Assessment of strontium immobilization in cement–bentonite matrices

Rahman, Rehab O. Abdel; Abidin, D.H.A. Zin El; Abou-Shady, H.

doi:10.1016/j.cej.2013.05.034

Cited by 49 publications

(14 citation statements)

References 44 publications

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“…The low values of boron’s normalized leach rates suggest the formation of smectite alteration phases in the three samples at extended leaching times [37]. From the abovementioned data, it can be concluded that the releases for all studied elements are monotonically increasing with time, and the changes in the slope of the release-time represent a possible change in the controlling leaching mechanisms [7,9,11,12,13,14,27].…”

Section: Resultsmentioning

confidence: 99%

“…Glass leaching mechanisms were evaluated based on the analysis of the experimental data to a collective model that represents the cumulative leach fraction (CLF i ) of the structural elements, modifiers, and waste oxides as superimposed leaching processes that include a first-order reaction exchange between the leaching solution and bounded element on the matrix or the formed colloides, bulk diffusion of elements throughout the matrix, congruent dissolution, and instantaneous release of loosely bounded element from the surface [6,7,9,10,11,12,13,14,36]:CLFi=QOi(1−e−Kinormalt)+(SV)(2Dinormaltπ+Uinormalt)+normalC, where Q oi is the initial exchangeable fraction of element on the surface of the waste form, K i is the rate constant for the exchange reaction (h −1 ), U i is the glass network dissolution rate (m·h −1 ), and D i is the effective diffusion coefficient of the element (m 2 ·h −1 ) .This equation is used in conditions when saturation effects are not important, such as the initial stage of glass dissolution.…”

Section: Methodsmentioning

confidence: 99%

“…Its main safety functions are to ensure structural stability, resist degradation, and limit water ingress and radio-contaminant releases. Several waste matrices have been proposed to stabilize the radioactive/nuclear wastes, including, cement-, bitumen- and polymer-, glass-, and ceramic-based matrices [4,6,7,8,9,10,11,12,13,14]. The main safety function of glass waste matrices is to slow down radionuclide releases from a geological disposal facility [15].…”

Section: Introductionmentioning

confidence: 99%

“…Generally, leaching characteristics of radioactive/nuclear waste matrices are highly dependent on the chemical compositions of the waste matrices and leaching experimental conditions [6,7,8,9,11,12,13,14,15,16,17]. A huge research effort was directed at studying the leaching characteristics of glass-based waste matrices using static and dynamic leaching experiments, i.e., PCT (product consistence test), MCC (Material Characterization Center), and single pass flow through tests, by investigating different waste matrices and leachant compositions at varying pH and temperature values and leachant-to-waste volumes [10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25].…”

Section: Introductionmentioning

confidence: 99%

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An Assessment of Initial Leaching Characteristics of Alkali-Borosilicate Glasses for Nuclear Waste Immobilization

et al. 2019

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Initial leaching characteristics of simulated nuclear waste immobilized in three alkali- borosilicate glasses (ABS-waste) were studied. The effects of matrix composition on the containment performance and degradation resistance measures were evaluated. Normalized release rates are in conformance with data reported in the literature. High Li and Mg loadings lead to the highest initial de-polymerization of sample ABS-waste (17) and contributed to its thermodynamic instability. Ca stabilizes non-bridging oxygen (NBO) and reduces the thermodynamic instability of the modified matrix. An exponential temporal change in the alteration thickness was noted for samples ABS-waste (17) and Modified Alkali-Borosilicate (MABS)-waste (20), whereas a linear temporal change was noted for sample ABS-waste (25). Leaching processes that contribute to the fractional release of all studied elements within the initial stage of glass corrosion were quantified and the main controlling leach process for each element was identified. As the waste loading increases, the contribution of the dissolution process to the overall fractional release of structural elements decreases by 43.44, 5.05, 38.07, and 52.99% for Si, B, Na, and Li respectively, and the presence of modifiers reduces this contribution for all the studied metalloids. The dissolution process plays an important role in controlling the release of Li and Cs, and this role is reduced by increasing the waste loading.

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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An Assessment of Initial Leaching Characteristics of Alkali-Borosilicate Glasses for Nuclear Waste Immobilization

et al. 2019

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“…Its precipitation has been promoted in order to immobilize radioactive elements and toxic metals [31][32][33], for instance strontium [34] and cesium [35]. In a such case, ettringite acts as a host to harmful elements or ions through crystal chemical substitution, both in the calcium and aluminum double hydroxide columns and in the channels among them [31,33].…”

Section: Introductionmentioning

confidence: 99%

Kinetic and thermal decomposition of ettringite synthesized from aqueous solutions

Guimarães

Oliveira

Leão

2016

J Therm Anal Calorim

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The kinetics of the thermal decomposition of a synthetic ettringite sample was studied between 298 and 820 K in an inert atmosphere for the present work. The ettringite and its thermal decomposition products were characterized using X-ray diffraction, infrared spectroscopy, and scanning electron microscopy. Four endothermic events were observed with thermogravimetry curves, the maxima of which occurred at 366, 397, 537, and 641 K. All events were associated with the loss of water molecules with different degrees of interaction within the ettringite structure. Chemical equations for each decomposition step were proposed based on the percentages of mass loss observed. In addition, for the first time, the activation energies of each ettringite decomposition events were determined by the isoconversional methods of Ozawa-Flynn-Wall, Friedman, and Kissinger-AkahiraSunose. The modeling revealed that the activation energy varied from *50 kJ mol -1 , characteristic of mass transfer control steps, to *150 kJ mol -1 , which is typical of chemical control, as the temperature increased and the ettringite structure lost water. A total of 32 mol of water was released equivalent to 43.1 % of the initial sample mass.

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