Two new articles have been accepted for publication in the journals Membrane and Desalination, entitled Enhancing Palladium Recovery Rates in Industrial Solutions through Electrodialysis and Selective recovery of ions from copper-contaminated effluents using electrodialysis. The main person behind these articles is PhD-candidate Pauline Zimmermann who is now nearly ready to deliver her thesis.
Palladium is a vital commodity in the industry. To guarantee a stable supply in the future, it is imperative to adopt more effective recycling practices. In the first article, we explore the potential of electrodialysis to enhance the palladium concentration in a residual solution of palladium recycling, thus promoting higher recovery rates. Experiments were conducted using an industrial hydrochloric acid solution containing around 1000 mg/L of palladium, with a pH below 1. Two sets of membranes, Selemion AMVN/CMVN and Fujifilm Type 12 AEM/CEM, were tested at two current levels. The Fujifilm membranes, which are designed for low permeability of water, show promising results, recovering around 40% of palladium within a two-hour timeframe. The Selemion membranes were inefficient due to excessive water transport. All membranes accumulated palladium in their structures. Anion-exchange membranes showed higher palladium accumulation at lower currents, while cation-exchange membranes exhibited increased palladium accumulation at higher currents. Owing to the low concentration of palladium and the presence of abundant competing ions, the current efficiency remained below 2%. Our findings indicate a strong potential for augmenting the palladium stage in industrial draw solutions through electrodialysis, emphasizing the importance of membrane properties and process parameters to ensure a viable process. Beyond the prominent criteria of high permselectivity and low resistance, minimizing the permeability of water within IEMs remains a key challenge to mitigating the efficiency loss associated with uncontrolled mixing of the electrolyte solution.
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. The study in the second article 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.
