The recovery of copper and tin from waste tin stripping solution: Part II: Kinetic analysis of synthetic and real process waste

Tin stripping is a key process step in printed circuit board fabrication. At the end of a tin stripping process, in general, metal concentration in the waste is 2–40 g/l Cu and 150 g/l SnO2 [D. McKeeson, Print. Circuit Fabr. 22 (7) (1999) 34–37] in addition to nitric acid, ferric ions and other complexants. In a previous work we had carried out a thermodynamic analysis to determine if copper can be recovered from a tin stripping process. In this paper we present a kinetic analysis to determine the current efficiency for copper electrodeposition from a tin strip waste solution. We have performed electrochemical stripping analysis from simulated and real waste tin strip solutions. Copper is electrodeposited from solutions containing only copper and nitric acid, copper and nitric acid with ferric and tin ions, or waste from tin-strip processes. Our results showed that copper can be recovered at reasonably high current efficiency from solutions containing nitrate ions. The presence of ferric ions, however, reduces current efficiency significantly. It was shown that the tin stripping solution is a mixed potential system. In order to develop a high efficiency electrochemical copper recovery system, the crucial criteria are to maintain a low concentration of ferric ions in solution and to suppress the generation of ferric ions by electro-oxidation.