Combined near-infrared and x-ray diffraction investigation of the octahedral sheet composition of palygorskite
Gionis, Vassilis (National Hellenic Research Foundation. Theoretical and Physical Chemistry Institute)
Kacandes, George H. (Geohellas S.A.)
Kastritis, Ioannis D. (Geohellas S.A.)
Chryssikos, Georgios D. (National Hellenic Research Foundation. Theoretical and Physical Chemistry Institute)

Data:	2007
Resum:	The octahedral composition of palygorskite in more than 300 samples from the Pefkaki deposit, W. Macedonia, Greece, has been studied by near-infrared (NIR) and X-ray diffraction (XRD), and evaluated according to the formula yMgSiO (OH)·xMgFe SiO(OH)·(1-x-y) MgAlSiO (OH). Included in the study were PFI-1 and several commercial palygorskites. Our analysis of 2nd derivative NIR spectra shows that the dioctahedral composition is adequately described by three sharp overtone bands representing AlAlOH, AlFeOH and FeFeOH in M2 dioctahedral sites, and that the summed intensity of these bands is proportional to the amount of dioctahedral component present (1-y). The samples show large variations in the degree of dioctahedral Fe-for-Al substitution with Fe occupying up to 70% of the dioctahedral M2 sites. Ternary analysis shows that the distribution of dioctahedral Al and Fe is not random, but displays a tendency towards homoionic pairing. An overtone band at 7214 cm and several combination bands are indicative of a trioctahedral MgOH component (y), and their appearance correlates with a distinct palygorskite signature in thermogravimetric analysis. Nevertheless, these bands cannot be used reliably for the quantification of a trioctahedral palygorskite component due to their close similarity to those of sepiolite. To circumvent this problem, we have evaluated y indirectly by calculating the difference between 1-y and the total concentration of palygorskite determined by the normalized intensity of the d XRD peak of palygorskite at 10. 4 Å. Using this methodology, we have found that the samples conform to a trioctahedral limit of y ≈ 0. 55, although within this limit they display large variations in octahedral character. Finally, we extend the above methodology to PLS chemometrics and show how NIR can be used to determine palygorskite content routinely in multimineralic geological samples.
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Llengua:	Anglès
Document:	Article ; recerca ; Versió publicada
Matèria:	Greece ; Near-infrared Spectroscopy ; Octahedral Composition ; Palygorskite ; X-ray ; Diffraction
Publicat a:	Clays and Clay Minerals, Vol. 55, Núm. 6 (2007) , p. 543-553, ISSN 1552-8367

DOI: 10.1346/CCMN.2007.0550601

11 p, 1.2 MB  Accés restringit a la UAB

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