GeolCarp_Vol63_No6_503

www.geologicacarpathica.sk

GEOLOGICA CARPATHICA

, DECEMBER 2012, 63, 6, 503—512 doi: 10.2478/v10096-012-0039-x

Stability of kaolin sand from the Vyšný Petrovec deposit

(south Slovakia) in an acid environment

MARTIN PENTRÁK

, JANA MADEJOVÁ

, SLÁVKA ANDREJKOVIČOVÁ

, PETER UHLÍK

and

PETER KOMADEL

Institute of Inorganic Chemistry, Slovak Academy of Sciences, SK-845 36 Bratislava, Slovak Republic; martin.pentrak@savba.sk

Department of Geology of Mineral Deposits, Comenius University, Mlynská dolina G, SK-842 15 Bratislava, Slovak Republic

(Manuscript received October 27, 2011; accepted in revised form June 13, 2012)

Abstract: Comprehensive characterization of kaolin sand from the Vyšný Petrovec (VP) deposit in Slovakia by a
variety of experimental methods was performed. The quantitative XRD analysis (RockJock software) revealed that the
acid-untreated sample contained mainly kaolinite ( ~ 60 wt. %), a considerable amount of dioctahedral micas ( ~ 32 wt. %)
and quartz ( ~ 7 wt. %). The Hinckley index (HI) and Aparicio-Galán-Ferrel index (AGFI) calculated from the 02l and
11l reflections showed medium-defect kaolinite to be present in the VP kaolin. The influence of the mineral composi-
tion of VP kaolin on its stability in 6 mol · dm

—3

HCl at 95 °C was investigated. The solid reaction products were exam-

ined by chemical analysis; XRD and infrared spectroscopy in both middle (MIR) and near (NIR) regions. Considerably
higher dissolution rate of Fe compared to Al indicated that Fe was bounded in a readily soluble phase rather than in
kaolinite. While the MIR spectra confirmed the gradual release of the central atoms from the clay minerals layers and
creation of amorphous silica upon acid treatment, the NIR spectra revealed the formation of Si-OH groups in the solid
reaction product. Relatively high dissolution rate of VP kaolin resulted from the presence of small-grains of medium-
defect kaolinite and clay admixtures in VP kaolin sand.

Key words: acid treatment, thermal analysis, SEM, XRD analysis, FTIR spectroscopy, kaolinite.

Introduction

Kaolins are raw materials extensively used in a wide variety
of industrial applications. The main constituent of kaolins is
the clay mineral kaolinite with specific properties and struc-
ture  determining  its  use  for  technological  utilization  of
whole  kaolin  ore  (He  et  al.  2011;  Ma  2011;  Moussi  et  al.
2011;  Yanik  2011),  for  example,  in  ceramic  production,  as
fillers for plastics and rubber (Lagaly 1999), but the largest
amounts  of  processed  kaolins,  more  than  60 %  of  the  word
production, are used in the paper industry as fillers within the
network of cellulose fibres and as coating particles (Harvey &
Lagaly 2006; Murray 2007). The next utilization of kaolinite
is  in  preparation  of  nanotubes  (Matusik  et  al.  2009,  2011)
and zeolites (Novembre et al. 2011). In contrast to smectites,
2 : 1 clay minerals with substantial isomorphous substitution
in  the  layers,  kaolinites  are  1 : 1  clay  minerals  with  layers
composed  of  one  tetrahedral  and  one  dioctahedral  sheet
(Brindley & Robinson 1946; Giese 1988; Murray et al. 1993)
in which isomorphous substitutions of central atoms are rare
(Evans  &  Guggenheim  1988).  However,  a  small  amount  of
octahedral  iron  in  natural  kaolinites  was  reported  (e.g.
Meads  &  Malden  1975;  Mestdagh  et  al.  1980;  Petit  et  al.
1999).  Particle  shape  of  kaolinite  is  regular  and  pseudo-
hexagonal. One of substantial parameters affecting the utili-
zation of kaolins is the “crystallinity” or degree of structural
ordering of kaolinite (Plançon & Tchoubar 1977a,b; Plançon
et al. 1988, 1989; Bookin et al. 1989). The level of kaolinite
ordering  is  usually  expressed  by  indices  calculated  from
their  X-ray  diffraction  patterns  (Hinckley  1963;  Plançon  &
Zacharie 1990; Aparicio et al. 2006).

The mean crystallite thickness of kaolinites, analysed by

Bertaut-Warren-Averbach (BWA) technique, is also a signif-
icant parameter for description of the “crystallinity” of kao-
linite minerals (Šucha et al. 1999). Another factor is the
purity of the kaolin ore since raw kaolin may contain admix-
tures, typically quartz, micas or mixed-layer clay minerals,
notably illite-smectite or Fe oxides and oxyhydroxides.

Acidification of the clays

Acid solutions (e.g. acid mine drainage water or acid

rain)  occurring  in  natural  environment  can  modify  proper-
ties  of  the  clays  and  thus  also  their  application  (Dubíková
et  al.  2002;  Egiebor  &  Oni  2007).  Acidity  is  an  important
factor  affecting  the  formation  of  clays  (e.g.  Sillitoe  2010;
Kadir  et  al.  2011;  Premović  et  al.  2012)  and  weathering
pathways  controlling  processes  of  clay-mineral  formation
in acidic soils (Uzarowicz et al. 2011). Many studies were
devoted  to  acid  treatment  of  bentonites  or  smectites  (Fijał
et al. 1975; Číčel & Novák 1976; Stoch et al. 1977; Novák
&  Číčel  1978;  Komadel  et  al.  1993,  1996;  Tkáč  et  al.
1994;  Breen  et  al.  1997;  Madejová  et  al.  1998;  Rožić  et
al. 2010, 2011; Sciascia et al. 2011), illites, micas or kao-
linites  (Bahranowski  et  al.  1993;  Ganor  et  al.  1995;  Kali-
nowski  &  Schweda  1996;  Dubíková  et  al.  2002;  Hradil  et
al. 2002; Jozefaciuk & Bowanko 2002; Pentrák et al. 2009,
2010;  Nguetnkam  et  al.  2011;  Valášková  et  al.  2011;
Worasith et al. 2011). Acid attack on clay minerals causes
very fast exchange of hydrated exchangeable cations mainly
in smectites, typically Ca

, Na

, Mg

and K

, with H

ions,

which attack structural OH groups simultaneously with

504

PENTRÁK, MADEJOVÁ, ANDREJKOVIČOVÁ, UHLÍK and KOMADEL

GEOLOGICA CARPATHICA

GEOLOGICA CARPATHICA, 2012, 63, 6, 503—512

depopulation  of  the  octahedral  Al,  Fe  and  Mg  from  the
structure. The presence of Mg and Fe (isomorphous substi-
tutions for Al) in octahedral sheets leads to enhancement of
the  clay  mineral  dissolution  due  to  higher  negative  layer
charge density (Pentrák et al. 2012). The tetrahedra are re-
arranged  from  layered  into  three-dimensional  adjustment.
The protonated amorphous silica phase is the final reaction
product  (Tkáč  et  al.  1994;  Madejová  et  al.  1998).  The
leaching effect of the acids on the clay minerals depends on
temperature, time, type and concentration of used acid, clay/
acid ratio and stirring of the reaction mixture. Solubility of
the  clay  minerals  in  acids  is  also  affected  by  type  of  clay
minerals  where  chemical  composition  and  swelling  ability
play  important  roles  (Gates  et  al.  2002;  Komadel  2003;
Pentrák et al. 2010).

Origin of the sample

Kaolins occur in several different types of deposit in Slo-

vakia. They were formed on weathering crusts of metamor-
phites  and  granitoids  and  rarely  also  on  neovolcanites.  The
main period of kaolinization was from Badenian to Pontian
(Kraus  &  Hano  1976;  Kraus  &  Horváth  1978;  Kraus  1989;
Novotná  et  al.  1993;  Madejová  et  al.  1997).  Paleoclimatic
development  in  this  time  span,  in  comparison  to  the  older
stage  in  the  Paleogene,  was  less  favourable  and  proceeded
under lower average temperature and humidity (Kováč et al.

2006). Consequently, the process of chemical weathering
showed lower intensity. Paleoenvironmental changes in the
Central-Carpathian Paleogene Basin have been discussed re-
cently in detail (Soták 2011). However, according to paleo-
vegetation cover, a subtropical climate with gradual transition
to warm temperate climatic conditions is still expected dur-
ing the Miocene in the Central Parathethys (Kováčová et al.
2011).

The Vyšný Petrovec deposit is situated in a 10 km long and

up to 1.5 km wide belt of kaolin sands with the greatest thick-
ness of 80 m in the NW part of the Lučenská kotlina Depres-
sion (Hano 1973). It represents a redeposited kaolin crust of
Horná  Prievrana  weathering  type,  situated  just  3 km  to  the
west-south  west  from  the  parent  deposit  (Fig. 1).  Kaolin
sands  form  an  overburden  of  kaolinized  sericitic-chloritic
and sericitic-graphitic phyllites of Gemericum and it overlies
sediments of the Poltár Formation (Kraus & Hano 1976).

Two distinct technological types of different mineralogical

composition  occur  in  both  the  primary  kaolin  of  Horná
Prievrana  and  the  secondary  sedimentary  kaolin  from  Vyšný
Petrovec (Kraus 1989). The first type, found only occasionally
in  the  lower  part  of  the  deposit,  consists  of  kaolinite,  bram-
malite  (Na-interlayer-deficient  dioctahedral  mica),  illite  and
muscovite.  The  presence  of  brammalite  indicates  kaoliniza-
tion on metarhyolites of Paleozoic age with a very high con-
tent  of  albite.  The  second  type,  a  product  of  weathering  of
sericite-chlorite phyllites, is remarkably dominant. It comprises
kaolinite, illite and muscovite, while brammalite and albite are
absent. Kaolin from the Vyšný Petrovec deposit is considered
to be the most promising source of domestic raw material for

Fig. 1. Location of Vyšný Petrovec (A) and Horná Prievrana (B) deposits on the simplified geological
map from Vass et al. 1992. 1 – Quaternary; 2 – Poltár Formation (Pont): variegated clays, sands and
gravels; 3 – Gemericum: Dobšiná Group (Visean—Namurian A): phyllites with metasandstones, ser-
pentinites; 4 – Veporicum: metamorphosed quartzy sandstones, sandstones, phyllites and interme-
diate to basic volcanoclastics; 5 – thrust lines.

the Slovak ceramic and glass in-
dustry.  Presence  of  both  kaolin
types,  the  weathering  and  sedi-
mentary, confirms that the most
extensive  kaolin  weathering  of
the  Western  Carpathians  took
place in SW part of the Vepori-
cum  and  Gemericum  (Kraus
1989).  New  potential  applica-
tion  of  kaolin  from  the  Vyšný
Petrovec  deposit  as  metakaolin
was reported recently. Metakao-
lin  is  a  reactive  aluminosilicate
pozzolan  obtained  by  thermal
treatment  of  kaolin  (at  about
650 °C)  and  by  grinding  it  to  a
high  fineness.  The  use  of  me-
takaolin as a partial replacement
for  Portland  cement  clinker
helps  to  obtain  more  eco-effi-
cient  cements  (Krajčí  et  al.
2007;  Janotka  et  al.  2010).  The
production  of  VP  kaolin  sand
was  about  20—30 kt  per  year.
However,  its  production  has
been  interrupted  since  2009
(Baláž  &  Kúšik  2010)  for  eco-
nomic  reasons.  The  deposit  is
very  heterogeneous,  predomi-

505

STABILITY OF KAOLIN SAND FROM VYŠNÝ PETROVEC DEPOSIT (SLOVAKIA)

GEOLOGICA CARPATHICA

GEOLOGICA CARPATHICA, 2012, 63, 6, 503—512

nantly from the grain size point of view, and the production of
raw material is connected with increased costs.

Kaolins KGa-1 (well-ordered) and KGa-2 (less-ordered)

are the samples available from the Source Clays Repository
of the Clay Minerals Society, used as reference materials
over the years (Van Olphen & Fripiat 1979). An extensive
amount of data is available in literature on these materials.

This study reports the stability of Vyšný Petrovec kaolin

consisting of various minerals (kaolinites, micas, quartz, etc.)
in HCl and the influence of components on its dissolution rate.

Materials and methods

Materials

The kaolin sand from Vyšný Petrovec (VP) (Slovakia) was

studied.  The  sample  was  collected  from  a  homogenized  re-
pository  of  mined  kaolin  sands  that  was  situated  directly  in
the deposit. To obtain the fine fraction of VP, 1 kg of the raw
material  was  suspended  in  distilled  water  and  treated  with
1 mol · dm

—3

CaCl

solution. After the sedimentation (using

Stokes’law) the  < 45 µm fraction was collected, washed free
of  excess  ions,  air-dried  at  60 °C  and  ground  to  pass  a
0.2 mm  sieve.  Its  chemical  and  mineralogical  compositions
are reported in Table 1 and Table 2, respectively.

Table 1: Chemical composition of < 45 µm fraction of VP kaolin
(in mass %) determined after drying at 105 °C.

Sample SiO

CaO MgO Na

O K

O TiO

O Total

50.20 32.47 1.61 0.22 0.44 0.06 1.93 1.33 9.98 98.24

dard  minerals  (the  calculated  pattern)  to  the  measured  pat-
tern by varying fraction of each mineral standard pattern, us-
ing  the  Solver  function  Microsoft  Excel  to  minimize  a
degree of fit parameter between the calculated and measured
pattern.  Samples  for  analysis  were  prepared  by  adding
0.111 g ZnO (internal standard) to 1.000 g sample. The mix-
ture  was  ground  in  a  McCrone  mill  for  5 min  with  4 ml  of
methanol then dried and sieved (Eberl 2003).

XRD profiles of 001 basal plane reflections of illite and

kaolinite  were  selected  for  crystallite  size  determination  of
acid-untreated and treated samples. Selected peaks were fitted
by pseudo-Voight function. This function is an analytical ap-
proximation of the Voigt function which in turn is the convo-
lution  product  of  a  Gaussian  and  a  Lorentzian  function  with
the mixing factors h = 1 and h = 0, respectively. It provides re-
finement stability and the possibility of a crude physical inter-
pretation of mixing factors h. The simple Scherrer equation, as
integral breadth method was utilized for crystallite size deter-
mination  by  software  Topas  V2.0  (Bruker  AXS,  2000).  Val-
ues of reliability for profile fitting (Rwp) were always  < 4 %.

Infrared spectroscopy. Fourier transform infrared (FTIR)

spectra in the middle IR (MIR) region (4000—400 cm

—1

) were

obtained using a Nicolet 6700 spectrometer and KBr pressed-
disc technique (0.5 mg of sample and 200 mg of KBr). The
discs were heated in a furnace overnight at 150 °C to mini-
mize the water adsorbed on sample and KBr. For the near IR
(NIR) region (12000—4000 cm

—1

) neat samples were measured

by a Smart Diffuse Reflectance (DRIFT) accessory from Ther-
mo Scientific. 128 scans with resolution of 4 cm

—1

were recor-

ded for each sample. Spectra manipulations were performed
using the Thermo Scientific OMNIC 8.0 software package.

Atomic emission spectroscopy (AES). The amounts of Al,

Fe and Si leached from the samples upon the acid treatment
were  calculated  from  the  data  obtained  on  a  Varian  Vista-
MPX  optical  emission  spectrometer  with  inductively  cou-
pled plasma (ICP—OES) equipped with a 40 MHz air-cooled
free  running  RF  generation  system,  power  (kW)  1.3 kW,
plasma flow rate 1.5 dm

· min

—1

and the nebulizer flow rate

0.7 dm

· min

—1

Scanning electron microscopy (SEM). The morphology of

the kaolin sand sample was displayed by an Electron micro-
scope SEM LEO 1450VP with resolution of 3.5 nm, acceler-
ating voltage of 30 kV, current probe of 20 pA and working
distance of 8 mm.

Thermal analysis (TA). Differential thermal analysis (DTA)

and thermogravimetric (TG) curves were obtained simulta-
neously using a TA Instruments SDT 2960 apparatus, sample
mass of 25 mg, platinum crucible, heating rate of 10 °C · min

—1

in air flow, temperature range 20—1100 °C and reference ma-
terial Al

Results and discussion

Characterization of the acid-untreated < 45 µm fraction of
the VP kaolin sample

XRD analysis. XRD powder pattern analysis was used to de-

termine the mineral composition of the acid-untreated sample.

Methods

Acid treatments were performed at 95 °C for 4, 8, 12, 18

and 36 hours. 2.5 g of the < 45 µm sample were mixed with
0.250 dm

of 6 mol · dm

—3

HCl. This high concentration of

acid, similarly as in Pentrák et al. (2009, 2010), was chosen to
achieve faster structural changes of the clays than in the natu-
ral environment with weaker reaction conditions (Lintnerová
et al. 1999; Dubíková et al. 2002). The suspensions were
heated in 0.5 dm

glass flasks with laps under reflux. The

mixtures were stirred every hour. The filtrate and wash super-
natant  solutions  were  analysed  for  Al,  Fe  and  Si  by  atomic
emission  spectroscopy,  yielding  the  amounts  of  the  elements
dissolved.  Dissolution  curves  were  constructed  by  plotting
the undissolved fraction of the respective cation versus time
(Komadel et al. 1996).

Powder X-ray diffraction. XRD profiles of pressed powder

samples were collected on a BRUKER D8 Advance diffracto-
meter equipped with CuK (

= 1.54060 Å) radiation and a

BRUKER LynxEye detector. The records were collected in
the 2-theta range from 2.5° to 65°, using step of 0.01° 2 ,
and counting time of 3 s per step.

Quantitative analysis of the acid untreated sample was per-

formed applying the RockJock program (Eberl 2003). The
program fits the sum of stored XRD patterns of pure stan-

506

PENTRÁK, MADEJOVÁ, ANDREJKOVIČOVÁ, UHLÍK and KOMADEL

GEOLOGICA CARPATHICA

GEOLOGICA CARPATHICA, 2012, 63, 6, 503—512

Besides a kaolinite and mica type minerals, including a

muscovite and an illite, the  < 45 µm fraction of the VP sample
also contains non-clay admixtures such as quartz (3.34 Å) and
probably also a siderite and a rutile (Fig. 2). The mineral com-
position  of  the  sample  reveals  that  it  belongs  to  the  second
type  of  kaolin  occurring  in  the  Vyšný  Petrovec  deposit.  The
results  from  quantitative  RockJock  analysis  of  the  acid-un-
treated sample are presented in Table 2.

The structural ordering of kaolinite was determined by

Hinckley index (HI) and Aparicio-Galán-Ferrel index (AGFI)
described  by  Hinckley  (1963)  and  Aparicio  et  al.  (2006),  re-
spectively. While HI needs performance of decomposition of
overlapped diffractions between 20° and 23° 2  to the distin-
guished peaks, AGFI requires only simple weighting peak in-
tensity ratios of the 020, 110, and 111 diffractions. Moreover,
the HI is influenced by the presence of quartz, feldspar, Fe-hy-
droxide gels, illite, smectite and halloysite, while the AGFI is
less  affected  by  the  admixtures  including  X-ray  amorphous
phases (Aparicio et al. 1999; Galán et al. 2006). The calculated
HI value of 0.63 for VP shows the presence of a medium defect
kaolinite. The AGFI value of 1.3 also classifies this kaolinite to
the medium defect kaolinite group (Aparicio et al. 2006).

Scanning electron microscopy. Figure 3 shows sharp edges

of pseudohexagonal isolated particles of kaolinite with maxi-
mum dimensions of ~1 µm.

These kaolinite grains are small compared to those in well-

ordered kaolinites KGa-1 and KGa-1b from Washington
County, Georgia. Pruett & Webb (1993) estimated that 58 %
of KGa-1b particles were smaller than 2 µm and 32 % were
< 0.5 µm, whereas in KGa-1 it was about 47 and 21 %, re-

Fig. 2. XRD pattern of VP acid-untreated sample (CuK radiation).

(mass %)

Kaolinite

Dioctahedral micas

Quartz

Siderite, Rutile

Table 2: Results of quantitative XRD analysis (RockJock) of
< 45 µm fraction of VP kaolin.

Fig. 3. SEM image of pseudohexagonal kaolinite particles in VP
sample.

Fig. 4. SEM images of irregular quartz grains in VP sample.

Fig. 5. SEM image of mica aggregates in VP sample.

507

STABILITY OF KAOLIN SAND FROM VYŠNÝ PETROVEC DEPOSIT (SLOVAKIA)

GEOLOGICA CARPATHICA

GEOLOGICA CARPATHICA, 2012, 63, 6, 503—512

spectively. Clearly identifiable irregular quartz grains had
larger sizes of ~ 210 µm (Fig. 4).

Mica grains represented platy aggregates (Fig. 5). In com-

parison to quartz, the aggregates are of smaller average size
( ~ 70 µm).

Thermal analysis. Dehydration, dehydroxylation and re-

crystallization  steps  were  found  by  thermal  analysis  of  the
acid-untreated  sample.  The  TG  curve  shows  two  steps  of
mass loss from 20 up to 1000 °C (Fig. 6). The first step be-
tween room temperature and 200 °C represents 2 % mass re-
duction  of  water  molecules  from  the  surface.  The  second
mass  decrease  of  about  10 %  occurring  between  350  and
900 °C  reflects  dehydroxylation  processes  of  kaolinite  and
mica type minerals. Due to very close dehydroxylation tem-
peratures  of  these  minerals  (Bish  &  Duffy  1990)  only  one
minimum  at  497 °C  related  to  metakaolinite  formation  was
observed  on  the  DTA  curve  (Siddique  &  Klaus  2009).  The
small  exothermic  peak  at  986 °C  corresponds  to  the  forma-

Fig. 7. MIR (b and c) and NIR (a) spectra of VP kaolin.

Fig. 6. TG and DTA experimental curves for VP sample.

tained by IR spectroscopy in both MIR and NIR regions. Four
resolved bands are observed in the OH stretching region
(Fig. 7b). The band at 3697 cm

—1

belongs to inner surface

AlAlOH groups and vibration at 3621 cm

—1

is attributed to in-

ner AlAlOH groups. Two bands at 3670 and 3653 cm

—1

are

usually resolved only in the spectra of well-ordered kaolinites,
disordered kaolinites show a single complex band near
3650 cm

—1

(Farmer 1974; Madejová et al. 2002). Less clear

resolution and lower intensity of the 3670 cm

—1

band in the

VP spectrum than in the spectrum of a well-ordered KGa-1b
(Madejová & Komadel 2001) also indicates only medium-or-
dering of the kaolinite in the VP sample. The absence of the
AlFeOH band near 3598 cm

—1

implies that iron determined

by chemical analysis of VP kaolin is not bound in the kaolin-
ite’s octahedral sheets (Petit et al. 1999). The absorption
bands at 936 and 916 cm

—1

correspond to bending vibration

of inner-surface and inner OH groups, respectively. Three
vibrations at 1105, 1034 and 1010 cm

—1

represent Si-O

stretching modes of tetrahedral sheets. Bending vibrations of
Si-O-Al a Si-O-Si are located at 539 and 471 cm

—1

, respec-

tively (Fig. 7c). The OH and Si-O absorption bands of mica
type mineral are overlapped by more intense bands of kaolin-
ite. A characteristic doublet at 798 and 779 cm

—1

confirms the

presence of quartz.

The NIR spectrum of VP shows bands corresponding to the

overtone 2

and combination ( + )

modes of the funda-

mental vibrations of OH groups (Fig. 7a). The 2

band near

7068 cm

—1

belongs to vibrations of the inner OH groups, while

the less intense band at 7171 cm

—1

is due to 2

overtone of

inner-surface OH groups. The presence of water molecules in
the sample is confirmed by the ( + )

H2O

band at 5225 cm

—1

This band is hardly recognized in the spectra of kaolins with
high kaolinite content due to very low amount of water ad-
sorbed on the particle edges (Pentrák et al. 2009). The combi-
nation bands of AlAlOH groups occur at 4622 and 4528 cm

—1

(Fig. 7a).

tion of mullite (Brindley & Nakahira
1959;  Slaughter  &  Keller  1959;  Bu-
lens  &  Delmon  1977).  Guggenheim
& Koster van Groos (2001) reported
that the clay mineral standards KGa-1b
(well-ordered)  and  KGa-2  (less-or-
dered) both containing  ~ 96 % kaolin-
ite  (Chipera  &  Bish  2001)  showed
dehydroxylation  maxima  at  518  and
513 °C,  respectively.  Similarly,  the
exothermic  maxima  were  found  at
993 °C  for  KGa-1b  and  984 °C  for
KGa-2,  which  is  just  above  and  be-
low the 986 °C found for VP kaolin.
These  small  differences  can,  at  least
partly, also be due to non-equal sam-
ple  preparation  and  different  instru-
ments  used.  The  admixtures  present
in  VP  kaolin  ( ~ 40 mass %)  could
have affected its thermal stability.

IR spectroscopy. Further informa-

tion on the chemical and structural
composition of VP kaolin was ob-

508

PENTRÁK, MADEJOVÁ, ANDREJKOVIČOVÁ, UHLÍK and KOMADEL

GEOLOGICA CARPATHICA

GEOLOGICA CARPATHICA, 2012, 63, 6, 503—512

Acid dissolution

Structural changes of VP kaolin dissolved in HCl were

monitored by XRD (Fig. 8). The intensities of the basal dif-
fractions of present phyllosilicates decreased gradually pro-
portionally to time of dissolution up to 12 hours (Fig. 8a—d).
More profound changes were observed after longer dissolu-
tion times. Treatment for 18 hours caused almost total de-
struction of mica’s structure, while the diffractions of
kaolinite were still clearly visible (Fig. 8e).

Only some traces of kaolinite and mica type mineral can

be detected after 36 hours of acid treatment. On the contrary,
the resistance of quartz against high molar hydrochloric acid
is well-documented mainly by absence of changes in the in-
tensities of diffraction maxima at 26.6° 2 (3.34 Å, Fig. 8f).

A similar trend in crystallite size reduction was determined

by analytical profile fitting of both, kaolinite and dioctahedral
mica, 001 peaks and calculation based on the Scherrer equa-
tion (Table 3). The crystallite size of the longest treated dio-
ctahedral micas was reduced to less than 15 % of those in the
acid-untreated sample. Kaolinite was confirmed as the more
stable phase; only less than 50 % reduction of crystallite size
was determined in the most extensively dissolved material. The
measured mean crystallite size of the untreated VP kaolinite is
more than twice as large as the mean thickness of VP kaolinite
and of other Slovak kaolinites determined by the BWA tech-
nique (Šucha et al. 1999). This discrepancy is caused by differ-
ent approach to the calculation of the mean values. The integral
breadth methods, applied in this study, use volume weighted
column heights, in contrast to the BWA analysis using area
weighted values (Klug & Alexander 1974; Drits et al. 1998).

Figure 9 shows dissolution of Al, Fe and Si from VP sam-

ples. The amount of individual elements remaining in the
solid reaction product is plotted vs. time of dissolution. Be-

Time of acid treatment

(hours)

Dioctahedral mica 001

Crystallite size (nm)

Kaolinite 001

Crystallite size (nm)

80.7

± 9.3

19.0

± 0.4

61.7

± 3.9

17.7

± 0.2

64.9

± 4.5

17.1

± 0.3

58.5

± 4.2

16.3

± 0.4

27.1

± 3.0

15.2

± 0.4

12.1

± 1.2

10.3

± 0.5

Table 3: Reduction of crystallite size of kaolinite and dioctahedral
mica upon acid dissolution as determined by profile fitting followed
by crystallite size calculation using Scherrer equation.

Fig. 8. XRD patterns of untreated (a) VP kaolin and treated in 6 mol · dm

—3

HCl at 95 °C

for 4 (b), 8 (c), 12 (d), 18 (e) and 36 h (f).

Fig. 9. Dissolution of Si, Al and Fe from VP kaolin in 6 mol · dm

—3

HCl at 95 °C.

cause  VP  kaolin  contains  besides  kaolin-
ite  also  other  clay  and  non-clay  minerals
more or less soluble in HCl, the resulting
acid dissolution (AD) curves represent the
sum  of  the  individual  elements  dissolved
from  all  minerals  present.  As  expected,
the  release  of  Si  atoms  into  the  solution
was minor due to formation of a protonated
amorphous  silica  phase  in  the  solid  reac-
tion product (Tkáč et al. 1994; Madejová et
al. 2009; Pentrák et al. 2009).

The dissolution curve for Al shows that

about  25 %  of  total  Al  is  dissolved  from
VP  kaolin  after  4  hours;  while  the  AD
curve  for  Fe  indicates  about  50 %  of  total
Fe released, implying that iron is bound in
a phase more soluble in HCl than kaolinite.
Higher extent of Fe release than that of Al
was observed also after 12 hours of VP dis-
solution.  The  final  solid  reaction  product
contains 13 % and 12 % of total Al and Fe
found in the starting material, respectively.

Pentrák et al. (2009) compared dissolu-

tion rates of two kaolins (GF, KGa-2)

509

STABILITY OF KAOLIN SAND FROM VYŠNÝ PETROVEC DEPOSIT (SLOVAKIA)

GEOLOGICA CARPATHICA

GEOLOGICA CARPATHICA, 2012, 63, 6, 503—512

with similar chemical composition and different structural
ordering (AGFI

KGa-2

= 0.8; AGFI

= 1.6) in 6 mol · dm

—3

HCl

at 95 °C. Although Fe occurred in both samples, the IR spec-
tra  confirmed  the  presence  of  Fe  in  the  octahedral  sheets
only  for  well-ordered  Golden  Field  (GF)  kaolinite.  About
50 % of total Al and Fe remained undissolved after 36 hours
of  treatment  of  the  well-ordered  GF,  in  contrast  to  less-or-
dered KGa-2, for which only 16 % of Al and Fe resisted the
dissolution process. It follows that a higher level of structural
ordering  of  GF  kaolinite  increases  its  stability  against  the
acid attack. Hradil et al. (2002) also described the same re-
sults. As both the HI and AGFI indices confirm, the mineral
in VP kaolin is a middle-ordered kaolinite. The AD curves of
VP kaolin, however, show an even larger extent of decompo-
sition  after  36  hours  in  HCl  than  less-ordered  KGa-2,  dis-
solved under the same conditions (Pentrák et al. 2009). The
presence of more soluble minerals (e.g. mica type minerals)
than kaolinite accelerates the dissolution of VP kaolin.

Useful information on the extent of VP kaolin dissolution

provides  IR  spectroscopy  in  both  MIR  (Fig. 10)  and  NIR
(Fig. 11) regions. The changes observed in the Si-O stretching
and bending regions reflect the transformation of the layered
structure  into  a  three-dimensional  framework.  Intensities  of
the  Si-O  stretching  bands  at  1034  and  1010 cm

—1

decrease

upon acid treatment and after 36 hours of dissolution they are
hardly distinguishable. Simultaneous appearance of the bands
at 1105 and 800 cm

—1

indicates formation of an amorphous

SiO

phase in the solid reaction product (Fig. 10).

Gradual release of octahedral atoms from the clay minerals

present in VP kaolin is reflected in a progressive decrease of the
intensities of the OH stretching bands in the 4000—3000 cm

—1

region and the AlAlOH bending bands at 936 and 913 cm

—1

Fig. 11. NIR spectra of untreated (a) VP kaolin and treated in
6 mol · dm

—3

HCl at 95 °C for 4 h (b), 8 h (c), 12 h (d), 18 (e) and 36 h (f).

Fig. 10. MIR spectra of untreated (a) VP kaolin and treated in 6 mol · dm

—3

HCl

at 95 °C for 4 h (b), 8 h (c), 12 h (d), 18 (e) and 36 h (f).

Liberation of Al atoms into HCl solution is also confirmed
by decreasing intensity of the Al-O-Si band at 539 cm

—1

(Fig. 10d). Although the absorption bands of amorphous silica
at 1100, 800 and 470 cm

—1

dominate in the MIR spectrum of

VP after 36 hours of dissolution in HCl, clearly resolved
bands of kaolinite prove the considerable stability of this clay

mineral. This is in agreement with the Al AD
curve indicating that about 13 % of total Al re-
mains in the solid reaction product (Fig. 10f).

Structural destruction of VP kaolin in HCl can

also be seen in the NIR spectra (Fig. 11). Signifi-
cant reduction in the intensities of the structural
OH overtones at 7171 and 7068

—1

and OH

combination modes near 4622 and 4528

—1

starts after 8 hours of acid treatment. In spite of
substantial decrease in the amount of AlAlOH
groups with prolonged time of dissolution, com-
plex OH overtone and combination bands can be
observed even in the NIR spectrum of VP kaolin
treated for 36 hours (Fig.

11f).

The appearance of the 2

Si—OH

overtone at

7315

—1

after 4 hours of acid treatment con-

firms partial protonization of Si-O bonds
(Fig.

11b). Enhancing intensity with prolonged

time of treatment indicates an increasing amount
of SiOH groups. Decomposition of VP kaolin in
HCl also influences the adsorption of water on
clay mineral surfaces. The combination band of
water molecules ( + )

H2O

is seen near 5225

—1

in the NIR spectrum of untreated VP kaolin.
Upon acid treatment, the position of the band is
shifted to ~ 5266 cm

—1

, namely to the same posi-

tion as observed in the NIR spectra of extensively

510

PENTRÁK, MADEJOVÁ, ANDREJKOVIČOVÁ, UHLÍK and KOMADEL

GEOLOGICA CARPATHICA

GEOLOGICA CARPATHICA, 2012, 63, 6, 503—512

acid-decomposed smectites and illites (Madejová et al. 2009).
The  shift  of  the  water  band  reflects  different  strength  of
H-bonds  between  water  molecules  and  acid-untreated  clay
minerals  and  between  H

O and amorphous silica, created

upon clay minerals dissolution. Moreover, the final position
of the ( + )

H2O

band confirms, like all bands observed in the

MIR and NIR spectra of the 36 hours treated VP, that disso-
lution of kaolinite results in the same reaction product as that
of other clay minerals.

Conclusions

The less than 45 µm fraction of kaolin sand from Vyšný

Petrovec deposit in Slovakia contains about 60 % of medium-
ordered  kaolinite,  32 %  of  dioctahedral  mica  type  minerals
and about 9 % of non-clay minerals, mainly quartz. However,
the stability of this kaolin in strongly acidic environment is
lower  than  that  of  less-ordered  KGa-2  kaolinite.  Chemical
analysis, XRD and IR spectroscopy confirm almost complete
decomposition  of  the  clay  minerals  present  in  the  acid-un-
treated VP kaolin upon a 36 hours treatment in 6 mol · dm

—3

HCl at 95 °C. The small-grain size of the middle-ordered ka-
olinite  and  the  presence  of  accessory  minerals  (illite,  sider-
ite),  more  soluble  than  kaolinite,  are  responsible  for  the
lower  stability  of  Vyšný  Petrovec  kaolin  in  HCl  than  pure
kaolinite samples under the same conditions.

Acknowledgments:  The  financial  support  of  the  Slovak
Grant Agency VEGA (Grant 2/0183/09) and Slovak Research
and  Development  Agency  (Grant  APVV-VVCE-0033-07)
are  highly  appreciated.  We  express  gratitude  to  Professor
V.N. Sokolov (Lomonosov Moscow State University) for his
excellent SEM measurements and Professor I. Kraus (Come-
nius  University,  Bratislava)  for  his  willingness  to  share  his
knowledge on kaolins.

References

Aparicio P. & Galán E. 1999: Mineralogical interference on kaolinite

crystallinity index measurements. Clays and Clay Miner. 47,
12—27.

Aparicio P., Galán E. & Ferrell R.E. 2006: A new kaolinite order

index based on XRD profile fitting. Clay Miner. 41, 811—817.

Bahranowski K., Serwicka E.M., Stoch L. & Strychalski P. 1993:

On the possibility of removal of non-structural iron from kao-
linite-group minerals. Clay Miner. 28, 379—391.

Baláž P. & Kúšik D. (Eds.) 2010: Slovak Minerals Yearbook. Sta-

tistical data to 2009. State Geological Institute of Dionýz Štúr,
1—158.

Bish D.L. & Duffy C.J. 1990: Thermogravimetric analysis of min-

erals. In: Stucki J.W. & Bish D.L. (Eds.): Thermal analysis in
clay science. CMS Workshop Lectures. Clay Minerals Society,
Boulder, Colorado, USA, 124—129.

Bookin A.S., Drits V.A., Plançon A. & Tchoubar C. 1989: Stacking

faults in kaolin-group minerals in the light of real structural
features. Clays and Clay Miner. 37, 297—307.

Breen C., Zahoor F.D., Madejová J. & Komadel P. 1997: Character-

ization and catalytic activity of acid-treated, size-fractionated
smectites. J. Physical Chemistry B 101, 5324—5331.

Brindley G.W. & Nakahira M. 1959: The kaolinite-mullite reac-

tions series. I. A survey of outstanding problems. II. Metakao-
lin. III. The high temperature phases. J. Amer. Ceramic Soc.
42, 311—324.

Bruker AXS 2000, TOPAS V2.0: General profile and structure

analysis software for powder diffraction data. User Manual,
Bruker AXS, Karlsruhe, Germany.

Bulens M. & Delmon B. 1977: The exothermic reaction of metakao-

linite in the presence of mineralizers. Influence of crystallinity.
Clays and Clay Miner. 25, 271—277.

Chipera S.J. & Bish D.L. 2001: Baseline studies of the Clay Minerals

Society Source Clays: Powder X-ray diffraction analyses.
Clays and Clay Miner. 49, 398—409.

Číčel B. & Novák I. 1976: Dissolution of smectites in hydrochloric

acid. I. Half-time of dissolution as a measure of reaction rate.
7-th Conference on Clay Mineralogy and Petrology, Karlovy
Vary.

Drits V.A., Eberl D.D. & Środoń J. 1998: XRD measurement of

mean thickness, thickness distribution and strain for illite and
illite-smectite crystallites by the Bertaut-Warren-Averbach
technique. Clays and Clay Miner. 46, 38—50.

Dubíková M., Cambier P., Šucha V. & Čaplovičová M. 2002: Ex-

perimental soil acidification. App. Geochem. 17, 245—257.

Eberl D.D. 2003: User’s guide to RockJock – a program for deter-

mining quantitative mineralogy from powder X-ray diffraction
data. U.S. Geol. Surv., Open-File Report, 3—78.

Egiebor N.O. & Oni B. 2007: Acid rock drainage formation and treat-

ment: a review. Asia-Pacific J. Chem. Engineering 2, 47—62.

Evans B.W. & Guggenheim S. 1988: Talc, pyrophyllite and related

minerals. In: Bailey S.W. (Ed.): Hydrous phyllosilicates (exclu-
sive of micas). Rev. in Mineralogy, 19, Mineral. Soc. Amer.,
Washington, D.C., 225—294.

Farmer V.C. 1974: Layer silicates. In: Farmer V.C. (Ed.): Infrared

spectra of minerals. Monograph. Mineral. Soc., London 4,
331—363.

Fijał J., Kłapyta Z., Ziętkiewicz J. & Żyła M. 1975: On the mecha-

nism of the montmorillonite acid activation. I. Degradation of
Ca-montmorillonite structure. Mineral. Pol. 6, 29—43.

Galán E., Aparicio P., La Iglesia A. & González I. 2006: The effect

of pressure on order/disorder in kaolinite under wet and dry
conditions. Clays and Clay Miner. 54, 232—241.

Ganor J., Mogollon J.L. & Lasaga A.C. 1995: The effect of pH on

kaolinite dissolution rates and on activation energy. Geochim.
Cosmochim. Acta 59, 1037—1052.

Giese R.F. 1988: Kaolin minerals: Structures and stabilities. In:

Bailey S.W. (Ed.): Hydrous phyllosilicates (exclusive of micas).
Rev. in Mineralogy, 19, Mineral. Soc. Amer., Washington, D.C.,
29—66.

Guggenheim S. & Koster van Groos A.F. 2001: Baseline studies of

the Clay Minerals Society Source Clays: Thermal analysis.
Clays and Clay Miner. 49, 433—443.

Hano V. 1973: Vyšný Petrovec, preliminary exploration – kaolin

sands. Report, Geofond, Bratislava, 1—74 (in Slovak).

Harvey C.C. & Lagaly G. 2006: Conventional applications. In: Ber-

gaya F., Theng B.K.G. & Lagaly G. (Eds.): Handbook of clay
science. Developments in clay science. Vol. 1. Elsevier Ltd.,
The Netherlands, 501—540.

He M.C., Zhao J., Fang Z.J. & Zhang P. 2011: First-principles

study of isomorphic (‘dual—defect’). Clays and Clay Miner.
59, 501—506.

Hinckley D.N. 1963: Variability in “crystallinity” values among the

kaolin deposits of the coastal plain of Georgia and South Caro-
lina. In: Swineford A. (Ed.): Clays and Clay Miner., Proc.
11th Natl. Conf., Ottawa, Ontario, 1962. Pergamon, New
York, 229—235.

Hradil D., Hostomský J. & Soukupová J. 2002: Aluminium release

511

STABILITY OF KAOLIN SAND FROM VYŠNÝ PETROVEC DEPOSIT (SLOVAKIA)

GEOLOGICA CARPATHICA

GEOLOGICA CARPATHICA, 2012, 63, 6, 503—512

rates from acidified clay structures: comparative kinetic study.
Geol. Carphathica 53, 2, 117—121.

Janotka I., Puertas F., Palacios M., Kuliffayová M. & Varga C.I.

2010: Metakaolin sand-blended-cement pastes: Rheology, hy-
dration process and mechanical properties. Construction and
Building Materials 24, 791—802.

Jozefaciuk G. & Bowanko G. 2002: Effect of acid and alkali treat-

ments on surface areas and adsorption energies of selected
minerals. Clays and Clay Miner. 50, 771—783.

Kadir S., Erman H. & Erkoyun H. 2011: Mineralogical and

geochemical characteristics and genesis of hydrothermal kao-
linite deposits within neogene volcanites, Kütahya (Western
Anatolia), Turkey. Clays and Clay Miner. 59, 250—276.

Kalinowski B.E. & Schweda P. 1996: Kinetics of muscovite, phlo-

gopite and biotite dissolution and alteration at pH 1—4, room
temperature. Geochim. Cosmochim. Acta 60, 367—385.

Klug H.P. & Alexander L.E. 1974: X-ray diffraction procedures for

polycrystalline and amorphous materials. 2

edition. Wiley,

New York, USA, 1—992.

Komadel P., Stucki J.W. & Číčel B. 1993: Readily HCl-soluble iron

in the fine fractions of some Czech bentonites. Geol. Carpathica
– Clays 44, 11—16.

Komadel P., Madejová J., Janek M., Gates W.P., Kirkpatrick R.J. &

Stucki J.W. 1996: Dissolution of hectorite in inorganic acids.
Clays and Clay Miner. 44, 228—236.

Komadel P. 2003: Chemically modified smectites. Clay Miner. 38,

127—138.

Kováč M., Baráth I., Fordinál K., Grigorovich A.S., Halásová E.,

Hudáčková N., Joniak P., Sabol M., Slamková M., Sliva  . &
Vojtko R. 2006: Late Miocene to Early Pliocene sedimentary
environments  and  climatic  changes  in  the  Alpine-Carpathian-
Pannonian junction area: A case study from the Danube Basin
northern  margin  (Slovakia).  Palaeogeogr.  Palaeoclimatol.
Palaeoecol. 238, 32—52.

Kováčová M., Doláková N. & Kováč M. 2011: Miocene vegetation

pattern and climate change in the northwestern Central Para-
tethys domain (Czech and Slovak Republic). Geol. Carphathica
62, 3, 251—266.

Krajči ., Janotka I., Kraus I. & Jamnický P. 2007: Burnt kaolin

sand as pozzolanic material for cement hydration. Ceramics-
Silikáty 51, 217—224.

Kraus I. 1989: Kaolins and kaolinite clays of the Western Car-

pathians. Western Carpathians, mineralogy petrography geo-
chemistry metalogensis series. Geological Institute of Dionýz
Štúr, Bratislava 13, 1—287.

Kraus I. & Hano V. 1976: Genetic classification and age of kaolinite

group minerals from the Western Carpathians deposits. Miner.
Slovaca 8, 431—436 (in Slovak).

Kraus I. & Horváth I. 1978: Mineralogy and age of Slovakian kao-

lins. Schrift. Geol. Wissenschaft. 11, 125—136.

Lagaly G. 1999: Introduction: from clay mineral—polymer interaction

to clay mineral-polymer nanocomposites. Applied Clay Sci. 15,
1—9.

Lintnerová O., Šucha V. & Streško V. 1999: Mineralogy and

geochemistry of acid mine Fe-precipitates from the main Slovak
mining regions. Geol. Carpathica 50, 395—404.

Ma M. 2011: The dispersive effect of sodium silicate on kaolinite

particles in process water: Implications for iron-ore processing.
Clays and Clay Miner. 59, 233—239.

Madejová J. & Komadel P. 2001: Baseline studies of The Clay Min-

erals Society Source Clays: Infrared methods. Clays and Clay
Miner. 49, 410—432.

Madejová J., Kraus I., Tunega D. & Šamajová E. 1997: Fourier trans-

form infrared spectroscopic characterisation of kaolinite group
minerals from the main Slovak deposits. Geol. Carpathica –
Clays 6, 3—10.

Madejová J., Bujdák J., Janek M. & Komadel P. 1998: Comparative

FT-IR study of structural modifications during acid treatment
of dioctahedral smectites and hectorite. Spectrochim. Acta,
Part A 54, 1397—1406.

Madejová J., Kečkéš J., Pálková H. & Komadel P. 2002: Identifica-

tion of components in smectite/kaolinite mixtures. Clay Miner.
37, 377—388.

Madejová J., Pentrák M., Pálková H. & Komadel P. 2009: Near-in-

frared spectroscopy: A powerful tool in studies of acid-treated
clay minerals. Vibrational Spectroscopy 49, 211—218.

Matusik J., Gaweł A., Bielańska E., Osuch W. & Bahranowski K.

2009: The effect of structural order on nanotubes derived from
kaolin-group minerals. Clays and Clay Miner. 57, 452—464.

Matusik J., Gaweł A., Bielańska E. & Bahranowski K. 2011: Surface

area and porosity of nanotubes obtained from kaolin minerals of
different structural order. Clays and Clay Miner. 59, 116—135.

Meads R.E. & Malden P.S. 1975: Electron-spin resonance in natural

kaolinites containing Fe

and other transition metal ions. Clay

Miner. 10, 313—345.

Mestdagh M.M., Vielvoye L. & Herbillon A.J. 1980: Iron in kaolin-

ites. II. The relationship between kaolinite crystallinity and
iron content. Clay Miner. 15, 1—13.

Moussi B., Medhioub M., Hatira N., Yans J., Hajjaji W., Rocha F.,

Labrincha J.A. & Jamoussi F. 2011: Identification and use of
white clayey deposits from the area of Tamra (northern Tunisia)
as ceramic raw materials. Clay Miner. 46, 165—175.

Murray H.H., Bundy W.M. & Harvey C.C. 1993: Kaolin genesis

and utilization. Spec. Publ. No. 1. Clay Miner. Soc., Boulder,
CO, 1—341.

Murray H.H. 2007: Applied clay mineralogy. Occurrences, process-

ing and application of kaolins, bentonites, palygorskite-sepio-
lite, and common clays. Elsevier, Developments in Clay Sci. 2,
1—180.

Nguetnkam J.P., Kamga R., Villiéras F., Ekodeck G.E., Razafitian-

amaharavo A. & Yvon J. 2011: Alteration of cameroonian
clays under acid treatment. Comparison with industrial adsor-
bents. Applied Clay Sci. 52, 122—132.

Novák I. & Číčel B. 1978: Dissolution of smectites in hydrochloric

acid: II. Dissolution rate as a function of crystallochemical
composition. Clays and Clay Miner. 26, 341—344.

Novembre D., Di Sabatino B., Gimeno D. & Pace C. 2011: Synthe-

sis and characterization of Na-X, Na-A and Na-P zeolites and
hydroxysodalite from metakaolinite. Clay Miner. 46, 339—354.

Novotná M., Kraus I. & Horváth I. 1993: Expression of kaolinite

ordering in selected kaolin deposits. Miner. Slovaca 25, 55—59
(in Slovak).

Pentrák M., Madejová J. & Komadel P. 2009: Acid and alkali treat-

ment of kaolins. Clay Miner. 44, 511—523.

Pentrák M., Madejová J. & Komadel P. 2010: Effect of chemical

composition and swelling on acid dissolution of 2 : 1 clay min-
erals. Philosophical Mag. 90, 2387—2397.

Pentrák M., Czímerová A., Madejová J. & Komadel P. 2012: Changes

in layer charge of clay minerals upon acid treatment as obtained
from their interactions with methylene blue. Applied Clay Sci.
55, 100—107.

Petit S., Madejová J., Decarreau A. & Martin F. 1999: Characteriza-

tion of octahedral substitutions in kaolinites using near infra-
red spectroscopy. Clays and Clay Miner. 47, 103—108.

Plançon A. & Tchoubar C. 1977a: Determination of structural de-

fects in phyllosilicates by X-ray powder difraction. I. Principle
of calculation of the diffraction phenomenon. Clays and Clay
Miner. 25, 430—435.

Plançon A. & Tchoubar C. 1977b: Determination of structural de-

fects in phyllosilicates by X-ray powder difraction. II. Nature
and proportion of defects in natural kaolinites. Clays and Clay
Miner. 25, 436—450.

512

PENTRÁK, MADEJOVÁ, ANDREJKOVIČOVÁ, UHLÍK and KOMADEL

GEOLOGICA CARPATHICA

GEOLOGICA CARPATHICA, 2012, 63, 6, 503—512

Plançon A., Giese R.F. & Snyder R. 1988: The Hinckley index for

kaolinites. Clay Miner. 23, 249—260.

Plançon A., Giese R.F., Snyder R., Drits V.A. & Bookin A.S. 1989:

Stacking faults in the kaolin-group minerals: defect structures
of kaolinite. Clays and Clay Miner. 37, 203—210.

Plançon A. & Zacharie C. 1990: An expert system for the structural

characterization of kaolinite. Clay Miner. 25, 249—260.

Premović P.I., Ciesielczuk J., Bzovska G. & Đor evič M.G. 2012:

Geochemistry and electron spin resonance of hydrothermal
dickite (Nowa Ruda, Lower Silesia, Poland): vanadium and
chromium. Geol. Carphathica 63, 3, 241—252.

Pruett R.J. & Webb H.L. 1993: Sampling and analysis of KGa-1B

well-crystallized kaolin source clay. Clays and Clay Miner. 41,
514—519.

Rožić L., Novaković T. & Petrović S. 2010: Modeling and optimi-

zation process parameters of acid activation of bentonite by re-
sponse surface methodology. Applied Clay Sci. 48, 154—158.

Rožić L., Grbić B., Radić N., Petrović S., Novaković T., Vuković Z.

& Nedić Z. 2011: Mesoporous 12-tungstophosphoric acid/acti-
vated bentonite catalysts for oxidation of 2-propanol. Applied
Clay Sci. 53, 151—156.

Sciascia L., Turco Liveri M.L. & Merli M. 2011: Kinetic and equi-

librium studies for the adsorption of acid nucleic bases onto
K10 montmorillonite. Applied Clay Sci. 53, 657—668.

Siddique R. & Klaus J. 2009: Influence of metakaolin on the prop-

erties of mortar and concrete: A review. Applied Clay Sci. 43,
392—400.

Sillitoe R.H. 2010: Porphyry copper systems. Econ. Geol. 105, 3—41.
Slaughter M. & Keller W.D. 1959: High temperature phases from

impure Kaolin clays. Bull. Amer. Ceramic Soc. 38, 703—707.

Soták J. 2011: Paleoenvironmental changes across the Eocene-Oli-

gocene boundary: insights from the Central-Carpathian Paleo-
gene Basin. Geol. Carphathica 61, 5, 393—418.

Stoch L., Bahranowski K., Budek L. & Fijał J. 1977: Bleaching

properties of non-bentonitic clay materials and their modifica-
tion. I. Acid activation of the miocene clays from Machów.
Miner. Pol. 8, 31—51.

Šucha V., Kraus I., Šamajová E. & Puškelová . 1999: Crystallite

size distribution of kaolin minerals. Periodico di Mineralogia
68, 81—92.

Tkáč I., Komadel P. & Müller D. 1994: Acid-treated montmorillo-

nites – a study by

Si and

Al MAS NMR. Clay Miner. 29,

11—19.

Uzarowicz Ł., Skiba S., Skiba M. & Michalik M. 2011: Clay-mineral

formation in soils developed in the weathering zone of pyrite-
bearing schists: A case study from the abandoned pyrite mine
in Wieściszowice, Lower Silesia, SW Poland. Clays and Clay
Miner. 59, 581—594.

Valášková M., Barabaszová K., Hundáková M., Ritz M. & Plevová

E. 2011: Effect of brief milling and acid treatment on two or-
dered and disordered kaolinite structures. Applied Clay Sci. 54,
70—76.

Van Olphen H. & Fripiat J.J. 1979: Data handbook for clay minerals

and other non-metallic materials. Pergamon Press, 1—346.

Vass D., Elečko M., Bezák V., Bodnár J., Konečný V., Lexa J.,

Molák B., Straka P., Stankovič J., Stolár M., Škvarka L.,
Vozár J. & Vozárová A. 1992: Geological map of the Lučenská
kotlina depression and Cerová vrchovina upland, 1 : 50,000.
Geol. Surv. of Slovak Republic, Bratislava.

Worasith N., Goodman B.A., Neampan J., Jeyachoke N. &

Thiravetyan P. 2011: Characterization of modified kaolin from
the Ranong deposit Thailand by XRD, XRF, SEM, FTIR and
EPR techniques. Clay Miner. 46, 539—559.

Yanik G. 2011: Mineralogical, crystallographic and technological

characteristics of Yaylayolu kaolin (Kütahya, Turkey). Clay
Miner. 46, 397—410.