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General Principles and processes of Isolation of Elements
normal
$NaCN$ is sometimes added in the forth flotation process as 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 $Na_2[Zn(CN)_4]$ while $PbS$ forms froth
C
$PbS$ forms soluble complex $Na_2[Pb(CN)_4]$ while $ZnS$ forms froth
D
$NaCN$ is never added in froth floatation process
Solution
Depressant is a substance that is added to suppress the floating characterisric of metal sulphide present as an impurity
$PbS\, + \,\mathop {ZnS}\limits_{(Impurity)} \,\,\xrightarrow{{4NaCN}}\,\mathop {N{a_2}\left[ {Zn{{\left( {CN} \right)}_4}} \right]}\limits_{Soluble\,\,Complex} \, + \,PbS$
Standard 12
Chemistry
