The mineral composition of an ore can directly affect the cyanidation process, while decomposition products of certain minerals can indirectly influence gold dissolution. Notable impacting minerals include copper minerals, iron sulfides, carbonaceous materials, zinc minerals, mercury minerals, lead minerals, arsenic-antimony minerals, and selenium-tellurium minerals. The following sections discuss several common associated minerals and their treatment methods.
01
Copper Minerals
Due to their similar geological characteristics, gold deposits often contain varying amounts of copper minerals. Primary copper sulfides are generally sparingly soluble in cyanide solutions. However, native copper, various copper oxides, and secondary copper sulfides are almost entirely soluble in cyanide solutions. Excluding primary copper sulfides from total copper content, the sum of copper from native copper, copper oxides, and secondary copper sulfides is defined as cyanide-soluble copper (Cu-sol).
Research indicates a correlation between cyanide consumption and Cu-sol content—lower Cu-sol results in lower cyanide consumption, while higher Cu-sol increases cyanide consumption. No such relationship exists with total copper content. Similarly, gold recovery rates show an inverse correlation with Cu-sol content, but no correlation with total copper. Thus, it is cyanide-soluble copper that significantly impacts the cyanidation of copper-bearing gold ores.
At higher cyanide concentrations, copper minerals react intensely with cyanide solutions, dissolving rapidly. As cyanide concentration decreases, this reaction intensity drops sharply. At cyanide concentrations of 0.05%–0.10%, copper dissolution is very slow, allowing gold to dissolve preferentially. However, when cyanide concentrations exceed 0.10%, copper dissolution rates surge and may surpass those of gold, leading to cyanide consumption primarily by copper minerals. Therefore, for gold ores with high Cu-sol content, a strategy of “controlling cyanide concentration to reduce copper dissolution” can be employed to improve gold recovery.
02
Iron Sulfide Minerals
Oxidized iron minerals such as hematite, magnetite, limonite, and siderite do not react significantly with cyanide and thus have minimal impact on leaching. In contrast, sulfide iron minerals—particularly pyrite, marcasite, and pyrrhotite—are common in gold ores and can react with cyanide solutions; their oxidation products also react with cyanide, significantly affecting the leaching process. Their reactivity with cyanide follows the order: pyrrhotite > marcasite > pyrite.
Most pyrite does not readily oxidize during cyanidation and only decomposes when pulp is aerated and in prolonged contact with the solution, thus having a minor effect. However, marcasite and pyrrhotite are easily oxidized during cyanidation.
Pyrrhotite decomposes rapidly in the presence of water and air, consuming significant amounts of cyanide. In an oxygen-saturated, weakly alkaline solution, pyrrhotite initially oxidizes to thiosulfates, which further oxidize to sulfates.
To mitigate the adverse effects of sulfide mineral oxidation products during leaching, an alkaline pre-treatment can be applied. This involves adding sufficient alkali and aerating the pulp before cyanidation to precipitate iron as insoluble ferric hydroxide, thereby reducing cyanide and oxygen consumption caused by iron during the process.
Adding lead nitrate during cyanidation can suppress the dissolution of minerals like pyrrhotite and enhance gold leaching. For example, an ore with 21% iron sulfide minerals, including 11% pyrrhotite, achieved a gold recovery of approximately 80% through conventional cyanidation. With lead nitrate as a leaching aid, the recovery increased to approximately 92%, demonstrating significant improvement.
Post time: Mar-30-2026
