Breakthrough experiments were carried out to study ion exchange separation of uranium isotopes. Four kinds of solutions containing natural uranium (mole fraction of ²³⁵U 0.720₀×10^-2),
(1) 0.05M TnOA/benzene solution saturated with U (IV)-chloro complex,
(2) mixture of 0.05M TnOA/benzene solution saturated with U (IV)-chloro complex and 0.05M TnOA/benzene solution saturated with U (VI)-chloro complex,
(3) 0.05M TBP/benzene solution with U (IV)-chloro complex,
(4) mixture of 0.05M TBP/benzene solution saturated with U (IV)-chloro complex and 0.05M TBP/benzene solution saturated with U (VI)-chloro complex, were passed through 100 cm long, 1.3cm diameter anion exchange resin columns until the composition of the effluents became equal to that of the feed solutions.
Near the front of the breakthrough of the solution (4) above, the ²³⁵U was found enriched to 0.732₄×10^-2 (enrichment factor 1.017), while in the case of the solution (2), ²³⁵U was depleted to 0.710₇×10^-2 (enrichment factor 0.987).
From the total amounts of ²³⁵U enriched or depleted by these breakthrough experiments, single process ion exchange separation factors of uranium isotopes were estimated to be 1.000000 for the solution (1), 1.00033 for the solution (2), 0.99989 for the solution (3), and 0.99988 for the solution (4).
Based on these data, the apparent equilibrium coefficients of the electron exchange reaction,
²³⁵U (VI)+²³⁸U (IV)_??_²³⁸U (VI)+²³⁵U (IV)
were estimated to be 1.0010 and 1.0013 for TnOA/benzene and TBP/benzene systems, respectively. These values are smaller than the value of 1.0020 obtained for 8M hydrochloric acid in the previous paper. The apparent equilibrium coefficient of the electron exchange reaction in the anion exchange resin (Dowex 21 K) was estimated to be 1.00101.0013.

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The breakthrough experiments of U(IV) and U(VI) have been done through an anion exchange resin column of 100 cm height and 1.2 cm diameter with 8_N-hydrochloric acid.
Uranous ions gave better separation factor (0.9993) than uranyl ions (1.0000) just as in the case of cation exchange resin reported in the previous paper. The mixed solutions of uranous and uranyl ions gave much favorite separation factors (0.99920.9986), which can be explained by effective contribution of the isotope effect of electron-exchange reaction.
²³⁵U(VI)+²³⁸U(IV)_??_²³⁸U(VI)+²³⁵U(IV)
The whole experimental results agreed with the theoretical values derived from the following fundamental equation by assuming ke=1.002.
ln S₂₃₈²³⁵(U)=ln S₂+ln{1+S₁keS₂^-1-1/1+ρ}+ln{1+(ke_-1-1)/1+ρ}
where S₁ is the separation factor with the system containing only uranous ions, S₂ is for uranyl; ρ and ρ are the ratios of uranyl ions to uranous ions in the solution and in the exchanger resin, respectively.

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The separation factors of nitrogen isotopes, S¹⁵₁₄(N), for 0.1M HN₃ in acetone-water mixtures were determined with differently cross-linked sulfonated polystyrene-divinylbenzene copolymers and synthetic inorganic exchanger (lonite C). The values for S¹⁵₁₄(N) lie between 1.023 and 1.034. The highest values 1.034 and 1.033 were obtained for 40% acetone with 55% DVB exchanger and for 80% acetone with lonite C, respectively. From the data obtained for aqueous solutions, the equilibrium coefficient, ¹⁵₁₄K_NH3, for the isotope exchange reaction between ammonia and ammonium ion, (Eq. (5)), was calculated to be 1.027 at 20°C.

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(1) The adsorbing capacity for uranium shown by titanic acid prepared in homogeneous and acidic solution was found larger than titanic acid prepared in nonhomogeneous and neutral solution. The uranium adsorbed on titanic acid increased with rising temperature of sea-water. The adsorption reached equilibrium within 2 days. The concentration of uranium in the titanic acid was found experimentally to have a maximum value of U/Ti=1, 500μg/g.
(2) The concentration of uranium adsorbed on the titanic acid at a given temperature was determined by the amount of sea-water and the concentration of uranium in seawater on the same titanic acid. An empirical formula was obtained for this relationship; the adsorption was applied to Freundlich's isotherm, and the distribution coefficients were found nearly constant within the range of sea-water volume covered by the present experiment.
(3) The adsorption capacity was estimated from the term of multiplication of the distribution coefficient and the concentration of uranium in sea-water. The maximum value evaluated was U/Ti=4, 200μg/g, with the titanic acid prepared by hydrolysis.
(4) The uranium adsorbed on the titanic acid increased with rising temperature of the sea-water, the empirical relationship being c=k exp (αtt²), (c: concn. of U, t: temp., k and α: const.).

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