Identification of phase transformation during conversion of Ca-bentonite into a low silica-based zeolite structure through fusion and hydrothermal processes

Abstract

The present study signified the phase transformation during the conversion of Ca-bentonite into zeolite LTA, and hydroxysodalite in the presence of boehmite through the fusion technique. Although opal CT, and other impurities could be easily eliminated by alkali fusion, leading to formation of relatively pure powder, the obtained zeolite structure effectively depends on boehmite content. The cation exchange capacity (CEC) of zeolite powders was found to be increased from 71 to 193 ​mg ​g−1 with rise in boehmite ratio from 0.40 to 0.53 due to formation of LTA structure. Moreover, to create a cubic-shaped morphology, the alkali ratio should be fixed at 1.67 otherwise, the precursor is converted to hydroxysodalite or amorphous phase, depending on boehmite ratio. The particles exhibited a mesoporous structure with mean pore size about 6 ​nm, providing a specific surface area ∼27 ​m2 ​g−1.