Transport selectivity of carbonate and chloride ions througha strongly alkaline anion-exchange membrane before and after its modification with sodium alginate

The transport selectivity of carbonate ions relative to chloride ions (left( {P_{Cl^ - }^{CO_3^{2 - } } } right)) through an anion-exchange membrane during electrodialysis is investigated before and after the membrane was modified by the electrolytic precipitation of sodium alginate on its surface, as well as by pretreating the membrane in a solution of sodium alginate. It is established that the experimental value of (P_{Cl^ - }^{CO_3^{2 - } } ) is appreciably smaller than the calculated value for the unmodified membrane at low values of current density. At large currents the calculated value of (P_{Cl^ - }^{CO_3^{2 - } } ) is 0.83, and the experimental value is 0.64. During electrodialysis of the working solution, which contains sodium alginate at a concentration of 1–2 g l^?1, (P_{Cl^ - }^{CO_3^{2 - } } ) decreases by 2–3 times in the current-density range 0.25–1 A dm^?2. Pretreatment of the membrane in a solution of sodium alginate having a concentration of 10 g l^?1 for 72 h decreases (P_{Cl^ - }^{CO_3^{2 - } } ) from 0.50 (unmodified membrane) to 0.35.