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

Abstract

• Mn x O y enhanced MW/PS oxidation is used to remedy pyrene polluted site. • Enhancement effect on pyrene removal by Mn x O y is explored. • Radical and non-radical processes both contribute to pyrene removal. • Conversion of Mn(IV) to Mn(III) promotes ROS formation and pyrene removal. • Pyrene degradation pathways involve ring-opening and hydroxylation. Polycyclic aromatic hydrocarbons (PAHs) contaminated sites have attracted worldwide concern due to their carcinogenic, mutagenic, and teratogenic natures. Crystallographic manganese oxides (Mn x O y ) are ubiquitous in soils. In this study, Mn x O y 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 Mn x O y , which ranked as β -MnO 2 > α -MnO 2 > γ -MnO 2 > Mn 2 O 3 . Pyrene removal efficiency was enhanced from 65.7% to 85.6% within 15 min of treatment when β -MnO 2 dosage increased from 0 to 0.1 g. Mn x O y 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. 1 O 2 played significant roles in pyrene degradation, whereas the presence of β -MnO 2 alleviated the shielding effects of SO 4 − 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 Mn x O y enhanced MW/PS oxidation, and highlighted new insights into the mechanism of PS activation by metal oxides.