Mineral phases and properties of alkali-activated metakaolin-slag hydroceramics for a disposal of simulated highly-alkaline wastes

Chen, Song; Wu, Mengqiang; Zhang, Shuren

doi:10.1016/j.jnucmat.2010.05.015

Cited by 29 publications

(12 citation statements)

References 24 publications

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“…Both zeolites are fully consumed after 7 d of reaction. Sodalite-type zeolites can be formed from zeolite NaA (which is a closely related framework structure) under highly alkaline conditions (Deng et al, 2006;Chen et al, 2010), which suggests that the increased alkalinity, compared with that reached when using sodium carbonate as Bernal et al, 2013;Escalante-García et al, 2003). The intensities of the reflections assigned to these phases increase substantially during the first 45 d of curing, with only minor variations at advanced age (180 d), consistent with the deceleration of the progressive activation process after the first months of reaction.…”

Section: Isothermal Calorimetrymentioning

confidence: 99%

Alkali-activated slag cements produced with a blended sodium carbonate/sodium silicate activator

Bernal¹,

Nicolas²,

Provis³

et al. 2015

Advances in Cement Research

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An alkali-activated slag cement produced with a blend of sodium carbonate/sodium silicate activator was characterised. This binder hardened within 12 h and achieved a compressive strength of 20 MPa after 24 h of curing under ambient conditions, which is associated with the formation of an aluminium substituted calcium silicate hydrate as the main reaction product. Carbonates including pirssonite, vaterite, aragonite and calcite were identified along with the zeolites hydroxysodalite and analcime at early times of reaction. The partial substitution of sodium carbonate by sodium silicate reduces the concentration of carbonate ions in the pore solution, increasing the alkalinity of the system compared with a solely carbonate-activated paste, accelerating the kinetics of reaction and supplying additional silicate species to react with the calcium dissolving from the slag as the reaction proceeds. These results demonstrate that this blend of activators can be used effectively for the production of high-strength alkali-activated slag cements, with a microstructure comparable to what has been identified in aged sodium-carbonate-activated slag cements but without the extended setting time reaction usually identified when using this salt as an alkali activator.

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Section: Isothermal Calorimetrymentioning

confidence: 99%

Alkali-activated slag cements produced with a blended sodium carbonate/sodium silicate activator

Bernal¹,

Nicolas²,

Provis³

et al. 2015

Advances in Cement Research

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“…A similar X-ray pattern (c) was observed from Class G/ quartz flour blend cement, implying that the failure of cement was brought about by the presence of portlandite in cement. [17,18], into the autoclaved cement, while the quartz detected came from the Class F fly ash. Since the hydrolysis of sodium silicate activator in water generated two major reactants, sodium hydroxide and silicic acid, the hydrothermal reactions between sodium hydroxide and mullite (3Al 2 To support information on the phase composition of the #80/Class F fly ash blended and nonblended cements described above, FT-IR analyses were carried out for the same cement as those used in the XRD study, over the frequency range of 4000-650 cm -1 ( Figure 11).…”

Section: Xrd and Ft-ir Analysesmentioning

confidence: 99%

Thermal Shock-resistant Cement

Sugama¹,

Pyatina²,

Gill³

2012

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We studied the effectiveness of sodium silicate-activated Class F fly ash in improving the thermal shock resistance and in extending the onset of hydration of Secar #80 refractory cement. When the dry mix cement, consisting of Secar #80, Class F fly ash, and sodium silicate, came in contact with water, NaOH derived from the dissolution of sodium silicate preferentially reacted with Class F fly ash, rather than the #80, to dissociate silicate anions from Class F fly ash. Then, these dissociated silicate ions delayed significantly the hydration of #80 possessing a rapid setting behavior. We undertook a multiple heating -water cooling quenching-cycle test to evaluate the cement's resistance to thermal shock. In one cycle, we heated the 200C-autoclaved cement at 500C for 24 hours, and then the heated cement was rapidly immersed in water at 25C. This cycle was repeated five times. The phase composition of the autoclaved #80/Class F fly ash blend cements comprised four crystalline hydration products, boehmite, katoite, hydrogrossular, and hydroxysodalite, responsible for strengthening cement. After a test of 5-cycle heat-water quenching, we observed three crystalline phase-transformations in this autoclaved cement: boehmite  -Al 2 O 3 , katoite  calcite, and hydroxysodalite  carbonated sodalite. Among those, the hydroxysodalite  carbonated sodalite transformation not only played a pivotal role in densifying the cementitious structure and in sustaining the original compressive strength developed after autoclaving, but also offered an improved resistance of the #80 cement to thermal shock. In contrast, autoclaved Class G well cement with and without Class F fly ash and quartz flour failed this cycle test, generating multiple cracks in the cement. The major reason for such impairment was the hydration of lime derived from the dehydroxylation of portlandite formed in the autoclaved cement, causing its volume to expand.4

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“…The mechanisms of immobilization are both physical and chemical, due to their dense microstructures and chemical sorption capacities . The amorphous or semi‐crystalline structures of geopolymers may even be developed to more stable crystal structures by high‐temperature sintering or hydrothermal synthesis, which would improve the immobilization of radioactive waste elements such as Sr or Cs. On the other hand, a sintering process for geopolymer radioactive waste forms may be regarded as an alternative process for improving the immobilization of a highly alkaline, sodium bearing waste containing large amounts of long‐lived radioactive nuclides ( 137 Cs and 90 Sr) and salts .…”

Section: Introductionmentioning

confidence: 99%

Sintering of metakaolin‐based Na/Ca‐geopolymers and their immobilization of Cs

et al. 2019

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Metakaolin‐based Na/Ca‐geopolymers with a designed composition close to feldspar were used as precursors of Cs immobilization form materials. The sintering behaviors of geopolymers and their sintered materials' immobilization of Cs ions were investigated; the results indicated that the major phases of sintered geopolymers are plagioclase feldspars and feldspathoid. With the addition of Cs to the geopolymers, Cs‐leucite phase and caesium silicates were formed at 1150°C and 1170°C, respectively. It was found that Cs addition can slightly decrease the sintering temperature of geopolymers and make the grains finer. In addition, in order to reduce the volatilization of Cs ions during sintering, sintering temperatures of Cs‐geopolymer were further decreased to 850°C by introducing B2O3. After the geopolymer and Cs‐geopolymer were sintered using a low‐temperature liquid‐phase process, they remained structurally plagioclase feldspars and feldspathoid. Leaching on Product Consistency Test indicates that the leaching concentrations of Cs‐geopolymer samples sintered at higher temperatures are lower than those of samples sintered at lower temperatures. Thus, the increased volatilization of Cs ions at the higher temperatures and the formation of Cs‐leucite phase and caesium silicates can lead to the decrease of leaching concentrations in leachates. Therefore, low sintering temperatures and the fabrication of Cs crystalline ceramics are the key factors toward improving the immobilization of Cs ions.

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Mineral phases and properties of alkali-activated metakaolin-slag hydroceramics for a disposal of simulated highly-alkaline wastes

Cited by 29 publications

References 24 publications

Alkali-activated slag cements produced with a blended sodium carbonate/sodium silicate activator

Alkali-activated slag cements produced with a blended sodium carbonate/sodium silicate activator

Thermal Shock-resistant Cement

Sintering of metakaolin‐based Na/Ca‐geopolymers and their immobilization of Cs

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