Design of ionic liquids for homogeneous liquid-liquid extraction and aqueous biphasic extraction of metal ions

Ionic liquids (ILs) are solvents that consist entirely of ions. They have special properties such as a negligible vapor pressure which makes them an excellent environmentally friendly alternative to organic solvents. Ionic liquids can be divided into hydrophilic ionic liquids which are totally miscible with water and hydrophobic ionic liquids which are immiscible with water. Ionic liquids can also show a temperature dependent miscibility with water. Some IL/solvent mixtures have an upper critical solution temperature (UCST). They form one homogeneous phase above the UCST and phase-separate below this temperature. Other IL/solvent mixtures have a lower critical solution temperature (LCST). They form one homogeneous phase below the LCST and phase-separate above this temperature. This project is about the development of solvent extraction systems for the separation of metal ions, based on non-fluorinated ionic liquids showing temperature dependent miscibility with water. Intense stirring can be avoided during extraction by the formation of a homogeneous phase above (below) the UCST (LCST). In the homogeneous phase, a fast reaction between the metal ion and the extraction agent can take place. Upon cooling, phase separation occurs with transfer of the metal complex to the IL phase. Such as separation process is called homogeneous liquid-liquid extraction (HLLE). The ionic liquid solvent extraction systems will be used for the recovery and separation of rare earths and other critical metals.status: publishe

Docusate Ionic Liquids: Effect of Cation on Water Solubility and Solvent Extraction Behavior

Ionic liquids with the docusate (dioctyl sulfosuccinate or DOSS) anion are described. Docusate is incorporated into several phosphonium ionic liquids, including tetrabutylphosphonium and phosphonium cations functionalized with an ester, carboxylic acid, or ethylene glycol group. All synthesized ionic liquids are immiscible with water except the compound with the ethylene glycol moiety in the cation, [P444E3][DOSS]. This ionic liquid exhibits a lower critical solution temperature phase behavior upon mixing with water, to yield a homogeneous phase at temperatures below 19 °C, resulting in fast kinetics for homogeneous liquid–liquid extraction. The metal extraction capabilities for both divalent and trivalent metal ions are compared for this thermomorphic ionic liquid and the other hydrophobic docusate ionic liquids in an initial screening test. [P444E3][DOSS] is selected to perform separations on the Sm/Co and La/Ni pairs, because of their relevance in the recycling of samarium cobalt magnets and nickel metal hydride batteries. The extraction mechanism is studied, and stripping of the metals is investigated.status: publishe

Overview of the Effect of Salts on Biphasic Ionic Liquid/Water Solvent Extraction Systems: Anion Exchange, Mutual Solubility, and Thermomorphic Properties

Hydrophobic (water-immiscible) ionic liquids (ILs) are frequently used as organic phase in solvent extraction studies. These biphasic IL/water extraction systems often also contain metal salts or mineral acids, which can significantly affect the IL through (un)wanted anion exchange and changes in the solubility of IL in the aqueous phase. In the case of thermomorphic systems, variations in the cloud point temperature are also observed. All these effects have important repercussions on the choice of IL, suitable for a certain extraction system. In this paper, a complete overview of the implications of metal salts on biphasic IL/water systems is given. Using the Hofmeister series as a starting point, a range of intuitive prediction models are introduced, supported by experimental evidence for several hydrophobic ILs, relevant to solvent extraction. Particular emphasis is placed on the IL betainium bis(trifluoromethylsulfonyl)imide [Hbet][Tf2N]. The aim of this work is to provide a comprehensive interpretation of the observed effects of metal salts, so that it can be used to predict the effect on any given biphasic IL/water system instead of relying on case-by-case reports. These prediction tools for the impact of metal salts can be useful to optimize IL synthesis procedures, extraction systems and thermomorphic properties. Some new insights are also provided for the rational design of ILs with UCST or LCST behavior based on the choice of IL anion.status: publishe

Solvent Extraction of Scandium(III) by an Aqueous Biphasic System with a Nonfluorinated Functionalized Ionic Liquid

The use of ionic liquids (ILs) as solvents for extraction of metals is a promising development in separation science and technology; yet, the viscosities of ionic liquids (ILs) can be so high that long reaction times are required to reach the equilibrium state. An aqueous biphasic system (ABS) consisting of the nonfluorinated carboxyl-functionalized phosphonium IL [P444C1COOH]Cl and a 16 wt % NaCl solution is described. The IL-rich phase of the aqueous biphasic system has a very low viscosity, in comparison to the pure IL [P444C1COOH]Cl. This system has excellent extraction properties for scandium. Different extraction parameters were investigated, including contact time and metal loading. The influence of the pH on the solubility of the IL cation in the water-rich phase was determined via quantitative 1H NMR. The stripping of scandium with oxalic acid from the IL phase was also investigated. A plausible extraction mechanism is proposed where three IL cations are deprotonated to form zwitterionic compounds that can coordinate scandium(III) ions.status: publishe

Base-stable triazolium ionic liquids for extractive separations of metals from waste streams

Poster presentation by Stijn Raiguelstatus: publishe

Halogen-free synthesis of symmetrical 1,3-dialkylimidazolium ionic liquids using non-enolisable starting materials

Imidazolium ionic liquids were synthesized from readily available molecules: aldehydes, 1,2-carbonyl components, alkyl amines and acids in a halogen-free procedure. Since the use of enolisable carbonyl functions is not compatible with the modified Debus–Radziszewski reaction, symmetrical 1,3-dialkylimidazolium ionic liquids were made. The use of strong acids, like sulfuric acid, leads to protonation of the amine, low yields and side products that are difficult to remove. Changing the acid in the synthesis to acetic acid greatly improved the isolated yield and produced pure imidazolium acetate ionic liquids. From these imidazolium acetate compounds, many other ionic liquids could be prepared using different metathesis strategies. These strategies were dependent on the acidity of the conjugate acid of the anion, the acid volatility and the hydrophilicity of the used reagents and resulting ionic liquid. The following anions were introduced: bis(trifluoromethylsulfonyl)imide ([Tf2N]−), p-toluenesulfonate (tosylate, [TsO]−), bis(2-ethylhexyl)phosphate ([DEHP]−) and nitrate ([NO3]−). The impact of the different anions on the properties of the ionic liquids was investigated.crosscheck: This document is CrossCheck deposited related_data: Supplementary Information copyright_licence: The Royal Society of Chemistry has an exclusive publication licence for this journal copyright_licence: The accepted version of this article will be made freely available after a 12 month embargo period history: Received 30 October 2015; Accepted 13 January 2016; Accepted Manuscript published 15 January 2016; Version of Record published 21 January 2016status: publishe

Homogeneous liquid–liquid extraction of metal ions with non-fluorinated bis(2-ethylhexyl)phosphate ionic liquids having a lower critical solution temperature in combination with water

Ionic liquids with an ether-functionalised cation and the bis(2-ethylhexyl)phosphate anion show thermomorphic behaviour in water, with a lower critical solution temperature. These ionic liquids are useful for homogeneous liquid–liquid extraction of first-row (3d) transition metals.crosscheck: This document is CrossCheck deposited related_data: Supplementary Information copyright_licence: The Royal Society of Chemistry has an exclusive publication licence for this journal copyright_licence: The accepted version of this article will be made freely available after a 12 month embargo period history: Received 8 July 2015; Accepted 30 July 2015; Accepted Manuscript published 31 July 2015; Advance Article published 10 August 2015; Version of Record published 3 September 2015status: publishe

Solvent Extraction of Scandium(III) by an Aqueous Biphasic System with a Nonfluorinated Functionalized Ionic Liquid

The use of ionic liquids (ILs) as solvents for extraction of metals is a promising development in separation science and technology; yet, the viscosities of ionic liquids (ILs) can be so high that long reaction times are required to reach the equilibrium state. An aqueous biphasic system (ABS) consisting of the nonfluorinated carboxyl-functionalized phosphonium IL [P₄₄₄C₁COOH]Cl and a 16 wt % NaCl solution is described. The IL-rich phase of the aqueous biphasic system has a very low viscosity, in comparison to the pure IL [P₄₄₄C₁COOH]­Cl. This system has excellent extraction properties for scandium. Different extraction parameters were investigated, including contact time and metal loading. The influence of the pH on the solubility of the IL cation in the water-rich phase was determined via quantitative ¹H NMR. The stripping of scandium with oxalic acid from the IL phase was also investigated. A plausible extraction mechanism is proposed where three IL cations are deprotonated to form zwitterionic compounds that can coordinate scandium­(III) ions

Metal extraction with a short-chain imidazolium nitrate ionic liquid

A short-chain symmetrical dihexyl imidazolium nitrate ionic liquid for conventional solvent extraction of metals was developed. Rare earths were found to be preferentially extracted over 1st row transition metals leading to the application of the ionic liquid system for separation of the Sm(III)/Co(II) and La(III)/Ni(II) pairs, which are relevant for the recycling of SmCo magnets and NiMH batteries.crosscheck: This document is CrossCheck deposited related_data: Supplementary Information identifier: Wim Dehaen (ORCID) identifier: Koen Binnemans (ORCID) copyright_licence: The Royal Society of Chemistry has an exclusive publication licence for this journal history: Received 4 March 2017; Accepted 29 March 2017; Accepted Manuscript published 29 March 2017; Advance Article published 3 April 2017; Version of Record published 9 May 2017status: publishe

Overview of the Effect of Salts on Biphasic Ionic Liquid/Water Solvent Extraction Systems: Anion Exchange, Mutual Solubility, and Thermomorphic Properties

Hydrophobic (water-immiscible) ionic liquids (ILs) are frequently used as organic phase in solvent extraction studies. These biphasic IL/water extraction systems often also contain metal salts or mineral acids, which can significantly affect the IL trough (un)­wanted anion exchange and changes in the solubility of IL in the aqueous phase. In the case of thermomorphic systems, variations in the cloud point temperature are also observed. All these effects have important repercussions on the choice of IL, suitable for a certain extraction system. In this paper, a complete overview of the implications of metal salts on biphasic IL/water systems is given. Using the Hofmeister series as a starting point, a range of intuitive prediction models are introduced, supported by experimental evidence for several hydrophobic ILs, relevant to solvent extraction. Particular emphasis is placed on the IL betainium bis­(trifluoromethylsulfonyl)­imide [Hbet]­[Tf₂N]. The aim of this work is to provide a comprehensive interpretation of the observed effects of metal salts, so that it can be used to predict the effect on any given biphasic IL/water system instead of relying on case-by-case reports. These prediction tools for the impact of metal salts can be useful to optimize IL synthesis procedures, extraction systems and thermomorphic properties. Some new insights are also provided for the rational design of ILs with UCST or LCST behavior based on the choice of IL anion