A transport mathematical model to describe the performance of ion exchange processes in fixed beds, to use the regeneration curves as a tool to optimize the regeneration process was developed. The model is based on both the Nernst-Planck equation and the mass action law. This model allowed to obtain the optimum amount of regenerant agent to be used, regardless the system considered. Therefore, it would be possible to minimize the final waste volume and maximize the recovered bed capacity without any additional consumption of regenerant agent. The results obtained allowed to conclude that the sodium chloride is better regenerant agent than chlorhydric acid for strong acid resins, because it requires a lower amount of equivalents to reach the same regeneration level and is cheaper. Finally, the concentration of regenerant agent required for copper elation is less than that required for the other ions (Cd2+ and Zn2+). These results were found to agree with the affinity of the resin. (c) 2005 Elsevier B.V. All rights reserved.