Semiconductor-Microbial Mechanism of Selective Dissolution of Chalcocite in Bioleaching

Chalcocite-dominant secondary copper ore with a high pyrite content had a rapidly increased iron concentration in the middle and later periods of bioleaching, which increased the difficulty of separating copper and iron ions in the leaching solution. In the two aspects of microbial community succession and energy band theory, the selective dissolution mechanism of chalcocite in this type of copper ore was analyzed and illustrated using experiments and first-principles calculations. The results showed that controlling the solution potential at a lower level was beneficial to the selective leaching of chalcocite, while bacteria promoted the leaching of pyrite and chalcocite simultaneously by oxidizing Fe²⁺ to Fe³⁺ in the solution. Below 700 mV of solution potential, the bacterial community, mainly consisting of Acidithiobacillus and Sulfobacillus, had a stronger promotion on the selective dissolution of chalcocite. The solution energy level of bioleaching was higher than ideal pyrite but lower than ideal chalcocite, which resulted in the accumulation of electrons on the surface of pyrite and the formation of holes at the top of the chalcocite valence band. When bacteria assisted the oxidation of Fe²⁺ to Fe³⁺ and caused the raise of the solution potential, the difference between the solution energy level and the top of the pyrite valence band would be smaller than the width of the pyrite energy gap. Below 700 mV, the assistance of Acidithiobacillus and Sulfobacillus on the oxidation of Fe²⁺ was weak. Chalcocite would be selectively dissolved by oxygen and a small amount of Fe³⁺ in the solution. Because of the existence of Fe, Cu, and S vacancies in real minerals, the atomic activity in the Cu-S bond and the Fe-S bond enhanced, and the reaction difficulty between chalcocite, pyrite, and electron acceptors in the solution reduced. The solution potential should be controlled at 600 mV or less to ensure the selective dissolution of chalcocite.