Sil Wellens

An environmentally friendlier approach to hydrometallurgy: highly selective separation of cobalt from nickel by solvent extraction with undiluted phosphonium ionic liquids

A green solvent extraction process for the separation of cobalt from nickel, magnesium and calcium in chloride medium was developed, using undiluted phosphonium-based ionic liquids as extractants. Cobalt was extracted to the ionic liquid phase as the tetrachlorocobaltate(II) complex, leaving behind nickel, magnesium and calcium in the aqueous phase. Manganese is interfering in the separation process. The main advantage of this ionic liquid extraction process is that no organic diluents have to be added to the organic phase, so that the use of volatile organic compounds can be avoided. Separation factors higher than 50 000 were observed for the cobalt/nickel separation from 8 M HCl solution. After extraction, cobalt can easily be stripped using water and the ionic liquid can be reused as extractant, so that a continuous extraction process is possible. Up to 35 g L−1 of cobalt can be extracted to the ionic liquid phase, while still having a distribution coefficient higher than 100. Instead of hydrochloric acid, sodium chloride can be used as a chloride source. The extraction process has been upscaled to batch processes using 250 mL of ionic liquid. Tri(hexyl)tetradecylphosphonium chloride, tri(butyl)tetradecylphosphonium chloride, tetra(octyl)phosphonium bromide, tri(hexyl)tetradecylphosphonium bromide and Aliquat 336 have been tested for their performance to extract cobalt from an aqueous chloride phase to an ionic liquid phase. Tri(hexyl)tetradecylphosphonium chloride (Cyphos IL 101) turned out to be the best option as the ionic liquid phase, compromising between commercial availability, separation characteristics and easiness to handle the ionic liquid.

A continuous ionic liquid extraction process for the separation of cobalt from nickel

A continuous ionic liquid extraction process using the ionic liquid trihexyl(tetradecyl)phosphonium chloride (Cyphos® IL 101) has been developed for the selective extraction of cobalt from nickel. The performance of this continuous extraction process is competitive with that of currently applied industrial processes. Moreover, the elimination of volatile odorous compounds from the extraction phase leads to environmentally friendlier and healthier working conditions.

Separation of cobalt and nickel by solvent extraction with two mutually immiscible ionic liquids

The proof-of-principle for the separation of metals by solvent extraction using two mutually immiscible ionic liquids is given. Cobalt was extracted from the ionic liquid 1-ethyl-3-methylimidazolium chloride to the ionic liquid trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl)phosphinate. A distribution ratio of 44 was obtained. Cobalt could be selectively separated from nickel, with a separation factor of 207. The extraction mechanism was elucidated using UV-VIS absorption measurements. The mutual solubility between the two ionic liquids was determined by (1)H NMR. Processing steps such as washing, stripping and regeneration of the ionic liquid phases are discussed.

Separation of rare earths and nickel by solvent extraction with two mutually immiscible ionic liquids

It is shown that rare earths can be distributed between two immiscible ionic liquids, allowing the transfer of the rare earths from one ionic liquid phase to another. The ionic liquid 1-ethyl-3-methylimidazolium chloride was used as the initial feed phase and the ionic liquid trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl)phosphinate (Cyphos IL 104) as the extracting phase. The rare earths could be recovered from the extracting phase by stripping with a 2 M HNO3 solution. The ionic liquids could be regenerated for reuse in the next extraction step. This ionic liquid–ionic liquid extraction system can be used for the separation of rare earths from nickel, because nickel is not extracted under these experimental conditions. Such a separation process is relevant for the recycling of valuable metals from nickel metal hydride (NiMH) batteries. Direct dissolution of rare-earth oxides in 1-ethyl-3-methylimidazolium chloride was possible, provided that a small amount of concentrated hydrochloric acid was added to the ionic liquid.

T-Shaped Ionic Liquid Crystals Based on the Imidazolium Motif: Exploring Substitution of the C-2 Imidazolium Carbon Atom

In this contribution the first examples of so-called rigid-core, T-shaped imidazolium ionic liquid crystals, in which the C-2 atom of the imidazolium ring is substituted with an aryl moiety decorated with one or two alkoxy chains, are described. The length of the alkoxy chain(s) was varied from six to eighteen carbon atoms (n=6, 10, 14-18). Whereas the compounds with one long alkoxy chain display only smectic A phases, the salts containing two alkoxy chains exhibit smectic A, multicontinuous cubic, as well as hexagonal columnar phases, as evidenced by polarising optical microscopy, differential scanning calorimetry, and powder X-ray diffraction. Structural models are proposed for the self-assembly of the molecules within the mesophases. The imidazolium head groups and the iodide counterions were found to adopt a peculiar orientation in the central part of the columns of the hexagonal columnar phases. The enantiotropic cubic phase shown by the 1,3-dimethyl-2-[3,4-bis(pentadecyloxy)phenyl]imidazolium iodide salt has a multicontinuous Pm ̄3m structure. To the best of our knowledge, this is the first example of a thermotropic cubic mesophase of this symmetry.

Determination of Halide Impurities in Ionic Liquids by Total Reflection X‑ray Fluorescence Spectrometry

The determination and quantification of halide impurities in ionic liquids is highly important because halide ions can significantly influence the chemical and physical properties of ionic liquids. The use of impure ionic liquids in fundamental studies on solvent extraction or catalytic reactions can lead to incorrect experimental data. The detection of halide ions in solution by total reflection X-ray fluorescence (TXRF) has been problematic because volatile hydrogen halide (HX) compounds are formed when the sample is mixed with the acidic metal standard solution. The loss of HX during the drying step of the sample preparation procedure gives imprecise and inaccurate results. A new method based on an alkaline copper standard Cu(NH3)4(NO3)2 is presented for the determination of chloride, bromide, and iodide impurities in ionic liquids. The 1-butyl-3-methylimidazolium ([C4mim]) ionic liquids with the anions acetate ([C4mim][OAc]), nitrate ([C4mim][NO3]), trifluoromethanesulfonate ([C4mim][OTf]), and bis(trifluoromethylsulfonyl)imide ([C4mim][Tf2N]) were synthesized via a halide-free route and contaminated on purpose with known amounts of [C4mim]Cl, [C4mim]Br, [C4mim]I, or potassium halide salts in order to validate the new method and standard.

Determination of Halide Ions in Solution by Total Reflection X-ray Fluorescence (TXRF) Spectrometry

An accurate quantitative determination of halide ions X (X = Cl, Br, I) in aqueous solution by total reflection X-ray fluorescence (TXRF) is not possible using the traditional acidic internal standards. In general, the standard solutions are highly acidic (e.g., Ga(NO3)3 in HNO3) to avoid precipitation of hydroxides of the standard element and to obtain a stable and reliable standard. In acidic solutions, dissolved halide salts can exchange their cation for a proton. The resulting volatile HX compounds can evaporate during the drying procedure of the TXRF sample preparation. In this technical note, we show that an alkaline Cu(NH3)4(NO3)2 standard can be used for the determination of chlorine, bromine and iodine without facing problems of HX evaporation.

Carbene formation upon reactive dissolution of metal oxides in imidazolium ionic liquids

Metal oxides were found to dissolve in different imidazolium ionic liquids with a hydrogen atom in the C2 position of the imidazolium ring, but not if a methyl substituent was present in the C2 position. The crystal structure of the product that crystallised from an ionic liquid containing dissolved silver(i) oxide showed that this was a silver(i) carbene complex. The presence of carbenes in solution was proven by (13)C NMR spectroscopy and the reactions were also monitored by Raman spectroscopy. The dissolution of other metal oxides, namely copper(ii) oxide, zinc(ii) oxide and nickel(ii) oxide, was also studied in imidazolium ionic liquids and it was found that stable zinc(ii) carbenes were formed in solution, but these did not crystallise under the given experimental conditions. A crystalline nickel(ii) carbene complex could be obtained from a solution of nickel(ii) chloride dissolved in a mixture of 1-butyl-3-methylimidazolium and 1-ethyl-3-methylimidazolium acetate.

How safe are protic ionic liquids? Explosion of pyrrolidinium nitrate

A batch of the protic ionic liquid pyrrolidinium nitrate exploded while drying it under reduced pressure at 110 °C, using a rotary evaporator with an oil bath.