School of Chemical Engineering and Technology, Tianjin University, Tianjin, PR China.
School of Chemistry and Chemical Engineering, Tianjin University of Technology, Tianjin, PR China.
J Hazard Mater. 2013 Jun 15;254-255:89-97. doi: 10.1016/j.jhazmat.2013.03.022. Epub 2013 Mar 16.
Manganese (hydr)oxides are powerful oxidants mediating the transformation of As(III) to As(V) under natural conditions, however, the presence of Mn(II) on the oxidation of As(III) in the pH range of 7.0-9.0 has not been reported so far. In this study, abiotic oxidation of Mn(II) to amorphous Mn(III, IV) (hydr)oxides (MnOx) on magnetite and hematite was confirmed, and the impact of newly formed MnOx on the fate of As(III) was investigated. With the addition of Mn(II) into As(III)-preloaded systems, the dissolved and the adsorbed As(III) was oxidized to As(V) at high pH, and Mn(II) mobilized the adsorbed As(III) and As(V) in hematite system. High production of dissolved As(V) and significant mobilization of As(III) were even more significant in hematite suspension (total As was 18.96 mgL(-1) after 60 h at pH 8.62) with simultaneous addition of Mn(II) and As(III), while magnetite showed a higher capacity for the retention of As(III) and As(V). It could therefore be deduced that the newly formed MnOx on iron oxides could oxidize the dissolved and the adsorbed As(III) to As(V). In addition, the MnOx formed at high pH would take up the sorption sites previously occupied by the adsorbed As(III), and then mobilized a fraction of the adsorbed As(III) into solution. The present study reveals that MnOx formed via abiotic oxidation on iron oxides plays an important role in the oxidation and mobilization of both dissolved and adsorbed As(III) in aquatic environment.
水合氧化锰是一种强有力的氧化剂，可在自然条件下将砷(III)转化为砷(V)，然而，目前尚未有报道表明在 pH 值为 7.0-9.0 的范围内，Mn(II)的存在会促进砷(III)的氧化。在本研究中，证实了磁铁矿和赤铁矿上的 Mn(II)非生物氧化为无定形的 Mn(III,IV)(水合)氧化物(MnOx)，并研究了新形成的 MnOx 对砷(III)命运的影响。在向预先加载有砷(III)的体系中添加 Mn(II)的情况下，高 pH 值下溶解态和吸附态的砷(III)被氧化为砷(V)，并且 Mn(II)使赤铁矿体系中吸附的砷(III)和砷(V)发生迁移。在同时添加 Mn(II)和砷(III)的情况下，赤铁矿悬浮液中溶解态砷(V)的高产量和吸附态砷(III)的显著迁移更为显著（在 pH 值为 8.62 时，60 小时后总砷含量为 18.96 mgL(-1)），而磁铁矿对砷(III)和砷(V)的保留能力更高。因此可以推断，氧化铁上新形成的 MnOx 可以将溶解态和吸附态的砷(III)氧化为砷(V)。此外，在高 pH 值下形成的 MnOx 将占据先前被吸附的砷(III)占据的吸附位点，然后将一部分吸附的砷(III)迁移到溶液中。本研究揭示了通过氧化铁上的非生物氧化形成的 MnOx 在水生环境中溶解态和吸附态砷(III)的氧化和迁移中发挥着重要作用。
