Recovery of Fe²⁺ from stainless steel scrap cathodes in the Fenton reaction

Fenton oxidation technology can generate highly reactive free radicals through a series of processes and is widely used for advanced mineralization treatment of industrial wastewater. However, its oxidation rate is limited by the regeneration of Fe²⁺. This research was based on the Fenton principle and combined with electrochemistry to develop a ferric ion recycling system using discarded stainless steel as the cathode. This system regenerates Fe²⁺ through electrochemical reduction, catalyzes hydrogen peroxide to produce hydroxyl radicals, and then degrades pollutants. Results show that after filling the cathode with stainless steel scrap, its electrochemical active area reaches 2633 cm². At a current density of 0.6 mA cm^-2 and an influent flow rate of 80 mL min^-1, the regeneration efficiency of iron ions reaches 83 % within 70 min, with a current efficiency of 93 % and energy consumption of 8.21 × 10^-4 kWh g^-1 Fe²⁺. After adding hydrogen peroxide at a COD:H₂O₂ ratio of 1:1.5, the electrochemical system could remove 97 % of phenol and 90 % of COD, with an energy consumption of 4.21 × 10^-5 kWh g^-1 COD. The reaction mechanism of the electrochemical system was verified through electrochemical analysis and quenching experiments. Results indicate that the direct oxidative degradation effect of the electrode on pollutants is minimal, and the degradation of pollutants primarily originates from the oxidation of ^•OH, which is generated by the Fenton reaction catalyzed by Fe²⁺. The electrochemical system developed in this study exhibits high stability, enabling the effective degradation of pollutants while achieving the resource utilization of metal waste and iron sludge. This provides technical support for its industrial application.