DESORPTION AND EXTRACTION OF SELECTED HEAVY-METALS FROM SOILS

The need for proper disposal of industrial wastes and for remediation methods for soils contaminated with heavy metals necessitates a better understanding of the processes involved in mobilizing, transporting, and retaining elements in surface soils. The objective of this study was to investigate the desorption in water and efficacy of several traditional extraction agents in removing Tc, Np, Mo, U, Cr, Pb, Cs, and Th. Selected slices were taken with depth in acidic sand (Dystrochrept) soil cores that were spiked for 4 yr. Similarly, Tc, Np, and U were desorbed and extracted from the clay subsoil of reed/sedge peat cores following a one-season migration study. Technetium and Mo behaved as anions, and the small amount of Tc retained was attributed to insoluble organic complexes and oxides in the sandy soil and carbonates in the clay subsoil. The retention of Mo was attributed to colloidal Fe(III) oxides and organic colloids or complexes. Neptunium sorption appears to be dependent on the variable charge of the soil, making organic matter and pH important factors. Uranium and Pb were associated with the oxides. Cesium and Cr took part in inorganic reactions that fixed them rigorously to the soil solids or formed precipitates; Th formed organic complexes. Results suggest that remediation techniques for soils contaminated with Tc, Mo, and Np could be quite successful using intense leaching with acidified water. Soils. containing U, Pb, and Th may be partially reclaimed by manipulation of the organic matter or leaching with organic acids; however, soils contaminated with Cs and Cr would require extensive chemical treatment.