A STUDY OF SELENIUM AND TIN SORPTION ON GRANITE AND GOETHITE

Sensitivity analyses based on an illustrative performance assessment c ase study of a disposal concept for nuclear fuel waste have shown that radioisotopes of Se and Sn could have a significant effect on cumulat ive radioactive dose if they were to be transported through the geosph ere without retardation. Static batch sorption methods, coupled with 2 (n) factorial experimental designs, were used to determine the extent to which Se and Sn can be sorbed by granite and goethite as a function of total dissolved solids concentration, [TDS], natural fulvic acid c oncentration as dissolved organic carbon, [DOC], pH and, for the studi es with Se, the Se concentration, [Se]. Aqueous speciation and the sat uration indices of solubility-controlling solid phases were estimated using the speciation code HARPHRQ with the HATCHES thermodynamic datab ase. The experimental results indicated that Se sorption on granite wa s low and not affected by changes in [DOC] or [TDS]. Increased [Se] an d increased pH decreased sorption. For Se sorption on goethite, the pH range was narrow but indicated that sorption decreased as pH increase d. Increased [TDS] and [Se] lowered sorption on goethite, but changes in [DOG] had no effect on sorption. For Sn, increased pH, [TDS] and [D OG] decreased sorption on granite. For Sn sorption on goethite, increa sed [DOG] resulted in decreased sorption, but differences in [TDS] and pH had little consistent effect on sorption.