Valorization of Geothermal Waters: the Development and Testing of a Supercritical Fluid Extraction Process for the Recovery of Lithium

Abstract

Many geothermal waters are enriched in a range of metals and minerals. Lithium has been identified as one of the more attractive metals for extraction and has also been defined by the U.S. Department of Energy as a critical material because of its use in batteries for electric vehicles and portable electronics. Extraction of lithium from geothermal waters has been attempted with a range of different methods, most depending on adsorption or ion exchange on a surface. Because of the dependence on surfaces, scaling can be severely detrimental to activity and silica removal is required for the processes to operate. Additionally, there has been a lack of focus on the concentration process necessary to make geothermal waters feasible for the production of lithium products, which are generally made from brines that have been concentrated to about 4,000-6,000 mg/L. We have developed an extraction and concentration method that is fast, environmentally friendly and not sensitive to silica scaling; a supercritical fluid extraction process with lithium selective crown ether extractants. The overall process takes about an hour and results in significant concentration of lithium into an aqueous solution. It takes place across a fluid interface and at high pressures and temperatures to both prevent silica scaling and limit the effect of scaling if it happens. The overall extraction efficiency of lithium from a 10 mg/L synthetic geothermal water solution is 30% in a batch operated process, at 60°C and 250 bar. In this talk key features in the development of the process will be presented, as well as the results of supercritical extraction of lithium from synthetic geothermal waters, and possibilities for the optimization of the process.