Question

Calcination and roasting are pre treatments in metallurgy before metal extraction. Differentiate between calcination and roasting.

Answer 1

Hint: Calcination is a thermal treatment process in the absence or in limited supply of air to ores to bring about thermal decomposition. Roasting is referred to as the heating of the sulphide ore in the presence of air.

Complete step by step answer:
The differences between calcination and roasting are given below.

Calcination	Roasting
1. Calcination is the process in which the ore is heated below its melting point in the absence or limited supply of air or oxygen in order to remove impurities like arsenic.	1. Roasting is the process of heating the ore below its melting point in the presence of air to oxidize the impurities. For example, carbon, sulphur are removed as their oxides.
2. This method is used for the treatment or thermal decomposition of carbonate ores.	2. This method is used for the treatment or thermal decomposition of sulphide ores.
3. Carbon dioxide is produced with the metal oxide.	3. Sulphur dioxide is produced with the metal oxide.
4. During calcination, moisture is driven out from an ore.	4. Roasting does not involve dehydrating of the ore.
5. No toxic acidic compounds are released.	5. During roasting, a large amount of metallic, toxic and acidic compounds are released.
6. Moisture organic impurities are removed.	6. Volatile impurities are removed.
7. When zinc carbonate is heated it gives zinc oxide and carbon dioxide.	7. When zinc sulphide reacts with oxygen it produces zinc oxide and sulphur dioxide.

Note: Both calcination and roasting are the processes which involve heating of the ore below its melting point. And both aim at removing the impurities present in the ore.