Answer: Selectively prevent certain minerals from floating (e.g., NaCN depresses ZnS allowing PbS to float separately).
- A Selectively prevent certain minerals from floating (e.g., NaCN depresses ZnS allowing PbS to float separately)
- B Promote every mineral present in the ore to float together indiscriminately in the majority of cases studied
- C Generally lower the pH of the flotation cell without affecting any mineral surface as widely reported in standard practice
- D Raise the temperature of the flotation cell to speed up bubble formation under most conditions encountered
Correct answer: A. Selectively prevent certain minerals from floating (e.g., NaCN depresses ZnS allowing PbS to float separately)
Explanation: Depressants (NaCN, ZnSO<sub>4</sub>) make certain mineral surfaces hydrophilic, preventing them from floating, allowing selective separation of one sulfide mineral from another.
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.