Part 2 - Extractive Metallurgy of Al

8/20/2019 Part 2 - Extractive Metallurgy of Al

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CRICOS Provider00111D

Extractive MetallurgyPart 3 – ExtractiveMetallurgy of Aluminium

A/Prof Akbar RhamdhaniDepartment of Mechanical andProduct Design Engineering

Universitas Indonesia

23 November – 4 December 2015


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SCIENCE | TECHNOLOGY | INNOVATION | BUSINESS | DESIGN

General References

1. C. Bodsworth, The Extraction and Refining of Metals, CRC Press, London,

1993

2. J.D. Gilchrist, Extraction Metallurgy, 3rd. Ed., Pergamon Press, Oxford, 1989

3. P.C. Hayes, Process Principles in Minerals & Materials Production, Hayes

Publishing, Sherwood, 1993

4. T.W. Swaddle, Inorganic Chemistry: An Industrial and EnvironmentalPerspective, Academic Press, San Diego, 1997.

5. K. Grjothiem and B.J. Welch, Aluminium Smelter Technology , Aluminium-

Verlag, Dusseldorf, 1988

6. J. Thonstad, P. Fellner, G.M. Haarberg, J. Hives, H. Kvande, A. Sterten, Aluminium Electrolysis, 3rd Edition, Aluminium-Verlag, Dusseldorf, 2001

7. I. Galasiu, R. Galasiu, J. Thonstad, Inert Anodes for Aluminium Electrolysis,

1st Edition, Aluminium-Verlag, Dusseldorf, 2007

2


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Topics to be covered

Part 1 – Fundamental of Light Metals Production

(focused on Al)

1. Overview of Light Metals Production

2. Analysis of Processes Routes and Ellingham Diagram

3. Carbothermic and Metallothermic Processes

4. Electrolysis from Molten Salts

What should you hope to gain?

An understanding of why metals are produced by certain

routes and what alternatives exist3


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Topics to be covered

Part 2 – Removal of Impurities and Refining of Al in Cast

House

1. Impurities in aluminium and their effect

2. Technique and method for impurities removal and

refining of aluminium

What should you hope to gain?

An understanding of impurities and their effect, and various

techniques for refining and removing of impurities in

CastHouse

4


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1.Fundamentals of Light Metals Production(focused on Al)


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Metals and Where do we get them?

6


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Why are Light Metals so expensive

7

050

100

150

200

250

300

350

400

Titanium Magnesium Aluminium Stainless

steel

Steel

GER(MJ/kgmetal)

0

10

20

30

40

50

GWP(kgCO2e/kgmetal)GER

GWPElectrolyticHall-

Heroult

Electric

furnaceBF &

BOF

Kroll

Norgate et al., Green Processing 2004, AusIMM


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EXTRACTION OF METALS FROM OXIDES

STAGE 1:

Physical processing to lower impurities form a “concentrate”

Grinding, crushing, gravity separation, froth flotation, electrostatic, and others

www.prlog.org http://www.goldorecrusher.com


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STAGE 2:

Route 1:

Reduce the concentrate to impure metal

product• Carbothermic reduction, Metallothermic

reduction, Gaseous reduction, etc

Example: Ironmaking through Blast Furnace

Refine the impure metal• Converting, zone refining, vacuum refining,

electrolysis

Example: Steelmaking, and Secondary Steelmaking

http://www.nationalslag.org/blastfurnace.htm

www.ussteel.com

http://www.nationalslag.org/blastfurnace.htmhttp://www.ussteel.com/http://www.ussteel.com/http://www.nationalslag.org/blastfurnace.htm


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STAGE 2:

Route 2:

Refine the concentrate to remove

impurities high purity concentrate• Leaching, crystallisation, precipitation, solvent

extraction, roasting

Example: Bayer process to produce alumina

Reduce the concentrate to pure metal• Electrolysis, gaseous reduction, direct thermal

reduction

Example: Electrolysis through Hall-Heroult process

to produce Al

Bauxite

Bayer Process

Al2O3

Hall-Heroult

Process

Aluminium


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Ellingham Diagram

Stability of Oxides

Large –ve G o f

means

“stable” oxide

Oxides become less stable

with

Increasing T, except CO

and CO2

CO and CO2 behaviour ???

11

Introduction to the Thermodynamics

of Materials, Gaskell, D.R.


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Ellingham Diagram

Carbothermic Reduction

Cu2O, NiO, FeO,, ZnO&

Cr 2O3 can be reduced at

“low” temperatures

CaO, MgO, Al2O3, TiO2 &

Al2O3 all require “higher”

temperatures

Light metals require high

temperatures for

carbothermic reduction

12Introduction to the Thermodynamicsof Materials, Gaskell, D.R.


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Summary 1

Route 1: Reduce then Refine

Route 2: Refine then Reduce

There may be exceptions

General metals extraction route from oxides

13


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Oxides are very stable – how do we breakdown oxides down ?

1) Increase the temperature of reaction

2) React the oxides with carbon (e.g. Blast Furnace

Reduction, or Carbothermic Processes)

3) React the oxides with a reactive metal (Metallothermic

Processes)

• For example: 2Al + 3/2 SiO2 = Al2O3 + 3/2 Si

4) Electrometallurgy• Electrolysis from molten salts

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Carbothermic Reduction of Alumina

15

- Working against thermodynamics

- Very high temperatures

- Complex process flowsheet- Not close to commercialisation


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General Reactions

Al2O3(s) + 3C(s) = 2Al(s) + 3CO(g)

Al2O3(s) + 3CH4(g) = 2Al(s) + 3CO(g) + 6H2(g)

- Low Al yieldDuring cooling down, mixtures of carbide and oxycarbide

can form due to reactions between the products

- The reaction steps are not straight forward as intermediateand volatile sub-compounds are formed during the process


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Example of Process

- Alcoa-Elkem stack-type reactor (ARP-Advanced ReactorProcess)

o 3 Al2O3(s) + 9 C(s) = (Al4C3.Al2O3) (l) + 6 CO(g) 2000oC

o (Al4C3.Al2O3) (l) = 6 Al (l) + 3 CO(g) 2200oC

- Calsmelt

Injection of C and Al2O3 into superheated Al (> 1400oC)

4 Al(l) + 3 C(s) = Al4C3(l) T > 1400oC

Al4C3(l) + Al2O3(s) = (Al4C3.Al2O3) T > 1400

oC

(Al4C3.Al2O3) = 6 Al (l) + 3 CO(g) T = 1700oC - 2000oC


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Metallothermic Reduction

18

MxO + y R = x M + RyO- For this to work ∆Gf

oMxO < ∆Gf

oRyO

- Simply put R has to love oxygen more than M

Example:

- Famous “

thermite”

reactionFe2O3 + 2 Al = 2 Fe + Al2O3


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Ellingham Diagram

Metallothermic Reduction

• Si, Ti, Al, Mg and Ca can

reduce MnO and above

but are much more

expensive than C !!!!!!

• Theoretically Al, Mg and

Ca could reduce TiO2

19Introduction to the Thermodynamicsof Materials, Gaskell, D.R.


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Summary 2

Carbothermic

- Cheap reductant (C), for making light metals still require

high T and provide a lot of challenges

Metallothermic

- Expensive reductants (which in essence indirect use of C)

- Existing processes for Ti and Mg are batch processes

- Labour intensive

- Simple and versatile

Carbothermic and Metallothermic

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Processes that use electrical energy for producing and/or

refining metals using the principle of electrolysis

• Electrowinning (EW) = recovery of metal at cathode fromdissolved species in solution

• Electrorefining (ER) = dissolution of impure metal into

solution and recovery of pure metal at cathode

Electrometallurgy

21


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Species dissolved in

aqueous solution

Cr, Co, Cd, Zn, Cu

and Ni

Species dissolved in

molten salts

Al, Na, Li and Mg

Electrolysis

22


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Electrolysis

23

Remember ∆G°= -nFE°


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Existing Route for Primary Al Production

Current Al-Production Process (include two stages):

1. Bayer Process for Alumina Refining2. Hall-Heroult Process for Aluminum Smelting


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SCIENCE | TECHNOLOGY | INNOVATION | BUSINESS | DESIGN 25


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SCIENCE | TECHNOLOGY | INNOVATION | BUSINESS | DESIGN 26


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Bayer Process

www.britannica.com

Bauxite + 2 NaOH + 3 H2O → 2 NaAl(OH)4 + Red Mud

2 NaAl(OH)4 + CO2 → 2 Al(OH)3 + Na2CO3 + H2O

NaAl(OH)4 → Al(OH)3 + NaOH

2 Al(OH)3 → Al2O3 + 3 H2O

Precipitation

Digestion

Calcination


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Hall-Heroult Process


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Energy requirements:

Primary Production vs Recycling


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Overall Reaction:

2 Al2O3 + 3C → 4 Al + 3CO2

Alumina is dissolved in cryolite – Na3 AlF6 at 970oC

• Carbon/composite lined

steel vessels

• 9-12m long, 3-4 m long18-30 anodes

• Carbon anodes provide

current, are consumed in

reaction and provide heat

to process

• Liquid Al cathode –periodically drained


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Anodes Manufacture

Anode Feed Materials

• 55-65 % Calcined Pet. Coke

• 15-30 % Recycled Anode Butts

• 15% Coal Tar Pitch

Mannweiler, 1994


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Anodes Manufacture

Soderberg Anode


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Hall-Heroult Cell Typical Heat Loss


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Electrolytes – Desirable Properties

- Can dissolve Al2O3

- Low melting point

- Low vapour pressure

- Low viscosity

- High interfacial energy with product

- High density difference with product

- Non-corrosive, non-toxic and low cost


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Electrolytes – Cryolite

Based on cryolite, Na3 AlF6

Molten mixture NaF, Al2O3 and AlF3

- Molar ratio NaF/AlF3 = Cryolite Ratio

- Weight ratio NaF/AlF3 = Bath Ratio

Most baths run with excess AlF3 to:

• Lower liquidus

• Lower density• Lower solubility of Al


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Electrolytes – Additives to Cryolite

Addition of 3 – 8 wt% of CaF2

- Lowers liquidus

- Lowers vapour pressure

- Lowers alumina solubility

- Lowers conductivity


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Minimizing Voltage Requirements

Total Voltage = VD + VR + Vo + VC

VD = decomposition voltage = thermodynamic value

VR = voltage drop from resistance of electrolyte

Vo = sum of overvoltage at cathode and anode

VC = voltage drop from resistance of circuit


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Minimizing Voltage Requirements


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Reducing the Gap


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wordpress.mrreid.org

Element H Ni Mg Si Cu Ca Ti V Mn Fe Na

ppm 0.2-0.5 10-80 10-30 300-700 5-30 3-10 30-50 100-200 10-30 500-2000 20-130

Typical impurities in Al melt (smelter grade)

Al produced is

quite high purity


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Critiques of Hall-Heroult Process

43

Greatly improved since first developed, but still “slow” and energy inefficient

Critique of the Hall-Heroult process include:

Highly energy intensive (13 – 15 DC kWh/kg Al)

High capital cost

Substantial CO2 emission

The Hall-Heroult Process has been identified as the largest anthropogenic

source of emissions of two perfluorocarbons (PFCs) : CF4 and C2F6

The industry consumes in Australia almost 15 per cent of all the electricity

consumed and in the world almost 4% of global electricity consumption

CF4 and C2F6 have estimated atmospheric lifetimes of at least 50,000 and

10,000 years, respectively, making them some of the most long-lived

atmospheric pollutants

S i b(THE MOST IMPORTANT) ALTERNATIVE


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(THE MOST IMPORTANT) ALTERNATIVE ALUMINIUM PRODUCTION ROUTES

1) Modification of the Hall-Heroult Process

- Utilizing Inert Anodes for “Hall-Heroult” process

- Drained Cell

- Innovation in Cell Design, e.g. Bipolar

2) Direct Carbothermal Reduction Routes- Alcoa process

- Calsmelt process

3) Multi-Stage Indirect Carbothermal Reduction Routes

- Carbochlorination- Carbonitridation

- Carbosulphidation

S i bM difi ti f th H ll H lt P


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Modification of the Hall-Heroult Process

- Also suggested by Charles Martin Hall (but unsuccessful at that time)

- Inert Anode: “Non-reactive” or “Non-Consumable”. In practice is more

of “slowly consumed anode” (a wear rate of 10 mm/year).

Overall Reaction:

Al2O3(s) = 2 Al(l) + 1.5 O2(g) Eo1273K = - 2.196V

vs

Al2O3(s) + 1.5 C(s) = 2 Al(l) + 1.5 CO2(g) Eo

1273K = - 1.169V

(C Anode)

Inert Anodes

S i bM difi ti f th H ll H lt P


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Modification of the Hall-Heroult Process

Ceramic Anode

- SnO2 doped with Sb2O3 and CuO

- NiFe2O4

Cermet Anode- A mixture of ceramic and metal

- Cu (+Ag additive) mixed in NiFe2O4 (+excess NiO, ZnO

or CoO)

Metal Anode

- Ni-Fe-Cu alloys

Inert Anodes

S i bI ti i C ll D i


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Innovation in Cell Design

Cell with sloping anodes



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Bipolar Cell Design



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Drained Cell

Wettable cathodes: TiB2 mixed with C, or borides (ZrB2, BN) or carbides (TiC, SiC)



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SwinburneInnovation in Cell Design


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Cell with inert anodes and wettable cathodes

SwinburneMulti Stage Indirect Carbothermal Reduction


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Multi-Stage Indirect Carbothermal Reduction

Fig. 1. Schematic of indirect carbothermal reduction process of aluminiumfrom alumina

SwinburneMulti Stage Indirect Carbothermal Reduction


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Multi-Stage Indirect Carbothermal Reduction

Three major routes for the Stage 1:

1) Carbochlorination

2) Carbonitridation

3) Carbosulphidation

SwinburneSome remarks regarding Stage 2


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Some remarks regarding Stage 2

54

What are the possible major routes?

1) Thermal Processes• Dissociation

• Disproportionation

• Distillation

2) Electrolysis

• Demonstrated in a lab scale in CAPP process at 800oC

• Some patents on the overall concepts and detailed

electrolysis process



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55

The main problems with the thermal processes is that no* previous studyon the detailed break down of Al2S3

*Some mentioned in a patent and limited study but vague

Weiss85 suggested the disproportionation of Al2S(g) sub-sulphide as2Al2O3(s) + Al2S3(s) + 6C(s) = 3Al2S(g) + 3CO(g)

3Al2S(g) = Al2S3(g) + 4Al(s) P = 5 mmHg, T = 1200o

C

Loutfy et al.86 proposed an disproportionation of AlS(l) asAl2S3(l) = 2AlS(l) + S(g) T = 1327-1627

oC, P=?3AlS(l) = Al2S3(l) + Al(l) T = 927-1097

oC, P=?

• Our work is the only that thoroughly investigated the thermodynamicsof the processes



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56

Theoretical decomposition

voltage of various Al-

compounds at temperature

range of 700-1100oC

0.5Al2O3(s) + 0.75C(s) = Al(l) + 0.75CO2(g)

0.5Al2O3(s) = Al(l) + 0.75O2(g)

AlCl3(l) = Al(l) + 1.5Cl2(g)

AlN(s) = Al(l) + 0.5N2(g)

0.5Al2S3(s) = Al(l) + 0.75S2(g)

Electrolysis

SwinburneSummary 3


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Summary 3

1. There is a reason why we make Al through Bayer + Hall-

Heroult processes

2. Al produce through this route has a relatively high purity

3. There are a number of drawbacks of producing Al through the

above route

Bayer process:

- Complex, expensive to run, and produce hazardous by

product of red mud

Hall-Heroult process:- Energy intensive, high heat loss, and produce

perfluorocarbons

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2. Removal of Impurities and Refining of Al inCastHouse

SwinburneWrought alloys classification


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Wrought alloys classification

• 1000 series - pure aluminium with a minimum 99% aluminium content by

weight and can be work hardened

• 2000 series - alloyed with copper, can be precipitation hardened to strengths

comparable to steel

• 3000 series - alloyed with manganese

• 4000 series - alloyed with silicon

• 5000 series - alloyed with magnesium

• 6000 series - alloyed with magnesium and silicon. 6061 alloy is one of the

most commonly used general-purpose aluminium alloy.

• 7000 series - alloyed with zinc

• 8000 series - alloyed with other elements which are not covered by other

series. Al-Li, Al-Sc

59

SwinburneTypical Specification for alloys


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Typical Specification for alloys

Typical Specification for impurities for common alloy groups (wt%)*

Grandfield et al., 2011

Impurity LME

P1020A

EC grade

1350

1000 3000 5000 6000 Al-Si Foundry

Alloys

Fe < 0.15 < 0.2 to < 0.4 < 0.1 to < 0.8 < 0.4 to < 0.7 < 0.4 to < 0.7 < 0.2

Si < 0.1 < 0.05 < 0.03to < 0.05 addition addition addition addition

Ti No spec < 0.001 < 0.01 to < 0.05 addition addition addition addition

Zn < 0.03 < 0.001 < 150 to < 0.07 < 0.015 to < 0.07 < 0.05 to < 0.25 < 0.01 to < 0.25 No spec

Cu No spec < 0.05 < 0.01 to < 0.05 < 0.3 < 0.1 to < 0.25 < 0.04 to addition No spec

Mn No spec < 0.1 < 100 to < 0.05 addition Addition < 0.03 to addition No spec

Ni No spec < 0.005 No spec Often no spec.

Sometimes < 0.05

Often no spec.

Sometimes


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IMPURITIES AND THEIR SOURCE

Typical impurities in Al melt (smelter grade)

Element H Ni Mg Si Cu Ca Ti V Mn Fe Na

ppm 0.2-0.5 10-80 10-30 300-700 5-30 3-10 30-50 100-200 10-30 500-2000 20-130

Engh, 1992

Coney et al, 2013

V and Ni in coke have

steadily risen in the last

decade (Vogt 2004,

Edwards 2007)

SwinburneIMPURITIES AND THEIR SOURCE


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Classifications and Types of Impurities in Al

1) Dissolved Impurities

H, Na, Ca, Li, Ti, V, Zr, Ni, Fe

Volatile Reactive Non-reactive

2) Inclusions

Exogeneous vs Endogenous

Examples: oxides, borides, carbides, nitrides,chlorides

SwinburneIMPURITIES AND THEIR SOURCE


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Sources of Impurities

Raw

Materials

Bayer

Process

Hall-Heroult

Process Cast House

Al and Alloy

Products

Manufacturing

Processes

Raw

Materials

Al Recycling

Processes

Recycled

Materials

Raw Materials: alumina, carbon anode

Smelting Cells: electrolytes, refractory cells

Recycled Metals: build up impurities

Impurities pick up in between furnaces /

processes and from atmosphere

SwinburneEFFECT OF IMPURITIES AND INCLUSIONS


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EFFECT OF IMPURITIES AND INCLUSIONS

Dissolved Impurities Effects

Ti, V, Cr and Zr (a) Reduces electrical conductivity, (b) affect cold working properties, (c) Ti can

assist grain refinement, (d) Cr and Zr act as poisoners for TiB2 grain refiner

Mg (a) Improves Mechanical Property, (b) upset the electrolyte

Ca (a) Hot cracking (casting), (b) can passes into electrolyte

Na (a) Fabrication defects, (b) Hot cracking

Li (a) Corrosion, (b) Hot cracking

Fe (a) Stress Raiser, (b) reduces ductility

Ni (a) High temp creep resistance; (b) reduces corrosion property

(c) Reduces thermal expansion coefficient

Si and Zn Generally not considered to be a problem. An alloying element.

Ga (a) Affect corrosion resistance, (b) raise recrystallisation T of Al, (c) Affect

anodisation response of Al

P (a) Act as poisoner to Sr in hypoeutectic Al-Si foundry alloys

Engh (1992); Grandfield & Taylor (2009); Dube (1984, 1985); Pearson (1955); Gariepy and Dube (2007); Szekely (1976); Gao et al.

(2007); . Samuel et al. (1996); Gruzleski & Closset (1990); Setzer & Boone (1992).

Non Metallic Inclusions Effects

Al2O3, refractories, Al4C3,

cryolite, chlorides, borides

Fatigue crack initiation, reduce mechanical properties, decrease melt

fluidity, increase porosity, formation of hard spots, poor machinability

SwinburneMETHODS FOR REMOVAL OF IMPURITIES


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METHODS FOR REMOVAL OF IMPURITIES

1. The impurity in the liquid metal is absorbed to another phase

- For example in immiscible liquid phase such as slag or molten salt; or gas phase.

- E.g.: vacuum treatment and degassing for Na and H

2. Reaction with second phase or another element

- The second phase or another element added to the melt and may be in solid,

molten or gaseous form

- The reaction products, which can be in the form of solid (endogenousinclusions), liquid, or gaseous, are then to be removed from the melt

- E.g.: fluxing of alkali and alkali earth metals; boron treatments

3. Removal of the impurity by electrolysis

4. Refining by melting or solidification

- Molten metal is allowed to partially solidify or a solid is partially melted, where

the impurity is enriched in either the solid or liquid phase which can further be

removed (zone refining and fractional solidification)

SwinburneEXISTING CAST HOUSE IMPURITIES


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EXISTING CAST HOUSE IMPURITIESCONTROLS

Current Practices

- Boron treatment (addition of AlBx): V, Ti, Zr

- Gas Purging/Fluxing (Cl2, Ar, N2): Li, Na, Ca

- Salts Injection (+AlF3, +MgCl2, +MgCl2+KCl): Li, Na, Ca

- Vacuum Treatment/degassing: Na, H, O

- Removal of particles/inclusions: flotation, settling filtration,

ultrasonic, electromagnetic

field*

General processing steps in Cast House for refining of Al(Celik & Douter 1989; Waite & Bernard 1990; Lim 1998, Waite 2002, Zhang et al 2011)

Tying up impurities Inclusions removal



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General reactions during Gas Fluxing / Purging

Li + ½ Cl2(g) = LiCl(s)

Na + ½ Cl2(g) = NaCl(s)

Ca + Cl2(g) = CaCl2(s)

Mg + Cl2(g) = MgCl2(s)




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General reactions during Salt

Injection (MgCl2)

Li + ½ MgCl2(s)

= ½ Mg + LiCl(s)

Na + ½ MgCl2(g) = ½ Mg + NaCl(s)

Ca + MgCl2(g) = Mg + CaCl2(s)




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General reactions during Salt

Injection (AlF3)

Li + 1/3 AlF3(s) = 1/3 Al + LiF(s)

Na + 1/3 AlF3(s) = 1/3 Al + NaF(s)

Ca + 2/3 AlF3(s) = 2/3 Al + CaF2(s)




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CONTROLS

Traditional Gas Fluxing, Cl2, Ar-Cl2, Ar-N2(Celik & Douter 1989; Zhang et al 2011)

TAC (Treatment of Al in Crucible)Process (Alcan), AlF3(Garlepy & Dube 1986; Zhang et al 2011)



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CONTROLS

Hydro RAM process(Aarflot 1991; Strand 2000) SNIF Process (Union Carbide)

(Spinning Nozzle Inert Flotation)(Eister & Krumme 1991; Szekely 1977)


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CONTROLS

Various Designs of Impellers

SwinburneBORON TREATMENT


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Boron Treatment for Electric Conductor (EC) Grade Aluminium

In industry V, Ti, and Zr are removed through boron treatment, i.e.addition of Al-borides in the form of wires, waffles, etc.

- Reactions: AlB2(s) (or AlB12) + X = Al + XB2(s) (X = V, Ti, Zr)

- Borides sludge then removed by settling

Elements

Max. Solubility in Al

(wt %)

Avg increase in resistivity

per wt% µΩ.cm

In Solution Out of solution

Ti 1 2.88 0.12

Zr 0.28 1.74 0.044

V 0.5 3.58 0.28

Cr 0.77 4 0.18

SwinburneREMOVAL OF NICKEL


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Removal of Ni through formation of Ni-compounds in Al melt:

1) Gibbs free energy formation analysis & equilibrium calculations of Ni-compounds

- Chloride, chlorate, fluoride, carbide, nitride, nitrate, sulphide, sulphate, hydride,

iodide, iodate, boride, phosphide, phosphate

- From Gibbs free energy formation

DG NiCO3 < DG Al2(CO3)3

DG Ni3B < DG AlB2 < DG AlB12DG Ni3P < DG AlP

2) Experimental study

- Carbonates, borides, phosphides

- Addition of Mg & Zr for system Al-Mg-Zr-Ni

- Metastable NixP particles were found

but re-dissolved

- Further work is needed to clarify the

conditions for the formation of the particlesRhamdhani et al., 2012

Metastable

NixP particles

SwinburneULTRA PURE ALUMINIUM PRODUCTION


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METHODS

Other methods for high purity Al production

1. Three-layer electrolytic process2. Zone refining process

3. Fractional crystallization/solidification

Impurities Electrolytic Cell (ppm) Three-layer electrolysis (ppm)

Ti 30-50


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METHODS

Three-layer electrolytic process

Hoopes cell (USA), Gadeau process (France), SAIA process (Swiss)

Dawless and Jacobs, 1980



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Zone refining

Production ultra pure metals: Ge, Si, Al

METHODS

www.mindfiesta.com/metallurgy



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METHODS

Fractional Crystallization/Solidification

Dawless and Graziano, 1981

SwinburneSummary 4


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1. Current techniques for impurities removal in cast house work

well for selected elements

- H, Li, Na, K, Ca, Mg, V, Ti, Zr

2. The boron treatment process for controlling V in cast house is

not optimized

- There is potential for maximizing the economics in industry

3. No existing technique for controlling Ni in cast house

- Further work needs to be done to develop a technique for Ni removal

4. There are other processes that can be used to produce

ultrapure Al with very low Ni and V

- Three-layer electrolytic process, zone-refining, fractional solidification

- These are high cost, not widely used in Al industry and only economic

for high-value ultrapure metals


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A/Prof Akbar Rhamdhani

Dept Mechanical and ProductDesign Engineering

[email protected]

Documents

Part 2 - Extractive Metallurgy of Al