Question

$NaCN$ is sometimes added in the forth flotation process as a depressant when $ZnS$ and $PbS$ minerals are expected because :

• A. $Pb(CN{)}_2$ is precipitated while no effect as $ZnS$
• B. $ZnS$ forms soluble complex $N{a}_2\left[Zn\right(CN{)}_4]$ while $PbS$ forms froth
• C. $PbS$ forms soluble complex $N{a}_2\left[Pb\right(CN{)}_4]$ while $ZnS$ forms froth
• D. $NaCN$ is never added in froth flotation process

Answer 1

The correct option is B $ZnS$ forms soluble complex $N{a}_2\left[Zn\right(CN{)}_4]$ while $PbS$ forms froth

When the minerals are expected to contain $PbS$ and $ZnS$, suitable depressants such as $NaCN$ are added.
The added $NaCN$, selectively prevents $ZnS$ from coming to the froth by forming soluble complex $N{a}_2\left[Zn\right(CN{)}_4]$ and $PbS$ is removed along with the froth.