Defluoridation from aqueous solution by cattle bone char and hydroxyapatite

Abstract

Water containing fluoride beyond 1 mg/L is harmful to human health. In this study, cattle bone char (BC) and hydroxyapatite (HAP) were used in fluoride removal from water. The BC and HAP surface characteristics were investigated by BET, FTIR, XRD,XPS and SEM analysis. BET analysis shows that BC had a higher specific area (59.62 m2/g) than HAP (45.69 m2/g), and their pores size are 9.52 nm and 9.51 nm respectively. XRD analysis reveals that Ca10(PO4)6(OH)2 is the major constituent of BC and HAP. The effects of adsorbent dose, pH, initial fluoride concentration, temperature, and ionic strength on adsorption capacity were explored. The adsorption capacity increases with initial fluoride concentration and decreases with pH, and the maximum adsorption capacities of BC and HAP are 10.23 and 12.90 mmol/g at pH 3 respectively. The adsorption isotherms were evaluated by Freundlich and Langmuir models across fluoride concentration. Based on XRD, XPS and FTIR pattern shown, the major mechanisms of the BC and HAP for fluoride removal with increasing fluoride concentrations are surface complex formation and electrostatic interactions between adsorbent surface and fluoride, then ion exchange, and then precipitation of CaF2