EPA/.742/B-97/005.
Poll ution P re vent io n
\ ' ^i. ' . - -':'
for the
Metal Finishing Industry
A Manual for
Pollution Prevention
Technical Assistance Providers
February 1997
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Acknowledgments
S'FWMOA is indebted 10 Ihe U.S. Environmental Protection Agency's Office of
'the peer review committee: .. .; .
Mark Arienti, Maine Metal Products Association
Daryl Beardsley, Beardsley & Associates
Bob Brown, ConnTAP
Jim DeWitt, GZA Environmental '
. Chris Ford, Printed Circuit Corporation
Peter Gallerani, ^Integrated Technologies
Gene Park, Rhode Island Pollution Prevention Program
'Jackie Peden. Waste Management and Research Center
Karen Thomas. Toxics Use Reduction Institute
Project Staff/Contributors
Lisa Regenstein. NEWMOA P2 Project Manager - Researcher/Author
Terri Goldberg. NEWMOA P2 Program Manager--Managing Editor
Jennifer Shearman, NEWMOA P2 Staff -Editor/Copy Editor
Beth Anderson. EPA - EPA Project Manager
Laurie Case. Waste Management Research Center-- Formatting and Layout
NEWMOA welcomes user, of.iht* mamal to cite and reproduce sccnons ^'
assistance to companies. Hoover, the Association requests that users ate the oAuSPA
reproducing or quoting so that appropriate credit tijgtven to original authors. NEWMOA and US EPA.
NEWMOA thanks you for cooperating with this request. .
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Northeast Waste Management Officials' Association
The Northeast Waste-Management Officials/ Association,(NEWMOA) is a non-profit, nonpartisan,'
interstate governmental association. The membership.iscomposed.of state environmental agency
directors .of the hazardous waste, solid waste, waste site cleanup and pollution prevention programs in
Connecticut, Maine, Massachusetts, Mew Hampshire, New Jersey, New York, Rhode Island, and
Vermont. " ' ;-. ".-:-.'
NEWMOA's mission is to help states articulate, promote and implement economically sound re-
gional programs for the enhancement of environmental protection. The group fulfills this, mission by.
orovidine a variety of support services that facilitate communication and-cobperation among member
states and between the states and EPA, and promote the efficient sharing of state and federal program
resources.
NEWMOA was established by the governors of the New England states as an official interstate
regional organization, in accordance with Section 1005 of the Resource Conservation^ Recovery
'Act (RCRA), The organization was formally recognized by the U.S. Environmental Protection
Agency (EPA) in 1986! It is funded by state membership dues and EPA grants.
NEWMOA established the Northeast States Pollution Prevention Roundtable, (NE P2 Roundtable) in
1989'to enhance the capabilities of member state environmental officials to implement effective
source reduction programs. TheNE P2 Roundtable's program involves the following components
V) managing a regional roundtabie of state pollution prevention programs; (2) pubhshmg.a newslefr
te r managing a clearinghouse of books, reports.case studies, fact sheets, notices of upcoming
meetm^ and conferences, and a list of P2 experts; (3) organizing training; and (4) conducting .
Larch and publishing reports and other documents. The clearinghouse provides pollution preven-
tion mformatL to st.te.and local government officials, the public, industry and others Fundmg for
the NE P2 Roundtable is provided by the NEWMOA member states and die: U.S. EPA. For more
information contact: Terri Goldberg, NEWMOA, 129 Portlands^
(617) 367-8558 x302 (Phone); (617) 367-0449 (Fax); NEPPR@TIAC.NET (e-mail).
The views expressed in this manual do not necessarily reflect those of NEWMO^WRG
or the NEWMOA member states. Mention of any company, process, or product name should not be
considered an endorsement by NEWMOA, NEWMOA member states, or the US EPA.
Printed on Recycled Paper
ii
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Table of Contents
' " ' . ' ' ' VI
List qf Figures .:.' ;:
List of Tables . - ............>.
._..,.. i , -... viii
Using This Manual.... ;...;........., ...........
Chapter 1: Overview of the Metal Finishing Industry..... 1
Types qf Shqps ..;... "''. - ' '""
. - , . '. " . - . - '.. ' ; 2
Types of Metal Finishing Processes .;
. ' . , ' - ' "''";. , 6
The Finishing Process... -
Metal Finishing Demographics ...I.:.......,:-.*
Characterization of the Metal Finishing Industry .._.. 1
Motivations for Implementing Pollution Prevention.... - 12
' 12
References. : ..............
Chapter 2: Regulatory Overview........... 1-5
Common Wastes from Metal Finishing Operations..... 15
Overview of Federal Regulations Affecting Metal Finishing... .,- - 17
;.........., 25
References "' """"
Chapter 3: Planning Pollution Prevention Programs at a
Metal Finishing Facility............... ...................27
.-,-.'' ! . ' '-, . '' ":'... 27
Planning ...........:. ; '
' .29
Assessing the Facility :.v r- "
32
Analyze and Select Options............ ; - "' ".".
''''' '-'. ' - . . "34
Keeping the Program Going .»... ' \ -r
, -. ' . .--- '; . .-.-'.,.'". ..-,."..' -.34
References ..;..... -
Chapter 4: Common Pollution Prevention Practices.....35
Emplqyee Training ........-..I............" .............
Hqusekeeping and Preventative Maintenance .,..........,.
'. 36
Leak Preventiqn ' ""
. !^ - ':' . . , .v 37
Spill. Preventiqn.....
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Inventory Management: Chemical Purchasing, Tracking, Storage, Use, and
Handling [[[ : ........... ............. .................... 37
Chemical Sample Testing ......................................... ........................................ 0/
Maintaining Incoming Water Quality ................................ ..... ............................ 38
References ............................................ ...................... ' ............. ; .......... ........... v
Chapter 5: Pre-Finishing Operations .................... ...... 41
42
Assessing the Cleaning Process [[[
'
, .
Cleaning Processes .................................. -
n , ' ............. ..:.51
References ............................... ..... ; ..... ............... .......... ..... .......
Chapter 6: Pollution Prevention in the Plating Process .53
* q-3 '
General Pollution Prevention Techniques for Plating Solutions ........... . ................. =><*
Cyanide-Based Plating Processes.... ....... ............................ : ....................... ........ 60
81
Non-Cyanide-Based Plating Processes ........................................... .................... °
92
Electroless Plating [[[ " ............................
1 : ' 97
Immersion (Displacement) Plating ....................................... .......................... '"
97
Chemical and Electrical Conversion ................................. ........... ................ ; 7
Issues Related to Aluminum Finishing [[[ '°
. . ......... ..... 107
Stripping ............ » .................... : ........... ; .............. ..........................
0, ' ................. ....108
References ....................................... .................................. "
Chapter 7: Pollution Prevention in Rinsing... .............. 1 13
113
Alternative Rinsing Practices ............... . ........................................ .................
118
Alternative Rinsing Methods [[[ ............
1 22
Rinsewater Flow Controls ................................... ........... ..... ....... f ............. "
1 9 *3
Rinsewater Recycling and Recovery Techniques .. .................................. ............ -
*
Recovery Technologies ...........................................
134
Membrane Technologies ................................................. ...............................
n , - ' ' :...... ............... 150
References ............................................ r ....... ................. ........
Chapter 8: Alternative Methods of Metal Deposition . 1 53
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References".^. .'.' .............;..... :- ; ;." ^ 59
Chapter 9: Design of a Modern Metal '
Finishing Facility 161
Process islands ..... - :.............. '6
Rinse lank Design ..........V.......:.. .....................,...:.. 161
Bath Makeup Transfers .......:.........,............ > '.
-| x r\
Rinse-to-Rinse Transfers , .- ....-.,
Enclosed Waste Lines. :........... ..............r : 162
-I X O
Secondary Containment ...., ..'......:..... -- o
. - . . .:..'' 163
Shop Design - -; -" <
' ..'-'.'' 1 AT
Facility Maintenance -.
'._., ' : .- ' . ...:... 164
References , ;--
Index .....~...-.^^^
Appendices ,......:....,. 167
T
Evaluation Form ;.....,..................-.......-. i-
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List of Figures
Figure 1 . Markets Served by Metal Finishers Percent of 1 992 Market ......... ........ ......... .. 1
Figure 2. Overview of -the Metal Fabricating Process ........................ ; ............ } ................ 3
Figure 3. Process for Surface Preparation for Electroplating ........................ . ................... 6
Figure 4. Overview of the Metal Finishing Process ........................... ......... .......... .......... 7
Figure 5. Waste Minimization/Pollution Prevention Methods and Technologies ................. 8
Figure 6. Multiple Reuse of Rinsewater ......................... ............................................... 57
Figure 7. Overview of the Electroless Plating Process ............................ .................. 93
Figure 8. Illustration of Dragout .............................. .............................................. | ]^
Figure 9. Illustration of Drainboards .......................................... ............................. ] ^°
Figure 10. Three-Stage Countercurrent Rinsing [[[ 120
Figure 1 1 . Example of Reactive Rinsing ............... . ......... ............... ............................ 1 21
Figure 12. Application of Conductivity Cells ................... . ........ ..... ...... ....... ....... ^
Figure 13. Configuration of Rinsewater Recycling in Open- and Closed-Loop Systems 125
Figure 14. Electrowinning ........................... ...................................... ...................
Figure 15. Two Common Configurations of Atmospheric Evaporators ................ .
Figure 16. Illustration of Membrane Flow ........................... .
Figure 17. Example of Microfiltration Application
Figure 18. Example of Ultrafiltration
Figure 19. Example of Reverse Osmosis ................................. .............. ............
Figure 20. Typical Reverse Osmosis Configuration-for Nickel Plating
'Figure 21. Two Common Configurations of Ion Exchange
Figure 22. Example of Ion Exchange ....................................... - .......
Figure 23. Common Ion Exchange Configurations for Chemical Recovery .
Figure 24. Example of Process Flow of a Nickel Plating Line Before and, After the Installation
of Electrodialysis ....................................... ...... ........................ - ............ ^°
Figure 25. Typical Acid Sorption Configuration ........ , .......... .................................. J4/
Figure 26. Typical Ion Transfer Configuration ........ .................. ........ ;-'; ............. \ *
Figure 27. Configuration of Membrane Electrolysis Application for Bath Maintenance . 1 4V
List of Tables
Table 1 . Waste Minimization Options for Metal Plating Operations ................................ -9
Table 2. Process Inputs and Pollution Generated .......................................... ..... .......... lo
Table 3. Overview of Federal Regulations Affecting the Metal Finishing Industry .......... 20
Table 4. RCRA listed Wastes ......... ,... ............................ .................. - ......... ................ ^2
Table 5. EPA Regulations for the Three Generator Classes ........................... ................. ^
Table 6. Overview of Assessment Information ........ . ........... : ........ ................................ ^
Table 7. Alternatives for Chlorinated Solvent Cleaning .................................................
TableS. Precipitators for Common Plating Solutions ................ .................................... ^
Table 9. Alternatives to Cadmium Cyanide Product Quality Issues.... .......................... °*
Table 10. Alternatives to Cadmium Cyanide Process Issues. ......... ........ .................... °j>
Table 1 1 . Overview of Alternatives for Copper Cyanide Plating .... ................................
Table 12. Overview of Alternatives for Gold Cyanide Plating ........................................ '_>
Table 13. Overview of Alternatives for Silver Cyanide Plating ................................. ..... ''
table 14. Alternatives to Zinc Cyanide Product Quality Issues .................... ............... -°JJ
Table 15. Alternatives to Zinc Cyanide Process Issues .. ............................. ............. °g
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Table 17. Common Uses of Chromate Conversion Coatings.' 0?
Table 18'. Results of MolypHos as a Substitute-for Chromating """ o/
Table 1 9. Overview of Applications for Recycling/Recovery Equipment - *>
Table 20. Overview of Recovery/Recycling Technologies ........ *'
Table 21. Potential of Metal Using Electrolytic Recovery '........ -.. ^
Table 22. Overview-of Membrane Processes -. ...................
'Table 23; Reverse Osmosis and Specific Metals'....: ...,....'....
Table 24 Overview of Alternative Methods for Metal Deposition - ^
Table 25 Comparison of Alternative Deposition Methods with Conventional Plating ...1 54
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Using This Manual
The Northeast Waste Management Officials' Association (NEWMOA) designed this manual to
provide environmental assistance staff with a basic reference on metal finishing. The purpose of the
manual is to enable assistance providers to rely on a single publication to jump start their research on
pollution prevention for metal finishers with whom they are working. The manual is explicitly
designed to be useful to assistance professionals with experience working with metal platers and
those who have never encountered metal finishing before. The O.S. Environmental Protection
Agency Pollution Prevention Division funded this manual as a model of a comprehensive packet of
information on a single industry.
'., ', ' , , , j '''
NEWMOA collaborates with state and local environmental assistance programs in the Northeast;
these programs have requested this manual to help them provide more efficient and effective help to
the numerous metal finishers in the region. Assistance providers have reported frustration with
having to search databases for materials only to obtain a list of citations and case studies that they
have to spend considerable time finding in order to provide information to their client companies. In
addition, these officials rarely have the opportunity to check the accuracy of the information they find
in databases to determine whether the material is still current. To avoid duplicating efforts and to
ensure that the information platers receive is up-to-date and accurate, NEWMOA developed this
manual as a model "synthesized" information packet that includes an exhaustive compilation and
synthesis of existing materials on P2 for the metal finishing industry.
To compile this manual, NEWMOA reviewed over 700 books, articles, fact sheets, reports and -,
guides on P2 for metal finishing. NEWMOA staff also sent a draft of the manual to more than 15
expert reviewers for their comments and suggestions. The result is an up-to-date compilation of
information on P2 options for metal finishing. However, pollution prevention is a rapidly changing
field, and all users should check with the various centers identified in Appendix B to determine
whether any new information is available.
The first three chapters of the manual include a'statistical characterization of the industry, overview
of federal regulations for metal finishing, pointers on implementing process planning and a descrip-
tion of general pollution prevention options. Chapter 4 covers general issues that apply to overall
facility operations. Chapters 5 through 7 address specific issues within each process line. These
three chapters focus on specific processes, pollution prevention options for these processes, issues
pertaining to the options and case studies highlighting the options. Chapter 8 covers alternative
deposition processes that replace traditional electroplating operations. Chapter 9 provides informa-
tion on integrating P2 into a facility's design. In order to reduce redundancy where topics overlap,
the text refers the reader to other sections within the document. The manualalso has an index to
facilitate quick information retrieval. The Appendices provide a glossary and resource listing.
Audience
NEWMOA designed this manual for individuals who are involved in providing some form of envi-
ronmental technical assistance to metal finishing companies. NEWMOA believes that the informa-
tion in this manual would be useful to environmental inspectors and permit writers that are involved
In regulatory compliance activities at metal finishing companies. This manual could help these
regulatory officials'identify possible pollution prevention opportunities at the firms that they are
inspecting or permitting.
NEWMOA designed this manual for assistance providers with little or no experience with metal
finishing NEWMOA suggests that these users pay particular attention to Chapters 1 through 4 to
gain a basic understanding of P2 for the industry. Chapters 5 through 9 will become increasingly
viii
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useful to these users as they work with specific companies on particular issues. To facihtat^search-
iri° for specific information and. topics, the last section of the manual includes an index. NENVMOA
expects users of this manual, who are, experienced assistance providers to metal finishers, to use only
those sections that pertain to their specific situations in client companies. These users may find the
information in Chapters 5 through 9 to be the most useful.
As stated above, this is a model for additional manuals that NEWMOA and other regional and
national-organizations are developing for other industry groups. NEWMOA is interested m obtaining
comments and suggestions from manual users on its content and format. Please take a moment and
complete the evaluation form at the end of the document to help us with future versions of this and
other manuals, or call NEWMOA at (617) 367-8558 ext. 304 and talk with us about the manual.
ix
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Overview of the Metal
Finishing Industry
These days everyone doing .pollution preven-
tion' assistance seems interested in helping the
metal finishing industry; ever wonder why? .
Metal finishing, when taken as a whole, is one.of
the largest users of many toxics chemicals in the
country. Electroplating alone is the second
largest end user "of nickel and nickel compounds,
and the third largest end user, of cadmium and
cadmium compounds.' Electroplating also
accounts for a substantial amount of chromium
use in the United States. In other words, this
industry is responsible for managing large
amounts of hazardous materials (Davis 1994).
Many industries use metal finishing in their
manufacturing processes including automotive,
electronics, aerospace, hardware, jewelry, heavy
equipment, appliances, tires, and telecommunica-
tions. Figure 1 shows the percent of markets
served by metal finishers in 1992.
Why is metal finishing so prevalent? Without
.metal finishing, products made from metals
would-last only a fraction of their present
lifespan because of'corrosion and wear. Finish-
ing is also used to enhance electrical properties,
to form and shape components, and to enhance ,
the bonding of adhesives or organic coatings.
Sometimes the finishes are used to meet con-
sumer demand for a decorative appearance.
Overall, metal, finishing alters the surface of
metal products to enhance: .
Corrosion resistance
Wear resistance -'.
Electrical conductivity .
Electrical resistance
Reflectivity and appearance (e.g., bright-
ness or'color)
40% T
Figure 1. Markets Served by Metal Finishers-Percent of 1992 Market (EPA 1995a)
' ' .' ''-. .'.- 1 '" - , ' ... '
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C".1C!4* I' Ove've* JT" ;ne M«3l Finishing Industry
Torque tolerance
Solderability
Tarnish resistance
Chemical resistance
Ability to bond to rubber (e.g., vulcaniz-
ing}
Hardness
Metal finishers use a variety of materials and
processes to clean, etch, and plate metallic and
non-metallic surfaces to create a workpiece that
has the desired surface characteristics. Electro-
lytic plating, electroless plating, and chemical
and electrochemical conversion processes are
typically used in the industry. Typical support-
ing processes can include degreasing, cleaning,
pickling, etching, and/or polishing.
Some of the materials used in metal finishing are
solvents and surfactants for cleaning, acids and
bases for etching, and solutions of metal salts for
plating the finish onto the substrate. Figure 2
presents an overview of the fabricated metal
products manufacturing process and shows the
types of emissions and wastes that are generated
during production.
Types of Shops
The electroplating, plating, polishing, anodizing,
and coloring industry is classified under the
Standard Industrial Classification (SIC) code
3471 and includes establishments primarily
engaged in all types of metal finishing. Compa-
nies that both manufacture and finish products
are classified according to products they make.
Nonetheless, they are still considered part of the
metal finishing industry.
Firms that rely on one customer or that conduct
metal finishing as part of a larger operation are
referred to as captive shops. These companies
tend to have larger operations than job shops:
Independent facilities, often referred to as job
shops, rely on a variety of customers and coat a
variety of workpieces and.substrates. In general,
job shops tend to be small and independently
owned. Enough similarities exist between the
job and captive shops that they are essentially
considered part of one industry. The job and
captive shops use the same types of processes
and fall within the same regulatory framework
(EPA 1995a).
However, the barriers they face in deciding upon
and implementing new technologies reflect the
differences in their environmental performance
and in the corporate capabilities of the two
segments. Captive operations, which are more
« specialized, can focus their operations because
they often work on a limited number of products
and/or use a limited number of processes. Job
shops, on the other hand, tend to be less focused
in their operations because they can have many
customers often with different requirements. In
general, captive shops tend to have greater access
to financial and organizational resources and, as
a result, tend to be more proactive in their
approach to environmental management.. How-
ever, this is not always the. case. The vastly
different cultures in these shops greatly affects
their perceived ability to implement pollution
prevention (EPA 1994).
Job shops and captive shops do not ordinarily
compete against each other because captive
finishers seldom seek contract work. However,
.captive facilities might use job shops as subcon-
tractors to perform tasks that their operations are
unable to or that they choose not to do. As a
nationwide trend, many manufacturers are
choosing to eliminate or reduce metal finishing
operations from their facilities because it is not
of strategic importance for their long-term
success. In some of these cases, the larger firms
have shifted their plating activities to job shops
(EPA I995a).
Types of Metal Finishing
Processes
Metal finishing comprises a broad range of
processes that are-practiced by most industries
which manufacture metal parts. Typically,
manufacturers perform the finishing after a metal
part has been formed. Finishing can be any
operation that alters the surface of a workpiece to
achieve a certain property. Common metal
finishes include paint, lacquer, ceramic coatings,
and other surface treatments. This manual
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Cnjpcer I ' Overview or the Mecj/. fir.isntng Indus
Techniques '
Rinsing. -
' - '- - . ' '
_/ ' "" s ' '"
Figure 2. Overview'of the Metal Fabricating Process (EPA 1995a)
' '. '/' ' ' ' ' 3 . _ . '
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f. e"A i( :** M*HI Finishing Industry
maini> addresses the plating and surface treat-
ment processes.
The metal finishing industry generally catego-
rizes plating operations as electroplating and
electroless plating. Surface treatments consist of
chemical and electrochemical conversion, case
harden :. metallic coating, and chemical
coatint. The following sections briefly describe
the major plating and surface treatment processes
in order to provide a context for the more in-
depth information in the chapters that follow.
Electroplating
Electroplating is achieved by passing an electric
current through a solution containing dissolved
metal ions and the metal object to be plated. The
metal object serves as the cathode in an electro-
chemical cell, attracting ions from the solution.
Ferrous and non-ferrous metal objects are plated
with a variety of metals including aluminum,
brass, bronze, cadmium, copper, chromium,
gold, iron, lead, nickel, platinum, silver, tin, and
zinc. The process is regulated by controlling a
variety of parameters including voltage and
amperage, temperature, residence times, and
purity of bath solutions. Plating baths are almost
always aqueous solutions, therefore, only those
metals that can be reduced in aqueous solutions
of their salts can be electrodeposited. The only
major exception to this principle is aluminum,
which can be plated from organic electrolytes'
(EPA"l995a).
Plating operations are typically batch operations
in which metal objects are dipped into a series of
baths containing various reagents for achieving
the required surface characteristics. Operators
can either carry the workpieces on racks or in
barrels. Operators mount workpieces on racks
that carry the part from bath to bath. Barrels
rotate in the plating solution and hold smaller
parts (Ford 1994).
The sequence of unit operations in an electroplat-
ing process is similar in both rack and barrel
plating operations. A typical plating sequence
involves various phases of cleaning, rinsing,
stripping, and plating. Electroless plating uses
similar steps but involves the deposition of metal
on metallic or non-metallic surfaces without the
use of external electrical energy (EPA 1995a).
Electroless Plating and Immersion
Plating
Electroless plating is the chemical deposition of
a metal coating onto an object using chemical
reactions rather than electricity. The basic
ingredients in an electroless plating solution are a
source metal (usually a salt), a reducer, a
complexing agent to hold the metal in solution,
and various buffers and other chemicals designed
to maintain bath stability and increase bath life.
Copper and nickel electroless plating commonly
are used for printed circuit boards (Freeman
1995).
Immersion plating is a similar process in that it
uses a chemical reaction to apply the coating.
However, the difference is that the reaction is
caused by the metal substrate rather than by
mixing two chemicals into the plating bath. This
process produces a thin metal deposit by chemi-
cal displacement, commonly zinc or silver.
Immersion plating baths are usually formulations
of metal salts, alkalis, and complexing agents
(e.g., lactic, glycolic, or malic acids salts).
Electroless plating and immersion plating
commonly generate more waste than other
plating techniques, but individual facilities vary
significantly in efficiency (Freeman 1995).
Chemical and Electrochemical
Conversion
Chemical and electrical conversion treatments
deposit a protective and/or decorative coating on
a metal surface. Chemical and electrochemical
conversion processes include phosphating,
chromating, anodizing, passivation, and metal
coloring. Phosphating prepares the surface for
further treatment. In some instances, this process
precedes painting. Chromating uses hexavalent
chromium in a certain pH range to deposit a
protective film on metal surfaces. Anodizing is
an immersion process in which the workpiece is
placed in a solution (usually containing meta!
salts or acids) where a reaction occurs to form an
insoluble metal oxide. The reaction continues
and forms a thin, non-porous layer that provides
good corrosion resistance. Sometimes this
-------
Chapcer \: Overview of the
process-is used as;apretreatment for painting.
Passivatihg also involves the immersion of the
\\orkpiece into an acid solution, usually nitric
acid or nitric acid with sodium d.ichromate. The
passivating process is used to prevent corrosion
and extend the life of the product. Metal
coloring involves chemically treating the
workpiece to impart a decorative.finish (EPA
I995a). ' ' "<'.:
Other Surface Finishing .':
Technologies
Other commonly used finishing technologies
that do not fall into the plating or chemical and <
electrochemical conversion processes include
cladding, case hardening, dip/galvanizing,
electropolishing, and vapor deposition. The
"following sections provide brief overviews of
these different processes, ' _
Cladding . :
Cladding is a mechanical process in which the
metal coating is metallurgically bonded to the
\vorkpiece surface by combining heat and
pressure. An example of cladding is a quarter.
The copper inside is heated and pressed between
two sheets of molten nickel alloy, bonding the
materials. Cladding is used to deposit a thicker
coating than electroplating, and requires less
preparation and emits less waste. However,
. equipment costs are higher than electroplating
(Freeman 1995). ,
Case Hardening
Case hardening is a metallurgical process that
modifies the surface of a metal. The process
produces a hard surface (case) over a metal core-
that remains relatively soft. The case is wear-
resistant and durable, while the core is left
strong and pliable. In case hardening, a metal is
heated and molded and then the temperature is
quickly dropped to quench the workpiece. An
example of a material made with case hardening
is the Samurai sword. The hardened surface can
be easily shaped, however, the sword remains
pliable. This method has low waste generation
and requires a low degree of preparation.
Operating difficulty and equipment cost are
approximately the same as for anodizing,
although case hardening imparts improved
toughness and wear (Freeman 1995).
Case hardening methodologies include carburiz-
' ing, nitriding, micro-casing, and hardening-usi-ng, [
localized heating and quenching operations.
Carburizing, the most widely used case harden-
ing operation, involves diffusion of carbon into^a
steelsurface at temperatures of 845 to 955
degrees Celsius, producing a hard case coating.
Nitriding processes diffuse nascent nitrogen into
a steel surface to produce case-hardening. .
Nitriding uses either a nitrogenous gas, usually
ammonia, or a liquid salt bath (typically consist-
ing of 60 to 70 percent sodium salts, mainly _
sodium cyanide, and 30 to 40 percent potassium
salts, mainly potassium cyanide). Carbon
' nitriding and_cyaniding involves the diffusion of -
both carbon and nitrogen simultaneously into a
steel surface.
Dip/Galvanized
Dip/galvanized coatings are applied primarily to
iron and steel to protect the base metal from
corroding. During the dipping process, the plater
immerses the part in a molten bath commonly
composed of zinc compounds. The metal part
' must be free of grease, oil, .Iubricants,and other
surface contaminants prior to the coating pro-
cess. Operating difficulty and equipment costs
are low, which makes dipping an attractive
coating process for most industrial applications.
However, dipping does not always provide a
high quality finish (Freeman 1995).
Electropolishing
In electropolishing, the metal surface is anodi-
cally smoothed in a concentrated acid or alkaline
solution. For this process, the parts are made
anodic (reverse current), causing a film forma-
tion around the part that conforms to the macro-
contours of the part. Because the film does not
conform to the micro-roughness, the film is
thinner oyer the micro-projections and thicker
over the micro-depressions. Resistance to the
current flow is lower at the micro-projections,
causing a more rapid dissolution. Many different
solutions are available for electropolishing
depending,on the substrate (Ford 1994).
Metallic Coatings (Vapor Deposition)
Metallic coatings change the surface properties
of the workpiece from those of the substrate to
that of the metal being applied, This process
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Copter t: Overview af Che Meut Fintshfng Industry
allots the workpiece to become a composite
material with properties that generally cannot be
achieved by either material alone. The coating's
function is usually as a durable, corrosion-
resistant protective layer, while the core material
provides a load-bearing function. Common
coating materials include aluminum, coated lead,
tin, zinc, and combinations of these metals..
Metallic coatings often are referred to as diffu-
sion coatings because the base metal is brought
into contact with the coating metal at elevated
temperatures, allowing the two materials to
interlace. These systems include various metal-
lic spraying applications, cladding (application
using mechanical techniques), hot dipping, vapor
deposition, and vacuum coating. The main
application for spray diffusion coatings is
workpieces that are difficult to coat by other
means because of their size, shape, or suscepti-
bility to damage at high temperatures. Cladding
uses a layer of metal that can be bonded to the
workpiece using high-pressure welding or
casting techniques. In some applications,
cladding can be used as an alternative to plating.
Hot dipping is another diffusion process that
involves partial or complete immersion of the
workpiece in a molten metal bath. The facility
applies the coating metal in a powdered form at
high temperatures (800 to 1,100 degrees Celsius)
in a mixture with inert particles such as alumina
or sand, and a halide activator. Vapor deposition
and vacuum coating produce high-quality pure
metallic layers, and can sometimes be used in
place of plating processes (EPA 1995b).
The Finishing Process
In general, objects to be finished undergo three
stages of processing, each of which involves
moving the workpiece through a series of baths
containing chemicals designed ,to complete
certain steps in the process. The following list
illustrates each of the three basic finishing stages
and the steps typically associated with them:
Surface preparation: Platers clean the
surface of the workpiece to remove greases,
soils, oxides, and other materials in prepara-
tion for application of the surface treatment.
The operator typically uses detergents,
solvents, caustics, and other media first in
this stage and then rinses the workpiece.
" Next, an acid dip is used to remove oxides
from the workpiece, which is then rinsed.
The part is now ready to have the treatment
applied. Figure 3 shows the steps in the
process of preparing a metal part/product for
electroplating.
Surface treatment: This stage involves the
actual modification of the workpiece surface,
including plating. The actual finishing
process includes a series of baths and rinses
to achieve the desired finish. For example, a
common three-step plating system is copper-
nickel-chrome. The copper is plated first to
improve the adhesion of the nickel to the
steel substrate and the final layer, chrome,
provides additional corrosion and tarnish
protection. Following the application of
each of the plate layers, workpieces are
rinsed to remove the process solution. The
final step in the process is drying. This step
can consist of simple air drying or a more
complex system such as forced air evapora-
tion or spin dry. Figure 4 presents an
overview of the metal finishing process.
Post treatment: The workpiece, having
been plated, is rinsed and further finishing
- operations cart follow. These processes are
Scale
Removal
Acid
Pickling
Surface Cleaning
^iRinse
i
Alkaline
Cleaning
> Rinse
»
Alkaline
Cleaning
* Rinse|
Figure 3. Process for Surface Preparation for Electroplating (EPA 1995a)
'. ' ' i
6
-------
Chapter. I : Overview of the Metal Fmisn'm? \naustr;
Alkaline
Cleaner
Rinse
A'cid ..
Dip
Rinsq
.1
Plating.
Drag-
out
Tanks
Rinse
- r~
Finishing
Treatment
Rinse
Surface Preparation
Surface Treatment
Figure 4. Overview of the Metal Finishing Process (EPA 1994)
used to enhance the appearance or add to the
properties of the workpiece. A common
example of a post-treatment process is heat
treating to relieve hydrogen embrittlement or
stress. Chromate conversion is another post-
treatment process that often follows zinc or
cadmium plating to increase corrosion
resistance (EPA 1995b).
In each of these stages, opportunities for pollu-
tion prevention exist. Chapters 5-8 provide '
information on specific techniques/technologies.'
For an overview of pollution prevention opportu-
nities, refer to Figure 5 and Table 1 on the
following pages. The two figures provide an
overview of the different pollution prevention
techniques/technologies that metal finishers can
use and their place on the waste management
hierarchy. Table,! presents more detailed
information on specific waste reduction tech-
niques and an overview of the applications and
limitations of each. The information provided in
this table is consistent with the United States
Environmental Protection Agency's (EPA)
environmental protection hierarchy and their
definition of pollution prevention.
EPA defines pollution prevention as any practice
which reduces the amount of any hazardous
substance, pollutant, or contaminant entering the
wastestream or otherwise released to the environ-
ment (including fugitive emissions) prior to
recycling, treatment, or disposal; and reduces the
hazards to public health and.the environment.
Pollution prevention practices can include
changes in the design, inputs, production, and
delivery of a product including:
Raw material substitution: Switching raw
materials to use jess hazardous materials
*' Process modificatio'n: Changing the produc-
tion process'to improve efficiency and
reduce the use of toxic substances
J
Equipment upgrade: Installing more
efficient equipment to reduce raw material
consumption and produce less waste
Product redesign: Reducing certain raw
', materials in products and packaging or
improving manufacturability ;'
What we call pollution prevention often can be
called something else in another profession. For
instance: l
Accountants call it loss control
Process engineers call it an efficient
process . .
Managers call it total quality .
management .
People unaccustomed to long definitions
call jt common sense
Many waste minimization options, including
process recovery and reuse as well as improved
operating procedures, represent significant
opportunities for waste reduction with relatively'
low investment costs. Similarly, such options as
product replacement can represent the ultimate
pollution prevention solution, however, the
implementation of these options is largely driven
by consumer preference and not favored by the
industry (EPA 1995b).
Often, technical assistance providers can have
greater success in getting companies to imple-
ment pollution prevention if they understand the
nature of the industry. The following sections
-------
!: Gverve* of the Meul Finishing Industry
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Chapter 1: Overview of me Mem Fwsv.n? An
provide background on metal finishing, demo-
graphics, characterization, and motivations to.
assist in gaining that understanding. >;-"
Metal Finishing
Demographics
There are an estimated 3,500 independently
owned metal finishing shops, mostly srriall
operations with limited capital and personnel
(EPA.1994). A typicaljob shop is a small single
establishment that employs 15 to 20 people,
receives their workplaces from an outside source,
, and generates $800,000 to $1 million in annual
gross revenues. .Between 1982 and 1987, the
number of smaller shops declined, while the _
number of larger metal finishers increased. This
development apffears to signal a trend toward
smaller shops closing down and medium and
larger shops incrementally increasing in number
(EPA 1995a). Overall, however, there has been a
, sharp decline in the number of job shops in the
United States. Moreover, there are an estimated
10,000 captive finishing operations in the United
States that are not listed under SIC 3471. ^
Although geographically diverse, the metal
finishing industry is concentrated in what are
usually considered the heavily industrialized
regions of the United States: .the Northeast,
Midwest, and California. This geographic
concentration has occurred in part because small
plating facilities locate near their customer base
to be cost effective (EPA I995a). '
Characterization of the
Metal Finishing Industry
In describing the industry, EPA sometimes
groups metal finishers into four categories or
tiers with regard to their environmental perfor-
mance. These groups each face different drivers
and barriers in their environmental performance.
' The list below characterizes these categories and
their most significant challenges. These chal-
lenges can affect a company's decision-making
process. Understanding the various types of
firms can help technical assistance providers
determine the most effective way for different
platers to implement pollution prevention.
» Tier 1: EPA characterizes Tier 1 companies
as environmentally proactive firms that are
actively pursuing and investing in strategic
environmental management projects. These
firms are in compliance with environmental
regulations,and are, actively pursuing and
1 investing capital in continuous improvement
projects that go beyond compliance.
* Tier 2A: These are firms that EPA charac-
terizes as consistently in compliance/but do
not or cannot look for opportunities to
improve environmental performance beyond
that level.
', Tier 2B: EPA characterizes these firms as
those that.would like to be in compliance but
are not able to do so.
\ Tier 3: EPA characterizes Tier 3 metal
" k finishing firms as companies that are older
and want to close operations; but stay in
operation because they fear the liability and
legal consequences.of shutting down.
Tier 4: EPA characterizes Tier 4 metal
finishing shops as shops that are out of .
compliance or "outlaw" firms that are not
substantial competitors but pull down the
reputation of the industry; they have little or
no interest in complying with environmental
regulations (EPA 1994). ,
"Some metal finishers (Tier 3 and some Tier 4
firms) might have a perverse incentive to oper-
ate, even in the face of disappearing profits,
because of the potentially high environmental
cleanup costs associated with shutting down and
liquidating. These facilities, although opera-
tional, are not making any additional capital
investments to improve environmental perfor-
mance. Because they lack internal capital and
cannot secure external financing to fund clean-
ups, these firms continue to perform poorly and
represent a significant barrier to entry for more
efficient firms that might have higher short-term
costs (EPA 1994).
11
-------
Cw. en. i( (Me Metal Finishing Industry
Motivations for
Implementing Pollution
Prevention
Assistance providers can use a number of
pollution prevention motivators in discussions
with company personnel. Using the information
provided in the previous section, combined with
the proper motivators, can help assistance
providers develop successful strategies to sell
pollution prevention to the facility management.
Drivers for metal finishers seem to depend on the
tier in which they are classified. The following
list contains the drivers for different tiers:
Tier 1: Top firms are driven by recognition
and pride in industry performance. They see
the economic payoffs of strategic environ
mental investments and contend that flexibil-
ity in compliance would promote innovative
approaches and increase their willingness to
help other firms.
«. Tier 2: Regulatory compliance is a strong
driver for this large middle tier. Barriers to
proactive performance include a lack of
capital and information, a lack of positive
reinforcement, and an uneven enforcement
playing field. Some job shops in this tier
depend on suppliers for ingredients and
process recipes that restrict their willingness
and/or ability to undertake environmental
improvement activities.
Tier 3: These are generally older, outdated
shops that have a strong fear of liability and
little ability to improve because they lack
capital, information, and skills to do so=
Some of these firms might want to go out of
business but, because of environmental and
financial liability concerns, they remain
open. The firms in Tiers 1 and 2 might have
an incentive to help close down these firms
rather than to help raise them to a higher tier.
Tier 4: These firms flagrantly disregard
compliance requirements and have no
incentive to improve their operations because
they gain no competitive advantage. They
' " !
do not fear enforcement because they are ,
difficult to track down. They operate
without permits and do not report discharges.
They profit by having a lower cost structure
that undercuts the higher tier firms.
The barriers that generally apply to some or all
of the tiers are:
Regulatory compliance and/or
enforcement actions: Many job shops lack
the personnel and capital resources to move
beyond compliance. Liability concerns are a
barrier to obtaining loans for capital im-
provements.
. Development of safer products: Metal
finfshers, while possessing much understand-
ing of the processes they use, rely heavily on
chemical suppliers to optimize existing
processes and to investigate new solutions.
In some cases, suppliers might be reluctant
to suggest environmentally proactive pro-,
cesses or product changes because these
could mean lower product sales in the short
term.
Uncertainty about future regulatory
activity: Inconsistency in existing regulatory
requirements/enforcement actions at the
federal, state, and local level creates, at least,
uncertainty and, at worst, competitive
imbalances throughout the industry. This
climate generates distrust of EPA and state
programs and can inhibit meaningful com-
munication.
«. Military and customer'specifications:
Some customers, especially those in the
military, continue to require the use, at least
indirectly, of environmentally harmful
products and processes even when safer
substitutes or processes are available.
Lack of awareness of changes in prod-
uct/process technology: Lower-tier firms
often lack any incentive to change because
existing liabilities can continue to over
whelm their ability to pay for remediation
(Haveman 1995).
T2
-------
CTupcer 1: p\eruewof the.Mewi F.inisnins; Industry
References
Davis, Gary A. et/al. 1994. The Product Side
of Pollution Prevention: Evaluating Potential /
Safe Suto/Yu/es,.Cincinnati, Ohio: Risk Reduc-
tion Laboratory, Office of Research and Devel-
' opment. ;
EPA. \995z. Profile of the Fabricated Metal
Products Industry. Washington, DC: Office of
Enforcement and Compliance Assurance.
EPA. 1995b. Metal Plating Waste Minimiza-
tion. Arlington, VA: Waste Management Office,
Office of Solid Waste. . , ~
EPA. 1994. Sustainable Industry: Promoting
Strategic Environmental Protection in the
Industrial Sector: Phase I Report Metal Finish-
ing Industry. Washington, DC: Office 6f Policy,
Planning and Evaluation. ^ -
\ ".- ,
' Ford, Christopher J., and Sean Delaney.
1994. Metal Finishing Industry 'Module. Lowell,
MA: Toxics Use Reduction Institute.
Freeman, Harry M. 1995. Industrial Pollu-
.tion Prevention Handbook. New York, NY:
McGraw-Hill, Inc. ' ', ' ' .
Haveman, Mark. 1995. Profile of the Metal
Finishing Industry. Minneapolis, MN: Waste
Reduction Institute for Training and Applications
Research. .
13
-------
-------
Regulatory Overview=
To varying degrees, all metal finishing
processes tend to have pollution problems .
and to generate hazardous and solid wastes.
Unlike other manufacturing operations, the vast
majority of chemicals that platers use end up as
waste. Of particular concern are those processes
-.that use highly toxic or carcinogenic ingredients
that are difficult to destroy or stabilize., Some of
these processes are: ; ; :,
Cadmium plating , ,
> Cyanide-based plating including zinc,
cadmium, copper, brass, bronze, and ,
silver plating ..'-'
Chromium plating and conversion coat-
ings using heXaval.ent chromium
compounds
V Lead and lead-tin plating ;
Common Wastes from
Metal Finishing
Operations
The metal finishing process often produces
undesirable byproducts or wastes including air
emissions, wastewater, and hazardous-and solid
wastes. These wastes predominately result from
organic halogenated solvents, ketones, aromatic
hydrocarbons, and acids used during the surface
preparation stage of the process and from metals
(primarily present in the form of dissolved salts
in the plating baths) used during the surface
treatment stage. Cyanide, used in many plating
baths,,is also a pollutant of concern. This
chapter provides an overview of wastes gener-
ated from the various processes found in a metal
finishing facility. Table 2 provides a summary
of these pollutants and their sources.
Wastewater
The rinsing process is the primary source of .
waste generated in metal finishing operations.
Rinsing removes plating solutions or cleaners
from the workpiece. Rinsewaters often contain
low concentrations of process chemicals carried
by the workpiece into the rinse (also known as
dragout).
Sourpes of wastewater that are typically treated
on site include:
, Cleaning rinsewater . ' :
Plating rinsewater ' . '
Tumbling and burnishing rinsewater '
Exhaust scrubber solution ' '
Wastewater that is typically regulated but not
'treated includes: .
> Non-contact cooling water
Steam condensate
Boiler blowdown
Stormwater
To meet air emission regulations, vapors and
mists, wli.ich are emitted from process baths, are
controlled by exhaust systems equipped with
mist collection and scrubbing systems. This
treatment process generally produces a metal
hydroxide sludge that must be managed as a
hazardous material. Once treated, wastewaters
are discharged to a sewer authority or to a body
of water (EPA 1995b). :
Solid and Hazardous Waste
Metal finishers periodically discharge process
baths when they lose their effectiveness because
of chemical depletion or contamination. Acci-
dental discharges of these chemicals also can
occur (e.g., when a tank is overfilled). These
concentrated wastes are either treated on site or
hauled to an off-site treatment or recovery
facility. In general,1 the sources of hazardous and
solid wastes at a plating shop include:
* Spent plating baths
S'pent etchants and cleaners
15
-------
R«p.ia::r/ O'.er.tew
Table 2. Process Inputs and Pollution Generated (EPA 1995b)
Material
Process Input
Air
Emission
Process
Wastewater
Surface Preparation
. Solvent Degreasing
and Emulsion
Alkaline and Acid
Cleaning
it
Solvents
Emulsifying agents
Mkalis
Acids
Solvents (associated
with solvent de-
greasing and
emulsion cleaning
only)
Caustic mists
Solvent
Alkaline
Acid wastes
i! Surface Finishing
j| - ~
! Anodizing
i
i
i
Chemical Conversion
Coatings
Electroplating
Plating
Other Metal
Finishing Techniques
(including polishing,
hot dip coating, and
etching)
Acids
Dilute metals
Dilute acids
Acid/alkaline
solutions
Heavy rrietal-
jearing solutions
Cyanide-bearing
solutions
Metals (e.g., salts)
Complexing agents
Alkalis
v\etal ion-bearing
mists
Acid mists
Metal ion-bearing
mists
Acid mists
Metal ion-bearing
mists
Acid mists
Metal ion-bearing
mists
Metal fumes
Acid fumes
Particulates
Acid wastes
v\etal salts
Acid
3ase wastes
Acid/alkaline
Cyanide
v\etal wastes
Cyanide
Metal wastes
Metal
Acid wastes
Solid
Waste
Ignitable Wastes
Solvent wastes
Still bottoms
Spent solutions
Wastewater
treatment sludges
Base metals
Spent solutions
Wastewater
treatment sludges
Base metals
Metal
Reactive wastes
Cyanide
Metal wastes
Polishing sludges
Hot dip tank dross
Etching sludges
Scrubber residues
Strip and pickle baths
Exhaust scrubber solutions
Industrial wastewater treatment sludge,
which can contain materials such as
cadmium, copper, ctiromium, nickel, tin,
and zinc
Miscellaneous solid wastes such as
absorbents, filters, empty containers,
aisle grates, and abrasive blasting
residue
Solvents used for degreasing
Spills, if they occur, can contribute significantly
to the volume of waste. Samples of plating
chemicals, which are provided by vendors but
not intended for manufacturing use, also can
contribute to the amount of waste that a metal
finisher generates, Outdated chemicals are
another example of wastes that platers and others
typically do not attribute to the production
process. These samples and obsolete or expired
materials often accumulate and can violate waste
storage requirements. These wastes eventually
must be returned to the supplier or disposed of
appropriately (EPA 1995b).
16
-------
.Chapter 2: Resuuwry Oversew.
Air Emissions ;
There.are several air emission sources at a metal
finishing facility. Those of greatest environmen-
tal concern are chrome plating and anodizing
processes that use hexavalent chromium and
solvents from vapor degreasing. Chromium
emissions frequently are controlled by wet .
scrubbers. The discharge of these systems is sent
to wastewater treatment and combined with other
wastewaters for processing.
Solvents evaporate substantially during
degreasing operations. Contaminated liquid
solvents are recovered either by distillation (on
site or, off site) or sent for disposal (incineration).
Most shops do not have controls for organics.
However, some larger plants use .carbon adsorp-
tion-units to remove hydrocarbons (EPA 1995b).
Metal finishing results in a variety of hazardous
compounds that are released to the land, air, and;
water. As a result, facilities are required to y
comply with numerous regulations. Regulations
for metal finishers are promulgated at the
federal, state, and local level. The requirements
are complex and can vary, not only from state to
state, but also from municipality to municipality.
Overview of Federal
Regulations Affecting
Metal Finishing
The metal finishing industry has made extensive
progress in improving operations in recent years -
as environmental regulations regarding dis-
charges have become more stringent. However,
in the future, platers will need to meet new
standards that require further reductions in the
amount and types of wastes that they discharge.
Increased costs for materials and discharges will
continue to cut profit margins and force .
businesses to search for new ways to reduce
these costs. ;.;
The metal finishing industry is regulated under
numerous federal, state, and local environmental
statutes. Three major federal laws regulate
releases and transfers from the metal finishing
industry: the Clean Air Act as amended in 1990
(CAAA), the Clean Water Act (CWA), and the
Resource Conservation and Recovery Act
(RCRA). Also, the emissions reporting require-
ments under EPA's Toxics Release Inventory
(TRI) cover many of the chemicals used in metal
finishing. Table 3 presents an overview of the
federal regulations affecting the metal finishing
industry'.
' / '
Environmental assistance providers should
consult with state and local regulatory authorities
to identify specific requirements that might be
more stringent than those promulgated under
federal law. A myriad of state'and local laws
pertain to metal finishers, and helping them to
understand all of these regulations can be an
important aspect of providing assistance. This
manual does not provide specific information on
state and local regulations because of the lack of
consistency across state and local programs.
Clean Air Act
With the enactment of the Clean Air Act
Amendments, air emissions have become a
greater concern for metal finishers. Any metal
finishing operation with processes that could
emit Hazardous'Air Pollutants (HAPs) or volatile
organic compounds (VOCs), as defined in the
CAAA, could be required to obtain an operating
permit and/or comply with other regulatory
requirements for those processes. Regulations
covering the use of halogenated solvents, a
common material in most metal finishing opera-
tions, will-directly affect most companies.
Facilities that have processes which emit airr
borne metals, particularly chromium, are also
going to be subject to increasing requirements'
(Haveman 1995).
Hazardous Air Pollutants
The Clean Air Act Amendments of 1990
established a list of 189 hazardous air pollutants.
Of the 56 SIC 34.71 substances reported in the
TRI database for 1990,33 are included on the list
of HAPs. Under the CAAA, Congress required
EPA to identify major and area source categories
associated with the emissions of one or more
listed HAPs. to date, EPA has identified 174
categories. Congress also required EPA to
promulgate emissions standards for listed source
categories within 10 years of the enactment of
the CAAA (November 15, 2000). These stan-
17
-------
" RegvaKry O'.e'-.'.ew
dards are called the National Emission Standards
for Hazardous Air Pollutants (NESHAPs).
The standards will require-regulated metal
finishers to apply Maximum Achievable Control
Technology (MACT) to all new sources of
HAPs, while existing sources could be in compli-
ance using less strict control measures. The
MACT determination processes is quite compli-
cated. Put simply, it is the lowest emission rate
or highest level of control demonstrated on
average by the top performing companies (top 12
percent) in the source category. MACT determi-
nation is subject to negotiation among industry,
environmental groups, and EPA (Haveman
1995). State environmental agencies will
determine exactly which businesses are subject
to the permit requirement as part of their State
Implementation Plans (SIPs).
Currently, EPA is finalizing three NESHAPs
(Chromium Electroplating, Solvent Degreasing,
and Steel Pickling) that will directly affect the
metal finishing industry (EPA 1995a). A sum- -
mary of these three NESHAPs follows.
NESHAP: Chromium Electroplating
These standards limit the air emissions of
chromium compounds in an effort to protect
public health. The promulgated regulation will
be a MACT performance standard that will set
limits on chromium and chromium compounds
emissions based upon concentrations (e.g., mg of
chromium/m3 of air).
The chromium electroplating process emits a
chromic acid mist in the form of hexavalent
chromium (Cr+6) and small amounts of trivalent
chromium (Cr+3). Human health studies suggest
that acute, intermediate, and chronic exposure to
hexavalent chromium results in various adverse
effects. EPA has developed a NESHAP for
chromium emissions for hard and decorative
chromium electroplating and chromium anodiz-
ing tanks. There is not one standard emission
limit. The proposed emission standards differ
according to the sources (e.g., old sources of
chromium emissions will have different stan-
dards than new ones). EPA argues that these
proposed performance standards allow facilities
a degree of flexibility because they recognize a
difference in facilities and allow facilities to
choose any technology that meets the emission
standards established by the MACT (EPA
1995a).
NESHAP: Organic Solvent Degreasing
EPA also has promulgated a NESHAP for the
halogenated solvent degreasing/cleaning source
category that will directly affect the metal
finishing industry. EPA has designed this .
standard to reduce halogenated solvent emissions
based on MACT. The standard will apply to new
and existing organic halogenated solvent clean-
ers (degreasers) that use any of the HAPs listed..
in the CAAA. Specifically, EPA is targeting
vapor degreasers that use the following HAPs:
methylene chloride, perchloroethylene, trichloro-
ethylene, 1,1,1-trichloroethane, carbon tetrachlo-
ride, and chloroform (EPA I995a).
This NESHAP sets two standards. Facilities can
meet these standards in a variety of ways. The
MACT-based equipment and work practice
compliance standard requires a facility to use a
designated type of pollution prevention technol-
ogy along with proper operating procedures.
Existing operations that use a performance-based
standard can continue to do so if they can
achieve the same level of control as the equip-
ment and work practice compliance standard
(EPA 1995a).
NESHAP: Steel Pickling, HCL
EPA has identified steel pickling processes that
use hydrochloric acid (HCL) and HCL
regeneration processes as potentially significant
sources of HCL and chlorine emissions. Hydro-
chloric acid and chlorine are among the pollut-
ants listed as HAPs in Section 112 of the CAAA.
EPA has drafted a presumptive MACT standard
for these processes, which is currently under
review. This standard is slated for promulgation
by November 15,1997, however, it might be
delayed (EPA 1995a).
Volatile Organic Compounds
In effort to control smog, the CAAA required
EPA to develop standards on the following
substances:
Inhalableparticulates(PM-lO)
18
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Chapter 2: Regulatory Overview
» Nitrogen oxides (NOx) ' ,
Ozone
Sulfur oxides (SOx) - .;
. Lead ' '-.''
+ Carbon monoxide1. : . ,
The standard of interest to metal finishers is
ozone. Ground level ozone results from the
reaction of VOCs with nitrogen oxides. Many
of the substances used in solvent cleaning and
degreasing, as well as stripping, are VOCs. The
' extent to which a small source of VOCs will be
regulated depends upon the air quality in the
region in which the source is located. Basically,
if a source is located in an "attainment" area (in
compliance with the National Ambient Air
Quality Standards (NAAQS)), it will be re-
quired to obtain a permit if its potential to emit
is greater than 100 tons of VOCs per year.
Special provisions for attainment areas have ,
been made for sources located in the Northeast
and Mid-Atlantic states. Facilities located in an
attainment area will be subject to a permit if
they have the potential to emit 50 tons of VOCs
per year (Haveman 1995). \.
For those facilities located in non-attainment
' areas, the regulatory thresholds are much lower.
How much lower depends on the degree of non-
compliance with the NAAQs in that region.
EPA classifies non-attainment areas into five
types: marginal, moderate, serious, severe, and
extreme. As-air problems increase, the
-likelihood that a small source of VOCs will be
required to obtain a perrnit will increase.
Clean Water Act
The Clean Water Act regulates the amount of
chemicals/toxics released via direct and indirect
wastewater/effluent discharges, EPA has
promulgated effluent guideline's and standards
for different industries under the CWA
provisions. These standards usually set concen-
tration-based limits for the discharge of a given
chemical. EPA defines two types of discharges:
direct arid indirect.. Both types have different
requirements.
Direct Dischargers
A facility that is'discharging directly into a body
of water is regulated under the National Pollution
Discharge Elimination System. (NPDES) and
'must apply for a NPDES permit. The permit
specifies what type of pollutants can be
discharged and includes a schedule for
compliance, reporting, and monitoring. The,
NPDES regulation limits the.amount of metajs,
cyanides, and total toxic' organics that a facility
can discharge. These limitations remain the
same whether the facility is discharging to a
body of water or to a treatment facility
(Haveman 1995). ; :. ',
Indirect Dischargers
Most metal finishing facilities discharge their .
wastewater to publicly-owned treatment works
(POTWs). These indirect dischargers must
adhere to specified pretreatment standards
because the POTWs are designed to deal mainly
with domestic sewage, not industrial discharges.
Often, specific state or local water regulations
require more stringent treatment or pretreatment
requirements than those in the federal effluent
guidelines because of local water quality issues ,
(Haveman 1995). All facilities discharging to a -
POTW are governed by the General Pretreatment
Standards. These standards state that discharges
must have a pH greater than 5..0 and cannot:
Create fire or explosion
Obstruct the flow of wastewater through
the system
«, Interfere with sewage plant operations
* Contain excessive heat
Contain excessive petroleum, mineral, or
nonrbiodegradable oils
In additidn, two CWA regulations affect the
metal finishing industry: the Effluent Guidelines
and Standards for Metal Finishing (40 CFR Part
433) and the-Effluent Guidelines and Standards
for Electroplating (40 CFR Part 413) (Haveman
1995). Companies regulated by the electroplat-.
ing standards before the metal finishing stan-
dards were promulgated become subject'to the
more stringent metal finishing standards when
.they make modifications to their facility's
19
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g'-;j:arv O«.e«-.tew
Table 3. Overview of Federal Regulations Affecting the Metal Finishing Industry (EPA 1995a)
Program I Application to Metal Finishing
Implications
Clean Air Act
EPA required to regulate 189 air toxics. Also has
authority to require pollution prevention mea-
sures (installation of control equipment, process
changes, substitution of materials, changes in
work practices, and operator certification
training). Industries addressed include metal
finishers.
Requires phase-out of the production of chloro-
fluorocarbons (CFCs) and several other ozone-
depleting chemicals. Imposes controls on CFC-
containing products.
New sources located in non-attainment areas
must use most stringent controls and emissions
offsets that compensate for residual emissions.
Air,toxics regulation increases cost
of controlling numerous air emis-
sions produced by metal finishers,
increasing incentives for waste
reduction.
Restriction on CFCs limit some
chemicals used by metal finishers
and force use of alternatives
including aqueous and semi-
aqueous degreasers.
i I
Offsets can be achieved through [j
pollution prevention.
Clean Water
Act
Imposes technology-based effluent limits on
pollutants for specific industries. Standards can
require in-plant water treatment systems.
Effluent limits raise cost of treat-
ment and disposal, creating
financial incentives for source
reduction.
In-house controls provide process/
procedural modifications that
achieve waste reduction.
Emergency
Planning and
Community
Rlght-to-
Know
Requires select industries to report environmen-
tal releases of specified toxic chemicals includ-
ing metal fabricating and other industries that
conduct metal finishing.
Reporting requirements have
created a strong incentive for
reducing waste generation and
releases for all industries.
Release data have spurred in-
creased industry and public
scrutiny of waste generation and
manufacturing operations.
Executive
Order
12843
Resource
Conservation
and Recovery
Act
Requires fedefal agencies to implement the
Montreal Protocol and the phase-out of ozone-
depleting substances including chmeicals used
by the metal finishing industry.
Directly regulates several metal finishing wastes
as hazardous wastes.
Requires all hazardous waste generators,
including metal finishers, to certify that they
have a program in place to reduce the volume
or quantity and toxicity of the waste they
generate.
Requires the phase-out of ozone-
depleting chemicals such as '1,1,1 ,-
trichloroethane. Forced metal ,
plating operations to identify
replacements such as aqueous and
semi-aqueous degreasers.
Rigorous regulator/ scheme
applicable to metal finishing wastes
that are hazardous wastes. Creates
strong financial and liability
incentives to pursue source
reduction.
20
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Chapter 2: Regulocory.CXerv'iew
operating functions (e.g., facility equipment and
process modifications). If these companies make
no such modifications, they remain subject to the
electroplating standards only. All new facilities
are subject to the metal finishing standard.
Metal Finishing Standard
The Effluent Guidelines and Standards for Metal"
Finishing are applicable to wastewater generated
byany of the following processes:
Electroplating ,
- Electroless plating' .
Anodizing ..
'« Coating . .
Chemical etching and milling
Printed circuit board manufacturing
If a facility performs any of the processes listed
above,, it is subject to this standard. In addition,
discharges from 40 additional processes
including cleaning, polishing, shearing, hot dip
coating, and solvent degreasing could be subject
to this standard.
The metal finishing'and electroplating standards
include daily maximum and monthly maximum
r average concentration limitations. .The stan-
dards, which are based on milligrams per square
meter of operation, determine the amount of
wastewater pollutants from various operations
that can be discharged (EPA 1995b).
Electroplating Standard
The Effluent Guidelines and Standards for
Electroplating cover wastewater discharges from
electroplating and related metal finishing opera-
tions. This standard was developed prior to the
metal finishing standard and has less stringent
requirements than the metal finishing standard.
Facilities that are currently regulated by the
electroplating standard can become subject to the
more stringent metal finishing standard if they
make-modifications to their facility's operations.
EPA has made some exceptions to this rule, for
example printed circuit board manufacturers
(primarily to minimize the economic impact of
regulation on these relatively small firms). EPA
defines independent printed circuit board manu-
facturers as facilities that manufacture printed
circuit boards primarily for sale to other compa-
nies. Also excluded from the metal finishing
standard are facilities that perform metallic
platemaking and gravure cylinder preparation
within printing and publishing facilities.
Operations similar to electroplating that are
specifically exempted from coverage under the
electroplating standards.include:
+ Continuous strip electroplating conducted
within iron and steel manufacturing
facilities .
» Electrowinni.ng and electrorefining con-
ducted as part of non-ferrous metal
smelting and .refining .
Electrodepojsition of active electrode ;
materials, electro-impregnation, and
electrofbrming conducted as part of
battery manufacturing
Metal surface preparation and conversion
coating conducted as part of coil coating
Metal surface preparation and imme'rsion
plating or electroless plating conducted
as part of porcelain enameling
Surface treatment including anodizing
and conversion coating conducted as part.
of aluminum forming
Congress is considering reauthorization of the
CWA that could change the standards affecting
metal finishing operations. In addition to
possible congressional changes to the CWA,
EPA also is reviewing the Effluent Guidelines
and Standards for Electroplaters and Metal
Finishers, which were promulgated in the 1970s
and amended in-the 1980s.
EPA also is developing effluent guidelines and
standards for a related industry, the metal
products and machinery industry. Phase 1 of
these regulations was due in-May 1996. These
regulations would have set new effluent limits
for some metal finishers. However, as a result of
comments received,.EP A is considering combin-
ing Phases 1 and 2 of these regulations and
promulgating them in 2 years. Although this
standard contains only cleaning and finishing
21
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" 2, RegLi-Kcrv CKerstew
operations as captKe processes, it is likely that
EPA might integrate the new regulatory options
for metal finishing processes into this guideline.
Under this, scenario, electroplaters and metal
finishers would most likely reference appropriate
sections of the Products and Machining Industry
Guideline to determine their effluent limits.
What is not clear is how this guideline will affect
job shop operations, which are not considered
part of this industry. If job shops are not in-
cluded, different requirements could be devel-
oped for them.
Resource Conservation and
Recovery Act
The Resource Conservation and Recovery Act
(RCRA) of 1976 addresses solid (Subtitle D) and
hazardous (Subtitle C) waste management
activities. Regulations promulgated under
Table 4. RCRA Listed Wastes (EPA 1995a)
Subtitle C establish a "cradle to grave" system
that governs these wastes from point of genera-
tion to disposal. A material is classified under
RCRA as a hazardous waste if the material meets
the definition of solid waste and exhibits one of
the characteristics of a hazardous waste (i.e.,
corrosiveness, flammability, toxicity, or reactiv-
ity, designated with the code "D") or if it is
specifically listed by EPA as a hazardous waste
(designated with the code "F"). Metal finishers
generate a variety of hazardous wastes during the
plating process. Within RCRA subtitle'C, EPA
includes hazardous waste from non-specific
sources in a series of "F" listings. Table 4
presents the F-listed wastes that might be rel-
evant to the electroplating industry.
The universe of RCRA listed wastes is constantly
changing. In some states, the list of specific
Listing
Waste Description
F001
F002
F003
F004
F005
Listings FOOT through F005 are for halogenated solvents. The listing for a particular
site will depend on the type of solvent used.
F006
F007
Wastewater treatment sludges from electroplating operations. This category refers to
sludges produced during the treatment of spent plating baths and rinsewaters.
Wastewater treatment sludges from specific operations not included in this classifica-
tion system are:
Sulfuric acid anodizing of aluminum
Tin plating or carbon steel
Zinc plating (segregated basis) on carbon steel
Aluminum or zinc-aluminum plating on carbon steel
Cleaning/stripping associated with tin, zinc, and aluminum plating on carbon steel
Chemical etching and milling of aluminum.
Spent cyanide plating bath solutions from electroplating operations.
F008
Sludges and residues from the bottom of plating baths where cyanides are used in the
process. »
F009
Spent stripping and cleaning bath solutions from electroplating operations where
cyanides are used in the process.
F011
Spent cyanide solutions from salt bath pot cleaning from metal heat-treating
operations. . . . _
F019
Wastewater treatment sludges from the chemical conversion coating of aluminum.
22
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Chapter 2:1 Regulatory Overview
wastes might be different because they have ' .
added to EPA's list of hazardous chemicals.
A waste can exhibit one or more of the RCRA
Subtitle C characteristics but not be listed as a
specific waste, Waste generated in electroplating
operations that are not specifically listed but
might exhibit a RCRA characteristic include:
* Plating bath sludges (not generated from
' cyanide baths), which might be toxic
because of metal content
Alkaline cleaning baths, which might be
corrosive because of high pH
Rinsewater, .which might have a low or
high pH depending on the contents of the
, preceding bath . . ;
Spent plating baths or cleaning and
pickling solutions containing acids, which
might be corrosive because of low pH or
dissolved metal content (EPA 1994)
To determine what a plater must do to comply
with RCRA requirements, the facility first must
determine its generator status. Generator status
is based upon the amount of waste generated on
a monthly basis. The following criteria
determine the quantity of waste that is regulated
by RCRA: ,
Material remaining in.a production,
process is not counted as wqste until it is
no longer being used.in that process.
Waste discharged directly arid legally to a
POTW in compliance with CWA pre-
treatment standards is not counted
toward RCRA generation total. -
Any-material that is characteristic.or listed
as a hazardous waste, and is accum-
ulated after its removal from the process
before being sent off site for treatment,
storage, or disposal, is counted toward
RCRA Subtitle C generation total.
In general, there are three classes of generators.
Although individual states might have different
names for them, EPA classifies them as:
Large quantity generators: Facilities that
generate more than i,000 kilograms (2,200
pounds) of hazardous waste per month or
that generate or accumulate more than 1
kilogram (2.2 pounds) of acute hazardous
waste at one time.
o Small quantity generators: Facilities that
generate between 100 kilograms (220'
pounds) and 1,000 kilograms (2,200 pounds)
of hazardous waste in any calendar month.
* Conditionally exempt small quantity
generators: Facilities that generate less
than 100 kilograms (220 pounds) of
hazardous waste per month or that generate ,
less than 1 kilogram (2.2 pounds) of acute "
hazardous waste in any calendar-month.
Each state has varying degrees of regulation for
the three generator classes. At a minimum,
however, EPA requires each class to comply
with the requirements listed in'Table 5.
Toxics Release Inventory Reporting
Metal finishers must publicly report many of the
chemicals they use in plating under the federal
Toxic Release Inventory (TRI) reporting require-
ment. Facilities report information on a TRI data
form (Form R) for each toxic chemical that is
used over the threshold amount. Basic informa-
tion that is reported in a Form R i nc 1 udes:
Facility identification ...-''
Parent company information.
"> Certification by corporate official ,
«. SIC code
«. Chemical activity and use information
Chemical release and transfers
Off-site transfer information
On-site waste treatment
« Source reduction and recycling activities
The releases and transfers reported on a Form R
include:
V Emissions of gases or partic'ulates to the
- , air ." '' ,
23
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Table 5: EPA Regulations for the Three Generator Classes
Category
Requirements
Large Quantity Generators
Notify the EPA and obtain an EPA ID number
Store waste for no more than 90 days
Comply with container standards and tank rules
Prepare and retain a written Contingency Plan
Prepare and retain written training plan including annual
training of employees
Prepare a written waste minimization plan'
Dispose of hazardous materials only at a RCRA permitted site
Only use transporters with EPA ID numbers
Use proper Department of Transportation (DOT) packaging .
and labeling
Use the full Uniform Hazardous Waste Manifest
Place a 24 hour emergency number on all manifests
Report serious spills or fires to the National Response Center
Obtain a DOT registration number for shipments over 5,000
pounds
' Keep all records for 3 years
Make sure that any treatment or recycling done onsite is
permitted
Report missing shipments in writing
Submit biennial reports of hazardous waste activities, including
' waste minimization ^^
1
Small Quantity Generators
Notify the USEPA and obtain an EPA ID number
Store waste for no more than 180 days (270 days if the waste
is shipped more than 200 miles)
Comply with container standards and tank rules
Dispose of hazardous materials only at a RCRA permitted site
Only use transporters with EPA ID numbers
Use proper Department of Transportation (DOT) packaging
and labeling
Use the full Uniform Hazardous Waste Manifest
Place a 24 hour emergency number on all manifests
Post- emergency response telephone numbers near telephones
Provide informed employee training
Make sure that any treatment or recycling -done onsite is
permitted
Report missing shipments in writing
Keep all records for 3 years
Conditionally Exempt Small
Quantity Generators
Avoid accumulating more than 1,000 kilograms (2,200
pounds) of hazardous waste onsite at any one time
Send waste to a facility that is at least approved to manage
municipal or industrial solid waste
24
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Chapter 1-, iUsuurar/ .Q\«\«Y<
Wastewater discharges into rivers',
streams, and other bodies of water
Releases to land on sife including landfill,
surface impoundment, land treatment, or
other mode of land disposal
Disposal of wastes in underground
injection wells
Transfers of wastewater to POTWs
Transfers of wastes to other off-site
facilities for treatment, storage, and
disposal ' ,' ' .
A facility must fill out Form R if it:
* Is included in SIC codes 20 to 39
* Has 1Q or more full-time employees
Manufactures, processes, or "otherwise
uses" any listed material in quantities
equal to or greater than the established
threshold for the calendar year '
The manufacturing and processing thresholds
have dropped over the reporting years from
75,000 pounds in 1987 to 25,000 pounds in 1989.
For a chemicaP'otherwise used," the threshold
amount is 10,000 pounds. The following list
presents the top 22 chemicals in the TRI database
for metal finishing (SIC 3471)Trom 1987
through 1990 (the list ranks the chemicals in
order of decreasing release quantities with
national TRI rankings presented in parentheses):
Acids ; '
Sulfuricacid (1) > , .
Hydrochloric acid, (2) _....'
.Nitric acid (7)
Phosphoric acid (17) . ' _
' Metals
Nickel compounds (8)
. Zinc compounds (11)
Chromium compounds (12)
Zinc (14)
Nickel'(16) V .' .:
' Copper (20)
Chromium (22) .
Copper compounds. (23)
Solvents
1,,1,1-trichloroethane (3)
Dichloromethane (methylene. chloride). (9)
Tetrachloroethylene (1-3) . .
; Methyl ethyl ketone (15)
Toluene(9)
Cyanide ,
Cyanide compounds (24)
'Other
Freon 113(10) :
Technical assistance providers can use TRI
data to develop an aggregate picture of the ;
releases and transfers from the metal'finishing
industry. ,' ' .
References
EPA. 1995a. Profile of the Fabricated Metal
Products Industry. Washington, DC: Office of
Enforcement and Compliance Assurance,
EPA. 1995b. Metal-Prating Waste Minimiza-
tion. Arlington, VA: Waste Management Office,
Office of Sol id Waste. '
EPA. 1994. Sustainable Industry: Promoting
Strategic Environmental Protection in the
Industrial Sector: Phase I Report Metal, Finish-
ing Industry. Washington, DC: Office of Policy,
. Planning and Evaluation.
Haveman, Mark. 1995. Profile of the Metal
. Finishing:Industry. Minneapolis, MN: Waste
Reduction Institute for Training and Applications
Research.
25
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-------
Planning Pollution
Prevention Programs at a
Metal Finishing Facility:
How can assistance providers and regulatory
compliance staff sell pollution prevention
options to a mejtal finisher?. The most important
point that an assistance provider can make to a
metal finisher is that pollution prevention can
help them achieve regulatory compliance while
saving money. The savings associated with
recapturing and reclaiming precious metals are
obvious; the value of the recovered metal in
many cases outweighs the:cost of reclamation
processes. Overall, the benefits associated with
pollution prevention include: :
, Reduced operating costs/overhead:
These savings result in reduced utility
charges, water/sewer fees, wastewater
treatment costs, waste disposal expenses, ,
permit discharge fees, analytical monitoring
and reporting costs, and increased potential
for chemical recovery. : .
Reduced manufacturing costs: Facilities
can save money on reduced materials costs
(e.g.", reduced plating bath solution pur-
chases), water costs, and anode loss.
Product quality improvements: Pollution
prevention techniques often increase the
quality of rinsing, reducing spotting and
staining of the workpiece. Often pollution
prevention increases the process controls of
the plating operation, improving the predict-
.. ability/performance of process solutions and
decreasing reject rates.
Environmental risk reduction: Pollution
prevention projects can result in reduced
non-compliance enforcement actions;
environmental and worker health liability;
and risk of on-site contamination via spills,
releases, and leaks. .
A facility potentially can realize other
benefits from the implementation of a compre-
hensive pollution prevention program. Source
reduction can lower insurance costs, protect
property values, and improve relationships with
financial institutions. Even though pollution
prevention has clear economic advantages and
the techniques are simple, inexpensive, and time
proven, many facilities still do not have signifi-
cant source reduction programs (Haveman 1995),
Planning
One of the keys to developing'a successful
pollution prevention program is planning.
Assistance providers can work with facilities to
implement planning programs, assist in estab-
lishing baseline measures, and identify potential
pollution prevention projects. The key steps to
starting a pollution prevention program include:
Obtaining management support and
involvement
Establishing an in-house pollution pre-
; ' ventidn team .
Getting companywide involvement
Management Support
The support of company management is essential
for developing a lasting and successful pollution
prevention program. The level of success that a
metal finishing plant can achieve in reducing
waste generation appears to depend more on
management interest and commitment than on
technical and economic feasibility, particularly
for source reduction technologies that require
process modifications or housekeeping improve-
ments (Noyes 1989).
At the outset of the program, management
endorsement is needed to help identify the
pollution prevention team and give credence to
the planning effort. Throughoutthe program,
company management, can support the team by
endorsing goals and implementation efforts,
communicating the importance of pollution
27
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3, P'Jrmrg Pc'lucion Prevention Programs at a Mecal Finishing- Facility
prevention, and encouraging and rewarding
employee commitment and participation in the
effort (Dennison 1996).
Some companies see only the barriers they face
in implementing a project and use these as
excuses for not implementing pollution preven-
tion. Other firms find solutions to overcome
obstacles and reap the benefits of a successful
pollution prevention project. Technical assis-
tance providers should stress to management that
a successful program has a wide range of ben-
efits. These benefits include cost savings as well
as reduced liability and enhanced company
image. Assistance providers also should inform
management that an initial labor cost is incurred
in organizing and implementing a pollution
. prevention program. Using a technical assis-
tance provider can minimize these costs but an
up-front resource commitment must still be
made. Case studies often can highlight the
benefits that other companies have realized from
implementing pollution prevention programs.
Providers can help facilitate management support
by developing a plan that sells pollution
prevention to a company's executives. The
presentation on pollution prevention drivers and
barriers in Chapter I should help users of this
manual to find the appropriate basis for selling
pollution prevention. Successful management
initiatives that have promoted pollution preven-
tion include developing a corporate policy that
makes pollution prevention a mandate, incorpo-
rating pollution prevention success into perfor-
mance evaluations, and offering financial
incentives for meeting pollution prevention goals
or for finding pollution prevention opportunities.
Obviously, each firm is different and, therefore,
the assistance provider's approach to each
company's leadership should attempt to address
their specific interests and priorities as
manifested by the corporate culture. Identifying
these interests and priorities is a challenge for
any assistance team. Many technical assistance
programs require active management participa-
tion in the assistance process as part of their
agreement to conduct an on-site visit. On these
visits the teams discuss their priorities and
pollution prevention in relation to those
priorities. Technical assistance providers should
also stress to management that planning is an
ongoing task.. Once the initial plan is completed
the facility should continue to re-evaluate their
facility to identify areas that can be improved
(CAMF 1995).
Establishing the Team
A successful pollution prevention program
requires not only support-from management but
also input and participation from all levels of the
organization. To champion the effort, every
pollution prevention program needs an effective
pollution prevention coordinator. Assistance
providers can identify the team leader and work
with them on developing their team and .suggest-
ing ways for the facility to implement its pollu-
tion prevention program.
The pollution prevention team should include
employees who are responsible for planning,
designing, implementing, and maintaining the
program. A team approach allows these tasks to
be distributed among several employees and
enables staff from different parts.of the company
to have input into the planning process.
Members of the tedm are typically responsible
for:
Working with upper management to set
preliminary and long-term goals
Gathering and analyzing information
relevant to the design and implementa-
tion of the program
» Promoting the program to employees and
educating them on how they can partici-
pate in the effort
Monitoring and reporting to manage- .
ment on the progress of the program
(Dennison 1996) ,
The ideal size of the team depends on the size of
the organization. In small companies, the team
can consist of one person who wears many hats
or the company manager and a technical person.
In larger companies, the team might include
environmental managers, building supervisors,
technical staff, maintenance staff, marketing
staff, purchasing staff, and other interested
employees (Dennison 1996).
28
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Chapter 3; Planning Pollution.Prevention Programs 31
External personnel such as technical assistance
providers or consultants-can complement the
team by providing expertise. These people often
can offer auditing expertise,as well as
knowledge of pollution prevention and environ-
mental laws and regulations. However; external
people will be unfamiliar with thefacility's '
operation. Once the team is established, assis-
tance providers and regulatory .staff should
encourage the facility to.take the following steps
to properly evaluate the options for reducing
pollution:
Define and identify the facility's -
objectives: Clearly identify/quantify, and
rank the facility's objectives. For example,
at some facilities compliance with effluent
limits and quality rinsing are primary
concerns while optimized worker efficiency
and cost are secondary concerns.
Define criteria for evaluating pollution
prevention options: Clearly define what
constitutes a feasible option. Items to
consider beyond technical feasibility include
economic feasibility, quality standards, and
the effect of the option on the overall
; process. '
Assessing the Facility
Once the team has defined its objectives and
criteria for a pollution prevention program, the
next step is to assess the facility. Beyond the ,
facility tour, useful information for the assess-
ment can be obtained from sources such as:
;_ \ - ' - - ' . -.
Engineering interviews and records
Accounting interviews and records
* Manifest documents
Vendor data
V Regulatory documents
Sampling data
The following pages provide an overview of the
typical steps involved in a facility assessment.
Characterize the Facility
Locate or prepare drawings of the layout of the
process and storage areas. These drawings
.should be to scale, showing the location of all
relevant equipment and tanks and identifying:
* Floor space of facility . ".> . ,
Plating and other process lines
Gutters, sumps, and sewer lines
Water lines, control valves, and flow
regulators .
Available rinse stafio'ns
Location of each process tank
Piping plans should be reviewed for cross .
connections and illegal connections. Facilities
can also use this information to develop process
flow diagrams to which baseline information can
be added, resulting in a diagram that represents
current operating practices. ' ,
Gather Baseline Information
Review all operations of the facility that relate to
chemical or water use. Some of the information
that should be collected includes:
General Facility Information
' Estimates of production units such as
square meters plated and number of
.'.'' parts; barrels, or racks to pass through a
line sequence
Types of parts plated
,«. . Chemical purchases
Chemical inventory
Chemical use rates (where each chemical
is used and how much is used in each
/ process)
» Quality of makeup water
Facility-wide water use rates
Wastewater treatment operating
procedures
Wastewater content
Sludge management procedures
» Sludge content analysis
Waste management costs
+ Raw material costs
29
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Ch3ct«r 3: Pljnmng-Pollution Prevention Programs at a Metal Finishing Facility
+ Compliance problems
* Control processes
* Sampling and analysis information
+ General amount of drippage onto the
floor
From Each Line
Rack/barrel design and condition
Actual operating procedures
Operating parameters
Production rates' (i.e., square feet pro-
cessed per "hour)
From Each Plating Process Bath
Batch dumps that result from the process
Dragout rates from each process tank
Bath evaporation rates
* Process solution composition
Actual operating parameters for each
process tank
+ Dump schedule for each process tank
From Each Rinsing Process
Rising and draining times on automatic
lines or efficiency of operator on manual
lines
Dragout measurements,
Dragin/contaminant loading rates
Rinsewater quality requirements
Flow control techniques
Wastewater flow rate from each rinse
tank
Dragout reduction techniques used .(Hunt
1988)
TableS summarizes the types of data and
information that is useful for conducting an
assessment.
Evaluate the Design of, the
Facility's Process
Some technologies might require the addition of
tanks or modifications to the plating process.
The facility should evaluate its ability to
dptimize the process and to accommodate
changes to the process (Ferrari 1995).
Developing a Process
Flow Diagram
Once all the information has been gathered and a
map of the facility exists, a process flow diagram
can be developed. Process flow diagrams break
down the facility into functional units, each of
which can be portrayed in terms of material
inputs, outputs, and losses. Developing a process
map helps the facility understand how the
production process is organized, providing a
focal point for identifying and prioritizing
pollution prevention opportunities (EPA 1996).
The process map should cover the main
operations of the metal finishing facility and any
ancillary operations (e.g., shipping and receiving,
chemical mixing areas, and maintenance opera-
tions). Separate maps can be generated for
ancillary operations. Another important area to
cover is "intermittent operations" or operations
that do not occur on a regular basis. The most
common intermittent operation is cleaning and
maintenance. A great many pollution prevention
opportunities can be found by examining inter-
mittent operations (EPA 1996).
It is also useful and important to include
operations that are upstream and downstream of
the metal finishing operation. Pollution and
waste issues often cross facility boundaries. An
understanding of where the pollution originates
from can assist in identifying pollution preven-
tion opportunities.
Identifying Pollution
Prevention Opportunities
Using the information obtained in the facility
assessment, the team should'compile a list of
technically feasible options. Brainstorming
sessions with the team can provide innovative
ideas. Researching case studies of other compa-
nies also can provide valuable information.
Other potential sources of ideas include suppliers
and consultants. At this point, all ideas should
be taken seriously and none should be rejected
automatically for reasons such as "that's already
30
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Chapter L Planning Pollution Prevention Programs 31 3 Meul f\wst\wl r
Table 6. Overview of Assessment Information (BCDNRP 1994)
Process
Data
! | Production Processes and
Operational Procedures
Material Use, Handling, and Storage
Waste Management
Production rates
* Process description and efficiencies
Condition of 'process equipment
Sources or potential sources of leaks/spills
> Operating procedures
Maintenance procedures and schedules
Energy/utility use and costs.
Operating and maintenance costs
Material inventory , : . .
Raw material accounting (how much of the'
material is used in the process, how much is^lost
through' evaporation or other means, and how
much enters the wastestream)
Raw material costs ',--' -
Material transfer and handling procedures
Storage procedures , .
Sources of leaks or spills in transfer and storage
areas , ,
Condition of pipes, pumps, Janks, valves, and
. storage/delivery areas
Activities, processes, or input materials that
generate wastestreams
> Physical and chemical characteristics of each stream:
* Hazardous classification of each wastestream
Rates of generation of each wastestream and
.variability in these rates ;
« Current treatment and disposal system for each
wastestream ,
* Cost pf managing wastestream (e.g., feesjabor, -
and disposal costs).
« Operating procedures for waste treatment units
Efficiency of waste treatment units
o.Quanfrty'and characteristics of all treated wastes,
sludges, and residues _
Wastestream mixing (hazardous wastes mixed with
non-hazardous waste)
«> Current waste reduction and recycling methods
being implemented ,
o Effectiveness of those methods
31
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C"3S5«' 3 f '*<*'"""2 Pollution Pra\encion Programs at a Metal Finishing Facility
been tried" or "it w ill ne'ver work" or "it's too
expensive."
After all options have been identified, the team
should screen the options based upon the
objectives and criteria set in the assessment
phase. It is likely that each option will fi.t into
one of the following categories:
'«'' u
«. Impractical idea
+ Ideas needing more detailed information
and study
*
Ideas that can be implemented with a
minimum of effort and cost
Each company will weigh an option differently
based upon its criteria (e.g., cost and compliance
issues). This initial evaluation will assist the
company in identifying a subset of options that
deserve further investigation. Generally, the
number of options requiring detailed information
and study should be pared to a minimum (Ferrari
1995).
When screening ideas keep in mind that an
important principle of manufacturing excellence
is maximizing the productivity of the plating
cycle. Some pollution prevention options can
increase productivity while others can increase
the cycle time, sometimes substantially. Produc-
tivity and output in plating operations are influ-
enced by a number of factors. Technical
assistance providers should be aware of how
their suggestions can affect the productivity of
the plating process when screening options. The
following is a description of the major factors
that can affect plating line efficiency:
* Part geometry: The shape and size of the
workpiece will greatly influence the
throughput of a plating, line. Larger complex
pieces usually must be rack plated whereas
small parts can be barrel plated together.
Part geometry also is an important factor in-
determining dragout rates.
« Solution concentration and temperature:
A change in the concentration of the plating
solution can have a critical impact on the
plating process. Concentrations that are not
high enough can result in increased reject
rates, while higher concentrations can
increase dragout and waste generation.
Plating specifications: Plating thickness,
corrosion resistance, and brightness are the
- primary quality specifications in
electroplating. These specifications and the
steps needed to accomplish them will greatly
affect the productivity of the line, and the
. waste generated.
Masking or plugging: The amount of
masking and plugging required to plate the
workpiece correctly also affects productivity.
Masking or plugging prevents metals from
being deposited on inappropriate areas of the
part. In many electroplating applications
only a portion of the part might need to be
plated.
Single load versus long runs: The need to
change processes frequently to accommodate
different plating jobs will reduce
productivity when compared to scheduling
long runs of the same part.
Rinsing methods: Productivity also is
affected by the type of rinsing method used.
For instance, countercurrent rinsing increases
cycle time significantly when compared with
other rinsing methods.
Unfamiliar parts: Familiarity with certain
substrates, process chemistries, particular.
production specifications, or similar
workpiece geometries will assist a facility in
increasing productivity. Although produc-
tion specifications often are available and
provide guidance, working with an un-
familiar plating line can decrease plating
productivity (Haveman 1995).
By gaining information on these types of issues,
technical assistance providers can provide better
suggestions on pollution prevention options
when assessing a facility.
Analyze and Select
Options
Once a short list of options has been identified,
the team should begin the process of deciding
which options are appropriate for the facility.
During this phase, the team should be clear on
32
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Chjpter 3: Pl3rmmg.Poilut.ion.Prevention Programs at a Meui F i
the company's objectives and criteria. Depending
oh the goafs of the company, cost effectiveness .
might not be the overriding goal. Option
screening should consider these questions:
V Which options will best achieve the goal
pf waste reduction? ,
What are the main benefits to be'gained
by implementing this option?
V- Does the technology exist to develop the
. option? ." - ' '
4 How much does it cost?
*
Can the option be implemented without
major disruptions in production?
* Does the option have a good track
, record.? ^ ' - . - ,
What are other areas that might be
affected by implementation of the option?
In addition/a company that believes cost
effectiveness is critical should consider the long-
term costs associated with a particular option.
For instance, the team might be inclined to .,
,.' disregard an option because the initial capital
outlay is high, hoV/ever, upon examining the
' total cost associated with the measure, the team
might find that it could yield impressive savings
in several years (Dennison 1996). In order to
identify the total costs associated with'both
existing processes and new processes, the facility
might have to consider costs that traditionally
have not been incorporated into capital acquisi-
tions. For more information on identifying.these
costs, assistance providers can refer to atraining
manual developed by the Northeast Waste
Management Officials'Association for conduct-
ing financial assessments of pollution prevention
projects. . .,.'.-;
Pilot Test or Validate Preferred
Options
Once the facility has determined its preferred
option(s), it should pilot test the program prior to
full facility implementation. A pilot test can
highlight any installation or implementation
issues. At this point, the technical assistance
! provider has completed his or her job. However,
if issues arise in the pilot test phase, he or she
can be called in to troubleshoot. or suggest other
alternatives.
Procure/Implement New System
Once the hew system is installed, employees
should be informed about the project and the
importance of.their cooperation and involve-
ment. Operators should'be trained on how to
properly operate the system. Companies should
update employees on the expected benefits and
the progress made in achieving the goals of the
system. Frequent updates on the progress of the
program can increase staffs stake in the pro-
gram. In order to sustain employee interest in
the, program, facilities should encourage employ-
ees to submit new ideas for increasing the -
effectiveness of the program. By working with
employees as a team, assistance providers can
aid in the development and successful implemenr
tation of a pollution prevention program.
: Following these steps can provide the facility
with the necessary information for determining
the best opportunities for implementing pollution
prevention projects. This methodology is useful
because the cost to correct a failed system can
greatly, exceed the cost .of proper initial imple-
mentation. A few critical rules should be kept in
mind when helping a company consider new
projects:
No single system or process is right for all
applications. A vast range of variables
can affect the physical and chenriical
characterization of process baths and.
rinses which in turn affects the selection
and performance of a pollution preven-
* tion system. Specific variables include
process bath formulations, work type,
work loading rate, and wbrkpiece
geometry.
Unless the scope of the application is
small, the new system will likely involve
more than one process unit or subsystem.
Prior to investing m any.'new system, the
team should take the time to evaluate
and understand the process, preferably
including a rigorous pilot test in the
facility.
33
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Ouoter 3: P'jnr-j Pci'uucn Prevention Programs at J Metal Finishing Facility
The team should recognize that the
provider of any new system (including
designer and sales staff) is a new partner
at the facility (Ferrari 1995).
The Canadian Association of Metal Finishers '
prepared a detailed document on planning a
pollution prevention program in a metal finishing
facility. Information on the document can be
found by calling the Metal Finishing Centre.
Their telephone number is located in the resource
section in Appendix B. .
Keeping the Program
Going
If the technical assistance provider uses the team
approach described earlier, many individuals
from all areas of the company will have a chance
to share their perspective on waste problems and
solutions. Working from the process map, the
team will go onto the plant floor to discuss the
process with those directly involved (i.e.,
supervisors and front-line production workers)
and develop a baseline to measure all future
efforts. The assistance providers can suggest to
the facility that they develop a mechanism for
soliciting input from all employees in the future.
Cc ' nunicating the success of the program also
can keep employees involved. The facility can
use the baseline information developed from the
facility assessment phase to communicate
progress that the facility has made.
References
Broward County Department of Natural
Resource Protection (BCDNRP). 1994. Pollution
Prevention and Best Management Practices for
t\fetal Finishing Facilities. Fort Lauderdale, FL:
Pollution Prevention and Remediation Programs
Division.
Canadian Association of Metal Finishers
(CAMF)etal. 1995. Metal Finishing Pollution
Prevention Guide. Ontario, Canada: Great Lakes
Pollution Prevention Initiative.
Dennison, Mark S. 1996. Pollution Preven-
tion Strategies and Technologies. Rockland,
MD: Government Institutes.
EPA. 1996. Draft CSI Metal Finishing
Compliance Manual. Washington, DC: United
States Environmental Protection Agency.
Ferrari, Robert F. 1995. Wastewater Recy-
cling: Myth vs. Fact. Providence, RI: Ferrari'
Engineering.
Haveman, Mark. 199'5. Profile of the Metal
Finishing Industry. Minneapolis, MM: Waste
Reduction Institute for Training and Applications
Research.
Hunt, Gary E. 1988. Waste Reduction in the
Metal Finishing Industry. The International
Journal of Air Pollution Control and Waste
Management. May. pp 672-680.
Noyes. 1989. Ha-ardous Waste Reduction in
the Metal Finishing'Industry. Park Ridge. NJ:
Noyes Data Corporation.
34
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Common Pollution
Prevention Practices
Pollution prevention has emerged as an
effective tool for companies to attain' compli-
ance with environmental requirements.. As stated
in the previous chapter/using pollution preven-
tion as the primary technique for attaining
compliance also can reduce operating costs and
increase profits. Metal finishing firms have
achieved widespread success in reducing pollu-
tion using everything from improved housekeep-
ing to advanced technologies. ,
The primary goal of this manual is to describe
the major pollution prevention techniques used in
the metal finishing industry. Some of the
technologies involve simple installations, for
example, retrofitting pipes or drainboards. These
methods are cost effective and can be imple-
mented in house without outside consultation.
Other methods such as metal removal from
liquids and total recycling in a closed-loop
system require large capital expenditures.
Although EPA and the states do'not mandate
recycling or zero discharge, urging companies to
plan new equipment purchases with these, goals
in mind should prove cost effective in the long
run and help companies sustain environmental
compliance and profitability. '
This manual does not attempt to make blanket
judgments as to the economic feasibility of the
pollution prevention options that are presented.
The conditions: in each facility vary, and the
characteristics and quantities of the platables are
diverse. However, loss of raw materials in metal
' finishing can affect at least five distinct cost
categories. Facilities should consider the
following in any financial evaluation of pollution
prevention options: ;
. Replacement of raw materials
Removal of the materials from the waste
water before discharge (i.e., pretreatment)
Disposal of removed materials
Replacement of water
,> Processing of wastewater by local sewer
authorities
Assistance providers should take advantage of-.
the expertise and knowledge of local conditions
that a facility operator possesses when working
with a firm. Assistance providers should also .
keep in mind that current practices are often the
result of emplo'yee training. Employees might
not know why the facility uses certain work
' practices. In some cases, the real reason, for a
practice no longer applies to the current
situation.
The following sections present some of the
overall strategies that a'company should incorpo-
rate into a successful pollution prevention
program including employee training, house-
keeping, leak prevention, spill prevention,
inventory management, chemical sample testing.
, and water quality monitoring.
Employee Training
Employee training can provide workers with the
information necessary to minimize waste
generation. Companies should train employees
in the proper handling of chemicals and the
reasons for implementing safer techniques.
Employee training should also cover safety,
rinsing techniques, and chemical hazards. For
instance, only trained employees should be
responsible for mixing bath solutions and setting
flowlevels.
Companies should realize that they might
experience increased training costs to capture
these benefits (APPU 1995). In general, this
training produces a quick payback.
35
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OJo:«r 4. CcTf^en Pollution Prevention Practices
Employee Training Case Study
EPA documented a firm that achieved a 32.
percent reduction in sludge and a savings of
52,000 in off-site treatment costs by a facility
that Implemented an employee training program
tn plating and wastewater treatment operations.
The changes improved control of water levels in
rinse tanks, improved sludge separation, and-
resulted in higher levels of surfactant being
recycled back into the process. No capital or
operating costs were incurred. (EPA 1989a)
In addition, firms could consider designating
specific employees to be responsible for specific
tasks and properly training them in appropriate
work practices so that they can do the job
correctly. The tasks could include inspections of
tanks, raw material distribution, and bath mixing.
Properly trained employees are more likely to:
Understand how to operate baths at peak
efficiency
Minimize spill generation
Improve the consistency of solution
formulation and minimize the number of
bad baths
Housekeeping and
Preventative Maintenance
Although the benefits of improved housekeeping
can be difficult to quantify, simple housekeeping
improvements often can provide low-to-no-cost
opportunities for reducing waste. Preventative
maintenance and proper equipment and materials
management can minimize leaks, spills,
evaporative losses, and other releases of
potentially toxic chemicals. A plant can reduce
waste by developing inspection and maintenance
schedules, controlling the purchasing and
handling of raw materials, removing dropped
parts quickly from baths, keeping filters and
other process equipment in good working order,
and authorizing a limited number of employees
to accept and test samples from chemical suppli-
ers (UNCE 1995).
Employees should quickly remove dropped parts
and tools from process baths to reduce contami-
nation of the bath. Firms can help speed up such
removal by having rakes located in handy
places. Shops also should coordinate
maintenance schedules with inspection schedules
to ensure that equipment is operating at optimal
efficiency. Some of the benefits of improved
housekeeping and preventative maintenance
include:
Optimal efficiency cff machinery and
equipment
i i
Prevention of production losses
Reduced reject rate
Reduced effluent violations
Decreased amounts of waste from spills
occurring as a result of'equipment failure
Increased worker safety
Companies that have effective maintenance
programs can see an increase in up-front labor
costs, however, these costs usually are offset by
decreased downtime (APPU 1995).
Leak Prevention
Inspecting tanks and pipes for leaks can lead to
immediate reductions in waste at little or no cost.
Firms should inspect production, storage, and
waste treatment facilities regularly to identify
leaks, improperly functioning equipment, and
other items that could generate waste.
Inspections can be as simple as walking by tanks
and visually inspecting them or as complex as
formal inspections that include checklists and a
log of findings. Frequent inspections can
identify problems before they become signifi-
cant. Piping systems, filters, storage tanks,
defective racks, air sparging systems, automated
Leak Prevention Case Study
EPA documented a firm that achieved a 40 percent
reduction in solvent loss and savings of $4,800
annually in raw material and disposal costs by.
changing operating procedures and scheduling of
two in-line degreasers that use tetrachloroethylene
(TCE). Prior to implementation, 3,510 gallons of
TCE were lost per year. No capital costs or operating
costs were incurred and the payback period was
immediate. (EPA 1994)
36
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Chapter 4: Commori.Poilviaon ?r«s
flow controls,and even operators" production
procedures (including drain time and-rinse
methods) should be inspected regularly: Inspec-
tion routines could include setting up calibration
schedules on all temperature, speed controls, and
pH meters; instituting-an .employee training
program; or implementing a computerised
tracking system for preventative maintenance
procedures (Cushnie 1994). ; ;
Spill Prevention
Spills can be reduced by training personnel in
improved material handling and spill prevention
methods. Training should include proper use of
spouts, funnels, and drip .pans during material
.transfer; design of drainboards to eliminate spills
and reduce dragout; maintenance of liquid levels
in tanks to reduce overflow spills; use of mops or
pigs to clean up spills (as opposed to the use of
' an absorbent that must be treated or disposed of
as a hazardous waste); and use of containment
berms to contain spills. Training employees in
proper spill prevention techniques can assist in
reducing waste;generation and disposal costs by
: eliminating spills and overflows (APPU '1995).
Spill Prevention Case Study
EPA documented a firm that achieved a 25.percent
reduction in hazardous waste shipmenfs, a .50
percent reduction in chrome waste production,
and a 95 percent reduction m chromic wastes as a
result of severai.improvements. These improve-
ments included installing a rain cover for outdoor -
tanks, repairing leaks in tanks and pipes, and
installing a new treatment system that uses
caustics and sodium bisulfite, at a metal finishing
facility, the capital cost was $30,000 and disposal
and feedstock savings, were $T5,QOO annually.
1 (EPA 1994
Chemical Handling Case Study
'EPA documented a company that achieved a
49 percent reduction in wastes from 310 to -
152 tons per year with a sayings of ,$7,200 in
disposal and feedstock costs. The company
limited access to solvents to the foreman and
reused solvent from upstream operations in
downstream machine shop operations.,Prior
to implementation, waste consisted of reactive
dnions> waste oils, ana1 halogenated solvents.
(EPA1989b)
Inventory Management:
Chemical Purchasing,
Tracking, Storage, Use,
and Handling
Controlling the purchasing and handling of
materials can significantly reduce Waste genera-
tion. Firms should purchase chemicals in the
smallest possible quantities, reducing stockpiles
of raw materials. Chemicals that are bought in
bulk can be cheaper up front, but material
remaining.after the product has expired will
require disposal. Companies should store
materials in a locked space and limit access to a
few designated employees. By controlling
access to raw materials, operators will ensure
that containers are completely empty before new
containers are opened,(Cushnie 1994).
Companies should label materials with shelf life ,
dates to ensure that they have not degraded.
Companies also should use a first-in, first-out
policy. These practices will reduce the potential
for spills, decrease the likelihood of mixing-poor
process baths; and minimize waste generated
from the disposal of obsolete materials. Man-
agement also should establish standard operating
procedures for inventory control and purchasing,
working with suppliers to take back empty or
off-spec containers (UN.CE 1995).
In addition, firms should develop strict proce-
dures for mixing chemicals. Mixing procedures
should be designed to minimize spills, to provide
correctly mixed baths, and to ensure that the
baths are operated at the lowest possible
concentration to reduce dragout loss.
Chemical Sample Testing
Many suppliers provide metal finjshers with a
variety of process chemicajs for testing.
However, the material that the company does not
use stockpiles at the site and must eventually be
disposed of, increasing waste generation. If
possible, metal finishers should stipulate that test
samples will be accepted only if the supplier
agrees to take back leftover samples. The
unused portion of analytical samples taken from
37
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Chapter 4. Ccmmon Potlut.on Prevention Practices
process baths should be returned to the process
baths. Furthermore, using a bench test rather
than implementing a full-scale test in a process
bath will reduce waste generated by chemical
testing (Cushnie 1994).
Maintaining Incoming
Water Quality
Surprisingly, few metal finishers scrutinize the
quality of incoming water in their facility.
Companies use water throughout the finishing
process, in the cleaning process; and, most
importantly, in the rinsing process. Water also
is used as process bath makeup. Water quality
can impact process efficiency and waste genera-
tion significantly. Whether a problem exists is
based on many factors including the level of
water cleanliness, the sensitivity of the plating
chemistry, and the evaporation rate of the
system. Hardness in the water decreases the
ability of the water to rinse effectively and
creates scales on heated surfaces. Some surface
water contains high concentrations of calcium,
magnesium, chloride, and other soluble con-
taminants that can build up in the bath and
possibly reduce bath life and increase sludge
generation. Companies should examine the
quality of their incoming water to determine if
some treatment of the water is required prior to
use in the metal finishing process. For instance,
in the Mid%vest the use of deionized water is
more common mainly because of the presence
of hard water. Companies can correct this
problem by using water softeners that are
relatively inexpensive or by deionizing their tap
water (Gallerani 1990).
In many baths," the total dissolved solids content
of the water tends to accumulate in the rinsing
system and plating bath. For example, in
closed-loop systems, impurities from many
sources tend to build up in process baths.
Common contaminants from tap water are
calcium carbonate or bicarbonate and, to a
lesser degree, chlorides or sulfates. Alkaline
baths especially tend to absorb carbon dioxide
from the air. Carbon dioxide combines with
carbonate contamination in tap water and can
cause carbonate levels in these baths to rise
quickly. When a firm is not able to discharge
Deionized Water
Advantages
Improves plating quality
Extends bath life
Increases rinsing efficiency
Reduces water use
Reduces sludge generation
Disadvantages
Increased costs
(APPU 1995)
bath as dragout, as is the case in closed-loop
systems, the level of carbonates will tend to rise
requiring additional treatment for the bath. In
this case, normal procedures for sodium baths
would be to chill a side stream from the bath to
precipitate the carbonates and regain control.
Similar problems exist for almost all baths in one
way or another. For example, metal impurities
can build up from dropped parts or anode
impurities. Organic additives combined with
metals in the tap water can increase containina-
tion. In each case, the question is the same:
How can the bath be treated, and does the
problem occur rapidly? In some cases, the
problem might never occur or might occur so
slowly that bath life is not a concern. For
example, baths that degrade themselves, such as
chromating baths, normally are changed fre-
quently so that water quality problems never
occur. As with all pollution prevention technolo-
gies, facilities have to examine their situation
and determine whether they prefer using deion-
ized water.
References
Arizona Pollution Prevention Unit (APPU).
1995. Metal Finishing in Arizona: Pollution
Prevention Opportunities, Practices and Cost
Benefits. Phoenix, Arizona: Arizona Department
of Environmental Quality.
Cushnie, George. 1994. Pollution Prevention
and Control Technology for Plating Operations.
Ann Arbor, Michigan; National Center for
Manufacturing Sciences.
EPA 1994. Summary of Pollution Preven-
tion Case Studies with Ecotiomic Data. Washing-
ton, DC: United States Environmental Protection
Agency.
38
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Chapter 4: Common Pollution Prevention Practices
EPA. 1989a. Case Studies from tht? Pollu-
tion Prevention-Information Clearinghouse:
Electroplating. Washington, DC: United States
Environmental Protection Agency.
" EPA. 1989b.. Pollution Prevention in Metal
Manufacturing - Saving Money Through Pollu-
tion Prevention. Washington, DC: United States
Environmental Projection. Agency.
Gallerani, Peter A. 1990. Good Operating
Practices in Electroplating: Rinsewaier and
Waste Reduction. Boston, MA: Massachusetts
Department of Environmental Protection.
University of Nebraska Cooperative Exten-'
sion(UNCE). 1995." ,4 Tool Kit/or Metal
Finishers. Lincoln, NE: University of Nebraska.
39
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-------
Pre-Finishing Operations
Virtually all products that are finished require
some pre-finishing procedure such as
cleaning, stripping, or pickling. Without a -
properly cleaned surface, even the most expen-.
sive coating will fail to adhere or protect the
workpiece. Depending on the process being
performed, the degree of cleanliness will vary.
Finishing operations such as, phosphating,
chromating, or electropolishing do not require as
high a degree of cleanliness as electroplating or,
electroless plating. For example, it would be
unreasonable to set up the same system for
phosphating and electroplating operations .
because the cleaning prior to phosphating is not
as critical to achieving a finish of high quality. In
some cases, cleaners that contain acids or alkalis
can actually reduce the quality of the finishing
process. In other words, the cleaning process
should match the finishing operation so that
cleaning is performed in the most economical
way to meet requirements (Innes 1993).
Assessing the Cleaning
Process
Technical assistance providers should help
companies determine feasible options by exam-
ining the overall cleaning operationsof a facility.
Often, workpieces in plating tines are cleaned
several times using water, acids*eau$ties> and: ,-..
detergents. An analysis of an ehlfj^jfkushing
process can identify redundant orusneBessary
cleaning steps» The cleanliness requirements
also shouldWi^aloated to see if they are too
stringent. Se^td; assess the technical feasibility
of the alteroa|r^Si,To determine the best
alternative;asfe^foHpwing questions: . \
What are the cleanliness requirements of
the part?
«. Does the alternative meet customer
specifications? .
Is the part/material/coating compatible
with the cleaning process?
, Can the new process meet required
production volumes? -
. Is the process easily installed, operated,
and maintained?
How does the hew process affect subse-,
quent production steps? ' ,
Then, compare the economics of technically
feasible options. When comparing the econom-
ics, consider capital outlay, process operating
costs, permit requirements, waste disposal costs,
labor costs, and energy costs. Many facilities
have substantially reduced waste generation by
implementing alternative cleaning systems.
Finally, considerany potential new regulatory
requirements that might.be required if the new-
process is instaIled.(NFESC 1995).
Factors Affecting Cleaning
Operations
In order to properly assess the cleaning opera-
tion, four parameters must be analyzed: the
substrate, the degree of cleanliness required, the
nature of the soil, and incoming water quality. . ,
Substrate
The composition, physical properties, and
chemistry of the base metal influence the selec-
tioivbfthe cleaning procedure. Hardness, -
porosity*; thermal coefficient of expansion,
conductivity,~melting point, specific heat, and the
effect o( hydrogen embrittlement must be
considered. For instance, hardened steels and
other metals, such as titanium, can become
embrittled by hydrogen. For this reason, these
metals must be handled appropriately to mini-
mize embrittlement (Innes 1993).
The condition of the base metal is equally
important. For example, a piece of metal with
heat or welding scale requires more processing
: than nonoxidized cold rolled steel. The cleaning
medium must be designed so that it is compatible
with the metal being processed. A cleaning
41
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*er Si
process that attacks the metal surface is undesir-
able, Therefore, select a process that does not
attack the metal or does so in a desirable way
(e.g., a satiny or frosty appearance might be
desirable on aluminum substrates). Other
problems can be encountered when working with
metals that have low melting points (200 degrees
Fahrenheit). Such alloys cannot be cleaned in
boiling aqueous solutions. Other metals can be
distorted or bent in heated solutions (Innes
1993).
Degree of Cleanliness Required
The degree of cleaning required varies depending
on the particular surface treatment it will receive.
For instance, parts plated with a cyanide-based
solution usually do not need a high level of
cleaning because cyanide-based plating solutions
clean the .part during the plating operation. For a
nickel plate to adhere to a metal surface, how-
ever, the surface must be extremely clean.
Because the plating bath does not contain
cyanide, it does not clean the part. Therefore,
thorough and rigorous cleaning operations are
needed prior to plating (EPA 1990).
Nature of the Contamination
In order to properly design the cleaning system
and sequence of baths or other operations, it is
important to know the composition of the
contaminants on the material surface. Generally,
soils can be broken down into two categories:
organic and inorganic.
Organic: Saponifiable animal and veg-
etable oils
Unsaponifiable mineral oils and
waxes
Miscellaneous contaminants
either formed in situ or inhibitors
from certain pickle acids redeposit-
ing on the metal
Inorganic Scale and smut oxide and metal-
lic residues
Polishing compounds abrasive,
grinding, and polishing residues or
grits
Miscellaneous contaminants shop
dust or soldering flux
Other soils are paints, cleaning residues, finger-
prints, inorganic coatings, and rust preventatives.
The method and medium used for soil removal
depends on the composition and condition of the
soil as well as its physical and chemical proper-
ties. Often a cleaning procedure can be recom-
mended based on the chemical properties of the
soil providing that a chemical change has not
occurred after application because of age or
drying out. For instance, alkaline cleaners often
are used to remove heavy soils and some solid
oils while caustics are good stripping agents.
Acid cleaners and abrasives are used mainly to
remove oxidation and rust. When parts have
been contaminated with several materiafs,
sequencing of cleaning operations can be impor-
tant. For instance, a layer of oily contamination
might be removed by an alkaline cleaner before
abrasives are used to remove a rust layer (EPA
1990).
Water Quality
The condition of the incoming water often is
overlooked in metal cleaning. Hard water can
decrease the effectiveness of a cleaning system.
Water with a hardness exceeding 25 grains is
definitely a problem and must be treated in order
to operate most cleaning systems adequately.
Many of the chemical additives that are used in
cleaning can be neutralized by minerals found in
tap water. Filtration and deionizing can be used
to correct water quality problems (Innes 1993).
Cleaning Processes
Four types of metal cleaning can be used by the
, metal finishing industry: solvents (both haloge-
nated and nonhalogenated), alkaline cleaners,
electrocleaning, and acid cleaners. Alkaline and
acid cleaners are generally referred to as aqueous
cleaners. Mixtures of solvents and alkalines
frequently used. Mixtures where water-immis-
cible solvent is emulsified in water are termed
emulsion cleaners (EPA 1990). Electrocleaning
uses electrical current to clean the workpiece.
Frequently, no one cleaning operation can be
specified as the best. Several cleaning methods
often appear appropriate and only through
experimentation can one be selected. Some
42
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Chioter S:
cleaning techniques involve the application'of ;
organic solvents to degrease the surface of the ,
workpiece. Other techniques such as emulsion.
cleaning use common organic solvents dispersed
in an aqueous medium.
; The cleaning process generally can be,divided.
into three distinct phases: immersion, power
spray, and electrocleaning. The purpose of
immersion and spray cleaning is to remove the
bulk of or all soil contamination prior ;to
electrocleaning, phosphating, pickling, or
chromating. In some,cases, the spray cleaner also
can be an activation process. In other cases,
spray cleaners can be used individually or in
conjunction with one another. In fact, in a
number of cleaning operations, success ulti-
mately depends upon the soak and spray combi-
nation (Innes 1993). An immersion or spray
cleaner can fall into any of the following
categories: " '
Solvent ' ':
V- Emuisifiable solvent . ,
Emulsion of oil in water (o/w) or water in
oil (w/o)
. . Diphase '-.'..; .
* Acid
Detergent '. ..'!""
Alkaline-built detergent
Solvent Cleaning
The most common form of eleaningin metal
finishing operations is chlorinated solvent vapor
degreasing and ambient-temperature solvent
immersion cleaning. The Clean Air Act Amend-
ments of 1990 required new standards for vapor
degreasing. These new regulations are pushing
metal finishers to investigate alternative cleaning
methods or improve current operating practices.
The University of Tennessee Center for Indus-
trial Services"has developed a manual to assist
manufacturers in complying with the CAAA
standards for vapor degreasing.
Traditionally, vapor degreasing using chlorinated
solvents such as trichloroethylene (TCE) or
perchloroetliylene (PERC) has been used to
remove oils, grease, and Wax-based soils. Unlike
other cleaning processes involving water, vapor.
degreasing does not require downstream drying
because the solvent vaporizes from the
workpiece over time. However, vaporization
results in significant VOC emissions and solvent
losses.
Conventional open-top vapor cleaners (OTVCs)
use an open tank where solvent vapor is main-
tained. A perforated basket containing soiled.
parts is retained in this vapor layer for a few
minutes, and rotated to expose all part surfaces to
the vapor. As vapor condenses on. the parts, the
soil is dissolved and carried away by condensate.
When the parts reach the temperature of the
vapor,.no more condensate is generated and the
parts are removed (Ford "1994).
Methods for Improving Solvent Vapor
Degreaser Efficiency
Certain equipment-related and operational
factors can reduce emissions from traditional
OTVCs including: >'.
' «' Installing of refrigeration coils in addition
to or as replacements.for water chillers;
'coils can help to reduce, vapor generation
by 40 percent or more in some cases. ,
'Covering the degreaser at all possible
times. Placing a co.ver on the OTVC
opening during idling and shutdown
reduces'emissions significantly. The best
type of cover is a motor-controlled cover'
that can be closed automatically.
. Keeping the tip of the spray warid below
the vapor level during spraying
operations.
> Removing parts from the degreaser unit
slowly. Lowering and raising the basket
of soiled parts gently (with a hoist) re-
duces-convective losses by minimizing
turbulence. The recommended hoist/
withdrawal speed is 11 linear feet per
minute.
;» Racking parts so that the solvent drains.
out of the holes> .joints, crevices, 'etc.,.,
, Retaining the basket of soiled parts over
43
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5- r't'f nt»n rj Operations
the tank opening for a short time allows
solvent condensate to drip back into the
tank instead of being dragged out.
* Increasing the freeboard ratio (the
height of the tank walls above the vapor
layer) from 0.5 to 0.75 or 1.0 feet can
cut vapor loss in half (Freeman 1995).
Alternatives to CFC Solvent
Cleaning
With the phaseout of chlorofluorocarbon (CFC)-
based cleaners, facilities have been investigating
chemical, mechanical, and specialty alterna-
tives. Chemical alternatives include replace-
ment solvenfs for use in existing cold cleaning
and vapor degreasing systems. In contrast,
mechanical alternatives commonly require
replacement of an entire process. Generally,
higher initial costs are offset by a safer work-
place and reduced operating costs. Specialty
alternatives include processes such as plasma
systems and supercritical cleaning. Table 6 lists
several methods to reduce the use of chlorinated
solvents.
Chemical Alternatives
Many alternatives to methylchlorofluoro-
carbons (MCF) and CFC-113 are available for
use in cold cleaning and vapor degreasing
applications such as wipe cleaning, dip cleaning,
immersion soaking, pressure washing, and vapor
degreasing. Some solvents are recommended
only for specific applications while others are
used for many applications. In general, the
following properties are desirable when consid-
ering solvent alternatives: low surface tension to
penetrate small spaces, high density to remove
small particles, high volatility to provide rapid
drying, good solvency to readily improve organic
soils, low cost, low toxicity, non-flammable,
little residue, and easy cleanup and disposal
(NFESC 1995).
Drop-in solvent replacement of traditional
solvents such as MCF and CFC-113 usually is
not possible. However, because vapor
degreasing is effective at cleaning delicate parts.
facilities might want to consider maintaining the
process with a substitute solvent. Some possible
CFC-free alternatives include:
«. Aliphatic hydrocarbons: Aliphatic com-
pounds comprise a wide range of solvents
such as mineral spirits and kerosene. These
. solvents have superior cleaning ability and
are compatible with most plastics, rubbers.
and metals and reusable when distilled.
However, aliphatic hydrocarbons are
Table 7. Alternatives for Chlorinated Solvent Cleaning (NFESC 1995)
Contaminant
Corrosion inhibitors
Fats and Fatty Oils
Fingerprints
Ink Marks
Hydrocarbon Greases and Oils
Machining (cutting fluids)
Polishing Compounds
Possible Alternatives
Consider alkaline-soluble compounds
Protective packaging can eliminate the need to clean
Hand wipe or use alkaline cleaners
Handle all fabricated parts with gloves
Use alkaline compounds for hand -wiping
Use water-soluble inks
Remove ink with water
Use labels or tags until final marking is applied
Hand wiping stations remove enough soil for alkaline cleaning
Use.water-soluble compounds
Substitute water-soluble fluids for use in machining
Use water-soluble compounds
Clean at polishing station
44
-------
S: Pre-Finisnirs Coentiorss
flammable, slow to dry, and have low
occupational exposure limits. As a result,
- aliphatics have not been a desirable substi-
tute for traditional solvents. '
Other .chlorinated solvents: The main
advantage to using a chlorinated solvent such
as trichloroethylene, perch loroethylene, or
methylene chloride is their similarity to CFC
solvents in both physical properties and
cleaning effectiveness,.especially in vapor
degreasing. However, all of the above three
have been classified as Hazardous Air
Pollutants (HAPs) by EPA and are targeted
by the Emergency Planning and Community
Right-to-Know Act as well. Furthermore,
'spent solvents are classified as a hazardous
waste.! As a result, handling and disposal of
these solvents is more involved and expen-
sive-than other cleaning alternatives. Future
regulations might ban the manufacture of all
chlorinated solvents. " '
Other organic solvents: Organic solvents
such as ketones, alcohols, ether, and esters
are effective, but dangerous. Many are
HAPS %vhile others have very low flash ;
.' points! For example, acetone has a
flashpoint of 0 degree's Fahrenheit. Extreme
caution is required when handling organic
solvents. Additionally, organic solvents can.
be toxic and malodorous and, as a result,.are
not generally used in vapor degreasing..
N-methyl-2-pyrolidone: Also known as
M-pyrol or NMP, N-methyl-2-pyrolidone
has high purity, a high flash point, and low
volatility. It is very effective in ultrasonic
applications. '-,,'
y Volatile methyl siloxanes: Volatile methyl
siloxahes (VMS) compounds are relative
newcomers to solvent cleaning. They are
low molecular-weight silicone fluids avail-
able in a variety of blends, exhibiting good
compatibility with plastics and elastomers.
However, all blends are either flammable or
combustible and somewhat toxic. Advan-
tages of VMS include good cleaning capa-
bilities for a wide variety of contaminants,
rapid drying without leaving residue on the
workpiece, rapid spreading, and good
penetration into tight spaces. This alterna-
tive cart use existing equipment. Another
advantage of VMS fluids is that they can. be
distilled for reuse. .
Hydrochlorofiuorocarbons: While,
hydrochlorofluorocarbons (HCFCs) are
similar to CFC-113, and MCF in solvency
and cleaning effectiveness, the use of HCFCs
is severely restricted because of their ozone
depleting potential and health effects. A
production ban on HCFCs is scheduled for
the year 2010, but could be accelerated at
any time. Emission controls are required for
safe operating conditions (NFESC 1995).
Aqueous Gleaning
^ . '
Aqueous cleaning uses a solution of water,
detergents, and acidic or alkaline chemicals to
clean parts. These cleaners also are made up of
builders, surfactants, inhibitors, and chelators.
Most cleaners include a variety of ingredients,
many of which are not needed for a firm's
cleaning process and can actually cause problems
.with cleaning systems. Before a facility pur-
chases any equipment for aqueous cleaning, it
should first identify an acceptable aqueous
cleaner. Some vendors will work with a facility
to develop a cleaner tailored to their application.
Below are some common additive types, what
they do, and the advantages and disadvantages of
each (FL DEP 1995). ,
V Builders: A builder is the basic ingredient of
;!an aqueous cleaner. The most common
builders are sodium hydroxide, potassium
hydroxide, and sodium silicates. All of these
are alkalines and are difficult to rinse.
Remember that proper rinsing is the key to
effective aqueous cleaning. Silicate-based
cleaners tend to be easier on substrates and
reduce worker exposure when compared to
hydroxides (FL DEP 1995).
Surfactants and emulsifiers: Surfactants,
also known as surface active agents or
wetting agents, are used to reduce the surface
tension of the cleaning solution. Unfortu-
nately; most surfactants are also emulsifiers.
Emulsifiers take ojls into solution and keep
them from re-contaminating the workpiece.
Traditional aqueous cleaners work by
breaking down organic soils with caustic
and/or solubilizing them with emulsifiers;
' either method tends to leave a large amount
45
-------
Chjpw S. Pre-r mshirj Operations
of spent useless wastewater. Before dis-
posal, the emulsion must be "cracked" or
processed via ultrafiltration to remove the
emulsified oils. Cracking requires either
heat or acid treatment.
The newest aqueous cleaners clean .by
subverting the soil. Non-emulsifying
surfactants have a higher affinity for the
substrate than the soil. The surfactant lifts
the soil from the part without chemically
reacting with it. Non-emulsifying cleaners
work well in spray applications. If a settling
tank and oil skimmer are added to the
system, soils can be removed and the clean-
ing solution can be reused, sometimes
indefinitely without contaminating the part.
In an irrfmersfon tank, however, non-emulsi-
fied oils rise to the surface. Parts can be
contaminated with oils as they are withdrawn
from the tank. This may be desirable
because the oil can act as a rust inhibitor, but
is not acceptable in most situations.
Weak emulsifiers offer the best of both
worlds. This type of cleaner will keep the
oils in suspension as long as the solution is
agitated, but the emulsion breaks when the
agitation stops, either in a holding tank or
when the system is shut down. The sojls can
be removed and the solution can be reused.
"I n ' ' ( i
Inhibitors: Inhibitors are used to reduce the
effect of highly alkaline or acidic cleaners-on
sensitive substrates. Inhibitors are also used
to prevent rusting or oxidation of parts after
cleaning. Chromates and silicates are
commonly used pH inhibitors, but chromates
have obvious environmental disadvantages.
Hydroxides and silicates prevent rust.
Inhibitors cart make rinsing more difficult
and can adversely affect subsequent plating
operations".
> Chelating agents: Chelators are designed
to keep metal ions in solution. These can
cause major problems with wastewater
treatment. Chelating agents should be
avoided if possible. A number of surfactants
are also chelators. For more information on
chelators, refer to Chapter 6.
Sequestering agents: Many alkaline
cleaners are sensitive to the condition of
incoming process water. Sequestering
agents are used to capture hard water ions
such as calcium and magnesium, allowing
the cleaner to work at maximum efficiency.
Saponifiers: Highly alkaline cleaners can
convert insoluble fatty oils to water soluble
soils. This will keep, the soils in solution and
the additional soap can aid cleaning, how-
ever, it also causes disposal problems similar
to those for emulsified solutions. Soaps
created by saponification can cause foaming
problems in spray and ultrasonic
applications.
The three most common equipment configura-
tions of conventional aqueous processes for
metal finishing are: immersion with ultrasonic
agitation, immersion with mechanical agitation.
and spray washing. Aqueous immersion clean-
ing with mechanical agitation or ultrasonics and
spray methods are being used most widely as
substitutes for solvent cleaning. Aqueous
cleaners are generally better than solvent clean-
ers at removing soils or paniculate matter.
However, when oils.or greases are part of the
contamination, other steps might be needed to
' provide adequate cleaning. The rinsing and
drying steps are of particular concern, especially
with parts that have complex geometries or that
are susceptible to corrosion because water can
remain on the part and cause flash rust.
v
Advantages of these systems include increased
safety and flexibility, decreased material and
waste disposal costs, and multiple cleaning .
mechanisms (chemical reaction, displacement,
emulsification, dispersion, and others). Aqueous
cleaning solutions can be tailored for specific
parts and contaminants. When compared with
solvents, aqueous systems generally have higher
capital costs and require elaborate rinsing and
drying procedures as well as tighter process
controls for optimum cleaning (NFESC 1995).
Alkaline, tumbling and hand-aqueous washing
are most often used although automated pro-
cesses are available. In alkaline tumbling, the
soiled parts are placed in ah open, tilted vessel
46
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Chjpcer 5: Pre-Fimsf-.ing Ccerittons
and an aqueous cleaning solution is introduced.
As the vessel rotates, the parts tumble over each
other. The cleaning solution overflows, and clean
tap water is added'to rinse the parts.
In the hand-aqueous .process, the workload ^
(perforated basket of parts) js dipped into a series
of tanks containing (successively) surfactant
solutions and rinsewater. A continuous clean
water flow must be maintained through the final
rinse tanks, but the surfactant and dragout tank.
contents can be used for an entire day without \
changing. Both aqueous processes require
drying at the end before further surface finishing
treatment (Freeman 1995)..
Automated aqueous washers use a helical screw
to transport soiled parts through the five com-
partments. The parts are sprayed successively
with solutions from the holding tanks.. The
helical screw agitates the parts as it carries them
forward. The automated washer is used mostly
for parts small enough to be conveyed by the
helical screw. For larger parts, such as engines
and transmissions, power washers can be used.
The part(s) are placed on a turntable for the
automatically timed cleaning cycle. High-
pressure, high-temperature water,.usually
containing a detergent, blasts the parts clean.
Rotation on the table and the numbenand angle
of the sprays enable the water to reach all
surfaces (Freeman 1995).
Regeneration of Aqueous Cleaners
Some of the cleaners used in aqueous cleaning .
can be regenerated for further use. Alkaline
cleaners, for example, often are regenerated with
micro filtration. In microfiltration, the membrane
is a physical barrier with a pore size of approxi-
' mately 1 to 2 microns. The microfiltration
membranes reject grease, oils, and dirt while
allowing the cleaning solution to pass through.
For a detailed discussion of microfiltration, see
Chapter?. ,
Wastewater Treatment from Aqueous
. Cleaning Systems . -
In many instances because of local, state, or
federal regulations, wastewater from aqueous or
semi-aqueous processes must be treated before
discharge to a municipal wastewater treatment
plant. Contaminants'of concern include organic
matter (grease and oil), metals (dissolved or in
suspension), and alkaline .cleaners, which raise
the pH to an unacceptable level. Pretreatment
technologies include gravity separators, ultrafil-
tration/chemical treatment, precipitation, and
carbon adsorption. For more information on
these technologies, refer to Chapter 6. '-
Acid Aqueous Solutions . , _
Acidic solutions effectively and rapidly remove
rust, scale, and oxides from metal surfaces. The
solutions actually etch the surface of the metal
and can improve coating adhesion. Inhibitors are
used to control the etching rate. However, acid
solutions are classified as hazardous waste and
can cause hydrogen embrittlement as hydrogen
gas formed during surface etching penetrates the
metal and reduces its strength (KSBEAP 1996). (
Aqueous Alkaline Cleaning
In alkaline cleaning, the cleaning action relies
mainly on the displacement of soils rather than .
the breakdown of the soil, as is the case with
organic solvents. Most alkaline cleaning solu-
tions are comprised of three-'major types of
components: builders such as alkali hydroxides
and carbonates, which make up the largest
portion of the cleaner; organic and inorganic .
additives, which promote better cleaning or act to
.' affect the-metal surface in some way; and
surfactants. Other additives can include antioxi-
dan.ts and stabilizers as well as a small amount of
solvents.
Mild alkaline detergent solutions such as sodium v
hydroxide, sodium carbonate, sodium phosphate,
sodium metasilicate, and borax are used to clean
many, substrates because no hydrogen
embrittlement results from alkaline cleaning
(IHWRIC 1992). Alkaline cleansers also remove
rust, scale, and oxides from metal surfaces. In
general, the stronger the solution, the faster it
cleans. However, relatively mild solutions often
are used to easily accomplish thorough rinsing
(KSBEAP 1996). Aqueous processes apply to a
wide range of products and are environmentally
safer than chlorinated solvent processes. Some
disadvantages of aqueous cleaning are its high
water consumption rate and its hazardous
wastewater discharges (Freeman 1995).
47
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CUMW 5
-f'n-»nirg Ooeraaons
Alkaline cleaning often is assisted by mechanical
action, ultrasonics, or by electrical potential (e.g.,
electrah tic cleaning). Alkaline cleaning also can
be used for the removal of organic soils. Alka-
line cleaners and strippers are used to remove
soil from metal parts, old paint, and plating.
These types of solutions are beginning to be used
in acid cleaning as well.
Regeneration of Alkaline Solutions
Most cleaning formulations resist treatment
because they are designed to keep dirt and oil in
suspension. If the concentration of cleaning
chemicals is high enough in an effluent, it can
prevent efficient removal of the precipitated
metals. Slugs of alkaline cleaner passing through
treatment systems are well known to upset the
systems.
While alkaline solutions are not currently
regulated by wastewater programs, they can have
a significant impact in wastewater systems. In
certain cases, large finishing operations on small
sewer systems or small receiving streams might
have a problem meeting organic content require-
ments because of wetting agents and detergents.
Cleaners are also important contributors to a
facility's total dissolved solids load in their
effluent.
" * ' '
Ultrasonic Cleaning
This method uses high-frequency sound waves to
improve the cleaning efficiency of aqueous and
semi-aqueous cleaners. By generating zones of
high and low pressure in the Ijquid, the sound
waves create microscopic vacuum bubbles that
implode when the sound wave moves and the
zone changes from negative to positive pressure.
This process, called eavitation, exerts enormous
localized pressures (approximately 10,000
pounds per square inch).and temperatures
(approximately 20,000 degrees Fahrenheit on, a
microscopic scale) that loosen contaminants and
actually scrub the workpiece,.especially in hard-
to-reach areas. Ultrasonic cleaning has allowed
aqueous/non-chlorinated degreasing to be
practiced in applications where solvents had been
the only effective degreasing tool. Ultrasonic .
cleaning can be used on ceramics, aluminum,
plastic, and glass as well as electronic parts,
wire, cables, rods, and detailed items that might
be difficult to clean by other processes (Freeman
1995). Ultrasonic cleaning can be used to
increase the efficiency of virtually any immer-
sion cleaning process.
Semi-Aqueous Cleaning
Semi-aqueous cleaning, a combination of a non-
aqueous cleaner with an aqueous rinse, is used
frequently in metal cleaning, especially where
aqueous methods alone are ineffective on heavy
grease, tar, and soils. However, precision and
electronics applications are limited. Primary
concerns generally focus on the properties of the
non-aqueous cleaners: volatility, flammability
(especially in heated applications), exposure
risks, residues requiring rinsing, and high costs
of disposal. A nitrogen blanket can reduce the
risk of combustion. Hydrocarbon and surfactant
mixtures, alcohol blends, terpenes, and petro-
leum distillates are solutions available for semi-
aqueous cleaning. Advantages include
compatibility with most metals, plastics, and rust
inhibitors. Other benefits include potential
decreases in solvent purchases, decreases in
evaporative losses, and reduction in metals
entering the waste stream because of the non-
alkaline nature of the cleaner.
Electrocleaning ' .
Electrocleaners are basically heavy-duty alkaline
types and are always used with an electric
current either reverse, direct, pr periodic reverse.
These systems are designed for soil removal and
metal activation. These solutions are heavily
alkaline and often heated. Typically, an initial
cleaning step precedes this operation, although
electrocleaning alone will suffice. In
electrocleaning, the work is immersed in the
solution and current is applied. When water is
electrolyzed by electric current, the following
reaction occurs:
H20 +H2+'/202
The objective of electrocleaning is to remove all
soils and activate the metal surface. Activation
is usually obtained by using reverse-current
electrocleaning. The gas scrubbing of the
oxygen assists in the removal of soils while the
reverse current aids in soil removal and prevents
the deposition of any metallic film or non-
48
-------
ChJDter 5: P'e-fimsmrg
adherent metallic particles. A dilute mineral acid
dip usually,follows the final cleaner to neutralize "
the alkaline film on the metal surface.
Reverse or Anodic Cleaning
In reverse cleaning, the workpiece is made the
anode. In this case, oxygen gas is evolved at the
surface of the piece and assists in oil and dirt
removal. Because of the reversed current, any
metallics in the bath cannot deposit on the piece,
making this method of cleaning preferable to
others (Ford 1994). In this process, the current
density, temperature,, and concentration, particu-
larly on non-ferrous'materials, must be con-
trolled to avoid etching and tarnishing. This
type of cleaning is not recommended for use on
aluminum, chromium, tin, lead, or other metals
that are soluble in alkaline electrocleaners (Innes
1993). ,
Direct or Cathodic Cleaning
If the workpiece is the cathode, the cleaning is
considered to be direct. In this case, hydrogen
gas is liberated'at the surface of the workpiece.
The volume of hydrogen liberated is twice that of
oxygen liberated at the anode for a given current
density. Therefore, more gas scrubbing is
achieved at the cathode than at the anode. For
this reason, cathpdic cleaning is sometimes used
as a precleaner followed by anodic cleaning
(Innes 1993). However, any.positively charged
particles (especially metallics) in the solution
will tend to adhere to the workpiece forming a
smut. This type of cleaning is generally used
when reverse cleaning is harmful to the work
; (Ford 1994).
Any workpiece that is subject to hydrogen
embrittlement should not be cleaned with this
> method unless adequate steps are taken after
processing to remove the hydrogen. Generally,
heat treatment for 1 hour at 400 degrees Fahren-
heit immediately after processing will remove
the embrittling effect of hydrogen.
Cathodic cleaning is used;for the following ,
applications:
To clean metals such as chromium, tin,
lead, brass, magnesium, and aluminum.
These metals are dissolved or etched by
--, anodic cleaning.,
To buff nickel prior to chromium plating.
The oxidation action of anodic cleaning
produces a passive film on the nickel.
This prevents the deposition of bright
chromium.
Periodic Reverse
Periodic reverse cleaning alternately makes the
workpiece anodic and cathodic. This cleaning
technique is used in oxide removal where acidic
processes are harmful to the base material (Ford
1994). This method of cleaning generally is used
to remove smut, oxide, and scale from ferrous .
metals. One of the advantages of this method is
the elimination of acid on certain types of work
" (hinges) where entrapment of acid aggravates
bleed-out during and after alkaline plating (brass,
copper, zinc, cadmium, and tin). Oxides also can
be removed without the danger of etching or the
development of smut usually encountered from
acid pickling (Innes 1993).
Solutions used in these types of cleaning opera-
tions often are sent off site for disposal because
the chemical nature of the surfactants, wetting -
agents, inhibitors, and wetting compounds is
such that they directly interfere with waste
treatment operations. "_.-.
Acid Cleaning (Pickling)
Acid cleaning, or pickling, often is used to
remove contaminants from the workpiece using
an acid. Acid pickling is used to remove oxides
(rust), scale, or tarnish as well as to neutralize
any base remaining on the parts. Acid pickling
uses aqueous solutions of sulfuric, hydrochloric,
phosphoric, and/or nitric acids. For instance,
most carbon steel is pickled in sulfuric or hydro-
chloric acids although hydrochloric acid can
embrittle certain types of steel and is used only
in specific applications.. In the pickling process,
the workpiece generally passes from the pickling
bath through a series of rinses and then onto
plating. Acid pickling is similar to acid cleaning,
but is more commonly used to remove the scale
from semi-finished mill products whereas acid
cleaning is usually used for near-final prepara-
tion of m'etai surfaces prior to finishing.
49
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f S, P-e-rr>;srupg Operations
Regeneration of Pickling and Bright
Dipping Solutions
Copper and Alloys
Straight electrolytic recovery as described earlier
is highly effective on many copper pickling and
milling solutions including sulfuric acid, cupric
chloride, and ammonium chloride solutions.
Solutions based on hydrogen peroxide generally
are regenerated best by crystallization and
removal of copper sulfate with the crystals sold
as byproducts or redissolved for further treat-
ment by electrolytic metal recovery (Steward
1985).
Highly concentrated bright dipping nitric/sulfuric
acids are a difficult challenge for regeneration
because of the small quantities (5 to 25 gallons)
used and the high dragout losses. Regeneration
is possible by distillation of nitric acid and
removal of copper salts, however, the economics
are usually not favorable.
Sulfuric and Hydrochloric Acid
Both sulfuric and hydrochloric acids are used
commonly for cleaning steel. Sulfuric acid can
be regenerated by crystallizing ferrous sulfate.
Hydrochloric acid can be recovered by distilling
off the acid and leaving behind iron oxide.
These techniques have been used for many years
in large facilities. The economics of these
processes, however, usually are not favorable for
smaller facilities (Steward 1985).
Waste pickle liquors from these operations often
can be of use to sanitary waste treatment systems
for phosphate control and sludge conditioning.
Some industrial firms can use spent process
waste from pickling operation. Iron in the waste
is used as a coagulant in wastewater treatment
systems (Steward 1985).
Specialty Alternatives
Vacuum De-oiling
A vacuum furnace uses heat and a vacuum to
vaporize oils from parts. Vacuum furnace de-
oiling can be applied where vapor degreasing
typically is used to clean metal parts. It also can
remove oil from no'nmetallic parts. Although
capital costs for vacuum de-oiling are high, the
operating costs are low. Unlike other clean
technologies, vacuum de-oiling does not leave
the cleaned parts water-soaked so they do not
need to be dried. Because the time and tempera-
Hire of the de-oiling process depends on the
material to be cleaned and the oil to be removed,
adjustments might be needed for each new
material, oil, or combination. Also, the parts
must be able to withstand the required tempera-
ture and vacuum pressure (Freeman 1995).
Laser Ablation.
In this method, short pulses of high-peak-power
laser radiation are used to rapidly heat and
vaporize thin layers of material surfaces that
' form a dense cloud of hot vapors that will
condense and recontaminate the surface if not
removed immediately. Ablation must be carried
out in an inert gas environment to avoid further .
contamination. Laser ablation can do localized
cleaning in a small area without affecting the
entire part. Laser ablation meets waste minimi-
zation goals with no solvents or even aqueous
solutions needed. The only waste is the small
amount of material removed from the surface of
the item being cleaned (Freeman 1995). The use
of laser ablation to clean metal surfaces is being
explored by Sandia National Laboratories. .
Pressurized Gas
This method uses clean,' dry, inert gas or air that
is fed to a pressurized gas .gun to physically
remove the contaminant from the substrate
surface. Advantages of this process are low
capital cost and the fact that nonflammable gases
are generally used. However, this technology
might not be effective in removing all soils, and
it might damage the substrate (Freeman 1995).
Supercritical Fluid Cleaning
This process involves the application of
supercritical fluids at temperatures and pressures
above their critical point to remove contaminants
from parts. Carbon dioxide (CO,) is the most
commonly used fluid in this process because it is
widely available and considered to be environ-
mentally sound. Supercritical fluid cleaning is
compatible with stainless steel, copper, silver,
porous metals, and silica. It leaves no solvent
50
-------
Gupier 5'. ?re-f;nisr.(0?'QQeri«Qns
residue after cleaning and has low operating.
costs. However, capital costs-are very high .
. (Freeman 1995).- ' "
Plasma Cleaning , ,
This metho'd uses an electrically charged gas
containing ionized atoms, electrons, highly
reactive free radicals, and electrically neutral,
species to remove soils. Plasmas can be used in
a wide range of temperatures and pressures. The
advantages of this'process include low operating
costs and lessened disposal costs. However,
. initialcapitalists can be high (Freeman 1995).
References
EPA. 1990. Guides to Pollution Prevention:
The Fabricated Metal Products Industry. Wash-
ington, DC: Office of Research and Develop-
ment.
Florida Department of Environmental
Protection (FL DEP). 1995. Fact Sheet: Aqueous
Cleaner Additives for Industrial Cleaning:
Jacksonville, FL: Florida Department pf Envi- .
ronmental Protection.
' . Ford, Christopher J., and Sean Delaney.
1994. Metal Finishing Industry Module, Lowell,
MA: Toxics Use Reduction Institute.
Freeman, Harry M. 1995. Industrial 'Pollu-
tion Prevention Handbook. New York, NY:
McGraw-Hill, Inc. , '
Illinois Hazardous Waste Research and
Information Center(IHWRIC>.,1992. Paint
Waste and Disposal Options. Champaign, IL:
Illinois Hazardous Waste Research ahd Informa-
tion Center.
Innes, Al,and William H. Toller. 1982.
Considering Recycling and Recovery:. Plating
and SurfaceFinishing. February, pp.. 26-27.
Kansas Small Business Environmental
Assistance Program (KSBEAP). 1996". Environ-
mentally Conscious Painting. Wichita, KS:
Kansas Small Business Environmental Assis-
tance Program.
Naval Facilities Engineering Service Center
(NFESC) 1995. ODS-Free Metal Cleaning
Overview. Department of Defense Pollution
Prevention Technical Library. (Downloaded
from Envirosense web site:
http://www.es.inel.gov).
:-. Steward, F.A., and W. J. McLay. 1985.
Waste Minimization and Alternate Recovery
Technologies! Warrendale, PA: Alcoa Separa-
tions Technology, Inc.
51
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-------
Pollution Prevention in the
Plating Process
This chapter provides an overview of pollution
prevention techniques that apply to plating
lines within metal finishing operations. As
described .in Chapter 1, the plating line is the part
of the metal finishing process where metal is
applied to a substrate. ;
The first section of this chapter describes general,
pollution prevention techniques for plating
solutions and covers housekeeping, monitoring,
additives, equipment modification, and on-site
recycling and recovery. The next section covers
general issues in pollution prevention for cya-
nide-based plating. The next seven sections
cover pollution prevention options for plating,
specific metals such as brass, cadmium, chro-
mium, copper, nickel, precious metals, and zinc.
The sections that follow cover additional types of
plating including electroless, aluminum, chemi-
cal and electrical conversion, and others.
General Pollution
Prevention Techniques for
Plating Solutions
Chapter 4 presented a number of general pollu-
tion prevention techniques for all types of metal
finishing operations. These general techniques
can apply in a variety ways to plating lines. The
following are some specific applications of these
techniques to plating baths.
General Housekeeping
Keeping the plating areas clean and preventing
foreign material from entering or remaining can
prolong the life of a bath. Companies can use a
number of simple and inexpensive techniques to
reduce contamination of the process bath. A part
that falls off the rack into a bath should be
removed quickly to reduce contamination.
Operators should maintain racks so that they are
clean and free of contaminants. Firms should
avoid using broken or crocked racks because they
can increase the amount of process solution that
is dragged intojthe rinse process, increasing
sludge generation. Other general housekeeping
'. methods include protecting anode bars from
corrosion, using corrosion-resistant tanks and :.-
equipment, and filtering incoming air to reduce
airborne contaminants. A clean process area also
makes detecting problems such as leaking tanks
or pipes much easier. For more information on
these techniques, refer to Chapter 4.
Monitoring Bath Composition/
Chemistry
Proper control of bath operating parameters can
result in more consistent workpiece quality as
well as longer bath life. This strategy is simple: ;
determine critical operating parameters and
maintain them within the acceptable limits. The
first step in this process is to determine optimum
operating parameters for the process. The next
step-is to ensure regular monitoring of bath
' chemistry, which is essential in determining the _
proper amount of chemicals to add to maintain
efficient operating parameters. For many
solutions, simple field test kits are available.
. Determining operating parameters on an indi:
vidual plating line basis is important because
suppliers sometimes set concentration specifica-
tions for levels higher than is required for
effective operation. Higher concentrations mean.
increased dragout and waste generation. Many
plating facilities rely heavily on suppliers to
provide them with optimum operating param-
eters. In some cases, shops send samples on a
monthly basis to their vendors in addition to the
daily analyses performed at facilities. The
following sections describe the operating param-
eters that a facility should establish and the ways
to determine those values (IAMS 1995).
53
-------
Quour 6:
Prevention tn the Placing Process
High Process Bath
Operating Temperature
Advantages
Reduces volume of dragout loss
» Allows the use of lower solution concentrations
Disadvantages
» Increases energy costs
»Increases evaporation as more water will
be needed to replenish process bath
Can increase worker exposure because of
higher emissions from process bath (e.g.,
cyanide baths) (APPU 1995)
Lower Plating Solution Concentration ,
Advantages
Reduces dragout losses
Reduces chemical use and costs
Reduces sludge generation rates
Disadvantages
Decreases tolerance to impurities
Might not be an option if contractual
specifications require a certain concentration
(APPU 1995)
Process Bath Operating Temperature
Increased bath temperatures will reduce the
viscosity of the plating solution, enabling faster
drainage from the workpiece and reducing the
amount of solution that is dragged into subse-
quent baths. Operators, however, should avoid
using very high temperatures because many
additives break down in high heat, and carbonate
buildup increases in cyanide solutions. Exces-
sive temperatures also can cause the process
solution to dry onto the workpiece during
removal, increasing dragout, water use, and labor
costs (APPU 1995).
Higher operating temperatures also'will increase
the evaporation rate of the process solution. A
facility can take advantage of the increased
evaporation rate by using solution from the
process line rinse tanks to replenish the process
bath and to maintain the proper chemical equilib-
rium. This replenishment reduces wastewater
and recovers dragout while maintaining a stable
plating solution. A facility might consider.using
deionized water when operating plating solutions
at higher temperatures since deionized water will
minimize the natural contaminant buildup in the
process bath. Increasing the operating tempera-
ture also can increase energy costs (EPA 1992).
Plating Solution Concentration
Facilities'should determine the lowest concentra-
tion of chemicals that can be used to obtain a x
quality finish. If the process line is operated at
higher temperatures, lower concentrations can be
used to obtain results equivalent to higher
concentrations at lower temperatures. Generally,
the greater the concentration of chemicals in a
solution, the greater the viscosity and dragout.
As a result, the film that adheres to the
workpiece during removal from the process bath
is thicker and does not drain back into the
process bath as quickly. Reducing the concentra-
tion of the plating solution can increase the
ability of process solution to drain efficiently
from a workpiece (EPA 1992).
Many chemical'product manufacturers recom-
mend an operating concentration that is higher
than necessary. To determine the lowest possible
process bath concentration, a facility should mix
a new process bath at the median recommended
concentration. As the process bath is replen-
ished, operators can continue to reduce the
chemical concentration until product quality
begins to deteriorate. Alternatively, operators
can mix the new bath at a low concentration and
gradually increase the concentration until the
bath cleans, etches, or plates the test pieces
adequately. Facilities can operate fresh cleaning
process baths at lower concentrations than used
baths. Makeup chemicals can be added to the
used bath increasing the concentration gradually
to maintain effective operation (EPA 1992).
Lower Concentration Plating Solution
Case Study
EPA documented a firm that used low concentra-
tion plating solutions instead of mid-point
concentrations in order to reduce total mass of
chemicals dragged out. This case involved five
nickel tanks and an annual dragout of 2,500
gallons. The capital cost was $0 and disposal
and feedstock savings were $1,300.
(APPU 1995
54
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Chapter 6: Pollution Prevention ,n :r.e P'Jtfrg ?-oc
Additives for Plating Baths
Platers commonly use several chemical addi- ;
tives to aid in the plating process and to reduce
waste generation. Most of these chemicals are .
used to reduce dragout of solution into rinsewa-
ter. Some of the more common additives are
described below.
Wetting Agents ;
Metal finishers have used wetting agents for
years in process solutions to aid in plating. A
wetting agent is a substance, usually a.surfac-
tant, that reduces surface'tension. The addition
of a very small amount of surfactant or wetting
agents can reduce dragout by as much.as 50
percent (EPA 1992). However, platers should
be careful to use only non-ionic wetting agents.
The use of certain ionic wetting agents can
reduce plating quality and limit reclamation of
metals in wastewater. If a shop' is considering
the use of wetting agents for dragout reduction,
they should conduct experiments to determine
.the potential benefit and to ensure compatibility
with,bath chemistry, especially for hard chro-
mium plating.
Wetting agents also can create foaming prob-
lems in process baths and might not ,be compat-
ible with waste treatment systems. For these
reasons, impacts on both the process bath and .
treatment system should be evaluated prior to
use (Ford 1994).
Wetting Agents
Advantages . -.....'
Reduces dragout loss by as much as 50
percent
Can improve quality of finish
Disadvantages
Can create foaming problems in process bath
Some bath chemistries are not compatible
with wetting agents . -(APPU1995)
Non-Chelated Process Chemicals
Firms use complexers, including chelators, in
chemical process baths to" control the concentra-
tion of free metal ions in the solution beyond
their normal solubility limit. Chelators are
usually found in baths used for rrietaletching,
cleaning, and electroless plating. However, once
chelating compounds enter the wastestream, they .
inhibit the precipitation of metals and additional
treatment must be used.- These treatment chemi-
cals end up as sludge and contribute to the
volume of hazardous waste. For example, when
platers use ferrous sulfate, a popular precipitant,
, the volume of sludge increases significantly. For
some applications, operators add ferrous sulfate-
at an 8:1 ratio. Also, many of the spent process
baths containing chelators cannot be treated on
site and are put into containers for off-site
disposal, adding to waste disposal costs (EPA
1992). - '
Metal finishers use a variety of chelators in
different processes. In general, mild complexors
such as phosphates and silicates are used for
most cleaning and etching processes. Electroless
'prating baths typically are chelated with stronger
'organic acid chelating compounds including
citric acid, maleic acid, and oxalic acid. Some
firms also use ethylenediaminetetraacetic acid
(EOTA), but with less frequency than the other
chelators (PRC 1989). However, EDTA is a
common component in many cleaning solutions.
Operators must make a trade off between extend-
ing bath life and removing chelated process
chemicals from wastewater to meet required
discharge levels. Often, the pH of wastestreams
must be adjusted to break down the metal
complexes formed by the chelators. EDTA, for
example, requires lowering the pH below 3.0 and
adding treatment chemicals (PRC 1989). In
some cases, even this form of treatment does not,
enable metals to precipitate.
Wetting Agents Case Study
EPA documented a firm that used wetting agents to reduce dragout by 50 percent. An
dragout reduction of 67 percent was achieved by increasing drainage time. No saving
was available, although operating and maintenance costs of $15 per 200 grams of wetting agents
and $1.5 per gallon misting reduction additives was reported. (c _^J_
55
-------
6 Pi-jt.cn Pretenuon in the Plating Process
Firms can use non-chelated process chemistries
for processes (e.g., alkaline cleaning and etching)
in \shich keeping the metals removed from the
\\orkpiece surfaces in solution for later treatment
might not be necessary. An application of the
above is dummy plating. In such cases, the
metals can be allowed to precipitate and the
process bath can be filtered to remove the solids.
However, non-chelated chemicals are not used
for electroless plating because the chelators play
a significant role in allowing the plating bath to
function (PRC 1989).
Non-chelated process cleaning baths usually
require continuous filtration to remove the solids.
These systems generally have a filter with pore
sizes 1 to 5 microns thick with a pump that can
filter the tank contents once or twice each hour
(PRC 1989). The cost of a filter system ranges
from approximately $400 to S1,000 for each
tank. Operating costs include filter element
replacement as well as disposal and maintenance
costs. However, firms will realize savings in
reduced waste treatment, sludge handling, and
disposal costs for spent baths. Another important
advantage of non-chelated process chemicals is
that the metal removal capability of wastewater
treatment usually is improved and the treated
effluent is more likely to meet discharge limits
(EPA 1992).
Equipment Modifications to
Prevent Pollution
A facility can implement several modifications
to reduce contamination of the process bath,
extending its life and reducing waste generation.
These techniques include using the proper anode
care, purified water, and ventilation/exhaust
systems.
Anodes: Purity, Bagging, and Placement
Anodes used in the plating process often contain
impurities that can contaminate'a process bath.
Anodes with higher grades of purity do not
contribute to bath contamination, however, their
cost might be higher than less pure anodes. In
addition, some contaminants are added to the
anode to aid in the plating process. Therefore,
properly matching the anode to the process is
critical. One method for reducing contamination
from anodes is placing cloth bags around them.
This technique can prevent insoluble impurities
from entering a bath. However, the bags must be
maintained and made of a material that is com-
patible with the process solution (EPA 1992).
For some process solutions, such as copper
cyanide, bagging is not a feasible option. Facili-
ties also can experiment with the placement of
the anode in the process bath. Proper placement
of the anode can increase the quality of the
plating process resulting1 in fewer rejects, and can
reduce the need to rework workpieces.
Purified Water
Firms can use deionized, distilled, or reverse
osmosis water to replace tap water for process
bath makeup and rinsing operations. Natural
contaminants such as calcium, iron, magnesium,
manganese, chlorine, carbonates, and phosphates
can reduce rinsewater efficiency, minimizing the
potential for dragout recovery and increasing the
frequency of process bath dumping. These
contaminants also contribute to sludge volume,
when removed from wastewater during treatment
(EPA 1992). Further information on issues
related to purified water are included in Chapter
4 in the section on water quality monitoring.
Ventilation/Exhaust Systems
Scrubbers, de-misters, and condensate traps
remove entrained droplets and vapors from air
passing through ventilation and exhaust systems.
If-segregated, operators can return some wastes
from scrubbers to process baths after filtering.
Updraft ventilation allows mist to collect in the
duct work and flow back to the process tank. For
example, hard chromium plating baths can
benefit from an updraft ventilation system (EPA
1992).
Process baths that generate mist (e.g., hexavalent
chromium plating baths and air-agitated nickel/
copper baths) should be in tanks that have more
freeboard in order to reduce the amount of mist
in the ventilation system. The added space at the
top of the tank (i.e., the freeboard) allows the
mist to return to the bath before entrainment in
the air entering the exhaust system. Platers also
can use foam blankets or floating polypropylene.
balls in hard or decorative chromium baths to
keep mists from reaching the exhaust system
(EPA 1992).
56
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Chaocer 6: Pollution Prevention m ;ne ?'j'.;ng P-ccass
Chemical Substitution
A plater can use several chemical substitutes to
reduce the amount of toxic materials. Detailed
information on these substitutes is presented in .
Chapters 5 and in upcoming'sections in Chapter
6. Substitutes are used most commonly for
cyanide because of its toxicity: |
Replace Cyanide-Based Plating with Non-
Cyanide-Based Processes
Converting process baths to non-cyanide process
chemistries can, in some cases, simplify waste-
water treatment, reduce treatment costs, and
decrease sludge generation. Alternatives are-
available for most cyanide-containing processes
including silver, cadmium, zinc, gold, and copper
plating, However, drawbacks often are associ- -
ated with switching to non-cyanide process ,
plating. For a more detailed description of
cyanide alternatives, refer to the Pollution ' ..
Prevention for Cyanide-Based Plating section in
this chapter. '
On-Site Recycling and Recovery
Several opportunities exist for platers to recycle
or reuse solutions in baths either within the same
tanks or in other processes: This section covers
acid solution regeneration, reactive rinsing,'and
spent solution reuse. ,
Acid Solution Regeneration
Firms can regenerate acid solutions using several
processes including distillation, acid sorption,
membrane electrolysis, crystallization, and .
diffusion dialysis. Technologies such as mem- .
brane electrolysis and diffusion dialysis rely on
the ability of a membrane to selectively diffuse
anions and hydrogen while at the same time
, rejecting metals. Diffusion dialysis functions by
passing water in a counterciirrent flow to the '
spent acid stream. The two streams meet at a
/membrane where anions and hydrogen diffuse
through the membrane into the water: Operators
end with an acid solution at the approximate
strength with which they started and a dilute acid
waste that contains the metal component. The
, acid then is reused and the waste is treated or
:sent off site for disposal. Acid solution regenera-
tion technologies are discussed in further detail
in Chapter 7.
Spent Acid Bath Reuse (Reactive Rinsing)
Companies might have opportunities to reuse
spent process baths in other facets of a metal
finishing operation. Used acid and alkaline ,
cleaners from the cleaning process are the most
common example of this technique. For ex-
ample, rinsewater from an acid dip process can
. be piped to the alkaline cleaning process for use
as rinsewater (or vice versa). If both systems
have the same flow' rate, water use would be
reduced by 50 percent. This system also can
increase rinsing efficiency by reducing the
viscosity of the alkaline dragout (EPA 1992).
However, facilities should make sure that rinse
tanks, pipes, plumbing, and bath chemistries are
compatible with the rinse solution (EPA 1992).
. Another use for spent acid cleaning rinsewater is
as an influent for rinsing after a mild etch
process. Furthermore, rinsewater from final or
critical rinses, which tend to be less contami-
nated, can be used in rinsing operations where a
high degree of rinsing efficiency is hot required.
Costs for implementing a system to reuse water
can vary greatly, Simple systems can cost as
'"" little as a few hundred dollars while a complex
system cart cost hundreds of thousands. Figure 6
illustrates rinsewater reuse for an alkaline
cjeaning, mild acid etch, and acid cleaning line.
. Fresh
water
Alkaline
Cleaner
4
Rinse
. Acid
Dip
>
Rinse
1
Nickel
Plating
Drag-
out
Tanks.
Rinse
Figure 6.- Multiple Reuse of Rinsewater (EPA 1992)
57
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Chiottr 6; Pailus-or- Prevention in the Plating Process
Spent Solution Bath Reuse
Process baths that have become too contaminated
to be used for plating operations often are
dumped. However, these solutions can have
valuable uses in other metal finishing operations
such as:
Metal precipitation: Non-chelated caustic
solutions can be used to precipitate metals.
However, cleaning solutions that contain
detergents, surfactants, and high concentra-
tions of wetting agents tend to destroy the
flocculating/settling ability of the precipi-
tated metal (Ford 1994).
Chrome treatment: Solutions can act as pH
adjusters in a precipitation tank (precipita-
lion is discussed in the next section). For
example, acid solutions can be used to adjust
the pH in chromium reduction treatment.
However, because these solutions typically
have a high metal content, they should not be
used for final pH adjustments. As with
reusing spent rinsewater, facilities should
check to make sure that the spent process
bath solutions are compatible before they are
used (EPA 1992).
Chelated metals treatment: Spent acids,
particularly those high in iron content such
as ferric chloride etchants and steel and iron
pickling solutions, are particularly desirable
for pH adjustment (Ford 1994).
Cyanide treatment: Non-chelated caustic
solutions can be used to raise the pH in the
first stage of cyanide treatment. In the
second stage, the pH can be lowered with
spent acid, but care must be taken not to use
spent acids that contain nickel or iron as
these metals; form complexes with cyanide
that are extremely.refractory to alkaline
chlorination (Ford 1994).
Waste Segregation
Platers can extend the life of process solutions by
removing impurities from the bath. The follow-
ing sections provide an overview of removal
techniques including filtration, carbonate freez-
ing, precipitation, electrolysis, and carbon
treatment.
Removal of Solids via Filtration
Filtration is one of the most common techniques
available for maintaining process bath purity.
Most frequently, platers use cartridge filters as
either in-tank or external units to remove sus-
pended solids from the process solution. The
majority of cartridges in use are disposable.
However, reusable filters also are available.
Filter systems also can be used on pre-fmishing
operations (mainly on larger tanks). The cost
varies depending on the size and type of filter the
shop uses (Cushnie 1994).
Removal of Salts via Carbonate Freezing -
Cyanide baths are adversely affected by the
formation of carbonate buildup during the
breakdown of cyanide. An excessive carbonate
concentration can affect the smoothness of
deposits, plating efficiency, and plating range.
Filtration
Advantages
Extends bath life '
Reduces chemical purchases for bath
makeup and neutralization
Reusable filters decrease operating
costs
Disadvantages
Takes'up tank space
(APPU 1995}
Filtration Case Study
An in-tank filtration unit reduced one company's
chemical costs and waste generation by 50
percent. Capital costs for a 1,200 gallon per
hour in-tank filter was $500. Operation and
maintenance costs were $1,391 with a payback
period of less than 5 months. Annual savings
were approximately $2.781. (APPU 1995)
Salt buildup can increase process solution
dragout by as much as 50 percent.
Carbonate freezing can prevent the buildup of
salts. The carbonate freezing process takes
advantage of the low solubility of carbonate salts
in the bath. Bath temperature is lowered to
approximately 26 degrees Fahrenheit to
58
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Chapter 6: Pollution Prevention :n :re
P-ocsss
Carbonate Freezing Case Study
The United States Army has developed a process
to reduce'carbonate concentration in cyanide
baths using'a techniques that involves freezing
the carbonates.out of solution, A-metal box
containing dry ice and acetone is immersed in;
the plating bath. Carbonates are precipitated -
directly onto the outside metal surface of the
box. The box is removed and the carbonates
scraped off the box and discarded as solid
waste. . (Cushniel994)
crystallize the salts. This1 process also can
remove sodium sulfate and sodium ferrocyanide.
Carbonate freezing is used most often in cad-
mium cyanide plating, zinc cyanide plating,
copper cyanide plating, and copper cyanide
strike. Sodium cyanide baths can be treated by
carbonate freezing or crystallization. However,
potassium cyanide baths must be treated by
precipitation rather than freezing (Cushnie 1994).
Removal of Metal Contaminants via Pre-
cipitation
Metal finishers use precipitation as an alternative
to carbonate freezing for cyanide baths. Table 7
lists common bath contaminants and precipita-
tors that platers can use to remove contaminants.
The process generally is performed in a spare
tank where the solution is chemically treated and
filtered and then returned to the original tank.
For example, in a zinc bath, zinc sulfide can be
used to precipitate lead and cadmiumt the .
precipitant then is removed via filtration. In
addition, iron and chromiijm contamination is
Precipitation
Advantages ..
Extends bath life
Disadvantages '
Eventually the process is no longer effective
and bath will need to be du,mped
'; , .- . (APPU 1995)
common in acidic nickel baths. In most formula-
tions, these contaminants can be removed with
peroxide combined with pH elevation and batch
filtration. As with all chemical reactions,
facilities must take care to ensure that the
precipitation reagents are compatible with the
bath constituents (Cushnie 1994).
Removal of Metal Contaminants via Low-
Current Electrolysis (Dummy Plating).
A common problem with plating baths is the
introduction of metal contaminants into the bath
that reduce the effectiveness of the solution.
Copper is a common metal contaminant that
builds up in plating baths. Copper can be
removed from zinc and nickel baths through a
process called dummy plating. Dummy plating
is an electrolytic treatment process in which
metallic contaminants in a metal finishing
'solution are plated out using low .current density
electrolysis, the process.is-based on the electro-
lytic principle that copper can be plated at a low
electrical current (Ford 1994).
When the copper concentration in a process bath
becomes too high, an operator can place.an
Table 8. Precipitatofs for Common Plating Solutions (ASM 1982)
Plating Bath
Silver Cyanide
Cyanide Baths
Nickel
Acid Chloride Zinc
Zinc
Electroless Nickel
Contamina
Carbonate's
Zinc and leac
Misc. metal c
(e.g., iron an
Soluble ferro
Iron
Phosphorous
Hydrogen peroxide
Potassium permanganate
59
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&. P;l'ut'«"' Prevention ;n the Plating Process
electrolytic panel in the bath (the bath must be
inoperative for 1 or 2 days). A trickle current
then is run through the system, usually at a
current density of 1 to 2 amperes per square foot.
At this current, the copper in the plating bath
solution will plate out onto the panel, but the
plating bath additives are unaffected. Some of
the plating metals also might be removed inad-
vertently, but the savings from extending the fife
of the bath usually justifies the metal loss. For
more information on this process, refer to the
recovery techniques section in Chapter 7.
Removal of Organics Using
Carbon Treatment
Carbon treatment of plating baths is a common
method of removing organic contaminants. The
carbon absorbs organic impurities that are
present as a result of introducing oil or breaking ,
down bath constituents. Carbon treatment can be
used on both a continuous and batch basis.
Various filtration methods are available, includ-
ing carbon filtration cartridges (restricted to use
on small applications), carbon canisters, pre-coat
filters, and bulk applicatioh/agitation/filtration.
Typical dosages are I to 4 pounds of carbon per
100 gallons of solution (Cushnie 1994).
Carbon Filtration Case Study
EPA documented a company that used acti-
vated carbon filtration to regenerate plating
baths. This method consisted of a holding
tank, a mixing tank, and a MEFIAG paper-
assisted filter operating in cf batch mode. This
project reduced the-volume of plating baths
disposed and the amount of virgin chemicals
purchased by 47 percent. The batch size was
2,400 gallons. Approximately 4 to 5.5 barrels
! of solids are generated annually from this
I process. Capital cost for the activated carbon
filtration unftwas $9,192 and operational/
maintenance costs were $7,973 per year.
Savings came from $67,420 in reduced waste
disposal costs and $55,000 in chemical
purchases savings. Waste generation was
reduced by 10,800 gallons a year. The
payback period was 3 months.
(APPU1995)
Cyanide-Based Plating
Processes
Perhaps the single most toxic chemical used in
metal finishing on a weight-for-weight basis is
cyanide. Electroplaters are most at risk for
exposure to hydrogen cyanide (HCN) through
ingestion and inhalation, either through a cata-
strophic event or low levels associated with
processing. Skin contact with dissolved cyanide
salts is somewhat less dangerous but will cause
skin irritation and rashes (Mabbett 1993).
This section contains information on the avail-
able alternatives to cyanide plating. The first
part discusses general information regarding the
substitution of non-cyanide solutions for tradi-
tional cyanide-based baths. The next section
addresses specific plating solutions (e.g.. brass.
cadmium, copper, precious metals, and zinc) and
provides information on alternative bath chemis-
tries and successful implementation of recycling
and recovery technologies.
Substitution of cyanide can have profound
effects on a metal finisher. Cyanide, in the form
of sodium or potassium cyanide, has been a key
component of plating solutions for many years,
particufarly in plating copper, zinc, and other
metals'. Cyanide is an excellent complexer and
has a wide tolerance for impurities and variations
in bath composition. Cyanide's principle disad-
vantages are toxicity and the high cost of waste-
water treatment (Ford 1994).
For these reasons, EPA and many states severely
limit the discharge of cyanide. Platers typically
use an alkaline chlorination process requiring
sodium hypochlorite or chlorine to treat wast-
estreams containing free cyanide. These chemi-
cals can contribute substantially to sludge
generation (Braun Intertec 1992). For complex
cyanides, platers typically use ultraviolet (UV)/
ozone or UV/peroxide treatment. This process is
simple and cost effective (Gallerani 1996).
Overview of Non-Cyanide
Substitutes
"' ,.,,',' ' ' . . . y ,
Many metal platers are seeking alternatives to
traditional cyanide-based plating. Concerns over
60
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Chapter 6: Pollution prevention .n tne P'jt.-r.g
occupational health and safety, waste treatment
costs, regulatory compliance requirements,,and
potential liability have encouraged process
managers to investigate new, non-cyanide plating '
technologies:' The earliest and most complete
cyanide substitution that has taken place in the
industry is the conversion from zinc cyanide to
zinc chloride or zinc alkaline (TURI 1994).
Non-cyanide alternatives generally have proven
to be base specific and, therefore, are not simple
to substitute. Also, non-cyanide plating solutions
are less forgiving than cyanide baths to soils left
on parts for plating. Firms must maintain higher
cleaning standards if they switch-to non-cyanide
solutions. Another disadvantage of non-cyanide
substitutes is that they tend to cost more than
conventional baths (Ford 1994). Also; some of
the common recovery technologies are more
difficult to use with non-cyanide substitutes.
Using non-cyanide process chemistries can
reduce hazardous waste sludge by eliminating a
treatment step. However, many non-cyanide
processes are difficult to treat and produce more
sludge than cyanide baths. Some platers also
have found that they need to install more than
one process line to replace a single cyanide line.
Usually, no substitute will meet all the require-
ments 'for replacing the single cyanide line.
Multiple substitutes must be used, and some
applications have no available substitute (TURI
' 1994). . . . ''
Non-cyanide^based alternatives are available for
cyanide copper, zinc, and cadmium plating
processes. These substitutes can reduce regula-
tory reporting requirements, lower risks to
' workers, decrease environmental impact, and
decrease corporate liability. .Platers should
weigh the advantages and disadvantages of non-
cyanide baths for specific applications (Braun
Intertec 1992). ,
The following list describes the factors that
technical assistance providers should consider
when recommending changes to a non-cyanide
solution:
Often, several non-cyanide solutions
replace the single cyanide line.
V Process controls and cleaning-practices ',
must be maintained within tighter limits.
* Without the completing ability of cyanide,
periodic removal of iron and other
potential contaminants might,be required
to ensure deposit quality. Filtration
generally is necessary when using non- _
cyanide-processes.
The color shades obtained in chromating
nonrcyanide deposits do not always
match those obtained with the same color
chrorhates over'cyanide deposits. CUST .
tofners should be notified when segregat-
ing products with color shade differences
is important.
Some non-cyanide processes do not
satisfactorily adhere to all surfaces and
tend to become brittle at high tempera- /
hires./. ' *
..», Alkaline non-cyanide processes generally
provide more ductile deposits for subse-
quent forming operations than do acid
non-cyanide processes.
» In both acid and alkaline non-cyanide
processes, higher levels of organic or
' non-organic brightening agents are
required to achieve a more cosmetically
appealing finish. However, residue left
on the workpiece can cause problems in
future finishing processes such as
. . chromating.
Acid substitutes require an approptiate
liner such as plastic (TURI 1994).
Technical assistance providers, should make sure
that companies that are considering a conversion
to a non-cyanide substitute understand the
inherent dangers in converting a cyanide line.
Many problems can be averted as long as compa-
nies develop a well thought-out plan. A majority
of the accidents involving cyanide in metal
finishing operations have occurred because of
badly planned conversions of a plating line from
cyanide to non-cyanide operations (Galleram
1996).
The following sections provide detailed descrip-
tions of commonly used cyanide plating
61
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Oiotcr 6. PC !'utiOn Prevention in :ne Plating'Process
processes (brass, cadmium, copper, precious
metals, tin, and zinc) and the available
alternatives.
Brass Plating
Common Uses
Brass plating is one of the most common alloy
plating processes in use today. Brass can be
plated in many applications arid in varying
thicknesses. Another property of brass plating is
its ability to provide good adhesion to steel and
rubber. Brass is, therefore, commonly used in
the manufacture of steel wire cord f6r use in
tires. Other applications of brass plating include
a variety of decorative and engineering finishes
(Strow 1982).
Brass plate comes in variety of colors from
yellow to various shades of bronze and brown.
In some cases, platers use brass as a very thin
plate over other bright plates. Nickel often is
used under a brass plate to level the surface. A
brass plate then is applied over the nickel to
provide a bright brass surface. Yellow brass is
the most common material used in brass plating.
Gold-colored brass often is used as a decorative
plate. The main problem in applying a brass
finish is rapid tarnishing. The conventional
solution to this problem is to apply a protective
layer of clear transparent powder coat or lacquer
(Strow 1982).
Common Bath Solutions
Typical brass plating solutions are cyanide-
based. The basic ingredients of a cyanide brass
plating solution are sodium cyanide, copper
cyanide, and zinc cyanide. Other constituents
include ammonia and carbonate. In some cases,
platers also add sodium carbonate to provide a
buffering action so that the plate color is consis-
tent. The ratio of cyanide to zinc is the key
, element in controlling plate color and alfoy
composition (Strow 1982).
Bath Content
Plating efficiency is controlled by copper content
(i.e., the higher the copper content, the higher the
efficiency). Temperature also plays a key role in
the efficiency of the" bath solution. For example,
plating at 95 degrees Fahrenheit is twice as
efficient as plating at 75 degrees Fahrenheit.
Process lines operated at higher than 95 degrees
Fahrenheit require more frequent additions of
ammonia; lines below, 95 degrees require less
frequent additions (Strow 1982).
Alternative Bath Solutions for Brass
Plating
Various non-cyanide brass solutions have been
developed in the past, however, cyanide brass
solutions are still the most prevalent solutions
used by metal finishers today. Some of the
original non-cyanide solutions had some prob-
lems including insufficient color in the deposit, -
poor appearance, narrow operating ranges, or
bath instability. One of the most critical disad-
vantages is the lack of uniformity of color or
appearance of the non-cyanide brass deposit
(Fujiwara 1993b). Currently, not much literature
is available for alternatives to brass cyanide
baths.
Brass Pyrophosphate
Among the non-cyanide brass plating baths,
pyrophosphate appears to be one of the most
promising. However, field reports have stated .
that additives are necessary to operate this'
application properly. Otherwise, problems
develop with unalloyed zinc getting contained in
the deposit. Metal finishers have used the
additive histidine in a pyrophosphate solution
successfully. The deposits have shown similar
qualities to the traditional copper zinc alloy
deposits (Fujiwara 1993a).
Brass Pyrophosphate-Tartare
Tests have been completed on. an alkaline
pyrophbsphate-tartare bath containing histidines
as an alternative to brass cyanide solutions.
Tests on these solutions have found that their
alloy composition was almost constant over a
wide range of current densities. Moreover,
' bright brass deposits having a uniform composi-
tion and color were obtained over almost the
entire cathode area. The tests were performed on
a bath solution that had a pH of 12.0 and a
constant temperature of 30 degrees Celsius.
Zirconium Nitride
Zirconium nitride is a coating that has similar
characteristics to brass and is applied using.an
62
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Chapter 6: Pollution Prevention m tne PU'.trg'P-ocess
alternative deposition process. This compound is
much easier .than,brass to plate and does not ,
tarnish. The surface has a metallic appearance . -
and a brass color tone. The solution uses a
deposition process call sputterion plating.
Sputterion'plating involves coating a thin film in
an even layer on a material to form a strong
atomic bond. The film provides good wear . .
resistance without color variation that can result
from tarnishing. In this process,' all or some
portions of the material to be deposited enter a
gas phase and condensation of the material takes
place under constant ion bombardment (Kopacz
1992). For additional information on sputterion
plating, refer to Chapter 8:
"Alternative Deposition Methods
Electrocoating
. The electrocoating process has been used as an
alternative to brass electroplating. This process
places the metal coating on the substrate via ^
electrocoating. It comes in a brass color and in-
clear and can be used for some decorative
applications. It does not involve metal plating,
however, the finished surface resembles a plated
finish. This finish provides excellent resistance
under salt spray tests. A plater in Illinois is using
this process on zinc die castings as a.replacement
for brass plate (Peden 1996).
Cadmium Plating
Cadmium is extremely toxic and tightly regu-
lated by EPA and OSHA. Because of its regula-,
tory status and the high cost of cadmium plating,
many platers are substituting cadmiurn with zinc
where possible. Metal finishers have; found some
problems with finding substitute bath solutions
or low-cyanide cadmium solutions for many
applications. No single cadmium substitute has
stood out as a drop-in solution. The primary
problems with, cadmium substitutes are customer
acceptance,, the characteristics of the finish, and
the higher cost of the plating solution in some
cases (Davis 1994).
Common Uses
Cadmium exhibits superior corrosion resistance
(especially in marine environments), lubricity,
and other specific engineering properties.
Cadmium.also is easily welded. Moreover, a
because of its toxicity, fungus or mold growth is
not a problem. Often, cadmium-plated material -
is chromated to increase corrosion resistance.
The largest segment of the cadmium plating
market is the military, which is beginning to
change its specifications to less toxic products
(H.aveman 1994).
Common Bath Solution ,
The most common method for electroplating
cadmium is an alkaline cyanide bath.- Cadmium
is supplied to the bath in the form of metallic
cadmium and cadmium compounds. An .all-
purpose, bright cadmium bath has a sodium
cyanide to 9admium ratio of 5:1. Sodium
hydroxide and sodium carbonate also are used in
the bath solution. Operating temperatures range
from 24 degrees Celsius to 32 degrees Celsius-
A current density of 20 to 40 amperes per square
foot is required to achieve a uniform plating
thickness (ASM 1982):
Alternative Process Solutions for Cadmium
Plating
Cadmium plating solutions that do not use
cyanide are commercially available. These
include cadmium acid.and cadmium alkaline .
plating solutions. Given the toxicity of cad-
miiirhi however, the most environmentally ;
preferrable substitutes do not.use either cadmium-
or cyanide. Replacing cyan.ide-based cadmium
coatings with one of the non-cadmium, non-
cyanide alternatives eliminates workplace
exposure to both cadmium and cyanide and
reduces environmental releases of both chemi-
cals. Tables 8 and 9 present an overview of the
available alternatives. These alternatives include
several non-cyanide based cadmium baths,
various combinations of zinc-based chemistries,
and two tin-based alternatives. Some of the
alternatives have improved performance when
compared to cadmium. These benefits include:
» Zinc substitutes exhibit improved corro-
sion resistance
» Zinc-nickel alloys have better wear
resistance
Zinc-cobalt deposits show good resis-
' tance to atmospheres containing -sodium
dioxide
63
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Quo!** &. Pigeon P'evention in the Placing Process
Table 9, Alternatives to Cadmium CyanideProduct Quality Issues (TURI 1994)
Alternatives
Cadmium
Neutral or
Acid Sulfate
Cadmium Acid
Fluoroborate
Zinc-Nickel
Alkaline
Zinc-Nickel
Acid
Zinc-Cobalt
Acid
Zinc-Cobalt
Alkaline
Zinc-Iron Acid
Tin-Nickel Acid
or Near
Neutral
Tin-Zinc Acid,
Alkaline or
Neutral
Corrosion
Protection i
(+)Good
(-t-)Good
+)Excellent
with chromate
conversion coating
(+) Good
(+)Good
(+) Good
(+) Good, but not
recommended for
high-temperature
applications
Finish
Appearance
-t-) Satisfactory
;+) Satisfactory
(+)Good
(+) Good bright-
ness at higher
efficiency
(+) Excellent
(+)Provides deep
uniform black
without use of
silver
(-t-)Provides deep
uniform black
without use of
silver
(+) Provides deef
uniform black
without use of
silver
(+) Good resistana|(+)Can be
to corrosion and decorative in
tarnish appearance
(+) Good with
chromate applied
(*) Does not
undergo bimetallic
corrosion
(-) Fair
Chromate
Colors
:ull line available
Full line available
Specialized chromates
bronze, yellow,
iridescent, and black
Specialized chromates
bronze, yellow,
iridescent, and black
Specialized chromates
bronze, yellow,
iridescent, and black
Specialized chromates
bronze, yellow,
iridescent, and black
Black; other limited
based on bath
conditions
N/A
Limited to yellow
: i
Ductility
(+) Good; little hydrogen
embrittlement
(+) Good; little hydrogen
embrittlement
(+) More ductile than acid
zinc
(-) Less ductile because of
higher brightener levels
. " 1
(+) Fair; lower hydrogen t'!
embrittlement than
alkaline
+) Better than acid bath .
(+) Good
' I
(-l-)Gobd
(+) Excellent (soft deposit)
64
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Chapter 6: Pollution Prevention '.n ;ne P'jors _?-ccess
Table 10. Alternatives to Cadmium CyanideProcess .Issues (TUR1 1994)
;i Alternatives
Plating
Uniformity
Process
Considerations
General Comments
Cadmium
(Neutral or,
AcidSulfate)
'-) Poor throwing power
(-) Liners required for acid;
preferred for neutral
(-) High toxicity, low discharge
limits for cadmium; not .
preferred toxic use reduction
(TUR) option'
Cadmium Acid
Fluoroborate
Poor throwing power
(+) High cathode efficiency
at high current densities
(+) Good stability
(+),Good data available;
widely used in. barrel plating
(-) High toxicity, low discharge
limits for cadmium; not
preferred TUR option
Zinc-Nickel
Alkaline
Zinc-Nickel
Acid
Zinc-Cobalt
Acid
+) More uniform thickness,
nd alloy distribution.than
n-nickel . _ ' ' ''
+) Good throwing power
-) Poor thickness distribu-
ion; alloy variation from
ligh to low current density
Poor throwing power
I Variable current density
(-) Chiller required to '
maintain optimum
temperature .
-} Slower plating speed
than zinc-nickel acid
(+) Faster plating speed
than alkaline nickel
(+") Good corrosion properties
maintained after forming and
heat treating
(-) Might contain chelators
(-) Requires additional
inert anodes and
segregated rectification
.(+) Faster plating speed
than alkaline nickel .
(+) Good corrosion properties
maintained after forming and
heat treating
.(-) Might contain chelators
Good .plqting speed
(+j High cathode efficiency
Zinc-Cobalt
Alkaline
Zinc-Iron Acid
or Alkaline
+) More uniform..than zincJ (-) Lower efficiency than
cobalt acid ''. '. zinc-cobalt acid
(+) Good throwing power
{-) Iron content must be
controlled to prevent
blistering
Tin-Nickel
Acid or Near
Neutral
(+) Deep throwing power
Tin-Zinc Acid,
Alkaline or
Neutral
(-) Chiller required
(-) Lined tanks
recommended
(+) No silver required for
black chromdting
(-)'Might contain chelators
, ; : -. ~~
(+) No silver required for
black chromating
(-) Might contain chelators
(+) No silver required for
black chromating
(-) Might contain chelators
(+) Good hardness (between
nickel and chromium) and
wear resistance, low contact
resistance
(+) Able to retain oil film for
lubrication
(r) Poor throwing power
.(+} Excellent covering
power
(-). Chiller required
(+) Excellent solderqbility
properties .
65
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C*Kttr 6 Pji'uiion Pre.«ncion in the Plating Process
Some of the limitations of cadmium alternatives
include;
* Increased electrical contact resistance for
zinc coatings
Reduced lubricity
Decreased throwing power
4. Decreased corrosion resistance in marine
environments
Cadmium Neutral or Acid Sulfate/Cad-
mium Acid Fluoroborate
Three non-cyanide, cadmium-based alternatives
are available: neutral sulfate, acid fluoroborate,
or acid sulfate. However, these cadmium-based
alternatives do not have the throwing power of
cadmium cyanide processes. The only substitute
that is capable of high cathode efficiency is acid
fluoroborate. but only at high current densities.
Since cadmium is also a highly regulated sub-
stance, non-cyanide alternatives that still use
cadmium are not as preferable as those substi-
tutes that contain neither Cadmium or cyanide
(Pearlstein 1991).
Zinc Alloys
Numerous zinc alloy processes are commercially
available including zinc-nickel, zinc-cobalt, zinc-
tin, and zinc-iron. The use of zinc alloys has.
grown because of their potential to replace
' cadmium, particularly in countries such as Japan
where the use of cadmium has been strictly ,
curtailed or prohibited. Zinc alloys were intro-
duced in the Japanese and German automotive
industry for use in fuel lines and rails, fasteners,
air conditioning components, cooling system
pumps, coils, and couplings. Improved warranty
provisions in 1989 from vehicle manufacturers
such as Honda, Toyota, and Mazda further
boosted the use of zinc-nickel and zinc- cobalt in
the automotive industry. Other industries that
use zinc alloys as a substitute for cadmium
include electrical power transmitting equipment,
lock components, marine, and aerospace indus-
tries. Metal finishers also have substituted zinc-
nickel coatings for cadmium on fasteners for
electrical transmission structures and on televir
sion.coaxial cable connectors (EPA l£94).
Plating with zinc alloys requires that operating
parameters are controlled and maintained at
much tighter standards than with cadmium
cyanide plating. Critical parameters include pH,
chemistry, temperature, and agitation level.
Zinc-nickel alloys can be plated from a chloride-
based process that is similar to chloride zinc
baths or from an alkaline non-cyanide zinc
solution. Brightening agents and other additives
make these alloy processes more expensive to
purchase and operate than cadmium baths. The
alloying metal usually is added as a chemical
concentrate, which is purchased from the sup-
plier. Zinc anodes generally are used with this .
solution, because alloy anodes are not readily
available (Altmayer 1993a).
For cadmium applications that require enhanced
corrosion resistance to salty environments, zinc
alloys are suitable substitutes. Pure zinc also can
be used as a substitute for heavy cadmium
deposits (more than 1 millimeter thick). How-
ever, zinc alloy deposits can fail to be suitable
substitutes when cadmium is specified for the
following characteristics: enhanced lubricity,
solderability, low electrical contact resistance,
ease of disassembly after corrosion has occurred.
or inhibition of fungus or mold growth (Bates
19-94).'
Treatment of rinsewater from zinc alloy electro-
plating usXially is simply adjusting the pH,
eliminating the need for cyanide oxidation. The
zinc-cobalt, zinc-tin, and zinc-iron processes do
not add any metals to the process that are pres-
ently regulated under federal water programs
(Altmayer 1993a). The following sections
provide a brief description of several of the most
common zinc alloys.
Zinc-Nickel Alkaline
Alkaline zinc-nickel baths produce a deposit that
tends to favor applications that do not require
bendability. Those applications are better suited
for the laminar structure of acid baths. Alkaline
zinc-nickel coatings, however, provide one of the
highest corrosion protection ratings available
with a chromate conversion coating. High
corrosion protection is a result of the chromate
solution dissolving some of the zinc from the
66
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ChJOter6i Ppflucion Prevention n'.he-Placing P-ccsss
surface, leaving a nickel-rich layer. Zinc-nickel
finishes provide good corrosion properties after .-
parts-forming operations and heat treating.
Other features of alkaline zinc-nickel are low '
metal formulation, limited range.of chromate
colors, difficulty in chromating because of nickel
content, and temperature constraints that require
a chiller for control (Zaki 1989).
Zinc-Cobalt
Zinc-cobalt deposits contain approximately 1
percent cobalt and 99 percent zinc. The acid
bath has a high cathode efficiency and high
plating speed. The deposit also has reduced
hydrogen embrittlement when compared to
alkaline systems. Thicknesses of the deposits
tend to vary substantially with the current density
of the process bath (Murphy 1993).
Zinc-Iron Acid or Alkaline
, The primary advantage of zinc-iron is its ability
to develop a deep uniform black conversion
coating. Additionally, the alloy is easily welded
and machined and is used easily on strip steel. .
This coating has been used successfully as a base
Substituting Zinc-Cobalt for Cadmium
Case Study '
The Foxboro Company, a manufacturer of
ndustrial process controls located in southeast-
ern Massachusetts/employs 3,500 people in
hree facilities. The company manufactures,a
wide range of production processes, from
electronic assembly to cleaning, plating,
painting, degreasing, and machining.
In 1992, the company focused attention on
eliminating the use of cadmium in its plating
operations. This was acomplished by eliminat-
ing unnecessary plating and substituting zinc-
cobalt solution for cadmium cyanide. The
change did not require any new plating equip-
ment and the vendor of the new plating bath
provided technical support and worker retrain-
ing to facilitate the switch. The switch not only
eliminated health and safety problems associ-
ated with cyanide, but also permitted the facility
to eliminate an entire process from waste
treatment operations. It is estimated that the
change in operations saves the company
$35,000 annually. (MA OTA 1995
coat prior to painting. The primary disadvantage
of zinc-iron coatings is their limited ability to .
provide corrosion resistance (Murphy 1993).
Zinc-Nickel Acid . - , ,
Zinc-nickel acid solutions provide bright coat- ;
ings that exhibit high throwing power. Good
corrosion properties are maintained after parts-
forming operations and heat treating because
acid zinc-nickel delivers a higher nickel content
than the alkaline zinc bath, which tends to '
increase corrosion. Unfortunately, acid solutions
also tend to produce deposits with poorer thick-
ness distribution and greater alloy variation
between high and low current density areas than
its. alkaline counterpart Other disadvantages
include the limited range of chromate colors,
required use of additional inert anodes, and
segregated treatment systems. For workpieces
that are being chromated after a cadmium plate.
this solution is difficult to work with because
higher brightener levels and nickel content create
a more brittle coating, making it more difficult to
chromate (Zaki 1989).
Tin-Zinc Alloy .
A tin-zinc alloy lias been developed in the United
Kingdom as an.alternative for cadmium plating.
The proprietary solution, Stanzec; was developed
by the International Tin Research Institute (ITRI)
in Uxbridge, Middlesex, United[Kingdom. It
contains 75 percent tin and 25 percent zinc and
can be used in either rack or barrel plating.
Research is underway to develop a high-speed
tin-zinc plating line for the continuous plating of
steel strip (Plating and Surface Finishing 1994).
Zinc Chloride
Zinc chloride process baths were tested to assess
the feasibility of using this solution as an alterna-
tive for cadmium cyanide in rack plating opera-
tions. Performance results demonstrated that
while the zinc chloride finish was similar to the
cadmium finish, the cadmium-plated parts,
however, exhibited superior corrosion resistance.
The main advantage of using the zinc chloride
over cadmiiim is a greatly reduced hazard risk at
the facility. High capital costs ($2 million for
the purchase of new equipment, cleanup costs for
old equipment, and waste disposal costs) gave
this investment a payback period of 115 years.
67
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ChJDtcr 6 ?:l;!i.! on P'e-.e-icon in the PUting Process
The process change, therefore, cannot be justi-
fied on economics alone (PNWPPRC 1996).
CorroBan .
CorroBan was developed by Boeing scientists in
the early 1980s. It is a proprietary zinc-nickel
alloy that is electrodeposited from a cyanide-free
solution. The process was licensed to Pure
Coatings, Inc. The zinc provides galvanic
protection similar to cadmium while the nickel
imparts extra hardness. Deposits from this
process pass 2,600-hour salt spray tests and
ASTM F 519 hydrogen embrittlement tests and
are compatible with aluminum. This deposit also
has lubricity (torque-tension) characteristics
similar to cadmium. Testing also has shown that
CorroBan provides better sacrificial corrosion
protection than cadmium because of the im-
proved electrode potential of the coating in a
sodium chloride solution (EPA Region 2 1995).
Alternative Deposition Processes for
Cadmium Plating
50/50 Zinc-Cadmium Alloy Using In-situ
Reclaim
The 50/50 zinc-cadmium alloy using an alterna-
tive deposition processes has shown promise as
an alternative to cadmium plating. This alloy
uses 50 percent less cadmium, but exhibits
superior corrosion resistance. The coating is
applied using a dry plating technique developed
bylonEdge Corporation for use specifically with
this alloy. In this dry plating" process, simulta-
neous plating of zinc and cadmium species is
conducted under neutral gas-flow discharge
conditions. Details of the process are of a
proprietary nature and, therefore, further infor-
mation is not available (Sunthankar 1994).
Ion Vapor Deposition of Aluminum
Aluminum coatings deposited through ion vapor
deposition (IVD) can replace cadmium coatings
in some applications, eliminating both the use of
cadmium and cyanide. This technology is suited
especially to applications that require cadmium
to protect steel substrates from corrosion and to
inhibit the growth of organisms such as mold and
fungus, ton Vapor deposition aluminum coat-
ings can be applied to a wide variety of metallic
substrates including aluminum alloys and plastic/
composite substrates, this process does not use
or create any hazardous materials.
This technology has been used mainly on high-
strength steels in the aerospace industry and in
marine applications. Some facilities have con-
verted to IVD coatings, eliminating the anodiz-
ing process on aircraft components that are '
subject to fatigue (EPA 1994). Ion Vapor
Deposition aluminum has found applications in
naval aircrafts, particularly those manufactured
by IVIcDonnell Douglas Corporation. This,
company has found IVD aluminum coatings are
especially suited'for parts where temperatures
can exceed 450 degrees Celsius and/or when
contact with titanium parts is expected. This
process also is used when working with high-
strength steels that preclude using cathodic
processes such as electroplating. However, IVD
coatings lack the frictional properties of cad-
mium and are expensive to implement (Lansky
1993).
The advantages of IVD aluminum coatings
include the uniformity in finish thickness and
excellent throwing power. Deposits can be
plated on difficult-to-reach places, making IVD
attractive for coating complex shapes. The
process is limited, however, in its ability to
deposit coatings into deep holes and recesses.
particularly in configurations where hole depth
exceeds the diameter (Pearlstein 1991). IVD
processes are discussed in more detail in
Chapter 8.
Copper Plating
Common Uses
Copper plating is widely used as an underplate in
multi-plate systems arid as stop-offs for carburiz-
ing as well as in electroforming and the produc-
tion of printed circuit boards. Although
relatively corrosion resistant, copper tarnishes
and stains rapidly when exposed to the atmo-
sphere. Copper alone is rarely used in applica-
tions where a durable and attractive surface is
required. Copper plating is used generally as an
unde.rplate or pre-plate before a final finishing
operation such as nickel or gold. Bright copper
is used as a protective underplate in multiple
68
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Chapter 6; Pollution pre,'.ent:cn «r. ;ne.Pbt.rg P'3cess
la'ver systems or \vhen a'decorative finish is
desired. The copper finish often is protected -
against tarnishing and'staining by the application
of a clear lacquer: Copper plating can change the
appearance, dimensions, or 'electrical conductiv-
ity of a metal part. Jewelry manufacturing,
aerospace, and electronics often use copper
plating (ASM 1982), .'. .
Common Bath Solutions and Waste
Treatment
The major constituents of copper cyanide baths
. are potassium cyanide, potassium hydroxide, and
copper cyanide. Cyanide copper plating requires
a two-stage \yaste.treatment procedure. The first
step is cyanide destruction using either chlorine
gas or less hazardous, but more expensive,
hypochlorite treatment. The second step is
precipitation of metals (i.e., pH adjustment with ,
a caustic). The sludge produced.from this
treatment contains trace amounts of cyanide,
increasing disposal costs significantly (ASM
1982). ';'..''_
The benefits of replacing cyanide^based copper
' . plating baths with a non-cyanide solution include
reduced environmental exposure and employee
health risks. Non-cyanide copper has the follow-
ing benefits: '
Greatly reduces safety risks to workers
Can reduce the costs and complexity of
treating spent plating solutions
Poses no risk of hydrogen cyanide (HCN)
evolution frorn dragoui to an acidic bath
Can increase plating speed . .
Eliminates a listed hazardous ; -
wastestreqm ,
Eliminates or reduces Toxics Release
Inventory (TR1) reporting requirements
» Can reduce sludge generation because
of reduced metal concentrations
Might not require treatment for carbon-
ates in the plating solution (EPA 1994)
Issues Related to Non-Cyanide Substitutes
Non-cyanide copper plating requires more
frequent bath analysis and adjustment than
cyanide-based plating. Cyanide-based copper.
plating baths are relatively forgiving to bath . , _ .
composition because they remove impurities.
Non-cyanide baths are less tolerant of poor
surface cleaning so thorough cleaning and
activation of the surface is critical to obtain a
quality finish. Personnel should be capable of
operating the non-cyanide process as easily as
. the cyanide-based process (EPA 1994).
Operating costs of the bath are substantially '
higher for the non-cyanide processes than the
cyanide process, however, replacing the cyanide-
based bath with a non-cyanide bath eliminates
the nee'd for treatment of cyanide-contaminated
wastewaters. This reduces substantially the
difference in cost between the two. solutions.
Given the higher operating costs, a facility might
not be able to justify this conversion on econom-
ics alone unless the facility, faces substantial
treatment costs for cyanide emissions.
Reported Applications
The use of non-cyanide copper plating baths is
not widespread-. The number of companies
running non-cyanide trials is small, but growing
(Altmayer 19.93). An application where non-
cyanide plating could be attractive from a cost
perspective is selective carbtirizing. This process
is used widely in the heavy equipment industry
for hardening portions of coated parts such as
gear teeth. Gears must be hard at the edges, but
not throughout because hardness throughout
could cause the part to become brittle. To
achieve this selective hardening,' the plater
applies a copper mask to that portion of the part
that is not targeted for hardening. The part then
is treated with carbon monoxide and other gases
(EPA 1994).
Limitations
, Alkaline non-cyanide processes are unable to
deposit adherent copper on zinc die castings and
zincated aluminum parts without a copper strike.
The one exception is a supplier that claims to be
able to plate these parts using a proprietary
process. Several facilities are currently testing
this method on avptlot scale (Altmayer 1993). Of
these pilot tests, two facilities reported that costs
are approximately .two to three times more than
other processes, even when waste treatment and
disposal costs are considered. One of these
-. 69
-------
C*"JD8«r 6: ?c«ut.op P'tvertton in the Placing Process .
facilities has discontinued the use of the process
while the other facility has continued with the
process believing that the benefits of increased
safety and compliance are worth the cost (EPA
1994"),
For plating copper, certain non-cyanide alkaline
baths of proprietary composition have been
developed. Four widely known alternatives to
copper cyanide plating are copper acid sulfate,
copper acid fluoroborate, copper alkaline, and
copper pyrophosphate. Table 10 provides a brief
overview of these four alternative bath solutions.
Specific Non-Cyanide Alternatives
Copper Alkaline Solutions
Non-cyanide alkaline baths yield fine grained,
dense deposits similar to cyanide copper depos-
its. The one area where they might differ is in
the purity of deposit. Additives in copper
alkaline solutions incorporate a trace of organic
material into the deposit. This solution is ideally
suited for wdrkpieces that require thick deposits
such as t''ose used as heat treating (carburizing)
stop-off on steel parts. The dense deposit is an
excellent diffusion barrier for carbon (Braun
tntertec 1992).
The non-cyanide alkaline copper solution uses
cupric copper ions while the cyanide process
contains monovalent copper. The chemical
composition of monovalent copper results in
faster plating at the same current density levels.
Platers can operate alkaline copper baths at
higher current densities than cyanide solutions to
yield faster plating overall. The throwing power
of the non-cyanide process is superior to the
cyanide process, especially in barrel plating.
.This process uses one-quarter to one-half of the
copper contained in cyanide solution, resulting in
lower sludge generation because of lower metal
concentrations (Mabbett 1993).
The alkaline substitute has significant draw-
backs. Copper alkaline non-cyanide baths
operate at significantly lower pHs (8.0 to 8.8)
than traditional cyanide copper lines. Despite the
lower pHs, non-cyanide baths have trouble
tolerating zinc contamination and have not been
Table 11. Overview of Alternatives for Copper Cyanide Plating (TURI 1994)
jj :; , -..
'Alternatives
Copper
Alkaline
Copper
Acid Sulfate
or
Fluoroborate
Copper
Pyrophosphate
Finish
Appearance
+) Good
appearance
4-) Good
appearance
(+) Excellent
eveling
[+) Good, fine
grained, and
semi-bright
Ductility
+) Good
4-) Good
to excellent
(+) Good
Plating
Uniformity
+) Better throwing
nan cyanide
-) Less macro -
hrowing power
than alkaline
[+) More micro-
throwing power
than alkaline
(4-)Good throwing
power
Process
Considerations
+) Operating pH 8.0
08.8
-) Lined tanks and
appropriate anode
gaskets required
(4-) Fluoroborate
allows use of higher
current densities
(+) Operating pH of.
8.0 to 9.8
(-) More sensitive to
organic contaminants
than acid copper
(-) Might require
longer plating time
General
Comments j j
4-) Can be used as
leat treat maskants
4-) Less corrosive
[+) Might be used
as a strike bath
(+) Good use 'data
available
(4-) Might be used a:
strike bath
(-) Might contain
ammonia
70
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Chapter 6; Pollution Prevention n tne P!j£.ng Process
successful at plating copper over zinc surfaces.
The alkaline copper process also is more sensi-
' tive to impurities and the chemistry can be .
' difficult to control. In addition, changing over to
alkaline-copper requires a lined tank and, in
some cases, the addition of a purification tank.
Overall, the cost for substitution is fairly high
when compared to the cost of copper cyanide
solutions (Mabbett 1993).
Copper Acid Sulfate
The copper sulfate bath is the most frequently
used of the acid copper electrolytes. An acidic
copper plating bath using sulfate ions has proved
versatile. However, the low pH can sometimes
Substituting Copper Alkaline Solutions
for Copper Cyanide Case Study
Tri-Jay Company is located in Johnston, Rhode
Island. The facility employs 45 people and
occupies .an 11,000 square foot facility. Tri-Jay
provides the jewelry industry with job, shop
plating services. In conjunction with the Rhode
Island .Department of Environmental Manage-
ment, Tri-Jay tested the feasibility of replacing
their copper cyanide lines with an alkaline
plating solution manufactured by Zinex Corpora
tion of Canard, California. .
n testing the solution, parts were placed in rack
and barrel processes under controlled condi-
iohs. Based on limited production runs, the
saths were scaled up to higher production .
quantities. The bath conditions were optimized
and data was taken on plate conditions after
quality control. ',..,' ,
' , I ' "s
Tri-Jay concluded that while the bath had
promise, the operation needs close.monitoring
and the solution might not be well suited for job
shop applications.. The process proved to be
trouble-free in plating brass and, with proper
cleaning, steel-as well. Castings, however,
presented too many contamination prpblems fo
this solution to be economically.feasible. Forth
electronics and automotive industries and for
reel-ta-reel plating operations/ this solution
might be extremely feasible. (Rl DEM 1995a)
attack the substrate and increase iron concentra-
tion in the process bath. The process is used
primarily in printed wire board manufacturing
and e'lectroforming operations arid for the -
application of copper "as an undercoating for
chromium. By altering the composition of the
. bath, platers can use copper sulfate in through-
hole plating of printed circuit boards where a
deposit ratio of 1:1 is desired. With additives,
the bath produces a bright deposit with good _
leveling characteristics or a semi-bright deposit
that is easily buffed (Braun Intertec 1992).
. In contrast to heavy copper cyanide plating
.baths, copper sulfate baths are highly conductive
and have simple chemistries. Sulfate baths are
economical to prepare, operate, and treat. Previ-
ous sulfate bath problems have been overcome
with new formulations and additives. The
copper cyanide strike might still be needed for
steel, zinc, or tin-lead base metals (Braun
Intertec 1992). ' '
,Copper Fluorobora te
Fluoroboric acid is the basis for another copper
plating bath that provides enhanced solubility
arid conductivity as well as high plating speeds.
This bath is simple to prepare, stable, and easy to
control. Operating efficiency approaches 100
percent. Deposits are smooth and attractive and
can be easily buffed to a high luster. The addi-
tion of molasses to the bath, when operated at
120 degrees Fahrenheit, results in deposits that
are stronger and harder (Weisenberger 1982).
Additional agents must be used to avoid exces-
sive porosity in thicknesses greater than 20 mils.
The drawbacks of this bath solution are that it is
more costly, has fewer additive systems avail-
able, and is more hazardous to use than other
non-cyanide alternatives. Treatment of waste-
water also is more costly (Murphy 1993).
Copper Pyrophosphate
Copper pyrophosphate is used, primarily to
produce thick deposits. These baths are used for
decorative multi-plate applications, through-hole
plating of printed circuit boards, and a stop-off in
selective case hardening of steels. The types of
plates obtained with this solution are similar to
those obtained with a high efficiency cyanide
bath. However, a strike is required if plating
over steel, magnesium, atuminum, or zinc.
Alkaline pyrophosphate baths exhibit good
throwing power, plating rates, and coating
71
-------
; PartuC.cn Prevent on in the Plating Process
ductility, In addition, the bath" normally operates
at an almost neutral pH. Deposits from this bath
are fine-grained and semi-bright. The main
disadvantage of copper pyrophosphate is that the
chemistry is expensive and wastewater is harder
to treat when compared to traditional copper
cyanide wastewater (Braun Intertec .1993).
Acid Copper Versus Alkaline
Copper Solutions
Plating of copper from acid baths is used exten-
sively for electroforming, electrorefming,
manufacturing of copper powder, and decorative
electroplating. Acid copper plating baths contain
copper in bivalent form and are more tolerant of
ionic impurities than alkaline baths. However,
they have less macro-throwing power and poorer
distribution rates than alkaline solutions. Acid
baths have excellent micro-throwing power,
which can be effective in sealing porous die
castings. As with the alkaline baths, the plater
must apply a strike to a workpiece prior to
plating on steel or zinc (Braun Intertec 1993).
Alternative Deposition Processes for
Copper Plating
The Department of Defense is testing the feasi-
bility of depositing copper using new deposition
technologies such as plasma spraying, ion
plating, and sputter deposition. For more infor-
mation on these technologies, refer to Chapter 8.
Waste Treatment of Alkaline Non-Cyanide
Copper '
Wastewater treatment of non-cyanide copper
solutions is simpler than those for copper cya-
nide processes because of the elimination of
cyanide removal. Another benefit is reduced
sludge generation because the non-cyanide
process contains one-half to one-fourth as much
copper as a full-strength cyanide copper bath.
Furthermore, non-cyanide alternatives eliminate
the two-stage chlorination system that uses
chemicals such as chlorine or sodium hypochlo-
rite that can increase sludge generation. One
potential disadvantage of the non-cyanide bath is
that it frequently can become contaminated
beyond control (as happened in pilot test),
requiring increased treatment and disposal for
the process line (Freeman 1995).
Separation Technologies for
Copper Plating . . ,' '
This section provides specific examples of
recycling and recovery technologies for copper
plating including ion exchange, electrodialysis,
electrolytic recovery, and reverse osmosis. A
more in-depth discussion of individual recycling
technologies is included in Chapter 7.
Ion Exchange
Copper platers can use ion exchange to recover a
high percentage of the copper from contaminated
plating baths and rinsewaters. For example,, a
Montreal plating shop sent rinsewater with
copper concentrations of about 300 parts per
million from a copper sulfate plating solution
(acid copper) to an ion exchange resin unit. The
unit reduced the concentration of copper to about
1 part per million. Every 20 to 30 minutes, the
. resin would be regenerated with dilute sulfuric
acid, exchanging copper ions in the resin with
hydrogen ions. The concentrated copper sulfate
solution produced from the regenerating process
was added to the plating tank as needed.
Through this ion exchange process, the company
recovered-95 percent of the copper from the
running rinse (RI DEM 1995a).
Electrodialysis
Used on a stagnant rinse line, electrodialysis can
recover 90 to 95 percent of the dragout from
heated copper plating solutions. This concen-
trated dragout goes back into the plating tank
while the dilute stream is returned to the rinse
tank. Electrodialysis can run continuously
without regeneration, requires only a DC power
source for operation, and consumes relatively
small amounts of electricity. A disadvantage of
electrodialysis is that it recovers plating bath
impurities along with the copper. The mem-
branes in this process also are prone to fouling
from either solids in the bath or from compounds
forming on the sheets (RI DEM 1995b).
Electrolytic Recovery
this process recovers only the metals that are
dragged into the rinsewater. Enough metal must
be present in the solution to form a usable strip.
A homogenous copper deposit requires the rinse
solution to have concentrations of 2 to 10 grams
72
-------
Ouocer 6: Pcilucicn Prevention m :r.e p'acirg p-?cess
'per liter, Cathodes with greater surface area can
recover copper from much lower concentrations
'(.in the 10- to 50-milligrams-per-liter range)..
*'-
An electroplater in Providence, Rhode Island,
reported recovery of 85 grams per minute over 9
days using a 5-square-foot electrode. The unit
received flow from a dragout tank and returned
the clean water to the same tank. This particular
tank's copper concentrations dropped from 150
to 10 milligrams per liter. Other companies have
experienced similar reductions of approximately
88 percent of the copper from both standing rinse
tanks and running rinses (RI DEM I995a).
Reverse Osmosis
EPA performance tests have shown reverse, ,
osmosis (RO) to be successful in recovering ,
metals from both acid copper and.copper cyanide
plating baths. Reverse osmosis membranes used
in cyanide applications might need pretreatment.
A copper cyanide plater reported that its RO unit
recovered 98 to 99 percent of the copper from: its
plating wastes and 92 to 98 percent of the
cyanide. The type of membrane used is a major
factor in determining the effectiveness of RO.
Cellulose membranes cannot withstand cyanide
and solutions .with either high or low pH. How-
ever, many membranes are resistant to these
conditions (RI DEM 1995a). ' ;
Copper Strike
Copper strikes often are used to deposit a thin '
intermediate layer (strike),of copper over a
variety of substrates including steel and zinc die
castings before those metals are plated with other
metals. This layer is required for successful
plating because it promotes adhesion on diffi-
cult-to-plate metals and protects some substrates
from degradation in subsequent plating solutions.
Because copper-strikes are applied frequently,
finding replacements for cyanide solutions can
greatly assist facilities in reducing the amount of
cyanide that they use (Hughes 1991). :
,.-*."'"' , "*
Copper Strike Alternatives
Copper Pyrophosphate
Dilute copper pyrophosphate has been viewed as
a feasible replacement for the cyanide strike .
because the solution does not degrade substrates.
The main disadvantage of this chemistry is that it
usually takes three times longer to plate than
traditional cyanide solutions (Hughes 1991).' For
.more information on this alternative, refer to the
previous section on copper cyanide'plating in
this chapter. . "
'
High-pH Nickel
High-pH nickel plating solutions have been
available for a long time as a substitute for
cyanide copper strike on zincated surfaces and
zinc die castings. To obtain optimum results
with high-pH nickel, the plater must balance the
ratio between nickel sulfate and sodium sulfate.
The proper ratio depends on several factors
including part geometry; parts-with complex -
shapes require higher sodium sulfate concentra-
tions than parts with simple geometry. For
plating operations above a 5.4 pH, platers use
ammonium hydroxide and sulfuric acid for pH .
control. Zinc contamination should be removed
continuously through low current density dum-
mying in a purification cell. Cleaning parts prior
to plating is more critical in high-pH nickel
plating than traditional copper cyanide strikes.
Because the bath chemistry is not proprietary and
requires no additives, facilities can mix their own
. solutions. This makes the cost of operating this
bath lower than operating cyanide copper strike
lines and significantly lower than the cost of
operating alkaline non-cyanide copper baths
(Freeman 1995). . ,
Using sodium in the. bath will affect the deposit
characteristics of the strike. The higher the
sodium content of this nickel-plating bath, the
more brittle the deposit becomes. The bath,
therefore, should be used only as a strike before
conventional nickel or copper plating. Parts that
undergo fatigue cycles or extreme temperature,
changes can experience early fatigue failures and
less corrpsion reststance.(Freeman 1995).
Substituting high-pH.nickel for a copper cyanide
strike will eliminate a cyanide wastestream.
However, the ammonium ion present in the high-
pH nickel formulation can cause waste treatment
problems unless the concentration can be mini-
mized through dragout recovery techniques.
Another disadvantage of this technique is that the
bath contains a higher metal content than the
73
-------
Oioser 6; PaiSution Prevention in the Plating Process
cyanide copper process and twice the metal
content of the alkaline non-cyanide process.
Sludge volume from wastewater treatment would
be affected accordingly (Freeman 1995).
Precious Metals
The etectrodeposition of precious metals for
decorative and engineering purposes is an
important part of the metal finishing industry.
Given the high cost for a gallon of precious
metal solution, platers have used many methods
to conserve and recover precious metal solutions.
Because of this, more information is available on
recovery technologies for precious metals than
common metals (e.g., copper, nickel, and zinc).
Common forms of metal recovery in precious
metal operations include ion exchange or elec-
trowinning (Ford 1994).
Gold Plating
Common Uses
Until recently, gold plating was used primarily
for decorative purposes in jewelry and flatware.
Currently, gold is widely used in the electronics
industry because of its good electrical contact
properties as well as corrosion and oxidation
resistance. Typical applications for gold plating
include printed circuit boards, contacts, connec-
tors, transistor bases, and integrated circuit
components. Gold plating also is widely used in
the chemical industry for reactors and heat
exchangers (ASM 1982).
Traditionally, gold has been plated from potas-
sium gold cyanide solutions, although many
different types of gold and gold alloys are
available. However, gold plates can be broken
down into eight general classes:-
Class A: Decorative 24K gold flash (2 to 4
millionths thick) plated In rack and barrel
operations
Class B: Decorative gold alloy flash (2 to 4
millionths thick) plated in rack and barrel
operations
Class C: Decorative gold alloy flash (20 to
40 millionths thick) plated in rack operations
* Class D: Industrial/electronic high-purity
soft gold plated in rack, barrel, and selective
plating operations
Class E: Industrial/electronic hard, bright,
and heavy 99.5 percent gold (20 to 200
millionths thick) plated in rack, barrel, and
selective plating operations
Class F: Industrial/efectronic gold alloy
heavy (20 to 400 millionths thick) plated in
rack and selective plating operations
Class G; Refinishing, repair, and general;
deposits are pure bright alloys (5 to 40
millionths thick) plated in rack and selective
' plating operations
Class H: Miscellaneous including electro
forming of gold and gold alloys, statuary,
and architectural applications (Weisberg
1993)
In general, platers use high gold contents at
heavy thickness because this permits higher
current densities and higher cathode efficiencies.
Other methods that platers can use to increase
plating speed include higher operating tempera-
tures and increased agitation (ASM 1982).
Common Bath Solutions
The four general groups of gold plating solutions
are alkaline gold cyanide, neutral gold cyanide,
acid gold cyanide, and non-cyanide solutions
(generally sulfite-based). Alkaline cyanide baths
have been used for the past century. Because of
the complexing action of cyanide, however,
obtaining consistent co-deposit of gold alloys is
difficult unless the process is operated at high
current densities. As a result, platers have
limited the use of alkaline cyanide baths to flash
deposits. Around the 1950s, bright baths were
developed using silver and selenium as alloying
agents. Some success has been demonstrated
with neutral baths. Free of cyanide at the start,
these baths build up potassium cyanide by
adding gold potassium cyanide to replenish the
gold in the process bath (Braun Intertec 1992).
Each of the groups can be paired with the
different classes of plating operations discussed
above.
74
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Chaocer 6: Pollution Prevention in (fie Pacing Process
* Alkaline gold cyanide:.Class A, B, C, D,
occasionally F, G, and H .
Neutral gold cyanidexThis is usually used
to achieve highrpurity gold plated for Class
' D and G. ' '
Acid gold cyanide: This is used for bright,
. hard gold and gold alloy plating. It is used
occasionally for Class B, C, E, F, arid.G.
*' Non-cyanide gold: Occasionally, it is used
for Class A, B, C, D, F, G, and H (Weisberg
1993).
Alternative Gold Plating Solutions
The high cost of gold has made conservation
critical and has led to a search for substitutes.
Table 11 provides an overview of the alternatives
to gold cyanide plating. -.-,-.
'Gold Sulfite "
In gold plating, firms can substitute a sulfite bath
for a cyanide bath. For example, a study per-
formed at Sandia National Laboratories com-
pared coatings on-microelectronic circuits
produced by the gold cyanide process and the
'gold sulfite process. The test results showed that
gold sulfite plating solutions are compatible with
a wide variety of substrates used in electronics
including quartz, aluminum oxide, silicon, glass,
cordierite, duriod, and gallium arsenide. The
study also found compatibility with surface
treatment compounds. The sulfite bath formed a
gold plate, with similar weld bond strength and a
coat density similar to pure gold. The study
concluded that the gold sulfite bath produced
nearly equal, if not slightly better, coatings and
was far less hazardous to use. Another study -
found that a non-cyanide sulfite gold plating
solution is capable of stable operations at pH
values as low as 4.0. At pH values lower than
6.5, sulfur dioxide is released at a controlled
level during operation (Hughes 1991). _
Palladium , ;
Palladium, a-precious metal, has emerged as a
feasible substitute for hard gold and, in some
instances, soft.gold finishes within the last
decade. Palladium's attributes include lower
cost, lower specific gravity, comparable at-
tributes to gold, and solution composition.
Palladium and palladium-nickel alloys have been
used primarily for separable connectors and
printed wiring board fingers. Recently, many
additional applications have been found includ-
ing contact finishing for edge card connectors,
lead frames for 1C packaging, solderable contact
and end terminations for multi-layered ceramic
capacitors, semiconductor optoelectronic devices
for packing, etch resists for printed wire boards,
battery parts, and decorative items for jewelry
and consumer hardware. These applications all
take advantage of palladium's lower cost and
material properties, which, in many instances,
are superior to gold. The use of palladium also
eliminates the use of cyanide because palladium
is plated from non-cyanide solutions. The two
major solutions for palladium are ammonia-
based and organic amihe-based (Abys 1993).
Alternative Deposition Processes for ,
Gold Plating
Several facilities are testing the use of alternative
deposition processesSor gold plating. Processes
Table 12. Overview of Alternatives for Gold Cyanide Plating (Braun Intertec 1992)
Alternative Solution
Gold Sulfite
I Cobalt-Hardened
I (No Free Cyanide)
Gold*
Advantages
Excellent throwing power
Can plate on complex parts
Performs as well as gold
cyanide solutions
Disadvantages
Solutions are less stable,
therefore, require more
monitoring and
conditioning
Works well on slide wear
applications .'
Deposits are brittle and
thermal shock can cause
cracking
Outlook for Solution
^ m '
For electronic applica-
tions, more research
is required
More research-is required
'Little information on this solution is available
75
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Chjotcr 6; Ps:'uiscn Prevention in the Plating Process
such as ion plating and sputter deposition are
being tested. For more information on these
processes, refer to Chapter 8.
Recovery Technologies for Gold Plating
Because of the high cost of the metal salts for
gold plating, recovery technologies are widely
used. Even with the high cost of some of the
technologies, it still is economically feasible for
companies to use technologies such as ion
exchange and reverse osmosis.
Silver
Common Uses
The largest use of silver plate is in the flatware
and hollowware trade. The second largest use is
in the electronics industry where large amounts
of silver.are plated onto conductors, wave
guides, and similar items because of silver's
unsurpassed electrical conductivity. In most of
these applications, silver is plated over copper
and copper alloys. The aerospace industry uses
silver as a plate over steel in aircraft engine
manufacturing (SME 1985).
Common Bath Solutions
Commercial silver electroplating has been
practiced since the middle of the nineteenth
century. The plating bath contains silver in the
form of potassium silver cyanides and free
potassium cyanide. Platers also can use sodium
cyanide, but they generally prefer the potassium
form. The amount of free cyanide in.silver
solutions is extraordinarily high. For example, a
common copper-cyanide bath has 2 ta4 ounces
of free cyanide per gallon while the amount of
free cyanide in silver solutions commonly is 16
to 22 ounces. Large quantities of cyanide are
required to increase the throwing power of the
solution. Usually, a small amount of potassium
carbonate and/or potassium hydroxide also is
added to the bath. Silver baths usually are
operated at room temperature-although high-
speed plating has been performed at tempera-
tures as high as 120 degrees Fahrenheit (SME
1985).
When hard, bright silver deposits are desired,
proprietary additives containing metals or
organic brighteners generally are used. Some
Closed-Loop Metal Recovery for Jewelry
Manufacturer Case Study
Howard H. Sweet crd Son is a 125-worker
jewelry manufactu": specializing in the produc-
tion of silver, gold, and gold-filled beads and
chains. The company's operations are widely
integrated spanning the design and manufac-
ture of the working parts for its chain-making
machines, the stamping of flat stock and tubing,
and bead and chain making to the soldering,
plating, and assembly of finished jewelry. In laie
1995, the company faced new regulations that
required them to implement further pollution
controls. The company determined that a major
source of hazardous waste was a burn-out
room where copper used in the fabrication of
gold beads was stripped.
paced with this requirement, the company first
examined traditional wastewater treatment
options. Problems with space and cost immedi-
ately became apparent. The company chose to
invest in an ACCA system, a virtually closed-
loop recovery system for gold and copper.
During the first year of operation, Sweet's new
system recovered 263 troy ounces of gold and
2,144 pounds of copper.
The total capital and engineering costs for the
ACCA Technologies system was $95,000. The
payback period from the recovery of additional
gold and copper was 12.6 months. After the
first year, the system yielded $95,000 annually
in recovered metals. In addition, the need for
sludge disposal was eliminated.
(Plating and Surface Finishing 1993)
additive combinations increase the tarnish
resistance of the silver deposit. As with all
bright solutions, the metal and free cyanide
content of the bath must be closely monitored
(SME 1985).
Alternative Solutions for Silver Cyanide
Given the large amounts of cyanide used in silver
plating, finding suitable alternatives could
greatly reduce cyanide levels in wastewater.
Several attempts have been made to introduce
non-cyanide alternatives. Most of these solu-
tions are based on ammonium, halide, and
aminothio complexes containing silver and a
variety of conductivity salts and brightening
agents. In almost all cases, the non-cyanide
76
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Qiopter 6: Pollution Prevention m the Pljcing Protest
solutions have had problems especially in
producing thick, bright deposits. Many of the
alternatives that have been tested are unsuitable
because of photosensitivity. However, some -
proprietary formulations are worthy of mention.
Table 13 provides an overview of the alternatives
for silver cyanide plating. "
RCA Silver Solution ,
RCA, Inc. obtained a-patent for silver iodide in
1977. Silver iodide is a stable and easy-to-use'
solution. However, the solution was unsuitable
for electronics and decorative coating because of
sensitivity to light and the high cost of the
solution. Another problem with this solution is
that it is toxic anxl is likely to complicate waste
treatment operations (Braun Intertec 1992).
Silver Ammonium ' '
, In 1968, IBM, Inc. obtained a patent for a bath
. that uses silver ammonium complexes. This
solution's optimum performance was found to be
in the pH range of '11.0 to 12.5. At this pH level,
the bath generates ammonium hydroxide, which
poses a concern for employee health and safety
(Braun Intertec 1992).
Silver Metfianesulfonate-Potassium Iodide
Researchers have investigated a silver
methanesulfonate-potassium iodide bath to study
the effects of additives. This bath produced a .
deposit with a ftne grain.structure and appear-
ance that"was comparable to or better than a
conventional cyanide bath.. However, this
solution has not been tested on a commercial
scale (Braun Intertec 1992).
Technic Non-Cyanide Silver Solution
Some platers have successfully applied Technic
Inc.'s proprietary non-cyanide silver solution for
applications where a thin deposit is required.
However, it has not been, applied universally. A
facility in New York tested Technics, Inc.'s non-
cyanide silver solution, Technic-SHver CyLess,
Table 13 Overview of Alternatives for Silver Cyanide Plating (Braun Intertec 1992)
Alternative
Solution
Ammonium
Silver*
Advantages
Amino or Thio-
Complex Silver
Disadvantages
Bath generates ammonium
hydroxide which poses an
exposure concern for line
operators
Outlook for Solution
Not promising because
of worker health
and safety Issues
» Readiness of thiosulfate
ions to be oxidized
»Low current density area
might be discolored
Halide Silver |Very stable
Easy to operate
Not promising; at
one time widely
marketed but
withdrawn
No Free Cyanide
Silver
Light-sensitive solution
Initial, cost is high for
decorative and electronic
applications
Solution is toxic
Limited application;
solution is fairly unstable
Developed specifically , :
for electronics applications
»Good contact properties
* Less, susceptible to tarnishing
^Silver can Be precipitated
and reused
^Neutral pH and no free
cyanide allows for free rinsing
Limited test application
Developed for high-
speed electronics plating
*No additional information on this solution is available
77
-------
CUB:** 6' Pe-utan P'*\e"t;cn m the Plating Process
as a replacement for their bright silver cyanide
line. The facility decided not to implement this
system for the following reasons:
+ Alternative is cost prohibitive: The facility
estimated that the cost of operation for the
non-cyanide system is three to four times
more expensive than a conventional silver
cyanide system.
Difficult-to-polish surface: The non-
cyanide silver plating process produces a
surface that is difficult to polish and not as
bright as conventional silver cyanide depos-
its. Customer specifications require that the
facility's silver-plated products are bright.
More work on Technic's non-cyanide solution is
being performed by Lawrence Livermore Na-
tional Laboratory through a cooperative research
and development agreement.
Silver in the Electronics Industry
Researchers have developed a new silver plating
bath with no free cyanide especially for high-
speed plating in the electronics industry. This
solution also can be formulated for standard
Systems. Silver coatings from the no free
cyanide bath have good contact properties and
are less susceptible to tarnishing than those from
conventional alkaline cyanide silver baths.
These solutions are easy to maintain and require
less complicated waste treatment procedures.
Silver can be precipitated as silver cyanide and
reused. The neutral pH and no free cyanide
properties cause the system to be less likely to
leave residuals on parts, a property known as free
rinsing (Braun Intertec. 1992).
Alternative Deposition Processes for Silver
Plating
Several facilities are testing alternative deposi-
tion processes for silver plating. Processes such
as sputter deposition are being tested. For more
information on this process, refer to Chapter 7 in
this manual.
Recovery Technologies for Silver Plating
Because of the high cost of the metal salts used
in,silver plating, recovery technologies are
widely practiced. Even with the high cost of the
* some of the technologies, it is still economically
feasible for companies to use technologies such
as ion exchange and reverse osmosis. Silver
cyanides can be quite problematic because the
complexed cyanide is somewhat resistant to
oxidation using conventional alkaline
chlorination.
Electrolytic Recovery Technology for Silver
Cyanide Recycling
Wastewater generated frdm the rinsing of silver
cyanide parts contain silver and cyanide-contain-
ing compounds. The wastestream requires
pretreatment to reduce these toxic materials prior
to discharge. Electrolytic recovery technology
uses an electrical current to plate out the silver
metal and oxidize the cyanides in spent rinsewa-
ter. The silver metal is recovered from the
electrolytic recovery unit (ERU) as a metal foil
that can be returned to the plating process bath as
an anode source. The purity of the recovered
silver should meet the specifications for anode
purity as long as the water from the rinse tanks is
used to rinse parts that are plated only in the
silver cyanide tank. The ERU should be
plumbed to a static rinse tank in a closed-loop
fashion. The cyanides,are partially oxidized to
cyanates in the electrolytic process. This technol-
ogy can be used to remove more than 90 percent
of the silver metal in the rinsestream and oxidize
50 percent of the cyanides (NFSESC 1995).
The benefits of electrolytic recovery for silver
cyanide recycling include cost savings and
reduced hazardous waste generation. The cost
savings will vary for. each installation, however,
cost savings can be expected from reduced use of
treatment chemicals for cyanides and heavy
metals in the wastewater treatment plant, reduced
costs for silver anodes arid chemicals, and
reduced cost for disposal of hazardous waste
sludge generated from the treatment process.
For more information on electrolytic recovery,
refer to the recycling/recovery section in
Chapter?.
Silver Recovery with Ion Exchange and
Electron/inning
Ion exchange systems can be used to remove
silver cyanide complexes from rinsewater.
These metal complexes are strongly retained by
anion resins and are difficult to remove with
78
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Chapter 6: Pollution Prevention m the Plilmfc ?roCKS
conventional strong base regeneration. Often, the .
exhausted resin is simply shipped off site for
silver recovery by incineration, resulting in high
operating costs for the ion exchange unit because
of resin costs. A study done in Wisconsin found
that by combining ion exchange and etectrpwirtr
ning technology facilities can expect that:
Greater than-99 percent of the silver .
cyanide can be removed from electroplat-
ing rinsewater using a strong base aniorv-
excharige resin. .
Ion exchange resins can be effectively
regenerated using sodium thiocyanate at
.a dosage of 40 to 50 pounds per cubic
foot of resin.
* Silver can be completely recovered from
spent thiocyanate regenerant using
electrowinning. Thiocyanate destruction
during electrowinning is fairly minimal so
that-regenerant can be reconstituted for
reuse.'Electrowinning also.cah^be used.
to remove 67 percent of the copper
contamination. . .- ,
Budgetary estimates for a 2 gallons-per-
minute system indicate a 3- to 4- year .
.payback is feasible (Lindstedt 1992). ,
For more information on ion exchange and
electrowinning, refer to the recovery/recycling
section in Chapter 7.
..Polymer Filtration
A new technology is under development at Los
Alamos National Laboratory to selectively
recover silver ions from electroplating
rinsewaters. The silver ions are recovered in a
concentrated form with the appropriate counter
ions ready for return to the original electroplating
bath. The technology is based on the use of
specially designed water-soluble polymers that
selectively bind with silver ions in the rinse bath.
The polymers have such a large molecular
weight that they can be separated using ultrafil-
tration technology. The advantages of this
technology are high metal selectivity with no
sludge formation, rapid processing,: low energy,
low capital costs, and small size.
Zinc Plating
The electroplating industry uses approximately
88,000 tons of zinc in the United States per year.
Approximately 40 percent is used in cyanide
baths And another 40 percent is used in chloride
zinc solutions. The remainder is used in alkaline
non-cyanide baths (Davis 1994 j.
Common Uses
Zinc plating is versatile and used for many
different applications. Because zinc is relatively
inexpensive and readily applied in barrel, tank,
or continuous plating, platers prefer it for coating '
iron and steel parts when protection from either. ,
atmospheric or indoor corrosion is the primary
/objective (Ford 1994). ..' -
Common Bath Solutions
As stated above, zinc is deposited electrolytically
from three different solutions: 'a cyanide bath, an
acid chloride bath, and an alkaline non-.cyanide
(or zincate) bath. Zinc, is also used in the galva-
nizing process. Workpieces usually are
chromated after plating. The conventional zinc
coating is dull gray in color with a matte finish.
Another common zinc coating is bright zinc with
a bleached chromate conversion coating or a
clear lacquer coating, which is sometimes used
as a decorative fin ish(Mabbett 1993). '
Alternatives to Cyanide Zinc Baths
Two bath solutions are currently used as alterna-
tives to zinc cyanide plating: zinc alkaline and
zinc acid chloride. Tables 13 and 14 present
these alternatives and their characteristics.
Proper matching of the bath solution to the
substrate characteristics is important to success-
fully implement a non-cyanide zinc plating
system. Regular steel and leaded; steel substrates
are both compatible with acid chloride and -
alkaline non-cyanideiprocesses. Substrates other
than steel tend to be more compatible with acid
chloride zinc than alkaline zinc (TURI 1994).
Zinc Alkaline
Alkaline n'on-cyanide electrolytes consist of
sodium and zinc hydroxide.. In the absence of
cyanide, platers sometimes use proprietary
79
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Oupser 6, Pjvuton Pre-.eT.:on in the Plating Process
Table 14. Alternatives to Zinc CyanideProduct Quality Issues (TURI 1994)
,
| Alternatives
Zinc Alkaline
Zinc Acid
Chloride
Corrosion
Protection
(+) Good, greater
protection in difficult-
to-rinse areas
(+} Good, but less
protection in difficult-
to -rinse areas
Finish
Appearance
(4-) Good brightness
(+) Excellent brightness
and leveling
Chromate
Colors
Full line available
Full line available
Ductility
(+) Good, can be
reduced at
higher thickness
(-) Higher brightener
levels can reduce
ductility
(H-) Little hydrogen
embrittlement
Table 15. Alternatives to Zinc CyanideProcess Issues (TURI '1994)
Alternatives
Zinc Alkaline
Z?nc Acid
Chloride
Plating Uniformity
(+) Good uniform in high
qnd low density areas
({-) Good throwing power
(-) Variable with current
density
Process Considerations
(-) Narrow optimum operating
range of bath parameters
(-) Lower conductivity than
zinc
(-) Liners necessary in steel or
porous tanks
(+) High cathode efficiency at
high current densities
(-) Agitation required
General Comments! I
(+) Better for some 1
forming operations |
(-) Harder to plate on
cast iron and carbon
nitride steel
I
(H-)Higher conductivity . !
results in energy savings
{-) Bleed out of entrapped
plating solution can limit j
use for complex parts - J
(.+) Plates readily on cast j
iron and carbon nitrided 1
steel
sequestering agents to yield grain refinement.
When operated with concentrations and other
parameters in control, zinc alkaline baths per-
form as well as cyanide-based baths and are the
least expensive of all the zinc plating baths. This
solution has excellent throwing power and
rinsewater generally is easy to treat Also,
sludge generation is low because of the low
metal content of the solution (Murphy 1993).
A common problem with alkaline baths is the
control of the zinc metal level. During idle
periods, the caustic is aggressive toward the zinc
anodes and metal concentration rises. Platers
often are forced to remove anode baskets at the
end of a work shift or prior to the weekend.
Some opt to store the solution in an anode-free
storage, tank. In the past, yellowing of the plate
has been a problem, however, advances in
technology have resolved this issue and many
proprietary bath solutions can provide excellent
brightness and good color. Another drawback
often cited about zinc alkaline baths is low
cathode efficiency. While this is a problem for
barrel platers, those that rack plate actually can
find that an increase in cathode current density
can provide excellent metal distribution on parts
with intricate designs. Blistering also can be a
problem with this solution, especially in thicker
deposits. Blistering can be attributed to poor
cleaning or high brightener levels. Good house-
keeping is imperative to avoid this problem
(Natorski 1992).
80
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Chapter 6; Pollution Prevention .n'cne Pbcip? P'
Alkaline zinc baths also form carbonate similar
to cyanide solutions,. Symptoms of this include
yellows in blue bright chfomate, a drop In
brightness,, and poor coverage. If carbonate
levels become too high, platers should consider
one of the following options:
Decant the bath and rebuild to
specifications _
Freeze out the carbonate
Mix the bath with a compatible barrel
plating bath to equalize carbonate
Zinc Add Chloride
Chloride zinc baths have been available since
the 1960s. The original baths used chelates or
ammonium chloride. Today', however, most
baths use either .potassium or ammonium chlo-
ride. The advantages of the chloride systems
' include brilliant deposits, high cathode effi-
ciency, good leveling^properties, low energy
consumption, and easily treated non-toxic
electrolyte. The. disadvantages are poor throwing
power-, higher initial equipment investment, and
higher brightener costs compared to the alkaline
processes. In the past, chloride solutions had'a
foaming problem, especially, in air-agitated rack
plating. However, new surfactants in the solu-
tion produce low-foaming electrolytes. Facilities
using atmospheric evaporators should use low-
foaming solutions. Another advancement in
chloride solutions are their ability to plate .
efficiently at highertemperatures (Murphy
1993). Higher temperature baths increase the
number of potential recycling/recovery applica-
tions that this process can use.
Alternative Deposition Processes
Autophoretic Coatings :
A number of electroapplied organic coatings,
also known as Ecoat, and at least one commer-
cially available autophoretic coating are feasible
as non-metallic substitutes for zinc electroplated
coatings, especially when they are used for
corrosion resistance on steel substrates
(Altmayer,1993a).
Replacing Zinc Plating-for Auto Deposition.
Case Study '". '' j
Steelcase/Inc., replaced four zinc plating lines with
an autophoretic'autodeposition line at its Desk
Division in Grand Rapids, Michigan. Steelcase
began investigating alternatives in' 1987 when it
determined that its.plating lines were outmoded and
'no longer efficient. Various coating processes were
tested for hardness, abrasion resistance, corrosion
resistance, finish consistency, and environmental
' impact. The company chose to install the'-
autodeposition line. Capital investment was similar
to the cost of installing four new zinc lines. The new
single line process, however, has doubled the
production capacity of the four original plating lines.
Maintenance and waste treatment costs have been
reduced substantially as a result of the new process
line. Other savings include energy costs, labor costs,
and reduced reject' rates. (Ohio EPA 1994)
Separation Technologies
Reverse Osmosis
In August 1988, Plating Inc., a subsidiary of
Superior Plating, installed a 5 gallons-per-minute
reverse osmosis system on their automated zinc
cyanide line to recover rinse and process bath
solution.' In a 7-month study funded by the
Minnesota Waste Management Board, the -
system achieved its objectives. It maintained
rinse quality standards, recovered 2,480 gallons
of plating solution, avoided shipment of thou-. -
sands of gallons of dead rinse for treatment, and
was projected to eliminate the need for shipment
of 700 cubic feet annually'of resins containing
cyanide. Payback for the system was expected to
be less than 1 year (Rich 1989).
Non-Cyanide-Based
Plating Processes
While cyanide is a major contributor to pollution
generation at a metal plating facility, other
constituents are of concern because of the
toxicity of the metal contained in the solution.
Most common of these processes include nickel,
. tin, and chrome. The following section covers
nickel and chromium plating..
81
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Gupur 6- Poi'ut.on Pre\ention in the Plating Process
Chromium Plating
Electroplating processes and aluminum finishing
use chromium plating heavily. The most com-
mon hexavalent chromium-bearing solutions
include decorative and hard chromium, alumi-
num conversion coating, bright dipping of
copper and copper alloys, chromic acid ahodiz-
ing, aluminum deox/desmut, chromate conver-
sion coatings on cadmium and zinc, and copper
stripping with chromic acid. This section will
cover hard and decorative electroplating. Con-
version coatings such as anodizing and
chromating are covered in this chapter. Chro-
mium use with aluminum and stripping are .
covered in this chapter.
Because of hexavalent chromium's high toxicity
and cost for treatment and disposal, the industry
has focused on reducing or eliminating its use.
Hexavalent chromium is a known carcinogen and
a designated hazardous air pollutant. Approxi-
mately 80 percent of the available power sup-
plied to hexavalent chromium processes
generates hydrogen gas. Evolution of the gas
produces a mist of fine water particles with
entrained hexavalent chromium. This mist is
regulated under the Clean Air Act and the .
Occupational Safety and Health Administration
(OSHA). Protection of employee health and
safety as well as the environment requires a high
level of emissions control (PTAPS 1995).
Chromium, especially hexavalent, also is very
easy to operate in a closed-loop system using
simple technologies (Gallerani 1996).
Common Uses
When the plater's goal is a pleasing appearance
that has durability, the plating is considered
decorative. Decorative chromium plate is almost
always applied over a bright nickel-plated
deposit, which is usually deposited on substrates
such as steel, aluminum, plastic, copper alloys,
and zinc die casting. Chromium has a pleasing
appearance when plated over bright nickel.
Decorative chromium plating typically ranges
from 0.005 mils to 0.01 mils in thickness.
Decorative chromium plating can be found on
numerous consumer items including appliances,
jewelry, plastic knobs, hardware, hand tools', and
automotive trim (EPA 1994).
When chromium is applied for almost any other
purpose, or when appearance is an incidental or
lesser feature, the process is commonly referred
to as hard chromium plating or functional
chromium plating. Functional chromium plating
normally is not applied over bright nickel plating
although, in some cases, nickel or other deposits
are applied first to enhance corrosion resistance.
Functional chromium plating tends to be rela-
tively thick, ranging from 0.1 mils to more than ,
10 mils. Common applications of functional
chromium include hydraulic cylinders and rods,
crankshafts, printing plate/rolls, pistons for.
internal combustion engines, molds for plastic
and fiberglass parts manufacture, and cutting
tools. Functional chromium commonly is
specified for rebuilding worn parts as rolls,
molding dies, cylinder liners, and crankshafts
(Chessin 1982).
Common Bath Solutions
The traditional chrome plating process,is the
100:1 bath, which means that the ratio of chro-
mic acid (CrO3) to sulfate (SO4) should be 100:1
by weight, that is, 250g/l CrO3 to 2.5 g/l SO4.
Excess sulfate in these solutions can affect
plating quality and should be removed by the .
addition of barium carbonate. The addition of
this chemical causes the formation of barium
sulfate, which can be precipitated. This solution
contains chrome in the hexavalent form, which is
regulated far more stringently than trivalent
chrome. For this reason, development of triva-
lent chromium plating solutions is proceeding
rapidly (Ford 1994).
Alternative Solutions
- '' i.
To function as a suitable substitute for chro-
mium, an alternative coating must offer a combi-
nation of wear resistance, corrosion resistance,
lubricity, high-temperature tolerance, low
friction coefficient, heavy thickness deposition,
and high impurity tolerance. No single coating
can replace the properties and processing ease of
traditional hexavalent chromium, however,
several alternatives have shown promise in
replacing chromium for specific applications.
Trivalent Chromium
In some applications, especially decorative
plating, the use of trivalent chromium has been
82
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Oupeer 6: Pollution Prevention in the Plating Process
proven successful as an alternative for
hexavalent chrome for certain thicknesses1..; Use
of trivalent chrome eliminates misting problems
'and the added reduction step in wastewater , .
treatment. Adherence, throw, and coverage also ^
, are improved. Higher rack densities also can be
achieved because bath concentration is much
lower, dragout is less, and the amount of sludge
produced by wastewater treatment is reduced
substantially. However, plating thickness Is
limited to 0.1 mil; coatings thicker than this
usually have problems with cracking-and palling.
Therefore, this technique usually is not suitable
for hard chromium coatings, which can require
finish thicknesses of 20 mils or more. Although
the color tones of trivalent chromium coatings
are different from those of hexavalent chromium,
additives to the trivalent chromium bath often
can ameliorate the difference. One of the main'
.barriers for increased use of this solution is
customer acceptance. Primarily, customer
concern'is related to the color of the deposit
(Shahin 1.992).
Electro/ess Nickel Phosphorous
The use of electrqless nickel finishes frqiii-
. conventional hypophosphitc solutions has been
investigated as an alternative. The use of clec-
troless nickel as an alternative is limited by its
somewhat poorer physical properties including
lessened hardness and abrasion resistance. The
corrosion and wear properties depend on the
phosphorous content, which can vary from 1 to
12 percent. Electroless nickel deposits from
borohydride chemistry rather than from
hypophosphite chemistry have shown better
wear, lower friction, and improved hardness
(Lindsay 1995). Additionally, heat treatment is
required to achieve full hardness. Brittleness of
the deposits makes-some final finishing applica-
tions, such as grinding, difficult on thick depos-
its. Also, thick deposits of electrpless nickel
cannot be plated as cost effectively as chrome.
. However, electroless nickel plates more evenly
so that the need for substantial overplating often
can be eliminated. An advantage of ele.ctroless
nickel is that the deposit follows all the contours
of 'the substrate without excessive buildup at the
edges and'corners, which is a common problem
in chrome plating (Meyers 1994).
Trivalent Chrome Case Study
Foss Plating in Sante Fe Springs, California, is
a family-run chrome plating shop that has
been in business more than 40-years. Today
about 30 people are employed in the shop. -
Their current plating line is a fully automated
.single chrome-cell (111) system that was con-
verted from.a hexavalent chromium line in
1989. The cost of conversion was approxi-
mately $30,000. . ' . -
As a result of the conversion, Foss Plating
'realized a return on their investment within the
first year of operating the chrome (HI) system.
They saw an increase in productivity/greater
system efficiency, fewer rejects, and lower
treatment costs, The better throwing power and
covering power of chrome (HI) allowed them tof
increase the surface area on the racks by 70
percent. At the same time, they experienced a
more than 90 percent decrease in the. number
of rejected parts and eliminated almost all
need for color buffing. Foss also found that
chrome (111) plated more efficiently from an
energy standpoint.
The two biggest disadvantages Foss Plating
experienced with chrome (III) were discolora-
tion from impurities in the bath and the need to
'passify the non-plated areas of the parts.
:, --- (CDTSC 1995)
The process bath, however, is more sensitive to
impurities than the chronic plating bath. As a
result, it must be monitored closely to maintain
the proper concentrations and balance of the
metal ions and reducing agents. In addition, the
bath life is finite and requires frequent disposal
and replenishment, especially when thick depos-
its are being applied. Deposition rates and
coating properties are affected by temperature,
pH, and metal ion-reducing agent concentrations
(Meyers 1994).
Electroless nickel has been %vell accepted for
ground-based hydraulic component use, how-
ever, it has not been used in aerospace applica-
tions. For more information on electroless
nickel, refer to the section on electroless plating
in this chapter. ' .
83
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ust*' 6. Pe.tuiion P-e'.enuori in, the PUting Process
Nickel-Tungsten Electroplating
1 '.I,,
Tuo nickel tungsten-based alloy electroplating
processes are available as potential alternatives
to chrome plating: nickel-tungsten boron (Ni-W-
B) and a nickel-tungsten silicon carbide compos-
ite (Ni-W-SiC). The two processes are similar in
that they are both electrolytic and they deposit a
coating of nickel and tungsten with minor
percentages of either boron or silicon carbide to
enhance the coating's properties (Meyers 1994).
Both substitutes use less energy than chrome
plating both for rectification and heating, result-
ing in-reduced energy costs. Additionally, the
deposits are more uniform than chrome, increas-
ing plating line throughput and reducing reject
rates. Each coating exhibits many of the same
desirable properties as chrome plating, but
additional testing is needed before widespread
use can be expected. The major disadvantages of
these two processes are their lack of maturity,
potential for increased chemical costs, and their
reliance on nickel (a metal targeted by EPA for
reduction) (Meyers 1994).
Nickel-Tungsten-Boron Alloy
Following several years of development, an alloy
of nickel, tungsten, and boron has been intro-
duced recently under the trade name AMPLATE.
The plating solution is mildly alkaline and far
less toxic than chromium. The alloy is reflective
and has an appearance similar to chromium,
bright silver, or bright nickel. The coating has
favorable chemical and abrasion resistance, high
ductility, a' low coefficient of friction, and a
uniform finish (Meyers 1994). Unlike most
metals that exhibit a crystalline structure at
ambient temperatures, the AMPLATE alloy is
structuretess so that the plate replicates the
appearance of the substrate. For instance, if the
substrate has a bright appearance so will the
finish, but if the substrate is etched or patterned,
the plated workpiece will appear etched (Scruggs
1992).
Nickel-Tungsten Silicon Carbide
This technology has been patented by Takada
Inc. to replace functional (hard) chromium
coatings. Nickel-tungsten silicon carbide is
similar to nickel-tungsten-boron, except that it
uses silicon carbide particles interspersed in the
matrix to relieve internal stress and improve
coating hardness (Meyers 1994). Nickel and
tungsten ions become absorbed-on the suspended
silicon carbide particles in the plating solution.
The attached ions are then adsorbed on the
cathode surface and discharged. The silicon
carbide particle becomes entrapped in the
growing metallic matrix (EPA 1994).
, This process has several advantages over hard
chromium plating including higher plating rates,
higher cathode current efficiencies, better
throwing power, and better wear resistance. The
main disadvantage of this process isits suscepti-
bility to metallic and biological contamination.
Much is still unknown about this process includ-
ing its susceptibility to hydrogen embrittlement.
fatigue, and corrosion as well as its maximum
finish thickness, lubricity, grinding characteris-
tics, and facility requirements (EPA 1994).
Tin-Cobalt Alloy
Tin-cobalt alloys provide a finish that is similar
in appearance to chromium. The tin-cobalt
appearance ranges in color from a bright, chro-
mium appearance to a warm, silvery gray color.
Color is controlled by varying the percent of tin
in the alloy. To achieve the appearance of a
chromium plate, the optimal tin-cobalt ratio in -
solution is 50:50. This ratio results in a plate that
is 80 percent tin and 20 percent cobalt. Reducing
the cobalt content of the plate below' 17 percent
results in a matte gray appearance. Additional
operating parameters include a pH of approxi-
mately 8.5 and an operating temperature of
between 38 and 43 degrees Celsius. The tin-
cobalt finish provides a hardness and wear
resistance that is sufficient for most indoor,
decorative applications. The process, either in
rack or barrel operations, uses an alkaline sulfate
system with optional wetter/amine-based liquid
brighteners. Current applications of this plating
alternative for chromium include automotive
interior parts, computer components, bicycle
spokes, flexible shower hoses, and screws (Davis
1994).
Tin-nickel Acid or Near Neutral
Tin-nickel alloy plating can be used as a replace-
ment for decorative chromium plating for both
indoor and outdoor applications because of its
84
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Chapter 6: Pollution Prevention in the ;Pl3tmg Process
faint rose pink cast. This alloy is resistant to
corrosion and tarnish and has good contact and
wear resistance. Tin-nickel's hardness lies
between that of chromium and nickel. Other
advantages of this coating include excellent ^
frictional resistance and ability to retain an oil
Film on'its surface. Tin-nickel alloy plating
solutions have a high throwing power, which
enables the solution to function where plating
chromium in deep recesses is a problem (Plating
and Surface Finishing 1994).
Alternative Deposition Methods
Aluminum Ion Vapor Deposition
Ion yapor deposition (IYD) produces a multi-
purpose coating that has excellent corrosion
protection and no embrittlement problems. This
technology has been used as an alternative to
chrotnium'coating in several applications. >
Extensive testing has shown that IVD aluminum
protects substrates better titan electroplated or
vacuum-deposited chromium in acetic salt fog
and outdoor environments. IVD also provides
greater resistance to cracking (Muchlbergcr
1983). For more information on IVD, refer to
the section on IVD in Chapter 8.
Metal Spray Coating .
Several metal spray coatings processes have ,
' shown promise as potential alternatives to ,
chrome plating. These technologies are not new,
however, recent regulation of chrome has made
these technologies economically desirable.
Variations on the spray technologies include arc
spray; flame.s'pray, plasma spray, and high
velocity oxy-fuel (HVOF) spray. From a materi-
als standpoint, HVOF spray results in coatings
with the best properties (Meyers 1994).
HVOF coatings are used currently in many
industrial applications because they develop very
hard, wear-resistant surfaces that are comparable
.to those of chrome plating. In HVOF coating
application, an explosive gas mixture ignites the
. barrel of the spray gun, which melts a powdered
coating material and propels it at supersonic
speeds toward the substrate. The superior
. properties achieved using this technology arc a
result of the high speed of the material. The
higher the velocity, the greater the force of
impact on the substrate,, resulting in fewer voids
in the coating. Several of the potential alterna-
tives contain chromium, yet .the HVOF coating
will generate a significantly smaller mass of
chromium-containing waste and will emit less.
chromium. The powdered dverspray can be
captured and recycled easily by a dry filter
system and, unlike conventional chrome electro-
plating, no chemicals are added to the total waste
volume when precipitating the metals (Meyers
1994).
A disadvantage of the HVOF process is that the
application is limited to line-of-sight areas of the
part. Complex shapes, threads, and bores/holes
cannot be coated. Unlike the chemical substitutes
that use conventional finishing methods, metal
spray coatings will require changes in finishing
and grinding operations. Given the hardness of
the coating, stripping and reworking these
finishes might prove difficult (Meyers 1994).
For more information on this" process, refer to
Chapters. .
Physical Vapor Deposition
Physical vapor deposition (PVD) is one of the
many emerging replacements for chromium
electroplating. PVD encompasses several
deposition processes in which atoms are physi-
cally removed from a source and deposited on a
substrate. Thermal energy and ion bombardment
methods are used to convert the source material
into a vapor. Specific processes for applying
chromium include ion plating dnd sputtering.
For more information on PVD, see Chapter 8.
Titanium nitride using PVD is a prime replace-
ment for chromium coatings. This material
exhibits greater hardness than chromium and can
be applied cost effectively in a thinner coating.
Titanium nitride applied with PVD is not subject
to hydrogen embrittiement. However, because of
its hard nature, titanium nitride coating cannot
replace chromium in highpo.int or line-load
- applications. This material also does not provide
the corrosion protection of the thicker chromium
plates (Lindsay 1995).
Other Emerging, Technologies
The government is evaluating several other
technologies as alternatives to hcxavalent
85
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6, Pcuulicn Prevention in Che Plating Process
chrome under the Environmental Technology
Initiative including:
Alloy deposition of hard coatings (nickel-
tungsten silicon carbide and electroless
nickel-tungsten)
Deposition of powdered chromium with
an inductively coupled radio-frequency
plasma torch
Sputterion deposition using hard
chromium (Lindsay 1995)
For more information on these alternative
deposition processes, refer to Chapter 8.
Process Modifications for
Chromium Plating
i '
Mist Reduction
Inhibiting the release of chromium into the air by
forming a physical barrier atop the plating bath
\\ith plastic balls or mist suppressants or by
altering the chemistry of the bath with the
addition of wetting agents is one way to prevent
pollution from a chromium plating line (PTAPS
1994).
Floating Plastic Ball
Placing solid polypropylene balls 3/4 to 1'/:
inches in diameter on top of the plating bath will
retard mist formation and evaporation. The balls
can prevent up to 70 percent of the mist from
escaping the plating solution and can be used
effectively in both decorative and hard chrome
plating processes. Polypropylene is reasonably
resistant to chromic acid solutions at tempera-
tures of up to 140 degrees Fahrenheit. Higher
temperatures can cause the balls to break.
Platers should use solid balls because hollow
ones tend to trap solution inside from seam
leakage (PTAPS 1994).
" ,, ' . ;
Polypropylene balls cost approximately $45 to
S200 per 1,000 balls depending on the ball size
and the total quantity purchased. An average
tank requires about 2,500 balls. There are no
additional operating costs for using this method.
However,-some of the balls might need to be
replaced on an annual basis depending on the
operating conditions of the tank (PTAPS 1994).
When using balls in a plating solution, pre-
cleaning of parts is essential. Small amounts of
oil and grease from workpieces can float onto the
bath surface and adhere to the balls. As parts are
raised and lowered in the bath, oil-covered balls
can drag across the workpiece surface and
prevent effective plating and rinsing1, resulting in
a flawed coating.
The most common problem associated with this
method is that the "balls become trapped in
recessed areas of parts or equipment (e.g.,
barrels) and prevent plating or cause burning or
dulling of the plated workpiece. Whether the
balls become entrapped usually is associated
with their size. To help prevent entrapment of
balls, platers can use plastic mesh bags. The
bags can keep the balls together on the surface
and reduce the likelihood of balls being carried
into subsequent tanks (PTAPS 1994).
Mist Suppressants
A mist (or fume) suppressant is a chemical that
forms a barrier on the surface of the bath solution
to prevent mist from escaping. During operation
of the plating or anodizing process, the mist
suppressant generates a foam blanket and traps
the process gases cither between the bath surface
and the blanket or within the foam blanket. Mist
suppressants can be more than 99 percent
effective in reducing emissions from decorative
chrome plating and anodizing (PTAPS 1994).
Suppressants arc chemical additives that can
affect the .chemical balance of the plating or
anodizing solution. For this reason, a generic
suppressant is not available for widespread use.
Depending on the various types of baths within a
shop (e.g., hard, decorative, or proprietary), a
different mist suppressant or concentration of
suppressant might be required for each bath to
achieve the desired result. Some mist
suppressants must be replaced because of the
degradation of the active ingredient. These are
know as temporary suppressants. Other mist
suppressants only have to be replaced when they
are diminished because of bath dragout (PTAPS
1994).
Another factor to consider when deciding
whether to usc.mist suppressants is the amount
of foam generated during bath use. Too much
86
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Chapter 6: Pollution Prevention in the Pljt/ng Process
mist suppressant will .cause a large foam-blanket
that can result in excessive dragout into subse-
quent rinse tanks. This dragout will lead to an
increase in the amount of materials necessary to
replenish the suppressant in the tank. The foam
blanket'also can be drawn into the exhaust
system, increasing the likelihood that a more -'
concentrated chromium mist will be released
from the stack. Finally, too much mist
suppressant can spill onto the facility floor or,
into other tanks, generating large amounts of
waste that require clean up and increase treat-
ment and disposal costs (PTAPS 1994).
Because hydrogen-is the primary gas formed
during plating, dissipation of the gas is impor-
tant. Build up of hydrogen with the foam or
under the foam poses a serious explosion risk,
especially when the parts are removed while
"hot" (i.e., the electric current is still on). When
hot parts are removed, the hydrogen gas can ,
ignite spontaneously, resulting in equipment
damage, serious personal injury, and an in- ,_
cr,ease"d risk, of fire (PTAPS 1994).
Mist suppressants come in liquid and free
compressed-powder form and range in cost from
$10 per pound to S60 per pound. The amount of
mist suppressant chemical necessary to form a
sufficient barrier varies depending on the type of
chemical mist suppressant, tank size, and fre-
quency of plating. According to manufacturers'
instructions for different mist suppressants, the
recommended amount of chemical to add ranges
from 0.001 percent of the total volume of the
plating bath to 0.1 percent (approximately 1
ounce per 500 gallons initially with infrequent
additions thereafter). When used in the appropri-
ate amount, dragout and replenishment costs are
minimal. Because mist suppressants also are
stand alone emission controls^ utility require-
ments are nonexistent, except perhaps for
makeup water in the case of free-form powders
(PTAPS 1994).
When using mist suppressants, operators should
start with half the manufacturer's recommended
-amount and increase levels slowly to determine
the actual amount required to achieve the desired
ScrubberModifictitions Case Study,
C&R Hard Chrome is-a small chrome and electrons nickel plating company .specializing m pkrtmg and
plastic injection molding apparatus and machined tool parts. To reduce the h,gh costs associated with
proper disposal of waste generated at the' facility, the company sought ways to keep wastes and liobih-
es to a minimum. .- ... ..
To control emissions from the chrome plating operation, the company installed a wet-packed fume
crubber with a ^circulation system in 1 990. The system collected chromium concentrate from two
plating tanks. The company, however, experienced several problems with th.s system , including .contami-
nation of the chrome concentrate from the.steel ducts that transported the washout. To address Jhis
ssue, the company installed polyvinyl chloride (PVC) pipes. The new system employed a «*"?
extractor, double-baffle mesh pad eliminator, and an in-line vert.cal mist ehmmator. The pat.ng , fumes
are collected by two plenum arms on either side of the tank. The tops of these arms slant towa d the-
tank to return dragout to-the solution. The collected fumes are directed to a mo-turf -Jn pdor oca ed
above the tank. Moisture removal is accomplished centrifugally as air passes through the , sel ^f statin -
ary blades. A spray system periodically washes these blades and the solution is returned to the plating
tank. ' ' '. ' '' ;';. '.' .'
The final treatment involves an in-line vertical mist eliminator. A mesh pad was «*£** °
jn case the washdown spray does not engage. A blower operating at a rate of 5,250 «*«£« per
minute is used for this system. Now, the chromium can be recaptured by the fume scrubbers and
recirculated back to the solution. r . -.;.'_
The PVC fume-scrubbing system eliminated the need to send 1 ,840 gallons
and wastewater off site each year for treatment, Chromic acid use fell by almost 90
to less than 600 pounds annually. Chromium emissions fell by 98 percent, from 61.4 to
pounds per year. The capital outlay for the system was $95,000 w,th an annual
year.
-------
6; PoilbS-on Pre\ention in the Placing Process
result, The necessary amount of suppressant
.often depends on the activity of the plating line.
Less active plating lines might require the use of
more suppressant while a similar amount on a
busy day might generate an unmanageable
foaming problem (PTAPS 1994).
Wetting Agents
Reduction of surface tension of the chrome
plating or anodizing bath reduces the rate of mist
generation by causing the gas bubbles to burst
with less intensity. For chrome finishing,
decreasing the surface tension to 40 dynes per
centimeter will achieve excellent chromium
emission reductions. However, wetting agents
can affect the quality of the deposit; too much
can cause burning, pitting, of poor adhesion; too
little can result in little or no reductions in
emissions (PTAPS 1994). For a complete
description of wetting agents, refer to the first
section in this chapter.
Static Rinse Tank
Many facilities use a static rinse tank (often
known as dead rinse) after the process bath.
Water from this tank is used as makeup water in
the process bath. Using this method has assisted
many facilities in closing the loop on chromium .
contamination.
Tank Covers
Thin plastic sheets can be placed over the plating
bath to reduce emissions by trapping and con-
densing vapors from the tank. The cover can be
placed almost directly on the chromic acid
solution, resulting in little free space between the
cover and the solution. Tank covers can be
constructed of plexiglass or other suitable plastic
and cut tafit the size of the tank. The facility
should determine how to remove the cover when
transferring workpieces during plating or anodiz-
ing operations. Rigid covers are most easily
made by using anchors and hinges that operate
like a window or door. Platers can use flexible
sheeting by mounting it on one side, rolling it
over the top, and anchoring it to the other side
like a window shade. A drawback of this method
is that chromium can dry out or corrode plastics.
Another consideration is how the covcr-will
affect the movement of parts through the process
line (PTAPS 1994).
Recycling and Recovery Technologies for
Chromium Plating
Porous Pots .
For hexavalent chromium plating baths, firms
can use porous pots to^extend bath life. During
plating, the concentrations of iron and other
cationic impurities build up in a hexavalent ,
chromium bath so that the finish is unsatisfac-
tory. When the solution reaches this point,
operators can use porous pot technology to
purify the process solution. This technology uses
a porous pot in which a semi-permeable mem-
brane separates a cathode from an anode along
with an applied power source. In this operation,
the iron and other contaminant metal ions pass
through the membrane and accumulate in the
cathode chamber. Once the contaminants are
contained in the chamber, they can be removed
. periodically for disposal. Chromate ions remain
in the anode compartment as part of an anolyte
that, after purification, can be returned to the
plating tank for further use. Using this tech-
nique, companies not only reduce waste but also
use less chromium. The liquid in the cathode
compartment must be handled as waste (I A.MS
1995).
Two basic design configurations exist for this
technology, One type consists of a tank holding
four to eight pots. Plating solution is pumped to
the tank on a continuous basis and returned by
gravity flow to the plating tank. The cells arc
powered by a rectifier (1,000 to 2,000 ampheres)
that is dedicated to the purification unit. A
second type of unit exists that consists of a single
pot that is suspended directly in the plating bath.
This unit is powered by the tank rectifier and
draws up to 240 ampheres. The advantage of the
smaller unit is that it does not require extra
equipment (e.g., rectifier, fume exhaust system,
and overhead hoist). However, there are disad-
vantages to the smaller units. They include
limited capacity and operation that only occurs
when the tank is energized. For more informa-
tion on this technology, refer to Chapter 8.
Membrane Electrolysis
Membrane electrolysis is similar to the ion
transfer technology used in porous pots, how-
ever, this technology is primarily used in chrome
88
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Chapcer 6: Pollution Prevention in the Pbtinj Process
Porous Pots Case Study ;
G&R Hard Chrome .is a'small chrome and
electroless nickel plating company specializing
in plating plastic injection mold apparatus and
machined tool parts. To reduce the high costs .
associated -with proper disposal of wastes
generated at the facility, the company sought
ways to keep wastes and liabilities to a .
minimum. One of the problems in the facility
was that the chrome plating solution was '
being contaminated from the workpieces. The
cohtaminants'reduced solution life'and :
lowered plating efficiency. The reduced
lifespan required frequent replacement and
disposal of the'chromium solution while lower
:plating efficiency reduced plating quality and
increased power consumption and plating
time. In 1987, the company pruchased a
chrome solution purifier called a porous pot.
During plating operations, impurities collect in
the pot rather than the solution. The porous
pot used the concept of electrodialysis in
conjunction with ceramic membranes. The
continual removal of impurities significantly
increased the bath life. Since the installatiorvo
the porous pots, they .have collected 55
'gallons of contaminant sludge and prevented
the disposal of at least four chrome baths
(2,300 gallons of-solution). The payback time
on the S600 pot was less than three months.
Annual savings for this project are approxi-'
'matety S2,375 a year. ( NC DEHNR1995). .
applications. The unit employs a separate tank
and power source for operation. Plating solution
is circulated through the unit, which contains an
anode compartment and 10 cathode modules.
When the unit is energized, bath cations pass
through .the membrane and deposit on the
" cathodes. The membrane is not anion or cation
selective. Selectivity is a result of the electrical
force. This selectivity distinguishes this technol-
ogy from electrodialysis equipment. For more
information on this technology, refer to the
recycling/recovery section in Chapter 7.
Ion Exchange
Ion exchange has been applied to chromium
solutions for the removal of trivalent chromium,
iron, and other metallic contaminants. Facilities
using this technology usually treat the solution
on a batch basis, requiring a shutdown of the
. chromium line. However, a continuous process
Has been used.'Generally, the plating solution is
cooled and diluted prior to treatment.
Eco-Tec Inc. in Canada has developed an ion ,
exchange system for use in hexavalent chrome
plating operations. Initial results are promising,
however, other platers have had problems in the
past with .other ion exchange systems.' Problems
usually are a result of fouling membranes and
sensitivity to chromiufn concentrations (Cushnie
1993). For more information on ion exchange,
refer to Chapter 7.
Nickel Plating
Companies have plated nickel since 1842, but
modern nickelplating began in 1916 with the
introduction of the Watts formulation. Typi-
cally, nickel ingots or balls are dissolved into a
metal salt solution that is used in the plating
baths. However, nickel salts have some negative
characteristics including aljergenic properties
and carcinogcnicity (ASM 1982).
Common Uses
Nickel plating commonly is used to impart
corrosion resistance or to act as an intermediate
layer prior to plating silver, chrome, or gold,.
Nickel also is Valued for its leveling and bright- .
. cning properties. Because of these properties,
nickel; can eliminate the need for polishing work
and can improve the quality of an inferior
substrate. Several types of electrolytic nickel
plating are available including sulfamate nickel
and bright nickel. Many industries use nickel
plating for decorative or functional purposes
including jewelry, automotive parts, tools/dies,
and lighting fixture manufacturing (Rl DEM
I995c).
Common Wastes
Typical wastes from nickel plating operations
include nickel-contaminated water from running
rinses and excess dragout solution. If a plater
uses traditional chemical precipitation to treat
the nickel-laden wastewater prior .to discharge,
. the resulting sludge automatically is classified as
a F006 hazardous %vastc. Iron and chromium
contamination is common in acidic nickel baths.
In most formulations, this contamination can be
-removed with peroxide combined with pH
, elevation and batch,filtration(SME 1985).,
89,
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6; Pa-'uwjn Prevention m the PlJting Process
Common Bath Solutions
Sulfamate Nickel
Sulfamate nickel, also known as dull nickel or
engineering nickel, .is used for engineering
(usually non-decorative) applications to produce
low-stress deposits. This plate is ductile and can
be used in many applications. This bath also is
useful for electroforming and for parts that are
susceptible to fatigue failure. The primary
constituents of this bath are nickel sulfamate,
nickel chloride, and boric acid (Ford 1994),
Bright Nickel
Another common nickel plate is bright nickel,
sometimes referred to as a Watts bath. This
solution imparts a bright and hard finish, which
is used mainly for decorative purposes. The
process bath in nickel plating contains both
inorganics (i.e., nickel-salts and acid) and
organics (i.'e., brighteners and wetting agents).
Additional chemicals ultimately determine the
characteristic of the plate. These include bright-
ening and wetting agents that account for the
brittle nature of the deposit (Ford 1994).
Alternative Metal Processes Baths for
Nickel Plating
Alternatives to nickel as intermediate layers
include bronze, palladium, and cobalt. Like
nickel, however, cobalt is under examination as
an allergen and carcinogen and might be rcgu-.
lated in the future.
Yellow/White Bronze .-..,
Processes available for white or yellow bronze
deposits include cyanide or alkaline-based
systems. Like the nickel baths, operators can add
buffers, brighteners, and levelers to the bath to
create the needed characteristics. Bronze exhib-
its better throwing power than nickel, resulting in
a more evenly distributed thickness. This alloy
can be used when superior solderability, hard-
ness, corrosion resistance, brightening properties,
.thickness distribution, wear resistance, brdia-
magnetic properties are needed. Bronze alloys
' also kill bacteria, just like copper, and have
better bactericidc properties than silver, making
them attractive plating materials for bathroom
fittings and door handles (Simon 1994).
White bronzes are hard and tarnish resistant.
This metal also is corrosion resistant. Yellow
bronzes are hard, but'do not have, the corrosion
resistance properties of white bronze because of
their high copper content. Yellow bronze
however, have the brightening and leveling
effects of nickel plating. Platers use a layer of
white bronze on top of a yellow bronze to replace
bright nickel of the same layer and thickness
.(Simon 1994).
Bronzes can provide a surface that is harder than
nickel and, in decorative applications, protect
workpieces from deterioration or tarnishing.
However, for technical applications where the
workpiece will be subjected to high tempera-
tures, bronzes are not an appropriate substitute.
Palladium
Metal finishers can use palladium as a substitute
for nickel as an intermediate layer when nickel's
property as an allergen is a consideration. Some
platers also consider palladium a feasible re-
placement for gold because of palladium's lower
cost. One of the benefits associated with substi-
tuting palladium is that it is not listed as a
chemical that facilities must report under flic TRI
reporting requirement.
A relatively new system for using palladium
chloride as a palladium salt combined with
proprietary additives exists. This system pro-
duces ductile deposits that are crack-free and
bcndable as well as resistant to corrosion. To
avoid contamination of the electrolyte, a gold
strike or palladium strike is recommended before
applying the main palladium layer (Simon 1994).
Issues Concerning Palladium and Bronze
as Nickel Substitutes
Many questions remain unanswered about the
feasibility of replacing,nickel with bronze and
palladium, but some advantages are well known.
Bronzes and palladium are comparable to nickel
with regard to hardness, color, corrosion protec-
tion, solderability, further plating ease, and wear
resistance. Bronzes, especially the yellow-white
combination, arc superior to palladium in this
area. However, palladium is similar to nickel in
its diffusion properties. The use of bronze as a
diffusion barrier is limited to decorative
90
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Chjpcer f>: Pollution Prevention in the PlatingProcess
"purposes. In regard to ductility, bright nickel is
the most brittle of the three applications. Palla-
dium is ductile, yellow bronze has average
ductility, and white bronze is brittle. With ;
. regard to cost, palladium is the most expensive
of the three processes (Simon 1994). ; -
Recycling/Waste Reduction Technologies
Common pollution prevention options in nickel
plating include electrolytic dummying, spill and;
leak prevention (especially from filtration
systems), countercurrent rinsing, evaporation,
and ion exchange. This section covers particular
recycling/recovery technologies for nickel
plating. For more detailed information on a
specific recycling/recovery technology, refer to
Chapter 7. * ,
Electrodialysis Reversal Process (EDR) in
Nickel Plating ' ,
Electrodialysis is an electrochemical separation
process in which ions arc transferred through a
pairof ion-selective membranes from a less
concentrated to a more concentrated solution as a
result of the flow of direct electric current.
Initially, these systems could only transfer ions
in one direction. Typical problems associated .
with the system included membrane fouling and
organic .buildup.-' Newer electrodialysis systems,
however, eliminate these problems by allowing
-the flow to periodically reverse itself in order to
clean the membrane. Recently, electrodialysis
has been considered a .promising method for the
recovery of nickel ions from rinsewater, recy-
cling them back to the plating solution and
simultaneously generating clean water for reuse
in the plant. Important parameters to evaluate
include limiting current density, current effi-
ciency, and water transport through the mem-
branes (RI DEM I995e). Small-volume shops
might find that the costs associated with elec-
trodialysis are too high. But effort to build
smaller systems that are feasible for all manufac-
turers is increasing (Girasole 1996).
Electrolytic Recovery in Nickel Plating
Nickel can be recovered from a variety of
concentrated solutions including dragout tanks,
ion exchange regenerants, and concentrated
membrane fluids. The metal that is recovered
can be sold as scrap metal or, as some facilities
| Atlantic Seaboard Case Study
' " " '''''' '" "
II Atlantic Seaboard realized they were losing 80
' to 100 pounds of. nickel per day as a result of
dragout from barrel plating operations follow-
ing, the installatibn of modern,control equip,-'
ment. Atlantic Seaboard installed an EDR unit
and reduced their annual costs for purchasing '
plating chemicals by approximately $110,000
based on costs of nickel sylfate at $1.10 per
pound, nickel chloride at$l .40 per pound, and
boric acid at $0.41 per pound. Annual sludge
disposal costs also were reduced by $6,600 per
year (sludge disposal costs were $250 per ton
at 95 percent solids). The company also real-
ized savings of.$2,200 from reduced sodium
hydroxide use. The total annual savings
amounted to more the :$ 118,000.
'.' '.... ' (Ohio EPA, 1994
have done, returned as reclaimed material to the '
plating bath for use as a solid material in the
anode.,Electrolytic recovery works best in nickel
plating applications when pH values are between
land 9. Generally, high energy is required (100
to 500 amphcres). Anode and cathode materials
arc important design parameters for this technol-
ogy. Stainless steel or graphite are the best
choices. Trace metal contamination in the
clectrpwinning solution can sometimes affect the
overall efficiency of this operation (Girasole
1996)." '''",-
Electrolytic recovery of nickel cannot eliminate
nickel because the nature of the process makes it-
less efficient with low metal concentrations.
However, it will have a significant effect on
sludge generation: In general, for every pound of
metal reclaimed, sludge generation is reduced by
4 pounds (Girasoleil996). For more information
on electrolytic recovery, refer to Chapter 8.
Ion Exchange in Nickel Plating
Ion exchange is a frequently used and effective
method to recycle nickel rinsewaters and capture
nickel metal either for reuse or recycling. Spe-
cifically made resins are manufactured to remove
particular metal ions from the solution through
the exchange of similarly charged ions. At some
point, the resin becomes saturated with the metal
' ions and must be regenerated with an acid to
remove the captured metals. The.metals some-
91
-------
6; Pi .«.:,ci Prs<.enuon in the Plating Process
times can be reused in'the nickel plating tank if
the ion exchange regenerant is matched correctly
because the residual material consists of concen-
trated nickel salts. Some companies also choose
to send die saturated resin off site for metal
recovery (RI DEM 1995c).
The final rinse in a nickel plating line can be
continuously processed through the resin col-
umns to ensure a nickel-free final rinsewater.
The upstream rinses and dragouts are returned to
the plating tank to make up for evaporative
losses. As a result, platers can reduce generation
of F006 hazardous waste sludge. Initial capital
costs for ion exchange can vary depending on the
size of the shop, and setup costs can range from
several thousand dollars for a small line to
510,000 to 520,000 for a larger facility. Operat-
ing expenses include chemical costs and labor
(R1DEM I995c).
Reverse Osmosis in Nickel Plating
While ion exchange is used more frequently,
interest among platers in reverse osmosis (RO) is
growing. Nickel is the most common plating salt
reclaimed with RO because it is expensive and
the p.H and temperature requirements arc handled
easily by a RO system. Reverse osmosis can
separate dissolved components such as nickel
Ions, significantly reducing or possibly eliminat-
ing F006 sludge. Depending on the type of RO
membrane used, the recycled rinsewater might
still contain some metal ions. While a perfect
membrane theoretically could separate 100
percent of metal ions, the commercially available
membranes are usually 95 to 99 percent effec-
tive. Whether this is clean enough depends on
the ultimate use of the platdd part (Cushnie
1994). .
For many non-decorative products, water pro- '
duced by RO is clean enough to return to the
process. However^ in decorative and electronic
applications where nickel is a base for precious
metals, a nickel-free final, rinse is necessary to
avoid contaminating the precious metal plating
solution. Modifying the RO process to ensure a
nickel-free final rinse is possible with the addi-
tion of a small ion exchange system. Operating
costs for these systems include membrane
replacement, electricity, and labor. Average
labor costs can total 52,000 to $3,'000 per year.
.Systems for smaller units are not yet commer-
cially available, however, they are under devel-
opment (RI DEM 1995c).
Recycling Nickel Rinsewater Using
Low-Temperature Evaporation, and
- Reverse Osmosis Case Study
A Connecticut facility evaluated low-tempera-
ture evaporation' and reverse osmosis (on a
pilot scale) for their ability1 to process rinsewa-
ter collected from a nickel electroplating
operation. Each system offers advantages.
under specific operating conditions. The low-
temperature evaporation system appeared
best suited to processing solutions with
relatively high nickel concentrations. The RO'
system appeared best adapted to conditions
where relatively dilute rinsewater solutions
must be concentrated to levels acceptable for
replacement in the-plating bath. The company
found that a combination of the two technolo-'
gies might provide the best process alterna-
tive. Initially, the RO system would be used to
co'nce'htrate the feed solution followed by low-
temperature evaporation processing to
concentrate the solution to levels acceptable -
for replacement in the plating bath.
; ' ' ' ' (EPA 1995)
II
Electroless Plating
General Issues in Electroless Plating
Electroless plating is a growing segment of metal
finishing, especially in the electronics industry.
In electroless plating, metals are deposited onto
the surface of a part without the use of electricity
as a source of electrons. Instead, the bath
solution supplies the electrons for the deposition
reaction. These baths are extremely complex
using a variety of chelating and/or complexing
agents that hold the metals in solution. Common
chelating agents include
ethylenediaminetetraacetic acid (EDTA), cit-
rates, oxalates, cyanides, and'1,2
diaminocyclohexanetetraacetic acid (DCTA).
Nickel,.copper, cobalt, and gold are the most
common metals plated in this process. Deposi-
tion rates arc controlled by the amount of reduc-
ing agent present and the type of chelating agent
92
-------
.Chapter 6: 'Pollution Prevention in the Pbting Proems.
used.. Fi'igure 7 presents a flowchart of a typical
electroless plating process.
Electroless plating resultsjn a fine-grained metal
deposit similar to traditional electroplating
finishes. Industries use this process to plate on
non-conductors such as plastic, electroformed. ,
dies, and printed circuit-boards or to obtain an
extremely uniform plate (ASM 1982).
Waste segregation is especially important in
electroless systems because of the presence of
chelators. Chelated metal solutions are not
responsive to conventional neutralization,
. precipitation, flocculation, and settling treatment
techniques. Therefore, electroless platers require
alternate treatment methods. Because of the
affinity of metallic ions for dictating agents,
combining waste streams w.ill cause .unchelated
metallic ions to mix with unreacted agents,
increasing the load of difficult-to-break dictated
metals to the recovery equipment (Jordan-1985).
. Although extremely similar to'electroplating,
electroless operations feature four rather distinc-
. live characteristics:
Electroless plating demands much tighter
control over process parameters than
electroplating. Critical parameters
include metal concentration, reducer
concentration, pH, temperature,-agita-
tion, and contamination control. Im-
proper control over these process vari-
ables can result in increased reject rates
of workpieces and substantial waste.
Chemical reactions in-the electroless
process bath cause plate-out in which
everything coming into contact with the
process solution, including the tank itself,
is coated with the plating material. .To
treat plate-out, the plating line must be
taken off-line and stripped. In the case of
"electroiess nickel, stripping is,accom-
plished with nitric acid. In some shops,
stripping is done every few days. The
nitric acid stripping process can cause
' significant air releases of nitrous oxides
(NOX) if the -stripping solution is too
dilute. The resulting nitric acid/nickel
waste also is difficult to treat for disposal
because of its high metal content.
Drag-out
Drag-out
Drag-out
Drag-out
Drag-out
Pretreatment
System
Figure 7. Overview of the Electroless Plating. Process (Cushnie 1994)
'" - . ' ' 93 ' '- ' ' '
Discharge 1
-------
Prevention in the Pbcing Process
The frequency of dumping electroless
baths is greater than that of electroplat-
ing. Electroless baths are extremely
sensitive to contamination, especially
those that-are brought into the solution
(dragin). Turnover is a measure of the
age of electroless plating baths and is the
term used for the number of times the
starting mass of metal at makeup is
replenished. Current process bath
technologies typically allow up to 10 to
12 turnovers, although 5 to 6 is common.
The concentration of organics in electro-
less process chemistries can create
special wastewater treatment problems.
The focus for most metal finishers is
metals. For electroless platers, the level
of chlorinated organics can be a prob-
lem as well. The amines used in the
process can break down to form chlori-
nated organics when combined with
other chemicals in the pretreatment
process (Haveman 1995).
Precipitators
A common method of treating electroless wastes
is the addition of reducing agents such as so-
dium borohydride, sodium hypophosphitc! or
sodium hydrosulfite at elevated temperatures to
reduce the soluble metals to their metallic or
oxide forms. Sludges produced in these pro-
cesses contain relatively impure metal powders
that are susceptible to air oxidation and require
further treatment because of the presence of
interstitial water containing relatively large
amounts of free dictating agents. Over a rela-
tively short period of time, these chelates can
cause redissolution of some,of the metal oxide in
the sludge. As a result, platers must consider this
sludge a hazardous waste and manage the waste
accordingly (Richmond 1991).
Housekeeping in Electroless Plating
Electroless solutions are especially susceptible to
impurities affecting the process solution. Impu-
rities in the solution can cause reduced ductility
and corrosion resistance as well as pitting,
adhesion, and roughness problems. Facilities
should identify sources of contamination and
take steps to avert them including worker
training or equipment modifications. Common
sources of contamination include cleaners,
pickling solutions,,airborne particulates, hard
water, and defective equipment (ASM 1982).
Metal Recovery in Electroless Plating
Electrolytic Recovery
Electrolytic techniques use high surface-area
cathodes and/or non-conductive fluidized beds to
recover metal that can be sold for scrap. The
process uses a high surface-area cathode that
attracts the metallic ions out of solution. Platers
then must strip the cathodes-and treat the res'ult-
ing solution by chemicai or conventional electro-
lytic means to remove the remaining metal
content. In some cases, concentrate can be
returned to the process solution. Using a process
such as this will result in decreased sludge
generation and increased production rates'from
the clectroless bath (Jordan 1985). Chapter 7
presents a more thorough review of electrolytic
recovery.
Electrodialysis
Electrodialysis uses a membrane that allows for
the separation, removal, or concentration of
ionized chemicals! These functions arc accom-
plished by selective transport of ions through ion
exchange. Electrodialysis uses two different
membranes: an anionic permeable (AP) mem-
brane that allows passage of only anions and a
cationic permeable (CP) membrane that allows
cation ions to pass through. The result is two
streams: a demineralized rinsewater stream
suitable fpr reuse and a concentration of metallic
salts usually returned directly to the plating
solution. For example, electroless nickel and
copper plate rinsewaters generated during the
production of printed circuit boards can be
directed to an electrodialysis unit. Processed
concentrate can be returned to the plating tank
and water reused in the rinse process
(Kampermart 1991).
Ion Exchange in Electroless Plating
The use of conventional ion exchange systems as
well as newly developed resin technology has
been proposed for the treatment of electroless
wastes. Conventional cation exchange resins are
extremely inefficient. Systems involving these
94
-------
Chjpter 6: Pollution Prevention in the Pbti.-g Process
resins, therefore, require large columns and
frequent regeneration. Most chelating,resin.
systems available today are not effective on all'
dictators! In addition, the regerierant from most
ion exchange or chelate resin systems requires
further treatment in order to reclaim or otherwise
remove the metal content (Cushnie 1994). ;
Electroless Copper
; . '
Common Uses
Electroless copper is used commonly to plate
parts for engineering applications, particularly to
provide conductivity for electronics and printed
circuit boards or plastics that are going to receive
further plates for decorative applications (ASM
1982).
Common Process Solutions
Electroless copper uses copper salt as the metal
salt, often cupric chloride, EDTA as a chelating
'agent, and formaldehyde (a suspected carcino-
aen) as the reducing agent. The reductive
reaction is favored at high pHs so caustic soda is
used to. keep the pH above 11.0. Reducing
agents often react with the bath, resulting in
slower deposition rates and poorer deposit :
quality. This also can mean that the bath will
need to be rejuvenated after several metal
turnovers. '.
This solution also is subject to spontaneous
decomposition-. Copper built up on.the tanks
from the process solution must be stripped with
an etching solution (e.g., sutfuric acid/hydrogen
peroxide etchant). This results in an additional
wastestream of copper and etching solution (Ford
1994).
Alternatives to Electroless Copper
/.'
Carbon Technology .
The printed circuit board industry is testing a
proprietary technology, called the Blackhole
Process, as an alternative to electroless copper
plating: This process-uses conventional plating
equipment and aqueous black carbon that is
dispersed at room temperature. The carbon film
that is obtained provides the conductivity needed
for the through-holes. The following qualities
make Blackhole environmentally attractive:
* Reduced process steps
.» Reduced health and safety concerns
Reduced waste treatment costs
-Reduced water use
Reduced air pollution
The chemistry in the Blackhole process^avoids
the use of metals (i.e., copper, palladium, and
tin) and formaldehyde (a suspected carcinogen) ^
used in electroless copper plating. Compared to
conventional electroless copper plating, the
.Blackhole technology uses fewer individual steps
than electroless plating. The smaller number of
process steps reduces the use of rinsewater,,
decreasing waste treatment requirements (EPA
1994). ,
Printed,circuit boards are prepared prior to
carbon coating in the same manner as electroless
copper including etchback. Immediately prior to
carbon coating, the boards are cleaned with
proprietary cleaners and conditioning solutions
which are alkaline and contain weak complexing
agents. The carbon coating solution also is .
:J slightly alkaline and contains extremely fine
carbon particles. The process has been available
commercially since 1989. It is used in many
printed circuit board facilities and has been
approved by the United States Military (MIL-
55110D)as a substitute for electroless copper in
military applications (Altmayer 1994). Making
the transition from an electroless copper plating
system to the Blackhole technology requires only
the disposal and cleaning df the existing electro-
less line and purchasing of the new solutions
(EPA 1994).
Elimination of electroless copper removes a
chelated process from wastewater, however, the
substitute might have some disadvantages. The
extremely fine, suspended carbon might cause
problems in wastewater treatment operations by
clogging filters, coating probes, and interfering
withctarificrpperations. Carbon cannot be
removed by precipitation and must be controlled
95
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O30W<; 6; Pdiiation Prevention in the Plating Process
at the source. Carbon in wastewater will in-
crease loading to the publicly owned treatment
uorks (POT\V) significantly. The carbon also
can act as an organic collector, increasing total
organic concentrations in the wastewater. In
areas where POTWs have excessive coloration
regulations, discharges containing carbon are
unlikely to meet this requirement (Altmayer
1993).
Electroless Nickel
Common Uses
Electroless nickel is used normally as an engi-
neering coating to impart corrosion and wear
resistance to a workpiece. Platers also com-
monly use the process on aluminum to provide a
solderable surface and to improve lubricity and
the release of molds and dies. Because of these
properties, this technology is used widely in
petroleum,'chemicals, plastics, optics, printing.
mining, aerospace, nuclear, automotive, electron-
ics, computers, textiles, paper, and food machin-
ery manufacturing (Fields 1982).
Common Bath Solutions
Metal finishers have used electroless nickel since
the 1950s. The most common baths use iiickcl
sulfate salts with sodium hypophosphite as the
reducing agent. Platers frequently use
hypophosphite in metal applications and a warm,
alkaline hypophosphite solution in plastics
applications. In either case, decomposition of
the sodium hypophosphite during the reduction
' reaction results in the formation of a compound
that increases deposition rates. Generally, this
occurs between five and seven metal turnovers
(Fields 1982).
Process Characteristics
Some advantages of this process include'.
Uniform deposition without variances in
thickness
Platable on non-conducting materials
such as plastic
Solderability
Good wear
Corrosion resistance
Some disadvantages of the system include:
High chemical costs
Embrittlernent
Poor welding characteristics of nickel
phosphorous deposits
Copper strike needed to plate certain
alloys
Slow plating rates
Another disadvantage is that the baths have a
tendency to decompose spontaneously causing
the entire tank to become nickel plated. When
this occurs, the tank must be drained of the
plating solution and filled with a nitric acid
solution to dissolve the metal and repacify the>
tank. The nitric acid solution can be retained and
used several times, but at some point it must be
disposed (Davis 1992).
Bath Life -Extension
Because of the frequency of bath change-out, the
primary pollution prevention goal in electroless
nickel baths is bath life extension. Bath life
extension technology performs two functions:
removal of the chemical byproducts formed
during the processing of parts and the continuous
addition of bath chemicals to maintain the
overall chemical balance of the bath. Typical
byproducts of the process are orthophosphite.
sulfate, and sodium ions. Process bath chemicals
and operating.parameters such as nickel concen-
tration, hypophosphite, reducing agents,
complexing agents, pH, temperature, and bath
stabilizers influence the effectiveness of different
bath life extension methods (DoD 1996).
" I'
Recovery technologies such as ion exchange and
reverse osmosis have been used to remove
contaminates. Other methods include the
precipitation of orthophosphite contaminants
with calcium or magnesium ions, however, this
method is only useful if the sulfate ion also is
removed. Some treatments have extended the
bath life from seven to ten times the original life
(extensions such as these can reduce waste
generation by 90 percent) while others have
claimed increases of 50 times the original.
Facilities should-be aware that the concentration
of inhibitors, catalysts, and exaltants will change
96
-------
Chapter 6: 'Pollution Prevention in .the Pljcinf Process
as the lifetime of the batli is extended, requiring
monitoring and additions of the chemicals;
(Bishop 1993)! . . V- '.':
Regeneration of Electroless Nickel Baths
Electroless: nickel solutions are degraded by the
buildup of orthophosphite, a breakdown product
.of sodium.hypophosphite that platers use in the
solution as a reducing agent. Studies are under-
way to see if electrpdialysis is capable of remov-
ing the orthophosphite selectively, increasing the
life of the solution vastly. Initial results for this
are not promising, however, research centers
such as the Toxics Use Reduction Institute
continue to. work with companies on making this
technology feasible (Palepu). .
Prolonging Bath Life with Lime
A pilot-scale study was .conducted by TecKote,
in Brampton, Canada, to determine if it is
possible to precipitate out phosphite contamina-
tion of electroless nickel baths using lime, the
test procedure was as follows:
A plating bath was prepared using a
proprietary electroless'nickel'solution'
Nickel salt, and hypophosphite solution
were mixed with de'ionized water :
' Parts (i.e., activated steel panels) were
'immersed in the solution
V A 1 5-percent lime slurry was pumped
" 'into the plating bath at a constant rate of
20 miltiliters perjninute. . -
The plating run lasted 44 hours and yielded some
promising results. The test found that the
addition of lime slurry doubled the life expect-
ancy of the plating solution, however, the
process also produced a sludge that was deter-
mined to be hazardous. The study did not
determine whether this process would yield cost
savings for plating-facilities (Richmond 1991).
Immersion (Displacement)
Plating
Immersion.plating is a process similar to electro-
less plating. In this process, the metal finish is
: pjaced on the workpiece by displacing base
metal from the workpiece with another metal ion
in the plating solution. The metal ions in the
plating solution have a lower oxidation potential
than the displaced metal. This process, like
electroless plating, uses chemical reactions to
apply a metal finish to the substrate. Immersion
plating'differs from electroless plating in that the
reducing agent.is the base metal of the workpiece
and not a chemical additive, as is the case in
electroless plating (Davis 1994).
The thickness of deposits obtained in immersion
plating is limited because.deposition stops when
the entire surface of the base metal is coated.
Higher temperatures and agitation can increase
the reaction rate of the immersion-process.
These baths usually are inexpensive to operate
and deposit well. Other benefits of immersion
include its ability to deposit on difficult surfaces
such as bores or holes. When working with this
solution, be aware of the safety hazards, associ-
ated.with bases and acids (Hirsch 1993). Table
16 identifies deposit-base pairs that can use this
plating technique without a cyanide solution.
Chemical and
Electrical Conversion
Chemical and electrochemical conversion
treatments are designed to deposit a coating on
, metal surfaces that'perform corrosion protection
and/or decorative functions and; in some cases,
to prepare for painting/Processes include
anodizing, chromating, passivation, phosphating.
metallic coating, and eiectropolishing. The
converted surface is not superimposed on the
underlying metal, but rather is a strongly adher-
ent chemical entity formed at the interface by an,
interaction between the chemical coating
solution and the ions formed from the metal
surface immersed in the solution.
Anodizing
As mentioned in the previous section, anodizing
is a specialized electrolytic surface finish for-
aluminum that imparts hardness*resists corro-
1 sion, increases paint adhesion, provides electrical
insulation, imparts decorative characteristics, and
aids in the detection of surface flaws on the .
aluminum, This process employs electrochemi-
cal means to develop a surface oxide film on the
workpiece, enhancing corrosion resistance.
97
-------
' 6. Po'lud'OP Prevention in the Plating Process
Table 16. Immersion Plating Formulations (Hirsch 1993}
Type of Deposit
i Bronze
'
Cadmium
Copper
Gold
Nickel
Silver
Tin
Zinc
Base Metal
Steel
Aluminum
Copper alloys
Steel
Aluminum
Steel
Zinc
Copper alloys
Copper alloys
Steel
Zinc
Copper alloys
Aluminum
Copper alloys
Steel
Zinc
Aluminum
Steel
Bath Ingredients
Stannous sulfate, copper sulfate, and sulfuric acid
Cadmium sulfate and hydrofluoric acid
Cadmium oxide and sodium hydroxide
Cadmium oxide and sodium hydroxide
Copper sulfate and ethylenediamme or hydrofluoric acid .
Copper sulfate and sulfuric acid ;
Copper sulfate, tartaric acid, and ammonia i
Hydrogen tetrachloroaurate and ethanol. 1
Nickel sulfate, ammonium nickel sulfate, and sodium thiosulfate j
Nickel sulfate
i . . ' i
Nickel sulfate and sodium chloride
Silver nitrate, ammonia, and sodium thiosulfate
Sodium stannate
Stannous chloride, thiourea, and sulfuric acid
Stannous sulfate and sulfuric acid
Stannous chloride
Zinc oxide and sodium hydroxide
Zinc chloride and ammonium chloride
Anodizing differs from electroplating in two
ways. First, the workpiecc is the anode rather
than the cathode as in electroplating. Second,
rather than adding another layer of metal to the
substrate, anodizing converts the surface of the
metal to form an oxide that, is integral to the
substrate (SME 1985).
Industry uses three principal types of anodizing:
chromic acid anodizing (called Type I anodiz-
ing), sulfuric acid anodizing (called Type II
anodizing), and hard coat anodizing, a combina-
tion of sulfuric acids with an organic acid such as
oxalic acids (called Type III anodizing). Be-
cause of the structure, the anodized surface can
be dyed easily. These dyes are organic or
organometallic and often contain chrome in the
trivalent state. Whether the pieces are dyed or
not, they need to be sealed. Sealing can be
performed with hot water, nickel acetate, or
sodium dichromate, depending on the required
properties (SME 1985).
Type I (Chromic Acid) Anodizing
Chromic acid anodizing takes place in a solution
of chromic acid. The hexavalent chrome solu-
tion creates a thin hard coating (Ford 1994).
Type II (Sulfuric Acid) Anodizing
Sulfuric acid anodizing takes place in a 15-
percent solution of sulfuric acid. During the
anodizing process, aluminum dissolves off the
surface of the part and changes the surface
characteristic! to an oxide coating. This process
creates a surface structure that is both porous and
harder than the base aluminum. Sealing this
coating provides greater corrosion protection.
When the aluminum concentration in the bath
solution builds up to a certain level (15 to 20
gallons per liter), the process becomes less
efficient and requires treatment (Ford 1994).
Type III (Hard Coat) Anodizing
Hard coat anodizing is a form of sulfuric acid
anodizing in which the acid content is slightly
98
-------
Chapter 6:' Pollution Pre'.ention in the.PUcing Process
higher (20 percent) and an organic additive is
added to the bath. This additive helps to create a
tighter pore structure that increases the hardness ,
of the oxide coating. Hard coat anodizing has a
high resistance to abrasion, erosion, and corro-
sion. This type of coating also can be applied in
much thicker layers than Type 1 or Type II.
anodizing (Ford" 1994). V
Platers use various methods to treat wastes
'generated from anodizing bath solutions. Tech-
nologies that have been employed successfully
include evaporation systems operating under
reduced pressure, sedimentation, reverse osmo-
sis, filtration, and anion and cation exchangers.
Substituting Type 1 Chromic Acid Anodiz-
ing with Type 11 Sulfuric Acid Anodizing
Because of federal and state mandates bei,ng
imposed on operations using hexavalent chrome,
.researchers have investigated the feasibility of
substituting Type I anodizing with Type II
sulfuric acid anodizing. The results of a NASA
study indicate that in applications where anodiz-
ing is used to impart corrosion protection' on
aluminum, Type II sulfuric acid anodizing is
superior to Type I chromic acid anodizing
(Danford 1992); : '
Conversion from chromic acid to sulfuric acid
anodizing is not a simple chemical substitution
/according to suppliers. The conversion requires
a complete changeover of anodizing equipment
and partial modifications to downstream waste
treatment facilities. Replacement of the .anodiz-
ing tank often is required because of the*liffer-
ences in acidity between sulfuric acid and
chromic acid. Sulfuric acid anodizing processes
also have different voltage and amperage re- . ,
quirements, necessitating replacement of the
rectifier. The operating temperature of the
electrolytic bath also is different for the two
processes. The chromic process is usually
maintained by steam heat at an operating tem-
perature of 90 to:100 degrees Fahrenheit whereas
the sulfuric acid process must be chilled using
cooling water to an operating temperature of 45
to 70 degrees Fahrenheit. ,
Operation and maintenance costs are typically
, much lower for sulfuric acid anodizing than for
chromic acid because of lower energy require-
ments. Wastewater treatment costs are lower as
well because sulfuric acid only requires removal
of copper whereas chromic acid requires more"
complex chrome reduction techniques. The
change in materials also means that the cost of
sludge disposal is greatly reduced: '
Substituting Chrom'iq Anodizing with
Sulfuric Acid Case Study
n December 1988, General Dynamics
eplaced a 35-year-old chromic acid/alumi-
num anodizing system with a new computer-
zed sulfuric acid anodizing system that used
computerized hoists and on-demand rinsing.
The new system, supplied by- NAPCO, Inc.,
enabled General Dynamics to eliminate a
major source of chromium emissions. In.
addition to the chemical substitution to :.
eliminate chromium releases, automated hoist
and onrdemand water rinse systems helped to
reduce wastewater treatment requirements.
The computerized automated hoists monitor
the time intervals during which the parts are
treated and allowed to drain. Compared with
manual immersion and draining of parts, this
system reduces treatment requirements by
avoiding unnecessary' dragout of immersion
fluids to downstream rinse, tanks. Subse-
quently, the on-demand water system reduces
ririsiwater use "and wastewater treatment
requirements by reducing waster consumption
xand monitoring the conductivity of the rinse-
water in the tank. Unlike manually operated
rinse tanks, which have constant overflows,
the on-demand system adds water only when
the conductivity of the tank exceeds a set
value. : (US EPA 1995)
!i
Ion Vapor Deposition as a Substitute for
Anodlzed Coatings
The brittle nature of anodized coatings can cause
fatigue failure on aluminum alloy structures.
However, the soft ductile ion vapor deposition
(I VD) aluminum coating will not affect mechani-
cal properties of the base metal detrimentally. In
addition, the IVD coating offers excellent
sacri ficial and stress-corrosion protection,
increasing the service life of products using this
coating. This coating can allow for stronger
99
-------
Cue:*' S: Pi 'i»V.an Prevention in the,Pacing Process
constructions that sa\e u eight, particularly
important in the design of new aircraft
iMuehlberger 1983). For more information on
1VD coatings, refer to Chapter 8.-
Chromic Acid Regeneration
Chromic acid anodizing solutions can'be regen-
erated by the use of a cation exchanger which
removes the accumulating aluminum together
with other impurities such as copper. The life
expectancy is much shorter than on normal waste
treatment applications, but the method is still
practical and economical (Steward 1985).
Chromic Acid Case Study
NASA conducted a case study comparing the
corrosion protection between Type I (chromic
acid) anodizing and Type II (sulfuric acid)
anodizing. After using several analytical
techniques, the study found the corrosion
protection obtained by Type II anodizing
superior to Type I anodizing. (Danford 1992)
Sulfuric Acid Anodize Regeneration with
Ion Exchange
Traditionally, platers use ion exchange to remove
metallic contaminants from wastewater streams.
However, ion exchange resins remove the
hydrogen and sulfate components of the sulfuric
acid/aluminum anodizing solution. As the
solution passes through the columns, the acid is
removed. Then the wastestream, which consists
of a small amount of acid plus all the aluminum
from the anodizing solution, flows to the waste-
water treatment system. To recover the acid,
platers use water to flush the acid components
from the resin, which forms a sulfuric acid
solution that is low in dissolved aluminum and
cart be used again in the anodizing process (Ford
1994),
Chromic acid anodizing solutions can be regen-
erated by the use of a cation exchanger that
removes the accumulating aluminum together
with metal impurities suclvas copper. The life
expectancy of the resin is much shorter than for
normal waste treatment applications, but the
method is still practical and economical (Kostura
1990).
Sulfuric Acid Anodize Regeneration with
Electrodialysis
Electrodialysis removes metal ions (cations)
from solutions using a selective-membrane, an
electrical current, and electrodes. This technol-
ogy uses a chemical mixture (catholyte) as a
capture and transport media for metal ions. This
catholyte will form a metal sludge and will
require periodic change-outs.. The recovered
sludge is hazardous, however, companies might.
want to work with an outside firm to recover the
metal in the sludge. Using electrodialysis,
facilities can remove all the metal impurities
from the anodizing bath, maintaining it indefi-
nitely. By keeping the concentration of contami-
nants in the process bath low, the rinsewater
potentially can be recycled back to the bath,
closing the loop on the process. The cost to
.' operate this system will depend on the size of the
acid anodizing bath, the level of metal concentra-
tion, the metal removal capacity of the electrodi-
alysis unit, and the ability to reclaim metals in
the sludge. For more information on this technol-
ogy, refer to the recycling/recovery section in
'Chapter?.'
Sulfuric Acid Anodize Regeneration Using
Acid Retardation
Theoretically, sulfuric acid anodizc solution and
the phosphoric acid bright dip bath can both be
regenerated using acid retardation, \shich is a
sorption process using ion exchange resins. The
cost for such a recovery operation is likely to be
economically feasible for only very large opera-
tions. For more information on acid sorption
technologies, refer to Chapter 7 (Steward 1985).
It is also possible to collect sludges from rinse-
water neutralization and from treatment of batch
dumps of anodizing and caustic soda etch, press
the sludges as dry as possible, and then dissolve
the sludge jn sulfuric acid to make a concentrated
alum solution, which can be sold as a byproduct
' for coagulation in wastewater treatment opera-
tions. Facilities should ensure that they have a
market for the alum cake prior to undertaking
this option (Steward 1985).
100
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Chapter 6: Pollution Prevention'in the Phung Process
Blackening (Antiquing) .
Common Uses
Creating an antique finish by coating a ;
workpiece.with a black substance and mechani-
cally relieving it so that the only black remains in
rece'sses has been a commo^practice in jewelry
electroplating shops for many years. Typically,
the black is applied in one of several ways: as a
paint, as an oxide coating (usually applied by
immersion), or as an electroplated deposit -.
'(METFAB 1995).
Common Bath Solutions
The paints are solvent-based, the oxide solutions
often contain hazardous materials (e.g., arsenic,
lead, permangate, antimony, and dichromate),.
and the most'popular electroplating process can
contain more than 1 pound per galloivof solution
of free sodium cyanide (METFAB 1995). ,
Alternative Bath Solutions for Blackening
The Versy Black process by Zinex Corporation
of Oxnard, California, is a feasible alternative
for traditional antiquing operations. This process
does not contain any cyanide or chelators and
contains only small quantities of zinc, copper,
and cobalt. Substitution of this process for ,
existing blackening operations eliminates
cyanide, arsenic, antimony, permanganate,
d'ichromate,.and tellurium from a facility's
wastestream. The proprietary nature of the Zinex
product imposes limits on discussing the chemis-
try behind it (METFAB 1995.). .
The Rhode Island Department of Environmental
Management in conjunction with METFAB
' Sales and Service tested the Versy Black solution
over a 14-month period at several locations. The
study showed that Versy Black is not only a
.feasible alternative, but also a superior product.
Versy Black outperformed traditional blackening
in the following ways:
» Easier to control ' .
Easy to relieve .
Easy to lacquer -.,,-.-
.; + Stable chemistry
» '. Excellent adhesion
Easier to rework
No safety risk .
»' No environmental risk
Waste .treatment of this process is.simple.
Because the process uses no chelators, treatment
can be accomplished simply be precipitation
with caustics (pH adjustment). The absence of
chelators in the process also means that treating
the metals that enter the wastestream from other
processes is less troublesome. Chelators make
the 'precipitation less effective because of their
ability to keep metals from reacting with caustics
to form insoluble hydroxides (METFAB 1995).
Chromating
' Platers often use chromate coatings to minimize
rust formation and to guarantee paint adhesion
after anodizing aluminum parts. These coatings
' also are used over zinc and cadmium to simulate
' the appearance of bright nickel and chromium.
Other applications include use as a coating over
zinc or cadmium-plated parts to prevent the
formation of white rust. Depending on the color,
, chromating takes place in a solution of chromic
acid and additives. Although these baths contain
hcxavalent chrome, they are not electrolytic
baths and, therefore, do not generate the same
Icvelof mist/fumes of chrome electroplating or
anodizing. For this reason._the chromating
process is not regulated under the Chrome
M ACT standard (Katz 1992).
Process Description
The operator immerses anodized parts in a
solution that contains a hexavalent chrome salt,
either chromic acid or chromate, and an acid,
often nitric acid. This solution dissolves the
outer.layers of the substrate and causes a pH
increase at the surface-liquid interface. This
change results in the precipitation of a thin
complex chromium gel on the surface. The ge] is
composed of hexavalent and trivalent chromium
and the substrate itself. These chromate films
* provide further corrosion resistance and are
formed in a wide range of colors: clear, yellow,
gold, and drab olive (Ford 1994). Table 17
presents an overview of the common chromating
uses for different substrates.
101.
-------
i. PoJiuuon Prevention in the Plating Process
, , , , i
Table 17. Common Uses of Chromate Conversion Coatings (Freeman 1995)
, Corrosion
, i;
" i>
Metal
Aluminum
. ,
Cadmium
Copper
Mag-
nesium
Silver
Zinc
Resistance
X
X
X
. ,
X
X
x
Paint
Base
X
*
X
X
X
Chemical
Polish
X
X
-
X '
Metal
Coloring
X
X
X
X
Remarks |j
Economical replacement for anodizing if
abrasion resistance is not required
Used to touch up damaged areas on
anodized surfaces
Thin coatings prevent spotting out of brass ]
and copper electrodeposits . ' 1
No fumes generated during chemical i
polishing
1
Unfortunately, like chromium plating,
chromating Involves highly carcinogenic and
toxic materials. If inhaled, chromate mists can
eventually cause lung cancer. Health and safety
considerations and the increasing cost of disposal
of chromium-containing wastes have prompted
users to evaluate alternative treatments. A
number of alternatives exist, however, few
provide the corrosion protection of chromate
conversion coatings. Sulfuric acid anodizing can
be substituted for some chromium conversion
coatings although the coatings are more brittle
and significantly thicker than those produced
with chromate (Freeman 1995).
Alternatives for Chromating
Cobalt/Molybdenum
Cobalt/molybdenum (Alodine 2000) is a devel-
opmental conversion coating process that was
originally developed and patented by Boeing
Aircraft Company. The process is being devel-
oped further "by Parker+Amchem in preparation
for commercial availability. The process uses an
undisclosed proprietary formulation identified
generally as cobalt- and molybdenum-based.
The cobalt and molybdenum ions arc much less
hazardous than chromium and behave similarly.
The coating does not have the ability to inhibit
pitting corrosion as effectively as chromium.
therefore, a second step is required to meet
military specifications. The second step is an
organic emulsion seal (Alodine 2000) that
enhances corrosion resistance and paint adhesion
characteristics. The process is estimated to cost
two to three times more than conventional
chromating. The process also requires an
additional tank for the sealing process (Meyers
1994).
Gardolene VP 4683
A new chrome-free, post-rinse called Gardolene
VP4683 has been developed for use on
phosphated steel zinc, and aluminum surfaces
prior to painting. The rinse contains only
inorganic metallic compounds as the active
ingredient with no hexavalent or trivalent
chrome. The rinse is applied at temperatures up
to 100 degrees-Fahrenheit and at a slightly acidic
pH. The manufacturer describes corrosion
protection and paint adhesion as equal to that of
hexavalent chrome (Finishers Management
1991).
102
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Chapter 6: .Pollution Prevention in the Plating Process
Oxide. Layer Growth in High-Temperature
Deio'nized Water . .;
The oxide layer growth system was developed
and refined within the past decade. The process
coating; is applied in a series of steps, including
an oxide layer growth step in boiling deionized
water, to build a corrosion-resistant paint base on
aluminum. Both immersion and steam spray >
methods are being developed. The process does
not use any hazardous materials and is com-
pletely inorganic and non-toxic. Depleted bath
and rinsevvaters require limited treatment before
discharge to a sanitary sewer. The process can
withstand greater temperature exposure than the,
chromate conversion coating and is .thin, yet
* abrasion resistant, the chemical solutions used
to apply the coatings are very dilute, facilitating
' long solution life and simple monitoring and
control (Meyers 1994).
- The major drawback with the oxide layer growth
process is cost. > The process requires many
additional steps involving numerous tanks of
' chemicals at elevated temperatures. Conse-
quently, energy and capital costs increase1 .
substantially. While energy costs are offset by
waste disposal reductions,'this.technology is
estimated to cost up to ten times more than
conventional chromating methods. A variation
on the process involves spray application within
a cabinet coater. This device is a chamber or
series of conveyerized chambers. This method
reduces some of the associated heating and
chemical requirements and requires much less
floor space (Meyers 1994).
Non-Chromate Passivation of Zinc
The Centre for Advanced Electroplating in
Denmark has developed two different treatment
methods, both based on passivation using.
molybdate and .phosphate (referred to as. .
MolyPhos) as alternatives to chromating.
Chromated zinc often is used in the automotive,
aerospace, and electronics industries. Platers can
use MolyPhos for passivation of electroplated"
zinc instead of chromate. Depending upon the
zinc substrate and the environment in which the
workpiece will be placed, this method will
function similarly to yellow chromate.
MolyPhos performs well in outdoor exposure
tests, adhesion tests, and GMT tests, but does .not
fair well in salt spray tests. The results of
numerous corrosion tests are summarized in
Table 18 (Tang 1993).
SANCHEM-CC ,
Another promising alternative is the
SANCHEM-CC chromium-free aluminum
pretreatment system. The following'is.a sum-
mary of the process: ... ' -
Stage One: Boil in deionized water or
steam to form a hydrated aluminum-oxide
film. , ''- '. / .
. Stage Two: Treat in a proprietary aluminum
salt solution for at least 1 minute at a'mini-
mum of 205 degrees Fahrenheit.
, Stage Three: Treat ina proprietary perman-
ganate solution at 135 to 145 degrees Fahr-'
enheit for at least 1 minute.
In cases where maximum corrosion resistance
for certain aluminum alloys is required, the
process requires a fourth stage. The developers
claim that this process closely matches the
Table 18. Results of Molyphos as a Substitute for Chromating (Tang 1993)
Substrate
Cyanide Zinc
Acidic Zinc
Zinc/Nickel
(15% Nickel)
Zinc/Cobalt
(0.8% Cobalt)
Yellow Chromate
Very good
Good
Good
Very good
MolyPhos 33
Very good
Not possible ,
Bad
Good
MolyPhos 66
Good
Very good
Good
1 Good
103
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Ps 'wlicn Prevention in the Placing Process
performance of a eliminate conversion process
(EPA 1994).
Zirconium Oxide
Zirconium oxide, an organic conversion coating,
is an alternative to chromating for some applica-
tions. This coating is one of the only commer-
cially available non-chromating treatments for
aluminum. This process usually involves
immersion of the substrate in an aqueous solu-
tion containing a polymeric material and a
zirconium salt. The" zirconium deposits on the
surface in the form of zirconium oxide. These
coatings have been used on aluminum cans for
some time, but they have not been tested in the
kinds of environments in which chromate
conversion coatings are typically used. Wider
application of this coating as a total replacement
for chromating must be based on further testing
(EPA 1994).
Alternative Conversion Coating
A facility using a traditional chromate system
generated many forms of hazardous waste
(airborne and wastewater). The facility
replaced their chromating process with a dry-
in-place waferborne emulsion conversion
coating. The product is completely chromium-
free and adaptable to heat spray applica-
tions. Thepermanganate-based product is
considered environmentally safe at ambient
temperatures. In fact, small residual amounts
of the potassium salt that are deposited as a
primary coat are desirable in the industrial
wastewater treatment system because they aid
in treatment of other common wastewater
contaminants.
Replacement of the chromate conversion
coating process resulted in a coating that
bonded strongly to the metal surface and
provided good corrosion resistance. Uniform
coverage was achieved easily, and the
unpointed surface does not rub off on
worker's hands or emit toxic fumes when
welded. The parts can be painted immedi-
ately, which reduces the time required to
complete the finishing process.
(Freeman 1995
Other Chromate Conversion Coating
Alternatives
Several additional processes might prove feasible
in eliminating chromium from conversion
coatings. These include SBAA and other emerg-
ing technologies.
SBAA, developed by Boeing, might prove
valuable as a replacement for chromating on
certain aircraft parts. The process imparts
excellent paint adhesion and corrosion protection
at a cost that is comparable to chromating.
However, because SBAA is an anodic process, it
might not be technically feasible to use it on all
parts, especially parts with steel inserts or those
having sharp edges, crevices,'or areas that entrap
fluids (Meyers 1994).
Several experimental and developmental tech-
nologies might lead to breakthroughs as replace-
ments for chromium in conversion coatings.
These technologies include hydrated alumina
coating, hydrated metal salt coating', oxyamon
analogs, potassium permanganate, rare earth
metal salts (cerium), zirconium oxide/yttrium
oxide in aqueous polymeric solution, and
lithium-inhibited hydrotalcitc coatings.
'Regeneration of Chromating Solutions
Both ion exchange and electrochemical methods
have been demonstrated as effective methods to
regenerate spent eliminates; however, in almost
all cases, the metal finisher relies on a propri-
etary chemical supplier for'the appropriate
balance in the chromating bath. Either of these
regenerating technologies make the metal
finisher responsible for the overall chemical
maintenance of all constituents in the bath.
Proprietary suppliers might provide this service
to further assist finishers in maintaining a proper
balance when one of these techniques is used
(Steward 1985).
Passivation
Passivation is a process by which protective
films are formed on metals through immersion in
an acid solution. In stainless steel passivation,
embedded ion particles are dissolved and a thin
oxide coat is formed by immersion in nitric acid.
104
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Chjpter.6: Pollution Prevention in the Plating Process
\\hich s9metimes contains sodium dichromate. .
During forming, machining, tumbling. lapsing,
and other processing operations, iron particles
can be embedded'or smeared onto the surface of
stainless steel. If these remain, the iron co'rrodes
and gives the appearance of rust spots on the
stainless steel. In order to prevent this, platers
irnmerse the parts in a so.lutioivof nitric acid that
sometimes contains oxidizing salts (generally
sodium dichromate) depending on the alloy. .
Generally; 300-series stainless steel and chro- .-
mium steel with 17 percent or more chromium
are passivated in a solution of nitric acid.: Series-
400 Stainless steel with less than 17 percent
chromium is passivated in nitric acid and sodium
' dichromate (Ford 1994).
Chelant-based Solutions for Passivation
Nitric acid is a fuming, suffocating, and corro-
sive liquid. The acid's fumes are toxic aijid the
liquid causes severe tissue burns. Because of
these attributes, Cal-chem of South El Monte.
California, has developed a safer substitute
solution for use with passivation on steel'. The
solution contains chelants as opposed to nitric
acid. Chelants'provide an attractive alternative
because they are non-toxic and biodegradable,
however, platers need to be careful of this
solution in waste treatment (Microcontai;nination
1993). For more information, refer to the~first
section of this chapter.
Phosphate Coatings
Phosphating is used to treat various metals
(mainly steel and iron) to impart corrosion
resistance and to promote the adhesion of
finishes such as paint and lacquers. Phosphating
treatments provide a coating of insoluble metal
phosphate crystals that adhere strongly to the
base metal. Generally, phosphating solutions are
prepared front liquid concentrations containing
one or more divalent metals, free phosphoric
acid, and an accelerator (Ford 1,994). ..
Iron and zinc phosphate coatings often:are used
.as paint bases and manganese phosphate coatings
are applied chiefly to ferrous parts for break-in
and galling (e.g., engine parts). Other metallur-
gical uses for phosphate coatings are aiding in
the forming of steel, wear resistance, and corro-
sion protection (with the addition of oils or
waxes)- The choice of iron, or zinc phosphate
coating depends on product specifications. In
general, the more extensive multi-stage zinc
phosphate processes provide better paint adhe-
sion, corrosion protection, arid rust protection
than iron phosphate processes. Zinc phosphate
baths, however, tend to be more expensive,.
require more maintenance, and often result in
more sludge disposal (SME 1985).
The phosphating process consists of a series of
application and rinse stages typically involving
the application of either an iron, manganese, or
zinc phosphate solution to a substrate. A simple
iron phosphating system is comprised of two
stages: an iron phosphate bath that both cleans
the part and applies the conversion coating
followed by a rinse bath to remove dissolved
salts from the treated surface. An advanced zinc
phosphating line might feature seven stages of
spray/dip and rinse baths. In addition, a final
seal rinse comprised of a low-concentrate acidic
chroniate or an organic non-chromate often is
applied to further enhance corrosion resistance.
Following the conversion application, the parts
arc dried to prevent flash rusting (Ford 1994).
Pollution Prevention in the
.Phosphating Process
Since the 1970s, a trend in the metal finishing '
industry toward reducing heating costs, improv-
ing working conditions, prolonging equipment
life, reducing sludge, and reducing processing
steps has resulted in low-temperature iron and -
zinc phosphate coatings and, to a limited degree.
solvent phosphating solutions.
Regeneration of Phosphating Baths
Precipitates are formed continuously in
phosphating operations presenting maintenance
headaches. Often, this results in dumping of the
, solution. Usually, the precipitates accumulate in
the tank, primarily on. the heating coils. When
the solution is removed from the tank, this ,
accumulation of sludge can be manually re-
moved. The solution should be decanted back
into the tank to minimize waste because this uses
space and time; this is rarely done. A more
" efficient system involves the use of a continuous
recirculation system through a clarifier with
gentle agitation in the sludge blanket zone. This
105
-------
6; Pollution Prevention in the Placing Process
Ultrafiltration in the Phosphating Process Case Study
lh ! ' " .... : ^ "
!jR B White Inc., of Bloomington, Illinois, operates a sheet-metal fabrication facility that manufac-
ures painted steel shelving units. The company uses a single stage, aqueous iron phosphatmg/
decreasing system to improve worker safety and reduce the generation of organic solvent emiss.ons
and hazardous waste.' Although the switch eliminated the risks and liabilities associated with
organic solvents, it introduced a new waste disposal problem. Simultaneous degreasmg and
phosphating in the same bath formed an oil-water emulsion. With extended use, the buildup of oil
n the bath reduced cleaning and phosphating efficiency and product quality was compromised.
Additionally, dragout of oil from the bath into the rinsewater eventually pushed oil and grease levels
n the discharge over the allowable limit.
n the past, the company used oil skimmers to control oil slicks on the surface and prolong the life of
he bath, but the skimmers were only partially effective. When oil in the bath began to sacrifice
product quality and discharge levels edges closer to the maximum aNowable limit the ba h had to
3e replaced. Depending on production rates, the bath typically lasted 3 to 4 months. Replacing the
bath required losing a full day of production time to take the process off-line, arrangingJ wrfh a
waste transporter to drain and dispose of the contents, and recharging the tank with 5,000 gallons ,
of fresh water and raw materials. Disposal costs alone were $15,000. .
The plant implemented a full-scale, in-plant field test of an ultrafiltration system- provided by Koch |
membrane equipped with four 1-inch tabular PVDF membranes. When the field test began, the iron
phosphating/degreasing bath had not been replaced in more than 3 months. The aqueous solution ,
was murky with dirt and oil, and large patches of free oil floated on the surface. Over the next 11 .
days, ultrafiltration produced dramatic changes. Surface oil slicks disappeared and were rep aced
by a clean, light foam. The bath solution was visiblyclearer and plant personnel testified that it
looked like a freshly recharged bath. Results of total organic carbon (TOC) analysis for the full-scale
test showed a change in oil and surfactant concentrations during the test. .
The company analyzed the costs and benefits associated with installing the ultrafiltration system to
determine the economic feasibility of this technology. Based on the estimated expenditures and
avings the payback period for this technology was only 6.9 months. The net present value and
nternal rate of return indices were $152,143 and 178 percent, respect.vely.
n summary, the findings of the evaluation indicated that:
il'" , , ' i ., , h, ' 1 '
. The application of ultrafiltration produced significant reductions in hazardous waste,
especially significant when compared to earlier methods that used separate degreasmg and
phosphating tanks and organic solvent. .
In most phosphating applications, ultrafiltration is econ6mically attractive alt hough.capital
investment is required. Applications for recycling/reusing wastewater via ultraf, tration have
good potential for pollution prevention improvements as well as good econom.cs. However,
firms first should carefully investigate highly sensitive parameters such as fouling on small-
scale systems and identify variability in their operation and .ts effect on the Process'
106
-------
Chapter 6: Pollution Prevention in the Pitting Process
allows for indefinite use of the solution and ,
allows easy removal of dewatered sludge from
the bottom of the clarifier (Steward 1985).' '
Issues Related to
Aluminum Finishing
Aluminum finishing uses mainly anodizing and
chromating treatments. Prior to anodizing or
chromating, a workpiece usually proceeds
through a cleaning and etching process. Both ,
anodizing and chromating use similar cleaning
schemes. If required, platers perform solvent or
less toxic immersion cleaning/ The cleaner used
for aluminum workplaces should not contain
sodium hydroxide because this chemical attacks
aluminum. An example of an acceptable clean-
ing solution is borax (sodium tetraborate):
Technical assistance providers should be aware
that, even if a cleaner is made of a non-toxic
substance, if-the cleaning solution becomes '
contaminated with oils and lubricants, the spent
solution can be classified as a hazardous waste
(SME 1985)T ' '
The next step prior to finishing is etching. The
surface is etched by an alkaline or acid-based
etchant. Platers perform this etch step to thor-
" oughly clean and prepare the surface for further
treatment. The caustic etch used in many
aluminum finishing lines and the chemical
milling solution used for aircraft components can
both be regenerated by crystallization and
removal of sodium aluminate. However, the
process must be carefully controlled and main-
tained. Many operations might not find this
option economically feasibe because the technol-
ogy is capital intensive (DOD 1993).
During the etching process, smut often is formed
on the aluminum workpiece. The smut must be
removed prior to further treatment. Usually this
.treatment is accomplished with a nitric omitric/
hydrofluoric acid dip, otherwise known as
.desmutting (Cushnie 1994). The desmutting
process involves, the use of large amounts of
acids. Several products currently on the market
use approximately 10 percent of the usual
amount of nitric acid. Commonly, ferric nitrate
is substituted as a desmutting agent in the
presence of small amounts of nitric acid. The
rate and desmutting action of ferric nitrate .are
comparable to the traditional 50-percent nitric'
acid.bath(Ford 1994),
Stripping
Occasionally, workpieces that have a metallic
coating must be stripped to the base metal. Most
immersion stripping is accomplished with
cyanide, which does not attack steel substrates
but dissolves many of the metals used as coat-
ings. There are seemingly as many different
stripping solutions as there are base metal/
applied coating combinations. In general, they ,
tend to be either acid-, alkali-, or cyanide-based.
They can be chelated-heavily or not at all. The
most important property of these solutions
(besides the ability to strip the coating) is that
they must not attack the base metal. .The use of
cyanide-based metal strippers results in the
generation of cyanide-contaminated solutions
and a host of associated occupational health and
hazardous waste compliance issues. These
solutions require special treatment and disposal
procedures. Interestingly, stripping can be a part
of the finishing process, particularly for complex
parts that only require plating on certain.sur-
faces. The entire part is plated and then the areas
where plating should remain are masked off and
the entire part is immersed in the stripping
solution to remove the undesired finish (Ford
1994).
Pollution Prevention in Stripping
Operations
As the baths used in stripping are similar to those
used in plating, similar techniques of pollution
prevention and waste minimization are appli-
cable.'Attention to cleanliness and process
control are important in reducing stripping
wastes. Stripping usually is accomplished either
by chemical immersion or, by electrolytic pro-
cesses. Although mineral acids, suitably inhib-
ited, are useful for stripping some coatings, they
tend to attack the metal substrates and, therefore,
are limited in their application. '
Alternatives to Cyanide Stripping
Several non-cyanide alkaline immersion strip-'
. ping baths arc available to remove copper or
' nickel from various substrates. These baths
107
-------
ast*' a Pi 'uaor Prevention in the Placing Process
t\picall\ use either the ammonium ion or an
amine to provide complexing. Persulfate or
chlorite anions can be used as well as proprietary
formulations. The use of non-cyanide strippers
eliminates cyanide from the spent stripper
solution. In general, these non-cyanide strippers
are less toxic than their cyanide-based counter-
parts and are more susceptible to biological and
chemical degradation, resulting in simpler and
less expensive treatment and disposal costs. In
addition, the use of a non-cyanide stripper can
simplify the removal of metals from spent
solutions. These metals are difficult to. remove
from cyanide-based solutions because they form
a strong complex with the cyanide ligand (EPA
1994).
Because non-cyanide stripping solutions are
t>pically proprietary formulations, the detailed
chemistry of coating removal is not available for
most solutions. Stripping solutions are available
for a wide variety of'coating metal/base metal
combinations and processing characteristics can
vary widely (EPA 1994).
Reported Applications
Non-cyanide strippers have been available for
many years. The major drawbacks of this
technology include1 lack of speed, etching of
some substrates, and the 'need for electronic
current. As the disposal costs for cyanide
strippers increase, many companies have con-
verted to non-cyanide stripping and have ad-
justed production cycles accordingly for the
slower stripping speed (EPA 1994).
Operating Features
The wide variety of non-cyanide strippers makes
it difficult to generalize about operating param-
eters. Some strippers are designed to operate at
ambient bath temperatures whereas others are
recommended for operating temperatures as high
as 180 degrees Fahrenheit. Stripping processes
range from acidic to basic. Bath life is longer
because higher metal concentrations can be
tolerated. In general, the same equipment can be
used for cyanide-based and non-cyanide strip-
ping, however, acidic solution tank liners might
be needed to prevent corrosion (EPA 1994).
Costs ,
The impacts on costs when using non-cyanide
strippers are:
No large capital outlay is required
Costs of makeup solution is likely to
increase slightly
Waste treatment costs are reduced
because of reduced cyanide treatment
' (EPA 1994)
Facilities should be aware that treatment costs
might not change or might increase if cyanide is
still used in other processes in the facility.
Hazards and Limitations
Non-cyanide metal strippers have some disad-
vantages. The stripping rates for some coatings
might be lower than for comparable cyanide
strippers. Some strippers can produce undesir-
able effects on substrate metals even if the
stripper has been recommended by, the manufac-
turer. Also., for some non-cyanide strippers, the
recommended operating temperatures are high .
enounh to cause safety.concerns and reduced
temperatures can lead to slower stripping times
and reduced effectiveness. (EPA 1994).
A major use for non-cyanide strippers is the
removal of nickel coatings. Advances in no'n-
cyanide alternatives have been spawned by the
difficulty in treating nickel cyanide waste-
streams. Opportunities for further improvement
still remain though as the non-cyanide process is
sisinificantly slower than cyanide (8 hours versus
1 hour) (EPA 1994).
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108
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6. PJ'i*tan p'eisntion in the.PUcing Process
Ford. Christopher, and Sean Delaney. 1994.
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i
Freeman, Harry J. 1995. Industrial Pollution
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Fujiwara, Yutaka, and Hidehiko Enomoto.
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Kamperman, David R., ancl Kevin Warheit.
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Armament Research, Development and Engi-
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Kostura, John. 1990. Recovery and Treat-
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Ko, C.H. et al. 1991. A Comparison of
Cadmium Electroplate and Some Alternatives.
Plating and Surface Finishing. October, pp. 46-
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Kopacz, Uwe. 1992. Better than Brass?
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Lansky, Deborah. 1993. Replacing Cadmium
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HazMat World. February, pp. 26-27.
Lindsay; James H. 1995. Special Conference
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Lindstedt, John, and Micheal Doyle. 1992.
Silver Recovery with Ion Exchange and Elec'-.
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Mabbett and Associates, Inc. 1993. Making
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'Massachusetts Office of Technical Assis-
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Emissions While Eliminating Cadmium and
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no
-------
METFAB Sales &,Service. 1995. Replace-
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Muehlberger, DiE. 1983. Ion l'apor Deposi-
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Murphy, Micheal (ed.). 1993. 'Metals Hand:
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Natorski, Theodore. 1992. Zinc and Zinc '
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Naval Facilities Engineering Service;Center
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->' '-..-'-'
Peden, Jackie. ,1996. Comments received
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Ill
-------
Chapter 6; Pii'uten p-evention in the Plating Process
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t .
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112
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Pollution Prevention
in Rinsing
Rinsing follows cleaning, plating, and strip-
ping operations.: Adequate rinsing is a
critical step within the plating process, Rinsing (
prepares .a part for subsequent finishing opera-
tions,-stops the chemical reaction, and prevents
cross contamination of subsequent plating'tanks.
Poor rinsing can result in staining, spotting,
blistering, or peeling of the workpiece. There- '
fore, rinsing must be effective and efficient.
Alternative rinsing practices succeed only if they
are properly designed, operated, and maintained;
In some cases, the only practical-means of
preventing or reducing pollution is by improving,
modifying, or installing recovery/reuse technolo-
gies to' the rinsing process (Pinkerton 1984).
Most of the hazardous waste in a metal finishing
operation comes from the wastewater generated
by rinsing operations. Two general strategies to
' reduce waste from rinsing operations are pre-
venting rinse contamination, and recovering and
recycling materials from the rinsing process.
Facilities should evaluate alternative rrnsing ,
practices prior to investigating recovery tech-
nologies. Nevertheless, facilities might need to
use a combination of the two strategies -for an
effective rinsing system that complies with the
regulations.
Alternative Rinsing
Practices
The goals of alternative rinsing practices are
two-fold: (1) to control the dragout of solution
from process baths into the rinsewater and (2) to
minimize water consumption. These.two goals
have a significant effect on the amount of waste,
mainly, sludge, generated by waste treatment
systems. The amount of wastewatep sludge
generated is directly proportional to the amount
of metal, organic, and other bath constituents in
the rinsewater: Therefore, any technique for
reducing dragout also will reduce sludge genera-
tion (EPA 1992). . ' ."'."'
Dragout Reduction
Dragout, the bath solution that is carried out of
the process bath and into succeeding tanks, is the
primary source of contamination in rinsewater.
Reducing dragout can be the single most effec-
tive way to reduce waste and conserve water in
rinsing operations. Figure 8 illustrates typical
generation of dragout. ;'
Reducing dragout extends the life of the process
baths and reduces sludge generation., The rate of
dragout varies considerably among different
parts and processes. For instance, barrel plating
commonly carries 10 times more solution into
the rinsing process than a typical rack plating, ,
' opcration"(Ford 1994)., Several factors contrib-
ute to dragout including workpiece size and
shape, bath viscosity and chemical concentration.
surface tension, and temperature of the process
solution.
Most dragout reduction methods are inexpensive
to implement and, in most-cases, have short - ,
payback periods. Savings are mainly in the area
of reduced use of plating and processing chemi-
cals. Additional savings, often many times the
cost of the pollution prevention project, include
decreased operating costs of pollution control
systems. Many of the methods to reduce dragout
- require only the cost to properly train-employees
with no capital expenditures. For example,
removing workpiece racks at a slower rate or
allowing the rack to drain over the process tank
for a longer time does not require capital outlays,
but the method does require a conscientious,
properly trained operator. Such procedures
should not significantly affect production and
should result in reducing process chemical
113
-------
C^JCJs* 7, ?o, -t:;e*> P'e'.encton in Rinsing
Water Out £
Figure 8. Illustration of Dragout (IAMS 1995)
purchases, water and sewer use fees, treatment
chemical purchases, and sludge handling costs
(Cushnie 1994).
Measuring the Dragout Rate
Measuring dragout allows facilities to determine
the extent of the problem and to monitor the
. iTcctivcncss of reduction techniques. Facilities
can use several methods to effectively monitor
dragout rates. Some facilities use a tcnsiometcr
to measure surface tension. A tcnsiometer
measures the force necessary to lift a metal wire
ring off the surface of a liquid. The cost for this
tool is approximately $2,000. A second method
for determining surface tension ts a
stalagmometer. While stalagmometers are much
less expensive than tensiometers, they are more
difficult to use. For instance, plating solution
tends to dissolve the ink marks on the meter that
are used to calculate surface tension.
Facilities also can use a conductivity meter to
determine dragout rates. Using conductivity
measurements to generate information on rinsing
can greatly reduce analytical fees and eliminate
the lag time between sampling and results since
samples do not need to be" sent to a lab. Most
plating facilities have combination pH/conduc-
tivity meters that can be used for this purpose or
they can purchase a portable unit for S200 to
S300 (Cushnie 1994).
Methods to Reduce Dragout
Platers can reduce dragout using a variety of
techniques that involve a combination of em-
ployee retraining and relatively simple technol-
ogy. These methods include:
Decreasing workpiece withdrawal while
increasing drain rates
Changing the bath concentration and
temperature
Improving racking and rack design
Using dfainboards and dragout tanks
Rinsing over the plating tank
Using air knives
Improving barrel plating
These techniques are described in detail in the
following sections.
Workpiece Withdrawal and Drain Rates
The speed at which workpieces are removed
from the process bath can have a substantial
impact on dragout volume. The more slowly a
114
-------
Chjpcer 7: Pollution Prevention ih Rinsing
wprkpiece.is removed from the bath, the thinner,
the film of process solution is on the.workpiece,
and the less solution is dragged into rinse tanks.
The effect is so significant that many experts
/believe that most of the time allowed for drain-
ing should instead be used for withdrawing the
workpiece: A recent case study demonstrated
that a drain time of 10 seconds reduced dragout
by 40 percent compared'to the industry average
of 3 seconds (IAMS' 1995). :
Facilities can control drain times by posting them
' on tanks as a reminder to employees on manual
lines or by building-delays into automated .
process lines. Smooth, gradual removal of parts
from the solution is the-preferred method. A bar
or rail above the process tank can ensure ad-
equate drain time prior to rinsing. If platers use
.drip bars, employees can work on more-than one
rack during an operation. In rotation plating, an
Workpiece Withdrawal Case Study
.The Institute of Advanced Manufacturing -
Sciences, increased the drain time to 10
seconds for workpiece withdrawal and found
that dragout was reduced by moe than 40
percent. The more slowly the workpiece was
removed from the solution, the' less solution
was removed with the workpiece. This
practice also reduced the amount of hazard-
ous waste generated. No information was
availpble in the case study on savings.,Costs.
include training personnel or slowing down
automatic process lines. (APPU 1995)
Decreased Workpiece
Withdrawal Rates
Advantages
Less contaminants in the rinsewater .
Posting drainage times on a tank will assist
operators in using the optimal drainage time
Disadvantages . ,
Hard to control drainage time if workpieces
are removed manually
Takes training if done manually
Quality control problems could occur if
allowed to dry
Might cause production delays (depending
on production schedule) . (APPU 1995)
. operator removes a rack from a plating bath and
lets it drain above the process tank while other
racks'are.handled. Increased drain time, though,
can have some negative effects such as drying,
which is especially problematic with hot cleaners ,
because it can cause spotting on the workpiece
(Cushnie 1994).
Bath Concentration and Temperature
, Lowering the viscosity of the bath can reduce
dragout. Facilities can lower the viscosity of a
plating solution Vtwo ways: (1) reducing the
chemical concentration of the process bath or (2)
increasing the temperature of the process bath.
For further information on this option, refer to
the general pollution prevention section on,
plating baths in Chapter 6.
Racking
The placement of workpieces on racks can have
a significant impact on the chemicals carried into
the rinse tanks. Positioning pieces so that
solution drains freely without being trapped in
grooves or cavities'reduces dragout. .Positioning
workpieces so that they face downward also can
improve drainage efficiency. However, proper
placement must take into account both proper
plating and rinsing. For example, a saucer-
shaped object placed upside down would drain
well, but the plating solution would not entirely
coat the inside of the cup because of entrapped
gas bubbles. Therefore, an angled position-is the
most efficient. This placement allows for proper
plating and efficient draining. Proper racking
also can reduce surface tension and improve
draining. The following are some suggestions
for properly orienting and positioning
workpieces (EPA 1992): '
« Parts should be tilted so that drainage is
consolidated. The part should be rwisted
or turned so that fluid will flow together
and off the part by the quickest route.
* Where possible, avoid positioning parts
directly over one another.
^
-» Tip parts to avoid table-like surfaces and,
pockets where solution will be trapped.
I f a workpiece is designed so that it does not
drain easily, facilities can work with their
designers or,4n the case of job shops, their
115
-------
Chios*' Pollution Prevention in Rinsing
Improved Racking
Advantages
Improves drainage
Reduces rinsewater contamination
Little or no cost
Disadvantages
Might require some time to seek innovative
measures to improve workpiece drainage
Miqht require redesign of customer
I (APPU 19951
workpiece (Atru iyyoj
customers to see if modifications are possible.
For example/a plater asked his customer whether
he could drill four holes in the workpiece to
improve drainage. The customer agreed and the
pollution prevention technique was successfully
implemented (JAMS 1995).
Design and Maintenance of Racks
Improving the design of racks, baskets, or barrels
can reduce the amount of dragbut. If equipment
is not properly maintained, it can increase
contamination both in terms of increased dragout
and contamination from residue on racks. These
contaminants include rust and salt deposits that
form on racks, barrels, and baskets.' Keeping
racks clean can reduce contamination of process
baths and rinsewaters (Ford 1994).
Drainboards
Metal finishing operators can use drainboards to
collect dragout and drippage when transferring
racks from one tank to the next. Boards should
be mounted so that they cover the entire space
between the two tanks, allowing the solution to
drain back into the previous bath. This method
prevents chemical solutions from dripping onto
the floor. Figure 9 presents the typical set up of
a drainboard. Many operators prefer removable
drainboards because they permit access to
plumbing and pumps. Drainboards should be
made of a compatible material such as
polyvinylchloride (PVC). Use of drainboards is
a cost-effective technique for reducing chemical
consumption and rinsewater contamination
(IAMS 1994).
Drainboards
Advantages
Reduces chemical consumption
Reduces amount of rinsewater needed
Disadvantages.
Might limit access to pipes and plumbing
(APPU 1995)
Drainboard Case Study
An EPA case study found that the use of
drainboards to reduce dragout, combined
with deionized water for bath makeup,
reduced waste generation by 50 percent at
one company. Prior to implementation, 300 to
400 gallons of sludge were pumped out
periodically and disposed of as waste. Capital
costs were $315, the payback period was 1.3
months, and disposal and new material
savings were S2.892. (APPU 1995)
Figure 9. Illustration of Drainboards (IAMS 1995)
Plating tank
Drip Tank
Cone. Sol.
Pumped Back to Tank
116
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Chapter 7: Pollution Prevention .n SL.nsing
':i Static Rinse Tank Case Study
!' PRC Environmental stated that since static.Hnse
', tanks are not used as flow-through tanks, they
! could be set up without plumbing. They
' ''returned, dragouisolution to'the process bath,
reducing waste generation. Capital costs were
$400 to SI ,500 depending upon tank capac-
ity No other'cost information w.as available.
. (APPU 1995)
Dragout Tanks (Dead or Static
Rinse Tanks)
Dragout tanks are essentially rinse tanks that -
operate without a continuous flow of feed water.
The workpiece is placed in the dragout tank
before the standard rinsing operation. Dragout
tanks are used primarily with process baths that
operate at an elevated temperature.
Chemical concentrations in the dragout tank
increase as the operator passes the work through
the tank. Because dragout tanks do not have feed
water flow to agitate the rinsewater, air agitation
often is used to enhance rinsing. Eventually, the
chemical concentration of the dragout tank
solution will increase so that it can replenish the
process bath. Adding the dragout solution back
to {he process bath compensates for evaporative
losses that occur, because of high evaporation
rates (EPA 1992). ',-" .
added ba'ck'to the process bath,manually. How-'
ever, automation 'is more efficient as it main-
tains' the best concentration in the dragout tank
(EPA 1992). ' -; .
Rinsing Over the Plating Tank
If the process tank has a high.evaporation rate,
svorkpieces can be rinsed directly over the
process solution, returning water and chemicals
directly to the process tank.' This form of rinsing
requires a high evaporation rate^ so that the work
can be done without splashing solution onto the
equipment. Rinsing often is practiced over
electroless plating tanks because,they have no .
buss bars or rectifiers that can be splashed.
However, operators can rinse over other plating
tanks if they are careful (EPA 1992). ,
Air Knives
Metal platers use air knives to blow air across the
surface of workpieces as they are withdrawn
from process or rinse solutions, physically
pushing.liquid off of workpieces. This technique
returns solution directly to the process bath,
reclaiming dragout and reducing the amount of .
rinscw-ater required to clean the workpiece,
which enhances the drying process. In some
applications, however, this rapid-dry method can
cause poor bonding, spotting, and staining
(APPU 1995). . -
Static Rinse Tanks
Advantages.
Replenishes bath with dragout solution
Reduces chemical replacement costs
-V Reduces rinsewater use by as much as 50
percent
Disadvantages ' i '
Returned solution can contaminate some
process baths, requiring the baths:to be
dumped (e.g., electroless copper baths). -
Pretreatmeht step required before dragout is
returned to process tank (APPU 1995)
Air Knives
Advantages
* Enhances drying process ,
Reduces amount of rinsewater used
Returns, solution to process tank
Disadvantages
Can cause poor bonding, staining, and.'
_ i » f+e+t i i m
spotting '
(APPU 1995)
The cost of a dragout tank depends on the. size of
the tank. Since these tanks are not used as flow-
through tanks, they can be installed without
plumbing. Typically, dragout solutions'are
Specific Techniques for Reducing Dragout
in Barrel Plating Operations
In barrel plating, floor spills are less likely to
occur since automation typically moves the
barrel from one tank to tlte next. However,
barrets potentially create more dragout sjnce they
hold more solution. In addition, although the
barrels are perforated, complete drainage can be
117
-------
CMOS*' '"" ?-
t Prevention in Rinsing
Air Knives Case Study
" US EPA, Mexico's SEDESOL, and the Institute of
Advanced Manufacturing Science found that air
\ * knives reduced dragout by 75 percent at a
|] particular facility because they pushed water off
I of the workp'iece back into the tank. This
technique reclaimed dragout and reduced
water use. The study found that facilities must
properly filter the compressed air to remove
contaminants. Capital costs were $500.
(APPU 1995)
difficult. As with rack plating, extending drip
times reduces dragout.
In order to reduce dragout, the correct barrel
must be used for the parts being plated. For
example, if the average part is 2 inches in
diameter and the barrel contains holes that are
, too small (less than '/; inch) drainage can be too
slow, resulting in significant dragout. In general,
using a barrel with the largest holes possible
minimizes dragout. Operators should make sure
that barrel holes are not plugged. If they become
plugged, they should be cleaned or redriHed and
deburred to ensure maximum drainage. The
most important technique for reducing dragout in
barrel plating is proper hole size and rotation of
the barrel in the upright position (Gallerani
1996).
Angled withdrawal from the plating solution also
can result in reduced dragout. However, no
producer/vendor of angled barrel technology has
been found for large, horizontal double-hung
barrels. Nevertheless, one'of the following
modifications of existing barrels might prove
useful in minimizing dragout:
Lengthen or shorten one arm so as to-
create an off-horizontal position that
allows for quicker runoff
Attach a drip bar at the bottom of the
barrel edges to facilitate droplet
collection and runoff
Design a slope at the top of barrel
carriers
Prior to implementing an angled or sloped barrel
technique, platers should check the design pf all
tanks to ensure proper clearance for the modified
system (JAMS 1995).
Alternative Rinsing
Methods
This section presents alternatives to traditional
rinsing techniques. Two strategies for reducing
water use are improving the efficiency of the
rinsing operation and controlling the flow of
water to the rinsing operations. Contact time and
agitation influence the effectiveness of the
rinsing operations.
Improving Rinsing Efficiency
Platers can-use several methods to improve
rinsing efficiency. These methods include
finding the optimal amount of contact time and
the correct level of agitation.
Contact Time
Contact time refers to the length of time
workpicces are in the tank. For a given
workpicce and tank size, the efficacy of rinsing
varies with contact time. Production rate.,
however, varies inversely with contact time.
Through experimentation, the operator should
find the contact time that satisfies production
requirements while providing the highest rinsing
efficiency (I AMS 1995).
Increased Contact Time
Advantages
Improves rinsing efficiency
Reduces contamination
If combined with agitation, can shorten
contact time
Disadvantages
Rinse efficiency varies with contact time
Experimentation is needed to find the
optimal rinse efficiency
» Can reduce production rate (this factor
varies and the production process should
be analyzed to see the effect of this
technique^on production) (APPU 1995)
118
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Chapter 7: Pollution Prevention in Rinsing
' Contact Time Case Study ; ,j-
PRC Environmental documented that by ; j
'I' increasing rinsewater contact time and agitat-
ing, workpieces manually, the rate of rinsewater
flow can be reduced-significantly without
affecting rinse efficiency. The only capital hosts'
incurred for this project were for training <
personnel, however, no financial'costs'or ,
savings Were provided in the case study., (APPU
1995) ' . ';--..
can reduce costs because they eliminate the
need for air cleaners'and filters to remove oils in
compressed air systems. An in-tan'k pump for
forced water agitation can be purchased for
$200 to $ 1,000 depending on the flow rate
Agitation
Rinses that are agitated reduce the required
amount of contact time and improve the
efficiency of the, rinsing process. Rinsewater can
be agitated by pumping either air or water into
the rinse tank. Air bubbles create the best
turbulence for removing chemical process
solution from the workpiece surface. However,
.misting as the air bubbles break the surface can
cause air emissions problems (Cushnie 1994).
A finishing shop can use many methods to
agitate rinse tanks. In manual plating, the
operator lifts and lowers the workpiece iij the
rinse tank, creating turbulence. In other tanks,
the most effective form of agitation involves a
propeller-type agitator, but this method requires
extra room to prevent parts from touching the
agitator blades. Good agitation also can be
obtained with, the use of a low-pressure blower.
The following is a list of other effective agitation
methods:
Filtered air pumped into the bottom of
the tank through a pipe distributor (air
sparger) . ,
^4 Ultrasonic agitation for complex parts
4 Mechanical agitation
- Recircutation of a sidestream from the
rinse tank ^
4 An in-tank pump (a process known as
forced water agitation) (EPA 1992) . -
Air spargers, water pumps, or agitators can be
installed in existing rinse tanks. Installation of
an air sparger with a blower costs approximately
$200 to $325 for a 50 gallon tank. Air blowers
Increased Agitation
Advantages
4 Improves rinsing efficiency by removing
process chemicals using turbulence (they
remain in the tank instead of being dragged
Out)
4 Reduces water fees, sewer fees, treatment
chemical costs,- and sludge generation
Disadvantages .
> Manual system requires operators coopera-
tion
4 Compressed air needs to be cbritaminant-
free otherwise contaminants could,enter the
water supply and affect'work quality (oil-
free, low-pressure blowers reduce the
.likelihood of contamination)
4 Might need an additional tank for water
reuse . (APPU 1995)
desired. Selection of the optimum method of
agitation entails balancing capital and operating
costs against revenues from increased production
rates'and decreased water use (I.AMS 1995).
Controlling Water Flow to Rinses
The following sections present rinsing methods
that use less water and increase the efficiency of
the rinsing operations.
Counter-current Rinsing
Countercurrent rinsing uses sequential rinse
tanks in which the water flows in the opposite
direction of the work flow (dirtiest to cleanest).
Fresh water is added only to the final rinse
station and is conveyed, normally by gravity
overflow, to the previous rinse tank. Wastewater
exits the system from the first rinse tank. Figure
10 illustrates a three-stage countercurrent rinse
system. In some cases, the water contained in
the first rinse can be used as makeup water for
the process bath (see discussion of water quality
in Chapter 4). Many shops have used this
technique successfully to minimize water con-
sumption. The amount of water conserved will
119
-------
ChJBt«r 7 Po;?uCiOr? P-r-emicm in Rinsing
depend en the number of tanks installed for
counteredrrent rinsing. In some cases, counter-
current rinsing can achieve 95 percent reductions
CQuntercurrent Rinsing Case Study
§PA documented a company^that installed^ _
11 counteYcurreht111 rinse system with conductivity
controls. The system reduced rinsewater from
43,000 to 8,000 gallons per day. Operation
and maintenance .costs were SI 0 per 1 ,000
gallons, and disposal and feedstock savings
were SI 70,000. (APPU 1995)
in rinse flow if the facility uses three rinse tanks;
90 percent is possible with two tanks (Hunt
1988).
Limitations governing the use of countercurrent
rinsing include:
Shop floor space and/or line space .
Increased cycle time
Genera! resistance to change
Limited shop floor space can present a signifi-
cant problem for the electroplater. However,
careful review of the shop often can reveal
opportunities for added rinse stations. The
following list presents some of the ways a shop
can make room for countercurrent rinsing:
Work Piece
Movement
Process
Tank
Rinse
Reduce the number, of plating stations by
one or two in order to increase space for
rinse tanks.
Eliminate obsolete processes (e.g., bright
dipping before chromating or nickel
.activation before chrome plating).
Evaluate rinse station sizing. Single
station rinses often are sized arbitrarily to.
match plating tanks. In many cases,
platers can install baffles in oversized
rinse tanks to create multiple rinse
stations.
Review shop floor layout and seek oppor-
tunities to combine processes.
Extend the line and add rinse stations
(Gallerani 1990).
Static Rinsing (Recovery Rinsing)
If direct countercurrent rinsewater overflow to
the process tank is not possible, the first rinse
tank after a process bath can be a static rinse that
builds up a concentration of dragin. Static rinse
tanks used with low-temperature processes can
be Used as pre-dip or post-dip rinses to recover
dragout (as much as 80 percent). Periodically.
the accumulation in this bath should be concen-
trated enough for reuse/recycling into the process
bath (EPA 1992).
Work
Piece
Rinse
Effluent to y , i _^_
Recycle. Resource
Recovery or Treatment
Figure 10. Three-Stage Countercurrent Rinsing (IAMS 1995)
120
Rinse
Rinsewater i
Influent »
-------
Chapter 7: Pollution Prevention In
Multistage Static Rinsing
'Multistage static rinsing uses multiple dead tanks
rather than a system where the-water flows from
one rinse tank'to the other. This process often is
used in cadmium plating to keep the metal from
: entering the waste treatment system. Solution
from the first rinse tank can be used to replenish
the process bath. However,'the solution might
need treatment prior to reuse such as filtration to
remove contaminants. -
Multistage Static Rinsing
Advantages
Increases contact time between the
workpiece and rinsewater; improves rinse
efficiency , , ;
Reduces water use' '''-
Disadvantages
Needs more process steps - '
Needs additional tanks . .
Needs more work space
Should use deionized water to-reuse
rinsewater'
Warm Rinsing
Warm rinsing is effective particularly in the case
of alkaline solutions such asxlcaners and cya-.
nidc plating baths. Alkaline solutions tend to
freeze onto parts when immersed in cold water,
making effective cleaning difficult. Warm rinses
reduce freezing rate and increase rinsing effec-
tiveness (Ford 1994).
Reactive Rinsing
Reactive rinsing uses less water and saves
chemicals. Most cleaning lines use an alkaline
cleaner followed by an acidic pickle. Taking
advantage of the chemical nature of the pickle
liquors and alkaline cleaner, reactive rinsing ,
feeds the water from the acid pickle to the
alkaline rinse. This step neutralizes the cleaner,
and also prevents alkaline material from being
dragged into the acid, prolonging the life of the
pickle solution. Reactive rinsing cuts water use
in half, and, in some cases, enables the plater to
plumb more than two rinses in a' series. How-
ever, acidic water should never be fed into a
rinse that contains cyanide solution (Hunt, 1988).
In the example in Figure 11, nickel rinsewater is
.recycled back to the acid dip rinse tank, allowing
nickel plating.solution dragged outofthe process '
bath to be dragged back into the bath. Such a
modification will not harm the rinse step and will
allow the fresh water feed to the acid rinse to be
turned off. The acid rinsewater then can be ', ,
recycled to the alkaline cleaner rinse tank.
Advantages include, allowing the feed water to be
shut off, improving the rinsing .efficiency by
neutralizing the dragged-in alkaline solution, and
prolonging the life of the acid rinse bath as the
rinsewater dragin already will, be partially
neutralized; This concept can be taken onp step
r further and the rinsewater can be recycled among
process lines (Hunt 1988). v ; ,
The reuse of rinsewater cannot be indiscriminate.
Facilities must avoid contaminating the process
baths and reducing the plating quality (e,g.,
pitting). However, following careful evaluation.
reactive rinsing can produce significant water
and chemical savings (Gallerani 1990):
Spray or Fog Rinsing ,
Installation of fixed or movable rinse spray
nozzles over the process tank can replace sepa-
rate rinse tanks: Overspray is returned to the
. WOHK FLOW .
WATER
ALKALINE
CLEANER
n
RINSE
7
AGIO
\
\ RINSE
1 . : : 1 \
1
NICKEL
T
. r
: , T
RINSE
Figure 11. Example of Reactive Rinsing (Hunt 1988)
121
-------
Poi'uticn Pre'vencion in Rinsing
process tank, resulting in reduced dragout. This
spray or fog rinsing can be used for either rack or
barrel plating (I AMS 1995).
Spray rinsing uses between 10 to 25 percent less
water than dip rinsing. However, this method is
not always applicable to metal finishing because
the spray rinse might not reach all of the parts of
the workpiece. The effectiveness of spray
rinsing depends upon part geometry and com-
plexity. Spray rinsing compares favorably with
single-dip rinses, but is not as effective as
countercurrent rinsing. To address this problem,
spray rinsing can be combined with immersion
rinsing. In this technique, the workpiece is spray
rinsed over the process tank as soon as the part is
removed from the process solution. The part
then is submerged in an immersion tank. As a
result, the spray rinse removes much of the
dragout. returning it to the process bath before
the workpicce.is placed in the dip rinse tank.
This allows facilities to use lower water flow
rates and reduce dragout (EPA 1992).
Platers also can use spray or fog rinse systems
above heated baths to recover dragout solutions.
Spray rinsing washes process solutions through
impa'ct and diffusion forces and can reduce water
use by 75 percent. If an operator can adjust the
spray rinse flow rate to equal the evaporation
loss rate, the spray rinse solution can be used to
replenish the process bath. Purified water should
be used for the spray systems to reduce the
possibility of contamination entering the bath.
Fog rinsing uses water and air pressure to reduce
concentration of dragout films. This method is
most useful in finishing simple pieces (Cushnie
1994).
jj Spray/Fog Rinsing Case Study
EPA documented a 50 percent reduction in
hazardous waste generation with spray rinsing,
and a savings in disposal and feedstock costs of
$5,280. Capital costs were $11,685 with no
operation or maintenance costs and a payback
period of 26 months. Prior to implementation,
650,000 gallons of waste were generated daily
with 5 percent from, cyanide-based plating
operations. (APPU 1995)
Spray/Fog Rinsing
Advantages
Reduces dragout by as much as 75 percent
Reduces waste management costs (i.e.,
lower sewer bills and less sludge generation)
Greater quality control (i.e., less chemical
use and cleaner rinses)
Disadvantages
Might not be effective in rinsing certain
workpieces and might not work in all plating
operations (APPU 1995)
Rinsewater Flow Controls
An important concept in rinsewater conservation
is to use only as much water as you need. Many
electroplaters use far more water than they need.
Reducing water flow also can make certain
recovery technologies (such as reverse osmosis)
economically feasible because of the linear
relationship between cost and flow rate. In tact.
most of these technologies will only be cost
effective if water flow rates arc reduced to the
lowest possible levels.
Typically, a rinse tank uses a wide-open, unre-
stricted water feed. Installing flow restrictors or
conductivity cells can result in a significant
reduction in water use. The operator should first
determine the current flow, rate and then the
optimum flow rate at which .the facility should be
functioning.
Determining the Appropriate
Flow Rates
Platers should size rinsewater flow requirements
according to contaminant loading (process
dragout) and required final rinsewater purity or
concentration. In a multiple rinse setup, the flow
requirements should be exponentially lower than
those in static tanks. Operators can determine
the required rinsewater flow for a single station
rinse using the following equation:
D x Cp = F x Cr
D =?' Dragin rinse or process dragout
Cp = Concentration of dragin
F = Rinsewater flow
Cr = Concentration of the rinse
(Gallerani.1990)
122
-------
Chapter 7: Pollution Prevention -
Once platers have determined the appropriate
flow rate, they can use several methods to ;,
control now rates in their facilities including
flow restrictors, conductivity cells, and pH
meters. '
Methods to Restrict Water Flow
A number of simple methods are available to
restrict water flow and conserve water including
flow restrictors and conductivity controllers.
Flow Restrictors
'Flow restrictors limit the volume of rinsewater
flowing through a rinse system by limiting the
volume of water that can enter'the rinse system.
this method will maintain a constant flow of
fresh water to the rinse process. > Since most
small- and medium-sized'metal finishers operate
batch process operations, pressure-activated flow
Flow Restrictors
Advantages
Reduces water use
,«. Maintains flow rates at predetermined levels
Disadvantages ,
Unable to adjust flow restrictors
Increases operator responsibility
Need to coordinate among operators to
survey the rinse tanks and shut off the flow
to tanks not in use .
Might not be suitable for shops where flow,
rates are variable. '. (APPU;1995)
'.control devices as foot-pedal-activated valves or
timers can be helpful to ensure that water is not ,
left on after completion of the rinse operation
(EPA 1992). ,:-..-
Conductivity Cells/pH Meters
Platers can use conductivity controllers in place
of flow restrictors on a rinse system where dragin
is highly variable or where monitoring the bath
for extreme conditions (over or under concentra-
tion) is desirable. Figure 12 shows atypical >
application of conductivity cells. These devices
control water flow through a rinse system by
means of a conductivity sensor that measures the
level of ions in the rinsewater,. When the ion
level reaches a preset minimum, the sensor
activates a valve that shuts off the flo%v of fresh
water into therinse system. When the concentra-
tion builds to a preset maximum level, the sensor
opens a valve to resume the flow of fresh water.
These meters can alert production line staff to
imbalances in rinsewater concentration so that
they can be replenished on an as-needed rather
than a continuous basis. These systems' are
relatively expensive and require a good deal of
maintenance (Gallcrani 1990). If these systems
are not maintained consistently, water use
actually can increase. If the solenoid valve
becomes clogged, it will remain open, allowing
water to flow freely. A conductivity meter
equipped with the necessary solenoid valve can
cost approximately $700 to $4,000 per system.
Flow Restricfor Cqse Study
Alpha Metal Finishing in Dexter;Michigan; is
a large job shop that specializes in chromate
conversion. The president of the company,
Robert Wood, designed a company plan to
minimize water use. Trie company's greatest
waste reduction success is the decrease in the
volume of wastewater discharged to a POTW.
By reconfiguring rinse tanks and decreasing
water flow rates,'Alpha Metal reduced Its
wastewater discharge by 50 percent. Follow-
ing an intern's recommendation, the facility
installed flow restrictors,on the,rinse tanks.
The installation resulted in direct savings of
more than $18,'OQO. Wastewater discharge
decreased from a daily average of 40^,000 to
11,000 gallons. (OWRS1992
Conductivity Cells/pH Meters
Advantages ,
Reduces the amount of overflow water
Extends bath life ,
Disadvantages
Expensive maintenance costs for sensing
probes because of the need'for regular
cleaning and maintenance
Rinsewater Recycling and
Recovery Techniques
Water conservation and metal recovery tech-
niques have become an integral component of
pollution prevention programs for platers. Many
techniques to recover water, metals, or acids that
have contaminated rinsewater are available. In
123
-------
Chaos*' ." Pjiitiuon P'e'.ention in Rinsing
Work
Solenoid
Valve
Controller
-J^3!'
Conductivity Cell
Figure 12. Application of Conductivity Cells (IAMS 1995)
some cases, the technologies merely recover
materials so that they can be sent off site for
easier disposal. In other cases, the technology
can return the material back to the process line
for reuse.
Rinsewater Recycling
Rinsewater can be recycled in cither a closed- or
open-loop system. In a closed-loop system, the
treated effluent is returned to the rinse system.
Recycling rinsewater can reduce water use and
the volume of water discharged to the wastcwa-
tcr treatment system significantly. Closed-loop
systems discharge a small amount of waste. An
open-loop system allows the treated effluent to
be reused in the rinse system, but the final rinse
is fed by fresh water to ensure high-quality
rinsing. Therefore, some treated effluent will
continue to be discharged to the sanitary sewer
(EPA 1995). These two systems are shown in
Figure 13.
To improve the economic feasibility of closed-
or open-loop systems, platers should first imple-
ment rinsewater efficiency techniques. In the
past, material recovery from metal finishing was
not considered economical. However, effluent
pretreatment regulations and treatment and
disposal costs are now a significant financial
factor. As a result, metal finishers now might
find reusing rinsewater as well as recovering
metals and metal salts from spent process baths
and rinsewater are cost effective.
After rinse solutions have become too contami-
nated for their original purpose, they can be used
in other rinse processes. For example, effluent
from a rinse system following an acid cleaning
bath sometimes can be reused as influent to a
rinse system following an alkaline cleaning bath
(reactive rinsing). If both rinse systems require
'the same flow rate, 50 percent less rinscuatcr
could be used to operate the system,
Chemical Recovery
Facilities can manage the captured dragout
solution from rinsewater recovery in three uays:
(1) recycling solution back into the process, (2)
on-sitc recovery, and (3) shipment off site for
disposal or recovery-. The choice will depend^
upon the type of process bath, composition of the.
dragout, and the cost of the technique.
Platers must understand the chemical properties
of a wastestream to assess the potential for
reusing the waste as a raw material. Although
the properties of process bath or rinsewater
solutions might make them unacceptable for
their original use, the waste material might still
be valuable for other applications. A common
reuse option in multiple-use rinses is using
rinsewater from one process as rinsewater in
another. For example, rinsewater from a clean-
ing rinse can be reused in a plating rinse line.
The primary cost associated with rinsewater
reuse is rcplumbing. Depending on the design of
the rinse system, .firms also might need to
purchase storage tanks and pumps.
124
-------
Worx Piece
*/o demerit
Open-Loop System ...
Evaporation,
Process
Tank
1 Drag-out Solution
' Recycle
Rinse
Chapter 7: Pollution Prevention i
['Makeup i ,, 1
* Water T ,
' ' i ; Rinsewater
Rinsewater , |n)|uent
(to treatment)
Work Piece
Movement
Closed-Loop System
Evaporation
Work
Piece
Process j : .
Tank
I
Rinse
Rinse
i
' Drag-out Solution
: Recycle
A Makeup
I Water
Figure 13. Configuration of Rinsewater Recycl
1995)
Typically, operators dump spent acid or alkaline
solutions when contaminants exceed an accept-
able level. However, these solutions might
remain sufficiently acidic or alkaline to act as pH
adjusters. For example, alkaline solutions can be
used to. adjust .the pH in a precipitation tank
while acid solutions can be used in chromium
reduction treatment. The operator must ensure
that the spent solutions are compatible. For
example, because spent cleaners often contain
high concentrations of metals, they should not.be
used for final pH adjustments. Facilities should
check with chemical suppliers to determine
whether they have reclamation services1 for _';
plating baths. Be aware that some states classify
reclamation as treatment under the RCRA
program, requiring compliance with additional
regulatory requirements (in some cases, an
abbreviated treatment license). . .
ing in Open- and Closed-Loop Systems (1AMS
Metal Recovery
Every year, the plating industry pours millions of
dollars down the drain in valuable metals.
Closed-loop systems, reduce rinsewater volumes
and facilitate the recovery of metal salts for reuse
in plating baths, using separation processes such
as evaporation, ion exchange, reverse osmosis,
electrolysis, and electrodialysis. An industry
consultant recently estimated that it would be
economically feasible to recover 80 to 90 percent
of copper, 30 to 40 percent of zinc, 90 to 95
percent of nickel, and 70 to 75 percent of chro-
mium presently disposed of as sludge (Gallerani
1990). Recovered metals can' be reused in
several ways: ,
* Returned to bath as makeup
Sold or returned to suppliers
125
-------
ChJBW 7; Pc!'-t.on Prevention in Rinsing
Sold to a reclaimer
* Used on site as plating metal anode
materials
The savings achieved through metal recovery are
site-specific. Factors that determine whether
metal recovery is economically justified include:
The volume of waste that contains metals
The concentration of the metals
The potential to reuse some of the metal
salts
Treatment and disposal costs
Table 19 highlights different technologies that
can be used for chemical recovery, metal recov-
ery, and chemical solution maintenance.
Table 20 provides aii overview of technologies
for recovering metals, plating solutions, and
water.
Recovery Technologies
A number of rinsewater recovery technologies
are available to platers. Many platers already use
these systems. The recovery systems include
various types of electrolytic recovery and
evaporators.
Electrolytic Metal Recovery
Electrolytic metals recovery (EMR) is used to
recover the metallic content of rinsewater. EMR,
one of the most common methods of recovering
metal from finishing operations, is capable of
recovering 90 to 95 percent of the available
metals in gold, silver, tin, copper, zinc, solder
alloy, and cadmium plating operations (Bennati
and McLay 1983). The basic unit of this tech-
nology is an electrolytic cell with two electrodes
(an anode and a cathode) placed in the solution.
Ions in the solution move toward the charged
electrode. The dissolved metal ions are reduced
and deposited on the cathode. The material that
is deposited onto the cathode is removed either
by mechanical or chemical means and then is
sent off site for refining, recycling, or disposal
(Cushnie 1995). Table 20 provides a summary
of the metals and their potential for successfully
applying electrowinning. The table also includes
an indication of the use of EMR for certain
groups of metals.
As shown in Table 21, some metals are not
particularly suited to EMR. The only common
metal salt that cannot use electrowinning is
chromium. This technology can recover nickel.
but it requires close monitoring of the pH.
Platers also can use electrowinning in electroless
Table 19. Overview of Applications for Recycling and Recovery Equipment (Hunt 1988)
Chemical Solution
Maintenance
Chemical
Recovery
Recycling/Recovery
Method
Metal Recovery
Acid Sorpfion
Diffusion Dialysis
Evaporators
Electrolytic Metal Recovery
Electrodialysis
Ion Exchange
Ion Transfer
Microfiltration
Membrane Electrolysis
126
-------
'Chapter .7; Pollution.Prevention in Rinsing
Table 20. Overview of Recovery/Recycling Technologies (Hunt 1.98.8)
Method
Advantages
Disadvantages
Successful
Applications
Electrolytic
Metal
Recovery
'
Recovers only metals
Results in salable,
non-hazardous
'products . s
Energy efficient
Low maintenance
Solution concentration must,be
: monitored
|Fumes can form and can
'require hood scrubbing system
Solution heating encouraged
to maximize efficiency
Cadmium cyanide, copper
cyanide, copper pre-etch,
copper final etch,
acid copper, electroless
copper, gold, electroless \
nickel, watts nickel, silver,
tin, and zinc
Reverse
Osmosis.
Achieves modest
concentration
Small floor space
requirement
Less energy intensive
than evaporation
>! Limited concentration range
"- of. operation t .
Fouled membranes because
} of feeds high in suspended.
solids
Feed filtration essential '
Membrane sensitive to pH
4 Some materials fractionally
rejected '
Might require further
concentration .
Copper, nickel, and zinc.
! lon ' ..
1 Exchange
Low-energy'demands
"Handles'dilute feed
Returns metal as
metal salt solution
Requires tight operation and
maintenance
Equipment complex
Limited-concentration'ability
Might require evaporation to
increase concentration '_
Excess regenerate required
Feed concentration must'be
monitored closely
Chromium, .chromium etch,
copper pre-etch, copper ,
final 'etch, acid copper,.
gold cyanide, nickel/ .
electroless nickel, silver,
tin, and zinc
It
Electro-
dialysis
Achieves higher
concentration than ,
reverse osmosis'or
, ion exchange
Energy efficient
Organics not
concentrated
Inorganic salts
transport at different
rates .
Minimizes return of
unwanted inorganics
Feed,must be fiftered
Membrane sensitive to flow
distribution, pH, and
suspended solids
Equipment uses multi-cell stacks
Incurs leakage
Chemical adjustment of
' recovered material'
Membrane life uncertain
Solution concentration .
must be monitored
Cadmium cyanide, copper
cyanide, gold, iron, nickel,
ilver, tin, zinc cyanide,
and zinc chloride
Evaporators
Established and
proven technology
Simple to operate
Widely applicable
Can exceed bath
concentration
Some units are energy intensive
« Multistage countercurrent
rinsing essential
Returns impurities to bath
Additional treatment might
be needed to control impurities
Might require pH control
127
Cadmium cyanide, - .
chromium, chromium etch,
acid copper, copper cyanide
gold, iron, lead, nickel,
silver, tin, and zinc
-------
~ Po.'Jt'on Pre-.ention in Rinsing
Table 21. Potential of Metal Using Electrolytic Recovery (Cushnie 1994)
Potential of Electrolytic
Recovery
Metals
Widespread
Use
J f f f * M
success
Brass cyanide, cadmium cyanide, copper acid,
copper cyanide, gold cyanide, silver cyanide,
and zinc cyanide
Yes
High Potential for Success
Antimony, cadmium ammonium sulfate, iridium,
lead acid, palladium, ruthenium, rhodium,
selenium, tin acid, and tin alkaline
No
Moderate Potential for
Success
Cobalt, electroless .copper, copper strong acid,
copper ammoniacal etch, gold strip, indium,
lead fluoroborate, nickel watts, and woods, nickel
sulfamate, electroless nickel, silver thiosulfate,
tin7lea3 fluoroborafe, zinc acid
No
Low Potential for Success
Aluminum, barium, beryllium, boron, calcium,
cadmium strip, chromium, iron, rnagnesi-um,
manganese, mercury, molybdenum, silicon,
tantalum, titanium, tungsten, vanadium
No
plating operations. However, this application is
not as straightforward because of the presence of
dictated metals, reducing agents, and stabilizers
(Cushnie 1994). The most common applications
of EMR include acid.copper plating, cyanide
cadmium plating, cyanide zinc plating, and
cyanide copper plating (Freeman 1994).
Electrolytic recovery is most effective when
metal concentrations are high. Platers can take
the residual metals and sell them or recycle them
in the plating process. Because plating becomes
inefficient at low metal-ion concentrations, it
alone is not suitable for producing wastewater
that complies with discharge regulations. EMR
can be an effective reclaim/recycle method with
lower capital costs in conjunction with another
technique such as ion exchange (EPA 1995).
Metal finishers also can use EMR for spent
plating bath solutions, recovered spills, discharge
from static rinse tanks, and regeneration solu-
tions from ion exchangers. Firms generally use
EMR for reducing the amount of inexpensive
regulated metals and cyanide that they discharge
to treatment systems or for recovering expensive"
metalsl both common and precious. In either
case, companies use EMR for gross metal
recovery from concentrated solutions such as
dragout rinses or ion-exchange regenerant
(Cushnie 1994). Figure 14 illustrates the EMR,
process. " , '
Electrolytic Case Study
Pioneer Industries of Stratford, Connecticut, is
a job shop that uses both rack and barrel
plating operations. The company, which
employs 10 people, works with nickel and
gold electroplating and electroless nickel
plating.
In 1989, Pioneer Industries conducted a pilot-
scale test of the lonnet electrolytic recovery
unit to plate out nickel from wastewater. They
processed nickel-bearing wastewater through
the unit until the nickel concentration was less
than 20 parts per million. The pilot test was
successful and Pioneer expected that full-
scale implementation of this project would
save the firm $ 17,000 per year in waste
treatment costs. The payback period on the
$11,900 investment was 8.4 months.
(ConnTAP 1992)
128
-------
.Chapter 7: Pollution Prevention in Rinsing
Electrolyte
Recovery
A: Recycle (ram primary rinse bath
A & B: Treatment of effluent before
ion exchange
C: Total effluent to. ion exchange.
treatment of ion exchange regenerant.
I. Regenerant
J , Tank
| Ion Exchange
Disposal
Waste .
Treatment
I' ' ' '
i Ion Exchange
v Electrolytic j_
Recovery j
_| Regenerant
j Tank
Figure 14, Electrowinning (IAMS 1995)
Several basic design features, which are well '
known to the electroplating industry, are used in
electrolytic recovery:
, Expanded cathode surface area . ,
Close spacing between cathode and
anode '
Recirculation of the rinse solution ,
(Cushnie 1994) . '...'.
Two electrolytic recovery methods are conven-
tional metal cathode (electrowinning or dummy
plating) and high surface-area cathode (HSAC).
Conventional electrowinning involves the .
placement of a cathode and an anode in the rinse
solution. As the current passes between the
cathode and the anode, metallic ions deposit onto
the cathode, generating a solid metallic slab that
can be reclaimed or used as an anode in an
electroplating tank. Electroplaters can make
their electrowinning.units by closely spacing
parallel rows of anodes and cathodes in a, plating
tank and circulating rinse solutions through the
tank(Cushnie 1994).
In HSAC, the operator pumps the metal-contain-
ing solution through a carbon fiber cathode or
conductive foam polymer, which is used;as the
plating surface.; To recover the metals, the
carbon fiber cathode assembly is removed and
placed in an electrorefiner, which reverses the
current and allows the metal to plate onto a
stainless steel starter sheet. These systems
recover a wide variety of metals and regenerate
many types of solutions. Platers use MS AC
recovery mainly with dilute solutions such as
rinscwatcr effluent.
The types of cathodes, used in electrowinning can
be classified into three categories in order of
increasing surface area: (1) flat plate; (2)
expanded metal, wire mesh, or reticulate plate;
Electrowinning
Advantages
4> Recovers metals that can be recycled or
reused in process, sometimes up to 90 to
95 percent
* Uses no chemicals
.o Recovers only metals
o Maintenance is low
« Misapplication is rare because of similarity
. with plating.process
Disadvantages
Energy inefficient at very low metal-ion
concentrations
Segregation of the rinsewater is. needed to
prevenf contamination of the anode with
mixed metals .
Incomplete recovery (will not recover total
metal-content)
Might have high energy consumption.
Might cause spontaneous combustion of
, plated metal '
(Ohio EPA 1994 and Freeman 1995
129
-------
Oupw / P- >"*<"»
in Rinsing
and (3) porous or woven carbon and graphite
plate, Platers use flat plates for applications of
gross metal recovery from concentrated solutions
including expanded metal, wire mesh or reticu-
late plates, and porous or woven types for
recovering metals with lower concentrations.
Facilities also use cathodes to recover metals
from spent process baths prior to wastewater
treatment (Cushnie 1994).
Restrictions on Applications
Strong oxidizing substances, such as nitric acid
or fluoroboric acid, generally are not feasible
options for electrowinning primarily because of
the short life of the anodes in such environments.
Hydrochloric acid or other compounds contain-
ing the chloride ion also might not be suitable
because of the generation of chlorine gas at the
anodes. However, ventilation can control gas
formation (EPA 1995).
Costs
In general, capital cost for electrolytic recovery
equipment is low. A unit equipped with a 100-
ampere rectifier can cost between $8,000 and
S15,000 'depending on the type of anodes and
cathodes. Such a unit can remove up to 500
grams of metal per day from a dragout tank
(EPA 1995).
' and overall operation, many installations require
little scheduled maintenance (EPA 1995).
Evaporators
Evaporation is widely used by platers to recover
a variety of plating bath chemicals. This tech-
nology separates water from dissolved solids
such as heavy metals. Evaporators create
additional room in a process bath so that dragout
can be returned to the process tank. They also
can concentrate rinsewater so that less volume
goes back to the process tank. Evaporators often
return recovered dragout to the process tank in
higher concentrations than that of the original
process solution. This technology is used most
often in decorative chromium, nickel, and copper
cyanide plating, although it is not limited to these
applications (Freeman 1995).
Evaporators arc most economical when the
amount of water is small and the product concen-
tration is high or when natural atmospheric
evaporation can be used. For instance, evapora-
tion is efficient with multistage countercurrent
rinsing because the quantity of rinsewater to be
processed is small. However, this energy-
intensive-technology is expensive when used for
large volumes of water. Another problem with
this technology is that when the water volume is
Electricity, electrode replacement, and mainte-
nance cos'ts are the most significant operating
costs. Electricity costs per unit mass of metal
recovered vary with the concentration of metal in
the electrolyte. A low concentration of metal
ions leads to lower efficiency and higher energy
costs. Anodes require replacement every 1 to 5
years depending on the nature of the electrolytes
being electrowinned. The cost of anodes varies
widely, from S600 to more than $3,000 per
square meter for platinum-coated titanium types,
although some anodes rarely require replace-
ment. For example, fiat plate steel cathodes can
be reused after being scraped free of metal
deposits. Wire mesh and reticulate cathodes
" usually are rated to hold more than 1 kilogram of
metal and generally cost less than $100 per
square meter. The labor costs for operating and
maintaining an electrowinning unit are generally
low. Besides daily checks for electrical settings
Evaporation
Advantages
Reuses recovered chemicals
Uses no chemicals
Reduces liquid waste for treatment and
disposal
Requires no maintenance
Widely applicable
* Low in cost
Can reuse rinsewater
Disadvantages
Energy intensive
Needs multi-stage countercurrent rinse
system to be economicql
High in cost
Plating chemicals can be corrosive to
evaporator
Atmospheric evaporators can degrade
.plating bath chemistry because of high
temperatures. ,,,
(Ohio EPA 1994}
130
-------
Chapter 7: Pollution Prevention
high, sludse generation rates increase as-the flow
volume increases. Effective rinsing and reduced
dragout, however, increases the effectiveness of
evaporation (see Section 1 in Chapter 6 for more
information). In cases where large volumes of
water have low metal concentrations, ion ex-
change, reverse osmosis, or electrodialysis are
more cost effective than evaporation. In some
cases where water volume is high, even precipi-
tation, settling,, and resolubilization can be more
efficient procedures (Veil 1989). '
Evaporators should not be confused with drying
devices, which produce a solid or semi-solid
product. While both dryers and evaporators use
volatilization, evaporators are designed to
concentrate a solution to ho greater than one-half
to three-quarters solubility (Veit 1989).
' -Evaporation Case Study
EPA documented a case in which evaporators
reduced waste generation by 50 percent from
56,000 to 2t5,000 pounds per year, and ail
plating-chemicals were recovered. Prior to
implementation, .rinsewater was treated with
neutralization, flocculation, clarification,
settling/filtration, and compaction. The capital
costs for two evaporators were $12,500.and
the operation/maintenance costs v
-------
" 7- P» 'utcn Prevention ,n Rinsing
Atmospheric Evaporators Case Study
Quality Roiling & Debarring Co., Inc., of
Thomaston, Connecticut, installed two
f4AP/AP atmospheric evaporators supplied by
NAPCO Inc. on its nickel plating line. Quality
Rolling & Debarring employs 70 people and
serves the aircraft, automotive, medical, and
consumer products industries. The production
department focuses on high-volume through-
put using barrel nickel plating, mass finishing,
alkaline finishing, vapor degreasing, and
mechanical plating. The company reduced the
amount of chemicals that they purchased and
the flow of rinsewater to the wastewater
treatment system with the evaporators.
The company purchased the two evaporators
at a total cost of 55,000. The company saved
S510 per week in raw materials costs alone
arid substantially more in off-site disposal
costs. The company experienced a 6-month
payback on this project. (ConnTAP 1990)
and duct modification requirements.- Operating
costs (e.g., electricity and labor) average S0.25 to
$0.35 per gallon. Many companies prefer
atmospheric evaporators to other types of
evaporators because they are relatively inexpen-
sive (EPA 1995).
Vacuum Evaporators
Vacuum evaporators' are closed systems that use
one or more vacuum chambers to reduce the
boiling point of water to volatilize water from
the wastestream. In practice, platers pump
preheated fluid into the vacuum chamber where
it quickly vaporizes. These units do not require
large air volumes and generally produce distilled
water as a byproduct. A number of different
designs are available. They differ in how the
vacuum is achieved (i.e., eductor or vacuum
pump) and how much energy is used (i.e., single
effect or double effect). These systems take
advantage of the depression of the boiling point
of water as air pressure decreases. The higher
01 Water
12SUH-
Ttreo Staga Counter-flowing Rinse.
Moderate Temperature
Dl Water
65L/HT
' Two Stage
Counter-flowing Rlrwe
City Water
420 L/Hr
-^- To Treatment
Heated
to 504C
Figure 15. Two Common Configurations of Atmospheric Evaporators (EPA 1995)
1 ' " ' " . ' 132
-------
Chapter 7-..?otatoh
'; Atmospheric Evaporators Case Study -
In 1989, the llco Unican facility in Rocky
Mount, North Carolina,' plated 800,000 key
blanks per day with nickel. Typically/.rinse
..tanks become contaminated with dragout ^
'from the nickel process solution, resulting in a
hazardbusisludge that required costly treat-
merit. ,
To eliminate this problem, llco Unican began
using an inexpensive and low-maintenance
atmospheric evaporator system. Sufficient
water is evaporated-so that rinsewafer can be
reused in th'e plating bath. Hep was using a"
carbon filtration system'in the plating bath
already to remove contaminants from the
process bath. Since adding the evaporator
equipment, lico Unican has reduced the use
of nickel chloride by 6,400 pounds .and nickel
sulfate by 22,000 pounds. The in-line recy-
cling loop also recovered 80 percent (7,040
pounds) of the boric acid used. The only waste
generated is plating' bath sludge from the
filtration system:
The installation of two evaporator systems cost
approximately $12,200. Maintenance and
energy costs are $24,741 per year. Reduction
in nickel chloride, nickel sulfate, and boric -.
acia1 saved the company $9,280, $19,360,
and $3,328, respectively. The project also
eliminated rinse tank sludge. Disposal and
handling of this waste cost $25,131 annually.
Given these savings, the payback for the
project was 7.3 months with subsequent
annual savings of $36,223 per year.
... (NCD.HSE1995)
the vacuum, the lower the boiling point for
water. By lowering the boiling point, vacuum
evaporation protects some of the ingredients in
the processing solution from degrading.
The four types of vacuum evaporators include:
Single-effect evaporators: A single-effect
unit usualjy uses steam or high-temperature
hot water to heat the process liquid to its
boiling point. The steam is passed through a
coil or jacket and the vapors produced by the
boiling liquid are drawn off and condensed.
The concentrated liquid then is pumped from
:;i the bottom of the vessel. This process
requires 1,200 BTUs per pound of water
evaporated (Freeman 1995).
. Multiple-effect evaporators: A multiple-
effect unit consists of a series of single-effect
'evaporators. Vapor from the first evaporator
is used as.the heat source to boil liquid in the .
second evaporator. Boiling is accomplished
,', ,by operating the second evaporator at a
lower temperature than the first. The process
can continue through evaporators (effects).
Depending on the number of effects, mul-
tiple units can require as little as 200 BTUs
per pound of water evaporated (Freeman
1995)'
t Vapor recompression units: The vapor
recompression evaporator uses steam ini-
tially to boil the liquid. The vapor produced
is compressed to a higher temperature. The
compressed vapor then is directed to the
jacketed side of the evaporator and used as a
lieat source to vaporize more liquid. These
units require as little as 40 BTUs per pound
; of water evaporated (Freeman 1995)
Cold vaporization units: A variation on
standard vacuum evaporation technology is
the cold vaporization process, which uses a
similar evaporation separation principle but
evaporates water at temperatures of 50 to 70
, degrees Fahrenheit. This type of evaporation
uses less energy than'electrically heated
systems because the system gets energy from
the air around the unit. This equipment uses
the heat generated from the vacuum system
to provide heat needed for evaporation
(Cushnie 1994). .
Applications and Restrictions
Metal finishers typically use vacuum evaporators
in those applications in which atmospheric
evaporators are not suitable. Operating expenses
favor vacuum evaporators when feed rates are
' 190 to 265 liters per hour. These systems offer
major advantages when configured to trap
condensate for reuse in rinsing operations (EPA
1995). The primary advantages are:
They operate at comparatively low tem-
peratures. This protects temperature-
133
-------
Oiete1* 7. Pi-ut.cn ?-it«it!cn .n Rinsing
sensitive constituents in the plating
solution,
* They are relatively safe for products that
are sensitive to air oxidation because the
process does not expose the solution to
large volumes of air. For example,
stannous tin might oxidize in an atmo-
spheric evaporator, which could cause
solubility problems in the system.
These systems do not act as air scrubbers.
Because these systems do not use air
movement for evaporation, they do not
scrub volatile components found in the
air, minimizing potential air pollution
problems (Veit 1989).
Capital costs for vacuum evaporators range from
3125,000 to SI75.000. Operating costs are lower
than atmospheric evaporators, averaging $0.05 to
S0.12 per gallon (EPA 1995).
Membrane Technologies
Overview of Membrane Filtration
Metal finishers use membrane filtration to
remove suspended solids, oils, and other impuri-
ties from wastewatcr as well as to recover/
recycle process solution. The membranes
separate suspended or dissolved solids by
applying pressure to one side of the membrane.
Water and low molecular-weight compounds
fiow through the pores while larger molecules
and suspended solids flow across the membrane
and become part of the concentrate. In mem-
brane Filtration systems, wastewater flows
parallel to the membrane surface. This cross
flow allows high filtration rates to be maintained
continuously (RI DEM 1994). Membrane flow
is illustrated' in Figure 16. Platers moving
toward zero discharge or total recycling should
consider these systems as a means to achieve that
goal.
Several different membrane filtration technolo-
gies are available including microfiltration,
ultrafiltration, and nanofiltration. These tech-
nologies differ in the size of the membrane's
pores and the amount of pressure that is applied
to the wastestream. Table 22 presents the
differences in the membrane processes.
Many industries use membrane technology for
filtration. Membrane materials can be organic
(e.g., polypropylene, polyethylene, polyester,
polyacrylonitrile, and polysulfone) or inorganic
(e.g., carbon fiber or ceramics). The choice of
membrane depends upon pH,.temperature, and
specific application (leronimo 1995).
In recent years, membranes have become the
preferred method of liquid/solid separation
because of the consistent permeate (filtrate)
quality achieved and lower pretreatmerit chemis-
try requirements. The membrane technologies
used most commonly by metal finishing shops
are microfiltration and ultrafiltration. However,
platers use.other membranes in specific applica-,
tions (leronimo 1995).
Where To Use Different Types Of
Membrane Filtration
hi general, microfiltration applications work best
for metal finishing shops that have large amounts
of oils in the wastestream. Ultrafiltration appli-
Flow Across a Membrane
Figure 16. Illustration of Membrane Flow (RI DEM 1994)
134
-------
Chapter 7: PolluiioivPfevenuon .n
Table 22. Overview of Membrane Processes (IA.MS 1995)
' Process
Microfiltration
Ultrafiltration
Nanofiltration
Reverse Osmosis
Pressure (psi)
10- 125 !
100-200
200-800
Particle Size Ranges
0.10 micron or greater
.002 to 0.005 micron or
molecular weight 1 ,000
molecular weight 300 to 1,000
molecular weight 1 00 to 1 ,000
Amount of Solid Captured
Dissolved solids pass through
Dissolved solids pass through
Blocks, some dissolved solids, but
allows some to pass through
Blocks almost all solids
1
cations are best for facilities with mixed wastes
containing emulsified oils from aqueous clean-
ers. Metal finishers use-other membranes in
specific waste minimization activities including
acid recycling (i.e., electrodialysis) or recycling
wastewater (i.e., reverse osmosis).
Nanofiltration membranes are becoming popular
for recycling systems as well and some mem-
brane suppliers offer them for polishing treated
. water for recycling (I AMS 1995).
Platers should conducts pilot test of any mem-
brane system to avoid problems with flow (flux)
rate deterioration or compatibility with trace
constituents.such as solvents or silicones. Manu-
facturers' warranties vary and many do not
guarantee that effluent limits will b'e met
(leronimo 1995).
Maintenance and Equipment Cost
Depending upon the application, membrane
systems require periodic flushing and cleaning.
Some require little maintenance while other
applications where a higher concentration of
materials that could foul the membrane is present
require additional maintenance. In all applica-
tions, the concentrate generated by the filtration
, system must be managed in one of three ways:
(1) companies can use the solution in another
application, (2) they can discharge the solution to
the sewer, or (3) they can hire a licensed hauler
to remove it (leronimo 1995).
The capital cost of a membrane system depends
on the processing rate and the type of membrane
material used. Cost can vary from $4,000 for a
50 gallon-per-day system to more than SIOO.,000
for a 50,000 gallqn-per-day system. Typical
annual operating costs, which include mainte-
nance, replacement membranes, and electricity,
are 10 percent of the initial investment (EPA
1995).
Microfiltration
Micro filtration is a relatively new technology for
the removal of oil'and grease from aqueous and -
semi-aqueous degreasing baths. Captive shops
and non-plating facilities such as metal fabrica-
tors and painters currently-use microfiltration.
Microfiltration separates emulsified oils and
suspended solids from cleaning solutions in the
'. process bath, extending the life of the solution.
Microfiltration also can remove cleaning solution
dragout from rinsewater lines (Cushnie 1994).
To remove large particulates, platers typically
filter the feed stream entering the microfiltration
unit with conventional methods (e.g., cartridge
filters). Facilities use various holding tank
designs to trap or skim floating oils, allowing
heavier solids to settle. Operators then pump
fluid into the membrane compartment of the unit.
The membrane separates the remaining oils and
grease while water, solvent, and cleaning bath
constituents pass through. Figure 17 illustrates a
microfiltration system.
Two common configurations for microfiltration
are dead-end filtration and cross-flow filtration.
In dead-end filtration units, flows are similar to
those in laboratory Buchner funnels, while in
cross-flow filtration units, flows are tangential to
135
-------
ChJOW* 7- Pci;ut:Cn Prevent-on in Rinsing
Evaporation
01 Water
Thra« Slags Couitsr-Ftowtng Rinse
> To Treatment
McroflltraUon
Unit
Proctiscd Ctaanar
Figure 17, Example of Microfiltration Application (EPA 1995)
the filter surface. Filters used in these systems
can be either membranes with pore sizes smaller
than the diameter of the suspended solids or
depth filters with pore sizes larger than the
particle size, but that can still trap particles in
interstices. Cross-flow filtration is used pre-
dominantly in metal finishing because of its self-
cleaning ability, low pressure .requirements, and
high permeate fluxes. The membranes can be .
polymeric or ceramic materials. Polymeric
membranes have service lives of 2 to 4 years
while ceramic membranes can last 10 years.
Despite a cost that is twice that of polymeric
membranes, ceramic membranes are becoming
more popular because of their high temperature
and chemical resistance. All microfiltration
systems require periodic cleaning to remove
deposits on the surface and unplug membrane
pores. Cleaning usually is accomplished by
circulating acid (for inorganic scales), detergents
(for colloids emulsions), alkali (for biological
materials), or solvents (for organics) through the
microfiltration membrane (Freeman 1995).
the equipment selected for microfiltration
should have a simple mechanical configuration
that is physically sturdy and compact. The unit
should be constructed of materials that can
withstand high alkalinity and temperatures and
that can tolerate temperature fluctuations. It also
should be impenetrable to soils and metal
shavings. Selection of the membrane and
designation of pressure, retentate flow rate, and
concentration of oil in the influent are the most
important factors in determining the appropriate
microfiltration system (leronimo 1995).
Applications and Restrictions
Microfiltration is used in the recovery of caustic
aqueous cleaners. As caustic cleaning solution is
used, it accumulates dirt, grease, grime, free and
emulsified oils, and metal particulates. With use.
caustic cleaners lose their ability to remove
contaminants. Rather than dumping the cleaning
bath, it can be sent to a microfiltration unit for
regeneration. Not all cleaners are good candi-
dates for microfiltration and a facility might need
to change its cleaning chemistry to use
microfiltration. For example, high silicate .
.cleaners that accumulate metal ions can foul
membranes. Because these membranes do not
remove dissolved ions such as aluminum or
copper, bath life remains limited (EPA 1995).
Microfiltration also can be used to polish waste-
water after hydroxide precipitation (Freeman
1995).
Costs
The cost of microfiltration systems varies
depending on the size of the machine. Systems
can range from $15,000 to $20,000 for a 1,000
liters-per-day unit to $25,000 to $35,000 for a
5,000 liters-per-day unit. Installation costs are
usually 10 to 30 percent of the equipment cost.
136
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Chapter 7: Pollution Prevention in Rinsing
Operating costs include membrane replacement,
labor, and energy. . The lifespan of a membrane
depends upon the application. Some facilities
might need to change the membrane every few
years while other facilities can expect the mem-
brane to function properly for more than 10
years. Companies can save money by reducing
or eliminating replacement of spent cleaners and
neutralization chemicals (EPA 1995).
Ultrafiltration
Ultrafiltration (UF) membranes have~smaller
pores than microfiltration .membranes with pore
sizes of 0.0025 to 0.01 microns. The layout of a
typical Ultrafiltration recycling system is de-
picted in Figure 1?. As shown, the operator ,
pumps .spent process water from a process tank
to a holding/settling tank. If the spent process
solution has a high solids content, the rinsewater
first passes through a prefiltration unit (e.g., bag
filter) before being pumped to a holding tank.
From the holding tank,.the. Ultrafiltration system
recirculates and concentrates the process solu-
tion,, providing a-steady stream of clean fluid for
reuse. The system then sends a stream of clean
fluid to the holding tank for the operator to draw
on.as necessary. Typically, Ultrafiltration
systems use higher pressure than m'icrofiltration
systems (60 to 80 pounds per square inch) (Rl
DEM 1994).
Ultrafiltration membranes are tubular, hollow
fiber, and spiral wound. Platers generally use
tubular membranes in small flow, high-solids
loading applications. The construction of tubular
membranes allows easy cleaning, making them
excellent applications where the operator expects
, severe fouling (Rl DEM 1994). ,
The hollow fiber design consists of a membrane
wound into a hollow cylinder. The expected
solids loading governs the size of the cylinder
that is needed for a specific application. Platers
usually use spiral-wound membranes for high-
volume applications. The spiral membrane
consists of a rolled flat membrane that is netted
together.with specially designed spacer material.
Spiral membranes cannot be mechanically
cleaned and usually are reserved for applications
where total suspended solids loading is low or
has been reduced by prefiltration (Rl DEM
1994). -
Oil to
,Recycler
Water
Figure 18. Example of Ultrafittration (EPA 1995)
Reverse Osmosis
Reverse osmosis (RO) is a pressure-driven
membrane filtration process. In RO, a semi-
permeable membrane permits the passage of
purified water under pressure, but does not allow
the passage of larger molecular-weight compo-
nents. Water that passes through the membrane
usually is recycled as rinsewater. Water that is
rejected by the membrane (Le., water containing
dissolved solids) is returned directly to the
process tank. Reverse osmosis is capable of
removing up to 98 percent of dissolved solids^ 99
percent of organic*, and 99 percent of bacteria.
Figure 19 illustrates a typicalRO system.
Reverse osmosis is a good component of a low-
or zero-discharge configuration. The equipment,
however, tends to be more expensive and less
effective at recycling rinsewater than other
technologies such as ion exchange (EPA 1995).
Reverse osmosis is especially suited for closing
the loop on plating operations and sending
concentrate back to the plating bath. Firms apply
137
-------
C**1C!*^ -T P;''-W p'«ve"l:0n m Rinsing
Process
Tank
Pure Water
Makeup
Concentrate (Qc )
%Rec6very =» Q P -x 100%
Figure 19. Example of Reverse Osmosis (EPA 1995)
RO to a variety of processes including brass
cyanide, copper cyanide, copper sulfate, nickel.
silver cyanide, non-cyanide alkaline zinc, and
zinc cyanide plating. Recovery of dragout from
acid nickel process bath rinses is the most
common RO application. Reverse osmosis also
is used to purify tap water, recover plating
chemicals from rinsewater, and polish wastewa-
"ter effluent. Although RO recovers a concen-
trated dragout solution, some materials (e.g.,
boric acid) cannot be fully recovered (Freeman
1995). Reverse osmosis generally is not suitable
for applications that have a highly concentrated
okidative solution such as chromic acid, nitric
acid, and peroxy-sulfuric ctchant. Also, the
membranes will not completely reject many non-
ionized organic compounds. Therefore, acti-
vated carbon treatment typically is required
before the rinsewater solution can be returned to
the rinse system, which can be costly (Cushnie
1994).
Only RO can concentrate dissolved salts
Reverse osmosis cannot tolerate large
concentrations of suspended solids
Reverse osmosis requires much higher
operating pressures, mandating the use
of heavy gauge stainless steel; other
filtration technologies can use lightweight
stainless steel or plastic (Cushnie 1 994)
Facilities must carefully consider the membrane
used in RO. The membrane must be specifically
matched with the process chemicals. For in-
stance, polyamide membranes work best on zinc
chloride and watts nickel baths, while
polyetheramide membranes work best with
chromic acid and acid copper solutions (EPA
1995).
Although similar to other filtration technologies.
RO is different in that:
The membranes in RO are unable to withstand
pH extremes and long-term pressures. Feed
concentrations can reach saturation, precipitate
on the membrane, and cause the membrane to
fail. Precipitation of contaminants must be
avoided or RO will fail. Feed stream concentra-
tions must be kept low by adding a pre-filtering
system to the RO unit, usually an ultrafiltration
unit(Warheit 1988). Reverse osmosis mem-
branes also can be damaged by some incoming
materials (e.g., iron and manganese).
Another concern is the potential for a reject rate
of more than 50 percent of incoming flow
depending on the characteristics of the influent
and membrane porosity. Such a high rejection
rate can be difficult to handle in a metal finishing
operation unless the firm is using RO to generate
deionized water where the disposal of rejected
flow is not expensive. In a waste application,
platers must treat discharge of concentrate,
increasing the cost of the system and limiting the
use of RO to wastewater recycling applications.
138
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Chapter 7: Pollution Prevention ,n '
Reverse Osmosis
Advantages _, ' '. ' -
Recovers process chemicals ' \'
Recycles process water '
Achieves high separation rate
Uses no chemicals
* Requires small floor space
Low-energy process
* Less expensive than other recovery
technologies for certain applications
Disadvantages
^Problems with membrane durability
Sensitive to hard water salts
Fouls membranes because of feeds high in
suspended solids "
Feed filtration .is essential ' -
In some applications does not concentrate
plating solution sufficiently for reuse
Returns ionic impurities to plating bath _
Operates efficiently in a limited
concentration range, (Ohio EPA 1994)
Costs
Since flux rates vary from application to applica-
tion, and customization and special engineering
can be necessary, cost estimates based simply on
flow .or flux rates are approximate. .Reverse
osmosis units can cost $50,000 to $75,000 for
flow rates of 75 liters per minute.with cost as
high as $300,000 for flow.rates of 800 liters per
minute. Operating costs include labor, energy,
and membrane cleaning and replacement (EPA
1995). ' , .
Reverse Osmosis in Specific Baths
Table 23 provides information on specific metals
used with RO.
Table 23. Reverse Osmosis and Specific Metals
(Nadeau 1986)
A typical application for process recovery using
RO is nickel plating as shown in Figure 20.
Because RO is such a deiicate^process, any
change in bath chemistry can affect the operation
of the RO unit. '
.While widely used in other industrial applica-
tions such as desalinization, RO is not used
frequently as a recovery technology, in metal
finishing. The limited number of baths in which
firms have successfully applied RO and the
availability of competing technologies might be
'reasons. Other technologies that are available at
much Ipwer costs, such as atmospheric evapora-
tion, often are more attractive options for metal
finishers (Cushnie 1994),
Metal
Nickel
Copper
Sulfate
V
Brass
Cyanide
Use with Reverse Osmosis
Most nickel plating lines with RO
units use cellulose acetate mem-
oranes with recovery rates between
90 and 97 percent.
Many of the copper sulfate RO units
use hollow-fiber polyamide and
cellulose triacetate membranes and
spiral wound thin-film composite
types, which offer a membrane life
of approximately 3 years. Because
of the low operating temperature of
the plating bath, operators can return
only a small portion of the concen-
trate back to the process bath: ' .
Platers have used both polyamide
and cellulose triacetate membranes
in brass cyanide appjications.
.Average recovery rates are approxi-
mately. 90 percent. Average mem-
brane life in these systems is 3 to 4
years.
Figure 20. Typical Reverse Osmosis Configuration for Nickel Plating (EPA 199.5)
.'.-"-' -' : . 139 ,. ".'.''
-------
% "42:4* " P1?" -t C"* P'evtr.t on in Rinsing
Ion Exchange
Man\ metal finishers are familiar with ion
exchange technology. This versatile technology
has been used for decades and can be a major
component of a low- or zero-discharge configu-
ration. The most common applications in plating
include:
I
Treatment of raw water to produce high-
quality rinsewater
Recovery of chemicals from rinsewater
Treatment of plating baths t6 remove
contaminants
Primary end-of-pipe treatment
End-of-pipe polishing for compl
with stringent effluent limits
liance
nt
The ion exchange process replaces sorne"
harmless ions located in a resin with ion,, ;'
concern (i.e., plating chemicals). The system is a
molecular process where metal ions in solution
are ramnved by a chemical substitution reaction
with the ions in a resin bed. Resins are normally
contained in vessels referred to as columns,
rinsewater is passed through a series of resin
beds that selectively remove both cations and
anions. As rinsewater passes through the resin
bed, the resin bed exchanges ions with organic
compounds in the rinsewater. Figure 21 presents
two typical configurations of ion exchange for
bath maintenance.
Basically, ion exchange processes are either
anionic or cationic. Anion resins exchange
hydroxyl ions for negatively charged ions such
as chromates, sulfates, and cyanides. Cation
resins exchange hydrogen ions for positively
charged ions such as nickel, copper, and sodium.
An example of ion exchange is shown in Figure
22. Ion exchange systems typically operate in
cycles consisting of the following four steps
(Cushnie 1994): ,
* Service (exhaustion):' Process effluent
passes through the resin column or bed.
Charged ions present in the wastestream are
attracted to the resin and exchange with
CM Water
Acid Regenerant
Bath
Rol'jm
Three Stage Counter-Flowing Rinse
-To Treatment
or Off-slta
Disposal
Drag-out
Return
Three Stage Counter-Flowing Rinse
Filer
Figure 21. Two Common Configurations of Ion Exchange (EPA 1995)
140
-------
1 Matal 8cav«oghg
Evaooradon
Chjpcer 7.'Pollution Prevention n
Add. Regenerant . ' <
ic~ir
f pH Adjust }-» Sew«f
i . I -
Return Regenarant to Process ' Jf ^ To Treatment
_,_ ..-.--- - - * " ^' Etectrowlnrtr
or
'Inning
2. Water Recydng
Evaporation
Dl Water
65 L/Hr
1
Dl Water
Acid
3.
Caustic
Return Cation Regenerant to Process * ' ,....* >- To
- "" EV
To Treatment
Treatment or
Sectrowlmlng
Figure 22. Example of Ion' Exchange (EPA 1995)
siitiilarly.charged ions, in thebcd. After the
majority of the exchange sites have been
used up, the resin is considered exhausted.
Although the resin could be discarded and ,
replaced at this point/typically it is regener-
ated for reuse because of the high cost of
resin. - . '. .
Backwash^ Water is flushed through the
resin bed in the reverse direction of the
service cycle to redistribute the resin.
Regeneration: The exchanger resin is
regenerated by passing a concentrated
solution of the original ion through the resin
bed. Usually, the solution contains a strong
mineral or acid.
* Rinse: Rinsing to remove excess regenerant
is accomplished by circulating deionized
water through the ion exchange column.
Metals held in the solution are recovered by
cleaning the resin with an acid or alkaline
solution. Operators can electrowin,metals from
the resin regeneration solution while the water
treated by ion exchange can be returned to the
rinse system for reuse (Cushnie 1994). Figure
23 presents a typical ion exchange configuration
for chemicalrecovery applications. .
Ion exchange can selectively remove contami-
nants from a wastestream. In recycling applica-
tions, however, contaminants are not recovered
along with the desired materials. Close control
of the influent is important with low pHs reduce
the capacity of the resin and high pHs tend to
clog the resin with solids. One disadvantage of
these systems is that no method exists to monitor
the.saturation of the resin. However, physical
indicators such as reduced effluent quality can
signify when the resin bed is saturated. Typi-
cally, facilities clean the cylinders on a time-
based schedule (Freeman 1995). The recovery of
chemicals from the resin columns generates
. significant volumes of regenerant and wash
solutions, which can add to the wastewater
treatment toad (1AMS 1995).
Ion exchange should only be applied to relatively
dilute streams and is best used in association
with other conventional dragbut recovery prac-
141
-------
to Rinsing
Parts Row . ^
Spent Carbon/
Bain Organics
_.
Rooenerant Discharge
ex Reclamation
Makeup and
Reqenerant Water
^*
Figure 23. Common Ion Exchange Configurations for Chemical Recovery (EPA 1995)
Recover of Zinc and Nickel Using Ion
Exchange Case Study
Walbridge Coatings of Walbridge, Ohio,
produces eledrogalvanized zinc and zinc-
nickel cold-rolled steel primarily for the
automotive industry. In 1989, the company
embarked on an aggressive metals recovery
and reclamation program. After a year of
engineering work, the firm decided that .
recovery of zinc and nickel was possible
through ion exchange.
i Initial tests indicated that a metals recovery
!! rate of 90 percent was possible. The firm
estimated that initial recovery efforts would
result in approximately a 500 tons-per-year
reduction in sludge generation. After Installing
he system on the zinc-nickel stream, the
company found that the system could reduce
sludge generation from zinc processes by an
additional 350 tons per year.
During 1991 the project eliminated 515 tons
of sludge. During 1992, with improved
methods and the addition of the system to the
zinc stream, more than 892 tons of sludge
were eliminated, exceeding engineering
expectations by 5 percent.
The total project costs were $3.2 million with
annual.savings of $2 million. The payback
period, based solely on cost avoidance, was
1.5 years.
(Ohio EPA 1994)
tices. Ion exchange systems are less delicate
than RO systems, however, operators must filter
the water to protect the resin, removing oil,
grease, and dirt. In addition, certain other metals
can foul the resin, requiring a special procedure
to remove the foulant (Hunt 1988). In some
.applications, the solution generated from ion
exchange (i.e., regenerant) is returned directly to
the process tank. In most cases', however,
regenerant is electrowinned or goes to traditional
waste treatment systems (EPA 1995).
Optimizing Ion Exchange System
Performance
A properly designed system will operate at
maximum efficiency. Conducting treatability
testing of specific wastestreams to ensure proper
resin selection and sizing of the system is critical
to the overall success. Treatability testing also
will ensure that the system is not undersized or
oversized and that interferences are not present
that will render the resin ineffective. Other items
that facilities should consider include:
Regeneration frequency and volume: A
properly designed system will minimize
regeneration frequency and the volume of
waste regenerant solution generated. Vari-
ous methods for regeneration are available
including in-column or continuous and out-
of-column batch techniques. From the
operator's standpoint, in-column methods are
142
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Chagcer 7: Pollution Prevention .n Rjnjinj
preferred. The batch in-column method (also
-known as the Hooded vessel.method).in-; .
- volves filling the column with regenerant
, solution; allowing it to sit for a specified .
. time period, and then repeating this step or
proceeding with deionized rinsing. The
continuous in-colum"n technique involves
passings specified amount of regenerant
through the resin bed in a continuous flow
(either up or down). Although operators
might prefer the ease of the .batch in-column
method, the continuous flow method gener-
ally requires lower volumes of regenerant
solution. , ;
Determining breakthrough: Breakthrough
is defined as the point at which the resin has
become spent or exhausted and must be
regenerated. In some applications, the
columns must be regenerated just prior to
breakthrough in order to meet effluent
quality standards. Various methods are
available to determine breakthrough includ-
ing timed-interval regeneration, on-line
' monitoring of ions and flow to identify
regeneration intervals, and periodic off-line
-, sampling to monitor effluent quality. Selec-
tion of the appropriate method depends on
the effluent requirements of the; facility.
Series versus parallel configuration: Ion
exchange systems can be designed in a series
or a parallel configuration. Parallel configu-
rations generally have higher flow rates: In
applications where final effluent standards
are high, the series configuration allows
operators to observe breakthrough in the
initial column(s) of the series prior to
breakthrough in the last stage. "
Charging, and recharging vessels with
resin: Resins must be added or replaced in
the vessels to prevent a premature loss in
-r capacity because of flow restrictions or
increased resin deterioration.
Storage.of resin: Resins should not dry out
during storage. "Re-wetting usually results in
cracking and/or deterioration of the resin.
Additionally, resin vessels should be
backwashed prior to shutting down the
system to prevent fouling or cementing of
parttculates in the resin bed. Prior to long-
term shutdown, anion resins should be rinsed
with brine solution to ensure conversion to
the more stable chloride form (versus the
, hydroxide form) (Wiik 1990). ;
> Cosrs - . '
Capital costs depend on the volume of flow and
the level of automation. The components of an
ion exchange system are relatively inexpensive
and, depending on the, application, can cost from.
$100 to $400 per cubic foot. Installation costs
can be quite high. Platers can purchase and
install small manual units, applied to flows of 20
liters per minute or less for $15,000 or less. A
fully automatic 75 liters-per-minute unit with an
integrated electrbwinning unit costs approxi-
mately $75,000 installed (EPA 1995),
Operation and maintenance costs are generally
. low for ion exchange. A major expense is resin
replacement. Resin should last 3 years or more.
however, in certain applications (e.g., chrome) it
.can have a shorter lifespan. Resin costs from $7
to $22 per liter. Labor costs depend on the level
of automation included with the unit and can cost
from more than $1 per 1,000 liters for manual or
undersized installations to less than $0.25 per
1,000 liters for fully automatic systems. Up-.
stream components such as sand, polypropylene,
and carbon filters also contribute to operationing
costs(EPA 1995). -
Electro/Diffusion Dialysis
Two types of membrane dialysis systems are
electrodialysis and diffusion dialysis. These
systems are becoming increasingly popular for
chemical solution recovery especially because
they are more efficient and less expensive than
other recovery technologies for reclaiming acid.
They also can remove metals and recycle water
in plating or anodizing shops (EPA 1995).
Electrodialysis
Platers commonly use electrodialysis to reclaim
nickel and gold from plating rinsewaters. Figure
24 presents a flow schematic for a nickel plating
line before and after installation of electrodialy-
sis. This process uses both anion- and cation-
charged selective membranes between a set of
non-corrosive electrodes. As the plater recircu-
lates contaminated rinsewaters between the
charged surfaces, salts containing the metals are
143
-------
Cadmium and Chromium Recovery from Electroplating Rinsewaters Case Study
amoanv based in Torrington, Connecticut, participated in a pilot study in conjunc-
Connecticut Hazardous Waste Management Service to test the feasibility of recovering
chromium with ion exchange. The objective of the study was to evaluate the effec-
tiveness ot ion exchange in cleaning rinsewater for reuse in the rinse tank the pollut.on prevent.on
potent al of this technology, and the cost of ion exchange versus the cost of trad,t,onal control.
nium system has the following steps. Water from the first rinse tank passes
hrough a ^f.Uer to prevent suspended solids from contacting the resin in the , on exchange column.
The anionic resin captures the cadmium cyanide complex and the second nnse tank receives the
watr An eme genc^ bypass valve allows this water to be discharged to the waste treatment system
h case cadmLm o^nide levels are found to be too high. The company Per,od,cal y regenerates
he resin wi^a^ 5 to 20 percent sodium hydroxide solution and takes the regenerant to the
recovery unit where cadmium is recovered on the cathode and returned to the
is destroyed by decomposition during electrolytc metal recovery.
. Some cyanide also is destroyed in the cadm.um recovery process.
od wilh lh= cost of capital at 1 5 percent) was less than I year.
pbck pod (wilh
I oharatorv analysis of the cadmium rinsewater samples found that ion exchange removed most of
oTdJcS SSToTSlSanTSX the company was primarily concerned with cadmium
S cyan de Before ion exchange, cadmium remained in the wastewater that was sent to an on-
in orasr TO reiuwa nwiwi»wi\-« / -ne H /
might be present in the rinsewater.
Total chromium and iron levels decreased significantly after ion exchange.
analysis of the chromium rinsewater samples showed that the "nsewate''£ Qnd Qther contami.
nllcnline (931 to 9.45) because the hydroxide ions replaced chromcne .;<.<»
aiKaiine^T.o i \v i _ e'due on the parts neutralized the alkaline pn in tne rinse
"aTksaTn\ncorn°panyeuses a cartridge filter in conjunction with the ion exchange unit, which
144
-------
Chapter 7: Pollution Prevention *n
' significantly reduces the suspended" solids. As in the cadmium test, the mass of dissolved solids
I* decreased significantly, but conductivity (i,e., current-carrying strength) remained constant after ion
M exchange because the lighter hydroxide .ions, replaced heavier chromates in the rinsewater.
Without1 ion exchange,' approximately 80 pounds of chromium were discharged annually. With ion
exchange, most of the chromium was captured on the resin. To regenerate the resin, sodium
hydroxide was passed through a cation exchange resin, converting sodium chromate to chromic
acid. However, when this recovery Was performed during the pilot test, the final regenerant liquid
had a pH of 13.08. If sodium chromate had been converted to chromic acid, it would have a much.
lower pH. An excess use of regenerate and/or insufficient resin might have caused these results.
The company plans to conduct further tests to determine'the feasibility of tfte chromic acid recovery
process. . . .
The purchase price.of the chromium exchange system was estimated at-$8,200. Installation costs
were approximately $3,500 including materials and labor. Additional capital is required for in-
house testing. , .',- , / '[ , ' - '' - , / ' . (EPA1995b)
retained and returned to the plating tank. Rinse-
water is reused in the dirtiest rinse or dragout
tank. Separation is accomplished by applying a
direct current across a stack of selective mem-
branes. The membranes are stacked in alternat-
ing cation/anion stacks. Each stack is separated
by a spacer through which solutions are allowed
to"flow (Cushnie 1994). ;.
When the solutio'n passes through a cation-
selective membrane, cations pass through and
anions are trapped. As the solution continues to.
migrate, it will encounter an anionrselective
membrane that will not allow the cations to pass.
In this way, the wasteslream is diluted of both
anions and cations. The solution, which is
returned to process tank, can be 10 times more
concentrated than the feed stream, but usually is
not as concentrated as the process bath (Cushnie
1994). " ;
Applications and Restrictions
- For electrodiaiysis to offer any advantages over
competing technologies, the process fluid must
tolerate the direct return of the concentrate.
Because the returned solution is usually less
concentrated than the bath itself, and because of
the evaporative .nature of the process, only heated
fluids are candidates for this process (EPA
1995). One advantage of electrodialysis is its
ability to selectively retard the recovery of
certain organic materials, especially nickel, tliat
build up in some baths. In so doing, electrodi-
Electrodialysis
Advantages
Energy efficient
Returns minimal amount of unwanted
inorganic material
Recovers higher concentrations of ions than
RO or ion exchange . '
Disadvantages
Sensitive to clogging and ruptures, flow
distribution, pH, and suspended solids'
Efficiency drops as purity increases
Must filter feed ' '
Uses multi-cell stacks
Uncertain membrane life
(Ohio EPA 1994)
alysis can reduce the frequency of bath purifica-
tion (Cushnie 1994). Most applications for
electrodialysis are nickel-related although
manufacturers have used this technology in
copper cyanide, cadmium cyanide, and zinc
phosphate applications (EPA 1995).
Costs
Capital costs are related to membrane surface
area or to feed flow volume and characterization.
Vendors customize most units for a particular
application. In general, electrodialysis is more
expensive than other recovery technologies.
Units range'in price from $75,000 to several
hundred thousand dollars depending on the
capacity of the unit. Operating and maintenance
costs include energy, labor, and membrane
145
-------
*'-*r'i0n '" Rinsins
&(«
CUy Water
StIUHr
Ttvee Stage Counter-Flowing Rlnsa
. SOO UHr to Treatment
M tow 1800 g/Hr
27UHr Drag-WDrag-out
27 uw Arrangam»nt
After
Thres Slage Coulter-Bowing'Rinsa
aty Water
511 UHr
4S4L/HT
26 mg/L (^ to Treatment
Nkkel Loss: 127 g/Hr
Figure 24. Example of Process Flow of a Nickel Plating Line Before and After Installation" of
Electrodialysis (EPA 1995)
Nickel Recovery from Electroplating Rinsewater by Electrodialysis Case Study
Plotingo. Bridgeport.APB) in
rtridge filter removes any carryover carbon particles
s systen,
resulted in a payback of 1 year
replacement (EPA 1995). One vendor estimated
that operating costs are S0.78 per gallon of ac.d
feed. Primarily/these costs are incurred from
operation and maintenance, labor, energy,
detomzed water, and membrane replacement
(Cushnie 1994)1
Diffusion Dialysis
Diffusion dialysis is an ion exchange membrane
technology used for the recovery of acids con-
taminated with metals from pickling, anodizing,
stripping, etching, or passivation baths. This
146
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Chjpcer 7: Pollution prevention n
technology.is commonly used in finisliing
facilitiesjn Europe and Japan, but not in the ,
United States. Companies use diffusion dialysis
to.purify some acid baths that are contaminated
by metals. This technology can separate mineral
acids and metals such as copper, chrome, nickel,
iron, and aluminum so that acid can be reused.
Recovery rates in some instances are as high as
95 percent for acid solutions and 60 to 90 percent
for metal contaminants (Cushnie 1994)r Cur-
rently," this technology is popular with anqdizers
that generate large amounts of waste sulfuric
acid (EPA-1995). ,
The efficiency of a membrane to concentrate
dilute acids in solution depends on the surface
area available and the type of acid. Diffusion
dialysis separates acids from metal contaminants
via an acid concentration gradient that is placed
between two solution compartments. These
compartments are divided-by an anion exchange
membrane. 'Water is metered through one side of
an anionic membrane, causing the acid to
migrate to one side and the metals to stay on the
other. Purified acid is sentback to the process
tank and contaminant-laden spent acid and
metals are sent to the metal recovery or waste
treatment system. This technology does not use
pressure or charge to move material across the
.membrane as do other membrane technologies.
Movement is caused by the different acid con-
centrations on either side of the membrane
(Cushnie 1994).
Capital costs for diffusion dialysis systems start
at $ 18,000 for a 50 gallons-per-day-system (EPA
1995).
, Diffusion Dialysis
Advantages ';--, . . ',
Energy efficient " ;
Considerable reduction in acid
. consumption .
Fully automatic
' Low-maintenance costs
» Long membrane life- .
Disadvantages
Sensitive to clogging and ruptures, flow
distribution, pH, and suspended solids
Efficiency drops as purity increases
(Ohio EPA 1994)
Acid Sorption
Acid sorption is an acid purification technology
used on a variety of acid solutions'including
pickling or sulfuric acid anodizing baths. Abed
of.alkaline. anion exchange resin separates the
. acid from the metal ions. The acid'is taken up by
the resin while the metal ions pass through the
membrane. The acid then is desorbed from the
resin by water. This technology is rarely used by
the'plating industry (Cushnie 1994).
Figure 25.shows the steps in the acid sorption
process. First, spent acid is pumped upward
through the resin bed. A metal-rich, mildly
acidic solution passes through the resin bed and
is. collected at the top of the bed. Second, water
is pumped downward through the bed and
dcsorbs the acid from the resin. The purified
acid solution is collected at the bottom of the bed
(EPA 1995).
Figure 25. Typical Acid Sorption Configuration (EPA 1,995)
147
^- By-product
to eeclrowfnrtng
or Treatment ;
-------
7. PJt'utcn Pre'.eniton in Rinsing
This technology can recover approximately 80
percent of the free acid remaining in a spent
Solution. Facilities can purify the acid solutions
in a batch mode, but using the technology in a
continuous mode can produce a steady metal
concentration, in the concentrate. The capacity of
a system is determined by the size of the resin
bed and usually is expressed in terms of the mass
of metal removed from the acid solution. Equip-
ment capacities range from 100 grams per hour
to several thousand per hour. Typically, vendors
size a unit to remove metal near or above'the rate
at which metal is being introduced (EPA 1995).
Applications and Restrictions
Many plating shops with acid solutions could use
acid sorption technology. Heated solutions and
those containing okidizers have to be cooled and
filtered respectively prior to purification. Platers
generally send the process byproduct (i.e., metal-
rich solution) to the treatment system, but some
electrowin the solution for metals recovery. In
addition to anodizing and pickling baths, compa-
nies can apply acid sorption. to non-chromic acid
copper, brass etch, bright dips, nitric acid strip-
pers, aluminum bright dips, and cation ion
exchange regenerant. Chromates, concentrated
acids, and some hydrochloric acid processes are
not good candidates for this technology (EPA
1995).
Costs
Capital costs of acid sorption range from $30,000
to S40.000 for capacities under 200 grams per
hour to more than 5100,000 for capacities of 1
kilogram per hour. Little data is available on
operating costs (EPA 1995).
Ion Transfer
Ion transfer generally is restricted to chromic
acid plating baths, etches, and anodizing baths.
As with the other chromic acid purification
technologies, this technology selectively re-
moves cations from chromic acid process fluids.
Designs range from low-Cost in-tank small
porous pots to large multi-cell automated units
with unified rectifiers and transfer pumps (EPA
1995).
Figure 26 presents a typical ion transfer arrange-
ment. Ion transfer units consist of one or several
membrane compartments that separate the
cathode from the anode of an electrolytic cell.
The membrane is usually a porous ceramic pot
that contains the cathode. The anode surrounds
the pot. The membrane also can be constructed
of a polyfluorocarbon material and the catholyte
compartment can be reinforced with polyethyl-
ene. The anode is in direct contact with the
process fluid while the cathode is separated from.
the process fluid by the membrane. Equipment
can be in-tank or external. Small in-tank units
often use a process rectifier and operate only
while parts are being plated. Operators must
remove these units when the rectifier is switched
off because the membrane will leak cations back
into the process tank. Automated ion transfer
units include a system that replenishes the
catholyte with fresh fluid at regular intervals
(Cushnie 1994).
TWo S'taga Counter-Flowing
Rinse
Dl Water
Catholyte to
Treatment
(on Transfer
UNI
Figure 26. Typical Ion Transfer Configuration (EPA 1995)
148'
-------
' Chuoter 7: Pollution Prevention ,n
.Vendors determine the cation remov'al rates by
the membrane area, the amperage applied to the
cell, and the concentration of cations in the ,
process fluid.. Small units remove 10 to 50
cations per day while a multi-cell unit can
remove up to, 1,000 grams per-day. Generally,
removal rates fall sharply when the concentration
of cations is below 3 grams per liter in the
process fluid. Units usually are sized to remove
cations at a rate near or somewhat faster than the
introduction rate (EPA-1995).
Applications and Restrictions
Because of relatively low cation removal rates,
ion transfer is best suited to maintaining rela-
tively clean baths rather than attempting to clean
highly concentrated ones. Tramp metal concen-
trations of 4 grams per liter can be achieved with
this technology. Achieving lower concentra-
tions, if possible, will result in higher energy
costs and an increase in the volume of waste
catholyte. The.waste catholyte can contain some
chromium, which is lost during catholyte
changes (EPA 1995). . \
Companies have applied ion transfer to alumi-
num and other cation removal operations such as
chromic acid etch or anodizing solutions, al-
though such applications are rare. In etch
solutions, the introduction rate is quite high and a
multi-cell external unit is required (EPA 1995).
Costs " , . . '.
tn-tank ceramic pot styles that operate with an
off-the-tank rectifier can be purchased for less
thanSl-,000. External units with 400 grams-per- .
liter removal capacities cost $30,000 or more
-depending on automation'and instrumentation.
Operating expenses include labor, electricity, and
membrane or pot replacement. Membranes can
last for several years. However/the' pots can be
broken during cleaning and handling. Manual
system's require frequent catholyte changes and
operators generally clean the pot during these
changes. Sludge buildup in the catholyte re-
quires frequent cleaning. Extending the bath life,
and thereby reducing chemical use and waste
generation, can produce significant savings (EPA
1995). / ...
Membrane Electrolysis
Membrane electrolysis, is one of the newer
technologies for recovery in metal finishing.
Membrane electrolysis units cdnsist of a tank
containing an anode .and a cathode compartment
separated by a selective membrane(s) and a
power source. Similar to. ion exchange, the,
resins in membrane electrolysis are ion specific.
Depending upon .the membrane, they allow the
passage of only negative or positive ions. The
use of ion-specific membranes rather than
ceramic pots or polyfluorocarbon materials
" differentiates this technology from ion transfer or
other non-ion permeable technologies (Cushnie
.1994). :,
The primary function of membrane electrolysis,
when applied as a bath maintenance technology,
is to lower or maintain acceptable Jeveis of
contaminates in plating, anodizing, etching,
Evaporation . , , r
.J^1 Drag-Oui/Rin Drag-Out/Rtn Drag-Out Recovery
i ' I _." ; 2.^." . Returns Tramp Metals
to Chrome Tank
~ v:.jTrr
'-'a Heated '
Ell Chrome
\--^ Tank
T_"I_._L_- _ '
Solution to
ME Unit and
< Return Row
1 j
: , 2-Ccll
i ; . i .
1 Recovery
; ! Rinse
i
i
Recover -,
Rinse, [
Recirculation
ofCathotyte
-«' *
< : ^
Catholytc
! Tank
: Mli Unit ''
Rectifier
Figure 27. Configuration of Membrane Electrolysis Application for Bath Maintenance
(Cushnie 1994) . . '.,
' . ' .: ' . 149 ;--' '.. V. '
-------
7 Pjtiji.cn P"«v«"HiOn in Rinsing
stripping, and other metal finishing solutions.
For the plating industry, membrane electrolysis
is most applicable to the maintenance of chromic-
acid solutions including hard chromium and
decorative chromium plating, chromic acid
etching, chromic acid anodizing, and chromic
acid stripping. Other potential-applications
include sulfuric and nitric acid and sodium
hydroxide-based solutions (e.g., pickling,
etching, stripping, and rust removal solutions),
chromate conversion coating, and sodium
dichromate deoxidizer (Cushnie 1994). Figure
27 illustrates a common configuration of mem-
brane electrolysis.
Costs
Costs for this technology are based on the
removal of capacity of the unit and can range
from 510,000 to $300,000. On average, how-
ever, the systems cost between $25,000 and
5100,000. Installation costs are approximately 5
to 20 percent of the equipment costs. The main
operating cost is labor. Other costs include
electricity, cathodes, anodes, catholyte, and
membranes.
References
Arizona Pollution Prevention Unit (APPU).
1995. Metal'Finishing in Arizona: Pollution
Prevention Opportunities, Practices and Cost
Benefits. Phoenix, AZ: Arizona Department of
Environmental Quality.
Bennati, C.A., and W.J. McLay. 1983.
Electrolytic Metal Recovery Conies of Age.
Plating and Surface Finishing. March, pp. 26-28.
ConnTAP. j 992. Pollution Prevention
Successes: A Compendium of Case Studies for
the Northeast States. Boston, MA: Northeast
Waste Management Officials' Association
ConnTAP. 1990. Pollution Prevention
Successes: A Compendium of Case Studies for
the Northeast States. Boston, MA: Northeast
Waste Management Officials' Association.
EPA. 1995. Wastf Minimization for Metal
Finishing Facilities. Washington, DC: Office of
Solid Waste.
EPA. 1995b. Pollution Prevention Possibili-
ties for Small and Medium-Sized Industries:
Results of the WRITE Projects. Washington, DC:
Office of Research and Development.
EPA. 1992. Guides te Pollution Prevention:
The Metal Finishing Industry. Washington, DC:
Office of Research and Development.
Ford, Chris J., and Sean Delaney. 1994.
Metal Finishing Industry Module. Lowell, MA:
Toxics Use Reduction Institute.
Freeman, Harry J. 1995. Industrial Pollution
Prevention Handbook. New York, NY: McGraw-
Hill. Inc.
Gallerani, Peter A. 1990. Good Operating
Practices in Electroplating Rinse water and
Waste Reduction. Boston, MA: Massachusetts
Department of Environmental Protection.
Hunt Gary E. 1988. Waste Reduction in the
Metal Finishing Industry. The International
Journal of Air Pollution Control and Waste
Management. May. pp. 672-680.
leronimo, Thomas. 1995. Membrane Tech-
nology Options in the Metal Finishing Industry.
Watcrtown, CT: Integrated Environmental
Resources.
, Institute of Advanced Manufacturing Sci-
ences, Inc (lAMS). 1995. A Pollution Prevention
Resource Manual for Metal Finishers: A Com-
petilive Advantage Manual. Cleveland, OH: Ohio
Environmental Protection Agency.
Nadeau, Tom and Mike Dejak. 1986, Cop-
per, Nickel, and Chromium Recovery in a Job
Shop. Plating and Surface Finishing. April.
Cushnie, George. 1994. Pollution Prevention
and Control Technology for Plating Operations.
Ann Arbor, MI: National Center for Manufactur-
ing Sciences.
North Carolina Department of Health and
Natural Resources (NCDNR): 1995./1 Compila-
tion of Successful Waste Reduction Projects
Implemented bv North Carolina Businesses and
150
-------
ChiO'wr ' Poiiuuon
Industries: December 1995 Update. Raleigh,
NC: North Carolina Office of Waste Reduction.
Ohio EPA. 1994;. Source Reduction and
Metal Recovery Techniques for Metal Finishers -
Fact Sheet No. 24. Columbus7OH: Office of
Pollution Prevention, Ohio Environmental
Protection Agency. ' \
Pinkerton, H.L., and Kenneth Graham. 1984.
Rinsing. Electroplating Engineering Handbook.
. Rhode Island Pollution Department of ,
Environmental Management (RI DEM). 1994.
Ultrafiltration Fact Sheet. Providence, RI:
Rhode Island Department of Environmental
Management. ; - :
V
Veit, P.L. 1989. The Evaporator A Great
Tool -but No Free Lunch. Metal Finishing.
November, pp. 31-34.
Warheit, Kevin E. 1988. Dicilylic Metal
Recovery front Surface Finishing Effluents.
- Lincolnwood, IL: IP Corporation. . - ;
Wilk, L.F., and R.S. Capacc,io. 1990. Appli-
cation of Ion Exchange Technology in Pollution
Prevention. Metal Finishing. April, pp. 25-28.
151
-------
-------
Alternative Methods of Metal
Deposition ' ' .-.
Methods for depositing metal coatings such
as chromium, nickel, cadmium, and copper
in traditional electroplating processes have
inherent pollution problems. Several alternative
technologies exist to coat a substrate with metal
without using electrolytic solutions or plating
baths. These technologies do not eliminate the
use of metal coatings, but they do eliminate the
use of non-metal toxic components such as
cyanide from the plating process. They also,can
reduce the amount of metal-contaminated
wastewater and sludge that is generated from.
plating. These alternative technologies include
thermal spray coating/vapor deposition, and
chemical vapor deposition (EPA 1995).
In the future, these technologies might play a
greater role in metal finishing operations.
However, many of these alternative processes
have high unit-plating costs and, therefore, are
used only for special applications where the cost
of coating is not a major consideration. Another
drawback to alternative metal deposition-meth-
ods is that metal overspray or tailings from
remachining thick coatings from the alternative
processes can actually increase waste generation
(Davis 1994).
Alternative technologies for metal finishing have
several features in common that distinguish them
from conventional technologies. A general
overview of each" feature is presented below:
' V Energy: Surface treatment energizes the
, surface of the workpiece so, that the coating
will adhere. Conventional surface finishing
methods involve heating the entire part. The
methods described in this section usually add
energy and material onto the surface only,
. / keeping the bulk of the object relatively cool
and unchanged. In so doing, surface proper-
ties are modified with minimal change to the
underlying structure of the substrate.
.Plasmas: The alternate technologies de-
scribed in this chapter (with the exception of
thermal spraying) use plasmas (e.g., clouds
of electrons and ions from which particles
can be extracted). Plasmas are used to
reduce process temperatures by adding .
kinetic energy to the surface rather than
. thermal energy.
Vacuum: Advanced surface treatments
require the use of vacuum chambers to
ensure proper cleanliness and control:
Vacuum processes are generally more
expensive and difficult to use than liquid or
air. processes. Facilities can expect less
complicated, vacuum systems to appear in the
future. ' , ' - .
Table 24 presents a summary of the various
alternative coating technologies and their appli-
"cations and limitations. Table 25 compares these
alternatives to their conventional counterparts
and presents information on the status of the
technology;.the surface preparation required: the
relative capital and operating costs; and the
relative environmental, health, and safety (EHSj
risks (EPA 1995). ;
Thermal Spray Coatings
The basic steps involved in any thermal coating
process are:
V Substrate preparation: This usually
involves oil/grease removal and surface
roughening. Surface roughening is necessary
for most of the thermal spray processes to
: ensure adequate bonding of the coating to the
workpiece. The most common method used
to perform this task is grit blasting with
alumina.
Masking and iixturing: Masking the part
reduces the amount of overspray that an
- operator must strip after deposition.
153
-------
A tj'-a: .« N1i:-ods of Metal Deposition
Table 24, Overview of Alternative Methods for Metal Deposition (Freeman 1995)
Technology
Thermal Spray Coating:
1 * Combustion torch
j| * Electric arc
Plasma sprays
Vapor Deposition:
*|on plating
;i"ion Implantation
Sputtering and sputter
deposition
Laser surface alloying
Chemical Vapor Deposition
| Applications
Vimarily repair operations although
some firms now incorporate thermal
spray coatings into original
manufacturing processes
Technologies in varying states of
development; commercial
availability might be limited in
certain cases
Primarily high technology
applications that can bear
additional costs; expected to
improve product quality and
increase lifespan
Used primarily for corrosion
and wear resistance in electronics
Limitations
Cost often limits application
to expensive parts; might require
improved process controls,
employee training, and
automation
Startup costs are high
Table 25. Comparison
of Alternative Deposition Methods with Conventional Plating (Freeman 1995)
I Replacement
Technology
Plasma and
Thermal
Spray
Ion Beam
' Techniques
1 - : -
Chemical Vapor
Deposition
Conventional
Technology
Plating (electrolytic)
Plating (electroless)
Cladding
Plating (electrolytic)
Plating (electroless)
Cladding
Case hardening
Dip/galvanizing
Plating (electrolytic)
Plating (electroless)
Cladding
Anodizing
1 -
Status
p
p
P
p
P
R
C
R
.P
P
P
R
Suface
Prep
Less
Less
More
Same
Same
More
More
More
Same
Same
More
Same ,
Oper-
ation
Ease
Same
Same
Same
Better
Better^
Better
Better .
Better
Better
Better
Better
Better
Relative
Capital
Cost
Higher
Higher
Higher
Higher
Higher
Higher
Higher
Higher
Higher
Higher
Higher
Higher
Relative
Operating
Cost
Same,
Same
Same
Higher
Higher
Higher
Higher
Higher .
Same
Same
Higher
Same
EHS Risk
. *
Lower ; \
Lower
Lower > -,
Lower ! i
Lower
Lower ;
Lower
Lower j 1
Lower
Lower
Same
Lower
OCommercial, P^Pilot plant, R=Research; EHS-Etwironmental, health, and safety
Coating application: Coatings can be
sprayed from rod or wire stock or from
powder material. Operators feed materials to
a flame that melts it. The molten stock then
is stripped from the end .of the wire and
atomized by a high-velocity stream of
compressed air or other gases, coating the
materials onto the workpiece. Depending on
the substrate, bonding occurs because of
mechanical interlock with a roughened
surface and/or because of Van der Waals
forces (i.e., mutual attraction and cohesion
between two surfaces).
Stripping: Stripping can be performed with
acids or bases or electrolytically. If none of
these techniques are possible, operators can
use a grinding process, but these .can be time-
consuming.
finishing: The final step is finishing the
workpiece. Most often it is accomplished by
grinding and lapping the workpiece.
154
-------
Chapter 3; Alternative
of M«;JI -ecc
The basic parameters that affect the deposition.of
metals in thermal spray applications include the
particle's temperature^ velocity, angle;of impact,
and -amount of reaction with gases during the
deposition process. As with traditional electro-
plating, part geometry also influences how the .
surface coating is deposited. Several industries
use thermal spray coatings as a substitute for
plating. They include:
Tungsten' carbide replacement of
chrome plating on oil field 'piston rods:
Prior to the adoption of thermal spraying, -
there were considerable problems with
chrome flaking. The flakes would work
themselves into the cylinders, causing
additional wear on the piston and cylinder.
The tungsten carbide substitute has shown
excellent wear characteristics and does not
require recoating as the chrome finish did
, (except when damaged externally, resulting
in longer operational life).
Replacement of chrome-plated water rolls
in the printing industry: Ceramic coatings
applied by thermal spraying have replaced
chrome-plated water rolls. Ceramic roHs are
used because of their excellent wetting
action. Chrome-plated rolls required acid
" etching and the use of volatile isopropyl
' alcohol to increase wetting action. The use
of the ceramic rolls has reduced or, in some
cases, eliminated the need for wetting agents.
Since the rolls do not flake, they do not
containihate the water or ink (Gansert 1989).
.Three basic categories of thermal spray technolo-
gies are combustion torch (e.g., flamespray,
high-velocity oxy fuel, and delonatipn gun),
electric (wire) arc, and plasma arc.
Combustion Torch/Flame. Spraying
Flame spraying involves feeding gas and oxygen
through a combustion flame spray tprch. A
coating material in powder or wire form is fed
into the flame. The coating is heated to nearer
above its melting point and accelerated by the
combustion of the coating material. The molten
droplets flow together on the surface of the
workpiece to form the coating. Platers can use
this technique to deposit ferrous-, nickel;, as well
as cobalt-based alloys and ceramics. Companies
.use combustion torches to repair machine-
bearing or seal areas and to .provide corrosion
and wear resistance for boilers and structures
(EPA 1995).
Combustion torch deposits are noted, for their .
relatively high porosity, low resistance to impact
or point loading, and limited thickness (0.5 to 3.5
millimeters). -Advantages include low capital
; costs, simplicity,of use, and relative ease of
operator training. In addition, the technique uses
materials efficiently and has low maintenance
requirements (EPA 1995).
Combustion Torch/High-Velocity
Oxy Fuel
With high-velocity oxy fuel (HVOF) systems,
the coating is heated to near or above its melting
point and is deposited by a high-velocity com-
bustion gas stream. Continuous combustion of
fuels typically occurs in a combustion chamber,
enabling higher gas velocities. Typical fuels
include propane, propylene, or hydrogen. This
technique might be an effective substitute for
hard chromium plating for certain jet engine
components. Typical applications include worn
parts reclamation and machine buildup, abrad-
able seals, and ceramic hard facings (EPA 1995).
This technique~has.higivve!ocity impact. Coat-.
ings applied with HVOF exhibit little or no
porosity. Deposition rates are relatively high,
and the coatings have acceptable bond strength.
Coating thicknesses range from 0.000013
millimeters to 3 millimeters. Some oxidation of
metallic? or reduction of oxides can occur,
altering coaling properties (EPA 1995).
Combustion Torch/Detonation Gun
Combustion torches and detonation guns mix
oxygen and acetylene with a pulse of powder
containing carbides, metal binders, and oxides.
This mix is introduced into a water-cooled barrel
about I meter in length and 25 millimeters in
diameter. A spark initiates detonation, resulting
in expanding gas that heats and accelerates-the
; powder materials so that they are converted into
a plastic-like state at temperatures ranging from
1,100 degrees Celsius to 19,000.degrees Celsius.
A complete coating is built up through repeated,
controlled detonations (EPA 1995).
155
-------
3; A ivnai .e MetncJs of Mewl Deposition
This technique produces some of the densest
thermal coatings. Platers can use almost any
metallic, ceramic, or cement materials that melt
without decomposing to coat parts. Typical
coatins thicknesses range from 0.05 millimeters
to 0.5 millimeters, but both thinner and thicker
coatings can be achieved. Because of the high
velocities in this application, the properties of the
coatings are much less sensitive to the angle of
deposition than most other spray coatings (EPA
1995).
This technology is used with a narrow range of
coating materials and substrates. Oxides and
carbides commonly are deposited. Because of
the high-velocity impact of depositing materials
such as tungsten carbide and chromium carbide,
combustion torches and detonation guns can be
used only on metal substrates (EPA 1995).
Electric Arc Spraying
During electric arc spraying, an electric arc
forms between the ends of two wires that are
made of coating material. The arc continuously
melts the ends of the wire while a jet of gas (e.g.,
air or nitrogen) blows the molten droplets toward
the substrate. Platers can use electric arc spray-
ing for simple metallic coatings such as copper
and zinc and for some ferrous alloys. Coating
deposits can be applied thinly or thickly depend-
ing on the end use. Electric arc spray coatings
have high porosity and low bond strength.
Industrial applications include coating paper,
plastics, and other heat-sensitive materials. It is
also used in the production of electromagnetic
shielding devices and molds (EPA 1995).
Plasma Spraying
Plasma spraying involves the introduction of a
flow of gas (usually argon-based) between a
water-cooled" copper anode and a tungsten
cathode. A direct current arc passes through and
is ionized to form a plasma. The plasma heats the
powder coating to a molten state. Compressed
gas propels the material to the workpiece at high
speeds. Materials suitable for plasma spraying
include zinc, aluminum, copper alloys, tin,
molybdenum, some steels, and numerous ce-
ramic materials. Platers can use plasma spraying
to achieve thicknesses from 0.3 to 6 millimeters
depending on the coating and substrate materials.
With proper process controls, this technique can
produce coatings with a wide range of selected
physical properties'including coatings with a
wide range of porosities (EPA 1995).
Companies can use plasma spraying to deposit
molybdenum and chromium on piston rings,
cobalt alloy on jet engine combustion chambers,
tungsten carbide on the blades of electric knives,
and wear coatings on computer parts (Kirk-
Othmer 1987). : ' .
Vapor Deposition
Technologies
Vapor deposition technologies include processes
that put materials into a vapor state via conden-
sation, chemical reaction, or conversion. Manu-
facturers use these processes to alter the
mechanical, electrical, thermal, optical, corrosion
resistance, and wear properties of substrates.
They also use vapor deposition technologies to
form freestanding bodies, films, and fibers and to
infiltrate fabric-forming composite materials
(EPA 1995).
This section describes physical vapor deposition
(PVD) and chemical vapor deposition (CVD). In
PVD, the workpiece is subjected to plasma
bombardment. In CVD, thermal energy heats
gases in a coating chamber, driving the-deposi-
tion reaction. Vapor deposition processes
usually take place within a vacuum chamber
(EPA 1995).
Physical Vapor Deposition
Physical vapor deposition involves dry vacuum
deposition methods in which a coating is depos-
ited over the entire object rather than in certain
areas. All reactive PVD hard coating processes
combine:
* A method for depositing the metal
An active gas such as nitrogen, oxygen,
or methane
* Plasma bombardment of the substrate to
ensure a dense, hard coating
The primary PVD methods are ion plating, ion
implantation, sputtering, and laser surface
156
-------
Crupcer 3: AXrruuve Mw.ods erf Msut
alloying.. The production of metals arid plasma
differs In each of these methods (EPA; 1995).
Ion Plating/Plasma-Based ; '
Plasma-based plating is the most common form
of ion plating. In plasma-based plating, the
substrate is placed in close proximity to a,
pl'asma. Ions then are accelerated from the
plasma by a negative bias onto the substrate.
The accelerated ions and high-energy neutrons
from the charge-exchange processes in the *
plasma deposit the coating on the surface sub-
strate with a spectrum of energies (EPA 1995).
This technique produces coatings that typically
range from 0,008 millimeters to 0.025 millime-
ters'. Advantages.of ion plating include the
excellent surface covering ability, good adhe-
sion, flexibility in tailoring film properties (e.g.,
morphology, density, and residual film stress);
and in-situ cleaning of the substrate prior to film
deposition. Disadvantages include tightly .
controlled processing parameters, potential ,
contamination activated in the plasma, and
potential contamination of bombarded gas
species into the substrate and coating (EPA
1995).; ;
Ion plating can deposit a wide variety of metals
including alloys of titanium, aluminum, copper,
gold, and palladium. Manufacturers use plasma-
based ion plating in .the production of X-ray
tubes, piping threads used in chemical environ-
ments, aircraft engine turbine blades, steel drill
bits, gear teeth, high-tolerance injection molds,
aluminum vacuum-sealing flanges, and decora-
tive coatings and for corrosion protection in
nuclear reactors. In addition, ion plating is
widely used as an alternative to cadmium for
applying corrosion-resistant aluminum coatings.
Compared to other deposition processes, ion
plating is relatively inexpensive (EPA 1995).
Capital costs are high for ion plating, creating a
significant barrier to its use. Ton plating is used
mainly in value-added equipment such as
expensive injection molds rather than inexpenr
sive drill bits (EPA 1995). ,
Ion Implantation
Ion implantation does not produce a discrete
coating; rather, the process alters the elemental
chemical composition of the surface of the
substrate by forming an alloy with .energetic ions.
A beam of charged ions of the desired element is
formed by feeding a gas into the ion source
where electrons, emitted from a hot filamenti
ionize the gas and form a plasma. An electri-
cally biased extraction electrode focuses the ions
into a beam. If the energy is high enough; ions
alloy with the substrate instead of onto the
surface, changing the surface composition. , .
Three variations of iori implantation have been
developed: beam implementation, direct ion
implantation, and plasma source implementation
(EPA 1995).
Cleaning is'-critical to the success of this technol-
ogy. Platers must pretreat (e.g., degrease,;rinse.
and ultrasonieally clean) the substrate to remove
any surface contaminants prior to implantation..
The process is performed at room temperature.
Deposition, time depends on the temperature
resistance of the workpiece and the required dose
(EPA 1995). ;. ;
Platers can use ion implantation for any element
.that can be vaporized and ionized in a vacuum '
chamber. The benefits of this process include
high reliability and reproducibility, elimination
of post-treatment, an easily controlled process.
and minimal waste generation. Ion implantation
does not produce a stable, finish if the coating is
exposed to high temperatures. When this
happens, implanted, ions diffuse from the surface
because of limited depth of penetration. Com-
.mercial availability of this technology is limited
by a lack of familiarity, scarcity of equipment,
and the need for strict quality control. Manufac-
turers commonly use nitrogen to increase the
wear resistance of metals because nitrogen easily
produces ion beams (EPA 1995).
Implantation is used primarily as an anti-wear
treatment for components of high value such as
biomedical devices (e.g., prostheses), tools (e.g.,
molds, dies, punches, cutting tools, and inserts),
and gears and balls used in the aerospace indus-
try. Other industrial applications include depos-
iting gold, ceramics, and other materials into
plastic, ceramic, and silicon and gallium arsenide
substrates for the semiconductor industry (EPA
1995). '.
157
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C"ip;er 3 A t*'"3
of Meul Deposition
The initial capital cost of ion implantation is
relatively high although large-scale systems have
proven cost effective. An analysis of six systems
manufactured by three companies found that
coating costs range from S0.04 to S0.28 per
square centimeter. Depending on throughput,
capital costs range from S400.000 to SI.4 million
and operating costs range from $ 125,000 to
$250,000 (EPA 1995).
Sputtering and Sputter Deposition
Sputtering is an etching process that alters the
physical properties of a surface. In this process,
a gas plasma discharge is set up between two
electrodes: a cathode plating material and an
cmode substrate. Positively charged gas ions are
attracted to and accelerated into the cathode.
The impact knocks atoms off the cathode, which
impact the anode and plate the substrate (Davis
1994). A film forms as atoms adhere to the
substrate. The deposits are thin, ranging from
0.00005 millimeters to 0.01 millimeters. The
most commonly applied materials are chromium,
titanium, aluminum, copper, molybdenum,
tungsten, gold, and silver. Three techniques for
sputtering are available: diode plasmas, RF
diodes, and magnetron-enhanced sputtering
(EPA 1995). ~
Sputter deposition provides a versatile process
for depositing metals, alloys, compounds; and
dielectrics on surfaces. Manufacturers have used
this technology to apply both hard and protective
industrial coatings. Areas requiring future
research and development include better methods
for in-situ process control, stripping, and under-
standing of process controls that affect coating
properties (EPA 1995).
Sputter-deposited films are used routinely in
decorative applications such as watchbands,
eyeglasses, and jewelry. The electronics industry
relies on heavily sputtered coatings and films
(e.g., thin film wiring.on chips and recording
heads as well as magnetic and magneto-optic
recording media). Companies also use sputter
deposition to produce reflective films for large .
pieces of architectural glass and decorative, films
for plastic used in the automotive industry. The
food packaging industry uses sputtering to
produce thin plastic films for packaging. Com-
pared to other deposition processes, sputter
deposition is.relatively inexpensive (EPA 1995).
Laser Surface Alloying/Laser Cladding
Increasingly, lasers are being used for surface
modification. Surface alloying is one of the
many kinds of alteration processes that use
lasers. This technology is similar to surface
melting, but it promotes alloying by injecting
another material into the melt pool that alloys
into the melt layer. Surface characteristics of
this technology include high-temperature perfor-
mance, wear resistance, improved corrosion
resistance, better mechanical properties, and
enhanced appearance (EPA 1995).
One of many methods of laser surface alloying is
laser cladding. The overall goal of laser cladding
is to selectively coat a defined area. In laser
cladding, a thin layer of metal (or powder metal)
is bonded with-a base metal via a combination .ot
heat and pressure. Specifically, ceramic or metal
powder is fed into a carbon dioxide laser beam
above the surface of a substrate, melted in the
beam, and transferred to the substrate. The beam
welds the material directly into the surface
region, providing a strong metallurgical bond.
Powder feeding is performed using a carrier gas
in a manner similar to that used for thermal spray
systems. Large areas are covered by moving the
substrate under the beam and overlapping
deposition tracks! Pretreatment is not'vital to the
successful application of laser cladding coatings
although the surface might require roughening
prior to deposition. Grinding and polishing
generally are required after the coating is applied
(EPA 1995).
This technique can apply most of the same
materials as thermal spraying technologies.
Materials that are easily oxidized are difficult to
deposit without using inert gas streams and
envelopes. Deposition rates depend on laser
power, power feed rates, and traverse speed.
Coating thicknesses can range from several
hundred microns to several millimeters. If the
density is too high, however, cracking and
delamination can occur as is the case with
aluminum and some steels. This technology also
is unable to coat areas that are out of the line of
sight. Although laser processing technologies
158
-------
Cfutner 3: Formation of the reactive gas.mixture
Mass transport of the reactant gas
through a boundary layer to the substrate
*" Adsorption of the reactants on the sub-
strate _ . .' - ;
» Reaction of the adsorbents to form the
'.deposit. . , . "
Substrate pretreatment is important in vapor
deposition, particularly in CVD. Pretreatment
involves using mechanical and chemical means
to minimize pretreatment before placing the
substrate in the deposition reactor. Substrates
must be cleaned prior to deposition and the
deposition reactor chamber must be clean, teak-
. tight, and free of dust and moisture. Cleaning is
usually performed using ultrasonic cleaning and/
or vapor degreasing. To improve adhesion,
vapor honing might follow. During the coating
process, operators must maintain surface cleanli-
ness to prevent particulates from accumulating in
the deposit. Manufacturers use mild acids or
gases to remove oxide layers formed during heat-
up. Post-treatment can include heat treatment to.
facilitate diffusion of the coating material (EPA
1995). ,
Companies use CVD mainly for corrosion and
wear resistance. CVD.usually is applied to
obtain specific properties that are difficult to'
obtain with other processes. CVD's ability to
control the microstructure and/or chemistry of
the deposited material makes it important for
some applications. The microstructure of CVD .
deposits depend on the chemical makeup and
energy of atoms, ions, or molecular fragments; '
chemical composition and surface properties of
the substrate; substrate temperature; and pres-
' ence or absence of a substrate bias voltage. The
most commonly used metals in CVD coatings
are-nickel, tungsten, chromium, and titanium
carbide (EPA 1995). .
Companies also use CVD to deposit coatings and
to form foils, powders, composite materials, free-
standing bodies, spherical particles, filaments.
and whiskers! The majority of applications are
in electronics production including structural
applications, optical, opto-electrical, photovol-
taic, and chemicalindustries. Startup costs are
high (EPA 1995). .
References
Davis, Gary A. et al. 1994. The Product Side
of Pollution Prevention: Evaluating the Potential
Safe Substitute. Cincinnati, OH: Risk Reduction
Laboratory, Office of Research and
Development. ,
EPA 1995. Waste Minimization for Metal
Finishing Facilities. Washington, DC: Office of
. Solid Waste./
Freeman, Harry J. 1995. Industrial Pollution
Prevention Handbook. New York, NY: McGraw
Hill, Inc.
Gansert, Daren, and George Grenier. 1989.
Substituting Thermal Spraying for Electroplat-
ing-
159
-------
C:"»:*' 3 A r*'"J; « M«trajj a? Metal Deposition
.\kuil H osw .\fui!ng<.'iii<.'iit Alternatives.
Pasadena. CA: Alternative Technology Section,
Toxic Substances Control Division. California
Department of Health Services.
Kirk-Othmer. 1^87.
160
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Design of a Modern Metal
Finishing
Rarely do technical assistance providers have
the opportunity to assist a facility in design-
ing or redesigning their shop. However, if this
opportunity does arise, some key points should
be incorporated in the layout and design of the
facility. The following section provides, informa-
tion on designing the overall facility and key
items to consider in tank design.
The first step in designing a modern shop is
containing chemicals so that the likelihood of
spills and property contamination is minimized.
Achieving this involves the following general *
requirements:
Process islands
Proper rinse tank design '
Bath makeup transfer systems
Rinse-to-rinse transfer systems .
Enclosed waste lines v
Secondary containment
-Shop design
Facility maintenance
Each of these characteristics is described in the
following sections. . -'
Process Islands
In the past, metal finishers generally designed
their shops with the cleaning line in one area, the
acid room in another, and the plating process in a
third. Operators carried work dripping wet from
one area to another with wastewater conse-
quently tracked around the facility. In designing
a facility, work should ideally enter the process
linexiry, stay on a single wet-processing island,
and dry before leaving that island and entering
the next process. Each processing line must be
independent and self-sufficient with its own
cleaning, pickling, plating, and post-treatment
tanks (Mooney 1994). ..
Rinse Tank Design
Rinse tanks used in the process islands also
should be properly designed. Proper rinse tank
design is a,basic component of a water conserva-
tibn program. If the tanks cannot provide
adequate rinsing, conservation techniques will be
ineffective. Good rinse tank design is based
upon the following concepts:
*" Agitate rinse tanks using an oil-free,, low-
pressure regenerative blower. Good
mixing ensures efficient equilibrium of
rinse water and part design.
"> Add water to,the final rinse tank atlhe
bottom of the rinse tank., The water feed
should be protected by a syphon breaker
and should be equipped with a flow
restrictor. Individual water,meters,also
might be incorporated.
Y Eliminate accidental tank overfill by using
automatic level controls.
Design process lines with segregated spill
controls.
» Minimize external piping and pumps.
(Hunt 1988)
Bath Makeup Transfers
The, methods for handling the transfer of liquids
among tanks and making up of fresh water varies
across facilities. The most primitive method is
the use of buckets and hoses. Unless operators
are conscientious, this method easily can result
1 in overflows. If tanks are filled to less than
adequate levels, the rinse will not be able to
-clean workpieces. Proper piping and valves to .
handle these problems are inexpensive and
should be considered standard equipment (Hunt
1988).
161
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0' 1 Me-* Meul Finishing Fjcilicy
The best method to transfer bath makeup, either
from a rinse tank or other tanks, is to incorporate
a small pump that is activated by a "dead-man's"
Switch. As long as the switch is depressed,
transfer occurs. If the operator leaves, the
transfer is shut off automatically. The best
pumps are magnetically driven and seamless to
preclude leaks. These systems are generally
available in the range of $200 to $300; the switch
is approximately S50. The complete system
including piping and wiring should cost approxi-
mately S500 (Hunt 1988).
In countercurrent rinsing, rinsewater makeup
comes from the final rinse tank. The simplest
\vay to maintain proper water levels for these
systems is to have a local float control valve in
the first rinse. This valve is similar to a toilet
float valve but is designed to control the water
level in the. rinse tanks with the discharge side of
the valve piped to the last rinse. The flow to the
final rinse should be no higher than actually
required. A small fixed valve or discharge pipe
can limit the flow. Facilities also can use an
orifice in the line to the valve. Putting a hand
valve on the inlet side of the water control valve
for shutoff during non-operating hours is a cost-
effective solution. Systems to automatically
control makeup water are inexpensive to buy and
easy to install. The float valve should cost $50
to $ 100; the entire system costs approximately
S300 including connections and labor (Hunt
1988).
Rinse-to-Rinse Transfers
The optimum equipment system for transfers
among rinse tanks is a weir box and baffle
arrangement. In this system, the rinse level is
controlled by diverting overflow water into a
weir box that contains a baffle system. This box
is piped to the bottom of the next rinse tank. The
baffle height in each tank should decrease about
I inch from the preceding tank. When parts are
immersed in a tank and the level rises, rinsewater
cannot flow into the cleaner rinse tank and flow
, can enter the box area only. The same result can
be achieved by installing baffling between the
compartments of rinse tanks. A facility also can
use a single baffle overflow, but this method is
not normally adequate because the liquid from
the surface of one tank simply goes to the surface
of the next. A'more effective technique is a
double baffle. Liquid overflows the first baffle,
which controls tank, level, then flows down a slot
that is created by a second baffle to the bottom of
the next tank. Baffles should be placed '/z to 1
inch apart. The second baffle must be higher
than the liquid level and should stop short of the
bottom of the next tank to allow liquid entrance
(Hunt 1988).
An important feature of a well-designed baffle
system is that liquid proceeds from the top of one
tank to the bottom of the next to avoid stratifica-
tion of water layers. Also, each successive tank
level (going toward the process bath) must be
lower by at least the maximum increase in water
level that is anticipated when parts are immersed
in the tank. In cases where only separate tanks
are available, the solution is simple: assuming
liner damage is not an issue, the plater can
simply drill a hole at the top and bottom on the
same side of each tank-and install soft-sealed,
screw-in bulkhead fittings (Viton seals are
available for highly corrosive situations). The
final rinse "tank normally does not need a bottom
fitting. The first tank does not need a top fitting
unless it is to control water levels by overflow.
Once holes are drilled and bulkhead fittings
installed, install pipes from the top of one rinse
to the bottom of the next, using in most cases
1!/:- or 2-inch fittings unless the counterfiow is
small (Hunt 1988). .
Enclosed Waste Lines
Traditionally, plating shops often had trenches
into which wastewater and waste solutions flow.
This setup allowed toxic materials to seep into
floor coatings and then leach into the ground.
Most floor coatings go unmaintained for years or
decades and, because the coating is on the floor
with no observable dry space, operators are not
able to detect leaks before damage is done.
Allowing wastewater to flow into open trenches
almost guarantees that the ground below will
eventually become contaminated. Conveying
waste in enclosed pipes is preferred. The pipes
should be elevated off the floor, creating a space
between the bottom of the pipe and the floor that
can be checked for leaks. While few plating
shops use double containment piping, design of
any shop'should allow enough space in the
162
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Chapter 9: Design of J -Modern Me;j; Fln!S.-;rg Fjaiicy
trenches for double contained piping to be
installed in the future (Mooney 1994),
Secondary Containment
Valves and piping occasionally fail and tanks'get
overfilled. For this reason, as well as compliance
with local sewer codes and OSHA safety rules, '
secondary containment is becoming increasingly
necessary. Some platers believe that 'a curbed
and coated floor is a good secondary contain- -
ment device, however, plastic containment pans
are often a better approach for two reasons.
First,-a leak in a containment pan elevated off the
floor is visible and can be corrected before.
contamination of the ground occurs while a
breech in a floor coating is almost undetectable.
Second, employees must understand that the
floor must be dry./ Installing a floor that is
designed to be wet appears to encourage operator
.' sloppiness. Alarm horns also should be installed
to detect, liquids in floor sumps or containment
pans (Mooney 1994)'. :
Shop Design
Materials
The use of the right materials is key to a modern
shop. Steel tanks and catwalks can be essentially
unmaintainable. Extensive rust.and corrosion
can be costly, condemn housekeeping programs
to failure, and demand impossibly high mainte-
nance levels. Even worse than steel is aluminum
and aluminized or galvanized materials because
they corrode. In some environments, these types
of products have a relatively impervious skin, but
in a humid and acidic plating shop, Aluminum
and zinc accelerate corrosion. Steel bolts, nuts,
and washers should riot be used in a plating tank.
Where a facility cannot easily use plastic,
stainless steel hardware should be a minimum
requirement.
More appropriate for use in a finishing facility is
polyvinylchloride (PVC), polypropylene, and
proper grades of fiberglass. These Materials will
last indefinitely in most plating environments
without significant maintenance. Metal electri-
cal conduits, pipes, pipe support clamps, and
patent channels can be impossible to maintain in
a plating environment. When ma'de of plastic,
these items can be installed and forgotten and,
'with'occasional cleaning, will perform like new
for'many years.
Depending on the process chemistry, nickel
plating the anode and cathode rods and saddles is
usually advantageous and results in improved
appearance, corrosion resistance, and durability
over copper. The copper in bus runs can be
lacquered to prevent corrosion and to enhance
cleanability (Mooney 1994). ,
Lighting
Trying to save energy at the cost of inadequate
lighting is inefficient in a metal finishing facility.
The energy requirements for lighting a plating
shop are minimal compared to rectification and.
tank heating. Inadequate lighting often can result
in increased reject rates. Appropriate lighting
' actually saves energy. In many areas, electric '
utilities help pay for energy-efficient lighting
fixtures (Mooney 1994).
1 ligh-prcssure sodium is adequate for outdoor
lighting at night, but for most operations, lighting
should be white, not orange. Fluorescent light-
ing is adequate, but metal halide lights are even
" better. These lights can be mounted in the rafters
so that their exposure to corrosive tank fumes is
lessened, reducing the need for constant cleaning
and maintenance. Another option facilities
should consider is natural lighting (Mooney
1994).
Color
Bright paint in varied colors can imply a sense of
organization and purpose. Acid tanks .could be
painted bright red while acid rinses could be
painted bright pink. Electrical panels should be
blue enamel, moving parts OSHA orange, and
aisles yellow. Ceilings and walls probably should
be brilliant white not only for a clean appear- .
ance, but also, for reflectivity (Mooney 199.4).
Facility Maintenance
A plating shop that is spotless will have far less "
trouble with the regulators and the public.
163
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1 **-' ^
Meul Finishing Facility
While enforcing a program of regular
cleaning is important, the shop also should be
designed so that cleaning is easy and practical:
Design the process islands for easy
access to all areas of the equipment.
When one side or end of a tank line is
inaccessible because it is against a wall,
cleaning and maintaining can be impos-
sible or dangerous. Platers should
maintain aisles between walls and
Ihe process lines.
4. Elevate tanks to a minimum of 12 inches
off the floor so that the underside of the
tanks can be readily inspected and
maintained and all areas can be swept
and mopped. If maintenance staff have
to climb ladders or install temporary
scaffolding to gain access to an area,
that area probably will not be cleaned
and maintained properly. Permanent
access platforms can be the solution.
Shape the contour of the floor and design
of the walkways so that the amount of
structure to clean, coat, and maintain is
minimized. Strive for an integrated
design where each piece of structure
serves multiple purposes rather than
tacking on this and that.
New shops should be planned with high
' headroom. Exhaust ventilation is neces-
sary for safety reasons as well as to
maintain cleanliness. Designing a draft-
free environment when high air-flow rates
are used in a shop with low headroom
can be impossible. Additionally, a high
headroom shop reduces corrosion of the
ceiling panels and roof supports, keeping
the work environment cleaner and easier
to maintain and providing better lighting
and cleaner air for employees (Mooney
1994).
References
Hunt, Gary. 1988. Proper Rinse Tank
Design. Raleigh^ NC: North Carolina Office of
Waste Reduction.
Mooney/Ted E. 1994. Plating Shops for the
'90s and Beyond. Plating and Surface Finishing.
January, pp. 35-37.
164
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-------
-------
Index
acid bath reuse 57 " ' , . '
acid cleaning 48, 49, 57, 124 ', .'
acidsorption 10, 57, 126, 147
agitation 46, 60, 93, 105, 117, 118, 119
air knives 114, 117, 118 : '
alkaline cleaning 47 _ ,
aluminum finishing 82. 107 ;
anodic cleaning 49 ;
anodizing 4, 16, 17, 68, 82, 86, 88,. 99,
101, 102, '146, 148, 154
antiquing. See blackening
aqueous cleaning 47
atmospheric evaporators 81, 132, 133
autophoretic coating 81 '",
B
4, 65, 67, 70, 113, 114, 117,
barrel plating
128 ' - ' _. .
blackening 101
blackhole process 95 '
brass plating 62 -
brass pyrophosphate 62
brass pyrophosphate-tartare 62
C . '_ '
cadmium acid fluoroborater 66
cadmium plating 7, 15, 61, 63, 67, 68
carbon technology 95
carbon treatment 58, 60, 138
carbonate freezing 58, 59 : .
case hardening 4. 5, 71, 154:
cathodic cleaning 49
chemical recovery 10
chemical vapor deposition 9, 153. 154, 159
chromating 4, 41,, 61.,82, 97, 101. 102.
103, 104, 120
chromic acid anodizing 82; 98, 100, 150
chromium plating 15. 49. 55,^ 82, 86, 88. 150
cladding 5. 154, 158
Clean Air Act 17, 20. 43, 82
cobalt/molybdenum 102 -.." '
conductivity cells 122, 123. 124.
contact time 118, 119. 121 i
copper acid sulfate 70, 71
copper alkaline 70, 71
copper fluoroborate 71 .:.
copper plating 57. 68, 69, 72
copper pyrophosphate. 70, 71, 73
CorroBan 68
countercurrent rinsing 32, 91, 119, 120, 130,
162 .
cyanide plating 22,"60, 66, 70, 75, 77, 121
detonation gun 155
diffusion dialysis 57, 126, 143, 146
dragout reduction 9, 30, 55, 113
dragout tanks 91, 114, 117
drainboards 114,'116
dummy plating 56, 59, 129
'electric arc spraying 156 .
electrocleaning 42, 48
electrocoating. -63'
electrodialysis 10, 72, 89, 91, 94, 10.0, 125,
126. 127, 135, 143, 145, 146 .
eiectroless copper 95, 128, 132-- j.
electroless nickel 59, 83, 87, 89, 93, 96, ,
97, 128, 132 .
electroless plating 2, 4. 21, 55, 92, 94,
117,134
electrolysis 10, 57, 58, 59, 88, 125, 149
electrolytic recovery 50, 72, 78, 91, 94, 128
electropolishing 5, 41, 97
electrowinning 10. 74, 78., 126, 129
employee training 9, 24, 154
evaporators 81, 126, .130, 131, 132, 133
filtration 56, 58. 60. 79, 121, 134
ftame spraying 155
galvanized coatings 5
Gardolene VP 4683 102
gold plating 74, 75
goldsulfite 75
H. : ' -..'. ." " .;.'.-
hard coat anodizing 98
.hexavalentchromium 4, 15, IB, 56, 82, 88
high-velocity oxy fuel 155
housekeeping 27. 35. 36. 53, 80. 94, 163
hydrochlorofluorocdrbons 45
165
-------
I
immersion plating 4, 97, 98
Inventory management 35, 37
Ion exchange 10. 72. 78. 89. 91. 94, 100.
125, 128. 140, 141, 142. 144
ion implantation 9, 154, 156, 157
loo transfer 10. 148, 149
ion vapor deposition 68, 85, 99
R
racking 43, 114/115, 116
RCA Silver 77
RCRA 17, 22, 125
reactive rinsing 57, 121
reverse cleaning 49
reverse osmosis 10, 72, 73, 76, 81, 92, 125,
135, 137, 138, 139
rinsewater recycling 123, 124, 125
taser ablation 50
laser cladding 158
leak prevention 35, 36, 91
M
membrane electrolysis 10, 57. 88, 126. 149
membrane filtration 134
metal recovery 76. 92. 94. 123. 125. 126,
144
metal spray coatings 85
metallic coatings 5, 6. 156 '
methyl siloxane 45
mlcrofiltration 10, 12. 47, 134. 135, 136
mist suppressants 86
N
N-methyl-2-pyrolidone 45
hanofiifration 134, 135
NESHAP 18
nickel plating 57. 73. 82. 89. 90. 91, 92,
121, 128, 139. 146. 163
nickel tungsten 84
non-chromate passivation 103
palladium 75. 90. 95, 128, 157
passivation 4, 97, 103, 104. 105. 146
periodic cleaning 136
pH Meters 123
pH meters 37, 123
phosphating 4. 41, 97, 105. V06
physical vapor deposition 85, 156
pickling 2, 6. 18, 58. 94, 146, 161
plasma cleaning 51
plasma spraying 72, 156
plating solution concentration 54
polymer filtration 79
porous pots 89, 148
precipitation 47, 55, 58, 59, 125, 138
pressurized gas 50
process bath operating temperature 54
SANCHEM-CC 103
SBAA 104
semi-aqueous cleaning 48
silver 50, 76. 77. 78, 127
silver ammonium 77
silver plating 15, 76, 78
solvent cleaning 43, 44
. spill prevention 35, 37
spray rinsing 122
sputter deposition 72, 158
sputtering 9, 85, 154, 156, 158, 159
static rinse tanks 117, 120
static rinsing 120, 121
stripping 4, 19, 22, 41, 107, 108, 154, 158
sulfuric acid anodizing 22, 98, 99, 102, 147
supercritical fluid cleaning 50
tank covers 88
thermal spray coatings 9
TRI 17, 23, 69
trivalent chromium 18, 82
U
ultrafiltration 46, 47, 79, 134, 137
ultrasonic cleaning. 159
W '
warm rinsing 121
water quality 35, 38, 41, 42. 119
wetting agents 45. 55. 88, 90, 155
withdrawal rates 115
zinc acid chloride 79, 81
zinc alkaline 61. 79, 80
zinc alloys 66
zinc chloride 61, 67, 98, 127
zinc plating 22, 79, 81
zinc-cobalt 63, 66, 67
zinc-iron 65. 66. 67
zinc-nickel 63. 64. 66. 67. 142
zirconium nitride 62
zirconium oxide 104
166
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Appendix A
Glossary==
abrasive blasting = A method to remove brittle
materials such as millscale oxide, remains of
paint, etc. More generally referred to as grit
blasting.
acid = Chemical substance whose water solu-
tions exhibit a pH less than 7. -.
acid descaling = An alternative name for "pick-
ling" a process using acid to dissolve;oxide and
scale ' . , ':
activation = Process of removing last trace of
oxide on a metal surface and a thin layer of the
metal itself to ensure that the metal surface to be
plated is elcctrochemically active, (see "etch-
ing") "" .' . .. ;'.."
addition agent = Material used to modify the,
character of the deposit, usually used only in
-small amounts.
alkaline descaling= A chemical process for
removing scale. A typical descaling solution
uses caustic'soda with additives such as deter-
gents and dictating agents. "
alloying = The addition of one metal to another
metal or non-metal or combinations of metals.
For instance, steel is an alloy of carbon and iron. .
Other metals are added to steels to impart
specific characteristics like strength or corrosion
resistance.
"Alochrom" = A proprietary process applied to
aluminum and its alloys to improve corrosion
resistance or to prepare surfaces for painting.
Treatment produces an adherent aluminum oxide
with some absorbed chromate.
'amalgamating = Process in whichialloysare
formed with mercury such as gold,:silver, iroin
copper and aluminum. Due to the toxicity of
mercury, use of the technique is declining
amorphous = Structure that is non-crystalline or
without a regular structure.
ampere = The current that will deposit silver at
the rate of 0.0011180 grams per second. Current
flowing at the rate of one coulomb.
annealing = A heat treatment process which may
be applied to all metals to soften them.
anode = The positive electrode in electrolysis, at
which negative and positive ions arc discharged.
positive ions are formed, or other oxidizing, "
reactions occur.
anodic coating = A protective, decorative, or
functional coating formed by conversion of the
surface of a metal in an electrolytic oxidation
process.-
anodic etching = A form of electrolytic etching
where the workpiece is being etched is anodic in
- the electrolytic circuit (in electroplating, the
workpiece is the cathode). ,:
anodizing = A process generally applied to
aluminum and its alloys to produce an adherent
oxide film to impart corrosion resistance or
surface hardness. . , . -
aholyte = The portion of an electrolyte in the
vicinity of.the anode. In a divided cell, the
portion of the electrolyte that is on the anode side
of the diaphragm.
aquablast = A surface cleaning process which
can be applied to any material where an abrasive
material is suspended in water. The resulting
slurry is pressurized and ejected through a
nozzle. .Since higher pressures can be used in
this process than in other types of blasting,
surface metal can be quickly removed and
leaving a good surface finish. . - .
167
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barrel plating (or cleaning) = Plating or clean-
ing in which the \\ork is processed in bulk in a
rotating container.
base metal = A metal that readily oxidizes or
dissolves to form ions. The opposite of a base
metal.
basis metal - Material upon which coatings are
deposited.
blasting » See listing by specific medium (e.g.,
abrasive, dry, grit, shot, aqua)
borax treatment» A method of coating steel
with a thin film of dry lubricant. After surface
cleaning or acid pickling, the material is placed
in a hot borax solution, allowed to come to
solution temperature and removed and dried. The
resulting alkaline coating imparts lubrication for
subsequent drawing operations and provides
minor corrosion protection.
bonding = A high temperature process used for
surface hardening of mild low carbon steels.
' ,, f
bright chrome plating = Decorative chromium
plate deposited directly on a nickel plate sub-
strate.
bright dip= A solution used to produce a bright
surface on a metal.
bright plating = A process that produces an
electrodeposit that is luminous.
bright throwing power = The measure of the
ability of a plating solution or a specified set of
plating conditions to uniformly deposit bright
electroplate upon an irregularly shaped cathode;
in particular, those areas that are recessed and
have a low current density area.
brightener = An addition agent that increases
the brightness of the deposit. '
bronzing = A chemical process generally
applied to steel to impart the appearance of
bronze (antimony chloride in hydrochloric acid
followed by ammonium chloride in dilute acetic
acid). The resulting "bronze" film does not have
the corrosion resistance of true bronze. ,
brush plating = A method of plating that is
applies the metal with a brush or pad within an
anode that is moved over the cathode to be
plated.
buffing = A specific type of mechanical polish-
ing using a high speed disc made from layers of
cloth, leather, or plastic impregnated with an
abrasive. The workpiece is pressed against the
disc for buffing.
building up = Electroplating for the purpose of
increasing the dimensions of an article.
''. burnishing = A form of metal finishing where
the surface is treated mechanically so that no
appreciable metal is removed but the surface is
smoothed.
burnt deposit = A rough or otherwise unsatis-
factory deposit produced by the application of an
excessive current density and usually containing
oxides or other inclusions.
^
carb'onitriding = A surface hardening technique
for steel in which a hydrocarbon (e.g., butane or
propane) and ammonia are injected into a
furnace (750 - 800 degrees Celsius) containing
the workpiece. The resulting atomic carbon and
nitrogen react with the surface iron to form iron
carbides and iron nitrides.
carburizing = A process used for certain types
of ductile steel wliich increase surface hardness
' from two to six times. It generally is conducted
in a heat resistant box containing an atmosphere
of carbon monoxide, carbon dioxide, water
vapor, methane, hydrogen, and butane in correct
ratios and heated to 900 degrees Celsius.
case hardening = A family of surface hardening
processes generally applied only to steels (see
specific listings for carbonitriding, carburizing,
chromium plating, cyanide hardening, electroless
nickel plating, and nitriding).
casting = A general term covering a production
technique where any metal is heated until it is
molten and then poured into a mold, allowed to
cool and solidify.
168
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catalyst = An element or ion that promotes or
assists in a reaction without affecting'or chang-
ing the element. ; ' ,
cathode = The negative electrode in.electrolysis
at which positive ions are discharged, negative
ions are formed, or other reducing actions occur,
cathodic etching = A technique applied to steel
.workpieces where the workpiece is rn'ake the
cathode in an electrolytic cell with sulfuric acid
as the electrolyte. The anode will generally be
lead or stainless steel. When a current is applied,
hydrogen will be evolved at the cathode and the.
surface metal oxide will be reduced. The tech-
nique is usually applied immediately prior.tp
electroplating.. ..-,...
cathodic protection = A technique .applied to
steel where metals anodic to iron (e.g., zinc,
aluminum, magnesium) are applied to the surface
on the steel %vorkpiece to provide a corrosion
resistant surface. The process relies on the fact
that where a cell exists between two metals with
an electrolyte, one of the metals will corrode and
in the process of corroding protect the other
metal. ; - '.,. ; ,
cation = A positively charged ion.
chemical polishing = A process carried out on
mild- and low-alloy.steel, stainless steel/alumi-
,num. Special solutions are'used to attack the
surfaces of these metals in such a manner that the
peaks or corners are affected in preference to the
concave surfaces. The result is a general
smoothing of the surface. - ,
chromate coating.(chromating) = A corrosion
protection technique which has many variations
and can be applied to steel, aluminum, magne-
sium, and zinc. It results in the formation of
metal oxide on the surface of the workpiece
which reacts to form metallic chromates.
Chromating of aluminum and magnesium
improves corrosion resistance considerably..
With steel it is much less permanent.
chromium plating = This electrodeposition of
chromium is generally applied to steel in all its
forms. It is*usually done for decorative purposes
(bright chromium) or to provide a hard surface
for engineering purposes (hard chromium).
Chromium plate is nearly always deposited on
top of a nickel deposit. The-nickel deposit
supplies corrosion resistance.
chromizing = A treatment applied to mild- and
low-alloy steel only. It is a surface diffusion
process in which chromium is alloyed with iron
to create a chromium-rich surface layer. Thor-
' oughly cleaned workpieces are placed in a heat
resistant box with a proprietary powder, of an'
unstable chromium compound. When the box is
heated to over 1,000 degrees Celsius, the chro-
mium decomposes into an active state \vhich -
reacts with the iron to produce an alloy. .The
longer the workpiece is retained in the heated
box the deeper the chromium alloy penetrates. -
cold galvanizing = A term sometimes used to
differentiate between electroplating zinc on steel
from the hot dipping,of steel in molten zinc.. It
can also refer to a form of painting with special-
ized paints which result in a film of up to 90 %
powdered zinc. The purpose of all these pro-
cesses is to provide corrosion resistance.
coloring = The production of desired colors
onto a the workpiece using chemical or electro-
chemical action.
-- « , . .
color anodizing = A process used only on
aluminum and its alloys using dyes to color the
anodic film, the anodic process produces a
porous film which when fresh will absorb dyes:
The anodizing is carried out using the sulfuric
acid process. After completion of the anodizing
the workpieces~are rinsed in.cold. water and
placed in a dye solution. After dyeing, the
workpieces are again rinsed in cold water
.followed by immersion in nearly boiling water.
The heat seals the anodic film and the surface
remains permanently colored.
complex ion = An ion composed of two or more
ions or radicals, both of which are capable of
independent existence, that imparts the property
of solubility necessary for electroplating.
complcxing agent = A compound that will
combine with metallic ions to form soluble ions.
See complex ion. '
169
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concentration polarization = The increase in
solution concentration at a membrane surface
because of solution retentation.
contact plating = Deposition of a metal with the
use of an internal source of current by immersion
qf the work in solution in contact with another
metal.
contact tin plating = A form of electroless
plating commonly used in the printed circuit
board and general electronics industries to
improve solderability of workpieces. The
workpieces are immersed in a hot chemical
solution containing unstable tin compounds. The
tin reduces on the surface of the workpieces.
conversion coating = A coating produced by
chemical or electro-chemical treatment of a
metallic surface that provides a superficial layer .
containing a compound of die metal; for ex-
ample, chromate coatings on zinc and cadmium
or oxide coatings on steel.
copper plating » Copper is electrode-posited for
conductivity in the printed circuit and electrical
industries and for decorative purposes. There are
four basic types of copper plating solutions;
copper sulfatc, copper cyanide, copper pyrophos-
phatc. and copper fluoroborate.
corrosion * Corrosion occurs in all metals at
some time and can be divided into four basic
forms. Room temperature oxidation, the most
common form, is most obvious in mild and low-
alloy steels. The process is accelerated dramati-
cally by comparatively small amounts of .
contaminants like chloride, sulfate, and fluoride.
When exposed to high temperatures, metals will
almost invariable result in oxidation of metal
surfaces. Chemical corrosion is the result of
attack by acids or alkaline compounds which
dissolve the metal surface. Electrolytic corrosion
occurs when two metals in contact with each
other have different electrode potentials. It is a
major contributor to most of the corrosion found
in steels.
or deep holes (to be distinguished from throwing
power).
cromodizing = A name given to the chromating
of steel where a film of iron chromate is formed
on the surface. The corrosion protection pro-
vided by this treatment is of a very low order.
"Phosphating" and oiling will probably provide
superior resistance without the use of chromium.
current density (cd) = Current per unit area;
usually expressed in amperes per square foot or
amperes per square decimeter.
cyanide hardening = A surface hardening
technique which uses molten cyanide salts to
give workpieces a case containing carbon and
nitrogen. Temperatures of 650 degrees to 800
degrees Celsius must be maintained for 20-30
minutes to be effective. The high toxicity of the
cyanide makes this an expensive process due
high treatment costs.
DC (Direct Current) - A flow of electricity
from a positively charged terminal to a nega-
tively charged terminal.
degrcasing= A form of cleaning which gener-
ally uses chlorinated solvents. In the most
common form, a liquid solvent is heated in an
open topped container. As it boils a hot vapor
rises above the liquid. The vapor is held within
the container by means of a cooling coil which
runs around the inside of the container a short
distance below the rim. This cold zone causes
the vapor to condense and return to the sump for
rebelling continuously distilling itself.
When any cold component is placed in the
container, the vapor immediately condenses on
" the surface. The solvent dissolves any grease on
the surface and as more solvent condenses it runs
off the workpiece carrying the soluble soils into
the sump.
deposit = Refers to the metal coating deposited
on the workpiece.
tions, to deposit metal on the surfaces of recesses
descaling = This term describes a process that
can be applied to all materials to remove scale.
Scale is generally produced during manufacture
170
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or storage.. Sometimes it is easily seeii in the
formof rustormiliscale, in-other instances it is
inconspicuous. Various methods are used/for
this process including blasting, pickling, acid or
alkaline sodium hydride treatments, and polish- -
ing. . .-'-.
die-casting = A method of casting in which
molten metal is poured, sometimes under pres-
sure, into a mold or die. The die is made of
metal and immediately after solidification of the
casting the die opens and the casting is ejected,
diffusion coating = An alloy coating produced
by applying heat to one or more metal coatings
deposited on a metal. . .
distribution = Refers to the. uniformity of the
metal deposited from a plating process.
dragin = The water or-solut.ion that'adheres to
workpieces introduced into a bath.
" ' '"">."'
dragout = The solution that adheres to a .
workpiece removed from a bath.. '
dry blasting = A general name given to any
form of blasting where the abrasive agent is not
carried in water.
dry-form lubrication = A form of painting
applied to steel surfaces of workpieces subject to
light wear or abrasion. It generally uses colloidal
or molybdenum disulfide carried in 'a phenolic
resin. '
ductility = Refers to the flexibility of an electro-
plated deposit; this parameter is critical when
bending and forming operations occur after
plating. .
dummy (dummy cathode) = A cathode in a
plating solution that is not to be used after
plating; often used for removal or decomposition
of impurities.
effluent = Any gas or liquid emerging from a
pipe or similar outlet; usually refers to" waste
products from chemical or industrial plants as
stack gases or liquid mixtures.
electrocleaning = An electrochemical cleaning
process by which a workpiece is first made the
cathode in an electrolytic cell. When current is
applied, the generation of hydrogen gas from the
electrolysis of water at the surface of the
workpiece results in a highly efficient scrubbing .
action: Following initial treatment as a cathode
the circuit is reversed so that the workpiece is the
anode. Oxygen gas^ which is generated at the
surface produces a final cleaning action.
electrode = A conductor through which current
enters or leaves an electrolytic cell at which there
is a change from conduction by electrons to
.conduction by charged particles of matter or vice
versa. . -
electrode potential = The difference in potential
' between an electrode and the immediately
adjacent electrolyte. -
elcctroforming = A specific form of electroplat-
ing used where intricate shapes and relatively
thin metal deposits are required. Molds of ;
plastic, wax, or sometimes metals are made
conductive by application of carbon or metallic
powder and are pjated by conventional methods.
Nickel, copper^ or precious metals are generally
selected for this form of plating. The mold is
generally removed at the completion of the
plating process by one of a number of methods
depending on the material from which the mold
is constructed. '
clectrogalvanizmg = Electrodeposition of zinc
coatings.
elcctroless plating = The process of depositing
metal from a water-based solution using chemi-
cal catalysts for the metal cation reduction
process. In this process no external potential
(electrical current) is applied.
electrolyte = A conducting medium in which the
flow of current is accompanied by movement of
matter;mdst often an aqueous solution of acids,
bases, or salts, but includes many other media
such as fused salts, ionized gases, and some
solids.
electrolysis = Production of chemical changes
by the passage of current through an electrolyte.
171
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electrolytic etch = A technique generally applied
to steels which attack the surface to produce a
clean, oxide free material. It is often used prior
to electroplating, especially chromium plating.
Since it preferentially attacks edges it will open
us small cracks in the surface of the workpiece.
Due to this, this process can be used to inspect
finishes for flaws.
electrolytic polishing = An electrochemical
process usually applied to steels, aluminum, and
aluminum alloys. This process produces .a
surface that is bright and highly reflective. In
most instances this is used for decorative pur-
poses and is often used in conjunction with some
other form of metal finishing such as anodizing,
plating, or lacquering.
electroplating = The process of depositing metal
from an aqueous solution using an external
potential (electrical current) for the metal cation
reduction process; usually, the potential applied
is DC, but can approach controlled AC with
some sophisticated switching devices (pulsed
electroplating).
electro-osmosis - See "reverse osmosis"
clcctrorcfining = The process of anodically
dissolving a metal from an impure anode and
depositing it cathodically in a purer form.
olcctrowinning = The production of metals by
electrolysis with insoluble anodes in solutions
derived from ores or other materials.
emulsion cleaning - A cleaning technique
which acts by emulsifying contaminants. Emul-
sions are mixtures of two liquids, with one.liquid
holding the other in a suspension similar to
colloidal suspension. The liquids will typically
have different polarities and will dissolve
different types of materials. One of the liquids is
usually water arid the other will have non-polar
properties. They can therefore be used to
dissolve non-polar contaminants like oil and
grease from metal surfaces.
etching s Etching is sometimes used a surface
preparation technique prior to electroplating or
for removal of metal such as in the printed circuit
industry where material not required on the
finished product is removed by a chemical
solution. It can also be used as an inspection
technique due to its ability to accentuate-surface
cracks and defects.
"fcrrostan" process = A method of continuous
electrolytic tin plating of steel strip in which cold
reduced strip is continuously fed through the
cleaning, etching, plating, and rinsing processes.
The solution is generally acid sulfate which
produces a matte finish.
filtration = A means of separation where con- , .
stituents are separated usually by physical
methods.
fire gilt process = A process used exclusively in
the jewelry trade in which gold dissolved in
mercury (gold amalgam) is wiped on surfaces to
be plated. When the article is heated the mer-
cury is driven off leaving a gold film. The
process represents a considerable health hazard
due to the emission of the mercury vapor.
flocculation = The combination or aggregation
of suspended colloidal particles in such a way
that they form small clumps; usually used in
conjunction with additive chemicals (flocculants)
to treat waste water.
fluxing = A process used in the heating of metals
which may be intended to reduce or eliminate
oxidation, confine the products of oxidation.
reduce their melting point, and improve fluidity
of surface metal layers. Fluxing is generally used
in casting, welding, and soldering.
foam blanket = An additive that forms a layer
on the surface of electroplating baths that have
poor anode/cathode efficiency, to prevent any
mist or spray from escaping.
fouling = Deposition of materials on a mem-
brane surface or within the pores because of
soluablility limits (at the surface) or pore size
and/or shape.
free cyanide = (1) Calculated - the concentration
of cyanide or alkali cyanide present in solution in
excess of that calculated as necessary to form a
specified complex ion with a metal or metals
present in solution. (2) Analytical - the free
172
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cyanide content of a solution as determined by a
specified analytical.method. -. :
frosting = A type of metal finishing where a fine
matte finish is produced by using techniques
such as.acid-
etching, blasting, scratch brushing or barreling.
galvanic cell = An electrolytic cell capable of
producing electrical energy by electrochemical
.action.
galvanic protection ~ A general term used in the
corrosion protection of steel. Technically, it
refers to a metal used to protect a metal higher
than itself in electrode potential. Inpractice.it
refers to the use of zinc to protect steel.
galvanizing = A corrosion protection technique
applied only to mild steel, cast iron, and steel
alloys in which workpieces are immersed in
liquid zinc at 50.0 degrees Celsius. A zinc/iron
alloy is formed at the surface of the \vorkpiece
giving it an adherent coating of zinc. Prior to
galvanizing, the metal surface must be in a.state
of moderate cleanliness. This is generally
accomplished by light acid pickling or blasting.
Galvanized coatings,are generally about 0.005 :
inches thick and can give protection for 10 to 20
' years. -..."' '
gilding = A process in which gold is coated on
the surface of another base metal. Gold leaf, a-
layer beaten so thin it is porous to light, is.glued
or beaten onto' the article to be gilded. A similar
method applies a fine gold powder mixed with a
flammable liquid solvent applied to the article
like a paint. The solvent is allowed to evaporate
or in some cases may be ignited.
gold p!ating-= gold has two specific properties
which make it valuable in industrial and com-
mercial uses, it resists oxidation and corrosion to
a very high degree and it retains its attractive
color. The main advantage of gold plating over
other methods of applying gold to surfaces, is
that electroplated coatings do not have pores as
gilded coatings do. This provides significantly
longer lifespans and corrosion resistance. .
grit blasting = A technique'of abrasive cleaning
or surface preparation using sharp particles (e.g.,
cast iron shot, aluminum oxide); It covers such
processes as removal of scale, corrosion, paint
and.other surface films. Use of free silica
presents a health"threat and should be avoided.
hard chromium = Chromium plate for engineer-
ing rather than decorative applications; not
necessarilyharder than the latter, but generally
'thicker or heavier: See "chromium plating"
hard facing = A term referring to processes used
to harden metal surfaces and impart wear resis-
tance by a variety of heat treatments. See "metal
spraying".
HCD (High Current Density) = High amperes
per surface area. .-
hot dip coating = See "galvanizing"
hydrogen cmbrittlement = A defect which
occurs during;the"electroplating process. Atomic
hydrogen is produced at the cathode of the
workpiece being plated. This atomic hydrogen is
extremely reactive and has the capability of
entering the interstices of the metal. Being
unstable in the atomic state, the hydrogen will
combine as rapidly as possible with other.atoms
to form molecular hydrogen. This molecular
hydrogen, having a higher unit volume than
atomic hydrogen results in internal pressure in
.the plated metal.
immersion plating = A plating technique similar
to electroless plating where a more electroposi-
tive metal is dissolved in an electrolyte and is
plated onto the surface of a less electronegative
metal workpiece. The term immersion plating is
used where a deposit is obtained and the plating
process then stops. This is distinguished from
electroless plating where the deposition of the
metal being plated continues to deposit as long as
the workpiece remains in the solution.
inchrom process = see "Chromizing"
indicator (pH) = A substance that changes color
when the pH of the, medium is changed; in.the
case of most useful indicators, the pH range
within which the color changes is narrow.
173
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indium plating = Indium is a metal not un-like
lead but with friction and corrosion resistance
properties that are unique. In fact, the sole
.purpose of indium plating is improving the
friction characteristics of very high-
rated bearings.
ion =" An electrified portion of matter of atomic
or molecular dimensions.
ion exchange = A reversible process by which
tons are interchanged between.a solid and a
liquid with no substantial structural changes in
the solid.
"kanigen plating" = First proprietary process
for electroless nickel plating.
LCD (Low Current Density) = Low amperes
per surface area.
lead plating = lead plating does not have many
common uses except in the production of elec-
trodes for lead acid batteries. Steel which has
been plated with lead is much stronger mechani-
cally and lighter than the same thickness of pure
lead. It is also used as a base layer for indium
plating. Lead plating solutions contain approxi-
mately 100 grams of lead per liter and 40 grams
per liter of fluordboric acid.
leveling = Electrodeposited materials tend to be
concentrated at sharp corners, peaks, and ridges,
due to the fact that current distributed on a
surface will tend to concentrate at these irregu-
larities more than in concave surfaces such as.
recesses. Therefore, when a workpiece with a
rough surface is electroplated, the rate
ofdeposition will be faster on convex irregulari-
ties resulting in an accentuation of the item's
original roughness. To counteract this effect,
additives are added to the electrolyte solution to
produce a polarization effect concentrated at the
peaks and ridges. This polarization effect lowers
the current density at the peaks and reduces
deposition rates. The net result is to smooth or
"level" the surface of the workpiece.
mandrel = A form used as a cathode in electro-
forming; a mold or matrix.
mechanical plating = The application of an
adherent metallic coating by mechanical means
involving the compacting of finely divided
particles of such metal to form coherent coatings.
membrane = A microporous structure that acts
as a highly efficient filter that allows passage of
water, but rejects suspended solids and
colloidals; depending on membrane type, ions
and small molecules might or might not be
' rejected.
metal spraying = The general term is applied to
the spraying of one of several metals onto a
metal substrate. In general, it is intended to
produce three effects. The first, corrosion
protection, usually involves the spraying of zinc
or aluminum on structural steel components. It is
also used on high tensile workpieces., such as
those used in the aerospace industry, that can not
be electroplated due to hydrogen embrittlement.
' The second purpose is "hard facing". Materials
used in hard facing are tungsten bearing-or
tungsten carbide materials, cobalt, and nickel
with small amounts of chromium, and high
manganese chrome materials. These materials
provide significant wear resistance. The third
application is for salvage purposes. When
engineering components are found to exhibit
wear while in service, technical and economic
. considerations may make metal spraying to
replace the wear a better alternative to replace-
ment.
The most common method of metal spraying is
"flame impingement". The technique uses
powdered metal continuously fed into a high
velocity flame. The flame atomizes the metal
powder into a molten,state and the particles are
projected by the energy of the flame onto a
prepared metal surface. Plasma coating is a
similar method which uses radio frequency-
induced plasmas at temperatures up to 30,000
degrees Celsius. This methods use is limited to
high integrity components where excellent
adhesion or sophisticated materials are required.
"Micro-chcm" = A proprietary electrocleaning
process used for "brightening" and "passivating"
stainless steel. It is a form of electropolishing
which gives a considerably smoother and shinier
finish.
1 74
-------
micro-throwing power = The ability of a
plating solution or a.specified set of plating ..
conditions to deposit metal in'tiny pores or
scratches. . . . '
mil = One thousandth of an inch. '
nickel plating = A very common form of
electrolytic deposition that is generally used as
an undercoating for subsequent deposits. There
are three common solution for nickel plating:
Watt's solution, Sulfuric acid, and electroless
plating. '
nitrlding = A. surface hardening process that is
applied only to certain types of steel.. This
process creates a finish that is the hardest surface
attainable using heat treatment processes. The
process consists of maintaining a workpiece in a
500 degree Celsius ammonia atmosphere.for up
to 100 hours./Under these conditions.atomic .
nitrogen combines with surface iron to form iron
nitride. The nitrogen slowly diffusesaway from
, the surface as long as the proper temperature is
maintained. The resulting case thickness is
.therefore dependent on length of heat treatment.
noble metal = A metal that docs not readily tend
to furnish ions and, therefore, does not readily
dissolve nor easily enter into such reactions as
oxidations; the ^opposite of a base metal. .
nodule = A rounded projection formed on a
cathode during electrodeposition. , '
passivation = The cleaning of stainless steel
with nitric acid to remove carbon and other
impurities. ' .
pH adjustment = The act of changing the pH of
'an aqueous solution by adding acid or caustic.
phosphating =-A process that converts the
surface of a steel workpiece to iron phosphate
jusually prior to painting. Before phosphating, .
the surface of the workpiece must be free of rust
and scale: This is usually accomplished with
acid pickling, mechanical wire brushing, or
. blasting. Phosphating is a relatively short
process, usually 5 to 20 minutes. Workpieces are
generally painted or chromated wiihin 24 hours
of treatment since the phosphating provides little
corrosion.resi'stance.. '
pickling = A chemical treatment which removes
oxidebr scale from the surface of a metal. It
most often refers to the use of sulfuric or hydro-
chloric acid to remove scale formed on mild and
low-alloy steel during hot forming operations. .
Treatment of stainless steel or high nickel alloys
is done with hydrofluoric acid, a particularly
hazardous material that must be handled with'
extreme care.
plating = An electroplating or electroless plating
process.
plating range = The current density range over
which a satisfactory electroplate can be depos-
ited.
pulse plating = A method of plating that uses a
power source capable of producing square-wave
current pulses. ,
rack plating = A frame for suspending and:
carrying current to articles during plating and
related operations.
reducing agent = A compound that causes
reduction thereby itself becoming oxidized.
rcflowing = A technique used in the printed
circuit board industry in which a component is
heated in order to melt solder deposits and
causing them to flow. I't produces a bright,
attractive looking material but its main purpose
is for quality control. With reflowing, any defect
on the substrate will not wet, clearly indicating
areas where solder is missing.
rustproofing = A general term that refers to
processes applied to steel. It can include paint-
ing or galvanizingt but most often refers to
phosphating and similar low duty rust
preventatives. -
sacrificial protection = A corrosion protection
technique that uses a metal of lower electrode
potential to protect a metal of higher electrode
potential. This is possible because in the pres-
ence of an electrolyte an electrochemical cell is
175
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established in which the lower potential metal
acts as an anode and the metal that is being
protected acts as the cathode. The anode cor-
rodes and deposits onto the surface of the
cathode. In practice, zinc and aluminum are the
two metals most commonly used for this process.
sealing or anodic coating = A term commonly
applied to any metal process having a subsequent
treatment capable of affecting a previous process
coating in order to reduce staining and corrosion
of the workpiece or to improve the durability of
color of the coating.
sensitizing = A relatively non-specific term used
to cover "a range of metal finishing processes that
improve the treatability of a workpiece for
subsequent processes. It often refers specifically
to a part of electroless plating procedure on
plastics or non-metal surfaces. After the surface
has been etched it is reacted with solution that
deposits a very thin film of a metal or metallic
compound. The surface is then referred to as
sensitized.
silver plating = Silver, the easiest metal to plate,
is deposited for decorative purposes on house-
hold and jewelry items. Sometimes it is used by
the electrical industry where it is plated over
copper to improve corrosion resistance.
solder plating = The term covers deposition of
an alloy of 60% tin and 40% lead that is widely
used in the electrical and electronics industries.
It provides two valuable features, corrosion
resistance and "solderability".
stop-off = Method of protecting portions of a
workpiece from chemical processes. Waxes,
lacquers, or special tapes are applied to areas to
prevent chemical attack or deposition.
strike = (1) A thin film of metal to be followed
by other coatings. (2) To plate for a short time,
usually at a high initial current density.
substrate = Surface material or electroplate
upon which a subsequent electrodeposit or finish
Is made. See basis metal.
surface hardening = A general term referring to
methods for making the surface of steel
vvorkpieces mechanically harder than their inner
portions. Also see: "nitriding", "carburizing",
"cyanide hardening", "carbonitriding".
throwing power = The ability to effect satisfac-
tory coverage in recessed or blind (hole) areas of
a part being plated.
total cyanide = The total content of cyanide
expressed as the radical CN or as alkali cyanide,
whether present as simple or complex ions; the
sum of both the combined and free cyanide
content of a solution.
ultrafiltration = The process that uses mem-
branes to achieve separation of various constitu-
ents; a typical ultrafiltration membrane allows
water, ions, and small molecules to pass through
while rejecting large molecules and suspended
solids.
vacuum deposition = A process in which certain
pure metals are deposited on a substrate. The
technique relies on the fact that, in a vacuum,
pure metals can be vaporized at a low tempera-
ture in a closed container. The.metal'vapor will
.condense evenly on all surfaces to produce a
metallic coating. Aluminum is tjie most success-
fully deposited material, producing a highly
reflective finish.
vapor deposition = (1) Chemical - process for
producing a deposit by chemical reaction.
induced by heat orgaseous reduction of a vapor
condensing on the substrate. (2) Physical - a
process for depositing a coating by evaporating
and subsequently condensing an element or
compound, usually in a higlvvacuum.
wetting agent = A substance that reduces the
surface tension of a liquid, causing it to spread
more readily on a solid surface without it bead-
ing up.
workpiece = The part that is being electroplated
or electroless plated. (
zinc coating = See "galvanizing"
zinc phosphating = A process applied to freshly
zinc plated workpieces that are immersed in a
zinc phosphate solution acidified with
176
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phosphoric,acid. .The-zinc surface deposit is
converted to zinc phosphate. The workpieces are
then immersed in a dilute chromic acid sblutibn
to seal the zinc phosphate'deposits and prevent
rust formation of unsightly zinc oxide. .
zinc plating = Common form of plating used to
provide corrosion resistance for steels. .
zincate treatment = A treatment necessary for
aluminum and its alloys before electroplating.
After cleaning, etching in chromic or phosphuric
acid to remove oxide and dipping in nitric acid to
activate the surface, workpieces are immersed in
a sodium zincate solution! Metallic zinc is.
deposited on the surface of the workpiece. It is
then rinsed and immediately brought the final
plating operation. :
177
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Appendix B
Resource List
the following pages provide further sources of
information on pollution prevention in metal
finishing. Information is provided on regional
information clearinghouses where assistance
providers can locate specific documents on metal
finishing. A list of technical assistance programs
with experience in metal finishing also is pro-
vided. Other federally funded organizations"
working on metal finishing, as well as, metal
finishing trade associations also are listed., A .
list of publications and periodicals and web sites
on the industry also is provided.
Clearinghouses
EPA's Pollution Prevention Information
Clearinghouse
401 M Street, SWMC 7409 -
Washington, DC 20460
(202)260-1023
- Waste Management and Research Center
Library and Clearinghouse
One East Hazelwood Drive
Champaign, Illinois 61820
(217)333-8940 ,
The Northeast Waste Management-Officials'
Association (NEWMOA) Clearinghouse
'' 129Portland Street, 6th Floor
Boston,'MA 02114- ' . 1
(617)367-8555
Toxics Use Redaction Institute
University of Massachusetts-Lowell
One University Avenue
Lowell, MA 01854 . ' .
.(508)934-3275
Waste Reduction Resource Center
3825 Barrett Drive, Suite 300
PO Box 27687
, Raleigh, NC 27611-7687
(919)715-6500 .
Technical Assistance
Programs with Expertise
in Metal Finishing
Arizona Department of Environmental Quality -
Pollution Prevention Program
3,033 North Central Avenue
Phoenix, AZ 85012
(602)207-4210 ' '
ConnTAP '.''':.
, 50 Columbus Blvd., 4th floor
' Hartford, CT 06106
Contact: Bob Brown (860) 241-0777
Delaware Pollution Prevention Program
DNREC
PO Box 1401, 89 Kings, Highway
Dover, DE 19903
.(302)739-3822 " ; , '
! Illinois Waste Management and^Research Center
One East Ilazelwdod Drive
Champaign, Illinois 61820
(217)333-8940 v -
Indiana Pollution Prevention and Site Materials
Institute ; ' ' '
Purdue University ,
1291 Cumberland Avenue .
Suite C-l - .
West Lafayette, IN 47906-1385
Contact: Shayla Barrett (317) 494-6450
Maine Metal Products Association
190 Riverside Street ,
Portland, ME 04103-1073
(207)871-8254 .','...
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Massachusetts Office of Technical Assistance
100 Cambridge Street, Room 2019
Boston, MA 02202
{617)727-3260
j
MnTAP
1315 5th Street SE, #207
Minneapolis, MN 55414
(612)627-4556
NIST Great Lakes Manufacturing Technology
Center
Environmental Services Program
Prospect Park Building
4600 Prospect Avenue
Cleveland, OH 44103-4314
{216)432-5300
North Carolina Division of Pollution Prevention
and Environmental Assistance
PO Box 29569
Raleigh, NC 27626-9569
(919)715-6500
Pacific Northwest Pollution Prevention Research
Center
1326 Fifth Avenue, Suite 650
Seattle, Washington 98101
(206)223-1151
Great Lakes Pollution Prevention Centre
265 N. Front St., Suite 112
Sarnia, ON N7T 7X1 CANADA
Tel: (519) 337-3423
Rhode Island Pollution Prevention Program
83 Park Street
Providence, RJ 02903
(401)277-3434
Solid and Hazardous Waste Education Center
University of Wisconsin - Madison
eiOLangdonStfeet
Madison, WI53703
(608) 262-0385
Other Information Centers
« ... i
Battcllc-Pacific Northwest Laboratory
The Pacific Northwest Laboratoroy (PNL) is a
.public/private partnership between the federal
government and Battelle Memorial Institute, and
includes almost 2 million square feet of consoli-
dated laboratory space. PNL can provide assis-
tance to metal platers in the following areas:
Development of waste acid distillation and
recovery systems used in reclaiming spent
plating and etching solutions
Development of supercritical CO2 cleaning
to eliminate solvent use in fine-surface
preparation prior to plating
* Development of biometic surface coatings
and other advanced materials technologies
that will eventually meet customer's needs
for surface modification and protection
without the need for chromium, cadmium, or
other regulated materials
These technologies can be developed further
with platers through a variety of technology
development and transfer mechanisms, depend-
ing on plater's specific needs. For more infor-
mation, contact Scott Butner at Battelle Seattle
Research Center: (206) 528-3290.
Canadian Pollution Prevention Resource
Centre for the Metal Finishing Industry
This resource offers easy access to technical and
information resources for the metal finishing
industry. Linkages with international informa-
tion resources provide a comprehensive range of
expertise to companies seeking pollution preven-
tion solutions. For more information, call: (800)
667-9790.
The Energy and Manufacturing Technology
Assess Project
The Energy and Manfacturing (EEM) project is a
2 year cooperative agreement between govern-
ment and industry that will help manufacturers
access energy, environmental, and manufacturing
improvement technologies. The EEM project
has produced an integrated EEM self-assessment
and benchmark tool that has been used by more
than 100 metal finishers to benchmark their EEM
performance. A series of pilot tests are currently
underway at metal finishing shops that will test a
number of technologies, .including a reduction of
180
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hexavalent chrome emissions. For'more,informa-
tion, contact Ken Saulteir: (313) 769-4234. ,-; ,
National Defense Center for Environmental
Excellence - Control Technologies Corpora-
tion
The .National'Defense Center for Environmental
Excellence (NDCEE) is a .technical assistance
organization that helps to integrate clean tech-
nologies into defense and private industrial
facilities: NDCEE's assistance"includes access
to a demonstration factory that has 28 clean
technologies that can be evaluated off-line, using.
a company's own parts. In many cases, NDCEE
demonstrates the technology, trains-personnel,
assists in startup, and researches additional
applications to achieve maximum performance.
Specific technology available through NDCEE
for research or testing that might be if interest to
a metal finishing facility include:
Inorganic finishing technologies such as
advanced electroplating, ion plating, ion
beam assisted deposition, ion implantation,
plasma spray, and high velocity-oxy fuel
Advanced cleaning technology including
power washer, rotary basket, duel-use
ultrasonic, advanced immersion, '
supercritical carbon dioxide, and honeycomb
cleaning
Water reuse/recycling technologies such as
diffusion dialysis, membrane electrolysis,
electrowinning, ion exchange, cross-flow
microfiltration, reverse osmosis, and vacuum
evaporation
The NDCEE's main demonstration'facilities are,
located in Johnstown, Pennsylvania.
Research Triangle Institute
The federal government, through the Environ-
mental Protection Agency and Departments of
Defense, Energy, and Commerce, has funded
numerous pollution prevention projects related to
metal finishing. Research Triangle Institute in
North Carolina developed a document called the
Summary of Federal Research on Pollution
Prevention in Electroplating and Surface Finish-
ing, which provides a project name, contact, and
brief description for 36 projects funded with
federal dollars. '
Web Sites
Department ofJJefense (DOD) P2 Tech
Library
Access: http://clean.rti.org/Iarry/nav_in.html
This site is actually part of EnviroSenSe. It
contains a variety of P2 information including .
data sheets on electroplating and finishing,
.hazardous materials/hazardous management,
ozone depleting substances, painting/depainting,
petroleum, oils, lubricants, and, more.
EnviroSenSe
Access: http://es.incl.gov/
' EnviroSenSe, funded by the US EPA and the
Strategic Environmental Research and Develop-
ment Program (SERDPa joint effort of DOD.
DOE, and EPA) is one of the largest and most
inclusive sites for pollution prevention informa-
tion.' Its features include: a pollution prevention ;
forum for all levels of government, researchers,
industry, and public interest groups; Solvent
Umbrella, a solvent alternative information
guide; ASK EPA. an interactive forum for P2
questions; a directory of federal, state, and local
P2 programs; international resources; technical/
research and development information; and
compliance and enforcement information.
Industry content guides for the commercial
printing and graphic arts, electronics assembly
and manufacturing, iron and .steel foundries and
'metal finishing"sectors have recently been
developed.
Finjshing.com, The Home Page of the Finish-
ing Industry
Access: http://www.finishing.com/
This site provides information about surface
: finishing, from anodizing to powder coating.
Metal Finishing - The On-Line Finishers
Resource
Access: http://www.Mctal-Finishing.com
Metal Finishing is a resource for suppliers, metal
finishers, engineers, end-users, specifiers and
other professionals that need metal finishing
information. This site contains searchable
databases for company and product data along
181
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vvhh related information for the metal finishing
industn., New features include web pages for
on-line catalogs, new products, announcements
for developments in technology, classifieds" for
used equipment, chemicals, and metals, and
much more.
The National Metal Finishing Resource
Center
Access: http://www.ncms.org/rimfrc/
The National Metal Finishing Resource Center
was created to serve the needs of the metal
finishing industry arid their technical assistance
providers. The Center offers pollution prevention
and compliance assistance information, and
creates a forum for information exchange.
Products Finishing - The Gardner Web
Access: http://www.gardnenveb.com
Gardner web was launched in 1995 to provide
nietalworking and Finishing specifiers the
information they need. Information on this site
includes supplier information, industry event
listings, and technical resources.
The Society of Vacuum Coatcrs
Access: http://www.svc.org/
The Society of Vacuum Coatcrs, a non-profit
professional, trade and educational organization,
is dedicated to the development of equipment
and processes for high-volume production of
coatings using vacuum-based processes. Its
unique industrial focus targets the processing
engineer and technician, end-user, equipment
manufacturer, and the materials supplier. SVC
seeks to disseminate knowledge, experience, and
techniques to the vacuum coating industry
through a variety of forums.
European Journal of Cleaner Production
Access: http://telebonn.gmd.de/chemsoft/
coatings
IAMS Industry Sector
Access: http://wvvw.iams.org/p2irisdc/
p2iris.htm
Thomas Register
Access: http://www.thomasrcgistcr.com
Trade Associations
The American Electroplaters and Surface Finish-
ers Society, Inc. (AESF)
12644 Research Parkway
Orlando, FL 32826-3298
(407)281-6441
National Association of Metal Finishers (NAMF)
401 N. Michigan Avenue
Chicago, IL 60611-4267
(312) 644-6610 ext. 3479
Metal Finishers Suppliers Association
801 N. Cass Avenue, Suite 300
. Westmqnt, IL 60559
(708)887-0957
Publications
Guide to Cleaner Technologies: Alternative
Metal Finishes
This publication discusses alternative processes
in metal plating including cleaning, material
' substitutes, and alternative deposition processes.
Industrial Pollution Prevention Handbook
' This is a general reference book for people
working on environmental projects. It contains
information on 53 subjects such as pollution
prevention planning, agile manufacturing, and
pollution prevention in specific industrial sec-
tors. The handbook is available from McGraw-
Hill, Inc. for $94.50. To order, call (800) 262-
4729 and reference ISBN #0-07-022148-0.
Metal Finishing Industry Pollution Prevention
Project: Second Progress Report
'The report presents 10 site-specific pollution
prevention case studies from Canada. Informa-
tion is provided on plant projects, target chemi-
cals, objectives, project descriptions, cost savings
and expected reductions. For a free copy, please
call the Great Lakes Pollution Prevention Centre
at (800) 667-9790.
Metal Finishing Pollution Prevention Guide
this manual provides guidance to metal finishers
for incorporating pollution prevention planning
into their everyday business activities. Stepwise
directions will help a P2 team in identifying,
182
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prioritizing, and'implementing solutions to - ..
pollution problems. Available for S25 (Cana- .
dian) by calling (800.) 667-9790. ; : .r '
Pollution Prevention and Control Technology
for Plating Operations
This publication is the result of a survey con-.
ducted with hundreds of electroplating compa-
nies of all sizes to determine the actual track
record pi" currently available pollution prevention
techniques and pollution control equipment. A
400-page report describes the available options
and summarizes the survey results. The report
and associated database enables users to match
their requirements and capabilities with the
experience of survey respondents. The report
costs S43'; the report and database cost S48.50.
To order contact GAI Engineering, 3433
Valewood Drive, Oaktpn, VA 22124, or call
George Cushnie: (710) 264-0039. . . .-
The Product Side of Pollution Prevention:
Evaluating the Potential Safe Substitutes
This publication evaluates substitutes fqr a
variety of processes in; metal plating*, including
cleaning, plating, and coating.
Profile of the Metal Finishing Industry
The report written by the Waste Reduction
Institute for Training and Applications Research
(WRITAR) provides an overview an analysis of
the competitive, process, and environmental
issues shaping the metal finishing industry.
Energy, environment, and manufacturing tech-
nologies are described in the plating and coating
areas. The report can be ordered from WRITAR
for S50 by calling (612) 379-5995. '.',-.'
Waste Minimization for Metal Finishing
Facilities
This publication provides a detailed description
of waste,issues* alternative processes, and policy
implications for metal finishing. To order, call
EPA's Pollution Prevention Information Clear-
inghouse (202) 260-1023
\ . '" . " ' ' " '
Periodicals
Metal Finishing
Metal finishing is a technical journal with
information on practical and technical issues for
finishing metal and plastic products, including
waste treatment and pollution control. For
information on subscribing, contact-Elsevier
Science/Metal Finishing: (212) 633-3950. ';
Plating and Surface Finishing
This journal focuses on a wide variety of infor-
mation related to finishing including plating,
painting and cleaning. For information on
subscribing contact AESF International Head-
quarters (407) 281-6441.
* . '
Pollution Prevention Review ,
This journal focuses on a wide variety of pollu-
tion prevention related topics including technical
case studies, environmental management, arid
regulatory issues. The journal'is published
quarterly. For subscription inquiries, call: (212).
850-6479. . .'..-
Product Finishing
Product Finishing is published oh a monthly
basis and provides technical'information on
electroplating, painting, and other finishing
operations. For subscription information contact
(513)527-8800.
Videos
Rinsing Process Modifications for Metal Finish-
' ers. lil minutes (VHS with audio script). S25.
Available from WRITAR: (612) 379-59,95,
Pollution Prevention in Metal Finishing Avail-
able from the North Carolina Office of Waste
Reduction: (919) 715,6500.
*s" , - * '
The following videos are available from AESF.
For prices and/or to place-an order call: (800)
334-2052. :
The Historyof Electroplating with Al
Weisberg. '.
The Basics of Wastewater Treatment
The Role of Microfiltration in Waste
Treatment
Avoiding Metal Finishing Disasters
The Basics of Tin Plating
Making Surface Tension Measurements
'Control of Chromium Emissions
Safety in Metal Finishing . ,
Introduction to Electroplating and Surface
Finishing
183
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Reader Response Survey
: ' . f - , ^ .
Pollution Prevention for the Metal Finishing Manual - Reader Response Survey
This manual has been published as a pilot project to develop a comprehensive pollution prevention
manual for technical assistance programs for the metal finishing sector. In order.to determine the,
utility and make improvements in future editions, we would like to hearfrom you. Your comments
will enable us to increase the- value of this document. Please take a few moments to answer .some
questions. When completed, simply fold in half staple and mail the survey back. We appreciate your
comments and suggestions. ' ' ' ' ' ' -..'.-',.
Where did you learn about .this report? - ' '_'.
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* Colleague , ' ,
E-mail announcement ' - ' . .
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. Other '1. ; i:-
For the following questions, please circle the number that best describes your level .of agreement
with each statement. .
1. The overall quality (organization, content) of the manual was high?
. " . ' -5- -4 " . ' ' 3 :; '"' 2 ^ * ' :'.
2. The manual provided a comprehensive overview of pollution prevention techniques for metal
finishing! -..'..' . - .
If you felt the manual was not comprehensive what information was lacking: -
Was there any information that was unnecessary or inaccurate?
3. ' Information., was easily located in the; Manual.
" . 5 .'.;* ''..' ' ' 3 -.
4. Additional comments regarding the Manual
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