United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/SR-94/071 July 1994
&EPA Project Summary
Evaluation of an Electrodialytic
Process for Purification of
Hexavalent Chromium Solutions
Dale W. Folsom, Jody A. Jones, and Robert F. Olfenbuttel
The evaluation summarized here ad-
dresses the waste reduction and eco-
nomics of an electrodialytic process
that can be used to selectively remove
impurities that build up in chromic acid
solutions with use. The removal of im-
purities extends the useful life of the
chromic acid solution and reduces pe-
riodic replacement of the solution. The
electrodialytic units tested in this evalu-
ation were manufactured by lonsep™*.
The units were tested at SL Modern
Hard Chrome in Camden, NJ, (a hard
chromium plating solution) and at
Paramax in St. Paul, MN, (a chromic
acid solution etching copper from
printed wire boards).
The electrodialytic process was found
to effectively remove the impurities that
build up in chromic acid solutions. The
rate of return on investment was not
cost effective for the hard chromium
plating bath but was cost effective for
the chromic acid etch bath, which had
a payback of less than 5 yr. In these
two examples, the payback was related
to the rate of contaminant buildup in
the solution — the more frequently a
solution was replaced when contami-
nants were not removed, the shorter
the payback after an electrodialytic pro-
cess had been installed. The chromium
plating operation annually reduced
chromium needing disposal by 73 kg
(161 Ib), and the copper etching opera-
tion projected an annual reduction of
4,410 kg (9,700 Ib).
* Mention of trade names or commercial products does
not constitute endorsement or recommendation for
use.
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
Technology Evaluation 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)
Waste Reduction and Innovative Technol-
ogy Evaluation (WRITE) Program, was a
cooperative effort among EPA's Risk Re-
duction Engineering Laboratory (RREL),
SL Modern Hard Chrome, and Paramax.
The goal of the WRITE Program is to
evaluate, in a typical workplace environ-
ment, examples of prototype or innovative
commercial technologies that have poten-
tial for reducing wastes and then to pro-
vide this information to potential users.
The objectives of the electrodialytic tech-
nology study were to evaluate (1) the
waste reduction potential of the technol-
ogy, (2) the economic feasibility of the
technology, and (3) the impact on product
quality.
SL Modern Hard Chrome was the site
for testing the electrodialytic process on a
hard chromium plating solution. SL Mod-
ern Hard Chrome has specialized in in-
dustrial hard chrome plating for over 35
years and plates a full spectrum of materi-
als, ranging from aluminum through the
copper, ferrous, and nickel base alloys to
zinc. The chromium thickness varies from
0.0001 in. to 0.030 in. or more on parts
ranging in size from a few ounces to sev-
Printed on Recycled Paper
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eral tons. Paramax (a Unisys company)
was the site for testing the electrodialytic
process on a chromic acid etching solu-
tion. Paramax manufactures multilayer
printed wire boards at this facility.
At SL Modern Hard Chrome, contami-
nation builds up in the chromium plating
solution. The contaminants typically are in
the form of cations, including iron, triva-
lent chromium, and lead. As the contami-
nants build up, the plating solution fails to
produce the required product quality and
must be replaced. The lonsep™ electrodia-
lytic process removes the cations from
the chromium plating solution and allows
it to be used longer. At SL Modern Hard
Chrome, it has been more than 3 yr since
a chromium plating bath was replaced.
Paramax uses a chromic acid solution
to etch copper from printed wire boards
(PWB). As copper builds up in the etching
solution, the etching rate becomes unac-
ceptably slow. Before lonsep™ installa-
tion, the chromic acid solution was
replaced with fresh solution from once a
day to once a week at the operator's dis-
cretion. The lonsep™ electrodialytic pro-
cess extends the usefulness of the etching
solution by removing copper from the
etching solution and converting some of
the trivalent chromium back to hexavalent
chromium electrolytically.
lonsep™ Electrodialytic
Process
The aim of this technology is to reduce
wastes by removing metals other than
chromium from the process solution. This
improves plating and etching product qual-
ity and extends process solution life.
Figure 1 shows a two-compartment cell
used for the purification of a chromium
plating solution. The lonsep™ electrodia-
lytic process uses a voltage gradient to
separate salt in a solution into cations and
anions. Chromium is present in the an-
ionic chromate form in the plating and
etching solutions. Metal contaminants (cat-
ions) migrate across a semipermeable
membrane, under the influence of the elec-
tric field. Conversion of the electroplatable
metal cations to insoluble hydroxides oc-
curs when the cations migrate through the
membrane; this migration eliminates the
buildup of metals on the cathode. Mem-
branes in the electrodialytic cells serve to
physically separate the acidic, basic, and
other process solutions.
Materials and Methods
One test site uses a chromium plating
solution and one a chromic acid for etch-
ing copper. At each site, metal analyses
were performed on the chromium solution
and the catholyte solution to determine
contaminant levels in the process solution
and the rate of metals buildup in the
catholyte solution. From the analyses, the
rate of metals buildup in the catholyte
solution was determined. This corre-
sponded with metals removal from the
process solution, which in turn was used
to determine the bath life-extending capa-
bilities of the lonsep™ process and the
waste reduction potential. Operating costs
with and without the lonsep™ process
were used along with installation costs to
determine the economics of the process.
Results and Discussion
The results from the two sites are dis-
cussed separately for each site because
the bath process and the lonsep™ pro-
cess used at the two sites were very dif-
ferent. For each site, the discussion is
divided into the three project objectives:
waste reduction potential, economic evalu-
ation, and product quality evaluation.
ANODE
MEMBRANE
CATHODE
+
ANIONS
00" F"
^*^SO"
SALTS
CATIONS —
r * * r_i* * — —
Cu. Cd
N^V
Al*** /^F***— -
TO4 JQ- A ACIDS Nl
H* T Cr^^CrO.'
H* PROCESS
SOLUTION
>•
>• C»|OH) j
> Cd(OH) 2
>> F«(OH) 3 BASES
>• AI(OH|, ^^
^. N!(OH), ((OHJ-)
K>NSEP*CATHOLYTE G)
Figure 1. lonsep™ electrodialytic process.
(Source: lonsep™ Corporation, 1989)
Chromium Plating
At SL Modern Hard Chrome's 1,400-gal
hard chromium plating bath, the chromium
plating solution was recovered continu-
ously by placing the lonsep™ unit (cell)
directly into the bath. The catholyte solu-
tion is contained in a plastic 55-gal drum
outside the bath and is circulated through
the lonsep™ cell.
Waste Reduction Potential
SL Modern Hard Chrome purchased the
lonsep™ system as part of its plan to
eliminate all industrial liquid waste dis-
charges to the city. To achieve zero liquid
discharge, SL Modern Hard Chrome ini-
tially rinses parts over the bath; the final
rinse is totally collected in a sump, fil-
tered, and then returned to the bath to
make up water lost to evaporation.
Impurities build up in the plating bath
because all rinse water is returned to it;
the lonsep™ system was purchased to
reduce this buildup. With use of lonsep™,
the only resulting waste discharge is the
sludge from the lonsep™ catholyte solu-
tion. This catholyte sludge contains levels
of chromium at 2000 to 3200 mg/L total
chromium and 760 to 1050 mg/L
hexavalent chromium and therefore must
be handled as a hazardous waste. With
the catholyte solution replaced monthly,
the annual discharge of total chromium is
6.5 kg (14.2 Ib).
The catholyte solution was analyzed af-
ter the solution had been in use for 1 to
2 months and immediately before disposal.
The metals in the catholyte solution were
removed from the plating bath. Analysis
indicates a removal rate of approximately
25 g total contaminants/day for a 250-
amp lonsep™ unit. If the contaminants
were not removed, levels would eventu-
ally reach the limit of 52 g/L in the plating
bath. The time estimated from these data
for a 1,400-gal bath to reach that limit is
52 g/L x 3.79 L/gal x 1,400 gal/25 g/day,
or 11,036 days. Therefore, the use of
lonsep™ extends bath life beyond 40
years, which results in approximately 35
gal of solution saved/yr (that would other-
wise be disposed of), based on an opera-
tion schedule of 250days/yr (1,400-gal
bath/40 yr).
Hexavalent chromium is significantly re-
duced with the use of the lonsep™ unit —
from 165lb to 14.2 Ib. The 14.2 Ib of
chromium is the small amount lost to the
catholyte solution. The reduction is the
result of not having to replace the bath
periodically and of having all rinse water
returned to the plating bath to make up
evaporative water losses.
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Chromium is saved not only through
reduced replacement of plating solution,
but also through the reduced number of
rejects. For every reject, the company must
strip and replate the part. The reject data
are based on estimates of plant person-
nel, because no records were maintained.
The 5% decrease in rejects experienced
by SL Modern Hard Chrome corresponds
to approximately 237 Ib chromium/yr that
is not disposed of with the stripper and
that need not be purchased for addition to
the plating solution. The 237 Ib of chro-
mium oxide is calculated from the
company's plating rate from this bath of
42,900 ft2/yr, at a plating amount of 1.77
oz CrO3 per ft2, and a 5% savings (0.05 x
42,900 ft2/yr x 1.77 oz/ft2 x 1/16 oz/lb).
Table 1 summarizes the waste reduc-
tion potential of the new technology. The
top part of Table 1 (without lonsep™) lists
the wastes from infrequent bath replace-
ment and the estimated amount of chro-
mium stripped from rejected parts. The
bottom part of Table 1 (with lonsep™)
lists the chemicals used to make the
lonsep™ catholytic solution and the addi-
tional barium carbonate used to adjust the
sulfate levels of the chromium plating bath.
Barium carbonate is used to precipitate
the sulfate as barium sulfate. The use of
barium carbonate increased when the
lonsep™ was installed.
The total waste without the use of
lonsep™ amounts to 317 Ib of CrO3 (165 Ib
Cr). The total waste with the use of lonsep™
increases to 451 Ib. This increase is the
result of the catholyte salts and sludge and
the increased use of barium carbonate to
reduce sulfate in the bath. The sulfate con-
centration builds up faster in the bath be-
cause rinse water is reused in the bath
when the lonsep™ unit is used. In a 1-yr
period, 36 Ib of barium carbonate was
used to form barium sulfate, which pre-
cipitates out in the bath. The precipitate is
either filtered out or allowed to collect at
the bottom of the plating bath. The 36 Ib
of barium carbonate would react to form
43 Ib of barium sulfate.
Economic Evaluation
SL Modern Hard Chrome provided eco-
nomic information for most aspects of its
operations. The annual operating costs
with and without the lonsep™ unit are
itemized in Table 2. Without the lonsep™
system, the operation of a 1,400-gal bath
costs $3,684/yr. The cost for the same
bath with an electrodialytic unit is $3,5787
yr.
According to SL Modern Hard Chrome
personnel, a major incentive for installing
the equipment was to improve product
quality by reducing contaminant buildup in
the plating bath. Fewer rejects result in
economic savings (e.g., faster turnaround
time, decreased need for stripping solu-
tion, and ease of operation). The costs for
rejects and additional plating are included
in the operation without lonsep™.
The capital cost of a 250-amp lonsep™
unit in the fall of 1991 was $20,000. Be-
cause there is a savings of $106 in an-
nual costs using the lonsep™ unit, there
is a payback on the unit of 189 yr.
Although economic considerations are
important, they are not the only justifica-
tion for installing waste reduction equip-
ment. SL Modern Hard Chrome has zero
discharge from its plating operations to
the city water treatment system because
Table 1. Waste Reduction of the Chromium Plating Line
Waste
Annual Generation
Without lonsep™
CrO3 in bath solution
CrO3 due to rejects
Total CrO,
With lonsep™*
Catholyte solution
Sodium sulfate
Sodium carbonate
Additional barium sulfate from sulfate reduction w/BaCO3
TotaP
80 Ib (41.6 Ib Cr)
237lb(123lbCr)
317lb(165lbCr)
120 Ib
288 Ib
43 Ib
451lb(14.2lbCr+e)
* Sludge from lonsep™ not included because it should equal the amount of metal contaminants
disposed of with the chromium plating solution without lonsep™.
f The sludge for 1 yr would contain 14.2 Ib Cr *6.
all rinsewater is returned to the plating
baths.
Product Quality Evaluation
Chemical analyses of the chromium plat-
ing solution were conducted to verify that
the solution met operational specifications
for hard chromium plating solutions. Analy-
sis of the bath showed it was within speci-
fications — the contaminant level was
below the maximum of 52 g/L and the
chromium level was above the minimum
of 140 g/L.
The products, chromium-plated parts,
are inspected for pits, blisters, other de-
formities, and chromium thickness. The
product quality is the plated part quality,
which correlates with the plating bath qual-
ity (specifications). Since installation of the
lonsep™ unit, the number of rejects has
decreased by about 5%, a key factor in its
continued use. The improved chromium
plating quality has produced more uniform
chromium deposit and fewer pits.
Chromium Etching
At the second company, Paramax, chro-
mium-based etchant was tested as a batch
process. Eight of the six cells in the pro-
cess line were used, and over a 2-day
period, 200-gal etchant baths were re-
moved from the process line to a treat-
ment tank and pumped through the
lonsep™ unit. The unit ran continuously
for 3 days. Paramax has since estab-
lished that the recovered etchant meets
its stringent requirements for etching solu-
tions. The company is currently using 12
cells to keep up with the buildup of copper
and has successfully recycled the etchant
during production.
Waste Reduction Potential
Calculation of the waste reduction po-
tential was based on the difference be-
tween the amount of chromic acid etch
solution disposed without lonsep™ treat-
ment and the amount of chromic acid etch
that can be reused after treatment with
the lonsep™ unit.
Experience at Paramax indicates that
use of the lonsep™ unit prevents disposal
of approximately 7.5 baths/wk. Paramax
currently disposes of 8.5 baths/wk and
estimates that, with the lonsep™ unit, dis-
posal will be reduced to one bath/wk. Each
bath contains 110 gal (the lonsep™ unit
can treat up to 500 gal, or about four
baths in 4 days), which means that 41,250
gal of etchant bath solution would not be
disposed of per year (7.5 bath/wk x 110
gal/bath x 50 wk/yr). The etchant concen-
trate is diluted 50% to make up the bath.
Therefore, the lonsep™ unit could reduce
20,625 gal of etchant concentrate per year
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Table 2. Economics of the Chromium Plating Line'
Description
Annual Use
Rate ($)
Annual Cost ($)
Without lonsep™
Cr bath
Bath disposal
CrO3 due to rejects
Labor due to rejects
Strip solution replacement
and disposal
Total without lonsep™
35 gal
35 gal
237 Ib
140 hr
100 gal
$11.30/gal
2/gal
1.13/lb
20/hr
1.50/gal
$396
70
268
2,800
150
$3,684
With lonsep™
Catholyte solution
Sodium sulfate
Sodium carbonate
Water
Barium carbonate
Sludge disposal'
Labor
Maintenance
Power
Total with lonsep™
Annual savings
120 Ib
288 Ib
660 gal
36 Ib
4 drums
41 hr
—
8,100kWh
1 8/100 Ib
1 8/100 Ib
2.66/1 000 gal
1.22/lb
205/drum
20/hr
—
.0902/kWh
$22
52
2
44
820
827
1,080
731
$3,578
$106
Wastewater discharge costs are not applicable. Analytical costs are assumed to be the same for both
cases.
needing disposal. This amount of etchant
contains approximately 7,154 Ib of chro-
mium that would otherwise have gone to
waste (80 g/L CrO3 in etchant x 52 g Cr/
100 g CrO3 x 20,625 gal x 3.785 L/gal).
Table 3 summarizes the items evaluated
in the waste reduction analysis.
To recover the etched copper, Paramax
acidifies the cake filtered from the catholyte
solution. Water use at Paramax is in-
creased to make up the catholyte solu-
tion. After acidification and copper
recovery, the resulting solution is nonhaz-
ardous.
Economic Evaluation
Paramax provided economic informa-
tion for its etching operations. Because
the lonsep™ unit at Paramax is still un-
dergoing testing, most of the cost analysis
was based on Paramax estimates derived
from economic information in plant records
and experience of Paramax personnel.
These estimates indicate that the unit can
prevent disposal of approximately seven
etchant baths/wk and, thus, save disposal
and replacement chemical costs.
Operating cost factors involved in the
economic analysis for Paramax include
labor, maintenance, chemicals, utilities
(water and electricity), and waste treat-
ment/disposal. Table 4 compares costs
with and without the lonsep™ unit.
Without the unit, costs of approximately
$198,000 are incurred for replacement and
disposal of the etchant baths. Estimates
for operating the unit are approximately
$72,000/yr, mostly for added labor and
maintenance on the unit. Thus, with the
lonsep™ system, an approximate annual
savings of $126,000 would be realized.
The capital cost of the unit (specific to
Paramax), including installation and modi-
fications, was $563,000. Dividing this by
the estimated annual savings results in a
payback period of 4.5 yr.
Table 3. Waste Reduction of the Etching Line
Description
Product Quality Evaluation
The lonsep™ unit at Paramax was in
the initial testing phases during this study.
The etchant was sampled and analyzed
for both chromium and contaminants at
the end of the 3-day treatment/recovery
process. These analyses were used to
determine whether the renovated bath was
within specifications and whether bath
quality was an indication of product qual-
ity. Although total chromium in the etchant
remained constant, hexavalent chromium
increased. The hexavalent chromium
started at approximately 74% of the total
and increased to about 99%. It is believed
that oxidation of the trivalent chromium
back to the hexavalent form caused the
increase in hexavalent chromium concen-
tration. The resulting hexavalent chromium
concentration of 30.3 g/L in the etchant
over the 3-day sampling period ap-
proached the minimum specification level
of 31 g/L. This could be increased further
by longer treatment or by adding etchant
concentrate. At the time this study was
conducted, the etchant had not been re-
used and the effect of recovered solution
on in-house printed wire board product
quality had not been evaluated.
The cationic contaminants were within
specification. The 10.8 g/L (mostly cop-
per) was below the maximum level of 25
g/L. Because the chromium and the con-
taminant levels are both near specifica-
tion levels, the etchant should be
acceptable.
The full report was submitted in partial
fulfillment of Contract Number 68-CO-
0003, Work Assignment 3-36, by Battelle
(Columbus) under the sponsorship of the
U.S. Environmental Protection Agency.
Amount Discarded
Per Year
Without lonsep™
Etchant
Water
Chromium
With lonsep™
Catholyte solution
Sodium chloride
Sodium sulfate
Soda ash
Water
Chromium
20,625 gal
20,625 gal
7,100 Ib
10,000 Ib
5,000 Ib
1,000lb
25,000 gal
42 Ib'
* Estimated.
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Table 4. Economics of the Etching Line
Description Annual Use Rate ($) Annual Cost ($)
Without lonsep™
Etchant (concentrate) 20,625 gal $ 4.85/gal $100,031
Etchant disposal 41,250 gal 2.31/gal 95,288
Labor for disposal 150 hr 20.00/hr 3,000
Water 20,625 gal 2.66/1000 gal ' 55
Total $198,374
With lonsep™
Catholyte solution
Sodium chloride 10,000 Ib 3.50/50 Ib 700
Sodium sullate 5,000 Ib 17.50/100 Ib 875
Soda ash 1,000 Ib 0.23/lb 230
Water' 25,000 gal 2.66/1000 gal 66
Labor 2,000 hr 20.00/hr 40,000
Maintenance — — 30000
Power 1,430kWh 0.045/kWh ' 65
Total $ 71,936
* Water costs include sewage fee.
•&LJ.S. GOVERNMENT PRINTING OFFICE: 1994 - 550-067/80277
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Dale W. Folsom, Jody A. Jones, and Robert F. Olfenbuttel are with Battelle,
Columbus, OH 43201.
Teresa Marten is the EPA Project Officer (see below).
The complete report, entitled "Evaluation of an Electrodialytic Process for
Purification of Hexavalent Chromium Solutions," (Order No. PB94-165214;
Cost: $17.50, 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
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EPA/600/SR-94/071
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