Preparation method and application of low-cost polyamine wood flour-based phosphorus locking agent applied to high-salinity soil

Abstract

The invention belongs to the field of application of biomass-based conditioners in saline soil, and particularly relates to a preparation method and application of a low-cost polyamine wood flour-based phosphorus locking agent applied to high-salinity soil. Comprising the following steps: carrying out alkali liquor pretreatment on wood flour to expose active groups in the wood flour so as to facilitate next-step modification and obtain pretreated wood flour; grafting a cross-linking agent and fatty amine on the pretreated wood flour to obtain a polyamine wood flour-based phosphorus locking agent; the polyamine wood flour-based phosphorus locking agent is used for adsorbing and recycling phosphate radicals; the adsorption-saturated polyamine wood flour-based phosphorus locking agent is applied to high-salinity soil. The biomass-based phosphorus locking agent is used, the optimal phosphorus adsorption effect can reach 1.86-2.27 mmol / g, meanwhile, 10%-25% of traditional phosphorus fertilizer can be replaced, the rapidly available phosphorus content in the saline soil can be increased by 31.8%-40.2%, meanwhile, the pH of the saline soil is reduced to 7.8-7.9, the EC value of the saline soil is adjusted to 1404-1891 [mu] s / cm, and growth of crops in the high-salinity soil is promoted.

Description

Technical Field

[0001] The invention belongs to the application field of biomass-based conditioners in saline soil, and specifically relates to a preparation method and application of a low-cost polyamine wood powder-based phosphorus-locking agent applied to high-salt soil. Background Art

[0002] Saline-alkali land is an important land reserve resource. It has attracted much attention from researchers because of its large area and poor soil conditions. Since saline-alkali soil is prone to compaction, the porosity of the soil will be affected, and salt stress leads to low utilization of soil phosphorus by plants. Agricultural and forestry wastes are widely available and have huge output, but the utilization rate is very low. Most of them are used for fuel combustion, which not only wastes resources but also affects the environment. Wood powder, as a type of agricultural and forestry waste, has inherent advantages such as porous structure and large specific surface area, and the cellulose molecules in wood powder contain a large number of active groups, which provide a basis for it to become an adsorbent matrix. At the same time, with the development of the breeding industry, the discharge of breeding wastewater is also increasing. Pig manure wastewater, as a typical breeding wastewater, is considered to be "three high wastewater", namely high organic matter, high nitrogen, and high phosphorus, and contains a large number of pathogens and residual veterinary drugs. Among them, phosphorus is one of the key factors causing eutrophication of water bodies, and the discharge of untreated breeding wastewater will cause serious environmental pollution. In the traditional livestock and poultry breeding wastewater treatment process, although COD and BOD 5 , TN and other emission indicators can meet the national standards, but TP often does not meet the emission standards, so how to deal with phosphorus in livestock and poultry wastewater has become an imminent issue of phosphorus pollution. Therefore, considering the use of low-cost biomass-based materials as adsorbents for phosphorus-containing wastewater, it can not only remove phosphorus from livestock and poultry wastewater, but also achieve efficient utilization of agricultural and forestry wastes.

[0003] Although unmodified biomass materials have good cost advantages, they face the problem of low adsorption capacity. Therefore, some papers have improved the adsorption performance of biomass materials by modification. Sowmya et al. used quaternary ammonium chloride functionalized chitosan-melamine-glutaraldehyde resin to modify the maximum adsorption capacity of 31.6 mg / g, which has a high efficiency in removing phosphate.

[0004] Since wood powder mainly contains a large amount of cellulose, hemicellulose and lignin, according to the structure of cellulose, it contains a large number of active groups such as hydroxyl and carboxyl groups, which give it the ability to be chemically modified, and the alkalinity and electronegativity of the amino group can form hydrogen bonds and electrostatic attraction with the phosphate group of the pollutant. Therefore, the amino group is introduced through the grafting method. This method not only retains the three-dimensional network structure of the wood powder, but also improves the adsorption performance of the adsorbent.

[0005] It can be seen that biomass-based materials have extensive research value as adsorbents for treating phosphorus-containing wastewater, and utilizing the structural characteristics of biomass itself to modify the performance can greatly enhance the material's ability to remove pollutants, while also improving the stability and regeneration performance of biomass materials.

[0006] In the prior art, high-salinity soil is generally improved by applying a mixture of various materials such as organic matter and microorganisms to enable it to grow plants. How to further harmlessly treat adsorption-saturated non-carbonized biomass-based materials is a problem, and there are few reports on the technology of reusing adsorption-saturated non-carbonized biomass-based materials alone in high-salinity soil. Because the transformation of high-salinity soil and the impact on crops grown on it are relatively complicated, when adsorption-saturated non-carbonized biomass-based materials are reused alone in high-salinity soil, it is often difficult to form an improvement on the high-salinity soil in a short period of time, resulting in poor growth of plants growing on high-salinity soil. Summary of the invention

[0007] The present invention proposes a preparation method and application of a low-cost polyamine wood powder-based phosphorus-locking agent for use in high-salt soil. Using low-cost wood powder to prepare a high-efficiency phosphorus-locking agent and applying it to high-salt soil has environmental significance of treating waste with waste.

[0008] In view of the above problems existing in the prior art, the present invention proposes a preparation method and application of a low-cost polyamine wood powder-based phosphorus-locking agent for high-salt soil. The polyamine wood powder-based phosphorus-locking agent prepared by the method not only efficiently removes phosphorus from livestock and poultry wastewater, but also improves the utilization of phosphorus by plants in saline soil.

[0009] In order 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 powder-based phosphorus-locking agent for use in high-salt soils comprises the following steps: 1) placing wood powder in a 1-2 mol / L alkaline solution, and pre-treating the solution at 70-90°C for 0.5-1.5 hours; then adding 0.5-2% (v / v) acid, treating the solution at room temperature for 1-2 hours, and washing the solution to obtain pre-treated wood powder; 2) sequentially grafting a cross-linking agent and a fatty amine onto the pre-treated wood powder at 75-90°C, wherein the grafting reaction time is 3-6 hours, wherein the cross-linking agent is epichlorohydrin, and the fatty amine is at least one of diethylenetriamine, triethylenetetramine, and tetraethylenepentamine, to obtain a polyamine wood powder-based phosphorus-locking agent (referred to as polyamine wood powder); when the pre-treated wood powder is grafted with the cross-linking agent and the fatty amine, the ratio of the pre-treated wood powder to the cross-linking agent is 1g:85-95mmol, and the ratio of the pre-treated wood powder to the fatty amine is 1g:27-33mmol; the polyamine wood powder-based phosphorus-locking agent is used for adsorbing phosphate;

[0011] The adsorption-saturated polyamine wood powder-based phosphorus lock agent is applied to high-salt soil.

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

[0013] Furthermore, in step 2), when the pretreated wood powder is grafted with the crosslinking agent and the fatty amine, the ratio of the pretreated wood powder to the crosslinking agent is 1 g:90 mmol, and the ratio of the pretreated wood powder to the fatty amine is 1 g:30 mmol.

[0014] In step 2), the pretreated wood powder is immersed in an organic solvent and grafted with a crosslinking agent and a fatty amine, the grafting reaction temperature is 85° C., the grafting reaction time is 5 hours, and the organic solvent is NN dimethylformamide.

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

[0016] Alkali treatment exposes more active groups in the material; acid is added and treated at room temperature for a period of time to treat the wood powder to a neutral or slightly acidic state, which is convenient for the next grafting reaction.

[0017] The preparation method, specifically, first pre-treats the ground and sieved wood powder, heats the wood powder in a sodium hydroxide solution in a water bath at 80°C, then treats the wood powder with sulfuric acid, and finally washes it to neutrality to complete the pre-treatment of the wood powder. The pre-treated wood powder is soaked in an organic solvent of NN dimethylformamide, and a cross-linking agent and a fatty amine group are added in sequence after heating in a water bath at 80°C. The grafting reaction is completed after 5 hours to obtain polyamine wood powder. Livestock and poultry pig manure wastewater is simulated, the pH is adjusted, polyamine wood powder is added, and the phosphate therein is statically adsorbed. After adsorption, a biomass-based phosphorus lock agent is obtained.

[0018] Furthermore, the wood powder is sieved with 10-80 meshes, 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 sawdust is sieved through a 10-80 mesh sieve to obtain wood powder. The wood powder is placed in a 1-2 mol / L NaOH solution, stirred continuously for 1 hour at 80°C, and the supernatant is removed after cooling and precipitation, leaving the wood powder. The discarded supernatant can be recycled and reused; a sulfuric acid solution with a volume fraction of 1% (i.e., sulfuric acid aqueous solution) is prepared, the wood powder is added to the 1% sulfuric acid solution, stirred continuously for 2 hours at room temperature, and the supernatant is removed after precipitation. The discarded supernatant can be recycled and reused, and pure water is added until the wood powder is washed to neutrality; the wood powder is obtained by suction filtration, and the wood powder is dried at 55°C, and then ground to obtain pretreated wood powder.

[0021] (2) The pretreated wood powder obtained in step (1) is placed in N-N-dimethylformamide, and stirred continuously for 1 hour at room temperature. After heating in a water bath and stabilizing at 85°C, 90 mmol / L of epichlorohydrin is added, and stirring is continued for 2 hours. 30 mmol / L of diethylenetriamine, triethylenetetramine, and tetraethylenepentamine are slowly added to the mixture, respectively, and stirring is continued for 3 hours. The mixture is cooled to room temperature, filtered, and the wood powder is washed with pure water several times until it is neutral. The obtained wood powder is placed in a freeze dryer for freeze drying, and after drying, 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 KH 2 PO 4 The pH of the solution is adjusted, and then the polyamine wood powder obtained in step (2) is added, and the solution is placed in a shaking table for static adsorption for 24 hours. After the adsorption is completed, the polyamine wood powder adsorbing phosphate is obtained.

[0023] Furthermore, the simulated livestock and poultry wastewater is a laboratory-prepared concentration of 0.1, 0.2, 0.25, 0.5, 1, and 1.5 mmol / L KH 2 PO 4 Solution.

[0024] Furthermore, the KH 2 PO 4 The pH of the solution is adjusted to 2-10.

[0025] Furthermore, the KH 2 PO 4 The coexisting substances in the solution are CaCl 2 NH 4 Cl, NaF, Na 2 SO 4 、NaNO 3 、FeCl 3 Prepared 1mmol / L and 5mmol / L solutions.

[0026] Furthermore, the adsorption temperatures in the static adsorption experiment 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] The present invention also provides a low-cost polyamine wood powder-based phosphorus-locking agent for use in high-salt soils, which is prepared by the above-mentioned preparation method and is suitable for soils with a total soil salt content of 2 to 6‰ (mass fraction).

[0029] Another object of the present invention is to disclose the use of the aforementioned low-cost polyamine wood powder-based phosphorus locking agent for high-salt soil in improving the salt content of high-salt soil, reducing the pH value of high-salt soil and increasing the content of available phosphorus in high-salt soil, so that the content of available phosphorus in high-salt soil is increased by 31.8% to 40.2%, the pH value of high-salt soil is reduced to 7.8 to 7.9, and the EC value of high-salt soil is adjusted to 1404 to 1891 μs / cm; or the use of the agent in increasing the biomass of plants in high-salt soil is used to increase the plant height of plants in high-salt soil by 11.9% to 33.5%, and the fresh weight is increased by 27.5% to 62.5%.

[0030] In a preferred embodiment, when applied to high-salt soil, the mass ratio of the polyamine wood powder-based phosphorus lock agent to the high-salt soil is 0.1-2:1000, and the mixture is uniform. When applied, the polyamine wood powder-based phosphorus lock agent is uniformly mixed with 1-10 cm thick surface high-salt soil; the polyamine wood powder-based phosphorus lock agent is applied as part of the base fertilizer on the 8th to 12th day after sowing; the polyamine wood powder-based phosphorus lock agent is used to replace 10% to 25% (w / w) of phosphorus fertilizers with equal phosphorus.

[0031] The polyamine wood powder-based phosphorus locking agent is evenly mixed with the 1 to 10 cm thick surface high-salt soil to ensure that nutrients can be effectively used by the plants.

[0032] Preferably, when applied to high-salt soil, the polyamine wood powder-based phosphorus-locking agent is a polyamine wood powder-based phosphorus-locking agent that does not absorb phosphorus (the polyamine wood powder-based phosphorus-locking agent itself also contains nitrogen and can provide nutrients for plants) or a polyamine wood powder-based phosphorus-locking agent that is saturated with phosphorus adsorption, and the mass ratio of the polyamine wood powder-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 into saline-alkali soil at a mass fraction of 0.2‰ and 0.4‰; or add polyamine wood powder after adsorption of saturated phosphate at a mass fraction of 0.2‰ and 0.4‰ and mix it evenly into saline-alkali soil, so as to replace traditional inorganic phosphate fertilizer (superphosphate).

[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 it stand for 30 minutes, and then use the glass electrode as the indicator electrode and the calomel electrode as the reference electrode. When the two electrodes are inserted into the soil filtrate to be tested, a battery reaction is formed, and a point difference is generated between the two. Weigh the air-dried soil sample, add water in a ratio of 1:5 (the mass ratio of air-dried soil sample to water is 1:5), extract by oscillation at room temperature, and measure the conductivity of the extract at 25°C.

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

[0037] (1) In the grafting process, the present invention cross-links the pretreated wood powder with an appropriate amount of cross-linking agent and a fatty amine group. When the polyamine wood powder-based phosphorus-locking agent obtained in this way is used in high-salt soil after saturation with phosphate adsorption, phosphorus is released from the polyamine wood powder-based phosphorus-locking agent into the high-salt soil, and the sites of the polyamine wood powder-based phosphorus-locking agent that release P can again adsorb salt ions such as chloride ions in the high-salt soil, thereby reducing the salt concentration in the saline soil. At the same time, the polyamine wood powder-based phosphorus-locking agent that is saturated with phosphorus adsorption also reduces the soil pH.

[0038] When the addition amount was less than 1‰, after a certain proportion of inorganic phosphate fertilizers were replaced by phosphorus such as polyamine wood powder-based phosphorus lockers with saturated phosphorus adsorption, the available phosphorus in saline soil and plant biomass increased, indicating that polyamine wood powder-based phosphorus lockers are better at fixing phosphorus in saline soil than ordinary phosphate fertilizers; and are more conducive to plant growth.

[0039] (2) The present invention uses waste biomass-based wood powder as raw material to prepare an efficient biomass-based phosphorus lock agent. The cellulose structure of wood powder contains a large number of active groups such as hydroxyl and carboxyl groups, which gives it the ability to be chemically modified. At the same time, the fatty amine group is grafted onto the macromolecular carbon chain through a grafting reaction. The alkalinity and electronegativity of the fatty amine group can electrostatically attract and hydrogen bond with the phosphate group of the pollutant in the wastewater, thereby achieving the purpose of removing phosphorus from the wastewater. This not only retains the three-dimensional network structure of the wood powder, but also improves the adsorption performance of the biomass-based phosphorus lock agent. The adsorption capacity of the biomass-based phosphorus lock agent for phosphate can reach up to 1.86-2.27mmol / g, which is significantly better than other common chemical precipitation adsorption and biofilm adsorption technologies, and lays a good foundation for the subsequent removal of phosphorus in livestock and poultry pig manure wastewater.

[0040] (3) The method selected for the pretreatment step of the raw materials used in the present invention before grafting modification is a simpler alkali treatment method compared to common pretreatment methods including physical methods (mechanical crushing, steam explosion), chemical methods (dilute acid treatment, ozone treatment), biological methods (microbial fermentation), etc. The wood powder is pretreated with alkali to expose more active groups in cellulose and improve the efficiency of the grafting reaction. The present invention uses a lower concentration of alkali solution, and the alkali solution can be reused.

[0041] (4) Application in saline soil: replace a certain proportion of conventional fertilizers with polyamine wood powder that statically absorbs phosphorus according to equal phosphorus and equal nitrogen, and measure the effective phosphorus content in the soil and plant growth indicators. The present invention uses a biomass-based phosphorus lock agent, which can not only achieve the optimal effect of phosphorus adsorption to reach 1.86-2.27mmol / g, but also can replace 10%-25% (w / w) of traditional phosphate fertilizers with equal phosphorus, which can not only increase the available phosphorus content in saline soil by 31.8%-40.2%, but also reduce the pH of saline soil to 7.8-7.9, and adjust the EC value of saline soil to 1404-1891μs / cm.

[0042] (5) Compared with biochar materials, the synthesis process of polyamine wood powder is simple, and the reaction can be completed at about 85°C. The pH of the polyamine wood powder product is neutral. Applying only 0.2‰ to 0.4‰ of polyamine wood powder can significantly increase the biomass of the plants. The height of plants in high-salt soil increases by 11.9% to 33.5%, and the fresh weight increases by 27.5% to 62.5%. In addition, polyamine wood powder can significantly increase the content of available phosphorus in saline soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 The effect of the polyamine wood powder-based phosphorus-locking agent of the present invention on phosphate adsorption under different pH conditions and different polyamine reagents;

[0044] Figure 2 The effect of the polyamine wood powder-based phosphorus-locking agent of the present invention on the adsorption capacity of phosphates with different initial concentrations;

[0045] Figure 3 The effect of the polyamine wood powder-based phosphorus-locking agent of the present invention on the phosphate adsorption capacity at different adsorption temperatures;

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

[0047] Figure 5 The effect of the polyamine wood powder-based phosphorus locking agent of the present invention on the phosphate adsorption capacity at different adsorption times;

[0048] Figure 6 is the zeta potential value of the polyamine wood powder-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 powder-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 amounts of the polyamine wood powder-based phosphorus-locking agent of the present invention on plant biomass;

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

[0052] Fig.10 This is a graph showing the effect of different application amounts of the polyamine wood powder-based phosphorus-locking agent of the present invention on the EC of saline soil. DETAILED DESCRIPTION

[0053] The present invention is further described below in conjunction with specific embodiments.

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

[0055] The specific test method of the molybdenum antimony anti-spectrophotometric method used in the following examples for determining the total phosphorus concentration of water samples is as follows: a water sample with a certain dilution factor is added to a 25 mL colorimetric tube, and after adding potassium persulfate solution, the sample is sterilized at 120°C for 30 minutes to reduce the phosphate in the water sample to orthophosphate. After the water sample is cooled, a certain amount of ascorbic acid and a color developer molybdenum antimony anti-solution are added, and after waiting for 15 minutes for color development, the sample is measured at 700 nm using an ultraviolet spectrophotometer.

[0056] Example 1

[0057] Step 1:

[0058] (1) Sieve the crushed sawdust through an 80-mesh sieve to obtain wood powder. Put 3 g of wood powder into 1 mol / L 100 mL NaOH solution, stir continuously for 1 h at 80°C, remove the supernatant after cooling and settling, and leave the wood powder; prepare a 1% sulfuric acid solution by volume, add the wood powder into 1% 100 mL sulfuric acid solution, stir continuously for 2 h at room temperature, remove the supernatant after precipitation, and add pure water until the wood powder is washed to neutrality; filter to obtain wood powder, dry the wood powder at 55°C, and grind to obtain pretreated wood powder after drying. The above-mentioned waste supernatant can be recycled and reused.

[0059] (2) Place 1 g of the pretreated wood powder obtained in step 1) in 50 mL of N-N-dimethylformamide, stir continuously at room temperature for 1 h, heat in a water bath until the temperature stabilizes at 85°C, add 90 mmol (7.027 mL) of epichlorohydrin, stir continuously for 2 h, slowly add 30 mmol of fatty amines (3.258 mL of diethylenetriamine, 4.477 mL of triethylenetetramine, 5.680 mL of tetraethylenepentamine) to the mixture, and stir continuously for 3 h; cool to room temperature, filter, and wash the wood powder with pure water several times until it is neutral; place the obtained wood powder in a freeze dryer for freeze drying, and grind to obtain diethylenetriamine wood powder, triethylenetetramine wood powder, and tetraethylenepentamine wood powder after drying.

[0060] Step 2: Mix deionized water and potassium dihydrogen phosphate reagent evenly to prepare a KH 2 PO 4 Stock solution, dilute to prepare 1mmol / L KH 2 PO 4 , add 1mol / L sodium hydroxide solution and 1mol / L hydrochloric acid solution to adjust KH 2 PO 4 The pH of the solution is adjusted to 2, 3, 4, 6, 8, 9, 10, and then the three polyamine wood powders are added at a dosage of 0.4 g / L, that is, 20 mg of the three polyamine wood powders are added to 50 mL of potassium dihydrogen phosphate solution at each pH condition, and the mixture is shaken at 160 rpm and 25° C. for 24 hours, and then the wood powder is filtered out with a 0.45 μm water filter membrane, and the supernatant is taken to determine the phosphorus content by molybdate colorimetric method, and the adsorption capacity of the polyamine wood powder for phosphate is calculated. The following steps are performed under the optimal pH conditions obtained in this step, that is, pH=6. Figure 1 This is a curve diagram showing the relationship between the adsorption capacity of three polyamine wood powders for phosphate under different pH conditions before and after modification.

[0061] Step 3: Use polyamine wood powder to adsorb phosphates at molar concentrations of 0.1, 0.2, 0.25, 0.5, 1, and 1.5 mmol / L, pH = 6, and the amount of polyamine wood powder added is 0.4 g / L. Mix deionized water and potassium dihydrogen phosphate reagent evenly to prepare a KH 2 PO 4 The stock solution was then diluted with deionized water to prepare 0.1, 0.2, 0.25, 0.5, 1, and 1.5 mmol / L KH 2 PO 4 Solution. The polyamine wood powder obtained in the previous step was weighed at a dosage of 0.4 g / L, that is, 20 mg was weighed and placed in 50 mL of potassium dihydrogen phosphate solution, and shaken at 160 rpm and 25 ° C for 24 hours, and then the wood powder was filtered out with a 0.45 μm water filter membrane, and the supernatant was taken to determine the phosphorus content by molybdate colorimetric method, and the adsorption capacity of polyamine wood powder for phosphate was calculated. Figure 2 This is the relationship curve between the initial phosphate concentration and the adsorption capacity.

[0062] Step 4: Set the constant temperature oscillating bed to a temperature gradient of 10°C, 20°C, and 30°C, and prepare KH 2 PO 4 Solution, under the condition of adding amount of 0.4g / L, that is, weigh 20mg and put it into 50mL of potassium dihydrogen phosphate solution, oscillate at 160rpm for 24h, then filter out the wood powder with a 0.45μm water filter membrane, take the supernatant and determine the phosphorus content with molybdate colorimetric method, and calculate the adsorption capacity of polyamine wood powder for phosphate. Figure 3 This is the adsorption isotherm curve of polyamine wood powder.

[0063] Step 5: Prepare KH with an initial concentration of 1 mmol / L and pH = 6 2 PO 4 Solution, under the condition of dosage of 0.4g / L, that is, 100mg was weighed and placed in 250mL of potassium dihydrogen phosphate solution, and sampling was carried out at 160rpm at time intervals of 5, 10, 20, 30, 60, 120, 360, 480, 960, 1080, 1440, 1960, and 2080min, with 2mL sampled each time, and then the wood powder was filtered out with a 0.45μm water filter membrane, and the supernatant was taken to determine the phosphorus content by molybdate colorimetric method, and the adsorption capacity of polyamine wood powder for phosphate was calculated. Figure 5 This is the kinetic curve of phosphate adsorption by polyamine wood powder.

[0064] Step 6: Prepare KH with an initial concentration of 1 mmol / L and pH = 6 2 PO 4 Solution, 1mmol / L KH 2 PO 4 The solution was prepared with CaCl at concentrations of 1 mmol / L and 5 mmol / L respectively. 2 NH 4 Cl, NaF, Na 2 SO 4 、NaNO 3 、FeCl 3 The solution was mixed evenly, and 20 mg was weighed and placed in 50 mL of a mixed solution containing coexisting substances at a dosage of 0.4 g / L. The mixture was shaken at 160 rpm and 25 °C for 24 h. The wood powder was then filtered out with a 0.45 μm water filter membrane, and the supernatant was used to determine the phosphorus content using the molybdate colorimetric method. The adsorption capacity of the polyamine wood powder for phosphate was calculated. Figure 4 This is a diagram showing the effect of interfering ions on the adsorption of phosphate by polyamine wood powder.

[0065] Step 7: prepare deionized water with pH values ​​of 2, 3, 4, 5, 6, 7, 8, 9, and 10 respectively, and add 1 g / L of polyamine wood powder, i.e., place 10 mg of wood powder in 10 mL of deionized water with adjusted pH value, and perform ultrasound treatment until the polyamine wood powder is completely dispersed and suspended in the centrifuge tube, and then measure the polyamine wood powder using a zeta potential meter. Figure 6 This is the zeta potential diagram of three polyamine wood powders.

[0066] Figure 1 The figure shows the changes in the adsorption capacity of phosphate by three polyamine modified wood powders under different pH conditions. It can be seen that the adsorption capacity of phosphate by the three polyamine wood powders is significantly improved before and after modification. In this article, DTWF refers to diethylenetriamine wood powder, TTWF refers to triethylenetetramine wood powder, and TPWF refers to tetraethylenepentamine wood powder; among them, DTWF shows excellent adsorption capacity at pH = 4, TTWF and TPWF show excellent adsorption capacity at pH = 6, which are 0.976mmol / g, 1.109mmol / g and 1.123mmol / g respectively. Compared with alkali-treated wood powder (WF), the adsorption amount increased by 83.6%, 85.5% and 85.7% respectively. Alkali-treated wood powder (WF) is the pretreated wood powder obtained in step 1 (1) of Example 1.

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

[0068] Figure 3 The figure shows the changes in the adsorption capacity of phosphate by three polyamine wood powders at different adsorption temperatures. It can be seen that as the temperature increases from 10°C to 30°C, the adsorption capacity of DTWF gradually decreases, and then increases with the increase in temperature; on the contrary, the adsorption capacity of TTWF and TPWF first decreases at 10-20°C, then increases at 30°C, and then decreases again at 40°C; this indicates that the different changes in DTWF, TTWF and TPWF with temperature are caused by different adsorption mechanisms.

[0069] Figure 5The contact time and phosphate adsorption capacity of three polyamine wood powders show that the adsorption process of phosphate by polyamine wood powder can be divided into three stages. In the initial stage of adsorption (the first 3 hours), the phosphate enrichment increases rapidly with the contact time, followed by a slow adsorption stage (3 hours to 6 hours), in which the phosphate enrichment trend gradually slows down and eventually reaches equilibrium. The three polyamine wood powders all reach adsorption equilibrium at 1500 minutes to 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 4 The effect of different coexisting ions on the adsorption of phosphate by three polyamine wood powders is shown in Figure 2. It can be seen that low concentrations of interfering ions have little effect on the adsorption. As the molar ratio of interfering ion concentration to phosphate increases from 2 times to 10 times, the adsorbent shows a more obvious loss of adsorption capacity, and the loss size is SO 4 2- >NO 3 - >Cl - >NH 4 + >Fe 3+ >F - Therefore, the more negatively charged anions are, the greater the effect on phosphorus removal. Figure 5 From left to right they correspond to DTWF, TTWF and TPWF.

[0071] Figure 6 The figure shows the change of Zeta potential of three polyamine wood powders 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 polyamine wood powder has the best adsorption effect on phosphate at pH = 4 to 6 is that the Zeta potential at pH = 4 to 6 is greater than zero, 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 three kinds of polyamine wood powder and the cost of polyamine reagents, the subsequent saline soil experiments all applied triethylenetetramine wood powder with lower cost and higher adsorption capacity. The specific surface area of ​​triethylenetetramine wood powder was measured to be 2.917m2 / g, and the contents of C, O, and N were 59%, 21.2%, and 19.6% (mass fraction), respectively. In the prior art, other cellulose-based grafted amine groups can only reach 5.17% nitrogen content (Hui Qiu et al., Fabrication and evaluation of a regenerable HFO-doped agricultural waste for enhanced adsorption affinity towards phosphate). It is proved that the present invention has more grafted amine groups, and the nitrogen content indicates the number of grafted amine groups. The nitrogen content of polyamine wood powder is the SEM-Mapping test result.

[0073] Embodiment 2:

[0074] Step 1: Considering the adsorption capacity of the three polyamine wood powders and the cost of polyamine reagents, triethylenetetramine wood powder was used for later saline soil applications. The saturated adsorption capacity of triethylenetetramine for phosphate is 2.08mmol / g. The triethylenetetramine wood powder after saturated phosphate adsorption (i.e., saturated adsorption of polyamine wood powder-based phosphorus-locking agent) was added at a mass fraction of 0.2‰ and 0.4‰ respectively and evenly mixed into the saline-alkali soil (except for CKU treatment, the polyamine wood powder-based phosphorus-locking agents of other treatments were evenly mixed with 10cm thick surface high-salt soil), and the traditional inorganic phosphate fertilizer (superphosphate) was replaced by equal phosphorus. The saline soil for the test was collected from Dongtai City, Yancheng City, Jiangsu Province. pH = 9.25; EC = 3070 μs / cm; total salt 3 g / kg, 8 kg of saline soil per pot, the amount of phosphorus fertilizer required for growing amaranth was 3.375 g / pot, 8 amaranth seedlings were thinned per pot, and five treatments were set up, namely the conventional fertilization group (CKU) (according to N 200 kg / ha, P 2 O 590 kg / ha, conventional fertilization and other treatment groups were applied on the same day, all applied 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), 0.4‰ saturated phosphorus-absorbing polyamine wood powder treatment group (H-ACP), hereinafter referred to as abbreviations, each treatment set 4 parallel. The 0.2‰ and 0.4‰ polyamine wood powder treatment groups used the triethylenetetramine wood powder obtained in step 1 of Example 1 to replace 7.3% (mass fraction) and 14.7% of the inorganic nitrogen fertilizer, respectively, and the remaining nitrogen fertilizers were supplemented with urea; the 0.2‰ and 0.4‰ saturated adsorption polyamine wood powder-based phosphorus lockers replaced 10.4% (mass fraction) and 20.7% of the inorganic phosphorus fertilizer, respectively. At the same time, the 0.2‰ and 0.4‰ saturated adsorption polyamine wood powder-based phosphorus lockers replaced 7.3% (mass fraction) and 14.7% of the inorganic nitrogen fertilizer, respectively, and the remaining phosphorus fertilizers were supplemented with superphosphate, and the remaining nitrogen fertilizers were supplemented with urea. The saturated adsorption polyamine wood powder-based phosphorus lockers were obtained by saturating the triethylenetetramine wood powder obtained in step 1 of Example 1 with phosphorus. The total nitrogen and total phosphorus application amounts of each treatment (N 200kg / ha, P 2 O 5 90 kg / ha) is consistent, and only one fertilizer is applied in one season of the amaranth growth cycle (as basal fertilizer). The amaranth growth cycle is 40 to 45 days per season. Phosphorus fertilizer and nitrogen fertilizer are applied as basal fertilizer, and no topdressing is required in the later period; polyamine wood powder-based phosphorus lock agent is used as part of the basal fertilizer. Ensure that the light and water of amaranth in each treatment group are uniform, and irrigate the soil moisture management according to 60% of the field. 0.2‰ and 0.4‰ refer to the mass ratio of polyamine wood powder or polyamine wood powder after saturated adsorption of phosphate to saline-alkali soil.

[0075] Step 2: Harvest the amaranth 40 days after thinning. At the same time, take samples of the saline-alkali soil to which the polyamine wood powder-based phosphorus lock agent was applied using the five-point sampling method. Weigh the air-dried soil sample that passed through a 20-mesh sieve and add 0.5 mol / L NaHCO 3 Solution 50mL, air-dried soil sample and NaHCO 3 The solution mass ratio is 1:20, shaken at room temperature for 30 minutes, immediately filtered with phosphorus-free filter paper, and the filtrate is colorimetrically determined at a wavelength of 700nm using the molybdenum antimony colorimetric method to determine the available phosphorus in the soil.

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

[0077] Step 4: 40 days after thinning the amaranth seedlings, the saline-alkali soil to which the polyamine wood powder-based phosphorus lock agent was applied was sampled using the five-point sampling method. 5g of air-dried soil sample was weighed into a 50mL small beaker, and 12.5mL of carbon dioxide-free water was added. Stir vigorously with a glass rod for 1 to 2 minutes, let it stand for 30 minutes, and then use a glass electrode as the indicator electrode and a calomel electrode as the reference electrode. When the two electrodes are inserted into the soil filtrate to be tested, a battery reaction is formed, and a point difference is generated between the two. Since the point position of the reference electrode is fixed, the size of the two-point difference depends on the hydrogen ion activity in the solution, and the negative logarithm of the hydrogen ion activity is the pH value.

[0078] Step 5: 40 days after thinning the amaranth seedlings, the saline-alkali soil to which the polyamine wood powder-based phosphorus lock agent was applied was sampled using the five-point sampling method. The air-dried soil sample was weighed, and water was added at a ratio of 1:5 (mass ratio). The sample was extracted by oscillation at room temperature, and the conductivity of the extract at 25°C was measured. When two electrodes are inserted into the extract, the resistance between the two electrodes can be measured. When the temperature is constant, the resistance value is inversely proportional to the conductivity. When the conductivity cell constant is known, the conductivity can be obtained by measuring the resistance of the extract. Fig. 9 , 10 They are the pH and EC values ​​of saline soil after the fertilization period.

[0079] Figure 7 This is the effect of different application amounts of polyamine wood powder-based phosphorus-locking agents on the available phosphorus content in the soil. It can be seen that compared with the CKU treatment group, the available phosphorus content of each treatment group after the application of the polyamine wood powder-based phosphorus-locking agent increased to a certain extent, and the available phosphorus content of the H-AC treatment group was the highest at 0.093 mg / g, an increase of 40.2% compared with the CKU treatment group. The available phosphorus content of 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 8 The effects of different application amounts of polyamine wood powder-based phosphorus-locking agents on plant height and fresh weight were studied. It was found that the H-ACP treatment group had significant advantages in both plant height and fresh weight. The plant heights 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 compared with the CKU treatment group. The fresh weights of 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] Fig. 9 , 10pH and EC are two indicators that respectively describe the acidity and salt content of saline soil. It was found that after applying polyamine wood powder to plant a season of amaranth, the pH of each treatment group was significantly different from that of the CKU treatment group (P < 0.05). The pH of the CKU treatment group was > 8, and the pH of each treatment group ranged from 7.8 to 7.9. The pH 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 pH of the H-AC treatment group was the lowest at 7.84. The EC values ​​of each treatment ranged from 1404 to 1891μs / cm. The EC values ​​of the L-AC, H-AC, L-ACP, and H-ACP treatment groups were 1509μs / cm, 1404μs / cm, 1782μs / cm, and 1891μs / cm, respectively. The EC values ​​of the two groups treated with AC were lower than those of the CKU treatment, and the EC values ​​of the two groups treated with AC-P were higher than those of the CKU treatment. This may be due to the fact that the polyamine wood powder that adsorbs phosphates carries phosphate and increases the conductivity of the soil. However, the L-ACP and H-ACP treatments were still significantly lower than the background value of the test saline soil EC = 3070μs / cm, which had a positive effect on plant growth.

[0081] The application amount of saturated phosphorus-absorbing polyamine wood powder is also important for the soil available phosphorus content, plant biomass, pH value of saline soil and EC value. The applicant simultaneously conducted an experiment on a treatment group with 0.8‰ saturated phosphorus-absorbing polyamine wood powder. The soil available phosphorus content, plant biomass, pH value of saline soil and EC value were not significantly different from those of the treatment group with 0.4‰ saturated phosphorus-absorbing polyamine wood powder, and some indicators even declined. However, for the treatments of the present invention with application amounts of 0.2‰ and 0.4‰, the improvements in soil available phosphorus content, plant biomass, pH value of saline soil and EC value increased with the increase in application amount.

[0082] The present invention discloses the preparation and application of a low-cost polyamine wood powder-based phosphorus locker for use in high-salt soils, including (1) the preparation of a biomass-based phosphorus locker: heating the ground and sieved wood powder in a sodium hydroxide solution in a water bath, adding sulfuric acid to obtain pretreated wood powder; then adding epichlorohydrin crosslinking agent and diethylenetriamine, triethylenetetramine, and tetraethylenepentamine to the pretreated wood powder soaked in NN dimethylformamide, heating in a water bath to complete the grafting reaction, filtering, and freeze-drying to constant weight. (2) static adsorption, the obtained polyamine wood powder simulates the adsorption of phosphates in pig manure wastewater, and the adsorption is completed. (3) Application in saline soil; the polyamine wood powder that statically adsorbs phosphorus replaces a certain proportion of conventional fertilizers according to equal phosphorus and equal nitrogen, and the effective phosphorus content in the soil and the plant growth index are determined. The present invention uses a biomass-based phosphorus-locking agent, which can not only achieve the optimal effect of phosphorus adsorption to reach 1.86-2.27 mmol / g, but also can replace 10%-25% (w / w) of traditional phosphate fertilizers with equal phosphorus, and can not only increase the content of available phosphorus in saline soil by 31.8%-40.2%, but also reduce the pH of the saline soil to 7.84-7.91, and adjust the EC value of the saline soil to 1404-1891 μs / cm.

[0083] The present invention has been described in sufficient detail with certain particularity. It should be understood by those skilled in the art that the description in the embodiments is merely exemplary, and all changes made without departing from the true spirit and scope of the present invention should fall within the scope of protection of the present invention. The scope of protection claimed by the present invention is defined by the claims, rather than by the above description in the embodiments.

Claims

1. A method for preparing a low-cost polyamine wood powder-based phosphorus-locking agent for use in high-salt soils, characterized in that: The method comprises the following steps: 1) placing wood powder in a 1-2 mol / L alkaline solution, and pre-treating the solution at 70-90° C. for 0.5-1.5 h; then adding 0.5-2% (v / v) acid, treating the solution at room temperature for 1-2 h, and washing the solution to obtain pre-treated wood powder; 2) Pre-treating wood powder by grafting a cross-linking agent and a fatty amine at 75-90° C. in sequence, with a grafting reaction time of 3-6 hours, wherein the cross-linking agent is epichlorohydrin, and the fatty amine is at least one of diethylenetriamine, triethylenetetramine, and tetraethylenepentamine, to obtain a polyamine wood powder-based phosphorus-locking agent; when the pre-treating wood powder is grafted with the cross-linking agent and the fatty amine, the ratio of the pre-treated wood powder to the cross-linking agent is 1 g: 85-95 mmol, and the ratio of the pre-treated wood powder to the fatty amine is 1 g: 27-33 mmol; the polyamine wood powder-based phosphorus-locking agent is used to adsorb phosphate; The adsorption-saturated polyamine wood powder-based phosphorus lock agent is applied to high-salt soil.

2. The method for preparing a low-cost polyamine wood powder-based phosphorus-locking agent for use in high-salt soil according to claim 1, characterized in that: In step 2), the pretreated wood powder is first grafted with a crosslinking agent and then with a fatty amine; when the pretreated wood powder is grafted with the crosslinking agent and the fatty amine, the ratio of the pretreated wood powder to the crosslinking agent is 1g:90mmol, and the ratio of the pretreated wood powder to the fatty amine is 1g:30mmol.

3. The method for preparing a low-cost polyamine wood powder-based phosphorus-locking agent for use in high-salt soil according to claim 2, characterized in that: In step 2), the pretreated wood powder is immersed in an organic solvent and grafted with a crosslinking agent and a fatty amine, the grafting reaction temperature is 85° C., the grafting reaction time is 5 hours, and the organic solvent is NN dimethylformamide.

4. The method for preparing a low-cost polyamine wood powder-based phosphorus-locking agent for use in high-salt soil according to claim 1, characterized in that: In step 1), the alkali solution in the pretreatment is 1-2 mol / L sodium hydroxide or potassium hydroxide solution; the acid is sulfuric acid or hydrochloric acid.

5. The method for preparing a low-cost polyamine wood powder-based phosphorus-locking agent for use in high-salt soil according to claim 4, characterized in that: In step 1), the ratio of wood powder to alkaline solution is 1 g: 20-50 mL; Wood powder is obtained by crushing sawdust and passing it through a 10-80 mesh sieve.

6. A low-cost polyamine wood powder-based phosphorus-locking agent for use in high-salt soils prepared by the preparation method according to any one of claims 1 to 5, characterized in that: Suitable for soils with a total soil salinity of 2 to 6‰.

7. The use of the low-cost polyamine wood powder-based phosphorus-locking agent for high-salt soil according to claim 6 in improving the salt content of high-salt soil, reducing the pH value of high-salt soil and increasing the content of available phosphorus in high-salt soil, characterized in that: The available phosphorus content in the high-salt soil is increased by 31.8% to 40.2%, the pH value of the high-salt soil is reduced to 7.84 to 7.91, and the EC value of the high-salt soil is adjusted to 1404 to 1891 μs / cm.

8. The use of the low-cost polyamine wood powder-based phosphorus-locking agent for high-salt soil according to claim 6 in increasing the biomass of plants in high-salt soil, characterized in that: It increases the plant height of plants in high-salt soil by 11.9% to 33.5% and the fresh weight by 27.5% to 62.5%.

9. The use according to claim 7 or 8, characterized in that: When applied to high-salt soil, the mass ratio of the polyamine wood powder-based phosphorus-locking agent to the high-salt soil is: 0.1-2:1000; when applied, the polyamine wood powder-based phosphorus-locking agent is evenly mixed with 1-10 cm thick surface high-salt soil; the polyamine wood powder-based phosphorus-locking agent is applied as a part of the base fertilizer on the 8th to 12th day after sowing; the polyamine wood powder-based phosphorus-locking agent is used to replace 10% to 25% (w / w) of the phosphate fertilizer with equal phosphorus.

10. The use according to claim 7 or 8, characterized in that: When applied to high-salt soil, the polyamine wood powder-based phosphorus-locking agent is a polyamine wood powder-based phosphorus-locking agent that does not absorb phosphorus or a polyamine wood powder-based phosphorus-locking agent that is saturated with phosphorus absorption, and the mass ratio of the polyamine wood powder-based phosphorus-locking agent to the high-salt soil is 0.2-0.4:1000.

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