Question

The chemical composition of slag formed during the smelting process in the extraction of copper is:
(A) $C{u_2}O + FeS$
(B) $FeSi{O_3}$
(C) $CuFe{S_2}$
(D) $C{u_2}S + FeO$

Answer 1

Copper is obtained from an ore chalcopyrite ($CuFe{S_2}$). During smelting the copper ore is strongly heated with silicon dioxide (silica), calcium carbonate ($CaC{O_3}$) and air inside a furnace. The iron present in the ore is removed in the form of slag and copper in the form of $C{u_2}S$ which is further blasted with air to extract pure Cu.

Complete step by step answer:
-First of all we will see what this smelting process is.
Smelting is basically the process by which a metal is extracted from its ore by heating it at a temperature beyond its melting point and is a form of extractive metallurgy. This process is used in the extraction of metals like iron, silver, copper, etc. In this process heat and a chemical reducing agent are used for the ore’s decomposition which removes other elements in the form of gases or slag and the metal base is left behind.

-We will now talk about how copper is extracted.
The most common source for extraction of copper is an ore named chalcopyrite ($CuFe{S_2}$). Since the percentage of copper in the ore for its direct extraction is quite low and so the ore undergoes concentration via the Froth Flotation method.

Ore concentration: The fine powder of the crushed ore is mixed in water and a suspension is created. Collectors and froth stabilizers are added to it. The collectors like pine oils, fatty acids, etc are used to increase the non-wettability of the metal part of the ore which allows the formation of froth and the froth stabilizers like aniline and cresols sustain the froth. The metal is made wet by oil while the gangue by water. The suspension is constantly stirred and paddled with air to create froth. The metal froth is then removed from the top and dried to extract the metal.

Copper-smelting: During this process the concentrated ore of copper is strongly heated with silicon dioxide (silica), calcium carbonate ($CaC{O_3}$) and air inside a furnace. This process can be shown in the following steps:

1. Chalcopyrite has copper which is reduced to copper sulphide.
2. Calcium carbonate ($CaC{O_3}$) is added as flux and slag is created.
3. The iron present in chalcopyrite gets removed as iron silicate slag ($FeSi{O_3}$).
4. The sulphur from chalcopyrite gets converted into sulphur dioxide ($S{O_2}$).
   The reaction involved in this process will be:
   $2CuFe{S_2} + 2Si{O_2} + 4{O_2} \to C{u_2}S + 2FeSi{O_3} + 3{O_2}$

Here we obtain Cu in the form of $C{u_2}S$ and slag in the form of $FeSi{O_3}$. The copper along with the slag is known as copper matte. The $C{u_2}S$ gets reduced to pure Cu by blasting of copper matte with air.
$C{u_2}S + {O_2} \to 2Cu + S{O_2}$

This is how we obtain Cu from the copper ore chalcopyrite ($CuFe{S_2}$).
-Hence the chemical composition of slag formed during the smelting process in the extraction of copper is $FeSi{O_3}$.
So, the correct answer is “Option B”.

Note: Slag is the rocky waste material separated from metals during smelting of the metal. Slag is used in cement and construction industries.
Also the copper obtained after smelting is known as Blister copper due to its blistery appearance caused by the appearance and bursting of bubbles formed by escaping $S{O_2}$. This copper obtained is of 98–99.5% purity.