As a relatively new extractant, di-（2,3-dimethylbutyl）-phosphinic acid （HYY-2） is more efficient to separate heavy rare earths Tm/Yb/Lu than Cyanex 272 and P507. In this paper, HYY-2 was synthesized in our lab, and the extraction equilibrium, thermodynamics and stripping acidity for La, Gd and Y, which stood for light rare earth elements （REE）, middle REE and heavy REE respectively, from nitrate media with this extractant were investigated. Meanwhile, extraction ability, capacity and stripping acidity of HYY-2 were investigated and compared with those of Cyanex 272 and P507. The separation performance for rare earth element couples Gd/Eu and Er/Y were also studied. Compared to Cyanex 272, it possessed higher extraction capacity; while compared with P507, it has lower stripping acidity. The maximum βGD/Eu 1.46 occurred at PHequilibrium=2.78 and the maximumβEr/Y was 1.47 when pHequilibrium= 2.01.
