Electrowinning/Electrostripping and Electrodialysis Processes for the Recovery and Recycle of Metals from Plating Rinse Solutions

Abstract

Two electrochemical-based methods have been evaluated to remove heavy metals from a tin/zinc electroplating rinse solution with subsequent recycle of the metals back into the original plating bath. The first method uses electrodialysis to move tin to the anolyte strip solution as an anionic citrato complex while zinc is distributed to both the anolyte and catholyte, showing it exists as both an anionic citrato complex and in free cationic form. Zinc can be recovered by scraping the loose deposit from the cathode and dissolving it in mineral acid.

The second method is a combined electrowinning/ electrostripping technique. The process involves continuously flowing the plating rinse solution through a porous graphite cathode and removing the metal ions via electrodeposition. When a sufficient quantity of metal has been deposited, the electrode is placed in a solution whose chemical composition is similar to that of the original plating bath and the metals ions are stripped from the electrode anodically. The resulting solution is then placed into the original plating bath.

Both methods were used to treat a surrogate rinse solution originally containing 100–300 parts per million of each metal and were successful in reducing the metal-ion concentrations to less than 15 parts per million each. Approximately 70% of the tin and 100% of the zinc are recoverable by either method.