Capacitive deionization(CDI)

Ionic particles transport - Water desalination

Capacitive deionization(CDI) is a novel desalination method with the potential to return a fraction of the input energy during the system regeneration. Capacitive deionization itself is an electro-adsorption process that is conducted in two stages: desalination and regeneration. During the desalination, an electric field is sustained between two high surface carbon electrodes pulling their respective counter ions towards them and out of the stream solution. The adsorbed ions are retained in the electrodes' surface and the salinity of the solution is lowered until the saturation of the adsorbing surfaces. Once the carbon aerogel has been saturated, it is possible to return the aerogel to an unsaturated state by removing the sustained electric field or inversing the polarity of the electrodes in a process called regeneration. The expulsion of the majority of ions to the solution stream leads to the return of energy from the CDI cell lowering the overall energy expenditure required in the system. Figure 1 shows a schematic of the desalination and regeneration processes in a flow-through CDI cell.

Our research objective is to understand the ionic transport and adsorption kinetics that occur in a CDI system to improve its overall performance and investigate other potential applications of electro-adsorption processes such as wastewater treatment and spent nuclear fuel reprocessing. To do so, a laboratory scale CDI system has been designed and built at the MTFL lab. Figure 2 shows a picture and schematic of the current experimental set-up. Current lab capabilities allow us to investigate long-term steady state tests and short-term transient tests to determine both, the adsorption rate and its capacity for different operational conditions. Figure 3 shows the characteristic conductivity and current of long-term desalination experiments.

It is also well known that electrochemical techniques such as DC voltammetry and impedance analysis can be used to characterize materials as potential electrodes in this type of system. Our laboratory counts with cutting-edge technology equipment to perform these type of tests. Figure 4 presents the Nyquist plot from an EIS analysis of a porous material under investigation. Both, desalination experiments and EIS tests would be combined to gain a deeper understanding of the ionic transport and adsorption kinetics occurring in a CDI system.