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

Acta Geodyn. Geomater., Vol. 8, No. 1 (161), 59–67, 2011 CHARACTERIZATION AND DIFFERENTIATION OF KAOLINITES FROM SELECTED CZECH DEPOSITS USING INFRARED SPECTROSCOPY AND DIFFERENTIAL THERMAL ANALYSIS . Lenka VACULÍKOVÁ 1), Eva PLEVOVÁ 1)*, Silvie VALLOVÁ 2) and Ivan KOUTNÍK 2) 1) Institute of Geonics, Academy of Sciences of the Czech Republic, v.v.i., Studentská 1768, 708 00 Ostrava, Czech Republic 2) Technical University of Ostrava, 17. listopadu 15, 708 33 Ostrava, Czech Republic *Corresponding author‘s e-mail: [email protected] (Received September 2010, accepted December 2010) ABSTRACT This paper reports the possibilities of using FTIR spectroscopy and simultaneous thermogravimetry and differential thermal analysis for examination of the structural order of 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). FTIR spectroscopy was used for the classification of the degree of structural order of kaolinite samples by empirical (IR-E) and numerical (IR-N) classification. Differential thermal analysis was used for the determinatio n of the kaolinite disorder degree according to decomposition peak temperature obtained from DTA curves. The resulting trend of decrease in orderliness is: KGA-1b (with the best orderliness) > Jimlikov > Sedlec > Olomucany > Unanov (with the worst orderliness). KEYWORDS: kaolinite, degree of structural order, infrared spectroscopy, thermogravimetry and differential thermal analysis a thickness of approximately 7 Å. 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 p atterns 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 Galán, 1999; Chmielová and Weiss, 2002; Aparicio, 2006). Less common used method for determination o f kaolinite disorder degree is an infrared spectroscopy. The structural disorder of kaolinites can be detected b y differences in position and relative intensity of OH stretching and bending bands in IR spectru m (Brindley, et al., 1986; Muller and Bocquier, 1987; Prost et al., 1989; Madejová et al., 1997). On the basis of change in the relative intensities of absorption b ands 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 an d poorly ordered structure. 1. INTRODUCTION Important deposits of high quality kaolin in the Czech republic (sedimentary rock, with a significan t proportion of kaolinite and other clay minerals) are in Karlovy Vary region. A more extensive deposits o f 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 fo r its high whiteness and low abrasion and it is also use d in the other industry branches like construction, ceramics, rubber and porcelain manufacturing. The empirical formula for kaolinite is Al2Si2O5(OH)4 and the theoretical chemical composition is SiO2, 46.54 %; Al2O3, 39.50 %; and H2O, 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 (Kühn an d Zamarský, 1984) is shown in Figure 1. The quality respectively the orderliness o f kaolinites strongly influence their physical an d chemical properties. The most often used metho d 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 DSpace VŠB-TUO http://hdl.handle.net/10084/84630 21/06/2012 L. Vaculíková et al. 60 Fig. 1 The kaolinite layered structure 1:1. modes obtained by FTIR measurements as well as the determination of the disorder degree according to pea k temperature values of kaolinite dehydroxilation an d transformation obtained by differential thermal analysis. 2. SAMPLES AND EXPERIMENTAL METHODS 2.1. TESTED SAMPLES Kaolinite samples (fraction under 5μm) fro m several different Czech kaolin deposit were used fo r 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. 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 (H2O), dehydroxilation (structural OHgroups) and the transformation to mullite and cristobalite (Főldvári, 1997; Hatakeyama and Liu, 1998; Guggenheim and Koster van Groos, 2001). The obtained temperature effects of dehydroxilation and p olymorphic transformation are strongly dependent on kaolinite sample structural order (Smykatz-Kloss, 1974; Kristóf et al., 2002). In the present paper is incorporated a detailed study of the degree of structural disorder for fou r Czech kaolinite samples (Jimlikov, Sedlec, Olomucany and Unanov deposits) and one kaolinite standard KGa-1b from Georgia deposit obtained fro m 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 p urity and its special properties (Pruett and Webb, 1993; Bereznitski et al., 1998; Sanchez-Soto et al., 2000; Mermut and Cano, 2001; Traoré, 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 CI1 and CI2 calculated from the intensities of selected vibrations DSpace VŠB-TUO http://hdl.handle.net/10084/84630 21/06/2012 CHARACTERIZATION AND DIFFERENTIATION OF KAOLINITES FROM … . 61 Table 1 Locality, mineralogical composition, genesis and classification according to XRD of tested kaolinite samples. XRD Deposit Kaolinite (%) Associated minerals Origin HI AGFI Class. Georgia (KGa-1b), USA 96 D sedimentary 1.120 - w-o Jimlikov u Chodova, CZ 98 Q weathered 1.060 1.180 o Sedlec u K. Varu,CZ 97 Q,I,Sm weathered 0.630 0.780 p-o Olomucany,Blansko, CZ 97 Q,I,Sm weathered 0.590 0.670 p-o Unanov u Znojma, CZ 96 Q,I,F weathered 0.480 0.640 p-o HI - the method of Hinckley (1963) AGFI -the method of Aparicio-Galán_Ferrell (1999) classified as poorly ordered structures (CI1 < 0.7, CI2 > 1.2); partially ordered structures (0.7 < CI1 < 0.8, 0.9 < CI2 < 1.2) and ordered structures (CI1 > 0.8, CI2 < 0.9) (Russell and Fraser, 1994; Madejová 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 measuremen t 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 p ossible to determine the degree of disorder in kaolinite samples. Well ordered sample has thei r decomposition peak temperature of quite high value (Td > 571 °C), ordered sample has their decomposition peak temperature Td at the temperature interval 561570 °C. For poorly ordered sample, the temperature decomposition varies from 546 to 560 °C and disordered sample decomposition temperature values is up to 545 °C. The decomposition peak below 540 °C seems to be quite low according to publishe d 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 o f kaolinites if the analysis were under the proposed conditions : heating rate 10 °C.min-1, sample fraction under 5 μm (the fraction from 0.5 to 5 μm with maximum in their grain size distribution curves laying for the fraction 2 – 3 μm) , sample mass about 50 mg, thermocouple Pt-Pt90/Rh10, inert material Al2O3, no pressing in crucible (loose packed), air atmosphere. With different conditions, the dehydroxilation pea k temperature Td can vary, so the temperature interval o f disorder degree can differ too. The most influencing factor for the Tdtemperature value is the heating rate 2.2. METHOD OF FTIR SPECTROSCOPY The infrared spectra were recorded on Nicole t 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 disperse d in 200 mg of KBr to record optimal spectra in the regions of 4000-3000 and 4000-400 cm-1 with a resolution of 4 cm-1 and 64 scans. Discs for the 4000-3000 cm-1 region were heated in the furnace overnight at 150 °C to minimize the water adsorbe d on KBr and clay sample (Madejová 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 a t 3670, 3650 and 938 cm-1 could be identified bu t their intensities were low; and • poorly ordered if only one band near 3660 o r inflexions near 3670, 3650 and 938 cm-1 were observed in the spectra (Madejová et al., 1997). A numerical approach (IRN ) based on crystallinity indices CI1 and CI2 calculated from the intensities of selected vibrations modes using the equations: CI1 = I(ν1) / I(ν3) (1) CI2 = I(ν4) / I(ν1) (2) where I(ν1) and I(ν4) are intensities of the OH stretching bands at 3695 cm-1 and 3620 cm-1 and I(ν3) is the intensity of the OH bending band at 915 cm-1. The twop oints baseline method was used to obtained the intensity of the OH bands. According to the obtained values of crystallinity indices kaolinites were DSpace VŠB-TUO http://hdl.handle.net/10084/84630 21/06/2012 L. Vaculíková et al. 62 3. RESULTS AND DISCUSSION 3.1. FTIR SPECTROSCOPY The infrared spectra of tested kaolinites are shown in Figures 2 and 3. The complete assignment o f the absorption bands in measured IR spectra is summarized in Table 2. Determination of degree of structural disorde r from IR spectra of kaolinites based on visual estimation of specific features (IR-E) and calculated (Gabbott, 2008). The difference between the dehydroxilation temperature with heating rates 3 °C.min-1 and 30 °C.min-1 for the same kaolinite sample is over 50 °C. Therefore the evaluation of the disorder degree of kaolinites by thermal analysis must be always adjusted to measurement conditions (Smykatz-Kloss, 1974). Table 2 Possition and assignment of the absorption bands in IR spectra of tested kaolinites. Assignment KGa-1b Jimlikov Sedlec Olomucany Unanov OH stretching of inner-surface hydroxyl groups1 3694 3695 3696 3696 3696 OH stretching of inner-surface hydroxyl groups2 3669 3669 3668 3668(s) 3669 OH stretching of inner-surface hydroxyl groups2 3653 3652 3653 3654 3652 OH stretching of inner hydroxyl groups 3618 3620 3620 3620 3620 Si-O stretching (longitudinal mode) 1113(s) 1112 1113 1111 1114 Si-O stretching (perpendicular mode) 1098 - - - - in-plane Si-O stretching 1033 1032 1032 1032 1032 in-plane Si-O stretching 1009 1008 1007 1006 1007 OH deformation of innersurface hydroxyl groups 937 935 937 936 935 OH deformation of inner hydroxyl groups 913 913 913 913 912 Si-O 791 793 793 793 794 Si-O, perpendicular 752 755 755 755 754 Si-O, perpendicular 694 699 699 698 697 Si-O 645 647 641 645 644 Al-O-Si deformation 540 538 537 538 537 Si-O-Si deformation 468 470 469 470 469 Si-O deformation 433 430 430 430 429 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 DSpace VŠB-TUO http://hdl.handle.net/10084/84630 21/06/2012 CHARACTERIZATION AND DIFFERENTIATION OF KAOLINITES FROM … . 63 Fig. 2 The infrared spectra of kaolinites (400 to 1200 cm-1). Fig. 3 The infrared spectra of kaolinites (3560 to 3750 cm-1). KGa-1b, Jimlikov, Sedlec and Unanov. The I R spectrum of kaolinite from Olomucany deposi t showed the replacement of the middle two bands by a single broad band at 3654 cm-1 with a shoulder nea r 3668 cm-1, that indicates partially ordered structure o f this sample (Fig. 3). IR spectrum of Unanov demonstrated general broadening of all bands (Fig. 2). This feature confirms high degree of disordering in crystallinity indices CI1 and CI2 (IRN ) according to N eal and Worral (1977) are given in Table 3. The 3695, 3620 cm-1 doublet is characteristic fo r the kaolin group general. Four clearly resolve d absorption bands at about 3695, 3670, 3650 and 3620 cm-1 reflect high structural ordering of the samples. Distinguishable four bands in OH stretching region were observed in IR spectrum of sample DSpace VŠB-TUO http://hdl.handle.net/10084/84630 21/06/2012 L. Vaculíková et al. 64 Table 3 Classification of the degree of structural order of kaolinite samples using empirical (IR-E) and numerical (IR-N) classification. Attributes IR-E IR-N Deposit 1st 2 nd 3 rd 4 th class CI1 CI2 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   937 (s)  pa-o 0.91 1.20 pa-o Olomucany, Blansko, CZ   937 (s)  p-o 0.74 0.82 pa-o Unanov u Znojma, CZ   937 (s)  p-o 0.72 0.81 pa-o Attributes: 1st - distinguishable four bands 3695, 3670, 3650, 3620 2 nd – general broadening of all bands is not observed 3 rd - OH deformation bands 938 and 916 are visible 4 th – two weak bands found at 795 and 758 are of about equal intensity CI1, CI2 – the method of Neal and Worral (1977) absorption at 3695 cm-1. The problem is that thei r contribution to the absorption at 915 cm-1 is significantly higher than to the absorption a t 3695 cm-1. When calculating the ratio of CI2 b ased on such affected values, the ratio can indicate an erroneously higher value for the crystallinity degree o f 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 °C and releasing of constitution water an d b reaking of crystal lattice at higher temperature interval 552-576 °C. The recrystallization and transformation of dehydrated substance to mullite, cristobalite and quartz was observed as the exothermic effect at about 982-1001 °C. Table 4 shows the thermal data obtained fro m DTA curves including dehydroxilation pea k temperature Tdand transformation peak temperature Tt. The first group of well ordered samples is represented by kaolinite KGa-1b with the highes t decomposition peak temperature value (above 571 °C). The sample classified as ordered (fro m 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 pea k temperature values up to 560 °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 peaks kaolinite. Two clearly resolved OH bending bands occuring at about 938 and 916 cm-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-1. In all IR spectra were found two weak bands at 795 and 758 cm-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 I R spectra (IR-E) into three groups: ordered (well ordered), partially ordered and poorly ordered. Firs t group is represented by kaolinite KGa-1b and Jimlikov whose IR spectra satisfy all the demands o f IR-E classification. IR spectrum of Sedlec kaolinite without clearly resolved OH deformation band at 938 cm-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-1 (CI1); and 3695 cm-1 (CI2), it is posible 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 represente d 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-1 and OH stretching DSpace VŠB-TUO http://hdl.handle.net/10084/84630 21/06/2012 CHARACTERIZATION AND DIFFERENTIATION OF KAOLINITES FROM … . 65 Table 4 Thermal data including dehydroxilation peak temperature Td , transformation peak temperature Ttand classification of disorder degree of kaolinite samples. Deposit Td Tt 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-o Fig. 4 DTA curves of kaolinite samples Georgia (KGa-1b) and Unanov. tested kaolinite samples at the heating rate 10 °C.min-1. With increase of peak temperature on DTG curve, activation energy of dehydroxilation process decreased. The values of activation energy Ea varied from 230 kJ.mol-1 (well ordered kaolinite sample KGa-1b) to 301 kJ.mol-1 (the poorliest ordere d sample Unanov) with the reaction order n varied fro m 0.9 to 1.5. Obtained results show, that better ordered samples display lower activation energy fo r dehydroxilation process estimated by Freeman-Carroll method. The possibilities and comparision o f Freeman-Carroll method with other used methods are described well by (Slovak, 2001). The disadvantage o f this method can lay in the fact, that the calculation is p erformed 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 are of the high intensity and quite narrow. For the poorly ordered sample, the transformation peaks are of low intesity, wider and smaller. The kinetic parameters of decomposition was studied using the Arrhenius equation applied to solid state reactions. The activation energy fo r dehydroxilation was evaluated by Freeman-Carroll method which enables, from the exploitation of one DTG peak, to determine besides activation energy o f reaction also the reaction order and the rate constan t (Freeman and Caroll, 1958). Table 5 summarized thermal data including maximal reaction velocity temperature Tr, activation energy Eawith orde r reaction n and correlation factor R2. It is evident, that values of maximal reaction velocity temperature Tr obtained from DTG curve correspond to the decomposition peak temperature T d obtained from DTA curves. Figure 5 shows the derivative thermogravimetric (DTG) curves for all DSpace VŠB-TUO http://hdl.handle.net/10084/84630 21/06/2012 L. Vaculíková et al. 66 Table 5 Thermal data including peak temperature Tr , activation energy Ea and reaction order n. Deposit Tr °C Ea kJ.mol-1 n R2 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 Fig. 5 DTG curves of kaolinite samples. 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 Georgi a (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 se t a reasonable agreement with published data obtaine d b y XRD diffraction method. In case of using FTI R spectroscopy, there is only a slight difference between IR data and data evaluated by DTA and XRD analysis. The OH stretching and bending vibrations o f 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 ordere d and poorly ordered; while IRN method divides process is possible. Therefore if the heterogenous character of dehydraxilation process is supposed, the dependance of activation energy on structural orde r can differ, mainly if we cosider that the dehydroxilation process is initiated in the defec t places. 4. CONCLUSIONS The obtained results from infrared spectroscop y and differential thermal analysis were compared with XRD results p reviously published by Hinckley (1963) and Aparicio et al. (1999). 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