Abstract
The effect of anode bismuth level and of concentrations of dissolved oxygen and bismuth ions in copper electrolyte were investigated to understand the formation mechanism of anode slime layer and its influence toward passivation behaviour. The metallic granular forms of bismuth were found in the anode at the lower bismuth content. However, the higher bismuth content of anode exhibited a hairy or meshes-like shape. The bismuth dissolved preferentially during electrolysis and the anode surface after electrolysis became excessively uneven. The slimes were classified into the adhering and the falling types. The amount of falling slimes was about 90% of total slime formed and it mainly consisted of copper powder mechanically separated from anode. On the other hand, the adhering slimes consisted of copper powder, Bi2O3 and Bi2 (SO4)3. The copper powder in the adhering slimes was the fine particles formed by the disproportionation reaction of Cu+ ions. Bi2(SO4)3 in the slimes were precipitated by the supersaturation of dissolved Bi3+ ions and observed in the inside of grain boundary.Under the electrolytic condition of high current density and in the case of the addition of Bi3+ ions into electrolyte, layer of needle-like precipitates of Bi2 (SO4)3 was observed on the adhering slime. This slime layer caused the anode to passivate sensitively.When Bi, As and Sb impurities were coexisted in the copper anode, the composition of the resulting anode slime was Bi2O3, BiAsO4 and SbAsO4.
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