How can we separate a mixture of two sulphide ores using froth floatation method? [closed]

As we know froth floatation method makes use of the wetting properties of mineral particles.

Mineral particles (sulphide) become wet with oils, while gangue particles get wet by water

According to my textbook (NCERT Class 12), we can use the froth-flotation method to separate a mixture of sulphide ores also using depressants.

How do these depressants actually work in this process?

closed as too broad by Gaurang Tandon, M.A.R., Tyberius, Mithoron, aventurinMar 28 '18 at 15:29

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Commonly used depressant is $\ce{NaCN}$. To separate two sulphide ores ($\ce{ZnS and Pbs}$), $\ce{NaCN}$ selectively allows $\ce{PbS}$ to come with froth, but prevents ZnS. This happens because of the reaction of $\ce{NaCN}$ with $\ce{ZnS}$ to form $\ce{Na2[Zn(CN)4]}$.
The complete reaction is, $$\ce{4NaCN + ZnS → Na2[Zn(CN)4] + Na2S}$$