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Study of the mechanism of anodic dissolution of Cu2S

par Brennet, Patrick ;Jafferali, Shiraz;Vanseveren, Jean-Marie ;Vereecken, Jean ;Winand, René
Référence Metallurgical Transactions, 5, 1, page (127-134)
Publication Publié, 1974-01

Article révisé par les pairs

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Résumé :

The anodic dissolution of Cu2S in sulfuric acid solutions was studied under galvanostatic and potentiostatic conditions. The anodic products were studied by mineralogical and X-ray diffraction methods. In every case, the formation of a digenite Cu1-8S layer is observed at the surface of Cu2S according to 5Cu2S → 5Cu1.8S + Cu++ + 2e A copper concentration gradient appears through the digenite layer whose thickness remains constant as soon as a Cu1.1S layer appears at its own surface according to 3Cu1.8S → 4Cu1.1S + Cu++ + 2e If the electrolysis conditions are such that the anodic potential remains low, the next reaction to occur is 10Cu1.1S → HCu++ + 10S + 22e But if under galvanostatic conditions, the current density is high enough at a given temperature to reach the sharp rise in anodic potential, or if under potentiostatic conditions the potential is kept high, two other reactions are possible: 10Cu1.1S → 10CuS + Cu++ + 2e followed by CuS → Cu++ + S + 2e Moreover, at high anodic potential, the following reaction occurs also to some extent CuS + 4H2O {mapping} Cu++ + SO4= + 8H+ +8e resulting in a decrease in anodic current efficiency for the copper dissolution. From a more practical point of view, it was shown that it is possible to deplete virtually completely the copper content of the anode (residue at less than 0.5 pct Cu)keepingthe electrode potential at a low value (less than +650 mV/ENH). Providing the temperature is high enough (75°C at least), the mean current density remains near to 2 A/dm2, a suitable value to obtain good cathodic deposits. © 1974 American Society for Metals, The Melallurgical Society of AIME.