A modified anion-exchange membrane applied to purification of effluent containing different anions. Pre-treatment before desalination

Previous works have been made on the improvement of selectivity of ion-exchange membranes using organic macrocation adsorbant on the surface of the materials. The formation of a smooth layer on the surface of an ionexchange membrane plays a role of a repulsive barrier towards ions of high valences. The modification of the surface material in the case of an anion-exchange membrane concerns the hydrophilic/hydrophobic balance properties and its relationship with the hydration state. Starting from this goal, an anion-exchange membrane has been modified by adsorption of branched polyethyleneimine. This modification permits to achieve separation and concentration of sulfuric, nitric and hydrochloric acids from acidic effluents which are rejected generally in the sea and may affect the efficiency of the desalination process. The low selectivity obtained towards SO42− anion allowed separation with nitrate and chloride anions in electrodialysis. A commercial anion-exchange membrane ARA favoured the transfer of monovalent acids. The transference of the three acids follow the sequence HNO3 > HCl > H2SO4. However, an increase of concentration of the initial acid leads to its decrease in an anodic compartment. This is due to a leakage of protons in the opposite direction of anions. The modification of the anion-exchange membrane leads to a reduction of transfer of divalent anions and thus to acidity. On the other hand, the higher the concentration of acid, the lower the transference number of anions.