Question

Which of the following ores can be concentrated by froth flotation method and why?
${\text{F}}{{\text{e}}_{\text{2}}}{{\text{O}}_{\text{3}}}$, ${\text{ZnS}}$, ${\text{A}}{{\text{l}}_{\text{2}}}{{\text{O}}_{\text{3}}}$

Answer 1

Hint: Froth flotation is based upon the observation that ore is wetted by oil whereas the gangue is wetted by water. So, the ore particles come into froth and gangue settle down in the water. Thus, the ore is separated from the gangue.

Complete answer:
Froth flotation process is a method used to concentrate the ore.
Froth flotation process is based upon the density and hydrophobic nature of the ore. The sulphide is lightweight and hydrophobic whereas the gangue is heavy and hydrophilic. So, the sulphide particles wrapped into the air come upward in froth whereas the gangue particles wrapped into water molecules settle down, and thus the ore is concentrated.
Zinc sulphide ${\text{ZnS}}$ is a sulphide ore. From the Zinc sulphide, the zinc is concentrated or separated by the froth flotation process. First, the Zinc sulphide is converted into powder and mixed with water. Forth stabilizers are added to stabilize the froth. Collectors are added to increase the hydrophobicity of the sulphide.
Then the mixture is rotated and the air is supplied. The rotation makes the froth.
The hydrophobic ore particles surround with air, so come into the froth and the gangue partials surround with water, so they become heavy.
The froth is separated and dried.
After concentrating the ore, zinc metal is separated by converting the ore into oxide the then reduction.

Therefore, the ${\text{ZnS}}$ is separated by froth flotation because sulphides are hydrophobic and impurities are hydrophilic thus sulphides can be separated from impurities.

Note: Froth floatation is mainly used for sulphide ores. Froth flotation separates the gangue from the ore but this method can also be used to separate the two sulphide ores. Leaching is used to concentrate the oxide ores such as ${\text{F}}{{\text{e}}_{\text{2}}}{{\text{O}}_{\text{3}}}$and, ${\text{A}}{{\text{l}}_{\text{2}}}{{\text{O}}_{\text{3}}}$.