No abstract

During low temperature hydrothermal alkaline conversion of kaolinite in the presence of sodium carbonate a disordered phase crystallizes showing structural features between the socialite and cancrinite minerals. A detailed study of its formation field and the kinetics of crystallization is the first step for fu~er investigations of this zenlite-like material. The crystallization kinetics was investigated in the early stage of the reaction for timesTul~, to 192 h at a temperature of 353 K. Besides X-ray powder diffraction A1 MAS NMR has been found to be the preferred method to follow the reaction kinetics because a signal assigned to six-coordinated almninium of the starting kaolinite can be clearly distinguished from a second resonance, being typical for aluminium in four-coordinate position of an aluminosilicate framework structure. Important conclusions can also be drawn from the experiments for the synthesis of ideal ordered cancrinites.