THE SUBSTITUTION OF CADMIUM CYANIDE ELECTROPLATING
WITH ZINC CHLORIDE ELECTROPLATING
by
B. C. Kim, P. R. Webb, J. A. Gurklis, and R. K. Smith
Battelle
Columbus, Ohio 43201
Contract No. 68-CO-0003
Work Assignment No. 3-36
Project Officer
Teresa Marten
Waste Minimization, Destruction, and Disposal
Research Division
Risk Reduction Engineering Laboratory
Cincinnati, Ohio 45268
RISK REDUCTION ENGBNEERING LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U. S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
pLT) Printed on Recycled Paper
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NOTICE
This material has been funded wholly or in part by the U.S. Environmental
Protection Agency (EPA) under Contract No. 68-CO-0003 to Battelle. It has been subjec-
ted to the Agency's peer and administrative review and approved for publication as an EPA
document. Approval does not signify that the contents necessarily reflect the views and
policies of the U.S. Environmental Protection Agency or Battelle; nor does mention of trade
names or commercial products constitute endorsement or recommendation of use. This
document is intended as advisory guidance only to the electroplating industry in developing
approaches to waste reduction. Compliance with environmental and occupational safety
and health laws is the responsibility of each individual business and is not the focus of this
document.
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FOREWORD
Today's rapidly developing and changing technologies and industrial products and
practices frequently carry with them the increased generation of materials that, if improperly
dealt wrth, can threaten both public health and the environment. The U.S. Environmental
Protection Agency (EPA) is charged by Congress with protecting the Nation's land, air, and
water resources. Under a mandate of national environmental laws, the agency strives to
formulate and implement actions leading to a compatible balance between human activities
and the ability of natural systems to support and nurture life. These laws direct the EPA to
perform research to define our environmental problems, measure the impacts, and search for
solutions.
The Risk Reduction Engineering Laboratory is responsible for planning
implementing, and managing research, development, and demonstration programs to provide
an authontative, defensible engineering basis in support of the policies, programs, and
regulations of the EPA with respect to drinking water, wastewater, • pesticides, toxic
substances, solid and hazardous wastes, Superfund-related activities, and pollution
prevents. This publication is one of the products of that research and provides a vital
communication link between the researcher and the user community.
Passage of the Pollution Prevention Act of 1990 marked a significant change in the
U.S. policies concerning the generation of hazardous and nonhazardous wastes. This Act
implements the national objective of pollution prevention by establishing a source reduction
program at the EPA and by assisting states in providing information and technical assistance
about source reduction. In support of the emphasis on pollution prevention, the "Waste
Reduct,on Innovative Technology Evaluation (WRITE) Program" has been designed to identify
evaluate, and/or demonstrate new techniques and technologies that lead to waste reduction
The WRITE Program emphasizes source reduction and on-site recycling. These methods
reduce or eliminate transportation, handling, treatment, and disposal of hazardous materials in
the-environment. The project discussed in this report evaluated the success of substituting
z,nc chlor.de electroplating for cadmium cyanide electroplating processes. The project
determined hazardous waste, reduction, economic benefits, and change in product quality
resulting from the process substitution.
E. Timothy Oppelt, Director
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
in
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ABSTRACT
This project evaluated the substitution of zinc chloride for cadmium cyanide in
electroplating at Aeroquip Corporation, Van Wert, Ohio. The evaluation looked at product
quality, waste volume and pollutant reduction benefits, and economic benefit resulting from the
process change. Battelle obtained data on the zinc-plating process by sampling and analyzing
waste streams and conducting corrosion tests on zinc-plated production parts. Aeroquip
provided data on the older cadmium-plating process for comparison with the zinc data.
It was concluded that the newer process is successful on the quality and the waste
volume/pollutant reduction aspects. It results in products whose quality satisfies customer
requirements for corrosion resistance. The process change greatly reduces worker hazards and
env,ronmental pollution because it eliminates 12,132 Ib of cadmium and 835 Ib of cyanide
annually from the waste streams and chlorine from the wastewater treatment process. The
change also reduced annual oil and grease waste from 14,615 Ib to 5,123 Ib by reducing the
oil concentration in the water-soluble oil bath by a factor of approximately ten. However, the
change had two negative impacts on waste generation. Wastewater and wastewater
treatment sludge increased by approximately 12 and 36 percent, respectively, because the
Plating bath concentration increased from about 3 oz/gal in the older cadmium process to
about 3.5 oz/gal in the newer zinc process. The change also increased total chromium in
treated wastewater and sludge from 677 Ib/yr to 4,421 Ib/yr, because there was a fivefold
increase in the chromate bath concentration.
The process substitution was less clearly beneficial from an economic standpoint
For a company with existing cadmium process lines, the substitution of zinc cannot be justified
on economic grounds and must be weighed with other factors, such as market, environmental
health, and safety considerations. At Aeroquip, capital cost was estimated to be $1,972 000
of which approximately 72 percent was the cost of cleaning old equipment and disposing of
r?™L9enerated bV P'ant modifications- The process change reduced operating costs by
§17,000/yr, for a simple payback period of about 115 years to recover the capital cost of the
process substitution. However, because the cadmium and the zinc-plating lines have similar
equipment requirements, the capital costs for new plating lines can be expected to be about
equal for either process. Thus, for a new installation, the zinc-plating process offers an
economic advantage of lower operating cost.
This report was submitted in partial fulfillment of Contract Number 68-CO-0003
Work Assignment 3-36, under the sponsorship of the U. S. Environmental Protection Agency'
Th,s report covers the period from September 1991 to January 1994, and work was
completed as of January 31, 1994.
IV
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CONTENTS
Page
NOTICE
FOREWORD ' "v •'". ••••••• n
ABSTRACT " ' ' ' " •' ' ' ' ' .'"
FIGURES..... "'"• " ™.
TABLES .;;;;;; :;•::::::;::::;:;;•;;•;•••••••: v
ACKNOWLEDGMENTS . .-....'.'.'. viii
SECTION 1
INTRODUCTION -,
GENERAL OVERVIEW . . . . . , .................. ' ' -j
DESCRIPTION OF THE SITE AND TECHNOLOGY STUDIED 2
LITERATURE SURVEY ..................... -| 7
STATEMENT OF OBJECTIVES '.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'. 18
SECTION 2
CONCLUSIONS AND RECOMMENDATIONS . . . . . "....' 19
SECTION 3
MATERIALS AND METHODS , 21
PRODUCT QUALITY .......'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'. '.'. '. '/. 21
Corrosion Resistance Requirements at Aeroquip 21
ASTM Method B117-90: Apparatus and Operating Conditions 22
Experimental Corrosion Property Evaluation Program 23
DTL Salt-Spray Tests -.'.'.'.'.'. . . 23
Aeroquip Salt-Spray Tests 25
Additional Aeroquip Salt-Spray Tests . 25
Comprehensive Program of Salt-Spray Testing of Zinc- and
Cadmium-Plated Parts at Aeroquip ........... 25
WASTE AND POLLUTANT REDUCTION . " 26
ECONOMIC EVALUATION 29
SECTION 4 .
RESULTS AND DISCUSSION 31
PRODUCT QUALITY 31
Experimental Corrosion Property Evaluation Program -. . . . 31
DTL Salt-Spray Test Data and Results 31
Aeroquip Salt-Spray Test Data and Results 34
Comparison of DTL and Aeroquip Salt-Spray Test Results 35
Additional Aeroquip Salt-Spray Test Data and Results 35
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CONTENTS (Continued)
Comprehensive Program of Salt-Spray Testing of Zinc- and
Cadmium-Plated Parts at Aeroquip 35
Summation Comments on Adequacy of Corrosion Resistance
Properties of Zinc-Plated Parts . 42
WASTE AND POLLUTANT REDUCTION . . . '.'.-'.'.'.'.'.'.'.'. 43
Waste Reduction 43
Pollutant Reduction . . 44
ECONOMICS . . . . . -.-../ . '.'.'.'.'.'. '.'.'. '.'.'.'."" 50
SECTION 5
QUALITY ASSURANCE
• , . . . . 54
ON-SITE SAMPLE COLLECTION . . 54
CHEMICAL ANALYSIS . ' 55
LIMITATIONS AND QUALIFICATIONS ..'.'.'.'.'.'.'.'. 57
SECTION 6
REFERENCES
58
APPENDIX
COMPARISON OF POWER CONSUMPTION VALUES FOR THE ZINC
VERSUS CADMIUM PLATING OPERATIONS . 59
FIGURES
Number 0
• . Page
1 Flowsheet of zinc chloride rack plating line . . 3
2 Flowsheet of zinc chloride single hoist barrel plating line 6
3 Flowsheet of zinc chloride double hoist barrel plating line ..'.'. 9
4 Material flows around electroplating and wastewater treatment
processes ., g
5 Zinc-plated parts salt-spray tested by Detroit Testing Laboratory and
Aeroquip (rack plated) . . . 24
6 Zinc-plated parts salt-spray tested by Aeroquip (barrel plated) .26
7 Cadmium- and zinc-plated parts salt-spray tested by Aeroquip . ... 27
TABLES
Number Paqe
1 Comparison of zinc chloride and cadmium cyanide rack plating processes ... 12
2 Comparison of zinc chloride and cadmium cyanide single hoist barrel
plating processes 13
VI
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TABLES (Continued)
Number _
Pagg
3 Comparison of zinc chloride and cadmium cyanide double hoist barrel
plating processes 14
4 Pollutants generated from cadmium- and zinc-plating processes (Ib/year
based on production rate of 3.39 million sq ft) . . . 20
5 Summary of primary and quality control samples for chemical analysis
and characterization 2g
6 Results of corrosion resistance tests on various parts rack plated with
zinc using 5-percent salt spray; tests performed by Detroit Testing
Laboratory using ASTM B117-90 . 32
7 Results of corrosion resistance tests on various parts rack plated with
zinc using 5-percent salt spray; tests performed by Aeroquip using ASTM
B117-90 .. ... ... 33
8 Results of corrosion resistance tests on various parts barrel plated with
zinc using 5-percent salt spray; tests performed by Aeroquip using ASTM
B117-90 . 3 ft
9 Results of corrosion resistance tests on various parts plated with zinc
using 5-percent salt spray; tests performed by Aeroquip using ASTM
B117-90 in 1991 37
10 Results of corrosion resistance tests on various parts plated with
cadmium using 5-percent salt spray; tests performed by Aeroquip using
ASTM B117-90 3g
11 Annual generation of treated wastewater and sludge from cadmium- and
zinc-plating processes (Aeroquip data) . . 44
12 Chemical analysis of treated wastewater from cadmium- and zinc-plating
processes (Aeroquip data) . . 45
13 Chemical analysis of treated wastewater from zinc- plating process
(Battelle data) . . 46
14 Chemical analysis of sludge from cadmium- and zinc- plating processes
(Aeroquip data) 4_
15 Chemical analysis of dewatered sludge from zinc-plating process (Batteile
data) ? . . . 48
16 Pollutant generation in Ib/yr from cadmium- and zinc- plating processes
based on 1989 production rate of 3.39 million sq ft . . . . . 49
17 Chemical analysis of field blank and laboratory blank (Battelle data) 51
18 Capital cost .' ^
19 Comparison of operating costs for cadmium- and zinc- plating processes . . 53
20 Summary of primary and quality control samples for chemical analysis
and characterization 5(.
21 Precision of sludge analysis . . 55
22 Precision of treated wastewater analysis . . . ••••••-.....
23 Accuracy of sludge analysis .!!...!...!.! 56
24 Accuracy of treated wastewater analysis
VII
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ACKNOWLEDGMENTS
The U.S. Environmental Protection Agency and Battelle wish to thank Aeroquip
Corporation for providing the site for this evaluation. The authors appreciate the
cooperation and assistance provided by the Aeroquip staff, particularly Mr. James
Bookman in the Metal Finishing Department. Mr. Bookman arranged the salt-spray
corrosion tests, provided assistance to Battelle project staff during collection of waste-
water and sludge samples, and collected and supplied data from Aeroquip files for
inclusion in the evaluation.
VIII
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SECTION 1
INTRODUCTION
GENERAL OVERVIEW
The objective of the U.S. Environmental Protection Agency's (U.S. EPA) Waste
Reduction Innovative Technology Evaluation (WRITE) Program is to evaluate in the work place
prototype technologies that have potential for reducing wastes at the source (also referred
to as preventing pollution). In general, each technology is evaluated on three issues.
First, the new technology's effectiveness is assessed, in terms of maintaining
product quality. Pollution prevention or waste reduction technologies usually recycle or reuse
materials, or use alternative materials or techniques. Therefore, it is important to verify
whether the quality of the feed materials and the quality, of the products are acceptable for
the intended purpose.
Second, the impact of the new technology on waste generation is measured. The
new technology is compared with the existing technology (baseline) or the process that it
replaces. The wastes generated from each technology are determined and compared.
Third, the economics of the new technology are quantified and compared with the
economics of the existing technology.
This study evaluated the zinc chloride electroplating process as a substitute for
cadmium cyanide electroplating in the manufacture of industrial connectors and fittings at
Aeroquip Corporation. The process substitution eliminates certain wastes, specifically
cadmium and cyanide, which are listed among the 17 priority toxic pollutants designated by
the U.S. EPA, although as will be seen, zinc and chromium wastes increased with the process
change.
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DESCRIPTION OF THE SITE AND TECHNOLOGY STUDIED
The site for this study was Aeroquip Corporation, in Van Wert, Ohio. Aeroquip
manufactures industrial connectors such as hose fittings. The specific area studied was the
zinc chloride plating operation, which includes a rack plating line and two barrel plating lines.
Plating operations at Aeroquip previously used cadmium cyanide plating baths to
deposit a 0.005-0.010-mm (0.0002-0.0004-inch) cadmium coating to provide protection
against corrosion. Both cadmium and cyanide/however, are toxic chemicals targeted for
reduction by the U.S. EPA. In December 1990 and January 1991/Aeroquip modified its
plating process to substitute zinc chloride plating for cadmium cyanide plating. This
substitution eliminated hazardous cadmium and cyanide wastes.
The zinc chloride plating processes for the rack plating and the two barrel plating
lines (single-hoist and double-hoist) are illustrated in Figures 1, 2, and 3, respectively. Each
step in the automated plating operation is carried out in a tank with racks or barrels of pieces
progressing through each step in sequence. The tanks are open at the top to allow the racks
or barrels to enter from above. Rinse water and chemicals are added continuously or
intermittently to appropriate tanks to maintain the desired tank levels and concentrations of
chemicals.
Comparisons of the cadmium cyanide and the zinc chloride plating processes for the
rack plating and the barrel plating lines are shown in Tables 1, 2, and 3 respectively.
Hydrochloric acid is used to condition parts {shown as step 12 in Table 1 and step 10 in
Tables 2 and 3) prior to plating in the zinc chloride process whereas sodium cyanide is used
in the cadmium cyanide process. The cadmium cyanide lines had separate tanks to apply
either clear chromate or yellow chromate coatings (e.g., steps 18 and 20 in Table 1).
Aeroquip used clear chromate coating on the majority (90-95 percent) of cadmium-plated
parts. Currently, Aeroquip use yellow chromate coating on all zinc-plated parts. The reasons
for the change were: (a) Aeroquip has adopted a worldwide standardization of yellow as the
color their fittings and (b) the corrosion protection of the zinc-plated fittings vastly improves
when the fittings are coated with yellow chromate. The yellow chromate solution used by
Aeroquip contained approximately five times greater chromium concentration than the clear
chromate solution. In the water-soluble oil application step (e.g., step 22 in Table 1), the
concentration of the oil was substantially reduced by a factor of approximately ten in the zinc
-------
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Figure 1. Flowsheet of zinc chloride rack plating line (continued).
Note: Letters A, B, C, and D refer to continuation of
flow lines between successive pages.
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CHEMICAL & WATER
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Figure 1. (continued).
Note: Letters A, B, C, and D refer to continuation of flow lines
between successive pages.
-------
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between successive pages.
-------
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Figure 2. Flowsheet of zinc chloride single hoist barrel plating line (continued).
Note: Letters A, B, C, and D refer to continuation of flow lines
between successive pages.
-------
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8
-------
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Figure 3. Flowsheet of zinc chloride double hoist barrel plating line (continued).
Note: Letters A, B, C, and D refer to continuation of flow lines
between successive pages.
-------
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successive pages.
11
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TABLE 1, COMPARISON OF ZINC CHLORIDE AND CADMIUM
CYANIDE RACK PLATING PROCESSES
~
Process
Step
=
1
2
3
4
5
6
II 7
I 8
II 9
II 1°
|_ 11
12
r 13
I— 14'
15
II 16
I 17
II 18
19
20
21
22
I* '
=====
Tank
No.
=====
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
I ..
Operation
Zinc Chloride
Plating Line
=============s==
Soak clean
Rinse
Electroclean
Rinse
Rinse
Hydrochloric acid pickle
Rinse
Rinse
Electroclean
Rinse
Rinse
Hydrochloric acid pre-dip
Zinc plating
Rinse
Rinse
Nitric acid dip
Yellow chromate dip(al
Rinse
Chromate seal
Rinse
Drip tank dip
Water-soluble oil dip(cl
Cadmium Cyanide
/ Plating Line
Soak clean
Rinse
Electroclean
Rinse
Rinse
Hydrochloric acid pickle
Rinse
Rinse
Electroclean
Rinse
Rinse
Sodium cyanide pre-dip
Cadmium plating
Rinse
Rinse
Rinse
Nitric acid dip
Clear ehromate dip(a)(b)
Rinse""
Yellow ehromate diplb)
Rinse""
Water-soluble oil dip(c)
(a) The Cr concentration in the yellow ehromate bath was approximately five times the Cr concentration in
the clear ehromate bath.
.(b) Approximately 90-95 of the cadmium-plated parts were coated with clear chromate, and the remainder
coated with yellow chromate.
(c) The oil concentration in the water-soluble oil bath in the zinc-plating process was approximately 1/10 of
the concentration used in the cadmium-plating process.
12
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TABLE 2. COMPARISON OF ZINC CHLORIDE AND CADMIUM CYANIDE
SINGLE HOIST BARREL PLATING PROCESSES
' =====
Process
Step
===========
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
=====
Tank
No.
==========
3
4-6
7
8
9
10
11
12
13
21
23-26
22
20
19
18
17
15
16
14
2
Operation
Zinc Chloride
Plating Line
===== , =======
Soak clean
Soak clean
Electroclean
Rinse
Rinse
Hydrochloric acid pickle
Acid salt clean
Rinse
Rinse
Hydrochloric acid pre-dip
Zinc plating
Dragout rinse
Rinse
Rinse
Nitric acid dip
Yellow chromate dip(a)
Rinse
Chromate seal
Rinse
Water-soluble oil dip(c)
Cadmium Cyanide
Plating Line
==============:====;
Soak clean
Soak clean
Electroclean
Rinse
Rinse
Hydrochloric acid pickle
Acid salt clean
Rinse
Rinse
Sodium cyanide pre-dip
Cadmium plating
Dragout rinse
Rinse
Rinse
Nitric acid dip
Clear chromate dip(a|(b)
Rinse""
Yellow chromate dip(b)
Rinselbl
Water-soluble oil dip(c)
(a) The Cr concentration in the yellow chromate bath was approximately five times the Cr
concentration in the clear chromate bath.
(b) Approximately 90-95 of the cadmium-plated parts were coated with clear chromate and the
remainder coated wrth yellow chromate.
(c) The oil concentration in the water-soluble oil bath in the zinc-plating process was approximately
1/10 of the concentration used in the cadmium-plating process.
13
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TABLE 3. COMPARISONI OF ZINC CHLORIDE AND CADMIUM CYANIDE
DOUBLE HOIST BARREL PLATING PROCESSES
Process
Step
Tank
No.
Zinc Chloride
Plating Une
=
Soak clean
...
Soak clean
i—
Electroclean
——™»™»,
Rinse
-
Rinse
-
^ydrochloric acid pickle
Acid salt clean
—
Rinse
•^—«a^>_
Rinse
^—«•—••—•.
Hydrochloric acid pre-dip
Zinc plating
—
Dragout rinse
™' ii .1
Rinse
Rinse
Nitric acid dip
———————
Yellow chromate dip(al
Rinse
___
Chromate seal
Rinse
—^—t^«^
Water-soluble oil dip(c|
=
bath
Operation
Cadmium Cyanide
Plating Une
Soak clean
~" -•
Soak clean
•"•
Electroclean
•—^"«™—™.
Rinse
—«^«—^-^
Rinse
»—»•••.
Hydrochloric acid pickle
'"
Acid salt clean
^•—.
Rinse
Rinse
' m
Sodium cyanide pre-dip
Cadmium plating
Dragout rinse
— —i...
Rinse
Rinse
—' • i-—
Nitric acid dip
—— _ _
Clear chromate dipla)(b)
Rinse""
"" i.—
Yellow chromate dip""
Rinse(b)
"^««.
Water-soluble oil dip(c)
chromate, ,
14
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chloride plating process from the level used in the cadmium cyanide plating process The
change was necessary to obtain improved adhesion of chromate coating during the
subsequent heat-curing step.
Rinse water and various cleaning and plating solutions are discharged continuously
or periodically dumped from the tanks and treated in an on-site wastewater treatment p.ant
Wastewater bearing chromium is collected separately and treated with sulfur dioxide to
convert hexavalent chromium to triva.ent chromium, after which it is combined with the rest
of the wastewater for further treatment. The combined wastewater is treated with sodium
hydrox.de to precipitate heavy metals as hydroxides. In the cadmium cyanide plating process
cyamde-bearing wastewater was collected separately and treated with chlorine gas to destroy
cyan.de; sodium sulfide was used to precipitate cadmium as a sulfide.
The wastewater with precipitated metal hydroxides is sent first to a gravity settler
The oversow from the gravity settler is c.arified further in a sand filter before discharge to a
sanitary sewer. The underflow from the gravity settler and the sand filter are sent to a sludge
th,ckener, from which the sludge is pumped every 3 working days and dewatered in a filter
press. The water-soluble oil is collected separately and treated with hydrochloric acid to form
an insoluble oil phase, which subsequently is separated from water by decantation. The water
•s returned to the wastewater treatment p.ant. Material flows around the plating process and
the wastewater treatment plant are illustrated in Figure 4.
All wastes from the plating operations eventually end up in three waste streams
(treated water, dewatered sludge, and waste oil) that are discharged from the wastewater
treatment plant. The treated water is discharged to a sanitary sewer and sent to the
mumcipa. wastewater treatment plant. The dewatered sludge is collected in a 20-cubic-yard
hopper and sent to an off-site hazardous landfill once a month. The waste oil is collected in
drums and sent to an off-site hazardous waste incinerator every 3 months.
Because the cadmium cyanide process is no longer in operation, its evaluation was
based entirely on information provided by Aeroquip from their historical files. Evaluation of
the present zinc chloride process was based on information provided by Aeroquip and on data
generated in this study from Battelle's sampling and analysis of selected waste streams and
from testing of zinc-plated parts for corrosion resistance. Aeroquip's analyses were not
subject to the same QA/QC as were the analyses by Battelle's subcontractor for ana.ytical
work. The only waste analysis data available from Aeroquip for the cadmium cyanide process
15
-------
CHEMICALS WATER
UNFINISHED
PIECES
CHEMICAIS
PLATING PROCESS
WASTEWATER TREATMENT
PRODUCT
TREATED WATER
DEWATERED SLUDGE
WASTE OIL
CD ^- SAMPLE
SANITARY SEWER HOPPER *- SAMPLE DRUMS
\
MUNICIPAL WWTP HAZARDOUS LANDFILL HAZARDOUS WASTE INCINERATOR
Figure 4. Material flows around electroplating and
wastewater treatment processes.
16
-------
a
were on the dewatered sludge and the treated water discharged from the wastewater
treatment plant. Therefore, these same two streams were sampled and analyzed for the
existing zinc chloride process so that the two processes could be compared.
LITERATURE SURVEY
The literature survey conducted on this project indicates that the search for
alternative processes for cadmium electroplating started in the 1970s. For example, the U.S.
EPA and seven other government agencies sponsored a government-industry workshop on
"Alternatives for Cadmium Electroplating" at the National Bureau of Standards (NBS) in
Gaithersburg, Maryland, during October 2-4, 1977 (Journal of Plating and Surface Finishing,
1977). At this workshop, the Food and Drug Administration presented the results from
survey study indicating that the average human intake of cadmium in the U.S. was estimated
at 72 micrograms per day from food and water and was approaching the maximum level
recommended by the World Health Organization. NBS estimated that the majority of cadmium
water pollution in the U.S. was caused by cadmium electroplating and stripping.
International Business Machines (IBM) reported at the workshop that they had begun
to look for an alternative to cadmium plating in 1973 for 2,500 IBM parts plated with
cadmium. After an eight-month engineering study, IBM had successfully switched from
cadmium to zinc plating over a five-month period for all but 60 out of 2,500 parts that
required corrosion protection only. The other IBM parts formerly plated with cadmium for
properties other than corrosion protection were switched to zinc plating followed by a water-
emulsion post treatment for parts requiring lubricity, to tin or tin-lead alloy for parts requiring
good solderability, and to electroless nickel for a few remaining parts.
Other alternatives to cadmium plating reported at the workshop included: zinc-nickel
alloy plating by Sandia Laboratories., a tin alloy containing about 35 percent zinc by Tin
Research Institute, and ion vapor deposited (IVD) aluminum by McDonnell Aircraft Co. and by
Air Force Materials Laboratory. Dini and Johnson (1979) from Sandia Laboratories describe
results from salt-spray corrosion tests performed on steel panels electroplated with zinc-nickel
alloy, cadmium and zinc. The data obtained at 2.5-micron coating thickness indicate the
appearance of red rust after 72 hours for zinc coating (with chromate treatment) and
17
-------
192 hours for cadmium coating (with chromate treatment), but no red rust after 500 hours
for zinc-nickel coating (with chromate treatment).
Hsu (1984) from Boeing describes another zinc-nickel plating process, which
produced coatings that were better than cadmium-titanium coatings for corrosion protection.
Salt-spray corrosion tests showed a steel panel plated with a 12.5-micron Boeing zinc-nickel
coating showed no corrosion after 7,604 hours whereas a steel specimen plated with
cadmium-titanium coating corroded completely in the center after 1,848 hours. Rizzi et al.
(1986) describe a new zinc based coating containing phosphates and silicon that
outperformed cadmium and zinc in salt-spray corrosion tests. The time to appearance of red
corrosion was 100 hours for commercial electrodeposited zinc, 300 hours for cadmium, and
1,150 hours for the new zinc coating. Evaluation of alternative coatings for bearings prepared
by the Kaydon Bearing Div., Keene Corp. (Iron Age, 1980) shows zinc plating to be equal to
cadmium plating in corrosion resistance.
Donakowski and Morgan (1983) from Ford Motor Co. describe the development of
zinc/graphite composite coatings to achieve the anti-galling properties of cadmium desired for
fasteners. Relative coefficients of friction determined by using the Ford Portable Joint
Analyzer were 0.13 for zinc/graphite and 0.12 for cadmium. Salt-spray corrosion tests on
nuts electroplated with a 12.7-micron coating showed first appearance of white corrosion
after 120 hours for zinc/graphite (with chromate treatment) and no corrosion after 288 hours
for cadmium (with chromate treatment).
The findings from the literature survey suggest that zinc or zinc-based coatings are
the most widely used alternatives to cadmium coating.
STATEMENT OF OBJECTIVES
The goal of this project was to evaluate the substitution of cadmium cyanide
electroplating with zinc chloride electroplating. This study had three primary objectives.
• Evaluate the effects of the process substitution on product quality.
• Evaluate the waste reduction/pollutant reduction effects of the
process substitution.
" Evaluate the economics of implementing the process substitution.
18
-------
SECTION 2
CONCLUSIONS AND RECOMMENDATIONS
Based on the product quality evaluation performed in this study and data provided
by Aeroquip, it was concluded that zinc-plated parts meet customer requirements of 96 hours
of corrosion test (ASTM Method B117-90) before the appearance of white corrosion products.
Further, the zinc-plated parts meet the Aeroquip process requirements of 360 hours of
corrosion test before the appearance of red rust. Cadmium-plated parts are superior in their
corrosion resistance properties (i.e., appearance of white corrosion products and red rust in
salt-spray tests) to zinc-plated parts. However, as indicated above, the corrosion resistance
of zinc-plated parts was considered satisfactory for Aeroquip's customer requirements. The
process substitution also satisfied the requirements of some domestic and foreign customers
for cadmium-free products,
The changes in waste generation from the process substitution were: (a) reduction
of cadmium by 12,100 Ib/yr, (b) reduction of cyanide (as CN) by 835 Ib/yr, (c) reduction of
oil and grease waste, including waste oil, from 14,600 Ib/yr to 5,120 Ib/yr, (d) increase of
zinc by 22,300 Ib/yr, (e) increase of chromium from 677 Ib/yr to 4,420 Ib/yr, (f) increase of
treated wastewater from 40,000,000 gal/yr to 44,900,000 gal/yr, and (g) increase of
wastewater treatment sludge from 282,000 Ib/yr to 383,000 Ib/yr. Table 4 shows the
pollutant generation from each process. The process substitution eliminated cadmium and
cyanide, which are priority pollutants. The increases in wastewater and sludge were due
increase in plating bath concentration from approximately 3 oz/gal cadmium in the cadmium-
plating baths to approximately 3.5 oz/gal zinc in the zinc-plating baths. The decrease in oil
and grease was due to approximately tenfold decrease in the concentration of oil used in the
water-soluble oil dip tank. The increase in chromium was due to approximately fivefold
increase in the chromate bath concentration. The chromium, which also is a priority pollutant,
is effectively converted from the toxic hexavalent form to a much less toxic trivalent form in
the wastewater treatment plant; therefore, it does not pose as great a health risk as cadmium.
19
-------
The overall hazard level of the waste, therefore, was substantially reduced by eliminating
cadmium and cyanide. The process substitution also eliminated the use of chlorine (96,500
Ib in 1989) for cyanide destruction in the wastewater treatment plant. The process substitu-
tion, therefore, significantly reduced personnel health risks from handling hazardous materials,
such as cadmium, cyanide and chlorine. Consequently, the process substitution has reduced
the company's potential liability for accidental worker exposure to and environmental release
of these hazardous materials.
TABLE 4. POLLUTANTS GENERATED FROM CADMIUM- AND ZINC-PLATING PROCESSES
(LB/YEAR BASED ON PRODUCTION RATE OF 3.39 MILLION SQ FT)
•-
Pollutant
Cd
Total CN
Total Cr
Zn
Oil & Grease
" ' " i_-_i— ••— •
Cadmium Plating
12,100
835
677
o
14,600
=================—==—-
Zinc Plating
0
0
4,420
22,300
5,120
The capital cost for the process change at Aeroquip was estimated to be
$ 1,972,000. About 72 percent of the capital cost was for expenses associated with cleaning
up the process equipment contaminated with cadmium and cyanide, and for disposal of the
waste generated from the cleanup activity, and the remaining 28 percent was for new
' equipment. The annual operating cost reduction that resulted from the process change was
estimated to be $17,100. Based on these costs, the estimated payback period is 115 years.
The process change, therefore, cannot be justified on economic grounds alone. Justification
would be based on the improved worker and environmental safety considerations plus the
market's requirements for zinc-plated rather than cadmium-plated parts in many applications.
However, in comparing the two for a new installation, the zinc chloride-plating process offers
obvious advantages over the cadmium cyanide-plating process.
20
-------
SECTION 3
MATERIALS AND METHODS
PRODUCT QUALITY
Product quality was measured by the corrosion resistance of plated parts determined
by salt-spray (fog) tests. Salt-spray tests were carried out in accordance with the ASTM
Method B117-90 [Standard Test Method of Salt Spray (Fog) Testing], Test specimens are
suspended in a chamber and exposed to a salt-spray (fog) under controlled conditions of
temperature, salt solution concentration and pH, and spraying rate. For the duration of the
test period, test specimens are visually inspected at 24-hour intervals (except weekends) for
the initial appearance of corrosion products on part surfaces and the subsequent progress of
corrosion.
Corrosion Resistance Requirements at Aerogiiip
As part of their quality acceptance criteria for zinc-plated parts, Aeroquip's
engineering process specification has adopted the ASTM Method B633-85 (Standard
Specification for Electrodeposited Coatings of Zinc on Iron and Steel) requirement of 96 hours
of freedom from white corrosion products in salt-spray testing. Most Aeroquip customers
require 96 hours before the first appearance of white corrosion on zinc-plated parts. ASTM
Method B633-85 requires the corrosion resistance of zinc-plated specimens to be determined
in accordance with ASTM Method B117-90. ASTM Method 8633-85 states that zinc
coatings with Type II treatment (i.e., with colored chromate conversion coating) shall show
corrosion products of neither zinc nor the substrate metal after 96 hours, when tested by
continuous exposure to salt spray in accordance with ASTM B117-90. The first appearance
within 96 hours of corrosion products visible to the unaided eye at normal reading distance
21
-------
shall be cause for rejection, except that white corrosion products at the edges of specimens
shall not constitute failure.
The process specification for some of Aeroquip's products has an additional accept-
ance criterion of 360 hours of salt-spray exposure before the first appearance of red rust.
Thus the salt-spray test requirements for Aeroquip zinc-plated (plus yellow
chromate) parts are as follows:
Appearance of White Corrosion: 96 hr (all parts)
Appearance of Red Rust: 360 hr (designated parts).
AST1V1 Method B117-9Q: Apparatus and Operating Cr
iditic
The apparatus required for salt-spray (fog) testing, in accordance with ASTM
Method B 117-90, consists of a fog chamber, a salt solution reservoir, a supply of suitably
conditioned compressed air, one or more atomizing nozzles, specimen supports, and the
necessary means for control. The size and construction details of the apparatus are optional,
provided the conditions obtained meet the requirements of this method.
According to ASTM Method B 117-90, the fog shall be such that, for each 80 cm2
of horizontal collecting area, there will be collected in each collector from 1.0 to 2.0 ml of
solution per hour, based on an average of at least 16 hours. B 117-90 states also that: (1)
the sodium chloride concentration shall be 5 ± 1 weight percent (specific gravity, 1.027-
1.041) and (2) the PH of the collected solution shall be 6.5 to 7.2. Other data on chamber
operation are provided later in this report in the section that covers the salt-spray tests carried
out by Detroit Testing Laboratory on zinc-plated specimens.
It should be noted that ASTM Method B117^90 prescribes neither the type of test
specimen and exposure periods to be used for a specific product nor the interpretation to be
given the results. It should be noted further that there seldom is a direct relation between
resistance to salt spray and resistance to corrosion in other media. This is because the
chemistry of the reactions, including the formation of films and their protective value,
frequently varies greatly with the precise conditions encountered by parts during use.
The reader should be aware also of possible wide variations in the quality and
thicknesses of coatings on plated items produced on the same racks at the same time and the
consequent need to use multiple specimens for testing.
22
-------
For the salt-spray corrosion tests, 12 pieces each of four representative types of
zinc-plated parts were obtained for use as test specimens. Each group of 12 pieces was split
into two smaller groups of six specimens each. This was done to provide two sets (consisting
of four groups each) for testing. One set was retained by Aeroquip for testing in its
laboratory; the other set was given to Battelle, which in turn sent the set to an independent
testing laboratory [Detroit Testing Laboratory, Inc. (DTL), Warren, Michigan]. Thus, the salt-
spray tests were conducted in parallel by Aeroquip and DTL. The parts evaluated in the salt-
spray test are shown in Figure 5.
All of the above parts were rack plated with zinc (thickness: 0.0002-0.0004 inch),
followed by a yellow chromate coating.
DTL Salt-spray Tests
A total of 24 zinc-plated specimens, comprising six pieces each of four
representative Aeroquip fittings (Figure 5), were subjected to 5-percent salt-spray (fog)
corrosion testing by DTL, in accordance with procedures designated in ASTM B 117-90.
Tests were carried out in a Singleton Corrosion Test Chamber. The specimens were
mounted with the significant surface inclined approximately 1 5 degrees from the vertical and
exposed for 360 hours, with evaluations every 24 hours (excluding weekends). After 360
hours, the test specimens were rinsed in running water (not warmer than 100°F) and dried
During the 360-hour (14 day) test period, the 11 readings (daily except for weekends) showed
that cabinet temperature was 95 ± 1 °F, tower temperature was 120-121 °F, and tower
pressure was 10 psi. All of these readings were in accordance with B117-90 test
requirements. Four separate solution collectors were employed in the cabinet. Examination
of the data for each of the four collectors showed that (1) the collection volume rates all were
within a range of 1.0 to 1.2 ml/hr; (2) the PH values of the collected solution were within a
range of 6.6 to 6.8; and (3) the specific gravities of the collected solutions were all within a
range of 1.031 to 1.032 (4.6 to 4.8 percent NaCI). These collection volumes, solution pH
values, and concentrations were all within the required ranges of B 117-90, as described
above.
23
-------
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27
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* - . s
zinc and total
The historical data supplied by Aeroquip included.- (a) wastewater and sludge
g—n d,,a from , 989 and , 9,, , (b) waste oil '
Baneile collected additional sampies of sludge and treated wastewater to determine
z,nc. -a, ohrom,um, and oi, and grease ,,or S,udge only, for comparison with the analysis
da a Prov,ded by Aeroquip. Table 5 shows the samples coliected by Battell, The samples
co,,ec,ed by BatteUe were ana,yzed by a subcontractor (Zande Environmental Service, The
generation of al, po,,u,an,s, in ,b/yr, including cadmium, cyanide, zinc, tota, ohromium, and
'"« -alysis data received from
Zande analyzed the sludge samples for zinc and total chromium using EPA Methods
3050 and 6010, for oi, and grease using EPA Method 807,. and for tota, solids ,! s,u
content, us.ng ASTM Method D22, 6. Zande analyzed the treated wastewater and tap water
samples for zinc and ,o,a, chrom,um using EPA Methods 30,0 and 60,0. Ba,,elle coHected
°f the water sampies at th
Battene collected all samples over a 2-week period. BatteUe collected dewatered
sludge samples as grab samples from the sludge hopper iocated a, the discharge of the ,i,,er
press. The sludge samples were taken from various locations in the hopper and mixed in a
glass beaker to obtain composite samples. Battelie collected all sludge samples within a week
after filter press operation.
28
-------
TABLE
Outlet of sand
filter
••
Sludge hopper
Tap water line
_
(a) Field blank.
Treated water
• .1.
Sludge
—' i
Tap water'3'
During the same week
the sludge was sampled
*"*'
Within a week after
filter press operation
• :
During the same week
the sludge was sampled
Zn, total Cr, pH
Zn, total Cr,
oil & grease,
total solids
"
Zn, total Cr
Ba,,el,e co,lec,ed the treated was«ewa,er sampies continuously over a
meanS °f thS eXMn9 S3mP"n9 P™P ^ '^ """'• Wh"h " - « Aer
These served as ft*, blanks. A .aboratory b,ank
s ervice- who performed
WM provided by Zande
ECONOMIC EVALUATION
per d • -"I* Payback
penod ana,ys,s, Usin9 the cos, data provided oy Ae,0qu,p. The eva.ua.ion induded es la, o
of cap,,a costs for ,he process conversion and of the reduction, „ any, in operatinToo
resul,,ng from ,he process substitution. Capital costs included.-
• plant modifications
• removal and disposai of the old cadmium cyanide plating solution
• the cost of a fresh zinc chloride plating solution
• cleanup of process tanks, piping and equipment.
29
-------
Operating costs included:
operating and maintenance labor
utilities
plating chemicals
wastewater treatment chemicals
waste disposal costs.
30
-------
SECTION 4
RESULTS AND DISCUSSION
PRODUCT QUALITY
For the salt-spray corrosion tests 12n'
zinc-plated parts Were obtained for
n
two smaHer 9roUps of six
inc (thickness: 0.0002-0 0004 i
use as test
~
'
discussed below.
repreSentative
' * »~
6 **** WW* fack plated
of
by DTL and
are presented and
DTL Salt-Spray Test Data and Results
corrosion testing by DTL i
•ha, ,he 96-hou, requ,remen, of no c 0
Vary siigh, WC was noted on
«».«-P««nt sait-spray ,fcg)
in As™ B 1 '
« 1 » ho.s, so
ye"OW ch™m=te. parts was
-------
120 hours and small WC at 144 hours on the Group C specimens, it is likely that the DTL
Group C specimens would have met the 96-hour requirement.
TABLE 6. RESULTS OF CORROSION RESISTANCE TESTS ON VARIOUS PARTS RACK
PLATED WITH ZINC USING 5-PERCENT SALT SPRAY; TESTS PERFORMED
BY DETROIT TESTING LABORATORY USING ASTM B117-90(a)
========
Date
07/09/92
07/1 0/92
07/13/92
07/1 4/92
07/1 5/92
07/1 6/92
07/17/92
07/20/92
07/21/92
07/22/92
07/23/92
"
======
Elapsed Hours
24
48
120
144
168
. 192 .
216
288
312
336
360
======
====================
Corrosion Test Ratings*1
Group A
2021-2-35
Adapter
0
0
0
0
1 WC
1 WC
1 WC
2 WC
2 WC
3 WC
3 WC
Group B
21 0204-1 2s
Swivel Nut
0
0
0
1 WC
1 WC
1 WC
2 WC
2 WC
4 WC
6 WC
6 WC
==================
Group C
206204-8-6S
Adapter
0
0
1 WC
2 WC
3 WC
3 WC
4 WC
5 WC
6 WC
6 WC/2 RR|C)
6 WC/4 RR!cl
Group D
2089-6-6$
Adapter
0
0
0
1 WC
2 WC
2 WC
3 WC
4 WC
5 WC
5 WC
5 WC
(a) Four different parts, which had been rack plated with zinc, were tested. Each group of parts consisted of six
specimens.
(b) The following corrosion rating system was employed by DTL:
WC = White Corrosion
RR = Red Rust
0 = No corrosion
1 = Very slight
2 = Slight
3 = Slight to moderate
4 = Moderate
5 = Moderate to heavy
6 = Heavy
7 = Very heavy.
(c) Two of the six specimens in Group C exhibited red rust (RR) at the 336-hour and 360-hour observation times.
32
-------
TABLE 7. RESULTS OF CORROSION RESISTANCE TESTS ON VARIOUS PARTS
RACK PLATED WITH ZINC USING 5-PERCENT SALT SPRAY;
TESTS PERFORMED BY AEROQUIP USING ASTM B117-90(8>
Data
07/1 3/92
07/14/92
07/1 5/92
07/1 6/92
07/1 7/92
07/20/92
07/23/92
07/24/92
07/27/92
07/28/92
07/29/92
07/31/92
08/03/92
08/04/92
08/05/92
08/06/92
08/07/92
Elapsed
Hours
0
96
120
144
168
240
264
288
312
336
408
432
456
480
504
576
600
624
648
672
Corrosion Test Results
Group A
2021-2-3S
Adapter
No signs of white
corrosion (WC)
No change
WC on threads and
near braze joint
No change
No change
No change
No change
More WC; black areas
No change
No change
No change
RR starting on two
parts; parts removed
....
—
—
- —
—
—
~~~
Group B
210204-12*
Swivel Nut
_ .
No signs of WC
No change
WC on threads and
cones
No change
No change
No change
No change
No change
No change
No change
One part RR on ext.
threads, RR on ID;
parts removed
—
•
...
...
—
—
• _
—
... ,
Group C
206204-8-6*
Adapter
—
No signs of WC
No change
No change
Small WC, small
specks on corners
No change
More WC
No change
More WC
No change
No change
No change
No change
No change
No change •
No change
No change
More WC
No change
Small discolored
spots on flats of hex.
RR spots; parts re-
moved
Group D
2089-6-6s
Adapter
—
No signs of WC
No change
WC on threads and
cones
No change
No change
No change
One part of six has
red rust (RR)
No change
No change
No change
No change; parts
removed
. ...
—
•
.
_.
...
—
" ' . —
—
(a)
Four different parts, which had been rack plated with zinc, were tested. Each group of parts consisted of six
specimens. Readings of cabinet temperatures and pressures and salt-spray conditions were generally in compliance
with B117-90 requirements for the overall test period. Some problems whh the D.I. water supply and pH meter were
encountered from 07/07/92 to 07/23/92, so that salt solution pH values were below 6.5. The effect of lower solution
pH values or corrosion results was not considered significant. If anything, the lower pH would have resulted in a more
corrosive salt-spray solution.
In the DTL tests, all specimens in Groups A, B, and D were free of red rust (RR) at
the end of the 360-hour observation period. Two of the six specimens in Group C showed
33
-------
RR at the 336-hour and 360-hour observation periods. In comparison, the Aeroquip tests
(Table 7) on the Group C specimens showed no RR until the observation at 672 hours.
Aeroquip Salt-Spray Test Data and Results
As was done at DTL, four comparable groups of six pieces each (Figure 5) were
subjected to 5 percent salt-spray (fog) corrosion testing at the Aeroquip Laboratory in
accordance with procedures designated in ASTM B117-90. Data and results of the Aeroquip
salt-spray tests are presented in Table 7.
Because there was no sign of white corrosion products on any of the specimens in
any of the groups at the 96-hour observation period, all specimens met the no WC
requirement at 96 hours. One of the six parts in Group D showed red rust (RR) at the 264-
hour observation point, but no other parts in Group D exhibited RR at the 408-hour
observation point, at which time all Group D specimens were removed from the test chamber.
Specimens in Groups A, B, and C exhibited good resistance to red rust; the first signs of red
rust for specimens in the three groups were as follows:
Group A: 432 hours
Group B: 408 hours
Group C: 672 hours.
The Aeroquip salt-spray test results (Table 7) showed that the zinc (plus yellow
chromate) plated parts exhibited very good performance with regard to freedom from white
corrosion products for 96-hours. Further, the extended-exposure tests showed that only one
of six specimens in Group D exhibited RR at 264 hours. Thus, of a total 24 specimens, only
one specimen definitely would not have met the Aeroquip internal requirement of freedom
from RR at 360 hours. One specimen in Group B exhibited RR at 408 hours; at 336 hours,
no specimens in this group showed RR. Whether that one specimen exhibited RR at 360
hours is not known, as no observation Was made at 360 hours, which occurred on a
weekend.
34
-------
Comparison of DTL and Aeroquip Salt-Spray Tes, ResuKs
The data and results shown in Tables 6 and 7 and discussed above demonstrate
very good agreement in results of the salt-spray tests conducted by the two Jaboratories on
the zmc-plated parts. In general, very good a9reemen, and full compliance with the
requ,rement for absence of white corrosion products for 96 hours was noted for the groups
of specimens tested a, both laboratories. Further, there was generally good agreement in
results with respect to the appearance of red rust. A, both laboratories, on,y 3 of 48 speci-
mens did no, meet Aeroquip's internal requirement of freedom from red rust for 360 hours of
exposure to salt spray.
Additional Aeroauip Salt-Sorav TV»st Data anri Roc..it?
^ In addition to the salt-spray testing of the rack-piated parts, carried out in parallel
by DTL and Aeroquipand reported above in Tables 6 and 7, Aeroquip also tested four groups
of barrel-plated parts. Each group of parts consisted of six specimens plated with zinc
Corros,on data and results of these latter tests are presented in Table 8. As can be seen from
Table 8, al! specimens in all four groups met the requirement of freedom from white corrosion
(WCI products a, 96 hours. WC had started to appear on mos, of the specimens a, the 168-
hour observation point.
All parts also met the requirement of no red rust (RR) at 360 hours. One specimen
m Group A exhibited RR at 432 hours. At 504 hours, RR was present on Group A and Group
C parts, but Group B and Group D specimens showed no RR. The tests were terminated at
504 hours. The above data and results show that excellent resistance to both white corrosion
and red rust was exhibited by all 24 specimens in the four groups of parts that had been barrel
plated with zinc. .
Comprehensive Program of Salt-Snrav Te.,tinq n<
Cadmium-Plated Parts at Aeroguip
From October 15 to November 5, 1991, Aeroquip carried out corrosion tests to
compare the salt-spray corrosion resistance of zinc-plated parts with cedmium-plated parts
These tests were done in accordance with ASTM Method B117-90. Seven groups of
representative parts p.ated with zinc and seven groups of identica, parts plated with cadmium
35
-------
Corrosion
^™™™^".™1
Group B
Test Results
Group C
Elapsed
Hours
FC1044
Nipple
FC3596-08s
Crimp Socket
FC1006-12s
Socket
FC1130-08s
Socket
10/05/92
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10/06/92
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10/07/92
— — in.
10/08/92
• • i.
10/09/92
~ ,
10/12/92
•
10/1 3/92
—. ,.-
10/14/92
~ i —-i i—
1 0/1 5/92
No corrosion
•
No corrosion
——————_
No corrosion
———«—«^__
No corrosion
•" • .1 —
WC starting
No change
—————__
No change
•————_
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No corrosion
—————_M...
No corrosion
-T——^—__
No corrosion
,
No corrosion
•————™_
WC starting
'
No change
•
No change
—
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No corrosion
•^———__
No corrosion
——^——__
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——^"—.^—-
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-"-^—_«
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•
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.—
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Slightly more WC I Slightly more
WC
No change
———•—_
More WC
—
No change
No change
10/1 6/92
10/21/92
10/22/92
10/23/92
No change
No change
••—••——^__
No change
No change
1
More WC
i.
No change
—™—>__«^H
No change
No change
1
More WC
••
No change
—•—^—^_»_
No change
Red rust (RR) on
one part
(a) Four different
specimens.
parts, which had been barrel plated
No change
._
with zinc, were tested.
RR in I.D. | NO change
=====
Each group of parts consisted of six
36
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be.ow: The reSU'tS °f the Salt-SpraV tests °n the Zinc-P'*ed parts (Table 9, are summarized
" Sf's'e to^J" th,eHSe,Ven Qr°UPS °f Parts Passed the requirement
of 96 hours before the first appearance of white corrosion products.
at^S^
at the 360-hour observation time, so that all specimens met the
requirement of freedom from RR for 360 hours.
" ^ SP^imrS in Gr°UpS A' B' D and G were stil1 free of red rust
after 504 hours of salt-spray exposure. Red rust was beginning
develop on specimens in Groups C, E, and F at 504 hours at which
point all tests were terminated.
The results of the salt-spray tests on cadmium-plated parts (Table 1 0) are
summarized below:
h« f« r the rec>uirement of 96
hours before the first appearance of white corrosion products The
appearance of white corrosion products in any of the seven groups
was delayed to 336 hours and beyond. seven groups
B KI/% *•!
f CA W3S observed on any of the cadmium-plated specimens
ttminated."0"8 °f 6XPOSUre' at Whlch P°int the tests were
The above results demonstrate that the cadmium-plated parts exhibit superior corrosion
^stance to zinc-plated parts with regard to the appearance of white corrosion products and
red rust in salt-spray tests.
Summation Comments nn Adequacy of Corrosion
Resistance Properties of Zinc-Ptgted Parts
In view of the results of salt-spray tests carried out on zinc-plated parts by the
Detroit Testing and the Aeroquip Laboratories during this project, along with the results from
earner Aeroquip tests on zinc- and cadmium-plated parts, the following generalized comments
can be made:
prclduces a Coatin9that ^tisfies customer requirements
before the appearance of white corrosion products.
42
-------
• These same zinc-plated parts also comply with Aeroquip process
requirements of 360 hours before the appearance of red rust.
• Cadmium-plated parts are superior in their corrosion resistance
properties (i.e., appearance of white corrosion products and red rust)
to zinc-plated parts.
In light of the above evaluations, the corrosion resistance properties of zinc-plated
parts are considered satisfactory to allow use of zinc as a substitute for cadmium in many
plating applications. The Aeroquip Corporation, after extensive evaluation, switched over to
acid zinc chloride plating to replace their existing cyanide cadmium-plating operations in early
1991. The Aeroquip acid zinc chloride plated coatings comply with ASTM and many industrial
company specifications for corrosion resistance.
WASTE AND POLLUTANT REDUCTION
Environmental effects of the process change were evaluated on the basis of waste
volume reduction and pollutant reduction. Waste volume reductions were estimated for the
treated wastewater and the dewatered sludge, which affect conservation of water and landfill
space, respectively. Pollutant estimates focused mainly on toxic pollutants/such as cadmium,
cyanide, and chromium.
Waste Reduction
The quantities of treated wastewater and dewatered sludge from the cadmium-
plating process generated in 1989 and from the zinc-plating process generated in 1991 were
estimated from the data provided by Aeroquip and shown in Table 11. The production rate
(i.e., number of parts or pieces plated) in 1989 was 31 percent higher than the production
rate in 1991. Therefore, the waste generation for 1991 was adjusted upward by a factor of
1.31 for direct comparison with the 1989 waste generation. The adjusted 1991 wastewater
generations were 40.0 million gallons from the cadmium-plating process and 44.9 million
gallons from the zinc-plating process. The wastewater generated from the zinc-plating
process was, therefore, 1 2 percent higher than the wastewater generated from the cadmium-
43
-------
plating process. The adjusted sludge generations were 282,000 Ib from the cadmium-plating
process and 383,000 Ib from the zinc-plating process, an increase of 36 percent due to the
process substitution. The increases in wastewater and sludge generations were due to
increase in plating bath concentration from approximately 3 oz/gal cadmium in the cadmium-
plating baths to approximately 3.5 oz/gal zinc in the zinc-plating baths. The increased zinc
metal concentration in the zinc chloride plating bath increased the dragout and rinse water and
thereby increased the wastewater and sludge generation. The waste oil generation data
provided by Aeroquip were 26 drums/year from the cadmium-plating process in 1989 and
6 drums/year from the zinc-plating process in 1991, or 9,542 Ib/year and 2,202 Ib/year,
respectively, based on a specific gravity of the waste oil at 0.8. The decrease in the waste
oil generation was probably due to approximately tenfold reduction in the concentration of oil
in the water-soluble oil dip tank used in the zinc chloride plating process compared with the
oil concentration used in the cadmium cyanide plating process.
TABLE 11. ANNUAL GENERATION OF TREATED WASTEWATER AND
SLUDGE FROM CADMIUM- AND ZINC-PLATING PROCESSES
{AEROQUIP DATA)
Year
1989
1991|a)
Plating
Process
Cd
Zn
Treated
Wastewater,
gal
40,000,000
44,900,000
Sludge,
Ib
282,000
383,000
(a) Adjusted to the 1989 production rate of the electroplating process.
Pollutant Reduction
Tables 12 and 13 show chemical analyses of treated wastewater discharged from
the plant. Table 12 includes the data obtained by Aeroquip during July-December 1989 for
the cadmium-plating process, and during July-December 1991 and June-August 1992 for the
zinc-plating process. The change from cadmium to zinc plating occurred during December
1990 and January 1991. The Aeroquip data shown in Table 1-2 indicate that all pollutant
concentrations are below the effluent discharge limits set by the municipal wastewater
treatment plant that receives the wastewater. The changes in the average wastewater ana-
44
-------
TABLE 12. CHEMICAL ANALYSIS OF TREATED WASTEWATER FROM
CADMIUM- AND ZINC-PLATING PROCESSES (AEROQUIP DATA)
Concentration,
Month
1 989 Cd Platinq
Jul
Aug
Sep
Oct
Nov
Dec
Average
1991 Zn Platina
Jul
Aug
Sep
Oct
Nov
Dec
Average
1992 Zn Platina
Jun
Jul
Aug
Average
Discharge Limits
pH
10.51
10.21
10.05
9.75
9.44
9.91
9.98
7.87
8.59
7.83
8.46
8.52
8.15
8.24
8.14
8.29
8.01
8.15
< 10.50
Cd
0.011
0.060
0.045
0.04
0.06
0.04
0.043
0.011
0.012
0.053
0.079
0.038
0.015
0.035
0.006
0.011
0.008
0.008
0.26
Total
Cr
0.07
0.025
0.008
0.018
0.46
0.09
0.11
0.161
0.042
0.111
1.01
0.249
0.104
0.28
0.104
0.065
0.092
0.087
1.71
Total
CN(a)
1.23
2.99
3.25
3.49
1.68
2.37
2.50
<0.02
0.030
<0.02
<0.02
<0.02
< 0.002
<0.019
<0.02
<0.02
<0.02
<0.02
(a)
mg/L
Amenable
CNla)
0.14
<0.18
0.13
0.17
0.12
0.19
0.16
<0.02
<0.01
<0.02
<0.02
<0.02
<0.002
< 0.0 15
<0.02
<0.02
<0.02
<0.02
0.32
Zn
< 0.003
0.017
< 0.007
< 0.008
< 0.003
0.008
< 0.008
0.366
0.345
0.510
0.580
0.659
0.264
0.454
0.515
0.322
0.356
0.398
1.00
(a) Aeroquip is required to report total cyanide but is regulated by the amenable cyanide limit of 0.32 mg/L.
45
-------
TABLE 13. CHEMICAL ANALYSIS OF TREATED WASTEWATER FROM
ZINC-PLATING PROCESS (BATTELLE DATA)
Concentration, mg/L
Sample No.
46325-05-05
46325-06-28
46325-10-07
46325-13-21
Average
Date of
Sampling
06/23/92
06/24/92
06/25/92
06/30/92
PH
8.41
8.21
8.44
8.61
8.42
Total
Cr
0.025
0.129
0.079
0.042
0.069
Zn
0.330
0.466
0.384
0.340
0.380
lyses from July-December 1989 to July-December 1991 shown by the Aeroquip data were:
(a) decrease in pH from 9.98 to 8.24, (b) decrease in Cd concentration from 0.043 to 0.035
mg/L, (c) increase in total Cr concentration from 0.11 to 0.28 mg/L, (d) decrease in total CN
concentration from 2.50 to less than 0.019 mg/L, (e) decrease in amenable CN from 0.16 to
less than 0.015 mg/L, and (f) increase in Zn concentration from less than 0.008 to 0.454
mg/L. The changes in pollutant concentrations were consistent with the process substitution.
The higher pH was used in the cadmium cyanide plating process to optimize removal of Cd
by sulfide precipitation. Increase in totalCr concentration was due to approximately fivefold
increase in the Cr concentration in the yellow chromate solution used in the zinc chloride
plating process compared with the Cr concentration in the clear chromate solution used in the
cadmium cyanide plating process. The Aeroquip data in Table 1 2 show further decrease in
Cd concentration from 0.035 mg/L during June-December 1991 to 0.008 mg/L during June-
August 1992, indicating the residual Cd left in the process tanks (mainly in the sludge
thickener in the wastewater treatment plant) continued to decline. Table 13 shows the
wastewater analysis data for the samples collected by Battelle from the zinc-plating process
during June 1992. The Battelle data generally agreed with the Aeroquip data reported for
June-August 1992.
Table 14 shows the sludge analysis data obtained by Aeroquip for the cadmium-
plating process during November 1987 and February 1988 and from the zinc-plating process
during July 1 991. The historical data provided by Aeroquip for the cadmium-plating process
46
-------
included one analysis each for moisture content (67 percent), Cd (43,000 mg/kg), hexavalent
Cr (below detection limit, 0.1 mg/kg), and oil and grease (18,000 mg/kg). The historical data
provided by Aeroquip for the zinc-plating process included one analysis each for total Cr
(5,900 mg/kg) and hexavalent Cr (below detection limit, <0.1 mg/kg). No data were
available on total Cr concentration of the sludge from the cadmium-plating process. The
extremely low concentration of hexavalent Cr in the sludge from either process indicates very
efficient operation of the chemical treatment step, which converts the toxic hexavalent Cr to
much less toxic trivalent Cr.
TABLE 14. CHEMICAL ANALYSIS OF SLUDGE FROM CADMIUM- AND
ZINC-PLATING PROCESSES (AEROQUIP DATA)
Concentration, mg/kg
Date of
Sampling
Nov/87(a)
Feb/88(a|
Jul/91(b)
Moisture,
percent
67
(c)
71
Total
Cd Cr
-------
wastewater analyzed by Battelle in June 1992 (shown as 0.069 mg/L in Table 13) than the
Cr concentration in the treated wastewater analyzed by Aeroquip in July 1991 (shown as
0.161 mg/L Table 12).
TABLE 15. CHEMICAL ANALYSIS OF DEWATERED SLUDGE FROM
ZINC-PLATING PROCESS (BATTELLE DATA){a)
Concentration, mg/kg
Sample No.
46325-01-12
46325-03-24
46325-06-22
46235-08-26
46235-12-08
46325-13-07
Average
Date of
Sampling
06/22/92
06/23/92
06/24/92
06/25/92
06/26/92
06/30/92
Moisture,
percent
67.5
72.8
70.4
69.6
69.1
70.6
70.1
Total
Cr
20,700
14,700
15,800
15,300
17,500
16,900
1 6,800
Zn
55,100
55,600
59,000
61,700
59,600
56,400
57,900 -&
Oil&
Grease
7,580
5,520
8,040
9,140
9,110
6,410
7,630
(a) Sludge samples were collected as grab samples.
Pollutant generations, estimated from the quantities of treated wastewater and
sludge and pollutant concentrations in each waste stream, are summarized in Table 16 for the
cadmium- and the zinc-plating processes. For example, the quantity of Cd generated in the
sludge was estimated by multiplying the annual sludge generation (281,820 Ib/yr from Table
11) and the Cd concentration in the sludge (43,000 mg/kg from Table 14) as follows:
281,820 x 43,000/1,000,000 = 12,118 Ib/yr. The pollutant generations were based on the
1989 production rate of the electroplating process. The 1989 production rate, expressed as
sq ft of electroplated surface area of production parts, was estimated from the quantity of Cd
metal coated and the coating thickness. The quantity of Cd metal coated was estimated as
44,400 Ib by subtracting the waste Cd metal (12,100 Ib from Table 16) from the actual Cd
consumption in 1989 reported by Aeroquip as 56,500 Ib. Based on an average coating
thickness of 0.0003 inches (the mean of the 0.0002- to 0.0004—inch coating thickness
specification) and the specific gravity of Cd metal at 8.64,the total surface area of production
48
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TABLE 16. POLLUTANT GENERATION IN LB/YR FROM CADMIUM-
AND ZINC-PLATING PROCESSES BASED ON 1989
PRODUCTION RATE OF 3.29 MILLION SQ FT<8)
Wastewater
Cadmium-Platinq Process
Cd
Total CN
Total Cr
Zn
Oil & Grease
Zinc-Platina Process
Cd
Total CN
Total Cr
Zn
Oil & Grease
14
835(b)
37(b)
0
_(d)
Ow
0
75(h)
16l(h)
_(d)
Sludge
12,100(c)
0
640(e)
0
5,070(c)
0(9)
0<9>
4,350(i)
22,200(i)
2,920(j)
Waste Oil Total
-(d> 12,100
-W 835
-W) 677
0 0
9,540(f) 14,600
_(d) 0
_(d) o
-(d) 4,420
-(
-------
parts electroplated in 1989 was estimated as 3.29 million sq ft. The estimated pollutant
generations were based on the following assumptions:
• Zero discharge of Cd and CN from the Zn plating process.
• Zero discharge of Zn from the Cd plating process.
• The concentration of CN in sludge was assumed to be equal to that
in wastewater. This assumption will result in overestimating CN in
the sludge because CN is present in both media in a soluble form.
In the cadmium cyanide plating process, Cd and Cr were predominantly discharged in the
sludge and the CN in the treated wastewater. In the zinc chloride plating process, Zn and Cr
are also discharged predominantly in the sludge stream. A complete comparison of Cr
discharges from the two processes was not possible due to lack of data on Cr analysis of
sludge from the Cd plating process. Since the Cr concentration in the clear chromate solution
used in the Cd plating process was approximately 1/5 of the Cr concentration In the yellow
chromate solution used in the Zn plating process, the quantity of Cr in the sludge from the Cd
plating process (shown as 640 Ib/yr in Table 16) was estimated by assuming that the Cr
concentration in the sludge from the Cd plating process was 1 /5 of the Cr concentration of
the sludge from the Zn plating process.
Chemical analysis of the field blank (tap water) and the laboratory blank are shown
in Table 1.7. The Cr and Zn levels in the blanks appeared to be low enough that they have
negligible effect on estimation of the Cr and Zn discharges from the Zn plating process.
ECONOMICS
Table 18 shows the capital cost for converting the plating lines at Aeroquip from
cadmium plating to zinc plating. The cost data were provided by Aeroquip and were adjusted
to 1992 dollars using a 5 percent/year escalation. Approximately 72 percent of the total cost
was for expenses related to cleaning up the Cd process equipment and for disposal of the
waste generated from the cleanup operation; the remaining 28 percent was for installation of
the new equipment. The work involved in converting the plating lines included: (a) removal
and off-site destruction of the cadmium cyanide plating bath, (b) cleanup of the plating areas
and the cyanide destruction tanks in the wastewater treatment plant, (c) stripping and relining
50
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of the plating and rinse tanks with a new resin liner, (d, replacement of process piping (e)
.nstal.at.on of a continuous filter for the new zinc chloride bath, (e) instal.ation of new heat
exchangers to dissipate additional heat generated from the zinc,-plating process, (f) instal.ation
of a new air agitation system for the zinc-plating bath, (g) installation of an acid resistant
epoxy liner on the concrete pit used in emergencies when the plating tanks need to be cleaned
of sludge, (h) replacement of the dryers on the barrel plating lines, and (i) extension of the
dryer on the rack plating line.
TABLE ,7. =CAL ANALYSIS OJRM BLANK ANO LABORATORY
Sample Sample No.
===============5====—====;;——..
Field Blank (Tap Water) 46325-06-12
46325-11-26
Average
Laboratory Blank
(a) Not determined.
— ^S!
Concentration,
mg/L
Date Sampled
._
06/23/92
06/24/92
06/24/92
— •
PH
=====
7.57
7.77
7.67
(a)
Total
Cr
0.019
0.041
0.030
0.017
Zn
-1- — — -~-~ — ; —
0.027
0.032
0.030
0.021
TABLETS. CAPITAL COST
Parameter
Expense (clean-up of old
equipment and waste dis-
posal)
New equipment
Subtotal
Total
Barrel
Plating Lines
$ 428,000
$ 424,000
$ 852,000
Rack
Plating Line
$ 999,000
$ 122,000
$ 1,121,000
Subtotal
$ 1,427,000
$ 546,000
$ 1,973,000
51
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Table 19 shows the annual operating cost data provided by Aeroquip, adjusted to
1992 dollars. The data for the cadmium-plating process were from actual 1989 expenses,
except for the cadmium anode cost, which was based on the actual amount of the anode
consumed in 1989 (56,500 Ib) and the 1992 price of cadmium anode at $0.99/lb.
Consumption of zinc anode was estimated as 59,000 Ib by adding the amount of Zn coated
(36,668 Ib based on 0.0003 inch coating thickness, 3.29 million sq ft of coating, and specific
gravity of Zn metal at 7.14) and the amount of Zn wasted (22,300 Ib from Table 16). The
cost for zinc anode was based on the above estimate and the 1992 price of the zinc anode
at $0.78/lb.
The cost of wastewater treatment chemicals for the zinc-plating process included
savings of $38,300, primarily due to elimination of chlorine for cyanide destruction, and an
increase of $13,900 due to increased consumption of sulfur dioxide for reduction of
hexavalent chromium. These changes resulted in a net cost savings of $24,400. The labor
cost was based on the number of operators (which has not changed between the two
processes) and a unit cost of $25/hr, including supervision and overhead. The cost of
electricity for the plating processes was estimated from the voltage and current data provided
by Aeroquip. Details of the electrical power consumption and cost calculations are provided
in the Appendix.
Incremental maintenance costs for the cadmium-plating process over the zinc-plating
process were listed under miscellaneous expenses, which included the costs for the
washdown of the plating department, treatment of the washdown water, blood tests for
workers, environmental monitoring, and record keeping. The cost of sludge disposal was
estimated from the sludge volumes (shown in Table 7) and a sludge disposal unit cost of
$178.50/ton, as provided by Aeroquip. The cost of waste oil disposal was estimated from
the waste oil generation (Table 16) and disposal cost of $600/drum for hazardous waste
incinerator charge estimated by Battelle.
The reduction in annual operating cost resulting from substitution of zinc plating for
cadmium plating was estimated to be $17,200. For a new installation, therefore, the zinc
chloride plating process has an economic advantage of lower operating cost over the cadmium
cyanide plating process. The payback period for the capital investment of $1,973,000 for
process substitution was estimated as 115 years. The process substitution, therefore, cannot
be justified solely on economic grounds. It should be based on improving worker safety and
52
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environmental pollution, as well as on greater acceptance of the zinc-plated components in
domestic and foreign industrial and consumer markets. However, in comparing the two for
a new installation, the zinc chloride plating process offers obvious advantages over the
cadmium cyanide plating process.
TABLE 19. COMPARISON OF OPERATING COSTS FOR CADMIUM-
AND ZINC-PLATING PROCESSES'8*
== — — —_
Electroplating Chemicals
Clear chromate
Brightener
NaOH flakes
Yellow chromate
Sodium cyanide
Cadmium anode @ $0.99/lb
Potassium chloride
Boric acid
Wetter
Zinc anode @ $0.78/lb
Wastewater Treatment Chemicals
Operating Labor, 14 persons @ $2-
r- it
5/hr
Electricity, @ $0.08/kwh
Miscellaneous
Blood Tests
Environmental monitoring
Record Keeping
Washdown of Plating Dept.
Treatment of washdown
water
Sludge Disposal Cost, @ $1 78.50/ton
Waste Oil Disposal, @ $600/drum
Total
Net Cost Reduction
======================
Cadmium
Plating
$ 3,840
3,180
3,330
16,900
42,800
55,900
$ 215,000
$ 728,000
$8,920
$ 3,240
2,320
463
6,370
4,050
$ 25,200
$15,600
$ 1,135,000
.,
Zinc
Plating
$ 49,800
28,900
6,680
4,050
46,000
$ 190,000
$ 728,000
$ 7,880
$ 34,200
$ 3,600
$ 1,118,000
$ 17,200
(a) Adjusted to 1 992 dollars.
53
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SECTIONS
QUALITY ASSURANCE
A Quality Assurance Project Plan (QAPP, Battelle, 1992} was prepared and approved
by the EPA before testing began. This QAPP contained a detailed procedure for conducting
this study. Collection and analyses of samples were performed according to the QAPP.
ON-SITE SAMPLE COLLECTION
All samples were collected as outlined in the QAPP. The original sampling plan
proposed in the QAPP is shown in Table 20. All samples were collected over a 2-week
period. Dewatered sludge samples were collected as grab samples from the sludge hopper
located at the discharge of the filter press. The sludge samples were taken from various
locations in the hopper and mixed in a glass beaker to obtain composite samples. All sludge
samples were collected within a week after filter press operation.
Treated waste water samples were collected continuously over a 24-hour period by
means of the existing sampling pump in the plant, which is used at Aeroquip to collect
composite water samples. The sample collection rate was varied in each shift in proportion
to the discharge rate of each shift (i.e., at a ratio of 2.6:1.9:1.0, corresponding to
first:second:third shifts). Tap water samples were collected as grab samples from a tap water
faucet. These served as field blanks. A laboratory blank was provided by Zande
Environmental Service, who performed the chemical analyses of treated wastewater and
sludge samples.
54
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TABLE 20. SUMMARY OF PRIMARY AND QUALITY CONTROL SAMPLES
FOR CHEMICAL ANALYSIS AND CHARACTERIZATION
~-
Sample
Location
Outlet of Sand
Filter
Sludge Hopper
Tap Water
1 inn
Line
=======
,
Sample Matrix
Treated Water
Sludge
Tap Water'31
=======
Time of Sampling
During the same week
the sludge was sampled
Within a week after
filter press operation
During the same week
the sludge was sampled
======
Number of
Samples*1
4
6
2
Measurements
Zn, Total Cr, pH
Zn, Total Cr, Oil &
Grease, Total Solids
Zn, Total Cr
(a) Field blank.
(b) Including one reserve sample for each sample matrix. Samples collected in the field did not include samples prepared
in the laboratory for QA, such as duplicates, matrix spikes, and method blanks.
CHEMICAL ANALYSIS
All analyses were performed as planned in the QAPP. The pH of the treated
wastewater and tap water was determined at the time of sample collection. The precision
of the chemical analysis of the sludge and the treated wastewater are presented in Tables 21
and 22, respectively. All precision data were in the acceptable range of 25 percent.
TABLE 21; PRECISION OF SLUDGE ANALYSIS
Parameter
Oil & Grease
Total Chromium
Zinc
Total Solids
1
Sample
No,
46325-6-22
46325-6-22
46325-6-22
46325-6-22
*'- ' " " ii"
Regular
Sample
8040 mg/kg
1 5800 mg/kg
5900 mg/kg
70.4 %
— --+-H--
Duplicate
8500 mg/kg
1 5800 mg/kg
5800 mg/kg
70.3 %
.
11111111 "—
Precision
(%)
5.6
0.0
1.7
0.1
.
55
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TABLE 22. PRECISION OF TREATED WASTEWATER ANALYSIS
Parameter
Total
Chromium
Zinc
PH
Sample
No.
46325-6-28
46325-6-28
46325-6-28
Regular
Sample
0.129 mg/L
0.466 mg/L
8.21
Duplicate
0.1 17 mg/L
0.434 mg/L
8.16
Precision (%)
9.8
7.1
0.6
The accuracy of the chemical analysis of the sludge and the treated waste water is
presented in Tables. 23 and 24, respectively. All matrix spike recoveries were in the
acceptable range of 75 to 125 percent.
TABLE 23. ACCURACY OF SLUDGE ANALYSIS
Parameter
Oil &
Grease
Total
Chromium
Zinc
Sample
No.
46325-8-26
46325-8-26
46325-8-26
Regular
Sample
(mg/kg)
9810
15300
61700
Matrix
Spike Level
(mg/kg)
50000
16600
33200
Matrix Spike
Measured
(mg/kg)
64150
, 32600
97500
Accuracy
{% Recovery)
107
1 02
103
TABLE 24. ACCURACY OF TREATED WASTEWATER ANALYSIS
Parameter
Total
Chromium
Zinc
Sample
No.
46325-10-7
46325-10-7
Regular
Sample
(mg/L)
0.079
0.384
Matrix
Spike Level
{mg/L)
1.000
1.000
Matrix Spike
Measured
(mg/L)
0.980
1 .342
Accuracy
(% Recovery)
91
97
56
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All samples collected and analyzed in accordance with the QAPP were judged to be
valid to achieve a 100 percent completeness. The detection limits of the methods used for
all chemical analyses were equal to or smaller than the minimum required detection limits
specified in the QAPP.
LIMITATIONS AND QUALIFICATIONS
Based on the above QA data, the results of the pn-site and laboratory testing can
be considered valid for drawing conclusions about the chemical compositions of the sludge
and of the treated wastewater discharged from the wastewater treatment plant at Aeroquip.
57
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SECTIONS
REFERENCES
Battelle. 1 992. Quality Assurance Project Plan for the Substitution of Zinc Chloride
Electroplating for Cadmium Cyanide Electroplating. Prepared for the U S
Environmental Protection Agency Risk Reduction Engineering Laboratory, Cincinnati,
Dini, J. W. and H. R. Johnson. 1979. "Electrodeposition of Zinc-Nickel Alloy
Coating." Metal Finishing 77(9):53-7.
Donakowski W. A. and J. R. Morgan. 1983. "Zinc-Graphite - A Potential Substitute
Tor Anti-Calling Cadmium." J. Plating and Surface Finishing 70(1 1 ):48-51 .
Hsu, G. F. 1984. "Zinc-Nickel Alloy Plating: An Alternative to Cadmium." J Platina
and Surface Finishing 7 1(4): 5 2-5.
ooo, !«8°- "Cadmium/s p«9ht Opens Field to Alternative Coatings." Iron Age
2.23(2.)'.oO.
Journal of Plating and Surface Finishing. 1977. "Cadmium Colloquy." J. Plating and
Surface Finishing 64( 1 1 ):8, 1 0, 1 2, 1 4.
Rizzi, K. W., N. J. Spiliotis, and K. F. Blurton. 1986. "Calling-Resistant
Zinc/Silicon/Phosphate Coating Protects Thread Connections in Hostile Service " Oil
and Gas Journal. July 1 5, 1 36-1 39.
58
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APPENDIX
COMPARISON OF POWER CONSUMPTION VALUES FOR
THE ZINC-VERSUS CADMIUM PLATING OPERATIONS
Aeroquip has indicated that the thickness of the zinc coating being applied now is the
same as the thickness of the cadmium coating applied previously; this thickness is 0.0002
to 0.0004 in. Therefore, comparison of power consumptions for the two processes was
based on the same coating thickness.
REPRESENTATIVE PLATING CONDITIONS
Representative electroplating conditions currently employed on the various lines at
Aeroquip for the deposition of zinc coatings from the zinc chloride bath and those used earlier
for deposition of cadmium from the cadmium cyanide bath are as follows:
Zinc Chloride Bath
Rack Plating Line
Cell Voltage: 2.5 - 3.0
volts
Current: 3200 amp
Single Hoist Barrel Line
Cell Voltage: 5-6 volts
Current: 1100 amps
Twin Hoist Barrel Line
Cell Voltage: 5-6 volts
Current: 1300 amps
Cadmium Cvanide
Cell Voltage: 5.0 volts
Current: No data provided
Cell Voltage: 6 to 8 volts
Current: No data provided
Cell Voltage: 6 to 8 volts
Current: No data provided
59
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The current values shown for the various lines are typical values employed in production at
Aeroquip; these values depend on the area of the work pieces being plated. No amperage
data for the cadmium plating operations were available from Aeroquip.
ELECTROCHEMICAL EQUIVALENCE AND OTHER DATA
The following are other data related to the electrodeposition of zinc and cadmium:
Electrochemical Equivalent (Theoretical):
Zinc: 2.6886 lb/1000 amp-hr
Cadmium: 4.6226 lb/1000 amp-hr
Specific Gravity or Density:
Zinc: 7.14 g/cc
Cadmium: 8.64 g/cc
Electrodeposition Factor (Theoretical):
Zinc: 13.7 amp-hr to deposit 0.001 inch/sq ft
Cadmium: 9.73 amp-hr to deposit 0.001 inch/sq ft.
Based on the electrochemical equivalence data, more pounds of cadmium theoretically are
deposited per 1000 amp-hr than for zinc by a factor of 4.6226/2.6886 or 1.719. However,
based on the metal density values, it requires more (i.e., a greater weight) cadmium than zinc
to provide an equivalent coating thickness by a factor of 8.64/7.14 = 1.21. The theoretical
electrodeposition factor data indicate that it requires more amp-hrs to deposit 0.001 inch/sq
ft of zinc than of cadmium by a ratio of 13.7:9.73 or 1.4:1.
POWER CONSUMPTION CALCULATION FOR ZINC ELECTROPLATING OPERATIONS
Using the plating line data provided above, the estimated annual power consumption data
for the zinc electroplating operations were calculated.
60
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The following plating schedule was assumed:
2 shifts/day; 8 hrs/shift
5 days/week; 50 weeks/year
Total annual hours of plating operation: (2)(8)(5)(50) = 4000
Rack plating line: (3200 amp)(2.8 v) = 8,960 watts or 8.96 kW
Combined barrel lines: (2400 amp)(5.5 v) = 13,200 watts or 13.20 kW
Combined rack and barrel lines = 22,160 watts or 22.16 kW
Estimated Annual Power Consumption:
Rack plating: (8.96){4000) = 35,840 kWh
Barrel plating: (13.20X4000) = 52,800 kWh
Combined plating: (22.16X4000) = 88,640 kWh.
The lack of current (amperage) data for the cadmium-plating operations precluded similar
direct calculation of power consumption data for cadmium plating. The method employed
to determine power consumption data for cadmium for comparison purposes is described
below.
POWER CONSUMPTION VALUES FOR ZINC AND CADMIUM PLATING OPERATIONS
To estimate the power requirements for depositing an equivalent coating thickness of
zinc compared to cadmium, it is necessary to take into account the respective cell voltages
and current efficiencies for the zinc chloride and cadmium-cyanide plating operations.
Data in the literature indicate that typical cathode current efficiency (CE) values for plating
zinc from zinc chloride are near 100 percent (Dini and Johnson, 1979); Geduld (1988)
states 95 to 98 percent. For the cadmium cyanide bath, typical CE values are generally in
the range of 85 to 95 percent (Dini and Johnson, 1979). For calculation purposes herein,
a CE value of 97 percent was assumed for zinc plating; a CE value of 90 percent was
assumed for cadmium plating.
The comparative power consumption values for the zinc and cadmium plating
operations were calculated using the data on electrodeposition factors, cell voltages, and
current efficiencies cited above. The results of these determinations are as follows:
61
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Rack Plating Power Consumption:
Zinc: 13.7(2.8)/0.97 = 39.5 watt-hr to deposit 0.001 inch/sq ft
Cadmium: 9.72(5.0)70.90 = 54.0 watt-hr to deposit 0.001 inch/sq ft
Barrel Plating Power Consumption:
Zinc: 13.7(5.5)/0.97 = 77.7 watt-hr to deposit 0.001 inch/sq ft
Cadmium: 9.72(7.0)70.90 = 75.6 watt-hr to deposit 0.001 inch/sq ft.
From the above, it can be seen that power consumption values for deposition of equivalent
thicknesses on work pieces are significantly higher for the barrel plating operations than for
the rack plating operations for both zinc and cadmium coatings. This is primarily because
of the higher cell voltages required for the barrel plating operations. About 27 percent less
power is required for the rack plating of zinc as compared to that for cadmium. For barrel
plating, about 3 percent more power is required for the plating of zinc as compared to that
for cadmium.
Assuming that the same proportional amounts of rack and barrel plating occurred in the
cadmium plating operations as in the zinc-plating operations, the estimated annual power
consumption data for deposition of cadmium coatings were calculated as follows:
Annual Power Consumption:
Zn Rack Plating = 35,840 kWh
Cd Rack Plating = 35,840 (54.0/39.5) = 49,000 kWh
Zn Barrel Plating = 52,800 kWh
Cd Barrel Plating = 52,800 (75.6/77.7) = 51,370 kWh
Zn Combined Rack and Barrel Plating = 88,640 kWh
Cd Combined Rack and Barrel Plating = 100,370 kWh.
The above data show that, for the combined rack and barrel operations, the power
expenditure is about 1-0 percent less for the electroplating of zinc from the zinc chloride
bath as compared with the previous electroplating of parts with cadmium from a cadmium
cyanide bath.
62
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ESTIMATED POWER COSTS OF ELECTROPLATING OPERATIONS
The above calculations of power consumption were based on direct current (DC)
amperage values. Assuming a rectifier efficiency of 90 percent for converting alternating
current (AC) to direct current, the power consumption values for the combined rack and
barrel operations are as follows:
Zinc: 88,640/0.90 = 98,490 kWh
Cadmium: 100,370/0.90 = 111,520 kWh.
At an electricity charge of $0.08/kWh, the estimated annual cost for the electrodeposition
of the coatings is as follows:
Zinc: 98,490(0.08) = $7879
Cadmium: 111,520(0.08) = $8922.
SUMMATION COMMENTS
The switch to plating parts at Aeroquip with zinc from a zinc chloride bath instead of
cadmium from a cadmium cyanide bath has resulted in a small (about 10 percent)
reduction in the consumption and consequent cost of electricity.
REFERENCES
Dini, J. W. andj-l. R. Johnson. 1979. "Electrodeposition of Zinc-Nickel Alloy
Coating." Metal Finishing 77(9):53-7.
Geduld, H. 1988. Zinc Plating. Finishing Publications, Ltd., Teddington, Middlesex,
England, or ASM, Metals Park, Ohio.
63
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