(a) Write the principle of vapour phase refining.
(b) Write the role of dilute `NaCN` in the extraction of silver.
(c) What is the role of collectors in the froth floatation process? Give an example of a collector.

Explanation

(a) Vapour phase refining : The crude metal is freed from impurities by first converting it into suitable volatile compound by heating it with a specific reagent at a lower temperature and then decomposing the volatile compound at some higher temperature to give the pure metal.
(b) `NaCN` oxidises silver to form soluble complex of cyanide while the impurities remain unaffected which are filtered off.
`4Ag+8CN^(-)+2H_(2)O+O_(2)to4[Ag(CN)_(2)]^(-)+4OH^(-)`
This process in known as leaching.
(c) Collectors enhance the non-wettability of the ore particles. Example, Pine oil, Xanthates.