The dissolution of gold in ammoniacal solutions cannot take place in the absence of oxidants. Cupric ammine can act as an oxidant in this system according to Equation 3.
The effect of cupric ammine concentration on the dissolution rate of gold was investigated in a solution of 0.6 M total ammonia concentration (0.1 M (NH4)2SO4 and 0.4 M NH3). The cupric ammine solution was prepared by adding known concentrations of copper sulfate (CuSO4.5H2O) and free ammonia in the ratio of 1:4. Figure 2 shows the Tafel polarization curves for the dissolution of gold at different cupric ammine concentrations. It can be observed from these curves that the dissolution potential of the system increases with the increase of the concentration of cupric ammine. Therefore, cupric ammine can be successfully used as an oxidant for the dissolution of gold in ammoniacal solutions.
It can also be seen from the curves in Figure 2 that variation in the cupric ammine concentration had no effect on the anodic portion of the curve. This suggests that cupric ammine has no effect on the anodic reaction which is given by Equation 1. Hence, it ….Read more