The interface mechanism of ball-milled natural pyrite activating persulfate to degrade monochlorobenzene in soil: Intrinsic synergism of S and Fe species

Ball-milled natural pyrite has been proven to be an efficient and economical catalyst for persulfate (PDS) activation; however, the synergistic interface mechanism between S and Fe species transformation remains a large challenge. Herein, ball-milled pyrite was used in the degradation of monochlorobenzene (MCB) from soil, and the surface characteristics and identification of the S and Fe species in the ball-milled natural pyrite during the Fenton-like reaction were reported. The pyrite/PDS system was found to eliminate 93.8 % of the 95.6 mg/kg MCB in the soil. Ball milling changed the fundamental pathway of reactive species (RS) generation, and the FeIV contribution increased to 33.0 % for MCB degradation. Compared with heterogeneous activation, homogeneous activation induced by dissolved Fe(II) played an important role. Self-oxidation induced by sulfur vacancy sites (SVs) also occurred during MCB degradation (30.8 %). An exploration of the mechanism of the interfacial reaction at the microscopic level revealed that ball milling promoted the formation of SVs and increased the reducibility of S(-II) on pyrite, thus accelerating Fe(III) reduction and Fe(II) dissolution, limiting the generation of an Fe(III) passivation layer at the pyrite-water interface and promoting RS generation for MCB degradation. These findings provide new insights into the interface mechanism for PDS activation in a ball-milled pyrite/PDS system.