Enhanced degradation of 2,4-dinitrotoluene by ozonation in the presence of manganese(II) and oxalic acid

Manganese catalytic ozonation of 2,4-dinitrotoluene (DNT) in the presence of oxalic acid was studied. The addition of manganese ion (Mn²⁺) or oxalic acid alone in ozonation process did not enhance DNT degradation, but the addition of Mn²⁺ coupled with oxalic acid accelerated degradation of DNT. The DNT degradation efficiency was influenced by carbonate in the catalytic ozonation process. Kinetics study showed that Mn²⁺ catalytic ozonation significantly promoted the decomposition of ozone. Experimental results of electron spin resonance (ESR) demonstrated that addition of Mn²⁺ and oxalic acid produced much hydroxyl radicals in catalytic ozonation system than that in single ozonation system. These results suggested that catalytic ozonation followed hydroxyl radical-type mechanism. Mn²⁺ promoted decomposition of ozone to produce hydroxyl radical and it was oxidized into manganese oxide. Manganese oxide was reduced into Mn²⁺ by oxalic acid, which is the key step of catalytic process. Based on above results, a cycle catalytic mechanism of Mn²⁺ was proposed. Intermediates were determined by HPLC and GC–MS, and they mainly included aromatic organics and aliphatic carboxylic acids.