Natural Materials as a Pathway to Affordable and Scalable Membrane Separation Technologies

This white paper focuses on developing affordable and scalable membrane separation technologies derived from natural materials for selective extraction of critical minerals (CMs), such as lithium, manganese, and barium, from geothermal brines. This approach integrates with geothermal power operations, enabling simultaneous energy generation and mineral recovery while minimizing water use and environmental impact.

Current CM extraction processes are energy- and water-intensive, and geothermal brines present additional complexity due to the low concentration of valuable species (Li ~200 mg L-1, Ba ~200 mg L-1, Mn ~1000 mg L-1) coexisting with high concentrations of interfering ions (Ca >50,000 mg L-1, Na >20,000 mg L-1). Existing direct lithium extraction (DLE) technologies remain immature, with no fully demonstrated commercial systems capable of achieving high selectivity, throughput, and stability in these harsh chemical environments. Conventional membrane materials, while showing promise in laboratory studies, often suffer from fouling, mineral scaling, and prohibitively high production costs, particularly when constructed from advanced materials such as metal-organic frameworks or carbon nanotubes.

The near-term opportunity lies in developing membrane systems fabricated from inexpensive, naturally abundant, and environmentally benign materials that can withstand geothermal conditions and be economically disposed of at the end of their service life, thus reducing costs associated with cleaning, regeneration, and fouling mitigation. This new class of natural-material membranes offers a low-cost, sustainable alternative to synthetic membranes and opens the door to rapid deployment in geothermal and other industrial systems. A key scientific challenge remains in achieving ion selectivity among chemically similar species, such as Li+, Na+, and K+, which share comparable ionic radii and hydration energies. Addressing this will require fundamental studies linking membrane chemistry and structure to ion transport and separation mechanisms.

In the near term, customized membrane designs can be optimized for different brine compositions and target minerals, with multiple selective membrane units potentially operating sequentially to extract specific elements. Integration with high-temperature heat pumps (HTHPs) offers additional efficiency gains by upgrading low-grade geothermal heat for industrial or district heating use, further increasing the economic and environmental value of geothermal operations.

Success will be measured by the lab-scale demonstration of these natural-material membranes, increasing their technology readiness level (TRL) from 1 to 5, with a target of achieving greater than 70% lithium recovery and more than 70% purity-suitable for subsequent ultra-refining to battery-grade quality. Additional success metrics include developing a fundamental understanding of how membrane chemistry and architecture influence separation performance, demonstrating adaptability to diverse waste streams (e.g., oil and gas produced water), and achieving measurable reductions in energy and water use compared to conventional extraction methods. By transforming geothermal brines into dual-use resources for both power generation and mineral recovery, this effort advances U.S. energy sovereignty, strengthens domestic supply chains for critical minerals, and supports the deployment of sustainable energy and materials technologies at scale.