ALTA 2014: The oxidized gold and its role in pressure oxidation of double refractory gold concentrates
The major part of gold in sulfide ores and concentrates is «invisible» to optical microscopy. In the last 20-30 years, it has been proved that “invisible” gold is associated with sulfides in the form of both nanoparticles and oxidized gold (as a solid solution in sulfides). The presence of at least two forms of «invisible» gold in sulfides makes it necessary to estimate the quantity of each form. However, the physical methods of examination of the sulfide’s single grains cannot provide a quantitative assessment of the gold forms due to an extremely uneven metal distribution in sulfide grains. In this paper, the chemical procedures are suggested in order to determine the forms of gold. The metallic gold that is not encapsulated in sulfides was determined by direct cyanidation of the feed material. The encapsulated gold nanoparticles and solid solution of gold Au+ in sulfides were determined in POX residues by applying cyanidation and sulfite leaching, respectively. The specific ability of sulfite is to dissolve only oxidized gold with no effect on the metallic gold. This makes sulfite a convenient solvent for the selective leaching of the oxidized gold.
The procedures were used to determine the forms of gold in ten concentrates samples from six different Russian deposits. The oxidized form of gold was detected in all tested samples. Furthermore, the oxidized gold is a major form of gold in three samples.
Proposed method for determining oxidized gold can be used to study the mechanism and principles of formation of sulfide gold ore deposits, as well as to improve the technology of gold recovery from refractory ores and concentrates.
The correlation between the amount of oxidized gold and the gold recovery in a presence of carbonaceous matter and chloride ion was revealed. The content of oxidized gold is a third important factor determining the gold recovery from concentrates along with two generally known the content of carbonaceous matter and the concentration of chloride ion.