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Title: Industrial Minerals


1
Industrial Minerals Commodity Study
PresentationBauxite Aluminum Ore John
Morkeh Mineral Engineering Department New Mexico
Institute of Mining and Technology
2
  • Presentation Outline
  • Introduction
  • Uses
  • Production
  • Geologic Description and Distribution
  • Processing

3
  • Introduction
  • What is bauxite?
  • Aluminum ore, most commonly formed in deeply
    weathered rocks.
  • A common residual or transported constituent of
    clay deposits in tropical and subtropical
    regions.
  • Composed of a mixture of various aluminium oxides
    and hydroxides (principally gibbsite (Al(OH)3),
    boehmite (AlO(OH)), and diaspore (AlO(OH))).

4
  • Introduction
  • Why is bauxite so important?
  • Bauxite is a product of near-surface alteration
    of aluminous rocks, creating a zone depleted of
    Fe and Si and enriched in Al bearing minerals.
  • Typical analysis of bauxite
  • 50 Al2O3
  • 5 SiO2
  • 15 Fe2O3
  • 3 TiO2 (Anatase)
  • Typical but not always .
  • It is THE raw material for ALL primary aluminium
    of the major producers.

5
There is no aluminium without bauxite
6
Introduction First discovered by les Baux,
France 1821 The first commercial extraction of
alumina (Al2O3) from bauxite has been attributed
to Henri Sainte-Claire Deville in about
1854 Bauxites soft/friable, variable textures,
colors, sizes
7
  • Introduction
  • Not all bauxites are equal
  • Can be divided generally into
  • three types
  • Gibbsitic Al(OH)3 Low Temp
  • Boehmitic, gt4 AlO(OH) Hi Temp
  • Diasporic, gt5 AlO(OH) Very Hi Temp

8
Introduction What makes a good deposit?
Proximity to processing plant or infrastructure
to export. Low extraction costs
Quality High extractible Al2O3 Low
reactive SiO2
9
  • Uses
  • Traditional uses of bauxite
  • Blast Furnaces
  • Iron/Steel Ladles
  • Electric Arc furnaces
  • Tundishes
  • Soaking Pits
  • Open Hearth
  • Cement

Blast furnace in Sestao, Spain. The actual
furnace itself is inside the centre girderwork.
10
Production Bauxite Mining
Ghana Bauxite Company Ltd- Awaso
11
  • Production
  • Bauxite Mining Method
  • Eighty percent of world bauxite production is
    from surface mines
  • Southern Europe and Hungary, produce from
    underground excavations
  • Some surface deposits has no overburden, and on
    others, the bauxite may be covered by 70 meters
    or more of rock and clay
  • Deposits that are hardened may require blasting
    in order to release the ore
  • Once the bauxite is loosened into manageable
    pieces it is generally loaded into trucks or
    railroad cars and transported to crushing or
    washing plants or to stockpiles

12
Ghana Bauxite Company Ltd- Awaso
13
Production
Source Mineral Zone, Worldwide Exchange
http//www.mineralszone.com/minerals/bauxite.html
14
(No Transcript)
15
Geologic Description and Distribution Geological
definition of bauxite
Classification of bauxites, ferrites and
transitional rocks. (Schellman 1983).
16
Geologic Description and Distribution Schematic
Bauxite Profile
17
  • Geologic Description and Distribution
  • Bauxitization
  • 1-Dissolution Processes
  • Hydrolysis of aluminosilicates (Fe,
    feldspathoids, clays, gibbsite)
  • Limestone dissolution
  • -abundant organics
  • -intense microbial activity
  • -high temperature
  • -well drained weathering
  • Oxidation of iron minerals
  • 4FeS215O210H2O 4FeOOH8H2SO4
  • (pyrite) (goethite)
  • Organic compounds chelates

18
  • Geologic Description and Distribution
  • Bauxitization
  • 2- Formation of New Minerals
  • Aluminium (Hypothesis function of pH)
  • lt 4.5, Al3
  • gt 8.0, Al(OH)-4
  • Al hydroxide (amorphous)
  • AlOOHH2OOH- Al(OH)-4 Al(OH)3OH
  • Diaspore and boehmite top of topographical
    profiles
  • Aluminium goethite along fractures

Gibbsite -acid
Pseudo-boehmite
Norstrandite
Bayerite -alkaline
19
Geologic Description and Distribution Bauxitizati
on 3- Mineral Synthesis
20
Geologic Description and Distribution Bauxite
Distribution Tropical regions high T (avg 22),
rainfall (1.2 m) SiO2 leached in dry season,
Fe2O3, Al2O3 formed during wet season
21
  • Processing
  • Crushing, Cleaning and Drying
  • Conversion of Bauxite Ore to Aluminum Metal
  • The bauxite is purified by the Bayer Process
  • First, ore is mixed with hot Concentrated NaOH
  • Insoluble materials such as iron oxides remain
  • The insoluble materials are removed by filtration
  • Solution with soluble materials such as Al and Si
    is treated with CO2 gas
  • Carbonic acid forms and neutralizes NaOH in
    solution
  • Neutralization selectively precipitates the
    aluminum oxide, but leaves the silicates in
    solution
  • Filtration is used for the separation. After this
    stage the purified aluminum oxide is heated to
    evaporate the water

22
References Mineral Zone, Worldwide
Exchange http//www.mineralszone.com/minerals/baux
ite.html Morkeh John, 2002. Internship Report,
Ghana Bauxite Company Limited Awaso, Personal
Unpublished Document Ophardt, C.E., 2003.
Elnhurst College, Virtual Chembook http//www.elmh
urst.edu/chm/vchembook/327aluminum.html Wikipedi
a Encyclopedia http//en.wikipedia.org/wiki/Blast_
furnace http//volcano.und.edu/vwdocs/minerals/b
auxite.html
23
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