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

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 impu-rities 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 similar to 27 m2 g(-1).

Automated summary

The phase transformation of Ca-bentonite into zeolite LTA and hydroxysodalite was studied using fusion technique. Alkali fusion effectively eliminated opal CT and impurities, resulting in relatively pure powder, but zeolite structure depended on boehmite content. Cation exchange capacity of zeolite powders increased from 71 to 193 mg g(-1) with rising boehmite ratio from 0.40 to 0.53 due to formation of LTA structure. To achieve a cubic-shaped morphology, an alkali ratio of 1.67 was necessary, otherwise the precursor converted to hydroxysodalite or amorphous phase. The particles exhibited a mesoporous structure with a mean pore size of 6 nm, providing a specific surface area of about 27 m2 g(-1).