Methods To Minimize Wastes From Electroplating Facilities · and necklaces can be gold or silver...

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


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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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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3


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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-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:

3 -6-

WETHODS TO WINIMIZE WASTES FROM ELECTROPLATING FACILITIES


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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3



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


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

3 -12-

METHODS TO MINIMIZE WASTES PROM ELECTROPLATING FACILITIES


( 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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i

METHODS TO I(INIl4IZE WASTES FROM ELECTROPLATING FACILITIES


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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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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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


(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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-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


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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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

3 -22-

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


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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3



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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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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-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


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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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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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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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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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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