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Characterization and differentiation of kaolinites from selected Czech deposits using infrared spectroscopy and differential thermal analysis.

1. INTRODUCTION

Important deposits of high quality kaolin in the Czech republic (sedimentary rock, with a significant proportion of kaolinite and other clay minerals) are in Karlovy Vary region. A more extensive deposits of kaolin are in the region of Horni Briza, Kaznejov, Chotikov and other places in the northern neighborhood of Pilsen. Low-quality kaolin deposits are situated in western Bohemia and also in Znojmo district. Kaolin is widely used in the paper industry for its high whiteness and low abrasion and it is also used in the other industry branches like construction, ceramics, rubber and porcelain manufacturing.

The empirical formula for kaolinite is [Al.sub.2][Si.sub.2][O.sub.5][(OH).sub.4] and the theoretical chemical composition is Si[O.sub.2], 46.54 %; [M.sub.2] [O.sub.3], 39.50 %; and [H.sub.2]O, 13.96 %. Kaolinite has a 1:1 sheet structure consisted by tetrahedral and octahedral sheets. Type 1:1 minerals generally do not have the charge or its value is extremely low (Murray, 2007). The kaolinite layered structure 1:1 according to (Kuhn and Zamarsky, 1984) is shown in Figure 1.

The quality respectively the orderliness of kaolinites strongly influence their physical and chemical properties. The most often used method for examination of the degree of structural disorder or "crystallinity" of the kaolinite samples is X-ray powder diffraction. Kaolinite tetrahedral and octahedral network forms a single layer with a thickness of approximately 7 [Angstorm]. The poor structural order commonly observed in kaolinites can be explained in terms of a series of stacking faults or defects in the ab plane and along the c-axis. The XRD patterns of ordered kaolinite samples are significantly different from those of disorder. Ordered kaolinite shows sharp and narrow peaks, while its disordered counterpart gives less well-defined, broad, and asymmetrical peaks (Brigatti et al., 2006). The crystallinity indices given by many authors are widely used for determination of kaolinite disorder degree using various approaches based on X-ray diffraction (Brindley et al., 1963; Plancon and Zacharie, 1990; Aparicio and Galan, 1999; Chmielova and Weiss, 2002; Aparicio, 2006).

Less common used method for determination of kaolinite disorder degree is an infrared spectroscopy. The structural disorder of kaolinites can be detected by differences in position and relative intensity of OH stretching and bending bands in IR spectrum (Brindley, et al., 1986; Muller and Bocquier, 1987; Prost et al., 1989; Madejova et al., 1997). On the basis of change in the relative intensities of absorption bands corresponding to the stretching and bending vibrations of structural OH groups, it was possible to divide the analyzed samples into three groups: with ordered structure, partially ordered structure and poorly ordered structure.

[FIGURE 1 OMITTED]

The least common used method for determination of kaolinite disorder degree is simultaneous thermogravimetry and differential thermal analysis. The DTA curves show the endothermic and exothermic reactions in a kaolinite sample during heating, such as desorption of surface water ([H.sub.2]O), dehydroxilation (structural OH-groups) and the transformation to mullite and cristobalite (Foldvari, 1997; Hatakeyama and Liu, 1998; Guggenheim and Koster van Groos, 2001). The obtained temperature effects of dehydroxilation and polymorphic transformation are strongly dependent on kaolinite sample structural order (Smykatz-Kloss, 1974; Kristof et al., 2002).

In the present paper is incorporated a detailed study of the degree of structural disorder for four Czech kaolinite samples (Jimlikov, Sedlec, Olomucany and Unanov deposits) and one kaolinite standard KGa-1b from Georgia deposit obtained from the Source Clays Repository of The Clay Minerals Society (USA). The kaolinite standard KGa-1b is the aim of the interest of many authors because of its purity and its special properties (Pruett and Webb, 1993; Bereznitski et al., 1998; Sanchez-Soto et al., 2000; Mermut and Cano, 2001; Traore, 2006). This standard kaolinite was chosen for comparision with Czech selected kaolinites mentioned above. The detailed study has included mainly an numerical approach based on crystallinity indices [CI.sub.1] and [CI.sub.2] calculated from the intensities of selected vibrations modes obtained by FTIR measurements as well as the determination of the disorder degree according to peak temperature values of kaolinite dehydroxilation and transformation obtained by differential thermal analysis.

2. SAMPLES AND EXPERIMENTAL METHODS 2.1. TESTED SAMPLES

Kaolinite samples (fraction under 5[micro]m) from several different Czech kaolin deposit were used for analysis:

(a) kaolinite sample from Karlovy Vary region, formed by kaolinization of granite (Jimlikov u Chodova locality)

(b) kaolinite sample from Karlovy Vary region, formed by kaolinization of granite (Sedlec locality)

(c) kaolinite sample from Moravian Karst, represented kaolinized clayey-sandy sediments in fosil-karst depressions (Olomucany locality)

(d) kaolinite sample from Znojmo region, formed by kaolinization of granitoid rocks (Unanov locality)

(e) kaolinite sample KGa-1b from Georgia (USA), represented sedimentary kaolinite with well ordered structure.

Following Table 1 shows the volume of kaolinite and type of associated minerals signed as : Q--quartz, I--illite, Sm--smectite, D--dickite, F--feldspar.

2.2. METHOD OF FTIR SPECTROSCOPY

The infrared spectra were recorded on Nicolet Avatar 320 FTIR spectrometer. The KBr pressed-disc technique was used for routine scanning of the spectra. Samples of 2 mg and 0.5 mg were dispersed in 200 mg of KBr to record optimal spectra in the regions of 4000-3000 and 4000-400 [cm.sup.-1] with a resolution of 4 [cm.sup.-1] and 64 scans. Discs for the 4000-3000 [cm.sup.-1] region were heated in the furnace overnight at 150[degrees]C to minimize the water adsorbed on KBr and clay sample (Madejova et al., 1997).

Two approaches were used to determine the degree of structural disorder of selected kaolinites from IR spectra. The firstly step, an empirical approach (IR-E) on the basis of resolution and relative intensities of the bands in OH stretching and bending region was used. The samples were classified as:

* ordered (well-ordered) if the OH stretching and bending bands were clearly resolved;

* partially ordered if the individual OH bands at 3670, 3650 and 938 [cm.sup.-1] could be identified but their intensities were low; and

* poorly ordered if only one band near 3660 or inflexions near 3670, 3650 and 938 [cm.sup.-1] were observed in the spectra (Madejova et al., 1997).

A numerical approach (IR-N) based on crystallinity indices [CI.sub.1] and [CI.sub.2] calculated from the intensities of selected vibrations modes using the equations:

[CI.sub.1] = I([V.sub.1]) / I([V.sub.3]) (1)

[CI.sub.2] = I([V.sub.4]) / I([V.sub.1]) (2)

where I([V.sub.1]) and I([V.sub.4]) are intensities of the OH stretching bands at 3695 [cm.sup.-1] and 3620 [cm.sup.-1] and I([V.sup.3]) is the intensity of the OH bending band at 915 [cm.sup.-1]. The two-points baseline method was used to obtained the intensity of the OH bands. According to the obtained values of crystallinity indices kaolinites were classified as poorly ordered structures ([CI.sub.1] < 0.7, [CI.sub.2] > 1.2); partially ordered structures (0.7 < [CI.sub.1] < 0.8, 0.9 < [CI.sub.2] < 1.2) and ordered structures ([CI.sub.1] > 0.8, [CI.sub.2] < 0.9) (Russell and Fraser, 1994; Madejova and Komadel, 2001).

2.3. METHOD OF THERMAL ANALYSIS

Simulatneous thermogravimetry and differential thermal analysis was carried out using multimodular thermal analyzer SETSYS 12-SETARAM instrument equipped with a measurement head TG ATD ROD according to below mentioned conditions. Measurement of each sample was carried five times to get predicative results.

Based on obtained DTA curves, respectively according to decomposition peak temperatures is possible to determine the degree of disorder in kaolinite samples. Well ordered sample has their decomposition peak temperature of quite high value ([T.sub.d] > 571[degrees]C), ordered sample has their decomposition peak temperature [T.sub.d] at the temperature interval 561-570 [degrees]C. For poorly ordered sample, the temperature decomposition varies from 546 to 560[degrees]C and disordered sample decomposition temperature values is up to 545[degrees]C. The decomposition peak below 540[degrees]C seems to be quite low according to published DTA data of kaolinites and belog to only a very few naturally occuring, extremely disordered samples.

The differentiation mentioned above can be used for the determination of the disorder degree of kaolinites if the analysis were under the proposed conditions : heating rate 10[degrees]C.[min.sup.-1] , sample fraction under 5 [micro]m (the fraction from 0.5 to 5 [micro]m with maximum in their grain size distribution curves laying for the fraction 2-3 [micro]m) , sample mass about 50 mg, thermocouple Pt-[Pt.sub.90] /[Rh.sub.10] , inert material [Al.sub.2][O.sub.3], no pressing in crucible (loose packed), air atmosphere. With different conditions, the dehydroxilation peak temperature [T.sub.d] can vary, so the temperature interval of disorder degree can differ too. The most influencing factor for the [T.sub.d] temperature value is the heating rate (Gabbott, 2008). The difference between the dehydroxilation temperature with heating rates 3[degrees]C.[min.sup.-1] and 30[degrees]C.[min.sup.-1] for the same kaolinite sample is over 50[degrees]C. Therefore the evaluation of the disorder degree of kaolinites by thermal analysis must be always adjusted to measurement conditions (Smykatz-Kloss, 1974).

3. RESULTS AND DISCUSSION

3.1. FTIR SPECTROSCOPY

The infrared spectra of tested kaolinites are shown in Figures 2 and 3. The complete assignment of the absorption bands in measured IR spectra is summarized in Table 2.

Determination of degree of structural disorder from IR spectra of kaolinites based on visual estimation of specific features (IR-E) and calculated crystallinity indices [CI.sub.1] and [CI.sub.2] (IR-N) according to Neal and Worral (1977) are given in Table 3.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

The 3695, 3620 [cm.sup.-1] doublet is characteristic for the kaolin group general. Four clearly resolved absorption bands at about 3695, 3670, 3650 and 3620 [cm.sup.-1] reflect high structural ordering of the samples. Distinguishable four bands in OH stretching region were observed in IR spectrum of sample KGa-1b, Jimlikov, Sedlec and Unanov. The IR spectrum of kaolinite from Olomucany deposit showed the replacement of the middle two bands by a single broad band at 3654 [cm.sup.-1] with a shoulder near 3668 [cm.sup.-1], that indicates partially ordered structure of this sample (Fig. 3). IR spectrum of Unanov demonstrated general broadening of all bands (Fig. 2). This feature confirms high degree of disordering in kaolinite. Two clearly resolved OH bending bands occuring at about 938 and 916 [cm.sup.-1]were observed in IR spectra of samples from Georgia (KGa-1b) and Jimlikov deposit (Fig. 2). Other samples in this spectral region showed only a very weak inflection located at 934 [cm.sup.-1]. In all IR spectra were found two weak bands at 795 and 758 [cm.sup.-1] with about equal intensity (Fig. 2). This attribute can help to distinguish between well-crystallized kaolinite and halloysite.

It is possible to divide tested kaolinites according to visual estimation of degree of crystallinity from IR spectra (IR-E) into three groups: ordered (well ordered), partially ordered and poorly ordered. First group is represented by kaolinite KGa-1b and Jimlikov whose IR spectra satisfy all the demands of IR-E classification. IR spectrum of Sedlec kaolinite without clearly resolved OH deformation band at 938 [cm.sup.-1]belongs to the second group with partial structural order. Kaolinite Olomucany and Unanov represent third group with poorly order structure. According to calculated values of IR-N classification, based on the ratio hydroxyl band absorbances 3695 and 915 [cm.sup.-1]([CI.sub.1]); and 3695 [cm.sup.-1] ([CI.sub.2]), it is possible to divide the kaolinites into two groups: ordered (well ordered) and partially ordered. Among ordered (well ordered) kaolinites belong KGa-1b and Jimlikov. In this case data from IR-E classification correspond well with IR-N classification. Second group is represented by kaolinite Sedlec, Olomucany and Unanov, whose CI1 and CI2 crystallinity indices corresponded to partially ordered structures. Discrepancy between IRN and IR-E classification arose probably thank to admixture of fine-grained illite or smectite present in kaolinite samples (see Table 1). Both minerals (illite and smectite) have their absorption bands at the same area and can contribute to the increasing of both OH bending absorption at 915 [cm.sup.-1]and OH stretching absorption at 3695 [cm.sup.-1]. The problem is that their contribution to the absorption at 915 [cm.sup.-1]is significantly higher than to the absorption at 3695 [cm.sup.-1]. When calculating the ratio of [CI.sub.2] based on such affected values, the ratio can indicate an erroneously higher value for the crystallinity degree of the kaolinite.

3.2. THERMAL ANALYSIS

The measured DTA curves of tested kaolinites showed the following endothermic effects: desorption of surface water at low temperature interval 105110 [degrees]C and releasing of constitution water and breaking of crystal lattice at higher temperature interval 552-576[degrees]C. The recrystallization and transformation of dehydrated substance to mullite, cristobalite and quartz was observed as the exothermic effect at about 982-1001[degrees]C.

Table 4 shows the thermal data obtained from DTA curves including dehydroxilation peak temperature [T.sub.d] and transformation peak temperature [T.sub.t]. The first group of well ordered samples is represented by kaolinite KGa-1b with the highest decomposition peak temperature value (above 571[degrees]C). The sample classified as ordered (from Jimlikov) belongs to the second group with middle decomposition peak temperature values. Among poorly-ordered samples in the third group belong kaolinite samples from Sedlec, Olomucany and Unanov with the lowest decomposition peak temperature values up to 560[degrees]C.

From obtained data is evident, that with increasing of decomposition peak temperature value, respectively with increasing of orderliness, the transformation exothermic peak temperature also increase (Fig. 4). DTA curves show, that for well ordered samples, the transformation exothermic peak are of the high intensity and quite narrow. For the poorly ordered sample, the transformation peaks are of low intesity, wider and smaller.

[FIGURE 4 OMITTED]

The kinetic parameters of decomposition was studied using the Arrhenius equation applied to solid state reactions. The activation energy for dehydroxilation was evaluated by Freeman-Carroll method which enables, from the exploitation of one DTG peak, to determine besides activation energy of reaction also the reaction order and the rate constant (Freeman and Caroll, 1958). Table 5 summarized thermal data including maximal reaction velocity temperature [T.sub.r], activation energy [E.sub.a] with order reaction n and correlation factor [R.sup.2].

It is evident, that values of maximal reaction velocity temperature [T.sub.r] obtained from DTG curve correspond to the decomposition peak temperature [T.sub.d] obtained from DTA curves. Figure 5 shows the derivative thermogravimetric (DTG) curves for all tested kaolinite samples at the heating rate 10[degrees]C[.min.sup.-1]. With increase of peak temperature on DTG curve, activation energy of dehydroxilation process decreased. The values of activation energy [E.sub.a] varied from 230 kJ.[mol.sup.-1] (well ordered kaolinite sample KGa-1b) to 301 kJ.[mol.sup.-1] (the poorliest ordered sample Unanov) with the reaction order n varied from 0.9 to 1.5. Obtained results show, that better ordered samples display lower activation energy for dehydroxilation process estimated by Freeman-Carroll method. The possibilities and comparision of Freeman-Carroll method with other used methods are described well by (Slovak, 2001). The disadvantage of this method can lay in the fact, that the calculation is performed from the difference of two discrete experimental points and consider rather homogenous character of reaction. MacKenzie (1978) and Cicel et al. (1981) assume, that homogeneous and inhomogeneous mechanisms of the dehydroxilation process is possible. Therefore if the heterogenous character of dehydraxilation process is supposed, the dependance of activation energy on structural order can differ, mainly if we cosider that the dehydroxilation process is initiated in the defect places.

[FIGURE 5 OMITTED]

4. CONCLUSIONS

The obtained results from infrared spectroscopy and differential thermal analysis were compared with XRD results previously published by Hinckley (1963) and Aparicio et al. (1999). Also according to Pruett and Webb (1993), kaolinite Georgia (KGa-1b) is signed as well-ordered and based on the calculated characteristic (Chmielova and Weiss, 2002), the kaolinites from Czech deposits can be divided into two groups. First group of medium-degree of structural order (ordered) samples contains kaolinite Jimlikov, the second group of low-degree of structural order (poorly ordered) samples contains kaolinites from Sedlec, Olomucany and Unanov deposits. According to our DTA results, kaolinite Georgia (KGa-1b) belongs to well-ordered group, kaolinite Jimlikov to ordered group and other tested samples to poorly-ordered group. It is evident, that DTA data set a reasonable agreement with published data obtained by XRD diffraction method. In case of using FTIR spectroscopy, there is only a slight difference between IR data and data evaluated by DTA and XRD analysis. The OH stretching and bending vibrations of structural water are sensitive enough to distinguish ordered (well ordered), partially ordered and poorly ordered kaolinites. Visual IR-E method for structural order determination provides basic classification into three groups: ordered (well ordered), partially ordered and poorly ordered; while IR-N method divides kaolinite samples into two groups: ordered (well ordered) and partially ordered. Unanov and Olomucany samples were evaluated as partially ordered kaolinite analogous to Sedlec. The cause of this discrepancy is probably the presence of clay mineral admixture (e.g. illite or smectite), which strongly influences the IR pattern in OH stretching and bending region. The OH bands are overlapped and thus may lead to incorrect deegre of structural order. But even though all three used methods give a slightly different distribution of the structure classification, the order respectively the resulting trend of decrease in orderliness is the same for all three methods: KGA-1b (with the best orderliness) > Jimlikov > Sedlec > Olomucany > Unanov (with the worst orderliness).

ACKNOWLEDGEMENTS

This study was supported by the Czech Science Foundation, the project No.105/08/1398 and No.105/07/P416, and by Research plan No. AVOZ 30860518. The authors would like to thank George Laynr for controlling and correcting the use of English in this article.

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Lenka VACULIKOVA (1), Eva PLEVOVA (1) *, Silvie VALLOVA (2) and Ivan KOUTNIK 2

(1) Institute of Geonics, Academy of Sciences of the Czech Republic, v.v.i., Studentska 1768, 708 00 Ostrava, Czech Republic

(2) Technical University of Ostrava, 17. listopadu 15, 708 33 Ostrava, Czech Republic

* Corresponding author's e-mail: plevova@ugn.cas.cz

(Received September 2010, accepted December 2010)
Table 1 Locality, mineralogical composition, genesis and
classification according to XRD of tested kaolinite
samples.

       Deposit           Kaolinite   Associated     Origin       XRD
                            (%)       minerals

                                                                 HI

Georgia (KGa-1b), USA       96           D        sedimentary   1.120
Jimlikov u Chodova, CZ      98           Q         weathered    1.060
Sedlec u K. Varu,CZ         97         Q,I,Sm      weathered    0.630
Olomucany,Blansko, CZ       97         Q,I,Sm      weathered    0.590
Unanov u Znojma, CZ         96         Q,I,F       weathered    0.480

       Deposit                XRD

                         AGFI    Class.

Georgia (KGa-1b), USA      -      w-o
Jimlikov u Chodova, CZ   1.180     o
Sedlec u K. Varu,CZ      0.780    p-o
Olomucany,Blansko, CZ    0.670    p-o
Unanov u Znojma, CZ      0.640    p-0

HI - the method of Hinckley (1963)

AGFI - the method of Aparicio-Galan Ferrell (1999)

Table 2 Position and assignment of the absorption bands in IR
spectra of tested kaolinites.

       Assignment            KGa-1b    Jimlikov   Sedlec   Olomucany

OH stretching of              3694       3695      3696      3696
  inner-surface hydroxyl
  groups (1)

OH stretching of              3669       3669      3668    3668 (s)
  inner-surface hydroxyl
  groups (2)

OH stretching of              3653       3652      3653      3654
  inner-surface hydroxyl
  groups (2)

OH stretching of inner        3618       3620      3620      3620
  hydroxyl groups

Si-O stretching             1113 (s)     1112      1113      1111
  (longitudinal mode)

Si-O stretching               1098        -         -          -
  (perpendicular mode)

in-plane Si-O stretching      1033       1032      1032      1032

in-plane Si-O stretching      1009       1008      1007      1006

OH deformation of             937        935       937        936
  inner-surface hydroxyl
  groups

OH deformation of inner       913        913       913        913
  hydroxyl groups

Si-O                          791        793       793        793

Si-O, perpendicular           752        755       755        755

Si-O, perpendicular           694        699       699        698

Si-O                          645        647       641        645

Al-O-Si deformation           540        538       537        538

Si-O-Si deformation           468        470       469        470

Si-O deformation              433        430       430        430

       Assignment           Unanov

OH stretching of             3696
  inner-surface hydroxyl
  groups (1)

OH stretching of             3669
  inner-surface hydroxyl
  groups (2)

OH stretching of             3652
  inner-surface hydroxyl
  groups (2)

OH stretching of inner       3620
  hydroxyl groups

Si-O stretching              1114
  (longitudinal mode)

Si-O stretching               -
  (perpendicular mode)

in-plane Si-O stretching     1032

in-plane Si-O stretching     1007

OH deformation of            935
  inner-surface hydroxyl
  groups

OH deformation of inner      912
  hydroxyl groups

Si-O                         794

Si-O, perpendicular          754

Si-O, perpendicular          697

Si-O                         644

Al-O-Si deformation          537

Si-O-Si deformation          469

Si-O deformation             429

(1) - in plane vibration with a transition moment nearly
perpendicular to the (001) plane

(2) - anti-phase vibration with a transition moment lying
in the (001) plane.

(s) - shoulder of absorption band

Table 3 Classification of the degree of structural order of
kaolinite samples using empirical (IR-E) and numerical (IR-N)
classification.

       Deposit                             Attributes

                                1st       2nd       3rd       4th

Georgia (KGa-1b), USA         [check]   [check]   [check]   [check]
Jimlikov u Chodova, CZ        [check]   [check]   [check]   [check]
Sedlec u Karlovych Varu, CZ   [check]   [check]   937 (s)   [check]
Olomucany, Blansko, CZ           x      [check]   937 (s)   [check]
Unanov u Znojma, CZ           [check]      x      937 (s)   [check]

       Deposit                IR-E    [CI.sub.1]   [CI.sub.2]   IR-N

                              class                             class

Georgia (KGa-1b), USA           o        0.96         0.78        o
Jimlikov u Chodova, CZ          o        0.93         0.78        o
Sedlec u Karlovych Varu, CZ   pa-o       0.91         1.20      pa-o
Olomucany, Blansko, CZ         p-o       0.74         0.82      pa-o
Unanov u Znojma, CZ            p-0       0.72         0.81      pa-o

Attributes: 1st--distinguishable four bands 3695, 3670, 3650, 3620

2nd--general broadening of all bands is not observed

3rd--OH deformation bands 938 and 916 are visible

4th--two weak bands found at 795 and 758 are of about equal intensity

[CI.sub.1], [CI.sub.2]--the method of Neal and Worral (1977)

Table 4 Thermal data including dehydroxilation peak
temperature [T.sub.d], transformation peak temperature
[T.sub.t] and classification of disorder degree of
kaolinite samples.

        Deposit               [T.sub.d]   [T.sub.t]   class

Georgia (KGa-1b), USA            576        1001       w-o
Jimlikov u Chodova, CZ           570         992        o
Sedlec u Karlovych Varu,CZ       560         989       p-o
Olomucany,Blansko, CZ            558         988       p-o
Unanov u Znojma, CZ              552         982       p-0

Table 5 Thermal data including peak temperature [T.sub.r],
activation energy [E.sub.a] and reaction order n.

         Deposit            [T.sub.r]    [e.sub.a]    n    [R.sup.2]
                            [degrees]C    kJ.mot1

Georgia (KGa-1b). USA          573          230      1.1    1.0000
Jimlikov u Chodova. CZ         568          242      1.4    0.9998
Sedlec u Karlovych Varu.CZ     563          277      1.5    0.9998
Olomucany.Blansko. CZ          559          274      1.0    0.9992
Unanov u Znojma. CZ            553          301      0.9    0.9996
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Author:Vaculikova, Lenka; Plevova, Eva; Vallova, Silvie; Koutnik, Ivan
Publication:Acta Geodynamica et Geromaterialia
Article Type:Report
Geographic Code:4EXCZ
Date:Jan 1, 2011
Words:4444
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