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 KNO3Cl, K2ClSO42− and K2NO3SO42−, thermodynamic constants, and separation factors were calculated and decreased with the increase of ionic strength.

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