Question

What is slag?

Hint:

Slag = Flux + Gangue → waste by-product that floats over molten metal during smelting.

Answer 1

Step 1: Definition.
Slag is the fusible (molten) waste material or by-product formed during the extraction of metals from their ores in a furnace. It mainly consists of impurities combined with flux.
Step 2: Formation.
In metallurgical processes, flux is added to combine with the gangue (earthy impurities like SiO$_2$, Al$_2$O$_3$) to form slag. This slag is lighter and floats on the molten metal surface, protecting it from oxidation.
\[ \text{Example: } CaO + SiO_2 \rightarrow CaSiO_3 \text{ (slag)} \] Step 3: Function of slag.
- Removes impurities.
- Acts as a protective layer for the molten metal.
- Prevents oxidation.
Step 4: Example.
In the extraction of iron from hematite in a blast furnace, limestone (CaCO$_3$) acts as flux and reacts with silica impurities to form calcium silicate (slag).