Electro-adsorption characteristics and mechanism of Sr2+ ions by capacitive deionization and CFD analysis study

The electro-adsorption characteristics and mechanism of Sr2+ ions by capacitive deionization (CDI) with activated carbon cloth/graphene oxide (ACC/GO) composite electrode were studied. The influence of initial concentration, applied voltage, and co-existing ion on Sr2+ removal was examined. The kinetic, isotherms, and mass transfer models as well as various surface characterization methods were employed to study the adsorption mechanism, and the computational fluid dynamics (CFD) was used to analyze the hydrodynamic performance of CDI process. The results showed that the removal efficiency of Sr2+ significantly increased from 11.38 to 41.45% when applied voltage increased from 0 to 1.2 V. The co-existing ions (Co2+ and Cs+) and increasing initial concentration of Sr2+ solution obviously reduced the removal efficiency. The PFO model could fit the experimental value better. The Freundlich model could better describe the adsorption isotherm with the highest R2 values (0.9589). The transfer of Sr2+ to active sites was the rate-limiting step based on mass transfer models. CFD analysis of circular CDI channel indicated that increasing flow rate could effectively decrease the stagnant zone, and suitable flow rate was 10 mL min−1 in this study. The adsorption mechanism of Sr2+ by CDI process included not only electro-adsorption but also non-electrostatic interaction adsorption, such as surface complexation and ion exchange.