The effect of trace lead on the coulombic efficiency of zinc electrowinning in high-purity synthetic solutions

• Published in: Journal of the Electrochemical Society 1988-10, Vol.135 (10), p.2465-2471
• Main Author: FRAZER, E. J
• Format: Article
• Language: English
• Subjects: Adsorption; Chemistry; Electrochemistry; Electrodeposition; Exact sciences and technology; General and physical chemistry; Study of interfaces; Transport phenomena
• ISSN: 0013-4651; 1945-7111
• DOI: 10.1149/1.2095359

Measurements of coulombic efficiency (QE) for Zn electrodeposition were carried out under mass-transfer controlled conditions using a rotating disk electrode. Zinc deposits were produced over 2 h in acidic zinc sulfate solutions prepared from analytical grade or high-purity reagents under the following conditions: 25 or 35 deg C, 400 A m exp --2 , and an electrode rotation rate of 20 s exp --1 . It was found that, on its own, trace Pb ( < = 5 mg l exp --1 initially) had only a small ( < = 1%) beneficial effect on QE, which was not expected to be significant at the levels encountered in practice. However, in combination with Sb, a strong interactive effect was observed with the Pb "masking" the deleterious effect of Sb on QE, to an extent dependent on the Pb concentration. The mechanism of action of trace Pb was investigated by both physical and electrochemical methods. Analysis of Zn deposits by scanning electron microscopy suggested that the Pb was uniformly distributed. Electrochemical measurements showed that under the above conditions Pb was deposited under mass-transfer control; it also increased the hydrogen overpotential of the electrodeposited Zn and made the deposition potential more negative. 50 ref.--AA