Synthesis of Na-4-mica from metakaolinite and MgO: characterization and Sr2+ uptake kinetics

Abstract

Na-4-mica, a high-charge-density sodium fluorophlogopite mica of ideal chemical composition Na₄Mg₆Al₄Si₄O₂₀F₄xH₂O has been prepared from a mixture of NaF, MgO and metakaolinite (the latter serving as an inexpensive aluminosilicate source). Highly crystalline Na-4-mica can be easily and economically synthesized from the above precursors in the temperature range 850–890 °C. ²⁷Al and ²⁹Si MAS NMR spectroscopy revealed that the Na-4-mica synthesized from metakaolinite is more close to the ideal nearest neighbor distribution of Al and Si compared to that prepared from magnesium aluminosilicate gel. Selective Sr exchange kinetic studies showed that the uptake was slow because of the somewhat large particle size as determined by scanning electron microscopy as well as restricted interlayer spacing.