Studies on Electrolytic Refining of Zinc. I : The Solubility of Lead in Zinc Sulfate-Sulfuric Acid Electrolyte

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The solubility of lead in zinc sulfate-sulfuric acid electrolyte was determined over the range of zinc concentration from 30 to 120g/l, and acid concentration from 50 to 300g/l, at the temperatures 30°, 40°, and 50℃. For each of the solubility determination lead sulfate was wet-ground with a little electrolyte and transferred to 80 ml portion of the latter in a stoppered 100ml conical flask. The electrolyte was mechanically stirred for 24 hours and then allowed to stand for 2 hours at a constant temperature. Five ml of the electorlyte was then taken as a sample and lead was extracted by dithizone in chloroform. The quantity of lead present in the dithizone solution was measured with Fisher Nefluoro Photometer through the 525mμ filter. The solubility of lead in zinc electrolyte is mainly affected by free sulfuric acid concentration and temperature. It decreases with increase in acid concentration, and it increases with rise in temperature, being scarcely affected by zinc concentration. The relationship between the lead solubility and the free sulfuric acid concentration is given by the following expression : logy=a+bx, where y is the concentration of lead, mg/l, x the free sulfuric acid concentration, in g/l unit, a and b constants which may be evaluated from zinc concentration and temperature of the electrolyte. Rise in temperature results in an increase of 0.11-0.16 mg Pb/℃.
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