Extraction Behaviors of Critical Rare Earth Elements with Novel Structurally Tailored Unsymmetrical Diglycolamides from Acidic Media

ABSTRACT

A series of eight new structurally related unsymmetrical diglycolamides (UDGA) were designed and compared based on REEs extraction and phase compatibility at high acidic media concentration. The structure–reactivity relationship with extraction of REEs was studied in HCl, HNO₃, and H₂SO₄ solutions. A symmetrical diglycolamide (DGA), N,N,N’,N’-tetradodecyldiglycolamide (TD²DGA), was synthesized for purpose of comparison. The influence of HCl, HNO₃, and H₂SO₄ concentrations on the distribution ratios of the studied metal ions was investigated. In all systems, the mutual separation of the investigated REEs as well as from Fe(III), Ni(II), and Co(II) was achieved in the whole range of acidic solutions used by N,N′‐diisobutyl‐N,N′‐didodecyldiglycolamide (DiBD²DGA). A systematic investigation of the extraction of La(III), Pr(III), Nd(III), and Dy(III) was carried out with DiBD²DGA from hydrochloric acid media. The stoichiometry of the extracted REEs-UDGA complex was determined by the slope analysis method and complexation was found to be exothermic. The FT-IR spectra of these extracted species were studied. The back extraction of La(III), Pr(III), Nd(III), and Dy(III) was carried out.

KEYWORDS:

• Rare earth elements
• base metal ions
• extraction/separation
• unsymmetrical
• diglycolamides

Acknowledgments

The authors wish to express their thanks to Prof. K. L. Nash, the Co-editor, Solvent Extraction and Ion Exchange as well as the reviewers, for their constructive suggestions.