Reactions of metakaolinite with NaOH and colloidal silica — Comparison of different samples (part 2)

The eight metakaolinites studied in Part 1 were reacted hydrothermally with NaOH and silica gel. After induction periods that were much longer than in the absence of additional silica the main products formed were zeolite A and X in different proportions, associated with minor amounts of zeolite P. The ratio of zeolite X to A formed after 120 h was greater in samples with longer induction periods. In samples with shorter induction periods crystals of zeolite X coated crystals of zeolite A, evidently shielding them from further reaction. No correlation could be established between any observed feature of the starting kaolinite and the product assemblages.