The schematic diagram of the expected ion exchange mechanism under the above mentioned conditions, in the simplest form, is represented in Fig. 4. The chemical reactions involved in the present systems first takes place at the interface between NH4+ and Nd3+ adsorption bands. When (NH4) n-Ligand reached the rear boundary of Nd3+ adsorption band, the ligands are transferred to Nd3+ because of the large stability constant of the Nd-Ligand complex compared to that of ammonium ion-Ligand complex. During the moving down of the solution phase, which contains Nd-Ligand complex species through the Nd3+ adsorption band in the column, the isotopic exchange reaction takes place between Nd3+ ions in the resin phase and Nd-Ligand complex species in the solution phase. After that the Nd-Ligand complex reaches the Cu2+ ion band, where ligand are transferred to Cu2+ ions and Nd3+ ions are adsorbed in the resin phase. The related chemical reactions for the three types of carboxylic acids, mono-basic (glycolate), di-basic (malate) and tri-basic (citrate) ligands can be expressed, in the simplest form, as: