Saline-alkali soil conditioning particles rich in humic acid and use method thereof

Abstract

The invention relates to the field of agricultural resource utilization, and particularly discloses saline-alkali soil conditioning particles rich in humic acid and a use method of the saline-alkali soil conditioning particles. According to the technical scheme, the particles are homogeneous particles prepared from the following raw materials in parts by weight through reactive extrusion granulation: 50-65 parts of weathered coal powder, 5-10 parts of maleic anhydride, 20-30 parts of calcium sulfite, 0.1-0.5 part of manganese sulfate, 5-10 parts of alkyl glycoside, 5-10 parts of sodium lignin sulfonate and 5-15 parts of water. The humic acid content of the weathered pulverized coal is greater than or equal to 50.0%, and the granularity of the weathered pulverized coal passes through a 80-120-mesh sieve; the grafting reaction is initiated by using free radicals generated by auto-oxidation of calcium sulfite, an additional organic initiator does not need to be added, organic residues are avoided, meanwhile, chemical modification of humic acid is achieved, the carboxyl content is increased, and the exchange capacity of conditioning particles for sodium ions in soil is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of agricultural resource utilization, more particularly, it relates to a saline-alkali soil conditioning granule rich in humic acid and a use method thereof. BACKGROUND

[0002] As an important reserve arable land resource, the management and utilization of saline-alkali soil has far-reaching significance for food security. The main characteristics of saline-alkali soil are high soil pH value, high proportion of exchangeable sodium ions in soil colloids, and hard soil structure, which leads to inhibited growth of crop roots and low water and fertilizer utilization efficiency. Among many improvement measures, the application of humic acid soil conditioning agent is widely adopted due to its good ion exchange performance and improvement effect on soil aggregate structure. Humic acid molecules contain active functional groups such as carboxyl and phenolic hydroxyl groups, which can replace sodium ions on soil colloids through ion exchange and adjust soil pH.

[0003] However, natural humic acid directly derived from weathered coal or lignite has a relatively low content of active functional groups in its molecular structure, resulting in a limited cation exchange capacity, and the improvement effect on severe saline-alkali soil is often unsatisfactory. In order to overcome this defect, the existing technology often uses graft copolymerization to chemically modify humic acid, that is, introducing monomers containing abundant carboxyl groups to increase the exchange capacity. However, the current graft modification process mainly has the following technical bottlenecks: On the one hand, most of the existing graft polymerization reactions rely on organic initiators to produce free radicals. The use of such organic initiators not only increases the cost of raw materials, but more importantly, the unreacted organic initiators and their decomposition products are easily left in the final soil conditioner, which brings potential organic pollution risk to the soil environment. On the other hand, traditional modification is usually carried out in an aqueous solution system, which has a long process flow, high energy consumption for subsequent drying, and is difficult to realize continuous industrial production. If only simple physical mixing or granulation process is used, although the use of organic initiators is avoided, chemical bonding at the molecular level cannot be achieved, the number of carboxyl groups on the humic acid backbone cannot be effectively increased, and the cation exchange capacity of the product cannot be substantially improved, which makes it difficult to meet the demand for efficient management of saline-alkali soil. SUMMARY

[0004] In order to solve the problem that the traditional graft modification in the prior art relies on organic initiators and is prone to residue, the present application provides a saline-alkali soil conditioning granule rich in humic acid and a use method thereof.

[0005] The saline-alkali soil conditioning granule rich in humic acid and the use method thereof provided by the present application adopt the following technical solutions: The present application provides a saline-alkali soil conditioning granule rich in humic acid.

[0006] The granules are prepared by reactive extrusion granulation of raw materials including the following weight parts: weathered coal powder 50-65 parts, maleic anhydride 5-10 parts, calcium sulfite 20-30 parts, manganese sulfate 0.1-0.5 parts, alkyl glycoside 5-10 parts, sodium lignosulfonate 5-10 parts, and water 5-15 parts.

[0007] In the technical solution of the present application, the granules are not a simple physical mixture of components, but a reactive extrusion product. Specifically, the humic acid in the weathered coal powder and the maleic anhydride undergo a chemical grafting reaction during the extrusion process. The grafting reaction is not initiated by an exogenous organic initiator, but by the intermediate radicals generated by the oxidation reaction of calcium sulfite under specific process conditions. By grafting maleic anhydride in situ on the molecular backbone of humic acid, a large number of carboxyl functional groups are introduced, thereby increasing the cation exchange capacity of the granule matrix.

[0008] Preferably, the humic acid content of the weathered coal powder is greater than or equal to 50.0%, and the particle size passes through an 80-120 mesh screen; the calcium sulfite is an industrial by-product with a purity greater than or equal to 90.0%. Using the industrial by-product calcium sulfite as a raw material, the initiation of free radicals is achieved by utilizing its instability, combining chemical reaction driving with waste utilization.

[0009] Preferably, the alkyl glycoside is a non-ionic surfactant with a carbon chain length of C8-C10 or C12-C14, and its solid content is greater than or equal to 50.0%; the total sulfonate content of the sodium lignosulfonate is greater than or equal to 50.0%. The alkyl glycoside is distributed in the granule matrix and used to reduce the surface tension of the soil solution during use; the sodium lignosulfonate plays a role in terminating the radical reaction and dispersion during preparation.

[0010] Preferably, the particle size of the granules is controlled to be 2-5 mm, and the final moisture content is less than 5.0%.

[0011] The second aspect of the present application provides a preparation method of the above-mentioned saline-alkali soil conditioning granules rich in humic acid.

[0012] The method uses a reactive extrusion process with multi-stage temperature control and shear control, including the following steps: Step S1: Dry mix the weighed weathered coal powder and maleic anhydride in a high-speed mixer to prepare a premix, and add the premix to a twin-screw extruder through the main feeding port.

[0013] Step S2: Mix the calcium sulfite, manganese sulfate, and water to prepare a wet material or slurry, and add it to the low-temperature mixing zone of the twin-screw extruder through the side feeding port.

[0014] Step S3: The material enters the high-temperature reaction section of the twin-screw extruder. In this stage, the high temperature and shearing action are used to induce the self-oxidation reaction of calcium sulfite in the presence of manganese sulfate catalysis and oxygen. The oxidation process produces active intermediates such as sulfite radicals, which attack humic acid and maleic anhydride, initiating in-situ graft polymerization of maleic anhydride on the surface and inside the pores of the weathered coal powder.

[0015] Step S4: Add alkyl polyglycoside and sodium lignosulfonate in the cooling and mixing section of the twin-screw extruder. The reducing property of sodium lignosulfonate consumes the residual free radicals in the system, terminates the grafting reaction, and prevents excessive crosslinking. After melt blending of the components, they are extruded through a die, cut into particles, and dried to obtain the finished product.

[0016] Preferably, in step S1, the temperature of dry mixing is controlled at 20-30℃, and the mixing time is 5-15 min. This step ensures uniform adhesion of maleic anhydride monomers to the surface of weathered coal powder.

[0017] Preferably, in step S2, the temperature of the low-temperature mixing zone is controlled at 40-70℃, and the screw rotation speed is set at 80-120 r / min. This region is not vacuumed, and oxygen exists in the barrel. The presence of oxygen is a necessary condition for the oxidation of calcium sulfite to produce free radicals.

[0018] Preferably, in step S3, the temperature of the high-temperature reaction section is controlled at 90-120℃, the residence time of the material in this section is 30-90 s, the screw rotation speed is set at 150-250 r / min, and the shearing pressure is controlled at 2-5 MPa. High temperature and high shearing force promote the oxidation rate of calcium sulfite and the grafting efficiency of maleic anhydride.

[0019] Preferably, in step S4, the temperature of the cooling and mixing section is reduced to 70-90℃, and the alkyl polyglycoside and sodium lignosulfonate are added in the form of solid powder or concentrated solution.

[0020] Preferably, in step S4, the drying process is carried out in a hot air environment at 60-85℃ until the moisture content of the particles is less than 5.0%.

[0021] In summary, the present application has the following beneficial effects: 1. By using the free radicals generated by the self-oxidation of calcium sulfite to initiate grafting reaction, no additional organic initiator is needed, avoiding organic residues, and at the same time realizing the chemical modification of humic acid, increasing the carboxyl content, and improving the exchange capacity of conditioning particles for sodium ions in the soil.

[0022] 2. The chemical grafting process is integrated with the granulation process by a reactive extrusion process, the introduction of sodium lignosulfonate as a reaction terminator ensures the controllability of the reaction and prevents uncontrollable crosslinking and solidification of the material during extrusion.

[0023] 3. The alkyl polyglycoside in the granules and the modified humic acid synergize, the alkyl polyglycoside reduces the soil water surface tension, and assists the modified humic acid and calcium ions to migrate to the deep soil, thereby improving the permeability of the saline-alkali soil. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a flowchart of the humic acid-rich saline-alkali soil conditioning granules provided by the present application and a method of using the same. DETAILED DESCRIPTION

[0025] The present application will be further described in detail below in combination with the drawings and examples.

[0026] The sources and specifications of the main raw materials and reagents used in the following examples and comparative examples are as follows, and the reagents not specifically described are commercially available analytical pure or higher grade products.

[0027] Weathered coal powder: commercially available industrial grade, humic acid content 55.0%, particle size passes through 100 mesh sieve; Maleic anhydride: chemical pure, purity greater than or equal to 99.0%, CAS number: 108-31-6; Calcium sulfite: industrial grade, purity greater than or equal to 90.0%, CAS number: 10257-55-3; Manganese sulfate: analytical pure, manganese sulfate monohydrate, purity greater than or equal to 99.0%, CAS number: 10034-96-5; Alkyl polyglycoside: industrial grade, type APG0810 (C8-C10 alkyl polyglycoside), solid content 50.0%, CAS number: 68515-73-1; Sodium lignosulfonate: industrial grade, total sulfonate content greater than or equal to 50.0%, CAS number: 8061-51-6; Deionized water: laboratory-made, electrical conductivity less than 5 μS / cm, CAS number: 7732-18-5.

[0028] Example 1 Referring to the accompanying Figure 1 , the present embodiment provides a humic acid-rich saline-alkali soil conditioning granule and a preparation method thereof.

[0029] Raw material formula (by weight): weathered coal powder 58 parts, maleic anhydride 7 parts, calcium sulfite 25 parts, manganese sulfate 0.3 parts, alkyl polyglycoside 7 parts, sodium lignosulfonate 8 parts, deionized water 10 parts.

[0030] Preparation method: Step S1: The weighed weathered coal powder and maleic anhydride were placed in a high-speed mixer and dry mixed at a temperature of 25°C for 10 minutes to prepare a premixed material. The premixed material was added to the twin-screw extruder through the main feeding port.

[0031] Step S2: The calcium sulfite, manganese sulfate, and deionized water were mixed to prepare a wet material, which was added to the low-temperature mixing zone of the twin-screw extruder through the side feeding port. The temperature of the low-temperature mixing zone was controlled at 55°C, the screw speed was set at 100 r / min, and the region was not vacuumed, keeping the cylinder in communication with the atmosphere.

[0032] Step S3: The material entered the high-temperature reaction section of the twin-screw extruder. The temperature of this section was controlled at 110°C, the screw speed was set at 200 r / min, the average residence time of the material in this section was 60 seconds, and the shear pressure was controlled at 3.5 MPa. Under these conditions, the oxidation of calcium sulfite produced free radicals to initiate graft polymerization.

[0033] Step S4: The material entered the cooling and mixing section of the twin-screw extruder, and the temperature of this section was reduced to 80°C. Solid powdered alkyl polyglycoside and sodium lignosulfonate were added here, and after melt blending, they were extruded through a die with a pore size of 3 mm. The extruded strips were cut into particles with a length of 4 mm by a pelletizer, and then dried under hot air at 75°C until the moisture content was less than 5.0%, obtaining the finished product.

[0034] Example 2 Raw material formula: weathered coal powder 50 parts, maleic anhydride 5 parts, calcium sulfite 20 parts, manganese sulfate 0.1 part, alkyl polyglycoside 5 parts, sodium lignosulfonate 5 parts, deionized water 5 parts.

[0035] The following method was used for preparation: Step S1: The weighed weathered coal powder and maleic anhydride were placed in a high-speed mixer and dry mixed at a temperature of 20°C for 5 minutes to prepare a premixed material. The premixed material was added to the twin-screw extruder through the main feeding port.

[0036] Step S2: The calcium sulfite, manganese sulfate, and deionized water were mixed to prepare a wet material, which was added to the low-temperature mixing zone of the twin-screw extruder through the side feeding port. The temperature of the low-temperature mixing zone was controlled at 40°C, the screw speed was set at 80 r / min, and the region was not vacuumed, keeping the cylinder in communication with the atmosphere.

[0037] Step S3: The material entered the high-temperature reaction section of the twin-screw extruder. The temperature of this section was controlled at 90°C, the screw speed was set at 150 r / min, the average residence time of the material in this section was 30 seconds, and the shear pressure was controlled at 2.0 MPa. Under these conditions, the oxidation of calcium sulfite produced free radicals to initiate graft polymerization.

[0038] Step S4: The material enters the cooling mixing section of the twin-screw extruder, and the temperature of this section is reduced to 70℃. At this point, solid powdered alkyl polyglycoside and sodium lignosulfonate are added, and after melt blending, the material is extruded through a die with a 2mm aperture. The extruded strip is cut into 3mm long particles by a pelletizer, and dried under hot air at 60℃ until the moisture content is less than 5.0%, thereby obtaining the finished product.

[0039] Example 3 The raw materials used in this example are as follows: weathered coal powder 65 parts, maleic anhydride 10 parts, calcium sulfite 30 parts, manganese sulfate 0.5 parts, alkyl polyglycoside 10 parts, sodium lignosulfonate 10 parts, and deionized water 15 parts.

[0040] The preparation method is as follows: Step S1: The weighed weathered coal powder and maleic anhydride are placed in a high-speed mixer and dry mixed at a temperature of 30℃ for 15 minutes to prepare a premixed material. The premixed material is added to the twin-screw extruder through the main feed port.

[0041] Step S2: The calcium sulfite, manganese sulfate, and deionized water are mixed to form a slurry, which is injected into the low-temperature mixing zone of the twin-screw extruder through a slurry pump. The temperature of this low-temperature mixing zone is controlled at 70℃, the screw speed is set at 120r / min, and this region is not vacuumed, maintaining the barrel in communication with the atmosphere.

[0042] Step S3: The material enters the high-temperature reaction section of the twin-screw extruder. The temperature of this section is controlled at 120℃, the screw speed is set at 250r / min, the average residence time of the material in this section is 90 seconds, and the shear pressure is controlled at 5.0MPa. Under these conditions, the oxidation of calcium sulfite generates free radicals to initiate graft polymerization.

[0043] Step S4: The material enters the cooling mixing section of the twin-screw extruder, and the temperature of this section is reduced to 90℃. At this point, concentrated solution of alkyl polyglycoside and sodium lignosulfonate is added, and after melt blending, the material is extruded through a die with a 5mm aperture. The extruded strip is cut into 5mm long particles by a pelletizer, and dried under hot air at 85℃ until the moisture content is less than 5.0%, thereby obtaining the finished product.

[0044] Example 4 This example provides a saline-alkali soil conditioning granule rich in humic acid and a preparation method thereof. This example aims to verify the implementation when the process parameters are varied within the protection range under the same formula.

[0045] The formula is exactly the same as that of Example 1; The preparation method is as follows: Step S1: Dry mixing temperature 25℃, time 10 minutes.

[0046] Step S2: low temperature mixing zone temperature 60℃, screw rotation speed 110 r / min, and the region is not vacuumized.

[0047] Step S3: high temperature reaction section temperature 100℃, screw rotation speed 180 r / min, average residence time 50 seconds, shear pressure 3.0 MPa.

[0048] Step S4: cooling mixing section temperature 85℃, subsequent extrusion, granulation and drying steps are the same as in Example 1.

[0049] Comparative Example 1 Compared with Example 1, the difference is that in Step S2, instead of adding calcium sulfite and manganese sulfate, equal weight parts of 200 mesh quartz sand are added as inert filler; the rest of the raw material formulation and preparation steps are the same.

[0050] Comparative Example 2 Compared with Example 1, the difference is that in Step S4, instead of adding alkyl glycoside, equal weight parts of deionized water are added; the rest of the raw material formulation and preparation steps are the same.

[0051] Comparative Example 3 Compared with Example 1, the difference is that the preparation process is different, this comparative example does not use a twin-screw reactive extrusion process, but uses a normal temperature disc granulation process. The specific operation is as follows: the weathered coal powder, maleic anhydride, calcium sulfite and manganese sulfate are mixed uniformly in a mixer, then added to a disc granulator, and sprayed with an aqueous solution containing sodium lignosulfonate and alkyl glycoside for granulation. The material temperature is maintained at 20-30℃ during the granulation process, and does not undergo high temperature shearing and initiation of grafting reaction process. After granulation, it is dried at 75℃ to a water content of less than 5.0%. The types and total weight parts of the raw materials used are the same as in Example 1.

[0052] Test Example 1: Cation Exchange Capacity Determination This test uses the ammonium acetate exchange method to determine the cation exchange capacity of the sample, and refers to the standard NY / T 295-1995 "Determination of Cation Exchange Capacity and Exchangeable Salt Base of Neutral Soil". The specific operation steps are as follows: Step 1: Select the granular samples prepared in Examples 1 to 4, Comparative Examples 1 to 3, and the raw material weathered coal powder as the objects to be tested. Grind each group of samples and pass through a 60 mesh sieve, and place in a 105℃ oven to dry to constant weight.

[0053] Step 2: accurately weigh 2.00g of the above dried sample, and place it in a 100mL centrifuge tube. Add 30mL of 1mol / L neutral ammonium acetate solution (pH 7.0), stir evenly, and soak for 24 hours, during which time the sample is intermittently shaken to replace all the exchangeable cations in the sample with ammonium ions.

[0054] Step 3: Centrifuge the soaked suspension and discard the supernatant. Continue to wash the precipitate with 30 mL of 1 mol / L neutral ammonium acetate solution for 3 times, centrifuge and discard the supernatant until no calcium ions are detected in the supernatant (using ammonium oxalate solution for detection), to ensure that the soil colloidal adsorption sites are completely saturated with ammonium ions.

[0055] Step 4: Add 30 mL of 95% ethanol solution to the precipitate, stir and wash, and centrifuge, repeat the washing operation until no ammonium ions are detected in the supernatant (using Nessler's reagent for detection), to wash off the excess physical adsorption of ammonium acetate.

[0056] Step 5: Transfer the washed precipitate to the distillation tube of the Kjeldahl apparatus, add a small amount of light magnesium oxide, and distill. The released ammonia gas is absorbed with boric acid solution.

[0057] Step 6: Titrate the absorption solution with a standard hydrochloric acid solution with a concentration of 0.05 mol / L, record the volume of hydrochloric acid consumed, and calculate the cation exchange capacity of the sample according to the amount of hydrochloric acid consumed.

[0058] The cation exchange capacity of each group of samples is shown in the following table.

[0059] Table 1 Cation exchange capacity CEC determination results of each group of samples

[0060] According to the data shown in Table 1, the cation exchange capacity of the granular samples prepared in Examples 1 to 4 is distributed between 758.3 cmol / kg and 824.7 cmol / kg, which is significantly higher than the raw material weathered coal of 308.4 cmol / kg. This numerical change indicates that the chemical modification of the humic acid molecular structure has occurred in the high temperature and shear environment of the twin-screw extruder. The introduction of maleic anhydride increases the number of carboxyl groups on the side chains of the humic acid molecules, thereby providing more active sites for adsorbing and exchanging cations, resulting in an increase in the cation exchange capacity of the final product.

[0061] Comparing the data of Comparative Example 1 with Comparative Example 1 and Comparative Example 3, it can be seen that the initiation system and the reaction process are the key factors determining the degree of chemical modification. Comparative Example 1 does not add calcium sulfite and manganese sulfate, which results in the inability to generate free radicals required for initiation grafting through the self-oxidation reaction of calcium sulfite in the system, and maleic anhydride mainly exists in the form of physical mixing, which cannot be effectively grafted onto the humic acid skeleton. Comparative Example 3 uses a normal temperature granulation process, which lacks the activation energy provided by high temperature and strong shear, which also limits the formation of chemical bonds. The data show that only when the free radicals generated by the oxidation of calcium sulfite and the high temperature and shear conditions of the extrusion process exist at the same time, maleic anhydride can occur in situ graft polymerization on the surface and pores of the weathered coal powder.

[0062] The determination results of Comparative Example 2 are close to those of Example 1 and significantly higher than those of other comparative examples. This indicates that the absence of alkyl polyglycoside does not affect the chemical grafting reaction process between humic acid and maleic anhydride. Under the condition of having a calcium sulfite initiation system and a suitable reaction temperature, even without adding a surface active component, the carboxylation modification of humic acid molecules can still be completed, thereby maintaining a high cation exchange capacity. This result further confirms that the improvement of CEC value in the preparation method described in the present application is mainly due to the free radical grafting reaction mechanism induced by calcium sulfite, rather than the simple physical superposition of each component.

[0063] Test Example 2: Soil Infiltration Performance Test This test uses soil column leaching method to determine the influence of different particle samples on the water infiltration rate of saline-alkali soil, to evaluate the ability of the material to improve soil structure and guide vertical water migration. The specific operation steps are as follows: Step 1: The experimental soil is taken from the surface layer (0-20 cm) of soda saline-alkali soil in Da'an City, western Jilin Province, dried naturally, ground and passed through a soil sieve with a pore size of 2 mm. The pH value of the soil is 9.6 and the total salt content is 1.35%.

[0064] Step 2: Prepare a transparent organic glass column with an inner diameter of 5.0 cm and a height of 30 cm as a soil column container, and lay a layer of nylon screen with a pore size of 0.15 mm at the bottom to prevent soil particles from being lost.

[0065] Step 3: The treated dry soil is layered into the organic glass column, and each layer is compacted after filling until the soil filling height reaches 20.0 cm. The soil bulk density of each soil column is strictly controlled to be consistent, set at 1.35 g / cm³, to ensure the same initial porosity.

[0066] Step 4: The particle samples prepared in Examples 1 to 4, Comparative Examples 1 to 3 are ground and passed through a 20 mesh sieve. Weigh the sample powder equivalent to 0.3% of the mass of the 0-2 cm soil layer of the soil column, and mix it evenly with the surface soil. The raw weathered coal control group only undergoes the same turning treatment but does not add any improvement material.

[0067] Step 5: Slowly add deionized water on top of the soil column, and use a Mariotte bottle device to control the water depth on the surface of the soil column to be constant at 3.0 cm.

[0068] Step 6: Start timing from the time when water is added and a stable water head is formed, and observe the vertical movement of the wetting front in the soil column. Record the time required for the wetting front to reach the bottom of the soil column, i.e. the infiltration depth reaches 20.0 cm.

[0069] The soil infiltration time determination results of each group of samples are shown in the following table.

[0070] Table 2 Results of soil infiltration performance test of each group of samples

[0071] According to the data shown in Table 2, the infiltration time of the treatment groups of Examples 1 to 4 is distributed between 41.5 minutes and 49.2 minutes, which is about 3 times faster than the raw weathered coal control group of 145.6 minutes. This significant difference is directly related to the introduction of the alkyl glycoside component in the formula. As a non-ionic surfactant, alkyl glycoside significantly reduces the surface tension of the liquid-solid interface when it dissolves into the soil solution with the particles, reduces the contact angle of water on the hydrophobic saline soil particle surface, thereby overcoming the infiltration resistance of the soda saline soil caused by colloidal dispersion and pore blockage, and accelerating the vertical migration of water to the deep soil.

[0072] Comparing the data of Comparative Example 1 and Comparative Example 2, there is a great difference between the two. Comparative Example 2 did not add alkyl glycoside during preparation, although it underwent a high-temperature grafting reaction, the hydrophilicity of humic acid molecules was improved, but the lack of surfactant adjustment of soil capillary force resulted in its limited ability to improve the permeability in the dense saline soil column. This confirms that in the treatment of severely hardened saline soil, relying solely on the chemical modification of humic acid is not enough to solve the problem of water infiltration difficulty, and a composite system containing a surface active component must be built to achieve the effective introduction of the modifier.

[0073] Comparing the data of Comparative Example 1 and Comparative Example 1 and Comparative Example 3, it can be observed that in the case of containing the same amount of alkyl glycoside, the infiltration speed of Example 1 treated by reactive extrusion grafting is still superior to that of Comparative Example which did not undergo chemical grafting. This is because in Example 1, the grafting of maleic anhydride onto the humic acid molecule introduces more hydrophilic carboxyl groups, improving the solubility and dispersion stability of humic acid in water, allowing it to migrate quickly with the water flow without easily flocculating and blocking soil pores. In contrast, the humic acid in Comparative Examples 1 and 3 mainly exists in a physical mixing state, with relatively poor solubility, which may be retained in the surface layer or pore throat during the infiltration process, causing a certain resistance to water flow. The results show that the chemical structure change brought about by the reactive extrusion process and the physical and chemical action of alkyl glycoside have a synergistic effect in improving the hydrodynamic properties of the soil.

[0074] Test Example 3: pH Buffering Capacity and Continuous Alkalinity Reduction Effect Test This test aims to evaluate the acid-base adjustment ability and duration of each group of particle samples in an alkaline environment. The experiment simulates a high-pH soil solution environment to measure the change in solution pH over time after adding the samples. The specific operation steps are as follows: Step 1: Prepare a dilute sodium hydroxide solution with pH value of 10.00 (±0.05) as the simulated alkaline soil solution.

[0075] Step 2: Weigh 1.00 g of each of the granular samples prepared in Examples 1-4, Comparative Examples 1-3, and the raw weathered coal.

[0076] Step 3: Place each group of samples into a conical flask containing 100 mL of the simulated alkaline solution, and place it in a constant temperature shaker at 25°C with a rotation speed of 150 r / min.

[0077] Step 4: At 1 hour, 24 hours, and 72 hours, respectively, measure the pH value of the supernatant of each group using a calibrated precision pH meter. Allow 5 minutes of standing time before each measurement, and continue the shaking culture after measurement. Record the pH data at each time point to reflect the progress and stability of the neutralization reaction.

[0078] The pH value measurement results of each group of samples at different time points are shown in the following table.

[0079] Table 3: pH Buffering Capacity Test Results of Each Group of Samples

[0080] As shown in Table 3, the pH values of the treated groups in Examples 1-4 all decreased to below 8.00 after 72 hours, showing significant acid buffering and alkaline reduction capacity compared to the raw weathered coal. This decrease in pH value is due to the graft copolymerization reaction that occurs during preparation, which bonds maleic anhydride to the humic acid skeleton and introduces a large number of carboxyl groups (-COOH). In an alkaline solution, these graft-introduced carboxyl groups dissociate to release hydrogen ions, which neutralize the hydroxide ions in the solution, effectively reducing the pH of the system. The raw weathered coal, which has not been chemically modified, carries a limited number of active acidic groups, so its buffering effect on high-alkaline solutions is weak.

[0081] Comparing the differences between Comparative Example 1 and Comparative Example 1, the sample lacking the calcium sulfite / manganese sulfate initiation system has significantly weakened alkaline reduction effect. In Comparative Example 1, the absence of free radicals generated by the initiator prevents maleic anhydride from being effectively grafted, resulting in low effective carboxyl content. In addition, the calcium sulfite added in Example 1 gradually oxidizes to form sulfate or acidic sulfite intermediates during the reactive extrusion process and subsequent hydrolysis and oxidation process, providing an additional sustained acid production mechanism. The pH value in the example data shows a continuous downward trend over time, verifying the synergistic release effect of the grafting carboxyl group and the oxidation of calcium sulfite to produce acid.

[0082] The data of comparative example 1 and comparative example 3 show that the chemical bonding structure constructed by the reactive extrusion process has more excellent stability and acid release efficiency than the simple physical mixing. In the physical mixture of comparative example 3, the maleic anhydride may be rapidly hydrolyzed or lost at the initial contact with the aqueous phase, and fails to form a stable macromolecular acidic skeleton, resulting in a less obvious pH decline than example 1. This shows that the fixation of the acid-producing component in the granular matrix through high-temperature shearing and radical reaction can ensure the long-term acid buffering capacity of the modifier in the soil solution, rather than short-term physical dissolution. The pH change trend of comparative example 2 is basically the same as that of example 1, indicating that the absence of the penetration aid does not affect the chemical acid-base neutralization performance of the material, and its role mainly reflects the physical penetration level, as shown in test example 2.

[0083] The specific embodiments are merely illustrative of the present application, and are not a limitation on the present application. Those skilled in the art can make modifications to the embodiments without creative contribution after reading the specification, and as long as the modifications are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A saline soil conditioner particle enriched in humic acid, characterised in that, It comprises the following weight parts: weathered coal powder 50-65 parts, maleic anhydride 5-10 parts, calcium sulfite 20-30 parts, manganese sulfate 0.1-0.5 parts, alkyl glycoside 5-10 parts, sodium lignosulfonate 5-10 parts, and water 5-15 parts; In the grafting reaction, humic acid in the weathered coal powder and maleic anhydride are grafted together, and the grafting reaction is initiated by free radicals generated by oxidation of calcium sulfite.

2. The humic acid-enriched saline soil conditioning granule of claim 1, characterized by: The humic acid content of the weathered coal powder is greater than or equal to 50.0%, and the particle size passes through an 80-120 mesh sieve; the calcium sulfite is an industrial by-product with a purity greater than or equal to 90.0%.

3. The humic acid-enriched saline soil conditioning granule of claim 1, characterized by: The alkyl glycoside is a C8-C10 or C12-C14 non-ionic surfactant with a solid content greater than or equal to 50.0%; and the total sulfonate content of the sodium lignosulfonate is greater than or equal to 50.0%.

4. The humic acid-enriched saline soil conditioning granule of claim 1, characterized by: The particle size of the granules is 2-5 mm, and the final moisture content is less than 5.0%.

5. A method of using humic acid-enriched saline soil conditioning granules, characterized in that, A method for preparing the humic acid-rich saline-alkali soil conditioning granules of any one of claims 1-4 comprises the following steps: S1. Dry mixing the weighed weathered coal powder and maleic anhydride in a high-speed mixer to obtain a premixed material, and feeding the premixed material into a twin-screw extruder through a main feeding port; S2. Mixing calcium sulfite, manganese sulfate, and water to obtain a wet material or slurry, and feeding the wet material or slurry into a low-temperature mixing zone of the twin-screw extruder through a side feeding port; S3. The material enters a high-temperature reaction section of the twin-screw extruder, and under the shearing action, the calcium sulfite undergoes self-oxidation to generate free radicals, which initiate the graft polymerization of maleic anhydride on the weathered coal powder; S4. Adding alkyl glycoside and sodium lignosulfonate to a cooling and mixing section of the twin-screw extruder, using sodium lignosulfonate to terminate the free radical reaction, and then extruding, cutting, and drying after melt blending.

6. A method of using the saline soil conditioner granules enriched with humic acids according to claim 5, characterized by: In step S1, the dry mixing temperature is 20-30°C, and the mixing time is 5-15 min.

7. A method of using the saline soil conditioner granules enriched with humic acids according to claim 5, characterized by: In step S2, the temperature of the low-temperature mixing zone is controlled at 40-70°C, the screw rotation speed is 80-120 r / min, and the zone is not vacuumed to maintain oxygen in the cylinder for oxidation reaction.

8. A method of using the saline soil conditioners of humic acid enriched particles according to claim 5, characterized in that: In step S3, the temperature of the high-temperature reaction section is controlled at 90-120°C, the material residence time is 30-90 s, the screw rotation speed is 150-250 r / min, and the shearing pressure is controlled at 2-5 MPa.

9. The method of using humic acid-enriched saline soil conditioning granules according to claim 5, characterized in that: In step S4, the temperature of the cooling and mixing section is reduced to 70-90°C, and the alkyl glycoside and sodium lignosulfonate are added in the form of solid powder or concentrated solution.

10. A method of using the saline soil conditioners of humic acid enriched particles according to claim 5, characterized in that: In step S4, the drying is performed under hot air at 60-85°C until the moisture content of the granules is less than 5.0%.

Images