The behaviour of lead in the anode during electrolysis was investigated in terms of impurity levels in the anode and the concentration of dissolved oxygen and H2SO4 in the electrolyte. The metallic granular forms of lead were found in the anode at a level of less than 5,000 ppm. The anode potential-time curves show discontinous steps based on the falling of slime from the anode surface during electrolysis, and passivation were not observed. The adhering slimes were dark-brown and consisted of PbSO4 and copper powder. The ratio of PbSO4 to copper powder in the adhering slimes increased with increasing lead level, and ranged from 50-80 wt%. The PbSO4 deposited around the undissolved metallic lead. On electrolysis with the Cu-As-Pb-O anode, the slime obtained was mainly PbSO4 and Cu3As. Trace amounts of As2O3 and PbO were detected in the slime. Undissolved lead was also present.
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