Preparation method and application of high phosphorus removal magnetic biochar

Abstract

The application relates to a high-phosphorus-removal magnetic biochar as well as a preparation method and application thereof. The preparation method of the magnetic biochar comprises the following steps: mixing biomass and a FeCl3 solution to obtain a biomass-FeCl3 mixed solution, dehydrating the biomass-FeCl3 mixed solution to a water content of 68-78%, then adding calcium oxide to mix and expand, pressing, calcining, and crushing to obtain the magnetic biochar. The present inventors accidentally find, through a large number of experiments, that the prepared magnetic biochar, which is obtained by baking a mixed solution of a ferric chloride solution and biomass to a specific water content, then adding calcium oxide to mix and expand, not only improves the adsorption capacity of the biochar, but also enhances the phosphorus adsorption capacity of the magnetic biochar in neutral and weak alkaline sewage, effectively solving the problem that the phosphorus removal effect of the magnetic biochar in weak alkaline sewage is poor.

Description

Technical Field

[0001] This invention belongs to the field of water pollution control and resource utilization technology, specifically relating to a method for preparing and applying high phosphorus removal magnetic biochar. Background Technology

[0002] Phosphorus cycles almost unidirectionally in nature, yet the demand for phosphate rock resources continues to rise annually, exacerbating the global phosphorus shortage. Wastewater contains large amounts of phosphorus, and direct discharge into water bodies not only wastes resources but also leads to eutrophication. Therefore, phosphorus recovery from wastewater, which combines waste resource utilization with environmental protection, has attracted significant attention both domestically and internationally.

[0003] Currently, commonly used methods for phosphorus removal from wastewater include biological methods, chemical methods, and adsorption methods. Biological methods are easily affected by changes in external factors, and produce high sludge yields with high water content, making recovery difficult. Chemical methods are costly, have difficult reagent control, and are prone to causing secondary pollution of water bodies. Adsorption methods for phosphorus removal are highly efficient, rapid, environmentally friendly, and enable the efficient recovery and utilization of phosphorus resources.

[0004] Activated carbon is an adsorbent material with a rich porous structure. It has the advantages of wide applicability, environmental friendliness, wide availability, and low cost, and is widely used in the field of water treatment. However, activated carbon has a relatively poor adsorption capacity for phosphates in water, and cannot achieve efficient adsorption and removal of phosphorus from wastewater. But by controlling the surface modification methods of activated carbon, its structure can be changed, thereby enhancing the phosphorus removal efficiency of activated carbon and facilitating rapid phosphorus recovery.

[0005] By modifying biochar with iron, magnetic biochar with phosphorus removal properties can be prepared, which can improve the phosphorus adsorption capacity of biochar and enhance its separation ability. For example, Chinese patent CN110882676A provides a method for preparing magnetic adsorption biochar material and its application. This method involves soaking biomass raw materials in ferric chloride solution, drying them until moist and ensuring no solution flows out when inverted, carbonizing them in the absence of air, and filtering them with distilled water until the pH value is constant to obtain magnetic biochar adsorbent material. This material is magnetic and can effectively remove nitrogen and phosphorus from water bodies, reducing eutrophication. It can be quickly separated from water bodies by magnetic separation. However, in practical applications, wastewater pH varies widely, and the phosphorus removal rate of magnetic biochar in alkaline wastewater is not ideal, indicating that its adsorption capacity remains limited. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for preparing magnetic biochar with a wider applicable pH range and better phosphorus removal effect, which addresses the shortcomings of the prior art.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing magnetic biochar includes the step of mixing biomass with FeCl3 solution to obtain a biomass-FeCl3 mixture. The preparation method further includes the step of dehydrating the biomass-FeCl3 mixture to a water content of 68-78%, then adding calcium oxide to mix and expand, pressing, calcining, and pulverizing to obtain magnetic biochar.

[0009] The inventors of this application unexpectedly discovered that soaking biomass in a ferric chloride solution, then dehydrating it to a specific moisture content, and finally adding calcium oxide for mixing creates a paste-like mixture. After mixing, the calcium oxide reacts with water to form Ca(OH)₂, releasing a large amount of heat and water vapor. This facilitates the rapid adhesion of FeCl₃ in the solution to the biomass. Simultaneously, the escape of water vapor creates numerous pores in the originally paste-like mixture, causing the system to expand like fermenting bread. This results in a more uniform mixing of calcium oxide and the biomass adsorbed with ferric chloride, while also increasing the loading of ferric chloride on the biomass. During the biomass loading process, calcium oxide and ferric chloride undergo a chemical reaction to generate magnetic substances such as Fe₃O₄. The magnetic biochar releases large amounts of iron and calcium ions into the wastewater, significantly improving phosphorus removal efficiency and enhancing its phosphorus adsorption capacity in neutral or weakly alkaline wastewater.

[0010] Traditional magnetic biochar is suitable for phosphorus removal in weakly acidic wastewater, while the magnetic biochar of this invention has a wider pH range and not only has a good phosphorus removal effect in weakly acidic wastewater, but also has an even better phosphorus removal effect in neutral or weakly alkaline wastewater.

[0011] Furthermore, the moisture content is 70-75%.

[0012] In some embodiments, the calcium oxide has a particle size of 100 to 200 mesh.

[0013] In some embodiments, the step of adding calcium oxide is carried out in an anaerobic chamber.

[0014] In some embodiments, the mass ratio of the biomass, FeCl3, and calcium oxide is 1:0.8–2.4:0.3–1.2.

[0015] Preferably, the mass ratio of the biomass, FeCl3, and calcium oxide is 1:1 to 2:0.4 to 1.

[0016] In some embodiments, the concentration of the FeCl3 solution is 0.8–1.8 mol / L.

[0017] In some embodiments, the dehydration is carried out in an oven at a temperature of 90–120°C.

[0018] In some specific embodiments, the particle size of the biomass is 40-70 mesh.

[0019] In some specific embodiments, the raw material for the biomass is peanut shells.

[0020] In some specific embodiments, the calcination temperature is 500–800°C.

[0021] In some specific embodiments, the preparation method includes the following steps:

[0022] (1) Dry, grind and sieve the peanut shells to obtain 40-70 mesh peanut shell powder biomass;

[0023] (2) Add the biomass to FeCl3 solution and stir for 20-30 h to obtain a biomass-FeCl3 mixture;

[0024] (3) The biomass-FeCl3 mixture is placed in an oven to dehydrate to a moisture content of 68-78%, and stirred every 0.3-1 hour.

[0025] (4) Cool down to room temperature, then add calcium oxide powder, stir to expand, press into blocks, calcine at 500-800℃ for 1.5-2.5h, cool, and pulverize to obtain the magnetic biochar.

[0026] The second technical solution adopted by the present invention is: a magnetic biochar prepared by the above-described method for preparing magnetic biochar.

[0027] The third technical solution adopted in this invention is: the application of the magnetic biochar described above in the adsorption of phosphorus in wastewater, wherein the wastewater is acidic, neutral or alkaline.

[0028] Preferably, the pH of the wastewater is less than or equal to 10.

[0029] More preferably, the pH of the wastewater is greater than or equal to 3 and less than or equal to 10.

[0030] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0031] The inventors of this application made an unexpected discovery through numerous experiments that by drying a mixture of ferric chloride solution and biomass to a specific water content, and then adding calcium oxide to expand the mixture, the prepared magnetic biochar not only improves the adsorption capacity of the biochar, but also enhances its phosphorus adsorption capacity in neutral and weakly alkaline wastewater, effectively solving the problem of poor phosphorus removal efficiency of magnetic biochar in weakly alkaline wastewater. Attached Figure Description

[0032] Figure 1SEM image of peanut shells after pyrolysis at 700℃ for 2 hours;

[0033] Figure 2 Here is a SEM image of the magnetic biochar from Example 1;

[0034] Figure 3 for Figure 2 SEM image of magnetic biochar magnified 5 times. Detailed Implementation

[0035] In practical applications, existing iron-modified magnetic biochar does not achieve ideal phosphorus removal rates in alkaline wastewater with a wide range of pH variations, and its adsorption capacity remains limited.

[0036] Compared with existing iron-modified magnetic biochar, the iron-calcium composite modified biochar of this application has a wider pH range. This is mainly because the calcium oxide supported on the biochar can regulate OH- in alkaline environments. - Concentration, reduce OH - The ability to compete for active sites in biochar, thereby enhancing the biochar's resistance to PO4 under alkaline conditions. 3- The adsorption capacity is [not specified]. Compared to calcium-modified biochar, the introduction of iron modification gives the biochar magnetic properties, making subsequent separation and recovery more convenient and efficient. Furthermore, the phosphorus crystal precipitate (blue iron ore) formed after adsorption by the magnetic biochar of this application has higher recovery value.

[0037] In the preparation of the magnetic biochar of this application, the water content of the modification solution is gradually reduced to allow the biochar to be loaded with a large amount of modifying material, thereby increasing the adsorption capacity of the biochar. Furthermore, during the process of modifying the biochar with CaO, the heat released during the reaction of CaO with water causes the system to expand rapidly, and in this process, the modifying material is more uniformly loaded onto the biochar.

[0038] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the technical solution of the present invention, but the present invention is not limited to the scope of the examples described.

[0039] Example 1

[0040] The method for preparing magnetic biochar provided in this embodiment includes the following steps:

[0041] (1) After thoroughly cleaning, drying and grinding the peanut shells, sieve them with a sieve and take 45-60 mesh peanut shell powder as biomass.

[0042] (2) Take 100g of biomass and add it to 800mL of FeCl3 solution with a concentration of 1mol / L. Stir for 24h to obtain biomass-FeCl3 mixture.

[0043] (3) Place the biomass-FeCl3 mixture in an oven and heat it at 105°C. Stir it with a glass rod every 1 hour to promote the gradual adsorption of ferric chloride by the peanut shell powder. After heating for 12 hours, a viscous paste is formed, and its moisture content is reduced to about 75%.

[0044] (4) Remove the paste from the oven, cool it to room temperature in the desiccator, and then transfer it to the anaerobic operating box. Add 50g of calcium oxide powder with a particle size of 100-120 mesh in batches, and stir evenly with a stirring rod to expand it. Then press the expanded material into blocks of 15×15×3mm.

[0045] (5) Place the block in a crucible and calcine it in a muffle furnace. The muffle furnace is gradually heated to 700°C at a heating rate of 5°C / min. After calcination for 2 hours, the temperature inside the muffle furnace drops to about 100°C after the pyrolysis reaction. The block is then removed, cooled to room temperature in a desiccator, and pulverized to obtain magnetic biochar.

[0046] See Figure 1 , Figure 1 This is a SEM image of peanut shells after pyrolysis at 700℃ for 2 hours. Figure 2 and Figure 3 This is a SEM image of magnetic biochar. Figure 1 It is evident that the biochar obtained from the pyrolysis of natural peanut shells has a smooth surface and rich layered and porous structures, which can provide a site for iron and calcium to be loaded on the surface of the biochar. Figure 2 and Figure 3 The magnetic biochar exhibits an irregular, coral-like structure with a rough surface and numerous aggregated particles, which may be calcium oxide particles embedded within the biochar. The rough surface and aggregated particles increase the specific surface area and reaction sites of the biochar, allowing it to continuously release iron and calcium ions in solution, thus enhancing the adsorption and recovery of phosphorus.

[0047] Example 2

[0048] The method for preparing magnetic biochar provided in this embodiment is basically the same as that in Example 1, except that:

[0049] In step (2), the concentration of FeCl3 solution is 1.5 mol / L.

[0050] Example 3

[0051] The method for preparing magnetic biochar provided in this embodiment is basically the same as that in Example 1, except that:

[0052] In step (3), the moisture content is reduced to 70%.

[0053] In step (5), the calcination temperature is 800℃.

[0054] Example 4

[0055] The method for preparing magnetic biochar provided in this embodiment is basically the same as that in Example 1, except that:

[0056] In step (4), the amount of calcium oxide powder used is 100g.

[0057] Comparative Example 1

[0058] The preparation method of magnetic biochar provided in this comparative example is basically the same as that in Example 1, except that:

[0059] In step (4), the amount of calcium oxide powder used is 150g.

[0060] Comparative Example 2

[0061] The preparation method of magnetic biochar provided in this comparative example is basically the same as that in Example 1, except that:

[0062] In step (4), the amount of calcium oxide powder used is 20g.

[0063] Comparative Example 3

[0064] The preparation method of magnetic biochar provided in this comparative example is basically the same as that in Example 1, except that:

[0065] In step (5), the calcination temperature is 400℃.

[0066] Comparative Example 4

[0067] The preparation method of magnetic biochar provided in this comparative example is basically the same as that in Example 1, except that:

[0068] In step (5), the calcination temperature is 900℃.

[0069] Comparative Example 5

[0070] The preparation method of magnetic biochar provided in this comparative example is basically the same as that in Example 1, except that:

[0071] In step (2), the concentration of FeCl3 solution is 0.5 mol / L.

[0072] Comparative Example 6

[0073] The preparation method of magnetic biochar provided in this comparative example is basically the same as that in Example 1, except that:

[0074] In step (2), the concentration of the FeCl3 solution is 2 mol / L.

[0075] Comparative Example 7

[0076] The method for preparing magnetic biochar provided in this comparative example differs from that in Example 1 in that it is dehydrated to a moisture content of 80%.

[0077] Comparative Example 8

[0078] The method for preparing magnetic biochar provided in this comparative example differs from that in Example 1 in that:

[0079] In step (3), the mixture is dehydrated in an oven until it remains moist and no solution flows out when inverted, at which point the water content is 65%.

[0080] Comparative Example 9

[0081] The method for preparing magnetic biochar provided in this comparative example includes the following steps:

[0082] (1) After thoroughly cleaning, drying and grinding the peanut shells, sieve them with a sieve and take 45-60 mesh peanut shell powder as biomass.

[0083] (2) Take 100g of biomass, then add the biomass to 800mL of FeCl3 solution with a concentration of 1mol / L, and add 50g of calcium oxide at the same time, and stir for 24h.

[0084] Performance testing

[0085] 1. Removal rate test at different phosphorus concentrations

[0086] The phosphate adsorption performance of the magnetic biochar from Examples 1-4 and Comparative Examples 1-9 was tested, specifically as follows:

[0087] 100 ml of solutions (prepared with potassium dihydrogen phosphate) with initial phosphorus concentrations of 5 mg / L, 20 mg / L, 50 mg / L, 100 mg / L, and 200 mg / L were added to each conical flask, with 13 aliquots prepared for each concentration. Then, 0.5 g of magnetic biochar was added to each conical flask, and the mixture was stirred at room temperature for 180 min. The phosphorus concentration in the supernatant was then measured, and the adsorption results are shown in Table 1.

[0088] Table 1 shows the adsorption and removal rates of magnetic biochar in Examples 1-4 and Comparative Examples 1-9.

[0089]

[0090]

[0091] As shown in Table 1, with the increase of ferric chloride solution concentration, the removal rate of magnetic biochar at the same initial phosphorus concentration showed a trend of first increasing and then decreasing. Furthermore, with the increase of initial phosphorus concentration, the adsorption effect of comparative examples 5 and 6 on phosphorus was poor. Examples 1 and 2 had better adsorption performance, and examples 3 and 4 also had better adsorption performance.

[0092] 2. Removal rate test at different pH levels

[0093] Add 100 ml of an initial phosphorus concentration of 40 mg / L solution to each conical flask, and adjust the pH to 3, 5, 7, and 9 with NaOH or HCl. Prepare 13 samples for each pH. Then, add 0.5 g of magnetic biochar to each conical flask, stir at room temperature for 180 min, and measure the phosphorus concentration in the supernatant. The adsorption results are shown in Table 2.

[0094] Table 2 shows the adsorption and removal rates of magnetic biochar in Examples 1-4 and Comparative Examples 1-9.

[0095]

[0096] As shown in Table 2, as the initial pH increases, Examples 1-4 can achieve a removal efficiency of over 99%, indicating that the magnetic biochar has a good pH range and can effectively remove phosphorus under different environmental conditions.

[0097] In summary, the magnetic biochar of this disclosure has the following advantages compared to existing magnetic biochar:

[0098] 1) This magnetic biochar has a very wide pH range, meaning it can effectively remove phosphorus in various environments. Unlike traditional magnetic biochar, the biochar of this disclosure exhibits higher phosphorus removal performance in neutral and alkaline environments. This makes it more advantageous in treating phosphorus pollution in various wastewaters and sewages.

[0099] 2) The magnetic biochar of this embodiment greatly improves the adsorption capacity of biochar, and iron and calcium can be effectively loaded onto biochar, which not only improves the adsorption efficiency, but also reduces the waste of resources in the biochar modification process.

[0100] 3) This embodiment uses peanut shells as raw material, modified with ferric chloride and calcium oxide. Both the raw materials and the modifying substances are readily available, simplifying the process and reducing costs. This low-cost, high-efficiency preparation method is expected to promote the widespread application of magnetic biochar in wastewater treatment and environmental protection, providing a feasible solution.

[0101] 4) By optimizing the method, the water content of the modification solution was gradually reduced during the modification process of magnetic biochar, which effectively increased the loading of the modified material on the biochar, allowing the magnetic biochar to release a large amount of iron and calcium ions into the wastewater, thereby improving the phosphorus removal effect.

[0102] 5) The mass ratio of iron, calcium, and biomass used in the modification was optimized. This resulted in the modified magnetic biochar having both a high specific surface area and a high loading of modified materials. This helps to improve the phosphorus adsorption capacity and rate of the biochar.

[0103] 6) This magnetic biochar adsorbs phosphates in water to produce lapis lazuli, and its magnetic properties are used to recover and reuse phosphorus. The preparation method of magnetic biochar uses readily available raw materials and has a simple process, realizing waste-to-waste treatment and making it suitable for phosphorus recovery and reuse in wastewater.

[0104] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

[0105] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

Claims

1. A method for preparing magnetic biochar, comprising the step of mixing biomass with a FeCl3 solution to obtain a biomass-FeCl3 mixture, characterized in that: The preparation method further comprises the steps of dehydrating the biomass-FeCl3 mixture to a water content of 68-78%, and then adding calcium oxide to mix and expand, pressing, calcining, and crushing to obtain the magnetic biochar. The mass ratio of the biomass, FeCl3, and calcium oxide is 1:0.8-2.4:0.3-1.

2.

2. The method of claim 1, wherein: The particle size of the calcium oxide is 100-200 mesh; and / or, the step of adding calcium oxide is performed in an anaerobic operation box.

3. The method of claim 1, wherein: The mass ratio of the biomass, FeCl3, and calcium oxide is 1:1-2:0.4-1.

4. The method of claim 1, wherein: The concentration of the FeCl3 solution is 0.8-1.8 mol / L.

5. The method of claim 1, wherein: The dehydration is performed in an oven at a temperature of 90-120°C.

6. The method of claim 1, wherein: The particle size of the biomass is 40-70 mesh; and / or, the raw material of the biomass is peanut shell; and / or, the calcination temperature is 500-800°C.

7. The method of claim 1-6, wherein, The preparation method comprises the following steps: (1) drying, grinding, and sieving peanut shell to obtain 40-70 mesh peanut shell powder biomass; (2) adding the biomass to a FeCl3 solution, stirring for 20-30 h to obtain a biomass-FeCl3 mixture; (3) dehydrating the biomass-FeCl3 mixture in an oven to a water content of 68-78%, and stirring every 0.3-1 h; (4) cooling to room temperature, then adding calcium oxide powder, stirring to expand, pressing into blocks, calcining at a temperature of 500-800°C for 1.5-2.5 h, cooling, and crushing to obtain the magnetic biochar.

8. A magnetic biochar prepared by the preparation method of any one of claims 1-7.

9. The magnetic biochar of claim 8 for use in adsorbing phosphorus in wastewater, wherein the wastewater is acidic, neutral, or alkaline.

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