General Principles and Processes of Isolation of Elements
Which of the following process does not involve heating?
Correct Answer: Option(d)
Solution: The process that does not involve heating is Levigation:
D: Levigation is the process of grinding an insoluble substance into a fine powder, while wet. The material is introduced into the mill together with water, in which the powdered substance remains suspended, and flows from the mill as a turbid liquid or thin paste, according to the amount of water employed.
A: The IUPAC defines it as 'Heating to high temperatures in air or oxygen'. However, calcination is also used to mean a thermal treatment process in the absence or limited supply of air or oxygen applied to ores and other solid materials to bring about a thermal decomposition.
B: Smelting is a form of extractive metallurgy; its main use is to produce a base metal from its ore. This includes the production of silver, iron, copper and other base metals from their ores. Smelting makes use of heat and a chemical reducing agent to decompose the ore, driving off other elements as gases or slag and leaving just the metal base behind. The reducing agent is commonly a source of carbon such as coke, or in earlier times charcoal. The carbon (or carbon monoxide derived from it) removes oxygen from the ore, leaving behind the elemental metal. The carbon is thus oxidized in two stages, producing first carbon monoxide and then carbon dioxide. As most ores are impure, it is often necessary to use flux, such as limestone, to remove the accompanying rock gangue as slag.
C: Roasting consists of thermal gas-solid 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 sulphur is released as sulphur dioxide, a gas.