(i) Zone refining is the method of refining to obtain silicon of high purity. This method is used generally to obtain semiconductors of high purity like silicon.
(ii) During metallurgy, a flux is added which combines with the gangue and forms slag, which is easily separated from the ore to remove the gangue. SiO2 combines with the iron in the copper ore to form iron (II) silicate slag which is easily removed. Thus it (SiO2) acts as a flux to remove the impurity of Iron oxide.
(iii) In froth flotation process, depressant prevents the formation of froth. It is used to separate two sulphide ores by preventing the formation of froth of one sulphide ore and allowing the other to form the froth. For example, in an ore containing ZnS and PbS, NaCN, a depressant selectively prevents ZnS from coming in froth but allows PbS to come with the froth.
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