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Title: An evaluation of factors affecting the solidification/stabilization of heavy metal sludge
Authors: Bricka, R. Mark
Jones, L. W. (Lawrence W.)
Keywords: Soils--Heavy metal content
Soil stabilization
Publisher: Environmental Laboratory (U.S.)
U.S. Army Engineer Waterways Experiment Station.
Series/Report no.: Technical Report;EL-93-4
Abstract: Solidification/stabilization of hazardous waste involves mixing the waste with a binder material to enhance the physical properties of the waste and to immobilize contaminants that may be detrimental to the environment. Many hazardous wastes contain materials that are known to inhibit the setting and strength development properties of cement and pozzolan binding agents commonly used in solidification/stabilization processes. This study presents the results of an evaluation into the effects of ten interfering substances (oil, grease, lead, copper, zinc, sodium hydroxide, sodium sulfate, phenol, trichloroethylene, and hexachlorobenzene) on the physical and contaminant mobility properties of a solidified/stabilized heavy metal sludge. Three binder materials (Portland cement, lime/fly ash, and cement/fly ash) were used to solidify/stabilize a synthetic metal plating waste sludge containing substantial concentrations of four metals (cadmium, chromium, nickel, and mercury). The effects of these interfering materials were evaluated using five physical tests: unconfined compressive strength (UCS), cone index, bulk density, wet/dry cycling, and permeability. Contaminant leaching properties were evaluated using the U.S. Environmental Protection Agency's Extraction Procedure test. Microchemical/micromorphological analyses were also performed on the treated sludges. Test results indicate that copper, lead, zinc, grease, oil, and phenol have a significant detrimental effect on the physical properties of the solidified/stabilized sludge. In contrast, the effects of hexachlorobenzene, trichloroethylene, and sodium sulfate on the physical properties were much less marked. Sodium hydroxide increased the rate of set and 28-day UCS of the fly ash-containing mixtures, but reduced the 28-day UCS of the cement specimens. The Extraction Procedure leaching tests indicated that contaminant leaching was highly dependent on the extraction solution's final pH, except for the mercury contaminant. The metal nitrate salts had the greatest effect on the extract solution's final pH and, thus, contaminant leaching. No definitive conclusions could be drawn from the results of the microchemical/micromorphological examinations. The results of this research confirm the need for waste and binder-specific studies prior to the selection of a chemical solidification/stabilization process for the treatment of hazardous waste.
Appears in Collections:Technical Report

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