No abstract

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.

No abstract

Evaluation of the partitioning of contaminant and nutrient elements between soil particles and their surrounding solution requires separation of the pore-water from the solids. Disposable soil-sample holders are described that can be used in low-and ultra-speed centrifuges. The pore-water sample is filtered of paniculate during centrifugation, thus eliminating the tedious step of separating the centrifugate from the soil using pipettes. The system is inexpensive, works for both fine mineral and peat soils, requires little preparation time and provides enough pore-water of sufficient quality for chemical analysis.

The environmental impact of accidental or chronic releases of contaminants to the unsaturated soil zone, either through surface spills or contaminated groundwater, has become a major concern. This study was designed to provide data after 1 and 4 yr to compare the leaching and upward transport of Tc, I, Np, Cs, U, Th, Cr, and Mo in cores of the same soil in outdoor lysimeters. Over the 4‐yr study a broad range of climatic, soil moisture, and temperature conditions existed, which were representative of long‐term means as well as some extremes. The amount of rainfall leached through the cores decreased with time. The leaching resulted in a downward movement of fine soil particles, especially in the lower horizons. Element mobility in the leaching cores for the 4 yr decreased in the order I > Tc ≫ Cr > Np > Mo > Cs ≥ U > Th. This differs slightly from the ranking predicted after 1 yr. After 1 yr, Mo appeared to be more mobile than Cr or Np. After 4 yr, I, Tc, Np, and Cs migrated to the soil surface from depth. Analysis of the soil solid/liquid partition coefficient, Kd, values indicates the retention of these elements is primarily related to soil organic matter content and dependent on porewater concentration. The Kd model is appropriate for I in all soil horizons and for Tc, Np, and Cs in the Ae horizon of the groundwater cores. The Freundlich isotherm or a kinetic expression best describes the sorption for all other elements and horizons.