Hydrothermal synthesis of zeolite-a from natural rhyolite for effective removal of Cr(VI) from wastewater

Abstract

Hexavalent chromium (Cr(VI)) is a toxic and carcinogenic pollutant that can adversely affect bone formation during fetal development and damage kidneys. Technologies, such as chemical precipitation, oxidation, and reduction, have been explored for removing Cr(VI) from wastewater. However, these methods are often expensive, futile, and have collateral effects on the environment. The objective of this study was to treat Cr(VI)-contaminated wastewater using zeolite-A crystals, which were synthesized from natural rhyolite through a hydrothermal process. The synthesized zeolite-A material was characterized using FTIR, XRD, and SEM analyses. The resulting zeolite-A exhibited high crystallinity (83.67%) and low amorphicity (16.33%). While treating Cr(VI)-contaminated wastewater with the synthesized zeolite-A, the zeolite-A crystals exhibited remarkable efficiency, achieving an impressive adsorption capacity of 94.33% for Cr(VI) ions. The adsorption isotherm data aligned perfectly with the Freundlich isotherm model, boasting a correlation coefficient (R²) of 0.99. This high correlation indicates that Cr(VI) ions were adsorbed in multiple layers onto the active sites of zeolite-A. The separation factor (RL) of 0.24 indicated that the adsorption process was favorable, as it fell within the range of 0–1. Furthermore, the adsorption kinetics adhered to a pseudo-first-order model, suggesting that physisorption was the main rate-determining step. This means the overall adsorption rate was primarily influenced by the concentration of the reactant. Therefore, zeolite-A crystals synthesized from natural rhyolite present an effective and economical solution for remediating Cr(VI)-contaminated wastewater through adsorption. This makes them a promising option for wastewater treatment.