1. Lecture 4:
Beneficiation and Mineral Processing
of Bauxite and Feldspar
Hassan Z. Harraz
hharraz2006@yahoo.com
Spring 2017
@ Hassan Harraz 2017
Beneficiation and Mineral Processing of Bauxite and Feldspar

2. OUTLİNE OF LECTURE 4:
Examples Mineral processing:
 BAUXITE:
 Raw Materials of Bauxite
 The World's Bauxite Sources
 Alumina Production:
 Bayer process;
 Hall-Héroult process
 Use of Cryolite
 Preparation of Fused Alumina
 Preparation of High Purity Alumina
 Feldspar:
 Feldspar in Glass Manufacture
 Feldspar in Ceramic Manufacture
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3. Bauxite:
 is main resource of the world’s aluminum.
 is an aluminum ore and is not actually a mineral.
 is the most abundant element found in the earth's crust, although the word bauxite
is used forms most commonly in deeply weathered rocks as a hydrated aluminum oxide
ore.
 formed in residual deposits; at or near the surface under tropical or Subtropical
conditions of weathering.
 extracted in many countries of the tropical belt.
4) BAUXITE
Introduction
 Although aluminium (Al) is the most abundant metal in the earth's crust and
the 3rd most abundant element, it occurs mainly in combinations that so far
have defined commercial extraction.
 It is an important constituent of all clays and soil and of the silicates of
common rocks.
 Alumina (Al2O3) is produced worldwide for the aluminum and ceramics
industries.
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4. The World's Bauxite Sources
Courtesy of: http://www.hs.wisd.org/ddaughenbaugh/Pictures/alcoa_aluminum_smelter_and_mine.htm
 Main producers: Australia, Guinea, Jamaica, Brazil, China, Guyana,
Indonesia, Cuba, Philippines, India, Surinam and Balkan Republics.
 Largest producers are Australia, Jamaica and Guinea.
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5. Raw Materials of Bauxite
 Bauxite ore consists of variable proportions of the following hydroxide minerals
Gibbsite (Al(OH)3),
Böehmite {AlO(OH)},and
Diaspore AlO(OH)
 The main impurities: clay mineral {Halloysite (Al2Si2O5(OH)4•2H2O), Kaolinite
(Al2Si2O5(OH)4), Montmorillonite ((Na,Ca)0.33(Al,Mg)2Si4O10(OH)2•nH2O)},
iron oxides, and small amounts of Anatase (TiO2) .
DecreaseAl2O3
Composition of bauxites:
35 to 65% Al2O3
2 to 10 % SiO2
2 to 20% Fe2O3
1 to 3 % TiO2
10 to 30% combined water.
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6. http://www.alcoa.com/australia/en/info_page/mining_homepage.asp
Jarrahdale bauxite mine (Australia, Alcoa)
For aluminium ore: bauxite should contain preferably at least 35% Al2O3 and
less than 5% SiO2, 6% Fe2O3 and 3% TiO2.
For the chemical industry: the percentage of silica is less important, but iron
and titanium oxides should not exceed 3% each; and
For abrasive use: SiO2 and Fe2O3 should be less than 6% each.
Commercial bauxite occurs in three forms:
Pisolitic or Oolitic, in which the kernels are much as a centimeter in diameter
and consist principally of amorphous trihydrate.
Aluminum ores
Ore minerals of aluminum are
gibbsite (Al2O3.3H2O), diaspore
(Al2O3.H2O), boehmite
(Al2O3.H2O), corundum (Al2O3),
kaolinite (Al2O3.2.SiO2.2H2O), etc.
Ores: The only commercial ore of
aluminum is bauxite. Bauxite is a
rock containing the hydrated oxides
of aluminum; gibbsite, diaspore and
boehmite (Al2O3.xH2O). Bauxites
contain 55 – 61 % Al2O3, 10 – 30 %
combined water, 1 – 25 % Fe2O3, 1
– 3 TiO2 and 1 – 12 % SiO2.
Bauxites with low SiO2 are
desirable.
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7. The traditional process to extract aluminium oxide (alumina) from
bauxite (aluminium ore) involves two major processes:
i) Bayer process extracts/purifies alumina from bauxite ore via a
chemical process and is usually done at the mine site.
 Chemical: Sodium hydroxide(NaOH), carbon
dioxide (CO2)
 Hydrometallurgical Production of Al2O3 (alumina) by the Bayer
Process
 Pure alumina (aluminium oxide: Al2O3) is exported to a
smelting operation.
 The alumina (aluminium oxide: Al2O3) is then dissolved in
cryolite. Once dissolved, the final process of metal
extraction involves ELECTROLYSIS.
ii) Hall-Héroult process uses electricity to de-oxidizes alumina
(aluminium oxide: Al2O3) into aluminum metal (Aluminum : Al).
It’s an electrolysis process that extracts aluminum metal out of
alumina.
 It’s usually done near a major electric power source.
Electrolysis: cryolite
 Overall cell reaction is
Alumina + Carbon = Aluminum + Carbon dioxide
4.2) ALUMINA PRODUCTION
Aluminum production
flow chart
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8. i) Bayer process
 Bayer process is Hydrometallurgical processing to extract aluminum oxide (Al2O3) from bauxite ore.
 Bauxite is powdered prior to the start BAYER process.
 Aluminum oxide (Al2O3) from bauxite ore dissolve in caustic soda (i.e., Sodium hydroxide (NaOH)) and lime (Ca(OH)2).
 Iron oxide, silicon oxide (SiO2), and titanium oxide (TiO2), and other materials don’t dissolve.
 As aluminum oxide is amphoteric, it dissolves in sodium hydroxide solution.
Al(OH)3(s) + NaOH (aq)  NaAlO2(aq) + 2H2O(l)
 During the digestion, most of the hydrated alumina goes into solution as sodium aluminate and insoluble impurities compounds impurities (SiO2,
TiO2, and Fe3O3) are removed/ separated by settling and filtration. This is waste is red in colour so is usually referred to as “Red Mud”.
 Then it is pumped into huge pressure containers and heated, after which more chemicals (lime to regenerate caustic soda) are added, and hydrate
alumina crystallizes from the solution after being seeded with other (trihydrate alumina) crystals.
 After cooling, the filtered sodium aluminate (AlO2Na) solution is seeded with very fine gibbsite (Al(OH)3), and at the lower temperature th
aluminum hydroxide reforms as the stable phase. Seeding with aluminum hydroxide then reverses the reaction.
 The solution is drawn off and CO2 is blown in under pressure “blown through”. This Carbon dioxide (CO2) dissolves to form carbonic acid whic
neutralizes the alkali causing aluminum hydroxide (AlOH) to precipitate. When pressure is released, CO2 gas bubbles off like soda pop.
 Alumina is collected and rinsed so the sodium hydroxide (NaOH) can be recycled.
 Calcination:
Alumina is calcinated, which means it’s baked hotter than boiling temperature of water but less than melting. This causes oxygen from the a
to combine with hydrogen from aluminum hydroxide to form alumina and water vapour. Aluminum hydroxide calcinates >1100oC.
2Al(OH)3 + O2 (air)  Al2O3(s) + 3H2O(l)
 The slurry from the precipitation thanks is filtered to extract the fines (recycled as seed crystals). The gibbsite is continuously classified, washed to
reduce the sodium content, and then calcined. The filter cake is than calcined at 1100oC (rotary kiln, or fluidized bed calciner) resulting in sandy
alumina with more than 90% of the particles >45µm. Material calcined at 1100-1200°C is crushed and ground to obtain a range of sizes (Fig.3).
 Tabular aluminas are obtained by calcining to a higher temperature, about 1650°C.
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9. Alumina: Bayer process I
http://www.qal.com.au/
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10. Fig.2: Flow chart Bayer process
Courtesy of:
http://www.hs.wisd.org/ddaughenbaugh/Pictures/alcoa_aluminum_smelter_and_mine.htm
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11. Fig.3: Bayer Process flow chart
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12. Extraction of Aluminum
Hydrometallurgical Production of Al2O3 (alumina) by the Bayer Process
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13. Opaque alumina: purity > 99.5%; grain size ~ 0.55 μm,
residual porosity 0.3%; transparent alumina: residual
porosity < 0.03%
(J. Am. Cer. Soc., 89(6), 1985-1992, 2006)
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14. Use of Cryolite
 Alumina has a very high melting point of 2045°C.
 Cryolite (sodium hexafluoroaluminate(III), Na3AlF6) melts
at ~950°C and the solution can dissolve alumina
sufficiently well.
 Considerable energy is still required to heat cryolite and
dissolve alumina, but it is much more energy-efficient
than melting the alumina itself.
 Natural cryolite is depleted long ago, thus synthetic
cryolite is needed.
 The aluminate solution (NaAlO2(aq)) from Bayer process
is used in separate process to make synthetic cryolite.
 Hydrogen fluoride and sodium carbonate is added to the
solution to precipitate cyrolite.
NaAlO2(aq) + 6HF(g) + Na2CO3(aq)  Na3AlF6(s) +3H2O(l) + CO2(g)
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15. ii) Hall-Héroult process
 Alumina is made up of aluminium and oxygen. To produce aluminium metal, these two elements need to be
separated. Two tonnes of alumina are needed to make one tonne of aluminium.
 Since alumina is an electrical insulator (i.e., Alumina is not conductive), the hall process uses cryolite
as a catalyst for electrolysis.
 Alumina is dissolved in an electrolytic bath of molten cryolite (Sodium Aluminium Fluoride: Na3AlF6) within a large
carbon or graphite lined steel furnace known as a ‘pot’. There are hundreds of pots at a typical smelter.
 Molten cryolite (Na3AlF6) dissociates into an ionic compound (3Na+ AlF6
3-) permitting electrical conduction.
 A high electric current is passed through the pot at low voltage, via carbon blocks called anodes. The strong electric
current flows continuously from the anode (positive), through the alumina/cryolite mixture to the carbon or graphite
lining of the pot (negative), and then to the next pot, and so on.
 The electricity enables the alumina to split into its components of aluminium and oxygen.
 The oxygen bubbles away and the aluminium settles to the bottom of the pot. The electricity also maintains the
temperature of the process at ~950°C. Aluminum is poured from a spout at the bottom.
2 Al2O3 → 4 Al + 3 O2
 Side reactions are a concern. Electricity is delivered to the molten cryolite via a graphite anode. Some of the oxygen
from air or oxygen released by electrolysis will combine with carbon from the anode to form carbon dioxide (CO2)
gas. This consumes the anode.
 Carbon can be regenerated from carbon dioxide via the Reverse Water Gas Shift (RWGS):
H2 + CO2 → H2O + CO
H2 + CO → H2O + C
 With enough heat and pressure the process will continue to consume carbon monoxide to form graphite soot.
 recover hydrogen reverse fuel cell:
2 H2O → 2 H2 + O2
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16. Hall Heroult process
http://image.tutorvista.com/content/p-block-elements/hall-heroult-process.jpeg
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17. 3) PREPARATION OF FUSED ALUMINA
 Fused alumina is trade names of Alundum and Aloxite.
 Fused alumina is used to made abrasive grains.
 Before processing, bauxite, the crude raw material, is calcined at ~950°C
to remove both free and combined water.
 The bauxite is then mixed with ground coke (~3 %) and iron borings (~2
%) in a pot-type, electric-arc furnaces for 24 hours at 2000oC.
 Melts the bauxite and reduces the impurities that settle to the bottom of
the furnace.
 The furnace is then emptied and the outer impure layer is stripped off.
 The core of aluminum oxide is then removed to be processed into
Abrasive Grains.
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18. 4) PREPARATION OF HIGH PURITY ALUMINA
 High purity: >99.50%
 High purity can be produced by Five processes, namely:
1) Selective crystallization: get ammonium alum or ammonium
alum carbonate hydrate (AACH) first, repeated dissolution-
crystallization, to remove impurities, e.g. Na, Mg, Ca, Fe, Ti,
SiO2; NH4Al(SO4)2 12H2O.
2) Distillation method: Al metal as source, reaction to get AlR3
or alkoxide Al(OR)3, then remove impurity by distillation,
calcination to get oxides.
3) Spark discharge: high purity Al as electrode, under high
electrical voltage, spark discharge to get oxide.
4) Chemical reaction: ethylene chlorohydrin process, sodium
aluminate solution as source, add organic acid ClCH2CH2OH,
slow neutralization reaction to get Al(OH)3, impurity such as
Na, Si, Fe difficult to enter oxide lattice; by-product ethylene
oxide, may react with HCl  to get ethylene hydrin to save
money.
5) Modified Bayer process: add large silica particle during
calcination, to trap evaporated Na2O to remove it; or flowing
HCl to form soluble NaCl to remove it.
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19. Transparent Alumina
 One potential application: to be used
in HID (high-intensity discharge) lamp;
for projectors, ….etc.
 Anti-corrosive, heat resistant, good
strength (better than fused silica)
HID lamp: greater
light output/watt
electrical input
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20. PROPERTIES OF ALUMINUM
 Malleable and can be shaped easily
 Excellent conductor of heat and electricity
 Has much a lower density than iron, yet can form alloys that are stronger than steel
 Resistant to corrosion due to its protective layer of aluminum oxide
 The thickness of the oxide layer can be further increased by a process known as
anodizing.
Use Examples
Transport Superstructures of trains, ships and airplanes. Alloy engines for cars.
Construction Window frames, doors roofing
Power transmission Overhead electricity cables, capacitor foil
Kitchen utensils Kettles, saucepans
Packaging Drink cans, foil wrapping
Chemical industry Al(OH)3 – flame retarder, paper making
Al2(SO4)3 – flocculant in sweage treatment and to precipitate P2O5-
Al2O3 – catalyst and catalytic support material, abrasive
USES OF ALUMINUM
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21. ENVIRONMENTAL IMPACT
Smelting processes of aluminum requires enormous amount of electricity.
Also, the main process which is the electrolysis emits carbon dioxide
which is greenhouse gas.
Recycling aluminum is an important method of saving energy and
minimizing the environmental damage.
Recycling aluminum requires only 5% of the energy to produce the same
amount of aluminum from bauxite.
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22. 5) FELDSPAR
Feldspars melt at ~1150oC.
Generally, feldspar is used in the manufacture of glass products (70%), in
ceramics and other products (30%).
Feldspar is also used Filler (in paint, in mild abrasives, urethane, latex foam, and
as a welding rod coating).
Feldspar does not have a strict melting point, since it melts gradually over a
range of temperatures. This greatly facilitates the melting of quartz and clays
and, through appropriate mixing, allows modulations of this important step of
ceramic making.
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23. 23

24. Feldspar (Naturally occurring forms of devitrified glass)
Potassium Feldspar (Orthoclase or
microcline)
K2O Al2O3 6SiO2
Sodium Feldspar (Albite) Na2O Al2O3 6SiO2
Lime Feldspar (Anorthite) CaO Al2O3 2SiO2
Flux
Stabilizer
Glass Former
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25. 5.1) Feldspar in Glass and Ceramic Manufacture
 Feldspar is an important ingredient in the manufacture of glass , because it acts
as a fluxing agent, reducing the melting temperature of quartz and helping
to control the viscosity of glass.
 The Raw material for Glass consists of:
 Silica sand (quartz), Soda ash (sodium carbonate) and Limestone
(calcium carbonate).
 Feldspar adds certain qualities to the process.
 Alumina in feldspar acts as a stabiliszer
 improves the finished product by increasing resistance to impact,
bending, and thermal shock,
 increases viscosity during glass formation and inhibits devitrification.
 provides hardness, workability, strength, and makes glass more
resistant to chemicals.
 Alkali content (Na2O + K2O) in feldspar acts as flux:
 lowering the glass batch melting temperature,
 reduce the melting temperature of quartz so less energy is used
 decrease the amount of soda ash needed
 helping to control the viscosity of glass,
 thus reducing production costs.
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26. 5.2) Feldspar in Ceramic Manufacture
 In the manufacture of ceramics, feldspar is the second most important ingredient after clay.
 In the fabrication of ceramic material, feldspars are used as fluxing agents to form a glassy
phase at low temperatures, and as a source of alkalies and alumina in glazes.
 In the manufacture of ceramics, feldspar is the second most important ingredient after clay.
 Feldspars are used as fluxing agents to form a glassy phase at low temperatures and as a source of
alkalis and alumina in glazes.
Because of their low melting point, feldspars are used as a melting agent in ceramic
mixtures, glass batches, glazes, enamels and also as casting powders.
 They improve the strength, toughness, and durability of the ceramic body and cements the
crystalline phase of other ingredients, softening, melting and wetting other batch
constituents.
 Fluxing temperature is depend on free silica content, body composition and the ratio of the
alkali oxides (Na2O, K2O, and Li2O).
 In the flooring sector, feldspar is used as a flux, lowering the vitrifying temperature of a
ceramic body during firing and forming a glassy phase. Surface tensions pull the remaining
solid particles together, giving a densification of the ceramic body. With rising temperatures
the alkalis become more active and first dissolve the clay particles and then the free silica.
Note: In ceramic, K-spar is prepared over Na-spar, since it form a highly viscous
melt even at very high temperatures and thus prevents distortion during firing.
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27. White calcic Feldspar (~13% CaO)
Gabal Abu Had- Southern Portion of
Eastern Desert
Total Cost: 10 Egyptian pound/ton
Sale: 500 Egyptian pound/ton
Gabal Abu Had- Southern
Portion of Eastern Desert
White calcic
Feldspar
Photo by: Mohamed Imam
Photo by: Mohamed Imam
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28. Feldspar Production line
(500 ton/ Day)
Ball Mill
Belt Conveyor
Belt Conveyor
Vacuum Filter
Floatation Machine
Electric- vibrating Feeder
GZD Series vibrating Feeder
PEX Series Jaw Crusher
Storage Bin
Classifier
Storage BinRaw Ore
PE Series Jaw Crusher
Blender
Concentrator
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29. ‫غارب‬ ‫رأس‬ ‫طريق‬ ‫شمال‬ ‫الشرقية‬ ‫الصحراء‬-‫المنيا‬
Quartz
Orthoclase
Mica
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30. 30

31. In the feldspar process, one may distinguish three
different flotation steps, namely the micas flotation, the
oxides flotation, and the feldspar flotation.
Each of these requires a different reagent regime.
The following flow sheet shows the steps
involved in the recovery of feldspar. 31

32. Thank You!
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