A critical analysis on ion transport of organic acid mixture through an anion-exchange membrane during electrodialysis

The effect of the composition and pH of solutions on the transport of organic acids species in the anion exchange membrane (AEM) and adjacent diffusion layers has been investigated using voltamperomertry and chronopotentiometry. Carboxylic acids of varying number of carboxylic groups (acetic, malic and citric acid) were selected and their individual concentration in the mixture was varied to understand the influence of one molecule on the transport of other molecule in their mixture. Shape of the I–V and chronopotentiometric curves was influenced by pH and concentration. Detection of two limiting current densities (LCD) in I–V curves and inflection points in chronopotentiometric curves are due to change in species that are being transported in boundary layers and membrane. Results showed that LCD, resistance to ionic transport and concentration polarization were related to molar concentration and anionic equivalent charge calculated from Hydra-Medusa. Smaller size, higher mobility and charge density delayed the formation of concentration polarization. Electrolytes having ionic species with more anionic equivalent charge and larger Stokes radii were responsible for an early activation of overlimiting mechanisms and shorter plateau in I–V curve.