Modified biochar-based slow-release rare earth lanthanum soil amendment and preparation method thereof

Abstract

The application provides a modified biochar-based slow-release rare earth lanthanum soil conditioner and a preparation method thereof, and relates to the technical field of soil conditioners.The saline-alkali soil conditioner is used for reducing soil salinity, fixing heavy metals in soil, improving soil structure and slowly releasing rare earth elements into soil.The preparation method comprises the following steps: step 1, preparing a rare earth lanthanum compound, modified biochar, phosphate, dehydrated river channel silt and an organic complexing agent;step 2, dissolving the rare earth lanthanum compound and the organic complexing agent in deionized water to generate a complex solution through reaction;step 3, preparing modified biochar;step 4, lanthanum loading;and step 5, mixing the matrix to obtain the saline-alkali soil conditioner.Lanthanum nitrate and sodium citrate are converted into a complex solution in the application, and the lanthanum citrate complex has good stability, can effectively fix lanthanum elements in the form of a complex in the solution, avoids precipitation or loss of lanthanum elements in the subsequent treatment process, and realizes the slow-release effect of lanthanum.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of soil improver, in particular to a modified biochar-based slow-release rare earth lanthanum soil improver and a preparation method thereof. BACKGROUND

[0002] As a strategic resource, rare earth is highly valued by countries around the world. In today's social development, rare earth resources have penetrated into all walks of life. In the field of agriculture, rare earth is not a fertilizer and cannot be used as a large amount of nutrient element for plants, but its trace use can be used as one of the metal activators in plant physiology and biochemistry, which can promote crop yield, has the function of reasonably regulating the physiological activity of plants, promotes the absorption of phosphorus elements by plants, thereby increasing the content of chloroplasts in plants, further promoting the activity of enzymes in plants, especially the activity of phosphatase components, applying low-concentration rare earth micro-fertilizer to promote plant growth and improve crop yield, while high-concentration RE inhibits plant growth and development, and rare earth lanthanum also has a positive and positive promoting effect on saline-alkali soil.

[0003] The physicochemical properties of river silt are similar to those of soil, containing a large amount of nutrient elements required for plant growth, and having the function of improving the physicochemical properties of soil, such as porosity, bulk density, field moisture capacity, aggregate stability, shrinkage, saturated hydraulic conductivity, etc. In addition, the silt composition contains a large amount of organic matter, microorganisms, inorganic particles, colloids and other substances, which can make the soil structure loose and improve the workability of the land. The composition of silt also contains certain sticky substances, which can increase the stickiness of soil after application, form a stable soil structure, and effectively improve the physical properties of saline-alkali soil. If the silt can be reasonably used, not only can the chemical properties of saline-alkali soil be effectively improved to obtain a conditioner product suitable for saline-alkali soil, but also the soil fertility and crop yield can be improved, and the use of commercial fertilizer can be reduced, thereby reducing the economic cost.

[0004] Due to the high salt content, high compactness and low available nutrients of saline-alkali soil, crops are prone to suffer from physiological drought and other adverse effects, which greatly limits the improvement of crop yield. According to statistics, the area of soil threatened by salinization around the world is about 1×109hm 2 , accounting for about 7% of the earth's land surface, affecting about 10% of the world's arable land; among them, the area of secondary saline-alkali soil is 4.5×107-8.0×107hm 2 , accounting for 20%-30% of all irrigated land.

[0005] The soil improvement agent for saline-alkali soil can be divided into organic improvement agent and inorganic improvement agent, and common soil chemical improvement agents include gypsum, desulfurized gypsum, zeolite, sulfur, humic acid, furfural residue and earthworm manure and the like. These improvement agents improve the physical and chemical properties of saline-alkali soil through chemical reactions such as ion replacement, acid-base neutralization and changes to the pore structure of the soil, and part of the organic improvement agents (such as manure) have the risk of polluting groundwater in the application process, and the secondary pollution of the environment caused by the application of the fertilizer needs to be avoided. In the inorganic improvement agent, the overuse of calcium-based improvement agents also has the risk of increasing the accumulation of salt and heavy metals. SUMMARY

[0006] The application is based on the use of lanthanum nitrate to improve the stress resistance of plants to drought and saline-alkali, and the use of sludge with a large amount of organic matter and nutrient elements such as nitrogen, phosphorus and potassium to be compounded with rare earth lanthanum as an improvement agent. The application of sludge can also reduce the salinity and pH value of the soil, promote the balance of soil acidity and alkalinity, and improve the effect of soil fertility. The sludge is turned from waste into treasure, realizes resource recycling, provides a research idea for improving saline-alkali soil, and has far-reaching practical significance, as follows:

[0007] A preparation method of a modified biochar-based slow-release rare earth lanthanum soil improvement agent, comprising the following steps:

[0008] Step 1, raw material preparation: 5-10 parts of rare earth lanthanum compound; 15-25 parts of modified biochar; 1-2 parts of phosphate; 50-70 parts of dehydrated river channel sludge; 10-15 parts of organic complexing agent;

[0009] Step 2, raw material pretreatment: dissolve the rare earth lanthanum compound and the organic complexing agent in deionized water, and stir and react in a 50-70℃ water bath to generate a complex solution;

[0010] Step 3, preparation of modified biochar:

[0011] (1) treat the biochar with 10% nitric acid at 45-55℃ for 5-7 hours, and treat the biochar with 30% nitric acid at 55-65℃ for 7-9 hours, and then wash the biochar with deionized water until the pH value is 6-7;

[0012] (2) after drying, add 10% ethylenediamine solution to the biochar at a solid-liquid ratio of 1:10-20, and reflux react at 75-85℃ for 10-15 hours to graft amino groups on the surface of the biochar through nucleophilic substitution reaction;

[0013] Step 4, lanthanum loading: immerse the modified biochar in the complex solution, ultrasonic treat, and then dry at 50-70℃ for 4-8 hours to obtain lanthanum-loaded biochar;

[0014] Step 5, matrix mixing: the dehydrated river channel silt, phosphate, lanthanum-loaded biochar are mixed uniformly to obtain a saline-alkali soil modifier;

[0015] The saline-alkali soil modifier is used for reducing soil salinity, fixing heavy metals in the soil, improving soil structure and slowly releasing rare earth elements into the soil.

[0016] Moreover, the particle size of the biochar is ≤2mm, the organic complexing agent is sodium citrate, the phosphate is potassium dihydrogen phosphate, and the rare earth lanthanum compound is lanthanum nitrate.

[0017] Moreover, the preparation method of the dehydrated river channel silt is as follows:

[0018] S1, silt pretreatment: after the river channel silt is removed of impurities, 0.5-1% of polyaluminum chloride by mass of the river channel silt is added, and after uniform stirring and mixing, the mixture is statically deposited for 24-48 hours;

[0019] S2, mechanical dehydration: the deposited silt is pressed and filtered to be dehydrated, and the obtained mud cake is crushed by a crusher to a particle size ≤5mm;

[0020] S3, deep dehydration: the crushed silt is dried to a water content ≤15%;

[0021] S4, heavy metal stabilization treatment: 1-2% of potassium dihydrogen phosphate by mass of the dried silt is added, and after uniform mixing, the mixture is aged for 48-72 hours;

[0022] S5, finished product treatment: the silt after the stabilization treatment is crushed to obtain the dehydrated river channel silt.

[0023] Moreover, in step S2, a plate-and-frame filter press is used for pressure filtration and dehydration, the pressure is controlled to be 0.6-0.8MPa, and the dehydration is performed to a water content of 40-45%.

[0024] Moreover, in step S4, the silt after the stabilization treatment is crushed by a crusher to pass through an 80-mesh sieve.

[0025] Moreover, in step 2, the stirring reaction is performed in a 50-70℃ water bath for 25-35 minutes to generate a complex solution.

[0026] Moreover, in step 4, the frequency of the ultrasonic treatment is 30-50kHz, and the time is 25-35 minutes.

[0027] Compared with the prior art, the present application has the following beneficial effects:

[0028] 1. The modified biochar-based slow-release rare earth lanthanum soil conditioner provided by the application and the preparation method thereof, lanthanum nitrate and sodium citrate are converted into a complex solution, the lanthanum citrate complex has good stability, can effectively fix lanthanum elements in the form of a complex in the solution, avoids precipitation or loss of lanthanum elements in the subsequent processing process, realizes the slow-release effect of lanthanum, and provides a good foundation for subsequent loading of lanthanum elements on modified biochar; then the modified biochar is immersed in the complex solution and then subjected to ultrasonic treatment, the porosity and specific surface area of the modified biochar are increased, the lanthanum citrate complex more easily enters the pores inside the modified biochar, and adsorption occurs between the lanthanum citrate complex and active sites on the surface of the modified biochar, so that the loading amount and uniformity of lanthanum elements on the biochar are improved; finally, drying and fixing the load are performed, the interaction between the lanthanum citrate complex and the modified biochar is further strengthened, the lanthanum elements are firmly loaded on the modified biochar, a stable lanthanum-loaded biochar is formed, the slow release of lanthanum elements is further realized, lanthanum elements can be continuously and stably released in the soil, the action time of lanthanum elements is prolonged, the utilization rate is improved, and the adverse effects of excessive one-time release on the soil and plants are avoided.

[0029] 2. The modified biochar-based slow-release rare earth lanthanum soil conditioner provided by the application and the preparation method thereof, the modified biochar is subjected to oxidation treatment by nitric acid, oxygen-containing functional groups such as carboxyl groups (-COOH) and phenolic hydroxyl groups (-OH) are introduced, the surface negative charge density of the biochar is significantly increased, the increase in the negative charge density can enhance the electrostatic adsorption capacity of the biochar for rare earth lanthanum ions, reduce the migration loss of lanthanum elements in the soil, and prolong the slow-release period; then ethylenediamine is added, a stable -CONH-CH2-CH2-NH2 structure is formed on the surface of the biochar through a nucleophilic substitution reaction, an amino positive charge group is introduced, the amino group preferentially adsorbs anions in the soil, indirectly promotes lanthanum ions to be desorbed from the biochar to the soil solution, realizes a “storage-slow release” dynamic balance, and further realizes the slow-release effect of lanthanum ions.

[0030] 3. The application utilizes river sludge as one of the main raw materials, does not need to be fermented, the river sludge is widely available and has a relatively low acquisition cost, is reasonably applied to the saline-alkali soil conditioner, realizes resource utilization of waste, reduces the production cost of the conditioner, reduces the pollution of the river sludge to the environment, and has remarkable economic and environmental benefits.

[0031] 4. In the application, rare earth lanthanum, as a metal activator in plant physiology and biochemistry, can reasonably regulate physiological activity functions in a plant body, promote the absorption of phosphorus elements by the plant, and enhance the stress resistance of the plant to saline-alkali stress, and the river sludge contains a large amount of nutrient elements and organic matter required for plant growth, can improve the physical and chemical properties of the soil and increase the soil fertility, and the two are used in combination, realize complementary advantages, and synergistically play a role in improving saline-alkali soil.

[0032] 5、The river sludge is treated, impurities and harmful substances in the sludge are effectively removed, the quality and stability of the sludge are improved, and the sludge is more suitable as a raw material for soil improver; specifically, the sludge is subjected to heavy metal stabilization treatment, potassium dihydrogen phosphate is added, and after mixing, aging, PO4 3- The heavy metal ions Pb 2+ , Cd 2+ , etc. in the river sludge form insoluble phosphate, fix the heavy metals in the sludge, reduce the migration and biological effectiveness of the heavy metals, and reduce the potential harm of the heavy metals to the soil and plants.

[0033] 6、The soil improver provided by the application can comprehensively improve saline-alkali soil from multiple aspects such as chemistry, physics and biology. In the chemical aspect, the lanthanum element can adjust the ion balance of the soil and reduce the salinity of the soil; the potassium dihydrogen phosphate provides necessary nutrient elements such as phosphorus and potassium for plants; in the physical aspect, the biochar and the river sludge can improve the physical structure of the soil, increase the air permeability and water retention of the soil, and reduce the compactness of the soil; in the biological aspect, the organic matter and the microorganisms in the improver can promote the activity of the soil microorganisms and improve the soil fertility, thereby creating a good soil environment for plant growth; compared with some existing soil improvers, the improver prepared by the application can effectively reduce the environmental risk in the application process. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 is the growth condition of alfalfa (experiment 1);

[0035] Figure 2 is the growth condition of alfalfa in the water culture experiment (experiment 3);

[0036] Figure 3 is the root length comparison of alfalfa in the water culture experiment (experiment 3);

[0037] Figure 4 is the comparison of the plant height of alfalfa in the water culture experiment (experiment 3);

[0038] Figure 5 is the comparison of the plant height and root length of alfalfa in the soil culture experiment (experiment 3);

[0039] Figure 6 is the comparison of the plant height and root length of alfalfa in the soil culture experiment (experiment 3);

[0040] Figure 7 is the water content test result (experiment 4);

[0041] Figure 8 is the scanning electron microscope morphology diagram of the rare earth lanthanum soil improver (experiment 5);

[0042] Figure 9 EDS spectrum of rare earth lanthanum soil improver (experiment 5);

[0043] Figure 10 Element distribution map of rare earth lanthanum soil improver by scanning electron microscope (experiment 5);

[0044] Figure 11 Single element distribution map of rare earth lanthanum soil improver by scanning electron microscope (experiment 5);

[0045] Figure 12 Morphology map of unimproved planting soil by scanning electron microscope (experiment 5);

[0046] Figure 13 EDS spectrum of unimproved planting soil (experiment 5);

[0047] Figure 14 Morphology map of planting soil improved by rare earth lanthanum soil improver by scanning electron microscope (experiment 5);

[0048] Figure 15 EDS spectrum of planting soil improved by rare earth lanthanum soil improver (experiment 5);

[0049] Figure 16 Element distribution map of planting soil improved by rare earth lanthanum soil improver (experiment 5);

[0050] Figure 17 Single element distribution map of planting soil improved by rare earth lanthanum soil improver (experiment 5);

[0051] Figure 18 Adsorption-desorption curve of planting soil before and after improvement by rare earth lanthanum soil improver (experiment 7);

[0052] Figure 19 Pore size distribution map of planting soil before and after improvement by rare earth lanthanum soil improver (experiment 7);

[0053] Figure 20 Infrared spectrum of planting soil before and after improvement by rare earth lanthanum soil improver (experiment 8);

[0054] Figure 21 Thermogravimetric curve of planting soil before and after improvement by rare earth lanthanum soil improver (experiment 9);

[0055] Figure 22 Differential thermogravimetric curve of planting soil before and after improvement by rare earth lanthanum soil improver (experiment 9). DETAILED DESCRIPTION

[0056] Example 1

[0057] A preparation method of a modified biochar-based slow-release rare earth lanthanum soil improver, comprising the following steps:

[0058] Step 1, raw material preparation: 10 parts of rare earth lanthanum compound; 25 parts of modified biochar; 2 parts of phosphate; 70 parts of dehydrated river channel silt; 15 parts of organic complexing agent;

[0059] Step 2, raw material pretreatment: dissolve the rare earth lanthanum compound and the organic complexing agent in deionized water, stir and react in a 50-70°C water bath to generate a complex solution;

[0060] Step 3, preparation of modified biochar:

[0061] (1) treat the biochar with 10% nitric acid at 55°C for 7 hours, and with 30% nitric acid at 65°C for 9 hours; wash with deionized water until pH=7;

[0062] (2) after drying, add 10% ethylenediamine solution to the biochar at a solid-liquid ratio of 1:20, and reflux at 85°C for 15 hours to graft amino groups on the surface of the biochar through nucleophilic substitution reaction;

[0063] Step 4, lanthanum loading: immerse the modified biochar in the complex solution, ultrasonic treatment, and then dry at 70°C for 8 hours to obtain lanthanum-loaded biochar;

[0064] Step 5, matrix mixing: mix the dehydrated river channel silt, phosphate, and lanthanum-loaded biochar uniformly to obtain a saline-alkali soil conditioner;

[0065] The saline-alkali soil conditioner is used to reduce soil salinity, fix heavy metals in the soil, improve soil structure, and slowly release rare earth elements into the soil.

[0066] Further, the particle size of the biochar is ≤2mm, the organic complexing agent is sodium citrate, the phosphate is potassium dihydrogen phosphate, and the rare earth lanthanum compound is lanthanum nitrate.

[0067] Further, the preparation method of the dehydrated river channel silt is as follows:

[0068] S1, silt pretreatment: after removing impurities from the river channel silt, add 1% of polyaluminum chloride by mass of the river channel silt, stir and mix uniformly, and then stand for 48 hours of sedimentation;

[0069] S2, mechanical dewatering: dewater the sedimented silt by filter pressing, and crush the obtained mud cake to a particle size of ≤5mm by a crusher;

[0070] S3, deep dewatering: dry the crushed silt to a water content of ≤15%;

[0071] S4, heavy metal stabilization treatment: add 2% of potassium dihydrogen phosphate by mass of the dried silt, mix uniformly, and then age for 72 hours;

[0072] S5, product processing: the stabilized sludge is crushed to obtain the dewatered river sludge.

[0073] Further, in step S2, the plate and frame filter press is used for pressure filtration and dewatering, the pressure is controlled to be 0.8 MPa, and the dewatering is performed to a water content of 45%.

[0074] Further, in step S4, the stabilized sludge is crushed by a pulverizer to pass through an 80-mesh screen.

[0075] Further, in step 2, the complex solution is generated by stirring in a 70°C water bath for 35 minutes.

[0076] Further, in step 4, the frequency of ultrasonic treatment is 50 kHz, and the time is 35 minutes.

[0077] Example 2

[0078] A preparation method of a modified biochar-based slow-release rare earth lanthanum soil conditioner, comprising the following steps:

[0079] Step 1, raw material preparation: 5 parts of rare earth lanthanum compound, 15 parts of modified biochar, 1 part of phosphate, 50 parts of dewatered river sludge, and 10 parts of organic complexing agent;

[0080] Step 2, raw material pretreatment: the rare earth lanthanum compound and the organic complexing agent are dissolved in deionized water, and a complex solution is generated by stirring in a 50-70°C water bath;

[0081] Step 3, preparation of modified biochar:

[0082] (1) The biochar is treated with 10% nitric acid at 45°C for 5 hours, and with 30% nitric acid at 55°C for 7 hours, and then washed with deionized water until the pH is 6;

[0083] (2) After drying, the biochar is added to 10% ethylenediamine solution at a solid-liquid ratio of 1:10, and refluxed at 75°C for 10-15 hours to graft amino groups on the surface of the biochar through nucleophilic substitution reaction;

[0084] Step 4, lanthanum loading: the modified biochar is immersed in the complex solution, and after ultrasonic treatment, it is dried at 50-70°C for 4 hours to obtain lanthanum-loaded biochar;

[0085] Step 5, matrix mixing: the dewatered river sludge, phosphate, and lanthanum-loaded biochar are mixed uniformly to obtain a saline-alkali soil conditioner;

[0086] The saline-alkali soil conditioner is used to reduce the salinity of the soil, fix heavy metals in the soil, improve the soil structure, and slowly release rare earth elements into the soil.

[0087] Further, the particle size of the biochar is ≤2mm, the organic complexing agent is sodium citrate, the phosphate is potassium dihydrogen phosphate, and the rare earth lanthanum compound is lanthanum nitrate.

[0088] Further, the preparation method of the dehydrated river sludge is as follows:

[0089] S1, sludge pretreatment: after removing impurities from the river sludge, 0.5% of polyaluminum chloride by mass of the river sludge is added, and after stirring and mixing uniformly, it is left to stand and settle for 24 hours;

[0090] S2, mechanical dewatering: the settled sludge is dewatered by filter pressing, and the obtained mud cake is crushed by a crusher to a particle size ≤5mm;

[0091] S3, deep dewatering: the crushed sludge is dried to a water content ≤15%;

[0092] S4, heavy metal stabilization treatment: 1% of potassium dihydrogen phosphate by mass of the dried sludge is added, and after mixing uniformly, it is aged for 48 hours;

[0093] S5, product treatment: the stabilized sludge is crushed to obtain the dehydrated river sludge.

[0094] Further, in step S2, a plate and frame filter press is used for filter pressing dewatering, the pressure is controlled at 0.6MPa, and the dewatering is performed to a water content of 40-45%.

[0095] Further, in step S4, the stabilized sludge is crushed by a crusher to pass through an 80-mesh sieve.

[0096] Further, in step 2, the reaction is stirred in a 50℃ water bath for 25 minutes to generate a complex solution.

[0097] Further, in step 4, the frequency of ultrasonic treatment is 30kHz, and the time is 25 minutes.

[0098] Example 3

[0099] A preparation method of a modified biochar-based slow-release rare earth lanthanum soil conditioner, comprising the following steps:

[0100] Step 1, raw material preparation: 8 parts of rare earth lanthanum compound; 20 parts of modified biochar; 1.5 parts of phosphate; 60 parts of dehydrated river sludge; 13 parts of organic complexing agent;

[0101] Step 2, raw material pretreatment: the rare earth lanthanum compound and the organic complexing agent are dissolved in deionized water, and the reaction is stirred in a 50-70℃ water bath to generate a complex solution;

[0102] Step 3, preparation of modified biochar:

[0103] (1) The biochar is treated with 10% nitric acid at 50°C for 6 hours, and with 30% nitric acid at 60°C for 8 hours, and then washed with deionized water until the pH is 6;

[0104] (2) After drying, the biochar is added with 10% ethylenediamine solution at a solid-liquid ratio of 1:15, and then refluxed at 80°C for 13 hours to graft amino groups on the surface of the biochar through nucleophilic substitution reaction;

[0105] Step 4, lanthanum loading: the modified biochar is immersed in a complex solution, ultrasonically treated, and then dried at 60°C for 6 hours to obtain lanthanum-loaded biochar;

[0106] Step 5, matrix mixing: the dehydrated river channel sludge, phosphate, and lanthanum-loaded biochar are uniformly mixed to obtain a saline-alkali soil conditioner;

[0107] The saline-alkali soil conditioner is used to reduce the soil salinity, fix heavy metals in the soil, improve the soil structure, and slowly release rare earth elements into the soil.

[0108] Further, the particle size of the biochar is ≤2 mm, the organic complexing agent is sodium citrate, the phosphate is potassium dihydrogen phosphate, and the rare earth lanthanum compound is lanthanum nitrate.

[0109] Further, the preparation method of the dehydrated river channel sludge is as follows:

[0110] S1, sludge pretreatment: after removing impurities from the river channel sludge, 0.8% of polyaluminum chloride by mass of the river channel sludge is added, and then the mixture is stirred and uniformly mixed, and then left to stand and settle for 36 hours;

[0111] S2, mechanical dewatering: the settled sludge is dewatered by filter pressing, and the obtained mud cake is crushed by a crusher to a particle size of ≤5 mm;

[0112] S3, deep dewatering: the crushed sludge is dried to a water content of ≤15%;

[0113] S4, heavy metal stabilization treatment: 1-2% of potassium dihydrogen phosphate by mass of the dried sludge is added, and then the mixture is uniformly mixed and aged for 48-72 hours;

[0114] S5, finished product treatment: the stabilized sludge is crushed to obtain the dehydrated river channel sludge.

[0115] Further, in step S2, the filter pressing dewatering is performed by a plate-and-frame filter press, and the pressure is controlled at 0.7 MPa to dewater the sludge to a water content of 43%.

[0116] Further, in step S4, the stabilized sludge is crushed by a crusher to pass through an 80-mesh sieve.

[0117] Further, in step 2, the reaction was stirred in a 60°C water bath for 30 minutes to form a complex solution.

[0118] Further, in step 4, the ultrasonic treatment was performed at a frequency of 40 kHz for 30 minutes.

[0119] Comparative Example 1

[0120] The difference between this comparative example and Example 3 is that no sodium citrate was added.

[0121] Comparative Example 2

[0122] The difference between this comparative example and Example 3 is that the biochar was not modified.

[0123] Comparative Example 3

[0124] The difference between this comparative example and Example 3 is that no dewatered river sludge was added in step 3.

[0125] Comparative Example 4

[0126] The difference between this comparative example and Example 3 is that no potassium dihydrogen phosphate was added in step 3.

[0127] Comparative Example 5

[0128] The difference between this comparative example and Example 3 is that no lanthanum nitrate was added in step 1 and step 3.

[0129] Comparative Example 6

[0130] The difference between this comparative example and Example 3 is that the dewatered river sludge was fermented in step 3, and the specific preparation method is as follows:

[0131] S1, sludge pretreatment: the river sludge was filtered through a 20-mesh screen to remove impurities, then 0.5-1% of polyaluminum chloride was added to the river sludge, and the mixture was stirred and mixed uniformly, then left to settle for 24-48 hours;

[0132] S2, mechanical dewatering: the settled sludge was pressed and dewatered, and the obtained mud cake was broken to a particle size of ≤5mm by a crusher;

[0133] S3, fermentation: 1-2% of calcium peroxide and 0.5-1% of humic acid were added to the broken sludge, and the mixture was mixed uniformly and then subjected to aerobic fermentation at 50-60°C for 7-10 days, with the pile being turned over every 24 hours during the fermentation;

[0134] S4, deep dewatering: the fermented sludge was dried to a water content of ≤15%;

[0135] S5, heavy metal stabilization treatment: 1-2% of potassium dihydrogen phosphate was added to the dried sludge, and the mixture was mixed uniformly and then aged for 48-72 hours;

[0136] S6, product processing: the sludge after stabilization treatment is crushed to obtain the dewatered river sludge.

[0137] Experimental section

[0138] Experiment 1

[0139] The seeds of alfalfa were planted in the saline-alkali soil improved by the soil improver prepared in Example 3 and Comparative Examples 1-6, 8 g of the soil improver was added to 100 g of the saline-alkali soil, and a control group was set. The soil improvers of Example 3 and Comparative Examples 1-5 were applied to the same soil, and a water control group was set. After 20 days, the growth of alfalfa was observed, and the results are shown in Table 1. Figure 1 As can be seen from the figure, the alfalfa in the control group did not show seedling emergence. The growth of alfalfa in Comparative Examples 1-6 was uneven, and the growth was not robust and the leaves were not lush. The growth of Comparative Example 4 was relatively better. The growth of alfalfa in Comparative Example 3 was far inferior to that in Example 3, and the growth of alfalfa in Comparative Example 6 was not as good as that in Example 3, which showed that the treatment method of the sludge had a significant effect on the fertilizer efficiency, and the soil improver prepared by directly adding river sludge had a better improvement effect on the saline-alkali soil than the soil improver prepared by adding fermented river sludge.

[0140] The growth of alfalfa in Example 3 was significantly better than that in the control group and Comparative Examples 1-6, and the plants were taller and the stems and leaves were more lush, which showed that the soil improver prepared in Example 3 had a significant improvement effect on the saline-alkali soil, and could effectively reduce the adverse effects of saline-alkali soil on the growth of alfalfa, and provided a more suitable growth environment for alfalfa, and promoted the growth and development of alfalfa.

[0141] Experiment 2

[0142] After the end of Experiment 1, the soil of each group was taken to determine the soil pH value, pH value, electrical conductivity (EC), organic matter content, available nutrients (nitrogen, phosphorus, potassium), cation exchange capacity (CEC), heavy metal content (such as Pb, Cd), and soil aggregate stability according to the Soil Agricultural Chemical Analysis.

[0143] Table 1 Soil improvement determination results

[0144]

[0145] As can be seen from Table 1, the pH and EC values of saline-alkali soil of Example 3 are significantly reduced, which is better than other groups, due to the synergistic effect of lanthanum citrate complex and sludge, so that the soil salt is effectively reduced, and the toxic effect of salt on crops is reduced. The content of available nitrogen, available phosphorus, available potassium and organic matter is also higher than that of other groups, and the content of Pb and Cd is reduced, which proves that the soil conditioner of the application has better effect on the nutrient composition and saline-alkali improvement of soil, and also has better effect on the removal of heavy metals in soil. At the same time, the CEC value of Example 3 is increased to 9.5 cmol+ / kg, which enhances the soil fertility and buffering performance, and is beneficial to the absorption and utilization of nutrients by crops. The aggregate stability of the control group is 0.5 mm, indicating that the soil structure is poor and easy to erode, and the aggregate stability of Example 3 is increased to 1.5 mm, which is also significantly increased compared with the comparative example, indicating that the soil conditioner provided by the application enhances the anti-erosion ability and water-retention ability of soil, which is beneficial to the growth and development of crop roots.

[0146] Experiment 3

[0147] 1. Water culture experiment

[0148] Prepare water and apply rare earth lanthanum soil conditioner conditioner prepared in Example 3 two groups of test, alfalfa seeds for water planting, for a week after taking pictures record (Fig. 1) Figure 2 ), the ruler is used to measure the root length (Fig. 2) Figure 3 ) and plant height (Fig. 3) Figure 4 ), the pH meter and conductivity meter are used to monitor the pH and EC value (conductivity) of the solution at the same time, see Table 2.

[0149] 2. Soil culture experiment

[0150] Prepare blank control group and add rare earth lanthanum soil conditioner two groups of test, take 150g of planting soil, the application amount of rare earth lanthanum soil conditioner is 10% of the mass of planting soil, alfalfa seeds for soil planting, repeat three groups, for two weeks after taking pictures record (Fig. 4) Figure 5 ), the ruler is used to measure the plant height and root length (Fig. 5) Figure 6 ), the pH meter and salt monitor are used to monitor the change of pH, EC value and salt content of soil at the same time, the growth condition of plants under these conditions and different effects are detected, and the change of pH and salt of soil in four groups of test is detected, see Table 2.

[0151] Table 2 Comparison of pH, EC and salinity of plants with and without adding conditioner in different tests

[0152]

[0153] Based on the comparative study of hydroponics and soil culture system, the improvement effect of rare earth lanthanum soil conditioner on salinized soil was systematically verified. As shown in Table 2, there was no significant change in the pH monitoring of the solution and water of the rare earth lanthanum soil conditioner in the hydroponics test, and the conductivity decreased from 1307 μS / cm to 1240 μS / cm, indicating that the rare earth lanthanum soil conditioner can improve the ion environment of the medium by releasing soluble electrons, which provides a theoretical basis for improving saline-alkali soil in the subsequent soil culture test. In the soil culture test, the salinity of the unimproved planting soil was 1132.5 ppm, the pH was 8.38, and after improvement, the pH decreased to 7.56 and the salinity decreased to 815 ppm, a decrease of 27.9%. Therefore, it is concluded that the rare earth lanthanum soil conditioner has a significant effect on "salt reduction and efficiency improvement" of salinized soil.

[0154] Experiment 4

[0155] The core indicator for evaluating water retention is the field moisture capacity, which is the stable water content after gravity water is drained from saturated soil, representing the maximum effective water amount that the soil can retain under natural conditions. In the soil sampling and pretreatment, a cutting ring is used to sample the same position of each soil culture pot with different factors added. The unimproved planting soil and the soil improved by the rare earth lanthanum soil conditioner in the soil culture test of Experiment 3 are sampled, respectively, to maintain the natural structure of the soil samples. Then the soil samples are soaked for 12 h until they are completely saturated. After that, the saturated soil samples are placed on filter paper and left for 2 h. Then the wet soil mass of the drained soil samples is measured using an electronic balance and recorded. Then the soil samples are dried at 105°C for 24 h until the constant weight is achieved. Subsequently, the dry soil mass of the soil samples is measured. Finally, the moisture content of the soil samples is calculated using the moisture content formula.

[0156] Moisture content formula:

[0157] ;

[0158] In the formula: : Moisture content, %; m w : Water mass, g; m s : Dry soil mass, g;

[0159] The calculated moisture content of the planting soil before and after improvement is shown in Table 3 and Figure 7 As can be seen from the results, under the same drainage time, the stable water content of the unimproved planting soil after gravity water is drained is 8.81%, while the moisture content of the soil with the rare earth lanthanum soil conditioner is 11.48%, which is significantly higher than the control group by 2.67%. Therefore, it is concluded that the rare earth lanthanum soil conditioner improves the water retention of the soil, and the increase in moisture content can further promote the formation of soil particle aggregates, enhance the soil's air permeability and water retention capacity, and improve the problem of salinized soil hardening.

[0160] Table 3 Moisture content test

[0161]

[0162] Experiment 5

[0163] The morphology of the rare earth lanthanum soil conditioner was detected by a scanning electron microscope (SEM) of GAIA 3XMN type, as shown in FIGS. 1-3. Figure 8 The energy spectrum of the conditioner is shown in FIG. 4. Figure 9 The element content detection is shown in Table 4. Figure 10 Figure 11

[0164] Table 4. Element content detection of the conditioner by scanning electron microscopy

[0165]

[0166] Table 4 shows that the atomic number of oxygen and carbon in the rare earth lanthanum soil conditioner accounts for 98.37%, indicating that the core component is an organic polymer. The atomic number of lanthanum accounts for 0.14%, which is enriched in the interface of organic matter in the form of La 3+ , and enhances the stability of the aggregate through the "ion bridge bond" (-COO-La 3+ ). The atomic number of nitrogen accounts for 0.80%, which provides nitrogen source for microbial metabolism. The atomic number of potassium accounts for 0.28%, which exists in the form of exchangeable K⁺, improves the content of soil available potassium, and activates urease activity. The rare earth lanthanum soil conditioner can directly input high content of exogenous organic carbon, and improve the total organic matter content of the soil. Figures 9-11 The distribution of the detected elements of the rare earth lanthanum soil conditioner was more directly observed.

[0167] The element scanning electron microscopy morphology of the unimproved planting soil is shown in FIG. 5. Figure 12 The element detection energy spectrum is shown in FIG. 6. Figure 13 The element content detection is shown in Table 5.

[0168] Table 5. Element content detection of the unimproved planting soil by scanning electron microscopy

[0169]

[0170] The element scanning electron microscopy morphology of the soil improved by the rare earth lanthanum soil conditioner is shown in FIG. 7. Figure 14 The element detection energy spectrum is shown in FIG. 8. Figure 15 The scanning electron microscopy element distribution diagram is shown in FIG. 9. Figure 16 The single element distribution diagram of the scanning electron microscopy is shown in FIG. 10. Figure 17 The element content detection is shown in Table 6.

[0171] Table 6. Element content detection of the improved planting soil by scanning electron microscopy​​

[0172]

[0173] Based on the characterization analysis of scanning electron microscopy, the rare earth lanthanum soil conditioner significantly optimizes the soil organic matter structure by restructuring the element occurrence form Figure 12 、 14 . As shown in Table 5, the total atomic ratio of C and O elements in the unimproved planting soil is 82.9%. As shown in Table 6, after being improved by the rare earth lanthanum soil conditioner, the atomic ratio of C and O is significantly improved to 95.0%, and a continuous and dense organic matter network structure is presented. The energy spectrum data further reveals the appearance of La3 + characteristic peak in the improved soil Figure 13 、 15 , accompanied by N, K; as shown in Table 6, the atomic percentage of lanthanum is 0.21%, the atomic percentage of nitrogen is 1.63%, and the atomic percentage of potassium is 0.04%, and other nutrient elements are directionally enriched; Figures 16-17 More intuitive observation of the distribution of the detected elements of the rare earth lanthanum soil conditioner.

[0174] Experiment 6

[0175] XRF detection is the excitation of atoms in the sample by primary X-rays emitted by an X-ray light tube, which causes the generation of characteristic X-rays. By accurately measuring the wavelength, energy and intensity information of the characteristic fluorescence X-rays released by each element in the sample, the elemental composition in the sample can be fully analyzed, and the content data of each element can be accurately obtained, thereby realizing the dual goals of qualitative and quantitative analysis. The following is the XRF detection analysis of the unimproved planting soil and the soil improved by the rare earth lanthanum soil conditioner in Experiment 3, and the specific data is shown as follows.

[0176] Table 7 Relative abundance and mass percentage of elements in unimproved planting soil

[0177]

[0178] The relative abundance of elements and the mass percentage (wt%) of corresponding oxides or elements of the unimproved planting soil in Table 7 are shown. The highest content component in the unimproved planting soil is SO3, accounting for 44.72 wt% of the total mass, indicating that the content of sulfate in the soil is extremely high. The mass percentage of Cl is 1.17 wt%, reflecting the enrichment of soil salt (such as NaCl). The mass percentage of SiO2 is 3.45 wt%, and the mass percentage of Al2O3 is 2.71 wt%, which is significantly lower than the normal soil SiO2 content of 40-70%, and the salt cover again proves the salinization characteristics. Since the high mass percentage of SO3 and the enrichment of Cl indicate that the soil is a sulfate-chloride type of saline soil. The mass percentage of Na2O is 1.14 wt%, which is relatively high. Combined with Cl and SO3, it can be inferred that the percentage of exchangeable sodium is over-standard and needs to be improved. The mass percentage of K2O is 2.605 wt%, and the mass percentage of CaO is 1.53 wt%, so the content of potassium and calcium oxides is relatively high. In the detection of heavy metals and trace elements, the mass percentage of Fe2O3 is 0.8174 wt%, and the mass percentage of MnO is 0.106 wt%, and the content of iron and manganese oxides is normal.

[0179] Table 8 Relative abundance of elements and mass percentage of soil improved by rare earth lanthanum soil improver

[0180]

[0181] The relative abundance of elements and the mass percentage (wt%) of the corresponding oxides or elements of the improved planting soil are shown in Table 8. The mass percentage of SO3 decreased from 44.72 wt% to 1.38 wt%, and the mass percentage of Cl decreased from 1.17 wt% to 0.333 wt%, so the content of chlorides was greatly reduced, and the soil was converted from “sulfate-chloride type” to slightly salinized. The mass percentage of CaO increased from 1.53 wt% to 8.906 wt%, and it was speculated that calcium ions replaced Na+ through ion exchange, enhancing the structural stability. The mass percentage of Na2O increased slightly from 1.14 wt% to 1.83 wt%, but combined with the decrease of Cl and SO3, the percentage of exchangeable sodium decreased, and the soil dispersion improved. The mass percentage of SiO2 increased from 3.45 wt% to 46.64 wt%, indicating that the addition of silicates in the rare earth lanthanum soil conditioner or the enhancement of mineral stability, and the mass percentage of Al2O3 increased from 2.71 wt% to 10.69 wt%, reflecting the enrichment of clay minerals, and the applied rare earth lanthanum soil conditioner improved the soil aggregate structure. The enrichment of silicate and aluminate minerals and calcium indicated that the soil structure stability and fertility were significantly improved. The mass percentage of K2O was 2.446 wt%, and the mass percentage of Fe2O3 was 4.774 wt%, which was due to the input of organic matter after the application of rare earth lanthanum soil conditioner, which promoted the absorption of plant nutrients, and the mass percentage of effective phosphorus P2O5 was 0.701 wt%, and the mass percentage of available potassium K2O was 2.446 wt%, which supported crop growth. The mass percentage of CuO was 0.0084 wt%, and the mass percentage of ZnO was 0.0115 wt%, which was extremely low, and the risk of heavy metals was low, and no pollution was shown.

[0182] Experiment 7

[0183] The multi-point BET specific surface area, adsorption-desorption average pore size, and pore volume of the unimproved planting soil and the soil improved by the rare earth lanthanum soil conditioner in the soil culture experiment in Experiment 3 were detected by the Micromeritics ASAP 2460 specific surface area instrument. The specific data are shown in Table 9.

[0184] Table 9 Specific surface area and pore size of the measured samples

[0185]

[0186] Based on the specific surface area and pore parameter analysis of Table 9, the specific surface area of the improved soil reaches 8.9237 m² / g, which is 30.5% higher than the specific surface area of the original planting soil (unimproved planting soil) of 6.8398 m² / g. The increase in specific surface area indicates a significant increase in adsorption sites, providing a physical basis for nutrient retention. The average pore size of the original planting soil is 9.9494 nm, while the average pore size of the rare earth lanthanum soil improver is 4.5740 nm. After the improvement of the rare earth lanthanum soil improver, the average pore size of the soil is 6.1099 nm, forming a pore structure dominated by mesopores, which has both micropore adsorption and macropore water conduction functions. The pore volume of the original planting soil is 0.013793 cm³ / g, while the pore volume of the improved soil decreases to 0.011581 cm³ / g, reflecting the transformation of the pore structure from disordered macropores to ordered mesopores, reducing the proportion of ineffective pores. Through a synergistic mechanism, the rare earth lanthanum soil improver transforms the planting soil from a loose and inefficient structure to a high-adsorption and slow-release functional substrate. The mesopore-dominated pore system exhibits multiple advantages in water retention, fertilizer retention, and growth promotion, and can quickly improve saline soil.

[0187] The working mechanism of the specific surface area instrument is based on gas adsorption theory. In an ultra-low temperature environment, reversible physical adsorption occurs between the surface of the solid sample and nitrogen molecules. The adsorption equilibrium state is regulated by the system pressure. At a constant temperature, the amount of gas adsorbed on the surface of the solid is related to the pressure, which changes with the pressure. Based on the adsorption and desorption principle, the equilibrium adsorption amount of adsorbate on adsorbent is determined at different pressures at a constant temperature, and the adsorption and desorption isotherm is drawn. The adsorption and desorption curve of the sample is shown in Figure 18 , and the pore size distribution analysis is shown in Figure 19 .

[0188] According to the International Union of Pure and Applied Chemistry (IUPAC) pore classification, in the stage of relative pressure P / P0 <0. 50, it is micropore N2 adsorption with pore size d<2 nm, and the curve shows a large upward state, indicating that the number of micropores of the planting soil increases rapidly; in the relative pressure range of 0. 50-0. 88, it is mesopore N2 adsorption with 2 nm≤d≤50 nm, and the curve shows an upward state, indicating that the content of mesopores of the planting soil is rich; in the high relative pressure P / P0>0. 88, the adsorption amount increases sharply, which is macropore N2 adsorption with d>50 nm. In this stage, due to the occurrence of capillary condensation phenomenon, the curve shows a leap upward state. Figure 18 For the N2 adsorption and desorption curves of the planting soil before and after improvement, it can be seen from the figure that the adsorption and desorption curves before and after improvement both show a concave low-pressure zone, capillary condensation in the high-pressure zone, and the adsorption and desorption do not coincide, there is a hysteresis loop, so it belongs to type IV curve. Under the same P / P0 conditions, the adsorption amount increases due to the incorporation of the rare earth lanthanum soil improver. The desorption branch curve of the soil before and after improvement does not completely coincide with the adsorption branch, and there is a significant drop in adsorption amount.

[0189] Figure 19 To improve the pore size distribution of the planting soil before and after, it can be seen from the figure that the pore size distribution of the soil before improvement is mainly distributed in the range of 2.5-3 nm, indicating that the sample has abundant mesoporous structure, and the mesoporous structure is very important for the adsorption performance and nutrient release characteristics of compound fertilizer. The pore structure of the improved soil is larger than that of the unimproved soil at the same pore width, and the pore size of the soil before and after improvement is concentrated in the range of 2.5-4 nm, and the pore capacity increases sharply in this range. The pore volume of the improved soil increases from 0.002 cm 3 / g to 0.0175 cm 3 / g, and the pore volume of the improved soil is larger than that of the unimproved planting soil in the range of 2.5-4 nm, so the mesopore of the soil increases after improvement, and the pore size of the soil before and after improvement decreases linearly in the range of 4-5 nm, and the pore volume increases in the range of 5 nm to 30 nm, but the pore volume of the improved soil is still larger than that of the unimproved soil, so the application of rare earth lanthanum soil conditioner can enhance the water conservation capacity, the expanded mesoporous structure can significantly improve the soil water holding capacity, reduce water seepage loss, and improve the soil aeration, accelerate oxygen diffusion and carbon dioxide discharge, provide a suitable habitat for microbial metabolism, drive organic matter mineralization and nutrient transformation.

[0190] Experiment 8

[0191] The principle of infrared spectrum analysis technology is based on the absorption of infrared light by molecules, and the formed infrared absorption spectrum is used to identify the molecular composition and structure, or to determine the quantitative method. Based on the selective absorption of specific wavelength infrared by molecules, the internal vibration energy level and rotation energy level will change, and by monitoring the infrared absorption information, the external absorption spectrum of the substance can be obtained. This spectrum can also be called vibration-rotation spectrum or molecular rotation spectrum. In this experiment, the improved planting soil was detected by TENSOR II of Germany Brueck, and the infrared spectrum of the planting soil before and after improvement is shown in Figure 20 .

[0192] Based on Figure 20The infrared spectrum data of the improved planting soil showed that the O-H / N-H stretching vibration at 3600-3200 cm⁻¹ was significantly enhanced at 3723.4 cm⁻¹ and 3601.8 cm⁻¹, indicating that the organic matter hydroxyl (-OH) and amino (-NH) functional groups introduced by the rare earth lanthanum soil conditioner were enriched, enhancing the soil water retention and ion exchange capacity; the C-H / CO3²⁻ vibration at 2950-2350 cm⁻¹ showed a weak peak at 2350.1 cm⁻¹ in the unimproved planting soil, which may be due to trace amounts of carbonate, while the improved soil showed no peak at this position, which was consistent with the previous thermogravimetric analysis results and indicated that the rare earth lanthanum soil conditioner inhibited the deposition of carbonate through pH adjustment; the C-H bending vibration at 1449 cm⁻¹ was enhanced in the improved planting soil, reflecting the input of exogenous organic matter and promoting the accumulation of aliphatic carbon pool; the Si-O-Si / Al-O-Si stretching vibration at 1019.8 cm⁻¹ was significantly higher in the improved planting soil than in the unimproved planting soil, indicating that the silicate component in the rare earth lanthanum soil conditioner formed a stable silicate network with clay minerals, enhancing the stability of soil aggregates; the metal-O bond vibration at 659.8 cm⁻¹ showed a La-O characteristic peak in the improved planting soil, which was related to the hydrolysis product La(OH)3 of La(NO3)3 in the rare earth lanthanum soil conditioner, confirming that La³ + The organic-mineral complex was stabilized by ionic bridge bonds, which was consistent with the analysis of the rare earth lanthanum soil conditioner by scanning electron microscopy. It was concluded that the rare earth lanthanum soil conditioner had a carbonate inhibition effect, and the disappearance of the peak at 2350 cm⁻¹ indicated that the salt content (CO3²⁻) was reduced, combined with the decrease in pH from 8.38 to 7.56, the risk of salinization was reduced by 35%; and it could promote the fixation of sodium ions, La³ + The Na⁺ adsorbed by clay minerals was replaced by ion exchange; the enrichment of hydroxyl and amino groups was enhanced, and the peaks at 3723.4 cm⁻¹ and 3601.8 cm⁻¹ were enhanced, which was directly related to the increase in organic matter content; the stability of the carbon pool was improved, and the peak at 1449 cm⁻¹ was strengthened, reflecting the increase in the proportion of recalcitrant organic matter and the decrease in carbon mineralization rate; it could also promote the stability of the structure.

[0193] Experiment 9

[0194] The principle of thermal gravimetric analysis (TG or TGA) is to place the sample in a temperature-programmed mass response, and obtain the initial decomposition temperature, termination temperature, weight loss rate and residual carbon content and other related information through the mass change of the sample with temperature or time. The thermal gravimetric curve (TG curve) is a curve directly obtained from the thermal gravimetric test, which records the relationship between the mass of the sample and the temperature or time. The differential thermal gravimetric curve (DTG curve) is a curve generated from the thermal gravimetric curve, which is the first derivative of the thermal gravimetric curve with respect to temperature or time. It reflects the rate of change of the mass of the sample. In the corresponding relationship between the DTG curve and the TG curve, the peak point of the DTG curve corresponds to the inflection point of the weight loss step of the TG curve. The peak position corresponds to the maximum value of the weight loss rate.

[0195] The thermal gravimetric experiment this time adopts the thermal gravimetric analysis system of Netzsch TG 209 F1 of Germany, and selects two soil samples in experiment 3 for comparative analysis: unimproved planting soil (mass 5.7832 mg) and soil improved by rare earth lanthanum soil improver (mass 5.4615 mg). The experimental parameter setting is: thermal gravimetric analysis is carried out at a temperature rising rate of 30 K / min in the temperature range of 30-800℃. The thermal gravimetric curve graphs before and after improvement are as shown in Figure 21 , and the differential thermal gravimetric curves before and after improvement are as shown in Figure 22 .

[0196] The unimproved planting soil has three weight loss stages, which are 33.4-100℃ low-temperature weight loss stage, weight loss rate is 1.69%, mainly due to the volatilization of adsorbed water in the soil, such as the loss of part of the weakly bound water or interlayer water in the clay mineral, the DTG curve appears a single peak near 80℃, the peak value is -0.25% / min, reflecting the desorption of interlayer water of montmorillonite; 250-632.1℃ medium-temperature weight loss stage, weight loss rate is 2.61%, due to the humus in the organic matter of the soil, decarboxylation of humic acid (-COOH→CO2↑) at 300-450℃, oxidation and pyrolysis of microbial residues and cleavage of aliphatic compounds, a single peak appears in the DTG curve near 400℃, the peak value is -0.18% / min; 632.1-700℃ high-temperature weight loss stage, weight loss rate is 1.37%, due to the removal of structural hydroxyl (-OH) of clay mineral and the decomposition of trace amount of carbonate to release carbon dioxide, a single peak appears in the DTG curve near 680℃, the peak value is -0.10% / min. The improved planting soil has three weight loss stages, which are 35-200℃ low-temperature weight loss, the mass increases by 0.38%, indicating that the La 3+The stable complex with clay minerals enhances the water binding capacity, and the oxidation of part of the organic matter at low temperature may also increase the weight; The weight loss rate in the medium temperature loss stage of 400-642.5 ℃ is 0.231%, which is 91.1% lower than that of the improved soil, i.e. the stability of soil organic matter is improved; The high temperature weight loss rate of 642.5-800 ℃ is 3.976%, and the increase in weight loss rate may be due to the high temperature reaction of silicate and clay minerals in rare earth lanthanum soil improver, rather than simple mineral decomposition. It is concluded that rare earth lanthanum soil improver improves the soil through the synergistic mechanism of "water adsorption enhancement-organic matter condensation stability-mineral reconstruction", which makes the improved soil have the advantages of water conservation, drought resistance and long-term carbon storage.

Claims

1. A method for preparing a modified biochar-based slow-release rare earth lanthanum soil conditioner, characterized in that, Includes the following steps: Step 1: Raw material preparation: 5-10 parts rare earth lanthanum compound; 15-25 parts modified biochar; 1-2 parts phosphate; 50-70 parts dehydrated river silt; 10-15 parts organic complexing agent; Step 2, Raw material pretreatment: Dissolve the rare earth lanthanum compound and the organic complexing agent in deionized water, and stir and react in a water bath at 50-70℃ to generate a complex solution; The biochar has a particle size ≤2mm, the organic complexing agent is sodium citrate, the phosphate is potassium dihydrogen phosphate, and the rare earth lanthanum compound is lanthanum nitrate. Step 3: Preparation of modified biochar: (1) Treat the biochar with 10% nitric acid at 45-55℃ for 5-7 hours; treat it with 30% nitric acid at 55-65℃ for 7-9 hours; wash it with deionized water until pH=6-7; (2) After drying, add 10% ethylenediamine solution to biochar at a solid-liquid ratio of 1:10-20, and reflux at 75-85℃ for 10-15 hours to graft amino groups onto the surface of biochar through nucleophilic substitution reaction. Step 4, Lanthanum loading: The modified biochar is impregnated in a complex solution, ultrasonically treated, and then dried at 50-70℃ for 4-8 hours to obtain lanthanum-loaded biochar. Step 5, Matrix Mixing: Mix dehydrated river silt, phosphate, and lanthanum-loaded biochar evenly to obtain a saline-alkali soil conditioner; the saline-alkali soil conditioner is used to reduce soil salinity, fix heavy metals in the soil, improve soil structure, and slowly release rare earth elements into the soil; The method for preparing the dehydrated river silt is as follows: S1. Silt pretreatment: After removing impurities from the river silt, add 0.5-1% of polyaluminum chloride by weight of the river silt, stir and mix evenly, and let it stand to settle for 24-48 hours. S2. Mechanical dewatering: The settled sludge is dewatered by filter press, and the resulting mud cake is crushed to a particle size of ≤5mm by a crusher. S3. Deep dewatering: Dry the crushed sludge to a moisture content of ≤15%; S4. Heavy metal stabilization treatment: Add 1-2% by weight of potassium dihydrogen phosphate to the dried sludge, mix well and age for 48-72 hours. S5. Finished product processing: The stabilized sludge is crushed to obtain dewatered river sludge.

2. The preparation method of the modified biochar-based slow-release rare earth lanthanum soil conditioner as described in claim 1, characterized in that, In step S2, a plate and frame filter press is used for dewatering, with the pressure controlled at 0.6-0.8 MPa, to dewater to a moisture content of 40-45%.

3. The preparation method of the modified biochar-based slow-release rare earth lanthanum soil conditioner as described in claim 1, characterized in that, In step S5, the stabilized sludge is crushed by a crusher until it passes through an 80-mesh sieve.

4. The preparation method of the modified biochar-based slow-release rare earth lanthanum soil conditioner as described in claim 1, characterized in that, In step 2, the mixture is stirred in a water bath at 50-70°C for 25-35 minutes to generate a complex solution.

5. The preparation method of the modified biochar-based slow-release rare earth lanthanum soil conditioner as described in claim 1, characterized in that, In step 4, the ultrasonic treatment frequency is 30-50kHz and the time is 25-35 minutes.

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