Sorption strategies for recovering critical raw materials: Extracting trace elements from saltworks brines

Rising population, industrialisation, and resource demand intensify resource limitations, particularly critical for European Union (EU) industries dependent on raw materials. Based on economic importance and supply risk, 32 Critical Raw Materials (CRMs) and two strategic raw materials were identified in 2023. With most CRMs sourced outside the EU, sea mining emerges as a promising secondary resource for CRMs extraction from seawater, although the harvest of Trace Elements (TEs) will require energy-intensive processes. Several EU-funded projects explore circular economy and resource recovery, considering sorption methods’ potential to extract TEs from brines. Commercial polymeric (IRC747, S940, MTX8010) and inorganic (SbTreat, SrTreat) sorbents, plus another synthesised inorganic one (CuHCF), were assessed for recovering TEs (cobalt, gallium, germanium, rubidium, strontium, caesium) from saltworks brines (bitterns). Polymeric sorbents, containing chelating functional groups, effectively targeted cobalt, gallium, and strontium, commercial inorganic sorbents favoured cobalt, gallium, germanium and strontium, and CuHCF targeted rubidium and caesium. Kinetic batch experiments demonstrated rapid element retention (≤30 min) by most sorbents. In dynamic column experiments, high sorption capacities were observed for cobalt and gallium with the polymeric sorbents, particularly for aminophosphonic sorbents (IRC747 and S940) (≥2.1 mg/g). SrTreat exhibited also a high sorption capacity of 7 mg/g for strontium, SbTreat achieved 20 mg/g for gallium and germanium and CuHCF retained rubidium (10 mg/g) and caesium (70 mg/g). Acidic desorption effectively recovered (>70 %) most of the elements from the sorbents, achieving concentration factors up to 708 for cobalt with IRC747 and S940, highlighting the potential valorisation of saltworks bitterns.