Role of dissolved Mn(III) in transformation of organic contaminants: Non-oxidative versus oxidative mechanisms

Mn(III) is a strong oxidant for one electron transfer, which may be important in the transformation of organic contaminants during water/wastewater treatment and biogeochemical redox processes. This study explored the reaction mechanisms of dissolved Mn(III) with organics. The role of dissolved Mn(III) either as a catalyst or an oxidant in reactions with organics was recognized. Aquo and/or hydroxo (or free) Mn(III), generated from the bisulfite activated permanganate process, facilitated efficient N-dealkylation of atrazine via a beta-elimination mechanism, resulting no net redox reaction. In contrast, free Mn(III) degraded 4-chlorophenol via intramolecular redox processes, the same as hydroxyl radical ((OH)-O-center dot), resulting in dechlorination, (OH)-O-center dot substitution, ring-opening and mineralization. Mn(III)-pyrophosphate compounds did not react with atrazine because complexation by pyrophosphate rendered Mn(III) unable to bond with atrazine, thus the electron and proton transfers between the reactants couldn't occur. However, it degraded 4-chlorophenol at a slower rate compared to free Mn(III), due to its reduced oxidation potential. These results showed two distinct mechanisms on the degradation of organic contaminants and the insights may be applied in natural manganese-rich environments and water treatment processes with manganese compounds. (C) 2017 Elsevier Ltd. All rights reserved.

三价锰（Mn(III)）是一种用于单电子转移的强氧化剂，这在水/废水处理以及生物地球化学氧化还原过程中有机污染物的转化方面可能具有重要意义。本研究探讨了溶解态三价锰与有机物的反应机理。认识到溶解态三价锰在与有机物反应中作为催化剂或氧化剂的作用。由亚硫酸氢盐活化的高锰酸盐过程产生的水合和/或羟基（或游离）三价锰通过β -消除机制促进了阿特拉津的高效N -脱烷基化反应，且没有净氧化还原反应发生。相比之下，游离三价锰通过分子内氧化还原过程降解4 -氯苯酚，这与羟基自由基（·OH）相同，导致脱氯、·OH取代、开环和矿化。焦磷酸锰（III）化合物不与阿特拉津反应，因为焦磷酸的络合作用使三价锰无法与阿特拉津结合，从而反应物之间无法发生电子和质子转移。然而，与游离三价锰相比，它以较慢的速率降解4 -氯苯酚，这是由于其氧化电位降低。这些结果表明了有机污染物降解的两种不同机制，这些见解可应用于富含天然锰的环境以及含锰化合物的水处理过程。（C）2017爱思唯尔有限公司。保留所有权利。