EPA-600/2-77-099
May 1977
Environmental Protection Technology Series
INNOVATIVE RINSE-AND-RECOVERY SYSTEM FOR
METAL FINISHING PROCESSES
Industrial Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
-------
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
• 7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL PROTECTION TECH-
NOLOGY series. This series-describes research performed to develop and dem-
onstrate instrumentation, equipment, and methodology to repair or prevent en-
vironmental degradation from point and non-point sources of pollution. This work
provides the new or improved technology required for the control and treatment
of pollution sources to meet environmental quality standards.
This doeumelt is available to the public through the National Technical Informa-
tion Service, Sprifigfjild, Virgiw^
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EPA-600/2-77-099
May 1977
INNOVATIVE RINSE-and-RECOVERY SYSTEM
FOR METAL FINISHING PROCESSES
by
Walter C. Trnka
Charles J. Novotny
Industrial Filter & Pump
Manufacturing Company
Cicero, Illinois 60650
Grant No. R-803723-01
Project Officer
Donald L. Wilson
Industrial Pollution Control Division
Industrial Environmental Research Laboratory
Cincinnati, Ohio 45268
INDUSTRIAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
-------
DISCLAIMER
This report has been reviewed by the Industrial Environmental Research
Laboratory - Cincinnati, U.S. Environmental Protection Agency, and
approved for publication. Approval does not signify that the contents
necessarily reflect the views and policies of the U.S. Environmental
Protection Agency, nor does the mention of trade names or commercial
products constitute endorsement or recommendation for use.
ii
-------
FOREWORD
When energy and material resources are extracted, processed, con-
verted, and used, the related pollutions! impacts on our environment
and even on our health often require that new and increasingly more
efficient pollution control methods be used. The Industrial Environ-
mental Research Laboratory - Cincinnati (lERL-Ci) assists in developing
and demonstrating new and improved methodologies that will meet these
needs both efficiently and economically.
This report is a product of the above efforts. It evaluates a
method of recovery of aqueous processing solution which, if not re-
covered, requires special treatment before it is eventually discharged
into the nations' sewers and waterways. In particular, the report
summarizes the effectiveness of this new method of recovery as applied
to the metal finishing industry. It incorporates a rinse and recovery
system different from the conventional counter-current rinses that
follow a finishing operation. This new technology is to be identified
as the Zero Discharge System™ (ZDS™). The ZDS™ is not only econ-
omically advantageous to the metal finishing industry but also is a
possible effort to conserve and protect the natural resources i.e.,
chromium. Ho deteriorization of the environment is possible if the
ZDS™ is implemented.
For further information on this subject, contact the Metals and
Inorganic Chemicals Branch, Industrial Pollution Control Division.
David G. Stephan
Director
Industrial Environmental Research Laboratory
Cincinnati, Ohio
iii
-------
ABSTRACT
This report describes the feasibility of a rinse-and-recovery system
that can be installed in almost any metal finishing line and does not
harm the environment because no plating solution exits to the sewer.
Most toxic pollutants from metal finishing operations are associated
with the water used to rinse the affected parts after successive
finishing operations.
A typical car bumper plating operation was chosen as opposed to a
barrel rolling operation. When a part emerges from the plating bath,
it "drags out" full-strength plating solution with the bumper. This
drag out is tremendously diluted by following rinse steps. The diluted
rinses are sent to the sewer and cause toxic deteriorization of the
waste waters.
The ZDS™ is an innovative rinse-and-recovery system for use in the
metal finishing industry. A conventional multistage aqueous rinsing
system is replaced by a 2-stage solvent spray rinse followed by a
single-stage aqueous immersion rinse. By continuously purifying and
recycling the baths, appreciable savings in operating chemical costs
can be realized.
An actual chrome plating bumper line was simulated for test purposes.
After 80 hours of testing, the data shows that the levels of toxic
hexavalent chromium was less than 2 PPM. Thus proving that the levels
of toxic drag out can be arrested.
This report was submitted by Industrial Filter and Pump Manufacturing
Company in fulfillment of Grant R803723-01, given to the Bumper Recycling
Association of North America, Inc., from the Industrial Environmental
Research Laboratory, U.S. Environmental Protection Agency. Work was
completed on May 19?6.
iv
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CONTENTS
Foreword
Abstract
List of Figures
List of Tables
SECTIONS
I
II
III
IV
V
VI
VII
VIII
Conclusions
Recommendations
Introduction
Design and Construction of the System
Process Discussion
Laboratory Analysis
Costs
Operational Problems, Solutions, and
Rec ommendations
PAGE
iii
iv
vi
vi
1
2
3
8
13
16
20
21
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FIGURES
NO. PAGE
1 AQUEOUS CONCURRENT RINSING SYSTEM 5
2 RINSE AND RECOVERY SYSTEM PLOW DIAGRAM 6
3 ZDS™ EQUIPMENT LAYOUT 9
h VAPOR RECOVERY EQUIPMENT DIAGRAM 11
5 SPRAY ARRANGEMENT lk
TABLES
NO. PAGE
1 SPACE REQUIREMENTS 8
2 PLATING BATH 16
3 RECOVERED CHROME 1?
k FIRST RINSE 17
5 SECOND RINSE 18
6 FINAL RINSE 18
7 TEMPERATURE DATA 19
vi
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SECTION I
CONCLUSIONS
rnu
The heart of the ZDS is the multistage solvent rinsing technique.
This technique exposes new technology which as its best application
in the plating and metal finishing industry. As a result of multi-
stage solvent rinsing, a non-polluted effluent exits the plant via
the sewer.
This rinse-and-recovery system not only has excellent rinsing efficien-
cies but also recovers dragged-out chromic acid and returns it to the
plating bath. In other words, a closed loop system has been achieved
through the use of multistage solvent rinsing system.
An immiscible organic displacing fluid (IODP) acts as the main solvent
flush that washes off the dragged out chromic acid. The solvent used
is perchloroethylene, which does not deteriorate in the presence of
inorganic acids and can be used repeatedly.
The goal of not degrading either air or water can be solved and full
utilization of metal finishing chemicals has been accomplished.
-------
SECTION II
RECOMMENDATIONS
TM
During the operating of the ZDS for over 80 hours, many suggestions
were offered regarding improvements, but limiting factors of this pilot
unit precluded making them. This is why it has been suggested and
anticipated continuing development of this project.
It is recommended that the next phase of this protect include the con-
struction, installation, and operation of the ZDS™ in an existing chrome
plating line. This prbject has given the necessary experience to suc-
cessfully complete the next phase. An important objective would be to
optimize the set-points and correct flaws as dictated by day to day
finding. Another goal would be to develop data on the feasibility of
a long-term (one month) recycling of plating baths and its effect on
finishing quality.
Finally, this next phase will reassess the conservational impact of the
ZDS on the National economy-chemical energy, and labor consumption.
It will also determine its ability to achieve the 1983 Effluent Guide-
lines.
-------
SECTION III
INTRODUCTION
GENERAL
The initial presentation of the multi-phase rinse and recovery method
came from the Allied Chemical Corporation. Industrial Filter and Pump
Manufacturing Company through the cooperation of the Bumper Recycling
Association of North America, Inc. operated this system in Cicero,
Illinois.
The ZDS™ operates to return drag-out from rinse steps to the original
process bath utilizing methods which economically collect and purify
the recovered fluids. The net effect is to achieve a zero discharge
system in an operation, such as plating, whose normal effluent dis-
charges are toxic, undesirable, and expensive to treat. The ZDS™
utilizes the best techniques previously available: countercurrent
rinsing, ion exchange, and, in some instances, evaporation and/or
reverse osmosis. It adds a further element of displacement by use of
an IODF. This fluid provides an additional facet of rinsing that
permits either fewer countercurrent stages or smaller deionization,
evaporation, or reverse osmosis equipment. The effect is to provide
rinsing in less space, time, and at less cost with a system that self
adjusts for abrupt changes in drag-out volume or water loss volume
from the process tank. For any process, there will be an economic
optimization for the choice of ZDS™ versus a simpler concept, such as
a plain countercurrent rinsing.
OBJECTIVE
The purpose of this project was to demonstrate the effectiveness of
a solvent rinse system. After a car bumper leaves the chromic acid
plating bath, acid is normally dragged out through a series of rinses.
However, by using an aqueous acid spray and an IODF spray, 99+$ of
this dragged-out plating solution is removed. The final rinse in
these tests contained less than 2 parts per million (PPM) of chromic
acid plating solution. After approximately 80 hours of testing, the
final rinse tank, RT3 of figure 2, was not contaminated with chromic
acid.
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THEORETICAL APPROACH
The ZDS™ overcomes the major problems that can occur in standard
countercurrent rinsing systems, such as the typical five rinse tanks
connected in cascade (Figure l). In such a system it has been dem-
onstrated that the rinse ratio between successive rinses remains the
same as that between the plating tank and the first rinse. By rinse
ratio is meant the ratio of the concentration of the plating tank
solution to the drag-out concentration after the first rinsing. This
rinse ratio can also be shown to be equivalent to the total rinse
water flow divided by the volume of the drag-out.
Assuming use of a chrome plating bath containing 200 of Cr03 (chromic
acid salt), with the initial rinse ratio at 10:1, the concentration in
the first rinse tank would be 20 g/1. If good quality rinsing dictates
that this be reduce* to 0.002 g/1 (2 ppm CrC3) dragout residue on the
work piece, using five rinse tanks with dragout volume being 100 I/day,
a continuous rinse flow of 100 I/day would be required at the 10:1
rinse ratio.
Applying this analysis to a countercurrent system designed to operate
at a rinse ratio of U:l (to equalize for a typical plating solution
evaporation loss of UOO I/day), it can be shown that nine counter-
current tanks would be needed to produce the final 2 ppm CrC3 concen-
tration. If there were space for only three tanks, the rinse flow
would have to be about 30,000 I/day, which would leave about 29,600
I/day excess water to be disposed of (if the evaporation loss from
the plating tank were only hOO I/day). Whether the excess water was
eliminated by restricted rinse flow (as with the k:I. rinse ratio) or
by another method, large capital outlays for equipment would be
required together with high energy costs.
ACTUAL APPROACH
The ZDS™ overcomes excess water usage and produces a final residual
of 2 ppm using only three tanks (Figure 2). It should be noted that
in the standard counter-current rinsing system, a fourth and possibly a
fifth rinse tank is used. Parts move from the plating tank to the
first rinse tank where they are sprayed with an acid pre-flush solu-
tion that is shown being returned from separator tank 1 at the first
rinse tank concentration. This Cj^ pre-flush increases the efficiency
of the IODF rinse. Perchloroethylene is immiscible with the plating
solution and, if used alone, would displace about 9<$ of the chromic
acid.
-------
E
D
PT
C = 200
g/1
t
FIGURE 1. AQUEOUS CONCURRENT RINSING SYSTEM
RT1
C = 20
g/1
TO SEWER
ACID
MAKE-UP
KT2
C = 2 g/1
I
RT3
C = 0.2
C = .02
g/1
RT5
C = .002
g/1
FEED
LEGEND
PT = -PLATING TANK
RT = R|nse Tank
D = Drag out of Acid on V/ork
Ł = Evaporation
C = Concent rat i.on of Acid
g/1 = Grams acid per liter water
-------
FIGURE 2. RINSE AND RECOVERY SYSTEM FLOW DIAGRAM
E
D (RT3)
PB = Plating Bath
RT = Rinse Tank
D = Drag out
DR = Drain
G = Genesolv-D
ST 1 ST 2
LEGEND
MA = Make Up Acid
PF = Preflush
WA = Water Advance
CC = Cation Column
AC = Anion Column
N = Needle Valve
IODF = Immiscible organic
displacing fluid
(Perchloroethylene)
F = Water Feed
E = Evaporation
ST = Separation Tank
CR = Chrome Concentration
-------
The first step, therefore, becomes a very important one. In the
second rinse tank most of the remaining IODF is removed along with
the plating residues. From separation tank 2 the recovered IODF is
sent to the first stage to be reused and the dilute acid (C^) is
used chiefly for flushing in the second rinse tank. It should be
noted that at the needle valve, some of the diluted acid is blended
with about 0.25-.50$ of the IODF. This dilute acid feed is identical
to the forward feed of a countercurrent system. In other words, the
dilute acid feed contains the same volume as the water advance as
shown in Figure 2.
From tank 3, the rinse water circulates through the anion column where
the hexavalent chrome is removed. The purified rinse is returned to
tank 3 with a portion being used as forward feed for the second stage.
Because the chromium recovered from regenerated anion resin must be
reprocessed for reuse in plating, the deionization step is used at
this point is only to achieve zero discharge with minimum outlay of
capital and to conserve space.
After leaving separation tank 1 where the IODF has been removed, the
aqueous effluent is sent to the Genasolv-D extraction unit (G in
figure 2) to remove any residual (dissolved) perchloroethylene.
(Perchloroethylene oxidation by Cr03 when containing chloride ions
could cause chloride ion buildup in the plating tank.) After the
residual perchloroethylene has been removed, the remainder of the
aqueous preflush (CRI) passes through the cation exchange resin to
remove zinc, iron, copper, and other metallics, as well as trivalent
chrome (Cr3).
An evaporator (not shown) is required only if adequate evaporation is
not occurring at the plating tank. This is relatively inexpensive when
compared to eliminating 29,600 I/day of excess water, as mentioned in
regard to the countercurrent rinsing example.
-------
SECTION IV
DESIGN AND CONSTRUCTION OF THE SYSTEM
GENERAL
The entire ZDS^M was constructed on four skids for shipment and ease
of assembly (Figure 3). Skid number one contained the first separa-
tion tank, control cabinet, and all the necessary pumps and solenoid
valves. The second skid contained the anion and the cation sub-
assembly and the Genesolv-D (tri-chloro, tri-fluoro, ethane) extraction
unit. A vapor adsorber was on the third skid, and the chiller unit
and second separation tank will be on the fourth skid. Vic Manufactur-
ing Company had supplied the activated carbon vapor adsorber that was
used.
SPACE REQUIREMENTS
The figures shown in Table 1 are approximate. Each system will ulti-
mately have to be custom designed (at which time a more standard size
layout can be developed).
TABLE 1. SPACE REQUIREMENTS
(sq. ft)
Component
Vapor adsorber* 35
Anion and cation 12
columns
Control cabinet and 36
separation tanks
Piping and chiller 7
Total 90
*Two may" be needed so that
one can be regenerating while
the other is being used.
8
-------
SKID 3
L- _
FIGURE 3. ZDS™ EQUIPMENT LAYOUT
TOP VIEW
SKID k SKID 2
CH
ST2
00
RT1
RT2
RT3
ST1
CO
SKID 1
LEGEND
VA = Vapor Adsorber A = Anion Column
P = Plating Bath C = Cation Column
RT = Rinse Tank G = Genesolv-D
ST = Separation Tank CH = Chiller
CO = Control Cabinet
-------
OPERATIONAL
Witlyproper float controls and automated ion exchange columns, the
ZDS is fully automatic. This means that there are no additional
skills required by the plating operator to run the system. Regular
checks of the final rinse tank can assure that zero discharge will
be met. Nothing other than normal maintenance is required to assure
dependable service and long life.
VAPOR ADSORBER
The vapor adsorber is used in this system to recover the sprayed
perchloroethylene. A mist is formed after the part has been sprayed
in the first rinse tank. There are two cycles that are to be dealt
with during the operation of the activated carbon adsorber; the ad-
sorption cycle and tite desorption cycle. When the adsorption cycle
is in proper operation, the vapor-laden air passes through the
activated carbon. AH of the solven vapors of perchloroethylene are
removed from the air stream (Figure U). The vapor adsorber system
together with tie lip vents (on the tanks) do an adequate job of
recovering the solvent vapors from the equipment and the processing
cycle. The unit was rated at 1100-1200 cubic feet per minute. In
the desorption cycle, the regeneration of the unit was fairly simple
and automated. Once the regeneration cycles have been determined,
they can be timed on the control timer. (Manual control was used
for this report.) The process requires that the unit be regenerated
after 10 to lU hours of processing, (150-200 bumpers rinsed) to
ensure a 50^ vapor-recovery efficiency. It is important to note
that the desorption cycle is a closed loop cycle. Steam passing
through the unit at a rate of 200-300 pounds per hour collects the
perchloroethylene from the activated carbon. The condenser water
required was 2500 pounds per hour. The decanter assembly allows no
perchloroethylene to pass into the sewer. The retention time in the
decanter assures proper separation of solvent and water to occur.
When the unit has been regenerated, it automatically cycles back to
the adsorption cycle. Any perchloroethylene that is not removed is
not allowed to escape because the flow is now reversed and the
perchloroethylene is sent back through the carbon. This unit has no
air pollution capabilities because the solvent recovery loop assures
clean air at low cost (figure h).
10
-------
FIGURE' u. VAPOR RECOVERY EQUIPMENT DIAGRAM
Solvent
Vapors
trapped
in
Carbon
Red
Decanter
Solvent
to
"storage"
ADSORPTION CYCLE
DESORPTION CYCLE
-------
ION EXCHANGE UNIT
This system requires a cation and an anion column assembly. In the
tests, both columns performed as expected. The cation column removed
all traces of trivalent chrome, iron, zinc, and copper in the recovery
section of the system regeneration. After passing through the cation
column, the chrome (Cr°) can be returned to the plating bath as make
up. To protect the plating bath and the cation column from being
contaminated by the perchloroethylene, the preflush chrome is passed
through a Genesolv-D extraction unit to remove any perchloroethylene
solvent. The anion column is used to remove any hexavalent chrome
(Cr°) in the final rinse. Less than 2 PPM of hexavalent chrome was
found in the final rinse after the first 80 hours of operation. Had
this column been regenerated weekly, only a trace of chrome would have
been recorded.
SEPARATION TANKS
After the bumpers are sprayed with the aqueous preflush and the IODP,
the effluent is allowed to drain into the separation tanks. Because
the specific gravity of the aqueous preflush is 1.0 and the specific
gravity of the IODF is 1.6, these two fluids will separate from each
other rather quickly. The solvent settles to the bottom of the
separation tank so that it can be used over and over again in the
spray tanks. The aqueous preflush floats to the top and is also re-
used.
COOLING SYSTEM
The main purpose of the chiller unit is to create a cold layer of air
in rinse tank 1 to reduce solvent vapor losses during the spray cycle.
If a heated plating bath is used, it and the rinse tank should be
physically separated to avoid unnecessary heat transfer. The chiller
unit also cools the solvent in the separation tank and the small
condenser on the Genesolv-D separator. The main cooling fluid used
is ethylene glycol and water (50^-50^) mixture. Regular factory water
is used in the vapor adsorber system. Although perchloroethylene
does dissolve in water, during short project, none was detected.
Special instrumentation is required to positively identify the dis-
solved perchloroethylene.
12
-------
SECTION V
PROCESS DISCUSSION
The ZDS™ was designed for use in the metal finishing industry. For this
particular design, car bumper sections were being plated. After leaving
the chromic acid plating bath, the bumper was sprayed in the rinse tanks.
The spray system is the heart of the ZDS™.
For the sake of clarity, it is necessary to define the terms that are used.
The "aqueous preflush" refers to a dilute 1% mixture of chromic acid and
water. The term "solvent rinse" refers to the perchloroethylene, which also
is called IODF.
As shown in Figure 5, the aqueous preflush S-l and solvent rinse S-2 are in
the first rinse tank (RTl). The aqueous flushes S-3 and S-k are in the
second rinse tank (RT2). And finally, the water rinse S-5 (water feed, F)
is in the third rinse tank (RT3).
As the work (in this case, a bumper section) is taken out of the plating
bath, it is carried over and into RTl. As the plating rack is lowered Into
it, the aqueous preflush S-l is manually (or automatically) actuated and
is in force for ^-5 seconds. The main purpose of this aqueous prespray is
to cool the work before the main solvent spray (this lowers the solvent
evaporation and losses). The prespray removes approximately 50% of the
chrome which is carried over on the work (drag-out) by replacing the drag-
out concentration by the spray concentration (which should be 25% to 50% of
the plating bath concentration). The spray rate is estimated to be 30-
kO gpm. The next spray, which is actuated automatically at the end of
spray S-l, is the main solvent spray, which is applied in such a way as to
cover all of the work and maintain low evaporation losses. In this appli-
cation, the solvent is sprayed at a rate of 18-20 gpm through *»8 nozzles
for 15-16 seconds. This volume is made up of 0.25 - 0.50% aqueous solution
which is advanced from the second rinse effluent by the actuation of a
pneumatic valve for the spray time. The work is then removed from RTl and
transported to the RT2. The data indicates that 95-97% of the chrome
(plating solution) which was carried out from the plating bath is removed
in the first rinse tank. Again, this depends on each individual applica-
tion, the shape of the work, rinse system, rinse cycle time, etc. It is
recommended, however, that a spray system always be employed in the first
rinse tank to remove as much of the chrome as is possible, preferably
97-98% of the dragout.
13
-------
FIGURE 5. SPRAY ARRANGEMENT
H
MH^H
s
-_/•
^ I
f 1\ /
f
SH
RT
CR!
IOE
sm.
* *9
2
-1
F
J
>
N
SH
^ SH
RT-
CR2
IODI
9 ' —
fc
2
/*
»
V_
•*
/
SH = Spray Header
AC = Anion Column
SH5
*^
RT-3
I
V
WA
LEGEND
F = Water Feed IODF = Perchloroethylene
WA = Water Advance Cg = Chrome Concentration
N = Needle Valve RT = Rinse Tank
-------
The main purpose of RT2 is to displace the solvent which was left on
the work after the first spray. Another reason is to remove some of
the chrome which is left on the work after the first rinse. Ihthis
application, the rinse is actuated by a foot switch after the work is
placed in the rinse tank R-2. The rinse system SHk is composed of U8
nozzles that spray at an approximate rate of 35-^0 gallons per minute
for 19-20 seconds. More impingment is required in RT-2 to remove the
solvent remaining on the work after the first spray rinse (solvent)
SH2. The concentration of the chrome on the work is again reduced to
the aqueous spray concentration of spray SI&. For good rinsing
efficiency, the SI& spray concentration should be a minimum of 100
times less the plating bath concentration. In this application a
rinse spray (SH*0 concentration of 1000-1500 ppm is acceptable. At
the same time the main aqueous spray (SH2) of the rinse tank is acti-
vated, a rack spray is also activated. The principal purpose of this
spray (SH3) is to advance water from the last rinse tank (RT3). This
water advancement maintains a threshold concentration of the aqueous
rinse in the second rinse system that is 100 times less than the plating
bath concentration. As chrome is carried into the second rinse system
as dragout, it is diluted to some concentration by the water which is
advanced from the rack spray SH3. The water volume which is advanced
through this spray is very small and varies depending on the water
losses (evaporation) for each application. This water volume will also
be approximately equal to the quantity which is advanced with each
solvent spray in RT1. This increases the aqueous level in RT-2. The
use of stainless steel nozzles (possibly having a smaller orifice)
in a smaller quantity is recommended. Besides serving the purpose of
water advancement, spray SH3 is a plating rack spray, i.e., the spray
removes any chrome carried over on the plating rack so that it is
washed off in RT2 and not carried over into RT3« In this application,
after the 19-20 second spray duration in RT2, the work is removed and
carried over to RT3. At this point (before the last rinse dip in RT3)
more than 99$ of the chrome should be removed from the work.
RT3 is an immersion water-rinse, whose concentration is maintained at
a minimum (2 ppm) to ensure the removal of virtually »-n the chrome
(99.99+$) from the work. Spray system SH5 over RT-3 serves as a rack
spray to remove any chrome remaining on the plating rack. It is also
a source of water supply to the system. Water feed may be continuous
or on demand, depending on evaporation rate, nozzle size, etc. The
chrome concentration is maintained low (<2 ppm) by continuously
recirculating the aqueous rinse through an anion exchange column.
During an 11-day test run, 1,125 bumpers were rinsed in the system.
15
-------
SECTION VI
LABORATORY ANALYSIS
To accurately evaluate the ZDS™, temperatures were recorded and samples
were taken dally and sent to the laboratory for analysis. The samples
were taken at: the plating bath (Table 2), the recovered chrome
(Table 3), the first rinse (Table U), the second rinse (Table 5), and
the final rinse (Table 6). The samples were taken at the beginning
and end of each day. Temperatures at these areas were also noted
(Table 6).
TABLE 2. ELATING BATH
Sample
Taken after hours
below
After 1
After HO
After 80
Cr4® = hexavalent chrome
Cr+3 = trivalent chrome
Fe = iron
Total Chrome
(ppm)
Cr1
Cr
•+3
Fe
(ppm) (lO-H+/liter)
NA
126,000
12^,000
NA
NA
NA
NA
NA
NA
iko
200
212
0.3
Q.k
0.2
LEGEND
pH = strength of acid (moles H*/liter)
ppm = parts per million
NA = Not Available
16
-------
TABLE 3- RECOVERED CHROME
Sample Total Chrome Cr*6 Cr^ pe |>H
Taken After Hours
below
After U
After 9
After 28
After 33
After U3
After 51
After 63
After 71
After 80
Sample
Taken After Hours
below
After to
After 80
(ppm)
1,1*50
3,100
9,000
20,500
29,500
32,000
38,500
1*7,000
55,000
TABLE 1*.
Total Chrome
(ppm)
28,000
55,000
(ppm)
1,1*00
2,900
7,800
17,000
26,000
28,000
38,500
1*3,000
50,000
(ppm)
50
200
1,200
3,500
3,500
1*,000
0
1*,000
5,000
(ppni)
6.5
20
120
320
368
381*
1*50
500
700
(lO-H+/liter)
1.7
1.5
1.3
1.0
1.0
1.0
0.9
0.7
0.6
FIRST R3MSE
Cr4^
(ppm)
28,000
50,000
Cr+3
(Ppm)
0
5,000
Pe
(ppm)
380
21*0
pH
(lO-H*/liter)
1.0
0.6
17
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TABLE 5. SECOND RINSE
^
Sample
Taken After Hours
below
kO
80
Sample
Taken After Hours
below
1
8
16
2U
32
ko
U8
56
6k
72
80
* Note: Here ia an indication that column regeneration is required.
This was not done during these tests.
Total Chrome
(ppm)
225
780
TABLE 6.
Total Chrome
(ppm)
0.0
0.0
0.0
0.0
0.0
0.0
0.0
1.0*
1.0
O.U
1.5
Crft>
(ppm)
210
725
FINAL RINSE
Cr*6
(PPtt)
0.0
0.0
0.0
0.0
0.0
0.0
0.0
NA
1.0
o.U
1.5
Cr"1^ Pe
(ppm) (ppm)
15 NA
55 NA
Cr+3
(ppm)
0.0
0.0
0.0
0.0
0.0
0.0
0.0
NA
0.0
0.0
0.0
ES
(lO-H+/liter)
U.O
2.5
ES
(lO-H+/liter)
6.2
11.5
11.2
11.0
11.0
10.8
11.0
10.5
10.6
10.5
10.5
18
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TABLE 7. TEMPERATURE DATA (°F) (AVERAGE 8-HOUR DAY)
Sample Start End
Solvent 68 52
Plating Bath 62 60
First Rinse 6? 62
Second Rinse 62 70
Final Rinse 62 70
Under the tests conditions, the samples taken were not returned to the
plating bath because it was at ambient temperature and required no
make up of recovered chrome. The discharge of chrome was controlled as
can be noted in Table 5 after 80 hours of operation. About 2 ppra of
chrome were maintained in the final rinse. During this 80-hour phase
of testing, the anion column was not regenerated. If it had been, no
chrome would have been present, as shown after U8 hours. Also, proper
column sizing is important to achieve maximum efficiency.
19
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SECTION VII
COST
EQUIPMENT COST
The complete cost of one ZDS™ module was $U6,UOO.OO as of May 19?6.
Assuming that proper care and maintenance are given to the equipment,
a 10-year life expectancy is anticipated. It is estimated that equip-
ment costs will be about the same as those for alternative systems,
except that the ZDS^ requires less instrumentation. The real saving
is realized in the recovery phase.
OPERATIONAL COSTS
Assuming 100 bumpers a day (500 bumpers a week) are run through the
plating line, the costs incurred per bumper are:
Sulfuric acid (cation column) $ O.OCk
Sodium hydroxide (anion column) $ 0.020
Perchloroethylene (spray loss) $ 0.130
Genesolv-D (solvent extraction at column $ 0.00^
Steam regeneration $ 0.010
$ 0.168
It is estimated that the power consumed is the same for the ZDS™ as it
would be for a countercurrent rinsing system. This includes all the
pumps and solenoid valves.
SOLVENT
As previously discussed, the system uses perchloroethylene, which is
available from several manufacturers at a cost of about $4 per gallon.
The test data indicate that the solvent cost in the actual system
application was approximately $0.13 per bumper. When compared with
the cost of cleaning up the environment, this expenditure is quite
reasonable.
20
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SECTION VIH
OPERATIONAL PROBLEMS, SOLUTIONS, AND RECOMMENDATIONS
ADVANTAGES
The advantage of the ZDS™ over conventional systems is in its rinsing
efficiency and recovery portion. The conventional countercurrent rinsing
system may require 2 pounds of sulfur dioxide (SOg) and one-half pound
of sulfuric acid (HjgSOli) to reduce one pound of chronic acid (CrOj).
In 1970, 2,080,000 pounds of chronic acid were used in the bumper-plat ing
industry, and it cost $1,250,000 to detoxify this acid. An additional
one million dollars was spent to adjust the pH levels before dumping.
Approximately Ul,000,000 pounds of chromic acid are used annually for
plating in general. Practically all this supply is imported from
South Africa, Turkey, Rhodesia, and Russia. The ZDS™ process recovers
the chrome and returns it to the plating bath. ZDS™ appears to be the
best available technology if:
1. The evaporation rate is low (low-temperature bath)
2. A countercurrent system requires an excessive number of tanks
3. A reasonable size countercurrent system requires the removal
of more than 5000 gallons/day of water
U. The magnitude of the difference in plating bath concentration
and final rinse concentration is significant
5. There are significant fluctuations in evaporation or drag out
volume
Therefore, the ZDS™ should be given due consideration if any of these
criteria are met. Finally, to date no adverse effects of this system
on product quality have been encountered.
PERCHLOROETHYLENE VS. FREON TF
The system cannot readily be converted to freon TF, therefore no state-
ment can be made on the possible advantages or disadvantages of using
freon TF. It is known that freon TF has a low boiling point, 118° F,
a characteristic that would cause it to flash off of the plated parts,
thus making its recovery more difficult.
21
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IRON CONTAMINATION
The first two-week test run disclosed that the recovered chrome con-
tained too much iron. This indicated that either the cation exchanger
was ineffective or too much iron was picked up in the unlined steel
tanks before the recovered chrome was passed through the cation ex-
change unit. Sample analysis of the recovered chrome indicated that
the iron and trivalent chrome (Cr+3) concentrations increased propor-
tionately, therefore, it can be assumed that the recovered chrome was
corroding the steel tank (RT-l). All of the tanks should have been
rubber lined at the outset to prevent the iron build up.
VAPOR ADSORBER
In the first series of tests (1000 cycles), approximately 32 gallons
of solvent were lost — over half of the total amount used. The
equipment and test process should allow a solvent recovery rate of
80-90^. It was determined that recovery efficiency was poor because
the vapor adsorber was not regenerated until the end of the two-week
test run. The unit should be regenerated at least every 1-1/2 days.
A different lip vent design could be used to increase air flow and
thus raise solvent recovery.
SPRAY ARRANGraffiNT
Problems were encountered with the spray system. The material used
to construct the spray headers in rinse tank Rl was chlorinated poly-
vinyl chloride (CPVC). It was attacked by the solvent perchloroethylene
and the spray header arrangement and fittings fell apart after 3-1* weeks
in continuous contact with the solvent. The other parts which were
constructed of PVC (poly-vinyl chloride) seemed to be very resistant
to the solvent and showed no signs of attack, cracking, softening, or
swelling. It is recommended that the spray system be constructed of
PVC or fiberglass.
ION EXCHANGE UNIT
No unusual problems were encountered with the anion exchange columns.
Additional modification of the equipment was made to allow for water
rinsing of the unit in a "downward" flow after the regeneration cycle.
This included the addition of valves and fittings. A small water
softener was constructed to permit the use of soft water for rinsing
after regeneration. Besides the problems of iron and trivalent chrome
buildup in the cation exchange column already described, additional
-------
problems were encountered with the cation exchange columns. One of the
columns began to leak before the test runs were strated. The problem
was finally resolved by using PVC glue generously at the leakage points.
As with the anion exchange columns, additional piping and valves were
required to allow for "downward" rinse action after regeneration. Before
the recovered chrome is passed through the cation exchange column, it
is passed through a column which is 3A filled with Allied Chemicals'
Genesolv-D (tri-chloro, tri-fluoro, ethane). This mixing of the re-
covered chrome with Genesolv-D removes any traces of solvent perchloro-
ethylene before the recovered chrone passes through the cation exchanger
and is returned to the plating bath. All traces of solvent are removed
to prevent the negative reaction of the solvent with the cation exchange
resin. Also any solvent carried over may be detrimental to the plating
bath. The Genesolv-D should be replaced once a week to maintain a high
solvent absorption capability.
SEPARATION TANKS
The separation tank seemed to operate as anticipated. Additional piping
was included to allow for the removal of solvent build up in the recover-
ed chrome section of the tank. This modification continuously recycles
the recovered chrome and any solvent which is carried over to the re-
covered chrome, thus preventing a large build up of solvent on the re-
covered chrome side. At the beginning of the two-week test run a leakage
problem arose with the separation tank. One of its compartments twice
had to be drained of the solvent and aqueous solution so that the tank
side could be patched with vyton and epoxy. The leaks occurred because
chlorine had attacked the steel at the spots where welding was used to
form compartment separation. The problem was probably caused by in-
sufficient rinsing of the system when the unit was not operating (left
dry). The chilling coils in the separation tank should be allowed to
cool the solvent to 65-70° F. It has to be maintained at that tempera-
ture to reduce evaporation losses and to prevent heat build up (from
pumps and process) from damaging the system pumps. Solvent feed to the
system is actuated by a level control. Depending on the solvent losses
incurred, the feed may be continuous or controlled manually on demand
(when level drops too low in the separation tank). It was found that
manual control (on demand) to be more satisfactory for solvent feed.
COOLING SYSTEM
The chiller unit experienced a freon leak prior at the beginning of the
test run. The unit was repaired and is working satisfactorily. The
main purpose of the chiller is to create a cold air layer in rinse tank
RT1 to reduce solvent vapor losses during the spray cycle. The heat
transfer coils on the sides of rinse tank RT1 seemed to do a good job
in maintaining a cold layer of air in the tank. It is recommended that
the plating bath and rinse tank RT1 be separated by an air space in an
actual plating installation. This would prevent or reduce the amount
of heat transferred from the plating tank to the first rinse tank. As
already mentioned, the chiller also cools the solvent in the separation
23
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tank and the small condenser on the cation exchange unit. The cooling
system is filled with an approximate 5OJ&-50$ ethylene glycol water
solution. The unit is automatically set to maintain the temperature
of the cooling fluid in the range of 15-30° F. Cooling water for the
chiller compressor must be provided for the compressor to operate
properly. In the two-week test run, only 1-2 gallons of cooling fluid
were lost, probably due to evaporation.
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/2-77-099
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
Innovative Rinse-and-Recovery System for Metal
Finishing Processes
5. REPORT DATE
May 1977 Issuing Date
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Walter C. Trnka
Charles J. Novotny
8. PERFORMING ORGANIZATION REPORT NO.
Project No. 98A
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Industrial Filter & Pump Manufacturing Company
5900 West Ogden Avenue
Cicero, 111inois 60650
10. PROGRAM ELEMENT NO.
1BB610
11. CONTRACT/GRANT NO.
R-803723-Ol
12. SPONSORING AGENCY NAME AND ADDRESS
Industrial Environmental Research Lab.-Cin.
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio A5268
OH
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
EPA/600/12
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This report describes the feasibility of a rinse-and-recovery system that can be
installed in almost any metal finishing line and does not harm the environment
because no plating solution exits to the sewer. Most toxic pollutants from metal
finishing operations are associated with the water used to rinse the affected parts
after successive finishing operations.
A typical car bumper plating operation was chosen as opposed to a barrel rolling
operation. When a part emerges from the plating bath, it "drags out" fulI-strength
plating solution with the bumper. This drag out is tremendously diluted by follow-
ing rinse steps. The diluted rinses are sent to the sewer and cause toxic deteriori-
zation of the waste waters.
TM
The ZDS is an innovative rinse-and-recovery system for use in the metal finishing
industry. A conventional multistage aqueous rinsing system is replaced by a 2-stage
solvent spray •"inse followed by a single-stage aqueous immersion rinse. By con-
tinuously purifying and recycling the baths, appreciable savings in operating chemi-
cal costs can be realized.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
COSATI Field/Group
Metal Finishing
Plating
Chromium coatings
Rinsing
Materials recovery
Zero Discharge System
13B
18. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
31
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
25
u. S. GOVERNMENT PRINTING OFFICE: l977-757-056/6A3't Region No. 5-11
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