Variations in adsorption mechanisms of radioactive cobalt and cesium in rocks

Abstract

Variations in adsorption mechanisms of 60Co and 137Cs in metamorphosed shale and chert, and granodiorite were examined under aerobic conditions in terms of different adsorption periods, salinity of solution and solid to liquid ratios. The mechanisms were investigated by means of selective extraction tests using: (1) distilled water; (2) 1 N ammonium acetate (pH 7), (3) 0.1 M hydroxylamine hydrochloride (pH 3.5); and (4) 0.2 M ammonium xalate + 0.2 M oxalate (pH 2.5). The increase in relative amounts of 137Cs and 60Co extracted by ammonium acetate was observed in the first 1-month period of adsorption. Then the conversion of the nuclides from ammonium acetate extractable to non-extractable was observed, which continued on the order of several years. It indicates that under aerobic conditions, remobilization of the nuclides once adsorbed to geologic media will become less probable as time elapses. Solid to liquid ratios and salinity of solution of the adsorption experiments did not influence the adsorption mechanisms of 60Co and 137Cs.