Which furnace is used for roasting?

Roasting is the process of heating a sulfide ore to a high temperature in the presence of air. It is an important step in the extraction of certain metals. More specifically, roasting is a metallurgical process involving gas–solid reactions at elevated temperatures, carried out to purify the desired metal components.

Before roasting, the ore is often partially concentrated by methods such as froth flotation. The concentrate is then mixed with other substances to facilitate the process. While roasting is an effective metallurgical technique, it is also a major source of air pollution.

Chemical Reactions During Roasting

Roasting involves various thermal gas–solid reactions, such as:

• Oxidation
• Reduction
• Chlorination
• Sulfation
• Pyrohydrolysis

In practice, the ore (generally a sulfide mineral) is treated with very hot air. The sulfide ore is converted into its oxide form, while sulfur is released as sulfur dioxide gas (SO₂).

Use of Blast Furnace

A blast furnace is often employed for roasting. It is a tall shaft furnace where:

• Air is forced under pressure at the bottom,
• A mixture of concentrated ore, coke, and flux is fed from the top,
• The reactions lead to the production of molten metals.