Corrosion and protection of lead anodes in acidic copper sulphate solutions

Abstract

It is known that lead anodes used in the industrial extraction of copper by electrolysis (electrowinning) suffer corrosion as a result of accidental or intended current interruptions. In order to improve understanding of the corrosion and protection of such anodes, the effects of the concentrations of copper, sulphuric acid, cobalt, iron, manganese, chloride and an organic additive (guar) on the corrosion of lead have been studied by means of weight loss tests and surface analysis techniques (X-ray photoelectron spectroscopy, X-ray diffraction, and wavelength dispersive spectroscopy). The rate of corrosion of lead during current interruptions increases with increasing concentration of sulphuric acid and copper, whereas it decreases markedly in the presence of cobalt and iron and, to a lesser extent, in the presence of chloride and the organic additive. Manganese is the only impurity whose presence does not reduce the rate of corrosion; it is also the only element which precipitates in significant amounts on the lead anode surface under the conditions studied. A method is proposed to establish the optimum anodic protection current density during current interruptions in electrowinning cells. Three current density ranges have been found, of which the 'high' protection range could be caused by the degree of compactness acquired by the PbO 2 layer at applied anodic current densities in excess of 60 A m 22 .

Zinc Electrowinning Using Reactive Electrodialysis (Red)

“…This process is performed using the electrochemical reactions of water oxidation on a lead anode 2,3,4 and zinc reduction in a solution on an aluminum cathode.Within the zinc electro-winning process, in spite of having being used for several years, there are two major drawbacks: the first is the generation of acid mist produced by the O 2 evolution reaction at the anode, which causes damage to the working plant. The second of these is the use of lead anodes.…”

The influence of tin and silver as microstructure modifiers on the corrosion rate of Pb–Ca alloys in sulfuric acid solutions

“…The corrosion products, from the samples, are removed by their dissolution in water solution of 100 g l À1 KOH þ 50 g l À1 KI þ 200 g l À1 Na-tartarate at 30 8C [11]. Samples, previously washed in deionized water and then in absolute methanol and dried in warm air, are weighted on the analytical balance.…”

“…It is seen from Figs. 4 and 5 that concentration of tin in the alloy should be !1.1 wt% to obtain its positive effect on the microstructure refinement, as well as the addition of 0.02 wt% of silver [1,5,6,10,11].…”

“…Alloy no. 4: Big grains and more regular grain boundaries with segregates at inter-crystalline zones are characteristics of quaternary alloy [10,11]. Rolling direction !…”

Corrosion of lead anodes in base metals electrowinning

“…Problems related to manganese in the electrolyte have been discussed by Miller (1995) and Hughes et al (1998). Cifuentes et al (2005) investigated the effect of various impurities in a copper electrowinning electrolyte on the rate of corrosion of lead anodes and found that manganese increased the corrosion rate of lead anodes more significantly during normal tankhouse operation than during current interruptions. The PbSO 4 formed in Equation [11] is also converted to PbO 2 at the anode but it will be in the form of loose, nonadherent flakes.…”