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 unique elements with diverse applications in energy, medicine, and technology. Increasing global demand and limited supplies have led to exploring the economic viability of domestic feedstock extraction from sources such as coal. Little is known about the release of REEs from coal due to the environmentally driven processes of photodissolution. In this study, the photodissolution of water-soluble REEs and dissolved organic carbon (DOC) from subbituminous coal was investigated using laboratory-simulated sunlight exposures. The effects of the solar intensity, temperature, and exposure time on photodissolution were also examined. Following irradiation, water-soluble REE and DOC concentrations increased significantly above nonirradiated controls, indicating photodissolution is a significant process. Both solar intensity and exposure time influenced photodissolution rates, while temperature did not. Results from this study provide motivation to further investigate the photodissolution pathways of REEs from subbituminous coal and interaction with DOC ligands, given that photosolubilized REEs may be organic associated. These findings may have implications, both positive and negative, for the environmental impact of REEs.