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.