Extraction of Metals
After separation of gangue, mineral is passed through some chemical process to extract the pure metal from it. Followings are main chemical processes used for extraction of metals.
a. Roasting
b. Smelting
c.
Refining or purification of metals
a. Roasting
The process in which minerals are converted into their oxides by heating in the air at temperature below their melting point is called roasting.
Examples of roasting are given below.
b. Smelting
Reduction of the metals ions to free metal is called smelting. The most common reducing agents are coke, carbon monoxide and hydrogen. Some examples are:
Smelting of copper ore is done in two steps.
i. In first step, the roasted copper ore is heated with coke and sand at about 1100 oC. The minerals melt and separate into it two layers. The bottom layer that contains mixture of CuS and FeS is also known as matte. The upper layer is a silicate slag formed by the reaction of FeO and sand.
ii. After separation of upper layer, molten copper (matte) undergoes bessemerization. In this process, air is passed through matte in Bessemer converter. Any remaining iron sulphide (FeS) is oxidized and removed as slag (FeSiO3). In this final step, cuprous sulphide (Cu2S) is oxidized to form cuprous oxide (Cu2O) which reacts with remaining cuprous sulphide to form metallic copper.
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