Degradation of 2,4-dinitrotoluene by persulfate activated with zero-valent iron

The oxidation of 2,4-dinitrotoluene (DNT) by persulfate (S2O82−) activated with zero-valent iron (Feo) was studied through a series of batch experiments. The mechanism for Feo activation was investigated by comparing with Fe2+, and the effects of persulfate-to-iron ratio and pre-reduction on DNT oxidation were examined. DNT was stable in the presence of persulfate and transformed only when Feo was added. Most DNT was degraded oxidatively by Feo-activated persulfate, whereas direct reduction of DNT by Feo was unimportant. The rate of DNT degradation increased with higher Feo dose, presumably due to increasing activation of persulfate by Feo and Fe2+. In contrast to the Feo-persulfate system, where complete oxidation DNT was achieved, only ≤ 20% of DNT was degraded and the reaction was terminated rapidly when Feo was replaced with equimolar Fe2+. This indicates that Feo is more effective than Fe2+ as activating agent and potentially more suitable for environmental applications. The reduction products of DNT were more rapidly oxidized by persulfate than DNT, suggesting that converting the nitro groups of NACs to amino groups prior to oxidation can greatly enhance their oxidation. This suggests that a sequential Feo reduction–persulfate oxidation process may be an effective strategy to promote NAC degradation.