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The world’s most abundant copper mineral, chalcopyrite (CuFeS2), experiences slow kinetics in atmospheric leaching using traditional acidic ferric sulfate lixiviants because of its unique physico-chemical properties and the passivating product layer formed during leaching. To overcome this, FLSmidth® has devised a novel process, which alters the properties of semiconducting minerals and increases chemical reactivity and dissolution kinetics. In the FLSmidth® Rapid Oxidative Leach (ROL) process, a combination of chemical and mechanical processes is responsible for enhancing the leach kinetics. The former comes about from a surface pretreatment that “activates” the mineral with 0.1 to 5 mol% of copper (II), and latter is assisted by using a Stirred Media Reactor to cleave fresh surfaces during leaching. As a result, surface passivation problems are diminished, and the process can achieve copper recoveries >95% in under 6 h. Since lattice restructuring can play a major role in semiconductor reactivity, it is critical to understand the associated physico-chemical phenomena and their influence in the ROL process. With respect to this, it is important to investigate the relationship between the activation steps and its impact on the chalcopyrite crystal lattice.In this study, it was found that the key markers of activation could be identified as changes in the physical structure and electrochemical properties of the mineral. Diffraction with transmission electron microscopy (TEM) was critical in uncovering the expansion of the crystal lattice after activation, which would facilitate the extraction of ions since the expanded structure would allow atoms to move more freely. Parts of the mineral, particularly the surface, had significant modification of the structure, which indicated a phase transformation to structural resembling the mineral covellite, CuS. Chemical analysis with x-ray photoelectron spectroscopy (XPS) was capable of proving that significant oxidation occurs in the copper and sulfur, corresponding to a change of phase on the surface and supporting the hypothesis of the formation of covellitic phase. Finally, calculations using density functional theory (DFT) gave fundamental foundations for the importance of electrochemical changes, whereby it was found that copper activation contributes to increased conductivity of the mineral. Increased conductivity has positive impacts on the flow of ions, which provides further proof for the influence on leaching kinetics. The combination of these three studies provides a better understanding on the role of activation than a single approach would. |
