Cyanide chemistry and its effect on mineral flotation

• Free cyanide depresses the flotation of pyrite, chalcocite, and sphalerite.
• Free cyanide activates galena flotation.
• Cyanide depression is through surface complexing and reducing mixed potential.
• Amine or lead nitride alleviates the depression effect of cyanide on pyrite.
• WAD cyanide may affect mineral flotation inadvertently due to its speciation.

Cyanide has been widely used as a depressant in sulphide mineral flotation. It occasionally activates mineral flotation as well. In addition, cyanide species in the water from gold cyanidation process may be recycled to flotation circuits and have an inadvertent effect on mineral flotation. Therefore, the investigation on mineral flotation in the presence of cyanide with different speciation is of great importance. Even after decades of research, the mechanisms of cyanide depression and activation processes are not fully understood and effective ways to solve problems encountered in minerals flotation plants using cyanide-containing recycled water are not currently available. In this paper, a review of previous literature on the effect of free cyanide, weak acid dissociable (WAD) cyanide and strong acid dissociable (SAD) cyanide on the flotation of base metal and precious minerals is presented, with a particular focus on the underpinning mechanisms and process solutions. Ultimately, an overall picture of current status of studies in this area is provided and the future research associated with using cyanide in mineral flotation is suggested.