(i) What is the role of $Si{{O}_{2}}$ in the extraction of copper?
(ii) What is the role of depressants in froth floatation process?
(i) Ores of copper contain iron oxide as impurity. Silica reacts with iron oxide and forms iron silicate, which is removed as slag.
(ii)Depressants are used to prevent one type of sulphide ore particles from forming the froth with air bubbles, e.g. Sodium cyanide is used as a depressant to separate lead sulphide (PbS) ore from zinc sulphide (ZnS) ore.