Reactions of kaolinites and metakaolinites with NaOH—comparison of different samples (Part 1)

Reactions with aqueous sodium hydroxide of eight different kaolinites and of metakaolinites derived from them were studied under hydrothermal conditions. All the kaolinites gave basic hydrosodalite 8:2:2 (8Na+/2OH−/2H2O) as the primary product. The metakaolinites reacted to produce mainly zeolite A, in some of the samples associated with minor amounts of zeolite X. After 5 days, all the metakaolinites were converted to hydrosodalite. The kinetics of the reactions of the samples differed, but no correlation could be established between the rates of the reactions and the crystallinity of the kaolinites, the impurities present or any other observed feature of the starting material.