United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/SR-94/050 April, 1994
EPA Project Summary
Cadmium and Chromium
Recovery from Electroplating
Rinsewaters
Arun R. Gavaskar, Robert F:. Olfenbuttel, and Jody A. Jones
This evaluation addresses the prod-
uct quality, pollution prevention po-
tential, and economic factors involved
in the use of ion exchange to recover
cadmium and chromium from elec-
troplating rinsewaters and to remove
contaminants for reuse of rinsewater.
Cadmium, chromium, and cyanide
(which is part of the cadmium bath)
are on EPA's 33/50 list of target
chemicals. Test results showed that
the water returned to the rinse after ion
exchange was of acceptable quality for
both the cadmium and chromium pro-
cesses. The ion exchange resins are
regenerated with sodium hydroxide
(NaOH). On the cadmium line, the
regenerant was subjected to electro-
lytic metal recovery (EMR) to recover
cadmium for reuse in the plating bath.
On the chromium line, the regenerant
was passed through a cation exchange
resin in an effort to recover chromic
acid. Although the recovery results
were good on the cadmium line, chro-
mic acid could not be recovered in this
test. The pollution prevention potential
of ion exchange on the cadmium and
chromium rinsewater is good; however,
further testing is needed to establish
good recovery of chromium as chro-
mic acid from the regenerant. The ion-
exchange processes also proved
economically viable.
This Project Summary was developed
by the U.S. EPA's Risk Reduction En-
gineering Laboratory (RREL), Cincin-
nati, OH, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction
This study, performed under the U.S.
EPA Waste Reduction and Innovative
Technology Evaluation (WRITE) Program,
was a cooperative effort among EPA's
RREL, the Connecticut Hazardous Waste
Management Service, and the Torrington
Company. The objective of the WRITE
Program is to evaluate, in a typical work-
place environment, examples of prototype
or innovative commercial technologies that
have potential for reducing waste. The
ion exchange system used in this study
was manufactured by CTEO Tek, Inc.*
and supplied by Plating Services, Inc.
Other ion exchange units and technolo-
gies applicable to the same wastestream
(electroplating rinsewaters) are also
commercially available.
The objectives of this study were to
evaluate (1) the effectiveness of the ion
exchange unit in cleaning the rinsewater
for reuse in the rinse tanks, \2.) the pollu-
tion prevention potential of this technol-
ogy, and (3) the cost of ion exchange
versus the cost of the former practice (dis-
posal).
Figure 1 shows the cadmium ion ex-
change system configuration. The water
from Rinse 1 tank is first passed through
a filter to prevent suspended solids from
contacting the resin in the ion exchange
column. The anionic resin captures the
cadmium-cyanide complex, and the water
Mention of trade names or commercial products does
not constitute endorsement or recommendation for
Printed on Recycled Paper
-------
is returned to the Rinse 2 tank. An emer-
gency bypass valve allows this water to
be discharged to waste in case cadmium
or cyanide levels are found to be too high.
The resin is periodically regenerated with
a 15 to 20% NaOH solution, and the
regenerant is taken to the electrolytic metal
recovery (EMR) unit, where cadmium is
recovered on the cathode and returned to
the plating tank. Some cyanide is de-
stroyed by decomposition during the EMR
process.
Figure 2 shows the chromium system
configuration. The primary ion exchange
resin is anionic to remove hexavalent
chrome. In the future, a cationic resin com-
ponent will be added to the primary resin
to remove any trivalent chrome that may
be present in the rinsewater. The anionic
resin is also regenerated with a 15 to 20%
NaOH solution. The resulting solution (so-
dium chromate) is run through a second-
ary (cationic) exchange unit that should
convert the regenerant back to chromic
acid and return it to the plating tank.
Product Quality Evaluation
The objective of this part of the evalua-
tion was to show that water processed
through the ion exchange system is clean
enough for use as rinsewater in the cad-
mium or chromium plating lines. Contami-
nant-free rinsewater ensures a good
workpiece finish. The approach was to
collect three samples each of the
rinsewater, before and after passing
through the ion exchange system. These
samples were analyzed in the laboratory
to evaluate the removal of contaminants.
In addition, batches of rinsewater (one
batch for cadmium and one for chromium)
were spiked with plating bath solution to
elevate contaminant levels (cadmium or
chromium), and the spiked rinsewater was
run through the ion exchange to test the
limits of the unit. Because rinsewater was
continuously circulated through the ion
exchange system during the day, three
samples of the rinsewater at the begin-
ning, middle, and end of a shift were
taken to ensure that water quality remained
relatively steady over time.
Table 1 presents the results of the labo-
ratory analysis of the cadmium rinsewater
Workpiece -.
.., .y' Metering \ ,.-*
". /Pump Make-up \ /
'"
u-JL^JLi ^_JLr~
*J Cadmium \stiilRin*r Ri 1 R,
\ I Plating Tank \(Dragout) | \ Rinse 1. j HOT
Recovered ป Emergency Bypass to
Cadmium | Cyanide Wastestream
Rinse 2
L ,
EMR Unit
Make-up Water
Regenerant
Tank
Legend
* Rinse Water
ป Workpiece
>. Regenerant
Filter
Cartridge
Figure 1. Ion exchange recovery of cadmium from plating rinsewater.
Workptecet Catering
''.% f'" Pump Make-up
Chromium
I Plating Tank
Recovered
Chromium
To Chrome
Reduction
Wastestream
KVJT
-+ซ-
Rinse 1 I Rinse 2
Secondary Catkin
Exchange
Make-up Water
Regenerant
Legend
* Rinse Water
ป Workpiece
ป Regenerant
Filter
Cartridge
Figure 2. Ion exchange recovery of chromium from plating rinsewater.
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Table 1. Cadmium Rinsewater Analysis
Sample No.
CD-X1-B1
CD-X1-B2
CD-X1-B3
CD-X1-A1
CD-X1-A2
CD-X1-A3
CD-XS-B1
CD-XS-A1
CD-R1-B1
CD-R1-B2
CD-R1-B3
CD-R2-B1
CD-R2-B2
CD-R2-B3
CD-X30-B1
CD-FB-1
Sample Description
Before ion-x, Run 1
Before ion-x, Run 2
Before ion-x, Run 3
After ion-x, Run 1
After ion-x, Run 2
After ion-x, Run 3
Spike, before ion-x
Spike, after ion-x
Rinse 1, 9:00 am
Rinse 1, 12:30 pm
Rinse 1, 4:00 pm
Rinse 2, 9:00 am
Rinse 2, 12:30 pm
Rinse 2, 4:00 pm
Rinse 1, 30-min
Field blank
pH
11.26
11.41
11.48
11.45
11.51
11.51
NA
NA
10.72
11.37
11.40
11.07
11.50
11.47
11.35
7.50
Conductivity
(umhos/cm)
783
864
936
867
845
885
NA
NA
278
823
985
360
860
970
760
65.3
Cadmium
(mg/L)
7.28
2.23
2.58
0.015
<0.01
0.01
38.7
3.69
1.80
3.55
4.71
0.067
0.105
0.269
4.31
<0.01
Cyanide
(mg/L)
35.60
9.26
13.80
0.037
0.047
0.041
117
14.6
8.55
15.60
24.70
0.28
0.62
1.23
17.60
<0.01
Iron
(mg/L)
0.57
0.22
0.31
0.06
0.06
0.02
NA
NA
0.28
0.34
0.41
0.11
0.07
0.09
0.33
0.21
Dissolved
Solids
(mg/L)
226
196
205
147
161
163
NA
NA
90
190
225
80
164
191
189
50
Suspended
Solids
(mg/L)
1
< 1
< 1
<1
2
<1
NA
NA
1
< 1
10
2
3
<1
3
1
(a) NA = not analyzed.
samples. Most of the cadmium and cya-
nide were removed by ion exchange in
some cases, to below detection levels.
The pH of the rinsewater remained steady
at alkaline levels throughout the testing.
A statistical t-test (95% significance
level) was performed based on the aver-
ages and standard deviations of the 1 -min
"before" and "after" (CD-X1-) data. Sus-
pended solids levels were very low in both
"before" and "after" samples. After ion ex-
change, concentrations of cadmium, cya-
nide, and iron in the rinsewater decreased
significantly. Overall dissolved solids lev-
els also' showed a significant decrease
after ion exchange; this indicated a de-
cline in dissolved mass levels. Interest-
ingly, conductivity did not show any
significant change after ion exchange, in-
dicating that the current-carrying capacity
of the rinsewater did not change. During
ion exchange, heavier ions (cadmium, iron,
etc.) transfer to the resin and lighter so-
dium ions are transferred to the water.
Thus, dissolved mass in the water de-
creases but conductivity remains relatively
constant. Small amounts of fresh makeup
water were added to the rinsewater loop
from time to time to compensate for the
water lost to evaporation and dragout with
the parts; this also helped control conduc-
tivity.
Table 2 describes the results of the
laboratory analysis of the chromium
rinsewater samples. After ion exchange,
the rinsewater pH levels were slightly al-
kaline (9.31 to 9.45) because chromate
ions (and any other contaminant anions)
had been substituted with hydroxide ions.
The alkaline pH was neutralized in the
rinse tanks by the chromic acid residue
on the parts (workpiece).
Similar statistical analyses were per-
formed on the chromium data as have
been described for the cadmium data. Sus-
pended solids levels were significantly re-
duced by the cartridge,.filter ahead of the
resin. Chromium (total chromium) and iron
levels decreased significantly after ion ex-
change. Iron removal may be due either
to removal of ferrous suspended particles
on the cartridge filter or fc> (deposition of
complexed iron on the resin. As in the
cadmium tests, dissolved solids mass de-
creased significantly, but conductivity (cur-
rent-carrying strength) remained constant
after ion exchange. This is because
heavier chromates in the rinsewater were
replaced with lighter hydroxide ions.
Pollution Prevention Evaluation
The pollution prevention potential of the
ion exchange technology was assessed
in terms of waste volume reduction and
pollutant reduction. Waste volume reduc-
tion addresses the gross wastestream
(e.g., Ib of wastewater treatment sludge)
and affects environmental resources (e.g.,
landfill space) expended through disposal.
Pollutant reduction addresses the specific
pollutants in the wastestream (e.g., chro-
mium in the sludge).
Table 3 summarizes the waste volume
reduction. By using ion exchange, large
volumes of water are saved from going to
waste. This water (an important resource)
can be reused as a rinse on the cadmium
and chromium lines. Without ion exchange,
Torrington must maintain high rinsewater
flow rates (8 gpm for the cadmium line
and 2 gpm for the chromium line). These
continuous flows generate large amounts
of wastewater that have to be treated on
site. With the ion exchange system on the
cadmium line, Torrington requires only 50
gal/day to make up for dragout losses. A
similar makeup rate is expected on the
chromium line. Therefore, with the addi-
tion of the ion-exchange system, the
amount of wastewater that must be treated
is reduced. Virtually eliminating the waste-
water stream also eliminates the hazard-
ous sludge (containing cadmium or
chromium) that has to be handled, trans-
ported, and disposed.
In terms of pollutant reduction on the
cadmium line, the pollutants of interest
are cadmium and cyanide. Before ion ex-
change, cadmium in the rinsewater was
lost to wastewater, which was sent to an
on-site wastewater treatment plant. The
wastewater was treated in a steel cyanide
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Tablt>2. Chromium Rinsewater Analysis
Sample No.
CR-X1-B1
CR-X1-B2
CR-X1-B3
CR-X1-A1
CR-X1-A2
CR-X1-A3
CR-XS-B1
CR-XS-A2
CR-X2-B1
CR-FB-1
Sample Description
Before ion-x, Run 1
Before ion-x, Run 2
Before ion-x, Run 3
After ion-x, Run 1
After ion-x, Run 2
After ion-x, Run 3
Spike, before ion-x
Spike, after ion-x
Rinse 1, 30-min
Field blank
PH
4.83
4.67
4.41
9.38
9.31
9.45
NA(a)
NA
4.68
7.50
Conductivity
(umhos/cm)
103
104
106
198
126
115
NA
NA
105
65.3
Total
Chromium
(mg/L)
20.0
18.2
21.3
0.048
0.111
0.271
33.6
0.294
19.9
0.04
Iron
(mg/L)
0.90
0.85
0.87
0.15
0.20
0.26
NA
NA
0.73
0.21
Dissolved
Solids
(mg/L)
93
99
106
96
70
71
NA
NA
87
50
Suspended
Solids
(mg/L)
9
8
6
<1
<1
< 1
NA
NA
2
1
(a) NA " Not analyzed.
Tablo 3. Waste Volume Reduction
Without Ion Exchange
With Ion Exchange
Waste
Description
Cadmium System
Wastewater
Chromium System
Wastewater
Amount
Generated per
Yearฎ
1,920,000 gal
480,000 gal
Waste
Description
Wastewater
Regenerant
Fitter cartridges
Wastewater
Regenerant
Filter cartridges
Amount
Generated per
Yearฎ
Ogal
660 gal
6
Ogal
840 gal
12
(a) Based on values of 16 hr/day, 5 days/wk, 50 wk/yr.
(b) Based on pilot tests conducted by the Torrington Company and resin capacity.
treatment tank using chlorine gas, sodium
hypoohlor'rte, calcium hypochlorite, and
NaOH to oxidize the cyanide. The cad-
mium and other metals formed hydrox-
ides that settled in the clarifier as sludge,
which was then hauled off site for dis-
posal. The treated water was discharged
to the municipal sewer under a permit.
At Torrington, prior to ion exchange,
approximately 69 Ib of cadmium,and 281 Ib
of cyanide were discharged annually. Now,
because most of the cadmium can be
recovered and reused, this pollutant is
virtually eliminated from the wastestream.
Some cyanide is also destroyed in the
cadmium recovery process.
On the chromium line, without ion ex-
change, approximately 80 Ib of chromium
Is discharged annually. With ion exchange,
most of the chromium will be captured on
the resin, which will be regenerated with
NaOH. The regenerant then will pass
through a cation exchange resin for con-
version of sodium chromate to chromic
acid. However; when this recovery was
performed during the pilot unit testing, the
final regenerant liquid still showed a pH of
13.08. This indicates that sodium chro-
mate had not been converted to chromic
acid; if it had been, the pH would have
been much lower. This may be because
(a) an excess of NaOH was used to re-
generate the resin and/or (b) insufficient
resin was available to exchange all the
.sodium in the regenerant. Further testing
is needed to determine the feasibility of
the chromic acid recovery process.
Economic Evaluation
The economic evaluation involves com-
paring the costs of the ion exchange op-
eration with those of the former practice
(counterflow rinse). These comparisons are
summarized in Tables 4 and 5. Operating
costs for ion exchange recovery are much
lower than those for counterflow rinse
alone. The main cost saving is the reduc-
tion in Wastewater treatment costs.
In addition to operating cost savings,
the recovered cadmium has value because
it is reused in the plaiting bath as a cad-
mium anode. The cost of cadmium an-
odes is approximately $15/lb. The resulting
value of the 69 Ib/yr of recovered cad-
mium is approximately $1,036/yr.
The chromium deposited on the ion ex-
change resin also has value if it can be
successfully recovered as chromic acid.
The cost of chromic acid is approximately
$2.50/lb. Approximately 80 Ib/yr of chro-
mium metal is deposited on the ion ex-
change resin. This corresponds to about
154lb of chromic acid (CrO3). However,
further testing is needed to establish the
feasibility of chromic acid recovery from
the chromium in the regenerant.
The purchase price of the cadmium ion
exchange system was $8,100 (including
ion exchange resin column, pumps, and
collection tanks). The EMR equipment
price was $4,125 (including rectifier, pump,
anodes, cathodes, and solution tank). In-
stallation cost at Torrington, including ma-
terials (piping, etc.) and labor, was
approximately $3,500, to which $5,000 was
added to approximate the cost of in-house
pilot testing to determine specifications for
the individual plant.
The purchase price of the chromium ion
exchange system is estimated to be $8,200
(including ion exchange resin column,
pumps, and tanks). Installation cost at
Torrington is expected to be $3,500, in-
cluding materials '(piping, etc.) and labor.
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Table 4. Operating Costs Comparison for Cadmium System
Item
Amount
Used
per Year
Unit
Cost
Total Annual
Cost
Without Ion Exchange
Freshwater
Wastewater treatment
With Ion Exchange
Freshwater
Chemicals (50% NaOH)
Energy
Labor
i
Routine maintenance
- filter cartridges
- EMR anode plates
- EMR cathode plates
- labor
Waste Disposal
- regenerant
- filters
1,920,000 gal
1,920,000 gal
12,500 gal
96 gal
1564 kWhr
173hr
6
1
12
24 hr
660 gal
6
$0.70/1000 gal
$22/1000 gal
Total
$0.70/1000 gal
$ 1.50/gal
$ 0.075/kWhr
$7/hr
$5
$30
$30
$7/hr
$22/1000 gal
$ 400/36 units
Total
$ 1,344
$42,240
$ 43,584
$9
$144
$117
$ 1,211
$30
$30
$360
$168
$15
$67
$ 2,151
Table 5. Operating Costs Comparison for Chromium System
Item
Amount
Used
per Year
Unit
Cost
TotalAnnual
Cost
Without Ion Exchange
Freshwater
Wastewater treatment
With Ion Exchange
480,000 gal
480,000 gal
Freshwater 12,5.00 gal
Chemicals (50% NaOH) 240 gal
Energy 1492kWhr
Labor 149 hr
$ 0.70/1000 gal
$15/1000 gal
Total
$0.70/1000 gal
$ 1.SO/gal
0.075/kWhr
$7/hr
$336
$7,200
$7,536
$9
$360
$112
$ 1,043
Routine maintenance
- filters
- labor '
Waste Disposal
- regenerant
- filters
12
24
840 gal
6
$5
$7/hr
$15/1 000 gal
$ 400/36 units
Total
$60
$168
$13
$67
$ 1,832
The approximate cost of $5,000 for in-
house testing was also added for this unit.
A rough estimate of the payback period
can be obtained by the following formula:
Payback, years =
capital costs
operating cost savings
+ recovery value
Therefore, the payback period for the
cadmium ion exchange system is less than
1 year. For the chromium system, the pay-
back period is approximately 3 years. Be-
cause chromic acid recovery from the
regenerant-is yet to be established, no
recycled chromium value is assumed.
The above payback period estimation is
a simple calculation that (does not take
into account such factors as> taxes, depre-
ciation, inflation, etc. A more detailed eco-
nomic evaluation, based on Ithe worksheets
provided in the Facility Pollution Preven-
tion Guide (EPA 600/R-92/088), was per-
formed that took these factors into account.
The results showed that, for the cadmium
process, the return on investment (with
cost of capital equal to 15%) was still less
than 1 year. For the chromium process,
the return on investment (with cost of capi-
tal equal to 15%) was over 5 years. This
includes capital costs of engineering and
installation as well as increased overhead
costs due to addition of the units.
Conclusions and Discussion
The evaluation showed that rinsewater
on both cadmium and chromium lines at
Torrington Company can be reused after
subjecting it to filtration and ion exchange
to remove impurities. Large volumes of
water are thus saved, and large amounts
of hazardous metals sludge are kept from
the environment. The sidestreams from
ion exchange are negligible compared with
the wastewater and sludge wastestreams
that are generated in the absence of ion
exchange. The ion exchange resin can be
regenerated with NaOH. On the cadmium
line, the regenerant can be subjected to
EMR and the cadmium recovered on the
cathode. This electrode, with the depos-
ited cadmium, is then inserted in the plat-
ing tank as a cadmium anode. Thus, a
hazardous pollutant, cadmium, is reused.
On the chromium line, further testing is
needed to establish the feasibility of re-
covering chromium as chromic acid for
reuse in the bath.
Without ion exchange, the rinsewater
must undergo an expensive wastewater
treatment process. The cost of operating
the ion exchange unit is more than offset
by the savings in wastewater treatment
costs and by the value of the recovered
product. In addition to the direct economic
benefits, the ion exchange system also
reduces Torrington Company's potential
liability by virtually eliminating the risks
involved during off-site transport and dis-
posal of hazardous sludge.
The full report was submitted in fulfill-
ment of Contract No. 68-CO-0003, Work
Assignment No. 3-36, by Battelle under
the sponsorship of the U.S. Environmen-
tal Protection Agency.
A-U.S. GOVERNMENT PRINTING OFFICE: 1994 - 55WW7/80Z22
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Awn R. Gavaskar, Robert F. Olfenbuttel, andJodyA. Jones are with Battelle
Memorial Institute, Columbus, OH 43201-2693
Lisa Brown Is the EPA Project Officer (see below).
The complete report, entitled "Cadmium and Chromium Recovery from
Electroplating Rinsewaters," (OrderNo. PB94-156395; 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-94/050
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