United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-82-099 Feb. 1983
&EPA Project Summary
Physical Properties and Leach
Testing of Solidified/Stabilized
Industrial Wastes
Environmental Laboratory, U.S. Army Engineer Waterways Experiment
Station
A study was conducted to investigate
a new waste treatment and
containment technology involving the
solidification and stabilization of
hazardous industrial wastes. Small-
scale laboratory tests were conducted
to determine the physical properties
and chemical leaching characteristics
of five industrial wastes that had been
chemically solidified or stabilized by
one or more of four processes. Basic
data are provided to help estimate the
potential for environmental pollution
from disposal of these industrial wastes
and to define the strength and durability
of the treated materials.
Results suggest that in some cases
solidification/stabilization may be a
useful technique for reducing
environmental pollution from these
wastes. But a great deal of work must
be done to optimize treatment
procedures for each waste being
disposed, and additional work is
required to understand the behavior of
treated industrial wastes under actual
field conditions.
This Project Summary was developed
by EPA's Municipal Environmental
Research Laboratory. Cincinnati. OH,
to announce key findings of the
research project that is fully documen-
ted in a separate report of the same title
(see Project Report ordering informa-
tion at back).
Introduction
As industry produces ever increasing
amounts of diff icult-to-handle hazardous
wastes, the need for finding solutions to
its disposal will become more and more
critical. In response to that need, this
study addresses a new waste treatment
and containment technology involving
the solidification and stabilization of
hazardous industrial wastes. Small-scale
laboratory tests were conducted to
determine the physical properties and
chemical leaching characteristics of both
untreated and chemically solidified or
stabilized industrial wastes. Basic data
are provided to help estimate the
potential for surface and groundwater
pollution from industrial waste disposal
and to define the strength and durability
of the treated materials.
Types of Hazardous Wastes
Those wastes that are classed as
hazardous because of their organic or
inorganic constituents can be dealt with
by somehow altering the offending
compound to produce a new, less toxic
material before disposal. But those
containing toxic or hazardous
constituents of an elemental nature pose
a very different problem since, short of
nuclear transmutation, no secondary
treatment can alter them. With such
wastes, the toxic elements must be
contained within the disposal facility
forever or, at least, losses must be kept so
low that the environment is not harmed.
The most common elemental
constituents of sludges in this category
are the heavy metals, many of which are
toxic in very small quantities. A second
type of waste with elemental
contaminants is that which contains very
high levels of moderately soluble to very
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soluble inorganic salts. Such wastes
often contain substantial levels of toxic
heavy metals as well.
Types of Waste Containment
Waste constituents can be contained
on several different levels. For example,
wastes can be placed unaltered in a
containment vessel or buried directly so
that the landfill itself ultimately provides
the containment. Or, on a smaller scale,
the wastes can be mixed with material
that will coat or encapsulate each
separate particle or grain with an
impervious, inert coating -- often termed
microencapsulation. Another method is
to mix the waste with a binder that bonds
the waste particles together without
necessarily coating each grain. The
smallest-scale containment systems use
the production of new, inert, insoluble
crystal lattices that bind the toxic
elements into a durable, solid material.
Techniques for embedding wastes in
concrete or pozzolan concrete are well
established and commercially available.
Macroencapsulation involves fusing an
impervious polymer coating to a large
block of solidified waste.
Methods and Materials
Four solidification/stabilization
techniques were selected for this study
as representative of those technologies
currently available commercially or under
extensive development. These
techniques are: (1) a lime-flyash,
pozzolanic cement process that yields a
solid microencapsulation system, (2) a
cement/soluble-silicate treatment
process that produces a soil-like product,
(3) an organic polymer system that
produces a hard, rubber-like solid, and (4)
a microencapsulation process that
solidifies the waste and then bonds it in a
polyethylene jacket.
Five sludges were selected for
treatment by the solidification/stabiliza-
tion techniques: electroplating sludge,
nickel-cadmium battery sludge, pigment
production sludge, chlorine production/
sludge, and glass etching sludge. All are
inorganic sludges with dangerous levels
of toxic, heavy metals and/or other
leachable ions, but with only traces of
organic materials. Furthermore, all are
difficult to dewater and represent
problems for disposal. High U.S.
production levels and lack of reclamation
facilities place these wastes in a category
of problem sludges. Their production
rates also make them prime candidates
for large-scale commercial solidification/
stabilization processes.
Four waste processors agreed to take
part in the test program to evaluate
and/or treat the selected sludges. They
are identified only by letter to protect their
anonymity. All were furnished a sample
of the test sludges to optimize their
treatment systems for each waste. After
these preliminary evaluations, the
participating vendors treated sludge
samples for laboratory evaluation and
physical testing at the U.S. Army
Waterways Experiment Station in
Vicksburg, Mississippi.
Results and Conclusions
Data from these investigations can be
used to evaluate the pollution potential of
the wastes studied when they are
disposed of in standard landfills or
shallow land burial. But the conditions in
such a landfill would favor the
containment of the treated wastes more
than did the conditions used in this study.
The small sample size and continuous
submersion in CO2-saturated leaching
solution used in this study appear to
represent very rigorous leaching
conditions. Most landfill operations on
the other hand, would allow the use of
much larger blocks of treated sludge and
would have only intermittent saturated
conditions occurring in the fill. This study
may thus overestimate the leaching
losses that might be expected under
actual disposal conditions.
Results of Various
Treatment Processes
The treatment processes used in this
study produced final products with a wide
array of physical properties varying from
moderate-strength solids to a soil-like
granular material. Process A, which was
the lime-flyash pozzalonic solidification,
produced a solid soil/cement-like
product with good structural integrity but
poor durability. Concentrations of
hazardous elements in leachates from
this treated product were actually higher
in about half the cases than they were in
leachates from similar untreated
material. The net benefit of treatment by
this method was marginal.
Process B, the cement/soluble-silicate
treatment process, produced a semi-
friable material with low strength and a
soil-like consistency. This process
produced more consistent containment
of hazardous elements with 60 to 70
percent of the constituents having lower
levels in the leachate from the treated
sludge than in the leachate from the
untreated control columns. Physical
property tests typical of structural solidi
could not be run on this material.
Process C attempted to contain th<
industrial wastes in a plastic matrix b\
polymerizing the waste directly in c
urea-formaldehyde monomer prepara-
tion. Only two wastes were treated by this
process -- the electroplating waste anc
the paint production sludge. Both losi
most constituents at much higher rates
than the control columns, possibly
because of the acidification and resulting
dissolution of the sludge that was
required to produce the polymerization
reaction used in this process.
Urea-formaldehyde as used here appears
to be counterproductive as a containment
procedure.
Process D, the macroencapsulation
process that solidifies the waste and then
bonds it in a polyethylene jacket, gave
excellent containment of all constituents
but cadmium. The high costs for material,
equipment, and labor associated with this
method probably preclude its use for all
but the most hazardous wastes, however.
Replication
Replicates of the leaching tests showed
remarkable repeatability between
columns using different samples from
one treatment batch of a particular sludge.
But the patterns of constituent loss from
different sludges treated by one
treatment process were not similar.
Since the sludges are primarily metal
hydroxide wastes, it would be assumed
that each treatment process would be
similarly effective in containing a
particular contaminant in most of the
sludge types tested. Results indicate,
however, that complete leaching tests
might be required for each new waste
even though similar constituents of other
wastes might have been contained by a
particular treatment system.
As might be expected, the same
variability was found for constituent
losses from samples of a single sludge
that was subjected to different treatment
processes. Thus, no generalizations
could be made concerning the probable
loss of a particular constituent, either
from different sludges treated by one
process or from a single sludgetreated by
different solidification/stabilization
systems.
Patterns of Constituent Loss
Two distinct patterns of constituent
loss from leaching emerged in both the
treated and control columns.
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First, when constituent concentrations
in the sludge greatly exceeded their
solubilities in the leaching medium (e.g.,
calcium, nickel, lead, and sulfate), their
concentrations were relatively constant
in the leachates collected over the entire
span of the test period. For these
constituents, the rate of loss depended on
the volume of leachate produced not on
the length of time over which the
leaching took place.
The second leaching pattern was
observed for those constituents whose
solubilities were large compared with
their concentrations in the sludge
(chloride, for example). These
constituents had very high concentra-
tions in the initial leachate samples,
followed by an asymptotic drop in
concentration as the element was
depleted from the sludge that was
exposed to the leaching medium.
Channelization of the leachate flow in
the control columns resulted in a rapid
decline in the concentration of soluble
constituents in the leachate. The reason
was that this process decreased the area
of sludge that came in contact with the
leaching medium.
A third, less common leaching pattern
showed low initial concentrations in the
early leachate samples and slow
increases as the experiment progressed.
This pattern was observed for
constituents in which a common ion
effect limited concentrations at first and
permitted them to increase as the levels
of interfering ion were depleted. This
pattern was also evident for constituents
whose solubility increased later because
of changes in pH or redox conditions in
the leachate. The loss of such
constituents would be missed completely
in short-term leaching tests, but they
might be of great consequence in the
evaluation of the waste for land disposal.
Recommendations
This study has indicated that
solidification/stabilization of potentially
hazardous industrial wastes may reduce
the losses of undesirable constituents to
environmental waters when the wastes
are disposed of by landfilling with proper
engineering techniques. But much more
study involving long-term, large-scale
operations, is required before the
behavior of treated industrial wastes
under actual field conditions can be
adequately understood. Such an
understanding is necessary before the
disposal of industrial wastes can be
carried out with confidence that no
environmental degradation will occur
over the long term.
The full report was submitted in
fulfillment of Interagency Agreement No.
EPA-IAG-D4-0569 by the U.S. Army
Engineer Waterways Experiment Station
under the sponsorship of the U.S.
Environmental Protection Agency.
Environmental Laboratory is at the U.S. Army Engineer Waterways Experiment
Station, Vicksburg, MS 39180.
Robert E. Landreth is the EPA Project Officer (see below).
The complete report, entitled "Physical Properties and Leach Testing of Solidified/
Stabilized Industrial Wastes," (Order No. PB 83-147983; Cost: $ 14.50, subject
to change) will be available only from:
National Technical Information Service
52.85 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
•feUS GOVERNMENT PRINTING OFFICE; 1983 659-O17/O893
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