Optimization of cation-doped nano-hydroxyapatite in combination with amorphous aluminum hydroxide for defluoridation

Abstract

Abstract Given widespread fluoride in the ground water, there is a need for effective defluoridation in several geographical areas. In this regard, we explored heavily doped cationic nano-composites of hydroxyapatite (HA) given its surface chemistry for adsorption of the specific anion. We synthesized and extensively characterized HA nano-rods (HA-NR), Al/Mg-HA nanocomposites and amorphous aluminum hydroxide, and optimized their efficient defluoridation. The kinetics and thermodynamics of adsorption were further evaluated to establish the mechanistic rationale and its spontaneity. We report the optimized ideal adsorbents for the near-total removal of fluoride that demonstrated 99.99% and 99.98% efficiency with adsorption capacities of 83.3 and 81.3mg/g respectively. The adsorbent composites were (Mg-HA)-Al(OH)3 and (HA-NR)-Al(OH)3 in 1:1 ratio. The optimal conditions for defluoridation were 25mg of adsorbent in 25ml (10mg/L) fluoride solution at room temperature agitated for 10h in the pH range of 4.88–7.20.