Isotope Effect in Extraction of Metals from Light
and Heavy Water Solutions

A. M. Rozen^†, V. I. Volk, Z. I. Nikolotova, N. A. Kartasheva, and A. Yu. Vakhrushin

State Scientific Center of the Russian Federation: Bochvar All-Russia Research Institute of Inorganic Materials,
ul. Rogova 5, Moscow, 123060 Russia

Received May 5, 1996

Abstract—A theory of the isotope effect observed in extraction of metals salts and acids from their solutions
in heavy water with extracting agents incapable of deuterium exchange is developed. It is necessary to dis-
tinguish between the thermodynamic isotope effect (the ratio of the extraction constants for the heavy- and
light-water systems) and the apparent effect _D (the ratio of distribution coefficients D), which is dependent
on conditions of the process. The isotope effect is related to change in the Gibbs energy of hydration of a salt
G_aq upon replacement of light by heavy water: RT ln = G_aq. It was shown that the effect is due to
weaker hydration of salts in heavy water (G_aq > 0). The isotope effect is positive ( > 1, G > 0) for
coordination extraction (formation of addition complexes) but may be negative for cation-exchange mecha-
nism of the process (<1). Theoretical predictions agree with the experimental data for extraction of
actinides. The isotope effect is positive for coordination extraction with tributyl phosphate and trioctylamine:
= 3.3 and G = 0.72 kcal/mol for americium nitrate and = 1.5 and G = 0.25 kcal/mol for uranyl
nitrate and nitric acid. The effect observed for cation-exchange extraction with di-2-ethylhexylphosphoric
acid is negative ( = 0.15 for americium). Theisotope effects are large, and it is possible to simplify deter-
mination of the hydration energy of salts in transition from light to heavy water by measuring instead of
calorimetric measurements.

Pleiades Publishing home page | journal home page | top

If you have any problems with this server, contact webmaster.