Solid transformation synthesis of zeolites from fly ash

Abstract

The solid transformation method was used to synthesize zeolites from fly ash (FA). The effects of the calcination temperature, alkali–fly ash ratio, liquid–solid ratio and crystallization reaction time on the formation of NaA type zeolites and the changes of mineralogy were investigated during the synthesis process. The crystal transformations, specific surface areas and pore sizes, and textural properties of the zeolite products were characterized using XRD, BET, SEM and TG. The experimental results indicated that a zeolite with three kinds of crystal morphology (NaA, SOD, and Ph zeolites) and a higher cation-exchange capacity (CEC) was obtained from coal fly ash at a calcination temperature of 650 °C, a crystallization temperature of 90 °C and a crystallization time of 3.5 h, a liquid–solid ratio of 2.7 : 1 and an alkali–fly ash ratio of 0.5 : 1. The CEC value and adsorption capabilities for Cr(VI) of the FA – derived zeolite synthesized using solid transformation technology were closely similar to those of a commercial grade NaA zeolite.