Use of response surface methodology for optimization of thorium(IV) removal from aqueous solutions by electrodeionization (EDI)

In this research, the thorium(IV) removal from the aqueous solution was conducted by electrodeionization (EDI). Thorium(IV) removal experiments with EDI are designed using RSM based on CCD, and three independent variables were scrutinized, including applied voltage (X-1), flow rate (X-2), and thorium(IV) concentration (X-3). A quadratic model with R-2 equal to 0.9825 was the best model for the analysis of variance, which was in a good agreement with experimental results. The X1X2 did have a significant effect, and other interactions had an insignificant effect. The optimal values of voltage, flow rate, and thorium(IV) concentration were obtained 9.8 V, 3.4 mL min(-1), and 63.1 mg L-1, respectively. In these conditions, the thorium(IV) removal was 99.06%, which was 0.31% different from the software prediction. The EDI efficiency was evaluated by calculating the current efficiency, mass flux and mass transfer coefficient. The results showed that the flow rate increment has a more significant effect on the increase of the mass flux and mass transfer coefficient than the impact of the voltage increases. Thorium(IV) removal with different resin configuration was as follow: layered < mixed < only cationic resin. EDI and electrodialysis comparisons showed that with EDI, thorium(IV) removal increased by more than 35%. Through this study, the desirable removal of thorium(IV) was achieved by EDI.