Ural Federal University named after the first President of Russia B. N. Yeltsin, Yekaterinburg, Russia:

A. V. Kritskii, PhD student, engineer, lecturer-assistant, Department of Non-Ferrous Metallurgy, e-mail: a.v.kritsky@urfu.ru

VTT Technical Research of Finland Ltd, Espoo, Finland:
S. Jafari, Lecturer and researcher

Fortum, Recycling and Waste, Pori, Finland:
P. Sinisalo, Development engineer

Aalto University, Espoo, Finland:
M. Lundström, Associate-professor, Department of Chemical and Metallurgical Engineering, Doctor of Technical Sciences

Manufacturing of nickel by hydrometallurgical technology at Harjavalta plant (Finland) had been caring out since 1960 by Outokumpu. Later on, the technology was modernized and currently Harjavalta plant belongs to PJSC “MMC Nornickel”. The plant is specializing on processing of copper-nickel mattes, converter mattes and by-products, originated from “Kola MMC” and third-party enterprises. Currently, the technology for the materials processing includes oxidative autoclave leaching (POX), solvent extraction, nickel electrowinning as well as solutions purification and metal salts obtaining stages. Selective POX produces nickel solution and copper cake (Cu-cake), which is a valuable by-product of the plant. The article presents the results on investigating the possibility of Cu-cake processing using POX in sulfate media at different temperature regimes. Low-temperature POX (105 ^oC) allowed to extract more than 95% Cu into solution within 30–60 min, while the dominating compound of solid residue was elemental sulfur; mass output of the solid residue was 20–25%. High-temperature POX (190 ^oC) allowed to extract more than 98% Cu in 60–80 min; mass output of the solid residue was 2.5–5%, which significantly increased a concentration of precious metals. Mid-temperature POX (150 ^oC) is characterized by increased duration. Copper extraction level of 95–98% is achieved at least after 120–180 minutes of leaching. Mass output of the solid residue was 6–10%. A detailed analysis of Cu-cake and the resulting products is provided. The behavior of precious metals was considered.
The work was supported by Act 211 Government of the Russian Federation, contract № 02.A03.21.0006.
The authors wish to also acknowledge the Circular Metal Ecosystem (CMEco) project (7405-31-2016) funded by Business Finland and thank the project partners, especially Mia Tiljander (XRD) and Sari Lukkari (FE-SEM) in GTK Research laboratory (Espoo, Finland) for conducting of the analysis and Jukka Marmo for collaboration. Nornickel Harjavalta are acknowledged for their support. Our gratitude also goes to RawMatTERS Finland Infrastructure (RAMI), supported by the Academy of Finland.

1. Reznik I. D., Ermakov G. P., Shneerson Ya. М. Nickel. Part 3. Мoscow : Nauka i Tekhnologii, 2000. 608 p.
2. Kshumaneva E. S., Kasikov A. G., Belyaevskii A. T., Neradovskii Yu. N. Pentlandite leaching in the FeCl₃ – CuCl₂ – HCl system. Russian Journal of Applied Chemistry. 2009. Vol. 82, No. 8. pp. 1327–1332.
3. Dutrizac J. E., Chen T. T. A mineralogical study of the phases formed during the CuSO₄ – H₂SO₄ – O₂ leaching of nickel-copper matte. Canadian Metallurgical Quarterly. 1987. Vol. 26. pp. 265–267.
4. Rademan J., Lorenzen L., Van Deventer J. The leaching characteristics of Ni–Cu matte in the acid-oxygen pressure leach process at Impala Platinum. Hydrometallurgy. 1999. Vol. 52. pp. 231–252.
5. Park K., Mohapatra D., Reddy B., Nam C. A study on the oxidative ammonia/ammonium sulphate leaching of a complex (Cu – Ni – Co – Fe) matte. Hydrometallurgy. 2007. Vol. 86, No. 3–4. pp. 164–171.

6. Kurokawa H., Takaishi K. Nickel and cobalt refining at Niihama nickel refinery. J. MMIJ. 2007. Vol. 123, No. 12. pp. 678–681.
7. Muir D., Ho E. Process review and electrochemistry of nickel sulphides and nickel mattes in acidic sulphate and chloride media. Mineral Processing and Extractive Metallurgy. 2006. Vol. 115, No. 2. pp. 57–65.
8. Yan F., Li B., Fan C., Zhai X., Zhang X., Li D. Selective leaching of nickel from low-sulfur Ni-Cu matte at atmospheric pressure. Transactions of Nonferrous Metals Society of China. 2010. Vol. 20. pp. 71–76.
9. Provis J., Van Deventer J., Rademan J., Lorenzen L. A kinetic model for the acidoxygen pressure leaching of Ni – Сu matte. Hydrometallurgy. 2003. Vol. 70, No. 1–3. pp. 83–99.
10. Tsymbulov L. B., Knyazev M. V., Tsemekhman L. Sh., Golov A. N. Pilot testing of a process treatment of Ni-containing copper concentrate after high-grade matte separation resulting in blister copper production in twozone Vaniukov furnace. Proceedings of the sixth international Copper-Cobre Conference, The Carlos Diaz Symposium on Pyrometallurgy. Toronto, Ontario, Canada, 25–30 August 2007. Vol. 3, Book 1. pp. 397–409.
11. Muinonen M., Plascencia G., Utigard T. High temperature oxidation of Bessemer matte. Canadian Metallurgical Quarterly. 2013. Vol. 49, No. 3. pp. 249–254.
12. Morcalia M. H., Khajavi L. T., Aktas S., Dreisinger D. B. Oxidative dissolution of nickel matte in dilute sulfuric acid solutions. Hydrometallurgy. 2019. Vol. 185. pp. 257–265.
13. Crundwell F., Moats M., Ramachandran V., Robinson T., Davenport W. Electrowinning of Nickel from Purified Nickel Solutions. Extractive Metallurgy of Nickel, Cobalt and Platinum Group Metals. Amsterdam : Elsevier, 2011. Vol. 26. pp. 327–345.
14. Naboychenko S. S., Ni L. P., Shneerson Ya. M., Chugaev L. V. Autoclave hyrometallurgy of non-ferrous metals. 2nd edition. Ed. S. S. Naboychenko. Ekaterinburg : GOU UGTU-UPI, 2002. 940 p.
15. Dorfling C., Akdogan G., Bradshaw S., Eksteen J. Determination of the Relative Leaching Kinetics of Cu, Rh, Ru and Ir during the Sulphuric Acid Pressure Leaching of Leach Residue Derived from Ni – Cu Converter Matte Enriched in Platinum Group Metals. Minerals Engineering. 2011. Vol. 24, No. 6. pp. 583–589.
16. McDonald R., Muir D. Pressure oxidation leaching of chalcopyrite. Part I. Comparison of high and low temperature reaction kinetics and products. Hydrometallurgy. 2007. Vol. 86, No. 3. pp. 191–205.
17. Marsden J. O., Wilmot J. C., Hazen N. Medium-temperature pressure leaching of copper concentrates — Part I: Chemistry and initial process development. Mining, Metallurgy and Exploration. 2007. Vol. 24, No. 4. pp. 193–204.
18. Nikolaeva S. A. Selection of corrosion resistant materials for autoclaves. Proceedings of the research and design institute Gipronikel. 1967. No. 16. pp. 197–212.
19. Chugaev L. V., Maslenitskii I. N. Features of the autoclave dissolution of fused sulfides of copper and nickel. Proceedings of the research and design institute Gipronikel. 1965. No 24. pp. 31–47.
20. Dreisinger D. Copper leaching from primary sulfides: Options for biological and chemical extraction of copper. Hydrometallurgy. 2006. Vol. 83. pp. 10–20.
21. Javed T., Xie M., Asselin E. Factors affecting hematite precipitation and characterization of the product from simulated sulphate-cloride solutions at 150 ^oC. Hydrometallurgy. 2018. Vol. 179. pp. 8–19.
22. Javed T., Abdul B., Ryan D., Raudsepp M., Asselin E. Amorphous iron phases in medium temperature sulphide concentrate leach residues from pilot and demonstration plants. International Journal of Mineral Processing. 2016. Vol. 148. pp. 65–71.
23. Zhao H., Zhang Y., Zhang X., Qian L., Sun M., Yang Y., Zhang Y., Wang J., Kim H., Qiu G. The dissolution and passivation mechanism of chalcopyrite in bioleaching: An overview. Minerals Engineering. 2019. Vol. 136. pp. 140–154.
24. Crundwell F. The semiconductor mechanism of dissolution and the pseudopassivation of chalcopyrite. Canadian Metallurgical Quarterly. 2015. Vol. 54, No. 3. pp. 279–288.
25. Tong L., Dreisinger D. Interfacial properties of liquid sulfur in the pressure leaching of nickel concentrate. Minerals Engineering. 2009. Vol. 22. pp. 456–461.