The pivotal role of particle size on REE enrichment and extraction efficiency: A multi-modal characterization and leaching study of bastnäsite ore

• REE enrichment quadrupled below 40 µm, validating size segregation as a critical pre-concentration step • Hydrometallurgical tests prove particle size is the governing control parameter for enhanced REE extraction • Automated Mineralogy confirmed bastnäsite content dramatically increased in the enriched fine fractions • Systematic multi-modal characterization offers a robust framework for optimizing global complex bastnäsite ores. A detailed multi-modal characterization and extraction investigation was performed on bastnäsite ore from Türkiye's Kızılcaören deposit to elucidate REE enrichment mechanisms across different particle sizes. The as-received ore was fractionated and rigorously analyzed using Automated Mineralogy (AM), ICP-MS, and XRD. Results revealed a strong dependency of REE concentration on particle size, particularly below 40 µm. Light REE content quadrupled from 2.5 wt.% (±0.83) to 10.6 wt.% (±3.00), while Heavy REE increased from 835.7 ppm (±346.33) to 3867.5 ppm (±1056.9), with high standard deviations suggesting uneven elemental distribution. Consistent with chemical data, AM analysis showed that the area occupied by REE minerals (bastnäsite, monazite, parisite, synchysite) increased from 2.6% to 3.8% in fractions <40 µm. Mineralogical mapping highlighted strong associations between REE phases and barite/Fe-Mn oxides rather than the primary fluorite phase. Furthermore, Rietveld refinement confirmed that bastnäsite content rose from 3.8 wt.% to 9.5 wt.% in fine fractions. Leaching experiments in two media indicated no significant performance difference; however, the finest fraction (<25 µm) yielded the highest extraction concentrations (1215 ppm Ce, 1062 ppm La, 134.3 ppm Nd). This study demonstrates that particle size is the paramount factor governing REE enrichment and hydrometallurgical extraction, providing critical data for optimizing pre-concentration and leaching flowsheets.