Theory of Isotope Separation in Counter-Current Columns: Review

This chapter discusses the theory of isotope separation in counter-current columns. Isotope separation in two-phase systems is based on the thermodynamic isotope effect (TDIE), the value of which is conventionally determined by the separation factor of a binary isotopic mixture. In chemical isotope exchange (CHEX) the aggregative states of working substances (X-material and Y-material) are either the same or different, and phase isotope exchange (PHEX) occurs among the molecules of only one material, forming a two-phase system. The values of the separation factor and equilibrium constant coincide only in the event of isotope exchange among molecules with only one exchangeable isotopic atom per molecule, as well as in the case of CHEX reactions of one atom. A peculiarity of heterogeneous systems is that several isotope exchange processes occur here simultaneously. It is found that of wide occurrence are the CHEX reactions between gases and liquids, complicated by either PHEX reactions between a gaseous phase substance and its liquid solution, or PHEX reactions between a liquid and its vapor in the gaseous phase. The kinetics of CHEX reactions and mass exchange in counter-current phase movement is also elaborated.