Treatment of Cyanide in Gold Leaching Tailings

The Prevalence of Cyanidation and the Danger of Cyanide

Cyanidation is widely used by the majority of gold mines globally and will likely remain prevalent in the coming years. However, Cyanide is a dangerous toxic pollutant. Its presence in wastewater and tailings can severely impact humans and the environment. Thus, it is essential to control these contaminants.

Cyanide Leaching Process and Its By - products

Cyanide leaching converts gold into water - soluble cyanide complexes and is currently the most common and effective process for extracting gold from ores. This process requires an excess of cyanide to enhance gold recovery, generating cyanide - containing waste in the form of tailings and water. Free cyanide, the primary by - product in the metallurgical process, is considered the most toxic form of cyanide as it can cause harmful effects even at relatively low concentrations. Other cyanide species can easily dissolve into free cyanide under acidic conditions.

The Necessity of Treating Cyanide - containing Tailings

The natural attenuation of cyanide in tailings to a bio - harmless level takes a long time. Therefore, cyanide - containing tailings should be treated before being discharged into the environment to avoid adverse impacts on the receiving environment. The decomposition of cyanide in Gold leaching tailings has been one of the greatest challenges faced by gold mines in the past few decades. Hence, proper treatment of cyanide in tailings is necessary to avoid or minimize environmental and health problems.

Existing Treatment Techniques for Cyanide

Over the years, several biological, physical, and chemical techniques, as well as electrolytic oxidation and other methods for decomposing or recovering cyanide, have been developed to treat cyanide solutions. Currently, techniques widely used in the industrial production of cyanide decomposition include the INCO process, the alkaline chlorination process, the activated carbon process, the ozonation process, the hydrogen peroxide oxidation process, and hydrogen cyanide recovery. The INCO and alkaline chlorination processes are used to remove high - concentration cyanide but cannot completely degrade cyanide. Activated carbon can adsorb and aggregate cyanide but cannot decompose it. The ozonation and hydrogen peroxide oxidation processes are used to treat low - concentration cyanide with less secondary pollution, but they are relatively costly. Hydrogen cyanide recovery can reduce cyanide content and costs but does not meet the requirements for tailings backfilling.

Backfilling Technology and Cyanide Removal Research

Backfilling technology is the best option for mines to break through the bottlenecks of resources, environment, and safety. However, harmful substances such as residual metal materials and solvents in gold - leaching tailings should be properly treated before backfilling to prevent groundwater pollution. Research on cyanide removal has mainly focused on industrial wastewater. Research on cyanide removal in gold - leaching tailings, including wastewater and tailings, is still limited. The mineral composition of gold ores is relatively complex, and chemical substances such as cyanide, activated carbon powder, and hydrogen peroxide are added to the beneficiation process, making the tailings composition even more complex. Most of the residual cyanide in tailings is strongly adsorbed on the mineral surface, and only a small amount of free cyanide and hydrolyzed complex cyanide can enter the leachate. Therefore, it is necessary to explore more effective methods for cyanide removal.

The Complexity of CN⁻ Decomposition and Future Research Direction

The proper decomposition of CN⁻ is a complex process. It requires the combination of multiple methods to improve treatment efficiency and consider treatment economics. Using combined methods to remove cyanide is a promising direction for future research.