Abstract
The adsorption behavior of thioarsenite (TAsIII) on the surface of hematite (α-Fe2O3) is unknown at present. In the present study, we have investigated the transformation and reactions of TAsIII [monothioarsenite (MTAsIII) and dithioarsneite (DTAsIII)] on the surface of α-Fe2O3 in the presence of sulfide at S/As = 1 and 3 by X-ray absorption spectroscopy (XAS) and Raman spectroscopy. The adsorption envelopes reveal that the adsorption of TAsIII on α-Fe2O3 is significantly less than that of arsenite (AsIII) in the pH range from 7 to 11 with the initial As concentration of 25 mg L−1. However, at the initial As concentration of 135 mg L−1, the uptake of TAsIII by α-Fe2O3 is higher at pH 7 but lower at pH 8–11 than that of AsIII. The adsorption isotherms show that the adsorption of As on α-Fe2O3 is largely inhibited by the presence of aqueous sulfide at pH 7 with low As equilibrium concentration (<40 mg L−1). Whereas the uptake of As by α-Fe2O3 is highly elevated compared with the value predicted by Langmuir model at pH 7 with high As equilibrium concentration (>40 mg L−1), implying the formation of As-bearing (surface) precipitate. The As and S K-edge XAS as well as Raman spectroscopy confirm the formation of As sulfide precipitate on the surface of α-Fe2O3 in MTAsIII system. It is worth to note that the oxidation of (thio)AsIII occurs on the surface of α-Fe2O3 in DTAsIII system under strictly anaerobic conditions. These results shed new light on the understanding of the interfacial behavior of As and point to the potential implication in immobilization and removal of arsenic in sulfidic environment.
Published Version
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