In this study, we demonstrate that Mn²⁺ can greatly promote the Cr(VI) reduction by oxalic acid at pH < 5 via an induction period and a subsequent auto-acceleration process. The Cr(VI) reduction rate constant during the late auto-acceleration process was about 10 times that of the initial induction period. Characterization results revealed that this interesting two-step Cr(VI) reduction phenomenon was attributed to the in-situ generated Mn³⁺ by the oxidation of Mn²⁺ with Cr(VI) in the presence of oxalic acid during the induction period. The in-situ generated Mn³⁺ might complex with oxalate and Cr(VI) to produce a ternary complex, thus facilitating the electron transfer from oxalate to Cr(VI) to automatically accelerate the Cr(VI) reduction process. These findings shed insight into the possible roles of widely existed Mn ions (Mn²⁺ and Mn³⁺) and oxalic acid in the transformation of Cr(VI) in natural aquatic environment, and also provided an efficient way to remediate Cr(VI)-containing acid wastewater.

中文翻译：

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Mn ²⁺促进草酸还原Cr（VI）：原位生成Mn ³⁺的必不可少的作用

在这项研究中，我们证明了Mn ²⁺可以通过诱导期和随后的自动加速过程，在pH <5时极大地促进草酸对Cr（VI）的还原。在后期的自动加速过程中，Cr（VI）的还原速率常数约为初始诱导期的10倍。表征结果表明，这种有趣的两步Cr（VI）还原现象归因于在诱导期间草酸存在下草酸存在下Mn ²⁺与Cr（VI）的氧化原位生成的Mn ³⁺。原位生成Mn ³⁺可能与草酸盐和Cr（VI）络合生成三元络合物，从而促进电子从草酸盐到Cr（VI）的转移，从而自动加速Cr（VI）的还原过程。这些发现使人们深入了解了广泛存在的锰离子（Mn ²⁺和Mn ³⁺）和草酸在自然水生环境中转化Cr（VI）的可能作用，并提供了一种有效的补救Cr（VI）的方法。含酸性废水。