Mechanical Performance, Heavy-Metal Leaching, and CO2 Emission Reduction in Cement–Copper Tailings Composites

Copper tailings are generated in large quantities, and their efficient utilization remains challenging because of their complex mineralogical composition and relatively low reactivity. This study investigated the feasibility of partially replacing cement with copper tailings, with particular emphasis on the combined effects of particle packing and potential alkaline dissolution. Unlike previous studies mainly focusing on the use of copper tailings as aggregates or cement raw materials, this work integrates mechanical performance, alkaline dissolution behavior, microstructural characteristics, Cu/Zn leaching behavior, and simplified embodied-carbon comparison. The results showed that a 10% copper tailings replacement yielded the highest 28 d compressive and flexural strengths of 46.5 MPa and 4.83 MPa, respectively. The improvement was mainly associated with particle filling and packing effects, while alkaline dissolution tests indicated that limited Si and Al species could be released from the tailings under alkaline conditions and potentially contribute to hydration. Excessive replacement reduced the cement content and weakened the mechanical performance. The prepared composites also exhibited low Cu and Zn leaching concentrations. Overall, the study demonstrates the potential of copper tailings for partial cement replacement while considering mechanical performance, environmental safety, and carbon-reduction potential. However, the conclusions are limited to one tailings source, 28 d mechanical properties, short-term leaching behavior, and a simplified embodied-carbon comparison.