Structure and properties of the liquid phase of the flotation
1. Structural characteristics of water molecules
Figure 4-6-10 Schematic diagram of water molecular structure
The water molecule consists of two hydrogen atoms and one oxygen atom. The three nuclei form an isosceles triangle with two protons as the base, as shown in Figure 4-6-10. Wherein the two unique electrons of oxygen do not form a bond, forming two negative electric centers, and the two hybrid orbitals form a bond with hydrogen to form two positive electrodes of water molecules, which become a quadrupole structure composed of two positive electrodes and two negative electrodes. The charge is concentrated on the top of the tetrahedron. It can be seen from the structure of water molecules that the positive and negative charge centers of water molecules are far apart, so they are strong dipoles, the dipole length is 0.386×10-10 m, and the dipole moment is [5.69~6.56]X 10-30 Cm. .
The macroscopic structural characteristics of water are mainly due to the “tetrahedral cage structure†and “flashing clusters†caused by hydrogen bond association and dipole association of water, see Figures 4-6-11 and 4-6-11. .
The water molecule has two positive electrodes and two negative electrodes, and is far apart. The two positively charged hydrogen atoms of the water molecule attract each other with the unique electrons of the oxygen atoms in the adjacent water molecules to form a hydrogen bond (hydrogen bond association). The hydrogen bond energy is about 18.9 kJ/mol, which is water. The main association energy of molecules. Each water molecule may form a tetrahedral cage structure by hydrogen bonding with four adjacent water molecules. In addition, as a strong dipole molecule, there is molecular energy between molecules. The molecular association energy is about 4~8 kJ/mol, of which 85% is the directional effect (permanent dipole-permanent dipole), 10% is the dispersion effect (instant dipole-instantaneous dipole), 5% is Inductive effect [permanent dipole-induced dipole]. It can be seen that water molecules are mainly related by hydrogen bond association (followed by molecular association) to form macromolecules as shown in Figure 4-6-12. characteristic.
According to the "flashing cluster" model proposed by 68%, (3), etc., water is a floating group of water composed of a tetrahedral cage structure in a slightly "free hydrogen bond disconnection, only molecular association" a mixture; the cluster itself is not constant, it is continuously formed and continuously destroyed, and has "flashing"; the water molecules in the non-clustered state have their hydrogen bonds broken, and only molecules collide with each other in the molecule. Weak, as shown in Figure 4-6-12.Due to the strong polar structural characteristics of water molecules, the main properties related to flotation are caused: high dielectric constant, high solubility and strong association between water molecules. These properties determine the important properties of some of the effects of the flotation phase interface.
2. The effect of water molecules on the mineral surface
After the mineral is broken, it has an unsaturated bond on the fracture surface. If the fracture surface is placed in a vacuum, no compensation can be obtained; if it is placed in the air, partial compensation can be obtained, but since the density of oxygen and nitrogen molecules is very low and there is no polarity, the compensation obtained is extremely small; When the fracture surface is placed in water, the unsaturated bond on the mineral surface acts on the water dipole and is partially compensated.
Because of the difference in the lattice structure of minerals, when the mineral is broken, the characteristics of the unsaturated bonds that are expected to be compensated on the fracture surface are different, and thus the polarity of the mineral surface is also different. The water molecules will be arranged in different forms on the surface according to the polarity of the mineral surface to form different types of hydration layer or hydration film, so that the free energy of the mineral surface changes.
When the degree of unsaturation on the fracture surface of the mineral is high, the water molecules are easy to interact with it, forming a hydration layer after the action, replacing the air on the original surface, and the interface energy of the solid-water interface after the action is smaller than the solid-air interface energy before the action, thus Spontaneous process; the surface with low degree of unsaturation is the opposite, the water molecules are not easy to interact with it, and the surface free energy increases before and after the action, so it is difficult for water to spontaneously replace the air on the surface of the original mineral to form a hydration layer. The role of water molecules and mineral surfaces seriously affects the contact process and steady state of minerals and bubbles.
3. Water solubility
The solubility of water plays a very important role in the flotation process. Since water dissolves some ions on the mineral surface, which changes the chemical composition of the mineral surface, the electrical properties of the interface, and the chemical composition of the liquid phase, the results also change the behavior of the mineral during the flotation process.
For general minerals, when the hydration energy is higher than its lattice energy, the mineral dissolves until the dissolved ions are equal in the chemical positions of the solid and liquid phases. Most minerals have low solubility, except for salts and minerals with a high degree of oxidation. In addition to the above-mentioned lattice energy and hydration energy, the solubility of minerals is also affected by solid particles and other chemical elements (commonly referred to as impurities) contained in water. When the water contains minerals of the same name, the ability of water to dissolve minerals is reduced; while other ions are included, the ability of water to dissolve minerals can be improved. For example, when Ca2+ and F- are contained in the solution, the solubility of water to fluorite is lowered, and when other ions are contained, the solubility of water to fluorite is improved, and the results are shown in Fig. 4-6-13.
The dissolution of minerals causes the pulp to contain a variety of ions. These so-called "inevitable ions" are one of the important factors affecting flotation. Although the solubility of most minerals is not large, the minerals entering the slurry are significant, such as the number of grams per ton of ore to be floated, which is comparable to the amount of flotation unit added conventionally used. The effects of “inevitable ions†are multifaceted: including the interaction of new compounds that are not present in the original ore and their interactions, which alter the composition and potential of the mineral surface; the “inevitable ion†and the flotation agent and the hardness present in the water. The salt ions [Na+, K+, Ca2+, Mg2+, Cl-, carbonate, sodium hydrogencarbonate, etc.] react to move the slurry value to a certain side. In each specific case, "inevitable ions" will have different effects on flotation.
Water dissolves most salt minerals more complicatedly. The dissolved ions also undergo a series of reactions such as hydrolysis and complex formation. Therefore, a large number of complex ions, molecules and complexes appear in the water, which greatly affects and changes the fraction. Selection process. Therefore, in the flotation process, attention should be paid to the effect of water on these minerals and the effect of the product on flotation.
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