Step-by-Step vs. Selective Leaching: Key Technologies for Gold Extraction from Copper-Bearing Ores

Copper-gold ores are typical refractory ores in the field of hydrometallurgy, as copper interferes with the cyanidation leaching process, often leading to high cyanide consumption and low gold leaching rate. To address this issue, the industry has developed two core gold extraction technologies: "step-by-step leaching" and "selective gold leaching". These technologies can be flexibly selected based on the copper content, mineral type and recovery value of the ore, enabling efficient extraction of gold resources.

Core Classification and Application of Gold Extraction Technologies

(1) Step-by-Step Copper-Gold Extraction Process: A Comprehensive Recovery Solution for High-Copper Ores

This process is suitable for copper-gold ores with high copper content (usually >0.5%) and recovery value. By first separating copper and then leaching gold, it fundamentally reduces the interference of copper on cyanide leaching while realizing the comprehensive utilization of copper resources. It mainly includes three technical paths:

1.    Sulfuric Acid Leaching of Copper + Cyanide Leaching of Gold Process

For ores dominated by copper oxide and secondary copper sulfide, dilute sulfuric acid (2%-3%) is first used for pretreatment to leach copper, with a copper leaching rate of over 70%. The resulting copper sulfate solution is displaced with iron filings to obtain sponge copper; then, alkaline medium conversion is carried out for cyanide leaching of gold. Tests by the Shaanxi Bureau of Geology and Mineral Resources on a copper-gold ore in Ji'an, Jilin, showed that after pretreatment, the consumption of sodium cyanide decreased from 20 kg/t to 2 kg/t, and the gold leaching rate reached 85%. This process does not require complex equipment and can also be adapted to heap leaching scenarios, but it needs to go through acid-alkali medium conversion, resulting in a long cycle and high sulfuric acid consumption.

2.    Roasting Step-by-Step Leaching Process
For copper-gold ores with high sulfur content, oxidative roasting is first used to convert copper sulfides into oxides, or sulfation roasting is carried out at controlled temperatures to generate copper sulfate (recoverable after water washing), followed by subsequent gold extraction. To solve the problem of sulfur and arsenic pollution in traditional roasting, the industry has developed the "sulfur and arsenic fixation roasting" technology. By adding reagents such as calcium oxide and magnesium oxide, the fixation rate of sulfur and arsenic exceeds 90%. A gold mine in Jidong, Heilongjiang, adopted shaft kiln sulfur-fixation roasting heap leaching, verifying the advantages of this process in low pollution and low cost. However, due to the need for roasting equipment and sulfur absorption systems, the initial investment is high, making it more suitable for medium and high-grade ores.

3.    Bioleaching Process
Acidophilic bacteria (such as Acidithiobacillus ferrooxidans) are used to oxidize copper sulfides into copper sulfate, followed by cyanide leaching of gold. This process is suitable for copper sulfide-type copper-gold ores. Dexing Copper Mine in China has an annual production capacity of 2000 tons of electrolytic copper through bacterial heap leaching-extraction-electrowinning; the Shaanxi Bureau of Geology and Mineral Resources conducted bio-oxidation pretreatment on a refractory gold concentrate with 15% copper and 150 g/t gold. After 102 days, the copper leaching rate was 45%, the gold leaching rate increased from 79% to 93%, and the cyanide consumption decreased from 57 kg/t to 35 kg/t. This process is green and environmentally friendly, but the heap leaching oxidation cycle is long. Moreover, minerals such as chalcopyrite are more difficult to oxidize, so it is necessary to enhance leaching efficiency by optimizing bacterial strains and adding catalytic ions.

Selective Gold Leaching Process: An Efficient Gold Extraction Option for Low-Copper Ores

When the copper content in the ore is low (no recovery value), the selective gold leaching process is adopted to directly inhibit copper dissolution and preferentially extract gold during leaching. The core technologies include non-cyanide gold leaching agent method and ammonia-cyanide method:

1.    Gold Extraction with Non-Cyanide Leaching Agents

Thiourea and thiosulfate are commonly used selective gold leaching agents. Thiourea uses Fe³⁺ as an oxidant in an acidic medium, and the copper dissolution rate is only 1/10 of that of the cyanidation method. It can achieve the leaching effect of the cyanidation method in 24 hours within 4-5 hours, but the reagent cost is high; thiosulfate uses copper ions and ammonia as adjuvants in an alkaline medium at 60°C, with low toxicity, fast leaching rate, and little interference from cations. It is especially suitable for ores containing copper and arsenic, but its leaching mechanism is still under further study.

2.    Selective Gold Leaching by Ammonia-Cyanide Method
The ammonia-cyanide system (optimal pH 9-11, ammonia-cyanide ratio 2:1-3:1) is used to inhibit copper dissolution and reduce cyanide consumption. The transformation of the copper-gold ore in Sishangcun, Lingbao by the Institute of Process Engineering, Chinese Academy of Sciences showed that when the gold leaching rate was maintained at 93%, the consumption of sodium cyanide decreased from 17.5 kg/t to 7 kg/t, and the copper leaching rate was only 5%. This process has achieved large-scale application and is the preferred solution for gold extraction from low-copper copper-gold ores.

 Technology Selection and Industry Value

The selection of gold extraction technology for copper-gold ores must be closely linked to ore characteristics: when the copper content is high and copper has recovery value, the step-by-step extraction process (such as sulfuric acid leaching of copper + cyanide leaching of gold) is preferred, taking into account both comprehensive resource utilization and economic benefits; when the copper content is low and copper has no recovery value, the selective gold leaching process (especially the ammonia-cyanide method) has more cost advantages. The development and application of these two types of technologies not only solve the refractory problem of copper-gold ores but also promote the green and efficient upgrading of the hydrometallurgy field, providing key technical support for the comprehensive development of gold resources.