Modelagem computacional de etapas da oxidação da calcopirita e do efeito spillover em superfície de TiO2 dopada com Ru

Abstract

Computational chemistry enables the investigation of reactive sites, structural and electronic studies, as well as the determination of thermodynamic and kinetic data on surfaces. In this thesis, we analyzed two distinct systems using Density Functional Theory (DFT). The first system involved the oxidation of chalcopyrite (CuFeS2), the primary form in which copper is found worldwide. Copper extraction from this mineral can be achieved through hydrometallurgical extraction, which encompasses various industrial stages. Our focus was on the leaching stage, which depends on the presence of a leaching agent that promotes the oxidation of chalcopyrite. We investigated the hydrated Fe³+ ion and O2 as possible leaching agents. Our results indicate that both species studied have oxidizing properties, with O2 being a stronger oxidant. Furthermore, our calculations indicate that the promotion of chalcopyrite oxidation by the Fe³+ ion occurs through the oxygen atoms of water molecules coordinated to the hydrated ion, rather than direct oxidation between the Fe³+ ion and the surface. It was also found that chalcopyrite oxidation predominantly occurs through the sulfur atoms present on the surface. The subsequent steps involving the formation of H2O and OH•, as well as hydrogen transfer between these species, accompanied by the simultaneous oxidation of sulfur on the chalcopyrite surface, were also investigated. Additionally, through NEB calculations, a kinetic study was performed, which demonstrated that the (001)-S surface is the most favorable for oxidation to occur, while the (112)-S surface presents an energy barrier of approximately 80 kcal mol-¹. In the second system analyzed, we investigated the adsorption mechanism of H2 on the surface of Ru-doped TiO2. This process is thermodynamically and kinetically favorable. It begins with the dissociative adsorption of H2 on the ruthenium site, and then hydrogen migrates to an oxygen site on TiO2, promoting the reduction of titanium atoms directly bonded to the ruthenium atom through, a process known as the spillover effect. This thesis demonstrates the importance of establishing an appropriate chemical model to enable the proper investigation of complex reactions through computational calculations.