Geochemical exploration for prospecting new rare earth elements (REEs) sources: REE potential in lake sediments around Eppawala Phosphate Deposit, Sri Lanka

Rare earth elements (REEs) are globally considered as critical elements due to their indispensable applications in various high-tech industries. With the ever-increasing demand, identified primary REE resources will not be able to fulfil the global requirements and thus exploration and exploitation of secondary REE deposits are essential. This work is designed to prospect REE potential in lake sediments in the proximity of the Eppawala Phosphate Deposit (EPD) in Sri Lanka. In this context, surface and core sediment samples were collected from 2 upstream lakes and one downstream lake (connected to a man-made water canal, namely Jaya-Ganga) with respect to the EPD. In the downstream, the average total rare earth element (TREE), light REE (LREE) and heavy REE (HREE) concentrations of the surface sediments were 1011.3, 904.6 and 66.6 mg/kg, respectively. The corresponding average values in downstream core sediments were 858.7, 719.3 and 100.2 mg/kg, respectively. The results suggested that the downstream lake sediments contained a high TREE content with a significant LREE enrichment compared to the upstream lake sediments. The EPD was identified as the main REE source and Jaya-Ganga, which flows across the EPD, was the main transport medium in this study. Phosphate-bearing minerals, such as fluorapatite and hydroxylapatite, derived from the EPD act as the REE carriers where REEs substitute isomorphous in the mineral lattice. Since REE grade is relatively high compared to some of the reported secondary REE sources, the downstream lake sediments could be a potential secondary source for REEs for future exploitation.