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.