Photodissolution of Rare Earth Elements and Dissolved Organic Carbon from Subbituminous Coal: Effects of Environmental Variables and Implications for Biogeochemical Cycling

Rare earth elements (REEs) make up a group of uniqueelements withdiverse applications in energy, medicine, and technology. Increasingglobal demand and limited supplies have led to exploring the economicviability of domestic feedstock extraction from sources such as coal.Little is known about the release of REEs from coal due to the environmentallydriven processes of photodissolution. In this study, the photodissolutionof water-soluble REEs and dissolved organic carbon (DOC) from subbituminouscoal was investigated using laboratory-simulated sunlight exposures.The effects of the solar intensity, temperature, and exposure timeon photodissolution were also examined. Following irradiation, water-solubleREE and DOC concentrations increased significantly above nonirradiatedcontrols, indicating photodissolution is a significant process. Bothsolar intensity and exposure time influenced photodissolution rates,while temperature did not. Results from this study provide motivationto further investigate the photodissolution pathways of REEs fromsubbituminous coal and interaction with DOC ligands, given that photosolubilizedREEs may be organic associated. These findings may have implications,both positive and negative, for the environmental impact of REEs.