Adsorption of radiostrontium by soil treated with alkali metal hydroxides

Twelve soils from areas used for the disposal of low-level radioactive solid waste at the Oak Ridge National Laboratory were examined for their ability to adsorb trace levels of Sr. Radiostrontium adsorption, in the presence of normal soil Ca levels, was determined following the addition of LiOH, NaOH, KOH, NaCl, and Na-polyacrylate. With soils from C horizons, the average thermodynamic equilibrium constant for the Na-Ca(Sr) exchange reaction decreased from 0.063 to 0.00041 after treatment with 0.4 meq/g of NaOH, indicating a large increase in the selectivity for Ca(Sr) adsorption. With samples from A or B horizons, this effect was not observed due to the dissolution of soil organic matter; Na-polyacrylate interfered with the adsorption of Ca(Sr) in the same manner as the NaOH-solubilized soil organic matter. Selectivity differences between trace levels of Sr and the macroamounts of soil Ca were quite small (<5%) in both the treated and untreated soils. A multiple regression analysis indicated that three soil properties (percent organic matter, exchangeable Ca + Mg, and exchangeable acidity) explained 77% of the variation in Sr adsorption by alkali-treated soils. In untreated soils, the exchangeable Ca + Mg and exchangeable acidity explained 70% of the variation in the adsorption of Sr. The response of the soils to alkali treatment generally followed the lyotropic series: Li > Na > K