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

Abstract

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.