Cyanide Recovery

Rising costs associated with cyanide consumption, strict environmental regulations and the need to ensure sustainable operations have led to increased interest in cyanide recovery technologies. SGS has the technical expertise and capital equipment to work with you to develop and demonstrate the safest, most effective process for recovering the cyanide from your gold circuit.

Cyanide recovery brings a number of important benefits to your operation including:

• Reduced detoxification costs for tailings
• Cost-effective recycling of cyanide which reduces the overall yearly requirements associated with purchase and delivery of new cyanide
• Increased revenue  as a result of the creation of saleable by-products
• Improved compliance with environmental regulations
• Enhanced social accountability arising from better cyanide transport procedures

SGS has been instrumental in developing and improving processes to safely recover cyanide from solutions or tailings. Gold mines around the world now use the following SGS cyanide recovery technologies in their gold recovery operations: 

• SART
• Hannah process 
• AVR
• MNR

Sulfidization, Acidification, Recycling and Thickening of precipitate (SART)

SART is an adaptation of the AVR process, and was developed to treat gold plant tailings that contain high concentrations of copper cyanide. During SART, sulfide ions are added to the gold tailings with the acid. The copper is converted to chalcocite, which is thickened and filtered.

Hannah Process

The new Hannah process for cyanide recovery was developed by SGS. The process uses strong resin technology to extract free cyanide radicals, as well as metal cyanide complexes, from gold tailings.  

Acidification, Volatilization, Reneutralization (AVR)

AVR was the first process used to recover cyanide from gold tailings and, more recently, pulps. The process has been in use for over 50 years.

During cyanide use, pH is always carefully controlled and maintained at a high level to avoid the production of highly toxic HCN (hydrocyanic acid gas). During the acidification stage of AVR, the pH level is lowered from approximately 10 to about 4 using sulfuric acid. Then free cyanide and weakly complexed metal cyanide complexes are converted to HCN. This is then volatilized in a sealed system by passing a vigorous stream of air bubbles through the solution or tailings pulp. The air/HCN gas stream is then treated using a lime slurry. This converts the HCN back to free cyanide ions for recycling.

Advantages

• High rates of cyanide recovery
• The only large-scale commercial cyanide regeneration facilities in use today
• Time-tested technology

Limitations

• Complex system, costly to operate
• Inefficient for tailings that are high in some copper cyanide complexes
• Processed tailings solids may contain high levels of cyanide (CuCn), which are unsuitable for discharge into the environment
• May lead to increased insurance rates as a result of the production of HCN during the process

Metallgesellschaft Natural Resources (MNR) Process

The MNR process is suitable for tailings containing copper cyanide complexes. In the MNR process, sulfide ions are added to the cyanide solution and the acid. 

Advantages

• Very high recovery rates, up to 100% of copper complexed cyanide
• Precipitate is saleable copper sulfide
• Less acid required as the reaction takes place at a lower pH

Limitations

• New technology is not extensively proven

SGS is a global leader in traditional and innovative new technologies for cyanide recovery that provide you with positive economics and environmental stewardship. Contact us early in the planning stage of your project. Our metallurgists will develop a flowsheet that includes testing, pilot plant demonstration and ongoing support for cyanide recovery that ensures regulatory compliance and improves your bottom line.