Fabrication of Manganese-Supported Activated Alumina Adsorbent for Defluoridation of Water: A Kinetics and Thermodynamics Study

Abstract

Fluoride pollution frequently occurs in many underground drinking water sources due to discrepancies in the geological environment. To address this problem, a manganese-supported activated alumina (MnOOH-supported AA) adsorbent was proposed in the present study. The adsorbent was prepared with an impregnation method, then the morphology and microstructure were systematically characterized. Further, the adsorption kinetics and thermodynamics were systematically explored through static experiments to confirm the adsorption mechanism. The results showed that MnOOH was successfully loaded on the activated alumina (AA), and irregular and convex spinous structures were formed on the surface of particles. Compared with the AA, MnOOH-supported AA exhibited a significantly higher defluoridation rate, which has been doubled. The kinetic behavior of fluoride adsorption on MnOOH-supported AA was governed by the quasi-second-order kinetics model with regression coefficients of 0.9862, 0.9978 and 0.9956, respectively. The adsorption rate was mainly ascribed to the intra-particle diffusion. Additionally, the Freundlich isotherm equation fitted the adsorption thermodynamic process reasonably well compared with the Langmuir adsorption model. Specifically, the correlation coefficients were 0.9614, 0.9383 and 0.9852 at 25 °C, 35 °C and 45 °C, respectively. The adsorption–desorption isotherm plot was similar to the Type V isotherm. The whole fluoride adsorption was a spontaneous endothermic reaction, and controlled by chemical adsorption. These results demonstrated that MnOOH-supported AA as an alternative to the conventional AA showed promising potential for defluoridation in drinking water treatment.