Evaluation of glycolipid functionalized organosilica media for adsorption of rare earth elements and uranium

Anthropogenic metal contamination in aqueous resources poses risks to human and environmental health. Such solutions can contain critical materials such as rare earth elements (REE) and uranium (U) that are vital for economic security and the green economy. One approach to remediate these solutions is "aqueous mining" to generate non-traditional metal resources. The practical implementation of such an approach requires the recovery of metals in an economical, green, and selective manner. Bioinspired glycolipid surfactants are promising materials for such an application because they are non-toxic, biodegradable, and selective for critical materials. Six glycolipid-functionalized media were examined for the recovery of REE and U as a function of pH. At pH 7, U adsorption exceeded REE in 5 of the 6 media with nearly 100 % of U absorbed by media containing either a single-chain galactolipid, two-chain rhamnolipid, or a two-chain xylolipid. REE sorption was the highest in the two-chain rhamnolipid medium reaching 96 %. The single-chain glucolipid medium sorbed little to no metal. Due to its good performance, the two-chain rhamnolipid medium was further evaluated at pH ranging from 7 to 2.75. Adsorption of both REE and U remained near 100 % from pH 7 to 3.25. At pH 3, REE adsorption dropped to similar to 20 % but U remained near 90 %. At pH 2.75 neither REE (similar to 0 %) nor U (similar to 10 %) were strongly bound. To examine glycolipid-media stability, the media were washed three times followed by total carbon analysis to examine glycolipid loss. Glycolipid loss ranged from <4 % to 26 % in the first wash with decreasing losses in the subsequent washing steps. Despite exhibiting the most loss, sorption activity of both the single and double chain rhamnolipids remained high, achieving nearly 100 % of theoretical maximum sorption. Future work will focus on further characterizing high-performing glycolipid sorbents to assess industrial applicability compared to existing technologies.