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.
The dissolution of metal oxides in an acid-saturated ionic liquid, followed by selective stripping of the dissolved metal ions to an aqueous phase is proposed as a new ionometallurgical approach for the processing of metals in ionic liquids. The hydrophobic ionic liquid trihexyl(tetradecyl)phosphonium chloride (Cyphos IL 101) saturated with a concentrated aqueous hydrochloric acid solution was used to dissolve CaO, NiO, MnO, CoO, CuO, ZnO and Fe 2 O 3. It was found that nickel(II) and calcium(II) could be separated from all other transition metals present in the ionic liquid phase by stripping at high chloride concentrations. By scrubbing the ionic liquid solutions phase with water, manganese(II) and cobalt(II) could be stripped together with a fraction of iron(III) and copper(II), leaving zinc(II) and the remainder of copper(II) and iron(III) in the ionic liquid phase. These metal ions could be removed from the ionic liquid using ammonia. Copper(II) and zinc(II) formed ammine complexes and were back-extracted, while iron(III) precipitated as iron(III) hydroxide. After removal of all the metals present in the ionic liquid phase, the ionic liquid was prepared for reuse. Unfortunately, the mutual separations nickel-calcium, cobaltmanganese, or zinc-copper could not be achieved. This system would be useful when nickel is the metal of interest, since separation of nickel from all other transition metals present in the solution is achieved by one stripping step.
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.
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