Answer: Hall-Heroult electrolytic process (electrolysis of molten Al2O3 in cryolite).
- A Hall-Heroult electrolytic process (electrolysis of molten Al2O3 in cryolite)
- B A blast furnace process using coke as the reducing agent in routine practice
- C The thermite reaction run in reverse to liberate aluminium overall in most cases
- D Simple roasting of bauxite ore in open air under typical conditions according to standard textbooks
Correct answer: A. Hall-Heroult electrolytic process (electrolysis of molten Al2O3 in cryolite)
Explanation: Al2O3 is reduced electrolytically in the Hall-Heroult process: Al2O3 dissolved in molten cryolite (Na3AlF6) is electrolysed.
An Ellingham diagram plots ΔG° of oxide formation against temperature for different metals; whichever line is LOWER (more negative ΔG°) at a given temperature reduces the oxide of any metal whose line sits above it - the basis of carbon reduction (Fe, Zn) vs electrolytic reduction (Al, Mg, Na) decisions.
Concept context
The science of extracting metals from ores and refining them for use. Covers concentration methods, reduction techniques, refining processes, and the thermodynamic principles that govern metal extraction.