Layered multi-metal oxide-based magnetic biochar for remediation of arsenic and cadmium contaminated soil, and preparation method and use thereof

Abstract

The present application relates to a layered multi-metal oxide-based magnetic biochar and a preparation method and use thereof, the preparation method comprising: S1, mixing biomass with an iron salt solution for impregnation, after solid-liquid separation, adjusting the first pH value of the solid phase material to obtain pretreated biomass; S2, pyrolyzing the pretreated biomass to obtain magnetic biochar, then mixing the magnetic biochar with a solution containing at least two metal salts and adjusting the second pH value, and then performing hydrothermal treatment to obtain the layered multi-metal oxide-based magnetic biochar. The obtained layered multi-metal oxide-based magnetic biochar has a large specific surface area, is magnetic, has a layered morphology, and has strong adsorption capacity, and can be applied to the treatment of water bodies containing arsenic and cadmium composite pollution, and can also be used for the passivation of arsenic and cadmium in farmland soil, reducing the health risk of food chain crops and ensuring food safety.

Description

Technical Field

[0001] This invention relates to the field of environmental remediation technology, specifically to a layered polymetallic oxide-based magnetic biochar, its preparation method and uses, and more particularly to a layered polymetallic oxide-based magnetic biochar, its preparation method, and a method for treating arsenic and / or cadmium pollution. Background Technology

[0002] Currently, arsenic and cadmium are (quasi-)heavy metal elements that are widely present in soil, posing a serious threat to the ecological environment and human health.

[0003] Waste biomass is an important type of agricultural waste with a wide range of sources, especially the straw of major crops (including wheat straw, rice husks, corn straw, bamboo shavings, etc.). Among these, converting waste biomass into biochar and applying it to agricultural production has shown good effects, such as fixing soil carbon, enhancing soil fertility, and reducing the greenhouse effect.

[0004] In recent years, numerous studies have shown that biochar has a good effect on cadmium-polluted water and soil environments. For example, CN114471463A discloses a biochar for adsorbing the heavy metal cadmium, its preparation method, and its application. It uses fast-growing grass biomass as raw material, which undergoes bacterial composting modification, fungal decomposition modification, and oxygen-free carbonization sequentially. Bacterial composting modification involves mixing fast-growing grass biomass with a bacterial nitrogen source and an inoculum of bacteria capable of degrading cellulose, followed by fermentation to obtain bacterially composted biomass. Fungal decomposition modification involves mixing the bacterially composted biomass with a fungal nitrogen source and lime water, sterilizing, cooling to room temperature, inoculating with fungal inoculum, and harvesting the residue after fungal fruiting bodies. However, this modified biochar was designed to verify its adsorption effect on arsenic.

[0005] CN107413296A discloses a biochar-iron-manganese spinel composite material for adsorbing heavy metals antimony and cadmium. The preparation method of the biochar-iron-manganese spinel composite material includes: uniformly adding solution B to suspension A, stirring for 2.5-3.5 hours, followed by centrifugation, washing, and drying to obtain the biochar-iron-manganese spinel composite material; wherein solution B is a 0.1 mol / L potassium permanganate solution, and suspension A is composed of water, ferrous sulfate heptahydrate, and tea twig biochar in a weight ratio of 100:(8.0-8.5):(0.8-1.2). This biochar composite material has a larger specific surface area and porosity, which is more conducive to the adsorption of heavy metals. It has a certain adsorption effect on arsenic and antimony polluted water bodies, but the adsorption effect on arsenic and cadmium combined polluted water bodies is unknown.

[0006] However, the alkaline nature of biochar can cause cadmium precipitation. Furthermore, due to electrostatic repulsion, the remediation effect of raw biochar on anionic arsenic pollution is limited, thus restricting its application in environments with combined arsenic and cadmium pollution. It is evident that current technologies using biochar to treat heavy metal pollutants such as arsenic and / or cadmium still suffer from poor adsorption and removal efficiency. Summary of the Invention

[0007] In view of the problems existing in the prior art, the purpose of this invention is to provide a layered polymetallic oxide-based magnetic biochar, its preparation method and uses. The obtained layered polymetallic oxide-based magnetic biochar has a large specific surface area, is magnetic, has a layered morphology, and has strong adsorption capacity. It can be applied to the treatment of water bodies containing arsenic and cadmium composite pollution, and can also be used for the passivation of arsenic and cadmium in farmland soil, reducing the health risks of food chain crops and ensuring food safety.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing layered polymetallic oxide-based magnetic biochar, the method comprising:

[0010] S1. The biomass is mixed with an iron salt solution and impregnated. After solid-liquid separation, the pH value of the solid material is adjusted to obtain pretreated biomass.

[0011] S2. The pretreated biomass is pyrolyzed to obtain magnetic biochar. Then, the magnetic biochar is mixed with a solution containing at least two metal salts and the pH value is adjusted. Finally, the mixture is subjected to hydrothermal treatment to obtain layered polymetallic oxide-based magnetic biochar.

[0012] The method for preparing layered polymetallic oxide-based magnetic biochar provided by the present invention utilizes iron salt pre-impregnation technology to pre-magnetize biomass and then perform pyrolysis treatment to enhance the activity of iron oxides. Then, a bimetallic oxide solution is cross-linked with magnetic biochar using a hydrothermal method to prepare modified biochar for the treatment of arsenic and cadmium pollution.

[0013] As a preferred technical solution of the present invention, the biomass includes any one or a combination of at least three of wheat straw, rice husks, bamboo shavings, sludge or garlic, preferably garlic, bamboo shavings and garlic.

[0014] Preferably, the biomass particles are 60-100 mesh.

[0015] As a preferred embodiment of the present invention, the iron salt solution comprises a mixed solution of ferrous iron and ferric iron.

[0016] Preferably, the molar ratio of ferric iron to ferrous iron in the iron salt solution is (1-4):1.

[0017] Preferably, the mass ratio of the biomass to the iron salt used in preparing the iron salt solution is (0.5-3):1.

[0018] As a preferred embodiment of the present invention, the stirring speed during the impregnation is 300-1000 r / min.

[0019] Preferably, the stirring time during the impregnation is 4-48 hours.

[0020] As a preferred technical solution of the present invention, the endpoint of the first pH value adjustment is that the pH value of the solid material is 6.5-7.5.

[0021] As a preferred embodiment of the present invention, the pyrolysis temperature is 400-800℃.

[0022] Preferably, the pyrolysis time is 1-6 hours.

[0023] As a preferred technical solution of the present invention, the metal ions in the solution containing at least two metal salts include a combination of at least two of magnesium ions, aluminum ions, iron ions, or calcium ions.

[0024] Preferably, the molar ratio of trivalent metal ions to divalent metal ions in the solution containing at least two metal salts is (1-4):1.

[0025] Preferably, the solid-liquid ratio (g / mL) of the magnetic biochar and the solution containing at least two metal salts is 1:(1-20).

[0026] As a preferred embodiment of the present invention, the second pH value is adjusted to adjust the pH value of the solution to 8-10.

[0027] Preferably, the hydrothermal treatment involves evaporating the material using a hydrothermal method.

[0028] Preferably, the evaporation temperature is 80-110℃.

[0029] In a second aspect, the present invention provides a layered polymetallic oxide-based magnetic biochar, which is prepared by the preparation method described in the first aspect;

[0030] The specific surface area (BET) of the layered polymetallic oxide-based magnetic biochar is 11.8-310.5 m². 2 ·g -1 .

[0031] Thirdly, the present invention provides an application of the layered polymetallic oxide-based magnetic biochar obtained by the preparation method described in the first aspect, specifically a method for treating arsenic and / or cadmium pollution, the method comprising using the layered polymetallic oxide-based magnetic biochar as described in the first aspect to treat arsenic and / or cadmium pollution;

[0032] In the treatment of arsenic and / or cadmium-containing solutions, the solid-liquid ratio (mg / L) of the layered polymetallic oxide-based magnetic biochar to the arsenic and / or cadmium-containing waste liquid is (0.5-5) g / L.

[0033] For the remediation of soil contaminated with arsenic and / or cadmium, the dosage of the layered polymetallic oxide-based magnetic biochar is 500-2000 kg / mu.

[0034] Compared with existing technical solutions, the present invention has the following beneficial effects:

[0035] (1) The bimetallic oxide-based magnetic biochar provided by this invention has a large specific surface area, reaching 310.55 m². 2 ·g -1 It is also easily recyclable, and the mass percentage of iron can be increased to 29.95%, the mass percentage of calcium to 20.55%, the mass percentage of magnesium to 21.52%, and the mass percentage of aluminum to 10.11%. The bimetallic oxide-based magnetic biochar exhibits good adsorption performance for arsenic (its adsorption capacity for arsenic can reach 85.77-206.58 mg·g). -1 The adsorption capacity for cadmium can reach 107.86-216.17 mg·g. -1 This modified biochar, a bimetallic oxide-based magnetic biochar, is highly efficient at treating arsenic and cadmium-contaminated wastewater. It effectively adsorbs arsenic and cadmium from the water (removal rate can reach over 85%). The treatment and safe utilization of this arsenic and cadmium-contaminated wastewater can reduce pollution and improve water quality, not only reducing the harm of polluted wastewater to the aquatic environment but also providing a new approach to the safe and efficient utilization of waste biomass. Furthermore, it can be applied to the remediation of arsenic and cadmium-contaminated sites or the safe utilization of arsenic and cadmium-contaminated farmland, enhancing soil fertility and agricultural productivity, and significantly contributing to the sustainable use of land resources.

[0036] (2) The preparation method of the bimetallic oxide-based magnetic biochar provided by the present invention is simple, easy to implement and highly adaptable to application. The modified biochar is treated at a temperature of 80-100℃, which consumes little energy. The rest are all treated under conventional conditions. Moreover, due to the stability of the raw materials, it has wide adaptability.

[0037] (3) The bimetallic oxide-based magnetic biochar provided by the present invention is prepared from biomass raw materials such as municipal sludge, bamboo powder, garlic, etc. Biomass raw materials are a large-scale and difficult-to-process biomass source. The sources are wide, the materials are easy to obtain, and the feasibility is high. It realizes the resource utilization of biomass waste and is a new agricultural production method in rural economy, which can generate huge economic benefits. Attached Figure Description

[0038] Figure 1This is a flowchart of a method for preparing layered polymetallic oxide-based magnetic biochar according to an embodiment of the present invention;

[0039] Figure 2 This is a scanning electron microscope image of the original biochar obtained from bamboo, a biomass raw material, in Example 3 of this invention;

[0040] Figure 3 This is a scanning electron microscope image of the magnetic biochar obtained in Example 1 of the present invention;

[0041] Figure 4 This is a scanning electron microscope image of the layered polymetallic oxide-based magnetic biochar obtained in Example 1 of the present invention.

[0042] The present invention will now be described in further detail. However, the examples described below are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims. Detailed Implementation

[0043] To better illustrate the present invention and facilitate understanding of its technical solutions, typical but non-limiting embodiments of the present invention are as follows:

[0044] This embodiment provides a method for preparing layered polymetallic oxide-based magnetic biochar, such as... Figure 1 As shown, the preparation method includes:

[0045] S1. The biomass is mixed with an iron salt solution and impregnated. After solid-liquid separation, the pH value of the solid material is adjusted to obtain pretreated biomass.

[0046] S2. The pretreated biomass is pyrolyzed to obtain magnetic biochar. Then, the magnetic biochar is mixed with a solution containing at least two metal salts and the pH value is adjusted. Finally, the mixture is subjected to hydrothermal treatment to obtain layered polymetallic oxide-based magnetic biochar.

[0047] In this invention, the product obtained by preparing the multi-metal oxide contains at least two metal oxides.

[0048] Specifically, the biomass is any one or a combination of at least three of the following: wheat straw, rice husks, bamboo shavings, sludge, or garlic, preferably garlic, bamboo shavings, and garlic. Typical but non-limiting combinations include wheat straw, rice husks, and garlic; sludge, rice husks, and bamboo shavings; and wheat straw, garlic, and sludge. Using biomass as a raw material has the advantages of stable yield, wide availability, and low application cost.

[0049] Sludge, bamboo shavings, and garlic are preferred because sludge char is widely available and has abundant ash content, which helps it bind with anions; bamboo char has a large specific surface area, making it a good modification carrier; and garlic char is rich in thiol groups, which is beneficial for binding with cadmium.

[0050] The biomass can be cleaned and dried before use to avoid the influence of other factors on the resulting product. The cleaning solution can be water or alcohol or other commonly used cleaning agents in the field. When washing with water, deionized water, tap water, industrial recycled water or other water that meets the requirements can be used. Drying can be done using conventional drying methods in the field, such as oven drying or air drying. When oven drying is used, the drying temperature can be selected as 60-80℃.

[0051] Specifically, the biomass particles are 60-100 mesh in size.

[0052] In this invention, the biomass particles can be any aggregate of particles within the defined range, such as aggregates of particles with uniform particle size, such as aggregates of 60-mesh particles, aggregates of 70-mesh particles, aggregates of 80-mesh particles, or aggregates of particles within a certain particle size range, such as aggregates of all particles within the particle size range of 60-80 mesh, aggregates of all particles within the particle size range of 70-90 mesh, aggregates of all particles within the particle size range of 80-1000 mesh, etc.

[0053] Specifically, the iron salt solution includes a mixed solution of ferrous and ferric iron.

[0054] Specifically, the molar ratio of ferric iron to ferrous iron in the iron salt solution is (1-4):1, for example, it can be 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1 or 4:1, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0055] Specifically, the mass ratio of the biomass to the iron salt used in the preparation of the iron salt solution is (0.5-3):1, for example, it can be 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1 or 3:1, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0056] In this iron salt solution, ferric iron can be prepared using ferric nitrate heptahydrate or other commonly used soluble ferric salts in the field. Ferric chloride or ferric sulfate can also be selected. The molar concentration of ferric iron in the solution is 0.2-0.4 mol / L, for example, 0.2 mol / L, 0.21 mol / L, 0.23 mol / L, 0.25 mol / L, 0.27 mol / L, 0.31 mol / L, 0.33 mol / L, 0.35 mol / L, 0.37 mol / L, 0.39 mol / L or 0.40 mol / L, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0057] In this iron salt solution, ferrous iron can be prepared using ferrous sulfate nonahydrate or other commonly used soluble ferrous salts in the field, such as ferrous chloride or ferrous nitrate. The molar concentration of ferrous iron in the solution is 0.1-0.3 mol / L, for example, 0.1 mol / L, 0.12 mol / L, 0.14 mol / L, 0.16 mol / L, 0.18 mol / L, 0.2 mol / L, 0.22 mol / L, 0.24 mol / L, 0.26 mol / L, 0.28 mol / L, or 0.3 mol / L, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0058] Specifically, the stirring speed during the impregnation is 300-1000 r / min, and the stirring method can be selected from commonly used stirring methods in the art, such as magnetic stirring or propeller stirring. For example, it can be 300 r / min, 400 r / min, 500 r / min, 600 r / min, 700 r / min, 800 r / min, 900 r / min or 1000 r / min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0059] Preferably, the stirring time during impregnation is 4-48 hours, for example, it can be 4 hours, 8 hours, 10 hours, 15 hours, 20 hours, 24 hours, 30 hours, 40 hours or 48 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0060] The solid-liquid separation after impregnation can be carried out by suction filtration, or by filtration, pressure filtration and other commonly used solid-liquid separation methods in this field, with the aim of separating the liquid phase in the material.

[0061] Specifically, the endpoint of the first pH adjustment is a pH value of 6.5-7.5 for the solid phase material. For example, it could be 6.5, 6.6, 6.8, 7, 7.2, 7.4, or 7.5, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. Controlling a specific pH range promotes the precipitation of iron ions on the biomass surface to form ferrohydrate, which is beneficial for the formation of goethite and magnetite during pyrolysis, thereby enhancing the adsorption performance of layered polymetallic oxide-based magnetic biochar. The pH value during this process involves measuring the pH of the residual liquid phase after pH adjustment. A pH of 6.5-7.5 for the residual liquid phase is considered acceptable.

[0062] Furthermore, the pretreated biomass obtained from S1 can be dried for better subsequent processing.

[0063] Specifically, the pyrolysis temperature is 400-800℃, for example, it can be 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃ or 800℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0064] Specifically, the pyrolysis time is 1-6 hours, for example, it can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours or 6 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0065] Specifically, the metal ions in the solution containing at least two metal salts include combinations of at least two of magnesium ions, aluminum ions, iron ions, or calcium ions. Examples, but not limited to, include magnesium ions and aluminum ions, calcium ions and aluminum ions, magnesium ions and iron ions, calcium ions, magnesium ions and aluminum ions, calcium ions, iron ions and aluminum ions, etc., with a preferred combination being calcium ions, magnesium ions and aluminum ions.

[0066] In this invention, the metal ions in the solution containing at least two metal salts should preferably include both trivalent and divalent metal ions.

[0067] Specifically, the molar ratio of trivalent metal ions to divalent metal ions in the solution containing at least two metal salts is (1-4):1, for example, it can be 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1 or 4, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0068] In this invention, the molar ratio of trivalent metal ions to divalent metal ions in a solution containing at least two metal salts is the molar ratio of all trivalent metal ions to all divalent metal ions.

[0069] Furthermore, during the mixing process of magnetic biochar and solution containing at least two metal salts in S2, the mass ratio of magnetic biochar to all metal salts used in preparing solution containing at least two metal salts is controlled to be 1:(0.5-3), for example, it can be 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5 or 1:3, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0070] Preferably, the solid-liquid ratio (g / mL) of the magnetic biochar and the solution containing at least two metal salts is 1:(1-20), for example, it can be 1:1, 1:2, 1:4, 1:6, 1:8, 1:10, 1:12, 1:14, 1:16, 1:18 or 1:20, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0071] Specifically, the second pH value adjustment is to adjust the pH value of the solution to 8-10, for example, it can be 8, 8.5, 9, 9.5 or 10, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0072] Preferably, the hydrothermal treatment involves evaporating the material using a hydrothermal method.

[0073] Preferably, the evaporation temperature is 80-110℃, for example, it can be 80℃, 85℃, 90℃, 95℃, 100℃, 105℃ or 110℃, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0074] In this invention, in order to make efficient and practical use of the layered polymetallic oxide-based magnetic biochar obtained by hydrothermal treatment, the product obtained after hydrothermal treatment can also be ground and sieved to obtain a powdered product that meets the usage requirements.

[0075] Furthermore, the present invention provides a layered polymetallic oxide-based magnetic biochar, which is prepared by the preparation method described above;

[0076] The specific surface area (BET) of the layered polymetallic oxide-based magnetic biochar is 11.8-310.5 m². 2 ·g -1 .

[0077] In this invention, the obtained layered polymetallic oxide-based magnetic biochar comprises, by mass percentage: C 0.00-83.75%, O 7.12-44.1%, Fe 6.15-29.52%, and M 1.28-52.18%, totaling 100%.

[0078] M includes one or a combination of at least two of Ca, Mg, or Al.

[0079] Among them, when the obtained layered polymetallic oxide-based magnetic biochar contains Ca, the Ca content is 3.33-20.55%; when it contains Mg, the Mg content is 2.66-21.52%; and when it contains Al, the Al content is 1.28-10.11%.

[0080] Furthermore, the present invention provides a method for treating arsenic and / or cadmium pollution, the method comprising using layered polymetallic oxide-based magnetic biochar as described above to treat arsenic and / or cadmium pollution;

[0081] In treating solutions containing arsenic and / or cadmium, the solid-liquid ratio (mg / L) of the layered polymetallic oxide-based magnetic biochar to the arsenic and / or cadmium-containing wastewater is (0.5-5) g / L.

[0082] For the remediation of soil contaminated with arsenic and / or cadmium, the dosage of the layered polymetallic oxide-based magnetic biochar is 500-2000 kg / mu.

[0083] To further illustrate the superior properties of the layered polymetallic oxide-based magnetic biochar prepared in this invention, the following specific examples are provided:

[0084] Example 1

[0085] This embodiment provides a method for preparing layered polymetallic oxide-based magnetic biochar, comprising the following steps:

[0086] (1) Crush the bamboo and pass it through an 80-mesh sieve to obtain the sieved biomass raw material;

[0087] (2) The crushed biomass raw material and the iron salt mixture with a molar ratio of 3:1 of ferric iron and ferrous iron were magnetically stirred at 500 r / min for 24 h at a mass ratio of 1:1 (biomass solid: iron salt). After that, the mixture was filtered and the pH value of the solid phase was adjusted to 7. Then it was dried at 60 °C and finally pyrolyzed at 400, 600 and 800 °C for 2 h respectively. The mixture was then crushed to 100 mesh to obtain magnetic biochar at the corresponding temperature.

[0088] (3) A calcium magnesium aluminum metal salt solution with a molar ratio of trivalent metal to divalent metal of 3:1 was mixed with magnetic biochar obtained at different pyrolysis temperatures at a loading ratio of 0.5:1, 1:1 or 2:1 and a solid-liquid ratio of 1g:20mL. The pH of the mixture was adjusted to 8 with 1mol / L sodium hydroxide. Then, the mixture was crosslinked at an evaporation temperature of 90℃ using a hydrothermal method until the water was evaporated. After that, it was washed with deionized water until the pH of the washing liquid was 7. After freeze drying, it was ground for 30min and pulverized to a particle size of 100 mesh to obtain layered polymetallic oxide-based magnetic biochar.

[0089] Example 2

[0090] The only difference from Example 1 is that the biomass is replaced with sludge and garlic respectively, resulting in polymetallic oxide-based magnetic sludge charcoal, polymetallic oxide-based magnetic garlic charcoal and polymetallic oxide-based magnetic bamboo charcoal respectively.

[0091] Example 3

[0092] This embodiment provides a process for preparing biochar, specifically using bamboo, sludge and garlic as biomass raw materials, crushing them and passing them through an 80-mesh sieve, and then pyrolyzing the screened products at 400℃, 600℃ and 800℃ for 2 hours to obtain pyrolytic biochar.

[0093] The main physicochemical properties of the biochar before and after modification in Examples 1-3 were analyzed. The specific surface area, pore volume and pore size were tested using a Micromeritics APSP2460 4-station fully automated specific surface area analyzer under 77K liquid nitrogen conditions. After the instrument analysis was completed, isothermal adsorption-desorption curves were obtained. The total specific surface area, pore volume and pore size of the material were obtained by BET method. The analytical results are detailed in Table 1.

[0094] Table 1

[0095]

[0096] Note: B-BC is bamboo-derived pyrolysis biochar at 800℃; B-MBC is bamboo-derived pyrolysis magnetic biochar at 800℃; G-BC is garlic-derived pyrolysis biochar at 800℃; G-MBC is garlic-derived pyrolysis magnetic biochar at 800℃; S-BC is sludge-derived pyrolysis biochar at 800℃; S-MBC is sludge-derived pyrolysis magnetic biochar at 800℃; LMBC is layered polymetallic oxide-based magnetic biochar; L... x MBC y In the figure, x represents the loading ratio (polymetallic oxide: magnetic biochar), such as x=0.5 means 0.5:1, x=1 means 1:1, x=2 means 2:1, and y represents the pyrolysis temperature, which is 400, 600 and 800℃, and it is derived from bamboo biomass; S-LMBC and G-LMBC represent layered polymetallic oxide-based magnetic biochar derived from sludge biomass and garlic biomass, respectively, and their preparation conditions are a polymetallic oxide loading ratio of 1:1 and pyrolysis at 800℃.

[0097] Table 1 shows that bamboo biomass exhibits the highest specific surface area upon pyrolysis at 800℃, making it an excellent carrier for modified cross-linking. Compared to unmodified biochar from various biomass sources, the modified biochar has a slightly lower specific surface area, but significantly increased iron, calcium, magnesium, and aluminum content, reaching 10-30% by mass. The introduction of metal elements signifies an increase in effective active adsorption sites, enabling effective bonding of arsenic and cadmium. Figures 2-4 It can be more clearly seen that the surface of the polymetallic oxide-based magnetic sludge carbon exhibits a layered, wrinkled morphology, which is due to the precipitation and loading of nano-layered polymetallic oxides on the surface of the biochar matrix.

[0098] Example 4

[0099] This embodiment provides a method for preparing layered polymetallic oxide-based magnetic biochar, comprising the following steps:

[0100] (1) Crush the bamboo and pass it through an 80-mesh sieve to obtain the sieved biomass raw material;

[0101] (2) The crushed biomass raw material and the iron salt mixture with a molar ratio of 3:1 of ferric iron and ferrous iron were magnetically stirred at 500 r / min for 24 h at a mass ratio of 1:1 (biomass solid: iron salt). After that, the mixture was filtered and the pH value of the obtained solid phase was controlled to be 7. Then the solid phase was dried at 60 °C and finally pyrolyzed at 400 °C for 2 h. The solid phase was then crushed to 100 mesh to obtain magnetic biochar.

[0102] (3) A calcium magnesium aluminum metal salt solution with a molar ratio of trivalent metal to divalent metal of 3:1 was mixed with magnetic biochar at a loading ratio of 1:1 and a solid-liquid ratio of 1g:20mL. The pH of the mixture was adjusted to 8 with 1mol / L sodium hydroxide. Then, the mixture was cross-linked at an evaporation temperature of 90℃ using a hydrothermal method until the water was evaporated. After that, it was washed with deionized water until the pH of the washing solution was 7. It was then freeze-dried, ground for 30min, and pulverized to a particle size of 100 mesh to obtain layered polymetallic oxide-based magnetic biochar.

[0103] Furthermore, this embodiment also provides the original biochar corresponding to the biomass raw material, and the preparation process is as follows:

[0104] Bamboo was crushed and passed through an 80-mesh sieve. The sieved product was then pyrolyzed in a muffle furnace at a temperature of 400°C for 2 hours. After cooling to 30°C, raw biochar was obtained.

[0105] Example 5

[0106] The only difference from Example 4 is that the pyrolysis temperature in step (2) of preparing layered polymetallic oxide-based magnetic biochar is changed to 600°C.

[0107] Furthermore, this embodiment also provides the original biochar corresponding to the biomass raw material, and the preparation process is as follows:

[0108] Bamboo is crushed and passed through an 80-mesh sieve. The sieved product is then pyrolyzed in a muffle furnace at a temperature of 600°C for 2 hours. After cooling to 30°C, raw biochar is obtained.

[0109] Example 6

[0110] The only difference from Example 4 is that the pyrolysis temperature in step (2) of preparing layered polymetallic oxide-based magnetic biochar is changed to 800°C.

[0111] Furthermore, this embodiment also provides the original biochar corresponding to the biomass raw material, and the preparation process is as follows:

[0112] Bamboo was crushed and passed through an 80-mesh sieve. The sieved product was then pyrolyzed in a muffle furnace at a temperature of 800°C for 2 hours. After cooling to 30°C, raw biochar was obtained.

[0113] Example 7

[0114] This embodiment provides a method for preparing layered polymetallic oxide-based magnetic biochar, comprising the following steps:

[0115] (1) Crush the bamboo and pass it through an 80-mesh sieve to obtain the sieved biomass raw material;

[0116] (2) The crushed biomass raw material was magnetically stirred at 500 r / min for 24 h with iron salt mixtures of ferric iron and ferrous iron in molar ratios of 0.5:1, 1:1 and 2:1 respectively, at a mass ratio of 0.5:1 (biomass solid: iron salt). After that, the mixture was filtered and the pH of the resulting solid phase was controlled to be 7. The solid phase was then dried at 60 °C and finally pyrolyzed at 800 °C for 2 h. The mixture was then crushed to 100 mesh to obtain magnetic biochar.

[0117] (3) A calcium magnesium aluminum metal salt solution with a molar ratio of trivalent metal to divalent metal of 3:1 was mixed with magnetic biochar at a loading ratio of 0.5:1 and a solid-liquid ratio of 1g:10mL. The pH of the mixture was adjusted to 9 with 1mol / L sodium hydroxide. Then, the mixture was cross-linked at an evaporation temperature of 90℃ using a hydrothermal method until the water was evaporated. After that, it was washed with deionized water until the pH of the washing solution was 7. It was then freeze-dried, ground for 30min, and pulverized to a particle size of 100 mesh to obtain layered polymetallic oxide-based magnetic biochar.

[0118] Example 8

[0119] The only difference from Example 7 is that in step (3) of preparing layered polymetallic oxide-based magnetic biochar, the loading ratio of calcium magnesium aluminum metal salt solution is adjusted to 1:1.

[0120] Example 9

[0121] The only difference from Example 7 is that in step (3) of preparing layered polymetallic oxide-based magnetic biochar, the loading ratio of calcium magnesium aluminum metal salt solution is adjusted to 2:1.

[0122] Example 10

[0123] The only difference from Example 7 is that in step (3) of preparing layered polymetallic oxide-based magnetic biochar, the calcium magnesium aluminum metal salt solution is replaced with a calcium aluminum metal salt solution, and the loading ratio is adjusted to 2:1.

[0124] Example 11

[0125] The only difference from Example 7 is that in step (3) of preparing layered polymetallic oxide-based magnetic biochar, the calcium magnesium aluminum metal salt solution is replaced with a magnesium aluminum metal salt solution, and the loading ratio is adjusted to 2:1.

[0126] Example 12

[0127] The only difference from Example 7 is that in step (3) of preparing layered polymetallic oxide-based magnetic biochar, the calcium magnesium aluminum metal salt solution is replaced with a calcium magnesium metal salt solution, and the loading ratio is adjusted to 2:1.

[0128] Example 13

[0129] The only difference from Example 6 is that the biomass is first pyrolyzed to obtain biochar, which is then mixed and impregnated with an iron salt solution, and then dried and pulverized. Step (3) remains unchanged.

[0130] Example 14

[0131] The only difference from Example 6 is that the molar ratio of trivalent metal to divalent metal in the preparation of polymetallic oxide-based magnetic biochar (3) is adjusted to 1:3.

[0132] Application examples

[0133] This application example specifically illustrates the treatment effect of the layered polymetallic oxide-based magnetic biochar obtained in Examples 4-14 on the heavy metal elements arsenic and cadmium, as detailed below:

[0134] 1. Adsorption performance of layered polymetallic oxide-based magnetic biochar for arsenic and cadmium under different pyrolysis temperatures

[0135] Weigh 0.2500 g each of the original biochar, magnetic biochar, and layered polymetallic oxide-based magnetic biochar from Examples 4-6, place them in 50 mL Erlenmeyer flasks, and add 25 mL of each flask with a concentration gradient of 10-250 mg·L⁻¹. -1 A mixed As(III) / Cd(II) solution, with pH adjusted to 4.5, was subjected to a reaction at 150 r·min at room temperature. -1 The mixture was shaken at a constant speed for 8 hours and then centrifuged. The supernatant was filtered and the arsenic content was determined by atomic fluorescence spectrometry, while the cadmium content was determined by inductively coupled plasma atomic emission spectrometry. The adsorption capacity was calculated based on the difference from the initial concentration. Each treatment was repeated 3 times.

[0136] Weigh 0.2500 g of each of the layered polymetallic oxide-based magnetic biochar from Examples 4-6, place them in 50 mL Erlenmeyer flasks, and add 25 mL of a 100 mg·L⁻¹ solution to each flask. -1An As(III) / Cd(II) mixed solution was prepared, with the pH adjusted to 4.5. The solution was shaken at 150 rpm for 8 hours at room temperature, followed by centrifugation. The supernatant was filtered, and the arsenic content was determined using atomic fluorescence spectrometry (AFS), while the cadmium content was determined using inductively coupled plasma atomic emission spectrometry (ICP-AES). The adsorption efficiency was calculated based on the initial concentration, with each treatment repeated three times. The adsorption capacity results are shown in Table 2, and the adsorption efficiency is shown in Table 3.

[0137] The adsorption capacity results are detailed in Table 2, and the adsorption efficiency results are detailed in Table 3.

[0138] The results, as shown in Table 2, indicate that the adsorption capacity of the original biochar for arsenic was 5.9-15.9 mg·g. -1 The adsorption capacity for cadmium is 20.1-39.2 mg·g. -1 The adsorption capacity of magnetic biochar for arsenic is 78.1-91.6 mg·g. -1 The adsorption capacity for cadmium is 76.0-108.1 mg·g⁻¹. -1 The adsorption capacity of layered polymetallic oxide-based magnetic biochar for arsenic is 105.1-189.6 mg·g⁻¹. -1 The adsorption capacity for cadmium is 152.1-206.8 mg·g. -1 The layered polymetallic oxide-based magnetic biochar prepared by this method has a 10-12 times higher adsorption capacity for arsenic and a 4-7 times higher adsorption capacity for cadmium compared to the original biochar.

[0139] The results, as shown in Table 3, indicate that the removal rates of arsenic by raw biochar were 6-17% and cadmium by 16-34%; the removal rates of arsenic by magnetic biochar were 46-69% and cadmium by 52-79%; and the removal rates of arsenic by layered polymetallic oxide-based magnetic biochar were 73-90% and cadmium by 75-91%. Among these, the layered polymetallic oxide-based magnetic biochar pyrolyzed at 800℃ showed the best removal effect for arsenic and cadmium, with removal rates exceeding 90%. The layered polymetallic oxide-based magnetic biochar pyrolyzed at 400℃ had a lower removal rate, but its removal efficiency for arsenic and cadmium was still above 70%. Therefore, the polymetallic oxide functionalization modification of biochar significantly improves its removal rate of arsenic and cadmium, greatly enhancing its ability to remove arsenic and cadmium from water bodies.

[0140] Table 2

[0141]

[0142] Table 3

[0143]

[0144] When the layered polymetallic oxide-based magnetic biochar obtained in Examples 4-6 adsorbs arsenic and cadmium wastewater of different concentrations, such as 60 mg·L⁻¹, the adsorption effect is achieved. -1 70 mg·L -1 80 mg·L -1 100 mg·L -1 150 mg·L -1 Even so, the removal efficiency of arsenic and cadmium in the solution is still above 80%.

[0145] 3. Adsorption performance of layered polymetallic oxide-based magnetic biochar for arsenic and cadmium under different loading ratios.

[0146] Weigh 0.2500 g of each layered polymetallic oxide-based magnetic biochar prepared under the conditions described in Examples 7-9, place them in a 50 mL Erlenmeyer flask, and add 25 mL of each flask with a concentration gradient of 10-250 mg·L⁻¹. -1 A mixed As(III) / Cd(II) solution, with pH adjusted to 4.5, was subjected to a reaction at 150 r·min at room temperature. -1 The mixture was shaken at a constant speed for 8 hours and then centrifuged. The supernatant was filtered and the arsenic content was determined by atomic fluorescence spectrometry, while the cadmium content was determined by inductively coupled plasma atomic emission spectrometry. The adsorption capacity was calculated based on the difference from the initial concentration. Each treatment was repeated 3 times.

[0147] Weigh 0.2500 g of each of the layered polymetallic oxide-based magnetic biochar from Examples 7-9, place them in 50 mL Erlenmeyer flasks, and add 25 mL of a 100 mg·L⁻¹ solution to each flask. -1 An As(III) / Cd(II) mixed solution was prepared, with the pH adjusted to 4.5. The solution was shaken at 150 r / min at room temperature for 8 hours, followed by centrifugation. The supernatant was filtered, and the arsenic content was determined by atomic fluorescence spectrometry (AFS), while the cadmium content was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES). The adsorption efficiency was calculated based on the initial concentrations, with each treatment repeated three times. The adsorption capacity results are shown in Table 4, and the adsorption efficiency is shown in Table 5.

[0148] As shown in Tables 4 and 5, a higher layered polymetallic oxide loading ratio results in higher adsorption capacity and removal rate. The adsorption capacity of the layered polymetallic oxide-based magnetic biochar under the (2:1) loading ratio preparation condition for arsenic and cadmium is about 1 times that under the (0.5:1) preparation condition, and the removal rate is increased by more than 30%. This indicates that the layered polymetallic oxide loading can improve the adsorption capacity of the modified biochar.

[0149] Table 4

[0150]

[0151] Table 5

[0152]

[0153] 4. Adsorption performance of layered polymetallic oxide-based magnetic biochar for arsenic and cadmium under different metal selection and ratio preparation conditions

[0154] Weigh 0.2500 g of each layered polymetallic oxide-based magnetic biochar prepared under the conditions described in Examples 10-14, place them in 50 mL Erlenmeyer flasks, and add 25 mL of each flask with a concentration gradient of 10-250 mg·L⁻¹. -1 A mixed As(III) / Cd(II) solution, with pH adjusted to 4.5, was subjected to a reaction at 150 r•min at room temperature. -1 The mixture was shaken at a constant speed for 8 hours and then centrifuged. The supernatant was filtered and the arsenic content was determined by atomic fluorescence spectrometry, while the cadmium content was determined by inductively coupled plasma atomic emission spectrometry. The adsorption capacity was calculated based on the difference from the initial concentration. Each treatment was repeated 3 times.

[0155] Weigh 0.2500 g of each of the layered polymetallic oxide-based magnetic biochar from Examples 10-14, place them in 50 mL Erlenmeyer flasks, and add 25 mL of a 100 mg·L⁻¹ solution to each flask. -1 An As(III) / Cd(II) mixed solution was prepared, with the pH adjusted to 4.5. The solution was shaken at 150 rpm for 8 hours at room temperature, followed by centrifugation. The supernatant was filtered, and the arsenic content was determined using atomic fluorescence spectrometry (AFS), while the cadmium content was determined using inductively coupled plasma atomic emission spectrometry (ICP-AES). The adsorption efficiency was calculated based on the initial concentration, with each treatment repeated three times. The adsorption capacity results are shown in Table 6, and the adsorption efficiency is shown in Table 7.

[0156] As shown in Tables 6 and 7, the adsorption effects of pre-impregnated calcium-magnesium-based, calcium-aluminum-based, and magnesium-aluminum-based magnetic carbon on arsenic and cadmium were all inferior to those of calcium-magnesium-aluminum-based magnetic carbon, indicating that the calcium-magnesium-aluminum-based compound formulation was the most effective in enhancing the adsorption of arsenic and cadmium by layered polymetallic oxide-based magnetic biochar. According to Tables 6 and 7, the adsorption capacity of calcium-magnesium-aluminum-based magnetic carbon for arsenic and cadmium was 65%-107% and 71%-123% higher than that of calcium-magnesium-based, calcium-aluminum-based, and magnesium-aluminum-based magnetic carbon, respectively, confirming the above conclusions. The removal rate results showed similar conclusions. Furthermore, the adsorption capacity of pre-impregnated calcium-magnesium-aluminum-based magnetic carbon for arsenic and cadmium was 26%-42% higher than that of post-impregnated calcium-magnesium-aluminum-based magnetic carbon, and the removal rate was increased by more than 10%. This indicates that iron salt pre-impregnation is the preferred method for improving the adsorption capacity of layered polymetallic oxide-based magnetic biochar for arsenic and cadmium.

[0157] Table 6

[0158]

[0159] Table 7

[0160]

[0161] In Tables 6 and 7, except for the (1:3) molar ratio of trivalent to divalent metals in the calcium-magnesium preimpregnated magnetic carbon, the molar ratio of trivalent to divalent metals in the other layered polymetallic oxide-based magnetic biochars is 3:1, which corresponds to the examples.

[0162] 5. The role of layered polymetallic oxide-based magnetic biochar in fixing arsenic and cadmium in soil.

[0163] (1) Soil samples: The soil samples were collected from contaminated farmland surrounding the site in Dalian, Liaoning Province. The collected soil samples were air-dried and sieved through a 2mm sieve before use. 100g of soil was sieved through a 0.149mm sieve, and relevant indicators were determined according to conventional soil agricultural chemistry analysis methods. The basic physicochemical properties of the soil were: total arsenic content 178.75 mg·kg⁻¹. -1 The arsenic content extracted from NaHCO3 was 8.56 mg·kg⁻¹. -1 The total cadmium content was 8.12 mg / kg. -1 The pH value is 8.02, and the organic matter content is 47.66 g·kg⁻¹. -1 The cation exchange capacity is 15.96 cmol·kg⁻¹ -1 In the mechanical composition of soil, particles with a diameter of 2.0-0.2 mm account for 51.51%, particles with a diameter of 0.2-0.02 mm account for 40.99%, and particles with a diameter of 0.02-0.002 mm account for 7.50%.

[0164] (2) Soil cultivation experiment

[0165] 100 g of air-dried soil sample, passed through a 2 mm sieve, was weighed into a 250 mL beaker. The original biochar, magnetic biochar, and layered polymetallic oxide-based magnetic biochar from Examples 6-13 were applied to the soil at a mass fraction of 3% (with blank soil as a control). After uniform mixing, a certain amount of ultrapure water was added to bring the moisture content to 70% of field capacity. The mixture was then placed in a constant temperature and humidity chamber at 25℃ and 70% humidity for incubation. Each treatment was repeated three times, with water replenished using the constant weight method to maintain 70% of field capacity. Samples were taken after 30 days of incubation, and the toxic leaching content of arsenic and cadmium in the soil was extracted using the TCLP method.

[0166] (3) Test indicators: TCLP toxicity leaching test: Prepare 500 mL of acetic acid extract with pH 2.88 using glacial acetic acid. Take 1 g of soil into 20 mL of acetic acid extract and shake for 18 h. Then centrifuge, filter, dilute, and measure the solution content using an instrument.

[0167] Results: Analysis of the TCLP toxicity leaching experiment of arsenic and cadmium showed that after 30 days of cultivation, the TCLP leaching content of arsenic in the soil decreased significantly after the addition of layered polymetallic oxide-based magnetic biochar. The passivation efficiency of arsenic and cadmium in the soil was over 85%, while the toxicity leaching of arsenic and cadmium in the soil was high under the original biochar treatment. Therefore, the application of layered polymetallic oxide-based magnetic biochar greatly reduced the toxicity leaching content of arsenic and cadmium in the soil, thus effectively fixing the active arsenic and cadmium in the soil.

[0168] The present invention is described in detail through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0169] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0170] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0171] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for treating arsenic and cadmium-contaminated soil, characterized in that, The method includes the remediation of arsenic and cadmium contaminated soil using layered polymetallic oxide-based magnetic biochar. For the remediation of arsenic and cadmium-contaminated soil, the dosage of the layered polymetallic oxide-based magnetic biochar is 500-2000 kg / mu. The preparation method of the layered polymetallic oxide-based magnetic biochar includes: S1. The biomass is mixed with an iron salt solution and impregnated. After solid-liquid separation, the pH value of the solid material is adjusted to obtain pretreated biomass. S2. The pretreated biomass is pyrolyzed to obtain magnetic biochar. Then, the magnetic biochar is mixed with a solution of calcium ion, magnesium ion, and aluminum ion metal salts and the pH value is adjusted. Then, it is subjected to hydrothermal treatment to obtain layered polymetallic oxide-based magnetic biochar. The biomass includes any one of wheat straw, rice husks, bamboo shavings, sludge, or garlic; The endpoint of the first pH adjustment is a pH of 7 for the solid phase material; The specific surface area (BET) of the layered polymetallic oxide-based magnetic biochar is 11.8-310.5 m². 2 •g -1 ; The iron salt solution comprises a mixed solution of ferrous iron (Fe2+) and ferric iron (Fe3+), wherein the molar ratio of ferric iron to ferrous iron in the iron salt solution is (1-4):

1. The pyrolysis temperature is 800℃, and the pyrolysis time is 1-6 hours; The molar ratio of trivalent metal ions to divalent metal ions in the calcium, magnesium, and aluminum ion metal salt solution is (1-4):

1. The second pH value is adjusted to a solution pH of 8-10; The solid-liquid ratio of the magnetic biochar and the calcium, magnesium, and aluminum ion metal salt solution is 1:(1-20) g / mL.

2. The method for treating arsenic and cadmium contaminated soil as described in claim 1, characterized in that, The biomass particles are 60-100 mesh in size.

3. The method for treating arsenic and cadmium contaminated soil as described in claim 1, characterized in that, The mass ratio of the biomass to the iron salt used in the preparation of the iron salt solution is (0.5-3):

1.

4. The method for treating arsenic and cadmium contaminated soil as described in claim 1, characterized in that, The stirring speed during the impregnation is 300-1000 r / min.

5. The method for treating arsenic and cadmium contaminated soil as described in claim 1, characterized in that, The stirring time during the impregnation is 4-48 hours.

6. The method for treating arsenic and cadmium contaminated soil as described in claim 1, characterized in that, The hydrothermal treatment involves evaporating the material using a hydrothermal method.

7. The method for treating arsenic and cadmium contaminated soil as described in claim 6, characterized in that, The temperature for evaporation is 80-110℃.

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