A pyrometallurgical alternative: The refining electrolysis of lead and solder

Conclusions

In refining electrolysis in hexafluorosilic acid with current densities of 100 A/m², it is possible to separate bismuth and antimony from prerefined lead bullion. Pure lead with less than 50 ppm bismuth and less than 100 ppm antimony was deposited at the cathode. The current efficiency was 99%, and the specific energy consumption was 30–40 kWh/t.

Under the same conditions, a lead-tin alloy with less than 300 ppm antimony can be produced by refining a Pb−Sn−Sb alloy with 30% tin and up to 5% antimony. In this case, antimony remains in the anode sludge.

Because of the high amount of anode sludge, the strong adhesion of the sludge on the anode surface, and its physical properties in the case of high antimony contents (i.e., more than 5% antimony in the anodes), some differences in the usual electrolysis technology are necessary to guarantee a long-term, stable, and trouble-free electrolysis. The tendency of anode passivation can be reduced by using a periodic current reversal technique. This technique results in a smaller amount of anode sludge, a reduced loss of lead in the anode sludge, and lower anodic polarization values.