**4. Conclusions**

A process to obtain a cobalt rich hydroxide from the processing of a Cu–Cd–Co residue produced by cementation on zinc dust is described in this paper. The process includes a water leaching of the residue to remove soluble Zn and Cd. The washed residue is leached for 30 min with sulfuric acid (100 g/L) at a pH of 0.2. The Fe and Mn of the leach solution are precipitated by increasing the Eh to 650 mV while maintaining a pH of 3.0 with sodium hydroxide. Cobalt hydroxide is finally precipitated by increasing the Eh to 1000 mV. Repetition of the whole processing flow sheet shows that the critical steps of the process are the control of the Eh at the precipitation stage and the solids/liquid filtration of the Fe–Mn precipitate. The cobalt recovery from the zinc residues to the cobalt hydroxide is 62 ± 14%. The cobalt content of the cobalt product is 45 ± 4%. The variability in the results is mainly due to the control and measurement of the solution Redox potential

**Author Contributions:** Conceptualization, investigation, formal analysis methodology, data curation, writing—review and editing, L.B.; conceptualization, investigation, formal analysis methodology, data curation, supervision, writing—review and editing, K.T. and J.-F.B.; writing—original draft preparation, writing—review and editing, formal analysis, supervision, project administration, C.B.; funding acquisition, conceptualization, review, G.H. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by Institut de recherche de Hydro-Québec.

**Acknowledgments:** The authors acknowledge the financial support of the Institut de recherche de Hydro-Québec and CEZinc for providing the zinc residues sample for the testwork. E. Benguerel, of CEZinc, is also acknowledged for reviewing the paper prior to publication.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


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