Statements on Metallurgical Processes in Metal Extraction

To determine the correct statement(s) regarding the metallurgical extraction of metals, we analyze each option individually:

1. Option (A):

   • Malachite is a basic copper carbonate mineral with the chemical formula $\text{CuCO}_3 \cdot \text{Cu(OH)}_2$.
   • Upon heating (calcination/roasting), it decomposes into copper(II) oxide ($\text{CuO}$), carbon dioxide, and water vapor: $\text{CuCO}_3 \cdot \text{Cu(OH)}_2 \xrightarrow{\Delta} 2\text{CuO} + \text{CO}_2 \uparrow + \text{H}_2\text{O} \uparrow$
   • $\text{CuO}$ is known as Tenorite, whereas Cuprite is copper(I) oxide ($\text{Cu}_2\text{O}$).
   • Therefore, Statement (A) is incorrect.

2. Option (B):

   • Calamine is zinc carbonate ($\text{ZnCO}_3$).
   • Calcination of calamine involves thermal decomposition in the absence or limited supply of oxygen: $\text{ZnCO}_3 \xrightarrow{\Delta} \text{ZnO} + \text{CO}_2 \uparrow$
   • The product $\text{ZnO}$ (zinc oxide) is mineralogically known as Zincite.
   • Therefore, Statement (B) is correct.

3. Option (C):

   • Copper pyrites ($\text{CuFeS}_2$) contains iron as a major impurity in the form of iron sulfide ($\text{FeS}$).
   • During heating in a reverberatory furnace, iron sulfide oxidizes to iron(II) oxide ($\text{FeO}$): $2\text{FeS} + 3\text{O}_2 \rightarrow 2\text{FeO} + 2\text{SO}_2 \uparrow$
   • Silica ($\text{SiO}_2$) is added as an acidic flux which reacts with the basic oxide $\text{FeO}$ to form a fusible slag, iron silicate ($\text{FeSiO}_3$): $\text{FeO} + \text{SiO}_2 \rightarrow \text{FeSiO}_3 \quad (\text{Slag})$
   • This allows iron to be removed as slag from the matte.
   • Therefore, Statement (C) is correct.

4. Option (D):

   • In the MacArthur-Forrest cyanide process (hydrometallurgy), silver is extracted by leaching the ore or impure silver with an aqueous solution of potassium cyanide ($\text{KCN}$) in the presence of atmospheric oxygen, forming a soluble complex: $4\text{Ag} + 8\text{KCN} + 2\text{H}_2\text{O} + \text{O}_2 \rightarrow 4\text{K}[\text{Ag(CN)}_2] + 4\text{KOH}$
   • Pure silver is subsequently recovered from the complex by displacement reduction using a more electropositive metal, zinc ($\text{Zn}$): $2\text{K}[\text{Ag(CN)}_2] + \text{Zn} \rightarrow \text{K}_2[\text{Zn(CN)}_4] + 2\text{Ag} \downarrow$
   • Therefore, Statement (D) is correct.

Conclusion: The correct statements are (B), (C), and (D).