Transforming of Pb-Zn mining waste into sustainable alkali-activated materials: Mechanical and environmental evaluation

Globally, mine wastes represent a major environmental concern because of their high levels of potentially toxic elements (PTEs). However, they also constitute an underexploited aluminosilicate resource for sustainable construction materials. This study examines the potential recovery and valorization of Pb-Zn mine wastes from the abandoned Bou Grine mine, northwestern Tunisia, which contain significant concentrations of Zn (8910 ppm) and Pb (3390 ppm), as a partial or total substitute for metakaolin in alkali-activated materials (AAMs) using NaOH as the sole activator. Six binary BG/MK mixtures (0–100 wt% BG) were prepared and cured at 25 °C for 28 days, and subsequently characterized at multiple scales using XRD, XRF, ATR-FTIR, TGA/DTA, SEM/EDS, UV-Vis spectroscopy, and nitrogen physisorption, whereas compressive strength and leaching behavior were systematically evaluated. Characterization results indicate that the BG mining waste exhibits a complex mineralogical composition, including calcite, dolomite, cerussite, sphalerite, gypsum, and phyllosilicates. Furthermore, incorporating 20–50 wt% BG enhances 28-day compressive strength to 19–21 MPa, more than double that of the AAM with 100 wt% MK (~10 MPa), due to the synergistic formation of N-A-S-H and C-A-S-H/N-A-S-H gels, which promotes matrix densification and improved particle packing. Moreover, leaching tests confirm that potentially toxic elements (PTEs) are effectively immobilized, with all analyzed elements meeting the NT 106.002 and USEPA regulatory limits except Pb. Although Pb leaching remained below the USEPA limit (5 mg/L), it exceeded the more stringent Tunisian NT 106.002 limit (0.1 mg/L), indicating partial Pb immobilization. These findings demonstrate that BG mine wastes are both technically and environmentally suitable precursors for geopolymer AAMs, provided that further optimization is undertaken to improve Pb immobilization.