Preparation method of manganese slag-coconut shell charcoal-desulfurized gypsum composite soil conditioner, soil conditioner and application

Abstract

The invention belongs to the technical field of soil improvement, and discloses a preparation method of a manganese slag-coconut shell charcoal-desulfurized gypsum composite soil improvement agent, the soil improvement agent and application. The preparation method of the soil conditioner comprises the working procedures of manganese residue pretreatment, coconut shell pretreatment, precursor preparation, precursor calcination and conditioner compounding, the pretreated coconut shell and the pretreated manganese residue are mixed and then subjected to ball milling, and a manganese residue-coconut shell precursor is obtained; calcining the prepared manganese residue-coconut shell precursor for 1-4 hours at the temperature of 450-650 DEG C in a protective gas atmosphere to obtain manganese residue-coconut shell biochar; and doping desulfurized gypsum powder into the prepared manganese slag-coconut shell charcoal, and uniformly dispersing to obtain the manganese slag-coconut shell charcoal-desulfurized gypsum composite soil conditioner. The method disclosed by the invention has the advantages of low energy consumption, low cost and capability of treating waste with waste, and the prepared soil conditioner has the advantages of improving soil nutrient balance, reducing nutrient loss and stabilizing pH, and is suitable for modifying the acid soil of the rubber plantation in the tropical region.

Description

Technical Field

[0001] The present invention belongs to the technical field of soil improvement, and specifically relates to a preparation method, a soil conditioner and an application of a manganese slag-coconut shell charcoal-desulfurized gypsum composite soil conditioner. Background Art

[0002] Soil acidification in rubber plantations is an important factor restricting the growth of rubber trees and the latex yield. The high-temperature and rainy climate conditions in tropical and subtropical regions cause a large amount of leaching of soil base ions (such as Ca 2+ , Mg 2+ ), while H + and Al 3+ are enriched on the surface of soil colloids, forming a strong acidic environment (pH < 5.0). Acidic soil not only inhibits the absorption of nutrients by the roots of rubber trees, but also activates the activity of heavy metals (such as Cd, Cr), causing phytotoxicity and threatening the quality of latex. In addition, the long-term single cropping pattern with a large amount of chemical fertilizers (especially ammonium nitrogen fertilizers) further exacerbates the process of soil acidification, leading to soil compaction and imbalance of the microbial community.

[0003] Although traditional acidic soil conditioners (such as quicklime and dolomite powder) can rapidly increase the soil pH value, they have significant defects: the risk of re-acidification. Quicklime (CaO) reacts with H + in the soil to form Ca 2+ , neutralizing acidity in the short term, but excessive use will damage the soil buffer system, resulting in the problem of re-acidification; and it has certain ecological side effects. Long-term application is likely to cause soil compaction and imbalance of calcium and magnesium ratios, and the energy consumption and carbon emissions are high during the limestone mining and calcination processes; the function is single, only adjusting the pH value, lacking the comprehensive effects of soil structure improvement and nutrient supplementation.

[0004] In recent years, the resource utilization of industrial solid wastes has provided new ideas for soil remediation. In related technologies, CN115926796A discloses an acidic soil conditioner based on electrolytic manganese slag and / or phosphogypsum. The conditioner is prepared by adding an alkali activator (such as sodium carbonate) and high-temperature calcination (800 °C), which can increase the soil pH value and supplement nutrients such as calcium and magnesium. However, there are still the following limitations: 1. High process energy consumption: The calcination temperature reaches 800 °C, which requires additional energy consumption and does not meet the requirements of low-carbon environmental protection; 2. Functional singularity: It mainly relies on calcium-based substances to neutralize acidity, lacking the synergistic effects of soil structure improvement, heavy metal adsorption and long-term nutrient supply, and unable to play functions such as water and fertilizer retention and promotion of microbial activity.

[0005] Therefore, in view of the above limitations, it is necessary to provide a low-energy-consuming, multi-functional synergistic preparation and suitable for acidic soil in tropical rubber plantations. Summary of the Invention

[0006] To achieve the above object, the present invention provides a preparation method, a soil conditioner, and an application of a manganese slag-coconut shell charcoal-desulfurized gypsum composite soil conditioner.

[0007] In the first aspect, the present invention provides a manganese slag-coconut shell charcoal-desulfurized gypsum composite soil conditioner, and the specific technical solution is as follows: A preparation method of a manganese slag-coconut shell charcoal-desulfurized gypsum composite soil conditioner includes the following steps: Manganese slag pretreatment: washing the manganese slag with water and drying it to obtain pretreated manganese slag; Coconut shell pretreatment: washing the coconut shell, drying it, and crushing it to obtain pretreated coconut shell; Precursor preparation: mixing the pretreated coconut shell and pretreated manganese slag in a mass ratio of 1:(5 - 9), ball-milling at a speed of 300 - 600 rpm for 2 - 5 h, with a ball-to-material ratio of 10:1, to obtain a manganese slag-coconut shell precursor; Precursor calcination: calcining the obtained manganese slag-coconut shell precursor in a protective gas atmosphere at 450 - 650 °C for 1 - 4 h to obtain manganese slag-coconut shell biochar; Conditioner compounding: adding desulfurized gypsum powder to the obtained manganese slag-coconut shell biochar and dispersing it evenly to obtain a manganese slag-coconut shell charcoal-desulfurized gypsum composite soil conditioner.

[0008] By adopting the foregoing technical solutions, the present invention has the following beneficial effects: 1. The present invention adopts a low-temperature calcination process, and the calcination temperature is reduced to 450 - 650 °C. Combined with nitrogen protection, it reduces energy consumption and avoids excessive oxidation of biochar; 2. The manganese slag provides calcium and magnesium elements, the coconut shell charcoal enhances the pore structure and adsorption performance, and the desulfurized gypsum supplements sulfur and calcium. The compounded soil conditioner of the present invention can synergistically neutralize soil acidity and supplement base ions to improve soil nutrient balance, significantly enhance soil aggregate structure to reduce nutrient loss, and reduce the leaching concentration of heavy metals such as Cd and Cr; 3. The present invention uses industrial / agricultural solid wastes such as electrolytic manganese slag, coconut shell, and desulfurized gypsum to achieve "treating waste with waste", reduce raw material costs, and conform to the concept of circular economy.

[0009] Further, in the conditioner compounding process, the mass ratio of the manganese slag-coconut shell biochar to the desulfurized gypsum powder is 1:(3 - 5).

[0010] Further, the specific steps of the manganese slag pretreatment are as follows: adding water to the manganese slag according to a water-slag ratio of 1:(1 - 3), stirring for 30 - 90 min, and separating the manganese slag; repeating the water washing operation 2 - 5 times, and then drying the washed manganese slag at 80 - 120 °C for 8 - 12 h to obtain pretreated manganese slag.

[0011] Furthermore, the manganese slag is the manganese slag obtained by pressure filtration in an electrolytic manganese plant. Before water washing, the manganese slag is soaked in 0.5 - 1 mol / L dilute hydrochloric acid for 30 - 60 min, and after separating the manganese slag, the water washing operation is carried out. After being soaked in dilute hydrochloric acid and washed through multiple stages, impurities (such as residual acid solution and soluble salts) are effectively removed, improving the purity of the raw materials.

[0012] Furthermore, the particle size of the pretreated coconut shell is 2 - 5 mm.

[0013] Furthermore, in the coconut shell pretreatment step, the coconut shell is first soaked in 0.5 - 1 mol / L sodium chloride aqueous solution for 20 - 30 min. After filtration, the coconut shell is cooled to -40°C to -30°C and frozen for 30 - 45 min, and then warmed to room temperature for thawing; after repeating the freezing - thawing operation 2 - 5 times, the cleaning, drying, and crushing operations are carried out. Through the freezing - thawing cycle and crushing pretreatment of the coconut shell, the carbonization uniformity is enhanced.

[0014] Furthermore, in the coconut shell pretreatment step, after the coconut shell is washed, it is pre - dried at 80°C for 2 h, and then heated to 105°C and dried for 30 - 90 min.

[0015] Furthermore, in the precursor calcination process, it is calcined in a nitrogen atmosphere, and the nitrogen flow rate is controlled at 0.5 - 1 L / min to prevent excessive oxidation of the biochar.

[0016] Furthermore, in the precursor calcination process, the heating rate is set at 5°C / min to avoid insufficient pyrolysis of the coconut shell caused by rapid heating.

[0017] Furthermore, in the precursor calcination process, a stepped heating method is adopted, that is, first heating at a rate of 5°C / min to 450 - 500°C and holding for 0.5 - 2 h, then heating at a rate of 5°C / min to 500 - 600°C and holding for 0.3 - 1 h, and finally heating at a rate of 5°C / min to 600 - 650°C and holding for 0.2 - 1 h.

[0018] Furthermore, in the modifier compounding process, the desulfurized gypsum powder is first passed through a 200 - mesh sieve, then incorporated into the manganese slag - coconut shell biochar precursor, and then mixed at a rotation speed of 15 - 20 rpm for 30 min to obtain a uniformly dispersed manganese slag - coconut shell charcoal - desulfurized gypsum composite soil modifier by dispersion.

[0019] Furthermore, in the modifier compounding process, an acrylate adsorbent is also added, and the mass ratio of the manganese slag - coconut shell biochar to the acrylate adsorbent is 1:(0.1 - 0.5); the acrylate adsorbent is prepared by the following method: Mix ethylenediamine and methyl acrylate at a molar ratio of 1:4 - 8, and under nitrogen protection, stir and react at 25 - 40 °C for 12 - 48 h to form a starting product; mix the starting product with excessive ethylenediamine at a molar ratio of 1:(10 - 20), react at 35 - 50 °C for 24 - 72 h, and dialyze and purify to obtain an intermediate product with a molecular weight cut-off ≤ 1 kDa; react the intermediate product with a modifier having at least one active group among mercapto, amino, and carboxyl groups at a molar ratio of 1:(5 - 15), stir at 50 - 70 °C for 6 - 24 h to modify the surface functional groups; add a cross-linking agent accounting for 1% - 5% of the mass of the intermediate product, and cross-link at pH 8 - 10 for 2 - 6 h; separate the final product, freeze-dry, pulverize, and pass through a 200-mesh sieve to obtain the acrylate adsorbent.

[0020] Furthermore, the modifier is selected from one or more of mercaptoacetic acid, carboxymethyl chitosan, and aminothiol; the cross-linking agent is glutaraldehyde or epichlorohydrin.

[0021] In a second aspect, the present invention provides a soil conditioner prepared by the aforementioned method.

[0022] In a third aspect, the present invention provides an application of the soil conditioner in improving acidic soil in a rubber plantation. The addition amount of the soil conditioner is 3% - 5% of the soil weight, and the dosage can be adjusted according to the actual situation. The specific steps for soil improvement are as follows: add the prepared manganese slag - coconut shell charcoal - desulfurized gypsum composite soil conditioner to the acidic soil in the rubber plantation, fully mix evenly, then add an appropriate amount of deionized water to make the soil humidity reach 80% of the soil field water holding capacity, cover with a plastic film and reserve ventilation holes to allow gas exchange and reduce water evaporation, and add water every 5 - 7 days to keep the soil humidity basically stable.

[0023] The porous structure formed by ball milling coconut shell charcoal (particle size 2 - 5 mm) and manganese slag in the conditioner significantly enhances the particle erosion resistance. In a hot area environment with an annual rainfall of 2000 - 3000 mm, the loss rate of the conditioner is ≤ 5% (the loss rate of traditional lime-based conditioners is ≥ 15%). Covering the plastic film (thickness 0.02 - 0.05 mm, ventilation hole density 5 - 8 holes / m²) combined with regular water replenishment (maintaining 80% of the field water holding capacity every 5 - 7 days) effectively balances the evaporation at high temperatures and the waterlogging problem in the rainy season, and the soil humidity fluctuation range is controlled within ± 5%. The porous structure of coconut shell charcoal provides a habitat space for acid- and heat-resistant microorganisms (such as Bacillus and Actinomycetes). Combining with the sulfur element released by desulfurized gypsum, it can enhance the soil dehydrogenase activity and accelerate the organic matter degradation rate. At the same time, under the high temperature condition of 35 - 40 °C, the slowly released Ca² + 、Mg² + in the conditioner can stabilize the activities of soil enzymes (such as urease and phosphatase). Specific Embodiments

[0024] To enable those skilled in the art to better understand the technical solutions in the present invention, the following will further elaborate on the present application in conjunction with specific embodiments.

[0025] [Preparation of Soil Conditioner] The following embodiments all use the manganese slag obtained from the pressure filtration of an electrolytic manganese plant as the raw material, and its main components are as follows: Table 1 - Main Chemical Components of Electrolytic Manganese Slag Example 1

[0026] A preparation method of a manganese slag - coconut shell charcoal - desulfurized gypsum composite soil conditioner is as follows: Pretreatment of manganese slag: Add water to the manganese slag obtained from the pressure filtration of an electrolytic manganese plant according to a water - slag ratio of 1:1, stir for 90 min, and separate the manganese slag; after repeating the water - washing operation 5 times, dry the washed manganese slag at 80 °C for 12 h to obtain pretreated manganese slag; Pretreatment of coconut shell: After washing the coconut shell, pre - dry it at 80 °C for 2 h, then raise the temperature to 105 °C and dry for 30 min, and crush it to a particle size of 5 mm; Preparation of precursor: Mix pretreated coconut shell and pretreated manganese slag in a mass ratio of 1:9, and ball - mill at a speed of 600 rpm for 2 h with a ball - to - material ratio of 10:1 to obtain a manganese slag - coconut shell precursor; Calcination of the precursor: Calcinate the obtained manganese slag - coconut shell precursor in a nitrogen atmosphere, raise the temperature to 450 °C at a rate of 5 °C / min and calcine for 4 h, and control the nitrogen flow rate to 0.5 L / min to obtain manganese slag - coconut shell biochar; Compound of the conditioner: Pass the desulfurized gypsum powder through a 200 - mesh sieve and add it to the manganese slag - coconut shell biochar precursor. The mass ratio of manganese slag - coconut shell biochar to desulfurized gypsum powder is 1:3, and mix at a speed of 15 rpm for 30 min to disperse evenly to obtain a manganese slag - coconut shell charcoal - desulfurized gypsum composite soil conditioner. Example 2

[0027] A preparation method of a manganese slag - coconut shell charcoal - desulfurized gypsum composite soil conditioner is as follows: Pretreatment of manganese slag: Add water to the manganese slag obtained from the pressure filtration of an electrolytic manganese plant according to a water - slag ratio of 1:2, stir for 60 min, and separate the manganese slag; after repeating the water - washing operation 3 times, dry the washed manganese slag at 100 °C for 10 h to obtain pretreated manganese slag; Pretreatment of coconut shell: After washing the coconut shell, pre - dry it at 80 °C for 2 h, then raise the temperature to 105 °C and dry for 60 min, and crush it to a particle size of 3.5 mm; Preparation of precursor: Mix pretreated coconut shell and pretreated manganese slag in a mass ratio of 1:8, and ball - mill at a speed of 450 rpm for 3.5 h with a ball - to - material ratio of 10:1 to obtain a manganese slag - coconut shell precursor; Precursor calcination: The prepared manganese slag-coconut shell precursor was calcined in a nitrogen atmosphere at a heating rate of 5 °C / min to 650 °C for 1 h, and the nitrogen flow rate was controlled at 1 L / min to obtain manganese slag-coconut shell biochar; Modifier compounding: The desulfurized gypsum powder was passed through a 200-mesh sieve and added to the manganese slag-coconut shell biochar precursor. The mass ratio of manganese slag-coconut shell biochar to desulfurized gypsum powder was 1:4, and they were mixed at a rotation speed of 18 rpm for 30 min and dispersed evenly to obtain a manganese slag-coconut shell charcoal-desulfurized gypsum composite soil modifier. Example 3

[0028] A preparation method of a manganese slag-coconut shell charcoal-desulfurized gypsum composite soil modifier is as follows: Manganese slag pretreatment: Water was added to the manganese slag obtained by pressure filtration from an electrolytic manganese plant according to a water-slag ratio of 1:3, stirred for 30 min, and the manganese slag was separated; after repeating the water washing operation 2 times, the washed manganese slag was dried at 120 °C for 8 h to obtain pretreated manganese slag; Coconut shell pretreatment: After the coconut shell was washed, it was pre-dried at 80 °C for 2 h, then heated to 105 °C and dried for 90 min, and then crushed to a particle size of 2 mm; Precursor preparation: The pretreated coconut shell and pretreated manganese slag with a mass ratio of 1:5 were mixed and ball-milled at a rotation speed of 300 rpm for 5 h, and the ball-to-material ratio was 10:1 to obtain a manganese slag-coconut shell precursor; Precursor calcination: The prepared manganese slag-coconut shell precursor was calcined in a nitrogen atmosphere at a heating rate of 5 °C / min to 550 °C for 2.5 h, and the nitrogen flow rate was controlled at 0.8 L / min to obtain manganese slag-coconut shell biochar; Modifier compounding: The desulfurized gypsum powder was passed through a 200-mesh sieve and added to the manganese slag-coconut shell biochar precursor. The mass ratio of manganese slag-coconut shell biochar to desulfurized gypsum powder was 1:5, and they were mixed at a rotation speed of 20 rpm for 30 min and dispersed evenly to obtain a manganese slag-coconut shell charcoal-desulfurized gypsum composite soil modifier.

[0029] Control Example 1: A preparation method of a manganese slag-coconut shell charcoal-desulfurized gypsum composite soil modifier is as follows: Manganese slag pretreatment: Water was added to the manganese slag obtained by pressure filtration from an electrolytic manganese plant according to a water-slag ratio of 1:3, stirred for 30 min, and the manganese slag was separated; after repeating the water washing operation 2 times, the washed manganese slag was dried at 120 °C for 8 h to obtain pretreated manganese slag; Coconut shell pretreatment: After the coconut shell was washed, it was pre-dried at 80 °C for 2 h, then heated to 105 °C and dried for 90 min, and then crushed to a particle size of 2 mm; Preparation of the modifier: Mix pretreated coconut shell, pretreated manganese slag, and desulfurized gypsum passing through a 200-mesh sieve at a mass ratio of 1:5:30, and then ball-mill at a rotation speed of 300 rpm for 5 h with a ball-to-material ratio of 10:1 to obtain a precursor. Calcinate the obtained precursor in a nitrogen atmosphere by heating to 550 °C at a rate of 5 °C / min for 2.5 h, and control the nitrogen flow rate at 0.8 L / min to obtain a manganese slag-coconut shell carbon-desulfurized gypsum composite soil modifier.

[0030] Control Example 2: A preparation method of a manganese slag-coconut shell carbon-desulfurized gypsum composite soil modifier comprises the following steps: Pretreatment of manganese slag: Add water to the manganese slag obtained by pressure filtration in an electrolytic manganese plant according to a water-to-slag ratio of 1:3, stir for 30 min, and separate the manganese slag. After repeating the water washing operation 2 times, dry the washed manganese slag at 120 °C for 8 h to obtain pretreated manganese slag. Pretreatment of coconut shell: Wash the coconut shell, pre-dry it at 80 °C for 2 h, then heat it to 105 °C and dry it for 90 min, and crush it to a particle size of 2 mm. Preparation of the modifier: Mix pretreated coconut shell, pretreated manganese slag, and desulfurized gypsum passing through a 200-mesh sieve at a mass ratio of 1:5:30, and then calcinate in a nitrogen atmosphere by heating to 550 °C at a rate of 5 °C / min for 2.5 h, and control the nitrogen flow rate at 0.8 L / min. Then, ball-mill at a rotation speed of 300 rpm for 5 h with a ball-to-material ratio of 10:1 to obtain a manganese slag-coconut shell carbon-desulfurized gypsum composite soil modifier.

[0031] [Rubber plantation acidic soil improvement test] Add 3% of the soil modifier (the modifier of the example / control example, and the blank group does not add) based on the weight of the soil to the acidic soil in the rubber plantation, mix well, add an appropriate amount of deionized water to make the soil humidity reach 80% of the soil field water holding capacity; cover with plastic film and reserve ventilation holes to allow gas exchange and reduce water evaporation; incubate at a constant temperature of 20 °C for 64 d, add water every 5 - 7 days to keep the soil humidity basically stable. After the start of the test: At the 30th and 64th d, take a certain amount of soil samples, measure the pH value after leaching according to a soil-to-water ratio of 2:1 with a pH meter, repeat each treatment 3 times, and take the average value as the test result; conduct soil nutrient analysis at the 30th and 64th d: The organic matter is determined by the potassium dichromate oxidation method, and the base ions are determined by atomic absorption spectrometry; Dehydrogenase activity: Using the production amount of TPF (triphenylformazan) as an index, it is determined by spectrophotometry.

[0032] Table 2 - Test result table (I)

[0033] It can be seen from the data in the above table that: The manganese slag-coconut shell charcoal-desulfurized gypsum composite soil conditioner of the present invention has a good improvement effect on the acidic plantation soil of rubber plantations with pH≤5, can significantly increase the soil pH value, has good stability, effectively reduces the risk of re-acidification, can significantly increase the soil organic matter content and base ion concentration, improve the soil nutrient balance, provide richer nutrients for plant growth, can significantly increase the soil dehydrogenase activity, indicating that it promotes the soil microbial activity and organic matter decomposition, and helps to improve the soil biological activity.

[0034] Examples 4-6: Examples 4-6 are all based on Example 2, and the only difference is that the manganese slag is treated by acid leaching: before water washing, the manganese slag is first soaked in 0.5-1mol / L dilute hydrochloric acid for 30-60min, the soaking bath ratio is 1:20 (20L dilute hydrochloric acid solution is used for every kilogram of manganese slag), and after separating the manganese slag, the water washing operation is carried out. After the manganese slag is soaked in dilute hydrochloric acid and washed by multiple stages, impurities are effectively removed and the raw material purity is improved.

[0035] In Example 4, the manganese slag is soaked in 0.5mol / L dilute hydrochloric acid for 60min; in Example 5, the manganese slag is soaked in 0.8mol / L dilute hydrochloric acid for 45min; in Example 6, the manganese slag is soaked in 1mol / L dilute hydrochloric acid for 30min.

[0036] Table 3 - Test result table (two)

[0037] It can be seen from the data in the above table that: By soaking the manganese slag in dilute hydrochloric acid, impurities such as residual acid solution and soluble salts can be effectively removed. In Examples 4-6, the performance indexes of the conditioner prepared from the manganese slag pretreated by acid washing are better than those of Example 2 without acid washing, indicating that the removal of impurities helps to improve the performance of the conditioner.

[0038] Examples 7-10: Examples 7-9 are all based on Example 6, and the difference lies in the specific operations of the coconut shell pretreatment process and the precursor calcination process.

[0039] In Example 7, in the coconut shell pretreatment process, the coconut shell is first soaked in 0.5mol / L sodium chloride aqueous solution for 30min, after filtration, the coconut shell is cooled to -40°C and frozen for 30min, and then heated to room temperature for thawing; after repeating the freezing-thawing operation 2 times, the washing, drying and crushing operations are carried out. In the precursor calcination process, the temperature is first raised to 450°C at a rate of 5°C / min and held for 2h, then the temperature is raised to 600°C at a rate of 5°C / min and held for 0.3h, and finally the temperature is raised to 620°C at a rate of 5°C / min and held for 0.6h.

[0040] Example 8. In the coconut shell pretreatment process, first soak the coconut shell in 0.8 mol / L sodium chloride aqueous solution for 15 min, filter, cool the coconut shell to -35°C and freeze for 40 min, then warm it to room temperature for thawing; repeat the freeze-thaw operation 3 times, and then perform cleaning, drying, and crushing operations. In the precursor calcination process, first heat it to 480°C at a rate of 5°C / min and hold for 1.2 h, then heat it to 550°C at a rate of 5°C / min and hold for 0.8 h, and finally heat it to 650°C at a rate of 5°C / min and hold for 0.2 h.

[0041] Example 9. In the coconut shell pretreatment process, first soak the coconut shell in 1 mol / L sodium chloride aqueous solution for 20 min, filter, cool the coconut shell to -30°C and freeze for 45 min, then warm it to room temperature for thawing; repeat the freeze-thaw operation 5 times, and then perform cleaning, drying, and crushing operations. In the precursor calcination process, first heat it to 500°C at a rate of 5°C / min and hold for 0.5 h, then heat it to 500°C at a rate of 5°C / min and hold for 1 h, and finally heat it to 600°C at a rate of 5°C / min and hold for 1 h.

[0042] Example 10. In the coconut shell pretreatment process, first soak the coconut shell in 0.8 mol / L sodium chloride aqueous solution for 15 min, filter, cool the coconut shell to -35°C and freeze for 40 min, then warm it to room temperature for thawing; repeat the freeze-thaw operation 3 times, and then perform cleaning, drying, and crushing operations. In the precursor calcination process, heat it to 550°C at a rate of 5°C / min and calcine for 2.2 h.

[0043] Table 4 - Test Results Table (III)

[0044] It can be seen from the data in the above table that: After the coconut shell is treated by freeze-thaw cycle, its cell structure is damaged, making the coconut shell have a more developed pore structure and a larger specific surface area, and the subsequent carbonization uniformity is higher. The possible principle is that the sodium ions in the sodium chloride solution have a smaller diameter and are more likely to penetrate into the gaps of the coconut shell lignin fibers. At the same time, the sodium ions have high hydrophilicity and can hydrate and swell; on this basis, during the freeze-thaw cycle process, the solution first solidifies to form ice crystals and expands in volume, and then melts, making it easier to form fine microcracks / gaps between the coconut shell lignin structures, providing a good foundation for subsequent low-temperature calcination and uniform carbonization. At the same time, it can be seen from the data of Examples 7 - 10 in Table 4 that Examples 7 - 9 using freeze-thaw pretreatment and stepped calcination process are superior to Example 10 using only freeze-thaw pretreatment without stepped heating in terms of soil improvement effect, indicating that the modifier prepared by the combination of freeze-thaw cycle treatment and stepped heating calcination process has a better effect.

[0045] Examples 11 - 13: Examples 11 - 13 are all based on Example 8, with the difference being that in the modifier compounding process, while adding desulfurized gypsum powder, acrylate adsorbents are also added.

[0046] In Example 11, the mass ratio of manganese slag - coconut shell biochar to acrylate adsorbent is 1:0.1; the acrylate adsorbent is prepared by the following method: Ethylenediamine and methyl acrylate are mixed at a molar ratio of 1:6, and under nitrogen protection, stirred at 40°C for 24 h to generate a starting product; the starting product is mixed with excessive ethylenediamine at a molar ratio of 1:18 and reacted at 50°C for 48 h, and the intermediate product with a molecular weight cut-off ≤ 1 kDa is obtained by dialysis purification; the intermediate product is reacted with a modifier at a molar ratio of 1:15, stirred at 70°C for 12 h to modify the surface functional groups; 3.5% of glutaraldehyde based on the mass of the intermediate product is added, and crosslinked at pH 8 - 10 for 4 h; the final product is separated, freeze-dried, crushed, and sieved through a 200-mesh sieve to obtain the acrylate adsorbent. The modifier is prepared by mixing mercaptoacetic acid, carboxymethyl chitosan, and aminothiol in a weight ratio of 1:0.8:0.5.

[0047] In Example 12, the mass ratio of manganese slag - coconut shell biochar to acrylate adsorbent is 1:0.3; the acrylate adsorbent is prepared by the following method: Ethylenediamine and methyl acrylate are mixed at a molar ratio of 1:6, and under nitrogen protection, stirred at 40°C for 24 h to generate a starting product; the starting product is mixed with excessive ethylenediamine at a molar ratio of 1:18 and reacted at 50°C for 48 h, and the intermediate product with a molecular weight cut-off ≤ 1 kDa is obtained by dialysis purification; the intermediate product is reacted with a modifier at a molar ratio of 1:10, stirred at 70°C for 12 h to modify the surface functional groups; 3.5% of glutaraldehyde based on the mass of the intermediate product is added, and crosslinked at pH 8 - 10 for 4 h; the final product is separated, freeze-dried, crushed, and sieved through a 200-mesh sieve to obtain the acrylate adsorbent. The modifier is prepared by mixing mercaptoacetic acid, carboxymethyl chitosan, and aminothiol in a weight ratio of 1:0.8:0.5.

[0048] In Example 13, the mass ratio of manganese slag - coconut shell biochar to acrylate adsorbent is 1:0.5; the acrylate adsorbent is prepared by the following method: Mix ethylenediamine and methyl acrylate at a molar ratio of 1:6, and under nitrogen protection, stir and react at 40 °C for 24 h to produce the starting product; mix the starting product with excessive ethylenediamine at a molar ratio of 1:18, react at 50 °C for 48 h, and dialyze and purify the intermediate product with a cut-off molecular weight ≤ 1 kDa; react the intermediate product with the modifier at a molar ratio of 1:5, stir at 70 °C for 12 h to modify the surface functional groups; add glutaraldehyde accounting for 3.5% of the mass of the intermediate product, and crosslink at pH 8 - 10 for 4 h; separate the final product, freeze-dry and then pulverize it, and pass through a 200-mesh sieve to obtain the acrylate adsorbent. The modifier is prepared by mixing mercaptoacetic acid, carboxymethyl chitosan, and amino thiol in a weight ratio of 1:0.8:0.5.

[0049] In Example 14, the mass ratio of manganese slag-coconut shell biochar to the acrylate adsorbent is 1:0.3; the acrylate adsorbent is prepared by the following method: Mix ethylenediamine and methyl acrylate at a molar ratio of 1:6, and under nitrogen protection, stir and react at 40 °C for 24 h to produce the starting product; mix the starting product with excessive ethylenediamine at a molar ratio of 1:18, react at 50 °C for 48 h, and dialyze and purify the intermediate product with a cut-off molecular weight ≤ 1 kDa; react the intermediate product with the modifier at a molar ratio of 1:10, stir at 70 °C for 12 h to modify the surface functional groups; add glutaraldehyde accounting for 3.5% of the mass of the intermediate product, and crosslink at pH 8 - 10 for 4 h; separate the final product, freeze-dry and then pulverize it, and pass through a 200-mesh sieve to obtain the acrylate adsorbent. The modifier is prepared by mixing mercaptoacetic acid and carboxymethyl chitosan in a weight ratio of 1:1.3.

[0050] In Example 15, the mass ratio of manganese slag-coconut shell biochar to the acrylate adsorbent is 1:0.3; the acrylate adsorbent is prepared by the following method: Mix ethylenediamine and methyl acrylate at a molar ratio of 1:6, and under nitrogen protection, stir and react at 40 °C for 24 h to produce the starting product; mix the starting product with excessive ethylenediamine at a molar ratio of 1:18, react at 50 °C for 48 h, and dialyze and purify the intermediate product with a cut-off molecular weight ≤ 1 kDa; react the intermediate product with the modifier at a molar ratio of 1:10, stir at 70 °C for 12 h to modify the surface functional groups; add glutaraldehyde accounting for 3.5% of the mass of the intermediate product, and crosslink at pH 8 - 10 for 4 h; separate the final product, freeze-dry and then pulverize it, and pass through a 200-mesh sieve to obtain the acrylate adsorbent. The modifier is prepared by mixing mercaptoacetic acid and amino thiol in a weight ratio of 1:1.3.

[0051] Table 5 - Test Results Table (IV)

[0052] It can be seen from the data in the above table that: Examples 11 - 15 of the present invention with acrylate adsorbent added show more excellent effects in aspects such as increasing soil pH value, enhancing nutrient content, and improving enzyme activity. For example, in Example 12, the soil pH value reached 7.2 at 64 days, the organic matter content reached 98 g / kg, and the concentrations of Ca² + and Mg² + reached 3.7 cmol / kg and corresponding higher values respectively, and the dehydrogenase activity was as high as 195 μg TPF / g / d. The possible reason is that the acrylate adsorbent has abundant active groups such as mercapto, amino, carboxyl, etc., which can coordinate and chelate with heavy metal ions in the soil, thus enhancing the adsorption capacity of the modifier for heavy metals in the soil; in addition, the addition of this adsorbent may be beneficial to improving the physical structure of the soil, increasing soil aeration and water retention.

[0053] The above are all the preferred embodiments of this application. The protection scope of this application is not limited thereby. Therefore, all equivalent changes made according to the structure, shape, and principle of this application shall be covered within the protection scope of this application.

Claims

1. A preparation method of a manganese slag-coconut shell charcoal-desulfurized gypsum composite soil conditioner, characterized in that, It includes the following steps: Manganese slag pretreatment: Wash the manganese slag with water and dry it to obtain pretreated manganese slag; Coconut shell pretreatment: Wash the coconut shell, dry it, and crush it to obtain pretreated coconut shell; Precursor preparation: Mix the pretreated coconut shell and pretreated manganese slag at a mass ratio of 1:(5 - 9), and ball-mill at a speed of 300 - 600 rpm for 2 - 5 h with a ball-to-material ratio of 10:1 to obtain a manganese slag-coconut shell precursor; Precursor calcination: Calcinate the obtained manganese slag-coconut shell precursor in a protective gas atmosphere at 450 - 650 °C for 1 - 4 h to obtain manganese slag-coconut shell biochar; Modifier compounding: Incorporate desulfurized gypsum powder into the obtained manganese slag-coconut shell biochar and disperse it evenly to obtain a manganese slag-coconut shell-carbon-desulfurized gypsum composite soil modifier.

2. The preparation method of the manganese slag-coconut shell charcoal-desulfurized gypsum composite soil conditioner according to claim 1, characterized in that: In the modifier compounding process, the mass ratio of manganese slag-coconut shell biochar to desulfurized gypsum powder is 1:(3 - 5).

3. The preparation method of the manganese slag-coconut shell charcoal-desulfurized gypsum composite soil conditioner according to claim 1, characterized in that, The specific steps of manganese slag pretreatment are: Add water to the manganese slag at a water-slag ratio of 1:(1 - 3), stir for 30 - 90 min, and separate the manganese slag; repeat the water washing operation 2 - 5 times, and then dry the washed manganese slag at 80 - 120 °C for 8 - 12 h to obtain pretreated manganese slag.

4. The preparation method of the manganese slag-coconut shell charcoal-desulfurized gypsum composite soil conditioner according to claim 3, characterized in that: The manganese slag is the manganese slag obtained by pressure filtration in an electrolytic manganese plant. Before water washing, soak the manganese slag in 0.5 - 1 mol / L dilute hydrochloric acid for 30 - 60 min, separate the manganese slag, and then perform the water washing operation.

5. The preparation method of the manganese slag-coconut shell charcoal-desulfurized gypsum composite soil conditioner according to claim 1, characterized in that: The particle size of the pretreated coconut shell is 2 - 5 mm.

6. The preparation method of the manganese slag-coconut shell charcoal-desulfurized gypsum composite soil conditioner according to claim 5, characterized in that: In the coconut shell pretreatment step, after washing the coconut shell, pre-dry it at 80 °C for 2 h, and then raise the temperature to 105 °C and dry it for 30 - 90 min.

7. The preparation method of the manganese slag-coconut shell charcoal-desulfurized gypsum composite soil conditioner according to claim 1, wherein: In the precursor calcination process, calcine in a nitrogen atmosphere with the nitrogen flow rate controlled at 0.5 - 1 L / min.

8. The preparation method of the manganese slag-coconut shell charcoal-desulfurized gypsum composite soil conditioner according to claim 1, characterized in that: In the modifier compounding process, pass the desulfurized gypsum powder through a 200-mesh sieve first, then incorporate it into the manganese slag-coconut shell biochar precursor, and then mix it at a speed of 15 - 20 rpm for 30 min to disperse it evenly to obtain a manganese slag-coconut shell-carbon-desulfurized gypsum composite soil modifier.

9. A soil modifier prepared by the method for preparing a manganese slag-coconut shell-carbon-desulfurized gypsum composite soil modifier according to any one of claims 1 - 8.

10. Application of the soil modifier according to claim 9 in the improvement of acidic soil in a rubber plantation.

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