Cross-section Analysis of Anode Slime Generated on Sn Anode Containing Sb and Bi for Elucidating passivation mechanism

Electrorefining is a method for recycling solder material. After applying constant current electrolysis to a Sn anode material containing Bi and/or Sb as impurities, we performed cross-sectional observation and mapping analysis of the generated anode slime layer. Our findings confirmed that the Sn anode electrode composition affects the generated anode slime shape. The anode slime layer generated from anode material containing Bi and Sb in a specific ratio exhibited a network-like structure. This structural change apparently has an anti-passivation effect. Mapping analyses of some samples used for this experiment revealed S-rich layers between the electrode and slime layer. We infer that S enrichment is attributable to the formation of Sn-S-O compounds and that the Sn-S-O compound formation causes passivation of electrodes. Ease of forming Sn-S-O might depend on the slime layer structure and other factors.