Selective recovery of silver from copper impurities by electrodialysis: Tailoring monovalent selective cation exchange membranes by monomolecular layer deposition

Selective recovery of silver from secondary resources enriched with copper impurities is a well-known challenge but is urgently needed by the industry. This study addresses the challenge by developing a highly efficient monovalent selective cation exchange membrane (CEM) with a specifically tailored polyelectrolyte deposition, enabling efficient Ag+/Cu2+ separation in electrodialysis. Based on the Ag+/Cu2+ separation mechanism in electrodialysis, a selected polyelectrolyte, polyethyleneimine (PEI), was deposited on a standard CEM as a monomolecular layer with precisely controlled polymer chain stretch patterns and optimized morphologies. The effects of deposition conditions, such as solution pH and ionic strength, were studied to ensure the desired surface properties. The selectivity performance of the developed membranes was tested using an equimolar binary mixture; a high Ag+/Cu2+ selectivity of > 20 was documented, exhibiting superior selectivity performance compared to commercial monovalent selective CEMs.