Preparation method and application of low-cost polyamine wood powder-based lock phosphate agent applied to high-salt soil

Abstract

The application belongs to the application field of biomass-based conditioning agent in saline soil, and particularly relates to a preparation method and application of a low-cost polyamine wood powder-based phosphorus locking agent applied to high-salt soil. The method comprises the following steps: pretreating wood powder with alkali liquor to expose active groups in the wood powder, so as to facilitate modification in the next step, and obtaining pretreated wood powder; grafting crosslinking agent and fatty amine to the pretreated wood powder, and obtaining a polyamine wood powder-based phosphorus locking agent; further applying the polyamine wood powder-based phosphorus locking agent to adsorb and recycle phosphates; and applying the saturated polyamine wood powder-based phosphorus locking agent to high-salt soil. The biomass-based phosphorus locking agent can not only achieve the optimal effect of adsorbing phosphorus of 1.86-2.27 mmol / g, but also replace 10%-25% of traditional phosphorus fertilizers, so as to not only increase the content of available phosphorus in the saline soil by 31.8%-40.2%, but also reduce the pH of the saline soil to 7.8-7.9, adjust the EC value of the saline soil to 1404-1891 μs / cm, and promote the growth of crops in the high-salt soil.

Description

Technical Field

[0001] This invention pertains to the application of biomass-based conditioners in saline soils, specifically relating to a method for preparing and applying a low-cost polyamine wood flour-based phosphorus-locking agent for high-salt soils. Background Technology

[0002] Saline-alkali land is an important land reserve resource, attracting significant research attention due to its large area and poor soil conditions. Because saline-alkali soils are prone to compaction, soil porosity is affected, leading to low phosphorus utilization by plants under salt stress. Agricultural and forestry waste is widely available and produced in large quantities, but its utilization rate is very low, with most being used for fuel combustion, wasting resources and impacting the environment. Wood flour, as a type of agricultural and forestry waste, possesses inherent advantages such as a porous structure and large specific surface area, and the cellulose molecules in wood flour contain numerous active groups, providing a basis for its use as an adsorbent matrix. Meanwhile, with the development of the livestock industry, the discharge of livestock wastewater is increasing. Pig manure wastewater, a typical example of livestock wastewater, is considered "high-emission wastewater"—high in organic matter, nitrogen, and phosphorus—and also contains large amounts of pathogens and residual veterinary drugs. Phosphorus is a key factor contributing to eutrophication, and the discharge of untreated livestock wastewater leads to serious environmental pollution. In traditional livestock and poultry wastewater treatment processes, while emission indicators such as COD, BOD5, and TN can meet national standards, TP often fails to meet emission standards. Therefore, how to treat phosphorus in livestock and poultry wastewater has become an urgent issue of phosphorus pollution. Thus, the use of low-cost biomass-based materials as adsorbents for phosphorus-containing wastewater is considered. This approach can not only remove phosphorus from livestock and poultry wastewater but also achieve efficient utilization of agricultural and forestry waste.

[0003] While unmodified biomass materials offer significant cost advantages, they suffer from low adsorption capacity. Therefore, some studies have explored modifications to improve the adsorption performance of biomass materials. For example, Sowmya et al. modified chitosan-melamine-glutaraldehyde resin with quaternary ammonium chloride functionalization, achieving a maximum adsorption capacity of 31.6 mg / g and demonstrating highly efficient phosphate removal.

[0004] Since wood flour mainly contains a large amount of cellulose, hemicellulose, and lignin, and based on the structure of cellulose, it is known that it contains a large number of active groups such as hydroxyl and carboxyl groups, which endow it with the ability to be chemically modified. Furthermore, the basicity and electronegativity of amine groups can interact with pollutant phosphate groups through hydrogen bonding and electrostatic attraction. Therefore, amine groups are introduced through grafting. This method not only preserves the three-dimensional network structure of wood flour but also improves the adsorption performance of the adsorbent.

[0005] Therefore, biomass-based materials have broad research value as adsorbents for treating phosphorus-containing wastewater. Furthermore, modifying the structure of biomass itself can significantly improve the material's ability to remove pollutants, while also enhancing the stability and regeneration performance of biomass materials.

[0006] In existing technologies, high-salinity soils are generally improved by applying a mixture of organic matter, microorganisms, and other materials to enable plant growth. However, the further harmless treatment of saturated non-carbonized biomass-based materials is a problem, and there are few reports on the technology of reusing saturated non-carbonized biomass-based materials alone in high-salinity soils. Because the modification of high-salinity soils and their impact on crops is complex, the reuse of saturated non-carbonized biomass-based materials alone often fails to achieve soil improvement in a short period, resulting in poor plant growth in high-salinity soils. Summary of the Invention

[0007] This invention proposes a method for preparing a low-cost polyamine wood flour-based phosphorus-locking agent for use in high-salt soils, as well as its application. Utilizing a low-cost wood flour-based agent to prepare a highly efficient phosphorus-locking agent and applying it to high-salt soils has environmental significance in turning waste into waste.

[0008] To address the aforementioned problems in existing technologies, this invention proposes a method for preparing and applying a low-cost polyamine wood flour-based phosphorus-locking agent for high-salt soils. The polyamine wood flour-based phosphorus-locking agent prepared by this method not only efficiently removes phosphorus from livestock and poultry manure wastewater but also improves phosphorus utilization by plants in saline soils.

[0009] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0010] A method for preparing a low-cost polyamine wood flour-based phosphorus-locking agent for high-salt soil includes the following steps: 1) Wood flour is placed in a 1-2 mol / L alkaline solution and pretreated at 70-90℃ for 0.5-1.5 h; then 0.5-2% (v / v) acid is added and treated at room temperature for 1-2 h, followed by washing to obtain pretreated wood flour; 2) The pretreated wood flour is grafted with a crosslinking agent and a fatty amine sequentially at 75-90℃ for 3-6 h. The crosslinking agent is epichlorohydrin, and the fatty amine is at least one of diethylenetriamine, triethylenetetramine, and tetraethylenepentamine to obtain a polyamine wood flour-based phosphorus-locking agent (referred to as polyamine wood flour); when grafting the crosslinking agent and fatty amine onto the pretreated wood flour, the ratio of pretreated wood flour to crosslinking agent is 1 g: 85-95 mmol, and the ratio of pretreated wood flour to fatty amine is 1 g: 27-33 mmol; the polyamine wood flour-based phosphorus-locking agent is used to adsorb phosphate ions;

[0011] Adsorption-saturated polyamine wood flour-based phosphorus-locking agents are applied to high-salt soils.

[0012] In a preferred embodiment, in step 2), the pretreated wood flour is first grafted with a crosslinking agent, and then with aliphatic amines.

[0013] Further, in step 2), when pretreating the wood flour grafting crosslinking agent and fatty amine, the ratio of pretreated wood flour to crosslinking agent is 1g:90mmol, and the ratio of pretreated wood flour to fatty amine is 1g:30mmol.

[0014] In step 2), the pretreated wood flour is soaked in an organic solvent and grafted with a crosslinking agent and aliphatic amine. The grafting reaction temperature is 85°C and the grafting reaction time is 5 hours. The organic solvent is N,N-dimethylformamide.

[0015] In a preferred embodiment, in step 1), the alkaline solution in the pretreatment is a 1-2 mol / L sodium hydroxide or potassium hydroxide solution; the acid is sulfuric acid or hydrochloric acid. The ratio of wood flour to alkaline solution is 1 g: 20-50 mL; the wood flour is obtained by crushing wood chips and then passing them through a 10-80 mesh sieve.

[0016] Alkali treatment exposes more active groups in the material; adding acid and treating at room temperature for a period of time treats the wood flour to a slightly acidic-neutral state, which facilitates the next grafting reaction.

[0017] The preparation method specifically involves pretreating ground and sieved wood flour by heating it in a sodium hydroxide solution at 80°C in a water bath, then treating it with sulfuric acid, and finally washing it until neutral. The pretreated wood flour is then soaked in N,N-dimethylformamide organic solvent, heated in an 80°C water bath, and a crosslinking agent and aliphatic amine groups are added sequentially. After 5 hours, the grafting reaction is completed, yielding polyamine wood flour. Simulating livestock and poultry manure wastewater, the pH is adjusted, and polyamine wood flour is added to statically adsorb phosphates. Once adsorption is complete, a biomass-based phosphate-locking agent is obtained.

[0018] Furthermore, the wood flour is wood flour sieved through a 10-80 mesh, the concentration of the sodium hydroxide solution in the pretreatment is 1-2 mol / L, and a sulfuric acid solution with a volume fraction of 1% is also used in the pretreatment.

[0019] Furthermore, the specific steps are as follows:

[0020] (1) The crushed wood chips are sieved through a 10-80 mesh sieve to obtain wood flour. The wood flour is placed in a 1-2 mol / L NaOH solution and stirred continuously at 80℃ for 1 h. After cooling and precipitation, the supernatant is removed, leaving the wood flour. The waste supernatant can be recycled and reused. A 1% sulfuric acid solution (i.e., sulfuric acid aqueous solution) is prepared, and the wood flour is added to the 1% sulfuric acid solution. The mixture is stirred continuously at room temperature for 2 h. After precipitation, the supernatant is removed. The waste supernatant can be recycled and reused. Pure water is added until the wood flour is washed to neutral. The wood flour is obtained by suction filtration and dried at 55℃. After drying, it is ground to obtain pretreated wood flour.

[0021] (2) The pretreated wood powder obtained in step (1) was placed in NN dimethylformamide and stirred continuously at room temperature for 1 h. After the temperature was stabilized at 85°C by water bath heating, 90 mmol / L epichlorohydrin was added and stirred continuously for 2 h. 30 mmol / L diethylenetriamine, triethylenetetramine, and tetraethylenepentamine were slowly added to the mixture and stirred continuously for 3 h. After cooling to room temperature, the wood powder was filtered and washed with pure water several times until neutral. The obtained wood powder was placed in a freeze dryer for freeze drying. After drying, it was ground to obtain diethylenetriamine wood powder, triethylenetetramine wood powder, and tetraethylenepentamine wood powder.

[0022] (3) Add sodium hydroxide solution and hydrochloric acid solution to adjust the pH of KH2PO4 solution, then add the polyamine wood powder obtained in step (2), and place it in a shaker for static adsorption for 24 hours. After adsorption is completed, polyamine wood powder with adsorbed phosphate is obtained.

[0023] Furthermore, the simulated livestock and poultry manure wastewater is a KH2PO4 solution with concentrations of 0.1, 0.2, 0.25, 0.5, 1, and 1.5 mmol / L, prepared in the laboratory.

[0024] Furthermore, the pH of the KH2PO4 solution of the simulated livestock and poultry manure wastewater is adjusted to be between 2 and 10.

[0025] Furthermore, the KH2PO4 solution of the simulated livestock and poultry manure wastewater contains coexisting substances of CaCl2, NH4Cl, NaF, Na2SO4, NaNO3, and FeCl3 in 1 mmol / L and 5 mmol / L solutions, respectively.

[0026] Furthermore, the adsorption temperatures in the static adsorption experiments were set to 10, 20, 30, and 40°C, respectively.

[0027] Furthermore, the adsorption times in the static adsorption experiment were set to 0, 5, 10, 30, 60, 180, 360, 720, 1080, 1440, 2160, and 2880 min, respectively.

[0028] This invention also provides a low-cost polyamine wood flour-based phosphorus-locking agent prepared by the aforementioned method for use in high-salt soils. It is suitable for soils with a total salt content of 2–6‰ (mass fraction).

[0029] Another objective of this invention is to disclose the application of the aforementioned low-cost polyamine wood flour-based phosphorus-locking agent for high-salt soils in improving the salinity of high-salt soils, reducing the pH value of high-salt soils, and increasing the available phosphorus content in high-salt soils, thereby increasing the available phosphorus content in high-salt soils by 31.8% to 40.2%, reducing the pH value of high-salt soils to 7.8 to 7.9, and adjusting the EC value of high-salt soils to 1404 to 1891 μs / cm; or in increasing plant biomass in high-salt soils, thereby increasing plant height by 11.9% to 33.5% and fresh weight by 27.5% to 62.5%.

[0030] In a preferred embodiment, when applied to high-salt soil, the mass ratio of polyamine wood flour-based phosphorus-locking agent to high-salt soil is 0.1–2:1000, and the mixture is homogeneous. During application, the polyamine wood flour-based phosphorus-locking agent is evenly mixed with a 1–10 cm thick layer of topsoil. The polyamine wood flour-based phosphorus-locking agent is applied as part of the base fertilizer 8–12 days after sowing. The polyamine wood flour-based phosphorus-locking agent is used to replace 10%–25% (w / w) of phosphate fertilizer.

[0031] The polyamine wood powder-based phosphorus-locking agent is mixed evenly with a 1-10cm thick layer of topsoil with high salinity to ensure that nutrients can be effectively utilized by the plants.

[0032] Preferably, when applied to high-salt soil, the polyamine wood flour-based phosphorus-locking agent is a non-phosphorus-adsorbed polyamine wood flour-based phosphorus-locking agent (the polyamine wood flour-based phosphorus-locking agent itself also contains nitrogen, which can provide nutrients for plants) or a phosphorus-adsorbed polyamine wood flour-based phosphorus-locking agent, and the mass ratio of the polyamine wood flour-based phosphorus-locking agent to the high-salt soil is 0.2-0.4:1000.

[0033] The specific steps are as follows:

[0034] Step 1: Add polyamine wood powder to the saline-alkali soil at a mass fraction of 0.2‰ and 0.4‰; or add polyamine wood powder that has been adsorbed with saturated phosphate at a mass fraction of 0.2‰ and 0.4‰ and mix it evenly into the saline-alkali soil, so as to replace traditional inorganic phosphate fertilizer (superphosphate) with phosphorus.

[0035] Step 2: Weigh 5g of air-dried soil sample into a 50mL beaker and add 12.5mL of carbon dioxide-free water. Stir vigorously with a glass rod for 1-2 minutes, let stand for 30 minutes, then use a glass electrode as the indicator electrode and a calomel electrode as the reference electrode. When both electrodes are inserted into the soil filtrate, a cell reaction is formed, creating a potential difference between them. Weigh the air-dried soil sample and add water at a ratio of 1:5 (mass ratio of air-dried soil sample to water is 1:5). Extract by shaking at room temperature and measure the conductivity of the extract at 25℃.

[0036] Compared with the prior art, the advantages of the present invention are:

[0037] (1) During the grafting process, this invention crosslinks the pretreated wood flour with an appropriate amount of crosslinking agent and aliphatic amine groups. When the resulting polyamine wood flour-based phosphorus-locking agent is applied to high-salt soil after phosphate adsorption saturation, phosphorus is released from the polyamine wood flour-based phosphorus-locking agent into the high-salt soil. The sites on which phosphorus is released in the polyamine wood flour-based phosphorus-locking agent can then adsorb chloride ions and other salt ions in the high-salt soil again, thereby reducing the salt concentration in the saline soil. At the same time, the phosphorus-saturated polyamine wood flour-based phosphorus-locking agent also lowers the soil pH.

[0038] When the amount added is less than 1‰, after the phosphorus saturated adsorption polyamine wood flour-based phosphorus locking agent replaces a certain proportion of inorganic phosphate fertilizer, the available phosphorus in saline soil and the biomass of plants both increase. This indicates that the polyamine wood flour-based phosphorus locking agent is better at fixing and locking phosphorus in saline soil than ordinary phosphate fertilizer, and is more conducive to plant growth.

[0039] (2) This invention uses waste biomass-based wood flour as raw material to prepare a highly efficient biomass-based phosphorus-locking agent. Utilizing the large number of active groups such as hydroxyl and carboxyl groups in the cellulose structure of wood flour, it is endowed with the ability to be chemically modified. Simultaneously, through a grafting reaction, aliphatic amine groups are grafted onto the carbon chain of the macromolecule. The basicity and electronegativity of the aliphatic amine groups can interact with phosphate ions in wastewater through electrostatic attraction and hydrogen bonding, thereby achieving the purpose of removing phosphorus from the wastewater. This not only preserves the three-dimensional network structure of wood flour but also enhances the adsorption performance of the biomass-based phosphorus-locking agent. The adsorption capacity of this biomass-based phosphorus-locking agent for phosphate ions can reach up to 1.86–2.27 mmol / g, significantly superior to other common chemical precipitation adsorption and biofilm adsorption technologies, laying a good foundation for the subsequent removal of phosphorus from livestock and poultry manure wastewater.

[0040] (3) The pretreatment method used in this invention before grafting modification is a simpler alkali treatment method compared to common pretreatment methods such as physical methods (mechanical crushing, steam explosion), chemical methods (dilute acid treatment, ozone treatment), and biological methods (microbial fermentation). Alkali pretreatment of the wood flour exposes more active groups in the cellulose, improving the efficiency of the grafting reaction. This invention uses a lower concentration of alkali solution, and the alkali solution can be reused.

[0041] (4) Application in saline soil: Polyamine wood powder with static phosphorus adsorption was used to replace a certain proportion of conventional fertilizer with equal phosphorus and nitrogen content, and the available phosphorus content in the soil and plant growth indicators were measured. This invention uses a biomass-based phosphorus-locking agent, which can not only achieve the optimal phosphorus adsorption effect of 1.86-2.27 mmol / g, but also replace 10%-25% (w / w) of traditional phosphate fertilizer with equal phosphorus content. This can not only increase the available phosphorus content in saline soil by 31.8%-40.2%, but also lower the pH of saline soil to 7.8-7.9 and adjust the EC value of saline soil to 1404-1891 μs / cm.

[0042] (5) Compared with biochar materials, polyamine wood powder has a simple synthesis process and can be completed at about 85°C. The pH of polyamine wood powder products is neutral. Applying polyamine wood powder at only 0.2‰ to 0.4‰ can significantly increase the biomass of plants. The plant height in high saline soil increases by 11.9% to 33.5%, and the fresh weight increases by 27.5% to 62.5%. In addition, polyamine wood powder greatly increases the available phosphorus content in saline soil. Attached Figure Description

[0043] Figure 1 This invention relates to the effect of polyamine wood flour-based phosphorus-locking agent on phosphate adsorption under different pH conditions and different polyamine reagents.

[0044] Figure 2 This invention relates to the effect of polyamine wood flour-based phosphorus-locking agent on the adsorption capacity of phosphates with different initial concentrations.

[0045] Figure 3 This invention relates to the effect of polyamine wood flour-based phosphorus-locking agent on phosphate adsorption capacity at different adsorption temperatures.

[0046] Figure 4 The effect of the polyamine wood flour-based phosphorus-locking agent of the present invention on the phosphate adsorption capacity under different concentrations of interfering ions;

[0047] Figure 5 This invention illustrates the effect of the polyamine wood flour-based phosphorus-locking agent on the phosphate adsorption capacity at different adsorption times.

[0048] Figure 6 The zeta potential values ​​of the polyamine wood flour-based phosphorus-locking agent of the present invention at different pH values;

[0049] Figure 7 This is a graph showing the effect of different application amounts of the polyamine wood flour-based phosphorus-locking agent of the present invention on the available phosphorus in saline soil;

[0050] Figure 8 This is a graph showing the effect of different application rates of the polyamine wood flour-based phosphorus-locking agent of the present invention on plant biomass;

[0051] Figure 9 This is a graph showing the effect of different application amounts of the polyamine wood flour-based phosphorus-locking agent of the present invention on the pH of saline soil;

[0052] Figure 10 This is a graph showing the effect of different application amounts of the polyamine wood flour-based phosphorus-locking agent of the present invention on the EC of saline soil. Detailed Implementation

[0053] The present invention will be further described below with reference to specific embodiments.

[0054] The biomass base used in the following examples is wood flour.

[0055] The specific test method of the molybdenum antimony spectrophotometric method used to determine the total phosphorus concentration in water samples in the following examples is as follows: A water sample diluted to a certain factor is added to a 25 mL colorimetric tube. After adding potassium persulfate solution, the tube is autoclaved at 120°C for 30 min to reduce the phosphate in the water sample to orthophosphate. After the water sample cools, a certain amount of ascorbic acid and the colorimetric reagent molybdenum antimony solution are added. After waiting for 15 min for color development, the concentration is measured at 700 nm using a UV spectrophotometer.

[0056] Example 1

[0057] Step 1:

[0058] (1) The crushed wood chips are sieved through an 80-mesh sieve to obtain wood flour. 3g of wood flour is placed in 100mL of 1mol / L NaOH solution and stirred continuously at 80℃ for 1h. After cooling and precipitation, the supernatant is removed, leaving the wood flour. A 1% (v / v) sulfuric acid solution is prepared, and the wood flour is added to 100mL of the 1% sulfuric acid solution. The mixture is stirred continuously at room temperature for 2h. After precipitation and removal of the supernatant, pure water is added until the wood flour is washed to neutral. The wood flour is obtained by suction filtration and dried at 55℃. After drying, it is ground to obtain pretreated wood flour. The waste supernatant can be recycled and reused.

[0059] (2) 1g of the pretreated wood powder obtained in step 1) was placed in 50mL of NN dimethylformamide and stirred continuously at room temperature for 1h. After the temperature was stabilized at 85℃ in a water bath, 90mmol of 7.027mL of epichlorohydrin was added and stirred continuously for 2h. 30mmol of fatty amines (3.258mL of diethylenetriamine, 4.477mL of triethylenetetramine, and 5.680mL of tetraethylenepentamine) were slowly added to the mixture and stirred continuously for 3h. After cooling to room temperature, the wood powder was filtered and washed with pure water several times until neutral. The obtained wood powder was placed in a freeze dryer for freeze drying. After drying, it was ground to obtain diethylenetriamine wood powder, triethylenetetramine wood powder, and tetraethylenepentamine wood powder.

[0060] Step 2: Mix deionized water and potassium dihydrogen phosphate reagent thoroughly to prepare a 5 mmol / L KH₂PO₄ stock solution. Dilute to prepare a 1 mmol / L KH₂PO₄ solution. Adjust the pH of the KH₂PO₄ solution to 2, 3, 4, 6, 8, 9, and 10 respectively by adding 1 mol / L sodium hydroxide solution and 1 mol / L hydrochloric acid solution. Then add the three types of polyamine wood powder obtained in the above steps at a dosage of 0.4 g / L (20 mg of each type of polyamine wood powder at each pH condition) to 50 mL of potassium dihydrogen phosphate solution. Shake at 160 rpm and 25 °C for 24 h. Filter the solution through a 0.45 μm aqueous filter membrane to remove the wood powder. Determine the phosphorus content of the supernatant using the molybdate colorimetric method and calculate the adsorption capacity of the polyamine wood powder for phosphate. The following steps are carried out under the optimal pH conditions obtained in this step, i.e., pH = 6. Figure 1 The graph shows the relationship between the adsorption capacity of three types of polyamine wood flour for phosphate under different pH conditions before and after modification.

[0061] Step 3: Utilizing polyamine wood powder to adsorb and treat phosphate molar concentrations of 0.1, 0.2, 0.25, 0.5, 1, and 1.5 mmol / L, pH=6, with a polyamine wood powder dosage of 0.4 g / L. Prepare a 5 mmol / L KH₂PO₄ stock solution by thoroughly mixing deionized water and potassium dihydrogen phosphate reagent. Then dilute with deionized water to prepare KH₂PO₄ solutions of 0.1, 0.2, 0.25, 0.5, 1, and 1.5 mmol / L. Weigh 20 mg of the polyamine wood powder obtained in the previous step at a dosage of 0.4 g / L and place it in 50 mL of potassium dihydrogen phosphate solution. Shake at 160 rpm and 25℃ for 24 h. Filter the solution through a 0.45 μm aqueous filter membrane to remove the wood powder. Determine the phosphorus content of the supernatant using the molybdate colorimetric method and calculate the adsorption capacity of the polyamine wood powder for phosphate. Figure 2 This is a curve showing the relationship between the initial phosphate concentration and the adsorption capacity.

[0062] Step 4: Set the constant temperature shaking bed to a temperature gradient of 10℃, 20℃, and 30℃. Prepare a KH2PO4 solution with an initial concentration of 1 mmol / L and pH=6. Under the condition of adding 0.4 g / L, weigh 20 mg and place it in 50 mL of potassium dihydrogen phosphate solution. Shake at 160 rpm for 24 h. Then filter out the wood flour using a 0.45 μm aqueous filter membrane. Take the supernatant and determine the phosphorus content using the molybdate colorimetric method. Calculate the adsorption capacity of polyamine wood flour for phosphate. Figure 3 The image shows the adsorption isotherm curves of polyamine wood flour.

[0063] Step 5: Prepare a KH2PO4 solution with an initial concentration of 1 mmol / L and pH = 6. Under the condition of adding 0.4 g / L, weigh 100 mg and place it in 250 mL of potassium dihydrogen phosphate solution. Take samples at 160 rpm at time intervals of 5, 10, 20, 30, 60, 120, 360, 480, 960, 1080, 1440, 1960, and 2080 min each time. After each sample is taken, filter it through a 0.45 μm aqueous filter membrane to remove the wood flour. Take the supernatant and determine the phosphorus content by the molybdate colorimetric method. Calculate the adsorption capacity of polyamine wood flour for phosphate. Figure 5 The kinetic curve of phosphate adsorption by polyamine wood flour is shown.

[0064] Step 6: Prepare a KH2PO4 solution with an initial concentration of 1 mmol / L and pH = 6. Mix the 1 mmol / L KH2PO4 solution with CaCl2, NH4Cl, NaF, Na2SO4, NaNO3, and FeCl3 solutions with concentrations of 1 mmol / L and 5 mmol / L, respectively. Under the condition of adding 0.4 g / L, weigh 20 mg and place it in 50 mL of the mixed solution containing the coexisting substances. Shake at 160 rpm and 25 °C for 24 h. Then filter out the wood flour using a 0.45 μm aqueous filter membrane. Take the supernatant and determine the phosphorus content using the molybdate colorimetric method. Calculate the adsorption capacity of polyamine wood flour for phosphate. Figure 4 The figure shows the effect of interfering ions on the adsorption of phosphate by polyamine wood flour.

[0065] Step 7: Prepare deionized water with pH values ​​of 2, 3, 4, 5, 6, 7, 8, 9, and 10 respectively. The dosage of polyamine wood powder is 1 g / L, that is, 10 mg of wood powder is placed in 10 mL of deionized water with the pH adjusted. Sonicate until the polyamine wood powder is completely dispersed and suspended in the centrifuge tube, and then measure it using a zeta potential meter. Figure 6 The diagram shows the zeta potential of three types of polyamine wood flour.

[0066] Figure 1The adsorption capacity of wood flour modified with three polyamine reagents for phosphate under different pH conditions was investigated. It can be seen that the adsorption capacity of the three polyamine wood flours for phosphate was significantly improved before and after modification. In this article, DTWF refers to diethylenetriamine wood flour, TTWF refers to triethylenetetramine wood flour, and TPWF refers to tetraethylenepentamine wood flour. Among them, DTWF showed better adsorption capacity at pH=4, and TTWF and TPWF at pH=6, with adsorption capacities of 0.976 mmol / g, 1.109 mmol / g, and 1.123 mmol / g, respectively. Compared with the alkali-treated wood flour (WF), the adsorption capacity increased by 83.6%, 85.5%, and 85.7%, respectively. The alkali-treated wood flour (WF) is the pretreated wood flour obtained in step one (1) of Example 1.

[0067] Figure 2 The adsorption capacity of three polyamine wood powders for phosphate at different initial concentrations is shown. It can be seen that under the same dosage (0.4 g / L), the adsorption capacity of polyamine wood powder for phosphate gradually increases with the increase of the initial phosphate concentration, and the maximum adsorption capacity is 1.86 mmol / g, 2.08 mmol / g, and 2.27 mmol / g when the maximum initial concentration is set at 1.5 mmol / L. Figure 2 From right to left, the numbers are DTWF, TTWF, and TPWF.

[0068] Figure 3 The adsorption capacity of three polyamine wood flours for phosphate at different adsorption temperatures shows that as the temperature increases from 10℃ to 30℃, the adsorption capacity of DTWF gradually decreases, and then increases again with increasing temperature. Conversely, the adsorption capacities of TTWF and TPWF decrease first at 10-20℃, then increase at 30℃, and then decrease again at 40℃. This indicates that the different temperature-dependent changes of DTWF, TTWF, and TPWF are due to different adsorption mechanisms.

[0069] Figure 5 The changes in contact time and phosphate adsorption capacity of the three polyamine wood powders are shown. It can be seen that the adsorption process of phosphate by the polyamine wood powders can be divided into three stages. In the initial stage of adsorption (first 3 hours), the enrichment of phosphate increases rapidly with increasing contact time. Subsequently, a slow adsorption stage (3 hours to 6 hours) occurs, during which the enrichment trend of phosphate gradually slows down, eventually reaching equilibrium. All three polyamine wood powders reach adsorption equilibrium between 1500 and 2000 minutes, and the adsorption capacities of the three polyamine wood powders at equilibrium are 1.043 mmol / g, 1.078 mmol / g, and 1.042 mmol / g, respectively.

[0070] Figure 4The effects of different coexisting ions on the adsorption of phosphate by three polyamine wood flours were investigated. It can be seen that low concentrations of interfering ions have little effect on adsorption. As the molar ratio of interfering ion concentration to phosphate increases from 2 to 10, the adsorbent exhibits a significant loss in adsorption capacity, with the loss order being: SO42-... 2- >NO3 - >Cl - >NH4 + >Fe 3+ >F - Therefore, the more negatively charged anions there are, the greater their impact on phosphorus removal. Figure 5 From right to left, the numbers correspond to DTWF, TTWF, and TPWF respectively.

[0071] Figure 6 The zeta potential of the three polyamine wood powders changes with pH. It can be seen that the isoelectric points of the three polyamine wood powders are all between 8 and 10. The reason why the polyamine wood powder has the best adsorption effect on phosphate at pH = 4 to 6 is that the zeta potential is greater than zero at pH = 4 to 6, which makes the polyamine wood powder carry a positive charge. Based on the porous structure of the wood powder, it electrostatically attracts phosphate anions.

[0072] Considering the adsorption capacity of the three polyamine wood powders and the cost of polyamine reagents, triethylenetetramine wood powder, which has a lower cost and higher adsorption capacity, was used in subsequent saline soil experiments. The specific surface area of ​​the triethylenetetramine wood powder was measured to be 2.917 m² / g, with C, O, and N contents of 59%, 21.2%, and 19.6% (mass fraction), respectively. In existing technologies, other cellulose-based grafted amine groups only achieve a nitrogen content of 5.17% (Hui Qiu et al., Fabrication and evaluation of a regenerable HFO-doped agricultural waste for enhanced adsorption affinity towards phosphate). This demonstrates that the present invention grafts more amine groups, and the nitrogen content indicates the amount of grafted amine groups. The nitrogen content of the polyamine wood powder is based on SEM-Mapping test results.

[0073] Example 2:

[0074] Step 1: Considering the adsorption capacity of the three types of polyamine wood powder and the cost of polyamine reagents, triethylenetetramine wood powder was selected for application in the subsequent saline soil treatment. The saturated adsorption capacity of triethylenetetramine for phosphate adsorption is 2.08 mmol / g. The triethylenetetramine wood powder after saturated adsorption of phosphate (i.e., the saturated adsorbed polyamine wood powder-based phosphorus-locking agent) was added at a mass fraction of 0.2‰ and 0.4‰ respectively and uniformly mixed into the saline-alkali soil (except for the CKU treatment, the polyamine wood powder-based phosphorus-locking agent of other treatments was uniformly mixed with a 10cm thick layer of top high-salt soil). Phosphorus was used to replace traditional inorganic phosphate fertilizer (superphosphate). The saline soil used in the test was collected from Dongtai City, Yancheng City, Jiangsu Province. The saline soil had a pH of 9.25, an EC of 3070 μs / cm, and a total salt content of 3 g / kg. Each pot contained 8 kg of saline soil. The amount of phosphate fertilizer required for planting amaranth was 3.375 g / pot. Eight amaranth seedlings were thinned out per pot. Five treatments were set up: conventional fertilization group (CKU) (applied according to N 200 kg / ha and P2O5 90 kg / ha, conventional fertilization was applied on the same day as other treatment groups, all on the 10th day after sowing), 0.2‰ polyamine wood powder treatment group (L-AC), 0.4‰ polyamine wood powder treatment group (H-AC), 0.2‰ saturated phosphorus-absorbing polyamine wood powder treatment group (L-ACP), and 0.4‰ saturated phosphorus-absorbing polyamine wood powder treatment group (H-ACP). All treatments will be referred to by abbreviations. Each treatment was set up in 4 replicates. The 0.2‰ and 0.4‰ polyamine wood powder treatment groups used triethylenetetramine wood powder prepared in step one of Example 1, which replaced 7.3% (mass fraction) and 14.7% of inorganic nitrogen fertilizer with equal nitrogen, respectively, and the remaining nitrogen fertilizer was supplemented by urea. The 0.2‰ and 0.4‰ saturated adsorption polyamine wood powder-based phosphorus-locking agents replaced 10.4% (mass fraction) and 20.7% of inorganic phosphate fertilizer with equal phosphorus, respectively. At the same time, the 0.2‰ and 0.4‰ saturated adsorption polyamine wood powder-based phosphorus-locking agents replaced 7.3% (mass fraction) and 14.7% of inorganic nitrogen fertilizer with equal nitrogen, respectively, and the remaining phosphate fertilizer was supplemented by superphosphate, and the remaining nitrogen fertilizer was supplemented by urea. The saturated adsorption polyamine wood powder-based phosphorus-locking agents were obtained by saturating phosphorus adsorption of triethylenetetramine wood powder prepared in step one of Example 1. The total nitrogen and total phosphorus application rates (N 200 kg / ha, P2O5 90 kg / ha) were kept consistent across all treatments. Amaranth was fertilized only once per season (as basal fertilizer). The amaranth growth cycle is 40–45 days. Phosphorus and nitrogen fertilizers were applied as basal fertilizers, and no subsequent topdressing was required. Polyamine wood powder-based phosphorus-locking agent was used as part of the basal fertilizer. Light and water conditions were kept uniform across all treatment groups, and soil moisture was managed with irrigation at 60% of the field level. 0.2‰ and 0.4‰ refer to the mass ratio of polyamine wood powder or polyamine wood powder saturated with phosphate adsorption to saline-alkali soil.

[0075] Step 2: Harvest amaranth 40 days after thinning. At the same time, take samples of the saline-alkali soil treated with polyamine wood flour-based phosphorus-locking agent using a five-point sampling method. Weigh out the air-dried soil sample that has passed through a 20-mesh sieve, add 50 mL of 0.5 mol / L NaHCO3 solution (mass ratio of air-dried soil to NaHCO3 solution is 1:20), shake at room temperature for 30 min, and immediately filter with phosphorus-free filter paper. Use the molybdenum antimony colorimetric method to determine the available phosphorus in the soil at a wavelength of 700 nm.

[0076] Step 3: Harvest the amaranth 40 days after thinning. Select four amaranth plants of equal growth for each treatment and measure their plant height and fresh weight. Measure the length of the above-ground part of the amaranth with a ruler in cm and weigh the fresh weight of the above-ground part of the amaranth with a micrometer electronic scale in g.

[0077] Step 4: Forty days after amaranth thinning, a five-point sampling method was used to sample the saline-alkali soil treated with polyamine wood flour-based phosphorus-locking agent. 5g of air-dried soil sample was weighed into a 50mL beaker, and 12.5mL of carbon dioxide-free water was added. The mixture was vigorously stirred with a glass rod for 1–2 minutes and allowed to stand for 30 minutes. Then, using a glass electrode as the indicator electrode and a calomel electrode as the reference electrode, a cell reaction was formed when both electrodes were inserted into the soil filtrate. A potential difference was generated between the two electrodes. Since the reference electrode's potential was fixed, the magnitude of this potential difference depended on the hydrogen ion activity in the solution; the negative logarithm of the hydrogen ion activity was the pH value.

[0078] Step 5: Forty days after thinning amaranth seedlings, samples were taken from saline-alkali soil treated with polyamine-based phosphorus-locking agent using a five-point sampling method. Air-dried soil samples were weighed and mixed with water at a 1:5 ratio (by mass). The mixture was then extracted by shaking at room temperature, and the conductivity of the extract was measured at 25°C. The resistance between the two electrodes was measured when both electrodes were inserted into the extract. At a constant temperature, this resistance is inversely proportional to the conductivity. Given the cell constant, the conductivity can be calculated by measuring the resistance of the extract. Figure 9 , 10 The values ​​represent the pH and EC values ​​of the saline soil after the fertilization period.

[0079] Figure 7 The study investigated the effects of different application rates of polyamine wood flour-based phosphorus-locking agents on the available phosphorus content in the soil. It was found that compared with the CKU treatment group, the available phosphorus content in all treatment groups with polyamine wood flour-based phosphorus-locking agents increased to a certain extent. The highest available phosphorus content was found in the H-AC treatment group, which was 0.093 mg / g, an increase of 40.2% compared with the CKU treatment group. The available phosphorus content in the L-AC, L-ACP, and H-ACP treatment groups increased by 33.7%, 31.8%, and 38.4% respectively compared with the CKU treatment group. Figure 8To investigate the effects of different application rates of polyamine wood flour-based phosphorus-locking agents on plant height and fresh weight, it was found that the H-ACP treatment group showed significant advantages in both plant height and fresh weight. Compared with the CKU treatment group, the plant height of the L-AC, H-AC, L-ACP, and H-ACP treatment groups increased by 11.9%, 17.6%, 14.9%, and 33.5%, respectively, while the fresh weight of the plants in the L-AC, H-AC, L-ACP, and H-ACP treatment groups increased by 27.5%, 56.3%, 43.6%, and 62.5%, respectively, compared with the CKU treatment group.

[0080] Figure 9 , 10 pH and EC were used to describe the acidity / alkalinity and salinity of saline soil, respectively. It was found that after planting amaranth with polyamine wood powder for one season, there were significant differences in pH between the treatment groups and the CKU treatment group (P < 0.05). The CKU treatment group had a pH > 8, while the pH range of the other treatment groups was between 7.8 and 7.9. The pH values ​​of the L-AC, H-AC, L-ACP, and H-ACP treatment groups were 7.90, 7.84, 7.91, and 7.86, respectively. Among them, the H-AC treatment group had the lowest pH at 7.84. The EC values ​​for each treatment ranged from 1404 to 1891 μs / cm. The EC values ​​for the L-AC, H-AC, L-ACP, and H-ACP treatment groups were 1509 μs / cm, 1404 μs / cm, 1782 μs / cm, and 1891 μs / cm, respectively. The EC values ​​of the two AC treatment groups were lower than those of the CKU treatment group, while the EC values ​​of the two AC-P treatment groups were higher than those of the CKU treatment group. This may be because the polyamine wood powder adsorbed with phosphate carries phosphate ions, increasing the soil's electrical conductivity. However, the EC values ​​of the L-ACP and H-ACP treatments were still significantly lower than the background value of 3070 μs / cm in the tested saline soil, indicating a positive effect on plant growth.

[0081] The application rate of saturated polyamine phosphate-absorbing wood powder is also important for soil available phosphorus content, plant biomass, soil pH, and EC value. The applicant conducted an experiment with a treatment group treated with 0.8‰ saturated polyamine phosphate-absorbing wood powder. The soil available phosphorus content, plant biomass, soil pH, and EC value were not significantly different from those treated with 0.4‰ saturated polyamine phosphate-absorbing wood powder, and some indicators even declined. However, the treatments of 0.2‰ and 0.4‰ in this invention showed that as the application rate increased, the improvement in soil available phosphorus content, plant biomass, soil pH, and EC value all increased.

[0082] This invention discloses the preparation and application of a low-cost polyamine wood flour-based phosphorus-locking agent for high-salt soil, including (1) preparation of biomass-based phosphorus-locking agent: grinding and sieving wood flour is heated in a sodium hydroxide solution in a water bath, and sulfuric acid is added to obtain pretreated wood flour; epichlorohydrin crosslinking agent and diethylenetriamine, triethylenetetramine, and tetraethylenepentamine are added to the pretreated wood flour soaked in N,N dimethylformamide, heated in a water bath to complete the grafting reaction, filtered, and freeze-dried to constant weight. (2) Static adsorption: the obtained polyamine wood flour simulates the adsorption of phosphate in pig manure wastewater, and the adsorption is completed. (3) Saline soil application: the polyamine wood flour that statically adsorbs phosphorus replaces a certain proportion of conventional fertilizer with equal phosphorus and nitrogen, and the available phosphorus content in the soil and plant growth indicators are measured. This invention uses a biomass-based phosphorus-locking agent, which can not only achieve the optimal phosphorus adsorption effect of 1.86-2.27 mmol / g, but also replace 10%-25% (w / w) of traditional phosphate fertilizer. It can increase the available phosphorus content in saline soil by 31.8%-40.2%, while lowering the pH of saline soil to 7.84-7.91 and adjusting the EC value of saline soil to 1404-1891 μs / cm.

[0083] The present invention has been described above in sufficient detail and with certain specificities. Those skilled in the art should understand that the descriptions in the embodiments are merely exemplary, and all changes made without departing from the true spirit and scope of the invention should fall within the protection scope of the invention. The scope of protection claimed by the present invention is defined by the claims, and not by the above descriptions in the embodiments.

Claims

1. The application of a low-cost polyamine wood flour-based phosphorus-locking agent for high-salinity soils in improving soil salinity, reducing pH, and increasing available phosphorus content, characterized in that... The preparation method of a low-cost polyamine wood flour-based phosphorus-locking agent for use in high-salt soils includes the following steps: 1) Place the wood flour in a 1-2 mol / L alkaline solution and pretreat it at 70-90℃ for 0.5-1.5 h; then add 0.5-2% v / v acid and treat it at room temperature for 1-2 h, wash it, and obtain the pretreated wood flour; 2) Pretreated wood flour is grafted with a crosslinking agent and a fatty amine sequentially at 75–90℃ for 3–6 hours. The crosslinking agent is epichlorohydrin, and the fatty amine is at least one of diethylenetriamine, triethylenetetramine, and tetraethylenepentamine to obtain a polyamine-based phosphate-locking agent. When grafting the crosslinking agent and fatty amine onto the pretreated wood flour, the ratio of pretreated wood flour to crosslinking agent is 1 g: 85–95 mmol, and the ratio of pretreated wood flour to fatty amine is 1 g: 27–33 mmol. The polyamine-based phosphate-locking agent is used to adsorb phosphate ions. When applied to high-salt soil, the polyamine wood flour-based phosphorus-locking agent is a phosphorus-adsorption-saturated polyamine wood flour-based phosphorus-locking agent, and the mass ratio of the polyamine wood flour-based phosphorus-locking agent to the high-salt soil is 0.2-0.4:1000; the polyamine wood flour-based phosphorus-locking agent is used to replace 10%-25% w / w of phosphate fertilizer with equal phosphorus content. The high-salt soil mentioned refers to soil with a total salt content of 2-6‰.

2. The application of the low-cost polyamine wood flour-based phosphorus-locking agent for high-salinity soil according to claim 1 in improving the salinity of high-salinity soil, reducing the pH value of high-salinity soil, and increasing the available phosphorus content in high-salinity soil, characterized in that, In step 2), the pretreated wood flour is first grafted with a crosslinking agent and then with a fatty amine. When grafting the pretreated wood flour with the crosslinking agent and the fatty amine, the ratio of pretreated wood flour to crosslinking agent is 1g:90mmol, and the ratio of pretreated wood flour to fatty amine is 1g:30mmol.

3. The application of the low-cost polyamine wood flour-based phosphorus-locking agent for high-salinity soil according to claim 2 in improving the salinity of high-salinity soil, reducing the pH value of high-salinity soil, and increasing the available phosphorus content in high-salinity soil, characterized in that, In step 2), the pretreated wood flour is soaked in an organic solvent and grafted with a crosslinking agent and aliphatic amine. The grafting reaction temperature is 85°C and the grafting reaction time is 5 hours. The organic solvent is N,N-dimethylformamide.

4. The application of the low-cost polyamine wood flour-based phosphorus-locking agent for high-salinity soil according to claim 1 in improving the salinity of high-salinity soil, reducing the pH value of high-salinity soil, and increasing the available phosphorus content in high-salinity soil, characterized in that, In step 1), the alkaline solution in the pretreatment is a 1-2 mol / L sodium hydroxide or potassium hydroxide solution; the acid is sulfuric acid or hydrochloric acid.

5. The application of the low-cost polyamine wood flour-based phosphorus-locking agent for high-salinity soil according to claim 4 in improving the salinity of high-salinity soil, reducing the pH value of high-salinity soil, and increasing the available phosphorus content in high-salinity soil, characterized in that, In step 1), the ratio of wood flour to alkaline solution is 1g: 20-50mL; the wood flour is obtained by crushing wood chips and passing them through a 10-80 mesh sieve.

6. The application of the low-cost polyamine wood flour-based phosphorus-locking agent for high-salinity soil according to claim 5 in improving the salinity of high-salinity soil, reducing the pH value of high-salinity soil, and increasing the available phosphorus content in high-salinity soil, characterized in that, It increases the available phosphorus content in high-salt soil by 31.8%–40.2%, lowers the pH of high-salt soil to 7.84–7.91, and adjusts the EC value of high-salt soil to 1404–1891 μs / cm.

7. The application of a low-cost polyamine wood flour-based phosphorus-locking agent in high-salt soils to improve plant biomass in high-salt soils, characterized in that, It increases plant height by 11.9%–33.5% and fresh weight by 27.5%–62.5% in high-salt soils; The preparation method of a low-cost polyamine wood flour-based phosphorus-locking agent for use in high-salt soils includes the following steps: 1) Place the wood flour in a 1-2 mol / L alkaline solution and pretreat it at 70-90℃ for 0.5-1.5 h; then add 0.5-2% v / v acid and treat it at room temperature for 1-2 h, wash it, and obtain the pretreated wood flour; 2) Pretreated wood flour is grafted with a crosslinking agent and a fatty amine sequentially at 75–90℃ for 3–6 hours. The crosslinking agent is epichlorohydrin, and the fatty amine is at least one of diethylenetriamine, triethylenetetramine, and tetraethylenepentamine to obtain a polyamine-based phosphate-locking agent. When grafting the crosslinking agent and fatty amine onto the pretreated wood flour, the ratio of pretreated wood flour to crosslinking agent is 1 g: 85–95 mmol, and the ratio of pretreated wood flour to fatty amine is 1 g: 27–33 mmol. The polyamine-based phosphate-locking agent is used to adsorb phosphate ions. When applied to high-salt soil, the polyamine wood flour-based phosphorus-locking agent is a phosphorus-adsorption-saturated polyamine wood flour-based phosphorus-locking agent, and the mass ratio of the polyamine wood flour-based phosphorus-locking agent to the high-salt soil is 0.2-0.4:1000; the polyamine wood flour-based phosphorus-locking agent is used to replace 10%-25% w / w of phosphate fertilizer with equal phosphorus content. The high-salt soil mentioned refers to soil with a total salt content of 2-6‰.

8. The application according to claim 7, characterized in that, When applying, the polyamine wood powder-based phosphorus-locking agent should be mixed evenly with the top 1-10 cm layer of high-salt soil; the polyamine wood powder-based phosphorus-locking agent should be applied as part of the base fertilizer 8-12 days after sowing.

Images