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 FENH3 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.