3.7.1. Air

In another study carried out by Cheng and Lawson [24], the effect of aeration on the leaching of chalcocite was seen, but in this case, agitating leaching was carried out, showing that there is no greater contribution. Moreover, by adding a greater flow of air to the system slightly lower recoveries are obtained. This is because the particles adhere to the bubbles generated and are dragged toward the walls of the reactor. On the other hand, in the research carried out by Liu and Granata [75], the effect of aeration was studied by analyzing historical data in two leaching piles of chalcocite as the main mineral present, one with and the other without aeration. In the results, they observed that in leaching in an aerated heap, better results were obtained, but there was only a comparative change after 200 days of leaching with respect to the non-aerated heap. For the aerated pile, from 200 days onward, there was no significant change in copper recovery. This is because aeration is no longer beneficial at this point. After all, we are in the second stage of the dissolution of chalcocite, which is a controlled chemical reaction. Furthermore, the authors mentioned that the total acid consumption per ton of ore processed was higher in the case of the aerated pile, but the net acid consumption per ton of copper produced was the same in both cases.

#### 3.7.2. Ferric Ions

The effect of the concentration of ferric ions in the leaching of chalcocite has also been studied. For the first reaction stage, there is a positive effect on the leaching kinetics with an increase in the concentration of ferric ions. When the concentration is lowered, the leaching rate of chalcocite is considerably lower. For the second stage, the ferric ions are not as noticeable as in the first stage. Still, better reaction rates are obtained by increasing their concentration because of the increase generated in the redox potential of the leaching solution [24,65,72].
