Copper smelting slag valorization in waste-derived clay ceramics: sintering behavior, microstructural evolution, engineering performance, and leaching behavior

The Fe- and Si-rich composition of copper smelting slag (CS) provides a basis for its utilization as a secondary raw material in high-temperature ceramic processing. This study investigates the effect of relatively low additions of untreated CS (5 and 10 wt%) on the sintering behavior, phase and microstructural evolution, engineering properties, and leaching behavior of waste-derived ceramics fired at 900-1200 °C. The effect of CS was strongly temperature-dependent, with no clear mechanical benefit at 900-1000 °C but pronounced improvement at 1100-1200 °C. At 1200 °C, 10 wt% CS increased compressive strength to approximately 135 MPa and bulk density to 2.23 g cm^-3, while reducing water absorption to 2.2%. XRD, FTIR, and SEM analyses indicated high-temperature structural reorganization and enhanced matrix densification without major changes in the dominant crystalline phase assemblage. CS incorporation did not systematically increase the release of potentially hazardous elements, with regulated concentrations remaining well below the corresponding TCLP limits. The results show that the partial replacement of SS and FA by low additions of untreated CS can improve ceramic performance while maintaining low leachability, supporting its valorization in high-performance ceramic materials. These findings provide a basis for further studies on the long-term durability and environmental performance of CS-containing ceramics under real service conditions, as well as for scaling-up toward industrial production.