Manganese(IV) oxides, and more especially birnessite, rank among the most efficient metal oxides for As(III) oxidation and subsequent sorption, and thus for arsenic immobilization. Efficiency is limited however by the precipitation of low valence Mn (hydr)oxides at the birnessite surface that leads to its passivation. The present work investigates experimentally the influence of chelating agents on this oxidative process. Specifically, the influence of sodium pyrophosphate (PP), an efficient Mn(III) chelating agent, on As(III) oxidation by birnessite was investigated using batch experiments and different arsenic concentrations at circum-neutral pH. In the absence of PP, Mn(II/III) species are continuously generated during As(III) oxidation and adsorbed to the mineral surface. Field emission-scanning electron microscopy, synchrotron-based X-ray diffraction and Fourier transform infrared spectroscopy indicate that manganite is formed, passivating birnessite surface and thus hampering the oxidative process. In the presence of PP, generated Mn(II/III) species form soluble complexes, thus inhibiting surface passivation and promoting As(III) conversion to As(V) with PP. Enhancement of As(III) oxidation by Mn oxides strongly depends on the affinity of the chelating agent for Mn(III) and from the induced stability of Mn(III) complexes. Compared to PP, the positive influence of oxalate, for example, on the oxidative process is more limited. The present study thus provides new insights into the possible optimization of arsenic removal from water using Mn oxides, and on the possible environmental control of arsenic contamination by these ubiquitous nontoxic mineral species.

锰（IV）氧化物，尤其是水钠锰矿，是用于As（III）氧化和后续吸附以及砷固定的最有效金属氧化物。但是，效率受到水钠锰矿表面低价锰（氢）氧化物的沉淀的限制，导致钝化。本工作通过实验研究了螯合剂对该氧化过程的影响。具体而言，使用批处理实验和在环境中性pH值下不同的砷浓度，研究了有效的Mn（III）螯合剂焦磷酸钠（PP）对水钠锰矿氧化As（III）的影响。在没有PP的情况下，在As（III）氧化过程中会连续生成Mn（II / III）物种并吸附到矿物表面。场发射扫描电子显微镜 基于同步加速器的X射线衍射和傅里叶变换红外光谱表明，形成了锰矿，钝化了水钠锰矿表面，从而阻碍了氧化过程。在PP存在下，生成的Mn（II / III）物质形成可溶性络合物，从而抑制了表面钝化并促进了用PP将As（III）转化为As（V）。Mn氧化物增强As（III）氧化的能力在很大程度上取决于螯合剂对Mn（III）的亲和力和Mn（III）配合物的诱导稳定性。与PP相比，草酸盐对氧化过程的积极影响更为有限。因此，本研究为使用Mn氧化物从水中去除砷的可能优化以及这些无处不在的无毒矿物对砷污染的可能环境控制提供了新的见识。