r
I
AN EXAMPLE OF ECONOMIC PLATING
WASTE TREATMENT BY
REVERSE OSMOSIS
A. GOLOMB
-&EFv-515
L S f 08
Department of Physical Chemistry, Ontario Research Foundation,
Sheridan Park, Ontario. Canada
/D/c
INTRODUCTION
The large volumes of water used in rinsing operations in the plating industry may
contain cyanides, chromium, nickel, and zinc, resulting in a substantial loss of valuable
plating chemicals. From an economic viewpoint, particular consideration should be given
to measures that will permit recovery of chemicals and water for reuse.
In view of the wide variety of conditions found in plating practice, treatment processes
have to be tailored to each installation (Barnes, 1968). A simple approach to conservation
of water and chemicals is the use of counter-current rinsing. Ideally, if a sufficiently large
number of stages can be installed, rinse water from the first stage can be returned to the
plating bath as make-up to balance the volumetric rate of evaporative loss. However, in an
existing plant, where it is impractical to install a sufficiently large number of rinse tanks,
some alternative method of reclamation must be sought. For instance, evaporative and
ion exchange recovery systems have been incorporated in many plants.
In the last few years, growing interest has been expressed in a relatively new chemical
engineering separation technique for water purification, Reverse Osmosis (RO), which
received much of its impetus from the work of Loeb and Sourirajan (1964). The various
types of commercially available RO modular units have been critically reviewed by
Golomb and Besik (1970).
LABORATORY TESTS ON WATTS NICKEL RINSES
Details o f the laboratory test unit used to evaluate the KO performance characteristics
of Loeb-Sourirajan type cellulose acetate membranes for nickel rinse waters have been
previously reported by Golomb (1970). Eastman Kodak cellulose acetate membranes
(type RO-97), a grade with very high rejection for inorganic salts, received most attention
in these experiments.
Simulated nickel rinse waters were prepared by dilution with distilled water of a Watts
bath formulation having the following composition:
NiS04 .6H20
NiC12 .GH20
H3 BO3
pH 4.0
337.5 g/l(45 oz/gal)
75 .O g/l (1 0 oz/gal)
37.5 dl(10 oz/gal)
A series of exploratory reverse osmosis tests was performed on diluted Watts bath
solutions (no organic addition agents) at levels of 100 ppm Ni"; I , IO, 25 and 50 per cent
of bath concentration.
T h e m e m b r a n e s from these experiments were subsequently stored in the
corresponding test solution and re-tested at intervals of several weeks to obtain an
568
'
A. Golomb
indication of membrane lifetime and performance characteristics. Some experiments were
conducted with rinse waters prepared by dilution of a Watts bath obtained from an
industrial source and in both cases the nickel rejections were of the order of 99+ per cent.
No significant deterioration in membrane properties occurred over a period of five
months for samples in contact with the test solutions.
RO tests were also made in the presence of selected organic addition agents. As
described by Jones and Kenez (1969), these fall into two broad categories, the so-called
semibriglit and bright nickel additives. Coumarin was selected as a representative of the
first system and a combination of sodium allyl sulphonate and N-allyl quinaldinium
bromide was chosen as representative of the second. The test solution was a simulated
rinse water at 1 per cent of Watts bath concentration. Table I summarizes the results of
RO tests with membranes after 20 weeks' storage in contact with the test solution.
In the presence of both types of organic addition agents, nickel rejection efficiencies
are again better than 99 per cent. However, the behaviour of the addition agents is quite
different. The retention of coumarin is low, suggesting coupled flow of this species with
water through the membrane. On the other hand, rejection of the sodium allyl
sulphonate/N-allyl quinaldinium bromide combination is the range 96-98 per cent. This
behaviour is typical of dissolved, highly dissociated ionic species.
a L A T E D NICKEL RINSE WATERS
DILUTED INDUSTRIAL WATTS BATH
0
0'
I
I
10
20
PERCENTAGE WATTS
I
I
40
50
BATH CONCENTRATION
30
Fig. 1.
Flux vs. percentage Watts bath concentration
- (laboratory
scale).
Ewnoniic Plutitig IVustc Treatment by Reverse Osriiosis
569
Table I
Typical Reverse Osmosis Test Data (Laboratory Scale)
for Watts Nickel Plating Rinse Water at 1% of Bath Concentration
Using Eastman RO-97 Membranes at 600 psi
Flux rate for permeating water: 14.6 gfd.
Species
Rejection Efficiency %
Ni ++
99.6
so4--
99.8
CI -
99.0
BOB
28.0
Coumarin
25.0
li3
Sodium allyl sulphonate/
N-allyl quinaldinium bromide
96.8
combination additive
.
570
A. Golomb
Fig. 1 illustrates the eifect upon flux rate* of increasing concentration a t operating
pressures of 600 psi and 1000 psi respectively, for laboratory prepared rinse waters and
for a diluted industrial Watts bath. It is necessary to determine the practical upper limit
of concentration that can be treated with the particular membrane employed, since this
factor is important in designing a recycle system in which chemicals are returned to the
plating bath as a concentrated solution. Apparently the practical upper limit for
concentration by reverse osmosis lies in the region of about one-third of the Watts bath
concentration. Consistently high rejection efficiencies for nickel ions, generally 99+ per
cent, were observed throughout these runs.
The different flux rates noted for laboratory and plant solutions are attributed to
relatively lower concentrations (and osmotic pressures) of the particular Watts bath
samples obtained from industrial sources.
ECONOMIC EVALUATION FOR A TYPICAL PROCESS DESIGN
Golomb (1970) outlined the rationale for design of a process, based on RO, for
recovery of nickel values from Watts rinse waters by reverse osmosis. As representative of
a typical industrial plating operation, a three stage counter-current rinse system was
chosen in which deionized water is used for rinsing, the concentration of total dissolved
solids (TDS) in the final rinse is 0.002 oz/gal, and part of the solution from the first tank
is returned to the plating bath to balance evaporative losses, the remainder going to drain.
Two levels of operation were considered, one in which the dragout is 500 gal/day and
evaporation from the plating tank is 5000 gal/day and the second at one-tenth of these
values.
For the higher level of operation (dragout rate 500 gal/day) the chemical loss as nickel
is 240 Ib/day and as plating salts, including water of hydration, is 1200 lb/day. These are
equivalent to dollar losses of $ 3 lO/day and $550/day respectively, based on chemical
costs of Ni - $1.30/lb; NiS04.6H20 -$0.46; NiClz.6H20 - $0.62 and H3BOJ $O.lO/lb. The losses are one-tenth of these values for the smaller scale operation (dragout
rate 50 gal/day).
A reverse osmosis treatment may now be applied to the nickel rinse waters such that
the volume of concentrate returned to the plating tank again equals the evaporative
losses. With the entire permeate being discharged as a waste stream, the total daily
amounts and concentrations of the various chemical components in the process streams
can be calculated. More than 99 percent of the nickel salts is returned to the plating bath,
but some deficiency of boric acid is anticipated, w h c h can be corrected by make-up. The
waste effluent contains only 32 ppm of nickel, the major component being boric acid. As
reported by McKee and Wolf (1963) most witer authorities have indicated no strong
objection t o the presence of boric acid in effluents being discharged to water courses,
(except where the water is to be used for irrigation of certain crops), but nickel is not
generally permitted at levels above 5 ppm in effluents entering sewage lines. A certain
degree of dilution would therefore be required, as appropriate.
Some saving in water and a reduction in the chemicals discharged to waste can be
achieved by recycle of part or all of the permeate to the rinse line. This will result in a
higher TDS in the final rinse tank which would need to be considered in relation t o its
* gfd = flux rate, U.S. gal/ft2 of membrane/24 hr day.
Ecorioiiiic Piatirig Waste Treatriienr by Reverse Osrnosis
571
effect 011 a subsequent plating step, for example, chromium plating.
A preliminary cost est illlate for reverse osmosis rccovery of plating chemicals, b x e d 011
the laboratory results, indicated favourable economics. It was recogniscd, however, that
#
pilot plant evaluation is a necessary prelude to plant application, both to evaluate long
term operational effects and t o obtain more accurate cost and design data.
FIELD TRIAL ON AN INDUSTRIAL NICKEL PLATING LINE
A field trial was commenced early July. 1971. on a small industrial automatic plating
located in a factory in the Toronto area. The existing nickel plating operation utilizes
a semibright Watts nickel bath, maintained at 140"F, with evaporative losses of ca. 150
gal/day. Dragout rates vary according to the number and shape of the piece parts being
plated, but are generally of the order of ca. 15 gal/day. Three rinse tanks follow the
nickel bath.
Operated as a 3-stage countercurrent system and processing the rinse water from the
first rinse tank by RO it was anticipated that 99+ percent of the nickel dragout losses
could be recovered, and, depending on the amount of permeate that could be recycled,
deionized water usage might be greatly reduced.
It was recognised, however, that permanent installation of an RO recovery unit might
be uneconomical in relation to this particular plating operation. Prior to the RO field
trial, the three rinse tanks were arranged, as is typical of many small plating shop
operations. as follows:( I ) A still rinse tank, filled initially with deionized'water and rising from 0-3 oz/gal
before return to the bath as make-up.
(2) & (3) Two rinse tanks arranged in countercurrent, with ca. 1500 gal/day of deionized
water entering the final rinse tank, and flowing as effluent to the acid waste drain from
the second. Deionized water is favoured for quality rinsing, with minimum staining or
spotting of the plated articles..
Operating in this way, about 85%of the dragout nickel losses are recoverable.
The objective of the field trial was to obtain sufficient data over a test period of
several hundred hours t o predict the feasibility of using RO to recover nickel values on a
larger scale, i.e. where nickel dragout losses are significantly hgh.
For several reasons, a commercial unit of the spiral wound configuration was selected
for the field trial. After preliminary studies in the laboratory, using a single spiral wound
module (50 ft2 cellulose acetate surface area), the principal engineering parameters were
determined at 300-600 psi, and a compact, commercial mobile unit of this type was
procured, of capacity rated for the field trial. The unit has 100 ft2 of cellulose acetate
membrane (2 X 50 ft2 modules), with a nominal permeation rate of 1000 gal/day at 600
psi.
After design modifications, the RO unit performed satisfactorily during preliminary
trials in the laboratory, and was later installed on-site in the plating shop. An operating
pressure of 450 psi was selected as optimum.
A schematic flow diagram of the RO nickel recovery system is given in Fig. 2. The data
presented are typical of measurements made during intermittent operation over a
3-month period on a one-shift-per-day basis. Concentrations given are for nickel only. The
boric acid rejection was found to vary appreciably during the test for reasons yet to be
determined; however, an average rejection efficiency of ca. 5055 for boric acid can be
taken as representative.
llrle
!
572
A. Golomb
LVAPN. I 5 0 golldoy
I 3 9 5 ml/mm 1
D = I5 gotldoy
( 40 m l /min I
\
HOLDING TANK
V,.
V , = 3 5 8 5 gallday
150 pol ldoy
I395 mllmin 1
(9420 ml/mm 1
C i a 8 3 4 0 ppm NI
c~~1200
ppm
0 Ni
V,
9
2 3 7 0 golldoy
Vp* 1065 p o l l d a y
( 6 2 2 0 mllmin)
C,
8
12000 ppm Ni
Cp' 2 0 ppm NI
BACK PRESSURE
REGULATOR
RECYCLE CONTROL VALVE
Fig. 2.
Flow diagram of reverse osmosis nickel reclamation system - (field test).
LEGEND
O OBSERVED 36-47'(
a CORRECTED TO 200
TRANSITION
ZONE
FOLLOWING FLUSH
4000
I
.E 3000
-E
\
.
- 2000
W
c
a
a
g
d
LL
t
I
1000
ACID
FLUSH
o ~ " ' t " '
I
5
I
"
'
"
'
I
I
13
17
EXPERIMENT NUMBER
9
a
b
*
I
21
I
(
I
.
I
,
L
25
Fig. 3.
Flux characteristics of industrial reverse osmosis unit operating at 450 psi - (ficld test).
-
1:iotiotrtic Platitig Wastc Treatmettt by Reverse Ostitosis
513
Table 11
Selected R.O. Performance Ddta for Industrial Nickel Recovery
Operating Pressure
Operating Temperature Range
pump Delivery Rate, Vi
Feed
DH
_..
Feed Flow Rate, Vf
Permeate Flow Rate, Vp
Concentrate Recovery Rate, Vc
K.0. Conversion Factor for Water
*Membrane Rejection Efficiency for Ni, R
**R.O.Retention Efficiency for Ni, q
*
**
450 psi
36 - 47°C (ambient frequently >32"C)
3585 gal/day (2.5 gal/min)
4.0 + O S
1 2 1 5 gal/day
1065 gal/day (corresp. t o 10.7 gfd)
150 gal/day
88%
99.8 +0.1%
98.3 +0.7%
R is defined as
qisdefinedas
Footnotes
(i)
(ii)
(iii)
VfCf - v p c p x 100
VfCf
CAV is the average concentration of Ni in the solution in contact with the membrane. It is taken, as a first approximation, to
be the arithmetic mean of Ci and Cc, the inlet and outlet concentrations across the modular assembly.
Ci is readily calculated from a mass balance over the recycle loop
of the R.O. unit (Fig. 2), assuming constant pumping rate Vi (this
was periodically checked)
Thus;ViCi = VrCc +- vfcf
Vr, the recycle flow rate is given b y Vr = Vi - Vf
where Vf = Vc t Vp
5 74
A. Golomb
After three months, the plhting shop foreman reported no detectable change in plating
quality. Nickel salt requirements for bath make-up were virtually eliminated, and boric
acid usage had dropped to below half the regular quantity. Deionized water usage was
minimal: the only water input exactly matched volumetric evaporative losses from the
bath. Perhaps even more significant in its wider implications, the system was, from a
pollution standpoint, essentially a ‘closed loop’.
A gradual decline in flux was observed during the initial 3-month test period (Fig. 3).
This is attributed, at least in part, to precipitation of ferric hydroxide as a fine film over
the membrane surface. The presence of iron in the bath and rinse waters results from
local galvanic action on steel piece parts which occasionally drop inadvertently from the
racks during plating and rinsing. (That the iron should be present in the ferric state rather
than ferrous is predictable from the known presence of hydrogen peroxide added t o the
plating bath as a depolarizing agent. Furthermore, oxygen levels close to saturation would
be anticipated, since air agitation of the bath and rinse tanks is used to promote efficient
mixing.) Experimentation indicated that membrane fouling could be kept well under
control by carefully adjusting the feed solution pH. Gradual addition of dilute sulphuric
acid to the feed holding tank maintained it a pH 4.0 ? 0.5. As can be seen from Fig. 3,
occasional acid flushing of the unit with a more strongly acidified feed at pH 2.0 for 30
minutes had a restorative effect on the flux rate. (Alternatively, flushing with a 0.3%w/w
aqueous solution of oxalic acid was found to be very effective, but can only be
conveniently accomplished during a lapse in plating production.) Typical results of the
RO field trial during the initial 3-month period (after 400 hrs of operation) are
summarized in Table 11. These results clearly lend weight to the predictions based on the
earlier laboratory experimental work.
PROJECTED COST ESTIMATES
A summary of an order-of-cost analysis for ‘closed loop’ reverse osmosis recovery of
nickel plating chemicals is given in Table 111. Three levels of operation are considered,
with dragout rates of 15, 50 and 500 gal/day respectively. The assumptions made are as
follows:(0 Relative to the field trial data, process flow rates are taken to be proportionately
higher for the larger scales of operation, where concentrations remain the same.
(ii) In estimating equipment size and cost, a flux rate of 10.7 gfd at 450 psi has been
used throughout.
(iii) Capital costs are based on straight line amortization over a five-year period at an
interest rate of 8.5 percent. Operation is assumed on 240 days per year, with three
8-hr. shifts per day.
(iv) As a first approximation, for the three levels considered, combined operating and
labour costs equivalent to 0, 5% and 25% respectively of 1 man per 23-hr day at
$8.00/hr have been applied. Membrane replacement costs are based on a membrane
life of 18 months.
Total operating and maintenance costs per 1000 gal of permeate are:
Table 111
Summary of Projected Cost Estimate for Nickel Recovery by R.O. ('Closed Loop') System
Toronto Installation:
D = 15 gal/day:
W = 150 gal/day
Flux Rate (gfd) at 450 psi
Permeation Rate (gal/day)
Nominal R.O. Unit Capacity (gal/day)
*Installed Capital Cost ($)
Amortized Capital Costll 000 gal permeate
*Operating & Maintenance Cost/lOOO gal permeate
Total Cost/lOOO gal permeate
Total Cost/day
Recovered Value/day Ni
Recovered Valuelday as Total Salts
Savings in Deionized Water Usage/day
Total Savings as (Total Salts + Water)/day
Net Savings/day
Payback on Capital Investment
Projected Scale:
D = 50 gal/day:
W = 500 gal/day
Projected Scale:
D = 500 gal/day:
W = 5000 gal/day
10.7
1,065
1,000
7,000
$6.96
$0.70
$7.66
$8.1 5
$9.46
$16.62
$0.49
$17.1 1
$8.96
10.7
3,550
3,500
9,000
$2.68
$3.40
$6.08
$21.60
$3 1S O
$55.30
$1.65
$56.95
$35.35
10.7
35,500
3 5,000
* 37,000
$1.03
$2.05
$3.08
S 109.30
$3 15.00
$5 53 .OO
$16.50
$569.50
$460.20
39 months
13 months
4 months
*Capital and Maintenance Costs can vary widely depending on the design of the unit.
576
A. Golomb
D = 15 galiday
D = 50 gal/day
D = 500 gal/day
Membrane replacement
$0.50
$0.50
$0.50
Power
$0.10
$0.10
$0.10
Labour
Nil
$2.70
$ I -35
Materials
$0.1 0
$0.10
$0.10
$0.70
$3.40
$2.05
From the projected cost data summarized in Table 111, it is evident that RO offers an
economically attractive treatment process for recovering nickel values from Watts nickel
plating waste rinse waters, particularly for those plating operations where dragout losses
are significantly high.
CONCLUSIONS
(1) On the basis of laboratory studies and subsequent plant trials on an industrial plating
line, Watts nickel plating rinse waters can be effectively treated by reverse osmosis to
reclaim reusable materials.
(2) Cellulose acetate membranes can be used to recover 99+ percent of nickel values
from the waste rinse streams.
(3) Depending on the level of nickel dragout losses’associated with the plating operation,
projected cost estimates indicate capital investment payback periods of the order of 13
months t o 4 months for medium to large industrial operations respectively. On the same
basis of assessment, small plating operations can expect payback after 3-4 years.
(4) It is emphasized that evaluation must be made in relation t o actual line operation,
and consideration given to any potential problem areas that could affect efficient running
of the RO unit, and the maintenance of good quality plating.
(5) In addition to the favourable economic aspects, the ‘closed loop’ reverse osmosis
reclamation system can make a significant contribution toward eliminating unnecessary
discharge of contaminants and total dissolved solids into the environment. With the
development of new, improved membrane systems, operable over a wider pH range, it is
anticipated that reverse osmosis will play an important r61e in electroplating waste
treatment practice in the near future.
ACKNOWLEDGEMENTS
This project was undertaken under the sponsorship of the American Electroplaters’
Society and the Department of Trade and Development, Province of Ontario, Canada. I
ani grateful to colleagues at thc Ontario Research Foundation, Dr. M.H. Jones, Director,
Department of Physical Chemistry, for helpful discussions, and Mr. D.A. Cobb for
technical assistance during the course of this work. 1 also th&k members of the AES
I:i.otioinic Plaring Waste Treatrileti f by Reverse Osmosis
577
Project Committee for their assistance in rechnical and economic aspects of electroplating
practice.
REFERENCES
1 .BARNES, G.E., "The Economics of Electroplating Wastes Disposal", Plafitig 55, 727-731 (1968).
2 GOLOMB, A., "Application o f Reverse Osmosis to Electroplating Waste Treatment, Part I Recovery o f Nickel", Plafitig57, 1001-1005 (1970).
3 GOLOMB, A., and BESIK. F., "Reverse Osmosis for Wastewater Treatment", lnd. Water Eng. 7,
(IO), 16-19(1970).
4 JONES,M.H., and KENEZ, M.G.,"Initial Stages of Nickel Deposition: 11 - Effect o f Addition
Agents". Plating 56. 537-542 (1969).
5 LOEB, S., and SOURIRAJAN, S. US.Patents 3, 133, 132 and 3, 133, 137, (1964).
6 McKEE, J.E., and WOLF, H.W. Water Quality Criteria. Calif:State Wafer Quality Bd Publ. No.
3-A, Sacramento, Colic, pp. 147, 222, (1963).