Formation mechanism of iron scale in membrane capacitive deionization (MCDI) system

Abstract In this study, we investigated the scaling behaviors of Fe in the membrane capacitive deionization (MCDI) systems through batch experiments. By analyzing the migration and transformation of Fe in the MCDI system, it was found that Fe scale was deposited on the ion exchange membrane rather than on the electrode. The characterizations of Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) showed that the FeOOH formed in the solution deposited on the anion exchange membrane, while the iron scale on the cation exchange membrane was mainly Fe2O3. In the presence of 1 mg/L iron ions, the amount of iron ions adsorbed by the MCDI system was about 25% less than that by the capacitive deionization (CDI). However, at 10 mg/L iron ions, the amount of iron ions absorbed by the MCDI system was almost twice that by the CDI system. This was because that the high concentration of iron ions produced a large number of yellow flocs which were adsorbed by the cation exchange membrane. Ion exchange membrane increased the adsorption capacity of the CDI system, but it did not alleviate the scaling caused by Fe.