Coal-based solid waste treatment and high-value utilization method

Abstract

The invention relates to the field of solid waste resource utilization, in particular to a coal-based solid waste treatment and high-value utilization method. The coal-based solid waste treatment and high-value utilization method comprises the following steps: carrying out thermal oxidation on lignite to obtain oxidized lignite; mixing the oxidized lignite with a chemical activator dispersion liquid, and carrying out a solvothermal reaction to obtain a turbid liquid; carrying out solid-liquid separation on the turbid liquid to obtain filter residues and filtrate; calcining the filter residues to obtain a medium element compound fertilizer; and adding an acidic solution into the filtrate to adjust the pH to be acidic, thereby obtaining the humic acid. According to the method, the humic acid is prepared, meanwhile, the medium element compound fertilizer is prepared from the residues, the process route is improved, the economic benefit is greatly improved, and high additional value and multi-path resource utilization of the lignite solid waste are achieved.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization, and in particular to a method for treating and utilizing coal-based solid waste at high value. Background Technology

[0002] Lignite is a low-rank coal with a low degree of coalification, appearing light black and dull throughout. Currently, the main uses of lignite are incineration for power generation and as fuel. However, lignite has disadvantages such as low calorific value, low carbon content, and high ash content. Compared with high-rank coal, it requires burning more lignite to achieve the same calorific value, producing more fly ash and increasing solid waste. Furthermore, the combustion process generates a large amount of gaseous pollutants, causing the flue gas to carry significant amounts of nitrogen oxides, sulfur oxides, and carbon dioxide, placing a heavy burden on subsequent flue gas denitrification processes. Currently, the coal industry is vigorously promoting the clean and efficient utilization of coal for non-fuel purposes, especially lignite, a low-rank coal, whose comprehensive utilization pathways have received widespread attention.

[0003] Lignite is rich in native humic acid, making it a high-quality raw material for humic acid extraction. Humic acid has wide applications in agriculture, environmental protection, and materials science, particularly in soil improvement, fertilizer enhancement, and heavy metal adsorption. Currently, industrial humic acid extraction primarily employs an alkaline dissolution and acid precipitation process. While this method is simple, it often requires pretreatment of the lignite with strong oxidants such as nitric acid and hydrogen peroxide to increase the humic acid dissolution rate. These chemical oxidants are costly and toxic, easily causing secondary pollution, thus limiting their green and large-scale application.

[0004] Furthermore, lignite is rich in silicon, comprising approximately 50% of its total content. Silicon is an essential nutrient for soils, ranking as the fourth largest nutrient after nitrogen, phosphorus, and potassium. Silicon fertilizer plays a crucial role in the growth of cash crops such as rice and wheat. However, the silicon in lignite exists primarily in an adapted form and cannot be absorbed by the soil and plants. These elements mostly exist in stable silicate forms, making them difficult for plants to directly absorb. Currently, technologies for converting silicon in lignite into usable secondary element fertilizers for plants are still relatively lacking.

[0005] Therefore, developing a clean, efficient, and simultaneous process for the extraction of humic acid and activation of medium-level elements in lignite is of significant environmental and economic importance. Summary of the Invention

[0006] This invention provides a method for the treatment and high-value utilization of coal-based solid waste. It uses lignite to produce humic acid while simultaneously preparing the residue into a compound fertilizer with medium-quantity elements, thereby achieving the goal of high-value utilization of solid waste through multiple pathways.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: This invention provides a method for the treatment and high-value utilization of coal-based solid waste, comprising the following steps: Lignite is thermally oxidized to obtain oxidized lignite; The oxidized lignite and the chemical activator dispersion were mixed and subjected to a solvothermal reaction to obtain a suspension; The suspension was subjected to solid-liquid separation to obtain filter residue and filtrate; The filter residue is calcined to obtain a compound fertilizer containing medium-quantity elements; An acidic solution was added to the filtrate to adjust the pH to acidic, thus obtaining humic acid.

[0008] In some specific embodiments, the conditions for thermal oxidation are: temperature of 100~280℃, time of 0.5~3h, atmosphere flow rate of 0.5~2L / min, and the atmosphere includes air.

[0009] In some specific embodiments, the mass ratio of the oxidized lignite to the chemical activator in the chemical activator dispersion is 1~7:1.

[0010] In some specific embodiments, the ratio of chemical activator to solvent in the chemical activator dispersion is 1g:(4~10)mL.

[0011] In some specific embodiments, the chemical activator dispersion contains sulfates, nitrates, or carbonates.

[0012] In some specific embodiments, the sulfates include calcium sulfate and / or magnesium sulfate.

[0013] In some specific embodiments, the nitrates include calcium nitrate and / or magnesium nitrate.

[0014] In some specific embodiments, the carbonates include calcium carbonate and / or magnesium carbonate.

[0015] In some specific embodiments, the conditions for the solvothermal reaction are: temperature of 90~160℃, time of 0.5~4h, and pressure of 25~30MPa.

[0016] In some specific embodiments, the calcination temperature is 700~1000℃, and the calcination time is 1~4h.

[0017] In some specific embodiments, the target pH value is 1.5 to 3.3.

[0018] In some specific embodiments, the acidic solution includes hydrochloric acid; the concentration of the hydrochloric acid is 5wt% to 15wt%.

[0019] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for the treatment and high-value utilization of coal-based solid waste, which simultaneously produces humic acid and prepares the residue into a compound fertilizer containing medium-element elements. This invention uses air thermal oxidation instead of traditional chemical oxidation, reducing reagent costs while avoiding equipment corrosion and secondary environmental pollution caused by strong oxidants, and significantly improving the extraction rate of humic acid. Furthermore, air thermal oxidation removes mineral impurities, adsorbed water, and free water from lignite through physical methods, improving the purity of the subsequently prepared compound fertilizer and humic acid products. Then, a solvothermal reaction is performed on the oxidized lignite using a chemical activator, enhancing the activation effect of the chemical activator on the oxidized lignite and its extraction of humic acid, thereby effectively increasing the solubility of humic acid and promoting the reaction between silicon-containing compounds in lignite and the chemical activator, thus increasing the content of available silicon. The resulting suspension after the solvothermal reaction is subjected to solid-liquid separation to obtain filter residue and filtrate. Humic acid is extracted from the filtrate, and compound fertilizer is prepared from the filter residue. This improved process route greatly enhances economic benefits and realizes high added value and multi-pathway resource utilization of lignite solid waste. Detailed Implementation

[0020] The present invention will be described below through specific embodiments. Those skilled in the art will understand that the specific embodiments described below are for illustrative purposes only and do not limit the scope of the invention in any way. Furthermore, in the following embodiments, unless otherwise specified, the reagents and equipment used are commercially available. If specific processing conditions and methods are not explicitly described in the following embodiments, conditions and methods known in the art can be used for processing.

[0021] This invention provides a method for the treatment and high-value utilization of coal-based solid waste, comprising the following steps: Lignite is thermally oxidized to obtain oxidized lignite; The oxidized lignite and the chemical activator dispersion were mixed and subjected to a solvothermal reaction to obtain a suspension; The suspension was subjected to solid-liquid separation to obtain filter residue and filtrate; The filter residue is calcined to obtain a compound fertilizer containing medium-quantity elements; An acidic solution was added to the filtrate to adjust the pH to acidic, thus obtaining humic acid.

[0022] The method of this invention first involves air-thermal oxidation of lignite. This decomposes some unstable organic matter, releasing products such as carbon dioxide and water vapor. Simultaneously, oxygen in the air reacts with the lignite macromolecules, introducing more oxygen-containing functional groups into its structure, while removing mineral impurities and moisture, thus modifying and initially purifying the lignite and creating conditions for subsequent activation reactions. The oxidized lignite is then subjected to a solvothermal reaction with a chemical activator. The resulting liquid product is rich in soluble humates and water-soluble nutrients such as silicon, potassium, and calcium. The solid product contains unreacted organic matter, a new silicate phase formed during the reaction, and other inherent minerals. Due to silicon activation, the content and activity of plant-available secondary elements in the solid phase are significantly enriched and increased. The suspension after the solvothermal reaction is then subjected to solid-liquid separation to obtain a filtrate and a filter residue. The filtrate is a humate solution, a raw material for extracting humic acid; the filter residue is a solid residue rich in active secondary elements and a small amount of organic matter, specifically used for preparing secondary element compound fertilizers. Calcination of the filter residue removes residual organic matter, improves product purity and nutrient concentration, and promotes the transformation of silicates and other minerals into stable forms that are more easily absorbed by plants and have a slow-release effect. Simultaneously, calcination effectively kills pathogens and weed seeds, ensuring the product meets fertilizer hygiene standards and ultimately yields a qualified compound fertilizer containing medium-quantity elements. Utilizing the extremely low solubility of humic acid under acidic conditions, acid is added to the filtrate, causing the humic acid to precipitate out as flocculent or colloidal precipitates. Subsequent washing and drying processes yield a high-purity humic acid product.

[0023] In this invention, the original organic matter of lignite is a complex three-dimensional macromolecular network with an aromatic core, cross-linked by bridging bonds and aliphatic side chains. This network is dense and poorly soluble in alkali. However, through air thermal oxidation in the presence of oxygen and gentle heating, these bridging bonds (especially aliphatic bridging bonds) become weaknesses in the oxidative attack. The large, insoluble coal macromolecules are broken down into smaller, more loosely structured fragments, which are closer to the size and structure of humic acid. Due to their smaller size and reduced steric hindrance, their accessibility and solubility in the subsequent alkaline solution are significantly improved. After oxidation, the total acidic group content of lignite, especially the carboxyl group content, increases significantly. This allows more organic matter to be converted into soluble humates, thereby directly and substantially increasing the humic acid extraction rate.

[0024] In this invention, the chemical activator, under solvothermal conditions, simultaneously enhances the solubility of humic acid and the effective silicon content through a dual synergistic effect.

[0025] In this invention, "effective silicon" refers to silicon that can be absorbed by plants.

[0026] In this invention, the lignite undergoes a pretreatment process before thermal oxidation. The pretreatment includes: sequentially crushing, grinding and sieving lignite to obtain lignite powder; The particle size of the lignite powder is 0.075~0.18 mm. As an example, the particle size of the lignite powder can be 0.075 mm, 0.08 mm, 0.09 mm, 0.1 mm, 0.15 mm and 0.18 mm, etc.

[0027] In this invention, the particle size of lignite powder mainly affects extraction efficiency through the specific surface area effect and mass transfer resistance mechanism. Smaller particle sizes significantly increase the contact area between lignite and the reaction medium, accelerating oxygen penetration and reaction during thermal oxidation, and promoting the role of chemical activators in the solvothermal stage. However, excessively fine lignite powder particle sizes easily lead to particle agglomeration, difficulty in filtrate separation, and increased pulverization energy consumption. This invention, by controlling the lignite powder particle size within the aforementioned range, achieves a balance between reaction kinetics, separation efficiency, and cost control, thereby maximizing the optimization of humic acid extraction rate and effective silicon activation degree.

[0028] In some specific embodiments, the conditions for thermal oxidation are: temperature of 100~280℃, time of 0.5~3h, and atmosphere flow rate of 0.5~2L / min, wherein the atmosphere includes air. As an example, the temperature in the thermal oxidation conditions can be 100℃, 120℃, 150℃, 180℃, 200℃, 220℃, 250℃, and 280℃, etc.; the time can be 0.5h, 1h, 1.5h, 2h, 2.5h, and 3h, etc.; and the atmosphere flow rate can be 0.5L / min, 0.8L / min, 1L / min, 1.2L / min, 1.5L / min, 1.8L / min, and 2L / min, etc.

[0029] In this invention, the thermal oxidation temperature within the aforementioned range is beneficial for promoting the oxidative degradation of lignite and increasing oxygen-containing functional groups while avoiding excessive decomposition or combustion loss of organic matter. If the temperature is too high, it can lead to excessive pyrolysis or even carbonization of the humic acid precursor, resulting in significant loss of organic matter and a decrease in specific surface area, thus reducing the yield of extractable humic acid. If the temperature is too low, the oxidation reaction kinetics will be slow, functional group proliferation will be insufficient, and the pore structure will not develop adequately, failing to effectively improve the subsequent extraction rate. The time within the aforementioned range is beneficial for ensuring that the oxidation reaction proceeds fully and uniformly, allowing the lignite particles to achieve the ideal oxidation depth and functional group modification level. If the time is too long, it will lead to increased energy consumption and may cause over-oxidation, resulting in the loss of some of the already generated active... Further decomposition of oxygen-containing structures reduces product yield. If the time is too short, oxidation will be incomplete, with only the surface of the lignite being modified and insufficient internal activation, resulting in limited improvement in overall extraction rate. An air flow rate within the above range is beneficial for maintaining sufficient oxygen concentration in the reaction system to drive the oxidation reaction and for timely removal of generated water vapor and volatile products, promoting the forward reaction. If the air flow rate is too fast, it will carry away too much reaction heat, making it difficult to maintain a stable furnace temperature. It may also cause fine lignite particles to be lost due to airflow, increasing material loss. If the air flow rate is too slow, it will lead to local oxygen deficiency, resulting in uneven oxidation. Furthermore, the retention of volatile products will inhibit reaction equilibrium and may cause partial pyrolysis rather than oxidation to dominate due to insufficient oxygen, affecting the formation of the target product.

[0030] In some embodiments, the mass ratio of the oxidized lignite to the chemical activator in the chemical activator dispersion is 1 to 7:1. As an example, the mass ratio of the oxidized lignite to the chemical activator in the chemical activator dispersion can be 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, and 7:1, etc.

[0031] In this invention, the mass ratio of the chemical activator in the oxidized lignite and the chemical activator dispersion is within the above range, which ensures that humic acid is fully extracted and silicon is effectively activated, so that the filter residue becomes a high-quality compound fertilizer rich in effective medium-quantity elements after calcination.

[0032] In some embodiments, the ratio of chemical activator to solvent in the chemical activator dispersion is 1 g: (4~10) mL. As examples, the ratio of chemical activator to solvent in the chemical activator dispersion is 1 g: 4 mL, 1 g: 5 mL, 1 g: 6 mL, 1 g: 7 mL, 1 g: 8 mL, 1 g: 9 mL, and 1 g: 10 mL, etc.

[0033] In some embodiments, the chemical activator in the chemical activator dispersion includes, but is not limited to, sulfates, nitrates, or carbonates.

[0034] In some embodiments, the sulfate includes, but is not limited to, calcium sulfate and / or magnesium sulfate.

[0035] In some embodiments, the nitrate includes, but is not limited to, calcium nitrate and / or magnesium nitrate.

[0036] In some embodiments, the carbonate includes, but is not limited to, calcium carbonate and / or magnesium carbonate.

[0037] In this invention, the chemical activator can be used alone or in combination with two or more salts that have different cations but the same anion.

[0038] As an example, the chemical activator can be a mixture of calcium sulfate and magnesium sulfate in a mass ratio of (3~1):1, a mixture of calcium nitrate and magnesium nitrate in a mass ratio of (3~1):1, or a mixture of calcium carbonate and magnesium carbonate in a mass ratio of (3~1):1.

[0039] In this invention, calcium and magnesium salts are used as chemical activators, and high-temperature calcination further promotes the conversion of effective silicon. In addition, a large amount of medium-quantity elements such as calcium, magnesium, and sulfur are incorporated to achieve the production of medium-quantity element compound fertilizer.

[0040] In some embodiments, the conditions for the solvothermal reaction are: temperature of 90~160℃, time of 0.5~4h, and pressure of 25~30MPa. As an example, the conditions for the solvothermal reaction can include temperatures of 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, and 160℃, times of 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, and 4h, and pressures of 25MPa, 26MPa, 27MPa, 28MPa, 29MPa, and 30MPa.

[0041] In some embodiments, the solvothermal reaction is carried out under stirring at a speed of 400-900 rpm. For example, the stirring speed can be 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm, and 900 rpm, etc.

[0042] In this invention, the chemical activator and lignite are fully reacted under high temperature, high pressure and continuous stirring conditions, which promotes the full mixing between the solid and liquid phases, strengthens the interaction between reactant molecules, shortens the reaction time, effectively improves the solubility of humic acid, promotes the reaction between silicon-containing compounds in lignite and the activator, and increases the effective silicon content.

[0043] In some embodiments, before calcining the filter residue, a first drying treatment is also included. The temperature and time of the drying treatment are not specifically limited, as long as the moisture in the filter residue is removed.

[0044] In some embodiments, the calcination temperature is 700~1000℃, and the calcination time is 1~4h. As examples, the calcination temperature can be 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, and 1000℃, etc., and the calcination time can be 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, and 4h, etc.

[0045] In this invention, by controlling the calcination temperature within the aforementioned range, it is beneficial to thoroughly decompose the small amount of residual organic matter in the filter residue, improve the purity and nutrient concentration of the compound fertilizer product, and simultaneously promote the transformation of minerals into stable oxides or mineral phases that can be slowly released and absorbed by plants. If the calcination temperature is too high, it will lead to increased volatilization loss of some nutrient elements, and some minerals may melt and sinter, forming glassy hard blocks, reducing the effective surface area and nutrient release of the product, and significantly increasing energy consumption. If the calcination temperature is too low, it will lead to carbonization of organic matter rather than complete combustion, resulting in a product with high residual carbon content, dark color, and mineral... Incomplete transformation of nutrients results in low activity of effective silicon, calcium, and other nutrients, leading to poor fertilizer efficiency. By controlling the calcination time within the above-mentioned range, it is beneficial to ensure sufficient heat transfer and thorough reaction, allowing the organic matter to be completely ashed and the mineral phases to reorganize and reach a stable state. If the calcination time is too short, the material center may not react completely, resulting in residual organic matter and uneven mineral transformation, leading to unstable product quality. If the calcination time is too long, it will lead to an unnecessary increase in energy consumption and may cause the already formed active mineral structure to be deactivated or sintered due to excessive heat treatment, reducing product porosity and nutrient availability, while increasing production costs.

[0046] In some embodiments, the target pH value is 1.5 to 3.3. As examples, the target pH value can be 1.5, 1.8, 2, 2.5, 2.8, 3, and 3.3, etc.

[0047] In some embodiments, the acidic solution includes, but is not limited to, hydrochloric acid.

[0048] In some embodiments, the concentration of the hydrochloric acid is 5 wt% to 15 wt%. As an example, the concentration of the hydrochloric acid solution can be 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 12 wt%, 13 wt%, and 15 wt%, etc.

[0049] In some embodiments, after adding an acidic solution to the filtrate to adjust the pH to acidic, the method further includes solid-liquid separation of the resulting solution to obtain a precipitate, and performing a second drying treatment on the precipitate.

[0050] In some embodiments, the method of solid-liquid separation is not specifically limited, and those skilled in the art can use conventional solid-liquid separation methods to separate the precipitate. In some embodiments, solid-liquid separation can be centrifugal separation.

[0051] In this invention, the temperature and time of the second drying process are not specifically limited; it is sufficient to remove the moisture from the precipitate.

[0052] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments. The embodiments of this application are only examples, and all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0053] Example 1 The lignite was crushed, ground, and sieved to obtain lignite powder with a particle size of 0.075~0.18mm; 20g of lignite powder was placed in an air thermal oxidation device and subjected to air thermal oxidation for 2 hours at an air flow rate of 1.5L / min and a temperature of 150℃ to obtain oxidized lignite. 5g of calcium sulfate was added to deionized water at a ratio of 1g:8mL to obtain a chemical activator dispersion. Oxidized lignite and the chemical activator dispersion were mixed at a mass ratio of 7:1. The mixture was subjected to a solvothermal reaction for 0.5h at a pressure of 28MPa, a temperature of 120℃, and a stirring speed of 500rpm to obtain a suspension. The suspension is subjected to solid-liquid separation to obtain filter residue and filtrate; The filter residue was placed in a drying oven and dried at 105℃ for 8 hours, and then calcined at 700℃ for 2 hours to obtain a calcium-silicon-sulfur compound fertilizer. While stirring, add 8wt% hydrochloric acid dropwise to the filtrate to adjust the pH to 2.8. Then, centrifuge the resulting solution and place the precipitate in a forced-air drying oven to dry at 105℃ for 8 hours to obtain humic acid.

[0054] The effective silicon content of the calcium-silicon-sulfur compound fertilizer prepared in Example 1 was determined to be 5048.58 mg / kg by the silicon-molybdenum-blue spectrophotometric method.

[0055] The yield of humic acid in Example 1 was found to be 26.84%.

[0056] Example 2 The lignite was crushed, ground, and sieved to obtain lignite powder with a particle size of 0.075~0.18mm; 20g of lignite powder was placed in an air thermal oxidation device and subjected to air thermal oxidation for 2h at an air flow rate of 1L / min and a temperature of 200℃ to obtain oxidized lignite. 5g of calcium sulfate and 5g of magnesium sulfate were added to deionized water at a ratio of 1g:8mL to obtain a chemical activator dispersion. Oxidized lignite was mixed with the chemical activator dispersion at a mass ratio of 4:1. The mixture was subjected to a solvothermal reaction at a pressure of 25MPa, a temperature of 150℃, and a stirring speed of 500rpm for 2 hours to obtain a suspension. The suspension is subjected to solid-liquid separation to obtain filter residue and filtrate; The filter residue was placed in a drying oven and dried at 105℃ for 8 hours, and then calcined at 900℃ for 2 hours to obtain a calcium-magnesium-silicon-sulfur compound fertilizer. While stirring, add 5 wt% hydrochloric acid dropwise to the filtrate to adjust the pH to 1.5. Then, centrifuge the resulting solution and place the precipitate in a forced-air drying oven to dry at 105℃ for 8 hours to obtain humic acid.

[0057] The effective silicon content of the calcium-magnesium-silicon-sulfur compound fertilizer prepared in Example 2 was determined to be 7865.91 mg / kg by the silicon-molybdenum-blue spectrophotometric method.

[0058] The yield of humic acid in Example 2 was found to be 30.65%.

[0059] Example 3 The lignite was crushed, ground, and sieved to obtain lignite powder with a particle size of 0.075~0.18mm; 20g of lignite powder was placed in an air thermal oxidation device and subjected to air thermal oxidation for 1 hour at an air flow rate of 2L / min and a temperature of 280℃ to obtain oxidized lignite. 5g of magnesium nitrate was added to deionized water at a ratio of 1g:8mL to obtain a chemical activator dispersion. Oxidized lignite and the chemical activator dispersion were mixed at a mass ratio of 2:1. The mixture was subjected to a solvothermal reaction at a pressure of 30MPa, a temperature of 100℃, and a stirring speed of 800rpm for 4h to obtain a suspension. The suspension is subjected to solid-liquid separation to obtain filter residue and filtrate; The filter residue was placed in a drying oven and dried at 105℃ for 8 hours, and then calcined at 1000℃ for 2 hours to obtain a calcium-magnesium-silicon-sulfur compound fertilizer. While stirring, add 5 wt% hydrochloric acid dropwise to the filtrate to adjust the pH to 3. Then, centrifuge the resulting solution and place the precipitate in a forced-air drying oven to dry at 105℃ for 8 hours to obtain humic acid.

[0060] The effective silicon content of the calcium-magnesium-silicon-sulfur compound fertilizer prepared in Example 3 was determined to be 8851.08 mg / kg by the silicon-molybdenum-blue spectrophotometric method.

[0061] The yield of humic acid in Example 3 was found to be 26.24%.

[0062] Example 4 The lignite was crushed, ground, and sieved to obtain lignite powder with a particle size of 0.075~0.18mm; 20g of lignite powder was placed in an air thermal oxidation device and subjected to air thermal oxidation for 1 hour at an air flow rate of 1.6L / min and a temperature of 200℃ to obtain oxidized lignite. 5g of magnesium carbonate and 5g of calcium carbonate were mixed with deionized water at a ratio of 1g:8mL to the total mass of magnesium carbonate and calcium carbonate, to obtain a chemical activator dispersion. Oxidized lignite was mixed with the chemical activator dispersion at a mass ratio of 2:1. The mixture was subjected to a solvothermal reaction for 3 hours at a pressure of 28MPa, a temperature of 150℃, and a stirring speed of 600rpm to obtain a suspension. The suspension is subjected to solid-liquid separation to obtain filter residue and filtrate; The filter residue was placed in a drying oven and dried at 105℃ for 8 hours, and then calcined at 800℃ for 2 hours to obtain a calcium-magnesium-silicon-sulfur compound fertilizer. While stirring, add 5 wt% hydrochloric acid dropwise to the filtrate to adjust the pH to 2.5. Then, centrifuge the resulting solution and place the precipitate in a forced-air drying oven to dry at 105℃ for 8 hours to obtain humic acid.

[0063] The effective silicon content of the calcium-magnesium-silicon-sulfur compound fertilizer prepared in Example 4 was determined to be 7911.37 mg / kg by the silicon-molybdenum-blue spectrophotometric method.

[0064] The yield of humic acid in Example 4 was found to be 27.33%.

[0065] Although preferred embodiments of the invention have been shown and described, it is conceivable that those skilled in the art can devise various modifications to the invention within the spirit and scope of the appended claims.

Claims

1. A method for treating and utilizing coal-based solid waste at high value, characterized in that, Includes the following steps: Lignite is thermally oxidized to obtain oxidized lignite; The oxidized lignite and the chemical activator dispersion were mixed and subjected to a solvothermal reaction to obtain a suspension; The suspension was subjected to solid-liquid separation to obtain filter residue and filtrate; The filter residue is calcined to obtain a compound fertilizer containing medium-quantity elements; An acidic solution was added to the filtrate to adjust the pH to acidic, thus obtaining humic acid.

2. The method for treating and utilizing coal-based solid waste according to claim 1, characterized in that, The conditions for thermal oxidation are: temperature 100~280℃, time 0.5~3h, atmosphere flow rate 0.5~2L / min, and the atmosphere includes air.

3. The method for treating and utilizing coal-based solid waste according to claim 1, characterized in that, The mass ratio of the oxidized lignite to the chemical activator in the chemical activator dispersion is 1~7:

1.

4. The method for treating and utilizing coal-based solid waste according to claim 1, characterized in that, The ratio of chemical activator to solvent in the chemical activator dispersion is 1g:(4~10)mL.

5. The method for treating and utilizing coal-based solid waste according to claim 1, characterized in that, The chemical activator in the dispersion includes sulfates, nitrates, or carbonates.

6. The method for treating and utilizing coal-based solid waste according to claim 5, characterized in that, The sulfates include calcium sulfate and / or magnesium sulfate; The nitrates include calcium nitrate and / or magnesium nitrate; The carbonates include calcium carbonate and / or magnesium carbonate.

7. The method for treating and utilizing coal-based solid waste according to claim 1, characterized in that, The conditions for the solvothermal reaction are: temperature 90~160℃, time 0.5~4h, and pressure 25~30MPa.

8. The method for treating and utilizing coal-based solid waste according to claim 1, characterized in that, The calcination temperature is 700~1000℃, and the calcination time is 1~4h.

9. The method for treating and utilizing coal-based solid waste according to claim 1, characterized in that, The target pH value is 1.5 to 3.

3.

10. The method for treating and utilizing coal-based solid waste according to claim 1, characterized in that, The acidic solution includes hydrochloric acid; the concentration of the hydrochloric acid is 5wt% to 15wt%.