Flotation of rare earth minerals from Italian granite waste: mineralogy, reagent evaluation and process optimization

The recovery of rare earth elements (REEs) from secondary sources is increasingly important for strengthening the European supply chain and reducing the environmental impact of primary mining. This study evaluates the potential of froth flotation to upgrade rare earth minerals (REMs) from Italian granite wastes, besides exploring alternative reagents beyond those traditionally employed for REM flotation. Three feed materials derived from magnetic pre-concentrates and grinding fines were characterised using TIMA-X automated mineralogy, which revealed contrasting liberation and association patterns of the REE bearing phases: monazite and xenotime are fine-grained and well liberated, whereas allanite-bearing particles are coarser, more poorly liberated, and strongly intergrown with biotite and chlorite gangue. Batch flotation tests conducted in a 2 L Outotec GTK cell assessed the influence of reagent selection, pH, temperature, and regrinding. Nouryon's glycinate-type collector Atrac 922 delivered the best combination of grade and recovery at pH 8 and 9. Controlled regrinding (20 min) significantly enhanced mineral liberation and TREEs grade, although overgrinding (40 min) and excessive ultrafine generation reduced concentrate purity and selectivity due to entrainment, despite yielding TREEs recoveries up to 85 %. Grinding fines exhibited superior flotation performance compared to magnetic concentrates, driven by finer grain sizes and better liberation of monazite and xenotime. Overall, the results demonstrate that flotation can effectively complement magnetic separation for rare earth minerals beneficiation from granite wastes. However, substantial REE losses - likely related to the surface chemistry and behaviour of allanite highlight the need for tailored reagent strategies, optimised size reduction, and improved understanding of the mineralogical impacts on flotation performance.