SUPERCRITICAL FLUID PROCESSING OF HEAVY METALS

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 INNOVATIVE TECHNIQUE PROPOSED HERE RENDERS CARBON DIOXIDE AND OTHER NONPOLAR SOLVENTS CAPABLE OF DISSOLVING METALS AND THEIR SALTS, AND EXTENDS THE PROCESSING CAPABILITIES OF SUPERCRITICAL TECHNOLOGY TO METAL-CONTAINING WASTES. IN THE ENVISAGED PROCESS, MIXTURES OF METALS WILL BE EXTRACTED FROM CONTAMINATED SLUDGES AND SOILS AND WILL BE SEPARATED AND CONCENTRATED INTO INDIVIDUAL METALS FOR RECYCLE, SALE OR DISPOSAL. FURTHERMORE, THE ORGANIC COMPLEXING AGENT USED TO SOLUBILIZE THE METALS REMAINS IN THE SOLVENT AND IS RECYCLED IN THE EXTRACTION STAGE. THE AVAILABILITY OF A PROCESS FOR EXTRACTING, SEPARATING AND CONCENTRATING METALS THAT DOES NOT REQUIRE A TOXIC SOLVENT WILL PROVIDE THE FEDERAL GOVERNMENT AND THE EPA WITH THE CAPABILITY NEEDED TO SUPPORT THE MORE STRINGENT CLEAN AIR AND CLEAN WATER ACTS CURRENTLY BEING LEGISLATED. THE DOD WILL BE ABLE TO PURIFY METAL-CONTAINING HAZARDOUS SLUDGES AND SANDS CONTAMINATED WITH DEPLETED URANIUM, AND TO RESTORE SOILS PREVIOUSLY CONTAMINATED WITH SPENT PLATING BATHS. COMMERCIAL APPLICATIONS INCLUDE HAZARDOUS WASTE PROCESSING SUCH AS SOLID WASTES FROM BOILERS AND FURNACES.