The ore of which metal is concentrated by leaching?
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Associate the concentration method with the type of ore:
- \textbf{Sulphide ores} (e.g., ZnS, CuFeS\(_2\), PbS): Froth Flotation.
- \textbf{Oxide ores}: Gravity separation (if dense), Magnetic separation (if magnetic, like Fe\(_3\)O\(_4\)), or Leaching (if amphoteric, like Al\(_2\)O\(_3\)).
- \textbf{Noble metals} (Ag, Au): Leaching with cyanide (MacArthur-Forrest process).
Leaching is a chemical method of concentrating an ore. It involves treating the powdered ore with a reagent that selectively dissolves the desired metal or its compound, leaving the impurities (gangue) undissolved.
Let's consider the options: Zn (Zinc): The main ore of zinc is zinc blende (ZnS). It is typically concentrated by froth flotation, which is a physical method based on differences in wettability. Cu (Copper): The main ore of copper is copper pyrites (CuFeS\(_2\)). It is also concentrated by froth flotation. Al (Aluminium): The main ore of aluminium is bauxite (Al\(_2\)O\(_3\)\(\cdot\)xH\(_2\)O). Bauxite is concentrated by the Baeyer's process, which is a leaching process. The powdered ore is treated with a hot, concentrated solution of sodium hydroxide (NaOH). The amphoteric aluminium oxide dissolves to form sodium aluminate, while impurities like iron oxides and silica remain undissolved.
Reaction: \( \text{Al}_2\text{O}_3(s) + 2\text{NaOH}(aq) + 3\text{H}_2\text{O}(l) \rightarrow 2\text{Na}[\text{Al(OH)}_4](aq) \).
The solution is then filtered, and pure hydrated alumina is precipitated, which is then heated to get pure alumina. Fe (Iron): The main ores of iron are hematite (Fe\(_2\)O\(_3\)) and magnetite (Fe\(_3\)O\(_4\)). These are typically concentrated by physical methods like hydraulic washing or magnetic separation (for magnetite).
Therefore, aluminium ore is the one concentrated by leaching among the given options.
