METHODS TO MINIMIZE WASTES FROM ELECTROPLATING FACILITIES
Prepared for:
Process Technology ’88 The Key to Hazardous Waste Minimization
Sacramento, California August 15-18, 1988
Prepared by:
Edvard R. Saltzberg, Ph.D. Science Aplications International Corporation
8400 Westpark Drive McLean, VA 22102
METHODS TO MINIMIZE WASTES FROM ELECTROPLATING FACILITIES
EDWARD R. SALTZBERG, PH.D
SCIENCE APPLICATIONS INTERNATIONAL CORPORATION
8400 WESTPARK DRIVE, MCLEAN, VA 22102 (703) 821-4671
TOPIC NUMBER: 1000
The majority of metals and cyanide discharged by industry into the
Nation’s waterways comes from metal-finishing facilities, primarily
from electroplating processes. The U.S. Environmental Protection
Agency (EPA) figures released a few years ago, show that of the 34
industries covered by EPA’s toxic wastewater regulations, metal
finishers contribute 57 percent of the metals released to sewers.
The degree of risk posed by these discharges is hard t o determine
because it depends on site-specific factors; however, small amounts
of the types of chemicals discharged by metal finishers are toxic
enough to cause EPA to set stringent, safe threshold levels for
these chemicals in surface waters.
I
Because of the toxicity of pollutants in metal-finishing wastes and
the amounts of these discharges, EPA established national wastewater
regulations for this industry. The goal of these regulations is to
reduce the contaminants in metal-finishing discharges to levels that
are environmentally acceptable while remaining technically feasible
and affordable for the industry. However, Federal wastewater regu-
lations could have a severe economic impact on the metal-finishing
industry. EPA has estimated that up to 20 percent of all electro-
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METHODS TO HINIMIZE WASTES FROM ELECTROPLATING FACILITIES
3 EDWARD R. SALTZBERG, PH.D.
2 plating firms may close due to wastewater regulations. Since the
conventional methods used to treat metal-finishing wastewater pro-
duce sludges that are subject to costly hazardous waste regulations,
even a larger percentage of this industry than was estimated by EPA
could go out of business.
Fortunately, the economic outlook for cleaning up metal-finishing
wastewater is not as dismal as EPA expected. Recently, some elec-
troplating firms have found that very inexpensive changes in pro-
cessing and waste control methods can greatly reduce the amount of
wastewater and hazardous waste they generate. These techniques
enable plating shops to avoid much of the cost of waste treatment
originally estimated by EPA. Moreover, these techniques can act-
ually pay for themselves in a very short period of time because they
save large quantities of water and process chemicals.
far less than 20 percent of the firms in the electroplating industry
should close because of EPA's wastewater regulations.
As a result,
The new methods of plating waste controls that are being used and
accepted by the industry are based on what energy conservationists
have been proclaiming for more than a decade:
and cheapest way t o save energy is t o avoid using it.
quickest, easiest and cheapest way to keep down pollution control
costs is not to pollute in the first place. Accordingly, the new
methods of pollution control for the electroplating industry rely on
the quickest, easiest
Likewise, the -
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METHODS TO MINIMIZE WASTES FROM ELECTROPLATING FACILITIES
EDWARD R. SALTZBERG, PH.D.
conservation practices - usually low cost technology methods that are inexpensive and easy to use.
change in attitude toward production than they do on expensive
hardware. The central theme of the new methods is to strictly
conserve and reuse water and chemicals, and to employ wastewater
treatment technologies for compliance only when absolutely neces-
sary.
The new methods depend more on a
The new methods depend on reducing the drag-out of chemicals from
plating baths and low rinse rates, but the techniques are slightly
different, more effective, and less costly than those traditionally
used in the industry.
The principal measures used in the new methods are:
(1) Multiple drag-outs -- a variation on single drag-out tanks;
Reactive rinsing -- a technique for reusing rinsewaters. (2)
Rather than reducing the size of end-of-pipe treatment equipment,
the new methods of plating waste controls use multiple drag-out
tanks and apply reactive rinsing techniques in order to avoid the
need for end-of-pi-pe treatment equipment altogether, resulting in
very small pollution control costs.
waste treatment is still necessary, the cost of the treatment is
still far less than i t would be using standard techniques.
In instances where some final
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METHODS TO MINIMIZE WASTES FROM ELECTROPLATING FACILITIES
EDWARD R. SALTZBERG. PH.D.
This paper explains how to use these new methods.
these new methods, a brief description of electroplating is pre-
sented to provide some background to those unfamiliar with this
industry.
Before examining
OVERVIEW OF THE ELECTROPLATING PROCESS
for applying a thin metal coating such as zinc, copper, nickel,
chromium, etc. to the surface of metal parts, which are usually made
of iron, steel, brass or aluminum. The coatings serve to protect
the metal from corrosion, to build up the surface thickness, or to
decorate the piece.
Automobile bumpers and door handles, for example, are often chrome
plated; printed circuit boards are copper plated, and watch bands
and necklaces can be gold or silver plated.
Electroplating is a process
Many commonly used items are electroplated.
PROCESS STEPS Most electroplating processes can be divided into
three principal work steps as shown in Figure 1.
Surface Preparation
before it is plated.
the work piece in a tank containing a solvent or alkaline solution,
and then in an acid dip to remove corrosion. Both the alkaline and
the acid dip are followed by rinsing in running water.
Surface preparation involves cleaning the part
Cleaning is usually accomplished by placing
Plating Application In the second work step, a metal coating is
applied from a solution containing the plating metal in dissolved
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Port Treatment
PICUlfK 1 OMXVIKY OF ELZC’IPOPUTINC PBocllSS
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HETHODS TO MINIMIZE WASTES FROM ELECTROPLATING FACILITIES
EDWARD R. SALTZBERG, PH.D. 7
form and other chemicals. The part to be plated is placed in the
solution and charged with electricity to attract the dissolved metal
to its surface much like a magnet attracts iron filings. Plating is
followed by rinsing with water to flush the process solution from
the work piece.
Post Treatment Some plating steps are followed by post treatment of
the work pieces to color it or to add corrosion resistance. Chro-
mate, for example, is a common post treatment for zinc and cadmium
plating. Post treatment steps are also followed by rinsing in
running water. Some electroplating processes are complete after the
plating step and do not require post treatment.
Sometimes the configuration of an electroplating process line will
appear to be complicated. Because of space constraints, work flow
requirements, ancillary components of a work step, or poor tank
layout, the three plating steps can be difficult to recognize. For
example, Figure 2 illustrates the layout of an anodizing line in the
shop of an east coast plater.
for finishing aluminum. The three work steps are not easy to dis-
tinguish because of the positioning of the tanks and because several
components comprise each work step. Nonetheless, there are still
only three steps as identified below.
Anodizing is an electrolytic process
The surface preparation step in the anodizing process begins with
degreasing (Tank 1) in a hot solvent. Next, parts are further
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METHODS TO MINIMIZE WASTES FROM ELECTROPLATING FACILITIES
-3 EDWARD R. SALTZBERG, PH.D.
cleaned in Tanks 2 and 3, which contain alkaline cleaners, and then
etched in Tank 4.
aluminum, can take place in any of five process tanks (8, 9, 10, 11,
12).
tanks (18, 19, 21, 24, 25, 27, 2 9 ) , and sealing of the dyes takes
place in tanks 32, 33, and 3 4 . Although the layout and number of
the tanks complicate the plating sequence, there are still only
three steps to this and all electroplating process lines.
every component of each step is followed by rinsing in running
The plating step, in this case the anodizing of
Finally, post treatment of aluminum takes place in the dye
Usually,
water.
SOURCES OF WASTE Wastes from electroplating shops originate in
several ways.
processing solution that clings to the work piece as it is removed
from the plating bath.
drag-out is a function of many factors including, the design of the
racks or barrels carrying the parts to be plated, and the shape of
the parts. Plating procedures and several interrelated parameters
of the process solution, such as concentration of toxic chemicals,
temperature, viscosity, and surface tension also affect drag-out
rates.
One source of pollution is from "drag-out," which is
The amount of pollutants contributed by
Rinsewater Large volumes of rinsewater are usually needed to clean
the drag-out from the work with conventional rinsing techniques.
Rinsing actually serves two purposes:
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WETHODS TO WINIMIZE WASTES FROM ELECTROPLATING FACILITIES
EDWARD R. SALTZBERG, PH.D.
1. It cleans the part, which prevents staining and other quality control problems:
minat ion. 2. It protects subsequent process baths from "drag-in" conta-
Because of high flow rates used in conventional rinsing techniques,
rinsewaters are contaminated with relatively dilute concentrations
of process solutions. Typically, rinsewaters that follow plating
solutions contain between 15 and 100 milligrams per liter (mg/l) of
the metal being plated.'
Host job shops operate several plating lines such as zinc, copper,
nickel, cadmium, and chromium. The rinsewaters discharged from each
line are usually combined in a common pipe or floor trench, and the
concentrations of the individual metals from each process are
diluted in the entire volume of the shop's wastewater, usually to
less than 40 mg/l for each metal.3
Spent Process Baths Another source of contamination from electro-
plating shops is used or spent process solutions. Platers routinely
discard spent cleaners, acids, and bright dips. Although these
solutions are not usually made up of metals, it is not uncommon to
find cyanide and heavy metals in concentrations of several thousand
milligrams per lirer in these solutions. This contamination is
caused by drag-in from previous process cycles and from metals
leached or dissolved from the work by the process chemicals.
Plating solutions and other process chemicals containing high metal
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METHODS TO MINIMIZE WASTES FROM ELECTROPLATING FACILITIES
EDWARD R. SALTZBERG. PH.D.
concentrations are rarely discarded. Instead, they are deconta-
minated or rejuvenated in place so they are not usually a hazardous
vaste problem.
Other Sources Accidental spills, leaks, and floor drips of process
solutions also can contribute to effluent contamination. Additional
pollution sources include sludges from the bottoms of plating baths
generated during chemical purifications, backwash from plating tank
filter systems, and stripping solutions. Although the contribution
from all pollution sources varies from shop t o shop, in almost every
case the most significant pollution problem is drag-out and the
resultant contaminated rinsewater. A recent survey in Cleveland
underscores this point. The average rate of rinsewater discharged
from 22 Cleveland electroplating shops was 18,500 gallons per day
(gpd), whereas spent process solution accounted for only 60 gpd. -
3
DRAG-OUT MINIMIZATION USING MULTIPLE DRAG-OUT TANKS Minimizing the
amount of plating solution that is dragged from work pieces upon
their removal from the process tank reduces the amount of conta-
mination in the rinse tanks. A single drag-out tank, installed
immediately following the plating process, will capture some of the
contamination. Two or more drag-out tanks will capture most of it.
The multiple drag-out technique is similar to counterflow rinsing -
a common water conservation method - because it uses several rinse
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METHODS TO MINIMIZE WASTES PROW ELECTROPLATING FACILITIES
EDWARD R. SALTZBERG, PH.D.
tanks in series. The difference is that instead of a single drag-
out tank and two or more running rinses, the multiple drag-out
method uses several drag-out tanks and single running rinse, as
Figure 3 illustrates.
tank, leaving the second tank less contaminated than the first. As
a result, the concentration of pollution in the discharge from the
running rinse tank is lower than i t would be if only one drag-out
tank is used. More drag-out tanks lower the discharge concentration
even further. As a rule of thumb, each drag-out tank reduces the
discharge concentration by 50 percent. Accordingly, two drag-outs
are twice as effective as one, and three drag-outs are four times as
effective as one.
Host of the drag-out is captured in the first
The concentration of pollutants in the running rinse tank does not
remain constant. As pollution builds up in the drag-out tanks, i t
also increases in the running rinse tank. However, the more drag-
out tanks used, the slower the buildup of contaminants in the
running rinse. This is the principle behind multiple drag-out tanks
and a key feature of the new methods of plating waste control.
Using two or more drag-out tanks, the concentration of pollutants in
the discharge from the running rinse tank can be held below effluent
limits for extended periods of time. The length of time depends on
five factors:
(1) Concentration of the process solution: (2) Rate of drag-out;
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3
Work Flow c I [ Plating Tank 1 1 D<:y 1.1 D ~ ~ ~ u c Rinse Tank
To pH Neutralization P I C W 3 MULTIPLE DRAG-Om
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METHODS TO MINIMIZE WASTES PROM ELECTROPLATING FACILITIES
EDWARD R. SALTZBERG, PH.D.
( 3 ) Number and size of the drag-out tanks: ( 4 ) Rinse rate; ( 5 ) The number of rinse tanks in the plating shop.
These factors and the handling of discarded drag-out solutions are
examined below.
THE FACTORS CONTROLLING POLLUTION CONCENTRATIONS IN RINSE-WATER
Figure 4 is a graph illustrating the effect of the factors identi-
fied above on the concentration of pollutants in a running rinse
tank. The upper solid curve plots the discharge concentration over
time from a rinse station without any drag-out tanks, and the lower
solid curve plots the concentration for one with two drag-out tanks.
The curve for one drag-out tank would fall between the two curves
shown in Figure 4 .
It takes longer for a two drag-out tank system to reach a certain
Concentration such as "CR" than a system without a drag-out tank o r
with only one drag-out. The curve for three or more drag-out tanks
would fall below the curve for two drag-outs and, consequently, take
longer to reach a concentration of C, in the discharge from the
rinse tank.
The strength of the process solution also affects the concentration
of pollutants in the rinse discharge. A high strength solution will
pollute more quickly than a low strength solution and, consequently,
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. CP
Concentration in Rinse Tank
No Drag-out Tanks c* Days
F I C W 4 EFFECTS OF CONTROL PAibUfSTgPs ON R I N S E TANK DISCEARCE CONCEHlgAIIOll
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METHODS TO I(INIl4IZE WASTES FROM ELECTROPLATING FACILITIES
EDWARD R. SALTZBERG, PH.D.
the rinsewater will reach C, sooner.
drag-out rate, the quicker the rinsewaters become contaminated.
Figure 4 illustrates these effects for the two drag-out tank case.
The solid curve is shifted upward for higher drag-out rates or
highly concentrated process solutions and is illustrated by the
upper dashed curve. Accordingly, the time to reach a specific
discharge concentration is reduced. Lower values for these factors
would shift the curve downward and increase the time to reach C,.
Likewise, the higher the
Rinse rates have just the opposite effect.
the curve shifts downward because dilution in the rinse tanks is
increased. The
lower dashed curve illustrates this effect.
At higher rinse rates,
As a result, the time to reach C, is increased.
If C, is the effluent limit for the metal being plated then "T,",
shown in Figure 4, indicates the time i t takes a double drag-out
rinse tank discharge system to reach this limit. This is also the
time at which the drag-out solutions must be replaced or purified if
C, is to be maintained in the discharge from the running rinse.
Using two drag-outs, T, usually ranges from 2 to 16 hours, depending
on the process concentration and the rinse rate.
Actually, drag-out solutions need replacement far less frequently
because government limitations apply to the firm's combined rinse-
waters from all processes and not to individual tank discharges.
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METHODS TO MINIMIZE WASTES FROM ELECTROPLATING FACILITIES
3 EDWARD R. SALTZBERG, PH.D.
3
Most processes have four rinse tanks (cleaner, acid, process, and
post-treatment), so there is a four to one natural dilution within
each process.
cesses, there is additional natural dilution within the rinsewaters
of the shop.
not uncommon, and natural dilution can increase T, by a factor of
"five times 4" or at least 20. Accordingly, the time for a parti-
cular drag-out solution (T,) to be replaced in order to keep a
firm's combined discharge below a government limitation (C,) will
range from 5 to 40 working days (assuming 8 hours of production per
day). Figure 5 illustrates this effect. If the drag-out solution
is replaced on schedule, then the rinsewater from that process can
be discharged without further treatment because it will meet govern-
ment wastewater limits. Accordingly the firm will save tens and
even hundreds of thousands of dollars because it will not need a
conventional end-of-pipe treatment system. In most cases, the pH of
the discharge will still have to be regulated, but pH control for
dilute rinsewater costs only a few thousand dollars even for large
flow rates.
Since plating shops generally provide several pro-
Electroplating shops with five or more processes are
3
Replacing each drag-out solution every 1 to 8 weeks is not a very
large burden on a plating shop and, considering the savings in
pollution control costs, it is certainly worth the extra effort.
Cleaners and acids, for example, are replaced on a similar schedule
anyway, so drag-out control can easily become part of a firm's
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Concentration in Combined
Discharge (MI)
3 Processes
10 Processes / -*
I 1 I I I 1 1
20 30 40 50 60 IO Days
PICURB 5 C O N C E ~ T I O N IA COWIWED D I S C U C I
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METHODS TO MINIMIZE WASTES FROM ELECTROPLATING FACILITIES
EDWARD R. SALTZBERG, PH.D.
routine process maintenance program. What to do with drag-out
solution (generally listed or characteristic hazardous waste) once
it is discarded is addressed below.
MANAGING DRAG-OUT SOLUTIONS There are two techniques for discarding
drag-out solution.
drag-out tank is drained before time "TR" is reached.
replaced with the entire volume of the second tank, and tank 2 is
filled with freshwater (in a two-tank system). If there are more
than two drag-out tanks, then the last one is filled with freshwater
and upstream tanks are replenished with solutions from the down-
stream tank.
In the first, the entire volume of the first
It is
Alternatively, drag-out solution can be trickled from the appro-
priate drag-out tank as in a very slow counterflow rinse tank
system.
is maintained in the running rinse instead of cycling from zero to
the value that assures that C, is not exceeded in the firm's com-
bined discharge.
because it requires electronic controls to maintain the proper
trickling rate. However, considering the convenience, it may be the
preferred approach at many plating shops.
The advantage of this method is that a steady concentration
This technique is more expensive than the first,
There are three ways to handle discarded drag-out solutions:
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NETHODS TO NININIZE WASTES FROM ELECTROPLATING FACILITIES
EDWARD R. SALTZBERG, PH.D.
(1) (2) Treatment in place; (3) Batch treatment on-site or off-site.
Recycle drag-out solution to the plating bath;
The application of these methods depends on the chemistry and
operating conditions of the processes and the size and geographic
location of the firm. Each technique is discussed below.
Recycle Drag-out Solution to the Plating Bath The best alternative
for managing drag-out solution is to return i t to the process bath
from which it came. Total recycle eliminates the drag-out from
being a hazardous waste problem and conserves process chemicals.
Returning drag-out directly to the process is possible if the pro-
cess bath is hot and there is sufficient evaporation to make room
for the amount of solution dragged out each day. For example,
nickel and chromium plating are both operated at or above 130'F and
drag-out solution can be returned to these processes.
Returning drag-out solution to the plating bath is a technique that
should not be used indiscriminately because it can impact plating
quality. For example, copper pyrophosphate plating is a heated
process but contaminants build up in the bath because of chemical
reactions that occur in the process solution.
There are many plating processes on the market, and one cannot
generalize about the application of drag-out recovery to all the
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METHODS TO MINIMIZE WASTES FROM ELECTROPLATING FACILITIES
-I EDWARD R. SALTZBERG, PH.D.
processes. However, in general, the technique can be used after
most heated plating baths. The manufacturer of the individual
process chemicals will usually advise platers on the application of
drag-out recovery to their processes.
Unfortunately, many plating baths are operated at room temperature,
and there is little evaporation from them. Accordingly, drag-out
cannot be returned directly to these processes. In instances in
which drag-out cannot be recycled directly, high technology recovery
techniques such as reverse osmosis and evaporation have been used in
plating shops to concentrate the drag-out into volumes small enough
to be returned to cold process baths. However, there are two pri-
mary drawbacks to these techniques:
o They are very expensive;
o These techniques not only concentrate the excess solution in the drag-out tank, but they also concentrate the impurities in the drag-out.
When the concentrate is returned to the process, the concentrated
impurities can contaminate the plating solution and impair the
quality of the plating.
exchange to selectively remove impurities, but this drives up the
already high cost-of recovery. In general, the following methods of
handling drag-out solutions which cannot be returned to the plating
bath are more cost effective than high technology controls.
The concentrate can be purified using ion
3
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HETHODS TO HINIHIZE WASTES FROM ELECTROPLATING FACILITIES
EDWARD R. SALTZBERG, PH.D.
Treatment in Place When the drag-out solution cannot be returned to
the plating tank the next best alternative is treatment in place. A
process called integrated treatment was developed several years ago
by Lancy Laboratories, Zelienpole, Pennsylvania. It was primarily
designed to complete in-process the first step in the two-step
treatment of chromium and cyanide.
out in the end-of-pipe treatment system.
The second step would be carried
Electrolytic recovery of metals from the drag-out tank has become
cost-effective in the last 2 years. This technique works best on
zinc, cadmium, copper, silver, gold and tin processes. It is not
effective on chromium and nickel.
Batch Treatment on Site If the drag-out solution cannot be returned
to the process tank or treated entirely in place, it has to be
chemically treated, usually in a batch treatment system. In these
cases, the drag-out solution can be handled like other spent elec-
troplating process baths.
In addition t o drag-out solutions, spent baths from plating shops
include cleaners, acids, and post treatment solutions. (Platers
rarely discard plating solutions.) Spent baths can be treated
on-site in the firm’s own bath treatment system or shipped off-site
to a private waste treater. Central processing facilities that
recover metals may be able to refine drag-out solutions and certain
other spent plating baths. 4
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HETHODS TO MINIMIZE WASTES FROM ELECTROPLATING FACILITIES
EDWARD R. SALTZBERG, PH.D.
A diagram of a batch treatment system for spent plating baths
(including drag-out solutions) is shown in Figure 6 . The solutions
to be treated are discharged on a schedule, and the size of the
treatment system is designed for the schedule specific to each
plating shop.
plating baths at a medium-sized shop.
Below is a typical weekly schedule for dumping
o AciddAlkalies 300 gallons/week o Cyanides 100 gallondweek o Chrome 100 gallons/week
o TOTAL 500 gallons/week
For this schedule, the firm would need:
o Three 5000 gallon holding tanks (one for each type of solution);
o A 750 gallon treatment tank;
o A filter to consolidate the sludge;
o A few chemical feed tanks;
o Some chemical control equipment.
The system would cost about $60,000 including engineering and
installation. If the firm used the new methods of plating waste
control, this would be the major portion of the firm’s waste
treatment bill. If it didn’t, the bill would be several hundred
thousand dollars.
5
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1
Acid/Alkali Holding Tank -
- I I
---h Treatment Chemicals
Cyanide Holding Tank - -
Chromium Holding Tank
Treatment * Tank Effluent to Drain -
Sludge Filter
T o Disposal
PICURX 6 BATCB T R E A " T SYSTEM
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METHODS TO HINIMIZE WASTES FROM ELECTROPLATING FACILITIES
EDWARD R. SALTZBERG. PH.D.
WATER CONSERVATION THROUGH REACTIVE RINSING
technique to reuse or recycle rinsewater one or more times before it
is discharged. This technique takes advantage of the chemical
reactivity of used rinsewater.
tion be greatly reduced by recycling, but rinsing efficiency can
actually be increased by this method, thus improving plating
quality.
Reactive rinsing is a
Not only can a firm's water consump-
Counterflow rinsing is the standard technique platers use to reduce
flow rates. However, rinse tanks are expensive and require space
for installation, while electroplating shops usually have trouble
raising capital and are often located in tight quarters.
rinsing is a very effective alternative to counterflow rinsing
without the cost or logistical constraints. Reactive rinsing does
not require additional rinse tanks, so it is less expensive than
counterflow rinsing. It also does not use any additional space, so
it has wider application than counterflow rinsing.
Reactive
INTRAPROCESS REACTIVE RINSING
diagrammed in Figure 7 . It is usually composed of three process
steps:
A typical nickel plating line is
o An alkaline cleaning tank; o An acid dip tank; o A nickel plating tank.
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Work Flow- Fresh Water Fresh Water Fresh Wale c c
--- Reuse Flow Scheme
FIGURE 7 INTBAPROCESS REACTIVE RINSIAG
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HETHODS TO MINIMIZE WASTES FROM ELECTROPLATING FACILITIES
EDWARD R. SALTZBERG, PH.D.
Each process step is followed by a running rinse tank, and each
rinse tank has a separate freshwater feed line. The rinse tanks run
at about 4 gpm, and the nickel plating line in Figure 7 uses a total
of 12 gpm.
single 8-hour production day, this line alone accounts for 5,700
gallons of water. Other types of plating lines have more than three
rinse tanks so they could use even more water than a nickel process.
Therefore, it is little wonder that each plating shop employing
standard rinsing methods uses tens of thousands of gallons of water
each day.
Twelve gallons per minute is a lot of water. In a
USING REACTIVE RINSING TO SAVE WATER The parts to be plated
"drag-in" to the nickel tank whatever is in the previous rinse tank.
If that rinse tank is fed with freshwater, the drag-in will be
comprised primarily of a dilute acid solution, which will reduce
both the nickel concentration in the process bath and, to a certain
extent, the acidity of the bath. (Nickel solutions are slightly
acidic.) Instead of using freshwater, the acid rinse tank could be
fed with the discharge from the nickel rinse tank. Since the nickel
rinse tank contains dilute process solution, it will feed the acid
rinse tank with slightly acidic water containing nickel salts and
other process additives. Accordingly, the drag-in from the acid
rinse tank will partially replenish process chemicals in the nickel
tank. This is an example of reactive rinsing. Nickel rinsewater
does not harm the rinsing step after the acid bath, and it helps to
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HETHODS TO HINIHIZE WASTES FROM ELECTROPLATING FACILITIES
EDWARD R. SALTZBERG, PH.D.
conserve chemicals in the nickel plating tank and the freshwater
feed line to the acid rinse tank can be turned off to save 4 gpm.
This reactive rinsing application reduces water use and saves pro-
cess chemicals without harming the rinse step.
rinsing applications actually aid rinsing and, therefore, improve
plating quality.
Some reactive
IMPROVING RINSING EFFICIENCY THROUGH REACTIVE RINSING
example of how this technique can be used to improve rinsing
efficiency is also illustrated in Figure 7. Cleaner solutions are
alkaline--soapy and, therefore, difficult to rinse. Imagine trying
t o rinse off dishwashing detergent from dinner plates in cold water.
It doesn’t work very well because the detergent clings to the
plates. In a kitchen, hot water is used to rinse dishes, but hot
water is too expensive to use in plating cleaning lines because so
much costly energy is needed to heat the water. Therefore, platers
rinse cleaning solutions in cold water tanks and depend on the
subsequent acid solutions to neutralize any cleaners still clinging
to work. However, cleaner solutions are neutralizing agents and
they reduce the useful life of the acid baths.
a very efficient rinsing system.
A good
Clearly, this is not
Acids are expensive, and their useful life should be prolonged, not
reduced. Moreover, spent acid solutions are a costly waste manage-
ment problem, which is a second compelling reason to lengthen the
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METHODS TO MINIMIZE WASTES FROM ELECTROPLATING FACILITIES
-I BDWARD R. SALTZBERG, PH.D.
time of service of acid baths. The answer to this problem is almost
obvious -- use the acid rinse tank discharge to feed the cleaner rinse tank. If this is done, then neutralization of the drag-out
from the cleaning process will occur in the cleaner rinse tank and
not in the acid process tank. The parts get very well rinsed, and
the life of the acid solution is prolonged. In this case, another 4
gpm of water is saved because the fresh feed to the cleaner rinse
tank can be turned off.
COST OF REACTIVE RINSING APPLICATIONS Reactive rinsing is not
expensive. In this example, two thirds of the original flow rate
vas saved without purchasing any additional tanks. Some plumbing is
required but it is not extensive.
elevated slightly in order to gravity flow rinsewater to the
receiving rinse tank.
raised above the acid rinse, which in turn would be raised above the
cleaner rinse.
water through the three tanks. The system will work if the nickel
tank is raised or even tilted on standard building bricks, and the
acid rinse tank is elevated half that distance. If it is not prac-
tical to elevate the tanks, then inexpensive submersible pumps can
be used to move the rinsewater. In either case, reactive rinsing
costs less than $250 per application. In contrast, counterflow
rinsing, the conventional flow reduction technique, is many times
more expensive than reactive rinsing, and its application is con-
strained by space limitations.
The nickel rinse tank could be
In this example, the nickel rinse would be
Very little head pressure is needed to run rinse-
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METHODS TO WINIWIZE WASTES FROM ELECTROPLATING FACILITIES
EDWARD R. SALTZBERG, PH.D.
INTERPROCESS REACTIVE RINSING
rinsewater within a process and is a powerful technique for reducing
water consumption. An even more powerful technique is interprocess
reactive rinsing in which rinsewater is used across plating lines.
Figure 8 diagrams this reactive rinsing concept.
includes three plating lines:
Interprocess reactive rinsing reuses
The Figure
o Copper/nickel; o Zinc; o Anodizing.
The plating shop in Figure 8 would require 12 freshwater feed lines
(indicated by the numbers inside the rinse tanks). Using reactive
rinsing, eight of these feed lines could be shut off. Some of the
savings is from intraprocess reuse. For instance, used acid rinse-
water is fed to the alkaline cleaning water rinse tanks in both
metal-plating lines. Also, the anodizing rinsewater, which is very
acidic, is used to feed the caustic etch rinse tank. The rest of
the savings is due to interprocess reuse.
cleaning rinsewater is reused in the zinc cleaning steps and then
again to feed the anodizing rinse tank for the nonetch cleaner.
Rinsewater from the zinc process also is used in the rinse tank
following the anodizing dye step.
The copper/nickel
Rinsewater cannot be reused indiscriminately, because i t could
contaminate plating baths and effect plating quality. Accordingly,
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Non-Etch UP To Drain
’$ Fresh Water Feed Lines
h I
t To Drain To Drain
FIGURE 8 EXAHPLE OF INTERPROCESS “IVE BIRSIAG SYSTHn
METHODS TO nINIHIZE WASTES FRON ELECTROPLATING FACILITIES
EDWARD R. SALTZBERC, PH.D.
reactive rinsing should be done with the guidance of a chemist or
chemical engineer experienced with the firm’s specific plating
process. However, there are many applications for interprocess
reactive rinsing that are safe similar to the ones shown in
Figure 8.
COST SAVINGS OF REACTIVE RINSING
shops a considerable amount of money. The 12 rinse tanks in
Figure 8, for example, would use 23,000 gpd if they each ran at 4
gpm. Reactive rinsing could cut the number of freshwater feed lines
to four, and the shop would reduce its water use by 15,000 gpd. In
Boston, Massachusetts, for example, water costs approximately $1.50
per 1.000 gallons. Using this value, reactive rinsing would save
$22.50 per day or $4,950 per year.
program for this example is $1,750 ($250 per application) and would
pay for itself in reduced water costs in less than 4 months.
Clearly, reactive rinsing is a very good investment.
Reactive rinsing can save plating
The cost of the reactive rinsing
SUMMARY -- A STRATEGY FOR APPLYING THE NEW METHODS OF PLATING WASTE
CONTROL
Electroplating firms typically discharge large amounts of rinse-
water. In Cleveland, Ohio, for example, the average water consump-
tion at 22 electroplating firms is 18,500 gpd. The discharge
volumes at these firms range from 10,000 gpd at small shops to
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METHODS TO MINIMIZE WASTES FROM ELECTROPLATING FACILITIES
3 EDWARD R. SALTZBERG, PH.D.
150,000 gpd for very large electroplating operations.
electroplaters do not discharge large volumes of spent process
solutions. The Cleveland firms each generate about 60 gpd of spent
bath. However, the concentration of certain contaminants in spent
baths is much higher than it is in plating wastewaters.
concentration for each pollutant ranges up to 20 mg/l. A typical
spent acid solution, for example, will contain three times the
amount of zinc and nickel as a typical rinsewater discharge.
Conversely,
The average
Although there are other sources of pollution in plating shops such
as leaks from process tanks and floor drippings, the major sources
of pollution are drag-out in rinsewaters and spent process solu-
tions. The most practical approach to controlling plating waste is,
therefore, to concentrate on these two sources. However, the pol-
lution load characteristics of rinsewater and spent baths differ.
Rinsewaters are generally dilute but are large in volume, while
spent solutions are usually small in volume but concentrated.
Accordingly, these two pollution sources should be handled differ-
ently. It is the different characteristics of the two pollution
sources that is the basis for the new methods of waste control for
electroplating shops.
POLLUTION LOAD CHARACTERISTICS OF RINSEWATER Typically, the concen-
trations of individual metals in the untreated discharge from elec-
troplating range from 10 to 20 mg/l. EPA regulations for individual
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METHODS TO MINIMIZE WASTES FROM ELECTROPLATING FACILITIES
EDWARD R. SALTZBERG, PH.D.
metals are about 1 mg/1.6
captured before the work piece is rinsed, then the rinsewater could
meet EPA standards without treatment. Platers have long used a
single drag-out tank to minimize the contamination of rinsewater and
to conserve process chemicals. However, a single drag-out tank can
rarely achieve enough drag-out control to meet discharge limits.
The new methods carry the older drag-out control techniques a step
or two further in order to achieve extra control of drag-out.
Instead of one drag-out tank and counterflow rinse tank, the new
methods use two or more drag-out tanks and one rinse tank. In
addition, the new methods make extensive use of recycled rinsewater.
The basic premise of the new methods for controlling wastewater is
if the solution is dilute to start with, take steps to make i t even
less concentrated so that i t can be discharged without end-of-pipe
treatment .
Accordingly, if most of the drag-out is
POLLUTION LOAD CHARACTERISTICS OF SPENT SOLUTIONS Spent process
solutions are small in volume, but they are concentrated. There-
fore, they should not be handled like rinsewaters.
tional treatment system, spent baths are trickled into the firm's
rinsewater discharge for treatment with the rinses. In doing so,
the concentrated solutions are first diluted in the rinsewater and
In a conven-
then their contaminants are removed and reconcentrated. It is more
straightforward to treat the concentrated solution separately
through chemical physical means, or recover and reuse the solution.
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HETHODS TO HINIHIZE WASTES FROM ELECTROPLATING FACILITIES
3 EDWARD R . SALTZBERG, PH.D.
The premise for the new method of controlling spent baths is
discharge is already concentrated, try to concentrate it further for
reuse, batch treatment, or disposal.
The goals of the new methods of plating waste control are to avoid
wastewater treatment and to minimize hazardous waste problems while
meeting environmental regulations.
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METHODS TO MINIMIZE WASTES FROM ELECTROPLATING FACILITIES
EDWARD R. SALTZBERG. PH.D.
LIST OF REFERENCES
'EPA, Assessment of the Impacts of Industrial Dischargers on Public'ly Owned Treatment Works, NTIS No. PB 82-15395 8, February
902.
'EPA, Economic Analysis of Proposed Pretreatment Standards for Existing Sources of the Electroplating Point Source Category, EPA-230/1-78-001, December 1977.
'EPA, Control and Treatment Technology for the Metal Finishing Industry, EPA-625/8-82-008, January 1982.
EPA, Third Conference on Advanced Pollution Control for the Metal I
Finishing Industry, EPA-600/2-81-028, February 1981.
5EPA, Development Document for Existing Point Source Pretreatment Standards for the Electroplating Point Source Category, EPA-440/1-79-003, August 1979.
6Federal Register, Effluent Guidelines and Standards: Electroplating Point Source Category Pretreatment Standards for Existing Sources, Federal Register, 16(18): 1981.
942-9473, January 28,
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