Auto-accelerating and auto-inhibiting phenomena in the oxidation process of organic contaminants by permanganate and manganese dioxide under acidic conditions: effects of manganese intermediates/products

摘要

Considering the confused/controversial kinetics law of organic contaminant oxidation by permanganate (MnO _(4) ~(?) ) and manganese dioxide (MnO _(2) ) under acidic conditions, this study was conducted to systematically investigate the oxidation kinetics and mechanisms of contaminants by MnO _(4) ~(?) and MnO _(2) under acidic conditions. The process of phenol oxidation by MnO _(4) ~(?) showed an auto-accelerating trend at pH 2.0–6.0, which was mainly associated with the generation of MnO _(2) , an oxidant more active than MnO _(4) ~(?) under acidic conditions. However, an auto-inhibiting trend was observed during phenol oxidation by MnO _(2) , which could be ascribed to the generation of Mn( II ) and its subsequent adsorption on the surface of MnO _(2) . The presence of excessive pyrophosphate (PP) greatly accelerated the oxidation of phenol by MnO _(4) ~(?) and MnO _(2) under acidic conditions due to the generation and accumulation of highly reactive Mn( III )–PP. The presence of PP also changed the manganese species at equilibrium from MnO _(2) and Mn( II ) to Mn( III )–PP, respectively, in the processes of organic contaminant oxidation by MnO _(4) ~(?) and MnO _(2) . In short, the reduction products of MnO _(4) ~(?) and MnO _(2) determined the auto-accelerating or auto-inhibiting phenomenon observed in the process of phenol oxidation by MnO _(4) ~(?) and MnO _(2) .