Geothermal brines are hydrothermal fluids naturally heated under the earth’s surface and are a known source of environmentally sustainable, renewable energy. Additionally, these brines can exhibit significant concentrations of valuable minerals and critical metals. While the exact chemical composition of geothermal brines can vary with location, most brines in the U.S. contain relatively high lithium (Li) content.

Li is used in advanced clean energy technologies including fuel cells, electric vehicles, and renewable energy applications. Because of its importance in energy storage devices, Li has been identified as a near-critical material (second highest ranking) in the US DOE 2011 Critical Materials Strategy. Currently, the U.S. largely relies on foreign sources of Li due to limited domestic production.

The conventional process used to extract Li from brines requires a series of football field-sized evaporation ponds and lengthy acid/base leaching processes. The multi-step method is extremely time consuming, taking 18‒24 months to produce Li compounds such as lithium carbonate (Li₂CO₃), lithium chloride, and lithium hydroxide. In addition, the process is expensive, energy intensive, and frequently requires brine transportation for processing steps that result in the in the emission of large quantities of carbon dioxide (CO₂).

This invention describes a two-step process for the extraction of Li from natural brines; directly generating Li₂CO₃, an industrially useful product. The method uses a unique carbon pressure-based process parameter to first concentrate Li as ions in the brine solution; followed by the extraction of Li as Li₂CO₃ through the application of CO₂ gas to the concentrated brine under predetermined conditions. The proposed approach is a combination of simple concepts, and can be implemented using existing geothermal technologies. The source of CO₂ used in the separation process can be waste gas from other industrial processes generating CO₂. This novel process significantly reduces the overall cost, time, and energy demand for Li extraction from geothermal brines while reducing CO₂ emissions.