Modified porous biochar material, preparation method thereof, adsorbent and application of adsorbent

Abstract

The invention discloses a modified porous biochar material, a preparation method thereof, an adsorbent and application of the adsorbent, and belongs to the technical field of environmental protection. The modified porous biochar material comprises porous biochar, and nano La (OH) 3 particles are loaded on the surface and in pores of the porous biochar; the average particle size of the porous biochar is 100-2000 [mu] m, the average pore size is 2-5 nm, the pore volume is 0.05-0.28 cm < 3 > / g, the ratio of the micropore volume to the pore volume is not less than 75%, and the specific surface area is 150-450 m < 2 > / g; the mass ratio of the La element to the porous biochar in the nano La (OH) 3 particles is (0.05-0.5): 1. The method provided by the invention can realize effective and efficient adsorption of phosphorus element in sewage.

Description

Technical Field

[0001] The present invention relates to a modified porous biochar material, a preparation method thereof, an adsorbent and an application of the adsorbent, and belongs to the technical field of environmental protection. Background Art

[0002] Nitrogen and phosphorus are essential elements for all living things, but they are also the primary culprits of water eutrophication. Therefore, controlling nitrogen and phosphorus emissions is crucial for preventing and controlling eutrophication. Compared to nitrogen, phosphorus emissions have limited control options, are more difficult, and are more expensive. Therefore, finding a cost-effective and efficient way to remove phosphorus has become a pressing challenge for the industry.

[0003] Research has found that wetlands are crucial for the balance and restoration of lake ecosystems. Wetlands can effectively improve the quality of sewage treatment plant effluent and intercept non-point source pollution from surface runoff, with wetland plants playing a key role in this process. However, pollutants absorbed by wetland plants after decay can be released back into the water, causing secondary pollution. Regular harvesting of wetland plants in constructed wetlands is crucial to prevent pollutant backflow and improve purification efficiency. However, their high moisture content, low calorific value, and high volatility significantly limit their further application. To overcome these limitations, developing suitable wetland plant resource utilization technologies is an urgent task. In recent years, researchers have used wetland plants to produce biochar. This low-cost, highly effective adsorption material has been widely used for the adsorption of heavy metals and organic impurities, but its physical and chemical properties limit its ability to adsorb phosphates. How to effectively and efficiently adsorb phosphorus using biochar, a low-cost adsorbent, has become a new research topic. Summary of the Invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present invention proposes a modified porous biochar material, a preparation method thereof, an adsorbent and an application of the adsorbent, which can achieve effective and efficient adsorption of phosphorus in sewage.

[0005] The first aspect of the present invention relates to a modified porous biochar material, comprising porous biochar, wherein the porous biochar is loaded with nano-La(OH)3 particles on the surface and in the pores;

[0006] The porous biochar has an average particle size of 100 to 2000 μm, an average pore size of 2 to 5 nm, and a pore volume of 0.05 to 0.28 cm 3 / g, the ratio of micropore volume to pore volume is not less than 75%, and the specific surface area is 150~450m 2 / g;

[0007] The mass ratio of La element in the nano La(OH)3 particles to porous biochar is 0.05-0.5:1.

[0008] Preferably, the average particle size of the porous biochar is 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm, 1000 μm, 1100 μm, 1200 μm, 1300 μm, 1400 μm, 1500 μm, 1600 μm, 1700 μm, 1800 μm, 1900 μm, 2000 μm, etc.

[0009] Preferably, the average pore size of the porous biochar can be 2 nm, 3 nm, 4 nm, 5 nm, etc.;

[0010] Preferably, the pore volume of the porous biochar can be 0.05 cm 3 / g, 0.08cm 3 / g, 0.10cm 3 / g, 0.14cm 3 / g, 0.15cm 3 / g, 0.17cm 3 / g, 0.19cm 3 / g, 0.22cm 3 / g, 0.25cm 3 / g, 0.26cm 3 / g, 0.28cm 3 / g etc.;

[0011] Preferably, the specific surface area of ​​the porous biochar is 150 m 2 / g, 200m 2 / g, 250m 2 / g、300m 2 / g、350m 2 / g, 400m 2 / g, 450m 2 / g, etc.

[0012] Preferably, the mass ratio of La element to porous biochar can be 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.10:1, 0.20:1, 0.30:1, 0.40:1, 0.50:1, etc.

[0013] The second aspect of the present invention relates to a method for preparing a modified porous biochar material, comprising the following steps:

[0014] S1, selecting clean and dry wetland plants, heating them to 700-800°C in an inert gas atmosphere such as nitrogen, then keeping the temperature for 1-2 hours for pyrolysis treatment, then cooling, and finally sieving to obtain a porous biochar material with an average particle size of 100-2000 μm;

[0015] S2, weighing a soluble lanthanum salt according to a mass ratio of La element to porous biochar material of 0.05 to 0.5:1, and mixing the soluble lanthanum salt with the porous biochar material in deionized water to obtain a mixed solution, wherein the lanthanum ions in the mixed solution are adsorbed by the porous biochar material;

[0016] S3, adding alkaline solution to the mixed solution, adjusting the pH value, until the adsorbed lanthanum ions are completely reacted to form La(OH)3, and then letting it stand for a period of time and filtering it out;

[0017] S4, washing and drying the filtrate obtained by the treatment in step S3 to obtain a modified porous biochar material.

[0018] In some specific embodiments, the wetland plants are pretreated to achieve a clean and dry state to prevent the introduction of impurities such as soil that could affect the synthesis and purity of the porous biochar material. Pretreatment includes at least washing and drying the wetland plants to a constant weight. Preferably, the pretreatment also includes dividing or pulverizing the large-sized raw materials into smaller ones.

[0019] For some specific embodiments, heating is performed at a heating rate of 10 to 15°C / min in step S1. Preferably, the heating temperature in step S1 can be 700°C, 710°C, 720°C, 730°C, 740°C, 750°C, 760°C, 770°C, 780°C, 790°C, 800°C, etc.; the holding time can be 1 hour, 1.2 hours, 1.5 hours, 2 hours, etc., and the heating rate can be 10°C / min, 11°C / min, 12°C / min, 13°C / min, 14°C / min, 15°C / min, etc.

[0020] In some specific embodiments, the soluble lanthanum salt in step S2 includes at least one of lanthanum nitrate, lanthanum carbonate, and lanthanum chloride.

[0021] In some specific embodiments, the alkaline solution in step S3 is an inorganic strong base solution, including at least one of potassium hydroxide and sodium hydroxide. Preferably, the pH value in step S3 is adjusted to not less than 11. For example, the pH value is adjusted to 11.0, 11.1, 11.2, 11.3, 11.4, 11.5, 11.6, 11.7, 11.8, 11.9, 12.0, 12.1, etc.

[0022] In some specific embodiments, the aging time in step S3 is 12 to 24 hours, for example, the aging time is 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours, 21 hours, 22 hours, 23 hours, 24 hours, etc.

[0023] For some specific implementation schemes, the cleaning treatment in step S4 is ultrapure water cleaning until the pH value is close to neutral, such as pH 7 to 8; by cleaning, impurity ions are removed to avoid affecting the adsorption effect of the modified porous biochar material.

[0024] In some specific embodiments, the drying treatment in step S4 is carried out by holding at 60-85°C for 8-24 hours. For example, the drying temperature is 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, etc., and the holding time is 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, 24 hours, etc.

[0025] The third aspect of the present invention relates to an adsorbent, which includes the above-mentioned modified porous biochar material.

[0026] The fourth aspect of the present invention relates to the use of the above-mentioned adsorbent in treating wastewater containing phosphate ions.

[0027] Compared with the prior art, the present invention has the following technical effects:

[0028] 1) This method provides a simple and easy method for the resource utilization of wetland plants, which has the advantages of simple operation, low cost, and wide applicability. By converting wetland plants into modified biochar and applying it to wastewater adsorption, it not only avoids the secondary pollution caused by the re-release of pollutants absorbed by the wetland plants after decay into the water body, but also effectively removes phosphates from the water body, achieving the goal of "waste treatment with waste, and green circular development";

[0029] 2) A porous biochar material with large pore volume and ultra-high specific surface area was prepared through a pyrolysis process. Lanthanum modification was then achieved through a specific modification process. This overcomes the defects of most biochars, such as negative surface charge, low anion exchange capacity, and insufficient effective functional groups. The surface functional groups, pore structure, and charge characteristics of the biochar were significantly improved, thereby significantly enhancing its phosphate adsorption capacity and making it more efficient and stable in phosphorus removal.

[0030] 3) Lanthanum-modified biochar has good pH adaptability and exhibits excellent adsorption performance for medium and low concentration phosphate solutions (≤20 mg / L). It can be widely used in the treatment of lakes, rivers, sewage treatment plant tail water and agricultural non-point source pollution, and can be applied to various water environment treatment needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Phosphate adsorption performance of biochars from Canna (a), Lotus pod (b), Phragmites australis (c) and Phragmites australis (d) at different carbonization temperatures;

[0032] Figure 2 These are the breakthrough curves of phosphate adsorption on lanthanum-modified canna biochar and lanthanum-modified lotus shell biochar packing beds;

[0033] Figure 3 The changes in adsorption capacity of lanthanum-modified canna biochar and lanthanum-modified lotus shell biochar at different reaction times;

[0034] Figure 4 The adsorption capacity changes of lanthanum-modified canna biochar and lanthanum-modified lotus shell biochar under different phosphate concentrations;

[0035] Figure 5 Effects of lanthanum-modified canna biochar (a) and lanthanum-modified lotus shell biochar (b) on phosphate adsorption performance under different pH conditions. DETAILED DESCRIPTION

[0036] The present invention will be described in detail below in conjunction with specific embodiments. Experimental methods without specific conditions specified in the examples were carried out according to conventional methods and conditions.

[0037] Example 1

[0038] Raw material selection

[0039] Wetland plants including Phragmites australis, Phragmites australis, Canna indica, and lotus pods without lotus seeds were selected as raw materials. After removing the leaves, the materials were cleaned, cut into 4-6 cm long segments, and dried at 80°C to constant weight. The dried raw materials were placed in a tube furnace, evacuated, and then purged with nitrogen. Under a nitrogen atmosphere (flow rate of 100 mL / min), the materials were heated at a heating rate of 10°C / min to the target carbonization temperatures (300°C, 400°C, 500°C, 600°C, 700°C, and 800°C). The temperature was maintained at the target carbonization temperature for 1 hour to complete the pyrolysis process. After the pyrolysis process, the resulting material was cooled to room temperature in the furnace, removed, crushed, and passed through a 35-mesh sieve to obtain wetland plant biochar samples prepared under different carbonization temperature conditions.

[0040] Static adsorption experimental screening

[0041] Batch phosphate adsorption experiments were conducted on the prepared biochar samples: 0.1000g of biochar was weighed into a 500mL reagent bottle, and 30mL of a KH2PO4 solution with an initial concentration of 20mg / L was added. The adsorption reaction was allowed to proceed at 25°C and 150rpm for 24 hours. After the reaction, the solution was filtered through a 0.45μm filter membrane, and the residual phosphate concentration was measured. The phosphate removal rate and adsorption capacity were calculated. The specific surface area, pore size, and micropore volume of the prepared biochar samples were also measured. The specific surface area was determined using the BET method, the pore size distribution was determined using the BJH method, and the micropore volume was determined using the T-Plot method.

[0042] The results are as follows Figure 1As shown in Table 1, the canna biochar and lotus biochar prepared at 800℃ carbonization conditions have larger specific surface areas of 193.1461m² / g and 429.5571m² / g, respectively, and the phosphate removal rates are 15.04% and 25.75%, respectively, which are significantly better than those of reed biochar and canna biochar. In view of this, the canna biochar and lotus biochar prepared at 800℃ carbonization conditions were further modified with lanthanum.

[0043] Table 1 Comparison of biochar properties

[0044] Lanthanum modification

[0045] A certain amount of each of the canna biochar and lotus pod biochar prepared at 800°C was weighed and placed in a 250 mL Erlenmeyer flask. A corresponding amount of La(NO₃)₃·6H₂O was dissolved in ultrapure water at a biochar to lanthanum mass ratio of 1:0.2 and slowly added to the biochar-containing flask. The mixture was stirred under magnetic stirring for 4 hours. After the reaction, 0.1 mol / L sodium hydroxide solution was added dropwise to adjust the pH to 11.5, and the mixture was allowed to age for another 24 hours. After aging, the modified biochar was repeatedly washed with ultrapure water until the filtrate reached a near-neutral pH. Finally, the filtrate was dried at 80°C for 24 hours to obtain lanthanum-modified canna biochar and lanthanum-modified lotus pod biochar, respectively.

[0046] After preparation, the adsorption performance was tested using a 20 mg / L phosphate solution. The specific method was as follows: 0.1000 g of modified biochar was weighed into a 500 mL reagent bottle, 30 mL of KH2PO4 solution was added, and the mixture was shaken at 25°C and 150 rpm for 24 hours to allow for adsorption reaction. After the reaction, the mixture was filtered through a 0.45 μm filter membrane, and the phosphate concentration in the filtrate was determined using ammonium molybdate spectrophotometry to calculate the removal rate and adsorption capacity. The adsorption test results showed that after lanthanum modification, the phosphate removal rates of both canna biochar and lotus biochar exceeded 99%, and the adsorption capacities increased to 11.15 mg / g and 12.27 mg / g, respectively, which were significantly better than those of unmodified biochar.

[0047] Dynamic adsorption experiment

[0048] The limitations of static adsorption make it difficult to meet the requirements of wastewater treatment in real-world production. However, fixed-bed dynamic adsorption is a more common method that can ensure efficient treatment and continuous effluent, which is of great significance for measuring the potential application value of adsorbents. Therefore, dynamic adsorption experiments using modified biochar adsorbents were conducted in a fixed-bed experimental apparatus to test the adsorption effect.

[0049] The fixed-bed experimental apparatus consists of an inlet tank, a dynamic pump, a packing column, and an outlet tank. The packing column is constructed of polyethylene tubing with an inner diameter of 1.1 cm. Glass beads are placed at each end of the packing column to prevent the adsorbent from escaping with the water flow, which could result in adsorbent loss. This experiment utilizes a bottom-in, top-out method to ensure sufficient contact between the solution and the packing. The treatment process involves pumping the phosphorus-containing solution to be treated into the packing column from the bottom via a dynamic pump. After sufficient contact with the adsorbent in the packing column, the solution flows through an outlet pipe connected to the top of the packing column into the outlet tank, completing the dynamic adsorption process.

[0050] The specific implementation process is as follows: 1.000g of lanthanum-modified canna biochar and lanthanum-modified lotus shell biochar were accurately weighed and loaded into the adsorption column, and the adsorbent height was accurately measured. A KH2PO4 solution with a concentration of 0.5mg / L (Class A discharge standard for urban sewage treatment plants) was added to the inlet tank. The peristaltic pump speed was adjusted to 1.8rpm (3mL / min), corresponding to a hydraulic retention time of 80s. The column was filled with water in a bottom-in, top-out manner, and after sufficient contact with the adsorbent, it flowed into the outlet tank. The phosphate content in the effluent was measured every three hours. The breakthrough and exhaust points of the packing column were set at 5% and 95%, respectively.

[0051] The experimental results show that both lanthanum-modified canna biochar and lanthanum-modified lotus shell biochar have good potential application value.

[0052] The effluent quality of the lanthanum-modified Canna biochar was always maintained in a low concentration range (<0.047 mg / L) in the first 99 hours. The removal rate was stable and approached 100% (below the national standard detection limit) in the initial operation of the device (the first 27 hours). In the subsequent operation process, the removal rate of the device gradually decreased and reached the exhaustion point of the adsorbent at 165 hours. Figure 2 When the lanthanum-modified Canna biochar reached the exhaustion point, a total of 29.70 L of phosphate solution was processed, 11.11 mg of phosphate was removed, the adsorption capacity of the adsorbent was 11110 mg / kg, and the total removal rate of the fixed packing bed could reach 74.81%.

[0053] Lanthanum-modified lotus shell biochar maintained a low effluent concentration (<0.01 mg / L) in the first 21 hours and crossed the breakthrough point at 27 hours, with a corresponding removal rate of 93%. The removal rate gradually decreased in the subsequent 81 hours and reached the exhaustion point at 108 hours. Figure 2 At this time, the lanthanum-modified lotus shell biochar treated 19.44 L of phosphorus-containing solution, removing a total of 5.41 mg of phosphate, with an adsorption capacity of 5410 mg / kg and a total removal rate of 55.66%.

[0054] Adsorption equilibrium time determination

[0055] Next, static phosphate adsorption experiments were conducted to determine the adsorption equilibrium time of lanthanum-modified canna biochar and lanthanum-modified lotus shell biochar. Specifically, 0.1000 g of lanthanum-modified canna biochar and 0.1000 g of lanthanum-modified lotus shell biochar were weighed and added to their respective 500 mL reagent bottles. 30 mL of KH2PO4 solution with an initial phosphate concentration of 20 mg / L was then added to each. The bottles were placed in a thermostatic oscillator at 25°C and 150 rpm. Samples were taken periodically after different reaction times (0.25, 0.5, 1, 2, 4, 8, 12, and 24 h), filtered through a 0.45 μm filter membrane, and the phosphate concentration in the filtrate was determined using ammonium molybdate spectrophotometry. Adsorption time curves were plotted based on the changes in phosphorus concentration to determine the adsorption equilibrium time.

[0056] The experimental results showed that the lanthanum-modified canna biochar and lanthanum-modified lotus shell biochar maintained a high adsorption rate in the first 4 hours. Figure 3 As shown in the figure, the lanthanum-modified canna biochar and the lanthanum-modified lotus shell biochar reached adsorption equilibrium at 8 h and 4 h, respectively.

[0057] Determination of maximum phosphate adsorption capacity

[0058] Next, batch adsorption experiments were conducted using phosphate solutions with initial concentrations ranging from 5 to 500 mg / L. Specifically, 0.1000 g of lanthanum-modified canna biochar and 0.1000 g of lanthanum-modified lotus shell biochar were weighed and added to their respective 500 mL reagent bottles. Phosphate solutions were prepared with initial concentrations of 5, 10, 20, 50, 100, 150, 300, and 500 mg / L. For each adsorption experiment, 30 mL of KH2PO4 solution of the corresponding concentration was added, and adsorption was allowed to proceed at 25°C and 150 rpm for 24 hours. After adsorption, the solution was filtered through a 0.45 μm filter, and the residual phosphate concentration in the solution was determined.

[0059] like Figure 4 As shown in the experimental results, the adsorption capacity of biochar modified with lanthanum was significantly improved. The maximum adsorption of lanthanum-modified canna biochar and lanthanum-modified lotus shell biochar was 37.37 mg / g and 37.89 mg / g, respectively. Lanthanum-modified canna biochar also demonstrated excellent adsorption performance under low and medium concentration conditions (P ≤ 50 mg / L), with phosphate removal rates exceeding 99%. Lanthanum-modified lotus shell biochar maintained a removal rate of over 99% in solutions with P ≤ 20 mg / L.

[0060] Adaptability evaluation

[0061] Finally, the pH adaptability of the modified biochar was evaluated. Phosphate solutions with different initial pH values ​​were prepared to examine the phosphate removal efficiency of the modified biochar under different pH conditions. Specifically, 0.1000 g of lanthanum-modified canna biochar and 0.1000 g of lanthanum-modified lotus shell biochar were added to their respective reagent bottles (500 mL) and divided into nine groups. KH2PO4 solutions with different pH values ​​(2, 3, 4, 5, 6, 7, 8, 9, and 10) were added to each group, with an initial phosphate concentration of 20 mg / L. The solution was adsorbed at 25°C and 150 rpm for 24 hours. After adsorption, the solution was filtered through a 0.45 μm filter membrane, and the residual phosphate concentration in the solution was determined. KH2PO4 solutions with different pH values ​​were adjusted using 0.1 mol / L HCl and 0.1 mol / L NaOH solutions.

[0062] like Figure 5 As shown, the experimental results show that the two lanthanum-modified biochars have a wide pH adaptability, and both maintain high adsorption performance between pH 3 and 9, with removal rates above 99%, which can meet the pH treatment conditions of most phosphorus-containing water bodies.

[0063] It should be emphasized that the above are only preferred embodiments of the present invention and do not limit the present invention in any form. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A modified porous biochar material, characterized in that: The porous biochar comprises nano-La(OH)3 particles loaded on the surface and in the pores of the porous biochar; The porous biochar has an average particle size of 100 to 2000 μm, an average pore size of 2 to 5 nm, and a pore volume of 0.05 to 0.28 cm 3 / g, the ratio of micropore volume to pore volume is not less than 75%, and the specific surface area is 150~450m 2 / g; The mass ratio of La element in the nano La(OH)3 particles to porous biochar is 0.05-0.5:

1.

2. A method for preparing a modified porous biochar material, characterized in that: The following steps are involved: S1, selecting clean and dry wetland plants, heating them to 700-800°C in an inert gas atmosphere, keeping the temperature for 1-2 hours for pyrolysis treatment, then cooling them, and finally sieving them to obtain porous biochar materials with an average particle size of 100-2000 μm; S2, weighing a soluble lanthanum salt according to a mass ratio of La element to porous biochar material of 0.05 to 0.5:1, and mixing the soluble lanthanum salt with the porous biochar material in water to obtain a mixed solution, wherein the lanthanum ions in the mixed solution are adsorbed by the porous biochar material; S3, adding alkaline solution to the mixed solution, adjusting the pH value, until the adsorbed lanthanum ions are completely reacted to form La(OH)3, and then letting it stand for a period of time and filtering it out; S4, washing and drying the filtrate obtained by the treatment in step S3 to obtain a modified porous biochar material; The modified porous biochar material comprises porous biochar, and the porous biochar is loaded with nano La(OH)3 particles on the surface and in the pores; The porous biochar has an average particle size of 100 to 2000 μm, an average pore size of 2 to 5 nm, and a pore volume of 0.05 to 0.28 cm 3 / g, the ratio of micropore volume to pore volume is not less than 75%, and the specific surface area is 150~450m 2 / g.

3. The preparation method according to claim 2, characterized in that The wetland plants are pretreated, which at least includes washing and drying. The dried wetland plants are in a constant weight state.

4. The preparation method according to claim 3, characterized in that The pretreatment also includes segmentation and / or pulverization.

5. The preparation method according to claim 2, characterized in that In step S1, heating is performed at a heating rate of 10 to 15°C / min.

6. The preparation method according to claim 2, characterized in that The soluble lanthanum salt in step S2 includes at least one of lanthanum nitrate, lanthanum carbonate, and lanthanum chloride.

7. The preparation method according to claim 2, characterized in that The alkaline solution in step S3 is an inorganic strong base solution, including at least one of potassium hydroxide and sodium hydroxide; Preferably, the pH value in step S3 is not less than 11 after adjustment; Preferably, the aging time in step S3 is 12 to 24 hours.

8. The preparation method according to claim 2, characterized in that In step S4, the cleaning process is washing with ultrapure water until the pH value is 7 to 8; the drying process is heat preservation at 60 to 85° C. for 8 to 24 hours.

9. An adsorbent, characterized in that The adsorbent includes the modified porous biochar material according to claim 1.

10. Use of the adsorbent according to claim 9 in treating wastewater containing phosphate ions.

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