Study on Cu(II) extraction process optimization and mechanism from acidic leaching solution using the deep eutectic solvent P507/Menthol

In this study, the selectivity of a hydrophobic deep eutectic solvent (HDES) comprising 2-ethylhexylphosphonic acid mono-(2-ethylhexyl) ester (P507) and L-menthol (Men) was assessed for the extraction and separation of Cu(II), Co(II), and Ni(II) from acidic leaching solutions, aiming to make the HDES system more consummate and provide a novel approach for metal extraction using HDES. The results indicated that under the conditions of a 2:1 M ratio of P507 to Men, an extraction temperature of 40℃, an extraction time of 40 min, an oil-water ratio(O/W, v/v) of 1, and a pH value of 4, the three-stage cross-flow extraction efficiency of the HDES for Cu(II) was over 99 %. Furthermore, successful selective separation of Cu(II), Ni(II), and Co(II) was demonstrated by separation coefficients βCu/Ni of 2150 and βCu/Co of 305. Molecular dynamics (MD) simulations and density functional theory (DFT) indicated that the formation of an HDES molecule involved the combination of two molecules of P507 and one molecule of Men through hydrogen bonding interactions. Moreover, compared to other cupric complex configurations, the tetrahedral cupric complex, synthesized using two molecules of P507 and two molecules of menthol with Cu(II), exhibited a lower single-point energy and a higher ΔE(LUMO-HOMO), demonstrating greater stability.