Strontium binding by calcium silicate hydrates

Tits, J.; Wieland, Erich; Müller, Christian J.; Landesman, Catherine; Bradbury, Michael E.

doi:10.1016/j.jcis.2006.03.043

Cited by 105 publications

(86 citation statements)

References 25 publications

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“…After an ageing period of at least 2 weeks, the C-S-H suspensions were ready for further use in sorption experiments. A detailed characterization of these C-S-H phases is provided in [38]. The composition of ACW is based on an estimate of the pore water composition in HCP before any degradation of the material had occurred.…”

Section: Methodsmentioning

confidence: 99%

“…The C:S ratio of C-S-H phases correlates with both the pH and the Ca concentration in solution (e.g., [30,[33][34][35]38]). An increase in the C:S ratio from 0.67 to 1.65 results in a pH increase from 10.1 to 12.5 and an increase in the Ca concentration from ∼5 × 10 −4 M to 2 × 10 −2 M. In ACW, at a constant pH of 13.3, the Ca concentration increases from ∼ 10 −5 M to 1.6 × 10 −3 M at increasing C:S ratios between 0.67 and 1.29 [38]. The change in the C:S ratio further induces changes in the structure of the C-S-H phases.…”

Section: Sorption Studies On C-s-h Phasesmentioning

confidence: 99%

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Influence of the redox state on the neptunium sorption under alkaline conditions: Batch sorption studies on titanium dioxide and calcium silicate hydrates

Tits¹,

Laube²,

Wieland

et al. 2014

Radiochimica Acta

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Influence of the redox state on the neptunium sorption under alkaline conditions: Batch sorption studies on titanium dioxide and calcium silicate hydrates Abstract: Wet chemistry experiments were carried out to investigate the effect of the redox state and aqueous speciation on the uptake of neptunium by titanium dioxide (TiO 2 ) and by calcium silicate hydrates (C-S-H) under alkaline conditions. TiO 2 was chosen as a reference sorbent to determine the surface complexation behaviour of neptunium under alkaline conditions. C-S-H phases are important constituents of cement and concrete. They may contribute significantly to radionuclide retention due to their high recrystallization rates making incorporation the dominating sorption mechanism for many radionuclides (e.g. the actinides) on these materials. The sorption of neptunium on both solids was found to depend strongly on the degree of hydrolysis. On TiO In addition to the effect of hydrolysis, the presence of Ca is found to promote Np(V) and Np(VI) sorption on TiO 2 whereas on C-S-H phases, the present wet chemistry data do not give unambiguous evidence. Thus, the aqueous speciation appears to have a similar influence on the sorption of the actinides on both types of solids despite the different sorption mechanism.The similar d values for Np(IV,V,VI) sorption at pH = 10 can be explained qualitatively by invoking inter-ligand electrostatic repulsion between OH groups in the coordination sphere of Np(V) and Np(VI). This mechanism was proposed earlier in the literature for the prediction of actinide complexation constants with inorganic ligands. A limiting coordination number for each Np redox state, resulting from the inter-ligand electrostatic repulsion, allows the weaker sorption of the highest hydrolysed Np(V,VI) species to be explained.

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Section: Methodsmentioning

confidence: 99%

Section: Sorption Studies On C-s-h Phasesmentioning

confidence: 99%

Influence of the redox state on the neptunium sorption under alkaline conditions: Batch sorption studies on titanium dioxide and calcium silicate hydrates

Tits¹,

Laube²,

Wieland

et al. 2014

Radiochimica Acta

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“…C-S-H phases with target CaO/SiO 2 (C/S) molar ratios of 0.7, 1.07 and 1.8 were synthesized in Milli-Q water (alkali-free solution) or ACW (alkali-rich solution), respectively. Details of synthesis of these C-S-H phases leading to effective C/S ratios of 0.75, 1.07 and 1.65 were reported elsewhere [13].…”

Section: Preparation Of U(vi)-doped Samplesmentioning

confidence: 99%

EXAFS investigation on U(VI) immobilization in hardened cement paste: influence of experimental conditions on speciation

Macé¹,

Wieland²,

Dähn³

et al. 2013

Radiochimica Acta

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U(VI) / Speciation / Cement / (Micro-)EXAFSSummary. Extended X-ray absorption fine structure (EXAFS) spectroscopy has been used to investigate the coordination environment of U(VI) in cementitious materials. The EXAFS measurements were carried out on U(VI)-doped samples prepared under varying conditions, such as samples from sorption, hydration and diffusion experiments, and using different cementitious materials, such as crushed hardened cement paste (HCP) and calcium silicate hydrates (C-S-H). The samples had U(VI) loadings ranging from 1700 μg/g to 45 000 μg/g. Applying principal component analysis (PCA) on 13 EXAFS spectra (each spectra corresponding to a minimum of five different scans) of the low loading samples, one single species is obtained indicating a similar U(VI) coordination environment for both HCP and C-S-H samples. This result confirms that C-S-H phases control the uptake of U(VI) in the complex cement matrix. The coordination environment of this species is similar to a U(VI) surface complex or to U(VI) in uranyl silicate minerals (two axial O atoms at 1.82 ± 0.02 Å; four equatorial O atoms at 2.25 ± 0.01 Å; one Si atom at 3.10 ± 0.03 Å). At high U(VI) loading, PCA revealed a second U(VI) species, with a coordination environment similar to that of U(VI) in calcium uranate (two axial O atoms at 1.94 ± 0.04 Å; five equatorial O atoms at 2.26 ± 0.01 Å; four Ca atoms at 3.69 ± 0.05 Å and five U atoms at 3.85 ± 0.04 Å).

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“…The effective C:S mol ratios were determined to be 0.75, 1.07, and 1.15 from mass balance calculations. Synthesis and characterization of the C-S-H phases prepared using the direct reaction method are described elsewhere [36].…”

Section: Synthesis Of C-s-h Phasesmentioning

confidence: 99%