ELECTRODIALYSIS OF AMMONIUM SULFATE SOLUTIONS: EXPERIMENTAL STUDY AND MATHEMATICAL MODELLING

The kinetic experimental study was carried out on a laboratory-scale electrodialysis (ED) unit of TS2-5 type from Eurodia-Tokuyama equipped with five cell pairs. The membranes used were the AMX type anion exchange membranes (AEM) and CMS type cation exchange membranes (CEM), each of 0.02 m(2) surface area. The feed was an aqueous ammonium sulfate solution with molar concentrations of 88 to 92 mol/m(3). The evolution with time of the solution concentration in both dilute and concentrate compartments has been determined for two feed rates and four voltages, at a 303 K constant temperature. A mathematical model has been derived to describe the concentration evolution with time. The model includes two empirical constants a and b. The constants have been identified by confronting the computed data with the experimental ones. The validated model has been finally used to extrapolate the ED process in order to determine the necessary time for a practically maximal removal of ammonium sulfate. This is equivalent to a final dilute concentration of less than 1.5 mol/m(3).