Q.Giving examples, differentiate between 'roasting' and 'calcination'.

Calcination example: $CaCO_3 \xrightarrow{\Delta} CaO + CO_2$ (limestone) or $Al_2O_3.2H_2O \xrightarrow{\Delta} Al_2O_3 + 2H_2O$ (bauxite) — no air/oxygen is required for the reaction itself. …

Step 1 – Calcination

Calcination is the process of strongly heating a concentrated ore, generally below its melting point, in a limited supply of air or in its absence, primarily to remove volatile constituents such as water of crystallisation (from hydrated oxides) or carbon dioxide (from carbonates), and to make the ore porous.

Examples:

No oxygen/air is chemically involved in these reactions — they are simple thermal decompositions.

Step 2 – Roasting

Roasting is the process of strongly heating a concentrated (usually sulphide) ore, below its melting point, in the presence of excess air/oxygen, converting the sulphide to the corresponding oxide and driving off sulphur as sulphur dioxide gas (and burning off other volatile impurities such as arsenic or antimony as their oxides).

Examples:

Step 3 – The essential difference

Contrast the two by (a) the typical ore type each is used on (carbonate/hydrated oxide vs sulphide) and (b) whether air/oxygen is supplied and particip …

• Saying both processes 'remove impurities' without distinguishing the key chemical difference — presence/absence of air/oxygen as a reactant. …