Question

Roasting of ore is done below its melting point but smelting is done above the melting point. Why?

Answer 1

Answer:

Smelting is a process of applying heat to ore in order to extract a base metal. It is a form of extractive metallurgy. It is used to extract many metals from their ores, including silver, iron, copper, and other base metals. Smelting uses heat and a chemical reducing agent to decompose the ore, driving off other elements as gases or slag and leaving the metal base behind. The reducing agent is commonly a source of carbon, such as coke—or, in earlier times, charcoal.

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Answer 2

This is so because they are different kinds of processes.

• While Roasting, Sulphide ores are converted into their oxides. The concentrated oxide ore is oxidized by heating it with excess oxygen below the melting point.

Example: 2PbS + 3O$_2$ = 2PbO + 2SO$_2$

• While Smelting, the roasted/calcinated ore is heated to convert into metal or matte by adding flux and reducing agent such as carbon, carbon monoxide, or aluminium is added to a concentrated ore and the mixture is melted by heating at a high temperature. Therefore it goes above the melting point.

Example: Fe$_2$O$_3$ + 3CO = 2Fe + 3CO$_2$

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