Hydrothermal chemistry of silicates. Part XVI. Replacement of aluminium by boron during zeolite growth

Abstract

The possibility of isomorphous replacement of Al by B during crystallisation of some zeolites has been investigated in the system Na₂O–Al₂O₃–B₂O₃–SiO₂–H₂O. Of the zeolites grown the compact analcite structure is essentially free of boron even when the borate concentration is very high. Zeolite A and the gismondite-type zeolite Na-P1 crystallise with significant amounts of boron, which however can readily be washed out again leaving the compounds with only minimal boron content. The faujasite-type zeolite X retains a significant amount of boron after thorough washing, while in sodalite hydrate this boron content is substantial. Various properties have been examined and it is probable that in zeolite X and sodalite hydrate boron is nearly all present as borate in the tetra-decahedra1 sodalite cages which occur in each. Thus substitution of Al by B in the above zeolite frameworks is considered to be insignificant during synthesis in alkaline aqueous media.