Chelyabinsk Zink Plant JSC, Chelyabinsk, Russia

M. S. Varganov, Head of the Technical Department, e-mail: mkv@zinc.ru
S. A. Zagrebin, Deputy Head of the Technical Department, Candidate of Chemical Sciences, e-mail: saz@zinc.ru

Chelyabinsk State University, Chelyabinsk, Russia

A. I. Biryukov, Associate Professor at the Department of Analytical and Physical Chemistry, Candidate of Chemical Sciences, Associate Professor, e-mail: st4857@yandex.ru

D. A. Zakharievich, Associate Professor at the Department of Condensed Matter Physics, Candidate of Physics & Mathematics Sciences, Associate Professor, e-mail: dmzah@csu.ru

This study looked at the dependence of the corrosion rate of rolled anodes made of lead alloys with different concentrations of alloying elements (such as silver, tin, calcium and indium) on the current density, temperature and the concentrations of chloride ions Cl^– and manganese Mn²⁺ in zinc electrowinning. The study also looked at the correlation between the corrosion rate and the surface microstructure and chemical composition of anodes. The anode structure was additionally influenced by changing the cooling rate of the specimens of alloys. Thus, slow cooling was applied to obtain a coarse-grained structure in anodes. When the corrosion properties of anodes were studied at low current densities (not exceeding 400 A/m²) and a temperature of 36 ^oC, no dependence was observed between the corrosion rate and the chemical composition or the alloy cooling mode. Rising current density, electrolyte temperature and concentration of chlorine and manganese ions stimulate the corrosion of alloyed lead anodes. The corrosion rate of lead anodes rose by 2 to 4 times when the current density increased from 385 to 450 A/m², and by 3 to 5 times when the concentration of Cl– ions increased from 200 to 600 mg/L. Experiments showed that silver is the key element governing the corrosion properties of the alloy. Doping of the alloy leads to a double decrease in the concentration of silver in anodes (from ~1 to ~0.5 % at.), which intensifies the corrosion rate. Lead anodes that contain indium and are characterized with the presence of the coarsest microcrystals at the surface have the maximum corrosion rate. The corrosion rate also rises when 0.6 to 1.8 % (at.) of tin is introduced in the alloy, even if to a lesser degree compared with the introduction of indium. Small additions (<0.1 % (at.)) of calcium produce no noticeable effect on the corrosion properties of lead anodes. The results of this study include some new data on the effect produced by indium on the corrosion resistance of lead-containing anodes with tin and calcium additions in three- and four-component systems with silver. The obtained results can be used in the practice of zinc electrowinning for predicting the lifespan of anodes as a function of the current density, the electrolyte temperature and the concentrations of chlorine and manganese ions.

The authors would like to thank A. V. Kolesnikov, T. V. Batmanova and E. I. Ageenko for their contribution to the project and this paper.

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