This document provides an overview of aluminum extraction and production. It discusses the abundance and useful properties of aluminum. The key extraction process is the Bayer process, which uses caustic soda to extract alumina from bauxite ore. The alumina is then used as the raw material input for the Hall-Héroult electrolysis process, which produces aluminum metal. This process uses carbon anodes and cathodes submerged in a cryolite bath containing dissolved alumina. An electric current is passed through the bath to electrolytically reduce the alumina to molten aluminum. Additives are used to optimize the electrolysis conditions. The process requires substantial energy and raw material inputs to produce aluminum on an industrial scale.

1. Non-ferrous Metal Extraction:
Principles and Practices
Department of Metallurgical and Materials Engineering
National Institute ofTechnology, Rourkela – 769008
Odisha, India
Archana Mallik, PhD
Course Instructor
Module – Aluminium Extraction and Indian scenario

2. ALUMINIUM
!................LIFE OF A METAL……………………!
Grey and white…………..friendly and mighty!!!!!

3. Introduction and uses

4. Why Aluminium?
▪ The most abundant metal (8.1% by weight)
▪ The second most widely used metal
▪ High strength to weight ratio – Transportation
▪ Good workability – infrastructure, household and transportation
▪ Good conductor of heat and electricity – Electrical and electronic
▪ Effective light and heat reflection – Coatings and paints
▪ Good corrosion resistance to common and marine atmospheres – Ships, Infrastructure
▪ It retains its toughness at very low temperatures – Petroleum refining, rubber manufacture
▪ Alloys can match or even exceed the strength of common construction steel
• Non-toxic – Food packaging and water purification
• Readily recyclable
% Al Designation
< 99 Low grade
99 – 99.9 Commercial purity
99.9 – 99. 95 High purity
99.95 – 99.996 Super purity
> 99.996 Extreme purity

5. Physical and chemical properties
Crystal structure FCC, - 269 to 660 C
MP 660 C
BP 2494 C
Density (Solid) 2.7 gm/cc
Density (Liquid) 2.3 gm/cc
Lattice constant 4.04 x 10 E-10 m
Electrical resistivity 2.65 x 10 E-8 Ωm
Thermal conductivity 2.37 W/cm K
Physical properties
Mechanical properties
Hardness 245 – 1250 MPa
Tensile strength 75 – 360 MPa
Compressive strength 30 – 280 MPa
Chemical properties
Valency +3
Dry oxidation  Growth of thin but
stable oxide layer
 Piling-Bedworth ratio:
1.3
Reaction with aq. Soln.  Resistant to acids
 Dissolves in bases
 Amphoteric oxide
 Extensive reaction with
water (molten Al)
Reaction at high temp. Can reduce metals
Corrosion
Reaction with gases
Adherent passive film
H2, CO, CO2 and vapor

6. Global and Indian scenario of
Alumina and Al extraction

7. Global scenario of Alumina and Aluminium

8. Indian scenario of Alumina and Aluminium
Indian market price – INR 143.67/kg
(Fig. 3: Al consumption in India)
 Main producers are
 HINDALCO (Hindustan Al)
 VAL (Vedanata Al)
 NALCO (National Al)
 IACL (India Al)
 Kennametal
 HZL
 Sujana metals etc.
 6th largest producer of alumina
 2nd largest producer of Al
 Total production is only 5% of
consumption
(Fig. 4: Bauxite deposits in India)

9. Production of Alumina and Al:
Extraction and refining

10. • 1807 : Sir Humphrey Davy, underlined the existence of Aluminium. Argued that Alum
(KAl(SO4)2·12H2O) was salt of an unknown metal, which he said should be called ‘Aluminium’.
• 1821: P. Bertiiier, discovered bauxite, named after Les Baux a village in France
• 1825 : H.C. Oersted, Developed a method to produce anhydrous aluminium chloride
• 1854 : Frenchman Henri Sainte-Claire Deville, developed a reduction process using sodium,
which led to production of high cost metal in limited quantities and was used throughout Europe.
• 1886 : Charles Martin Hall of Ohio, USA
and Paul Lois Toussaint Héroult of New Orleans, France discovered electrolytic smelting
Fig 6: Charles Martin Hall(1863-1914) and Paul Lois Toussaint Héroult(1863-1914)
• 1888 : Karl Bayer, an Austrian, invented a better method for making Aluminium Oxide from Bauxite. This method reduced
the cost of Aluminium by some 80% from Deville’s process.
A glance on the history
Fig. 5: Sir Humphrey Davy(1778-
1829)

11. BAUXITE (Al2O3.xH2O)
FELDSPAR (KAlSi3O8)
CRYOLITE (Na3AlF6)
ALUMINITE (Al2S)4(OH)4.7H2O) KAOLINITE (Al2i2O5(OH)4)
(Fig. 7: Different ores of aluminium)
Resources of Al: Primary

12. 2
Resources of Al: Secondary
Al scrap:
 Old scrap
 New scrap
 Sheet Al
 Dirty Al
 Al can
 Al gutters
 Al wires

13. Aluminium production
Conventional process:
 Hall-Heroult electrolysis
Newer processes:
 ALCOA process
 TOTH process
 ALCAN process
 Lime-sinter process
 Deville-Pechiny
 Serpeck process
(Fig. 8: Electrolysis of Aluminium)
Raw materials:
 Carbon (Anode:0.4-0.5 kg
and cathode 0.02-0.04 kg/kg of
Al)
 Auminium oxide (1-6%,
1.9 – 1.95 kg/kg of Al)
 Electrolyte material
 Na3AlF6 ( > 75%)
 CaF2 (4 – 8%)
 AlF3 (5-15%)
 LiF (0-5%)
 MgF2 (0-5%)

14. Description of raw materials: Carbon
Anodes
Cathodes
 Average anode life: 20 – 30 hours
 Pure form of carbon: Coke from petroleum refining
 Coke+Spent anode+coal-tar pitch – Baked at 1000-1200 C
 Steel stub+cast iron pouring
 Pure Al spraying
 Average cathode life: 2 -6 years
 Purity is not the focus: Anthracite/Mett.
Coke/Graphite
 Coke+coal-tar pitch – Baked at 1000-1200 C
 Mortared, mixed with seam mix – sent for pot lining
 Pure Al spraying

15. Description of raw materials: Ore/Bauxite/Alumina
Bauxite -The major ore
• Mixture of hydrated Aluminium oxides - Gibbsite[Al(OH)3] + Boehmite /Diaspore[AlO(OH)], 50-70% Alumina
• Claylike and earthy
• White to deep brown or red
• The major impurities in Bauxite are:-
 Iron oxides (goethite & haematite)
 Silicon dioxide (< 5%)
 kaolinite (Al2Si2O5(OH)4 )
 Anatase (TiO2)
RED MUD
Alumina extraction:
 MP – 2800 C
 Density - 3.96gm/cm3
 Lime sinter process
 Deville-Pechiny process
 Serpeck process
 Bayer process
Lime sinter process:
Alumina clay reacts with limestone to produce
alumina
(Al2O3.2SiO2)(c) + 2CaCO3 2CaSiO3 + Al2O3
Deville-Pechiny process
Low grade bauxite mixed with sodium
carbonate to produce alumina
Serpeck process
Low grade bauxite mixed with carbon in
presence of nitrogen/aluminium
nitride/hydrolyzation/Al(OH)3 or Al2 O3

16. (Fig. 8: Simplified Bayer circle)
 Crushing and grinding of Bauxite by jaw crushers/hammer
 Silica in fine fractions
 Alumina in coarse fractions
 Milling with caustic soda in a ball mill, yielding a slurry
 Pressure leaching in autoclave/digesters
 Temperature: 180-220 o C
 Pressure: 5-25 atm
 Time: 2-2.5 hours
 86-88% of alumina gets digested
 Reactions involved:
 Al2 O3.H2O + 2NaOH =2NaAlO2 +2H2O
 Al2O3 .3H2O + 2NaOH= 2NaAlO2 +4H2O
 1 ton of Al2O3 - 2.2-2.4 tonnes of bauxite
0.08-0.12 tonnes of caustic soda
8-10 tonnes of steam
0.18-0.2 tonnes of fuel oil
Bayer’s process: The path

17. Bayer’s process in action
Factors affecting the process:
 Size of bauxite
 Medium of grinding
 Temperature of digestion
 Sensible heat of the process
 %of precipitation
 Calcination temperature

18. Description of raw materials: Electrolyte
Cryolite + Additives
Requirements of electrolysis process
▪ Lower liquid temperature (for higher current efficiency.
We don’t want current to generate heat)
▪ Decrease solubility of metal (in fused salt)
▪ Increase solubility of Al2O3
▪ Increase electrical conductivity
▪ Decrease density (for better separation of metal/salt i.e
between cryolite and Al)
▪ Decrease vapor pressure and metal loss
Cryolite:
Role and properties:
 Dissolution of alumina
 Induce conductivity
 High dissociation voltage
 MP – 1010 C
 Density – 2.10 gm/cc (Vs. Alumina)
Source/Occurrence:
 Natural (Exhausted)
 Used pot linings
 Byproduct of red. Cell
3Na2O+4AlF3 = 2NA3ALF6+Al2O3
 Synthetic
6HF+2NaOH+NaAlO2 = Na3AlF6 + 4H2O
Cryolite ratio (Rc): NaF/AlF3 = 3:1

19. ▪ Reduction in MP of the bath
▪ Decreased solubility of reduced ions
▪ Decrease in vapor pressure
▪ Increase in current efficiency
▪ Decreases the solubility of Al2O3 in cryolite
▪ Decrease the electrical conductivity.
▪ Increase the density of the bath
▪ Most common additives – CaF2, AlF3
Description of raw materials: Electrolyte
CaF2: Natural occurrence
AlF3: To compensate shortage of AlF3 in the
bath
 Loss due to vaporization (NaAlF4)
 Hydrolysis loss –
2AlF6+3H2O = 2Al2O3+6HF
 Evolution of CCl4 during anode effect
 Byproduct reaction (cryolite production)
Additives:

20. Hall-Heroult’s process
Process characteristics:
 Cell dimension: 5 x 2 x 1 m
 Three layer process:
1st layer - Al2O3 (3.96 gm/cc)
2nd layer - Na3AlF6(2.1 gm/cc)
3rd layer - Al (2.3 gm/cc)
 Temperature: 940 - 980 C
 Continuous addition of alumina from top
 Al2O3 dissolution upto 15% at 1000 C in cryolite
 Al purity: 99.5 – 99.8%
(Fig. 9: The Hall-Heroult process)
Anode Carbon
(Prebaked/Soderberg)
Cathode Carbon
Electrolyte Alumina+Cryolite+Additives

21. The operation
Step 1: Addition of cryolite – V, CD on/Electrothermics and Electrodics/1010 C
Na3AlF6  3Na+ + [AlF6]3- ………(1)
[AlF6]3-  [AlF4]- + 2F- ………(2)
Step 2: Addition of alumina – constant V, CD/Electrodics/ 980 C
2Al2O3 + 2[AlF6]3-  3[Al2O2F4]2- ………(3)
Al2O3 + 4[AlF6]3-  3[Al2OF6]2- + 6F- ………(4)
[AlF6]3-  [AlF4]- + 2F- ………(5)
Ionic structure of the
melt
Na+
[AlF4]-
2F-
[Al2O2F4]2-
[Al2OF6]2-
Cations
Anions
Step 3: Electrode reactions – constant V, CD/Electrodics/ 980 C
At cathode:
[AlF4]- + 3e−  Al + 4F- ………(6)
3Na+ + e- = Na, no reaction as E0 is active then Al
η𝑐=
𝑅𝑇 (1.375 −0.125 𝑅𝑐)
1.5 𝐹
ln
𝑖
0.257
At anode:
C + O2 → CO2 + 4e− (Gas) ………(7)
[Al2O2F4]2- = O2- +Al2O2F4 ………(7i)
Al2O2F4 + [Al2OF6]2- = [Al2O2F4]2- + 2AlF3..(7ii)
F- = F + e− (Gas), COF4, CF4 ………(8)
η𝑎=
𝛾𝑅𝑇
𝑝𝑛𝐹
ln
𝑖
𝑖𝑙𝑖𝑚
1/2Al2O3 + 3/4 C → Al + 3/4 CO2

22. The operation
Operating voltage:
𝐸𝑂𝑃 = 𝐸
0
+ η𝑐 + η𝑎 − I (𝑅𝐴 + 𝑅𝐵 + 𝑅𝐶 + 𝑅𝑋 )
1.19 V 3.81 V
Current efficiency:
CE = 254.92 - 1.7CAl2O3+0.39C2
Al2O3+0.45XAlF3+0.055X2
AlF3+0.3CCaF2 - 0.23T+ 129/(D+1)+25i
Al2O3 + 3/2 C → 2 Al + 3/2 CO2
Consumption
of carbon
Anode effect
Consumption of carbon:
 H2 and CH4 injection
 Reduction in
decomposition
potential
 Cheap availability
Anode effect:
 Alumina < 2%
 Formation of gas
clouds near anode
 No wetting of anodes
 Increase in V/CD
 Florine reaction
 Florine based gases
 Electrolysis ceases
 Electrical sparks
Remedies for AE:
 Restore alumina
 Liquid Al splashing
 Fresh anode
 Repositioning anode
Deciding factors of electrolysis:
 Bath temperature
 V, CD
 Density
 Interpolar distance
 Additives

23. Material and heat consumption/ton of Al produced
Material consumption in tons
Alumina 2
Cryolite 0.035
AlF3 0.04
Soda ash 0.7 (for new pot)
Coke 0.5
Hard pitch 0.13
Calcined anthracite 7 (for new pot)
Soft pitch 1 (for new pot)
Fuel oil (for baking furnace) 0.12
Energy consumption in 105 kCal/t
Metal from primary ore 61.5
Metal from secondary resources 3
Metal ingot 49.6

25. Electrolytic refining of Aluminium
Production of super purity Al
36% AlF + 30% Na3AlF6+ 18% BaF2 + 18% CaF2
99.99%
Al-Cu (28-30% Cu) (density 4.5)
Electro-Chemical
Changes:
Na3AlF6 → 3NaF + AlF3
AlF3 → Al+3 + 3F-
At the cathode:
Al+3 + 3e- → Al
At the anode:
Al → Al+3 + 3e-
Overall reaction:
Al+3 + Al → Al + Al+3
(Fig. 10: Three layer process/Hoopes process)

26. Newer processes of Al
extraction
…….because electricity is getting expensive and scarce

27. ALCOA Process
▪ This process does not rely on direct use of Alumina and cryolite
▪ Here alumina obtained from Bayer’s process is chlorinated to form AlCl3
▪ Chlorination is done under reducing condition
▪ Al2O3(c) + 2C(c) + 3Cl2(g) = 2AlCl3(g) + CO(g) + CO2(g)
(Fig. 11: ALCOA process)

28. Monopolar (HH) vs bipolar(Alcoa) process
▪ Bipolar cells is equivalent to five conventional monopolar cells in series
▪ Productivity of bipolar is five times that of monopolar cells
▪ Cell voltage of bipolar is five times those of conventional monopolar cells
▪ Biplolar enhances the surface area of electrode enormously
▪ Less electrode gap (1.3 cm)
▪ No emission of CO or CO2
▪ Electrodes are not consumable
▪ Energy efficient (30% higher then HH process)
▪ AlCl3 is highly toxic, forms HCl
▪ May be expensive, to handle the toxicity

29. TOTH process
 Named after Charles Toth
 Indirect carbothermal reduction of alumina
 Can deal with low grade ore
 Energy concumption – 5% of HH process
 Step 1: At 925 C
Al2O3(in clay) + 2C(C) + 3Cl2(g) = 2AlCl3(g) + CO(g)
 Step 2: At 230 C and 15 atm
3Mn (C)+2Al3Cl3 = 2Al + 3MnCl2
 Step 3: At 600 C
2MnCl2 + O2 = 2MnO + 2Cl2
 Step 4: At 1750 C
MnO + C = Mn + CO
 High pressure – expensive
 Feasibility of Mn reduction
 Mn contamination
 Carbon consumption

30. ALCAN Process
▪ Reduce Al2O3 (direct from bauxite)by Carbon at 2000 C in electric furnace to produce carbide
▪ Alloy produce has 50% Al, 30%Fe, 5% Si, 5%Ti and 5% C
▪ Why Fe and Si, because you are starting with bauxite
▪ 2Al (alloy carbide) + AlCl3 = 3AlCl
▪ As AlCl temp is reduced , Al droplets forms that are collected
▪ Stress corrosion by AlCl3
1300 C
700 C

31. Environmental aspects of Al use
extraction and use

32.  Perfluorocarbons (PFC) during the aluminum smelting process
are 9,200 times more harmful than carbon dioxide in
terms of their affect on global warming
Environmental concerns
 Air emissions
 Cell room:
Particulate and gaseous florides,Alumina,
Carbon dust, SO2, CO, CO2
 Anode plant:
Coke dust, pitch fume and fluorides
 Water discharge
 Fume collection system
Acid, Fluoride and organic materials
 Hydrometallurgical Effluents
 Sodium ions introduced during NaOH
leaching
 Pot wash water
 Plant runoff
 Solid waste
 Spent potlining (Fig. 12: Production of Al and emission of PFC)

33. Al production in India

34. Aluminium production in India
Producer and
technology
Smelter location Deposit location Plant
capacity
Final products
HINDALCO (AP-36)  Renukoot
 Mahan Al
 Hirakud
 Aditya Al
Utkal Alumina 1.3 MTPA
 Primary Al (Ingots,
wire rods and billets)
 Flat rolled products
 Foils and packaging
 Extrusions
NALCO
(AP-16)
Angul Damanjodi 0.22 MTPA  Primary Al
 Cast strips
 Cold rolled sheets
VAL  Jharsuguda
 Korba
Jharsuguda 2.3 MTPA  Primary Al
 Alloy ingots
 Chequered sheets
 Hot and cold rolled
sheets
Ingot
Wire rod
Billet
Sheets

35. (Fig. NALCO overview)
CPP
PORT FACILITIES
VIZAG
10x120MW Power Plant
Alumina: 45%
Alumina: 55% for Export
Power to Grid
Power to Smelter
Import caustic soda & export Alumina
REFINERY
SMELTER
Cast Metal: 4.6 lakhTPA
Alumina: 21 lakhTPA
MINES
Bauxite 63 lakhTPA
Aluminium production in NALCO

36. Smelter Process Flow Diagram
CPC & PITCH
VCU
BAKING FURNACE RODDED ANODE
ATV
ALUMINA,
BATH & ALUMINA FLOURIDE
180KA POT
POT SHELL
POWER FROM CPP
DC POWER
ALUMINA
SILO
FUME TREATMENT
ALUMINA
ALUMINA
ALUMINA
STACK
MTT
FURNACE
CAST HOUSE
DESPATCH
ALUMINA WAGON FROM
DAMANJODI
2MT TAPPING EVERY 32/HR
PER POT
150 ANODES/ SHIFT
GREEN ANODE
1235KG
27 ANODES/HR
45T/35T HOLDING FURNACE
4 X 13,500MT
(Fig: Smelter flow design)

37. Smelter Process Flow Diagram: VAL

38. Inside a potline
▪ Technology : AP-16
▪ No of pot lines : 4
▪ No of pots : 240 x 4 = 960
▪ Anodes : Prebaked
▪ Cathodes : Semigraphite/
graphite block
▪ Prodn.Capacity : 4,60,000 tpa
▪ Env.Control : dry scrubbing
▪ Alumina feed : Alpsys (Point feed)
regulation

39. References
 H. S. Ray, R. Sridhar and K. P. Abraham, Extraction of non-ferrous metals, Affiliated
east-west press private limited, New Delhi, 2015.
 Fathi Habashi, Handbook of Extractive Metallurgy, Wiley VCH, Germany, 1997.
 http://www.world-aluminium.org/statistics/alumina-production/12-23-2017
 http://www.hindalco.com/12-23-2017
 http://www.ambicaaluminium.com/top-10-aluminium-manufacturing-companies-in-
india/12-23-2017
 https://www.nalcoindia.com/12-23-2017
 http://www.vedantaaluminium.com/12-23-2017
 https://www.youtube.com/watch?v=fa6KEwWY9HU/12-23-2017

40. Acknowledgements
My undergraduate students
Siddharth Padhee (114MM0509)
Anvesh Nathani (114MM0644)
Priyansha Nikita (115MM0081)
Nishant Kumar (115MM0177)
B Anjali (115MM0200)
Saurav Mishra (115MM0389)
V.Rajan Kumar Raju (115MM0395)
Kakarasri Pushpa (115MM0474)
Himanshu Sekhar (115MM0659)
Laxmidhar Majhi (114MM0507)
2015-2019 undergraduate batch

41. THANKYOU