イオン交膜面付着物層内における濃度分極 Concentration Polarization in the Substance Layer Attached to an Ion Exchange Membrane
In order to prevent fouling of ion exchange membranes, the ionic transport and concentration polarization in the substance layer attached to the membrane surface was analyzed in an NaCl solution using the extended Nernst-Planck equation. The ionic diffusion coefficient in a non-infinitely diluted region withn the layer was obtained ushlg the diffusion coefficient equation taken from the Nernst-Einstein equation, and the same coefficient in an infinitely diluted region was expressed using the values in the infinitely diuted region. When the NaCl concentration in the substance layer is increased in the non-infinitely diluted region, the ionic concentration change is expressed linearly. This is because the effbct of convection on the ionic transport is neghgible. When the NaCl concentration is reduced in the non-infinitely diluted region, the ionic concentration is expressed by a curved line and the concentration polarization is moderated to some extent. This is because of the increase in the ionic diffusion codfficient in the low NaCl concentration. In the infinitely diluted region, the ionic diffhsion coefficient being co nstant, the concentration polarization is promoted by the sharp linear decrease of the NaCl concentration neaf the membrane surface. Accordingly, the possibility of trouble occurrhlg, such as water dissociation, increases as a result of the formation of the infinitely diluted region. The concentration polarization is promoted in the substance Iayer because the convection is less and the effect of the 3rd term (convection term) in the extended Nernst-Planck equation decreases. The convection in the layeroccur only as a result of the electro-osmotic flow and convection diffbrence osmotic flow in the membranes. It is important to remove the substance layer attached to the membrane surface in the electrodialysis, because of the cel voltage increase Qwing to the promotion of concentration polarization.
日本海水学会誌 51(4), 228-236, 1997-09-01