MISiS National University of Science and Technology, Moscow, Russia:

P. V. Aleksandrov, Associate Professor at the Department of Non-Ferrous Metals and Gold, e-mail: alexandrovpv@mail.ru
A. S. Medvedev, Professor at the Department of Non-Ferrous Metals and Gold, e-mail: medvedev@splav.dol.ru
V. A. Imideev, Assistant at the Department of Non-Ferrous Metals and Gold, e-mail: vimideev@gmail.com
A. O. Berbenev, Post-Graduate Student at the Department of Non-Ferrous Metals and Gold, e-mail: elsilvano86@gmail.com

Low-temperature roasting (400–450 ^оС) with sodium chloride and further hydrometallurgical processing of the roasted product deliver a promising processing option for copper sulphide concentrates. One of the advantages of this approach to the processing of sulphide concentrates of non-ferrous and rare metals is that sodium sulphate is produced during roasting, which helps significantly against the production of sulfurous gases. Other advantages include: reduced energy costs due to relatively low temperatures used; formation of the water-soluble compounds of recoverable metals, which helps simplify the subsequent leaching process and reduce the consumption of leaching reagents. This research was carried out for 24.1% copper sulphide flotation concentrate produced as a result of Udokan ore testing. The basic minerals included chalcosine and covellite. The study helped verify the composition of solid roasted products and dump cake. It was found that the roasting of Udokan copper sulphide concentrate with sodium chloride results in an almost complete exposure of copper sulphides with both copper chlorides and copper oxides forming. The authors analysed how the roasting regimes (roasting temperature and time and sodium chloride consumption) can influence the sulphides exposure, as well as copper distribution between water-soluble and insoluble forms. It was established that the roasting temperatures of 400–500 оС, the roasting time of 60–120 min. and the sodium chloride consumption of 25–150% enable an almost complete exposure of sulphides, and copper, in the form of copper chlorides, accounts for 40–60% of the roasted product. It was found that copper oxides form as a result of sulphatisation, which takes place in the first 30 minutes of the process. The paper also presents a principal process flow chart for the Udokan copper sulphide concentrate. The process includes roasting, 1st stage water leaching of the roasted product, pH correction to 5–6 to help all leached copper to transform to a solid phase (as copper hydroxides), 2^nd phase sulfuric acid leaching of the roasted product followed by the correction of pH to 2–3. At this pH level, all copper stays in the solution while iron precipitates as iron hydroxides thus ensuring product separation.

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