To solve the problem that polychlorinated biphenyls (PCBs) in soil are difficult to be removed by conventional oxidation methods, this work tried to use FeS-activated persulfate (PS) combined with KMnO4 to treat the contaminated soil. Compared with Fe0/PS and KMnO4/PS systems, the FeS/PS system significantly improved the degradation efficiency of PCB77, reaching 79.2 ± 2.54% after 8 h. Adding KMnO4 after reacting 4 h to FeS/PS system could promote the degradation of PCB77, while the degradation of PCB77 was inhibited if adding KMnO4 at 0 h. At the same time, the degradation efficiency of PCB77 was directly proportional to the concentration of FeS. Under the same oxidant dosage, the increase of spiked soil decreased the degradation efficiency of PCB77, but increased the degradation amount of PCB77. Through electron paramagnetic resonance analyzation and quenching experiments, four radicals containing hydroxyl group, sulfate radical, singlet oxygen and superoxide radical, were determined to play an important role in the oxidation experiment. Gas chromatograph mass spectrometer (GC-MS) and liquid chromatograph mass spectrometer (LC-MS) were used to identify possible intermediate products in the FeS/PS/KMnO4, and the possible reaction mechanisms were predicted. According to the theoretical calculation, 2(C) and 4(C) had higher 2E2HOMO and E2HOMO+E2LUMO, which were easy to be attacked in the oxidation reaction.Hydroxyl and sulfate radical attacked the lowest energy of transition state (TS) at 2(C) site and the energy of TS4C was lower than TS3C, so 2(C) was the first to be attacked by free radicals, followed by Cl at 4(C) which was replaced by hydroxyl and sulfate radical. Therefore, four main possible reaction pathways were proposed, which was involved mainly dechlorination, hydroxylation, sulfonation and C-C bridge bond cleavage. This work suggested that FeS/PS/KMnO4 is applicable to treat large amounts of PCB77 contaminated soil, which has a great potential for remediation of PCBs-contaminated soil.

Enhanced the degradation of PCB77 in soil by FeS activated persulfate coupling with permanganate

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