Selective separation of rare earths and aluminum from low-concentration rare earth solution via centrifugal extraction

The separation of rare earths (REs) and aluminum (Al) has always been a practical challenge in the rare earth industry. In this paper, the effects of contact time, the concentrations of Al3+ and RE3+ on the extraction and separation of REs and Al during the solvent extraction of low-concentration rare earth sulfate solution using P507 were investigated. Significant differences in the extraction kinetics between REs and Al can be observed at the same contact time. For instance, when the contact time is 10 s, the extraction efficiency of Y reaches up to 97.5 %, whereas that of Al is only 9.1 %. Under the conditions of initial pH of the rare earth solution 4.0, Al3+ concentration 0-20.0 mmol/L, and RE3+ concentration 1.5-12.0 mmol/L, both the separation factors of Gd/Al (beta Gd/Al) and Y/Al (beta Y/Al) are higher than 100 at the contact time of 10-300 s, indicating that M-HREs can be easily separated from Al through solvent extraction using P507. The separation factors of La/Al (beta La/Al) and Nd/ Al (beta Nd/Al) are 10.8-12.3 and 40.5-58.7, respectively, at the contact time of 15-30 s, which are much lower than those of M-HRE (such as Gd and Y), but are much higher than those at the contact time of 300 s (beta La/Al = 2.8, beta Nd/Al = 31.5). It means that the separation of LRE and Al serves as the key for the separation of REs and Al in the low-concentration rare earth solution, and controlling the contact time in the range of 15-30 s is conducive to the separation of LREs from the Al. The increase in the Al3+ concentration in the rare earth solution has no significant impact on the separation of REs and Al at the contact time of 10-60 s, but the increase in the RE3+ concentration induces the separation of REs and Al. In conclusion, REs in the low-concentration rare earth solution can be selectively separated from the Al via centrifugal extraction technology.