Key Engineering Materials
ISSN: 1662-9795, Vols. 512-515, pp 648-651
doi:10.4028/www.scientific.net/KEM.512-515.648
© 2012 Trans Tech Publications, Switzerland
Online: 2012-06-04
Study on Mineral Composition and Main Mineral Morphology of Bauxite
from ZhongXiang, HuBei Province
Yan Li1, a, Zhaohui Huang2, b and Yan-gai Liu3,c
School of Materials Science and Technology,
China University of Geosciences, Beijing 100083, China
a
[email protected], [email protected]
Keywords: Bauxite; Morphology; Mineral composition; ZhongXiang
Abstract. In this paper, the mineral composition and main mineral morphology of bauxite were
studied from ZhongXiang deposit, HuBei province. Through Electron Microscope Identification,
there are two main rock types, oolitic, bean-like and aphanitic or fine crystalline structure of bauxite.
The main mineral morphology is micro-crystalline or flake, crumby forms. The mineral and chemical
compositions of samples were investigated by XRD, EPMA analysis tests. The EPMA results showed
that Al2O3 content is 47.95% ~ 75.04%, in association with other isomorphous impurities, such as Si,
Fe, Ti and Mg in varying proportions. The mineral compositions of bauxite ore are mainly aluminum,
iron, silicon minerals, which totally account for from 83.01% to 86.40%. The XRD revealed that
diaspore, hematite and kaolinite are the major mineral components in the bauxite ores. The bauxite
from ZhongXiang deposits is a type of high diaspore bauxite, partly with clay minerals. Furthermore,
the function of bauxite as a good fire-resistant material was discussed.
Introduction
Bauxite is an aluminium ore and is the main source of aluminium. This form of rock consists mostly
of the minerals gibbsite Al(OH)3, boehmite γ-AlO(OH), and diaspore α-AlO(OH), in a mixture with
the two iron oxides goethite and hematite, the clay mineral kaolinite, and small amounts of anatase
TiO2. Bauxite deposits can be classified into two main categories according to the bedrock lithology.
Bauxite deposits overlying on carbonates are identified with the karstic category, regardless of
whether the bedrock surface is karstified or not, or the degree of karstification; those overlying
alumosilicate rocks can be subdivided in lateritic bauxites and Tikhvin-type bauxites. Karst bauxites
take 14% of world bauxite resources [1,2]. China has abundant bauxite resources, taking the fifth
place in the world, and the bauxite deposits are mostly the karstic type.
Most lateritic bauxites can be directly related to the underlying source rocks through their textures
and compositions [2,3,4], although this is rarely true for karstic bauxites. Therefore, the precursor
rock of karstic bauxites is difficult to determine.
For karst bauxites, a wide variety of subtypes have been distinguished via different criteria
[2,4,5,6]. Among them, the subdivision of Combes (1990) and Combes et al. (1993) based on the
uplift rate of the craton include four genetic subtypes: autochthonous, allochthonous,
para-autochthonous and para-allochthonous.
In this study an attempt is made to reveal more details of the mineral composition and morphology
of bauxites from ZhongXiang Deposit, HuBei province, obtained by polarized light microscopy
observation and XRD, EPMA analysis tests.
Samples and Analytical Methods
The bauxite samples were collected from the strip mine in LengShui Town , Zhongxiang City. Ore
body has an extension of 2835-2855 meters long, slope angle with the extension of 5-10 meters. The
bauxite ores are irregularly scattered in the orebody layer making them show an even chemical
distribution; therefore, this research randomly collected samples in each ferrallitic soil profile.
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Key Engineering Materials Vols. 512-515
649
The main textures of this bauxite ore are pelitomorphic, clastic shape, oolitic shape, rough shape,
etc. The mineral structure has lump, caities, thin layer shape, primarily big block in shape. Among
those textures, the pelitomorphic texture is dominant in the bauxite ores, and abundant ooids and
minor clastic assemblages are scattered within the pelitomorphic matrix. The area is sedimentary
bauxite deposits, according to the mineral structure, it can be divided into oolitic or bean like, clastic,
coarse, three kinds of natural type, clastic and coarse shape are the main type.
The mineralogy and texture of the ores were studied by microscope (four samples), while the
mineral composition were studied by X-ray diffraction (two samples) and EPMA(five samples )
analysis.
Identification by Electron Microscope
There are two rock types after carefully watching by polarizing microscope, one is oolitic, bean-like
bauxite, and the other is aphanitic or fine crystalline structure of bauxite.
(1) Oolitic, bean-like structure bauxite: rock mainly consists of diaspore, goethite and clay mineral
composition. The diaspore is mainly aphanitic crystal, partly crystallizing into a subhedral granular
aggregates, gathering into oolitic, beans and other clot.
Oolitic, bean-like structure bauxite formed the cylindrical lenticular spherical, spindle-shaped,
concentric structure. Individual diaspora crystal is thick, translucent, with the size of 0.2mm or more.
Mostly aphanitic clay minerals can form interstitial material between the oolitic and beans, or with a
mixed composition of diaspora and other gelatinous clot. Water goethite was brown, which was
uneven disseminated in rocks.
(2) Aphanitic and fine-grain quality bauxite: the rock is consisted of diaspore, clay minerals and
water goethite composition. The diaspore is aphanitic or fine-grained subhedral crystals into a tabular
crystal, colorless and transparent under the single-polarized, bright interference colors under crossed
polarized light (three interference color). Clay minerals are mostly aphanitic or small scale-like
crystals. The water goethite is brown which is spread like goethite gel in the rocks.
The morphology of bauxite is micro-crystalline or flake, crumby forms, and the bauxite is
disseminated by iron or organic materials. After observation in the electron microscope, we can get
the results the main mineral components of bauxite from ZhongXiang are diaspore, which is crumby
with the diameter about 2µm-3µm. And sometimes the aggregates are flower-like or flake-like, single
scaly, film diameter between about 0.8µm-1.5µm.
The Mineral Composition of ZhongXiang Bauxite
Through EPMA analysis testing, the results show that the mineral compositions of bauxite ore are
mainly aluminum, iron, silicon mineral, these three ore mineral contents account for 83.01%,
86.15%, 86.40%, 85.01%, 84.62%, and the rest are a few titanium and trace minerals minerals. The
mining bauxite ore mineral composition is primarily diaspore, taking account for the total amount of
ore by 50% ~ 95%, and generally greater than 85%. Some rare hydrargillite and kaolinite minerals
associated, has an inverse correlation with diaspore. The Al2O3 content is 47.95% ~ 75.04%, in
association with other isomorphous impurities, such as Si, Fe, Ti and Mg in varying proportions.
samples
S1
S2
S3
S4
S5
Table 1 Major elements compositions of bauxite rock samples
Chemical composition (%)
SiO2
Al2O3 Fe2O3
TiO2
MgO
CaO
Na2O
K2O
9.30
70.00
3.71
1.84
0.21
0.05
0.03
1.20
7.30
75.04
3.81
2.03
0.16
0.05
0.02
1.04
20.13 55.52 10.75
2.41
0.24
0.06
0.06
0.31
25.40 47.95 11.66
1.66
0.45
0.15
0.05
0.24
10.13 70.09
4.40
1.97
0.15
0.07
0.02
0.34
else
13.30
10.60
11.07
12.00
13.48
Total
99.64
100.05
100.55
99.20
100.65
650
High-Performance Ceramics VII
Bauxite is an aluminium ore and is the main source of aluminium and consists mostly of the
minerals gibbsite,boehmite, and diaspore, the properties of monohydrate bauxite and gibbsite are as
follows:
Table 2 The properties of monohydrate bauxite and gibbsite
Mineral
diaspore
boehmite
gibbsite
Chemical
α-AlO(OH)
γ-AlO(OH)
Al(OH)3
formula
crystal system
Orthorhombic
Orthorhombic
Monoclinic
shape
Long-plate,columnar,
tiny-rhombohedrons
Similar to hexagonal
needle
flake
plate
hardness
Strong, 6-7
Weak, 3.5-4
Weak, 2.5-3.5
Gravity
3.3-3.5
3.01-3.06
2.3-2.4
cleavage
// {010} complete
// {010} complete
// {001}totally complete
Refractiv Ng
1.745
1.651
1.587
e index
Nm
1.722
1.645
1.566
Nv
1.075
1.638
1.565
Table 3 Chemical analysis ( LOI : loss on ignition)
LOI wt%=14.78-15.10%
sample SiO2 Al2O3 CaO MgO K2O Na2O MnO P2O5 TiO2 Fe2O3 FeO LOI
Y-1
43.36 31.60 2.94 0.47 1.45 1.40 0.009 0.17 1.75 0.22
0.62 14.94
Y-2
43.25 33.76 3.08 0.66 0.80 1.20 0.012 0.062 1.38 0.46
0.31 14.74
The XRD revealed that diaspore, hematite and kaolinite are the major mineral components in the
bauxite ores; gibbsite, goethite, anatase, chamosite and illite are minor minerals, and zircon, quartz
and pyrite are accessories. According to the mineralogical classification of Bárdossy (1982), most
bauxite samples in the studied areas fall within the bauxite field, the rest within low-iron bauxite,
iron-rich bauxite and clayey bauxite fields (Fig.1).
Fig.1. XRD patterns of four typical bauxite ore samples.
Discussion
Bauxite is the most important raw material for aluminum production, accounting for more than 90%
of world bauxite production. The non-metallic application is used for refractory, abrasive materials,
chemical products and raw materials of high alumina cement. The bauxite from ZhongXiang, a type
of high diaspore bauxite, which is abundant in Al2O3 content, can be used for producing refractory
materials, such as mullite and corundum.
Key Engineering Materials Vols. 512-515
651
Conclusion
(1) There are two main rock types, one is oolitic, bean-like bauxite, and the other is aphanitic or
fine crystalline structure of bauxite.
(2) The morphology of bauxite is micro-crystalline or flake, crumby forms, and the bauxite is
disseminated by iron or organic materials.
(3) The mineral compositions of bauxite ore are mainly aluminum, iron, silicon minerals, and
these three ore mineral contents account for from 83.01% to 86.40%, with impurities of titanium and
trace minerals.
(4) The Al2O3 content is 47.95% ~ 75.04%, in association with other isomorphous impurities, such
as Si, Fe, Ti and Mg in varying proportions.
(5) The XRD revealed that diaspore, hematite and kaolinite are the major mineral components in
the bauxite ores; gibbsite, bauxite, chamosite are minor minerals, and zircon, quartz and pyrite are
accessories.
(6) The bauxite from ZhongXiang, which is abundant in Al2O3 content, can be used for producing
refractory materials mullite.
Acknowledgements
The authors greatly appreciate the National Natural Science Foundation of China (51032007), the
Fundamental Research Funds for the Central Universities (2010ZD12), the Key Projects in the
National Science & Technology Pillar Program (2011BAB03B08), the New Star Technology Plan of
Beijing (2007A080).
References
[1] A. Holmes, Laterites and bauxites of Antrim, Nature. Vol. 173 (1954), p. 812.
[2] A. Horbe, M. Costa, Geochemical evolution of a lateritic Sn- Zr - Th - Nb -Y-REE-bearing ore
body derived from apogranite: the case of Pitinga, Amazonas-Brazil, J. Geochem. Explor. Vol.
66 (1999), p. 339.
[3] M. K. D. Mutakyahwa, J. R. Ikingura and A. H. Mruma, Geology and geochemistry of bauxite
depositsin Lushoto District, Usambara Mountains, Tanzania, J. Afr. Earth. Sci. Vol. 36, (2003) p.
357.
[4] J. P. Combes, Recherches sur la genese des bauxites dans le Nord-Est de l'Espagne,le Languedoc
et l'Ariege (france)-Mém, Centre Etudes Rech. Geol. Hydrogeol. Montpellier. (1969), p. 342.
[5] R. A. Berner, Authigenic mineral formation resulting from organic matter decomposition in
modern sediments, Fortschr, Miner Vol. 59 (1981), p. 117
[6] G. H. Brimhall, C. J. Lewis, J. J. Ague, W. E. Dietrich, J. Hampel, T. Teague, and P. Rix,
Metalenrichmentin bauxites by deposition of chemically mature Aeolian dust, Nature Vol. 333
(1988), p. 819.
[7] G. I. Bushinsky, Case of natural bleaching of bauxites, Travaux du ICSOBA. Vol. 5 (1968), p.
17.
[8] A. A. Calagari, A. Abedini, Geochemical investigations on Permo-Triassic bauxite horizon at
Kanisheeteh, east of Bukan, West-Azarbaidjan, Iran, J. Geochem. Explor. Vol. 94 (2007), p. 1.
High-Performance Ceramics VII
10.4028/www.scientific.net/KEM.512-515
Study on Mineral Composition and Main Mineral Morphology of Bauxite from ZhongXiang, HuBei
Province
10.4028/www.scientific.net/KEM.512-515.648
DOI References
[2] A. Horbe, M. Costa, Geochemical evolution of a lateritic Sn- Zr - Th - Nb -Y-REE-bearing ore body
derived from apogranite: the case of Pitinga, Amazonas-Brazil, J. Geochem. Explor. Vol. 66 (1999), p.339.
10.1016/S0375-6742(99)00002-3