Kinetics of Technetium Reactions: XV. Tc(IV) Oxidation with Persulfate Ions in HClO4 Solution

Koltunov, V. S.; Gomonova, T. V.; Koltunov, G. V.

doi:10.1007/s11137-005-0065-y

Cited by 3 publications

(5 citation statements)

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“…Thus, considering the rate-determining stages (3), (4), and (9), the expression for the rate of U(IV) oxidation can be written in the form (10) where k 1 and k 2 are the rate constants of oxidation of U 4+ aqua ion and complex ion U 4+ . CO(NH 2 ) 2 according to Eqs.…”

Section: Resultsmentioning

confidence: 99%

“…(10), we assumed that the urea concentration remains constant in oxidation of U(IV). However, with increasing initial concentration of U(IV), the amount of HNO 2 formed increases; this HNO 2 reacts with urea by reaction (8) and decreases its concentration, and thus the urea concentration does not remain constant in the course of the reaction.…”

Section: Resultsmentioning

confidence: 99%

“…To prevent U(IV) oxidation, a compound rapidly reacting with HNO 2 , e.g., hydrazine, is added to the solution [2]. However, when solutions contain technetium ions, which catalyze the reaction between U(IV) and HNO 3 (nitrate ions), U(IV) is oxidized even in the presence of hydrazine [3]. Similar trends are also observed with another stabilizing agent for U(IV), hydroxylamine [4].…”

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Oxidation of U(IV) in HNO3 Solutions Containing Urea and Tc(VII)

2005

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The kinetics of U(IV) oxidation with nitric acid in aqueous solutions containing urea, catalyzed with technetium ions, were studied by sampling with subsequent colorimetric determination of the U(IV) concentration. At the constant ionic strength of the solution m = 2 in the range of the initial concentrations of U(IV) from 2 0 10 !3 to 1.28 0 10 !2 , Tc(VII) from 5 0 10 !5 to 1 0 10 !3 , urea from 0.01 to 0.1, and hydrogen ions from 0.4 to 1.96 M, the reaction rate is described by the equation 3d[U(IV)]/dt = k 1 [U(IV)][Tc] 0.5 [CO(NH 2 ) 2 ] 0 {[H + ] 2 + b 1 [H + ] + b 2 } !1 3 k 2 [U(IV)] 2 [H + ] 0.4 [CO(NH 2 ) 2 ] 1.6 {[H + ] 2 + b 1 [H + ] + b 2 } !2 , where k 1 = 172 + 10 mol 0.5 l !0.5 min !1 and k 2 = (9.4 + 1.2) 0 10 2 mol l !1 min !1 at 25oC, b 1 and b 2 are the hydrolysis constants of U 4+ ions. The activation energy is 63 + 2 kJ mol !1 . A reaction mechanism is proposed, in which in the slow stages the complex ion U(OH) 2 2+ . CO(NH 2 ) 2 reacts with TcO 2+ and TcO 2+ . CO(NH 2 ) 2 ions.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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confidence: 99%

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Oxidation of U(IV) in HNO3 Solutions Containing Urea and Tc(VII)

2005

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“…The extract and stripping solution were fed at rates of 800 and 78 ml h -1 , respec- However, in this case α also tends to decrease. One of the causes is high acidity of the aqueous phase (~2.5 M HNO 3 ; in the other experiments, from 0.7 to 0.8 M), which accelerates the Tc-catalyzed oxidation of U(IV) with nitric acid (nitrate ions) [7].…”

Section: Technetium Strippingmentioning

confidence: 96%

Stripping of Pu and Tc from tributyl phosphate solutions with carbohydrazide

Alekseenko¹,

Marchenko²,

Dvoeglazov³

et al. 2012

Radiochemistry

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Stripping of Pu from 30% tributyl phosphate solutions with carbohydrazide was studied. The degree of the Pu stripping drastically decreases with an increase in acidity and increases with an increase in the carbohydrazide concentration and in temperature. The Pu(IV) reduction rate in the two-phase system is sufficiently high to perform the reductive stripping of Pu with carbohydrazides both in mixer-settlers and in centrifugal extractors. Stripping of Тс at high phase ratio (O/W = 30) with carbohydrazide, hydrazine, and U(IV) in a mixture with hydrazine was studied. At low acidity (<1 M HNO 3 ) and 30-35°C, carbohydrazide allows more than 80% stripping of Tc from 30% TBP solutions even at high volume ratio of the phases.One of the lines in improving aqueous technology for SNF reprocessing is search for new effective reagents for performing redox processes involving Pu and Np ions [1]. The results of our previous studies [2,3] show that carbohydrazide (NH 2 NH) 2 CO can be a candidate reagent for the Pu and Np reduction. Its advantages are high rate of the reaction with Pu(IV) and Np(VI) in aqueous solution, resistance to oxidation in HNO 3 solutions, and the absence of HN 3 among products of its reactions with HNO 3 and HNO 2 . Furthermore, thanks to a high rate of the reaction with HNO 2 , the use of carbohydrazide (CH) does not require introduction of any antinitrite agent (hydrazine) for stabilization of lower valence states of U, Pu, and Np.Another possible application of carbohydrazide is decontamination of U from Tc by the reduction of Tc(VII) to nonextractable Tc(IV) in the final step of the extraction reprocessing of SNF, because specifically 99 Tc (along with 106 Ru) is the nuclide determining the purity of the final uranium product.The goal of this study was to examine the possibility of using carbohydrazide in two-phase extraction systems with TBP for the Pu and Tc reduction and to perform laboratory trials of the reductive stripping of Pu under the conditions of the first extraction cycle and of the U decontamination from Tc in the step of extraction refining of U.The experimental procedure was as follows. A temperature-controlled separating funnel was charged with an aqueous nitric acid solution of carbohydrazide of known concentration, and an equal volume of a 30 vol % solution of TBP in n-dodecane, containing 0.9 to 1.1 g l -1 Pu(IV), was added. The contents were mechanically stirred for a definite time, after which the phases were separated by settling, and the Pu concentration in the organic phase was determined radiometrically, and that in the aqueous phase, spectrophotometrically. In each experiment, we also determined the concentration of H + ions in the aqueous phase by potentiometric titration. The Pu distribution ratio D and the degree of Pu stripping α were calculated by the formulas D = [Pu] org /[Pu] aq and α = (1 -[Pu] org /[Pu] org,init ) × 100%, where [Pu] org and [Pu] aq are the Pu concentrations in the organic and aqueous phases after the phase separation, and [Pu] org, init is the P...

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“…55 In related work, the reduction of Pu(VI) to Pu(III) by acetaldoxime, also in HNO 3 occurs by a 3-stage process from Pu(VI) to Pu(V) to Pu(II), together with a ''reproportionation'' of Pu(IV). 56 Similarly, there has been a mechanistic study of oxidation of Tc(IV) by S 2 O 8 2À and H 2 SO 5 57 and reduction of Np(V) with hydroxyethylhydrazine. 58 In the latter, an autocatalytic pathway is invoked.…”

Section: àmentioning

confidence: 99%

Mechanisms of reactions in solution

Davies

2006

Annu. Rep. Prog. Chem., Sect. A: Inorg. Chem.

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Kinetics of Technetium Reactions: XV. Tc(IV) Oxidation with Persulfate Ions in HClO4 Solution

Cited by 3 publications

References 8 publications

Oxidation of U(IV) in HNO3 Solutions Containing Urea and Tc(VII)

Oxidation of U(IV) in HNO3 Solutions Containing Urea and Tc(VII)

Stripping of Pu and Tc from tributyl phosphate solutions with carbohydrazide

Mechanisms of reactions in solution

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