UMMC Technical University, Verkhnyaya Pyshma, Russia:

P. A. Kozlov, Deputy Director Responsible for Research, Doctor of Technical Sciences, e-mail: p.kozlov@tu-ugmk.com

Chelyabinsk Zinc Plant PJSC, Verkhnyaya Pyshma, Russia:
V. Yu. Nesmelov, Head of the Engineering Centre, Candidate of Technical Sciences

Institute of Metallurgy at the Ural Branch of the Russian Academy of Sciences, Yekaterinburg, Russia:
D. P. Ordinartsev, Senior Researcher, Candidate of Technical Sciences, e-mail: denis_ordinartsev@mail.ru

This paper describes a technique to recover cobalt from zinc-cobalt cake. The initial concentration of cobalt in the cake is around 0.3 wt%, and according to the X-ray diffraction analysis data, the prevailing cobalt-containing phase includes cobalt (II) sulphate. Through surface analysis of a zinc-cobalt cake section on a scanning electron microscope, it was found that zinc-cobalt cake is a heterogenous multiphase material with multiple inclusions. On the basis of these data, a solution has been designed that involves two main stages: Stage 1 — sulphuric acid leaching, Stage 2 — adjustment of the solution pH and precipitation of cobalt with 1-Nitroso-2-naphthol. Sulphuric acid was selected as the principal leaching reagent to recover cobalt from zinc-cobalt cake. It is due to the fact that sulphuric acid solutions do not interfere with the electrolysis process or require a lot of resources for their disposal. To determine the leaching environment that would enable maximum recovery, variations of the two most critical parameters were used — i. e. sulphuric acid concentration and temperature. It should be noted that approximately 30% of cobalt recovery can be achieved by aqueous leaching, which is indicative of water-soluble cobalt compounds. During sulphuric acid leaching, 91.3 wt% of cobalt recovery was reached and cobalt was concentrated to copper and zinc. The sodium salt of 1-Nitroso-2-naphthol was used to precipitate cobalt from the leach liquor as cobalt tends to bond with this reagent forming poorly soluble complexes. 1-Nitroso-2-naphthol also bonds with Cu, Zn, Ni, Cd, Pb. However, when interacting with cobalt, it builds most stable complex compounds which form an insoluble deposit of bright red colour. It was established that cobalt 1-Nitroso-2-naphtholate would not dissolve even in strong mineral acid solutions, whereas complexes built with other metals would be easily soluble in a similar environment. That’s why to remove impurities (i.e. other metals) the precipitated cobalt/1-Nitroso-2-naphthol complex was flushed with sulphuric acid solution. It is due to this stage that a high-purity cobalt oxide Co₃O₄ could be obtained, that would correspond to the KO-1 grade per GOST 18671–73. As a result of the conducted study, a principal process diagram was created that encompasses all the process stages enaling to produce cobalt concentrate.

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