Question:medium

Which of the reaction is suitable for concentrating ore by leaching process?

Updated On: Mar 23, 2026
  • \(2 Cu _2 S +3 O _2 \rightarrow 2 Cu _2 O +2 SO _2\)
  • \(Fe _3 O _4+ CO \rightarrow 3 FeO + CO _2\)
  • \(Al _2 O _3+2 NaOH +3 H _2 O \rightarrow 2 Na \left[ Al ( OH )_4\right]\)
  • \(Al _2 O _3+6 Mg \rightarrow 6 MgO +4 Al\)
Show Solution

The Correct Option is C

Solution and Explanation

To determine which reaction is suitable for concentrating ore by leaching, we need to understand the concept of leaching in metallurgy. Leaching is a process used to extract metals from their ores by dissolving the ore in a liquid (usually a solvent) to form a solution, from which the metal can be easily extracted.

The correct answer is the reaction:

\(Al_2O_3 + 2 NaOH + 3 H_2O \rightarrow 2 Na\left[Al(OH)_4\right]\)

Here's the step-by-step explanation:

  1. This reaction represents the Bayer process, which is an example of hydrometallurgy. In this process, the ore of aluminum, bauxite (\(Al_2O_3\)), is digested in a concentrated solution of sodium hydroxide (\(NaOH\)).
  2. The aluminum oxide in bauxite dissolves in the sodium hydroxide solution to form a soluble complex, sodium aluminate (\(Na[Al(OH)_4]\)), while impurities remain in solid form and can be removed by filtration. This step is crucial because it separates aluminum from impurities.
  3. The resulting sodium aluminate solution is further processed to recover aluminum hydroxide, which can then be thermally decomposed to produce pure aluminum oxide.

Let's consider why the other options are not suitable for the leaching process:

  • \(2 Cu_2S + 3 O_2 \rightarrow 2 Cu_2O + 2 SO_2\): This is a smelting or roasting process where copper sulfide is converted to copper oxide; it is not suitable for leaching because it involves high-temperature treatment rather than solution-based extraction.
  • \(Fe_3O_4 + CO \rightarrow 3 FeO + CO_2\): This represents a reduction process using carbon monoxide; typically involved in blast furnaces for iron extraction, not leaching.
  • \(Al_2O_3 + 6 Mg \rightarrow 6 MgO + 4 Al\): This reaction is a reduction of alumina using magnesium, known as the Goldschmidt process. It's a pyrometallurgical process and not leaching.

Thus, \(Al_2O_3 + 2 NaOH + 3 H_2O \rightarrow 2 Na\left[Al(OH)_4\right]\) is the correct reaction for ore concentration by leaching.

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