Question

Process of roasting

Answer 1

Roasting is a process of heating of sulphide ore to a high temperature in presence of air. It is a step of the processing of certain ores. More specifically, roasting is a metallurgical process involving gas–solid reactions at elevated temperatures with the goal of purifying the metal component(s).

Roasting consists of thermal gas–liquid reactions, which can include oxidation, reduction, chlorination, sulfation, and pyrohydrolysis. In roasting, the ore or ore concentrate is treated with very hot air. This process is generally applied to sulfide minerals. During roasting, the sulfide is converted to an oxide, and sulfur is released as sulfur dioxide, a gas. For the ores Cu₂S (chalcocite) and ZnS (sphalerite), balanced equations for the roasting are:

2 Cu₂S + 3 O₂ → 2 Cu₂O + 2 SO₂ 2 ZnS + 3 O₂ → 2 ZnO + 2 SO₂

The gaseous product of sulfide roasting, sulfur dioxide (SO₂) is often used to produce sulfuric acid. Many sulfide minerals contain other components such as arsenic that are released into the environment.