Which of the following metals can be extracted through alkali leaching technique?

Leaching is a chemical concentration process where the ore is selectively dissolved in a suitable chemical reagent while the gangue (impurities) remains insoluble.

Alkali Leaching utilizes a strong aqueous base (such as NaOH). For a metal or its ore to dissolve in a strong alkali, it must exhibit amphoteric behavior to form a soluble complex.

Evaluation of the Options:

• A) Sn (Tin)

  Tin is a distinctly amphoteric metal. Its ores (like Cassiterite, $$SnO_2$$) react smoothly with concentrated aqueous sodium hydroxide ($$NaOH$$) to form a soluble sodium stannate complex, leaving insoluble gangue behind:

• B) Pb (Lead)

  While lead oxides are amphoteric, lead ores (primarily Galena, $$PbS$$) are typically concentrated via froth floatation and extracted through roasting/smelting rather than commercial alkali leaching loops.

• C) Au (Gold)

  Gold is a noble metal and is extracted via Cyanide Leaching (MacArthur-Forrest Process) using dilute $$NaCN$$ or $$KCN$$ in the presence of oxygen, not simple alkali leaching.

• D) Cu (Copper)

  Low-grade copper ores are typically extracted using Acid Leaching (with dilute sulfuric acid, or Ammonia Leaching, rather than an alkaline sodium hydroxide treatment.