Fluoride removal efficiency from aqueous solution by synthetic iron(III)–aluminum(III)–chromium(III) ternary mixed oxide

Abstract

Hydrated iron(III)–aluminum(III)–chromium(III) ternary mixed oxide (HIACMO) was synthesized and characterized. FTIR studies confirmed the presence of M–O–M 1 type bond in HIACMO. Use of it for investigating fluoride removal efficiency at varied conditions showed that the reaction was pH sensitive, and optimum pH (initial) was between 4.0 and 7.0. The time required to attain dynamic equilibrium was 1.5 h. The pseudo-second order equation described all kinetic data very well. The rate of reaction was multistage diffusion phenomena. The Langmuir isotherm equation described the equilibrium well. Thermodynamic analyzes of equilibriums indicated that the adsorption reaction of fluoride with HIACMO from water was endothermic and spontaneous in nature. The equilibrium solution pH analyzes suggested ion/ligand exchange mechanism for fluoride adsorption. Regeneration of fluoride adsorbed material could be possible up to 90.0 (± 2.0)% with 0.5 M NaOH. 0.2 g of HIACMO reduced fluoride level well below the maximum permissible value from 50.0 ml of fluoride spiked tap water (10.0 mg F − dm − 3 ) sample.