Why Is It More Difficult to Leach Gold from Carbonaceous Gold Ores?

Contents:

・Types of Carbonaceous Materials in Gold Ores

・Pre-treatment Methods for Carbonaceous Gold Ores

・How to Enhance Gold Leaching?

・Conclusion

Gold extraction from carbonaceous gold ores, which are prevalent in black (or carbonaceous) rock series and sedimentary rock series, presents significant challenges due to the presence of organic carbon. This type of ore has been recognized since the early 20th century for its detrimental impact on cyanide leaching. Carbonaceous gold ores are typically defined as those containing organic carbon that interacts with gold cyanide complexes, making conventional cyanide leaching ineffective. Some of the most famous carbonaceous gold deposits include the Carlin gold mine in the United States and the Muruntau gold mine in Uzbekistan, with significant deposits also found in Canada, Australia, New Zealand, and China.

Studies have shown that carbonaceous materials in primary ore deposits, especially those in sedimentary rock-hosted gold deposits, play a crucial role in their formation. When organic carbon compounds exceed 0.2%, they significantly hinder the cyanide leaching process, leading to the classification of such ores as carbonaceous gold ores. Besides the harmful effects of carbonaceous materials, these ores also exhibit mineralogical characteristics typical of refractory ores, such as gold encapsulation in sulfides or clay minerals. In many carbonaceous gold ores, gold coexists with pyrite or other sulfides. In certain finely disseminated and metamorphic rock-type gold deposits, carbonaceous material is a primary gold carrier.

Types of Carbonaceous Materials in Gold Ores

Carbonaceous materials in gold ores are categorized into three types: elemental (solid) carbon, polymeric hydrocarbon mixtures, and organic acids similar to humic acids, collectively referred to as organic carbon. The presence of carbonaceous material in the ore is generally attributed to the introduction of small amounts of organic matter (potentially including hydrocarbons) during hydrothermal activity. Elemental carbon occurs in forms such as graphite, amorphous carbon, and poorly crystallized pseudo-graphite (a mixture of amorphous and graphite structures), primarily composed of carbon and generally gold-free. Solid carbon, particularly amorphous carbon, exhibits activated carbon-like properties during cyanide leaching, adsorbing dissolved gold-cyanide complexes. The organic components of carbonaceous ore include long-chain hydrocarbons that do not interact with gold cyanide complexes and organic acids that form complexes with gold-cyanide salts. Chinese researchers classify organic carbon in finely disseminated gold ores into chloroform-soluble organic matter and insoluble organic matter (kerogen).

Pre-treatment Methods for Carbonaceous Gold Ores

Pre-treatment methods for carbonaceous gold ores include removing or decomposing the carbonaceous material or rendering it inactive during cyanide leaching. The latter approach eliminates the harmful effects of carbonaceous material on cyanide leaching without destroying the carbonaceous content of the ore, and therefore does not liberate gold initially encapsulated in carbonaceous materials.

Roasting is the most commonly used method for the pretreatment of carbonaceous gold ores. By roasting these ores in the air, the gold locked within the minerals can be effectively exposed, eliminating the adsorption of gold cyanide complexes by carbonaceous matter, and thereby successfully increasing the gold leaching rate. Currently, the primary focus in the development and utilization of carbonaceous gold mines is on the single recovery of gold, rather than the effective comprehensive recovery or utilization of other components. With the high energy consumption and the need to treat SO2 emissions, the cost pressures associated with the conventional roasting process are becoming increasingly prominent. Due to its strong applicability, simple technological process, and remarkable recovery rates, the roasting method will continue to be widely used in the industrial production of carbonaceous gold mines for a long time to come. Therefore, increasing the comprehensive recovery and utilization rate of carbonaceous gold ores and reducing the cost of waste gas treatment are two key future development directions for roasting pretreatment technology.

How to Enhance Gold Leaching?

To address the challenges posed by conventional cyanide leaching, Y&X Beijing Technology Co., Ltd. has developed the eco-friendly gold leaching reagent YX500. This innovative reagent effectively replaces sodium cyanide and can be used in various gold beneficiation and smelting processes. YX500 offers numerous advantages, including low toxicity, environmental friendliness, high recovery rates, stability, and ease of operation, making it a superior alternative for gold extraction.

Conclusion

In summary, the presence of carbonaceous materials in gold ores presents significant challenges to gold extraction using conventional cyanide leaching methods. To enhance gold leaching efficiency, it is crucial to minimize the impact of carbon on the process. Additionally, addressing environmental and health concerns associated with cyanide use is essential. YX500 by Y&X Beijing Technology Co., Ltd. offers an effective and environmentally friendly alternative to sodium cyanide, enhancing gold recovery while reducing environmental and health risks.