Question

What is the role of silica in the metallurgy of copper?

Answer 1

Hint: Some of the impurities in copper are the iron oxide and the reaction of iron oxide with silica results in the formation of the compound which floats on the top of the pure metal resulting in the removal of the iron oxide . Some of the major ores of copper, like Chalcopyrite and Bornite contain iron.

Complete step by step solution:
- Let us first understand what is meant by metallurgy. The various scientific and technological processes that are involved in extraction of a metal from its ore is called metallurgy. The type of process used to extract the metal varies, and the cheapest technique is always used for extracting the metals.
- The extraction of metals from their ores involves 3 main steps. They are –
(A) Concentration of ore
(B) Isolation of metal from the concentrated ore
(C) Purification of metal.
- The ores used for metallurgy of copper include Chalcocite ($C{{u}_{2}}S$), Covellite (CuS), Chalcopyrite ($CuFe{{S}_{2}}$), Cuprous oxide ($C{{u}_{2}}O$) etc.
- For oxides ores of copper (cuprous oxide -$C{{u}_{2}}O$), the extraction is easy. Cu is easily obtained by the reduction of $C{{u}_{2}}O$. The reduction process is done by heating $C{{u}_{2}}O$ with coke.
- The role of silica comes in the case of sulphide ores.
For sulphide ores of copper, the steps needed to be followed are,
(A) Froth flotation method to concentrate the sulphide ore. This method is helpful in removing gangue from sulphide ore.
(B) The next step is roasting of the sulphide ore. This is where the role of silica comes in. The roasted sulphide ores give rise to oxides of copper, iron and sulphur.
$2C{{u}_{2}}S+3{{O}_{2}}\to 2C{{u}_{2}}O+2S{{O}_{2}}$
$2FeS+3{{O}_{2}}\to 2FeO+2S{{O}_{2}}$
- In the reverberatory furnace, the ore is roasted only after mixing with silica. The role of silica is to react with the iron oxide leading to the formation of iron silicate (slag), which can easily be removed.
$FeO+Si{{O}_{2}}\to FeSi{{O}_{3}}(slag)$
- This leads to production of copper in the form of copper matte - $C{{u}_{2}}S$ and $FeS$ .
(C) Silica plays a role in the next step of the process too. The copper matte is charged into a silica lined convertor. More silica is also added into the convertor.
- This step leads to the formation of solidified copper called blister copper (has blistered appearance).
- Therefore, we can say that silica plays a role in removing the iron oxide as slag.

Note: Silica plays a role only for extraction of ores of copper iron and sulphur. It has the role of reacting with the iron oxide resulting in the formation of iron silicate, which is easily removed. It does not play any role in extraction of oxide ores.