J. Mod. Phys., 2010, 1, 206-210
doi:10.4236/jmp.2010.14031 Published Online October 2010 (http://www.SciRP.org/journal/jmp)
Fourier Transform Infrared Spectroscopic
Characterization of Kaolinite from Assam and
Meghalaya, Northeastern India
Bhaskar J. Saikia1, Gopalakrishnarao Parthasarathy2
1Department of Physics, Dibrugarh University, Dibrugarh, I ndia & G B Pant Institute of Himalayan
Environment & Development, Almora, India
2National Geophysical Research Institute, (Council of Scientific and Industrial Research)
Hyderabad, India
Received June 10, 2010; revised July 27, 2010; accepted August 9, 2010
Abstract
This study demonstrates the Fourier transform infrared (FTIR) spectroscopic characterization of natural kao-
linite from north-eastern India. The compositional and structural studies were carried out at room tempera-
ture by using X-ray fluorescence (XRF), electron microprobe (EPMA) analyses and Fourier transform infra-
red (FTIR) spectroscopic techniques. The 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. Few peaks of infrared
spectra inferred to the interference peaks for quartz as associated minerals. The present study demonstrates
usefulness of the spectroscopic techniques in determining quality and crystalline nature of kaolinite from the
Assam and Meghalaya, northeastern India.
Keywords: Kaolinite, Spectroscopic Characterization, FTIR
1. Introduction
Kaolinite is an economically important clay mineral that
is common in the weathering, diagentic, hydrothermal,
and very low grade metamorphic environments. Kaolin-
ite is one of the most abundant aluminosilicate minerals,
occurring primarily as a clay sized particles with high
surface-area to volume ratios. Hence kaolinite weather-
ing may play an important role in controlling the chemi-
cal characteristics such as degree of crystallinity, con-
centration of impurities, particles size distribution. De-
spite its economic and geological importance, the spec-
troscopic characterization is not well documented. Clay
is widely utilized for different industrial applications,
and as such any of its occurrences is worth proper
chemical, mineralogical and technological investigations.
Its current market price (about US $0.04–0.12/kg) is
considered to be 20 times cheaper than that of activated
carbon [1]. In recent years, there has been an increasing
interest in utilizing kaolin for its capacity to adsorb not
only inorganic but also organic molecules. It showed that
kaolinite and some other naturally occurring clay mineral
(such as bentonite, smecttite ,diatomite and fullers earth)
could use as a substitute for activated carbon as an ad-
sorbent due to its availability and low cost, and its good
sorption properties [2]. Clays are layered aluminosilicate
minerals forming important components of soils and
sedimentary rocks. Their layers consist of TO4 tetrahedra
(T = Si4+, Al3+, etc.) and MO6 octahedra (M = Al3+, Fe3+,
etc.). Layers in 1:1 family of clay minerals hold together
by hydrogen bonds formed between hydroxyl groups
attached to coordinately unsaturated oxygen sites of the
MO6 side of each layer and oxygen atoms terminating
the opposite SiO4 side of the next layer [3]. A natural
clay consists of one or different type of clay minerals
together with some impurities. The most common impu-
rities in natural clay are quartz, calcite, feldspar, mica
and organic matter while hydrated iron oxide, ferrous
carbonate and pyrite are being the minor impurities. The
factors that affect most of the physical properties of clay
are particle size, shape, cation exchange capacity and the
type of impurities present. Clay particle sizes are in the
micrometer to nanometer range length scale. The basic
structural units in clays consist of the silica sheet formed

B. J. SAIKIA ET AL.
207
of silica tetrahedra and the octahedral units formed of
octahedrally coordinated cations with oxygens or hy-
droxyls octahedra [3].
A number of works has been carried out on the quan-
titative clay mineral analysis using infrared spectroscopy.
Vibrational spectroscopic investigations yield useful in-
formation about hydration characteristics, interlayer
cations and moisture content in clays. The structural dif-
ferences of kaolin can be detected by spectroscopic
method. The FTIR spectroscopy applied to clay miner-
alogy lies in its ability to characterize the functional
group and fingerprint region of very small quantities of
samples [4]. The studied samples are collected from six
clay occurrence locations of Assam and Meghalaya, viz.
Sheelveta, Silanijan and Deopani area of Assam and
Khasi Hills, Jaintia Hills and East Garo Hills of Megha-
laya. This study demonstrates the complementary role of
both FTIR and XRF spectroscopy in characterizing the
kaolin of Assam and Meghalaya.
2. Experimental
The composition of the clays was determined by using
Philips X-ray fluorescence (XRF) machine. The samples
were powdered in dry conditions using agate mortar and
pestle. The chemical composition of the calumetite was
also determined by electron probe micro-analyzer
(EPMA). Energy Dispersive X-ray (EDAX) measure-
ments were carried out by using scanning electron mi-
croscope (JEOL JSM-840 A) in EDAX mode with a
filament current of 100 μA and an accelerating voltage of
20 kV. Five independent measurements were carried out
and the average composition of the calumetite sample is
presented here. The chemical constituents and LOI at
800˚C were determined by the Indian standard method [5]
and differential thermal analyses. Differential thermal
analysis (DTA) and thermo gravimetric studies were
performed on powder samples using a Mettler Toledo
star System apparatus. The temperature was measured
with platinum sensors. Temperature precision and accu-
racy are ± 0.1˚C. Thermo gravimetric method is used to
quantify the percentage of hydroxyl/water content in the
sample. The calibration and reproducibility of this appa-
ratus is discussed elsewhere [6]. In X-ray fluorescence
method, typical uncertainty involved in oxide analyses
was about 0.01 wt %. The clay samples were crushed
into fine powder for analysis. The powdered sample was
homogenized in spectroscopic grade KBr (1:20) in an
agate mortar and pressed into 3 mm pellets with a hand
press. We tried to minimize the grinding time to avoid
the deformation of the crystal structure, the ion exchange
and the water absorption from atmosphere as suggested
by [4]. The infrared spectra was acquired using Perkin-
Elmer system 2000 FTIR spectrophotometer, with He-Ne
as the reference, at a resolution of 4 cm–1. The spectra
were taken in the region 400-4000 cm–1. The room tem-
perature was 28˚C during the experiment.
3. Results and Discussion
The compositional analysis of the clay samples are per-
formed by XRF analysis (Table 1). It is obvious from
Table 1, that improvement on the chemical composition
of kaolin as result of beneficiation was marginal. The
XRF result shows the major constituents of the samples
are silica, alumina, which confirms the chemical analysis
of clay. The infrared and compositional analyses indicate
that the clay samples belong to kaolin.
The loss on ignition (LOI) was determined at 800˚C.
The kaolin sample dehroxylate at about 600˚C, with an
intense endothermic peak on the DTA trace. The resul-
tant anhydrous phase transforms into mullite and gamma
alumina at about 980˚C, with an exothermic peak in the
DTA trace. The relatively large difference in the LOI
values between the sample-1 (10.32 wt %) and sample-3
(4.10 wt %) indicates that greater loss on ignition took
place during the calcination step. This is largely due to
the giving off of structural hydroxyl water and volatile
organic components.
Figure 1 is the IR spectrum of six kaolin samples. The
Table 1. Compositions of the studied kaolin samples (in Weight (%)).
Sample SiO2 Al2O3 Fe2O3 TiO2 CaO MgO K2O Na2O LOI
Sample 1 44.71 36.34 2.03 1.01 0.37 -- 0.07 0.01 10.32
Sample 2 46.81 32.59 4.18 -- 3.04 0.71 -- -- 9.47
Sample 3 43.79 37.37 1.94 0.38 0.77 0.89 1.11 0.02 4.10
Sample 4 44.66 34.04 0.95 1.23 1.56 -- -- -- 6.51
Sample 5 42.96 33.71 1.17 1.45 1.25 0.36 -- -- 4.54
Sample 6 45.58 36.33 1.97 0.18 0.49 -- 0.02 -- 7.11

B. J. SAIKIA ET AL.
208
(a) (b)
(c) (d)
(e) (f)
Figure 1. The infrared spectra of the studied kaolin samples. A: Sample 1, B: Sample 2, C: Sample 3, D: Sample 4, E: Sample
5, F: Sample 6.

B. J. SAIKIA ET AL.
209
FT-IR technique investigates OH vibrations, whose ab-
sorption bands appear at different frequencies depending
on the cations directly linked to the hydroxyls. This per-
mits the determination of cation distribution around hy-
droxyls and thus allows assessing short-range cation or-
dering. The band position is compared with the Gadsden
(1975) [7] and possible assignments of the samples are
presented in the Table 2. The structure of kaolin miner-
als consist of a sheet of corner-sharing tetrahedra, shar-
ing a plane of oxygens and hydroxyls (inner hydroxyls)
with a sheet of edge-sharing octahedral with every third
site vacant (dioctahedral). The general features of the OH
stretching absorption bands are well established for kao-
lin [8]. A typical spectrum of kaolin show four bands, at
3697, 3669, 3645 and 3620 cm–1, and these characteristic
bands are observed in the studied kaolin samples as men-
tioned in the Ta ble 2. The band observed at around 3620
cm-1 has been ascribed to the inner hydroxyls, and the
bands observed at around the other three characteristic
bands are generally ascribed to vibrations of the external
hydroxyls. The studied kaolin sample exhibits the bands
near the three characteristic bands at 3669, 3645 and
3620 cm–1. The absorption bands observed at 3420-3445
cm–1 and 1620-2642 cm–1 could be assigned to the OH
Table 2. Infrared band positions of the studied kaolin samples.
Wavenumber (cm-1)
Theoritical Kaoline Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Sample 6 Assignments
3670-56 -- -- -- 3640 3661 -- Al---O-H stretching
3645 3630 3630 3634 3624 -- 3597 OH Stretching,
Crystalline hydroxyl
-- 3420 3440 3435 3445 3429 3432 H-O-H stretching,
Absorbed water
-- 2925 2958 2920 2920 2926 2931 C-H stretching
-- 2850 2854 2855 2855 2864 2867 C-H stretching
-- -- 1875 -- -- 1835 -- --
-- 1620 1642 1637 1634 1635 1634 H-O-H bending of water
-- -- 1520 -- -- -- -- aromatic nitrate
-- 1470 1475 -- -- -- -- C-H stretching
-- -- -- 1347 -- 1356 1360 Al-O as Si cage (TO4)
1117-05 -- 1175 -- 1179 1175 -- --
-- -- -- 1079 -- -- -- Si-O quartz
1035-30 1038 -- 1038 1038 1031 1033 Si-O stretching,
Clay minerals
1019-05 -- 1005 1008 -- -- -- Si-O stretching
918-09 912 910 -- 915 891 893 OH deformation,
linked to 2Al3-
800-784 840 840 847 -- -- -- OH deformation,
linked to Al3-,Mg2-
-- 788 779 797 778 777 799 Si-O quartz
700-686 693 690 -- 694 691 696 Si-O quartz
-- -- 635 673 -- 635 642 Si-O-Si bending
542-35 544 535 535 527 539 543 Fe-O, Fe2O3
Si-O-Al stretching
475-68 470 468 470 467 469 467 Si-O-Si bending

B. J. SAIKIA ET AL.
210
vibrational mode of the hydroxyl molecule, which is ob-
served in almost all the natural hydrous silicates. The
bands between 3450 and 3670 cm–1 are attributed to the
OH stretching mode. In ferric saponite hydroxyl peaks at
3610 and 3400 cm–1 are characteristic [6,9].
The H-O-H bending of water is observed at 1620-1642
cm-1. In the 1000cm-1(10 μm) and 500 cm-1(20 μm) re-
gion, main functional groups were Si-O and Al-OH.
Muscovite and possibly quartz interference could be ob-
served at 1031-1038 cm-1 for the studied kaolin. The
Al-OH absorption peak was identified at 891-915 cm-1
for the studied sample. The band at 914-936 cm-1 cor-
responding to Al-OH bending vibrations of kaolinite, the
doublet at 780-798 cm-1 is due to Si-O-Si inter tetrahe-
dral bridging bonds in SiO2 and OH deformation band of
gibbsite at 1000 cm-1 are finger-prints of the typical vi-
brational modes which are recognized easily. In the car-
bonate and C-H bending vibration region, the kaolin
samples exhibit some weak peaks (Table 2).The band
found at 1347-1360 cm-1 arises due to 2vs, overtone of
Al-O as Si cage (TO4). The carbonate structure contains
isolated CO32– group with a doubly degenerate symmet-
ric stretch (ν3) at the region 1508-1560 cm–1 [10]. This
band is observed in the studied kaolin at 1520cm-1. An-
other band found at 1470-1475 cm-1 is arising due to
Na+….CO32- vibration [11]. The OH deformation of wa-
ter is found in between 1620-2642 cm-1. The kaolin sam-
ples exhibits the C-H stretching bands in between
2850–2958 cm-1 indicating polyatomic Cn-H-O entitles
with C bonded to two or three H. The strongest CH band
in between 2920-2931 cm-1 assigned to symmetrical
stretch of C-H mode of –CH2-group. The bend between
2850-2867 cm–1 is assigned to anti symmetrical stretch of
–CH2-group. Another peak is found at 2954cm-1 in one
kaolin sample due to symmetric stretch of –CH3 group.
4. Conclusions
The compositional analysis (XRF) exhibits that kaolin of
the study area are constituted of alumina and silica in
major quantities. The minor and trace oxide composi-
tions are iron, calcium, magnesium and other elements.
The presence of quartz and organic matter as minor
phases were confirmed by FTIR analysis. The infrared
spectra of the kaolin samples exhibits, the Si-O stretch-
ing vibrations at around 778 cm–1, 695 cm–1 and 468
cm–1 which is indicative of the presence of quartz in the
kaolin samples.
5. Acknowledgements
We thank Directors, National Geophysical Research In-
stitute (NGRI), Hyderabad, North East Institute of Sci-
ence and Technology (NEIST), Jorhat and G. B. Pant
Institute of Himalayan Environment and Development
(GBPIHED), Almora, for their cooperation during this
work. We also thank Dr. P. K. Baruah, Gauhati Univer-
sity, Guwahati, for his assistance in the FTIR analysis.
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