There are many kinds of minerals in nature, about 3,500. Due to the difference in material composition, temperature, pressure and other conditions during crystallization, the crystal lattice of minerals varies widely, and the floatability of minerals has a great relationship with the crystal structure. Practice has shown that there are not many minerals with natural floatability, only a few kinds of paraffin, graphite , talc , pyrophyllite and molybdenite . Mica , quartz, etc. are minerals that are not naturally floatable. The relationship between crystal structure and floatability is very complicated. The relationship between several typical mineral crystal structures and floatability can be listed below.
(1) Paraffin Paraffin is a natural organic hydrocarbon having a molecular formula of Cn+H 2n+2 . The basic unit of paraffin crystals is a molecule, each molecule consisting of zigzag-connected carbon atoms. When these paraffin molecules form crystals, they are linked by molecular bonds, which are caused by the attraction of positive and negative charges in the instantaneous dipoles of two molecules, that is, the dispersive force acts, the intensity is small, and it is the permanent dipole of water molecules. The effect is small. Therefore, no matter whether the paraffin crystal is intact or broken, water molecules rarely align in the vicinity of it. This is why paraffin wax is small in hydrophilicity, large in hydrophobicity, and has good natural floatability. It is also the reason why many floating mineral processing agents with hydrocarbon groups have hydrophobicity.
(2) Graphite The composition of graphite is carbon, and the crystal structure of a graphite is shown in Fig. 6-5. The carbon atoms in the graphite crystal are arranged in a hexagonal annular layer. The two adjacent carbon atoms in the layer are combined by a covalent bond, and the force is strong. The carbon atoms between the two layers are linked by molecular bonds, and the force is weak. The graphite crystals are ruptured along the plane to form small pieces. The ends of the graphite fragments are broken covalent bonds, which have great attraction to water molecules. Some water molecules are arranged around them, so the two ends of the fragments are hydrophilic. But the plane of the fragment is a weak molecular bond, which is hydrophobic and has a great advantage. Therefore, crystalline graphite has good hydrophobicity and natural floatability.
The molybdenum ore (M o S 2 ) in the sulfide ore and the pyrophyllite in the silicate are similar in structure to the graphite and have a certain natural floatability. However, not all layered minerals have natural buoyancy. For example, although mica has a smooth flaky cleavage surface, its layer exists as an ionic bond in the water, and the layer and both ends are hydrophilic.
(3) Quartz quartz is the most common gangue mineral in the beneficiation process. It is composed of a plurality of silicon oxytetrahedrons connected to each other at an apex angle to form a frame structure extending in a three-dimensional space, as shown in Fig. 6-6. When cracking, the covalent bond between Si and O is broken, so there is strong hydrophilicity in the cross section, and there is no natural floatability. Si after the fracture often adsorbs OH-, and O- often breaks after adsorption H+.
(4) galena (PbS), copper, lead, zinc, iron sulfide minerals type crystals more, wherein the copper more representative square lattice having a simple cube, shown in Figure 6-7.
These metal sulfide particles bond force between the crystal lattice, usually both the nature of metallic and covalent bonds. Water molecules are easily aligned around the atoms or ions on the rupture surface, lacking natural floatability, but their surfaces are also easy to adsorb oxygen or organic agents, which is a very favorable condition for floating beneficiation.
In short, the relationship between the lattice and floatability of minerals depends mainly on what bonds are exposed on the surface. If the surface is ionic, that is, the surface force is a strong electrostatic field. Such minerals ( calcite , fluorite, etc.) ) is hydrophilic. Its natural floatability is poor, and it is necessary to add a different polarity of the collector to change the hydrophilicity of the mineral surface, so that it is possible to float the beneficiation. If the mineral surface is a covalent lattice or a molecular lattice, the surface after the fracture may be a covalent bond, a molecular bond, or both. If the surface is covalent, the surface has a strong valence energy. Such minerals (such as beryl, quartz, etc.) are hydrophilic, not easy to float, and also need to be added with a different polar collector to float the beneficiation.
Only the surface exposed is a molecular bond that is hydrophobic. As mentioned above, there are three kinds of molecular bond forces, among which the surface mainly based on dispersive force is the most hydrophobic, such as paraffin, graphite, molybdenite and the like.
It should be noted that in the practice of floating beneficiation, whether the mineral can float is not only related to the inherent wettability of the mineral surface, but also depends on whether it acts with the collector.
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