LLC Science-Research Center “Gidrometallugriya”, Saint Petersburg, Russia:

S. Yu. Polezhaev, Junior Researcher, e-mail: polezhaev@gidrometall.ru 

I. V. Fomenko, Researcher

M. A. Pleshkov, Leading Researcher

L. V. Chugaev, Leading Researcher

Gold in refractory ores and concentrates is mainly associated with sulfides, while its significant part is usually presented in the form of so-called “invisible” gold. This gold occurs in the sulfides as Au0 nanoparticles and in oxidized state (in the solid solution form). Presence of at least two forms of “invisible” gold in sulfides requires the quantitative determination of each form. Physical methods of analysis, applied to single mineral grain, cannot provide a quantitative assessment of particular gold forms due to extremely uneven metal distribution in grains. This paper offers a method of sulfite leaching for oxidized gold determination. The sulfite leaching incorporates the pressure oxidation of sulfide gold concentrate at 200–225ºC and oxygen overpressure of 0.5–0.7 MPa. The oxidized “liberated” gold-containing residue is treated with hot solution of sodium sulfite Na₂SO₃, which allows to extract only the oxidized gold to the solution. The sulfite ability to dissolve only oxidized gold with no influence on metallic gold makes it a convenient solvent for selective leaching of oxidized gold. The method was applied to eight refractory sulfide gold concentrates, derived from Russian ore deposits. A significant amount of oxidized gold was discovered in four of eight tested concentrates, and oxidized gold predominates in three materials. The offered method for determination of oxidized gold could be applied to study the mechanism and principle of sulfide gold ore deposits' geological generation, as well as to improve the gold recovery from refractory materials.

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