Recycling of mine tailings as supplementary cementitious material: Impact of mine tailings’ mineralogy on hydration behaviour and phase assemblage of Ordinary Portland cement blends

• Dehydroxylation of alunite enabled sulphate regulation and delayed induction. • Dehydroxylation of Fe-Chlorite had hydraulic properties influencing early hydration properties. • Tailing reactivity was mainly through phyllosilicate minerals. • Tailing crystalline phases through ion-exchange influenced hydrates formed. • 60% OPC replacement can be achieved in a ternary blend with tailings and BFS. This study investigated the influence of mineral tailings’ mineralogy on hydration behaviour and phase assemblage of cured cement in ternary blends comprising Ordinary Portland cement (OPC), blast furnace slag (BFS) and tailings. The identification and quantification of mineral phases was achieved through Quantitative X-ray diffraction (QXRD) analysis, while the evaluation of mineral thermal stability was conducted using thermogravimetric analysis with mass spectrometry (TGA-MS). Isothermal calorimetry revealed that the tailings influenced the OPC heat flow profile during early-stage hydration, with minerals like dehydroxylated Fe-chlorite and alunite hydraulic properties contributing to the early-stage reaction mechanism. The bulk slow-reacting minerals in the tailings affected both the phase assemblage and the hydration mechanism of OPC by releasing elemental species that could be incorporated in the C-S-H phases. The chemical composition of the C-S-H formed in the blended cement varied and had a low Ca/Si ratio < 1.3, enabling guest elements to be incorporated. Correlative Electron Microscopy Automated Mineralogy (CEM-AM) was utilised to analyse and map the distribution of the secondary C-S-H phases within the paste matrix. The findings give insight into the nature of hydrates formed in a ternary blend with tailings, which directly affect the cured cement’s performance and service life properties.