Janine RICHTER1, Michael RUCK1,2
1Technische Universitšt Dresden, Inorganic Chemistry II, Dresden, Germany
2Max Planck Institute for Chemical Physics of Solids, Dresden, Germany
Numerous naturally occurring ores as well as industrial waste products consist of metal oxides. Due to their typically low reactivity, their activation often requires high temperatures of around 1000 °C, generating immense amounts of CO2. Therefore, products of such energy-intensive processes, for example metals, as of today, have to be regarded as significant contributors to climate change.
A promising, more energy- and resource-efficient alternative could be an ionometallurgical approach, implying metal extraction by means of ionic liquids or deep eutectic solvents. Especially betainium bis(trifluoromethylsulfonyl)imide ([Hbet][NTf2]) proved to be a suitable ionic liquid for this purpose. In the first stage of this approach, metal oxides are dissolved at low temperature. In the second stage, metals are electrochemically deposited from the resulting solution. After the application of this approach to the examples of copper, zinc and lead, we here present our results in the cobalt system.
In the first stage, CoO, Co3O4 and LiCoO2 readily dissolve in the ionic liquid. Thereby, a complete reduction to cobalt(II) occurs, as indicated by three crystal structures of precipitated complexes and UV/Vis spectra. Interestingly, cobalt can only be electrodeposited from solutions of CoO and Co3O4 in the second stage. LiCoO2 solutions, in contrast to this, require additives, such as water or alkanoic acids for successful cobalt electrodeposition. This beneficial effect is attributed to additives influencing complex equilibria, which facilitates the formation of suitable complex species for cobalt deposition.
These findings demonstrate that cobalt can directly be produced ionometallurgically from different oxides, but also that a thorough understanding of the actual complex equilibria is essential. This approach could industrially be highly relevant for the processing of cobalt-containing ores as well as the recycling of lithium ion batteries. Furthermore, its application to other metal systems is of great interest. In the course of these ongoing works, we investigate the possibilities to recycle or even replace the expensive and toxic IL [Hbet][NTf2] by more benign reaction media. Thereby, toxicity, thermal and chemical stability, recyclability and costs have to be critically discussed.