United States
Environmental Protection
Agency
Hazardous Waste Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-87/106 Feb. 1988
Project Summary
Technical Resource Document:
Treatment Technologies for
Metal/Cyanide-Containing
Wastes, Volume III
Stephen A. K. Palmer, Marc A. Breton, Thomas J. Nunno, David M. Sullivan,
and Norman F. Surprenant
The full document provides informa-
tion that can be used by environmental
regulatory agencies and others as a
source of technical information for
waste management options for hazard-
ous liquid wastes containing heavy
metals and/or cyanide compounds.
These options include waste minimiza-
tion, recycling, and treatment of waste
streams. Emphasis has been placed on
the collection and interpretation of
performance data for proven technol-
ogies. These include: Metals: precipi-
tation, coagulation/flocculation,
chemical reduction, membrane separa-
tion technologies, activated carbon
adsorption, ion exchange, electrolytic
recovery, thermal recovery; Cyanides:
alkaline chlorination, ozonation, bio-
logical treatment, thermal destruction.
These, and other potentially viable
technologies, are described in terms of
their actual performance in removing
constituents of concern, their asso-
ciated process residuals and emissions,
and those restrictive waste character-
istics that impact their ability to effec-
tively treat the metal/cyanide wastes
under consideration. Although empha-
sis is placed on performance data, cost
and capacity data are also provided to
assist the user of the document in
assessing the applicability of technol-
ogies to specific waste streams.
This Project Summary was devel-
oped by EPA's Hazardous Waste Engi-
neering Research Laboratory, Cincin-
nati, OH, to announce key findings of
the research project that is fully doc-
umented in a separate report of the
same title (see Project Report ordering
information at back).
Background
Heavy metals and cyanides are widely
used by all segments of American
industry. Because of this, they are
frequently detected in all media, includ-
ing ground water. To combat the negative
effects of environmental release that
these and other hazardous materials may
have on the environment, the 1984
amendments to the Resource Conserva-
tion and Recovery Act (RCRA) were
promulgated. These amendments
directed the U.S. Environmental Protec-
tion Agency (EPA) to ban certain wastes
from land disposal to the extent required
for the protection of human health and
the environment. The ban for concen-
trated metal/cyanide wastes went into
effect on July 8, 1987, 2-1/2 years
following enactment of the amendments.
EPA has taken steps to meet this
deadline by characterizing metal/cya-
nide waste generation, identifying waste
management alternatives through case
study development and literature sur-
veys, and determining available capacity
of disposal options. From these investi-
gations, the Agency concluded that
industry would be able to comply with
the land disposal ban as scheduled.
Although currently permitted treatment
units are insufficient to accommodate
the quantities of these metal/cyanide
wastes currently land disposed, the
Agency determined that sufficient capac-
ity could be brought on-line by the
statutory deadline.
The categories of wastes subject to the
July 8, 1987 land disposal ban are
identified in the May 28, 1986 Federal
Register. They include any RCRA wastes
with liquid fractions that contain heavy
-------
metals or total cyanides above the
concentrations specified in Table 1. For
the purposes of this regulation, the EPA
has proposed use of the Paint Filter Test
to determine liquid content and use of
the Toxicity Characteristics Leaching
Procedure (TCLP) to determine constit-
uent concentrations. Any waste contain-
ing a carbon-nitrogen triple bond is
considered to be a cyanide-containing
waste. Metal/cyanide RCRA wastes
containing concentrations below the
threshold levels specified in Table 1 may
be subject to land disposal restrictions
at a later date; i.e., between 1988 and
1990.
Scope
The full Technical Resource Document
provides information that can be used by
environmental regulatory agencies and
others as a source of technical informa-
tion describing waste management
options for wastes containing metals
and/or cyanides. These options include
waste minimization (i.e., source reduc-
tion, recycling/reuse) and use of various
physical, chemical, thermal, and biolog-
ical treatment processes. Emphasis has
been placed on the collection and inter-
pretation of performance data for proven
technologies, however, the report also
examines promising technologies which
are still in the developmental stage.
The full document begins with a brief
statement of purpose (Section 1.0) and
a review of regulatory background (Sec-
tion 2.0), which have been summarized
above. This is followed by a review of
the currently available data regarding
metal/cyanide waste sources, charac-
teristics (Section 3.0), quantities gener-
ated, existing management practices,
and available unused treatment capacity
(Section 4.0). This is followed by a
summary of documented waste minimi-
zation practices (Section 5.0) and an
evaluation of a wide range of treatment/
recovery processes (Sections 6.0 through
15.0). In order of their presentation, the
latter include:
• Metal Waste Treatment/Recovery
Processes:
—Membrane Separation
Technologies
—Liquid Extraction
—Adsorption Technologies
—Electrolytic Recovery
—Chemical Treatment
—Biological Treatment
—Thermal Destruction/Recovery
• Cyanide Waste Treatment/
Destruction
—Physical Removal Processes
—Chemical Destruction Techniques
—Biological Treatment
—Thermal Destruction
These technologies are examined with
emphasis placed on identifying process
design and operating factors and waste
characteristics that affect process per-
formance and applicability. Cost data are
also presented, as available, to assist the
Table 1 . Concentration Limits for Defining Waste Management Alternatives (mg/L)"
Constituent
Total Cyanide
As
Cd
Cr**
Pb
Hg
Ni
Se
Tl
Ba
Ag
Maximum Allowable
Concentration for
Land Disposal in
RCRA Facilities
1,000
500
100
500
500
20
20
134
130
No limit
No limit
Maximum Allowable
Concentration for
Exclusion from RCRA
Management Provisions*
NA
5.0
1.0
5.0
5.0
0.2
NA
1.0
NA
100
5.0
*AII concentrations refer to the liquid fraction of these wastes.
"Federal Register. 40 CFR Subpart C §261.24. 45 FR 33119. May 19, 1980.
user in evaluating and selecting options
The report concludes with an algorithm-
presenting considerations for the selec
tion of treatment/recovery alternative:
(Section 16.0). A brief synopsis of the
contents of each technical section is
provided below.
Metal/Cyanide Waste Sources
and Characteristics
(Section 3.0)
Available information describing
important industrial uses, waste sources,
and characteristics for metal/cyanides is
summarized. An understanding of these
topics is a prerequisite for evaluating the
applicability of waste management
alternatives, particularly source reduc-
tion and recycling options. Recognizing
the wide variability of metal/cyanide
waste characteristics and the lack of a
comprehensive national data base des-
cribing these data, an industry by indus-
try approach is taken to categorize waste
sources. Industries that are high volume
generators of RCRA metal/cyanide
wastes are targeted. These include metal
surface treatment and electroplating
facilities, printed circuit board manufac-
turers, inorganic pigment manufactur-
ers, petroleum refineries, wood preserv-
ing facilities, and others. These same
industrial categories are used later to
discuss industry specific waste minimi-
zation options.
Waste Quantity, Management
Practices, and Treatment
Capacity (Section 4.0)
The current status and limitations of
the data base relative to existing RCRA
waste generation, management practi-
ces, and available alternative treatment
capacity are reviewed, noting that EPA
is currently in the process of updating
this data base. Much of the currently
available data rely on recent interpreta-
tions of the EPA's 1981 RIA National
Survey of large quantity generators and
TSDFs and 1983 survey of small quantity
generators. These data indicate that
roughly 13 billion gallons of metal/
cyanide RCRA waste is generated annu-
ally, the vast majority of which is
wastewater streams from relatively few,
very large generators.
Unfortunately, these data do not permit
an assessment to be made regarding the
characteristics of these wastes. Specif-
ically, it cannot be determined what
fraction of these wastes will be subject
to the land disposal restrictions. A review
-------
f available waste characterization data
suggests that, provided wastes are
segregated prior to treatment, the quan-
tity affected by the July 8,1987 statutory
provisions will be a modest fraction of
the total waste generation figure stated
above.
As part of its proposal to codify the land
disposal restrictions for metal/cyanide
wastes, the EPA estimated demand and
supply of available alternative treatment
capacity. Since the Agency lacked data
on waste concentrations, it conserva-
tively assumed that all liquid wastes
currently land disposed require alterna-
tive capacity. Currently available capacity
falls far short of this quantity. However,
the EPA believes that by the statutory
deadline, industry will be able to install
treatment units (e.g., precipitation,
chromium reduction, cyanide oxidation)
which are capable of meeting the effluent
concentrations specified by the land
disposal restrictions. Other than present-
ing the EPA's analysis, no attempt was
made in the full document to make
national projections regarding the adop-
tion of waste management alternatives.
The extreme variability in physical,
chemical, and flow characteristics
between waste streams, and the lack of
reliable data quantifying these variables,
precludes making reliable projections.
Waste Minimization Practices
(Section 5.0)
Waste minimization is discussed from
the standpoint of two distinct areas of
activity; recycle/reuse and source reduc-
tion; e.g., process modification and raw
material substitution. These topics are
described in general as they pertain to
metal/cyanide wastes and then in terms
of specific practices available to the
industrial categories identified in Section
3.0. This section also provides informa-
tion on Governmental and privately
operated waste exchanges and a sum-
mary of documented waste minimization
applications and their cost-effectiveness.
It is noted that waste minimization
activities are widely applied, particularly
to metal-containing wastes, and will
receive further impetus as a result of the
land disposal ban.
Metal Waste Treatment/
Recovery Technologies
(Section 6.0 Through 12.0)
Table 2 summarizes commonly used
technologies for the treatment of metal-
containing wastes, which were dis-
cussed in this document. These have
Table 2. Summary of Treatment Technologies for Metal-Bearing Waste Streams
Process Applicable Waste Streams Stage of Development
Performance
Residuals Generated
Physical Treatment Technologies
Membrane Separation Aqueous waste streams
containing 10-20 percent
metals depending on the
technology used.
Liquid-Liquid
Extraction
Carbon Adsorption
Ion Exchange
DeVoe-Holbein
Electrolytic Treatment
Aqueous, sludge, and solid
wastes.
Aqueous waste streams
containing metal ions at
low pH. Effective in
treating chelated metals as
well as metal cations.
Effective for treating dilute
aqueous waste streams as
an end-of-pipe or polishing
treatment.
Similar to ion exchange
except capable of treating
both dilute and
concentrated solutions.
Aqueous streams; high
concentrations (greater
than 1.000 ppm) are most
efficiently removed.
Demonstrated technology
for many process and
waste streams.
Limited use in hazardous
waste field but widespread
in mining and smelting
industries.
Largely experimental with
some field applications for
treating hexavalent
chromium and mercury
containing waste streams.
Used in metal finishing and
electroplating industries
for recycling rinse
solutions and
concentrating waste metal
solutions for efficient
treatment.
Newly developed process
used in metal finishing
industries, ore
benefication, precious
metals recovery, and chlor-
alkali plants.
Well developed and readily
available from commercial
vendors.
Greater than 99 percent if
properly utilized.
Capable of yielding a
solution which is 20-30
times more concentrated
than feed.
Used as a primary
treatment for removal of
hexavalent chromium.
With a Cr8* influent
concentration of 6 ppm.
effluent concentration of
CV8+ remained below 0.05
ppm.
Performance influenced by
nature of functional group.
ions available for
exchange, and pH.
Performance reportedly
shows high specificity.
However more data are
needed to assess utility.
Performance varies greatly
depending on the
application and the
particular electrolytic unit
used; some units may
remove over 90% of metals
such as Cu, Pb, In, Av, Ag,
andCd.
Generally none except for
solids from ultrafiltration.
Raffinate and regenerant
stream may require post-
treatment to remove
residual extractsnt and
metal, respectively.
Spent carbon requires
disposal or reactivation.
Regeneration solution
requires treatment or
disposal.
Regenerant required but
has good potential for
recycling since typically
high in metals content.
Generally the metal is
recovered in a usable form
and no residual solids are
generated.
-------
Table 2. Continued
Chemical Treatment Methods
Precipitation
Coagulation/
Flocculation
Reduction
Flotation
Aqueous streams;
restrictions based on
physical form, viscosity,
and metal solubility.
Aqueous streams; forppb
concentrations two-stage
process required, not
readily applied to small,
intermittent flows.
Primarily, aqueous
chrome-bearing waste
streams although sodium
borohydride can treat most
metals.
Aqueous streams
containing 100 mg/L or
less of metals. Restrictions
based on physical form, oil
and grease content.
Well developed, reliable
process, suitable for
automatic control.
Well developed and readily
available from commerical
vendors.
Well developed.
Not fully developed,
primarily at pilot plant
stage of development.
Heavy metals; Cd. Cu, Pb,
Hg, Ni, Ag, andZn
removed to 0.01 to 0.5
mg/L.
Not considered a primary
treatment but can achieve
low residual levels.
Chromium removal to 0.01
mg/L. Sodium borohydride
able to remove Cu, Ni, Pb,
Zn, Hg. Ag. Cd in the 0.01
to 1.0 mg/L range.
Heavy metals Pb. Cu. Zn.
Cr3* removed to 0.03 to 0.4
mg/L.
Effluent stream will requii
secondary processing to
remove and dispose of
precipitated solids.
Requires secondary
processing and disposal.
Effluent stream will requir
secondary processing to
remove and dispose of
reduced metal. Sodium
borohydride introduces
boron into the effluent
stream.
Requires secondary
treatment of metals-laden
foamate.
Biological Treatment Methods
Aerobic and anaerobic
technology suitable for
dilute aqueous wastes;
metal removal due to
partitioning or
precipitation.
Generally not used as
primary treatment
technology for metals.
May be used as final
treatment for low
concentrations of heavy
metals (10 mg/L or lessl,
may be used as
pretreatment for resistant
species.
Residual contamination
likely, will usually require
secondary treatment.
Thermal Treatment Methods
Incineration
Pyrometallurgy
(smelting, calcination)
Evaporation
Crystallization
Organometalllics, metal
wastes containing organics
(e.g., solvent wastes
containing metals).
Pyrometallurgy is
applicable to most metal-
bearing wastes.
Effectiveness is directly
proportional to metal
content of waste.
Aqueous wastes with low
non-volatile metals
content, or wastes with
high volatile metals
content.
Primarily used for v.sstes
from electroplating,
pickling containing high
levels of acids, water, or
low molecular weight
organics.
Well developed reliable
process. Numerous
technologies available
which can be opti-mixed
according to waste
characteristics. Process
costs are high.
Well developed and widely-
available. Some
commercial capacity
available. Process costs are
high (although typically
lower than for
incineration).
Well developed and widely-
available.
Well developed. Often used
in conjunction with
evaporation.
Can oxidize organic portion
of metal-waste to virtual
completion.
Can effect high-level (i.e.,
greater than 90 percent)
recovery of metal or metal
oxides from waste matrix.
Can effect high-level
recovery of volatile metals
or significant volume
reduction of aqueous
wastes.
Can effect high level
recovery.
Air emissions, ash,
scrubber effluents.
Potential formation of toxic
sludges.
Air emission sludges.
Sludges.
-------
been categorized in terms of treatment
mechanism; i.e., physical, chemical,
biological, and thermal processes. Phys-
ical and chemical processes apply to all
waste types whereas biological methods
are appropriate for dilute wastewaters
containing metals (but not as a primary
treatment method) and thermal tech-
niques are applicable to organo-
metallics. Each technology is discussed
in terms of the following generalized
areas: (1) process description; (2) theo-
retical considerations; (3) applicable
waste types; (4) pretreatment and post-
treatment requirements; (5) demon-
strated performance in metal waste
treatment; (6) cost of treatment; and (7)
status and availability of the technology.
The limited scope of the full document
did not permit a comprehensive evalua-
tion of cradle-to-grave management of
metal wastes. In particular, topics which
are covered in limited detail include
general waste pretreatment (e.g., sedi-
mentation, filtration, flow equalization,
trace organic removal) and post-
treatment (e.g., sludge consolidation, pH
adjustment, solidification) technologies.
These topics have been considered in
other EPA sponsored Technical Resource
Documents produced as part of this and
other series.
The following is a summary of metal
treatment/recovery technologies consi-
dered in the full document.
Physical Treatment
Technologies
(Sections 6.0 Through 8.0)
Membrane Separation
Technologies (Section 6.0)
Membrane technologies such as
reverse osmosis (RO) and electrodialysis
(ED) are used commercially to recover
dissolved metals from aqueous wastes
generated through electroplating or
metal etching processes. The technolo-
gies are applicable to specific waste
streams, provided pretreatment mea-
sures can be used to remove suspended
and dissolved solids and ensure accepta-
ble membrane lifetimes. Ultrafiltration
(UF) is often used as a pretreatment for
RO and ED. UF also is used to remove
suspended solids following precipitation
of metals from waste streams. RO and
ED usually do not generate residuals
providing the reject stream is recyclable.
Liquid-Liquid Extraction
(Section 7.0)
Liquid-Liquid extraction involves the
separation of a component from a waste
solution by transfer to a second, immis-
cible solution, typically an inexpensive
organic acid (e.g., kerosene). The process
has gained widespread acceptance in the
mining industry for metal recovery from
aqueous discharges and in the smelting
industry for metal recovery from
sludges/solids in hydrometallurgical
operations. However, due in part to the
specificity of system design to particular
applications, adoption of this processing
technique for hazardous metal waste
treatment has been limited. Performance
capabilities are difficult to predict
through generalized equations and,
instead, require isotherm and kinetic
data determinedthrough laboratory scale
studies. However, through support from
equipment suppliers, successful systems
have been designed for metal recovery
from chlor-alkali plant discharges (Hg),
pickling, plating, and etching baths, and
metal finishing sludges including recov-
ery of both heavy metals (Ni, Cr, Zn, Cu,
Cd, and Ag) and cyanide.
Residuals generated from this process
include the treated waste feed (raff inate),
which may require post-treatment to
remove residual extractant concentra-
tions, and the regenerant, which will
require treatment (e.g., electrolytic
recovery) to recover the metals and
permit reuse of the acid extractant.
Adsorption Technologies
(Section 8.0)
Adsorption technologies for metals
wastes include activated carbon, ion
exchange, and DeVoe-Holbein treat-
ment. Activated carbon adsorption
involves separation of a substance from
one phase, typically an aqueous solution,
and the concentration of the substance
at the surface of an activated carbon
adsorbate. Activated carbon is generally
used in granular form either in batch,
column (both fixed-bed and countercur-
rent bed), or fluidized-bed operations,
with fixed-bed being the most common.
Although promising results have been
reported, activated carbon for inorganic
compound removal from water is largely
in the experimental stage. In addition, the
number of commercial applications is
small and data for full scale applications
are limited.
Ion exchange is a versatile separation
process used to remove metal contam-
inants from aqueous waste streams and
to recycle or discharge the treated
solution. Ion exchange techniques
involve the use of an ion selective resin
to remove ionic contaminants (metals)
from solution. Three basic types of resins
are employed; cation exchange resins,
anion exchange resins, and metal selec-
tive chelating resins.
The major attraction of ion exchange
is the broad range of resins manufac-
tured to treat specific waste streams. The
ion exchange resin will selectively
remove only the toxic compound while
allowing the nontoxic dissolved ionic
solids to remain in solution. With proper
resin selection, ion exchange can provide
an effective pollution control method in
a wide range of applications such as
water purification and recycle end-of-
pipe treatment, and chemical recovery.
DeVoe-Holbein is a technology similar
to ion exchange using insoluble chelating
compounds based on microbial sidero-
phores which reportedly display a high
degree of metal sequestering specificity.
This technology has been successfully
applied to recover concentrated metal/
cyanide solutions such as plating and
etching baths. However, due in part to
the waste specific nature of its formu-
lations and the fact that it has a single
industrial supplier, estimates of cost and
performance applicable to a range of
industrial waste streams proved to be
very difficult to obtain. Additional work
is needed to demonstrate this
technology.
Electrolytic Recovery
(Section 9.0)
The primary use of electrolytic pro-
cesses is for the removal of dissolved
metals from rinsewaters generated by
metal plating and etching processes. In
this situation, an electrolytic cell is
attached to the rinse bath following the
plating or etching tank, and the rinse
solution is circulated through the elec-
trolytic cell. As the solution passes
through the cell, dissolved metals ions
are reduced and deposited on the
cathode in elemental form. If cyanides
are present, they may also be removed
by oxidation at the anode forming carbon
dioxide, ammonia and nitrogen.
There exist a number of different
electrolytic cell designs. Some use very
simple flat plate anode and cathode.
Other, more complex designs, incorpo-
rate granular or porous cathodes. These
designs increase the mass transfer of
metal ions to the cathode by increasing
the surface area of the cathode, and
therefore have the ability to remove
metals to a much lower concentration
than flat plate electrodes. The use of one
-------
djsign over another depends upon the
application. Noble metals such as gold
and silver are not difficult to remove
electrolytically, and therefore flat plate
electrodes can be used. Metals such as
copper, tin, lead, and cadmium are more
difficult to remove and sometimes may
require the use of the more complex
electrolytic cell designs.
Chemical Treatment
Technologies (Section 10.0)
Chemical treatmeht methods for
metals wastes include precipitation,
coagulation/flocculation, reduction, and
flotation processes. Precipitation
involves the alteration of the ionic
equilibrium of a dissolved metallic
compound to produce an insoluble
precipitate. The process typically uses an
alkaline reagent to cause the solubility
of the metal ions to decrease, and thus
precipitate out of solution. The chemicals
most frequently used for precipitation of
metals are hydroxides, sulfides, and
carbonates. The overwhelming majority
of present technology is based on hydrox-
ide precipitation. However, in certain
cases where heavy metals are com-
plexed, or at concentrations below the
level of minimum hydroxide solubility,
sulfide precipitation is a viable alterna-
tive. Carbonate precipitation is also
sometimes used in cases where it
provides superior precipitation properties
(cadmium) or lower effluent concentra-
tions (nickel).
Precipitation is used most commonly
to remove heavy metals from aqueous
wastes. The precipitation process produ-
ces a sludge composed of metal hydrox-
ides, metal carbonates or metal sulfides
as well as the precipitating agent used.
In some instances, precipitation can be
used for organic-based liquids, although
this application is very limited due to
sedimentation problems in viscous
media.
Coagulation/flocculation is aimed at
removal of colloidal particles. A stable
suspension of colloidal particles is
characterized by a balance of repulsive
forces and attractive forces. The coag-
ulation process involves the destabiliza-
tion of the suspension by neutralizing or
decreasing the repulsive forces so that
the particles will approach each other
and agglomerate.
The coagulants/flocculants currently
in commerical use are classified as
inorganic, synthetic organic and natu-
rally occurring polymers. The principal
coagulants available are inorganics such
as aluminum sulfate, lime, and iron salts.
Synthetic organics such as anionic and
cationic polyelectrolytes are typically
added as coagulation/flocculation aids.
Naturally occurring organics have seen
limited use since the composition of
natural products tends to fluctuate and
they are susceptible to microbial degra-
dation during storage.
The coagulation/flocculation process
is usually performed after a precipitation
step and the treated water is then
permitted to settle. 1 he precipitated
sludge from the settling vessel is
removed at 1 to 2 percent solids for
further treatment while the overflow is
typically polished by a multi-media filter
and then discharged.
Chemical reduction as a waste treat-
ment process is an established and well-
developed technology. The reduction of
hexavalent chromium's valence (oxida-
tion) state to decrease toxicity and
encourage precipitation is presently used
as a treatment technology in numerous
electroplating facilities. Major advan-
tages of chemical reduction when used
to reduce hexavalent chromium is oper-
ation at ambient conditions, automatic
controls, high reliability, and modular
process equipment.
The reduction reaction is one in which
one or more electrons are transferred to
the chemical being reduced (reductant)
from the chemical initiating the transfer
(the reducing agent). Hexavalent chro-
mium can be reduced to trivalent chro-
mium, which can then be removed by
precipitation. The pH of the aqueous
solution is reduced to about 2.0 with
hydrochloric or sulfuric acid. The aque-
ous pH controls the reaction rate, which
is extremely slow above pH 3. Then
reducing agents such as sulfur dioxide
and sodium metabisulfite are added.
Lime or caustic soda is added to raise
the pH and precipitate trivalent chro-
mium. Precipitation is carried out at pH
8.5 to 9.5; in this range chromium
hydroxide solubility is minimal.
An alternate reducing agent applicable
to most heavy metals is sodium borohy-
dride. Sodium borohydride has recently
shown promise for reducing and remov-
ing soluble lead, including organo-lead
salts.
Chemical flotation is a well established
and developed technology for separating
finely ground valuable minerals in the ore
processing industry. However, recent
research efforts have centered on apply-
ing this technology to the removal of low
concentrations (100 mg/L or less) from
industrial wastewaters. The advantage:
of chemical flotation include simplicity
effectiveness, and moderate costs. Ir
addition, low space requirements and i
concentrated, easily handled sludge are
major advantages over comparable
metallic contaminant removal through
chemical precipitation. While still prim-
arily in the pilot plant stage of develop-
ment, chemical flotation and most not-
ably adsorbing colloid foam flotation,
represents a feasible and economical
method for removing heavy metals from
wastewaters.
Biological Treatment
(Section 11.0)
A large number of companies special-
ize in the design and construction o1
biological treatment systems. Aerobic
systems are the most readily available,
and their design and operation are
complex, but manageable. The total
number of biological treatment systems
used for inorganic compound removal is
unknown. However, the total number oi
facilities using some sort of aerobic
biological treatment for biodegradable
wastes is large, in excess of 2,000. The
number of companies offering expertise
in bioaugmentation and anaerobic treat-
ment is relatively small, but this segment
is expected to grow rapidly.
Biological treatment of metals using
conventional equipment and acclimated
strains is typically only capable of
treating combined heavy metal influents
of 10 mg/L. While improvements in
reported values for biological treatment
process tolerance limits for inorganic
priority pollutants is encouraging, most
processes are still in the developmental
stage and have yet to be widely applied.
In addition, the difficulty of disposing of
a large, voluminous sludge-containing
heavy metals limits available disposal
options. Since the biological matrix
surrounding the accumulated metallic
species can readily degrade and release
the entrapped metals into the environ-
ment, fixation, encapsulation, or other
forms of secure disposal may be
necessary.
Thermal Treatment/Recovery
Technologies (Section 12.0)
Thermal treatment technologies such
as incineration, calcination, smelting,
evaporation/distillation, and crystalliza-
tion have been used extensively to effect
recovery of metals from certain metal-
bearing hazardous wastes. Incineration
processes are primarily used to handle
-------
organic wastes containing metals such
as solvent rinses from metal treating or
organometallic wastes such as tetraethyl
lead. Pyrometallurgical processes (calci-
nation and smelting) are primarily used
to manage wastes from metal refining
industries, e.g., specialty steelmaking.
Evaporation/distillation and crystalliza-
tion are often used to manage corrosive
wastes from electroplating, pickling, or
other metal finishing operations, or low-
molecular weight organic wastes (e.g.,
solvents) containing metals.
All of the thermal treatment systems
applicable to metal-bearing hazardous
wastes employ well-developed technol-
ogies, with readily-available commercial
capacity. However, the incineration of
many metal wastes will require air
pollution control devices to assure
incineration emission compliance.
Cyanide Treatment/
Destruction Technologies
(Sections 13.0 Through 15.0)
Table 3 summarizes information on
technologies used for this treatment and
destruction of cyanide-containing
wastes which have been covered in this
document. Concentrated cyanide solu-
tions are sometimes recovered, generally
by membrane and other separation
technologies which are capable of segre-
gating metal contaminants from the
solution. Typically, however, cyanides
are destroyed due to their low cost and
relative ease of destruction. Processes
for cyanide waste management are
covered in the full document in similar
fashion to metal wastes. A summary of
these technologies is provided below.
Physical Separation Processes
(Section 13.0)
Physical separation methods for cya-
nide bearing wastestreams include ion
exchange and foam flotation. Ion
exchange for the removal of cyanide has
been limited to applications involving the
treatment of low organic concentration
waste streams. Anion exchange resins,
in particular, are susceptible to severe
fouling by insoluble oil and dissolved
organic compounds. Therefore, the use
of ion exchange is not practicable unless
extensive pretreatment of the organics
is practiced. Typically, ion exchange for
cyanides removal has been applied as a
polishing step to sorb any ferricyanide
or other complexed cyanide residuals
from oxidation processes such as alka-
line chlorination. The environmental
impact from this technology is that it
concentrates cyanides in the regenera-
tion step, creating a secondary stream
that needs to be treated.
The advantages of this technology are
that it has been demonstrated at both
the bench-scale and pilot-scale. The
equipment is compact, versatile, and is
generally applicable to many different
waste treatment situations. Limitations
include the high cost of regenerative
chemicals and the waste streams orig-
inating from the regeneration process
are relatively high in pollutant concen-
tration. In addition, if more than 25 mg/L
of suspended solids and/or more than
20 mg/L of oil exists in the influent,
filtration is required as pretreatment.
Also, the stream to be treated should not
contain any materials that cannot be
removed by the backwash operation.
Some organic compounds, particularly
aromatics, will be irreversibly adsorbed
by the resins, and this will result in
decreased capacity.
Ion flotation/foam separation of cya-
nide bearing wastewaters has not yet
been tested on a pilot-scale at an actual
commercial facility. Most of the research
.hat has been performed to date with
flotation has focused on equipment
development and process parameter
definition. Although preliminary
research has demonstrated the technical
feasibility of the process, pilot-scale
testing is needed to determine if suffi-
cient cyanide recoveries can be achieved.
Flotation could prove to be a cost-
effective alternative to conventional
treatment practices because of its min-
imal operating requirements.
Limited work has been done on the
secondary treatment and disposal of the
flotation concentrate. Since the concen-
trate contains precipitated ferri- and
ferrocyanide which are not amenable to
conventional oxidation technologies
such as alkaline chlorination, alternate
technologies such as wet air oxidation
or UV/ozonation may be more appropri-
ate. In addition, solidification and
encapsulation of the residuals may be
required prior to land disposal.
Chemical Destruction
Processes (Section 14.0)
Chemical destruction methods for
cyanide wastes include alkaline chlori-
nation, ozonation, wet air oxidation, and
sulfur-based treatment technologies.
Alkaline chlorination systems have
generally proven reliable if well main-
tained and equipped with well-designed
Oxidation Reduction Process (ORP)
control. The treatment technology cannot
oxidize stable cyanide complexes such as
ferrocyanides and has difficulty treating
nickel cyanides. The most widespread
application of cyanide oxidation through
alkaline chlorination is in facilities using
cyanides in electroplating operations.
A major environmental impact of this
technology is the potential for evolution
of toxic hydrogen cyanide gas at low pH
levels. In cases where alkaline chlorina-
tion is used to treat dissolved complex
cyanides and dissolved cyanides of heavy
metals, sludges or metal hydroxides and
carbonates are generated. These sludges
can be recovered by filtration and treated
by chemical fixation/solidification. This
is particularly true in cases where the
cyanide complex has not been destroyed
and instead has been merely rendered
insoluble and precipitated.
Ozonation appears best suited for
treatment of very dilute waste streams,
similar to those streams treated by the
ozone based water disinfection pro-
cesses now used in Europe. It does not
appear to be cost competitive or tech-
nically viable for most industrial waste
streams where organic concentration
levels are 1 percent or higher. However,
it may be viable for certain specific
wastes with high levels of a contaminant
of special concern and high reactivity.
Assuming adequate destruction of a
contaminant by ozonation, the principal
environmental impact would appear to
be associated with ozone in the effluent
vapor and liquid streams. However,
thermal decomposition of ozone is
effective and is used commercially to
destroy ozone prior to discharge.
Unreacted contaminants or partially
oxidized residuals in the aqueous efflu-
ent may be a problem necessitating
further treatment by other technologies.
Presence of many such residuals will
generally result in selecting a more
suitable alternative technology.
The WAO process is available commer-
cially, and reportedly well over 150 units
are now operating in the field treating
municipal and various industrial sludges.
The process is used predominately as a
pretreatment step to enhance biodegrad-
ability. Only a few units are now being
used to treat industrial cyanide wastes.
These include a unit in California and six
other units currently operating in Japan
and Europe.
The oxidation of specific contaminants
in waste streams by the wet oxidation
process is not highly predictable. Equip-
-------
Table 3. Summary of Treatment Technologies for Cyanide-Bearing Waste Streams
Process
Applicable Waste Streams Stage of Development
Performance
Residuals Generated
Physical Treatment Methods
Ion Exchange
Foam Flotation
Aqueous wastes
containing less than 25
mg/L suspended solids
and 20 mg/L of oil and
grease.
Aqueous wastes:
restrictions based on oil
and grease, chelator
complexant, and
competing ion
concentrations.
Primarily pilot plant stage
with a few commercial
plants.
Laboratory-scale.
Able to treat 48 mg/L of
total cyanides to 0.5 mg/L.
Ninety-nine percent
removal of amenable
cyanide.
Secondary processing and
disposal required for spent
regenerant and byproduct
streams.
Cyanide laden concentrate
will require secondary
treatment and/or disposal.
Chemical Treatment Methods
Alkaline Chlorination
Ozonation
Wet Air Oxidation
Sulfur-Based
Oxidation
Aqueous wastes:
restrictions based on
physical form, oil and
grease content, suspended
solids, viscosity, and iron
content.
Aqueous wastes requires 1
percent or lower
contaminant
concentration.
Aqueous and sludge
wastes containing up to
25,000 mg/L of cyanide.
Aqueous wastes.
Well developed, reliable
process, suitable for
automatic control.
Well developed and widely-
available.
Well developed and
available at over 150
installations.
Not fully developed but has
demonstrated potential.
Can oxidize all free and
most fixed cyanides to
below 1 mg/L.
Able to oxidize free and
fixed cyanides to low
concentrations.
Ninety-nine percent
destruction of total
cyanide.
Ninety-nine percent
oxidation of simple
cyanides.
Possible process emissions
and toxic sludges requiring
secondary treatment
Unreacted ozone may be
present in effluent vapor
and liquid streams.
Post-treatment will be
required of both I/quid and
vapor streams.
Post-treatment will be
required of both liquid and
solid streams.
Biological Treatment Methods
Suitable for dilute
aqueous waste streams.
Well developed for dilute
streams, pilot plant stage
for more concentrated
wastes.
Able to completely oxidize
cyanide concentrations of
10 mg/L if cyanides are
amenable.
Residuals are generally
non-toxic.
Thermal Treatment Methods
Incineration
Evaporation
Crystallization
Organic cyanide-bearing
wastes (e.g., acrylonitrile
wastes), liquid wastes from
cyanides production.
Wastes containing low-
molecular weight organics.
Typically used for metal-
finishing wastes.
Typically used for plating
wastes.
Well developed, and
widely-available. Process
costs are high.
Well developed and widely-
available.
Well developed and
generally used in
combination with
evaporation system.
Cyanide compounds have
been destroyed to levels
exceeding 99.99 percent.
Capable of high level
recovery of cyanides.
Capable of high level
recovery of cyanides.
Air emissions, scrubber
effluents, ash.
Air emissions, sludges.
Sludges
-------
ment manufacturers rely largely on the
result of bench-scale results to tailor the
design of full-scale WAO continuous
units for specific wastes. Full-scale data
confirm the results of WAO performance
data obtained in bench- and pilot-scale
studies.
Sulfur-based cyanide treatment tech-
nologies, while not fully developed, have
demonstrated potential as a cyanide
waste treatment process. Both reagents
and equipment requirements are
straightforward and simple. Application
to industrial wastes is presently limited,
but both polysulfide and sulfur dioxide
based technologies have demonstrated
high efficiencies in treating dilute and
concentrated aqueous cyanide waste
streams. Careful control of the treatment
via multistaging of the reaction, careful
control of pH, reagents, etc., are required.
The environmental impact of the
processes discussed here relate to the
unreacted contaminants and byproducts
(thiocyanates) remaining in the waste
stream. Additional treatment to prevent
corrosion and meetthiocyaniate effluent
guidelines usually will be required. Air
emissions associated with the use of
these technologies will be minimal,
although some care must always be
observed in pH adjustments to prevent
hydrogen cyanide evolution.
Miscellaneous Cyanide
Destruction Processes
(Section 15.0)
The main miscellaneous cyanide des-
truction processes are biodegradation
and thermal treatment. Biodegradation
as a process for treating wastes contain-
ing cyanide is still in the developmental
stage. Certain types of microorganisms
have shown the ability to completely
degrade low concentrations of simple
cyanides. The major obstacle to imple-
mentation has been the inability of most
conventional biosystems even when
acclimated, to degrade fixed cyanides or
simple cyanides in high concentrations.
However, since the end products of
complete biodegradation are nontoxic,
continued research is advisable. In
addition, many of the new bioaugmen-
tation processes which can degrade fixed
and/or concentrated cyanide wastes,
may render biological treatment as a
feasible alternative to conventional
chemical or thermal destruction
technologies.
Thermal treatment technologies which
may be applied to cyanide-bearing
hazardous wastes include incineration,
evaporation, and crystrallization. The
processing systems involved in each of
these technologies are similar to those
described for management of metal-
bearing hazardous wastes. Test studies
have indicated high potential levels of
waste destruction (i.e., in excess of 99.99
percent) for the incineration of cyanide
wastes. Incineration is most typically
used to destroy cyanide wastes gener-
ated in organic chemical manufacturing,
e.g., acrylonitrile production. Other
cyanide waste candidates for incinera-
tion are waste organic cyanide com-
pounds such as cyanogen.
Considerations for System
Selection (Section 16.0)
The final section of the Technical
Resource Document presents a compre-
hensive approach for the selection of a
recovery/treatment process or pro-
cesses for metal/cyanide hazardous
waste management. The ultimate objec-
tive is to meet land disposal or discharge
standards with the lowest possible cost,
recognizing that waste minimization is
a key aspect of cost benefit.
Process selection criteria are pre-
sented in the form of a generic algorithm,
outlining pertinent considerations such
as waste characteristics, cost, equipment
availablility, and regulatory and institu-
tional constraints. The importance of
modeling and the need for experimental
data are noted, and likely sources of such
information are identified. Generaliza-
tions of the applicability of waste man-
agement alternatives are not empha-
sized, recognizing the limitations of this
approach. Although each technology
possesses certain definable ranges in
cost and applicable waste types, as
identified in the technology sections,
suitability in a particular application is
overwhelmingly dependent on site spe-
cific factors. In addition to wide variability
in waste characteristics, these site
specific factors include considerations
such as potential for source reduction or
waste reuse, availability of ancillary
equipment and other onsite resources,
and availability of offsite waste manage-
ment services.
Stephen A. K. Palmer. Marc A. Breton, Thomas J. Nunno, David M. Sulllivan,
and Norman F. Surprenant are with Alliance Technologies Corp., Bedford,
MA 01730.
L. H. Garcia and Robert C. Thurnau are the EPA Project Officers (see below).
The complete report, entitled "Technical Resource Document: Treatment
Technologies for Metal/Cyanide-Containing Wastes, Volume III," (Order No.
PB 88-143 896/AS; Cost: $56.95, subject to change! will be available only
from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officers can be contacted at:
Hazardous Waste Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
-------
« 1 1
3 18
X
------- |