Pollution Control Technologies for Sodium Cyanide in the Gold Industry

Introduction

The gold industry has long relied on sodium cyanide in the extraction process due to its efficiency in dissolving gold from ores, even low - grade ones. Since its first application in 1887 for gold and silver extraction, the cyanidation method has become mainstream in the global gold mining sector. The basic chemical reaction involved is 4Au + 8NaCN + O₂+ 2H₂O → 4Na(Au(CN)₂)+ 4NaOH, where gold in the ore reacts with cyanide ions in the presence of oxygen to form soluble gold cyanide complexes. However, the use of Sodium Cyanide brings significant pollution risks, making the development and implementation of pollution control technologies crucial.

Environmental and Safety Concerns Associated with Sodium Cyanide

Toxicity and Environmental Pollution

Cyanide is a highly toxic substance. Sodium cyanide waste liquid can cause severe pollution to the environment. Even in small amounts, it can be lethal to aquatic life and pose a threat to human health if it contaminates water sources. In the gold extraction process, the improper disposal of cyanide - containing waste can lead to the contamination of soil, surface water, and groundwater. For example, in some gold - mining areas, the leakage of cyanide - rich tailings has resulted in the death of fish in nearby rivers and the decline of water quality, affecting the livelihoods of local communities that depend on the water.

Safety Risks in Handling

The transportation, storage, and use of Sodium cyanide require strict safety measures. It is a special chemical that demands an import license and an end - user certificate before importation. During storage, it should not be placed together with acids, nitrites, nitrates, and other substances, as exposure to an acidic environment can cause the release of toxic hydrogen cyanide gas, reducing the product quality and use effect. It must be stored in a ventilated and dry place, preferably in a special warehouse or a double - locked special cabinet. Regular checks, maintenance, and control of the temperature and humidity of the storage place are necessary, along with appropriate ventilation or dehumidification measures. The storage area should also be equipped with corresponding gas masks, masks, personal protective equipment, and fire - fighting equipment. Accidents during handling, such as spills or leaks, can have disastrous consequences for workers and the surrounding environment.

Pollution Control Technologies

Source Reduction

1.Process Optimization

• Some gold mines are adopting new extraction processes to reduce the use of sodium cyanide. For example, the development and application of non - cyanide leaching agents are being explored. Although the cyanidation method is dominant, alternative technologies like the use of thiosulfate - based leaching agents show potential. These non - cyanide agents can extract gold under certain conditions without the high toxicity risks associated with cyanide.

• Another approach is to improve the ore - dressing process. By using more efficient grinding and separation techniques, the gold in the ore can be more concentrated before the leaching step. This reduces the amount of ore that needs to be treated with cyanide, thus decreasing the overall cyanide consumption.

2.Equipment Upgrades

• Upgrading equipment can also contribute to source reduction. For instance, modern gold - extraction equipment is designed to be more closed - loop, minimizing the potential for cyanide leakage. High - tech leaching tanks with advanced sealing mechanisms can prevent the escape of cyanide - containing gases and liquids during the extraction process.

Process Control

1.Monitoring and Adjusting Cyanide Usage

• Real - time monitoring systems are being installed in many gold - mining operations to control the amount of cyanide used. These systems can analyze the composition of the ore and adjust the cyanide dosage accordingly. For example, if the gold content in the ore is lower, the system can reduce the amount of cyanide added, while still ensuring efficient extraction.

• In addition, continuous monitoring of the cyanide concentration in the leaching solution allows for prompt adjustment. If the cyanide concentration is too high, it not only wastes resources but also increases the pollution risk. By maintaining the optimal cyanide concentration, the extraction efficiency can be maximized while minimizing the environmental impact.

2.Treatment of Intermediate Wastes

• Technologies for treating intermediate wastes generated during the gold - extraction process are also part of process control. For example, in the case of waste solutions containing cyanide and other impurities, methods such as ion - exchange can be used to remove and recover valuable metals while reducing the cyanide content. This not only helps in resource recovery but also reduces the toxicity of the waste before further treatment or disposal.

Wastewater Treatment

1.Chemical Oxidation

• Chemical oxidation is a common method for treating cyanide - containing wastewater. Hydrogen peroxide treatment is widely used. When hydrogen peroxide reacts with sodium cyanide waste liquid, sodium bicarbonate and ammonia gas are generated. This oxidation and degradation process is efficient and relatively economical. Other oxidizing agents such as ozone can also be used. Ozone has a strong oxidizing ability and can quickly break down cyanide compounds in wastewater, converting them into less harmful substances.

2.Biological Treatment

• Biological treatment methods are also emerging as a viable option. Certain bacteria and microorganisms can metabolize cyanide compounds. In a well - designed biological treatment system, these microorganisms can be cultured in a reactor where the cyanide - containing wastewater is passed through. The microorganisms break down the cyanide into carbon dioxide, ammonia, and other harmless substances. This method is more environmentally friendly as it does not introduce additional chemical pollutants, but it requires careful control of environmental conditions such as temperature, pH, and nutrient availability to ensure the proper growth and activity of the microorganisms.

Solid Waste Management

1.Safe Disposal of Cyanide - Containing Tailings

• For cyanide - containing tailings, proper disposal is essential. One approach is to use secure landfills that are designed to prevent the leakage of cyanide into the environment. These landfills are lined with multiple layers of impermeable materials, such as clay and synthetic membranes, to stop the migration of cyanide - containing contaminants.

• Another option is the treatment of tailings to reduce their cyanide content before disposal. Techniques such as chemical stabilization can be used to bind the cyanide in the tailings, making them less likely to leach into the environment.

2.Resource Recovery from Tailings

• In addition to safe disposal, efforts are being made to recover valuable resources from cyanide - containing tailings. By using advanced separation techniques, gold and other metals that may still be present in the tailings can be extracted. This not only reduces the environmental impact of the tailings but also provides an additional economic benefit. For example, some mines are using flotation and magnetic separation methods to recover gold and other minerals from the tailings, minimizing waste and maximizing resource utilization.

Case Studies

Zijin Mining's Application

Zijin Mining has successfully applied the cyanidation method using sodium cyanide in the Zijinshan Gold Mine. By spraying a cyanide solution (sodium cyanide solution) onto the crushed low - grade gold ores, they have achieved low - cost gold extraction. However, they also pay great attention to pollution control. They have installed advanced wastewater treatment systems that use a combination of chemical oxidation and biological treatment methods to ensure that the cyanide - containing wastewater meets the strict environmental standards before discharge. In terms of solid waste management, they have established secure tailings storage facilities with proper lining and monitoring systems to prevent cyanide leakage.

Western Arid Region Gold Mine

In a gold mine in the western arid region, historical legacy heap - leaching cyanide tailings were a major environmental concern. The tailings, which had been left untreated for a long time, posed a risk of contaminating the surrounding soil and groundwater. To address this issue, an in - situ sealing and blocking method was adopted. The tailings were covered with multiple layers of impermeable materials, including clay and geomembranes. This effectively blocked the diffusion and seepage of pollutants through rainfall. After the project was implemented, the monitoring results showed that the concentration of cyanide and other pollutants in the surrounding environment decreased significantly, achieving the expected engineering goals.

Future Trends

1.Development of Non - Cyanide Extraction Technologies

• The gold industry is expected to see more research and development efforts focused on non - cyanide extraction technologies. As environmental regulations become stricter and public awareness of environmental protection grows, the demand for non - toxic extraction methods will increase. This may lead to the commercialization of new non - cyanide leaching agents and processes in the near future.

2.Integration of Advanced Monitoring and Control Systems

• Advanced monitoring and control systems will play an increasingly important role in the gold industry. The use of Internet of Things (IoT) technology, for example, can enable real - time monitoring of cyanide usage, wastewater quality, and the condition of tailings storage facilities. This data can be analyzed in real - time, allowing for immediate adjustments to the extraction process to minimize pollution and ensure safety.

3.Circular Economy Approaches

• There will be a greater emphasis on circular economy approaches in the gold industry. This includes not only the recovery of gold and other valuable metals from tailings but also the recycling and reuse of water and other resources in the extraction process. By reducing waste and maximizing resource utilization, the gold industry can become more sustainable and environmentally friendly.

In conclusion, pollution control technologies for sodium cyanide in the gold industry are essential for reducing the environmental and safety risks associated with gold extraction. Through a combination of source reduction, process control, wastewater treatment, and solid waste management, the gold industry can continue to operate while minimizing its impact on the environment. With the development of new technologies and the adoption of more sustainable practices, the future of the gold industry can be more environmentally friendly and sustainable.