Leaching is used for the concentration of

Options

A. Ag
B. Au
C. Al
D. All of these

Answer

**Step-by-Step Solution:**

1. **Understanding Leaching:**
Leaching is a process used to extract metals from their ores by treating them with suitable leaching agents. The leaching agents dissolve the desired metal, leaving behind the impurities.

2. **Identifying Leaching Agents:**
Common leaching agents include sodium hydroxide (NaOH), sodium cyanide (NaCN), and potassium cyanide (KCN). These agents help in solubilizing the metal from its ore.

3. **Leaching Process for Aluminium:**
- In the case of aluminium extraction, alumina (Al2O3) is treated with sodium hydroxide.
- The reaction is as follows:
\[ \text{Al}_2\text{O}_3 + 2 \text{NaOH} + 3 \text{H}_2\text{O} \rightarrow 2 \text{NaAl(OH)}_4 \]
- Here, sodium aluminate is formed, and impurities remain insoluble.

4. **Leaching Process for Silver:**
- For silver extraction, silver ore is treated with sodium cyanide.
- The reaction is:
\[ \text{Ag}_2\text{S} + 4 \text{NaCN} \rightarrow 2 \text{NaAg(CN)}_2 + \text{Na}_2\text{S} \]
- Silver is solubilized as sodium argentocyanide, while impurities remain insoluble.

5. **Leaching Process for Gold:**
- Similarly, gold ore is treated with sodium cyanide.
- The reaction is:
\[ 4 \text{Au} + 8 \text{NaCN} + 2 \text{H}_2\text{O} \rightarrow 4 \text{NaAu(CN)}_2 + 2 \text{NaOH} \]
- Gold is solubilized as sodium auricyanide, with impurities left behind.

6. **Conclusion:**
Leaching is used for the concentration of metals such as silver, gold, and aluminium. Therefore, the correct answer to the question is "all of these."

**Final Answer:**
Leaching is used for the concentration of silver, gold, and aluminium.

---