Recovery of rare earth elements minerals from iron oxide–silicate rich tailings – Part 1: Magnetic separation

Abstract

This work is part of an ongoing investigation being conducted to recover and upgrade rare earth elements (REE) minerals from iron oxide and silicate rich tailings generated at a South Australian mining operation. Detailed mineralogical characterisation via Quantitative Evaluation of Minerals by Scanning electron microscopy (QEMSCAN) of the tailings established the presence of low grade (<1 wt% REE), fine-sized REE minerals. The REE minerals (bastnäsite, monazite, florencite, stillwellite, brannerite, and stetindite) identified were in intimate associations with weakly ferromagnetic/strongly paramagnetic iron oxides (mainly hematite and goethite) and diamagnetic silicate (quartz, illite, and annite) minerals. Chemical analysis showed the tailings comprised 26.2% Fe, 18.6% Si, 3.9% Al, and 1.07% total rare earth oxides (TREO). A rougher–scavenger–cleaner magnetic separation process was deployed to produce two useful streams of REE minerals concentrate and tails using a wet high-intensity magnetic separator (WHIMS). Typical metallurgical results indicated the rejection of 25% of the iron oxides at 0.11 T, whilst producing a magnetic concentrate with TREO recovery of 51% at a grade of 1.25% and non-magnetic tails with TREO recovery of 41% at a grade of 1.08%, both at 1.74 T. Bastnäsite, monazite, florencite, and stillwellite minerals were confirmed to be paramagnetic, whilst stetindite and brannerite were found to be diamagnetic. Whilst the applied magnetic field intensity was the most important factor in the minerals’ magnetic separation efficacy, particle size distribution and mineralogical characteristics of ores also had significant effect. The findings exemplify both the challenges and opportunities for the beneficiation of complex, low grade REE-bearing iron oxide silicate rich tailings using WHIMS. They indicate that magnetic separation may be used to achieve modest preconcentration, the success of which is limited by the complex nature of the tailings and its concomitant magnetic properties, and thus warranting the need for further downstream processing (e.g., froth flotation) to produce cleaner, higher grade REE minerals concentrates for subsequent values extraction.