A modified magnetic biochar, preparation method and application thereof in adsorbing heavy metals in composting

Abstract

The present invention proposes a modified magnetic biochar, a preparation method and an application thereof in adsorbing heavy metals in compost, belonging to the technical field of heavy metal treatment in solid phase. The modified magnetic biochar preparation method comprises the following steps: (1) first loading active metal magnesium on biochar, then loading amino groups and sulfonic acid groups to obtain preliminary modified biochar; (2) loading magnetic nano zero-valent iron on the preliminary modified biochar to obtain modified magnetic biochar. The prepared modified magnetic biochar material not only has strong adsorption capacity and rich functional groups, but also has magnetic adsorption force, and can adsorb heavy metal pollutants in the solid phase of compost.

Description

Technical Field

[0001] The invention belongs to the technical field of heavy metal treatment in a solid phase, and in particular relates to a modified magnetic biochar, a preparation method and application thereof in adsorbing heavy metals in composting. Background Art

[0002] Heavy metal pollution refers to environmental pollution caused by heavy metals or their compounds. It is mainly caused by human factors such as mining, exhaust gas emissions, sewage irrigation and the use of products with excessive heavy metals. Due to human activities, the content of heavy metals in the environment has increased beyond the normal range, directly endangering human health and causing deterioration of environmental quality. Heavy metals mainly exist in the solid phase (soil or manure, etc.) or liquid phase (various types of wastewater). Most adsorption materials or adsorption methods target heavy metals in solution. Compared with liquid phase, solid phase heavy metals cannot be extracted and recovered and have low mobility, which is the main reason for their difficulty in treatment. Therefore, how to remove heavy metals in the solid phase has become a difficult point in environmental governance.

[0003] Biomass waste is widely available, low-cost, environmentally friendly and renewable. Biochar materials prepared by biomass carbonization show great potential in the control of heavy metal pollutants. However, due to the underdeveloped pore structure of native biochar and the unreasonable distribution of surface functional groups, their performance in the adsorption of heavy metal pollutants is poor. The active metal elements loaded on the surface of biochar can react with the target and improve the adsorption performance of biochar. However, the characteristics of biochar loaded with active metal elements are that it is dispersed in the solid phase, does not aggregate, and is not easy to recover, which makes it perform poorly in the adsorption of solid-phase heavy metal pollutants. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes a modified magnetic biochar, a preparation method and its application in the adsorption of heavy metals in compost. The modified magnetic biochar material not only has strong adsorption capacity and rich functional groups, but also has magnetic adsorption force, and can adsorb heavy metal pollutants in the solid phase of compost.

[0005] The present invention has a unique advantage in recycling. The magnetic material can absorb the solid phase heavy metals around the material through magnetic force, and the certain shape and size are convenient for recycling, so as to achieve the purpose of removing the solid phase heavy metals.

[0006] To achieve the above object, the present invention provides a method for preparing modified magnetic biochar, comprising the following steps:

[0007] (1) first loading active metal magnesium on biochar, then loading amino groups and sulfonic acid groups to obtain preliminary modified biochar;

[0008] (2) Loading magnetic nano zero-valent iron onto the preliminary modified biochar to obtain modified magnetic biochar.

[0009] Furthermore, the preparation method of the biochar is as follows:

[0010] The biomass raw material is dried, carbonized at 600° C. for 1.5 h, the heating rate is controlled to be 10° C. / min, washed, and dried to obtain the biochar.

[0011] Furthermore, the particle size of the biomass raw material is 0.05 to 1 mm, preferably 0.1 to 0.5 mm. In the present invention, corn stalks are preferably used as the biomass raw material, which has a wide range of raw material sources and low production costs.

[0012] Furthermore, after washing, the drying temperature is 45-75° C. and the drying time is 8 hours.

[0013] Further, the method of loading active metal magnesium is as follows:

[0014] a. preparing a saturated magnesium donor solution;

[0015] b. Soaking the biochar in the saturated magnesium donor solution, heating in a water bath, drying, and carbonizing at high temperature to obtain biochar loaded with active metal magnesium.

[0016] Furthermore, the mass concentration of the magnesium donor solution is 20-28%, preferably 25-28%, most preferably 27-28%, preferably a saturated magnesium chloride solution. The present invention has no particular limitation on the amount of the magnesium donor solution, as long as it can immerse the biomass raw material.

[0017] Furthermore, the magnesium donor solution is preferably a magnesium chloride solution, and the preparation method is as follows: 500 mL of pure water is taken, and at 20° C., a solid magnesium chloride sample is added into the pure water at once to prepare a saturated magnesium chloride solution.

[0018] Furthermore, in step b, the water bath heating temperature is 60-90°C, and the water bath heating time is more than 8 hours. Within this water bath heating condition range, the reaction can be completed; however, based on economic cost considerations, in some preferred schemes, the water bath heating temperature is 80°C, and the time is 8 hours. The high temperature carbonization temperature is 300-900°C, and the high temperature carbonization time is 15-120 minutes.

[0019] Furthermore, in step b, the immersion temperature of the biochar in the saturated magnesium donor solution is 10-40°C, preferably 20-30°C; the immersion temperature is preferably room temperature; the immersion time is preferably 5-10h, more preferably 6-8h, and most preferably 7-8h.

[0020] Furthermore, in step b, the drying temperature is preferably 45 to 75° C., more preferably 55 to 65° C.; the drying time is preferably 15 to 120 min, more preferably 60 to 90 min.

[0021] Further, in step b, high-temperature carbonization is preferably carried out in a protective atmosphere; the present invention has no special limitation on the protective atmosphere, and a protective atmosphere well known in the art can be used. In the present invention, the protective atmosphere is preferably nitrogen. In the present invention, the temperature of the high-temperature carbonization is 300-900°C, preferably 400-800°C, and most preferably 500-700°C; the time of the high-temperature carbonization is 15-120min, preferably 30-90min, and most preferably 50-80min. The present invention has no special limitation on the equipment used for high-temperature carbonization, and a high-temperature carbonization equipment well known in the art can be used; in an embodiment of the present invention, high-temperature carbonization is preferably carried out in a tubular furnace.

[0022] Further, the method of loading the amino group and the sulfonic acid group is as follows:

[0023] The biochar loaded with active metal magnesium is placed in a donor solution containing amino groups and sulfonic acid groups, stirred evenly and then allowed to stand, washed and dried to constant weight to obtain a preliminary modified biochar.

[0024] Furthermore, the mass concentration of the amino and sulfonic acid donor solution is 32-50%, preferably 35-40%, and most preferably 38-40%. The present invention has no particular limitation on the amount of the amino and sulfonic acid donor solution, as long as it can immerse the biomass raw material.

[0025] Furthermore, the amino group and sulfonic acid group donor solution includes a solution containing sodium persulfamate, magnesium sulfamate or sulfamic acid.

[0026] Furthermore, the method of loading the magnetic nano zero-valent iron onto the preliminarily modified biochar is as follows:

[0027] The preliminary modified biochar is placed in a solution containing a trivalent iron donor, and after a period of contact, an ethanol solution is added, stirred evenly, and then a NaBH4 solution is added while stirring. After the addition is completed, stirring is continued, centrifugation, filtration, washing, and drying are performed to obtain a modified magnetic biochar material for adsorbing heavy metals in compost. In this step, the role of the ethanol solution is to allow the iron ions to be loaded better, because ethanol contains a large number of free strong polar hydroxyl groups, and these groups form chelate bonds with metal ions in the aqueous solution, tightly encapsulating around the metal ions to form a limited structure with a limited shape, so that the size of the synthesized nanoparticles is limited, thereby achieving the purpose of modification. The principle of the loading sequence is to first extract and load magnesium and aminosulfonyl groups, and then reduce the iron ions to zero-valent iron. First, this conforms to the law from simple to complex. Secondly, after loading iron, it needs to be stored under dry anaerobic conditions. If iron is loaded first, it will be exposed to air again, so that the iron is oxidized.

[0028] Furthermore, the ferric iron donor solution is a ferric chloride solution; the contact time is 3 hours; the volume fraction of the ethanol solution is 50%, and after adding the ethanol solution, stirring is performed for 10 minutes; after adding the NaBH4 solution, stirring is performed for 30 minutes; the mass ratio of the ferric chloride solution to the NaBH4 solution is 16.2:0.684.

[0029] Furthermore, the method for loading active metal magnesium is specifically performed as follows: 500 mL of pure water is taken, and at 20°C, a solid sample of magnesium chloride is added to the pure water at one time to prepare a saturated magnesium chloride solution. 20 g of corn straw biochar is placed in the saturated magnesium chloride solution and soaked at 25°C for 7 hours, heated in a water bath at 80°C for 8 hours, and the modified corn straw biochar is taken out after heating, and dried at 60°C for 80 minutes to obtain a semi-modified material. The semi-modified material is placed in a quartz tube furnace, carbonized at 600°C for 0.5 hours under nitrogen atmosphere protection, and the heating rate is controlled at 10°C / min. The material obtained after carbonization is rinsed with deionized water 3 to 5 times and then dried.

[0030] Furthermore, the method of loading amino groups and sulfonic acid groups is specifically performed as follows: 20 g of biochar loaded with active metal magnesium is added to 500 mL of 0.05 g / mL sodium peraminosulfonate solution, stirred evenly, and allowed to stand at 25°C for 8 hours or more, rinsed repeatedly with deionized water several times, and dried in a drying oven at 105°C until the mass no longer changes, thereby obtaining a preliminary modified biochar.

[0031] Furthermore, the method of loading the magnetic nano zero-valent iron onto the preliminarily modified biochar comprises the following specific operations:

[0032] Take 600mL of pure water, pass nitrogen for 30min to remove dissolved oxygen in the water, put 16.2g FeCl3 into 500mL of the above pure water to prepare a 32.4g / L ferric chloride solution (FeCl3 solution), put 20g of the above preliminary modified biochar into the above FeCl3 solution, add 50mL of 50% (volume fraction) ethanol solution after contact for 3h, and stir for 10 minutes after adding to make the preliminary modified biochar more evenly dispersed in the solution. At 25℃, add 30mL of 22.8g / L NaBH4 solution dropwise to the reaction system through a pipette while stirring, and continue stirring for 30min after the NaBH4 solution is completely added. After the reaction is completed, the mixture is centrifuged, vacuum filtered, the residual ions are rinsed with deionized water, and vacuum freeze-dried to obtain modified magnetic biochar.

[0033] A modified magnetic biochar is prepared according to the above preparation method.

[0034] The modified magnetic biochar is used in adsorbing heavy metals in composting.

[0035] Mechanism of modified magnetic biochar of the present invention: Fe 0 and -NH2 were successfully loaded onto the new modified biochar. The new modified biochar material containing -NH2 functional groups can react with Fe 0 Working together, with the participation of water, Fe 0 Oxidized to Fe 2 + , then Fe 2+ Reacts with -NH2 to generate ≡FeNH2, which can react with Cd 2+ Combined to form a stable complex, and in this reaction process, the shell of the new modified biochar material will also produce FeOOH, which can react with Cd 2+ Forming bidentate complexes also serves to adsorb heavy metal Cd 2+ role.

[0036] Compared with the prior art, the present invention has the following advantages and technical effects:

[0037] (1) The modified magnetic biochar of the present invention has high internal porosity, large specific surface area, and contains a variety of functional groups on the surface, which can adsorb solid-phase heavy metal pollutants; at the same time, it has magnetic adsorption force, which is easy to recover.

[0038] (2) The preparation method provided by the present invention has simple process, low energy consumption, low cost, and is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0040] Figure 1 The scanning electron microscope images of the modified magnetic biochar prepared in Example 1 at different magnifications, a is 50 μm, b is 10 μm, c is 5 μm, and d is 2 μm;

[0041] Figure 2 The modified magnetic biochar Cd prepared in Example 1 was treated with different addition amounts. 2+ Effect of adsorption amount and adsorption rate;

[0042] Figure 3 The modified magnetic biochar Cd prepared in Example 1 was subjected to different solution pH values. 2+ The influence of adsorption effect. DETAILED DESCRIPTION

[0043] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0044] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0045] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0046] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0047] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0048] The room temperature in the present invention refers to 25±2°C.

[0049] In the present invention, unless otherwise specified, all raw material components are commercially available products well known to those skilled in the art.

[0050] Example 1

[0051] Preparation of biochar: The biomass raw material corn straw with a particle size of 0.1-0.5 mm (passing through an 80-mesh sieve) was dried in a drying oven, and the dried corn straw was placed in a quartz tube furnace under nitrogen atmosphere and carbonized at 600°C for 1.5 h, with the heating rate controlled at 10°C / min, washed, and dried at 60°C for 8 h to obtain corn straw biochar.

[0052] Loading active magnesium metal: Take 500mL of pure water, add the solid sample of magnesium chloride to the pure water at 20°C to prepare a saturated magnesium chloride solution. Soak 20g of corn straw biochar in the saturated magnesium chloride solution at 25°C for 7h, heat it in a water bath at 80°C for 8h, take out the modified corn straw biochar after heating, and dry it at 60°C for 80min to obtain a semi-modified material. The semi-modified material is placed in a quartz tube furnace and carbonized at 600°C for 0.5h under nitrogen atmosphere protection, with the heating rate controlled at 10°C / min. The material obtained after carbonization is rinsed with deionized water 3 times and then dried to obtain biochar loaded with active magnesium metal.

[0053] Loading amino and sulfonic acid groups: Add 20 g of biochar loaded with active metal magnesium into 500 mL of 0.05 g / mL sodium peraminosulfonate solution, stir evenly and let stand at 25 °C for 8 h. Rinse repeatedly with deionized water until neutral and dry in a drying oven at 105 °C until the mass no longer changes to obtain preliminary modified biochar.

[0054] Preparation of modified magnetic biochar: Take 600mL of pure water, pass nitrogen for 30min to remove dissolved oxygen in the water, put 16.2gFeCl3 into 500mL of the above pure water to prepare a 32.4g / L ferric chloride solution (FeCl3 solution), put 20g of the above preliminary modified biochar into the above FeCl3 solution, add 50mL of 50% (volume fraction) ethanol solution after contact for 3h, and stir for 10 minutes after adding to make the preliminary modified biochar more evenly dispersed in the solution. At 25℃, add 30mL of 22.8g / L NaBH4 solution dropwise to the reaction system through a pipette while stirring, and continue stirring for 30min after the NaBH4 solution is completely added. After the reaction is completed, the mixture is centrifuged, vacuum filtered, the residual ions are rinsed with deionized water, and vacuum freeze-dried to obtain modified magnetic biochar.

[0055] The particle size of the modified magnetic biochar obtained in this example is 872 nm and the specific surface area is 16.88 m 2 / g, total pore volume 0.047cm 3 / g, the atomic percentage of iron is 13.7%, the average pore size is 9.59nm, and the surface functional groups include amino groups, iron atoms, carboxyl groups, hydroxyl groups and magnesium ions. The scanning electron microscope image of the modified biochar prepared in this example is shown in Figure 1 ,Depend on Figure 1 It can be seen that its surface has a large number of irregular particles and is very rough, which is due to the loading of functional groups. At the same time, there are many crystalline substances, which are the debris of biochar. After being modified in various ways, the composite material has diversity, which is more advantageous for the adsorption of heavy metals.

[0056] Example 2

[0057] Preparation of biochar: corn straw, a biomass raw material with a particle size of 0.1 to 0.5 mm, was dried in a drying oven, and the dried corn straw was placed in a quartz tube furnace under nitrogen atmosphere and carbonized at 600°C for 1.5 h, with the heating rate controlled at 10°C / min, washed, and dried at 45°C for 8 h to obtain corn straw biochar.

[0058] Loading active magnesium metal: Take 500mL of pure water, add the solid sample of magnesium chloride to the pure water at 20°C to prepare a saturated magnesium chloride solution. Soak 20g of corn straw biochar in the saturated magnesium chloride solution at 10°C for 10h, heat it in a water bath at 80°C for 8h, take out the modified corn straw biochar after heating, and dry it at 45°C for 120min to obtain a semi-modified material. The semi-modified material is placed in a quartz tube furnace and carbonized at 300°C for 120min under nitrogen atmosphere protection, with the heating rate controlled at 10°C / min. The material obtained after carbonization is rinsed with deionized water 5 times and then dried to obtain biochar loaded with active magnesium metal.

[0059] Loading amino and sulfonic acid groups: Add 20 g of biochar loaded with active metal magnesium into 500 mL of 0.05 g / mL aminosulfonic acid solution, stir evenly and let stand at 25 °C for 8 h. Rinse repeatedly with deionized water until neutral and dry in a drying oven at 110 °C until the mass no longer changes to obtain preliminary modified biochar.

[0060] Preparation of modified magnetic biochar: Take 600mL of pure water, pass nitrogen for 30min to remove dissolved oxygen in the water, put 16.2gFeCl3 into 500mL of the above pure water to prepare a 32.4g / L ferric chloride solution (FeCl3 solution), put 20g of the above preliminary modified biochar into the above FeCl3 solution, add 50mL of 50% (volume fraction) ethanol solution after contact for 3h, and stir for 10 minutes after adding to make the preliminary modified biochar more evenly dispersed in the solution. At 25℃, add 30mL of 22.8g / L NaBH4 solution dropwise to the reaction system through a pipette while stirring, and continue stirring for 30min after the NaBH4 solution is completely added. After the reaction is completed, the mixture is centrifuged, vacuum filtered, the residual ions are rinsed with deionized water, and vacuum freeze-dried to obtain modified magnetic biochar.

[0061] The particle size of the modified magnetic biochar obtained in this example is 789 nm, and the specific surface area is 14.11 m 2 / g, and the total pore volume is 0.041cm 3 / g, the atomic percentage of iron is 13.7%, the average pore size is 8.23nm, and the surface functional groups include amino groups, iron atoms, carboxyl groups, hydroxyl groups and magnesium ions.

[0062] Example 3

[0063] The same as Example 1, except that the method for loading active metal magnesium is as follows: 500 mL of pure water is taken, and a solid sample of magnesium chloride is added to the pure water at 20°C to prepare a saturated magnesium chloride solution. 20 g of corn straw biochar is placed in the saturated magnesium chloride solution and soaked at 40°C for 8 hours, heated in a water bath at 80°C for 8 hours, and the modified corn straw biochar is taken out after heating, and dried at 75°C for 90 minutes to obtain a semi-modified material. The semi-modified material is placed in a quartz tube furnace and carbonized at 700°C for 80 minutes under nitrogen atmosphere protection, with the heating rate controlled at 10°C / min. The material obtained after carbonization is rinsed with deionized water 5 times and then dried.

[0064] The particle size of the modified magnetic biochar obtained in this example is 727 nm and the specific surface area is 14.11 m 2 / g, and the total pore volume is 0.033 cm 3 / g, the iron atom content is 12.9%, the average pore diameter is 8.41nm, and the functional groups include amino, iron atom, carboxyl, hydroxyl and magnesium ion.

[0065] Example 4

[0066] The same as Example 1, except that the method for loading active metal magnesium is as follows: 500 mL of pure water is taken, and a solid sample of magnesium chloride is added to the pure water at 20°C to prepare a saturated magnesium chloride solution. 20 g of corn straw biochar is placed in the saturated magnesium chloride solution and soaked at 30°C for 7 hours, heated in a water bath at 80°C for 8 hours, and the modified corn straw biochar is taken out after heating, and dried at 65°C for 70 minutes to obtain a semi-modified material. The semi-modified material is placed in a quartz tube furnace and carbonized at 400°C for 50 minutes under nitrogen atmosphere protection, with the heating rate controlled at 10°C / min. The material obtained after carbonization is rinsed with deionized water 3 times and then dried.

[0067] The particle size of the modified magnetic biochar obtained in this example is 754 nm, and the specific surface area is 14.87 m 2 / g, and the total pore volume is 0.039 cm 3 / g, the iron atom content is 13.21%, the average pore size is 8.23nm, and the surface functional groups include amino groups, iron atoms, carboxyl groups, hydroxyl groups and magnesium ions.

[0068] Example 5

[0069] Preparation of biochar: corn straw, a biomass raw material with a particle size of 0.05 to 0.2 mm, was dried in a drying oven, and the dried corn straw was placed in a quartz tube furnace under nitrogen atmosphere and carbonized at 600°C for 1.5 h, with the heating rate controlled at 10°C / min, washed, and dried at 75°C for 8 h to obtain corn straw biochar.

[0070] Loading active magnesium metal: Take 500mL of pure water, add the solid sample of magnesium chloride to the pure water at 20°C to prepare a saturated magnesium chloride solution. Soak 20g of corn straw biochar in the saturated magnesium chloride solution at 25°C for 6h, heat it in a water bath at 80°C for 8h, take out the modified corn straw biochar after heating, and dry it at 65°C for 70min to obtain a semi-modified material. The semi-modified material is placed in a quartz tube furnace and carbonized at 550°C for 50min under nitrogen atmosphere protection. The heating rate is controlled at 10°C / min. The material obtained after carbonization is rinsed with deionized water 3 times and then dried to obtain biochar loaded with active magnesium metal.

[0071] Loading amino and sulfonic acid groups: Add 20 g of biochar loaded with active metal magnesium into 500 mL of 0.05 g / mL magnesium sulfamate solution, stir evenly and let stand at 25 °C for 10 h. Rinse repeatedly with deionized water until neutral and dry in a drying oven at 105 °C until the mass no longer changes to obtain preliminary modified biochar.

[0072] Preparation of modified magnetic biochar: Take 600mL of pure water, pass nitrogen for 30min to remove dissolved oxygen in the water, put 16.2gFeCl3 into 500mL of the above pure water to prepare a 32.4g / L ferric chloride solution (FeCl3 solution), put 20g of the above preliminary modified biochar into the above FeCl3 solution, add 50mL of 50% (volume fraction) ethanol solution after contact for 3h, and stir for 10 minutes after adding to make the preliminary modified biochar more evenly dispersed in the solution. At 25℃, add 30mL of 22.8g / L NaBH4 solution dropwise to the reaction system through a pipette while stirring, and continue stirring for 30min after the NaBH4 solution is completely added. After the reaction is completed, the mixture is centrifuged, vacuum filtered, the residual ions are rinsed with deionized water, and vacuum freeze-dried to obtain modified magnetic biochar.

[0073] The modified magnetic biochar obtained in this example has a particle size of 742 nm and a specific surface area of ​​14.51 m 2 / g, and the total pore volume is 0.033 cm 3 / g, the iron atom content is 13.1%, the average pore size is 8.27nm, and the surface functional groups include amino groups, iron atoms, carboxyl groups, hydroxyl groups and magnesium ions.

[0074] Comparative Example 1: Ammonia-iron modified biochar (without active metal magnesium loading)

[0075] Preparation of biochar: The biomass raw material corn straw with a particle size of 0.1-0.5 mm (passing through an 80-mesh sieve) was dried in a drying oven, and the dried corn straw was placed in a quartz tube furnace under nitrogen atmosphere and carbonized at 600°C for 1.5 h, with the heating rate controlled at 10°C / min, washed, and dried at 60°C for 8 h to obtain corn straw biochar (marked as BC).

[0076] Loading amino and sulfonic acid groups: Add 20 g corn straw biochar into 500 mL 0.05 g / mL sodium persulfamate solution, stir evenly and let stand at 25 °C for 8 h. Rinse repeatedly with deionized water until neutral and dry in a drying oven at 105 °C until the mass no longer changes to obtain preliminary modified biochar (labeled as NS@BC).

[0077] Preparation of modified magnetic biochar: Take 600mL of pure water, pass nitrogen for 30min to remove dissolved oxygen in the water, put 16.2gFeCl3 into 500mL of the above pure water to prepare a 32.4g / L ferric chloride solution (FeCl3 solution), put 20g of the above preliminary modified biochar into the above FeCl3 solution, add 50mL of 50% (volume fraction) ethanol solution after contact for 3h, and stir continuously for 10 minutes after adding to make the preliminary modified biochar more evenly dispersed in the solution. At 25°C, add 30mL of 22.8g / L NaBH4 solution dropwise to the reaction system through a pipette while stirring, and continue stirring for 30min after the NaBH4 solution is completely added. After the reaction is completed, the mixture is centrifuged, vacuum filtered, the residual ions are rinsed with deionized water, and vacuum freeze-dried to obtain modified magnetic biochar (NS-Fe 0 @BC).

[0078] Comparative Example 2 Magnesium-iron modified biochar (without amino and sulfonic acid groups)

[0079] Preparation of biochar: The biomass raw material corn straw with a particle size of 0.1-0.5 mm (passing through an 80-mesh sieve) was dried in a drying oven, and the dried corn straw was placed in a quartz tube furnace under nitrogen atmosphere and carbonized at 600°C for 1.5 h, with the heating rate controlled at 10°C / min, washed, and dried at 60°C for 8 h to obtain corn straw biochar (marked as BC).

[0080] Loading active metal magnesium: Take 500mL of pure water, add the solid sample of magnesium chloride to the pure water at 20°C to prepare a saturated magnesium chloride solution. Soak 20g of corn straw biochar in the saturated magnesium chloride solution at 25°C for 7h, heat it in a water bath at 80°C for 8h, take out the modified corn straw biochar after heating, and dry it at 60°C for 80min to obtain a semi-modified material. The semi-modified material is placed in a quartz tube furnace and carbonized at 600°C for 0.5h under nitrogen atmosphere protection, with the heating rate controlled at 10°C / min. The material obtained after carbonization is rinsed with deionized water 3 times and then dried to obtain biochar loaded with active metal magnesium (labeled as Mg@BC).

[0081] Preparation of modified magnetic biochar: Take 600mL of pure water, pass nitrogen for 30min to remove dissolved oxygen in the water, put 16.2gFeCl3 into 500mL of the above pure water to prepare a 32.4g / L ferric chloride solution (FeCl3 solution), put 20g of the above biochar loaded with active metal magnesium into the above FeCl3 solution, add 50mL of 50% (volume fraction) ethanol solution after contact for 3h, and stir continuously for 10 minutes after adding to make the biochar loaded with active metal magnesium more evenly dispersed in the solution. At 25°C, add 30mL of 22.8g / L NaBH4 solution dropwise to the reaction system through a pipette while stirring, and continue stirring for 30min after the NaBH4 solution is completely added. After the reaction is completed, the mixture is centrifuged, vacuum filtered, the residual ions are rinsed with deionized water, and vacuum freeze-dried to obtain modified magnetic biochar (Mg-Fe 0 @BC).

[0082] Loading amino and sulfonic acid groups: Add 20 g of biochar loaded with active metal magnesium into 500 mL of 0.05 g / mL sodium peraminosulfonate solution, stir evenly and let stand at 25 °C for 8 h. Rinse repeatedly with deionized water until neutral and then dry in a drying oven at 105 °C until the mass no longer changes to obtain modified biochar (NS-Mg@BC).

[0083] Comparative Example 3 Iron-modified biochar

[0084] The biomass raw material corn straw with a particle size of 0.1-0.5 mm (passing through an 80-mesh sieve) was dried in a drying oven, and the dried corn straw was placed in a quartz tube furnace under nitrogen atmosphere and carbonized at 600°C for 1.5 h. The heating rate was controlled at 10°C / min, washed, and dried at 60°C for 8 h to obtain corn straw biochar (marked as BC).

[0085] Take 600mL of pure water, pass nitrogen for 30 minutes to remove dissolved oxygen in the water, add 16.2g FeCl3 into 500mL of the above pure water to prepare a 32.4g / L ferric chloride solution, add 20g of biochar into the above FeCl3 solution, add 50mL of 50% ethanol solution after contact for 3h, stir continuously for 10 minutes after adding, so that the biochar is more evenly dispersed in the solution. At 25°C, add 22.8g / L NaBH4 solution dropwise to the reaction system through a pipette while stirring, add about 30mL, and continue stirring for 30min after the NaBH4 solution is completely added. After the reaction is completed, the mixture is centrifuged, vacuum filtered, the residual ions are rinsed with deionized water, and dried to obtain zero-valent iron modified biochar (labeled as Fe 0 @BC).

[0086] The element contents of pure biochar and the biochar products obtained from Comparative Examples 1-4 are shown in Table 1, the pore structure parameters are shown in Table 2, and the changes in functional groups are shown in Table 3.

[0087] Table 1

[0088]

[0089] Table 2

[0090]

[0091]

[0092] Table 3

[0093]

[0094] Taking the modified magnetic biochar prepared in Example 1 as an example, the effect of dosage on the adsorption effect was studied:

[0095] Take 25mL of 30mg / L cadmium standard solution and add it to a 100mL conical flask. Add 0.05, 0.10, 0.15, 0.20, 0.25, and 0.30g of dried modified magnetic biochar solid powder samples respectively and seal it with a sealing film. Place it in a constant temperature oscillator and oscillate it for 4 hours at 25℃ and 180r / min. After the oscillation, filter it with a syringe filter to obtain a clear solution, and determine its concentration by atomic absorption. 2+ The effect of adsorption amount and adsorption rate can be seen in Figure 2 .

[0096] Depend on Figure 2 It can be seen that with the increase of the amount of modified magnetic biochar added, the 2+ The adsorption capacity of modified biochar per unit mass of Cd 2+ The adsorption amount of Cd 2+ The adsorption rate of Cd 2+ The adsorption rate reaches 93.87%, and the saturated adsorption capacity is 2.816 mg / g. This is because the amount of adsorbent increases and the total adsorption sites increase. The amount of cadmium in the solution is certain, so the removal rate will increase when the adsorption sites increase, while the unit adsorption amount is constantly decreasing.

[0097] Taking the modified magnetic biochar prepared in Example 1 as an example, the effect of solution pH on the Cd 2+ Influence of adsorption effect:

[0098] Take 25 mL of 30 mg / L cadmium standard solution and place it in a 100 mL beaker. Use 0.1 mol / L hydrochloric acid and sodium hydroxide solution to adjust the pH of the solution to 5, 6, 7, 8, 9, and 10, respectively. Then transfer it to a 100 mL conical flask, add 0.25 g of modified magnetic biochar solid powder sample to each, and seal it with a sealing film. Oscillate in a constant temperature oscillator at 25°C and 180 r / min for 4 hours. After the oscillation, filter with a syringe filter to obtain a clear solution, and determine its concentration by atomic absorption. The results are shown in Figure 3 .Depend on Figure 3 It can be seen that with the increase of solution pH, the modified magnetic biochar has a greater 2+ The adsorption showed a trend of first increasing and then decreasing, and reached the optimum at pH=9.

[0099] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. Application of modified magnetic biochar in adsorbing heavy metals in composting, characterized in that: The method for preparing the modified magnetic biochar comprises the following steps: Preparation of biochar: corn stalks with a particle size of 0.1 to 0.5 mm were dried in a drying oven, and the dried corn stalks were placed in a quartz tube furnace under nitrogen atmosphere and carbonized at 600°C for 1.5 h, with the heating rate controlled at 10°C / min, washed, and dried at 60°C for 8 h to obtain corn stalk biochar; Loading active metal magnesium: Take 500 mL of pure water, add a solid sample of magnesium chloride to the pure water at 20°C to prepare a saturated magnesium chloride solution, put 20 g of corn straw biochar into the saturated magnesium chloride solution, soak it at 25°C for 7 hours, heat it in a water bath at 80°C for 8 hours, take out the modified corn straw biochar after heating, dry it at 60°C for 80 minutes to obtain a semi-modified material, place the semi-modified material in a quartz tube furnace, carbonize it at 600°C for 0.5 hours under nitrogen atmosphere protection, and control the heating rate at 10°C / min. Rinse the material obtained after carbonization with deionized water 3 times and dry it to obtain biochar loaded with active metal magnesium; Loading amino and sulfonic acid groups: Add 20 g of biochar loaded with active metal magnesium into 500 mL of 0.05 g / mL sodium peramate solution, stir evenly, and let stand at 25 °C for 8 h. Rinse repeatedly with deionized water until neutral, and then dry in a drying oven at 105 °C until the mass no longer changes, to obtain preliminary modified biochar; Preparation of modified magnetic biochar: 600 mL of pure water was taken, nitrogen was introduced for 30 min to remove dissolved oxygen in the water, 16.2 g of FeCl3 was added to 500 mL of the above pure water to prepare a 32.4 g / L ferric chloride solution, 20 g of the above preliminary modified biochar was added to the above FeCl3 solution, and after contact for 3 hours, 50 mL of 50% ethanol solution was added, and stirring was continued for 10 minutes after adding to make the preliminary modified biochar more evenly dispersed in the solution, and 30 mL of 22.8 g / L NaBH4 solution was added dropwise to the reaction system through a pipette while stirring at 25 ° C. After the NaBH4 solution was completely added, stirring was continued for 30 min. After the reaction was completed, the mixture was centrifuged, vacuum filtered, and the residual ions were rinsed with deionized water. After vacuum freeze drying, the modified magnetic biochar was obtained. The particle size of the modified magnetic biochar was 872 nm and the specific surface area was 16.88 m 2 / g, total pore volume 0.047cm 3 / g, the atomic percentage of iron is 13.7%, the average pore size is 9.59nm, and the surface functional groups include amino groups, iron atoms, carboxyl groups, hydroxyl groups and magnesium ions.

Images