Selective recovery of silver ions from copper-contaminated effluents using electrodialysis

With the growing demand for silver, the recycling of this precious metal from secondary sources has become imperative. However, the presence of copper impurities poses a significant challenge. This study aims to explore electrodialysis for selectively recovering silver ions from copper-contaminated effluents, elucidating the effect of low pH on the process performance. Electrodialysis of 10 mM equimolar solutions of silver nitrate and copper nitrate was performed at various pH levels, using nitric acid for pH adjustment. Adjusting the operational current to the limiting current resulted in similar silver fluxes and copper leakages at pH 1, 2, and 4.5. The energy requirement was governed by proton abundance, competing with silver ions for charge transport in the electrodialysis cell. The specific energy consumption for silver removal decreased from 751 kJ/mol at pH 1 to 36 kJ/ mol at pH 4.5, with the energy efficiency rising from 2 % at pH 1 to 37 % at pH 4.5. Copper leakage was approximately 20 % in all cases, yielding silver-copper separation efficiencies of 55 % at pH 1 and 80 % at pH 2 and 4.5. This study highlights electrodialysis as a promising technique for purifying hydrometallurgical effluents, emphasizing the need for case-specific assessment depending on feed water properties. Notably, the limitations associated with low pH suggest potential advantages of adjusting the pH of the solution.