Effect of CaO-Induced Mechanothermal Activation on the Reactivity of Copper Tailings and the Mechanical Performance of Mortars

Copper tailings (CTs), characterized by high crystallinity and low pozzolanic activity, are a type of solid waste generated in large quantities with significant environmental hazards. Due to their inert nature, single-activation methods are often insufficient to markedly enhance their reactivity. Existing studies mainly focused on individual activation techniques, and the reactivity improvement and underlying mechanisms of compound activation remain insufficiently explored. To address this gap, this study investigates the potential of CTs as supplementary cementitious materials (SCMs) by employing a CaO-induced mechanothermal activation method. The optimal activation parameters were determined using response surface methodology (RSM). The effects of CaO-induced mechanothermal activation on the physicochemical properties of CTs were systematically analyzed. Results indicated that under the conditions of 600°C calcination, 120 min ball milling, and 4% by weight CaO addition, the activated CTs replacing 30% of cement resulted in a 28-day compressive strength of 36.07 MPa and a reactivity index of 83.01%, representing improvements of 18.70 MPa and 43.03%, respectively, compared with untreated CTs. High-temperature calcination removed free water and interlayer water from muscovite, inducing microcrack formation on the CTs surface. Ball milling generated new interfaces, defects, and active sites. Additionally, CaO promoted Si─ O bond cleavage at newly formed interfaces, significantly enhancing the activation efficiency. This study offers a novel approach for the valorization of CTs in construction materials, contributing to the development of green building materials and sustainable resource utilization.