The equilibria associated with the solvent extraction of trivalent rare earth elements (REEs) with 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (EHEHPA) have been previously studied by many researchers because of the industrial importance of REEs. However, quantitative analysis has been limited to relatively low concentrations of EHEHPA because of the nonideal characteristics of the organic phase. In the present paper, we used an empirical equation to correct the nonideality of the organic phase and calculated extraction equilibrium constants for some trivalent REEs (La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, and Y) that are particularly important in RE recycling from end-of-life products and in-plant scraps. Calculations based on use of EHEHPA in a nonpolar diluent and a nitrate medium were used to systematically investigate equilibria at a constant ionic strength of 1 mol/L, temperature of 298 K, EHEHPA dimeric concentrations that ranged from 0.04 to 0.33 mol/L, and a range of pHs. Apparent extraction equilibrium constants that reproduced the distribution ratios of the REEs with good accuracy were obtained. Further experiments at higher EHEHPA concentrations revealed that the empirical equation was effective up to an EHEHPA dimer concentration of 0.5 mol/L, which is significantly higher than the upper bound for the conventional dimer model. Separation factors defined as the ratios of the distribution ratios of two REEs were calculated from the extraction equilibrium constants for the possible pairs of REEs and compared critically with literature values. Differences in the separation factors depended on the measurement conditions and were most pronounced when the difference in atomic numbers of the REEs was large. The results are expected to facilitate designing processes for the separation and purification of REEs.

以前由于稀土元素的工业重要性，许多研究人员已经研究了用2-乙基己基膦酸单-2-乙基己基酯（EHEHPA）溶剂萃取三价稀土元素（REE）的平衡。但是，由于有机相的非理想特性，定量分析仅限于相对较低浓度的EHEHPA。在本文中，我们使用经验公式校正了有机相的非理想性，并计算了一些三价稀土元素（La，Ce，Pr，Nd，Sm，Eu，Tb，Dy和Y）的萃取平衡常数。在报废产品和厂内废料的可再生能源回收中很重要。基于在非极性稀释剂和硝酸盐介质中使用EHEHPA的计算，系统地研究了在恒定离子强度1 mol / L，温度298 K，EHEHPA二聚体浓度范围为0.04至0.33 mol / L和pH值范围。获得了表观提取平衡常数，该常数以良好的精度再现了稀土元素的分布比。在较高的EHEHPA浓度下进行的进一步实验表明，经验公式在EHEHPA二聚体浓度为0.5 mol / L时有效，该浓度明显高于常规二聚体模型的上限。分离因子定义为两个REE的分配比之比，由可能的REE对的提取平衡常数计算得出，并与文献值进行严格比较。分离因子的差异取决于测量条件，当REE原子序数差异较大时，差异最明显。预期结果将有助于设计用于分离和纯化REE的过程。