Sustainable lithium recovery from geothermal brine via integrated membrane distillation – selective electrodialysis

Abstract

The escalating global demand for lithium, driven by its crucial role in energy storage systems and the transition to renewable energy, necessitates sustainable extraction methods from innovative sources such as geothermal brines, salt lakes and recycled batteries. Geothermal brine offers a dual advantage as a source of clean energy and lithium, with higher lithium concentrations (0.01–0.48 g L⁻¹) compared to seawater (0.18 mg L⁻¹) and levels comparable to salt lakes (0.04–3 g L⁻¹). Additionally, it features a much lower Mg/Li ratio (∼35.33) compared to seawater (∼7588), though still higher than that of salt lakes (∼6.4). Despite these advantages, lithium recovery from geothermal brines is challenging due to low lithium concentrations and the presence of competing ions. Herein, we introduce a novel approach that integrates Membrane Distillation (MD) and Selective Electrodialysis (S-ED) for efficient lithium extraction and water recovery from geothermal brines. The focus is on optimizing performance at both stages: The MD process was optimized to reduce brine volume and specific thermal energy consumption, while the ED process was focused on minimizing voltage and specific energy consumption at the optimal concentration. The hybrid system demonstrates strong potential for energy-efficient lithium recovery. At MD stage, geothermal water was concentrated at different volume reduction factors (VRFs) of 15.1, 28.1 and 43.11, resulting in feed concentrations of 1 M, 2 M, and 3 M, respectively, for the subsequent ED stage. Operating the MD process with geothermal water at its natural temperature of 40 °C rendered it energy-neutral, leading to specific thermal energy savings of up to 1980.5 kW h m⁻³. At S-ED stage, higher feed concentrations improved lithium selectivity but increased specific energy consumption. The optimal performance was observed at a feed concentration of 2 M (corresponding MD-VRF of 28.1) and an applied voltage of 2 V, achieving a specific energy consumption of 0.04 kW h per gram of Li⁺ and a current efficiency of 4.1%. Overall, the integrated MD–S-ED approach demonstrates strong potential for energy-efficient lithium recovery, paving the way for innovative research and offering key insights for sustainable lithium extraction methods that support the principle of Circular Blue Economy and Green Process Intensification.