Coupling effect of NaOH and NaNO3 on the solidified fly ash-cement matrices containing Cs+: Reaction products, microstructure and leachability

Zheng, Zhao; Li, Yuxiang; Sun, Haolin; Zuguo, Zhang; Xue, Ming

doi:10.1016/j.jnucmat.2020.152252

Cited by 14 publications

(13 citation statements)

References 37 publications

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“…Indeed, the content of other sodium salts is rather low, which does not appear in the XRD pattern and does not affect the types of crystal products phase in the cement waste forms. As seen from Figure 1(b), the main crystal phase obtained from the fly ash/cement waste forms mixed with simulated LILRW is not different from the waste forms with pure NaNO 3 solution under low content of NaOH in previous study [23].…”

Section: Transformation Of Products and Pore Structuresmentioning

confidence: 52%

“…However, under the condition of high NaOH, the phase was slightly different from the waste forms with NaNO 3 solution, and only the chabazite phase was generated but there was no Na-P1 zeolite which existed in the condition of NaNO 3 solution. Combined with previous studies about the effect of NaOH contents on the product and structure of fly ash/ cement waste forms and the leaching rate of simulated radionuclides [23,25], the NaOH content in the fly ash/ cement waste forms of simulated LILRW in the study below was determined to be 10%.…”

Section: Transformation Of Products and Pore Structuresmentioning

confidence: 89%

“…e low-Ca fly ash and Portland cement (P•O 42.5, China standard: GB175-2007) were used in this study. Table 1 shows the corresponding composition of oxides in the two kinds of raw powder materials, while the particle size and morphology can be seen in reference [23]. e water used in this study was ultrapure water in order to eliminate the influence of impurities on the leaching data.…”

Section: Materials and Preparationmentioning

confidence: 99%

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The Transformation and Leachability of Fly Ash/Cement Waste Forms Subjected to the Simultaneous Effect of Heat and Chemistry

Zheng

Hua

et al. 2022

Advances in Materials Science and Engineering

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The utilization of cement waste forms with high content of fly ash is a potential method in large-volume immobilization of low- and intermedium-level radioactive waste at near-surface. However, the migration behavior of radionuclides in fly ash/cement waste forms under geological environment is still unclear. This study researched the transformation of products, pore structure as well as the leachability of Ca2+, Na+, and simulated radioactive nuclides (Sr2+ and Cs+) in fly ash/cement waste forms under simultaneous effect through X-ray diffractometer (XRD), mercury intrusion porosimetry (MIP), and inductively coupled plasma optical emission spectroscopy (ICP-OES). Furthermore, the relationship between the decalcification and the leaching of Sr2+ and Cs+ was established by the fitting curves of apparent diffusion coefficient. The results indicated that the products of fly ash/cement waste forms were kept stable under simultaneous effect and the pore structure has excellent resistance to temperature. The increasing salt concentrations of leachant and temperature promoted the leaching of radionuclides while the protection layer formed at 60–80°C inhibited this phenomenon. The relationship of apparent diffusion coefficient between Sr2+ and Ca2+ was quadratic nonlinear, while the relationship between Cs+ and Ca2+ showed a linear relationship. Compared to cement waste forms, fly ash/cement waste forms were more stable. In addition, the long-term retention ability of fly ash/cement waste forms to Cs+ was more outstanding than Sr2+.

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Section: Transformation Of Products and Pore Structuresmentioning

confidence: 52%

Section: Transformation Of Products and Pore Structuresmentioning

confidence: 89%

Section: Materials and Preparationmentioning

confidence: 99%

See 1 more Smart Citation

The Transformation and Leachability of Fly Ash/Cement Waste Forms Subjected to the Simultaneous Effect of Heat and Chemistry

Zheng

Hua

et al. 2022

Advances in Materials Science and Engineering

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“…The appearance of distinct diffraction peaks at 2θ = 13.93°, 24.23°, 34.43° after 3 days of curing is indicative of rearrangement of the amorphous phase into crystalline phases. The observed diffraction peaks may be attributed to a zeolite from a chabazite family with a relatively low SiO 2 :Al 2 O 3 ratio of 2, NaAlSiO 4 •XH 2 O (PDF #00-044-0248), which was previously reported to form in FA-based geopolymeric systems [37,38]. Additional peaks belonging to the same crystalline phase at 2θ = 9.33° and 20.63° are observed after a 3 month curing period.…”

Section: Characterization Techniquesmentioning

confidence: 57%

Alkali Activation of Fly Ash in the Presence of Sodium Nitrate

Ofer-Rozovsky

Bar-Nes²,

Katz

et al. 2021

Preprint

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The use of fly ash as a precursor for geopolymer has been investigated during the last decades for various applications. The aim of this research was to study the effect of nitrate on the formation and evolution of fly ash-based geopolymers, in order to assess their applicability as waste immobilization matrices. These may be of interest in order to treat waste streams from agricultural runoff and various industries including the nuclear industry. Fly ash was alkali-activated using NaOH solutions of various alkalinities, to which nitrates were added as NaNO3. The samples were cured at 40֯C for different periods and characterized by X-Ray diffractometry, Fourier transform mid-Infrared spectroscopy, scanning electron microscopy (SEM), and compressive strength measurements. The content of neo-formed crystalline phases in fly ash-based geopolymers was found to be lower than in metakaolin-based systems studied previously. The nature of the minerals formed in nitrate-free samples differed from those obtained in corresponding metakaolin-based geopolymers. Nevertheless, the dominant phase formed in the presence of nitrate at sufficiently high alkalinity was nitrate-cancrinite, as reported for metakaolin-based geopolymers, regardless of the type of fly-ash used. Although the presence of nitrates was found to have a promoting effect on the geopolymerization process of metakaolin-based geopolymers, it was found to inhibit the processes in fly-ash-based geopolymers.The formation of crystalline phases in FA-based geopolymers suggests that these materials may be used for immobilizing various hazardous species, while FA-based geopolymers containing the nitrate-cancrinite can be considered as a promising candidate for immobilizing radionuclides from radioactive wastes.

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“…Alkali can activate fy ash to produce the zeolite phase at high temperature, especially chabazite and P-type zeolite, which have good adsorption and retention efects on simulated radionuclides of Sr and Cs [15,26,27]. Due to the limitation of the ILLRW immobilization process, the way of adding sodium silicate solution is not easy to implement, while the way of adding sodium hydroxide powers is relatively simple.…”

Section: Introductionmentioning

confidence: 99%

In Situ Synthesis of Zeolites in Solidified Fly Ash/Cement Matrices with High Na Content: Products, Pore Structure, and Leaching Behavior

Zheng

Bao

Wang

et al. 2022

Advances in Materials Science and Engineering

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Due to its high retention capacity and well durability, fly ash-based geopolymers rich of zeolites are considered to be potential solidified materials for low- and intermediate-level radioactive waste stream. This study mainly focused on the phase transformation, pore structure, and leaching characteristic of Sr2+ and Cs+ in solidified fly ash/cement matrices under different sodium hydroxide contents or sodium nitrate concentrations after thermal curing of 28 d. The results obtained from the experiments indicated that the geopolymers prepared from pure fly ash had the potential to transform into ordered structures at high temperatures of 90°C instead of room temperature, such as Na-P1 zeolite and chabazite. With the increase in sodium hydroxide contents, more sodium nitrate participated in the reaction to form a zeolite phase in solidified fly ash/cement matrices, while the coexistence phenomenon of chabazite and Na-P1 zeolite appeared under the condition of high sodium hydroxide contents of more than 5%. Just a proper number of zeolites can effectively inhibit the leaching of radionuclides Sr2+, as too many zeolites would lead to the increase in porosity, which was harmful to the retention of radionuclides. Solidified fly ash/cement matrices at a sodium hydroxide content of 5% or at a sodium nitrate concentration of 300 g/L obtained the lowest cumulative leaching fraction of Sr2+. Moreover, sodium hydroxide increased the cumulative leaching fraction of Cs+ which reversely decreased significantly with the increase in sodium nitrate concentrations.

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Coupling effect of NaOH and NaNO3 on the solidified fly ash-cement matrices containing Cs+: Reaction products, microstructure and leachability

Cited by 14 publications

References 37 publications

The Transformation and Leachability of Fly Ash/Cement Waste Forms Subjected to the Simultaneous Effect of Heat and Chemistry

The Transformation and Leachability of Fly Ash/Cement Waste Forms Subjected to the Simultaneous Effect of Heat and Chemistry

Alkali Activation of Fly Ash in the Presence of Sodium Nitrate

In Situ Synthesis of Zeolites in Solidified Fly Ash/Cement Matrices with High Na Content: Products, Pore Structure, and Leaching Behavior

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