Industrial Minerals

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

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• 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))).

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• 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.

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There is no aluminium without bauxite
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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
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• 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

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Introduction What makes a good deposit?
Proximity to processing plant or infrastructure
to export. Low extraction costs
Quality High extractible Al2O3 Low
reactive SiO2
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• 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.
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Production Bauxite Mining
Ghana Bauxite Company Ltd- Awaso
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• 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

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Ghana Bauxite Company Ltd- Awaso
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Production
Source Mineral Zone, Worldwide Exchange
http//www.mineralszone.com/minerals/bauxite.html
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(No Transcript)
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Geologic Description and Distribution Geological
definition of bauxite
Classification of bauxites, ferrites and
transitional rocks. (Schellman 1983).
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Geologic Description and Distribution Schematic
Bauxite Profile
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• 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

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• 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
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Geologic Description and Distribution Bauxitizati
on 3- Mineral Synthesis
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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
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• 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

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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
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Questions?