Uptake of cesium and strontium cations by potassium-depleted phlogopite

Phlogopite mica was equilibrated with 1.0 N sodium chloride (NaCl)–0.2 N sodium tetraphenylborate (NaTPB)–0.01 M disodium ethylenediaminetetraacetic acid (EDTA) solution at room temperature resulting in an almost complete removal (92%) of the micaʹs interlayer K. X-ray powder diffraction analysis provides additional evidence that hydrated Na+ ions had almost completely replaced the interlayer K+. Following equilibration, the c-axis spacing of the mica increased from 10.0 Å to approximately 12.2 Å. Cesium and Sr ion exchange isotherms indicate that K-depleted phlogopite is highly selective for both elements, the Cs+ exchange capacity is 1.26 meq/g or 65% of the theoretical cation exchange capacity and the Sr2+ exchange capacity is 1.94 meq/g or 100% of the theoretical exchange capacity of the mica. Kielland plots indicated that the mica was selective for Cs+ when the equivalent exchange capacity of Cs+ in the exchanger phase (X¯Cs) was < 0.66 and selective for Sr2+ when X¯Sr < 0.41. At equivalent fractions greater than these levels, layer collapse and/or steric effects limit the diffusion of these ions into the interlayers of the mica. Analysis of the Cs+ equilibrated mica utilizing XRD indicated that a collapse of the c-axis spacing had occurred. Based on the high selectivity of < 45-μm K-depleted phlogopite for Sr2+ and Cs+, this material may prove useful as an inorganic ion exchanger for these radioactive isotopes.