Challenges associated with the recovery of Co– and As-bearing minerals from aged mine tailings

The global demand for cobalt (Co), essential for “clean” energy technologies, has raised interest in identifying secondary sources, including mine tailings. This study evaluates the potential of historic silver (Ag) mine tailings in Ontario, Canada, as a secondary Co source and for arsenic (As) mitigation, offering economic and environmental benefits. Physico–chemical and mineralogical characterization revealed promising Co (1 310 mg/kg) and As (5 245 mg/kg) contents in fine silty tailings (D₈₀ = 55 μm), with key Co-As-bearing minerals (e.g., safflorite, skutterudite, cobaltite, erythrite) exhibiting significant alteration and association with silicates (i.e., albite, quartz, chlorite). The complex mineralogy and fine particle size are challenging for conventional processing methods.

Tests using gravity separation achieved limited Co and As recoveries (4.2% and 7.3%, respectively), despite effective preconcentration (x24.8 and x38, respectively). Flotation experiments, performed in Denver cell with xanthate and hydroxamic acid collectors, achieved concentration factors of 2.5 for Co (70% recovery) and 3.0 for As (80% recovery). Pre-treatment with sonication further enhanced flotation efficiency. Analysis of entrainment index and particle size distribution emphasized the role of hydroxamate in particle recovery.

The study highlights the need for innovative processing strategies to overcome challenges posed by fine particle size, mineral alteration, and complex associations. However, Co grades comparable to global smelter concentrates were achieved, suggesting the potential for sustainable reprocessing of aged mine tailings. Future research should focus on optimizing reprocessing techniques to enhance resource efficiency and sustainability.