High-efficiency process of aluminum removal from rare earth solutions using a readily industrialized ionic liquid

Aluminum (Al) is often associated with rare earth resources, and the removal of Al3+ from rare earth elements (REEs) is a difficult task due to its amphoteric properties. Aluminum ions (Al3+) enrich in Sm3+-Gd3+ solution with the traditional 2-Ethylhexylphosphoric acid mono-2-ethylhexyl ester (P507)-kerosene-HCl system, emulsifying the phases, polluting the rare earth products and reducing the separation efficiency. A readily industrialized ionic liquid (IL) was synthesized with methyltrioctylammonium chloride ([N1888]Cl) and industrial naphthenic acid (NA) for the purification of Al3+ from GdCl3 solution. Under the experimental conditions, the extraction properties of diluted [N1888][NA], diluted NA and saponified NA were comparatively investigated and the separation factors (βAl/Gd) of Al/Gd were 23.0, 3.5 and 1.3, respectively. The effects of the salting-out agent, extraction agent, pH value and phase ratio on metal extraction efficiency were optimized. Finally, the industrial GdCl3 feed with a high Al3+ impurity of 889 mg/L was lowered to 5 mg/L. The removal efficiency of Al3+ was 99.4%, and the purity of Gd3+ was 99.998%. It provides a potential method for Al3+ purification from rare earth solutions with advantages of high efficiency, raw materials availability and ready industrialization.