managemen
t of metal-finishing sludge
-------
An environmental protection publication (SW-561) in the solid waste
management series. Mention of commercial products does not constitute
endorsement by the U.S. Government. Editing and technical content of this
report were the responsibilities of the Hazardous Waste Management Division
of the Office of Solid Waste Management Programs. *
Single copies of this publication are available from Solid Waste
Information, U.S. Environmental Protection Agency, Cincinnati, Ohio 45268.
-------
MANAGEMENT OF METAL-FINISHING SLUDGE
This publication (SW-561) was prepared by
E. P. CRUMPLER, JR.
U.S. ENVIRONMENTAL PROTECTION AGENCY
1977
-------
CONTENTS
SUMMARY 1
THE METAL FINISHING INDUSTRY 2
Sources of Waste 2
1977 Effluent Guidelines 3
Estimated Quantities of Sludge 4
WASTE TECHNOLOGY REVIEW 7
A. Disposal Technology Potentially 9
Environmentally Adequate
1. Encapsulation 10
2. Heat Treatment 12
3. Chemical Lining of Disposal Cells 15
4. Chemical Fixation 18
B. Water Treatment Processes Producing 21
Nonhydroxide Sludge
1. Sulfide Precipitation 22
2. Starch Xanthate Precipitation 24
C. Internal Recycle of Rinse Water Dragout 26
1. Evaporative Recovery 27
2. Reverse Osmosis 30
3. Ion Exchange 33
4. Electrodialysis 35
5. Freeze Separation 38
6. Solvent Rinsing 40
7. Ion Flotation 43
111
-------
Page
D. External Recovery of Segregated Metals 46
From Sludges and Solutions
1. Integrated Treatment 47
2. Kastone Treatment Process 49
3. Single Metal Sludge Recovery 51
4. Spent Bath Recovery 53
E. Recovery of Metals from Mixed Hydroxide 55
Sludges
1. Solvent Extraction 56
2. Electrochemical and Roasting 58
REFERENCES 60
LIST OF TABLES
Table
1. Estimated Aggregate Electroplating Sludge. ... 6
Composition
2. Matrix of Sludges and Processes Under 19
Study by Corps of Engineers, Vicksburg, Miss..
LIST OF FIGURES
Figure
1. Solubility of Metal Hydroxides vs pH 5
2. Water Solubility of a Heat Treating 13
Plating Sludge
3. Limestone Containment of Heavy Metal Sludge. . . 16
4. Closed-Loop Evaporative Recovery System 28
5. Closed-Loop Reverse Osmosis Recovery System. . . 31
6. Closed-Loop Electrodialysis Recovery System. . . 36
7. Solvent Rinsing System 41
8. Integrated Waste Treatment System 47
IV
-------
ABSTRACT
The disposal of metal-bearing sludges from treatment of metal
finishing wastewaters is causing increased concern. Implementation
of metal precipitation as the best available technology to meet
effluent guidelines will increase the amounts of sludge requiring
disposal. This report discusses the state-of-the-art of technology
which can potentially manage the sludge. Disposal techniques, recycle
and waste reduction technology are reviewed. The major advantages
and disadvantages of each technique are presented. Current EPA research
and demonstration efforts are also discussed.
-------
The Metal Finishing Industry
Metal finishing operations are found throughout the primary
metal and metal fabrication industries. The metal finishing
process contains any or all of the following operations:
1. Cleaning and pickling
2. Buffing and polishing
3. Electroplating
4. Immersion plating (metal deposit by
chemical exchange)
5. Phosphating and oxidizing
6. Painting
7. Electropainting
8. Anodizing
9. Annealing and case hardening
The metal finishing industry consists of two types of shops:
captive and job. A captive shop is a part of a larger manufacturing
operation requiring metal finished parts. The automobile industry is
an example. A job shop performs contract metal finishing on parts
owned by its customers. Its sole business is metal finishing. The
technology discussed in this report applies to both captive and job
shops.
Sources of Waste
Metal finishing operations are batch operations. The parts to be
treated are immersed in a chemical bath where one step in the finishing
process takes place. After the treatment is completed, the part is
removed and the process solution is rinsed off before the next step.
An example of a typical metal finishing line is the plating of an auto-
mobile bumper. The basic steel bumper passes through the following steps:
1. Solvent cleaning
2. Acid cleaning
3. Zinc plating
4. Copper plating
5. Nickel plating
6. Chromium plating
After each step, the bumper is rinsed with water to remove the process
solution. The rinse minimizes contamination of the subsequent process
solutions as well as maintaining a quality finish. The large volume of
contaminated rinse water containing dilute quantities of process solutions
(dragout) is one source of waste.
-------
A second source of waste is the dumping of spent process solutions.
Process baths accumulate impurities during their use and bath additives
deteriorate with time. In many cases, these baths cannot be satisfactorily
reclaimed and require disposal. This is a major source of waste.
Other wastes in metal finishing shops come from process spills, tank
leaks, and air pollution control systems. All of these wastes contain
metals, acids, bases, organics and solvents in solution. To meet discharge
water standards, treatment of some type is necessary to remove most
of the pollutants.
1977 Effluent Guidelines
The 1977 Effluent Guidelines for the Electroplating Industry
identify the Best Practical Control Technology Currently Available
(BPCTCA). The waste treatment process produces a sludge high in
metal content. The BPCTCA treatment process is described below:
a. The hexavalent chromium stream is segregated for
chemical reduction to trivalent chromium. This
reduction is most frequently accomplished by using
sulfur dioxide gas. Other reducing agents may be
used such as sodium bisulfate, ferrous sulfate, or
sulfuric acid, but sulfur dioxide is preferred due
to its lower cost. The chemical reduction is
necessary since hexavalent chromium will not
precipitate by pH adjustment.
b. The cyanide bearing streams are segregated for
chemical destruction of the cyanide. The cyanide
is oxidized by use of chlorine gas or sodium
hypochlorite in an alkaline solution. The cyanide
radical (CN+) is broken down into nitrogen and
carbon dioxide which are vented as gases. Metal
hydroxide solids are also formed during the
destruction reaction due to the alkalinity of
the solution.
c. The treated chromium and cyanide streams are
combined with the remaining acid-alkali waste
waters and pH is adjusted to the 7.0 to 9.5 range.
The pH adjustment causes the metal ions to preci-
pitate as hydrated metal oxides. Lime is the
preferred pH adjustment reagent due to both lower
cost and superior settling properties. The
solubilities of most metals are at their minimum
-------
in the pH range of 8.0 to 11.0 as illustrated in
Figure 1. The water-sludge mixture passes into
a clarifier where sludge thickening occurs. The
decanted water is passed through a sand filter
before discharge to receiving waters. The sludge,
normally two to three percent solids, is usually
disposed of in a lagoon, drying bed, or a land-
fill. In some cases, the sludge may be dewatered
to reduce the amount of water to be handled. The
damage potential inherent in disposal of the water
treatment sludges involves resolubilizing of the
metal hydroxides in water or leachate with pH's
at or below 7.0. The solubility curve shown in
Figure 1 indicates the rapid increase in metal
solubility as the pH drops. Even rainwater at
a pH value of 5.5 to 6.5 will accelerate
resolubilization.
The metal content of a typical electroplating
sludge is shown in Table 1. Eighty-five percent
of the sludge, on a dry basis, is estimated to
be metal hydroxides.
Estimated Quantities of Sludge
Battelle estimates that 19,792 metric tons (dry weight) of water
treatment sludge were produced in 1975 from United States job shops.
The 1977 estimate is 56,549 metric tons and the 1983 estimate
is 74,080 metric tons (dry weight).1 Although no estimate of the quan-
tities of sludge produced by captive shops was made, the tonnage is
expected to be much greater.
This quantity of metal-containing sludge presents a major
environmental problem for disposal. Surface and groundwater will
certainly be threatened by inadequate disposal.
This paper will attempt to review the significant technological
alternatives potentially capable of addressing the wastewater sludge
problem. It is part of the Hazardous Waste Management Division's mission
to identify an economical technology for (1) disposing safely of these
sludges, (2) recycling the wastes, or (3) eliminating the waste.
-------
Figure 1. Solubility of Metal Hydroxides vs. pH*
1.0
too
a
•»
.— I
cd
-t->
0)
0.1
O
I?
3 o.oi
o
CQ
0.001
10
u
12
pH of Solution
*Development document for proposed effluent limitations guidelines
and new source performance standards; copper, nickel, chromium, and zinc
segment of the electroplating point source category. Washington, U.S.
Environmental Agency, Office of Air and Water Programs, Effluent
Guidelines Division, Aug. 1973. 206 p.
-------
TABLE 1
Estimated Aggregate Electroplating Sludge Composition
Compound
Cu (OH)
Cr (OH) 3
Ni (OH) .
Zn (OH) 2
Cd(OH)2
Impurities
Total
Dry Weight %
12.3
14.8
39.1
17.1
1.7
15.0
100.0
Metal
Cu
Cr
Ni
Zn
Cd
Non-metals
Total
Dry Weight %
8.0
7.5
21.0
11.0
1.0
51.5
100.0
*Hezir, J. S. Impacts of new water pollution
regulations on solid waste management: New York City.
Washington, U.S. Environmental Protection Agency, Office
of Solid Waste Management Programs, Sept. 1973. 103 p,
(Unpublished report.)
-------
WASTE TECHNOLOGY REVIEW
For purposes of presentation, the various technologies can be
grouped into five categories. Each category represents a specific
approach to solving the metal hydroxide sludge disposal problem.
1. Disposal techniques which have the potential
for environmentally adequate disposal of metal
hydroxide sludges,
2. Processes that produce a modified metal containing
sludge,
3. Internal recycle processes for recovery of chemicals
removed in rinse water,
4. Recovery of metal from mixed metal hydroxide sludges,
and
5. Recovery of metals from segregated solutions and
sludges.
Detailed information on each process containing descriptions, known
state-of-the-art, economics, and major advantages and disadvantages
are presented.
Some processes which are being developed for electroplating
waste treatment are not included in this assessment. Specifically,
the following have not been addressed:
1. Cyanide destruction by ozone,
2. Cyanide destruction by electrolysis,
3. Hexavalent chromium reduction using iron, and
4. Waste-plus-waste techniques developed by the
Bureau of Mines.
These processes, while having operational cost advantages
over the 1977 BPCTCA, do not affect the composition or quantity of
hydroxide sludge formed. These are only modified destruction
methods, resulting in the same sludge.
-------
In a similar manner, the various techniques to reduce rinse
water consumption are not presented in this report. Rinse water
reduction will affect the size of the wastewater treatment facilities
and affect treatment economies, but the quantities of sludge produced
are not reduced, since the dragout from the plating bath is not
reduced. Techniques such as spray rinsing, reduced plating bath
concentration, spill prevention controls, and improved housekeeping
are not presented since these do not represent new technology. These
are well developed process modification techniques which require
minimal capital investment and can reduce sludge formation only to
a certain degree.
-------
A' Disposal Technology Potentially Environmentally Adequate
Four techniques have been identified as having the potential to
dispose of electroplating wastewater sludge. These are:
1. Encapsulation
2. Heat Treatment
3. Chemical Lining of Disposal Cells
4. Chemical Fixation
Individual summaries follow.
-------
ENCAPSULATION
Description
Encapsulation of a waste involves packaging and containment of
a specific quantity of a hazardous waste to prevent leaching. The
technique can range from disposal in sealed concrete crypts or
missile silos to the two-stage process being developed by TRW System
Inc., under EPA contract.2-*3 The TRW process incorporates the waste into
a solid inner matrix to reduce the solubility and the surface area
available for dissolution. The solid matrix is then coated with an
impervious encapsulation medium. The encapsulation medium water-
proofs the inner matrix and protects it from external physical and
chemical attack after disposal. It should be noted that the current
practice of burying waste material in steel drums, without further
encapsulation is not adequate, since the steel is readily corroded,
releasing the hazardous contents.
State-of-the-Ar t
Hazardous Wastes are being disposed of in concrete underground
missile silos in Idaho which are expected to be environmentally sound.
However, this technique is dependent on the availability of abandoned
underground military installations and is, therefore, not a generally
usable disposal method. Several Mississippi disposal sites are using
sealed concrete culvert pipe to dispose of pesticide containers and
residues.2 However, this technique is considered a temporary method
until a more permanent disposal method can be devised.
The TRW work being sponsored by the Solid and Hazardous Waste
Research Division, Cincinnati, is currently examining a series of
organic polymers as encapsulating materials. Polybutadiene resins
are being tested as inner matrices, and polyvinylchloride plastisols,
epoxies and polyethylene resins are being evaluated for use as outer
encapsulation media. The materials have been tested in bench-scale
studies and results have been promising. Current activities are
encapsulation of actual industrial wastes and testing under varied
environmental conditions.
10
-------
Economics
TRW has estimated the cost of the organic resin encapsulation
process to be $85.10 per ton of dry waste.3 Work now underway is
focused on reduction of costs by the use of waste polymers. The
hoped-for reduction in cost is expected to bring the unit cost down
to approximately $40/ton.3
Advantages
1. Encapsulation may be the only usable method for ultimate
disposal of environmentally persistent toxic elements
such as arsenic.
Disadvantages
1. Encapsulation in concrete pipe or crypts may not be an
environmentally sound practice.
2. The TRW technique appears to be expensive and complex.
3. Land disposal is still required.
4. No resource recovery is practiced.
11
-------
HEAT TREATING OF SLUDGE
Description
High temperature heat treatment is capable of reducing the
solubility of metal finishing sludge, rendering the sludge
potentially safe for land disposal. The sludge could be heated
to a temperature where the metal hydroxide would thermally convert
to metal oxides. The oxides of metals tend to be much less water
soluble than their hydroxides. The sludge would take on the form of
a slag with a reduced volume, and should present less of an environ-
mental hazard after disposal.
State-of-the-Art
Laboratory work to determine the conditions required to convert the
metal hydroxides to metal oxides has been done in Zurich, Switzerland,
by Dr. R. Braun of EAWAG.1* Actual plating sludges were subjected to
controlled temperature conditions followed by water solubility tests.
A plot of the temperature-solubility relationship for an actual plating
shop sludge is shown in Figure 2. From his laboratory work, Dr. Braun
concluded:
1. 1,100 to 1,200 C temperatures are required to achieve
chemically stable, water insoluble structures.
2. Treatment of metallic sludges in conventional incinerators
at 800 to 1000 C is inadequate to achieve sufficient
reduction in water solubility.
Economics
From the laboratory work, Dr. Braun concluded that a full-scale
heat treatment process would be expensive although no cost estimates
are given.
Advantages
1. The solubility of the metals is greatly reduced by
converting to metal oxides, thus reducing the potential
leachability.
2. The volume of the sludge is reduced by drying.
12
-------
O
CO
(M
200 300 400 500 600 700 800 900 1000 1100 1200 1300
TEMPERATURE, C
Figure 2 Water Solubility of a Heat Treated Plating Sludge.*
*Braunf R. Problems in the removal of inorganic
industrial slurries. In_ Wastes: solids, liquids a,nd gases,
ACHEMA Symposium, 1970, Frankfurt. New York, Chemical
Publishing Company, Inc., 1974. p. 203.
13
-------
Disadvantages
1. The cost to heat treat sludges is expected to be
expensive.
2. Land disposal of the treated sludge is still required.
3. No recovery of resources is practiced.
4. Heat treating appears to be energy intensive.
14
-------
CHEMICAL CONTAINMENT
Description
One potential environmentally adequate method to dispose of
electroplating wastewater sludge involves surrounding the sludge
with a medium which will ensure alkalinity of any liquids coming
into contact with the sludge. The object is to keep the pH of any
leachate within a range of 7.0 to 10.0 to minimize the metal solu-
bility. By maintaining this pH range, the rate of release of the
metals is lowered to a level which will not impact the groundwater
significantly.5 This technique cannot provide total containment
of the sludge since the metal hydroxides cannot be maintained totally
insoluble by pH adjustment.
To illustrate the technique, a sketch of a disposal method
currently being used at the Armstrong Cork Company Carpet plant near
Lancaster, Pennsylvania, is shown in Figure 3. The Carpet Plant
accumulates a heavy metal sludge mixed with rubber latex in storage
tanks at the plant site until sufficient quantity is obtained to fill
a sludge cell. A trench is opened about every six months, lined with
a minimum of three inches of limestone and the sludge mixed with fly
ash or soil is dumped into the trench. The sludge is immediately
covered with soil and contoured to minimize percolation of runoff
through the trench.
State-of-the-Art
The site at Lancaster, Pennsylvania, has been in operation since
March 1971. Quarterly testing of the groundwater at the site has
revealed no increase in heavy metals. The company has been unable
to obtain any samples to date from test lysimeters buried under two
of the beds. The Pennsylvania Department of Environmental Resources
is requiring the separate landfilling of heavy metal sludge using
the limestone envelope for all new landfill permits.6
Economics
No data are available on the increase in land disposal cost due
to use of this technique. Cost data are needed.
15
-------
-Excess Cove r Final Contour
Top Cover
Top
-SLUDGE -
3" min. Limeston^-
Tailings ' >
(Dust Jo 3/16")
Figure 3 Limestone Containment of Heavy Metal Sludge
Water Level.
*Drawing no, MR-A-12, Lancaster, Pa., Armstrong Cork
Company, Central Engineering Department, 1971.
-------
Advantages
1. Limestone containment is a land disposal technique which
can be applied in a very short time due to its simplicity.
2. Proper inventory of sludges being buried would allow for
future recovery.
Disadvantages
1. This technique requires land for disposal.
2. The environmental adequacy has not been fully demonsti ated,
17
-------
CHEMICAL FIXATION
Description
Chemical fixation uses a physical-chemical matrix structure
to tie up hazardous liquids and solids for disposal. The matrix
structure prevents or retards leaching of the waste into the
environment. A number of commercial fixation processes are avail-
able. These processes use materials such as cement, fly ash, and
limestone with the addition of organic polymers or inorganic sili-
cates to produce a friable, soil-like material. The fixation
product may or may not be suitable for landfills or construction
materials.
State-of-the-Art
A number of firms offer chemical fixation commercially. Some
processors have portable equipment which can be used for on-site
treatment at a customer's plant.7 Units are also sold for permanent
installation at sites requiring continuing processing of wastes.8
The significant gap in the state-of-the-art is the lack of
supportable data which accurately identifies the effectiveness of
the fixation, i.e., the leachability of the fixed product. A joint
EPA-Army Corps of Engineers project to identify the pollution potential
of a number of chemically fixed industrial wastes is being conducted
at the U.S. Army Engineers Waterways Experiment Station, Vicksburg,
Mississippi.9 Ten industrial sludges, including an electroplating
sludge are being fixed by seven different commercial fixation processes.
A matrix of the sludge-fixation process combination being studied is
shown in Table 2. Four of the seven processes will be used on the
electroplating sludge chosen for the study.
Experimental work is being done both in the laboratory and in
the field. The project is expected to be completed by June 1977.
The environmental adequacy of chemical fixation of electroplating
sludges will be known with more certainty after completion of the
project.
18
-------
Sludges
TABLE .2
MATRIX OF SLUDGES AND PROCESSES
UNDER STUDY BY CORPS OF ENGINEERS. VICKSBURG. MISS.
Chemfix Lancy NECO IUCS
WEHRAN
Dravo
TRW
1. Flue gas desulfurization-
lime scrubber-Eastern Coal
2. Electroplating
3. Nickel -cadmium battery
4. Flue gas desulfurization
limestone scrubber-eastern
coal
5. Flue gas desulfurization-
double alkali -eastern coal
6. Flue gas desulfurization-
limestone scrubber-western
coal
7. Pigment manufacturing
8. Chlorine manufacturing
sludge
9. Flue gas desulfurization
double alkali -western coal
0. Calcium fluoride manufacturing
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
w
X
X
X
X
X
VO
-------
Economics
The charges for fixation of industrial wastes will vary widely
depending on a number of factors. Among the factors determining cost
are the process selected, the character of the waste, whether equipment
is purchased or provided periodically by the vendor, trucking charges,
and landfilling costs. A typical price range quoted by several
processors is $8.00 to $20.00 per metric ton of waste. 11J 12.) i1* The
disposal site for the fixation product is supplied by the waste generator,
Advantages
1. Chemical fixation is commercially available from several
sources.
2. Applicable to both large and small sludge generators.
3. Cost of fixation is reasonable.
4. No capital is tied up other than land for disposal.
5. Wastes may be stabilized so that metal ions are not
available (readily) to the environment.
Disadvantages
1. Environmental adequacy of fixation products not yet fully
established, although the product is certainly environmentally
superior to raw sludge.
2. Landfilling is still required.
3. No resource recovery is practiced.
4. Sludges must be pumpable to feed mixing and discharge
equipment.
20
-------
B. Water Treatment Process Producing a Nonhydroxide Sludge
Two wastewater treatment processes have been identified which
produce a nonhydroxide metal sludge. These are:
1. Sulfide Precipitation
2. Starch Xanthate Precipitation
Individual process summaries follow.
21
-------
SULFIDE PRECIPITATION
Description
The sulfides of many metallic ions have very low solubilities
in water, usually much lower than the corresponding hydroxide. An
example is nickel. Nickel hydroxide has a water solubility of
1.3xlO-lgm/l @ 18 C.11 Nickel sulfide has a solubility of
3.6xlO-2gm/l @ 18 C. 1J The sulfide is only 27 percent as soluble as
the hydroxide. A soluble sulfide such as ferrous sulfide is added to
the wastewater at a pH range of 5 to 7. The heavy metals form sulfides
which precipitate readily. The sludge formed is reported to be more
dense than a corresponding hydroxide and easily dewatered to 50 percent
solids with gravity filtration.12
The long-term stability of the sulfide sludge is not known.
Speculation on the weathering of sulfide sludges indicates that sulfuric
acid might be formed by oxidation and metal release would follow.5
State-of-the-Art
The process has been demonstrated on a pilot-scale. The number of
installations, if any, is not known. The Industrial Waste Treatment
Laboratory, Edison, New Jersey, has granted $30K to the Metal Finishers'
Foundation to conduct a pilot plant investigation designed to optimize
the process and evaluate economic feasibility of a novel sulfide
precipitation process. This project is currently in the draft report
stage. The Edison Lab intends to fund a full-scale demonstration in
the near future.12
Economics
Exact data comparing the costs of hydroxide precipitation vs
sulfide precipitation are not available. The Edison grant work will
give detailed projections of costs.
Advantages
1. Sulfide Precipitation will give better water effluent
quality than hydroxide precipitation.
2. Sulfide sludge is reportedly easier to dewater than
hydroxide sludge.
22
-------
Disadvantages
1. A sludge is formed which requires disposal.
2. No recovery of metals is practiced.
3. The long-term stability of the sludge under landfill
conditions is unknown.
23
-------
STARCH XANTHATE PRECIPITATION
Description
A process to effectively remove metal ions from solution has
been developed at the Northern Regional Laboratory of the United States
Department of Agriculture. An insoluble cross-linked xanthate compound
derived from corn starch acts as an ion exchange resin to remove heavy
metals in water. The starch xanthate is slurried with vigorous agitation
into the metal bearing solution. A contact time as short as five minutes
is sufficient to ensure removal. For example, a solution containing
31,77001^/1 (ppb) of copper was reduced to 22qg/l (ppb) of copper in
five minutes. 13 The insoluble starch settles very rapidly once agitation
is stopped. Residual heavy metal concentration in solutions treated are
typically much lower than existing effluent guideline concentrations.
The metals are reported to be reclaimable from the starch solids
by treatment with nitric acid. The starch can be reused, but must be
processed to regenerate the active site cross-linking. The stability
of the starch-metal complex under landfill conditions has not been
studied but speculation seems to indicate that the organic structure
would break down rapidly and release the metals to the environment.
State-of-the-Art
Starch xanthate treatment development is still in the laboratory
stage. No full-scale applications are known. The Industrial Waste
Treatment Laboratory, Edison, New Jersey, has granted $39K to the United
States Department of Agriculture, Peoria, Illinois, to conduct a pilot
plant evaluation. This project is expected to be completed by July 1976.
Economics
The United States Department of Agriculture estimates the cost
to manufacture starch xanthate at $0.20 to $0.22 per pound.13 The
claimed high capacity to bind metals indicates that the starch process
may provide significant savings over conventional destruction processes.
The Edison grant work due July 1976 will provide additional cost
projections.
Advantages
1. Initial cost estimates indicate a potential reduction
in waste treatment costs.
24
-------
2. Metal removal from the starch compound is efficient.
3. The technique may have potential for treatment of
segregated metal streams and subsequent recovery
of pure metals.
Disadvantages
1. The ion exchange reaction is non specific for metals
in a mixed metal solution.
2. The sludge is probably unsuited for land disposal due
to its organic nature.
25
-------
C. Internal Recycle of Rinse Water Dragout
Seven processes which can recycle the plating metal dragout have
been identified. These processes are in various stages of development
ranging from bench-scale to widespread commercialization. These are:
1. Evaporative Recovery
2. Reverse Osmosis
3. Ion Exchange
4. Electrodialysis
5. Freeze Separation
6. Solvent Rinsing
7. Ion Flotation
26
-------
EVAPORATIVE RECOVERY
Description
Evaporative recovery of processing chemicals from plating rinse
waters is an established method for reducing electroplating effluents.
Evaporative recovery concentrates rinse waters containing the dilute
plating chemicals up to the concentration of the plating bath and
returns this concentrated solution to the plating tank. The evaporated
water is condensed and reused in the rinsing tanks. Figure 4 illus-
trates the principle of evaporative recovery in a closed loop counter
current rinsing system. The closed loop system is capable of recovering
for reuse in excess of 95 percent of the chemicals lost from dragout.
No external rinse water is added except to replace losses to atmospheric
evaporation and spills. The only chemicals supplied to the plating bath
are those needed to replace what is actually deposited on parts and that
lost by spillage.
In metal plating systems, dragout serves to purge baths of
contaminants resulting from the processing operation. The buildup of
impurities, which can cause serious quality problems in evaporative
recovery operations, may be prevented by the incorporation of techniques
such as ion exchange, filtration, precipitation, and activated carbon
treatment.
The benefits of this type of operation are the elimination of
contaminated rinse water discharges which reduces metal sludge formation
in wastewater treatment, the recovery and reuse of processing chemicals,
the reduction in water consumption for rinsing, and the production of
a small amount of waste from the associated impurity purge system.
State-of-the-Art
Evaporative recovery is a fully developed technology with an
estimated 200 to 300 installations in the United States.11* EPA's
Industrial Waste Treatment Research Laboratory at Edison, New Jersey,
has a grant in progress to demonstrate Evaporative Recovery of
chromium rinse waters at Advanced Plating Company, Cleveland, Ohio.
This demonstration will establish the effectiveness and economics
of treating chromic acid rinse waters with a new evaporator design
expected to be attractive for small platers. The project report is
expected in April 1976.
27
-------
EVAPORATOR
Recovered
Chemicals
Work Flow
00
Dragout
Water
Recovery
ff
PLATING TANK
RINSE TANKS
Figure 4 Closed-Loop Evaporative Recovery System
-------
Economics
A typical evaporator unit costs $37K installed.15 The operating
cost of a unit sized to produce 10 gpm of distilled water for reuse
will be approximately $2.50 per 1000 gal. of water distilled.15 The
savings in chemical cost will often offset the operating cost. One
installation operating on a chromic acid bath has an annual operating
cost of $9,301 per year but recovers $61,380 per year of chromic acid.16
Adding an additional savings of $30,073 per year in reduced wastewater
treatment cost, the net annual savings to the operation is $82,152. l 6
Current economic data for an evaporative recovery system in a small
plating shop will be available from the EPA/Advanced Plating Demonstration
in April 1976.
Advantages
1. The loss of valuable chemicals is eliminated.
2. The water treatment sludge from treating the rinse
water is eliminated. Treatment of a bleed stream
is necessary to remove buildup impurities.
3. Water use in the rinsing operation is greatly reduced.
Disadvantages
1. Application to many plating baths is limited due to the
buildup of degraded organic additives and heat sensitivity
of some bath components.
2. Energy requirements are high where a waste heat source
is not readily available.
3. Initial capital costs may be high for a small shop.
29
-------
REVERSE OSMOSIS
Description
Reverse osmosis is a membrane technique which accomplishes pollution
abatement by purifying the rinse water for reuse and concentrating the
dragout chemicals for return to the plating bath. This technique is
normally used in conjunction with counter current rinsing to minimize
water volume. The system, when set up in a closed loop (see Figure 5),
is designed to recover 95+ percent of the chemicals lost in the rinse
water for reuse in the plating bath. No external rinse water is added
except to replace evaporative and spill losses. Chemicals are added
to the plating bath to replace only the chemicals actually plated onto
parts plus any spills.
In reverse osmosis, pressure is used to force the water molecule
through a membrane, while the larger plating chemical molecules are
rejected and concentrated. The structure and durability of the membrane
is the key to successful applications.18 Use of a filter ahead of the
membrane is required to prevent blinding of the membrane with solid
particles. Impurity buildup in the closed system may be reduced by ion
exchange, chemical precipitation and activated carbon.
This system impacts on sludge formation by reclaiming the plating
chemicals and reducing water treatment sludge. Reduction in water
consumption is an added benefit.
State-of-the-Art
The technology of reverse osmosis is in a relatively advanced state
of development. Commercial units are available and electroplating rinse
water recycle installations are operating with varying degrees of success.
The lack of membrane materials capable of handling the wide pH and tempera-
ture range encountered in electroplating baths has hindered widespread
use of reverse osmosis. New membranes are being developed with assistance
from .EPA. The Industrial Waste Treatment Research Laboratory at Edison has
a development grant to investigate new membranes at Celanese Corp. Also,
the Cincinnati Industrial Waste Treatment Research Laboratory has a pilot
plant study grant to evaluate new membranes. In addition, Edison has
two current demonstration grants to evaluate reverse osmosis on zinc
cyanide plating rinse water and on nickel plating rinse water. Completion
of the nickel recovery system demonstration was scheduled for April 1975
and the zinc cyanide demonstration for October 1975.
30
-------
R. O. Cell
1
Membrane
*s
Recovered
Chemicals
/
fc
A
Chemicals /
/
ffi ^
Pressure /
H
H
•m
A
!
i
t
>
Water
^
^
* Lo
Pressure
( Rinse
. Water
Work Flow
1
.__,
1
1
1
1
.
'
.
1
1
1
to 1 1
Dragout ' / • *-
^--
i
^•^^ i
L_i ff
^
Water
Recovery
PLATING TANK
RINSE TANKS
Figure 5 Closed-Loop Reverse Osmosis Recovery System
-------
Economics
Capital and operating costs compared to evaporation are relatively
low for reverse osmosis technology. One installation returning 500 gal.
per day of concentrated nickel sulfate solution to the plating bath
cost $10K to install and $13 per day to operate.19 A recovery of $548
per day of nickel sulfate from the rinse waters produces very favorable
economics. Current data on economics will be available from the two
EPA sponsored demonstrations.
Advantages
1. Valuable chemicals are recovered and recycled to the
plating process.
2. Sludge formation at wastewater treatment is reduced
or eliminated. Treatment costs are also reduced.
3. Water use in the rinsing operation is greatly reduced.
4. Energy consumption is low.
Disadvantages
1. Like all recycle systems, closed loop reverse osmosis is
susceptible to buildup of impurities.
2. Solids in rinse water will "blind" the reverse osmosis
membrane unless filtered out.
3. Current membranes have limited operating ranges for
temperature, pH and chemical attack.
4. Maintenance costs and downtime tend to be excessive.
32
-------
ION EXCHANGE
Description
Ion exchange is a well developed process which uses a packed bed
of resin to selectively capture anions or cations from solution. The
retention of specific ions results from the exchange of one ion from
the surface of the solid resin particle for another in solution. A
specific example is the two-step recovery of chromic acid from a
rinse water.17 The chromic acid is removed from rinse water by an
ion exchange resin as follows:
+ 2HOR > CrO=R + 2HJD
Where: R=ion exchange resin.
After the resin is saturated with chromate, sodium hydroxide solution
is used to regenerate the resin as follows:
2NaOH + CrO.=R > Na0CrO. + HO=R
4 24
The regenerated sodium chromate is passed through a cation exchanger
to yield chromic acid suitable for reuse in the plating operation:
NA2C04 + 2H=R > H2Cr°4 + 2Na=R
The cation exchanger resin is regenerated with an acid such as hydrochloric:
2HCL + 2Na=R > 2H=R + 2NaCl
Ion exchange is a versatile, inexpensive technique which can be
applied to many dilute metal bearing wastes in metal finishing. Most
ion exchange operations are batch-wise processes going through the ion
exchange and regeneration cycle consecutively. Continuous ion exchange
units are available but are more capital intensive and complex to operate.
33
-------
State-of-the-Art
Ion exchange technology is highly developed with general application
installations numbering in the millions. Ion exchange has been used in
electroplating applications for a number of years handling a variety of
tasks. However, ion exchange is limited to dilute solutions since the
resins are destroyed by excessive pH ranges.17 In addition, cyanides
are a problem since anion resins are readily poisoned by cyanide
levels above 200mg/l.17 EPA has funded a full-scale demonstration at
the Singer Company, Elizabeth, New Jersey, to recycle cyanide, chromium
and other toxic materials by ion exchange and ultra filtration. This
project was funded for $29K and is scheduled to be completed in November
1976.
Economics
Capital expenditure for ion exchange would be expected to vary greatly
since each system must be engineered for the particular application.
Operating cost should be moderate, the regeneration chemicals being the
major cost. Energy costs are low. A detailed economic study will be
available from the EPA demonstration at the Singer Company in November
1976.
Advantages
1. Moderate capital and operating expenditures are required.
2. Recycle of chemicals can be practiced.
3. Sludge formation can be reduced by recycling.
D isadvantages
1. Ion exchange is applicable to dilute metal wastes only.
2. Resin beds are rapidly destroyed by strong oxidizing and
reducing conditions.
34
-------
ELECTRODIALYSIS
Description
Electrodialysis is a membrane cell process which can be applied
to recover plating chemicals from rinse water. The electrodialysis
cell consists of a series of compartments separated by alternating
anion and cation permeable membranes (see Figure 6). A direct
current is passed through the cell which causes the positive and
negative ions to migrate through the membranes. The correct placing
of the alternating membranes in relation to the electrical current
flow causes the alternating cells to become more concentrated or less
concentrated respectively. The cells are drawn off to produce deionized
water for recycling and a concentrated solution. The concentrated chemi-
cal solution is returned to the plating tank and the deionized water is
reused in the rinsing tanks.
In the closed loop configuration, chemicals are added to the plating
bath to replenish the chemicals actually plated on the work pieces (or
spilled). Water is added only to make up for spills and losses due to
evaporation. As in any membrane process the key to successful operation
is the membrane material.
A filter is used ahead of the cell to protect the membranes, although
membrane blinding is not as serious in electrodialysis as in reverse osmosis.
Impurity buildup in the system may be handled by ion exchange, chemical
precipitation or activated carbon.
State-of-the-Art
Electrodialysis for rinse water recovery is in the early stages of
demonstration on a full scale. The Industrial Waste Treatment Research
Laboratory at Edison, New Jersey, has two grant programs in progress to
demonstrate electrodialysis. One demonstration at the Keystone Lamp
Manufacturing Corporation, Slatington, Pennsylvania, will use electro-
dialysis to recover cyanides from rinse water to produce zero discharge.
This demonstration, funded at $15K, is scheduled for completion December
1975. The second demonstration, at the Risdon Manufacturing Company,
Waterbury, Connecticut, will demonstrate electrodialysis recovery of
nickel rinse water. The Risdon demonstration is funded at $25K and is
scheduled for completion June 1976.
35
-------
Recovered
Chemicals
Cu(CN)2
ELECTRODIALYSIS CELL
t t
4-"-| ----A---7 ,
(q) ! (A) 1 (c) ; (A) 1 !
Cathode ^ Cu
^"^ r-TVT~ -
CJN
CNr_3
i
4 Cu Anode '
• J CN -> ,
' r + '
Cu (
^ ^ T T ^ x-\ ' Water
• | ! * I (AJ--Anion , Recovery
L ' ' ' J Permeable
1 (G)- Cation t
I Permeable
' Rinse r i
. Water j
Work Flow ! i
fc. .
D]
r
F • '
1 ^___*-_ -
^^^ ! _^-_J^
! ,
____ L—^M
PLATING TANK
RINSE TANKS
Figure 6 Closed-Loop Electrodialysis Recovery System
-------
Economics
Full-scale operating costs and efficiencies are not available at
this time. The two EPA funded demonstrations will develop economic
and operating data.
Advantages
1. The plating chemicals in rinse water are recovered.
2. Sludge formation at wastewater treatment is reduced
or eliminated.
3. Water usage is reduced in the rinsing operation.
Disadvantages
1. The closed loop system is susceptible to build-up
of impurities.
2. Considerable electrical energy is consumed.
37
-------
FREEZE SEPARATION
Principle
Freezing of wastewater to separate pure water and concentrate the
dissolved waste is a technically feasible method of recycling dragout
in rinse water. When water freezes, the solute is excluded from the
ice crystal. When the ice is separated and remelted, relatively pure
water is obtained. The remaining unfrozen solution becomes more concen-
trated due to the loss of water. A freezing unit would be required for
each plating bath and rinse system analogous to an evaporation or reverse
osmosis unit.
State-of-the-Art
Freezing technology is quite new and has not been applied to a full
scale plating line. One manufacturer has reported successful completion
of pilot-plant work on electroplating solution.20 Full-scale applica-
tions of freeze separation have been limited to sea water desalinization.
Economics
Capital cost of current freeze separation units ($200 to $300K) is
the major stumbling block to application for electroplating chemical
recycling. Operating costs are also said to be significantly lower than
evaporative separation due to lower energy consumption per pound of
water separated.20 Specific data on electroplating chemical recovery
is lacking. However, unless the cost of freeze separation units becomes
much lower, this technique will be of little interest to all but a few
large electroplaters.
Advantages
1. The plating chemicals are recovered and recycled.
2. Heat sensitive plating solutions can be recycled.
3. Sludge formation at wastewater treatment is reduced
or eliminated.
4. Water used for rinsing is reduced.
5. Energy operating costs are lower than for evaporative
recovery.
38
-------
Disadvantages
1. Current cost of freeze separation units is very high,
discouraging all but very large plating operations.
2. The closed loop system is susceptible to buildup of
impurities.
39
-------
SOLVENT RINSING
Description
Solvent rinsing is a recycle technique which replaces the water
in the first rinse after the plating bath with a water immiscible
solvent. The dragged out water-plating chemical solution is removed
from the work pieces with the solvent. The plating solution can then
be phase separated from the solvent and returned to the plating bath.
The solvent is returned to the rinse bath. In the second rinse, the
solvent is rinsed from the parts with water and the water-solvent
mixture is separated in a phase separator. The solvent phase is
returned to the solvent rinse tank and the water is discharged to
treatment. Figure 7 illustrates the process in diagram form.
State-of-the-Ar t
Solvent rinsing as a technique to recycle plating dragout is
untried on a commercial scale. The key to the success of solvent
rinsing is the selection of an appropriate solvent. Primary considera-
tions for a solvent are:
1. Very low mutual solubility with water,
2. Chemical inertness,
3. Low surface tension to minimize emulsion formation, and
4. Flammability and toxicity.
The Industrial Waste Treatment Research Laboratory in Cincinnati
has granted the Bumper Recycling Association of North America, Incor-
porated, $30K to study solvent rinsing using perchloroethylene. The
pilot-plant study is being conducted in Cicero, Illinois. Completion
of the study is expected in June 1976.
Economics
No economic data are currently available for solvent rinsing.
However, the Bumper Recycling Association pilot-plant study with
economic projections is expected after June 1976.
40
-------
PHASE
SEPARATOR
Bath
Chemicals
Mixed:
Sol vent-
Chemicals
PLATING BATH
SOLVENT
RINSE
TANK
|
1
Waste
Water
i
Rinse
Water
Water
I
I
I
I
1 WATER
| RINSE
| TANK
[
1 Mixed-
| Solvent
41
PHASE
SEPARATOR
Figure 7 Solvent Rinsing System
-------
Advantages (Anticipated)
1. Valuable chemicals are recycled.
2. Water use and waste treatment cost are reduced.
3. Sludge formation is reduced or eliminated.
4. The process does not involve complex technolgy.
5. The consumption of energy is minimal.
Disadvantages
1. Solvent contamination of the plating bath may cause
product quality to deteriorate, depending on the
solubility of the solvent in the plating solution
and the efficiency of the liquid-liquid phase
separation.
42
-------
ION FLOTATION
Description
Ion flotation or foam flotation is a relatively well developed unit
operation in the metal extraction industry. Application to electroplating
wastewaters has not been demonstrated. The process uses a foaming agent
and an inorganic ionic agent in water. An air pump called a foam generator
injects the foaming and ionic agents with air into the bottom of a column
filled with the solution to be extracted. A foam is generated in the
column and the metal ions are captured by electrochemical forces in the
foam. The foam is collected and removed on the liquid surface and the
metal ions are recovered. A unique feature of this technique is that
chromium may be recovered without reduction, and cyanides do not require
destruction before treatment.12 The foam is treated with caustic soda,
soda ash or sodium silicate to break the foam and cause a separation.
The separated metals are left concentrated in solution and can be recycled
or recovered. The technique is anticipated to be simple, economical and
effective for removal of pollutants at low concentrations in wastewater.
State-of-the-Art
Foam flotation for recovery and recycle of metals in solutions from
electroplating operations is in the laboratory development phase. The
Industrial Waste Treatment Laboratory, Edison, New Jersey, has granted
$20K to Vanderbilt University, Nashville, Tennessee, to study electro-
plating waste recovery by foam flotation. This laboratory scale
investigation was completed in December 1975. A final report is
expected in April 1976.
Economics
No economic data for foam flotation of electroplating wastes are
available. The laboratory study by Vanderbilt University will provide
preliminary cost projections after December 1975.
Advantages
1. Foam flotation is expected to be a relatively low cost
process for wastewater treatment and metals recovery.
2. The process may be potentially selective for certain
metals.
43
-------
3. The process has the potential for recovery and recycle
of plating chemicals.
4. The potential for reduction or elimination of water
treatment sludge is good.
Disadvantages
1. Foam flotation is an unproven technique for electroplating
waste treatment.
44
-------
D. External Recovery of Segregated Metals from Sludges and Solutions
Four processes or techniques to recover metal values from unmixed
electroplating sludges and waste solutions are discussed. These
processes/techniques are:
1. Integrated Treatment
2. Kastone Treatment Process
3. Single Metal Sludge Recovery
4. Spent Bath Recovery
45
-------
INTEGRATED TREATMENT
Description
The integrated system treats the plating bath dragout at the
source and allows segregation of individual metals as sludge. The
treatment is accomplished by substituting a chemical precipitation
bath in place of the first rinse after the plating bath. The dragout
on the work piece is removed and reacted to form a sludge in the
treatment tank. The treatment tank is circulated to a settling tank
where the precipitate is allowed to settle and form a sludge.
The settling tank is also used as a make-up tank for addition of
the treatment chemicals to maintain the system concentration. The treatment
settling tank can be used for several plating lines which are plating
the same metal, otherwise each plating bath requires a separate settling
tank. Figure 8 illustrates the integrated system in block diagram.
The integrated system offers a distinct advantage over "end of the line"
conventional treatment because the metal sludges can be segregated and
therefore offer much greater potential for recovery.
State-of-the-Art
The integrated treatment system is a fully developed technique and
has received widespread applications. An EPA grant demonstration at
Beaton and Corbin Company, a small captive shop, was published in 1973.21
The Beaton and Corbin Company of Southington, Connecticut, installed
integrated chemical treatment in its plant on two chromium lines, a copper
cyanide bath and a nickel sulfate bath. An additional system was added
to handle floor spills, acid rinse and alkali rinse baths. The effluent
leaving the plant was upgraded to meet Connecticut discharge limits. The
sludge formed from the four treatment systems was combined and pumped
to drying beds before disposal. The prospects for sale and reclamation
of segregated sludges from integrated treatment is unknown at this time.
Economics
The EPA demonstration at Beaton and Corbin yield the following
cost data for the year 1970.21
Cost of installation $47,337.00
Annual operating cost (including amortization) $11,828.00
Treatment cost as percent of value added by 5.7%
the plating process
46
-------
Work Flow
PLATING BATH
Treatment
Chemicals"
//J
TREAT-
MENT
BATH
1
TREATMENT
SETTLING TANK
Water
I WATER
I RINSE
I TANKS
I Rinse
f Water
Sludge
Figure 8 Integrated Waste Treatment System
-------
The above economic data indicates that integrated treatment may well
be within the cost capability of many small platers. A potential credit
for metal recovery would offset part of the operating cost.
Advantages
1. Integrated treatment appears to be attractive to the small
shop operator.
2. The operation of the treatment system is not complex and is
within the capabilities of the small shop.
3. This technique appears to have good potential for recovery of
metals since the metals are segregated in individual treatment
systems.
Disadvantages
1. Feasibility of sale and recovery of the segregated metal sludges
is not known.
2. If segregated sludges cannot be sold and/or recovered, this
process offers little or no advantage over conventional
treatment regarding land protection.
48
-------
KASTONE PROCESS
Description
A new process referred to as "Kastone," marketed by E.I. du Pont,
Incorporated, Wilmington, Delaware, uses a proprietary peroxygen
compound in the presence of formaldehyde to oxidize cyanide to cyanate
in rinse waters from zinc or cadmium metal finishing operations. By
treating wastewater with the proprietary solution, zinc and/or cadmium
precipitates out as metal oxides. The precipitates are filtered. After
treatment, the clarified water contains cyanate, ammonia and a glycolic
acid amide. Since the cyanate ion is ten times less toxic than the
cyanide ion, the treated effluent is normally discharged to a municipal
sewer for further treatment. The process is finding some acceptance by
small finishing shops.
The oxidized zinc and cadmium potentially may be recycled or reclaimed.
The process to date is only applicable to zinc and cadmium cyanide solutions,
State-of-the-Art
The Kastone process is a full-scale treatment process being actively
marketed by E.I. du Pont, Incorporated. The Industrial Waste Treatment
Research Laboratory, EPA, Edison, New Jersey, has a $15K grant with
Metal Plating Corporation, Connersville, Indiana, to demonstrate zinc
cyanide removal and zinc oxide recycle. The zinc oxide precipitated is
directly redissolved into the alkaline cyanide plating bath.22 The
final draft report from this demonstration is expected in November 1975.
Economics
Economic data for the Kastone process will be published in the
Edison grant final report due in November 1975. Initial indications
are that the process is competitive with other treatment technology.
Advantages
1. Zinc and cadmium sludge can be recycled to the
plating bath.
2. The process is commercially available and reasonably
pr iced.
Registered Trademark, E.I. du Pont, Inc.
49
-------
Disadvantages
1. Due to the presence of the toxic cyanate ion, the
Kastone process will probably be limited to pre-
treatment prior to discharge to municipal treatment
systems.
2. The process is currently applicable to zinc and cadmium
cyanide only.
50
-------
SINGLE METAL SLUDGE RECOVERY
Description
Since metal recovery is relatively simple from a single metal
sludge, rinse water from a single bath can be treated individually,
as in the integrated system to produce a pure metal-containing
sludge. One major electroplating supply company (OMI, Udylite,
Detroit, Michigan) is recovering nickel from sludges produced at their
customer's plants.23 Nickel, which has a high value (approximately
$3.00 per Ib) is removed from nickel sulfate bath rinse water by precipi-
tation with sodium bicarbonate as an insoluble nickel carbonate. The
precipitate is settled and then dewatered by a filter press to 50 percent
solids. The dry filter cake is shipped back to the supplier at one of
four regional centers. The nickel carbonate is converted back to a high-
grade nickel sulfate plating solution by a proprietary process. Pilot
plant work to develop a similar copper recovery process is proceeding
at Udylite.28
State-of-the-Art
Nickel recovery from nickel sulfate rinse waters is being practiced
by a number of electroplating shops, such as General Motors, and Wald
Manufacturing Company in Kentucky. OMI, Udylite, is handling the nickel
sludge for recycle into high-grade nickel sulfide. Other metals may
well lend themselves to this technique as their prices continue to increase.
Economics
The capital cost to the electroplating shop involves purchase and
installation of a system to precipitate nickel in rinse waters and
produce a 50 percent solids nickel carbonate sludge. This amounts to
about $40K.23 The sodium carbonate is purchased from the supplier/
reclaimer. Shipping costs (the key to any regional recovery approach)
are minimized by the high solids content obtained (~50%). The electro-
plater receives a credit against future nickel sulfate purchases based
on the sludge shipment's weight and nickel assay. The credit reportedly
averages 50 percent of the purchase price of new nickel sulfate baths.
Reported recovery of nickel is about 95 percent for the complete process.
Advantages
1. This recycle technique potentially can handle many
plating baths not amenable to direct recycling due to
rapid breakdown of organic additives.
51
-------
2. Sludge recovery is practical and economical for an
external reprocessor operating on a regional basis.
3. Sludge generation in the wastewater treatment process
is reduced.
Disadvantages
1. Probably not attractive to small shops due to capital
requirements for each metal plated.
2. Economics depend on increasing metal prices and on a
regional metal reprocessor.
52
-------
SPENT BATH RECOVERY
Description
The periodic dumping of plating baths and stripping solutions is
required to eliminate impurities dragged into the bath and thereby
maintaining minimum quality standards. In many shops, the spent baths
are bled into the wastewater at low enough rates to avoid upsets to
treatment systems. Thus, these baths end up as sludge.
Due to the fact that spent baths are concentrated, compared to
rinse waters, there is commercial interest by some waste processing
firms in the recovery of metals from these unmixed baths.21* 25 26 Waste
processors may be in a position to collect sufficient quantities of
spent baths from a number of platers, so as to make recovery and sale
of salvaged metals economically practical. The recovery of the metals
from the spent baths may be accomplished by several processes.
Conventional cyanide destruction followed by hydroxide precipitation
may be practiced for cyanide baths. Ion exchange recovery may be
practiced for a number of metal salts. In some cases, the bath
chemicals are reacted to form saleable byproducts such as the process
by Nieuwenhuis, U.S. Patent 3,443,328, which converts chromium waste
solutions to lead chrornate, which is sold as a paint pigment.2 6
State-of-the-Art
Several-waste processors are reclaiming electroplating baths with
varying degrees of success.2k The market for the reclaimed metals or
derivatives is the controlling factor in the profitability of this
business.
Economics
The electroplater using a waste processor to dispose of his spent
baths would require storage tanks to store sufficient quantities to
justify a pickup. The waste processor would set his fee to produce a
reasonable return on his investment. If the price of the recovered
metals is high enough and the recovery process efficient enough, the
cost to the electroplater might be reduced. Also, the reduction of
the cost of waste treatment and sludge disposal would help offset
the disposal fee.
53
-------
Advantages
1. The technique is widely applicable to large and small
shops due to minimal capital investment required.
2. Sludge from spent bath treatment would be eliminated.
3. Metals can be reclaimed for reuse.
Disadvantages
1. Some investment in storage tanks to hold spent baths
before pickup is required.
54
-------
E. Recovery of Metals From Mixed Hydroxide Sludges
Two types of potential processes have been identified as having
the potential to recover metals from hydroxide wastewater treatment
sludges. These are:
1. Solvent Extraction
2. Electrochemical and Roasting
55
-------
SOLVENT EXTRACTION
Description
A potential process technique for recovery of metals from hydroxide
sludges is solvent extraction. The process depends on organic reagents
which are selective for specific metals. The basic process involves
leaching of the sludge to solubilize the metals. The leach liquor is
contacted with an organic solvent containing a selective reagent. The
reagent extracts a specific metal ion. The organic phase is then separated
and treated further to recover the metal.
State-of-the-Art
Solvent extraction of metal containing sludge is currently in the
laboratory state of development. In the United States, EPA has funded
a grant for $80K to Texas Southern University to develop a solvent
extraction process. The project is being monitored from the Industrial
Waste Treatment Research Laboratory at Edison, New Jersey, and completion
is expected in May 1976.
A Swedish firm, MX Processer in Gotenborg, has announced a process
developed by their company which will recover metals from electroplating
sludges.27 The process, named MAR for "Metals and Acid Recovery," recovers
copper, zinc and nickel for sale. HWMD has been in contact with the
inventor, Dr. Reinhardt of MX Processers, to obtain additional information.
However, patent considerations preclude release of information by MX
Processers at this time.28
Economics
The initial prototype MAR process is expected to break even
economically assuming hydroxide sludges are delivered to the plant
free of cost.27 No other information on potential economics is
known at this time. The Texas Southern University grant report, due
May 1976, will contain some economic projections.
Advantages
1. The recovery of metals from the sludge reduces the
hazard of disposal.
2. The metals are recovered for recycle.
56
-------
3. The economics of the process may be favorable.
4. Energy usage is expected to be low.
Disadvantage
1. Although the sludge can be detoxified, disposal of
a residual sludge will still be required.
57
-------
METAL RECOVERY - ELECTROCHEMICAL AND ROASTING
Description
Another proposed approach to recover the metals from electroplating
sludges and metal bearing solutions is the use of electrolysis and high
temperature roasting techniques. In this recovery approach, the sludge
is leached with a strong reducing agent such as ammonium carbonate or
sulfuric acid to solubilize the metal hydroxides. The leach liquor is
then subjected to controlled potential electrolysis to remove copper.
A roasting technique separates chromium and zinc. A detailed process
description is not possible due to the preliminary state of development.
State-of-the-Art
Wbrk on this approach to recovery of metals from sludges and waste
solutions is still in the laboratory stage. The Bureau of Mines, Rolla
Metallurgy Research Center, is conducting active experimental work into
process approaches for metals recovery.29
Battelle-Columbus Laboratories is developing a process to recover
metal values from water treatment sludge under a $104K EPA grant from
the Industrial Waste Treatment Laboratory, Edison, New Jersey. The
current study started July 1975, following a preliminary study completed
April 1975. Battelle plans to build a small pilot plant which will be
portable, for on-site evaluations.30 The project is expected to be
completed by July 1976.
Economics
Economics are uncertain. The evaluation report from Battelle-
Columbus Laboratories indicated unfavorable economics.31 Operating
costs for a plant processing five tons per day (dry basis) of sludge
were estimated at $1,740 per day. The recovered metals could be sold
for $640 per day leaving a cost deficit of $1,090 per day. The current
study, expected to be completed by July 1976, should give more accurate
projections of operating and capital costs for the Battelle process.
Advantages
1. The sludge will be detoxified, eliminating the
environmental hazard arising from land disposal.
2. The metal values can be recovered for sale.
58
-------
Disadvantages
1. A detoxified sludge will still require disposal,
2. Present economic projections are not favorable.
59
-------
References
1. Battelle-Columbus Laboratories. Assessment of industrial
hazardous waste practices; electroplating and metal
finishing industries-job shops. U.S. Environmental
Protection Agency, 1976. (In preparation; to be
distributed by the National Technical Information
Service, Springfield, Va.)
2. Ghassemi, Mv and S. Quinlivan, [TRW Systems Group], Study of
selected landfills designed as pesticide disposal sites.
U.S. Environmental Protection Agency, 1976. (In press; to
be distributed by the National Technical Information Service,
Springfield, Va., as PB-250 717.)
3. Buck, M., R. Derham,and H. Lubowitz [TRW Systems Group]. Recommended
methods of reduction, neutralization, recovery, or disposal of
hazardous waste. v.lY. Hazardous waste encapsulation techniques.
Washington, U.S. Environmental Protection Agency, Nov. 22, 1974.
87 p. (Unpublished report.)
4. Braun, R. Problems in the removal of inorganic industrial slurries.
In Wastes: solids, liquids and gases. ACHEMA Symposium, 1970,
Frankfurt. New York, Chemical Publishing Company, Inc., 1974.
p. 197-206.
5. The capabilities and costs of technology associated with the
achievement of the requirements and goals of the Federal Water
Pollution Control Act, as amended, for the metal finishing
industry; survey and study conducted for the National Commission
on Water Quality. Zelienople, Pa., Lancy Division of Dart
Environment and Services Company, Oct. 1975. 284 p., app.
6. Personal communication. G. Merrit, Pennsylvania Department
of the Environment and Resources, to E. Grumpier, Office
of Solid Waste Management Programs, August 24, 1975.
7. Fields, T., and A. W. Lindsey. Hazardous waste technology assessment
summary; chemical fixation of industrial wastes, Chemfix Division
of Environmental Sciences, Inc., Pittsburgh, Pa. [Washington,
U.S. Environmental Protection Agency, Office of Solid Waste
Management Programs, Jan. 1974.] 4 p. (Unpublished report.)
8. Personal communication. R. Wisniewski, Chemfix Company, to E. Grumpier,
Office of Solid Waste Management Programs, July 3, 1975.
60
-------
9. The pollutant potential of raw and chemically fixed industrial waste
and air abatement sludges; progress report. [Vicksburg, Miss.],
U.S. Army Engineer Waterways Experiment Station, June 1975. [7 p.]
(Unpublished report.)
10. Personal communication. E. M. Ross, Crossford Pollution Services, Ltdv
to D. Farb, Office of Solid Waste Management Programs, Dec. 11, 1974.
11. Hodgmen, C.D., et al., eds. Handbook of chemistry and physics. 44th ed.
Cleveland, The Chemical Rubber Publishing Co., [1962/63.] 3604 p.
12. Personal communication. M. K. Stinson, Industrial Waste
Treatment Laboratory, Edison, N.J., to E. P. Grumpier,
Office of Solid Waste Management Programs, October 8,
1975.
13. Water-insoluble starch xanthate; preparation and use in heavy
metal recovery. CA-NRRL-41 (Rev.) Peoria, 111, U.S.
Department of Agriculture, Agricultural Research Service,
Northern Regional Research Laboratory, Aug. 1974. 5 p.
14. Personal communication. J. Ciancia, U.S. Environmental
Protection Agency, Edison N. J., to E. P. Grumpier, Office
of Solid Waste Management Programs, May 5, 1975.
15. Personal communication. D. Deaton, Warsaw Plating Company,
to E. P. Grumpier, Office of Solid Waste Management Programs,
July 28, 1975.
16. The electroplaters are polishing up. Environmental Science
& Technology, 8 (5):406-407, May 1974.
17. Watson, M. R. Pollution control in metal finishing. Park Ridge,
N. J., Noyes Data Corporation, 1973. 295 p. (Pollution
Technology Review no. 5.)
18. Personal communication. D. Furakawa, UOP Corporation, to
E. P. Grumpier, Office of Solid Waste Management Programs,
July 6, 1975.
19. Pay for pollution control by recovering waste metals! Canadian
Paint and Finishing, 45 (3):90-91, Mar. 1971.
20. lammartino, N. R. Freeze crystallization: new water-processing
tool. Chemical Engineering, 82 (13):92-93, June 23, 1975.
61
-------
21. Martin, J. J., Jr. Chemical treatment of plating waste for
removal of heavy metals. Washington, U.S. Government Printing
Office, May 1973. 40 p. (Distributed by National Technical
Information Service, Springfield, Va., as PE-227 363.)
22. Personal communication. J. Ciancia, U.S. Environmental Protection
Agency, Edison, N. J., to E. P. Grumpier, Office of Solid Waste
Management Programs, Oct. 16, 1975.
23. Personal communication. A. Olsen, Udylite Corporation, to
E. P. Grumpier, Office of Solid Waste Management Programs,
July 29, 1975.
24. Personal communication. L. H. Ersted, Conservation Chemical Co.,
to E. P. Grumpier, Office of Solid Waste Management Programs,
July 11, 1975.
25. Personal communication. A. Prevdon, Alexandria Metal Finishing
Co., to E. P. Grumpier, Office of Solid Waste Management
Programs, July 19, 1975.
26. Personal communication. N. J. Nieuwenhuis, Western Processing,
Seattle, Wash., to E. P. Grumpier, Office of Solid Waste
Management Programs, Mar. 21, 1975.
27. Reinhardt, H. Solvent extraction for recovery of metal waste.
Chemistry and Industry, 5:210-213, Mar. 1, 1975.
28. Personal communication. H. Reinhardt, MX Processer AB, Goteborg,
Sweden,, to E. P. Grumpier, Office of Solid Waste Management
Programs, July 24, 1975.
29. Cochran, A. A. and L. C. George. Recovery of metals from chromium
etching/bright dip wastes. Rolla, Mo., U.S. Bureau of Mines,
Rolla Metallurgy Research Center, 1975. 15 p. (Unpublished
draft report.)
30. Personal communication. J. Hollawell, Battelle-Columbus Laboratory,
to E. P. Grumpier, Office of Solid Waste Management Programs,
July 1, 1975.
31. Tripler, A. B., Jr., R. H. Cherry, Jr., and G. R. Smithson, Jr.
[Battelle-Columbus Laboratories]. Reclamation of metal values
from metal-finishing waste treatment sludges. Washington, U.S.
Environmental Protection Agency, Apr. 1975. 97 p. (Distributed
by National Technical Information Service, Springfield, Va., as
PB-242 018.)
1101341
62
ft U. S. GOVERNMENT PRINTING OFFICE : 1977 720-116/5706
------- |