Dithionite accelerated copper slag heterogeneous-homogeneous coupled Fenton degradation of organic pollutants

The heterogeneous-homogeneous coupled Fenton (HHCF) processes combine the advantages of rapid reaction and the catalyst reuse, which makes them attractive for wastewater treatment. Nevertheless, the lack of both, cost-effective catalysts and the desirable Fe3+/Fe2+ conversion mediators limit the development of HHCF processes. This study investigates a prospective HHCF process, in which solid waste copper slag (CS) and dithionite (DNT) act as catalyst and mediator of Fe3+/Fe2+ transformation, respectively. DNT enables controlled leaching of iron and a highly efficient homogeneous Fe3+/Fe2+ cycle by dissociating to SO2- • under acidic conditions, leading to the enhanced H2O2 decomposition and •OH generation (from 48 μmol/L to 399 μmol/L) for p-chloroaniline (p-CA) degradation. The removal rate of p-CA in the CS/DNT/H2O2 system increased by 30 times in comparison with the CS/H2O2 system (increased from 1.21 × 10-3 min-1 to 3.61 × 10-2 min-1). Moreover, batch dosing of H2O2 can greatly promote the yield of •OH (from 399 μmol/L to 627 μmol/L), by mitigating the side reactions between H2O2 and SO2- •. This study highlights the importance of the iron cycle regulation for improvement of the Fenton efficiency and develops a cost-effective Fenton system for organic contaminants elimination in wastewater.