Cyanide Removal from Wastewater, Mining Dam Water, Gold Processing Mines

Cyanide is a highly toxic chemical that is widely used in various industries, including gold mining, electroplating, and chemical production. While cyanide has several important applications, it can also pose a significant threat to human health and the environment if it is not properly managed. Cyanide is a fast-acting poison that can be lethal to humans and animals even in small doses. It is soluble in water and can easily leach into groundwater, rivers, and other water sources, causing widespread harm to the environment and wildlife. This is why cyanide treatment is an essential step in many industrial processes to remove cyanide and prevent environmental contamination. Cyanide can enter the environment from various sources, including gold mines, electroplating facilities, and chemical manufacturing plants. In gold mining, for example, cyanide is used to extract gold from ore, and it is released into the environment in the form of wastewater, tailings, and process water. This release of cyanide can contaminate water sources, harm aquatic life, and pose a threat to human health if it is not properly treated.

Cyanide Removal and Treatment

Cyanide removal refers to the process of removing cyanide from water, air, soil, or any other contaminated material, while, cyanide treatment refers to the process of neutralizing or reducing the concentration of cyanide. Both methods aim to either reduce or eliminate the concentration of cyanide in contaminated materials, making them safer for the environment and human exposure.

There are several methods for removing and treating cyanide, including chemical treatment, bioremediation, physical separation, adsorption, and others. The choice of method depends on the specific characteristics of the contaminated material, such as the concentration of cyanide and the type of material it is in. By effectively handling cyanide, it is possible to reduce the environmental impact of industrial processes and ensure the safety of the environment and human health. Some of the notable technologies are listed as below.

1. Chemical Oxidation

Chemical oxidation is a process that uses chemicals to oxidize cyanide and convert it into less toxic or non-toxic compounds. This process is often used in conjunction with physical or biological processes to achieve complete cyanide removal.

Sodium hypochlorite, hydrogen peroxide, and calcium polysulfide are some chemicals used in chemical treatment to remove cyanide from tailing dam waters, oxidizing cyanide to cyanate and releasing nitrogen gas.

The procedure and technique for cyanide removal in tailing dam water by chemical oxidation typically involves the following steps:

• Collection of water sample: A water sample is taken from the tailing dam to determine the concentration of cyanide. This information is used to design an appropriate treatment plan.
• Preparation of treatment solution: The treatment solution is prepared by mixing chemicals such as hydrogen peroxide, calcium hypochlorite, or sodium hypochlorite with water. The appropriate chemical and concentration is selected based on the cyanide concentration in the tailing dam water.
• Mixing and aeration: The treatment solution is mixed with the tailing dam water, either by manual mixing or through aeration. The aeration process helps to increase the rate of chemical oxidation and the effectiveness of the treatment.
• Monitoring and adjustment: The treated water is monitored for changes in pH, temperature, and cyanide concentration. If necessary, the treatment solution may be adjusted to optimize the removal of cyanide.
• Filtration and discharge: The treated water is then filtered to remove any residual solids, such as activated carbon or sludge, that may have been generated during the treatment process. The treated water is then discharged into the environment, ensuring that the concentration of cyanide is within acceptable levels.

It is imperative to mention that chemical oxidation is a highly technical process that should be performed by trained and experienced professionals. Improper handling and use of chemicals can result in serious environmental and health impacts, so it is important to follow proper safety procedures and regulations when performing chemical oxidation for cyanide removal.

Advantages of Chemical Oxidation Method

• High Efficiency

One of the biggest advantages of chemical oxidation method is its high efficiency in removing cyanide from waste water and process water. When chemical oxidation is used in conjunction with other treatment methods, such as physical treatment and biological treatment, it is possible to achieve complete cyanide removal.

• Cost-Effective

Chemical oxidation method is also a cost-effective solution for removing cyanide from waste water and process water. When compared to other treatment methods, chemical oxidation is relatively low-cost and does not require significant investments in equipment or infrastructure.

• Easy to Implement

Chemical oxidation method is also easy to implement, making it a practical solution for removing cyanide from wastewater and process water. This method can be carried out on site, without the need for complex equipment or infrastructure.

Disadvantages of Chemical Oxidation Method

• Chemical Residues

One of the disadvantages of chemical oxidation method is the potential for chemical residues. When chemical oxidation is used to remove cyanide from wastewater and process water, it may also generate other toxic compounds that can pose a threat to human health and the environment.

• Requires Careful Management

Chemical oxidation method also requires careful management to ensure that it is carried out safely and effectively. This includes the proper handling and storage of chemicals, as well as the proper disposal of waste generated during the process.

• Limited Applications

Another disadvantage of chemical oxidation method is its limited applications. This method is only effective for removing cyanide from waste water and process water, and it may not be suitable for removing other toxic compounds.

Conclusion

Chemical oxidation method is a cost-effective and efficient solution for removing cyanide from waste water and process water. However, it is important to be aware of the potential disadvantages, such as the potential for chemical residues and the need for careful management, before implementing this method. By taking the time to understand the advantages and disadvantages of chemical oxidation method, it is possible to choose the best solution for removing cyanide from wastewater and process water, and prevent environmental contamination.

2. Physical Treatment

Physical treatment is a process that uses physical methods to remove cyanide from wastewater. One of the most common physical methods is adsorption, which uses a material with a high affinity for cyanide to remove the chemical from the wastewater. Other physical methods include ion exchange, reverse osmosis, and ultrafiltration.

3. Biological Treatment

Biological treatment is a process that uses microorganisms to degrade cyanide in wastewater. This process involves adding a mixture of microorganisms to the wastewater, which oxidizes the cyanide and converts it into less toxic compounds.

Introduction

Tailing dams are large structures used in the mining industry to store waste materials that are generated during the extraction of minerals and precious metals and are typically built in areas where there is sufficient land and water resources to support the storage of the tailings. Tailings are typically stored in the dam as a slurry or a paste, and can contain a variety of chemicals, including cyanide, sulfuric acid, and heavy metals.

Cyanide in Tailing Dam Waters

Cyanide is frequently used in the gold mining industry for the extraction of gold from its ore. The process, known as cyanide leaching, involves the dissolution of gold from the ore using a solution of sodium cyanide. The resulting tailings, which contain residual cyanide, are then disposed of in tailing dams.

The presence of cyanide in tailing dam water poses significant risks to the environment, humans and aquatic life. To minimize the risk of cyanide release from tailing dams, it is important to implement best management practices, including proper storage and containment of the tailings, live monitoring of the tailing dam waters, and the implementation of measures to prevent or minimize the release of cyanide into the environment.

Why recycles cyanide?

Cyanide recycling is a process that involves reusing the cyanide rather than disposing of it. This approach not only reduces the amount of waste produced, but also reduces the costs associated with removing and treating the cyanide. By recycling the cyanide in tailing dam water, it is possible to minimize its impact on the environment and reduce the overall cost of mining operations.

There are various methods for cyanide recovery in tailing dam water, including adsorption, precipitation, and ion exchange.

1. Adsorption:

This method involves the use of adsorbent materials, such as activated carbon, that bind to the cyanide and remove it from the water. The adsorbent material can then be separated from the water, and the cyanide can be recovered for reuse in the mining process.

Adsorption is a relatively simple and low-cost method for removing cyanide. In fact, it is a highly effective method, capable of removing high concentrations of cyanide from the water. Additionally, adsorption does not produce harmful byproducts and can be easily integrated into existing mining operations.

However, there are some limitations to the use of adsorption for cyanide recovery. For example, the adsorbent material can become saturated with cyanide over time, reducing its effectiveness. Additionally, the adsorbent material must be disposed of properly after use to prevent contamination of the environment.

The procedure and techniques for cyanide recovery by adsorption are as follows:

• Preparation: The first step in the process is to prepare the adsorbent material. This typically involves activation of the material, such as carbon activation, to increase its surface area and enhance its ability to adsorb the cyanide.
• Contact: The next step is to bring the adsorbent material into contact with the tailing dam water containing the cyanide. This can be done through batch or continuous processes, depending on the specific requirements of the mining operations.
• Adsorption: The adsorbent material binds to the cyanide in the tailing dam water, removing it from the water. The adsorption process can take several hours, depending on the concentration of cyanide in the water and the specific characteristics of the adsorbent material.
• Separation: After the adsorption process is complete, the adsorbent material containing the cyanide is separated from the tailing dam water. This can be done through filtration, sedimentation, or centrifugation, and can be tailored for the specific requirements of the mining operations.
• Recovery: The final step in the process is to recover the cyanide from the adsorbent material. This can be done through desorption, which involves the use of chemicals or heat to release the cyanide from the material. The recovered cyanide can then be reused in the mining process.

2. Precipitation

This method involves the addition of chemicals to the tailing dam water that cause the cyanide to react and form solid particles. The obtained solid particles are then separated from the water, and the cyanide can be recovered for reuse in the mining process.

Some commonly used chemicals for precipitation include metal salts, such as iron, aluminum, and zinc, and basic compounds, such as lime (calcium hydroxide) or sodium hydroxide. Metal salts are commonly employed for the precipitation of cyanide since they react with the cyanide to form solid metal cyanide complexes. For example, the reaction of iron with cyanide can form iron cyanide precipitates, which can then be separated, recovered, and reused in the process.

Other basic compounds, such as lime or sodium hydroxide, can also be employed for precipitation. For instance, the reaction of cyanide with lime can form calcium cyanide precipitates, which can then easily be recovered.

The procedure and techniques for cyanide recovery by precipitation are as follows:

• Preparation: The first step in the process is to prepare the batch of chemicals that will be used for precipitation. This typically involves the mixing of chemicals, such as metal salts or lime, to create a solution that will cause the cyanide to react and form solid particles.
• Contact: The next step is to bring the chemical solution into contact with the tailing dam water containing the cyanide. This can be done through batch or continuous processes.
• Precipitation: The added chemical solution causes the cyanide to react and form solid complexes. The precipitation process can take several hours, depending on the concentration of cyanide in the water and the specific characteristics of the chemical solution.
• Separation: After the precipitation process is complete, the solid particles containing the cyanide are separated from the tailing dam water. This can be done through filtration, sedimentation, or centrifugation, depending on the specific requirements of the mining operation.
• Recovery: The final step in the process is to recover the cyanide from the precipitated solid complexes. This can be done through the use of chemicals or heat to dissolve the solid particles and release the cyanide. Thus, enabling the recovery of cyanide for the reuse in the mining process.

3. Ion Exchange

Ion exchange is a process in which ions in a solution are exchanged for ions of a different type, which can then be easily recovered/removed. In the case of cyanide recovery from tailing dam water, ion exchange resin is used to remove the cyanide ions from the tailings.

The ion exchange process begins with the treatment of the tailing dam water with a suitable resin that has been specially designed for the removal of cyanide ions. The water is then passed through a column filled with the resin, which acts as an ion exchange medium. The cyanide ions in the water are exchanged with ions of a different type, such as hydrogen ions, which are then easily removed from the water. The advantage of using ion exchange for cyanide recovery is that it is a relatively simple and efficient process that can effectively remove cyanide ions from tailing dam water. Additionally, ion exchange resins can be reused multiple times, making the process more sustainable and cost-effective.

The method for cyanide recovery from tailing dams using ion exchange technique typically involves the following steps:

• Resin selection: An ion exchange resin that is specifically designed for the removal of cyanide ions must be selected. This resin should have high affinity for cyanide ions, and should be able to effectively remove them from the water.
• Pretreatment: The tailing dam water is subjected to pretreatment, which typically involves pH adjustment, filtration, and clarification. This helps to remove any suspended solids and other impurities that may interfere with the ion exchange process.
• Column preparation: The selected ion exchange resin is loaded into a column. This column is then sealed and connected to a water supply and discharge system.
• Ion exchange process: The pretreated tailing dam water is then passed through the column filled with the resin. The cyanide ions in the water are exchanged with ions of a different type, such as hydrogen ions, which are then easily removed from the water. The water is continuously circulated through the column until the desired level of cyanide removal is achieved.
• Elution: The resin is then subjected to elution, which involves the removal of the cyanide ions from the resin. This is typically done by passing an eluent, such as an acidic or basic solution, through the column. The eluent strips the cyanide ions from the resin and releases them into the solution.
• Recovery: The cyanide ions in the eluent can then be recovered by various methods, such as precipitation, electro-winning, or evaporation. The recovered cyanide can then be recycled and reused in the mining process.