Coal chemical looping gasification (CLG) is a clean coal technology that combines efficient fuel conversion with inherent CO₂ separation, in which the oxygen carrier (OC) determines reaction efficiency, syngas quality, and cycling stability. To address the sintering and agglomeration, insufficient mechanical stability, and high cost of Cu-based OCs, this work develops a composite OC using coal gasification slag (CGS), an industrial solid waste, as both the supporting framework and the source of functional components. CGS was pretreated by high-temperature calcination and stepwise acid leaching to remove residual carbon and impurities, reduce the SiO₂ content, and enrich Fe₂O₃. A series of Cu/CGS OCs with different compositions was then prepared by impregnation and characterized by XRD, SEM, temperature-programmed reduction, TG-DTG, and XPS. Their CLG performance was evaluated by thermodynamic equilibrium analysis and fixed-bed experiments, and density functional theory (DFT) calculations were performed to investigate lattice oxygen migration. Cu interacted with the Fe species in CGS to form a spinel CuFe₂O₄ active phase that improved reducibility and oxygen-transfer capacity over a wide temperature range and promoted the conversion of coal char into CO and H₂. Elevating the temperature favored syngas formation, while moderate steam and OC loadings improved the oxygen potential, enhanced H₂ production, and suppressed CH₄; the introduction of CuO promoted the water-gas shift reaction, broadly consistent with thermodynamic predictions. A favorable balance between syngas selectivity and carbon conversion was achieved at 950 °C, an O/C ratio of 2, and a steam flow rate of 0.04 mL/min, with the C33F66 OC performing best under the tested conditions. After reaction, CuO was reduced to metallic Cu, while Fe species existed as Fe and Fe₃O₄ accompanied by a CuFeO₂ composite phase, indicating synergistic Cu–Fe redox behavior. DFT calculations showed that CuFe₂O₄ possesses lower oxygen vacancy formation energy and a lower lattice oxygen migration barrier owing to multimetal synergistic coordination and interfacial coupling. The spinel CuFe₂O₄-based composite OC exhibits superior structural stability and oxygen-release performance, confirming that CGS is a viable low-cost feedstock for high-performance oxygen carriers in coal chemical looping gasification.

coal chemical looping gasification; coal gasification slag; Cu-based oxygen carrier; CuFe2O4; lattice oxygen migration