Novel lead–cobalt composite anodes for copper electrowinning

Abstract

PbO2–CoOx and PbO2–Co3O4 composite-coated anodes, using titanium and nickel substrates, have been successfully prepared and tested under typical copper electrowinning conditions. The aim of depositing a well-adhered composite coating onto the surface of the titanium and nickel substrate materials was pursued using three different coatings. The performance of the produced anodes was examined in terms of oxygen evolution potential and service life. Both of the anodes with PbO2–CoOx or PbO2–Co3O4 deposited on titanium resulted in reduction of the oxygen evolution potential of 300 to 400mV compared with a conventional PbCaSn anode. The anodes prepared by applying the same coatings onto a nickel substrate showed poor stability in the acidic electrolyte media used in this experiment to represent typical copper electrowinning conditions. Of the different coatings tested, a combination of thermal deposition of a SnO2–Sb2O3 interlayer on the surface of a titanium substrate followed by electrodeposition of the top layer of the composite coating resulted in the best electrochemical activity and service life for the anodes. A Tafel slope of 88mV dec−1 was recorded for the anode with a top coating of PbO2–CoOx and 47mV dec−1 for the anode with a top coating of PbO2–Co3O4, which both compare favourably to the 122mV dec−1 which was observed for a conventional PbCaSn anode. Anodisation tests were carried out for a period of 16h both in the presence and in the absence of the organic additive thiourea in the electrolyte. Corrosion rates were estimated from these tests and the results showed that the titanium-based anode with a SnO2–Sb2O3 interlayer and PbO2–CoOx coating has a lower corrosion rate than a conventional PbCaSn anode, whereas the corrosion rate of the titanium-based anode with same interlayer and PbO2–Co3O4 coating might be much greater but this remains to be confirmed. The results also showed that the addition of thiourea appears to increase the corrosion rate of the composite-coated anodes although it reduces the corrosion rate of a PbCaSn anode. Thiourea showed no obvious effect on the anode potential.