Abstract
For the both purposes of improving the efficiency and preventing the deposition of scales, the ion exchange membrane used for sea water concentration undergoes in most cases a treatment which gives it permselectivity among counter-ions (the permselectivity treatment).
However, it has less effectiveness in decreasing the permeability of total carbonates (CO2+HCO3-+CO3-) through anion exchange membranes treated under general conditions of sea water concentration. In the process of the permselectivity treatment, the permeability of sulfate ion showed a gradual decline, but the permeability of the total carbonates was kept almost unchanged. This was due to the fact that most of the total carbonates migrated through the membrane as univalent hydrogen carbonate ion under the general conditions. At higher pH, on the other hand, divalent carbonate ion became dominant form, promoting the effect of the permselectivity treatment prominently. Therefore, the effect of the permselectivity treatment was considered to depend upon the valencies of migrating ions. At pH<2, the permeability of total sulfates (HSO4-+SO4-) showed a rise because appreciable part of sulfate became hydrogen sulfate form.
Therefore, much attention is paid when acidified sea water is concentrated.
