A Ion Exchange Isotope Separation
The isotope effect in ion exchange process was first observed by Taylor and Urey. They found that the isotopic abundance ratios of lithium, potassium, and nitrogen were changed when lithium, potassium, and ammonium ions were eluted from inorganic ion exchanger "zeolite" packed in a stainless steel pipe.79 Isotope effects of lithium were intensively studied by Lee, Begun, and Drury by using organic cation exchange resin.80-82 They determined single stage separation factors of lithium isotopes between the phases of an aqueous solution and synthetic cation exchange resin at different experimental conditions of temperature, concentration of eluent, crosslinking and functional groups of resin, etc.
Ion exchange was applied for nitrogen isotope separation by Spedding et al. They were successful in enrichment of 15N and obtained highly enriched 15N starting from natural abundance of 0.366% by ion exchange chromatography.83 Since then several works have been carried out on nitrogen isotope separation by cation exchange resins. The observed single stage separation factor of the NH3-NH^ system is in the range 1.020 ~ 1.025. The experimentally determined isotope separation factor arises from the equilibrium constant of the following isotopic exchange reaction
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