Mass Transfer Phenomena during Electrodialysis of Multivalent Ions: Chemical Equilibria and Overlimiting Currents

Abstract

Electrodialysis is utilized for the deionization of saline streams, usually formed by strong electrolytes. Recently, interest in new applications involving the transport of weak electrolytes through ion-exchange membranes has increased. Clear examples of such applications are the recovery of valuable metal ions from industrial effluents, such as electronic wastes or mining industries. Weak electrolytes give rise to a variety of ions with different valence, charge sign and transport properties. Moreover, development of concentration polarization under the application of an electric field promotes changes in the chemical equilibrium, thus making more complex understanding of mass transfer phenomena in such systems. This investigation presents a set of experiments conducted with salts of multivalent metals with the aim to provide better understanding on the involved mass transfer phenomena. Chronopotentiometric experiments and current-voltage characteristics confirm that shifts in chemical equilibria can take place simultaneous to the activation of overlimiting mass transfer mechanisms, that is, electroconvection and water dissociation. Electroconvection has been proven to affect the type of precipitates formed at the membrane surface thus suppressing the simultaneous dissociation of water. For some electrolytes, shifts in the chemical equilibria forced by an imposed electric field generate new charge carriers at specific current regimes, thus reducing the system resistance.

A protocol for quantifying mono- and polysaccharides in seawater and related saline matrices by electro-dialysis (ED) – combined with HPAEC-PAD

“…The majority of organic matter (OM) in oceanic seawater can be assigned to the chemical classes of proteinogenic amino acids, carbohydrates and lipids (Benner and Kaiser, 2003;Kaiser and Benner, 2009;Kuznetsova and Lee, 2002;Marty et al, 1979;Skoog et al, 1999;Wakeham et al, 1997). Previous studies uncovered that combined amino acids are the most abundant organic substances in fresh particles sinking within the water column (Wakeham et al, 1997), although more recent studies indicate that carbohydrates may be equally abundant (Cisternas-Novoa et al, 2019), while hydrolyzable carbohydrates dominate the chemical composition of dissolved organic matter (DOM) (Kaiser and Benner, 2009;McCarthy et al, 1996).…”

A protocol for quantifying mono- and polysaccharides in seawater and related saline matrices by electro-dialysis (ED) – combined to HPAEC-PAD

“…Previous studies explained these unfavorable changes of pH by a strong concentration polarization at the membranes surface leading to water splitting to H + and OHions, when a certain limiting current is exceeded. This phenomenon has been preferably observed at anion exchange membranes with quaternary amino groups in the presence of divalent cations, such as Mg 2+ and Ca 2+ (Cowan, 1962;Martí-Calatayud et al, 2018;Ottosen et al, 2000). The described phenomena exclusively occurred when (synthetic) seawater was desalinated and not during the desalination of NaCl standard solutions.…”

Electrodialysis Applications in Wastewater Treatment for Environmental Protection and Resources Recovery: A Systematic Review on Progress and Perspectives

“…Several studies have focussed on transport phenomena by assessing IEMs properties, pH effect, complexes formation and ions competition, and by developing modified or novel IEMs. Among them, experiments with aqueous solutions of Ni [ 153 , 154 , 155 , 156 , 157 ], Cu [ 158 , 159 , 160 , 161 , 162 ], Zn [ 157 , 163 , 164 ], Cr [ 154 , 156 , 165 , 166 , 167 , 168 , 169 , 170 ], Fe [ 154 , 156 ] and Pb [ 155 , 157 ] have been conducted, as well as with mixtures (e.g., Ni, Cu and Pb, or Cu and Zn) [ 171 , 172 ], thus providing important insights on basic phenomena and ED processes. Another crucial aspect is the identification of optimal operative conditions.…”