A modified biochar and a preparation method and application thereof

Abstract

The application discloses a novel modified biochar and a preparation method and application thereof, and preparation comprises the following steps: placing calcium-rich solid waste raw materials in a crusher for crushing treatment, fully mixing the biochar with the removed dissolved organic matter at a mass ratio of 1:(1-4), adding pure water at a mass-volume ratio of 1g:(60-100)mL, and adding diammonium hydrogen phosphate and ammonium dihydrogen phosphate at a calcium-phosphorus ratio of 1:(2.5-3.34); all raw materials are placed in a ball mill jar, the mass ratio of the raw materials to zirconia balls before ball milling is 1:(10-15), and ball milling is carried out at a rotating speed of 250-600 r / min for 6-12 h; the biochar slurry after ball milling is moved to a centrifuge tube, and centrifugation is carried out at a rotating speed of 5000 r / min for 10 min; the solid precipitate is washed with pure water for 3 times to remove excessive phosphate, and is placed in an oven for drying, so as to obtain the ball-milled novel modified biochar; the novel modified biochar has the advantages of simple synthesis method, low energy consumption, easy separation by using a centrifuge, and high adsorption performance on heavy metals.

Description

Technical Field

[0001] This invention belongs to the field of new material preparation technology, specifically relating to a novel modified biochar, its preparation method, and its application. Background Technology

[0002] Biochar has a rich porous structure with abundant oxygen-containing functional groups on its surface, enabling it to effectively adsorb cationic heavy metals through adsorption mechanisms such as complexation, electrostatic adsorption, and cation exchange. Using biochar to adsorb heavy metals is a common method; however, some biochars have limited adsorption capacity and, due to their small particle size and low density, remain in suspension, making separation difficult through centrifugation or filtration after adsorption. Therefore, biochar is often modified by loading to improve its adsorption performance and increase its density, enabling rapid separation.

[0003] Cadmium is a common harmful metallic element. Various industrial activities, such as dyeing, battery production, plastics processing, and chemical processing, inevitably discharge cadmium-containing wastewater. Due to cadmium's high mobility and strong bioaccumulation, it easily accumulates in ecosystems and poses a significant threat to human health. Adsorption, chemical precipitation, ion exchange, and membrane separation are commonly used methods to remove cadmium from wastewater. Adsorption is widely used due to its flexibility, high removal rate, and low operating cost. Selecting a suitable adsorbent is the most important factor determining adsorption efficiency.

[0004] In the prior art, CN119327857 A discloses a method for remediating cadmium-contaminated soil by intercropping water spinach with marigold and applying a passivating agent. HAP-modified biochar is prepared by reacting hydroxyapatite and biochar as a passivating agent. The passivating agent is first added to the cadmium-contaminated soil. The effective cadmium content of the soil is reduced by 34.52% to 40.13% when biochar is applied alone or HAP-modified biochar is applied alone.

[0005] Developing a modified biochar with high adsorption capacity for cadmium by utilizing common calcium-rich solid waste materials and agricultural biomass materials is of great significance. Summary of the Invention

[0006] To address at least one of the aforementioned problems, this invention provides a novel modified biochar, its preparation method, and its applications. This novel modified biochar not only has a simple synthesis method and saves thermal energy, but also can effectively adsorb cadmium from water.

[0007] To achieve the above objectives, the present invention employs the following technical means:

[0008] The first aspect of the present invention provides a novel method for preparing modified biochar, comprising the following steps:

[0009] (1) Place the calcium-rich solid waste raw material in a crusher and crush it until the particle size is less than 5 mm;

[0010] (2) After drying the crop straw powder in an oven at 60℃ for 3 h, pass it through a 60-mesh sieve. Place the sieved powder in a ceramic crucible, wrap it tightly with tin foil, and then put it into a muffle furnace for pyrolysis at 300-600℃ for 3 h. Take out the product and place it in pure water. Shake it at 30℃ and 200r / min for 24 h, then filter and dry it to obtain biochar with dissolved organic matter (DOM) removed.

[0011] (3) The crushed calcium-rich solid waste raw material in (1) is thoroughly mixed with biochar to remove dissolved organic matter (DOM), and pure water, diammonium hydrogen phosphate and diammonium dihydrogen phosphate are added to obtain the ball mill pre-processing raw material;

[0012] (4) Place the raw materials for ball milling in a ball mill jar for ball milling. After ball milling, a mixed slurry is obtained.

[0013] (5) Transfer the mixed slurry in (3) to a centrifuge tube for centrifugation. Wash the solid precipitate with pure water to remove excess phosphate, and dry it in an oven. Grind and sieve to obtain the new modified biochar.

[0014] In some preferred embodiments of the present invention, the pyrolysis temperature is 600°C.

[0015] In the embodiments of the present invention, the calcium carbonate-rich solid waste in step (1) includes, but is not limited to, solid waste with calcium carbonate as the main component, such as oyster shells, seashells, and eggshells.

[0016] In the embodiment of the present invention, in step (3), the mass ratio of calcium-rich solid waste raw material to biochar is 1:(1-2), the calcium-to-phosphorus ratio is 1:(2.50-3.34), and the mass-to-volume ratio of calcium-rich solid waste raw material to pure water is 1g:(60-100)mL. Excess phosphate ensures that calcium carbonate is completely converted into calcium hydrogen phosphate dihydrate (Brushite) mineral, which adheres to the surface of biochar.

[0017] In an embodiment of the present invention, the conditions for ball milling in step (4) are ball milling at a speed of 250-600 r / min for 6-12 hours, and the mass ratio of raw material to zirconia balls before ball milling is 1:(10-15).

[0018] In an embodiment of the present invention, the crop straw in step (2) is selected from one or a mixture of corn straw, wheat straw, rice straw, rapeseed straw, cotton straw, and sugarcane straw.

[0019] This invention provides a novel application of modified biochar in adsorbing heavy metal cadmium in water.

[0020] In an embodiment of the present invention, the mass-to-volume ratio of the novel modified biochar to the water polluted by heavy metal cadmium is 1:(1000-1500).

[0021] In some embodiments of the present invention, the pH value of the cadmium-polluted water is 2-7; the adsorption time is 15 min-24 h.

[0022] This invention provides an application of a novel modified biochar in the remediation of cadmium-contaminated soil.

[0023] In an embodiment of the present invention, the mass ratio of the novel modified biochar to cadmium-contaminated soil is (1-3):20, and the biochar is cultured in a greenhouse for 30-60 days.

[0024] Beneficial effects of the present invention

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] This invention utilizes the pyrolysis of agricultural and forestry solid waste to prepare primary biochar, employing ammonium dihydrogen phosphate and diammonium hydrogen phosphate as phosphorus sources, and shellfish and other solid waste as calcium sources. A novel modified biochar is prepared using ball milling with deionized water. This method simplifies the preparation process and reduces energy consumption. After ball milling to remove dissolved organic matter, the biochar undergoes modification. Ball milling increases the specific surface area of ​​the biochar, enriches its pore structure and surface charge, and enhances both physical and electrostatic adsorption. During ball milling, intermediate crystals CaHPO4·2H2O are formed on the surface and within the pores of the biochar. These intermediate crystals adhere to the biochar surface, increasing adsorption sites. CaHPO4·2H2O can effectively adsorb cadmium ions through mechanisms such as co-precipitation. The formation of these intermediate crystals alters the density of the biochar, allowing for easy centrifugation and facilitating its separation and recovery.

[0027] Biochar, as a porous carbon material, possesses a large specific surface area, pore volume, and abundant functional groups, exhibiting a high adsorption rate for the heavy metal Cd. Modification of biochar generates a new intermediate crystal, CaHPO4·2H2O, which effectively enhances the adsorption efficiency of biochar for Cd and improves the surface charge distribution, thus facilitating Cd adsorption. Both biochar and CaHPO4·2H2O are slightly alkaline; their combination promotes the conversion of free Cd ions into insoluble precipitates, thereby reducing the Cd content in the soil. Furthermore, the novel modified biochar can reduce the mobility and availability of Cd ions in the environment through surface complexation. Attached Figure Description

[0028] Figure 1 This is a comparison chart showing the Cd removal efficiency of the materials prepared in Examples 1-6 and Comparative Examples 1-2 of the present invention on water.

[0029] Figure 2 This is a comparison chart showing the Cd removal efficiency of the materials prepared in Examples 2-4 and Examples 7-8 of this invention on water.

[0030] Figure 3 The images shown are SEM images of the materials prepared in Comparative Examples 1-2, Examples 2 and 4, and Examples 7-8 of this invention.

[0031] Figure 4 The XRD patterns are of the materials prepared in Comparative Examples 1-2, Examples 2 and 4, and Examples 7-8 of this invention.

[0032] Figure 5 The adsorption capacity of the materials prepared in Comparative Examples 1-2, Examples 2 and 4, and Examples 7-8 of this invention for Cd at different pH values;

[0033] Figure 6 The following are Cd adsorption kinetic diagrams of the materials prepared in Comparative Examples 1-2, Examples 2 and 4, and Examples 7-8 of this invention for water.

[0034] Figure 7 The images shown are SEM-EDS analysis images of the material prepared in Example 8 of this invention after adsorbing Cd. The upper left image is the SEM image of the biochar prepared in Example 8 after adsorbing Cd; the upper right image is the EDS analysis image of the biochar after adsorbing Cd; the lower left image is the SEM image of the mineral particles loaded with Cd after the material obtained in Example 8 adsorbs Cd; and the lower right image is the EDS analysis image of the mineral particles loaded with Cd.

[0035] Figure 8 These are XRD comparison images of the materials prepared in Examples 6 and 8 of this invention before and after Cd adsorption.

[0036] Figure 9 This is an EDS analysis diagram of the hydroxyapatite prepared in Comparative Example 3 of this invention after adsorbing Cd.

[0037] Figure 10 This is a comparison chart showing the effect of the materials prepared in Comparative Examples 1-2, Example 2 and Example 4, and Example 7-8 of this invention on the available cadmium content in soil. Detailed Implementation

[0038] 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.

[0039] 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 and cited therein are incorporated herein by reference. Many equivalent techniques of specific embodiments of the invention described herein will be recognized or can be understood by ordinary experimentation by those skilled in the art. These equivalents will be included in the claims.

[0040] A novel method for preparing modified biochar includes the following steps:

[0041] (1) Place the calcium-rich solid waste raw material in a crusher and crush it until the particle size is less than 5 mm to obtain crushed calcium-rich solid waste raw material;

[0042] (2) Dry the crop straw powder in an oven at 60℃ for 2-3 h and then pass it through a 60-mesh sieve. Place the sieved powder in a ceramic crucible, wrap it tightly with tin foil, and put it into a muffle furnace for pyrolysis at 300-600℃ for 3 h. Take out the product and place it in pure water. Shake it at 25-30℃ and 200-300r / min for 20-24 h, then filter and dry it to obtain DOM-removed biochar.

[0043] (3) Mix the crushed calcium-rich solid waste raw material in (1) with the DOM-removed biochar in (2) at a mass ratio of 1:(1-4), and mix it with diammonium hydrogen phosphate and diammonium dihydrogen phosphate at a calcium-to-phosphorus ratio of 1:(2.50-3.34). The mass-to-volume ratio of the calcium-rich solid waste raw material to the added pure water is 1g:(60-100)mL to obtain the ball mill pre-processing raw material;

[0044] (4) Place the raw material for ball milling in (3) into a ball milling jar for ball milling treatment. The ball milling is carried out at a speed of 250-600 r / min for 6-12 h. The mass ratio of the raw material for ball milling to the zirconium oxide balls is 1:(10-15) to complete the ball milling and obtain a new type of modified biochar mixed slurry.

[0045] (5) Transfer the mixed slurry in (4) to a centrifuge tube for centrifugation. Wash the solid precipitate with pure water to remove excess phosphate, dry it in an oven, grind and sieve it to obtain a new type of modified biochar.

[0046] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the technical solutions of the present invention are further described below with reference to embodiments. However, the present invention is not limited to the listed embodiments, but should also include any other known modifications within the scope of the claims of the present invention.

[0047] The term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the invention. The phrase "in one embodiment" appearing in different places throughout this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0048] The technical solution of this patent will be further described in detail below with reference to specific embodiments.

[0049] Example 1

[0050] Oyster shells are placed in a crusher and crushed until the particle size is less than 5 mm to obtain crushed calcium-rich solid waste raw material.

[0051] Corn stalk powder was dried in an oven at 60°C for 3 hours and then passed through a 60-mesh sieve. The sieved powder was placed in a ceramic crucible, tightly wrapped in tin foil, and then placed in a muffle furnace for pyrolysis at 300°C for 3 hours to obtain biochar.

[0052] Place 1.25g of biochar in a ball mill jar, add 1.25g of shell powder, 3.5g of ammonium dihydrogen phosphate, and 3.5g of diammonium hydrogen phosphate, and pour in 100mL of deionized water to obtain the ball milling pre-processing material. The mass ratio of the ball milling pre-processing material to the zirconia balls is 1:12, and the ball milling conditions are 250r / min for 6h.

[0053] The ball-milled product was filtered, washed, and dried in an oven at 60°C. It was then passed through a 0.2 mm sieve to obtain modified biochar, denoted as HBC3-1.

[0054] Example 2

[0055] The seashells are placed in a crusher and crushed until the particle size is less than 5 mm to obtain crushed calcium-rich solid waste raw materials.

[0056] Rice straw powder was dried in an oven at 60°C for 3 hours and then passed through a 60-mesh sieve. The sieved powder was placed in a ceramic crucible, tightly wrapped in tin foil, and then placed in a muffle furnace for pyrolysis at 300°C for 3 hours to obtain biochar.

[0057] Place 2.5g of biochar in a ball mill jar, add 1.25g of shell powder, 3.5g of ammonium dihydrogen phosphate, and 3.5g of diammonium hydrogen phosphate, and pour in 100mL of deionized water. The mass ratio of raw material to zirconia balls is 1:12. The ball milling conditions are 250r / min for 6h.

[0058] The ball-milled product was filtered, washed, and dried in an oven at 60°C. It was then passed through a 0.2 mm sieve to obtain modified biochar, denoted as HBC3-2.

[0059] Example 3

[0060] Eggshells are placed in a crusher and crushed until the particle size is less than 5 mm to obtain crushed calcium-rich solid waste raw material.

[0061] Cotton stalk powder was dried in an oven at 60°C for 3 hours and then passed through a 60-mesh sieve. The sieved powder was placed in a ceramic crucible, tightly wrapped in tin foil, and then placed in a muffle furnace for pyrolysis at 300°C for 3 hours to obtain biochar.

[0062] Place 3.75g of biochar in a ball mill jar, add 1.25g of shell powder, 3.5g of ammonium dihydrogen phosphate and 3.5g of diammonium hydrogen phosphate, pour in 100mL of deionized water. The mass ratio of raw material to zirconia balls is 1:12. The ball milling conditions are 250r / min for 6h.

[0063] The ball-milled product was filtered, washed, and dried in an oven at 60°C. It was then passed through a 0.2 mm sieve to obtain modified biochar, denoted as HBC3-3.

[0064] Example 4

[0065] Oyster shells are placed in a crusher and crushed until the particle size is less than 5 mm to obtain crushed calcium-rich solid waste raw material.

[0066] Corn stalk powder was dried in an oven at 60°C for 3 hours and then passed through a 60-mesh sieve. The sieved powder was placed in a ceramic crucible, tightly wrapped in tin foil, and then placed in a muffle furnace for pyrolysis at 600°C for 3 hours to obtain biochar.

[0067] Place 1.25g of biochar in a ball mill jar, add 1.25g of shell powder, 3.5g of ammonium dihydrogen phosphate, and 3.5g of diammonium hydrogen phosphate, and pour in 100mL of deionized water. The mass ratio of raw material to zirconia balls is 1:12. The ball milling conditions are 250r / min for 6h.

[0068] The ball-milled product was filtered, washed, and dried in an oven at 60°C. It was then passed through a 0.2 mm sieve to obtain modified biochar, denoted as HBC6-1.

[0069] Example 5

[0070] The seashells are placed in a crusher and crushed until the particle size is less than 5 mm to obtain crushed calcium-rich solid waste raw materials.

[0071] Rice straw powder was dried in an oven at 60°C for 3 hours and then passed through a 60-mesh sieve. The sieved powder was placed in a ceramic crucible, tightly wrapped in tin foil, and then placed in a muffle furnace for pyrolysis at 600°C for 3 hours to obtain biochar.

[0072] Place 2.5g of biochar in a ball mill jar, add 1.25g of shell powder, 3.5g of ammonium dihydrogen phosphate, and 3.5g of diammonium hydrogen phosphate, and pour in 100mL of deionized water. The mass ratio of raw material to zirconia balls is 1:12. The ball milling conditions are 250r / min for 6h.

[0073] The ball-milled product was filtered, washed, and dried in an oven at 60°C. It was then passed through a 0.2 mm sieve to obtain modified biochar, denoted as HBC6-2.

[0074] Example 6

[0075] Eggshells are placed in a crusher and crushed until the particle size is less than 5 mm to obtain crushed calcium-rich solid waste raw material.

[0076] After drying cotton stalk powder in an oven at 60°C for 3 hours, the powder was passed through a 60-mesh sieve. The sieved powder was placed in a ceramic crucible, tightly wrapped in tin foil, and then placed in a muffle furnace for pyrolysis at 600°C for 3 hours to obtain biochar.

[0077] Place 3.75g of biochar in a ball mill jar, add 1.25g of shell powder, 3.5g of ammonium dihydrogen phosphate and 3.5g of diammonium hydrogen phosphate, pour in 100mL of deionized water. The mass ratio of raw material to zirconia balls is 1:12. The ball milling conditions are 250r / min for 6h.

[0078] The ball-milled product was filtered, washed, and dried in an oven at 60°C. It was then passed through a 0.2 mm sieve to obtain modified biochar, denoted as HBC6-3.

[0079] Comparative Example 1

[0080] After drying corn stalk powder in an oven at 60℃ for 3 hours, the powder was passed through a 60-mesh sieve. The sieved powder was placed in a ceramic crucible, wrapped tightly in tin foil, and placed in a muffle furnace for pyrolysis at 300℃ for 3 hours to obtain biochar BC3.

[0081] Comparative Example 2

[0082] After drying corn stalk powder in an oven at 60℃ for 3 hours, the powder was passed through a 60-mesh sieve. The sieved powder was placed in a ceramic crucible, wrapped tightly in tin foil, and placed in a muffle furnace for pyrolysis at 600℃ for 3 hours to obtain biochar BC6.

[0083] Example 7

[0084] The seashells are placed in a crusher and crushed until the particle size is less than 5 mm to obtain crushed calcium-rich solid waste raw materials.

[0085] Rice straw powder was dried in an oven at 60°C for 3 hours and then passed through a 60-mesh sieve. The sieved powder was placed in a ceramic crucible, tightly wrapped in tin foil, and then placed in a muffle furnace for pyrolysis at 300°C for 3 hours to obtain biochar.

[0086] Take 2.5g of biochar and put it into an Erlenmeyer flask. Add 100mL of deionized water and place it in a water bath constant temperature shaker. Shake at 200r / min for 2 days at 30℃. After filtration and drying, DOM-free biochar is obtained.

[0087] Place 2.5 g of DOM-free biochar in a ball mill jar, add 1.25 g of shell powder, 3.5 g of ammonium dihydrogen phosphate, and 3.5 g of diammonium hydrogen phosphate, and pour in 100 mL of deionized water. The mass ratio of raw material to zirconia balls is 1:12. The ball milling conditions are 250 r / min for 6 h.

[0088] The ball-milled product was filtered, washed, and dried in an oven at 60°C. It was then passed through a 0.2 mm sieve to obtain a novel DOM-free modified biochar, denoted as NDHBC3.

[0089] Example 8

[0090] Oyster shells are placed in a crusher and crushed until the particle size is less than 5 mm to obtain crushed calcium-rich solid waste raw material.

[0091] Corn stalk powder was dried in an oven at 60°C for 3 hours and then passed through a 60-mesh sieve. The sieved powder was placed in a ceramic crucible, tightly wrapped in tin foil, and then placed in a muffle furnace for pyrolysis at 600°C for 3 hours to obtain biochar.

[0092] Take 2.5 g of biochar and put it into an Erlenmeyer flask. Add 100 mL of deionized water and place it in a water bath constant temperature shaker. Shake at 200 r / min for 2 days at 30℃. After filtration and drying, DOM-free biochar is obtained.

[0093] Place 2.5g of DOM-free biochar in a ball mill jar, add 1.25g of shell powder, 3.5g of ammonium dihydrogen phosphate, and 3.5g of diammonium hydrogen phosphate, and pour in 100mL of deionized water. The mass ratio of raw material to zirconia balls is 1:12. The ball milling conditions are 250r / min for 6h.

[0094] The ball-milled product was filtered, washed, and dried in an oven at 60°C. It was then passed through a 0.2 mm sieve to obtain a novel DOM-free modified biochar, denoted as NDHBC6.

[0095] Comparative Example 3

[0096] Oyster shells are placed in a crusher and crushed until the particle size is less than 5 mm to obtain crushed calcium-rich solid waste raw material.

[0097] Take 1.25 g of shell powder, 3.5 g of ammonium dihydrogen phosphate and 3.5 g of diammonium hydrogen phosphate and place them in a ball mill jar. Pour in 100 mL of deionized water. The mass ratio of raw material to zirconia balls is 1:12. The ball milling conditions are 250 r / min and 6 h.

[0098] The ball-milled product was filtered, washed, and dried in an oven at 60°C to obtain hydroxyapatite.

[0099] (1) Pre-experiments on Cd adsorption were conducted on the materials prepared in Examples 1-6 and Comparative Examples 1-2 to determine the Cd removal efficiency, such as... Figure 1As shown.

[0100] Depend on Figure 1 It is evident that, compared to biochar BC, the novel modified biochar HBC significantly improves Cd removal efficiency. HBC3 and HBC6 show improvements of 21.26%-22.49% and 23.70-24.85%, respectively, with HBC6 exhibiting a significantly higher Cd removal efficiency than HBC3, improving by 20.72%-23.08%. The study found that different calcium-rich solid waste raw materials and different straw biochar formulation ratios did not significantly affect the novel modified biochar.

[0101] (2) Pre-experiments on Cd adsorption were conducted on the materials prepared in Examples 2-4 and 7-8 to determine the Cd removal efficiency, such as... Figure 2 As shown.

[0102] Depend on Figure 2 It is evident that NDHBC significantly improves Cd removal efficiency compared to HBC. NDHBC3 shows a 30.74% improvement over HBC3, while NDHBC6 shows a 7.37% improvement over HBC6. The study found that novel modified biochar prepared from biochar with DOM removal exhibits better Cd removal efficiency, with NDHBC3 showing a more significant improvement.

[0103] (3) The materials prepared in Comparative Examples 1 and 2, Examples 2 and 4, and Examples 7 and 8 were subjected to electron microscopy scanning, such as... Figure 3 As shown.

[0104] Depend on Figure 3 As can be seen, the surface morphology of the modified biochar HBC / NDHBC, compared with that of the BC biochar in the figure, shows that its surface and pores are covered with white substances, indicating that hydroxyapatite-like substances were successfully loaded onto the biochar during the modification process. Moreover, after ball milling modification, the specific surface area of ​​the biochar was effectively increased, enriching the pore structure and surface charge, increasing the loading sites of hydroxyapatite-like substances, and indirectly improving the adsorption performance.

[0105] (4) BET analysis was performed on the materials prepared in Comparative Examples 1 and 2, Examples 2 and 4, Examples 7 and 8 to obtain the specific surface area and pore structure parameters of biochar, as shown in Table 1.

[0106] As shown in Table 1, the specific surface area (SSA) of biochar continuously increases with increasing pyrolysis temperature. Furthermore, compared to the original biochar BC, the pore volume of the novel modified biochar NDHBC is increased, thus increasing the number of adsorption sites. In particular, NDHBC6, compared to BC6, shows an increase in pore volume without a significant change in specific surface area. Moreover, the material is modified with hydroxyapatite-like substances, greatly enhancing its adsorption potential for the heavy metal Cd.

[0107] Table 1. Specific surface area, pore volume, and pore size of biochar

[0108]

[0109] (5) XRD analysis was performed on the materials prepared in Comparative Examples 1 and 2, Examples 2 and 4, and Examples 7 and 8. The results are as follows: Figure 4 As shown.

[0110] Depend on Figure 4 It is evident that, compared to biochar, the presence of CaHPO4·2H2O on modified biochar indicates that intermediate crystals of CaHPO4·2H2O have been loaded onto the biochar.

[0111] (6) Batch adsorption experiments were conducted on the materials prepared in Comparative Examples 1 and 2, Examples 2 and 4, and Examples 7 and 8. The method was as follows: 0.03 g of biochar was placed in a 50 mL centrifuge tube, and a 50 mg / L Cd solution with a pH of 2-7 was added. The mixture was shaken at 30°C and 200 r / min for 24 h. After centrifugation and filtration, the Cd concentration was measured. Alternatively, 0.03 g of biochar and 30 mL of a 50 mg / L Cd solution with a pH of 6 were added to a 50 mL centrifuge tube. The mixture was shaken at 30°C and 200 r / min for 15 min-24 h. After centrifugation and filtration, the Cd concentration was measured. Results are shown in Table 2. Figure 5 and Figure 6 As shown.

[0112] Depend on Figure 5 It is evident that, compared to biochar, modified biochar exhibits better resistance to pH changes, and NDHBC shows better performance than HBC; as shown in Table 2, Figure 6 It is evident that, compared to biochar, the novel modified biochar exhibits significantly improved adsorption performance, and the adsorption capacity of NDHBC becomes more stable with prolonged adsorption time.

[0113] Table 2 Adsorption kinetic parameters of biochar

[0114]

[0115] (7) The material prepared in Example 8 was subjected to SEM-EDS analysis after adsorbing Cd, as shown in the results. Figure 7 As shown.

[0116] Depend on Figure 7 As shown in the top left and top right images, the weight percentage of Cd significantly increased by 2.51% after adsorption by the novel modified biochar, indicating successful Cd adsorption on the biochar surface. Figure 7 As shown in the lower left figure, the novel modified biochar exhibits a flower-like crystal structure after adsorbing Cd. Figure 7As shown in the lower right figure, Cd, P, and O elements account for a relatively large proportion of the weight in this crystal, at 29.82%, 6.41%, and 33.31%, respectively, while Ca accounts for a relatively small proportion, at 0.34%. This is because Ca atoms on the intermediate crystal CaHPO4·2H2O were replaced by Cd atoms, leading to the formation of the crystal.

[0117] (8) XRD analysis was performed on the materials prepared in Examples 4 and 8 before and after Cd adsorption, such as... Figure 8 As shown.

[0118] Depend on Figure 8 As can be seen, by comparing the XRD patterns of HBC6 / NDHBC6 before and after Cd adsorption, it can be observed that the peak intensity of CaHPO4·2H2O decreases, and Cd4P8O is present. 12 • 12H2O crystals are formed. This proves that after Cd is adsorbed by CaHPO4·2H2O, Ca ions are replaced, and new crystals are formed.

[0119] (9) The hydroxyapatite prepared in Comparative Example 3 was analyzed by X-ray energy dispersive spectroscopy (EDS) after adsorbing Cd. Figure 9 As shown.

[0120] Figure 9 The analysis of surface elemental composition of hydroxyapatite prepared by ball milling after Cd adsorption shows that the adsorption performance of cadmium dihydrate (brushite) in the novel modified biochar is significantly better than that of hydroxyapatite. The cadmium content on the surface of the mineral after cadmium adsorption by the novel modified biochar is 29.92%, while the cadmium content on the surface of hydroxyapatite prepared by ball milling is only 14.43%.

[0121] Will Figure 9 Results and Figure 7 The comparison of results in the lower right figure shows that hydroxyapatite's adsorption of Cd is weaker than that of the intermediate crystal CaHPO4·2H2O supported in the novel modified biochar of this application. Compared with biochar modified with hydroxyapatite, biochar modified with CaHPO4·2H2O exhibits superior adsorption performance for cadmium.

[0122] (10) Soil culture experiments were conducted on the samples prepared in Comparative Examples 1 and 2, Examples 2 and 4, Examples 7 and 8. The method was as follows: soil samples without biochar were cultured as the control group, and biochar prepared in Comparative Examples 1 and 2, Examples 2 and 4, Examples 7 and 8 were added as the experimental group.

[0123] At 25℃, 1g of biochar material was weighed into 50mL centrifuge tubes, along with 10g of cadmium-containing soil and 20mL of pure water. The centrifuge tubes were placed in a constant-temperature shaker and shaken at 200r / min for 2 hours. Afterward, they were placed in a constant-temperature incubator and cultured for 60 days. The concentration of available cadmium was determined by ICP-MS. The results are as follows: Figure 10 As shown.

[0124] Depend on Figure 10 As can be seen from the results, the novel modified biochar in the examples has a significant effect on improving the available cadmium in the soil. Compared with the control group (CK), the available cadmium content in the soil of the HBC treatment group decreased by 29.09%-34.81% mg / kg, while that of NDHBC decreased by 54.03%-55.06% mg / kg, with NDHBC showing the best effect.

[0125] 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 modified biochar for the adsorption of heavy metal cadmium, characterized in that, Includes the following steps: (1) Place the calcium-rich solid waste raw material in a crusher and crush it until the particle size is less than 5 mm; (2) Dry the crop straw powder and pass it through a 60-mesh sieve. Place the sieved powder in a muffle furnace and pyrolyze it at 300-600℃ for 3-4 h. Take out the product and place it in pure water. Shake it at 25-35℃ and 200-300r / min for 20-24 h, then filter and dry it to obtain biochar with dissolved organic matter removed. (3) Mix the crushed calcium-rich solid waste raw material in (1) with the biochar in (2) after removing dissolved organic matter, and add pure water, diammonium hydrogen phosphate and diammonium dihydrogen phosphate to obtain the ball mill pre-processing raw material; (4) Place the raw materials for ball milling in a ball mill jar for ball milling. After ball milling, a mixed slurry is obtained. (5) Transfer the mixed slurry in (4) to a centrifuge tube for centrifugation. Wash the solid precipitate with pure water to remove excess phosphate, dry it in an oven, grind and sieve it to obtain modified biochar. In step (3), the mass ratio of calcium-rich solid waste raw material to biochar for removing dissolved organic matter is 1:(1-4), the calcium-to-phosphorus ratio is 1:(2.50-3.34), and the mass-to-volume ratio of calcium-rich solid waste raw material to pure water is 1g:(60-100)mL; the calcium-rich solid waste raw material in step (1) includes shells, oyster shells and eggshells.

2. The method for preparing modified biochar for adsorption of heavy metal cadmium according to claim 1, characterized in that, The conditions for ball milling in step (4) are: ball milling at a speed of 250-600 r / min for 6-12 hours, and the mass ratio of raw material to zirconia balls before ball milling is 1:(10-15).

3. The method for preparing modified biochar for adsorption of heavy metal cadmium according to claim 1, characterized in that, In step (2), the crop straw is selected from one or more of the following: corn straw, wheat straw, rice straw, rapeseed straw, cotton straw, and sugarcane straw.

4. A modified biochar prepared by the method according to any one of claims 1-3.

5. The application of the modified biochar according to claim 4 in the adsorption of heavy metal cadmium in water.

6. The application according to claim 5, characterized in that: The mass-to-volume ratio of modified biochar to cadmium-contaminated water is 1:(1000-1500); the pH value of cadmium-contaminated water is 2-7.

7. The application of the modified biochar according to claim 4 in the stabilization of heavy metal cadmium in soil.

8. The application according to claim 7, characterized in that: The weight ratio of the modified biochar to the soil is (1-3):20.

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