(i) What is the principle behind the zone refining of metals? (ii) What is the role of silica in the extraction of copper? (iii) How is ‘cast iron’ different from ‘pig iron’?
Answers
(i) Zone refining: This method is based on the principle that impurities are more soluble in the molten state of metal (the melt) than in the solid state. In the process of zone refining, a circular mobile heater is fixed at one end of a rod of impure metal.Then, the end with the impurities is cut off.
(ii)During the roasting of pyrite ore, a mixture of FeO and Cu2O is obtained. The role of silica in the metallurgy of copper is to remove the iron oxide obtained during the process of roasting as 'slag'.Then, FeO combines with silica to form iron silicate, FeSiO3 (slag).
(iii) The iron obtained from blast furnaces is known as pig iron. ... Cast iron is obtained by melting pig iron and coke using a hot air blast. It contains a lower amount of carbon (3%) than pig iron. Unlike pig iron, cast iron is extremely hard and brittle.