Abstract: A Cu-based material 5 is immersed into an alkali hydroxide solution with a concentration of 3.0 to 37.5 mass % and a H2O2 solution with a concentration of 3.0 to 50.0 mass % is added in the alkali hydroxide solution, a temperature of the alkali hydroxide solution when the Cu-based material is immersed ranges from 60 to 105° C., a ratio A/B between a mol number A of alkali hydroxide in the alkali hydroxide solution and a mol number B of H2O2 in the H2O2 solution is 10 or more, and where a mol number of Sn in the Sn layer is C and a mol number of Sn in the CuSn layer is D, B?C×2+D×6.

Abstract: The present invention relates to a method for treating spent tin or tin/lead stripping solution used in the electronic industry, particularly in the manufacture of printed circuit boards or a lead frames. Said method comprises (i) electrolytically reducing copper ions in the solution to copper at a low temperature; (ii) electrolytically oxidizing Sn2+ and Pb2+ in the solution at a high temperature to form solid tin and lead oxides and hydroxides; (iii) separating solid tin and lead oxides and hydroxides from the solution; (iv) dissolving tin and lead oxides and hydroxides obtained in step (iii) in a strong alkali or acidic solution; and (v) electrolytically reducing the alkali or acidic solution obtained in step (iv) at a high temperature to recover metallic tin and lead. Also, the filtrate obtained in step (iii) above is useful for preparing fresh tin or tin/lead stripping solution.