Assessing the Effects of Specific and Electro-Induced Sorption in an Asymmetric Capacitive Deionization Device Operating in Continuous Cycles
Previous testing of this CDI system in a “Single Pass” (passing the water through the device only once) operational mode using a CaSO4 solution showed reductions in both Ca2+ and SO42- concentrations . However, issues related with ion desorption and faradaic reactions (due to high cell potentials) were also observed. In this work, cycles of consecutive adsorption/desorption tests were performed to evaluate the long-term performance of this CDI system. Ion sorption and electrode stability were analyzed in terms of variables such as influent concentration, flow rate, and regeneration potential. These analyses also included performance metrics related with charge efficiency and energy consumption. For comparison purposes, CDI cells with uncoated carbon electrodes were evaluated following similar protocols.
The results showed that increasing the concentration of CaSO4 in the feed solution (from 1.5 to 4.5 mM) increased the ion removal to values up to 3.29 ± 0.25 mg·g-1 and reduced energy consumption from 0.16 down to 0.09 kWh·mol-1. It was also observed that electric charge efficiencies increased by 15-30 % when asymmetrically coated configurations were employed. Nevertheless, the presence of SO42- significantly hindered salt desorption; conversely, recovery values close to 95 % were achieved using NaCl electrolyte. Finally, the evaluation of the long-term CDI performance revealed a slight but progressive loss in the ion electrosorption capability, probably due to the oxidation of the positive electrodes.
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