Hydrous ferric oxide doped alginate beads for fluoride removal: Adsorption kinetics and equilibrium studies

Abstract A new biopolymer beads, composite of hydrous ferric oxide (HFO) and alginate were synthesised, characterised and studied for its fluoride efficiency from water. The beads were characterised by chemical analysis, BET surface area, pH PZC and X-ray diffraction (XRD) analysis. The optimum conditions for fluoride removal were determined by studying operational variables viz. pH, contact time, initial F − concentration, bead dose and temperature. Presence of other anions like SO 4 2− , PO 4 3− , NO 3 − , Cl − and HCO 3 − effect on fluoride removal efficiency of prepared beads was also tested. The beads were 0.8–0.9 mm in size and contain 32–33% Fe (III) and showed specific surface area of 25.80 m 2 g −1 and pH PZC of 5.15. Modified beads demonstrated Langmuir F − adsorption capacity of 8.90 mg g −1 at pH 7.0. The adsorption kinetics were best described by the pseudo-second order kinetic model followed by intra-particle diffusion as the rate determining step. It was found that about 80% of the adsorbed fluoride could be desorbed by using 0.05 M HCl. The FTIR, Raman and SEM-EDAX analysis were used to study the fluoride adsorption mechanisms on beads. Studies were also conducted to test the potential application of beads for F − removal from drinking water and the treated water quality.