Fourier Transform Infrared Spectrophotometry and X-ray powder Diffractometry as Complementary Techniques in characterizing Clay size fraction of Kaolin

This study aimed at demonstrating complementary roles offered by both Fourier transform infrared (FTIR) spectrophotometry and x-ray powder diffraction (XRPD) techniques in characterizing clay size fraction of kaolins. The clay size fraction of kaolin samples obtained from Kgwakgwe, Makoro, Lobatse and Serule kaolin occurrences and deposits in Botswana were characterized using laser diffraction particle size analyzer (LDPSA), FTIR spectrophotometry and XRPD techniques. More than 70 wt % of the clay size fraction of these samples were < 4 μm. Main peaks in the infrared spectra reflected Al-OH, Al-O and Si-O functional groups in the high frequency stretching and low frequency bending modes and were those for kaolinite but possible absorption interference peaks for quartz, smectite and muscovite are inferred. The XRPD results identified kaolinite as the major mineral phase with confirmed presence of quartz, smectite and muscovite as minor quantities in the samples. The findings therefore suggest that XRPD technique could be used as a complementary tool when characterizing the clay fraction of kaolin using FTIR spectrophotometry. @JASEM Kaolin is both a rock and clay mineral term consisting of pure kaolinite or related minerals such as halloysite, nacrite and dickite as well as associated mineral assemblages which include quartz, smectites, feldspars and micas. Its deposits could be primary (hydrothermal, residual or mixed hydrothermal and residual deposits) or secondary (erosion and transportation of clay particles and their deposition in lacustrine, paludal, deltaic and lagoonal environments) depending on their genesis. Kaolin genesis has a direct bearing on its industrial applications. Kaolin is utilized in the paper, paint, rubber, ceramic and plastic industries. Other applications include pharmaceutics, cosmetics, wine and vegetable clarifiers, insecticides, pesticides, fungicides, crayons and pencils, oil absorbers, fertilizers, polish, cat litter, cosmetics, and iron smelting (Ekosse, 2000, 2001; Murray, 1986). Brick making, pottery chinaware and porcelain, and the construction industry are major consumers of kaolin. Kaolin is widely utilized for different industrial applications, and as such any of its occurrences is worth proper chemical, mineralogical and technological investigations. Tests for its characterization include FTIR spectrophotometry technique. This technique has been well used for the identification of functional groups in kaolin. The strength of FTIR spectrophotometry applied to clay mineralogy lies in its ability to characterize the functional group and fingerprint regions of very small quantities of samples (Tan, 1998). Unfortunately, due to its sensitivity, FTIR spectrophotometry has draw backs such as absorption peak interferences whereby two or more minerals share same absorption peaks in the high frequency stretching and/or low frequency bending modes (Ojima, 2003); thereby possibly affecting the interpretation of results. In eliminating ambiguity caused by interferences of peaks, complementary analytical techniques should be applied. In this regard, XRPD technique could be used in the identification and characterization of mineral phase components present in kaolins. Its limitation in identifying phases below instrument detection limit is equally recognized. This study demonstrates the complementary role of both FTIR spectrophotometry and XRPD techniques in characterizing the clay size fraction of kaolins. MATERIALS AND METHODS Samples were obtained from four kaolin occurrences and deposits in southeastern Botswana: Kgwakgwe, Lobatse, Makoro and Serule. The Kgwakgwe kaolin occurs at latitude 25 00′ 05′′ S and longitude 25 19′ 30′′ E. Lobatse kaolinitic mudstones are located at latitude 25 41’ 02” S and longitude 25 12’ 04” E. Makoro kaolinitic mudstones are found at latitude 22 39′ 50′′ S and longitude 27 05′ 05′′ E. Serule kaolin occurs at latitude 21 59’ 06” S and longitude 2720’16” E. Clay size fraction in this study was defined as particles being < 4 μm in particle size. The clay size fraction of the samples for minerals identification and characterization was obtained based on the principle of sedimentation according to Stoke’s law (Gaspe et. al., 1994). The particle size distribution (PSD) analyses of the clay size fraction of kaolin samples were carried out using a Beckman Coulter LS 200 laser diffraction particle size analyzer (LDPSA) with a Fraunhofer Rf 780z optical mode. Analyses were JASEM ISSN 1119-8362 All rights reserved J. Appl. Sci. Environ. Mgt. 2005 Vol. 9 (2) 43 48 Full-text Available Online at www.bioline.org.br/ja Fourier Transform Infrared Spectrophotometry and X-ray powder Diffractometry... Georges-Ivo E. Ekosse 44 performed in the dry powder module from a free flowing position, following the procedures described in the manual. Calculations for particle sizes were from 0.375 μm to 101.1 μm. The procedure used for FTIR spectrophotometry analysis is that mentioned by Ojima (2003) and Madejova et. al. (1997). The infrared spectra were acquired using a Perkin Elmer system 2000 FTIR spectrophotometer at a resolution of 4 cm. The dried powdered samples were homogenized in spectrophotometric grade KBr in an agate mortar and pressed at 3 mm pellets with a hand press. In order not to distort the crystallinity of kaolinite in the samples, the mixing was set to 3 min allowing for minimal grinding as suggested by Tan (1998). Peaks were reported based on % transmittance to given wavelengths. For XRPD analysis, the dried samples were gently crushed in an agate mortar to a fine texture in order not to affect kaolinite crystallinity (Ekosse, 2004). The powder samples were mounted on the sample holder with very little pressure, and later scanned in the Philips PW 3710 XRPD system which was operated at 40kV and 45 mA, with a Cu-Kα radiation and a graphite monochromator. A PW 1877 Automated Powder Diffraction, X'PERT Data Collector software package was employed to capture raw data, and a Philips X'PERT Graphics & Identify software package was used for qualitative identification of the minerals from both the data and patterns obtained by scanning at a speed of 12θ / min. Samples were scanned from 22θ to 40 2θ and their diffractograms recorded. The interpreted results were compared with data and patterns available in the Mineral Powder Diffraction File, data book and the search manual issued by the ICDD (1986, 2002) for confirmation. RESULTS AND DISCUSSION The PSD curves for Lobatse, Makoro, Kgwakgwe and Serule kaolins are presented in Figures 1A, 1B, 1C and 1D respectively, and the wt % of the clay size and silt fractions (silt defined as > 4 μm <20 μm) are given in Figure 2. The smallest particle size for Lobatse kaolin was 0.72 μm and biggest one was 15.26 μm with a median of 2.15 μm and a mean of 5.53 μm. The Makoro kaolin, being finer than Lobatse, had 0.52 μm for the smallest particle size and 5.799 μm for the biggest one, with a median of 1.07 μm and a mean of 2.53 μm. The Kgwakgwe kaolin was finer than both Makoro and Lobatse kaolins. Its smallest particle size was 0.48 μm and the biggest one was 4.50 μm with a median of 0.88 μm and a mean of 1.92 μm. The Serule kaolin was the finest of all. Its smallest particle size was 0.48 μm and the biggest one was 4.00 μm with a median of 0.81 μm and a mean of 1.62 μm. The clay size fraction for the kaolin samples were as follows: Lobatse = 70 wt %, Makoro = 82, Kgwakgwe = 86 and Serule = 90 (Figure 2). Fig 1A: PSD curve of the clay fraction of Kgwakgwe kaolin sample Fig 1B: PSD curve of the clay fraction of Lobatse kaolin sample Fig 1C: PSD curve of the clay fraction of Makoro kaolin sample Fourier Transform Infrared Spectrophotometry and X-ray powder Diffractometry... Georges-Ivo E. Ekosse 45 Fig 1D: PSD curve of the clay fraction of Serule kaolin sample