Heavy metal pollution control method and system based on fulvic acid type potassium sulfate

Abstract

The invention belongs to the technical field of environmental protection, and relates to a heavy metal pollution control method and system based on fulvic acid type potassium sulfate. The method comprises the following steps: firstly, obtaining the variety and content of heavy metal ions in soil and the complexing ratio of the heavy metal ions to fulvic acid, calculating the amount of fulvic acid required by complete complexing, determining the sowing amount by combining the content of fulvic acid in the fulvic acid type potassium sulfate fertilizer, uniformly sowing the fertilizer, drawing a heavy metal ion complexing reaction curve, and judging the pollution risk according to the residual amount after reaction equilibrium. If yes, recalculating the fulvic acid demand quantity and adjusting the sowing quantity. Heavy metal ions in soil can be effectively complexed, the activity and bioavailability of the heavy metal ions are reduced, and harm to crops is reduced; meanwhile, in the heavy metal pollution control process, soil nutrients are adjusted according to crop requirements, soil fertility is improved, and healthy growth of crops is guaranteed.

Description

Technical Field

[0001] The present invention belongs to the technical field of environmental protection, and specifically relates to a method and system for controlling heavy metal pollution based on potassium sulfate of fulvic acid type. Background Art

[0002] With the rapid development of industry and the unreasonable use of chemical fertilizers and pesticides, the problem of heavy metal pollution in soil is becoming increasingly serious. Heavy metals such as lead, cadmium, copper, etc. accumulate in the soil, which will not only affect the activity of soil microorganisms and damage the soil structure, but also endanger human health through the food chain. At present, the control methods for soil heavy metal pollution mainly include physical remediation, chemical remediation, and biological remediation, etc. Among them, chemical remediation has attracted attention because of its relatively simple operation and fast effect. Using complexing agents to form stable complexes with heavy metal ions is one of the common chemical remediation means.

[0003] Fulvic acid is a natural organic complexing agent that can react with a variety of heavy metal ions to reduce the activity and bioavailability of heavy metal ions. At the same time, potassium sulfate is an important potassium fertilizer that can provide potassium nutrition for crops and promote crop growth. However, when using potassium sulfate of fulvic acid type to control soil heavy metal pollution at present, there are problems such as how to accurately determine the application rate of potassium sulfate of fulvic acid type to ensure that heavy metal ions are effectively complexed, and at the same time avoid the content of potassium sulfate in the soil being too high or too low, which affects crop growth and soil environment. In addition, the existing methods do not fully consider the synergistic effect of soil nutrient requirements and heavy metal pollution control, resulting in possible imbalance of soil nutrients while controlling heavy metal pollution. Summary of the Invention

[0004] To solve the above technical problems, the present invention is achieved through the following technical solutions: First aspect, a heavy metal pollution control method based on potassium sulfate of fulvic acid type is proposed, including: S1: Obtain the types of heavy metal ions in the soil, the content of each heavy metal ion, and the complexation ratio of each heavy metal ion to fulvic acid; S2: According to the content of each heavy metal ion and the corresponding complexation ratio, obtain the fulvic acid demand corresponding to the complete complexation of all heavy metal ions in the soil; S3: According to the fulvic acid demand and the content of fulvic acid in the potassium sulfate fertilizer of fulvic acid type, obtain the spreading amount of the potassium sulfate fertilizer of fulvic acid type; S4: Spread the potassium sulfate fertilizer of fulvic acid type evenly on the soil according to the spreading amount, and record the current content of the potassium sulfate fertilizer of fulvic acid type in the soil; S5: Obtain the residual amount of each heavy metal ion in the soil after reaching the complexation equilibrium with fulvic acid; S6: Execute S7 for each heavy metal ion; S7: Judge whether the residual amount is greater than the screening value of agricultural land soil pollution risk. If so, add a risk label to the heavy metal ion and execute S8. Otherwise, execute S9; S8: According to the residual amount of each heavy metal ion with a risk label and the corresponding complexation ratio, obtain the fulvic acid demand corresponding to the complete complexation of all heavy metal ions with risk labels in the soil, and return to S3; S9: Obtain the current content of potassium sulfate in the soil according to the current content of the potassium sulfate fertilizer of fulvic acid type; S10: Judge whether the current content of potassium sulfate falls within the required range. If so, end the current heavy metal pollution control. Otherwise, adjust the soil nutrients according to the current content of potassium sulfate.

[0005] Further, the heavy metal pollution control method further includes: S11: Collect a second soil sample from any sampling unit, and extract various complexes and various components from the second soil sample; the components include: minerals and organic matter; S12: Extract the initial concentration of each heavy metal ion and the initial concentration of each ligand from any first soil sample; S13: Obtain the decomposition time of each complex; S14: Extract the maximum crop waiting time from the decomposition times of various complexes; S15: After the waiting time, return to S1.

[0006] In a second aspect, a heavy metal pollution control system based on potassium sulfate of fulvic acid type is proposed, including: a central processing unit, a first soil detection device, a fertilizer spreading device and a soil improvement device; the central processing unit is respectively connected to the first soil detection device, the fertilizer spreading device and the soil improvement device; the first soil detection device is used to obtain the types of heavy metal ions in the soil and the content of each heavy metal ion; the central processing unit includes: a data acquisition module, which is used to obtain the complexation ratio of each heavy metal ion and fulvic acid; a first data processing module, which obtains the fulvic acid demand corresponding to the complete complexation of all heavy metal ions in the soil according to the content of each heavy metal ion and the corresponding complexation ratio; a second data processing module, which is used to obtain the spreading amount of potassium sulfate of fulvic acid type according to the fulvic acid demand and the content of fulvic acid in potassium sulfate of fulvic acid type; the fertilizer spreading device is used to evenly spread potassium sulfate of fulvic acid type on the soil according to the spreading amount; the central processing unit further includes: a data recording module, which is used to record the current content of potassium sulfate of fulvic acid type in the soil; the first soil detection device is also used to obtain the residual amount of each heavy metal ion in the soil after reaching the complexation equilibrium with fulvic acid; the central processing unit further includes: a first function call module, which is used to call the first analysis and control module to work for each heavy metal ion; the first analysis and control module is used to judge whether the residual amount is greater than the screening value of agricultural land soil pollution risk. If so, it controls the label adding module and the second analysis and control module to work. Otherwise, it controls the third data processing module to work; the label adding module is used to add a risk label to the heavy metal ion; the second analysis and control module is used to obtain the fulvic acid demand corresponding to the complete complexation of all heavy metal ions with risk labels in the soil according to the residual amount of each heavy metal ion with a risk label and the corresponding complexation ratio, and sequentially controls the second data processing module, the fertilizer spreading device, the data recording module, the first soil detection device, the first analysis and control module and the label adding module to work; the third data processing module is used to obtain the current content of potassium sulfate in the soil according to the current content of potassium sulfate of fulvic acid type; the third analysis and control module is used to judge whether the content of potassium sulfate falls within the required range. If so, the current heavy metal pollution control is ended. Otherwise, it controls the soil improvement device to work; the soil improvement device is used to adjust the soil nutrients according to the current content of potassium sulfate.

[0007] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. By the types, contents and complexing ratios of heavy metal ions in the soil, the application rate of the fulvic acid type potassium sulfate fertilizer is obtained to ensure that the heavy metal ions are effectively complexed. At the same time, the effects of the contents of potassium ions and sulfate ions in the soil under complexing equilibrium on soil crops are considered. Combining risk screening values and residual amount analysis, soil nutrient regulation is carried out to avoid affecting crop growth due to improper potassium sulfate content, realizing the coordinated treatment of heavy metal pollution control and soil nutrient balance. Through multiple cycles of adjusting the application rate and nutrient regulation, the effect of heavy metal pollution control and the stability of the soil environment are improved.

[0008] 2. Considering the secondary damage caused by heavy metal ions to the environment after the decomposition of the complex, the decomposition time is obtained through the prediction of complex decomposition, and the heavy metal ions are controlled regularly according to the decomposition time to prevent the reactivation of heavy metal ions. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, form a part of this application, and do not limit the embodiments of the present invention. In the drawings: Figure 1 It is a schematic flowchart of a method for controlling heavy metal pollution based on fulvic acid type potassium sulfate provided in Embodiment 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0010] To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments. The illustrative embodiments and descriptions thereof of the present invention are only used to explain the present invention and are not intended to limit the present invention. The following described embodiments are some embodiments of the present invention, not all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0011] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it is obvious to those of ordinary skill in the art that: the present invention does not have to employ these specific details. In other embodiments, well-known structures, materials or methods are not specifically described to avoid obscuring the present invention. The materials, instruments and reagents used in the following embodiments can be obtained from commercial sources unless otherwise specified. The technical means used in the embodiments are conventional means well-known to those skilled in the art unless otherwise specified.

[0012] In addition, the terms "first" and "second" are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of this application, "a plurality" means two or more unless otherwise specifically defined.

[0013] Example 1: A method for controlling heavy metal pollution based on fulvic acid potassium sulfate is proposed, including Figure 1 the following steps shown: S1: Obtain the types of heavy metal ions in the soil, the content of each heavy metal ion, and the complexation ratio of each heavy metal ion with fulvic acid.

[0014] S2: According to the content of each heavy metal ion and the corresponding complexation ratio, obtain the fulvic acid demand corresponding to the complete complexation of all heavy metal ions in the soil.

[0015] S3: According to the fulvic acid demand and the content of fulvic acid in the fulvic acid potassium sulfate fertilizer, obtain the application rate of the fulvic acid potassium sulfate fertilizer.

[0016] The following is an explanation of S1 to S3: Fulvic acid potassium sulfate is a new type of high-efficiency fertilizer, which takes potassium sulfate as the main component and adds fulvic acid or potassium fulvate. Among them, fulvic acid has a complex functional group structure, such as carboxyl group, hydroxyl group, etc. These functional groups can adsorb and complex with heavy metal ions, fix the heavy metal ions in the soil, reduce their activity and mobility in the soil solution, and thus reduce the possibility of heavy metals being absorbed by crops. Potassium sulfate can provide potassium and sulfur elements for crops, promote the growth and development of crops, enhance the stress resistance of crops, and improve the quality of crops.

[0017] The purpose of this method is to control heavy metal pollution by applying fulvic acid potassium sulfate fertilizer to the soil and using the fulvic acid in it to complex with heavy metal ions in the soil. However, if the applied fulvic acid potassium sulfate fertilizer is excessive, it will cause soil compaction and antagonism among various nutrients in the soil. If the applied fulvic acid potassium sulfate fertilizer is insufficient, it will lead to the residue of heavy metal ions in the soil and fail to achieve a good heavy metal control effect. Therefore, it is necessary to accurately control the amount of fulvic acid potassium sulfate fertilizer applied to the soil. This method is achieved by reverse deduction, and the specific implementation method is as follows: First, obtain the types of heavy metal ions in the soil, the content of each heavy metal ion, and the complexation ratio of each heavy metal ion with fulvic acid.

[0018] Determining the content of different heavy metal ions in the soil and their complexation ratios with fulvic acid is a prerequisite for accurately calculating the amount of fulvic acid required to completely complex all heavy metal ions. For example, if the soil contains lead ions and cadmium ions, with the lead ion content being X mol and its complexation ratio with fulvic acid being 1:1, and the cadmium ion content being Y mol with a complexation ratio of 1:2, then based on these data, it is possible to accurately calculate that X mol and 2Y mol of fulvic acid are required to complex lead ions and cadmium ions respectively, and further obtain the fulvic acid demand corresponding to the complete complexation of all heavy metal ions in the soil. This method uses experimental determination to obtain the types of heavy metal ions in the soil and the content of each type of heavy metal ion. The specific steps are as follows: S1.1: Divide the target area into multiple sampling units.

[0019] The 3D radar scan image of the target area can be obtained by radar scanning and imported into image processing software (QGIS or ArcGISPro). Use the image processing software to convert its 3D radar scan image into a raster format. Crop the corresponding part of the target area from the format-converted 3D radar scan image. The target area refers to the area where the soil to be controlled for heavy metal pollution is located. In the image processing software, use the "Create Grid" tool to generate a regular grid, and set the size of the grid according to actual needs (for example, 10m×10m), with one grid corresponding to one sampling unit. Crop the generated grid within the boundaries of the target area.

[0020] S1.2: Obtain the coverage area and average soil thickness of each sampling unit.

[0021] (1) Calculate the coverage area Extract the elevation information of the soil surface from the 3D radar scan image (which can be completed through a raster calculator, for example, using the "Raster Calculator" tool in QGIS). For each grid, calculate its projected area on the horizontal plane (in QGIS, a new field can be added using the "Field Calculator" to store the area of each grid).

[0022] (2) Calculate the average soil thickness Extract the soil depth information from the 3D radar scan image (which can be completed through a raster calculator, for example, using the "Raster Calculator" tool in QGIS). For each grid, calculate the average value of the soil depths of all pixel points within it (in QGIS, the "Raster Statistics" tool can be used to calculate the average value of each grid).

[0023] S1.3: Collect a first soil sample from each sampling unit and detect the soil density of each first soil sample.

[0024] (1) Collect soil samples Soil samples can be collected using a soil auger or shovel. Put the collected soil samples into sampling bags and record the sampling point numbers.

[0025] (2)Detect soil density Place the collected soil samples in the laboratory in the order of their numbers. Put the soil samples into a drying oven, set the temperature to 105 - 110 °C, and dry for 24 hours to remove the moisture in the soil. Grind the dried soil samples into fine powder and sieve through a 2 - millimeter sieve to remove larger particles and impurities. Use a balance to weigh the mass of the sieved soil samples and record the mass of each sample. Insert a core cutter vertically into the soil to collect a complete soil columnar sample, ensuring that the soil in the core cutter is compact and void - free. Weigh the core cutter and the soil together and record the total mass M1. Take out the soil in the core cutter and weigh the mass of the empty core cutter M2. Calculate the mass of the soil M = M1−M2. The soil density ρ = VM, where V is the volume of the core cutter (100 cubic centimeters).

[0026] S1.4: Extract the types of heavy metal ions and analyze the heavy metal ion content in each first soil sample to obtain the test data of each first soil sample.

[0027] Among them, the test data includes: the amount of substance of each heavy metal ion in the soil per unit mass.

[0028] The specific implementation of S1.4 is detailed in steps A1 to A3.

[0029] Step A1: Extract the heavy metal ions in the first soil sample into the solution.

[0030] Use acid extraction method to extract heavy metal ions - accurately weigh a certain amount of dry soil sample (such as 1.0 gram) using a balance. Put the weighed soil sample into a beaker and add an appropriate amount of extractant (such as 10 milliliters of aqua regia or nitric acid). Place the beaker on a hot plate and slowly heat it to gentle boiling, and maintain the gentle boiling state for about 1 hour to fully dissolve the heavy metal ions in the soil into the solution. Cool the solution to room temperature and filter it with filter paper to remove the insoluble residues.

[0031] Step A2: Determine the types of heavy metal ions in the solution and the concentration of each heavy metal ion.

[0032] Determination by atomic absorption spectrometry - Dilute the sampled extract with a diluent (such as 1% nitric acid solution) to a certain volume (such as 10 mL). Filter the diluted solution through a 0.45-micron filter membrane. Feed the diluted sample into the atomizer of the AAS through an injector to measure the intensity of light absorption at a specific wavelength, identify the types of heavy metal ions in the solution, and determine the concentration of each heavy metal in the solution. Record the wavelength and absorption intensity of each heavy metal ion. Match the detected absorption intensity with the standard curve to determine the types of heavy metal ions in the solution and the concentration of each heavy metal ion.

[0033] Step A3: Perform Steps A31 to A32 for each heavy metal ion.

[0034] Step A31: Convert the concentration to molar concentration.

[0035] Find the molar mass of the heavy metal ion. For example, the molar mass of lead (Pb) is 207.2 g / mol, and the molar mass of cadmium (Cd) is 112.4 g / mol. Convert the mass concentration (mg / L) to g / L, i.e., mass concentration (g / L) = mass concentration (mg / L) ÷ 1000. Calculate the molar concentration, i.e., molar concentration (mol / L) = mass concentration (g / L) ÷ molar mass (g / mol). For example, if the measured mass concentration of lead (Pb) in a solution is 50 mg / L and the molar mass is 207.2 g / mol, convert the mass concentration (mg / L) to g / L, i.e., mass concentration (g / L) = 50 (mg / L) ÷ 1000 = 0.05 g / L. Calculate the molar concentration, i.e., molar concentration (mol / L) = 0.05 g / L ÷ 207.2 g / mol = 0.000241 mol / L.

[0036] Step A32: Obtain the amount of substance of the heavy metal ion in the unit mass of soil based on the soil density, molar mass, and molar concentration.

[0037] The amount of substance in the unit mass of soil = C × V ÷ m. Where C is the molar concentration (mol / L), V is the volume of the solution (L), m is the mass of the soil (g / kg), V = m ÷ ρ, and ρ is the soil density (kg / m³). For example, if the soil density is 1.5 g / cm³ (or 1500 kg / m³) and the molar concentration of the heavy metal ion is 0.000241 mol / L, then the amount of substance in the unit mass of soil = 0.00024 (mol / L) ÷ 1.5 (g / cm³) = 0.00016067 mol / g.

[0038] S1.5: Obtain the amount of substance of each heavy metal ion in each sampling unit based on the detection data.

[0039] For the specific implementation of S1.5, please refer to Steps B1 to B2.

[0040] Step B1: Obtain the soil mass of the sampling unit according to the coverage area, soil density, and average soil thickness.

[0041] Step B2: Obtain the amount of substance of each heavy metal ion in the sampling unit according to the detection data and the soil mass of the sampling unit.

[0042] According to the detected amount-of-substance concentration and the soil mass of the sampling unit, calculate the total amount of substance of each heavy metal ion in the sampling unit. The calculation formula is N = C × M, where N is the total amount of substance of the heavy metal ion in the sampling unit (mol), C is the amount-of-substance concentration of the heavy metal ion (mol / kg or mol / g), and M is the soil mass of the sampling unit. For example, if the amount-of-substance concentration of the heavy metal ion C = 0.00016067 mol / g and the soil mass of the sampling unit M = 1000 g, then the total amount of substance of the heavy metal ion in the sampling unit N = 0.00016067 mol / g × 1000 g = 0.16067 mol.

[0043] S1.6: Sum up the amount of substance of each heavy metal ion in each sampling unit to obtain the content of each heavy metal ion in the soil of the target area.

[0044] Then, according to the content of each heavy metal ion and the corresponding complexation ratio, obtain the demand for fulvic acid corresponding to the complete complexation of all heavy metal ions in the soil.

[0045] The demand for fulvic acid corresponding to the complete complexation of all heavy metal ions in the soil, that is, the amount of substance of fulvic acid required for the complete complexation of all heavy metal ions in the soil, is the product of the amount of substance of the heavy metal ion and the complexation ratio.

[0046] Finally, according to the demand for fulvic acid and the content of fulvic acid in the fulvic acid type potassium sulfate fertilizer, obtain the application rate of the fulvic acid type potassium sulfate fertilizer.

[0047] The demand for fulvic acid and the content of fulvic acid in the fulvic acid type potassium sulfate fertilizer refer to the mass percentage of fulvic acid in the fulvic acid type potassium sulfate fertilizer. On the premise of calculating the demand for fulvic acid, the application rate of the fulvic acid type potassium sulfate fertilizer = demand for fulvic acid ÷ mass percentage.

[0048] Through the above S1 to S3, the amount of fulvic acid type potassium sulfate fertilizer that needs to be applied theoretically for the complete complexation of all heavy metal ions in the soil can be accurately calculated. On this basis, perform the following steps: S4: Evenly spread the fulvic acid type potassium sulfate fertilizer in the soil according to the application rate, and record the current content of the fulvic acid type potassium sulfate fertilizer in the soil.

[0049] After S4, fulvic acid begins to undergo complexation reactions with various heavy metal ions in the soil. However, the application rate of fulvic acid-based potassium sulfate fertilizer calculated through S1 to S3 is a theoretical value. On the one hand, the complexation reaction is a reversible process that follows the principle of chemical equilibrium. According to Le Chatelier's principle, even if the amount of fulvic acid is increased, the equilibrium can only shift in the direction of forming complexes, but it cannot completely convert heavy metal ions into complexes, and there will inevitably be a certain amount of heavy metal ions remaining. On the other hand, due to the complex structure system of the soil, components such as minerals and organic matter in the soil will compete with heavy metal ions for the complexation sites of fulvic acid. For example, clay minerals in the soil have a charged surface and can adsorb heavy metal ions. After some heavy metal ions are adsorbed by clay minerals, it is difficult for them to come into full contact with fulvic acid to undergo complexation reactions, resulting in the remaining of some heavy metal ions. Moreover, conditions such as the soil pH and redox potential will also affect the progress of the complexation reaction. In acidic soils, the hydrogen ion concentration is relatively high, which will compete with heavy metal ions for the active groups on fulvic acid, inhibiting the complexation reaction and causing more heavy metal ions to remain. Therefore, after S1 to S4, the heavy metal ions in the soil cannot be completely complexed, and the heavy metal ions in the soil need to be further controlled through the following steps. Specifically as follows: S5: Obtain the residual amount of each heavy metal ion in the soil after reaching complexation equilibrium with fulvic acid.

[0050] This method predicts the residual amount of each heavy metal ion in the soil after reaching complexation equilibrium with fulvic acid through experimental detection and numerical fitting. Specifically, it includes the following steps: S5.1: Extract a unit mass of soil sub-samples from each first soil sample.

[0051] S5.2: According to the detection data and the corresponding complexation ratio, obtain the amount of fulvic acid added corresponding to the complete complexation of all heavy metal ions in each soil sub-sample.

[0052] The amount of fulvic acid added in this step refers to the amount of fulvic acid required to completely complex all heavy metal ions in a unit mass of soil sub-sample. Since the detection data includes the amount of substance of each heavy metal ion in the unit mass of soil, by multiplying the amount of substance of each heavy metal ion in the unit mass of soil by the corresponding complexation ratio, the amount of fulvic acid added corresponding to the complete complexation of all heavy metal ions in each soil sub-sample can be obtained.

[0053] S5.3: According to the amount of fulvic acid added and the content of fulvic acid in the fulvic acid-based potassium sulfate fertilizer, obtain the application rate of the fulvic acid-based potassium sulfate fertilizer.

[0054] Refer to S3.

[0055] S5.4: Set multiple test time points.

[0056] Experimentally determine the time required for the complexation reaction between different heavy metal ions (such as lead, cadmium, copper, zinc, etc.) and fulvic acid to reach equilibrium and the residual amount respectively. Set multiple test time points, such as 15 minutes, 30 minutes, 1 hour, 2 hours, 4 hours, 8 hours, 12 hours, 24 hours, etc. Measure the amount of heavy metal ions at each test time point until the amount of heavy metal ions no longer changes. The corresponding time is the maximum duration of the complexation reaction, and the finally measured concentration of the heavy metal ions is the residual amount.

[0057] S5.5: Obtain the residual amount of each heavy metal ion in each soil subsample.

[0058] For the specific implementation of S5.5, see Steps C1 to C3 for details.

[0059] Step C1: Mix the soil subsample and fulvic acid type potassium sulfate fertilizer in an amount equal to the addition amount evenly in a reaction dish.

[0060] Step C2: At each test time point, measure and record the concentration of each heavy metal ion in the reaction dish.

[0061] Refer to Step A2.

[0062] Step C3: Use time as the abscissa and the concentration of heavy metal ions as the ordinate to plot the complexation reaction curve of each heavy metal ion.

[0063] Organize the concentration data of each heavy metal ion measured at different time points and establish a data table. The first column of the table records the time, and each subsequent column corresponds to the concentration data of a heavy metal ion. Use professional drawing software (such as Origin, Excel, etc.) to establish a coordinate system with time as the abscissa and the concentration of heavy metal ions as the ordinate. Plot the organized data in the form of scatter points in the coordinate system, where the concentration of heavy metal ions corresponding to each time point is a scatter point. Use the curve fitting function of the drawing software or manually draw a curve to connect the scatter points into a smooth curve.

[0064] Step C4: Obtain the ordinate corresponding to the point with a slope of zero on the complexation reaction curve of each heavy metal ion to obtain the residual amount of each heavy metal ion.

[0065] In the initial stage of the reaction, due to the high concentrations of fulvic acid and heavy metal ions, the reaction proceeds rapidly in the direction of forming complexes. At this time, the concentration of heavy metal ions decreases rapidly, and the slope of the complexation reaction curve is relatively large. As the reaction continues, fulvic acid and heavy metal ions continuously combine to form complexes, their concentrations gradually decrease, the reaction rate also gradually slows down, and the slope of the curve gradually becomes smaller. When the reaction reaches equilibrium, the rate of the forward reaction is equal to the rate of the reverse reaction, and the concentrations of all substances in the system no longer change. At this time, the slope of the complexation reaction curve becomes zero. Therefore, the ordinate corresponding to the point with a slope of zero on the complexation reaction curve is the concentration of the heavy metal ion after the complexation reaction reaches equilibrium.

[0066] S5.6: Obtain the residual amount of each heavy metal ion in each sampling unit according to the soil quality of the sampling unit and the residual amount of each heavy metal ion in the soil sub-samples.

[0067] Refer to step B2.

[0068] S5.7: Sum up the residual amounts of each heavy metal ion in each sampling unit to obtain the residual amount of each heavy metal ion in the soil of the target area after reaching complexation equilibrium with fulvic acid.

[0069] Refer to S1.6.

[0070] S6: Execute S7 for each heavy metal ion.

[0071] S7: Determine whether the residual amount is greater than the screening value of the agricultural land soil pollution risk. If so, add a risk label to the heavy metal ion and execute S8; otherwise, execute S9.

[0072] China has clear reference standards for whether the heavy metal content in the soil exceeds the standard, mainly based on the "Soil Environmental Quality Risk Control Standards for Agricultural Land (Trial)" (GB15618-2018). When the heavy metal content in the soil is equal to or lower than the risk screening value, the soil pollution risk is low; when the heavy metal content in the soil is higher than the risk screening value but lower than the risk control value, there may be a soil pollution risk; when the heavy metal content in the soil is higher than the risk control value, safety utilization measures should generally be taken. According to the above reference standards, only when the heavy metal content in the soil is less than or equal to the screening value of the agricultural land soil pollution risk can it be determined that the heavy metal content in the soil meets the standard. Therefore, in this method, the residual amount of each heavy metal ion is compared with the corresponding screening value of the agricultural land soil pollution risk to determine whether the residual amount is greater than the screening value of the agricultural land soil pollution risk. If so, a risk label is added to the heavy metal ion, and the content of the heavy metal ion with the risk label exceeds the standard. Then execute S8.

[0073] S8: Obtain the demand for fulvic acid corresponding to the complete complexation of all heavy metal ions with risk labels in the soil based on the residual amount of each heavy metal ion with a risk label and the corresponding complexation ratio, and return to S3.

[0074] The purpose of this step is to obtain the amount of fulvic acid theoretically required for the complete complexation of each heavy metal ion with an excessive content in the soil, that is, the amount of fulvic acid that needs to be further added to the soil. After obtaining the amount of fulvic acid that needs to be further added, the fulvic acid and potassium sulfate are further spread according to the above method to control the content of heavy metal ions in the soil, and to detect whether the content of heavy metal ions in the soil exceeds the standard after further implementing the control measures. This cycle continues until the content of heavy metal ions in the soil reaches the national standard.

[0075] S9: Obtain the current content of potassium sulfate in the soil based on the current content of fulvic acid-type potassium sulfate.

[0076] After S7 and S8, the residual amount of each heavy metal ion in the soil is less than or equal to the screening value of agricultural land soil pollution risk, indicating that the heavy metal content in the soil has reached the national standard at this time. However, after multiple additions of fulvic acid-type potassium sulfate, it is possible that the content of potassium sulfate in the soil is still insufficient or the content of potassium sulfate in the soil has exceeded the limit. Whether the content of potassium sulfate in the soil is insufficient or exceeds the standard may have a series of adverse effects on the soil environment and crop growth. For example: (1) Sulfate ions (SO4²⁻) react with water in the soil to form sulfuric acid (H2SO4), resulting in soil acidification; (2) Excessive sulfur elements will have an antagonistic effect with other nutrients (such as calcium, magnesium, potassium, etc.), affecting the absorption of these nutrients by crops. Insufficient sulfur elements in the soil may lead to insufficient sulfur supply for plants, affecting the growth and development of plants. Furthermore, excessive potassium and sulfur elements in the soil will also have adverse effects on crop growth and soil health. For example: (1) Excessive potassium in the soil will have an ion antagonistic effect with other cations (such as calcium, magnesium, etc.), affecting the absorption of these elements by crops, resulting in symptoms of deficiency of elements such as calcium and magnesium in crops. (2) Insufficient potassium in the soil affects crop growth. Therefore, it is necessary to obtain the current content of potassium sulfate in the soil and further judge whether the current content of potassium sulfate meets the requirements of crop growth.

[0077] S10: Judge whether the current content of potassium sulfate falls within the demand range. If so, end the current heavy metal pollution control. Otherwise, adjust the soil nutrients according to the current content of potassium sulfate.

[0078] The required range refers to the adaptation range of the potassium sulfate demand in the soil for crops at different growth stages. If the current content of potassium sulfate falls within the required range, it indicates that the nutrient components in the soil are suitable for the growth of crops. Otherwise, it is necessary to adjust the soil nutrients according to the current content of potassium sulfate. It should be noted that the premise of S10 is that after S7 and S8, the heavy metal ions in the soil have reached the national detection standard through complexation reactions.

[0079] Regarding how to adjust the soil nutrients according to the current content of potassium sulfate, first, it is necessary to know the amount of potassium element and sulfur element required for the normal growth of crops, corresponding to the amount of potassium ions and sulfate ions required for crop growth. This method is realized by using the QUEFTS model for simulation. The QUEFTS model, namely the quantitative evaluation model of soil fertility, can predict crop yields by analyzing soil chemical characteristics and crop fertilizer requirements, and then evaluate soil fertility and guide fertilization decisions. Using the QUEFTS model to simulate the demand ranges of potassium ions and sulfate ions for crops at different stages, the specific implementation method is to perform the following steps before S10: Obtain multiple potassium ion demands and multiple sulfate ion demands of crops at each growth stage. Specifically, it includes steps D1 to D4.

[0080] Step D1: Determine the physical and chemical characteristic parameters of the first soil sample.

[0081] Among them, the physical and chemical characteristic parameters include: initial potassium ion content, initial sulfate ion content, contents of various macronutrients, contents of various micronutrients, pH value, redox potential, cation exchange capacity, and organic matter content. These data are the basis for understanding the soil fertility status and can provide a basis for calculating the amount of potassium ions and sulfate ions that crops can absorb in the subsequent steps.

[0082] The potentiometric method can be used to measure the soil pH value to understand the soil acidity and alkalinity, providing a basis for reasonable fertilization and soil improvement. To measure the soil organic matter content, the potassium dichromate oxidation method can be used. Organic matter affects soil fertility, fertilizer retention and water retention capacity, and microbial activity. Analyze the soil nutrient content, including macronutrients (nitrogen, phosphorus) and micronutrients (iron, zinc, manganese, etc.). Among them, the Kjeldahl method is used to measure the total nitrogen content; the sodium bicarbonate extraction-molybdenum antimony anti-colorimetric method is used to measure the available phosphorus. When analyzing micronutrients, atomic absorption spectrometry, inductively coupled plasma mass spectrometry, etc. are commonly used.

[0083] Step D2: Obtain the growth characteristic parameters and ion absorption characteristic parameters of crops through web crawlers.

[0084] Among them, the growth characteristic parameters include: the growth duration of each growth stage and the growth rate of each growth stage; the ion absorption characteristic parameters include: the potassium ion absorption rate, the potassium ion accumulation amount, the sulfate ion absorption rate, and the sulfate ion accumulation amount. These characteristic parameters help to clarify the demand characteristics of the target crop for potassium element at different growth stages. For example, for some crops, the demand for potassium in the early growth stage is mainly used for the growth of roots and stems and leaves, while in the later stage, it is more used for the development of fruits or grains.

[0085] The data sources of web crawlers can be websites of agricultural research institutions, where research results on crop planting and growth are published, including detailed data on various growth stages of crops. For example, the websites of relevant research institutes of the Chinese Academy of Agricultural Sciences have published research reports on a variety of crops, covering crop growth characteristic parameters. Academic databases such as CNKI and Web of Science have collected a large number of academic literatures in the agricultural field, including research papers on crop growth and element absorption. Key parameters can be extracted from them through crawlers.

[0086] In addition, crop growth characteristic parameters can also be obtained through direct measurement methods (using tools such as rulers and calipers to directly measure morphological indicators such as the plant height, stem diameter, leaf length, and leaf width of crops), image analysis methods (using cameras or other imaging devices to obtain images of crops, and analyzing the morphological characteristics of crops through image processing software, such as canopy width, plant height, leaf number, leaf area index, etc.), sensor monitoring methods (using sensors to monitor the physiological state and environmental parameters of crops, and then obtaining relevant growth characteristic parameters), etc. And ion absorption characteristic parameters of crops can be obtained through solution culture methods (planting crops in nutrient solutions containing known concentrations of ions, and calculating the ion absorption amount of crops by regularly measuring the changes in ion concentrations in the nutrient solutions), ion selective electrode methods (using ion selective electrodes to measure the activity or concentration of specific ions in solutions), isotope tracer methods (using radioactively or stably isotope-labeled ions, adding them to the environment where crops grow, and then studying the absorption, transportation, and distribution laws of ions by crops by detecting the absorption, distribution, and accumulation of isotopes in different parts of crops), etc.

[0087] Step D3: Set the target yield and climate parameters.

[0088] Among them, the target yield is determined according to actual needs. The climate parameters include: temperature, precipitation, and sunshine duration, which are determined according to the actual local climate conditions.

[0089] Step D4: Use the QUEFTS model to analyze the physical and chemical characteristic parameters, growth characteristic parameters, ion absorption characteristic parameters, target yield, and climate parameters to obtain the potassium ion demand and sulfate ion demand of the crop at each growth stage.

[0090] The QUEFTS model, based on a large amount of experimental data and theoretical research, establishes a mathematical relationship among soil parameters, crop growth stages, yield targets, and potassium element uptake. By inputting physical and chemical characteristic parameters, growth characteristic parameters, ion uptake characteristic parameters, target yield, and climate parameters into the QUEFTS model, the QUEFTS model calculates the input data and outputs the uptake amounts of potassium ions and sulfate ions by the crop at each stage.

[0091] Extract the maximum and minimum values from multiple potassium ion demand amounts to obtain the demand range of potassium ions; extract the maximum and minimum values from multiple sulfate ion demand amounts to obtain the demand range of sulfate ions.

[0092] On the basis of obtaining the amounts of potassium ions and sulfate ions required for crop growth, S10 then judges whether the current content of potassium ions and the current content of sulfate ions in the soil meet the normal growth requirements of the crop based on the demand amounts of potassium ions and sulfate ions. If it is excessive or insufficient, the nutrients in the soil are adjusted accordingly to meet the crop growth requirements. The specific method is as follows: S10.1: Obtain the current content of potassium ions according to the current content of potassium sulfate and the proportion of potassium ions in potassium sulfate; obtain the current content of sulfate ions according to the current content of potassium sulfate and the proportion of sulfate ions in potassium sulfate.

[0093] S10.2: Judge whether both the current content of potassium ions and the current content of sulfate ions fall within the corresponding demand ranges. If so, end the current heavy metal pollution control. Otherwise, add fertilizers or ion exchange resins according to the potassium ion content and sulfate ion content.

[0094] Specifically, it includes the following steps: S10.2.1: Judge whether both the current content of potassium ions and the current content of sulfate ions fall within the corresponding demand ranges. If so, end the current heavy metal pollution control. Otherwise, judge whether both the current content of potassium ions and the current content of sulfate ions do not fall within the demand range of potassium ions. If so, execute S10.2.2 to S10.2.3. Otherwise, judge whether the current content of potassium ions does not fall within the demand range of potassium ions. If so, execute S10.2.4. Otherwise, execute S10.2.5.

[0095] S10.2.2: Judge whether the current content of potassium ions is on the left side of the demand range. If so, add potassium fertilizer to the soil according to the current content of potassium ions. Otherwise, add cation exchange resin to the soil according to the current content of potassium ions.

[0096] S10.2.3: Determine whether the current content of sulfate ions is on the left side of the required range. If so, add sulfate fertilizer to the soil according to the current content of sulfate ions; otherwise, add anion exchange resin to the soil according to the current content of sulfate ions.

[0097] S10.2.4: Execute S10.2.1.

[0098] S10.2.5: Execute S10.2.2.

[0099] It should be noted that: (1) If the current contents of potassium ions and sulfate ions both fall within the corresponding required ranges, it means that the current contents of potassium ions and sulfate ions in the soil both meet the requirements for normal growth, and there will be no shortage of potassium ions affecting crop growth or excess potassium ions causing ion antagonism with other cations in the soil. Nor will there be a shortage of sulfate ion content leading to insufficient sulfur supply for plants or excess sulfate ions causing soil acidification and antagonism with other nutrients. At this time, the heavy metal ions in the soil have undergone a complexation reaction with fulvic acid, and the content has reached the national detection standard, and both the potassium ion content and the sulfate ion content meet the requirements for normal crop growth. Then, the coordination of soil nutrient requirements and heavy metal pollution control is achieved, and while completing heavy metal pollution control, normal crop growth is ensured. (2) If the current contents of potassium ions and sulfate ions do not both fall within the corresponding required ranges, then three situations occur. The first situation is that the current contents of both potassium ions and sulfate ions do not fall within the corresponding required ranges; the second situation is that the current content of potassium ions does not fall within the corresponding required range, while the current content of sulfate ions falls within the corresponding required range; the third situation is that the current content of potassium ions falls within the corresponding required range, while the current content of sulfate ions does not fall within the corresponding required range. The three situations need to be judged separately.

[0100] Furthermore, for the first situation, if the current contents of both potassium ions and sulfate ions do not fall within the corresponding required ranges, it is necessary to further determine whether the current content of potassium ions is insufficient (on the left side of the required range) or whether the current content of potassium ions is excessive (on the right side of the required range), that is, corresponding to the second situation above; and determine whether the current content of sulfate ions is insufficient (on the left side of the required range) or whether the current content of sulfate ions is excessive (on the right side of the required range), that is, corresponding to the third situation above.

[0101] Furthermore, for the situation where the current content of potassium ions is insufficient, potassium fertilizer needs to be added to the soil according to the current content of potassium ions. The addition amount of potassium fertilizer can be determined with reference to the following method: First, obtain the first difference between the current potassium ion content and the lower limit of the demand range, and obtain the second difference between the current potassium ion content and the upper limit of the demand range.

[0102] Then, determine the potassium ion supplementation amount according to the first difference and the second difference. For example, the potassium ion supplementation amount = (the first difference + the second difference) ÷ 2. The purpose is to make the current potassium ion content after supplementation fall within the corresponding demand range.

[0103] Finally, determine the amount of potassium fertilizer to be supplemented according to the potassium ion supplementation amount and the proportion of potassium ions in the potassium fertilizer.

[0104] Furthermore, for the case where the current potassium ion content is excessive, cation exchange resin needs to be added to the soil according to the current potassium ion content. The cation exchange resin is used to adsorb potassium ions in the soil and reduce its antagonistic effect on other cations. The addition amount of the cation exchange resin can be determined with reference to the following method: First, obtain the potassium ion absorption amount according to the first difference and the second difference. For example, the potassium ion absorption amount = (the first difference + the second difference) ÷ 2. The purpose is to make the current potassium ion content after absorption fall within the corresponding demand range.

[0105] Then, obtain the adsorption efficiency of the cation exchange resin for potassium ions through a web crawler.

[0106] Finally, calculate the addition amount of the cation exchange resin according to the formula R = K × M ÷ E. Wherein, R represents the addition amount of the cation exchange resin, K represents the amount of potassium ions to be absorbed per unit mass of soil, M represents the soil mass, and E represents the absorption efficiency of the cation exchange resin for potassium ions.

[0107] Furthermore, for the case where the current sulfate ion content is insufficient, sulfate fertilizer needs to be added to the soil according to the current sulfate ion content. The addition amount of the sulfate fertilizer can refer to the method for determining the addition amount of the above potassium fertilizer.

[0108] Furthermore, for the case where the current sulfate ion content is excessive, anion exchange resin needs to be added to the soil according to the current sulfate ion content. The anion exchange resin is used to adsorb sulfate ions in the soil. The anion exchange resin is a kind of polymer material with ion exchange function, which can adsorb and exchange anions. The addition amount of the anion exchange resin can refer to the method for determining the addition amount of the above cation exchange resin.

[0109] Up to the above S1 to S10, the control of heavy metal pollution is completed, and the synergy between soil nutrient requirements and heavy metal pollution control is achieved. However, under the conditions of soil environment (acidity and alkalinity, redox potential and temperature), microbial action and competition of other substances, the complexes in the soil will decompose into heavy metal ions, ligands and new compounds. After decomposition, the heavy metal ions will be released back into the soil, causing secondary pollution. Therefore, after S10, it is also necessary to detect the content of heavy metal ions within a specified time. If the content of heavy metal ions exceeds the national detection standard, the heavy metal pollution control needs to be carried out according to the methods of S1 to S10. This method uses a model simulation method to detect the content of heavy metal ions in the soil after the decomposition of the complex. The specific method is as follows: S11: Collect a second soil sample from any sampling unit, and extract various complexes and various components from the second soil sample.

[0110] The components refer to various minerals and various organic matters in the soil.

[0111] (1) Complex extraction The complexes are extracted by the chemical reagent extraction method. Use 0.05mol / L EDTA (ethylenediaminetetraacetic acid) solution as the extractant. Put the second soil sample into a conical flask, add the EDTA solution according to the ratio of soil to extractant of 1:5 - 1:10 (mass ratio), then place the conical flask on an oscillator and oscillate for 1 - 3 hours at a certain temperature (such as 25°C) and oscillation speed (such as 150 - 200r / min). After oscillation, centrifuge the sample (usually centrifuge at a speed of 3000 - 5000r / min for 10 - 15 minutes), take the supernatant to obtain an extract containing metal-organic complexes. For some specific complexes, chelating agents can also be used for extraction, such as DTPA (diethylenetriaminepentaacetic acid) for extracting available zinc, iron, manganese and other metal complexes in the soil.

[0112] (2) Mineral extraction The minerals are extracted by the acid dissolution method. Put the second soil sample into a polytetrafluoroethylene crucible, add hydrofluoric acid and perchloric acid, and heat it at a low temperature on a hot plate (the starting temperature is about 100 - 120°C) to carbonize and decompose the organic matter in the soil, then gradually raise the temperature to 200 - 250°C until white smoke of perchloric acid appears and the soil is completely digested. After cooling, dissolve the residue with dilute hydrochloric acid and transfer it to a volumetric flask for volume fixation to obtain a solution containing mineral components. For the types and contents of minerals in the solution, the atomic absorption spectrometry can also be used, referring to the operation methods of step A2 or step D2 above, which will not be elaborated here.

[0113] (3) Organic matter extraction Organic matter was extracted by potassium dichromate oxidation method. The second soil sample was placed in a test tube, potassium dichromate solution and concentrated sulfuric acid of known concentration were added, and heated to boil in an oil bath at 170-180°C for 5 minutes. After the test tube was cooled, the solution was transferred to a conical flask. The remaining potassium dichromate was titrated with ammonium ferrous sulfate standard solution, and ferrochlore was used as an indicator. The end point of the titration was when the color of the solution changed from orange-yellow to blue-green to brick red. The volume of ammonium ferrous sulfate standard solution consumed was recorded, and the content of organic matter in the solution was calculated based on the blank test (same operation but without adding solution sample) and sample titration data.

[0114] S12: extracting the initial concentration of each heavy metal ion and the initial concentration of each ligand from any first soil sample.

[0115] Refer to step A2 or step D2.

[0116] S13: Obtain the decomposition time of each complex.

[0117] The specific implementation of S13 is detailed in S13.1 to S13.3.

[0118] S13.1: Obtain the thermodynamic characteristic parameters of the complex and the interaction parameters of the complex with each component through web crawlers.

[0119] Among them, thermodynamic parameters include: composition, structure, stability constant and dissociation constant.

[0120] The interaction parameters reflect the degree to which two or more substances deviate from the ideal state when interacting, and can help scientists more accurately understand and predict the behavior of substances in complex systems. For example, when studying the interaction between complexes and soil, the interaction parameters can reflect the combined influence of factors such as the strength of the binding between the complex and the soil mineral surface, organic matter, etc., the affinity, and steric hindrance. The interaction parameters between the complex and each component include: thermodynamic interaction parameters, kinetic interaction parameters, and structural interaction parameters.

[0121] The data source of web crawlers can be academic databases, such as Web of Science, CNKI, etc., which include many research papers in the fields of chemistry and materials science, including a large number of thermodynamic parameters of complexes and related parameter data such as the interaction between various components in the soil. In addition, professional chemical websites, such as the official website of the American Chemical Society (ACS) and the official website of the German Chemical Society (GDCh), also publish chemical data information.

[0122] In addition, thermodynamic characteristic parameters and interaction parameters between the complex and each component can also be determined by experimental methods such as calorimetry (obtaining thermodynamic parameters by measuring the heat change during the complexation reaction) and spectroscopy (studying the structure and composition of the complex using spectroscopic techniques to obtain thermodynamic parameters).

[0123] S13.2: Analyze the physical and chemical characteristic parameters of the soil, the initial concentration of each heavy metal ion, the initial concentration of each ligand, the thermodynamic characteristic parameters of the complex, and the interaction parameters between the complex and each component using the PHREEQC model to obtain the decomposition curve of the complex concentration over time.

[0124] PHREEQC comes with a variety of thermodynamic databases, such as phreeqc.dat, etc. These databases contain thermodynamic data of various chemical substances, such as standard free energy of formation, enthalpy, entropy, etc., which are used to calculate the equilibrium constant of the reaction and the change in Gibbs free energy. Input the physical and chemical characteristic parameters of the soil, the initial concentration of each heavy metal ion, the initial concentration of each ligand, the thermodynamic characteristic parameters of the complex, and the interaction parameters between the complex and each component into the PHREEQC model. The PHREEQC model will calculate the chemical equilibrium between the complex and other ions in the soil solution under the given soil conditions according to the input parameters and thermodynamic data. The calculation results include information such as the equilibrium concentration of the complex, the activity of various ions, and the saturation index. In addition, the PHREEQC model simulates the change of the decomposition process of the complex in the soil over time. The simulation results will give the concentration change of the complex at different time points, so that the decomposition curve of the complex can be obtained.

[0125] S13.3: Obtain the abscissa corresponding to the point with a slope of zero on the decomposition curve to get the decomposition time of the complex.

[0126] S14: Extract the maximum value from the decomposition times of various complexes as the waiting time for the crop.

[0127] S15: After the waiting time, return to S1.

[0128] In summary, a heavy metal pollution control method based on potassium sulfate of fulvic acid type proposed in this embodiment can effectively complex heavy metal ions in the soil by accurately determining the application rate of potassium sulfate fertilizer of fulvic acid type, and adjust according to the soil nutrient requirements to ensure the health of the soil environment and the growth requirements of crops.

[0129] Embodiment 2: Corresponding to Embodiment 1, this embodiment proposes a heavy metal pollution control system based on potassium sulfate of fulvic acid type, including: a central processor, a first soil detection device, a fertilizer spreading device, and a soil improvement device; the central processor is respectively connected to the first soil detection device, the fertilizer spreading device, and the soil improvement device.

[0130] The first soil detection device is used to obtain the types of heavy metal ions in the soil and the content of each heavy metal ion; The central processing unit includes: A data acquisition module, which is used to obtain the complexation ratio of each heavy metal ion with fulvic acid; The first data processing module, according to the content of each heavy metal ion and the corresponding complexation ratio, obtains the demand for fulvic acid corresponding to the complete complexation of all heavy metal ions in the soil; The second data processing module is used to obtain the spreading amount of fulvic acid type potassium sulfate fertilizer according to the demand for fulvic acid and the content of fulvic acid in the fulvic acid type potassium sulfate fertilizer; The fertilizer spreading device is used to evenly spread the fulvic acid type potassium sulfate fertilizer on the soil according to the spreading amount; The central processing unit further includes: A data recording module, which is used to record the current content of fulvic acid type potassium sulfate fertilizer in the soil; The first soil detection device is also used to obtain the residue amount of each heavy metal ion in the soil after reaching the complexation equilibrium with fulvic acid; The central processing unit further includes: The first function call module is used to call the first analysis and control module to work for each heavy metal ion; The first analysis and control module is used to judge whether the residue amount is greater than the screening value of agricultural land soil pollution risk. If so, it controls the label adding module and the second analysis and control module to work. Otherwise, it controls the third data processing module to work; The label adding module is used to add risk labels to heavy metal ions; The second analysis and control module is used to obtain the demand for fulvic acid corresponding to the complete complexation of all heavy metal ions with risk labels in the soil according to the residue amount of each heavy metal ion with a risk label and the corresponding complexation ratio, and sequentially controls the second data processing module, the fertilizer spreading device, the data recording module, the first soil detection device, the first analysis and control module and the label adding module to work; The third data processing module is used to obtain the current content of potassium sulfate in the soil according to the current content of fulvic acid type potassium sulfate fertilizer; The third analysis and control module is used to judge whether the content of potassium sulfate falls within the required range. If so, it ends the current heavy metal pollution control. Otherwise, it controls the soil improvement device to work; The soil improvement device is used to adjust the soil nutrients according to the current content of potassium sulfate.

[0131] Further, the first soil detection device includes: A 3D scanning device, which is used to obtain a 3D scanning image of the target area; An image processing unit for dividing a target area into multiple sampling units according to a 3D scanned image, and obtaining the coverage area and average soil thickness of each sampling unit; A first sample collection device for collecting a first soil sample from each sampling unit; A soil density detection device for detecting the soil density of each first soil sample, and performing heavy metal ion type extraction and heavy metal ion content analysis on each first soil sample to obtain the detection data of each first soil sample; the detection data includes: the amount of substance of each heavy metal ion in the soil per unit mass; A first data processing unit for obtaining the amount of substance of each heavy metal ion in each sampling unit according to the detection data; A second data processing unit for summing up the amount of substance of each heavy metal ion in each sampling unit to obtain the content of each heavy metal ion in the soil of the target area.

[0132] Furthermore, the first soil detection device further includes: A second sample collection device for extracting a unit mass of soil sub-sample from each first soil sample; A fourth data processing unit for obtaining the amount of fulvic acid added corresponding to the complete complexation of all heavy metal ions in each soil sub-sample according to the detection data and the corresponding complexation ratio, and obtaining the amount of fulvic acid type potassium sulfate fertilizer added according to the amount of fulvic acid added and the content of fulvic acid in the fulvic acid type potassium sulfate fertilizer; A time setting unit for setting multiple test time points; A fourth data processing unit for obtaining the residual amount of each heavy metal ion in each soil sub-sample; A fifth data processing unit for obtaining the residual amount of each heavy metal ion in each sampling unit according to the soil quality of the sampling unit and the residual amount of each heavy metal ion in the soil sub-sample, and summing up the residual amount of each heavy metal ion in each sampling unit to obtain the residual amount of each heavy metal ion in the soil of the target area after reaching complexation equilibrium with fulvic acid.

[0133] Furthermore, the heavy metal pollution control system further includes: A fourth data processing module for obtaining multiple potassium ion demands and multiple sulfate ion demands of the crop at each growth stage; A second soil detection device for measuring the physical and chemical characteristic parameters of the first soil sample; the physical and chemical characteristic parameters include: initial potassium ion content, initial sulfate ion content, contents of multiple macronutrients, contents of multiple micronutrients, pH value, redox potential, cation exchange capacity and organic matter content; The first data acquisition module is used to obtain the growth characteristic parameters and ion absorption characteristic parameters of crops through web crawlers; the growth characteristic parameters include: the growth duration of each growth stage and the growth rate of each growth stage; the ion absorption characteristic parameters include: potassium ion absorption rate, potassium ion accumulation amount, sulfate ion absorption rate, and sulfate ion accumulation amount; The parameter setting module is used to set the target yield and climate parameters; the climate parameters include: temperature, precipitation, and illumination duration; The first numerical analysis module is used to analyze the physical and chemical characteristic parameters, growth characteristic parameters, ion absorption characteristic parameters, target yield, and climate parameters by using the QUEFTS model to obtain the potassium ion demand and sulfate ion demand of crops in each generation stage; The fourth data processing module is used to extract the maximum value and the minimum value from multiple potassium ion demands to obtain the potassium ion demand interval, and extract the maximum value and the minimum value from multiple sulfate ion demands to obtain the sulfate ion demand interval.

[0134] Further, the soil improvement device includes: The sixth data processing unit is used to obtain the current content of potassium ions and the current content of sulfur ions according to the current content of potassium sulfate and the proportions of potassium ions and sulfate ions in potassium sulfate respectively; The data analysis and control unit is used to judge whether the current content of potassium ions and the current content of sulfate ions both fall within the corresponding demand intervals. If so, end the current heavy metal pollution control. Otherwise, control the fertilizer addition device or the resin addition device to work; The fertilizer addition device is used to add fertilizers to the soil; The resin addition device is used to add exchange resins to the soil.

[0135] Further, the heavy metal pollution control system further includes: The third sample collection device is used to collect a second soil sample from any sampling unit; The third soil detection device is used to extract various complexes and various components from the second soil sample; the components include: minerals and organic matter; The third concentration determination device is used to extract the initial concentration of each heavy metal ion and the initial concentration of each ligand from any first soil sample; The sixth data processing module is used to obtain the decomposition time of each complex; The seventh data processing module is used to extract the maximum value crop waiting time from the decomposition times of various complexes; The system restart module is used to restart the system work after the waiting time.

[0136] It should be understood that the "system", "device", "unit" and / or "module" used in this specification are a way to distinguish different components, elements, parts, portions or assemblies at different levels. However, if other words can achieve the same purpose, the said words can be replaced by other expressions.

[0137] As shown in this specification and the claims, unless the context clearly indicates otherwise, words such as "a", "an", "one" and / or "the" are not specifically singular and may also include the plural. Generally speaking, the terms "comprising" and "including" only indicate the inclusion of the steps and elements that have been clearly identified, and these steps and elements do not constitute an exclusive list. The method or device may also include other steps or elements.

[0138] The specific embodiments described above further elaborate on the purpose, technical solution and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

[0139] It should be noted that the structures, ratios, sizes, etc. shown in the drawings of this specification are only used to cooperate with the content disclosed in the specification for those skilled in the art to understand and read, and are not used to limit the implementation conditions of the present invention. Therefore, they do not have a substantial technical meaning. Any modification of the structure, change of the proportional relationship or adjustment of the size, without affecting the efficacy that the present invention can produce and the purpose that can be achieved, should still fall within the scope that can be covered by the technical content disclosed in the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle", etc. cited in this specification are only for the convenience of clear narration and are not used to limit the implementation scope of the present invention. The change or adjustment of their relative relationship, without substantial change in the technical content, should also be regarded as the scope in which the present invention can be implemented.

Claims

1. A method for controlling heavy metal pollution based on potassium sulfate of fulvic acid type, characterized in that, Including: S1: Obtain the types of heavy metal ions in the soil, the content of each heavy metal ion, and the complexation ratio of each heavy metal ion with fulvic acid; S2: According to the content of each heavy metal ion and the corresponding complexation ratio, obtain the fulvic acid demand corresponding to the complete complexation of all heavy metal ions in the soil; S3: According to the fulvic acid demand and the content of fulvic acid in the fulvic acid type potassium sulfate fertilizer, obtain the spreading amount of the fulvic acid type potassium sulfate fertilizer; S4: Evenly spread the fulvic acid type potassium sulfate fertilizer on the soil according to the spreading amount, and record the current content of the fulvic acid type potassium sulfate fertilizer in the soil; S5: Obtain the residual amount of each heavy metal ion in the soil after reaching complexation equilibrium with fulvic acid; S6: Execute S7 for each heavy metal ion; S7: Judge whether the residual amount is greater than the screening value of agricultural land soil pollution risk. If so, add a risk label to the heavy metal ion and execute S8. Otherwise, execute S9; S8: According to the residual amount of each heavy metal ion with a risk label and the corresponding complexation ratio, obtain the fulvic acid demand corresponding to the complete complexation of all heavy metal ions with risk labels in the soil, and return to S3; S9: Obtain the current content of potassium sulfate in the soil according to the current content of the fulvic acid type potassium sulfate fertilizer; S10: Judge whether the current content of potassium sulfate falls within the demand range. If so, end the current heavy metal pollution control. Otherwise, adjust the soil nutrients according to the current content of potassium sulfate.

2. The heavy metal pollution control method based on potassium sulfate of fulvic acid type according to claim 1, characterized in that S1 includes: Divide the target area into multiple sampling units; Obtain the coverage area and average soil thickness of each sampling unit; Collect a first soil sample from each sampling unit and detect the soil density of each first soil sample; Extract the types of heavy metal ions and analyze the content of heavy metal ions from each first soil sample to obtain the detection data of each first soil sample; The detection data includes: the amount of substance of each heavy metal ion in the soil per unit mass; According to the detection data, obtain the amount of substance of each heavy metal ion in each sampling unit; Sum up the amount of substance of each heavy metal ion in each sampling unit to obtain the content of each heavy metal ion in the soil of the target area.

3. A heavy metal pollution control method based on potassium sulfate of fulvic acid type according to claim 2, characterized in that S5 Including: Extract a soil sub-sample of unit mass from each first soil sample; According to the detection data and the corresponding complexation ratio, obtain the fulvic acid addition amount corresponding to the complete complexation of all heavy metal ions in each soil sub-sample; According to the fulvic acid addition amount and the content of fulvic acid in the fulvic acid type potassium sulfate fertilizer, obtain the addition amount of the fulvic acid type potassium sulfate fertilizer; Set multiple test time points; Obtain the residual amount of each heavy metal ion in each soil sub-sample; According to the soil quality of the sampling unit and the residual amount of each heavy metal ion in the soil sub-sample, obtain the residual amount of each heavy metal ion in each sampling unit; Sum up the residual amount of each heavy metal ion in each sampling unit to obtain the residual amount of each heavy metal ion in the soil of the target area after reaching complexation equilibrium with fulvic acid.

4. A heavy metal pollution control method based on potassium sulfate of fulvic acid type according to claim 2 or 3, characterized in that, Before S10, the following steps are included: Obtain multiple potassium ion demands and multiple sulfate ion demands of the crop at each growth stage; Extract the maximum and minimum values from multiple potassium ion requirements to obtain the demand range of potassium ions; extract the maximum and minimum values from multiple sulfate ion requirements to obtain the demand range of sulfate ions.

5. A heavy metal pollution control method based on potassium sulfate of fulvic acid type according to claim 4, characterized in that, S10 includes the following steps: Obtain the current content of potassium ions according to the current content of potassium sulfate and the proportion of potassium ions in potassium sulfate; obtain the current content of sulfate ions according to the current content of potassium sulfate and the proportion of sulfate ions in potassium sulfate. Judge whether the current content of potassium ions and the current content of sulfate ions both fall within the corresponding demand ranges. If so, end the current heavy metal pollution control. Otherwise, add fertilizers or ion exchange resins according to the potassium ion content and sulfate ion content.

6. A heavy metal pollution control method based on potassium sulfate of fulvic acid type according to claim 4, characterized in that It also includes: S11: Collect a second soil sample from any sampling unit, and extract various complexes and various components from the second soil sample; The components include: minerals and organic matter; S12: Extract the initial concentration of each heavy metal ion and the initial concentration of each ligand from any first soil sample; S13: Obtain the decomposition time of each complex; S14: Extract the maximum crop waiting time from the decomposition times of various complexes; S15: Return to S1 after the waiting time.

7. A heavy metal pollution control system based on potassium sulfate of fulvic acid type, characterized in that It includes: A central processing unit, a first soil detection device, a fertilizer spreading device, and a soil improvement device; the central processing unit is respectively connected to the first soil detection device, the fertilizer spreading device, and the soil improvement device; The first soil detection device is used to obtain the types of heavy metal ions in the soil and the content of each heavy metal ion; The central processing unit includes: A data acquisition module, which is used to obtain the complexation ratio of each heavy metal ion and fulvic acid; A first data processing module, which obtains the demand for fulvic acid corresponding to the complete complexation of all heavy metal ions in the soil according to the content of each heavy metal ion and the corresponding complexation ratio; A second data processing module, which is used to obtain the spreading amount of fulvic acid type potassium sulfate according to the demand for fulvic acid and the content of fulvic acid in fulvic acid type potassium sulfate; The fertilizer spreading device is used to evenly spread the fulvic acid type potassium sulfate on the soil according to the spreading amount; The central processing unit also includes: A data recording module, which is used to record the current content of fulvic acid type potassium sulfate in the soil; The first soil detection device is also used to obtain the residual amount of each heavy metal ion in the soil after reaching complexation equilibrium with fulvic acid; The central processing unit also includes: A first function call module, which is used to call the first analysis and control module to work for each heavy metal ion; The first analysis and control module is used to judge whether the residual amount is greater than the screening value of agricultural land soil pollution risk. If so, control the label adding module and the second analysis and control module to work. Otherwise, control the third data processing module to work; The label adding module is used to add risk labels to heavy metal ions; The second analysis and control module is used to obtain the fulvic acid demand corresponding to the complete complexation of all heavy metal ions with risk labels in the soil according to the residual amount of each heavy metal ion with a risk label and the corresponding complexation ratio, and sequentially control the second data processing module, the fertilizer spreading device, the data recording module, the first soil detection device, the first analysis and control module, and the label adding module to work; The third data processing module is used to obtain the current content of potassium sulfate in the soil according to the current content of fulvic acid type potassium sulfate fertilizer; The third analysis and control module is used to judge whether the content of potassium sulfate falls within the demand range. If so, end the current heavy metal pollution control. Otherwise, control the soil improvement device to work; The soil improvement device is used to adjust the soil nutrients according to the current content of potassium sulfate.

8. A heavy metal pollution control system based on fulvic acid type potassium sulfate according to claim 7, characterized in that The first soil detection device includes: A 3D scanning device for obtaining a 3D scan image of the target area; An image processing unit for dividing the target area into multiple sampling units according to the 3D scan image, and obtaining the coverage area and average soil thickness of each sampling unit; The first sample collection device for collecting a first soil sample from each sampling unit; A soil density detection device for detecting the soil density of each first soil sample, and extracting the types of heavy metal ions and analyzing the heavy metal ion content of each first soil sample to obtain the detection data of each first soil sample; the detection data includes: the amount of substance of each heavy metal ion in the soil per unit mass; The first data processing unit for obtaining the amount of substance of each heavy metal ion in each sampling unit according to the detection data; The second data processing unit for summing up the amount of substance of each heavy metal ion in each sampling unit to obtain the content of each heavy metal ion in the soil of the target area.

9. A heavy metal pollution control system based on potassium sulfate of fulvic acid type according to claim 8, characterized in that, The first soil detection device further includes: A second sample collection device for extracting a unit mass of soil sub-sample from each first soil sample; The third data processing unit for obtaining the fulvic acid addition amount corresponding to the complete complexation of all heavy metal ions in each soil sub-sample according to the detection data and the corresponding complexation ratio, and obtaining the addition amount of fulvic acid type potassium sulfate fertilizer according to the fulvic acid addition amount and the content of fulvic acid in the fulvic acid type potassium sulfate fertilizer; A time setting unit for setting multiple test time points; The fourth data processing unit for obtaining the residual amount of each heavy metal ion in each soil sub-sample; The fifth data processing unit for obtaining the residual amount of each heavy metal ion in each sampling unit according to the soil mass of the sampling unit and the residual amount of each heavy metal ion in the soil sub-sample, and summing up the residual amount of each heavy metal ion in each sampling unit to obtain the residual amount of each heavy metal ion in the soil of the target area after reaching the complexation equilibrium with fulvic acid.

10. A heavy metal pollution control system based on fulvic acid type potassium sulfate according to claim 8 or 9, characterized in that, It further includes: The fourth data processing module for obtaining multiple potassium ion demands and multiple sulfate ion demands of the crop at each growth stage; The fifth data processing module is used to extract the maximum value and the minimum value from multiple potassium ion demand amounts to obtain the demand range of potassium ions, and extract the maximum value and the minimum value from multiple sulfate ion demand amounts to obtain the demand range of sulfate ions.

11. A heavy metal pollution control system based on fulvic acid type potassium sulfate according to claim 10, characterized in that, The soil improvement device comprises: The sixth data processing unit is used to obtain the current content of potassium ions and the current content of sulfur ions according to the current content of potassium sulfate and the proportions of potassium ions and sulfate ions in potassium sulfate respectively; The data analysis and control unit is used to judge whether the current content of potassium ions and the current content of sulfate ions both fall within the corresponding demand ranges. If so, end the current heavy metal pollution control. Otherwise, control the fertilizer adding device or the resin adding device to work; The fertilizer adding device is used to add fertilizers to the soil; The resin adding device is used to add ion exchange resins to the soil.

12. A heavy metal pollution control system based on fulvic acid type potassium sulfate according to claim 10, characterized in that, It further comprises: The third sample collection device is used to collect a second soil sample from any sampling unit; The third soil detection device is used to extract various complexes and various components from the second soil sample; the components include: minerals and organic matter; The third concentration measurement device is used to extract the initial concentration of each heavy metal ion and the initial concentration of each ligand from any first soil sample; The sixth data processing module is used to obtain the decomposition time of each complex; The seventh data processing module is used to extract the maximum value, i.e., the crop waiting time, from the decomposition times of various complexes; The system restart module is used to restart the system operation after the waiting time.

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