Essence of coal flotation sludge to be hydrophobic by the action of the coal collector, adhere to the bubbles, and the gangue particles hydrophilic remain in the water, separated from each other in order to achieve the process. The surface of the coal particles is mainly hydrophobic and has good natural floatability. Non-polar hydrocarbon oils are widely used as collectors in flotation, especially kerosene, light diesel oil and modified kerosene, accounting for 80%-90% of the collector consumption during coal flotation flotation.
Most of the hydrocarbon oils come from petroleum products, which are mainly fractionated and processed according to different boiling points depending on the purpose of industrial use. They are liquid, have a symmetrical molecular structure, are inactive in nature, do not dissociate into ions in water, are hardly soluble in water, have high hydrophobicity, and generally do not chemically interact with mineral surfaces.
First, the capture of non-polar hydrocarbon oil
The capture of non-polar hydrocarbon oils is due to its ability to adsorb on the surface of non-polar minerals and to spread out on its surface and form an oil film. The main components of non-polar hydrocarbon oils are aliphatic hydrocarbons, cycloalkanes and aromatic hydrocarbons. The molecules are composed of carbon and hydrogen atoms. The atoms have non-polar carbon-carbon bonds and weakly polar carbon-hydrogen. Bond bonding, belonging to non-polar molecules. In the process of slime sorting, most of the surface of the coal particles is non-polar. Therefore, the coal particles are more attractive to oil molecules than the strong polar water molecules, and the oil droplets are adsorbed to the surface of the coal particles. The force between the oil molecules and the oil molecules is greater than the force between the oil molecules themselves, and the oil droplets spread on the surface of the coal particles to form a hydrophobic thin oil film, which further improves the hydrophobicity of the surface of the coal particles. (See Figure 2c). The majority of the surface of the vermiculite particles is a polar surface and has a strong hydrophilicity. The surface of the vermiculite is less attractive to oil molecules than the water molecules. The surface of the vermiculite is covered by water molecules to form a hydrated membrane. Hydrocarbon oils are not easily adsorbed on the surface of vermiculite [see Figure 2(a)], or only a very small amount of hydrocarbon oil can be adsorbed to the local hydrophobic part, which basically does not increase the hydrophobicity of the vermiculite, thereby expanding the surface of the coal particles and vermiculite. The difference in wettability prompted the sorting to proceed smoothly. If polar mineral impurities are contained on the surface of the coal particles or locally oxidized, a discontinuous oil film can be formed [see Fig. 2(b)].
Figure 2 Fixation of non-polar hydrocarbon oil on mineral surface
The collection of non-polar hydrocarbon oils is mainly manifested in the following three aspects:
(1) Non-polar hydrocarbon oils can increase the adhesion of coal particles and bubbles. Since the non-polar hydrocarbon oil is unfolded on the surface of the coal particles, the degree of hydrophobicity on the surface of the coal particles is increased, and the hydration is weakened, so that when the coal particles collide with the bubbles, the hydrated film is easily broken, and the adhesion process is easy to proceed.
(2) The non-polar hydrocarbon oil can effectively improve the adhesion of the coal particles to the bubbles. This is caused by the enrichment of non-polar hydrocarbon oils along the periphery of the three-phase contact to form an oil ring. When the surface of the bubble is in contact with the coal particles, the gap between the two causes the oil droplets to rapidly aggregate due to the capillary force, and then expands the area to form an oil film, and gathers into an oil ring to the wetted periphery in contact with the bubble, thereby promoting the coal particle. Firmly adhere to the bubbles. As shown in Figure 3.
Figure 3 Formation of the oil ring under the bubble
(3) The surface of the fine-grained coal adheres to the oil droplets and merges with each other to form a floc.
Second, the impact of the chemical composition of non-polar hydrocarbon oil on the capture
Among organic compounds, any substance containing only carbon and hydrogen atoms is called a hydrocarbon compound. Hydrocarbon compounds are generally divided into two major categories, saturated hydrocarbons and unsaturated hydrocarbons, depending on their molecular structure.
The saturated hydrocarbon refers to a hydrocarbon compound in which all carbon atoms are connected by a single bond, and includes two kinds of alkane composed of a linear chain and a cycloalkane composed of a cyclic chain. When the number of carbon atoms in an alkane reaches four or more, the arrangement of carbon atoms in the molecule will be different when the number of carbon atoms is the same, and this phenomenon is called normal or heterogeneous of an alkane.
The unsaturated hydrocarbon means a hydrocarbon compound formed by a partial double bond between carbon atoms, an unsaturated hydrocarbon containing a linear double bond is called an olefin, and an unsaturated hydrocarbon containing a benzene ring is called an aromatic hydrocarbon (abbreviated as an aromatic hydrocarbon).
The capture performance of non-polar hydrocarbon oils is related to their chemical composition, and their composition varies greatly depending on the origin, processing method and fraction temperature.
(1) Effect of non-polar components on flotation
The non-polar hydrocarbon oils can be classified into aromatic hydrocarbons, olefins, and alkanes according to the hydrocarbon group composition. Alkanes can be further divided into normal alkanes, isoparaffins and naphthenes. There are also some oxygen-containing, nitrogen-containing compounds in hydrocarbon oils. The long-term practical use and research shows that the order of capture of non-polar hydrocarbon oil components is: aromatics > olefins > isoparaffins > cycloalkanes > normal paraffins; heavy aromatics (polycyclic) > light aromatics (single ring).
(2) Effect of heteropolar compounds on flotation
In the hydrocarbon oil composition, there are a small amount of non-hydrocarbon impurities other than the polar component, for example, a heteropolar compound such as pyridine, quinoline, pyrrole, phenol, fatty acid, alcohol ester, and carbonyl compound. Due to the presence of these impurities, the floatability is greatly improved, which not only saves the amount but also improves the process effect.
The reason why the heteropolar substances have a catching effect on the coal particles is because the heteropolar molecules can be aligned at the polar parts of the surface of the coal particles, and the polar groups are directed to the surface of the coal particles, and various oxygenates on the surface of the coal particles. The functional group interacts; the non-polar group faces the water, makes the small polar part of the coal particle surface hydrophobic, improves the floatability of the coal particle, and then promotes the hydrocarbon oil to adhere to the surface, further improving the hydrophobicity [see Figure 4 ( a)]. However, after the content of the heteropolar substance exceeds a certain amount, a reverse adsorption layer is formed on the surface of the coal particle, so that the surface of the already-hydrophobic coal particle becomes hydrophilic again [see Fig. 4(b)].
Figure 4 Schematic diagram of the action of heteropolar substances on coal particles
Third, the types and properties of commonly used collectors
(1) Kerosene
Kerosene is one of the most widely used non-polar hydrocarbon collectors for slime flotation. It is a distillate product in the cracking of petroleum. The main component is C11-C26 alkane, which is basically insoluble in water and only has a trapping property. The amount of kerosene is generally 1-2 kg/t.
According to different uses, kerosene is classified into lamp kerosene, tractor kerosene, and aviation kerosene. According to product quality standards, the distillate content of less than 270 ° C is not less than 70%, and the distillate content of more than 310 ° C should be less than 2%. Kerosene often contains a small amount of aromatic hydrocarbons, olefins, etc., but its properties vary greatly depending on the source. From the economic point of view, kerosene for lamps is generally used in the flotation of coal slime.
(2) Light diesel oil
Light diesel oil can be divided into catalytic diesel, straight-run diesel, hot cracked diesel and coking diesel according to different processing methods. The light diesel carbon chain length is usually C15-C18, the fractionation temperature is about 165 ° C - 365 ° C, and the density is 0.74 - 0.95 g / cm 3 .
Light diesel oil is dissolved in some paraffin waxes with a relatively large molecular weight. When the temperature drops, it will "crystallize" and precipitate out of the oil in a network structure, that is, the solidification phenomenon of light diesel oil is produced. The coal preparation plant should use light diesel oil with different freezing points according to different seasons.
Commercial light diesel oil is divided into 10th, 0th, -10th, -20th, -35th grades according to the freezing point. Flotation generally uses No. 0 or No. 10 light diesel oil, and the dosage is usually 1 - 2 kg / (ton dry coal slime), which is related to the amount of coal flotation flotation agent.
The composition of light diesel oil is larger than that of kerosene, especially the aromatic content. For example, the content of aromatic hydrocarbons in catalytic cracking light diesel oil is much higher than that of straight-run light diesel oil. The collection performance is higher than that of kerosene, but the selectivity is not as good as kerosene. Light diesel oil has a high molecular weight, so the viscosity is high. The size of the oil beads dispersed in water is large, and the oil film is spread on the surface of the coal particles at a slow rate, but its hydrophobicity is strong. Therefore, it is used as a coal with a lower degree of deterioration during flotation. Collectors are advantageous.
(3) shale light diesel oil
The product obtained by shale light diesel oil shale tar is subjected to cold dewaxing and acid-base washing. Shale light diesel oil contains more unsaturated hydrocarbons (olefins, aromatics), as well as oxygen and nitrogen-containing substances, so shale light diesel oil has strong collection performance and certain foaming performance. Usually used for easy or medium easy selection of slime, the amount is about 1 - 2kg / (ton dry coal slime).
(4) MB series flotation agent
MB series of flotation agents are used in coal preparation floating collector of the series, a brown, a density of 0.93 g / cm3, consisting essentially hydrocarbons (C9 - C15) n structure, and aromatic hydrocarbons isomers, polyalkylbenzenes Class, alkyl indane, and contains other ingredients. There are 5 kinds of flotation agents in this series, which have both harvesting performance and foaming performance, which can meet the flotation needs of different floatable coals. Which, MB1 is suitable for medium and fine mud volatile content is more difficult to float coal, collector performance is stronger than MB2, suitable for warm southern region of China; MB2 suitable for medium and fine mud volatile content of the coal easier to float, should for cold regions of the north; MB12 for medium-fine clay content difficult floated coal; MB25 for medium-volatile coal is easy to float, floatation speed; MB275 for medium and high volatile content of coal fine mud.
(5) (ZF) synthetic flotation agent
It is a product of liquid phase catalytic oxidation of kerosene as raw material under normal pressure. The composition contains hydrocarbons and hydrocarbon oxides. The ratio of the two is about 60:40. The appearance is brownish yellow transparent liquid with a density of 0.85 g/ Cm3, PH value is 6~7. The flotation agent has both collectibility and foaming properties.
(6) MZ series flotation agent
MZ series flotation agent is a coal collector with different functional groups and foaming properties. It is made by processing, modifying, formulating and removing odor of petrochemical by-products. Its main component is (C8). - C13) of alkanes, aromatic hydrocarbons, fatty alcohols, hydrocarbon derivatives and small amounts of surfactants. The flotation agent has good trapability, selectivity and certain solubility, and the flotation effect is better than using a single hydrocarbon oil.
(7) OC additive
OC additive is an auxiliary collector for improving the flotation effect of slime. It can be used together with all the collectors, foaming agents and composite flotation agents currently used to significantly improve the flotation effect of oxidized coal.
(8) Slime flotation promoter
The accelerator is a flotation agent that can improve the effect of the collector and the foaming agent, and is an important auxiliary agent for floating coal preparation.
The accelerator has the properties of a modifier and an emulsifier, so the role in the flotation process is to promote and enhance the dispersion of the hydrocarbon oil in the coal slurry, to generate fine oil droplets, and to increase the chance of the oil droplets contacting the coal particles. The oil droplets are evenly adhered to the surface of the coal particles to enhance the strength of the oil droplets adhering to the surface of the coal. At the same time, mixing with other flotation agents can enhance the use of various flotation agents, and improve the selectivity and flotation speed. Improve the yield of clean coal
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