Aluminum Extraction from Feldspar: Bytownite Process

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Al

Aluminum extraction from

Feldspar

by Robert Dyck

Ardeco Consulting Ltd.

Traditional ore

Aluminum ore on Earth is bauxite

Bauxite is formed by tropical rain forests:

• igneous minerals weathered by water

• tropical ecosystem depletes their needs

 iron oxide, silicon dioxide, aluminum oxide

We aren’t going to find a rainforest on Mars.

MGS-TES

Microcline1

Andesine

Bytownite

Bronzite

Augite1

Augite3

Serpentine

Gypsum

Calcite

Dolomite

Kaolinite

Illite

Surface type 1

Model-derived modes (%)

5.8

22

21.5

5.4

12.4

11.3

4.8

1.8

3.7

0.9

2.4

9.9

RMS error

(emissivity) = 0.179

Surface type 2

Microcline1

Bytownite

Actinolite

Muscovite

Bronzite

Augite1

Forsterite

Gypsum

Dolomite

Fe-smectite

Illite

Obsidian Glass

Model derived modes (%)

5.7

27

6.1

5.7

1.6

8.4

2.9

4.5

3.3

9.2

2.2

22.8

RMS error

(emissivity)= 0.089

Plagioclase feldspar

Anorthite

Bytownite

Labradorite

Andesine

Oligoclase

Albite

CaAl

2

Si

2

O

8

70-90% anorthite, 10-30% albite

50-70% anorthite, 30-50% albite

30-50% anorthite, 50-70% albite

10-30% anorthite, 70-90% albite

NaAlSi

3

O

8

Orthoclase feldspar

Microcline KAlSi

3

O

8

Traditional smelting

• Bayer process extracts/purifies alumina from ore

– chemical

• Sodium hydroxide, carbon dioxide

• Hall-Héroult process de-oxidizes alumina into metal

– electrolysis

• cryolite

Bayer process

• Aluminum & silicon oxides dissolve in alkali NaOH

• Iron oxide and others don’t (red mud)

• Solution drawn off, CO

2

“blown through”

• Aqueous CO

2

→ carbonic acid, neutralizes alkali

• AlOH precipitates

• CO

2 gas released

• NaOH recycled

• Calcination:

2 AlOH + O

2

→ Al

2

O

3

+ H

2

O

HallHéroult process

• Alumina is not conductive, cryolite is catalyst

• Na

3

AlF

6

• 2 Al

2

O

3 dissociates into 3 Na + AlF

6

3-

→ 4 Al + 3 O

2

• Some carbon of the anode will form CO

2

• Anode regeneration: RWGS

H

2

H

2

+ CO

2

→ H

+ CO → H

2

2

O + CO

O + C

• Bake soot under pressure to form graphite

• recover hydrogen reverse fuel cell:

2 H

2

O → 2 H

2

+ O

2

Bytownite to Alumina

• Bytownite is an alkali feldspar so an alkali like sodium hydroxide will not dissolve it. Hydrochloric acid will.

• 1.8 Al 3+ , 0.8 Ca 2+ , 0.2 Na + , 2.2 SiO

2

• Ammonia will raise pH, and evaporate when released

• Ammonium chloride pH 5.0 @ 10%

• AlOH will between pH 4.5 and 9.2

• AlOH can be calicinated: 2 AlOH + O

2

• NaCl, KCl, CaCl

2

→ Al

2

O

3

+ H

2

O are salts, they will remain in solution

• Silica scale is a problem in the Bayer process it will be more so with bytownite

Side reactions: ammonium chloride

NH

3

NH

4

+

+ H

2

O ↔ NH

4

+ (aq) + OH (aq)

(aq) + Cl (aq) ↔ NH

4

Cl(s)

Ammonium chloride can be contained with a spray scrubber

Acid Recycling

Working solutions have to be recycled.

Hydrochloric acid will have to be remade from salt.

Electrolysis across a membrane:

2 NaCl + 2 H

2

O → 2 NaOH + H

2

H + Cl → HCl

+ 2 Cl

K + & Ca + will not cross membrane

KOH & CaOH in diaphragm cell

Precipitating Silica

SiO

2 or Si(OH)

4

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