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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