3.1.1. Preliminary leaching and electrowining findings
Fig. 3 shows a 3D plot of copper recovery versus the ratio of cupric to cuprous ions and ratio of ferric to ferrous ions, which has been drawn using STATISTICA 9 software. The fraction of copper dissolved for eight different experiments (See Table 2) is presented in graphical form. The leaching solution with low ferric ion, high ferrous ion, high cupric ion, low cuprous ion and high acid concentration (Cu09-01Fe01-09H15), results in maximum leaching. It was observed that maximum 2-day recovery was∼ 0.005 g Cu/g Ore from an ore with a copper content of∼ 0.0074 g Cu/g Ore. Thus, the extraction of copper reached 68% in 2 days. 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.