Zero-valent iron-aluminium co-corrosion: A potential comprehensive low-cost method for water defluoridation

Abstract

Climate change coupled with population increase has forced communities in fluoride rich areas to turn to fluoride contaminated groundwater to fill in the water deficit created by drying of water sources and increasing water demand. Application of low-cost materials such as iron and aluminium hydroxides in the field is limited by expensive preparation steps involved. This study investigated the applicability of Fe and Al, in their metallic states, in water defluoridation by allowing simultaneous corrosion of zero-valent aluminium (ZVA) and iron (ZVI) to form in situ hydroxides. The effect of time, dose, concentration and pH was studied by varying one parameter at a time while controlling others. Findings reveal that, mixing the two materials in their metallic state have the same synergistic effect on their fluoride removal properties as their corresponding (hydr)oxides. Whereas in their pure metallic states, iron and aluminium lowered the concentration of fluoride from 15 - 13.09 mg/L and 15 - 14.9 mg/L respectively, their mixture lowered fluoride levels from 15 - 7.74 mg/L in the period of seven (7) days. Spiking the fluoride solution with Fe3+ ions was found to enhance fluoride removal by lowering Fluoride levels from 15 - 0.8 mg/L in the same period. This could imply that a fluoride removal mechanism in this process involves precipitation of fluoro-complexes of iron rather than those of aluminium. These findings, therefore, suggest that a step involving conversion of ZVA and ZVI into their (hydr)oxides can be skipped in water defluoridation without significantly affecting their fluoride removal capacities.