Cation exchange equilibria of cesium and strontium with K-depleted biotite and muscovite

Cation exchange selectivity for Cs⁺ and Sr²⁺ with K-depleted biotite (Na-biotite) and K-depleted muscovite (Na-muscovite) was determined with equilibration for 4 weeks at room temperature. The cation exchange isotherms and Kielland plots indicated that both K-depleted micas show high selectivity for Cs⁺ at low equivalent fraction of Cs⁺ on solid. The K-depleted micas took up Cs up to approximately 50% of their theoretical cation exchange capacities. The XRD patterns after Na⁺ → Cs⁺ exchange reactions with K-depleted biotite showed that the d(001)-spacings collapsed from ~ 12.2 to ~ 11.2 Å with high Cs⁺ concentrations. This collapse suggests that K-depleted biotite is able to immobilize or fix Cs ions in the interlayers. In case of 2Na⁺ → Sr²⁺ exchange, K-depleted biotite showed high selectivity for Sr ions at low equivalent fraction of Sr²⁺ on solid. The XRD patterns showed that the main d(001)-spacing of the K-depleted biotite slightly increased from 12.16 Å to ~ 12.3 Å after the exchange reactions with the high Sr²⁺ concentrations. These results suggest that K-depleted biotite could be used as an ion exchanger to remove radioactive ¹³⁷Cs as well as ⁹⁰Sr from groundwater.