Question

Copper is extracted from copper pyrites. After roasting, the ore is mixed with silica and coke and then smelted into a blast furnace. The matte obtained from the blast furnace is charged into a silica lined converter. Some silica is also added and a hot air blast is thrown into the mixture to obtain blister copper which is purified by electrorefining.
During roasting, copper pyrites are ultimately converted into a mixture of:
(A) FeS + $C{u_2}S$
(B) FeS + $C{u_2}O$
(C) FeO + $C{u_2}S$
(D) $FeS + C{u_2}S \to FeO + C{u_2}O$

Answer 1

During the roasting process, the copper ore is allowed to be heated in regular supply of air. The temperature of the reaction is kept under the melting temperature of the metal. Iron also reacts similarly with oxygen like copper.

Complete answer:
Let’s take a look at the roasting process in order to find the answer.
- The ore is heated in regular supply of air in the furnace at a temperature below the melting temperature of the metal. This process is called roasting of a metal.
- So, generally, we obtain oxides of the metals as we are allowing the regular supply of air during the reaction. So, atmospheric oxygen gas reacts with the metal compounds in ore to give metal oxides. Here, in the case of copper pyrites, the reverberatory furnace is used.
- Copper pyrites is the ore of copper in which copper is present in the form of its sulphide. So, this gives a roasting reaction to give copper oxide as a main product. But alongside this, the ore also contains iron. So, we add some amount of silica in order to remove iron as slag. The reaction can be given as under.
$C{u_2}S + FeS\xrightarrow{{{O_2}}}C{u_2}O + FeO + 2S{O_2}$
- Here, FeO reacts with Silica ($Si{O_2}$) to form iron silicate which gets collected at the bottom of the vessel. The reaction can be given by
$FeO + Si{O_2} \to FeSi{O_3}$
- In this process, the sulphur dioxide gas produced is collected and used in the production of sulphuric acid.

Thus, we can conclude that the correct answer of this question is (D).

Note: Note the copper metal is present in copper pyrites in +1 oxidation state. Its oxidation state does not change in the roasting process. Remember that sulphur gets oxidized to sulphur dioxide$(S{O_2})$. So, do not get confused between other sulphur oxides.