Chemical treatments of soil to decrease radiostrontium leachability

摘要

The ready leachability of radiostrontium from radioactive waste 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, for periods up to thirty years, has led to contamination of significant volumes of soil with /sup 90/Sr. The goal of the present investigation was to evaluate methods to effect the in situ fixation or decrease the leachability of /sup 90/Sr from soil. Small columns of three soils, collected from the solid waste disposal areas at ORNL, were labelled with /sup 85/Sr as a convenient tracer for /sup 90/Sr. After this labelling 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 0.1 N CaCl/sub 2/ (calcium chloride), and fractions of the leachate were analyzed for /sup 85/Sr. The CaCl/sub 2/ solution was selected to qualitatively simulate groundwater which contains Ca as the dominant dissolved cation. With two soils which were high in indigenous exchangeable Ca, only 30 to 35% of the /sup 85/Sr could be leached from the carbonate-treated columns. Presumably, the /sup 85/Sr was coprecipitated with the nascent CaCO/sub 3/ formed during this treatment. In contrast, greater than 98% of the /sup 85/Sr was readily leached from all untreated soils. Other anions fixed variable but generally less /sup 85/Sr than the carbonate treatment. Thus, sodium carbonate appears to have potential application to immobilize /sup 90/Sr in situ in contaminated soil.