Aqueous-phase composition affects the extraction selectivity of N, N, N', N'-tetraisobutyldiglycolamide for light rare earth elements

Abstract

The current separation process of light rare earth elements (La, Ce, Pr, Nd) faces the persistent challenge of low separation coefficients. Efficient separation of mixed light rare earths was investigated using (N, N, N', N')-tetraisobutyldiglycolamide as the extractant in a mixed aqueous medium of hydrochloric acid and sodium chloride. Single-factor experiments systematically examined the effects of extraction time, temperature, diluent type, hydrochloric acid concentration, and sodium chloride concentration on extraction performance. Results indicate that, at fixed chloride ion concentration, the ratio of hydrochloric acid to sodium chloride significantly influences extraction selectivity. Under identical aqueous phase conditions, compared with (N, N, N', N')-tetrabutyldiglycolamide (TBDGA), (N, N, N', N')-tetraoctyldiglycolamide (TODGA), and (N, N, N', N')-tetra(2-ethylhexyl)diglycolamide (T2EHDGA), (N, N, N', N')-tetraisobutyldiglycolamide (TIBDGA) demonstrates superior selective extraction capability for La3+ and Ce3+ from mixed light rare earths under the present non-redox chloride conditions. The extraction mechanism was elucidated by analyzing the effect of TIBDGA concentration, supported by infrared spectroscopy and XPS characterization. Experimental results show that under conditions of 2.0 mol/L sodium chloride and 3.0 mol/L hydrochloric acid, the separation factor βLa/Pr reaches 192.67, and βCe/Pr equals 55.58. These results demonstrate that systematic variation of the NaCl/HCl composition can significantly affect the extraction selectivity of TIBDGA toward light rare earth elements in this system.