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 ------- 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. ------- 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 3 ------- United States Environmental Protection Agency Center for Environmental Research Information Cincinnati OH 45268 Fee^Paid Agency EPA 335 Official Business Penalty for Private Use $300 RETURN POSTAGE GUARANTEED _. , „ Third-Class Bulk Rate ------- |