Complete separation of aluminium from rare earths using two-stage solvent extraction

To remove aluminum (Al) from rare earth element (REE) especially light rare earth element (LREE), octyl-phenoxy isopropionic acid (OPIPA) has been developed for the liquid-liquid extraction separation of Al from REE in this study. Using specific extraction experiment and infrared spectra analysis, the stoichiometry of saponified octyl-phenoxy isopropionic acid (S-OPIPA) to Al is indicated to be 3:1. The results of extraction investigation show that the separation effects of Al and REE arrive best when the initial water solution is pH = 3. The stripping experiment shows that sodium hydroxide is the best stripping agent. The extraction abilities of Al by OPIPA, naphthenic acid (NA), saponified OPIPA (S-OPIPA) and saponified naphthenic acid (S-NA) are compared at the pH values of 1, 2, 3, which indicates the importance of saponification. The loading capacities of S-NA and S-OPIPA reach the maximum values of 1.82 g/L and 1.85 g/L, respectively. It is found that S-NA is easy to be emulsified, while S-OPIPA reveals excellent phase separation behavior for the Al solution with the high concentration. The difference indicates that S-OPIPA is more suitable for the massive removal of Al. In the separation process of simulated REE ore leaching solution, the Al concentration can be lowered to zero after two stages of Al removal with S-OPIPA and S-NA sequentially, and REE recovery rate of 86.43% with a purity of 99.69% is achieved.