Under the oxidative roasting process, pyrite, as a major mineral in sulfidic mine tailings, can transform to iron oxides. Generated iron oxides, if exhibiting enough magnetic properties, can be recovered via magnetic separation resulting in partial mine tailings valorization. However, due to the presence of various minerals and sintering possibility, it is advantageous to remove impurities and increase the pyrite content of mine tailings prior to the roasting procedure. In this case, hydrofluoric acid that has no influence on pyrite can be used to leach most inorganic minerals, including aluminosilicates. Therefore, this study investigated and compared the influence of the roasting process with and without hydrofluoric acid leaching pretreatment on mineralogical phase transformation of pyrite and magnetic properties of thermally generated minerals. Several tests and analyses were performed to study mineralogical phase transformation, morphology, elemental composition, surface characterization, and magnetic properties. Results of this study indicated that without acid leaching pretreatment, pyrite was mainly transformed to hematite. However, via acid leaching, fluorine, as a more electronegative element over oxygen, entered the compound and neglected the role of oxygen in thermal oxidation, instead reducing sulfur content of pyrite to only form pyrrhotite.

In this study, the basic principles of paste technology which has been implemented successfully in the mining industry for both waste volume reduction and environmental impact reduction were investigated. In the past two decades, paste technology has progressed from a research-based mine backfill idea to a widely accepted and cost-effective fill system with the potential to totally change the approach tailings are disposed on the surface. Application of paste tailings for modern mines was shown experimentally by laboratory and field testing, focusing on intrinsic (e.g., tailings, cement and mix water properties) and extrinsic (e.g., in situ mixing, placement and curing conditions) parameters. Results indicate that use of paste tailings as backfilling and disposal in the mining industry as an innovative and environmentally sound system can guarantee operational continuity by reducing environmental (e.g., tailings dam failure, acidic water formation) and financial concerns over the mine’s life. Finally, paste technology enables mining operators to better manage their problematic tailings produced in the mineral processing plants.