United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/SR-94/074 May 1994
EPA Project Summary
Substituting Cadmium Cyanide
Electroplating with Zinc Chloride
Electroplating
B.C. Kim, P.R. Webb, J.A. Gurklis, and R.K. Smith
The environmental and economic im-
plications of substituting zinc chloride
electroplating for cadmium cyanide
electroplating were evaluated. The pro-
cess substitution successfully achieved
product quality to satisfy the customer
requirements for corrosion resistance.
Corrosion resistance was determined
by salt-spray tests in accordance with
the ASTM Method B117-90. Not only
did the process substitution eliminate
cadmium and cyanide from the wastes
and chlorine from the wastewater treat-
ment process, thereby greatly reduc-
ing hazards to plant personnel and
pollution of the environment, the pro-
cess substitution also reduced oil and
grease waste. On the negative side,
however, the process change increased
the generation of wastewater, waste-
water treatment sludge, and chromium.
For a new installation, the zinc-plating
process offers an economic advantage
of slightly lower operation cost over
the cadmium-plating process.
This Project Summary was developed
by EPA's Risk Reduction Engineering
Laboratory, Cincinnati, OH, to announce
key findings of the research project
that is fully documented in a separate
report of the same title (see Project
Report ordering information at back).
Introduction
This study, performed under the U.S.
Environmental Protection Agency's (EPA's)
Waste Reduction Innovative Technology
Evaluation (WRITE) Program, was a co-
operative effort between EPA's Risk Re-
duction Engineering Laboratory (RREL)
and Aeroquip Corporation. The objective
of the WRITE program is to evaluate, in a
typical workplace environment, examples
of prototype technologies that have po-
tential for reducing wastes. Substitution of
zinc chloride electroplating for cadmium
cyanide electroplating was evaluated at
Aeroquip's Industrial Connectors Division*
in Van Wert, OH. The goal of this project
was to evaluate (1) the effects of the pro-
cess substitution on product quality, (2)
the waste reduction/pollutant reduction ef-
fects of the process substitution, and (3)
the economics of the process substitution.
The Processes
The cadmium cyanide and the zinc chlo-
ride plating processes for the rack plating
line at Aeroquip are compared in Table 1.
Hydrochloric acid is used to condition parts
(shown as step 12 in Table 1) before
plating in the zinc chloride process
whereas sodium cyanide is used in the
cadmium cyanide process. The cadmium
cyanide plating line had separate tanks to
apply either clear chromate or yellow chro-
mate coatings (steps 18 and 20 in Table
1). Previously, Aeroquip used clear chro-
mate coating on most (90% to 95%) of
the cadmium-plated parts. Currently,
Aeroquip uses yellow chromate coating
on all zinc-plated parts because (1)
Aeroquip has adopted a worldwide stan-
dardization of yellow as the color for their
fittings and (2) yellow chromate coating
vastly improves the corrosion protection
* Mention of trade names or commercial products does
not constitute endorsement or recommendation for
use.
Printed on Recycled Paper
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Tab/a 1. Comparison of Zinc Chloride and Cadmium Cyanide Back Plating Processes
Operation
Process
Step
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
Tank
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
'22
Zinc Chloride
Plating Line
Soak clean
Rinse
Electroclean
Rinse
Rinse
Hydrochloric acid pickle
Rinse
Rinse
Electroclean
Rinse
Rinse
Hydrochloric acidpre-dip
Zinc plating
Rinse
Rinse
Nitric acid dip
Yellow chromate dip
Rinse
Chromate seal
Rinse
Drip tank dip
Water-soluble oil dip
Cadmium Cyanide
Plating Line
Soak clean
Rinse
Electroclean
Rinse
Rinse
Hydrochloric acid pickle
Rinse
Rinse
Electroclean
Rinse
Rinse
Sodium cyanide pre-dip
Cadmium plating
Rinse
Rinse
Rinse
Nitric acid dip
Clear chromate dip
Rinse
Yellow chromate dip
Rinse
Water-soluble oil dip
of the zinc-plated fittings. The yellow chro-
mate solution used by Aeroquip contained
approximately a five times greater chro-
mium concentration than did the clear chro-
mate solution. In the water-soluble oil
application step (step 22 in Table 1), the
concentration of the oil was reduced by a
factor of approximately ten in the zinc
chloride plating process from the level used
In the cadmium cyanide plating process.
The change was necessary to obtain im-
proved adhesion of chromate coating dur-
ing the subsequent heat-curing step.
Rinse water and various cleaning and
plating solutions are discharged continu-
ously or periodically dumped from the
tanks and treated in an on-site wastewa-
ter treatment plant. All wastes from the
plating operations eventually are in three
waste streams — treated wastewater, de-
watered sludge, and waste oil — that are
discharged or disposed from the waste-
water treatment plant. The treated waste-
water is discharged to a sanitary sewer.
The dewatered sludge is collected in a
20-yd3 hopper and sent to an off-site haz-
ardous landfill once a month. The waste
oil Is collected in drums and sent to an
off-site hazardous waste incinerator every
3 mo.
Product Quality Evaluation
Product quality was measured by the
corrosion resistance of plated parts deter-
mined by salt-spray (fog) tests carried out
In accordance with the ASTM Method
B117-90 (Standard Test Method of Salt
Spray [Fog] Testing). As part of their qual-
ity acceptance criteria for zinc-plated parts,
Aeroquip's engineering process specifica-
tion has adopted the ASTM Method B633-
85 (Standard Specification for Electro-
deposited Coatings of Zinc on Iron and
Steel) requirement of 96 hr of freedom
from white corrosion products in salt-spray
testing. Most Aeroquip customers require
96 hr before the first appearance of white
corrosion on zinc-plated parts. The pro-
cess specification for some of Aeroquip's
products has an additional internal accep-
tance criterion (not required by custom-
ers) of 360 hr of exposure to salt spray
before the first appearance of red rust.
In the first series of tests, four repre-
sentative types of parts plated with zinc in
the rack plating line were tested in parallel
by Aeroquip and an independent testing
laboratory (Detroit Testing Laboratory, Inc.
[DTL], Warren, Ml). These parts, shown in
Figure 1, included swivel nut (Group B)
and three types of adapter (Groups A, C,
and D). In the DTL tests, all of the Group
A, B, and D specimens were free of white
corrosion products at 120 hr, so that the
96-hr requirement of no white corrosion
for zinc-plated parts was met. Very slight
white corrosion was noted on some Group
C specimens at 120 hr. In the DTL tests,
all specimens in Groups A, B, and D were
free of red rust at the end of the 360-hr
observation period; two of the six speci-
mens in Group C showed red rust at the
336-hr and 360-hr observation periods. In
the Aeroquip tests, there was no sign of
white corrosion products on any of the
specimens in any of the groups at the 96-
hr observation period. Further, the ex-
tended-exposure tests showed that only
one of six specimens in Group D exhib-
ited red rust at 264 hr. Thus, of a total 24
specimens tested by Aeroquip, only one
specimen definitely would not have met
Aeroquip's internal requirement of free-
dom from red rust at 360 hr. One speci-
men in Group B exhibited!red rust at 408
hr; at 336 hr, no specimens in this group
showed red rust. In general, very good
agreement and full compliance with the
requirement for absence of white corro-
sion products for 96 hr was noted for the
groups of specimens tested at both labo-
ratories. Further, there was generally good
agreement in results with respect to the
appearance of red rust. At both laborato-
ries, only 3 of 48 specimens did not meet
the Aeroquip's internal requirement of free-
dom from red rust for 360 hr of exposure
to salt-spray.
Aeroquip also tested four groups of parts
platedjwith zinc in the barrel plating lines.
The parts included nipple (Group A), crimp
socket (Group B), and two other types of
socket (Groups C and D). All specimens
in all four groups met the requirement of
freedom from white corrosion products at
96 hr. White corrosion started to appear
on most of the specimens at the 168-hr
observation point. All parts also met the
requirement of no red rust at 360 hr. One
specimen in Group A exhibited red rust at
432 hr. At 504 hr, red rust was present on
Group A and Group C parts, but Group B
and Group D specimens showed no red
rust.
From October 15 to November 5,
1991, Aeroquip carried out corrosion
tests to compare the salt-spray corro-
sion resistance of zinc-plated parts with
cadmium-plated parts. Seven groups of
representative parts plated with zinc and
" seven groups of identical parts plated
with cadmium were tested. The parts
included two types of barrel-plated reus-
able sockets (Groups A and B), two types
of barrel-plated reusable nipples (Groups
C and D), two types of rack plated nuts
(Groups E and F), and a rack-plated crimp
fitting (Group G). The results of the salt-
spray tests on the zinc-plated parts were
as follows: (1) all specimens in the seven
groups of parts passed the requirement of
96 hr before the first appearance of white
corrosion products; (2) no red rust ap-
peared on any of the specimens in the
seven groups at the 360-hr observation
time; (3) all specimens in Groups A, B, D,
and G were still free of red rust after 504
hr of salt-spray exposure; red rust was
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Group A: Part No. 2021-2-35; Pipe to 37 ° mate Hare adapter
Group B: Part No. 210204-12s; swivel nut (crimp type)
Group C: Part No. 206204-8-6s; SAE male to 37' male flare adapter
Group D: Part No. 2089-6-6s; 90 ° male to female pipe adapter
Figure 1. Zinc-plated parts salt-spray tested by Detroit Testing Laboratory andAeroquip (rack plated).
beginning to develop on specimens in
Groups C, E, and F at 504 hr. The results
of the salt-spray tests on cadmium-plated
parts were as follows: (1) all specimens in
the seven groups passed the requirement
of 96 hr before the first appearance of
white corrosion products, and the appear-
ance of white corrosion products in any of
the seven groups was delayed to 336 hr
and beyond and (2) no red rust was ob-
served on any of the cadmium-plated
specimens after 504 hr of exposure, at
which point the tests were ended. These
results demonstrated that the cadmium-
plated parts exhibit superior corrosion re-
sistance to zinc-plated parts with regard
to the appearance of white corrosion prod-
ucts and red rust in salt-spray tests.
Waste Reduction Potential
Waste reduction potential of the pro-
cess substitution was determined on the
basis of waste volume reduction and pol-
lutant reduction. Waste volume reduction
was estimated for the treated wastewater
and the dewatered sludge, which, respec-
tively, affect conservation of water and
landfill space. Pollutant generation focused
mainly on toxic pollutants such as cad-
mium, cyanide, chromium, and chlorine.
Tables 2 and 3 show the changes in the
total waste and pollutant generation, re-
spectively.
The increases in wastewater and sludge
were due to an increase in plating bath
concentration from approximately 3 oz/gal
of cadmium in the cadmium-plating baths
to approximately 3.5 oz/gal zinc in the
zinc-plating baths. The decrease in oil and
grease was due to an approximately ten-
fold decrease in the concentration of oil
Table 2. Annual Generation of Treated Wastewater and Sludge from Cadmium- and Zinc-Plating
Processes (Aeroquip Data)
Year
1989
1991«»
Plating
Process
Cd
Zn
Treated
Wastewater,
gal
40,000,000
44,900,000
Sludge,
Ib
282,000
383,000
(a) Adjusted to the 1989 production rate of the electroplating process.
Table 3. Pollutant Generation from Cadmium- and Zinc-Plating Processes (Ib/yr based on production
rate of 3.29 million ft2)
Pollutant
Cadmium Plating
Zinc Plating
Cd
Total CN
Total Cr
Zn
Oil & grease
12, 100
835
677
0
14,600
0
0
4,420
22,300
5,120
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used in the water-soluble oil dip tank. The
increase in chromium was due to an ap-
proximately fivefold increase in the chro-
mate bath concentration. The chromium,
which also is a priority pollutant, was ef-
fectively converted from the toxic
hexavalent form to a much less toxic triva-
lent form in the wastewater treatment plant;
therefore, it does not pose as great a
health risk as does the cadmium. Thus,
the overall hazard level of the waste was
substantially reduced by eliminating cad-
mium and cyanide. The process substitu-
tion also eliminated the use of chlorine
(95,900 Ib in 1989) for cyanide destruc-
tion in the wastewater treatment plant.
Personnel health risks were reduced sig-
nificantly by eliminating the handling of
hazardous materials such as cadmium,
cyanide, and chlorine. Consequently, the
process substitution has reduced the
company's potential liability for accidental
worker exposure to and environmental re-
lease of these hazardous materials.
Economic Evaluation
Economic evaluation of the process sub-
stitution was based on a simple payback
period analysis with the use of the cost
data provided by Aeroquip. The evalua-
tion included estimation of capital costs
for the process conversion and operating
costs of both processes. Table 4 shows
the capital cost (in 1992 dollars) for con-
verting the plating lines at Aeroquip from
cadmium plating to zinc plating.
Approximately 72% of the total cost was
for expenses related to cleaning up the
cadmium process equipment and for dis-
posal of the waste generated from the
cleanup operation; the remaining 28% was
for installing new equipment. Table 5
shows the annual operating cost (in 1992
dollars) for the two plating processes. The
operating cost for the zinc-plating process
was slightly lower than that for the cad-
mium-plating process. For a new installa-
tion, therefore, the lower operating cost of
the zinc chloride plating process results in
an economic advantage over that of the
cadmium cyanide plating process. The
payback period for the capital investment
required for converting an existing cad-
mium-plating process to a zinc-plating pro-
cess was estimated at 115 yr. The process
conversion, therefore, cannot be justified
solely on economic grounds. It should be
based on worker safety and environmen-
tal pollution, as well as on greater accep-
tance of the zinc-plated components in
domestic and foreign industrial and con-
sumer markets.
Table 4. Capital Cost to Convert (1992)
Parameter
Barrel
Plating Lines
Hack
Plating Line
Subtotal
Expense (cleanup of old $428,000 $999,000 $1,427,000
equipment and waste
disposal)
New equipment $424,000 $122,000 $646,000
Subtotal $852,000 $1,121,000
Total $ 1,973,000
Table 5. Comparison of Operating Costs for Cadmium- and Zinc-Plating Processes (1992)
Expenditure
Cadmium
Plating
Zinc
Plating
Electroplating chemicals
Clear chromate $3,840
Brightener 3,180
NaOH flakes 3,330
Yellow chromate 16,900
Sodium cyanide 42,800
Cadmium anode @ $0.99/lb 55,900
Potassium chloride
Boric acid
Wetter
Zinc anode @ $0.78/lb
Wastewater treatment chemicals $215,000
Operating labor, 14 persons @ $25/hr $728,000
Electricity, @ $0.08/kwh $8,920
Miscellaneous
Blood tests • $3,240
Environmental monitoring 2,320
Record keeping 463
Washdown of plating dept. 6,370
Treatment of washdown water 4,050
Sludge disposal cost, @ $178.50/ton $ 25,200
Waste oil disposal, @ $600/drum $15,600
Total $1,135,000
Net cost reduction
$49,800
28,900
6,1580
18,200
4,050
46,000
$ 190,000
$ 728,000
$ 7,880
$34,200
$3,600
$1,118,000
$ 17,200
Conclusions
The results from the corrosion tests per-
formed in this study and from historical
data provided by Aeroquip indicate that
zinc-plated parts meet customer require-
ments of 96 hr of exposure to salt spray
(ASTM Method B117-90) before the ap-
pearance of white corrosion products. Fur-
ther, the zinc-plated parts meet the
Aeroquip process requirements, of 360 hr
of exposure to salt spray before the ap-
pearance of red rust. Although the corro-
sion resistance properties of cadmium-
plated parts are superior to that of zinc-
plated parts, the corrosion resistance of
zinc-plated parts can be considered satis-
factory to allow use of zinc as substitute
for cadmium in many plating applications.
The process substitution also satisfied the
requirements of some domestic and for-
eign customers for cadmium-free prod-
ucts.
The changes in the waste generation
from the process substitution were as fol-
lows:
-------
decrease of cadmium by 12,100 Ib/
yr.
decrease of cyanide by 835 Ib/yr,
decrease of oil and grease waste,
including waste oil, from 14,600 Ib/yr
to 5,120 Ib/yr,
increase of zinc by 22,300 Ib/yr,
increase of chromium from 677 Ib/yr
to 4,420 Ib/yr,
increase of treated wastewater from
40,000,000 gal/yr to 44,900,000 gal/
yr, and
increase of wastewater treatment
sludge from 282,000 Ib/yr to 383,000
Ib/yr.
The use of chlorine for destruction of
cyanide in the wastewater treatment plant
was also eliminated.
The capital cost for the process change
at Aeroquip was estimated to be
$1,973,000. The annual operating cost re-
duction that resulted from the process
change was estimated to be $17,200.
Based on these costs, the estimated
payback period is 115 yr. The process
change, therefore, cannot be justified on
economic grounds alone. Justification
would be based on the improved worker
safety and reduced environmental pollu-
tion plus the market's requirements for
zinc-plated rather than cadmium-plated
parts in many applications. In comparing
the two processes for a new installation,
the zinc chloride plating process offers
obvious advantages over the cadmium
cyanide plating process.
The full report was submitted in partial
fulfillment of Contract Number 68-CO-0003,
Work Assignment 3-36, under the Spon-
sorship of the U.S. Environmental Protec-
tion Agency.
•&IU.S. GOVERNMENT PRINTING OFFICE: MM - SSO-067/80247
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B.C. Kim, P.R. Webb, J.A. Gurklis, and R.K. Smith are with Battelle, Columbus,
OH 43201-2693.
Teresa Harten is the EPA Project Officer (see below).
The complete report, entitled "Substituting Cadmium Cyanide Electroplating
with Zinc Chloride Electroplating," (Order No. PB94-165321; Cost: $19.50
subject to change) will be available only from
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use
$300
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
EPA/600/SR-94/074
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