Physicochemical Aspects on Fluoride Adsorption for Removal from Water by Synthetic Hydrous Iron(III) – Chromium(III) Mixed Oxide

Fluoride removal with varying different parameters at 303 ± 1.6 K and pH 6.5 ± 0.2 was investigated by hydrous iron(III)-chromium(III) bimetal oxide. The kinetic and equilibrium data fitted with the pseudo-second order and Langmuir isotherm equations very well (R2 = 0.99−1.00), respectively. The Langmuir capacity (θ) and free energy (EDR) of adsorption evaluated were 16.34 (±0.50) mg·g−1 and 15.81 kJ·mol−1, respectively. The estimated thermodynamic parameters viz. ΔH0, ΔG0, and ΔS0 indicated that the reaction was endothermic but spontaneous for entropy increase. The small-scale column filtration of high fluoride (C0 = 7.37 mg·L−1) water gave encouraging results.