Method and system for separating high-kaolin coal gangue from coal gangue, and high-kaolin coal gangue prepared by the method

Abstract

This invention relates to the field of kaolinite technology, specifically to a method and system for separating kaolinite-rich coal gangue from coal gangue, and the kaolinite-rich coal gangue obtained by this method. The method includes: sequentially passing coal gangue with a particle size <200mm through screening, ultrasonic washing, rinsing, X-ray-image recognition, and pneumatic separation to obtain kaolinite-rich coal gangue. The kaolinite-rich coal gangue obtained by the method provided by this invention has the characteristics of high kaolinite content, low loss on ignition, and high calcination whiteness; at the same time, this method reduces the raw material requirements for coal gangue, simplifies the process flow, reduces energy consumption, and thus expands the scope of application.

Description

Technical Field

[0001] This invention relates to the field of kaolinite technology, and more specifically to a method and system for separating kaolinite-rich coal gangue from coal gangue, as well as kaolinite-rich coal gangue obtained by the method. Background Technology

[0002] Coal gangue is a solid waste generated during coal mining, washing, and processing. It is a hard rock with low carbon content. In my country, most of the coal gangue generated during coal mining is dumped as waste without treatment, typically in gullies, slopes, and even arable farmland. This not only occupies a large amount of land but also causes serious pollution and harm to the soil, groundwater, and air environment.

[0003] Coal gangue has a complex composition, low utilization rate, and low added value. Minerally, it is a sedimentary rock composed of various rocks and minerals. In terms of the ratio of organic to inorganic matter, it has a low organic matter content and a high inorganic matter content, which increases as the carbon content decreases. Regarding the composition of metallic and non-metallic elements, most elements in coal gangue exist in oxide form, with SiO2 and Al2O3 being the most abundant. Although coal gangue is currently widely used in power generation, roadbeds, brick making, landfill lining materials, cement, and concrete production, its low added value and the generally long distance from the target market significantly limit its utilization.

[0004] Coal-series kaolinite is an important non-metallic mineral resource associated with coal. my country possesses abundant kaolinite resources in coal-series strata, interbeds, and roof and floor formations. Higher purity kaolinite yields downstream products with superior physicochemical properties and processing performance, making it suitable for industries such as construction, printing and dyeing, plastics, chemicals, electronics, agriculture, and refractory materials. Currently, coal-series kaolinite resources are not mined separately but are extracted along with coal during mining as interbeds. It is then processed in coal preparation plants, with some kaolinite (+50mm) manually sorted before being sent to kaolinite processing plants for further processing. Because kaolinite has a similar density to other ores in coal gangue, and due to coal dust adhesion, it is difficult to distinguish kaolinite by appearance. Consequently, most coal preparation plants do not separate kaolinite, instead treating it as waste along with other gangue minerals in the coal gangue waste, polluting the environment and wasting resources.

[0005] CN105110439A discloses a method for separating fine kaolinite from coal slime water. This method not only separates fine kaolinite from coal slime water, realizing the resource utilization of kaolinite, but also reduces the ash content of coal slime. However, the cost of flotation of coal slime water by adding reagents is high, and this method faces significant economic problems.

[0006] CN106379909A discloses a method for producing coal-series kaolin from waste burnt coal gangue. The method includes: sequentially performing preliminary classification (i.e., manual sorting, crushing, washing, screening, centrifugal dewatering, concentration and pressure filtration), secondary classification, photoelectric color sorting, and ultrafine pulverization to obtain ultrafine kaolin. This method is cumbersome, does not sort materials larger than 5mm, and only sorts materials between 0.1-5mm. It also has high requirements for the color of the material, and can only sort out white materials. In reality, only burnt coal gangue can produce white materials, while most coal gangue does not meet the requirements.

[0007] The sorting of kaolinite generally involves energy-intensive processes such as manual screening, multi-stage crushing, flotation, and centrifugal dewatering, as well as long process flows and high requirements for the characteristics of coal gangue raw materials.

[0008] Therefore, there is an urgent need for a new method to separate kaolinite-rich coal gangue from coal gangue. Summary of the Invention

[0009] The purpose of this invention is to overcome the problems of existing methods for separating kaolinite from coal gangue, which involve high-energy-consuming processes such as manual screening, multi-stage crushing, flotation, and centrifugal dewatering, as well as long process flow and high requirements for the characteristics of coal gangue raw materials. This invention provides a new method and system for separating kaolinite-rich coal gangue from coal gangue, and a kaolinite-rich coal gangue produced by this method. This method reduces the requirements for coal gangue raw materials, simplifies the process flow, and reduces energy consumption.

[0010] To achieve the above objectives, the first aspect of the present invention provides a method for separating kaolinite-rich coal gangue from coal gangue, the method comprising: sequentially passing coal gangue with a particle size <200mm through screening, ultrasonic washing, rinsing, X-ray-image recognition, and pneumatic separation to obtain kaolinite-rich coal gangue.

[0011] Preferably, the method includes the following steps:

[0012] (1) The coal gangue with a particle size <200mm is screened to obtain coal gangue with a particle size ≥25mm as material I;

[0013] (2) The material I and the washing solvent are subjected to ultrasonic washing to obtain material II and washing liquid;

[0014] (3) The material II and the rinsing solvent are rinsed to obtain material III and rinsing solution;

[0015] (4) Perform X-ray image recognition on material III to identify the kaolinite content in material III;

[0016] (5) When the threshold of the X-ray image recognition is less than or equal to the set value, the material III is subjected to the pneumatic sorting to obtain the rich kaolin coal gangue and low carbon coal gangue;

[0017] Wherein, the set value is ≤1.06.

[0018] The second aspect of the present invention provides a kaolin-rich coal gangue prepared by the method provided in the first aspect.

[0019] A third aspect of the present invention provides a system for separating kaolin-rich coal gangue from coal gangue, the system comprising: a screening unit, an ultrasonic washing unit, a rinsing unit, an identification unit, and a pneumatic separation unit connected in sequence;

[0020] The screening unit is used to screen coal gangue with a particle size <200mm to obtain coal gangue with a particle size ≥25mm as material I;

[0021] The ultrasonic washing unit is used to ultrasonically wash the material I and the washing solvent to obtain material II and washing liquid.

[0022] The rinsing unit is used to rinse material II and rinsing solvent to obtain material III and rinsing liquid;

[0023] The identification unit is used to perform X-ray-image recognition on the material III to identify the kaolinite content in the material III;

[0024] The pneumatic sorting unit is used to pneumatically sort the material III with a kaolinite content ≥80wt% to obtain kaolinite-rich coal gangue and low-carbon coal gangue.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] (1) Compared with the prior art, the method provided by the present invention adopts the technical means of screening, ultrasonic washing, rinsing, X-ray-image recognition and pneumatic sorting, and the obtained kaolinite-rich coal gangue has the characteristics of high kaolinite content, low loss on ignition and high calcination whiteness; in particular, by limiting the threshold parameter of X-ray-image recognition, the physical property parameters of kaolinite-rich coal gangue can be further improved.

[0027] (2) The method provided by the present invention reduces the raw material requirements of coal gangue, simplifies the process flow, reduces energy consumption, and thus expands the scope of application. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of a system for separating kaolinite-rich coal gangue from coal gangue, provided by the present invention.

[0029] Explanation of reference numerals in the attached figures

[0030] I. Screening Unit II. Ultrasonic Washing Unit III. Rinsing Unit

[0031] IV. Identification Unit V, Pneumatic Sorting Unit VI, Settling Unit

[0032] 1. Coal gangue with a particle size < 200mm 2. Coal gangue with a particle size ≥ 25mm (i.e., Material I)

[0033] 3. Coal gangue with a particle size <25mm 4. Carbon-rich coal gangue 5. Material II

[0034] 6. A mixture of washing and rinsing solutions 7. Material III 8. Rinsing solution

[0035] 9. Materials with kaolinite content ≥ 80 wt% (III) 10. Low-carbon coal gangue

[0036] 11. Rich kaolin coal gangue; 12. Coal slime; 13. Clear liquid.

[0037] 14. Circulating solvent Detailed Implementation

[0038] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0039] The first aspect of the present invention provides a method for separating kaolinite-rich coal gangue from coal gangue, the method comprising: sequentially passing coal gangue with a particle size <200mm through screening, ultrasonic washing, rinsing, X-ray-image recognition, and pneumatic separation to obtain kaolinite-rich coal gangue.

[0040] The inventors of this invention have discovered that, compared to existing technologies that use flotation to separate fine coal gangue from coal slime, or to extract white kaolinite from overburned coal gangue through multi-stage crushing, flotation, centrifugal dewatering, and photoelectric separation, this invention employs screening, ultrasonic washing, rinsing, X-ray-image recognition, and pneumatic separation techniques. This simplifies the process, reduces the requirements for coal gangue raw materials, expands the scope of application of the method, and reduces energy consumption.

[0041] In some embodiments of the present invention, preferably, the method includes the following steps:

[0042] (1) The coal gangue with a particle size <200mm is screened to obtain coal gangue with a particle size ≥25mm as material I;

[0043] (2) The material I and the washing solvent are subjected to ultrasonic washing to obtain material II and washing liquid;

[0044] (3) The material II and the rinsing solvent are rinsed to obtain material III and rinsing solution;

[0045] (4) Perform X-ray image recognition on material III to identify the kaolinite content in material III;

[0046] (5) When the threshold of the X-ray image recognition is less than or equal to the set value, the material III is subjected to the pneumatic sorting to obtain the rich kaolin coal gangue and low carbon coal gangue;

[0047] Wherein, the set value is ≤1.06.

[0048] In this invention, unless otherwise specified, a set value ≤ 1.06 corresponds to a kaolinite content ≥ 80 wt% in material III. That is, when the threshold ≤ the set value, i.e., the threshold ≤ 1.06, corresponding to a kaolinite content ≥ 80 wt% in material III, material III will undergo pneumatic sorting; when the threshold > the set value, i.e., the threshold > 1.06, corresponding to a kaolinite content < 80 wt% in material III, material III will not undergo pneumatic sorting.

[0049] In this invention, because coal gangue is harder than coal and not easily crushed or pulverized, the coal content in the fine particles is high, while the gangue content in the large particles is relatively high. Therefore, in step (1), the screening aims to separate the coal gangue into carbon-rich coal gangue and material I.

[0050] In this invention, the screening method has a wide range of options. Preferably, coal gangue with a particle size <200mm is passed through a vibrating screen with a screen aperture of 25mm to obtain coal gangue with a particle size ≥25mm as material I, and coal gangue with a particle size <25mm as carbon-rich coal gangue.

[0051] In some embodiments of the present invention, preferably, in step (1), the screening further obtains coal gangue with a particle size <25mm as carbon-rich coal gangue; more preferably, the carbon content in the carbon-rich coal gangue is 10-30wt%.

[0052] In this invention, unless otherwise specified, the carbon-rich coal gangue obtained by this invention can be used as solid fuel due to its certain calorific value; the low-carbon coal gangue can be used as building material or mine backfill material.

[0053] In this invention, the ultrasonic washing aims to remove coal powder adhering to the surface of material I. Preferably, in step (2), the ultrasonic washing conditions include: a frequency of 20-100 kHz, preferably 45-60 kHz; and a time of 1-30 min, preferably 5-10 min. Using these preferred conditions is more conducive to removing coal powder adhering to the surface of material I and improving the accuracy of X-ray identification.

[0054] In some embodiments of the present invention, preferably, in step (2), the ratio of material I to washing solvent is 1:2-6, for example, 1:2, 1:3, 1:3.5, 1:4, 1:6, and any value in any range of any two components, preferably 1:3-4.

[0055] In this invention, a wide range of washing solvents can be selected. Preferably, the washing solvent is water, including but not limited to industrial water, domestic water, etc.

[0056] In this invention, the rinsing is intended to further remove residual coal dust from the surface of material II. Preferably, in step (3), the rinsing time is 2-10 minutes, more preferably 3-5 minutes. Using the preferred conditions is more conducive to removing coal dust from the surface of coal gangue and saves energy.

[0057] In some embodiments of the present invention, preferably, in step (3), the ratio of material II to rinsing solvent is 1:0.5-3, for example, 1:0.5, 1:1, 1:1.5, 1:3, and any value in any range of any two values, preferably 1:1-1.5.

[0058] In this invention, a wide range of options are available for the rinsing solvent. Preferably, the rinsing solvent is water, including but not limited to industrial water, domestic water, etc.

[0059] In this invention, unless otherwise specified, the X-ray image recognition mainly uses dual-energy X-rays to irradiate material III. Through signal acquisition and algorithm optimization, the obtained image is converted into a grayscale image. Based on the difference in the ratio of the maximum grayscale value of high-energy X-rays to the maximum grayscale value of low-energy X-rays for different contents of kaolinite, the content of kaolinite in material III is obtained.

[0060] In some embodiments of the present invention, preferably, in step (4), the process of X-ray-image recognition includes: recognizing the material III with high-energy X-rays and low-energy X-rays respectively, and processing the obtained high-energy X-ray image and low-energy X-ray image respectively to obtain a high-energy X-ray grayscale image and a low-energy X-ray grayscale image.

[0061] According to the present invention, preferably, the threshold is the gray-scale peak ratio of the high-energy X-ray grayscale image and the low-energy X-ray grayscale image; more preferably, the threshold is 0.8-1.2, for example, 0.8, 0.9, 1, 1.06, 1.1, 1.2, and any value in the range of any two values, preferably 0.9-1.1.

[0062] In some embodiments of the present invention, preferably, the voltage of the high-energy X-ray is 100-160kV, more preferably 140-150kV; and the current is 1-3mA, more preferably 2-3mA.

[0063] In some embodiments of the present invention, preferably, the voltage of the low-energy X-ray is 50-90kV, more preferably 70-80kV; and the current is 1-3mA, more preferably 2-3mA.

[0064] According to the present invention, preferably, the material III is dried before the X-ray image recognition is performed; more preferably, the moisture content of the material III is ≤30wt%, preferably ≤20wt%.

[0065] In this invention, a wide range of drying methods can be selected, as long as the moisture content parameter of material III meets the above-mentioned limitations. Preferably, compressed air is used to dry material III.

[0066] In some embodiments of the present invention, preferably, the drying time is 5-20 min, more preferably 10-15 min.

[0067] In some embodiments of the present invention, preferably, the method further includes: returning the rinsing liquid and mixing it into the washing solvent as a replenishment of the washing solvent.

[0068] In some embodiments of the present invention, preferably, the method further includes: contacting the mixture of the washing liquid and the rinsing liquid with a flocculant and allowing it to settle to obtain a clear liquid and coal slime. In the present invention, the settling can separate the residual coal slime in the mixture; the flocculant includes, but is not limited to, polyaluminum chloride, polyacrylamide, etc.

[0069] In some embodiments of the present invention, preferably, the clarified liquid is returned as a circulating solvent and mixed with the washing solvent and rinsing solvent; the product obtained after filtering and dewatering the coal slime is used as the carbon-rich coal gangue.

[0070] The second aspect of the present invention provides a kaolin-rich coal gangue prepared by the method provided in the first aspect.

[0071] According to the present invention, preferably, the physical properties of the kaolinite-rich coal gangue satisfy the following: kaolinite content of 80-95wt%, loss on ignition of 5-15%, calcined whiteness ≥85, and coloring element content <1.8wt%.

[0072] In this invention, unless otherwise specified, the kaolinite content parameter and the coloring element content parameter are based on the total weight of the kaolinite-rich coal gangue; the coloring elements include, but are not limited to, Fe and / or Ti. Preferably, the Fe element content is <0.6wt% and the Ti element content is <1.2wt%.

[0073] In this invention, unless otherwise specified, the kaolinite content and color-developing element content are measured using the XRF method; the loss on ignition is measured using a thermogravimetric analyzer; and the calcined whiteness is measured using a whiteness meter.

[0074] A third aspect of the present invention provides a system for separating kaolin-rich coal gangue from coal gangue, the system comprising: a screening unit, an ultrasonic washing unit, a rinsing unit, an identification unit, and a pneumatic separation unit connected in sequence;

[0075] The screening unit is used to screen coal gangue with a particle size <200mm to obtain coal gangue with a particle size ≥25mm as material I;

[0076] The ultrasonic washing unit is used to ultrasonically wash the material I and the washing solvent to obtain material II and washing liquid.

[0077] The rinsing unit is used to rinse material II and rinsing solvent to obtain material III and rinsing liquid;

[0078] The identification unit is used to perform X-ray-image recognition on the material III to identify the kaolinite content in the material III;

[0079] The pneumatic sorting unit is used to pneumatically sort the material III with a kaolinite content ≥80wt% to obtain kaolinite-rich coal gangue and low-carbon coal gangue.

[0080] According to the present invention, preferably, the rinsing unit further includes a drying section for drying the material III.

[0081] According to the present invention, preferably, the flushing liquid outlet of the flushing unit is connected to the inlet of the ultrasonic washing unit for returning the flushing liquid and mixing it with the washing solvent.

[0082] According to the present invention, preferably, the device further includes: a sedimentation unit connected to the washing liquid outlet of the ultrasonic washing unit, for settling the mixture of the washing liquid and the rinsing liquid to obtain a clear liquid and coal slurry; more preferably, the clear liquid outlet of the sedimentation unit is independently connected to the inlet of the ultrasonic washing unit and the rinsing unit, for returning the clear liquid as a circulating solvent and mixing it with the washing solvent and the rinsing solvent.

[0083] This invention provides a system for separating kaolin-rich coal gangue from coal gangue, such as... Figure 1 As shown, by Figure 1 It can be seen that the system includes: a screening unit I, an ultrasonic washing unit II, a rinsing unit III, an identification unit IV, and a pneumatic sorting unit V connected in sequence;

[0084] The unit comprises: screening unit I for screening coal gangue 1 with a particle size <200mm to obtain coal gangue 2 with a particle size ≥25mm as material I and coal gangue 3 with a particle size <25mm as carbon-rich coal gangue 4; ultrasonic washing unit II for ultrasonically washing material I 2 with washing solvent to obtain material II 5 and washing liquid; rinsing unit III for rinsing material II 5 with rinsing solvent to obtain material III 7 and rinsing liquid 8; identification unit IV for performing X-ray-image recognition on material III 7 to identify the kaolinite content in material III; and pneumatic separation unit V for pneumatically separating material III 9 with a kaolinite content ≥80wt% to obtain kaolinite-rich coal gangue 11 and low-carbon coal gangue 10.

[0085] The rinsing unit III also includes a drying section for drying the material III 7;

[0086] The flushing fluid outlet of the flushing unit III is connected to the inlet of the ultrasonic washing unit II, and is used to return the flushing fluid 8 and mix it with the washing solvent.

[0087] The device further includes: a settling unit VI connected to the washing liquid outlet of the ultrasonic washing unit II, used to settle the mixture 6 of washing liquid and rinsing liquid to obtain clear liquid 13 and coal slime 12; the clear liquid outlet of the settling unit V is independently connected to the inlet of the ultrasonic washing unit II and the rinsing unit III, used to return the clear liquid 13 as a circulating solvent 14 and mix it with the washing solvent and rinsing solvent.

[0088] The present invention will be specifically illustrated below through examples.

[0089] The kaolinite content and colorimetric element content parameters were both determined using the XRF method.

[0090] Loss on ignition parameters were measured using a thermogravimetric analyzer.

[0091] The whiteness parameters of calcination were measured using a whiteness meter.

[0092] Example 1

[0093] (1) Coal gangue with a particle size <200mm (the properties of the raw materials are listed in Table 1) is screened through a sieve with a pore size of 25mm to obtain coal gangue with a particle size ≥25mm as material I, and coal gangue with a particle size <25mm as carbon-rich coal gangue.

[0094] (2) The above material I and the washing solvent (water) are ultrasonically washed at a weight ratio of 1:3 (frequency 50kHz, time 10min) to obtain material II and washing liquid.

[0095] (3) The above material II and the rinsing solvent (water) are rinsed at a weight ratio of 1:1 to obtain material III and rinsing solution;

[0096] (4) After drying the above material III, the moisture content of material III is <25wt%; then X-ray image recognition is performed. High-energy X-rays (voltage 150kV, current 3mA) and low-energy X-rays (voltage 80kV, current 3mA) are used to identify the material III, and the obtained high-energy X-ray images and low-energy X-ray images are processed to obtain high-energy X-ray grayscale images and low-energy X-ray grayscale images. The threshold is obtained according to the grayscale peak ratio of the high-energy X-ray grayscale images and low-energy X-ray grayscale images; the set value is 1.04.

[0097] (5) When the above threshold is lower than 1.04, material III is pneumatically separated to obtain kaolinite-rich coal gangue and low-carbon coal gangue with a kaolinite content of >80wt%.

[0098] The property parameters of carbon-rich coal gangue, kaolin-rich coal gangue, and low-carbon coal gangue are listed in Table 2.

[0099] Table 1

[0100]

[0101] Note: 1 - refers to the molar ratio of SiO2 / Al2O3.

[0102] Table 2

[0103]

[0104] Note: 1 - refers to the molar ratio of SiO2 / Al2O3.

[0105] As shown in Table 1-2, compared to coal gangue raw materials, the dry basis ash content of the kaolinite-rich coal gangue prepared by the method provided in this invention is increased to 84.42 wt%, indicating a significant increase in kaolinite content. Furthermore, the SiO2 / Al2O3 molar ratio is closer to the theoretical molar ratio of kaolinite (2), and the calcination whiteness reaches 87. In addition, compared to coal gangue raw materials, the dry basis ash content of the carbon-rich coal gangue is reduced by 9.31 wt%, while the calorific value is increased by 3.41 kJ / kg. It also contains enriched coloring elements TiO2 and Fe2O3, indicating that coloring elements are more abundant in fine-grained coal gangue, resulting in lower calcination whiteness. The dry basis ash content of the low-carbon coal gangue is increased to 78.86 wt%, indicating that the organic carbon content is still relatively high.

[0106] Example 2

[0107] The method of Example 1 is different except that in step (2), the ultrasonic washing frequency is replaced with 10kHz, and the other conditions are the same, to obtain rich kaolin coal gangue, rich carbon coal gangue and low carbon coal gangue; the relevant parameters of rich kaolin coal gangue, rich carbon coal gangue and low carbon coal gangue are listed in Table 3.

[0108] Table 3

[0109]

[0110] Note: 1 - refers to the molar ratio of SiO2 / Al2O3.

[0111] Comparing the data in Tables 2 and 3, it can be seen that limiting the ultrasonic washing frequency in step (2) to 20-100kHz can effectively increase the dry basis ash content and calcination whiteness of kaolinite coal gangue, and effectively reduce the calorific value of kaolinite coal gangue; in particular, limiting the ultrasonic washing frequency to 45-60kHz can more effectively improve the physical property parameters of kaolinite coal gangue.

[0112] Example 3

[0113] The method of Example 1 is different in that the value in step (4) is set to 1.25. That is, when the above threshold is 1.25, material III is directly pneumatically sorted, and the other conditions are the same, to obtain rich kaolin coal gangue, rich carbon coal gangue, and low carbon coal gangue. The relevant parameters of rich kaolin coal gangue, rich carbon coal gangue, and low carbon coal gangue are listed in Table 4.

[0114] Table 4

[0115]

[0116] Note: 1 - refers to the molar ratio of SiO2 / Al2O3.

[0117] Comparing the data in Tables 2 and 4, it can be seen that by limiting the set value to ≤1.06, the dry basis ash content and calcination whiteness value of kaolinite gangue can be effectively improved, and the SiO2 / Al2O3 molar ratio is closer to the theoretical molar ratio of kaolinite.

[0118] Comparative Example 1

[0119] Using a conventional process, black coal gangue larger than 100mm is manually removed on a horizontal conveyor belt. The remaining gangue is fed into a primary crusher via a guide plate, where it is crushed to a particle size of 50-100mm. The gangue is then conveyed to a jigging washing machine, where materials with a specific gravity greater than 2.6 and those with a diameter greater than 100mm are separated and returned to the primary crusher for further crushing. The intermediate products enter a screening process. Kaolinite larger than 5mm on the screen is directly sent to a centrifugal dewatering unit to reduce the moisture content from 18-30wt% to 7-10wt%, and then conveyed to the kaolinite concentrate silo. Kaolinite undersized (0.1-5mm) undergoes color sorting. The color sorter receives signals from colored kaolinite via a CCD sensor, and a robotic arm discharges the colored particles to a waste bin. White kaolinite continues to fall into a receiving hopper, achieving the goal of finely selecting kaolinite. Washing waste liquid smaller than 0.1mm enters the thickening tank, which has a cylindrical structure with a conical bottom. The concentrated sludge is continuously discharged from the bottom and enters the filter press to form a sludge cake, which is then discharged. The clean water is reused.

[0120] The property parameters of kaolinite larger than 5 mm and non-ferrous coal gangue of 0.1-5 mm are listed in Table 5.

[0121] Table 5

[0122]

[0123] Comparing the data in Tables 2 and 4, it can be seen that the kaolin-rich coal gangue prepared by the method provided in this invention has a higher dry basis ash content, that is, the kaolin yield obtained by calcination using the method provided in this invention is higher, increasing by 3.43-7 wt% compared to conventional methods. At the same time, the content of visible elements (TiO2 and Fe2O3) in the kaolin-rich coal gangue prepared by the method provided in this invention is 1.32 wt%, while the contents in conventional methods are 2.94 wt% and 1.83 wt%, respectively. The whiteness of calcination will decrease due to the higher content of visible elements, thus affecting the value of kaolinite.

[0124] Comparative Example 2

[0125] The method of Example 1 is different except that steps (2)-(3) are omitted. That is, the material I obtained in step (1) is directly subjected to X-ray image recognition, and the other conditions are the same to obtain rich kaolin coal gangue, rich carbon coal gangue, and low carbon coal gangue. The relevant parameters of rich kaolin coal gangue, rich carbon coal gangue, and low carbon coal gangue are listed in Table 6.

[0126] Table 6

[0127]

[0128] Note: 1 - refers to the molar ratio of SiO2 / Al2O3.

[0129] By comparing the data in Tables 2 and 6, it can be seen that, compared with Comparative Example 2, the kaolin-rich coal gangue prepared by the method provided in Example 1 has a higher dry basis ash content and calcination whiteness, as well as a lower calorific value and lower content of revealed elements; the low-carbon coal gangue prepared also has a higher dry basis ash content and a lower calorific value.

[0130] Test case

[0131] The electricity consumption and circulating water consumption of the process equipment for producing 1000 tons of kaolinite using the methods provided in Example 1 and Comparative Example 1 are listed in Table 7.

[0132] Table 7

[0133] Electricity consumption, kWh Circulating water consumption, t Example 1 2500 10 Comparative Example 1 3100 15

[0134] As shown in Table 7, the method provided by this invention reduces electricity consumption by 19.35% and circulating water consumption by 33.33% when producing kaolinite-rich coal gangue. Therefore, for a plant that processes 200,000 tons of kaolinite annually, based on an industrial electricity cost of 1 yuan / ton and a water cost of 10 yuan / ton, the method provided by this invention can save 130,000 yuan annually.

[0135] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various specific technical features in any suitable manner. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately. However, these simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for separating kaolin-rich coal gangue from coal gangue, characterized in that, The method includes: passing coal gangue with a particle size <200mm through screening, ultrasonic washing, rinsing, X-ray-image recognition, and pneumatic sorting in sequence to obtain kaolin-rich coal gangue; The method includes the following steps: (1) The coal gangue with a particle size <200mm is screened to obtain coal gangue with a particle size ≥25mm as material I and coal gangue with a particle size <25mm as carbon-rich coal gangue. (2) The material I and the washing solvent are subjected to ultrasonic washing to obtain material II and washing liquid; the conditions for ultrasonic washing include: frequency of 20-100 kHz and time of 1-30 min; (3) The material II and the rinsing solvent are rinsed to obtain material III and rinsing solution; (4) The material III is dried so that the moisture content is ≤30wt%, and the X-ray image recognition is performed to identify the kaolinite content in the material III; (5) When the threshold of the X-ray image recognition is less than or equal to the set value, the material III is subjected to the pneumatic sorting to obtain the rich kaolin coal gangue and low carbon coal gangue; Wherein, the set value is ≤1.06; The X-ray-image recognition process includes: identifying the material III using high-energy X-rays and low-energy X-rays respectively, processing the obtained high-energy X-ray images and low-energy X-ray images respectively to obtain high-energy X-ray grayscale images and low-energy X-ray grayscale images, and using the grayscale peak ratio of the high-energy X-ray grayscale images and low-energy X-ray grayscale images as the threshold; wherein the voltage of the high-energy X-rays is 100-160kV and the current is 1-3mA; the voltage of the low-energy X-rays is 50-90kV and the current is 1-3mA; Alternatively, the rinsing solution may be returned and mixed with the washing solvent; or, The mixture of the washing liquid and rinsing liquid is contacted with a flocculant and allowed to settle to obtain a clear liquid and coal slurry; wherein, the clear liquid is returned as a circulating solvent and mixed with the washing solvent and rinsing solvent, and the coal slurry is filtered and dehydrated to obtain the product as the carbon-rich coal gangue.

2. The method according to claim 1, wherein, In step (1), the carbon content in the carbon-rich coal gangue is 10-30 wt%; In step (2), the conditions for ultrasonic washing include: a frequency of 45-60 kHz and a time of 5-10 min; The ratio of material I to washing solvent is 1:2-6.

3. The method according to claim 2, wherein, The ratio of material I to washing solvent is 1:3-4.

4. The method according to claim 1, wherein, In step (3), the ratio of material II to rinsing solvent is 1:0.5-3; The rinsing time is 2-10 minutes.

5. The method according to claim 4, wherein, In step (3), the ratio of material II to rinsing solvent is 1:1-1.5; The rinsing time is 3-5 minutes.

6. The method according to claim 1, wherein, In step (4), The threshold value is 0.8-1.2; The high-energy X-rays have a voltage of 140-150 kV and a current of 2-3 mA. The low-energy X-rays have a voltage of 70-80 kV and a current of 2-3 mA.

7. The method according to claim 6, wherein, In step (4), the threshold is 0.9-1.

1.

8. The method according to claim 1, wherein, The moisture content of material III is ≤20 wt%.

9. The method according to any one of claims 1-8, wherein, The physical properties of the kaolinite gangue meet the following requirements: kaolinite content of 80-95wt%, loss on ignition of 5-15%, calcined whiteness ≥85%, and coloring element content <1.8wt%.

10. The method according to claim 9, wherein, The kaolinite gangue contains Fe content < 0.6 wt% and Ti content < 1.2 wt%.

11. The method according to any one of claims 1-8, wherein, The method is carried out in a system for separating kaolin-rich coal gangue from coal gangue, characterized in that the system comprises: a screening unit, an ultrasonic washing unit, a rinsing unit, an identification unit, and a pneumatic sorting unit connected in sequence. The screening unit is used to screen coal gangue with a particle size <200mm to obtain coal gangue with a particle size ≥25mm as material I; The ultrasonic washing unit is used to ultrasonically wash the material I and the washing solvent to obtain material II and washing liquid. The rinsing unit is used to rinse material II and rinsing solvent to obtain material III and rinsing liquid; The identification unit is used to perform X-ray-image recognition on the material III to identify the kaolinite content in the material III; The pneumatic sorting unit is used to pneumatically sort the material III with a kaolinite content ≥80wt% to obtain kaolinite-rich coal gangue and low-carbon coal gangue.

12. The method according to claim 11, wherein, The rinsing unit also includes a drying section for drying the material III; The flushing fluid outlet of the flushing unit is connected to the inlet of the ultrasonic washing unit, and is used to return the flushing fluid and mix it with the washing solvent.

13. The method according to claim 11, wherein, The system also includes a sedimentation unit connected to the washing liquid outlet of the ultrasonic washing unit, used to settle the mixture of washing liquid and rinsing liquid to obtain clear liquid and coal slime; The clear liquid outlets of the sedimentation units are independently connected to the inlets of the ultrasonic washing unit and the rinsing unit, respectively, for returning the clear liquid as a circulating solvent and mixing it with the washing solvent and rinsing solvent.

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