The potential of REEs in the Eppawala Phosphate Deposit, Sri Lanka: REE enrichment, mineralization, and economic significance

The significant role in high-tech and green technologies, recent outstripping demand, and constrained global supply of rare earth elements (REEs) have led to the exploration of phosphate deposits worldwide as a sustainable source for the recovery of REEs as by-products. In this context, the Eppawala Phosphate Deposit (EPD) in Sri Lanka can be considered a potential source for recovering REEs as a by-product. The REE geochemistry and mineralogy of sixty representative samples from the weathered regolith (primary apatite crystals and secondary phosphate matrix) and the carbonatite source rock at the EPD were analyzed. The average total REE content (Sigma REE) in the weathered regolith ranged from 2500 to 6092 ppm, with higher enrichment of light REEs than heavy REEs. The weathered regolith was highly enriched in REEs compared to the parent carbonatite due to residual enrichment of apatite with calcite and dolomite dissolution. Furthermore, REE immobilization during matrix formation results from the retention of REEs in fluorapatite and hydroxylapatite. Mineralogical analyses revealed that the major REE ore minerals in the EPD are apatite group minerals. Despite the relatively low REE grade (similar to 0.48% total rare earth oxide) compared to the other phosphate deposits in the world, this deposit is significantly enriched in critical and highly demanded REEs, such as Nd (54,468 tonnes), Pr (17,994 tonnes), and Tb (2,897 tonnes). Therefore, with upgraded extraction techniques, the EPD could become a potential source of REEs that could contribute to maintaining a sustainable REE supply chain in the future.