Question

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

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

Answer 1

Answer: (A)

$ZnS$ forms soluble complex ${Na}_2\left[Zn{\left(CN\right)}_4\right]$ while $PbS$ form froth

$NaCN$ is used as a depressant in the separation and concentration of $ZnS$ and $PbS$ ore. Here, $NaCN$ acts as a depressant for $ZnS$ but does not prevent $PbS$ from forming the froth.