Diglycolamide-functionalized resorcinarene for rare earths extraction
A C-methylcalix(4)methylresorcinarene–DODGA ligand, derived from calixmethylresorcinarene functionalized with four diglycolamide (DGA) binding units, was synthesized and characterized by NMR and MS. The ligand was investigated with respect to the extraction of rare earth elements (REEs) from nitric acid solution. High sensitivity was observed, particularly toward heavy rare earth elements. The acidity effects, as well as the concentration of the extractant, were evaluated with regard to the extraction and separation efficiencies. The results showed that the distribution coefficient values increase with an increase in nitric acid concentration in the range from 0.1 to 5 mol L−1. A slope analysis method and spectrophotometric titrations showed clear complexation of the REEs with the ligand. An extraction mechanism is proposed from the estimation of the thermodynamic parameters (ΔH, ΔS, and ΔG). The extraction and stripping of REEs from a simulated leaching solution of a Nd/Fe/B/Dy magnet have been studied.