Third Phase Formation in Extraction of Nd(Ⅲ) by (DdO)₂DGA

N,N′-di-octyl-N,N′-di-dodecyl-3-oxapentane-1,5-diamide ((DdO)₂DGA) is a new unsymmetrical diglycolamide extractant for the separation of trivalent actinides and lanthanides from high level liquid waste. In this paper, the representative element Nd in lanthanides was taken as the research object to study the third phase formation behavior of Nd(Ⅲ) in (DdO)₂DGA, the influence of aqueous phase acidity, temperature and co-existing metal ion concentration on the limiting organic concentration (LOC) of Nd(Ⅲ) in (DdO)₂DGA/n-dodecane solution was investigated. The structural variation of (DdO)₂DGA-Nd(Ⅲ) complex formed in the organic phase before and after third phase formation was also studied by infrared spectra, UV-vis spectra and fluorescence spectra. The results show that LOC of Nd(Ⅲ) increases with temperature, and decreases with increase of aqueous acidity and co-existing metal ion concentration. However, the structure of (DdO)₂DGA-Nd(Ⅲ) complex is not varied before and after third phase formation, and the reason for third phase formation is the variation of aggregation behavior of extracted complexes.