Efficient conversion and enrichment method for natural mineral source raw material humic acid

Abstract

The invention belongs to the technical field of agricultural chemical products and application, and particularly relates to a natural mineral source raw material humic acid efficient conversion and enrichment method which comprises the steps that S1, a natural mineral source raw material is dried and crushed until the particle size is smaller than 100 meshes, and crushed materials are obtained; s2, mixing the crushed material obtained in the step S1 with a nitric acid solution with the mass concentration of 15-30% to obtain a mixed solution; s3, carrying out water bath ultrasonic treatment on the mixed solution obtained in the step S2 in an ultrasonic machine with the power of 200W-600W at room temperature for 5-60 minutes to obtain a mixture; and S4, carrying out suction filtration or filter pressing on the mixture obtained in the step S3 to realize solid-liquid separation, wherein the obtained solid is a target humic acid product. The humic acid product prepared by the method can be used for improving soda saline-alkali soil. According to the method, double breakthrough of raw material quality and preparation efficiency is achieved, under the optimal process, the yield of humic acid reaches up to 706.72%, high-valued application of low-grade raw materials is achieved, the reaction time is shortened to 5 min and is shortened by 95.83% compared with a traditional process (2 h or above), the production efficiency is improved by 1099%, and energy consumption is reduced by 50% or above.

Description

Technical Field

[0001] This invention belongs to the field of agricultural chemical products and application technology, specifically relating to a method for the conversion and enrichment of humic acid from natural mineral raw materials (peat, lignite, weathered coal), and the application of this humic acid in improving soda saline-alkali land. Background Technology

[0002] Soil salinization of arable land is a major problem facing humanity, seriously threatening the sustainable development of agriculture. Currently, there are over 412 million hectares of saline-alkali arable land worldwide. Based on different causes and chemical compositions, saline-alkali land can be divided into various types. Among them, soda saline-alkali soil is the most difficult to manage, characterized by high pH (usually >9.0, even exceeding 10.5), high sodium alkalinity (ESP>15%), and rich bicarbonate and carbonate ions. This high-salt, strongly alkaline environment exerts a dual stress on soil and plants: on the one hand, excessive exchangeable Na⁺ damages soil colloids, leading to loose soil structure and extremely poor aeration and permeability; on the other hand, the strongly alkaline environment fixes various trace elements such as phosphorus, iron, and zinc, while the high salt concentration creates osmotic stress, affecting plant growth.

[0003] Among the measures for improving saline-alkali soil, humic acid, with its huge specific surface area and abundant functional groups, can chelate metal ions, improve the physical structure of the soil and increase nutrient availability, stimulate plant growth, and act as a buffer to alleviate drastic fluctuations in pH. In recent years, it has shown great application potential in the field of soil improvement, especially in the treatment of saline-alkali soil.

[0004] Humic acid extracted from natural mineral raw materials such as peat, lignite, and weathered coal is currently the primary source of humic acid products. According to the coal industry standard MT / T 1159-2011 "Technical Conditions for Coal-Based Humic Acid," raw materials with a humic acid content below 45% are considered "unqualified," and those with a humic acid content below 40% are generally considered commercially worthless. Although my country has abundant coal reserves, high-grade weathered coal and lignite humic acid raw materials suitable for production are becoming increasingly scarce. Peat is mainly imported, leading to a continuous rise in the cost of humic acid raw materials and limiting industry development. At the same time, while a large amount of low-grade natural mineral humic acid raw materials have high carbon content, existing humic acid extraction technologies cannot efficiently enrich and convert the "stable carbon" in the raw materials into active humic acid, resulting in significant resource waste. Therefore, efficient enrichment and conversion of low-grade mineral humic acid raw materials to improve humic acid yield is crucial to overcoming the technological bottleneck in the humic acid industry.

[0005] Currently, the preparation of mineral-derived humic acid is primarily aimed at weathered coal, lignite, or peat with a humic acid content of at least 40%, and mostly employs alkaline extraction. The main product is potassium / sodium humate, with a pH between 9 and 11. Due to its alkalinity and high salt ion content, this type of humic acid is unsuitable for saline-alkali land, especially for the improvement of soda soil saline-alkali land. Existing processes mainly extract humic acid from raw materials already containing it, and the yield is limited by the humic acid content of the raw materials themselves. For example, the humic acid extraction methods disclosed in Chinese patents CN102181064A and CN1304659A both require the raw material to have a humic acid content of at least 40%.

[0006] In order to increase the humic acid content or carbon dissolution rate in raw materials, existing technologies have also attempted to use mechanical grinding, strong oxidant oxidation, or ultrasonic pretreatment before alkaline solution dissolution to improve the yield of humic acid.

[0007] Strong oxidants such as nitric acid, potassium permanganate, and hydrogen peroxide treat raw materials under certain conditions, breaking chemical bonds in the coal body through oxidation and degrading insoluble macromolecular organic matter into soluble small-molecule humic acid. This method can improve the yield of humic acid to a certain extent and increase the oxygen-containing functional groups in the product. However, it faces problems such as harsh reaction conditions, high cost, serious environmental pollution, and easy over-oxidation of the product. The nitric acid oxidation method disclosed in Chinese patent CN1304659A has a nitric acid concentration of 43% and a reaction time of 1-9 hours; or it can be used as a pre-oxidation treatment at a lower concentration, such as the nitric acid oxidation method disclosed in Chinese patent CN102181064A. Although the nitric acid concentration is only 1-2%, the reaction temperature is as high as 70-80℃, and purification with alkaline solution is required after the reaction. In the prior art, Chinese Patent Publication No. CN107337510A discloses a method for activating lignite humic acid and preparing a slow-release coated organic fertilizer. This method includes the following steps: oxidizing lignite with nitric acid; bioactivating the lignite humic acid using a compound enzyme preparation (lignin peroxidase, laccase, and manganese peroxidase) to reduce its molecular size; and then nitrifying and dissolving the lignite humic acid under the action of ammonia. This preparation process uses nitric acid oxidation as a pretreatment and ultimately requires extraction with ammonia and alkaline solution. It does not explicitly improve the grade of humic acid in the raw material, and the patent document does not record corresponding data. Furthermore, the humic acid obtained after ammonia treatment is unsuitable for use in soda-saline-alkali land.

[0008] Korean Patent Publication No. KR1020150105509A discloses a method for separating humic acid from lignite, which includes: oxidizing the lignite with a nitric acid solution, mixing the oxidized lignite with an alkaline solution, adjusting the pH value to 7.5-8, and further separating the humic acid. In this scheme, nitric acid is also used as a pretreatment, and the final process is still strong alkali extraction. The separated humic acid cannot be used for the improvement of saline-alkali land. Chinese Patent Publication No. CN109111578A discloses a method for preparing an aqueous solution of humic acid, which mainly uses an alkaline solution to dissolve the humic acid in weathered coal or lignite. However, the resulting solution still cannot be used for the improvement of saline-alkali land.

[0009] Ultrasonic oxidation technology generates cavitation, and the extreme high temperature and pressure produced by the collapse of cavitation bubbles simultaneously triggers the cleavage of water molecules, generating a large number of highly oxidizing substances such as hydroxyl radicals in situ. This can be used for the extraction of humic acid from mineral sources. Currently, ultrasonic processes are mainly used as pretreatment, and alkaline extraction is still required in the final stage. Moreover, the ultrasonic process mainly employs probe ultrasonic technology.

[0010] Existing patent literature does not document a method for enriching humic acid from low-grade natural mineral raw materials, converting inert organic matter in the raw materials into active humic acid. Current humic acid extraction processes cannot achieve yields exceeding the humic acid content of the raw materials themselves. Therefore, developing a proprietary activation and enrichment method that is mild, highly controllable, and capable of efficiently converting large quantities of low-grade humic acid mineral raw materials into high-grade humic acid, while also increasing the extraction rate of humic acid from high-grade raw materials to varying degrees, and simultaneously producing humic acid products free from high salt and high pH issues, suitable for saline-alkali land improvement, is of significant practical importance for the high-value utilization of low-grade coal resources and improving the quality of raw materials for the humic acid industry. Summary of the Invention

[0011] This invention aims to overcome the shortcomings of existing technologies and provide a simple, mild, and highly efficient method for the conversion and enrichment of humic acid. It overcomes the challenge of stable and efficient conversion and enrichment of humic acid from low-grade natural mineral raw materials (humic acid content 8.8% to no more than 40%), and can also promote further increases in humic acid content from high-grade raw materials (humic acid content greater than 40%). Furthermore, the produced humic acid product solves the problems of strong alkalinity and high salinity, and can be effectively used to improve soda saline-alkali soils.

[0012] To achieve the above objectives, this invention provides a method for the efficient conversion and enrichment of humic acid from natural mineral raw materials, the method comprising: S1: Dry the natural mineral raw materials and crush them to a particle size of less than 100 mesh to obtain crushed materials; S2: Mix the fragments obtained in step S1 with nitric acid solution to obtain a mixture; S3: The mixture obtained in step S2 is ultrasonicated in a water bath in an ultrasonic machine to obtain a mixture; S4: The mixture described in step S3 is subjected to vacuum filtration or pressure filtration to achieve solid-liquid separation, wherein the obtained solid is the target humic acid product.

[0013] Preferably, in step S1, the humic acid content in the natural mineral raw material is less than 30%.

[0014] Preferably, in step S2, the concentration of the nitric acid solution is 5%-30%.

[0015] Preferably, in step S3, the ultrasound is a water bath ultrasound, and the ultrasound power is 200W-600W, the ultrasound temperature is room temperature, and the ultrasound time is 5min-60min.

[0016] Preferably, in step S2, the solid-liquid mass ratio of the crushed material to the nitric acid solution is 1:0.5-1:6.

[0017] Preferably, step S4 further includes drying the resulting solid at a temperature of 65°C.

[0018] Furthermore, in step S1, the humic acid content in the natural mineral raw material is greater than 40%, and step S1 also includes the operation of ball milling the crushed material together with an ammonium activator.

[0019] Preferably, the humic acid content in the natural mineral raw material is greater than 50%.

[0020] Preferably, the ammonium activator is ammonium chloride, ammonium sulfate, or ammonium nitrate.

[0021] This application also provides humic acid products prepared using the above-described transformation and enrichment method.

[0022] This application also provides the application of the above-mentioned humic acid products in the preparation of organic fertilizers, soil conditioners, soil conditioning agents or crop growth stimulants.

[0023] This application also provides a soil conditioner, comprising the above-mentioned humic acid product after treatment.

[0024] Preferably, the soil conditioner is used in soda-saline-alkali land.

[0025] Compared with the prior art, the present invention has the following significant advantages: (1) Significantly improved humic acid yield: The humic acid preparation method of the present invention breaks through the transformation of inert organic matter in humic acid raw materials into active humic acid, and the humic acid yield exceeds the original humic acid content (the extraction rate of humic acid in existing technologies does not exceed 100%). It can make high-value utilization of a large amount of low-grade humic acid ("unqualified" raw materials as defined in MT / T 1159-2011 "Technical Conditions for Coal-based Humic Acid", the low-grade natural mineral raw materials are raw materials with humic acid content of 8.8%-40%). For low-grade natural mineral sources, the highest humic acid yield can be achieved at 706.72%, and no heating is required at room temperature, which is much better than the traditional process, realizing a breakthrough in the yield and efficiency of low-grade to high-grade humic acid raw materials. At the same time, there is also a different degree of improvement for high-grade raw materials with humic acid content of 52.33% (increased to 68.9%, with a yield of 131.63%).

[0026] (2) Shorter reaction time: Traditional methods require more than 2 hours, while this method only requires 5 minutes, increasing production efficiency by 1099%.

[0027] (3) The reaction conditions and equipment are easier to achieve: the reaction is carried out under normal temperature and pressure conditions, and the ultrasonic process is water bath ultrasonic, which overcomes the problems of high energy consumption, local overheating and local overreaction of the current probe ultrasonic. It does not require complex equipment and can achieve large-scale production.

[0028] (4) High economic benefits: The raw materials are solid waste, the conditions are mild and the reaction time is short, which improves both the cost of raw materials and energy consumption, and reduces energy consumption by more than 50%.

[0029] (5) Wide range of product applications: It has many functional active groups, does not contain salt ions, and is acidic, thus overcoming the current problem of lack of humic acid products for saline-alkali land. The humic acid product has higher stability than biochemical humic acid, higher activity than natural humic acid, and can be adapted to various scenarios, enabling the rapid construction of high-quality tillage layers.

[0030] (6) The method of the present invention has a wide range of applications. It can activate natural mineral humic acid raw materials such as peat, lignite, and weathered coal. It can further increase the humic acid content on the basis of humic acid modification for both low-grade and high-grade mineral sources.

[0031] On the other hand, the enrichment method of this invention is process-controllable and produces stable products. This method achieves precise control over the oxidation and activation process, ensuring that the humic acid yield consistently reaches over 100% (the specific yield is affected by the organic carbon content of the raw materials themselves), and is rich in functional groups, highly active, and reproducible. Furthermore, the reaction conditions of this invention are mild and easy to implement: the reaction temperature is room temperature, requiring no high pressure or special equipment, the process route is simple, and post-processing is straightforward, making it suitable for industrial-scale production. Simultaneously, this invention overcomes the common problems of high salt ion concentrations and pH levels, as well as poor activity, in existing humic acid products prepared via alkali dissolution.

[0032] Furthermore, the humic acid product prepared by the enrichment method of this invention has broad application prospects. Testing revealed that its various indicators are significantly superior to those of conventional raw materials, and its application to soil can increase soil nutrients such as nitrogen, phosphorus, potassium, and sulfur. The mineral-derived calcium humic acid complex fertilizer provided by this invention has promising applications in improving soda-saline-alkali land. The Ca in the mineral-derived calcium humic acid complex fertilizer... 2+ It can effectively replace Na on soil colloids + This directly reduces soil alkalinity (ESP) and pH value; the mineral-derived calcium humate complex fertilizer helps promote soil colloid aggregation, forming a stable granular structure, thereby improving soil aeration and permeability, and alleviating the common compaction problem in soda saline-alkali soils. In summary, the mineral-derived calcium humate complex fertilizer provided by this invention can effectively improve the soil organic matter, soil nutrients, and soil structure of soda saline-alkali land, thus providing a good material and means for soil improvement of soda saline-alkali arable land. Attached Figure Description

[0033] Figure 1 This is a process flow diagram of the humic acid enrichment method of the present invention.

[0034] Figure 2 This is a comparison chart showing the humic acid content of products obtained from lignite activated with different concentrations of nitric acid in the embodiments and comparative examples of this application. 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 accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0036] This invention provides a method for the conversion and enrichment of humic acid in low-grade natural mineral raw materials, wherein the low-grade natural mineral raw materials are natural mineral raw materials with a humic acid content of less than 45%. Figure 1 The method includes: S1: The natural mineral raw material is dried and crushed to a particle size of less than 100 mesh; S2: Mix the material obtained in step S1 with a nitric acid solution with a mass concentration of 15%-30%; S3: The mixed solution obtained in S2 is ultrasonicated in a water bath at room temperature for 5 min-60 min in a 200W-600W ultrasonic machine to obtain a mixture; S4: The mixture described in S3 is subjected to vacuum filtration or pressure filtration to achieve solid-liquid separation, wherein the obtained solid is the target humic acid product.

[0037] S5: Mix the material obtained in step S1 with a nitric acid solution with a mass concentration of 5%-20%; S6: The mixed solution obtained in S5 is ultrasonicated in a 200W-600W ultrasonic machine in a water bath at room temperature for 5min-60min to obtain a mixture; S7: The mixture described in S6 is dried directly, and the resulting solid is the target humic acid product.

[0038] S8: Products from S4 or S7 can be used for the improvement of soda soil saline-alkali land, with a dosage of 210 kg / mu. S9: Products from S4 or S7 can be used to quickly construct a high-quality topsoil layer on newly reclaimed farmland. They can be used in conjunction with desulfurized gypsum and organic matter, with an addition of 150 kg per acre, in conjunction with deep plowing.

[0039] Preferably, in steps S2 and S5 above, nitric acid mainly plays the role of oxidation and activation. If the concentration of nitric acid is too low, the oxidation and activation effect will be insufficient; if the concentration of nitric acid is too high, the oxidation reaction will be too violent, which will easily lead to excessive destruction of the humic acid structure.

[0040] Preferably, in steps S2 and S5, the solid-liquid mass ratio of the natural mineral raw material to the nitric acid solution is 1:0.5-1:6. This ratio ensures a complete reaction while also saving costs.

[0041] Another aspect of the present invention provides the application of the above-mentioned humic acid product for improving soda saline-alkali land.

[0042] Humic acid can chelate, adsorb, and exchange ions with salt ions in the soil, thereby increasing the soil's ability to absorb calcium. 2+ Mg 2+ Fe 3+ The adsorption capacity of plasma accelerates the adsorption of Na. +Humic acid, rich in various functional groups and hydrophilic in nature, can promote the formation of soil aggregates, improve soil physical structure, increase soil permeability, aeration and water retention, and reduce soil moisture evaporation. Simultaneously, humic acid contains hydroxyl and carboxyl groups, which have a certain buffering capacity for soil pH. It can neutralize or exchange alkaline ions such as carbonate and bicarbonate in saline-alkali soils, reducing soil alkalinity and maintaining soil pH stability. Furthermore, humic acid can activate and release insoluble phosphorus, mineral potassium, and slow-release potassium in the soil, converting them into readily available phosphorus and potassium, enhancing nutrient availability and improving soil fertility.

[0043] Although humic acid can increase soil nutrient content and has a good binding capacity with soil minerals, its effect on improving soil aggregate structure may not be significant if there is a lack of sufficient bridging ions (such as calcium ions).

[0044] Nitrohumic acid is a class of nitro derivatives formed by the reaction of humic acid and nitric acid. It combines the soil-improving and plant-growth-promoting effects of humic acid with the fast-acting nutritional functions of the nitro functional group, making it a highly efficient, green, and environmentally friendly fertilizer and soil conditioner. Traditional methods for preparing nitrohumic acid often use high-quality weathered coal or peat as raw materials, employing concentrated nitric acid under heating conditions for nitration oxidation. This method suffers from problems such as high energy consumption, vigorous reaction that easily produces toxic nitrogen oxide gases, high requirements for raw material quality, and unstable product performance.

[0045] Specifically, the humic acid product prepared by this invention can be used for the improvement of soda soil saline-alkali land, with a usage of 210 kg / mu; it can also be used for the rapid construction of a high-quality topsoil layer in newly reclaimed farmland, in synergy with desulfurized gypsum and organic matter, with an addition of 150 kg per mu, in conjunction with deep plowing.

[0046] The present application will be further explained and illustrated below through specific embodiments.

[0047] Lignite from a local producer in Inner Mongolia was measured to have a humic acid content of 8.93% on a dry basis. The procedure described in this example is as follows: The lignite was crushed to a particle size of less than 100 mesh. 100g of the lignite raw material was weighed and placed in a 1000mL Erlenmeyer flask. 400mL of nitric acid solutions with different mass concentrations (5%, 10%, 15%, 20%, and 30%, respectively) (solid-liquid ratio 1:4) were added, and water was used as a negative control. The flask was placed in an ultrasonic cleaner (450W, model KQ-500VDE) and ultrasonicated for 5 minutes at room temperature.

[0048] After the reaction was completed, the resulting mixture was filtered, and the solid filter cake was dried in an oven at 65°C until constant weight. After pulverization, a brownish-black powder was obtained, which is the target humic acid product.

[0049] The test results of humic acid content corresponding to different concentrations of nitric acid are as follows: Figure 1 As shown.

[0050] Under ultrasonic treatment with 15% nitric acid, the humic acid content reached 63.11%, and the humic acid yield was 706.72%. Meanwhile, from... Figure 1 It can also be seen that 20% nitric acid and 30% nitric acid correspond to 63.58% and 63.98% humic acid content, respectively.

[0051] Therefore, 15%-30% nitric acid is the optimal concentration range.

[0052] The lignite obtained from a certain location in Inner Mongolia was measured to have a humic acid content of 33.30% on a dry basis. The procedure for this example is as follows: Crush the raw lignite to a particle size of less than 100 mesh, weigh 100g of lignite raw material, and place it in a 1000mL conical flask. Add 400mL of 15% nitric acid solution (solid-liquid ratio 1:4), place the flask in an ultrasonic cleaner, and sonicate for 5 minutes at room temperature.

[0053] After the reaction was completed, the resulting mixture was dried in an oven at 65°C until constant weight, and then pulverized to obtain a brownish-black powder, which is the target humic acid product.

[0054] After the reaction, the humic acid content was measured to be 45.13%, which is an increase of 35.53%, and the yield was 135.53%.

[0055] Weathered coal from a certain area in Henan Province was measured to have a humic acid content of 40.96% on a dry basis. The procedure for this example is as follows: The material was crushed to a particle size of less than 100 mesh. 100g of weathered coal raw material was weighed and placed in a 1000mL Erlenmeyer flask. 400mL of 15% nitric acid solution (solid-liquid ratio 1:4) was added, and the flask was placed in an ultrasonic cleaner and ultrasonicated for 5 minutes at room temperature.

[0056] After the reaction was completed, the resulting mixture was filtered, and the solid filter cake was dried in an oven at 65°C until constant weight. After pulverization, a brownish-black powder was obtained, which is the target humic acid product.

[0057] After the reaction, the humic acid content was measured to be 52.51%, and the yield was 128.20%, which significantly increased the humic acid content of the raw material.

[0058] Weathered coal from a local Xinjiang source was tested and found to contain 52.33% humic acid on a dry basis, indicating a relatively high humic acid content. The coal was crushed to a particle size of less than 100 mesh and then ball-milled with ammonium chloride (an ammonium activator) for 15 minutes.

[0059] Weigh 100g of the above weathered coal raw material and place it in a 1000mL Erlenmeyer flask. Add 400mL of 15% nitric acid solution (solid-liquid ratio 1:4), place the flask in an ultrasonic cleaner, and sonicate for 5 minutes at room temperature.

[0060] After the reaction was complete, the mixture was filtered. The solid filter cake was dried in an oven at 65°C to constant weight, and then pulverized to obtain a brownish-black powder product.

[0061] After the reaction, the humic acid content was further activated to 68.9%, with a yield of 131.63%, indicating that the method is also applicable to mineral materials with high humic acid content.

[0062] Lignite from a local producer in Inner Mongolia was measured to have a humic acid content of 8.93% on a dry basis. The procedure described in this example is as follows: The raw lignite was crushed to a particle size of less than 100 mesh. 100g of the lignite raw material was weighed and placed in a 1000mL Erlenmeyer flask. 400mL of 15% nitric acid solution (solid-liquid ratio 1:4) was added, and water was used as a negative control. The flask was placed in an ultrasonic cleaner (450W, model KQ-500VDE) and ultrasonicated for 60min at room temperature.

[0063] After the reaction was completed, the resulting mixture was filtered, and the solid filter cake was dried in an oven at 65°C until constant weight. After pulverization, a brownish-black powder was obtained, which is the target humic acid product.

[0064] Under ultrasonic treatment with 15% nitric acid for 60 minutes, the humic acid content reached 62.96%, and the humic acid yield was 705.04%.

[0065] Peat obtained from a foreign country was measured to have a humic acid content of 44.29% on a dry basis. The procedure for handling this peat in this example is as follows: The peat raw material was crushed to a particle size of less than 100 mesh. 100g of the above peat raw material was weighed, ball-milled separately for 15 minutes, and then placed in a 1000mL Erlenmeyer flask. 400mL of 15% nitric acid solution (solid-liquid ratio 1:4) was added, and the flask was placed in an ultrasonic cleaner and ultrasonicated for 5 minutes at room temperature.

[0066] After the reaction was completed, the resulting mixture was filtered, and the solid filter cake was dried in an oven at 65°C until constant weight. After pulverization, a brownish-black powder was obtained, which is the target humic acid product.

[0067] After the reaction was completed, the humic acid content was measured to be 47.08%, and the humic acid yield was 106.30%, which further improved the humic acid content of the raw material.

[0068] The content and yield of humic acid before and after treatment in the above embodiments are shown in Table 1. Table 1. Humic acid yield in Examples 1-4 Comparative Example 1 Using the same lignite raw material as in Example 1, and with the same operating steps, conditions, and parameters, except for the concentration of nitric acid (10% dilute nitric acid was used instead), the mixture was sonicated at room temperature for 5 minutes. The resulting product had a humic acid content of 23.4%, which, although higher than the raw material, still failed to meet the acceptable standard. This indicates insufficient oxidizing strength and limited activation effect.

[0069] Figure 2 This is a comparison chart of the detection results of the above embodiments and comparative examples.

[0070] Using the same lignite raw material, 15% nitric acid concentration, and solid-liquid ratio as in Example 2, but without ultrasonic assistance, the product was mechanically stirred for 5 minutes at room temperature and then soaked at 30°C for 48 hours. The resulting product had a humic acid content of 46.86%, slightly higher than in Example 2, but the reaction time was longer and the reaction temperature was higher. This comparison demonstrates that "simultaneous ultrasound + nitric acid oxidation" under mild conditions is the key to this technology. It can significantly enhance mass transfer, promote the microscopic reaction between nitric acid and coal particles, and achieve efficient activation at room temperature and lower nitric acid concentrations, while simple stirring cannot achieve the same effect in the same time.

[0071] Take lignite with a humic acid content of 8.9%, crush it to a particle size of less than 100 mesh, and ball mill it together with calcium hydroxide (an alkaline activator, added in an amount of 1 / 5 of the lignite mass) for 15 minutes. After ball milling, the humic acid content is measured to be 10.10%. Weigh 100g of the above lignite raw material and place it in a 1000mL Erlenmeyer flask. Add 400mL of 15% nitric acid solution (solid-liquid ratio 1:4), place it in an ultrasonic cleaner, and sonicate it at room temperature for 5 minutes.

[0072] After the reaction was completed, the resulting mixture was dried in an oven at 65°C until constant weight. After pulverization, a brownish-black powder was obtained, which was the target humic acid product. The total humic acid content in the product was 45.78%.

[0073] Take lignite with a humic acid content of 8.9%, crush it to a particle size of less than 100 mesh, and ball mill it together with ferric sulfate (an alkali activator, added in an amount equal to 1 / 5 of the lignite mass) for 15 minutes. After ball milling, the humic acid content is 7.23%. Weigh 100g of the above lignite raw material and place it in a 1000mL Erlenmeyer flask. Add 400mL of 15% nitric acid solution (solid-liquid ratio 1:4), place it in an ultrasonic cleaner, and sonicate it at room temperature for 5 minutes.

[0074] After the reaction was completed, the resulting mixture was dried in an oven at 65°C until constant weight. After pulverization, a brownish-black powder was obtained, which was the target humic acid product. The total humic acid content of the final product was 45.15%.

[0075] Take lignite with a humic acid content of 8.9%, crush it to a particle size of less than 100 mesh, weigh 100g of the above lignite raw material, and place it in a 1000mL conical flask. Add 400mL of 10% nitric acid solution (solid-liquid ratio 1:4), place it in an ultrasonic cleaner, and sonicate for 5 minutes at room temperature.

[0076] After the reaction was completed, the resulting mixture was dried in an oven at 65°C until constant weight. After pulverization, a brownish-black powder was obtained, which was the target humic acid product. The humic acid content of the final product was determined to be 59.97%. This example demonstrates the enrichment effect of vacuum filtration.

[0077] Weathered coal from a local Xinjiang source was tested and found to contain 52.33% humic acid on a dry basis, indicating a relatively high humic acid content. The coal was crushed to a particle size of less than 100 mesh and then ball-milled separately for 15 minutes.

[0078] Weigh 100g of the above weathered coal raw material and place it in a 1000mL Erlenmeyer flask. Add 400mL of 15% nitric acid solution (solid-liquid ratio 1:4), place the flask in an ultrasonic cleaner, and sonicate for 5 minutes at room temperature.

[0079] After the reaction was complete, the mixture was filtered. The solid filter cake was dried in an oven at 65°C to constant weight, and then pulverized to obtain a brownish-black powder product.

[0080] After the reaction, the humic acid content was further activated to 42.23%, indicating that ball milling with ammonium activator is the key operation to improve the humic acid content of the weathered coal.

[0081] The above examples and comparative examples fully demonstrate that the "room temperature ultrasonic synergistic nitric acid oxidation" process system determined in this invention is key to achieving efficient activation of low-grade natural mineral humic acid raw materials. The cavitation and mechanical effects of ultrasound solve the problem of slow reaction kinetics at room temperature. Synergistically, with nitric acid solutions within a specific concentration range, it can stably convert substandard natural mineral raw materials (raw materials with humic acid content below 30%) into high-value humic acid raw materials with a humic acid content of over 45% within a very short time (5-60 minutes). This method avoids the thermal degradation of active ingredients that may occur with traditional heating methods, and has outstanding advantages such as low energy consumption, high efficiency, and good product activity.

[0082] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for the conversion and enrichment of humic acid from natural mineral raw materials, the method comprising: S1: Dry the natural mineral raw materials and crush them to a particle size of less than 100 mesh to obtain crushed materials; S2: Mix the fragments obtained in step S1 with nitric acid solution to obtain a mixture; S3: The mixture obtained in step S2 is ultrasonicated in a water bath in an ultrasonic machine to obtain a mixture; S4: The mixture described in step S3 is subjected to vacuum filtration or pressure filtration to achieve solid-liquid separation, wherein the obtained solid is the target humic acid product.

2. The transformation and enrichment method according to claim 1, characterized in that, In step S1, the humic acid content in the natural mineral raw material is less than 30%.

3. The transformation and enrichment method according to claim 1, characterized in that, In step S2, the concentration of the nitric acid solution is 5%-30%.

4. The transformation and enrichment method according to claim 1, characterized in that, In step S3, the ultrasound is a water bath ultrasound, with an ultrasound power of 200W-600W, an ultrasound temperature of room temperature, and an ultrasound time of 5min-60min.

5. The transformation and enrichment method according to claim 1, characterized in that, In step S2, the solid-liquid mass ratio of the crushed material to the nitric acid solution is 1:0.5-1:

6.

6. The transformation and enrichment method according to claim 1, characterized in that, Step S4 also includes drying the resulting solid at a temperature of 65°C.

7. The transformation and enrichment method according to claim 1, characterized in that, In step S1, the humic acid content in the natural mineral raw material is greater than 40%, and step S1 also includes the operation of ball milling the crushed material together with an ammonium activator.

8. The transformation and enrichment method according to claim 7, characterized in that, The humic acid content in the natural mineral raw material is greater than 50%.

9. The transformation and enrichment method according to claim 7, characterized in that, The ammonium activator is ammonium chloride, ammonium sulfate, or ammonium nitrate.

10. Humic acid products prepared by the conversion enrichment method according to any one of claims 1-9.

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