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Mineralogy and chemistry of Fe-rich bentonite from the

Lieskovec deposit (Central Slovakia)















Institute of Inorganic Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, 845 36 Bratislava, Slovak Republic;;;;


Envigeo, Kynce ová 2, 974 11 Banská Bystrica, Slovak Republic;


State Authority for Mining, Energy and Geology (LBEG), Federal Institute for Geosciences and Natural Resources (BGR), Stilleweg 2,

D—30655 Hannover, Germany;

(Manuscript received December 5, 2005; accepted in revised form March 16, 2006)

Abstract: Powder X-ray diffraction and infrared spectroscopy were used to identify the mineralogical composition of
clay obtained from a systematically sampled bentonite deposit at Lieskovec (Central Slovakia), developed from andesitic
pyroclastics. The main mineral is an iron-rich montmorillonite, the admixtures present in all samples include kaolinite,
quartz, cristobalite and plagioclase, while muscovite/illite and orthoclase appear in most samples. This bentonite deposit
is relatively homogeneous as is demonstrated by its chemical composition and quantitative analysis using Rietveld
refinement. Total Fe




 content (5—9 %) in the Lieskovec samples is higher than in most other Slovak bentonites.

Mössbauer spectroscopy shows that Fe(II) covers less than 5 % of total Fe. Goethite and/or hematite are not present in all
< 2   m fractions separated from the raw bentonite and they contain up to 26 % of total Fe. Low tetrahedral Al and
octahedral Mg substitutions cause that the smectite is of lower charge than montmorillonite separated from the best
known Slovak bentonite: Stará Kremnička-Jelšový potok. This is in accord with the absence of the AlMgOH bending
vibration in the IR spectra of Lieskovec samples.

Key words: infrared spectroscopy, thermal analysis, cation exchange capacity, Rietveld quantification, iron—rich


The quality of bentonitic raw materials depends on numer-
ous parameters such as colour, rheological and exchange
properties, adsorption abilities and swelling behaviour.
The mineralogical and chemical composition of bentonite
as well as the morphological parameters of smectites influ-
ence these properties. Bentonites are used due to their
unique features in various fields of technical applications:
in civil engineering as well as in the food, chemical and
pharmaceutical industries or geomedicine. Bentonites are
widely utilized in environmental protection as sealing ma-
terials in landfill liners as a result of their excellent sealing
ability and long-term stability (Alther 1987; Luckham &
Rossi 1999; Janotka et al. 2002).

Geological research and industrial utilization of bento-

nites in Slovakia were focused on the deposits in the eastern
part of the country (Kuzmice, Fintice, Lastovce) and later
mainly to the bentonite from Stará Kremnička-Jelšový po-
tok in Central Slovakia. Important experimental data on
Slovak bentonites were published by Kraus et al. (1989),
Číčel et al. (1992), Madejová et al. (1992), Šucha et al.
(1996), etc.

The Central-Slovak deposits are connected with two

types of neovolcanic rocks: rhyolites and andesites. The
bentonite from Stará Kremnička-Jelšový potok was devel-
oped from rhyolitic pyroclastics, the main component is a
montmorillonite. The bentonite from Lieskovec has as par-

ent rocks andesitic pyroclastics; so the main mineral is an
iron-rich smectite (Šucha et al. 1996). The Lieskovec depos-
it is located in the western part of the Zvolen—Slatina Basin,
near to Lieskovec Ridge. The basin is filled with volcanic
rocks and non-marine sediments of Badenian to Sarmatian
(the main Carpathian molasses), covered with Pliocene to
late Miocene, partly tuffitic nonsaline sediments (late mo-
lasse). The problem of the genesis of the Lieskovec deposit
has not been solved yet (Galko & Gembalová 1996).

The purpose of the present paper was to obtain basic in-

formation on the mineralogical and chemical composition
of the bentonite in the Lieskovec deposit, primarily on the
main mineral and other phases containing iron.

Materials and methods


Thirty samples (L1—L30) were systematically collected

from various parts of the deposit; steps on the line were
10—30 m (Fig. 1). Raw samples and selected  < 2  m  frac-
tions were used in this work. To obtain the fine frac-
tions, the raw material was suspended in distilled water,


-saturated by repeated treatments with 1 M CaCl


lution, washed free of excess ions and the  < 2  m  fraction
was collected, air-dried at 60 ºC and ground to pass
a 0.2 mm sieve. Ca

2 +

 is the prevailing exchangeable cation

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in this bentonite, therefore Ca


 saturation was used to ob-

tain a homoionic form.


Powder X-ray diffraction (XRD): A Phillips model PW

1050 X-ray diffractometer (40 kV, 18 mA, CuK  radiation,
Ni—filter) was used to analyse randomly oriented speci-
mens. A Philips diffractometer PW 3710 (40 kV, 30 mA)
with CuK  radiation, equipped with a goniometer of
183 mm radius, a fixed divergence slit and a secondary
graphite monochromator was used for samples selected for
quantitative analysis by the Rietveld method. ‘Random
powder’ samples were scanned with a step of 0.02º 2 theta
and counting time of 10 s per step over a measuring range
of 1 to 90º 2 theta.

Rietveld refinement: Starting from the qualitative XRD

analysis, quantitative analysis of bentonites was performed
applying Rietveld refinement using AutoQuan® (GE In-
spection Technologies, SEIFERT Analytical X-ray, Germa-
ny). For smectites the new model of Ufer et al. (2004) was
applied, where turbostratic disordering can be described
within a Rietveld calculation of multiphase mixtures.

Infrared spectroscopy (IR): Fourier transform infrared

(FTIR) spectra in the 4000—400 cm


 region were obtained

using a Nicolet Magna 750 spectrometer with a DTGS de-

tector and a KBr beam splitter. KBr pressed-disc technique
(1 mg of sample and 200 mg of KBr) was used. Discs were
heated in a furnace overnight at 150 ºC to minimize the
water adsorbed on KBr and the clay sample.

Thermal analysis (TA): Differential thermal analysis

(DTA) and thermogravimetric (TG) curves were ob-
tained simultaneously using TA Instruments SDT
2960 apparatus, sample mass 25 mg, platinum cruci-
ble, heating rate 10 ºC · min


 in air flow, temperature

range 20—1100 ºC, reference material – Al





Cation exchange capacity (CEC): Three different meth-

ods were used to determine the CEC of the samples dried
overnight at 105 ºC. The solutions used for exchange of cat-
ions included ammonium acetate, barium chloride and the
complex of copper(II) triethylenetetramine [Cu Trien]

2 +


Ammonium acetate: Approximately 10 grams of sample

were shaken with 200 ml of 1 M CH





allowed to stand for 24 hours and then filtered. The clay
was washed with ethanol until no free ammonium cations
were present. The clay sample was transferred into a distil-
lation balloon and two grams of MgO and 200 ml of re-
distilled water were added. 100 ml of obtained distilled
solution were collected into an Erlenmeyer flask with
50 ml of 4% boric acid and 5 drops of bromocresol green
and titrated with 0.1 M HCl. The amount of spent HCl was
used to calculate the CEC (Oliveira 1998).

Fig. 1.  Location of Lieskovec deposit (below) and sampling of L1—L30 (above).

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Barium chloride (Gillman 1979): 200 mg of sample

were mixed with 10 ml 0.1 M aqueous BaCl


 solution. Af-

ter 24 hours, the supernatant was removed, new salt solu-
tion was added and the whole procedure was repeated five
times. All fractions of the supernatant were collected for
analysis. After each ion exchange, 10 ml of redistilled wa-
ter was added in order to remove the excess of ions
present. All the liquid fractions were combined and analy-
sed using atomic absorption spectroscopy (AAS) for Ca,
Mg, Na and K; their sum was used for CEC calculation.

Complex of copper(II) triethylenetetramine: 0.01 M solu-

tion of the complex [Cu Trien]

2 +

 was prepared according to

Meier & Kahr (1999). 200 mg ( ± 0.5 mg) of clay samples
were added to 50 ml of distilled water and 10 ml solution of
[Cu Trien]

2 +

, then subjected to an ultrasonic treatment for 5

minutes, filtrated and the concentration of Cu(II) complex
was determined by UV—VIS spectrophotometry (Cary 100,
Varian), at 578 nm (Meier & Kahr 1999). The amount of ad-
sorbed [Cu Trien]

2 +

 was determined using molar absorption


= 0.245 mol


· dm


· cm


 (Kaufhold & Dohr-

mann 2003) and the CEC values were calculated.

Results and discussion

X-ray diffraction

Powder X-ray diffraction data prove that the samples

L1—L30 are similar to some extent; however, their compo-
sition is not the same. Three representative X-ray diffrac-
tion patterns are shown in Fig. 2. Smectite is the dominant
mineral in all samples. The d


 diffraction at 62.2º 2 theta

shows that it is a dioctahedral smectite (Brindley & Brown
1980). Identified admixtures include kaolinite, quartz,
cristobalite and plagioclase, present in all samples, while
muscovite/illite and orthoclase were found in most sam-
ples, including L11 and L15, respectively. The intense
diffraction of calcite is present only in the patterns of sam-
ples L22 and L24.

Figure 3  shows the XRD-patterns of raw sample L3 and

its < 2   m  fraction. As expected, the fine fraction contains
much less non—clay minerals than the raw bentonite. How-
ever, size fractionation did not lead to pure smectite. Ad-
mixtures of kaolinite and anatase were identified in the
< 2   m  fractions of several Czech bentonites (Číčel et al.
1992). Therefore, structural formula, which have frequent-
ly been used for simple comparison of different smectites,
cannot be correctly calculated from the chemical analysis
of this  < 2  m  fraction. More information on the chemical
composition of the dominant mineral in this bentonite was
obtained from the IR spectra (see below).

The results of the Rietveld refinement of four samples

L1, L10, L11, and L15 are listed in Table 1. The mineral-
ogical composition is relatively homogeneous. An evalua-
tion test of the credibility of the quantitative XRD
analysis was performed. On the basis of the results of the
XRD Rietveld calculation, the theoretical chemical com-
position of each bentonite was calculated assuming a the-
oretical chemical composition for each mineral. This is

Fig. 2.  X-ray diffraction patterns of randomly oriented samples of
bentonite from Lieskovec. S – smectite, K – kaolinite, Q – quartz,
Cr – cristobalite, O – orthoclase, M – muscovite/illite, P – pla-
gioclase, C – calcite.

Fig. 3. X-ray diffraction patterns of raw sample L3 and its  < 2  m

Table 1:  Mineralogical composition (in mass %) of raw samples
L1, L10, L11 and L15 obtained using Rietveld refinement.

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straightforward for minerals like K-feldspar, kaolinite or
plagioclase (albite), which provided better fits than anor-
thite. However, it is not possible to distinguish between
different plagioclases in the powder XRD pattern of these
admixtures and therefore to ascertain the real Na/Ca ratio
in their structure.

Some assumptions were used for the  2 :1 minerals. It was

impossible to obtain directly the chemical composition of
muscovite/illite. It is a minor component (content
< 5  wt. %) in all samples. A simplified chemical composi-
tion based on the data of Lippmann & Berthold (1992)
with slightly increased Fe




 and MgO and reduced





 contents was used: 50% SiO


, 22% Al




, 8% K



5% Fe




 and 4% MgO.

The composition of smectite was taken from the chemical

analysis of the < 2 µm fraction of the respective sample,
though these fractions are not monomineralic. However,
only traces of kaolinite, cristobalite, quartz and feldspar are
present, which does not affect the credibility of this test sub-
stantially. This theoretical chemical composition was sub-
tracted from chemical analysis data; the differences are
shown in Fig. 4. They are small enough to accept the results
obtained. The biggest discrepancy is for Fe




, present in

the concentration range of 6.3—9.6 wt. %, and not complete-
ly recovered in all four samples. This can be a consequence
of Fe-oxides or oxohydroxides present in the samples. The
Mössbauer spectra of raw L15 sample taken at liquid nitro-
gen and room temperatures prove that about 7 % of total Fe
is bound in hematite. Inclusion of hematite in the Rietveld
refinement leads to substantial decrease in the discrepancy
for Fe




 (Fig. 4). Mössbauer spectroscopic assay of  < 2  m

fractions of several Czech bentonites from deposits Blšany,
Braňany, Černý vrch, Hroznětín, Krásný Dvoreček (KD),
Rokle, Stebno and Střimice showed that microcrystalline
and/or Al-substituted goethite comprised 8 to 72 % of total
Fe present in these samples, while KD also had 2 % of total
Fe bound in hematite (Komadel et al. 1993; Lego et al.

1995). Fe(III) in goethite was the main source of readily
HCl-soluble Fe in six out of seven investigated samples,
while it was Fe(II) from smectite and Fe(III) from goethite in
the seventh sample, Hroznětín (Komadel et al. 1993).

Infrared spectroscopy

Further information on mineralogical composition was

obtained by IR spectroscopy. For example, substantial dif-
ference was observed between the spectra of the samples
L4, L11 and L22 (Fig. 5). Absorption bands of dioctahe-
dral smectite dominate in the spectra of all samples. The
band near 3620 cm


is due to stretching vibrations of

structural OH groups shared by two octahedral atoms,
mainly Al. The strong band near 1036 cm


 is typical for

stretching Si—O vibrations of smectites (Madejová et al.
1992); however, it may include contributions due to ab-
sorption bands of other silicates (Farmer 1974). Bending
vibrations of OH groups absorb in the 930—800 cm



gion, while those of the tetrahedral sheets appear near
525 cm


 (Al—O—Si) and 470 cm



The IR spectra helped to identify non-smectitic phases

present in the studied samples. The characteristic band near
3698 cm


, assigned to stretching vibration of surface OH

groups, indicates the presence of kaolinite. This band can
be simply used to identify low content of kaolinite admix-
tures in bentonites, because it is not affected by other bands
of smectites or other minerals commonly present in bento-
nites (Madejová et al. 2002). Variation in the intensity of
this band suggests that the amount of kaolinite differs in
samples L1—L30. For example, the spectra of L4 and L22
signify higher content of kaolinite in these samples com-
pared to L11. Other kaolinite bands at 755 and 693 cm


(Farmer 1974) are observed in the spectrum of L22 (Fig. 5).
The typical doublet of quartz at 797 and 779 cm


, well

resolved in the spectrum of L4, is overlapped with the
band of microcrystalline SiO


 in the spectra of L11 and

L22. Consequently, the resolution of the quartz doublet is
decreased and the complex band is shifted to 795 cm



Admixtures of calcite identified in XRD patterns of sam-
ples L22 and L24 (Fig. 2), are also visible in their IR spec-
tra. The band near 1430 cm


 in the spectrum of L22

(Fig. 5) is ascribed to stretching vibration of CO





The IR spectra of raw sample L3 and its fine fraction are

shown in Fig. 6. In accordance with the XRD data (Fig. 3),
the < 2  m  fraction contains more smectite and less non-
clay minerals. The kaolinite content is not influenced sig-
nificantly by fractionation, as can be seen from very
similar intensities of the bands at 3695 cm


 in both spec-

tra. The shape of the absorption near 800 cm


 with partly

resolved doublet at 799 and 779 cm


 indicates the pres-

ence of both quartz and microcrystalline SiO


 in the raw

sample. The content of these admixtures is considerably
lower in the fine fraction, as is clearly indicated by de-
creased absorbance in this region in the spectrum of the
< 2   m  fraction (Fig. 6).

IR spectroscopy also provides information on the chem-

ical composition of the octahedral sheets of clay minerals
as the occupancy of the octahedra by different central at-

Fig. 4. Plausibility test for quantitative XRD Rietveld results.
Amounts and theoretical chemical composition of minerals used in
Rietveld refinement (Table 1) were subtracted from the measured
chemical composition of the samples, the results for the main com-
ponents SiO


, Al




, Fe




, CaO, MgO, K


O and Na


O are shown.

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Fig. 5. Infrared spectra of three representative samples of bento-
nite from Lieskovec deposit.

Fig. 6. Infrared spectra of raw sample L3 and its  < 2  m  fraction.
K – kaolinite, Q – quartz, SiO


microcrystalline phase.

than that of beidellite Stebno (Fig. 7b), but is lower in
comparison with the spectrum of montmorillonite SWy-2
(Fig. 7c). The intensity of the AlFeOH band in the L11
spectrum is slightly stronger than that of SWy-2, but clear-
ly less intense than the corresponding band in the spectra
of both Stebno (Fig. 7b) and SWa-1 (Fig. 7d). No AlMgOH
vibration near 845 cm


 is observed in the spectrum of

L11, thus proving relatively low Mg content in the octa-
hedral sheets. The intense band at 819 cm


 due to

FeFeOH bending vibrations confirms high content of octa-
hedral Fe in SWa-1.

The presence of aluminium in the tetrahedral sheets of

layer silicates, such as beidellites or micas can be recog-
nized by Si—O—Al(t) absorption near 830 cm


 as is illus-

trated in the spectrum of Fe—beidellite Stebno. Absence of
such a band in the L11 spectrum indicates lower Al for Si
substitution in the tetrahedra of L11. Detailed analysis of

Fig. 7. The IR spectra of a – Lieskovec ( < 2  m fraction of sample
L11), b – Fe—beidellite Stebno, c – montmorillonite SWy-2 and
d – ferruginous smectite SWa-1. K – kaolinite, Q – quartz.

oms has an effect on the positions of the OH stretching
and bending bands (Farmer 1974). Structural formula of
smectite present in Lieskovec bentonite cannot be reliably
calculated from the chemical analysis of any of the sepa-
rated < 2  m  fractions due to the presence of admixtures.
However, comparison of the spectra of these fractions with
the spectra of clay minerals of well known structure, such
as the SWy-2 and SWa-1 samples from the Source Clay
Repository of the Clay Minerals Society, can offer valu-
able information on its composition.

The IR spectra of dioctahedral smectites of different

chemical composition are given in Fig. 7. In the OH
stretching region a complex band composed of two strong
components at 3697 and 3626 cm


 appears in the spec-

trum of  < 2  m fraction of L11. While the 3697 cm



is due to vibrations of surface OH groups of kaolinite, the
component at 3626 cm


 results from absorption of both,

inner OH groups of kaolinite and OH groups of smectite.
The presence of kaolinite is also clearly visible in the
spectrum of Fe-beidellite Stebno (bands at 3697 and
3620 cm


); however, in this sample the OH absorption of

smectite is shifted to 3600 cm


. The position of the band

indicates that AlFeOH groups prevail in the octahedral
sheets of Fe-beidellite Stebno, which is in agreement with
its structural formula (Číčel et al. 1992). The position of
the OH stretching band of SWy-2 (3635 cm


) is typical

for montmorillonite with prevailing Al in the octahedral
positions, while the band at 3570 cm


 in the spectrum of

ferruginous smectite SWa-1 is characteristic for FeFeOH
grouping and reflects high content of octahedral iron in
the sample (Madejová et al. 2000; Mermut & Cano 2001).

Two discrete peaks at 916 and 880 cm


 associated with

the AlAlOH and AlFeOH bending vibrations, respectively,
are present in the L11 spectrum. Though the band near
916 cm


 corresponds to AlAlOH bending vibrations of

smectite, the OH bending vibrations of kaolinite and mus-
covite/illite may contribute to this band. The intensity of
the AlAlOH band in the L11 spectrum (Fig. 7a) is higher

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the IR spectrum of L11 shows that the dominant mineral
in this sample is a Fe—montmorillonite with rather low iso-
morphous substitution in the octahedral (Mg


 for Al



and tetrahedral (Al


 for Si


) sheets.

Thermal analysis

Thermal analysis was used to study dehydration and de-

hydroxylation of the samples; however, the samples show
very similar traces, as is illustrated in Fig. 8 for the repre-
sentative raw sample L15 and its  < 2  m  fraction. For both
samples, the mass loss from room temperature up to
1000 ºC can be divided into three steps. The first one, up
to 300 ºC, represents escape of water molecules from the
surface and from the interlayer space, including water mol-
ecules coordinating exchangeable cations (e.g. Bish &
Duffy 1990). As  < 2  m  fractions contain more smectite
than the raw samples and smectite is the dominant hydrat-
ed phase in bentonites, the mass loss shown in the trace of

2   m of L15  is higher than in the raw sample, with losses

of 8.8 % and 5.7 %, respectively (Fig. 8). Both, the second
and the third steps in the 300—550 ºC and 550—700 ºC re-
gions, respectively, are connected with dehydroxylation of

Fig. 9. DTA curves of  < 2  m fraction and raw sample from Lieskovec deposit.

Fig. 8. TG curves of  < 2  m fraction and raw sample from Lieskovec deposit.

clay minerals, including iron—rich smectite (400—800 ºC),
kaolinite (450—700 ºC) and muscovite/illite  (350—600 ºC).
The dehydroxylation temperatures of these minerals are
too close to each other to distinguish these individual pro-
cesses on the TG curve. Progress of dehydroxylation also
depends on the chemical composition of smectite and its
crystallinity (Číčel et al. 1981).

Additional information on the changes in the samples

upon heating provide DTA curves, similar for raw sample
L15 and its  < 2  m  fraction (Fig. 9). Four endothermic
peaks near 80, 460, 640 and 880 ºC and one exothermic
peak near 920 ºC appear. The first most intense endother-
mic peak shows a shoulder at about 160 ºC, distinguish-
ing removal of water molecules from the inner hydration
shell of exchangeable cations, mostly Ca

2 +

, from less

strongly bound water (Greene-Kelly 1957). Two endot-
hermic peaks, near 460 ºC and 640 ºC, on the DTA
curves confirm that the changes observed on the TG
curves in the 300—700 ºC region are due to two partly
overlapping dehydroxylation processes. Brandley &
Grim (1951) have noted that the endothermic peak near
880 °C is associated with the breakdown of the anhy-
drous montmorillonite to an “amorphous” material from

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Table 2: Chemical composition of L1—L30 samples from Lies-
kovec bentonite.

Table 3: Cation exchange capacities in meq/100 g.

which new high-temperature phases crystallize near
920 ºC (e.g. Číčel et al. 1981).

Chemical analysis

Chemical analyses of samples are given in Table 2. SiO


content varies between 53—65 %, suggesting possible
presence of free SiO


 phases, as is confirmed by XRD and

IR spectroscopy. Al




 is in the range 16—22 %, an ex-

emption is L28 with its 25% abundance. The total Fe




content of 5—9 % is medium to high for bentonites; how-
ever, several Czech bentonites contain more Fe





et al. 1992). The content of octahedral iron is higher than
in most other Slovak bentonites. Mössbauer spectroscopy
data prove that Fe(II) covers less than 5 % of the total Fe
both in raw samples and in the  < 2  m  fractions. The
amount of Fe—oxides or oxohydroxides is variable, repre-
senting up to 26 % of total Fe present. Low MgO content
causes that the smectite is of relatively lower charge, as is
also shown by the absence of the AlMgOH bending vibra-
tion in the IR spectra (Fig. 7). Higher CaO content in sam-
ples L22 and L24 is due to calcite contamination, also
confirmed by XRD and IR spectroscopy.

Cation exchange capacity

Solutions of ammonium acetate, barium chloride and

copper(II) complex of triethylenetetramine [Cu Trien]

2 +

were used for determination of CEC. Table 3 shows the
CEC values with the standard deviations for three raw
samples and their  < 2  m fractions as attained from dif-
ferent ion-exchange reactions. The obtained data prove
that all three methods used provide very similar results.
The CECs for raw samples range between 58.1 and

61.1 meq/100 g, thus proving that the CECs of these ben-
tonite samples are similar and rather low. The CEC values
of the  < 2  m fractions of L10, L11 and L15 samples were
higher by about 6.4 %, 6.5 % and 10.0 %, respectively,
than the data obtained for the raw samples. This is caused
by higher amount of smectite in the fine fractions. How-
ever, the values of 62—68 meq/100 g (Table 3), are lower
in comparison with the  < 2  m fractions separated from
other  bentonites, for example 85 meq/100 g for SWy-2,
89 meq/100 g for STx-1, or 123 meq/100 g for SAz-1
(Borden & Giese 2001). Low CECs are in agreement with
the low Mg content (Table 2) proving lower isomorphic
Mg for Al substitution in the octahedral sheets of smectite
and thus its lower octahedral charge. They are also typical
for smectites with increased amount of octahedral Fe
(Šucha et al. 1996). Low cation exchange capacity and
low octahedral charge suggest that the substitution of Al
for Si in the tetrahedra is also not high. Substantial tetra-
hedral substitution would cause absorption near 750 cm



but it is not observed in the IR spectra (Fig. 7). According
to these observations, the main mineral in Lieskovec ben-
tonite is Fe-montmorillonite rather than Fe-beidellite.

Lieskovec bentonite is currently used mainly in civil

engineering, where the colour and Fe-content is not an im-
portant parameter. However, most recent applications in
the chemical industry and in agriculture show that other
uses may become more important in the following years.


Fe-montmorillonite of relatively low charge is the domi-

nant mineral in Lieskovec bentonite. Admixtures of kaolin-
ite, quartz, cristobalite and plagioclase are present in all
samples, while muscovite/illite and orthoclase occur in
most samples. Lieskovec bentonite deposit is relatively ho-
mogeneous as demonstrated by quantitative analysis using
Rietveld refinement, though some differences in the sam-
ples obtained from different parts occur. Size fractionation
did not lead to pure smectite. The  < 2  m fractions contain
smectites, kaolinite and traces of crystalline non-clay min-
erals. Total Fe




 content (5—9 %) in Lieskovec bentonite

is higher in comparison with Stará Kremnička-Jelšový po-
tok bentonite. Fe(II) content is low and Fe(III) occurs domi-
nantly in smectite. Goethite and/or hematite, containing up
to 26 % of total Fe, are present in some samples.

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 The authors acknowledge Professor

Lipka for obtaining and analysis of the Mössbauer spectra
and the financial support of the Grant Agency APVT
(Grant APVT-51-018502).


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