Soil improvement material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of soil improvement, and discloses a soil improvement material as well as a preparation method and application thereof. The soil improvement material comprises ferrous phosphate minerals doped and modified by metal ions, the metal ions are selected from at least one of Mn < 2 + >, Mg < 2 + >, Ni < 2 + >, Ca < 2 + > and Al < 3 + >. The soil improvement material provided by the invention has slow-release phosphorus and soil organic carbon immobilization performance under anaerobic and aerobic conditions, can be used as a slow-release fertilizer in soil to provide phosphorus elements required by crop growth, and can also be used as a carbon immobilization material to improve soil carbon sink; the slow release property of phosphorus in the material is utilized, the fertilizer efficiency period can be prolonged, the phosphorus utilization rate of crops is increased, meanwhile, manganese, magnesium and other trace elements in the material can be slowly released and absorbed and utilized by the crops, and the yield and quality of the planted crops are improved; while the slow release of phosphorus in anaerobic and aerobic stages is realized, the efficient, stable and lasting storage of organic carbon in the soil is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of soil improvement, and in particular to a soil improvement material and a preparation method and application thereof. Background Art

[0002] Phosphorus is one of the essential elements for plant growth and development. Phosphorus in the soil plays an irreplaceable role in ensuring crop growth and yield. On the one hand, phosphorus can promote the root development of crops and improve the absorption and utilization of soil nutrients by crops. On the other hand, phosphorus can participate in the growth and metabolism of crops. Therefore, in agricultural production activities, the application of phosphorus-containing mineral fertilizers is particularly important.

[0003] In addition to phosphorus-containing fertilizers, the content and stability of organic carbon in the soil are also key factors affecting crop growth and development. However, soil soluble organic carbon is highly mobile and difficult to exist stably and be absorbed and utilized by crops. Therefore, improving the stability of soil organic carbon and increasing soil carbon sequestration will help crop growth and yield. In addition, as the largest carbon pool in terrestrial ecosystems, small changes in the soil organic carbon pool will lead to large fluctuations in the concentration of carbon dioxide in the atmosphere. The enhancement of soil organic carbon sequestration is of great significance to reducing atmospheric greenhouse gas emissions and mitigating global warming.

[0004] In the research of slow-release phosphate fertilizer, blue iron ore has been widely used in chemical, environmental and agricultural industries due to its high phosphorus content, strong reaction activity and certain slow-release phosphorus characteristics. CN 109626570A discloses a blue iron ore crystallization pre-phosphorus removal method based on AAO / AO process, which synthesizes blue iron ore by recovering phosphorus from sewage, but the blue iron ore synthesized by this method has a high impurity content and cannot be directly applied to farmland soil as a slow-release phosphate fertilizer. In addition, the cycle of preparing blue iron ore by this method is long, the efficiency is low, the cost is high, and it is not suitable for large-scale promotion and use. In addition, pure blue iron ore has a low solubility product, which leads to a very slow efficiency of releasing phosphorus when it is used as a fertilizer, and has a certain pH dependence, which limits the application of traditional blue iron ore phosphorus-based fertilizers in soil.

[0005] In the study of soil carbon fixation materials, the sequestration of soil dissolved organic carbon is mainly achieved through three ways: physical, chemical and biological. Soil active iron minerals are secondary minerals commonly found in soil, with high surface activity, and can fix soil dissolved organic carbon through cation bridging and coordination exchange, and the stability of soil organic carbon fixed in this way is the highest, so more carbon fixation materials are related to soil active iron and aluminum minerals. CN 116875323A discloses a method for promoting soil carbon sink by using nano-hematite, wherein a carbon fixation additive formed by mixing herbaceous organic matter with nano-magnetic minerals is applied to the soil to increase the soil carbon sink, but the synthesis cost of nano-magnetite is high, the particle size is small, and the mobility is strong, resulting in a low stability of the nano-particle material after fixing organic carbon, which is easy to cause the original fixed soil organic carbon to be released again. In addition, it is difficult to find pure nano-iron mineral particles or blue iron ore in the soil, which generally exist in the form of minerals doped with other ions (such as manganese or magnesium). Directly adding pure nano-iron mineral particles or blue iron ore to the soil may cause damage to the local soil ecological environment, which is not conducive to the growth of crops.

[0006] The existing technology usually directly adds organic matter-rich amendments to the soil, but this method is highly dependent on external organic matter, and most of the added organic matter is easily lost, resulting in low soil carbon sequestration efficiency and difficulty in achieving slow-release phosphorus coupled with synchronous sequestration of organic carbon. By maximizing the development and utilization of the characteristics of natural minerals in the soil, it is possible to maximize the slow release of phosphorus coupled with the sequestration of soil dissolved organic carbon, achieve effective release of phosphate fertilizers and long-term stable sequestration of soil organic carbon, which is of great significance for improving soil, enhancing soil carbon sinks, providing the phosphorus elements required for crop growth, ensuring crop growth and increasing yields. Summary of the invention

[0007] The present invention aims to solve at least one of the above-mentioned technical problems existing in the prior art. To this end, one of the purposes of the present invention is to provide a soil improvement material; the second purpose of the present invention is to provide a method for preparing the soil improvement material; the third purpose of the present invention is to provide an application of the soil improvement material.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is:

[0009] The first aspect of the present invention provides a soil improvement material, comprising a ferrous phosphate mineral doped with a metal ion; the metal ion is selected from Mn 2+ Mg 2+ 、Ni 2+ , Ca 2+ 、Al 3+ At least one of .

[0010] In some embodiments of the present invention, the metal ion is selected from Mn2+ and Mg 2+ At least one of .

[0011] In some embodiments of the present invention, the doping amount of the metal ions is less than or equal to 50 mol % of the total amount of doped metals and ferrous elements in the soil improvement material.

[0012] In some specific embodiments of the present invention, the doping amount of the metal ions is 10 mol%-50 mol% of the total amount of the doped metal and ferrous elements in the soil improvement material.

[0013] In some embodiments of the present invention, the soil improvement material includes the following preparation raw materials: ferrous salt, phosphorus source, doping ion source and water.

[0014] In some embodiments of the present invention, the ferrous salt is selected from at least one of ferrous sulfate, ferrous chloride, ferrous perchlorate, and ferrous ammonium sulfate.

[0015] In some specific embodiments of the present invention, the ferrous salt is ferrous chloride.

[0016] In some embodiments of the present invention, the phosphorus source is selected from at least one of disodium hydrogen phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, ammonium dihydrogen phosphate, and tripotassium phosphate.

[0017] In some specific embodiments of the present invention, the phosphorus source is sodium dihydrogen phosphate.

[0018] In some embodiments of the present invention, the doping ion source is selected from at least one of manganese chloride, manganese sulfate, manganese nitrate, magnesium chloride, magnesium sulfate, magnesium nitrate, nickel chloride, nickel sulfate, nickel nitrate, calcium chloride, calcium sulfate, calcium nitrate, aluminum chloride, aluminum sulfate, and aluminum nitrate.

[0019] In some specific embodiments of the present invention, the doping ion source is selected from at least one of manganese chloride and magnesium chloride.

[0020] In some embodiments of the present invention, the water is deoxygenated deionized water.

[0021] The second aspect of the present invention provides a method for preparing the soil improvement material according to the first aspect of the present invention, comprising the following steps:

[0022] S1, dissolving ferrous salt, phosphorus source and doping ion source in water respectively to form ferrous salt solution, phosphate solution and doping ion solution;

[0023] S2. Firstly, the ferrous salt solution and the phosphate solution are mixed, diluted with water, and then the doping ion solution is added to obtain a suspension, and the solid-liquid separation is performed, and the solid phase is collected to obtain the soil improvement material.

[0024] In some embodiments of the present invention, the concentration of the ferrous salt solution is 0.4-0.6 mol / L.

[0025] In some specific embodiments of the present invention, the concentration of the ferrous salt solution is 0.4-0.5 mol / L.

[0026] In some embodiments of the present invention, the concentration of the phosphate solution is 0.2-0.4 mol / L.

[0027] In some specific embodiments of the present invention, the concentration of the phosphate solution is 0.2-0.3 mol / L.

[0028] In some embodiments of the present invention, the concentration of the doping ion solution is 0.2-0.3 mol / L.

[0029] In some specific embodiments of the present invention, the concentration of the doping ion solution is 0.2-0.25 mol / L.

[0030] In some embodiments of the present invention, in step S2, the volume ratio of the ferrous salt solution, the phosphate solution, water and the doping ion solution is 1:(2-4):(12-15):(0.1-1.5).

[0031] In some specific embodiments of the present invention, in step S2, the volume ratio of the ferrous salt solution, the phosphate solution, water and the doping ion solution is 1:(2-3):(12-14):(0.1-1.3).

[0032] In some embodiments of the present invention, in step S2, after the dilution with water, a stirring and mixing operation is further included; the stirring and mixing is performed at a rotation speed of 250-300 r / min and a time of 50-70 min.

[0033] In some embodiments of the present invention, after adding the doping ion solution, a stirring and mixing operation is further included; the stirring and mixing is performed at a speed of 250-300 r / min and a time of 50-70 min.

[0034] In some embodiments of the present invention, the pH of the suspension is 7-8.

[0035] In some embodiments of the present invention, a pH adjuster is added to adjust the pH of the suspension.

[0036] In some embodiments of the present invention, the pH adjuster includes a deoxygenated alkali solution or a deoxygenated acid solution.

[0037] In some embodiments of the present invention, the alkali source of the alkali solution comprises an alkali metal hydroxide.

[0038] In some specific embodiments of the present invention, the alkali source of the alkali solution is selected from at least one of potassium hydroxide and sodium hydroxide.

[0039] In some embodiments of the present invention, the concentration of the alkali solution is 4-6 mol / L.

[0040] In some embodiments of the present invention, the acid solution comprises hydrochloric acid.

[0041] In some embodiments of the present invention, the concentration of the acid solution is 1-3 mol / L.

[0042] In some embodiments of the present invention, the process of adjusting the pH of the suspension is assisted by stirring.

[0043] In some embodiments of the present invention, the stirring speed is 250-300 r / min, and the stirring time is 40-50 h.

[0044] In some embodiments of the present invention, the preparation of the soil improvement material is carried out under light-proof conditions.

[0045] In the present invention, the pH value of the suspension is ensured to be stable at 7-8 and is fully stirred, so that the hydrolysis rate of divalent iron and phosphate can be controlled to obtain the ferrous phosphate mineral doped and modified by metal ions.

[0046] In some embodiments of the present invention, after the solid-liquid separation, the process further comprises washing and drying to obtain the soil improvement material.

[0047] In some embodiments of the present invention, the solid-liquid separation method includes centrifugation and filtration to remove the supernatant.

[0048] In some embodiments of the present invention, the centrifugal rotation speed is 7500-8500r / min.

[0049] In the present invention, after the solid phase is collected by solid-liquid separation, deoxygenated deionized water is added to wash the solid phase to remove other impurities remaining on the surface of the material, and then the solid powdered soil improvement material is obtained by drying.

[0050] The third aspect of the present invention provides the use of the soil improvement material described in the first aspect of the present invention in slow-releasing phosphorus and / or improving soil carbon sequestration capacity.

[0051] In some embodiments of the present invention, the soil improvement material is used to slowly release phosphorus and simultaneously enhance the soil carbon sequestration capacity.

[0052] In some embodiments of the present invention, the mass ratio of the soil improvement material to soil is 1:(10-20).

[0053] In some specific embodiments of the present invention, the mass ratio of the soil improvement material to the soil is 1:(10-15).

[0054] In some embodiments of the invention, the pH of the soil is 3-10.

[0055] In some specific embodiments of the present invention, the pH of the soil is 4-9.

[0056] Compared with the prior art, the present invention has the following beneficial effects:

[0057] 1) The soil improvement material provided by the present invention has the performance of slow-release phosphorus and soil organic carbon sequestration under both anaerobic and aerobic conditions, and can be used as a slow-release fertilizer in the soil to provide the phosphorus element required for crop growth, and can also be used as a carbon sequestration material to improve soil carbon sink; the present invention modifies the ferrous phosphate mineral by metal ion doping, so that the zero-point charge and specific surface area of ​​the ferrous phosphate mineral are increased, and the increase in zero-point charge can increase the electrostatic attraction between the soil improvement material and organic matter, thereby improving the physical adsorption effect to promote the sequestration of soil organic carbon, and inhibiting the release of dissolved organic carbon already sequestered by the soil improvement material; the increase in specific surface area provides more adsorption sites for the sequestration of soil organic carbon, so that the soil improvement material can fix more soil active organic carbon through surface adsorption;

[0058] 2) The preparation method of the soil improvement material provided by the present invention has simple steps, uses low-cost, easily available iron salts and phosphates and water-soluble doped metal salts as main materials, and controls the hydrolysis rates of ferrous ions, phosphates and doped metal ions by adjusting the pH of the solution to obtain soil improvement materials doped with different metal ions and with different doping amounts. By developing and utilizing the characteristics of natural soil minerals and regulating their properties, phosphorus slow release coupled with the sequestration of soil soluble organic carbon is achieved;

[0059] 3) The soil improvement material provided by the present invention can utilize the slow release of phosphorus in the material to increase the fertilizer effect period and improve the utilization rate of phosphorus by crops. At the same time, trace elements such as manganese and magnesium in the material can also be slowly released and absorbed and utilized by crops, thereby improving the yield and quality of crops.

[0060] 4) The soil improvement material provided by the present invention can simultaneously promote the fixation of active organic carbon in the soil during the anaerobic and aerobic periods, and increase carbon sinks; under aerobic conditions, the iron minerals in the soil improvement material undergo phase changes to generate secondary iron minerals, which can promote the release of part of the phosphorus. At the same time, the phase change further increases the specific surface area of ​​the material and improves the adsorption capacity of active organic carbon in the soil. During the phase change process, the secondary iron minerals can also fix organic matter through physical encapsulation and nanopores, thereby enhancing the stability of the fixed soil organic carbon, solving the problems of low soil carbon fixation efficiency and carbon release during the anaerobic period in the prior art, and ensuring efficient, stable and long-lasting storage of soil organic carbon while achieving phosphorus slow release in the anaerobic and aerobic stages;

[0061] 5) The soil improvement material provided by the present invention can exert the performance of slow-release phosphorus and soil organic carbon sequestration in acidic, neutral and alkaline soils, and has a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 TEM images of the soil improvement materials prepared in Comparative Example 1 (a), Example 10 (b) and Example 9 (c);

[0063] Figure 2 The X-ray diffraction patterns of the soil improvement materials prepared in Comparative Example 1, Example 9 and Example 10;

[0064] Figure 3 is the zero point charge of the soil improvement materials prepared in Comparative Example 1, Example 9 and Example 10;

[0065] Figure 4 is the specific surface area of ​​the soil improvement materials prepared in Comparative Example 1, Example 9 and Example 10;

[0066] Figure 5 It is a diagram of mineral components in different reaction systems under aerobic and anaerobic conditions in Experimental Example 1;

[0067] Figure 6 This is a comparison diagram of phosphorus release effects in different reaction systems under aerobic and anaerobic conditions in Experimental Example 1;

[0068] Figure 7 This is a comparison chart of organic carbon sequestration performance in different reaction systems under aerobic and anaerobic conditions in Experimental Example 1;

[0069] Figure 8 A comparison diagram of the phosphorus release effect (a) and organic carbon sequestration performance (b) in the reaction system of soil pH = 4.6 under aerobic and anaerobic conditions in Experimental Example 2;

[0070] Fig. 9A comparison diagram of the phosphorus release effect (a) and organic carbon sequestration performance (b) in the reaction system of soil pH = 6.8 under aerobic and anaerobic conditions in Experimental Example 2;

[0071] Fig.10 This is a comparison chart of the phosphorus release effect (a) and organic carbon sequestration performance (b) in the reaction system of soil pH = 8.4 under aerobic and anaerobic conditions in Experimental Example 2. DETAILED DESCRIPTION

[0072] The present invention is further described in detail below by specific examples. Unless otherwise specified, the raw materials, reagents or devices used in the examples and comparative examples can be obtained from conventional commercial sources or can be obtained by prior art methods. Unless otherwise specified, the experiments or test methods are conventional methods in the art.

[0073] In the following examples and comparative examples, ferrous chloride tetrahydrate is used as ferrous salt, sodium dihydrogen phosphate is used as phosphorus source, manganese chloride or magnesium chloride is used as doping ion source to prepare soil improvement materials, and a 5 mol / L deoxygenated sodium hydroxide solution is used as pH regulator, and the deionized water used to prepare the solution has been deoxygenated. The preparation process of each solution is as follows:

[0074] Ferrous salt solution: weigh 8.35g of ferrous chloride tetrahydrate into a 250mL glass beaker, add 100mL of deoxygenated deionized water to fully dissolve it, and prepare 100mL of ferrous salt solution with a concentration of 0.42mol / L;

[0075] Phosphate solution: weigh 3.96 g of disodium hydrogen phosphate solid into a 250 mL glass beaker, and add 100 mL of deoxygenated deionized water to fully dissolve it to prepare 100 mL of phosphate solution with a concentration of 0.279 mol / L;

[0076] Doping ion solution: weigh 2.58 g of manganese chloride or 1.95 g of magnesium chloride solid into a 250 mL glass beaker, add 100 mL of deoxygenated deionized water to prepare 100 mL of a doping ion solution with a concentration of 0.205 mol / L.

[0077] The boric acid-sodium borate buffer, sodium chloride and hydrochloric acid used in the above reagents and test examples were purchased from Sinopharm Reagents and were of analytical grade.

[0078] Example 1

[0079] In this example, a Mn 2+ The steps of doping and modifying the ferrous phosphate mineral soil improvement material are as follows:

[0080] 11.90 mL of 0.42 mol / L ferrous salt solution was added to a 250 mL glass beaker, which was placed on a magnetic stirrer, and 27.95 mL of 0.279 mol / L phosphate solution was added, and 157.37 mL of deoxygenated deionized water was added, and the solution was stirred at a speed of 280 r / min for 60 min to obtain a mixed solution containing ferrous and phosphate ions;

[0081] Add 2.78 mL of 0.205 mol / L manganese chloride doped ion solution to the mixed solution to obtain a suspension, and stir the suspension at a speed of 280 r / min for 60 min;

[0082] After the stirring is completed, 5 mol / L deoxygenated sodium hydroxide solution is gradually added dropwise to the suspension, and the color of the suspension gradually turns white and turbid. The deoxygenated sodium hydroxide solution is continuously added dropwise to the suspension until the pH value of the suspension increases to 7.0. The stirring is continued for 48 hours, during which the pH value of the suspension is kept constant at 7.0.

[0083] The suspension obtained above was centrifuged, the supernatant of the precipitate was discarded, and the same volume of deoxygenated deionized water was added, mixed thoroughly and then centrifuged, and the washing step was repeated three times to remove excess ions on the solid surface;

[0084] The wet solid obtained after washing was placed in an anaerobic box and dried naturally at room temperature. After 48 hours, the dry solid powder was collected to obtain 10 mol% Mn 2+ Doped and modified ferrous phosphate mineral soil improvement material, denoted as V_0.1Mn.

[0085] Example 2

[0086] This example prepares a Mg 2+ The steps of doping and modifying the ferrous phosphate mineral soil improvement material are as follows:

[0087] 11.90 mL of 0.42 mol / L ferrous salt solution was added to a 250 mL glass beaker, which was placed on a magnetic stirrer, and 27.95 mL of 0.279 mol / L phosphate solution was added, and 157.37 mL of deoxygenated deionized water was added, and the solution was stirred at a speed of 280 r / min for 60 min to obtain a mixed solution containing ferrous and phosphate ions;

[0088] Add 2.78 mL of 0.205 mol / L magnesium chloride doped ion solution to the mixed solution to obtain a suspension, and stir the suspension at a speed of 280 r / min for 60 min;

[0089] After the stirring is completed, 5 mol / L deoxygenated sodium hydroxide solution is gradually added dropwise to the suspension, and the color of the suspension gradually turns white and turbid. The deoxygenated sodium hydroxide solution is continuously added dropwise to the suspension until the pH value of the suspension increases to 7.0. The stirring is continued for 48 hours, during which the pH value of the suspension is kept constant at 7.0.

[0090] The suspension obtained above was centrifuged, the supernatant of the precipitate was discarded, and the same volume of deoxygenated deionized water was added, mixed thoroughly and then centrifuged, and the washing step was repeated three times to remove excess ions on the solid surface;

[0091] The wet solid obtained after washing was placed in an anaerobic box and dried naturally at room temperature. After 48 hours, the dry solid powder was collected to obtain 10 mol% Mg 2+ Doped and modified ferrous phosphate mineral soil improvement material, denoted as V_0.1Mg.

[0092] Example 3

[0093] In this example, a Mn 2+ The steps of doping and modifying the ferrous phosphate mineral soil improvement material are as follows:

[0094] 11.90 mL of 0.42 mol / L ferrous salt solution was added to a 250 mL glass beaker, which was placed on a magnetic stirrer, and 27.95 mL of 0.279 mol / L phosphate solution was added, and 154.95 mL of deoxygenated deionized water was added, and the solution was stirred at a speed of 280 r / min for 60 min to obtain a mixed solution containing ferrous and phosphate ions;

[0095] Add 5.56 mL of 0.205 mol / L manganese chloride doped ion solution to the mixed solution to obtain a suspension, and stir the suspension at a speed of 280 r / min for 60 min;

[0096] After the stirring is completed, 5 mol / L deoxygenated sodium hydroxide solution is gradually added dropwise to the suspension, and the color of the suspension gradually turns white and turbid. The deoxygenated sodium hydroxide solution is continuously added dropwise to the suspension until the pH value of the suspension increases to 7.0. The stirring is continued for 48 hours, during which the pH value of the suspension is kept constant at 7.0.

[0097] The suspension obtained above was centrifuged, the supernatant of the precipitate was discarded, and the same volume of deoxygenated deionized water was added, mixed thoroughly and then centrifuged, and the washing step was repeated three times to remove excess ions on the solid surface;

[0098] The wet solid obtained after washing was placed in an anaerobic box and dried naturally at room temperature. After 48 hours, the dry solid powder was collected to obtain 20 mol% Mn 2+Doped and modified ferrous phosphate mineral soil improvement material, denoted as V_0.2Mn.

[0099] Example 4

[0100] This example prepares a Mg 2+ The steps of doping and modifying the ferrous phosphate mineral soil improvement material are as follows:

[0101] 11.90 mL of 0.42 mol / L ferrous salt solution was added to a 250 mL glass beaker, which was placed on a magnetic stirrer, and 27.95 mL of 0.279 mol / L phosphate solution was added, and 154.95 mL of deoxygenated deionized water was added, and the solution was stirred at a speed of 280 r / min for 60 min to obtain a mixed solution containing ferrous and phosphate ions;

[0102] Add 5.56 mL of 0.205 mol / L magnesium chloride doped ion solution to the mixed solution to obtain a suspension, and stir the suspension at a speed of 280 r / min for 60 min;

[0103] After the stirring is completed, 5 mol / L deoxygenated sodium hydroxide solution is gradually added dropwise to the suspension, and the color of the suspension gradually turns white and turbid. The deoxygenated sodium hydroxide solution is continuously added dropwise to the suspension until the pH value of the suspension increases to 7.0. The stirring is continued for 48 hours, during which the pH value of the suspension is kept constant at 7.0.

[0104] The suspension obtained above was centrifuged, the supernatant of the precipitate was discarded, and the same volume of deoxygenated deionized water was added, mixed thoroughly and then centrifuged, and the washing step was repeated three times to remove excess ions on the solid surface;

[0105] The wet solid obtained after washing was placed in an anaerobic box and dried naturally at room temperature. After 48 hours, the dry solid powder was collected to obtain 20 mol% Mg 2+ Doped and modified ferrous phosphate mineral soil improvement material, denoted as V_0.2Mg.

[0106] Example 5

[0107] In this example, a Mn 2+ The steps of doping and modifying the ferrous phosphate mineral soil improvement material are as follows:

[0108] 11.90 mL of 0.42 mol / L ferrous salt solution was added to a 250 mL glass beaker, which was placed on a magnetic stirrer. 27.95 mL of 0.279 mol / L phosphate solution was added, and 151.82 mL of deoxygenated deionized water was added. The solution was stirred at a speed of 280 r / min for 60 min to obtain a mixed solution containing ferrous and phosphate ions.

[0109] 8.33 mL of 0.205 mol / L manganese chloride doped ion solution was added to the mixed solution to obtain a suspension, and the suspension was stirred at a speed of 280 r / min for 60 min;

[0110] After the stirring is completed, 5 mol / L deoxygenated sodium hydroxide solution is gradually added dropwise to the suspension, and the color of the suspension gradually turns white and turbid. The deoxygenated sodium hydroxide solution is continuously added dropwise to the suspension until the pH value of the suspension increases to 7.0. The stirring is continued for 48 hours, during which the pH value of the suspension is kept constant at 7.0.

[0111] The suspension obtained above was centrifuged, the supernatant of the precipitate was discarded, and the same volume of deoxygenated deionized water was added, mixed thoroughly and then centrifuged, and the washing step was repeated three times to remove excess ions on the solid surface;

[0112] The wet solid obtained after washing was placed in an anaerobic box and dried naturally at room temperature. After 48 hours, the dry solid powder was collected to obtain 30 mol% Mn 2+ Doped and modified ferrous phosphate mineral soil improvement material, denoted as V_0.3Mn.

[0113] Example 6

[0114] This example prepares a Mg 2+ The steps of doping and modifying the ferrous phosphate mineral soil improvement material are as follows:

[0115] 11.90 mL of 0.42 mol / L ferrous salt solution was added to a 250 mL glass beaker, which was placed on a magnetic stirrer. 27.95 mL of 0.279 mol / L phosphate solution was added, and 151.82 mL of deoxygenated deionized water was added. The solution was stirred at a speed of 280 r / min for 60 min to obtain a mixed solution containing ferrous and phosphate ions.

[0116] 8.33 mL of 0.205 mol / L magnesium chloride doped ion solution was added to the mixed solution to obtain a suspension, and the suspension was stirred at a speed of 280 r / min for 60 min;

[0117] After the stirring is completed, 5 mol / L deoxygenated sodium hydroxide solution is gradually added dropwise to the suspension, and the color of the suspension gradually turns white and turbid. The deoxygenated sodium hydroxide solution is continuously added dropwise to the suspension until the pH value of the suspension increases to 7.0. The stirring is continued for 48 hours, during which the pH value of the suspension is kept constant at 7.0.

[0118] The suspension obtained above was centrifuged, the supernatant of the precipitate was discarded, and the same volume of deoxygenated deionized water was added, mixed thoroughly and then centrifuged, and the washing step was repeated three times to remove excess ions on the solid surface;

[0119] The wet solid obtained after washing was placed in an anaerobic box and dried naturally at room temperature. After 48 hours, the dry solid powder was collected to obtain 30 mol% Mg 2+ Doped and modified ferrous phosphate mineral soil improvement material, denoted as V_0.3Mg.

[0120] Example 7

[0121] In this example, a Mn 2+ The steps of doping and modifying the ferrous phosphate mineral soil improvement material are as follows:

[0122] 11.90 mL of 0.42 mol / L ferrous salt solution was added to a 250 mL glass beaker, which was placed on a magnetic stirrer. 27.95 mL of 0.279 mol / L phosphate solution was added, and 149.04 mL of deoxygenated deionized water was added. The solution was stirred at a speed of 280 r / min for 60 min to obtain a mixed solution containing ferrous and phosphate ions.

[0123] 11.11 mL of 0.205 mol / L manganese chloride doped ion solution was added to the mixed solution to obtain a suspension, and the suspension was stirred at a speed of 280 r / min for 60 min;

[0124] After the stirring is completed, 5 mol / L deoxygenated sodium hydroxide solution is gradually added dropwise to the suspension, and the color of the suspension gradually turns white and turbid. The deoxygenated sodium hydroxide solution is continuously added dropwise to the suspension until the pH value of the suspension increases to 7.0. The stirring is continued for 48 hours, during which the pH value of the suspension is kept constant at 7.0.

[0125] The suspension obtained above was centrifuged, the supernatant of the precipitate was discarded, and the same volume of deoxygenated deionized water was added, mixed thoroughly and then centrifuged, and the washing step was repeated three times to remove excess ions on the solid surface;

[0126] The wet solid obtained after washing was placed in an anaerobic box and dried naturally at room temperature. After 48 hours, the dry solid powder was collected to obtain 40 mol% Mn 2+ Doped and modified ferrous phosphate mineral soil improvement material, denoted as V_0.4Mn.

[0127] Example 8

[0128] This example prepares a Mg 2+ The steps of doping and modifying the ferrous phosphate mineral soil improvement material are as follows:

[0129] 11.90 mL of 0.42 mol / L ferrous salt solution was added to a 250 mL glass beaker, which was placed on a magnetic stirrer. 27.95 mL of 0.279 mol / L phosphate solution was added, and 149.04 mL of deoxygenated deionized water was added. The solution was stirred at a speed of 280 r / min for 60 min to obtain a mixed solution containing ferrous and phosphate ions.

[0130] 11.11 mL of 0.205 mol / L magnesium chloride doped ion solution was added to the mixed solution to obtain a suspension, and the suspension was stirred at a speed of 280 r / min for 60 min;

[0131] After the stirring is completed, 5 mol / L deoxygenated sodium hydroxide solution is gradually added dropwise to the suspension, and the color of the suspension gradually turns white and turbid. The deoxygenated sodium hydroxide solution is continuously added dropwise to the suspension until the pH value of the suspension increases to 7.0. The stirring is continued for 48 hours, during which the pH value of the suspension is kept constant at 7.0.

[0132] The suspension obtained above was centrifuged, the supernatant of the precipitate was discarded, and the same volume of deoxygenated deionized water was added, mixed thoroughly and then centrifuged, and the washing step was repeated three times to remove excess ions on the solid surface;

[0133] The wet solid obtained after washing was placed in an anaerobic box and dried naturally at room temperature. After 48 hours, the dry solid powder was collected to obtain 40 mol% Mg 2+ Doped and modified ferrous phosphate mineral soil improvement material, denoted as V_0.4Mg.

[0134] Example 9

[0135] In this example, a Mn 2+ The steps of doping and modifying the ferrous phosphate mineral soil improvement material are as follows:

[0136] 11.90 mL of 0.42 mol / L ferrous salt solution was added to a 250 mL glass beaker, which was placed on a magnetic stirrer, and 27.95 mL of 0.279 mol / L phosphate solution was added, and 146.35 mL of deoxygenated deionized water was added, and the solution was stirred at a speed of 280 r / min for 60 min to obtain a mixed solution containing ferrous and phosphate ions;

[0137] 13.8 mL of 0.205 mol / L manganese chloride doped ion solution was added to the mixed solution to obtain a suspension, and the suspension was stirred at a speed of 280 r / min for 60 min;

[0138] After the stirring is completed, 5 mol / L deoxygenated sodium hydroxide solution is gradually added dropwise to the suspension, and the color of the suspension gradually turns white and turbid. The deoxygenated sodium hydroxide solution is continuously added dropwise to the suspension until the pH value of the suspension increases to 7.0. The stirring is continued for 48 hours, during which the pH value of the suspension is kept constant at 7.0.

[0139] The suspension obtained above was centrifuged, the supernatant of the precipitate was discarded, and the same volume of deoxygenated deionized water was added, and the mixture was thoroughly mixed and then centrifuged again. The washing step was repeated three times to remove excess ions on the solid surface;

[0140] The wet solid obtained after washing was placed in an anaerobic box and dried naturally at room temperature. After 48 hours, the dry solid powder was collected to obtain 50 mol% Mn 2+ Doped and modified ferrous phosphate mineral soil improvement material, denoted as V_0.5Mn.

[0141] Example 10

[0142] This example prepares a Mg 2+ The steps of doping and modifying the ferrous phosphate mineral soil improvement material are as follows:

[0143] 11.90 mL of 0.42 mol / L ferrous salt solution was added to a 250 mL glass beaker, which was placed on a magnetic stirrer, and 27.95 mL of 0.279 mol / L phosphate solution was added, and 146.35 mL of deoxygenated deionized water was added, and the solution was stirred at a speed of 280 r / min for 60 min to obtain a mixed solution containing ferrous and phosphate ions;

[0144] 13.8 mL of 0.205 mol / L magnesium chloride doped ion solution was added to the mixed solution to obtain a suspension, and the suspension was stirred at a speed of 280 r / min for 60 min;

[0145] After the stirring is completed, 5 mol / L deoxygenated sodium hydroxide solution is gradually added dropwise to the suspension, and the color of the suspension gradually turns white and turbid. The deoxygenated sodium hydroxide solution is continuously added dropwise to the suspension until the pH value of the suspension increases to 7.0. The stirring is continued for 48 hours, during which the pH value of the suspension is kept constant at 7.0.

[0146] The suspension obtained above was centrifuged, the supernatant of the precipitate was discarded, and the same volume of deoxygenated deionized water was added, mixed thoroughly and then centrifuged, and the washing step was repeated three times to remove excess ions on the solid surface;

[0147] The wet solid obtained after washing was placed in an anaerobic box and dried naturally at room temperature. After 48 hours, the dry solid powder was collected to obtain 50 mol% Mg 2+Doped and modified ferrous phosphate mineral soil improvement material, denoted as V_0.5Mg.

[0148] Comparative Example 1

[0149] This comparative example prepares a ferrous phosphate mineral soil improvement material that has not been modified by metal ion doping, and the steps are as follows:

[0150] 11.90 mL of 0.42 mol / L ferrous salt solution was added to a 250 mL glass beaker, which was placed on a magnetic stirrer. 27.95 mL of 0.279 mol / L phosphate solution was added, and 160.15 mL of deoxygenated deionized water was added. The solution was stirred at a speed of 280 r / min for 60 min to obtain a mixed solution containing ferrous and phosphate ions.

[0151] Gradually add 5 mol / L deoxygenated sodium hydroxide solution to the mixed solution, the color of the mixed solution gradually turns white and turbid, continue to add deoxygenated sodium hydroxide solution until the pH of the solution rises to 7.0, continue stirring for 48 hours, during which the pH of the solution is kept constant at 7.0;

[0152] The solution obtained above was centrifuged, the supernatant of the precipitate was discarded, and the same volume of deoxygenated deionized water was added, mixed thoroughly and then centrifuged, and the washing step was repeated three times to remove excess ions on the solid surface;

[0153] The wet solid obtained after washing was placed in an anaerobic box and dried naturally at room temperature. After 48 hours, the dry solid powder was collected to obtain an unmodified ferrous phosphate mineral soil improvement material, which was recorded as V_pure.

[0154] Material characterization

[0155] The soil improvement materials prepared in Examples 1-10 and Comparative Example 1 were characterized by transmission electron microscopy, X-ray diffraction and specific surface area. The specific methods are as follows:

[0156] 1) Transmission electron microscopy characterization

[0157] 10 μL of the suspension containing soil improvement materials in Examples 1-10 and Comparative Example 1 was added dropwise to anhydrous ethanol solution, and ultrasonicated for 8 minutes to fully disperse the suspension for preparing samples for transmission electron microscopy analysis. In order to prevent changes in the solid phase components during the ultrasonication process, the entire ultrasonication process was carried out in water at 25°C. The uniform suspension obtained after ultrasonication was added dropwise to an ultra-thin C film supported by a 200-mesh molybdenum mesh, and then placed in an anaerobic box to dry naturally. The soil improvement materials were analyzed using a transmission electron microscope (FEITalos F200X). In order to ensure reliable experimental results, multiple areas of the sample were selected for analysis.

[0158] 2) X-ray diffraction and specific surface area characterization

[0159] The solid powder of the soil improvement material after freeze drying in Examples 1-10 and Comparative Example 1 was placed in a mill and ground thoroughly, and the solid powder was collected and placed in a 2.0 mL centrifuge tube. The solid powder was analyzed using an X-ray powder diffractometer (XRD, Rigaku Smart Lab). In order to obtain reliable experimental data, during the test of the solid powder sample, the collection range of all diffraction spectra was set to 5°-80°, the instrument tube flow was set to 40 mA, the tube voltage was set to 40 kV, the step length was set to 0.02°, and the step speed was set to 2° / min.

[0160] In order to determine the specific surface area of ​​soil improvement materials doped with different ions, 35 mg of solid powder samples of Examples 1-10 and Comparative Example 1 were weighed and placed in glass tubes. -3 mbar) for 48 h to remove moisture, gas and impurities adsorbed on the surface. After degassing, the powder sample was analyzed using a specific surface area analyzer (Micromeritics ASAP 2460) under a nitrogen protection atmosphere at 77 K, and the adsorption and desorption isotherms in the 0.01-0.995P / P0 partial pressure region were collected. The desorption and adsorption isotherms were analyzed using the BET equation to obtain the specific surface area of ​​the solid powder sample.

[0161] In the present invention, soil improvement materials with different metal ion doping amounts are synthesized and characterized and analyzed, and it is found that when the doping amount of metal ions in the soil improvement material is greater than 50 mol% of the total amount of doped metals and ferrous elements in the soil improvement material, impurities such as manganese hydroxide and magnesium hydroxide will appear in the synthesized material, and the specific surface area and zero-point charge of the material show a downward trend, resulting in a poor phosphorus slow-release effect, a reduced storage amount of soil soluble organic carbon, and a weakened fixation effect. Therefore, when the doping amount of metal ions is less than or equal to 50 mol% of the total amount of doped metals and ferrous elements in the soil improvement material, the soil improvement material has the best effect of slow-release phosphorus coupling to enhance the soil carbon sink capacity.

[0162] Figure 1 TEM images of the soil improvement materials prepared in Comparative Example 1 (a), Example 10 (b) and Example 9 (c) are shown in FIG. Figure 1 It can be seen that the ferrous phosphate mineral soil improvement material in Comparative Example 1 that is not modified by metal ion doping is rhombic in shape, and the crystal size is about 10-15 μm. 2+ and Mg 2+After modification, as manganese / magnesium doped ions entered the ferrous phosphate mineral structure, the diamond boundaries of the synthesized soil improvement material became blurred, the roughness and disorder increased, and the crystal size generally decreased to about 8-12μm. This shows that metal ion doping modification can change the morphology and structure of ferrous phosphate minerals, and then change their adsorption capacity, providing more space for the sequestration of soil organic matter.

[0163] Figure 2 is the X-ray diffraction pattern of the soil improvement materials prepared in Comparative Example 1, Example 9 and Example 10, Figure 2 It can be seen that compared with the soil improvement material (V_pure) in Comparative Example 1 that was not doped with metal ions, no other impurity minerals appeared in the soil improvement materials of Example 9 (V_0.5Mn) and Example 10 (V_0.5Mg), indicating that the synthesized metal ion-doped and modified ferrous phosphate mineral soil improvement material has a higher purity.

[0164] Figure 3 is the zero-point charge of the soil improvement materials prepared in Comparative Example 1, Example 9 and Example 10, and is Figure 3 It can be seen that compared with the soil improvement material (V_pure) in Comparative Example 1 which is not doped with metal ions, the soil improvement materials in Example 9 (V_0.5Mn) and Example 10 (V_0.5Mg) are doped with Mn 2+ and Mg 2+ After addition, the zero-point charge of the materials increased from 5.4 to 6.9 and 6.3 respectively. Since organic carbon carries a negative charge, the increase in zero-point charge can increase the electrostatic attraction between minerals and organic matter, promoting the adsorption of organic matter by minerals.

[0165] Figure 4 is the specific surface area of ​​the soil improvement materials prepared in Comparative Example 1, Example 9 and Example 10, Figure 4 It can be seen that compared with the soil improvement material (V_pure) in Comparative Example 1 which is not doped with metal ions, the soil improvement materials in Example 9 (V_0.5Mn) and Example 10 (V_0.5Mg) are doped with Mn 2+ and Mg 2+ After that, the specific surface area of ​​the material increased from 34.25m 2 / g increased to 63.83m 2 / g and 52.36m 2 / g, the increase in specific surface area can effectively promote the surface complexation of modified ferrous phosphate mineral soil improvement materials and organic matter, increase its adsorption of soil organic carbon, and at the same doping amount, Mn 2+ Doped and modified soil improvement materials have the best effect.

[0166] Test Example 1

[0167] 1) Extraction of soil dissolved organic carbon:

[0168] Weigh 25g of paddy field soil into a 250mL glass bottle and add 125mL of deionized water. Place the glass bottle in a 25℃ oscillating box, set the speed to 280r / min, and oscillate for 48h; after the oscillation, transfer the soil-water mixture to a 50mL centrifuge tube and centrifuge at a speed of 8000r / min for 30min; filter the supernatant after centrifugation with a 0.45μm filter membrane to remove other impurities, collect the filtrate in a brown glass bottle, which is the soil dissolved organic carbon solution, and store it in a 4℃ refrigerator.

[0169] 2) Test on the sequestration performance of soil improvement materials on soil dissolved organic carbon:

[0170] Take 4 100mL serum bottles, numbered 1-4, with a total experimental volume of 50mL. The system contains 30mL of borax-boric acid buffer with a pH of 7.0 and a concentration of 30mmol / L, and 20mL of soil soluble organic carbon solution with a concentration of 50mg C / L. 0.3g of the soil improvement material prepared in Comparative Example 1, Example 9 and Example 10 is added to bottles 1-3 respectively as the experimental group, and no soil improvement material is added to bottle 4 as the control group.

[0171] The substances in each bottle were fully mixed to form a suspension, and the pH of the suspension was adjusted to 7.0 in an anaerobic box. Then, all serum bottles were placed in a constant temperature oscillating box for oscillation, with the speed set to 280r / min, and fully oscillated for 72h under anaerobic conditions at 25°C in the dark to complete the anaerobic phosphorus slow release and organic matter adsorption equilibrium experiments, and the forms of organic carbon, phosphorus and mineral components in each culture system under anaerobic conditions were determined respectively, and each experimental condition was repeated three times. Then, the serum bottle stopper was replaced with a breathable sealing film, and it was continued to be placed in an oscillation box with a speed of 280r / min for full oscillation for 72h to complete the aerobic phosphorus slow release coupled with organic matter sequestration enhancement experiment, and the forms of organic carbon, phosphorus and mineral components in each culture system under aerobic conditions were determined respectively, and each experimental condition was repeated three times.

[0172] Among them, the quantification method of different forms of iron minerals is:

[0173] After the experiments on phosphorus slow release and organic carbon sequestration kinetics of soil improvement materials under anaerobic and aerobic conditions are completed, the supernatant is taken out after centrifugal filtration to determine the concentration of solution iron ions, which is the concentration of dissolved iron minerals; the suspension is fully shaken, 5 mL of the suspension is taken out and mixed with oxalic acid liquid, and oscillated and extracted at room temperature for 5 hours, and then centrifuged and filtered to determine the concentration of solution iron ions, which is the sum of the concentrations of amorphous and dissolved iron minerals; the suspension is fully shaken, 5 mL of the suspension is taken out and mixed with 6 mol / L hydrochloric acid solution, and oscillated and extracted at room temperature for 2-3 hours, and then centrifuged and filtered to determine the iron ion concentration of the supernatant, which is the total iron mineral concentration, and the concentrations of iron minerals in different forms are calculated based on the law of mass conservation.

[0174] The phosphorus concentration was determined by:

[0175] Mix the suspension in the serum bottle thoroughly, pipette 1.5 mL of the suspension sample through a 0.45 μm filter membrane, add 1 mL of the filtrate into a colorimetric tube, add 20 μL of ascorbic acid, and shake thoroughly for 30 seconds. Then, add 40 μL of molybdate color developer to the colorimetric tube, shake thoroughly, and color for 30 minutes. Then, quantify the absorbance of the sample at a wavelength of 880 nm, and calculate the phosphorus concentration in the sample based on the phosphate mark.

[0176] The extraction and quantification methods of different types of organic carbon are:

[0177] After the experiment of phosphorus slow release and organic carbon sequestration kinetics of soil improvement materials under anaerobic and aerobic conditions, 10 mL of suspension sample was taken from the serum bottle and placed in a centrifuge tube for centrifugation. The supernatant was filtered with a 0.45 μm filter membrane, and the filtrate was used to determine the dissolved organic carbon content; then, 10 mL of sodium pyrophosphate with a concentration of 150 mmol / L was added to the centrifuge tube, and after sufficient mixing, the serum bottle was placed in an oscillating box with a speed of 280 r / min for 24 hours, and the solution was filtered with a 0.45 μm filter membrane. The filtrate was used to determine the content of adsorbed organic carbon. The total organic carbon concentration, dissolved organic carbon concentration and adsorbed organic carbon concentration in the initial system were determined using a total organic carbon analyzer, and the mineralized organic carbon concentration was calculated as follows: degraded organic carbon concentration = total organic carbon concentration - dissolved organic carbon - adsorbed organic carbon concentration.

[0178] Figure 5 The mineral composition diagram of different reaction systems under aerobic and anaerobic conditions in Experimental Example 1, where: Figure 5 (a) is the mineral components under aerobic and anaerobic conditions in the reaction system in which the soil improvement material in Comparative Example 1 is added, Figure 5 (b) adding the mineral components under aerobic and anaerobic conditions in the reaction system of the soil improvement material in Example 9, Figure 5 (c) is the mineral components under aerobic and anaerobic conditions in the reaction system in which the soil improvement material in Example 10 is added. Figure 5 It can be seen that under anaerobic conditions, the iron minerals in different treatment groups basically exist in the form of crystals, and only a small amount exists in the form of solubility and weak crystals. Under aerobic conditions, in the reaction system of the soil improvement material added in Comparative Example 1, the proportion of dissolved iron minerals that are difficult to fix organic carbon is 0.67%, the proportion of weakly crystalline iron minerals is 6.39%, and the proportion of crystalline iron minerals is 92.94%; in the reaction system of the soil improvement material added in Example 9, the proportion of dissolved iron minerals is 1.18%, the proportion of weakly crystalline iron minerals is 14.89%, and the proportion of crystalline iron minerals is 83.93%; in the reaction system of the soil improvement material added in Example 10, the proportion of dissolved iron minerals is 0.94%, the proportion of weakly crystalline iron minerals is 10.32%, and the proportion of crystalline iron minerals is 88.74%. The quantitative results show that ferrous phosphate minerals modified by doping with different metal ions basically do not undergo phase change during the anaerobic phosphorus release coupled with organic carbon sequestration; under aerobic conditions, the doping of metal ions can change the morphology of modified ferrous phosphate minerals, promote the transformation of modified ferrous phosphate minerals into weakly crystalline iron minerals, and slow down the transformation of ferrous phosphate minerals into crystalline iron minerals. Since weakly crystalline iron minerals have stronger soil-soluble organic carbon sequestration capacity, the doping of metal ions can enhance the sequestration of soil-soluble organic carbon by soil improvement materials under aerobic conditions.

[0179] Figure 6 This is a comparison chart of phosphorus release effects in different reaction systems under aerobic and anaerobic conditions in Experimental Example 1, where: Figure 6 (a) is the phosphorus release in the reaction system after adding the soil improvement material in Comparative Example 1, Figure 6 (b) is the phosphorus release in the reaction system after adding the soil improvement material in Example 9, Figure 6 (c) shows the phosphorus release in the reaction system after adding the soil improvement material in Example 10. Figure 6 It can be seen that under anaerobic conditions, in the reaction systems in which the soil improvement materials in Comparative Example 1, Example 9 and Example 10 were added, 3.82%, 19.43% and 15.76% of phosphorus were released into the solution, respectively; under aerobic conditions, in the reaction systems in which the soil improvement materials in Comparative Example 1, Example 9 and Example 10 were added, 2.65%, 15.38% and 11.23% of phosphorus were released into the solution, respectively. The quantitative results show that the soil improvement material provided by the present invention has the effect of promoting the slow release of phosphorus, and after Mn 2+ The slow-release phosphorus effect of soil improvement materials doped with modified ferrous phosphate minerals is the best.

[0180] Figure 7 This is a comparison chart of organic carbon sequestration performance in different reaction systems under aerobic and anaerobic conditions in Experimental Example 1, where: Figure 7(a) is the type and content of organic carbon in the reaction system in which the soil improvement material in Comparative Example 1 is added, Figure 7 (b) is the type and content of organic carbon in the reaction system in which the soil improvement material in Example 9 is added, Figure 7 (c) is the type and content of organic carbon in the reaction system in which the soil improvement material in Example 10 is added. Figure 7 It can be seen that under anaerobic conditions, in the reaction systems to which the soil improvement materials in Comparative Example 1, Example 9 and Example 10 were added, 64.58%, 74.45% and 70.25% of the soil dissolved organic carbon were sequestered, respectively; under aerobic conditions, in the reaction systems to which the soil improvement materials in Comparative Example 1, Example 9 and Example 10 were added, 69.59%, 83.75% and 77.14% of the soil dissolved organic carbon were sequestered, respectively. The quantitative results show that, whether under aerobic or anaerobic conditions, the soil improvement materials provided by the present invention can enhance the sequestration of soil dissolved organic carbon and reduce its mobility, and the doping of metal ions can enhance the soil dissolved organic carbon sequestration capacity of ferrous phosphate minerals, among which, after Mn 2+ Doped and modified ferrous phosphate mineral soil improvement materials have the best effect on the sequestration of organic carbon.

[0181] Test Example 2

[0182] 1) Prepare the reaction solution:

[0183] Take three 150mL serum bottles, numbered 1-3, add 80mL of deoxygenated borax-boric acid buffer respectively to maintain the constant pH of the reaction system, add 20mL of soil soluble organic carbon solution with a concentration of 50mg C / L to each serum bottle, and then add 0.6g of soil improvement materials in Comparative Example 1, Example 9 and Example 10 to bottles 1-3 respectively. Under anaerobic room temperature conditions, the serum bottles were placed in an oscillation box with a rotation speed of 280r / min. After the oscillation was completed, the suspension was filtered using a 0.45μm filter membrane, and the wet solids trapped on the filter membrane were washed 3-5 times with deionized water. The wet solids were placed at room temperature to dry naturally, and the solids were collected to obtain a composite precipitate. The composite precipitate obtained after the adsorption reaction was divided into 2 parts, one for determining the content of fixed organic carbon in the solid phase, and one for verifying the release of organic carbon fixed by the soil improvement material in soil solutions of different pH values ​​and the slow release of phosphorus.

[0184] 2) Evaluation test of stability effect after phosphorus slow release and organic carbon sequestration:

[0185] Three paddy field soils with different pH values ​​were selected, located in Shaoguan City, Guangdong Province, Zunyi City, Guizhou Province, and Zigong City, Sichuan Province. The pH values ​​of the three soils were 4.6, 6.8, and 8.4, respectively. The extracts of the three soils were used to carry out the stability evaluation test of soil improvement materials after phosphorus slow release and organic carbon sequestration under anaerobic and aerobic conditions. Weigh 80 g of each of the three soils in a serum bottle, add 400 mL of deionized water, shake and extract at a rate of 280 r / min for 18 hours, then let stand for 60 minutes, and absorb 350 mL of the upper solution in the serum bottle, which is the soil extract.

[0186] 10 mL of soil extract was placed in a 100 mL serum bottle, and then 40 mL of borax-boric acid buffer was added. 0.3 g of the dried composite precipitate was added to each treatment group, and the blank group was not treated. Samples were taken at 90 days in aerobic conditions and 15 days in anaerobic conditions, and the dissolved phosphorus and organic carbon content in the system were determined. The difference between the phosphorus and organic carbon in the solution of the treatment group and the blank group was the release of phosphorus and organic carbon in the soil improvement material.

[0187] Among them, the phosphorus slow-release rate of soil improvement materials = solution phosphorus release / initial phosphorus fixation * 100%;

[0188] The sequestration rate of soil active organic carbon by soil improvement materials = (initial organic carbon sequestration - solution organic carbon release) / initial organic carbon sequestration * 100%.

[0189] Figure 8 This is a comparison chart of the phosphorus release effect (a) and organic carbon sequestration performance (b) in the reaction system of soil pH = 4.6 under aerobic and anaerobic conditions in Experimental Example 2. Figure 8 It can be seen that in a slightly acidic soil system, after 90 days of anaerobic culture, the organic carbon release in the treatment groups containing the composite precipitates corresponding to the soil improvement materials in Comparative Example 1 (V_pure), Example 9 (V_0.5Mn) and Example 10 (V_0.5Mg) was 4.25%, 3.06% and 1.43%, respectively, and the phosphorus content released into the solution was 2.3%, 4.5% and 8.3%, respectively; after 15 days of aerobic culture, the organic carbon release in the treatment groups containing the composite precipitates corresponding to the soil improvement materials in Comparative Example 1 (V_pure), Example 9 (V_0.5Mn) and Example 10 (V_0.5Mg) was 4.46%, 3.27% and 1.64%, respectively, and the phosphorus content released into the solution was 1.2%, 3.7% and 6.8%, respectively.

[0190] Fig. 9 This is a comparison chart of the phosphorus release effect (a) and organic carbon sequestration performance (b) in the reaction system of soil pH = 6.8 under aerobic and anaerobic conditions in Experimental Example 2. Fig. 9It can be seen that in a slightly acidic soil system, after 90 days of anaerobic culture, the organic carbon release in the treatment groups containing the composite precipitates corresponding to the soil improvement materials in Comparative Example 1 (V_pure), Example 9 (V_0.5Mn) and Example 10 (V_0.5Mg) was 5.13%, 3.94% and 2.31%, respectively, and the phosphorus content released into the solution was 3.8%, 10.4% and 14.4%, respectively; after 15 days of aerobic culture, the organic carbon release in the treatment groups containing the composite precipitates corresponding to the soil improvement materials in Comparative Example 1 (V_pure), Example 9 (V_0.5Mn) and Example 10 (V_0.5Mg) was 5.54%, 4.35% and 2.72%, respectively, and the phosphorus content released into the solution was 2.6%, 8.9% and 12.1%, respectively.

[0191] Fig.10 The figure is a comparison of the phosphorus release effect (a) and organic carbon sequestration performance (b) in the reaction system of soil pH = 8.4 under aerobic and anaerobic conditions in Experimental Example 2. Fig.10 It can be seen that in a slightly acidic soil system, after 90 days of anaerobic culture, the organic carbon release in the treatment groups containing the composite precipitates corresponding to the soil improvement materials in Comparative Example 1 (V_pure), Example 9 (V_0.5Mn) and Example 10 (V_0.5Mg) was 6.28%, 5.09% and 3.46%, respectively, and the phosphorus content released into the solution was 4.5%, 15.7% and 19.4%, respectively; after 15 days of aerobic culture, the organic carbon release in the treatment groups containing the composite precipitates corresponding to the soil improvement materials in Comparative Example 1 (V_pure), Example 9 (V_0.5Mn) and Example 10 (V_0.5Mg) was 6.65%, 5.46% and 3.83%, respectively, and the phosphorus content released into the solution was 3.4%, 11.2% and 15.3%, respectively.

[0192] Depend on Figure 8-Figure 10 It can be seen that the soil improvement material provided by the present invention has a phosphorus slow-release effect in soil environments with different pH values, and the fixed soil organic carbon is relatively stable, with only a small amount of organic carbon being released, which can achieve long-term and stable storage of soil organic carbon. 2+ The phosphorus slow-release coupled with organic carbon sequestration effect of soil improvement materials doped with modified ferrous phosphate minerals is the best.

Claims

1. A soil improvement material, characterized in that: It includes a ferrous phosphate mineral doped with a metal ion; the metal ion is selected from Mn 2+ Mg 2+ 、Ni 2+ , Ca 2+ 、Al 3+ At least one of .

2. The soil improvement material according to claim 1, characterized in that: The doping amount of the metal ions is less than or equal to 50 mol% of the total amount of the doped metals and ferrous elements in the soil improvement material.

3. The soil improvement material according to claim 1 or 2, characterized in that: The soil improvement material comprises the following preparation raw materials: ferrous salt, phosphorus source, doping ion source and water.

4. The soil improvement material according to claim 3, characterized in that: The ferrous salt is selected from at least one of ferrous sulfate, ferrous chloride, ferrous perchlorate, and ferrous ammonium sulfate; And / or, the phosphorus source is selected from at least one of disodium hydrogen phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, ammonium dihydrogen phosphate, and tripotassium phosphate; And / or, the doping ion source is selected from at least one of manganese chloride, manganese sulfate, manganese nitrate, magnesium chloride, magnesium sulfate, magnesium nitrate, nickel chloride, nickel sulfate, nickel nitrate, calcium chloride, calcium sulfate, calcium nitrate, aluminum chloride, aluminum sulfate, and aluminum nitrate.

5. The method for preparing the soil improvement material according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1, dissolving ferrous salt, phosphorus source and doping ion source in water respectively to form ferrous salt solution, phosphate solution and doping ion solution; S2. Firstly, the ferrous salt solution and the phosphate solution are mixed, diluted with water, and then the doping ion solution is added to obtain a suspension, and the solid-liquid separation is performed, and the solid phase is collected to obtain the soil improvement material.

6. The preparation method according to claim 5, characterized in that: The concentration of the ferrous salt solution is 0.4-0.6 mol / L; And / or, the concentration of the phosphate solution is 0.2-0.4 mol / L; And / or, the concentration of the doping ion solution is 0.2-0.3 mol / L.

7. The preparation method according to claim 6, characterized in that: In step S2, the volume ratio of the ferrous salt solution, the phosphate solution, the water and the doping ion solution is 1:(2-4):(12-15):(0.1-1.5); And / or, the pH of the suspension is 7-8.

8. Use of the soil improvement material according to any one of claims 1 to 4 in slow-releasing phosphorus and / or improving soil carbon sequestration capacity.

9. The use according to claim 8, characterized in that: The mass ratio of the soil improvement material to the soil is 1:(10-20).

10. The use according to claim 8, characterized in that: The pH of the soil is 3-10.

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