(382f) High-Throughput Experiments Elucidate the Effect of Multicomponent Feed Streams on Solute Transport

Critical minerals, such as the rare earth elements (REEs), are crucial components in green energy technologies and electronics. Unfortunately, the current processes used to purify these resources are at odds with the technologies they inspire. For instance, REEs in primary and secondary sources are commonly separated through liquid-liquid extraction (LLE). LLE separations cannot be rapidly re-optimized to account for site-specific variability in the feed streams and require copious amounts of harmful organic solvents. In this regard, membrane technologies offer modular design platforms and an environmentally-responsible alternative for critical mineral separations. Membrane cascades have demonstrated the ability to fractionate solutes into distinct streams, yet their optimization has assumed that membrane performance is independent of feed composition. As such, the application of staged membrane designs is hindered by the lack of knowledge related to multicomponent interactions in relevant feed streams.

Motivated by the presence of lanthanum and sodium in fluorescent lamps and acid mine drainage, this study systematically explores the effect of feed composition on solute transport through commercial polyamide nanofiltration membranes. The feed stream will contain two salts with a shared anion, chloride, to reduce the complexity of the experiment. We design high-throughput experiments to keep one solute concentration constant over the course of the experiment and increase the concentration of the other unique ion. These experiments allow us to collect information-dense data sets. Therefore, fewer experiments can be used to explore the concentration phase space and create topological maps that relate solute transport to ionic strength and molar ratio. This enables us to identify the concentration ranges where interesting transport phenomena are occurring. For example, we demonstrate that the transport of the monovalent ion is enhanced while that of the multivalent ion is relatively unaffected. At low Na⁺:La³⁺ ratios, these multicomponent interactions result in negative sodium ion rejections. We subsequently extended our study to a feed containing lanthanum and calcium. This extension sheds light on the influence of ion-ion and ion-membrane interactions in multicomponent feeds.