Efficient extraction of Nd(III) by calix[4]arene derivatives containing diethyl phosphite

Abstract

Calix[4]arene derivatives including diethyl phosphite groups were used for the first time for separating Nd(III) from nitrate media. Calix[4]arene derivatives were synthesized and characterized by infrared spectroscopy (IR), mass spectroscopy (MS), and 1H NMR. Four calix[4]arene derivatives, CalixF (①), DCalixF (②), PCalixF (⑤), and POCalixF (⑥), were used in a solvent extraction method. The effects of aqueous acidity, diluent, temperature, shaking time, and Nd(III) concentration were investigated. The results showed that the extraction ability of ⑤ and ⑥ with a phosphate functional group at the upper rim were best for the extraction of Nd(III). Derivative ⑥ had better complexing capacities than ⑤ for the generation of a phenolic hydroxyl group at the lower rim. The enthalpy (∆HO), Gibbs free energy (∆GO), and entropy (∆SO) changes for the extraction were obtained from a thermodynamic study. The results showed that the extraction of Nd(III) from a nitric acid system might be an endothermic reaction since the process was naturally spontaneous and increasing the temperature during extraction was determined to be thermodynamically feasible. The extraction of Nd(III) was governed by a two-stage chemical reaction and diffusion process. In the first stage, the process was controlled by a fast chemical reaction at the liquid-liquid interface. The composition of the Nd(III)-calix[4]arene derivative complex was determined to be [Nd(NO3)3]2 [L]. The second stage was the diffusion of extracted products towards equilibrium. Calix[4]arene derivative ⑥ was found to be an efficient extractant for the separation of Nd(III) and would be a potential extractant for the disposal of radioactive waste in spent fuel.