Cow dung biochar composite material for saline-alkali soil improvement, preparation method and application

Abstract

The invention discloses a cow dung biochar composite material for saline-alkali soil improvement, and a preparation method and application thereof, and belongs to the technical field of cow dung material treatment. The method comprises the following steps: (1) air-drying cow dung, then carrying out oxygen-limited cracking, cooling and crushing to obtain cow dung original biochar; (2) mixing the cow dung original biochar with a calcium nitrate solution, and stirring for modification; and (3) after modification is finished, drying, carrying out oxygen-limited cracking, cooling, and crushing to obtain the cow dung biochar composite material. The calcium nitrate modified cow dung biochar composite material which can be popularized on a large scale and is low in cost is produced through the raw materials wide in source and the method easy to operate, and no pollutant is generated in the preparation process. The prepared composite material can reduce the pH value of saline-alkali soil, improve the physical and chemical properties of soil, has higher adsorption capacity on Na < + > in the soil, reduces the salt content of the soil, increases the nitrate nitrogen content of the soil, promotes plant growth, and meanwhile achieves the effect of recycling livestock waste.

Description

Technical Field

[0001] The present invention belongs to the technical field of cow dung material treatment, and particularly relates to a cow dung biochar composite material for saline-alkali soil improvement, a preparation method and uses thereof. Background Art

[0002] Saline-alkali soil refers to a type of land where soluble salts in the soil accumulate to a relatively high concentration, and it is the general term for different types of saline soils, salt soils, and alkali soils.

[0003] The application of livestock and poultry manure as an exogenous organic material has a good improvement effect on saline-alkali soil. The research by Ji et al. shows that organic fertilizer is beneficial to the restoration of soil organic matter and the increase of soil fertility, and can effectively improve the physical and chemical properties of the soil, promote the absorption and utilization of nutrients by plants, and promote the degree of soil humification. Quite a number of studies have found that cow dung can effectively increase the ratios of easily oxidizable carbon, light fraction organic carbon, and soluble organic carbon to organic carbon in soda saline-alkali soil; applying cow dung can increase the content and storage of surface organic carbon in alkaline soil, and improve the content of soil active organic carbon components such as EOC, POC, and MBC. The compound application of different modifiers by using livestock and poultry manure to enhance the activity and capacity of the organic carbon pool in soda-alkalized soil is also one of the current trends in improving saline-alkali soil. However, after untreated livestock and poultry manure is applied to saline-alkali soil, its high-concentration soluble salts (especially Na + , Cl - etc.) produce a superimposed effect with the inherent salts in the soil, resulting in a 15-30% increase in the sodium adsorption ratio (SAR) of the soil, significantly exacerbating soil compaction and deterioration of permeability. More seriously, the heavy metals remaining in the manure (such as the average contents of Cu and Zn reaching 150-450 mg / kg) form stable complexes in the high-pH environment of saline-alkali soil, causing a 2-3-fold increase in the biological availability of heavy metals and threatening food safety through crop enrichment. At the same time, the environmental problems caused by direct field return are becoming increasingly prominent: during the open storage process, the ammonia volatilization loss rate of livestock and poultry manure is as high as 30-50%, and the NH3 and CH4 released account for 26% and 14% of the agricultural source emissions respectively; the nitrogen and phosphorus loss caused by rainy season runoff can reach 45 kg N / ha and 8 kg P / ha, becoming the main inducement for water eutrophication. These negative effects show a significant amplification phenomenon in the ecologically fragile saline-alkali soil area.

[0004] Biochar is a stable porous solid mainly composed of carbon (accounting for about 23.6% - 88.0%) and ash, which is formed by pyrolyzing biomass at high temperature (≤700°C) under anaerobic or low-oxygen conditions. Compared with the direct return of livestock and poultry manure to the field, biochar has the following advantages: salt regulation, the stable mineral elements in biochar can reduce the soil exchangeable sodium percentage (ESP) by 40 - 60%, and the pore structure promotes the leaching of salt ions; heavy metal passivation, the abundant oxygen-containing functional groups (-COOH, -OH) on the surface increase the complexation capacity of heavy metals by 5 - 8 times; environmentally friendly, more than 90% of carbon elements are fixed during the carbonization process, reducing the greenhouse gas emission potential by 70 - 85%; soil improvement, the addition of biochar increases the aggregate stability index of saline-alkali soil by 35 - 50% and the water-holding capacity by 20 - 30%. By reducing soil bulk density and promoting aggregate formation, the application of biochar can increase crop yields, improve soil quality and reduce salinity, while increasing soil organic carbon content and improving the soil's water storage and fertilizer retention capacity.

[0005] Some studies have shown that adding different amounts of biochar can increase the cation exchange capacity, organic matter and nutrient content in the 0 - 40 cm soil layer, aboveground and underground parts during the seedling and harvest periods, effectively promoting root growth and development, root area and volume, and having a significant impact on plant height, stem diameter, leaf area and yield per plant. There are also studies indicating that applying 2.0% and 2.5% of biochar can improve the physical, chemical and biological properties of saline-alkali soil and significantly affect the soil bacterial structure and diversity, thus affecting the soil N and P cycles, improving soil physical and chemical properties, and promoting crop growth by alleviating salt stress. However, traditional biochar has a low surface functional group density (<1.2 mmol / g) and a single pore structure (the proportion of micropores >70%), resulting in insufficient ion exchange capacity for Na + in saline-alkali soil (0.3 - 0.8 cmol / kg), and low salt ion interception efficiency due to the mismatch between pore size and hydrated ion size. Modification can improve the improvement effect of biochar: for example, HNO3 oxidation increases the carboxyl density to 2.5 - 4.8 mmol / g, and the Na + exchange capacity is increased by 4 - 6 times (up 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 mesopores increases to 55%), reducing the migration resistance of salt ions (Na + , Cl - ) by 40 - 60%, and combining with rain leaching to increase the desalination efficiency by 2 - 3 times; Fe-Mn oxide loading modification regulates the surface charge of the material (pH drops from 6.8 to 3.2), and can adsorb and fix Cl - , NO3 -The anions can be removed and the interception rate can be increased to 85-92%. The acid-base modification, oxidant modification and metal salt modification of biochar will affect the properties of biochar, thus affecting the effect of biochar in improving saline-alkali land.

[0006] Currently, only 2-3% of cow dung resources are effectively utilized, and the remaining 97% of untreated manure is accumulated for a long time or discharged illegally, forming severe environmental stress. At present, there are significant shortcomings in the research and industrial application of cow dung resource technology.

[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 merged into a wastewater collection pool and then pumped into an acid adjustment pool to adjust the pH value to 5.0-6.0. After that, a methane inhibitor is added and mixed evenly and then pumped into a wastewater storage pool for storage. After hydrolysis and acidification, solid residue and hydrolysis acidification liquid are generated, and the solid residue is made into biochar. When the pH value of the wastewater in the wastewater storage pool is higher than 6.5, hydrolysis acidification liquid and biochar are added to the pool, mixed and stored continuously, and the stored wastewater is diluted and returned to the field for application.

[0008] In the Chinese utility model patent application "An environmentally friendly treatment system for manure water from pig and cattle farms" (application number: CN202120575135.6), the harmful elements in the manure are dissolved in the stirring tank by the manure of pig and cattle farms, and then separated by sedimentation; the solid manure undergoes aerobic and anaerobic reactions to reproduce the microorganisms in the manure, and the harmful components are converted into trace elements that are beneficial to plant growth; after drying, they are stored in the fertilizer base material warehouse. The separated liquid is transported to the sedimentation tank for sedimentation, and the pigments and colloids in the manure are added through the three-stage mixer. The manure pollutants such as pigments and colloids in the manure are discharged through the bottom valve; after the manure water is settled in the second level, the clean water discharged from the overflow is transported to the clean water tank for storage, and then repeatedly recycled.

[0009] In the Chinese invention patent application "An iron-modified cow dung biochar material and its preparation method and application" (application number: CN202411709133.6), the cow dung solid waste biomass raw material is placed in a K2FeO4 solution, immersed in a water bath, heated, and then dried to obtain a K2FeO4 composite biomass material, and then carbonized at high temperature in a tubular furnace to obtain a K2FeO4 modified cow dung biochar material (FCBC). The K2FeO4 modified cow dung biochar material (FCBC) of the present invention has better Cd removal than the unmodified cow dung biochar (CBC). 2 + Elimination of treatment capacity, at the same time, compared with traditional modified or unmodified plant-derived biochar, it also has incomparable 2+ adsorption effect.

[0010] In the Chinese invention patent application "A Preparation Method and Application of High-quality Sludge Biochar" (Application No.: CN202311350100.2), sludge and cow dung are chemically activated. After sedimentation separation, supernatant A and precipitate B are obtained. After precipitate B is separated by low-speed centrifugation, supernatant C and precipitate D are obtained. Precipitate D is dried to obtain pyrolysis precursor E. The precursor E is pyrolyzed under a nitrogen atmosphere. The pyrolyzed biochar is washed with an acid solution, and some useful substances are recovered. After pickling, the biochar and the pickling solution are separated. The biochar is washed with clean water. The pickled biochar is dried and screened, and can generate superoxide anion radicals in the way of adsorption, conversion and transfer.

[0011] The above patent has problems such as cumbersome engineering and high cost in the utilization of cow dung resources. Moreover, the existing preparation of cow dung biochar and its modified composite materials is mainly used for adsorbing heavy metals and repairing polluted soil, and there is a gap in the treatment of saline-alkali land with cow dung biochar modified composite materials and large-scale popularization and utilization. Summary of the Invention

[0012] Aiming at the above deficiencies in the prior art, the present invention provides a cow dung biochar composite material, a preparation method and a use for saline-alkali land improvement. The present invention uses widely sourced raw materials and an easy-to-operate preparation method to produce a calcium nitrate modified cow dung biochar composite material that can be widely promoted on a large scale and has a low cost, and no pollutants are generated during the preparation process. The prepared modified biochar can reduce the pH of saline-alkali land, improve the physical and chemical properties of the soil, has a stronger adsorption capacity for Na + in the soil, reduce the soil salt content, increase the soil nitrate nitrogen content, promote plant growth, and at the same time achieve the effect of recycling livestock waste.

[0013] To achieve the above object, the technical solution adopted by the present invention to solve its technical problems is:

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

[0015] (1) Air-dry the cow dung, then carry out oxygen-limited pyrolysis at 380-450 °C for 3-6 h, cool and crush to obtain the original cow dung biochar;

[0016] (2) Mix the original cow dung biochar with a calcium nitrate solution and modify it under stirring conditions for 22-30 h;

[0017] (3) After the modification is completed, dry and carry out oxygen-limited pyrolysis at 150-320 °C for 3-5 h, cool and crush to prepare the cow dung biochar composite material.

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

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

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

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

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

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

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

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

[0026] Further, in step (3), the temperature is 180-200 °C, oxygen-limited pyrolysis is carried out while drying, and the oxygen-limited pyrolysis time is less than the drying time.

[0027] Further, in step (3), the temperature is 200 °C.

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

[0029] Another object of the present invention is to provide a preparation for saline-alkali land improvement, which comprises the above cow dung biochar composite material.

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

[0031] Advantages of the present invention:

[0032] The whole preparation process has a short time, quick effect on improving saline-alkali land, is easy to promote, and has no environmental pollution.

[0033] The preparation steps are simple and easy to operate, and the raw materials are widely sourced. At the same time, the cow dung from free-range fencing grazing is effectively utilized, increasing the recycling of livestock and poultry manure.

[0034] The calcium chloride-loaded modified biochar composite material simultaneously loads Ca 2+ and NO 3-, while effectively alleviating the process of soil salinization, it can also increase the content of nitrate nitrogen in the soil and improve the soil nutrient status.

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

[0036] The present invention has improved the salinized soil, while alleviating the problem of grassland livestock manure pollution, reducing the costs of saline-alkali land improvement and cow dung treatment, and can achieve large-scale production and adapt to the treatment of large areas of saline-alkali land. Brief Description of the Drawings

[0037] Figure 1 It is the process flow chart of the present invention. Detailed Embodiments

[0038] The following describes the detailed embodiments of the present invention to facilitate those skilled in the art of the present technology to understand the present invention. However, it should be clear that the present invention is not limited to the scope of the detailed embodiments. For those of ordinary skill in the art of the present technology, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions and creations using the concept of the present invention are within the scope of protection.

[0039] Example 1

[0040] A preparation method of a cow dung biochar composite material for saline-alkali land improvement, which comprises the following steps:

[0041] (1) After the collected cow dung is air-dried, it is pyrolyzed under limited oxygen at 400 °C in a stainless steel muffle furnace for 4 h. After natural cooling, the biochar is pulverized with a pulverizer and passed through a 10-mesh sieve to obtain the original cow dung biochar;

[0042] (2) The original cow dung biochar is added to a 0.5 mol / L calcium nitrate solution according to a solid-liquid ratio of 1:15, and stirred with a shaker at 180 r / min for 24 h;

[0043] (3) It is dried at 200 °C in a stainless steel muffle furnace for 4 h and pyrolyzed under limited oxygen for 2 h to obtain a calcium nitrate-modified composite material of cow dung biochar.

[0044] Example 2

[0045] A preparation method of a cow dung biochar composite material for saline-alkali land improvement, which comprises the following steps:

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

[0047] (2) Add the original cow dung 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) Dry at 150 °C in a stainless-steel muffle furnace for 5 h and pyrolyze under limited oxygen for 2 h to obtain a cow dung biochar calcium nitrate modified composite material.

[0049] Example 3

[0050] A preparation method of a cow dung biochar composite material for saline-alkali soil improvement, which comprises the following steps:

[0051] (1) After the collected cow dung is air-dried, pyrolyze it under limited oxygen at 450 °C in a stainless-steel muffle furnace for 3 h. After natural cooling, crush the biochar with a pulverizer and pass through a 10-mesh sieve to obtain the original cow dung biochar;

[0052] (2) Add the original cow dung 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) Dry at 320 °C in a stainless-steel muffle furnace for 3 h and pyrolyze under limited oxygen for 2 h to obtain a cow dung biochar calcium nitrate modified composite material.

[0054] Comparative Example 1

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

[0056] Comparative Example 2

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

[0058] Comparative Example 3

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

[0060] Comparative Example 4

[0061] Compared with Example 1, the difference lies in that no limited oxygen pyrolysis is carried out during the drying process in step (3), and the rest of the process is the same as that of Example 1.

[0062] Comparative Example 5

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

[0064] Comparative Example 6

[0065] Compared with Example 1, the difference lies in that only step (1) is carried out to obtain the original cow dung biochar.

[0066] Test Example

[0067] 1. A field addition experiment was carried out on saline-alkali land at 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 5 t / ha. Sampling was carried out 7 days and 14 days after adding the materials to measure the soil pH, total alkalinity, and alkalization degree. The results are shown in Tables 1 and 2.

[0068] Table 1 Data for 7 days of soil cultivation

[0069]

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

[0071]

[0072]

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

[0074] 2. To further explore the effect of different application amounts of cow dung biochar composite materials on the improvement of saline-alkali land, on the basis of the above experiment with an application amount of 5 t / ha, the calcium nitrate-modified cow dung biochar composite material prepared in Example 1 was added to the above saline-alkali land at an application amount of 25 t / ha, which were used as Experiment 1 and Experiment 2 respectively, and the treatment without adding the calcium nitrate-modified cow dung biochar composite material was used as the blank control. A soil cultivation experiment was carried out for 14 days, and sampling was carried out on the 7th day and the 14th day after adding the calcium nitrate-modified cow dung biochar composite material to measure data such as soil pH, conductivity, total alkalinity, alkalization degree, and salt content. The results are shown in Table 3 (7 days) and Table 4 (14 days) respectively.

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

[0076]

[0077] Table 4 Results of Experiment 1-2 in Soil Culture (14 days)

[0078]

[0079] According to the test results in Table 3 and Table 4, it can be seen that after 7 days of soil culture, the soil pH and total alkalinity of Experiment 1 and Experiment 2 are both lower than those of the blank control. Although indicators such as soil conductivity, salt content, and soluble Na + content increase compared with the blank control, they decrease with the increase in the application rate of the calcium nitrate-modified cow dung biochar composite. And after 14 days of soil culture, the soil pH, conductivity, total alkalinity, and salt content of the blank control group increase, and the degree of salinization becomes more serious. However, after being treated with the prepared calcium nitrate-modified cow dung biochar composite of the present invention, soil salinization indicators such as soil pH, conductivity, total alkalinity, alkalinity, and salt content are significantly reduced, and the reduction effect increases with the increase in the dosage. It can be seen that the calcium nitrate-modified cow dung biochar composite prepared by the present invention can effectively improve the properties of saline-alkali soil and improve the salinization status of the soil.

[0080] 3. After 14 days of soil culture, oats at 15 kg / ha and Chinese wildrye at 3 kg / ha were sown in the improved saline-alkali land in mixture, and after growing naturally for 50 days, the average plant height and aboveground and underground biomass of the forage grasses in Experiment 1, Experiment 2, Comparative Examples 1-6, and the blank control saline-alkali land were measured, and the results are shown in Table 5.

[0081] Table 5 Experimental Data of Forage Grass Growth in Experiment 1-2

[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, it can be seen that after the saline-alkali land is treated with the cow dung biochar composite prepared by the present invention, not only the degree of salinization is alleviated, but also the growth of forage grass can be 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 them. Although the present invention has been described in detail with reference to the examples, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered by the scope of the claims of the present invention.

Claims

1. A preparation method of a cow dung biochar composite material for saline-alkali land improvement, characterized in that, It includes the following steps: (1) Air-dry the cow dung, then carry out oxygen-limited pyrolysis at 380-450 °C for 3-6 h, cool and crush it to obtain the original cow dung biochar; (2) Mix the original cow dung biochar with a calcium nitrate solution and modify it under stirring conditions for 22-30 h; (3) After the modification is completed, dry it at 150-320 °C and carry out oxygen-limited pyrolysis for 3-5 h, cool and crush it to prepare 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 °C and the pyrolysis time is 3-6 h.

3. The preparation method according to claim 1, wherein, In step (1), the particle size of the original cow dung biochar obtained after crushing is 1-3 mm.

4. The preparation method according to claim 1, wherein In step (2), the mass-volume ratio of the original cow dung biochar to the calcium nitrate solution is 1:10-15.

5. The preparation method according to claim 4, wherein In step (2), the concentration of the calcium nitrate solution is 0.5-0.8 mol / L.

6. The preparation method according to claim 1, characterized in that, In step (2), the modification reaction time is 24 h.

7. The preparation method according to claim 1, wherein In step (3), the temperature is 180-200 °C, oxygen-limited pyrolysis is carried out while drying, and the oxygen-limited pyrolysis time is less than the drying time.

8. A cow dung biochar composite material for saline-alkali land improvement, characterized in that, Prepared by the method according to any one of claims 1-7.

9. A preparation for improving saline-alkali land, characterized in that, It includes the cow dung biochar composite material according to claim 8.

10. Use of the cow dung biochar composite material according to claim 8 or the preparation according to claim 9 in saline-alkali land improvement.

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