Extraction of Iron in Blast Furnace Temperature Zones

To determine the correct statements regarding the extraction of iron in a blast furnace operating in the temperature range of $900 - 1500\text{ K}$, we analyze each option based on the chemical reactions and metallurgical principles involved:

1. Option (A): Removal of Silicate Impurity by Limestone In the temperature range of $900 - 1500\text{ K}$, limestone ($\text{CaCO}_3$) decomposes thermally to yield calcium oxide ($\text{CaO}$), which acts as a basic flux: $\text{CaCO}_3(s) \xrightarrow{\Delta} \text{CaO}(s) + \text{CO}_2(g)$ The basic flux $\text{CaO}$ reacts with the acidic silicate impurity ($\text{SiO}_2$) present in the ore to form a molten slag of calcium silicate ($\text{CaSiO}_3$): $\text{CaO}(s) + \text{SiO}_2(s) \rightarrow \text{CaSiO}_3(l) \quad \text{(slag)}$ Therefore, Statement (A) is correct.

2. Option (B): Carbon Content in Pig Iron The iron collected directly from the bottom zone of the blast furnace is known as pig iron. It contains approximately $4\%$ carbon along with minor amounts of other impurities such as $\text{S}$, $\text{P}$, $\text{Si}$, and $\text{Mn}$. Therefore, Statement (B) is correct.

3. Option (C): Conversion of $\text{CO}_2$ to $\text{CO}$ by Coke In the middle-to-lower temperature region ($900 - 1500\text{ K}$) of the furnace, carbon (coke) reduces carbon dioxide ($\text{CO}_2$) to carbon monoxide ($\text{CO}$), which acts as a primary reducing agent: $\text{C}(s) + \text{CO}_2(g) \rightarrow 2\text{CO}(g)$ Therefore, Statement (C) is correct.

4. Option (D): Composition of Exhaust Gases The exhaust gas mixture escaping from the top of the blast furnace predominantly consists of carbon monoxide ($\text{CO}$), carbon dioxide ($\text{CO}_2$), and nitrogen gas ($\text{N}_2$) introduced via the hot air blast. Nitrogen dioxide ($\text{NO}_2$) is not a major constituent of the exhaust gases. Therefore, Statement (D) is incorrect.

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