Question

What are fluxes? Which flux is used to remove impurity of FeO?

Answer 1

The process of metallurgy involves several steps like crushing and grinding of ore, concentration of ore, extraction of metal and finally, refining of metal. The process of removing impurities like sand, earthly impurities from the extracted ore is called concentration of ore or enrichment of ore or ore dressing. Gravity separation, froth floatation, leaching and magnetic separation are the different techniques of concentration of ore.

Complete Solution :
- Flux is any substance introduced in the smelting of ores to promote fluidity and to remove objectionable impurities in the form of slag. Limestone is commonly used for this purpose in smelting iron ores. Other materials used as fluxes are silica, dolomite, lime, borax, and fluorite. In soldering, a flux is used to remove oxide films, promote wetting, and prevent reoxidation of the surfaces during heating.
- Gangue and flux are mixed to form slag. Nature of flux depends upon the nature of gangue material. If the gangue material is acidic and basic flux is used and if gangue material is basic than acidic flux is used. Sometimes neutral flux is used to lower the melting point of the ore. In the electroreduction of Na from NaCl.
$Si{{O}_{2}}$ flux is used to remove impurity of FeO.
$Si{{O}_{2}}+FeO\to FeSi{{O}_{3}}$
Here, $Si{{O}_{2}}$ is an acidic flux and FeO is the basic gangue and $FeSi{{O}_{3}}$ is the Slag.

Note: Gangue are the impurities that are mixed closely with the ores. It is unwanted material which is of no market value and it is waste rock or mineral or sand etc. Metal ores are generally oxides, sulphides, and silicates.