Separation of Critical Metals by Membrane Technology under a Circular Economy Framework: A Review of the State-of-the-Art

The demand for critical metals for net-zero technologies, including electric vehicles and wind/solar energy, puts pressure on extraction and recycling processes. As the treatment of solutions is becoming more and more complex and associated with the decreasing concentration of critical metals and the concentration of contaminants increasing, the development of separation techniques is required. Among them, membrane separation has been evaluated for hydrometallurgical processes with similar results to traditional techniques. This work aimed at reviewing the literature on membrane applications to obtain critical metals—lithium (Li), cobalt (Co), and rare earth elements (scandium—Sc, yttrium—Y, lanthanum—La, and neodymium—Nd). The main novelty is that this literature review focuses on the application of membrane techniques in industrial processes, not only water and wastewater treatment. For this, we searched a scientific database for different keywords, and the bibliometric analysis demonstrated a strong linkage between membrane separation and critical metals. The application of membranes to obtain critical metals from primary and secondary sources, acid mine drainage (AMD), industrial wastes, and the recycling of electronic wastes (e-wastes) and brine was revised. Among these traditional technologies, no relation was found with reverse osmosis. The outstanding use of membranes included combinations of solvent extraction techniques, including supported liquid membranes and polymer inclusion membranes.