SRC Hydrometallurgy (LLC), Saint Petersburg, Russia:

I. V. Fomenko, General Director, Сandidate of Technical Sciences, e-mail: fomenko-i@gidrometall.ru
M. A. Pleshkov, Principal Researcher, Сandidate of Сhemical Sciences, e-mail: pleshkov-m@gidrometall.ru
S. I. Lyakh, Chief Engineer, Сandidate of Technical Sciences, e-mail: lyakh-s@gidrometall.ru
S. I. Laevskiy, Junior Researcher, e-mail: laevskiy-s@gidrometall.ru

This paper shows the results of laboratory tests of autoclave oxidation of double-refractory flotation concentrates. The presence of organic carbon (0,7–2,6%), which has a high sorption activity in relation to gold complexes is the main processing problem. Gold recovery from the autoclave oxidation cakes of such materials at a temperature of 200–225 ^oC does not exceed 80–90%. High temperatures (225–250 ^oC) and the duration of the material's residence time in the autoclave can influence the indicators of the process. Gold recovery from carbonaceous concentrates depends on the amount of organic carbon oxidized and removed to the vent gas in the form of carbon dioxide. Carbon oxidation process goes simultaneously at a low rate with the destruction of sulfides. The active phase of organic carbon oxidation occurs after the oxidation of sulfides when redox potential in a solution reaches about 530–540 mV. It is shown that organic carbon oxidation requires several hours of slurry residence time in the autoclave at operating parameters after the oxidation of sulfides (>99%). The optimal duration of overoxidation depends on the content and sorption activity of carbon in the material and the operating temperature. The almost full elimination of organic carbon is required to increase the gold recovery up to 96–98% from the tested concentrates. Concentrates with carbon content up to 1,5% must be overoxidized for 30–60 minutes, with content of 1,5–3,0% – for about 120 minutes at a temperature of 250 ^oC. Reducing the operating temperature in the autoclave by 10–25 ^oC leads to increase in overoxidation period by 1,5–2 times. The authors would like to thank the leadership of the Petropavlovsk Group for the possibility to carry out this research study and publish the findings.

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