Estudo morfológico e redução eletroquímica da calcopirita em solução salina de biolixiviação

The chalcopyrite (CuFeS2) is the most abundant copper sulfide in nature and belongs to the most explored group of copper minerals, accounting for about 70% of the total copper available. The electrochemical studies of chalcopyrite greatly alter the exploration and use of sulfides, not surprisingly, a large number of papers have been published on the electrochemical behavior of chalcopyrite [1-2]. The objective of this work was to study the reduction process of chalcopyrite by means of different electrochemical techniques: cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS). The surface morphology of the mineral surface was investigated after the different reduction events. The electrochemical studies were performed in salt solution of containing 0.5 g L-1 of each salt: MgSO47H2O, (NH4)2SO4 and KH2PO4, pH 1.8. Electrochemical tests were performed using solid chalcopyrite. The CV and LSV measurements were carried out at different potential intervals, started in to the open circuit potential (EOCP) until -1.0 V/Ag|AgCl|KCl3mol L-1at 0.01 mV s-1. Different potential pulses were applied at: -0.40, -0.60, -0.70 and -0.80 V/Ag|AgCl|KCl3mol L-1 to chalcopyrite reduction in saline solution for 12 h. After upon the CV, LSV and CA tests, the EIS diagrams were acquired. After different electrochemical tests, the total Cu and Fe concentrations in the electrolyte was determined by atomic absorption spectrometry (AAS). After CV tests, the SEM analysis of the surface showed a sulfur rich layer. The analysis of the solution detected higher concentration of iron and copper ions. LSV measurements showed reduction peaks of low intensity. Afterwards, SEM images and surface analysis by X-ray energy dispersion found a large amount of copper, indicating that at potentials below -0.50 V, the reduction of copper and copper sulfides (covelite, chalcocite and bornite) occurred on the surface of chalcopyrite. CA results showed that the more negative the applied potential, the higher the cathodic current. In negative potentials the concentration of copper in solution was much lower than iron ions, suggesting the formation of metallic copper and copper sulfides on the surface. For EIS tests, the more negative the potential, the smaller the Z real values, indicating a lower resistance to the mineral decomposition. (Part of the Master thesis of R. N. Peres, IQ-UNESP, 2016)