| In this study, the effects of Mn(II) on the oxidation and mobilization of As(III) on the synthetic lepidocrocite(γ-FeOOH) was investigated.Firstly, abiotic oxidation of Mn(II) on γ-FeOOH was studied in kinetics and characterization. Secondly, the effects of Mn(II) on the adsorption and oxidation of As(III) were explored through Mn(II)-As(III) simultaneous oxidation, As(III) pre-treated and Mn(II) pre-treated processes. Lastly, the effects of Mn(II) on the adsorption and oxidation of As(III) on γ-MnOOH were investigated.Our results showed that Mn(III)(hydr)oxides were detected on γ-FeOOH in the abiotic oxidation of Mn(II) and its amount increased with the increase of pH ranging from7.5to8.4. In Mn(II)-As(III) simultaneous oxidation and As(III) pre-treated processes, the presence of Mn(II) promoted the removal of aqueous As(III)(including adsorption and oxidation). Considering the oxidation of As(III) by MnOx produced on γ-FeOOH, aqueous As(V) increased as a function of time. Due to the release of As(V), an increase of total As in solution after a rapid decrease was found in both processes. The release of As(V) came from the growing MnOx on γ-FeOOH, which would take up the adsorption sites and push As(V) into solution. However, in Mn(II) pre-treated process, less As(III) was adsorbed compared with the other two processes because the adsorption sites were occupied by MnOx. The concentrations of As(V) in solution reduced accordingly, suggesting oxidation of the adsorbed As(III) was oxidized to As (V). The extent of removal of As(III) and the release of As(V) correlated positively with pH values and initial Mn(II) concentrations in all process.In the study of the interaction among Mn(II), As(III) and γ-MnOOH, the presence of Mn(II) promoted the removel of As(III) and total As, while inhibited the release of As(V) into solution. This observation was more significant with the increase of pH and initial Mn(II) concentration. |
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