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UBC Theses and Dissertations

Corrosion and passivation behaviour of noble metal coated anodes in copper electrowinning applications Wensley, Donald Arthur


Evaluation of the changes in loading and composition of platinum/ iridium alloy coated titanium anodes employed in conditions comparable to those encountered in electrowinning of copper from highly acidic electrolytes, typical of those produced from sol vent-extraction treatment of leach liquors, was accomplished by means of an X-ray fluorescence spectroscopic technique. Under continuous operation at a constant anode current in 2M H₂SO₄ or in 2M H₂SO₄ + 0.5M CuSO₄ electrolytes, the loss of coating metal from the particular anode material chosen for this study is predominantly electrochemical in nature, with platinum showing preferential attack. Anode materials from other sources, of nominally similar composition and manufacture, show varying degrees of mixed mechanical and electrochemical corrosion. Operation with pulsed current or addition of thiourea is found to promote accelerated dissolution of the coating metals. On imminent anode falure the mechanism of coating metal loss becomes predominantly mechanical in nature. The development of surface oxygen coverage on the alloy coatings during anodic polarization in sulfuric acid solutions, which in turn determines the nature of the corrosion and passivation (defined as the increase in anode potential with time) is analogous to the case of unalloyed platinum metal, showing growth of oxygen coverage to the equivalent of only 2-3 monolayers with prolonged anodization. In particular, the alloy coatings behave in a similar manner to platinum metal with respect to the formation and removal of surface oxygen coverage, thus permitting the determination of electrochemically active surface areas by means of formation and stripping of oxygen monolayers.

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