Which method of metal refining is generally used when a metal of high degree of purity is needed?

Give one example where hydro-metallurgy is used for metal extraction.

How does NaCN act as a depressant in preventive ZnS from forming the froth?

What is the major role of fluorospar (CaF₂) which is added in small quantities in the electrolytic reduction of alumina dissolved in fused cryolite?

Name the oxide ores of (a) iron  (b)  zinc,  (c) manganese  (d) aluminium.

Which process is used for the concentration of Bauxite (Al₂O₃.2H₂O)?

29.

Ultra pure silicon is needed by electronic industry. By which method of refining, such a high purity silicon is obtained?

Sulphide ores usually concentrated by froth flotation process. Why?