Nitrate Cancrinite Research Articles

Experimental determination of solubility constants of saponite at elevated temperatures in high ionic strength solutions

Abstract Saponite occurs in a wide range of environments from hydrothermal systems on the Earth to surface deposits on Mars. Of practical importance is that Mg-saponite forms when glasses for nuclear waste are altered in Mg-bearing aqueous solutions. In addition, saponite is favorably considered as candidate buffer material for the disposal of high-level nuclear waste and spent nuclear fuel in harsh environments. However, the thermodynamic properties, especially for Mg-saponites, are not well known. Here the author synthesized Mg-saponite (with nitrate cancrinite) following a previously reported procedure and performed solubility experiments at 80 °C to quantify the thermodynamic stability of this tri-octahedral smectite in the presence of nitrate cancrinite. Then, in combination with the equilibrium constant at 80 °C for the dissolution reaction of nitrate cancrinite from the literature, the author determined the solubility constant of saponite at 80 °C based on the solution chemistry for the equilibrium between saponite and nitrate cancrinite, approaching equilibrium from the direction of supersaturation, with an equilibrium constant of –69.24 ± 2.08 (2σ) for dissolution of saponite at 80 °C. Furthermore, the author extrapolated the equilibrium constant at 80 °C to other temperatures (i.e., 50, 60, 70, 90, and 100 °C) using the one-term isocoulombic method. These equilibrium constants are expected to have applications in numerous fields. For instance, according to the extrapolated solubility constant of saponite at 50 and 90 °C, the author calculated the saturation indexes with regard to saponite for the solution chemistry from glass corrosion experiments at 50 and 90 °C from the literature. The results are in close agreement with the experimental data. This example demonstrates that the equilibrium constants determined in this study can be used for reliable modeling of the solution chemistry of glass corrosion experiments.

Cesium immobilization in nitrate-bearing metakaolin-based geopolymers

Low-level nuclear wastes containing radioactive cesium (Cs) are often highly alkaline and rich in sodium nitrate. The goal of the present study was to examine immobilization of cesium in nitrate-bearing geopolymers with low Si/Al ratio (SiO2:Al2O3 < 2.0), which are known to have relatively high crystalline phase content.Geopolymers were prepared by activating metakaolin with a mixed NaOH-CsOH solution containing NaNO3 where Cs+ ions make up 7% of the total alkali content. Geopolymer samples were cured at 40±3 °C for up to 3 months. The structure of the cured geopolymers after varying curing times was characterized by XRD and FTIR, and the immobilization efficiency for Cs+, Na+ and NO3− was determined from leaching tests following the ANSI/ANS-16.1 standard procedure for low and intermediate level nuclear wasteforms.The first phase crystallized from the amorphous gel was zeolite A. This phase gradually undergoes further transformations to yield the nitrate-bearing feldspathoids, nitrate sodalite and nitrate cancrinite. The leaching curves for Cs+, Na+ and NO3− ions were clearly not linear with t1/2, suggesting a change in leaching mechanism after the initial 24 hours of the leaching experiment. The apparent diffusion constants, Da, as well as leaching indices for Cs+ and Na+ were therefore calculated separately for the 1st and 2nd time domains of the experiment (t1/2 < 1 days1/2 and t1/2 > 2.65 days1/2, respectively). The leachability indices for Cs+ were found to increase with increasing curing time (from 7.4 and 11.2 for the 1st and 2nd time domains after 1 month of curing to 9.6 and 12.6 for the 1st and 2nd time domains after 3 months of curing). The enhanced immobilization of Cs+ is correlated with the formation of the nitrate-bearing feldspathoid phases.

A simple synthesis of nitrate cancrinite from natural bentonite

A nearly pure, pale brown, spherical, nitrate cancrinite zeolite was successfully synthesized from natural bentonite as starting material with acidic activation treatment via hydrothermal method at 368 K for 24 h. The effect of different NaOH concentrations (pH at around 12) was investigated without addition of silica and aluminum sources. The effect of different NaOH concentrations (pH at around 12) was investigated without addition of silica and aluminum sources. The final products were characterized by powder X-ray diffraction, scanning electron microscopy, elemental and thermal analyses, infrared (IR) spectroscopy, and Brunauer–Emmett–Teller (BET) surface area measurements. While the Si/Al ratio of ideal cancrinite is 1.0, the Si/Al ratio of the product framework is approximately 1.76, apart from trace components. Unique single nitrate band was observed in both IR and thermogravimetric measurements, indicating that pure cancrinite was synthesized. This study showed that pure nitrate cancrinite was obtained with NaOH concentrations from 8 to 12 M, independent of NaOH contents on crystallization. Through this study, we proposed a simple synthesis method for pure nitrate cancrinite from bentonite for the purpose of recycling natural clay minerals.

The formation of crystalline phases in metakaolin-based geopolymers in the presence of sodium nitrate

Geopolymers generated by alkali-activation of amorphous aluminosilicate sources are considered as an alternative immobilizing matrix for hazardous and nuclear wastes. Low and intermediate level nuclear waste streams are often highly alkaline saline solutions containing various concentrations of nitrate salts. The aim of the research project presented here was to study the effect of nitrate ions on the formation and evolution of metakaolin-based geopolymeric systems at moderate temperatures, i.e., at 40 °C. Metakaolin was alkali-activated using NaOH solutions of varying concentrations, yielding H2O:OH- ratios of 5.50, 9.15, 13.75, and 27.50. Sodium nitrate was added to the activation solutions at a constant [NO3 −]: [OH−] ratio of 0.25. Most geopolymeric mixtures were designed to obtain a Na2O:Al2O3 ratio of 1.00 for nitrate-free mixtures, or 1.25 for those including sodium nitrate. In addition, the effect of deviation from these values (Na2O:Al2O3 ratios of 0.84 and 1.20 for nitrate-free samples, 1.04 and 1.50 for nitrate-bearing samples) was also studied. The samples were cured in sealed containers at 40 °C for periods ranging from 1 day to 3 months. The products were characterized by X-ray diffractometry, Fourier transform mid-infrared spectroscopy, and scanning electron microscopy as well as by compressive strength measurements. The results demonstrate the influence of composition, alkalinity, SiO2:Al2O3 ratio, Na2O:Al2O3 ratio, nitrate concentration, and curing times on the mineralogy of the geopolymeric matrix. Various crystalline phases such as zeolite A, zeolite X, and nitrate-bearing phases, namely nitrate sodalite and nitrate cancrinite, were identified among the reaction products. The sequence of phase evolution in these geopolymeric systems was elucidated.

Effect of solution composition on the recrystallization of kaolinite to feldspathoids in hyperalkaline conditions: limitations of pertechnetate incorporation by ion competition effects

AbstractThe incorporation of pertechnetate (TcO4–) into feldspathoids produced by alkaline alteration of aluminosilicate clays may offer a potential treatment route for 99Tc-containing groundwater and liquors. Kaolinite was aged in NaOH to determine the effect of base concentration, temperature, and solution composition on mineral transformation and pertechnetate uptake. In all reactions, increased temperature and NaOH concentration increased the rate of kaolinite transformation to feldspathoid phases. In reactions containing only NaOH, sodalite was the dominant alteration product; however, small amounts (6–15%) of cancrinite also formed. In experiments containing NaOH/Cl and NaOH/NO3 mixtures, sodalite and nitrate cancrinite were crystallized (at 70°C), with no reaction intermediates. The addition of SO42– crystallized sulfatic sodalite at 40 and 50°C, but at higher temperatures (60 and 70°C) sulfatic sodalite transforms to vishnevite (sulfatic cancrinite). In experiments where a pertechnetate tracer was added (at ∼1.5 μmol l–1), only 3–5% of the 99Tc was incorporated into the feldspathoid phases. This suggests that the larger pertechnetate anion was unable to compete as favourably for the internal vacancies with the smaller OH–, NO3–, SO42– or Cl– anions in solution, making this method likely to be unsuitable for groundwater treatment.

Crystal structure of nitrate cancrinite synthesized under low-temperature hydrothermal conditions

Crystal structure of nitrate cancrinite synthesized under low-temperature hydrothermal conditions

ChemInform Abstract: Synthesis, X-Ray Diffraction and MAS NMR Characteristics of Nitrate Cancrinite Na7.6 [AlSiO4] 6(NO3)1.6(H2O)2.

Abstract Investigations on the hydrothermal formation and the crystal structure of nitrate cancrinite have been carried out in the system Na2O–xSiO2–Al2O3–NaNO3–H2O, 1

One‐Pot Synthesis, X‐Ray Diffraction and MAS NMR Spectroscopic Study of Gallosilicate Nitrate Cancrinite Na8[GaSiO4]6(NO3)4(H2O)6

One‐pot synthetic gallosilicate nitrate cancrinite (CAN) framework topology have been synthesized under hydrothermal conditions at 100 °C. The synthesized product was characterized by, X‐ray powder diffraction, IR, Raman and 29Si, 23Na MAS NMR spectroscopy, SEM and thermogravimetry. The crystal structure refinement of pure nitrate cancrinite has been carried out from X‐ray data using Rietveld refinement method. Gallosilicate cancrinite Na8[GaSiO4]6(NO3)4(H2O)6 crystalline hexagonal with space group P63 and a = 12.77981 Å (2), c = 5.20217 Å (1), (Rwp = 0.0696 Rp = 0.0527). The results by MAS NMR spectroscopy confirmed the alternating Si, Ga ordering of the gallosilicate framework for a Si/Ga ratio of 1.0. A distribution of the quadrupolar interaction of the sodium cations caused by the enclatherated water molecules and motional effects can be suggested from the 23Na MAS NMR. Thermogravimetric investigation shows the extent of nitrate entrapment, stability within the cancrinite cage and decomposition properties. SEM clearly shows the hexagonal needle shaped crystals of nitrate cancrinite.

Influence of the alkalinity and [formula omitted]/Cl − anionic composition on the synthesis of the cancrinite–sodalite system

The formation conditions of nitrate–cancrinite and chlorosodalite-type zeolites were studied by investigating the influence of the pH and NO 3 - /Cl − ratios on the synthesis of these compounds. The pH was varied by using different NaOH concentrations i.e., 3, 8 and 16 mol/L (aqueous solution) and the ratio of NO 3 - /Cl − ions was defined by different weight fractions of NaNO 3/(NaNO 3 + NaCl) i.e., 0, 25, 50, 75 and 100%. In the case of 3 M NaOH one additional experiment with 2% NaNO 3 was carried out in order to investigate that area of the phase system in more detail. All of the reactions were carried out at 80 °C and under autogenous pressure for 40 h. Zeolite X was used as silicon and aluminum source. The obtained solids were characterized by powder X-ray diffraction (XRD), FTIR-spectroscopy, scanning electron microscopy (SEM) including elemental analyses using the EDX method and BET surface area measurements. The study shows that pure nitrate–cancrinite was obtained with all NO 3 - /Cl − compositions with NO 3 - contents from 2% to 100% and independently of the NaOH concentration. With 3 M NaOH and 0% NO 3 - (=100% Cl −) the reaction lead to a mixture of chlorosodalite and the starting material zeolite X. Pure chlorosodalite could only be synthesized if the reaction gel was formulated with 0% NO 3 - and at higher NaOH concentrations (8 and 16 M). These results allowed to deduce a dependency of the formation of the different phases in the studied zeolite system of the NaOH and the NO 3 - concentration.

Nitrate cancrinite: Synthesis, characterization, and determination of the enthalpy of formation

Nitrate cancrinite, with an ideal formula of Na 8[Al 6Si 6O 24](NO 3) 2 · 4H 2O, is an important constituent of high-level nuclear wastes at several US Department of Energy (DOE) storage sites. A simple synthesis route for this material is described. Pure nitrate cancrinite has been prepared using a mixed solution of sodium silicate, sodium aluminate, sodium nitrate, and sodium hydroxide. Crystallization took place rapidly at 90 °C and the cancrinite phase emerged within a few hours of aging. Both X-ray diffraction and composition analyses indicated the formation of pure nitrate cancrinite. Solution calorimetric measurements of this material were performed with a Calvet-type calorimeter operated at 701 °C using molten lead borate (2PbO · B 2O 3) as the solvent. Enthalpies of formation from the constituent oxides and from the elements are −903.3 ± 15.7 kJ/mol and −14,258.3 ± 17.3 kJ/mol, respectively, for a sample with the analyzed formula of Na 7.282[Al 5.854Si 6.146O 24](NO 3) 1.336(CO 3) 0.046 · 3.365H 2O.

Sodium cation dynamics in nitrate cancrinite: A low and high temperature23Na and1H MAS NMR study and high temperature Rietveld structure refinement

Static and 23 Na MAS and 1 H MAS NMR experiments at temperatures down to 100 K as well as high temperature static and 23 Na MAS NMR experiments up to 873 K were carried out to study the dynamics of the sodium cation in nitrate cancrinite. In addition, X-ray powder data were recorded at 296 K and 673 K to obtain information about long-range order changes in the structure. Low temperature 23 Na NMR experiments show almost no change in signal, whereas the 1 H MAS NMR spectra show the freezing of cage water motion. The two different crystallographic sodium sites cannot be distinguished in the 23 Na MAS NMR spectra at low and room temperature. In contrast, two 23 Na NMR signals exist at high temperatures above 673 K, a quadrupolar pattern and a Lorentzian signal. Rietveld structure refinements of powders show no change in the local environment of sodium. The strong quadrupolar coupling results from the loss of cage water and the near planar O atom coordination of Na in the ε-cage, while the interaction of Na + in the channel remains similar. Thus the change in quadrupolar interaction is mainly caused by the absence of electrostatic shielding of cage water after dehydration

Synthesis, X-ray diffraction and MAS NMR characteristics of nitrate cancrinite Na 7.6[AlSiO 4] 6(NO 3) 1.6(H 2O) 2

Investigations on the hydrothermal formation and the crystal structure of nitrate cancrinite have been carried out in the system Na 2O– xSiO 2–Al 2O 3–NaNO 3–H 2O, 1< x<6. Various starting materials have been examined to find the best reaction system for cancrinite formation under low temperatures and pressures (473 K, autogenous pressure). Additional experiments were performed at elevated conditions at 773 K and 0.15 GPa. Polycrystalline nitrate cancrinite and various amounts of unchanged educts were obtained in all low-temperature experiments. In contrast, in the high-temperature/high-pressure experiments a crossover of sodalite and cancrinite formation was observed as a function of the Si/Al ratio within the starting system for x=1.0, 2.0, 4.0 and 6.0 (i.e. at Si/Al ratios of 0.5, 1.0, 2.0 and 3.0). Structural investigations of nitrate cancrinite were performed by IR and MAS NMR spectroscopy of the nuclei 29Si, 27Al and 23Na. The results confirmed the alternating Si, Al ordering of the alumosilicate framework for a Si/Al ratio of 1.0 for all samples, independent of the Si/Al ratio of the educts as well as the temperature and pressure of crystallization. A distribution of the quadrupolar interaction of the sodium cations caused by the enclathrated water molecules and motional effects can be suggested from the 23Na MAS NMR spectrum. The single line with its slightly asymmetric shape makes it impossible to distinguish the sodium cations inside the structure channel from those located in the ε-cages of the cancrinite structure. In order to complete the study on nitrate cancrinite a single crystal structure refinement was carried out. As in the case of carbonate cancrinite, NO 3 − anions are distributed over two nonequivalent positions in the hexagonal channel of the framework. All the crystal water molecules were found to be arranged in the ε-cages of the cancrinite structure.

Spectroscopic Studies of Aluminosilicate Formation in Tank Waste Simulants

ABSTRACTAluminosilicates are one of the major class of species controlling the volume of radioactive high-level waste that will be produced from future remediation at Hanford site. Here we present studies of the phases and structures of aluminosilicates as a function of sludge composition using X-ray powder diffraction, solid state 27Al and 29Si NMR, and Raman spectroscopy. The results show that the content of NaNO3 in solution has significant effects on the nature of the insoluble aluminosilicate phases produced. It was found that regardless of the initial Si:Al ratio, nitrate cancrinite was the main phase formed in the solution with pH of 13.5 and 5 MNaNO3. However, at lower NaNO3 concentration with initial Si:Al ratios of 1.1, 2.2, and 11.0 in the solutions, a range of aluminosilicate zeolites was produced with Si: Al ratios of 1.1, 1.3, and 1.5, respectively. Lowering the solution pH appears to promote the formation of amorphous aluminosilicates. The results presented here are important for the prediction of the solubility and dissolution rate of Al in tank wastes.