Abstract
Scandium (Sc) and rare earth elements (REEs) hosted in silicate-rich ores are difficult to extract due to their strong association with refractory mineral phases. This study evaluates an integrated processing approach for ore concentrate samples from Scandium Canada’s Crater Lake project (Québec, Canada) that combines alkali cracking with supercritical CO2 extraction (SCFE) using a TBP–HNO3 extractant system. Direct SCFE of untreated concentrates resulted in negligible scandium recovery, highlighting the need for an effective pretreatment step. Several alkali-cracking conditions were investigated, including NaOH roasting at elevated temperatures and a lower-temperature NaOH–KOH eutectic treatment. Both approaches significantly improved metal accessibility and enabled efficient scandium and REE extraction during subsequent SCFE. Under optimized conditions, scandium recoveries approaching 90% were achieved, with similar trends observed for total rare earth elements. Mineralogical analyses confirmed selective removal of metal-bearing phases, while refractory gangue minerals remained in the solid residues. From a process perspective, the NaOH–KOH eutectic route delivered metallurgical performance comparable to high-temperature NaOH cracking while operating at substantially lower thermal input. Preliminary economic considerations indicate that this lower-temperature pathway offers advantages in energy consumption and overall processing costs, improving its attractiveness for scale-up. The results demonstrate the potential of combining alkali cracking with SCFE as a viable and energy-efficient route for scandium recovery from refractory silicate concentrates.