Acid-free countercurrent chromatographic separation of lanthanide nitrate salts using water / chloride ionic liquid biphasic systems

The separation of lanthanide compounds typically relies on acidic media, complexing agents and multi-stage solvent extraction processes. Here we report an acid-free approach to lanthanide nitrate separation using liquid-liquid countercurrent chromatography with a hydrophobic chloride ionic liquid stationary phase and pH-neutral aqueous mobile phases. Using praseodymium(III) and erbium(III) nitrates as a model system, selective partitioning within simple water/ionic liquid biphasic solvent systems enables efficient chromatographic resolution without added mineral acids, buffers or specialised chelators. Under optimised conditions, up to 93% of Pr(NO₃)₃ and 85% of Er(NO₃)₃ were recovered in chromatographically unmixed form. The results demonstrate that distribution-driven separations in recyclable ionic-liquid systems can provide a conceptually simple and potentially cleaner route to lanthanide fractionation.