Chemical Treatments of Soil to Decrease Radiostrontium Leachability

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AbstractThe leachability of radiostrontium from radioactive waste and through soil is one of the most salient problems with shallow‐land burial as a disposal method. The continuous leaching of buried waste at the Oak Ridge National Laboratory (ORNL), for periods up to 30 years, by lateral ground water flow has led to the contamination of surrounding soils and streams with 90Sr. The goal of the present investigation was to evaluate methods to effect either the in situ fixation or reduced leachability of 90Sr in soil. Small columns of three soils, collected from the solid waste disposal areas at ORNL, were labeled with 85Sr as a convenient tracer for 90Sr. After this labeling, but prior to leaching, the soil columns were percolated with equivalent amounts of sodium salt solutions of hydroxide, fluoride, carbonate, phosphate, silicate, or aluminate. Leaching was then initiated with 0.1N CaCl2 which was selected to qualitatively simulate ground water which contains Ca as the dominant dissolved cation. With two soils, high in indigenous exchangeable Ca2+, only 30–35% of the 85Sr could be leached from the carbonate‐treated columns. Presumably, the 85Sr was coprecipitated with the nascent CaCO3 formed during this treatment. In contrast, >98% of the 85Sr was readily leached from all untreated soils. Other anions fixed variable but generally less 85Sr than the carbonate treatment. Thus, sodium carbonate appears to have a potential application to immobilize 90Sr in situ in contaminated soil.