J Pak Mater Soc 2009 3 (1)
D.
BAUXITE DEPOSITS IN PAKISTAN: AN INTRODUCTION
Muhammad Fahad, Yaseen Iqbal, Rick Ubic
Material Connection Centre, Institute of Electronics & Physics, University of Peshawar, Pakistan
1.
Introduction
This introductory talk was focused upon
Bauxite, its deposits in Pakistan and
economical potential. Preliminary findings
regarding the phase and microstructure of
Bauxite were also described.
A mineral is basically defined as a naturally
occurring, inorganic substance formed
through geological processes. Each
mineral has a characteristic chemical
composition,
highly
ordered
atomic
structure and specific physical properties.
Almost all minerals are crystalline and form
the basic component of the earth‟s crust.
So far more than 2000 minerals are known
[1]
. Mineral may be Rock Forming Minerals
or Ore-Forming. Rock Forming Minerals
are those which are found in abundance in
the rocks of the earth‟s crust whereas the
Ore-Forming minerals are those which are
of economic value and usually do not occur
in abundance in rocks.
Figure 5. Mr. M Fahad giving his talk on Bauxite.
Rocks are aggregates or mixtures of
minerals, generally in the form of
interlocking crystals or grains. They may
comprise of one mineral only (e.g. limestone) or a mixture of minerals (e.g.
granite, sand stone). Rocks may include
organic remains as well. Rocks are further
divided into igneous and sedimentary rocks
[1]
. Igneous rocks are formed by cooling &
solidification of magma which is a hightemperature solution of silica, silicates,
metallic oxides, hot liquids and gases.
Typical Igneous rocks are granite and
basalt. Sedimentary rocks on the other
hand, are formed by consolidation and
cementation of sediments deposited under
water or land surface. Normally, they are
deposited in layers, progressively with
younger upwards and older downwards.
Such stratified layers are called “beds” and
a group of beds is called a “formation”.
Typical sedimentary rocks are sand stone
and limestone [1]. Another type of rock
referred to as “Metamorphic rocks” are
formed when the pre-existing rocks have
been changed in texture and composition
by changing conditions of temperature and
pressure. Substances formed on the earth
surface (such as clay) when subjected to
increased pressure and temperature,
change to more stable forms such as mica
or other silicates. Typical rocks of this type
are schist and gneiss [1]. Mineral are also
classified into various categories such as
a) metallic minerals which include
antimony, bauxite & laterite, chromite,
Muhammad Fahad, Yaseen Iqbal, Rick Ubic: D. Bauxite Deposits in Pakistan:….
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J Pak Mater Soc 2009 3 (1)
copper, gold, silver, platinum, iron ore, lead
and zinc, b) mineral used as fuel e.g. coal,
petroleum and natural gas, c) precious and
decorative stones e.g. garnet, peridot,
quartz, ruby and topaz, and d) silicates
such as china clay, fluorite, fire clay,
feldspar, limestone and silica sand.
Bauxite is a metallic mineral named after
the village “Les Baux” (Southern France)
where it was first discovered by “Pierre
Berthier” in 1821. Bauxite is the most
important aluminum ore consisting largely
of gibbsite [Al(OH)3], boehmite [γ-AlO(OH)]
and diaspore [ά-AlO(OH)] along with iron
oxides such as goethite, hematite and clay
mineral kaolinite [Al2Si2O5(OH)4] and small
amount of anatase [TiO2][5]. Bauxite may
be lateritic (i.e. silica bauxite) or karst (i.e.
carbonate bauxite). Bauxite may be white,
grey, yellow or red with white streak and
dull to earthy luster [2]. On mohs scale of
hardness, its hardness is 1 to 3 with 2 to
2.5 specific gravity. The crystal structure of
Diaspore and Boehmite is orthorhombic
whereas Gibbsite is monoclinic [2].
2.
Processing
Bauxite is strip mineral as it is found at the
surface with little or no over burden.
Approximately 85-95% of the world‟s
bauxite production is processed into
aluminum. In 2007, Australia was the top
producer of bauxite with almost one third of
the world share, following China, Brazil and
Jamaica [3]. The Bayer process is the
principal industrial means of refining
bauxite to produce alumina [8]. Bauxite
contains only 30 to 54% alumina and is
obtained by filtering off the solid impurities.
The mixture of the residual solid impurities
is called “red mud”.
Figure 6. A Camera photograph from the AJK‟s
Bauxite sample, showing its general appearance.
High-Alumina bauxite deposits, categorized
as “commercial bauxite” mainly occur in the
following areas of Pakistan [1]:
a) Katha-Pail Deposits (> 100 m.t) which
contains 35.5-72.5% alumina, 8.6850% silica and 10-20% iron along with
boehmite and kaolinite and trace
amount of diaspore and gibbsite.
b) Chhoi-Akhori Deposits (46.5 m.t) which
contains ~32-76% Al2O3, 2.5-43%
SiO2, 0.25-12% Fe2O3 and 2.2 - 4.2%
TiO2.
Bauxite deposits have also been
reported in Muzaffarabad-Kotli, Bandi
Kapla-Khanpur Hazara, Margalla Hills
(0.86 m.t) and Attock Surge area (0.25
m.t). An ordinary camera photograph of
as-mined stones of Azad Jammu &
Kashmir (AJK) bauxite is shown in
Figure 6.
To assess the „Processability‟ of a mineral,
its chemical and phase composition must
be known because this determines the
quality of the mineral and the required
process for its up-gradation. In addition to
alumina extraction, the residues or
Muhammad Fahad, Yaseen Iqbal, Rick Ubic: D. Bauxite Deposits in Pakistan:….
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J Pak Mater Soc 2009 3 (1)
byproducts can be used for other purposes
[4]
. The characterization of bauxite ore, in
particular, the iron mineralogy, is critical
when determining its processability [5]. Iron
oxides and hydro oxides are common
constituents of bauxite, in which they are
undesirable because their presence
increases the cost of aluminum production
[6]
. The iron oxides are unchanged by the
processing of bauxite with in a low
temperature (<150C) Bayer plant and
hence make up the major phase of the
bauxite residue material that needs to be
separated from the process liquor [5].
Globally, manganiferous karst bauxite is
rare which in general, contains 0.2% of
MnO2 [7].
3.
Other Applications
Red mud is the residue of bauxite
processing for alumina production and its
major constituents are Fe2O3, Al2O3, SiO2,
Na2O, CaO with trace amounts of Zr, Y, Th
and U [8-9]. Red mud is used in the
production of glazes in Ceramic industry
e.g. sanitary ware, tiles and electrical
porcelain glazes [9]. Low-cost mullite based
ceramics are also produced from the
mixture of natural bauxite and industrial
waste fly ash[10]. Dense alumina ceramics
are widely used for structural applications
(such
as
armor,
wear
resistance
applications and in situations with severe
mechanical stresses coupled with corrosive
and thermal action) [11]. Similarly, ordinary
glass-ceramics and nano-crystalline glassceramics can be prepared from red mud in
the aluminum industries [12-13]. Red mud is
a potential ceramic body initial ingredient
and influences the forming procedure,
sintering and final properties [14]. Ceramic
Microsphere are prepared using Chinese
bauxite through centrifugal spray drying
method, with applications in medicine,
chemical,
environmental
protection,
nuclear technology and war industry [15].
Red mud and barium compounds have
been utilized for making X-ray radiationshielding
material
through
ceramic
processing
route
using
phosphate
bounding [16]. In brief, bauxite is a mineral
with diverse applications and is abundant
in Pakistan; therefore, its detailed phase,
chemical and microstructural analysis is
required.
Secondary electron scanning electron
microscope images of AJK bauxite samples
are shown in Figure 7. In Figure 5a, energy
dispersive X-ray electron spectroscopy
(EDS) revealed that the grains with bright
contrast (labelled as A), dark grey contrast
(labelled as S) and light grey contrast
(labelled as I) comprised Al, Si only and Fe
respectively. Similarly in Figure 5b, the
grains or micro-regions labelled as “A”, “M”,
“T” and “S” comprised Al, Mg, Ti and Si
respectively.
Figure 7. SEI of AJK Bauxite sample,
showing, a) grains with bright contrast (A),
Muhammad Fahad, Yaseen Iqbal, Rick Ubic: D. Bauxite Deposits in Pakistan:….
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J Pak Mater Soc 2009 3 (1)
dark grey contrast (S) and light grey
contrast (I). EDS detected Al in microregion “A”, Si only in region “S” and Fe in
region labelled “I”, and b) grains of different
shapes and compositions where the grains
or micro-regions labelled as “A”, “M”, “T”
and “S” comprised Al, Mg, Ti and Si
respectively.
4. Conclusions
Sufficient reserves of high quality Bauxite
are present in Pakistan which requires
systematic characterization and upgradation for economical development of
the region and country. SEM of as-mined
Bauxite samples revealed the presence of
grains and micro-regions of varying
morphology and contrast. EDS analysis
revealed the presence of iron in microregions with grey contrast, silica in dark
grey micro-regions and alumina in microregions with bright contrast.
8.
9.
10.
11.
12.
13.
References
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7.
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