Question

Iron oxide ore is purified by magnetic separation, but iron sulphide is separated from impurities by froth flotation. Why?

Answer 1

To purify the sulphide ores we can use froth flotation method

Ores: The compound from which the metal can be extracted economically and conveniently.

Gangue: The impurities present in the ore are called as gangue particles

Sulphide Ores

These are types of ores containing sulphide $\left({\mathrm{S}}^{2-}\right)$ part in it

Example: galena $\left(\mathrm{PbS}\right)$, cinnabar $\left(\mathrm{HgS}\right)$

Oxide Ores

These are types of ores containing oxide ion $\left({\mathrm{O}}^{2-}\right)$ in it

Example: Iron oxide $\left({\mathrm{Fe}}_2{\mathrm{O}}_3\right)$ called hematite

In froth flotation method

• To a mixture of impure sulphide ore and water, we have to add pine oil and ethyl xanthate.
• The air starts to bubble from the lower portion of the tank and froth formation takes place.
• Since the sulphide ores are lighter and insoluble in water, they will be taken up by the froth to the surface and skimmed off
• The impurities which are soluble in water (heavy) leave at the bottom
• In this way, we can separate sulphide ores

The main reason behind choosing froth flotation method to purify sulphide ore is that, sulphide ores can be wetted by the oil (insoluble in water) and impurites are wetted by the water (soluble in water), so that separation of impurities becomes easier.

Magnetic separation

• For the separation of impurities from iron oxide ore we can take magnetic separation
• In this method, two rollers are present one of them is magnetic and the other is nonmagnetic in nature
• When the mixture of substances is put in a conveyor belt magnetic particles get attracted to the magnetic roller and fall to one side and nonmagnetic particles fall into another side
• Substances that have magnetic properties can be purified by magnetic separation, iron oxide can show magnetic properties where the impurities do not.

Thus, Iron oxide ore is purified by magnetic separation and iron sulphide is separated from impurities by froth flotation method.