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In the progress of integrating alkaline recovery of valuable metals from the waste catalyst and the regeneration of alkali liquor by electro-dialysis processes, the back-diffusion of anions through the cation-exchange membrane is one of the key issues that limit the effect of electro-dialysis. Parameters of current efficiency and desalination rate reveal that the back-diffusion quantity of hydroxide ions (OH–) enhanced along with the change of cathode: anode sodium concentration ratio. The presence of CO2can decrease the back-diffusion quantity of OH–owe to OH–had been transformed into carbonate ions (CO32–). Ionic coefficient also showed that their ionic concentration difference in concentration polarization layers. Therefore, the back-diffusion of CO32–is more difficult than OH–because of their different interactions with the functional groups of membrane. Different back- diffusion quantity of two anions (OH–and CO32–) through cation-exchange membrane may be owe to their different ionic diffusion capacity and interactions with the functional groups of membrane.