Homogeneous liquid–liquid extraction of neodymium(iii) by choline hexafluoroacetylacetonate in the ionic liquid choline bis(trifluoromethylsulfonyl)imide

Abstract

The ionic liquid choline bis(trifluoromethylsulfonyl)imide, [Chol][Tf2N], was used for the extraction of neodymium(III), in combination with choline hexafluoroacetylacetonate, [Chol][hfac], as the extractant. The binary mixture of [Chol][Tf2N] and water shows temperature-dependent phase behavior, with an upper critical solution temperature of 72 °C. A novel extraction technique, homogeneous liquid-liquid extraction (HLLE), was applied to this solvent system. HLLE is based on the use of thermomorphic solvent mixtures and has the advantage of forming a homogeneous phase during mixing. Extraction is not kinetically hindered by an interface and the extraction equilibrium is reached faster than in the case of heterogeneous mixing in conventional solvent extraction. Several extraction parameters were studied for the extraction of neodymium(III) with [Chol][hfac]: temperature, pH, extractant concentration and loading of the ionic liquid phase. A speciation study was performed to determine the stoichiometry of the extracted neodymium(III) complex and a plausible extraction mechanism is proposed. Neodymium is extracted as a tetrakis hexafluoroacetylacetonate complex with one choline cation as counter ion. The crystal structure of the extracted complex showed the presence of a coordination bond between the choline counter ion and the neodymium(III) center, resulting in a coordination number of nine. The stripping of the loaded neodymium and the influence of acid and extractant concentrations on the phase behavior of the [Chol][Tf2N]-H2O system were investigated.

Selective Single‐Step Separation of a Mixture of Three Metal Ions by a Triphasic Ionic‐Liquid–Water–Ionic‐Liquid Solvent Extraction System

“…From these results, it can be concluded that [Hbet][Tf 2 N] system is of more interest than the [Chol][Tf 2 N] system because the phases in the latter system are less pure and thus less interesting for solvent extraction systems. Moreover, choline is a very weak solvating ligand and extraction without the addition of an extra extractant is very difficult 16…”

Chemical Tuning of Zwitterionic Ionic Liquids for Variable Thermophysical Behaviours, Nanostructured Aggregates and Dual‐Stimuli Responsiveness

“…[22] With regard to thermoresponsive IL-waters ystems, UCST-type systemsa re more popular as they can be utilised as extraction and separation solvents, which further broadens their applicationsi nc atalysis. [34][35][36] However,o nly few UCST-type IL-water systems are reported so far. [34][35][36][37] The most important one is the binary mixture of imidazolium-based ILs ([C n mim]BF 4 , n = 4, 6,8) and water,w hich shows tuneable UCST-type transitions depending on the length of the alkyl chain and also on the hydrophobicity of the anions.…”

“…[34][35][36] However,o nly few UCST-type IL-water systems are reported so far. [34][35][36][37] The most important one is the binary mixture of imidazolium-based ILs ([C n mim]BF 4 , n = 4, 6,8) and water,w hich shows tuneable UCST-type transitions depending on the length of the alkyl chain and also on the hydrophobicity of the anions. [37] The reportso fb oth UCST-and LCST-type transitions of [P 4,4,4,4 ]-type ILs with fumarate and maleatei ons, respectively,f urthere nriched this area.…”

Fast selective homogeneous extraction of UO22+ with carboxyl-functionalised task-specific ionic liquids

“…This system showed that effective extraction of trivalent rare-earth, indium, gallium, neodymium ions18, and uranyl species33 can be achieved by homogeneous extraction without additional any extractant. Homogeneous liquid–liquid extraction of neodymium(III) has also been achieved using choline hexafluoroacetylacetonate in the ionic liquid choline bis(trifluoromethylsulfonyl) imide34. Recently, Dupont et al .…”