Question

Describe the role of the following:
(i)${\text{Si}}{{\text{O}}_{\text{2}}}$ in the extraction of copper from copper matte.
(ii)${\text{NaCN}}$ in the froth floatation process.

Answer 1

Hint: If copper ore contains another metal oxide then a chemical compound is used which reacts with metal oxide and helps it to separate from the copper ore. In froth flotation, the ore is separated from the gangue. If the two sulphide ores are needed to be separated then some compounds are used which selectively cause one sulphide ore to come into forth.

Complete step by step answer:
(i) For the extraction of metal the concentrated ore of copper is converted into oxide by heating. If the copper ore contains iron oxide then the copper ore is mixed with the silica that is ${\text{Si}}{{\text{O}}_{\text{2}}}$. So, the iron oxide reacts with silica and forms a compound of iron and silicon that is known as slag.
The reaction of formation of slag is as follows:
${\text{FeO}}\,{\text{ + }}\,\,{\text{Si}}{{\text{O}}_{\text{2}}}\, \to \,{\text{FeSi}}{{\text{O}}_{\text{3}}}$
The slag discrete from the copper ore easily.
Therefore, ${\text{Si}}{{\text{O}}_{\text{2}}}$ forms slag with iron oxide which separates from copper matte easily.

(ii)Froth flotation process is based upon the density and hydrophobic nature of the ore. The metal is lightweight and hydrophobic whereas the gangue is heavy and hydrophilic. So, the metal particles wrapped into the air come upward in froth whereas the gangue particles wrapped into water molecules settle down. The fourth is separated and dried. Thus the ore is concentrated.
This method can also be used to separate the two sulphide ores. For this depression is used. The depressants prevent one ore to come into forth so, one ore comes into gangue and another comes into forth.
To separate the ${\text{ZnS}}$ and ${\text{PbS}}$, the ${\text{NaCN}}$ depressants are used. ${\text{NaCN}}$ prevent ${\text{ZnS}}$ to come forth.
Therefore,${\text{NaCN}}$ in the froth floatation process is used as depressants.

Note:
Copper is converted into oxide by heating in a reverberatory furnace. The formed copper oxide ${\text{C}}{{\text{u}}_{\text{2}}}{\text{O}}$ is known as copper matte. The 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.