Cooperative effect of 2-(dibutylcarbamoyl)benzoic acid and 2-thenoyltrifluoroacetone for the synergistic extraction of lanthanide ions

Selective extraction equilibria of Sc(III), Y(III), Fe(III) and Al(III) from acidic media with toluene mixture of deep eutectic solvent (DES) composed of TOPO and isostearic acid

A deep eutectic solvent (DES) composed of isostearic acid and TOPO was newly found out and investigated for selective recovery of scandium. The four elements used in this study are scandium, iron, yttrium, and aluminum. It was difficult to separate the four elements owing to the overlap of extraction behavior when isostearic acid or TOPO alone in toluene was used, respectively. However, scandium was able to be selectively extracted from other metals using DES prepared by 1:1 mol ratio of isostearic acid and TOPO without toluene. In DES consisting of isostearic acid and TOPO, synergistic and blocking effects with three extractants acted on the extraction selectivity for scandium. Both effects are proved also from the fact that scandium was easily stripped with diluted acidic solutions such as 2 M HCl and H₂SO₄. Thus, DES extracted selectively scandium and back-extraction was easily achieved. In order to elucidate these phenomena above, the extraction equilibria of Sc(III) using DES dissolved in toluene was investigated in detail. The extraction mechanism of scandium by DES in toluene indicates that the extracted chemical species vary with pH, and that trivalent scandium is extracted by forming stable metal complexes with DESs consisting of five molecules of isostearic acid and five molecules of TOPO.

Selective Extraction of Light Lanthanides(III) by N,N-Di(2-ethylhexyl)-diglycolamic Acid: A Comparative Study with N,N-Dimethyl-diglycolamic Acid as a Chelator in Aqueous Solutions

The complexation and selectivity of N,N-di(2-ethylhexyl)-diglycolamic acid (HDEHDGA/kerosene, HA) toward the light lanthanides, La(III), Ce(III), Pr(III), and Nd(III), are presented for the extraction from chloride media. In the low pH region (pH 1.8-2.8), the obtained data reveal that the extraction of Ln(III) is governed by cation-exchange mechanism and is driven by the negative change in enthalpy. The results from the slope analysis method suggest the formation of LnA₃·(HA)_1or2 in the extraction process. As major extracted species with a core of LnA₃ in the first coordination sphere, LnA₃ might connect with one or two additional HA molecules in the second coordination sphere by hydrogen bonding. The LnA₃ core might share similar coordination geometry to those of 1:3 Ln(III) complexes (LnA'₃) with water-soluble N,N-dimethyl-diglycolamic acid (HDMDGA, HA') formed in aqueous solutions or in solid-state compounds. The correlation between the extraction with HDEHDGA (HA) as an extractant and the complexation with HDMDGA (HA') as a chelator has been explored by interpreting the separation factors for HA with the difference in the stability constants for HA'. Consequently, the ratios of the stability constants of the corresponding 1:3 complexes (LnA'₃) with HDMDGA could be reasonably translated to the separation factors (SFs) with HDEHDGA, providing a valuable approach for understanding the origin of the extraction/separation mechanism. By comparing the extraction selectivity of HDEHDGA with that of the currently deployed extractants in the industry such as P204, P507, and Cyanex 272, HDEHDGA offers outstanding selectivity with considerable SFs (SF_Ce/La = 6.68, SF_Pr/Ce = 2.79, and SF_Nd/Pr = 2.65) for light Ln(III) pairs under conditions of low acid concentrations.