Uranyl ions hydrolysis

A review (91 references) on electrophilic and nucleophilic reactions of trivalent phosphorus acid derivatives, reactions of two-coordinate phosphorus compounds, and miscellaneous reactions has appeared.228 Earlier in this review we looked at the heavy-atom isotope effects on reactions of Co(III)-bound /vnitrophenyl phosphate,186 the uranyl ion hydrolysis of /vnitrophcnyl phosphodiesters (218)-(220),190 and the Th(IV) hydrolysis of these.191... 

S.V. (1984) Study of uranyl ion hydrolysis reaction equilibria in potassium nitrate solutions. Vest. Mosk. Univ. Khim., 39, 551-554. 

Hexavalent. As with most reactions, the hydrolysis of U02 + is the best studied of the hexavalent actinides. The hydrolysis of U02 + begins at pH 3, while the onset for the hydrolysis of Np02 + and Pu02 + each occur at a higher pH. The monomeric hydrolysis products of the uranyl ion, U02(0H) n = 1, 2) can be studied in solutions with uranimn concentrations less than 10 M. For solutions with higher uranium concentrations, multinuclear cationic species dominate the speciation, for example, (U02)2(0H)22+, (U02)3(0H)42+, and (U02)3(OH)s+. These cations have been crystallized from solutions with the formulas (U02)2(at2-OH)2(OH2)6 + and (U02)3(M3-0)(/x2-0H)3(0H2)6+ (21). For Np and Pu, the dimer of the first hydrolysis product, (An02)2(OH)2 + (22), has also been identified but not fully stracturally characterized. 

Ce(IV) ions efficiently catalyse the hydrolysis of phospho monoesters in nucleotides under physiological conditions. The proposed mechanism for the hydrolysis is illustrated in (217). Uranyl cations (UOj" ) catalyse the hydrolysis of aggregated and non-aggregated / -nitrophenyl phosphodiesters such as (218)/(219) and (220), respectively. Bis(/ -nitrophenyl) phosphate (218) hydrolysis is accelerated ca 2.8 X 10 -fold by Th(IV) cations in aqueous Brij micelles. The reactivity of Th(TV) towards (219) and (221 R = Et, C16H33) also exceeds that of uranyl ion and is comparable to that of Ce(IV) and exceeds that of other metal cations. 

Gupta, A.R. and Venkataramani, B., Sorption of uranyl ions on hydrous oxides. A new surface hydrolysis model. Bull. Chem. Soc. Jpn, 61, 1357, 1988. 

Some metal cations absorb sufficiently in the UV spectral range to be detected directly. By working at a sufficiently acidic pH hydrolysis is inhibited and an additional buffer does not need to be added. Sharp peaks were obtained for U02 in an aqueous HCl electrolyte with direct detection at 214 nm [10]. Uranium(V) had not been separated previously as the uranyl ion. 

The low concentration of radioactive tracers can lead to the formation of solute species that are not observed at equilibrium with macro amounts. For example, the hydrolysis of uranyl ions corresponds to the equilibrium... 

For this latter reason, for example, it was not possible to use spectroscopy to evaluate the various equilibria in the hydrolysis of uranyl ion in perchlorate media. Without assignment of all bands to their appropriate transitions it was not possible to rule out band crossing or overlapping, with pH change. 

Solution pressurizers. Solution steam pressurizers must satisfy rather strict chemical criteria. Stainless-steel surfaces in contact with solutions must not exceed temperatures at which heavy-li(juid-phasc. solutions form, giving rise to rapid corrosion [20]. Undesirable reduction of uranium must be avoided by the presence of some dissolved oxygen. Undesirable hydrolysis of uranyl ion must be avoided by control of the chemistry and temperature in pressurizer solutions [21]. The vapor-phase concentration of deuterium should be maintained below the explosive limit. One solution to these problems, used in the HRE-2, is the generation of steam from distilled water rather than from fuel solution. Another solution is the boiling of solutions in corrosion-resistant titanium. A third solution is the use of fission-product heating rather than external heating to reach the desired temperature. 

Effect of nitric acid. The addition of nitric acid to the aqueous phase favors the extraction of uranium by preventing or decreasing the hydrolysis of uranyl Ion and by Increasing the nitrate Ion concentration. Nitric acid 1s extracted also by the organic solvents. This requires... 

Ahrland, S. (1949) On the complex chemistry of the uranyl ion. I. The hydrolysis of the six-valent uranium in aqueous solution. Acta Chem. Scand., 3, 374—400,... 

L.G. (1963) Studies on the hydrolysis of metal ions. 46. Uranyl ion, in chlo-... 

Milic, N.B. and Suranji, T.M. (1982) Hydrolysis of the uranyl ion in sodium nitrate medium. Z. Anorg. Allg. Chem., 489, 197-203. 

The hydrolysis of the uranyl(VI) ion, UO " 2> has been studied extensively and begins at about pH 3. In solutions containing less than lO " M uranium, the first hydrolysis product is the monomeric U02(OH)", as confirmed using time-resolved laser induced fluorescence spectroscopy. At higher uranium concentrations, it is accepted that polymeric U(VI) species are predominant in solution, and the first hydrolysis product is then the dimer, (U02)2(0H) " 2 (154,170). Further hydrolysis products include the trimeric uranyl hydroxide complexes (U02)3(0H) " 4 and (1102)3(OH)(154). At higher pH, hydrous uranyl hydroxide precipitate is the stable species (171). In studying the sol-gel U02-ceramic fuel process, O nmr was used to observe the formation of a trimeric hydrolysis product, ((U02)3( -l3-0)(p.2-0H)3) which then condenses into polymeric layers of a gel based on the... 

At higher temperatures the monomer is the predominant species although the rate of hydrolysis to U03 is increased. U03 dissolves in uranyl solutions to give U02OH+ and polymerised hydroxo-bridged species. Polynuclear species could arise from U4+ as it hydrolyses in dilute acid solutions. Complex ions are formed with thiocyanate, phosphate, citrate and anions of other organic acids. 

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