Fly ash-based saline-alkali soil modifier as well as preparation method and application thereof

Abstract

The invention discloses a fly ash-based saline-alkali soil modifier and a preparation method and application thereof.The preparation method comprises the steps that firstly, fly ash is modified under the hydrothermal condition through an ammonia-carboxyl complexing agent, modified fly ash is obtained, the content of main heavy metal in the fly ash is reduced, and the pH value of the fly ash is adjusted; adding potassium sulfate, calcium sulfate, humic acid, a bio-organic fertilizer and a bacillus subtilis compound microbial fertilizer into the modified fly ash, uniformly mixing, putting into a constant-temperature rotary furnace, keeping the rotary furnace rotating at a constant speed, spraying hot water into materials in the rotary furnace at the same time in good time, enabling the materials to react for a period of time under the conditions of constant temperature and water content control, and preparing into particles, so as to obtain the coal ash-based saline-alkali soil modifier with the pH value of 6.5-8.0 and the particle size of 1-4mm. According to the preparation method, the comprehensive treatment cost of saline-alkali soil improvement is reduced, the industrialization of the modifier is promoted, the long-term ecological influence of the modifier on the soil is reduced, and the digestibility of the fly ash is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of saline-alkali soil improvers, and relates to a method for improving saline-alkali soil, its preparation and application. Background Art

[0002] Saline-alkali soil is a non-zonal soil type widely distributed on the earth and is an important land resource. The improvement and comprehensive management of saline-alkali soil are related to a series of major strategic issues such as the country's reserve cultivated land resources, regional food security, and economic development. However, the traditional ideas, methods, and technologies for saline-alkali soil treatment and transformation are far from meeting the current national strategic needs for saline-alkali soil improvement. According to the principles of restoration ecology, from a new perspective of the effective utilization of local resources, through ecological restoration, reasonable utilization, and industrial development, it is of great significance to effectively promote the sustainable economic development of saline-alkali soil areas.

[0003] The chemical composition of fly ash is highly similar to soil minerals, mainly composed of aluminum and silicon, and rich in medium and trace elements such as calcium, magnesium, and potassium, which can supplement the nutrient imbalance in saline-alkali soil. In addition, the alkaline oxides (such as CaO and MgO) in fly ash can react with sodium ions in saline-alkali soil to reduce the sodium adsorption ratio of the soil; fly ash particles are loose and porous. After being incorporated into the soil, it can significantly reduce the bulk density, increase the porosity, improve the soil aeration and water permeability, break the hardpan layer, and inhibit the upward movement of salts through capillary action. Using fly ash-based improvers to improve saline-alkali soil is a commonly used method. At present, when using fly ash to improve saline-alkali soil, either directly screen fly ash and mix it with desulfurized gypsum / phosphogypsum and organic fertilizers, or modify fly ash and then add organic fertilizers. The technology related to the present invention is the technology of using modified fly ash to condition or improve saline-alkali soil.

[0004] Chinese Patent Application No. 202310593152.6 discloses a modified fly ash, a saline-alkali soil improvement material, a preparation method and an application thereof. It uses ultrasonic waves and alkali solution to modify the screened fly ash, remove heavy metals in the fly ash and activate the silicate structure. The obtained modified fly ash is mixed with organic fertilizer and then ripened to obtain a saline-alkali soil improvement material for application in saline-alkali soil improvement. Although this method shows certain effects in saline-alkali soil improvement, ultrasonic activation destroys the particle structure of fly ash, affecting the persistence of its promotion of soil aggregate formation. Alkali treatment may change the release rate of elements such as calcium and magnesium in fly ash, resulting in a mismatch between soil nutrient supply and crop requirements. For the above reasons, on the one hand, a large amount of accumulated fly ash cannot be digested, and on the other hand, the fly ash-based saline-alkali soil conditioner developed at the laboratory stage cannot be widely promoted. Facing the current difficulties, there is an urgent need to research and develop a new method with local and sufficient supply of modifier raw materials, simplified manufacturing process, combination of organic and inorganic materials, in line with the current national agricultural industrial policy, products that can effectively improve saline-alkali soil, reduce the number of harmful ions in the solution, adjust the pH value of the saline-alkali soil solution, and at the same time have water retention, fertilizer retention, fertilizer enhancement, increase the air permeability of saline-alkali soil, suitable for large-scale production of saline-alkali soil conditioner products, supporting saline-alkali farmland engineering measures, comprehensive management, and providing new ideas for the effective treatment of saline-alkali soil. Summary of the Invention

[0005] In order to reduce the comprehensive treatment cost of saline-alkali soil improvement, promote the industrialization of the conditioner, reduce the long-term ecological impact of the conditioner on the soil, and increase the digestion rate of fly ash, the present invention provides a preparation method of an organic and inorganic combined fly ash-based saline-alkali soil conditioner suitable for soil treatment in vast saline-alkali areas, which is environmentally friendly, ecological, and conducive to the healthy treatment of saline-alkali soil.

[0006] The present invention also provides a fly ash-based saline-alkali soil conditioner prepared by this preparation method and its application.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] A preparation method of a fly ash-based saline-alkali soil conditioner, characterized in that the preparation method is as follows:

[0009] S1: Modify fly ash with an aminocarboxylic complexing agent under hydrothermal conditions to obtain modified fly ash, reduce the content of main heavy metals in the fly ash and adjust the pH value of the fly ash; the hydrothermal conditions refer to controlling the reaction temperature and the water content of the material during the reaction, and once the water content decreases, hot water is replenished in a timely manner;

[0010] S2: Add potassium sulfate, calcium sulfate, humic acid, biological organic fertilizer, and Bacillus subtilis compound microbial fertilizer to the modified fly ash, mix them evenly, and then place them in a constant-temperature rotary kiln. The rotary kiln rotates at a constant speed, and at the same time, hot water is sprayed onto the materials in the rotary kiln in a timely manner, so that the materials react for a period of time under the conditions of constant temperature and controlled water content to obtain a saline-alkali soil conditioner;

[0011] S3: Granulate the saline-alkali soil conditioner in step S2 to facilitate the slow release of the conditioner in the soil.

[0012] Furthermore, the soluble aminocarboxylic complexing agent described in step S1 is sodium EDTA, preferably EDTA-2Na·2H2O.

[0013] Furthermore, in step S1, the modification method is: mix the fly ash raw material with the aminocarboxylic complexing agent in a certain proportion and react under the conditions of controlling the temperature at 60°C - 85°C and the water content of the material at 20 - 30 wt%; preferably react for 1 - 2 h, and preferably control the temperature at 70°C - 80°C.

[0014] Furthermore, the mass ratio of each material is: fly ash raw material: aminocarboxylic complexing agent: potassium sulfate: calcium sulfate: humic acid: biological organic fertilizer: Bacillus subtilis compound microbial fertilizer = 1000:(2 - 4):20:100:(2 - 5):(200 - 400):(1 - 3).

[0015] Furthermore, the rotary kiln in step S2 rotates at a constant speed for 1 - 2 h.

[0016] Furthermore, in step S2, the water content of the material is controlled at 20 - 30 wt%, and the temperature of the rotary kiln is 70°C - 80°C.

[0017] Furthermore, after step S3, it also includes a static step after discharging the materials from the rotary kiln. The purpose is to allow the aminocarboxylic complexing agent, humic acid, biological organic fertilizer, and Bacillus subtilis compound microbial fertilizer to continue to react chemically with the harmful heavy metals in the fly ash, and adjust the harmful heavy metals and pH value in the materials.

[0018] The pH of the saline-alkali soil conditioner prepared by the above method is in the range of 6.5 - 8.0 (optimally 6.8 - 7.5), and the particle size is 1 - 4 mm.

[0019] The particle size of the fly ash raw material described in the present invention is generally controlled below 80 mesh.

[0020] The method for improving saline-alkali soil with the saline-alkali soil conditioner prepared by the above method is as follows:

[0021] Apply the saline-alkali land conditioner to the surface layer of the saline-alkali land to be improved, then deeply plow the soil, turn the saline-alkali land conditioner into the soil 40 - 60 cm below the surface of the saline-alkali land and level it. Then, dig ditches at intervals on the saline-alkali land where the saline-alkali land conditioner has been applied, and use the ditches to drain and wash the salt irregularly to suppress the capillary action of the saline-alkali land. At the same time, deeply plow the soil of the saline-alkali land to 40 - 60 cm below the surface irregularly; continuously improve according to the above method until the concentration and quantity of some harmful cations Na+ and anions CO3 2- are reduced to the soil conditions suitable for the growth of most crops. Generally, moderately or slightly saline-alkali land requires 2 - 3 years of improvement, and severely or moderately saline-alkali land requires 3 - 5 years of improvement.

[0022] Furthermore, the application rate of the saline-alkali land conditioner per mu is 700 - 1000 Kg. The application rate per mu of the conditioner for severely saline-alkali land is large, generally 1000 Kg, and the application rate per mu of the conditioner for moderately and slightly saline-alkali land is small, generally 700 Kg.

[0023] Furthermore, the method of draining and washing the salt is as follows: constantly fill the ditches with treated water (that is, water without harmful cations or anions). Usually, according to the concentration of harmful ions in the soil, conduct field sprinkler irrigation or flood irrigation irregularly. After the sprinkler irrigation or flood irrigation, pump out the excess water in the ditches, and then fill the ditches with treated water again. That is to say, when improving the saline-alkali land in the present invention, the ditches should always be filled with treated water. When conducting field sprinkler irrigation or flood irrigation, it is necessary to pump out the water in the ditches and then fill them with treated water.

[0024] After applying the saline-alkali land conditioner of the present invention and taking corresponding supporting farmland engineering measures, in the 3rd year, measure the concentrations of Na + , K + , Ca 2+ , CO3 2- , HCO -3 , Cl - ions in the 0 - 60 cm soil layer of the improved saline-alkali land to test the effect of the improvement of the saline-alkali land soil, and then timely adjust the quantity of the saline-alkali land conditioner used and the supporting agricultural engineering measures taken (including the number of deep plowing times, the depth of deep plowing, the frequency of draining and washing the salt, etc.);

[0025] The purpose of the regular irrigation and drainage in the present invention is to wash the salt. Through irrigation and drainage, the soluble salts in the saline-alkali land (including the replaced cations Na + , Ca 2+ , Mg 2+ , etc., and the removed anions Cl - , SO 2- 4, CO3 2-Etc., and leach to the deep layer of saline-alkali soil, or move out of the saline-alkali land with water. The purpose of deep plowing the saline-alkali soil in the present invention is to fully mix the saline-alkali soil improver with the soil at all levels of the saline-alkali soil, cause a chemical reaction, and reduce the harmful ions at all levels of the saline-alkali soil. The operation of deep plowing the saline-alkali soil regularly is carried out 1-2 times a year. Combining with the irrigation and drainage of the saline-alkali soil can effectively reduce the concentration and quantity of harmful cations in the saline-alkali soil at 40-60 cm.

[0026] The advantages of the present invention will be described below in combination with the process and the mechanism of action:

[0027] 1. The present invention uses a complexing agent to modify fly ash under the conditions of controlling temperature and controlling the water content of the material. Its reaction mechanism is that high temperature (60°C - 85) promotes the complexation reaction between sodium EDTA and residual heavy metal ions (such as Pb, Zn, Cd, etc.) in fly ash to form stable water-soluble complexes, reducing the bioavailability of heavy metals.

[0028] 2. The present invention places the mixture constituting the soil improver in a rotary kiln and controls the temperature and the water content of the material, so that the soil improver mixture rotates and stirs uniformly under humid and hot conditions. On the one hand, it promotes the complexation reaction to be more complete, further reducing the content of harmful heavy metals and the pH value; on the other hand, the porous structure of fly ash is fully combined with organic fertilizer and humic acid to form a complex with a high specific surface area, enhancing the adsorption performance of the soil improver. Adding a small amount of potassium sulfate (K2SO4) under humid and hot conditions will dissolve and release K + , promoting the reaction between fly ash and added calcium sulfate (gypsum) to generate ettringite or zeolite-like minerals, and enhancing the ion exchange capacity. The added humic acid undergoes physical dehydration, colloid loosening, and increased solubility under humid and hot conditions. The added Bacillus subtilis complex microbial fertilizer plays the role of a "soil doctor" in saline-alkali soil improvement, achieving the effects of salt reduction, alkali adjustment, fertilizer increase, and growth promotion through multi-channel synergistic effects.

[0029] 3. The most harmful cation in saline-alkali soil is Na + , and the soil improver of the present invention replaces Na + in the saline-alkali soil with K 2+ or Ca + to form Na2SO4, and then combines with irrigation and drainage measures to wash and remove Na + from the soil. The replacement of harmful metal elements in the saline-alkali soil solution is carried out according to the replacement order of metal elements. The replacement order is:

[0030] K>Ca>Na>Mg>AI>Zn>Fe>Sn>Pb>Cu>Hg>Ag>Pt>Au; for example:

[0031] K2SO4 + Na + → Na2SO4 + K +Utilize K + to displace Na in the saline-alkali land, and NaCl is displaced into Na2SO4; +

[0032] CaSO4 + Na + → Na2SO4 + Ca 2+ Utilize Ca 2+ to displace Na in the saline-alkali land + ;

[0033] K2SO4 + Mg 2+ → MgSO4 + K + Utilize K + to displace Mg in the saline-alkali land 2+ ;

[0034] Utilize gypsum CaSO4 in the modifier to undergo a chemical reaction with the saline-alkali land soil solution to remove CO3 in the saline-alkali land 2- ;

[0035] CaSO4 + Na2CO3 → CaCO3 + Na2SO4

[0036] H2SO4 + Na2CO3 → Na2SO4 + H2O + CO2

[0037] The toxicity of the displaced Na2SO4 is smaller than that of Na2CO3;

[0038] Utilize the organic matter in the modifier to improve the soil structure of the saline-alkali land, increase the activity of soil microorganisms in the saline-alkali land, and promote the removal of harmful ions in the saline-alkali land soil solution.

[0039] ​4. Since salinized soil has strong water absorption, the salt in the soil dissolves when it encounters water, causing the saline-alkali land to become soft, and the surface shrinks and hardens after evaporation, and the soil structure is destroyed. The porosity of the soil becomes smaller, the capillary action becomes stronger, and the salt in the saline-alkali underground layer rises with the capillary. At the same time, due to evaporation, the salt in the capillary is analyzed, further aggravating the salinization of the soil. After the saline-alkali land improver of the present invention is applied to the surface of the saline-alkali land soil, it is deep-turned to 40-60cm underground. The fly ash finished product and biological organic fertilizer and other materials form a similar "sandy soil barrier", which can effectively improve the soil structure of the saline-alkali land. This is mainly because the "sandy soil barrier" formed by the fly ash finished product and biological organic fertilizer forms a "salt isolation layer" in the saline-alkali land, destroying the capillary action of the saline-alkali land soil water. The "sandy soil barrier" formed by the fly ash finished product and biological organic fertilizer has a large porosity and a reduced capillary force, which inhibits the capillary rise of the saline-alkali groundwater and the upward movement of salt with water. At the same time, the process of "sandy soil barrier" formed by fly ash products and biological organic fertilizers loosens the cultivated layer of saline-alkali land soil, accelerates the rate of water infiltration from the surface downward during irrigation or natural precipitation, and the salt in the cultivated layer of saline-alkali land is more likely to move down to the soil depth of 60 cm below the surface with the water. Field test observations have found that the saline-alkali land improver of the present invention applied 60 cm below the surface of saline-alkali land is better than the saline-alkali land improvement effect of 40 cm below the surface. The saline-alkali land improver of the present invention has a good water retention function. For saline-alkali land management, it retains the soil moisture of the saline-alkali land cultivated layer, which is a very important content for the effective management of saline-alkali land. At the same time, it supplements the beneficial middle and trace elements of saline-alkali land soil, increases the air permeability and porosity of saline-alkali land soil, and is used for the management of different types of saline-alkali land in a wide range of areas.

[0040] 6. The present invention uses fly ash as the main raw material, removes harmful heavy metals and reduces the pH value of fly ash raw materials, and then adds organic materials to form an environmentally friendly and healthy product combining organic and inorganic materials. The production process is simple, the production process is simplified, and the "hot water catalysis method" is used without high temperature, high humidity, and high pressure, and does not produce "three wastes". It is innovative, universal, and advanced. In addition, no additional investment in new equipment is required, which is convenient for reducing industrialization costs. The rotary kiln used is the equipment used in the compound fertilizer production line, which can be slightly modified. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is an electron microscope scan of fly ash raw material.

[0042] Figure 2 This is an electron microscope scan of fly ash after modification. DETAILED DESCRIPTION

[0043] The technical solution and positive effects of the present invention are further described below through the accompanying drawings and specific embodiments.

[0044] The preparation method of the saline-alkali land conditioner of the present invention is as follows:

[0045] Step A: First, weigh the above raw materials according to the mass ratio of fly ash raw material: complexing agent (EDTA-2Na·2H2O): potassium sulfate: calcium sulfate: humic acid: biological organic fertilizer: the Bacillus subtilis compound microbial fertilizer containing Bacillus subtilis = 1000:(2-4):20:100:(2-5):(200-400):(1-3). In practice, the proportioning can be adjusted according to the types of saline-alkali land and the requirements of improvement intensity in the use area to meet the improvement needs. For example, due to the differences in harmful cations such as Na + and anions such as Cl - , HCO - 3, etc., after comprehensively evaluating the pH value of the saline-alkali land soil solution, the types of crops planned to be planted, the improvement intensity, etc., adjust and formulate the corresponding refined formula of the saline-alkali land conditioner and the supporting farmland project. However, in any case, the mass of fly ash accounts for 65.27% - 75.47% of the total material mass, which needs to be strictly controlled.

[0046] The fly ash raw material is a waste generated during the combustion of bituminous coal; the potassium sulfate is a chemical fertilizer with a potassium oxide content of not less than 52% and a fineness of 0.5 mm; the calcium sulfate is commonly known as gypsum with a calcium oxide content of more than 95%; the humic acid is a finished product of agricultural humic acid, an organic matter formed by microbial fermentation of plant stems, leaves and branches; the EDTA-2Na·2H2O is a derivative of EDTA with good solubility; the biological organic fertilizer is an organic material, mainly the organic material obtained after harmless treatment of animal manure such as cattle, sheep, pigs, etc. or the powder obtained by mechanical crushing of plant straws, branches and withered leaves; the Bacillus subtilis compound microbial fertilizer is a compound microbial fertilizer containing Bacillus subtilis.

[0047] Step B: First, put fly ash and complexing agent into a reaction tank (the reaction tank is semi-closed) and mix them for a certain period of time. During this period, control the temperature of the reaction tank at 60°C - 85°C. At the same time, add hot water to the reaction tank. The purpose of adding hot water is to control the water content of the materials in the tank at (20 - 30) wt% (the temperature of the hot water should ensure that the temperature of the reaction tank is still controlled at 60°C - 85°C after adding). Make the fly ash and complexing agent undergo a complexation reaction under hydrothermal conditions for 1 - 2 hours to modify the fly ash, so as to reduce the content of the main harmful heavy metal elements of lead, chromium, cadmium, arsenic, and mercury in the fly ash to the industry standard, and reduce the pH value to 6.5 - 8.0 (optimally 7 - 8). The measurement results are shown in Table 1. The fly ash raw material is taken from Dingzhou Power Plant in Hebei Province, and the measurement unit is the National Key Laboratory of Wheat Breeding, Shandong Agricultural University. The results in the table are the results of treating the fly ash raw material and the complexing agent according to a mass ratio of 1:0.02, with a material water content of 25 wt%, a water temperature of about 75°C, and a reaction time of 1.5 hours.

[0048] Table 1 (the unit of harmful heavy metal content in the table is mg / Kg)

[0049] Project \ Heavy metal content and pH value Hg AS cd cr pb pH Fly ash raw material 4.31 44.93 16.45 57.53 56.16 12.14 Treated fly ash 1.3 4.90 2.95 21.16 16.95 7.2

[0050] It can be seen from the table that the contents of the five heavy metals and the pH value in the treated fly ash have been greatly reduced, and are far lower than the contents specified in the national standard GB / T8196 - 2003 for agricultural fly ash. It also meets the group standard - Soil Water Retention Conditioner (Fly Ash Based) issued on April 26, 2019 and implemented on May 26 by the China Chemical Industry Enterprise Management Association, and is suitable for acidic, neutral, and alkaline soils.

[0051] Further, conduct electron microscopy scanning on the fly ash before and after improvement. The scanning results are shown in Figure 1-2 . Figure 1 shows the electron micrograph of the untreated fly ash raw material, Figure 2 shows the electron micrograph of the fly ash after the hydrothermal reaction with the complexing agent. Comparing Figure 1 and Figure 2 it can be seen that before the fly ash was treated, the particles were basically spherical and quasi-spherical, and the sphere diameters were basically in the range of 1 - 50 um. After being treated by the modification method of the present invention, there are fewer small crystal balls in the finished product, and a large number of flocs beneficial to water storage are formed.

[0052] Step C: Add potassium sulfate, calcium sulfate, humic acid, biological organic fertilizer, and nano-calcium microbial fertilizer to the modified fly ash according to the required proportions, and then stir and mix evenly. At this time, the pH value of the mixed materials is in the range of 7.0 - 8.5, and the optimal value is 7.0 - 7.5.

[0053] Step D: Transfer the uniformly mixed materials into a rotary kiln at 70 - 80 °C. Let the rotary kiln rotate at a constant speed with a constant temperature duration of 1 - 4 h. Meanwhile, spray hot water (the actual temperature of the hot water sprayed is higher than 80 °C in practice so as to maintain the temperature of the rotary kiln at 70 - 80 °C) into the mixed materials in the rotary kiln as appropriate, so that the moisture content of the mixed materials is maintained at 25 - 30%. After the reaction, the pH value of the materials is in the range of 6.5 - 8.0, and optimally 6.8 - 7.5.

[0054] The rotary kiln used is the equipment in the compound fertilizer production line. There is a return pipe inside the rotary kiln. The hot gas is transported to the return pipe at the kiln mouth. The materials are directly in contact with the return pipe and are heated. The rotary kiln rotates while a pressurized water gun is used to timely inject hot water into the kiln.

[0055] Step E: Discharge the materials from step C from the rotary kiln and store them statically for 24 - 48 h at a temperature of 20 - 30 °C in a semi - enclosed place without direct sunlight. Cover the materials with a plastic sheet to keep the moisture content of the materials from decreasing too fast. The purpose is to let the aminocarboxylic complexing agent, humic acid, biological organic fertilizer, etc. continue to react chemically with the harmful heavy metals in the fly ash, reduce the harmful heavy metals in the materials and adjust the pH value; do not stir the materials during the static storage period of the materials.

[0056] Step F: Check the moisture content of the materials from step D. When the moisture content of the materials is 18% - 25%, they can be transferred to a granulator for granulation. The particle size is 1 mm - 4 mm; after passing the finished product inspection, they can be weighed, packaged, sold and used, and finally a saline - alkali soil conditioner with a pH in the range of 6.5 - 8.0 (optimally 6.8 - 7.5) and a particle size of 1 - 4 mm is obtained.

[0057] The usage method of the saline - alkali soil conditioner of the present invention is as follows:

[0058] First step. Take stratified soil samples from the saline - alkali land to be improved, from 0 - 60 cm, every 10 cm as a layer, take 5 points in the field by the plum blossom sampling method. Register, number, air - dry, grind, sieve and pre - treat the retrieved soil samples, and measure the total salt, alkalinity, total nitrogen, harmful cations, anions, soil ESP (percentage of exchangeable sodium), organic matter, soil porosity, soil bulk density, pH value and other indicators in the soil solution; based on these indicators, accurately calculate the amount of potassium sulfate, calcium sulfate, aminocarboxylic complexing agent, etc. required in addition to the types and amounts of beneficial metal elements contained in the fly ash for thorough chemical reaction, and conduct the material ratio. At the same time, consider factors such as the season of applying the conditioner, the intensity requirements of improvement, and farmland engineering measures.

[0059] Step 2. Apply the saline-alkali land conditioner to the surface layer of the saline-alkali land to be improved (usually from October of each year to March of the following year). The dosage per mu of the saline-alkali land conditioner is 700 - 1000 Kg, 1000 Kg per mu for severely saline-alkali land, and 700 Kg per mu for moderately and mildly saline-alkali land. Use a tractor to deeply plow and turn over the soil, turning the saline-alkali land conditioner 40 - 60 cm below the surface of the saline-alkali land to break the hard layer of the saline-alkali land, and then use a rotary tiller to till and level the land. At the same time, dig ditches in the saline-alkali land. The distance between ditches is 15 - 30 m, the depth of the ditch is 1 - 1.2 m, and the width is 0.8 - 1 m. Sprinkler irrigation facilities can be installed in the field. The agricultural engineering measures after applying the saline-alkali land conditioner mainly include:

[0060] (1) Drainage and desalination. Through irrigation and drainage, the soluble salts in the saline-alkali land (including the released Na + , the released Mg 2+ , the removed carbonate ion CO3 2- , etc.) are leached to the deep layer of the saline-alkali land soil or drained outside the saline-alkali land with the water flow. Drainage and desalination means filling the ditches with treated water (treated water refers to water without harmful cations or anions) to suppress the capillary action of the saline-alkali land, then timely carry out field sprinkler irrigation or flood irrigation, and pump out the excess water in the ditches, and then fill the ditches with treated water again. Generally, the number of operations throughout the year is 2 - 4 times, and the specific number of operations is determined according to the local natural precipitation and the requirements of the improvement intensity;

[0061] (2) Deeply plow the soil of the saline-alkali land to 40 - 60 cm, which can turn the salts on the surface layer of the saline-alkali land soil to the deep layer, reducing the carbonate ion CO3 2- , etc. on the surface layer of the saline-alkali land soil. Regularly deep plow the saline-alkali land soil 1 - 2 times a year. Combined with the irrigation and drainage of the saline-alkali land soil, it can effectively reduce the concentration and quantity of harmful cations Na + and anions CO3 2- in the 40 - 60 cm layer of the saline-alkali land soil;

[0062] (3) From May to September of each year, the above methods can be adopted to deep plow the soil and irrigate the saline-alkali land once again to remove the concentration and quantity of harmful cations Na + and anions CO3 2- in the 40 - 60 cm layer of the saline-alkali land soil;

[0063] Step 3. From October of the second year to March of the following year, continue to apply the saline-alkali land conditioner and carry out supporting agricultural engineering measures, irrigation measures, etc., and the method is the same as step 2;

[0064] Step 4. From October of the third year to March of the following year, continue the operation content of step 3.

[0065] The application rates of the saline-alkali soil conditioner in the second and third steps can be adjusted according to the content of harmful ions and the pH value in the soil after improvement.

[0066] Evaluate the improvement effect of the already improved saline-alkali soil. Generally, if the method of this invention patent can be strictly followed and there are no other harmful cations and anions input, usually after 2 - 3 years of effective improvement, the slightly and moderately saline-alkali soil can be improved into healthy farmland suitable for growing crops; after 3 - 5 years of effective improvement, the severely saline-alkali soil can be improved into healthy farmland suitable for growing crops.

[0067] The following further illustrates the operation process of the present invention through two field examples.

[0068] Example 1. The saline-alkali soil in the management area of Hekou District, Dongying City, Shandong Province. The area where the test plot is located is in the north temperate East Asian monsoon continental climate zone, with an annual precipitation of 810 mm. The salt content (Nacl) of the soil solution sampled at 0 - 30 cm is 0.86%, the pH value is 7.48, and the harmful cations and anions contained are: Na + , Mg 2+ , Ca 2+ , CO3 2- , HCO3 - , Cl - and other ions are relatively abundant, and the soil type belongs to severely saline-alkali soil formed after the ebb of seawater intrusion. In March 2022, the improvement agent experiment of the present invention was carried out. 1000 Kg of saline-alkali soil conditioner was applied per mu, evenly spread on the surface layer of the saline-alkali soil, and deep plowed by a tractor for 40 - 60 cm to turn the saline-alkali soil conditioner into the ground at 40 - 60 cm, level the land, dig ditches at intervals of 30 meters in the saline-alkali soil, the ditches are 1 - 1.2 m deep and 0.8 - 1 m wide, and fill them with treated water, 40 - 60 cubic meters. At intervals of 1 month - 3 months, irrigate the saline-alkali soil by sprinkler irrigation, 5 - 10 cubic meters of water per mu, and sprinkle 3 - 5 times a year. In March 2023, continue to carry out the saline-alkali soil improvement experiment, applying 700 Kg of saline-alkali soil conditioner per mu, and the improvement method and supporting farmland engineering measures are the same as those of the previous year. In March 2024, continue to carry out the saline-alkali soil improvement experiment according to the method of 2023. After each year's improvement, soil samples are taken in time for testing and analysis of the harmful cations and anions in the saline-alkali soil: Na + , Mg 2+ , Ca 2+ , HCO3 -- , Cl -The content of ions and the like. After three years of improvement, the content of harmful cations and anions in the saline-alkali land has decreased significantly. For the cotton variety Zhongmian 45 planted in 2024, the yield of seed cotton per mu is 416 jin, while the yield of seed cotton per mu of the control is 292 jin, with an increase of 42.47%. The changes in the soil solution after three years of improvement are shown in Table 2.

[0069] Table 2 Experimental plot in Dongying, Shandong

[0070]

[0071] Example 2: The saline-alkali land of farmers introduced by the agricultural department of Wuyuan County, Bayannao'er City, Inner Mongolia. The area where the experimental plot is located has a temperate continental monsoon climate, with an average annual precipitation of 186 mm. The soil type is moderately saline-alkali wasteland. The salt content (NaCl) of the soil solution sampled at 0 - 30 cm is 1.98%, and the pH value is 9.83. The harmful cations and anions it contains are: Na + , Mg 2+ , Ca 2+ , CO3 2- , HCO3 - , Cl - There are relatively many ions, etc., and the trees planted in the saline-alkali land have all withered. In April 2022, the improvement agent experiment of the present invention was carried out. 800 Kg of saline-alkali land improvement agent was applied per mu, evenly spread on the surface layer of the saline-alkali land, and deep plowed 40 - 60 cm with a tractor to turn the saline-alkali land improvement agent into the ground 40 - 60 cm. The land was leveled. In the saline-alkali land, ditches were dug at intervals of 30 meters. The ditches were 1 - 1.2 m deep and 0.8 - 1 m wide, and 50 - 60 cubic meters of treated water was filled. At intervals of 1 to 3 months, the saline-alkali land was irrigated by sprinkler irrigation with treated water, 10 - 15 cubic meters of water per mu, and sprinkler irrigation was carried out 4 - 6 times a year; In April 2023, the saline-alkali land improvement experiment was continued. 700 Kg of saline-alkali land improvement agent was applied per mu. The improvement method and supporting farmland engineering measures were the same as those of the previous year, and soil was taken and the harmful cations and anions contained in the soil solution were measured. In April 2024, the saline-alkali land improvement experiment was continued, soil was taken, tested, and the harmful cations and anions contained were analyzed. After three years of improvement, the content of harmful cations and anions in the saline-alkali land has decreased significantly. For the sunflower variety Mengkui 23 planted in 2024, the yield of sunflower seeds per mu is 1460 jin, while the yield of seed cotton per mu of the control is 897 jin, with an increase of 62.76%. The changes in the soil solution are shown in Table 3.

[0072] Table 3 Experimental plot in Wuyuan County, Bayanzhuo'er, Inner Mongolia

[0073]

[0074] It should be noted that while applying the saline-alkali land conditioner using the method of the present invention, corresponding farmland engineering measures must be taken. Only by implementing them together can the improvement purpose of the saline-alkali land conditioner of the present invention be achieved. Taking only one of them alone will lead to misjudgment of the improvement effect. Moreover, it takes a certain amount of time to wait until all the chemical reactions in the saline-alkali land soil solution are completed, rather than seeing immediate improvement effects after application.

[0075] In addition, the given ratios of the components of the conditioner of the present invention are the results of optimization and have universality. However, in practice, they can also be adjusted in a timely manner according to factors such as the type of saline-alkali land, the degree of salinization, the intensity of improvement to be achieved, the composition of fly ash raw materials and the types and quantities of harmful heavy metal elements, the concentrations of harmful cations and anions in the saline-alkali land soil, the comprehensive evaluation of the quantity and frequency of using the conditioner, and the intensity and measures of the supporting agricultural engineering measures for targeted improvement. Therefore, any polishing and modifications without creative labor based on the present invention are within the protection scope of the present invention.

Claims

1. A preparation method of a fly ash-based saline-alkali soil conditioner, characterized in that, It includes the following preparation steps: S1: Modify fly ash with an aminocarboxylic complexing agent under hydrothermal conditions to obtain modified fly ash, reduce the content of main heavy metals in the fly ash and adjust the pH value of the fly ash; the hydrothermal conditions refer to controlling the reaction temperature and the water content of the material during the reaction process; S2: Add potassium sulfate, calcium sulfate, humic acid, bio-organic fertilizer and Bacillus subtilis compound microbial fertilizer to the modified fly ash and mix evenly, then place it in a constant-temperature rotary kiln. The rotary kiln rotates at a constant speed, and at the same time, hot water is sprayed onto the material in the rotary kiln in a timely manner, so that the material reacts for a period of time under the conditions of constant temperature and controlled water content to obtain a saline-alkali soil conditioner; S3: Granulate the saline-alkali soil conditioner obtained in step S2 to facilitate the slow release of the conditioner in the soil.

2. The preparation method of the fly ash-based saline-alkali soil conditioner according to claim 1, wherein, In step S1, the aminocarboxylic complexing agent is sodium EDTA, preferably EDTA-2Na·2H2O.

3. The preparation method of the fly ash-based saline-alkali soil conditioner according to claim 1, characterized in that In step S1, the modification method is: mix the fly ash raw material with the aminocarboxylic complexing agent in a certain proportion, and react under the conditions of controlling the temperature at 60°C - 85°C and the water content of the material at 20 - 30 wt%; the controlled temperature is preferably 70°C - 80°C.

4. The preparation method of the fly ash-based saline-alkali soil conditioner according to any one of claims 1-3, characterized in that, The mass ratio of each material is: fly ash raw material: aminocarboxylic complexing agent: potassium sulfate: calcium sulfate: humic acid: bio-organic fertilizer: Bacillus subtilis compound microbial fertilizer = 1000:(2 - 4):20:100:(2 - 5):(200 - 400):(1 - 3).

5. The preparation method of the fly ash-based saline-alkali soil conditioner according to claim 1, characterized in that, The rotary kiln in step S2 rotates at a constant speed for 1 - 2 h.

6. The preparation method of the fly ash-based saline-alkali soil conditioner according to claim 1, characterized in that, In step S2, the water content of the material is controlled at 20 - 30 wt%, and the temperature of the rotary kiln is 70°C - 80°C.

7. The preparation method of the fly ash-based saline-alkali soil conditioner according to claim 1, characterized in that, After step S3, it also includes a step of standing the material after discharging it from the rotary kiln.

8. A saline-alkali land conditioner prepared by the preparation method according to any one of claims 1 to 7, characterized in that, The pH of the saline-alkali soil conditioner is 6.5 - 8.0, and the particle size is 1 - 4 mm.

9. A method for improving saline-alkali land by using the saline-alkali land improver described in claim 8, characterized in that, During improvement, apply the saline-alkali land conditioner to the surface layer of the saline-alkali land to be improved, then deeply plow the soil, turn the saline-alkali land conditioner into the soil 40 - 60 cm below the surface of the saline-alkali land and level it. Then, dig ditches at intervals on the saline-alkali land where the saline-alkali land conditioner has been applied, and use the ditches to drain and wash salts irregularly to suppress the capillary action of the saline-alkali land. At the same time, deeply plow the soil of the saline-alkali land to 40 - 60 cm below the surface irregularly; continuously improve according to the above method until the concentration and quantity of some harmful cations Na + and anions CO3 2- are reduced to the soil conditions suitable for the growth of most crops.

10. The method for improving saline-alkali land by using a saline-alkali land conditioner according to claim 9, characterized in that, The method of draining and washing salts is: constantly fill the water ditch with water that has been treated and does not contain harmful cations or anions. Usually, according to the concentration of harmful ions in the soil, carry out field spraying irrigation or flooding irrigation irregularly. After the spraying irrigation or flooding irrigation, pump away the excess water in the water ditch, and then fill the water ditch with the treated water again.

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