(388j) Capacitive Deionization of High-Salinity Solutions

Desalination of high salinity solutions has been studied using a novel experimental technique and a theoretical model. Neutron imaging has been employed to visualize lithium ions in mesoporous carbon materials, which are used as electrodes in capacitive deionization for water desalination. Experiments were conducted with a flow-through capacitive deionization cell designed for neutron imaging and with lithium chloride (⁶LiCl) as the electrolyte. Sequences of neutron images have been obtained at a relatively high concentration of lithium chloride (⁶LiCl) solution to provide information on the transport of ions within the electrodes.

A new model that computes the individual ionic concentration profiles inside mesoporous carbon electrodes has been used to simulate the capacitive deionization process. The volume averaging method has been used to derive the equations that simulate the charge-discharge process in mesoporous materials. An electroneutrality condition has been derived to relate concentrations and potential at the macroscopic scale. Ion-size based activity coefficients have been introduced into the simulation model to calculate results at moderate/high electrolyte concentrations. The model predicts ion distributions for a wide range of pore sizes and operating conditions.

Experimental data and simulation results provide insight into why capacitive deionization is less effective for desalination of high ionic-strength solutions. The combination of experimental information, obtained through neutron imaging, with the theoretical model will help in the design of capacitive deionization devices, which can improve the process for moderate/high ionic-strength solutions.