Zeolite Synthesis under Insertion of Silica Rich Filtration Residues from Industrial Wastewater Reconditioning

Abstract

Zeolite synthesis was studied using two silica rich filtration residues (FR 1 and FR 2) as Si-source and sodium aluminate in a direct synthesis at 60˚C at strong alkaline conditions (8 M - 16 M NaOH). In addition to these one-pot syntheses, a two-step process was investigated. Here, an alkaline digestion of FR at 60˚C was followed by gel precipitation with sodium aluminate and gel crystallization under usual conditions of 80˚C - 90˚C. The results show that the substitution of chemical reagent sodium silicate by a waste material like FR as Si-source is possible but requires fine tuning of the reaction conditions as zeolite crystallization is a process under kinetic control. The solubility behaviour and impurities of the inserted filtration residues strongly influenced the course of reaction. Thus zeolites like hydrosodalite or intermediate zeolite between cancrinite and sodalite, or zeolite NaA or Z-21 in cocrystallization with hydrosodalite could be observed in the one pot...