Chelated trace element complex liquid fertilizer and its preparation method

Abstract

The present application relates to the field of fertilizer preparation, and discloses a chelated medium and trace element composite liquid fertilizer and a preparation method thereof, which comprises the following steps: preparing a medium element pre-chelated mother liquor with residual complexing capacity; in the presence of amino acid chelating components, degradable polycarboxylic acid chelating components and antioxidant stabilizers, adding iron salt, manganese salt, zinc salt and copper salt in sequence to prepare a trace metal chelated mother liquor; adding a boron source to a sugar alcohol chelating component to form a boron-polyhydroxy complex system, and then adding a molybdenum source to prepare a boron-molybdenum buffer mother liquor; adding the trace metal chelated mother liquor to the medium element pre-chelated mother liquor in sections, and adding a reserved chelating agent according to the turbidity increase value, the conductivity change rate and the proportion of free metal ions; then adding the boron-molybdenum buffer mother liquor and performing a stabilization treatment to obtain the chelated medium and trace element composite liquid fertilizer. The present application is suitable for the preparation of a composite liquid fertilizer containing calcium, magnesium, iron, manganese, zinc, copper, boron and molybdenum.

Description

Technical Field

[0001] This invention relates to the field of fertilizer preparation, specifically to a chelated micronutrient compound liquid fertilizer and its preparation method. Background Technology

[0002] Micronutrient liquid fertilizers are a type of fertilizer used in agriculture to supplement nutrients such as calcium, magnesium, iron, manganese, zinc, copper, boron, and molybdenum. They are usually in the form of an aqueous solution and are suitable for foliar spraying, drip irrigation, fertigation, and fertigation systems. Because micronutrients such as calcium and magnesium, as well as micronutrients such as iron, manganese, zinc, and copper, are easily affected by pH, hardness ions, phosphate ions, carbonate ions, and competition for coordination among different metal ions in aqueous solutions, existing products typically use sugar alcohols, amino acids, organic acid salts, and polycarboxylic acids as complexing or chelating components to improve the solubility and stability of each nutrient in the liquid phase system.

[0003] Existing chelated micronutrient liquid fertilizers are mostly prepared by mixing different elements separately into mother liquors, or by reacting chelating agents with various micronutrient salts under specific temperature and pH conditions. While these methods can reduce the precipitation of single elements to some extent, when multiple metal elements coexist and the product concentration is high, coordination competition or exchange may still occur between calcium, magnesium, iron, manganese, zinc, and copper. Especially at the moment of mixing the micronutrient mother liquor and the micronutrient mother liquor, changes in the local metal ion concentration and the state of the chelating agent can easily cause some metal ions to be in a free or weakly complexed state, leading to turbidity, precipitation, or crystallization during storage, low-temperature placement, dilution with hard water, or contact with phosphate-containing water.

[0004] Therefore, existing technologies still have the following problems: the preparation process of existing chelated micronutrient compound liquid fertilizers usually focuses on the selection of chelating agents and the final formulation, lacking the requirements for complexation capacity reservation, segmented compounding detection, and supplementary correction control during the compounding process of medium-element mother liquor and trace metal mother liquor. This results in the multi-element high-concentration compound system still exhibiting problems such as increased free metal ion ratio, increased turbidity, and insufficient stability during preparation and subsequent dilution and use. Therefore, it is necessary to provide a chelated micronutrient compound liquid fertilizer and its preparation method that can control the compounding state during preparation and improve the stability of the finished liquid phase. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a chelated micronutrient compound liquid fertilizer and its preparation method, thereby solving the technical problems existing in the prior art.

[0006] The above-mentioned technical objective of the present invention is achieved through the following technical solution: A method for preparing a chelated micronutrient compound liquid fertilizer includes the following steps: S1: Prepare a medium-element prechelation mother liquor. Mix and dissolve the sugar alcohol chelating component, the hydroxycarboxylic acid chelating component and water, then add calcium salt and magnesium salt for prechelation to obtain a medium-element prechelation mother liquor. Control the remaining complexing capacity in the medium-element prechelation mother liquor that is not occupied by calcium ions and magnesium ions to be 8% to 25% of the theoretical total complexing capacity. The theoretical total complexing capacity is calculated according to the molar amount of chelable metal ions corresponding to the sugar alcohol chelating component and the hydroxycarboxylic acid chelating component. S2: To prepare a trace metal chelating mother liquor, amino acid chelating components, biodegradable polycarboxylic acid chelating components and antioxidant stabilizers are dissolved in water, and iron salt, manganese salt, zinc salt and copper salt are added sequentially under pH conditions of 4.8 to 5.6 to carry out segmented chelation and obtain a trace metal chelating mother liquor. S3: To prepare a boron-molybdenum buffer mother liquor, a boron source is added to an aqueous solution containing sugar alcohol chelating components to form a boron-polyhydroxy complex system, and then a molybdenum source is added to obtain the boron-molybdenum buffer mother liquor. S4: Add the trace metal chelating mother liquor to the medium element prechelating mother liquor in segments. After each segment is added, detect the increase in turbidity, the rate of change in conductivity, and the proportion of free metal ions in the compound solution. When at least one of the following conditions is met: the increase in turbidity is greater than 5 NTU, the rate of change in conductivity is greater than 3%, and the proportion of free metal ions is greater than 2% of the total metal molar amount, add a retaining chelating agent to the compound solution. The retaining chelating agent is one, two, or three of the following: sugar alcohol chelating components, hydroxycarboxylic acid chelating components, and amino acid chelating components. S5: After all the trace metal chelating mother liquor is added, boron-molybdenum buffer mother liquor is added to the compound solution to adjust the pH to 5.8-6.2 and then stabilized to obtain chelated trace element compound liquid fertilizer.

[0007] Preferably, when preparing the medium-element prechelation mother liquor, the sugar alcohol chelating component, the hydroxycarboxylic acid chelating component and water are stirred at 45-65°C for 20-40 min, then calcium salt is added and the reaction is kept at the temperature for 15-30 min, then magnesium salt is added and the reaction is kept at the temperature for another 20-50 min. The sugar alcohol chelating components include sorbitol and mannitol, the hydroxycarboxylic acid chelating components include potassium citrate and sodium gluconate, the calcium salt is calcium nitrate or calcium acetate, and the magnesium salt is magnesium nitrate or magnesium acetate.

[0008] Preferably, the remaining complexing capacity is calculated as the difference between the theoretical total complexing capacity and the complexing capacity occupied by calcium and magnesium ions, and the complexing capacity occupied by calcium and magnesium ions is calculated as the molar amount of metal ions corresponding to the added calcium and magnesium salts.

[0009] Preferably, when preparing the trace metal chelating mother liquor, the amino acid chelating component includes glycine, glutamic acid and aspartic acid, the degradable polycarboxylic acid chelating component is iminodisuccinate or polyaspartate, and the antioxidant stabilizer is ascorbic acid or sodium isoascorbate. After adding iron salts, the reaction time is 20–35 minutes; after adding manganese salts, the reaction time is 15–30 minutes; after adding zinc salts, the reaction time is 15–30 minutes; and after adding copper salts, the reaction time is 10–25 minutes.

[0010] Preferably, the iron salt is ferrous sulfate or ferric nitrate, the manganese salt is manganese sulfate or manganese nitrate, the zinc salt is zinc sulfate or zinc nitrate, and the copper salt is copper sulfate or copper nitrate. The iron salt, manganese salt, zinc salt, and copper salt are added after being prepared into aqueous solutions with a mass concentration of 10% to 35%.

[0011] Preferably, when preparing the boron-molybdenum buffer mother liquor, the sugar alcohol chelating component is first added to water and heated to 45-65°C, then the boron source is added and stirred for 20-50 minutes, then the temperature is lowered to 35-50°C and the molybdenum source is added, and the pH is adjusted to 6.0-6.8. The boron source is boric acid, sodium octaborate tetrahydrate, or potassium tetraborate tetrahydrate, and the molybdenum source is ammonium molybdate or sodium molybdate.

[0012] Preferably, the trace metal chelation mother liquor is added to the medium element prechelation mother liquor in 3 to 6 stages, with each stage being 15% to 35% of the total mass of the trace metal chelation mother liquor. The stirring interval between two adjacent stages is 8 to 20 minutes, and the test after each stage is added is carried out within 3 to 8 minutes after the stage is added. The turbidity increase value is the difference between the turbidity of the compound solution measured within 3 to 8 minutes after the addition of each segment of trace metal chelate mother liquor and the turbidity of the compound solution measured before the addition of that segment. The conductivity change rate is the percentage of the difference between the conductivity of the compound solution measured within 3-8 minutes after the addition of each segment of trace metal chelate mother liquor and the conductivity of the compound solution measured before the addition of that segment, relative to the conductivity of the compound solution measured before the addition of that segment. The free metal ion ratio is the percentage of the molar amount of free metal ions after ultrafiltration separation to the total molar amount of metals in the compound solution.

[0013] Preferably, when the increase in turbidity is greater than 5 NTU, a sugar alcohol chelating component is added; When the rate of change in conductivity is greater than 3%, add hydroxycarboxylic acid chelating components; When the proportion of free metal ions is greater than 2% of the total metal molar amount, amino acid chelating components are added. The amount added at one time is 0.05% to 0.5% of the mass of the compound solution; The stabilization treatment includes: stirring the compound solution after adding boron-molybdenum buffer mother liquor at 35-50°C for 30-90 minutes, and then filtering it through an 80-200 mesh filter.

[0014] A chelated micronutrient compound liquid fertilizer includes: Water, calcium, magnesium, iron, manganese, zinc, copper, boron, molybdenum, sugar alcohol chelates, hydroxycarboxylic acid chelates, amino acid chelates, and biodegradable polycarboxylic acid chelates; The sugar alcohol chelating components include sorbitol and mannitol, the hydroxycarboxylic acid chelating components include potassium citrate and sodium gluconate, the amino acid chelating components include glycine, glutamic acid and aspartic acid, and the degradable polycarboxylic acid chelating components are iminodisuccinate or polyaspartate. The pH of the chelated trace element compound liquid fertilizer is 5.8-6.2, and the proportion of free metal ions measured after separation by a 500Da molecular weight cutoff ultrafiltration membrane is no more than 2% of the total metal molar amount. The chelated micronutrient compound liquid fertilizer was diluted 100 times with a hard water simulation solution with a calcium carbonate hardness of 300-500 mg / L and a pH of 7.0-8.0 and allowed to stand for 24 hours. The turbidity increase of the diluted solution was no more than 10 NTU. The chelated micronutrient compound liquid fertilizer uses a phosphate-containing simulated solution with a phosphate concentration of 0.005–0.05 mol / L and a pH of 6.5–7.5. After diluting 100 times and letting it stand for 24 hours, the increase in turbidity of the diluted solution is no more than 10 NTU.

[0015] Preferably, the calcium content is 2.0%–8.0% by mass, the magnesium content is 0.5%–4.0% by mass, the zinc content is 0.1%–2.0% by mass, the iron content is 0.05%–1.5% by mass, the manganese content is 0.05%–1.5% by mass, the copper content is 0.01%–0.5% by mass, the boron content is 0.05%–1.0% by mass, and the molybdenum content is 0.005%–0.2% by mass. The chelated trace element compound liquid fertilizer is prepared by the preparation method according to any one of claims 1-8.

[0016] In summary, the present invention has the following main beneficial effects: By first preparing a medium-element prechelating mother liquor with residual complexing capacity, and controlling this residual complexing capacity to be 8%–25% of the theoretical total complexing capacity, calcium and magnesium ions retain a complexing margin that can be used for subsequent compounding after prechelation. At the same time, by adding the trace metal chelating mother liquor in stages to the medium-element prechelating mother liquor, trace metal elements such as iron, manganese, zinc, and copper can gradually transfer and combine with the residual complexing capacity when entering the compounding system. This achieves the purpose of reducing the enrichment, turbidity, and precipitation of free metal ions caused by local concentration abrupt changes under high-concentration compounding conditions.

[0017] By detecting the increase in turbidity, the rate of change in conductivity, and the proportion of free metal ions in the compound solution after each addition of trace amounts of metal chelating mother liquor, and by adding sugar alcohol chelating components, hydroxycarboxylic acid chelating components, or amino acid chelating components when the corresponding indicators exceed the process control threshold, the compounding process is transformed from a one-time feeding reaction into a preparation process with segmented detection and segmented correction. This achieves the goal of timely adjusting the complexation state of the compound solution during the preparation process and reducing coordination exchange and metal ion release after compounding.

[0018] By first forming a boron-polyhydroxy complex system with a boron source and a sugar alcohol chelate, and then adding a molybdenum source to form a boron-molybdenum buffer mother liquor, and then adding the boron-molybdenum buffer mother liquor after the segmented transfer and compounding of the trace metal chelate mother liquor, the boron and molybdenum sources are prevented from directly participating in complex side reactions in the early high-concentration calcium, magnesium, iron, manganese, zinc, and copper coexisting system. At the same time, by dilution and testing with hard water simulation solution and phosphate-containing simulation solution, as well as rework stabilization treatment, the liquid phase stability of the obtained chelated trace element compound liquid fertilizer in hard water dilution environment and phosphate-containing environment is improved. Attached Figure Description

[0019] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] refer to Figure 1 A method for preparing a chelated micronutrient compound liquid fertilizer includes the following steps: S1: Prepare a medium-element prechelation mother liquor. Mix and dissolve the sugar alcohol chelating component, the hydroxycarboxylic acid chelating component and water, then add calcium salt and magnesium salt for prechelation to obtain a medium-element prechelation mother liquor. Control the remaining complexing capacity in the medium-element prechelation mother liquor that is not occupied by calcium ions and magnesium ions to be 8% to 25% of the theoretical total complexing capacity. The theoretical total complexing capacity is calculated according to the molar amount of chelable metal ions corresponding to the sugar alcohol chelating component and the hydroxycarboxylic acid chelating component. S2: To prepare a trace metal chelating mother liquor, amino acid chelating components, biodegradable polycarboxylic acid chelating components and antioxidant stabilizers are dissolved in water, and iron salt, manganese salt, zinc salt and copper salt are added sequentially under pH conditions of 4.8 to 5.6 to carry out segmented chelation and obtain a trace metal chelating mother liquor. S3: To prepare a boron-molybdenum buffer mother liquor, a boron source is added to an aqueous solution containing sugar alcohol chelating components to form a boron-polyhydroxy complex system, and then a molybdenum source is added to obtain the boron-molybdenum buffer mother liquor. S4: Add the trace metal chelating mother liquor to the medium element prechelating mother liquor in segments. After each segment is added, detect the increase in turbidity, the rate of change in conductivity, and the proportion of free metal ions in the compound solution. When at least one of the following conditions is met: the increase in turbidity is greater than 5 NTU, the rate of change in conductivity is greater than 3%, and the proportion of free metal ions is greater than 2% of the total metal molar amount, add a retaining chelating agent to the compound solution. The retaining chelating agent is one, two, or three of the following: sugar alcohol chelating components, hydroxycarboxylic acid chelating components, and amino acid chelating components. S5: After all the trace metal chelating mother liquor is added, boron-molybdenum buffer mother liquor is added to the compound solution to adjust the pH to 5.8-6.2 and then stabilized to obtain chelated trace element compound liquid fertilizer.

[0022] This method first prepares a medium-element prechelating mother liquor with residual complexing capacity, then prepares a trace metal chelating mother liquor and a boron-molybdenum buffer mother liquor; subsequently, the trace metal chelating mother liquor is added to the medium-element prechelating mother liquor in stages, and the increase in turbidity, change in conductivity, and proportion of free metal ions of the compound solution are detected after each stage is added, and a retaining chelating agent is added according to the detection results; finally, the boron-molybdenum buffer mother liquor is added and stabilized to obtain a chelated medium-trace element compound liquid fertilizer.

[0023] The chelated micronutrient compound liquid fertilizer obtained in this application includes water, calcium, magnesium, iron, manganese, zinc, copper, boron, molybdenum, sugar alcohol chelating components, hydroxycarboxylic acid chelating components, amino acid chelating components, and biodegradable polycarboxylic acid chelating components. Among them, the sugar alcohol chelating components include sorbitol and mannitol; the hydroxycarboxylic acid chelating components include potassium citrate and sodium gluconate; the amino acid chelating components include glycine, glutamic acid, and aspartic acid; and the biodegradable polycarboxylic acid chelating components are iminodisuccinate or polyaspartate.

[0024] The medium-element prechelating mother liquor described in this application is a liquid-phase system prepared from sugar alcohol chelating components, hydroxycarboxylic acid chelating components, water, calcium salts, and magnesium salts. This medium-element prechelating mother liquor is not a fully chelated mother liquor in which all sugar alcohol and hydroxycarboxylic acid chelating components are used for the complexation of calcium and magnesium ions. Instead, after the prechelation of calcium and magnesium ions, 8% to 25% of the theoretical total complexing capacity is retained as a residual complexing capacity.

[0025] In this application, the theoretical total complexing capacity is calculated based on the batch calibration results of sugar alcohol chelate components and hydroxycarboxylic acid chelate components from the same batch. During calibration, the chelate component to be calibrated is dissolved in water, the pH is adjusted to the pH range used in preparing the pre-chelation mother liquor of medium-quantity elements, titration is performed using a calcium salt standard solution, and the complexation endpoint is defined as the rate of change of free calcium ion concentration measured by a calcium ion selective electrode being less than 5% after two consecutive detections. The molar amount of metal ions that can be complexed by the chelate component is calculated based on the molar amount of calcium ions corresponding to the consumed calcium salt standard solution. When the raw material supplier provides complexation equivalent data, this data is only used as a basis for feeding estimation, and the final calculation of the theoretical total complexing capacity is based on the calibration results of the same batch of raw materials.

[0026] The theoretical total complexing capacity is calculated using the following formula: ; in, The theoretical total complexing capacity is expressed in mol. The mass of the added sugar alcohol chelating component is expressed in grams. The molar amount of complexable metal ions obtained by batch standardization of sugar alcohol chelate components, in mol / g; The mass of the hydroxycarboxylic acid chelating component added is expressed in grams. The molar amount of complexable metal ions obtained by batch standardization of the hydroxycarboxylic acid chelating component is expressed in mol / g. The remaining complexing capacity ratio is calculated according to the following formula: ; in, The percentage of remaining complexing capacity relative to the theoretical total complexing capacity, expressed as a percentage. The theoretical total complexing capacity is expressed in mol. This represents the molar amount of calcium ions corresponding to the addition of calcium salt, expressed in mol. The value represents the molar amount of magnesium ions corresponding to the addition of magnesium salt, expressed in mol.

[0027] The turbidity increase value mentioned in this application refers to the difference between the turbidity of the compound solution measured within 3-8 minutes after the addition of each segment of trace metal chelating mother liquor and the turbidity of the compound solution measured before the addition of that segment. During testing, a sample of the compound solution is placed in a clean colorimetric tube and measured using a turbidity meter, with the unit being NTU.

[0028] The conductivity change rate mentioned in this application refers to the percentage difference between the conductivity of the compound solution measured within 3 to 8 minutes after the addition of each segment of trace metal chelate mother liquor and the conductivity of the compound solution measured before the addition of that segment, relative to the conductivity of the compound solution measured before the addition of that segment.

[0029] The free metal ion ratio mentioned in this application refers to the percentage of the molar amount of free metal ions after ultrafiltration separation to the total molar amount of metals in the compound solution. The free metal ion ratio is calculated according to the following formula: ; in, The percentage of free metal ions is expressed as a percentage (%). The molar amount of free metal ions measured in the filtrate after ultrafiltration separation, in mol. This represents the total molar amount of calcium, magnesium, iron, manganese, zinc, and copper in the compound solution, expressed in mol.

[0030] When determining the proportion of free metal ions, the compound solution sample was taken out and allowed to stand at 25°C for 5 minutes without dilution. It was then ultrafiltered through a 500 Da molecular weight cutoff ultrafiltration membrane at a pressure of 0.1–0.3 MPa for 10–20 minutes. The initial filtrate was discarded, and the intermediate filtrate was collected. The intermediate filtrate was used to determine the molar amount of free metal ions using either a metal ion colorimetric method or inductively coupled plasma atomic emission spectrometry (ICP-AES). Separately, a sample from the same batch of compound solution was digested with acid, and the total molar amount of calcium, magnesium, iron, manganese, zinc, and copper in the compound solution was determined.

[0031] In this application, the turbidity increase of 5 NTU, conductivity change of 3%, free metal ion ratio of 2%, and turbidity increase of 10 NTU in the dilution solution are all process control thresholds during the preparation process. These thresholds were determined by screening the turbidity, conductivity, free metal ion content, and dilution turbidity of the compound solution during small-scale compounding of the same raw material system. They are used to determine whether additional chelating agents need to be added or if stabilization treatment should be repeated, and are not used as fertilizer efficiency indicators.

[0032] Example 1 This embodiment provides a method for preparing a chelated micronutrient compound liquid fertilizer. The liquid fertilizer contains calcium, magnesium, iron, manganese, zinc, copper, boron, and molybdenum.

[0033] In preparing the prechelation mother liquor for medium-element elements, water was added to the first reaction vessel, stirring was started, and the reaction solution was heated to 55°C. While stirring, sorbitol, mannitol, potassium citrate, and sodium gluconate were added, allowing sorbitol and mannitol to form the sugar alcohol chelate component, and potassium citrate and sodium gluconate to form the hydroxycarboxylic acid chelate component. Stirring was continued for 30 minutes to dissolve the sugar alcohol and hydroxycarboxylic acid chelate components.

[0034] Before feeding, the complexation capacity of the sugar alcohol chelate and hydroxycarboxylic acid chelate components from the same batch was determined, and the theoretical total complexation capacity was calculated according to the aforementioned formula. After dissolution, the pH of the reaction solution was adjusted to 5.7–5.9 using potassium hydroxide aqueous solution and citric acid aqueous solution. After the pH stabilized, calcium nitrate aqueous solution was slowly added to the first reaction vessel, and the reaction was maintained at the temperature for 20 min after the addition was completed; then magnesium nitrate aqueous solution was added, and the reaction was maintained at the temperature for another 35 min after the addition was completed, to obtain the medium-element pre-chelation mother liquor.

[0035] The remaining complexing capacity ratio is calculated based on the actual amounts of calcium nitrate and magnesium nitrate added. The ratio is controlled between 8% and 25% by adjusting the amounts of calcium nitrate and magnesium nitrate aqueous solutions added. If the calculated remaining complexing capacity ratio is below 8%, the amount of calcium or magnesium salt added is reduced, or sugar alcohol chelating components and hydroxycarboxylic acid chelating components are added and the calculation is repeated. If the calculated remaining complexing capacity ratio is above 25%, the amount of calcium or magnesium salt added is increased to ensure that the medium-element pre-chelation mother liquor meets the requirements for subsequent staged compounding.

[0036] In preparing the trace metal chelate mother liquor, water was added to the second reaction vessel, stirring was started, and the reaction solution was heated to 45°C. Glycine, glutamic acid, and aspartic acid were added while stirring to form an amino acid chelate component; then iminodisuccinate was added as a biodegradable polycarboxylic acid chelate component; subsequently, ascorbic acid was added as an antioxidant stabilizer. After adding the above materials, stirring was continued until dissolved, and the pH was adjusted to 5.0–5.3.

[0037] Ferrous sulfate, manganese sulfate, zinc sulfate, and copper sulfate were prepared into aqueous solutions with a mass concentration of 10%–35%. First, the ferrous sulfate aqueous solution was added to the second reaction vessel, maintaining the pH at 4.8–5.6 during the addition process. After the addition was complete, the reaction was allowed to proceed for 25 minutes. Next, the manganese sulfate aqueous solution was added, and the reaction was allowed to proceed for 20 minutes. Then, the zinc sulfate aqueous solution was added, and the reaction was allowed to proceed for 20 minutes. Finally, the copper sulfate aqueous solution was added, and the reaction was allowed to proceed for 15 minutes, yielding a trace metal chelation mother liquor.

[0038] In this embodiment, iron salt, manganese salt, zinc salt, and copper salt are added sequentially, allowing the iron salt to enter the system containing amino acid chelating components, biodegradable polycarboxylic acid chelating components, and antioxidant stabilizers first, and chelation to occur under conditions of pH 4.8–5.6; copper salt is added last. This order of addition ensures that the trace metal chelating mother liquor forms a segmented chelation state before entering the medium element prechelating mother liquor.

[0039] In preparing the boron-molybdenum buffer mother liquor, water and a sugar alcohol chelating component were added to the third reaction vessel, and the temperature was raised to 55°C while stirring. After the sugar alcohol chelating component dissolved, boric acid was added, and the mixture was stirred for 35 minutes to form a boron-polyhydroxy complex system with the boron source and the sugar alcohol chelating component. Subsequently, the temperature was lowered to 40°C, ammonium molybdate was added, and the pH was adjusted to 6.2–6.5. The mixture was stirred until dissolved to obtain the boron-molybdenum buffer mother liquor.

[0040] In this embodiment, the boron source first forms a boron-polyhydroxy complex system with the sugar alcohol chelating component, and then forms a boron-molybdenum buffer mother liquor together with the molybdenum source. The boron-molybdenum buffer mother liquor is added after the trace metal chelating mother liquor has been transferred and compounded in stages.

[0041] During the staged transfer and compounding process, the medium-element prechelation mother liquor in the first reaction vessel was maintained at 40°C, and stirring was started and kept constant at the stirring speed. The trace metal chelation mother liquor in the second reaction vessel was added to the medium-element prechelation mother liquor in four stages. The first stage added 25% of the total mass of the trace metal chelation mother liquor, and stirring was performed for 10 minutes after the addition was completed; the second stage added 25% of the total mass of the trace metal chelation mother liquor, and stirring was performed for 10 minutes after the addition was completed; the third stage added 25% of the total mass of the trace metal chelation mother liquor, and stirring was performed for 10 minutes after the addition was completed; the fourth stage added 25% of the total mass of the trace metal chelation mother liquor, and stirring was performed for 10 minutes after the addition was completed.

[0042] Before adding each segment of the trace metal chelating mother liquor, the turbidity and conductivity of the compound solution were measured, and a sample was taken to determine the total molar amount of metal in the compound solution. Within 3–8 minutes after adding each segment of the trace metal chelating mother liquor, the turbidity and conductivity of the compound solution were measured again, and a sample was taken for ultrafiltration separation to determine the molar amount of free metal ions. Based on the test results, the increase in turbidity, the rate of change in conductivity, and the proportion of free metal ions were calculated.

[0043] When the turbidity increase exceeds 5 NTU, add sugar alcohol chelating agents to the compound solution; when the conductivity change exceeds 3%, add hydroxycarboxylic acid chelating agents; when the proportion of free metal ions exceeds 2% of the total metal molar amount, add amino acid chelating agents. The single addition amount is 0.05%–0.5% of the compound solution mass. If two or three indicators simultaneously exceed their corresponding thresholds after the same addition, add the corresponding chelating agents respectively. After addition, continue stirring for 8–20 minutes before adding the next stage of trace metal chelating mother liquor. If none of the three indicators exceed their corresponding thresholds, do not add retention chelating agents; directly add the next stage of trace metal chelating mother liquor.

[0044] After the trace metal chelating mother liquor was added in stages, the boron-molybdenum buffer mother liquor from the third reaction vessel was added to the compound solution. During the addition process, the temperature of the compound solution was maintained at 35–50°C, and stirring was continued. After the boron-molybdenum buffer mother liquor was added, the pH was adjusted to 5.8–6.2 using potassium hydroxide aqueous solution or citric acid aqueous solution, and the mixture was stirred at 35–50°C for 30–90 minutes. After stabilization treatment, the solution was filtered through an 80–200 mesh filter to obtain the chelated trace element compound liquid fertilizer.

[0045] The resulting chelated micronutrient compound liquid fertilizer is a homogeneous liquid-phase system containing water, calcium, magnesium, iron, manganese, zinc, copper, boron, molybdenum, sugar alcohol chelates, hydroxycarboxylic acid chelates, amino acid chelates, and biodegradable polycarboxylic acid chelates. The sugar alcohol chelates are derived from sorbitol and mannitol; the hydroxycarboxylic acid chelates are derived from potassium citrate and sodium gluconate; the amino acid chelates are derived from glycine, glutamic acid, and aspartic acid; and the biodegradable polycarboxylic acid chelates are derived from iminodisuccinate. The calcium, magnesium, iron, manganese, zinc, copper, boron, and molybdenum elements in the finished product are introduced from their corresponding calcium salts, magnesium salts, iron salts, manganese salts, zinc salts, copper salts, boron sources, and molybdenum sources.

[0046] The elemental content of the finished product is determined by calculating the amount of raw materials fed into the sample and combining this with the elemental analysis results after acid digestion. During testing, a sample of the finished product is acid-digested, and the elemental contents of calcium, magnesium, iron, manganese, zinc, copper, boron, and molybdenum are determined using inductively coupled plasma atomic emission spectrometry (ICP-AES) or atomic absorption spectrometry (AAS). For a qualified finished product, the mass content of calcium is controlled at 2.0%–8.0%, magnesium at 0.5%–4.0%, zinc at 0.1%–2.0%, iron at 0.05%–1.5%, manganese at 0.05%–1.5%, copper at 0.01%–0.5%, boron at 0.05%–1.0%, and molybdenum at 0.005%–0.2%. When there is a discrepancy between the acid digestion test results and the calculated amount of raw materials fed into the sample, the test results after acid digestion are used as the basis for determining the elemental content of the finished product.

[0047] The pH of the finished product was measured at 25℃. Before measurement, the finished product sample was stirred evenly and tested using a calibrated pH meter. For a qualified finished product, the pH of the chelated micronutrient compound liquid fertilizer is 5.8–6.2. If the pH is below 5.8, it is adjusted with potassium hydroxide aqueous solution; if the pH is above 6.2, it is adjusted with citric acid aqueous solution. After adjustment, the mixture is stirred at 35–50℃ for 30–90 minutes, and the pH is measured again.

[0048] The proportion of free metal ions in the finished product was determined according to the aforementioned method for detecting the proportion of free metal ions. For a qualified finished product, the proportion of free metal ions measured after separation by a 500 Da molecular weight cutoff ultrafiltration membrane should not exceed 2% of the total metal molar amount.

[0049] The stability of the finished product was tested separately using hard water and phosphate-containing simulated solutions. The hard water simulated solution had a hardness of 300–500 mg / L (calculated as calcium carbonate) and a pH of 7.0–8.0; the phosphate-containing simulated solution had a phosphate concentration of 0.005–0.05 mol / L and a pH of 6.5–7.5. The obtained chelated micronutrient compound liquid fertilizer was diluted 100 times with both the hard water and phosphate-containing simulated solutions, and the turbidity of the diluted solutions was measured after standing for 24 hours. For a qualified finished product, the increase in turbidity of the diluted solution after 100 times dilution with the hard water simulated solution and standing for 24 hours should not exceed 10 NTU, and the increase in turbidity of the diluted solution after 100 times dilution with the phosphate-containing simulated solution and standing for 24 hours should not exceed 10 NTU.

[0050] If the proportion of free metal ions in the finished product is greater than 2%, or the increase in turbidity after dilution with hard water simulation solution or phosphate-containing simulation solution is greater than 10 NTU, the same batch of finished product shall be returned to the stabilization treatment step. A retaining chelating agent shall be added at 0.05%–0.3% of the batch's mass, the pH shall be adjusted to 5.8–6.2, and the mixture shall be stirred at 35–50°C for 30–90 minutes, filtered, and the finished product shall be retested. Each batch shall be reworked no more than twice; if the above-mentioned finished product testing conditions are still not met after two rework treatments, the batch shall not be considered a qualified finished product.

[0051] Example 2 This embodiment provides another method for preparing a chelated micronutrient compound liquid fertilizer. The difference from Embodiment 1 is that the calcium salt in the micronutrient prechelation mother liquor is calcium acetate, and the magnesium salt is magnesium acetate; the biodegradable polycarboxylic acid chelating component in the micronutrient chelation mother liquor is polyaspartate, and the antioxidant stabilizer is sodium isoascorbate; the boron source is sodium octaborate tetrahydrate, and the molybdenum source is sodium molybdate.

[0052] When preparing the prechelation mother liquor for medium-quantity elements, sorbitol, mannitol, potassium citrate, sodium gluconate, and water are stirred at 45–65°C for 20–40 min. Calcium acetate is added first and the reaction is maintained at this temperature for 15–30 min. Then, magnesium acetate is added and the reaction is continued at this temperature for another 20–50 min. By adjusting the amounts of calcium acetate and magnesium acetate added, the remaining complexing capacity ratio is controlled at 8%–25%.

[0053] In preparing the trace metal chelate mother liquor, glycine, glutamic acid, aspartic acid, polyaspartate, and sodium isoascorbate were dissolved in water. After adjusting the pH to 4.8–5.6, ferric nitrate aqueous solution, manganese nitrate aqueous solution, zinc nitrate aqueous solution, and copper nitrate aqueous solution were added sequentially, with the mass concentration of each metal salt aqueous solution ranging from 10% to 35%. The reaction time was 20–35 min after the addition of ferric nitrate aqueous solution, 15–30 min after the addition of manganese nitrate aqueous solution, 15–30 min after the addition of zinc nitrate aqueous solution, and 10–25 min after the addition of copper nitrate aqueous solution.

[0054] When preparing boron-molybdenum buffer stock solution, first add the sugar alcohol chelating component to water and heat to 45-65℃, then add sodium octaborate tetrahydrate and stir for 20-50 min, then lower the temperature to 35-50℃ and add sodium molybdate, and adjust the pH to 6.0-6.8.

[0055] During the segmented transfer and compounding process, the trace metal chelating mother liquor was added to the medium element prechelating mother liquor in three stages. Each stage consisted of one-third of the total mass of the trace metal chelating mother liquor, with a stirring interval of 8–20 minutes between each stage. Within 3–8 minutes of each stage's addition, the increase in turbidity, the rate of change in conductivity, and the proportion of free metal ions were measured. The chelating agent was then replenished in the same manner as in Example 1. After all stages were added, a boron-molybdenum buffer mother liquor was added to adjust the pH to 5.8–6.2. The mixture was stirred at 35–50°C for 30–90 minutes. After filtration through an 80–200 mesh filter, the chelated trace element compound liquid fertilizer was obtained.

[0056] The chelated micronutrient compound liquid fertilizer prepared according to this embodiment is a homogeneous liquid phase system, containing water, calcium, magnesium, iron, manganese, zinc, copper, boron, molybdenum, sugar alcohol chelating components, hydroxycarboxylic acid chelating components, amino acid chelating components, and biodegradable polycarboxylic acid chelating components. The biodegradable polycarboxylic acid chelating components are derived from polyaspartate. The pH, free metal ion ratio, dilution stability in hard water simulated solution, dilution stability in phosphate-containing simulated solution, and mass content of each element of the obtained chelated micronutrient compound liquid fertilizer were all tested and determined according to the finished product testing method described in Example 1.

[0057] Example 3 This embodiment provides a method for preparing chelated trace element compound liquid fertilizer suitable for batches with high trace metal content. The difference from Embodiment 1 is that the trace metal chelating mother liquor is added to the medium element pre-chelating mother liquor in six stages, with each stage added successively at 15%, 15%, 20%, 20%, 15%, and 15% of the total mass of the trace metal chelating mother liquor. After each stage is added, the mixture is stirred for 8–20 minutes, and turbidity, conductivity, and free metal ion concentration are measured within 3–8 minutes after the addition of that stage.

[0058] When the conductivity change rate exceeds 3% after the addition of the first or second stage, add a hydroxycarboxylic acid chelating component; when the proportion of free metal ions exceeds 2% after the addition of the third or fourth stage, add an amino acid chelating component; when the turbidity increase exceeds 5 NTU after the addition of the fifth or sixth stage, add a sugar alcohol chelating component. The amount added at one time is 0.05% to 0.5% of the mass of the compound solution at that time. If the same detection index still exceeds the corresponding threshold after the addition, continue stirring for 8 to 20 minutes, then test again, and add a second time at 0.05% to 0.3% of the mass of the compound solution. The next stage is added after the second addition. The remaining steps are the same as in Example 1.

[0059] The chelated trace element compound liquid fertilizer prepared according to this embodiment is tested in the same way as in Embodiment 1. When the proportion of free metal ions in the finished product, the increase in turbidity after dilution with hard water simulation solution, or the increase in turbidity after dilution with phosphate-containing simulation solution exceeds the corresponding control range, it is processed according to the rework treatment method described in Embodiment 1.

[0060] Compare with Implementation Method 1 This comparative embodiment uses the same raw material types and total feed amount as Example 1, but instead of controlling the remaining complexing capacity of the medium element mother liquor, calcium and magnesium salts are added in such a way that all sugar alcohol chelating components and hydroxycarboxylic acid chelating components are used for calcium and magnesium ion complexation, making the medium element mother liquor nearly completely chelated. Then, a small amount of trace metal chelating mother liquor is added to the medium element mother liquor all at once, followed by the addition of boron-molybdenum buffer mother liquor. This comparative embodiment does not perform the detection of turbidity increase, conductivity change rate, and free metal ion ratio after each addition, nor does it perform the step of adding retaining chelating agent according to the detection results.

[0061] Compare with Implementation Method 2 This comparative embodiment uses the same types of raw materials and total feed amount as Example 1, but adds calcium salt, magnesium salt, iron salt, manganese salt, zinc salt, copper salt, boron source, molybdenum source, sugar alcohol chelating component, hydroxycarboxylic acid chelating component, amino acid chelating component, biodegradable polycarboxylic acid chelating component, and antioxidant stabilizer to the same reactor at once, and stirs the reaction at pH 5.8–6.2 and temperature 35–50°C. This comparative embodiment does not separately prepare the medium-element prechelation mother liquor, trace metal chelation mother liquor, and boron-molybdenum buffer mother liquor.

[0062] Compare with implementation method three This comparative embodiment uses the same medium-element prechelating mother liquor, trace metal chelating mother liquor, and boron-molybdenum buffer mother liquor as in Example 1. The trace metal chelating mother liquor is also added to the medium-element prechelating mother liquor in four stages. However, after each stage is added, only stirring is performed; the increase in turbidity, the rate of change in conductivity, and the proportion of free metal ions are not measured, and no additional retaining chelating agent is added based on the test results. After all the trace metal chelating mother liquor has been added, the boron-molybdenum buffer mother liquor is added directly to complete the stabilization treatment.

[0063] The products obtained in the same ways as in Example 1 were compared with those obtained in Examples 1 to 3. The pH, free metal ion ratio, increase in turbidity after dilution with hard water simulation solution and increase in turbidity after dilution with phosphate-containing simulation solution were tested using the same finished product testing method as in Example 1. This was done to compare the effects of different preparation routes on the state parameters of the finished product.

[0064] Example 1, Control Implementation 1, Control Implementation 2, and Control Implementation 3 were prepared using the same total metal element input amount, and the increase in turbidity, change in conductivity, proportion of free metal ions, and increase in turbidity after dilution of the finished product were measured at each stage of the compounding process. The test items included: the increase in turbidity, change in conductivity, and proportion of free metal ions after each addition in the compounding process; the increase in turbidity of the finished product after dilution 100 times with a hard water simulation solution and standing for 24 hours; the increase in turbidity of the finished product after dilution 100 times with a phosphate-containing simulation solution and standing for 24 hours; the visible crystallization of the finished product after being placed at 5°C for 7 days; and the precipitation of the finished product after being placed at 25°C for 30 days. These test items were used to evaluate the impact of different preparation routes on the stability of the compounding process and the stability of dilution.

[0065] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a chelated micronutrient compound liquid fertilizer, characterized in that, Includes the following steps: S1: Prepare a medium-element prechelation mother liquor. Mix and dissolve the sugar alcohol chelating component, the hydroxycarboxylic acid chelating component and water, then add calcium salt and magnesium salt for prechelation to obtain a medium-element prechelation mother liquor. Control the remaining complexing capacity in the medium-element prechelation mother liquor that is not occupied by calcium ions and magnesium ions to be 8% to 25% of the theoretical total complexing capacity. The theoretical total complexing capacity is calculated according to the molar amount of chelable metal ions corresponding to the sugar alcohol chelating component and the hydroxycarboxylic acid chelating component. S2: To prepare a trace metal chelating mother liquor, amino acid chelating components, biodegradable polycarboxylic acid chelating components and antioxidant stabilizers are dissolved in water, and iron salt, manganese salt, zinc salt and copper salt are added sequentially under pH conditions of 4.8 to 5.6 to carry out segmented chelation and obtain a trace metal chelating mother liquor. S3: To prepare a boron-molybdenum buffer mother liquor, a boron source is added to an aqueous solution containing sugar alcohol chelating components to form a boron-polyhydroxy complex system, and then a molybdenum source is added to obtain the boron-molybdenum buffer mother liquor. S4: Add the trace metal chelating mother liquor to the medium element prechelating mother liquor in segments. After each segment is added, detect the increase in turbidity, the rate of change in conductivity, and the proportion of free metal ions in the compound solution. When at least one of the following conditions is met: the increase in turbidity is greater than 5 NTU, the rate of change in conductivity is greater than 3%, and the proportion of free metal ions is greater than 2% of the total metal molar amount, add a retaining chelating agent to the compound solution. The retaining chelating agent is one, two, or three of the following: sugar alcohol chelating components, hydroxycarboxylic acid chelating components, and amino acid chelating components. S5: After all the trace metal chelating mother liquor is added, boron-molybdenum buffer mother liquor is added to the compound solution to adjust the pH to 5.8-6.2 and then stabilized to obtain chelated trace element compound liquid fertilizer.

2. The method for preparing a chelated micronutrient compound liquid fertilizer according to claim 1, characterized in that, When preparing the medium-element prechelation mother liquor, the sugar alcohol chelating component, the hydroxycarboxylic acid chelating component and water are stirred at 45-65°C for 20-40 min, then calcium salt is added and the reaction is kept at the temperature for 15-30 min, then magnesium salt is added and the reaction is kept at the temperature for another 20-50 min. The sugar alcohol chelating components include sorbitol and mannitol, the hydroxycarboxylic acid chelating components include potassium citrate and sodium gluconate, the calcium salt is calcium nitrate or calcium acetate, and the magnesium salt is magnesium nitrate or magnesium acetate.

3. The method for preparing a chelated micronutrient compound liquid fertilizer according to claim 2, characterized in that, The remaining complexing capacity is calculated as the difference between the theoretical total complexing capacity and the complexing capacity occupied by calcium and magnesium ions. The complexing capacity occupied by calcium and magnesium ions is calculated based on the molar amount of metal ions corresponding to the added calcium and magnesium salts.

4. The method for preparing a chelated trace element compound liquid fertilizer according to claim 3, characterized in that, When preparing the trace metal chelate mother liquor, the amino acid chelating component includes glycine, glutamic acid and aspartic acid, the degradable polycarboxylic acid chelating component is iminodisuccinate or polyaspartate, and the antioxidant stabilizer is ascorbic acid or sodium isoascorbate. After adding iron salts, the reaction time is 20–35 minutes; after adding manganese salts, the reaction time is 15–30 minutes; after adding zinc salts, the reaction time is 15–30 minutes; and after adding copper salts, the reaction time is 10–25 minutes.

5. The method for preparing a chelated micronutrient compound liquid fertilizer according to claim 4, characterized in that, The iron salt is ferrous sulfate or ferric nitrate, the manganese salt is manganese sulfate or manganese nitrate, the zinc salt is zinc sulfate or zinc nitrate, and the copper salt is copper sulfate or copper nitrate. The iron salt, manganese salt, zinc salt, and copper salt are added after being prepared into aqueous solutions with a mass concentration of 10% to 35%.

6. The method for preparing a chelated micronutrient compound liquid fertilizer according to claim 5, characterized in that, When preparing the boron-molybdenum buffer mother liquor, the sugar alcohol chelating component is first added to water and heated to 45-65°C, then the boron source is added and stirred for 20-50 minutes. Then the temperature is lowered to 35-50°C and the molybdenum source is added, and the pH is adjusted to 6.0-6.

8. The boron source is boric acid, sodium octaborate tetrahydrate, or potassium tetraborate tetrahydrate, and the molybdenum source is ammonium molybdate or sodium molybdate.

7. The method for preparing a chelated micronutrient compound liquid fertilizer according to claim 6, characterized in that, The trace metal chelation mother liquor was added to the medium element prechelation mother liquor in 3 to 6 stages. The amount added in each stage was 15% to 35% of the total mass of the trace metal chelation mother liquor. The stirring interval between two adjacent stages was 8 to 20 minutes. The test after each stage was added was carried out within 3 to 8 minutes after the stage was added. The turbidity increase value is the difference between the turbidity of the compound solution measured within 3 to 8 minutes after the addition of each segment of trace metal chelate mother liquor and the turbidity of the compound solution measured before the addition of that segment. The conductivity change rate is the percentage of the difference between the conductivity of the compound solution measured within 3-8 minutes after the addition of each segment of trace metal chelate mother liquor and the conductivity of the compound solution measured before the addition of that segment, relative to the conductivity of the compound solution measured before the addition of that segment. The free metal ion ratio is the percentage of the molar amount of free metal ions after ultrafiltration separation to the total molar amount of metals in the compound solution.

8. The method for preparing a chelated micronutrient compound liquid fertilizer according to claim 7, characterized in that, When the increase in turbidity is greater than 5 NTU, add sugar alcohol chelating components; When the rate of change in conductivity is greater than 3%, add hydroxycarboxylic acid chelating components; When the proportion of free metal ions is greater than 2% of the total metal molar amount, amino acid chelating components are added. The amount added at one time is 0.05% to 0.5% of the mass of the compound solution; The stabilization treatment includes: stirring the compound solution after adding boron-molybdenum buffer mother liquor at 35-50°C for 30-90 minutes, and then filtering it through an 80-200 mesh filter.

9. A chelated micronutrient compound liquid fertilizer, applicable to the preparation method of the chelated micronutrient compound liquid fertilizer according to any one of claims 1-8, characterized in that, include: Water, calcium, magnesium, iron, manganese, zinc, copper, boron, molybdenum, sugar alcohol chelates, hydroxycarboxylic acid chelates, amino acid chelates, and biodegradable polycarboxylic acid chelates; The sugar alcohol chelating components include sorbitol and mannitol, the hydroxycarboxylic acid chelating components include potassium citrate and sodium gluconate, the amino acid chelating components include glycine, glutamic acid and aspartic acid, and the degradable polycarboxylic acid chelating components are iminodisuccinate or polyaspartate. The pH of the chelated trace element compound liquid fertilizer is 5.8-6.2, and the proportion of free metal ions measured after separation by a 500Da molecular weight cutoff ultrafiltration membrane is no more than 2% of the total metal molar amount. The chelated micronutrient compound liquid fertilizer was diluted 100 times with a hard water simulation solution with a calcium carbonate hardness of 300-500 mg / L and a pH of 7.0-8.0 and allowed to stand for 24 hours. The turbidity increase of the diluted solution was no more than 10 NTU. The chelated micronutrient compound liquid fertilizer uses a phosphate-containing simulated solution with a phosphate concentration of 0.005–0.05 mol / L and a pH of 6.5–7.

5. After diluting 100 times and letting it stand for 24 hours, the increase in turbidity of the diluted solution is no more than 10 NTU.

10. A chelated trace element compound liquid fertilizer according to claim 9, characterized in that, The calcium content is 2.0%–8.0% by mass, the magnesium content is 0.5%–4.0% by mass, the zinc content is 0.1%–2.0% by mass, the iron content is 0.05%–1.5% by mass, the manganese content is 0.05%–1.5% by mass, the copper content is 0.01%–0.5% by mass, the boron content is 0.05%–1.0% by mass, and the molybdenum content is 0.005%–0.2% by mass. The chelated trace element compound liquid fertilizer is prepared by the preparation method according to any one of claims 1-8.

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