Theoretical and experimental comparison of rare earths extraction by [P6,6,6,1,4][Decanoate] bifunctional ionic liquid and D2EHPA acidic extractant

Abstract

The extraction behavior of two lanthanides (La3+ and Y3+) in the nitric acid solution was studied using a bifunctional ionic liquid, namely Trihexyl-tetradecyl-phosphonium Decanoate ([P6,6,6,1,4] [Decanoate]). On comparative study on D2EHPA as a molecular extractant, the ionic liquid revealed remarkably higher extraction capacity of the total are earth elements. The ionic liquid had a separation factor for La/Y smaller than that of the molecular extractant. A high yttrium extraction with an efficiency of > 99% was observed for both extractants, even in low concentrations. The highest efficiency of D2EHPA (20%) equaled 75.04% in the extraction of lanthanum, while this magnitude was > 99% for lanthanum extraction by the ionic liquid. In this study, the Density Functional Theory (DFT) connected to Born Haber Thermodynamics was used along with the solvent effect, imported by the Conductor-like Screening Model (COSMO), for confirming and interpreting the selectivity results, which were observed in the laboratory during the extraction of lanthanum and yttrium. Calculation of the difference in the energy levels of the molecular orbitals of [P6,6,6,1,4] [Decanoate] in the extraction of the neutral complexes of [La.(NO3)3. (H2O)3] ΔEorbital = 0.16 eV) and [Y.(NO3)3. (H2O)2] (ΔEorbital = 0.17 eV) with the neutral or ion pair exchange has shown that this ionic liquid was more efficient than D2EHPA with a cation exchange mechanism in the extraction of the ionic complexes of these elements.