Preface

Chapman, Neil; McCombie, Charles

doi:10.1016/s0713-2743(03)80001-6

Cited by 9 publications

(9 citation statements)

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“…Stabilization and conditioning by cementitious materials has been recognized as technology well suited for the immobilization of cationic and anionic species present in these waste forms . Cement-based materials are foreseen to be used for the construction of the engineered barrier systems in deep geological repositories in conjunction with disposal strategies for long-lived radioactive waste . Knowledge of the chemical mechanisms governing the interaction of metal cations and anionic species with the cement matrix, thus, is essential for predicting the long-term behavior of waste ions in these repositories.…”

Section: Introductionmentioning

confidence: 99%

Strontium Uptake by Cementitious Materials

Wieland

Tits

Kunz

et al. 2007

Environ. Sci. Technol.

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Wet chemistry experiments and X-ray absorption fine structure (XAFS) measurements were carried out to investigate the immobilization of nonradioactive Sr and 85Sr in calcite-free and calcite-containing Portland cement. The partitioning of pristine Sr between hardened cement paste (HCP) and pore solution, and the uptake of 85Sr and nonradioactive Sr were investigated in batch-type sorption/desorption experiments. Sr uptake by HCP was found to be fast and nearly linear for both cements, indicating that differences in the compositions of the two cements have no influence on Sr binding. The partitioning of pristine Sr bound in the cement matrix and 85Sr between HCP and pore solution could be modeled in terms of a reversible sorption process using similar Kd values. These findings allow 85Sr uptake to be interpreted in terms of an isotopic exchange process with pristine Sr. Sr K-edge EXAFS measurements on Sr doped HCP and calcium silicate hydrate (C-S-H) samples reveal no significant differences in the local coordination environments of pristine Sr and Sr bound to the cement matrix upon sorption. The first coordination sphere consists of five to six oxygen atoms located at a distance of about 2.6 A, which corresponds to Sr-O distances in the hydration sphere of Sr2+ in alkaline solution. Sr binds to the cement matrix via two bridging oxygen atoms located at a distance of about 3.6 A. No further neighboring atoms could be detected, indicating that Sr is taken up as a partially hydrated species by HCP. Wet chemistry and spectroscopic data further indicate that Sr binding to C-S-H phases is likely to be the controlling uptake mechanism in the cement matrix, which allows Sr uptake by HCP to be predicted based on a Ca-Sr ion exchange model previously developed for Sr binding to C-S-H phases. The latter finding suggests that long-term predictions of Sr immobilization in the cementitious near field of repositories for radioactive waste can be based on a simplified sorption model with C-S-H phases.

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Section: Introductionmentioning

confidence: 99%

Strontium Uptake by Cementitious Materials

Wieland

Tits

Kunz

et al. 2007

Environ. Sci. Technol.

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“…The safety of repositories for radioactive waste is based on the multiple barrier concept, whereby both engineered and natural barriers between the waste and the surface act in concert to contain the wastes [1]. Deep geological repository concepts for nuclear waste disposal may include a clay barrier around the waste containers, which is the main retarding/retention component once the failure of the canister and the oxidation/dissolution of the combustible matrix are produced.…”

Section: Introductionmentioning

confidence: 99%

Changes in the microstructure of compacted bentonite caused by heating and hydration

et al. 2016

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Abstract. Two twin 40-cm long columns of compacted FEBEX bentonite were tested in Teflon cells; water was supplied through the top surface of the columns and in one of them a heater was placed at the base and set to 100°C. The purpose of these tests was to simulate the behaviour of an engineered barrier in a radioactive waste repository and investigate the effect of the thermal gradient on saturation. In particular, changes in the pore size distribution and interlayer size have been investigated in this work. The thermal gradient had a strong influence on the water intake and distribution. Water content and dry density gradients persisted in the two columns after 12 years of testing. These changes gave place to the modification of the bentonite microstructure, overall increasing the microstructural void ratio and the proportion of adsorbed, interlayer water.

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“…In Switzerland, for example, it is planned to dispose of cement-stabilized radioactive wastes arising from electricity production in nuclear power plants as well as medicine, industry, and research in a deep geological repository. Hardened cement paste (HCP) is used to condition and stabilize the waste materials and to construct the engineered barrier systems (container, backfill, and liner materials) of repositories for radioactive waste . Therefore, a mechanistic understanding of the processes governing the binding and retention of heavy metals in cement systems is essential for long-term predictions of the environmental impact of cement-stabilized waste forms.…”

Section: Introductionmentioning

confidence: 99%

Soft X-ray Spectromicroscopy of Cobalt Uptake by Cement

Dähn¹,

Vespa²,

Tyliszczak³

et al. 2011

Environ. Sci. Technol.

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Scanning transmission X-ray microscopy was used to investigate the speciation and spatial distribution of Co in a Co(II)-doped cement matrix. The aim of this study was to improve the understanding of the heavy metals immobilization process in cement on the molecular level. The Co-doped cement samples hydrated for 30 days with a Co loading of 5000 mg/kg were prepared under normal atmosphere to simulate conditions used for cement-stabilized waste packages. Co 2p(3/2) absorption edge signals were used to determine the spatial distributions of the metal species in the Co(II)-doped cement. The speciation of Co was determined by collecting near-edge X-ray absorption fine structure spectra. On the basis of the shape of the absorption spectra, it was found that Co(II) is partly oxidized to Co(III). The correlation, respectively the anticorrelation with elements such as Al, Si, and Mn, show that Co(II) is predominantly present as Co-hydroxide-like phase as well as Co-phyllosilicate, whereas Co(III) tends to be incorporated only into a CoOOH-like phase. Thus, this study suggests that thermodynamic calculations of Co(II)-immobilization by cementitious systems should take into consideration not only the solubility of Co(II)-hydroxides but also Co(III) phases.

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Preface

Cited by 9 publications

References 0 publications

Strontium Uptake by Cementitious Materials

Strontium Uptake by Cementitious Materials

Changes in the microstructure of compacted bentonite caused by heating and hydration

Soft X-ray Spectromicroscopy of Cobalt Uptake by Cement

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