In the absence of SART Process, cyanide is consumed by the leaching of cyanide-soluble zinc minerals present in the ore, generating a WAD cyanide-zinc complex (Zn(CN)42-) in solution. This dissolved WAD CN-Zn complex circulates back to the leach in the recycled Barren Leach Solution (BLS), and further reacts with Ag2S in the fresh ore to form insoluble Zn(CN)2 according to the following reaction:
Ag2S + Zn(CN)42- → Ag(CN)2- + Zn(CN)2 (S)
The formation of this insoluble Zn(CN)2 precipitate will reduce the amount of free cyanide available for silver leaching and therefore represents a net consumption of cyanide reagent from the process.
The application of SART in a high zinc leached solution feeding a Merrill Crowe process would break the Zn(CN)42- complex, thereby avoiding the formation of insoluble Zn(CN)2, and liberating 4 moles of free cyanide for active leaching of Ag2S. In addition, sale-able ZnS concentrate is also recovered.