Nano ardealite-based saline-alkali soil modifier and preparation method thereof

Abstract

The invention discloses a nano ardealite-based saline-alkali soil modifier and a preparation method thereof, and relates to the technical field of soil improvement, the method comprises the following steps: uniformly mixing humic acid, charcoal and a halophilic microbial agent, and then fermenting at 28-32 DEG C for 115-125 hours to obtain a fermentation system; the preparation method comprises the following steps: grinding ardealite into nano ardealite, dispersing the nano ardealite under the action of a surfactant and deionized water, and carrying out surface etching by using acid to form microdot vacancies on the surface of the nano ardealite, so as to obtain chemically modified nano ardealite; the nano phosphogypsum-based saline-alkali soil modifier is obtained by uniformly mixing the chemically modified nano phosphogypsum with a fermentation system, has the advantages of multiple effects, low cost and environmental friendliness, can significantly reduce the salinity and alkalinity of soil, improve the soil structure and promote the growth of crops, realizes the resource utilization of the phosphogypsum, and reduces the environmental pollution.

Description

Technical Field

[0001] The present invention relates to the technical field of soil improvement, and particularly relates to a nano-phosphogypsum-based saline-alkali soil conditioner and a preparation method thereof. Background Art

[0002] The content of soluble salts in the soil of saline-alkali land is too high, which often leads to the growth inhibition or even death of crops, and is a major obstacle in agricultural production. However, as a potential reserve cultivated land resource, the improvement and utilization of saline-alkali land not only helps to expand the cultivated land area, improve land use efficiency, but also promotes the sustainable development of agriculture, so it has extremely important significance.

[0003] A large amount of soluble sodium salts are available for exchange in saline-alkali land, mainly including neutral sodium chloride and sodium sulfate, and alkaline sodium carbonate and sodium bicarbonate. The high content of exchangeable sodium in saline-alkali land results in small soil porosity, poor water permeability and air permeability, and affects the absorption of water and nutrients by plants. At present, the main methods for improving saline-alkali land include physical improvement, chemical improvement and biological improvement. Relatively speaking, the chemical improvement method is simple to operate, quick to take effect and easy to popularize. Gypsum is a commonly used chemical conditioner. The main component of gypsum is calcium sulfate. After being applied to the soil, the calcium ions generated by dissolution can react with the exchangeable sodium in the soil, replace it with soluble sodium, and combine with irrigation measures to drain away the soluble sodium salts, so as to achieve the improvement effect. However, the improvement effect of gypsum can only last for less than 5 years and needs to be applied repeatedly. Therefore, in order to reduce the cost of the conditioner, it is a good choice to make full use of industrial waste phosphogypsum.

[0004] The main component of phosphogypsum is calcium sulfate dihydrate, which is similar to natural gypsum. Its pH is usually between 1 and 4. It is a by-product of wet-process phosphoric acid production and can be applied in the field of soil improvement. However, the current main treatment methods of phosphogypsum are open stacking and mine backfilling. The stacking of a large amount of phosphogypsum wastes land resources. In addition to calcium sulfate dihydrate, phosphogypsum also contains a large amount of nutrients such as phosphorus, silicon, magnesium, and nitrogen, which are beneficial to plant growth. However, traditional phosphogypsum has large particles, small specific surface area and low reaction activity, and its effect in improving saline-alkali land is limited. Chinese Patent with publication number CN118879336A and name "A Soda-Type Saline-Alkali Soil Conditioner and a Preparation Method Thereof" discloses the following content: 10-50 parts of organic fertilizer, 20-40 parts of furfural residue, 10-40 parts of phosphogypsum, 0.1-5 parts of water-retaining agent, and 0.1-5 parts of organic acid complexing agent are mixed evenly according to the ratio, and then 0.1-2.5 parts of Bacillus mucilaginosus powder is sprayed and mixed evenly to obtain a soda-type saline-alkali soil conditioner. The soda-type saline-alkali soil conditioner prepared by this invention improves the chemical properties of saline-alkali soil after treatment, significantly increases the corn yield, but it is difficult to efficiently and quickly improve the properties of saline-alkali soil, and the added microbial inoculant has poor activity in the soil. Summary of the Invention

[0005] In view of the problems existing in the prior art, the present invention provides a nano-phosphogypsum-based saline-alkali soil conditioner and a preparation method thereof, so as to solve the problems that the current saline-alkali soil conditioners are difficult to efficiently and rapidly improve the properties of saline-alkali soil and the activity of microbial agents in the soil is poor. It has multiple functions, low cost, and is environmentally friendly. It can significantly reduce soil salinity and alkalinity, improve soil structure, promote crop growth, and at the same time realize the resource utilization of phosphogypsum and reduce environmental pollution.

[0006] The present invention is realized through the following technical solutions: A preparation method of a nano-phosphogypsum-based saline-alkali soil conditioner includes the following steps: S1, by mass, mix 15-25 parts of humic acid, 10-15 parts of biochar, and 3-8 parts of halophilic microbial agent evenly, and then ferment at 28-32 °C for 115-125 h to obtain a fermentation system; Grind phosphogypsum into nano-phosphogypsum, then disperse it under the action of a surfactant and deionized water, and then use an acid for surface etching to form microdot vacancies on the surface of the nano-phosphogypsum to obtain chemically modified nano-phosphogypsum; S2, mix the chemically modified nano-phosphogypsum with the fermentation system evenly, and the mass ratio of the chemically modified nano-phosphogypsum to humic acid is (60-70):(15-25) to obtain a nano-phosphogypsum-based saline-alkali soil conditioner.

[0007] Preferably, the halophilic microbial agent described in S1 is a bacterium solution of halophilic bacillus or halophilic slender bacillus with a concentration of 10 7 -10 8 cfu / mL.

[0008] Preferably, the biochar described in S1 is obtained through the following process: Under the protection of nitrogen, heat corn straw from room temperature to 440-460 °C at a heating rate of 4-6 °C / min, and then keep it for 3.5-4.5 h to obtain the biochar.

[0009] Preferably, the particle size range of the chemically modified nano-phosphogypsum described in S1 is 10-100 nm.

[0010] Furthermore, the chemically modified nano-phosphogypsum is obtained through the following process: First, the phosphogypsum is crushed, and then phosphogypsum particles with a particle size less than 2 mm are obtained through screening. Then, grinding media and a dispersant are added. The grinding media are zirconia balls or stainless steel balls, and the dispersant is polyethylene glycol or triethanolamine. The ball milling speed is controlled at 300 - 500 r / min. The mass ratio of the grinding media to the phosphogypsum particles is (3 - 5):1, and the ratio of the phosphogypsum particles to the dispersant is 1 kg:(40 - 60) mL. After grinding for 4 - 8 h, centrifugal separation is finally carried out to remove the excess dispersant, and wet nano-phosphogypsum powder is obtained. Then, the wet nano-phosphogypsum powder is subjected to the above-mentioned dispersion and surface etching to obtain chemically modified nano-phosphogypsum.

[0011] Further, the surfactant is sodium dodecyl sulfate or cetylammonium chloride, and the acid is sulfuric acid or nitric acid with a mass percentage of 30% each.

[0012] Further, based on every 1 kg of wet nano-phosphogypsum powder, the surfactant is 0.1 - 0.5 g, the acid is 0.5 - 2 g, and deionized water is 1800 - 2000 g.

[0013] Further, the wet nano-phosphogypsum powder is added to the chemical modification solution composed of the above-mentioned amounts of surfactant, acid, and deionized water, and stirred and reacted at 40 - 60 °C for 1 - 2 h. Then, drying and pulverization treatments are carried out in sequence to obtain chemically modified nano-phosphogypsum.

[0014] Further, the drying is carried out at 60 - 80 °C, and the pulverization is carried out using a jet mill or an ultrafine mill.

[0015] A nano-phosphogypsum-based saline-alkali soil conditioner obtained by the preparation method of the nano-phosphogypsum-based saline-alkali soil conditioner described in any one of the above.

[0016] Compared with the prior art, the present invention has the following beneficial technical effects: The preparation method of a nano-phosphogypsum-based saline-alkali soil conditioner of the present invention. Biochar and humic acid have a porous structure and a large specific surface area, which can provide good attachment sites and living spaces for halophilic microorganisms. The halophilic microorganisms utilize the nutrients in biochar and humic acid to promote their own reproduction, and enhance the activity and stability of halophilic microorganisms after fermentation. Halophilic microorganisms can secrete growth factors to promote plant growth and metabolism, and at the same time secrete more small-molecule organic acids to improve the soil texture and enhance the water retention and root penetration ability in the soil. In addition, halophilic microorganisms can decompose complex organic substances in humic acid and biochar to promote their conversion into simpler organic acids, such as oxalic acid, acetic acid, etc., to improve the fertility of the conditioner and further reduce the pH, thereby enhancing the improvement effect. Phosphogypsum is ground and dispersed, and then further subjected to surface etching with an acid to form microdot vacancies on the surface of the physically ground nano-phosphogypsum to produce the effect of surface etching of phosphogypsum. The modified nano-phosphogypsum has a larger specific surface area and reaction activity compared with ordinary phosphogypsum. There is a significant synergistic effect among the components of the conditioner of the present invention. Humic acid has acidic functional groups, and its synergistic effect with nano-phosphogypsum can effectively reduce the soil pH value and alleviate soil alkalinity. Calcium sulfate in nano-phosphogypsum can quickly react with the salts (sodium chloride, sodium sulfate) and alkaline substances (sodium carbonate and sodium bicarbonate) in the saline-alkali soil, displace sodium ions in the soil, and generate soluble sodium salts. At the same time, biochar and humic acid can reduce the soil bulk density, promote the formation of soil aggregates, enhance the soil air and water permeability, and promote the soil to discharge the sodium salts displaced by nano-phosphogypsum, thereby improving the soil structure and efficiently reducing soil salinity. Humic acid and biochar are rich in organic matter and trace elements, which can supplement nutrients for the soil and improve the fertility of saline-alkali soil. And biochar can adsorb the nutrients released by phosphogypsum, prevent nutrient loss, and slowly release them when needed to improve nutrient utilization efficiency. In addition, the nano-phosphogypsum-based conditioner of the present invention can also stimulate the activity of soil microorganisms, accelerate the decomposition of organic matter and the release of nutrients, further improve the soil ecological environment, and promote crop growth. Halophilic microorganisms can adapt to the high-salt environment of saline-alkali soil, decompose macromolecular organic substances in the conditioner and soil, release organic acids, improve the soil microenvironment, and promote the reproduction of the original microbial community in saline-alkali soil. In summary, the conditioner can effectively improve the physical and chemical properties of saline-alkali soil, increase soil fertility, promote the reproduction of soil microorganisms, and thus provide good conditions for crop growth, significantly improving the emergence rate, growth rate and yield of crops.

[0017] The nano-phosphogypsum-based saline-alkali soil conditioner of the present invention still contains elements such as calcium, sulfur, nitrogen, and phosphorus in the chemically modified nano-phosphogypsum. The fermentation components are rich in organic matter and trace elements, which can supplement nutrients for the soil and improve the fertility of saline-alkali soil. Phosphogypsum is a solid waste generated in the process of phosphochemical production, with a wide source and low cost. Using phosphogypsum as the main raw material, through grinding, dispersion, and surface etching, chemically modified nano-phosphogypsum is obtained, which greatly reduces the production cost of the conditioner. By recycling phosphogypsum, the pollution of land and environment caused by its accumulation is reduced, and the environmental protection goal of treating waste with waste is achieved. The conditioner can effectively improve the soil environment of saline-alkali soil, provide good conditions for crop growth, and significantly improve the emergence rate, growth rate, and yield of crops. Detailed implementation mode

[0018] The following further elaborates on the present invention in combination with specific embodiments, which is an explanation rather than a limitation of the present invention.

[0019] The present invention provides a nano-phosphogypsum-based saline-alkali soil conditioner and its preparation method. The nano-phosphogypsum-based saline-alkali soil conditioner mainly consists of the following components: 60 - 70 parts of nano-phosphogypsum and auxiliary improvement components (15 - 25 parts of humic acid, 10 - 15 parts of biochar, 3 - 8 parts of halophilic microbial inoculant): The phosphogypsum is prepared into nano-scale particles with a particle size range of 10 - 100 nm according to the following steps.

[0020] Raw material pretreatment: Select the phosphogypsum generated in industrial production, carry out crushing and screening, remove large impurities, and obtain phosphogypsum particles with a particle size less than 2 mm.

[0021] Mechanical grinding: Put the pretreated phosphogypsum particles into a ball mill, add grinding media (zirconia balls or stainless steel balls) and dispersants (polyethylene glycol or triethanolamine). The rotation speed of the ball mill is controlled at 300 - 500 r / min, the mass ratio of balls to materials is (3 - 5):1, the ratio of phosphogypsum particles to dispersant is 1 kg:(40 - 60) mL, and the grinding time is 4 - 8 h to obtain nano-phosphogypsum slurry.

[0022] Chemical modification: Centrifuge the nano-phosphogypsum slurry to remove the excess dispersant and obtain wet nano-phosphogypsum powder. Then add the wet powder into the chemical modification solution, which consists of the following components (per 1 kg of nano-phosphogypsum): 0.1 - 0.5 g of surfactant (sodium dodecyl sulfate or cetyl ammonium chloride), 0.5 - 2 g of acid (sulfuric acid or nitric acid with a mass percentage of 30% each), and 1800 - 2000 g of deionized water. Further disperse the nano-phosphogypsum particles with the surfactant to prevent the nano-gypsum particles from caking; at a certain temperature (40 - 60 °C), stir and react for 1 - 2 h. React the acid with impurities such as iron and aluminum oxides on the surface of phosphogypsum to form soluble sulfates, creating microvoids on the surface to produce an etching effect on the phosphogypsum surface, thus forming a honeycomb-like structure, further expanding the reaction surface area of nano-phosphogypsum and further improving the reaction activity to obtain chemically modified nano-phosphogypsum.

[0023] Drying and pulverization: Dry the chemically modified nano-phosphogypsum, control the drying temperature at 60 - 80 °C, and dry to constant weight. Then pulverize the dried nano-phosphogypsum lumps, which can be done using a jet mill or an ultrafine mill to pulverize the nano-phosphogypsum into nano-scale particles.

[0024] The biochar is prepared from corn straw. The preparation method is to heat the corn straw under nitrogen protection at a heating rate of 5 °C / min to 450 °C and hold for 4 hours to obtain a porous biochar.

[0025] The halophilic microbial agent can be a bacterial solution of halophilic alkalibacillus and halophilic gracilibacillus with a concentration of 10 7 -10 8 cfu / mL.

[0026] The preparation method of a nano-phosphogypsum-based saline-alkali soil conditioner of the present invention includes the following steps: Mix the auxiliary improvement components evenly according to the ratio of 15 - 25 parts of humic acid, 10 - 15 parts of biochar, and 3 - 8 parts of halophilic microorganisms, ferment at 28 - 32 °C for 115 - 125 h, and then fully mix evenly with nano-phosphogypsum by stirring or grinding to obtain the nano-phosphogypsum-based saline-alkali soil conditioner.

[0027] Example 1 A nano-phosphogypsum-based saline-alkali soil conditioner, and its raw material weight ratio is: 60 parts of nano-phosphogypsum, 20 parts of humic acid, 15 parts of biochar, and 5 parts of a bacterial solution of halophilic alkalibacillus with a concentration of 2×10 7 cfu / mL.

[0028] The preparation method of the conditioner is as follows: 1. Preparation of nano-phosphogypsum: Raw material pretreatment: Take 1 kg of phosphogypsum, crush and screen it to obtain particles with a particle size less than 2 mm.

[0029] Mechanical grinding: Put 1 kg of phosphogypsum particles into a ball mill, add 3 kg of zirconia balls and 50 mL of polyethylene glycol (molecular weight 400), set the rotation speed of the ball mill to 400 r / min, the ball-to-material ratio to 3:1, and grind for 6 h to obtain nano-phosphogypsum slurry.

[0030] Chemical modification: Centrifuge the nano-phosphogypsum slurry to obtain wet powder. Add the wet powder to a solution containing 0.3 g of sodium dodecyl sulfate, 1 g of 30% sulfuric acid and 2000 mL of deionized water, and stir and react at 50 °C for 1.5 h to obtain chemically modified nano-phosphogypsum.

[0031] Drying and pulverization: Dry the chemically modified nano-phosphogypsum at 70 °C to constant weight, and then pulverize it with a jet mill to obtain nano-phosphogypsum particles.

[0032] 2. Addition of auxiliary improvement components: Take 200 g of humic acid, 150 g of biochar, and mix them evenly with 50 g of a bacterium solution of Halophilic bacillus with a concentration of 2×10 7 cfu / mL, and ferment at 30 °C for 5 days. Then mix it with 600 g of nano-phosphogypsum particles to obtain a nano-phosphogypsum-based saline-alkali soil improver.

[0033] Example 2: 70 parts of nano-phosphogypsum, 17 parts of humic acid, 10 parts of biochar, and 3 parts of a bacterium solution of Gracilibacillus halophilus with a concentration of 10 8 cfu / mL.

[0034] The preparation method of the improver is as follows: 1. Preparation of nano-phosphogypsum: Raw material pretreatment: Take 900 g of phosphogypsum, crush and screen it to obtain particles with a particle size less than 2 mm.

[0035] Mechanical grinding: Put the phosphogypsum particles into a ball mill, add 4.5 kg of stainless steel balls and 40 mL of triethanolamine, set the rotation speed of the ball mill to 300 r / min, the ball-to-material ratio to 5:1, and grind for 8 h to obtain nano-phosphogypsum slurry.

[0036] Chemical modification: Centrifuge the nano-phosphogypsum slurry to obtain wet powder. Add the wet powder to a solution containing 0.2 g of cetylammonium chloride, 0.8 g of 30% nitric acid and 1800 mL of deionized water, and stir and react at 40 °C for 2 h to obtain chemically modified nano-phosphogypsum.

[0037] Drying and grinding: The chemically modified nano-phosphogypsum is dried to a constant weight at 80 °C and then ground using an ultrafine grinder to obtain nano-phosphogypsum particles.

[0038] 2. Addition of auxiliary improvement components: Take 170 g of humic acid, 100 g of biochar, and 30 g of Bacillus gracilis halophilus bacterial solution with a concentration of 10 8 cfu / mL. After mixing evenly, ferment at 30 °C for 5 days, and then mix with 700 g of nano-phosphogypsum particles to obtain a nano-phosphogypsum-based saline-alkali soil improver.

[0039] Comparative example 1: 70 parts of phosphogypsum (without nano-treatment, i.e., compared with Example 2), 17 parts of humic acid, 10 parts of biochar, and 3 parts of Bacillus gracilis halophilus bacterial solution with a concentration of 10 8 cfu / mL.

[0040] The preparation method is as follows: Phosphogypsum crushing treatment: Take 1000 g of phosphogypsum, and after crushing and screening, obtain particles with a particle size less than 2 mm.

[0041] Addition of auxiliary improvement components: Take 170 g of humic acid, 100 g of biochar, and 30 g of Bacillus gracilis halophilus bacterial solution with a concentration of 10 8 cfu / mL. After mixing evenly, ferment at 30 °C for 5 days, and then mix with 700 g of nano-phosphogypsum particles to obtain Comparative example 1.

[0042] Comparative example 2: Only contains the nano-phosphogypsum in Example 2 The preparation method is as follows: Raw material pretreatment: Take 900 g of phosphogypsum, and after crushing and screening, obtain particles with a particle size less than 2 mm.

[0043] Mechanical grinding: Put the phosphogypsum particles into a ball mill, add 4.5 kg of stainless steel balls and 40 mL of triethanolamine, set the rotation speed of the ball mill to 300 r / min, the ball-to-material ratio to 5:1, and grind for 8 h to obtain nano-phosphogypsum slurry.

[0044] Chemical modification: Centrifuge the nano-phosphogypsum slurry to obtain wet powder. Add the wet powder to a solution containing 0.2 g of cetylammonium chloride, 0.8 g of 30% nitric acid, and 1800 mL of deionized water, and stir and react at 40 °C for 2 h to obtain chemically modified nano-phosphogypsum.

[0045] Drying and grinding: Dry the chemically modified nano-phosphogypsum to a constant weight, and then grind it using an ultrafine grinder to obtain nano-phosphogypsum particles.

[0046] Test conditions and results According to the embodiments, pot experiments were carried out. The experimental site was located at the Innovation Port Campus of Xi'an Jiaotong University in Xi'an, Shaanxi Province. The tested soil was taken from Hexipu, Jinchang City, Gansu Province. After passing through a 2-mm sieve, the soil was air-dried for later use. In the pot experiment, the flowerpots had a diameter of 15 cm and a height of 15 cm. 1.5 kg of saline-alkali soil was filled into each pot, and the addition amount of the modifier was 0.2% of the mass of the saline-alkali soil; no modifier was added to the blank control group. Five replicate treatments were set for each experimental group. After watering and pre-culturing for 3 days, 20 wheat seeds of uniform size were sown in each pot. The germination rate was measured after 7 days, and the plant height and fresh weight of the plants, as well as the pH and electrical conductivity of the soil, were measured after 30 days.

[0047] Experimental results: Result 1 is shown in Table 1: Changes in the pH of saline-alkali soil The soil pH values of Example 1 and Example 2 were 7.88 and 7.82 respectively, which were significantly lower than those of the blank control (8.35), Comparative Example 1 (8.12), and Comparative Example 2 (8.17). This shows that the nano-phosphogypsum-based saline-alkali soil modifier has a significant effect on reducing the alkalinity of saline-alkali soil. Moreover, the addition of the modifier in Example 1 and Example 2 reduced the soil pH value to near neutral or weakly alkaline. Such a soil pH value is more conducive to the growth of most crops, indicating that the modifier can effectively improve the alkaline obstacle of saline-alkali land, optimize the soil acid-base environment, promote the growth of crop roots and nutrient absorption. Although Comparative Example 1 and Comparative Example 2 had a certain reducing effect, it was not as obvious as that of the examples.

[0048] Table 1 Table of changes in the pH of saline-alkali land

[0049] Result 2: Changes in the electrical conductivity of saline-alkali soil The soil electrical conductivities of Example 1 and Example 2 were significantly reduced to 451 μm / cm and 512 μm / cm compared with the blank control (854 μm / cm). The electrical conductivities of Comparative Example 1 (633 μm / cm) and Comparative Example 2 (653 μm / cm) were relatively lower but still higher than those of the examples. After applying the modifier, the soil salinity was significantly reduced, and the degree of soil salinization was improved. Soil electrical conductivity is an important indicator of soil salt concentration. The lower the value, the less the content of soluble salts. This shows that this modifier can effectively reduce the stress of soil salts on plants, promote crop growth, improve soil quality, and the synergistic effect of nano-phosphogypsum and auxiliary modification components is better than that of ordinary phosphogypsum modifiers and single nano-gypsum. (See Table 2) Table 2 Table of changes in the electrical conductivity of saline-alkali land

[0050] Result 3: Effect on the germination rate of wheat The germination rate of the control group was only 47%. The germination rates of Example 1 (98%) and Example 2 (96%) with the additive were significantly increased. The germination rates of Comparative Example 1 (64%) and Comparative Example 2 (72%) also increased but the increase was less than that of the examples. This indicates that the nano-phosphogypsum-based additive provides a good environment for wheat seed germination (such as reducing soil salinity and improving pH value). The improvement of soil structure and physical and chemical properties is conducive to seed water absorption and expansion, respiration, and elongation of radicle and plumule, resulting in a significant increase in germination rate. Its effect is better than that of ordinary phosphogypsum additive and nano-gypsum alone. (See Table 3) Table 3 Changes in wheat germination rate

[0051] Result 4: Effects on wheat plant height, fresh weight, and dry weight The plant height of the blank control wheat was 17.34 cm, while that of Example 1 reached 23.61 cm and that of Example 2 was 24.24 cm. The plant heights of Comparative Example 1 (18.5 cm) and Comparative Example 2 (19.44 cm) also increased to a certain extent but were much lower than those of the examples.

[0052] The fresh weight of the blank control wheat was 1.934×10⁻¹ g and the dry weight was 2.83×10⁻² g. After applying the additive, the fresh weight of Example 1 increased to 3.124×10⁻¹ g and the dry weight to 4.64×10⁻² g. The fresh weight and dry weight of Example 2 also increased significantly. Although the fresh weight and dry weight of Comparative Example 1 and Comparative Example 2 increased, the increase was small. The results show that the nano-phosphogypsum-based additive can effectively increase the wheat biomass. The effect of the nano-phosphogypsum-based additive is significantly better than that of ordinary phosphogypsum additive and nano-gypsum alone. (See Table 4) Table 4 Changes in wheat fresh weight and dry weight

[0053] In summary, the nano-phosphogypsum-based saline-alkali land additive significantly improves soil salinity and alkalinity by reducing soil pH value and conductivity. At the same time, the nano-phosphogypsum in the additive and the auxiliary improvement components act synergistically to promote soil fertility and structure optimization, greatly improving the wheat germination rate and growth rate and increasing the wheat biomass. Therefore, this additive has broad application prospects in saline-alkali land treatment and agricultural production increase, and can provide an effective solution for solving the problems of saline-alkali land ecological environment and food security.

Claims

1. A method for preparing a nano-phosphogypsum-based saline-alkali land improver, characterized in that: The following steps are involved: S1, by weight, 15-25 parts of humic acid, 10-15 parts of biochar and 3-8 parts of halophilic microbial agent are mixed evenly, and then fermented at 28-32° C. for 115-125 hours to obtain a fermentation system; The phosphogypsum is ground into nano-phosphogypsum, and then dispersed under the action of a surfactant and deionized water, and then the surface is etched with an acid to obtain chemically modified nano-phosphogypsum; S2, mixing the chemically modified nano phosphogypsum and the fermentation system evenly, wherein the mass ratio of the chemically modified nano phosphogypsum to humic acid is (60-70): (15-25), and a nano phosphogypsum-based saline-alkali land improver is obtained.

2. The method for preparing the nano-phosphogypsum-based saline-alkali land improver according to claim 1, characterized in that: The halophilic microbial agent described in S1 is 10 7 -10 8 cfu / mL of halophilic alkaline bacillus solution or halophilic tenuis bacillus solution.

3. The method for preparing the nano-phosphogypsum-based saline-alkali land improver according to claim 1, characterized in that: The biochar described in S1 was obtained by the following process: The corn stalks are heated from room temperature to 440-460° C. at a heating rate of 4-6° C. / min under nitrogen protection, and then maintained for 3.5-4.5 hours to obtain the biochar.

4. The method for preparing the nano-phosphogypsum-based saline-alkali land improver according to claim 1, characterized in that: The particle size of the chemically modified nano-phosphogypsum described in S1 is in the range of 10-100 nm.

5. The method for preparing the nano-phosphogypsum-based saline-alkali land improver according to claim 4, characterized in that: The chemically modified nano phosphogypsum is obtained according to the following process: The phosphogypsum is first crushed, and then sieved to obtain phosphogypsum particles with a particle size of less than 2 mm, and then a grinding medium and a dispersant are added. The grinding medium is a zirconia ball or a stainless steel ball, and the dispersant is polyethylene glycol or triethanolamine. The ball mill speed is controlled at 300-500r / min, the mass ratio of the grinding medium to the phosphogypsum particles is (3-5):1, and the ratio of the phosphogypsum particles to the dispersant is 1kg: (40-60)mL. The grinding is performed for 4-8h, and finally centrifugation is performed to remove excess dispersant to obtain wet nano-phosphogypsum powder. The wet nano-phosphogypsum powder is then dispersed and surface etched to obtain chemically modified nano-phosphogypsum.

6. The method for preparing the nano-phosphogypsum-based saline-alkali land improver according to claim 5, characterized in that: The surfactant is sodium dodecyl sulfate or hexadecyl ammonium chloride, and the acid is sulfuric acid or nitric acid with a mass percentage of 30%.

7. The method for preparing the nano-phosphogypsum-based saline-alkali land improver according to claim 6, characterized in that: Based on 1 kg of wet nano-phosphogypsum powder, the surfactant is 0.1-0.5 g, the acid is 0.5-2 g, and the deionized water is 1800-2000 g.

8. The method for preparing the nano-phosphogypsum-based saline-alkali land improver according to claim 7, characterized in that: The wet nano-phosphogypsum powder is added to a chemical modification solution consisting of the surfactant, acid and deionized water in the amount mentioned above, stirred for reaction at 40-60° C. for 1-2 hours, and then dried and crushed in sequence to obtain the chemically modified nano-phosphogypsum.

9. The method for preparing the nano-phosphogypsum-based saline-alkali land improver according to claim 8, characterized in that: The drying is carried out at 60-80°C, and the pulverization is carried out by a jet mill or an ultrafine pulverizer.

10. A nano-phosphogypsum-based saline-alkali land improver obtained by the preparation method of the nano-phosphogypsum-based saline-alkali land improver according to any one of claims 1 to 9.

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