Method for preparing ultra-pure coal through grinding and flotation combination

Abstract

The invention relates to a method for preparing ultra-pure coal through combination of grinding and flotation. The method comprises the following steps: carrying out primary surface modification and flotation to remove most of gangue; fine silt on the surfaces of the coal particles is removed through scrubbing and ore grinding, and the hydrophobicity of the coal is improved by combining secondary surface modification and flotation; the coal quality is judged according to the ash content of secondary flotation clean coal, if the ash content is larger than 3%, dissociation ore grinding and grading are conducted, and it is guaranteed that coal and gangue are fully dissociated; double-emulsion surface modification is adopted to enhance the dispersibility of the agent, and finally, the ultra-pure coal with the ash content smaller than 1% is obtained through three-time flotation and four-time flotation. Through the synergistic effect of scrubbing ore grinding, dissociation ore grinding and multi-section flotation, the dissociation efficiency and flotation selectivity of coal and gangue are effectively improved, the method adapts to coal quality fluctuation, and the yield of ultra-pure coal is increased.

Description

Technical Field

[0001] This invention relates to the field of coal mining technology, specifically a method for preparing ultrapure coal using a combination of grinding and flotation. Background Technology

[0002] Ultra-pure coal refers to coal products with an ash content of less than 1% and an organic matter purity of >99.9%. It is widely used in high-end fields such as coal-based battery anode materials, and its ash content must be strictly controlled below 1% to avoid performance degradation. Some raw coal from existing coal mines can be used as high-quality carbon material feedstock, but traditional coal preparation plants usually lack flotation processes, and the coal slime after gravity separation is directly sold as power coal, resulting in resource waste.

[0003] Traditional flotation processes typically involve a simple single-stage flotation, where coal slime slurry is mixed with reagents and directly fed into the flotation machine. For example, a small coal preparation plant using this single-stage flotation process struggles to effectively separate fine-grained coal slime with fluctuating ash content based on different particle sizes and ash characteristics. This results in unstable flotation performance, significant fluctuations in clean coal quality, and an inability to meet stringent market requirements for clean coal quality. Some coal preparation plants employ a two-stage flotation process: roughing and cleaning. In the roughing stage, higher doses of collectors are used, but their adaptability to complex coal qualities is limited. For example, for coal slime containing large amounts of high-ash fine mud that is closely intertwined with coal, two-stage flotation still struggles to achieve deep deashing and efficient recovery. Furthermore, coal slime quality naturally fluctuates. When coal quality deteriorates, insufficient separation of coal and gangue in the slime makes it difficult for existing single-stage flotation processes to achieve efficient separation of coal and gangue, resulting in an inability to consistently obtain ultra-pure coal products with ash content ≤1%. Therefore, there is an urgent need to develop a new process that can adapt to fluctuations in coal slime quality, promote efficient separation of coal and gangue, and improve flotation selectivity for the preparation of raw materials in high-end fields such as coal-based battery anode materials, so as to meet the long-term stable production needs of ultrapure coal. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing ultrapure coal by combining grinding and flotation processes. By combining grinding and flotation processes, this method solves problems such as insufficient separation of coal and gangue in coal slime, low flotation selectivity, and poor adaptability to coal quality fluctuations. It adapts to changes in coal slime quality and achieves stable production of ultrapure coal with ash content of less than 1%.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] The method for preparing ultrapure coal by combined grinding and flotation includes the following steps:

[0007] Step 1: Mix coal slime and flotation reagent in the first surface modifier. The interaction time between the flotation reagent and coal slime is 3-5 minutes to obtain the first surface-modified slurry.

[0008] Step 2: The first surface-modified slurry enters the first flotation device to obtain the first flotation concentrate;

[0009] Step 3: The first flotation concentrate enters the scrubbing and grinding equipment for scrubbing and grinding operations to obtain scrubbing and grinding products; during the scrubbing and grinding operation, the residence time of the first flotation concentrate in the equipment is ≤5min, and the increase in particles smaller than 0.074mm after the operation is ≤15%;

[0010] Step 4: The scrubbing and grinding products and flotation reagents are mixed in the second surface modifier. The interaction time between the flotation reagents and coal slime is 3-5 minutes to obtain the second surface-modified slurry.

[0011] Step 5: The second surface-modified slurry enters the second flotation equipment to obtain the second flotation concentrate;

[0012] Step Six: Determine the ash content of the second flotation concentrate: If the ash content is ≤3%, proceed to Step Seven; if the ash content is >3%, first perform the dissociation grinding and classification operations, then proceed to Step Seven; the dissociation grinding operation involves feeding the second flotation concentrate into the dissociation grinding equipment for grinding, so that the content of particles >0.074mm in the dissociated product is ≤25%; the classification operation involves classifying the dissociation grinding product by a classifying hydrocyclone with a particle size of 0.25mm, with particles ≥0.25mm returned to the dissociation grinding equipment, and particles <0.25mm proceeding to Step Seven;

[0013] Step 7: The product from Step 6 is mixed with the dual-emulsion flotation reagent, and the interaction time between the dual-emulsion flotation reagent and the product from Step 6 is 3-5 minutes; the modified dual-emulsion product is obtained.

[0014] Step 8: The modified product of the double emulsion enters the third flotation equipment, and the height of the tailings pipe relative to the feed inlet is ≥15cm, to obtain the third flotation clean coal;

[0015] Step 9: The third flotation concentrate enters the fourth flotation unit, with the tailings pipe height relative to the feed inlet ≥ 20cm, to obtain ultrapure coal;

[0016] The first and second flotation times are 3 to 4 minutes, the stirring speed is 2000 to 2200 r / min, and the aeration rate is 0.25 to 0.5 m3 / h; the third and fourth flotation concentrations are 40 to 60 g / L, and column flotation equipment is used with a circulation pressure ≥0.16 MPa.

[0017] The scrubbing and grinding equipment and the dissociation grinding equipment mentioned in step three of the above method are vertical stirred mills, rod mills or ball mills. The mill speed, grinding concentration and grinding media diameter are adjusted according to the properties of the feed.

[0018] The dual-emulsion flotation reagent mentioned in step seven of the above method is an oil-in-water-in-oil dual-emulsion or a water-in-oil-in-water dual-emulsion, which is prepared by mixing the flotation reagent with water using a dual-emulsification dosing device.

[0019] In steps two and three of the above method, the flotation time for the first and second flotation operations is 3 minutes, the stirring speed is 2000 r / min, and the aeration rate is 0.25 m³ / min. 3 / h.

[0020] In step three of the above method, the slurry concentration of the scrubbing and grinding operation is 100 g / L; the grinding media are zirconia balls with diameters of 2 mm and 3 mm, the mass ratio of 2 mm and 3 mm zirconia balls is 1:2, and the grinding speed is 60 r / min.

[0021] In step six of the above method, the concentration of the dissociated grinding slurry is 180 g / L, and the grinding media are zirconia balls of 5 mm, 4 mm, and 3 mm in size, with a mass ratio of media balls of 1:1:1.

[0022] The beneficial effects of this invention are:

[0023] 1. This invention, by selecting the differentiated application of scrubbing grinding and dissociation grinding according to the coal quality, can remove fine mud from the surface of coal particles through scrubbing grinding, and can achieve sufficient dissociation of coal and gangue through dissociation grinding when the coal quality is poor. It is flexible in operation and solves the problem of insufficient dissociation of coal and gangue in coal slime.

[0024] 2. This invention improves the effect of the second surface modification through scrubbing and grinding, providing a low-ash basis for the second flotation; the double emulsion surface modification enhances the dispersibility of the reagents, promotes the interaction between coal and reagents, and significantly improves the selectivity of the third and fourth flotations.

[0025] 3. By judging the ash content of the second flotation concentrate, the present invention flexibly selects whether to perform liberation grinding, ensuring that ultra-pure coal with ash content <1% can still be stably obtained even when the coal quality fluctuates.

[0026] 4. This invention promotes the entry of gangue into tailings through dissociative grinding, reduces clean coal pollution, and increases the yield of ultrapure coal; the grading operation avoids over-grinding and improves separation efficiency. Attached Figure Description

[0027] Figure 1 This is a process route diagram for the present invention;

[0028] Figure 2 This is a process flow diagram of the present invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0030] Reference Appendix Figure 1 This invention employs two process routes based on the quality of the coal slime. When the coal quality is good, the coal slime enters the flotation system and first undergoes surface modification by interacting with flotation reagents in a first surface modifier. The surface-modified slurry then enters the first flotation unit for the first flotation. The flotation concentrate obtained from the first flotation enters a scrubbing and grinding unit for scrubbing and grinding. The product after scrubbing and grinding enters a second surface modifier for further surface modification, and then enters the second flotation unit for the second flotation. The second flotation concentrate enters a flotation pretreatment unit for surface modification with flotation reagents that form a double emulsion. The surface-modified product then enters a third flotation unit for the third flotation. The third flotation concentrate enters a fourth flotation unit for the fourth flotation, and the fourth flotation concentrate is the ultrapure coal. The tailings from the first, second, third, and fourth flotation processes are mixed and used as flotation tailings.

[0031] When the coal quality is poor, the second flotation concentrate enters the dissociation grinding equipment for dissociation grinding, and the dissociation grinding product enters the classifying hydrocyclone for classification. The particles smaller than 0.25 mm obtained from classification are surface modified in the flotation pretreatment equipment with flotation reagents that form a double emulsion. The particles larger than 0.25 mm obtained from classification are returned to the dissociation grinding equipment for grinding again. The remaining steps are the same as the flotation process when the coal quality is good.

[0032] Coal slime is classified by particle size distribution in a classifying hydrocyclone using centrifugal force. Coarse particles (e.g., larger than 0.5 mm) are discharged from the underflow outlet and can proceed to subsequent gravity separation or other suitable coarse particle treatment processes; fine particles (e.g., smaller than 0.5 mm) are discharged from the overflow outlet and enter the flotation stage. Its function is to separate coal slime of different particle sizes so that more suitable separation processes can be used subsequently, improving separation efficiency.

[0033] Coal slime and flotation reagents are thoroughly mixed in a stirred tank. If collectors and frothers are added to the stirred tank in a certain proportion, stirring ensures the reagents are evenly dispersed in the coal slime slurry, increasing the contact opportunities between the reagents and coal particles, promoting reagent adsorption on the coal particle surface, and preparing for subsequent flotation.

[0034] Reference Appendix Figure 2 As can be seen from S1 to S11, the present invention prepares ultrapure coal according to the following steps:

[0035] Step one is the first surface modification operation: coal slime and flotation reagents are mixed in the first surface modifier. The surface modifier has a stirring effect, which can disperse the reagents, which helps to reduce the amount of reagents used and promotes the adsorption of reagents to coal, thereby increasing the difference in hydrophobicity between coal and gangue. The interaction time between the reagents and coal slime is 3 to 5 minutes to obtain the first surface modified slurry. The coal slime is provided by the coal preparation plant.

[0036] Flotation reagents can be formulated by combining kerosene with ester-based nonionic surfactants. Taking the combination of kerosene and ethyl oleate as an example, the viscosity, surface tension, and dispersibility of the reagent change after mixing. The ester functional groups in ethyl oleate can interact with certain active sites on the surface of coal particles, enhancing the adsorption effect and resulting in smaller dispersed particle size of kerosene in the slurry, higher adsorption heat, and further improved hydrophobicity of the coal particles. For example, kerosene and NP10 can be mixed in a 10:1 ratio.

[0037] Step two is the first flotation operation: the surface-modified slurry from the first flotation stage enters the first flotation equipment for the first flotation, yielding first-flotation clean coal and first-flotation tailings. The first flotation removes most of the gangue from the coal slime, which helps reduce the amount of gangue entering subsequent separation stages, avoids contamination of the clean coal product by gangue crushing and grinding, and also reduces the energy consumption of the separation system. The flotation time is 3–4 minutes, the stirring speed is 2000–2200 r / min, and the aeration rate is 0.25–0.5 m³ / min. 3 / h;

[0038] Step three is the scrubbing and grinding operation: the first flotation concentrate enters the scrubbing and grinding equipment for scrubbing and grinding to obtain the scrubbing and grinding product; during the scrubbing and grinding operation, the residence time of the slurry in the equipment is ≤5min, the slurry concentration is 100g / L, the grinding media are zirconia balls with diameters of 3mm and 2mm, the mass ratio of the media balls is 2:1, and the grinding speed is 60r / min; after scrubbing, the fine mud covering the coal surface is effectively removed; analysis shows that the increase in particles smaller than 0.074mm after the scrubbing and grinding operation is ≤15%;

[0039] Step four is the second surface modification operation: the scrubbed and ground ore product enters the second surface modifier and is mixed with flotation reagents for the second surface modification operation, resulting in a second surface-modified slurry. During the second surface modification, the flotation reagents adsorb onto the fresh surface of the scrubbed coal slime, further improving the hydrophobicity of the coal. The interaction time between the reagents and the coal slime is 3-5 minutes. The second surface modification stage further adjusts the surface properties of the scrubbed and ground ore product. By adding specific surface modifiers, such as those that can change the surface potential or chemical composition of coal particles, the difference in surface properties between coal particles and impurities can be further increased, enhancing the selectivity of flotation. For example, for coal particles whose floatability is reduced due to surface oxidation, secondary surface modification can restore some of their hydrophobicity and improve the flotation recovery rate.

[0040] Step five is the second flotation operation: The second surface-modified slurry enters the second flotation equipment for the second flotation, yielding second-flotation clean coal and second-flotation tailings. The second flotation operation removes the fine mud and coal particles with a large content of gangue embedded in the scrubbing operation, which is beneficial for subsequent processes to obtain low-ash clean coal. The flotation time is 3-5 minutes, the stirring speed is 2000-2200 r / min, and the aeration rate is 0.25-0.5 m³ / min. 3 / h;

[0041] Step six involves analyzing the coal quality to determine if liberation grinding is necessary. The method is to analyze the ash content of the second flotation concentrate. If the ash content is ≤3%, the coal quality is considered good and liberation grinding is unnecessary; if the ash content is >3%, the coal quality is considered poor and liberation grinding is required. When the coal quality is determined to be poor, the second flotation concentrate enters the liberation grinding equipment for liberation grinding. The content of particles larger than 0.074mm in the liberation grinding product should be ≤25%, but this can be adjusted based on the actual liberation situation. The product from the grinding process enters a classifying hydrocyclone for classification, with a classification particle size of 0.25mm. Particles larger than 0.25mm are returned to the grinding and dissociation equipment for further dissociation and grinding, while particles smaller than 0.25mm enter the next processing stage. After dissociation grinding, coal and gangue are fully dissociated, solving the problem of increased ash content in flotation concentrate caused by the intergrowth of coal and gangue. The slurry concentration of the dissociation grinding is 180g / L, and the grinding media consists of 5mm, 4mm, and 3mm zirconia balls with a mass ratio of 1:1:1.

[0042] The unique oil-water emulsion structure of the dual-emulsion flotation reagent more effectively encapsulates coal particles, enhancing their hydrophobicity and adhesion to air bubbles. The addition point is determined experimentally based on the needs of the flotation process to ensure the reagent functions optimally at the appropriate stage, thus improving flotation efficiency.

[0043] Dual-emulsion flotation reagents include oil-in-water emulsifiers such as Span, glyceryl monostearate, sodium oleate, and sodium erucic acid, and water-in-oil emulsifiers such as Tween, fatty alcohol polyoxyethylene ether, polyoxyethylene stearate, and sodium fatty alcohol polyoxyethylene ether carboxylate.

[0044] Step seven is the double emulsion surface modification operation: After dissociation grinding, the particle size becomes finer. A double emulsification dosing device is used to prepare flotation reagents and water into an oil-in-water-in-oil double emulsion or a water-in-oil-in-water double emulsion to improve the dispersion effect of the flotation reagents and promote the interaction between the reagents and the dissociated fine coal particles, thereby improving the selectivity of subsequent flotation. The interaction time between the double emulsion flotation reagents and coal slime is 3-5 minutes. The double emulsion is used to perform surface modification on the product of the previous operation to obtain the double emulsion modified product. When the water-in-oil-in-water double emulsion is not effective, it indicates that the hydrophobicity of the coal slime is poor. By setting the double emulsification dosing device program and changing the reagent formula and ratio, an oil-in-water-in-oil double emulsion can be prepared to improve the hydrophobicity of the coal.

[0045] Step eight is the third flotation operation: the double emulsion modified product enters the third flotation equipment for the third flotation to obtain the third flotation clean coal and the third flotation tailings; through the third flotation, gangue in the coal slime is further removed; the flotation column is used as the third flotation equipment in the experiment, and the separation effect is adjusted by adjusting the circulation pressure and the height of the tailings pipe. The circulation pressure is ≥0.16MPa, and the height of the tailings pipe relative to the feed inlet is ≥15cm.

[0046] Step nine is the fourth flotation operation: the clean coal from the third flotation enters the fourth flotation equipment for the fourth flotation to obtain ultrapure coal and tailings from the fourth flotation; the gangue in the coal slime is fully removed through the fourth flotation to obtain ultrapure coal with an ash content of less than 1%; the flotation column is used as the fourth flotation equipment in the experiment, and the separation effect is adjusted by adjusting the circulation pressure and the height of the tailings pipe. The circulation pressure is ≥0.16MPa, and the height of the tailings pipe relative to the feed inlet is ≥20cm.

[0047] The tailings from the first, second, third, and fourth flotation processes are called flotation tailings. Vertical stirred mills, rod mills, or ball mills are used for scrubbing and grinding, and the mill speed, grinding concentration, and grinding media diameter are adjusted according to the properties of the feed. Column flotation equipment is used for the third and fourth flotation operations, with a flotation concentration of 40–60 g / L.

[0048] Example 1

[0049] The coal slime used in this embodiment has good quality, and the steps are as follows:

[0050] Step 1: Mix the coal slime and flotation reagent in the first surface modifier. The interaction time between the reagent and the coal slime is 3 minutes.

[0051] Step 2: The surface-modified slurry from the first flotation stage enters the first flotation unit for the first flotation, yielding first-stage flotation concentrate and first-stage flotation tailings; flotation time is 3 minutes, stirring speed is 2000 r / min, and aeration rate is 0.25 m³ / min. 3 / h.

[0052] Step 3: The first flotation concentrate enters the scrubbing and grinding equipment for scrubbing and grinding to obtain the scrubbing and grinding product. During the scrubbing and grinding operation, the slurry stays in the equipment for 3 minutes, the slurry concentration is 100 g / L, the grinding media are zirconia balls with diameters of 3 mm and 2 mm, the mass ratio of the media balls is 2:1, and the grinding speed is 60 r / min. After scrubbing, the fine mud covering the coal surface is effectively removed. Analysis shows that the increase in particles smaller than 0.074 mm after the scrubbing and grinding operation is 10.14%.

[0053] Step 4: The scrubbing and grinding products are fed into the second surface modifier and mixed with flotation reagents for the second surface modification operation to obtain the second surface-modified slurry; the interaction time between the reagents and the coal slime is 3 minutes.

[0054] Step 5: The second surface-modified slurry enters the second flotation equipment for the second flotation, with a flotation time of 3 minutes, a stirring speed of 2000 r / min, and an aeration rate of 0.25 m3 / h; the second flotation clean coal and the second flotation tailings are obtained.

[0055] Step Six: The ash content of the clean coal from the second flotation was measured to be 2.6%, proceed directly to Step Seven.

[0056] Step 7: Using a dual emulsification dosing device, the flotation reagent and water are mixed to form a water-in-oil-in-water dual emulsion, which is then mixed with the dissociated fine coal particles. The interaction time between the reagent and the coal slime is 3 minutes.

[0057] Step 8: Use a flotation column to perform a third flotation to obtain third-flotation clean coal; the circulation pressure is 0.16MPa, and the height of the tailings pipe relative to the feed inlet is 15cm.

[0058] Step Nine: The third flotation of clean coal uses a flotation column with a circulation pressure of 0.16 MPa and a tailings pipe height relative to the feed inlet of 20 cm. The fourth flotation is then performed to obtain ultrapure coal with an ash content of less than 1%.

[0059] Example 2

[0060] The coal slime used in this embodiment is of poor quality, and the steps are as follows:

[0061] Step 1: Mix coal slime and flotation reagent in the first surface modifier. The interaction time between the reagent and coal slime is 5 minutes to obtain the first surface-modified slurry.

[0062] Step 2: The first surface-modified slurry is fed into the first flotation device for the first flotation. The flotation time is 5 minutes, the stirring speed is 2200 r / min, and the aeration rate is 0.5 m³ / min. 3 / h, to obtain the first flotation concentrate and the first flotation tailings.

[0063] Step 3: The first flotation concentrate enters the scrubbing and grinding equipment for scrubbing and grinding to obtain the scrubbing and grinding product. During the scrubbing and grinding operation, the slurry stays in the equipment for 5 minutes, the slurry concentration is 150 g / L, the grinding media are zirconia balls with diameters of 3 mm and 2 mm, the mass ratio of the media balls is 2:1, and the grinding speed is 60 r / min. After the scrubbing and grinding operation, the increase in particles smaller than 0.074 mm is 14.33%.

[0064] Step 4: The scrubbing and grinding products are fed into the second surface modifier and mixed with flotation reagents for the second surface modification operation to obtain the second surface-modified slurry; the interaction time between the reagents and the coal slime is 5 minutes.

[0065] Step 5: The second surface-modified slurry enters the second flotation equipment for the second flotation, with a flotation time of 5 minutes, a stirring speed of 2200 r / min, and an aeration rate of 0.5 m3 / h; the second flotation clean coal and the second flotation tailings are obtained.

[0066] Step Six: The second flotation concentrate enters the liberation grinding operation with a pulp concentration of 180 g / L. The grinding media are 5 mm, 4 mm, and 3 mm zirconia balls in a mass ratio of 1:1:1. After liberation, the content of particles >0.074 mm is <25%. The liberation product enters the classifying hydrocyclone. Particles <0.25 mm proceed to the next step, while particles ≥0.25 mm are returned to the liberation grinding.

[0067] Steps seven through nine are the same as in Example 1. The final product is ultra-pure coal with an ash content of 0.7%.

[0068] This invention achieves efficient liberation and separation of coal and gangue in fine coal slime; the scrubbing and grinding operation improves the effect of secondary surface modification, which is beneficial for obtaining low-ash clean coal products in secondary flotation; the liberation grinding operation fully liberates coal and gangue, which is beneficial for increasing the yield of ultrapure coal products and promoting the inclusion of gangue in tailings; the dual-emulsion surface modification operation improves the dispersion effect of reagents in the slurry, promotes the interaction between coal and reagents, and is beneficial for improving the selectivity of tertiary and quaternary flotation operations; the combination of the above processes in a specific manner can effectively promote the liberation of coal and gangue in coal slime, improve the selectivity of flotation methods, and obtain low-ash clean coal products.

[0069] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing ultrapure coal by combined grinding and flotation, characterized in that, Includes the following steps: Step 1: Mix coal slime and flotation reagent in the first surface modifier. The interaction time between the flotation reagent and coal slime is 3-5 minutes to obtain the first surface-modified slurry. Step 2: The first surface-modified slurry enters the first flotation device to obtain the first flotation concentrate; Step 3: The first flotation concentrate enters the scrubbing and grinding equipment for scrubbing and grinding operations to obtain scrubbing and grinding products; during the scrubbing and grinding operation, the residence time of the first flotation concentrate in the equipment is ≤5min, and the increase in particles smaller than 0.074mm after the operation is ≤15%; Step 4: The scrubbing and grinding products and flotation reagents are mixed in the second surface modifier. The interaction time between the flotation reagents and coal slime is 3-5 minutes to obtain the second surface-modified slurry. Step 5: The second surface-modified slurry enters the second flotation equipment to obtain the second flotation concentrate; Step Six: Determine the ash content of the second flotation concentrate: If the ash content is ≤3%, proceed to Step Seven; if the ash content is >3%, first perform the dissociation grinding and classification operations, then proceed to Step Seven; the dissociation grinding operation involves feeding the second flotation concentrate into the dissociation grinding equipment for grinding, so that the content of particles >0.074mm in the dissociated product is ≤25%; the classification operation involves classifying the dissociation grinding product by a classifying hydrocyclone with a particle size of 0.25mm, with particles ≥0.25mm returned to the dissociation grinding equipment, and particles <0.25mm proceeding to Step Seven; Step 7: The product from Step 6 is mixed with the dual-emulsion flotation reagent, and the interaction time between the dual-emulsion flotation reagent and the product from Step 6 is 3-5 minutes; the modified dual-emulsion product is obtained. Step 8: The modified product of the double emulsion enters the third flotation equipment, and the height of the tailings pipe relative to the feed inlet is ≥15cm, to obtain the third flotation clean coal; Step 9: The third flotation concentrate enters the fourth flotation unit, with the tailings pipe height relative to the feed inlet ≥ 20cm, to obtain ultrapure coal; The first and second flotation times are 3 to 4 minutes, the stirring speed is 2000 to 2200 r / min, and the aeration rate is 0.25 to 0.5 m3 / h; the third and fourth flotation concentrations are 40 to 60 g / L, and column flotation equipment is used with a circulation pressure ≥0.16 MPa.

2. The method according to claim 1, characterized in that, The scrubbing and grinding equipment and the dissociation grinding equipment mentioned in step three are vertical stirred mills, rod mills or ball mills. The mill speed, grinding concentration and grinding media diameter are adjusted according to the properties of the feed.

3. The method according to claim 1, characterized in that, The dual-emulsion flotation reagent mentioned in step seven is an oil-in-water-in-oil dual-emulsion or a water-in-oil-in-water dual-emulsion, which is prepared by mixing the flotation reagent with water using a dual emulsification dosing device.

4. The method according to claim 1, characterized in that, The flotation time for the first and second flotation operations described in steps two and three is 3 minutes, the stirring speed is 2000 r / min, and the aeration rate is 0.25 m³ / min. 3 / h.

5. The method according to claim 1, characterized in that, The slurry concentration for the scrubbing and grinding operation described in step three is 100 g / L; the grinding media are zirconia balls with diameters of 2 mm and 3 mm, respectively, with a mass ratio of 2 mm to 3 mm zirconia balls of 1:2, and the grinding speed is 60 r / min.

6. The method according to claim 1, characterized in that, In step six, the concentration of the dissociated grinding slurry is 180 g / L, and the grinding media are zirconia balls of 5 mm, 4 mm, and 3 mm in mass ratio of 1:1:1.

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