The problem of low manganese content in the coating on new anodes for electrolytic zinc production
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During the coating process of new anodes for electrolytic zinc production, a large amount of chlorine is generated in the electrolytic cell, causing the solution to become turbid and the environment to deteriorate. The concentration of manganese ions also drops significantly; for example, the fresh solution contains 5 g/L of manganese, while the waste solution contains 1–1.5 g/L. The same applies to chloride ions: the zinc solution contains 400 mg/L of chloride, whereas the waste solution contains 150–200 mg/L. I believe this phenomenon is caused by the electrode potentials of lead and lead dioxide – the new anodes produce a large amount of oxygen, which oxidizes chloride ions into chlorine gas, causing it to escape from the cell. Manganese ions are also oxidized by this excess oxygen into manganese dioxide. It takes about a week for the oxide layer on the anode plates to thicken enough for normal conditions to be restored. I would like to hear any different opinions from fellow enthusiasts; let’s discuss this together.
This year, making electrolytic zinc has been very profitable. Our factory sold off the anodes and cathodes at the beginning of the year, and we dismantled the zinc melting furnaces. As the price of zinc kept rising, we managed to sell dozens of tons; although we didn’t have time to convert them into zinc oxide, we still made a small profit. Selling zinc sulfate early on didn’t yield any profit
Anodic coating usually involves a low current level of 40–60 A/m2, over a period of 24 hours. There seems to be an issue with your procedure !
I have participated in four times in the coating process for new systems at large factories; in most cases, a good oxide layer is formed within 24–48 hours (a reddish-brown layer appears after 4–5 hours)