Answer: Low-grade ores by dissolving the metal selectively (e.g., gold in NaCN solution, Al 2 O 3 in NaOH).
- A Low-grade ores by dissolving the metal selectively (e.g., gold in NaCN solution, Al<sub>2</sub>O<sub>3</sub> in NaOH)
- B Every type of ore that exists, regardless of grade or actual metal content present during normal conditions
- C Mainly sulfide ores, which in practice are concentrated instead by froth flotation as generally observed
- D Mainly ores that are already high-grade and therefore need no further concentration step in typical laboratory settings
Correct answer: A. Low-grade ores by dissolving the metal selectively (e.g., gold in NaCN solution, Al<sub>2</sub>O<sub>3</sub> in NaOH)
Explanation: Leaching dissolves the metal from the ore matrix; e.g., Bayer process (Al<sub>2</sub>O<sub>3</sub> in NaOH), cyanide leaching (Au in NaCN/O<sub>2</sub>).
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.