Investigation on the dissolution of 30 metal oxides in the water-free ionic liquid [Hbet][NTf2] and the catalytic effect of chloride for the application in green ore processing.

Ionic liquids (ILs) and deep eutectic solvents (DESs) have proven to be suitable solvents and reactants for low-temperature reactions. To date, several attempts were made to apply this promising class of materials to metal oxide chemistry, which, conventionally, is performed at high temperatures. This review gives an overview about the scientific approaches of the synthesis as well as the dissolution of metal oxides in ILs and DESs. A wide range of metal oxides along with numerous ILs and DESs are covered by this research. With ILs and DESs being involved, many metal oxide phases as well as different particle morphologies were obtained by means of relatively simple reactions paths. By the development of acidic task-specific ILs and DESs, even difficultly soluble metal oxides were dissolved and, hence, made accessible for downstream chemistry. Especially the role of ILs in these reactions is in the focus of discussion.

Ionometallurgy is a new development aiming at the sustainable low‐temperature conversion of naturally occurring metal ores and minerals to their metals or valuable chemicals in ionic liquids (ILs) or deep eutectic solvents. The IL betainium bis((trifluoromethyl)sulfonyl)imide, [Hbet][NTf2], is especially suited for this process due to its redox‐stability and specific‐functionalization. The potentiostatic electrodeposition of zinc and lead starting directly from ZnO and PbO, which dissolve in [Hbet][NTf2] in high concentrations is reported. The initial reduction potentials of zinc(II) and lead(II) are about −1.5 and −1.0 V, respectively. The ionic conductivity of the solution of ZnO in [Hbet][NTf2] is measured and the effect of various temperatures and potentials on the morphology of the deposited material is explored. The IL proves to be stable under the chosen conditions. From IL‐solutions, where ZnO, PbO, and MgO have been dissolved, metallic Zn and Pb are deposited under potentiostatic control either consecutively by step‐electrodeposition or together in a co‐electrodeposition. Using the method, Zn is also deposited on 3D copper foam and assembles into high‐voltage zinc‐graphite battery. It exhibits a working‐voltage up to 2.7 V, an output midpoint discharge‐voltage of up to 2.16 V, up to 98.6% capacity‐retention after 150 cycles, and good rate performance.

The application of ionic liquids for the dissolution of metal oxides is a promising field for the development of more energy‐ and resource‐efficient metallurgical processes. Using such solutions for the production of valuable chemicals or electrochemical metal deposition requires a detailed understanding of the chemical system and the factors influencing it. In the present work, several compounds are reported that crystallize after the dissolution of copper(II) oxide in the ionic liquid [Hbet][NTf2]. Dependent on the initial amount of chloride, the reaction temperature and the purity of the reagent, copper crystallizes in complexes with varying coordination geometries and ligands. Subsequently, the influence of these different complex species on electrochemical properties is shown. For the first time, copper is deposited from the ionic liquid [Hbet][NTf2], giving promising opportunities for more resource‐efficient copper plating. The copper coatings were analyzed by SEM and EDX measurements. Furthermore, a mechanism for the decomposition of [Hbet][NTf2] in the presence of chloride is suggested and supported by experimental evidence.