Novel modified biochar as well as preparation method and application thereof

Abstract

The invention discloses novel modified biochar and a preparation method and application thereof.The preparation method comprises the following steps that calcium-rich solid waste raw materials are placed in a crusher to be crushed and fully mixed with biochar with dissolved organic matter removed according to the mass ratio of 1: (1-4); adding pure water with the mass volume ratio of 1g: (60-100) mL, diammonium hydrogen phosphate with the calcium-phosphorus ratio of 1: (2.5-3.34) and ammonium dihydrogen phosphate with the calcium-phosphorus ratio of 1: (2.5-3.34); all the raw materials are placed in a ball milling tank, the mass ratio of the raw materials to zirconium oxide balls before ball milling is 1: (10-15), and ball milling is conducted for 6-12 h at the rotating speed of 250-600 r / min; transferring the biochar slurry subjected to ball milling into a centrifugal tube, and centrifuging for 10 minutes at the rotating speed of 5000 r / min; the solid precipitate is washed with pure water three times to remove excessive phosphate, the solid precipitate is placed in a drying oven to be dried, and the novel ball-milled modified biochar is obtained, the novel modified biochar is simple in synthesis method and low in energy consumption, can be easily separated through a centrifugal machine and has high adsorption performance on heavy metal.

Description

Technical Field

[0001] The present invention belongs to the technical field of new material preparation, and particularly relates to a novel modified biochar and its preparation method and application. Background Art

[0002] Biochar has a rich pore structure on its surface and is rich in oxygen-containing functional groups. It can 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, but the adsorption performance of some biochars is limited, and due to their too small particle size and light density, they are in a suspended state and are not easily separated by centrifugation or filtration after adsorption. Usually, people modify biochar and improve its adsorption performance and increase its density by loading to enable rapid separation.

[0003] Cadmium is a common harmful metal element. In various industrial activities such as printing and dyeing, battery production, plastic processing, and chemical engineering, the inevitable discharge of cadmium-containing wastewater. Due to the high mobility and strong bioaccumulation of cadmium, it is easily accumulated in the ecosystem and poses a great threat to human life and health. Methods such as adsorption, chemical precipitation, ion exchange, and membrane separation are commonly used to remove cadmium from wastewater, and the adsorption method is widely used due to its flexibility, high removal rate, and low operating cost. Selecting a suitable adsorbent is the most important factor determining the adsorption efficiency.

[0004] In the prior art, CN119327857 A discloses a method for repairing cadmium-polluted soil by intercropping water spinach with marigold and applying a passivator. HAP-modified biochar prepared by reacting hydroxyapatite and biochar is used as a passivator. First, the passivator is added to cadmium-polluted soil, and the effective cadmium content in the soil treated with biochar and HAP-modified biochar alone is reduced by 34.52% - 40.13%.

[0005] It is of great significance to develop a modified biochar with high adsorption capacity for cadmium using common calcium-rich solid waste raw materials and crop biomass raw materials in life. Summary of the Invention

[0006] In order to solve at least one of the above problems, the present invention provides a novel modified biochar and its preparation method and application. This novel modified biochar not only has a simple synthesis method and saves heat energy, but also can effectively adsorb cadmium in water.

[0007] In order to achieve the above object, the present invention adopts the following technical means: The first aspect of the present invention provides a preparation method of a novel modified biochar, comprising the following steps: (1) Place the calcium-rich solid waste raw material in a crusher and crush it to a particle size less than 5 mm; (2) The crop straw powder is dried in an oven at 60 °C for 3 h and then sieved through a 60-mesh sieve. The sieved powder is placed in a ceramic crucible, tightly wrapped with tin foil, and then put into a muffle furnace for pyrolysis at 300 - 600 °C for 3 h. The product is taken out and placed in pure water, shaken at 30 °C and 200 r / min for 24 h, and then filtered and dried to obtain biochar with dissolved organic matter (DOM) removed. (3) The crushed calcium-rich solid waste raw material in (1) is fully mixed with the biochar with dissolved organic matter (DOM) removed, and pure water, diammonium hydrogen phosphate, and ammonium dihydrogen phosphate are added to obtain the raw material before ball milling. (4) The raw material before ball milling is placed in a ball mill tank for ball milling treatment, and a mixed slurry is obtained after ball milling is completed. (5) The mixed slurry in (3) is transferred to a centrifuge tube for centrifugation. The solid precipitate is washed with pure water to remove excess phosphate, placed in an oven for drying, ground and sieved to obtain the novel modified biochar.

[0008] In some preferred embodiments of the present invention, the pyrolysis temperature is 600 °C.

[0009] In the embodiments of the present invention, the calcium carbonate-rich solid waste in step (1) includes but is not limited to solid wastes mainly composed of calcium carbonate such as oyster shells, shells, and eggshells.

[0010] In the embodiments of the present invention, the mixing mass ratio of the calcium-rich solid waste raw material to the biochar in step (3) is 1:(1 - 2), the calcium-phosphorus ratio is 1:(2.50 - 3.34), and the mass-volume ratio of the calcium-rich solid waste raw material to pure water is 1 g:(60 - 100) mL. Excess phosphate can ensure that calcium carbonate completely reacts to form brushite minerals attached to the surface of the biochar.

[0011] In the embodiments of the present invention, the conditions for the ball milling treatment in step (4) are ball milling at a rotation speed of 250 - 600 r / min for 6 - 12 h, and the mass ratio of the raw material before ball milling to the zirconia balls is 1:(10 - 15).

[0012] In the embodiments of the present invention, the crop straw in step (2) is selected from one or more mixtures of corn straw, wheat straw, rice straw, rapeseed straw, cotton straw, and sugarcane straw.

[0013] The present invention provides an application of a novel modified biochar in adsorbing heavy metal cadmium in water bodies.

[0014] In the embodiments of the present invention, the mass-volume ratio of the novel modified biochar to the heavy metal cadmium-polluted water body is 1:(1000 - 1500).

[0015] In some embodiments of the present invention, the pH value of the cadmium-polluted water body is 2 - 7; the adsorption time is 15 min - 24 h.

[0016] The present invention provides an application of a novel modified biochar in the remediation of cadmium-polluted soil.

[0017] In the embodiments of the present invention, the mass ratio of the novel modified biochar to the cadmium-polluted soil is (1 - 3):20, and it is cultured under greenhouse conditions for 30 - 60 d.

[0018] Advantages of the present invention Compared with the prior art, the present invention has the following advantages: The present invention prepares the original biochar by pyrolyzing agricultural and forestry solid wastes, uses ammonium dihydrogen phosphate and diammonium hydrogen phosphate as phosphorus sources, and solid wastes such as shells as calcium sources, and combines deionized water to prepare the novel modified biochar by ball milling. This method simplifies the preparation process and reduces the preparation energy consumption. After the biochar removing dissolved organic matter is modified by ball milling, ball milling increases the specific surface area of the biochar, enriches the pore structure and surface charge, enhances physical adsorption and electrostatic adsorption. During the ball milling process, intermediate crystal CaHPO4·2H2O is formed on the surface and inside the pores of the biochar. The intermediate crystal CaHPO4·2H2O adheres to the surface of the biochar, increasing the adsorption sites; the intermediate crystal CaHPO4·2H2O can effectively adsorb cadmium ions through mechanisms such as coprecipitation. Due to the formation of the intermediate crystal CaHPO4·2H2O, the density of the biochar is changed, making it easy to centrifuge, which is conducive to the separation and recovery of the biochar.

[0019] Biochar itself, as a porous carbon material, has a large specific surface area, pore volume and rich functional groups, and has a large adsorption rate for heavy metal Cd; after the biochar is modified, a new intermediate crystal CaHPO4·2H2O is generated, effectively improving the adsorption efficiency of the biochar for cadmium, improving the surface charge distribution of the biochar, and being beneficial to the adsorption of Cd by the biochar; both the biochar and the CaHPO4·2H2O mineral are slightly alkaline, and the combination of the two can promote the conversion of free Cd ions into insoluble precipitates, thereby reducing the Cd content in the soil; the novel modified biochar can also reduce the mobility and availability of Cd ions in the environment through surface complexation. Description of the drawings

[0020] Figure 1 It is a comparison chart of the Cd removal efficiency of the materials prepared in Examples 1 - 6 and Comparative Examples 1 - 2 of the present invention for water bodies; Figure 2 It is a comparison chart of the Cd removal efficiency of the materials prepared in Examples 2 - 4 and Examples 7 - 8 of the present invention for water bodies Figure 3 It is the SEM diagram of the materials prepared in Comparative Examples 1 - 2, Example 2, Example 4, and Examples 7 - 8 of the present invention; Figure 4 XRD patterns of the materials prepared in Comparative Examples 1-2, Example 2, Example 4, Example 7-8 of the present invention; Figure 5 Adsorption capacities of the materials prepared in Comparative Examples 1-2, Example 2, Example 4, Example 7-8 of the present invention for Cd at different pH values; Figure 6 Adsorption kinetic diagrams of the materials prepared in Comparative Examples 1-2, Example 2, Example 4, Example 7-8 of the present invention for Cd in water; Figure 7 SEM-EDS analysis diagrams of the material prepared in Example 8 of the present invention after adsorbing Cd; among them, the upper left is the SEM diagram of the whole biochar adsorbing Cd prepared in Example 8; the upper right is the overall EDS analysis diagram of the biochar after adsorbing Cd; the lower left is the SEM diagram of the loaded mineral particles after the material obtained in Example 8 adsorbs Cd; the lower right is the EDS analysis diagram of the loaded mineral particles.

[0021] Figure 8 XRD comparative analysis diagrams of the materials prepared in Example 6 and Example 8 of the present invention before and after adsorbing Cd; Figure 9 EDS analysis diagram of the hydroxyapatite prepared in Comparative Example 3 of the present invention after adsorbing Cd; Figure 10 Comparison diagrams of the effects of the materials prepared in Comparative Examples 1-2, Example 2, Example 4, Example 7-8 of the present invention on the available cadmium content in soil. Detailed implementation manners

[0022] The following examples are used here to demonstrate the preferred implementation manners of the present invention. Those skilled in the art will understand that the technologies disclosed in the following examples represent the technologies discovered by the inventor that can be used to implement the present invention, and thus can be regarded as the preferred solutions for implementing the present invention. However, those skilled in the art should understand according to this specification that many modifications can be made to the specific embodiments disclosed here, and still obtain the same or similar results without departing from the spirit or scope of the present invention.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs. The materials cited herein and the materials they cite will be incorporated by reference. Those skilled in the art will realize or through routine experiments can understand many equivalent technologies of many specific embodiments of the invention described here. These equivalents will be included in the claims.

[0024] A preparation method of a novel modified biochar, comprising the following steps: (1) placing the calcium-rich solid waste raw material in a crusher and crushing it to a particle size of less than 5 mm to obtain crushed calcium-rich solid waste raw material; (2) Dry the crop straw powder in an oven at 60°C 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 place it in a muffle furnace for pyrolysis at 300-600°C for 3 h. Take out the product and place it in pure water. Oscillate it at 25-30°C and 200-300 r / min for 20-24 h, then filter and dry it to obtain biochar with DOM removed. (3) The crushed calcium-rich solid waste raw material in (1) and the DOM-removed biochar in (2) are fully mixed in a mass ratio of 1:(1-4), and mixed with diammonium hydrogen phosphate and ammonium dihydrogen phosphate at a calcium-phosphorus ratio of 1:(2.50-3.34), and the mass volume ratio of the calcium-rich solid waste raw material to pure water is 1g:(60-100)mL, to obtain a ball mill pre-raw material; (4) placing the pre-milling raw materials in (3) in a ball mill for ball milling at a speed of 250-600 r / min for 6-12 h, and completing the ball milling with a mass ratio of the pre-milling raw materials to the zirconia balls of 1:(10-15) to obtain a novel modified biochar mixed slurry; (5) The mixed slurry in (4) is transferred to a centrifuge tube for centrifugation. The solid precipitate is washed with pure water to remove excess phosphate, dried in an oven, ground and sieved to obtain a new modified biochar.

[0025] In order to make the above-mentioned objects, features and advantages of the present invention more clearly understood, the technical solutions of the present invention are further described below in conjunction with embodiments. However, the present invention is not limited to the embodiments listed, and should also include any other known changes within the scope of the rights claimed by the present invention.

[0026] The term "one 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 present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0027] The technical solution of this patent is further described in detail below in conjunction with specific implementation methods.

[0028] Example 1 The oyster shells are placed in a crusher and crushed to a particle size of less than 5 mm to obtain crushed calcium-rich solid waste raw materials.

[0029] The corn straw powder was dried in an oven at 60°C for 3 h and then passed through a 60-mesh sieve. The sieved powder was placed in a ceramic crucible, wrapped tightly with tin foil, and placed in a muffle furnace and pyrolyzed at 300°C for 3 h to obtain biochar.

[0030] Take 1.25 g of biochar and place it 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. Pour in 100 mL of deionized water to obtain the raw material before ball milling. The mass ratio of the raw material before ball milling to zirconia balls is 1:12, and the ball milling conditions are ball milling at 250 r / min for 6 h.

[0031] The ball milled product is filtered by suction, washed, placed in an oven and dried at 60 °C, and sieved through a 0.2 mm sieve to obtain modified biochar, denoted as HBC3-1.

[0032] Example 2 Place the shells in a crusher and crush them until the particle size is less than 5 mm to obtain the crushed calcium-rich solid waste raw material.

[0033] Dry the rice straw powder in an oven at 60 °C for 3 h and then sieve it through a 60-mesh sieve. Place the sieved powder in a ceramic crucible, tightly wrap it with tin foil, and put it into a muffle furnace to pyrolyze at 300 °C for 3 h to obtain biochar.

[0034] Take 2.5 g of biochar and place it 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. Pour in 100 mL of deionized water. The mass ratio of the raw material to zirconia balls is 1:12, and the ball milling conditions are ball milling at 250 r / min for 6 h.

[0035] The ball milled product is filtered by suction, washed, placed in an oven and dried at 60 °C, and sieved through a 0.2 mm sieve to obtain modified biochar, denoted as HBC3-2.

[0036] Example 3 Place the eggshells in a crusher and crush them until the particle size is less than 5 mm to obtain the crushed calcium-rich solid waste raw material.

[0037] Dry the cotton straw powder in an oven at 60 °C for 3 h and then sieve it through a 60-mesh sieve. Place the sieved powder in a ceramic crucible, tightly wrap it with tin foil, and put it into a muffle furnace to pyrolyze at 300 °C for 3 h to obtain biochar.

[0038] Take 3.75 g of biochar and place it 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. Pour in 100 mL of deionized water. The mass ratio of the raw material to zirconia balls is 1:12, and the ball milling conditions are ball milling at 250 r / min for 6 h.

[0039] The ball milled product is filtered by suction, washed, placed in an oven and dried at 60 °C, and sieved through a 0.2 mm sieve to obtain modified biochar, denoted as HBC3-3.

[0040] Example 4 Place the oyster shells in a crusher and crush them until the particle size is less than 5 mm to obtain the crushed calcium-rich solid waste raw material.

[0041] The corn straw powder was dried in an oven at 60 °C for 3 h and then sieved through a 60-mesh sieve. The sieved powder was placed in a ceramic crucible, tightly wrapped with tin foil, and put into a muffle furnace for pyrolysis at 600 °C for 3 h to obtain biochar.

[0042] Take 1.25 g of biochar and place it 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. Pour in 100 mL of deionized water. The mass ratio of the raw materials to the zirconia balls is 1:12, and the ball milling condition is ball milling at 250 r / min for 6 h.

[0043] The ball milled product was filtered by suction, washed, placed in an oven and dried at 60 °C, and sieved through a 0.2 mm sieve to obtain modified biochar, denoted as HBC6-1.

[0044] Example 5 The shells were placed in a crusher and crushed to a particle size less than 5 mm to obtain crushed calcium-rich solid waste raw materials.

[0045] The rice straw powder was dried in an oven at 60 °C for 3 h and then sieved through a 60-mesh sieve. The sieved powder was placed in a ceramic crucible, tightly wrapped with tin foil, and put into a muffle furnace for pyrolysis at 600 °C for 3 h to obtain biochar.

[0046] Take 2.5 g of biochar and place it 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. Pour in 100 mL of deionized water. The mass ratio of the raw materials to the zirconia balls is 1:12, and the ball milling condition is ball milling at 250 r / min for 6 h.

[0047] The ball milled product was filtered by suction, washed, placed in an oven and dried at 60 °C, and sieved through a 0.2 mm sieve to obtain modified biochar, denoted as HBC6-2.

[0048] Example 6 The eggshells were placed in a crusher and crushed to a particle size less than 5 mm to obtain crushed calcium-rich solid waste raw materials.

[0049] The cotton straw powder was dried in an oven at 60 °C for 3 h and then sieved through a 60-mesh sieve. The sieved powder was placed in a ceramic crucible, tightly wrapped with tin foil, and put into a muffle furnace for pyrolysis at 600 °C for 3 h to obtain biochar.

[0050] Take 3.75 g of biochar and place it 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. Pour in 100 mL of deionized water. The mass ratio of the raw materials to the zirconia balls is 1:12, and the ball milling condition is ball milling at 250 r / min for 6 h.

[0051] The ball milled product was filtered by suction, washed, placed in an oven and dried at 60 °C, and sieved through a 0.2 mm sieve to obtain modified biochar, denoted as HBC6-3.

[0052] Comparative Example 1 The corn straw powder was dried in an oven at 60 °C for 3 h and then sieved through a 60-mesh sieve. The sieved powder was placed in a ceramic crucible, tightly wrapped with tin foil, and put into a muffle furnace for pyrolysis at 300 °C for 3 h to obtain biochar BC3; Comparative Example 2 The corn straw powder was dried in an oven at 60 °C for 3 h and then sieved through a 60-mesh sieve. The sieved powder was placed in a ceramic crucible, tightly wrapped with tin foil, and put into a muffle furnace for pyrolysis at 600 °C for 3 h to obtain biochar BC6; Example 7 The shells were placed in a crusher and crushed to a particle size less than 5 mm to obtain a crushed calcium-rich solid waste raw material.

[0053] The rice straw powder was dried in an oven at 60 °C for 3 h and then sieved through a 60-mesh sieve. The sieved powder was placed in a ceramic crucible, tightly wrapped with tin foil, and put into a muffle furnace for pyrolysis at 300 °C for 3 h to obtain biochar.

[0054] 2.5 g of biochar was taken and put into a conical flask, 100 mL of deionized water was added, and it was placed in a water bath constant temperature oscillator and oscillated at 200 r / min for 2 d at 30 °C. After filtration and drying, DOM-free biochar was obtained.

[0055] 2.5 g of DOM-free biochar was taken and placed in a ball mill jar, 1.25 g of shell powder, 3.5 g of ammonium dihydrogen phosphate, and 3.5 g of diammonium hydrogen phosphate were added, 100 mL of deionized water was poured in, the mass ratio of the raw material to the zirconia balls was 1:12, and the ball milling condition was ball milling at 250 r / min for 6 h.

[0056] The ball-milled product was filtered, washed, placed in an oven and dried at 60 °C, and sieved through a 0.2 mm sieve to obtain DOM-free novel modified biochar, denoted as NDHBC3.

[0057] Example 8 The oyster shells were placed in a crusher and crushed to a particle size less than 5 mm to obtain a crushed calcium-rich solid waste raw material.

[0058] The corn straw powder was dried in an oven at 60 °C for 3 h and then sieved through a 60-mesh sieve. The sieved powder was placed in a ceramic crucible, tightly wrapped with tin foil, and put into a muffle furnace for pyrolysis at 600 °C for 3 h to obtain biochar.

[0059] 2.5 g of biochar was taken and put into a conical flask, 100 mL of deionized water was added, and it was placed in a water bath constant temperature oscillator and oscillated at 200 r / min for 2 d at 30 °C. After filtration and drying, DOM-free biochar was obtained.

[0060] Take 2.5 g of DOM-free biochar and place it 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. Pour in 100 mL of deionized water. The mass ratio of the raw materials to zirconia balls is 1:12, and the ball milling conditions are ball milling at 250 r / min for 6 h.

[0061] The ball-milled product is filtered by suction, washed, placed in an oven, and dried at 60 °C, and then sieved through a 0.2 mm sieve to obtain a novel modified DOM-free biochar, denoted as NDHBC6.

[0062] Comparative Example 3 Place the oyster shells in a crusher and crush them to a particle size less than 5 mm to obtain a crushed calcium-rich solid waste raw material.

[0063] 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 the raw materials to zirconia balls is 1:12, and the ball milling conditions are ball milling at 250 r / min for 6 h.

[0064] The ball-milled product is filtered by suction, washed, placed in an oven, and dried at 60 °C to obtain hydroxyapatite.

[0065] (1) Conduct a Cd adsorption pre-experiment on the materials prepared in Examples 1-6 and Comparative Examples 1-2, and measure the Cd removal efficiency, as Figure 1 shown.

[0066] As Figure 1 can be seen, compared with the biochar BC, the novel modified biochar HBC has a significantly improved Cd removal efficiency. HBC3 and HBC6 have increased by 21.26%-22.49% and 23.70-24.85% respectively. At the same time, the Cd removal efficiency of HBC6 is significantly higher than that of HBC3, and the effect has increased by 20.72%-23.08%. It is found that under the preparation conditions of different calcium-rich solid waste raw materials and different straw biochar mixing ratios, it has no significant effect on the novel modified biochar.

[0067] (2) Conduct a Cd adsorption pre-experiment on the materials prepared in Examples 2-4 and Examples 7-8, and measure the Cd removal efficiency, as Figure 2 shown.

[0068] As Figure 2 can be seen, compared with HBC, the Cd removal efficiency of NDHBC is significantly improved. NDHBC3 has increased by 30.74% compared with HBC3, and NDHBC6 has increased by 7.37% compared with HBC6. It is found that the novel modified biochar prepared from the biochar removing DOM has a better Cd removal efficiency, and the efficiency improvement of NDHBC3 is more significant.

[0069] (3)The materials prepared in Comparative Example 1, Comparative Example 2, Example 2, Example 4, Example 7, and Example 8 were subjected to electron microscopy scanning, as Figure 3 shown.

[0070] As can be Figure 3 seen from Figure 3 , compared with the surface morphology of BC biochar in the figure, it can be found that white substances cover the surface and pores of the modified biochar HBC / NDHBC, indicating that hydroxyapatite-like substances were successfully loaded onto the biochar during the modification process; moreover, after the biochar was modified by ball milling, the specific surface area was effectively increased, the pore structure and surface charge were enriched, the loading sites of hydroxyapatite-like substances were increased, and the adsorption performance was indirectly improved.

[0071] (4)The materials prepared in Comparative Example 1, Comparative Example 2, Example 2, Example 4, Example 7, and Example 8 were subjected to BET analysis to obtain the relevant parameters of the specific surface area and pore structure of the biochar, as shown in Table 1.

[0072] As can be seen from Table 1, the specific surface area (SSA) of the biochar continuously increased with the increase of the pyrolysis temperature. At the same time, compared with the original biochar BC, the pore volume of the new modified biochar NDHBC increased, increasing the adsorption sites of the biochar. Especially for NDHBC6, compared with BC6, under the condition that the specific surface area did not change significantly, the pore volume increased, and the material was modified with hydroxyapatite-like substances, greatly improving the adsorption potential of the material for heavy metal Cd.

[0073] Table 1 Specific surface area, pore volume, and pore diameter of biochar

[0074] (5)The materials prepared in Comparative Example 1, Comparative Example 2, Example 2, Example 4, Example 7, and Example 8 were subjected to XRD analysis, and the results are as Figure 4 shown.

[0075] As can be Figure 4 seen from Figure 4 , compared with the biochar, CaHPO4·2H2O appeared on the modified biochar, indicating that the intermediate crystal CaHPO4·2H2O was loaded onto the biochar.

[0076] (6)Batch adsorption experiments were carried out on the materials prepared in Comparative Example 1, Comparative Example 2, Example 2, Example 4, Example 7 and Example 8. The method was as follows: 0.03 g of biochar was placed in a 50 mL centrifuge tube, and 50 mg / L Cd solution with a pH value of 2 - 7 was added. It was oscillated at 30 °C and 200 r / min for 24 h, and the Cd concentration was measured after centrifugation and filtration; 0.03 g of biochar and 30 mL of 50 mg / L Cd solution with a pH of 6 were added to a 50 mL centrifuge tube, and it was oscillated at 30 °C and 200 r / min for 15 min - 24 h, and the Cd concentration was measured after centrifugation and filtration. The results are shown in Table 2, Figure 5 and Figure 6 shown below.

[0077] It can be seen from Figure 5 that compared with biochar, the modified biochar has better resistance to pH environmental changes, and NDHBC has better effect than HBC; from Table 2, Figure 6 it can be seen that compared with biochar, the adsorption effect of the new modified biochar is significantly improved, and with the extension of the adsorption time, the adsorption performance of NDHBC is more stable.

[0078] Table 2 Adsorption kinetic parameters of biochar

[0079] (7)SEM-EDS analysis was carried out on the material prepared in Example 8 after adsorbing Cd, as Figure 7 shown below.

[0080] It can be seen from Figure 7 the upper left and upper right figures in that after the new modified biochar adsorbed Cd, the weight percentage of Cd increased significantly by 2.51%, indicating that Cd was successfully adsorbed on the biochar surface. It can be seen from Figure 7 the lower left figure in that a flower-like crystal structure appeared after the new modified biochar adsorbed Cd, Figure 7 and it can be seen from

[0081] the lower right figure in that the weight percentages of Cd, P, and O elements in this crystal are relatively large, being 29.82%, 6.41%, and 33.31% respectively, while the proportion of Ca element is relatively small, being 0.34%. It is because Ca on the intermediate crystal CaHPO4·2H2O is replaced by Cd atoms, resulting in the formation of the crystal. Figure 8 shown below.

[0082] It can be seen from Figure 8 that by comparing the XRD patterns of HBC6 / NDHBC6 before and after adsorbing Cd, it can be found that the peak intensity of CaHPO4·2H2O weakened, and there was Cd4P8O 12The generation of CaHPO₄·12H₂O crystals was demonstrated. After Cd was adsorbed by CaHPO₄·2H₂O, Ca ions were replaced, resulting in the formation of new crystals.

[0083] (9)The hydroxyapatite prepared in Comparative Example 3 after adsorbing Cd was analyzed by X-ray energy spectrometer (EDS), as Figure 9 shown.

[0084] Figure 9 Figure 9 is the surface element analysis of hydroxyapatite prepared by the ball milling method after adsorbing Cd. By comparison, it can be seen that the brushite in the novel modified biochar has significantly better Cd adsorption performance than hydroxyapatite. The proportion of Cd content on the mineral surface after the novel modified biochar adsorbed Cd is 29.92%, while the Cd content on the surface of hydroxyapatite prepared by the ball milling method is only 14.43% after adsorbing Cd.

[0085] Compare the Figure 9 results with Figure 7 the results in the lower right figure, and it shows that the adsorption of Cd by hydroxyapatite is weaker than that of the intermediate crystal CaHPO₄·2H₂O loaded in the novel modified biochar of this application. Compared with the biochar modified by hydroxyapatite loading, the biochar modified by CaHPO₄·2H₂O loading has better Cd adsorption performance.

[0086] (10)Soil culture experiments were carried out on the samples prepared in Comparative Example 1, Comparative Example 2, Example 2, Example 4, Example 7, and Example 8. The method is as follows: The soil sample without adding biochar was used as the control group, and the biochars prepared in Comparative Example 1, Comparative Example 2, Example 2, Example 4, Example 7, and Example 8 were added as the experimental groups.

[0087] Under the condition of 25 °C, in the experimental groups, 1 g of biochar material was weighed into a 50 mL centrifuge tube, and 10 g of cadmium-containing soil and 20 mL of pure water were added. The centrifuge tube was placed in a constant temperature oscillator and shaken at a speed of 200 r / min for 2 h and then taken out and placed in a constant temperature incubator for 60 days. The effective cadmium concentration was measured by ICP-MS. The results are as Figure 10 shown.

[0088] It can be Figure 10 seen that the results show that the novel modified biochar in the examples has a significant improvement effect on soil available cadmium. Compared with the CK control group, the soil available cadmium content in the HBC treatment group decreased by 29.09% - 34.81% mg / kg, while the NDHBC decreased by 54.03% - 55.06% mg / kg, and the NDHBC has the best effect.

[0089] All documents mentioned in this invention are cited herein as references, as if each document was individually cited as a reference. In addition, it should be understood that after reading the above teachings of this invention, those skilled in the art can make various changes or modifications to this invention, and these equivalent forms also fall within the scope defined by this application.

Claims

1. A method for preparing a novel modified biochar, characterized in that: The steps include: (1) Place the calcium-rich solid waste raw materials in a crusher and crush them to a particle size of 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°C for 3-4 hours. Take out the product and place it in pure water. Oscillate it at 25-35°C and 200-300 r / min for 20-24 hours, then filter and dry it to obtain biochar with dissolved organic matter removed. (3) fully mixing the crushed calcium-rich solid waste material in (1) with the biochar from which dissolved organic matter has been removed in (2), and adding pure water, diammonium hydrogen phosphate and ammonium dihydrogen phosphate to obtain a ball mill pre-raw material; (4) placing the raw materials before ball milling in a ball milling tank for ball milling, and obtaining a mixed slurry after the ball milling is completed; (5) The mixed slurry in (4) is transferred to a centrifuge tube for centrifugation. The solid precipitate is washed with pure water to remove excess phosphate, and is placed in an oven for drying. The solid precipitate is ground and sieved to obtain a novel modified biochar.

2. The method for preparing a novel modified biochar according to claim 1, characterized in that: The calcium-rich solid waste raw materials in step (1) include shells, oyster shells and egg shells.

3. The method for preparing a novel modified biochar according to claim 1, characterized in that: In step (3), the mass ratio of the calcium-rich solid waste raw material to the biochar from which dissolved organic matter has been removed is 1:(1-4), the calcium-phosphorus ratio is 1:(2.50-3.34), and the mass-volume ratio of the calcium-rich solid waste raw material to pure water is 1 g:(60-100) mL.

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

5. The method for preparing a novel modified biochar according to claim 1, characterized in that: In step (2), the crop straw is selected from one or a mixture of corn straw, wheat straw, rice straw, rape straw, cotton straw, and sugarcane straw.

6. A novel modified biochar prepared by the method according to any one of claims 1 to 5.

7. Use of the novel modified biochar according to claim 6 in the adsorption of heavy metal cadmium in water bodies.

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

9. Use of the novel modified biochar according to claim 6 in stabilizing heavy metal cadmium in soil.

10. The use according to claim 9, characterized in that: The weight ratio of the novel modified biochar to soil is (1-3):20.

Images