Transcript Aluminum extraction from Feldspar

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
Surface type 1
Microcline1
Andesine
Bytownite
Bronzite
Augite1
Augite3
Serpentine
Gypsum
Calcite
Dolomite
Kaolinite
Illite
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
CaAl2Si2O8
Bytownite
70-90% anorthite, 10-30% albite
Labradorite
50-70% anorthite, 30-50% albite
Andesine
30-50% anorthite, 50-70% albite
Oligoclase
10-30% anorthite, 70-90% albite
Albite
NaAlSi3O8
Orthoclase feldspar
Microcline
KAlSi3O8
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, CO2 “blown through”
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Aqueous CO2 → carbonic acid, neutralizes alkali
AlOH precipitates
CO2 gas released
NaOH recycled
Calcination:
2 AlOH + O2 → Al2O3 + H2O
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Hall-Héroult process
Alumina is not conductive, cryolite is catalyst
Na3AlF6 dissociates into 3 Na+ AlF632 Al2O3 → 4 Al + 3 O2
Some carbon of the anode will form CO2
Anode regeneration: RWGS
H2 + CO2 → H2O + CO
H2 + CO → H2O + C
• Bake soot under pressure
to form graphite
• recover hydrogen
reverse fuel cell:
2 H2O → 2 H2 + O2
Bytownite to Alumina
• Bytownite is an alkali feldspar so an alkali like sodium
hydroxide will not dissolve it. Hydrochloric acid will.
• 1.8 Al3+, 0.8 Ca2+, 0.2 Na+, 2.2 SiO2
• 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 + O2 → Al2O3 + H2O
• NaCl, KCl, CaCl2 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
NH3 + H2O ↔ NH4+(aq) + OH-(aq)
NH4+ (aq) + Cl-(aq) ↔ NH4Cl(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 H2O → 2 NaOH + H2 + 2 Cl
H + Cl → HCl
K+ & Ca+ will not cross membrane
KOH & CaOH in diaphragm cell
Precipitating Silica
SiO2 or Si(OH)4