Re-use of Montorfano granite waste (Verbania, Piedmont, Italy) for REEsrecovery along the feldspar industrial chain. Results from pre-concentration tests

Granite quarry waste from the “Graniti dei Laghi” plutons in Piedmont (Italy), underwent laboratory-scale beneficiation tests to optimise the concentration of Rare Earth Elements (REEs) for a potential recovery in the context of circular economy and sustainable mining. Preliminary analyses using ICP-MS, XRPD, SEM-EDS and Automated Mineralogy revealed that the magnetic waste generated during granite industrial processing for feldspar production is significantly enriched in REEs, prompting further testing to simulate and refine a lab-scale treatment to enhance the concentration of Rare Earth Minerals (REMs). Monazite-(Ce) was identified as the primary target mineral, predominantly locked within Fe-rich biotite (annite-siderophyllite). The feed material was milled to various grain sizes and subjected to multiple stages of dry magnetic separation employing different instruments to determine optimal conditions for REMs beneficiation. Results show that approximately 80% of REEs are associated with paramagnetic fractions recovered at 0.4 A using a Frantz Isodynamic Separator, with 75-150 µm and 150-250 µm of feed grain size. Although comminution below 600 µm helped reject diamagnetic gangue minerals from the monazite-bearing annite-siderophyllite, SEM-EDS observations underscored that monazite liberation issues persisted for particles above 100 µm, due to their smaller size relative to annite-siderophyllite. This suggests that additional grinding below 100 µm is necessary for effective monazite liberation. However, dry electromagnetic separation on fine material yielded poor monazite recovery, indicating the need for wet magnetic separation and flotation for a more effective recovery of REMs from fine-grained pre-concentrates.