Composite biochar material for adsorbing heavy metals in soil and preparation method of composite biochar material

Abstract

The invention relates to the technical field of soil remediation, and particularly discloses a composite biochar material for adsorbing heavy metals in soil and a preparation method. The composite biochar material comprises 30-60 parts of cocoanut active charcoal, 10-15 parts of nano-hydroxyapatite, 5-10 parts of magnetic iron oxide / porous ceramic particles, 10-15 parts of shell powder and 5-10 parts of sea sludge. The preparation method comprises the following steps: uniformly mixing the raw materials, granulating and drying to obtain mixture particles; placing the mixture particles in an inert gas atmosphere, heating the mixture particles to 350-750 DEG C, carrying out heat preservation calcination for 1.5-3 hours, and naturally cooling the mixture particles to room temperature to obtain carbonized particles; and washing, drying and sieving to obtain the composite biochar material. By adopting the coconut shell activated carbon, the nano-hydroxyapatite, the magnetic iron oxide / porous ceramic particles, the shell powder and the sea sludge in a specific proportion, the adsorption efficiency of the biochar material on heavy metals can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of soil remediation, and in particular to a composite biochar material for adsorbing heavy metals in soil and a preparation method thereof. Background Art

[0002] In the field of environmental protection and soil remediation, heavy metal pollution has always been an urgent problem to be solved. The accumulation of heavy metals such as lead, cadmium, and mercury in the soil not only affects the soil quality, but may also enter the human body through the food chain, posing a serious threat to health. Composite biochar material is a new type of environmentally friendly material with good adsorption performance and stability. It can adsorb heavy metals and has received widespread attention in the field of soil remediation in recent years.

[0003] In the related art, a biochar material is disclosed, which is made of the following raw materials: straw, nano iron powder, nano magnetic iron oxide, domestic sludge, phosphate rock, diatomaceous earth and deionized water. By selecting specific biomass raw materials, it has the ability to adsorb heavy metals in the soil. This material not only has a large specific surface area and rich pore structure, which is convenient for the adsorption and fixation of heavy metal ions, but also enhances the selective adsorption capacity of heavy metals by introducing specific functional groups and trace elements.

[0004] However, in the process of preparing the above-mentioned biochar material, nano iron powder and nano magnetic iron oxide may agglomerate, reducing the effective surface area of ​​the biochar material and resulting in a decrease in the adsorption efficiency of heavy metals. Summary of the invention

[0005] In order to improve the adsorption efficiency of heavy metals, the present application provides a composite biochar material for adsorbing heavy metals in soil and a preparation method thereof.

[0006] In the first aspect, the present application provides a composite biochar material for adsorbing heavy metals in soil, which adopts the following technical solution:

[0007] A composite biochar material for adsorbing heavy metals in soil comprises the following raw materials in parts by weight: 30-60 parts of coconut shell activated carbon, 10-15 parts of nano hydroxyapatite, 5-10 parts of magnetic iron oxide / porous ceramic particles, 10-15 parts of shell powder and 5-10 parts of sea silt.

[0008] By adopting the above technical scheme, coconut shell activated carbon has a high specific surface area and rich microporous structure, which can increase the adsorption sites of biochar materials for heavy metal ions, and also help to disperse other raw materials and reduce agglomeration. Nanohydroxyapatite has excellent adsorption performance for heavy metal ions, and can be filled in the pores of coconut shell activated carbon, which helps to further increase the surface area of ​​biochar materials. The uniform dispersion of nanohydroxyapatite can also effectively prevent the agglomeration of raw materials. Magnetic iron oxide / porous ceramic particles are composite materials formed by magnetic iron oxide and porous ceramics. They are not only magnetic, but also have a porous structure with a stable structure. They can serve as a skeleton structure to support the entire biochar material, prevent the biochar material from agglomerating or collapsing during use, and further increase the surface area of ​​the biochar material, providing more adsorption space. Shell powder is rich in chitin, which can not only improve the adsorption capacity of biochar materials, but also form a good interface with other raw materials to reduce the possibility of agglomeration. The particle structure of sea silt is relatively fine, which helps to fill the tiny pores in the material and improve the density and surface area of ​​the biochar material. Therefore, the present application can reduce the occurrence of raw material agglomeration and increase the effective surface area of ​​the biochar material and the adsorption efficiency of heavy metals by adopting the above-mentioned raw material ratio.

[0009] In a specific embodiment, based on the total weight of the magnetic iron oxide / porous ceramic particles, the magnetic iron oxide / porous ceramic particles include the following raw materials in parts by weight: 10-20 parts of aluminum oxide, 0.2-0.5 parts of pore formers, 0.3-0.6 parts of sintering aids, 5-10 parts of nano-magnetic iron oxide, 0.5-1 parts of surfactants, and 50-80 parts of water.

[0010] By adopting the above technical solution, alumina, pore formers, and sintering aids can form ceramic particles with rich pore structures. The pore structure not only increases the specific surface area of ​​the material and provides more adsorption and reaction sites, but also helps the diffusion and adsorption of heavy metal ions inside the material, which is beneficial for capturing and fixing heavy metal ions in the soil, thereby improving the removal efficiency of heavy metals by composite biochar materials. Nano-magnetic iron oxide has good adsorption properties and magnetism. In a system of water and surfactants, it can form a suspension, so that the nano-magnetic iron oxide is evenly dispersed and loaded on porous ceramic particles to obtain magnetic iron oxide / porous ceramic particles.

[0011] In a specific embodiment, the method for preparing the magnetic iron oxide / porous ceramic particles comprises the following steps:

[0012] Preparation of porous ceramics: ceramic powder is uniformly mixed with a pore-forming agent and a sintering aid, ball-milled, granulated to obtain ceramic particles, calcined to obtain a calcined product, and the calcined product is ground and sieved to obtain porous ceramic particles;

[0013] Preparing a precursor solution: adding nano-magnetic iron oxide and a surfactant into water, uniformly dispersing them to obtain a suspension, adding porous ceramic particles into the suspension, and mixing them uniformly to obtain a precursor solution;

[0014] Loading: Add the precursor solution into the reactor, seal the reactor, heat at 120-160°C for 10-16h, cool naturally to room temperature, separate the solid and liquid, wash the separated solid with ethanol and water alternately, and dry to obtain loaded particles;

[0015] Sintering: Place the loaded particles at 400-500°C, keep the temperature for 2-6 hours, and naturally cool to room temperature to obtain magnetic iron oxide / porous ceramic particles.

[0016] By adopting the above technical scheme, by first adding nano-magnetic iron oxide and surfactant into water to form a suspension, and then mixing with porous ceramic particles, it is helpful for nano-magnetic iron oxide to be evenly dispersed and loaded on porous ceramic particles, thereby maximizing the synergistic effect of magnetic iron oxide and porous ceramics. The precursor solution is subjected to hydrothermal treatment at the above heating temperature and heating time, and the pore structure and specific surface area of ​​the porous ceramic particles can be further optimized. It can not only improve the adsorption efficiency and capacity of the material, but also help to improve its mass transfer performance, making it easier for heavy metal ions to enter the material and be adsorbed. After the loaded particles are subjected to high-temperature insulation treatment at the above temperature and time, the bond between the magnetic iron oxide and the porous ceramic particles is more firm, which helps the magnetic iron oxide / porous ceramic particles to maintain excellent adsorption performance for a long time and reduce the frequency of maintenance and replacement. By the method of alternating washing with ethanol and water, impurities and unreacted products generated during the preparation process can be effectively removed to ensure the purity and quality of the final product.

[0017] In a specific embodiment, in the step of preparing porous ceramics, the ceramic particles are dried, calcined at 600-800°C for 60-120 min, heated to 1200-1400°C, calcined for 3-5 h, and naturally cooled to room temperature to obtain a calcined product.

[0018] By adopting the above technical solution and calcining within the above temperature range, ceramic particles with rich pore structure can be formed. Moreover, through the calcination process, the ceramic particles can obtain higher mechanical strength, maintain good stability and durability in applications such as soil remediation, and maintain their adsorption performance even under harsh environmental conditions. Through the steps of ball milling, granulation, drying and calcination, porous ceramic particles with uniform size and shape can be prepared.

[0019] In a specific embodiment, the pore former is polymethyl methacrylate ceramic pore former or ammonium bicarbonate.

[0020] By adopting the above technical solution, polymethyl methacrylate ceramic pore former and ammonium bicarbonate can be quickly decomposed or volatilized during the pyrolysis process, thereby leaving a rich pore structure in the biochar material. Moreover, polymethyl methacrylate ceramic pore former and ammonium bicarbonate are non-toxic and harmless, meet environmental protection requirements, and have relatively low costs, which helps to reduce the production cost of composite biochar materials.

[0021] In a specific embodiment, the sintering aid includes phosphoric acid and carbonate in a weight ratio of 1:(1.4-1.8).

[0022] By adopting the above technical solution, the above weight ratio of phosphoric acid and carbonate can reduce the sintering temperature of the material. At a lower temperature, the material can achieve the required densification and strength, thereby saving energy and reducing production costs. In addition, phosphoric acid and carbonate will decompose at high temperatures and release gases. These gases form tiny pores between ceramic particles, promoting the fusion and connection between particles. It helps to enhance the mechanical strength of the material and optimize the microstructure.

[0023] In a specific embodiment, the composite biochar material for adsorbing heavy metals in soil also includes bentonite.

[0024] By adopting the above technical solution, bentonite has a strong cation exchange capacity, can effectively adsorb and fix heavy metal ions, and further improve the adsorption efficiency of heavy metals.

[0025] In a second aspect, the present application provides a method for preparing a composite biochar material for adsorbing heavy metals in soil, which adopts the following technical solution:

[0026] A method for preparing a composite biochar material for adsorbing heavy metals in soil comprises the following steps:

[0027] The coconut shell activated carbon, nano-hydroxyapatite, magnetic iron oxide / porous ceramic particles, shell powder and sea silt are uniformly mixed, granulated and dried to obtain mixed material particles;

[0028] The mixed material particles are placed in an inert gas atmosphere, heated to 350-750°C, kept warm and calcined for 1.5-3 hours, and naturally cooled to room temperature to obtain carbonized particles;

[0029] The carbonized particles are washed with ethanol and water in sequence, dried and sieved to obtain a composite biochar material for adsorbing heavy metals in soil.

[0030] By adopting the above technical scheme, coconut shell activated carbon is further carbonized during the heating process, enhancing its pore structure and specific surface area. Nanohydroxyapatite remains stable during the heating process. Magnetic iron oxide / porous ceramic particles combine with coconut shell activated carbon during the heating process to form a more uniform composite material. At the same time, the porous ceramic particles may further increase their internal porosity due to the thermal expansion effect, which helps to improve the adsorption capacity of biochar materials. The organic matter in shell powder and sea silt will decompose and release gas during the heating process, which will help to form more micropores and mesopores inside the composite biochar material, thereby increasing the specific surface area of ​​the composite biochar material. In addition, the functional groups such as carboxyl and hydroxyl introduced after the decomposition of organic matter can complex or chelate with heavy metal ions, thereby improving the adsorption efficiency of the material for heavy metals. Through the ethanol and water washing steps, surface impurities can be further removed, exposing more active sites, thereby improving the effective surface area of ​​the material and the adsorption capacity for heavy metals.

[0031] In summary, this application has the following beneficial effects:

[0032] 1. This application can improve the adsorption efficiency of heavy metals by biochar materials by using a specific ratio of coconut shell activated carbon, nano-hydroxyapatite, magnetic iron oxide / porous ceramic particles, shell powder and sea silt.

[0033] 2. In this application, the magnetic iron oxide / porous ceramic particles prepared by a specific raw material ratio and preparation method are preferably used, which can not only improve the adsorption efficiency and capacity of the material, but also help to improve its mass transfer performance, making it easier for heavy metal ions to enter the material and be adsorbed, and not easy to desorb.

[0034] 3. The method of the present application can further improve the adsorption capacity of biochar materials. DETAILED DESCRIPTION

[0035] The raw materials used in this application are all purchased from the market unless otherwise specified. Among them, coconut shell activated carbon is powdered coconut shell activated carbon with a particle size of 100 mesh. Nano hydroxyapatite is hydroxyapatite with an average particle size of 20nm. Nano magnetic iron oxide is powdered iron oxide with an average particle size of 100nm. Shell powder is calcined shell powder with a particle size of 325 mesh, produced in Lingshou, Hebei. Sea silt is powdered sea silt with a particle size of 50 mesh, produced in Shanghai.

[0036] The present application is further described in detail below in conjunction with embodiments and comparative examples.

[0037] Example

[0038] Example 1

[0039] The present embodiment provides a composite biochar material for adsorbing heavy metals in soil, comprising the following raw materials: 45 kg coconut shell activated carbon, 12.5 kg nano-hydroxyapatite, 7.5 kg magnetic iron oxide / porous ceramic particles, 12.5 kg shell powder and 7.5 kg sea silt.

[0040] Wherein, the magnetic iron oxide / porous ceramic particles are prepared according to the following steps:

[0041] The following raw materials were weighed: 15 kg of aluminum oxide, 0.35 kg of ammonium bicarbonate, 0.45 kg of sintering aid, 7.5 kg of nano-magnetic iron oxide, 0.75 kg of n-propyl gallate, and 65 kg of water. The sintering aid includes phosphoric acid and carbonate in a weight ratio of 1:1.6.

[0042] The ceramic powder is mixed evenly with ammonium bicarbonate and a sintering aid, ball-milled, and then mixed with water for granulation to obtain ceramic particles. After the ceramic particles are dried, they are placed in a calcining furnace, heated to 700°C, calcined for 90 minutes, then heated to 1300°C, calcined for 4 hours, and naturally cooled to room temperature to obtain a calcined product. The calcined product is ground and sieved to obtain porous ceramic particles.

[0043] Nano-magnetic iron oxide and n-propyl gallate are added into water and dispersed uniformly to obtain a suspension, and porous ceramic particles are added into the suspension and mixed uniformly to obtain a precursor solution.

[0044] The precursor solution was added into the reactor, and after the reactor was sealed, it was heated at 140° C. for 13 h. After naturally cooling to room temperature, the solid and liquid were separated, and the separated solid was washed alternately with ethanol and water, and dried to obtain loaded particles.

[0045] The loaded particles were placed at 450° C., kept warm for 4 hours, and naturally cooled to room temperature to obtain magnetic iron oxide / porous ceramic particles.

[0046] A method for preparing a composite biochar material for adsorbing heavy metals in soil comprises the following steps:

[0047] The coconut shell activated carbon, nano-hydroxyapatite, magnetic iron oxide / porous ceramic particles, shell powder and sea silt are uniformly mixed, granulated and dried to obtain mixed material particles;

[0048] The mixed material particles are placed in a calcining furnace, nitrogen is introduced into the calcining furnace, and the mixed material particles are heated to 550° C. in a nitrogen atmosphere, kept calcined for 2.2 hours, and then naturally cooled to room temperature to obtain carbonized particles;

[0049] The carbonized particles are washed with ethanol and water in sequence, dried and sieved to obtain a composite biochar material for adsorbing heavy metals in soil.

[0050] Example 2

[0051] The only difference between this embodiment and embodiment 1 is that the composite biochar material for adsorbing heavy metals in soil includes the following raw materials: 30 kg coconut shell activated carbon, 10 kg nano hydroxyapatite, 5 kg magnetic iron oxide / porous ceramic particles, 10 kg shell powder and 5 kg sea silt.

[0052] Example 3

[0053] The only difference between this embodiment and embodiment 1 is that the composite biochar material for adsorbing heavy metals in soil includes the following raw materials: 60 kg coconut shell activated carbon, 15 kg nano hydroxyapatite, 10 kg magnetic iron oxide / porous ceramic particles, 15 kg shell powder and 10 kg sea silt.

[0054] Example 4

[0055] The only difference between this embodiment and embodiment 1 is that, during the preparation of magnetic iron oxide / porous ceramic particles, the following raw materials are weighed: 10 kg of aluminum oxide, 0.2 kg of ammonium bicarbonate, 0.3 kg of sintering aid, 5 kg of nano-magnetic iron oxide, 0.5 kg of n-propyl gallate, and 50 kg of water.

[0056] Example 5

[0057] The only difference between this embodiment and embodiment 1 is that, during the preparation of magnetic iron oxide / porous ceramic particles, the following raw materials are weighed: 20 kg of aluminum oxide, 0.5 kg of ammonium bicarbonate, 0.6 kg of sintering aid, 10 kg of nano-magnetic iron oxide, 1 kg of n-propyl gallate, and 80 kg of water.

[0058] Example 6

[0059] The only difference between this embodiment and embodiment 1 is that, in the preparation process of magnetic iron oxide / porous ceramic particles, the sintering aid includes phosphoric acid and carbonate in a weight ratio of 1:1.2.

[0060] Example 7

[0061] The only difference between this embodiment and embodiment 1 is that, in the preparation process of magnetic iron oxide / porous ceramic particles, the sintering aid includes phosphoric acid and carbonate in a weight ratio of 1:1.4.

[0062] Example 8

[0063] The only difference between this embodiment and embodiment 1 is that, in the preparation process of magnetic iron oxide / porous ceramic particles, the sintering aid includes phosphoric acid and carbonate in a weight ratio of 1:1.8.

[0064] Example 9

[0065] The only difference between this embodiment and embodiment 1 is that, in the preparation process of magnetic iron oxide / porous ceramic particles, the sintering aid includes phosphoric acid and carbonate in a weight ratio of 1:2.

[0066] Example 10

[0067] The only difference between this embodiment and embodiment 1 is that, in the preparation process of magnetic iron oxide / porous ceramic particles, the ceramic powder is mixed with ammonium bicarbonate and a sintering aid, ball-milled, and then mixed with water and granulated to obtain ceramic particles. After the ceramic particles are dried, they are placed in a calcining furnace, heated to 600°C, calcined for 120 minutes, then heated to 1200°C, calcined for 5 hours, and naturally cooled to room temperature to obtain a calcined product. The calcined product is ground and sieved to obtain porous ceramic particles.

[0068] Embodiment 11

[0069] The only difference between this embodiment and embodiment 1 is that, in the preparation process of magnetic iron oxide / porous ceramic particles, the ceramic powder is mixed evenly with ammonium bicarbonate and a sintering aid, ball-milled, and then mixed with water and granulated to obtain ceramic particles. After the ceramic particles are dried, they are placed in a calcining furnace, heated to 800°C, calcined for 60 minutes, then heated to 1400°C, calcined for 3 hours, and naturally cooled to room temperature to obtain a calcined product. The calcined product is ground and sieved to obtain porous ceramic particles.

[0070] Example 12

[0071] The only difference between this embodiment and embodiment 1 is that, during the preparation process of magnetic iron oxide / porous ceramic particles, the precursor solution is added into the reactor, the reactor is sealed, heated at 120°C for 16 hours, naturally cooled to room temperature, the solid and liquid are separated, and the separated solid is washed alternately with ethanol and water and dried to obtain loaded particles.

[0072] Embodiment 13

[0073] The only difference between this embodiment and embodiment 1 is that, during the preparation process of magnetic iron oxide / porous ceramic particles, the precursor solution is added into the reactor, the reactor is sealed, heated at 160°C for 10 hours, naturally cooled to room temperature, the solid and liquid are separated, and the separated solid is washed alternately with ethanol and water and dried to obtain loaded particles.

[0074] Embodiment 14

[0075] The only difference between this embodiment and embodiment 1 is that, during the preparation process of magnetic iron oxide / porous ceramic particles, the loaded particles are placed at 400° C., kept warm for 6 hours, and naturally cooled to room temperature to obtain magnetic iron oxide / porous ceramic particles.

[0076] Embodiment 15

[0077] The only difference between this embodiment and embodiment 1 is that, during the preparation process of magnetic iron oxide / porous ceramic particles, the loaded particles are placed at 500° C., kept warm for 2 hours, and naturally cooled to room temperature to obtain magnetic iron oxide / porous ceramic particles.

[0078] Example 16

[0079] The only difference between this embodiment and embodiment 1 is that, during the preparation of magnetic iron oxide / porous ceramic particles, an equal amount of polymethyl methacrylate ceramic pore former (Mitsui, specification: 25) is used to replace ammonium bicarbonate.

[0080] Embodiment 17

[0081] The only difference between this embodiment and embodiment 1 is that, during the preparation process of magnetic iron oxide / porous ceramic particles, the composite biochar material used to adsorb heavy metals in the soil includes the following raw materials: 45 kg of coconut shell activated carbon, 12.5 kg of nano-hydroxyapatite, 7.5 kg of magnetic iron oxide / porous ceramic particles, 12.5 kg of shell powder, 7.5 kg of sea silt and 5 kg of bentonite.

[0082] The method for preparing a composite biochar material for adsorbing heavy metals in soil comprises the following steps:

[0083] The coconut shell activated carbon, nano-hydroxyapatite, magnetic iron oxide / porous ceramic particles, shell powder, sea silt and bentonite are uniformly mixed, granulated and dried to obtain mixed material particles;

[0084] The mixed material particles are placed in a calcining furnace, nitrogen is introduced into the calcining furnace, and the mixed material particles are heated to 550° C. in a nitrogen atmosphere, kept calcined for 2.2 hours, and then naturally cooled to room temperature to obtain carbonized particles;

[0085] The carbonized particles are washed with ethanol and water in sequence, dried and sieved to obtain a composite biochar material for adsorbing heavy metals in soil.

[0086] Embodiment 18

[0087] The difference between this embodiment and embodiment 1 is that the preparation method of the composite biochar material for adsorbing heavy metals in soil comprises the following steps:

[0088] The coconut shell activated carbon, nano-hydroxyapatite, magnetic iron oxide / porous ceramic particles, shell powder and sea silt are uniformly mixed, granulated and dried to obtain mixed material particles;

[0089] The mixed material particles are placed in a calcining furnace, nitrogen is introduced into the calcining furnace, and the mixed material particles are heated to 350° C. in a nitrogen atmosphere, kept at this temperature for 3 hours, and then naturally cooled to room temperature to obtain carbonized particles;

[0090] The carbonized particles are washed with ethanol and water in sequence, dried and sieved to obtain a composite biochar material for adsorbing heavy metals in soil.

[0091] Embodiment 19

[0092] The difference between this embodiment and embodiment 1 is that the preparation method of the composite biochar material for adsorbing heavy metals in soil comprises the following steps:

[0093] The coconut shell activated carbon, nano-hydroxyapatite, magnetic iron oxide / porous ceramic particles, shell powder and sea silt are uniformly mixed, granulated and dried to obtain mixed material particles;

[0094] The mixed material particles are placed in a calcining furnace, nitrogen is introduced into the calcining furnace, and the mixed material particles are heated to 750° C. in a nitrogen atmosphere, kept at this temperature for 1.5 hours, and then naturally cooled to room temperature to obtain carbonized particles;

[0095] The carbonized particles are washed with ethanol and water in sequence, dried and sieved to obtain a composite biochar material for adsorbing heavy metals in soil.

[0096] Comparative Example

[0097] Comparative Example 1

[0098] The only difference between this comparative example and Example 1 is that an equal amount of coconut shell activated carbon is used to replace nano hydroxyapatite in the preparation process of the composite biochar material for adsorbing heavy metals in soil.

[0099] Comparative Example 2

[0100] The only difference between this comparative example and Example 1 is that an equal amount of coconut shell activated carbon is used to replace the magnetic iron oxide / porous ceramic particles in the preparation process of the composite biochar material for adsorbing heavy metals in soil.

[0101] Comparative Example 3

[0102] The only difference between this comparative example and Example 1 is that an equal amount of coconut shell activated carbon is used to replace shell powder in the preparation process of the composite biochar material for adsorbing heavy metals in soil.

[0103] Comparative Example 4

[0104] The only difference between this comparative example and Example 1 is that an equal amount of coconut shell activated carbon is used to replace sea silt in the preparation process of the composite biochar material for adsorbing heavy metals in soil.

[0105] Performance testing

[0106] The following performance tests were performed on the composite biochar materials for adsorbing heavy metals in soil prepared in Examples 1-19 and Comparative Examples 1-4:

[0107] A 750 mg / L Cr6+ solution was prepared, and the composite biochar material of each embodiment or comparative example was added at an amount of 1 g / L. Under the conditions of 25°C and pH 7.5, the supernatant and the filtered composite biochar material were filtered using a 0.45 μm filter membrane. The Cr6+ concentration in the supernatant was determined by an atomic absorption spectrophotometer, and the adsorption efficiency at 12 h and 15 h of adsorption was calculated according to the following formula. Adsorption efficiency = (Co-Ce) × V÷M÷T, Co (mg / L) is the initial concentration of the Cr6+ solution before adsorption, Ce (mg / L) is the concentration of the remaining Cr6+ solution in the solution after a certain period of adsorption, V (L) is the volume of the Cr6+ solution, M (g) is the mass of the composite biochar material, and T (h) is the adsorption time.

[0108] The filtered composite biochar material was dried to constant weight, added to 100 mL and 0.01 mol CaCl2 solution respectively, shaken for 4 hours, and filtered with a 0.45 μm filter membrane to obtain the filtrate, and the desorption amount of Cr6+ in the filtrate was calculated. Desorption amount (mg / g) = Ce×V / M, Ce (mg / L) is the concentration of Cr6+ in the desorption solution, V (L) is the volume of the desorption solution, and M (g) is the mass of the composite biochar material after filtration.

[0109] The test results are shown in Table 1.

[0110] Table 1

[0111]

[0112]

[0113] Combining Example 1 and Comparative Examples 1-4 and Table 1, it can be seen that compared with Example 1, the 12h adsorption efficiency and 15h adsorption efficiency of Comparative Examples 1-4 are significantly reduced, and the difference between the 12h adsorption efficiency and 15h adsorption efficiency of the same comparative example is small; the desorption amount of Comparative Examples 1-4 is significantly increased. This shows that the raw material ratio and preparation method of Example 1 can improve the adsorption efficiency of the composite biochar material for heavy metals, and the adsorbed heavy metals are more solid and not easy to desorb.

[0114] Combining Examples 1-5 and Table 1, it can be seen that the 12h adsorption efficiency and 15h adsorption efficiency of Examples 1-5 are both relatively large, and the desorption amount is relatively small. This shows that by using the raw material ratios within the range of Examples 1-5, a composite biochar material with high heavy metal adsorption efficiency can be obtained.

[0115] Combining Examples 1, 6-9 and Table 1, it can be seen that the proportion of carbonate in the burning aids of Examples 1 and 6-9 is Example 6 < Example 7 < Example 1 < Example 8 < Example 9 from small to large, the 12h adsorption efficiency and 15h adsorption efficiency of Examples 6-7 are both lower than those of Example 1, the 12h adsorption efficiency and 15h adsorption efficiency of Example 8 are both higher than those of Example 1, but the 12h adsorption efficiency and 15h adsorption efficiency of Example 9 are both lower than those of Example 8. This shows that if the proportion of carbonate in the burning aid is too small or too large, the adsorption efficiency of the composite biochar material will be reduced. Therefore, using the ratio within the range of Examples 1, 7-8 will help to further improve the adsorption efficiency of the composite biochar material.

[0116] It can be seen from Examples 1, 10-19 and Table 1 that Examples 10-19 have greater 12h adsorption efficiency and 15h adsorption efficiency and smaller desorption amount, which means that the raw material ratio, process conditions or preparation method of Examples 10-19 can also improve the adsorption efficiency of composite biochar materials for heavy metals.

[0117] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A composite biochar material for adsorbing heavy metals in soil, characterized in that: The invention comprises the following raw materials in parts by weight: 30-60 parts of coconut shell activated carbon, 10-15 parts of nano hydroxyapatite, 5-10 parts of magnetic iron oxide / porous ceramic particles, 10-15 parts of shell powder and 5-10 parts of sea silt.

2. The composite biochar material for adsorbing heavy metals in soil according to claim 1, characterized in that: Based on the total weight of the magnetic iron oxide / porous ceramic particles, the magnetic iron oxide / porous ceramic particles include the following raw materials in parts by weight: 10-20 parts of aluminum oxide, 0.2-0.5 parts of pore formers, 0.3-0.6 parts of sintering aids, 5-10 parts of nano-magnetic iron oxide, 0.5-1 parts of surfactants, and 50-80 parts of water.

3. The composite biochar material for adsorbing heavy metals in soil according to claim 2, characterized in that: The method for preparing the magnetic iron oxide / porous ceramic particles comprises the following steps: Preparation of porous ceramics: ceramic powder is uniformly mixed with a pore-forming agent and a sintering aid, ball-milled, granulated to obtain ceramic particles, calcined to obtain a calcined product, and the calcined product is ground and sieved to obtain porous ceramic particles; Preparing a precursor solution: adding nano-magnetic iron oxide and a surfactant into water, uniformly dispersing them to obtain a suspension, adding porous ceramic particles into the suspension, and mixing them uniformly to obtain a precursor solution; Loading: Add the precursor solution into the reactor, seal the reactor, heat at 120-160°C for 10-16h, cool naturally to room temperature, separate the solid and liquid, wash the separated solid with ethanol and water alternately, and dry to obtain loaded particles; Sintering: Place the loaded particles at 400-500°C, keep the temperature for 2-6 hours, and naturally cool to room temperature to obtain magnetic iron oxide / porous ceramic particles.

4. The composite biochar material for adsorbing heavy metals in soil according to claim 3, characterized in that: In the step of preparing porous ceramics, the ceramic particles are dried, calcined at 600-800° C. for 60-120 min, heated to 1200-1400° C., calcined for 3-5 h, and naturally cooled to room temperature to obtain a calcined product.

5. The composite biochar material for adsorbing heavy metals in soil according to claim 2, characterized in that: The pore-forming agent is polymethyl methacrylate ceramic pore-forming agent or ammonium bicarbonate.

6. The composite biochar material for adsorbing heavy metals in soil according to claim 2, characterized in that: The sintering aid comprises phosphoric acid and carbonate in a weight ratio of 1:(1.4-1.8).

7. The composite biochar material for adsorbing heavy metals in soil according to claim 1, characterized in that: The composite biochar material for adsorbing heavy metals in soil also includes bentonite.

8. A method for preparing a composite biochar material for adsorbing heavy metals in soil according to any one of claims 1 to 7, characterized in that: The steps include: The coconut shell activated carbon, nano-hydroxyapatite, magnetic iron oxide / porous ceramic particles, shell powder and sea silt are uniformly mixed, granulated and dried to obtain mixed material particles; The mixed material particles are placed in an inert gas atmosphere, heated to 350-750°C, kept warm and calcined for 1.5-3 hours, and naturally cooled to room temperature to obtain carbonized particles; The carbonized particles are washed with ethanol and water in sequence, dried and sieved to obtain a composite biochar material for adsorbing heavy metals in soil.

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