| Acid birnessite was treated with Na4P2O7 at pH 2, 4, 5 respectively. After the treatments, the species and content of manganese ion in the complex solution, and the variation of average oxidation state (AOS) of Mn in birnessite, and the amount of adsorbed Pb2+ and released Mn2+, H+ during the Pb2+ adsorption were investigated. The results indicate that after acid birnessite, the AOS of Mn is 3.670 which is treated by Na4P2O7 at different pH, Mn(Ⅲ) located in the layer edge and part of Mn(Ⅲ) located in the interlayer are released to the solution through complexation with Na4P2O7.The content of Mn(Ⅱ) in the structure of original birnessite is very low. Small amount of Mn(Ⅱ), which accounts for 4.70%-7.46% in the molar percentage of total released Mn, is also released simultaneously. The AOS of Mn of birnessites after treatment increases to 3.783 (pH 2), 3.786 (pH 4), 3.824 (pH 5) respectively. While the crystal structure of birnessite does not change after treatment, the amount of Mn(Ⅲ) located above or below vacant cation sites decreases, and the amount of H+ located above or below vacant cation sites goes up in the structure of birnessites. The amount of vacant cation sites responsible for Pb2+ adsorption increases, which lead to the increase of the maximum amount of adsorbed Pb2+. Additionally, the distribution of Mn(Ⅲ) in the structure of acid birnessite is deduced. About one sixth of Mn(Ⅲ) locates in the layer edge, and five sixths of Mn(Ⅲ) locates in the interlayer and the non layer edge. |
