Synthesis of N-zeolite and chabazite from kaolinite and bentonite

Due to their chemical composition, clay minerals have been widely used as raw materials for zeolite synthesis. However, although numerous data have documented the crystallization of sodium zeolite, to our knowledge, very few studies have investigated and compared the synthesis of zeolite from kaolinite and bentonite by hydrothermal processing after KOH pre-fusion. This article moves in this direction. The Clay Mineral Society kaolinite standard (KGa-1) and a commercial bentonite sample (C-Bent-1) were used as raw materials for zeolite synthesis using distilled water or natural seawater. The laboratory tests were carried out progressively doubling the solid to liquid ratio (S/L) from 0.1 to 1.7. The effect of stirring prior to the hydrothermal process was also studied. The results indicate that with S/L = 1.7 and S/L = 0.8, N-zeolite (EDI type) is formed using both raw materials, both solutions, and without stirring. At S/L equal to 0.4, EDI type zeolite is predominant in KGa-1 although the no-stirring action and seawater improve chabazite (CHA type) crystallization which is the most abundant newly formed phase in C-Bent-1. Reduction of solid to liquid ratio (S/L = 0.1 and S/L = 0.2) controls the predominant formation of chabazite along with chabazite-merlinoite intergrowth (CHA-MER).