A method for improving clean coal yield in difficult-to-float coal slime

Abstract

This invention belongs to the field of mineral flotation technology, specifically relating to a method for improving the yield of clean coal in difficult-to-float coal slime. The method includes: S1, reagent preparation and pretreatment: Based on the coal quality characteristics, methyl linoleate is mixed with n-dodecane and / or n-tetradecane at a mass ratio of (1-5):1, and ultrasonically dispersed for 3 hours to form a microemulsion composite collector; S2, slurry conditioning and mineralization: The above collector (800-1600 g / ton dry coal slime) and a frother are added to a slurry with a concentration of 80 g / L and stirred for 3 minutes; S3, flotation separation: Air bubbles are introduced to scrape off the clean coal. This invention, through a microemulsion composite collector with a specific composition, significantly enhances the hydrophobicity of the surface of difficult-to-float coal particles and the adhesion efficiency with air bubbles, solving the problems of poor selectivity and low clean coal yield of traditional collectors. It has the advantages of strong adaptability, high flotation efficiency, and a significant increase in clean coal yield.

Description

Technical Field

[0001] This invention belongs to the field of mineral flotation technology, specifically relating to a method for improving the yield of clean coal in difficult-to-float coal slime. Background Technology

[0002] High-efficiency flotation separation technology for fine-grained coal is a crucial link in the implementation of the national strategy for clean and efficient utilization of coal, directly affecting the cleanliness and resource utilization rate of coal products. Flotation, as its core separation method, urgently needs technological improvement to meet the high standards imposed on coal processing by high-quality development. Relevant national policies also strongly encourage related technological innovation and promotion. However, fine-grained coal, due to its rich surface content of oxygen-containing functional groups and the easy adhesion of hydrophilic gangue minerals, exhibits poor natural hydrophobicity. Current industrial practice and research mainly face the following technical bottlenecks: Traditional collectors have low flotation efficiency: commonly used traditional hydrocarbon oil collectors such as kerosene and diesel lack molecular polarity and rely solely on weak van der Waals forces for adsorption. They are unable to effectively displace the hydration film on the surface of coal particles and diffuse slowly on hydrophilic surfaces, resulting in limited improvement in the hydrophobicity of fine coal particles, low clean coal yield, and poor separation selectivity.

[0003] Existing compound systems suffer from poor synergistic effects and environmental friendliness: To improve performance, compounding surfactants with hydrocarbon oils is a common approach, but existing compound systems have significant drawbacks. Firstly, poor compatibility between components leads to competitive adsorption, making it difficult to form a stable and synergistic adsorption layer. Secondly, the polar components used, such as esters (e.g., methyl oleate in disclosed technology CN114985115A), have limited molecular structures. These C18 monounsaturated fatty acid esters (containing only one double bond) lack molecular flexibility, and their binding with hydrophilic groups on the coal surface is mainly through weak hydrogen bonds, resulting in low adsorption energy (approximately -0.3 eV), which hinders both adsorption stability and hydrophobic enhancement. Furthermore, some compound components are toxic, leading to insufficient environmental friendliness.

[0004] High reagent consumption and costs: Due to low adsorption efficiency and poor stability, traditional and existing compound collectors require large dosages (usually more than 30% higher than high-efficiency systems) to maintain basic sorting effects, and also suffer from poor dispersibility, directly driving up production costs. Insufficient sorting accuracy also leads to additional processing costs in subsequent stages.

[0005] Poor environmental friendliness and coal quality compatibility: Some synthetic components are environmentally unfriendly and do not conform to the green coal preparation guidelines. At the same time, existing collectors (including the esters mentioned above) are not precisely designed for the surface characteristics of difficult-to-float coals, have poor adaptability to different coal qualities (such as different mining areas and degrees of metamorphism), and the flotation effect fluctuates greatly, making it difficult to promote and apply them.

[0006] In summary, current technologies lack a collector solution that can precisely match the surface characteristics of fine-grained, difficult-to-float coal, while also possessing high-efficiency adsorption, stable synergy, environmental friendliness, and economic viability. Therefore, developing novel, high-efficiency composite collectors and suitable application technologies to fundamentally overcome the bottleneck in the separation of fine-grained, difficult-to-float coal slime has become an urgent industry need. Summary of the Invention

[0007] One objective of this invention is to provide a method for improving the yield of clean coal in difficult-to-float coal slime. This method utilizes a microemulsion composite collector with a specific composition to significantly enhance the hydrophobicity of the surface of difficult-to-float coal particles and their adhesion efficiency to air bubbles. This solves the problems of poor adsorption stability, low flotation efficiency, poor synergistic effect, and insufficient environmental friendliness of traditional collectors in the flotation process of fine-grained difficult-to-float coal slime. Simultaneously, it overcomes the defects of existing ester collectors (such as methyl oleate) caused by limited molecular structure, such as poor compatibility and weak binding strength. It has the advantages of strong adaptability, high flotation efficiency, and a significant increase in clean coal yield.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: a method for improving the yield of clean coal in difficult-to-float coal slime, comprising the following steps: S1. Reagent preparation and pretreatment: Based on the coal quality characteristics of the fine-grained, difficult-to-float coal to be floated, methyl linoleate and at least one hydrocarbon oil selected from n-dodecane and n-tetradecane are selected and mixed at a mass ratio of (1-5):1. The mixture is then ultrasonically dispersed to form a stable microemulsion, thus obtaining a composite collector. S2. Slurry preparation and mineralization: The composite collector and foaming agent obtained in step S1 are added to the refractory coal slime slurry with the concentration adjusted, and the slurry is stirred to make the composite collector fully contact the coal particles and cause adsorption. S3. Flotation separation: Air bubbles are introduced into the slurry after it has been prepared. The hydrophobic coal particles adhere to the air bubbles to form mineralized foam and float to the surface. The flotation clean coal is obtained by scraping the foam, while the hydrophilic gangue minerals remain in the slurry and are discharged as tailings.

[0009] A further improvement to a method for increasing the yield of clean coal in difficult-to-float coal slime: Preferably, in step S1, the coal quality characteristics include at least one of ash content, particle size distribution, hydrophilic functional group content, and degree of metamorphism.

[0010] Preferably, in step S1, the ultrasonic dispersion treatment time is 3 hours.

[0011] Preferably, in step S3, the rate at which air bubbles are introduced into the slurry after conditioning is 0.25 m³ / h.

[0012] Preferably, in step S2, the amount of the composite collector added is 800-1600 grams per ton of dry coal slime; and the concentration of the pre-adjusted refractory coal slime slurry is 80 g / L.

[0013] Preferably, in step S2, the foaming agent is 2-octanol, and the addition amount is 250 g / t.

[0014] Preferably, in step S2, the stirring and mixing time is 3 minutes.

[0015] Preferably, the flotation separation process in step S3 also includes an effect monitoring and parameter adjustment step: monitoring the clean coal yield and tailings ash content, and making real-time or batch-by-batch fine adjustments to the ratio and / or dosage of the composite collector based on the monitoring results.

[0016] Preferably, the parameter adjustment specifically involves: increasing the proportion of methyl linoleate in the composite collector in subsequent batches when the yield of clean coal is lower than expected; and / or extending the ultrasonic dispersion time in step S1 and / or increasing the total amount of composite collector in subsequent batches when the ash content of tailings is lower than expected.

[0017] Preferably, after the flotation separation in step S3 is completed, the equipment cleaning and maintenance steps are also included: stopping stirring and aeration, cleaning the flotation cell and the bubble scraping device, and sealing and storing the remaining composite collector.

[0018] The advantages of this invention compared to the prior art are as follows: 1. Through molecular structure design and process control, the problem of low flotation efficiency of traditional difficult-to-float coal slime has been effectively solved, achieving a synergistic improvement in technical, economic and environmental benefits.

[0019] (1) Overall efficiency has been significantly improved

[0020] Comprehensive optimization of flotation parameters: Based on the specific hydrogen bond adsorption of highly flexible methyl linoleate molecules onto the hydrophilic units of coal surface (adsorption energy -0.46 eV), and its synergistic effect of "chain-to-chain entanglement" with hydrocarbon oils (composite adsorption energy -0.84 eV), highly selective collection of difficult-to-float coals was achieved. Ultimately, the clean coal yield was increased to a maximum of 89.20% (10-15% higher than the traditional ester compound system), while the ash content of tailings was significantly enriched to 80.32% (an increase of 8-12%), simultaneously improving both clean coal recovery rate and tailings disposal quality.

[0021] The process is highly adaptable and stable: Through molecular dynamics simulation optimization of three precise compound ratios (1:1, 3:1, 5:1) and 3-hour ultrasonic dispersion pretreatment, the reagent can be widely adapted to different coal qualities, and the fluctuation of clean coal yield is controlled within 3%, which solves the problems of poor adaptability and unstable effect of existing technologies.

[0022] (2) Dual benefits of economic and environmental protection

[0023] Significantly reduced overall costs: The powerful adsorption mechanism reduces the total amount of reagents used by 20-30%, directly reducing raw material costs; higher clean coal yield and lower tailings treatment load lead to a 15-20% reduction in overall production costs.

[0024] Green production and efficient resource utilization: The core component, methyl linoleate, is a bio-based material with a biodegradability of >95% and extremely low toxicity, significantly reducing the environmental burden. This technology improves the recovery rate of low-grade, difficult-to-float coal resources, extends the resource service life, and aligns with the national strategy for clean and efficient utilization and sustainable development of coal.

[0025] 2. The process of this invention is a holistic system with tightly coupled links and driven by a mechanism. The specific steps are as follows: Step 1: Precise formulation and activation of the composite collector; methyl linoleate is selected as the core, utilizing its high flexibility and strong polar functional groups provided by its double bonds to achieve strong hydrogen bond anchoring with hydrophilic sites (such as phenolic hydroxyl and carbonyl groups) on the coal surface. It is combined with n-dodecane / tetradecane to form a hydrophobic synergy through van der Waals forces. Based on the hydrophilicity of the coal, a (1-5):1 mass ratio is used for compounding. Subsequently, ultrasonic dispersion is performed for 3 hours to utilize the cavitation effect to form a stable microemulsion, reducing droplet self-adhesion by 90% and ensuring uniform and efficient subsequent adsorption.

[0026] Step 2: Enhanced Adsorption and Slurry Conditioning; At the optimal slurry concentration of 80 g / L, add 800-1600 g / t of the above-mentioned composite agent and stir for 3 minutes. At this time, methyl linoleate preferentially adsorbs onto hydrophilic sites and repels water molecules, while its long chain simultaneously "fixes" hydrocarbon oil molecules, constructing a stable composite hydrophobic film on the surface of coal particles.

[0027] Step 3: Selective flotation and separation; the modified coal particles have significantly enhanced hydrophobicity and rapidly mineralize and float to the surface after colliding with air bubbles. Gangue minerals, however, remain hydrophilic and retained in the slurry because they are not adsorbed by the reagents, thus achieving efficient separation.

[0028] Step 4: Dynamic Optimization and System Maintenance; Based on real-time clean coal yield and tailings ash content data, fine-tune the reagent ratio or dosage in reverse (increase the ester ratio if the yield is insufficient) to form a closed-loop optimization. Thoroughly clean the equipment and seal the reagents after operation to ensure long-term process stability.

[0029] In summary, this method starts with "specific adsorption molecule design" and, through the precise coordination of "simulation optimization of compound ratio", "ultrasonic dispersion and activation", "concentration-stirring intensity synergy" and "process dynamic control", it constitutes a complete process solution for the technical problem of efficient separation of fine-particle, difficult-to-float coal. Attached Figure Description

[0030] Figure 1 It is the molecular structure of methyl linoleate.

[0031] Figure 2 It is the molecular structure of n-dodecane.

[0032] Figure 3 It is the molecular structure of n-tetradecane.

[0033] Figure 4 This is a schematic diagram of the hydrogen bonding interaction between methyl linoleate and hydrophilic groups on the coal surface.

[0034] Figure 5 This is a schematic diagram of the synergistic adsorption of methyl linoleate and hydrocarbon oils through "chain-chain entanglement". Detailed Implementation

[0035] 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 embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0036] Example 1

[0037] This embodiment provides a method for improving the yield of clean coal in difficult-to-float coal slime, used to process a low-level difficult-to-float coal slime with fine particles, high ash content, and a large number of oxygen-containing functional groups on its surface.

[0038] Step S1, reagent preparation and pretreatment: Based on the characteristics of this coal slime, such as high ash content and strong hydrophilicity, methyl linoleate (molecular structure formula as shown) was selected. Figure 1 (as shown) and n-dodecane (molecular structural formula as shown) Figure 2 The two components (as shown) were combined to form a composite collector. They were mixed at a preset mass ratio of 1:1. The mixture was then placed in an ultrasonic disperser and subjected to ultrasonic dispersion for 3 hours to form a stable and homogeneous microemulsion, thus obtaining the composite collector.

[0039] Step S2, Slurry preparation and mineralization: The difficult-to-float coal slime ore was prepared into a slurry with a concentration of 80 g / L and pumped into the flotation cell. First, the composite collector prepared in step S1 was added to the slurry at a dosage of 800 g / ton of dry coal slime. Then, the frother 250 g / t of octanol was added. The agitator was turned on and stirred at a constant speed for 3 minutes to ensure that the composite collector and frother were fully dispersed in the slurry and fully contacted and adsorbed onto the surface of the coal particles, thus completing the mineralization process.

[0040] Step S3, Flotation Separation: Air is introduced into the prepared slurry to generate uniform bubbles. Hydrophobic coal particles adhere to the bubbles, forming mineralized foam that floats to the surface and is collected by a skimmer to obtain the flotation concentrate. The hydrophilic gangue minerals remain at the bottom of the slurry and are discharged as tailings.

[0041] During the flotation process, the yield of clean coal and the ash content of tailings were monitored. Under the conditions of this embodiment, the yield of clean coal basically met expectations, but the ash content of tailings was slightly lower than expected (i.e., more clean coal was lost in the tailings). Therefore, in the next batch of processing, it was decided to increase the total dosage of the composite collector to 900 grams per ton of dry coal slime to enhance the collection capacity for coal particles.

[0042] After flotation separation is complete, stop stirring and aeration. After draining the slurry, thoroughly rinse the flotation cell and skimmer with clean water. Store the remaining composite collector in a sealed, light-proof container for future use.

[0043] Example 2

[0044] This embodiment provides a method for improving the yield of clean coal in difficult-to-float coal slime, used to treat a difficult-to-float coal slime with medium metamorphism, wide particle size distribution, and medium ash content.

[0045] Step S1, reagent preparation and pretreatment: Based on the characteristics of this coal slime, methyl linoleate (molecular structural formula as shown) was selected. Figure 1 (as shown) and n-tetradecane (molecular structural formula as shown) Figure 3 The two components (as shown) were mixed at a preset mass ratio of 3:1. The mixture was then placed in an ultrasonic disperser and subjected to ultrasonic dispersion for 3 hours to form a stable and homogeneous microemulsion, thus obtaining the composite collector.

[0046] Step S2, Slurry preparation and mineralization: The difficult-to-float coal slime ore was prepared into a slurry with a concentration of 80 g / L and pumped into the flotation cell. The composite collector prepared in step S1 was added to the slurry at a dosage of 1200 g / ton of dry coal slime. Then, the frother 250 g / t of octanol was added. The agitator was turned on and the slurry was stirred at a constant speed for 3 minutes to complete the mineralization process.

[0047] Step S3, Flotation Separation: Air is introduced into the slurry to perform flotation separation. The mineralized froth is scraped off to obtain flotation concentrate, and the tailings are discharged from the bottom.

[0048] Monitoring results showed that the yield of clean coal and the ash content of tailings both met the expected targets, indicating good flotation performance. Therefore, under the current coal quality conditions, the operating parameters should be maintained at a compound collector ratio of 3:1 and a dosage of 1200 g / t dry coal slime.

[0049] After flotation, the equipment is stopped according to standard procedures and then cleaned and maintained. Remaining reagents are sealed and stored.

[0050] Example 3

[0051] This embodiment provides a method for improving the yield of clean coal in difficult-to-float coal slime, which is used to treat a high-ash, difficult-to-float coal slime with a high degree of oxidation and extremely strong surface hydrophilicity.

[0052] Step S1, reagent preparation and pretreatment: To address the extremely difficult flotation characteristics of this coal slime, methyl linoleate (molecular structure formula as shown) was selected to enhance its surface hydrophobicity. Figure 1 As shown in the figure, it is used as the main active ingredient, along with n-dodecane (molecular structure formula shown in the figure). Figure 2 (As shown) The two are mixed at a preset ratio of 5:1 by mass (i.e., a high proportion of methyl linoleate). The mixture is then placed in an ultrasonic disperser and subjected to ultrasonic dispersion for 3 hours to ensure the formation of a highly stable microemulsion, thus obtaining the composite collector.

[0053] Step S2, Slurry preparation and mineralization: The difficult-to-float coal slime ore was prepared into a slurry with a concentration of 80 g / L and pumped into the flotation cell. The composite collector prepared in step S1 was added to the slurry at a dosage of 1600 g / ton of dry coal slime. Then, the frother 250 g / t of octanol was added. The agitator was turned on and stirred at a constant speed for 3 minutes to ensure that the reagents and coal particles reacted fully.

[0054] Step S3, Flotation Separation: Air is introduced into the slurry to perform flotation separation. The mineralized froth is scraped off to obtain flotation concentrate, and the tailings are discharged from the bottom.

[0055] Initial flotation tests revealed a lower-than-expected clean coal yield. Analysis suggested severe coal slime oxidation, necessitating stronger polar collecting. Therefore, subsequent adjustments increased the proportion of methyl linoleate in the composite collector to 6:1 (a slight adjustment exceeding the original claims but reflecting the underlying design principles), and extended the ultrasonic dispersion time in step S1 to 3.5 hours to further enhance the dispersibility and efficacy of the reagent.

[0056] After flotation separation is completed, the equipment cleaning procedure must be strictly followed. Because the composite collector contains a high proportion of methyl linoleate, which is easily oxidized, the remaining composite collector must be strictly sealed and stored in a cool place.

[0057] Comparative Example 1

[0058] This comparative example uses an ester-based compound system with methyl oleate as the polar component. It lacks the highly flexible molecular design of methyl linoleate and has a short ultrasonic dispersion time. However, it lacks the synergistic optimization of "chain-to-chain entanglement." The specific steps are as follows: Preparation and pretreatment of the reagent: Take 15 parts methyl oleate, 20 parts kerosene, 10 parts diethyl phthalate, 5 parts waste hot pot oil, 5 parts waste cooking oil, 1 part dodecyl dimethyl ammonium bromide, and 50 parts water. After boiling and separating the waste hot pot oil, and evaporating it under reduced pressure, mix it with the other components and ultrasonically disperse it for 10 minutes (not 3 hours) to obtain the composite collector. Slurry preparation and mineralization: Add the above collector to 80 g / L slurry at an addition rate of 1200 g / t dry coal slime (consistent with Example 2), add 0.05 g / L 2-octanol, and stir for 3 minutes; Flotation separation: Air is introduced for flotation, mineralized foam is scraped off to collect clean coal, and indicators such as clean coal yield, clean coal ash content, and tailings ash content are tested.

[0059] Technical defects: Methyl oleate is a C18 monounsaturated fatty acid ester (with only one double bond), which has insufficient molecular flexibility. It binds to the hydrophilic groups on the coal surface as a weak hydrogen bond (adsorption energy of about -0.3 eV), resulting in poor adsorption stability. The ultrasonic dispersion time is only 10 minutes, which cannot form a stable microemulsion. The agent is not evenly dispersed, and there is no "chain-chain entanglement" synergistic effect, resulting in limited hydrophobic enhancement effect.

[0060] Comparative Example 2

[0061] This comparative example uses a compound collector specifically designed for weakly caking coal. It lacks the specific hydrogen bond design of methyl linoleate and relies on benzene ring π-bond bonding and the polar effects of ethers. The specific steps are as follows: Reagent preparation and pretreatment: Take 75% diesel oil, 15% phenylacetic acid, 3% ethylene oxide, and 7% n-pentyl ether, mix them, and stir at 1000 rpm for 15 minutes (without ultrasonic dispersion) to obtain a composite collector; Slurry preparation and mineralization: Add 1200 g / ton of collector to 80 g / L of slurry, add 0.05 g / L of 2-octanol, and stir for 3 minutes; Flotation separation: Air is introduced (air flow rate 0.8 cm / s), the bubbles are scraped for 3 minutes, the clean coal is collected and the indicators are tested.

[0062] Technical defects: This collector is designed for CO functional groups on the surface of weakly caking coal and is combined with aromatic nuclei through benzene ring π bonds. It has poor compatibility with medium-level metamorphic and difficult-to-float coals in this application. There is no ultrasonic dispersion step, the agent does not form a microemulsion, and it is unevenly spread on the surface of coal particles. The collection selectivity is lower than the "hydrogen bond anchoring + hydrophobic synergy" system in this application.

[0063] Comparative Example 3

[0064] This comparative example uses a vegetable oil-based compound system, with rice bran oil as the main component. It features a precise compounding and ultrasonic activation process without methyl linoleate and short-chain alkanes. The specific steps are as follows: Preparation and pretreatment of the agent: Take 50 parts of rice bran oil, 20 parts of methyl laurate, 5 parts of diethyl phthalate, and 15 parts of oleic acid, and ultrasonically disperse and mix them evenly (without 3 hours of ultrasonication) to obtain the compound collector. Slurry preparation and mineralization: Add 1200 g / ton of collector to 80 g / L of slurry, add 0.05 g / L of 2-octanol, and stir for 3 minutes; Flotation separation: Air is introduced for flotation, clean coal is collected and its parameters are tested.

[0065] Technical defects: This system relies on the hydrophobic effect of the long-chain fatty acids in vegetable oils. The combination of methyl laurate and oleic acid lacks the synergistic effect of "strong hydrogen bond anchoring + chain-chain entanglement". In addition, it has not been ultrasonically dispersed for 3 hours, so the reagent droplets are prone to agglomeration. The coverage efficiency of hydrophilic groups on the surface of difficult-to-float coal is lower than that of this application.

[0066] Figure 4 This is a schematic diagram illustrating the hydrogen bonding interaction between methyl linoleate and hydrophilic groups on the coal surface. Figure 4 It is evident that the introduction of methyl linoleate significantly increases the stability of the adsorption system. The formation of hydrogen bonds weakens the adsorption force between n-dodecane and n-tetradecane molecules and the coal surface, making it easier for n-dodecane and n-tetradecane molecules to desorb from the coal surface. However, they preferentially adsorb with methyl linoleate through van der Waals forces, excluding water molecules from the system and enhancing hydrophobicity, thereby leading to enhanced flotation effect.

[0067] Figure 5 This is a schematic diagram of the synergistic adsorption of methyl linoleate and hydrocarbon oils via "chain-to-chain entanglement". Figure 5 It is known that methyl linoleate molecules (long-chain fatty acid esters containing polar functional groups) and hydrocarbon oil (n-dodecane / n-tetradecane) molecules (non-polar hydrophobic long chains) are not independently adsorbed on the surface of coal particles. Instead, they are "chain-chain entangled" through hydrophobic interactions between the long chains of molecules. The hydrophobic carbon chains of methyl linoleate and the linear carbon chains of hydrocarbon oil intertwine and entangle with each other to form a continuous network covering layer, rather than an isolated monolayer or discrete oil droplets.

[0068] Methyl linoleate forms specific hydrogen bonds with oxygen-containing hydrophilic groups (such as CO and -OH) on the surface of coal particles through polar functional groups (ester groups) in its molecule, thereby achieving "anchoring adsorption" and fixing the entire molecule to the surface of the coal particles. Its hydrophobic long chains further intertwine with the hydrophobic long chains of hydrocarbon oils, which is equivalent to forming a "reinforced structure" on the basis of "anchoring", avoiding the problems of easy detachment of single molecules and uneven spreading, making the adsorption layer more stable.

[0069] The adsorption layer formed by "chain-chain entanglement" has high density and continuity: compared with the monolayer of methyl linoleate (incomplete hydrophobic coverage) or the discrete adsorption of a single hydrocarbon oil (easy to aggregate and uneven coverage), the entangled network structure can completely cover the hydrophilic sites on the surface of coal particles, effectively displace the surface hydration film, greatly improve the hydrophobicity of the coal particle surface, and the hydrophobic film is not easily washed away by water flow.

[0070] The schematic diagram intuitively illustrates the synergistic value of the composite system: methyl linoleate solves the problem of hydrocarbon oils being "difficult to anchor and easy to fall off", while hydrocarbon oils compensate for the shortcomings of single methyl linoleate in "single hydrophobic chain and non-dense coverage" by winding. The combination of the two achieves the dual effect of "firm anchoring + hydrophobic enhancement", providing structural support for the subsequent efficient adhesion of coal particles and bubbles.

[0071] The composite collector of Example 1 was subjected to coal slime flotation core performance tests, and the test standards were "Coal Preparation Laboratory Unit Flotation Test Method" (GB / T 4757-2001) and "Coal Flotation Evaluation Method".

[0072] Table 1. Flotation data of methyl linoleate and n-tetradecane

[0073] Table 1 shows that the clean coal yield ranged from 80.63% to 89.20% across the nine test data sets, with an average yield of 85.47%. The optimal clean coal yield reached 89.20%, significantly higher than that of traditional hydrocarbon oil collectors and existing ester-based compound systems (typically below 75%). This result fully validates the effectiveness of the "chain-to-chain entanglement" synergistic adsorption mechanism between methyl linoleate and n-tetradecane. The strongly polar functional groups of methyl linoleate form stable hydrogen bonds with the hydrophilic groups on the coal surface (adsorption energy -0.46 eV), while the hydrophobic long chains of n-tetradecane entangle with them to construct a dense hydrophobic film. This significantly improves the adhesion efficiency between difficult-to-float coal particles and bubbles, achieving highly efficient collection of fine-grained, difficult-to-float coal.

[0074] The composite collector of Example 2 was subjected to coal slime flotation core performance tests, and the test standards were "Coal Preparation Laboratory Unit Flotation Test Method" (GB / T 4757-2001) and "Coal Flotation Evaluation Method".

[0075] Table 2 Flotation data of methyl linoleate and n-dodecane

[0076] As shown in Table 2, the ash content of the clean coal in the nine test groups ranged from 14.26% to 22.55%, with an average ash content of 17.35%. Among these, the ash content of the clean coal in five groups was below 18%, and the clean coal yield and ash content showed a significant positive optimization trend: when the clean coal yield was higher than 84% (e.g., 84.07%, 84.15%, 84.14%, 85.74%), the ash content was controlled below 16%, indicating that the composite collector can accurately distinguish between coal particles and gangue minerals, effectively preventing ash impurities from mixing into the clean coal. Comparing the test data of "n-dodecane and n-tetradecane compound" in Table 3 (clean coal yield only 67.20%-75.88%), the separation selectivity of this invention is significantly improved, fully demonstrating the effectiveness of the synergistic mechanism of "specific hydrogen bond adsorption + chain-chain entanglement".

[0077] The composite collector of Example 3 was subjected to coal slime flotation core performance tests. The test standards were "Coal Preparation Laboratory Unit Flotation Test Method" (GB / T 4757-2001) and "Coal Flotation Evaluation Method".

[0078] Table 3. Flotation data of n-dodecane and n-tetradecane composites

[0079] As shown in Table 3, the clean coal yield of the nine test groups ranged from 67.20% to 75.88%, with an average yield of only 72.23%, which is more than 8 percentage points lower than the expected clean coal yield (above 80%) of the composite collector in Example 3. Among them, the lowest clean coal yield was only 67.20%, while the corresponding tailings yield was as high as 32.80%, indicating that a large number of difficult-to-float coal particles were lost to the tailings due to ineffective collection. The core reason for this result is that n-dodecane and n-tetradecane are both non-polar hydrocarbon oils, which rely solely on weak van der Waals forces for adsorption. They lack the strong polar functional group (ester group) of methyl linoleate and cannot form specific hydrogen bond anchoring with the large number of hydrophilic groups (such as hydroxyl and carboxyl groups) on the surface of oxidized coal. This makes it difficult to displace the thick hydration film on the surface of coal particles, resulting in insufficient improvement in the hydrophobicity of coal particles and extremely low adhesion efficiency with air bubbles. They are completely unsuitable for the characteristics of highly oxidized and difficult-to-float coal slime.

[0080] The composite collector of Example 4 was subjected to coal slime flotation core performance tests. The test standards were "Coal Preparation Laboratory Unit Flotation Test Method" (GB / T 4757-2001) and "Coal Flotation Evaluation Method".

[0081] Table 4 Comparison of flotation effects of methyl linoleate and methyl oleate composite systems

[0082] As shown in Table 4, the clean coal yield of the methyl linoleate + n-tetradecane system reached 89.20%, an increase of 16.55% compared to the 76.53% of the methyl oleate + n-tetradecane system, and far exceeded the minimum requirement of GB / T 4757-2001 for the clean coal yield of difficult-to-float coal slime (usually ≥65%). This significant improvement stems from the essential difference in molecular structure design: methyl linoleate contains two double bonds, making it more flexible. The specific hydrogen bond adsorption energy formed with the hydrophilic groups on the coal surface reaches -0.46 eV, which is much higher than the weak hydrogen bond of methyl oleate (about -0.3 eV), greatly enhancing the adsorption stability. At the same time, its "chain-chain entanglement" synergistic effect with n-tetradecane (composite adsorption energy -0.84 eV) constructs a dense and stable hydrophobic film, which significantly improves the adhesion efficiency of difficult-to-float coal particles and bubbles, completely overcoming the defects of insufficient molecular flexibility and easy adsorption detachment of methyl oleate. The methyl linoleate + n-tetradecane system exhibits a biodegradability of 95.6%, a 19.2% improvement over the methyl oleate + n-tetradecane system's 80.2%, and significantly exceeds the minimum environmental standard requirement for biodegradability of flotation reagents (≥80%). The core reason is that methyl linoleate is a bio-based material with extremely low toxicity, while the synthesis process of methyl oleate is more complex, and some byproducts affect its biodegradability. This indicator validates the "green production" design concept of this invention, reducing the environmental burden of the coal preparation process and aligning with the national strategy for the clean and efficient utilization of coal.

[0083] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of the present invention, and not all embodiments. It should be noted that many modifications and improvements can be made by those skilled in the art, and all modifications or improvements not exceeding the scope of the claims should be considered within the protection scope of the present invention.

Claims

1. A method of improving clean coal yield from a difficult-to-float coal slime, characterized in that, Includes the following steps: S1. Reagent preparation and pretreatment: Based on the coal quality characteristics of the fine-grained, difficult-to-float coal to be floated, methyl linoleate and at least one hydrocarbon oil selected from n-dodecane and n-tetradecane are selected and mixed at a mass ratio of (1-5):

1. The mixture is then ultrasonically dispersed to form a stable microemulsion, thus obtaining a composite collector. S2. Slurry preparation and mineralization: The composite collector and foaming agent obtained in step S1 are added to the refractory coal slime slurry with the concentration adjusted, and the slurry is stirred to make the composite collector fully contact the coal particles and cause adsorption. S3. Flotation separation: Air bubbles are introduced into the slurry after it has been prepared. The hydrophobic coal particles adhere to the air bubbles to form mineralized foam and float to the surface. The flotation clean coal is obtained by scraping the foam, while the hydrophilic gangue minerals remain in the slurry and are discharged as tailings.

2. The process for improving the clean coal yield from the difficult-to-float coal slime according to claim 1, characterized in that, In step S1, the coal quality characteristics include at least one of ash content, particle size distribution, hydrophilic functional group content, and degree of metamorphism.

3. The process for improving clean coal yield from the low floatability coal slime as claimed in claim 1 wherein, In step S1, the ultrasonic dispersion treatment time is 3 hours.

4. The process for improving clean coal yield from the low floatability coal slime as claimed in claim 1 or 2 wherein, In step S3, the rate at which air bubbles are introduced into the slurry after conditioning is 0.25 m³ / h.

5. The process for improving clean coal yield from low floatability coal slime as claimed in claim 1 wherein, In step S2, the amount of the composite collector added is 800-1600 grams per ton of dry coal slime; the concentration of the pre-adjusted refractory coal slime slurry is 80 g / L.

6. The process for improving clean coal yield from low floatability coal slime as claimed in claim 1 wherein, In step S2, the foaming agent is 2-octanol, and the addition amount is 250 g / t.

7. The process for improving clean coal yield from low floatability coal slime as claimed in claim 1 wherein, In step S2, the stirring and mixing time is 3 minutes.

8. The process for improving clean coal yield from low floatability coal slime as claimed in claim 1 wherein, In the flotation separation process of step S3, there is also an effect monitoring and parameter adjustment step: monitoring the clean coal yield and tailings ash content, and making real-time or batch-by-batch fine adjustments to the ratio and / or dosage of the composite collector based on the monitoring results.

9. The process for improving clean coal yield from the low floatability coal slime as claimed in claim 8 wherein, The parameter adjustment specifically refers to: when the clean coal yield is lower than expected, increasing the proportion of methyl linoleate in the composite collector in subsequent batches; and / or, when the tailings ash content is lower than expected, extending the ultrasonic dispersion time in step S1 and / or increasing the total amount of composite collector in subsequent batches.

10. The process for improving clean coal yield from low floatability coal slime as claimed in claim 1 wherein, After the flotation separation in step S3 is completed, the equipment cleaning and maintenance steps are also included: stop stirring and aeration, clean the flotation cell and the foam scraping device, and seal and store the remaining composite collector.

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