Arsenate removal from aqueous solutions using modified red mud

Red mud (RM), a waste tailing from alumina production, was modified with FeCl3 for the removal of arsenate from water. The RM and modified red mud (MRM) were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD) microanalysis. Adsorption of arsenate on modified red mud (MRM) was studied as a function of time, pH, and coexisting ions. Equilibrium time for arsenate removal was 24 h. Solution pH significantly affected the adsorption, and the adsorption capacity increased with the decrease in pH. Langmuir and Freundlich isotherms equation were used to fit the adsorption isotherms. The Langmuir isotherm was the best-fit adsorption isotherm model for the experimental data. Adsorption capacity of MRM was found to be 68.5 mg/g, 50.6 mg/g and 23.2 mg/g at pH 6, 7 and 9, respectively. NO3− had little effect on the adsorption. Ca2+ enhanced the adsorption, while HCO3− decreased the adsorption. MRM could be regenerated with NaOH, and the regeneration efficiency reached 92.1% when the concentration of NaOH was 0.2 mol/L.