A method for preparing an iron-based clay mineral composite and its use in the strengthening of humic acid formation and passivation in compost

Abstract

This invention discloses a method for preparing an iron-based clay mineral composite and its application in enhancing the formation and passivation of humic acid in composting. It belongs to the field of organic solid waste treatment and resource utilization technology. The invention prepares an iron-based clay mineral composite by loading ferrous sulfate onto clay minerals. This composite synergistically leverages the strong adsorption properties of clay minerals and the excellent catalytic performance of ferrous sulfate, enhancing the active sites on the clay mineral surface and thus improving the formation and retention capacity of humic acid in composting. Simultaneously, the iron oxides formed under aerobic composting conditions can strengthen its catalytic condensation performance of humic acid precursors. The ferrous sulfate and clay minerals used in this invention are low-cost, non-toxic, and harmless. Furthermore, the impregnation method used is simple to operate, fundamentally solving the problem of low adsorption and catalytic efficiency of clay minerals themselves. This invention improves both the quality and quantity of humic acid in organic solid waste composting by enhancing adsorption and catalysis, thereby increasing the agricultural and environmental value of the compost product.

Description

Technical Field

[0001] This invention belongs to the field of organic solid waste treatment and resource utilization technology, specifically relating to a method for preparing an iron-based clay mineral composite and its application in enhanced composting humic acid formation and passivation. Background Technology

[0002] With the acceleration of urbanization and the intensive development of agricultural production in my country, the output of organic solid waste such as livestock and poultry manure, agricultural straw, kitchen waste, and urban sludge has increased rapidly. The spread and leakage of toxic substances contained in these wastes have made the resource-based treatment of organic solid waste a significant challenge for environmental protection and economic development. Aerobic composting, a biological treatment technology aligned with the concept of a circular economy, can transform the complex organic components in organic solid waste into stable humus under the action of microorganisms, offering advantages such as low cost, ease of operation, and high resource utilization. As a key indicator for evaluating the maturity and agricultural value of compost products, humic acid has advantages such as improving soil water and fertilizer retention capacity, repairing damaged soil, and enhancing plant growth; its stable carbon structure plays a crucial role in fixing global carbon components. However, problems such as organic component loss due to microbial mineralization and low humic acid formation efficiency during aerobic composting limit the improvement of compost product quality and its subsequent application in soil. Therefore, developing aerobic composting-oriented humification and humic acid stabilization technologies is currently a key research direction for the resource-based treatment of organic solid waste.

[0003] To enhance the formation and retention of humic acid in compost, the application of exogenous substances is widely used due to its simplicity, cost-effectiveness, and good results. Among the many exogenous substances, iron-related conditioners and clay minerals exhibit excellent enhancing effects, but their individual application has significant limitations. Clay minerals are widely used in composting due to their large specific surface area and strong cation exchange capacity. They can adsorb organic components in the compost pile and catalyze the condensation of amino acids with sugars and phenols, thereby accelerating the humification process. However, the adsorption and catalytic abilities of clay minerals for organic components are limited, resulting in insufficient driving force for the polymerization and stabilization of humic acid components. Meanwhile, iron conditioners play an important role in redox and complexation reactions. Among them, iron oxides have excellent adsorption and catalytic properties, and can complex with carboxylic acids and polyphenolic organic components to enhance the efficiency of polymerization reactions. Furthermore, the cycling of ferrous and ferric iron can cause Fenton reactions in the compost pile to generate free radicals, driving the degradation of recalcitrant organic matter such as lignin into small molecule monomers and their conversion into humic acid. However, applying iron salt solution alone can easily cause rapid precipitation and deactivation, which increases the concentration of soluble salt ions in the pile, ultimately leading to problems such as unstable catalytic efficiency and insufficient adsorption of organic components. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method for preparing an iron-based clay mineral composite and its application in enhancing the formation and passivation of humic acid in composting.

[0005] This invention can effectively enhance the formation and retention capacity of humic acid in aerobic composting through a relatively simple application method.

[0006] A method for preparing an iron-based clay mineral composite is specifically carried out according to the following steps:

[0007] 1. Add clay minerals to deionized water and stir under nitrogen protection to obtain a suspension:

[0008] 2. Add ferrous sulfate heptahydrate to the suspension and stir until dissolved. Then add ascorbic acid and stir continuously under nitrogen protection. Ferrous ions fully penetrate into the montmorillonite interlayer and complete ion exchange and surface adsorption. Then let stand for aging, centrifuge, wash, dry, grind, and sieve to obtain iron-based clay mineral complex, which is then sealed and stored.

[0009] Application of an iron-based clay mineral composite in enhancing the formation and passivation of humic acid in compost.

[0010] The principle of this invention:

[0011] This invention prepares an iron-based clay mineral composite by loading ferrous sulfate onto clay minerals. This composite synergistically leverages the strong adsorption properties of clay minerals and the excellent catalytic performance of iron-based substances, enhancing the active sites on the clay mineral surface and thus improving the formation and retention capacity of humic acid in compost. Ferrous sulfate impregnation is a low-cost and easy-to-operate modification method that allows iron to penetrate the interlayer of clay minerals or form an iron oxide coating on the surface, ultimately resulting in more complex and stable humic acid components in the compost. Aerobic composting using the iron-based clay mineral composite prepared by this invention can enhance the decomposition of recalcitrant organic components by microorganisms and reduce the loss of carbon and nitrogen components in the compost pile due to carbon-nitrogen imbalance, thereby promoting the maturation of compost products.

[0012] This invention has significant theoretical and practical implications for enhancing the application value of compost products and contributing to carbon sequestration in agricultural systems.

[0013] Effects of the invention:

[0014] I. This invention provides a method for preparing iron-based clay mineral composites by modifying clay minerals with ferrous sulfate, thereby enhancing the adsorption and catalytic efficiency of clay minerals and applying them to different stages of aerobic composting to improve the formation and retention capacity of humic acid.

[0015] II. The complex formed by modifying clay minerals by ferrous ion impregnation can activate their active centers and increase their specific surface area, thereby enhancing their complexation ability with humic acid components during composting. At the same time, the iron oxides formed under aerobic composting conditions can enhance their catalytic performance in condensing humic acid precursors.

[0016] Third, the ferrous sulfate and clay minerals used in this invention are low in cost, non-toxic and harmless, and the impregnation method used is simple to operate, fundamentally solving the problem of low adsorption and catalytic efficiency of clay minerals themselves, and improving the quality and quantity of humic acid in organic solid waste compost from both the aspects of enhanced adsorption and catalysis.

[0017] IV. The iron-based clay mineral complex prepared by this invention has a larger specific surface area and more active iron sites, which can adsorb organic components such as humic acid and enhance their retention capacity; it can also provide a reaction interface, catalyze the polymerization of humic acid precursors, and improve the stability of humic acid; and the phased application of microbial activity and microenvironmental changes that match the composting process can achieve precise control of the humic acid formation process; using the method of this invention, various organic solid waste raw materials were subjected to aerobic composting for 60 days. Compared with the control group that did not apply iron-based clay mineral complex composting, the humic acid concentration of the iron-based clay mineral complex applied during the warming period of composting increased by 17.6%~33.7%, and the fluorescence intensity (Fmax value) characterizing the degree of humification increased by 3.7%~4.6%; the experiment shows that the iron-based clay mineral complex has a significant improvement on the formation and retention of humic acid in aerobic composting of organic solid waste.

[0018] V. The iron-based clay mineral composite prepared by this invention improves the humic acid content and structural stability of aerobic composting of organic solid waste. This invention can not only enhance the properties of clay minerals themselves, increase the specific surface area and adsorption center activity, but also catalyze the polymerization of sugars, amino acids and phenolic substances into humic acid, thereby enhancing the stability and carbon sequestration capacity of humic acid components and improving the agricultural and environmental value of compost products. Attached Figure Description

[0019] Figure 1 This is a composting temperature curve. Detailed Implementation

[0020] Specific Implementation Method 1: This implementation method is a preparation method for an iron-based clay mineral composite, specifically completed according to the following steps:

[0021] 1. Add clay minerals to deionized water and stir under nitrogen protection to obtain a suspension:

[0022] 2. Add ferrous sulfate heptahydrate to the suspension and stir until dissolved. Then add ascorbic acid and stir continuously under nitrogen protection. Ferrous ions fully penetrate into the montmorillonite interlayer and complete ion exchange and surface adsorption. Then let stand for aging, centrifuge, wash, dry, grind, and sieve to obtain iron-based clay mineral complex, which is then sealed and stored.

[0023] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the clay mineral mentioned in step one is sepiolite, attapulgite, montmorillonite, or calcite. The other steps are the same as in Specific Implementation Method One.

[0024] This embodiment does not impose any special restrictions on the source of the sepiolite, attapulgite, montmorillonite, and calcite; any source of sepiolite, attapulgite, montmorillonite, and calcite known in the art may be used.

[0025] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that: the mass ratio of clay minerals to deionized water in step one is 1g:40mL; the stirring in step one is performed using magnetic stirring at room temperature for 20-30 minutes at a speed of 400-500 rpm. Other steps are the same as in Specific Implementation Method One or Two.

[0026] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in the following ways: the mass ratio of ferrous sulfate heptahydrate in step two to the clay minerals in step one is 3:5; the initial stirring time in step two is 10-20 minutes, and the initial stirring speed is 400-600 rpm; the mass ratio of ascorbic acid in step two to the clay minerals in step one is 1:20. Other steps are the same as in Specific Implementation Methods One to Three.

[0027] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that: the continuous stirring time in step two is 6 to 8 hours; the settling and aging time in step two is 20 to 24 hours; the centrifugation speed in step two is 5000 r / min, and the centrifugation time is 5 to 10 minutes. Other steps are the same as in Specific Implementation Methods One to Four.

[0028] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in the following ways: the washing in step two uses deionized water until no sulfate ions are detectable in the washing solution; the drying temperature in step two is 45℃~60℃, and the drying time is 10h~12h; the particle size of the iron-based clay mineral composite in step two is 200nm~500nm. Other steps are the same as in Specific Implementation Methods One to Five.

[0029] Specific Implementation Method Seven: This implementation method is an application of an iron-based clay mineral composite in enhancing the formation and passivation of humic acid in composting.

[0030] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One through Seven in that: the application of an iron-based clay mineral composite in enhancing the formation and passivation of humic acid in composting is specifically accomplished through the following steps:

[0031] 1. Crush organic solid waste to obtain aerobic compost material; adjust the carbon-nitrogen ratio and moisture content of the aerobic compost material; add iron-based clay mineral complex to the aerobic compost material in one stage of composting and carry out aerobic composting; the iron-based clay mineral complex enhances the formation and passivation of humic acid in the compost.

[0032] One stage of composting described in step one is the heating period, high temperature period, or cooling period of composting;

[0033] 2. After composting, organic fertilizer is obtained. The other steps are the same as those in specific implementation methods one through seven.

[0034] This embodiment utilizes this raw material for composting, which not only enhances the decomposition of recalcitrant organic components by microorganisms, but also reduces the loss of carbon and nitrogen components in the compost pile due to carbon-nitrogen imbalance, thus promoting the maturation of compost products.

[0035] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that: the organic solid waste mentioned in step one is one or more of straw, kitchen waste, industrial organic waste, domestic waste, poultry and livestock manure, and municipal sludge; in step one, the organic solid waste is crushed to a length of 2cm to 3cm. Other steps are the same as in Specific Implementation Methods One to Eight.

[0036] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One to Nine in that: the carbon-nitrogen ratio in step one is 25-30; the water content in step one is 50%-60%; and the amount of iron-based clay mineral composite added in step one is 5% of the aerobic compost material. Other steps are the same as in Specific Implementation Methods One to Nine.

[0037] The following detailed description, with reference to embodiments, illustrates a method for enhancing the formation and retention of humic acid in composting using iron-based clay mineral composites, as provided by this invention. Obviously, the described embodiments are merely a portion of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0038] The beneficial effects of the present invention are verified using the following embodiments:

[0039] Example 1: A method for preparing an iron-based clay mineral composite, specifically carried out according to the following steps:

[0040] 1. Add 2.5g of clay mineral to 100mL of deionized water and stir for 30min under nitrogen protection to obtain a suspension:

[0041] The clay mineral mentioned in step one is montmorillonite;

[0042] 2. Add 1.5g of ferrous sulfate heptahydrate to the suspension and stir at 400r / min for 20min until the ferrous sulfate heptahydrate dissolves. Then add 0.075g of ascorbic acid to inhibit the oxidation of ferrous ions. Stir continuously for 8h under nitrogen protection at a stirring speed of 500r / min to allow ferrous ions to fully penetrate into the montmorillonite interlayer and complete ion exchange and surface adsorption. Let stand and age for 24h, centrifuge at 5000r / min for 10min, wash with deionized water until no sulfate ions are detected in the washing liquid, dry at 60℃ for 12h, grind, and pass through a 200-mesh sieve to obtain the iron-based clay mineral composite (ferrous sulfate modified montmorillonite), and store in a sealed container.

[0043] Application Example 1: The iron-based clay mineral composite prepared in Example 1 is applied in the enhanced formation and passivation of humic acid in composting, specifically by following these steps:

[0044] 1. Chicken manure (fresh samples collected from a chicken farm and dried) was crushed to 2cm. Then, the carbon-nitrogen ratio was adjusted to 25-30 using sawdust to obtain aerobic compost material. The moisture content of the aerobic compost material was adjusted to 60%-65% using tap water. During the heating period of composting, the iron-based clay mineral complex prepared in Example 1 was added to the aerobic compost material and aerobic composting was carried out. The iron-based clay mineral complex enhanced the formation and passivation of humic acid in the compost.

[0045] The amount of iron-based clay mineral composite added in step one is 5% of the aerobic compost material;

[0046] 2. After composting, organic fertilizer is obtained.

[0047] The humic acid components of organic fertilizers were extracted and their concentration and structure were characterized. The methods for extraction, concentration and structure determination of humic acid components are as follows:

[0048] Humic acid was extracted from the decomposed organic fertilizer using the following method: 3g of air-dried organic fertilizer was weighed into an Erlenmeyer flask, and a mixture of Na₄P₂O₇·10H₂O (0.1mol / L) and NaOH (0.1mol / L) was added at a solid-liquid ratio of 1:20 (W / V). After mixing, the mixture was shaken on a shaker at room temperature for 24 hours (180 r / min). The mixture was then centrifuged at 12000 r / min for 10 minutes, and the supernatant was filtered through a 0.45 μm filter membrane to obtain the humic acid solution. Three replicates were set up for each sample. The humic acid content was determined using a TOC analyzer, and the structure of the humic acid was characterized using fluorescence spectroscopy.

[0049] Comparison with Application Example 1: The difference between this example and Application Example 1 is that in step one, during the warming period of composting, unmodified montmorillonite (raw montmorillonite) is added to the aerobic composting material and aerobic composting is carried out. All other steps and parameters are the same as in Application Example 1.

[0050] Following the above experiments, using the unmodified montmorillonite (original montmorillonite) composting system applied during the heating period in Example 1 as a control group, a 60-day aerobic composting experiment was initiated, and the concentration and structure of humic acid in the resulting organic fertilizer were measured. The results showed that the final humic acid concentration in the experimental group was 71.9±1.5 g / kg, and the Fmax value of the stable humic acid component HAC3 was 28.4%, while in the control group it was 58.2±2.9 g / kg, and the Fmax value was 24.6%. Compared with the control group, the humic acid concentration and humification degree in the experimental group applying the iron-based clay mineral complex (ferrous sulfate-modified montmorillonite) prepared in Example 1 during the heating period were increased by 23.5% and 3.8%, respectively, compared to the control group that only applied montmorillonite. This indicates that the application of the iron-based clay mineral complex during the heating period can effectively improve the concentration and structural stability of humic acid in aerobic composting.

[0051] Example 2: The difference between this example and Example 1 is that the clay mineral mentioned in step one is calcite; and step two yields an iron-based clay mineral composite (ferrous sulfate-modified calcite). All other steps and parameters are the same as in Example 1.

[0052] Application Example 2: The iron-based clay mineral composite prepared in Example 2 is used in the enhanced formation and passivation of humic acid in composting, specifically by following these steps:

[0053] 1. Crush rice straw (from the residue after the previous year's rice harvest) to a length of 2-3 cm. Use chicken manure (2-3 cm long, fresh sample from a chicken farm, dried) to adjust the carbon-nitrogen ratio to 27-29 to obtain aerobic compost material. Adjust the moisture content of the aerobic compost material to 60%-65% using tap water. During the high-temperature period of composting, add the iron-based clay mineral complex prepared in Example 2 to the aerobic compost material and carry out aerobic composting. The iron-based clay mineral complex enhances the formation and passivation of humic acid in the compost.

[0054] The amount of iron-based clay mineral composite added in step one is 5% of the aerobic compost material;

[0055] 2. After composting, organic fertilizer is obtained.

[0056] Comparison with Application Example 2: The difference between this example and Application Example 2 is that in step one, unmodified calcite (raw calcite) is added to the aerobic compost material during the high-temperature period of composting, and aerobic composting is carried out. All other steps and parameters are the same as in Application Example 2.

[0057] Humic acid was extracted from organic fertilizer, and the total organic carbon content of the humic acid solution was determined using a TOC analyzer to obtain the humic acid carbon content. The structure of humic acid was characterized by fluorescence spectroscopy analysis. Samples were collected from three random locations in the compost for testing.

[0058] Following the above experiments, using the unmodified calcite composting system applied during the high-temperature period in Example 2 as a control group, a 60-day aerobic composting experiment was initiated, and the concentration and structure of humic acid in the final compost product were measured. The results showed that the final humic acid concentration in the experimental group was 68.3±3.5 g / kg, with an Fmax value of 19.7%, while the control group had a concentration of 51.6±2.9 g / kg and an Fmax value of 15.2%. Compared to the control group, the humic acid concentration and humification degree in the experimental group applying the iron-based clay mineral composite (ferrous sulfate-modified calcite) prepared in Example 2 during the high-temperature period were increased by 32.4% and 4.5%, respectively, compared to the control group that only applied calcite. This indicates that the application of the iron-based clay mineral composite during the high-temperature period can effectively improve the concentration and structural stability of humic acid in aerobic composting.

[0059] Example 3: The difference between this example and Example 1 is that the clay mineral mentioned in step one is sepiolite; and step two yields an iron-based clay mineral composite (ferrous sulfate-modified sepiolite). All other steps and parameters are the same as in Example 1.

[0060] Application Example 3: The iron-based clay mineral composite prepared in Example 3 is applied in the enhanced formation and passivation of humic acid in composting, specifically by following these steps:

[0061] 1. The kitchen waste (from the canteen of Changchun Normal University) was crushed to a length of 2-3 cm. Rice husks (from the farm) were used to adjust the carbon-nitrogen ratio of the kitchen waste to 29-30 to obtain aerobic compost material. The moisture content of the aerobic compost material was adjusted to 60%-65% using tap water. During the cooling period of composting, the iron-based clay mineral complex prepared in Example 3 was added to the aerobic compost material and aerobic composting was carried out. The iron-based clay mineral complex enhanced the formation and passivation of humic acid in the compost.

[0062] The amount of iron-based clay mineral composite added in step one is 5% of the aerobic compost material;

[0063] 2. After composting, organic fertilizer is obtained.

[0064] Comparison with Application Example 3: The difference between this example and Application Example 3 is that in step one, during the cooling period of composting, unmodified sepiolite (raw sepiolite) is added to the aerobic composting material and aerobic composting is carried out. All other steps and parameters are the same as in Application Example 3.

[0065] Humic acid was extracted from organic fertilizer, and the total organic carbon content of the humic acid solution was determined using a TOC analyzer to obtain the humic acid carbon content. The structure of humic acid was characterized by fluorescence spectroscopy analysis. Samples were collected from three random locations in the compost for testing.

[0066] Following the above experiments, using the unmodified sepiolite composting system applied during the cooling period in Example 3 as a control group, a 60-day aerobic composting experiment was initiated, and the concentration and structure of humic acid in the final compost product were measured. The results showed that the final humic acid concentration in the experimental group was 78.6±3.1 g / kg, with an Fmax value of 27.6%, while the control group had a concentration of 60.3±2.8 g / kg and an Fmax value of 23.7%. Compared to the control group, the humic acid concentration and humification degree in the experimental group applying the iron-based clay mineral composite (ferrous sulfate-modified sepiolite) prepared in Example 3 during the cooling period were increased by 30.3% and 3.9%, respectively, compared to the control group that only applied sepiolite. This indicates that the application of the iron-based clay mineral composite during the cooling period can effectively improve the concentration and structural stability of humic acid in aerobic composting.

[0067] Example 4: The difference between this example and Example 1 is that the clay mineral mentioned in step one is attapulgite; and step two yields an iron-based clay mineral composite (ferrous sulfate-modified attapulgite). All other steps and parameters are the same as in Example 1.

[0068] Application Example 4: The iron-based clay mineral composite prepared in Example 4 is used in the enhanced formation and passivation of humic acid in composting, specifically by following these steps:

[0069] 1. Chicken manure (fresh samples collected from a chicken farm) was crushed to a length of 2-3 cm. Rice straw (residues after the previous year's rice harvest) of 2-3 cm length was used to adjust the carbon-nitrogen ratio to 25-30 to obtain aerobic compost material. The moisture content of the aerobic compost material was adjusted to 65% using tap water. During the heating period of composting, the iron-based clay mineral complex prepared in Example 4 was added to the aerobic compost material and aerobic composting was carried out. The iron-based clay mineral complex enhanced the formation and passivation of humic acid in the compost.

[0070] The amount of iron-based clay mineral composite added in step one is 5% of the aerobic compost material;

[0071] 2. After composting, organic fertilizer is obtained.

[0072] Comparison with Application Example 4: The difference between this example and Application Example 4 is that in step one, during the warming period of composting, unmodified attapulgite (raw attapulgite) is added to the aerobic composting material and aerobic composting is carried out. All other steps and parameters are the same as in Application Example 4.

[0073] Humic acid was extracted from organic fertilizer, and the total organic carbon content of the humic acid solution was determined using a TOC analyzer to obtain the humic acid carbon content. The structure of humic acid was characterized by fluorescence spectroscopy analysis. Samples were collected from three random locations in the compost for testing.

[0074] Following the above experiments, using the unmodified attapulgite (original attapulgite) composting system applied during the heating period in Example 4 as a control group, a 60-day aerobic composting experiment was initiated, and the concentration and structure of humic acid in the final compost product were measured. The results showed that the final humic acid concentration in the experimental group was 68.4±2.0 g / kg, with an Fmax value of 27.6%, while the control group had a concentration of 53.8±1.2 g / kg and an Fmax value of 23.7%. Compared to the control group, the humic acid concentration and humification degree in the experimental group applying the iron-based clay mineral composite (ferrous sulfate-modified attapulgite) prepared in Example 4 during the heating period were increased by 27.1% and 3.9%, respectively, compared to the control group that only applied attapulgite. This indicates that the application of the iron-based clay mineral composite during the heating period can effectively improve the concentration and structural stability of humic acid in aerobic composting.

[0075] Comparative Application Example 5: The difference between this example and Application Example 1 is that in step one, during the high-temperature period of composting, the iron-based clay mineral composite prepared in Example 1 is added to the aerobic composting material and aerobic composting is carried out. All other steps and parameters are the same as in Application Example 1.

[0076] Humic acid was extracted from organic fertilizer, and the total organic carbon content of the humic acid solution was determined using a TOC analyzer to obtain the humic acid carbon content. The structure of humic acid was characterized by fluorescence spectroscopy analysis. Samples were collected from three random locations in the compost for testing.

[0077] Following the above experiments, an aerobic composting experiment was conducted for 60 days, using an unmodified montmorillonite composting system applied during the high-temperature period as the control group. The concentration and structure of humic acid in the final compost product were measured. The results showed that the final humic acid concentration in the experimental group was 55.6±2.5 g / kg, and the Fmax value of the humic acid stable component HAC3 was 27.2%, while the control group had a concentration of 65.4±3.4 g / kg and an Fmax value of 23.5%. Compared with the control group, the humic acid concentration and humification degree in the experimental group with ferrous sulfate-modified montmorillonite applied during the high-temperature period increased by 17.6% and 3.7%, respectively, compared with the control group with only montmorillonite applied. Combined with the relevant data in Application Example 1, this invention demonstrates that the application of iron-based clay mineral composites during the heating period can effectively improve the concentration and structural stability of humic acid in aerobic composting.

[0078] Comparative Application Example 6: The difference between this example and Application Example 2 is that in step one, during the cooling period of composting, the iron-based clay mineral composite prepared in Example 2 is added to the aerobic composting material and aerobic composting is carried out. All other steps and parameters are the same as in Application Example 2.

[0079] Humic acid was extracted from organic fertilizer, and the total organic carbon content of the humic acid solution was determined using a TOC analyzer to obtain the humic acid carbon content. The structure of humic acid was characterized by fluorescence spectroscopy analysis. Samples were collected from three random locations in the compost for testing.

[0080] Following the above experiments, an aerobic composting experiment was conducted for 60 days, using an unmodified calcite composting system applied during the cooling period as the control group. The concentration and structure of humic acid in the final compost product were measured. The results showed that the final humic acid concentration in the experimental group was 61.8±4.1 g / kg, with an Fmax value of 17.7%, while the control group had a concentration of 49.2±3.8 g / kg and an Fmax value of 13.5%. Compared with the control group, the humic acid concentration and humification degree in the experimental group with ferrous sulfate-modified calcite applied during the cooling period were increased by 25.6% and 4.2%, respectively, compared with the control group with only calcite applied. Combined with the relevant data in Application Example 2, this demonstrates that the application of the iron-based clay mineral composite during the high-temperature period effectively improves the concentration and structural stability of humic acid in aerobic composting compared to application during the cooling period.

[0081] Comparative Application Example 7: The difference between this example and Application Example 3 is that in step one, during the warming period of composting, the iron-based clay mineral composite prepared in Example 3 is added to the aerobic composting material and aerobic composting is carried out. All other steps and parameters are the same as in Application Example 3.

[0082] Humic acid was extracted from organic fertilizer, and the total organic carbon content of the humic acid solution was determined using a TOC analyzer to obtain the humic acid carbon content. The structure of humic acid was characterized by fluorescence spectroscopy analysis. Samples were collected from three random locations in the compost for testing.

[0083] Following the above experiments, an aerobic composting experiment was conducted for 60 days, using the unmodified sepiolite composting system applied during the warming period as the control group. The concentration and structure of humic acid in the final compost product were measured. The results showed that the final humic acid concentration in the experimental group was 83.8±4.2 g / kg, with an Fmax value of 30.2%, while the control group had a concentration of 62.7±3.6 g / kg and an Fmax value of 25.6%. Compared with the control group, the humic acid concentration and humification degree in the experimental group with ferrous sulfate-modified sepiolite applied during the high-temperature period were increased by 33.7% and 4.6%, respectively, compared with the control group with only sepiolite applied. Combined with the relevant data in Application Example 3, this indicates that adding ferrous sulfate-modified sepiolite during the warming period is more effective than adding it during the cooling period when comparing different addition times.

[0084] Comparative Application Example 8: The difference between this example and Application Example 4 is that in step one, during the high-temperature period of composting, the iron-based clay mineral composite prepared in Example 4 is added to the aerobic composting material and aerobic composting is carried out. All other steps and parameters are the same as in Application Example 4.

[0085] Humic acid was extracted from organic fertilizer, and the total organic carbon content of the humic acid solution was determined using a TOC analyzer to obtain the humic acid carbon content. The structure of humic acid was characterized by fluorescence spectroscopy analysis. Samples were collected from three random locations in the compost for testing.

[0086] Following the above experiments, an aerobic composting experiment was conducted for 60 days, using the unmodified attapulgite composting system applied during the high-temperature period as the control group. The concentration and structure of humic acid in the final compost product were measured. The results showed that the final humic acid concentration in the experimental group was 64.2±3.2 g / kg, with an Fmax value of 26.4%, while the control group had a concentration of 50.6±2.6 g / kg and an Fmax value of 22.6%. Compared with the control group, the humic acid concentration and humification degree in the experimental group with ferrous sulfate-modified attapulgite applied during the high-temperature period were increased by 26.9% and 3.8%, respectively, compared with the control group with only attapulgite applied. Combined with the relevant data in Example 4, this demonstrates that the application of iron-based clay mineral composites during the heating period, as involved in this invention, effectively improves the concentration and structural stability of humic acid in aerobic composting compared to application during the high-temperature period.

[0087] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing an iron-based clay mineral composite, characterized in that... The preparation method is specifically carried out according to the following steps:

1. Add clay minerals to deionized water and stir under nitrogen protection to obtain a suspension:

2. Add ferrous sulfate heptahydrate to the suspension and stir until dissolved. Then add ascorbic acid and stir continuously under nitrogen protection. Ferrous ions fully penetrate into the montmorillonite interlayer and complete ion exchange and surface adsorption. Then let stand for aging, centrifuge, wash, dry, grind, and sieve to obtain iron-based clay mineral complex, which is then sealed and stored.

2. The method for preparing an iron-based clay mineral composite according to claim 1, characterized in that... The clay minerals mentioned in step one are sepiolite, attapulgite, montmorillonite, or calcite.

3. The method for preparing an iron-based clay mineral composite according to claim 1, characterized in that... The mass ratio of clay minerals to deionized water in step one is 1g:40mL; the stirring in step one is magnetic stirring at room temperature for 20min~30min and at a speed of 400r / min~500r / min.

4. The method for preparing an iron-based clay mineral composite according to claim 1, characterized in that... The mass ratio of ferrous sulfate heptahydrate to the clay minerals in step one is 3:5; the initial stirring time in step two is 10 min to 20 min, and the initial stirring speed is 400 r / min to 600 r / min; the mass ratio of ascorbic acid to the clay minerals in step one is 1:

20.

5. The method for preparing an iron-based clay mineral composite according to claim 1, characterized in that... The continuous stirring time in step two is 6h~8h; the settling and aging time in step two is 20h~24h; the centrifugation speed in step two is 5000r / min, and the centrifugation time is 5min~10min.

6. The method for preparing an iron-based clay mineral composite according to claim 1, characterized in that... The washing described in step two involves using deionized water until no sulfate ions are detected in the washing solution; the drying temperature described in step two is 45℃~60℃, and the drying time is 10h~12h; the particle size of the iron-based clay mineral composite described in step two is 200nm~500nm.

7. The application of an iron-based clay mineral composite prepared by the preparation method according to claim 1, characterized in that... Application of an iron-based clay mineral composite in enhancing the formation and passivation of humic acid in compost.

8. The application of the iron-based clay mineral composite according to claim 7, characterized in that... The application of an iron-based clay mineral composite in enhancing the formation and passivation of humic acid in composting is specifically accomplished through the following steps:

1. Crush organic solid waste to obtain aerobic compost material; adjust the carbon-nitrogen ratio and moisture content of the aerobic compost material; add iron-based clay mineral complex to the aerobic compost material in one stage of composting and carry out aerobic composting; the iron-based clay mineral complex enhances the formation and passivation of humic acid in the compost. One stage of composting described in step one is the heating period, high temperature period, or cooling period of composting; 2. After composting, organic fertilizer is obtained.

9. The application of the iron-based clay mineral composite according to claim 8, characterized in that... The organic solid waste mentioned in step one is one or more of the following: straw, kitchen waste, industrial organic waste, domestic waste, poultry and livestock manure, and municipal sludge; in step one, the organic solid waste is crushed to a length of 2cm to 3cm.

10. The application of the iron-based clay mineral composite according to claim 8, characterized in that... The carbon-nitrogen ratio mentioned in step one is 25-30; the moisture content mentioned in step one is 50%-60%; and the amount of iron-based clay mineral composite added in step one is 5% of the aerobic compost material.

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