To assist mining companies in managing and recovering cyanide, engineering consultancy AZMET Technology & Projects developed the AZMET cyanide recovery process (AZ-CRP) to provide an alternative to cyanide detoxification.
AZMET’s focus is to provide a simpler and more cost-effective solution for existing cyanide detoxification and recovery processes, says AZMET director Barry Beylefeld.
“On-site testwork showed that the AZ-CRP can achieve cyanide levels on solution and slurry streams of less than 1 parts per million (ppm) free cyanide, and less than 5 ppm weak acid dissociable (WAD) cyanide into the tailings storage facilities (TSFs),” he points out.
While the existing cyanide detoxification processes will be an expense to the mine, AZMET cyanide recovery process will result in a cost reduction by recovering the cyanide and metal cyanide complexes from the leach tails.
The AZ-CRP will ensure that mines discharge less cyanide into the TSFs and the natural degradation in the TSFs will ensure that the cyanide levels are further reduced.
“The much lower levels – compared with the International Cyanide Management Code’s (ICMC’s) level of 50 ppm WAD in a lined TSF – will, therefore, guarantee that safer levels are maintained for any possible impact on humans and wildlife,” he explains.
As an additional precaution, another AZ-CRP module can be installed on the overflow of a TSF to further reduce the cyanide concentration in effluent stream before discharge to the environment.
Key advantages of the process include the AZ-CRP’s using proven gold processing technologies, which will ensure that it will be easy to operate. Using reagents currently used at gold processing facilities, as well as cyanide recovery from leach tails, can result in very low cyanide concentrations and no further detox requirement.
The process also allows for the recovery of cyanide for direct use in the main leach circuit, the recovery of valuable base metal by-products if in the feed ore and the additional recovery of precious metals from the carbon-in-leach (CIL) and carbon-in-pulp tails.
Additionally, the AZ-CRP is more cost effective, compared with a cyanide detox process that will add costs. Savings are calculated at around $2/t treated based on a typical two-million-tonne-a-year CIL plant operating at 45% solids with 100 ppm free cyanide, 5 ppm copper and 0.015 ppm of gold in solution. The additional cashflow could be applied by the mine to develop and sustain social development projects.
Beylefeld emphasises that environmental damage can be prevented by attending to problems in the plant before it is transferred to the TSF. “Don’t wait to reduce the cyanide levels in the TSF or when the effluent is being discharged into the downstream environment,” he states.
Meanwhile, cyanide has been and continues to be used by the mining industry in gold extraction. Depending on ore mineralogy, cyanide can form various harmful species in plant effluent and its use should, therefore, be monitored to ensure compliance to regulations bodies.
Beylefeld explains that most mines volunteer to follow the ICMC, which is an industry volun- tary programme for gold mining companies that promotes the responsible management of cyanide used in gold mining to enhance the protection of human health and reduce the potential environmental impact.