Cobalt Deposition from Ionothermally Dissolved Cobalt Oxides

Abstract

Owing to the environmental problems of numerous metal production processes, there is a growing need for more energyefficient approaches. Cobalt is considered a strategic element that is extracted not only from ores but also from spent Li-ion batteries. One promising new approach is ionometallurgy, which is the extraction of metal oxides by ionic liquids (ILs). This study concerns new investigations into ionometallurgical processing of CoO, Co 3 O 4 , and LiCoO 2 in the IL betainium bis(trifluoromethylsulfonyl)imide, [Hbet][NTf 2 ]. Three crystal structures of cobaltÀ betaine complex compounds and combined spectroscopic and diffraction studies provide insights into the dissolution process. In addition, an optimized dissolution procedure for metal oxides is presented, avoiding the previously reported decomposition of the IL. Subsequent cobalt electrodeposition is only possible from cationic complex species, highlighting the importance of a thorough understanding of the complex equilibria. The presented method is also compared to other recently reported approaches.

Critical Investigation of Betaine Hydrochloride‐Based Deep Eutectic Solvent for Ionometallurgical Metal Production

“…This slightly differs from the electrochemical window of [Hbet][NTf 2 ], −2.0 V to 1.4 V, measured in the same set‐up [9] . The measurements were performed without ferrocene as internal reference due to previously reported interactions with traces of water in the IL [Hbet][NTf 2 ] [10] . As [Hbet]Cl/4U/2.5GLY is hygroscopic and cannot be dried at elevated temperatures without promoting decomposition, the water content is even higher than in the referenced IL.…”

“…However, chloride could also play a significant role, as previous investigations on cobalt oxide dissolution showed [10] . Since [Hbet]Cl/4U/2.5GLY is a chloride‐rich solvent, metal oxide solubilities were compared to an equimolar mixture of [Hbet][NTf 2 ] and [Hbet]Cl, that is, [Hbet] 2 [NTf 2 ]Cl, [40] instead of the binary IL.…”

“…Among them, BaO, CaO, MnO, PbO, PbO 2 , SrO and ZnO dissolve very fast in the DES (within minutes as listed in Table 3). A reason could be a higher water content in the DES, which clearly facilitates the dissolution reaction [10,36] . MnO 2 behaves differently with purity: 85–90 % pure MnO 2 dissolves completely within 3 h, forming a brown solution.…”

“…ILs and DESs have also been employed in metal separation processes, and direct electrodeposition of metals from such solutions has been demonstrated. [2,4,9,10,19,20] Although ILs and DESs are often considered as similar classes of solvents, different interactions are effective on the molecular level, having significant implications for their properties. ILs are salts with a melting point below 100 °C, that is, they consist of defined cations and anions interacting electrostatically with each other.…”

“…Both can dissolve, usually under moderate heating, many metal oxides and sulfides, [16–18] that is, compounds that occur in, or are very similar to, common natural metal resources. ILs and DESs have also been employed in metal separation processes, and direct electrodeposition of metals from such solutions has been demonstrated [2,4,9,10,19,20] …”