What Is Surface Force?

Surface force is a force that acts on the outer surface of the fluid in question and is proportional to the surface area, that is, the force of the surrounding fluid on the surface of the separator. The surface force is proportional to the surface area of the fluid. The forces acting on any minute surface in a fluid can be divided into two types, namely, forces perpendicular to the surface and forces parallel to the surface. The former is pressure, and the latter is shear (cutting force). Stationary fluids are subject to pressure only, while flowing fluids are subject to both types of surface forces. Surface force can be divided into normal component force along the surface normal direction and friction force along the surface tangential direction.

Surface force is a force that acts on the outer surface of the fluid in question and is proportional to the surface area, that is, the force of the surrounding fluid on the surface of the separator. The surface force is proportional to the surface area of the fluid. The forces acting on any minute surface in a fluid can be divided into two types, namely, forces perpendicular to the surface and forces parallel to the surface. The former is pressure, and the latter is shear (cutting force). Stationary fluids are subject to pressure only, while flowing fluids are subject to both types of surface forces.

Surface force can be divided into normal component force along the surface normal direction and friction force along the surface tangential direction. Per unit area

In the mineral sorting system, there are many forces acting on the ore particles in the sorting area, such as gravity, magnetic force, buoyancy, centrifugal force, pressure gradient force, fluid flow resistance, false force, van der Waals force between ore particles, and ore particles. Structural force, hydrophobic interaction between ore particles, surface tension, etc. By nature, these forces can be divided into two categories: mass forces and surface forces. The former is related to mass, and the latter exists between molecules, atoms or molecular (atomic) aggregates, and is related to the particle surface, including van der Waals force, structural force, hydrophobic force, surface tension, etc. between ore particles, and the range of action generally does not exceed 100nm. Therefore, when the ore particles are fine to sub-micron level, the effect of surface force is dominant; when the ore particle size is greater than 10 m, the mass force is dominant; for micron-level particles, surface force and mass force coexist. In short, the surface force is of great significance for the classification of fine-grained minerals (typically less than 10 m or 20 m). This is not only manifested in surface-force-based flotation, agglomeration separation, and filtration of particles and ultrafine particles, but also in other methods such as gravity and magnetic separation. ^[2]

In terms of general flotation, surface forces play an important role in the collision and attachment of ore particles and bubbles. As the distance between ore particles and bubbles gradually decreases, when the distance between them is within 100 nm, various surface forces begin to take effect. These forces are Van der Waals force, electric double layer force, hydrophobic force, and structural force.

When hydrophilic ore particles interact with air bubbles, van der Waals force, electric double layer force, and structural force work. In most cases, all three appear as repulsive forces. When hydrophobic ore particles interact with air bubbles, Van der Waals force, electric double layer force, and hydrophobic force work, the former two appear as repulsive forces, and hydrophobic force is a strong attraction of hydrophobic ore particles in water. , The action distance is 10nm, and its value is usually one to two orders of magnitude greater than the Van der Waals force or the double-layer electrostatic force, so the hydrophobic action force is the key force for the interaction of hydrophobic ore particles and bubbles. ^[2]

The main characteristics of fine-grained minerals are large specific surface area and low mass. The physical characteristics are not significant, it is impossible to use physical methods to sort, and even the flotation method is difficult to work. The agglomeration of fine-grained ore particles in a dispersed state to reduce surface free energy is a spontaneous thermodynamic process, and intercoagulation is a very common phenomenon. However, the co-coagulation of particulate minerals inevitably affects the mineral sorting process, reducing or even destroying the selectivity of the sort. Therefore, in terms of effective sorting of fine-grained minerals, it is a necessary prerequisite for successful fine-grained sorting to prevent the coagulation of the fine-grained particles in anti-coagulation. Solving the contradiction between them is effective way. These approaches include: (1) Selective agglomeration flotation. Among them, polymer flocculation and hydrophobic agglomeration flotation is one of the effective ways to recover fine-grained minerals, and its essence is the process of sorting using the difference in surface force between solid particles (solid phase-solid phase); (Reselection, magnetic separation) The magnetic seed agglomeration-selective flocculation-overlap method combined with interface sorting; the new selective magnetic cover-magnetic separation separation process combining magnetic separation and interface sorting all uses minerals An example of surface properties (force) for effective sorting of fine-grained materials. In addition, the selection of appropriate force fields (including composite force fields) and process conditions (such as chemical separation with chemical agents to enhance separation and suitable pulp pH) can also achieve effective separation of fine-grained minerals. ^[2]