*3.1. The E*ff*ect of Particle Size on CuFeS2 Dissolution*

Figure 2 shows the effect on CuFeS2 dissolution of particle size with the addition of MnO2 (5/1 MnO2/CuFeS2 ratio, at different concentrations of H2SO4 and wastewater. It can be observed that no differences in copper dissolution rates can be obtained at particle size of −75 + 53 to −47 + 38 μm (Figure 2a,b). At small increases in the dissolution rate can be obtained by increasing the sulfuric acid concentration, with the best results obtained at 3 mol/L. This concurs with Skrobian et al. [36], who stated that particle size is irrelevant in chalcopyrite leaching in stirring reactors. However, the copper extraction rate increases with smaller particles (−20 μm), which could be due to the mechanical-chemical activation of the mineral resulting from extended milling [19], which Juhász and Opoczky [46] termed electrochemical activation. At this size, the concentration of H2SO4 is irrelevant.

**Figure 2.** *Cont*.

**Figure 2.** Effect of particle size and sulfuric acid concentration on copper dissolution. Particle size of: (**a**) −75 + 53 μm; (**b**) −47 + 38 μm; (**c**) −20 μm (acid concentration of 1, 2 and 3 mol/L and 25 ◦C).
