A NEW VALENCE STATE OF AMERICIUM, Am(VI)

Asprey, L.B.; Stephanou, S. E.; Penneman, R. A.

doi:10.2172/4416555

Cited by 9 publications

(9 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…7 The socalled autoreduction of Am(VI) was reported to occur via an autocatalytic mechanism where americium reacts with its own radiolysis products formed by α-decay. 16,17,[19][20][21][22][23][24] The varied experimental procedures and multiple aqueous media investigated previously have resulted in the report of inconsistent reduction mechanisms and rate constants. Given this group's interest in the chemistry of Am(VI) its autoreduction kinetics have been re-investigated.…”

Section: Introductionmentioning

confidence: 99%

Kinetics of the Autoreduction of Hexavalent Americium in Aqueous Nitric Acid

et al. 2017

View full text Add to dashboard Cite

The rate of reduction of hexavalent Am due to self-radiolysis was measured across a range of total americium and nitric acid concentrations. These so-called autoreduction rates exhibited zero-order kinetics with respect to the concentration of hexavalent americium, and pseudo-first-order kinetics with respect to the total concentration of americium. However, the rate constants did vary with nitric acid concentration, resulting in values of 0.0048 ± 0.0003, 0.0075 ± 0.0005, and 0.0054 ± 0.0003 h for 1.0, 3.0, and 6.5 M HNO, respectively. This indicates that reduction is due to reaction of hexavalent americium with the radiolysis products of total americium decay. The concentration changes of Am(III), Am(V), and Am(VI) were determined by UV-vis spectroscopy. The Am(III) molar extinction coefficients are known; however, the unknown values for the Am(V) and Am(VI) absorbances across the studied range of nitric acid concentrations were determined by sensitivity analysis in which a mass balance with the known total americium concentration was obtained. The new extinction coefficients and reduction rate constants have been tabulated here. Multiscale radiation chemical modeling using a reaction set with both known and optimized rate coefficients was employed to achieve excellent agreement with the experimental results, and indicates that radiolytically produced nitrous acid from nitric acid radiolysis and hydrogen peroxide from water radiolysis are the important reducing agents. Since these species also react with each other, modeling indicated that the highest concentrations of these species available for Am(VI) reduction occurred at 3.0 M HNO. This is in agreement with the empirical finding that the highest rate constant for autoreduction occurred at the intermediate acid concentration.

show abstract

Section: Introductionmentioning

confidence: 99%

Kinetics of the Autoreduction of Hexavalent Americium in Aqueous Nitric Acid

et al. 2017

View full text Add to dashboard Cite

show abstract

“…The rst reported preparation of Am VI was by Asprey et al, in 1951. [1][2][3] They used an excess of solid ammonium peroxydisulfate, (NH 4 ) 2 S 2 O 8 , added to 0.2 M nitric, perchloric or sulfuric acid solutions containing 0.002-0.035 M Am III . At 85 C, the pink Am III color was replaced by a straw-yellow color, and a sharp UV/Vis absorbance peak was reported at 992 nm, with another minor peak at 666 nm.…”

Section: Introductionmentioning

confidence: 99%

Recent advances in f-element separations based on a new method for the production of pentavalent americium in acidic solution

et al. 2015

View full text Add to dashboard Cite

The peroxydisulfate anion has long been used for the preparation of hexavalent americium (Am VI ) from the normally stable Am III valence state in mildly acidic solutions. However, there has been no satisfactory means to directly prepare the pentavalent state (Am V ) in that medium. Some early literature reports indicated that the peroxydisulfate oxidation was incomplete, and silver ion catalysis in conjunction with peroxydisulfate became accepted as the means to ensure quantitative generation of Am VI . Incomplete oxidation would be expected to leave residual Am III , or to produce Am V in treated solutions. However, until recently, the use of peroxydisulfate as an Am V reagent has not been reported. Here, parameters influencing the oxidation were investigated, including peroxydisulfate and acid concentration, temperature, duration of oxidative treatment, and the presence of higher concentrations of other redox active metals such as plutonium. Using optimized conditions determined here, quantitative Am V was prepared in an acidic solution and the UV/Vis extinction coefficients of the Am V 513 nm peak were measured over a range of nitric acid concentrations. The utility of Am V for separations from the lanthanides and curium by solvent extraction, organic column chromatography and inorganic ion exchangers was also investigated.

show abstract

“…The standard potential for the Am(III)/Am(VI) redox couple under acidic conditions is about 1.7 V, and thus strong oxidizing agents are required [1,11]. Several oxidants have been explored including peroxydisulfate [12,13], copper(III) periodate [14,15], electrochemical techniques [16], and sodium bismuthate [5][6][7][8]17]. Once oxidized the Am(VI) exists as the americyl AmO 2 2+ ion and behaves similarly to the other hexavalent actinyl cations.…”

Section: Theorymentioning

confidence: 99%

Oxidation and extraction of Am(VI) using a monoamidic extractant in 3D printed centrifugal contactors

Law

Mincher

Tillotson

et al. 2018

J Radioanal Nucl Chem

View full text Add to dashboard Cite

A series of tests were performed using centrifugal contactors to evaluate the separation of Am(VI) from cerium, as well as to determine the efficiency of the contactors. All experiments were performed using 2-cm, acrylic 3D-printed centrifugal contactors.Solvent extraction tests were performed using 1 M N,N-di(2-ethylhexyl)butyramide (DEHBA)/dodecane and a nitric acid feed solution spiked with 243 Am and 139 Ce and oxidized with 60 mg mL -1 sodium bismuthate. Approximately 72 % of the Am was extracted with a single contactor stage. Co-stripping of Am and Ce was demonstrated but attempts at selective stripping were not successful. Successful recycle of the used organic phase was demonstrated. Contactor efficiencies of 95 % to 100 % were obtained.

show abstract

A NEW VALENCE STATE OF AMERICIUM, Am(VI)

Cited by 9 publications

References 0 publications

Kinetics of the Autoreduction of Hexavalent Americium in Aqueous Nitric Acid

Kinetics of the Autoreduction of Hexavalent Americium in Aqueous Nitric Acid

Recent advances in f-element separations based on a new method for the production of pentavalent americium in acidic solution

Oxidation and extraction of Am(VI) using a monoamidic extractant in 3D printed centrifugal contactors

Contact Info

Product

Resources

About