**2. Surface energy in Froth flotation**

The concept of surface energy provides a satisfactory basis for explaining a wide range of "capillary phenomena", many of which are pertinent to the flotation process.


#### **Figure 3.**

*Surface and Interfacial tensions for the molecules in bulk liquid.*

According to molecular theory, different crystal structures have different surface energy [9–11]. Interface is the boundary between two or more phases exist together. The properties of the molecules forming the interface are different from those in the bulk that these molecules are forming an interfacial phase. Several types of interface can exist depending on whether the two adjacent phases are in solid, liquid or gaseous state.

### **2.1 Interfacial tension**

In the liquid state, the cohesive forces between adjacent molecules are well developed. There are various forces present between surface and interfaces molecules presented in **Figure 3.**

Cohesive forces are present with the other molecules which are situated below or adjacent to them. Adhesive forces are being developed with the molecules of other phases in the interface. Surface tension (γ) is the force per unit length that must be applied parallel to the surface so as to counter balance the net inward pull. Interfacial tension is the force per unit length existing at the interface between two different phases.
