[Degradation of α-HCH in Soil Washing Solutions with nZVI and CaO₂]

Nano zerovalent iron (nZVI) and CaO₂ were used to construct a heterogeneous Fenton-like system to degrade α-hexachlorocyclohexane (α-HCH) in soil solution, and the degradation efficiency and mechanism were investigated. The results showed that nZVI/CaO₂ can degrade α-HCH in an extensive pH range. When the dosage of nZVI and CaO₂ was 1 g·L^-1 and pH was 5, the degradation rate of α-HCH reached 93.23%. The degradation process of nZVI, CaO₂, and nZVI/CaO₂ treatments accorded with the first-order reaction kinetics model. The reaction rate constant of nZVI/CaO₂ was greater than the sum of individual treatments, showing that nZVI/CaO₂ has a synergistic effect on the degradation of α-HCH. Through quenching free radical experiments, the contribution rate of superoxide radicals was shown to be greater than that of hydroxyl radicals. Intermediates, including trichlorobenzene and chlorobenzene, were detected. The content of trichlorobenzene showed a sharp increase initially, and then decreased quickly. The chlorobenzene content was low and showed little change. The α-HCH in the soil washing solution was first reduced to trichlorobenzene, which was further reduced to chlorobenzene or mineralized into CO₂ and water directly.