Solid Waste Considerations for Lithium Extracted from Geothermal Brines

Geothermal lithium presents an opportunity for securing new sources of Li, a critical mineral with increasing demand. Lithium extracted from geothermal brines potentially has fewer environmental impacts than other Li resources and occurs concurrently with renewable energy production. Despite the benefits, the impacts of geothermal Li need to be further explored before commencement of full-scale operations. One such impact is the generation of solid wastes. Geothermal brines contain solid-forming minerals that interfere with direct lithium extraction (DLE) technologies and must be removed prior to Li extraction. In this study we developed a systematic method for evaluating existing datasets on brine chemistry to predict solid waste production from DLE projects. The method was implemented on geothermal brine chemistry datasets from the U.S. and Europe. We found that geothermal brines contain many potentially interfering elements such as SiO₂, Fe, Mn, and Zn at concentrations high enough to warrant treatment and removal before DLE. Brine chemistry varies between resources and the concentrations of solid-forming minerals vary relative to the quantities of Li and other critical minerals present. Data on Pb, As, and other contaminants were examined due to the challenges that these minerals present for solid waste disposal. Data on other critical minerals that could be extracted with the Li were also identified. Results indicate that some brines have higher concentrations of minerals with solid waste potential compared with other brines. Both U.S. and European brines contain elements such as arsenic that could complicate solid waste disposal options. Overall, the systematic method presented for evaluation of brine chemistry is useful for providing information needed to assess environmental impacts and inform decision-making in future geothermal Li projects.