&ER&
United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-81-130 Oct. 1981
Project Summary
Nickel Recovery from
Electroplating Rinsewaters by
Electrodialysis
John L. Eisenmann
A program to demonstrate the feasi-
bility of metal salt recovery and pollu-
tion control on a Watts-type nickel
plating line by electrodialysis was
conducted at Risdon Manufacturing
Co., Waterbury, CT. Each of two
reclaim rinse tanks, arranged in series
following plate tanks, was treated by
recirculating the rinse solutions
through separate electrodialysis
stacks. The first rinse solution was
maintained at 2-5 g/l nickel and the
second rinse held at 0.3-0.4 g/l nickel
over several months of plating opera-
tions. The nickel salts recovered from
the rinse solutions were concentrated
20-fold by the electrodialysis treat-
ment and could be returned directly to
the plate tanks for reuse. Several
operational problems are discussed
and recommendations made. It is con-
cluded that electrodialysis can be a
useful and economically viable
process for the treatment of at least
some types of electroplating rinses.
Both plating-metal recovery and
pollution control are accomplished.
A cost estimate based on the data
obtained during the demonstration
indicates that 95% of the nickel lost
from untreated rinses could be recov-
ered and that ancillary benefits in
sludge disposal, use of treatment
chemicals, etc. could be realized. Pay-
back periods of less than 18 months
are anticipated for commercial units.
This report was submitted in fulfill-
ment of Grant No. R803742 by
Risdon Manufacturing Co. under the
sponsorship of the U.S. Environmen-
tal Protection Agency. This report
covers the period June 1, 1975 to
December 31, 1976, and work was
completed as of February 22, 1977.
This Project Summary was develop-
ed by EPA's Industrial Environmental
Research Laboratory, Cincinnati. 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
information at back).
Introduction
Electrodialysis (ED) is a membrane
process that can be used for the separa-
tion, removal, or concentration of
ionized species in water solutions.
These operations are accomplished by
the selective transport of ions through
ion-exchange membranes under the
influence of an electrical potential
applied across the membrane. Ion-
exchange membranes, permeable to
either anions or cations, but not both,
are thin sheets of ion-exchange mate-
rial normally reinforced by forming on a
synthetic fabric backing. They range
between 0.1 to 0.6 mm in thickness and
are available in standard sheets up to 1 x
1.5 meters. As in the case of paniculate
ion-exchangers, the resin matrix is
usually copolymerized styrene-divinyl-
benzene, and exchange capacity is
imparted by sulfonic acid groups
(cation-selective membranes) or
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quaternary ammonium or pyridinium
groups (anion-selective membranes).
The terms cation-exchange, cation-
selective, and cation-permeable are
used interchangeably in membrane
terminology as are the corresponding
terms anion-exchange, anion-selective
and anion-permeable.
In the usual configuration employed
for ED, hundreds of alternating anion-
selective and cation-selective
membranes are arrayed in parallel
between two electrodes to form an ED
multicell or "stack." Specially designed
spacer/gaskets separate the
membranes by forming leak-tight, flow-
directing compartments or cells
between adjacent membranes. The
solutions to be treated are distributed to
and collected from these cells by two
internally manifolded hydraulic circuits,
one for the ion-depleting or diluting
cells and one for the alternating ion-
receiving or concentrating cells. The
repeating stack unit of a cation-
selective membrane, a diluting spacer,
an anion-selective membrane, and a
concentrating spacer is termed a cell-
pair, and the size and demineralizing
capacity of ED equipment can be
characterized by indicating the number
of cell-pairs comprising a multicell.
The passage of a direct current
through the ED stack causes the anions
and cations in the raw process solution
fed to the diluting cells (the feed) to
move in the direction of the anode and
cathode, respectively. Because of the
alternating membrane arrangement
they leave the diluting cells and accu-
mulate in the concentrating cells. This
process is shown schematically in
Figure 1 where the concentrating cells
are odd numbered and the diluting cells
have even numbers. As indicated, posi-
tive cations are attracted to the negative
cathode and pass from the diluting
compartments, through the cation-
selective membranes forming the
cathode side of the cell, into the concen-
trating compartments where they
accumulate, since their further trans-
port is prevented by anion-selective
membranes on the cathode side of the
concentrating cells. Anions move in the
opposite direction, passing through the
anion-selective membranes and being
excluded by the cation-selective mem-
branes. The partially deionized effluent
from the diluting cells may be suitable
for use after a single pass through the
stack or recirculated for further demin-
eralization. The solution introduced to
the concentrating cells is usually the
same process stream as that fed to the
diluting cells, but only 20-25% of its
volume, and is eventually discarded at 3
or 4 times the original concentration
having acquired the ions removed from
the solution passing through the dilu-
ting cells. A separate solution, which
may also be drawn from the raw stack
feed, is used to rinse the electrode
compartments and remove the gases
formed by the electrode reactions. It
may be recirculated or pumped on a
once-through basis and is usually acidi-
fied to prevent scaling. Use of the multi-
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To
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Collection or
Disposal
Key:
Membrane
A Anion-Selectiv
Diluting . Membrane
M? Cations
y Anions
Figure 1. Electrodialysis multicell schematic.
2
-------
cell concept makes it possible to obtain a
deionizing effect equal to many times
the electrical equivalents passed
between the electrodes.
In the late 1940's, the development of
highly selective and physically strong
synthetic ion-exchange membranes
made feasible commercial application
of the ED multicell. The first and still
largest use of ED is for desalinization of
brackish water; the second major
application is de-ashing whey. Besides
these now conventional uses, in which
the desired product is the deionized feed
to the diluting cells, an interesting and
important application of ED is the delib-
erate use of the concentrating steam to
concentrate and recover ionic constitu-
ents from the waste or process water
fed to the stack. In this modification the
recovered concentrate can also be
considered a product solution from the
ED treatment, and the recovered mate-
rial is available for reuse in the original
process or for further treatment and/or
disposal. In the latter case subsequent
handling of the recovered solution is
substantially simplified, since it is
typically 1-2% of the original volume.
Electrodialytic corrcentration of sea-
water is widely used in Japan in con-
junction with solar evaporation to
produce table salt and has great
potential utility in the electroplating and
metal finishing industries both for pollu-
tion control and metal recovery. The
Japanese have extended their work on
concentration by ED to exploratory
studies on waste liquors from copper
and nickel plating operations, and
laboratory tests in this country have also
indicated the possibility of electrodia-
lyzing nickel solutions (Figure 2).
Another recent laboratory investigation
has looked at the ED of a copper cyanide
plating bath rinse for recovery of plating
chemicals and elimination of toxic dis-
charges. Our own preliminary studies
have indicated that nickel can be recov-
ered as a valuable product solution from
a simulated plating rinse bath at many
times its concentration in the bath by
using especially designed ED multi-
cells and appropriate operating condi-
tions. Based on these laboratory data, a
prototype ED unit was constructed for a
field test and demonstration program at
Risdon Manufacturing Co.
Conclusions
The field test program demonstrating
the recovery of nickel from plating bath
rinse waters by ED has shown that ED
can be a useful and economically viable
process for the treatment of at least
some types of electroplating rinses,
specifically those from Watts-type
nickel plating lines. The process is
capable of reducing nickel content in
plating line effluents to the ppm range,
can recover 95% of the nickel salts lost
with conventional rinsing techniques
and substantially reduce other raw
material usage, can minimize the effort
and space required for operation of
standard destruct equipment, and can
return a concentrated nickel solution
directly to the plate tanks.
ED treatment of a reclaim rinse
immediately following the nickel plate
tanks held the rinse concentration at 2-
3 g/l nickel. A second reclaim tank in
series with the first was maintained at
approximately 0.3 g/l nickel. Lower
concentrations appear to be easily
attainable with appropriate equipment
sizing. Metal losses via drag-out to the
destruct system following the reclaim
rinses were drastically reduced com-
pared to those expected with a counter-
current or unmodified reclaim rinsing
sequence. For plating operations similar
to the demonstration line yearly savings
are estimated to be at least $16,000 in
raw materials with a concomitant de-
crease of about 2,300 kg (5,000 Ib.) in
sludge from pollution control facilities.
Net cost savings should increase as
chemicals become more expensive and
pollution regulations more stringent.
Depending on the operation of the plat-
To Spray
Rinse and
Drying
Electrodialysis
Concentrate
Reservoir
Figure 2. Electrodialysis treatment of nickel plating line.
-------
ing line, additional savings may be
realized on water usage, storing and
handling of chemicals, improved
rinsing, and additive recovery.
In contrast to reverse osmosis, ED can
concentrate the nickel 50- to 100-fold,
permitting direct return to the plating
solutions without the necessity of an
extra evaporation step or increase in
plate tank evaporation rate. The mem-
branes employed are mechanically
stronger and more resistant chemically
than typical reverse osmosis mem-
branes. The concentration of the
reclaim rinse can be held at any desired
value and the recovery rate adjusted to
remove nickel to match any drag-out
rate. ED is a continuous process and
requires no interruption for regenera-
tion for ion-exchange material or
disposal of regenerating solution as do
conventional ion-exchange systems.
The program has also demonstrated
that maintenance and operation of ED
equipment by plating room personnel
are completely satisfactory with a mini-
mum of training. Other than for start-up
and shut-down procedures only
intermittent attention by the operator is
required and much of his time can be
spent on other duties.
Recommendations
The success of the electrodialytic
treatment of nickel rinse solutions
described in this report suggests that
further investigations aimed at
broadening its applicability would be
desirable. Recommendations are made
that demonstration programs be carried
out on other types of nickel plating
systems, particularly on those systems
that use organic brighteners or other
classes of additives not employed on the
test line at Risdon. Extension of the
technique to additional plating
solutions, i.e., copper and chromium,
would be of considerable interest.
Simple salt or "acid" baths are the
obvious choices for initial efforts.
Demonstration of ED on plating lines
using countercurrent rinsing and/or
automatic barrel handling would also be
valuable in estimating the potential
savings (Table 1) and in water and space
requirements, in defining system
versatility, and in generalizing
experience with the process. Improved
maintenance schedules and more
accurate estimates of costs and com-
ponent life would be developed.
At Feast two employees familiar with
the individual plating operation should
be trained in ED technology to insure
full-time monitoring capability. Respon-
sibility for the ED equipment must be
recognized as an integral part of their
job and an appropriate percentage of
their time assigned to recovery opera-
7able 1. Estimated Operating Costs
for 50 Cell-Pair Nickel
Recovery Unit (1976
Dollars)
$/day $/year
Electric power
Labor
Chemicals
Filter cartridges
Replacement
membranes
Total
.70
3.75
.02
.91
1.25
$6.63
168
900
5
219
300
$1592
tions. Adequate filtration of the influent
to the ED stack is a reauired pretreat-
ment, and some cooling may be neces-
sary. Wide fluctuations in ambient
temperature should be avoided. Besides
the safety precaution in the intercon-
nection of the stack current/feed pump
circuitry, additional DC cutoffs based on
flow attenuation and feed conductivity
are desirable.
John L. Eisenmann is with Chemical Recovery Systems, Hanover, MA 02339.
Fred Ellerbusch and Mary K. Stinson are the EPA Project Officers (see below).
The complete report, entitled "Nickel Recovery from Electroplating Rinsewaters
by Electrodialysis," (Order No. PB 81-227 209; Cost: $8.00, 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 Officers can be contacted at:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati. OH 45268
US GOVERNMENT PRINTING OFFICE, 1981 —559-017/7368
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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