Question

NaCN used in the froth flotation method for the purification of ore is:-

• A. $ZnS$ which contain $PbS$
• B. $C{u}_{2}S$ which contain $F{e}_2{S}_3$
• C. $PbS$ which contain $ZnS$
• D. $PbS$ which contain $Si{O}_2$

Answer 1

Answer: (C)

$PbS$ which contain $ZnS$

FROTH FLOATATION PROCESS - This method is used when a higher ore contains impurities with higher density. This method is used for the concentration of Sulphide ores (e.g.: Copper pyrites, iron pyrites, Galena, Zinc blende etc.,)

In this process, collectors and froth stabilisers are added.

Collectors - (e.g., pine oils, fatty acids, xanthates, etc.); Froth Stabilisers - (e.g., cresols, aniline)

The mineral particles become wet by oils while the gangue particles by water. A rotating paddle agitates the mixture and draws air in it. As a result, froth is formed which carries the mineral particles. The froth is light and is skimmed off. It is then dried for recovery of the ore particles.

Sometimes, it is possible to separate two sulphide ores by adjusting proportion of oil to water or by using 'depressants'. Example: In case of an ore containing $ZnS$ and $PbS$, the depressant used is $NaCN$. It selectively prevents $ZnS$ from coming to the froth but allows $PbS$ to come with the froth.