Arsenate removal from aqueous solutions: thermodynamic and kinetic study on iron hydroxide-impregnated corn cob

The contamination of water resources with arsenic is a serious environmental problem. This research investigated the use of a strategic agricultural waste for Brazil, i.e., corn cob as a low-cost, biodegradable, and eco-efficient material for As(V) adsorption. Arsenate removal from an aqueous solution with iron hydroxide impregnated corn cob (IHCC) was investigated under different pH values (2-10). FTIR spectra revealed that monodentate complexes were formed during the adsorption of arsenate on IHCC. Furthermore, SEM micrographs revealed a uniform distribution of Fe(III) and also As(V) on the IHCC. IHCC was efficient in the removal of arsenic from acidic solutions, mainly those having pH values between 2 and 3 at temperatures below 50°C. The adsorption kinetics followed the pseudo-second order model with an activation energy of 39.35 ± 6.99 kJ mol<sup>-1</sup> implying that chemical reaction was the controlling step of arsenic adsorption by IHCC. In addition, arsenic adsorption on IHCC was (i) an entropically driven, (ii) spontaneous, and (iii) endothermic phenomenon (+23.82 kJ mol<sup>-1</sup>) and involved electrostatic adsorption and chemosorption (Qmax = 40 mg/g, at 25°C). Therefore, a promising sustainable and environmentally friendly solution for the use of IHCC was devised in the current work.