Question

AOD process is mainly used in

• A. Copper production
• B. Aluminium refining
• C. Stainless steel refining
• D. Zinc extraction

Hint:

Using argon dilution in the AOD process allows the steelmaker to utilize cheaper high-carbon ferrochromium instead of expensive low-carbon ferrochromium, vastly improving process economics.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks to identify the industrial metal refining process where the Argon Oxygen Decarburization (AOD) process is utilized.

Step 2: Key Formula or Approach:
The primary challenge in manufacturing stainless steel is to remove carbon (decarburize) to very low levels without oxidizing and losing valuable chromium (Cr) to the slag.
The competitive oxidation reactions are:
\[ 2\underline{\text{Cr}} + 3\underline{\text{O}} \rightarrow \text{Cr}_2\text{O}_3\text{(s)} \]
\[ \underline{\text{C}} + \underline{\text{O}} \rightarrow \text{CO(g)} \]

Step 3: Detailed Explanation:

• Thermodynamics of AOD: The equilibrium constant for the decarburization reaction is:
\[ K = \frac{P_{\text{CO}}}{a_{\text{C}} \cdot a_{\text{O}}} \]
By diluting the oxygen injection gas with an inert gas like Argon, the partial pressure of carbon monoxide (\( P_{\text{CO}} \)) inside the rising bubbles is significantly reduced.
This low \( P_{\text{CO}} \) shifts the chemical equilibrium to favor the decarburization reaction over chromium oxidation, allowing carbon to be removed while preserving chromium in the steel.

• Process Sequence: The AOD converter operates by blowing a mixture of oxygen and argon (or nitrogen) through submerged tuyeres.
The ratio of \( \text{O}_2 \text{ to } \text{Ar} \) is progressively changed from \( 3:1 \) at the start to \( 1:3 \) near the end of the process to achieve ultra-low carbon levels (\( \lt 0.03\text{ wt\%} \)).

• Incorrect Options: AOD is not utilized in non-ferrous metal extraction or refining like copper (Option A), aluminium (Option B), or zinc (Option D).


Step 4: Final Answer:
Therefore, the AOD process is mainly used in stainless steel refining, which matches Option (C).