Question

What is the role of limestone during the extraction of iron from haematite ore?
A. Leaching agent
B. Oxidizing agent
C. Reducing agent
D. Flux

Answer 1

Hint: To answer this question we should know that limestone is used to promote fluidity and to remove objectionable impurities in the form of slag. Leaching is used to extract precious metal. Oxidizing and reducing agents is used to get pure iron from its ores.

Step by step answer:
To answer this question, we should study every option.
Leaching agent: We should know that leaching is a process widely used in extractive metallurgy where ore is treated with chemicals to convert the valuable metals within into soluble salts while impurity remains insoluble. These can then be washed out and processed to give the pure metal; the material left over is commonly referred to as tailings. But we should know that limestone is not used as a leaching agent.
Oxidising and reducing agent: We should know that carbon is used as a reducing agent, especially at higher temperatures, because it is a non-metal and it combines with oxygen and forms its gaseous non-metallic oxides. The monoxide CO being a reducing agent also reduces the metal oxide ores to its metal. For example: in the smelting of the iron ore in the blast furnace.

Flux: We should know that flux in metallurgy is a substance introduced in the smelting of ores to promote fluidity and to remove objectionable impurities in the form of slag. Limestone is commonly used for this purpose in smelting iron ores.
Basically, limestone is used as a slag former. We should now that iron ore normally contain gangue materials such as silica ($Si{{O}_{2}}$), Alumina ($A{{l}_{2}}{{O}_{3}}$) along with sulphur (S) and Phosphorus (P). Removal of these impurities is done by combining the gangue materials with CaO to form slag which consists of low melting point complex compounds such as calcium silicate, calcium aluminate etc. CaO is charged along with other raw materials in the form of limestone. This limestone is first decomposed into CaO, which then combines with gangue to form slag. Further lime from limestone reacts with sulphur present in the raw materials to form CaS which goes into slag.
So, from the above discussion we say that flux is used to remove impurity in the form of slag. Limestone is used as flux, during the extraction of iron from haematite ore. So, our correct answer is option D.

Note: We should also know that lime is used for other purposes also, such as follows: In flue gas treatment: During combustion of coal and petroleum products there is a high level of $S{{O}_{2}}$ emissions. To control these emissions within norms it becomes necessary to treat the flue gases for $S{{O}_{2}}$ and other acid gases. Lime is used effectively for this purpose. Water treatment: Lime is used to treat wastewater for adjustment of pH levels and precipitation of heavy metals in the form of hydroxides, sulphates and phosphates as insoluble salts. It is added as a neutralizing agent for acidic water before its discharge. Sludge treatment: Lime is widely used to coagulate and to stabilize sludge in the sludge treatment units.