Insight into the scaling behavior of capacitive deionization for the removal of multiple cation components in the single-pass mode

Abstract

Capacitive deionization (CDI) can effectively remove various ions in seawater and brackish water. However, due to the complex cation components in natural water, the desalination stability of CDI is challenged by cation scaling. In this study, the scaling behavior of CDI for the removal of multiple cation components in the single-pass mode was investigated. Three feed solutions containing various compositions (FS1 for Na+, FS2 for Na+/Ca2+/Mg2+, and FS3 for Na+/Ca/Mg2+/Fe3+) were tested. The results showed that the desalination stability was affected by cation components. Especially, the salt adsorption capacity for FS3 dramatically decreased from 7.16 to 3.53 mg/g over multiple cycles. Characterization demonstrated that the scaling of Ca and Mg for FS2 was slight while the scaling of Fe for FS3 was noticeable. Additionally, compared to FS2 scale, Fe significantly aggravated the scaling of Ca and Mg. The severe scaling behavior led to a decrease in specific capacitance, and an increase in charge transfer resistance and ion diffusion resistance of CDI electrodes. Finally, the correlation between scaling behavior and Faradaic reactions was comprehensively explored. The study provides insight into the scaling behavior of CDI, which is crucial for desalination stability in actual operation.