Sorption behavior of neptunium(V) ion on clay sorbent.

Yamamoto, Koichiro; Yanagi, Tadashi; Senoo, Muneaki; Sakamoto, Yoshiaki

doi:10.3327/jnst.27.626

Cited by 5 publications

(4 citation statements)

References 3 publications

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“…Previous kinetics experiments (Yamamoto et al 1990;Hart et al 1994;Bertetti et al 1998) suggest that Np(V) sorption reactions are --98% complete within 48 h, but the solutions used in this study typically required up to 10 d for equilibration of pH when equilibrating with atmospheric Pcoz due to relatively slow mass transfer of CO2 between the gas and aqueous phases, similar to the times reported for pH equilibration in uranium solutions (Pabalan and Turner 1991).…”

Section: Methodsmentioning

confidence: 48%

Neptunium(V) Sorption on Montmorillonite: An Experimental and Surface Complexation Modeling Study

Turner

1998

Clays and clay miner.

118

121

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Abstract--Batch sorption experiments at fixed initial Np(V) concentration (-1 • 10 6 M 237Np), M/V ratio (4 g L-l), and ionic strength (0.1 molal NaNO3) were conducted to determine the effects of varying pH and Pco2 on Np(V) sorption on SAz-1 montmorillonite. The results show that Np(V) sorption on montmorillonite is strongly influenced by pH and Pco2. In the absence of CO2, Np(V) sorption increases over the entire pH range examined (~3 to --10), with measured sorption coefficients (Ko) of about 10 mL g-1 at pH < 6 to K o ~ 1000 mL g-~ at a pH of 10.5. However, for experiments open to atmospheric CO2 (Pco2 = 10 3.5 arm), Np(V) sorption peaks at Ko -100 mL g-1 at pH of 8 to 8.5 and decreases at higher or lower pH. A comparison of the pH-dependence of Np(V) sorption with that of Np(V) aqueous speciation indicates a close correlation between Np(V) sorption and the stability field of the Np(V)-hydroxy complex NpO2OH ~ (aq). In the presence of CO2 and aqueous carbonate, sorption is inhibited at pH > 8 due to formation of aqueous Np(V)-carbonate complexes. A relatively simple 2-site DiffuseLayer Model (DLM) with a single Np(V) surface complexation reaction per site effectively simulates the complex sorption behavior observed in the Np(V)-H20-CO2-montmorillonite system. The good agreement between measured and DLM-predicted sorption values suggests that surface complexation models based on parameters derived from a limited set of data could be useful in extrapolating radionuclide sorption over a range of geochemical conditions. Such an approach could be used to support transport modeling and could provide a better alternative to the current use of constant K o values in performance assessment transport calculations.

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Section: Methodsmentioning

confidence: 48%

Neptunium(V) Sorption on Montmorillonite: An Experimental and Surface Complexation Modeling Study

Turner

1998

Clays and clay miner.

118

121

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“…Under the pH condition (pH 5.5) of the sandy soil column, the chemical form of Np(V) is expected to be NpO 2 + as shown in Table 3. The migration behavior of NpO 2 + in soil column is obeyed by equilibrium sorption model, that is K d model, because of its cation exchange sorption reaction [1,4]. The major chemical form of Np(V) in the presence of the humic substances is also estimated as NpO 2 + because the complexation of Np(V) with humic substances is very low in low pH region [4,11,15].…”

Section: Migration Behavior Of Np(v) In the Absence And Presence Of Tmentioning

confidence: 99%

“…centration between in geological formation and groundwater [1,2]. However, the sorption of Np(V) is influence by groundwater composition, for example, carbonate ion [3], calcium ion [1], and dissolved organic substances [4,5]. Especially, the effect of dissolved organic substances, which are mainly humic or fulvic acids, in ground water on the sorption and migration behavior of Np(V) in geologic formation has not been clarified because a lack of information of coordination between Np ion and the humic substances.…”

Section: Introductionmentioning

confidence: 99%

“…Sorption and migration behavior of Np(V) is generally quantified by using simple thermodynamic equilibrium: distribution coefficient that is defined by ratio of Np(V) con-*Author for correspondence (E-mail: sakamoto@sparclt.tokai.jaeri.go.jp). centration between in geological formation and groundwater [1,2]. However, the sorption of Np(V) is influence by groundwater composition, for example, carbonate ion [3], calcium ion [1], and dissolved organic substances [4,5].…”

Section: Introductionmentioning

confidence: 99%

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The migration behavior of Np(V) in sandy soil and granite media in the presence of humic substances

Sakamoto¹,

Nagao²,

Ogawa³

et al. 2000

Radiochimica Acta

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Migration behavior of Np(V) in sandy soil and granite media was studied in the presence of humic substances using a column method. Two kinds of naturally occurring fulvics were isolated from groundwater at the Chalk River Laboratories of AECL (hereafter, CRL-fulvics) and at the Underground Research Laboratory of AECL (hereafter, URL-fulvics). The commercial humics from Aldrich Co. (hereafter, Aldrich-humics) was also used to compare the influence of humics from different origin on the migration behavior of Np(V). The dominant molecular size of these humic substances was under 5,000 daltons for the fulvics, and in the range from 30,000 to 100,000 daltons for Aldrich-humics. An enhanced elution of Np(V) from the sandy soil column under coexistence of CRL-fulvics at 20 mg/L was observed in comparison with the studies in the absence of humic substances. On the other hand, Np(V) under coexistence of Aldrich-humics was retarded. The difference in the effects of the humic substances on the migration behavior of Np(V) may be caused by the difference in the molecular size distribution of the humic substances. That is, the CRL-fulvics, being smaller in size, has lower sorption ability on the sandy soil than the Aldrich-humics, and thereby Np-fulvics complexes may be able to easily migrate through the sandy soil column. In the case of granite column experiments, again an enhanced elution of Np(V) under the coexistence of URL-fulvics was found and this observation was similar to that found with the CRL-fulvics. From these observations, it is likely that the migration behavior of Np(V) is influenced by the presence of humic substances.

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Sorption of Neptunium on Clays and Clay Minerals — A Review

Fröhlich

2015

Clays and clay miner.

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During recent decades, the search for possible repositories for high-level nuclear waste has yielded large amounts of sorption data for actinides on different minerals. Clays and clay minerals are of special interest as potential host-rock formations and backfill materials, by virtue of their good retardation properties. Neptunium (Np) is one of the actinides which is considered in long-term scenarios due to its long-lived nuclide 237Np (t1/2 = 2.1 × 106 y). Because neptunium sorption is heavily dependent on the experimental conditions, comparison of sorption data from different experiments is challenging. Normalizing reported data with respect to the surface area of the sorbent enables conversion of conventional distribution coefficients (Kd) to normalized (Ka) values, which improves comparability among the results of different experiments. The present review gives a detailed summary of sorption data of Np on clays and clay minerals and examines critically the applicability of the Ka approach.

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Sorption behavior of neptunium(V) ion on clay sorbent.

Cited by 5 publications

References 3 publications

Neptunium(V) Sorption on Montmorillonite: An Experimental and Surface Complexation Modeling Study

Neptunium(V) Sorption on Montmorillonite: An Experimental and Surface Complexation Modeling Study

The migration behavior of Np(V) in sandy soil and granite media in the presence of humic substances

Sorption of Neptunium on Clays and Clay Minerals — A Review

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