From the results of the factorial design analysis of electrowinning xperiments, which are graphically presented in Fig. 4, it can be concluded that a low ferric to ferrous ion ratio leads to maximum current efficiency of approximately 70%. This corresponds to 0.7 copper atoms per electron, which is much higher than the copper yield of only 0.49 atoms per electron in conventional electrowinning from sulfate media assuming 98% current efficiency. Fig. 4 also shows that a high ferric to ferrous ion ratio has the maximum adverse effect on electrodeposition current efficiency.