Effects of NaOH concentration on zeolite synthesis from fly ash with a hydrothermal treatment method

Abstract

Effects of NaOH concentration on the crystal structure and the reaction rate of the zeolite synthesized from fly ash with a hydrothermal treatment method was investigated. The fly ash or the mixture of fly ash and silica powder was hydrothermal treated using NaOH aqueous solutions of various concentrations. As a result, a decrease in the NaOH concentration raises the selectivity of phillipsite to the generated zeolite, and lessens that of hydroxysodalite. The reaction rates of them increase consistently with the NaOH concentration. It is clarified that the dependence of crystal structure of generated zeolite on NaOH concentration is not only induced by the dependence of the dissolution rates of silicate ion and aluminate ion from fly ash on it. The fraction of additive silica powder required to synthesize phillipsite selectively increases with increase in the NaOH concentration, and the required treatment time decreases with it.