Characterization of Finnish Carbonatite-Type Mine Tailings and Preconcentration of Rare Earth Elements

This study investigates the recovery and concentration of rare earth elements (REE) from mine tailings, addressing the growing demand fueled by the green energy transition and shifting geopolitical landscapes. Focusing on carbonatite-type tailings from a Finnish closed Pb-REE mine, containing mostly light REE (0.23 wt% neodymium and praseodymium), the research aims to characterize the material and evaluate mechanical preconcentration methods through sieving, as well as magnetic, gravity, and electrostatic separation techniques. The results reveal that REE concentrations are strongly influenced by particle size. Smaller particles have higher REE grade; for instance, 0.3 and 0.8 wt% REE at sizes of 250–500 µm and 0.45–0.63 µm, respectively. Furthermore, the complex mineral composition, minerals associations, and presence of gangue minerals make concentration of tailings particularly challenging. For example, the presence of silicon-containing REE minerals hampered efficient silicon separation, causing loss of 58–77% of REE along with silicon during density-based separations. Fe separation was also inefficient, 4 and 20% separation efficiency by low intensity magnetic and electrostatic separations, respectively, because REE minerals including monazite, with weak paramagnetic properties, are hard to separate from iron oxides using low intensity magnetic or electrostatic methods. Overall, mechanical separation methods show that a multi-step process improves REE recovery from low-grade mine tailings, with particle size and mineral properties affecting efficiency. Future work should target multi-cycle approaches and high-intensity magnetic separation for better concentration of fine REE minerals. Understanding mineralogy and optimizing preconcentration from tailings helps promote sustainable resource use and lessen dependence on primary sources.