Abstract
• Effects of various parameters on mass transport and membrane resistance were studied. • A simplified model was developed to describe mass transport and membrane resistance. • Counter flow electrodialysis may not be superior to parallel flow electrodialysis. • Membrane resistance increased dramatically at an extremely high salt concentration. • Appropriate concentration ranges were suggested for electrodialysis concentration. There is a growing demand for efficient and economical concentration of high salinity solutions, either to recover valuable salts from non-traditional sources or to reduce the environmental impact of brines from desalination plants. Electrodialysis is one of the most promising technologies for treating high salinity solutions with outstanding performance and energy conservation potential. This paper demonstrated the overall performance of mass transport and membrane resistance in electrodialysis for concentrating several high salinity solutions. The effects of various parameters on mass transfer performance and membrane resistance were examined. A simplified mathematical model for the characterization of mass transport and membrane resistance was developed. The initial concentration was found to play a dominant role in the salt transport and hydration number, whereas the current density, volume ratio and flow rate were negligible. A higher volume ratio and greater current density contributed to a greater maximum achievable concentration. In addition, the counter flow electrodialysis did not perform better than the parallel flow electrodialysis in experiments, likely caused by a non-uniform difference in pressure between the concentrated and diluted compartments. The initial concentration was also found to have a significant effect on the membrane resistance, which increased dramatically at an extremely high salt concentration probably due to the membrane shrinkage. Depending on the salt transport number, extractable water content and membrane resistance, appropriate concentration ranges of several high salinity solutions were suggested for electrodialysis concentration and desalination.
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