Why are impure tin slabs used as anodes in electrolytic refining?

In electrolytic refining, impure tin slabs are used as anodes to facilitate the purification of the metal through an electric current.12

When these anodes are immersed in an acidic electrolyte alongside high-purity starting cathodes, the application of a direct current causes the tin atoms in the anode to dissolve into the solution as ions. These ions then migrate through the electrolyte and deposit onto the cathode as high-purity metal.12

This process is essential for treating products derived from complex ores, allowing for the production of tin with a purity level of up to 99.999 percent. Furthermore, this method enables the recovery of valuable by-product metals that may be present as impurities, which are left behind as an insoluble sludge in the electrolytic cell.12