Problem 15 - Chemistry in 30 days

Question

Calcination is the process of heating the ore (a) in inert gas (b) in the presence of air (c) in the absence of air (d) in the presence of \(\mathrm{CaO}\) and \(\mathrm{MgO}\)

Step-by-Step Solution

Answer

(c) in the absence of air

Step 1: Explanation of Calcination

Calcination is a thermal treatment process applied to ores and other solid materials to bring about a thermal decomposition, phase transition, or removal of a volatile fraction.

Step 2: Determine the Correct Condition

Calcination specifically occurs in the absence or limited supply of air or oxygen. The primary purpose is to remove volatile substances, moisture, or to cause thermal decomposition without combustion.

Step 3: Examine the Options

Look at the list of conditions given: (a) in inert gas (b) in the presence of air (c) in the absence of air (d) in the presence of CaO and MgO We know that during calcination air is limited or absent, matching option (c).

Key Concepts

Thermal Decomposition

Thermal decomposition is a process where heat is used to break down a compound into simpler substances. During calcination, the heat energy causes this breakdown in the ore.
- No new energy source, like combustion, is needed. - The main purpose is to transform the material into a simpler form by removing volatile components.
When a compound undergoes thermal decomposition, it often forms solid products and gases. This process is endothermic, meaning it requires continuous input of energy.
An example in calcination is when a carbonate ore decomposes to form an oxide and carbon dioxide.
Understanding thermal decomposition helps predict the changes in chemical structure during calcination.

Phase Transition

Phase transition involves changing the physical state of a material without altering its chemical composition. In calcination, this transition affects the solid-state materials.
- Materials can change from solid to another form, like a powder. - Often occurs alongside thermal decomposition.
The heat supplied during calcination might induce these phase changes by disrupting the structural integrity of the ore.
For example, a crystalline material might convert into a more stable amorphous form, which can significantly alter its physical properties.
Recognizing phase transitions is crucial because it can affect the extraction and further processing of metals.

Removal of Volatile Substances

One main goal of calcination is to remove volatile substances from the ore.
- Volatile substances include moisture and gases embedded within the material. - Their removal is essential to purify the material.
Heating the ore causes these volatile compounds to evaporate or sublimate—turn directly from solid to gas.
Eliminating these substances not only purifies the ore but can also prevent unwanted chemical reactions during later processing stages.
By emphasizing the removal of volatile substances, calcination becomes a preparatory step, optimizing the material for subsequent refining.