Graphene Oxide Membranes for Critical Raw Materials Recovery and Water Purification: From Cleanroom Wastewater to Fluorite

The European Union has identified fluorite (CaF2) as a critical raw material (CRM) due to its economic importance, negligible recycling, and high import dependency. This study investigates a functionalized graphene oxide (fGO) membrane for purifying wastewater containing dissolved fluorides below the solubility limit of CaF2 and the subsequent CRM recovery. While the fundamental interaction is known in batch systems, closed-loop recovery processes using this kind of membrane remain unexplored. Utilizing fGO synthesized via a scalable, green approach, we transition beyond conventional adsorption to a dynamic membrane-stripping cycle. Comprehensive material characterization is provided. The fGO membranes were tested in a real-case scenario using cleanroom facility wastewater. Fluorine concentration was successfully reduced from 21 down to 1.4 mg L−1, meeting the EU/USA discharge and drinking water standards. High-purity CaF2 powder was recovered. This work establishes a viable, non-conventional membrane-based approach for waste valorization, advancing circular economy principles in the semiconductor and microelectronics industries by transforming a hazardous waste into a strategic resource.