Sustainable valorization of copper mine waste into construction materials by alkali activation

Large volumes of copper mine waste (CMW) are stockpiled worldwide, posing long-term environmental risks but also offering a potential aluminosilicate resource for low-CO₂ binders. Alkali-activated materials (AAMs) provide a promising route to valorize such wastes, yet most previous studies have used copper tailings blended with Portland cement or supplementary precursors, and the performance of binders produced solely from CMW remains insufficiently explored. This study investigates the alkali activation of CMW from the Sarcheshmeh copper mine in Iran, used as the sole aluminosilicate precursor. Cylindrical specimens (38 × 76 mm) were prepared by mixing the dry waste with 10 M NaOH, 2.5 M Na₂SiO₃, and their blends at dosages up to 10 wt.% of CMW, and cured at 25 °C for 7 and 28 days. Unconfined compressive strength (UCS), secant modulus, freeze-thaw durability (up to 12 cycles), leaching behavior (pH, EC, TDS, ICP-OES), and microstructure (FE-SEM/EDS) were evaluated. Na₂SiO₃ activation produced the highest UCS, reaching 16.5 MPa at 28 days, more than twice that of NaOH-activated mixtures. Freeze-thaw cycling caused a moderate strength loss of ~ 23% after 12 cycles, while leaching tests showed near-neutral pH (6.97-7.11), low ionic release (79-185 µS/cm; 53-116 mg/L), substantially reduced heavy metals concentrations, indicating effective immobilization within dense N-A-S-H/C-A-S-H/ N-Fe-A-S-H gels. The results demonstrate that CMW can be transformed into a mechanically robust, chemically stable alkali-activated binder without any supplementary materials, providing a viable route for sustainable valorization of copper mine tailings within a circular economy framework.