(a) Write the principle of electrolytic refining.
(b) Why does copper obtained in the extraction from copper pyrites have a blistered appearance?
(c) What is the role of depressants in the froth floatation process?

Explanation

(a) Impure metal is converted into block to form anode while cathode is made up of pure strip of the same metal suspended into electrolyte of a soluble salt of the metal when electric current is passed, metal ions from electrolyte are deposited at the cathode in the form of pure metal while an equivalent amount of metal dissolves from the anode and goes into the electrolyte solution as metal ion.
(b) In thhe extraction of copper from copper pyrites, molten metal is poured in sand moulds and when metal cools, dissolved `SO_(2)` escapes. some of the gas bubbles are entrapped during solidification giving blister like appearance to the metal.
(c) Depresent prevents one type of sulphide ore particles from forming the froath with air bubbles. Example, NaCN is used as depresent to separate lead sulphide ore from zinc sulphide ore.
`4NaCN+ZnStoNa_(2)[Zn(CN)_(4)]+Na_(2)S`