Application of microwave-irradiated manganese dioxide in the removal of polychlorinated biphenyls from soil contaminated by capacitor oil

<div><p>The removal of polychlorinated biphenyls (PCBs) from soil contaminated with capacitor oil, using microwave (MW)-irradiated manganese dioxide (MnO₂), was examined under different conditions. The effects of different types of MnO₂ added as oxidant, as well as the initial amount of water, MnO₂, and sulphuric acid solution, were also investigated. The removal efficiencies for dichlorobiphenyls, trichlorobiphenyls, tetrachlorobiphenyls, pentachlorobiphenyls, hexachlorobiphenyls, heptachlorobiphenyls, and octachlorobiphenyls were approximately 95.9%, 82.5%, 52.0%, 71.6%, 62.5%, 28.6%, and 16.1%, respectively, by 800 W MW irradiation for 45 min with the assistance of 0.1 g δ-MnO₂ and 0.2 mL water in 1.0 g severely PCB-contaminated soil (∑PCB=1560.82 mg/kg); meanwhile, the concentrations of Mn²⁺ ions detected were from 10.6±1.9 mg/kg at 0 min to 108.2±7.8 mg/kg after 45 min MW irradiation, indicating that MnO₂ acted as not only a MW absorber but also an oxidizer. Removal efficiencies of PCBs from contaminated soil increased with increasing the amounts of water and MnO₂ added. The type of MnO₂ also affected the removal of PCBs, following an order of . The addition of low concentration of sulphuric acid (such as 1.0 mol/L) solution was favourable for the removal of low chloro-substituted PCBs, but the addition of more than 1.0 mol/L sulphuric acid reduced the removal of all PCBs. The pronounced removal of PCBs from contaminated soil in a short treatment time indicates that MW irradiation with the assistance of MnO₂ is an efficient and promising technology for the remediation of PCB-contaminated soil.</p>