Institut Gipronikel LLC, Saint Petersburg, Russia:

S. L. Tsapakh, Lead Researcher, Hydrometallurgy Laboratory, Candidate of Chemical Sciences, e-mail: TsapakhSL@nornik.ru
A. Yu. Chetverkin, Research Fellow

Kola Mining and Metallurgical Company JSC, Monchegorsk, Russia:
P. V. Smirnov, Head of the Hydrometallurgical Research Department, Control and Analytics Centre

I. E. Malts, Deputy Head of Control and Analytical Center for Research and Development – Head of Research and Development Group

The adoption of chlorine technology at the nickel production facilities of Kola Mining and Metallurgical Company determines the use of highly concentrated nickel chloride solutions. Purification of the solutions, i.e. iron removal, would require a fundamental modification and intensification of the existing process. The authors determined the iron (II) ion oxidation rates for air, oxygen and oxygen-air mixtures used as oxidizing agents. The experimental results were approximated with dependences calculated on the basis of reversable reaction equation, with the reaction controlled by the charge transfer velocity. Oxidation rates were determined for copper (I) and iron (II) in solutions with one impurity and when both of them were present. The authors analysed how the iron concentration in the solution and the transition from air to oxygen would change the oxidation rate. Acceleration of the oxidation process is shown during iron (III) deposition. It is noted that most of the iron precipitates within 20 to 30 min, while extensive purification would require much more time. Parameters of hydrolytic purification with oxygen-air mixture have been determined (oxidation-reduction potential, рН), which ensure reaching the required purification level and producing iron cakes with a good filtering capacity. It is demonstrated that for the most part of iron the following deposition parameters should be observed: рН 1.4–2.0 and oxidation-reduction potential (ORP) 380–430 mV, whereas the final process stage should be conducted at the minimum ORP of 450–500 mV and the pH not exceeding 3.0. The authors demonstrate the possibility of carrying out extensive purification at higher rate, which is achievable when using chlorine with no copper ions present in the solution. The product includes a deposit with a good filtering capacity.

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