Thiosulfate offers a nontoxic alternative to cyanide for processing gold or
es. The mechanism of leaching gold using ammoniacal thiosulfate solution is
2 driven by the Cu(II)-Cu(I) redox couple and is complicated by competing
ligands such as NH3 and S2O32-. It is shown that an understanding of the co
pper speciation and sulfur speciation is required to optimize this system.
This paper presents Eh-pH and speciation diagrams for varying concentration
s of Cu(II), S2O32- and NH3 and discusses the conditions under which variou
s copper and sulfur species are stable.