Process Description

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Solidification and stabilization are nevertheless used interchangeably in the field [2,4]. In actual site remediation operation, the process immobilizes contaminants in soils and sludges by binding them in a concretelike, leach-resistant matrix. Contaminated hazardous waste materials are collected, screened to remove oversized material, and introduced to a batch mixer. The hazardous waste material is then mixed with water; a chemical reagent; some selected additives; and fly ash, kiln dust, or cement. After it is thoroughly mixed, the treated waste is discharged from the mixer. Treated waste is a solidified mass with significant unconfined compressive strength (UCS), high stability, and a rigid texture similar to that of concrete.

This process treats soils and sludges contaminated with toxic organic compounds, hazardous metals, inorganic compounds, and oil and grease. Batch mixers of various capacities can treat different volumes of hazardous waste.

The solidification and stabilization process (Fig. 1) was once demonstrated in December 1988 at the Imperial Oil Company, Champion Chemical Company Superfund site, in Morganville,



Figure 1 Solidification process equipment. (Courtesy of USEPA.)

New Jersey. This location formerly contained both chemical processing facilities and oil reclamation facilities. Soils, filter cake, and oily wastes from an old storage tank were treated during the demonstration. These wastes were contaminated with petroleum hydrocarbons, polychlorinated biphenyls (PCB), other organic chemicals, and hazardous heavy metals.

A Technology Evaluation Report [5], an Applications Analysis Report [6], and a Demonstration Bulletin [7] are available from the USEPA, Washington, DC, United States. Long-term chemical and physical monitoring and mineralogic analyses have also been conducted by USEPA.

Key findings from the solidification and stabilization process demonstration are summarized below:

1. Extract and leachate analyses showed that heavy metals in the untreated waste were immobilized.

2. The process solidified both solid and liquid wastes with high organic content (up to 17%), as well as oil and grease.

3. Volatile organic compounds in the original waste were not detected in the treated waste.

4. Physical test results of the solidified waste showed: (a) UCS ranging from 390 to 860 pounds per square inch (psi); (b) very little weight loss after 12 cycles of wet and dry and freeze and thaw durability tests; (c) low permeability of the treated waste; and (d) increased density after treatment.

5. The solidified waste increased in volume by an average of 22%. Because of solidification, the bulk density of the waste material increased by about 35%.

6. Trace amounts of semivolatile organic compounds were detected in the treated waste and the toxicity characteristic leaching procedure (TCLP) extracts from the treated waste, but not in the untreated waste or its TCLP extracts. The presence of these compounds is believed to result from chemical reactions in the waste treatment mixture.

7. The oil and grease content of the untreated waste ranged from 2.8 to 17.3% (28,000 to 173,000 ppm). The oil and grease content of the TCLP extracts (USEPA, 1980) from the solidified waste ranged from 2.4 to 12 ppm.

8. The pH of the solidified waste ranged from 11.7 to 12.0. The pH of the untreated waste ranged from 3.4 to 7.9.

9. No PCBs were detected in any extracts or leachates from the treated waste.

10. Visual observation of solidified waste revealed dark inclusions about 1 mm in diameter. Ongoing microstructural studies are expected to confirm that these inclusions are encapsulated wastes.

The USEPA Risk Reduction Engineering Laboratory, Cincinnati, OH, United States, may be contacted for further information on this stabilization and solidification process.

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