Iron extraction from copper slag constructs oxygen vacancy–containing Fe₂O₃ for electrocatalytic nitrate reduction to ammonia

The synergistic treatment of copper slag valorization and nitrate wastewater remediation represents a critical pathway toward the high–value utilization of metallurgical solid waste and nitrogen resource recovery. This study employs a strategy synergistically coupling thermal reconstruction with surface defect engineering to convert the Fe–containing phases in copper smelting slag into an Fe₂O₃–based electrocatalyst, designated as WCS600. At −0.6 V vs. RHE, WCS600 achieves an NH₃ production rate of 7.16 mg h⁻¹ cm⁻² and a FE NH3 of 91.56%. Characterization and DFT calculations reveal that cathodic polarization induces the electrochemical reconstruction of surface oxygen vacancies, dynamically generating an interface enriched with mixed–valence Fe²⁺/Fe³ ⁺ species and hydroxylated Fe–OH. This interface promotes the directional conversion of nitrogen–containing intermediates, thereby enhancing NH₃ selectivity. In a simulated acidic smelting wastewater system, WCS600 exhibits excellent stability and resistance to interference, with Fe leaching remaining below the safety threshold. Further techno–economic analysis indicates that, under specific scenarios coupling low–carbon hydrogen sources, the NH₃ production cost of WCS600 could be reduced to below 1.15 $ kg⁻¹ . This study provides a theoretical foundation and practical guidance for the synergistic resource–oriented treatment of solid waste and nitrate wastewater, as well as for the development of scalable electrochemical ammonia synthesis.