Answer: React with gangue to form fusible slag that can be separated from the metal.
- A React with gangue to form fusible slag that can be separated from the metal
- B Chemically reduce the metal oxide directly to the free metal in the majority of cases studied
- C Deliberately oxidise the molten metal during the smelting stage as widely reported
- D Lower the overall furnace temperature needed for smelting in standard practice
Correct answer: A. React with gangue to form fusible slag that can be separated from the metal
Explanation: Flux (e.g., limestone for silica gangue) reacts with gangue to form a low-melting slag that floats on molten metal.
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.