Aqueous hydroxylation mediated synthesis of crystalline calcium uranate particles

Ding, Weixuan; Botha, Johannes A.; Hanson, Bruce; Burke, Ian T.

doi:10.1016/j.jallcom.2016.07.140

Cited by 9 publications

(2 citation statements)

References 57 publications

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“…Although the calcium uranate phase identified in this system is a high-temperature phase (Takahashi et al, 1993), hydrous forms of calcium uranate exist (e.g. CaU 2 O 7 ÁxH 2 O (cr) ) and calcium uranate phases are typically solubility limiting for U/Ca at high pH (Finch & Ewing, 1997;Valsami-Jones & Ragnarsdo ¨ttir, 1997;Sutton et al, 2003;Ding et al, 2016;Ding, 2017 The geochemical modelling predictions were evaluated upon XRD analysis of the U VI -contacted phases (Fig. 4).…”

Section: Phase Analysis Before and After U VI Contactmentioning

confidence: 99%

Spectroscopic evaluation of U^VI–cement mineral interactions: ettringite and hydrotalcite

Yorkshire¹,

Stennett²,

Walkley³

et al. 2022

J Synchrotron Rad

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Portland cement based grouts used for radioactive waste immobilization contain high replacement levels of supplementary cementitious materials, including blast-furnace slag and fly ash. The minerals formed upon hydration of these cements may have capacity for binding actinide elements present in radioactive waste. In this work, the minerals ettringite (Ca6Al2(SO4)3(OH)12·26H2O) and hydrotalcite (Mg6Al2(OH)16CO3·4H2O) were selected to investigate the importance of minor cement hydrate phases in sequestering and immobilizing UVI from radioactive waste streams. U L III-edge X-ray absorption spectroscopy (XAS) was used to probe the UVI coordination environment in contact with these minerals. For the first time, solid-state 27Al magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy was applied to probe the Al coordination environment in these UVI-contacted minerals and make inferences on the UVI coordination, in conjunction with the X-ray spectroscopy analyses. The U L III-edge XAS analysis of the UVI-contacted ettringite phases found them to be similar (>∼70%) to the uranyl oxyhydroxides present in a mixed becquerelite/metaschoepite mineral. Fitting of the EXAFS region, in combination with 27Al NMR analysis, indicated that a disordered Ca- or Al-bearing UVI secondary phase also formed. For the UVI-contacted hydrotalcite phases, the XAS and 27Al NMR data were interpreted as being similar to uranyl carbonate, that was likely Mg-containing.

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Section: Phase Analysis Before and After U VI Contactmentioning

confidence: 99%

Spectroscopic evaluation of U^VI–cement mineral interactions: ettringite and hydrotalcite

Yorkshire¹,

Stennett²,

Walkley³

et al. 2022

J Synchrotron Rad

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“… 13 also noted that at higher Ca/Si ratios of C–S–H, and increased U(VI) loadings, a calcium uranate phase was observed due to oversaturation. It is well understood that calcium uranate phases will be solubility limiting for U(VI) in cementitious waters with high Ca content 16 , 43 , 44 . Geochemical modelling identified the formation of calcium uranate in all of the U(VI)/C–S–H systems studied here and the results from XANES linear combination fittings were indicative of signal contributions from calcium uranate phases (CaUO 4 or Ca 3 UO 6 ).…”

Section: Resultsmentioning

confidence: 99%

Spectroscopic identification of Ca-bearing uranyl silicates formed in C–S–H systems

Yorkshire

Stennett

Walkley

et al. 2023

Sci Rep

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Portland cement-based grouts used for radioactive waste immobilisation contain a Ca- and Si-rich binder phase, known as calcium–silicate–hydrate (C–S–H). Depending on the blend of cement used, the Ca/Si ratio can vary considerably. A range of C–S–H minerals with Ca/Si ratios from 0.6 to 1.6 were synthesised and contacted with aqueous U(VI) at 0.5 mM and 10 mM concentrations. Solid-state 29Si MAS-NMR spectroscopy was applied to probe the Si coordination environment in U(VI)-contacted C–S–H minerals and, in conjunction with U LIII-edge X-ray absorption spectroscopy analysis, inferences of the fate of U(VI) in these systems were made. At moderate or high Ca/Si ratios, uranophane-type uranyl silicates or Ca-uranates dominated, while at the lowest Ca/Si ratios, the formation of a Ca-bearing uranyl silicate mineral, similar to haiweeite (Ca[(UO2)2Si5O12(OH)2]·3H2O) or Ca-bearing weeksite (Ca2(UO2)2Si6O15·10H2O) was identified. This study highlights the influence of Ca/Si ratio on uranyl sequestration, of interest in the development of post-closure safety models for U-bearing radioactive waste disposal.

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ChemInform Abstract: Aqueous Hydroxylation Mediated Synthesis of Crystalline Calcium Uranate Particles.

et al. 2016

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Aqueous hydroxylation mediated synthesis of crystalline calcium uranate particles

Cited by 9 publications

References 57 publications

Spectroscopic evaluation of U^VI–cement mineral interactions: ettringite and hydrotalcite

Spectroscopic evaluation of U^VI–cement mineral interactions: ettringite and hydrotalcite

Spectroscopic identification of Ca-bearing uranyl silicates formed in C–S–H systems

ChemInform Abstract: Aqueous Hydroxylation Mediated Synthesis of Crystalline Calcium Uranate Particles.

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Aqueous hydroxylation mediated synthesis of crystalline calcium uranate particles

Cited by 9 publications

References 57 publications

Spectroscopic evaluation of UVI–cement mineral interactions: ettringite and hydrotalcite

Spectroscopic evaluation of UVI–cement mineral interactions: ettringite and hydrotalcite

Spectroscopic identification of Ca-bearing uranyl silicates formed in C–S–H systems

ChemInform Abstract: Aqueous Hydroxylation Mediated Synthesis of Crystalline Calcium Uranate Particles.

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Spectroscopic evaluation of U^VI–cement mineral interactions: ettringite and hydrotalcite

Spectroscopic evaluation of U^VI–cement mineral interactions: ettringite and hydrotalcite