Adsorption of antimony(III) on goethite in the presence of competitive anions

• PO43 − significantly decreased the adsorption of Sb(III) on goethite.
• Both NO3− and SO42 − had no effect on the adsorption of Sb(III) on goethite.
• Significant oxidation of Sb(III) bound to the surface of goethite had occurred.
• The adsorption processes is spontaneous and exothermic.

Adsorption of antimony (Sb) on goethite affects its mobility and bioavailability in the environment. In natural systems, competitive anions may compete with Sb adsorption sites on goethite surface. Accordingly, the adsorption of Sb(III) on goethite was investigated in the presence of competitive anions. Kinetic studies suggest that adsorption reaction of Sb(III) on goethite is rapid initially and becoming slow after 8 h both in binary Sb(III)–goethite system and in ternary Sb(III)-competitive anions–goethite system. Kinetic and adsorption isotherm studies show that PO43 − significantly decreased the adsorption of Sb(III) on goethite, while both NO3− and SO42 − had no effect. The adsorption data of Sb(III) on goethite in the absence and presence of competitive anions at three temperatures were successfully modeled using Langmuir (r2 > 0.932) and Freundlich (r2 > 0.975) isotherms. The thermodynamic parameters (∆G, ∆H, and ∆S) were calculated from the temperature dependence, suggesting that the adsorption process is spontaneous and exothermic. Accompanied by the adsorption of Sb(III) on goethite, significant oxidation of Sb(III) bound to the surface of goethite had occurred under the experimental conditions used in this study. Consequently, Sb(V) was released into the solution.

Adsorption isotherms for Sb(III) on goethite in the absence and presence of competitive anions at different temperatures.In this study, the adsorption of Sb(III) on goethite in the presence of competitive anions was examined. Adsorption experiments indicated that the presence of NO3− and SO42 − had no apparent effect on the adsorption of Sb(III) on goethite, while the presence of PO43 − induced an apparent decrease in Sb(III) adsorption on goethite. The adsorption data of Sb(III) on goethite in the absence and presence of competitive anions at 283, 298, and 318 K were fitted well by both Langmuir and Freundlich isotherms, with regression r2 of > 0.932 and > 0.975, respectively.Figure optionsDownload as PowerPoint slide