Thermal transformation of Cs-clinoptilolite to CsAlSi5O12

Brundu, Antonio; Cerri, Guido

doi:10.1016/j.micromeso.2015.01.029

Cited by 27 publications

(18 citation statements)

References 37 publications

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“…The beneficiation process enabled a powder to be obtained with a clinoptilolite content of about 89 wt %, along with residual amounts of feldspars, glass, opal-CT, biotite, and quartz. This result confirms that the beneficiation process here adopted is effective and replicable [20,22,29,30]. The high ammonium content (2.21 meq/g), along with the low sodium, potassium, calcium, and magnesium contents, indicate that a near end-member of NH 4 -clinoptilolite was obtained.…”

Section: Resultssupporting

confidence: 77%

“…On the other hand, this is the case for a material containing 63 wt % of mullite obtained from zeolite A [13], that shows the morphology of the precursor even if the zeolite structure has been destroyed. The phases nucleated from ES-NH cannot inherit the habitus of clinoptilolite because it is destroyed during the enrichment process [20].…”

Section: Discussionmentioning

confidence: 99%

“…The rock was subjected to the beneficiation process described in previous papers [20,22,29,30], aimed to increase the zeolite content. Briefly, the material was submitted to autogenous comminution and dry sieving.…”

Section: Starting Materials and Beneficiation Processmentioning

confidence: 99%

“…The use of natural zeolites in ceramic production has been evaluated by different research groups, highlighting the advantages, generally a lowering of sintering temperatures and limits, mainly linked to the dark color often observed in the fired products [15][16][17][18][19]. Recent papers show that crystalline materials can be obtained by thermally induced transformation of Cs-and Pb-exchanged clinoptilolite [20][21][22], whereas only an amorphous phase has been achieved from the thermal treatment of a NH 4 -clinoptilolite [23].…”

Section: Introductionmentioning

confidence: 99%

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Thermal Transformation of NH4-Clinoptilolite to Mullite and Silica Polymorphs

2017

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Clinoptilolite is a natural zeolite used for the abatement of ammonium in the treatment of urban wastewater. By considering that mullite was obtained through thermal treatment of NH 4 -exchanged synthetic zeolites, this work aimed to evaluate if this phase can be obtained from NH 4 -clinoptilolite. A material containing about 90 wt % of clinoptilolite, prepared using a Sardinian zeolite-rich rock, was NH 4 -exchanged and subjected to treatments up to 1200 • C. After dehydration, de-ammoniation, and dehydroxylation processes, the clinoptilolite structure collapsed at 600 • C. An association of mullite, silica polymorphs, and glass, whitish in color, was obtained for treatments between 1000 and 1200 • C. The higher degree of crystallinity was reached after a 32 h heating at 1100 • C: mullite 22 wt %, cristobalite 59 wt %, tridymite 10 wt %, glass 9 wt %. It is possible to speed up the kinetics of the transformation by increasing the temperature to 1200 • C, obtaining the same amount of mullite in 2 h, but increasing the residual amorphous fraction (16 wt %). These results indicate that NH 4 -clinoptilolite could represent a raw material of potential interest in the ceramic field, in particular in the production of acid refractory, opening scenarios for a possible reuse of clinoptilolite-based exchangers employed in ammonium decontamination.

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Section: Resultssupporting

confidence: 77%

Section: Discussionmentioning

confidence: 99%

Section: Starting Materials and Beneficiation Processmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Thermal Transformation of NH4-Clinoptilolite to Mullite and Silica Polymorphs

2017

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“…Zeolites are crystalline aluminosilicate microporous minerals and are considered widely used in many potential applications, such as adsorption, ion exchange, drug delivery, and catalysis [1][2][3][4][5][6][7][8][9]. 2 of 16 In particular, Cs-pollucite is interesting because it has strong basic sites due to the presence of the alkali Cs + cation [10,11]. In addition, it has a three-dimensional open channel with an eight-membered ring pore size (pore opening 2.43 Å) forming a high thermally stable ANA framework structure [12].…”

Section: Introductionmentioning

confidence: 99%

Hierarchical Cs–Pollucite Nanozeolite Modified with Novel Organosilane as an Excellent Solid Base Catalyst for Claisen–Schmidt Condensation of Benzaldehyde and Acetophenone

et al. 2020

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Cs–pollucite can be a potential solid base catalyst due to the presence of (Si-O-Al)−Cs+ basic sites. However, it severely suffers from molecular diffusion and pore accessibility problems due to its small micropore opening. Herein, we report the use of new organosilane, viz. dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride (TPOAC), as a promising pore-expanding agent to develop the hierarchical structure in nanosized Cs–pollucite. In respect to this, four different amounts of TPOAC were added during the synthesis of hierarchical Cs–pollucite (CP-x, x = 0, 0.3, 1.0, or 2.0, where x is the molar ratio of TPOAC) in order to investigate the effects of TPOAC in the crystallization process of Cs–pollucite. The results show that an addition of TPOAC altered the physico-chemical and morphological properties of hierarchical Cs–pollucite, such as the crystallinity, crystallite size, pore size distribution, surface areas, pore volume, and surface basicity. The prepared solids were also tested in Claisen–Schmidt condensation of benzaldehyde and acetophenone, where 82.2% of the conversion and 100% selectivity to chalcone were achieved by the CP-2.0 catalyst using non-microwave instant heating (200 °C, 100 min). The hierarchical CP-2.0 nanocatalyst also showed better catalytic performance than other homogenous and heterogeneous catalysts and displayed a high catalyst reusability with no significant deterioration in the catalytic performance even after five consecutive reaction runs.

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New insights on pressure, temperature, and chemical stability of CsAlSi5O12, a potential host for nuclear waste

et al. 2016

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A Cs-bearing polyphase aggregate with composition\ud (in wt%): 76(1)CsAlSi5O12 + 7(1)CsAlSi2O6 + 17(1)amorphous,\ud was obtained from a clinoptilolite-rich epiclastic\ud rock after a beneficiation process of the starting material\ud (aimed to increase the fraction of zeolite to 90 wt%),\ud cation exchange and then thermal treatment. CsAlSi5O12\ud is an open-framework compound with CAS topology;\ud CsAlSi2O6 is a pollucite-like material with ANA topology.\ud The thermal stability of this polyphase material was\ud investigated by in situ high-T X-ray powder diffraction,\ud the combined P–T effects by a series of runs with a singlestage\ud piston cylinder apparatus, and its chemical stability\ud following the “availability test” (“AVA test”) protocol.\ud A series of additional investigations were performed by\ud WDS–electron microprobe analysis in order to describe\ud the P–T-induced modification of the material texture, and\ud to chemically characterize the starting material and the\ud run products. The “AVA tests” of the polyphase aggregate\ud show an extremely modest release of Cs+: 0.05 mg/g. In response to applied temperature and at room P, CsAlSi5O12\ud experiences an unquenchable and displacive Ama2-\ud to-Amam phase transition at about 770 K, and the Amam\ud polymorph is stable in its crystalline form up to 1600 K; a\ud crystalline-to-amorphous phase transition occurs between\ud 1600 and 1650 K. In response to the applied P = 0.5 GPa,\ud the crystalline-to-amorphous transition of CsAlSi5O12\ud occurs between 1670 and 1770 K. This leads to a positive\ud Clapeyron slope (i.e., dP/dT > 0) of the crystallineto-amorphous\ud transition. When the polyphase aggregate\ud is subjected at P = 0.5 GPa and T > 1770 K, CsAlSi5O12\ud melts and only CsAlSi2O6 (pollucite-like; dominant) and\ud Cs-rich glass (subordinate) are observed in the quenched\ud sample. Based on its thermo-elastic behavior, P–T phase\ud stability fields, and Cs+ retention capacity, CsAlSi5O12 is a\ud possible candidate for use in the immobilization of radioactive\ud isotopes of Cs, or as potential solid hosts for 137Cs\ud γ-radiation source in sterilization applications. More in\ud general, even the CsAlSi5O12-rich aggregate obtained by a\ud clinoptilolite-rich epiclastic rock appears to be suitable for\ud this type of utilizations

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Thermal transformation of Cs-clinoptilolite to CsAlSi5O12

Cited by 27 publications

References 37 publications

Thermal Transformation of NH4-Clinoptilolite to Mullite and Silica Polymorphs

Thermal Transformation of NH4-Clinoptilolite to Mullite and Silica Polymorphs

Hierarchical Cs–Pollucite Nanozeolite Modified with Novel Organosilane as an Excellent Solid Base Catalyst for Claisen–Schmidt Condensation of Benzaldehyde and Acetophenone

New insights on pressure, temperature, and chemical stability of CsAlSi5O12, a potential host for nuclear waste

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