**2. Ion exchange system**

Enriched stable isotopes of many elements have been widely used in agriculture, medicine, biochemistry and industry, especially in nuclear industry. Such isotopes have been primarily used as the tracer for agricultural and biochemical studies and the availability of the isotopically labeled compounds have been now extensively increasing. In order to meet the demand, the need of developing a practical cost-effective process has been enlarged. The most heavy stable isotopes are produced in relatively small quantities, many light isotopes

© 2012 Ding and Liu, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Ding and Liu, licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

are used in large quantities. Distillation is used in industry to separation the isotopes of hydrogen, carbon, boron, nitrogen and oxygen. Chemical exchange is the satisfactory technique for separating isotopes of light elements because of their relatively high simple process factors (separation factors).

Chemical exchange separation of isotopes is based on the equilibrium fractionation of isotopes between two phases, i.e. one of the isotopes is concentrated more abundantly in one of the phases than in the other phase if two chemical species are distributed in each phase. In this method, the enrichment of the isotopes concerned is achieved when the simple process of isotope separation is multiplied, by arranging the countercurrent contacting of two substances. The countercurrent contacting of the two different chemical substances is most easily realized in vapor-liquid or liquid-liquid system. The contacting takes place in conventional systems such as packed columns, mixer-settlers, etc. In this process it is necessary to provide reflux at the product end of a chemical exchange plant; the end which the desired isotope being enriched. In general, chemical refluxing is used to complete the conversion of one chemical species into the other at the end of the multi-stage contactor system.

Ion exchange isotope separation, which is one of the chemical exchange methods, is based on the chemical equilibrium between a stationary phase and a mobile fluid phase. In the past, many researchers have studied isotope fractionation on the isotopes both for light and heavy elements in this liquid solid system[1-5] and several isotopes especially for nitrogen isotope have been successfully enriched in laboratory scale by using displacement chromatographic technique [6, 7]. In this process a band of adsorbate is eluted through the column by a displacing solution, which the rate of movement of the band is determined by the equilibrium between solution and adsorbent, not of the material of the band but of the displacing adsorbate. Displacement always results in a sharp boundary between the bands of eluted solution and displacing solution. Thus, the adsorption band moves with keeping a constant band length. During the migration the isotopes in the band are rearranged in order of the distribution coefficients.
