| Summary: | Solvent extraction is the most widely used method for separation and purification of rare earth elements, and organic extractants such as di(2-ethylhexyl) phosphoric acid (P204) and di(1-methyl-heptyl) methyl phosphonate (P350) are most commonly used for industrial applications. However, the presence of impurity ions in the feed liquid during extraction can easily emulsify the extractant and affect the quality of rare earth products. Aluminum ion is the most common impurity ion in the feed liquid, and it is an important cause of emulsification of the extractant. In this study, the influence of aluminum ion was investigated on the extraction of light rare earth elements by the P204-P350 system in hydrochloric acid medium. The results show that Al<sup>3+</sup> competes with light rare earths in the extraction process, reducing the overall extraction rate. In addition, the Al<sup>3+</sup> stripping rate is low and there is continuous accumulation of Al<sup>3+</sup> in the organic phase during the stripping process, affecting the extraction efficiency and even causing emulsification. The slope method and infrared detection were utilized to explore the formation of an extraction compound of Al<sup>3+</sup> and the extractant P204-P350 that entered the organic phase as AlCl[(HA)<sub>2</sub>]<sub>2</sub>P350<sub>(o)</sub>.
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