Study On The Extractive Separation Of Heavy Rare Earths With Organo-phosphinic Acid

As an important strategic resource, rare earths are applied widely in the fields of military, aerospace, energy, medicine, agriculture, functional materials and so on. With the development of sophisticated technology, the demand of high-purity rare earths rise violently. Solvent extraction is an important method of separation and purification for rare earth.In this thesis, high-purity bis (2,4,4-trimethylpentyl) phosphinic acid (L272) prepared by our research group was used as extractant for heavy rare earths (Er, Tm, Yb and Lu) and 1-methylheptyl alcohol (octanol) was used modifier to improve the extractive performance of L272. The extractive separation performance and mechanism of L272/octanol systems with different proportions were investigated. The extrantants were characterized by NMR (31P) and infrared spectra (IR). ICP analysis was performed to examine concentration of rare earth ions. In addition, the density, surface tension and solubility of extractants were also measured. The results indicates that the extractants (L972) with the volume ratio of 9:1 (L272:octanol) exhibits the best performance for the separation of heavy rare earths:average separation coefficient β≈8.05, and average saturation capacity about 0.14mol/L. Most of extraction process adopts cation exchange mechanism, and a few associative mechanism. The general formula of the cpmplex of L272-RE3+ were LnCl3-n(HA2)n (n=the slope of logD-pH).Extraction performance of L972 for heavy rare earths in HCl medium was studied systematically. It is shown that the maximal extraction rate of the heavy rare earths can be obtained under the following conditions:pH=2, O/A=1:1, t=12 min with other conditions fixed. The maximal stripping rate for saturated loaded organic phase rate is achieved with 3mol/L HCl. Moreover, the maximal separation factor (β) of the heavy rare earths can be obtained under the following conditions:pH=1.5, O/A=1:1, t=9 min with other conditions fixed.In addition, the effects of non-rare earth impurities such as iron, aluminum and si licon on extraction performance of L972 for heavy rare earths were also studied. It is shown that extraction rate of heavy rare earths was significantly reduced and emulsification occurs at lower pH value in the presence of iron and aluminum which are more difficult to strip. As for L972, the extraction rate of silicon is relatively low. But the loaded silicon was extremely difficult to remove with maximum stripping ratio only 40% after stripping again and again with 3M HCl. Therefore, silicon would accumulate in the organic phase during continuous extraction process, which would severely affect the performance of L972. Moreover, once formed during the extraction process, the silica gel is difficult to removed or break.Compared with well-known rare earth extractants, the extraction performance of L972 on heavy rare earth is superior to that of Cyanex 272 and P507 in many ways such as selectivity, saturation capacity, phase separation and stripping; The results of this thesis are expected to promote the development of separation and purification technology for heavy rare earths.