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How does the Betts process recover bismuth from lead bullion?

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A labeled periodic table element box for bismuth shows atomic number 83, symbol Bi, atomic weight 208.9804, electron configuration, and properties including solid state, rhombohedral crystal structure, and weakly acidic oxides. — bismuth Properties of bismuth.

The Betts process is an electrolytic method used to refine lead bullion that contains impurities such as bismuth. In this process, the lead bullion is cast into large plates that serve as anodes in electrolytic tanks.1

The refining takes place in an electrolyte solution consisting of lead fluosilicate and free fluosilicic acid. During electrolysis, the lead bullion anodes dissolve, and pure lead is deposited onto a thin sheet of lead acting as the cathode. Bismuth, along with other impurities present in the bullion, does not deposit with the lead but instead remains behind as part of the anode sludge. This sludge is then collected, and the bismuth is recovered from it through subsequent complex operations.231