The spheroidal mechanism of iron concentrates--the role of liquids and solids (2)

(3) The form and function of water in mineral powder
Dried mineral powder particles are generally hydrophilic. Under the action of molecular force and electric field on the surface of the particle, water molecules are adsorbed on the surface. Since the water molecule has a dipole polarity, its arrangement has a certain order. See Figure 5 for the thickness of the adsorbed water layer is extremely small, generally only a few The thickness of the water molecules. It is related to the hydrophilicity of the particles and the partial pressure of water vapor in the surrounding medium. Although the radius of action of the electric molecular force is small, the force is extremely large, for example, the first layer of water molecules adsorbed on the surface of the solid particles, the force thereof Equivalent to 10,000 atmospheres (98066.5 × 10 ⁴ Pa). Therefore, the adsorbed multi-layer water molecules are firmly attached to the surface of the particles, and the properties of the adsorbed water are different from those of ordinary water. For example, it cannot flow freely, the density is greater than 1.0, and the freezing point is much lower than 0 °C. When the relative humidity reaches 100%, the amount of adsorbed water reaches a maximum, which is called the maximum adsorbed water. Generally, when the particles only contain adsorbed water, they are still loose sand and cannot be combined into agglomerates unless the particles are very fine (about 1 micron).

After the particle surface reaches the maximum adsorbed water, there is also unbalanced molecular gravitational force. Therefore, in addition to adsorbing water, a thin film of water is formed. The binding force between the film water and the particle surface is weaker than that of the adsorbed water, and the inner layer is close to the adsorbed water. The layer is strongly affected by the particles, which is called strong binding water. Although the strong binding water is not as close as the binding of the adsorbed water to the particles, it is also quite strong, for example, it cannot be excluded under the centrifugal force of 70,000 times of the acceleration of the large dry gravity. It can migrate from the surface of one particle to the surface of the other, see Figure 6, without being affected by gravity. The freezing point of strong combined water is also below 0 °C.

The sum of the adsorbed water and the strongly bound water held by the ore particles is called the maximum molecular water. The largest molecular water can shape the powder, but it still has no plasticity.
The outer layer of film water is called weakly bound water. It is closer to free water, and after the mineral powder has weakly bound water, it can be plastically deformed under the action of external force.
The adsorbed water and the thin film water can be regarded as the outer shell of the mineral powder particles, and under the action of an external force, it moves together with the particles, and the particles are combined with each other. Therefore, the ore powder begins to roll into a ball and has a certain strength. [next]
When the ore fines are wetted by the water beyond the film water, capillary water appears between the particles, which begins to appear as contact state capillary water, see Figure 7(a), which binds the particles. Continue to increase the water, as well as the surface tension or external force of the capillary water, bringing the particles closer together, thus forming a cellular capillary water between them, see Figure 7(b).

At this time, the capillary water starts to join between the particles and can migrate. Further wetting occurs with saturated capillary water, see Figure 7(c), at which point the maximum capillary water content is reached.

 

The concentrate powder is formed into a ball, and the capillary water plays a leading role. The optimum water content is between the contact state and the cellular capillary water. If the mineral powder particles are set to two spheres of the same diameter, the connection force of the capillary water between them can be expressed by the following formula (Fig. 8).

Where a———the coefficient of surface tension of water;
R—the radius of the sphere;
θ———The corresponding angle of capillary water.
The ball speed of the concentrate powder is determined by the migration speed of the capillary water. The hydrophilic material can accelerate the migration of capillary water.

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