Effect of ionic strength on the ion exchange equilibrium between AMX membrane and electrolyte solutions

Abstract

The effect of ionic strength variation on the ion exchange equilibrium between AMX anion exchange membrane and electrolyte solutions containing the most dominant anions on natural waters (Cl−, NO3−, and SO42−) was studied. All experiments were carried out at a constant temperature of 25 °C. Ion exchange isotherms were established, at different ionic strengths from 0.1 to 0.5 M, for the systems (Cl−/NO3−), (Cl−/SO42−) and (NO3−/SO42−). Obtained results showed that for I = 0.1 M the affinity order is SO42 −>NO3−>Cl−. For I = 0.2 M this order is NO3−>SO42−>Cl−. For 0.3 and 0.5 M the AMX membrane becomes more selective for chloride than for nitrate or sulfate. Selectivity coefficients KNO3−Cl−, K2Cl−SO42− and K2NO3−SO42−, thermodynamic constants, and separation factors were calculated and decreased with the increase of ionic strength.

Ceramic thin-film composite membranes with tunable subnanometer pores for molecular sieving

“…This observed dependence of ion-ion selectivity on the pore size is different from our expectation, where a monotonic increase of the selectivity should be obtained with enhanced confinement (i.e., with smaller pore size) due to the higher extent of ion dehydration. Considering that SO 4 2− and Cl − ions have respectively hydrated diameters of 7.6 and 6.6 Å 44,45 , this observed selectivity trend suggests that the state of hydration/dehydration, rather than the extent of dehydration (i.e., the number of surrounded H 2 O molecules lost), plays the predominant role in determining the selective ion transport (Fig. 3e) 46 .…”

Study of Polyaniline/Poly(Sodium 4-Styrenesulfonate) Composite Deposits Using an Electrochemical Quartz Crystal Microbalance for the Modification of a Commercial Anion Exchange Membrane

“…Among the most important characteristics that ion exchange membranes must have, for a successful application, are adequate selectivity and/or resistance to biofueling, for example, for ions of similar charge and size or for bacteria to be present in the solution [1]. In the literature, several different approaches exist to handle these disadvantages that are a feature of membranes [1][2][3][4][5][6]. For example, one approach is to produce a novel membrane with suitable selective properties; however, this is a complex multistep process [7][8][9].…”

“…For example, one approach is to produce a novel membrane with suitable selective properties; however, this is a complex multistep process [7][8][9]. Another approach consists of modifying a characteristic of a commercial membrane [4][5][6]. This method is less expensive, since the membranes conserve most of their transport properties and only the properties related to selectivity or resistance to fouling change.…”