Question

What is the role of depressants in the Froth Floatation Process?

Answer 1

Froth flotation process

• ‘’This method is used for removing gangue from sulfide ores.''
• In this process, a suspension of the powdered ore is made with water.
• Collectors and froth stabilizers are added to it.
• Collectors (e.g., pine oils, fatty acids, xanthates, etc.) enhance nonwettability of the mineral particles and froth stabilizers (e.g., cresols, aniline) stabilize the froth.
• While the gangue particles are moistened by water, the mineral particles are moistened by oils.
• The mixture is stirred by a rotating paddle, which also sucks air into it.
• The outcome is the formation of froth, which transports the mineral particles. The light froth is scraped off.
• The ore particles are then recovered by drying the material.

Role of depressants

• Separating two sulfide ores can sometimes be done by changing the percentage of oil to water or by using 'depressants.'
• The depressant used in the case of an ore containing $\mathrm{ZnS}$ and $\mathrm{PbS}$ is $\mathrm{NaCN}$.
• $\mathrm{NaCN}$ reacts with $\mathrm{ZnS}$and forms a layer of ${\mathrm{Na}}_2\left[\mathrm{Zn}{\left(\mathrm{CN}\right)}_4\right]$ complex on the surface of $\mathrm{ZnS}$and thus prevents it from the formation of froth.
• It selectively prohibits $\mathrm{ZnS}$from reaching the froth while allowing $\mathrm{PbS}$ to do so.