Innovative Geothermal Mining through Membrane Technologies

Critical raw materials (CRMs) are crucial for technological advancements and the global energy transition, especially in sectors such as renewable energy, electronics, and electric mobility. The sustainable and secure management of these materials is increasingly important. Geothermal springs represent a promising source of CRMs, offering valuable materials such as lithium, magnesium, strontium, and boron in addition to clean energy. Depending on where they come from geologically, geothermal springs can have lithium levels that are at least 10 times higher than seawater (0.18 mg/L) and about the same as salt lakes (0.04–3 g/L). The moderate Mg2+/Li+ molar ratio (~35) also shows that the two elements might be better separated, which would allow for more Mg2+ recovery. This study introduces a novel method for the recovery of CRMs from geothermal brines, combining Reverse Osmosis (RO), Nanofiltration (NF), and Membrane Distillation (MD) for efficient separation of water and valuable materials. The experiments are conducted using a synthetic laboratory-reproduced geothermal spring solution, which accurately replicates the pH, temperature, and ionic composition typical of natural geothermal waters. This experimental approach ensures that the results reflect real-world conditions, which is critical for evaluating the feasibility and scalability of the proposed method. The process begins with RO and NF to concentrate the brine and selectively separate multivalent ions (e.g., Mg) from monovalent ions (e.g., Li), leveraging differences in ionic valence. Following this, MD is applied to reduce brine volume and minimize thermal energy consumption, thereby optimizing both water recovery and the concentration of CRMs. A key innovation of this work is the exploitation of the elevated temperature of geothermal brines (> 35°C), which allows the use of MD with minimal external heating. This significantly reduces energy requirements and operational costs. The process minimizes Specific Thermal Energy Consumption (STEC), highlighting its efficiency and sustainability. This method not only enhances the recovery of lithium and magnesium from geothermal springs, but it also offers a cleaner, more sustainable approach to CRM extraction by utilizing renewable geothermal heat.