A cow dung biochar composite material for saline-alkali land improvement, its preparation method and uses.

Abstract

This invention discloses a cow dung biochar composite material for saline-alkali land improvement, its preparation method, and its uses, belonging to the field of cow dung material processing technology. It includes the following steps: (1) air-drying cow dung, then performing oxygen-limited pyrolysis, cooling, and pulverizing to obtain raw cow dung biochar; (2) mixing the raw cow dung biochar with calcium nitrate solution and then stirring for modification; (3) after modification, drying and performing oxygen-limited pyrolysis, cooling, and pulverizing to obtain the cow dung biochar composite material. This invention uses widely available raw materials and an easy-to-operate method to produce a calcium nitrate-modified cow dung biochar composite material that can be widely promoted and is inexpensive, and the preparation process generates no pollutants. The prepared composite material can lower the pH of saline-alkali land, improve the physical and chemical properties of the soil, and reduce the sodium content in the soil. + It has a stronger adsorption capacity, reduces soil salinity, increases soil nitrate nitrogen content, promotes plant growth, and achieves the effect of recycling livestock waste.

Description

Technical Field

[0001] This invention belongs to the field of cow dung material treatment technology, specifically relating to a cow dung biochar composite material for saline-alkali land improvement, its preparation method, and its uses. Background Technology

[0002] Saline-alkali soil refers to a type of soil in which soluble salts accumulate to a high concentration. It is a general term encompassing different types of saline soil, saline soil, and alkaline soil. According to incomplete statistics from UNESCO and FAO, the global area of ​​saline-alkali soil reaches 955 million hectares. 2 Saline-alkali soils, accounting for approximately 11% of the total land area, are a significant environmental problem worldwide, particularly in arid and semi-arid regions characterized by widespread distribution, high salinity, and diverse soil types. This leads to severe land degradation, reduced agricultural productivity, and even food security issues. In my country, saline-alkali soils are distributed across 18 provinces and regions, including North China, Northeast China, Northwest China, and parts of the coastal plains, exhibiting diverse soil types. Currently, my country has developed over 40 practical technologies across eight major systems for the comprehensive utilization of saline-alkali land, including soil desalination technology and soil biological and organic salt-remediation and soil improvement technologies. In terms of crop varieties, my country has cumulatively promoted over 50 salt-tolerant crop varieties. Strengthening the management and comprehensive utilization of saline-alkali land, and awakening dormant reserve resources of arable land, will contribute to the expansion, improvement, and efficiency of arable land resources.

[0003] The application of livestock and poultry manure as an exogenous organic material has a good effect on improving saline-alkali soil. Studies by Ji et al. have shown that organic fertilizer is beneficial for the recovery of soil organic matter and the increase of fertility, and effectively improves soil physicochemical properties, promotes plant nutrient absorption and utilization, and promotes soil humification. A considerable number of studies have found that cow manure can effectively increase the ratio of easily oxidized carbon, light organic carbon, and soluble organic carbon to organic carbon in soda-alkali soils; the application of cow manure can increase the content and storage of organic carbon in the surface layer of alkalized soils, and increase the content of active organic carbon components such as EOC, POC, and MBC. The use of livestock and poultry manure to enhance the activity and capacity of the organic carbon pool in soda-alkali soils, combined with the application of different amendments, is also one of the current trends in improving saline-alkali soils. However, when untreated livestock and poultry manure is applied to saline-alkali soils, its high concentration of soluble salts (especially Na+) results in... + Cl -The combined effect of manure and inherent soil salinity leads to a 15-30% increase in soil sodium ion adsorption ratio (SAR), significantly exacerbating soil compaction and permeability deterioration. More seriously, residual heavy metals in manure (such as Cu and Zn, with average contents of 150-450 mg / kg) form stable complexes in the high pH environment of saline-alkali soil, increasing heavy metal bioavailability by 2-3 times and threatening food safety through crop accumulation. Simultaneously, the environmental problems caused by direct application to the field are becoming increasingly prominent: during open-air storage, the ammonia volatilization loss rate of livestock and poultry manure is as high as 30-50%, and the released NH3 and CH4 account for 26% and 14% of agricultural emissions, respectively; nitrogen and phosphorus losses due to rainy season runoff can reach 45 kg N / ha and 8 kg P / ha, becoming a major cause of eutrophication in water bodies. These negative effects are significantly amplified in ecologically fragile saline-alkali soil areas.

[0004] Biochar is a stable, porous solid material formed by the pyrolysis of biomass under anaerobic or low-oxygen conditions at high temperatures (≤700℃). Its main components are carbon (approximately 23.6%–88.0%) and ash. Compared to directly returning livestock manure to the field, biochar offers the following advantages: salt regulation – the stable mineral elements in biochar can reduce the percentage of exchangeable sodium (ESP) in the soil by 40-60%, and its porous structure promotes salt ion leaching; heavy metal passivation – the abundant oxygen-containing functional groups (-COOH, -OH) on its surface increase the complexation capacity of heavy metals by 5-8 times; environmental friendliness – the carbonization process fixes more than 90% of the carbon, reducing greenhouse gas emission potential by 70-85%; soil improvement – ​​the addition of biochar increases the stability index of saline-alkali soil aggregates by 35-50% and increases water retention capacity by 20-30%. By reducing soil bulk density and promoting aggregate formation, the application of biochar can increase crop yield, improve soil quality and reduce salinity, while also increasing soil organic carbon content and improving soil water and fertilizer retention capacity.

[0005] Some studies have shown that adding different amounts of biochar during the seedling and harvest stages can increase the cation exchange capacity, organic matter, and nutrient content in the 0-40 cm soil layer and both aboveground and belowground parts, effectively promoting root growth and development, root area and volume, and significantly affecting plant height, stem diameter, leaf area, and yield per plant. Other studies have shown that applying 2.0% and 2.5% biochar improves the physicochemical and biological properties of saline-alkali soils and significantly affects soil bacterial structure and diversity, thereby influencing soil N and P cycles, improving soil physicochemical properties, and promoting crop growth by alleviating salt stress. However, traditional biochar, due to its low surface functional group density (<1.2 mmol / g) and simple pore structure (micropores >70%), has limited effectiveness in improving the Na+ content in saline-alkali soils. +The ion exchange capacity is insufficient (0.3-0.8 cmol / kg), and the salt ion retention efficiency is low due to the mismatch between pore size and hydrated ion size. Modification can improve the effect of biochar: for example, HNO3 oxidation increases the carboxyl density to 2.5-4.8 mmol / g, and Na... + The exchange capacity is increased by 4-6 times (to 2.3-3.5 cmol / kg), which can significantly reduce the soil SAR value; KOH activation constructs a hierarchical pore system (the proportion of mesoporous pores increases to 55%), and salt ions (Na+) are separated. + Cl - Migration resistance is reduced by 40-60%, and combined with rain leaching, desalination efficiency is increased by 2-3 times; Fe-Mn oxide-loaded modification regulates the surface charge of the material (pH decreases from 6.8 to 3.2), enabling the adsorption and fixation of Cl in high-pH saline-alkali soils. - NO3 - The presence of anions increases the rejection rate to 85-92%. Modification of biochar through acid-base, oxidant, and metal salt processes affects its properties, thus influencing its effectiveness in improving saline-alkali land.

[0006] As the world's largest livestock producer, my country generates over 4 billion tons of livestock and poultry manure annually, with cow manure accounting for more than 35%. Currently, only 2-3% of cow manure resources are effectively utilized, while the remaining 97% of untreated manure accumulates or is illegally discharged, posing a severe environmental threat. Significant shortcomings exist in current research and industrial application of cow manure resource utilization technologies.

[0007] In the Chinese invention patent application "A method for storing livestock and poultry breeding wastewater based on farmland utilization" (application number: CN202110767069.7), the wastewater is collected and then pumped into an acidification tank to adjust the pH value to 5.0-6.0. After that, a methane inhibitor is added and mixed evenly before being pumped into a wastewater storage tank for storage. After hydrolysis and acidification, solid residue and hydrolysis acidification liquid are generated. The solid residue is made into biochar. When the pH value of the wastewater in the wastewater storage tank is higher than 6.5, the hydrolysis acidification liquid and biochar are added to the tank, mixed evenly, and then stored. The stored wastewater is diluted and then returned to the field for application.

[0008] The Chinese utility model patent application "An Environmental Protection System for Pig and Cattle Farm Manure Treatment" (application number: CN202120575135.6) describes a system where pig and cattle farm manure is dissolved in a mixing tank to separate harmful elements through sedimentation. Solid manure undergoes aerobic and anaerobic reactions, promoting the growth of microorganisms and converting harmful components into beneficial trace elements for plant growth. The manure is then dried and stored in a fertilizer silo. The separated liquid is transported to a sedimentation tank for further sedimentation. A three-stage mixer is used to add chemicals to remove pigments and colloids from the manure, which are then discharged through a bottom valve. After secondary sedimentation, the overflowing clear water is transported to a clear water tank for storage and reuse.

[0009] Chinese invention patent application "An Iron-Modified Cow Dung Biochar Material and Its Preparation Method and Application" (application number: CN202411709133.6) describes a method for preparing K2FeO4 composite biochar material by immersing cow dung solid waste biomass raw material in a K2FeO4 solution, heating it in a water bath, and then drying it. This material is then carbonized at high temperature in a tubular furnace to obtain K2FeO4-modified cow dung biochar material (FCBC). The K2FeO4-modified cow dung biochar material (FCBC) of this invention exhibits better Cd saturation than unmodified cow dung biochar (CBC). 2 + It eliminates the need for processing Cd, and at the same time, it has unparalleled advantages over traditional modified or unmodified plant-derived biochar in terms of Cd treatment capacity. 2+ Adsorption effect.

[0010] In the Chinese invention patent application "A method for preparing high-quality sludge biochar and its application" (application number: CN202311350100.2), sludge and cow dung are chemically activated, and after sedimentation separation, supernatant A and precipitate B are obtained. After low-speed centrifugation, supernatant C and precipitate D are obtained. Precipitate D is dried to obtain pyrolysis precursor E. Precipitate E is pyrolyzed under N2 atmosphere. The pyrolyzed biochar is washed with acid solution, and some useful substances are recovered. After acid washing, the biochar and acid washing solution are separated. The biochar is washed with water. The acid-washed biochar is dried and sieved, and can generate superoxide anion free radicals through adsorption, transformation and transfer.

[0011] The aforementioned patents have problems such as complicated engineering and high cost in utilizing cow dung resources. Furthermore, the existing methods for preparing cow dung biochar and its modified composite materials are mainly used to adsorb heavy metals and remediate polluted soil, leaving a gap in the large-scale application of cow dung biochar modified composite materials for the treatment of saline-alkali land. Summary of the Invention

[0012] To address the aforementioned shortcomings of existing technologies, this invention provides a cow dung biochar composite material for saline-alkali land improvement, its preparation method, and its applications. This invention utilizes widely available raw materials and an easy-to-operate preparation method to produce a low-cost, large-scale-scale-producible calcium nitrate-modified cow dung biochar composite material, with no pollutants generated during the preparation process. The prepared modified biochar can lower the pH of saline-alkali land, improve soil physicochemical properties, and reduce sodium content in the soil. + It has a stronger adsorption capacity, reduces soil salinity, increases soil nitrate nitrogen content, promotes plant growth, and achieves the effect of recycling livestock waste.

[0013] To achieve the above objectives, the technical solution adopted by the present invention to solve its technical problem is as follows:

[0014] The purpose of this invention is to provide a method for preparing a cow dung biochar composite material for saline-alkali land improvement, which includes the following steps:

[0015] (1) Air dry the cow dung, then decompose it at 380-450℃ under limited oxygen for 3-6 hours, cool it and then crush it to obtain the original cow dung biochar.

[0016] (2) After mixing the raw cow manure biochar with calcium nitrate solution, the mixture was modified for 22-30 hours under stirring conditions;

[0017] (3) After modification, the mixture is dried at 150-320℃ and subjected to oxygen-limited pyrolysis for 3-5 hours. After cooling, it is pulverized to obtain the cow dung biochar composite material.

[0018] Furthermore, in step (1), the oxygen-limited pyrolysis temperature is 400–420 °C, and the pyrolysis time is 3–6 h.

[0019] Furthermore, in step (1), the oxygen-limited pyrolysis temperature is 400℃ and the pyrolysis time is 4h.

[0020] Furthermore, the particle size of the raw cow dung biochar obtained after crushing in step (1) is 1-3 mm.

[0021] Furthermore, in step (2), the mass-to-volume ratio of raw cow dung biochar to calcium nitrate solution is 1:10-15 (g:mL).

[0022] Furthermore, in step (2), the mass-to-volume ratio of cow dung biochar to calcium nitrate solution is 1:15 (g:mL).

[0023] Furthermore, the concentration of the calcium nitrate solution in step (2) is 0.5–0.8 mol / L.

[0024] Furthermore, the concentration of the calcium nitrate solution in step (2) is 0.5 mol / L.

[0025] Furthermore, the modification reaction time in step (2) is 24 hours.

[0026] Furthermore, in step (3), the temperature is 180-200℃, and oxygen-limited pyrolysis is carried out simultaneously with drying, and the oxygen-limited pyrolysis time is less than the drying time.

[0027] Furthermore, the temperature in step (3) is 200℃.

[0028] Another object of the present invention is to provide a cow dung biochar composite material for improving saline-alkali land, which is prepared by the above method.

[0029] Another object of the present invention is to provide an agent for improving saline-alkali land, comprising the above-mentioned cow dung biochar composite material.

[0030] Another object of the present invention is to provide the use of the above-mentioned cow dung biochar composite material or preparation in the improvement of saline-alkali land.

[0031] The beneficial effects of this invention are:

[0032] The entire preparation process is short, it is effective in improving saline-alkali land, it is easy to promote, and it causes no environmental pollution.

[0033] The preparation process is simple and easy to operate, and the raw materials are widely available. At the same time, it effectively utilizes the manure from free-range grazing and fenced-off cattle, increasing the recycling and utilization of livestock and poultry manure.

[0034] The calcium chloride-modified biochar composite material is simultaneously loaded with Ca 2+ and NO 3- It can effectively alleviate soil salinization while increasing soil nitrate nitrogen content and improving soil nutrient status.

[0035] It can stably absorb salts in the soil, continuously reduce the degree of salinization, and improve the physical and chemical properties of the soil.

[0036] This invention improves saline soil, alleviates grassland pollution caused by livestock and poultry manure, reduces the cost of saline-alkali land improvement and cattle manure treatment, and enables large-scale production and is adaptable to the treatment of large areas of saline-alkali land. Attached Figure Description

[0037] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0038] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0039] Example 1

[0040] A method for preparing a cow dung biochar composite material for saline-alkali land improvement includes the following steps:

[0041] (1) After the collected cow dung was air-dried, it was decomposed in a stainless steel muffle furnace at 400℃ under limited oxygen for 4 hours. After natural cooling, the biochar was crushed by a pulverizer and passed through a 10-mesh sieve to obtain the original cow dung biochar.

[0042] (2) Add the raw cow manure biochar to a 0.5 mol / L calcium nitrate solution at a solid-liquid ratio of 1:15 and stir with a shaker at 180 r / min for 24 h.

[0043] (3) The mixture was dried at 200°C for 4 hours and subjected to oxygen-limited pyrolysis for 2 hours in a stainless steel muffle furnace to obtain a cow dung biochar calcium nitrate modified composite material.

[0044] Example 2

[0045] A method for preparing a cow dung biochar composite material for saline-alkali land improvement includes the following steps:

[0046] (1) After the collected cow dung was air-dried, it was subjected to oxygen-limited pyrolysis at 380°C in a stainless steel muffle furnace for 5 hours. After natural cooling, the biochar was pulverized by a pulverizer and passed through a 10-mesh sieve to obtain the original cow dung biochar.

[0047] (2) Add the raw cow manure biochar to a 0.8 mol / L calcium nitrate solution at a solid-liquid ratio of 1:12 and stir with a shaker at 180 r / min for 22 h;

[0048] (3) The cow dung biochar calcium nitrate modified composite material was obtained by drying at 150°C for 5 hours and then performing oxygen-limited pyrolysis for 2 hours in a stainless steel muffle furnace.

[0049] Example 3

[0050] A method for preparing a cow dung biochar composite material for saline-alkali land improvement includes the following steps:

[0051] (1) After the collected cow dung was air-dried, it was subjected to oxygen-limited pyrolysis at 450°C in a stainless steel muffle furnace for 3 hours. After natural cooling, the biochar was pulverized by a pulverizer and passed through a 10-mesh sieve to obtain the original cow dung biochar.

[0052] (2) Add the raw cow manure biochar to a 0.6 mol / L calcium nitrate solution at a solid-liquid ratio of 1:10 and stir with a shaker at 180 r / min for 24 h.

[0053] (3) The cow dung biochar calcium nitrate modified composite material was obtained by drying at 320°C for 3 hours and oxygen-limited pyrolysis for 2 hours in a stainless steel muffle furnace.

[0054] Comparative Example 1

[0055] Compared with Example 1, the difference is that the oxygen-limited pyrolysis temperature in step (1) is 520°C and the pyrolysis time is 6h, while the rest of the process is the same as in Example 1.

[0056] Comparative Example 2

[0057] Compared with Example 1, the difference is that the oxygen-limited pyrolysis temperature in step (1) is 320°C and the pyrolysis time is 4h, while the rest of the process is the same as in Example 1.

[0058] Comparative Example 3

[0059] Compared with Example 1, the difference is that in step (2), the solid-liquid ratio of cow dung biochar to calcium nitrate solution is 1:8, while the rest of the process is the same as in Example 1.

[0060] Comparative Example 4

[0061] Compared with Example 1, the difference is that step (3) does not involve oxygen-limited pyrolysis during the drying process, while the rest of the process is consistent with Example 1.

[0062] Comparative Example 5

[0063] Compared with Example 1, the difference is that oxygen-limited pyrolysis is carried out throughout the drying process in step (3) at a temperature of 380°C, while the rest of the process is consistent with Example 1.

[0064] Comparative Example 6

[0065] Compared with Example 1, the difference is that only step (1) is performed to obtain raw cow manure biochar.

[0066] Test case

[0067] 1. A field addition experiment was conducted in the saline-alkali land of the National Grassland Ecosystem Field Observation Station in Guyuan County, Zhangjiakou City, Hebei Province. The materials prepared in Examples 1-3 and Comparative Examples 1-6 were added to the saline-alkali land at a rate of 5 t / ha. Samples were taken 7 days and 14 days after the addition of the materials, and the soil pH, total alkalinity, and alkalinity were measured. The results are shown in Table 1 and Table 2.

[0068] Table 1. Data from 7 days of soil cultivation

[0069]

[0070] Table 2 Data from 14 days of soil cultivation

[0071]

[0072]

[0073] Although the addition of biochar materials will bring certain saline and alkaline substances to the soil, according to the test results in Tables 1 and 2, the calcium nitrate modified cow dung biochar composite material prepared in this invention still has excellent efficacy compared with the blank control group and the comparative example. It can effectively improve the properties of saline-alkali soil and improve its salinity and alkalinity.

[0074] 2. To further investigate the effects of different application rates of cow dung biochar composite material on the improvement of saline-alkali land, based on the above experiment with an application rate of 5 t / ha, a cow dung biochar calcium nitrate modified composite material prepared in Example 1 was added to the above saline-alkali land at an application rate of 25 t / ha, serving as Experiment 1 and Experiment 2, respectively, with the treatment without the addition of cow dung biochar calcium nitrate modified composite material serving as a blank control. A soil cultivation experiment was conducted for 14 days, and samples were taken on the 7th and 14th days after the addition of cow dung biochar calcium nitrate modified composite material to measure soil pH, electrical conductivity, total alkalinity, alkalinity, and salinity. The results are shown in Table 3 (7 days) and Table 4 (14 days), respectively.

[0075] Table 3 Results of soil cultivation in Experiments 1-2 (7 days)

[0076]

[0077] Table 4 Results of soil cultivation in Experiments 1-2 (14 days)

[0078]

[0079] According to the test results in Tables 3 and 4, after 7 days of soil cultivation, the soil pH and total alkalinity in Experiments 1 and 2 were lower than those in the blank control, although the soil electrical conductivity, salinity, and soluble Na+ were lower. +The content and other indicators increased compared to the blank control, but decreased with increasing application of the calcium nitrate-modified cow dung biochar composite material. Furthermore, after 14 days of soil cultivation, the soil pH, electrical conductivity, total alkalinity, and salinity increased in the blank control group, indicating a worsening of salinization. In contrast, the soil treated with the calcium nitrate-modified cow dung biochar composite material prepared in this invention showed significant reductions in soil salinization indicators such as pH, electrical conductivity, total alkalinity, alkalinity, and salinity, with the reduction effect increasing with increasing application rate. Therefore, the calcium nitrate-modified cow dung biochar composite material prepared in this invention can effectively improve the properties of saline-alkali soils and alleviate soil salinization.

[0080] 3. After 14 days of soil cultivation, the forage grass was mixed and sown in the improved saline-alkali land at a ratio of 15 kg / ha of oats and 3 kg / ha of sheepgrass. After 50 days of natural growth, the average plant height and aboveground and belowground biomass of the forage grass in Experiment 1, Experiment 2, Comparative Examples 1-6 and the blank control saline-alkali land were measured. The results are shown in Table 5.

[0081] Table 5. Data from Experiments 1-2 on Pasture Growth

[0082] Plant height (cm) <![CDATA[Aboveground biomass (g m -2 )]]> <![CDATA[Underground biomass (g m -2 )]]> Blank control 18.58 448 32 Experiment 1 30.94 468 34 Experiment 2 39.63 582.8 48

[0083] According to the test results in Table 5, after the saline-alkali land was treated with the cow dung biochar composite material prepared by this invention, not only was the degree of salinization alleviated, but the growth of pasture grass was also effectively promoted.

[0084] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a cow dung biochar composite material for saline-alkali land improvement, characterized in that, Includes the following steps: (1) Air dry the cow dung, then decompose it at 380~450℃ under limited oxygen for 3~6h, cool it and then crush it to obtain the original cow dung biochar; (2) Mix the raw cow manure biochar with calcium nitrate solution at a mass-to-volume ratio of 1:10~15 and modify it for 22~30 hours under stirring. (3) After modification, the mixture is dried at 180~200℃ for 3~5h, and oxygen-limited pyrolysis is performed for 2h during drying. After cooling, it is pulverized to obtain the cow dung biochar composite material.

2. The preparation method according to claim 1, characterized in that, In step (1), the oxygen-limited pyrolysis temperature is 400~420℃ and the pyrolysis time is 3~6h.

3. The preparation method according to claim 1, characterized in that, The particle size of the raw cow dung biochar obtained after crushing in step (1) is 1~3mm.

4. The preparation method according to claim 1, characterized in that, In step (2), the concentration of calcium nitrate solution is 0.5~0.8 mol / L.

5. The preparation method according to claim 1, characterized in that, The modification reaction time in step (2) is 24 hours.

6. A cow dung biochar composite material for improving saline-alkali land, characterized in that, It is prepared by the method described in any one of claims 1 to 5.

7. A formulation for improving saline-alkali land, characterized in that, Includes the cow dung biochar composite material as described in claim 6.

8. The use of the cow dung biochar composite material of claim 6 or the formulation of claim 7 in the improvement of saline-alkali land.

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