Pyrite-activated persulfate for simultaneous 2,4-DCP oxidation and Cr(VI) reduction

Organic pollutants and heavy metals often coexist in wastewater, their simultaneous and effective removal from wastewater has a particular significance for environmental remediation. In this study, pyrite (FeS2), the most abundant iron mineral in the Earth’s crust, was selected as a catalyst to activate persulfate for the simultaneous removal of 2,4-dichlorophenol (2,4-DCP) and Cr(VI), two common contaminants in wastewater. The results indicated that 76.2% of 2,4-DCP and 80.1% of Cr(VI) were simultaneously removed within 120 min in the pyrite/persulfate system. The simultaneous removal efficiency of 2,4-DCP and Cr(VI) by the pyrite/persulfate system was influenced by the contaminant concentration, solution pH and organic acids. The radicals SO4·− and ·OH were detected as the oxidative species in the pyrite/persulfate combined system using electron spin resonance (ESR) spectroscopy, and quenching experiments with methanol and tert-butanol indicated that SO4·− played a predominant role in the degradation of 2,4-DCP. The radicals (SO4·− and ·OH) produced from the activation of persulfate by pyrite principally contributed to 2,4-DCP disintegration, while the removal of Cr(VI) was primarily attributed to the reduction ability of pyrite. Experiments and density functional theory (DFT) calculation results indicated that Fe is the main catalytic site, and the reductive sulfides of the pyrite surface mediated Fe2+ recovery as donors during reaction processes. This work presented a ubiquitous natural sulfide mineral with excellent catalytic performance in the heterogeneous persulfate activation, implying a new strategy in wastewater treatment for simultaneous removal of heavy metal and organic compounds.