(1) Formation of hydrated film (layer)
From the macroscopic contact angle of minerals to the microwetting property of the interface between minerals and aqueous solutions, wetting is considered to be the hydration of water molecules (dipoles) on the adsorption of mineral surfaces. Water molecules are polar molecules, mineral surfaces The unsaturated bond energy also has different degrees of polarity. Therefore, polar water molecules adsorb on the surface of the polar mineral and form a hydrated film on the mineral surface. The water molecules in the hydrated film are oriented and densely arranged. They are different from the random and sparse arrangement of ordinary water molecules. The first layer of water molecules closest to the mineral surface is attracted by the surface bond energy, and the arrangement is the most tidy. As the bond energy is weakened, the distance from the surface is weaker. The order of the layers of water molecules is gradually confusing, and the surface bond energy can not reach the point where the water molecules have been in an unordered state like ordinary water. Therefore, the hydrated film is actually a transition between the surface of the solid mineral and ordinary water. The layer is also referred to as the "intermediate layer." Figure 4-6-18 is a schematic diagram of the hydrated film.
(2) Hydration film (layer) properties and floatability
It is known from surface chemistry that the thickness of the hydrated film is proportional to the wettability of the mineral. The surface hydration membrane of hydrophilic minerals (such as quartz and mica ) can reach 10-6 ~ 10-7cm. This layer of hydrated film is affected by the surface energy of the mineral. Its viscosity is larger than ordinary water and has similar elasticity to solid. Therefore, the appearance of the hydrated film is liquid phase, but its properties are similar to solid phase. The water molecules in the hydration layer adhere firmly to the mineral surface due to the bond energy of the mineral surface, so the viscosity is larger than ordinary water and the stability is high. To achieve the adhesion of the mineral particles to the bubbles, the mineral surface must be discharged. The hydration layer must have a certain energy added to it.
Whether the mineral surface can be hydrated depends on the change of free energy before and after mineral hydration. Before the mineral is hydrated, its surface is in contact with air. Its free energy is represented by ESA. After hydration, the mineral surface is in contact with water molecules, and its free energy is expressed by ESW. The hydration process can only proceed spontaneously when the system's free energy is reduced, ie water molecules can be aligned on the mineral surface only with ESW ---ESA. Therefore, the size of the ESW--ESA value can be used to measure the strength of water molecules and mineral surfaces. The greater the negative value of ESW--ESA, the easier it is for water molecules to interact with the surface of the mineral, and the stronger the hydration of the mineral. So can you approximate ESW ---ESA as a hydration of mineral surfaces?When coal flotation mud, since the surface of the non-polar surface of coal, which is the surface of the molecular bonds unsaturated bonds, hydration is the interaction between the coal surface molecules with a polar water molecules belonging to the biasing force of the induction effect and the dispersion effect The orientation force and hydrogen bonding between the water molecules are much weaker, so the hydration is weaker and the surface is not easily wetted by water. When the coal particles collide with the air bubbles, the coal particles easily adhere to the surface of the bubbles and enter the foam product. The surface of vermiculite is mainly a polar surface. The interaction between the surface and water molecules is mainly the interaction between ions and polar water molecules. Within a certain range, the force exceeds the force between water molecules. Therefore, in the meteorite The surface energy can adsorb a large amount of water molecules to form a thick hydration layer. When the surface collides with the bubbles, the hydration layer is difficult to be broken, and the vermiculite particles are difficult to adhere to the surface of the bubbles, so the vermiculite remains in the slurry. Separation of coal particles from vermiculite particles in coal slime can be achieved.
B&B EC CO., Ltd. , https://www.hi-cfm.com