Abstract
The use of iron ore tailings (IOT) is a trend for the future of mining. The adoption of alternatives that minimise the disposal of natural resources and add value to production processes strongly supports this effort. Hydrometallurgy, by means of acid leaching, has been investigated as a processing route for iron recovery from IOT. After the separation of the liquor, a solid fraction of insoluble quartz and kaolinite remains (the main mineralogical phases). In the same way, the cement industry is an intensive consumer of raw materials and a major emitter of greenhouse gases. As one of the main alternatives for reducing these impacts, clinker substitution by wastes from other industries is being extensively considered. Thus, this work aims to evaluate the properties of the solid product of IOT leaching (L-IOT) and its potential to produce sustainable cements. L-IOT main composition is based on silicon (≈35%), aluminium (≈8%) and iron (2%). After thermal activation, the L-IOT was incorporated into pastes, replacing the cement by up to 20 wt%. The rheological parameters, hydration kinetics, compressive strength, mineralogy through X-ray diffraction (XRD) and thermogravimetric analysis (TGA) of cement pastes were assessed. L-IOT increased cement pastes' dynamic yield stress and viscosity and anticipated its main heat flow peak by up to three hours. Replacement contents of up to 20 wt% showed an equivalent 28-d compressive strength in the control sample, associated with carboaluminates formation. Finally, a simplified carbon dioxide equivalent emission (CO2-eq) analysis was conducted to evaluate the L-IOT’s environmental feasibility. Reductions of up to 21% CO2-eq emissions were observed for an L-IOT content of 20 wt%, compared to plain cement. The hydrometallurgical route allowed the recovery of 95% of the iron content in IOT, and its by-product presented technical and environmental feasibility for cement replacement in cementitious matrices.
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