In the extraction of metallic Zn from calamine ore \((ZnCO_3)\) following steps are involved:

(A) Distillation of impure Zn

(B) Calcination of the ore

(C) Hydraulic washing of ore

(D) Reduction of ZnO using coke

Choose the correct order of steps from the options given below:

(C), (B), (D), (A)

The correct answer is option 2. (C), (B), (D), (A).

Let us dive into the detailed steps involved in the extraction of metallic zinc from calamine ore \((ZnCO_3)\), focusing on why the processes are carried out in a specific order.

C. Hydraulic Washing of Ore

Hydraulic washing is a concentration technique used to remove the lighter, unwanted materials such as sand, dust, and clay from the ore. This process is also known as gravity separation and is typically the first step in metal extraction. Since calamine ore (ZnCO₃) is found mixed with various impurities in the natural environment, this method helps concentrate the ore by exploiting the difference in densities between the metal-containing ore and the impurities.

Why this step first: Before any chemical treatment (calcination or reduction) can be done, it's essential to remove unwanted impurities to make the process more efficient.

B. Calcination of the Ore

Calcination is a thermal decomposition process where the concentrated zinc carbonate \((ZnCO₃)\) ore is heated in the absence of air to remove volatile components like carbon dioxide \((CO₂)\). The purpose of this step is to convert zinc carbonate into zinc oxide \((ZnO)\):

\(ZnCO_3 \overset{{\text{heat}}}{\longrightarrow} ZnO + CO_2\)

Why is calcination necessary: Zinc carbonate is not easily reduced by coke, so it needs to be converted to zinc oxide, which can then be reduced to zinc metal in the next step.

D. Reduction of ZnO Using Coke

Once the ore is converted to zinc oxide \((ZnO)\), it is ready for reduction. In this step, zinc oxide is mixed with coke (carbon) and heated in a furnace. The coke acts as a reducing agent, reducing zinc oxide to metallic zinc. The reduction reaction proceeds as follows:

\(ZnO + C \overset{{\text{heat}}}{\longrightarrow} Zn + CO\)

Carbon (in coke) reacts with zinc oxide, removing oxygen and leaving behind metallic zinc.

Why is coke used: Coke is an effective reducing agent that removes oxygen from the zinc oxide, leaving behind pure zinc.

A. Distillation of Impure Zn

The zinc obtained from the reduction process still contains some impurities, especially due to the presence of carbon and other substances from the furnace. To purify the zinc, distillation is used. Zinc has a relatively low boiling point (907°C) compared to other metals. The impure zinc is heated until it vaporizes, and then the vapors are condensed to obtain pure zinc

Why distillation: Since zinc vaporizes at a lower temperature than most impurities, distillation effectively separates pure zinc from unwanted substances. This step ensures the zinc obtained is in its pure form.

The correct order of steps for extracting zinc from calamine ore is:

(C) Hydraulic washing of ore → (B) Calcination of the ore → (D) Reduction of ZnO using coke → (A) Distillation of impure Zn

Thus, the correct answer is Option (2).