Agricultural waste-based recyclable ore-based carbon sphere preparation method and application thereof

Abstract

The application belongs to the field of adsorbing materials, and relates to a preparation method and application of recyclable mineral-based carbon balls based on agricultural waste, and comprises the following steps: preparation of magnesium-modified peanut shells: magnesium salt solution is used to modify and load broken peanut shells, and then KOH solution is added for treatment to obtain magnesium-modified peanut shells; preparation of recyclable mineral-based carbon balls: magnesium-modified peanut shells, starch, potassium bicarbonate, and attapulgite, bauxite and water are mixed to granulate and form balls, and the balls are preheated at 150 DEG C to 200 DEG C for 1 h to 2.5 h to form pores; after preheating, the balls are calcined at 500 DEG C to 700 DEG C for 0.5 h to 1.5 h, and then cooled to form recyclable mineral-based carbon balls. The mineral-based carbon balls are used for intercepting or adsorbing nitrogen and phosphorus in farmland runoff during the fertilization period and / or the heavy rain period; when the mineral-based carbon balls are saturated with nitrogen and phosphorus, the mineral-based carbon balls can be recycled for aerobic composting to increase soil fertility.

Description

Technical Field

[0001] This invention belongs to the field of adsorption materials and relates to a method for preparing reusable mineral-based carbon spheres based on agricultural waste and its application. Background Technology

[0002] Nitrogen and phosphorus are the most important limiting factors for plant growth. Point-source and non-point-source pollution from agricultural fertilization, industrial production, livestock and poultry farming, and residential life generates large amounts of nitrogen- and phosphorus-containing wastewater. Some of this wastewater is discharged directly or indirectly into rivers, lakes, reservoirs, and seawater without treatment. Nitrogen and phosphorus are important growth limiting factors for algae in rivers and lakes, and are also significant contributors to eutrophication, which can lead to ecological disasters such as algal blooms and cyanobacterial outbreaks, a typical example being the 2007 Taihu Lake cyanobacterial bloom. Therefore, my country's "Surface Water Environmental Quality Standards" sets the water quality standards for ammonia nitrogen, total nitrogen, and total phosphorus at 2.0 mg / L, 2.0 mg / L, and 0.4 mg / L (Class V water), respectively, to control the input of nitrogen and phosphorus nutrients from surface water into lakes and reservoirs. Therefore, controlling nitrogen and phosphorus in water bodies is of significant practical and strategic importance for improving the water environment, controlling eutrophication, and maintaining the health of aquatic ecosystems.

[0003] Currently, the main intercepting media for pollutants in water bodies are zeolite, aerated concrete, and volcanic rock. These materials primarily rely on their abundant pore structure and adsorption sites to achieve physical or chemical adsorption of nitrogen and phosphorus. However, the interception effect of these media on phosphorus is relatively limited, mainly because phosphorus exhibits the same negative charge as the media and the pore structure is relatively small. Therefore, it is necessary to develop a novel intercepting media for nitrogen and phosphorus pollution. In practical interception processes, the cost of the media is also a crucial factor. High prices are another significant limiting factor hindering the large-scale application of intercepting media. Therefore, pursuing a low-cost strategy for intercepting media is of great importance for their mass production and widespread application.

[0004] In addition, how to deal with saturated fillers remains a thorny issue. Simple dumping will occupy a lot of land, and the threat that its leachate or degradation products may pose to the soil cannot be ignored. Therefore, developing recyclable fillers is of great significance for resource recycling. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing reusable mineral-based carbon spheres based on agricultural waste and its application.

[0006] A first aspect of the present invention is to provide a method for preparing reusable mineral-based carbon spheres based on agricultural waste, comprising the following steps:

[0007] Preparation of magnesium-modified peanut shells: Crushed peanut shells were modified by spraying with magnesium salt solution, and then further modified by spraying with KOH solution to obtain magnesium-modified peanut shells;

[0008] Preparation of reusable mineral-based carbon spheres: Magnesium-modified peanut shells, starch, potassium bicarbonate, attapulgite, bauxite, and water are mixed in proportion and granulated into spheres. After sphere formation, the mixture is preheated at 150℃-200℃ for 1-2.5 hours (to form pores). After preheating, the mixture is calcined at 500℃-700℃ for 0.5-1.5 hours and then cooled to form reusable mineral-based carbon spheres.

[0009] The mass ratio of magnesium-modified peanut shells, starch, potassium bicarbonate, attapulgite, bauxite, and water is 35:(1-3):(1-3):(35-45):(4-6):(15-25);

[0010] The total molar ratio of magnesium ions in the magnesium salt solution to hydroxide ions in the KOH solution is 1:(2.3-2.7).

[0011] In a preferred embodiment, during the preparation of magnesium-modified peanut shells, the crushed peanut shells are sieved, and the peanut shells are sprayed with a 0.2-1.5 mol / L magnesium salt solution to uniformly wet the surface of the peanut shells. After standing for 18-28 hours (preferably 24 hours), the peanut shells are uniformly sprayed with a 1-2 mol / L KOH solution and then stirred and mixed.

[0012] Furthermore, the total molar ratio of magnesium ions in the magnesium salt solution to hydroxide ions in the KOH solution is 1:2.5; the magnesium salt is MgCl2.

[0013] In a preferred embodiment, the peanut shell is swollen within its pores through magnesium modification and pyrolysis to form nanoscale magnesium oxide (MgO).

[0014] Preferably, after pelleting, the pellets are preheated using the recovered heat from carbonization.

[0015] In a preferred embodiment, the reusable mineral-based carbon spheres have a specific surface area >150 m². 2 / g, fixed carbon >30%, iodine value >600mg / g, compressive strength 5-10MPa, methylene blue value >100mg / g; mineral-based carbon spheres have a particle size of 2-10mm.

[0016] The more specific preparation steps are as follows:

[0017] Preparation of Mg-modified peanut shells: Crushed peanut shells are passed through a 60-mesh sieve. A 0.5 mol / L MgCl2 solution is sprayed onto the peanut shells, and the mixture is stirred simultaneously until the surface of the peanut shells is evenly moistened. Generally, 100 kg of peanut shells can be spread out, sprayed at a rate of 10 L / h for approximately 10 minutes. After prolonged standing (preferably overnight), a 1.25 mol / L KOH solution (the concentrations of MgCl2 and KOH can be adjusted within a certain range, but a molar ratio of 1:2.5 must be maintained) is sprayed evenly following the same steps as for MgCl2. The spraying speed and time are the same as for MgCl2. The two reagents are sprayed alternately twice. After spraying, the mixture is slowly stirred for 1-2 hours.

[0018] Preparation of reusable mineral-based carbon spheres: Raw materials include magnesium-modified peanut shells, starch, potassium bicarbonate, attapulgite, and bauxite. The raw material ratio (by weight) for preparing the mineral-based carbon spheres is 35 parts magnesium-modified peanut shells, 2 parts starch, 2 parts potassium bicarbonate, 40 parts attapulgite (as a binder) + 5 parts bauxite (as a filler skeleton). After all raw materials are thoroughly mixed, 20 parts water are added, and the mixture is granulated into spheres using a disc granulation process (sphere diameter 0.2-1 cm, sphere formation time approximately 30 minutes). After sphere formation, the recovered heat from carbonization is used for preheating (to achieve pre-reaction between raw materials) at 150℃-200℃ for 2 hours. Then, the spheres are fired in a carbonization kiln at 500℃-700℃ for 1 hour. After natural cooling, the desired mineral-based carbon spheres are formed. Their relevant parameters (such as elemental composition, porosity, and strength) are as follows: specific surface area > 150 m². 2 / g, fixed carbon >30%, iodine value >600mg / g, compressive strength 5-10MPa, methylene blue value >100mg / g.

[0019] Furthermore, starch absorbs water and expands, enlarging the original pore structure of peanut shells. During preheating, potassium bicarbonate decomposes and dehydrates to form a pore structure. During calcination, starch pyrolyzes to form a pore structure, and bauxite decomposes, dehydrates, and recrystallizes to form a hardened skeleton. During the pyrolysis of peanut shell biochar, the MgO structure formed by the thermal dehydration of Mg(OH)2 is loaded into the porous structure of biochar.

[0020] In a second aspect, the present invention discloses reusable mineral-based carbon spheres prepared by the aforementioned preparation method.

[0021] A third aspect of the invention provides an interception dam filled with the aforementioned reusable mineral-based carbon spheres.

[0022] Preferably, the interception dam is used to intercept or adsorb nitrogen and phosphorus in farmland runoff during fertilization and / or rainstorm periods; after the reusable mineral-based carbon balls have completed saturated adsorption of nitrogen and phosphorus, they can be reused for aerobic composting to increase soil fertility.

[0023] The fourth aspect of the present invention discloses the aforementioned preparation method or the use of the aforementioned reusable mineral-based carbon balls in intercepting or adsorbing nitrogen and phosphorus in farmland runoff.

[0024] The fifth aspect of this invention discloses a method for treating saturated mineral-based carbon balls for aerobic composting. The method involves adding 5-10% carbon ball powder (the mass ratio of the saturated mineral-based carbon ball powder to the initial compost material composed of wheat straw and chicken manure) at a mass ratio of 1:1.5. The initial wet weight of the compost material is 8.0 kg, and the mixture is uniformly mixed with wheat straw at a mass ratio of 1:1.5. The moisture content is adjusted to approximately 60.0%. The composting process begins with the mixing of raw materials and involves turning the compost pile four times throughout the process. Turning is performed on days 11, 16, 24, and 33, and composting is completed on day 36. During turning, the compost in the incubator is poured out and stirred evenly in a mixer. An appropriate amount of water is added during stirring to maintain the moisture content of the compost at 55.0%-60.0%. The final product is the finished compost.

[0025] The significant advantages of this invention compared to existing technologies are:

[0026] The production process of the mineral-based carbon balls of the present invention is simple and convenient. The reagents required, such as MgCl2 and KOH, are inexpensive. KOH and MgCl2 are preferred as spraying reagents. KOH is chosen over alkaline reagents such as NaOH mainly because K is a major essential element for crops and can promote crop growth. MgCl2 is chosen over MgNO3 mainly because of its significant price advantage. In addition, residual metal chlorides are more easily decomposed than oxides and sulfides.

[0027] More importantly, the spraying and wetting process can effectively save chemical reagents, reduce reagent waste and environmental problems and preparation costs caused by solution impregnation or solution coprecipitation methods.

[0028] A spraying ratio of 1:2.5 can reduce Mg content. 2+ Theoretically, the concentration ratio of MgCl2 and KOH in the reaction should be 1:2 to achieve a complete reaction with OH-. However, because the surface co-precipitation reaction is achieved through alternating spraying (first spraying MgCl2, then spraying KOH, which is beneficial to the formation of MgO), Mg is present. 2+In cases where the reaction is incomplete, sufficient OH- is provided to ensure the complete co-precipitation reaction. Through optimized experiments, the applicant of this invention discovered that a molar ratio of 1:2.5 (i.e., sufficient KOH) can promote the complete reaction, thereby promoting the formation of cross-linked Mg(OH)2 products inside the peanut shell. Furthermore, the modification process using MgCl2 and KOH can increase the number of adsorption sites on the surface of the carbon spheres, improving the retention capacity for pollutants.

[0029] The metal loading material, agricultural waste raw materials, and their addition amount for this product were determined through a large number of experiments. After analyzing different metal loading materials (Mg, Fe, Ca, La), as well as agricultural waste such as wheat straw, rice straw, peanut shells, corn cobs, iris, poplar sawdust, and coffee grounds, cross-validation analysis showed that peanut shells loaded with Mg can achieve the largest nitrogen and phosphorus adsorption capacity. Peanut shells buried underground are characterized by their loose and breathable structure and abundant pores, possessing an interconnected pore structure not found in other biological wastes. Through Mg modification, widely distributed Mg oxide components can be formed within the pores during pyrolysis. These Mg oxide components formed within the pores have also been shown to form nanoscale MgO structures through swelling, thereby expanding the original pores of the peanut shells (i.e., MgO and water vapor formed by the pyrolysis of Mg(OH)2 can expand the channels of biochar and promote the cross-linking structure of the pores). The formed MgO can provide a large number of adsorption sites for phosphates and nitrates. After preheating and high-temperature pyrolysis, through the water absorption and swelling process of peanut shell biochar with MgO and added starch, and the pyrolysis and foaming process of potassium bicarbonate, the resulting network structure has a higher nitrogen and phosphorus binding capacity than traditional fillers such as carbon balls and zeolites.

[0030] my country has abundant bauxite resources with a significant price advantage. Furthermore, the Al2O3 in bauxite can form crystalline components under high-temperature conditions, improving the compressive strength and durability of the packing material, providing basic rigidity, and preventing it from being washed away in water. Preferably, the bauxite mass ratio is approximately 5%. Too high a bauxite ratio makes the carbon spheres difficult to crush during composting and recovery, hindering the release of trapped nitrogen and phosphorus nutrients. Conversely, too low a bauxite ratio results in poor rigidity of the carbon spheres, leading to breakage and degradation in flowing water environments.

[0031] This invention uses low-cost pore-forming agents starch and potassium bicarbonate. The pore structures and gases generated by their water absorption and pyrolysis can produce a large number of effective pore structures during preheating, increasing the specific surface area of ​​the carbon spheres. Specifically, starch absorbs water and expands, enlarging the original pore structure of the peanut shell; during preheating, potassium bicarbonate decomposes and dehydrates to form pore structures; and during calcination, starch pyrolyzes to form pore structures.

[0032] Attapulgite is a natural clay mineral whose main structure is a crystalline hydrous magnesium aluminum silicate mineral. Its microporous and channel structure has a large specific surface area and cation exchange capacity, giving it considerable adsorption and interception capacity for pollutants.

[0033] The preheating temperature is set at 150℃-200℃ for 2 hours, during which potassium bicarbonate decomposes and dehydrates, promoting the formation of internal pore structures. The calcination temperature of the mineral-based carbon spheres is 500-700℃. At this temperature range, bauxite decomposes, dehydrates, and recrystallizes, forming a hardened carbon sphere framework. Biochar undergoes extensive pyrolysis, with Mg(OH)₂ pyrolyzing to create abundant MgO adsorption sites, and starch decomposing and carbonizing to form a porous structure. Higher temperatures may cause the cross-linked pore structure of the biochar to begin collapsing, while lower pyrolysis temperatures may make it difficult for bauxite to dehydrate and decompose, weakening its rigidity; or the starch may not decompose and carbonize sufficiently.

[0034] The mineral-based carbon spheres of this invention have better nitrogen and phosphorus interception effects than similar modified biochars, while the cost is only about 1 / 3 to 1 / 2 of similar modified biochars.

[0035] After the mineral-based carbon spheres of this invention are saturated with adsorption, they can be used for composting and reuse after a safety assessment, thereby realizing the safe reuse of nitrogen and phosphorus resources. The main components, such as MgO, attapulgite, biochar, bauxite, starch, and potassium bicarbonate, can all be applied to the soil. The nitrogen and phosphorus pollutants bound to them can provide necessary nutrients for crops and achieve a slow-release effect of nutrient release. Attached Figure Description

[0036] Figure 1 SEM images of the mineral-based carbon spheres from Examples 1 and 2;

[0037] Figure 2 The pore volume and specific surface area of ​​carbon spheres, wherein: a and b correspond to Example 1, c and d correspond to Example 4, e and f correspond to Example 7, and g and h correspond to Example 8;

[0038] Figure 3 Infrared spectra of different mineral-based carbon spheres, a corresponds to Example 8, b corresponds to Example 4, c corresponds to Example 7, and d corresponds to Example 1;

[0039] Figure 4 Changes in N, P, K and total nutrients in compost samples;

[0040] Figure 5 The content of humic substances, fulvic acid, and humic acid, as well as the changes in HA / FA ratio, in organic fertilizers under various treatments. Detailed Implementation

[0041] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0042] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, and instruments used in the following examples are commercially available.

[0043] Example 1

[0044] Crushed peanut shells were passed through a 60-mesh sieve and sprayed with a 0.5 mol / L MgCl2 solution at a rate of 0.1 L / (h*kg) (i.e., 0.1 mol / L MgCl2 solution per kg of crushed peanut shells per hour) for 10 minutes. The mixture was stirred simultaneously at 200 rpm. After standing overnight, a 1.25 mol / L KOH solution was sprayed uniformly using the same steps as the MgCl2 spray, alternating between the two solutions twice. After spraying, the mixture was stirred at 200 rpm for 1 hour. The magnesium-modified peanut shells were then removed and dried for later use.

[0045] Preparation of reusable mineral-based carbon spheres:

[0046] Magnesium-modified peanut shells (35 parts), starch (2 parts), and potassium bicarbonate (2 parts) were mixed beforehand. Then, attapulgite (40 parts) and bauxite (5 parts) were added and thoroughly mixed. Finally, 20 parts of water were added, and the mixture was granulated into balls using a disc granulation process (ball diameter 0.2-1 cm, granulation time 30 min). After granulation, the balls were preheated using the recovered heat from carbonization at 150°C for 2 h. Then, they were calcined in a carbonization kiln at 600°C for 1 h. Finally, they were naturally cooled to form the desired mineral-based carbon balls.

[0047] Example 2:

[0048] The preparation method is similar to that in Example 1, except that there is no surface modification process using metal MgCl2 and KOH, and the product is mineral-based carbon spheres 2.

[0049] Example 3:

[0050] The preparation method is similar to that in Example 1, except that no attapulgite is added, and the product is mineral-based carbon spheres 3.

[0051] Example 4:

[0052] The preparation method is similar to that in Example 1, except that peanut shells are replaced with rice straw, and the product is mineral-based carbon spheres 4.

[0053] Example 5:

[0054] The preparation method is similar to that in Example 1, except that the modified Mg biochar is prepared by impregnation, and the product is mineral-based carbon spheres 5.

[0055] Example 6:

[0056] The preparation method is similar to that in Example 1, except that the metals sprayed are Fe (ferric chloride solution) and La (lanthanum chloride), and the products are mineral-based carbon spheres 6 and 7, respectively.

[0057] Example 7:

[0058] The preparation method is similar to that in Example 1, except that no potassium bicarbonate is added, and the product is mineral-based carbon spheres 8.

[0059] Example 8:

[0060] The preparation method is similar to that in Example 1, except that no starch is added, and the product is mineral-based carbon spheres 9.

[0061] Example 9:

[0062] The preparation method is similar to that in Example 1, except that there is no preheating process, and the product is mineral-based carbon spheres 10.

[0063] For modified biochar prepared from different biomass raw materials (only the biomass material was modified, and no carbon balls were made), the phosphate adsorption rate of biochar modified with different metals was determined by experiment. Suitable raw materials and types of modified metals were analyzed and screened. The results are shown in Table 1.

[0064] Table 1. Adsorption rate (%) of modified biochar powder (0.5 g) prepared from different raw materials for phosphate (1 L, 10 mg / L)

[0065]

[0066] The data in Table 1 show that the adsorption effect of peanut shell raw material on phosphate after Mg modification is much higher than that of other raw materials and modified metal types. Therefore, peanut shell and Mg modification are preferred conditions of the present invention.

[0067] like Figure 1 As shown, A corresponds to mineral-based carbon sphere 1, and B corresponds to mineral-based carbon sphere 2. Figure 1 The results show that, compared with mineral-based carbon spheres that have not been loaded with MgCl2 and KOH, the surface loading process can effectively increase the uneven pore structure of the material surface, thereby improving the material's ability to absorb pollutants.

[0068] Figure 2The results showed that replacing magnesium-modified peanut shells with magnesium-modified rice straw, and the absence of starch and potassium bicarbonate, all led to a significant reduction in the specific surface area and pore volume of the carbon spheres. However, in Example 1, the combined use of magnesium-modified peanut shells, starch, and potassium bicarbonate greatly increased the pore structure and specific surface area of ​​the carbon spheres, thereby enhancing their ability to reduce pollutants. This is mainly because starch and potassium bicarbonate enter the loose, porous structure of the peanut shells. Starch absorbs moisture and swells, increasing its volume by tens to hundreds of times. During the preheating stage, potassium bicarbonate acts as a foaming agent, generating a large amount of carbon dioxide gas, which promotes the formation of pores in the carbon spheres. These pores also facilitate further pyrolysis and expansion of the starch, playing a complementary role in improving the porosity of the carbon spheres. During the calcination stage, the starch and peanut shells entering the pores undergo differential carbonization due to differences in pyrolysis difficulty, further increasing the porosity of the carbon spheres. Therefore, in this invention, the expansion and carbonization of starch in the porous structure of peanut shells, combined with the foaming agent function of potassium bicarbonate, can effectively improve the pore size structure of carbon spheres and achieve a synergistic effect.

[0069] Figure 3 The results show that the surface functional groups of the mineral-based carbon spheres using the complete formulation have a richer functional group structure than those in other embodiments, while the mineral-based carbon spheres lacking other components lack functional groups corresponding to specific wavelengths, such as 750 cm⁻¹. -1 Carbonate, a functional group, can immobilize nitrogen and phosphorus pollutants in water through ion exchange. Therefore, the combined use of multiple formulations can increase the abundance of functional groups on the surface of the packing material, thereby providing more adsorption sites during pollutant reduction.

[0070] Application Example 1: Laboratory Interception and Purification Experiment

[0071] The experimental water was artificially cultivated simulated polluted water: COD 30 mg / L, total nitrogen 15 mg / L, ammonia nitrogen (NH4) + -N) 5mg / L, total phosphorus 1mg / L.

[0072] An adsorption device was constructed in the laboratory for testing. 50g of each of the different test packing materials was added to 50L of simulated wastewater. The pH was maintained at 7.5±0.2 at room temperature. After 24 hours of stirring and adsorption, the changes in the content of different pollutants in the supernatant before and after adsorption were measured, and the adsorption removal rate was calculated accordingly. The results in Table 2 show that surface Mg loading, attapulgite addition, peanut shell matrix, modified metallic MgO, a certain preheating process, and especially the synergistic effect of starch, potassium bicarbonate, and peanut shells, can increase the purification capacity of mineral-based carbon balls for nitrogen and phosphorus in water.

[0073] In Example 5, since the impregnation method requires the use of a large-volume container to immerse the raw material, the amount of waste liquid generated by the impregnation method is about tens of times that of the spraying method. In other words, the spraying method can significantly reduce production costs.

[0074] The addition of bauxite can increase the mechanical strength of mineral-based carbon balls, making them more resistant to impact in ditch water.

[0075] Table 2 Adsorption of TN, ammonia nitrogen, and TP by different mineral-based carbon spheres

[0076] Adsorption rate (%) TN ammonia nitrogen TP Mineral-based carbon spheres 1 69.5 64.5 63.5 Mineral-based carbon spheres 2 62.1 52.2 52.1 Mineral-based carbon spheres 3 70.5 42.1 56.8 Mineral-based carbon spheres 4 62.3 56.9 54.0 Mineral-based carbon spheres 6 63.1 50.6 53.2 Mineral-based carbon spheres 7 56.5 55.5 53.1 Mineral-based carbon spheres 8 49.1 49.0 57.8 Mineral-based carbon spheres 9 51.7 49.7 62.4 Mineral-based carbon spheres 10 39.4 47.1 49.5

[0077] Application Example 2: Ditch Interception and Purification Experiment

[0078] Interception dams filled with mineral-based carbon balls were installed in actual ditches, and their interception effect on nitrogen and phosphorus in farmland runoff during fertilization and heavy rain periods was monitored and analyzed. The dams were installed at a rate of 0.01 cubic meters of filler per mu (approximately 0.067 hectares) of paddy field. The specific location was an interception ditch in the Zhaojiatang area of ​​Xinkang Village, Wujin District, Changzhou, my country. The results are shown in Table 3.

[0079] Table 3. The interception effect of mineral-based carbon balls on nitrogen and phosphorus in farmland runoff during fertilization and heavy rain periods.

[0080]

[0081]

[0082] Application Example 3: Experiment on the Recycling of Adsorbed Saturated Carbon Balls for Composting

[0083] This study designed four treatments: CK0 (control, no additives), T1, T2, and T3. T1 involved the addition of 10% saturated Mg-modified peanut shell biochar powder; T2 involved the addition of 10% saturated mineral-based carbon spheres (1) obtained by crushing. In T3, the modified biochar spheres were the mineral-based carbon spheres (10%) prepared in Example 1, which were then reused after adsorption saturation. The 10% mass fraction refers to the mass ratio of biochar powder or carbon spheres to the initial compost material.

[0084] Chicken manure is processed, crushed, and passed through a 5mm sieve; wheat straw is processed and crushed to 1-2cm.

[0085] The composting reactor was a PP insulated box with an inner diameter of 52.5×40×29 (cm) and an outer diameter of 64×48×36 (cm). The composting process lasted 36 days. The initial wet weight of the compost material was 8.0 kg, uniformly mixed with wheat straw and chicken manure at a ratio of 1:1.5. The moisture contents of the wheat straw and chicken manure were 10.9% and 12.6%, respectively. The conditioner was mixed evenly with the compost, and the moisture content of each treatment was adjusted to approximately 60.0%. The composting process began with the mixing of raw materials and was turned four times during the entire composting process. Turning was carried out on days 11, 16, 24, and 33, and composting was completed on day 36. During turning, the compost in the incubator was poured out and stirred evenly in a mixer. An appropriate amount of water was added during stirring to maintain the moisture content of the compost at 55.0%-60.0%. After turning, the fertilizer in the mixer was poured out and placed back into the original insulated box for continued composting. Rinse the agitator three times with water, then continue turning the compost for the next treatment until all treatments have been turned. After each turning, collect samples during the theromphilic phase and cooling phase. Adjust the moisture content of the compost to 55.0-60.0% after each sampling. Do not add moisture during the maturation period when turning the compost.

[0086] like Figure 4 As shown, the variation patterns of total nitrogen among the treatments are similar, with the highest content during the high-temperature period (average 2.50%), gradually decreasing during the cooling period (average 2.00%), and slightly increasing during the maturation period (average 2.25%).

[0087] At the end of the decomposition period, compared with the control group, the TK content in the T2 treatment increased by nearly 25%. Figure 4 In treatment c), the high-temperature heating period was 50%-75% longer than that of treatment CK0, but the TK content in treatment T3 did not change much (increasing by about 1.2%). At the end of composting, the total nutrient content of the control group increased by 35.3%, the total nutrient content of treatment T1 increased by 35.7%, the total nutrient content of treatment T2 increased by 25%, and the total nutrient content of treatment T3 increased by 28.6%. The experimental results showed that the total nutrients in composting treatments with modified biochar powder (T2 treatment) and modified biochar balls (T3 treatment) were close to the total nutrients in treatment T1.

[0088] The degree of humification reflects the extent of biodegradation and the stability of compost products. The humic acid (HA) content in organic acids is as follows: Figure 5As shown in Figure a, compared with the control group, the HA content of the T2 treatment (with added Mg-modified biochar powder) increased (by 1.01%), while the HA content of the T1 and T3 treatments decreased slightly (by 1.0%). Compared with the control, the humic acid / fulvic acid (HA / FA) ​​ratio of the T2 compost treatment was significantly higher, increasing by 2.2%, while there were no significant differences in other compost treatments (p<0.05).

[0089] In summary, the addition of 10% adsorption-saturated mineral-based carbon spheres does not weaken nitrogen and phosphorus nutrients in compost and contributes to increasing the degree of humification (HA / FA ratio). In particular, the use of modified saturated biochar ground into powder in composting can maintain and enhance the fertilizer efficiency of compost when there is an input of exogenous substances, which is beneficial to the recycling of adsorption-saturated mineral-based carbon spheres.

[0090] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any way, and any technical solutions obtained by equivalent substitution or equivalent transformation fall within the protection scope of the present invention.

Claims

1. The use of a reusable mineral-based carbon ball based on agricultural waste, characterized in that, The preparation of reusable mineral-based carbon spheres based on agricultural waste includes the following steps: Preparation of magnesium-modified peanut shells: The crushed peanut shells were modified by spraying with magnesium salt solution, and then treated with KOH solution to obtain magnesium-modified peanut shells; Preparation of reusable mineral-based carbon spheres: Magnesium-modified peanut shells, starch, and potassium bicarbonate are mixed, and then attapulgite, bauxite, and water are added and mixed. The mixture is then granulated into spheres. After sphere formation, the mixture is preheated at 150℃-200℃ for 1-2.5 hours. After preheating, the spheres are calcined at 500℃-700℃ for 0.5-1.5 hours and then cooled to form reusable mineral-based carbon spheres. The mass ratio of magnesium-modified peanut shells, starch, potassium bicarbonate, attapulgite, bauxite, and water is 35:(1-3):(1-3):(35-45):(4-6):(15-25); The total molar ratio of magnesium ions in the magnesium salt solution to hydroxide ions in the KOH solution is 1:(2.3-2.7). The interception dam is filled with the reusable mineral-based carbon balls; the interception dam is used to intercept or adsorb nitrogen and phosphorus in the runoff from farmland during the fertilization period and / or the rainstorm period; after the reusable mineral-based carbon balls have completed saturated adsorption of nitrogen and phosphorus, they are crushed and reused in composting to increase soil fertility. The mass of the mineral-based carbon ball powder after adsorption saturation accounts for 5-10% of the mass of the initial compost material composed of wheat straw and chicken manure.

2. The use of a reusable mineral-based carbon ball based on agricultural waste according to claim 1, characterized in that, In the preparation of magnesium-modified peanut shells, the crushed peanut shells are sieved, and the peanut shells are sprayed with a 0.2-1.5 mol / L magnesium salt solution to make the surface of the peanut shells uniformly wetted by the magnesium salt solution. After standing for 18-28 hours, the peanut shells are sprayed evenly with a 1-2 mol / L KOH solution and then stirred and mixed.

3. The use of a reusable mineral-based carbon ball based on agricultural waste according to claim 1, characterized in that, The total molar ratio of magnesium ions in the magnesium salt solution to hydroxide ions in the KOH solution is 1:2.5; the magnesium salt is MgCl2.

4. The use of a reusable mineral-based carbon ball based on agricultural waste according to claim 1, characterized in that, Magnesium modification and pyrolysis cause the pores of peanut shells to swell and form nano-sized magnesium oxide (MgO).

5. The use of a reusable mineral-based carbon ball based on agricultural waste according to claim 1, characterized in that, The reusable mineral-based carbon spheres described above have a specific surface area >150 m². 2 / g, fixed carbon >30%, iodine value >600 mg / g, compressive strength 5-10 MPa, methylene blue value >100 mg / g; mineral-based carbon spheres with a particle size of 2-10 mm.

6. The use of a reusable mineral-based carbon ball based on agricultural waste according to claim 1, characterized in that, Starch absorbs water and swells to form a porous structure. During preheating, potassium bicarbonate decomposes and dehydrates to form a foamed structure. During calcination, magnesium-modified peanut shells pyrolyze to form biochar, starch decomposes and carbonizes to form a porous structure, and bauxite decomposes, dehydrates, and recrystallizes to form a hardened framework. At the same time, during the pyrolysis of biochar, the sprayed Mg(OH)2 forms abundant MgO structures that are loaded into the porous structure of biochar.

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