Question

8. Which substance is added as a depressant in froth floatation method to separate only Pbs
from the ore containing PbS and ZnS?
(A) ZnSO4
(B) NaOH
(C) NaCN
(D) NH4Cl​

Answer 1

Answer:

NaCN

Explanation:

in order to separate two sulphide ores (ZnS and Pbs), NaCN is used as a depressant. It selectively allows PbS form froth, but prevents ZnS from coming to froth. This happens due to the fact that NaCN reacts with ZnS to form Na2[Zn(CN)4].

4 NaCN + ZnS  →  Na2[Zn(CN)4] + Na2S

Answer 2

Answer:

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.