pH effect on Re(VII) and Se(IV) diffusion in compacted GMZ bentonite

Wang, Zhifen; Wang, Hai; Li, Qingmei; Xu, Minhong; Guo, Yuhai; Li, Jinying; Wu, Tao

doi:10.1016/j.apgeochem.2016.07.015

Cited by 37 publications

(12 citation statements)

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“…Se(IV) can also hardly enter the interlayer space of bentonite. A lower D e value was obtained in this work, compared to our previous results (Wang et al, 2016;Wu et al, 2014). This is probably caused by the lower experimental temperature and the different compositions of the pore water.…”

Section: Effect Of Ionic Strength On Se(iv) Diffusioncontrasting

confidence: 85%

Salt effects on Re(VII) and Se(IV) diffusion in bentonite

Wang

et al. 2017

Applied Clay Science

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The through-diffusion method was employed to investigate the effect of the salt concentration on the diffusion behaviour of Re(VII) and Se(IV) in compacted bentonite. The accessible porosity,  acc , of Re(VII) increased from 0.25 to 0.38 with an increase of the ionic strength from 0.1 to 1.0 mol/L. The dependency of the accessible porosity  acc on the salt concentration could be described approximately by a first-order decay exponential function. The interlayer porosity of GMZ bentonite was 21 % of the total porosity at a bulk dry density of 1600 kg/m 3 at 12 C. The D e values of Re(VII) and Se(IV) increased from 2.6  10 -11 to 6.1  10 -11 m 2 /s and from 1.6  10 -11 to 4.7  10 -11 m 2 /s in GMZ bentonite with an increase of the ionic strength from 0.1 to 1.0 mol/L, respectively. In the case of Se(IV), the adsorption showed a different ionic strength dependency in GMZ bentonite and montmorillonite. The ionic strength has no significant effect on the sorption (K d =1.8  10 -4 m 3 /kg) on GMZ bentonite, indicating the formation of inner-sphere surface complexes. In the case of synthetic montmorillonite, the K d values increased with increasing ionic strength. This can be explained by the fact that the electric potential of surface sites becomes less negative with increasing ionic strength resulting in an increase in the adsorption of Se(IV) at a pH

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Section: Effect Of Ionic Strength On Se(iv) Diffusioncontrasting

confidence: 85%

Salt effects on Re(VII) and Se(IV) diffusion in bentonite

Wang

et al. 2017

Applied Clay Science

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“…The compositions of granite will greatly affect the sorption behaviors of Se(IV) and therefore provides an information for selecting the sites and the host rock’s type for HLW repository, since many nuclides can be immobilized on biotite. ,, For the host rock surrounding the HLW repository, the deposited level of Se is relatively low. Some previous studies about diffusion were conducted with relatively large selenium concentrations to obtain the diffusion parameters, ,, which may lead to an overestimation or an inadequate mechanism of matrix diffusion. In this work, the diffusion experiments were conducted with a 7.03 × 10 –8 mol/L Se(IV) concentration to provide relatively reliable diffusion and sorption parameters.…”

Section: Environmental Implicationsmentioning

confidence: 99%

“…10,56,57 For the host rock surrounding the HLW repository, the deposited level of Se is relatively low. Some previous studies about diffusion were conducted with relatively large selenium concentrations to obtain the diffusion parameters, 4,5,20 which may lead to an overestimation or an inadequate mechanism of matrix diffusion. In this work, the diffusion experiments were conducted with a 7.03 × 10 −8 mol/ L Se(IV) concentration to provide relatively reliable diffusion and sorption parameters.…”

Section: Environmental Implicationsmentioning

confidence: 99%

“…Under well-oxidized geochemical environments, the most frequently encountered Se species is in the form of selenate, Se(+VI)O 4 2– . In less oxidizing conditions, selenite (Se(+IV)O 3 2– ) and biselenite (HSe(+IV)O 3 – ) dominate. , Upon more reducing environments, Se is reduced to elemental selenium(0) . In highly reducing conditions, oxidation states – I and -II dominate and usually present as solid states that have low mobility, such as FeSe 2 (-I) and FeSe(-II). , Overall, the higher oxidation states Se(IV) and Se(VI) prevail as more mobile aqueous oxyanions .…”

Section: Introductionmentioning

confidence: 99%

“…These minerals exhibit various porosities and pores’ surface sorption properties that have different effects on diffusion. Withal several diffusion experiments that have been conducted with relatively large selenium concentrations (approximately mmol/L magnitude) to obtain the diffusion parameters may lead to an overestimation or an inadequate mechanism of matrix diffusion. ,, Conducting a series of diffusion experiments with concentrations close to realistic situations is vital to an understanding of the diffusion behaviors of selenium in granite.…”

Section: Introductionmentioning

confidence: 99%

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Effects of Mineral Compositions on Matrix Diffusion and Sorption of ⁷⁵Se(IV) in Granite

Yang

et al. 2018

Environ. Sci. Technol.

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Exploring the migration behaviors of selenium in granite is critical for the safe disposal of radioactive waste. The matrix diffusion and sorption of Se(IV) (analogue forSe) in granite were systematically studied to set reliable parameters in this work. Through-diffusion and batch sorption experiments were conduct with four types of Beishan granite. The magnitudes of the obtained apparent diffusion coefficient (D) values are of the following order: monzogranite > granodiorite-2 > granodiorite-1, which is opposite to the sequence of the K values obtained from both the diffusion model and batch sorption experiments. The EPMA results of the granitic flakes showed that there was no obvious enrichment of Se(IV) on quartz, microcline and albite. Only biotite showed a weak affinity for Se(IV). Macroscopic sorption behaviors of Se(IV) on the four types of granite were identical with the sequence of the granitic biotite contents. Quantitative fitting results were also provided. XPS and XANES spectroscopy data revealed that bidentate inner-sphere complexes were formed between Se(IV) and Fe(III). Our results indicate that biotite can be representative of the Se(IV) sorption in complex mineral assemblages such as granite, and the biotite contents are critically important to evaluate Se(IV) transport in granite.

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