Electrochemical Oxidation of Cobalt at a Platinum Electrode in a Chloride Medium
Authors: Makarava Iryna , Wang Zulin , Wilson Benjamin , Yliniemi Kirsi , Lundström Mari 
Published: February 2024

Cobalt is a highly important metal that is widely used in lithium-ion batteries, cemented carbide, magnetic materials, chemical, and medical industries. The current global cobalt reserves (in total around 6.9 million tons) are unevenly distributed mainly between the Democratic Republic of Congo (48%) and Australia (21%) [1]. One of the main sources of cobalt is nickel production where Co is as a byproduct. Nevertheless, research related to cobalt extraction from both primary or secondary resources must be accelerated to address the current imbalance between supply and demand, that has resulted in cobalt being classified as highly critical by the EU [2]. Currently, primary and secondary raw materials are refined using pyro-hydrometallurgical or hydrometallurgical processing routes, followed by e.g. cobalt crystallization, or electrowinning. Battery grade cobalt salts can be further subjected for calcination to form battery grade oxides. In the current study, we investigate a novel approach of electrifying metallurgy - attempting for direct electrochemical cobalt recovery as cobalt oxide from a hydrometallurgical chloride based process solution.
Potentiostatic electrolysis was performed in synthetic cobalt chloride solution, mimicking the industrial concentrations. SEM and EDX were used for microstructural characterization and determination of sample compositions, respectively. Cyclic voltammetry (CV) was also carried out to understand the anodic behavior of cobalt on the Pt electrode. CV studies suggested the formation of different cobalt-containing phases and the obtained precipitates in potentiostatic experiments were identified as Co3O4 and CoOOH. However, the precipitate composition was strongly dependent on the conditions of electrolysis, such as potential, temperature, and pH. At the highest studied potential (1150 mV vs. Ag/AgCl) the precipitate obtained had a saturated black color indicating desired formation of Co3O4, while at lower potentials the brown colour indicated dominance of other phases. The microstructure of the electrodes due to different potentials was investigated by SEM, indicating also morphology changes as a function of recovery potential. EDX analysis suggested that the precipitates recovered included not only cobalt and oxygen but also traces of chloride ions.
Overall, this study highlights the possibility of cobalt recovery in oxide form in a chloride medium as an alternative method for the recovery of cobalt from industrial process solutions. The proposed approach can be suggested as an alternative to the traditional process of crystallization or electrowinning. In addition, cobalt obtained in a form of oxide is an important class of materials characterized by good electrochemical, catalytic, and optical properties and can be used as a final product in a variety of applications if quality requirements can be achieved.

Acknowledgment

The ENICON project (https://enicon-horizon.eu/) has received funding from the European Union’s Framework Program for Research and Innovation Horizon Europe under Grant Agreement No. 101058124

References

Rahimpour Golroudbary, S.; Farfan, J.; Lohrmann, A.; Kraslawski, A. Environmental Benefits of Circular Economy Approach to Use of Cobalt. Global Environmental Change (2022) 76, doi:10.1016/j.gloenvcha.2022.102568.

Blengini, G.A.; EL Latunussa, C.; Eynard, U.; Torres de Matos, C.; Wittmer, D.; Georgitzikis, K.; Pavel, C.; Carrara, S.; Mancini, L.; Unguru, M.; et al. Study on the EU’s List of Critical Raw Materials (2020) Final Report., doi:10.2873/904613.