Ural Federal University named after the first President of Russian Federation B. N. Yeltsin (UrFU), Institute of new materials and technologies, Department of non-ferrous metallurgy, Yekaterinburg, Russia:

A. V. Kritskii, PhD Student, Lecturer-Assistant, Engineer of Non-ferrous Metals Metallurgy Department, e-mail: a.v.kritsky@urfu.ru
S. S. Naboichenko, Professor-Consultant of Non-ferrous Metals Metallurgy Department, Doctor of Technical Science

OJSC “Uralmekhanobr”, Yekaterinburg, Russia:
A. M. Klyshnikov, Senior Researcher, Candidate of Technical Science
V. V. Musaev, Head of the Laboratory of Hydrometallurgy, Candidate of Technical Science

Pressure oxidative leaching (POX) of chalcopyrite concentrates originated from Mikheevskii enrichment plan (Mikheevskoye deposit of copper-porphyry ore) allow to obtain autoclave cakes of the following composition, (wt.) %: 56–65 Fe₂O₃; 25–30 SiO₂; 2.7 Ca; 0.3–1 Cu; 2–7 Stotal, 0.6–0.8 Pb; 5–12 Au (ppm); 30–70 Ag (ppm); its mass loss of 38–44%. By performing an additional operation of autoclave treatment (AT) of cakes under neutral atmosphere it is possible to achieve significant mass loss of the cakes (up to 65–70%) due to the dissolution of iron, and, as a result, to increase the content of precious metals (PM). The subsequent treatment of the cakes is reasonable for the extraction of gold and silver, which is most often carried out using cyanidation process. The effect of cake quality on the cyanidation process efficiency was evaluated. POX-cakes were obtained at the following parameters: t = 190–240 ^оC, PO₂ = 0.5–0.7 MPa, τ = 120 min. The extraction of gold by cyanidation increases significantly with the increase in temperature of the POX stage from 190 to 240 ^оC and reaches 93% in 8 hours of the process. The extraction of silver doesn't exceed 20% and with an increase in temperature of POX from 220 to 240 ^оC, it decreases from 20 to 1.5%. This phenomenon is apparently associated with the presence of silver in the form of AgFe₃(SO₄)(OH)₆. Cyanidation of POX-cakes after AT allows to increase the precious metals extraction rate — more than 85% of gold is recovered in less than 2 hours. The cyanidation of POX-cakes is characterized by an increased consumption of NaCN (>10 kg/t), apparently due to the presence of undissolved sulfides and elemental sulfur. A moderate NaCN consumption of about 6 kg/t was registered only at cyanidation of POX-cakes obtained at t = 240 ^оC and PO₂ = 0.6 MPa. The cyanidation parameters are given; the efficiency of using the cyanidation process to extract PM from POX-cakes is discussed. Options to increase the extraction of silver are proposed, as well as alternative approaches for precious metals recovery.
The research was funded by the Russian Science Foundation, grant number 18-19-00186.

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