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Clay Minerals; March 2008; v. 43; no. 1; p. 107-115; DOI: 10.1180/claymin.2008.043.1.08
© 2008 Mineralogical Society of Great Britain and Ireland
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Iron phases identified in bentonite from the Lieskovec deposit (Slovakia) by variable-temperature Mössbauer spectroscopy

P. KOMADEL1,*, A. S. ANASTÁCIO2, S. ANDREJKOVICOVÁ1 and J. W. STUCKI2

1 Institute of Inorganic Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, SK-845 36 Bratislava, Slovakia, and 2 Department of Natural Resources and Environmental Sciences, University of Illinois, Urbana, IL 61801, USA

* E-mail: uachkomp{at}savba.sk

(Received 5 July 2007; revised 19 October 2007)

The clay-mineral fraction of samples from a bentonite deposit in the Zvolenská kotlina Basin (Slovakia), formed by the alteration of andesitic pyroclastics, was dominated by Fe-bearing montmorillonite of relatively low charge. The total Fe content of the samples ranged from 3.58 to 5.81 wt.% Fe. Variable-temperature Mössbauer spectroscopy revealed that structural Fe(III) in smectite accounts for 70–90% of the total Fe in the unfractionated samples. No structural Fe(II) was observed by Mössbauer spectroscopy, but a small amount was detected by wet chemical analysis. The remainder of the Fe is present in oxide and/or oxyhydroxide phases dominated by poorly ordered goethite and hematite. The hyperfine parameters of the Mössbauer spectra for the raw bentonite are consistent with structural Fe(III) in an aluminosilicate phase mixed with varying quantities of hematite, goethite and possibly maghemite. Except in the fine fraction of sample L28, the hematite failed to undergo the Morin transition, as shown by the negative values for quadrupole splitting at 298 K and 6 K.

KEYWORDS: variable-temperature Mössbauer spectroscopy, Fe-bearing smectite, structural iron, hematite, goethite






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