The removal of chromium ions from water in Donnan dialysis process

摘要

The paper presents results of the studies on the removal of chromium ions (Cr2O72-) from multicomponent water solutions in the process of Donnan dialysis with anion-exchange membrane. The feeding solution contained the following salts: NaNO3, NaHCO3, NaCl (with a concentration of 3 mM for each component), and Na2Cr2O7 (with concentrations of 100, 300, or 500 mu g Cr(VI)/L). The Donnan dialysis process was conducted using a laboratory dialytic set-up equipped with 10 cell pairs with anion-exchange membranes, Selemion AMV (Asahi Glass, Japan) or Neosepta ACS (ASTOM Corp., Japan). The total working area of the membranes was 0.0756 m(2). NaCl solutions with concentrations of 100, 200, or 300 mM were used as receivers. The best effects of the anion exchange were obtained in the process with Selemion AMV membrane. Dichromate ions were efficiently removed from solutions with initial concentrations of 100 and 300 mu g Cr(VI)/L, at a relatively low salt concentration in the receiver equal to 100 mM NaCl. As a result of the anion exchange, chromium(VI) concentration was reduced to the value of 14 and 45 mu g Cr(VI)/L, respectively, that is, below the admissible value for potable water (50 mu g Cr(VI)/L). Mono-anion-selective membrane Neosepta ACS allowed to achieve satisfactory results of dichromate ion removal from the solution with a concentration of 100 mu g Cr(VI)/L - chromium(VI) concentration was reduced to the value of 13 mu g Cr(VI)/L (at the salt concentration of 100 mM NaCl). It should be underlined that for Neosepta ACS dichromate ions flux was three times lower than it was for Selemion AMV (0.030 x 10(-3) and 0.089 x 10(-3) mol/m(2) h, respectively). It standed for an adequately longer time of the anion exchange process with Neosepta ACS membrane.