Spectroelectrochemical Study of Uranium and Cerium in Carbonate Media

Redox reactions of actinides in carbonate and alkaline solutions

“…Taking into account the final proportion of Am(III), it can be concluded that the second-order reaction (7) prevailed. The rate constant of this reaction increased from 6.6610 72 to 262 litre mol 71 s 71 as pH was increased from 10.39 to 12.…”

“…41 Americium(IV) was prepared by irradiating a solution of Am(III) containing the BrO 7 ions with UV light. After termination of irradiation, Am(IV) was transformed spontaneously into Am(III) and Am(V) according to the reactions ( 6) and (7) in a time varying from a few minutes to 3 ± 4 days (depending on pH). The conversion of Am(IV) into Am(III) was 50% ± 65%.…”

“…Judging from the slopes of the plots of 2k d vs. pH (on the logarithmic coordinates), the disproportionation reaction of Am(IV) in KHCO 3 + K 2 CO 3 and NaHCO 3 + Na 2 CO 3 solutions is second order with respect to the OH 7 ions. This is attributable to the fact that the first step involves hydrolysis of americium carbonate complexes: Am(CO3)n(H2O) 2nÀ4À m + OH 7 (8) Am(OH)(CO3)n(H2O)…”

“…The same phenomena are observed in KHCO 3 + K 2 CO 3 or NaHCO 3 + Na 2 CO 3 mixtures at pH 4 10.9. At higher pH (including 1.5 M K 2 CO 3 or Na 2 CO 3 solutions without additives of bicarbonate), the addition of a stoichiometric amount of Np(VII) leads to complete oxidation of Am(III) to Am(IV), which then disappears due to disproportionation [see the reaction (7)]. This is evidenced by the appearance of Am(III) in an amount half as large as the initial value.…”

Electrochemical Characterisation of the Ce(IV) Limiting Carbonate Complex

“…8- [10,11,12,13,14,15] have been proposed for the Ce(IV) limiting complex. As the chemistry of Ce(III) [16] and Am(III) [7,8] in carbonate medium is well known, the reversible (or quasi-reversible) M(IV/III) redox couple may be used to study the chemistry of Ce(IV) and Am(IV) in concentrated bicarbonate/carbonate media.…”