抄録
Reduction and oxidation reactions of chromium (Cr) have attracted the interest of environmental scientist because the toxicity and mobility of Cr in soils and geologic materials are depending on its oxidation state. In this study, the oxidation of immobile and nontoxic Cr (III) to mobile and toxic Cr (VI) by a series of synthesized birnessites (σ-MnO2) with different crystallinity in aqueous environment was tested. The oxidation rates were initially fast and followed by a sharp rate decline after 1 hour equilibration. The oxidation of Cr (III) to Cr (VI) by birnessites favored lower pH, higher initial Cr (III) concentration, and higher ratio of birnessite surface area to solution volume when the other two factors are fixed. The combination of high pH and high initial Cr (III) concentration reduced Cr oxidation rate. Chromium oxidation capacity of birnessite increased with a decreased crystallinity.
