The arsenic bearing gold concentrate is known as refractory gold concentrate and the direct cyanide leaching produces very low gold extraction. It is because gold particles are extremely fine and encapsulated in sulfides (pyrite and arsenopyrite) and the exposure of gold particles is difficult by the mechanical method only.
Oxidation roasting, bio-oxidation and autoclave oxidation are used for pretreatment of refractory gold ore. The method of autoclave oxidation for this purpose has certain advantages in production cost and environmental protection, but it needs huge investment in equipment. Bio-oxidation is another choice in view of low cost and environmental friendliness. However, it is inefficient and too sensitive to the environment. Compared to these methods, oxidation roasting is brief in operation and the period of production is short. And the amount of treatment is large and the cost is low. In roasting processes, pyrite and arsenopyrite are oxidized to reduce the cyanide and dissolved oxygen consumption, and porous calcine is formed to increase gold extraction.
Two-stage roasting process is commonly used to pretreat arsenic bearing gold concentrate. The first stage is carried out in weakly oxidative atmosphere to release arsenic in the gaseous phase as As2O3. The second stage roast is performed in oxidative atmosphere to produce porous hematite.
Kim Yong Min, a section head at the Faculty of Metallic Engineering, investigated the effect of protective alkali and pH on gold extraction in the cyanide leaching process of two-stage roasting calcine of arsenic bearing gold concentrate.
The results showed that gold extraction was independent of protective alkali such as caustic soda, sodium carbonate and lime, and the effect of pH on gold extraction was obvious. If the pH of pulp is high, the arsenic concentration of cyanide leaching solution is increased to decrease gold extraction.
He also investigated the effect of arsenic concentration of solution on gold extraction. He found that when the leaching solution has no lead ion, the arsenic has no effect on gold extraction, but when the arsenic and lead exist in solution simultaneously, the effect of arsenic on gold extraction is remarkable.
For more information, please refer to his paper “Effect of Protective Alkali and pH on Gold Extraction in Cyanide Leaching Process of Two Stage Roasting Calcine of Arsenic Bearing Gold Concentrate” in “Russian Journal of Non-Ferrous Metals” (SCI).