Preparation and application of calcium-rich hierarchical porous biochar

Abstract

The application discloses a preparation method and application of calcium-rich hierarchical porous biochar, wherein the pulverized biomass powder, shell particles and ammonium oxalate monohydrate are ball milled according to a mass ratio of 10: (2-4) : (20-40), the product is pyrolyzed at 750 DEG C-850 DEG C, then HNO3 solution is added and stirred, the filtrate is collected by filtration, and the solid powder is washed to obtain acid-washed activated biochar; humic acid solution is added to the acid-washed activated biochar, NaOH solution is used to maintain the pH of the system, and a suspension is obtained by stirring; the acid-washed filtrate is slowly added to the suspension, and stirring is continued; and the solid powder is dried to obtain the calcium-rich hierarchical porous biochar. The method is simple in synthesis method, controllable in effective micro-morphology, can effectively adsorb air carbon dioxide and improve the soil carbon sequestration capacity, has good stability, exhibits excellent regeneration performance, and the adsorption capacity of carbon dioxide only decreases by 1.3% after 5 cycles of adsorption.

Description

Technical Field

[0001] This invention belongs to the field of new materials technology, specifically relating to the preparation and application of calcium-rich hierarchical porous biochar. Background Technology

[0002] Carbon dioxide, a common greenhouse gas, has been emitted unavoidably by various industrial activities since the Industrial Revolution, such as coal combustion, dyeing and printing, plastics processing, and chemical production. Its continuous accumulation in the atmosphere has led to a rise in ambient temperature, posing a significant threat to human survival. Therefore, reducing carbon emissions from industrial activities is crucial for lowering global CO2 concentrations. Meanwhile, soil carbon pools influence the global carbon balance of terrestrial ecosystems. The soil carbon pool refers to the total organic and inorganic carbon stored in the soil, representing the largest carbon pool in terrestrial ecosystems. It is vital for regulating global climate, maintaining ecosystem functions, and agricultural productivity. Organic carbon pools can be divided into unstable and stable organic carbon pools. Soil carbon sequestration efficiency is closely related to various factors, including climate, temperature, humidity, and soil management practices. Soil carbon pools are easily depleted due to continuous climate change, which in turn reinforces the negative positive feedback loop in the global climate system. Among these methods, altering soil carbon sequestration efficiency through exogenous inputs into the soil is a widely adopted approach.

[0003] Solid adsorbents are widely used for carbon dioxide capture, including porous carbon zeolites, clays, metal-organic frameworks, metal oxides, covalent organic polymers, and biochar, among other advanced materials. Biochar, as an emerging material, has attracted significant attention. Biochar possesses a well-developed porous structure and abundant functional groups, enabling it to adsorb carbon dioxide through numerous surface adsorption sites, contained minerals, and surface functional groups. However, its adsorption capacity for carbon dioxide and its effect on improving soil carbon sequestration are limited. Increasing the percentage of stable carbon in biochar is one way to increase its carbon sequestration ratio. Studies have shown that doping biochar with minerals can enhance its carbon dioxide adsorption capacity. This method improves the carbon sequestration capacity of traditional biochar, but it suffers from problems such as complex operation, high preparation costs, and unstable technology.

[0004] Therefore, there is an urgent need to develop a modified biochar that can improve soil fertility and structure, enhance soil water and fertilizer retention, and increase carbon sequestration capacity. Summary of the Invention

[0005] To address at least one of the aforementioned problems, this invention provides a calcium-rich graded porous biochar, its preparation method, and its application. This method not only features a simple synthesis process and controllable microstructure, but also effectively adsorbs carbon dioxide from the air and enhances the soil's carbon sequestration capacity.

[0006] To achieve the above objectives, the present invention employs the following technical means: The first aspect of this invention provides a method for preparing calcium-rich hierarchical porous biochar, comprising the following steps: S1. Agricultural and forestry solid waste biomass and shell waste raw materials are washed and dried, and then crushed in a crusher. S2. Weigh the biomass powder, shell pellets and ammonium oxalate monohydrate in a mass ratio of 10:(2-4):(20-40) and place them in a ball mill jar for ball milling. S3. After filtering and drying the ball-milled product, place it in a quartz tube furnace and heat it to 750 °C-850 °C at a heating rate of 10 °C / min under N2 atmosphere. After holding at this temperature for 1-2 hours, allow it to cool naturally to room temperature. S4. The black solid obtained after pyrolysis is added to HNO3 solution and stirred at 40-60°C for 1-2 h. After filtration, the filtrate is collected, and the solid powder is washed with deionized water to obtain acid-washed activated biochar. S5. Add humic acid solution to the obtained acid-washed activated biochar, while using NaOH solution to maintain the pH of the system within the range of 7.0±0.5, and stir for 30-60 min to obtain a suspension; S6. The acid washing filtrate from step S2 is allowed to stand and filtered, and the pH is adjusted to within the range of 7.0±0.5. It is then slowly added dropwise to the suspension from step S5 and stirred for 1-2 hours. After filtration, the solid powder is washed with deionized water and dried to obtain calcium-rich graded porous biochar.

[0007] In some embodiments of the present invention, in step S2, the ball milling speed is 300-600 rpm and the ball milling time is 1-3 hours.

[0008] In some embodiments of the present invention, in step S4, the concentration of the HNO3 solution is 0.5-1 mol / L, and the solid-liquid ratio is 1:(10-15).

[0009] In some embodiments of the present invention, in step S5, the concentration of humic acid solution is 5-8%, and the amount of humic acid added is 2-4 wt% of the biochar mass.

[0010] In some embodiments of the present invention, in step S6, the acid washing filtrate is added at a rate of 1-2 mL / min.

[0011] A second aspect of the present invention provides a calcium-rich hierarchical porous biochar, which is prepared using the method described in the first aspect.

[0012] The third aspect of the present invention provides an application of calcium-rich graded porous biochar prepared by the method described in the first aspect or the method described in the second aspect in flue gas treatment, wherein the application steps are as follows: a raw gas containing CO2 is introduced into a fixed bed containing calcium-rich graded porous biochar.

[0013] The fourth aspect of the present invention provides the application of calcium-rich graded porous biochar prepared by the method of the first aspect or the method of the second aspect in soil carbon sequestration.

[0014] In some embodiments of the present invention, the application steps are as follows: calcium-rich graded porous biochar is added to low-quality farmland soil and mixed evenly, water is added to 50-60% of the saturated moisture content, and the soil is cured at room temperature for 50-60 days.

[0015] In some embodiments of the present invention, the weight ratio of the calcium-nitrogen-rich modified biochar to soil is (0.5~1.5):100.

[0016] Beneficial effects of the present invention In existing technologies, the pores of calcium-modified biochar prepared by either co-pyrolysis or the loading method are blocked by minerals. Compared with existing technologies, the present invention has the following advantages: The preparation method of this application can not only prepare hierarchical porous biochar and prevent the biochar pores from being blocked, but also uniformly load the Ca source on the surface of the biochar through bridging.

[0017] Compared to original biochar, calcium-rich graded porous biochar exhibits a significant improvement in CO2 adsorption performance. The surface of the calcium-rich graded porous biochar shows a prominent honeycomb-like porous structure with no obvious blockage. Furthermore, some of the CaO generated during the high-temperature reaction adheres to the biochar, and a humic acid-calcium complex film forms on the surface, greatly increasing the number of adsorption sites and demonstrating excellent CO2 adsorption performance: at 80℃, the CO2 adsorption capacity of calcium-rich graded porous biochar is 54.87% higher than that of original biochar. Simultaneously, the improved pore structure and the adhesion of CaO crystals increase the stability of the biochar, exhibiting excellent regeneration performance; after 5 cycles of adsorption, the adsorption capacity decreases by only 1.3%.

[0018] Meanwhile, calcium-enriched graded porous biochar also demonstrated excellent carbon sequestration performance in soil carbon fixation experiments. The thermal decomposition resistance of calcium-enriched graded porous biochar was improved by 73.28%–121.85%, increasing the carbon retention rate and carbon stability of the biochar. Furthermore, the calcium adhering to the biochar surface acted as a physical barrier and adsorbent, hindering carbon release, all of which contribute to improving soil carbon sequestration capacity. Simultaneously, it improved soil water retention and fertility, and improved the distribution structure of soil aggregates, further promoting soil carbon sequestration capacity. While improving soil structure, compared to the control group (CK), the organic carbon content in the calcium-enriched graded porous biochar treatment group increased by 22.18–33.07%; the proportion of large aggregates in the soil of the calcium-enriched graded porous biochar treatment group increased by 4–7%, indicating that calcium-enriched graded porous biochar can significantly change soil structure, improve soil stability, and promote soil carbon sequestration capacity. Attached Figure Description

[0019] Figure 1 SEM images of the materials prepared in Examples 1, 3, and 5-8 of this invention; Figure 2 Thermogravimetric analysis (TGA) diagrams of the materials prepared in Examples 1, 3, and 5-8 of this invention are shown. Figure 3 The graphs show the comparison of CO2 adsorption capacity and cyclic adsorption of the materials prepared in Examples 1, 3, and 5-8 of this invention. Figure 4 The results of soil organic carbon determination are shown for the materials prepared in Examples 1, 3 and 5-8 of this invention after being applied to the soil. Figure 5 The results show the distribution of soil aggregates after the materials prepared in Examples 1, 3 and 5-8 of this invention were applied to the soil. Detailed Implementation

[0020] The following examples are used to illustrate preferred embodiments of the invention. Those skilled in the art will understand that the techniques disclosed in the examples represent techniques discovered by the inventors that can be used to implement the invention, and therefore can be considered preferred embodiments for implementing the invention. However, those skilled in the art should understand from this specification that many modifications can be made to the specific embodiments disclosed herein, still yielding the same or similar results, without departing from the spirit or scope of the invention.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains, and all materials disclosed herein are incorporated herein by reference. Many equivalent techniques of specific embodiments of the invention described herein will be recognized or can be understood by those skilled in the art through conventional experimentation. These equivalents will be included in the claims.

[0022] The preparation and application of a calcium-rich hierarchical porous biochar are characterized by comprising the following steps: (1) Wash and dry the agricultural and forestry solid waste biomass and shell waste raw materials with deionized water, crush the agricultural and forestry solid waste biomass in a crusher to obtain biomass powder, and crush the shells in a crusher to ≤2 mm particles. (2) Weigh the biomass powder, shell pellets (CaCO3) and ammonium oxalate monohydrate (NH4)2C2O4·H2O in a mass ratio of 10:(2-4):(20-40) and place them in a ball mill jar for ball milling. The rotation speed is 300-600 and the ball milling time is 1-3 hours. During ball milling, the shell particles can enhance the crushing of biomass. After ball milling, the shell powder is dispersed as fine powder, which will not cause local large blocks to sinter and block the pores during pyrolysis. At the same time, the shell powder and ammonium oxalate monohydrate (NH4)2C2O4·H2O are evenly distributed on the surface of the biomass powder. (3) After filtering and drying the ball milling product, place it in a corundum ceramic boat and put it in a quartz tube furnace. Heat it to 750 °C-850 °C at a heating rate of 10 °C / min under N2 atmosphere, keep it at the temperature for 1 h and then let it cool naturally to room temperature. (4) The black solid obtained after pyrolysis was added to 0.5 mol / L HNO3 solution (solid-liquid ratio 1:10-15), stirred at 40-60°C for 1-2 h, filtered and the filtrate was collected. The solid powder was washed with deionized water to obtain acid-washed activated biochar. (5) Add humic acid solution (concentration of 5-8%) to the obtained acid-washed activated biochar. The amount of humic acid added is 2-4 wt% of the biochar mass (corresponding to 40ml-80ml of humic acid solution). At the same time, use 0.1 mol / L NaOH solution to maintain the pH of the system within the range of 7.0±0.5 to ensure that the humic acid carboxyl groups (-COO) are intact. - (The humic acid is in a dissociated state. Stir for 30-60 minutes to pre-adsorb and anchor the humic acid on the surface of the biochar.) (6) After the acid washing filtrate (containing Ca(NO3)2) from step (4) is allowed to stand and filtered, the pH is adjusted to 7.0±0.5 and slowly added to the suspension at a rate of 1-2 mL / min. Stirring is continued for 1-2 h. After filtration, the solid powder is rinsed with deionized water and dried at 60-80°C to obtain calcium-rich graded porous biochar.

[0023] One application of calcium-rich graded porous biochar in flue gas treatment involves passing raw gas containing CO2 into a fixed bed containing calcium-rich graded porous biochar.

[0024] The application of calcium-rich graded porous biochar in soil carbon sequestration involves the following steps: calcium-rich graded porous biochar is added to low-quality farmland soil and mixed evenly, pure water is added to 60% of the saturated water content, and the soil is cured at room temperature for 60 days; the weight ratio of calcium-rich nitrogen-modified biochar to soil is (0.5~1.5):100.

[0025] The technical solution of this application will be further described in detail below with reference to specific embodiments.

[0026] Example 1 After drying the biomass straw in an oven at 60°C, it was crushed in a pulverizer and passed through a 60-mesh sieve. The straw powder was placed in a corundum ceramic boat and placed in a high-temperature quartz tube furnace. It was heated to 850°C at a heating rate of 10°C / min and kept at a constant temperature for 2 hours. Then, it was carbonized and pyrolyzed under a nitrogen atmosphere to obtain biochar.

[0027] Example 2 Biomass powder, CaCO3, and (NH4)2C2O4·H2O were weighed at a mass ratio of 10:3:30 and thoroughly ground in a mortar to obtain a homogeneous mixture. The mixed powder was then placed in a tube furnace and heated to 850°C at a heating rate of 10 °C / min under a N2 atmosphere. After holding at this temperature for 1 h, it was naturally cooled to room temperature to obtain calcium-modified biochar.

[0028] Example 3 Biomass powder, CaCO3, and (NH4)2C2O4·H2O were weighed at a mass ratio of 10:3:30 and placed in a ball mill jar for ball milling at a speed of 300-600 rpm for 3 hours. The mixed powder was then placed in a tube furnace and heated to 850°C at a heating rate of 10 °C / min under a N2 atmosphere. After holding at this temperature for 1 hour, it was allowed to cool naturally to room temperature to obtain calcium-modified biochar.

[0029] Example 4 Biomass powder, CaCO3, and (NH4)2C2O4·H2O were weighed at a mass ratio of 10:3:30 and thoroughly ground in a mortar to obtain a homogeneous mixture. The mixed powder was then placed in a tube furnace and heated to 850°C at a heating rate of 10 °C / min under a N2 atmosphere. After holding at this temperature for 1 h, it was naturally cooled to room temperature to obtain calcium-modified biochar. The black solid obtained after pyrolysis was added to a 0.5 mol / L HNO3 solution at a solid-liquid ratio of 1:10, stirred at 40-60°C for 1-2 h, filtered, and washed with deionized water to obtain acid-washed activated calcium-modified biochar.

[0030] Example 5 Biomass powder, CaCO3, and (NH4)2C2O4·H2O were weighed at a mass ratio of 10:3:30 and placed in a ball mill jar for ball milling at a speed of 300-600 rpm for 3 hours. The mixed powder was then placed in a tube furnace and heated to 850°C at a heating rate of 10 °C / min under a N2 atmosphere. After holding at this temperature for 1 hour, it was naturally cooled to room temperature to obtain calcium-modified biochar. The black solid obtained after pyrolysis was added to a 0.5 mol / L HNO3 solution at a solid-liquid ratio of 1:10 and stirred at 40-60°C for 1-2 hours. After filtration, the solid powder was washed with deionized water to obtain acid-washed activated calcium-modified biochar.

[0031] Example 6 Biomass powder, CaCO3, and (NH4)2C2O4·H2O were weighed at a mass ratio of 10:3:30 and placed in a ball mill jar for ball milling at a speed of 300-600 rpm for 3 hours. The mixed powder was then placed in a tube furnace and heated to 850°C at a heating rate of 10 °C / min under a N2 atmosphere. After holding at this temperature for 1 hour, it was naturally cooled to room temperature to obtain calcium-modified biochar. The black solid obtained after pyrolysis was added to a 0.5 mol / L HNO3 solution at a solid-liquid ratio of 1:10 and stirred at 40-60°C for 1-2 hours. After filtration, the solid powder was washed with deionized water to obtain acid-washed activated calcium-modified biochar.

[0032] Add 40 mL of a 5% humic acid solution to the acid-washed and activated biochar. The amount of humic acid added is 2 wt% of the biochar mass. Simultaneously, maintain the pH of the system at 7.0 ± 0.5 using a 0.1 mol / L NaOH solution to ensure the humic acid carboxyl groups (-COO) are properly aligned. - (The humic acid is in a dissociated state. Stir for 30-60 minutes to allow the humic acid to be pre-adsorbed and anchored on the surface of the biochar.) After the pickling mother liquor (containing Ca(NO3)2) from step (6) was allowed to stand and filtered, the pH was adjusted to 7.0±0.5 and slowly added dropwise to the suspension at a rate of 1-2 mL / min. Stirring was continued for 1-2 h. After filtration, the solid powder was rinsed with deionized water and dried at 60-80°C to obtain calcium-rich graded porous biochar.

[0033] Example 7 Biomass powder, CaCO3, and (NH4)2C2O4·H2O were weighed at a mass ratio of 10:3:30 and placed in a ball mill jar for ball milling at a speed of 300-600 rpm for 3 hours. The mixed powder was then placed in a tube furnace and heated to 850°C at a heating rate of 10 °C / min under a N2 atmosphere. After holding at this temperature for 1 hour, it was allowed to cool naturally to room temperature to obtain calcium-modified biochar.

[0034] The black solid obtained after pyrolysis was added to a 0.5 mol / L HNO3 solution at a solid-liquid ratio of 1:10, stirred at 40-60°C for 1-2 h, filtered, and the solid powder was washed with deionized water to obtain acid-washed activated calcium modified biochar.

[0035] Add 60 mL of a 5% humic acid solution to the obtained acid-washed and activated biochar. The amount of humic acid added is 4 wt% of the biochar mass. Simultaneously, maintain the pH of the system within the range of 7.0 ± 0.5 using a 0.1 mol / L NaOH solution to ensure the presence of humic acid carboxyl groups (-COO). - (The humic acid is in a dissociated state. Stir for 30-60 minutes to allow the humic acid to be pre-adsorbed and anchored on the surface of the biochar.) After the pickling mother liquor (containing Ca(NO3)2) from step (6) was allowed to stand and filtered, the pH was adjusted to 7.0±0.5 and slowly added dropwise to the suspension at a rate of 1-2 mL / min. Stirring was continued for 1-2 h. After filtration, the solid powder was rinsed with deionized water and dried at 60-80°C to obtain calcium-rich graded porous biochar.

[0036] Example 8 Biomass powder, CaCO3, and (NH4)2C2O4·H2O were weighed at a mass ratio of 10:3:30 and placed in a ball mill jar for ball milling at a speed of 300-600 rpm for 3 hours. The mixed powder was then placed in a tube furnace and heated to 850°C at a heating rate of 10 °C / min under a N2 atmosphere. After holding at this temperature for 1 hour, it was allowed to cool naturally to room temperature to obtain calcium-modified biochar.

[0037] The black solid obtained after pyrolysis was added to a 0.5 mol / L HNO3 solution at a solid-liquid ratio of 1:10, stirred at 40-60°C for 1-2 h, filtered, and the solid powder was washed with deionized water to obtain acid-washed activated calcium modified biochar.

[0038] 120 mL of a 5% humic acid solution was added to the obtained acid-washed and activated biochar. The amount of humic acid added was 6 wt% of the biochar mass. Simultaneously, a 0.1 mol / L NaOH solution was used to maintain the pH of the system within the range of 7.0 ± 0.5 to ensure the carboxyl groups (-COO) of the humic acid were intact. - (The humic acid is in a dissociated state. Stir for 30-60 minutes to allow the humic acid to be pre-adsorbed and anchored on the surface of the biochar.) After the pickling mother liquor (containing Ca(NO3)2) was allowed to stand and filtered, the pH was adjusted to 7.0±0.5 and slowly added dropwise to the suspension at a rate of 1-2 mL / min. The mixture was stirred for 1-2 h. After filtration, the solid powder was washed with deionized water and dried at 60-80°C to obtain calcium-rich graded porous biochar.

[0039] (1) The specific surface area and calcium content of Examples 1-5 were analyzed, and the results are shown in Table 1.

[0040] Table 1. Specific surface area and calcium content of Examples 1-5

[0041] The results showed that although CaCO3 and (NH4)2C2O4·H2O can decompose into intermediates and gases such as NH3, H2O, CO2, and CO in the early stage of pyrolysis, promoting the formation of numerous micropores and mesopores on the biochar surface, when the pyrolysis temperature exceeds 700°C, the CaO produced by the decomposition of calcium carbonate begins to interact with the inner pore walls of the biochar, leading to pore blockage. Therefore, the prepared calcium-modified biochar generally has a small specific surface area and a low degree of pore exposure.

[0042] The results showed that surface ball milling and acid washing activation had a significant synergistic regulatory effect on the pore structure of calcium-modified biochar. Ball milling mechanically dispersed calcium carbonate and ammonium oxalate uniformly on the surface of biomass powder, avoiding local agglomeration and sintering of the calcium source during pyrolysis. This resulted in calcium species covering the carbon matrix surface with finer particles, thus alleviating physical blockage of micropores while retaining certain calcium-rich characteristics. Subsequent acid washing with dilute nitric acid selectively dissolved surface-accessible calcium oxides (CaO), clearing pore blockages and exposing covered micropore channels, significantly increasing the specific surface area and micropore volume. When used in combination (i.e., ball milling + acid washing), calcium-modified porous biochar with a high specific surface area of ​​up to 871.4 m² was obtained. 2 / g. However, after acid washing, the calcium content in the calcium-modified biochar decreased significantly. Although dilute nitric acid can effectively dissolve accessible CaO / CaCO3 distributed on the pore walls and outer surface of the biochar, the Ca-Al-Si-O glassy phase and calcium silicate (CaSiO3) formed by the silicon-aluminum components of biomass ash and calcium at high temperatures cannot be dissolved by dilute nitric acid. Therefore, compared with biochar, the calcium content of the acid-washed activated calcium-modified biochar prepared in Example 5 is increased.

[0043] (2) The materials prepared in Examples 1, 3 and 5-8 were subjected to electron microscopy scanning, and the obtained SEM images are shown below. Figure 1 As shown in Table 2, the loading, specific surface area, Ca content, and porosity of the materials in Examples 3 and 5-8 were analyzed.

[0044] Table 2 shows the loading, specific surface area, Ca content, and porosity of the materials in Examples 3 and 5-8.

[0045] Depend on Figure 1It can be seen that the original biochar in Example 1 has relatively small pores, while the pore structure of the co-pyrolytic calcium-modified biochar in Example 3 is significantly blocked by minerals. Compared with Example 3, the surface of the acid-washed calcium-modified biochar in Example 5 shows a significant honeycomb-like pore structure, with macropores and mesopores interlocking, and no pore blockage was found. Compared with Example 5, the pore structures of Examples 6-7 are similar, and no pore blockage was found, but the pore structure of Example 8 is significantly smaller.

[0046] Specific surface area analysis of the materials in Examples 1, 3, and 5-8 also confirms this. Furthermore, analysis of the calcium content in different examples shows that the method of this invention can recover most of the calcium source from the pickling mother liquor (containing Ca(NO3)2). Therefore, compared to Example 1, the calcium-rich hierarchical porous biochar prepared by this invention has an optimized pore structure and a significantly increased specific surface area.

[0047] This application's method involves etching the pores of biochar with HNO3 solution to expose the pores. After etching with HNO3 solution, an alkaline solution is typically added to adjust the pH. In this method, the shell powder generates CO2 and CaO during pyrolysis, which not only promotes the formation of macropores in the biochar but also reacts with the HNO3 solution to neutralize the pH. At this point, a humic acid solution is added to pre-adsorb and anchor the humic acid onto the biochar surface. Then, recovered pickling mother liquor (containing Ca(NO3)2) is added, allowing the humic acid to pass through the Ca... 2+ The bridging effect forms a stable humic acid-calcium complex film loaded on the biochar surface, effectively preventing CaO from blocking the pores of the biochar while ensuring the loading of Ca.

[0048] (3) Thermogravimetric analysis was performed on the materials prepared in Examples 1, 3 and 5-8 of the present invention, and the results are as follows: Figure 2 As shown.

[0049] The results showed that the thermal decomposition resistance of calcium-rich graded porous biochar was improved by 73.28% to 121.85% compared with that of the original biochar, which increased the carbon retention rate and carbon stability of the biochar.

[0050] (4) The materials obtained in Examples 1, 3, and 5-8 were loaded into a thermogravimetric crucible, and N2 was introduced. The temperature was increased to 120°C at a rate of 5-10°C / min, and the samples were purged at a constant temperature for 30 min to perform sample degassing pretreatment. When the N2 atmosphere cooled to 25°C, the flowing gas changed from N2 to CO2, and the mass change of the sample was monitored. At the same time, the CO2 concentration at the outlet was continuously monitored. When the outlet concentration was consistent with the inlet concentration, adsorption saturation was reached. The results of CO2 adsorption capacity of different materials are as follows: Figure 3 As shown in the figure. The results indicate that the CO2 adsorption capacity of calcium-rich hierarchical porous biochar was significantly improved.

[0051] (5) Perform the above adsorption process on the materials obtained in Examples 1, 3, and 5-8 until the sample is saturated with adsorption. Switch to N2 purging, program the temperature to 120°C, and desorb at a constant temperature for 30 min. Continuously introduce N2, cool the system to 25°C, introduce CO2 to start the next round of adsorption, and repeat the entire process for the preset number of cycles. Figure 3 As shown, after five cycles of regeneration adsorption, the performance of the materials obtained in Examples 6-8 is significantly better than that in Examples 1, 3 and 5. In particular, the CO2 adsorption capacity of the material obtained in Example 7 decreased by only 1.3% after five cycles of adsorption and desorption, demonstrating excellent regeneration performance.

[0052] (6) Soil culture experiments were conducted on the materials prepared in Examples 1, 3, and 5-8. The method was as follows: 1% biochar material was added to the soil and thoroughly mixed. The mixture was cultured at room temperature for 90 days, with soil moisture maintained at 60%. Soil organic carbon and available nitrogen were measured. The distribution of soil aggregates was analyzed by wet sieving. The results are as follows: Figure 4 and Figure 5 As shown.

[0053] Figure 4 The results showed that the calcium-enriched graded porous biochar in Examples 6-8 had a more significant impact on soil organic carbon after application, while there were no significant differences among Examples 1, 3, and 5. Compared to Example 1, the calcium-enriched graded porous biochar increased soil organic carbon by 22.18-33.07%.

[0054] Figure 5 The results showed that, compared with Example 1, the application of calcium-rich graded porous biochar to the soil significantly increased the structure of large soil aggregates, with the proportion of large aggregates in the soil increasing by 4-7%, thereby improving soil stability and promoting soil carbon sequestration capacity.

[0055] All documents mentioned in this invention are incorporated herein by reference as if each document were individually incorporated by reference. Furthermore, it should be understood that after reading the foregoing teachings of this invention, those skilled in the art can make various alterations or modifications to this invention, and these equivalent forms also fall within the scope defined by this application.

Claims

1. A method for preparing calcium-rich graded porous biochar, characterized in that, Includes the following steps: S1. Agricultural and forestry solid waste biomass and shell waste raw materials are washed and dried, and then crushed in a crusher. S2. Weigh the biomass powder, shell pellets and ammonium oxalate monohydrate in a mass ratio of 10:(2-4):(20-40) and place them in a ball mill jar for ball milling. S3. After filtering and drying the ball-milled product, place it in a quartz tube furnace and heat it to 750 °C-850 °C at a heating rate of 10 °C / min under N2 atmosphere. After holding at this temperature for 1-2 hours, allow it to cool naturally to room temperature. S4. The black solid obtained after pyrolysis is added to HNO3 solution and stirred at 40-60°C for 1-2 h. After filtration, the filtrate is collected, and the solid powder is washed with deionized water to obtain acid-washed activated biochar. S5. Add humic acid solution to the obtained acid-washed activated biochar, while using NaOH solution to maintain the pH of the system within the range of 7.0±0.5, and stir for 30-60 min to obtain a suspension; S6. The acid washing filtrate from step S2 is allowed to stand and filtered, and the pH is adjusted to within the range of 7.0±0.

5. It is then slowly added dropwise to the suspension from step S5 and stirred for 1-2 hours. After filtration, the solid powder is washed with deionized water and dried to obtain calcium-rich graded porous biochar.

2. The method for preparing calcium-rich graded porous biochar according to claim 1, characterized in that, In step S2, the ball milling speed is 300-600 rpm and the ball milling time is 1-3 hours.

3. The method for preparing calcium-rich graded porous biochar according to claim 1, characterized in that, In step S4, the concentration of the HNO3 solution is 0.5-1 mol / L, and the solid-liquid ratio is 1:(10-15).

4. The method for preparing calcium-rich graded porous biochar according to claim 1, characterized in that, In step S5, the concentration of humic acid solution is 5-8%, and the amount of humic acid added is 2-4 wt% of the biochar mass.

5. The method for preparing calcium-rich graded porous biochar according to claim 1, characterized in that, In step S6, the acid washing filtrate is added at a rate of 1-2 mL / min.

6. A calcium-rich, graded porous biochar, characterized in that: It is prepared by the method described in any one of claims 1-5.

7. The application of calcium-rich graded porous biochar prepared by the method according to any one of claims 1 to 5 or the method according to claim 6 in flue gas treatment, characterized in that, The application steps are as follows: Pass the raw gas containing CO2 into a fixed bed containing calcium-rich graded porous biochar.

8. The application of calcium-rich graded porous biochar prepared by the method according to any one of claims 1 to 5 or the method according to claim 6 in soil carbon sequestration.

9. The application according to claim 8, characterized in that: The application steps are as follows: Add calcium-rich graded porous biochar to low-quality farmland soil and mix evenly. Add water to 50-60% of the saturated moisture content and cure at room temperature for 50-60 days.

10. The application according to claim 8, characterized in that: The weight ratio of the calcium-nitrogen-enriched modified biochar to soil is (0.5~1.5):100.

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