Question

13. In the froth floatation process, NaCN is added as
depressant when galena is associated with impurity
of Zns, because
(1) Pb(CN)2 is precipitated while ZnS remains
unaffected
(2) ZnS forms soluble complex Na [Zn(CN):) while
PbS combines with frother
(3) PbS forms soluble complexNa [Pb(CN)") while
ZnS combines with frother
(4) NaCN regenerates ZnS from complex
[Zn(CN):1:​

Answer 1

Explanation:

Correct option is

B

ZnS forms soluble complex Na

2

[Zn(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 Na

2

[Zn(CN)

4

] and PbS is removed along with the froth.