Question

What is the role of depressant in the froth floatation process?

Answer 1

Hint: This question is asked from the topic of metallurgy. Froth floatation is a technique that is used in the mineral processing in the extraction of metals. Froth flotation separates hydrophobic substances from hydrophilic.

Complete step by step answer:
 We know that Froth-Floatation is one of the techniques of mineral beneficiation. In this process, separation of desired minerals from the impurities and other minerals by collecting them on a surface of a froth layer. By using this froth floatation method, selectively separate different minerals.
 The role of depressant in the froth flotation process is very important. Depressants change the chemical properties of the mineral surface in order to deactivate the mineral surface towards the action of collectors. Depressant will prevent one mineral from flotation and allow another mineral to float and thus depressants increase selectivity of the flotation process.
So, the main role of depressant in the froth flotation process is deactivating the mineral surfaces towards the action of collectors and they increase the selectivity.
For example, depressant is used to separate two sulphide ores let's say ZnS and PbS. NaCN is the depressant used. PbS is allowed to froth and ZnS is prevented from forming froth. ZnS reacts with NaCN as shown below:
$\text{4NaCN + ZnS }\to \text{ N}{{\text{a}}_{2}}\text{ }\!\![\!\!\text{ Zn(CN}{{\text{)}}_{4}}\text{ }\!\!]\!\!\text{ + N}{{\text{a}}_{2}}\text{S}$

Additional Information: There are mainly two types of depressants, they are inorganic depressants and organic depressants. Examples for inorganic depressants are sodium cyanide, zinc sulphate and examples for organic depressants are starch, tannin, Dextrin, etc.

Note: You must notice that there are several other substances required for maintaining uniform quality froth in the froth flotation process. They are collector, Frother, Regulator, Activator and pH modifiers.