Arsenic adsorption onto aluminium-substituted goethite

Abstract

Environmental contextGoethite, commonly found in soils, is often partially substituted by Al and strongly influences the mobility of arsenic in the environment. The adsorption of AsV onto goethites with increasing Al substitution was explored, finding that Al incorporation decreases AsV sorption per gram of adsorbent, and that a low level of Al incorporation enhances the adsorption per unit area. Structures of the complexes formed between AsV and the oxy(hydr)oxide surface, at different pH values, are proposed by studying the changes in the surface charges of the adsorbed and non-adsorbed substituted and non-substituted goethites. AbstractAluminium and iron oxy(hydr)oxides in nature are often partially substituted by other elements and strongly influence the mobility of arsenic in the environment. Because goethite is commonly found in soils, and the oxide is easily substituted, in the present work, the adsorption of AsV onto several Al-substituted goethites was explored in order to determine how substitution affects the adsorption process. Three samples with increasing Al content (GAl0, GAl3.78 and GAl7.61) were prepared and fully characterised. The variations in AsV adsorption under different conditions, as well as the variations of the particle surface charge, were analysed. The results showed that the removal capacity of Al-goethites is determined by the Al content. The adsorption maxima per gram followed the trend GAl0> GAl3.78> GAl7.61, indicating that Al incorporation decreases AsV sorption. Adsorption per surface area decreased in the order GAl3.78> GAl0> GAl7.61, implying that a small incorporation of Al enhances the adsorption properties of the surface. The stoichiometry of the probable surface complexes formed with the contaminant at different pH values is proposed, by analysis of all the experimental results obtained before and after AsV adsorption. These surface complexes were used to fit the experimental data with good agreement, and the formation and acidity constants were also estimated.