Probing cleaner production opportunities of the Lac Tio pyrite-enriched tailings generated to alleviate sulfur dioxide emissions

Abstract

Sulfur dioxide (SO2) emissions following mineral roasting of sulfide bearing ore should be maintained as low as possible to avoid adverse air pollution and to fulfill the government pledge. The hematite–ilmenite deposit near Havre-Saint-Pierre in Quebec, Canada, mined by Rio Tinto Iron and Titanium encompasses naturally occurring high cut-off grades of hemo-ilmenite. The ore is directly sent to mineral roasting to recover titanium oxide used as feedstock for further processing. To mitigate sulfur dioxide emissions, magnetic separation preceding mineral roasting was explored to retrieve sulfides from the ore. This upstream solution is constrained by several challenges linked to the concentrate quality, the operating costs and the environmental risk of the generated solid waste (tailings). Scoping surveys of the magnetic separation revealed that Rare-Earth roll magnetic separation technology (RERMS) yields encouraging trade-offs among the feasibility driving factors. This technology allowed the removal of 23% of the initial sulfur mass and recovered 97.74% of the initial mass of hemo-ilmenite in the concentrate product. It was also selected owing to its technical and economical assets. Tailings generated upon the magnetic separation underwent detailed physico-chemical and mineralogical characterization to highlight its inherent environmental risk. Quantitative Evaluation of Materials by Scanning electron microscopy (QEMSCAN) was conducted to identify the potential contaminants that could be released in water during the oxidation of sulfides. Results revealed that 50% of pyrite grains, the sole sulfide detected, encompass Ni grades higher than 0.2%. Accordingly, batch sorption tests were performed to identify the sorption properties of the gangue minerals in the presence of 30 mg/L of Ni. Using a liquid to solid ratio 3:1, only 1% of the initial concentration is detected in the liquid phase after 6 h. Accordingly, the Lac Tio tailings could effectively attenuate the Ni leaching even with up to 30 mg/L of Ni. In addition to acid-base accounting, kinetic modeling was performed to unravel the pH buffering capacity associated to the gangue minerals. Results revealed that the mineral assemblage of the tailings produced by the magnetic separation exhibits a neutralization potential that could offset acidity generated by pyrite oxidation. However, long-term kinetic tests are required to validate that the magnetic separation offers cleaner production opportunity for both the atmosphere and the mine drainage.