Question

Which of the following steps is/are involved in roasting?

• A. remove water of hydration
• B. remove arsenic and sulphur impurities
• C. convert sulphide to oxide and sulphate
• D. None of these

Answer 1

Answer: (A), (B), (C)

remove arsenic and sulphur impurities
remove water of hydration
convert sulphide to oxide and sulphate

Roasting 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). Often before roasting, the ore has already been partially purified, e.g. by froth floatation.
The concentrate is mixed with other materials to facilitate the process. The technology is useful but is also a serious source of air pollution.

Roasting consists of thermal gassolid 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 sulphide mineral. During roasting, the sulfide is converted to an oxide, and sulfur is released as sulfur dioxide, a gas. For the ores $C{u}_{2}S$ (chalcolite) and ZnS (sphalerite), balanced equations for the roasting are:

$2C{u}_{2}S+3O_2\to 2C{u}_{2}O+2S{O}_2$

$2ZnS+3O_2\to 2ZnO+2S{O}_2$
Hence options A,B & C are correct.