The distribution of cyanide species as a function of pH at CN/Cu mole ratio of 3/1 is presented in Fig. 1. The initial cyanide concentration was fixed at 10 ppm and the calculation suggests that there is no influence on cyanide speciation when Eh ranges from 0 mV to 550 mV (SHE) which is consistent with the expected pulp potential in flotation. At pH 10, the dominant cyanide species is cuprous tricyanide Cu(CN)32− (accounting for 81% of the initial cyanide) while Cu(CN)2− accounting for 13%. This agrees with the previous study on the copper cyanide system (Lu et al., 2002). It is noted from Fig. 1 that both HCN and Cu(CN)2− become dominant in the solution when pH drops down to 7, which is commonly observed during the grinding process. This suggests that H+ ions at low pH compete with Cu(CN)2− to complex with CN− following Eq. (6).