A mineralogical study of one anode and four anode slimes was carried out to elucidate possible Pb-Sb-Bi interactions occurring when Pb is added to copper anodes to reduce the Sb and Bi concentrations of the cellhouse electrolyte. About one-fifth of the Pb and Sb, and one-third of the As, in copper anodes occurs in solid solution in the copper matrix. The remainder of these impurities, and most of the Bi, are present as Cu-Pb-As oxide and Cu-Pb-As-Sb-Bi oxide inclusions at the copper grain-boundaries. During electrorefming, the Pb, As, Sb and Bi in solid solution dissolve completely, and the oxide inclusions dissolve extensively. The dissolved Pb reprecipitates as PbSO_4, Pb_5(AsO_4)_3(Cl,OH) or a complex oxidate phase which contains minor amounts of Sb and Bi. Most of the dissolved Sb and Bi reprecipitate as SbAsO_4, or Sb-Bi-As-O species. Although As additions to the anodes clearly promote the precipitation of Sb-Bi-As oxide species, it is not apparent that Pb additions behave similarly. Trace amounts of Pb-Sb oxide and Pb-Bi oxide are detected, but the morphologies suggest that the oxides were present in the as-cast anodes. High Pb contents seem to retard the dissolution of the Cu-Pb-As-Sb-Bi oxide inclusions, with the formation of a Pb-Sb-As-Bi-S-O phase which remains closely associated with the selenide-PbSO_4 inclusions in the anode slimes. However, there is little mineralogical evidence to suggest the significant precipitation of Pb-Sb oxide or Pb-Bi oxide species.
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