Isotope electromigration

The progress achieved in the field of isotope electromigration in metals, salts, and aqueous solutions since the meeting on isotope separation in Paris in 1963 is reported. It is shown that the temperature dependence of the isotope effect in liquid metals leads to the conclusion that it is a result of classical atom—atom interactions. Isotope effects in molten salts are smaller than in classical ionic gases. A three stage model is proposed for an explanation of the temperature dependences of the isotope effects in molten salts. The available data of the relative difference in mobilities of isotopes in aqueous solutions are summarized. 

The internal transport numbers may be measured most accurately and precisely by the Klemm method, which was developed for the purpose of isotope separation. This method has the following merits (1) It is insensitive to a small amount of impurities, such as water. (2) Even in the region of very small concentration of an ion of interest, 12 can be measured accurately. (3) It can be applied to additive ternary systems. An apparatus for the Klemm method of measuring 12 in nitrate mixtures is shown in Fig. I. This cell developed for nitrates by Okada s group has the following advantages compared with other electromigration cells ... 

Phenomenologically the mass effect of electromigration can be written, in a linear approximation in relative isotopic differences, as (25)... 

In the last few years isotope separation in aqueous solutions by counter-current electromigration has found renewed interest. The reason for this renaissance is the hope that isotope effects in dissociation equilibria might substantially increase the effective relative difference in mobilities and make aqueous solutions a medium for a successful separation of isotopes. In this review we have summarized the available relevant data. 

In liquid salts the isotope factor is in principle measurable by electrotransport (electromigration). Since many such measurements are available (13), it is especially tempting to study thermotransport in molten ionic media. One must bear in mind, however, the possibility of the following complications (a) the mechanisms of electrotransport, thermotransport, and self-diffusion may be non-identical see Reference 16) b) the isotope factors, as determined by electrotransport, are dependent, via transport numbers, on the reference system and (c) severe experimental difficulties may be encountered in liquid salt thermotransport, mainly corrosion and convection effects. 

Fujii, Y. et al., Separation of isotopes of lithium and uranium by electromigration using cation-exchange membranes, Isotopenpraxis, 15, 7, 203, 1979. 

Okamoto, M. et al., Dependencies of pH and current density on the isotope effect occurred by the electromigration of uranyl ions in a... 

S. Hirai and H. Kakihana, Continuous separation of lithium isotopes by a simultaneous use of ion-exchange chromatography and electromigration, Nihon Genshiryoku Gakkaishi, 1976, 18, 373 Chem. Abst. 1983, 99, 29622j. 

The principle used for the counter-current ion-exchange isotope separation by electromigration in a column is the balancing of the hydraulic flow of the ions X, the isotopes of which are to be separated, by the opposite flow of ions Y in an electric field. The X ions should be the more strongly sorbed on the ion exchanger and the Y ions should be the more mobile ones in the field. A sharp boimdary between the two kinds of ions is attained at some place in the column and is maintained there by the balancing of the flows. The steady passage of electric current is equivalent to movement of the sorbed band of X (which is actually... 

Fujii and co-workers (1985) used such a membrane configuration to separate calcium isotopes with a migration length of 0.70m for a 0.5moll CaCli feed solution, resulting in enrichment factors smaller than those achieved by electromigration on the column. 

Diffusion, electromigration experiments and isotope effect 2.5.1. Diffusion and electromigration ofH... 

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