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Minerals 2018, 8(1), 28; https://doi.org/10.3390/min8010028

Thermal Stability of Woolly Erionite-K and Considerations about the Heat-Induced Behaviour of the Erionite Group

1
Department of Earth Sciences, Sapienza University of Rome, Piazzale A. Moro 5, I-00185 Rome, Italy
2
Rectorial Laboratory Fibres and Inorganic Particulate, Sapienza University of Rome, Piazzale A. Moro 5, I-00185 Rome, Italy
3
Department of Biology, Ecology and Earth Sciences, University of Calabria, Via Pietro Bucci, I-87036 Rende, CS, Italy
4
Department of Pure and Applied Sciences, University of Urbino Carlo Bo, Piazza della Repubblica 13, I-61029 Urbino, PU, Italy
*
Author to whom correspondence should be addressed.
Received: 30 December 2017 / Revised: 15 January 2018 / Accepted: 17 January 2018 / Published: 19 January 2018
(This article belongs to the Special Issue Natural Zeolites)
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Abstract

The thermal behavior of a woolly erionite-K sample (Lander County, NV, USA), chemical formula (Ca2.03Na0.73K2.52Mg0.26)[Al8.22Si27.78O71.80]·35.94H2O, was investigated in the 303–1173 K thermal range by in situ X-ray powder diffraction. Present data suggest a general thermally-induced volume contraction whose magnitude increases as S i S i + A l ratio becomes smaller. An inverse correlation between S i S i + A l ratio and Tdehydr is observed because higher S i S i + A l ratio values are associated to lower dehydration temperatures. A positive dependence exists between S i S i + A l ratio and Tbreak. A higher Si content results in a greater thermal stability, in agreement with the general trend observed in zeolites. On the contrary, no correlation has been found between Tbreak and weighted ionic potential (Z/r)wt as suggested by reference data. Heating produces a general depletion of the Ca1, Ca2, Ca3, and K1 sites, which is counterbalanced by an increase of the K2 site scattering, even though the latter is not populated at RT. No “internal ion exchange” mechanism was apparently acting in the present sample differently from other erionite samples analysed in the past. At 303 K approximately 20 e allocated at the OW H2O sites might be assigned to (extra-framework) EF cations. Such fraction increases due to their migration from the extra-framework cation sites following the same mechanism reported in reference data. View Full-Text
Keywords: erionite-K; ERI; zeolites; malignant mesothelioma (MM); high-temperature X-ray powder diffraction; Rietveld method erionite-K; ERI; zeolites; malignant mesothelioma (MM); high-temperature X-ray powder diffraction; Rietveld method
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Ballirano, P.; Pacella, A.; Bloise, A.; Giordani, M.; Mattioli, M. Thermal Stability of Woolly Erionite-K and Considerations about the Heat-Induced Behaviour of the Erionite Group. Minerals 2018, 8, 28.

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