| dc.description.abstract | The metal-processing industry faces the challenge of depleting raw materials, forcing companies to accept ores of declining quality. Consequently, energy and chemical demands for extracting the metals of interest are increasing, prompting the need for advanced purification methods. This thesis explores the application of electrodialysis in Norway's hydrometallurgical industry to promote sustainable resource management and a circular economy. Electrodialysis, a separation technique that selectively transports ions through ion-exchange membranes under an electric field, is gaining interest thanks to innovations in membrane design. Particularly, monovalent-selective ion-exchange membranes are proving effective for separating single-charged ions from multi-charged ones.
In this study, electrodialysis was applied to address specific industrial challenges faced by two collaborating metal-producing companies. For resource recovery, electrodialysis was employed on the residual solutions from palladium recycling, achieving higher recovery rates. It was found that both the type of membrane and the current density significantly influenced recovery rates and energy consumption.
Further investigation into the effects of current density focused on the removal of fluoride and chloride from sulfate-based electrolytes in zinc processing. A semi-empirical model was developed to determine ion-specific limiting current densities, which were then used to estimate the optimal current density for removing target ions from multi-ionic mixtures. This approach yielded separation efficiencies of 93% between chloride and sulfate, and 81% between fluoride and sulfate.
In addition, the influence of solution pH on copper-ion impurities during silver electrorefining was studied. A lower pH reduced the energy efficiency of the electrodialysis process, as highly mobile hydrogen ions consumed a significant portion of the applied current.
One of the challenges encountered was membrane clogging by metal ions, particularly during the recovery of palladium and silver. Palladium trapping varied with current density and membrane type, highlighting the importance of optimizing membrane properties and process design to scale up electrodialysis in metal processing. | en_US |
