Estudo da dissolução da calcopirita em soluções aquosas de ácido sulfúrico, clorídrico e nítrico, usando a técnica de espectroscopia de impedância eletroquímica

Abstract

The chalcopyrite, copper and iron sulphide (CuFeS2), is the most abundant copper mineral. The dissolution rate of this sulfide is slow at low temperatures and decreases with time. Most of the studies ascribe such slow rate to the formation of a non-porous layer and insoluble, which hinders the progress of dissolution. However, the formation of this layer and its characteristics are not yet fully established. In this work, electrochemical and surface analysis were used to carry out a comparative study of leaching of chalcopyrite in hydrochloric, nitric and sulfuric acids, aiming to increase the extraction of copper from low-grade, chalcopyrite ores. Unpublished results include the use of electrochemical impedance spectroscopy (EIS) in characterizing the surface of chalcopyrite. Potentiodynamic polarization coupled to atomic absorption showed that HCl is the best leaching because efficiency is almost five times that HNO3 e H2SO4. The EIS data showed greater impedance (175,190 Ω.cm2) for H2SO4, therefore, greater resistance which confirms the previous analysis. The electrochemical techniques used indicated the formation of a film on the electrode surface. The impedance spectra and their representations in the form of electrical equivalent circuit suggest that the process of dissolution of chalcopyrite is controlled by the diffusion layer of the film. The use of Raman spectroscopy and SEM / EDS allowed the partial identification of lead sulfide and bismuth as impurity and helped in the identification of two corrosion products formed, sulfur and covellite.