Open Journal of Physical Chemistry, 2011, 1, 23-27
doi:10.4236/ojpc.2011.12004 Published Online August 2011 (http://www.SciRP.org/journal/ojpc)
23
Production of γ-Al2O3 from Kaolin
Seyed Ali Hosseini*, Aligholi Niaei, Dariush Salari
Department of Applied Chemistry, Faculty of Chemistry, University of Tabriz, Tabriz, Iran
Received April 21, 2011; revised June 8, 2011; accepted July 12, 2011
Abstract
The paper reports a process for synthesis of γ-alumina from kaolin. Kaolin was transformed to meta-kaolin
by calcination at 800˚C for 2h. γ-alumina powder was synthesized through extracting alumina from meta-
kaolin via H2SO4 and meta-kaolin reactions and consequently precipitation in ethanol, which led to form the
aluminum sulfate. The precipitated aluminum sulfate was dried and calcined at 900˚C for 2h, which resulted
the formation of γ-alumina. The structure of γ-alumina was confirmed by XRD and FTIR and the mean par-
ticles size of γ-alumina was determined by SEM to be 0.5 - 0.9 µm. The study revealed the kaolin could be
promising material for preparation of γ-alumina.
Keywords: Kaolin, γ-Alumina, Aluminum Sulfate, Calcination
1. Introduction
Alumina has enormous technological and industrial ap-
plication. It exists in a variety of meta-stable structures
including γ-, η-, δ-, θ-, κ- and χ-aluminas, as well as its
stable α-alumina phase [1]. Bauxites have been widely
used in industry to produce alumina via the Bayer proc-
ess. On the other hand, nonbauxitic materials, which are
more abundant in many countries than bauxite resources,
also have been processed in attempts to develop alterna-
tive technologies for producing alumina [2-4].
Some examples of nonbauxitic raw materials are
alunite, sillimanite, andalusite, kyanite, kaolin, mica, and
fly ash. Significant advances in alumina purity have been
achieved using materials such as sulfates, nitrates, and
chlorides as alumina precursors, to obtain high purity
alumina [5-8].
Among various structures for alumina, γ-alumina is
one kind of extremely important nano sized materials. It
is used as a catalyst and catalyst substrate in automotive
and petroleum industries, structural composites for
spacecraft, and abrasive and thermal wear coatings [9].
Recent studies have shown that γ-alumina is thermo dy-
namically stable relative to α-alumina when a critical
surface area is achieved [10], and that nano γ-alumina
powder can promote the sintering behaviour of alumina
and silicon carbide fibbers [11], and also that the use of
single phase of γ-alumina powders makes the densifica-
tion temperature shift to lower temperature as compared
with the sample consisting of γ- and χ-alumina [12].
Those outcomes can open up endless possibilities for the
applications of γ-alumina, so it is of significance to in-
vestigate the preparation of γ-alumina. Until now, a large
variety of methods such as sol-gel synthesis from calci-
nation of boehmite [9], poly hydroxo aluminum-poly
vinyl alcohol [10], laser ablation of an aluminum target
in an oxygen atmosphere [13], hydrolysis of alumina
alkoxide [14], thermal decomposition of aluminum sul-
fate [15], metal organic chemical vapor deposition with
Al(CH3)3 [16] have been used to prepare γ-alumina.
Kaolinite is a clay mineral, part of the group of industrial
minerals, with the chemical composition Al2Si2O5(OH)4. It
is a layered silicate mineral, with one tetrahedral sheet
linked through oxygen atoms to one octahedral sheet of
alumina octahedral [17]. Kaolin contains 20 - 26 percent
by weight of alumina. Therefore, it can be suitable mate-
rial for production of γ-alumina because of its abundance
and having considerable content of alumina in kaolin
structure. In this study we report a production of γ-alu-
mina from kaolin using a simple and commercial method.
All materials used in this methods, are relatively cheap
and are found in industrially scale.
2. Experimental
2.1. Instrumentation
X-ray diffraction (XRD) studies were carried out on a
Siemens D500 diffractometer, working with the Kα line of
copper (k = 0.154 nm). Measurements of the samples were

24 S. A. HOSSEINI ET AL.
carried out in the range 2θ of 0˚ - 70˚, at a scanning rate of
1˚/min. Infrared (IR) spectra were recorded with a Bruker
27 FT-IR spectrometer using the Universal ATR Acces-
sory in the range from 3650 to 400 cm–1 with 4 cm–1
resolution. SEM characterization of gamma alumina was
carried out with scanning electron microscopy (model
EQ-C1-1). The composition of materials was analyzed by
X-ray fluorescence spectroscopy (spectro MIDEX).
2.2. Synthesis
The Kaolin, used as a starting material was supplied
from Zonoz mines (Marand, Iran). The chemical compo-
sition of Zonoz kaolin is given in Table 1. After extract-
ing from mine and grinding the kaolin, it was ground in
an agate mortar to particles below 0.5 mm in size. The
powdered kaolin was calcined at 800˚C for 2 h in an
electric furnace to loosen the alumina components. Then,
the kaolin powder was dispersed in a 2.0 N H2SO4 solu-
tion to attain a solid/liquid ratio of 1:20 by weight. The
mixture of kaolin powder and acid (250 mL) was con-
tained in a 500 mL round flask. The reaction flask fitted
with a reflux condenser and the mixture was mixed with
magnetic stirrer for 18h. The temperature of mixture was
set at 70˚C.
After the mixture of kaolin and acid had been leached,
it was cooled to room temperature and filtered to remove
leach residue, which mainly consisted of silica. The fil-
tered leach liquor then was added dropwise at a rate of
6.0 mL/min into 600 mL of ethanol while the ethanol
was stirred with a magnetic stirrer. Ethanol was used as a
precipitating agent because aluminum sulfate can be se-
lectively precipitated by ethanol from the ionic solution
[1]. The precipitates were washed again with the ethanol
and with distilled water and then dried at 70˚C for 10 h.
Finally, the precipitates were calcined at 900˚C for 2 h in
an electric furnace.
3. Results and Discussion
Figure 1 shows the XRD pattern of kaolin and calcined
Table 1. Chemical composition of marand kaolin.
Material Weight percentage
SiO2 61.5
Al2O3 24.5
Fe2O3 0.55
CaO 1.55
Na2O 0.8
MgO 0.6
L.O.I 10
kaolin (800˚C). It is observed that the kaolin shows all
the characteristic peaks of kaolinite. On calcination,
these peaks disappear giving a featureless band of X-ray
amorphous meta-kaolin. Kaolin-type clays undergo a
series of phase transformations upon thermal treatment in
air at atmospheric pressure. Endothermic dehydroxyla-
tion (or alternatively, dehydration) begins at 550˚C -
600˚C to produce disordered meta-kaolin, Al2Si2O7, but
continuous hydroxyl loss (-OH) is observed up to 900˚C
and has been attributed to gradual oxolation of the meta-
kaolin [18]. In this study, calcination of kaolin at 800˚C
led to form the meta-kaolin, which is transient and more
active and reacts easier than kaolin. Equation (1) shows
the changes during calcination and formation of meta-
kaolin. During the calcination the structure of kaolin was
degraded and two molecule waters were released.


2522 272
4
Si OOHAlAlSi O2H O (1)
During the leaching of meta-kaolin in sulphuric acid,
the alumina in meta kaolin is extracted and dissolves in
H2SO4 which leads to formation of aluminum sulfate
(Equation (2)).


232 4
3+ 2
42
AlOin metakaolin3HSO
2Al3SO3HO



(2)
Addition of aluminum sulfate in ethanol led to pre-
cipitate the aluminum sulfate, as shown in Equation (3).

3+ 2
42 242
3
Al3SO3H OAlSO3H O

  (3)


900 C
24 22
3
AlSO3H OAl O 

 

3
(4)
Evaporation of ethanol and consequently calcination
in 900˚C led to transform the aluminum sulfate to γ-
alumina (Equation 4). XRF analysis confirmed the high
purity of γ-alumina (98% by weight) and the other metal
oxides and also SiO2 were trace. It has been reported in
literature that decomposition of aluminium sulfate occur
at temperature range 680˚C - 1030˚C [1,19].
The results of XRD analysis of resulted sample con-
firmed the formation of γ-alumina through comparing
with JCPDS 29-63. The result of the analysis is shown in
Figure 2. The characteristic peaks of γ-alumina are
Figure 1. XRD pattern of kaolin and meta-kaolin.

S. A. HOSSEINI ET AL.
25
As we know, gamma alumina is used as catalyst and
catalyst support because of its higher specific surface
area and thermal stability. γ-alumina is stable until tem-
perature of 1030˚C. It has been reported that the thermal
stability of γ-Al2O3 was greatly improved in the presence
of some additives such as alkaline-earth ions, rare-earth
ions, silicon and phosphor or a combination of both [21].
Si was more effective than other elements in stabilizing
alumina and significantly retarded the transformation of
γ-A12O3 into α-A12O3. The presence of TiO2 could also
improve the thermal stability of alumina [22,23].
Figure 2. XRD pattern of synthesized gamma-alumina. 4. Conclusions
shown in the figure. In addition, the formation of γ-alu-
mina was approved by FTIR spectrum (Figure 3). Ref-
erence [20] showed that γ-alumina is known to have a
spinel structure which exists over a range of hydrogen
content captured by the empirical formula H3mAl2–mO3.
According to this result, the IR spectra of Figure 3 ob-
tained in our experiment could be readily explained.
γ-alumina powders were successfully synthesized by
alumina extraction processes through reaction of meta-
kaolin with H2SO4 solution. Direct precipitation in etha-
nol was a crucial step for synthesis of γ-alumina. It is
concluded that kaolin can be used as promising material
to preparation of γ-alumina. In agreement with other
works, it is resulted that the main factor in obtaining of
different alumina phases is the calcination temperature.
Calcination at 680˚C - 1030˚C leads to form the γ-alu-
mina [1].
The stronger broadening band 3800 - 3000 cm–1 oc-
curs due to the hydrogen bond between the various hy-
droxyl groups in the product. The stronger broadening
band 1000 - 400 cm–1 correspond to Al-O vibration ex-
isted under the temperature of 750˚C, one of which was
between 1000 - 500 cm–1, the other between 500 - 400
cm–1.
5. Acknowledgements
The authors wish to thank Tabriz pharmaceutical Tech-
nology Incubator for encouraging support and Mr. Reza
Masomi from Tabriz University of Medicine Science for
his assistance in obtaining of kaolin.
The particle sizes of synthesized gamma alumina were
determined by Scanning electron microscopy. The SEM
images are shown in Figure 4. The resulted particles are
in the range of 0.5 - 0.9 micrometer.
Figure 3. FTIR spectrum of synthesized gamma-alumina.

S. A. HOSSEINI ET AL.
26
Figure 4. SEM image of synthesized gamma-alumina.
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