Characterization of natural enargite aqueous solution systems by electrochemical techniques

The electrochemical behavior of natural enargite electrodes in stirred and quiescent aqueous solutions covering a wide pH range was investigated using ac and dc electrochemical techniques. It is proposed that in the first stage of enargite oxidation the release of copper ions takes place and a copper-depleted passivating film is formed on the electrode surface. At more positive potential the film becomes oxidized but depending on solution pH, a secondary passivation can be attained due to the precipitation of cupric arsenate. The electroreduction of enargite or a possible oxidized film formed during the preliminary treatment of the mineral surface initially releases S(II-) species and generates a surface film containing As2S2 and Cu2S. At more negative potentials the electroreduction of As2S2 to metallic As predominates. A dynamic system analysis carried out at pH 9.2 using electrochemical impedance spectroscopy gave additional information about the processes occurring on the enargite surface under anodic polarization.