Characterization of natural tetrahedrite/aqueous solution system by electrochemical techniques

The electrochemical behavior of the natural tetrahedrite in quiescent solutions covering a wide pH range was investigated using cyclic voltammetry (CV), open circuit potential (OCP), stationary polarization (SP) and electrochemical impedance spectroscopy (EIS) techniques. During the electrooxidation, the following processes might occur: (i) a redox internal process through which Cu(I) ions, present in the mineral tetrahedrite structure, are oxidized to Cu(II) ions, the possible mechanism for this process would be a hopping electron diffusion, (ii) the formation of a surface copper-depleted polysulfide film together with a release of Cu(I) from the mineral structure, and (iii) the Cu(I) ions freed from the tetrahedrite structure, according to pH solution and potential applied to the interface electrode/solution, can evolve to cupric ion or oxygen-containing Cu(II) species (oxo-hydroxo compounds). When the formation of oxo-hydroxo compounds takes place, the surface film becomes more complex but the electrode surface does not become fully passive possibly due to an irregular arrangement of its constituent species. During the electroreduction of tetrahedrite, the release of sulfur occurs and the consequent formation of Cu₂S and antimony sulfurs with different stoichiometry would take place.