Steps involved in Extraction of Copper:
i. Concentration: The finely powdered ore is concentrated by the froth floatation process by which % of Cu increases from 2% to 30-35%.
ii. Roasting: The concentrated ore is heated strongly in presence of air. The volatile impurities are removed as their oxides and the ore is converted into a mixture of cuprous and ferrous sulfides.
iii. Smelting: The roasted ore is mixed with sand (flux), little CaCO3, and coke (fuel) and then heated in a smelter in presence of excess air. FeS is oxidized to FeO which combines with SiO2 to form ferrous silicate slag, FeSiO3
iv. Self-Reduction: Molten matte is heated with SiO2 in a Bessemer converter and a blast of air is blown through the charge. Here FeS is completely removed as slag. It is a part of Cu2S that is oxidized to Cu2O and the unchanged Cu2S reduces Cu2O to metallic Cu by self-reduction process.
v. Refining: There are two types of the refining process:
i. Poling: The molten blister Cu is heated in presence of air and stirred with a pole of green wood. Impurities are removed as their volatile oxides, Fe is oxidized and forms a slag. The Cu2O is reduced to Cu by CO and H2 from green wood and contains – 99.5% Cu.
ii. Electrolytic Refining: Cu of the highest purity suitable for use in the electrical industry is obtained by electrolytic refining. Thick slabs of thermally refined Cu (Anode) are placed in between thin sheets of pure Cu (Cathode) in an electrolytic bath containing an acidified solution of CuSO4 at 50°C.
On electrolysis Cu-dissolves from the anode and is deposited at the cathode which gradually grows in size. The impurities like Zn, Fe, Ni, Co, etc. dissolve in the solution as sulfates, and others like Au and Ag settle down below the anode mud. This Cu is 99.99% pure.