The Use of 24-Crown-8's in the Solvent Extraction of CsNO3and Sr(NO3)2

Abstract

The feasibility of a solvent extraction process for removing strontium and cesium from acidic high activity nuclear waste is shown. Both strontium and cesium can be extracted from an aqueous HNO₃ phase containing the metal nitrates into an organic phase containing kerosene or CCl₄ as a diluent and complexing agents dissolved in the diluent. The most promising results obtained thus far have required the use of a mixture of three metal complexing agents: tributyl phosphate, di-2-ethylhexyl phosphoric acid, and 4,4′(5′)-di-tert-butylbenzo-24-crown-8. The highest distribution coefficients obtained (organic/aqueous) were 1.45 ± 0.05 for Cs⁺ and 200 for Sr²⁺. The extraction is reversible and is strongly dependent on the pH of the aqueous phase. The metal can be removed from the organic phase by lowering the pH to 1, while raising the pH above 3 causes the metal to return to the organic phase. The utility of this extraction technique for nuclear processing will depend on the radiation stability of the complexing agents and the degree of selectivity obtained when extracting strontium and cesium from mixed fission products.