Ionometallurgy: The Processing of Metals Using Ionic Liquids
2016-08-08T12:29:44Z (GMT) by
Metal processing is commonly carried out using hydrometallurgy or pyrometallurgy. These two techniques, whilst widespread, have inherent issues associated with selectivity and efficiency. The aim of this study is to investigate the use of ambient temperature ionic liquids (IL) to dissolve and recover metals from ionic media. The first stage of the study involved the development of a new stable reference electrode for use in IL media. This was used to obtain activity coefficients for three different silver salts in three different imidazolium-based ILs containing matching anions. Activity coefficients were also obtained for silver chloride, anhydrous copper (II) chloride and trifluoromethanesulfonic acid in the deep eutectic solvent (DES) Ethaline and it was found that these solutions displayed ideal behaviour, even at high concentrations. The electrochemistry of metal complexes in ionic liquids was studied using cyclic voltammetry in an ethylene glycol: choline chloride eutectic (Ethaline) and these potentials were plotted against the corresponding redox potentials in aqueous media to try to determine how speciation affected the reactivity of metals in solution. The speciation of a range of metal chlorides in a range of DESs was investigated and it was found that the majority of the metal ions tended towards chloride speciation, with a few exceptions for the more oxophilic early transition metals. The addition of a substantial amount of water in the form of hydration shells did not affect the metal speciation significantly. In IL media, the speciation tended towards the anionic component of the liquid, depending on its strength as a ligand. The fundamental redox behaviour and speciation data were used to develop a practical method to separate copper from gallium in waste semiconductor scrap. Lumps of the alloy were electrodissolved in Ethaline and this was followed by selective electrowinning of the copper as metal and precipitation of the gallium as a gelatinous white hydroxide. In addition, iodine could be used as a powerful oxidising agent in DES media to oxidise a small amount of gold and recover valuable paleontological microfossils.