Aqueous solutions of polyethylenimines (PEI) are usually used in the manufacture process of paper from pulps to improve the physical strength, and the ink and coatings fixation and to facilitate the printing. When PEI is used as a liquid cationic flocculant in water treatment it is supplied as a cheaper hydrochloride salt. The hydrochloride salt form is easier to handle and may be converted into the free amine form for adhesive purposes by some separation processes. Ion exchange is one of the easiest and cheapest ways to remove chlorides from different aqueous solutions. The strongly basic ion exchanger Amberlite IRA-420 has demonstrated that it can be used for chloride removal. The equilibrium isotherms of chloride ions i PEI-HCl at 20 and 40 degrees C, and NaCl and HCl at 30 degrees C in aqueous solution on Amberlite IRA-420 have been obtained. The presence of HPEI+ as coion exerts an important influence on the ion exchange equilibrium. This behavior can be explained by the competition between the protonated amine groups of PEI and the quaternary groups of the resin for the chloride ions that tends to promote a slightly non-favorable equilibrium. In the same way, the kinetic studies indicated that the chloride ions are slowly removed in presence of polyethylenimine. Finally, the Nernst-Planck homogeneous model allowed obtaining the self-diffusion coefficients for both the chloride and hydroxide ions in the Amberlite IRA-420 and the values are in the same order of magnitude as those reported in the literature. (C) 2008 Elsevier Ltd. All rights reserved.