Enhanced Salt Removal by Unipolar Ion Conduction in Ion Concentration Polarization Desalination

Abstract

Chloride ion, the majority salt in nature, is ∼52% faster than sodium ion (DNa+ = 1.33, DCl− = 2.03[10−9m2s−1]). Yet, current electrochemical desalination technologies (e.g. electrodialysis) rely on bipolar ion conduction, removing one pair of the cation and the anion simultaneously. Here, we demonstrate that novel ion concentration polarization desalination can enhance salt removal under a given current by implementing unipolar ion conduction: conducting only cations (or anions) with the unipolar ion exchange membrane stack. Combining theoretical analysis, experiment, and numerical modeling, we elucidate that this enhanced salt removal can shift current utilization (ratio between desalted ions and ions conducted through electrodes) and corresponding energy efficiency by the factor ∼(D− − D+)/(D− + D+). Specifically for desalting NaCl, this enhancement of unipolar cation conduction saves power consumption by ∼50% in overlimiting regime, compared with conventional electrodialysis. Recognizing and utilizing differences between unipolar and bipolar ion conductions have significant implications not only on electromembrane desalination, but also energy harvesting applications (e.g. reverse electrodialysis).

Purification of High Salinity Brine by Multi-Stage Ion Concentration Polarization Desalination

“…Since majority of ions existed in salty water sources ( e.g. seawater, produced water) are sodium and chloride ( D Na +  = 1.33, D Cl−  = 2.03[10 −9  m 2  s −1 ]), ICP utilizing CEMs can enhance salt removal ratio up to 20% compared to electrodialysis under constant current applied, along with other advantages compared with related electrodialysis technique19. Motivated by this analysis, we continue to develop and customize ICP desalination for high salinity water treatment further.…”

Rapid pre‐concentration of Escherichia coli in a microfluidic paper‐based device using ion concentration polarization

“…And it is the amount of co‐ions repelled by the Nafion ® membrane that defines the depletion of ions/charged particles in the system. Hence, as we increase the concentration of NaCl where E. coli is suspended, the pre‐concentration of E. coli happens faster .…”

Spatial distribution of mechanical forces and ionic flux in electro-kinetic instability near a permselective membrane

“…Ionic transport in the presence of a charged wall is used in numerous applications such as electro-dialysis, fuel cells, micro-mixers, biochemical analysis, etc. [1][2][3][4] In microand nano-technologies, electro-kinetic mechanisms, such as electro-osmosis and electro-convective instability, play a role all the more important that the specific surface is important and the Debye length to the characteristic length ratio is not so small, i.e., the volume where the electro-neutrality is not fulfilled cannot be neglected.…”

“…Direct numerical simulations are also used in the chemical engineering context. Kwak et al 2,17 and Urtenov et al 38 studied the electro-convective instability in the case of a pressure driven shear flow between two ion-exchange membranes. A scaling of the vortex size and of the vortex advection speed was found, and several modes of instability have been investigated by chrono-potentiometry from the Dukhin-Mishchuk mode to the unsteady Rubinstein-Zaltzman one.…”