Chemistry Books | Extraction of Copper From Copper Pyrites | Froth Floatation | Bessemerisation

Extraction of copper from copper pyrites involves the following steps. This tutorial is created based on plus two Chemistry Books.

Crushing and concentration
The ore is crushed and then concentrated by froth-floatation process.

What is froth floatation process?
In this process the powdered ore is mixed with water and a little pine oil, that is a foaming agent and the whole mixture is then stir vigorously by blowing compressed air. The oil forms the foam or froth with the air. The ore particles stick to the froth which rises to the surface. While the rocky and earthy impurities that is the gangue or matrix are left in water. The froth is skimmed of collected and allow to subside to get the concentrated ore.

Roasting
The concentrated ore is heated strongly in the reverberatory furnace, in excess of air. During roasting,
i) Moisture is removed.
ii) The volatile impurities are removed.
iii) Sulphur, phosphorus, arsenic and antimony which are present as impurity are removed as volatile oxides.

Sulphur plus oxygen gives sulphur dioxide.
Phosphorus plus oxygen gives phosphorus pentoxide.
Arsenic plus oxygen gives arsenic trioxide.

The copper pyrite is partly converted into sulphides of copper and iron.

Copper pyrire plus oxygen gives copper sulphide plus iron sulphide plus sulphur dioxide.

Iron sulphide plus oxygen gives iron two oxide plus sulphur dioxide.

Smelting
The roasted ore is mixed with powdered coke and sand and is heated in a blast furnace. It is made of steel plates lined inside with fire clay bricks. Hot air at 800 degree Celsius is introduced from the tuyers near the base of the furnace. As a result, the following changes occur.

Iron sulphide plus oxygen gives iron two oxide plus sulphur di oxide.

Iron oxide plus silicon dioxide gives ferro-silicate. that is a fusible slag.

Copper glance plus oxygen gives cupride plus sulphur di oxide.

Cupride plus iron sulphide gives copper glance plus iron oxide.

Iron oxide plus silicon dioxide gives ferro-silicate. That is a fusible slag.

As a result of smelting, two separate molten layers are formed at the bottom of the furnace. The upper layer consists of slag and is removed as a waste while the lower layer is called matte. It chiefly consists of cuprous sulphide and some unchanged ferrous sulphide.

Bessemerisation
The molten matte is transfered to a Bessemer converter as shown in the visual. The Bessemer is mounted on a horizontal axis and is fitted with small pipes called tuyeres through which a blast of hot air and fine sand is admitted.

Any sulphur, arsenic and antimony still present escape as their respective oxides. Ferrous sulphide present in matte is oxidised to ferrous oxide which combines with silica to form slag.

Iron sulphide plus oxygen gives Iron two oxide plus sulphur di oxide.
Iron oxide plus silicon dioxide gives ferrosilicate. That is a fusible slag.

Some of the cuprous sulphide undergoes oxidation to form cuprous oxide which then reacts with more cuprous sulphide to give copper metal. The impure metal thus obtained is called blister copper and is about 98% pure.
Cuprus sulphide plus oxygen gives cuprus oxide plus sulphur dioxide.
Cuprus oxide plus cuprus sulphide gives copper plus sulphur dioxide.

Refining
Blister copper contains about 2% of impurities and it is purified by electrolytic refining.

Electrolytic Refining
This method is used to get metal of high degree of purity. For electrolytic refining of copper,

A block of impure copper metal acts as anode

A thin plate of pure copper metal acts as cathode

Copper sulphate solution acidified with sulphuric acid is taken as electrolyte.

When electric current is passed through the electrolytic solution pure copper get deposited on the cathode ,impurities settle near the anode in the form of sludge called anode mud.