Name the method of refining to obtain silicon of high purity. What is the role of SiO2 in the extraction of copper?

(i) Zone Refining is the method of refining to obtain silicon of high purity (ii) SiO2 combined with the iron in the copper ore to form iron (II) silicate slag which is easily removed. FeO + SiO2 → FeSiO3 (iii) In froth flotation process, depressant prevents the formation of froth. It is used to separate two sulphide ores and allowing the other to form the froth, e.g., NaCN as depressant selectively prevents ZnS from coming in froth but allows PbS to come with the froth.