Hydrothermal chemistry of silicates. Part XX. The question of phosphorus substitution for silicon during zeolite synthesis

Abstract

Isomorphous replacement of framework silicon (or aluminium) by phosphorus during zeolite synthesis, which has been the subject of conflicting reports, has been investigated under low-temperature hydrothermal conditions. As sources of Al and Si, blends of AlPO₄ and silica were prepared from metakaolinite and phosphoric acid, in some instances with further additions of silica. Samples of zeolites A, Na–P (gismondine-type), sodalite hydrate and K–F (edingtonite-type) thus obtained were analysed for phosphorus. The content of this element was extremely low, the maximum possible extents of framework substitution ranging from about 0·00056 to 0·0117 atoms of phosphorus per atom of aluminium. Some or all of this low content could merely represent discrete anions trapped in cavities within the frameworks.