Question

In the metallurgy of iron, the upper layer obtained in the bottom of the blast furnace mainly _____
(a)- $CaSi{{O}_{3}}$
(b)- Spongy iron
(c)- $F{{e}_{2}}{{O}_{3}}$
(d)- $FeSi{{O}_{3}}$

Answer 1

Haematite is an oxide ore of iron. In extracting the ore, there is a step wise step method followed that includes concentration of ore, calcination, and smelting. The calcined ore is reduced with carbon. Slag is lighter in weight and is separated from the slag hole in the bottom layer of the blast furnace.

Complete step by step answer:
The main ore that is used for the extraction of Iron is Haematite. It involves the following steps:
-Concentration: First, the ore is crushed in jaw crushers. Now the crushed ore is concentrated using the gravity separation process which involves the washing of crushed ore in a stream of water where lighter sand and clay particles are washed away but the heavier ore particles will settle down. Froth flotation process is used in the case of sulfide ore for concentration.
-Calcination: Now the calcination process takes place i.e., heated strongly the ore in the presence of a limited supply of air in a reverberatory furnace. During calcination, the following changes occur.
i)- Moisture is removed
ii)- Impurities of sulfur, phosphorus, and arsenic escape as their volatile oxides.
$\begin{aligned} & {{S}_{8}}+8{{O}_{2}}\to 8S{{O}_{2}}\uparrow \\\ & {{P}_{4}}+5{{O}_{2}}\to {{P}_{4}}{{O}_{10}}\uparrow \\\ & 2As+5{{O}_{2}}\to A{{s}_{2}}{{O}_{5}}\uparrow \\\ \end{aligned}$
iii)- Ferrous oxide is oxidized to ferric oxide thereby preventing the loss of iron as slag during melting.
$4FeO(s)+{{O}_{2}}(g)\to 2F{{e}_{2}}{{O}_{3}}(s)$
iv)- The ore becomes porous and hence is more suitable for reduction to the metallic state.
$\begin{aligned} & FeC{{O}_{3}}(s)\to FeO(s)+C{{O}_{2}}(g) \\\ & 4FeO(s)+{{O}_{2}}\to 2F{{e}_{2}}{{O}_{3}}(s) \\\ \end{aligned}$
-Smelting: Reducing the calcined ore with carbon i.e. smelted in a blast furnace. It is a tall cylindrical furnace made of steel and lined inside with fire bricks. At the top, the furnace is also provided with an outlet for waste gases. At the base, the furnace is provided with:
(i)- Small pipes called tuyeres through which a blast of hot air is admitted
(ii)- A tapping hole for withdrawal molten iron
(iii)- A slag hole for withdrawing
-From the top through cup and cone arrangement, the charge that has calcined ore, coke, and limestone is introduced into the furnace. As fuel and as a reducing agent the coke is used and limestone is used as a basic flux.
-The flux is lighter in weight so it is removed in the upper layer from the slag hole. The slag is formed between calcium oxide and silicon oxide. The reaction is given below:
$CaO(s)+Si{{O}_{2}}(s)\xrightarrow{1123K}\underset{slag}{\mathop CaSi{{O}_{3}}}\,(s)$

So, the correct answer is an option (a)-$CaSi{{O}_{3}}$.

Note: The final reaction of formation of iron is:
$FeO(s)+C(s)\to Fe(s)+CO(g)$
The final reduction of iron oxide with carbon is a redox reaction. The iron oxide is reduced to iron metal and the carbon is oxidized to carbon dioxide.