EPA-440/1-75/040
GROUP I, PHASE II
Development Document for Interim
Final Effluent Limitations Guidelines
and Proposed Nkw Source
Performance Standards
for the
COMMON AND PRECIOUS METALS
Segment of the
ELECTROPLATING
Point Source Category
UNITED STATES ENVIRONMENTAL PROTECTION AGENC
April 1975
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DEVELOPMENT DOCUMENT
for
INTERIM FINAL EFFLUENT LIMITATIONS
and
NEW SOURCE PERFORMANCE STANDARDS
for the
COMMON AN^ PRECIOUS METALS SEGMENT OF THE
ELECTROPLATING MANUFACTURING POINT SOURCE CATEGORY
V
Russell Train
Administrator
James L. Agee
Assistant Administrator for Water
and Hazardous Materials
Allen Cywin
Director, Effluent Guidelines Division
Kit R. Krickenberger
Project Officer
April, 1975
Effluent Guidelines Division
Office of Water and Hazardous Materials
U. S. Environmental Protection Agency
Washington, D.C. 20460
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ABSTRACT
This document presents the findings of an extensive study of
the electroplating industry by the Environmental Protection
Agency for the purpose of developing effluent limitations
guidelines. Federal standards of performance, and
pretreatment standards for the industry, to implement
Sections 304, 306, and 307 of the Federal Water Pollution
Control Act, as amended (33 USC 1251, 1314, and 1316; 86
Stat 816) .
Effluent limitations guidelines contained herein set forth
the degree of effluent reduction attainable through the
application of the best practicable control technology
currently available and the degree of effluent reduction
attainable through the application of the best available
technology economically achievable which must be achieved by
existing point sources by July 1, 1977 and July 1, 1983
respectively. The standards of performance for new sources
contained herein set forth the degree of effluent reduction
which is achievable through the application of the best
available demonstrated control technology, processes,
operating methods, or other alternatives.
In developing the data and recommendations in this document
the electroplating processes have been considered as one
subcategory. Reasons for this decision may be found in
section IV of this document. This subcategory consists of
processes for electroplating of copper, nickel, chromium,
zinc, tin, lead, cadmium, cobalt, iron, silver, gold,
platinum, palladium, indium, antimony, rhodium, iridium,
ruthenium, titanium, or combination thereof and the
salvaging process of stripping. The electroplating of
copper, nickel, chromium and zinc was covered in the first
development document. The remainder are covered in this
document.
Chemical treatment of waste waters to destroy oxidizable
cyanide, reduce hexavalent chromium, and remove all but
small amounts of the metals represents the best practicable
control technology currently available for existing point
sources in this subcategory.
Chemical treatment of waste waters to destroy oxidizable
cyanide, reduce hexavalent chromium, and remove all but
small amounts of metals, augmented by in-process procedures
to further reduce the amount of waste water and the total
pollutional load is the new source performance standard for
point sources in this subcategory.
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The best available technology economically achievable to be
achieved by 1983 is no discharge of process waste water
pollutants to navigable waters.
Supportive data and rationale for development of the
proposed effluent limitations guidelines and standards of
performance are contained in this report.
11
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CONTENTS
II
III
IV
V
VI
CONCLUSIONS
RECOMMENDATION*
Tecnnology
Achievable e standards
New Source Pen
Page_
1
3
3
3
6
INTRODUCTION
Authority Development
st^11""
introduction orization
Objectives £ C»ctlon —
factor** Considered in
introduction Waste
—.t^f wfte? Uses
WaSt£epoflutional Significance
n o£ Efu
Chemical Treatmen^ Qpera
Wafefconservation Through Cont
Technology
11
11
12
13
17
17
17
17
27
37
37
37
37
44
81
81
81
82
95
95
98
111
114
121
iii
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Methods of Achieving No Discharge
of Pollutants 149
VIII COSTS, ENERGY, AND NONWATER QUALITY ASPECTS 153
Introduction 153
Treatment and Control Costs 153
Nonwater Quality Aspects 175
IX BEST PRACTICABLE CONTROL TECHNOLOGY
CURRENTLY AVAILABLE, GUIDELINES, 181
AND LIMITATIONS " ~>1
Introduction 181
Identification of Best Practicable
Control Technology Currently
Available 182
Rationale for Selecting the Best
Practicable Control Technology
Currently Available 184
X BEST AVAILABLE TECHNOLOGY ECONOMICALLY
ACHIEVABLE, GUIDELINES AND LIMITATIONS 273
Introduction 273
Industry Category and Subcategory
Covered 274
Identification of Best Available
Technology Economically Achievable 274
Rationale for Selection of Best
Available Technology Economically
Achievable 275
Effluent Limitations Based on the
Application of Best Available
Technology Economically Achievable 277
Guidelines for the Application of
Effluent Limitations 277
XI NEW SOURCE PERFORMANCE STANDARDS 279
Introduction 279
Industry Category and Subcategory
Covered 280
Identification of Control and Treatment
Technology Applicable to Performance
Standards and Pretreatment Standards
of New Sources 281
Rationale for Selection of Control and
Treatment Technology Applicable to
New Source Performance Standards 282
Standards of Performance Applicable
to New Sources 283
Guidelines for the Application of
New Source Performance Standards 283
IV
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XII ACKNOWLEDGEMENTS 285
XIII REFERENCES 287
XIV GLOSSARY 293
v
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TABLES
Number
1 BPCTCA Limitations for Electroplating
of Common Metals and Precious Metals
Subcategories 4 5
2 NSPS Limitations for Electroplating of
Common and Precious Metals Subcategories 7,8
3 Processes for Plating on Plastics 22
U Processes for Plating on Steel 23
5 Processes for Plating on Substrate Materials
Other Than Steel 24
6 Processes for Chemical Conversion Coatings 28
7 Processes for Metal Coloring 29
8 Estimated Daily Raw Waste Load of Principal
Salts Used In Cu, Ni, Cr, Zn Plating and
Related Processes 41
9 Wastewater Constituents from Treatment
Before Plating 42
10 Principal Wastewater Constituents in
Wastes Generated During Pretreatment for
Electroless Plating on Metals and Plastics 43
11 Alkaline Cleaners for Aluminum 45
12 Representative Deoxidizing and Desmutting
Treatments for Aluminum 47
13 Representative Alkaline Cleaners for
Magnesium 4g
1U Representative Constituents from Plating
Operations 5Q
15 Chromate Coating of Magnesium By The
Chrome Pickle Process 63
16 Dichromate Process Cycle for Magnesium Alloys 65
VI
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17 Principal Wastewater Constituents in Wastes
Generated During Phosphating Operations
on Various Metals and Alloys 68
18 Principal Wastewater Constituents in Wastes
Generated During Immersion Plating of Tin,
Copper, Gold and Nickel 70
19 Principal Wastewater Constituents in Wastes Generated
During Preparation for Immersion Plating on
Various Basis Metals 71
20 Principal Wastewater Constituents in Wastes
Generated During Pretreatment for Metal
Coloring 73
21 Principal wasatewater Constituents in Wastes
Generated During Coloring of Copper
and Brass 74
22 Principal Wastewater Constituents in Wastes
Generated During Coloring of Iron and Steel 75
23 Principal Wastewater Constituents in Wastes
Generated During Coloring of Zinc 76
24 Principal Wastewater Constituents in Wastes
Generated During Coloring of Cadmium 77
25 Principal Wastewater Constituents in wastes
Generated During Coloring of Silver, Tin
and Aluminum 78
26 Comparison of Soluble Pollutant Parameters
After Precipitation by Iron Sulfide or by
Hydroxide 107
27 Decomposition Products of Cyanide us
28 Costs for Waste Treatment Facilities 154
29 Treatment Equipment Costs 157
30 Annual Operating Costs 158
31 Investment and Annual Operating Costs for
Average Plant 161
32 Cost Effectivenss of control Alternatives 176
Vll
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33 Cost of Power Relative to Total Operating
Costs for Chemical Treatment 177
3>\ Effluent Discharges - Plant 11-8 i87
35 Cyanide Treatment Results - Plant 11-8 188
36 Chromium Reduction Results - Plant 11-8 191
37 Effectiveness of Clarifier - Plant 11-8 192
38 Summarized Effluent Flow - Plant 11-8 194
39 Summarized Data on Areas Plated -
Plant 11-8 196
40 Water Use Factors - Plant 11-8 197
41 Cyanide Treatment Results - Plant 33-20 200
42 Chromium Reduction Results - Plant 33-20 202
43 Effectiveness of Clarifier - Plant 33-20 204
44 Effluent Flow Data - August 20, 197U -
Plant 33-20 206
45 Effluent Flow Data « August 21, 1974 -
Plant 33-20 207
46 Effluent Flow Data - August 22, 1974 -
Plant 33-20 208
47 Flow Leaving Cyclator - Plant 33-20 209
48 Holding Tank Levels - Plant 33-20 2ll
49 Areas Plated - August 20, 1974 -
Plant 33-20 214
50 Areas Plated - Tin Lines - August 20, 1974 -
Plant 33-20 215
51 Collection Rates and Volumes of Sampling -
Plant 36-1 218
52 Volume Discharged - Plant 36-1 219
53 Effluent Discharged - Plant 36-1 220
viii
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54 Area Plated - Plant 36-1 222
55 Analysis of Raw and Treated wastes - 236
56 Effluent Quality and Standards -
Plant 33-5 237
57 Plant Parameters - Plant 33-5 238
58 Summary of Plant Data 248
59 concentration Factors of Limitations 250
60 Monthly Data - Plant 15-1 252,253
61 Monthly Data - Plant 12-6 254
62 Monthly Data - Plant 33-15 255
63 Electrochemical Equivalents 260
IX
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FIGURES
Number „
Page
1 Water Uses for Common and Precious
Metals Subcategories 34
2 Typical Flow of Water Through A
Plating Line 3
3 Typical Continuous Treatment Plant 97
4 Typical Integrated Treatment System 99
5 Batch Treatment of Cyanide 100
6 Sulfide Precipitation of Cadmium 117
7 Treatment of Cadmium 119
8 Ion Exchange System 129
9 Evaporation System 135
10 Reverse Osmosis System 140
11 Freezing System 142
12 Ion Flotation System 14g
13 Investment Costs
166
It Operating Costs
15 Chemical Treatment-Coprecipitation Only 162
16 Chemical Treatment-Cyanide Destruction
and coprecipitation ,,_
J-b J
17 Chemical Treatment-Chromium Reduction and
Coprecipitation ,, .
Xb4
18 Chemical Treatment-Cyanide Oxidation, Chromium
Reduction, Coprecipitation 165
19 Master Flow Pattern ,c-
ID /
20 Combined Treatment 168
21 Combined Treatment ]?ollowed By Reverse
Osmosis
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22 Batch Treatment 170
23 Combination Batch and Continuous Treatment 189
21 Continuous Treatment 198
25 Cyanide and Acid Wastes Treatment 217
26 waste Treatment - Plant 36-12 226
27 Tin Plating Line - Plant 36-12 227
28 Cu and Sn Plating Lines - Plant 36-12 228
29 Cu and Ag or Cu and Ni Plating Line -
Plant 36-12 229
30 Effect Bright Dipping on Cu and Zn
Concentrations 231
31 Change in Average Effluent Concentrations
and pH - Plant 36-12 232
32 Process Diagram 235
33 Example 1 266
34 Example 2 269
35 Example 3 271
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SECTION I
CONCLUSIONS
For the purposes of establishing effluent limitations
guidelines and standards of performance for the
electroplating industry, the electroplating point source
category has been considered as three subcategories. They
are the electroplating of common metals, electroplating of
precious metals, and the electroplating of speciality
metals. The industry was separated into these three
categories on the basis of volume of metal plated, economics
of plating and differences of treatment technologies. The
consideration of the age of the plant, processes employed,
geographical location, and wastes generated support this
conclusion. Guidelines for the application of the effluent
limitations and standards of performance take into account
the plant size in that the allowable amount of pollutant
that can be discharged is proportic al to the size of the
plant.
Phase I of the study covered only the electrop. \ting of
copper, nickel, chromium and zinc. The results of this
study may be found in the "Development Document for Effluent
Limitations Guidelines and New Source Performance Standards
for the Copper, Nickel, Chromium and Zinc Segment of the
Electroplating Point Source Category" March, 1974. Phase II
- common metals subcategory applies to the electroplating of
tin, lead, aluminium, cadmium, and iron. Phase II
precious metals subcategory applies to the electroplating of
silver, gold, platinum, rhodium, iridium, and ruthenium.
Phase II - speciality metals subcategory applies to the
electroplating of beryllium, magnesium, calcium, tellurium,
rhenium, cobalt and mercury. At publication, limitations
will be recommended only for electroplating of common and
precious metals.
The average cost for waste treatment reported by 30 plants
was $1.06/1000 liters of waste water treated. Investment
costs ranged from $1.15 to $43.39/l/hr. Estimates made from
two modeled waste treatment plants carrying out cyanide
destruction, chromate reduction, precipitation,
clarification and filtering were $1.09 and $1.41/1000 liters
of waste water treated. Investment costs ranged from
$22,980 for a 5-man plant plating 75 sq m/hr and treating
wastes only by neutralizing it to $378,U55 for a 47-man
plant plating 815 sq m/hr and treating for cyanide,
chromate, and metals including clarification and filtering.
A minimum cost batch waste treatment system was designed for
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$17,700. This system treats cyanide, chromate, and metals
but relies heavily on an operator for proper functioning and
many manual operations. Operating costs were estimated to
be $10,186/yr exclusive of analytical costs.
The best practicable control technology for this
subcategory, is chemical treatment. It is estimated that a
water use of 160 1/sq m/operation can be achieved in
existing sources for the processes in this subcategory.
The best available technology economically achievable by
1983 is no discharge of process waste water pollutants to
surface waters. The technology involved consists of both
in-process and end-of-process methods of minimizing and
eliminating water use and eliminating effluent.
The new source performance standards are based upon chemical
treatment and a water use estimated to be 80 1/sq
m/operation.
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SECTION II
RECOMMENDATIONS
Best_Practicable control Technology Currently Available
Recommended effluent limitations for the electroplating
industry applicable to existing sources discharging to
navigable waters are summarized in Table 1 and the specific
effluent limitation guidelines and rationale are discussed
in greater detail in Section IX of this report. The
guidelines to be achieved by July 1, 1977 have been derived
from the product of concentrations and water uses considered
achievable. Chemical treatment of waste waters to destroy
oxidizable cyanide, reduce hexavalent chromium, and remove
all but small amounts of the metal pollutants by chemical
coprecipitation represents the best practicable control
technology currently available (BPCTCAJ for existing point
sources. A water use of 160 1/sq m per operation has been
found to be achievable by the industry.
Additional currently available in-process control technology
designed to recover and reuse process chemicals and water
and reduce water consumption may be required to meet the
effluent limitations depending upon the kind of parts being
finished or the nature of available process facilities.
Best_Ayailable Technology EconomicallyAchievable
The effluent limitations attainable through the application
of the best available technology economically achievable by
existing point sources in the subcategories listed in
Section I is no discharge of process waste water pollutants
to navigable waters by July lr 1983. The achievement of no
aqueous discharge of process waste water pollutants to
navigable waters is believed to be possible through a
combination of technologies that are being employed
throughout the industry and are in the process of being
developed and demonstrated. There is considerable
information available on how to reduce water use in the
plant through proper design of processing lines and correct
operating procedures. Minimizing this water use minimizes
the problem of treating the waste water that is produced.
Reverse osmosis, electrodialysis, and special ion-exchange
systems are under development to recycle water in process
loops and thereby reduce water to be treated and are also
being tested for recovery of process water from waste
effluent. Already some electroplaters have been able to
eliminate discharges from one or more lines within a
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Table 1 - BPCTCA Limitations
for Electroplating of Common Metals
Subcategory
Effluent Effluent
Characteristic Limitations
Maximum for Average of daily
any one day values for thirty
consecutive days
shall not exceed
(Metric units) milligrams per sq m
per operation
Copper 160 80
Nickel 160 80
Cr,Total 160 80
CrVI 16 8
Zinc 160 80
CN,Total 160 80
CN,A 16 8
Fluoride 6400 3200
Cadmium 96 18
Lead 160 80
Iron 320 160
Tin 320 160
Phosphate 320 160
TSS 6400 3200
pH Within the range 6.0 to 9.5.
(English units) pounds per million sq ft
per operation
Copper 32.7 16.4
Nickel 32.7 16.4
Cr,Total 32.7 16.a
CrVI 3.3 1.6
Zinc 32.7 16.4
CN,Total 32.7 16.4
CNrA 3.3 1.6
Fluoride 1308 654
Cadmium 19.2 9.6
Lead 32.7 16.4
Iron 6!>.4 32.7
Tin 6!i.4 32.7
Phosphate 65.4 32.7
TSS 130IJ 654
pH Within the range 6.0 to 9.5.
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Table 1 - BPCTCA Limitations
for Electroplating of Precious Metals
Subcategory
Effluent Effluent
Characteristic Limitations
Maximum for Average of daily
any one day values for thirty
consecutive days
shall not exceed
(Metric units) milligrams per square meter
per operation
Ag
Au
CN,A
CN,Total
Cr,Total
CrVT
Ir
Os
Pd
Pt
Rh
Ru
Phosphate
TSS
pH Within the range 6.0 to 9.5,
(English units) pounds per million square
feet per operation
Ag
Au
CN,A
CN,Total
Cr,Total
CrVI
Ir
Os
Pd
Pt
Rh
Ru
Phosphate
TSS
Within the range 6.0 to 9.5.
16
16
16
160
160
16
16
16
16
16
16
16
320
6400
8
8
8
80
80
8
8
8
8
8
8
8
160
3200
3.3
3.3
3.3
32.7
32.7
3.3
3.3
3.3
3.3
3.3
3.3
3.3
65.4
1308
1.6
1.6
1.6
16.4
16.4
1.6
1.6
1.6
1.6
1.6
1.6
1.6
32.7
654
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facility. Additional techniques for water recovery should
come from the broad scientific and engineering base in the
United States, although it is difficult to pinpoint what
specific technologies will be most widely used in 1983.
New TSource Performance Standards
Recommended standards of performance applicable to new
sources discharging to navigable waters are summarized in
Table 2. The limitations are applicable to sources
constructed after publication of proposed regulations
prescribing a standard of performance. The new source
performance standards are based on an average water use of
80 1/m. per operation as it is possible to design and
economically install in-process systems that can be operated
with a lower water use than can be achieved in many existing
plants.
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Table 2 - NSPS Limitations
for Electroplating of Common Metals
Subcategory
Effluent Effluent
Characteristic Limitations
Maximum for Average of daily
any one day values for thirty
consecutive days
shall not exceed
(Metric units) milligrams per square meter
per operation
Copper
Nickel
Crr Total
CrVI
Zinc
CN, Total
CN,A
Fluoride
Cadmium
Lead
Iron
Tin
Phosphate
TSS
pH
(English
Copper
Nickel
Cr, Total
CrVI
Zinc
CN, Total
CN,A
Fluoride
Cadmium
Lead
Iron
Tin
Phosphate
TSS
PH
80
80
80
8
80
80
8
3200
48
80
160
160
160
3200
Within the range
40
40
40
4
40
40
4
1600
24
40
80
80
80
1600
6.0 to 9.5.
units) pounds per million square
_ feet per
16. 4
16. 1
16. a
1.6
16.4
16.4
1.6
654
9.6
16.4
32.7
32.7
32.7
654
Within the range
7
operation
8.2
8.2
8.2
0.8
8.2
8.2
0.8
327
4.8
8.2
16.4
16.4
16.4
327
6.0 to 9.5.
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Table 2 - NSPS Limitations
for Electroplating of Precious Metals
Subcategory
Effluent
Characteristic
Effluent
Maximum for
any one day
Average of daily
values for thirty
consecutive days
shall not exceed
(Metric units) milligrams per sq m
Ag
Au
CN,A
CNr Total
Cr,Total
CrVI
Ir
Os
Pd
Pt
Rh
Ru
Phosphate
TSS
PH
8
8
8
80
80
8
8
8
8
8
8
8
160
3200
4
4
4
40
40
4
4
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FOOTNOTES FOR TABLES 1 AND 2
(a) The effluent limitations and standards of performance
are defined as the weight of pollutant in milligrams
discharged per square meter per operation (Ibs per million
sq ft per operation). An operation is defined as any step
followed by a rinse in the electroplating process in which a
metal is electrodeposited on a basis material. In Subparts
A and B the electroless plating on non-metallic materials
for the purpose of providing a conductive surface on the
basis material, past plating steps of chromating,
phosphating and coloring forming an integral step in the
electroplating line and stripping where conducted in
conjunction with electroplating for the purpose of salvaging
improperly plated parts may be included under the term
"operation" for the purpose of calculting effluent
discharges. The term "sq m"("sq ft") sahll mean the area
plated expressed in square meters (square feet).
(b) Single-Day Maximum is the maximum value for any one
day.
(c) Thirty-Day Average is the maximum average of daily
values for any consecutive 30 days.
(d) Total metal (in solution and in suspended solids) in
sample.
(e) Chromium (total) is the sum of hexavalent and trivalent
chromium, in solution and in suspended solids.
(f) Oxidizable cyanide is defined as all detectable cyanide
amenable to oxidation by chlorine as described in 1972
Annual Book of ASTM Standards, 1972, Standard D 2036-72,
Method B, p. 553.
(g) Total cyanide is defined as all detectable cyanide in
the sample following distillation according to methods of
analyses as set forth in HO CFR 401.
(h) Total suspended solids retained by a filter according
to standard analytical procedures.
(i) A pH in the range of 8 to 9 is the best range for
minimizing the soluble metal concentration during co-
prec ipita ti on.
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SECTION III
INTRODUCTION
Purpoge uand Authority
Section 301 (b) of the Act requires the achievement by not
later than July 1, 1977, of effluent limitations for point
sources, other than publicly owned treatment works, which
are based on the application of the best practicable control
technology currently available as defined by the Administra-
tor pursuant to Section 304(b) of the Act. Section 301(b)
also requires the achievement by not later than July 1,
1983, of effluent limitations for point sources, other than
publicly owned treatment works, which are based on the
application of the best available technology economically
achievable which will result in reasonable further progress
toward the national goal of eliminating the discharge of all
pollutants, as determined in accordance with regulations
issued by the Administrator pursuant to Section 304 (b) to
the Act. Section 306 of the Act requires the achievement by
new sources of a Federal standard of performance providing
for the control of the discharge of pollutants which
reflects the greatest degree of effluent reduction which the
Administrator determines to be achievable through the
application of the best available demonstrated control
technology, processes, operating methods, or other
alternatives, including where practicable, a standard
permitting no discharge of pollutants.
Section 304(b) of the Act requires the Administrator to
publish within one year of enactment of the Act, regulations
providing guidelines for effluent limitations setting forth
the degree of effluent reduction attainable through the
application of the best practicable control technology cur-
rently available and the degree of effluent reduction
attainable through the application of the best control
measures and practices achievable including treatment
techniques, process and procedure innovations, operation
methods and other alternatives. The regulations proposed
herein set forth effluent limitations guidelines pursuant to
Section 304(c) of the Act for the electroplating category.
Section 306 of the Act requires the Administrator, within
one year after a category of sources is included in a list
published pursuant to Section 306 (b) (1) (A) of the Act, to
propose regulations establishing Federal standards of
performance for new sources within such categories. The
11
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Administrator published in the Federal Register of January
16, 1973 (38 FR 1624), a list of 27 source categories.
Publication of the list constituted announcement of the
Administrator's intention of establishing, under Section
306, standards of performance applicable to new sources
within the electroplating subcategory of the electroplating
industry which was included within the list published
January 16, 1973.
Summary of Methods Used for Development of the Effluent
Limitation Guidelines and Standards of Performance
The effluent limitations guidelines and standards of
performance recommended herein were developed in the
following manner. The electroplating industry was a major
point source reviewed first for subcategorization for the
purpose of determining whether separate limitations and
standards would be appropriate for different segments.
Phase I of the program was limited to the electroplating of
copper, nickel, chromium, and zinc on ferrous and nonferrous
or combination thereof, materials and the associated
preplating and postplating operations. Phase II - common
metals subcategory has been expanded include tin, lead,
aluminium, cadmium and iron. Phase II - precious metals
subcategory applies to the electroplating of silver, gold,
platinum, rhodium, osmium, palladium, iridium and ruthenium.
Such subcategorization was based upon raw material used,
operations employed, and other factors. The raw-waste
characteristics were identified by analyses of the source
and volume of water used in the process employed and the
sources of waste and waste waters in representative plants
and the constituents of all waste waters.
The full range of control and treatment technologies along
with their existing problems, limitations, and reliability
and cost and energy reguirements were identified. This
included in-plant and end-of-process technologies,, which are
existent or capable of being designed for waste control.
The quantity and the chemical and physical characteristics
of each pollutant were identified as well as the reduction
associated with the application of each of the treatment and
control technologies. In addition, the nonwater quality
environmental impact, such as the effects of the application
of such technologies upon other pollution problems,
including air, solid waste, and noise were also identified.
The information, as outlined above, was then evaluated in
order to determine what levels of technology constituted the
"best practicable control technology currently available".
12
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the "best available technology economically achievable", and
the "best available demonstrated control technology,
processes, operating methods, or other alternatives". In
identifying such technologies, the factors considered
included the total cost of application of technology in
relation to the effluent reduction benefits to be achieved
from such application, the age of equipment and facilities
involved, the process employed, the engineering aspects of
the application of various types of control techniques and
process changes, nonwater quality environmental impact
(including energy requirements), and other factors.
Sources of information utilized for developing the data in
this document include the following:
(1) Published literature (References appear in
Section XIII)
(2) Trade literature
(3) EPA Technology Transfer Seminar on Upgrading
Metal-Finishing Facilities to Reduce Pollution,
Braintree, Massachusetts, October 30-31, 1973
(H) Three EPA regional offices and eight state
pollution abatement offices
(5) Representatives of approximately 75 companies
with facilities for electroplating who returned
mailed questionnaires and who were subsequently
contacted by telephone or further correspondence
in many cases.
(6) Representatives of 17 companies who were visited
by BCL staff for development of detailed data
(7) Analytical verification of effluent data for
13 plants engaged in electroplating processes.
The decision as to which companies to contact was a matter
of judgement combined with information from the prior
sources listed. A plant or company was contacted if there
was any evidence that it was engaged in any of the
electroplating processes of interest and that it was
treating the wastes from these processes. Plants were
identified and contacted over a period of approximately 3
months, after which further activity of this sort was
minimal and most effort was devoted to summarizing the
information that had been obtained. Thus, a number of
plants were identified that could be classified as
exemplary.
General Description of the Electroplating Industry
The electroplating industry, as included in Standard
Industrial Classification (SIC) 3U71, is defined for the
13
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purpose of this document as that portion of industry
applying coatings on surfaces by electrodeposition.
Pretreatment of the basis material and post plating
operations are included and are carried out by both
independent (job) platers and captive facilities associated
with product fabrications and assemblies. The annual
dollars added value by electroplating exceeds
$2,000,000,000. Approximately 20,000 companies are engaged
in electroplating and metal finishing. Of these, 3400 are
job shops supplying only plating services. About 25 percent
of this segment is concentrated in the middle western
states of Illinois, Michigan, and Ohio. Another 20 percent
is concentrated in eastern Pennsylvania and the Atlantic
coastline states of Connecticut, Rhode Island, New York, and
New Jersey. The location of captive plating facilities
follows the same general geographic pattern. Of the
multimillion dollar added value, the 3241 companies in SIC
3471 accounted for $574,800,000 and the value of shipments
was $791,100,000 in 1967. In 1947, there were approximately
1,800 job shops, in 1963, 3,000 and 1974, 3,400.
Electroplating facilities of the kind in SIC 3471 vary
greatly in size and character from one plant to another. A
single facility for plating individual parts formed by
stamping, casting, machining„ etc., may employ plating or
processing solutions (excluding water rinses) ranging in
total volume from less than 380 liters (100 gallons) to 132
liters (500 gallons). The area of the products being
electroplated in these facilities varies as much as three
orders of magnitude from less than 10 to more than 1000 sq
meters/day (100 to 10,000 sq ft/day). The power consumed by
a single facility varies from a few kilowatt-hours/day to as
much as 20,000 kilowatt-hours/day. Products being plated
vary in size from less than 6.5 sq cm (1 sq inch) to more
than 1 sq meter (10 sq ft) and in weight from less than 30 g
(1 oz) to more than 9000 kg (10 tons). Continuous strip and
wire are plated in some plants on a 24-hour/day basis. Some
companies have capabilities for electroplating ten or twelve
different metals and alloys, but others specialize in just
one or two. Because of differences in character, size and
processes, few or no similar plants exist at the present
time. Construction of facilities have been custom tailored
to the specific needs of each individual plant.
The energy consumed by industry in the electroplating
subcategory was estimated to be 1.7 x 109 kilowatt hours.
It also cites that from 90,718 to 108,861 metric tons
(100,000 to 120,000 short tons) of metal (principally
copper, nickel, zinc, and tin) are converted annually to
electroplated coatings. The figures for sheets, strip, and
14
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wire include nonelectropiated coatings, applied by hot
dipping. All the aluminum is applied by hot dipping, as is
about 90 percent of the zinc, as are significant but
unidentified percentages of the tin and lead.
These coatings provide corrosion protection, wear or erosion
resistance, antifrictional characteristics, lubricity,
electrical conductivity, heat and light reflectivity or
other special surface characteristics, which enable the
industry to conserve several millions of tons of critical
metals. In the finishing of individual products,
electroplated coating thickness usually ranges from 0.0006
to 0.004 cm (0.00025 to 0.0015 inch), but thicker coatings
to 0.025 or 0.04 cm (0.010 or 0.015 inch) are sometimes
required for special engineering purposes or for salvaging
worn or mismachined parts. Tin and chromium coatings from
0.3 to 1 mm (1 x 10-« to a x 10~5 inch) and 0.003 mm (1 x
10~7 inch) thickness respectively are applied to continuous
steel strip as a prefinish before coating with an organic
material by the container industry.
An electroplating process includes cleaning, electroplating,
rinsing, and drying. The cleaning operation consists of two
or more steps that are required for removing grease, oil,
soil, and oxide films from the basis metal surface and
insuring good electroplate adhesion. Sequential treatments
in an alkaline solution and an acid solution with
intermediate rinsing are the minimum number customary for
these purposes. In the electroplating solution, metal ions
in either acid, alkaline or neutral solutions are reduced on
cathode surfaces, which are the workpieces being plated.
The metal ions in solution are usually replenished by the
dissolution of metal from anodes in bar form or in small
pieces contain in inert wire or expanded metal baskets. But
replenishment with metal salts is also practiced, especially
for chromium plating. In this case, an inert material must
be selected for the anodes. Hundreds of different
electroplating solutions have been adopted commercially, but
only two or three types are utilized widely for a single
metal or alloy. Cyanide solutions are popular for copper,
zinc, brass, cadmium, silver and gold, for example, yet
noncyanide alkaline solutions containing pyrophosphate or
another chelating agent have come into use recently for zinc
and copper. Acid sulfate solutions also are used for zinc,
copper, tin and nickel, especially for plating relatively
simple shapes. Cadmium and zinc are also being
electroplated from neutral or slightly acid chloride
solutions.
15
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Barrel plating is used for small parts that tumble freely in
rotating barrels. Direct current loads up to several
hundred amperes are distributed to the parts being plated.
Parts may be rack plated by attaching them to plastic coated
copper frames designed to carry current equally to a few
hundred small parts, several medium-sized shapes or just a
few large products through spring-like rack tips affixed to
the rack splines. Racks fabricated for manual transfer from
cleaning, plating, and rinsing tanks usually contain .5 to 1
sq m (5 to 10 sq ft) . Larger racks for holding heavier parts
are constructed for use with mechanical hoist and transfer
systems. Mechanized transfer systems for both barrels and
racks, which range in cost from $50,000 to more than
$1,000,000 are being utilized for high-volume production
involving six to thirty sequential operations. In some
instances, dwell time and transfer periods are programmed on
magnetic tape or cards for complete automation. Facilities
for plating sheets will be in the higher end of this cost
range.
Continuous strip and wire plating facilities cost in the
multimillions of dollars. A single tin plating line will
electroplate 139 to 186 sq im/min (1500 to 2000 sq ft/min of
steel strip.
16
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SECTION IV
INDUSTRY CATEGORIZATION
Introduction
This section discusses in detail the scope of the
electroplating industry. The rationale is developed for
considering the electroplating industry as a single
subcategory for the development of effluent limitations
guidelines and standards of performance.
Objectives of gategorization
The primary purpose of industry categorization is to develop
quantitative effluent limitations and standards of
performance for discharge of pollutants that are uniformly
applicable to a specific category or subcategory. This does
not preclude further classification within a category for
the purpose of monitoring to insure compliance.
Electroplating is one of several processes in the broader
category of metal finishing. It is listed under SIC 3471
(Standard Industrial Classification Manual) along with
numerous other metal finishing processes. The metal
finishing industry was divided into two segments,
electroplating and metal finishing, for the purposes of
developing effluent limitations guidelines. Phase I covered
the electroplating of copper, nickel, chromium and zinc or
combination thereof. Phase II covers tin, lead, cadmium,
iron, silver, gold, platimun, palladium, rhodium, iridium,
ruthenium, titanium, or any combination thereof. It also
covers stripping. This addition is justified because all
electroplating shops have a stripping line to salvage poorly
plated or badly corroded parts. This usually exists as a
separate line. Also considered are the pre and
posttreatment operations of alkaline cleaning, acid
pickling, conversion coatings, coloring, and descaling.
Although these processes are not strictly electroplating,
they usually form an integral part of an electroplating line
and therefore must be considered under the auspices of
electroplating. Other metal finishing operations which are
an end unto themselves and stand as a separate line are
considered in separate documents. These are anodizing,
immersion plating, chromating, phosphating, chemical milling
and etching.
Profile of production Processes
17
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The electroplating industry utilizes chemical and
electrochemical operations to effect an improvement in the
surface and structural properties of metals and other
materials. In practice, the operations are put together in
sequences that become the processes which effect the
improvement. Thus, electroplating operations may be both
process and materials oriented.
Those segments of the industry identified in SIC 3471 are
processes performed on products owned by a second party.
Such work is done in job or contract shops. The same
processes may also be performed by other manufacturers of
several different end products. These are known as captive
shops. The processes are the same for both facilities and
this document is applicable to both facilities.
Conceptually, an electroplating line may be broken down into
three types of steps - pretfeatment involving the
preparation of the metal for plating, actual application of
the electroplate, and post treatment steps.
Pretreatment
Pretreatment steps involve cleaning, pickling, degreasing,
descaling, desmutting, vapor blasting, surface activation,
etching, abrasion and bright dipping. Plating steps are
strikes and electroplates, coatings and metal coloring.
Post treatment steps are conversion and drying. Stripping,
while performed separately, is an integral part of an
electroplating shop. It is employed for the reclamation of
badly plated parts.
Cleaning
Cleaning involves the removal of oil, grease and dirt from
the surface of the basis material. Cleaning or degreasing
may be accomplished in one of several ways. These include
alkaline electrolytic (anodic and cathodic), diphase,
emulsion, soak, solvent, and ultrasonic cleaning.
Alkaline cleaners are the most widely used in preparing the
basis material. A good alkaline or soak cleaner must be
soluble in water, wet the surface of the basis material, wet
and penetrate soil, saponify or dissolve oil and greases or
emulsify or suspend insoluble or nonsaponifiable oils and
greases, prevent formation of calcium and magnesium deposits
from hard water, prevent tarnish and corrosion of basis
material, rinse freely and minimize foaming. For possible
compositions of alkaline cleaners, see Chapter V. Ferrous
metals and alloys can be cleaned using heavy duty (pH = 12.1
18
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13.5) uninhibited alkaline solutions. Usually, though,
weaker solutions (pH = 10.5 - 12) are used to avoid etching
and pitting. When cleaning nonferrous materials, an
inhibitor must be added to stop the corrosive action of the
cleaner.
Small volumes of work are usually cleaned by hand.
Solutions are applied by brushes, swabs, or cloth. Parts
may also be immersed in cleaning tanks which may be agitated
or heated to increase efficiency. The fastest method of
cleaning is by spraying the cleaning solution in an
automatic or semi-automatic washing machine. The mechanical
force of the spray combined with the chemical and physical
action of the cleaning solution increases efficiency.
Electrolytic cleaning is best employed when plating with
brass, cadmium, chromium, copper, gold, lead, nickel,
silver, tin, and zinc. The basis metal acts as either the
cathode or the anode and a low voltage current for each
square foot of metal is passed through the alkaline cleaning
solution. The generation of gases (H2 at the cathode and O2
at the anode) cause increased agitation and the removal of
soil particles.
Diphase cleaning is composed of a two layer system of water
soluble and a water insoluble organic solvent. This set up
is particularly useful where soil removal requires the
action of water and organic compounds and when temperature
may not be elevated. Usually, the organic solvent is
chlorinated. Because they are non-flammable and are denser
than water, trichloroethylene, methylene chloride, and
perchloroethylene are in common use. This is also known as
solvent cleaning. Emulsion cleaning uses water, organic
solvents and emulsifying agent.
Ultrasonic energy is finding increased use in the agitation
of cleaning solutions. Although it is more expensive to
install, there are substantial savings in labor and time.
It is used to remove difficult inorganic and organic soils
from intricate parts.
Descaling
Descaling involves the removal of oxide films and the
buildup of other contaminants on the surface of the basis
material. Such removal may be accomplished through
mechanical or chemical means.
Pickling
19
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During the production of metals, oxides build up on their
surface during such operations as heat treating and welding.
Also rust may have built up if the part is not used
immediately. Acid pickling is used to remove these oxide
films and involves dissolution of oxide scale in an acid. A
generalized reaction may be written.
MO2 +2HA MA2 + H2O
where M = metal
HA = acid
Sulfuric, hydrochloric, phosphoric and chromic acids all
find use in this regard. Sulfuric is most often used
because it is the least expensive. Rates of reactions are
increased by an increase in acid concentration, temperature
and degree of agitation.
Hydrochloric acid is more costly and there is a fuming
problem. Nevertheless, many small establishments use it
because it works well without the addition of heat. It is
also used for light acid dips before plating.
Phosphoric acid is intermediate in cost, but it forms
phosphates at the surface of the basis material. This is
desirable if rust resistance is needed but not if an
electroplate is to follow.
Mechanical
Removal of scale through mechanical means consists of
tumbling, (barrel finishing), burnishing, dry rolling,
buffing, deburring, polishing, desmutting, and blasting.
Such mechanical treatment eliminates or minimizes the
pickling to follow.
Activation
Activation involves the elimination of a condition on the
surface of the basis material which would preclude the
adhesion of an effective electroplate.
Bright Dipping
Bright dipping is used to impart a shiny, clean appearance
to the basis material. Solutions are comprised of mixtures
of nitric, sulfuric, phosphoric, chromic and hydrochloric
acids.
Electroless Plating on Non-Metallic Materials
20
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Electroless plating on non-metallic materials involves
impregnating the basis material with a metal, usually copper
or nickel, to provide a conductive surface. Table 3 shows
the processes involved in electroless plating on plastics.
Tables 4 and 5 give the processes for plating on steel and
other materials.
The most commonly used basis materials are steel, zinc
castings, brass, aluminum and plastics such as ABS and
polypropylene.
Electroplating
This document covers the electroplating of common and
precious metals and their alloys.
Cadmium Plating
Cadmium plating was first used commercially in 1915,
although laboratory work began in 1819. Cadmium plating
provides a corrosion protective coating over the basis
material. Iron and steel are most commonly used. Since
cadmium is relatively high priced, only thin coatings are
applied. It is sometimes used as an undercoating for Zn.
Cd plating is often used on parts consisting of two or more
metals to minimize galvanic corrosion.
Cadmium cyanide baths are by far the most popular because
they cover completely and give a dense, fine-grained deposit
which can be made very lustrous by the use of stable
brighteners. Because of the toxicity of cyanide, many
people have tried to find baths which produce plates of the
same superior quality. Although success has been limited, a
bath containing fluoroborate in place of cyanide has been
used.
Gold Plating
Gold has been applied for decorative purposes since man
first began to leave traces of his activities.
Electrodeposition of gold began in 1805. The electronics
industry found that gold was the metal best suited for the
specialized qualities needed in electronic component
manufacture. Gold plated surfaces not only provide
decorative finishes and corrosion protection, but are also
important in providing electrical contact surfaces, bonding
surfaces and electroformed conductors.
Plating baths have been developed for each use. Of these,
there are four types. Three of these are cyanide baths
21
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TABLE 3
PROCESSES FOR ELECTROLESS PLATING ON METALS AND PLASTICS
Operation
Alkaline clean/rinse
Acid dip/rinse
Zincate/rinse
Activate/ rinse
Catalyze /rinse
Electroless Deposit/rinse
Basis Materials
Iron, Nickel, Cobalt Copper Aluminum
X XX
X XX
X
X
X
X XX
Plastics
X
X
X
X
X
-------
TABLE 4 PROCESSES FOR PLATING ON STEEL
Tin Lead Cadmium Gold Silver Brass Bronze
Operation Plating Plating Plating Plating Plating Plating Plating
Alkaline clean/rinse
Acid dip/rinse
Neutralizer rinse
1-Strike plate/rinse
2-Strike plate/rinse
Electroplate/ rinse
Conversion coat/rinse
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
x x
X
X
X
X
X
X
X
X
X
X
-------
TABLE 5 PROCESSES FOR PLATING ON SUBSTRATE
MATERIALS OTHER THAN STEEL
Silver Lead
Gold on Gold Alloy Indium
on Nickel on on on
Copper Silver Plastic Aluminum Lead
Operation Substrate Substrate Substrate Substrate Plate
Alkaline clean/rinse
Acid dip/rinse
Neutralizer rinse
Strike plate/rinse
Activate/rinse
Catalyze/rinse
Electroless copper/rinse
Electroless nickel/rinse
Electroplate /rinse
Heat diffusion
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
.X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
24
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unbuffered alkaline containing Na or K with pH = 8.5 - 13,
acid buffer with pH = 3 - 6, and a neutral buffer with pH =
6 - 8.5. The fourth type of bath is non-cyanide.
Silver Plating
The first patent offered for plating was for Ag in 1840.
The initial use of silver plating was for decoration. Today
it is used for ball bearings, electronic components, slip
rings, wave guides and hot gas seals.
The cyanide bath is by far the most widely used. However,
in recent years other baths such as nitrate, iodide,
thiourea, thiocyanate, sulfamate and thiosulfate have come
into recognition.
Tin Plating
At first, tin coatings were applied by hot dipping. In
1930, electrodeposition began replacing the hot dip method
and by 1973 almost all tin plate was electrically deposited.
Tin is resistant to corrosion and tarnish is solderable,
soft and ductile. It is used as a coating on food-handling
equipment, refrigerator evaporators, washing machine parts,
builders1 hardware, electronic components, piston rings,
copper wire, and bearing surfaces.
Tin plating baths may produce either a bright or a matte
finish. The three most common baths are alkaline stannate,
sulfate and halogen.
Iron Plating
Iron was first electrodeposited during World War I on
driving bands for shells. Since iron is very magnetic, it
has been used in the manufacture of induction coils. It was
used extensively during World War II when Cu and Ni were in
short supply to make electrotypes. It has also been used to
cover soldering tips.
There are several difficulties in the maintenance of an iron
plating line. Special non-corrosive equipment is needed to
heat and agitate the plating bath. Also, care must be taken
that the plating solution does not oxidize. However, this
may be offset by the great abundance and low cost of iron.
Iron may be deposited as a hard and brittle or soft and
ductile coat. It is also corrosion resistant.
25
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Almost all iron is plated from solutions of ferrous salts
and low pH's. The most common plating baths contain
sulfate, chloride, fluoroboreite and sulfamate.
Lead Plating
Lead was first plated from fluorine acids in 1886. Lead is
most resistant to hydrofluoric and sulfuric acids. Thus, it
is used for protective linings as well as coatings on nuts
and bolts, storage battery parts and bearings. Lead is
often an undercoat for indium plating. Lead-tin and lead-
antimony alloys are used.
Fluorosilicate and fluoroborate baths are the most widely
used. Fluoroborate bath is more expensive but it gives
finer grained denser deposits, adheres better to steel and
will not decompose as readily.
Indium Plating
Indium plating first came into recognition during World War
II. It is used largely in the manufacture of aircraft
engine bearings. Corrosion of the originally plated Cd-Ag-
Cu bearings is reduced by an indium overlayer and heat
treating. It is also used in. the electronics industry as a
doping agent in the production of transistors. Indium is
often alloy plated with Cu, Sn, Pb, cd, Zn, Ni, Bi and Rh.
Initially, indium baths were composed of cyanide and sugar.
Today the sulfate bath is the most widely used along with
alkaline, fluoroborate, sulfamate, chloride, perchlorate and
tartrate baths.
Aluminum Plating
Application of aluminum plating on a commercial basis is
limited. It has been used for coating uranium and steel
strip, electrorefining and electroforming.
Because it is more reactive than hydrogen, aluminum cannot
be plated from aqueous solutions or any solution containing
acidic hydrogens. Only plating from a hydride bath with the
basic ingredients of diethyl ether, aluminum chloride and
lithium aluminum hydride has had any commercial
applications.
Platinum Metals Plating
Platinum metals include ruthenium, rhodium, palladium,
osmium, iridium, and platinum. They are particularly
26
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resistive to oxidation, corrosion and tarnish. Since the
platinum metals are quite expensive, thicknesses are minimal
ranging from 0.1 urn to 5 urn. Consequently, concentrations
of the metals in baths are very low. Plating by replacement
is to be avoided. Basis materials of more reactive metals
are usually preplated with nickel followed by a precious
meta1 strike.
Post Treatment
Coatings
Coatings are produced by either immersion plating,
chromating or phosphating aluminum, zinc, (die castings,
hot-dipped or electroplated) , steel, copper, or magnesium.
When applied to a basis material, chemical conversion
coatings comprise an integral step of an electroplating
line. It is for this reason that they are covered under the
electroplating guidelines. Ions in the waste water are
reduced to low concentrations by chemical treatment, water
use is similar to that for electroplating processes.
Operations involved in producing chemical conversion
coatings are shown in Table 6.
Metal Coloring
Coloring of the basis metals copper, brass, steel, zinc,
cadmium, silver, and tin, generally involves dissolution of
part of the basis metals to form an insoluble oxide or
sulfide on the surface. Zinc and cadmium plate may be
chromated and colored with organic dyes. Dyes are not
removed from waste water by chemical treatment, but may be
by adsorption techniques, i.e., activated carbon.
Coloring of aluminum involves inhibition of organic dyes
into a colorless aluminum oxide film produced by anodizing
or chemical conversion. The organic dyes may be bleached
from waste water by chemical treatment. When applied to a
basis material, metal collorings comprise an integral step
of an electroplating line. It is for this reason that they
are covered under the electroplating guidelines. Water use
for metal coloring processes is similar to that for
electroplating processes. Operations involved in metal
coloring are shown in Table 7.
Factors Considered in Categorization
When the nature of the industry and the operations performed
were analyzed, consideration was given to the further
27
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TABLE 6
PROCESSES FOR CHEMICAL CONVERSION COATINGS
Operation
Basis Metal
Steel
Zinc
Aluminum
Steel
Tin
Alkaline clean/rinse
Acid dip/rinse
Desmut/rinse
Phosphate/rinse
Chromate/rinse
X X
X X
X X
X
X X
X X
X
X X
X
X
X
X
X
X
X
X
28
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TABLE 7 PROCESSES FOR METAL COLORING
Operation
Copper Brass Silver Steel Tin Zinc Cadmium Aluminum
Alkaline clean/rinse
Acid dip /rinse
1-Cbloring solution/rinse
2-Coloring solution/rinse
Fixing solution/rinse
Brush
Chromat-e solution/rinse
Organic
-------
categorization of electroplating processes according to one
or more of the following:
(1) Type of basis material
(2) Product design
(3) Raw materials used
(U) Size and age of facility
(5) Number of employees
(6) Geographic location
(7) Quantity of work processed
(8) Waste characteristics
(9) Rack plating versus barrel plating
(10) water use
(11) Treatment technology
(12) Processing differences.
Type of Basis Material
The wastes produced by processing all common basis materials
are similar. A single facility can process all basis
materials without significant change in the raw materials
consumed or the waste-treatment technique adopted for
control of end-of-pipe water discharge. Any materials
dissolved from the surface of: the customary basis metals
during processing are removed from waste water discharge by
the chemical treatment processes described in Section VII.
Furthermore, the basis materials selected for most consumer
products frequently are interchanged from one model year to
another. Therefore, the type of basis material does not
constitute a basis for subcategorization.
Product Design
Product design concepts for minimizing electroplating costs
also reduce wastes created by electroplating processes.
Furthermore, the in-process controls and rinsing techniques
described in Section VII for minimizing the wastes generated
by electroplating processes have been adopted for canceling
the effect of the shape factor. Therefore, product design
variance is not a basis for subcategorization.
Raw Materials Used
Raw materials do not provide a basis for subcategorization,
because practical waste-treatement technology identified in
Section VII is applicable to all of the usual procedures and
solutions described previously for electroplating. In any
facility carrying out one or more of the processes shown,
the same waste treatment needs arise. Such variations as
30
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exist for each operation are not unique and do not affect
the waste-treatment technology and control.
Size and Age of Facility
The nature of electroplating is the same in all facilities
regardless of size and age. For example, copper plating is
technically the same in 190 liters (50 gallons), as in
19,000 liters (5000 gallons), or larger installations. The
age of the facility does not alter this situation. Other
electroplating operations follow the same pattern. Thus,
the characteristics of the waste will be the same for plants
of all ages and sizes. Only the quantity of waste per unit
time will differ. Yet, this factor is not a basis for
subcategorization, because waste discharge after treatment
is directly proportional to the size of the facility
expressed as surface area processed per unit time. The
guidelines recommended in this document provide for variable
production volume with no need to differentiate plant
capacity as a subcategory.
It is recognized that some small electroplating
installations may have insufficient space for accommodating
effective inprocess controls for minimizing water use and
conventional chemical waste treatment equipment. The
capital investment for installing waste control facilities
may be greater for small companies relative to their
investment in the remaining production facilities than for
larger plants. In such cases, heavy metal pollutants can be
adsorbed on resins in small ion-exchange units available.
At least one vendor of such equipment will replace the resin
beds, back wash the used beds in their own facilities and
regenerate the resins for reuse. Alternatively, both local
and regional organizations equipped with large tank trucks
supply a hauling and treating service in several areas. It
is also possible that a small electrodialysis system would
provide recycling of cyanide. Costs depend on water volume
and the concentration of pollutants.
Based upon data contained in the Economic Analysis of
Proposed Guidelines and a report prepared by Booz-Allen and
Hamilton, Inc., three alternative non-automated
establishment size groups were considered in developing the
general variance for small platers, 1-4 man shop, 5-9 man
shop, and 10-19 man shop. It was concluded that few
independent shops with less than 10 employees could afford
to install physical-chemical treatment. While it was also
apparent that a significant number of shops in the 10-20
employee size group would face adverse impacts due to BPT
requirements, the pollution potential created by granting a
31
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variance to this size group was felt to be larger than the
benefits of alleviating the adverse economic impact. This
flow could be expected to contain 2.0 kg/day (H.U Ibs/day)
of each metal plated and total cyanide. A total flow of
400,000 I/day (100,000 gal/day) could be discharged from a
shop in this size category. Hence, after extensive
deliberation the variance was established at the 10 employee
size level.
Number of Employees
The number of employees engaged in electroplating does not
directly provide a basis for subcategorization because
electroplating operations can be carried out manually or in
automatic machines which greatly conserve labor. For
example, an operation with 3800 liter (1000 gallon)
processing tanks may require six people if operated
manually, whereas a plant of the same tank size and carrying
out the same operations in an automatic machine would need
only two people. The same amount of waste would be
generated in each case if the products being plated were
equal in total area. Other examples could be cited to show
that no basis exists for relating the number of employees to
the electroplating processes carried out and to the waste
that results from those processes. However, it is believed
that one can relate the number of employees to the
production capacity of a non-automatic facility.
Geographic Location
Geographic location is not a basis for subcategorization.
No condition is known whereby the choice of electroplating
processes is affected by the physical location of the
facility, except availability of process water. If water is
not available, no modification of electroplating procedures
can compensate for this deficiency. No electroplating
facilities would be installed in such a location. The waste
treatment procedures described in Section VII can be
utilized in any geographical area. In the event of a
limitation in the availability of land space for
constructing a waste treatment facility, the in-process
controls and rinse water conservation techniques described
in Section VII can be adopted for minimizing the land space
required for the end-of-process treating facility. Often a
compact package unit can easily handle end-of-process waste
if the best in-process techniques are utilized to conserve
raw materials and water.
Quantity of Work Processed
32
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Quantity of work processed is analogous to plant size.
Therefore, the discussion about plant size is equally
applicable to the quantity of work processed. The
application of the guidelines provides for the production
volume of a particular facility.
Waste Characteristics
The physical and chemical characteristics of all wastes
generated by electroplating processes are similar.
Specifically, all wastes are amenable to the conventional
waste-treatment technology detailed in Section VII. The
characteristics of treated waste are the same throughout the
industry. Thus, waste characteristics do not constitute a
basis for subcategorization.
Rack Plating Versus Barrel Plating
The choice of rack or barrel methods for plating is based on
the size and quantity of the parts to be processed per unit
of time. Neither of these conditions imposes a significant
technical change in the operations for electroplating. The
selection is always based on economic considerations because
hand racking of small parts is usually more costly than
barrel processing in bulk. Sometimes plating bath
compositions will be modified by altering the concentration
of solution constituents. However, the same types of salts,
acids, and additives will be used. Thus, the impact on
waste characteristics is not changed. The volume of waste
water (dragout) is frequently greater in barrel plating
operations but the final effluent quality is not a function
of influent concentration. Techniques are available to
reduce the rinse water volumes in barrel plating to the
levels of rack plating. These techniques are detailed in
Section VII. Therefore, rack plating and barrel plating are
not appropriate subcategories.
Water Use
Water use formed a major basis for the differentiation
between electroplating and other metal finishing processes.
The water use in 1/sq m and the cumulative percentile has
been plotted in Figure 1. The median water use value is 120
1/sq m. However, it is not known to what extent rinsing
technique and product size and shape contribute to this
factor. Therefore 160 1/sq m is chosen as the water use
factor to allow for these factors.
Treatment Technology
33
-------
FIGURE 1
*J 00 tD o
COMMON & PRECIOUS METALS
l/m2 - op
M
o
CO
o
ju tn o viooto2
o o o oooo
M
§
•& CJI 01 *^J OOtOO
O O O O OOO
O O O O OO O
M CO
o o
o o
o o
ft U1
§ i
o o
U)
01
o
a>
o
00
o
0
-------
As no peculiarity exists between raw materials and waste
characteristics as a basis to separate facilities into
subcategories, none exists for treatability of wastes as a
basis for subcategorization. All of the principal treatment
procedures and in-process controls are technically
applicable by choice for any given waste and all operations
generate the same type of raw waste regardless of the
facility.
However, due to the high costs of some metals there has been
increasing impetus to recover and reuse them. This is
almost universally true of the precious metals, silver, gold
and the platinum metals. It is increasingly the case for
chromium and nickel. Thus, the treatment technologies
employed for the wastes generated from electroplating of
precious metals include electrolytic recovery evaporation,
ion exchange, and segregation and chloride precipitation for
silver. For this reason, electroplating of common metals
and electroplating of precious metals have been separated
into separate subcategories.
Processing Differences
Although the basic notion of electroplating remains the same
whether plating common or precious metals, there is a great
difference in the care with which they are handled.
Precious metal plating involves more hand work. Precious
metals are far more expensive to purchase which is offset by
greater worth per item. Also, the volume of business is
much smaller for precious metal plating. For these reasons,
electroplating of common metals is separated from
electroplating of precious metals.
Categorization Summary
The electroplating industry consists of two subcategories of
the electroplating point source category for the purpose of
establishing effluent limitations guidelines and standards
of performance. This subcategorization is based upon water
use and differences in treatment technologies and
processes.
35
-------
SECTION V
WASTE CHARACTERIZATION
Introduction
Water flow and the sources, nature and quantity of the
wastes dissolved in the water during electroplating
processes are described in this section. Water is a major
material in the electroplating industry and is associated
with every process. Yet, none of the water enters the
products so that it does not directly add to the product
value.
Characteristics of Waste
Waste water from electroplating processes comes from
cleaning, pickling, plating, etching, etc., operations and
includes constituents coming from the basis material being
finished as well as from the components in the processing
solution. Predominant among the waste water constituents
are the metal cations (sometimes complexed as anions) such
as copper, nickel, chromium, zinc, lead, tin, cadmium, gold,
silver, platinum metals, and anions that occur in cleaning,
pickling, or processing baths such as phosphates, and
chlorides, and various metal complexing agents.
Specific Water Uses
Water is used in the following ways:
(1) Rinsing to remove films of processing solution
from the surface of work pieces at the site of
each operation
(2) Washing away spills in the areas of the
operations
(3) Washing the air that passes through ventilation
ducts so as to remove spray from the air
before it is exhausted
(t») Dumps of pretreatment and posttreatment solutions,
(5) Rinse water (and dumps) of solutions from
auxiliary operations such as rack stripping
(6) Washing of equipment (e.g., pumps, filters,
tanks, ion-exchange units)
(7) Cooling water used in heat exchangers to
cool solutions in electroplating processes.
(8) Rinsing of activated carbon filters used in most
decorative plating solutions.
37
-------
Rinsing
A large portion (perhaps 90 percent) of the water usage is
in the rinsing operations. That used as cooling water
usually does second duty in rinsing steps. The water is
used to remove the films of processing solutions from the
surface of the work pieces. In performing this task, the
water becomes contaminated with the constituents of the
operating solutions and is not directly "reusable". Thus,
the cost of water is an operating expense to which is added
the cost of treating the water prior to reuse or discharge.
Dilute water solutions result from the raw waste from each
operation. Therefore, the location of rinse steps is
important relative to the operations performed in the
electroplating process.
Some plants use more water than the minimum required to
maintain good quality work, others use a smaller quantity to
achieve the same result. Figure 2 shows a schematic for
water flow in an electroplating facility.
Spills and Air Scrubbing
The extent of leakage from any source and the magnitude and
frequency of spills is directly related to plant management
and operating philosophy. These sources of waste can and
are being minimized to the level where they can be easily
handled. As of this date, there is no known relationship
between these sources and a unit of production or raw
material used. The water from washing away spills and from
washing down ventilation exhaust air is added to the acid
alkali stream and then treated.
Dumps
Exhausted or spent operating solutions to be dumped are
slowly trickled into rinse water following the operation and
prior to treatment. Alternatively, the operating solutions,
which are much more concentrated than the rinse water, may
be processed batchwise in a treated facility. Subsequent
discussion of waste treatment of rinse water covers all the
water in the facility.
Water from Auxiliary Operations
Cyanide solutions are used for stripping deposits and rack
tips to form cyanide compounds that are not decomposed by
treatment with chlorine, i.e., nickel cyanide. However,(
there are suitable alternatives to cyanide stripping
38
-------
Work flow
FIGURE 2. SCHEMATIC FLOW CHART FOR WATER FLOW IN CHROMIUM
PLATING ZINC DIE CASTINGS, DECORATIVE
39
-------
solutions with which the formation of stable cyanide
compounds can be avoided in many cases.
Washing Equipment
Water used for washing filters, pumps, and tanks picks up
residues of concentrated solutions or salts and should be
routed to the appropriate rinse water stream for chemical
treatment.
Cooling Water
As noted previously, cooling water used in heat exchangers
for cooling electroplating solutions should be used for
rinsing purposes in the interest of conserving water. A
further advantage of this practice is that if the cooling
water is contaminated by the electroplating bath due to
leaks in the heat exchanger, the contaminated water will be
subjected to treatment to remove the contaminants before the
water is discharged.
At least 95 percent of the products being electroplated (or
electroformed) to provide resistance to corrosion, wear, and
other destructive forces are processed in medium sized or
large plants (4,000 to 5,000 in number) , each deploying at
least 11 kg/day (25 pounds/day) of raw waste into rinse
water. The potentially toxic waste in the form of heavy
metal salts and cyanide salts from these sources is
approximately 340,000 kg/day (750,000 pounds/day). This is
equivalent to about 110,000 kg/day (250.000 pounds/day) of
heavy metal and cyanide ions.
At least 450,000 kg/day (1,000,000 pounds/day) of acids are
contributed to the total waste by cleaning and pickling
operations that precede electx opiating. The proportion of
phosphates in alkaline cleaning chemicals is believed to be
25 percent of the total alkalies.
Some of the alkaline solution waste and nearly all of the
acid solution waste contain metals resulting from the
dissolution of metal products to be plated. Hence, the
total amount of waste water constituents generated by the
electroplating industry probably exceeds 1,350,000 kg/day
(3,000,000 pounds/day).
The estimated alkali load of 230,000 kg/day (500,000
pounds/day) and acid load of 450,000 kg/day (1,000,000
pounds/day) are usually in about the same ratio in most
40
-------
TABLE 8 ESTIMATED DAILY RAW WASTE LOAD OF PRINCIPAL SALTS
USED IN COPPER, NICKEL, CHROMIUM, ZINC PLATING
AND RELATED PROCESSES
Operation
Principal Salts
Identity
kg/day pounds/day
Percent of
Total Salts
Consumed by
Plating
Copper plating Copper cyanide, 54,000 120,000
sodium cyanide, and
copper sulfate
Nickel plating
Nickel chloride and 54,000 120,000
nickel sulfate
Chromium plating Chromic acid
Zinc plating
Zinc oxide, zinc
cyanide, sodium
cyanide, and
zinc sulfate
45,000 100,000
68,000 150,000
Zinc chromating Sodium chromate and
sodium dichromate
6,800 15,000
227,800 505,000
13
17
13
23
2
68
(a) Data from a survey conducted by Battelle's Columbus
Laboratories in 1965.
41
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TABLE 9 WASTEWATER CONSTITUENTS FROM PREPARATION OF METAL BEFORE PLATING
K>
Constituent
Iron, Fe"^
Codmium
Copper
Lead
Tin
Silver
Nickel
Aluminum
Zinc
Silicates
Phosphates
Borates
*V~V
Wetting Agents
Chlorides
Sulfates
Nitrates
Fluoborates
Cyanides
Steel
X
X
X
X
X
X
X
X
X
Copper Lead
Alloys Alloys
X
X
X
X X
X
X X
X X
X X
X X
X X
X X
X
X
Basis Material*
Gold
Silver Alloys
X X
X X
X
X X
X X
X X
X X
X X
X X
X X
Nickel
Silver
X
X
X
X
X
X
X
X
X
X
Aluminum Zinc
X
X X
X X
X X
X X
X X
X X
X X
X
* The metal plated may be considered a basis material due to its presence on rack tips that are
recycled to pretreatment operations. For example, cadmium or lead may appear in wastewater
constituents for any basis metal plated with cadmium or lead.
** Wetting agents are represented by a variety of organic surface active agents, many of them
oroprietary.
-------
TABLE 10 PRINCIPAL WASTEWATER CONSTITUENTS IN WASTES
GENERATED DURING PRETREATMENT FOR ELECTROLESS
PLATING ON METALS AND PLASTICS
Pollutant
Pollutant
Copper Silver Aluminum Magnesium Plastics
Alkaline Cleaning
Copper, Cu+2 x
Iron, ferrous, Fe+2 X
Nickel, Ni+2 X
Cobalt, Co+2 X
Aluminum, Al+3 ^
Magnesium, Mg+2
Silicate, Si03~2 XXXXXX X X
X
- J o — •"• •"• A A X A
Carbonate, C03~^ XXXXXX X X
Phosphate, P04~3 XXXXXX X X
Organics XXXXXX X X
Acid Dipping
Iron, ferrous, Fe+2 x
Nickel, Ni+2 X
Cobalt, Co+2 X
Copper, Cupric, Cu+2 X
Silver, Ag+1 x
Aluminum, Al+ y
Magnesium, Mg+2 „
Chloride, Cl"1 x
Sulfate, 504-^ X X X X
Nitrate, NOo"1 Y Y v
Fluoride, F3 X X ^
A
Conditioning, Sensitizing,
Activating
Zinc, Zn+2 X X
Tin, Sn+2 x
Palladium, Pd+2 XX X
Chromate, Cr03~ x
Chloride, Cl~ XX X
-------
plants (i.e., combined acid/a.lkali wastewaters are mostly
acid). Assuming the alkalinity as sodium hydroxide (NaOH)
and acidity as sulfuric acid (H2SOU),
combination/neutralization (about 0.9 kg NaOH/kg H2S04)
would indicate a total net acid load of 350,000 kg/day
(750,000 pounds/day). Table 8 shows the estimated daily raw
waste load of principal salts used in electroplating and
metal finishing.
Sources of Waste
Preparation of Basis Metal
Tables 9 and 10 list the waste water constituents resulting
from the preparation of metals prior to plating operations.
Acids and alkalis must be neutralized prior to discharge
into navigable waters.
Alkaline Cleaners
Cleaners are made up with one or more of the following
chemicals regardless of the material to be electroplated:
sodium hydroxide, sodium carbonate, sodium metasilicate,
sodium phosphate (di- or trisodium), sodium silicate, sodium
tetraphosphate, and a wetting agent. Compositions for
cleaning steel are more alkaline and active than those for
cleaning brass, zinc die castings, and aluminum. Therefore,
cleaners vary with the type of basis metal being cleaned and
also with the type of soil being removed.
Wastes contain not only the chemicals found in the alkaline
cleaners but also soaps from the saponifications of greases
left on the surface by polishing and buffing operations.
Some oils and greases are not saponified, but nevertheless,
emulsified. The raw wastes from the basis materials and
process solutions for cleaning the work show up in the rinse
waters, spills, dumps of concentrated solutions, wash waters
from air-exhaust ducts, and leaky heating and cooling coils
and heat exchangers.
Alkaline cleaning of zinc die castings is generally carried
out in a proprietary solution, or a solution such as given
below, under the conditions shown.
Sodium carbonate 7.5 g/1 (1 oz/gal)
Sodium hydroxide 7.5 g/1 (1 oz/gal)
Temperature 93 C (200 F)
Time 30-60 seconds.
44
-------
This cleaned work is rinsed thoroughly and then dipped in 1
to 2 percent sulfuric or phosphoric acid for 15-30 seconds
at room temperature to assure neutralization of any
remaining alkaline films. Following another thorough rinse,
it is then chromated.
Conventional cleaning procedures involving solvent cleaners
or vapor degreasing are used routinely on aluminum for
removal of grease and other organic contaminants. The
removal of soil from aluminum is most frequently achieved by
using alkaline cleaners, that function by dissolving or
dispersing soils, augmented in some instances by etching of
the metal. Two representative cleaner formulations for
aluminum are shown in Table 11. The silicate in the second
formulation works as both a detergent and corrosion
inhibitor; the kerylbenzene sulfonate is a wetting agent.
An etching-type cleaning treatment may be used prior to
other treatments when a mat or nonspecular surface is
desired. Inhibited nonetching cleaners are employed when
attack or roughening of the aluminum part surface are
undesirable. Prolonged operations with aggressive alkaline
cleaners such as those containing caustic soda frequently
cause the precipitation of a flocculant hydrated aluminum
oxide which can interfere with effective rinsing of the
work. Several additional agents, which contain gluconates,
citrates, or tartrates, have been developed to avoid or
minimize such effects. These agents work by sequestering
the hydrated aluminum oxide to yield a more granular
precipitate which is less likely to cake and responds better
to rinsing.
Aluminum alloys containing copper, manganese, or silicon are
especially susceptible to smut on their surfaces during
alkaline cleaning operations. The smut generally consists
of loosely adherent, finely divided particles of the
aluminum alloy metals or their oxides. Table 12 lists some
typical deoxidizing and desmutting treatments for aluminum.
Nitric acid (Formulation A) is a general-purpose reagent for
removal of smut from aluminum and other metals. Formulation
B, containing about 75 percent nitric acid and 25 percent
hydrofluoric acid is especially effective in the removal of
smut formed on high silicon (5 percent or more) alloys. The
chromic acid-phosphoric acid (Formulation D) mixtures are
generally used for the selective removal of oxide without
significant attack of the metal surface. Proprietary
desmutting and deoxidizing solutions are extensively used.
Alkaline cleaning is generally the most satisfactory method
for degreasing and cleaning magnesium prior to chromating.
Representative alkaline cleaner compositions and operating
45
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TABLE
ALKALINE CLEANERS FOR ALUMINUM
Type
Composition
Temp, C
Time
•Ji
cr. Etching
Inhibited-
Nonetching
SC'M"ni "-r^"0*-" /"Mo^m.^ • 99 R rr/l (I. n n7/oa1">
^ s^^j/ • *~ "•' ~" o' ~^ v—-— — / o~ — /
Sodium orthophosphate (Na3P04'12H20: 22.0 g/1 (2.9 oz/gal)
Sodium carbonate (Na2C03): 22.5 g/1 (3.0 oz/gal)
Sodium orthophosphate (Na3PC>4 '12H20: 22.5 g/1 (3.0 oz/gal)
Sodium metasilicate (Na2Si03.9H20: 15.0 g/1 (2.0 oz/gal)
Kerylbenzene sulfonate (40%): 2.5 g/1 (0.3 oz/gal)
71-8?
71-82
As Reoiiired
As Required
-------
TABLE 12 REPRESENTATIVE DEOXIDIZING AND DESMUTTING
TREATMENTS FOR ALUMINUM
Formulation
Temp, C
Time
Purpose
(A) Cone. HNO (10 to 50% by vol) Ambient
(B) 75% vol cone HN03 Ambient
257o vol HF (48 wt%)
(C) 20 g/1 (2.66 oz/gal) Cr03 88-93
35 ml/1 85 wt% H3PC>3
(D) 100 ml/I 96 wt% H2S04
35 g/1 (4.66 oz/gal) Cr03 64-82
30 to 60 sec
5 to 10 sec
2 to 10 min
1 to 5 min
Smut removal
Smut removal,
especially for high
silicon Al alloys
Oxide removal
Oxide removal
47
-------
conditions for processing magnesium are presented in Table
13.
Pretreatment of copper, copper alloys, and silver is similar
to the procedures described for zinc, cadmium, and aluminum.
Acid Dips
Acid solutions are made up from one or more of the
following: hydrochloric acid, sulfuric acid, phosphoric
acid, fluoboric acid, chromic acid, and nitric acid. The
solution compositions vary according to the nature of the
basis metals, the type of tarnish or scale. The acid
dipping baths for treating metal substrates prior to plating
usually have a relatively short life. When these solutions
are dumped and replaced large amounts of chemicals must be
treated or reclaimed. Water used for rinsing following acid
dipping collects impurities, including metal waste from
dragout of acid solutions into the rinse water.
Acid solutions used for pickling, acid dipping, or
activating accumulate appreciable amounts of metals, as a
result of metal dissolution from metallic work pieces or
uncoated areas of plating racks that are recycled repeatedly
through the cleaning, acid treating, and electroplating
cycle. The copper (and zinc) accumulate in acid bright dip
solutions used to prepare electrical copper and brass
contacts for plating.
The amount of waste contributed by preplate preparation
steps varies appreciably from one facility to another
depending on the substrate material, the formulation of the
solution adopted for cleaning or activating the material,
the solution temperature, the cycle time, and other factors.
The initial condition of the substrate material affects the
amount of waste generated during preplate treatment. A
dense, scalefree copper alloy article can be easily prepared
for plating by using a mild hydrochloric acid solution that
dissolves little or no copper, whereas products with a heavy
scale require stronger and hotter solutions and longer
treating periods for insuring the complete removal of any
oxide, prior to plating.
Deposition and Posttreatment
Table m gives the principal waste water constituents
present in plating rinse waters by way of dragout from
plating solutions. The major contributions are marked by
"X" and are those elements or ions which are constituents in
a given plating bath. In many instances a metal cannot be
48
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TABLE 13 REPRESENTATIVE ALKALINE CLEANERS FOR MAGNESIUM
Type
Bath
Procedure
Heavy Duty
Alkaline
(a)
Sodium hydroxide (NaOH): 15-60 g/1 (2-8 oz/gal)
Trisodium phosphate (Na3P04 • 12H20) 11 g/1 (1-1/2 oz/gal)
.(a)
Caustic Soakv ' Sodium hydroxide (NaOH): 98 g/1 (13 oz/gal)
Immerse parts 3 to 10 minutes
in bath at 88-100C; clean
until no water break occurs
in rinse; rinse thoroughly
Immerse parts in bath at 88-
100C; soak for 10-20
minutes; rinse thoroughly
(a) Add 0.1 oz soap or wetting agent per gallon if heavy mineral oil films are to be removed.
-------
TABLE M. WASTEWATER CONSTITUENTS FROM PLATING OPERATIONS
P,1W WaH t e-
Constituent
Arro-. ia
A 1 ur. 1 r.um
Antimony
Arn'rn Ic
Cadmium
Cal' lu=
Chro-.ium
Cobalt
Confer
Gallium
Gold
Indium
Irldlum
Iron
Lead
Magnesium
Ma-i/ar e«e
Molybdenum
Klci-el
Palla-Jlun
Platinu-n
Potassium
Rhenium
»h',-l ! i-i
Ruthenium
Selenium
Silver
Sod lum
Tin
Zinc
Acetate
Borate
Cyanide
Phosphate
Fluor Me
Chloride
BronHe
Sulfate
Sulf Ide
Thiosulfate
C 1 1 r i. I e
Sulf ite
Carbonate
Tar t rat t-
Sul fa-ate
Nitrate
f.arbo-. •iluulf id*
Fer ro'-yan ide
phosphorous
Anlr.o nitrite
Organic addition
agents
Topper nn'l Niil'il nti'l Lead and Tin and Gold and Silver and Platinum
Copper Alloys Nickel Alloys Chromium Zinc Cadmium Indium l.rnd Alloys Tin Alloys Cold Alloyti Sllvei Alloys Metals Iron
X X X XXX
X
AX A
A AX
AX AX
X
X X
X A A AX
OX 0 0 X X X 0
AX
X
X X
X
X
OX X XX AX
X
A A X
OX 0 A A X OX 0
X
X
OX OOXXX XX OX
X
A
A A
X OX
ox ooxx x oxxx
X X XX
X X X
X X
xxoxxxx x
OX OOXXX X X OXX
x XX
x x x x
XX X X X X X
X 0 X X X XX
X
XX OX XX X XX
x x
X
X
X XX XX
XX A
XXX X
X
A X
X
X
A AAAAAAA A
Because of the use of acid and/or alkaline dips In the pretreatment for plating, basli metal constituent* arc expected to also be present In small
la the waste (treaa.
ounts (>10 »g/l)
-------
plated directly onto some basis metals and a precoating or
"strike" is required to achieve adhesion. An "O" before an
"X" indicates additional wastes originating from such strike
solutions. For example, silver on brass may be preplated
with copper, and/or nickel and silver on steel may be
preplated with nickel. Many plating baths contain metallic,
metallo-organic, or organic additives to induce grain
refining and level and brighten deposits. Such additives
are generally present in a bath at concentrations of less
than 1 percent by volume or weight, and are marked by "A".
The conversion solutions are generally very dilute as
compared to concentrations in normal electrodeposition
baths.
Iron Plating
Applications of iron deposits include electroformed parts
such as printing plates and surface-hardened tools, dies and
cylinder liners. Iron is plated from chloride,
sulfate/chloride and fluoroborate baths with concentrations
of 55 to 110 g/1 (7.5 to 15 oz/gal) of iron. A most useful
bath is the one containing 127 g/1 (17 oz/gal) FeCl2 and 111
g/1 (15 oz/gal) CaCl2. The sulfate/chloride bath contains
up to 20 g/1 (3 oz/gal) of ammonium chloride in addition to
250 g/1 (33 oz/gal) ferrous sulfate and small amounts of
ferrous chloride (30 g/1 or 4oz/gal). The fluoroborate bath
contains typically 225 g/1 (30 oz/gal) ferrous fluoroborate,
10 g/1 (1.3 oz/gal) sodium chloride and 22.5 g/1 (3 oz/gal)
of boric acid. The cathode current efficiency for all
solutions is between 95 to 100 percent.
Dragin to rinse water after plating is the major source of
waste; floor spills and leakage from filter systems are a
secondary source. Fluoborate ions will have to be treated
where such a bath is used. A small concentration of ferric
ion is present in the sulfate and chloride baths from
oxidation, but this generally precipitates in the bath as a
hydroxide or oxide.
Cadmium Plating
Cadmium deposits are used for preventing rusting of ferrous
metals. In some instances they are used as an undercoat for
zinc plating. Deposits from the cyanide baths are used on
moving parts, such as communications equipment and
instruments where corrosion products from a zinc deposit
would be objectionable. In the case of steels, hydrogen
embrittlement is a problem with some baths and is avoided by
use of a fluoroborate bath.
51
-------
Cadmium is electroplated from cyanide solutions, containing
cadmium as oxide or cyanide, sodium cyanide and sodium
hydroxide or fluoroborate solutions which are purchased as
liquid concentrates containing cadmium fluoroborate,
fluoboric acid, boric acid and ammonium fluoroborate.
Brighteners and grain refiners in the cyanide bath can be
metallic, such as nickel, cobalt, molybdenum and selenium,
or organic such as gelatin, coumarin, sugars, sulfonic acid
derivatives, and aromatic aldehydes. Licorice is suggested
for use in fluoroborate solutions. Most additives are
proprietary. The cyanide bath has the lower cadmium
concentration of 26 g/1 (3.5 oz/gal) with a total cyanide
concentration nearly four times as great as the cadmim
concentration. The fluoroborate bath contains 95 g/1 (12.6
oz/gal) cadmium and therefore contributes four times the
amount of cadmium to raw waste than does the cyanide bath.
Water use may be further increased because of the greater
viscosity of the fluoroborate baths and the resulting higher
dragout.
The major source of waste is from dragout into rinse waters.
A secondary source can be leakage from filters, pumps, and
piping from the cyanide solutions. Accidental spills and
poor housekeeping may in some instances lead to increased
waste; dumping of cadmium solutions is not practiced.
Lead and Lead Alloy Plating
Lead and Lead alloy coatings are used to improve the
solderability and coating properties and performance of such
basis metals as steels, copper and copper base alloys,
aluminum, and for strip plating of steel mill products.
They are also applied to copper and copper alloy coatings.
Lead and lead alloys (mainly lead-tin) are plated from
fluoroborate baths, which are purchased as concentrates and
then diluted to the desired strength. The lead
concentration may range from 112 to 255 g/1 (15 to 34
oz/gal) free fluoboric acid content from 20 to 45 g/1 (2.5
to 6 oz/gal) and the boric aicid concentration from 20 to 60
g/1 (2.5 to 8 oz/gal). Additives, such as glue, resorcinol,
and gelatine are present in small amounts (0.15 to 0.3 g/1)
to improve deposit structure, or sometimes hydroquinone is
used in concentrations of 10 g/1 (1.3 oz/gal).
In the alloy baths part of the lead is replaced with tin in
the form of fluoroborate. Normally lead and tin
fluoroborate concentrates are purchased separately and mixed
in the plant in proportions that achieve the alloy
composition desired. The raitio of Pb: Sn may vary from 16:1
52
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to 0.7:1 to deposit alloys containing from 6 to 60 percent
tin. The most concentrated baths are used for plating on
wire and strip.
Cathode current efficiencies are near 100 percent and the
baths are operated at temperatures between 22 and 38°C (70-
100°F). Continuous filtration of the baths is recommended
and precautions should be taken to collect leaks from the
filtering systems, as well as accidental spills. The main
source of waste should be dragout of plating bath into rinse
water. Spills and leaks constitute secondary sources.
Tin and Tin Alloy Plating
Tin and tin alloy electrodeposits are applied to improve
solderability, provide corrosion protection and give
j antifriction properties. Plating is done on piston
cylinders and rings, electrotypes, refrigerator parts, and
kitchen ware. A large amount of tin is plated on continuous
strip and wire. Tin-nickel alloy deposits have found
application as substitutes for bright nickel-chromium
plating. A copper undercoat, deposited from cyanide baths
is required when tin is to be plated on ferrous metals. The
tin-lead alloy is plated extensively on printed circuit
boards.
Tin is deposited from both acid and alkaline solutions.
Three types of acid tin baths are used in industry (1) the
sulfate/sulfuric acid bath, (2) the fluoroborate/fluoboric
acid bath, and (3) the halide bath. The sulfate bath
contains 30 g/1 (4 oz/gal) of tin or stannous sulfate, 50
g/1 (6.7 oz/gal) sulfuric acid or cresol sulfonic acid. The
latter reagents inhibit the oxidation of divalent tin to
quadrivalent tin. Gelatin is used at a concentration of 6
g/1 (0.8 oz/gal) and B-naphthol at a concentration of 1 g/1
(0.11 oz/gal) .
The fluoroborate bath is marketed in concentrate form, which
is diluted to concentrations of 8U g/1 (11 oz/gal) of tin,
56 g/1 (7 oz/gal) of fluoboric acid, 30 g/1 (4 oz/gal) boric
acid. A number of organic additives are present; gelatin is
used in concentrations of 6 g/1 (0.8 oz/gal) and B-naphthol
at a low concentration of 1 g/1 (0.11 oz/gal).
The halide bath consists of a solution of chlorides and
* fluorides. The tin concentration is approximately 35 g/1
* (U.6 oz/gal) and 1.5 g/1 (0.2 oz/gal) of an organic agent
are added.
53
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The acid baths deposit tin twice as fast as the stannate
baths, because the valence off tin is two rather than four.
Tin is present as stannate in alkaline bath compositions in
concentrations from 40 to 160 g/1 (5.3 to 21.2 oz/gal).
Sodium or potassium hydroxide concentrations are less than
15 g/1 (2 oz/gal).
Tin-Copper and tin-zinc alloys are plated from the same
stannate formulations, except that part of the tin is
replaced by either zinc or copper cyanides. The relative
amounts of each metal in the baths determine the alloy
composition of the deposits. Sometimes addition agents such
as gelatin, thiourea or ammonium molybdate. for brightening
and grain refining are used in small amounts (1 g/1).
The tin-nickel bath is acidic with a pH of 2.5 and contains
stannous chloride, nickel chloride, ammonium fluoride or
sodium fluoride or ammonium bifluoride and possibly
hydrochloric acid. The metal concentrations are 27 g/1 (3.6
oz/gal) of tin and 75 g/1 (10.0 oz/gal) of nickel. The
total fluoride content is 39 g/1 (5.2 oz/gal). A bright
alloy is deposited at 100 percent current efficiency without
the need for an addition agent. The only posttreatment is
"hot-flowing" in hot oil.
The major source of waste for all the tin and tin-alloy
baths is from dragout into rinse waters. Since the
solutions are generally filtered, leakage from pumps,
filters, and piping could be a secondary source of waste
together with accidental spills.
Silver Plating
Silver is used for decorative, protective, and engineering
coatings. Thin deposits of 2.5 urn (.0001 inch) and applied
over novelty items, jewelry and lighting fixtures. Thicker
deposits of 25 to 50 urn (.001 to .002 inch) are used for
tableware and hollowware and the thickest deposits up to
1500 m (.060 inch) are applied for bearings and
electroforms. Thin deposits are generally plated from
dilute baths. Concentrated, high-speed baths are used for
plating thicker coatings or electroforms.
Silver plating solutions contain potassium silver cyanide,
potassium cyanide, and potassium carbonate. The baths vary
in silver concentration from 25 to 75 g/1 (3.5 to 10 troy
oz/gal), depending upon their application. Modern silver
plating solutions also contain additives in small amounts
for grain refining and brightening, which are generally
54
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proprietary, i.e., reaction products of carbon disulfide,
ketones, turkey red oil, potassium antimony glycerol
complexes, gluconates or tartrates of lead and antimony,
ammonium thiosulfate and wetting agents. Cyanide solutions
are used for electrorefining silver.
Since silver will precipitate as a loose deposit by
immersion on metals to be plated, strike solutions are
generally employed to assure adhesion of the silver to the
basis metal. Strike solutions have a very low silver
content 1 g/1 (0.3 troy oz/gal), but a high cyanide content
of 75 to 90 g/1 (10 to 12 oz/gal) ; the solution may be
modified by the addition of copper cyanide. If silver is
plated on ferrous materials both types of strike solutions
are generally used. For other basis metals the type
containing silver cyanide only is considered sufficient.
When nickelr nickel alloys, or stainless steels are plated,
precautions must be taken to activate the nickel surface.
This may be accomplished by immersion in hydrochloric acid
or by striking in a Wood's nickel bath which is composed of
250 g/1 (32 oz/gal) nickel chloride and 120 ml/1 (16 oz/gl)
hydrochloric acid. Stainless steel can also be activated by
an anodic treatment in sulfuric acid solutions. In many
instances the parts to be plated are composed of more than
one metal, requiring both a copper strike and silver strike,
before silver plating. Consequently, more process steps are
required for plating silver than for plating the metals and
alloys discussed earlier. This, of course, requires a
greater use of water for rinsing.
Because of the high price of silver, the metal in solution
is generally recovered for refining and extra precautions
are taken to avoid spills and leaks. Dumping of solutions
is not practiced. The main concern, therefore, is the
treatment of cyanides present in the waste. The bath
additives, cited earlier, are present in amounts of less
than 10 mg/1 in the baths and are present in only trace
amounts in the rinse waters. Because silver tarnishes
readily in the atmosphere, posttreatments are sometimes
employed in the form of chromate conversion coatings.
Tarnished coatings are produced on silverware by immersion
in a hot solution of sulfur. Chromate and sulfide present
in rinse waters are removable by chemical treatment.
Gold Plating
Gold plating is divided into engineering and decorative
applications. Engineering coatings thicker than 1 urn
(O.OOOOU inch) are used for electronic switches,
semiconductors, surfaces of improved solderability and
55
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weldability, electroformed shapes. The coatings inhibit
galling and corrosion, and increase wear resistance.
Decorative coatings are applied on jewelry, watches, and
novelty items. The base metal can be a gold or silver alloy
or gold-filled. When ferrous and other nonferrous materials
are used an undercoat of copper and/or nickel is applied
first.
Gold and gold-alloys are plated from (1) cyanide
formulations, (2) neutral electrolytes, and (3) slightly
acidic baths. The deposits may contain as much as 99.99
percent or as little as 50 percent gold. Gold plating baths
are generally proprietary. All baths contain from 4 to 12
g/1 (0.5 to 1.5 troy oz/gal) of gold as an auro-cyanide or
sulfide. The cyanide formulations contain free potassium
cyanide, potassium carbonate, and potassium diphosphate all
at a concentration of about 30 g/1 (4 oz/gal) . The acid
baths contain small concentrations (0.1 to 2 g/1) of
cyanides complexed with approximately 90 g/1 (12 oz/gal) of
citrates. A sulfide-sulfate mixture of 150 g/1 (20 oz/gal)
is used in one of the cyanide-free baths.
A number of alloying elements are used in gold baths of
varying concentrations. In order to obtain specific
physical properties in gold deposits, cobalt, indium,
antimony, gallium, manganese, and arsenic are present in
solution in concentrations from 0.005 to 0.150 g/1 (0.0007
to 0.02 oz/gal) while other metals, such as silver, cadmium,
copper and nickel can have concentrations from 0.025 g/1 to
3 g/1 (0.003 to 0.4 oz/gal). These coatings have also found
application for decorative finishes.
Plating times for decorative coatings are comparatively
short being from 5 to 15 seconds for cyanide baths and up to
5 minutes for neutral or acid baths. Therefore, dragout
rates are high, compared to the amount of metal deposited,
especially for the case of the cyanide bath. Besides gold,
all the previously listed alloy elements are present in the
raw waste. Cyanide concentrations in the bath can range
from 15 to 30 g/1 (2 to U o:s/gal) .
Save rinses are generally used after gold plating. The
concentrated rinse can be returned to the bath or sent to
refiners for the recovery of gold. The succeeding diluted
rinses can be treated by ion exchange for metal recovery
before treatment of the cyanide.
Platinum Metals Plating
56
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Of the six metals in the platinum group only platinum,
rhodium, and palladium are plated to any extent. Of these,
rhodium is most often deposited. Decorative coatings for
silverware, jewelry, and watches are very thin (0.1 urn) and
are used to prevent tarnish and excessive wear of silver and
to enhance the color of gold and gold-filled products. When
the basis metal is not a silver or a gold alloy an undercoat
of nickel is generally used. Coatings 25 urn thick (0.001
inch) are used for wear and corrosion resistance in the
electronics industry and provide a surface of high optical
reflectivity.
Platinum is plated on titanium and similar metals, which are
used as insoluble anodes in other plating operations
(rhodium, gold). Electroplated platinum is used as an
undercoat for rhodium plate. Ruthenium plating is used on
high intensity arc electrodes to improve electrical contact.
Commercial plating of osmium and iridium are believed to be
nonexistant.
Rhodium plating baths are supplied as phosphate or sulfate
concentrates. The only additions made to the diluted
concentrate are phosphoric and/or sulfuric acids at
concentrations of 25 to 75 ml (3.2 to 9.6 fl oz/gal) per
liter of plating bath. A rhodium concentration of 2.0 g/1
(5 dwt/gal) is used for decorative coatings. Concentration
is increased to 10 to 20 g/1 (25 to 50 dwt/gal) for
achieving thicker deposits.
The platinum content in plating solutions ranges from 2.5 to
10 g/1 (6 to 25 dwt/gal) in the form of an amino nitrite
complex. Other constituents are 11 g/1 (1.5 oz/gal) sodium
nitrite and 50 ml/1 (6.U oz/gal) of concentrated ammonium
hydroxide. Palladium bath compositions are similar to those
for the platinum bath discussed above. Iridium deposition
has been accomplished from chloride or bromide solutions and
from a molten cyanide bath.
Very little, if any, waste from platinum metals baths is
expected to reach the final effluent from a plating plant.
The baths have generally very small volumes. Dragout is
minimized by using some rinses which are returned to the
plating baths and minor amounts of metal left in low flow-
running rinses are recovered by ion exchange. Solutions are
never dumped, but are returned to the refineries for
recovery of the metals.
Electroless Plating on Non-Ferrous Materials
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D ^criBtion of the Process. The term "electroless plating"
is used to describe a chemical plating process which can be
operated continuously to build up a relatively thick
deposit. The ability to build up thick deposits
distinguishes electroless plating from other chemical
deposition processes, such as immersion (displacement)
plating, which can produce only thin deposits. Electroless
plating occurs by catalysis rather than by interchange with
the basis metal characteristic of immersion processes.
Electroless plating can be used for special applications
where conventional electroplating processes are unsuitable.
For instance, electroless plating can deposit metal
uniformly on complex shapes and in deep holes that are
relatively difficult to coat uniformly by conventional
electroplating techniques.
Electroless plating is used to deposit metals on molded
plastic parts. If desired, a plastic part with metal
coating applied by electroless plating can be subsequently
plated by conventional electrodeposition techniques.
Solutions have been reported for electroless deposition of
the following metals: Arsenic, cobalt, copper, gold, iron,
nickel, palladium, and alloys of nickel-cobalt and nickel-
iron. However, only electroless copper and nickel plating
appear to have achieved commercial applicability.
Preparation for Finishing. Alkaline cleaning to remove soil
and grease is common practice for plastic substrates prior
to electroless plating. Parts are soak cleaned without
electrolysis. Cleaners contain silicates, carbonates,
and/or phosphates or combinations of these. Although the
solutions are inhibited to prevent etching or pitting of the
basis material, small amounts of basis metals are dissolved
and are therefore waste water constituents. Grease and oil
removed from the basis material constituents and organic
constituent in the waste water.
Acid pickling follows alkaline cleaning of basis metals and
the pickling solution may contain hydrochloric, sulfuric,
hydrofluoric and nitric acid. Some of the base metal is
dissolved by the pickling solution and therefore becomes a
waste water constituent. Metals such as copper and silver
require catalysis by dipping in an acidified solution of
palladium chloride.
Plastics to be electroless plated are roughened by abrasive
wet blasting or tumbling or chemically with chromic acid.
Roughening is followed by sensitizing in a strongly acid
58
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solution of stannous chloride. A further step is to
activate the surface in an acid solution of palladium
chloride. Thorough rinsing is required after each step.
Pretreatment. Plastic substrates require conditioning in
concentrated chromic acid solution, sensitizing in stannous
chloride solution, and activation in palladium chloride
solution before electroless plating.
Electroless nickel deposits spontaneously on catalytic
metals such as iron, nickel, and cobalt after alkaline
cleaning and acid dipping. Metals such as copper and silver
can be catalyzed by dipping them into a dilute solution of
palladium chloride to produce a thin immersion deposit of
palladium on the metal surface prior to electroless plating.
Aluminum and magnesium are attacked by electroless nickel
plating solutions resulting in blistered deposits. To
overcome this attack, a zincate immersion coating is used.
Alternatively, an electroless nickel solution containing
fluoride can be used directly on magnesium.
The primary use of electroless copper deposits is to produce
conductive layers on plastic substrates such as printed
circuit boards and flexible circuitry used in electronic
equipment. It has a very important function in providing a
conductive path through holes in double-sided circuit
boards. In the "additive" method of preparing printed
circuits electroless plating is used exclusively to form and
build up the circuit pattern. The volume of additive
circuits is growing slowly. The sensitization operation for
electroless deposition of copper on plastics is the same as
that used for electroless nickel.
Electrpless Deposition Treatment
There are two distinct types of electroless nickel baths:
(1) acid baths operated at pH 4-7 and (2) ammoniacal baths
operated at pH 8-11. The acid baths are more commonly used.
A variety of acid electroless nickel baths have been
described. These baths are all based on a composition of
nickel chloride or sulfate, sodium hypophosphite as the
reducing agent, and an organic acid. The organic acts both
as a buffer to help maintain the pH of the bath and as a
complexing agent for the nickel ions in solution. The rate
of nickel deposition is dependent upon the specific organic
acid in the bath and its concentration. Hydroxyacetic acid,
lactic acid, and propionic acid are commonly used.
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A typical ammoniacal electroless nickel bath contains nickel
chloride, sodium hypophosphite, sodium citrate, ammonium
chloride, and ammonium hydroxide. A variation of the
ammoniacal electroless nickel bath is the pyrophosphate bath
containing nickel sulfate,, sodium hypo phosphite, sodium
pyrophosphate, and ammonium hydroxide. The pyrophosphate
bath deposits nickel at a lower temperature than other
electroless nickel baths and at a faster rate than the
citrate nickel bath.
Electroless copper baths contain copper sulfate with either
Rochelle salt (sodium potassium tartrate) or EDTA
(ethylenediaminetetraacetic acid, sodium salt) as the
complexing agent and formaldehyde as the reducing agent. A
major application of electroless copper is in the
manufacture of printed circuit boards for electronic
equipment. The electroless copper is deposited on selected
activated areas to form the conductive leads between the
electronic components that are subsequently mounted on the
board.
Unlike conventional electroplating solutions which are
commonly used for many years and are seldom discarded,
electroless plating baths have a finite life and must be
periodically discarded or recovered when the concentration
of reaction products becomes too great. For instance, when
the phosphite concentration in an electroless nickel bath
has increased through oxidation of hypophosphite to 1 to 1.5
moles per liter, nickel ortho-phosphite will begin to
precipitate. Methods have been developed to periodically or
continuously remove the phosphite. However, such methods
have been considered too expensive for all but companies
using large volumes of solution. Therefore, electroless
plating solutions are either discarded or sent to suppliers
or other service companies for recovery. Where waste
treatment is employed discarded solutions are usually
trickled slowly into a rinse tank prior to waste treatment.
Post treatment of Electroless Deposits
Posttreatment of electroless deposits, when used, is usually
limited to electrodeposition of metal onto the electroless
deposit as often follows the metallization of plastics.
Consequently, wastes from treatments following electroless
deposition are considered in the context of the various
metals that are electrodeposited onto the electroless
deposit.
Posttreatment
60
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Chromating
Chromate conversion coatings are protective films formed on
metal surfaces. A portion of the base metal is converted to
one of the components of the film by reaction with aqueous
solutions containing hexavalent chromium and other active
organic or inorganic compounds. Chromate coatings are most
frequently applied to the following metals: zinc, cadmium,
aluminum, magnesium, copper, brass, bronze, and silver.
Generally the chromating solution is acidic and contains
chromic acid or its sodium or potassium salts, plus other
organic or inorganic compounds as activators, accelerators,
or catalysts. Although chromate conversion coatings can be
applied by chemical or electrochemical action, the bulk of
the coatings are usually applied by a chemical immersion,
spray or brush treatment. Most chromate treatments used in
industry employ proprietary solutions. With these
processes, a wide variety of decorative and protective films
ranging from colorless to iridescent yellow, brass, brown
and olive drab can be produced. The coating appearance will
depend on the basis metal and the processing procedures
employed. Additional coloring of the coatings can be
achieved by dipping the parts in organic dye baths to impart
red, green, blue and other colors. Besides their use as
protective or decorative films, chromate conversion coatings
are extensively employed to provide an excellent base for
paint and other organic finishes, which do not adhere well
to untreated metal surfaces.
Chromate coatings are widely used on aluminum in the
aircraft, electronics, and home appliance industries. The
process, being lower in cost than anodizing, is generally
employed for applications where the abrasion resistance or
highly decorative colors of anodized aluminum are not
required. The coatings have good adhesion properties for
subsequent organic coatings, offer good resistance to
corrosion, especially in chloride environments, and range
from clear to yellow, depending mostly on immersion time,
pH, solution composition, and to some extent on the
particular aluminum alloy treated.
Bright chromate treatments have advantages over conventional
acid bright dips for copper alloys, in that they produce a
passive film and also a surface with a high luster or
polish. The chromate film provides good protection against
corrosion and sulfide tarnishing on unplated parts. The
film also provides a good paint base.
Chromate coatings are applied to silver electroplates to
prevent sulfide tarnishing using proprietary formulations.
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Table 15 lists the principal waste water constituents
generated during pretreatment, coating and posttreatments
steps in chromating zinc, cadmium, aluminum and other
metals.
Chromate conversion coatings are frequently applied to zinc
or cadmiumrplated parts immediately following
electrodeposition. No preparation is necessary. In some
cases, a baking operation to eliminate hydrogen from the
deposit is carried out following electrodeposition.
Alkaline cleaning and an acid dip may then be necessary
before chromating.
Zinc and cadmium may be chromated to provide
(1) Bright chromates on zinc and cadmium
electrodeposits
(2) Colored coatings on zinc and cadmium
electrodeposits
(3) Colored coatings on zinc die castings.
The bright chromate treatments impart a high luster to zinc
or cadmium plates and also provide tarnish and corrosion
resistance. The chromate treatment of electrodeposits
generally follows immediately after the last rinse in the
plating cycle. The chromate bath for coating zinc and
cadmium parts is an acid solution containing hexavalent
chromium, such as chromic acid, plus other inorganic and
organic compounds to promote or catalyze the reaction.
The chromate coating solution for aluminum usually contains
hexavalent chromium, a fluoride, and an accelerator, such as
ferrocyanide or ferricyanide. The pH range is usually 1.0
to 2.5. Nitric acid frequently is added as an acidifying
agent. The fluoride, in the acidified solution, is the
active reagent; it dissolves the existing oxide film and
reacts with the aluminum. During the coating process, some
of the hexavalent chromium is reduced to the trivalent
state, and a gel-like film consisting primarily of aluminum
and chromium chromates is formed. As freshly formed, the
gel-like coating is dissolved readily in nitric acid. If
desired, the yellow chromate can be leached with hot water.
With aging, the film becomes insoluble. For many
applications, rinsing and drying complete the overall
chromating operation.
Much of the development work on chromate coatings on
magnesium has been carried out by the Dow chemical company.
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TABLE 15 CHROMATE COATING OF MAGNESIUM BY
THE CHROME PICKLE PROCESS
Step Bath Procedure or Comments
Cleaning Alkaline Immersion
Rinse Cold Water Rinse thoroughly in
cold running water
Chrome Pickle Sodium dichromate Immerse parts 1/2 to
(Na2Cr20y • 2^0) : 2 minutes in room
180 g/1 (24 oz/gal) temperature solution.
Concentrated nitric After dip, hold parts
acid (to Wt% HNO.,) : above tank for about
187 ml/1 (24 fl oz/gal) 5 seconds.
Rinse Cold Water Rinse thoroughly in
cold running water
Rinse Hot Water Hot water rinse used
to facilitate drying
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Chemical Treatment No. 1, also known as "chrome pickle", is
the most commonly used chemical treatment developed for
magnesium. It can be used on all magnesium alloys. The
coatings have good qualities as a paint base and protect
magnesium parts during shipment and storage. A typical
chrome-pickle procedure is shown in Table 15. The coating
appearance is usually mat gray to yellow red, and about
0.00006 inch of metal is removed from the magnesium.
The dichrornate treatment (Dow No. 7) for processing
magnesium alloys (except the thorium containing alloy)
produces a brassy to dark brown film, which provides a good
combination of protective and paint-base qualities. The
dichromate procedure is described in Table 16.
Generally, a cold rinse followed by a hot rinse to
facilitate drying complete the overall chromating process on
magnesium alloys.
Chromating treatments for copper, copper alloys, and silver
are similar to those described for zinc and cadmium.
Posttreatment of chromated parts, when used, can involve
bleaching or dying operations to produce or impart special
characteristics to the film. Clear bright finishes for zinc
and cadmium can be obtained by bleaching or leaching the
yellow coloring from the chromate film. Various mildly
acidic or alkaline aqueous solutions are employed, such as
(1) Sodium hydroxide 23 g/1 (3 oz/gal), room
temperature 5 to 10 seconds
(2) Sodium carbonate 15 to 23 g/1 (2 to 3 oz/gal) 19 to
54 C (120 to 130 F)
(3) Phosphoric acid, 1.0 ml/1 (.13 fl oz/gal), room
temperature, 5 to 30 seconds.
Dyed coatings can also be applied.
Phosphating
Phosphating is the treatment of ironr steel, zinc plated
steel, and other metals by immersion in a dilute solution of
phosphoric acid plus other reagents to produce an integral
conversion coating on the surface. Phosphate coatings are
used to: (1) provide a good base for paints and other
organic coatings, (2) condition the surfaces for cold
forming operations by providing a base for drawing compounds
and lubricants, and (3) impart corrosion resistance to the
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TABLE 16 BICHROMATE PROCESS CYCLE FOR
MAGNESIUM ALLOYS
-------
metal surface by the coating itself or by providing a
suitable base for rust-preventative oils or waxes.
The amorphous aluminum phosphate films are used extensively
as a base for organic coatings. Crystalline aluminum
phosphate coatings are used chiefly for paint bonding to
aluminum and also to provide lubrication for cold forming.
Commerical phosphating solutions are frequently proprietary
and usually consist of metal phosphates dissolved in
phosphoric acid solutions containing accelerators and other
special reagents to improve bath performance. Commonly used
accelerators include nitrites, nitrates, chlorates, and
peroxides. Phosphating occurs as follows:
3Me(H2P04)2 + Fe Me3 (POU) 2 + FeHPOU + 3H3PC4 + H2
where:
Me = Zn, Mn, or Fe.
The metal is provided by the basis material or from the
phosphating solution.
Cleaning of iron or steel parts is generally accomplished by
alkaline cleaning or solvent degreasing. Pickling in
phosphoric acid or other mineral acid solutions is used for
removal of rust or other corrosion products. Rinsing in hot
water, or in special activating solutions, generally
completes the pretreatment. In some instances, cleaning is
carried out simultaneously in the same solution.
The pretreatment procedures for phosphating aluminum alloys
include alkaline cleaning, and sometimes acid or caustic
etching, desmutting or deoxidizing dips, along with the
attendant rinses. These procedures were described in the
earlier sections of the report dealing with anodizing and
chromating of aluminum.
Table 17 lists lists the principle waste water constituents
generated during preparation, coating, and posttreatment
operations in phosphating iron, steel, and aluminum.
Zinc and iron phosphate coatings are applied by spray and
immersion techniques. Parts are immersed in a 2-1/2 percent
by volume zinc phosphate solution at (90 F) for 30 seconds
or sprayed with a 4 percent by volume zinc phosphate
solution at (140 to 180 F) for 3 to 5 minutes. Zn phosphate
may be applied to parts in an automatic barrel line by
66
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immersion in a proprietary solution containing zinc
phosphate, phosphoric acid, and nitrates. Iron phosphate is
applied by immersion in a 5 percent by volume solution at
(125 F to 160 F) and pH 3.5 to U.5 for 3 to 5 minutes or
spraying with a (1/2 to 2 oz/gal) solution at (90 to 160 F)
and pH 3.5 to 5.0 for 1 to 2 minutes. Manganese phosphate
is applied by immersion in a solution at (200 F) for 10 to
20 minutes.
A typical solution for producing amorphous phosphate
coatings on aluminum contains 70 g/1 phosphoric acid and a
ratio of fluoride ion to chromic acid of 0.25. The fluoride
removes the oxide film on the surface and attacks the
aluminum base metal to provide the ions needed to form
aluminum phosphate. The treatment times for temperatures of
100 to 130 F vary from a few seconds to several minutes.
The coating weights can be varied from 0.11 to 1.3 g/sq m
(10 to 400 mg/sq ft) .
Crystalline phosphate coatings on aluminum are produced
using solutions containing zinc or manganese acid
phosphates, an oxidizing agen such as nitrate, and a complex
fluoride to serve as the activating agent. A typical
phosphating solution contains: 0.7 percent zinc ion, 1.0
percent phosphate ion (Pcm)3~, 2.0 percent nitrate ion
(NO31-, and fluoroborate ion (BFU)»~. A satisfactory film
can be produced by spraying solution for 1 to 2 minutes at
SH to 57 C (130 to 135 F), or by immersing for 5 minutes in
a solution at 5U to 57 C (130 to 135 F) .
The final rinse after phosphating of iron, steel, and zinc
is usually carried out in a dilute chromic acid-phosphoric
acid solution (0.1 percent by volume) . This rinse removes
unreacted chemicals and improves the corrosion resistance of
the phosphated surface. The rinse step is frequently
followed by a dip in a suitable oil, wax, or other lubricant
before drying in hot air.
Immersion Plating
Immersion tin plating is used to "whiten" pins, hooks,
eyelets, screws, buttons, and other hardware items made of
copper, brass, or steel. In addition, aluminum alloy
pistons for internal combustion engines are coated with an
immersion deposit of tin. All immersion tin plating baths
for copper, brass, and steel are based on stannous chloride
solutions. Immersion tin solutions contain, in addition to
stannous chloride, cream of tartar (potassium bitartrate),
ammonium aluminum sulfate, or sodium cyanide and sodium
hydroxide.
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TABLE 17 PRINCIPAL WASTEWATER CONSTITUENTS IN WASTES
GENERATED DURING PHOSPHATING OPERATIONS ON
VARIOUS METALS AND ALLOYS
Basis
Constituent
Preparation-Cleaning
and Activating
Sodium, Na+
Aluminum Al+3
Zinc, Zn+2+2
Iron, Fe+2
Carbonate, C0o~2
Phosphate, P04~3
Silicate, Si02~2
Gluconate
Sulfate
Chloride
Nitrate
Chromate
Titanium, Ti+3
Antimony, Sb+3
Phosphating
Sodium, Na+
Aluminum, A1+3
Zinc , Zn+2
Iron, Fe+2
Manganese , Mn+2
Phosphate, P04~3
Chromate, Cr04~2
Fluoride, F~l
Fluoborate, BF4~1
Nitrite, N02"1
Nitrate, N03"1
Chlorate, C103~l
Posttreatment
Chromate, Cr04~2
Phosphate, P04~2
Metals and Alloys
Iron, Steel, and
Zinc-Plated Steel
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Aluminum
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Water soluble oils
and waxes
X
X
68
-------
Copper is immersion deposited on steel wire prior to drawing
in order to reduce wear on the dies. Copper is deposited
from an acid copper sulfate solution. Copper-tin alloy is
obtained on steel wire by adding tin salts to the copper
sulfate solutions.
Gold is immersion deposited on copper and brass to gild
inexpensive items of jewelry. Typical immersion gold
plating solutions contain gold chloride and potassium
cyanide or pyrophosphate.
Nickel is immersion deposited on steel prior to ceramic
enameling to improve the adhesion of the enamel. Immersion
nickel solutions contain nickel sulfate, or nickel chloride
and boric acid.
Tables 18 and 19 list the principal constituents in
wastewater generated during immersion plating of tin,
copper, gold, and nickel on various basis metals.
Metal Coloring
This section on metal coloring covers only chemical methods
of coloring in which the metal surface is converted into an
oxide or other insoluble metal compound. Coloring by
chemical deposition (immersion), electrodeposition, and
electrolytic conversion are covered elsewhere in this report
and thermal oxidation and lacquering are beyond the scope of
this report.
Metal coloring by chemical conversion methods provides a
large group of decorative finishes. The most common
finishes are used on copper, steel, zinc, and cadmium.
Application of the color to the cleaned basis metal involves
only a brief immersion in a dilute aqueous solution. The
colored films produced on the metal surface are extremely
thin and delicate. Consequently, they lack resistance to
handling and the atmosphere. A clear lacquer is often used
to protect the colored metal surface.
Preparation procedures for metal coloring are similar to
those used in the metal finishing processes, consisting of
alkaline cleaning and acid dipping. In addition to these
operations, polishing is often used to obtain the desired
surface prior to coloring. Mechanical polishing,
electropolishing, and chemical polishing are used singly or
in combination. Etching and bright dipping are also used to
obtain specific surface finishes. If mechanical polishing
is used, a degreasing operation must be included to remove
the polishing compound.
69
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TABLE 18 PRINCIPAL WASTEWATER CONSTITUENTS IN WASTES
GENERATED DURING IMMERSION PLATING OF TIN,
COPPER, GOLD, AND NICKEL
Basis Metal
Pollutant
Immersion Tin Plating
Tin
Chloride
Tartrate
Cyanide
Ammonium
Aluminum
Sulfate
Sodium
Immersion Copper Plating
Copper
Sulfate
Brass
X
X
X
X
X
X
X
X
Copper
X
X
X
X
X
X
X
X
Steel
X
X
X
X
X
X
X
X
X
X
Aluminum
X
X
Immersion Gold Plating
Chloride
Bicarbonate
Pyrophosphate
Cyanide
Potassium
Immersion Nickel Plating
Nickel
Sulfate
Borate
Chloride
X
X
X
X
X
X
X
X
X
X
X
X
X
X
70
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TABLE 19 PRINCIPAL WASTEWATER CONSTITUENTS IN WASTES GENERATED DURING
PREPARATION FOR IMMERSION PLATING ON VARIOUS BASIS METALS
Basis Metal
Pollutant Brass
Alkaline Cleaning
in
Iron, ferrous, Fe *•
+3
Aluminum , Al
Silicate, SK>3~2 X
Carbonate, C03~2 X
Phosphate, P0^~3 X
Organics X
Acid Dipping
Iron, Ferrous, Fe"*"2
Aluminum, Al -^
10
Copper, Cupric, Cu X
Zinc, Zn+2 X
Sulfate, S04~2 X
Chloride, Cl" X
Copper Steel Aluminum
X
X
XXX
XXX
XXX
XXX
X
X
X
XXX
XXX
71
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Table 20 lists the principal waste water constituents
generated during pretreatment steps prior to metal coloring.
A large amount of copper and brass is colored to yield a
wide variety of shades and colors. Shades of black, brown,
gray, green, and patina can be obtained on copper and brass
by use of appropriate coloring solutions. Table 21 shows
the constituents of the waste water obtained from rinsing
copper and brass after various coloring operations.
The most important colors for ferrous metals are based on
oxides which yield black, brown, or blue colors. Table 22
shows the constituents of the waste water used for rinsing
iron and steel after various coloring operations.
A number of colors can be developed on zinc depending on the
length of immersion in the coloring solution. For instance,
in a solution of ammonium chlorate the color sequence is
yellow, brown, violet, deep blue, and blue-black. Ammonium
molybdate solutions give a gold to brown to black color
sequence. Other colors that can be developed on zinc are
listed in Table 23, which also shows the constituents in
water used for rinsing after the coloring operations.
Although cadmium is not a structural metal, its use as a
protective deposit on ferrous metals provides applications
for decorative coloring. The most important surface
treatment for cadmium is chrornate passivation which improves
its resistance to the atmosphere and to finger prints as
well as providing color. In most instances, the color of
chromate-passivated cadmium is yellow, bronze, or dark
green. Black and brown colors can also be produced on
cadmium. Table 2H lists the principal constituents in waste
waters for rinsing after the coloring operations on cadmium.
Silver, tin, and aluminum are also colored commercially.
Silver is given a gray color by immersion in a polysulfide
solution such as ammonium polysulfide. Tin can be darkened
to produce an antique finish on pewter by immersion in a
solution of nitric acid and copper sulfate. Coloring of
aluminum is done by dyeing following anodizing as discussed
in the section of this report on anodizing of aluminum.
Waste water constituents from these processes are shown in
Table 25.
Because the colored layers on metal surfaces are so
delicate, they are usually protected by a coat of lacquer
applied by spraying or dipping. When water emulsions are
used, the lacquer or polymer is a waste water constituent.
72
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TABLE 20 PRINCIPAL WASTEWATER CONSTITUENTS
IN WASTES GENERATED DURING PRE-
PARATION FOR METAL COLORING
Metal Basis
Pollutant Copper/Brass Steel Cadmium Zinc
Alkaline Cleaning
•4-2
Iron, Ferrous, Fe X
Cadmium, Cd+2 X
Zinc, Zn+2 X
Silicate, Si03-2 X XXX
Carbonate, C03~2 X XXX
Phosphate, P04~3 X XXX
Organics X ,X XX
Acid Dipping
Iron, Ferrous, Fe+2 X
Cadmium, Cd X
Copper, Cupric, Cu+2 X
Zinc, Zn+2 X X
Sulfate, SOA~2 X XXX
Electro and Chemical Polishing
Phosphate, P04~3 X XX
Nitrate, N03*"1 X
Acetate, C2H302"1 X
Carbonate, C03~^ X
Sulfate, S04~2 X
73
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TABLE 21 PRINCIPAL WASTEWATER CONSTITUENTS
IN WASTES GENERATED DURING
COLORING OF COPPER AND BRASS
Pollutant
+2
Copper, Cu
_2
Carbonate, CO,,
+1
Ammonium, NH,
+2
Nickel, Ni
-2
Sulfate, SO,
-1
Chlorate, CIO
-1
Chloride, Cl
+3
Arsenic, As
+3
Antimony, Sb
-2
Thiosulfate, S.O,
2 3
+3
Iron, Ferric, Fe
Nitrate, NO ~
+2
Zinc, Zn
Color
Black Brown Gray Green
XX X
X X
XX X
X X
X
X
X X
X
X
X
X
X
X
Patina
X
X
X
X
X
X
Chlorite, CIO
Acetate,
-1
-1
Barium, Ba
Sulfide, S
+2
-2
X
X
X
X
74
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TABLE 22 PRINCIPAL WASTEWATER CONSTITUENTS IN WASTES
GENERATED DURING COLORING OF IRON AND STEEL
Pollutant
Black
Color
Brown
Blue
Nitrate, NO
Bichromate,
Nitrite, N02"1
Copper, Cu+2
4-2
Mercury, Hg
Iron, Ferric, Fe
Sulfate,
Chloride, Cl"1
Thiosulfate,
Lead, Pb+Z
Acetate, C2H302
+3
"1
in
Arsenic, As °
Chlorate, C103
Cyanide, CN"1
"1
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
75
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TABLE 23 PRINCIPAL WASTEWATER CONSTITUENTS IN WASTES
GENERATED DURING COLORING OF ZINC
Pollutant
4-9
Copper , Cu
Chlorate, d03~
Nitrate, N03~
Sulfate, SO^
Ammonium, NH^ •*-
Chloride, Cl"1
Carbonate, C03~2
Nickel, Ni+2
Malybdate, Mo^~
Color
Black Brown Green
XXX
X X
X
XXX
XXX
X
X
X
X X
Blue
X
X
X
76
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TABLE 24 PRINCIPAL WASTEWATER CONSTITUENTS IN
WASTES GENERATED DURING COLORING OF
CADMIUM
Pollutant
Chromium, Cr+6
Nitrate, W^"1
Copper , Cu
Sulfate, SO^"2
Chlorate, ClOo"-'-
Chloride, Cl"1
Arsenic, As+3
Ammonium, NH/
o
Dichromate, C^Oy *•
Permanganate, Mn04~-'-
Cadmium, Cd+2
Iron, Ferric, Fe+3
Color
Chromate Black Brown
X
X X
X
X
X
X X
X
X
X
X
X
X
77
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TABLE 25 PRINCIPAL WASTEWATER CONSTITUENTS IN WASTES
GENERATED DURING COLORING OF SILVER, TIN,
AND ALUMINUM
Pollutant
Gray on
Silver
Color
Antique on
Pewter (Sn)
Color on
Anodized Al
NH4+
S=
N03~
Cu+
so4=
Organic dyes
X
X
X
X
X
X
78
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Water Usaofe in the Electroplating Industry
The 1967 Census of Manufacturers estimated the total yearly
intake of water to be 3.27 x 10*° liters (8.7 x 10» gallon).
Of this amount 2.78 x 10»o liters (7.4 x 10« gallon) was
discharged as follows:
2.10 x 10»o liters
6.02 x 109 it
3.76 x 10* "
7.14 x 10« "
(5.6 x 10« gal) to public sewers
(L6 x 1Q9 galj to surface water bodies
(1.0 x 10« gal) to ground
(1.9 x 10« gal) treated before discharge.
This segment of industry, in 1967, had 55,100 employees,
an average of about 503,840 liters (134,000 gal)
employee.
or
per
Of the firms with captive electroplating facilities, 2191 of
them had a few more than 25,709 total employees. However,
the number of employees was not cited where one or two firms
were present. At the same water use rate these firms would
discharge over 1.182 x 1Qio liters (3.144 x 10« gal) and
assuming the same average rate the remaining 14,500
companies would discharge over 7.802 x 10^° liters (2.075 x
10»o
79
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SECTION VI
SELECTION OF POLLUTANT PARAMETERS
Introduction
This section of the report reviews the waste character-
ization detailed in Section V and identifies in terms of
chemical and physical constituents that which constitutes
pollutants as defined in the act. Rationale for the
selection and, more particularly, the rejection of waste
water constituents as pollutants are presented.
First, consideration was given to the broad range of
chemicals used in the electroplating industry. Those
considered to be amenable to treatment are identified.
Electroplating. Waste Water Constituents
A large variety of chemicals that become waste water
constituents are used in the electroplating industry. The
important ones were identified in Section V. Not all of
these constituents will be found in the waste waters from
every facility, since the number of processes in a single
facility varies as well as the number of basic materials
pretreated and types of posttreatment operations. The
nonmetallic cations, anions (hydrogen, ammonium, sulfate,
phosphate, chloride, etc.) can be considered typical of the
electroplating industry.
Each waste water constituent is additive to the
concentration of that constituent in the raw water supply if
the latter is not deionized. Sometimes constituents in the
effluent originate from the raw water supply.
Good chemical treatment will oxidize over 99 percent of the
cyanide and normally remove 85 to 99 percent of the metals.
The other constituents in the raw waste having much higher
solubilities than metal hydroxides are usually not removed,
and contribute to the total dissolved solids of the treated
effluent.
Some soluble constituents are adsorbed on the insoluble
material and removed during clarification. The
concentrations of total dissolved solids and each soluble
constituent depend on the degree of water conservation used
in the facility.
81
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Waste Water Constituents..and Parameters of Pollutions!
Significance
The waste water constituents of pollutional significance are
total suspended solids, phosphate, oxidizable cyanide, total
cyanide, fluoride, cadmium, hexavalent chromium, total
chromium, copper, iron, nickel, tin, zinc, color and pH.
These constituents are the subject of effluent limitations
and standards of performance regardless of the physical form
(soluble or insoluble metal) or chemical form (valence state
of a metal and whether or not it is complexed).
The pH is subject to effluent limitations because it affects
the solubility of metallic compounds such as zinc hydroxide
and the soluble metal content of the treated effluent.
Thus, the major chemical, physical, and biological waste
water constituents and parameters of pollutional
significance are as follows
Total suspended solids
Phosphate
Oxidizable cyanide
Total cyanide
Fluoride
Cadmium
Hexavalent Chromium
Total Chromium
Lead
Iron
Tin
Silver
Gold
Indium
Osmium
82
-------
Paladium
Platinum
Rhodium
Ruthenium
pH.
Other waste water constituents of secondary importance that
are not the subject of effluent limitations or standards of
performance are as follows
Aluminum
Total dissolved solids
Chemical oxygen demand
Oil and grease
Turbidity
Color
Temperature
Ni trate
Ammonia
RatipnaJ.e for the Selection of Waste Water Constituents
and Parameters
Total Suspended Solids
Suspended solids include both organic and inorganic
materials. The inorganic components include sand, silt, and
clay. The organic fraction includes such materials as
grease, oil, tar, animal and vegetable fats, various fibers,
sawdust, hair, and various materials from sewers. These
solids may settle out rapidly and bottom deposits are often
a mixture of both organic and inorganic solids. They
adversely affect fisheries by covering the bottom of the
stream or lake with a blanket of material that destroys the
fish-food bottom fauna or the spawning ground of fish.
Deposits containing organic materials may deplete bottom
83
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oxygen supplies and produce hydrogen sulfide, carbon
dioxide, methane, and other noxious gases.
In raw water sources for domestic use, state and regional
agencies generally specify that suspended solids in streams
shall not be present in sufficient concentration to be
objectionable or to interfere with normal treatment
processes. Suspended solids in water may interfere with
many industrial processes, and cause foaming in boilers, or
encrustations on equipment exposed to water, especially as
the temperature rises. Suspended solids are undesirable in
water for textile industries; paper and pulp; beverages;
dairy products; laundries; dyeing; photography; cooling
systems, and power plants. Suspended particles also serve
as a transport mechanism for pesticides and other substances
which are readily sorbed into or onto clay particles.
Solids may be suspended in water for a time, and then settle
to the bed of the stream or lake. These settleable solids
discharged with man's wastes may be inert, slowly
biodegradable materials, or rapidly decomposable substances.
While in suspension, they increase the turbidity of the
water, reduce light penetration and impair the
photosynthetic activity of aquatic plants.
Solids in suspension are aesthetically displeasing. When
they settle to form sludge deposits on the stream or lake
bed, they are often much more damaging to the life in water,
and they retain the capacity to displease the senses.
Solids, when transformed into sludge deposits, may do a
variety of damaging things, including blanketing the stream
or lake bed and thereby destroying the living spaces for
those benthic organisms that would otherwise occupy the
habitat. When of an organic and therefore decomposable
nature, solids use a portion or all of the dissolved oxygen
available in the area. Organic materials also serve as a
seemingly inexhaustible food source for sludgeworms and
associated organisms.
Turbidity is principally a measure of the light absorbing
properties of suspended solids. It is frequently used as a
substitute method of quickly estimating the total suspended
solids when the concentration is relatively low.
Phosphorus
During the past 30 years, a formidable case has developed
for the belief that increasing standing crops of aquatic
plant growths, which often interfere with water uses and are
nuisances to man, frequently are caused by increasing
84
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supplies of phosphorus. Such phenomena are associated with
a condition of accelerated eutrophication or aging of
waters. It is generally recognized that phosphorus is not
the sole cause of eutrophication, but there is evidence to
substantiate that it is frequently the key element in all of
the elements required by fresh water plants and is generally
present in the least amount relative to need. Therefore, an
increase in phosphorus allows use of other, already present,
nutrients for plant growths. Phosphorus is usually
described, for these reasons, as a "limiting factor."
When a plant population is stimulated in production and
attains a nuisance status, a large number of associated
liabilities are immediately apparent. Dense populations of
pond weeds make swimming dangerous. Boating and water
skiing and sometimes fishing may be eliminated because of
the mass of vegetation that serves as an physical impediment
to such activities. Plant populations have been associated
with stunted fish populations and with poor fishing. Plant
nuisances emit vile stenches, impart tastes and odors to
water supplies, reduce the efficiency of industrial and
municipal water treatment, impair aesthetic beauty, reduce
or restrict resort trade, lower waterfront property values,
cause skin rashes to man during water contact, and serve as
a desired substrate and breeding ground for flies.
Phosphorus in the elemental form is particularly toxic, and
subject to bioaccumulation in much the same way as mercury.
Colloidal elemental phosphorus will poison marine fish
(causing skin tissue breakdown and discoloration). Also,
phosphorus is capable of being concentrated and will
accumulate in organs and soft tissues. Experiments have
shown that marine fish will concentrate phosphorus from
water containing as little as 1 ug/1.
Cyanide^ Amenable to Oxidation by. chlorine. Oxidizable
cyanide may be present in significant amounts in the waste
water from this segment of the electroplating industry and
is amenable to oxidation by chlorine under alkaline
conditions.
Cyanide^_Total
Cyanides in water derive their toxicity primarily from
undissolved hydrogen cyanide (HCN) rather than from the
cyanide ion (CN-). HCN dissociates in water into H+ and CN~
in a pHdependent reaction. At a pH of 7 or below, less than
1 percent of the cyanide is present as CN-; at a pH of 8,
6.7 percent; at a pH of 9, 42 percent; and at a pH of 10, 87
percent of the cyanide is dissociated. The toxicity of
85
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cyanides is also increased by increases in temperature and
reductions in oxygen tensions. A temperature rise of 10°C
produced a two- to threefold increase in the rate of the
lethal action of cyanide.
Cyanide has been shown to be poisonous to humans, and
amounts over 18 ppm can have adverse effects. A single dose
of about 50-60 mg, is reported to be fatal.
Trout and other aquatic organisms are extremely sensitive to
cyanide. Amounts as small as .1 part per million can kill
them. Certain metals, such as nickel, may complex with
cyanide to reduce lethality especially at higher pH values,
but zinc and cadmium cyanide complexes are exceedingly
toxic.
When fish are poisoned by cyanide, the gills become
considerably brighter in color than those of normal fish,
owing to the inhibition by cyanide of the oxidase
responsible for oxygen transfer from the blood to the
tissues.
Fluorides
As the most reactive non-meteil, fluorine is never found free
in nature but as a constituent of fluorite or fluorspar,
calcium fluoride, in sedimentary rocks and also of cryolite,
sodium aluminum fluoride, in igneous rocks. Owing to their
origin only in certain types of rocks and only in a few
regions, fluorides in high concentrations are not a common
constituent of natural surface waters, but they may occur in
detrimental concentrations in ground waters.
Fluorides are used as insecticides, for disinfecting brewery
apparatus, as a flux in the manufacture of steel, for
preserving wood and mucilages, for the manufacture of glass
and enamels, in chemical industries, for water treatment,
and for other uses.
Fluorides in sufficient guantity are toxic to humans, with
doses of 250 to 450 mg giving severe symptoms or causing
death.
There are numerous articles describing the effects of
fluoride-bearing waters on dental enamel of children; these
studies lead to the generalization that water containing
less than 0.9 to 1.0 mg/1 of fluoride will seldom cause
mottled enamel in children,, and for adults, concentrations
less than 3 or U mg/1 are not likely to cause endemic
cumulative fluorosis and skeletal effects. Abundant
86
-------
literature is also available describing the advantages of
maintaining 0.8 to 1.5 mg/1 of fluoride ion in drinking
water to aid in the reduction of dental decay, especially
among children.
Chronic fluoride poisoning of livestock has been observed in
areas where .water contained 10 to 15 mg/1 fluoride.
Concentrations of 30 - 50 mg/1 of fluoride in the total
ration of dairy cows is considered the upper safe limit.
Fluoride from waters apparently does not accumulate in soft
tissue to a significant degree and it is transferred to a
very small extent into the milk and to a somewhat greater
degree into eggs. Data for fresh water indicate that
fluorides are toxic to fish at concentrations higher than
1.5 mg/1.
Cadmium
Cadmium in drinking water supplies is extremely hazardous to
humans, and conventional treatment, as practiced in the
United States, does not remove it. Cadmium is cumulative in
the liver, kidney, pancreas, and thyroid of humans and other
animals. A severe bone and kidney syndrome in Japan has
been associated with the ingestion of as little as 600
ug/day of cadmium.
Cadmium is an extremely dangerous cumulative toxicant,
causing insidious progressive chronic poisoning in mammals,
fish, and probably other animals because the metal is not
excreted. Cadmium could form organic compounds which might
lead to mutagenic or teratogenic effects. Cadmium is known
to have marked acute and chronic effects on aquatic
organisms also.
Cadmium acts synergistically with other metals. Copper and
zinc substantially increase its toxicity. Cadmium is
concentrated by marine organisms, particularly molluscs,
which accumulate cadmium in calcareous tissues and in the
viscera. A concentration factor of 1000 for cadmium in fish
muscle has been reported, as have concentration factors of
3000 in marine plants, and up to 29,600 in certain marine
animals. The eggs and larvae of fish are apparently more
sensitive than adult fish to poisoning by cadmium, and
crustaceans appear to be more sensitive than fish eggs and
larvae.
Chromium
Chromium, in its various valence states, is hazardous to
man. It can produce lung tumors when inhaled and induces
87
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skin sensitizations. Large doses of chromates have
corrosive effects on the intestinal tract and can cause
inflammation of the kidneys. Levels of chromate ions that
have no effect on man appear to be so low as to prohibit
determination to date.
The toxicity of chromium salts toward aquatic life varies
widely with the species, temperature, pH, valence of the
chromium, and synergistic or antagonistic effects,
especially that of hardness. Fish are relatively tolerant
of chromium salts, but fish food organisms and other lower
forms of aquatic life are extremely sensitive. Chromium
also inhibits the growth of algae.
In some agricultural crops, chromium can cause reduced
growth or death of the crop. Adverse effects of low
concentrations of chromium on corn, tobacco and sugar beets
have been documented.
Lead
Lead is a cumulative poison to the human system and
concentrates itself primarily in bones. Symptoms of
advanced lead poisoning are anemia, abdominal pain, and
gradual paralysis. Immunity to lead does not develop but
reaction grows more acute. It is not an elemental essential
to the metabolism of animals.
Lead poisoning has been reported in humans drinking water
with a concentration as small as 0.0H2 mg/1. However,
concentrations of 0.16 mg/1 seem to have had no effect over
long periods. It is generally felt that 0.1 mg/1 can cause
poisoning if ingisted regularly.
Chronic lead poisoning among animals has been caused by
concentrations less than 0.18 mg/1. Changes have been noted
in nervous systems of laboratory rats after ingistion of
0.005 mg/ per kg of body weight.
Lead concentrations of approximately of 0.5 mg/1 appear to
be the maximum safe limit.
Studies on the effect of lead on fishes indicate that lead
reacts with an organic constituent causing a mucus to
obstruct the gills and body. The fish ultimately dies of
suffocation. Concentrations between 0.1 mg/1 and 0.41 mg/1
have resulted in a TL 50 within HQ hours to sticklebacks,
guppies, minnous, brown trouts and coho salmon.
Silver
88
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Silver may be found occurring naturally in the elementl
state as aggentite, Ag2S, proustite, Ag3AsS3, horn silver,
AgCl, and pyrargyrite, Ag3SbS3.
Although silver is harmful to humans only in very large
doses, very small amounts have proved toxic for fish. The
uthal concentration for sticklebacks was 0.003 mg/1. The
average survival time at 0.004 mg/1 was one week, at 0.01
mg/1 was four days and at 0.1 mg/1 was one day. For salmon
fry silver nitrate was definitely toxic at 0.44 mg/1.
For Daphnja and Mjcroregma the median threshold effect
occurred at 0.03 mg/1 of silver. For one species of
flatworm it occurred at 0.15 mg/1.
Gold
Gold is widely distributed in trace amounts in rocles, aris,
and sea water. The pure metal is extremely unreactive and
insoluble. Gold has not been found to the harmful to
humans, but the lethal concentrations to the stickleback has
been reported as 0.40 mg/1.
Iron
Iron in small amounts is an essential constituent to animal
diets. The daily nutritional requirement is 1-2 mg and most
people intake an average of 16 mg. However, drinking water
becomes umpalatable at approximately 1.0 mg/1. Ferrous iron
imparts as taste at 0.1 mg/1 and ferric iron at 0.2 mg/1.
It also tends to precipitate causing stains and
discoloration of water. For these reasons drinking water
limitations have been recommended at 0.1 mg/1.
Very high concentrations of iron have been toxic to fish.
Iron hydroxides have been known to precipitate on the gills
of fish causing obstruction. Also heavy precipitation may
smother eggs.
Tin
Tin is not a nutritional requisite but neither does it
appear harmufl to human or animal life. The average diet
contains 17.14 mg/day. Very large doses of 30-50 mg/kg of
body weight caused much loss of weight in cats. Trace
amounts of tin appear beneficial to some fish.
oH, Acidity and Alkalinity
89
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Acidity and alkalinity are reciprocal terms. Acidity is
produced by substances that yield hydrogen ions upon
hydrolysis and alkalinity is produced by substances that
yield hydroxyl ions. The terms "total acidity" and "total
alkalinity" are often used to express the buffering capacity
of a solution. Acidity in natural waters is caused by
carbon dioxide, mineral acids, weakly dissociated acids, and
the salts of strong acids and weak bases. Alkalinity is
caused by strong bases and the salts of strong alkalies and
weak acids.
The term pH is a logarithmic expression of the concentration
of hydrogen ions. At a pH of 7, the hydrogen and hydroxyl
ion concentrations are essentially equal and the water is
neutral. Lower pH values indicate acidity while higher
values indicate alkalinity. The relationship between pH and
acidity or alkalinity is not necessarily linear or direct.
waters with a pH below 6.0 are corrosive to water works
structures, distribution lines, and household plumbing
fixtures and can thus add such constituents to drinking
water as iron, copper, zinc, cadmium and lead. The hydrogen
ion concentration can affect the "taste" of the water. At a
low pH water tastes "sour". The bactericidal effect of
chlorine is weakened as the pH increases, and it is
advantageous to keep the pH close to 7. This is very
important for providing safe drinking water.
Extremes of pH or rapid pH changes can exert stress
conditions or kill aquatic life outright. Dead fish,
associated algal blooms, and foul stenches are aesthetic
liabilities of any waterway. Even moderate changes from
"acceptable" criteria limits of pH are deleterious to some
species. The relative toxicity to aquatic life of many
materials is increased by changes in the water pH.
Metalocyanide complexes can increase a thousand-fold in
toxicity with a drop of 1.5 pH units. The availability of
many nutrient substances varies with the alkalinity and
acidity. Ammonia is more lethal with a higher pH.
The lacrimal fluid of the human eye has a pH of
approximately 7.0 and a deviation of 0.1 pH unit from the
norm may result in eye irritation for the swimmer.
Appreciable irritation will cause severe pain.
Rationale for the Selection_of^Total Metal as a Pollutant
Parameter for ElectroBlating^Processes
90
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Chemical treatment as presently developed is able to reduce
the concentration of metals in solution to low values and to
remove the precipitated form of the metal (clarification).
There is no a priori reason why soluble metal, insoluble
metal, complexed metal, etc., should be regarded as separate
pollutant parameters in view of the fact that technology is
capable of reducing the total metal content to low values.
It is practical, as part of chemical treatment, to remove
insoluble metal precipitate from the effluent by
sedimentation, clarification, filtering, or centrifuging
prior to the discharge of liquid effluent to streams. Large
amounts of metal hydroxides in the streams are further
sources of metal ions if the water later becomes acidic
relative to the pH at which the metal hydroxides were
originally precipitated. If this happens, the original
purpose in precipitating hydroxides is defeated. Therefore,
removal of precipitated metal hydroxides by efficient
clarification prior to discharge of the effluent to
navigable waters is assumed.
With removal of total suspended solids to levels of less
than 50 mg/1, significant removal of metal hydroxides
occurs. However, some portion of the total suspended solids
contains metals either as metal hydroxides or adsorbed metal
ions. Regardless of the form, the metal content of
suspended solids represents a significant pollutant in the
water.
Metals are considered pollutants regardless of form. The
standard method of analysis for total metal involves
acidification of the sample to analyze for total metal
content (dissolved metal plus any metal in suspended solids
left from clarification). For the purpose of establishing
effluent limitations and standards of performance it is
herein specified, in the absence of any qualifying
statement, that the concentration of metals in mg/liter
means total metal, as analytically determined by acid
digestion prior to filtering.
Rationale for Rejection of Other Waste Water Constituents as
Pollutants for Subcategory (1) Processes
Metals
than those described as a pollutant above is based on one or
more of the following reasons:
(1) They are not normally present in the processing
91
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solutions used in the electroplating
industry. It would be redundant to
make a long list of materials that
can be controlled but that are not
present.
(2) Insufficient data exist upon which
to base effluent limitations and
standards of performance. Waste-
water constituents such as sodium,
potassium, nitrate and ammonia are
present in many processing solutions
and waste waters, but there is no
practicable method at present of
removing them from solution.
Dissolved Solids
Dissolved solids are not a significant pollution parameter
in this industry. Although the concentration of total
dissolved solids will become higher as efforts are directed
to reducing water use and volume of effluent discharged, the
total quantity of dissolved solids will remain unchanged.
Chemical Oxygen Demand
The chemical oxygen demand can be significant in some cases
because of the oil and grease removed from the work in the
cleaning operation, which then constitutes a part of the
cleaner when it is dumped. It is possible to minimize
chemical oxygen demand in some cases by use of organic vapor
degreasers prior to alkaline cleaning. However, if there is
a high chemical oxygen demand practicable technology to
lower it has not been demonstrated in the electroplating
industry.
Biochemical Oxygen Demand
Biochemical oxygen demand is usually not an important
pollution parameter in this subcategory. An electroplating
plant in a suburban location not discharging to a publicly
owned system must treat its own sanitary sewage in a
separate treatment facility. If the plant chooses to mix
the treated sanitary effluent with process wastes prior to
treatment BOD would be considered a major parameter.
Turbidity
Turbidity is indirectly measured and controlled
independently by the limitation on suspended solids.
92
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Temperature
Temperature is not considered a significant pollution
parameter in this subcategory. However, cooling water used
to cool process tanks and/or evaporative recovery systems
that are not subsequently used for rinsing could contain
pollutants from leaks in the system.
Aluminum
Aluminum may be present in significant amounts in the waste
water stream. Limits are not placed on aluminum at this
time due to insufficient data. However, it is believed that
significant removal will result when conventional chemical
treatment techniques are employed.
93
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-------
SECTION VII
CONTROL AND TREATMENT_TECHNQLQGY
Introduction
The control and treatment technology for reducing the
discharge of pollutants from electroplating operations is
discussed in this section.
In process controls of electroplating waste waters included
material substitutions, good housekeeping practices, and
water conservation techniques. The in-plant control
techniques discussed are generally considered to be normal
practice in these industries.
Chemical treatment technology is discussed first in this
section because some treatment of this type is required of
many waste waters generated by electroplating operations
before discharge into navigable streams. After chemical
treatment the amount of pollutants discharged to navigable
waters is roughly proportional to the volume of water
discharged.
Advanced treatment of electroplating waste water includes
techniques for the removal of pollutants and techniques for
the concentration of pollutants in the waste waters for
subsequent removal by treatment or recovery of chemicals.
Although all of the treatment technologies discussed have
been applied to waste waters from electroplating processes,
some may not be considered normal practice in this industry.
The proper design, operation, and maintenance of all waste
water control and treatment systems are considered essential
to an effective waste management program. The choice of an
optimum waste water control and treatment strategy for a
particular electroplating facility requires an awareness of
numerous factors affecting both the quantity of waste water
produced and its amenability to treatment.
Possible Treatment Designs
Continuous Treatment. The chemical treatment process may be
made continuous by (1) sizing and baffling treatment tanks
to provide sufficient hold times to complete chemical
reactions; (2) providing continuous monitoring of pH and
oxidation/reduction potentials and controls for regulating
reagent additions by means of these monitors; and (3)
95
-------
providing a continuous overflow settling tank that allows
sludge to be pumped off periodically through the bottom.
A flow diagram for a large continuous-treatment plant is
shown in Figure 3. The dilute acid-alkali stream originates
from rinses associated with alkaline cleaners, acid dips,
and baths containing metal ions, but no cyanide or
hexavalent chromium. When concentrated acid and alkali
baths are to be discarded they are transferred to a holding
tank and added slowly to the dilute stream. In this
manner, sudden demands on the reagent additions and
upsetting of the treatment conditions are avoided. The
dilute acid-alkali stream first enters a surge tank to
neutralize the waste water and equalize the composition
entering the precipitation tank. The hexavalent chromium is
reduced at a pH of 2.0 to 2.5, and the addition of the SO2
and HCl are controlled by suitable monitors immersed in the
well-agitated reduction tank. Cyanide is destroyed in a
large tank with compartments to allow a two-stage reduction.
Reaction time is about 3 hours.
The treated chrome, cyanide, and neutralized acid-alkali
streams are run into a common tank where pH is automatically
adjusted to optimize the precipitation of metal hydroxides.
The stream then enters a solids contact and settling unit
where mixing, coagulation, flocculation, recirculation,
solids concentration, sludge collection, and sludge removal
are accomplished. Flocculants are usually added to this
tank. The overflow from the settling unit constitutes the
discharge from the plant. The sludge may be dewatered by
filtering and the filtrate returned to the settling unit, if
the solid content of this filtrate is higher than the
overflow from the clarifier.
Integrated Treatment. The integrated system uses a
reservoir tank in conjunction with the rinse tanks for each
type of plating bath. A common solution is circulated
through the chemical wash tank (which replaces what is
normally the first rinse tank) and the reservoir. The
solution contains an excess of treatment chemical so that,
for example, cyanide destruction takes place in the wash
tank and directly on the film of dragout solution on the
part itself. Therefore, no cyanide is dragged into the
subsequent rinse tank and the effluent requires no further
treatment for cyanide.
Because metals are precipitated separately at a relatively
high concentration, the metal hydroxide settled in the
reservoir may be recovered, dissolved, and returned to the
plating bath from which it originated. In contrast to batch
96
-------
strong
vo
1.8 gpm
sludge
FIGURE 3 DIAGRAM OF A TYPICAL CONTINUOUS-TREATMENT PLANT
-------
and continuous treatments, which are generally carried out
in a separate facility, the reservoir in the integrated
system is in proximity to the plating room because of the
necessity for circulation. The layout of an integrated
system for treating rinse water waste from a cyanide plating
solution and a chromium plating bath is shown in Figure H.
Batch Treatment
The batch method is generally used for small or medium-sized
plants. Batch treatment is useful not only for rinse waters
but for expendable process solutions containing high
concentrations of chemicals or spills, leaks, or other
accidental discharge of process solutions. Holding tanks
collect the waste water and are large enough to provide
ample time to treat, test, and drain a tank while another is
being filled. Analytical tests are made before treatment to
determine the amount of reagent to add and after treatment
to establish that the desired effluent concentrations have
been obtained. A flow diagram for batch treatment is shown
in Figure 5.
Chemical Treatment Technology
Applicability
Chemical treatment processes for waste water from
electroplating facilities are based upon chemical
precipitation reactions, many of which have been known since
the beginning of modern chemistry over 200 years ago. These
reactions have been used as the basis for the design and
engineering of systems capable of treating waste water
containing a large variety of pollutants and reducing the
concentration of metals below 1 mg/1. Control procedures
have been devised to assure the effectiveness of the
processes.
Cy.§£i3§ _ Oxidation. Cyanide in waste waters is commonly
destroyed by oxidation with chlorine or hypochlorite prior
to precipitation of the metals. The method is simple,
effective, and economically feasible for most waste waters,
even for small volume installations. A factor in how
rapidly cyanide is destroyed, if at all, is how strongly the
cyanide is complexed to metal ions and how rapidly the
complex can be broken. Therefore, some waste waters present
special problems, A comprehensive study of the method was
made by Dodge and Zabban. The results have been used to
work out the practical processes. The following are
proposed reactions for chlorine oxidation.
98
-------
Reuse woter
Cyanide solutions
Drag out
Cyanide
waste
treatment
Water
rinse
Chromic
acid
process
Chromic
acid waste
treatment
t<
Sodium
hypochlorite
Feed
pump
—CxJ-
Water
rinse
**
To pH control
clarif ier
Water reuse pump
Water slow down
to sewer
Cyanide
waste
treatment reservoir
5
?
5
<
7>
Chromium waste
treatment reservoir
5
r^
Feed
pump
Sodium carbonate
Sodium hydro-
sulfite
To sludge bed
FIGURE 4 INTEGRATED TREATMENT SYSTEM
-------
•- Water from first
rinse tank
Air-*-
^.;;;M ^ ^ ^;iUn tanks) v:^ ^ ^0^
^VvH^-'$:\^
•^•.:^.-.**:''.--:-:\-'.t ::':,:
" ' • • ; • t: •_•'-''•'••'.: v • ' - • .VT ni»»iiy ^r ~" 'T—^» TA TI tar ' '. ''
.''Measurement
^V-'r-y-y^
^•V;^.-:'^:;"-^:'^5;-^
To sewer
FIGURE D BATCH TREATMENT OF CYANIDE RINSE WATERS BY THE KASTONE PROCESS
100
-------
(1) NaCn + C12 = CNC1 + NaCl
(2) CNC1 * 2NaOH = NaCNO + NaCl * H20
(3) 2NaCNO + 3C12 + 4NaOH = N2 + 2CO2 + 6NaCl + 2H2O.
Reaction (2) goes rapidly at pH 11.5, under which conditions
build up of the toxic gas CNCl by Reaction (1) is avoided.
Treatment of dilute rather than concentrated solutions also
minimizes its formulation. Oxidation to cyanate (NaCNO) is
completed in 5 minutes or less. Reaction (3) goes more
slowly, requiring an hour in the preferred pH range of 7.5
to 9.0, and a longer time at higher pH. After the
conversion to nitrogen and carbon dioxide, excess chlorine
is destroyed with sulfite or thiosulfate.
Sodium hypochlorite may be used in place of chlorine.
Recent technical innovations in electrochemical hypochlorite
generators for on-site use raise the possibility of
controlling the addition of hypochlorite to the cyanide
solution by controlling the current to the electrochemical
generator, using sodium chloride as the feed material.
Concentrated solutions, such as contaminated or spent baths,
cyanide dips, stripping solutions, and highly concentrated
rinses, are normally fed at a slow rate into a dilute
cyanide stream and treated with chlorine. However,
concentrated solutions may also be destroyed by electrolysis
with conventional equipment available in the plating shop.39
In normal industrial practice the process is operated
batchwise, whereas the optimum system, from an operating
standpoint, would be a cascaded one in which successively
larger tanks are operated at successively lower current
densities. This is the more efficient system. In addition
to the oxidation of cyanide at the anode, valuable metal can
be recovered at the cathode. The process becomes very
inefficient when the cyanide concentration reaches 10 ppm,
but at this point the solution can be fed into the process
stream for chemical destruction of cyanide to bring the
concentration to the desired level. The addition of
chloride ions to the concentrated solutions, followed by
electrolysis, produces chlorine or hypochlorite in solution,
which can then destroy the cyanide to the same low levels as
obtained by direct chlorination. With the provision that
chlorine or hypochlorite be formed at a rate equal to the
concentration of cyanide passing through the system, the
process can be operated continuously:
2NaCN * 2NaOCl = 2NaCNO * 2NaCl
101
-------
2NaCNO + 3NaOCl + H2O = 2CO2 + N2. + 2NaOH + 3NaCl
2NaCN + 5 NaOCl + H2O 2CO.2 + N2 + 2NaOH + 5NaCl.
One proprietary process (A), based on the above principles,
produces 1 kg of active chlorine per 5.5 Kwh. Equipment
needs are the same with the exception that the tanks must be
lined, and graphite or platinized anodes must be used.
Polysulfide-cyanide strip solutions containing copper and
nickel do not decompose as readily and as completely as do
plating solutions. Although the cyanide content can be
reduced from 75,000 to 1000 mg/1 during two weeks of
electrolysis anode scaling prevents further cyanide
decomposition unless anodes are replaced or freed from
scale. Minimum cyanide concentration attainable is about 10
mg/1 after which the solution can be treated chemically.
The electrolysis of dilute cyanide solutions can be improved
by increasing the electrode area. Area can be increased by
filling the space between flat electrodes with carbonaceous
particles. The carbon particles accelerate the destruction
process 1000 times, but flow rate through the unit must be
carefully adjusted, if used on a continuous basis to achieve
complete destruction (Plant 30-1).
Although cyanide can be destroyed by oxygen or air under
suitable conditions, cyanide concentrations in the effluent
are reported to be 1.3 to 2.2 mg/1, which is high for
discharge to sewers or streams. A catalytic oxidation unit
using copper cyanide as a catalyst and activated carbon as
the reactive surface has been described for oxidizing
cyanide with air or oxygen, and at least two units were put
in operation. Catalytic oxidation units must be custom
designed for each installation for maximum effectiveness.
Ozone will oxidize cyanide to below detectable limits
independent of the starting concentration or of the complex
form of the cyanide. Decomposition can be achieved with
cyanides such as those of nickel and iron that are not
readily oxidized by chlorine. Systems that will oxidize the
cyanides that are usually treated, i.e., copper and zinc
compounds have been installed in production units and
demonstrated. Development work is continuing to enhance the
efficiency and reliability of modern ozone generators and to
decompose the more stable cyanides with the help of
ultraviolet radiation and heat.
A method employing thermal decomposition for cyanide
destruction has been recently announced. Cyanide solutions
102
-------
are heated to 160 to 200 C under pressure for 5 to 10
minutes. Ammonia and formate salts are formed. No
information is available at this time on the final cyanide
concentration.
Another proprietary process (B), destroys cyanides of
sodium, potassium, zinc, and cadmium and also precipitates
zinc and cadmium. The process is discussed later in this
section.
Precipitation of cyanide as ferrocyanide is restricted to
concentrated wastes. Ferrocyanide is less toxic than
cyanide, but is converted back to cyanide in sunlight.
Treatment is accomplished by adding an amount in excess of
stoichiometry (2.3 kg of FeSO4 per kg of cyanide). Large
amounts of sludge are produced which add to the pollution
load. Complex cyanides do not break down readily and the
reaction stops when a concentration of 10 mg/1 of cyanide is
reached. No benefits can be foreseen in terms of reducing
waste volume and concentration.
Cyanide is also destroyed by reaction with polysulfides.
Reasonable reaction rates are obtained only if the solution
is boiled. Since the reaction does not destroy all of the
cyanide further treatment is necessary.
For a small electroplating facility, it is conceivable that
an electrodialysis system for the destruction of cyanide
could be installed. Experimental work has been performed on
copper cyanide plating baths and is applicable to cyanide
baths of zinc, cadmium, silver and gold.
Reduction of Hexayalent Chromium. Hexavalent chromium
(Cr+*) is usually reduced to trivalent chromium at a pH of 2
to 3 with sulfur dioxide (SO2), sodium bisulfite, other
sulfite-containing compounds, or ferrous sulfate. The
reduction makes possible the removal of chromium as the
trivalent hydroxide which precipitates under alkaline
conditions. Typical reactions for SO2 reduction are as
follows:
S02 + H20 =H2S03
2H2CrOfi + 3H2S03 =Cr2 (SOU) 3 «• 5H2O.
Representative reactions for reduction of hexavalent
chromium under acid conditions using sulfite chemicals
instead of SO2 are shown below:
(a) Using sodium metabisulfite with sulfuric acid:
103
-------
4H2CrOj» + 3Na2S205 + 3H2SO4 = 3Na2SO4 + 2Cr2(SO4)3
+ 7H2O
(b) Using sodium bisulfite with sulfuric acid:
4H2CrOU + 6NaHS03 + 3H2SO4 = 3Na2S04 + 2Cr 2 (SOU) 3
+ 10H20
(c) Using sodium sulfite with sulfuric acid:
2H2CrO4 + 3Na2S03 + 3H2SO4 = 3Na2SO4 * Cr2(SO4)3
+ 5H20.
Reduction using sulfur dioxide is the most widely used
method, especially with larger installations. The overall
reduction is readily controlled by automatic pH and ORP
(Oxidation-Reduction Potential) instruments. Treatment can
be carried out on either a continuous or batch basis.
Hexavalent chromium can also be reduced to trivalent
chromium in an alkaline environment using sodium hydro-
sulfite as follows:
2H2Cr04 + 3Na2S2O4 + 6NaOH ~ 6Na2SO3 + 2Cr(OH)3 + 2H2O.
As indicated in the above equation, the chromium is both
reduced and precipitated in this one-step operation.
Results similar to those obtained with sodium hydrosulfite
can be achieved using hydrasiine under alkaline conditions.
Na2C03
UH2CrO4 + 3N2HU = 4Cr(OH)3 + 3N2 + 4H2O.
Sodium hydrosulfite or hydrazine are frequently employed in
the precipitation step of the integrated system to insure
the complete reduction of any hexavalent chromium that might
have been brought over from the prior reduction step
employing sulfur dioxide or sodium bisulfite. Where ferrous
sulfate is readily available (e.g., from steel pickling
operations), it can be used for reduction of hexavalent
chromium; the reaction is as follows:
2CrO3 + 6FeSO4.7H2O «• 6H2SO4 = 3Fe2(SO4)3 + Cr2 (504)3
+ 48H2O.
104
-------
Cr+* may be reduced at a pH as high as 8.5 with a
proprietary compound. It is not necessary to segregate
chromate-containing waste waters from the acid-alkali
stream, and the use of acid to lower pH is eliminated in
this case. Precipitation of chromic hydroxide occurs
simultaneously in this case with the reduction.
Cr+* ions may be reduced electrochemically. A concentration
of 100 mg/1 was reduced to less than 1 mg/1 with a power
consumption of 1.2 kwh/1000 liters. The carbon bed
electrolytic process previously described for cyanide2* may
also be used for chromate reduction in acid solution and
Plant 30-1 has achieved a Cr+* concentration of .01 mg/1
using this method. Electrolysis may also be used to
regenerate a reducing agent. A process51 has been described
involving the reduction of Fe+3 to Fe+2 electrochemically
and the reduction of Cr+* by Fe+2. The method should be
capable of achieving low Cr+6 levels.
The simultaneous reduction of Cr+* and oxidative destruction
of cyanide finds limited application in waste treatment
practice. The reaction requires mixing of Cr+* and CN~ in
ratios between 2 and 3 using Cu+2 as a catalyst in
concentrations of 50 to 100 mg/1. The catalyst introduces
additional pollutant into the waste stream. Reaction rates
are generally slow, requiring from 6 to 24 hours for cyanide
concentrations ranging from 2,000 to less than 50 mg/1 at a
solution pH of 5. The slowness of the reaction and the high
initial concentrations of reactants required make the method
unsuitable for treating rinse waters. Its use is limited to
batch treatment of concentrated solutions. No benefits are
obtained in terms of water volume and pollution reduction.
Destruction is not as complete as obtained by the more
common chemical methods.
Unit Operations
Precipitation. The effluent levels of metal attainable by
chemical treatment depend upon the insolubility of metal
hydrolysis products in the treated water and upon their
settling and filtering characteristics which affect the
degree to which they can be separated. The solubilities of
the hydrolysis products are dependent upon many conditions
during precipitations such as pH, presence of other cations
and anions, time allowed before separating out the solids,
the precipitation agent used, the degree of agitation, etc.
Schlegel and Hartinger have studied precipitation reactions
extensively and have been able to obtain low concentrations
of metal ions in solution within 2 hours.
105
-------
When metal ions are precipitated separately the pH may have
to be adjusted differently for each ion. This immediately
raises the question of whether the metals can be efficiently
precipitated tocrether at a common pH. This is possible as
shown in Table 2 6-
It is apparent that it is difficult to predict in detail the
conditions that will give the best precipitation results in
a practical situation. However, just as several parameters
can be adjusted in the laboratory to obtain optimum results,
suitable conditions may be found in the field. Flocculating
agents, added to aid in settling the precipitate, play a
significant role in reducing concentration of suspended
solids.
When solubilizing complexing agents are present, the
equilibrium constant of the complexing reaction has to be
taken into account in determining theoretical solubility
with the result that the solubility of the metal is
generally increased. Cyanide ions must be destroyed not
only because they are toxic but also because they prevent
effective precipitation of copper and zinc as hydroxides.
If cyanide is replaced in a plating bath by a nontoxic
complexing agent such as EDTA (ethylenediaminetetraacetic
acid), the new complexing agent could have serious
consequences as far as the removal of metal ions by
precipitation. Ammonium ion, present in many electroplating
baths, will complex copper, zinc, and other metal ions and
interfere with their precipitation as hydroxides.
Theory and experimental results confirm that it is not
possible to achieve complete removal of metal ions from
waste water by precipitation as hydroxides even if
separation of precipitate were 100 percent effective. Thus,
a finite concentration of pollutant will remain in the
effluent. The best indication of what can be achieved in
reducing metal concentration is the results of daily
operation in exemplary plants rather than theory or
laboratory experiments.. Clarification efficiency is an
important factor in determining the total metal content of
the effluent. It is safe to say that the soluble metal
content will be no greater than the total content achieved
in practice and may be less..
Solids _Separation. The first step in separating the pre-
cipitated metals is settling, which is very slow for gel-
like zinc hydroxide, but is accelerated by coprecipitation
with the hydroxides of copper and chromium. Coagulation can
also be aided by adding metal ions such as ferric iron which
forms ferric hydroxide and absorbs some of the other
106
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TABLE 26 COMPARISON OF SOLUBLE POLLUTANT
PARAMETERS AFTER PRECIPITATION
BY IRON SULFIDE OR BY HYDROLYSIS
Pollutant residues from--
Waste
compo-
sition
in ppm
Unknown
Cu, 100
Ni, 7.7
NH3, 475
NH3, 475
Cr(VI), 4.8
Zn, 3.5
Sulfide
precipi-
tation
in ppm
Cu, 0.1
Zn, negligible
Cu, 1.8
Cu, 0.4
Ni, 2.0
Cr(VI), negligible
Zn, 0.03
Hydroxide
precipi-
tation
in ppm
0.8
2.0
95.8
5.9
1.0
2.0
0.05
2.0
107
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hydroxide, forming a floe thcit will settle. Ferric iron has
been used for this purpose in sewage treatment for many
years as has aluminum sulfate. Ferric chloride is
frequently added to the clarifier of chemical wastetreatment
plants in plating installations. Flocculation and settling
are further improved by use of polyelectrolytes, which are
high molecular weight polymers. Due to their ionic
character they are capable of swelling in water and
adsorbing the metal hydroxide which they carry down during
settling.
Settling is accomplished in the batch process in a stagnant
tank, and after a time the sludge may be emptied through the
bottom and the clear effluent drawn off through the side or
top. The continuous system uses a baffled tank such that
the stream flows first to the bottom but rises with a
decreasing vertical velocity until the floe can settle in a
practically stagnant fluid.
Although the design of the clarifiers has been improved
through many years of experience, no settling techniques or
clarifier will completely remove solids from the effluent
which contains typically 5 to 20 mg/1 of suspended solids.
This floe contains some metal.
Sludge Disposal. Clarifier underflow or "sludge" contains
typically 1 to 2 percent solids and can be pumped to a
lagoon.
Metal ions in the liquid associated with the sludge can
percolate through porous soil and become a potential source
of groundwater contamination. Impervious lagoons require
evaporation into the atmosphere. However, in many parts of
the U.S., the average annual rainfall equals or exceeds the
atmospheric evaporation. Additionally, heavy rainfalls can
fill and overflow lagoons. Metal ions may be leached from
metal hydroxides and the surface run-off to adjacent streams
or lakes may be in sufficient quantity to be detrimental.
A case in point is contamination of groundwater by plating
wastes held in lagoons in Nassau County, New York. Plating
wastes have seeped down from the lagoons into the aquifier
intermittently since 1941. This seepage has resulted in a
plume of contaminated water some 4,300 feet long, up to
1,000 ft wide, and as much as 70 feet deep, extending
downgrade to the headwater of Massapequa Creek. Originally
the plating waste water was untreated and the concentration
of hexavalent chromium in the groundwater was about 40 mg/1.
Since the start of chromium treatment, concentrations have
decreased to less than 5 mg/1 in most of the plume.
108
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Treatment of the plating waste effluent results in discharge
of sludge to the lagoons, and the sludge forms a lining on
the bottoms and sides which retards infiltration. At
another location core-drilled samples were obtained from the
shale structure underlying the bed used for disposal of
sludge resulting from chemical treatment. The disposal side
had been in use for several years. Metal concentrations two
feet into the shale structure, were of the order of 50 to
100 ppm.
Lagooning can be avoided by dewatering the sludge to a
semidry or dry condition. Several devices are available for
dewatering sludge. Rotary vacuum filters will concentrate
sludge containing 4 to 8 percent solids to 20 to 25 percent
solids. Since the effluent concentration of solids is
generally less than 4 percent a thickener tank is often
employed between the clarifier and the filter. The filtrate
often contains excessive suspended solids and is
recirculated to the clarifier.
Centrifuges will also thicken sludges to the above range of
consistency and have the advantage of using less floor
space. The effluent contains excessive suspended solids and
is returned to the clarifier.
Pressure filters may be used. In contrast to rotary filters
and centrifuges, pressure filters will produce a filtrate
with less than 3 mg/1 of suspended solids so that return to
the clarifier is not needed. The filter cake contains
approximately 20 to 25 percent solids. Pressure filters are
usually designed for a filtration rate of 2.04 to 2.44
liters/min/sq m (0.05 to 0.06 gpm/sq ft) of clarifier
sludge.
Solids contents from 25 to 35 percent in filter cakes can be
achieved with semicontinuous tank filters rated at 10.19 to
13.44 1/min/sq m (0.25 to 0.33 gpm/sq ft) surface. A solids
content of less than 3 mg/1 is normally accepted for direct
effluent discharge. The units require minimum floor space.
Plate and frame presses produce filter cakes of 40 to 50
percent dry solids and a filtrate with less than 5 mg/1
total suspended solids. Because automation of these presses
is difficult, labor costs tend to be high. The operating
costs are partially offset by low capital equipment costs.
Automated tank type pressure filters are just now finding
application. The solids content of the cake can reach as
high as 60 percent while the filtrate may have up to 5 mg/1
of total suspended solids. The filtration rate is
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approximately 2.04 1/min/sq m (0.05 gpm/sq ft) filter
surface area. Pressure filters containing from 300 to 500
mg/1 suspended solids at design of U.88 to 6.52
liters/min/sq m (0.12 to 0.16 gpm/sq ft) and still maintain
a low solids content in the filtrate.
Filter cakes can easily be collected in solid waste
containers and hauled away to landfills. There may be
situations, however, where the metal in the filter cake
could be redissolved if it came into contact with acidic
water. Careful consideration should be given to where such
a material is dumped.
A proprietary process is available for solidifying sludge by
addition of chemical fixing agents. Relative to filtration,
the amount of dried sludge to be hauled away is increased.
The fixing process appears to insolublize the metal ions so
that in leaching tests only a fraction of a part per million
is found in solution. A fill is produced that is similar to
dried clay.
The possibility of recovering metal values from sludges
containing copper, nickel, chromium, and zinc have been
considered but such a system appears to be uneconomic under
present circumstances. It may be profitable to recover metal
values if 900 to 2300 kg (2,000 to 5,000 pounds) of dried
sludge solids can be processed per day with a thoroughly
developed process. To attain this capacity would almost
certainly require that sludge from a large number of plants
be brought to a central processing station. The recovery
would be simpler if the metallic precipitates were
segregated, but segregation would require extensive
modification, investment, and increased operating expense
for precipitation and clarification. Laboratory experiments
showed that zinc could be leached from sludge with caustic
after which copper, nickel, and chromium were effectively
dissolved with mineral acids. Ammonium carbonate dissolved
copper and nickel but not trivalent chromium, thus giving a
method of separation. Electrowinning of the nickel and
copper appeared to be a feeisible method of recovering these
metals.
Precipitation of Metal Hydroxides
Applicability. Chemical treatment was used by every plant
contacted during the effluent guidelines study with the
exception of those that are allowed to discharge plating
waste effluents into sewers or streams without treatment.
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_ TreatingjTechnigues. The
effectiveness of chemical treatment techniques depends on
the nature of the pollutant, the nature and concentration of
interfering ions, the procedure of adding the appropriate
amount of chemicals (or adjusting pH), the reaction time and
temperature and the achievement of effective separation of
precipitated solids. Effective removal of metal pollutants
is inhibited by some types of chelating ions such as
tartrate or ethylene diamine tetracetate ions.
The concentrations of metals and cyanide achievable by the
chemical techniques employed for treating waste from copper,
nickel, chromium, and zinc electroplating and zinc
chromating processes are summarized in Table 25.
Concentrations lower than those listed as maximum in Table
57 were reported by companies using all three (continuous,
batch, and integrated) treating systems.
Higher-than-normal concentrations of metals, when they
occur, are usually caused by: (1) inaccurate pH adjustment
(sometimes due to faulty instrument calibration); (2)
insufficient reaction time; (3) excessive concentrations of
chelating agents that complex the metal ions and prevent
their reaction with hydroxyl ions to form the insoluble
metal hydroxides; or (4) lack of suitable coprecipitating
agents. The causes for higher-than-normal concentrations of
cyanide are similar, but another important factor must be
added to the list of potential causes for incomplete cyanide
destruction. In this case, sodium hydroxide and chlorine
must be added continuously during the reaction to maintain
the optimum pH and provide sufficient reagent to complete
the reaction, which is normally monitored by an Oxidation-
Reduction-Potential (ORP) recorder-controller. The
maintenance of this system is a critical factor affecting
the effectiveness of chemical oxidation.
Practical_Operating_Sxstems. In Plant 33-2 the discharge of
cyanide is eliminated by electrochemical decomposition in a
tank held at sufficiently high temperatures to evaporate the
waste water as rapidly as it is introduced. Therefore, no
liquid stream leaves the tank. Fluorides and fluoroborate
containing waste waters in Plant 31-16 are collected
separately and treated with lime.
Plant 36-8 disposes of sludge in a pit lined with special
concrete blocks that filter out solids and allow liquid to
permeate into the surroundings. Relatively few finishing
plants have installed filters, although the problem of
disposing of unfiltered sludge in many cases should provide
an impetus for the use of one or more filters in the future.
Ill
-------
Plants 12-8 and 31-16 use large rotary filters to
concentrate sludge from a clarifier. Plant 33-30 is able to
filter the solution from the neutralizer directly, without a
preceding clarification step. A settling tank centrifuge
combination is in use in over 200 waste treatment
installations, including those in electroplating plants. A
proprietary system for solidifying sludge is in use at
several plants.
Demonstration.Status. The US Bureau of Mines has done some
development on a process in which the acid wastes and
alkaline cyanide wastes neutralize each other. The acid
wastes are slowly added to the alkaline wastes in a closed
reactor to form easily filtered metal cyanide precipitates.
The precipitates are heated in air to form stable metal
oxides.
Suspended^Solids. The suspended solids discharged after
treatment and clarification sometimes contribute more metal
than the dissolved metal. The concentration of total
suspended solids in the end-of-pipe discharge from typical
chemical treatment operations sampled during this study
ranged from 20 to 24 mg/1. Lower values are reported for
some facilities. Maintaining conditions so as not to exceed
these amounts requires (1) a properly designed settling or
clarifying facility, (2) effective use of flocculating
agents, (3) proper control of the rate of removal of settled
solids, (4) sufficient retention time for settling, and (5)
rate of overflow of clarified effluent. of course,
minimum retention time depends on the facility size and
design and the rate of solution flow through the facility.
In practice, this time ranges from about 2 to 8 hours for
plants that are able to reduce suspended solids to about 25
mg/1 or less.
Precipitation of Metal Sulfides
Applicability. The sulfides of metals are much less soluble
than their corresponding hydroxides. However, direct
precipitation of metal ions with hydrogen sulfide or sodium
sulfide involves the problem of excess sulfide ion which can
then become an additional pollutant parameter. A sulfide
precipitation system has recently been developed that avoids
the possibility of excess sulfide ion being present in
treated effluent. Iron sulfide, which itself has a very
small solubility, is used as the reagent to precipitate
copper, zinc, and nickel sulfides of even lower solubility.
Experimental results are shown in Table 26 indicating that
low concentrations can be achieved with sulfide
precipitation even when metals are complexed with ammonia.
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The disposal of sulfide solid wastes is a serious and
unsolved problem. Unlike the metal oxides, metal sulfides,
in the presence of air, decompose to sulfates and the metal
ions can thereby be solublized. This commonly happens to
ferrous sulfide as a result of coal mining operations and
contamination of streams with acid and iron is a result.
However, there is insufficient information available to
determine whether any significant oxidation will occur with
mixed metal sulfide sludges disposed of properly on
landsites. The lower solubility of metal sulfides should
reduce the amount leached directly into rainwater.
Therefore, if significant oxidation is found to occur, means
will have to be found to contain the sulfide precipitates or
insolublize them by some system such as the Chemfix Process.
Practical Operating. SYgt^s. Plant 9-2 is segregating its
plating streams and precipitating cadmium as the sulfide.
Demonstration Status. The process described is still being
developed, and it is anticipated that a demonstration plant
will be built and operating in the near future.
Combined Metal Precipitation and Cyanide
Destruction-Proprietary Process B
Applicability. This process is applicable to zinc and
cadmium cyanide solutions. The metal hydroxide is
precipitated and cyanide is decomposed. Applicability
depends upon deciding whether the products of cyanide
decomposition are suitable for discharge or not. The
effluent is considered suitable for discharge to sewers in
some states. A modified process may be applicable to copper
cyanide.
Process _ Principles __ and __ Equipment • Cyanide in zinc and
cadmium plating baths is destroyed by a mixture of formalin
and hydrogen according to the formula:
3CN- + 2H202 + HCOH + 2H2O = CNO~ + OH~ + NH3
+ H2C (OH) CONH2) (glycolic acid amide) .
The metal hydroxide is also precipitated. The hydrogen
peroxide is contained in the reagent (41%) which contains
stabilizers and additives to promote the reactions and help
in settling the metal hydroxide precipitate. The process
may be carried out on a batch or continuous basis, and is
particularly convenient for the small shop. However, the
glycolic acid generated is not a desirable constituent for
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discharge to streams and the use of the process should be
restricted to plants discharging to sewers.
Figure 1 shows the apparatus for batch treatment. To be
economical the rinse water should contain at least 55 mg/1
of cyanide, and sufficient counter-flow rinses are normally
installed to assure a sufficient cyanide concentration. The
typical treated effluent contains 0.1 mg/1 of cyanide and 1
to 2 mg/1 of zinc. Table 27 shows an analysis of the
products for decomposing 79<* ppm of cyanide.
Practical Ope rating Systems^ This process is well
established as a practical means for pollution control and
is being used in approximately 30 installations.
Chemical Treatment of Effluents From Specific
Process operations
Constituents
Iron. Iron baths have relatively simple compositions and
neutralization of waste water constituents will reduce the
soluble iron concentration well below 1 mg/1. Ferric
chloride is a common constituent in such baths and is used
as a flocculating agent in clarification systems for Phase I
metals following neutralization, to give an effluent
suitable for discharge. The waste waters (dilute acid) and
the concentrated plating baths (concentrated but weakly
acidic) enter the waste treatment system via the "dilute
acid-strong acid" streams of Figure 2.
Cadmium. After oxidation of cyanide or in noncyanide waste
water, cadmium can be precipitated as the hydroxide by
adjustment of pH. The waste water and strong solution
discharge streams are shown as "weak cyanide" and "strong
cyanide" in Figure 2. Alkalinity has a significant effect
on solubility of cadmium. The theoretical solubility values
according to Ponrbaix are approximately
Solubility
pH mg/1
8 3000
9 30
10 0.03
11 0.003 (minimum)
Therefore, soluble cadmium might not be reduced to a low
level by coprecipitation with Cu, Ni, Cr, Zn at pH 8 to 9.
Should a pH of 11 be used, there is danger that the zinc
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TABLE 27 DECOMPOSITION PRODUCTS OF CYANIDE IN
RINSE WATER(1) FROM A CYANIDE ZINC
ELECTROPLATING OPERATION AFTER TREATMENT
WITH "KASTONE"(2) PEROXYGEN COMPOUND
Amount Formed
Products Formed Actual Cyanide Equivalent
by Treatment ppm ppm percent
Cyanate 351 265 33
Ammonia (free
Dissolved 57 164 21
Volatilized(3) 32 91 11
Combined Ammonia .
Calc'd as NH3 95
Calc'd as glycolic 274 35
acid amide 419
794 100
(1) Analysis of water before treatment:
Cyanide* 794 ppm
Cyanate* 336 ppm
Ammonia * 41 ppm
¥Cyanide calculated as NaCN, cyanate as NaOCN, and
ammonia as NH^.
(2) Du Pont trademark.
(3) Not determined; estimated by difference.
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concentration in the effluent will be too high.
Consideration of the above theoretical data suggests that
cadmium might not be reduced to a low level when
coprecipitated with Cu, Ni, Cr, Zn at pH 8 to 9. The
insolubility of cadmium carbonate suggests that
precipitations with soda ash may reduce soluble cadmium to
very low levels in effluent.
Separation of Streams
Prior to chemical treatment, waste waters from different
operations in a electroplating process may be combined in
some cases and kept separate in other cases. The nature of
the waste waters and the pollutants present will determine
where segregation is desirable and where combination is
practical. Some pollutants cannot be properly removed in
the presence of others, while some are better removed when
combined with others. Combination of some streams will
result in a reaction to form additional pollutants and ones
that can be of immediate danger to personnel involved in the
electroplating operations, e.g., a cyanide containing stream
combined with an acid stream may cause evolution of gaseous
hydrogen cyanide. In general, waste waters containing
cyanide are segregated and treated separately, waste waters
containing hexavalent chromium are segregated and treated
separately. After treatment the cyanide, chrome, and metal
ion streams are combined for further treatment to
precipitate metal hydroxides which are settled out,
sometimes filtered, and disposed of on land. The treatment
facilities may be engineered for batch, continuous, or
integrated operations. However, the treatment methods for
several pollutants can deviate considerably from this
general plan. The design of a suitable procedure and system
to treat a specific pollutant mix requires considerable care
and experience.
Since many combined waste waters contain some carbonate it
is very possible that cadmium carbonate rather than cadmium
hydroxide is precipitated when waste waters are neutralized
with caustic or lime. Some reported values that seem
unrealistically low for hydroxide precipitation may be
achieved by this mechanism. Cadmium sulfide is very
insoluble (solubility product K = 10~2«), so that a
precipitation system based upon sulfides, combined with
efficient removal of dissolved solids, may provide
acceptable effluent. A schematic of the treatment scheme is
shown in Figure 6. In this figure, the cadmium sulfide
sludge is recovered. If segregated treatment of a cadmium
stream is required, the best way of holding the sludge may
116
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Water
I
Adjust
PH
Sulfide
Precipitate
Liquid effluent
Metal
Recovery
FIGURE 6 SCHEMATIC FOR SULFIDE PRECIPITATION
OF CADMIUM IN WASTEWATERS
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be to ship it to a metal recovery unit, or convert it to a
form suitable for return to the plating bath.
Alternative to recovering sulfide precipitate, an evaporator
can be installed to recover plating bath and reusable water.
A small bleed-off may be required to decrease contaminants
in the plating bath, as shown in Figure 7.
When cadmium plating is done in noncyanide baths, the waste
treatment is the same except that the cyanide oxidation step
is omitted. Fluoborate containing wastes come from a small
amount of cadmium plating. Fluoborate is covered in a
separate section.
Lead. There is a possibility that an adequately low
concentration of dissolved lead cannot be achieved by pH
adjustment. Pourbaix gives the following solubility data
for lead hydroxides.
Solubility
22
8 500
9 6
9.U 3 (minimum)
The chloride and sulfate are too soluble to achieve a
sufficiently low lead concentration, but sulfide
precipitation should reduce the concentration adequately.
Lead carbonates and basic carbonates have low solubilities
and therefore carbonate present incidentally in the
neutralization process or deliberately added may reduce lead
to low levels in effluent. The problem of suspended solids
remains. Sludge would most appropriately be sent to a metal
recovery unit or be converted to a form suitable for return
to the plating bath. Waste treatment operations are similar
to those shown for cadmium in Figures 6 and 7, omitting the
cyanide oxidation. Lead plating wastes contain fluoroborate
which is covered in a subsequent section.
Tin. The tin concentration can be reduced to low levels by
neutralization between pH 8 amd 9 whether the tin is present
in the divalent form from acid baths or the quadrivalent
form from alkaline baths. Therefore, chemical treatment is
adequate for this constituent. In principle, the sulfide
precipitation method, as discussed for cadmium and lead, is
applicable to tin.
Precious, Metals. Silver, gold, and platinum metals in rinse
waters generally are recovered by some method such as ion
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Water
1
Dry Sludge
to Recovery
FIGURE 7 SCHEMATIC OF CADMIUM WASTEWATER
TREATMENT WITH MINIMUM SOLID
DISPOSAL
119
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exchange, evaporation, or electrodeposition. Concentrates
as well as unusable baths are returned to a salvage company
for recovery of metal values by methods involving chemical
treatment.
Processes
Since several of the plating baths (those for
lead, tin, and their alloys) contain the fluoroborate ion,
the applicability of chemical treatment to remove this ion
from liquid effluent is of interest. Upon dilution the
fluoroborate hydrolyzes:
H2O = HF + BF3 + OH~.
The BF3 is very stable.
Thus, the problem is to reduce the concentration of HF in
the waste water. The fluoride may be precipitated with
lime, but the concentration can be reduced only to
approximately 15 mg/1. This suggests that fluoroborate
plating baths be operated as closed-loop systems with
recovery by evaporation, and that spills and leaks be
segregated so that they can be treated separately. In this
way, the fluoride discharged in liquid effluent can be held
to a very small amount.
Wire and.. Strip. Effluent constituents from copper, nickel,
chromium, zinc, and tin plating of wire and strip are
amenable to the same chemical treatment methods as discussed
previously.
Activation_and_Cataly^ing. Chemical precipitation is the
method generally used for treating wastes from these
operations for preparing plastics and nonconductors for
plating. Rinse waters contain tin for activating and palla-
dium from catalyzing operations. Waste Waters are
segregated and treated separately by neutralization and
precipitation. The tin is precipitated at pH 8 and removed
by settling or filtration. The palladium is precipitated at
pH 8 to 9 and recovered by settling or filtration.
s. Effluents from chromating operations
_
are amenable to chemical treatment to reduce the hexavalent
chromium and precipitate trivalent hydroxide as done in
treating waste water from chromium plating. Phosphates from
phosphating operations can be reduced to the 1 mg/1 level by
addition of aluminum ions. Removal of phosphate can occur
when aluminum sulfate is added to the clarifier as a
flocculating agent. Heavy metals, such as iron and zinc,
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derived from the basis metals and solution formulations, are
removed by neutralization and precipitation.
Water ConservationTIn Process_ContrQls
The volume of effluent is reduced if water is conserved
during rinsing operations. The solubility limit of effluent
constituents is essentially constant, so that a reduction in
the effluent volume accomplishes a reduction in the amount
of effluent constituents discharged. Water conservation can
be accomplished by in-plant process modifications requiring
little capital or new equipment, materials substitutions,
and good housekeeping practice. Further water conservation
is obtained by installing counterflow rinse tanks and ion-
exchange, evaporative recovery, or reverse osmosis systems.
Other systems that may accomplish water conservation are
freezing, electrodialysis, electrolytic stripping, carbon
adsorption, and liquid-liquid extraction.
Process Modifications
Substitution of low-concentration electroplating solutions
for high-concentration baths has been adopted in recent
years, principally for reducing the cost of chemicals used
for cyanide destruction. The dilute solutions require less
water for rinsing when electroplating parts are transferred
to rinse tanks. Assuming a 50 percent reduction in total
dissolved solids in the plating solution and two rinse tanks
in series, a 30 percent reduction in rinse water
requirements is achieved. Waste Water constituents
requiring treatment are reduced by the same amount. Adverse
effects in terms of lower efficiency and reduced
productivity per unit facility may be encountered when
dilution is adopted to conserve rinse water and reduce waste
water constituents requiring treatment, unless other factors
affecting plating rate are modified to adjust for the
effects of dilution. Thus, dilution should not be adopted
before a complete analysis is made of all pertinent factors.
The advent of effluent limitations is expected to encourage
research and development on other processes that will
eliminate or reduce water waste. A dry process for applying
chromate coatings, which is currently being developed, may
prove useful for such a purpose, for example. Chemical
vapor deposition processes partially developed a few years
ago may be revived for plating hard chromium.
Material Substitutions
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Noncyanide solutions, which have been developed for metal
finishing operations in place of cyanide solutions, reduce
the costs of treatment by eliminating cyanide destruction,
but do not eliminate treatment to precipitate and separate
the metals. The chelating agents employed in some non-
cyanide baths to keep the metal in soluble form are
precipitated when rinse water waste is treated with lime to
precipitate the metals, but other agents such as ethylene
diamine tetraacetic acid inhibit the precipitation of zinc
and contribute organic matter to the treated water waste.
Thus, the applicability of. the noncyanide solutions as
replacements for cyanide baths must be considered carefully.
Trivalent chromium baths have recently been introduced to
the electroplating industry. They eliminate the need for
sulfur dioxide reduction of waste water associated with
chromium plating. The trivalent chromium baths appear to
have other advantages for decorative plating such as better
throwing power, current efficiency and plating rate. The
dark color of the deposits is cited as a disadvantage by
some purchasers, however., Nevertheless, this process
modification may ultimately prove to be significant for
reducing waste treatment costs. No details have been
released on the treatment required for minimizing the
soluble chromium concentration in treated effluent, however.
Good Housekeeping Practices
Good housekeeping practices that reduce the waste generated
in electroplating facilities include the following:
(1) Maintain racks and rack coatings to prevent
the transfer of chemicals from one operation
to another. (Loose rack coatings are
noteworthy as an example of poor practice.)
(2) Avoid overcrowding parts on a rack, which
inhibits drainage when parts are removed
from a process solutions.
(3) Plug all floor exits to the sewer and con-
tain spills in segregated curbed areas or
trenches, which can be drained to direct
the spills to rinse water effluent with the
same chemicals.
(H) Wash all filters, pumps and other auxiliary
equipment in curbed areas or trenches,
which can be drained to direct the wash
water to a compatible holding tank or
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rinse water stream.
(5) Install anti-syphon devices on all inlet
water lines to process tanks.
(6) Inspect and maintain heating and cooling coils
to avoid leaks.
(7) Inspect and maintain all piping installed for
waste water flow, including piping from fume
scrubbers.
Water Conservation by Reducing Dragout
Dragout. Dragout is defined as solution on the workpiece
carried beyond the edge of the processing tank. The dragout
of concentrated solution from the processing tank can vary
over a wide range depending on the shape factor of the part.
A value of 16.3 1/1000 sq m (0.4 gal/1000 sq ft) is
considered a minimum for vertical parts that are well
drained. The practical range for parts of various shapes
that are well drained is about HO to 400 1/1000 sq m (1 to
10 gal/1000 sq ft) .
2£§32]Jt_Beductign. Water used for rinsing can be conserved
by" (if "improving the racking procedure to improve drainage
from surfaces over the process tank, prior to transfer to
the subsequent rinse tank, (2) increasing the drainage time
over the process tank, (3) reducing the viscosity of the
process solution by diluting it or increasing its
temperature, (t) adding a wetting agent to the process
solution to reduce surface tension, (5) installing fog
nozzles above the process tank to return a part of the
solution remaining on work surfaces to the process solution,
and (6) installing a drip-save (reclaim) tank between the
process and rinse stations to collect dragout that is pumped
back to the process solution. A mixture of air and water is
utilized in one version of a fog nozzle claimed to be
especially effective for removing most of the solution from
surfaces lifted above process tanks. With the above
techniques, the water needed for rinsing can be reduced as
much as 50 to 60 percent.
Reduction of dragout with the above methods is not without
problems. By returning chemicals to the processing tank,
impurities tend to build up in the processing solution.
Therefore, purification systems, such as ion exchange,
batch-chemical treatments, or electrolytic purification are
required to control impurities. The purification systems
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create some effluents which must be treated prior to end-of-
pipe discharge.
Water Conservation During Rinsing
Water conservation procedures that are used after processed
work is transferred to a rinse tank include (1) adding a
wetting agent to the rinse water, (2) installing air or
ultrasonic agitation and (3) installing counterflow rinses
whereby water exiting the last tank in the rinsing operation
becomes feed water for the preceding rinse. With two
counterflow rinses, water consumption is reduced 96 percent
in comparison with a single rinse, assuming that the dragout
solution mixes immediately with the rinse water. This
assumption is incorrect. While a part of the dragout
solution mixes rapidly with the rinse water, particularly if
agitation is used, the remaining film on the work comes off
rather slowly by a diffusion process. A more typical value
for the water reduction might be 85%t corresponding to a
rinsing efficiency of approximately 90%. Use of
conductivity meters in the final rinse provides automatic
control of water use according to need. Rinse water flow is
shut off automatically when no work is being processed.
Excessive use of water can also be avoided by use of flow
restrictors in the water feed lines.
Although multitank, counterflow rinsing imposes capital
investment costs for tanks, pumps, and floor space, these
costs are compensated for by a savings in water (and sewer)
charges. Further incentive is provided when regulatory
agencies require pollutional control. When end-of-process
chemical treatment is used, design of waste treatment
facilities usually indicates the economic advantage of
reducing rinse-water flow by installing two or more
counterflow rinses.
Because waste treatment facilities are usually over designed
to handle future expansion in production, there is a
tendency to use the water flow capacity of the treatment
facility whether or not it is needed for effective rinsing.
Furthermore, rinse water flows set by an orifice are not
always turned off when plating production is shut down. It
is probably more economical to reduce rinse water usage by
use of good rinsing practice than to increase water-
treatment facilities in the event of an increase in
production.
Rinsing can be carried out beyond the point consistent with
good practice, even though there is an economic incentive to
save water. The result is unnecessary pollution. Typical
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concentration levels permitted in the rinses following
various process tanks, should not be decreased unless
definite quality problems can be associated with the dis-
solved solids concentrations listed below for representative
rinsing systems:
Max Dissolved Solids
Process in Final Rinse^mg/1
Alkaline cleaners 750
Acid cleaners, dips 750
Cyanide plating 37
Copper plating 37
«' Chromium plating 15
Nickel plating 37
Chromium bright dip 15
Chromate passivating 350-750
A problem not considered in proposing a maximum dissolved
solids in the final rinse, is the dragin of these rinses
into a subsequent processing operation. If the dragin
attained from the concentration proposed is deleterious to
the following processing operation, the dissolved solids in
the final rinse would have to be decreased or means for
purification provided.
The following is an example, using various rinse
combinations, of the reduction in water volume that can be
obtained for rinsing assuming that the dragout and the rinse
water mix immediately. A Watts-type plating bath typically
contains 270,000 mg/1 of total dissolved solids. Obtaining
37 mg/1 in the final rinse requires 27,600 (7300 gallons) of
rinse water if a single rinse tank is used, in order to
dilute 3.78 liters (1 gallon) of a Watts-type plating
solution containing 270 g/1 of dissolved solids. The same
degree of dilution in a final rinse tank may be obtained
with less water by use of series and counterflow arrangement
of two or more rinse tanks. If the tanks are arranged in
series and fresh water is fed in parallel to each tank in
equal volume, the ratio, r of rinse water to dragout is:
1
n
Co
r = n CF ,
•
where Co = concentration in the process solution
CF = concentration in last rinse tank and
n = number of rinse tanks.
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If the tanks are arranged in the same way, but flow proceeds
from the last rinse tank to the first rinse tank
(count erf low) ,
1
n
Co
r = CF
By feeding water to counterflow tanks instead of in series,
the reduction in water varies n-fold. Values of n
calculated for several rinsing combinations, using the Co
and CF values given above for a nickel bath are as follows:
Rinse Combination Rinse_Ratiof r
Single rinse 7300
Two rinses, parallel feed 171
Three rinses, parallel feed 58.3
Two rinses, counterflow feed 85.5
Three rinses, counterflow feed 19.5
There is a significant reduction in water use by addition of
a second rinse tank, and at least two rinse tanks can be
considered normal practice. These should best be fed in
counterflow. Counterflow rinse tanks increase the
concentration of a metal or other constituent in the first
rinse tank following the plating or process bath. The water
in the first rinse tank can be used to supply makeup water
for the plating bath. As the concentration in the first
rinse tank increases, more of the dragout from the plating
bath can be returned to the bath in the makeup water, and
less will require treatment and disposal. Therefore, the
addition of countercurrent rinse tanks can decrease both the
volume of water to be treated and the amount of dissolved
metal that must be removed, at least in some cases. A
problem not considered in using counterflow rinses is that
the concentration in the first rinse tank can become so high
that the diffusion of the dragout from the film on the
workpiece can be slowed considerably and, therefore, the
rinsing efficiency decreased substantially. Therefore, the
more countercurrent rinse tanks that are used, the less
126
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accurate is the calculation assuming that the dragout and
rinse water mix immediately.
The rate of evaporation from the plating bath is a factor in
determining how much makeup water must be added. Operating
a bath at a higher temperature will allow more of the
dragout to be returned to the bath because of the higher
rate of evaporation. However, the temperature at which a
bath may be operated is sometimes limited because of the
decomposition of bath components. Progress has been made in
developing bath components that allow higher bath
temperatures to be used. For example, brighteners for zinc
cyanide baths have been developed which allow bath operation
at 50° C (120° F) as compared to 32« C (90° F) . The new
brighteners permit the return of more of the dragout to the
plating bath and a lessened load on the waste treatment
system, in addition to what other processing advantages they
may offer.
Advanced Treatment Technologies
Ion Exchange
Applicability.. Ion exchange is currently a practical com-
mercially accepted method for the in-process treatment of
(1) raw water, (2) processing baths, (3) rinse waters. Raw
water is treated to provide deionized water for both makeup
and critical final rinsing operations. Plating baths are
treated to remove impurities, i.e., removal of nickel ions
from a chromic acid bath with a cation exchange resin.
Rinse waters are treated to provide water that can be
returned to the process solution. The concentrated
regenerant can be chemically treated more easily than the
original volume of rinse water and in some cases the
chemicals can be recovered and returned to the bath. The
in-process treatment of chromium and nickel plating
effluents by ion-exchange techniques are the more econom-
ically attractive treatment operations currently being
carried out. Ion exchange also is beginning to find
increased use in combination with evaporative and reverse
osmosis systems for the processing of electroplating rinse
waters.
Advantages ^and^ Limitations. Some advantages of ion exchange
for treatment of plating effluents are as follows:
(1) Ion exchange is an economically attractive
method for the removal of small amounts
of metallic impurities from rinse waters
and/or the concentration for recovery
127
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of expensive processing chemicals.
(2) Ion exchange permits the recirculation
of a high-quality water for reuse in the
rinsing operations, thus saving on water
consumption.
(3) Ion exchange concentrates processing bath
chemicals for easier handling, treatment,
subsequent recovery, or disposal operations.
Some limitations or disadvantages of ion exchange for
treatment of process effluents follow:
(1) The limited capacity of parallel bed ion
exchange systems means that relatively
large installations are necessary to provide
the exchange capability needed between
regeneration cycles. Continuous ion exchange
units reduce the size compared to dual-bed
units.
(2) Parallel-bed ion exchange systems require
periodic regeneration with expenditures
for regenerant chemicals. Unless regeneration
is carried out systematically or continuous
ion exchange units are used, leakage of
undesirable components through the resin
bed may occur. In addition, the usual
treatment methods must be employed to
dispose of the regenerated materials.
(3) Cyanide generally tends to adversely affect
the resin performance because of tightly
held metal cyanide complexes on strongly
basic anion resins, so that processing of
cyanide effluents (except for very dilute
solutions) does not appear practical at
the present time.
(U) Resins, which are not highly cross-linked
(or macroreticular), slowly deteriorate with
use under oxidizing conditions.
Process Principles and Equipment. Ion exchange involves a
reversible interchange of ions between a solid phase and a
liquid phase. There is no permanent or substantial change
in the structure of the solid resin particles. The capacity
128
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Waste from
contaminated
rinse overflow
Waste-water
reservoir
To clean water
reservoir and
process rinse tanks
Caustic
soda
£x
• Hydrochloric
acid
rtx
LO
To recovery
or waste
treatment
FIGURE 8 ., SCHEMATIC PRESENTATION OF ION-EXCHANGE APPLICATION
FOR PLATING-EFFLUENT TREATMENT(7,25)
-------
of an ion exchange material is equal to the number of fixed
ionic sites that can enter into an ion exchange reaction,
and is usually expressed as milliequivalents per gram of
substance. Ion exchange resins can perform several
different operations in the processing of waste water,
including:
(1) Transformation of ionic species
(2) Removal of ions
(3) Concentration of ions.
The performance of some of these functions is illustrated in
Figure 8, which is a generalized schematic presentation of
the application of ion exchange to treatment of electro-
plating effluents. In practice, the solutions to be treated
by ion exchange are generally filtered to remove solids such
as precipitated metals, soaps, etc., which could
mechanically clog the resin bed. Oils, organic wetting
agents, brighteners, etc., which might foul the resins, are
removed by passage through catrbon filters.
During processing, the granular ion exchange resin in the
column exchanges one of its ions for one of those in the
rinse water or other solution being treated. This process
continues until the solution being treated exhausts the
resin. When this happens, solution flow is transferred to
another column with fresh resin. Meanwhile, the exhausted
resin is regenerated by another chemical which replaces the
ions given up in the ion exchange operation, thus converting
the resin back to its original composition. With a four-
column installation consisting of two parallel dual-bed
units, as shown in Figure 8, the ion exchange process can be
applied continuously by utilizing the regenerated units
while the exhausted units are being regenerated.
Most ion exchange systems depend upon regenerating with acid
and base to form the acid and base forms of the resin.
These are capable of exchanging with and thereby removing
from solution both metals and dissolved salts such as sodium
chloride. However, resins can be regenerated with salts,
i.e., sodium chloride to form sodium and chloride forms of
the resin. These will exchange with metals but not the
soluble salts. Since exchange capacity is reserved for
metals only, the frequency of regeneration is decreased as
is the cost of metal removed.
Practical Operating Systems. The Phase I report described
systems in use to remove nickel ions and trivalent chromium
ion from chromium plating baths. The more dilute baths for
producing chromium conversion coating are treated in a
130
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similar manner to remove, zinc ions. Aluminum is removed
from chromic acid anodizing baths, and from phosphoric acid
baths used for bright dipping. Cyanides may also be
removed, in a 3-bed system, consisting of strongly acidic,
weakly basic, and strongly basic ion exchangers. The system
provides ease of regeneration and little chance of cyanide
leaking through5*. The three-bed system has been in
commercial operation in Europe and only recently introduced
in the US. Several of the systems are being installed one
of which will be supported to a limited extent under an EPA
grant to obtain performance and economic information.
Demonstration Status. An ion exchange system using a short
30-minute cycle, including a 3 to 4-minute back wash to
recover chromic acid from rinse waters has been in operation
for over a year. The resin undergoes very little
performance deterioration since the chromic acid is not
deeply absorbed into the resin during such a short cycle.
Another system under development uses an ion exchange column
to achieve separation of components in much the same manner
that chromatographic columns are used. For example, a
solution for bright dipping of aluminum, containing
phosphoric acid and aluminum ions, is fed through a strongly
basic ion exchange column. The phosphate ions interact with
the ion exchange sites and flow of the phosphoric acid is
retarded in comparison to that of the aluminum ions, which
flow unimpeded through the column. Water, which may be
considered a very weak base, is adequate for regenerating
the ion exchange resin and eluting the phosphoric acid with
much of the aluminum removed. The phosphoric acid is
returned to the brightening bath.
Evaporative Recovery
Applicability. When rinse water from one type of bath is
distilled in an evaporative unit, the concentrate may be
returned to the plating bath and the distillate to the cor-
responding rinse tank, which is useful for closing the loop
on a single plating operation. The economics of
distillation, from the standpoint of either investment or
operating costs imposes a constraint on the size range of
distillation equipment. Units with a capacity of the order
of 300 gph are used in practice. Such a low rate of flow of
rinse water is achieved in many plating operations only by
the use of at least three countercurrent rinses, which by
itself reduces the waste water. Evaporative recovery units
for all of the rinse cycles would reduce the effluent to
zero. So far, recovery units have been installed on rinse
tanks following plating baths in order to recover plating
131
-------
chemicals and return them to the bath and thereby reduce
plating costs. The units have not been installed on cleaner
or acid dip lines because the cost of chemicals is not
sufficient to make recovery worthwhile, and the build up of
contaminants, i.e., oil and grease, makes use of a closed
system difficult.
Evaporation is a firmly established industrial procedure for
recovering plating chemicals and water from plating waste
effluents. Commercial units for handling zinc, copper,
nickel, chromium, and other metal plating baths have been
operating successfully and economically for periods of one
to 10 years or longer. Packaged units for evaporative
treatment of plating wastes are available from some
manufacturers.
At least 100 evaporative units have been installed, which
means that their use in industry is limited to a very small
percentage of the shops. Nevertheless, announcements of new
installations and savings through their use keep recurring
and evaporative recovery appears to be a method that will
grow in use. However, if these units are to pay off
strictly on the basis of savings in chemicals such factors
as value of the chemicals, their concentration in the
process bath, and the dragout rate are important in
determining whether a savings is possible
Advantages and _Limitations. The following are some of the
advantages of using evaporation for handling plating waste
effluents:
(1) Recovers expensive plating chemicals, which
were either lost by discharge to a sewer or
effluent which would have to be treated or
destroyed prior to disposal; chemicals
concentrated to plating strength can be
returned to the plating tank.
(2) Recovers distilled water for reuse in the rinse
operations, thus lowering water and sewer
disposal.
(3) Eliminates or greatly minimizes the amount of
sludge formed during chemical treatment and
eliminates or reduces the amount requiring
disposal by hauling or lagooning.
(H) The use of vacuum allows evaporation to accur
at relatively low temperatures (e.g., 110°F)
so that destruction of cyanides or other heat-
132
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sensitive materials is lessened.
(5) The technology of evaporators (conventional and
vapor recompression units) is firmly established,
so their capabilities are well known and their
performance should be readily predictable and
adaptable to plating effluent handling.
Some of the limitations or disadvantages of evaporative
recovery systems are given below:
(1) The rinse water saving (e.g., 1100 1/hr (300 gph))
is rather small, and by itself does not signifi-
cantly lighten the rinse water load on the final
chemical treatment plant.
(2) Evaporative units have relatively high capital
and operating costs, especially for the vacuum
units. Steam and coolant water are required.
(3) The evaporative units are fairly complex and
require highly trained personnel to operate
and maintain them.
(4) Separate units are required for handling the
waste effluent from each line, since various
solutions, such as zinc, nickel, copper,
chromium, cannot be mixed for chemical
recovery.
(5) As with all closed-loop systems, evaporation
in most cases results in a build-up of impurities
which must be taken care of by a bleed stream
or directly in the closed-loop system.
The advantages offered by evaporative recovery often
outweigh the disadvantages. Evaporative recovery is a
promising method currently available for handling plating
waste effluents and limiting treatment plant size. Where
existing chemical treatment (cyanide destruction, chromate
reduction, and chemical precipitation) facilities are
operating at less than capacity, the economics and
practicality of installing new evaporative equipment must be
closely evaluated. The small decrease in the rinse water
effluent (e.g., 1100 1/hr (300 gph)) by itself does not
warrant the installation of an evaporative system. The
savings produced by the recovery of plating chemicals plays
the significant role in judging the overall merits of the
evaporative system for a specific operation.
1-33-.
-------
Process Principles and Equipment. A representative closed
loop system for recovery of chemicals and water from a
plating line with a single-effect evaporator is shown in
Figure 9. A single-effect evaporator concentrates flow from
the rinse water holding tank. The concentrated rinse
solution is returned to the final rinse tank. With the
closed-loop system, no external rinse water is added except
for makeup of atmospheric evaporation losses. The system is
designed for recovering 100 percent of the chemicals,
normally lost in dragout, for reuse in the plating process.
Single-, double-, and multiple-effect evaporators, and
vapor-recompression evaporator units are used for handling
plating effluent. Open-loop and combined evaporation (i.e.,
evaporation combined with ion exchange, reverse osmosis, or
other systems) are also employed for handling plating
effluent.
A single-effect evaporator is preferred, if relatively
untrained operating personnel are involved, or low initial
capital outlay is desired. It's the simplest in design and
therefore the easiest to operate. However, it is less
economical than a double-effect or vapor recompression unit
with regard to utility costs. A double-effect evaporator
should be considered when lower operating cost is desired
with a modest increase in capital investment.
A vapor-recompression evaporator should be considered if no
steam or cooling water is available. Where utilities for a
conventional steam evaporator are available, the high
initial cost of the vapor recompression unit is not
economically justified. Its operating cost is the lowest of
the three systems. Its dependence on an expensive and
complex mechanical compressor is the main disadvantage.
Some sources report considerable maintenance and down time
and have dispensed with use of evaporator units. Other
sources report little or no trouble and are very satisfied
with the operation. It appears that the units can perform
very satisfactorily if the installation is properly
engineered, and if preventive maintenance and trouble-
shooting are carried out by knowledgeable personnel.
In some instances, evaporation procedures must be used in
combination with chemical or other methods in order to
handle small amounts of impurity build-up (e.g.,
brighteners, carbonates, extraneous metal ions, etc., in
closed loop operation) or for treatment of minor bleed-off
streams (open-loop).
134
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Concentrate hold tank
Distillate hold tank
I Plating work travel »•
Plating bath Rinse tanks (2
Rinse water
holding tank
IlSLJr
Condenser
Separator
Recirculafion concentrate pump
Vacuum jet
C.W. out
CW. in
Reboiler
Steam
Distillate pump
Condensate
FIGURE 9 REPRESENTATIVE CLOSED-LOOP SYSTEM FOR
RECOVERY OF CHEMICALS AND WATER WITH
A SINGLE-EFFECT EVAPORATOR
135
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Atmospheric evaporation, which uses air flow through packing
media in an evaporator, can concentrate plating solution
such as chromic acid up to 480 g/1 (H Ib/gal).
The Corning Glass company has introduced a new concept for
evaporative recovery. A glass shell and tube heat exchanger
is mounted vertically and the solution is fed through the
bottom. The boiling causes liquid surges that produce a
"rising film" effect and an improvement in heat transfer.
Vapor and liquid overflow the top of the tubes and are
separated in a cyclone. Water with less than 0.05 ppm of
chromic acid has been produced from chromium plating rinse
water.
Practical Operating Systems. Systems operating on copper
cyanide, nickel, chromium, and zinc cyanide plating lines
were described in the Phase I report. Systems have also
been installed on lines using the following baths: brass
cyanide, cadmium cyanide, Pb-Sn-Cu fluoroborate, and gold.
The practicality of using this system on cadmium and lead
plating baths means there is at least one way of eliminating
discharge of polluted water from these processes. Small
amounts of spills, leaks, if segregated, are evaporated to
dryness, and the solid waste sent to a metal recovery unit.
Falling film atmospheric evaporators have been installed in
a few plants.
Demonstration Status. The "rinsing film" units are
undergoing pilot and plant test.
Reverse osmosis
Applicabi1ity« Reverse Osmosis uses a pressure differential
across a membrane to separate a solution into a concentrate
and a more dilute solution that may approach the purity of
the solvent. It therefore accomplishes the same type of
separation as distillation and has been applied in plating
installations in the same manner. Small units under 300 gph
have been installed to recover plating baths chemicals and
make closed-loop operation of a line possible.
There are limitations on the acidity and alkalinity of
solutions suitable for treatment by reverse osmosis that
eliminate some alkaline baths and chromic acid baths from
consideration unless modifications are made to the solutions
prior to treatment. Another use of reverse osmosis is for
end-of-process water recovery following chemical treatment.
A recently designed system for Plant 11-22 offers promise
that large capacity reverse osmosis systems are possible and
therefore not subject to the* size constraints of evaporative
136
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systems. If so, they should play a key role in the design
of plants that will have no liquid effluent.
Most of the development work and commercial utilization of
the reverse osmosis process, especially for desalination and
water treatment and recovery, has occurred during the past
10 years. There is a steadily growing number of commercial
installations in plants for concentration and recovery of
plating chemicals along with recovery of water under
essentially closed-loop conditions. Most of the existing
commercial installations are for treatment of nickel plating
solutions, since reverse osmosis is especially suited for
handling nickel solutions and also because of the favorable
economics associated with recovery and reuse of expensive
nickel chemicals. commercial reverse osmosis units for
handling acid zinc and acid copper processes also have been
installed, however. Laboratory pilot plant and full-scale
in-plant studies directed at handling cyanide and chromium-
type effluents are under way.
Reverse osmosis is especially useful for treating rinse
water containing costly metals and other plating salts or
materials. Generally, the purified water is recycled to the
rinse, and the concentrated salts to the plating bath. In
instances where the concentrated salts cannot be recycled to
the plating tank, considerable savings will be achieved
because of the reduced amount of waste-containing water to
be treated.
Advantages and Limitations. Some advantages of reverse
osmosis for handling process effluents are as follows:
(1) Ability to concentrate dilute solutions
for recovery of salts and chemicals
(2) Ability to recovery purified water for
reuse
(3) Ability to operate under low power require-
ments (no latent heat or vaporization or
fusion is required for effecting separa-
tions; the main energy requirement is for
a high-pressure pump)
(t») Operation at ambient temperatures (e.g.,
about 60° to 90° F)
(5) Relatively small floor space requirement
for compact high-capacity units.
137
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Some limitations or disadvantages of the reverse osmosis
process for treatment of process effluents are listed below:
(1) Limited temperature range for satisfactory
operation. (For cellulose acetate systems
the preferred limits are 65° to 85° F;
higher temperatures will increase the rate
of membrane hydrolysis, while lower temper-
ature will result in decreased fluxes but
not damage the membrane).
(2) Inability to handle certain solutions
(strong oxidizing agents, solvents and
other organic compounds can cause dissolu-
tion of the membrane) .
(3) Poor rejection of some compounds (some
compounds such as borates and organics of
low molecular weight exhibit poor rejection).
(4) Fouling of membranes by slightly soluble
components in solution.
(5) Fouling of membranes by feeds high in sus-
pended solids (such feeds must be amenable
to solids separation before treatment by
reverse osmosis).
(6) Inability to treat highly concentrated
solutions (some concentrated solutions may
have initial osmotic pressures which are so
high that they either exceed available
operating pressures or are uneconomical to
treat).
Process Principles and Equipment. Water transport in
reverse osmosis (RO) is opposite to the water transport that
occurs in normal osmosis, where water flows from a less
concentrated solution to a more concentrated solution. In
reverse osmosis, the more concentrated solution is put under
pressure considerably greater than the osmotic pressure to
drive water across the membrane to the dilute stream while
leaving behind most of the dissolved salts. Salts in
plating baths such as nickel sulfate or copper sulfate can
be concentrated to solutions containing up to 15 percent of
the sa.lt, by weight.
Membrane materials for reverse osmosis are fairly limited
and the bulk of the development work has been with specially
prepared cellulose acetate membranes, which can operate in a
138
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pH range of 3 to 8 and are therefore useful for solutions
that are not strongly acid or alkaline, i.e., rinses from
Watts nickel baths. More recently, polyamide membranes have
been developed that will operate up to a pH of 12, and
several of these units are operating in plants for the
treatment of cyanide rinse waters.
Figure 10 is a schematic presentation of the reverse osmosis
process for treating plating-line effluent. The rinse
solution from a countercurrent rinse line is pumped through
a filter, where any suspended solids that could damage or
foul the membrane are removed. The rinse solution is then
raised to the operating pressure by a high-pressure pump and
introduced into the reverse osmosis unit. The concentrated
salt stream is returned to the plating tank, while the
dilute permeate stream is returned to the second rinse tank.
Currently, several different configurations of membrane
support systems are in use in commercial reverse osmosis
units. These include plate and frame, tubular, spiral
wound, and hollow fine fiber designs.
Practical .Operating _Systems. Reverse osmosis units are in
operation for recovering nickel from rinse waters. The
concentrate is returned to the plating bath.
Demonstration Status. The reverse osmosis units installed
at the Rock Island Arsenal as part of an end-of-process
water recovery system, is currently undergoing full scale
testing of performance as part of a total waste treatment
system. A project sponsored by the American Electroplating
Society has demonstrated that cellulose acetate membranes
can operate successfully on nickel and copper sulfate rinse
waters and that spiral wound and hollow fiber polyamide
membranes can be used to treat copper, zinc, and cadmium
cyanide baths. A second phase of this study is a
demonstration in a plating shop of a full scale reverse
osmosis system on copper cyanide rinse water.
Freezing
Applicability. The freezing process would be capable of
recovering metal and water values from plating rinse water
to permit essentially closed-loop type operation if fully
developed. The feasibility of using freezing for treatment
of plating rinse waters was demonstrated on a laboratory
scale using a mixed synthetic solution containing about 100
mg/1 each of nickel, cadmium, chromium, and zinc, along with
30,000 mg/1 of sodium chloride. Greater than 99.5 percent
removal of the metallic ions was achieved in the
experiments, with the purified water product containing less
139
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Rinse
1
= High-
p pressure
pump
Parts
Low-pressure
pump
Makeup
water
Concentrate
Reverse-osmosis
unit
Permeate
FIGURE 1° SCHEMATIC DIAGRAM OF THE REVERSEOSMOSIS PROCESS
FOR TREATING PLATING EFFLUENTS
-------
than 0.5 mg/1 each of the individual plating metals. The
separation tests were carried out using the 9500 1/hr (2500-
gpd) pilot plant unit at Avco Systems Division, Wilmington,
Massachusetts.
Process Principles and Equipment. The basic freezing
process for concentration and recovery of water from plating
effluents is similar to that used for recovery of fresh
water from the sea. A schematic diagram of the treatment of
plating rinses by the freezing process is shown in Figure
11. The contaminated reuse water is pumped through a heat
exchanger (where it is cooled by melted product water) and
into a freezer. An immiscible refrigerant (e.g., Freon) is
mixed with the reuse water. As the refrigerant evaporates,
a slurry of ice and concentrated solution is formed. The
refrigerant vapor is pumped out of the freezer with a
compressor. The slurry is pumped from the freezer to a
counterwasher, where the concentrated solution adhering to
the ice crystals is washed off.
The counterwasher is a vertical vessel with a screened
outlet located midway between top and bottom. Upon entering
the bottom, the slurry forms a porous plug. The solution
flows upward throught the plug and leaves the counterwasher
through the screen. A small fraction of the purified
product water (less than 5 percent) flows countercurrently
to the ice plug to wash off concentrated solution adhering
to the ice. The ice is pumped to a condenser and melted by
the release of heat from the refrigerant vapor which had
been originally evaporated to produce the ice, and which had
been heated by compression to a saturation temperature
higher then the melting point of the ice.
Because of the pump work, compressor work, and incomplete
heat exchange, a greater amount of refrigerant is vaporized
than can be condensed by the melting ice. Consequently, a
heat removal system is needed to maintain thermal
equilibrium. This system consists of a compressor which
raises the temperature and pressure of the excess vapor to a
point where it will condense on contact with ambient cooling
water.
The freezing process offers several advantages over some
other techniques. Because concentration takes place by
freezing of the water in direct contact with the
refrigerant, there is no heat-transfer surface (as in
evaporation) or membrane (as in reverse osmosis) to be
fouled by the concentrate or other contaminants. Suspended
solids do not affect the freezing process and are removed
141
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Cooling
water
To rinse
tank
Compressor
Refrigerant
vapor
Heat exchanger
FIGURE 11 SCHEMATIC DIAGRAM OF FREEZING PROCESS FOR RECOVERY
OF WATER AND CHEMICALS FROM PLATING RINSES (37,38)
-------
only as required by the end use to be made of the recovered
products.
The heat of crystallization is about 1/7 the heat of
vaporization, so that considerably less energy is
transferred for freezing than for a comparable evaporation
operation. Because freezing is a low-temperature process,
there will be less of a corrosion problem than with
evaporation, and less expensive materials of construction
can be employed. The freezing process requires only
electrical power, as opposed to the evaporation process
which also requires steam generating equipment. The cost of
the freezing method may be only 1/3 that for evaporative
recovery.
A method of freeze drying electroplating solutions has been
demonstrated in the laboratory. Droplets of the solutions
are injected into cold liquid-hexane where they are
immediately frozen. The droplets were separated out and the
water removed at subfreezing temperature. The method leaves
a dry chemical residue, and the pure vaporized water could
be recycled to process. The economics of the process on a
practical scale are unknown.
Practical Operating, Systems. No commercial utilization of
freezing"?or treatment of~waste water from electroplating is
known at this time.
Demonstration Status. No demonstrations are in progress in
electroplating plants. However, a 9500 liters/day (2500
gpd) unit is in operation to demonstrate desalination of
water.
Electro dialysis
Applicability. Electrodialysis removes both cations and
anions~from solution and is most effective with multi-valent
ions. It is capable of reducing the concentration of metal
ions from solutions whether they are complexed or not.
Chromate and cyanide ions may also be removed.
Process Principles and Equipment. The simplest
electrodialysis system consists of an insoluble anode and an
insoluble cathode separated by an anion permeable membrane
near the anode and a cation permeable membrane near the
cathode. An anode chamber, cathode chamber, and middle
chamber are thereby formed. Upon electrolysis anions pass
from the middle chamber to the anode compartment and cations
pass from the middle chamber to the cathode compartment.
The concentration of salt in the central compartment is
143
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thereby decreased. By employing several anion and cation
permeable membranes between the electrodes several chambers
are created. A stream may then be run through several of
these chambers in which the concentration is successively
increased. The net effect is similar to that of a
continuous moving bed ion exchange column with electrical
energy used for regeneration rather than chemicals.
Practical Operating Systems. No practical operating systems
have been reported. However, development has resulted in
several demonstrations, discussed below.
Demonstration Status. Several demonstrations have shown
that electrodialysis is a promising method. Further
development and use of the method may be expected. Copper
cyanide rinse water may be concentrated sufficiently to be
returned to the bath by using two units on a double
counterflow rinse system i.e., between the first and second
rinse tank and between the bath and first rinse tank.
Copper may be recovered and chromic acid regenerated in a
spent etching solution for printed circuits. The Metal
Finishers Foundation has put priority on a future project on
cyanide removal by electrodialysis.
Ion-Flotation Techniques
Applicability. Ion-Flotation techniques have not been
developed for application to process rinse water effluents.
If successfully developed into a practical method for
effluent treatment, ion flotation offers possibilities of
reducing the amount of water discharged by 60-90 percent for
some operations. These savings are based on results of
small-scale laboratory studies on solutions containing
cyanides or hexavalent chromium.
Process Principles and Equipment, Separation of ions from
aqueous solutions by a flotation principle is a concept
first recognized about 25 to 30 years ago. In the ion-
flotation operation a surface active ion with charge
opposite to that of the ion to be concentrated is added to
the solution and bubbles of air or other gas are introduced
into the solution to form a froth of the surface-active
materials. The foam is separated and collapses to form a
scum containing an ion concentrate. Ion flotation combines
the technologies of mineral flotation and ion exchange. A
schematic diagram of an ion-flotation cell is shown in
Figure 12.
Experimental results indicate that 90 percent of the
hexavalent chromium in a 10 to 100 ppm solution can be
144
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Air in
-— 6
Foam concentrate
take-off
Purified
solution — »
removal
Tnjprtiop port
for collector ^-
agent
0 *
t) 0
0 6
6 0
o\ f
t>( 0 t
I
0
•-•^y— • -,^_^
1^-— ~- *»>-V
*-*">^— ^/II-'-N'""
-^/"s*-^X-^V
Q A
» /
t o
o 0
at
K;
t
,—-•—
_^-*--
-^^^-«
if— NtftH
)
)
Air out
—^^*
*^*^*
~-«^*
— Foam level
— Solution level
v/ ' Solulion sumpliny
poi 1
FIGURE 12 SCHEMATIC DIAGRAM OF ION-FLOTATION CELL
FOR TREATMENT OF PLATING EFFLUENT
145
-------
removed with primary amine surface-active agents. However,
the amine suffered deterioration when regenerated for reuse,
since the removal efficiency dropped to 60 percent after two
regenerations of the amine.
Grieves, et al., have demonstrated the feasibility of using
ion flotation on dichromate solutions with a cationic
surfactant (ethylhexadecyldimethylammonium bromide) . A
continuous operation with a retention time of 150 minutes
was devised. The feed stream contained 50 mg/1 of
dichromate. Approximately 10 percent of the feed stream was
foamed off to produce a solution containing U50 mg/1 of
dichromate, while the stripped solution contained 15 mg/1.
Cyanides have been removed from dilute solutions with mixed
results. The extraction efficiency from a cadmium cyanide
solution containing 10 ppm of cyanide was 57 percent, using
primary, tertiary, and quaternary ammonium compounds as
collectors. Extraction efficiencies for nickel and iron
cyanide solutions were approximately 90 percent, but these
systems are of relatively little interest.
Operating Systems. There are no practical
operating systems.
Demonstration Status. The process has not been demonstrated
in an operating plant.
Electrolytic Stripping
AEEiisabiJLity. Electrolytic stripping is not in general use
for removing metals although some procedures have been
employed for recovering precious metals.
Process Principles and Equipment. in order to strip a solu-
tion by electrodeposition it. is necessary that the metallic
ions in a dilute solution reach the cathode surface at a
sufficient rate so that essentially all of the ions can be
deposited in a reasonable time. Surfleet and Crowle have
discussed several methods of accomplishing this. One method
called the "integrated" system uses baffles in a tank to
create a very long path through which the water may be
recirculated at a high velocity. The method is suitable
only for metals having a relatively high limiting current
density for dilute solutions, such as gold, silver, and tin.
The fluidized bed electrode is a bed of metal spheres or
metal-coated glass spheres that is fluidized by pumping the
dilute solution through it and causing an expansion of 5 to
10 percent. With spheres of 100 to 300 microns in diameter,
a total geometric area of 75 cm2/cm3 is obtained. Thus, the
146
-------
current density is very low and the flow of electrolyte
through the bed provides the forced convection to support
high currents. Another system employs electrodes made of
expanded metal and the turbulence around this structure
enhances the rate of deposition of metal when solution is
pumped past it. Turbulence and an increase in the rate of
deposition at a plane electrode may also be promoted by
filling the space between electrodes with a woven plastic
screen, glass beads, etc.
In another system the electrode is introduced into a narrow
gap between two porous carbon electrodes. The bulk of the
solution (99%) is forced through the cathode where copper is
deposited out. Predeposited copper on the anodic electrode
is dissolved into the 1 percent of the electrolyte that
permeates through this electrode and a copper concentrate is
produced. The two electrodes are periodically reversed so
that copper deposited from a large volume of solution is
dissolved into a small volume of electrolyte. Copper in
solution has been reduced from 670 mg/1 to 0.55 mg/1 in the
cathode stream and concentrated to 4U g/1 in the anode
stream. A similar system has been used for depositing
metallic impurities from strong caustic solutions.
Practical O]3e rating ^Syst ems. There are many systems in
operation for the recovery of precious metals.
Demonstration Status. The porous electrode system 76 is
still under development at the University of California and
has been scaled up to handle 250 gpd of copper sulfate
solution. The Metal Finishers Foundation has established
priority for a future project to remove zinc from effluent
by electrodeposition.
Water Conservation by Carbon Adsorption
Applicability. Activated carbon has been used for the
adsorption of various materials from solution, including
metal ions. Experimental data show that up to 98 percent of
the chromium can be removed from waste water. The treated
water can be recycled to the rinse tanks.
§ and Eguipjnent. The process relies upon
the adsorption of metal ions on specific types of activated
carbon. In the case of Chromium VI, a partial regeneration
of the carbon can be accomplished with caustic solution
followed by an acid wash treatment to remove residual
caustic and condition and carbon bed for subsequent
adsorption cycles. The equipment consists of holding tanks
for the raw waste, pumps and piping to circulate the waste
147
-------
through adsorption columns similar to those used for ion
exchange.
Practical Qperating^Systems. Systems based on adsorption
and desorption are still under laboratory development and no
practical operating systems are known.
Demonstration. Status. Pilot plant equipment has been
operated successfully in an electroplating plant treating
chromium rinses at a flow rate of 19 liters/min (5 gpm) at
concentrations from 100 to 820 mg/1 hexavalent chromium.
Adsorption was continued until the effluent reached
concentrations of 10 ppm of Or*6.
Liquid-Liquid Extraction
Applicability. Liquid-liquid extraction has been used on an
experimental basis only for the extraction of hexavalent
chromium from waste waters. The effect is to concentrate
impurities in a smaller volume, which in turn will have to
be treated by other means or suitably disposed of. The
fully extracted aqueous phase may be recycled to the rinse
tanks. Water savings from 50 to 73 percent appear to be
possible.
Process Principles and Equipment. The metal-ion pollutant
is reacted with an organic phase in acid solution, which
separates readily from the aqueous phase. Metal is subse-
quently stripped from the organic phase with an alkaline
solution. Hexavalent chromium, for example, has been
extracted from waste water at pH 2 with tertiary and
secondary amines dissolved in kerosene. After the reaction
of the chromium with the amine and phase separation, the
chromium is stripped with alkaline solution from the organic
phase restoring the amine to its original composition. For
liquid-liquid extraction to be feasible the following
conditions would have to be met:
(1) The extraction of chromium should be virtually
complete
(2) Reagent recovery by stripping would be efficient
(3) The stripping operation should produce a
greatly concentrated solution
(U) The treated effluent solution should be
essentially free from organic solvents
148
-------
(5) Capital and operating costs should be
reasonable.
The equipment required consists basically of mechanically
agitated mixing and settling tanks, in which the phases are
intimately dispersed in one vessel by agitation and then
permitted to flow by gravity to a settling vessel for
separation. Holding tanks for extractant and stripper and
circulating pumps for these solutions, as well as the
purified waste water, are necessary. Equipment for liquid-
liquid extraction would also include horizontal and vertical
columns, pulsed columns and centrifuges.
Practical Operating Systems. Liquid-liquid extraction
systems are not known to" be operating for treatment of
electroplating wastes.
DemQnstration_Status« Experimental evidence exists indi-
cating that up to 99 percent of chromium can be successfully
extracted from rinse waters containing 10 to 1000 mg/1 of
Cr*+. With 10 ppm of Cr«+ in the rinse water, the treated
effluent contained as little as 0.1 mg/1 of the ion; with
100 ppm in rinse water concentration was reduced to 0.4
mg/1. Stripping was effective as long as the amines were
not allowed in contact with the chromium for a prolonged
period of time which would allow oxidation by Cr*+ ions.
The effluent, however, contained from 200 to 500 mg/1 of
kerosene, which is undesirable.
Methods of Achieving No Discharge^of Pollutants
Although chemical methods of treating waste waters are
achieving the low effluent discharges recorded in this
report, they are not improvable to the point of achieving
zero discharge of pollutants. Also the problem of
recycling sludges or solid wastes remains. It is easy to
design systems that will in principle close the process loop
and prevent discharge. In practice, however, this can only
be done with considerable forethought and experience, since
closed systems are in general subject to impurity buildup.
Progress in achieving no-discharge systems is likely to take
place in a series of steps in which the amount of discharge
is consistently reduced until it is negligible,
A major problem with a series of electroplating processes in
a closed cycle is that of dragin. After a closed cycle has
been run long enough any stagnant tank, i.e., a plating
solution that is normally not discarded, will contain the
same concentration of contaminant as the preceding tank in
the cycle, the assumption being that the volume of dragin
149
-------
and dragout are equal. Therefore, if the final rinse
following nickel plating contains 12 ppm of nickel and
chromium plating follows, the chromium bath will ultimately
contain 12 ppm of nickel. Nickel is frequently removed from
chromium plating baths by ion exchange, but since the ion
exchanger requires periodic regeneration, the regenerant
must somehow be returned to the system if it is to be
considered a closed one. The nickel in the regenerant might
be recovered and returned to the nickel bath, but the
dissolved solids, i.e., sodium sulfate, and sodium chloride
are really excess products that cannot be completely
returned to the process. While the main process loop may be
closed, the secondary purification loops may be more
difficult to close. With some process baths, it may not be
possible to find a method for purification that is as
adaptable as is ion exchange to the removal of nickel from a
chromium bath. Alternatives then are to (1) develop
processing baths that can tolerate the impurity buildup or
(2) to design rinse systems in which the concentration of
impurity in the final rinse tank is reduced to a tolerable
level.
Some systems, designed to remove a specific impurity, are
found to remove other components as well, which may require
further treatment. An example of such a system is that used
for removing carbonates from cyanide baths. Whether
freezing or precipitation with calcium is used, the
carbonates occlude and adsorb significant quantities of
cyanide that must then be further treated, with the result
that cyanide is not maintained in a closed system.
Therefore, with present technology, it is likely that there
will be some discharge from a. process loop in spite of the
best efforts that are made to close it. Some waste water
effluent will be produced and the next consideration is how
well a waste treatment system can be closed.
The effluent will contain metals, cyanide, and chromate all
of which can be treated to relatively low levels to give (1)
liquid containing small amounts of metals, cyanide and
chromate and larger amounts of soluble salts such as sulfate
and chlorides, and (2) sludge containing metals, phosphate,
carbonates, flocculating agents, etc. The liquid, if large
in volume may be concentrated further by evaporation,
reverse osmosis, ion exchange, or some other process
followed by a further purification to reduce the metal
effluent to a negligable value. The liquid may
alternatively be passed through a salt loaded ion-exchange
column to remove all traces of heavy metals and yield an
effluent containing essentially soluble salts that may be
discharged to the ocean if not to a stream or sewage
150
-------
facility. Alternatively, solutions of soluble salts may be
evaporated to dryness and the solid salt contained or fixed
in cement, etc.
Sludge, obtained either directly from waste water or from
ion-exchange regenerants, cleaning and pickling baths, etc.,
would need to be reclaimed for metal values or the metal
salts separated out for return to process tanks in order to
provide a closed or recycle system.
Thus, to attain the ideal of providing a system where input
is energy and materials and output is solely a finished
product will require further research and development,
considerable ingenuity, and expert engineering and design.
However, the capability for progressing towards this goal is
available.
151
-------
SECTION VIII
gQ§T§x_gNERGYr AND NONWATER QUALITY ASPECTS
Introduction
In this section, costs associated with the degree of
effluent reduction that can be achieved by exemplary
treatment methods are discussed. The nonwater quality
aspects concerning disposal of solid waste and the energy
impact of the waste treatment technologies also are
discussed.
Treatment and Control Costs
Chemical Treatment to Achieve Low Levels of Pollutants
BPCTCA Limitations (Table_l)_- Costs associated with control
technology consistent with the exemplary practice of
chemical treatment in 32 plants averaged $1.06/1000 liters
treated with a standard deviation of $1.91/1000 liters
(Table 28). Operating costs include a cost of capital equal
to 8 percent of the investment and depreciation equal to 10
percent of the investment.
The operating cost of waste treatment as a percent of cost
of electroplating for 13 companies is 7.4 percent with a
standard deviation of 5.4 percent. The figures were arrived
at from estimates by the plants themselves concerning the
relative cost of waste treatment.
The plot in Figure 13 shows the large variation in
investment costs for individual plants and reflects the
large deviations reported above. Thus, there are no typical
plants. Rather, costs are highly dependent upon local
conditions. Costs were calculated in terms of volume of
waste water treated rather than surface area finished
because costs are believed to be more closely related to the
volume treated. Water use is highly variable and relating
waste treatment costs to area finished would have provided
even more variable results. For a nominal water use of 80
liters/sq m (2 g/sq ft) the cost of $1.06/1000 liters is
equivalent to $0.085/sq m ($.0079/sq ft).
In addition to the cost data collected from plants with
waste treatment facilities, costs were also estimated by
modeling electroplating facilities together with waste
treatment facilities providing effluent that would meet
153
-------
TABLE 28 COSTS FOR WASTE TREATMENT FACILITIES
Plant
No.
20-24
33-24
33-26
36-12
33-2
33-4
8-5
6-37
19-11
15-3
9-7
>-. 4~9
ol 4-5
** 30-19
8-8
33-22
33-23
20-22
20-20
33-35
20-23
4-8
6-35
9-2
23-7
36-13
33-30
19-24
6-36
31-16
46-4
33-29
Investment
Processes (1971)
Plating Common Metals
Plating Common Metals
Plating Common Metals
Plating Com. , Free. Metals
Plating Prec. Metals
Plating Prec. Metals
Plating Prec. Metals
Plating Prec. Metals
Plating Prec. Metals
Plating Prec. Metals
Electropainting, Anodizing
Electroless Plating
Electroless Plating
Electroless Plating
Electroless Plating
Anodizing
Anodizing
Anodizing
Anodizing
Anodizing
Anodizing
Chemical Milling
Chemical Milling
Chemical Milling 2
Chemical Milling
Chemical Milling
Phosphating
Etching
Immersion
Printed Circuits 1
Electropolishing
Elect romachining
34,000
172,000
27,932
200,000
25,000
66,000
300,000
400,000
110,000
66,113
100,000
45,325
23,292
217,725
51,679
193,846
167,575
180,902
155,300
125,000
123,414
17,469
300,000
,908,000
582,306
29,232
94,500
295,615
58,985
,050,000
41,926
Operating
Cost/Year
(1971)
14,195
80,430
10,694
72,809
14,968
18,205
115,995
121,905
49,985
25,552
32,249
45,312
9,746
168,312
13,430
51,515
49,658
113,370
84,481
28,244
41,855
16,675
83,758
685,867
333,216
11,119
59,726
120,211
15,702
237,623
14,368
Hours
Operated
Per Year
4,800
4,000
7,200
7,520
1,025
1,800
2,400
2,250
2,000
2,000
4,000
4,000
4,000
8,400
4,000*
4,000
6,000
6,000
7,200
7,200
6,000
4,800
2,000
6,000
6,000
3,850
3,600
2,000
2,250
4,000
4,170
4,000
Volume to
Treatment
Plant, 1/hr
26,497
15,897
4,163
6,813
12,615
24,224
34,065
113,562
45,424
57,727
30,851
1,741
3,985
104,087
36,794
9,000
18,925
79,485
129,447
3,028
22,712
7,570
7,570
189,250
159,000
6,813
54,509
6,813
11,356
90,849
30,659
22,710
Volume to
Treatment
Plant, 1/yr
1.271 x 108
6.359 x 107
2.997 x 10?
5.123 x 10?
1.293 x 10?
4.366 x 10?
8.176 x 10?
2.555 x 108
9.08 x 107
1.154 x 108
1.234 x 108
6.964 x 106
1.594 x 107
8.743 x 108
1.471 x 108
3.600 x 107
1.136 x 108
4.769 x 108
9.320 x 108
2.180 x 107
1.362 x 108
3.634 x 107
1.514 x 107
1.136 x 109
9.540 x 108
2.623 x 10?
1.962 x 108
1.362 x 107
2.555 x 107
3.633 x 108
1.278 x 108
9.084 x 107
Invest-
ment/
1/hr
$ 1.28
10.82
6.71
29.36
1.98
2.72
8.81
3.52
2.42
1.15
3.24
26.03
5.84
2.09
1.40
21.54
8.85
2.28
1.20
41.28
5.43
2.31
39.63
15.36
3.66
4.29
1.73
43.39
5.19
11.56
1.37
Operating
Cost/
1000 liters
$ 0.30
1.26
0.36
1.42
1.15
0.42
1.42
0.48
0.55
0.22
0.26
6.51
0.61
0.19
0.09
1.43
0.44
0.24
0.09
1.30
0.31
0.46
5.53
0.60
0.35
0.43
0.30
8.83
0.62
0.65
0.11
Treating
Cost/
Processing
Cost
14
3
6
5
0.65
7
7.5
13
4.7
16
3
7.4
1.0
18
1.6
4.4
* Assumed 16 hours per day, 5 days per week.
-------
4 u
U1
U1
to
i_
o
o
T3
in
O
c
0>
E
U)
o>
10
Capacity Liters.hr
FIGURE 13 INVESTMENT COSTS OP WASTE TREATMENT PLANTS
WITH VARYING VOLUME CAPACITY
-------
BPCTCA standards. By modeling plants it was possible to
derive selfconsistent costs for various degrees of treatment
and for various plant sizes. Plants were sized according to
the number of employees, which is desirable if data are to
be used for cost impact studies. Tables 29 and 30 summarize
the results of one cost estimate.
The lowest investment cost of $22,980 is for a 5-employee
urban plant that precipitates metals, does not treat cyanide
or hexavalent chromium, and does not clarify. This plant
also has the lowest operciting cost of $12,29U/yr. The
highest investment cost of $378,455 is for a plant with 47
employees carrying out complete waste water treatment
including clarification and filtering of sludge. This plant
also has the highest operating cost of $157,894/yr. The
operating cost probably could be reduced somewhat by using a
filter press directly on the neutralized waste water.
However, this technology is not as well established as that
of clarification.
Costs per area are $1.02/1000 liters for the 5-man plant
neutralizing only and $1.09/1000 liters for the 47-man plant
doing complete waste treatment. These figures compare
favorably with the $1.06/1000 liters average value for the
plants listed in Table 28.
The operating costs as a function of plant size have been
plotted in Figure 14 and show that in the size range studied
costs are roughly linear with the number of employees. The
makeup of the production processes varies somewhat, both
with the extent of treatment and with plant size. Processes
using cyanide or chromate were not included where treatment
for cyanide and/or chromate was omitted. The smaller plants
were assumed to be concerned with electroplating only while
processes such as anodizing and electroless plating were
confined to the largest plant. Even among the smaller
plants there are some variations in plating processes. Some
of the 5-man plants included cadmium plating as a specialty
while the 10-man plant omitted cadmium but concentrated more
on tin plating. The product mixes listed are only one of
many sets that might have been chosen but reflect in general
the amount of finishing that can be accomplished in the
various sized plants with diverse operations. The amount of
waste water to be treated, and the amount of waste produced
are thus typical of the various size plants.
The productivity of a plant, measured in area processed/
hour will vary with the process mix even though the number
of employees is not changed. Thus, in Table 30 the 5-man
plants that require only coprecipitation (A) or cyanide
156
-------
TABLE 25
TREATMENT EQUIPMENT COSTS. VALUES IN U. S. DOLLARS. 1974
5 Employees
A.
B.
C.
D.
E.
f.
a.
Item
Concrete Holding Pits
Valves. Controls, Monitor* & Recorders
Stirrers
Pumps
Tanks
Clarifies
Lagoons (Soil)
Polishing Filters
Evaporator
Ion -exchanger
Sulfonator
Chlorinalor
Subtotal A
Treatment Building
Land Cost, Urban
Rural
Land Cost, Pirs& Lagoons. Urban
Rural
Subtotal B
Urban
Rural
Total A&B
Urban
Rural
Equipment Installation
Total C&D Urban
Rural
C&D, Less Clanfier, Urban
Sludge Filter (Option)
Urban
Rural
Total E&F
Urban
Rural
A
410
2,600
1,100
3,740
2,945
12,550
100
2,600
--
--
--
--
26,045
3,990
245
50
40
10
4,275
4,050
30,320
30,095
5,210
35,530
35,305
22, 980
3,860
3,890
39,390
39, 195
B
420
4,850
1,100
4,770
3,550
12, 550
130
2.700
--
--
--
3.550
33, 620
5,910
365
75
30
10
6,305
5,995
39,925
39,615
6,725
46,650
46.340
34,100
4.590
4.620
51.240
50.960
C
550
5,080
1.100
4,845
4.930
14,900
230
2,700
--
--
3,550
--
37,885
8,160
500
100
30
10
8,690
8,270
46.575
46, 155
7,580
54,155
53.735
30,255
4,850
4,880
59.005
58,615
D
605
7.215
1.100
6,300
5,300
14,900
230
3,300
--
--
3,550
3.550
46,050
9,960
610
125
45
10
10,615
10,095
56,665
56. 145
9,210
65,875
65, 355
50,975
4,300
4.330
70,175
69, 685
A
950
2,945
1,100
4,940
2.780
19. 100
100
3,150
--
--
--
--
35,065
9,660
595
120
225
45
10,480
9,825
45.545
44.890
7,015
52,560
51,905
33,460
7,750
7.880
60, 310
59,785
10 Employees
B
945
5,080
1,100
6,390
3.700
19,000
130
3.200
--
--
—
3,550
43,095
11,760
720
145
185
40
12,665
11,945
55,760
55.040
8,620
64.380
63, 660
4,538
7.720
7,850
72,100
71,510
C
1,335
5,310
1,100
6,800
4,605
22,400
230
5.100
--
--
3,550
--
50,430
15,060
925
185
285
60
16,270
15,305
66,700
65,735
10,090
76,790
75,825
54.390
7,745
7.880
84,535
83,705
D
1,350
7,445
1,100
7,890
5,105
22,400
230
5.100
--
--
3,550
3,550
57,720
16,710
1,025
205
275
55
18,010
16,970
75,730
74,690
11,545
87,275
86.235
64, 875
7,745
7.880
95,020
94,115
A
1.545
2.945
1.100
5,650
3,895
25,400
160
5,600
• -
—
--
--
46,295
13,020
795
160
240
45
14, 025
13,225
60,320
59,520
9,260
69,580
68,780
44,180
11,380
11,510
80. 960
80,290
20 Employees
B
1.525
5,310
1.100
7.110
3.440
25,400
160
6.500
--
—
--
3.550
54.095
18.540
1.135
230
370
75
20.045
18.845
74. 140
72.940
10,820
84.960
83,760
59. 560
11.240
11.490
96.200
95.250
C
1,725
S.310
1,100
7,880
5.715
28, 000
230
6,500
--
--
3,550
--
60,010
19,050
1,170
235
300
60
20,520
19,345
80,530
79,355
12,005
92,535
91,360
64,535
12,380
12,580
104,915
103,940
D
1.740
7,445
1.100
12.340
7,200
28, 000
230
6,500
--
--
3.550
3,550
71,665
21, 180
1,300
260
310
65
22,790
21,505
94.455
93. 170
14,335
108.790
107,505
80,790
12. 380
12, 580
121. 170
120,085
A
2.490
7.786
2.200
9,300
8.355
47. 100
470
14.000
146,000
550
..
--
243,200
29,520
1.810
365
475
95
31.805
29, 980
275.005
273.180
48,640
323.645
321,820
276.545
12,930
13,220
336,575
335.040
47 Employees
B
2.535
10,610
2,200
11,610
13.955
47, 100
470
14, 000
146.000
550
3,550
252,580
33, 150
2,030
410
520
105
35,700
33, 665
288, 280
286,245
50,520
338, 800
336,765
291.700
12.930
13,220
351.730
349, 985
C
2,890
9,690
2,200
11,880
12.230
49, 600
600
15,600
146.000
—
3.550
..
254.240
44.370
2,720
545
765
155
47.855
45.070
302,095
299. 310
50,850
352,945
350,160
30,335
12,550
13, 050
365. 495
363,210
D
2. MS
14.485
2,200
12, 740
11,730
60.600
710
15.600
146,000
3.550
3,550
264,130
45,360
2.780
560
805
160
48,945
46,080
313, 07S
310, 210
52,830
365,905
363,040
315, 305
12,650
13,050
378.455
376.090
B-Cyanide oxidation plus neutralization.
C'Chromate reduction plus neutralization.
D-Cyanide oxidation chromate reduction, neutralization.
-------
TABiiE 30
ANNUAL OPERATING COSTS. WASTE TREATMENT, U. S. DOLLARS. 1914
Ul
00
Fr:?.
20
2-
I'tban
u. -'os
19.706
:3.S97
:o.75i
36.513
34.S--5
4J.057
43, :52
50. >0
65.601
110.970
125 S12
122.495
142.^94
(L'iints Filter Pieal
Rural
lo 14$
Is. -50
19 553
2f .VI
36.3:3
34. 0:4
4: S5-1
4- ???
Sc.113
65.2S4
111' Oil
r.t as
121 366
141. 1SJ
O SO. IV^ahom for sludge containing 4 percent solidi
(ei Equal to lnvtitrrifi.! com
) Bated on a d.ag'wt raw c-f 2 gu/IOOQ iq ft plated and a wlution COM of 2. so/gallon
(11) Difference between urban and rural Is the COM of Kwage charge only
(U> Credited for the com at ilodge removal. UK In conjunction with Equipment Co«t Da
-------
160,000
S-i
>*
CO
[fl
o
o
00
c
OJ
ex
o
140,000
120,000
100,000
80,000
60,000
40,000
20,000
O Coprecipitation only
d Oxidation of cyanide +
Coprecipitation
A Reduction of chromate +
Coprecipitation
X Oxidation of cyanide, reduction
of chromate, Coprecipitation
10
20
30
40
50
No. of Employees
FIGURE 14, OPERATING COSTS RELATED TO PLANT SIZE AND
EXTENT OF WASTE TREATMENT
159
-------
oxidation plus coprecipitation for treatment of wastes can
process 75 sq m/hr, while 5-man plants that include chromium
plating and chromating (C,D) can process 100 sq m/hr.
It was concluded that costs for a captive or independent
shop would be similar if the waste treatment plant was sized
for the electroplating operation only. Captive
electroplating operations may discharge waste waters into
large systems that handle other plant wastes, but it would
be difficult to estimate what volume percent of waste water
typically came from the electroplating operations and what
portion of total waste treatment costs should be allocated
to them. Flow sheets of the waste treatment plants that
were costed are shown in Figures 14, 15, 16, and 17.
Another plant was modeled to ascertain investment and
operating costs of a medium large plant employing (1)
segregated chemical treatment of waste waters containing
individual metals, and (2) no discharge of pollutants.
Costs for a waste treatment employing destruction of
cyanide, reduction of chromate wastewaters and
coprecipitation of all metals were also developed as a basis
of comparison. Table 31 summarizes both investment and
operating costs of the waste treatment plants. Investment
and operating costs increase in the order
(1) Combined chemical treatment and
coprecipitation
(2) Segregated chemical treatment and
coprecipitation
(3) combined chemical treatment plus
end-of-pipe treatment to eliminate
discharge of pollutants.
The operating cost for combined chemical treatment and
coprecipitation is equivalent, to $1.41/1000 liters, which is
approximately 30 percent higher than the $1.09/1000 liter
figure for a similar model in the previous discussion.
While the two models are slightly different the difference
is mainly due to the fact that the two cost values were
arrived at by two cost analysts, each of whom assumed what
he considered were the most realistic costs. Such a
discrepancy is not surprising and indicates the necessity
for making analysis self-consistent. Thus, the results in
Tables 29 and 30 were made by one analyst and are set of
cost factors and the cases (1) through (3) above by another
analyst with a different, set of cost factors. The
160
-------
TABLE 31 INVESTMENT AND ANNUAL OPERATING COSTS TOR VARIOUS TYPES OF WASTE
TREATMENT FOR REPRESENTATIVE AVERAGE PLANT (38 EMPLOYEES)(a)
Electroplating
Atcas Schc "j:u- re-n. -, tit to -> of the \ IIIOIK trciimcnt i> stems used arc
m"/hr
m
775
775
775
775
Build lng uth.n shipped.
i for urban and
tnpmont. emju
Instrument
Equip-
ment6) Total
142.500 219,200
142.500 215,100
366,300 461.000
366 300 453,700
276.300 302.570
276,300 358,610
c.i Task 2. Equipment
Annual Annual
Deprccla- Interest
lion**', Charge(0.
dollars dollars
21,900 17,540
21,500 17,200
46,100 36,880
45,370 36,300
36,260 29.010
35,870 28,690
LaboKg).
dollars
Maintenance Electric
Charge(h), PowerO),
dollars dollars
28,000(a> 6,580 2600
28,000(fl
32,000
32,000
32,000
32.000
) 6,450 2600
13, 830 2860
13.610 2860
10.880 2970
10,760 2970
and tanks, etc. were sized to 150 percent of normal operating c
Water and
ChflrgesO).
dollars
1040
520
1040
520
1040
520
UsedW.
dollars
26.300
26,300
29. 820
29,820
28, 100
28, 100
apactty. Cons are based
Osmosis Water and R.O. Cor.c. Dried
(R.O.) Sewer Sav- E^aporatoi Salt 10:2.
Disposal^). rWn), R.O.O). CoW™, r.oafb. r-y^.
dollars dollars dollars dollars dollars da.ian
6460 — -- -- -- 11- .4^,
6460 -- — -- — lJ*.0*i
4400 15.700 9920 25,44-3 1670 15a. Z-j
4400 15,700 4960 25,440 16"0 2:2.73^
7400 -- — — — 147. c£3
7400 -- -- -- - 144.311
on an 8-hour day, S days/ week (I.e. , 2000 hi/year).
, plating and rinsing sequences, bath compositions, etc.
rural locations, respectively.
u-cnne, and other items associated with setting up a wasti
ips, pH and ORP monitor/
: treatment plant were arri
ved at by i
controllers, electric mixers, and other items which were sized for the overall plant
jsing a factor of 1.40 times the purchased
design). A factor of 1. 15 v
cost of the
main equipment items (e.g.. tanks, reaction vessels.
/as used on the R.O. unit and the R.O. concentrate evaporator, since the* ufiia
,;! TV i. a-r-? tr. a—-vn UVi charge u>cd \. as ?3.00/hr. a 1-3/4 man/day figure was used for Phase 1 and a 2 man/day figure was used for Phases IA and II.
,b* \ r-a.-tt -j-ve c^-arce of 3 percent of the total m\e!tment was employed.
(i* A pov,er cost oi ^ ^15 K*.hr was used. A \alue of UO gal water treated per Kwhr was used for Phase I calculations, this basic value was adjusted lower for the Increased processing uied in Phases IA and II.
,l\ T>e co«t oi\atcr vaj taken as JO.25 '1000 5al for both urban and rural plants. A sewer charge of $0.25 gal/1000 gal of water used in the WT operations was applied. These same costs were used to determine the urtngi achieved by the ute of the R.O. Ireatmem.
-------
High-end low-level control
High-and low-level control
, Stream
FIGURE 15-TYPICAL PLANT OPERATION
CO PRECIPITATION ONLY
- CHEMICAL TREATMENT (A);
162
-------
Acid-alkali
holding and
mixing
Cyanide
holding and
mixing
Neutralization
and
precipitation
Cyanide
oxidation
Filter)
Stream
FIGURE 16 .TYPICAL PLANT OPERATION - CHEMICAL TRFATMEI-- (B)-
CYANIDE OXIDATION AND COPRECIPITATION
163
-------
H and L
Acid-alkali
holding and
mix'ng
H and L
Chromium
holding and
mixing
Plating
Non-CN/Non-Cr
Flocculant
o o
Overflow
H and L
Filter
ir
To stream
Pump pump
Filter
Backwash
FIGURE 17. TYPICAL PLANT OPERATION - CHEMICAL TREATMENT (C)-
CHROMIUM REDUCTION AND CO PRECIPITATION
164
-------
H and L
Neutralization
and
precipitation
Filter Pump
H and L1
O,
I
Lagoon
Circ.'
Pump
*—O
NaOH
pH
CH
S02
Pump
Sump
Settling
Pump
Flocculant
Overflow
H and L
Filter
Pump
PumpQ Q Pump
Filter
Backwash
To stream
FIGURE 18 .TYPICAL PLANT OPERATION - CHEMICAL TREATMENT (D);
CYANIDE OXIDATION, CHROMIUM REDUCTION, AND
CO PRECIPITATION
165
-------
difference is actually much smaller than that of actual
costs reported in Table 28.
The use of a system to eliminate pollutant discharge
requires approximately twice the investment and operating
cost as a system for combined chemical treatment. The costs
can be reduced in some situations by in-process recovery
systems where the savings in chemicals more than compensate
for the costs of operating the recovery system. Evaporative
recovery systems were not economical to use in the plants
assumed since the value, bath concentration, and dragout of
chemicals were not sufficient to make their in-process
recovery worthwhile. The costs of installing more counter-
current rinse tanks, evaporative equipment, and steam more
than offset the savings in chemicals.
In-process reverse osmosis systems may have lower operating
costs than evaporative systems, but are still in a
demonstration stage for baths other than nickel. Use of
reverse osmosis systems on the nickel lines in the plant
model would not be expected to reduce overall in operating
costs by more than 5 percent.
Figure 19 shows the operations in the plant and a schematic
diagram of a segregated waste treatment system. Figure 20
shows a coprecipitation system and Figure 21 the
modifications made at the end of the coprecipitation system
with a reverse osmosis unit and salt evaporator to eliminate
the discharge of pollutants.
Preliminary calculations indicated that use of evaporators
in-process and at the end-of-pipe to eliminate pollution
would be more expensive than use of reverse osmosis at end-
of-pipe for the particular electroplating lines considered.
With the installation of a reverse osmosis system the
neutralizing agent was sodium hydroxide rather than the lime
used with the coprecipitation and segregated precipitation
systems. Lime was used to precipitate phosphate as well as
metals, but precipitation products with lime are likely to
foul the reverse osmosis membranes. These membranes remove
phosphate directly and lime is not needed.
The cost of a minimum batch treatment system was also
estimated. The layout is shown in the schematic diagram of
Figure 22. The system was sized to handle 4500 1/hr of
waste water, which is less than produced by the 5-man plant
discussed above. For calculating operating costs an 8-hour
day and 5-day week were assumed.
166
-------
SEGREGATED STREAM TREATMENT
Line 1
(Aut. RavM
CuCN 180 gph
Ni 270 cph Combined CuCN
Ct 10-, , |, * 18° * 55 = 235 SP*1 *"
A A 1730 cph
Line 1
Cu- \'i-Cr
Man Ra«k
<~r HO
CN
Cu PPP.
NiNeut
PPT
it
* A 435
Lii'o J
Aut Raik
C rumaiL
Barrel
i~';;o Mate
Line 5
Man. CaJmm •
CX Line
&
Manual Hard Cr
1 i^T- 1
Vanual Rark
An Lid Line
Line 3
Lire y
Elc.tMc-
/.n(( M_, 3f,s ,-ph romhitud Cr Plat
fc 495+ 140 +75 = 710 gph """
Z.IIK i L hroinaie 110 ppli
* A 10oO gpli
Combined Zn{CN)2
ZHR i rhromate llu sjph
A A lu50 ^Ptl r*tr\i\
Cd(CN) 115gph "^
Cliruiiiiuni
Reduction
CN Desr,
&
Zn PPT
Cr Ntut
PPT
»- Underflow to Centrifuge #1
•-• Effluent to Stream
^ Underflow to Centrifuge /I
-—— »»- Effluent to Stream or Sewer
/rTentMX
~\.M) *" °"' S'Udl?ClOU?00riSl0ra?e
1
CN Dest
&.
Cd PPT
»- Clanfie
i. d-( hr.uiiaie 40 i^pii
A -A 4(KJj;ph Comb. Chtomate Streams
110 + 110 + 40 = 260 gph
i f 7S cph
Acid/AIk Streams 7060 gph
1730 + 995 + 1050 +1050
flr. Pip - Al CfiO cph
An .id - Al 130 uph
M Ac,t. - Al 3.5 cph ^ Combined Al Anod.
Zn Phosp. 130 gph
Clirom
Iteduction
A/A Neittraltza
and Precipnat
NCUC&
Elect. Ni 30 gph
A A 70i cph
Elect Ni 3i) gph
A 'A 375 gph
Raise pU to
13 0 to
Destroy
Complex
Cr, Zn, &
& PPT
tion
r
i . — •-=.
— »- Clanfier 1
C
t
i •
. /^""^
^i '"H1- 1 ^ idOJ/o Sludge to Lagoon Storage
^ UnderQcw to Centrifuge /I
| — ' ^ Effluent to Stream or Sewer
arificr — — ~ ^- Underflow to Centrtfugt /2
/f entri-\ 20^0 SlLtdge
*^ fuge I ^ To Lagoon Storage and
X/4/ Later Haul Away
/TemriN
\^ / 3 y To Lag00" Storage
FIGURE 19. PHASE I, IA, AND II MASTER FLOW PATTERN
-------
Clj
NaOH
00
Cone.
4(5 mg/1 CM
Combined Cjranide Streams 108 /, Ca
Cu » Zn •, Cd 288 "g/1 z"
235* 710 f 115 = 1060 gph S4 mg/1 Cd
HoSO«-
Combined Cr «• Chromate Stream
Or riatinc- 4;>S . 140 » 75 - 710 gph
Chroma! ing: 110 + 110 * 40 = 2SO gph
Total s^O cph
L1K-.C —
Combined Anodizing £ Zn Phocphating
•:«o » :so * 345 = S35 ,:pii
Zn rhoip. * 130 gph
NaOH — •.
Elect. Xi 150 gph
Nl rutirK ,t Acid 'Alk Streami
350 » 7060 gph
T T
Cyanide
Denuctlon
^^
i r802 ^-^
Chromium
1
NeutraUuilon
and
Precipitation
of Phosphatei
Destruction of
pH 13
HjS02 Lime. Ca(OH)2
I 1
^-^
,—
Combined
Neutralization
and
necipiuiion
or Sewer
-/ Clarlfler \
2H Solid!
Underflows
1 ( Centrifuge I «» 2«; slu
V J To Ugc
N»«_^' for Late
Tot « "410 gph
FIGURE 20. COMBINED CHEMICKL TREATMENT AND NEUTRALIZATION-PRECIPITATION
-------
(Ti
Combined Cyanide Streams
Cu + Zn + Cd
235 + 710 + 115 = 1060 gph
HjSC
Combined Cr Plating and Chromating Streams
Ct Plating: 495 + 140 t 75 « 110 gph
Chromating- 110 + 110 + 40 = 260 gph
Total 910 gph
Combined Anodizing aad Zn Phosphating Stream!
Anodizing- 260 » 230 + 345-835 gph
7-n Phosphating 130 gph
Total 965 gph
Electroleu Ni 150 gph
Nl Plating & Combined Acld/Alk Streams
Combined Acid 'Alk 7060 gph
Dried Salti
lot Haul-
Away Dupoial
udge
To LAgoon Storage
for Haul Away Diapoul
Ni Plating 350 gph
Total 1410 gph
FIGURE 21 COMBINED CHEMICAL TREATMENT AND PRECIPITATION FOLLOWED BY END-OF-LINE
REVERSE OSMOSIS TREATMENT FOR ZERO LIQUID EFFLUENT DISCHARGE
-------
Acid Alkaline
1000 gph
Cyanide
100 gph
—CftX'Qroate
100 gph
<
Q,
,
^
k
r
f" ' '
*
j
800g
800g
800g
o r\ r\~
duug
— ^5—
V3*
/Qv
Neutralization
i^.UUUy
m-^^... n i- <^ Effluent
vy Jlarifier x>
Slungp?
FIGURE 22. BATCH TREATMENT SYSTEM FOR SMALL PLANT
-------
Small Platers
Costs have been estimated for the 1-4 man shop and 5-9 man
shop and may be found with accompanying assumptions in the
following tables:
Sizing Assumptions
. 1-4 employee shop (3 employees)
. 30 sq m plated per hour
. 80 1/sq m per hour
. 1/4 of the flow is cyanide bearing (and can be
segregated)
. The cyanide concentration is 20 ppm
The concentrations in the rest of the flow are equivalent
to 100 ppm of FS+++
Engineering Assumptions
. Complete manual operation utilizing minimal equipment
. Store 1 day of cyanide containing waste and treat overnight
. Equalize flow in a tank corresponding to 1/2 of the
daily output. Operate in backmix with adjustment every
two hours.
. All adjustment from carboys or drums.
Manual_Handling pf chemicals Verification
Cyanide Total waste flow 2400 1/hr
Cyanide flow 600 1/hr
Total cyanide waste 4800 I/day
Total cyanide in waste 98 gm per day
Chlorine requirement approximately 700 gm per
day or 1.5 Ib
Using hypochlorite (1 Ib C12 1 gal hypochlorite)
1.5 gallons per day.
Using caustic 1 lb/1 Ib of chlorine - say,
1.5 Ibs/day
Neutralization (Assume that the caustic from cyanide treatment
is used in the first 1/2 day)
Total caustic required - about 2 gm per gm of iron (120/56)
1/2 day flow 9600 1 960 gm of iron
Caustic required - 2800 gm/or 4.5 Ib.
Additional - 4.5-1.5=3 Ibs.
Rest of day - 4.5 Ibs.
Total per day - 7.5 Ibs
O.K. to add by hand (drum of caustic - approximately 400 Ibs)
O.K. to use a small bucket (8 gals, approximately or 80 Ibs)
171
-------
Residence time - U hours (nominal or actual) for equalization
Egujpment_List
Equalization tank - 2500 gals.
Agitator - 5 HP
Chlorination tanks - 2 x 800 gals.
2 Agitators - 1 HP
1 Transfer pump
High level alarm - 3
Valves - 5
Other piping and supplies
Installation - 25%
$8500
Instrument
pH meter
colorimeter
400
200 600
Total $9100
Area required - 400-500 square feet (assumed available)
Assume that there is room for equipment, e.g. a 2500 gal. tank
of normal configuration is 6.51 in diameter and 10* in
height (without legs) .
Sizin3_Assumptions
5-9 employee shop (7 employees)
70 sq m plated per hour
80 1/sq m 5600 1/hr of flow
1/4 flow is cyanide bearing (and can be segregated)
Cyanide concentration = 20 ppm
The concentrations in rest of waste flow are equivalent
to 100 ppm FS+-H-
Engineering Assumptions
. Cyanide flow - 1400 1/hr - say, 350 gals/hr.
. Assume that a hand operation once a day is used for cyanide
(Automatic continuous unit would cost about $18,000-22,000).
. Equalize daily flow in a 1/2 day tank.
. Check for hand addition - or cheapest equivalent.
Hajjdling_Of_Chemicals
Cyanide . Cyanide total - 11,200 I/day 2800 gals. (3000)
. Total cyanide in wash - 22U gm/day
. Chlorine required - 1500 gm/day say 3.5 Ibs.
. Hypochlorite - 1 gal/lb of chlorine 3.5 gallons
172
-------
(can be added out of a plastic lined 55 gallon
drum with a hand pump)
Caustic - 3.5 Ibs.
Out of a 55 gallon drum ( 500 Ib) with a
scoop, (a big scoop is about 5 Ib)
2g_Adjust 2 gm per gm of iron
1/2 day flow (total) 22,400 1. (say 6000 gals)
Iron 2,210 gm
Caustic 4,500 gm 10 Ibs.
2 to 3 scoops.
Manual addition from a drum appears feasible.
Material handling equipment - 1 chlorine resistant
hand pump - say $200
Equipment List
1 Equalization tank - carbon steel 6000 gals. $ 4,100
2 Cyanide treat tanks - carbon steel, epoxy lined* 7,200
(3000 gal)
3 Agitators (1) 10 HP, (2) 5 HP (3500) (2 x 1000) 5,500
Transfer pump 300
High level alarms 400
Valves (5) 500
Other piping and supplies _,m-.-^300
18,300
Installation - 25% 4.600
Total $22,900
Instruments
Hand pump 200
pH meter 400
Colorimeter 29.0
$23,700
*Add 20% for epoxy lining.
If a 2 hour equalization is required
use a 3000 gal tank + 5 HP agitator (3000 + 1000) 4,000
instead of 4100 + 3500 (7600)
thus, 18300 - 3600 14,700
3.700
18,400
Save 4,500
Total 19^000
The total capital investment and operating and maintenance costs
for both size plants are as follows:
173
-------
No. of Capital Investment ($1000) Annual O&M Costs ($1000)
employees 80 1/sq m 160 1/sq m 80 1/sq m 160 1/sq m
min max miin max min max min max
1-1 9.1 13.7 13.7 20.5 3.9 6.5 3.9 6.5
5-9 23.7 35.6 35.6 53.3 4.3 7.1 4.3 7.1
New Source ^Performance_StandardsjNSPS^. New sources that
are required to meet the recommended standards of
performance have the opportunity of designing and building
plants that reduce water flow. Such systems as counterflow,
spray, and fog rinses, interlocks to provide water flow only
during processing sequences, drip tanks, etc., can be
provided. The capital investment for installing an extra 31
x 31 tank in each rinsing sequence of a plating line to
reduce further the water use in counterflow rinsing is of
the order of $3,000. The plant modeled in Figure 18 has 22
rinses so adding one more tank for each rinse would increase
capital investment $81,000 for a total of $300,200 for
combined chemical treatment and precipitation in an urban
plant. It is probable that water use can be reduced 100
percent by installing only half this number of tanks at a
cost of $40,000 or an increase in capital investment of 18
percent over a plant meeting BPCTCA standards. Operating
costs would increase $7200/yr minus a credit of $520 for
water and sewer charges or $6680/yr. The increase in
operating cost is 6 percent as compared to those for a plant
meeting BPCTCA standards.
No Discharge of Pollutants
The elimination of liquid discharge from electroplating
processes has not been demonstrated with present technology.
Anticipating that future development will make this
elimination possible, it is desirable to have a rough
estimate of the cost impact of doing this. Technically,
evaporative recovery, reverse osmosis, and ion exchange can
concentrate wastes after which the concentrate can be
evaporated essentially to dryness. Purified water can be
returned to process. Approximate cost analysis have been
made for a medium large plant 240 sq m (2600 sq ft) per hour
assuming use of 80 liters/sq m of water. The effects of
closing the liquid loop without a purge on the buildup of
impurities are not known and the cost of solving problems
connected with impurity buildup will depend greatly upon how
much impurity must be removed, the development of efficient
systems for their removal, and how many of the components
that are recovered can be recycled rather than discarded.
To determine the cost effectiveness of various control and
treatment alternatives much of the data developed for Plant
174
-------
33-1 in Phase I was used. For those examples involving
evaporative recovery, an additional investment of $150,000
was allowed for a unit to evaporate concentrate to dryness.
Results of the calculations are shown in Table 32. A
finishing cost of $2.70/sq m ($0.25/sq ft) is equivalent to
$644/hr, and all of the projected costs for waste treatment
are less than 10 percent of this figure. Of course, the
$2.70/sq m figure is too high for some processes, but
provides a basis for at least a rough estimate of the cost
impact of waste treatment.
Nonwater. Quality Aspects
Energy Requirements
Introduction. Energy requirements will be discussed for
chemical treatment, evaporative recovery, ionexchange, and
reverse osmosis.
Chemical,, Treatment. Energy requirements for chemical
treatment~are low,"the main item being electrical energy for
pumps, mixers, and control instruments. Electrical costs
have been tabulated for several plants in Table 33. Data
for Plants 33-1 through 33-6 were obtained from the Phase I
study. Results indicate that approximately 5 percent of the
waste treatment cost is for electric power.
It is estimated in the Phase I study that electrical energy
for treating 2.271 x 10* liters per hour by a reverse
osmosis unit for 4000 hours per year would cost $6,400. The
electrical energy cost is therefore 7.045 x 10-s. The
liters per year processed by all plants listed in Table 61
add up to 3.964 x 10« liters and the cost of electricity for
processing this water by reverse osmosis is $279,200. The
total electrical cost for chemical treatment for the plants
listed in Table 31 is $75,330. These figures can be used to
roughly estimate the increases in electrical power
requirements in going to a system with no liquid effluent.
For best practical control technology currently available
the electrical cost would be essentially that of current
estimates or $75,330. For the best available technology
economically achievable the combination of chemical
treatment and reverse osmosis plus evaporation of the
concentrate (that would require little electrical energy)
the electrical cost would be $75,330 plus $279,200 or
$354,530. The ratio of $354,530/75,330 is 4.70. On this
basis going to a system without discharge of liquid effluent
will increase the use and cost of electrical energy 5-fold.
175
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TABLE 32 COST EFFECTIVENESS OF
CONTROL ALTERNATIVES
(247 Sq M/Hr)
Type of Control
Water Operating
Investment Operating Treated Cost per
Cost Cost/Year 1/Hr 100 Sq M
Plant 33-1
Rinse System - $264,274
Chemical treatment
Three countercurrent 330,000
rinses - chemical
treatment
Single stage evapor- 890,000
ators (21 units)
Dry evaporator
Five single stage 400,000
evaporative units
and one vapor com-
pression unit - dry
evaporator
Chemical treatment 560,000
plus reverse osmosis
Sludge drier and dry
evaporator for
concentrate
$112,361
121,387
327,895
109,913
161,328
25,210
9,766
$17.30
18.68
50.47
16.92
24.83
176
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TABLE 33 COST OF POWER RELATIVE TO TOTAL OPERATING
COST FOR CHEMICAL TREATMENT
Plant
No.
33-1
11-8
36-1
20-14
20-17
3-4
33-3
33-6
33-22
20-20
20-22
33-24
36-12
33-2
33-4
8-5
6-35
30-19
Processes
Plating Cu, Ni, Cr, Zn
Plating Cu, Ni, Cr, Zn
Plating Cu, Ni, Cr, Zn
Plating Cu, Ni, Cr, Zn
Plating Cu, Ni, Cr, Zn
Plating Cu, Ni, Cr, Zn
Plating Cu, Ni, Cr, Zn
Plating Cu, Ni, Cr, Zn
Anodizing
Anodizing
Anodizing
Plating Common Metals
Plating Precious Metals
Plating Precious Metals
Plating Precious Metals
Plating Precious Metals
Chemical Milling
Chemical Milling
Electric
Cost/Year
$ 4,100
668
5,220
6,000
8,940
600
240
1,460
1,948
4,763
12,623
1,212
1,894
1,082
120
16,239
3,897
4,330
x - 4,185
a = 4,454
Waste
Treatment
Operating
Cost/Year
$112,361
391,406
221,009
93,240
798,840
4,064
18,019
77,460
51,515
83,481
113,370
80,430
72,809
14,968
18,205
115,995
83,758
168,312
x = 139,957
a - 187,688
Electric
Cost x
100/Waste
Treatment
Cost
$ 3.65
0.17
2.36
6.44
1.12
14.76
1.33
1.88
3.78
5.71
11.13
1.51
2.60
7.23
0.66
14.00
4.65
2.57
x = 4.75
a = 4.44
177
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Evaporative Recovery. From the Phase I report the cost of
steam for operating a 300 gph single-stage evaporator is
approximately $2100/yr corresponding to approximately
1,900,000 Ib of steam. The single-effect evaporators
require considerable energy. This requirement can be
diminished by use of multiple stage or vapor-compression
evaporators.
Ion Exchange. The few pumps required for ion-exchange
systems should consume very little power.
Reverse Osmosis. The energy requirement for reverse osmosis
systems is the electricity for operating the high pressure
across the membrane and for operating low pressure transfer
pumps. The estimate is $6400/yr for a 6000 gph facility
operating 4000 hours/yr.
Impact of Power Requirements for Waste
Treatment. Domestic production of electrical energy in 1971
was 1.717 x 10*2 kwh. For the plating industry the
electrical energy requirement is estimated to be 9.75 x 108
kwh. The electroplating industry as a whole is estimated to
consume no more than twice this value, which would be 1.950
x 10» kwh. The percentage of annual power that is used for
electroplating operations should be no more than:
1.950 x 10»i/1.717 x 10»2 = 0.114 percent.
Power for pumps, lights, fans, etc., and waste treatment
should not more than double this figure to 0.228 percent.
Cost of Recovery of Metal Values from Sludge
Reference (32) is a report on the feasibility of recoverying
metal values from sludge by digesting the sludge with acid
to dissolve it followed by electrolysis and neutralization
procedures to recover metal values. The case considered was
a sludge containing primarily copper, nickel, chromium, and
zinc values. A cost estimate was included for a small plant
that would treat 45 kg of dry sludge during a 12 hour day to
yield 2.27 kg of copper, 0.09 kg of nickel, and 4.54 kg of
chromium. However, the chromium was obtained as an oxide
mixed with some iron. The investment for a small plant was
estimated to be $15,130. Operating cost per day was
estimated to be $85.30. This did not include a cost of
capital, which if assumed to be eight percent of the
investment per year, would raise the daily operating cost to
$91.35. The total weight of metal recovered per day is 6.90
kg so that the cost is estimated to be $13.23 kg. The cost
178
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is obviously very high compared to market prices so that the
small operation would be far from economic. Undoubtedly,
the cost of processing would be less with a larger
installation, but if more than one electroplating
installation were served there would be an additional cost
for transporting sludge to the recovery operation.
179
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SECTION IX
BEST PRACTICABLE CONTROL TECHNOLOGY CURRENTLY
AVAILABLEl GUIDELINEST^AND LIMITATIONS
Introduction
The effluent limitations which must be achieved by July 1,
1977, are to specify the degree of effluent reduction
attainable through the application of the best practicable
control technology currently available. Best practicable
control technology currently available is generally based
upon the average of the best existing performance by plants
of various sizes, ages, and unit processes within the
industrial category and/or subcategory.
Consideration must also be given to:
(a) the total cost of application of technology
in relation to the effluent reduction benefits
to be achieved from such application
(b) the size and age of equipment and facilities
involved
(c) the processes employed
(d) the engineering aspects of the application of
various types of control techniques
(e) process changes
(f) nonwater quality environmental impact
(including energy requirements).
The best practicable control technology currently available
emphasizes treatment facilities at the end of a
manufacturing process but includes the control technologies
within the process itself when the latter are considered to
be normal practice within an industry.
A further consideration is the degree of economic and
engineering reliability which must be established for the
technology to be "currently available". As a result of
demonstration projects, pilot plants and general use, there
must exist a high degree of confidence in the engineering
and economic practicability of the technology at the time of
commencement of construction or installation of the control
facilities.
181
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Industry_Category and Subcateqgry Covered
The pertinent industrial category is the electroplating
category which is part of the metal finishing industry.
This category includes plants using electroplating processes
as defined by SIC 3471 (1972) and includes the pretreatment
and posttreatment steps associated with the electroplating
processes.
The identification of best practicable control technology
currently available and recommended effluent limitations
presented in this section cover the subcategories of
electroplating of common metals and electroplating of
precious metals. Guidelines for the electroplating of
copper, nickel, chromium and zinc were developed in another
effort and the results may be found in the "Development
Document for Effluent Limitations Guidelines and New Source
Performance Standards for the copper. Nickel, Chromium, and
Zinc Segment of the Electroplating Point Source Category"
March 1974. Guidelines for the remainder of the metal
finishing industry will be developed in a similar document.
Identificatign^of_Best_Practicable_Control
Technology^Currently Available
The best practicable control technology currently available
for the electroplating of common and precious metals is the
use of chemical methods of treatment of waste water at the
end of the process combined with the best practical in-
process control technology to conserve rinse water and
reduce the amount of treated waste water discharged.
Chemical treatment methods are exemplified by the
segregation of the acid-alkali stream, cyanide stream and
chromium stream. Cyanide is destroyed by oxidation and
hexavalent chrominum is reduced to the trivalent state. The
waste streams are then combined and there follows pH.
neutralization and coprecipitation of metals as hydroxides
or hydrated oxides with settling and clarification to remove
suspended solids prior to discharge or prior to dilution
with other nonelectroplating process water before discharge.
However, the above technology cannot achieve zero discharge
of metals because of finite solubility of the metals. In
addition, it is not practicable to achieve 100 percent
clarification and some small amount of metal is contained in
the suspended solids. By optimum choice of pH and efficient
clarification it is possible to achieve a significant re-
duction in the metal pollutional load.
182
-------
Although coprecipitation of metals as hydroxides or hydrated
oxides is most widely practiced in the electroplating
industry, much greater reduction could be achieved by stream
segregation and sulfide precipitation. However, there are
greater problems in the disposal of sludge sulfide
precipitation. Metallic sulfides are much less soluble than
hydroxides and offer a far greater level of removal.
Best practicable control technology currently available also
includes water conservation through rinsing. A water use of
160 1/m 2/operation (H gal/m2/operation) has been estimated
as that achievable by the industry. This figure precludes
the use of countercurrent or series rinses. Exclusive use
of single stage rinsing will not meet this water use. It
has been calculated that for 186 sg m/hr (2000 sq ft/hr)
proudction the rinse water need for various rinsing
techniques are:
1 - single rinse 1/hr 499,620 (132,000 gal/hr)
2 - tank countercurrent 2800 1/hr (1UO gal/hr)
3 - tank countercurrent 477 1/hr (126 gal/hr)
H - tank countercurrent 201 1/hr (53 gal/hr)
5 - tank countercurrent 121 1/hr (32 gal/hr)
This corresponds to a water use of:
1 - single rinse 2686 l/m2 (66 gal/sq ft)
2 - tank countercurrent 15 l/m2 (.37 gal/sq ft)
3 - tank countercurrent 2.56 l/m2 (.06 gal/sq ft)
U - tank countercurrent 1.2 l/m2 (.026 ga/sq ft)
5 - tank countercurrent .65 l/m2 (.016 gal/sq ft)
A 3 stage series rinse consumes approximately the same
quantity of water as a 2 - stage countercurrent.
The 160 Im2 (U gal/sq ft) takes into account the
contributions made by the pretreatment steps of alkaline
cleaning and acid pickling and allows some use of single
rinses.
Good management techniques considered normal practice in the
industry are:
(1) Manufacturing process controls to minimize
dragout from concentrated solutions such as
(a) proper racking of parts for easy
drainage
183
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(b) slow withdrawal of parts from the
solution
(c) adequate drip time or dwell time
over the tank
(d) use of drip collection devices.
(2) Effective use of water to reduce the
volume of effluents such as
(a) use of rinse water for makeup of
evaporation losses from solutions
(b) use of cooling water for noncritical
rinses after cleaning
(c) use of treated waste water for
preparing solutions for waste-
treatment chemicals.
(3) Recovery and/or reuse of waste water
constituents such as
(a) use of reclaim tanks after metal
finishing operations to recover
concentrated solutions for return
to the plating tank to make up
evaporation losses
(b) reduction in waste water volume by the
use of at least two series flow rinse
tanks after each finishing operation
with return of as much rinse water as
possible to the finishing tank.
Rationale rfor Selecting the Best Practicable
Control_Technoloqy Currently Available
Identification of Best Waste Treatment Facilities
There are approximately 20,000 facilities for electroplating
and metal finishing in the United States and identification
of the best plants within the short period of this study
required a rational screening and approach. The initial
effort was directed toward identifying those companies that
had well engineered and operated electroplating process and
waste treatment methods. Such companies were identified on
the basis of personal knowledge, and referrals by people
well acquainted with the industry (EPA regional
184
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representatives, state pollution control authorities, trade
associations, equipment suppliers, consultants) . Three
hundred nine companies were identified based on referrals by
cognizant people associated with the industry (EPA. regional
representatives, state pollution control authorities, trade
associations, equipment suppliers) and review of permit
applications were distributed geographically. About 90
percent of the companies were in the three principal regions
expected to have high concentrations of electroplating
industry: 38 percent in the Northeast (principally EPA
Regions I, II and III); 28 percent in the Midwest (EPA
Region V) ; 25 percent in the Southeast (Region IV).
Of these leads, the 129 companies initially contacted by
telephone were primarily in the principal electroplating
regions. The telephone contacts were made to verify the
existence of adequate waste treatment facilities and the
type of plating operations pertinent to Phase I. Sufficient
information was obtained to characterize the facility and if
pertinent to the scope of coverage desired operational data
were obtained. From the questionnaires returned, seventeen
plants were identified which are engaged in the
electroplating of the metals concerned. These seventeen
plants are 6-7, 6-37, 11-8, 15-3, 19-11, 19-24, 20-17, 20-
24, 23-7, 30-3, 30-21, 33-2, 33-5, 33-20, 33-2U, 36-1, and
36-12. Visits were made to six plants (11-8, 33-20, 36-1,
36-12, 33-5, 15-3) for the gathering of samples and plant
data on several of the processes at these plants and
analyzed. Of these six, three (11-8, 33-20, and 36-1) were
studied in great detail. The results of these visits are
compiled in the following pages.
Plant 11-8
Plant 11-8 is representative of a large job shop (about 170
employees) which contracts to do electroplating of copper,
nickel, chromium, zinc, and cadmium, along with chromating
and phosphating on a large variety of parts. This plant
operates automatic rack, automatic barrel, manual hoist and
barrel lines, and other specialized manual lines.
Plant 11-8 was identified as achieving good waste-effluent
control by a combination of batch and continuous chemical
treatment on mixed wastes from the electroplating
operations. Waste treatment also includes the special in-
process control operations of ion exchange and evaporation.
A combination anion-cation exchanger processes the chromium
plating rinse waters from three separate lines for reuse. A
300-gph evaporator serves two large zinc plating lines on an
open loop basis.
185
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Most of the plant processes were operated 20 hours a day
(two 10-hour shift basis), with some plating units running
as many as 22 hours a day. Working hours were also
staggered to some extent, so that the load on the waste
treatment plant was fairly uniform throughout the entire
day.
Figure 23 is a schematic presentation of the waste treatment
operation at Plant 11-8. The triangulated points indicate
waste stream sampling points. The figure also shows the
estimated flow rates for the various waste streams.
Effluent analyses are presented in Table 34. The table
shows data for the first 24-hour period, the second period
of 9 hours, and the combined period of 33 hours. As the
average flow rates for the 24-hour and 9-hour periods were
very close, (i.e., 25,565 gph and 25,000 gph, respectively)
the chemical analyses for the two periods were combined in
the ratio of their total flows to provide an analyses for
the combined period. The weighted percentages employed to
arrive at an analysis for the total 33-hour period were as
follow:
1st period 613,600 x 100 = 73.17 percent
838,600
2nd period 2.2.5x000 x 100 =26.83 percent
838,600
Cyanide_Treatment^System_Results
Cyanide waste treatment is carried out automatically on a
batch basis in either of two 25,000 gallon tanks. Sodium
hydroxide is automatically added by a pH-controller unit,
while an oxidation-reduction potential unit (ORP) controls
the chlorine addition. Each tank is equipped with its own
control units.
Samples of several batches of untreated cyanide wastes were
taken from the tank contents while the tank was filling at
sample point 1. Samples of treated batches of waste were
taken upon completion of the destruction step when the tank
was being emptied at sample point 2. Data on sampling times
and the compositing of grab samples taken from the cyanide
waste stream before and after treatment, along with
analytical results, are given in Table 35. The percent
cyanide destruction was as follows:
38^.9
42.T x 100 = 92.4 percent
186
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TABLE 34 COMPARISON OF TREATMENT RESULTS WITH EFFLUENT GUIDELINE REQUIREMENTS
FROM SAMPLING PROGRAM ON PLANT 11-8 OPERATIONS
Metric
Units
Guideline
Item
Cd
CrVI
Cr,
total
Cu
Fe
Ni
Zn
CN
(oxid)
CN,
total
POi
TSS
pH
(a) The
(b) The
Value,
mg/sq m
80
8
80
80
160
80
80
8
80
160
3,200
6.0 to 9.5
English
/•„ N
24-Hour Period^'
Units
Guideline Cone, in
Value,
lb/106 sq
16.4
].6
16.4
16.4
32.7
16.4
16.4
1.6
16.4
32.7
654
—
water/area processed
effluent
sample for
Effluent^),
ft mg/1
0.21
0.03
0.05
0.11
0.11
0.60
0.74
0.47
0.48
0.08
230 (b)
—
relationships for
the 24-hour period
Effluent
Discharge
mg/
sq m
27.0
3.9
6.4
14.1
14.1
77.0
95.0
60.3
61.6
10.3
(b)
—
the
was
lb/10b
sq ft
5.5
0.80
1.31
2.9
2.9
15.8
19.5
12.35
12.6
2.1
(b)
—
r _\
9-Hour Period^'
Cone.
Combined
33-Hour Period(a)
Combined
Effluent Weighted Effluent
in Discharge Cone, in Discharge
Effluent*^), mg/
lb/10b Effluent, mg/
mg/1 sq m sq ft
0.21
0.03
0.03
0.16
0.03
0.60
0.35
0.26
0.27
0.05
<10
8.8
three periods are
collected
22.7
3.2
3.2
17.3
3.2
64.7
37.8
28.1
29.1
5.4
<1,079
—
given in Table
in a 2-1/2-gallon jug
4.7
0.66
0.66
3.5
0.66
13.2
7.7
5.8
6.0
1.1
<221
— —
11-8-11
to which
mg/1
0.21
0.03
0.045
0.12
0.09
0.60
0.635
0.41
0.42
0.07
(b)
— —
later
about
sq m
25.7
3.7
5.5
14.7
11.0
73.3
77.6
50.1
51.3
8.6
(b)
__
lb/106
sq ft
5.3
0.76
1.13
3.0
2.3
15.0
15.9
10.3
10.5
1.8
(b)
__
in the report.
20-25 pellets of
sodium hydroxide had been added by Plant 11-8 personnel to preserve the cyanide. Sample collection was made
using the Plant 11-8 Sigmamotor WA-2 composite sampler which withdrew a small volume of effluent at 5-minute
intervals. The pH of the collected sample for the 24-hour period (volume - 2.5 gallons) was 10.8. The pH of a
grab sample of effluent taken during this period by Plant 11-8 personnel was measured at 8.5. The presence of
the caustic pellets in the collection jug is believed responsible for the high TSS value, as it caused precipi-
tation of solids which analyzed mostly calcium and magnesium. Analysis of the suspended solids (TSS) for the
24-hour period showed 51.0 mg/1 of calcium and 42.0 mg/1 of magnesium. Durirg the second period, the sample
was collected in a container without caustic pellets and a TSS value of <10 mg/1 was obtained. The actual
collection time for the second period was from 0810 to 1610 (6/7/74), as a container without caustic pellets
was used to replace the caustic containing jug put into use at 0700 (6/7/74).
-------
TABLE 35
CYANIDE TREATMENT RESULTS
Sample No. and Description
Concentration, mg/1
Total
Cyanide
Oxidizable
Cyanide
11-8-CN-B-COMP (Before CN Treatment)
This was a composite of 2 grab
samples mixed in equal proportions;
the samples were taken at the
following times: 6/6/74 (0845) and
6/7/74 (1035).
43.0
42.1
11-8-CN-A-COMP (After CN Treatment)
This was a composite of 4 grab
samples mixed in equal proportions;
the samples were taken at the
following times: 6/6/74 (1058) and
6/7/74 (0100,0940, and 1450).
3.2
3.2
188
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*>.
fr-
VO
Cyanide A
25,000 gal
Strong
Acid
Dilute Acid-Alkali
^18,000
Neutralization
120,000 gal
Clarifier
60,000 gal
Sludge
To Lagoon
^25,500 gph
FIGURE 23
Strong
Alkali
WASTE TREATMENT OF PLANT 11-8 EFFLUENTS EY COMBINATION BATCH-CONTINUOUS CHEMICAL TREATMENT
Flows shown are approximate for treatment of 25,500 gph effluent.
-------
Results^of ^Chromate Reduction
As indicated in Figure 23, treatment of the chromium wastes
is carried out automatically on a batch basis in either of
two 6000-gallon tanks using sulfur dioxide (SO2) and
sulfuric acid. The acid and SO2 additions are automatically
controlled by- the use of pH and ORP units, respectively.
Grab samples of several batches of untreated chromium stream
wastes were taken while the tank was filling at sampling
point 3. Grab samples of treated batches of waste were
taken upon completion of the reduction step when the tank
was being emptied at sampling point U.
Data on sampling times and compositing of grab samples taken
from the chromium waste stream before and after treatment,
along with analytical results, are given in Table 36. The
percentage reduction of Cr*6 to Cr*3 was as follows:
2^97
3.00 x 100 = >99.0 percent
This result indicates very efficient reduction of hexavalent
chromium with the batch SO2 treatment.
The arrangement of Plant 11-8's piping did not permit
sampling of the acid/alkali stream before treatment.
Analysis of samples taken at points 5 and 6 give total metal
concentrations before and after clarification. See Table 37
Effectiveness of Clarifier^in Lowering^Waste
Content of Effluent Stream
An analysis of the metal content of grab sample from the
neutralization tank contents (sample taken at Triangulated
Point 5, Figure 23) was carried out to determine the
effectiveness of the precipitation and clarification
procedures in removing wastes from the effluent stream. The
analytical data on the effluent stream before and after
clarification are shown in Table 37. Although a grab and
composite sample are being compared in Table 37 , it gives an
approximation of clarifier efficiency. The reduction for
the various metals ranged from 89 to 98 percent, which
indicates that the clarifier was doing an effective job in
lowering the waste content in the effluent stream.
Sampling Effluent
190
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TABLE 36 CHROMIUM TREATMENT RESULTS
Concentration, mg/1
Hexavalent Total
Sample No. and Description Cr Cr
11-8-Cr-B-l (Before S02 Reduction) 3.1 5.2
[This was a composite of 4 grab
samples taken at the following
times: 6/6/74 (0900, 1310, 2250)
and 6/7/74 (0710); equal amounts
from each grab sample were used
to make the composite.]
11-8-Cr-A-l (After S02 Reduction) <0.03 17.0
[This was a composite of 7 grab
samples mixed in equal proportions;
the samples were taken at the following
times: 6/6/74 (0914, 1113, 1330, 1540,
and 2230) and 6/7/74 (0745, 1535).]
191
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TABLE 37 EFFECTIVENESS OF CLARIFIER IN LOWERING THE
METALLIC PRECIPITATE CONTENT IN THE EFFLUENT
STREAM
Metal Concentration, mg/1
Total
Item Cu Cr Ni Cd Fe Zn
Neutralization Tank Effluent 1.64 1.95 5.65 3.10 7.81 15.0
(Grab sample taken 6/6/74 at 1415)
Clarified Effluent 0.11 0.05 0.60 0.21 0.11 0.74
6/6/74 (0700) to 6/7/74 (0700)
Reduction in Metal Content of Effluent 93.3% 97.4% 89.4% 93.2% 98.6% 95.1%
192
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Plant effluent was sampled with a Sigmamotor WA=2
(Sigmamotor Inc, Middleport, New York 14105) sampler
belonging to Plant 11-8. This unit collected about 33 ml of
effluent at 5.5 minute intervals throughout the first 24-
hour sampling period from 6/6/74 (0700) to 6/7/74 (0700) .
The rate of withdrawal was about 1 ml per second. The
frequency of effluent withdrawal was increased for the
following 9-hour sampling period in order to provide a
greater amount of sample. About 33 ml of effluent were
withdrawn at about 2.5 minute intervals, at a rate of about
1 ml per second. The effluent sampling location is shown as
Triangulated Point 6 on the waste treatment flowsheet
presented in Figure 23.
Waste Stream Flow Data
Effluent Flow Data
Instantaneous effluent flow rates were read periodically
from a recording chart and cumulative flowmeter readings
were also taken periodically during the visit.
Instruments for measuring and recording instantaneous flow
and for indicating cumulative volume were operating in the
plant. The cumulative meter was used to calculate average
flow except during a malfunction from 0700 to 1800 on 6/6/74
for which period readings on the instantaneous flowmeter
were averaged.
Summarized effluent flow data for the 24-hour and the 9-hour
sampling periods are presented in Table 38.
Intermediate Stream Flow Data
The following estimates of flow rates for the intermediate
streams making up the total plant effluent were obtained
from discussions with plant personnel:
Cyanide Stream 5,200 gph
Chromium Stream 2,300 gph
Acid/Alkali Stream 18,000 gph
Combined Stream Total 25,500 gph
Area^Processed
The estimation of the areas processed at Plant 11-8 was
based on measurements on representative parts on each line
and tying in these areas with processing rates. The
individual part areas, together with data on the number of
parts processed per unit time either on racks or in barrels,
193
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TABLE 3 8
SUMMARIZED EFFLUENT FLOW DATA
Time Interval
Average Hourly
Total Flow, Flow Rate,
gal gph
6/6/74 (0700 to 1800)
6/6/74 (1800) to 6/7/74 (0700)
24-Hour Period
6/6/74 (0700) to 6/7/74 (0700)
9-Hour Period
6/7/74 (0700 to 1600)
Total 33-Hour Period
6/6/74 (0700) to 6/7/74 (1600)
289,600
324,000
613,600
225,000
838,600
25,565
25,000
25,410
194
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were used to determine an average value of area processed
per hour. This hourly value multiplied by the number of
operations on the line and then multiplied by the hours of
operation during the sampling period, gave the total
processed area for the particular line.
Summarized data on the areas processed on each of the lines
are presented in Table 39. The area processed on each part
was taken as the total area that was rinsed on the part.
Thus, with tubular products, in which the inner surfaces
receive little or no plate but are rinsed, the inner surface
areas were counted as processed area. The qualifying
operations in the overall plating or coating operations
carried out on each line are indicated in the line-
description column of Table 39.
Water^Use/Area,Processgd Relationship
Summarized data on water use/area processed relationships
for the Plant 11-8 operations during the three periods are
presented in Table HO.
SAMPLING AND ANALYSIS TOF PLANT 33-20
Introduction^and Rationale for Sampling PlantT33-20
Plant 33-20 is a medium-sized manufacturing facility for the
fabrication and assembly of refrigeration thermostats,
temperature controls, valves, and other hardware. The
captive electroplating shop when operating under normal two-
shift conditions employs about 16 people, but under the
reduced work load during the latter part of August when the
visit was made, the number of employees was down to 10. The
waste treatment plant, which is run in conjunction with a
water-purification operation employs one man on each of
three shifts, plus supervision.
The main operation producing effluents are two tin automatic
rack lines and several bright dipping processes on brass and
copper parts. Other operations contributing to waste
effluents include: zinc barrel and rack plating, copper
barrel and rack plating, cadmium barrel plating, tin barrel
plating, and nickel rack plating.
Plant 33-20 was identified as achieving good waste effluent
control by continuous chemical treatment on mixed wastes.
Figure 24 is a flow sheet for the waste treatment operations
at the plant. The Cyclator is a combination precipitation-
195
-------
TABLE 39
SUMMARIZED DATA ON AREAS PROCESSED ON VARIOUS PLANT 11-8 LINES
10
a\
m ,__, Total Processed Area During Period
Line Description
Zinc Automatic Rack Line
(Zn + Chromate)
Stevens Ni-Cr Automatic Rack Line
Cu-Ni-Cr Manual Hoist Rack Line
(Cu + Ni 4- Cr, Ni -f Cr, or Ni + brass)
Zinc Manual Hoist Rack Line
(Zn -i- Chromate)
Cadmium Automatic Rack Line
(Cd 4- Chromate)
Hard Chromium Rack Line
M&T Zinc and Cadirium Aut. Barrel Line
(Zn + Chromate)
VIP Zinc Automatic Barrel Line
(Zn + Chromate)
Cu-Ni and Cd Manual Barrel Line
(Cu 4- Ni or Cd 4- Chromate)
Nickel Manual Barrel Line
(Cu 4- Ni)
Phosphating Line
(Line uses barrels or baskets)
Combined Lines (Total Area Processed)
Number
of
Operations
2
2
2 or 3
2
2
1
2
2
2
2
1
—
XU LCU.
Area
Processed
per Hour,
sq ft/hr
570
1510
1530
270
550
2
1355
1835
885
360
1105
—
Period
6/6(0700) to
Hr of
Operation
20
20
22
12
12
15
22
22
20
10
16
—
6/7(0700)
Area,
sq ft
11,400
30,200
33,700
3,240
6,600
30
29,810
40,370
17,700
3,600
17,680
E194,330
Period
6/7 (0700 to
Hr of
Operation
9
9
9
9
—
9
9
9
9
9
9
—
1600)
Area,
sq ft
5,130
13,590
13,770
2,430
—
30
12,195
16,515
7,965
3,240
9,945
284,800
-------
TABLE 40
WATER USE/AREA PROCESSED FACTORS FOR THREE PERIODS
H
vo
Period
1st
2nd
Combined
Duration,
hr
24
9
33
Water Used
B-al
613,600
225,000
838,600
liters
2,319,410
850,500
3,169,910
Area Processed
sq ft
194,330
84,800
279,130
s q m
18,060
7,880
25,940
Water Use-
Area Factor,
gal/sq ft
3.16
2.65
3.00
1/sq -m
128.4
107.9
122.2
-------
OT
/^
\
j
1 Alkali-Cyanide ,
i Holding Tank {-
j ~14,000 gal |
L i
Liquid
Causti
ci2
'? T >..
-3600 gph
c
... !
Cyanide-
Treatment
Tank No. 1
~2800 gal
__
I
i
i
i
Cyanide
Treatment
Tank No. 2
-2700 gal
|Acid-Chromium i
Holding Tank
[ -13,000 gal
-2400 gph
Chromium
Treatment Tank
-4800 gal
Lime
Lime
Coagulant
i
i _ i. _.
\ | Mix
i Tank
/ ; -2600 gal
•
\
• I/
I
Solids to
FIGURE 24 WASTE TREATMENT OF PLANT 33-20 EFFLUENTS BY CONTINUOUS CHEMICAL TREATMENT
Flows shown are approximate for treatment of 6000 gph of effluent.
-------
clarification unit; it was 20 ft in diameter and 20 ft high.
The triangular points indicate waste stream sampling
locations. Estimated flow rates for the various streams are
also shown on the flow diagram.
The overall plant visit covered a period of 72 hours, or 3
separate days in which the treatment plant processed wastes
on the average of 7 hours each day, while the electroplating
and bright dipping operations required 17 hours each day.
The holding tanks served to collect and store wastes during
the low electroplating production hours when the treatment
plant was shut down and not processing wastes.
Cyanide^Destruction Results
Cyanide treatment is carried out on a continuous basis using
a series of two tanks; the wastes flow through Tank No. 1
and then Tank No. 2. As indicated in Figure 24r chlorine is
metered into the alkali-cyanide stream at a rate of about
8.4 Ib/hour and liquid caustic (50 percent NaOH) is added to
maintain the pH in the treatment tanks between 9.0 and 10.0,
and preferably between 9.0 and 9.5. The Tank No. 2 contents
are checked for pH hourly, and also checked by the ortho-
tolidin test for the persistence of residual chlorine
indicating completion of the destruction reaction. Chlorine
and/or caustic feed rates are adjusted manually. The total
retention time taking into account both treatment tanks with
an estimated alkali-cyanide stream flow of 3600 gph was
about 90 minutes.
Thirteen 1-liter samples over a period of four days were
taken at sampling point 1 of untreated cyanide wastes in the
holding tank.
Equal portions of these samples were combined to provide the
composite sample of untreated cyanide submitted for analyses
(Table 41, Sample No. 33-20-CN-B-1-COMP.).
The treated alkali-cyanide stream was sampled for three
consecutive days at sampling point 2 with a Sigmamotor WA-2
(Sigmamotor Inc, Middleport, New York 14105) unit which
collected about 42 ml of treated waste at 5.4 minute
intervals during the treatment plant processing periods.
Equal portions of these samples were combined to provide the
composite sample submitted for analysis (Table 41, Sample
No. 33-20-CN-A-1-COMP).
199
-------
TABLE 41
CYANIDE TREATMENT RESULTS
Sample
No.
Description
Concentration, mg/1
Oxidizable Total
Cyanide Cyanide
33-20-CN-B-l-COMP
33-20-CN-A-l-COMP
Composite Sample, before
cyanide treatment
Composite sample: after
cyanide treatment
67.0
0.01
67.4
0.05
200
-------
The low oxidizable cyanide content of 0.01 in the treated
cyanide stream shows that effective cyanide destruction was
achieved. The percent cyanide destroyed was as follows:
67.0 - 0.01
67.0 (100) = 99.98 percent.
This high percent removal further attests to effective
cyanide treatment at Plant 33-20.
Chromium^Reduction^Results
The treatment of the acid-chromium waste stream is carried
out on a continuous basis using a single flow-through tank
(4800 gal). Addition of the sulfur dioxide (SO2) is
controlled manually. An ORP unit is used to monitor the
reduction, and a reading of 400 mv is maintained. The
reduction is carried out at the pH of the incoming acid-
chromium waste stream, which normally runs about 0.8 to 1.0.
The retention time in the chromium treatment tank based on
an estimated flow of 2100 gph was 120 minutes.
Thirteen 1-liter samples over a period of four days were
taken at sampling point 3 of the untreated acid-chromium
wastes in the holding tank.
Equal portions of these samples were combined to provide the
composite sample of untreated chromium submitted for
analyses (Table 42, Sample No. 33-20-Cr-B-1-COMP) .
The treated acid-chromium stream was sampled for three
consecutive days at sampling point 4 with a Sigmamotor WA-2
unit which collected about 34 ml at 5.3 minute intervals
during the treatment plant processing periods.
Equal portions of the samples of treated chromium stream
wastes were combined to provide the composite sample
submitted for analysis (Table 42, Sample No. 33-20-CR-A-1-
COMP).
The analytical results, presented in Table 41, showed that
effective reduction of the hexavalent chromium was achieved,
since the Cr+* concentration in the treated stream was <0.05
mg/1. Using the data from Table 41, the percentage
reduction of Cr*6 to Cr+3 was as follows:
3.8 - 0.05
3.8 ~ x 100 = >98.7 percent
201
-------
TABLE 42
CHROMIUM REDUCTION RESULTS
Sample
No.
Description
Concentration, mg/1
Hexavalent Cr
Total Cr
33-20--CR-3-1-COMP
33-20-CR-A-l-COMP
Composite sample before
S02 reduction of
chromium
Composite sample after
S0£ reduction of
chromium
3.8
<0.05
11.1
7.9
202
-------
The above results indicate effective reduction of hexavalent
chromium with the continuous SO2 treatment.
Effectiveness of .Precipitation(Treatment_of_Acid-Alkali
StreamL-ClarificatiQn^Operations in Lowering the
Waste contentmofthejEffluent_Stream
An analysis of the metal content of a composite of periodic
grab samples of mix tank contents (samples taken at
Triangular Point 5, Figure 24) was carried out to determine
the effectiveness of the precipitation and clarification
procedures in removing wastes from the effluent stream. As
shown in Figure 24, the alkali-cyanide and acid-chromium
streams flow together into the mix tank where lime is added
to maintain the pH between 4.0 and 6.0, and preferably
between 5.0 and 6.0. The addition of lime to the pH tank is
governed by a pH controller.
Nine 1-liter samples were taken over a period of three days
of the mix tank contents.
Equal portions of the above 9 grab samples were combined to
provide the composite sample of mix tank contents submitted
for analyses (Table 43, Sample No. 33-20-MN-1-COMP).
The analytical data on the effluent waste stream before and
after precipitation-clarification are given in Table 42.
The reduction in concentrations for six of the seven metals
ranged from 80 to 95 percent, which indicates that the
precipitation-clarification are given in Table 42. The
reduction in concentrations for six of the seven metals
ranged from 80 to 95 percent, which indicates that the
precipitation-clarification steps were effective in
substantially lowering the waste content in the effluent
stream. Even with the seventh metal, nickel, the reduction
was 61 percent which was good considering the low influent
concentration of 0.23 mg/1 Ni and the final effluent
concentration of 0.09 mg/1 Ni.
Plant effluent was sampled with a B.I.F. (Builder Industrial
Factory, Providence, Rhode Island) sampler belonging to
Plant 33-20. This unit collected about 36 ml of effluent at
5.0 minute intervals during the actual periods when the
waste treatment processing was being carried out. The rate
of collection is about 2 ml per second. The effluent is
sampled immediately after the effluent leaves the Cyclator
and the location is shown as Triangular Point 6 on the waste
treatment flow sheet of Figure 24.
Waste Stream Flpw_Data
203
-------
TABLE 43 EFFECTIVENESS OF PRECIPITATION-CLARIFICATION
OPERATIONS IN LOWERING WASTE CONTENT OF
EFFLUENT STREAM
Metal Concentration, mg/1
Total
Item Cd Cr Cu Fe Ni Sn Zn
Mix tank contents composite sample 0.15 1.4 22.4 1.9 0.23 6.0 4.1
(Sample No. 33-20-MN-l-COMP)
Clarified effluent (Combined 0.03 0.20 1.5 0.18 0.09 0.33 0.39
effluent for August 20 to 22,
see Table 33-20-1, right side
columns)
Reduction in metal content of 80.0% 85.7% 93.3% 90.5% 60.9% 94.5% 90.5%
effluent
204
-------
Intermediate Stream and Effluent Flow Data
Plant 33-20 personnel combine the flow rate data from the
alkali-cyanide and the acid-chromium streams to arrive at
the total effluent flow. The plant is equipped with an
instantaneous flow indicator and also a cumulative flow
meter on each stream. Unfortunately, at the time of the
visit the instantaneous flow indicator on the acid-chromium
stream was not functioning, and the instantaneous readings
on the alkali-cyanide stream unit, although not accurate
(too low by about 20-25 percent) served to indicate that the
pumping conditions on the stream were being maintained to
provide a steady flow rate.
Plant 33-20 personnel adjust the pressure settings governing
the Conoflow valves to regulate the pumping rates of each of
the two streams. By keeping these pressure settings
properly adjusted, steady pumping rates on each stream can
be maintained during the treatment period cycles which
averaged about 7 hours each day during the 3 days of the
plant visit. Flow rate and pH data during the days of the
visit for the periods in which the waste treatment plant was
processing waste streams are presented in Tables 44, 45, and
46, respectively. Plant 33-20 personnel indicated that from
experience with their known pressure settings governing the
Conoflow valves, the cumulative flowmeter readings on the
alkali-cyanide stream were about 5 percent higher than
actual flows and the cumulative flowmeter readings on the
acid-chromium stream unit were about 10 percent low.
The flow rates of the total effluent leaving the Cyclator
were measured by going down into a man-hole pit about 50 or
60 feet downstream from the Cyclator and noting the time
required for 5 gallons of effluent to be caught in a
calibrated container. The effluent flow data for the three
days are presented in Table 47. As can be seen from the
tabulated flow data. Plant 33-20 personnel by carefully
controlling the pressures governing the Conoflow valves were
able to maintain steady flows on the two streams during the
waste treatment plant operating periods. The alkali-cyanide
stream accounts for about 60 percent and the acid-Cr stream
for about 40 percent of the total effluent flow.
From an examination of the pH values of the Cyclator
contents listed in Tables 44, 45 and 46, it can be seen that
the plant experienced some problems at times in maintaining
the pH in the range of 7.0 to 8.5, and preferably at about
8.0. Even though the lime additions were governed by a pH
controller, somewhat erratic lime feeds occurred at times.
As can be seen from Tables 43 and 44 the pH was above 10 at
205
-------
TABLE 44 WASTE STREAM AND EFFLUENT FLOW DATA CORRESPONDING
TO THE ELECTROPLATING PRODUCTION FOR AUGUST 20,
1974(a)
Alkali-Cyanide Sl.ream
Date Time(a)
8/20/74 0815
0833
1007
1030
1125
1155
1225
1325
1335
1407
1436
1530
Instantaneous
Flow-Rate
Reading (fe), gpm
~45
43
44
44
45
44
45
45
44
44
44
44
Cumulative
1'lowmeter
Reading (c), 10 gal
8:.26889
8:.26999
7547
7676
8014
8196
8376
8749
8781
8980
9160
8129538(d)
Acid-Chromium
Stream(b)
Cumulative
Flowmeter
Reading
-------
TABLE 45 WASTE STREAM AND EFFLUENT FLOW DATA CORRESPONDING TO THE
ELECTROPLATING PRODUCTION FOR AUGUST 21, 1974(a)
to
o
Date Time
8/21/74 0845
0908
0938
1010
1100
1125
1143
1215
1300
1420
1502
1516
1530
Alkali-Cyanide
Stream
Instantaneous Cumulative
Flow Rate Reading (b), Flowmeter Reading'0',
gpm 10 gal
-44
44
44
44
44
43
44
44
44
43
43
43
43
8129538
8129652
8129832
8130030
0378
0470
0574
0772
1045
1454
1696
1772
8131882 (d)
Acid-Chromium Stream
Cumulative
Flowmeter Reading (c',
10 gal
0191500
0191568
1670
1784
1983
2036
2094
2208
2362
2626
2767
2812
01912873 W)
Effluent in
Cyclator,
pH
10.2
10.2
10.6
10.4
9.5
9.0
8.6
8.2
8.0
7.8
7.8
7.8
7.8
(a)(b)(c) See corresponding footnotes to Table 33-20-5.
(d) The stream flows for the period are given below:
Stream
Alk-CN
Acid-Cr
Flow From Meter
Readings, gal
23,440
13,730
Estimated Flow
Correction
5% High
10% Low
Corrected
Flow, gal
22,268
15,103
Total 37,371
-------
TABLE
WASTE STREAM AND EFFLUENT FLOW DATA CORRESPONDING TO THE
ELECTROPLATING PRODUCTION FOR AUGUST 22, 1974 (a)
o
00
Alkali- Cyanide Stream
Instantaneous
Flow Rate Reading^
Date Time
8/22/74 0845
0922
0930
0940
1005
1030
1050
1100
1120
1150
i22j
1320
1342
1415
1443
150.6
1520
1530
gpm
-44
44
44
44
44
44
44
44
44
44
44
44
44
44
44
44
44
44
(a)(b)(c) See corresponding footnotes
(d) The stream flows
Stream
Alk-CN
Acid-Cr
Cumulative ,
'', Flowmeter Reading^0 ,
10 gal
8131882
8132116
2170
2230
2382
2518
2642
2702
2819
3012
3214
3565
3683
3904
4054
4189
4289
8134370
to Table 33-20-5
Acid-Chromium Stream
Cumulative
Flowmeter Reading (°',
10 gal
0192873
0193005
3055
3092
3181
3262
3334
3368
3435
3546
3660
3865
3932
0194055
4140
4217
4271
0194320
Effluent in
Cyclator ,
PH
7.8
9.7
9.3
9.2
8.5
8.2
8.1
8.3
8.1
8.2
7.5
7.1
7.6
7.7
6.9
7.1
6.9
for the period are given below:
Flow From
Readings ,
24,880
14,470
Meter Estimated Flow
gal Correction
5% High
10% Low
Corrected
Flow, gal
23,636
15,917
Total 39,552
-------
TABLE 47 FLOW RATE DATA FOR TOTAL EFFLUENT
STREAM LEAVING THE CYCLATOR
Date
8/20/74
8/21/74
8/22/74
-_,.
Flow
Volume,
Time gal
1350 5
5
5
5
0925 5
5
5
1410 5
5
5
0940 5
5
5
1400 5
5
5
Time,
sec
3.0
3.2
2.8
3.0
3.0
3.2
3.1
3.0
3.2
3.0
3.0
2.8
3.1
2.8
3.0
3.0
Average Average Time Average Hourly
Time, For Day, Flow Rate,
sec sec gal
3.0 3.0 6000
3.1
3.08 5844
3.07
2.97
2.95 6102
2.93
209
-------
the end of the first treatment period and above 10 for about
2 1/2 hours at the start of the second treatment period.
These high pH values may have been responsible for the
highest TSS concentration in the effluent for the second
period, in that it may have produced a precipitate that
settled less readily.
Table 48 gives the holding tank levels at the start and end
of the waste treatment processing periods for the various
days of the visit. These readings were used in conjunction
with measured effluent outflows to calculate the volumes of
the waste streams for each day of the visit.
The total waste stream generated in the electroplating and
metal finishing operations for the various days were
determined using the flow rate and holding tanks liquid
level data presented in Tables 47 and 48, respectively.
The total waste flow corresponding to the production for
August 20 was determined as follows:
Hours of waste treatment plant processing: 0815
to 1530 = 7.25 hr
Average hourly effluent flow rate (Table 33-20-8)
= 6,000 gph
Total effluent flow during 7.25-hour period =
6,000 (7.25) = 43,500 gal
Corrections for changes in holding tank levels
(Table 33-20-9)
Alkali-CN tank level rise: 69.4 - 54.0 =
+15.4 in; 15.4 (133 gal) = + 2,048 gal
Acid-Cr tank level drop: 42.0 - 36.0 = 6.0;
-6.0 (117) = -702 gal
Adjustment for 30 minutes extra operation time
(i.e., 0815 to 0845) = 2550 gal
(It was assumed that inflow to holding
tank was 85 percent of outflow during
the 30 minute period; i.e.,
6000
2~ x 0.85 = 2550 gallons).
Total waste flow for 24-hour period (i.e., summation
of above) = 42,295 gallons.
The total waste flow corresponding to electroplating and
finishing production for August 21, was determined as
follows:
Hours of waste treatment plant processing:
210
-------
TABLE 48 HOLDING TANK LEVELS AT THE START AND END
OF THE WASTE TREATMENT PROCESSING
PERIODS ON VARIOUS DAYS
Alkali-Cyanide Acid-Chromium
Holding Tank Level(a), Holding Tank Level (b),
Date Time inches inches
8/20/74
8/21/74
8/22/74
8/23/74
Start:
End:
Start:
End:
Start:
End:
Start:
0815
1530
0845
1530
0845
1530
0845
54.0
12.0
69.4
33.5
86.5
38.7
86.5
42.0
6.0
36.0
16.7
46.0
30.5
52.5
(a) The alkali-cyanide holding tank is 14.50 x 14.75 ft so that 1 inch of liquid
level corresponds to a volume of 133 gal.
(b) The acid-chromium holding tank is 13.60 x 13.75 ft so that 1 inch of liquid
level corresponds to a volume of 117 gal.
211
-------
0845 to 1530 = 6.75 hour.
Average hourly effluent flow rate (Table 33-20-8)
= 5844 gph
Total effluent flow during 6.75-hour period
= 5844 (6.75) = 39,447 gallons
Correction for change in level of holding
tanks (Table 33-20-9)
Alkali-CN level rise: 86.5 - 69.4 =
+17.1 in; 17.1 (133) = + 2274 gallons
Acid-Cr level rise: 46.0 - 36.0 = +10.0
(1.17) = + 1170 gallons
Total waste flow for 24-hour period (i.e.,
summation of above) = 42,891 gallon
Similarily, the total waste flow corresponding to
electroplating and finishing production for August 22, was
determined as follows:
Hours of waste treatment plant processing:
0845 to 1530 = 6.75 hr
Average hourly effluent flow (Table 33-20-8)
=6102 gph
Total effluent flow during 6.75-hour period
= 6102 (6.75) = 41,189 gallon
Corrections for changes in holding tank levels
(Table 33-20-9)
Alkali-CN tank level change: no change in level
Acid-Cr tank level rise: 52.5 - 46.5 = +6.5
in; +6.5 (117) = +760 gallons
Total waste flow for 24-hr period (i.e., summation
of above) = 41,949 gallons.
The total waste flow values as determined above for the
three periods were as follows:
1st period - 42,891 gallon
2nd period - 41,949 gallon
3rd period - 42,295 gallon
These values were used to calculate the water use/area
processed factors for evaluating plant compliance with
guidelines.
Area Plated^Data
The values of area plated for the various lines were
determined from production data on parts processed supplied
by plating room personnel and from areas of individual parts
calculated from measurements made.
212
-------
Summarized data on the part description, number of parts
processed, the individual part areas, the number of
qualifying operations, total processed area, etc., on the
various lines are presented in Table 49. Table 50 gives
similar data for the two tin automatic rack plating lines.
With the exception of the tin automatic rack plating lines,
all the rest of the lines are manually operated. The area
processed on each part was taken as the total area that was
rinsed on the part.
The following is the total area processed data for Plant 33-
20 on one day:
Item Total Processed Area
Combined Lines (Table 33-20-10) 7713 sq ft
Tin Automatic Rack
Lines (Table 33-20-11) 1874 sq ft
TOTAL 9587 sq ft
The above values of 9587 sq ft was used to calculate the
water use/area processed factors for each of the three
sampling periods during the plant visit. Plant 33-20
personnel indicated that plating production the other two
days was similar to that done on the first day. However,
this figure is a little below normal due to recent reduced
demand.
SAMPLING AND ANALYSIS OF PLANT„36-1
Introduction and Rationale for Sampling Plant_36-1
Plant 36-1 is an example of a captive shop with cyanide,
chromium, copper, nickel, zinc, aluminum, and iron
contributing to the pollution of the plant stream. The
electrochemical operations include copper, brass, nickel,
cadmium, and zinc plating and aluminum anodizing. Chromate
conversion coatings are applied in two processes: (1)
following zinc plating, and (2) as preparation for painting.
Bright dipping of brass, nickel and aluminum in a
dichromate-sulfuric acid solution is a sizeable contributor
of heavy metals to the waste stream. Soap from burnishing
operations and metal stripping solutions is also carried in
the waste for treatment. The raw wastes are treated by a
batch system using chemical methods with FeSOU-reduction of
chromium and cyanide oxidation by C12. Hexavalent chromium
and cyanide concentrations are determined before and after
treatment. Treatment chemicals are added in excess (50 ppm)
to assure completion of the reactions.
213
-------
TABLE 49
SUMMARIZED DATA ON AREAS PROCESSED ON VARIOUS LINES ON AUGUST 20 1974
Line
Zinc rack
(Br. Dip + Zn +
Chromate)
Zinc rack
(Br. Dip + Zn +
Chromate)
Zinc barrel
(Zn + Chromate)
Zinc barrel
(Zn + Chromate
Cadmium barrel
(Br Dip + Cd +
Chromate)
Copper barrel
(Cu)
Tin barrel (Sn)
Nickel rack
(Br Dip + Hi)
Bright dip
Wax dip
"Hybrite" dip
(a)
Bright dip
Bright dip(a)
Bright dip and
rack copper
plate selected
areas 'a)
Part No.
34203-970
333049-2
60441-7
50333-4
54333-2
56508-1
55322-7
62019-1
55704-1
50363-1
—
—
Part Name
Bellows assembly
Bellows assembly
Dial shaft
Pivot point
Spring washer
Piston disc
Terminal
Bellows assembly
Valve seat
Insulator
3-way pilot
valve sub-
assembly
Copper tube
End cover
Valve body and
connection
tube assembly
Number of
Parts
Processed
2,000
300
1,325
32,236
42,000
33,200
28,000
661
6,000
113,000
3,000
25,500
8,400
3,200
3,200
Measured
Area per
Part,
sq in.
23.36
6
1
0
1
1
1
26
3
1
16
7
2
65
(Br.
3
(Cu
.663
.78
.397
.334
.368
.80
.49
.93
.139
.30
.47
.46
.70
Dip)
.902
plate)
Combined Lines Total
Total
Number of Processed
Qualifying Area(b),
Operations sq ft
3 973
3 42
2 33
2 178
3 1,167
1 315
1 350
2 243
1 164
1 894
1 340
1 1,323
1 144
1 1,460
1 87
I 7,713
(a) The area processed data corresponds to the aroduction on the various lines for August 20, 1974.
Kith Lha exception 01 the last four operations at the bottom of the table, the work was all
done in the one shift from 0645 to 15]5. The last four operations were carried out on a 2-shift
basis, and the processed areas shown correspond to the total production for the 2 shifts.
(b) The total processed area values shown in this column take into account the number of qualifying
operations involved lor the particular part.
214
-------
TABLE 50
SUMMARIZED DATA ON AREAS PROCESSED ON TWO TIN AUTOMATIC
RACK PLATING LINES ON AUGUST 20, 1974(a)
Part No.
24203-975
-982
-985
-620
-515
-976
-802
-527
- 77
-440
-545
-787
- 21
-785
34007-174
- 33
-241
34599-3
— 1
-161
- 39
322978-25
321609-2
35495-39
34433-21
34433-133
320597-1
36799-28
Part Name
Bellows Assembly
Ditto
ii
n
n
ii
n
n
M
n
ti
n
ii
n
Bellows Assembly
Ditto
n
Bellows Assembly
Ditto
M
n
Bellows Assembly
Bellows Assembly
Bellows Assembly
Bellows Assembly
Bellows Assembly
Bellows Assembly
Bellows Assembly
Number of
Parts
Processed
2,035
3,553
1,995
200
148
700
15
89
84
479
857
217
99
600
194
209
205
1,844
800
149
125
361
148
97
325
210
600
1,800
Individual
Part
Area,
sq in.
10.08
22.35
15.92
22.64
26.44
10.08
37.00
29.50
22.64
7.74
10.66
10.08
17.70
11.54
24.70
22.90
9.50
7.70
9.66
12.10
18.20
27.50
14.52
15.20
10.95
9.20
23.50
12.90
Total Total Area
Processed For Entire
Area, Sub Group,
sq ft sq ft
142 1,221
552
221
31
27
49
4
18
13
26
63
15
12
48
33 80
33
14
99 182
54
13
16
69 391
15
10
25
13
98
161
Combined Areas for Lines 1,874
(a) These data correspond to the entire production of the two tin plating lines for
August 20, 1974. The production was done on one shift from 0645 to 1515. The
number of qualifying operations on this line is one (i.e., tin plating).
215
-------
Sampling
The batch-type treatment system for plating wastes employed
by Plant 36-1 dictates a different approach to sampling than
the one applied to other plants. Where in normal cases
production and treatment are simultaneous and a constant
effluent flow is encountered, the batch treatment shows
considerable lag time from production to treatment to
discharge. Cyanide wastes, for example, are collected over
a 5 to 6-day period in the treatment tank, treated, and then
discharged after settling over an 8-hour working period.
The sampling data was, therefore, fixed for the day of
cyanide discharge. A raw waste cyanide sample was collected
before treatment and the treated cyanide was continuously
sampled during the time of discharge. Within the same time
period a treated acid-alkali-chromium tank, was discharged
and combined with the treated cyanide waste. A continuous
sample was also taken at this point. Other treated acid-
alkali-chromium wastes, originating during the same
production period as the cyanide wastes were also obtained
from plant personnel. These samples had been collected
earlier from a continuous sampler, collecting 35 ml every 9
minutes. Table 51 shows the collection rates used, and the
sampling points are indicated on the treatment diagram of
Figure 25.
Effluent Discharge
The time intervals from production through discharge of
effluent are shown in Table 52. The effluent discharges
achieved are shown in Table 53. The treated cyanide stream,
discharged during the day of the plant visit was actually
the result of filling over a period of 7 days almost 2 weeks
earlier. Reduction of CN-concentration in the (automatic)
zinc bath, reduction of water use, and a drop in production
have limited CN-waste treatment to once a week. Of the
27,900 gallons treated, 25,850 gallons were discharged as a
combined effluent with 40,800 gallons of acid-alkali-
chromium waste. The balance of 2050 gallons from the CN-
waste treatment and 5440 gallons treated acid waste were
transferred as 2 to 4 percent sludge to a holding tank from
where it is hauled to a nearby company-owned landfill. The
effluent volume hauled away as liquid sludge is considered
egual to the volume of liquid feed of treatment chemicals.
Consequently, the plant water use is equal to the volume
discharged.
Cyanide effluent is never discharged by itself, but always
in conjunction with one or more acid tanks. During the
sampling period the combined effluent was 66,650 gallons.
216
-------
I—,-
R.F.
VATn
SVPPLY
CHIC'!:::
cw.r TAJ.-,.
• A;:i5 A:"T'.^Tis.t
o-
PAW ACID ruy.rs
CKLORIWTOR
•o
6 AC 10
Tp.r^ryEJ.T
TA:.XS
5Q.CC3 CALS. EACH
Cii.-MCAL
j iVWS
j SIUOCE
L_J£!L
""" I>
,
4 SL'JKI
30.C.13 CMS.
f-O
Sl'.nCE
n"x?s
2 CY.V:IDE
TREATX£NT TA7.TC3
**
3
I
SLtliCt TU'CK
^ RATE OF FLC'-/
C,) CONT'O'-L!*
90 CW
«^TE or rtcw
CONIRO'-LHl
45 CPX
PL-yj-S
SLL'DCE DIUV OFF
TO R.SW ACID LINE
STOW Sr-T
FIGURE 25
DIAGRAM FOR CYANIDE AND ACID WASTES TREATMENT
* Sampling point 1 is used for sampling of acid effluents and combined acid-cyanide effluent.
** Raw waste was taken directly from tank after mixing of the weekly accumulated volume.
-------
TABLE 51 COLLECTION RATES AND VOLUMES OF SAMPLING
July 31, 1974 - Plant 36-1
Time
Composite 09:30
09:45
10:10
13:40
15:50
Cyanide 09:30
09:40
09:50
10:10
13:40
15:50
ON TIME,
sec
37
46
49
50
Sampling
59
45
46
46
48
Sampling
OFF TEME,
sec
235
236
234
233
Complete
21:.
254
216
216
210
Complet.e
TOTAL TIME,
sec
272
282
283
283
270
299
262
262
258
ml
40
47
51
51
90
64
49
49
49
ml/hr
529
600
649
649
1200
770
673
673
684
Total
Volume , ml
__
132
250
2.271
1406
4059
__
200
128
224
2355
1482
4389
218
-------
TABLE 52 WASTE TREATMENT SCHEDULE AND WASTE VOLUME FOR THE
PRODUCTION PERIOD FROM JULY 19 TO JULY 25, 1974
VO
Discharge Sampling Rate
Waste Stream
Acid No. 4
5,6
1,2,3,5
4,6
2
Cyanide No. 7
1,3
5
6
4
1,2,3
5
6
2
4
1.3
5
Cyanide No. 8
Tank Filling
7/18 to 7/19
7/19
7/19 to 7/22
7/22
7/23
7/12 to 7/19
7/23 to 7/24
7/24
> 7/24 to 7/25
7/25 to 7/26
7/26 to 7/27
7/27 to 7/28
7/28 to 7/29
7/28
7/29
7/29 (15:00)
to
7/30 (06:00)
7/30
(10:30 to 12:30)
7/19 (11:00)
to
7/26 (09:30)
Tank Treated
7/19
7/19
7/22
7/23
7/24
7/19 to 7/23
7/24
7/25
>7/25
7/26
7/28
7/29
7/29
7/29
7/29
7/30
(12:30 to 13:45)
7/26 (09:30)
to
7/30 (10:45)
Volume,
Settling Tank Discharged gal
7/19 #5
7/19 #4,6
7/22 n
#1,3
5
7/23 #4
#6
7/24
7/23 to 7/24
7/24
I""
>7/2",
7/26 02
#3
7/28
7/29
7/29
7/29
7/29
7/30 (13:45)
to (09
7/31 (09:30)
7/30 (10:45)
to (09
7/31 (09:30)
7/19 42,160
7/19 to7/22 89,530
7/22 43,066
»
7/22 to 7/23 127,610
7/23 to 7/24 41,253
7/24 42,160
7/24 43,293
7/24 25,850
7/24 to 7/25 85,000
I 7/25 to 7/26 >85,453
'7/26 40,800
7/26 to 7/28 87,720
7/28 43,520
7/29 40,346
• 7/29 to 7/30 122,622
7/30 to 7/31 82,053
7/31 40,800'
:30 to 15:50)
'66,65(
7/31 25,850
:30 to 15:50)
Rate, Volume,
gal/min ml/hr ml
90 230
24 230
90 230
133 230
43 230
175 230 ~
175 230
50 230
90 230
90 230
90 230
23 230
90 230
90 230
128 230
85 230
107 } 529- 645 4060
) '175
58 j 673-1200 4390
-------
TACLE 53 COMPARISON OF TREATMENT RESULTS WITH EFFLUENT GUIDELINE REQUIREMENTS FROM SAMPLING
PROGRAM ON PLANT 36-1 OPERATIONS
166-1/2- Hour Period
-------
discharged at a rate of 175 gal/min. Acid wastes are
discharged irregularly, depending on need, varying from one
to three combined tanks with a discharge rate from about 20
to 175 gal/min, depending on daylight, overnight, or over
weekend discharge. Lowest flow rates are measured on
weekends and highest during daytime with normal production.
Over a 96-hour period 417,065 gallons (1,578,591 1) of acid
waste only were discharged, while for a weekly period
consisting of 184 hours, 640,352 gallons (2,423,630 1) of
acid waste and 25,800 gallons 97,653 1) for a total of
666,125 gallons (2,521,283 1) were discharged.
Re suits
Analytical data show a raw waste concentration of 304 mg/1
of cyanide. After treatment by chlorination at two pH
levels, the total cyanide concentration is 0.52 mg/1 showing
that the cyanide oxidation reaction goes 99.83 percent to
completion.
Similar data for hexavalent chromium reduction could not be
determined, because a meaningful raw waste sample from Tank
No. 5 or any previously treated chromium wastes was not
available.
WaterUseandPrcess
In order to correlate process rates and water use for
ultimate determination of effluent parameters (mg/sq m) ,
water use was calculated within definite time periods for
which plant production was determined. The production
schedule is summarized in Table 54.
For one 8-hour period the water use was 252,270 liters. The
sq m processed are composed of the following operations:
(1) Chromate conversion coating of 123 and 195
sq m from C- shift on 7/29 , and A-shift on
7/30 for a total of 318 sq m
(2) Bright dip production of 5029 and 6767
sq m on 7/29 and 7/30 divided by 3
to take into account a one-shift pro-
duction on each day for a total of 3932 sq m
(3) Strand anodizing of 1541 sq m composed
of 868 sq m on 7/29 and 673 sq m on 7/30
(4) Chromate conversion coating following zinc
221
-------
NJ
TABLE 54 SUMMARY OF PRODUCTION SCHEDULE FOR THE PERIOD FROM
JULY 19 TO JULY 30, 1974
/Automatic
Barrel Zinc
Date
7/19
7/22
7/23
7/24
7/25
7/26
7/29
7/30
7/19 to 7/26
7/24 to 7/29
sq m
1669
2523
2673
2973
1205
1744
1490
1126
12787
5926
sq ft
17966
27156
28778
31994
12972
18776
16036
12120
137642
63781
C&D Line Strand Nickel
sq m
495
638
533
510
554
497
522
885
3227
182,8
sq ft sq m sq ft
5326 811 8732
6867 643 6917
5735
5485
5966
5346
5623
9529
34725 1454 15649
19678
Strand Anodizing
sq m
--
--
3994
3702
2138
1738
1736
1354
11572
7453
sq ft
--
--
42992
39846
22022
18708
18574
14570
124568
80227
Total Electro-
chem. Proc.
sq rn
2975
3804
7200
7183
3897
3979
3748
3365
29040
15207
sq ft
32024
40940
77505
77325
41960
42830
40233
36219
312584
163686
C'nromate
Processes
sq m
808
931
652
764
647
970
884
780
4772
2868
sq ft
8700
10020
7020
8220
6960
10440
9360
8400
51360
30870
Bright Dip
sq m
12060
6290
5090
4045
1893
5793
5029
6767
35171
14738
sq ft
129817
6774
54792
43542
20376
62361
54141
72895
378599
158649
Total
Processes
sq m
15843
11025
12942
11994
6437
10742
9661
10795
68983
32813
sq ft
170541
118671
139317
129087
69296
115631
103734
117464
742543
353205
-------
plating, which is 1/2 of 1490 + 1126 = 1308 sq m
(5) Strand Nickel plating 352 sq m
Totals (1) through (5) = 7442 sq m. Because three tanks
were filling simultaneously, only 1/3 or 2481 sq m will be
applicable processed area.
(6) Miscellaneous barrel plating operations,
called C&D line, consisting of copper,
nickel, cadmium and brass plating.
For the period from 7/19 to 7/26, 3277 sq m
were processed, 1/4 of which was acid
waste from the nickel plating, (5) above,
for a total of 2420 sq m.
(7) Cyanide barrel zinc plating from 7/19
to 7/26 amounted to 12,787 sq m.
Disallowing for the chromate coating following
zinc plating, the actual area processed
is 6393 sq m.
Total cyanide production is then 8813 sq m. When combined
with the acid-lines, a total process rate of 11,294 sq m
(121,572 sq ft) is obtained. The calculated water use
factor equals:
252^270 liters = 22.337 = 22.4 1/sq m.
"11,294 sq m
This factor is considered applicable whenever cyanide and
acid wastes are discharged together. In the above case,
only one acid tank was combined with the cyanide tank, so
that the cyanide concentration can be expected to be at its
maximum in the effluent, assuming consistent cyanide
destruction efficiency in the waste treatment.
A second type of effluent is being discharged from the plant
on 5 out of every 6 days from wastes excluding cyanide. The
second period (96 hours) in Table 53 provides such an
effluent. The concentrations given are the averages from
the analysis of four samples collected continuously from
7/26 to 7/31. The total water use corresponding to this
period was 417,065 gallons (1,578,591 1) and coincides with
the production period from 7/24 to 7/29 with 1/2 of the
production rate on 7/24. The sq m processed are as follows:
(1) Chromate from zinc barrel line for 2963 sq m
(2) Barrel nickel from the C&D line for 457 sq m
223
-------
(3) Strand anodizing processing 7453 sq m
(4) Chromate conversion coating prior to painting for
2868 sq m
(5) Bright dip operations of 14,738 sq m.
The total area processed is 28,479 sq m and the water use
factor is then:
Ix518«.591_liter = 55.43 1/sq m
28, 479 sq m
This factor is considerably greater than the other two,
which can be attributed to the fact that water use from
burnishing operations, electrolytic alkali cleaning of 586
sq m of wire, and the volume of water from cleaning and acid
pickling prior to zinc plating are included in the total
water flow. In this respect, this water use factor is
likely to be a maximum for the plant operations.
In order to calculate an average 30-day effluent discharge,
the production and water use of one total work-week
including both cyanide and acid effluents were correlated.
In the seven day period during which the cyanide treatment
tank was filling, (Table 36-1-3), was taken to be the norm.
In the 166-1/2-hour working period the total water use was
2,038,457 1 (538,562 gallons]! composed of 97,842 1 (25,800
gallons) of cyanide waste and 1,940,615 1 (512,712 gallons)
of acid waste, including water from burnishing and wire
cleaning operations for which an area value is not included
in the total area processed of 68,983 sq m. The
corresponding water use factor is:
2.038,457 1 = 29.6 l/m*
68,983 sq m
The concentrations in the effluent are weighted in the
ratios of acid and cyanide wastes from the analytical
results of the cyanide stream and the average of the acid
streams of the 96-hour period. The 30-day average should,
therefore, closely agree with the discharge values of 166-
1/2-hour period.
Considering that the production of Plant 36-1 is compared of
a number of electrochemical operations (plating and
anodizing), and chemical operations (conversion coatings and
bright dipping), as well as burnishing and wirecleaning,
approximate water use factors for these operations may be
calculated. Evaluations during a number of plant visits and
224
-------
water flow measurements indicate that approximately 45
percent of the water is being used for electrochemical
operations. Taking the production for the 166-1/2-hour
period from Table 54 and the water use for the same period
from Table 52, one obtains a water use factor of
2^038^457 i x 45
29,040 x TOO ~ = 31.6 1/sq m
for electrochemical processes and 28.1 1/sq m for chemical
operations. Taking these units as separate entities and
applying it to any of the concentrations of the three
periods show that the plant could meet guideline values were
it to operate on electrodeposition or chemical finishing
only.
Operation§_and Area Processed
The nickel finishing operations and the sq m or sq ft
processed are summarized in Table 54 for each day from July
19 to July 30. The products consist of small stamped parts
and continuous wire or wire coils. Areas of small parts
were calculated by plant personnel. Shaped wire areas were
calculated by measuring cross-sectional areas multiplied by
unit length. In some instances, weights and listed specific
gravities for common brass, nickel and aluminum were used to
compute processed areas. In the case of zinc barrel
plating, the process areas shown are twice that of the
production rate, taking into account the conversion coating
step on the zinc plate. In all other instances, process and
production rates are equal. Not included in the area
calculations are burnishing or deburring operations and
electrolytic wire cleaning. These operations are not
considered to be within the scope of the guideline, although
the rinses contribute directly to the waste stream.
Summary -^Plant 36-12
Introduction
The data represented in this section are representative of a
captive shop dealing in a specific product. All wastes
originate from electroplating and bright dipping processes,
and include silver, tin, copper, zinc, and nickel, as well
as cyanide. Figure 26 shows the schematic of the total
plant layout and Figures 27 to 29 show the individual lines
contributing waste and the subsequent waste treatment. The
electroplating facilities consist of four production lines.
Ampere capacities, amperes used, and production rates are
tabulated below.
225
-------
LINE 1
TIN-PLATING
332,000 SQ. FT.
PER MONTH
ELECTROLYTIC
TIN RECOVERY
It
ALKALI AND
FLOOR SPILL
COLLECTION
LINE 2
COPPER-TIN
PLATING
333,000 SQ. FT.
PER MONTH
LINES
COPPER-TIN
PLATING
144,000 SQ. FT.
PER MONTH
LINE 4
COPPER SILVER
COPPER-BARREL
PLATING
1 20,000 SQ. FT.
PER MONTH
LINES
BARREL-TIN
PLATING
15,00080. FT.
PER MONTH
LINE 6
ACID-PICKLING
205,000 SQ. FT.
PER MONTH
TIN
TREATMENT
RESERVOIR
ELECTROLYTIC
SILVER
RECOVERY
SILVER
TREATMENT
RESERVOIR
CYANIDE
DESTRUCT
NICKEL
TREATMENT
RESERVOIR
COPPER
TREATMENT
RESERVOIR
ALL USED
ALKALINE
CLEANER
TALL ACIDIC RINSES
ACID
COLLECTION
T ALL ALKALINE STEAM RE-USE WATER
pH ADJUSTMENT
SETTLING
TANK
SLUDGE
FILTER
CLEANER
NEUTRALIZATION
(FROM DUMPS)
FIGURE 26
* NOT IN OPERATION DURING PLANT VISIT
SCHEMATIC OF WASTE TREATMENT -
PLANT 36-12
TO STORM SEWER
TO SANITARY
SEWER
2 - 3 gpm
TO SANITARY SEWER
-------
'2gpm
r-o
NJ
TIN PLATING TIN-PLATING
CONTINUOUS STRIP
I = 720 AMPERE AVG.
COIL SPEED 19DR/HINAVG.
PRODUCTION 133 MILLION PARTS
PER MONTH
= 332,000 SQ FT/MON.
RATE 24 MRS/DAY
7 DAYS/WEEK
= 461 SOFT/MR
EFFICIENCY, % ~60
TO SANITARY
SEWER
F (2-3 gpm)
(COMBINED)
TO SANITARY
SEWER
FIGURE 27 SCHEMATIC OF TIN PLATING LINE AND WASTE TREATMENT
-------
COPPER - TIN PLATING
CONTINUOUS STRIP
ULTRA
SONIC
ALKALINE
CLEAN
ELECTRO-
LYTIC
CLEAN
SPRAY
RINSE
RE USE
WATER
TO SANITARY
SEWER
(COMBINED)
10%
H2SO4
COPPER
TREAT
SPRAY
RINSE
REUSE
WATER
COPPER
PLATE
COPPER
TREAT
SPRAY
RINSE
RE-USE
WATER
RECRYST
DUMPS i
ACID
TO SANITARY
SEWER
FIGURE 28 SCHEMATIC OF TWO COPPER AND TIN PLATING
LINES AND WASTE TREATMENT
-------
NICKEL
TREAT
NICKEL
PLATE
1%
H2SO4
i ALTERNATE
PROCESS LINE
COPPER - SILVER OR NICKEL PLATING
CONTINUOUS STRIP
I = 200 AMP. AVG
COIL SPEED = 50 TO 140 FT/MIN SQM/MONTH
PRODUCTION . Cu - Ag 100.000 SQM/MONTH
Cu Ni 20,000 SOFT/MONTH
16 MRS/DAY; 5 DAYS/WEEK
TO SANITARY
SEWER
(COMBINED)
FIGURE 29 SCHEMATIC OF COPPER AND SILVER OR COPPER AND NICKEL PLATING LINE AND WASTE TREATMENT
-------
ELECTROPLATING LINES AT PLANT 36-12
Line
NO.
1
2
3
4
Metal Product ion_Rate Amperes
Plated ft2/hr
Tin 461
Copper, (2x) 461
Tin
Copper, (2x) 200
Tin
Copper, (2x) 340
Silver,
Tin
m2/hr Capacity
42.8 1,500
42.8 2,000
1,500
18.6 500
600
31.6 500
600
1 ,000
Use
720
220
680
140
400
220
220
Geometric Area
Processed
1,662
135.8
237.7
8,200
2,580
8,200
2,580
Geometric Area 2,462
Prgcessed^x^Q^ operations
WASTE WATER TREATMENT SYSTEM
The waste treatment is an integrated, continuous chemical
one assisted by a preceding electrolytic recovery of silver
and tin. Silver and tin are electrolytically recovered from
a concentrated, recirculating raw waste solution containing
about 3 g/1 (0.1 oz/gal) of metal. Integrated chemical
precipitation, using hydrazine in a solution of sodium
carbonate and sodium hydroxide, takes out the remaining
traces of thse metals plus copper, zinc, and nickel. Only
one fresh rinse in each production line at the end of the
process line flowing at a rate of 2 gpm account for the
total water use of 480 gph. A hot deionized rinse before
drying is regenerated and not discharged. The barrel tin
and bright dipping process lines do not use any fresh water.
The sludges from the treatment reservoirs are collected in
the sludge filter outside the building. The water is
allowed to seep through special types of concrete block
widewalls from where it is carried to the sanitary sewer.
All acid-alkali rinses, floor spills, and overflows from the
metal treatment reservoir tanks end up in the concrete
settling tank from where the sludges are pumped over to the
sludge filter. The clean water flows over into a smaller
tank which serves as a reservoir from where the water is
recycled to the rinses.
230
-------
Date
2.4
23
22
O.I
20
1.9
i.e
I 7
16
I 5
14
1.3
1.2
I I
10
09
08
0.7
06
05
04
03
02
01
0
I 8
1.7
1.6
15
14
13
1.2
I I
1.0
09
0.8
O7
0.6
05
04
0.3
02
O.I
0
16
1.5
14
13
1.2
I I
10
09
08
07
06
05
04
0 3
0.2
01
0
TI I i i i
June
.11
'i
/i
' i
' i
A
Bright Dip-** ',
I i
i i
i i
i «
ft t «' \
j -^PPM Cu ,' \/ '( \
i • ' i\ '\ »
.' v ' !\i\ *
1 - - ;ji\ k
r*. f- <£ 00 00 (£> fcT)
CO 00 CO 00 GO
PPM Cu
01 f- r-
00 CO CD
ODCOODODOOODCOCOCOCDCOaD
rO iO f^ *T> (J)
CD CO CO CO CO
PH
August
f
l'
I >
PPM Cu
k /
/V- : L.-»—
/ . k-l " ' V
Bright Dip
,< /
^
W7
.V
.^
' ¥^
ID ^ CT) in
CO CO CD CD
*•••*
'*1*
48
4.6
44
4.2
40
38
3.6
3 4
32
30
28
:.e
24
22
20
i 8
16
I 4
: 2
iO
OS
06
04
02
0
3 6
34
32
30
28
2.6
2.4
22
20
I 8
i 6
4
I 2
.0
08
06
04
02
0
T f
30
28
26
2 4
2 2
20
18
I 6
I 4
I 2
I 0
08
06
04
02
0
00000000 00 00 CD CO 00 00
O C7> CD CD
PH
•o
o
a.
Q
CD
00 oo CD cococoaDcoaDoof- r~-
FIGURF 30
FFFFCT OF RRTGTIT DIPPING ON
Cu AND Zn CONCENTRATIONS IN
EFFLUENT
231
-------
d> V 6 0 10 «
O
-3 4-
FIGURE 31
CHANGE OF AVERAGE EFFLUENT CONCENTRATION AND pH
-------
The amount of bright dipping Of brass is believed by plant
personnel to be responsible for the variations of copper and
zinc concentrations in the final effluent (Figure 30). The
treatment cycle lags about 24 hours behind bright dip
operation. Figure 30 shows the monthly average effluent
concentration of copper and zinc. Figure 31 shows the
monthly average concentrations of copper and zinc and the
change of pH in the effluent. A direct correlation between
bright dip processing or pH for the amounts of copper or
zinc discharged cannot be established. All treatment cycles
are monitored and controlled by automatic pH and ORP
instruments.
Calculation of Effluent Parameters
Plant 36-12 shows a total water flow of 2160 gph to a stream
and 400 gph to the sanitary sewer. Of the 2160 gph, only
480 gph originate from four continuous strip plating lines,
one barrel plating line, and one bright dip line. On the
average, 1460 sq ft of phosphor bronze and cartridge brass
and minor amounts of steel are electroplated and bright
dipped per hour. The average water use is
480 gal
hr
1460 ft£
hr
= .329 gal/sq ft
= 13.40 1/mz
Summary - Plant.,33-5
Introduction
The data presented in this section show the efforts made by
a captive shop towards treatment of waste waters from
plating processes involving lead, tin, fluoroborate, and
fluoride, as well as copper, nickel and alkaline, and acid
wastes.
Waste Treatment^Facilities
All treatment is achieved by batch chemical precipitation,
without aid of evaporators, reverse osmosis, ion exchange,
or any other form of waste treatment. All wastes
originating from the plant are combined in one of two
concrete tanks having a capacity of 20,000 gallons each.
Treatment consists simply of hydroxide precipitation for 15
233
-------
to 30 minutes. Settling time; is eight hours, and drainage
takes about 1 hour. Each tank is drained once each day.
The produced sludge of about 1,600 ftVyear is pumped twice
a year to adjacent company-owned land.
Table 55 shows data for the waste concentration of treated
and untreated effluent and the typical ppm of each waste in
the rinse stations.
Table 56 shows analytical data from 1970 to 1972 indicating
variations in the treatment achieved. The data are for
monthly composite samples collected daily from each treated
tank, mixed, and then shipped once a month to a company
laboratory for analysis.
The total average water flow for two automatic production
lines plating 46.2 m*/hr (497 ft*/hr) is 10,900 1/hr (2,880
gph) for an average water use of 235 1/m2 1/m2 (5.80
gal/ft2). Table 57 shows an average effluent composition.
Figure 33-5-1 shows the plating plant layout and the nominal
water use of 4,088 1/hr (1,080 gph) which when properly
maintained by plant personnel would reduce the discharge by
a factor of 0.375. All effluent limitations and production
parameters are summarized in Table 57.
Plant_15-3
The production rates for all of the indicated plating lines
vary and are less than a 40 hour work week. In order to
make comparisons with other plants, these rates were
converted to a weekly volume:
A- Silver-plating
Water usage 365 gph = 1382 1/hr
0.2083* x 365 gph = 76.0 gph
= 288 1/hr
*From supplemental calculations.
B. Cadmium Plating
Water usage 944 gph = 3573 1/hr
0.3375 x 944 gph =319 gph
= 1207 1/hr
234
-------
Igpm 2gpm 2gpm
»1 » 1 11
T
HOT
RINSE
RINSE
Pb-Sn
FLASH
IUIT
STA-
TION
•^^^^^^
RINSE
(jj
Ln
1 \ \
LOAD & RACK AUTOMATIC PLATING MACHINE FOR PLATING \Pb-Sn-Cu
UNLOAD ON BEARING MATERIAL (Pb25/Sn1/Ar74) JALLOY
V
V
^-s^
12gpm
A 6gpm
-------
TABLE 55
ANALYSIS OF RAW AND TREATED WASTE
CO
OJ
Waste Constituent
Lead
Tin
Copper
Nickel
Fluoride
Fluoborate*
Chloride
Suspended Solids
Dissolved Solids
PH
Raw Waste
Concentration
mg/1
98
50
4
88
134
160
180
1720
3.40
Treated
Effluent
Concentration
mg/1
39
20
2
36
65
160
190
1630
7.70
Acid Rinse
Waste Waste Concentration
Removal Discharge Percent of
Percent kg/hr mg/1 Raw Waste
39.8 6 6.1
40.0 5 10.0
50.0 1 25.0
40.9
48.5
0
860
—
—
«-•«
* Tentative values, based on a spectrographic determination of Boron in the sample.
-------
TABLE 56
PLANT EFFLUENT QUALITY AND STANDARDS*
Sample
Date
4/12/72
3/24/72
3/1/72
1/3/72
1/5/72
11/23/71
12/10/71
10/26/71
9/16/71
6/22/71
10/6/71
7/12/71
12/17/70
Average
Stream
Standards
Effluent
Average Effluent Concentration, mg/1
Pb
7.0
0.69
0.29-
0.12 •
15.8 *
0.05 .
13.5 .
4.5
3.2
6.2
2.9
10.3 .
2.0
5.12
0.05
0.05
Sn
4.0
0.05
0.05
0.05
0.01
0.31
0.05
0.05
1.2
0.15
2.6
0.10
0.718
Cu
0.2
0.5
0.10
0.75
0.50
0.05
0.25
0.40
0.15
0.60
0.45
0.90
0.35
0.365
2.0
1.0
Ni
4.4
3.1
7.2
5.2
8.7
5.9
4.9
1.8
2.8
10.9
4.9
5.4
8.84
5.70
2.0
1.0
Fe F
59
0.04
0.08
0.40
0.01
3.9
0.19
0.66
0.63
0.21
0.44
0.26
0.62 .-59
1.0
5.0 2.0
pH
7.4
6.85
6.9
7.5
7.25
7.18
5.5-9.0
5-9
Standards
* The data are for monthly composite samples collected daily at the
plant and shipped once a month to a company laboratory for analysis,
237
-------
TABLE 57
EFFLUENT LIMITATIONS AND PLANT PARAMETERS
N)
U)
CO
Plant No. 33-5
Water use 1/hr
gal/hr
kg/rn2
lb/ft2
Effluent volume I/year x 106
gal/year x 10°
Production hours/year*
Mur. ber of plating operations
Nu-ber of rinses
Arc-a processed m^/hr
ft2/hr
ypste Constituent Pb Sn
Average constituent
Concentration mg/1 5.12 0.72
Discharge g/hr 55.8 7.83
Ib/hr 0.12 0.02
Eg/m2 1,208 170
lb/106 ft2 241 40
10,900 (total to waste treatment)
2,380
236
48
1,970
520
7,200
4
8
46.2
497
Cu Ni Fe F BF^** S.S.
0.37 5.70 0.62 59 160 33
3.98 62.3 6.76 643 1,744 360
0.009 0.14 0.015 1.42 3.85 0.79
87.3 1,345 146 13,920 37,749 7,786
18 282 30 2,857 7,746 1,590
D.S.
.1.059
11,543
25.5
249,850
51,308
* Based on 50 work-weeks per year.
** From BMI analysis; all other values are riant 33-5 values.
-------
Water usage 631 gph = 2388 1/hr
0.30 x 631 gph = 189.3 gph
=717 1/hr
Total water flow for the three metals plated
= 584 gph
= 2210 1/hr
D- Nickel Plating
Water usage 1830 gph =6927 1/hr
0.3375* x 1830 gph =618 gph
= 2339 1/hr
The total average water flow is 1202 gph = 4550 1/hr
= 1202 gph x 2000 hrs/yr = 2,404,000 gal/yr
= 9,099,140 1/yr.
If all the rinses are running all at the same time, then the
total water use would be 3770 gph = 14,270 1/hr
= 3770 gph x 2000 hrs/yr = 7,540,000 gal/yr
= 28,538,900 I/year.
However, company data show a raw waste volume of 3000 gph
= 11,355 1/hr = 3000 gph x 2000 hrs/yr = 6,000,000 gal/yr
= 22,710,000 I/year.
Area processed average hourly production based on a 40
hour week:
A. Silver
161 ft2 x 0.2083 = 33.5 ft*/hr
= 3. 12 m«/hr
B. Cadmium
239
-------
280 ftz x 0.3375 = 94.5 ftz/hr
= 8.78 mz/hr
C. Tin
215 ftz x 0.30 = 64.5 ftz/hr
= 5.99 mz/hr.
Total hourly production rate ~ 192.5 ftz/hr = 17.89 m2/hr
HO hr/wk x 50 wks/yr = 2000 hrs/yr x 192.5 ftz/hr
= 385,000 ftz/yr = 35,767 mz/yr.
D- NickelJPlating
206 ftz/hr x 0.3375 = 69.5 ftz/hr
= iS.46 mz/hr.
The total average area processed = 262 ftz/hr
= 24.35 mz/hr.
The total number of plating operations are:
A-C 12
A-D 18
and the number of rinses are
Acid-Alkali Metal
Acid-Alkali Integrated Integrated Total
A-C
A-D
12
20
4
4
5
5
21
29
Three of the above rinses are following posttreatment of
cadmium in a total flow of 201 gph x 0.3375 = 67.8 gph = 257
1/hr.
Effluent from the waste treatment system goes to the east
pond to the west pond to the lake water pond, from where it
goes to the streams. Analyses from this point are used for
the discharge parameter calculations. This is precipitated
by pH in the ponds, but is not analyzed.
240
-------
The production rate is 90 ftz/hr for each of three plating
operations in the Pb-Sn-Cu line for a total of 270 ftz/hr
and 227 ft^/hr for one plating operation in the Sn line.
The associated number of rinses are five and three,
respectively. These production rates are based on 48 second
indexing of an automatic rack plater and 18 baskets every
two minutes (510 baskets per hour) operating 70 percent of
the time. The water use is not controlled on either
production line, but is left to the need of individual
operators by simply opening faucets on each water line.
This procedure accounts for the discrepancy of actual water
use (2,880 gph) and proposed water use (1,080 gph).
Water Use Per Area Plated
A. Silver
B. Cadmium
C. Tin
76_gal/hr _
33.5 ft2/hr =2.27 gal/ ft*
288 1/hr
3.2 m2/hr = 92.3 1/m2
__
94.5 ft2/hr = 3.38 gal/ft*
J207_l/hr_
8.78 m2/hr = 137.5
189_c[al/hr
64.5 mz/hr = 2.93 gal/ft*
717 1/hr
D. Nickel
5.99 m*/hr = 119.7 l/m*
618_gal/hr.
69.5 ft2/hr = 8.89 gal/ft*
2339 1/hr
6.46 m2/hr = 362.1 1/m*
584_aal/hr 22!2_l/hr __
Total A-C = 192 ft2/hr = 3.04 gal/ftz 17.89 m2/hr
= 123.6 l/m2
4551 1/hr
A-D = 261.5 ft2/hr = 4.60 gal/ft2 24.35 mz/hr
= 186.9 l/m2
241
-------
Plant 20-24 is an automatic rack plater doing chromium,
copper and copper alloys, lead and lead alloys, nickel, tin
and tin alloys and zinc plating.
Plant 20-24 employs a continuous treatment system involving
pH adjustment, precipitation and settling. Also,
evaporative recovery is employed on Cu, Pb, Sn. Cr is
reduced by metabisulfite and then precipitated. Cyanide is
recovered by evaporation. Sludge is pumped to a drying
basin and subsequently removed by a licensed hauler to an
approved dump. Effluent concentrations achieved by plant
20-24 are as follows:
mg/1
Cu 0.17
Pb 0.60
Sn <2.0
Ni 1.9
Cr 0.54
Zn 0.25
Cd <0.01
CN 0.02
PO4 0.02
F 11.0
pH 8.5-9.5
SS 4
The production rate for 20-24 is 1200 sq ft/hr. The plant
operates 16 hr/day except for one line which operates 8
hr/day. The total effluent flow is 7000 gal/hr. This
corresponds to a water use of 5.8 gal/sq ft.
Summary of 33-24
Plant 33-24 does manual barrel plating of zinc and automatic
rack plating of tin and tin alloys. It employs a continuous
treatment system involving pH adjustment, precipitation with
hydrated lime and clarification. Hexavalent chromium is
adjusted to a pH of <3 and reduced to trivalent chromium
with sodium bisulfite, cyanide is totally destroyed to CO2
and N2 through chlorination. Sludge is hauled to a
landfill.
Effluent concentrations achieved by plant 33-24 are as
follows:
mg/1
Cu <1.0
Fe < 1.0
242
-------
Cr+3 <1.0
Zn <1.0
*CN <.025
*Cr+« <.05
SS <25
*dissolved solids
The production rate for 33-24 is 1300 sq ft/hr. The plant
operates 16 hrs/day, 5 days/week. Total effluent flow is
4200 gal/hr. This corresponds to a water use of 3.2 ^al/sq
ft.
SummarY_of_33-2
Plant 33-2 is a manual rack and barrel plater of coppei
cadmium, gold, silver and rhodium. Wastes from the platingN
of Cu, Cd and Ag in cyanide solutions are pumped into two
100 gallon lined tanks which are equipped with steam coils
to maintain a solution temperature of 205-210° F. A
rectifier is wired in series so that each tank is a plating
tank. The solution is plated out continuously. Cu, Cd, and
Ag plated out on the cathode are scraped into a lined barrel
and sent out for reclaim. No solution is ever discharged.
Metal bearing acid wastes are collected into a non-flowing
rinse tank. The tank is treated manually twice every eight
hour shift. Sodium hydroxide is added and the pH is
adjusted to 8.4-9.0. The contents then flow into a 100,000
gallon three stage sediment basin where metals precipitate.
This basin is cleaned annually.
A non-flowing tank is also located adjacent to each gold
plating tank. Here the pH is maintained at 4.4. During
non-working hours, gold is plated out on aluminum cathode
from which it is reclaimed. The liquid is then discarded to
the sediment basin after raising the pH to 8.5-9.0.
The rhodium rinse tank is also non-flowing. The rinse tank
is used until the metal concentration reaches 2 gm/gal. The
volume is then carbon treated and used to replenish the
rhodium solution.
Effluent concentrations attained by plant 6-37 are as
follows:
mg/1
Au Trace
Ag Trace
CN .1
243
-------
Rh
pH
TSS
Trace
5-10
6
The production rate for 33-2 is 30 sq ft/hr of gold/silver
for 8 hr/day 5 days/week and 30 sq ft of rhodium/silver for
1 hr/day 1 day/week. The total effluent flow is 3333 gph.
This corresponds to a water use of 111 gal/sq ft.
Summary of_6-37
Plant 6-37 is an automatic and manual rack plater of copper,
nickel and silver. It employs a batch electrolytic plate
out for silver and copper and nickel go through closed loop
vacuum distillation. Cyanide is electrolytically destroyed
followed by alkaline chlorination. pH is adjusted to 9.5
with N2OH or lime, sludge is dewatered and mixed with paper
refuge for landfill disposal. Effluent concentrations
achieved by plant 6-37 are as follows:
Ag
CN
Cu
Ni
pH
DS
mg/L
<5
<1
<5
<5
7-10
2760
The production rate for 6-37 is 3080 sq ft/hr for 9 hr/day 5
days/week. The total effluent flow is UOOO gal/hr. This
corresponds to a water use of 1.3 gal/sq ft.
Summ ary o f _ Pi ant _ 19_-11
Plant 19-11 is an automatic and manual rack and barrel
plater of gold, silver and rhodium. It employs electrolytic
recovery of gold and silver. Rhodium passes through an ion
exchange unit. Cu is reduced by hydrazine and precipitated
with the nickel. Cyanide is alkaline chlorinated. pH is
adjusted by the addition of Na^OH and H2SOJ*. Sludge is
disposed to municipal sewer beds.
Effluent concentrations are as follows:
Au
Ag
CN
Rh
Ni
mg/1
0
0
0
0
244
-------
Cu <-5
SS <20.0
pH 7.0-8.0
Company._6::7
Company 6-7 is a manual rack and barrel plater of silver,
copper and tin. The metal waste stream is treated by
adjusting the pH through addition of either acid or alkali
stream and then flowed into a settling tank. Two-thirds of
plating rinse water is recycled. Sludge is disposed by a
licensed contractor. Effluent concentrations achieved by
plant 6-7 are as follows:
Ag
CN
SS
pH
mg/1
0.20
0.12
0.01
25
6.8-8.7
The plant operates 16 hrs/day 5 days/week, except for silver
line which operates 2 hrs/day. The total flow is 1920
gal/hr.
Plant 19-24 is a plater of Cu, Cr, Ni, Cd, Pb, Sn, Ag and
gold. Metals are treated by neutralization and
precipitation of hydroxides with lime. Cr** is reduced to
Cr*3 with sulfur dioxide and then precipitated, cyanide is
batch treated by a two-step oxidation process utilizing N2OH
and chlorine. Finally, the waste stream is clarified and
sand filtered. Effluent concentrations achieyed by this
treatment system may be found below.
mg/1
Cu .15
Cr*6 <-03
Cr*3 <.05
Zn 2.2
F- 2.2
H <.0005
Ag -05
Cd <.02
Summary of 20-17
Plant 20-17 is an automatic rack and barrel plater of Ni,
Zn, Sn and Sn alloys. The treatment system is a continuous
245
-------
one involving neutralization and clarification. Sludge is
pumped to a drying lagoon or landfill.
Effluent concentrations achieved by this treatment method
may be found below:
mg/1
Cd .01
Cu .02
Fe .85
Pb .05*
Ag 0*
Ni .31
Cr .06
Zn .17
pH 7.18
SS 20
*grab
Summary_Qf Company 23^7
Company 23-7 is a large plater of Cu, Cr, Ni, Cd, and
precious metals. The waste treatment system is a continuous
one. The waste stream is treated with anti-foam and
coagulating agents before entering air mixing tank. N2OH or
H2SOU is added to maintain pH between 5.5 and 10.5. "After
aeration waste water flows to a series of settling tanks.
Excessive concentrations of Cr+« are reduced with ferrous
chloride. Sludges are collected by a vendor and hauled to a
landfill. The effluent concentrations achieved by this
treatment system may be found below:
mg/1
Fe .5
Al 0.5
Cr+* 5.0
Cr+3 5.0
Cu .01
CN .01
Cd .05
Summary of Plant 30-3
Plant 30-3 is a small manual rack plater of gold, silver and
rhodium. The treatment system involves alkaline
precipitation of metals. Cyanide is treated by N2OC1 and pH
is adjusted by N2OH. Sludge is disposed of by a~ scavenger
to an approved local source. The concentrations achieved by
this system may be found below.
246
-------
mg/1
Au N.D.
Ag <0.01
CN 1.0
Rh N.D.
pH 8.3
SS 31
Summary of^30-21
Company 30-21 is a manual and automatic rack plater of
silver and gold. Gold is treated by a continuously
operating in process ion exchange unit. Silver is batch
precipitated as a chloride. Any basis metals added to the
waste stream through cleaning operations are precipitated
with lime and ferric chloride and then filtered. Cyanide is
destroyed in a two step batch chlorine oxidation to CO2 and
N2. pH is adjusted in the final effluent by lime slurry
addition. Sludge is pumped to impoundment for slow
dewatering and land disposal. Effluent concentrations
achieved by this process may be found below:
mg/1
Au .003*
Ag .03
CN .03-.1+
P04 0.3+
SS~ 30
*estimated
+DS
due largely to algal growth
The production rate for plant 30-21 is approximately 1150 sq
ft/hr. The total flow is 35,000 gal/hr. This corresponds
to a water use of 30 gal/sq ft.
Waste Treatment Results
Volume Capacity of Treatment Plant Studied. Figure 27 shows
the volume capacity of the waste treatment plants for which
data were received, as measured by the amount of waste water
treated per hour. The range of capacities covers
approximately two orders of magnitude.
The plot is a cumulative one indicating how many plants have
a water use less than the volume corresponding to the
cummulative number. Thus, 25 plants have a volume of
100,000 liters/hour or less and 4 plants have a greater
volume.
247
-------
PLANT
*ll-8
*33-20
(+36-1
(+36-12
33-5
115-3
20-24
33-24
33-2
115-1
(12-6
1133-15
ff!2-3
6-37
43-1
19-11
6-7
19-24
20-17
23-7
30-21
l/m2-op
120
176
29
13
232
184
232
128
4440
132
60
211
80
52
-
_
_
-
-
-
_
(gal/ft2-op)
(3.0)
(4.4)
(.733)
(.329)
(5.8)
(4.6)
(5.8)
(3-2)
(111)
(3.3)
(1.5)
(5.3)
(2.0)
(1.3)
_
_
_
-
-
-
_
Table 58
mg/i
Cu Ni CrT Cr+6 Zn Pb Sn cd Au *£ Rh
.12 .60 .045 .03 .635 - - .21 - - -
1.5* .09 .20 .10 .48* - .20 -03 - - -
.14 .08 .06 .06 .34 - - .03 - - -
f 01
.73 - .52 - 0.5 - - <-01
.365 5.7 - 5.12 .718 - - - -
.26 .14 .07 .023 .12 - " •°09 "
.17 1.9 .54 - .25 - - .01 - - -
0
<1.0 - <1.0 - <1.0 < .05 - " - " "
Tr Tr Tr
.-- - . 15 ------
.8 .8 .4 .13 .3 - - - - - -
.09 .27 .30 .28 - - - -
.SO — .72 - .58 —
c
<5<5- - - -- - = --
1 — — —
.2 .5 .05 - - '3
on o
<.5- - - -- -00 U
.20
.15 - .05 .03 2.2 - - .02 - .05
.02 .31 - - .17 .05 - .01 - 0
.01 - 5.0 5.0 - - .05
- .003 .03
Al 32. CUT CNA
.42 .41*
.04 .04
13 - .025 .014
- < 01 -
_
.06 .06
<.02
.025°
.1
.16
.14
.01
- - .11 -
< 1
.1 .001 .01
- - 0 -
- - .12 -
- - -
.06
-
.07°
P04 F^ TSS gH
.07 - < 10 6.0 -
.13 - 10 8.2
.02 - <10 6.0 -
< 10 8.0
59 - 7.18
- - - 4.55
.02 11 4 6.5 -
< 25
6 5 -
- - - 6 -
20.5 7.9-
5.1 8.67
- - - C -
_ — — 7 —
6.5 -
20 7 -
.01 - 25 6.8 -
2.2 -
20 7.18
-
.3° - 30 -
9.5
9.5
9.5
10
10
8.7
9
10
8.0
8
8.7
# = xn compliance w/ 1977 standards
+ = in compliance w/ new source performance standards
* = out of compliance on parameters starred
0 = dissolved solids
-------
Concentrations of Pollutants and Water Use Factors in
Plants. The concentration of constituents in the treated
effluent, the pH, and the water use factor for each of the
previously described plants are shown in Table 58. The
concentrations are for soluble plus suspended constituents
in the effluent, unless otherwise noted. These results
appear to have little relation to the type of process from
which waste waters are derived with the possible exception
of electroless plating. The complexing agents, such as
ammonia, that are dragged into waste waters from electroless
plating baths are capable of inhibiting the precipitation of
metals such as copper and nickel.
Determination of Effluent Limitations
Effluent limitations were established from three parameters:
(1) constituent concentration in the effluent, (2) water
use, and (3) area processed or plated. Some dependence
among these parameters is known, i.e., coagulation of
precipitates out of dilute solution is more difficult than
out of more concentrated solutions and area processed in a
given line increases with complex shapes that give higher
dragout and require more water for rinsing. The plant data
obtained show no evident correlation between the three
factors probably because variations in water use and
concentration due to other factors mask out the relationship
between the three factors mentioned. Within the accuracy of
the information available the three factors will be
considered independent, that is the concentration achievable
in the effluent by exemplary chemical treatment is not
related to the amount of water used for processing. The
best water use is not necessarily found in a plant operating
an exemplary waste treatment facility and vice versa.
However, once exemplary values for both water use and
concentrations have been established the product of the two
represents an overall figure of merit that takes into
account both parameters. Therefore, the guidelines can be
expressed in terms of the product of the two parameters:
(mg/1) x (1/sq m) = mg/sq m. More water may be used if
lower concentrations are achieved and vice versa.
Concentrations of Effluent Constituents and Eg. Table 59
lists the proposed concentration portion of the guidelines
for each parameter to be limited. It also shows the
fraction of the fraction of analysis meeting these proposed
concentrations. The values proposed are for the total
amount of constituent, dissolved or suspended. Therefore,
both proper precipitation and efficient clarification and/or
filtration are required to meet the concentrations
considered achievable.
249
-------
TABLE 59 - Achievable Effluent Concentrations (mg/1)
TSS 20
Phosphorus 1.0
Cyanide (oxidizablc) 0.05
Cyanide (total) 0.5
Fluoride 20
Cadmium 0.3
Chromium (Hexavalent) 0.05
Chromium (total) 0.5
Copper 0.5
Iron 1.0
Lead 0.5
Nickel 0.5
Tin i.o
Zinc 0.5
Platinum 0.05
Rhodium 0.05
Iridium 0.05
Osmium 0.05
Palladium 0.05
Ruthenium 0.05
pH 6-9
250
-------
Figure 1 is a plot of water use values of 1/sq m-operation
for fourteen plants. Thirteen of these are less than 250
1/sq m-operation (6.3 gal/sq ft-operation) . The median
value is 125 1/sq m-operation (3.1 gal/sq ft-operation).
Because the influence of shape and design and the possible
greater contributions made by precious metal platers the
65th percentile of 160 1/sq m-operation (U.O gal/sq ft-
operation) is chosen as the water use factor.
Effluent Limitations Guidelines
To derive guideline values, the water use factor of 160 1/sq
in/operation is multiplied by the concentrations achievable
by coprecipitation as listed in Table 59. This is the 30
day average value.
Recognizing that controls may not allow attainment of the
average effluent limitation guidelines on a daily basis due
to variation in both water flow and concentration, the
maximum for any single-day average is specified to be two
times the 30-day average.
Five months of daily data were obtained from plant 15-1.
This data appears in Table 60. In this time period the 30-
day average value of 80 mg/m2 operation for Zn was exceeded
on two occasions, December 4, 1971 and December 10, 1974.
The thirty day average of 80 mg/m2 - operation for CNT was
never exceeded. The one-day maximum of 160 mg/m2
operation was never exceeded by Zn or CN.
One month1s effluent data was chosen at random from plant
12-6. It appears in Table 61. Ni, TSS, Cu, Zn, CNT are not
out of compliance with the thirty day average or one-day
maximum. Cr+* is not out of compliance with the 30-day
average but i s out on the one-day maximum three times during
the month.
Five months of twice weekly sampling TSS, for plant 33-15 is
shown in Table 62. CrT, Ni, Cu never exceed the 30-day
average or one-day maximum. Cr+* is not in compliance for
30-day average or one day maximum.
Plants Meeting the Guidelines
The effluent concentrations and water use factors have been
collected for 21 plants in Table 58. Except as indicated on
the table, all values are in total solids. Plants 36-1, 36-
12, 15-3, 15-1, 12-6, 33-15 and 12-8 met the 1977 standards.
Plants 36-1 and 36-12 met the new source performance
251
-------
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-
VD VO VO 'O VO VO VO VO VO '-O VO VO VO UD M3 V^O ^-O >-
I I I I I I I I I I I I I I I1 I I I
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I
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-------
TABLE 60
PLANT 12-6
mg/m2-0peratlon
DATE pH Zn CNT
11-13-7^ 8 1.3 27.7
11-14-74 7 11.9 14.5
ll_l8-7U 6 15.8 18.5
11-19-74 7 13.2 22.4
11-20-74 7 48.8 14.5
11-25-711 8 15.8 29.0
11-26-74 10 6.6 31.7
Average 7.6 17-4 23.3
12-02-74 8 10.6 30.4
12-03-74 7 14.5 46.2
12-04-74 7 12.1 29.0
12-05-74 6 55.4 17.2
12-06-74 6 17.2 21.1
12-09-74 9 15.8 31.7
12-10-74 9 92.4 23.8
12-11-74 7 29.0 21.1
12-12-74 10 5-3 23.8
12-13-74 8 37.0 37.0
12-16-74 8 01.1 22.4
12-18-74 7 9.2 19.8
12-19-74 7 25.1 17.2
Average 7.6 38.4 26.2
1-03-75 6 10.6 23.8
1-06-75 9 11.9 15.8
1-07-75 7 6.6 19.8
1-08-75 7 7.9 13.5
1-09-75 7 33.0 15.3
1-10-75 8 66.0 18.5
1-13-75 8 13.2 29.0
1-14-75 10 11.9 52.8
1-15-75 8 15.8 27.7
1-16-75 7 13.2 14.5
1-17-75 7 48.8 13.2
1-20-75 6 15.8 18.5
1-22-75 8 6.6 15.8
1-23-75 7 6.6 15.8
1-24-75 8 38.3 22.4
1-27-75 8 9.2 17.2
1-28-75 6 7.9 18.5
1-29-75 7 1.3 14.5
1-30-75 7 26.4 29.0
1-31-75 7 21.1 26.4
Average 7.4 18.6 20.9
253
-------
DATE
7-03-74
7-09-74
7-11-74
7-15-74
7-17-74
7-23-74
7-26-74
7-30-74
Average
8-02-74
8-06-74
8-09-74
8-12-74
8-14-74
8-19-74
8-23-74
8-26-74
8-28-74
Average
9-04-74
9-06-74
9-10-74
9-12-74
9-16-74
9-19-74
9-24-74
9-27-74
Average
10-02-74
10-04-74
10-07-74
10-10-74
10-15-74
10-18-74
10-21-74
10-23-74
10-29-74
10-31-74
Average
11-04-74
11-06-74
11-12-74
11-15-74
11-19-74
11-21-74
11-25-74
11-27-74
7-5
8.6
8.8
8.6
8.3
8.4
8.4
8.5
8.4
8.7
8.5
8.8
8.9
8.7
8.5
8.8
8.6
8.5
8.7
8.8
8.8
8.6
8.7
8.7
8.8
8.9
9.1
8.8
8.9
8.9
8.7
9.0
8.6
8.6
8.9
8.9
8.9
9.0
8.8
8.7
8.3
8.3
8.7
8.5
8.6
8.3
8.7
Average
3.5
TABLE
PIANT
61
33 - 15
mg/m2-0perat ion
Cu
18.5
29.3
16.2
11.6
31.7
17-5
16.3
30.6
21.5
16.3
10.2
14.3
11.0
16.3
19-7
16.2
48.2
23.2
21.9
18.3
28.6
21.9
19.7
15.3
13.9
15.3
30.2
20.4
24.1
18.6
30.6
16.2
18.5
17.5
36.7
21.9
26.3
32.8
30.4
18.4
24.5
26.5
22.4
20.2
34.9
35.0
17.2
24.9
Ni
95
34.3
37-1
44.1
95
35
36.7
49.0
53-3
42.8
49.0
40.8
44.2
57.1
39.4
51.0
122.6
74.2
65.1
89.7
65.3
21.9
55.7
7S.8
46.4
37.2
74.2
5E.6
4-,. 8
37.1
96.4
4t .1
89.8
87.6
7-1.4
65-7
63.3
48.2
80.9
40.8
81.6
73.4
57.1
71.8
33.1
8:..o
55-0
6:.. 7
Cr+6
89.8
39.6
46.4
23.2
52.8
61.3
53.0
65.3
53.9
75.5
65.3
55.1
25.8
61.2
46.0
71-9
74.5
69.6
68.1
75.5
36.7
32.9
50.8
61.3
69.6
37.4
60.3
53-1
50.4
32.5
21.9
32.5
23.7
24.1
20.4
15-3
6.6
11.0
29.3
18.4
30.6
4.1
53.0
7.4
25.8
9.2
24.1
21.6
CrT
95
44.9
48.7
27.8
55.4
63.5
61.2
71.4
58.5
77.5
73.4
61.2
27.6
63.2
70.1
81.2
48.2
83.5
73.2
77-5
63.2
54.8
55.7
63.5
83.5
59.1
65.0
65-3
65.7
39.^
21.9
32.5
23-7
26.3
24. "S
19.7
11.0
30.7
36.9
24 . 5
34.7
14.3
75.5
117.8
42.3
31.3
46.4
48.4
CNT
10.6
2.9
3.2
2.8
2.6
8.7
4.9
4.1
5.0
6.7
2.2
5.3
1.8
2.0
2.0
3-0
2.6
2.1
3-5
8.2
4.1
8.1
13.2
8.1
4.9
3.7
6.5
7-1
7.9
7.9
7.7
4.9
3.4
8.3
8.8
13.8
8.5
8.1
9.9
5.1
4.3
- .2
6.9
2.4
8.8
2.4
3.3
4.3
TSS
845
1637
858
766
1109
1226
734
877
1006
653
714
898
2594
1102
1489
974
1862
766
1382
836
714
701
1067
460
742
548
928
750
1621
742
1051
557
818
635
612
701
876
1007
883
449
1204
1775
1408
1398
626
3864
877
1450
254
-------
TABLE
62
PLANT 15-1
mg/m2-0peration
DATE
6-01-74
6-02-74
6-03-74
6-04-74
6-05-74
6-06-74
6-07-74
6-08-74
6-09-74
6-10-74
6-11-74
6-12-74
6-13-74
6-14-74
6-15-74
6-16-74
6-17-74
6-18-74
6-19-74
6-20-74
6-21-74
6-22-74
6-23-74
6-24-74
6-25-74
6-26-74
6-27-74
6-28-74
6-29-74
6-20-74
pH
Hi
9.3
8.6
8.4
8.6
8.1
8.1
8.7
9.5
8.2
9.0
7.9
8.0
8.6
8.9
9.0
8.6
8.1
8.2
8.5
9.1
8.3
9.5
7.9
8.9
8.8
8.9
9.6
9.8
9.5
8.1
Lo
7.5
6.9
6.9
6.3
6.6
6.8
7.8
8.0
6.8
7.1
6.6
6.4
7.4
6.4
7.5
7.2
6.9
6.6
7.3
7-3
7.5
8.3
6.6
7.3
7.2
7.6
7.8
8.0
8.3
7.0
CN
5.7
7.4
5.3
6.2
6.6
7.2
10.6
16.6
35.3
22.3
19.2
7.0
6.6
10.1
6.2
7.0
5.7
5.7
6.2
5-7
6.6
8.4
7.4
5.7
6.2
6.2
6.2
5.7
5.7
3.1
Cr+6
.52
5.4
.48
2.2
1.8
1.3
4.8
.52
4.2
.62
.60
1.3
.60
.92
.56
1.3
1.0
1.0
2.8
8.3
8.4
40.3
46.2
.52
5.6
2.2
1.7
7-6
78.0
.28
CrT
5.2
6.8
4.8
5.6
6.0
6.5
9.6
5.2
6.0
.72
6.0
6.4
6.0
9.2
5.6
6.4
5.2
5.2
5.6
10.4
30.0
15.2
170.
10.4
16.8
5.6
5.6
6.8
130.
22.4
Zn
5.2
12.6
19.2
11.2
12.0
19-5
28.8
5.2
12.0
7.2
12.0
19.2
24.0
36.8
16.8
12.8
5.2
10.4
11.2
20.8
12.0
15.0
20.4
10.4
5.6
16.8
11.2
15.6
15.6
11.2
Cu
5.2
20.4
48
44.8
48.0
58.5
67.2
31.2
42.0
50.4
48.0
57.6
60
73.0
39.2
38.0
41.0
36.4
44.8
41.6
42.0
22.8
61.2
52.
50.4
50.4
33.6
52.0
57.2
19.6
Ni
15.6
13.6
38.4
56.0
60.0
84.5
96.0
20.8
42.0
21.6
36.0
57.6
66.0
110.4
56.0
25.6
46.8
36.4
67.2
31.2
66.0
30.4
61.2
41.6
56.0
44.8
39.2
31.2
20.8
8.4
TSS
1508
408
696
476
930
813
3984
2392
690
806
360
536
1560
3588
1736
832
416
806
308
1196
810
2546
1156
1378
1316
980
644
1040
1950
794
Average
.7
7.2
8.6
8.0
22.4 16.2 44.6
46.0
1170
255
-------
standards. Plants 11-8 and 33-20 were out of compliance on
only one or two parameters.
Engineering Aspects of the Application of Various Types of
Control Technology
Advanced in-process controls for recovery of plating
chemicals are rapidly gaining acceptance and often show a
net cost savings compared to chemical treatment. However,
the applicability of these in-process controls is dependent
on first achieving reduction in water use by multitank
countercurrent rinsing. Such installation is not practical
in all cases.
Process Changes
Process changes are not currently available for the
electroplating industry that would lead to greater pollution
reduction than can be achieved by the recommended effluent
limitations. Some possible process changes such as use of
noncyanide plating baths may eliminate one pollution
parameter, but do not eliminate all and may cause other
problems. They may be useful in some facilities for
reducing the cost of meeting the effluent limitations
recommended in this document.
Nonwater Quality Environmental Impact
As discussed in Section VIII of this report, the principal
nonwater quality aspect of electroplating waste treatment is
in the area of solid waste disposal. Disposal of sludges
resulting from metal removal by chemical treatment is a
current problem in many states that have a high
concentration of facilities. The problem might be partially
alleviated by disposal of drier sludge.
The use of advanced technology to recover metal plating
chemicals from rinse water rather than chemical treatment
which adds to the sludge is being applied in areas where the
sludge-disposal problem is greatest. Further impetus in the
direction of recovery rather than disposal is expected to be
provided by authorities responsible for solid waste
disposal. This will have an overall beneficial effect on
water pollution because of the concurrent requirements for
water conservation for economic application of recovery
techniques.
It is estimated that many of the existing sources dis-
charging to navigable waters are already using chemical
treatment methods with a high percentage removal of metals.
256
-------
This is particularly true in geographic areas where water
pollution reduction has been emphasized and the sludge-
disposal problem is most evident.
There will be no direct effect on air quality as a result of
the application of recommended technology for water
pollution reduction. Indirect effects related to increased
energy use are estimated to be modest.
Guidelines ,for the^Application of^Effluent_Limitations
Selection of Production Unit
Effluent limitations are intended to specify the maximum
quantity of pollutants which may be contained in the
discharged treated effluent from a point source. This
quantity must be related to a unit of production so that the
effluent limitations can be applied broadly to various
plants in the same category regardless of their production
capacity. For example, an effluent limitation for a
particular wastewater constituent in mg/unit times the
production rate in units/hr equals the maximum amount of
that constituent that can be discharged in mg/hr. Thus, for
any production unit:
ma X Unit = mg X 1_
unit hr 1 hr Equation 1
The right-hand side of the above equation represents the
normal method of monitoring based on analysis of
concentration of individual pollutants in the effluent in
mg/1 and measurement of the effluent discharge rate in 1/hr.
Expressing the effluent limitation as a function of a
production unit compensates for change in production rate,
which changes the effluent discharge rate. The effluent
rate in the electroplating industry is closely related to
the rinse water rate which is in turn related to the
production rate of electroplated parts.
The effluent discharge rate as volume per day is commonly
reported by electroplating and other industrial sources.
Because many plants do not work on a 24-hour-day basis at
all times, it would be preferable to use the next smaller
unit of time, which is an hour. This avoids the uncertainty
associated with the daily unit which often requires further
definition as to the number of shifts worked per day and the
hours per shift.
The most appropriate production unit in some industries is
the weight of product produced or the weight of raw
257
-------
materials purchased. Neither a unit quantity of product
produced nor a unit quantity of raw material use is
appropriate for the electroplating industry, because the
quantity of product expressed as the weight of products
plated does not bear any relation to raw waste produced.
Electroplating is a surface process that is not invluenced
by the volume or density of the part plated. The raw waste
load is related to surface area (not volume) of
electroplated parts which determines the concentrated
solution dragout, rinse water use, and ultimately the degree
of pollution reduction achievable. While it is common in
barrel plating of small parts to weigh the plated parts as a
control measure for basket loading, the optimum weight of
parts was originally determined by trial and error plating
or precalculation of the part per unit weight in order to
achieve the correct total area.for optimum plating current
density. Regardless of the method of controlling the
plating operation, the dragout is related to the total area
of parts plated and not the weight. Solution adhering to
the surface of small parts causes dragout. Although some
cup-shape parts that are difficult to drain or rinse may
cause high dragout not directly related to area, weight
would not be a good unit quantity applicable to both rack
and barrel plating.
Although the amount of raw material used or chemicals
purchased was considered as a possible unit quantity related
to production, neither unit appeared suitable as a reliable
measure of production. The weight of material purchased and
used as soluble anodes ends up on the parts plated, but this
weight must be divided by the thickness plated to obtain a
correlation with production rate in area plated per unit
time which is the true determinant of raw waste load. In
the case of chemicals purchased for bath make up and
particularly for chromium salts purchased for plating with
insoluble anodes, there is a further complication. A
material balance will show that the difference between the
chromium purchased and the chromium on the plated parts
produced equals the chromium in the precipitated sludge
minus the small amount of chromium discharged with the
treated effluent. Thus, chromium in chromium salts
purchased in excess of that on plated parts reflects dragout
and increased sludge but not necessarily increased water
pollution. The same reasoning applies to all other metal-
containing chemicals purchased for bath make up which
primarily end up as precipitated and separated sludge.
Although the amount of chemicals purchased indicates total
dissolved salts in the treated effluent, total dissolved
solids is not considered an important pollutant parameter in
the electroplating industry. (See Section VT.)
258
-------
Consideration of the above factors led to the conclusion
that the unit of production most applicable to the
electroplating industry is surface area. The surface area
withdrawn from a concentrated solution in a plating
operation is the paramount factor influencing dragout of
solution constituents, some portion of which ends up in the
waste water and treated effluent. Surface area influencing
dragout includes not only the surface area receiving an
electroplate but also the surface area of nonsignificant
surfaces receiving little or no electrodeposit plus the
surface area of racks or barrels which hold the parts.
The total surface area is rarely known and impractical to
measure in some cases in the electroplating industry. In
this case, the plated area is the alternative logical unit
of production. However, plated area is not a measurement
that has been historically recorded by the industry and may
not be readily available from all plants. Alternative units
of production based on amperes and water use, which are more
easily measured, were developed and correlated with plated
area and ultimately to the total surface area in
establishing effluent limitations. These alternative means
of calculating the area plated should only be used until the
industry does have ample records of area plated.
Plated Area Unit of Production
The plated area is the primary unit of production on which
the effluent limitations in Table 1 are based. Plated area
is defined with reference to Faraday1s Law of electrolysis
by the following equation:
_EIT
S = 100 kt Equation 2
where s = area, sq m (sq ft)
E = cathode current efficiency, percent
I = current used, amperes
T = time, hours
t = average thickness of deposit, mm (mil)
k = a constant for each metal plated based on the electro-
chemical equivalent for metal deposition, amp-hr/mm-sq m
(amp-hr/mil-sq ft).
The numerical product of current and time (IT) is the value
that would be measured by an ampere-hour meter. Values of
the constant k based on equivalent weight and the valance of
the metal deposited are shown in Table 63.
259
-------
TABLE 63 ELECTROCHEMICAL EQJIVALENTS AND RELATED DATA*
(All figures In this table are based on 100% current efficiency)
Element
Aluminum
Antimony
Arsenic
Bismuth
Cadmium
Chromium
Cobalt
Copper
Gallium
Germanium
Gold
Indium
Iridium
Iron
Lead
Manganese
Mercury
Nickel
Palladium
Platinum
Polonium
Rhodium
Rhenium
Selenium
Silver
Tellurium
Thallium
Tin
Zinc
Atomic
weight
26.97
121.76
74.91
209.0
112.4
52.01
58.94
63.57
69.72
72.60
197.2
U4.76
193.1
55.84
207.2
54.93
200.61
58.69
106.7
195.23
210
102.9
186.31
78.9
107.88
127.61
204.39
118.7
65.38
Valence
3
5
3
5
3
5
3
2
6
3
2
2
1
3
4
2
3
2
t
3
4
3
2
2
2
2
1
2
4
3
2
4
2
4
4
3
2
7
4
1
4
2
1
4
2
nig/cou-
lomb
0.0932
0.2523
0.4206.
0.1525
0.2587
0.4332
0.7219
0.5824
0.0898
0.1796
0.3054
0.3294
0.6588
0.2408
0.1881
0.3762
0.6812
1.0218
2.0435
0.3964
0.5003
0.6670
0.2893
1.074
0.2846
1.0394
2.0788
0.3041
0.2764
0.3686
0.5528
0.5058
1.0115
0.5440
0.2666
0.3555
0.5332
0.2758
0.2046
1.1179
0.3306
0.6612
2.1180
0.3075
0.6150
0.3387
g/amp hr
0.3354
0.9085
1.5141
0.5589
0.9315
1.5594
2.5990
2.097
0.323
0.646
1.099
1.186
2.372
0.8670
0.6771
1.3542
2.4522
3.6783
7,3567
1.4271
r.sooi
2.4012
1.042
3.865
1.0746
3.7420
7.4839
1.095
0.9951
1.3268
1.9903
1.8208
3i6416
1.958
0.9598
1.2797
1.9196
0.9929
0.7364
4.0245
1.1901
2.3803
7.6249
1.1070
2.2141
1.2195
oz/atnp hr
0.0118
0.032
0.0535
0.0197
0.0328
0.055
0.0915
0.074
0.0114
0.0228
0.0388
0.0418
0.0837
0.0306
0.02388
0.04776
0.0865
0.1297
0.2595
0,05033
0.06349
O.C8469
0.0368
0.1362
0.0362
0.1320
0.2640
0.0386
0.035
0.0467
0.0703
0.0645
0.1284
0.0691
0.0338
0.0451
0.0677
0.0350
0.0260
0.142
0.0420
0.0840
0.2583
0.039
0.078
0.043
lb/1,000
amp hr
0.7394
2.0028
3.3380
1.2322
2.0536
3.4378
5.7297
4.6226
0.7129
1.4258
2.4236
2.6142
5.2283
1.9114
1.4928
2.9855
5.406
8.1094
16.2187
3.1461
3.9704
5.2938
2.2963
8.5210
2.2588
8.2496
16.4992
2.4135
2.1939
2.9252
4.3878
4.0142
8.0283
4.318
2.1160
2.8213
4.2319
2.1890
1.6235
8.8726
2.6238
5.2476
16.8000
2.4406
4.8812
2.6886
oz/sq ft for
sp gr 0.001 in.
2.7
6.68
6.68
5.73
5.73
9.8
9.8
8.64
7.1
7.1
8.9
8.92
8.92
5.9
5.35
5.35
19.3
19.3
19.3
7.31
22.42
22.42
7.9
11.3
7.2
13.55
13.55
8.9
12.0
12.0
12.0
21.4
21.4
12.5
12.5
12.5
20.53
4.81
10.5
6.25
6.25
11.85
7.3
7.3
7.1
0.225
0.557
0.557
0.475
0.475
0.816
0.816
0.72
0.591
0.591
0.74
0.74
0.74
0.491
0.445
0.445
1.61
1.61
1.61
0.608
1.869
1.869
0.66
0.94
0.598
1.129
1.129
0.742
0.998
0.998
0.998
1.78
1.78
1.04
1.04
1.04
1.710
0.400
0.875
0.520
0.520
0.986
0.61
0.61
0.59
amp hr to
deposit 0.001
in./sq ft
19.05
17.4
10.4
24.1
14.5
14.8
8.93
9.73
51.8
25.9
19.0
17.7
8.84
16.0
18.6
9.31
18.6
12.4
6.2
12.1
29.4
22.1
17.9
6.91
16.5
8.55
4.27
19.0
28.6
21.4
14.2
27.6
13.85
30.8
23.1
15.37
48.8
15.4
6.16
12.4
6.19
3.82
15.63
7.82
13.7
amp hr to
Symbol of aepOSlt .1 %
element mm/sq m Eff
Al
Sb
As
Bi
Cd 4.12 90-100
Cr 21.9 13
Co 8.05 100
Cu 7.50 100
3.74 50-100
Ga
Ge
Au
2.63 100
In 5.13 50-80
Ir
Fe 7.58 100
Pb 2.93 100
Mn
Hg
Hi 8.05 100
Pd 12.12
9.07
6.02
Pt 11.69 60
5.85 60
Po
Rh 13.05
9.79 60
6.53
Re
Se
Ag 2.61 100
Te
Tl
Sn 6.62 90
3.31 100
Zn 5.80 100 (ACID)
60-90 (CD)
From Electroplating Engineering Handbook
260
-------
Average thickness can be approximated by averaging thickness
measurements at several points on a single plated part, to
establish the ratio of average to minimum thickness.
Minimum thickness is customarily monitored to meet the
specifications of purchasers of electroplated parts, based
on service requirements.
This equation was used in this study to determine the plated
areas per unit time in each plating operation when the only
available information was the current used and the average
thickness of deposit. This equation was also used as a
check on estimates of surface area plated provided by the
plants contacted.
To calculate the total plated area on which the effluent
limitations are based for a specific plant, it was necessary
to sum up the area for each electroplating process line
using Equation (2). For process lines containing two or
more electroplating operations (such as in copper-nickel-
chromium decorative plating) the plated area is calculated
by Equation (2) for each plating operation in the process.
The results should be the same, since the same parts are
processed through each operation. However, if the
calculated plated area differed for each plating operation
in a single process line, the average of the calculated
plated areas for the operations was used. The sum of the
plated area for each process line is the total plated area
for the plant.
Small discrepencies in the above calculation for two or more
plating operations in the same process line might be related
to a difference in the actual current efficiencies from
those in Table 37 which are to be used for the calculation.
However, experience with data from several plants indicated
that the more likely cause of the discrepancy is the
accuracy of the reported values of average plate thickness.
The use of ampere-hour on rectifiers might have value for
monitoring or record keeping for some plants in lieu of
measuring the area of the parts plated provided the average
thickness plated is known or determined.
Records of plating voltage and ampere-hours on each
rectifier (or watt-hours) plus thickness deposited might be
correlated with watt-hours of electricity consumed per day
or month with allowance for other electricity uses
(lighting, pumps, etc) to estimate total plated area per day
or month. The total effluent could be approximated by the
plant water purchases if mainly for electroplating. Thus,
the information on electric power consumption and water
261
-------
consumption from monthly bills for these services might be
used in an approximation of daily plated area for a cross
check against plated area determined by more direct means.
In practice, it should be possible for electroplaters to
readily adapt to keeping records of plated area for
reporting purposes. The fact that many platers do not
presently know their production rate in terms of surface
area plated is not a valid consideration since there has
been no prior requirement to keep such records. Determining
plated area should not be difficult for platers whose
process operation is dependent on use of the correct current
density for optimum plating results.
"Process";
A process is the accumulation of steps
required to bring about an electroplating
result.
"Operation"; The concept of an operation is a crucial
one in the formation of limitations
for each individual installation plant.
For this purpose, an operation shall
be defined as any step followed by
a rinse in the electroplating process
in which a metal is electrodeposited
on a basis material. Electroless
plating on non-metallic materials
for the purpose of providing a
conductive surface on the basis
material and preceding the actual
electroplating step, and the past
treatment steps of chromating,
phosphating and coloring where an
integral part of the plating line
and stripping where conducted in
conjunction with electroplating for
the purpose of salvaging improperly
plated parts may be included under
the term operation for the purpose
of calculating effluent discharge.
"Rinse";
A rinse is a step in a process used
to remove components of a bath from
262
-------
the work following an operation.
A rinse may consist of several
sequences such as successive
countercurrent rinsing or hot
rinsing followed by a cold
rinsing with deionized water.
Nevertheless, there is only one
rinse after an operation.
Applying Effluent Limitation Guidelines
The application of the effluent limitation guidelines
will be illustrated by examples. In all cases, certain
basic information is needed from a plant:
(1) The number of operations in each process line
including initial cleaning and pickling
operations and all rinses
(2) The sq m/hr through each process line (average
for 30 sequential days)
(3) The volume of effluent from the plant
due to electroplating processes (average
for 30 sequential days)
The concentrations of waste water constituents
in the effluent that are limited by the
guidelines. These are the concentrations
in the effluent due to electroplating
processes before dilution by effluent
from other processes (average for 30
sequential days).
Determination^Qf,Plated Area/Hr/Operatjon
The area for each line will be determined from information
on the (1) average amperes used, (2) the sequence of plating
operations, and (3) the average thickness in mil of each
type of plate. If complete data on thickness is lacking,
the following value will be used:
Copper 0.3 mil
Nickel 0.3 mil
Zinc 0.3 mil
Chromium 0.015 mil
Where chromating follows plating, the area will be the same
as that of the primary plating operation. The equation:
263
-------
S = EIT/100 kt
is then used to calculate plated area/hr/operation. In a
line with several sequential operations, it is likely that
the calculated plated areas for each plating operation will
vary from each other although the actual area plated should
be the same. The difference in calculated areas may vary by
a factor of two or three. When applying the guidelines,.the
figure used for area plated should be the arithmetic average
of the calculated plated areas.
Where actual amperes are not known, a value equal to 2/3 of
the installed capacity for the line should be used. Where
information on amperes is completely lacking for a line but
water use is available, the sq m/hr may be determined by:
Sq m/hr = 1/hr^used,on the^line
(200 1/sq m)(no. of operations)
Sq ft/hr = gal/hr_used 011 the line
(5 gal/hr) (no,, of operations)
Once the plated area has been measured the guidelines can be
used to determine the total allowable discharge of waste
water constituents from the plant. Every time the surface
is rinsed, following some operation in the process line, it
is assumed that more waste water is produced, and a greater
quantity of waste water constituents may be discharged under
the guidelines. The cleaning and pickling rinses are
therefore incorporated into the rinse following the first
plating operation for purposes of calculating the allowable
amount of waste water constituents discharged. The total
allowable discharge in g/day will be:
(103) (sq m plated/hr) (effluent limitation in mg/sq m)
(No. of oper.)(hr/day)
The total allowable discharge in Ib/day is:
(10«) (sq ft plated/hr) (effluent limitation
in Ib/million sq ft (No. of oper.) (hr/day) = Ib/day
These relations hold for each effluent limitations guideline
value listed in Table 1. The relations apply to each
process line or part of a process line if the area plated/hr
changes in the line.
The actual discharge from the plant is the product of the
volume of effluent/hr and the concentration of waste water
constituent in the effluent.
264
-------
Thus,
g/day = (liters/hr) (mg/1) (10-3) (hr/day)
Ib/day = (8.33 x 10-*) (gal/hr) (mg/1) (hr/day)
Several examples will show how the guidelines are applied to
specific processes.
Example I. This example of plating on steel has three
operations as shown in Figure 33. For the purpose of
effluent limitations the nickel strike, nickel plate, and
chromium plate are the three included operations and the
alkaline cleaning and acid pickling operations are the
excluded operations. The line processes an estimated 10 sq
m/hr of work and the treatment plant discharges 3000 1/hr.
Next consideration must be given to what waste water
constituents can appear in the water from the line so that
one can be sure that the analysis of the effluent accounts
for these constituents.
Base Metal Dissolution - Iron
Cleaning and Pickling - Phosphates, Cyanide
Electroplating - Nickel, Chromium (Total and
Hexavalent)
The concentrations of waste water constituents in the
effluent were reported as follows:
Phosphate 2 mg/1
Cyanide (oxidizable) 0.2
Cyanide (total) 0.3
Nickel 0.6
Chromium (total) O.U
Chromium (hexavalent) 0.03
Total Suspended Solids 10
pH 7.5
The above data are adequate to determine whether effluent
limitations are being met. The actual discharge may be
compared with the allowable discharge.
Actual Discharge:
(Effluent concentration, mg/1)x(Effluent discharge, 1/hr)
(hr/day) = mg/day.
Allowable Discharge:
(Guideline, mg/m2/operation) x S± (m2/day) x operations!
265
-------
Electrolytic
Alkaline Clean
Ftinse
Acid Pickle
Rinse
Nickel Strike
Rinse
Nickel Plate
Chromiium Plate
FIGURE 33 OPERATION OF A NICKEL AND
CHROMIUM PLATING LINE
266
-------
= mg/day.
Phosphate:
Actual discharge = 2.0 x 3000 x 1/106 = 0.048 kg/day
Allowable discharge = (160) x 10 x 8 x 3/106 0.0384 kg/day
Guideline not met.
Cyanide (oxidizable)
Actual discharge = 0.2 x 3000 x 8/106 = 4.80 x 10-* kg/day
Allowed discharge = 8 x 10 x 8 x 3/106 = 1.92 x 10~* kg/day
Guidelines not met.
Cyanide (total)
Actual discharge = 0.3 x 3000 x 8/106 = 7.20 x 10-* kg/day
Allowed discharge = 80 x 10 x 8 x 3/106 = 1.92 x 10~3 kg/day
Guidelines met.
Nickel:
Actual discharge = 0.6 x 3000 x 8/106 = 1.44 x 10~3 kg/day
Allowed discharge = 80 x 10 x 8 x 3/106 = 1.92 x 10~3 kg/day
Guidelines met.
Chromium (total):
Actual discharge = 0.4 x 3000 x 8/106 = 9.60 x 10~* kg/day
Allowed discharge = 80 x 3000 x 8/106 = 1.92 x 10-3 kg/day
Guidelines met.
Chromium (hexavalent) :
Actual discharge = 0.03 x 3000 x 8/106 = 7.20 x 10~5 kg/day
Allowed discharge = 8 x 10 x 8 x 3/106 = 1.92 x 10~* kg/day
Guidelines met. ~"
Suspended Solids:
Actual discharge = 10 x 3000 x 8/106 = 2.40 x 10-2 kg/day
Allowed discharge = 3200 x 10 x 8 x~3/10~* = 7.68 x 10-2 kg/day
Guidelines met.
pH effluent limitation guidelines of 6-9 met by pH 7.5.
Example II. Example I considered one line to which
guidelines for one subcategory applied. Plants almost
invariably involve more than one line and process. Where
one subcategory is involved for several lines and processes
267
-------
for calculation to determine effluent limitations guidelines
is essentially identical to that of Example I. A flow sheet
for two electroplating lines (and processes) is shown in
Figure 34. The base metal is steel.
Zinc plating is the included operation in Line 1 and copper
plating is the included operation in Line 2 for the purpose
of establishing effluent limitations guidelines. Line 1
processes 10 sq m/hr of work and Line 2 processes 5 sq m/hr
of work. Effluent volume due to both lines is 1000 1/hr.
The plant operates 16 hr/day.
Constituents subject to effluent limitations guidelines
expected in waste water are
Base Metal Dissolution - Iron
Cleaning and Pickling - Phosphate, Cyanide
Electroplating - Zinc, Copper, Cyanide
The concentrations of waste water constituents in the
effluent were reported as follows:
Phosphate 1 mg/1
Cyanide (total) 0.1 mg/1
Cyanide (oxidizable) 0.02 mg/1
Chromium (total) 0.1 mg/1
Chromium (hexavalent) 0.06 mg/1
Total Suspended Solids 15 mg/1
pH 6,5 mg/1
Calculations are similar to those for Example I.
Phosphate:
Actual Discharge = 1.0 x 1000 x 16/106 = 1.60 x 10-3 kg/day
Allowed Discharge = 160 x (10 x 1 + 5 x 1) x 16/106 =
3.84 x 10-3 kg/day
Guidelines met.
Calculations for other constituents are identical, except
for changes in concentrations for determining actual
discharge and changes in effluent limitation guidelines for
determining allowed discharge.
Actual Discharge, Allowed Discharge,
Constituent Ka^lY. kg /day
Phosphate 1.60 x 10-3 3.84 x 10-3
Cyanide (total) 1.60 x 10~* 1.92 x 10- 3
Cyanide (oxidizable) 3.20 x 10-s 1.92 x 10-*
268
-------
Line 1
Line 2
Electrolytic Clean
Rinse
Acid Pickle
Rinse
Copper Plate
(cyanide bath)
I
Rinse
FIGURE 34 SIMULTANEOUS OPERATION OF ZINC
AND COPPER PLATING LINES
269
-------
Chromium (total) 1.60 x 10-* 1.92 x 10-3
Chromium (hexavalent) 9.60xlO~5 1.92x 10-*
Total Suspended Solids 2.40 x 10~2 7.68 x 10~«
pH 6.5 6-9
Actual discharge amounts meet guidelines in all cases.
Example III. A more complex situation is encountered when
more than one process is operating simultaneously in a plant
but processes may be found in more than one subcategory. In
such a case, the effluent limitation guideline for more than
one subcategory must be considered. Figure 35 shows a line
for electroless plating on plastics (Subcategory (2)) and an
electroplating nickelchromium line (Subcategory (1))
operating in sequence. The plant may consider both
processes as one line, but for purposes of considering
whether effluent limitations guidelines are being met, the
sequence must be considered as made up of two separate
processes.
The electroless process plates 10 sq m/hr of work. Of this,
9 sq m/hr continue through the electroplating process while
1 sq m/hr is finished after the electroless process or is
rejected. The volume of effluent from the two processes is
5000 1/hr. The plant operates 10 hours per day. The
included operations for determining whether effluent
limitations guidelines are met are, for the electroless
process
Sensitize
Activate
Electroless Nickel
and for the electroplating process
Acid copper Strike
Nickel Electroplate
Chromium Electroplate.
Constituents subject to effluent limitations guidelines
expected in waste waters are
Cleaning and Pickling - Phosphate, Chromate
Electroless Plating - Nickel
Electroplating - Copper, Nickel, Chromium.
The concentrations of waste water constituents in the
effluent were reported as follows
Phosphate 2 mg/1
270
-------
Soak Clean
Rinse
Acid Dip
Rinse
Sensitize
Rinse
Rinse
Electroless Nickel
Rinse
Acid Copper Strike
Rinse
Nickel Electroplate
Rinse
Chromium Electroplate
Rinse
FIGURE 35 ELECTROLESS NICKEL PLATING OF PLASTIC PLUS
NICKEL-CHROMIUM ELECTROPLATING
271
-------
Chromium (total)
Chromium (hexavalent)
Copper
Nickel
Total Suspended Solids
pH
0.3
0.03
0.
0
25
8.0
5
7
The actual amount of discharge is calculated as in the
previous examples. The allowable discharge is calculated by
determining the mg/day for the elctroless plating process,
which is in Subcategory (2) and adding to the mg/day for the
nickel and chromium processes, which are in Subcategory (1).
±(320) (10) (10) (3)
kg/day.
(160) (9) (10) (3) 1/10* = 1.39 x
Allowable discharges for other constituents are made in the
same manner, using appropriate values for the effluent
limitations.
Phosphate
Chromium (total)
Chromium (hexavalent)
Copper
Nickel
Total suspended Solids
pH
Actual Discharge
kg/day.
1.00 x 10-2
1.50 x 10-3
1.50 x 10-*
2.50 x 10-3
3.50 x 10-3
1.25 x 10-»
8.0
Allowed Discharge
_kg/day
1.39 x 10-2
6.96 x 10-3
6.96 x 10-*
6.96 x 10-3
6.96 x 10-3
2.78 x 10-»
6-9
It is apparent from Example III how a plant with diverse
processes can be analyzed. All of the electroplating is
divided into individual processes; each process is assigned
to the appropriate Subcategory; the square meters going
through each process is estimated; the total volume of
effluent due to the electroplating processes and the
concentration of waste water constituents in the treated
effluent are determined. The calculations are than made as
shown in Example III.
272
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SECTION X
BEST AVAILABLE TECHNOLOGY ECONOMICALLY
Introduction
The effluent limitations which must be achieved July 1,
1983, are to specify the degree of effluent reduction
attainable through the application of the Best Available
Technology Economically Achievable. This technology can be
based on the very best control and treatment technology
employed by a specific point source within the industry
category and/or subcategory or technology that is readily
transferable fron one industry process to another. A
specific finding must be made as to the availability of
control measures and practices to eliminate the discharge of
pollutants, taking into account the cost of such elimina-
tion.
Consideration must also be given to
(a) the age of the equipment and facilities
involved
(b) the process employed
(c) the engineering aspects of the application
of various types of control technologies
(d) process changes
(e) cost of achieving the effluent reduction
resulting from the technology
(f) nonwater quality environmental impact
(including energy requirements).
The Best Available Technology Economically Achievable also
assesses the availability in all cases of in-process
controls as well as the control or additional treatment
techniques employed at the end of a production process.
A further consideration is the availability of processes and
control technology at the pilot plant, semiworks, or other
levels, which have demonstrated both technological
performances and economic viability at a level sufficient to
reasonably justify investing in such facilities. Best
Available Technology Economically Achievable is the highest
273
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degree of control technology that has been achieved or has
been demonstrated to be capable of being designed for plant
scale operation up to and including no discharge of
pollutants. Although economic factors are considered, the
costs for this level of control are intended to be top-of-
the-line of current technology subject to limitations
imposed by economic and engineering feasibility. However,
Best Available Technology Economically Achievable may be
characterized by some technical risk with respect to
performance and with respect to certainty of costs and thus
may necessitate some industrially sponsored work prior to
its application.
Industry Category and Subcateorory Covered
The pertinent industry category is the electroplating
industry as previously discussed in Section IV.
Qf Best Available Economically Achievable
No discharge of metals in effluent may be achieved only by
eliminating the effluent itself by such techniques as
reverse osmosis and evaporation, which offer the possibility
of purifying all waste water to a sufficient degree to be
recycled to process or by evaporating to dryness so that
waste water constituents are disposed of as solid waste.
No generalization regarding degree of metal pollution
reduction is possible because of the mix of finishing
processes possible in a single plant and variety of metals
in the raw waste of most plants. Because of this fact and
the high cost of inplant segregation of all waste streams
according to metal, coprecipitation of metals is the general
practice. There is an optimum pH for precipitating each
metal that results in the greatest removal by clarification.
There are several advanced recovery methods available for
closing up the rinse water cycle on individual
electroplating operations. These methods (evaporation, ion
exchange, reverse osmosis, counter current rinsing) have not
yet been applied to rinse waters from pretreatment and
posttreatment operations. The corresponding rinse waters
plus concentrated solution dumps and floor spills may
contain one or all of the pertinent metals (copper, nickel,
chromium, and zinc) in significant amounts requiring
chemical treatment. Thus, chemical treatment of at least
the typical acid/ alkali stream from pretreatment and
posttreatment operations represents the best practicable
control technology currently available to achieve the
effluent limitations recommended.
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The Best Available Technology Economically Achievable is the
use of in-process and end-of-process control and treatment
to achieve no discharge of pollutants. By the use of in-
process controls to reduce the volume of waste water, it
becomes economical to use end-of-process treatment designed
to recover water and reuse the water within the plant thus
avoiding any discharge of effluent to navigable waters.
Solid constituents in the wastewater are disposed of to
landfill or otherwise. A line in Plant 30-21 plating silver
has eliminated liquid effluent discharge for several months,
and continued demonstration of this operation will support
the fact that technology is available to achieve this.
Plant 11-22, which does mostly chromium plating, studied in
Phase I, is using a system designed to eliminate liquid
effluent by subjecting effluent from the clarifier of the
chemical treatment plant to reverse osmosis and recycling
water to process. The concentrate from the reverse osmosis
unit is evaporated to dryness. It is expected that other
methods will be developed during the next five years to
avoid discharge of effluent to navigable waters and thus
achieve no discharge of pollutants in an economical manner.
Batignale_for selection^of Best Available
TechnologY_EconomicallY_Achievable ~" ~~
Age of Equipment and Facilities
Replacement of older equipment and facilities will permit
the installation of modern multitank countercurrent rinsing
systems after each operation in each process line with
conservation of water use for rinsing. The use of reclaim
and recovery systems after each finishing operation should
be possible. Use of inprocess controls to the maximum
extent will reduce the volume of effluent to the point that
recovery and reuse of water is economically feasible.
Process Employed
The application of the technology for end-of-process
recovery and reuse of water to the maximum extent possible
is not dependent on any significant change in the processes
now used. Most water recovery technology can produce a
higher quality of water than normally available from public
or private water supplies. High purity water for the final
rinse after electroplating operations is desirable to
improve the quality of the product.
Engineering Aspects of the Application of Various Types of
Control Techniques
275
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Many plants are successfully using evaporative recovery
systems after one or more plating operations with a net
savings compared to chemical treatment. Evaporative systems
are in current use after copper, nickel, chromium, zinc,
brass, tin, lead, and gold plating operations. Some plants
have succeeded in using recovery systems after all plating
operations in their facility,, The engineering feasibility
of in-process controls for recovery of chemicals and reuse
of water are sufficiently well established. Sufficient
operational use has been accumulated to reduce the technical
risk with regard to performance and any uncertainty with
respect to costs.
The technical feasibility of end-of -pro cess water recovery
systems has been established by extensive development of the
recovery of pure water in many related industrial processes.
Although some uncertainty may remain concerning the overall
costs when applied to electroplating wastewaters, such
uncertainty primarily relates to the volume of water that
must be processed for recycling and reuse. The fact that
the technology as applied to the electroplating industry has
progressed beyond the pilot plant stage and has been
designed and is being built for fullscale operational use
indicates that the technology is available and probably
economical. These systems are equally applicable to
processes other than electroplating due to the similarity in
the waste water produced.
Application of the technology is not dependent on any
process changes. However, process changes and improvements
are anticipate to be a natural consequence of meeting the
effluent limitations in the most economic manner.
Nonwater^ Quality Environmental Impact
Application of technology to achieve no discharge of
pollutants to navigable waters by July 1, 1983, will have
little impact on the solid waste disposal problem with
regard to metal removal as sludge beyond that envisioned to
meet effluent limitations recommended for July 1, 1977. The
volume of soluble salts will be substantially increased.
In general, it is anticipated that the technology will be
applied in a manner such that no discharge of effluent to
surface waters occurs. Thus,, metal oxide sludges would be
disposed of either on land with suitable precautions. The
soluble salts, largely innocuous should be suitable for
disposal in the salt water. Because these salts are not
276
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large in amount and can be dewatered to dry solids (by
incineration if necessary) very little additional impact on
the solid waste disposal problem is anticipated.
No impact of air pollution is expected as the result of
achieving no discharge of pollutants to surface water. The
available technology creates no air pollutants.
Ef^uenj^Ljjnita^j^ns_Ba^eJ^n_^e_Aj3Bcjtion of gest
Available_Technoloiy._iS2U2nii£lily
The recommended effluent limitations to be achieved by July
1, 1983, for existing sources based on the application of
Best Available Technology Economically Achievable is no
discharge of pollutants to navigable waters for Subcategory
1.
guidelines for the Application of Effluent Limitations
Achieving the effluent limitations of no discharge of
pollutants by achieving no discharge of effluent to surface
waters is the most direct methods that eliminates the need
for sampling and analysis. If there is other effluent
discharge to surface waters from the plant not associated
with electroplating, a determination is required that no
waste waters originating from metal finishing processes are
admixed with this other plant effluent.
211
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SECTION XI
NEW SOURCE PERFORMANCE STANDARDS
Introduction
The standards of performance which must be achieved by new
sources are to correspond to the degree of effluent
reduction attainable through the application of higher
levels of pollution control than those identified as Best
Available Technology Economically Achievable for existing
sources. The added consideration for new sources is the
degree of effluent reduction attainable through the use of
improved production processes and/or treatment techniques.
The term "new sources" is defined by the Act to mean "any
source, the construction of which is commenced after
publication of proposed regulations prescribing a standard
of performance".
New Source Performance Standards are based on the best in-
plant and end-of-process technology identified as Best
Available Technology Economically Achievable for existing
sources. Additional considerations applicable to new source
performance standards take into account techniques for
reducing the level of effluent by changing the production
process itself or adopting alternative processes, operating
methods, or other alternatives. The end result will be the
identification of effluent standards which reflect levels of
control achievable through the use of improved production
processes (as well as control technology) , rather than
prescribing a particular type of process or technology which
must be employed. A further determination must be made as
to whether a standard permitting no discharge of pollutants
is practicable.
Consideration must also be given to:
(a) The type of process employed and process
changes
(b) operating methods
(c) batch as opposed to continuous operations
(d) use of alternative raw materials and mixes
of raw materials
(e) use of dry rather than wet processes
(including substitution of recoverable
solvents for water)
279
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(f) recovery of pollutants as by-products.
Standards of Performance for New Sources are based on
applicable technology and related effluent limitations
covering discharges directly into waterways.
Consideration must also be given to the fact that Standards
of Performance for New Sources could require compliance
about three years sooner than the effluent limitations to be
achieved by existing sources by July 1, 1977. However, new
sources should achieve the same effluent limitations as
existing sources by July 1, 1983.
Industry Cateqory^and^SubcategorY,Covered
The pertinent industry category is the electroplating
industry as previously discussed in Section IV.
Identif3,cation_Qf Control and^Treatment
Technology Applicable to Performance
Standards and Pretreatment Standards of
New Sources
The technology previously identified in Section IX as Best
Practicable Control Technology Currently Available is also
applicable to New Source Performance Standards. In addition
a New Source can utilize the best practice in multitank
rinsing after each operation in the process as required to
meet the effluent limitations at the time of construction.
Thus, with no practical restrictions on rinse water
conservation after each operation by multitank rinsing,
there are fewer restrictions on the use of advanced
techniques for recovery of bath chemicals and reduction of
wastewater from rinsing after pretreatment and
posttreatment. Maximum use of combinations of evaporative,
reverse osmosis, and ion exchange systems for in-process
control currently available should be investigated. A small
end-of-pipe chemical treatment system can be used to treat
spills, concentrated solution dumps, and any other water
flows not economically amenable to in-process water and
chemical recovery.
The net result of the improvements cited should be a
reduction in water use as compared to that considered
achievable for Best Practicable Control Technology Currently
Available. This reduction should result in a lower
discharge of waste water constituents. Although methods are
being developed that may make possible a further reduction
in the concentration of constituents and a reduction in the
280
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discharge of waste water constituents in chemically treated
effluents, present technology is capable only of achieving
the concentrations listed in Table 66 by exemplary chemical
treatment. It would be anticipated that some plants now
operating, due to having been designed recently to minimize
water use or because of other favorable circumstances such
as adequate space to make modifications, are attaining a
water use well below 160 1/sq m/operation. Table 64 shows
16 lines involving processes that achieve a water use of
less than 80 1/sq m/operation. These are found in Plants
36-12, 30-2, 33-24, 15-3, 6-36, 33-23, 33-35, 20-22, 30-9,
9-2, 6-37, 20-25, and 23-8. The processes involved are rack
and barrel plating of common metals, rack and strip plating
of precious metals, anodizing, chemical milling, and
phosphating. It is estimated that a new source can easily
achieve a water use of 80 1/sq m/operation by use of the
technology described above for reducing water use.
Rationale for Selection of Control and
Treatment Technology Applicable to New
Source Performance Standards
The rationale for the selection of the above technology is
applicable to new sources discharging to navigable waters is
as follows:
(1) In contrast to an existing source, a new
source has complete freedom to choose the
most advantageous equipment and facility
design to maximize water conservation by
use of as many multitank rinsing operations
as necessary. This, in turn, allows for
economic use of in-process controls for
chemical and water recovery and reuse.
(2) In contrast to an existing source which may
have at present a large capital investment
in waste treatment facilities to meet
effluent limitations by July 1, 1977, a new
source has complete freedom in the selection
the design of new waste treatment facilities.
(3) In contrast to an existing source, a new
source has freedom of choice with regard to
geographic location.
281
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Standards of Performance Applicable to New Sources
The recommended Standards of Performance to be achieved by
new sources discharging to navigable waters was shown
previously in Table 2 of Section II.
The quantitative values for the 30-day average standard for
each parameter in mg/sq m (lb/10° sq ft) is based on a
nominal water use one-half as large as those used to develop
BPCTC guidelines combined with the concentrations achievable
by chemical treatment as previously shown in Table 66 of
Section IX. For example, 0.5 mg/1 for copper, nickel, total
chromium, zinc, and total cyanide, 0.05 mg/1 for hexavalent
chromium and oxidizable cyanide, 15 mg/1 for suspended
solids, when combined with an effluent factor of 40 1/sq m
are the basis for the 30-day average standards of
performance found in Table 2.
In effect, Standards of Performance for New Sources as shown
in Table 2, are 1/2 of the values of the Effluent
Limitations for existing sources to be achieved by July 1,
1977, as shown in Table 1. The rationale for selection of
Standards of Performance is based on the technical
feasibility of achieving greater reduction in water use by
multitank rinsing at the time of construction of new
facilities in contrast to the present limitations for some
existing sources. For example, if an existing source can
achieve water use of 80 1/sq m, a new source should be able
to design a new facility to achieve a water use of 40 1/sq
m. As discussed previously in Section IX, the Standard of
Performance in mg/sq m is the product of the water use in
1/sq m and the concentration of the parameter in the treated
effluent in mg/1. The choice of whether to reduce
concentration by emphasis on optimum chemical treatment and
clarification or whether to reduce effluent volume by water
conservation or a combination of both approaches is left to
the discretion of the new source.
The rationale for establishing the daily maximum value of
Standards of Performance at 2.0 times the 30-day average is
based on the arguments given in Section IX.
It is recommended that new sources meet the same effluent
limitations as required for existing sources by July 1,
1983, based on the effluent reduction believed to be
attainable by the application of the Best Available
Technology Economically Achievable.
282
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Guidelines for the Application of
New Source Performance Standards
The recommended guidelines for the application of Standards
of Performance for New Sources discharging to navigable
waters are the same as those in Section IX relating to
existing sources based on use of the Best Practicable
Control Technology Currently Available and those in Section
X based on use of Best Available Technology Economically
Achievable.
283
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SECTION XII
ACKNOWLEDGEMENTS
The Environmental Protection Agency was aided in the
preparation of this Development Document by Battelle
Columbus Laboratories under the direction of William H.
Safranek, Luther Vaaler, John Gurklis and Carl Layer on
Battelle1s staff made significant contributions.
Kit R. Krickenberger served as project officer on this
study. Allen Cywin, Director, Effluent Guidelines Division,
Ernst P. Hall, Deputy Director, Effluent Guidelines Division
and Walter J. Hunt, Chief, Effluent Guidelines Development
Branch, offered guidance and suggestions during this
program.
The members of the working group/steering committee who
coordinated the internal EPA review are:
Walter J. Hunt, Effluent Guidelines Division
Kit R. Krickenberger, Effluent Guidelines Division
Devereaux Barnes, Effluent Guidelines Division
Murray Strier, Office of Permit Programs
John Ciancia, NERC, Cincinnati, (Edison)
Alan Eckert, Office of General Counsel
James Kamihachi, Office of Planning and Evaluation
Acknowledgement and appreciation is also given to Nancy
Zrubek, Kaye Starr, and Alice Thompson of the Effluent
Guidelines Division for their effort in the typing of drafts
and necessary revisions, and the final preparation of this
document.
Appreciation is extended to the following organizations
associated with the electroplating industry:
American Electroplaters1 Society, East Orange,
New Jersey
Aqua-Chem, Milwaukee, Wisconsin
Artisan Industries, Inc., Waltham, Massachusetts
E.I. duPont de Nemours and Co., Wilmington,
Delaware
Heil Process Equipment corporation, Cleveland,
Ohio
Haviland Products Company, Grand Rapids, Michigan
Industrial Filter and Pump Manufacturing Co.,
Cicero, Illinois
285
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Institute of Printed Circuits, Chicago, Illinois
Ionic International, Incorporated, Detroit,
Michigan
Lancy Laboratories, Zelienople, Pennsylvania
MOT Chemicals, Incorporated, Matawan, New Jersey
Electroplating Suppliers" Association, Incorporated,
Birmingham, Michigan
National Association of Metal Finishers, Upper
Montclair, New Jersey
Osmonics, Incorporated, Minneapolis, Minnesota
Oxy Electroplating Corporation, Warren, Michigan
The Permutit Company, Paramus, New Jersey
Pfaudler Sybron Corporation, Rochester, New York
286
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SECTION XIII
References
(1) Table 3, pg 36, "1967 Census of Manufacturers",
U.S. Bureau of Commerce.
(2) "Where to Buy Electroplating Services", Modern
Metals, 28 (6), p. 71 (July, 1972).
(3) Institute of Printed Circuits, Chicago, Illinois.
CO Electroplating, p. 42, March 1972.
(5) Sidney B. Levinson, J. Paint Technology, 44 (569) 49.
(6) J. Schrantz, Industrial Finishing, 20-29, October, 1972.
(7) Table 3, p. 7-45, "1967 Census of Manufacturers",
U.S. Bureau of Commerce.
(8) Modern_Electroplating, Edited by F.A. Lowenheim,
2nd Ed., John Wiley~and Sons (1963), Chap. 7,
pp 154-205.
(9) ^Electroplating^Guidebook and Directory, Metals
and Plastics Publications, Inc., 1973.
(10)^Electroplating .Guidebook and Directory, Metals
and Plastics Publications, Inc. 1972.
(11) Modern Electroplating, p 698.
(12) Modern Electroplating, p 708.
(13) Electroplating^Engineerinq Handbook, A Kenneth Graham,
Ed.,""van Nostrand RhelnholdT 3rd Ed., 1971, p 486.
(14) Schrantz, J. Industrial Finishing, April, 1973,
pp 37-40.
(15) Stiller, Frank P..r Metals Finishing Guidebook and
Directory, Metals and Plastics Publications, Inc. ,
pp 548-553, 1972.
(16) George, D.J., Walton, C.J., and Zelly, W.G., Aluminum
Fabrication_and_Finishinc[, Vol 3, Am Soc for Metals,
19677 pp~387-622.
287
-------
(17) Innes, W.P.r Electroplating Guidebook. and Directory,
1972, p 554."
(18) Pocock, Walter, E. Electroplating Guidebook and
and Directory, 1972, pp 568-575. ~
(19) Ostrander, C.W. , Electroplating Engineering Handbook,
pp 437-447.
(20) Maher, M.F. , and Prodel, A.M. , Electroplating_6uidebook
and Directory. 1972, pp 590-603.
(21) ASM Handbook. Vol 2, 8th Ed., 1964, pp 531-547.
(22) Olsen, Alan E., Upgrading Electroplating Facilities
to Reduce Pollution, EPA Technology Transfer Seminar,
New York, New York, December, 1972.
(23) George, D.J. , Walton, c. J. , Zelley, W.G., Aluminum
Fabrication and Finishing. Vol 3, pp 587-622.
(24) Fishlock, D., Metal Coloring, Robert Draper, Ltd.,
Teddington, Great Britain, 1962, pp 300-353.
(25) Safranek, W.H., Colored .Finishes for Copger ..and
Copper All oys , Copper Division Association, New
York, New York, 1968.
(26) Metals Handbook, American Society for Metals, 8th Ed.,
1964, Vol 2, pp 611-660.
(27) Faust, C.L. , Metals Handbook, 1964, pp 484-488.
(28) Pourbaix, Marcel, Atlas of Electrochemical Equilibria
s, Pergamon Press, New York (1966).
(29) H. Schlegel, Metallqher f lache , 17, 129 (1963).
(30) Hartinger, Ludwig, Baender, Bleche, Rohre, 1963,
pp 535-540; 1963, pp 638-647; 1964, pp 14-21;
1965, pp 524-533.
(31) Personal communication from Dr. Coleman, Western
Electric Company, Indianapolis, Indiana.
(32) Tripler, A. B. , Cherry, R.H., Smithson, G. Ray,
"Summary Report on the Reclamation of Metal Values
from Electroplating Waste Treatment Sludges",
Battelle Columbus Laboratories report to Metal
Finisher's Foundation, July 6> 1973.
288
-------
(33) Environmental Sciences, Inc., "Ultimate Disposal
of Liquid Wastes by Chemical Fixation".
(34) Dodge, B.F., and Zabban. W., "Disposal of Plating
Room wastes. III. Cyanide Wastes" Treatment with
Hypochlorites and Removal of Cyanates", Plating
38 (6), 561-586 (June, 1951).
(35) Dodge, B.F., and Zabban, W., "Disposal of Plating
Room Wastes. III. Cyanide Wastes: Treatment with
Hypochlorites and Removal of Cyanates. Addendum",
Plating, 39 (4) , 385 (April, 1952) .
(36) Dodge, B.F., and Zabban, W., "Disposal of Plating
Room Wastes. IV. Batch Volatilization of Hydrogen
Cyanide From Aqueous Solutions of Cyanides",
Plating, 39 (10), 1133-1139 (October, 1952).
(37) Dodge, B.F., and Zabban, W., "Disposal of Plating
Room Wastes. IV. Batch Volatilization of Hydrogen
Cyanide From Aqueous Solutions of Cyanides.
Continuation", Plating, 39 (11), 1235-1244 (November,
1952).
(38) "Overflow", Chemical Week, 111 (24), 47 (December,
1972) .
(39) Oyler, R.W., Disposal of Waste Cyanides by Electro-
lytic Oxidation", Plating, 36 (4), 341-342 (April,
1949) .
(40) Kurz, H., and Weber, W., "Electrolytic Cyanide
Detoxication by the CYNOX Process", Galvanotechnik
and oberflaechenschutz, 3, 92-97 (1962).
(41) "Electrolysis Speeds Up Waste Treatment", Environmental
Science and Technology", 4 (3), 201 (March, 1970).
(42) Thiele, H., "Detoxification of Cyanide-Containing
Waste Water by Catalytic Oxidation and Adsorption
Process", Fortschritte Wasserchemie Ihrer
Grenzgebiete, 9, 109-120 (1968): CA, 70, 4054
(1969) .
(43) Bucksteeg, W., "Decomposition of Cyanide Wastes by
Methods of Catalytic Oxidation Absorption", Proceedings
of the 21st Industrial Waste conference, Purdue
University Engineering Extension Series, 688-695
(1966) .
289
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(44) "Destroy Free Cyanide In Compact, Continuous Unit",
Calgon Corporation Advertisement, Finisher*s
Management, 19 (2) , 14 (February, 1973) ,.
(45) Sondak, N.E., and Dodge, B.F., "The Oxidation
of Cyanide Bearing Plating Wastes by Ozone.
Part I", Plating, 48 (2) 173-180 (February,
1961).
(46) Sondak, N.E., and Dodge, B.F., "The Oxidation
of Cyanide Bearing Plating Wastes by Ozone.
Part II", Plating, 48 (3), 280-284 (March,
1961).
(47) Rice, Rip G., letter from Effluent Discharge
Effects Committee to Mr. All-en Cywin, Effluent
Guidelines Division, July 9, 1973.
(48) "Cyanide Wastes Might Be Destroyed at One-Tenth
the Conventional Cost", Chemical Engineering,
79 (29), 20 (December 25, 1972).
(49) Manufacturers1 Literature, DMP Corporation,
Charlotte, North Carolina (1973).
(50) Ible, N., and Frei, A.M., "Electrolytic Reduction
of chrome in Waste Water", Galvanotechnik and
Oberflaechenschutz, 5 (6), 117-122 (1964).
(51) Schulze, G., "Electrochemical Reduction of
Chromic Acid-Containing Waste water", Galvanotechnik,
58 (7), 475-480 (1967): CA, 68, 15876t (1968).
(52) Anderson, J.R., and Weiss, Charles 0., "Methods
for Precipitation of Heavy Metal Sulfides",
U.S. Patent No. 3,740,331, June 19, 1973.
(53) Lancy, L.E., and Rice, R.L., "Upgrading Metal
Finishing Facilities to Reduce Pollution",
Paper presented at the EPA Technology Transfer
Seminar, New York, New York (December, 1972).
(54) Ele£tro2la^ijiGLEjigineer;inc[_Handbook, Edited by
A.K. Graham, 3rd Edition, Van~Nostrand Reinhold
Company, New York (1971).
(55) Olsen, A.E., "Upgrading Electroplating Facilities
to Reduce Pollution; In-Process Pollution Abatement
Practices", paper presented at the EPA Technology
290
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Transfer Seminar, New York, New York (December, 1972).
(56) Novotny, C.J., "Water Use and Recovery", Finishers'
Management, 18 (2), H3-H6 + 50 (February, 1973).
(57) Rushmere, J.D., "Process for Brightening Zinc
and Cadmium Electroplates Using an Inner Salt
of a Quaternary Pyridine Carboxylic Acid and
Composition Containing the Same", U.S. Patent
3,411,996, November, 1968.
(58) Ceresa, M., and Lancy, L.E., "Electroplating
Waste Disposal. Part II", Electroplating,
66 (5) , 60-65 (May, 1968) .
(59) Ceresa, M., and Lancy, L.E., "Electroplating
Waste Disposal. Part III", Electroplating,
66 (6) , 112-118 (June, 1968) .
(60) Brown, C.J., et al., "Plating Waste Recovery by
Reciprocating-Flow Ion Exchange", Technical
Conference of the American Electroplaters1
Society, Minneapolis, Minnesota, June 18, 1973.
(61) Metal Market, April 17, 1972, p 21.
(62) Oh, C.B., and Hartley, H.S., "Recycling Plating
Wastes by Vapor Recompression", Products
Finishing, 36 (8), 90-96 (May, 1972).
(63) Kolesat, T.J., "Employment of Atmospheric Evaporative
Towers in the Electroplating Industry as a Means
of Recycle and Waste Elimination", Technical
Conference of the American Electroplaters1 Society,
Minneapolis, Minnesota, June 18, 1973.
(6U) McLay, W.J., Corning Glass Company, Personal Communi-
cation.
(65) Spatz, D.D., "Industrial Waste Processing With
Reverse Osmosis", osmonics. Inc., Hopkins, Minnesota
(August 1, 1971).
(66) Spatz, D.D., "Electroplating Waste Water Processing
With Reverse Osmosis", Products Finishing, 36 (11),
79-89 (August, 1972).
(67) Campbell, R.J., and Emmerman, O.K., "Recycling of
Water From Electroplating Wastes by Freezing
Processes", ASME Paper 72-PID-7 (March, 1972) .
291
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(68) Campbell, R.J., and Emmerman, D.K., "Freezing and
Recycling of Plating Rinse Water", Industrial water
Engineering, 9 (4), 38-39 (June/July, 1972).
(69) A.J. Avila, H.A. , Sauer, T.J. Miller, and R.E.
Jaeger, Plating, 60 239 (1973) .
(70) Dvorin, F., "Dialysis for Solution Treatment in
the Electroplating Industry", Electroplating,
57 (4), 52-54 + 62 (April, 1959).
(71) Ciancia, John, Plating 60, 1037 (1973).
(72) Communication with P. Peter Kovatis, Executive
Director, National Association of Metal Finishers.
(73) "An Investigation of Techniques for Removal of
Chromium From Electroplating Wastes", Battelle,
Columbus Laboratories Report on Program No.
12010 EIE to the Environmental Protection Agency
and Metal Finishers' Foundation (March, 1971).
(74) Grieves, R., et al.r "Dissolved-Air Ion Flotation
of Industrial Wastes. Hexavalent Chromium",
Proc. 23rd Industrial Waste Conference, Purdue,
University. 1968, p 154.
(75) Surfleet, B., and Crowle, V.A., "Quantitative
Recovery of Metals from Dilure Solutions",
Transactions of the Institute of Electroplating,
50, 227 (1972).
(76) Bennion, Douglas N., and Newman, John, "Electro-
chemical Removal of Copper Ions from Very Dilute
Solutions", Journal of Applied Electrochemistry,
2, 113-122 (1972).
(77) Carlson, G.A., and Estep, E.E., "Porous Cathode
Cell for Metals Removal from Aqueous Solutions",
from Electrochemical Contributions to Environmental
Protection, a symposium volume published by the
Electrochemical Society, Princeton, New Jersey,
p 159.
(78) "Water Quality Criteria 1972," National Academy of
Sciences and National Academy of Engineering for the
Environmental Protection Agency, Washington, D.C.
1972 'U.S. Government Printing Office Stock no.
5501-00520).
292
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SECTION XIV
GLOSSARY
Acid_Dip.
An acidic solution for activating the workpiece surface
prior to electroplating in an acidic solution, especially
after the workpiece has been processed in an alkaline
solution.
Alkaline Cleaning
Removal of grease or other foreign material from a surface
by means of alkaline solutions.
Anodizing
The production of a protective oxide film on aluminum or
other light metals by passing a high voltage electric
current through a bath in which the metal is suspended. The
metal serves as the anode. The bath usually contains
sulfuric, chromic, or oxalic acid.
Automatic Plating
(1) full - plating in which the cathodes are automatically
conveyed through successive cleaning and plating tanks.
(2) semi - plating in which the cathodes are conveyed
automatically through only one plating tank.
Barrel Plating
Electroplating of workpieces in barrels (bulk).
BasisJ Metal_or Material
That substance of which the workpieces are made and that
receives the electroplate and the treatments in preparation
for plating.
Batch Treatment
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Treatment of electroplating rinse waters collected in
adjacent tanks. Water is not allowed to leave the tank till
treatment is completed.
Best_Available TechnglogY_Ec<)ngmicallY_Achievable
Level of technology applicable to effluent limitations to be
achieved by July 1, 1983, for industrial discharges to
surface waters as defined by Section 301(b) (2) (A) of the
Act.
Level of technology applicable to effluent limitations to be
achieved by July 1, 1977, for industrial discharges to
surface waters as defined by Section 301 (b) (1) (A) of the
Act.
Bright Dip
A solution used to produce a bright surface on a metal.
Captiye^Operation
Electroplating facility owned and operated by the same
organization that manufacturers the workpieces.
Chemical Brightening
Process utilizing an addition agent that leads to the
formation of a bright plate, or that improves the brightness
of the deposit.
Chemical Etching
To dissolve a part of the surface of a metal or all of the
metal laminated to a base.
ChemicalmMetaljColoring
The production of desired colors on metal surfaces by
appropriate chemical or electrochemical action.
Chemical^Polishing
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The improvement in surface smoothness of a metal by simple
immersion in a suitable solution.
Chromatjzing
To treat or impregnate with a chrornate or dichromate
especially with potassium dichromate.
Chrome-Pickle Process
Forming a corrosion-resistant oxide film on the surface of
magnesium-base metals by immersion in a bath of an alkali
bichromate.
Closed-Loop. jEvaporation System
A system used for the recovery of chemicals and water from a
plating line. An evaporator concentrates flow from the
rinse water holding tank. The concentrated rinse solution
is returned to the plating bath, and distilled water is
returned to the final rinse tank. The system is designed
for recovering 100 percent of the chemicals, normally lost
in dragout, for reuse in the plating process.
Continuous_Treatment
Chemical waste treatment operating uninterruptedly as
opposed to bath treatment; sometimes referred to as flow
through treatment.
Conversion Coating
A coating produced by chemical or electrochemical treatment
of a metallic surface that gives a superficial layer
containing a compound of the metal, for example, chromate
coatings on zinc and cadmium, oxide coatings on steel.
Deoxidizing
The removal of an oxide film from an alloy such as aluminum
oxide.
Descaling
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The process of removing scale or metallic oxide from
metallic surfaces.
The removal of smut, generally by chemical action.
Dragin
The water or solution that adheres to the objects removed
from a bath.
Dragout
The solution that adheres to the objects removed from a
bath, more preciously defined as that solution which is
carried past the edge of the tank.
EDTA
Abbreviation for ethylenediamine-tetraacetic acid.
Effluent
The waste water discharged from a point source to navigable
waters.
Electrobrightening
Electrolytic brightening (electropolishing) produces smooth
and bright surfaces by electrochemical action similar to
those that result from chemical brightening.
Machining (ECM)
A machining process whereby the part to be machined is made
the anode and a shaped cathode is maintained in close
proximity to the work. Electrolyte is pumped between the
electrodes and a potential applied with the result that
metal is rapidly dissolved from the work in a selective
manner and the shape produced on the work complements that
of the cathode.
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Membrane dialysis under the influence of direct current
electricity.
Electroless Plating
Deposition of a metallic coating by a controlled chemical
reduction that is catalyzed by the metal or alloy being
deposited.
Electropa jntj ng
A coating process in which the coating is formed on the
workpiece by making it anodic or cathodic in a bath that is
generally an aqueous emulsion of the coating material.
Electroplating
The electrodeposition of an adherent metallic coating upon
the basis metal or material for the purpose of securing a
surface with properties or dimensions different from those
of the basis metal or material.
Electroplating Process
An electroplating process includes a succession of
operations starting with cleaning in alkaline solutions,
acid dipping to neutralize or acidify the wet surface of the
parts, followed by electroplating, rinsing to remove the
processing solution from the workpiece, and drying.
Electrolytic corrosion process that increases the percentage
of specular reflectance from a metallic surface.
Electrostatic Precipitation
Use of an electrostatic field for precipitating or rapidly
removing solid or liquid particles from a gas in which the
particles are carried in suspension.
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Heavy Metals
Metals which can be precipitated by hydrogen sulfide in acid
solution, e.g., lead, silver, gold, mercury, bismuth,
copper, nickel, iron, chromium, zinc, cadmium, and tin.
A method of coating one metal with another to provide a
protective film.
Hydrogen Embr ittlement
Embrittlement of a metal or alloy caused by absorption of
hydrogen during a pickling, cleaning, or plating process,
A metallic deposit produced by a displacement reaction in
which one metal displaces another from solution, for
example:
Fe * Cu-n- Cu + Fe++
Independe a t _O pe ration
Job shop or contract shop in which electroplating is done on
workpieces owned by the customer.
Integrated Chemical Treatment
A waste treatment method in which a chemical rinse tank is
inserted in the plating line between the process tank and
the water rinse tank. The chemical rinse solution is
continuously circulated through the tank and removes the
dragout while reacting chemicals with it.
Ion-Flotation Technique
Treatment for electroplating rinse waters (containing
chromium and cyanide) in which ions are separated from
solutions by flotation.
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Iridite Dip_Process
Dipping process for zinc or zinc coated objects that
deposits an adherent protective film that is a chrome gel,
chrome oxide or hydrated chrome oxide compound.
Phosphatizing
Process of forming rust-resistant coating on iron or steel
by immersing in a hot solution of acid manganese, iron, or
zinc phosphate.
Pickle
An acid solution used to remove oxides or other compounds
related to the basis metal from its surface of a metal by
chemical or electrochemical action.
Pickling
The removal of oxides or other compounds related to the
basis metal from its surface by immersion in a pickle.
Point,Source
A single source of water discharge such as an individual
plant.
Precious Metals
Gold, Silver, Platinum, etc.
Back_Plating
Electroplating of workpieces on racks.
Reyerse_0smosis
A recovery process in which the more concentrated solution
is put under a pressure greater than the osmotic pressure to
drive water across the membrane to the dilute stream while
leaving behind the dissolved salts.
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Rochell Salt
Sodium potassium tartrate: KNaC4H4O6 . 4H2O.
Shgt_Peening
Dry abrasive cleaning of metal surfaces by impacting the
surfaces with high velocity steel shot.
Sludge
Residue in the clarifier of a chemical waste treatment
process.
Strike
(1) noun - a thin coating of metal (usually less than
0.0001 inch in thickness) to be followed by other coatings.
(2) noun - a solution used to deposit a strike. (3) verb
- a plate for a short time, usually at a high initial
current density.
Stripping
Removal of an electrodeposit by a chemical agent or reversed
electrodeposition.
Wgrkpiece
The item to be electroplated.
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Conversion Table
co
O
MULTIPLY (ENGLISH UNITS)
English Unit
Abbreviation
by TO OBTAIN (METRIC UNITS)
Conversion Abbreviation Metric Unit
acre
acre - feet
British Thermal Unit
British Thermal Unit/pound
cubic feet/minute
cubic feet/second
cubic feet
cubic feet
cubic inches
degree Fahrenheit
feet
gallon
gallon/minute
horsepower
inches
inches of mercury
pounds
million gallons/day
mile
pound/square inch (gauge)
square feet
square inches
tons (short)
yard
ac
ac ft
BTU
BTU/lb
cfm
cfs
cu ft
cu ft
cu in
°F
ft
gal
gpm
hp
in
in Hg
Ib
mgd
mi
psig
sq ft
sq in
ton
yd
0.405
1233.5
0.252
0.555
0.028
1.7
0.028
28.32
16.39
0.555(°F-32)*
0.3048
3.785
0.0631
0.7457
2.54
0.03342
0.454
3785
1.609
(0.06805 psig+D*
0.0929
6.452
0.907
0.9144
ha
cu m
kg cal
kg cal/kg
cu m/ir.in
cu m/min
cu nv
1
cu cm
°C
m
1
I/sec
kw
cm
atm
kg
cu m/day
km
atm
sq m
sq cm
kkg
m
hectares
cubic meters
kilogram - calories
kilogram calories/kilogram
cubic meters/minute
cubic meters/minute
cubic meters
liters
cubic centimeters
degree Centigrade
meters
liters
liters/second
kilowatts
centimeters
atmospheres
kilograms
cubic meters/day
kilometer
atmospheres (absolute)
square meters
square centimeters
metric tor.s (1000 kilograms)
meters
* Actual conversion, not a multiplier
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