Defluoridation of Water Using Cu-Mg-Binary-Metal-Oxide-Coated Sand

Abstract

Defluoridation of water was evaluated using a copper–magnesium (Cu-Mg) coated sand (CMCS) as a sustainable adsorbent containing binary metal oxides. The CMCS sorbent coating contained mostly amorphous copper and magnesium oxides in the Cu-Mg coating on the crystalline sand surface. Pseudo-second-order kinetics was observed where most fluoride was removed rapidly within an hour. Favorable adsorption occurred according to the Langmuir and Freundlich adsorption equations, while physisorption occurred according to the Dubinin–Radushkevich (D-R) adsorption equation. The adsorption capacity of the CMCS sorbent based on sorbent surface was similar to various other adsorbents with larger adsorbent surface areas, likely due to the efficacy of the Cu-Mg coating despite the CMCS sorbent’s much smaller surface area. Fluoride was adsorbed effectively from pH 3 to pH 11 through adsorption of anionic fluoride onto the CMCS sorbent’s protonated surface with a pHPZC of 10.5, indicative of electrostatic attraction as the main adsorption mechanism. The CMCS sorbent’s re-coating was conducive to successful recycling and reuse of the CMCS sorbent as a sustainable adsorbent for water defluoridation.