Question

NaCN is sometimes added in the froth flotation process as a depressant when ZnS and PbS minerals are expected because __________.

• A. $Pb(CN{)}_2$ is precipitated while no effect on 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

Answer: (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.