Rapid Microwave Irradiation-Enhanced Detoxification and Mineralization of Cr(VI) by FeS2/ZVI Composites

The rapid detoxification and mineralization of Cr(VI) in aqueous environments hold critical importance for emergency response and resource recovery yet remain technically challenging. Herein, we report the synthesis of FeS2/ZVI composites through ethanol-assisted wet ball-milling and their application in Cr(VI) removal under microwave (MW) irradiation. This study systematically investigates the effects of MW irradiation on the removal efficiency of Cr(VI) using FeS2/ZVI composites, with particular focus on key parameters including composite dosage, initial pH, MW temperature, and Cr(VI) concentration. Notably, 1 g/L FeS2/ZVI composites achieved near-complete removal (>99%) of 50 mg/L Cr(VI) within 7 min at a MW irradiation temperature of 333 K, which exhibited 5.9-fold and 13.1-fold superior performance compared to pure pyrite and ZVI, respectively. Additionally, there is a 96.1% reduction in reaction time in comparison to non-MW irradiation system. In real electroplating wastewater samples, Cr(VI) concentration was reduced from 38.93 to 0.42 mg L−1 by MW irradiation-assisted treatment, validating its potential for practical applications in industrial Cr(VI) pollution control. The activation energy determined by fitting the Arrhenius equation showed a 39.7% reduction for the MW-assisted FeS2/ZVI system (16.0 kJ mol−1) compared to conventional thermal heating (from 25.6 kJ mol−1), indicating that MW irradiation induced catalytic enhancement of FeS2/ZVI, thereby lowering the energy barrier for Cr(VI) reduction. Moreover, MW irradiation-assisted processes facilitated the mineralization of reduced Cr(III) to stable spinel FeCr2O4. These findings collectively establish a synergistic mechanism between MW activation and FeS2/ZVI composites, offering innovative pathways for efficient Cr(VI) detoxification and resource recovery from high-strength industrial wastewaters.