Studies On Extraction Technology Of Pr/Nd In D₂EHPA-HCl-LA-H₃cit Synergistic Coordination System

The separation of the rare earth (RE) elements is known to be difficult because of their similar chemical properties.In some traditional extraction separation system, the separation coefficient of light rare earth elements is low, especially Pr and Nd is only1.3to1.5, and the saponification system produces high levels of ammonia, high pollution of water resources problem.In this experiment, the non-saponified D2EHPA as the extractant, the citric acid was added in the rare earth solution containing lactic acid to form a synergistic coordination agent, and the extraction process of Pr and Nd in D2EHPA-HCl-LA and D2EHPA-HCl-LA-H3cit was studied.The distribution ratio and separation coefficient were determined in the D2EHPA-HCl-LA and D2EHPA-HCl-LA-H3cit system at different raw solution acidity, lactic acid and citric acid concentration. Comparing with distribution ratio and separation coefficient in two kinds of extraction system, the results showed that:high separation coefficient and extraction capacity is the advantages in both extraction systems. Comparing the D2EHPA-HCl-H3cit system, the addition of lactic acid not only inhibited the precipitation of rare earth citrate effectively, but aslo reduced the extraction acidity, and made the reextraction easier.Further researches are made for the two systems to separate Pr and Nd, and the optimized conditions were found as follows:In D2EHPA-HCl-LA system, under the pH value3.5, lactic acid concentration of0.6mol/L conditions, the distribution ratio DPr=7.1298, DNd=11.4078, separation coefficient βNd/Pr=1.6; In D2EHPA-HCl-LA-H3cit system, under the pH value3.5, lactic acid concentration of0.6mol/L, citric acid is lactic acid concentration of1/10conditions, the distribution ratio DPr=121.8571, DNd=221.7799, separation coefficient βNd/Pr=1.82.Infrared spectroscopy is used to analyze the organic phase loading RE in D2EHPA-HCl-LA and D2EHPA-HCl-LA-H3cit system. The results show that:the extraction mechanism of the first system is cation exchange extraction simply; While the latter lactic acid and citric acid also exist in the system, it shows a rare earth and the extractant solvent effect, the process of extraction presents the dual for cation exchange and solvent extraction reaction mechanism, increasing the extraction capacity of D2EHPA.Therefore, the results of experiments will provide the theory and technical basis for the realization of a green clean way to extract and separate the rare earth.