A Review on Recovery of Copper and Cyanide From Waste Cyanide Solutions

Abstract

The mainstream technology for leaching gold from gold ore is still leaching in aqueous alkaline cyanide solution. However, when copper minerals are present in the gold ore, high levels of free cyanide must be maintained during leaching because many common copper minerals react with cyanide, forming copper cyanide complexes that deplete the solution of free cyanide. This results in a significant economical penalty through excessive cyanide consumption and loss of valuable copper in tails. Environmental constraints controlling the discharge of cyanide from mining industry are being tightened by local governments worldwide. The solution chemistry of copper in cyanide solution and various technologies for the recovery of copper and cyanide from barren gold cyanide solutions were reviewed in the paper. Direct recovery methods are mainly based on the acidification–volatilization–reneutralization (AVR) process or its modifications. These processes are not very efficient for treating low cyanide solutions and high metal cyanide solutions due to their substantial operational cost. Indirect recovery technologies by activated carbon, ion-exchange resins (IX) and solvent extraction (SX) have been extensively studied. The basic principle of these technologies is to pre-concentrate copper (and part of cyanide) into a small volume of eluant or stripping solution. The copper and cyanide in the resulted solutions can be further recovered by AVR or similar processes or by the electrowinning process. Activated carbon is only suitable for use as a polishing process to remove cyanide to lower levels from those cyanide solutions where the cyanide content is already low. Compared to activated carbon, ion exchange resins are less easily poisoned by organic matter and can usually be eluted at room temperature, and selectivity for particular metals can be achieved by the choice of the functional group incorporated into the bead or by the selective elution process. Solvent extraction process developed base on guanidine and modified quaternary amines exhibit relative fast extraction kinetics and can be operated in a continuous manner. It will be necessary to thicken and wash the solids in order to produce a clarified feed solution while treating the slurry from operations using carbon-in-pulp (CIP) for the recovery of gold. Other copper and cyanide recovery technologies such as biosorption or direct electrowinning were also proposed, but they have still not found their way to practical application.

Keywords:

• copper
• cyanide
• recovery

Acknowledgments

Feng Xie is currently affiliated with the University of British Columbia.

Notes

*Data of Cu–C and C–N bond length is from Kuznetsov et al. 2002 and other properties from Flynn and McGill (1995).

N: No information available.