Preparation, characterization, and cation exchange selectivity of synthetic and topotactically altered naturally occurring trioctahedral micas

The large quantity of high level nuclear waste held in underground stainless steel storage tanks around the country has necessitated the need for inorganic ion exchange materials with the ability to selectively remove radioactive species such as 137Cs and 90Sr in the presence of large concentrations of competing cations. Sodium expandable micas, such as sodium fluorophlogopite and K-depleted phlogopite have shown promise for this purpose. During this research highly charged sodium fluorophlogopite micas, Na_x(Mg₃)[Al_xSi_4−x]O ₁₀F₂·yH₂O, with layer charges of −2, −3, and −4 per unit cell were synthesized from a dry mix of poorly crystalline kaolinite, Mg(NO3)2, and NaF. Additional silicon was also added to the reaction mixture in the form of amorphous SiO₂ to increase the Si:Al ratio as needed. Talc was also utilized for the first time as Si and Mg sources in the synthesis of Na-2-mica. Potassium-depleted phlogopite, K_1−xNa_x(Mg₃)[AlSi₃]O ₁₀(OH)₂, was prepared by conventional and microwave assisted equilibration of <45μm phlogopite mica with a solution containing sodium tetraphenylborate.; The synthesized materials were characterized using X-ray diffraction, scanning electron microscopy, magic angle spinning nuclear magnetic resonance, and wet chemical techniques. Three synthetic sodium fluorophlogopite micas and one K-depleted phlogopite sample were selected for ion exchange studies. Ion exchange isotherms for the synthetic sodium fluorophlogopite micas were obtained for Cs+, Sr2+, Ba2+, and Co2+. For the K-depleted phlogopite ion exchange isotherms for Cs+ and Sr2+ were determined.; The ion exchange studies indicated that only the Na-2-mica was selective for Cs+, all three micas were selective for Sr2+. All three mica also appeared to be highly selective for both Ba2+ and Co2+. The ion exchange studies indicated that the K-depleted phlogopite was highly selective for both Cs+ and Sr 2+. The ion selectivity of all of these micas indicates that they may be useful not only for removal of radioactive isotopes from the nuclear waste stream, but also removal of transition metal cations from industrial wastes.