ARSENATE ADSORPTION ONTO ALUMINIUM AND I

The geochemical fates of iron and arsenic are so closely correlated that methods of arsenic removal from water are in general based on the high adsorptive affinity of this metalloid with iron (hydr)oxides. Under anoxic conditions, however, reductive dissolution of iron (hydr)oxides can take place, and arsenic may be released into the surrounding environment. The purpose of this study was to investigate the potential of Al-substituted goethites in adsorbing arsenic compared with other Fe and Al (hydr)oxides. Hematite (Hm), goethite (Gt), 2-line ferrihydrite (Fh), gibbsite (Gb), aluminium hydroxide, and three Al-substituted goethites (AlGt) were synthesized and characterized by X-ray powder diffraction (XRD), particle size analysis, and diffuse reflectance (DR) spectroscopy. Adsorption isotherms were obtained after shaking the samples with increasing concentrations of arsenate (40 - 1600 mg L-1) in a 10 mmol L-1 CaCl2 solution for 24 hours. The adsorption envelope was measured at pH ranging from 3 to 9. The As(V) adsorption maxima decreased in the following order: Al(OH)3 > Fh > AlGt-15 > AlGt-25 > AlGt-35 > Hm > Gb > Gt. No relationship was observed between particle diameter and maximum adsorption, suggesting that re-aggregation could have taken place, or possibly that imperfections on the surface of the particles increased their surface net charge, resulting in high adsorption density. The behaviour of all samples was strongly dependent on pH, and the maximum adsorption was achieved in slightly acidic conditions. In general, Al-substituted goethites showed promising results for their potential use as an adsorbent to remove arsenic from water.