Free-radical redox reactions of uranium ions in sulphuric acid solutions

Abstract

A. JOHN ELLIOT, SHAHSULTAN PADAMSHI, and JANA PIKA. Can. J. Chem. 64, 314 (1986).The radiolytic reductio? of uranyl ions in degassed sulphuric acid solutions containing various organic solutes was studied. It was shown that while COOH, C02-, and a-hydroxy-alkyl radicals reduced uranyl ions, the P-hydroxy-alkyl radicals and those derived from gluconic acid could not affect the reduction. The oxidation of uranium(1V) by hydrogen peroxide at pH 0.7 involves hydroxyl radicals in a chain mechanism but at pH 2.0 the oxidation proceeds by a non-radical reaction pathway. From the enhancement of the rate of oxidation of uranium(1V) by oxygen in the presence of 2-propanol, a mechanism involving the perhydroxyl radical, which reconciles earlier published data on kinetics and oxygen tracer studies, is proposed for the oxygenuranium(1V) reactions.A. JOHN ELLIOT, SHAHSULTAN PADAMSHI et JANA PIKA. Can. J. Chem. 64, 314 (1986). On Ctudie la reduction radiolytique des ions uranyles dans des solutions dCgazCes d'acide sulfurique contenant divers solutks organiques. On montre que, contrairement aux radicaux COOH, COz-et a-hydroxy-alkyles qui rCduisent les ions uranyles, les radicaux P-hydroxy-alkyles et ceux provenant de l'acide gluconique ne peuvent effectuer la rkduction. L'oxydation de I'uranium(1V) par le peroxyde d'hydrogtne i un pH de 0,7 fait intervenir des radicaux hydroxyles dans un mCcanisme en chaine; toutefois, i un pH de 2,0, la rCaction d'oxydation s'effectue par une voie non-radicalaire. En se basant sur le fait que la vitesse d'oxydation de l'uranium(1V) par l'oxygtne est plus grande en presence de propanol-2, on propose pour cette rCaction un mCcanisme qui implique le radical perhydroxyle. Ce mkcanisme permet de concilier les donntes publites anttrieurement tant sur la cinCtique que sur les Ctudes par marqueurs d'ox>g' ene.[Traduit par le journal]

Heterogeneous photocatalytic removal of U(VI) in the presence of formic acid: U(III) formation

“…In addition, the U(IV) peak centered at 850 nm was certainly higher, while the peak at 650 nm seemed to be more defined. A very similar change of the U(IV) spectra during U(VI) radiolytic studies was found by Elliot et al, who also ascribed this change to U(III) [36]. Although U(III) is unstable, its half-life has been reported to be at least 755 h under similar conditions to ours [37], enough to be spectroscopically detected.…”

“…Similarly to other electron donors, HCOOH 1) accelerates uranyl reduction by reducing the recombination rate of e CB − /h VB + pairs, and 2) is able to indirectly reduce U(VI) by • COO − [36]. Photochemical experiments at acid pH (< 2) with TiO 2 nanoparticles in the presence of high HCOOH concentrations (Fig.…”

Photochemical reduction of U(VI) in aqueous solution in the presence of 2-propanol

“…• COH, a strong reducing radical [57] (E 0 ranges from −1.8 to −1.39 V [62]), which can reduce UO 2 2+ to UO 2 + , U(IV) and even to U(III) [41,63] (see however below).…”

Magnetic amino-sulfonic dual sorbent for uranyl sorption from aqueous solutions – Influence of light irradiation on sorption properties

“…(1b)), which are highly reactive for uranyl reduction to U(V) (Eq. (1c)) followed by disproportionation into U(VI) and U(IV) species [80] (Eq. (1d)).…”