(Mixed Waste Treatment Process)
IT Corporation's mixed waste treatment process integrates thermal desorption, gravity separation, water treatment, and chelant extraction technologies to treat soils contaminated with hazardous and radioactive constituents. The process separates these contaminants into distinct organic and inorganic phases that can then be further minimized, recycled, or destroyed at commercial disposal facilities. The decontaminated soil can be returned to the site. Each technology has been individually demonstrated on selected contaminated materials. The process flow diagram below shows how the technologies have been integrated to treat mixed waste streams.
During the initial treatment step, feed soil is prepared using standard techniques, such as screening, crushing, and grinding to remove oversized material and provide a consistent feed material.
Thermal treatment removes volatile and semi-volatile organics from the soil. Soil is indirectly heated in a rotating chamber, volatilizing the organic contaminants and any moisture in the soil. The soil passes through the chamber and is collected as a dry solid. The volatilized organics and water are condensed into separate liquid phases. The organic phase is decanted and removed for disposal. The contaminated aqueous phase is passed through activated carbon, which removes soluble organics before combining with the thermally treated soil.
Inorganic contaminants are removed by three physical and chemical separation techniques: (1) gravity separation of high density particles; (2) chemical precipitation of soluble metals; and (3) chelant extraction of chemically bound metals.
Gravity separation is used to separate higher density particles from common soil. Radionuclide contaminants are typically found in this fraction. The gravity separation device (shaker table, jig, cone, or spiral) depends on contaminant distribution and the physical properties of the thermally treated soil.
Many radionuclides and other heavy metals are dissolved or suspended in the aqueous separation media. These contaminants are separated from the soils and are precipitated. A potassium ferrate formulation precipitates radionuclides. The resulting microcrystalline precipitant is removed, allowing the aqueous stream to be recycled.
Some insoluble radionuclides remain with the soil following the gravity separation process. These radionuclides are removed by chelant extraction. The chelant solution then passes through an ion-exchange resin to remove the radionuclides and is recycled to the chelant extraction step.
The contaminants are collected as concentrates from all waste process streams for recovery or off-site disposal at commercial hazardous waste or radiological waste facilities. The decontaminated soil can be returned to the site as clean fill.
This process treats soils contaminated with organic, inorganic, and radioactive material.
The mixed waste treatment process was selected for the SITE Emerging Technology Program in October 1991. Bench- and pilot-scale testing was completed in late 1995; a report detailing evaluation results will be available from EPA in 1997. Individual components of the treatment process have been demonstrated on various wastes from the U.S. Department of Energy, (DOE), the U.S. Department of Defense, and commercial sites. Thermal separation has removed and recovered polychlorinated biphenyls from soils contaminated with uranium and technetium. These soils were obtained from two separate DOE gaseous diffusion plants.
Gravity separation of radionuclides has been demonstrated at pilot scale on Johnston Atoll in the Pacific. Gravity separation successfully removed plutonium from native coral soils.
Water treatment using the potassium ferrate formulations has been demonstrated at several DOE facilities in laboratory and full-scale tests. This treatment approach reduced cadmium, copper, lead, nickel, plutonium, silver, uranium, and zinc to dischargeable levels.
Chelant extraction has successfully treated surface contamination in the nuclear industry for more than 20 years. Similar results are expected for subsurface contamination.
EPA PROJECT MANAGER:
Douglas Grosse
U.S. EPA
National Risk Management Research Laboratory
26 West Martin Luther King Drive
Cincinnati, OH 45268
513-569-7844
Fax: 513-569-7585
TECHNOLOGY DEVELOPER CONTACT:
Ed Alperin
IT Corporation
312 Directors Drive
Knoxville, TN 37923-4709
423-690-3211
Fax: 423-694-9573