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• The effect of operating conditions on the desalination rate was studied. • Under various conditions, ion adsorption follows a quasi-first order kinetic model effectively. • MCDI outperforms other CDI methods in desalination rate and ion adsorption. • Optimal conditions: 1.6 V voltage, 30 mL/min flow rate, 1000 mg/L initial concentration. Membrane Capacitive Deionization (MCDI) is an efficient desalination technology using ion-selective membranes and capacitive principles to remove ions. Highly mineralized water flows through parallel electrode plates separated by ion-selective membranes. An applied electric field adsorbs ions onto electrodes, creating an electric double layer, and periodic field reversals release enriched ions back into the water while discharging ions on the electrode surfaces, enabling continuous deionization. This study aims to investigate the feasibility of using MCDI technology with Prussian blue analog (PBA)/carbon electrodes to treat highly mineralized water in oilfields. The desalination rate under different operating conditions is experimentally analyzed and compared. A comparison is made between the Capacitive De-Ionization (CDI) systems in terms of changes in conductivity, desalination rate, ion adsorption capacity, and ion adsorption rate. Results showed that compared to conventional CDI and Hybird-CDI (HCDI), MCDI demonstrates the highest desalination rate, ion adsorption capacity, and ion adsorption rate. It indicates that MCDI has significant advantages in treating highly mineralized water. At a voltage of 1.6 V, a flow rate of 30 mL·min−1, and an initial concentration of 1000 mg·L−1, the MCDI system exhibited the highest desalination efficiency. Under these conditions, the desalination rate was 43.4%, the electrosorption capacity was 54.75 mg·g−1, and the electrosorption rate was 0.018 mg·g−1·s−1. The study provides a viable solution for the treatment of highly mineralized water in oilfields and serves as a reference for further improvement and application of MCDI technology. [ABSTRACT FROM AUTHOR]

[Display omitted] • Divergent/convergent CDI cells are established and compared with straight ones. • The spacer geometry shifts the location of the initial adsorption and the depletion zone. • The channel slope mainly affects the desalination output rate. • Convergent channels show a faster ASAR than the regular straight geometry. • Steeper slopes give larger benefits. This research aims to explore the impact of tilted channel configurations of CDI cells on desalination performance. The results reveal that the titled convergent channels have a faster average salt adsorption rate (ASAR) than the regular straight geometry. For desalination operations that end at a quarter of the equilibrium salt adsorption capacity (SAC), the convergent spacer with a slight slope of 1.5 degrees has a 20 % higher ASAR than the typical straight geometry (0.15 mg/g/min for convergent and 0.12 mg/g/min for straight). This gain increases to about 24, 29.5, and 33%, respectively, for slopes of 3.5, 5.5, and 7 degrees, compared to the straight geometry with the same spacer thickness. By looking at the underlying mechanisms, the spacer geometry is found to shift the location of the initial adsorption. This affects how quickly the device outputs the cleaned water. Interestingly, the geometry angle can also affect the location of the depletion zone, so tilted spacers can also affect the behavior during electrode starvation. Specifically, the convergent geometry has the depletion zone in the middle of the electrode instead of the corner near the outlet, as seen for straight and divergent channels. Together, these findings indicate how to construct tilted spacers to enhance CDI performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cyclic voltammetry (CV) measurements were performed for the MCDI cell. • The potential of minimum charge (PMC) of the MCDI cell was measured as −0.22 V. • The desorption rate was not significantly affected by the desorption potential. • The water splitting reaction occurred at a desorption potential below the PMC value. • The optimal desorption potential was equivalent to the PMC value for stable and effective operation of the MCDI cell. The optimal desorption potential (DP) for maximizing the salt adsorption capacity of a carbon electrode while maintaining the stable operation of a membrane capacitive deionization (MCDI) cell was studied. Cyclic voltammetry (CV) measurements were performed for the MCDI unit cell. Additionally, the adsorption and desorption characteristics of the MCDI cell were analyzed while changing the DP. The potential at which the charges of the carbon electrode become the minimum was defined as the potential of minimum charge (PMC). The PMC value was measured as −0.22 V from the cyclic voltammogram. In addition, as the cell potential increased, the adsorption capacity of the carbon electrode increased. However, the effect of the DP on the desorption rate was negligible. In DPs below the PMC value, all adsorbed ions were desorbed, but the effluent pH rapidly decreased due to the occurrence of a water splitting reaction at the interface between the carbon electrode and the ion exchange membrane. When the DP was set as greater than the PMC value, some ions remained on the carbon electrode, resulting in a decrease in the amount of adsorbed ions during the subsequent adsorption process. When the DP was equivalent to the PMC value, the adsorption capacity of the carbon electrode was maximally utilized, and the pH of the effluent was maintained in a stable state. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) is an emerging technology for energy-efficient water desalination, and attracts more and more attention in recent years. It has been concluded that CDI technology shows competitiveness and perspectives on seawater desalination and wastewater treatment. The ionic adsorption mechanism can be clarified by electric double-layer capacitive adsorption and pseudocapacitive adsorption. The performance of CDI depends on both device and materials. The adsorption capacity and energy efficiency was improved significantly with fast growth of researches on material and novel energy storage techniques. This review summarizes researches on CDI technologies with an emphasis on electrode material design and improved adsorption performance. This review outlines the ion storage mechanisms and electrode materials of capacitive deionization. Unlabelled Image • Electrochemical extraction of ions from seawater/brine was reviewed systematically. • An emphasis on electrode material design thought has been analyzed. • The performance of various extraction devices has been summarized and compared. • Future challenge on this technology has been clarified. [ABSTRACT FROM AUTHOR]