Hydrophobic nano carbon particle as well as preparation method and application thereof
Superhydrophobic nano-carbon particles were prepared through pyrolysis carbonization, mechanical grinding, steam oxidation and surface modification, which solved the problems of dispersion and high cost of traditional collectors in coal slime flotation, and improved the flotation efficiency and clean coal quality of coal slime.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ANHUI UNIV OF SCI & TECH
- Filing Date
- 2026-01-29
- Publication Date
- 2026-04-28
AI Technical Summary
In the existing coal slime flotation process, traditional collectors have poor dispersibility, require large amounts, and are costly. Furthermore, the surface hydrophobicity of coal-based nanoparticles is insufficient, making it difficult to meet the requirements for efficient utilization.
Superhydrophobic carbon nanoparticles were prepared through pyrolysis carbonization, mechanical grinding, steam oxidation and surface modification. By using a stepwise synergistic and in-situ anchoring strategy, micro and nano-level rough structures were constructed and CF bonds were introduced to enhance the hydrophobicity of the particle surface.
The strong hydrophobicity of nano-carbon particles was achieved, which reduced the preparation and use costs of collectors, improved the clean coal recovery rate of coal slime flotation, and realized the cascade utilization of coal resources and environmental protection.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of nanomaterials technology, specifically relating to a hydrophobic carbon nanoparticle, its preparation method, and its application. Background Technology
[0002] Coal, as a crucial basic energy source and industrial raw material in my country, is widely used in thermal power generation, metallurgy, and coal chemical industries. In 2025, my country's raw coal production reached a record high of 4.83 billion tons. However, raw coal contains a large amount of gangue, necessitating washing and processing for clean and efficient utilization. While producing high-grade clean coal, the washing process also generates a large amount of coal slime. Coal slime is characterized by high ash content, fine particle size, strong caking properties, and low calorific value, making it difficult to use directly for combustion. Currently, large quantities of coal slime remain abandoned or stored in the open, not only wasting valuable coal resources but also causing serious pollution to the atmosphere, soil, and water bodies.
[0003] Flotation is the primary method for recovering clean coal from coal slime, helping to improve coal resource utilization efficiency and reduce environmental pollution. Currently, non-polar hydrocarbon oils (such as diesel oil) are commonly used as collectors in coal slime flotation. However, their dispersibility in the slurry is poor, with droplet sizes mostly between 70 and 150 μm, resulting in low contact probability with coal particles, large collector dosages, and high operating costs. Hydrophobic nanoparticle collectors can enhance the hydrophobicity of coal particle surfaces and achieve selective adsorption, thereby improving flotation yield and clean coal quality. Previous studies have prepared two types of polystyrene nanoemulsions—anionic and cationic—with particle sizes of 53 nm and 63 nm, respectively, using emulsion polymerization. Compared to traditional kerosene collectors, their clean coal recovery rate is improved, but the raw materials for synthesis largely rely on chemical products, resulting in high costs. Coal, as a low-cost raw material, has been explored for preparation into nanoparticles, but the prepared nanoparticles typically lack sufficient surface hydrophobicity, making it difficult to meet the requirements of coal slime flotation. Summary of the Invention
[0004] The technical problem to be solved by the present invention is to address the shortcomings of the existing technology by providing a hydrophobic nano-carbon particle, its preparation method and application. Using coal as raw material, after a series of treatments, the final prepared nano-carbon particle has strong hydrophobicity and can be directly used as a collector for coal slime flotation, providing an economical and efficient new reagent solution for coal slime flotation.
[0005] To address the technical problem proposed in this invention, this invention provides a method for preparing hydrophobic carbon nanoparticles, specifically comprising the following steps: 1) Pulverized coal is pyrolyzed and carbonized once in a low oxygen atmosphere, and then ball-milled once in an inert atmosphere to obtain the first nano-carbon particles; 2) The first nano-carbon particles are subjected to surface oxidation treatment in humid air to obtain the second nano-carbon particles; 3) The second nano-carbon particles are subjected to secondary pyrolysis in an inert atmosphere to obtain the third nano-carbon particles; 4) The third nano-carbon particles were fluorinated and then ball-milled again in an inert atmosphere to obtain hydrophobic nano-carbon particles.
[0006] In the above scheme, the particle size of the pulverized coal is less than 0.5 mm.
[0007] In the above scheme, the volume fraction of oxygen in the low oxygen atmosphere is 8%~15%, and the remainder is nitrogen.
[0008] In the above scheme, the inert atmosphere is one of nitrogen, argon, and helium.
[0009] In the above scheme, the pyrolysis temperature of the first pyrolysis is 900~1100 ℃, and the pyrolysis time is 30~90 min.
[0010] Furthermore, the heating rate of the first pyrolysis is 5~10 ℃ / min.
[0011] In the above scheme, during the first pyrolysis, coal powder is loaded into a container and filled to 60% to 80% of the container volume. Then, the container is covered but not sealed, and placed into the pyrolysis equipment.
[0012] In the above scheme, the ball milling speed is 350~600 r / min and the ball milling time is 30~90 min.
[0013] In the above scheme, the grinding balls used in the primary ball mill have a particle size of 0.1~8mm and fill 40%~50% of the volume of the ball mill equipment.
[0014] Furthermore, the grinding ball gradation of the primary ball mill, by mass fraction, is as follows: 80-85% of the particles are 0.1-1.5 mm in diameter, and 15-20% are 3-8 mm in diameter.
[0015] In the above scheme, the particle size of the first nano-carbon particles is 200~500 nm and the oxygen content is 1~3%.
[0016] In the above scheme, the volume fraction of water vapor in the humid air is 10%~30%.
[0017] In the above scheme, the surface oxidation treatment temperature is 200~500 ℃ and the time is 20~30 min.
[0018] Furthermore, the heating rate of the surface oxidation treatment is 5~10 °C / min.
[0019] In the above scheme, the oxygen content of the second nano-carbon particles is 10%~20%.
[0020] In the above scheme, the pyrolysis temperature of the secondary pyrolysis is 600~800℃, and the pyrolysis time is 10~30 min.
[0021] Furthermore, the heating rate of the secondary pyrolysis is 5~10 ℃ / min.
[0022] In the above scheme, the oxygen content of the third nano-carbon particles is 3%~8%.
[0023] In the above scheme, the fluorination modification is carried out by mixing the third nano-carbon particles with ammonium fluoride evenly and then performing heat treatment in an inert atmosphere.
[0024] Furthermore, the mass ratio of the third nano-carbon particles to ammonium fluoride is 1:(0.4~1).
[0025] Furthermore, the heat treatment temperature is 250~400 ℃, and the time is 1~2 h.
[0026] Furthermore, the heating rate of the heat treatment is 5~10 °C / min.
[0027] In the above scheme, the ball milling speed of the secondary ball mill is 400~600 r / min, and the ball milling time is 5~10 min.
[0028] In the above scheme, the grinding balls of the secondary ball mill have a particle size of 0.1~8 mm and fill 20~40% of the volume of the ball milling equipment.
[0029] Furthermore, the grinding ball gradation of the secondary ball mill, by mass fraction, is as follows: 60-70% of the particles are 0.1-1.5 mm in diameter, and 30-40% are 3-8 mm in diameter.
[0030] In the above scheme, the hydrophobic carbon nanoparticles have a particle size of 50~300 nm, an oxygen content of 2~5%, and a specific surface area of 100~200 m². 2 / g, contact angle ≥150°.
[0031] This invention provides a hydrophobic carbon nanoparticle, which is prepared by the above-described preparation method.
[0032] The present invention also provides the application of the hydrophobic nanocarbon particles as a collector in mineral flotation. The application method is as follows: the hydrophobic nanocarbon particles are added to the slurry, and after stirring and aeration, the target mineral is separated by flotation.
[0033] In the above scheme, the amount of hydrophobic nano-carbon particles added is 600~800 g / t slurry.
[0034] The main technical concept of this invention is as follows: This invention, based on a step-by-step synergistic and in-situ anchoring strategy, prepares nano-carbon particles with superhydrophobic properties through the tight coupling and sequential synergy of steps such as pyrolysis carbonization, mechanical grinding, steam oxidation, and surface modification. 1) Pyrolysis carbonization: Coal is used as raw material and pyrolyzed in an inert atmosphere. This step removes volatiles and forms a large number of microcracks inside the particles through high temperature. This structure significantly reduces the energy consumption and time of subsequent mechanical grinding to a particle size of 200~500 nm, and provides a nano-carbon particle substrate with high reactivity for subsequent processing.
[0035] 2) Steam oxidation: The nano-carbon particles obtained by pyrolysis carbonization are placed in a steam atmosphere for controlled oxidation. This step has a dual function: on the one hand, the steam selectively etches the carbon surface, constructing micro and nano-level rough structures based on the microcracks formed by pyrolysis; on the other hand, oxygen-containing functional groups such as carboxyl groups and hydroxyl groups are introduced into the active sites such as protrusions, edges and defects of the rough structure. These functional groups serve as highly active "chemical anchors", providing preset reaction sites for subsequent directional fluorination.
[0036] 3) Deoxidation and roughening: The nano-carbon particles oxidized by water vapor are placed in an inert atmosphere and selectively removed from the surface by controlled pyrolysis (such as some hydroxyl and carbonyl groups). At the same time, carbon surface reconstruction is induced to form richer micro and nano-level rough structures in situ. This structure can effectively enhance the air trapping capacity of the particle surface, thereby significantly improving its apparent hydrophobicity.
[0037] 4) Fluorination Modification: The deoxidized and roughened nanocarbon particles are fluorinated under mild conditions. The oxygen-containing functional groups, such as carboxyl groups, pre-defined and partially retained in the second step, act as "chemical anchors" on the particle surface, selectively covalently bonding with the fluorine source. This efficiently introduces highly electronegative CF bonds into the carbon skeleton. This directional bonding mechanism avoids the random etching of the carbon skeleton by drastic fluorination, achieving superhydrophobic surface functionalization while perfectly preserving the micro- and nano-level roughened structure constructed in the previous steps. The resulting nanocarbon particles possess both types of functional groups: oxygen-containing functional groups ensuring good dispersion in the slurry, and CF bonds imparting superhydrophobic properties, thus comprehensively optimizing their performance as a flotation collector. This method also reduces the amount of ammonium fluoride required for the fluorination reaction.
[0038] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) This invention uses coal as raw material and, through a series of treatments, effectively solves the problem of insufficient hydrophobicity of existing coal-based nanoparticles. It achieves precise control over the surface chemical properties (hydrophobicity) and physical structure (particle size, specific surface area) of carbon nanoparticles. The prepared carbon nanoparticles have strong hydrophobicity and can be directly used as collectors for coal slime flotation, providing an economical and efficient new reagent solution for coal slime flotation.
[0039] 2) Compared with polystyrene nanoemulsion collectors that rely on chemical raw materials for synthesis, the present invention has a wide range of raw material sources and extremely low acquisition costs, which can significantly reduce the preparation and use costs of collectors; at the same time, it realizes the cascade utilization of coal resources, avoids resource waste, meets the needs of low-cost industrial production, and solves the dual pain points of high synthesis cost of existing hydrophobic nanoparticle collectors and high operating cost due to large dosage of traditional non-polar hydrocarbon oil collectors. Detailed Implementation
[0040] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.
[0041] Example 1 The preparation method of hydrophobic carbon nanoparticles in this embodiment specifically includes the following steps: 1) Take a coal powder sample with a particle size of less than 0.5 mm and an oxygen content of 18%. Put the coal powder into a container and fill it to 70% of the container volume. Then cover the container with a lid, but do not seal it. Place it in a muffle furnace and heat it to 1000 ℃ in a low oxygen atmosphere with an oxygen volume fraction of 8% and the remainder being nitrogen. Pyrolyze it for 30 min at a heating rate of 5 ℃ / min. The pyrolysis sample was placed in a ceramic jar and milled using zirconia balls with a particle size range of 0.1–8 mm. The particle size distribution, by mass fraction, was 80% for particles with a diameter of 0.1–1.5 mm and 20% for particles with a diameter of 3–8 mm. The jar filled 50% of the ball mill volume, and nitrogen was introduced as a protective atmosphere for milling at 520 r / min for 30 min to obtain the first nano-carbon particles. The particle size was measured to be 400 nm and the oxygen content was 3%. 2) The first nano-carbon particles were placed in a vertical fluidized tube furnace, and the temperature was raised to 300 ℃ at a heating rate of 7 ℃ / min in an air atmosphere with a water vapor volume fraction of 20%. The particles were oxidized at this temperature for 30 min to obtain the second nano-carbon particles. The oxygen content of the sample was tested and found to be 18%. 3) The second nano-carbon particles were placed in a muffle furnace and heated to 800 ℃ at a heating rate of 5 ℃ / min under a nitrogen atmosphere. The particles were then pyrolyzed at this temperature for 10 min to obtain the third nano-carbon particles. The oxygen content of the sample was tested and found to be 8%. 4) After mixing the third nano-carbon particles with ammonium fluoride at a mass ratio of 1:1, the mixture was loaded into a reaction vessel and heated to 400 °C at a heating rate of 5 °C / min under a nitrogen atmosphere for 1.5 h. The treated sample was placed in a planetary ball mill, using zirconia balls as the milling medium. The ball milling media had a particle size range of 0.1–8 mm, with a mass fraction of 60% for particles 0.1–1.5 mm and 40% for particles 3–8 mm. The balls filled 40% of the mill's volume. Nitrogen gas was introduced as a protective atmosphere for milling at 400 r / min for 8 min to obtain hydrophobic carbon nanoparticles. Samples were taken and tested, and the particle size was 120 nm, the oxygen content was 2%, and the specific surface area was 148 m². 2 / g, with a contact angle of 165.7°.
[0042] Example 2 The preparation method of hydrophobic carbon nanoparticles in this embodiment specifically includes the following steps: 1) Take a coal powder sample with a particle size of less than 0.5 mm and an oxygen content of 18%. Put the coal powder into a container and fill it to 70% of the container volume. Then cover the container with a lid, but do not seal it. Place it in a muffle furnace and heat it to 1100 ℃ in a low oxygen atmosphere with an oxygen volume fraction of 10% and the remainder being nitrogen. Pyrolyze it for 90 min at a heating rate of 8 ℃ / min. The pyrolysis sample was placed in a ceramic jar and milled using zirconia balls with a particle size range of 0.1–8 mm. The particle size distribution, by mass fraction, was 85% for particles with a diameter of 0.1–1.5 mm and 15% for particles with a diameter of 3–8 mm. The balls filled 40% of the volume of the milling equipment, and nitrogen was introduced as a protective atmosphere for milling at 600 r / min for 50 min to obtain the first nano-carbon particles. The particle size was measured to be 350 nm and the oxygen content was 1%. 2) The first nano-carbon particles were placed in a vertical fluidized tube furnace, and the temperature was raised to 400 ℃ at a heating rate of 10 ℃ / min under an air atmosphere with a water vapor volume fraction of 30%. The particles were oxidized at this temperature for 20 min to obtain the second nano-carbon particles. The oxygen content of the sample was tested and found to be 12%. 3) The second nano-carbon particles were placed in a muffle furnace and heated to 800 ℃ at a heating rate of 8 ℃ / min under a nitrogen atmosphere. The particles were then pyrolyzed at this temperature for 20 min to obtain the third nano-carbon particles. The oxygen content of the sample was tested and found to be 6%. 4) After mixing the third nano-carbon particles with ammonium fluoride at a mass ratio of 1:0.4, the mixture was loaded into a reaction vessel and heated to 250 °C at a heating rate of 7 °C / min under a nitrogen atmosphere for 1 h. The treated sample was placed in a planetary ball mill, using zirconia balls as the milling medium. The ball media had a particle size range of 0.1–8 mm, with a mass fraction of 70% for particles 0.1–1.5 mm and 30% for particles 3–8 mm. The balls filled 30% of the mill's volume. Nitrogen gas was introduced as a protective atmosphere for milling at 600 r / min for 5 min to obtain hydrophobic carbon nanoparticles. Samples were taken and tested, revealing a particle size of 100 nm, an oxygen content of 4%, and a specific surface area of 169 m². 2 / g, with a contact angle of 151.8°.
[0043] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that steps 2), 3), and 4) are omitted, and only step 1) is performed, with the first nano-carbon particles as the final product.
[0044] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that steps 2), 3), and 4) are omitted, and the first nano-carbon particles obtained in step 1) are used instead of the third nano-carbon particles.
[0045] Comparative Example 3 The only difference between Comparative Example 3 and Example 1 is that step 2) and step 3) are not performed, and the first nano-carbon particles obtained in step 1) are used instead of the second nano-carbon particles.
[0046] Comparative Example 4 The only difference between Comparative Example 4 and Example 1 is that the third nano-carbon particles used in steps 3) and 4) are replaced by the second nano-carbon particles obtained in step 2).
[0047] The performance of the nano-carbon particles obtained in each embodiment and comparative example was tested, and the results are shown in Table 1.
[0048] Table 1
[0049] Application examples The nano-carbon particles prepared in each embodiment and comparative example were used as collectors for coal slime flotation. The experimental procedures for each group were as follows: 120 g of coal slime was weighed and slowly poured into the flotation cell, moistened with 1.5 L of water, and stirred for 2 min to form a slurry with a concentration of 80 g / L; nano-carbon particles were added at a rate of 600 g / t of slurry (no addition was made in the blank group), and after stirring for 1 min, a frother was added, and the air valve was opened at the same time; after 10 s, the scraper was opened to start skimming the bubbles; and the process was stopped after 3 min. The clean coal and tailings after flotation were filtered, dried, weighed, and ashed. The experimental results are shown in Table 2.
[0050] Table 2
[0051] Table 2 shows that the nano-carbon particles prepared by the complete process in Examples 1 and 2 both exhibit hydrophobicity (water contact angle) exceeding 150°. Based on the tight coupling and sequential synergy between the steps, the nano-carbon particle collector can achieve a clean coal recovery rate of over 60% in mineral flotation applications, demonstrating excellent comprehensive performance.
[0052] In contrast, the comparative examples showed a significant decline in material performance due to the absence or improper sequence of key steps: Comparative Example 1 underwent only one pyrolysis and ball milling process, failing to construct a rich rough structure and introduce hydrophobic CF bonds, resulting in insufficient hydrophobicity and poor collection effect of the obtained particles; Comparative Example 2 underwent fluorination treatment directly after one pyrolysis and ball milling process, similarly failing to construct a rich rough structure, and the particle surface lacked pre-set oxygen-containing functional groups as fluorination "anchors," resulting in low fluorination reaction efficiency, unsatisfactory particle hydrophobicity, and thus poor collection effect; Comparative Example 3 lacked core surface oxidation treatment, resulting in a lack of active sites in the subsequent secondary pyrolysis, and the fluorination reaction lost its "chemical anchor," resulting in insufficient specific surface area and hydrophobicity of the obtained particles; Comparative Example 4, after surface oxidation treatment, did not undergo secondary pyrolysis to selectively remove some unstable oxygen-containing functional groups on the surface, leading to random etching of the carbon skeleton by severe fluorination, destroying the constructed micro and nano rough structures, resulting in a significant reduction in particle hydrophobicity.
[0053] The above embodiments are merely examples for clear illustration and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations, and any obvious variations or modifications derived therefrom are still within the scope of protection of this invention.
Claims
1. A method for preparing hydrophobic carbon nanoparticles, characterized in that, Includes the following steps: 1) Pulverized coal is pyrolyzed and carbonized once in a low oxygen atmosphere, and then ball-milled once in an inert atmosphere to obtain the first nano-carbon particles; 2) The first nano-carbon particles are subjected to surface oxidation treatment in humid air to obtain the second nano-carbon particles; 3) The second nano-carbon particles are subjected to secondary pyrolysis in an inert atmosphere to obtain the third nano-carbon particles; 4) The third nano-carbon particles were fluorinated and then ball-milled again in an inert atmosphere to obtain hydrophobic nano-carbon particles.
2. The method for preparing hydrophobic carbon nanoparticles according to claim 1, characterized in that, The oxygen volume fraction in the low-oxygen atmosphere is 8%~15%, with the remainder being nitrogen; the pyrolysis temperature of the first pyrolysis is 900~1100℃, and the pyrolysis time is 30~90 min; the particle size of the first nano-carbon particles is 200~500 nm, and the oxygen content is 1~3%.
3. The method for preparing hydrophobic carbon nanoparticles according to claim 1, characterized in that, The ball milling speed of the first ball mill is 350~600 r / min, and the ball milling time is 30~90 min; the particle size of the grinding balls in the first ball mill is 0.1~8 mm, and the grinding ball gradation by mass fraction is: 80~85% of the particles with a particle size of 0.1~1.5 mm, and 15~20% of the particles with a particle size of 3~8 mm.
4. The method for preparing hydrophobic carbon nanoparticles according to claim 1, characterized in that, The volume fraction of water vapor in the humid air is 10%~30%; the temperature of the surface oxidation treatment is 200~500℃ and the time is 20~30 min; the oxygen content of the second nano-carbon particles is 10%~20%.
5. The method for preparing hydrophobic carbon nanoparticles according to claim 1, characterized in that, The pyrolysis temperature of the secondary pyrolysis is 600~800℃, and the pyrolysis time is 10~30 min; the heating rate of the secondary pyrolysis is 5~10 ℃ / min; and the oxygen content of the third nano-carbon particles is 3%~8%.
6. The method for preparing hydrophobic carbon nanoparticles according to claim 1, characterized in that, The fluorination modification involves uniformly mixing third-nano carbon particles with ammonium fluoride and then heat-treating them in an inert atmosphere; the mass ratio of the third-nano carbon particles to ammonium fluoride is 1:(0.4~1); the heat treatment temperature is 250~400℃ and the time is 1~2h.
7. The method for preparing hydrophobic carbon nanoparticles according to claim 1, characterized in that, The ball milling speed of the secondary ball mill is 400~600 r / min, and the ball milling time is 5~10 min; the particle size of the grinding balls in the secondary ball mill is 0.1~8 mm, and the grinding ball gradation by mass fraction is: 60~70% of the particle size is 0.1~1.5 mm, and 30~40% of the particle size is 3~8 mm.
8. The method for preparing hydrophobic nanocarbon particles according to claim 1, characterized in that, The coal powder has a particle size of less than 0.5 mm; the inert atmosphere is one of nitrogen, argon, or helium; the hydrophobic carbon nanoparticles have a particle size of 50-300 nm, an oxygen content of 2-5%, and a specific surface area of 100-200 m². 2 / g, contact angle ≥150°.
9. A hydrophobic carbon nanoparticle prepared by any one of claims 1 to 8.
10. The application of the hydrophobic nanocarbon particles as described in claim 9 as a collector in mineral flotation.