TREATMENT OF SOILS CONTAMINATED BY EITHER MERCURY OR DEPLETED URANIUM BY SUPERCRITICAL FLUID EXTRACTION

Some Department of Defense facilities have soils contaminated by mercury and depleted uranium. The proposed program addresses the removal of these metals by depleted uranium. The proposed program addresses the removal of these metals by supercritical carbon dioxide fluid extraction using an innovative technique that solubilizes the metals in the carbon dioxide solvent. Supercritical extraction has several advantages over conventional processes including benign solvents, enhanced mass transfer, and the inherent capability of separating mixtures of extracted material. However, supercritical extraction is not generally applied to inorganic substances because these are relatively insoluble in non-polar solvents such as supercritical carbon dioxide. Up to now, this has excluded the possibility of treating by supercritical solvent extraction the many metal-containing hazardous waste streams generated in DOD operations. The proposed program involves (a) the synthesis of a number of CO2-soluble complexing agents specific to either mercury or depleted uranium, (b) measurements of the solubility of the complelxing agents in CO2 and the metal extraction efficiencies in soil, and (c) estimating the capital and operating cost of the super-critical solvent extraction process.