Extraction of copper from copper pyrite.

Q. Write down the extraction of copper from copper pyrite. [8 marks]

Answer: It can be extracted from copper pyrite which goes through the following step:

1. Crushing and pulverization: The big size of the ore is crushed and it is changed into a fine powder then it is taken for concentration.

2. Concentration: The obtained powder ore is concentrated by the froth floatation process. Then it is taken for roasting.

3. Roasting: It is then heated strongly in a reverberatory furnace. The volatile impurities such as sulphur, arsenic, etc are removed and pyrite ore is converted into a mixture of cuprous sulphide, iron sulphide and ferrous oxide.

$$S+O_2 \underset{\Delta}\longrightarrow SO_2\uparrow$$

$$4As+3O_2\underset{\Delta}\longrightarrow 2As_2O_3\uparrow$$

$$CuFeS_2 + O_2 \underset{\Delta}\longrightarrow Cu_2S+2FeS+SO_2\uparrow$$

$$2Cu_2S+3O_2\longrightarrow 2Cu_2O+2SO_2\uparrow$$

$$2FeS+3O_2\longrightarrow2FeO+2SO_2\uparrow$$

4. Smelting: The obtained ore is mixed with sand and coke then it is heated in a blast furnace then ferrous sulphide is oxidized to give ferrous oxide which combines with SiO2 (sand) to give the fusible silicate slag.

$$2Cu_2S+3O_2\longrightarrow 2Cu_2O+2SO_2\uparrow$$

$$2FeS+3O_2\longrightarrow2FeO+2SO_2\uparrow$$

$$\underset{non-fusible}{Fe}+\underset{(flux)\,basic\,impurities}{SiO_2}\longrightarrow \underset{(fusible\,slag)}{FeSiO_3}$$

Thus, obtained fusible slag is removed.

Then, cuprous oxide again reacts with carbon (coke) to give few amounts of copper and again it reacts with ferrous sulphide to give cuprous sulphide.

$$Cu_2O+C\underset{\Delta}\longrightarrow2Cu+CO\uparrow$$

$$Cu_2O+FeS \underset{\Delta}\longrightarrow Cu_2S+FeO$$

The lower layer is molten mass containing about 40-50% of metal, Cu2S, and some trash amount of FeS is called matte (molten matte) which is transferred to a Bessemer converter for Bessemerization.

5. Bessemerization: The obtained matte is heated. Then FeS (ferrous sulphide) is oxidized to give ferrous oxide. It again reacts with SiO2 to give fusible slag.

$$2FeS+3O_2 \longrightarrow 2FeO + 2SO_2\uparrow$$

$$FeO+SiO_2\longrightarrow \underset{(fusible\,slag)}{FeSiO_3}$$

Here, the total FeS (fusible slag) is removed.

Then, cuprous sulphide begins to be oxidized. When about two-thirds of the Cu2S is oxidized then the oxide of copper reacts with the remaining Cu2S to give copper and sulphur dioxide.

$$2Cu_2S + 3O_2 \underset{\Delta}\longrightarrow 2Cu_2O + 2SO_2\uparrow$$

$$Cu_2O+Cu_2S \underset{\Delta}\longrightarrow 6Cu+SO_2\uparrow$$

Then, molten mass is cooled then dissolved SO2 gas is obtained in the form of a bubble. This gives the shape of a blister to the surface of solidified copper. For this reason, it is also called blister copper which contains 2% impurities like Ag, Ni, Zn, etc. Then it is taken for purification.

6. Purification (Electrolytic refining): For this, a thin sheet of impure crude metal is made anode and the thin sheet of another metal (sheet) is made the cathode. Both are replaced in acidified copper sulphate solution when an electric current is passed then impure copper from the anode goes into the solution and then pure copper from the solution gets deposited at the cathode and impurities are collected below the anode.

$$CuSO_4 \longrightarrow Cu^{++}+SO_4^{- -}$$

At anode: $$Cu\longrightarrow Cu^{++}+2e^-$$

At cathode: $$ Cu^{++}+2e^-\longrightarrow Cu$$

THE END

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