Abstract
Rare earth (RE) metals (Dy, Sm, Nd, etc.) are indispensible and widely used elements in advanced technology fields, especially of dysprosium. It is, therefore, important to recycle RE metals including dysprosium from the waste magnet in Japan.
The equilibrium distribution of dysprosium(III) between aqueous nitric acid solution and 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (PC88A) has been measured in the range of an initial aqueous Dy (III) concentration from 1.0 × 10-3 to 1.0 × 10-1 kmol∙ m-3 and PC88A concentration from 0.16 to 0.65 kmol∙ m-3 in Shellsol D70 as the diluent. The data obtained were used to develop a chemically-based model in order to correlate the equilibrium distribution ratios of Dy(III) between aqueous and organic phases. In this model, (i) Dy(III) was assumed to be extracted with PC88A as a 1:6 complex, (ii) the activities were considered for the aqueous species, and (iii) the effective concentration of the PC88A dimer was calculated by the Alstad’s empirical equation. As a result, the apparent extraction equilibrium constant was determined to be 253 (kmol∙m-3)-2 with the excellent correlation between the experiment and calculation results in the wide range of logarithm of the distribution ratio from -2 to 3.5.
