Selective Exchange and Fixation of Strontium Ions with Ultrafine Na-4-mica

A simple preparation process of Na-4-mica (ideal brittle mica composition of Na 4 Mg 6 Al 4 Si 4 O 20 F 4 · x H 2 O) from kaolinite yielded a nearly pure and very fine Na-4-mica with a crystallite size of about 0.2 μm. Strontium−sodium ion exchange in the hydrated interlayers of the Na-4-mica was demonstrated with this fine mica. The forward ion exchange of Sr 2+ → 2Na + (Sr-ion adsorption) was determined after equilibration for 4 weeks, and the Sr exchange capacity reached a value of about 200 mequiv (100 g) - 1 . The parabolic diffusion or modified Freundlich model described the forward exchange process well. Only a small reverse exchange 2Na + → Sr 2+ (Sr-ion desorption) occurred from the hydrated Sr 2+ -saturated sample in 4 weeks. The irreversible sodium−strontium ion-exchange isotherm was obtained at room temperature after 4 weeks of equilibration. This mica showed much higher selectivities for Sr and Ba than for Mg and Ca, as expected. This selective Sr-ion exchanger with a large ion-exchange capacity and extremely low Sr leachability is expected to be useful for 90 Sr removal followed by its immobilization at room temperature.