Migration of liquid waste 137Cs and 60Co in calcareous soils

Abstract

Two experiments were carried out to determine the leaching characteristics and distribution of liquid waste 137Cs and 60Co in three calcareous soils varied in clay contents. The liquid waste as raw (RLW), diluted (DLW), and diluted then pH adjusted (ADLW) was applied to either large undisturbed soil columns (in 200 mL) and leached for 180 d with deionized water and groundwater or to small packed soil columns (in several pore volumes). Distribution of 137Cs and 60Co in the large columns was determined nondestructively (with the aid of correction curve) by scanning of gamma radiation along the soil columns. However, their distribution in the small columns were determined by sectioning and measuring their content. Most of the radionuclides were retained by the upper 10 cm of the large soil columns of which approximately 70% of 137Cs and 55% of 60Co were held by the surface 1 cm of the columns, suggesting the irreversible sorption of both radionuclides. Differences in leachability of 137Cs and 60Co were attributed to the differences in sorption mechanisms associated with the varied experimental conditions. The dilution and/or pH adjusting of the liquid waste greatly reduced the mobility of both radionuclides applied in several pore volumes. For instance, the amount of 137Cs retained by the upper 1 cm of river sediment was approximately 10 and 20 folds greater with ADLW and DLW, respectively than RLW. Greater mobility of 60Co than 137Cs was observed in the form RLW.