Characterization of Ion Transport and -Sorption in a Carbon Based Porous Electrode for Desalination Purposes

Abstract

New and more efficient water desalination technologies have been a topic of incipient research over the past few decades. Although much of the attention and efforts have focused on the improvement of membrane-based desalination methods such as reverse osmosis, the development of new high-surface area carbon-based-electrode materials have brought substantial interest towards capacitive deionization (CDI), a novel technique that uses electric fields to separate the ionic species from the water. Part of the new interest on CDI is its ability to store and return a fraction of the energy used in the desalination process. This characteristic is not common to other electric-field-based desalination methods such as electro-deionization (EDI) and electro-dialysis reversal (EDR) where none of the input energy is recoverable. This paper presents work conducted to analyze the energy recovery, thermodynamic efficiency, and ionic adsorption/desorption rates in a CDI cell using different salt concentration solutions and various flow-rates. Voltage and electrical current measurements are conducted during the desalination and porous electrode regeneration processes and used to evaluate the percentage of energy recovery.. Salinity measurements of the inflow and outflow stream concentrations using conductivity probes, alongside the current measurements, are used to calculate ion adsorption/desorption efficiencies. Correlation of these measurements with an analytical species transport model provides information about the net ionic adsorption/desorption rates in non-saturated-carbon-electrode scenarios. The results show a strong dependence of the net electrical energy requirements with the number of carbon electrodes regeneration cycles. Finally, a non-dimensional number that compares the convective and electro-kinetic transport times is presented. The energy requirements and adsorption/desorption rates analyses conducted for this water-desalination process could be extended to other ion-adsorption applications such as the re-process of spent nuclear fuels in a near future.

Cadmium Removal From Aqueous Solution by Capacitive Deionization with Nano - Porous Carbon Electrodes

“…Various treatment processes such as adsorption, biosorption, ion exchange and electrochemical cadmium from aqueous waste streams. Capacitive deionization or otherwise called electrosorption is an electrochemical ion collection/discharge process which relies on the formation of double-layer supercapacitors at the solution /electrode interface [3][4][5][6]. When an electric field is applied between two carbon aerogel electrodes, cations and anions are held in the electric double-layers formed at the cathode and anode surface respectively.…”

Macro Analysis of the Electro-Adsorption Process in Low Concentration NaCl Solutions for Water Desalination Applications

“…1,8,[12][13][14] More specifically published papers on CDI assume an ideally stirred solution within a unit cell 9 or approximate important parameters (such as Stern capacitance, a transport coefficient, or a chemical attraction energy) by best fitting z E-mail: hidrovo@mail.utexas.edu the temporal variation of the outlet solution concentration obtained from the compilation of a full desalination-regeneration cycle. [9][10][11]15 This procedure however, might provide misleading estimates because the temporal variation of outlet solution conductivity is sensitive to a diverse range of variables such as the inclusion of remnant ions from previous desalination cycles during regeneration, 16,17 the state of the electrodes, 18,19 and the sensitivity of the conductivity probes employed. Additionally, there is a large sensitivity of the outlet conductivity profile to the solution flow rate, as this paper will show.…”