Polarized behaviour of lead anode with 0,8 % silver in synthetic solution for electrollytic zinc precipitation in presence of depolarized substances

Abstract

At density current of 400A/m2, average voltage of electrolytic cell in zinc industrial production is approx. 3,7V, making anode potential approx. 2,0V. In the process of electrolysis, almost 80% of electric energy is spent, so there is a great economic interest to reduce specific electric energy consumption per zinc mass unit. The solution of this problem can be found in reducing anode potential (depolarization) by adding, in electrolyte, the substances that oxidize at potentials lower than the one of water oxidation. This paper examined the behaviour of anode potential by adding 1, 3, 5 and 8% (vol) methanol, i.e. 1, 3 and 5% (vol) formic acid in synthetic industrial electrolyte with 150g/dm3 H2SO4, as well as the influence of chloride presence in electrolyte on anode polarization effects. Lead anode alloyed with 0,8% silver was used, being a standard for zinc industrial production. Corrosion behavior of such an anode was examined in presence of methanol in synthetic industrial electrolyte with 150g/dm3 sulphuric acid. The results show that in the field of industrial relevant density current, depolarization effect while adding methanol exists, that the presence of methanol doesn't affect adversely on corrosion stability of anode, but the acceptable content of chloride in electrolyte cancels the effects of depolarization in the presence of methanol. The presence of formic acid in synthetic electrolyte doesn't show clear and uniform depolarization effects.