The redox chemistry of neptunium in<i>γ</i>-irradiated aqueous nitric acid

Mincher, Bruce J.; Přeček, Martin; Mezyk, Stephen P.; Elias, Gracy; Martin, Leigh R.; Paulenová, Alena

doi:10.1524/ract.2013.2013

Cited by 22 publications

(32 citation statements)

References 21 publications

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“…The absorbance of AmIII, AmV and AmVI were measured by UV/Vis spectroscopy using techniques previously developed under INL LDRD funding for observing the effects of irradiation on Np redox chemistry. [3] Briefly, samples were removed from the irradiator and the Uvvis absorbance spectra were recorded over the wavelength range 450-1050 nm using a Cary 6000 spectrophotometer. These were then returned to the irradiator to receive additional exposure to the source.…”

Section: Experimental Methodsmentioning

confidence: 99%

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The Radiolysis of AmVI Solutions

Mincher¹

2013

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SUMMARYThe reduction of bismuthate-produced AmVI by 60 Co gamma-rays was measured using post-irradiation UV/Vis spectroscopy. The reduction of AmVI by radiolysis was rapid, producing AmV as the sole product. Relatively low absorbed doses in the ~0.3 kGy range quantitatively reduced a solution of 2.5 x 10 -4 M AmVI. The addition of bismuthate to samples during irradiation did not appear to protect AmVI from radiolytic reduction during these experiments. It was also shown here that AmV is very stable toward radiation. The quantitative reduction of the AmVI concentration here corresponds to 1.4 hours of exposure to a process solution, however the actual americium concentrations will be higher and the expected contact times short when using centrifugal contactors. Thus, the reduction rate found in these initial experiments may not be excessive.

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Section: Experimental Methodsmentioning

confidence: 99%

“…This indicates that radiolytic reduction of AmVI to AmV occurred, probably caused by radiolytic generation of HNO 2 , which INL LDRD work previously showed was also capable of reducing NpVI. [3] The decrease in absorbance of AmVI at 997 nm versus absorbed dose is shown in Fig. 3.…”

Section: Samples Nominally Containing Only Trace Residual Bismuthatementioning

confidence: 99%

The Radiolysis of AmVI Solutions

Mincher¹

2013

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“…A former study [6] mentioned that nitrous acid catalyzed Np(V) oxidation, and another study [23] reported binuclear rate constant of Np(V) oxidation by nitric acid. Since the temperature dependencies of these effects were not reported, we did not take into account of these effects in the present calculation for Np(V) and Np(VI) concentrations.…”

Section: Oxidation Kinetics Of Np(v) To Np(vi) In 3 M Nitric Acidmentioning

confidence: 99%

“…Guillaume et al have reviewed the redox properties of Np, such as its reactions with nitric acid and hydrazinium nitrate [20]. Moreover, studies on the redox chemistry of Np, such as heterogeneous catalytic oxidation of Np(IV) [21], Np(V) disproportionation and cation-cation interactions in TBP/kerosene solvent [22], and redox chemistry of Np in gamma-irradiated nitric acid [23], have recently been performed.…”

Section: Introductionmentioning

confidence: 99%

Spectroscopic study of Np(V) oxidation to Np(VI) in 3 mol/dm³ nitric acid at elevated temperatures

et al. 2014

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Optical absorption spectra of Np in 3 mol/dm 3 nitric acid at elevated temperatures were measured using an optical glass cell with a water jacket having a light path of 1 cm. Molar extinction coefficients of Np(VI), T M −1 cm −1 , were obtained at various temperatures (297, 313, 334, 352, and 372 K). The values of T were found to decrease with increasing temperature and could be described by the equation T = −0.14 + 85.5, where is the temperature. Oxidation of Np(V) to Np(VI) in 3 M nitric acid at elevated temperatures (336, 342, 354, and 362 K) was observed using the optical glass cell. Oxidation of Np(V) was promoted by increasing the temperature and proceeded as a pseudo-first order reaction with respect to Np(V) concentration. The rate equation in the temperature range of 336-362 K was obtained as follows: − d[Np(V)] / d = 2.2 × 10 7 exp[−65 × 10 3 /( )][Np(V)] , where , , and [Np(V)] indicate the gas constant, temperature, and Np(V) concentration at time , respectively.

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“…The value probably falls in the range (0.017)*[HNO 3 ] to 0.031*[HNO 3 ] µmol J -1 . [8,9] It should also be a reducing agent for Am(VI), based on analogy with its reduction of Np(VI), [9] however, no rate constants have been reported. Nitrous acid and H 2 O 2 effects on americium redox chemistry are partially mitigated by their reaction with each other: [7]…”

Section: Introductionmentioning

confidence: 99%