Synergistic Solvent Extraction of Erbium(III) using a Mixture of Neodecanoic Acid with 1-(2-Neononylamidoethyl)-2-Neononyl-2-Imidazoline

The solvent extraction of erbium(III), representing heavy lanthanides, from nitrate solutions has been studied using a novel mixture of neodecanoic acid (HA) with 1-(2-neononylamidoethyl)-2-neononyl-2-imidazoline (L) in toluene with 15 % (v/v) of n-decanol. The synergistic extraction of erbium(III) has been found in the equilibrium pH range from 6.0 to 6.5. The effects of the equilibration time, the temperature, the nature of diluent, the aqueous phase acidity, and variation of one extractant at a fixed concentration of the other extractant have been investigated. The temperature had no effect on the extraction process in the range of 0–45°C. FT-IR spectra of the mixed extractant before and after extraction of erbium were examined, and the loading capacity of the mixed extractant for Er(III) was determined. The experimental data indicated that the erbium ion is not directly coordinated by L, and the nitrate ions are not involved in the extraction of erbium(III). In the equilibrium pH range between 5.0 and 6.0, the extracted species were determined to be [Er(OH)A2·L] by the slope analysis method. The increase in the pH leads to the dominance of [Er(OH)2A·L] as the main extracted species. The extraction mechanism is discussed. The Nd/Pr, Y/Pr, Dy/Y, Ho/Y, and Er/Y separation factors were calculated, and the possibility of the separation of the Er–Y pair was demonstrated.