Electrochemical dissolution of chalcopyrite: Detection of bornite by synchrotron small angle X-ray diffraction and its correlation with the hindered dissolution process

The formation of bornite (Cu5FeS4), an iron-deficient sulfide, and its correlation with the slow oxidation rate of chalcopyrite (CuFeS2) in acidic media under atmospheric conditions is demonstrated. Chalcopyrite electrodes oxidized in 0.1 mol/L H2SO4 solutions at room temperature (25 ± 1 °C) were analyzed by micro Raman spectroscopy and synchrotron small angle X-ray diffraction (S-SAXRD), techniques indicated for thin films analysis. Anodic polarization curves of chalcopyrite electrodes showed two well-defined behaviors: quasi-potential-independent regime and potential-dependent regime. When the critical potential (Ec) is attained, which ranged from 0.75 to 0.90 V vs. Standard Hydrogen Electrode (SHE), the mineral oxidation rate becomes strongly dependent on potential. Potentiostatic current-time profiles at 0.60 and 0.70 V vs. SHE indicated a current decay, which suggests the formation of a progressively thickening protective layer. The profiles at 0.80 V vs. SHE showed a similar current decay, but also an active oxidation process for some samples. After chronoamperometry at 0.70 and 0.80 V vs. SHE, respectively, for 6 and 2 h, analyses by using S-SAXRD revealed peaks of bornite on oxidized chalcopyrite electrodes. Elemental sulfur (S8) was also detected by S-SAXRD at 0.80 and 1.00 V vs. SHE, respectively, for 2 and 0.5 h. An unidentified metal-deficient phase and covellite (CuS) were detected on chalcopyrite by micro Raman spectroscopy after chronoamperometry at 0.60 and 0.80 V vs. SHE, respectively. The formation or absence of these product phases under a constant applied potential correlated well with a hindered dissolution or active oxidation processes. The results of this work support the hypothesis that the formation of intermediate iron-deficient sulfides contributes to the slow oxidation rate of chalcopyrite under atmospheric conditions.

The formation of iron-deficient sulfides and covellite contributes to the slow dissolution rate of chalcopyrite under atmospheric conditions. There is no evidence to ascribe the mineral’s hindered dissolution to the formation of elemental sulfur.Figure optionsDownload as PowerPoint slideHighlight
► First experimental evidence of bornite films on oxidized chalcopyrite.
► The formation of bornite is correlated with the slow oxidation rate of chalcopyrite.
► The mechanism of formation of iron-deficient sulfides, as bornite, was proposed.