Q1: Limestone addition in the blast furnace is done to flux __________ present in the raw materials.

ANS:A - SiO₂

Limestone addition in the blast furnace is done to flux SiO2 present in the raw materials. In the blast furnace process for ironmaking, iron ore (typically hematite or magnetite), coke (carbon), and fluxes (such as limestone) are charged into the furnace. The limestone serves as a fluxing agent, reacting with impurities in the iron ore to form slag. One of the primary impurities in iron ore is silica (SiO2). The addition of limestone (CaCO3) to the blast furnace serves multiple purposes:

1. Fluxing: Limestone reacts with silica (SiO2) present in the iron ore to form calcium silicate (CaSiO3), which is a slag. This slag has a lower melting point than iron and helps to separate impurities from the molten iron, promoting the formation of liquid slag that can be easily removed from the furnace.
2. Desulfurization: Limestone also reacts with sulfur compounds present in the iron ore or coke to form calcium sulfide (CaS), which is then removed as part of the slag, aiding in desulfurization of the iron.
3. Heat generation: The decomposition of limestone into calcium oxide (CaO) and carbon dioxide (CO2) during the high-temperature conditions in the blast furnace contributes to the heat required for the reduction of iron ore to molten iron.