LLC “Scientific-Research Center “Gidrometallurgiya”, Saint Petersburg, Russia:

P. V. Zaytsev, Researcher, e-mail: peter.zaytsev@gidrometall.ru
I. V. Fomenko, Researcher
L. V. Chugaev, Leading Researcher
Ya. M. Shneerson, Chief Executive Officer

Pressure oxidation allows to carry out the efficient processing of goldbearing sulfide materials. However, application of this method for processing of double refractory raw materials leads to irreversible gold losses due to autoclave preg-robbing of gold by organic carbon. Thermodynamic and experimental data indicate that almost complete sulfide decomposition leads to a high value of reduction-oxidation potential. At this value, the partially oxidized gold, revealed from sulfides, is further oxidized and dissolved within formation of tetrachloroaurate (III) (even in the presence of small amounts of chloride ion). Gold (in the form of chloride complex) is sorbed by organic carbon and becomes unavailable for subsequent cyanidation. In this paper, there are reviewed the methods, practiced in the gold industry to remove the autoclave preg-robbing. Laboratory studies demonstrate that limestone or lime addition to double refractory concentrate before pressure oxidation lead to decrease of the POX solution acidity. Furthermore, the limestone addition reduces the oxygen partial pressure due to formation and evolution of carbon dioxide to autoclave gaseous phase. These leads to the decrease of redox potential of oxidized slurry thereby reducing the gold solubility, gold preg-robbing by organic carbon under POX conditions, and allows to increase precious metal recovery via cyanidation.

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