Preparation method of goethite-boron complex mineral for soil improvement

Abstract

The invention provides a preparation method of goethite-boron complex minerals for soil improvement, and belongs to the technical field of preparation of artificial minerals for soil improvement, the preparation method comprises the following steps: 1, mixing solutions; 2, stirring the mixed solution; 3, dropwise adding a sodium hydroxide solution; step 4, centrifugal washing; 5, drying the precipitate; and 6, grinding and screening. According to the goethite-boron composite artificial mineral prepared through the method, the boron loss rate is reduced, the boron slow release performance is improved, the ecological environment effect is improved, the boron fertilizer utilization efficiency is improved, iron nutrition is synchronously provided, and the iron deficiency symptom of calcareous soil is relieved.

Description

Technical Field

[0001] This invention relates to the field of controllable synthesis of composite artificial minerals, specifically to a method for preparing goethite-boron composite minerals for soil improvement. Background Technology

[0002] Boron is an essential micronutrient for plant growth. It is absorbed by the roots in the form of borate ions. It stabilizes cell wall pectin by forming borate-diester bonds, strengthens xylem vessels, promotes long-distance transport of sucrose-boron complexes in sieve tubes, and regulates pollen tube callose deposition and ovule development. Boron deficiency leads to thinning of cell walls, disordered enzyme activity, decreased pollen germination rate, ovary abortion, corky malformation of fruits, necrosis of root tip meristems, reduction of lateral roots, and ultimately reduced yield or even crop failure.

[0003] In my country, approximately 60% of arable land has available boron levels below the critical value of 0.5 mg / kg. In the rainy southern regions, 30%–50% of boron can be lost each season due to intense leaching. In the calcareous soils of the north, high pH levels cause boron to be fixed by clay particles and calcium carbonate. Traditional borax and boric acid are fast-acting and easily soluble, with a utilization rate of less than 20% in the current season. Excessive application can pollute water bodies through runoff, leading to crop failure to bear fruit, corky fruit pulp, and root tip necrosis. Therefore, there is an urgent need to develop slow-release boron carriers. Summary of the Invention

[0004] To address the problems existing in the prior art, the purpose of this invention is to provide a method for preparing goethite-boron composite minerals for soil improvement.

[0005] The objective of this invention is achieved through the following technical solution: A method for preparing goethite-boron composite minerals for soil improvement includes the following steps: Step 1, Mixing the solution: Place the reaction vessel on the main unit, add boric acid (H3BO3) solution to the reaction vessel, let it stand for 10 seconds after adding, and then add ferric nitrate [Fe(NO3)3·9H2O] solution to the reaction vessel to obtain a mixture of boric acid solution and ferric nitrate solution; Preferably, in the first step, the main unit is equipped with a power button, four display windows, and three knobs. The four display windows are for displaying the flow rate of the pumped liquid, the rotation speed of the stirring rotor, the temperature of the mixture in the reaction vessel, and the pH / OPR of the mixture in the reaction vessel, respectively. The three knobs are for adjusting the flow rate of the pumped liquid, the rotation speed of the stirring rotor, and the temperature of the mixture heating, respectively. The main unit is equipped with a magnetic stirring device, a heating device, a pH / OPR measuring device, and a pump device. An external liquid addition container is installed on the outside of the main unit. A cover plate is built on the reaction vessel. The cover plate can be made of glass, stainless steel, or polytetrafluoroethylene. A temperature control probe, a pH / OPR composite electrode, and a liquid drop inlet are installed on the cover plate. The external liquid addition container and the main unit are connected through a liquid delivery pipe A. The main unit and the liquid drop inlet are connected through a liquid delivery pipe B. The main unit and the temperature control probe are connected through a wire A. A wire B is provided between the main unit and the pH / OPR composite electrode. Preferably, in the first step, a stirring rotor is provided inside the reaction vessel. The stirring rotor is a magnetic rotor and is placed at the center of the bottom of the reaction vessel. Preferably, in the first step, the boric acid is a solution with a concentration of 1.0 mol / L to 2.0 mol / L; Preferably, in the first step, the ferric nitrate is a solution with a concentration of 0.1 mol / L to 0.2 mol / L. Preferably, in the first step, the molar ratio of boric acid solution to ferric nitrate solution is 10:1; Preferably, in the first step, the reaction vessel can be made of glass, stainless steel, or polytetrafluoroethylene.

[0006] Step 2: Stir the mixture: Turn on the main power and start the magnetic stirring device. The magnetic stirring device drives the stirring rotor in the reaction vessel to rotate, and the stirring rotor stirs the mixture of boric acid solution and ferric nitrate solution in the reaction vessel. Preferably, in the second step, the rotational speed of the stirring rotor is 500 rpm to 800 rpm; Preferably, in the second step, the stirring time of the stirring rotor on the mixture of boric acid solution and ferric nitrate solution is 3-5 hours; Third step: Add sodium hydroxide solution dropwise. Under the condition of continuous stirring of the mixture of boric acid solution and ferric nitrate solution, sodium hydroxide (NaOH) solution is added dropwise to the reaction vessel. The pH value of the reaction system is monitored in real time, the stirring rate is adjusted, and sodium hydroxide solution is continuously added dropwise according to the set requirements. The mixture is stirred until the reaction system is stable. Preferably, in the third step, a 2.5 mol / L sodium hydroxide solution is added dropwise to the reaction vessel at a constant rate of 5 mL / min. Preferably, in the third step, the pH value of the reaction system is monitored in real time and the stirring rate is adjusted. That is, when the pH is ≥ 4.4, the stirring rate needs to be increased to 800 rpm to 1200 rpm due to the increase in solution viscosity, so as to avoid local agglomeration. Preferably, in the third step, sodium hydroxide solution is continuously added dropwise according to a set requirement, that is, the addition of sodium hydroxide solution is stopped when the pH value of the final solution reaches the range of 11.5~12.0. Preferably, in the third step, the stirring time of the mixture is 6-8 hours.

[0007] Step 4, centrifugal washing: The supernatant of the reaction solution was removed by centrifugation; the precipitated minerals were added to deionized water, stirred and washed, and then centrifuged again; this washing process was repeated until the conductivity of the washing solution was ≤2 μS / cm. Preferably, in the fourth step, the centrifugal force is 3000 g to 4000 g, and the centrifugation time is 5 to 10 min; Preferably, in the fourth step, the precipitated minerals are added to deionized water at a solid-liquid ratio of 1:100 to 1:150 (W / V); Preferably, in the fourth step, the stirring and washing speed is 500 rpm to 800 rpm, and the stirring and washing time is 30 minutes. Preferably, in the fourth step, this washing process is repeated 10 to 15 times; Step 5: Dry the precipitate: Precipitates with an electrical conductivity ≤2 μS / cm are dried to obtain dried minerals; Preferably, in the fifth step, the drying temperature is 50℃~70℃; Step 6, Grinding and Screening: The dried minerals were ground and screened to obtain a goethite-boron composite artificial mineral. Preferably, in the sixth step, the dried minerals are ground in an agate mortar; Preferably, in the sixth step, the screening device is a nylon sieve with a mesh size of 200.

[0008] The beneficial effects of this invention are as follows: Goethite (α-FeOOH), a widely distributed iron oxide in soil, has surface hydroxyl groups (-OH) that form monodentate / bidentate complexes with boric acid (H3BO3) through coordination exchange, with the strongest adsorption at pH 7–9. The adsorption energy of goethite for boron lies between physical and chemical adsorption, allowing boron to be gradually desorbed when roots secrete organic acids (such as citric acid) or when soil pH decreases, thus achieving a continuous supply of boron.

[0009] By precisely controlling the crystal form, specific surface area, and boron loading of goethite through artificial synthesis, a quantitative model of the relationship between "mineral structure-boron release kinetics-crop absorption efficiency" can be established, overcoming the research bottleneck caused by the heterogeneity of natural minerals. Compared with traditional boron fertilizers, the composite mineral can reduce boron loss by 70% under simulated rainfall conditions, effectively improving the slow-release performance of boron and increasing its ecological and environmental benefits. The organic acids secreted by roots dissolve the composite mineral, triggering targeted release of boron and improving boron fertilizer utilization efficiency. At the same time, the goethite carrier can simultaneously provide iron nutrition, alleviating iron deficiency symptoms in calcareous soils.

[0010] This preparation method achieves atomic-level composite of boron (H3BO3) and goethite (α-FeOOH) through chemical crystallization. Boron exists stably in the mineral lattice in a structural substitution form. The composite mineral slowly releases boron into the soil, solving the problem of easy leaching loss of traditional boron fertilizers. It is especially suitable for sandy soils or areas with high rainfall.

[0011] The minerals prepared using this method have a total boron content of 87.4 mg / kg. After extraction with deionized water, the remaining minerals have a total boron content of 65.8 mg / kg. The water-soluble boron content is 21.6 mg / kg, accounting for 24.7%, while the fixed boron content is 75.3%. In contrast, other goethite-bound boron minerals prepared using this method have a water-soluble boron content of 35.5% and a fixed boron content of only 64.5%. Therefore, the minerals prepared using this method reduce the problem of boron leaching when applied to soil. Attached Figure Description

[0012] Figure 1 This is a flowchart of the preparation method of the present invention.

[0013] Figure 2 This is a schematic diagram of the preparation apparatus of the present invention.

[0014] The components are: 1. pH / OPR window, 2. Power button, 3. Temperature knob, 4. Temperature window, 5. Speed ​​knob, 6. Speed ​​window, 7. Flow rate knob, 8. Flow rate window, 9. Stirring rotor, 10. Reaction vessel, 11. Wire A, 12. Temperature control probe, 13. Liquid drop inlet, 14. pH / OPR composite electrode, 15. Infusion pipe B, 16. Cover plate, 17. Wire B, 18. Infusion pipe A, 19. Main unit, 20. External liquid addition container. Detailed Implementation

[0015] Example 1: As Figure 1 and Figure 2 As shown, a method for preparing a goethite-boron composite mineral for soil improvement includes the following steps: Step 1, Mixing the solution: Place reaction vessel 10 on main unit 19, add boric acid (H3BO3) solution to reaction vessel 10. The boric acid solution has a concentration of 1.0 mol / L to 2.0 mol / L. After adding the boric acid solution and letting it stand for 10 seconds, add ferric nitrate [Fe(NO3)3·9H2O] solution to reaction vessel 10. The ferric nitrate solution has a concentration of 0.1 mol / L to 0.2 mol / L. The molar ratio of boric acid solution to ferric nitrate solution is 10:1, resulting in a mixture of boric acid solution and ferric nitrate solution.

[0016] The reaction vessel 10 can be made of glass, stainless steel or polytetrafluoroethylene. The reaction vessel 10 is equipped with a stirring rotor 9, which is a magnetic rotor and is placed at the center of the bottom of the reaction vessel 10.

[0017] The main unit 19 is equipped with a power button 2, four display windows, and three knobs. The four display windows are for displaying the flow rate of the pumped liquid (window 8), the rotation speed of the stirring rotor 9 (window 6), the temperature of the mixture in the reaction vessel 10 (window 4), and the pH / OPR of the mixture in the reaction vessel 10 (window 1). The three knobs are for adjusting the flow rate of the pumped liquid (knob 7), the rotation speed of the stirring rotor 9 (knob 5), and the temperature of the mixture for heating (knob 3). The main unit 19 contains a magnetic stirring device, a heating device, a pH / OPR measuring device, and a pump device. An external device is added to the main unit 19. An external liquid addition container 20 is provided; a cover plate 16 is installed on the reaction vessel 10. The cover plate 16 can be made of glass, stainless steel or polytetrafluoroethylene. A temperature control probe 12, a pH / OPR composite electrode 14 and a liquid drop inlet 13 are installed on the cover plate 16. The external liquid addition container 20 and the main unit 19 are connected by a liquid inlet pipe A18. The main unit 19 and the liquid drop inlet 13 are connected by a liquid inlet pipe B15. The main unit 19 and the temperature control probe 12 are connected by a wire A11. A wire B17 is provided between the main unit 19 and the pH / OPR composite electrode 14.

[0018] Step 2: Stir the mixture: Turn on the power of the main unit 19 and start the magnetic stirring device. The magnetic stirring device drives the stirring rotor 9 in the reaction vessel 10 to rotate. The speed of the stirring rotor 9 is 500 rpm to 800 rpm. The stirring rotor 9 stirs the mixture of boric acid solution and ferric nitrate solution in the reaction vessel 10. The stirring time of the stirring rotor 9 is 3 to 5 hours.

[0019] Third step: Add sodium hydroxide solution dropwise. Under continuous stirring of the mixture of boric acid solution and ferric nitrate solution, 2.5 mol / L sodium hydroxide (NaOH) solution was added dropwise to reaction vessel 10 at a constant rate of 5 mL / min. The pH value of the reaction system was monitored in real time, and the stirring rate was adjusted accordingly. When the pH value was ≥ 4.4, the stirring rate needed to be increased to 800 rpm to 1200 rpm due to the increased viscosity of the solution to avoid local agglomeration. Sodium hydroxide solution was continuously added dropwise as required. When the pH value of the solution was in the range of 11.5 to 12.0, the addition was stopped, and the mixture was stirred for 6 to 8 hours until the reaction system stabilized.

[0020] Step 4, centrifugal washing: After the reaction, the supernatant was removed by centrifugation at a force of 3000 g to 4000 g for 5 to 10 min. The precipitated minerals were added to deionized water at a solid-liquid ratio of 1:100 to 1:150 (W / V), stirred and washed, and then centrifuged again. This washing process was repeated 10 to 15 times until the conductivity of the washing solution was ≤2 μS / cm.

[0021] Step 5: Dry the precipitate: Precipitates with an electrical conductivity ≤2 μS / cm were dried at a temperature of 50℃~70℃ to obtain dried minerals.

[0022] Step 6, Grinding and Screening: The dried minerals were ground in an agate mortar and sieved using a nylon sieve with a mesh size of 200 to obtain a goethite-boron composite artificial mineral.

[0023] Experimental example: The goethite-boron composite mineral maintains structural stability over a wide pH range (3~10) and at high temperatures (≤300℃), with a low boron release rate (compared to >30% for traditional borates under the same conditions). In addition, high-purity washing (conductivity ≤2 μS / cm) effectively removes free ions, avoiding secondary pollution in subsequent applications.

[0024] Boron extraction was performed on the prepared minerals using solutions of different pH values. After 7 days of extraction, the pH values ​​of the solutions and the boron content in the remaining minerals were as follows: Effect of different solution pH values ​​on the release efficiency of boron from composite minerals When the solution pH is neutral (6.47–7.75), the release efficiency of water-soluble boron from the mineral is 4.5%–4.8%. When the solution pH is below 5 (2.29–4.31), the release efficiency is only 9.1%–15.0%. This indicates that when the goethite-boron complex is applied to the soil, even with the effects of plant root exudates and microorganisms lowering the soil pH, the composite mineral still has a low dissolution efficiency while meeting the boron requirements of plants. This suggests that the prepared mineral can reduce the waste of boron resources and avoid boron pollution of soil and groundwater.

Claims

1. A method for preparing goethite-boron composite minerals for soil improvement, characterized in that, Includes the following steps: Step 1, Mixing the solution: Place the reaction vessel on the main unit, add boric acid solution to the reaction vessel, let it stand for 10 seconds after adding, and then add ferric nitrate solution to the reaction vessel to obtain a mixture of boric acid solution and ferric nitrate solution. In the first step, the main unit is equipped with a power button, four display windows, and three knobs. The four display windows are used to display the flow rate of the pumped liquid, the rotation speed of the stirring rotor, the temperature of the mixture in the reaction vessel, and the pH / OPR of the mixture in the reaction vessel. The three knobs are used to adjust the flow rate of the pumped liquid, the rotation speed of the stirring rotor, and the temperature of the mixture. The main unit is equipped with a magnetic stirring device, a heating device, a pH / OPR measuring device, and a pump device. An external liquid addition container is installed on the outside of the main unit. A cover plate is built on the reaction vessel. The cover plate can be made of glass, stainless steel, or polytetrafluoroethylene. A temperature control probe, a pH / OPR composite electrode, and a liquid drop inlet are installed on the cover plate. The external liquid addition container and the main unit are connected through a liquid delivery pipe A. The main unit and the liquid drop inlet are connected through a liquid delivery pipe B. The main unit and the temperature control probe are connected through a wire A. A wire B is provided between the main unit and the pH / OPR composite electrode. In the first step, a stirring rotor is provided inside the reaction vessel. The stirring rotor is a magnetic rotor and is placed at the center of the bottom of the reaction vessel. In the first step, the boric acid is a solution with a concentration of 1.0 mol / L to 2.0 mol / L; In the first step, the ferric nitrate solution has a concentration of 0.1 mol / L to 0.2 mol / L; In the first step, the molar ratio of boric acid solution to ferric nitrate solution is 10:1; In the first step, the reaction vessel can be made of glass, stainless steel, or polytetrafluoroethylene. Step 2: Stir the mixture: Turn on the main power and start the magnetic stirring device. The magnetic stirring device drives the stirring rotor in the reaction vessel to rotate, and the stirring rotor stirs the mixture of boric acid solution and ferric nitrate solution in the reaction vessel. In the second step, the stirring rotor rotates at a speed of 500 rpm to 800 rpm. The second step involves stirring the mixture of boric acid solution and ferric nitrate solution with a stirring rotor for 3-5 hours. Third step: Add sodium hydroxide solution dropwise. Under the condition of continuous stirring of the mixture of boric acid solution and ferric nitrate solution, sodium hydroxide solution is added dropwise to the reaction vessel. The pH value of the reaction system is monitored in real time, the stirring rate is adjusted, and sodium hydroxide solution is continuously added dropwise according to the set requirements. The mixture is stirred until the reaction system is stable. In the third step, a 2.5 mol / L sodium hydroxide solution is added dropwise to the reaction vessel at a constant rate of 5 mL / min. The third step involves monitoring the pH value of the reaction system in real time and adjusting the stirring rate. Specifically, when the pH value is ≥ 4.4, the stirring rate needs to be increased to 800 rpm to 1200 rpm due to the increased viscosity of the solution to avoid local agglomeration. The third step involves continuously adding sodium hydroxide solution as required, i.e., continuously adding sodium hydroxide solution until the pH value of the final solution is in the range of 11.5~12.0, and then stopping the addition. In the third step, the mixing time of the mixture is continued for 6-8 hours; Step 4, centrifugal washing: The supernatant was removed from the reacted solution under centrifugal force. The precipitated minerals were added to deionized water, stirred and washed, and then centrifuged again. Repeat this washing process until the conductivity of the washing solution is ≤2 μS / cm; In the fourth step, the centrifugal force is 3000 g to 4000 g, and the centrifugation time is 5 to 10 min. In the fourth step, the precipitated minerals are added to deionized water at a solid-liquid ratio of 1:100 to 1:150 (W / V); In the fourth step, the stirring and washing speed is 500 rpm to 800 rpm, and the stirring and washing time is 30 minutes. The fourth step involves repeating this washing process 10 to 15 times. Step 5: Dry the precipitate: Precipitates with an electrical conductivity ≤2 μS / cm are dried to obtain dried minerals; In the fifth step, the drying temperature is 50℃~70℃; Step 6, Grinding and Screening: The dried minerals were ground and screened to obtain a goethite-boron composite artificial mineral. In the sixth step, the dried minerals are ground in an agate mortar; In the sixth step, the screening device is a nylon sieve with a mesh size of 200.

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