Crystallographic manganese oxides enhanced pyrene contaminated soil remediation in microwave activated persulfate system

Polycyclic aromatic hydrocarbons (PAHs) contaminated sites have attracted worldwide concern due to their carcinogenic, mutagenic, and teratogenic natures. Crystallographic manganese oxides (MnxOy) are ubiquitous in soils. In this study, MnxOy enhanced PAHs contaminated soil remediation in a microwave activated persulfate (MW/PS) system was conducted, and pyrene was selected as a target pollutant. Significant enhancement performance on pyrene removal was observed after adding MnxOy, which ranked as β-MnO2 > α-MnO2 > γ-MnO2 > Mn2O3. Pyrene removal efficiency was enhanced from 65.7% to 85.6% within 15 min of treatment when β-MnO2 dosage increased from 0 to 0.1 g. MnxOy in the MW/PS system improved the production of active substances and converted radical process into non-radical process via conversion of Mn(IV) to Mn(III) and Mn-O-Mn to Mn-O-X. 1O2 played significant roles in pyrene degradation, whereas the presence of β-MnO2 alleviated the shielding effects of SO4− and OH scavengers. Pyrene molecular structures were destroyed, and some ring-opening and/or lower ring byproducts were generated. Residual toxicity of pyrene and its degradation byproducts was predicted. This work provided a potential pathway to promote PAHs contaminated soil remediation via MnxOy enhanced MW/PS oxidation, and highlighted new insights into the mechanism of PS activation by metal oxides.