Strength performance and leachability of cement-stabilised copper tailings as land reclamation geomaterial for sustainable copper tailings disposal

This study focuses on the ultimate utilisation of copper tailings as a sustainable land reclamation geomaterial, simultaneously addressing the adverse environmental impacts that they cause and the scarcity of land resources. Unlike the limited approach of using copper tailings as partial replacements for natural fine aggregates in concrete, land reclamation demands far larger volumes of geomaterial. The primary objectives were to determine the optimal replacement ratio of natural fine aggregate with copper tailings, assess the development of mechanical and microstructural strength, and evaluate the leachability of heavy metals. The study also explored the enhancement of tensile strength through the incorporation of basalt fibre. Using Excel Solver, the optimal replacement ratios were determined for tailings from four different sources. Mechanical performance of cement-stabilised Dexing copper tailings was tested in compression, tension, and flexure, while microstructural properties were analysed using X-ray Diffraction and Scanning Electron Microscopy. Results showed optimal replacement rates of about 9 % for Dexing, Kakosa, and Mindola tailings, and 15 % for Muntimpa tailings. The 28-day compressive strength of Dexing tailings treated with 15 % cement exceeded the required 1.2 MPa for stockpile engineering applications. Microstructural analysis confirmed the formation of strength-contributing compounds, including calcium hydroxide, ettringite, and calcium silicate hydrate. Additionally, incorporating 0.5 % of 9 mm basalt fibres notably improved tensile strength. Toxicity characteristic leachability tests confirmed that heavy metal concentrations remained within safe limits for both drinking water and seawater (Category III). Therefore, this study concludes that using 100 % copper tailings in land reclamation offers a more sustainable solution than their limited use in concrete applications.