(1) The basic composition of coal
The composition of the coal has significant unevenness. Coal is a composite of organic matter and various inorganic minerals, and its composition varies greatly with the degree of coalification. Therefore, different coals have different floatability. According to coal rock science, coal has four main components: silk charcoal, dark coal, mirror coal and bright coal. The silk charcoal has a fibrous structure, and the fibers in each small block are arranged in parallel, brittle, and the appearance is very similar to charcoal, showing a dull luster. Dark coal has less obvious bedding, is generally denser, and sometimes has a granular structure, and its hardness and toughness are relatively large. Other components of lentils that are often embedded in bright coal are often gradually converted to dark coal. Under the microscope, bright coal is very similar to dark coal but has a large amount of unstructured matrix. Mirror coal is very different from the other three components. It has a uniform structure, a shell-like fracture, and a bright luster. Because the cleavage surface is completely different, it is easy to distinguish the mirror coal from other components. It should be pointed out that the various components of coal have the property of continuous transformation with each other, which makes the composition of the surface of the coal particles more complicated and more uneven, and it is difficult to carry out preferential flotation of different components.
In the flotation of coal slime, the nature of the associated minerals has a great impact on the flotation effect. Further research on the types of minerals embedded in coal and their embedding is very important for coal flotation. The oxides contained in the coal are mainly quartz , and the quartz particles are mostly round, sometimes angular and white transparent. The carbonates in the coal are mainly oval-shaped calcite calcite . Coal often mixed with gypsum, pyrite, marcasite and clay minerals. Among these associated minerals, quartz and calcite have poor natural floatability, so they are easily separated from coal particles. Pyrite is a sulfide mineral, which is relatively easy to float. Its flotation activity is similar to that of coal particles, so it floats. When the selection method is removed, the appropriate pharmaceutical system must be selected; if a large amount of clay mineral is mixed in the coal, the flotation process will be greatly deteriorated. Clay minerals will muddy the slurry. At the same time, it often adheres to the surface of the coal particles due to electrostatic attraction, causing the zeta potential of the coal particles to change and cannot be floated and mixed into the tail coal. In recent years, many researchers have consistently pointed out that the chemical composition of coal has a great influence on the flotation properties of coal after studying the chemical composition and flotation properties of coal.
( 2) Structural model of coalCoal is not a crystal structure, its surface is not uniform, but it is composed of various irregular organic compounds. There are a large number of voids on the surface of the coal, so it is easy to adsorb a large amount of inorganic and organic substances from the liquid; in addition, the surface of the coal is easily oxidized, which affects the flotation property of the coal and complicates the flotation activity of the coal surface.
Regarding the structural model of coal, the structure proposed by Kleve is more comprehensive. It considers the physical, physical and chemical properties and chemical properties of coal (see Figure 4-6-8), pointing out that coal is mainly composed of aromatic networks. The composition is a polycyclic aromatic polymer compound, which is an aromatic compound in which a large amount of benzene nuclei are combined, and is composed of a multilayer planar carbon network, but also has a side chain. . During the metamorphism of coal, the side chains are easily decomposed to form oxygen, sulfur and nitrogen-containing functional groups, as shown in Figure 4-6-9. Studies have shown that there are a large number of polycyclic aromatic structural components in coal. As the degree of metamorphism increases, the spacing of carbon network layers decreases, the number of carbon atoms forming an aromatic group increases, and the side chain portion decreases. In addition to the structural components of polynuclear aromatics, bituminous coal also contains a hydrogenated aromatic nucleus with a fatty chain. Infrared spectroscopy can prove the existence of hydrogen bonds in bituminous coal, which is of great significance to the mechanism of action of coal and polar agents. The polycyclic aromatic nucleus of coal is often associated with each other by a 0-bond, a CH2-bond, or by a hydrogen bond in an oxide formed by an alkane ring and an aliphatic chain. The bright coal and mirror coal components contain more phenolic groups than the silk and dark coal components, which gives bright coal and mirror coal a greater adsorption activity. It must be pointed out that the oxygen-containing functional group has a strong adsorption activity, which inevitably has a great influence on the interaction between coal and water, coal and flotation reagents, and even has a decisive influence.
The aromatic nucleus is chemically inert and hydrophobic, but the carboxyl, carbonyl, hydroxyl, hydroxyl and phenol functional groups mentioned above are all hydrophilic.
(3) The floatability of coal
Coal is a polycyclic aromatic compound, and each basic unit and surrounding side chains and functional groups vary greatly depending on the degree of metamorphism. Therefore, coal has the following properties:
1 The composition is different, the components can not be separated in practice, and the flotation quality has a great relationship with the content and properties of each component;
2 The main body of coal is a polyphenyl aromatic nucleus, and the aromatic nucleus is chemically inert and hydrophobic. Therefore, the main surface of the coal is hydrophobic;
3 On the carbon network of the aromatic nucleus, there are a number of side chains, which are easy to generate oxygen-containing functional groups during oxidation, so that certain parts of the coal are hydrophilic;
4 The structure of coal also contains a certain amount of minerals, most of which have a certain polarity, thus making the surface of coal part hydrophilic;
Although the oxygen-containing functional groups and inorganic minerals on the surface of coal have certain hydrophilicity, these parts also have high chemical activity, and some heteropolar molecules in the collector can be adsorbed on these active sites. Thereby increasing the hydrophobicity of the entire coal particle;
The degree of metamorphism of coal 6 has a great influence on the floatability of coal. Generally, moderately metamorphic coal has the best floatability. Coal with high degree of metamorphism and low degree of deterioration has a decrease in floatability. When the degree of metamorphism is low, the number of oxygen-containing functional groups is large, and the porosity is more than 10%. When the degree of metamorphism is high, the number of hydrophilic oxygen-containing functional groups is decreased, but the side chain content is also decreased, and the side chains are shortened to make hydrophobic. The degree of porosity is also increased, and the porosity is also increased compared with the degree of moderate metamorphism. Therefore, in both cases, the floatability is poor;
7 coal surface is easy to oxidize. After the oxidation of coal, the floatability deteriorates. The presence or absence of functional groups on the coal surface is an important factor in determining whether coal can be oxidized. The oxidation of coal in water is much more intense than in air, so the soaking time of coal has a great influence on the floatability of coal.
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