In froth-floatation process, what is the depressant used in the separation of sulphide ores of zinc and lead?

Options

A. NaCl
B. `Na_(2)CO_(3)`
C. NaCN
D. `Na_(2)SO_(4)`

Answer

C

Explanation

In froth-floatation process, depressants help to separate two sulphide ores by selective prevention of froth formation by one ore and allowing the other to come into froth.
For example, in order to separate two sulphide ores (ZnS and PbS), NaCN is used as a depressant. It selectively allows PbS to from the froth, but prevents ZnS from coming to froth. This happens due to the fact that NaCN reacts with ZnS to form `Na_(2)[Zn(Cn)_(4)]`.
`" "4NaCN+ZnS rarr Na_(2)[Zn(CN)_(4)]+Na_(2)S`