Immobilization of Pb and Zn from mining waste using alkali‐activated materials: Physico‐chemical properties and leaching behavior

Abstract

The management of mining waste containing potentially toxic elements represents a major environmental concern. In this study, mining residues from the Boujaber abandoned Pb–Zn mine (northwest Tunisia) were valorized through alkali activation in order to develop environmentally safe construction materials. Mining waste was used as a partial replacement for metakaolin in the synthesis of alkali‐activated materials. Different formulations were prepared using sodium hydroxide solutions with concentrations ranging from 6 to 12 M and cured for up to 28 days. The materials were characterized in terms of compressive strength, Fourier‐transform infrared spectroscopy (FTIR), apparent density, water absorption, and microstructure (SEM). Particular attention was given to the immobilization of potentially toxic elements through leaching tests. The raw mining waste exhibited high concentrations of hazardous elements, especially Pb (3710 ppm) and Zn (14,860 ppm). The results showed that high waste contents (>50 wt%) or low alkaline activator concentrations led to poor mechanical and physico‐chemical properties. Conversely, formulations incorporating ≤50 wt% mining waste and activated with 10–12 M NaOH demonstrated improved performance. Leaching tests confirmed the effective immobilization of Zn within the alkali‐activated matrix, while Pb leaching was significantly reduced but remained above the NT 106.002 limit (0.1 mg/L), although still compliant with the less restrictive USEPA threshold (5 mg/L), indicating partial immobilization of this element. Among the tested formulations, the 80% metakaolin–20% mining waste composition showed the most advantageous performance, combining the highest compressive strength with the lowest Pb and Zn leaching concentrations, in compliance with regulatory limits, while offering a cost‐effective and environmentally beneficial valorization of mining waste. This study highlights the potential of alkali‐activated materials as a sustainable solution for the stabilization and reuse of mining waste, contributing to both environmental protection and resource efficiency.