AN ELECTROCHEMICAL STUDY OF NATURAL ENARGITE UNDER CONDITIONS RELATING TO THOSE USED IN FLOTATION OF SULFIDE MINERALS

The electrochemistry of natural enargite (Cu3AsS4) in an alkaline solu tion of berate buffer is studied. Photoelectrochemical experiments con firm that the samples studied are p-type semiconductors. The potential range in which the photocurrent is noticeable (below -0.4 +/- 0.2 V v s. SCE) is more negative than the potential range of flotation (near 0 .0 V vs. SCE). The electrochemical behaviour of the electrode is studi ed by electrochemical impedance spectroscopy (EIS) around this potenti al and by voltammetry. The time dependence of the impedance over some tens of minutes leads us to believe that a surface layer forms over th e potential range studied, and the law for the growth of this layer co rresponds to two processes: the formation and dissolution of the layer . The voltammetric study, interpreted in the light of a treatment assu ming two successive transfers with a surface intermediate, supports th is interpretation. Between 1 Hz and 10 kHz, the impedance spectra coul d be analysed with an equivalent circuit including a constant phase el ement, valid whatever the applied potential in the range from -0.1 to 0.2 V vs. SCE in the presence or absence of a collector (ethyl xanthat e), while an equivalent circuit with simple elements was found with ga lena under similar conditions. This result is tentatively discussed in relation to particular structural properties of ternary compounds bef ore and after electrochemical oxidation. The effects of xanthate addit ions are studied by voltammetry and EIS, also. No proof of the underpo tential deposition of xanthate is observed. It seems that surface oxid ation and reactivity with the collector are closely linked, and a proc ess of ion exchange occurring at potentials more positive than 0.0 V i s proposed to explain our results.