Effect of the equilibria of multivalent metal sulfates on the transport through cation-exchange membranes at different current regimes

Ion transport through homogeneous and heterogeneous ion-exchange membranes in single salt and multicomponent electrolyte solutions

“…The voltage remaining after switching off the current and the slow restoration of the membrane potential is characteristic of bipolar membranes and has been attributed to the recombination of water dissociation products [23,24]. Moreover, this characteristic has also been reported for monopolar membranes when a layer of precipitates is formed at the membrane surface, a quasi-bipolar structure is developed and the dissociation of water is catalyzed by the deposited metal hydroxides [25,26].…”

“…In connection with the atypical response observed for both membranes with solutions of Fe(III), it has to be noted that the shape of the chronopotentiograms obtained in a previous study for the Nafion membrane with solutions of Fe(III) was significantly dependent on the initial salt concentration [25]. Therefore, in order to confirm that this difference is originated from the characteristics of the electrolyte, additional experiments were conducted with 0.001M Fe 2 (SO 4 ) 3 .…”

Sulfuric acid recovery from acid mine drainage by means of electrodialysis

“…Therefore, as the concentration in the depleting compartment decreases, the i lim of the CEM could diminish up to the point of reaching the same value as the applied current [24]. At this moment, the formation of Fe(OH) 3 precipitates at the anodic surface of a cationic membrane can be enhanced, thus acting as a blocking mechanism for the ionic transfer through the membrane [26,27]. The precipitates formed under the conditions of 15 mA·cm -2 were observed at the anodic side of the CEM at the end of the experiments.…”

“…In addition, the specific energy consumption per each kg of SO 4 2-ions recovered in the anolyte (E s ) was also calculated using Eq. (26).…”

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

“…In addition to membrane surface properties, the type of electrolyte has been also demonstrated to be an influencing parameter in the early onset and intensification of electroconvection. Several researchers have concluded from experimental studies that multivalent ions with larger Stokes radii are able to create larger vortices and boost electroconvection [13][14][15]. However, these ions also entail an additional complexity, since they can appear as free ions or combined in the form of complex species.…”