Copper recovery from tin stripping solution: Galvanostatic deposition in a batch-recycle system

Abstract

Tin stripping is employed widely for the manufacture of printed circuit boards. At the end of stripping process, in general, 2–40g/l of Cu along with 150g/l SnO2 and ferric and nitrate ions remain in solution. The performance of an electrochemical batch recycle reactor for copper recovery from simulated tin stripping waste solutions was examined by galvanostatic plating. Galvanostatic control was achieved by the application of decreasing constant current steps which followed the concentration decay of metal ions in solution. The concentration decay was predicted by a model based on the batch recycle reactor operating under mass transport control. The current required to reduce the copper ions at the mass transfer limit at each time step was predicted from the model. These were matched against copper reclamation experiments from simulated tin stripping waste solutions using a single volumetric mass transfer coefficient as a fitting parameter. The prediction of the concentration decay of copper ions was in good agreement with the experimental data. It was found that the current efficiency for copper deposition was lowered by nitrates and oxygen present in the electrolyte due to their co-reduction at the cathode. Dissolved Fe3+ ions also influenced current efficiency for copper recovery due to the simultaneous reduction of ferric ions. The current efficiency was between 70% and 90% throughout the electrolytic process, which suggests that electrochemical copper reclamation may be a viable process.