(i) Name the method of refining to obtain silicon of high purity.
(ii) What is the role of SiO_2 in the extraction of copper?
(iii) What is the role of depressants in froth floatation process ?

Explanation

(i) Zone refining to obtain silicon of high purity. Zone melting is a group of similar methods of purifying crystals, in which a narrow region of a crystal is molten, and this molten zone is moved along the crystal and it is based on the priniciple that the impurities are more soluble in molten state than in the sqlid state of metal.
(ii) The sulphide ores of copper are heated in reverberatory furnace. If the ore contains iron, it is mixed with silica before heating. Iron oxide "slags of" as iron silicate and copper is produced in the form 9f copper matte which contains `Cu_(2)S` anmd FeS.
`FeO+SiO_(2)rarrunderset("(Slag)")(FeSiO_(3))`
It is utilised for manufacturing `H_(2)SO_(4)`.
(iii) Sometimes, it is possible to separate two sulphide ores by adjusting proportion of oil to water or by using" depressants". It selectively prevents ZnS from coming to the froth but allows PbS to come with the froth.