Magnetic properties of REE fluorcarbonate minerals and their implications for minerals processing

Rare earth elements (REE) are considered as critical metals for electronics and green technology. The REE fluorcarbonates are one of the main REE ore minerals, common in many different types of REE deposit and yet some of their fundamental properties have still not been determined. This study measured the magnetic properties of pure REE fluorcarbonate single crystal minerals using a vibrating sample magnetometer (VSM) and determined their elemental compositions using electron probe microanalysis (EPMA). The results provide the first measurements of the magnetic behaviour and susceptibility of REE fluorcarbonates other than bastnäsite-(Ce). The magnetic susceptibility of REE fluorcarbonates varies systematically from one mineral to another and is highly dependent on the mineral chemistry. It is positive (paramagnetic) for bastnäsite-(Ce) and gradually decreases as the amount of Ca increases in parisite-(Ce), becoming negative (diamagnetic) for the Ca-rich member of the series, röntgenite. Synchysite-(Ce) is difficult to measure, generate good signal and acquire accurate readings because it practically always occurs as <5 mg crystals. Its magnetic susceptibility in samples from a REE ore deposit was experimentally determined by magnetic separation and checked by an associated study using a SQUID magnetometer, synchysite-(Ce) behaved as a diamagnetic mineral. This can be explained by the increase of Ca content and decrease of REE content, in addition to the variations in the layered structure common to the REE fluorcarbonate series minerals. Given the wide range of magnetic susceptibility of REE fluorcarbonates, it is important that the mineralogy is determined carefully before setting up a mineral processing flow sheet.