Effect of tartaric acid complexing agent on the extraction and separation of Pr and Nd by HDEHP in hydrochloric acid medium

As the most important method for the separation and purification of rare earth elements, solvent extraction is widely used in industry. HDEHP (Di(2-ethylhexyl) phosphoric acid) has become the most commonly used organic extractant because of its high separation factor for rare earth elements and large processing capacity. However, the large amount of ammonia nitrogen wastewater generated during the extraction process creates huge pressure on the environment. The tartaric acid complexing agent has been added to the aqueous phase to improve the extraction performance of HDEHP without saponification. This can effectively avoid the generation of ammonia nitrogen wastewater, which is more in line with the concept of green production. In this study, the effect of tartaric acid on the separation of Pr and Nd by HDEHP in hydrochloric acid and the corresponding mechanism are investigated. This study showed that the addition of tartaric acid could significantly increase the separation coefficient of HDEHP for Pr and Nd. When the tartaric acid concentration was 0.4 mol/L and the solution pH was 2.5, the separation coefficient reached β Nd/Pr  = 1.85, which was higher than the separation coefficient of HDEHP for Pr and Nd in the saponification system. Combining Fourier-transform infrared spectroscopy, nuclear magnetic spectroscopy other analysis and detection methods, and in-depth exploration of the extraction mechanism, the final extraction of the compound structures was determined.