United States
Environmental Protection
Agency
Water Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-86/094 Jan. 1987
&EPA Project Summary
Evaluation of the HSA Reactor
for Metal Recovery and
Cyanide Oxidation in
Metal Plating Operations
The electrochemical removal of heavy
metals and cyanide from the wastewaters
from electroplating shops is one alter-
native available to plating shops in achiev-
ing compliance with effluent regulations.
Several of such systems manufactured by
HSA Reactors*, Ltd., have been installed
since 1981 with varying degrees of suc-
cess. This report is the result of a brief
survey of the effectiveness of several of
these installations.
Six installations of electrochemical re-
covery systems were tested to establish
the performance that may be expected
from the technology. Results showed that
performance varied widely ranging from
nearly ineffective to a metal removal and
cyanide destruction capability sufficient
to achieve compliance with effluent reg-
ulations. The tests conclude that the
technology is a viable solution to the
pollution control problem under certain
circumstances.
This Project Summary was developed
by EPA's Water Engineering Research
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 order-
ing information at back).
Introduction
Regulations promulgated by the U.S.
Environmental Protection Agency (EPA)
govern the allowable pollutant content of
discharges from industrial processes. The
•Mention of trade names or commercial products does
not constitute endorsement or recommendation for
use.
metal finishing industry is one of the major
sources of heavy metal and cyanide pollu-
tion. The capital expenditures for equip-
ment to remove these pollutants from
wastewaters and wastes impose a con-
siderable economic burden on the industry.
In addition, the disposal of metallic slud-
ges produced by conventional waste treat-
ment systems is becoming increasingly
more difficult and costly. A system such
as the HSA (high surface area) Reactor,
which permits recovery and recycle of the
plating metals and destruction of cyanide
in plating wastewaters, holds great poten-
tial for providing a cost-effective solution
to this environment problem.
Conventional electrolytic control of
spent plating baths and rinse waters is
costly because the removal efficiency of
electrolytic processes is decreased as the
solution becomes more dilute. The metal
concentration of plating rinse streams is
very dilute compared with that of the
plating tank solution. One method of in-
creasing the removal efficiency in dilute
solutions is to increase the surface area
of the electrode upon which the metal is
plated (cathode).
The HSA Reactor, based upon just such
a technology, is capable of removing toxic
pollutants from metal finishing waste-
waters by electrodeposition. The system
utilizes a special carbon fiber cathode and
a metallic anode, both nonconsumable.
This system provides dramatically im-
proved performance, in terms of metal
removal rates, compared with competitive
electrochemical techniques. The reactor
also can electro-oxidize and destroy
cyanides to levels below detection limits
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at a cost that appears much lower than
that of the conventional alkali-chlorination
process.
Findings
Analytical results of the testing of the
HSA Reactor at six installations showed
that the technology is capable of remov-
ing cadmium, zinc, and the cyanide associ-
ated with these solutions from electro-
plating dragout. The concentration of the
metal and cyanide in the discharge from
the following rinse was usually low
enough to meet current effluent regula-
tions (Table 1). Those shops where reduc-
tion of concentrations in the rinse
overflows to effluent regulation levels was
not achieved were experiencing equipment
and/or operational problems at the time of
testing. However, the metal concentration
of the running rinse overflow from the
plating line being tested does not reflect
the metal concentration in the plant
effluent. Rinses from other plating opera-
tions such as cleaners, acid dips, etc.,
would dilute the plating rinse stream
further. Therefore, even those shops that
were experiencing abnormal conditions
would likely be in compliance with dis-
charge limitations.
Plating shops using the HSA recovery
systems have been reluctant to reuse
metal recovered from the HSA cathodes
in their plating baths because of possible
contamination with other metals. In addi-
tion, metal recycling firms have refused
to accept the metals because of the
unknown content of the metal. Therefore,
samples of the recovered metal were col-
lected during the testing and analyzed,
and the results as reported are given in
Table 2. The recovered cadmium proved to
be 99.34 to 99.94 percent pure; zinc,
98.74 to 99.39. These results indicate
that the metals removed from the waste
plating solutions are recovered in a form
highly suitable for recycling into primary
or secondary metals markets.
An attempt was made to determine the
quantity of metal recovered during each
cycle of the HSA Reactor. At some shops,
the metal from the spent cathodes is
redissolved by reversing the current in a
stripping solution. Other shops transfer
the metal to stainless steel cathodes by
electrolytic means. The stainless plates are
then mechanically stripped of the metal.
Depending on the procedure used at the
particular shop, the weight of recovered
metal is determined by either analyzing the
stripping solution before and after strip-
ping or weighing the cathodes before and
after stripping.
Table 1. HSA Reactor Performance
Metal
Cyanide
Shop*
1
2
3
4
5
6
Sample
Set
1
2
3
1
2
3
1
2
3
4
1
2
3
1
2
1
2
Source
mg/L
13400
15000
6980
538
538
538
1980
2770
1640
1580
20400
20400
18900
4560
7400
29730
17950
HSA Tank
mg/L
154
68
21
122
218
345
2.5
0.59
0.46
0.61
140
5.45
29
3200
1240
900
3470
Rinse
mg/L
1.06
0.45
0.14
1.29
2.3
3.65
B.D.n
B.D.
B.D.
B.D.
0.22
0.01
0.05
11.67
4.52
3.57
13.7
Source
mg/L
+
2990
4690
+
10000
+
10250
10750
12250
11250
86500
+
72000
26000
36000
60430
59330
HSA Tank
mg/L
111
49.45
30.0
950
949
951
0.4
0.6
0.1
0.2
0.02
0.02
0.02
20000
28OOO
8770
25280
"Metal concentration is for cadmium for all shops except shop 2, for which zinc removal is
given.
•^Sample analysis is not given.
ttB.D. = below detection limit.
Table 2. Purity of Recovered Metal
Composition, %
Shop No.
2
3
4"
5
6
Plated Metal
Zinc
Zinc
Cadmium
Cadmium
Cadmium
Cadmium
Cd
.08
.04
99.94
25.08
99.63
99.34
Cr
.32
.11
.00
1.59
.01
.00
Cu
.02
.02
.01
43.86
.07
.14
Fe
.75
.41
.02
13.48
.05
.34
Ni
.08
.04
.02
14.53
.08
.10
Zn
98.74
99.39
.01
1.10
.15
.07
* The HSA system had been used to dispose of a solution of nickel/copper stripping solution.
The weight of metal recovered at the
various test sites showed a variation of
159 to 44723 grams/cycle for cadmium
and 150 to 559 for zinc (Table 3). This
wide range is attributed to the operation
of the HSA cycle based on a fixed time
rather than on cathode capacity. Wide
variations in dragout rate are experienced
because of the type of parts plated and
production fluctuations. Such variations
reduce the removal efficiency of the HSA
system.
All personnel at the shops visited felt
that the HSA systems "as-delivered"
required modification for industrial use.
Specifically, extensive changes in piping
and/or equipment were necessary before
acceptable operation was attained. Some
operators felt that there were still
operating problems that needed to be
solved. The most obvious shortcoming of
the equipment is the lack of instrumenta-
tion to clearly indicate to the operator the
status of the cathodes. Regeneration
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cycles, determined on a trial-and-error
basis, have generally been based on a fixed
time rather than cathode capacity.
Conclusions
The HSA Reactor is an effective means
of removing cadmium, zinc, and cyanides
from the dragout of electroplating opera-
tions. Based on observations and/or
analytical results of samples from the test
sites, the following conclusions were
reached.
1. Any process change that will reduce
the chemical load on the HSA system
will improve its performance. The
average concentration can be
lowered in the HSA tank and in the
solution dragged from it by using a
dragout, or a dragin/dragout tank be-
tween the plating tank and the HSA
tank.
2. System performance at Site #3 was
outstanding because this is a captive
shop that has little variation in the
parts plated; therefore, the chemical
load on the HSA system is relatively
constant. Conversely, job shops ex-
periencing widely varying load rates
from the wide variety of parts plated
saw reduced performance of the
HSA Reactors. This reduced perform-
ance is thought to be related to
operator interaction with the HSA
system under variable conditions.
3. Additional development of the tech-
nology is needed to produce systems
that will indicate when regeneration
is required. Also the development of
systems to remove other metals as
well as cadmium and zinc is
desirable.
The full report was submitted in fulfill-
ment of Contract No. 68-03-1721 by
CENTEC Corporation under the sponsor-
ship of the U.S. Environmental Protection
Agency and Environment-Canada.
Table 3. Metal Recovered
Shop No.
1
1
1
2
2
2
3*
3*
3*
3*
4
4
5
5
6
6
Metal
Cadmium
Cadmium
Cadmium
Zinc
Zinc
Zinc
Cadmium
Cadmium
Cadmium
Cadmium
Cadmium
Cadmium
Cadmium
Cadmium
Cadmium
Cadmium
Metal (wt, g)
159
273
1272
229
150
559
227
227
227
227
5299
926
44723
8945
1923
3830
Recovered metal at this shop was
determined by weighing the cathode
before and after stripping.
The Project Report was authored by personnel of CENTEC Corporation, Reston,
VA 22090. The Project Summary was authored by John O. Burckle (also
the EPA Project Officer, see below), who is with the Water Engineering
Research Laboratory, Cincinnati, OH 45268.
The complete report, entitled "Evaluation of the HSA Reactor for Metal Recovery
and Cyanide Oxidation in Metal Plating Operations," {Order No. PB 87-111
167'/AS; Cost: $11.95, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 221611
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Water Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
The representative of Environmental Canada, Wayne Bissett, may be contacted
at:
The Industrial Programs Branch
Place Vincent Massey
Hull, Quebec, Canada K1A-1C8
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