Question

In metallurgy of iron, limestone provides flux and impurities for removing as slag.
(A) True
(B) Flase

Answer 1

Flux is an agent which is added for the formation of slag. It forms slag with those impurities which are more soluble in it then in the molten metal. In iron metallurgy, we have acidic impurity for which we use a basic flux. The flux used here is also known as quicklime.

Complete step by step answer:
Before answering the question, we must understand the term slag and flux.
Flux is basically a chemical agent that we use to get rid of impurities. We use different flux for removal of different kinds of impurity. By getting rid of the impurity, we receive pure metal at the end of the process.
For example, we use iron ore as a flux during smelting of copper, other fluxes like borax, lime, sodium carbonate etc. are used during different processes.
Slag is the by-product remaining after we have separated the desired metals from its raw ore.
Now, let’s discuss the metallurgy of iron very briefly.
Iron is obtained from Hematite and magnetite. These two are the most common ore of iron.
Iron is extracted from hematite by introducing the ore along with limestone and coke in the blast furnace. The main impurity in hematite is iron bearing metal silicates.
- Extraction process begins by adding carbon or coke to the molten ore in a blast furnace where reduction of ferrous oxides takes place.
- Then, a flux mainly limestone is added to form lime-silica slag which floats on top of the furnace and can be removed. Limestone decomposes due to the heat in the furnace and forms calcium oxide which reacts with silicon based impurity.
$CaC{{O}_{3}}(s)\rightleftharpoons CaO(s)+C{{O}_{2}}(g)$
- Calcium oxide reacts with the impurity and forms a slag which can be removed from the molten metal. We can write the reaction as:
$CaO+Si{{O}_{2}}\to CaSi{{O}_{3}}$
The slag helps to protect steel from re-oxidation and also removes the impurities whose solubility is greater in slag than in ferrous metal.
We can understand from the above discussion that in metallurgy of iron, limestone provides flux and impurities for removing as slag thus the assertion is true.

Therefore, the correct answer is option (A) True.

Note: Every impurity has a different flux that we use to remove it. Flux can be acidic or basic depending on the type of impurity new are aiming to remove with it.
We use acidic flux for the removal of basic impurities like oxides of calcium and magnesium. On the other hand, we use basic flux for the removal of acidic impurity like silicon dioxide and diboron trioxide.
Here we have the impurity of silicon dioxide which we can remove by using a basic flux like calcium oxide.