Chemistry of soil minerals. Part XI. Hydrothermal transformations of metakaolinite in potassium hydroxide

Abstract

Metakaolinite, or metakaolinite with added silica, has been treated with potassium hydroxide solutions to yield six zeolites and the two felspathoids kaliophilite and kalsilite. Among the zeolites K–F, K–M (near-phillipsite), and K–G (near-chabazites) were abundantly and consistently formed. The properties of these zeolites and of their ion-exchange forms have been particularly examined. The near-chabazites were prepared with ratios SiO₂/Al₂O₃ from 2·13 to 4·51; the most siliceous of these in their Li- or Ca- exchange forms were excellent sorbents with the molecule-sieving characteristics of calcium-rich natural chabazites. The yields of crystals (K–G or K–F) declined with increasing excess of KOH of constant molality; and the ratios SiO₂/Al₂O₃ were always less than these ratios in the reactant mixture except when SiO₂/Al₂O₃= 2. Whatever the ratio SiO₂/Al₂O₃ in the parent mixture this ratio in the resultant crystals approached more and more nearly to 2 the greater the alkali concentration.