Compound activation of iron ore tailings using industrial solid Wastes: Pozzolanic Activity, Microstructure, and mechanism

This study aimed to develop a lower-burden activation strategy for iron ore tailings (IOTs) by replacing conventional chemical activators with industrial solid wastes (ISWs) and systematically comparing mechanical activation (MA), chemical–mechanical compound activation (CMA), and chemical–thermal–mechanical compound activation (CTMA) within a unified framework. Calcium carbide slag (CCS), flue gas desulfurized gypsum (FGDG), and coal gangue (CG) were selected as waste-derived activators representing alkaline, sulfate, and reactive aluminosilicate functions, respectively. Activation performance and mechanisms were evaluated using compressive strength testing, particle-size analysis, XRD, SEM–EDS, and TG–DSC. Grinding improved IOT reactivity, with an optimum grinding time of 2 h. Appropriate additions of CCS and FGDG enhanced the activity of CMA-IOTs and CTMA-IOTs, whereas excessive dosages reduced activation efficiency. CG exhibited the strongest activation effect because mechanical and thermal treatment increased the reactivity of its Si- and Al-bearing phases. For CG-assisted CTMA-IOTs, activity first increased and then decreased with increasing heating temperature, reaching an optimum at 600 °C. At 600 °C and 40 wt% CG, the 28-day activity index reached 90.0 %. A preliminary screening assessment further showed that CMA provided a favorable balance between activity enhancement and processing burden, whereas CTMA achieved higher activity but required substantially greater thermal-energy input, cost, and carbon burden under an electric-heating scenario. Overall, the results demonstrate the effectiveness of functionally distinct ISWs for IOT activation and highlight the need to balance reactivity enhancement with practical, economic, and environmental burdens.