Arsenate Desorption From Synthetic Goethite Promoted by Competitive Adsorbents.

Arsenic toxicity in biological systems is well established and the understanding of its adsorption-desorption in mineral surfaces is critical for predicting As behavior in many important soil-water systems around the world. Although the adsorption of arsenate on Fe (oxyhydr)oxides has been extensively studied, its strength of retention on these mineral surfaces remains unsolved. Accordingly, we studied the kinetics of arsenate desorption from goethite induced by anion exchange resin (IRA 400). Synthetic goethite was prepared and its phase purity was checked by XRD using the Rietveld method for structure refinement. Langmuir adsorption maximum for arsenate on goethite and the resin were 0.103 and 1.667 mmol/g, respectively in 20 mM sodium acetate at pH 5. Arsenate was pre-adsorbed on goethite to obtain 25, 50, 75 and 100% of the Langmuir maximum at pH 5 in 20 mM sodium acetate. After 24 hours equilibration, resin was added and samples were collected periodically. Dissolved As, As remaining on goethite and As obtained on the resin were determined. In general, the dissolved concentration of As decreased in an exponential fashion, reaching low equilibrium concentrations and the As shifted from being retained on goethite to the resin.