Aluminum extraction from Feldspar Al 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.
Plagioclase feldspar Orthoclase feldspar
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” • Aqueous CO2→carbonic acid, neutralizes alkali • AlOH precipitates • CO2 gas released • NaOH recycled • Calcination: 2 AlOH + O2→ Al2O3 + H2O
Hall-Héroult process • Alumina is not conductive, cryolite is catalyst • Na3AlF6 dissociates into 3 Na+ AlF63- • 2 Al2O3 → 4 Al + 3 O2 • Some carbon of the anode will form CO2 • Anode regeneration: RWGSH2 + CO2 → H2O + COH2 + CO → H2O + C • Bake soot under pressureto form graphite • recover hydrogenreverse 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 processit 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