A magnesium oxide modified surface-enhanced biochar adsorbent material and a preparation method thereof

Abstract

The present application relates to a kind of magnesium oxide modified surface reinforced biochar adsorbent material and its preparation method.The method comprises: biomass material is pre-carbonized, and biochar is obtained;Biochar is stirred and impregnated in gallic acid hot solution, impregnation solution is obtained, then the impregnation solution is filtered, and the biochar coated with gallic acid layer is obtained;The biochar coated with gallic acid layer is stirred and impregnated with magnesium salt solution, then dried, and a mixture is obtained;The mixture is sequentially heated and treated at 120-150 DEG C and pyrolyzed at 400-600 DEG C in inert gas, and magnesium oxide modified surface reinforced biochar adsorbent material is prepared.The biochar adsorbent material obtained by the present application can efficiently and quickly treat low-concentration heavy metal wastewater, ammonia-nitrogen wastewater and phosphorus-containing wastewater, has excellent adsorption performance, reduces the use of auxiliary reagents such as flocculants, has low sludge production, and can optimize the separation of pollutants and the reuse of heavy metals.

Description

Technical Field

[0001] This invention relates to the field of adsorbent materials technology, and in particular to a magnesium oxide-modified surface-strengthened biochar adsorbent material and its preparation method. Background Technology

[0002] Adsorption is a common method in wastewater treatment. It has a wide range of applications, is easy to operate, produces low effluent concentrations, generates less secondary pollution and less hazardous solid waste, and is one of the main methods for treating heavy metal wastewater, ammonia nitrogen wastewater and phosphorus-containing wastewater.

[0003] MgO, as an adsorbent, possesses relatively green and environmentally friendly characteristics. It can immobilize heavy metal ions through ion exchange and precipitation, and its low solubility and slow hydroxide ion release rate avoid precipitation dissolution caused by excessive alkalinity. Furthermore, MgO also exhibits strong removal capabilities for pollutants such as ammonia nitrogen and phosphate in wastewater. However, the slow reaction rate results in longer treatment times and larger dosages when using MgO to treat heavy metal and nitrogen-phosphorus wastewater. MgO-based adsorbents typically require activation before use to increase their specific surface area and improve adsorption efficiency. However, general activation methods are costly and energy-intensive, requiring preparation temperatures exceeding 1000℃; or they involve excessively adhesive preparation processes and equipment (spray drying, sol-gel methods, etc.) and excessive reagent consumption (such as precipitation methods, sol-gel methods, etc.), thus increasing costs. Simultaneously, because the active MgO adsorbent particles and the resulting precipitates are too small, they are highly dependent on auxiliary agents such as flocculants and flotation agents, further increasing sludge production, making subsequent treatment difficult, and they are prone to coagulation and inactivation during use. When MgO is loaded onto a porous carbon substrate, the adsorbent condensation problem can be reduced to some extent, and the adsorption activity of magnesium oxide can be improved. However, when an unactivated substrate is used for loading, the activation degree of magnesium oxide particles is still low, and the adsorption rate is still insufficient. Therefore, the preparation of magnesium oxide / biochar adsorbent materials requires high surface properties of the biochar material. The original biochar has insufficient support and dispersion effect on magnesium oxide, and the activation degree of magnesium oxide is also low. It is usually necessary to improve the activation degree of magnesium oxide to further improve the adsorption performance of magnesium oxide / biochar adsorbent materials for heavy metal wastewater, ammonia nitrogen wastewater, and phosphorus-containing wastewater.

[0004] In summary, in order to solve one or more of the technical problems mentioned above, it is necessary to provide a magnesium oxide-modified surface-strengthened biochar adsorbent material and its preparation method. Summary of the Invention

[0005] To address one or more technical problems existing in the prior art, this invention provides a magnesium oxide-modified surface-strengthened biochar adsorbent material and its preparation method. The biochar adsorbent material obtained by this invention can efficiently and rapidly treat low-concentration heavy metal wastewater, ammonia nitrogen wastewater, and phosphorus-containing wastewater, exhibiting excellent adsorption performance, reducing the use of auxiliary reagents such as flocculants, producing low sludge, and optimizing pollutant separation and heavy metal reuse.

[0006] In a first aspect, this invention provides a method for preparing a magnesium oxide-modified surface-strengthened biochar adsorbent material, the method comprising the following steps:

[0007] (1) Pre-carbonize biomass materials to obtain biochar;

[0008] (2) The biochar was stirred and impregnated in a hot gallic acid solution to obtain an impregnation solution. The impregnation solution was then filtered to obtain biochar coated with a gallic acid layer.

[0009] (3) The biochar coated with gallic acid layer was stirred and impregnated in magnesium salt solution, and then dried to obtain a mixture;

[0010] (4) The mixture is subjected to heating treatment at 120-150℃ and pyrolysis treatment at 400-600℃ in an inert gas to obtain magnesium oxide modified surface-strengthened biochar adsorbent material.

[0011] Preferably, in step (1): the biomass material is a lignocellulosic biomass material. More preferably, the lignocellulosic biomass material is one or more of agricultural and forestry waste, grass leaves and wood materials. More preferably, the lignocellulosic biomass material is one or more of corn cobs, straw, grass leaves, fruit shells and wood materials. More preferably, the lignocellulosic biomass material is corn cobs.

[0012] Preferably, in step (1): before pre-carbonization, the biomass material is pretreated. The pretreatment of the biomass material is as follows: the biomass material is washed and cut into blocks, dried, crushed and sieved to obtain biomass material with a particle size of less than 18 mesh.

[0013] Preferably, in step (1): the pre-carbonization is carried out under the protection of an inert gas, preferably in a nitrogen atmosphere, or the pre-carbonization is carried out in a closed space after oxygen has been removed by limited combustion; and / or the temperature of the pre-carbonization is 300-600°C and the time is 1-3 hours, preferably the temperature of the pre-carbonization is 400°C and the time is 2 hours.

[0014] Preferably, in step (2): the gallic acid concentration of the gallic acid hot solution is 50-150 g / L, the temperature of the gallic acid hot solution is 70-90℃, preferably 80-90℃; the ratio of the amount of biochar to the gallic acid hot solution is (25-75) g: 1 L; the mass ratio of the biochar to the gallic acid in the gallic acid hot solution is 1: (1-3); and / or the stirring and impregnation time is 12-24 h.

[0015] Preferably, in step (2): the temperature of the impregnation solution is not lower than 70°C before filtration, and the filtration time is not more than 5 minutes. Preferably, the filtrate after filtration is recycled and reused until no solid precipitates when cooled to 40°C.

[0016] Preferably, in step (3): the magnesium salt in the magnesium salt solution is one or more of magnesium nitrate, magnesium sulfate and magnesium chloride, preferably magnesium chloride; the temperature of the magnesium salt solution does not exceed 30°C, preferably not exceeding 20°C; the concentration of the magnesium salt solution is 200-500 g / L; the mass ratio of magnesium in the magnesium salt solution to the biochar in step (2) is (0.1-0.3):1; and / or the stirring and impregnation time is 1-2 h.

[0017] Preferably, in step (3): the drying temperature is 60-75°C; and / or drying is performed to obtain a slurry-like mixture with a moisture content of 20-40%.

[0018] Preferably, in step (4): heat treatment at 120-150°C for 1-2 hours; and / or pyrolysis treatment at 400-600°C for 1-2 hours.

[0019] In a second aspect, the present invention provides a magnesium oxide-modified surface-strengthened biochar adsorbent material prepared by the preparation method described in the first aspect of the present invention.

[0020] Compared with the prior art, the present invention has at least the following beneficial effects:

[0021] (1) This invention provides a method for preparing a surface-enhanced biochar adsorbent material by highly activating and dispersing magnesium oxide onto the surface of biochar coated with a gallic acid layer containing a large number of carboxyl and phenolic hydroxyl groups. This material is used for the rapid and efficient removal of lead, cadmium ions, ammonia nitrogen, and phosphate ions from heavy metal wastewater. The method uses biomass materials as raw materials and utilizes the difference in solubility of gallic acid in hot and cold water, as well as the affinity of its aromatic structure for the directional surface of biochar. A hot solution impregnation method is used to uniformly coat the biochar surface with gallic acid (surface enhancer). Subsequently, the interaction between the enhanced biochar surface and the magnesium salt solution, i.e., the presence of phenolic and carboxyl groups, allows magnesium ions to be highly uniformly dispersed on the biochar surface during the magnesium salt impregnation process. Through pyrolysis under an inert atmosphere, the highly activated magnesium oxide is then used to remove lead, cadmium ions, ammonia nitrogen, and phosphate ions from heavy metal wastewater. Magnesium salts dispersed on the surface of biomass carbon are transformed into highly dispersible and activated magnesium oxide, achieving high dispersibility and high activity of magnesium oxide loading, ultimately yielding a magnesium oxide-modified surface-strengthened biochar adsorbent material. When using the magnesium oxide-modified surface-strengthened biochar adsorbent material of this invention to adsorb lead and cadmium ions, the complexation provided by the phenolic hydroxyl groups and carboxyl groups uniformly distributed on the surface of biochar concentrates and fixes heavy metal ions, causing them to react with the active magnesium oxide dispersed on the adsorbent surface to produce precipitation. The precipitate is captured by the pores of biochar, the hydrophobic surface of biochar, and the carboxyl / phenolic hydroxyl groups, thereby obtaining easily separable large-sized heavy metal precipitate particles. The biochar adsorbent material obtained by this invention can efficiently and rapidly treat low-concentration heavy metal wastewater, reduce the amount of auxiliary reagents such as flocculants, and produce low sludge.

[0022] (2) Compared with traditional methods for preparing active magnesium oxide, the method of the present invention requires a lower heating temperature (for example, the temperature of magnesium oxide prepared by calcination is reduced from about 1000℃ to about 400-600℃), and consumes less energy. At the same time, compared with methods such as precipitation, sol-gel and spray drying, this method is simpler and has fewer steps. The method provided by the present invention is relatively simple, consumes less energy, has good adsorption effect, and has a wide range of applications.

[0023] (3) Compared with using only magnesium oxide for modification, the present invention pre-coats the surface of biochar with gallic acid layer, thereby improving the dispersion of magnesium ions on the surface of biochar during impregnation, enhancing the activation effect of biochar, and making the surface pore distribution more uniform. While improving the utilization rate of magnesium oxide during activation, it also improves the adsorption performance of biochar adsorbent material for low-concentration heavy metal wastewater, ammonia nitrogen wastewater and phosphorus-containing wastewater, which is conducive to the rapid and efficient removal of lead, cadmium ions, ammonia nitrogen and phosphate ions in heavy metal wastewater.

[0024] (4) Compared with biochar adsorbents modified only with magnesium oxide, the magnesium oxide-modified surface-strengthened biochar adsorbent material in this invention has significantly improved adsorption capacity and adsorption rate when treating nitrogen and phosphorus wastewater; when treating lead and cadmium wastewater, the lead and cadmium precipitation rate is faster and the adsorption rate is significantly improved. Under the combined action of surface carboxyl groups, phenolic hydroxyl groups and active magnesium oxide, the adsorption capacity of this adsorbent exceeds the sum of the adsorption capacity of biochar loaded only with magnesium oxide and biochar surface-strengthened only with gallic acid, indicating that gallic acid surface strengthening and magnesium oxide modification have achieved effective coupling and played a good synergistic role.

[0025] (5) The present invention found that biochar materials coated with surface strengthener (gallic acid) and impregnated with magnesium salt solution in sequence have a stronger adsorption performance than those subjected to surface strengthener and magnesium salt impregnation at the same time. After adsorption using the biochar adsorbent material prepared by the present invention, the size of heavy metal precipitate particles increases significantly and they adhere to the adsorbent substrate, thereby obtaining larger particle products, reducing the difficulty of recycling, and reducing costs and energy consumption. Attached Figure Description

[0026] Figure 1 This is a photograph of the magnesium oxide-modified surface-strengthened biochar adsorbent material prepared in Example 1 of this invention.

[0027] Figure 2 These are SEM images of the magnesium oxide-modified surface-strengthened biochar adsorbent material prepared in Example 1 of this invention at different magnifications.

[0028] Figure 3 This is the XRD pattern of the magnesium oxide-modified surface-strengthened biochar adsorbent material prepared in Example 1 of this invention;

[0029] Figure 4 The images show SEM images of lead and cadmium adsorbed directly using magnesium oxide adsorbent and using the magnesium oxide-modified surface-reinforced biochar adsorbent material prepared in Example 1. In the images, a is the SEM image of lead adsorbed directly using magnesium oxide adsorbent, b is the SEM image of cadmium adsorbed directly using magnesium oxide adsorbent, c is the SEM image of lead adsorbed using the magnesium oxide-modified surface-reinforced biochar adsorbent material prepared in Example 1, and d is the SEM image of cadmium adsorbed using the magnesium oxide-modified surface-reinforced biochar adsorbent material prepared in Example 1. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0031] In a first aspect, this invention provides a method for preparing a magnesium oxide-modified surface-strengthened biochar adsorbent material, the method comprising the following steps:

[0032] (1) Biomass material is pre-carbonized to obtain biochar; in this invention, biochar is also referred to as original biomass carbon material; in this invention, for example, the pre-treated biomass material is pre-carbonized under oxygen-limited conditions (e.g., nitrogen atmosphere) to obtain original biomass carbon material (i.e., biochar).

[0033] (2) The biochar is stirred and impregnated in a hot gallic acid solution to obtain an impregnation solution. The impregnation solution is then filtered to obtain biochar coated with a gallic acid layer (a thin layer of gallic acid) (also referred to as surface-strengthened biochar). In this invention, a hot solution impregnation method is used to coat the surface of the biochar with a gallic acid layer (also referred to as a thin layer of gallic acid). For example, the biochar is stirred and impregnated in a hot gallic acid solution of a certain concentration for a certain period of time, and then filtered in a room temperature environment (e.g., a room temperature environment with a temperature not exceeding 30°C). The characteristic that gallic acid has different solubility in hot and cold water is utilized to allow gallic acid to precipitate on the surface of the biochar during the filtration process, achieving a uniform and dense coating effect. In step (2), the filtration is carried out using a filtration device. The pore size of the filter membrane, filter paper, filter cloth, or filter screen used in the filtration device needs to ensure that the biochar particles can be retained. In this invention, the hot gallic acid solution uses water as a solvent and gallic acid as a solute.

[0034] (3) The gallic acid-coated biochar is stirred and impregnated in a magnesium salt solution (cold magnesium salt solution), and then dried to obtain a mixture; In this invention, the stirring and impregnation in step (3) ensures that the gallic acid-coated biochar and the magnesium salt solution are fully mixed; In this invention, for example, drying at an appropriate temperature yields a slurry-like mixture; In this invention, the magnesium salt solution uses water as a solvent and magnesium salt as a solute; This invention does not specifically limit the stirring and impregnation speed in steps (2) and / or (3), and those skilled in the art can conventionally select it, for example, it can be 200 to 1000 r / min;

[0035] (4) The mixture is subjected to heating treatment at 120-150°C (e.g., 120°C, 130°C, 140°C or 150°C) and pyrolysis treatment at 400-600°C (e.g., 400°C, 500°C or 600°C) in an inert gas to obtain a magnesium oxide-modified surface-strengthened biochar adsorbent material; In this invention, both the heating treatment at 120-150°C and the pyrolysis treatment at 400-600°C are carried out in an inert gas; In this invention, the inert gas may be, for example, nitrogen and / or argon.

[0036] Unlike existing magnesium salt impregnation techniques, this invention uses gallic acid as a surface strengthener. It leverages the temperature-dependent solubility of gallic acid in water (its different solubility in hot and cold water) and the affinity of its aromatic structure for the directional surface of biochar to uniformly coat the biochar surface, forming a uniform gallic acid layer. Utilizing the phenolic hydroxyl and carboxyl groups it contains, magnesium ions are highly dispersed on the biochar surface during magnesium salt impregnation, thus significantly improving the dispersibility of magnesium oxide on the biochar surface. This results in highly dispersed and active magnesium oxide loading, enhancing the adsorption of heavy metal ions. Furthermore, the delocalized π bonds formed by the aromatic structure of gallic acid can be utilized to conjugate with heavy metal ions, thereby achieving rapid adsorption of heavy metal ions. In addition, the complexation of phenolic hydroxyl and carboxyl groups can also achieve rapid adsorption of heavy metal ions. After the enhanced surface functional groups concentrate heavy metal ions near the surface of biochar, the heavy metal ions are converted into solid precipitate particles under the ion exchange and precipitation promotion provided by magnesium oxide on the biochar surface. These particles are then captured by the porous structure and surface functional groups of the biochar, increasing particle size, reducing recovery difficulty, reducing the use of flocculants and other auxiliary reagents, and reducing sludge production.

[0037] This invention utilizes the difference in solubility of gallic acid in hot and cold water. By dissolving gallic acid in hot water and then adding biochar to the system, followed by cooling, gallic acid is precipitated on the surface of the biochar, thereby forming a uniform gallic acid layer on the surface of the biochar. Compared to the traditional method of directly coating organic acids onto the surface of biochar by stirring without controlling the impregnation loading temperature, this invention utilizes the precipitation process formed by the thermal-cold dissolution difference to significantly improve the uniformity and density of the coating. This avoids the problem of uneven deposition of polyphenolic hydroxyl compounds on the biochar surface. Gallic acid, which has high solubility in hot water, can fully dissolve and penetrate into the surface of biochar pores. Subsequently, cooling reduces its solubility, causing it to precipitate on the biochar surface and form a uniform and dense thin layer coating. In addition, this invention induces precipitation through alternating thermal and cold treatment, promoting the preferential deposition of gallic acid on the biochar surface rather than leaving it in the solution. This improves the utilization rate of gallic acid, effectively reducing raw material waste. Furthermore, the thin layer formed by cooling after hot water dissolution usually has better crystallinity or agglomerated structure, enhancing its adhesion to the biochar surface. The resulting gallic acid layer is more firmly bonded to the biochar surface, giving it better stability and elution resistance. Ultimately, this significantly improves the adsorption performance of the magnesium oxide-modified surface-strengthened biochar adsorbent material.

[0038] Compared to using only magnesium oxide for modification, this invention pre-coats the biochar surface with a gallic acid layer, thereby improving the dispersion of magnesium ions on the biochar surface during impregnation. This results in more thorough and uniform activation of the biochar surface, enhancing the activation effect and making the surface pore distribution more uniform. This improves the distribution of effective adsorption sites in the prepared surface-enhanced biochar adsorbent material, increasing the surface area that can participate in the adsorption reaction. While improving the utilization rate of magnesium oxide during activation, it also enhances the adsorption performance of the biochar adsorbent material for low-concentration heavy metal wastewater, ammonia nitrogen wastewater, and phosphorus-containing wastewater. Compared to biochar adsorbents modified only with magnesium oxide, the magnesium oxide-modified surface-strengthened biochar adsorbent material of this invention exhibits significantly improved adsorption capacity and adsorption rate when treating nitrogen and phosphorus wastewater. When treating lead and cadmium wastewater, lead and cadmium precipitation occurs more rapidly, and the adsorption rate is significantly improved. Under the combined action of surface carboxyl groups, phenolic hydroxyl groups, and activated magnesium oxide, the adsorption capacity of this adsorbent exceeds the sum of magnesium oxide-supported biochar and gallic acid-modified biochar alone, indicating that gallic acid surface strengthening and magnesium oxide modification achieve effective coupling and a good synergistic effect. In this invention, when the dosage of the magnesium oxide-modified surface-strengthened biochar adsorbent material is 300 ppm, the removal rate exceeds 99.9% when treating 200 mg / L lead wastewater, with an effluent concentration below 0.1 mg / L; when the dosage is 600 ppm, the effluent concentration is below 0.02 mg / L when treating 100 mg / L cadmium wastewater.

[0039] According to some preferred embodiments, in step (1): the biomass material is a lignocellulosic biomass material, preferably, the lignocellulosic biomass material is one or more of agricultural and forestry waste, grass leaves and wood materials, more preferably, the lignocellulosic biomass material is one or more of corn cobs, straw, grass leaves, fruit shells and wood materials, and even more preferably, the lignocellulosic biomass material (agricultural waste) is corn cobs.

[0040] According to some preferred embodiments, in step (1): before pre-carbonization, the biomass material is pretreated. The pretreatment of the biomass material is as follows: after cleaning the biomass material, it is cut into blocks, dried, crushed and sieved to obtain biomass material with a particle size of less than 18 mesh. Specifically, the pretreatment is as follows: first, the biomass material is cleaned to remove excess mud and sand and other attachments on the surface, then the biomass material is cut into small pieces, dried to remove most of the moisture, crushed using a crusher, and the biomass material with a size (particle size) of no more than 18 mesh is selected by sieving and naturally air-dried for later use.

[0041] According to some preferred embodiments, in step (1): the pre-carbonization is carried out under the protection of an inert gas, preferably in a nitrogen atmosphere, or the pre-carbonization is carried out in a closed space after oxygen has been removed by limited combustion; and / or the temperature of the pre-carbonization is 300-600°C (e.g., 300°C, 400°C, 500°C or 600°C), and the time is 1-3h, preferably 1-2h, and preferably the temperature of the pre-carbonization is 400°C and the time is 2h; in step (1), the pre-carbonization can be carried out, for example, in a static or dynamic inert gas, and when carried out in a dynamic inert gas, the inert gas flow rate does not exceed 10L / h, preferably 5-10L / h.

[0042] According to some specific implementation methods, step (1) is as follows: the pretreated biomass material powder can pass through an 18-mesh sieve. The material that can pass through the 18-mesh sieve is pre-carbonized at 300-600℃ (e.g., 300℃, 400℃, 500℃ or 600℃) for 1-3 hours under oxygen-limited conditions to obtain the original biomass carbon material (biochar). In this invention, the oxygen-limited conditions can be obtained by introducing inert gases such as nitrogen into a tube furnace or a high-temperature reactor, or by pyrolysis in a closed environment, and the oxygen-limited effect is achieved by consuming a limited amount of oxygen through excessive biomass raw materials. The biochar obtained under these different oxygen-limited pre-carbonization conditions has no significant difference in properties and has no significant impact on the performance of the subsequent activated biochar.

[0043] According to some preferred embodiments, in step (2): the gallic acid concentration of the gallic acid hot solution is 50-150 g / L (e.g., 50, 60, 70, 80, 90, 100, 110, 120, 130, 140 or 150 g / L), and the temperature of the gallic acid hot solution is 70-90℃ (e.g., 70℃, 75℃, 80℃, 85℃ or 90℃), preferably 80-90℃ (e.g., 80℃, 85℃ or 90℃). In this invention, within the range of 50-150 g / L concentration of the gallic acid hot solution, even if there is slight precipitation in the gallic acid hot solution, it will not have a significant impact on the properties of the obtained material. This invention discovers that during the stirring and impregnation process in the hot solution, the temperature of the hot solution is 70-90℃, preferably 80-90℃. Excessive temperature can easily cause the hot solution to boil, affecting the coating effect, while excessive temperature can easily lead to excessive precipitation of the surface strengthening agent, ultimately making it difficult for magnesium oxide to adhere to the biochar surface. The ratio of the biochar to the gallic acid hot solution is (25-75) g:1 L (e.g., 25 g:1 L, 30 g:1 L, 35 g:1 L, 40 g:1 L, 45 g:1 L, 50 g:1 L, 55 g:1 L, 60 g:1 L, 65 g:1 L, 70 g:1 L, or 75 g:1 L), preferably (25-50) g:1 L (e.g., 25 g:1 L). L, 30g:1L, 35g:1L, 40g:1L, 45g:1L or 50g:1L); the mass ratio of biochar to gallic acid in the gallic acid hot solution is 1:(1-3) (e.g. 1:1, 1:1.5, 1:2, 1:2.5 or 1:3), preferably 1:(1.2-3); in this invention, it is preferred that the mass ratio of biochar to gallic acid is 1:(1-3). If there is too much gallic acid, it is easy to precipitate excessively on the surface of biochar, making it difficult for magnesium oxide to adhere to the surface of biochar; while if there is too little, it will not have a sufficient effect; and / or the stirring and impregnation time is 12-24h (e.g. 12, 14, 16, 18, 20, 22 or 24h).

[0044] According to some preferred embodiments, in step (2): before filtration, i.e. when the impregnation solution enters the filtration device and contacts the filter layer, the temperature of the impregnation solution is not lower than 70°C, preferably 70-90°C, more preferably 80-90°C, and the filtration time is not more than 5 minutes. Preferably, the filtrate after filtration is recycled and reused until no solid precipitates when cooled to 40°C. In this invention, during the process of separating the gallic acid-coated biochar from the impregnation solution through filtration, filtration is performed using a filtration device at a room temperature not higher than 30°C. The time for all impregnation solutions to pass through the filtration device should be controlled within 5 minutes to control the amount of gallic acid precipitated on the surface of the biochar and ensure that the thickness of the coating layer is appropriate. However, before filtration, the temperature of the impregnation solution needs to be controlled not lower than 70°C. If the temperature of the impregnation solution is too low, it is easy to cause excessive precipitation of gallic acid, making it difficult for magnesium oxide to adhere to the surface of the biochar.

[0045] To ensure the magnesium oxide modification and surface strengthening effects of biochar, this invention requires gallic acid coating under appropriate conditions and process parameters. This coating ensures a uniform gallic acid layer of suitable thickness on the biochar surface, resulting in a more uniform distribution of magnesium oxide on the biochar surface. This invention has found that both excessively low and excessively high gallic acid (thickness) loadings (layers) can reduce surface activation, leading to decreased adsorption performance. If the loading is too low, sufficient surface activation cannot be guaranteed, resulting in reduced adsorption. Conversely, if the loading is too high, gallic acid may detach from the biochar surface during magnesium salt solution impregnation, making it difficult for magnesium oxide to adhere to the biochar surface, similarly reducing activation and adsorption. To ensure effective gallic acid coating, the impregnation solution temperature, gallic acid concentration, biochar to gallic acid mass ratio, impregnation time, filtration time, and filtration temperature must be controlled during the coating process to ensure a uniform gallic acid layer of suitable thickness on the biochar surface.

[0046] According to some preferred embodiments, in step (3): the magnesium salt in the magnesium salt solution is one or more of magnesium nitrate, magnesium sulfate and magnesium chloride, preferably magnesium chloride; in the present invention, the magnesium salt can be, for example, magnesium nitrate, magnesium sulfate and magnesium chloride, or a mixture of multiple magnesium salts; in some other embodiments, if the magnesium salt also contains non-magnesium ions, for example, the molar percentage of magnesium in the mixed salt cation is not less than 80%, if it contains non-magnesium ion cations, the non-magnesium ion cations are one or more of sodium, potassium and calcium.

[0047] According to some preferred embodiments, the temperature of the magnesium salt solution does not exceed 30°C, preferably not exceeding 20°C; in this invention, it is preferred that the temperature of the magnesium salt solution does not exceed 30°C. This invention has found that excessively high magnesium salt solution temperatures can easily cause gallic acid to dissolve and detach from the biochar surface; the concentration of the magnesium salt solution is 200–500 g / L (e.g., 200, 250, 300, 350, 400, 450, or 500 g / L), preferably 200–300 g / L; the mass ratio of magnesium in the magnesium salt solution to the biochar in step (2) is (0.1–0.3):1 (e.g., 0.1:1, 0.15:1, 0.2:1, 0.25:1, or 0.3:1); and / or the stirring and impregnation time is 1–2 hours; in this invention… In this invention, preferably, the temperature of the magnesium salt solution does not exceed 30°C, the concentration of the magnesium salt solution is 200–500 g / L, and the stirring and impregnation time in the magnesium salt solution is 1–2 hours. This invention has found that excessively high magnesium salt solution temperatures can easily cause gallic acid to dissolve and detach from the biochar surface. Conversely, excessively low magnesium salt concentrations correspond to larger solution volumes, which can also easily cause gallic acid to dissolve and detach from the biochar surface, increasing subsequent drying time. Excessively high magnesium salt concentrations correspond to smaller solution volumes, which can easily lead to insufficient dispersion of biochar in the solution, ultimately resulting in uneven dispersion of magnesium oxide on the biochar surface. Furthermore, excessively long stirring times can also easily cause gallic acid to dissolve and detach from the biochar surface, while excessively short stirring times can easily lead to insufficient interaction between gallic acid and magnesium oxide.

[0048] According to some preferred embodiments, in step (3): the drying temperature is 60-75°C (e.g., 60°C, 65°C, 70°C, or 75°C), more preferably 60-70°C, and the drying time is 12-24 hours (e.g., 12, 18, or 24 hours); and / or drying to obtain a slurry-like mixture with a moisture content (relative moisture content) of 20-40%; in this invention, it is preferred that the drying temperature is 60-75°C, and drying is performed to obtain a slurry-like mixture with a moisture content (relative moisture content) of 20-40%. This invention has found that... Excessive drying temperature can lead to over-dissolution of gallic acid, causing it to detach from the biochar surface and rendering it ineffective. Conversely, excessively low drying temperature can lead to excessively long drying time, also resulting in excessive dissolution of gallic acid and detachment from the biochar surface, thus rendering it ineffective. If the moisture content after drying is too low, the mixture may become too dense during pyrolysis, affecting the pore-forming process. On the other hand, if the moisture content is too high, water may not be removed in time during pyrolysis, causing the surface strengthener to lose contact with the biochar surface and resulting in insufficient surface strengthening effect on the biochar.

[0049] According to some preferred embodiments, in step (4): heating treatment at 120-150°C for 1-2 hours; and / or pyrolysis treatment at 400-600°C for 1-2 hours; in step (4), for example, the heating treatment and pyrolysis treatment can be carried out in a static or dynamic inert gas, and when carried out in a dynamic inert gas, the inert gas flow rate does not exceed 10 L / h, preferably 5-10 L / h (e.g., 5, 6, 7, 8, 9 or 10 L / h).

[0050] In a second aspect, the present invention provides a magnesium oxide-modified surface-strengthened biochar adsorbent material prepared by the preparation method described in the first aspect of the present invention.

[0051] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise specified, all raw materials used in the embodiments of the present invention and comparative examples can be obtained commercially or synthesized by existing methods.

[0052] Example 1

[0053] ① First, clean the biomass material (corn cob) to remove excess mud and sand from the surface. Then, cut the corn cob into small pieces, dry them to remove most of the moisture, crush them with a pulverizer, and screen them to select materials with a size (particle size) of less than 18 mesh to obtain pretreated biomass material. Let it air dry naturally for later use.

[0054] ② The pretreated biomass material obtained in step ① is transferred to a heating device, and the temperature is raised to 400℃ for pre-carbonization for 2 hours under the condition of introducing inert gas to obtain biochar; wherein, the inert gas is nitrogen, and the flow rate is 8L / h.

[0055] ③ Add the biochar obtained in step ② to a gallic acid hot solution at a temperature of 90℃ and a concentration of 60g / L. Stir and impregnate for 12 hours while maintaining the solution temperature at 90℃ to obtain an impregnation solution. The ratio of biochar to gallic acid hot solution is 30g:1L, that is, the amount of biochar added is 30g per liter of gallic acid hot solution. While still hot, pour the obtained impregnation solution (at 90℃ before filtration) into a filtration device (vacuum filtration device) equipped with an aqueous filter membrane (pore size 0.45μm). Filter at room temperature of 25℃, controlling the filtration time to not exceed 5min, and separate the solid to obtain biochar coated with a gallic acid layer.

[0056] ④ The gallic acid-coated biochar obtained in step ③ is stirred and impregnated in a magnesium salt cold solution (temperature 20℃) for 1 hour, and then dried at 70℃ to obtain a slurry-like mixture with a water content of 25%; wherein, the magnesium salt in the magnesium salt cold solution is magnesium chloride hexahydrate, the concentration of magnesium chloride hexahydrate is 200g / L, and the amount of magnesium salt used is 1 times the mass of the biochar added in step ③.

[0057] ⑤ The slurry mixture obtained in step ④ is transferred to a heating device and heated under the condition of passing an inert gas. First, the temperature is raised to 135°C at a rate of 3°C / min and heated for 1.5 hours. Then, the inert gas is continued to be passed through, and the temperature is raised to 600°C at a rate of 3°C / min for pyrolysis for 1.5 hours. Finally, the obtained material is rinsed with water and dried at 70°C to constant weight to obtain a magnesium oxide modified surface-reinforced biochar adsorbent material. The inert gas is nitrogen, and the flow rate is 8 L / h.

[0058] Example 2

[0059] Example 2 is basically the same as Example 1, except that:

[0060] The corn cobs used in step ① were replaced with wheat straw.

[0061] Example 3

[0062] Example 3 is basically the same as Example 1, except that:

[0063] In step ④, the magnesium salt is replaced with magnesium nitrate hexahydrate with the same magnesium content.

[0064] Example 4

[0065] Example 4 is basically the same as Example 1, except that:

[0066] Change the 600℃ pyrolysis for 1.5h in step ⑤ to 400℃ pyrolysis for 2h.

[0067] Example 5

[0068] Example 5 is basically the same as Example 1, except that:

[0069] ③ Add the biochar obtained in step ② to a gallic acid hot solution at a temperature of 80℃ and a concentration of 150g / L. Stir and impregnate for 24 hours while maintaining the solution temperature at 80℃ to obtain an impregnation solution. The ratio of biochar to gallic acid hot solution is 75g:1L, that is, the amount of biochar added is 75g per liter of gallic acid hot solution. While still hot, pour the obtained impregnation solution (at 80℃ before filtration) into a filtration device (vacuum filtration device) equipped with an aqueous filter membrane (pore size 0.45μm). Filter at room temperature of 25℃, controlling the filtration time to not exceed 5min, and separate the solid to obtain biochar coated with a gallic acid layer.

[0070] ④ The gallic acid-coated biochar obtained in step ③ is stirred and impregnated in a magnesium salt cold solution (temperature 20℃) for 2 hours, and then dried at 70℃ to obtain a mud-like mixture with a water content of 40%; wherein, the magnesium salt in the magnesium salt cold solution is magnesium chloride hexahydrate, the concentration of magnesium chloride hexahydrate is 300g / L, and the amount of magnesium salt used is 2.5 times the mass of the biochar added in step ③.

[0071] Comparative Example 1

[0072] ① First, wash the biomass material (corn stalks) to remove excess mud and sand from the surface. Then, cut the corn stalks into small pieces, dry them to remove most of the moisture, crush them with a pulverizer, and screen them to select materials with a size (particle size) of less than 18 mesh to obtain pre-treated biomass material. Let it air dry naturally for later use.

[0073] ② The pretreated biomass material obtained in step ① is transferred to a heating device, and the temperature is raised to 400℃ for 2 hours under the condition of passing in an inert gas to obtain biochar (adsorbent material); wherein, the inert gas is nitrogen, and the flow rate is 8L / h.

[0074] Comparative Example 2

[0075] ① First, wash the biomass material (corn stalks) to remove excess mud and sand from the surface. Then, cut the corn stalks into small pieces, dry them to remove most of the moisture, crush them with a pulverizer, and screen them to select materials with a size (particle size) of less than 18 mesh to obtain pre-treated biomass material. Let it air dry naturally for later use.

[0076] ② The pretreated biomass material obtained in step ① is transferred to a heating device, and the temperature is raised to 400℃ for pre-carbonization for 2 hours under the condition of introducing inert gas to obtain biochar; wherein, the inert gas is nitrogen, and the flow rate is 8L / h.

[0077] ③ The biochar obtained in step ② is stirred and impregnated (mixed) in a magnesium salt solution (temperature 20℃) for 1 hour, and then dried at 70℃ to obtain a mud-like mixture with a water content of 25%; wherein, the magnesium salt in the magnesium salt solution is magnesium chloride hexahydrate, the concentration of magnesium chloride hexahydrate is 200g / L, and the amount of magnesium salt used is 1 times the mass of the added biochar.

[0078] ④ The slurry mixture obtained in step ③ is transferred to a heating device and heated under the condition of passing an inert gas. First, the temperature is raised to 135℃ at a rate of 3℃ / min and heated for 1.5h. Then, the inert gas is continued to be passed through and the temperature is raised to 600℃ at a rate of 3℃ / min for pyrolysis for 1.5h. Finally, the obtained material is rinsed with water and dried at 70℃ to constant weight to obtain magnesium oxide modified biochar adsorbent material. The inert gas is nitrogen and the flow rate is 8L / h.

[0079] Comparative Example 3

[0080] ① First, wash the biomass material (corn stalks) to remove excess mud and sand from the surface. Then, cut the corn stalks into small pieces, dry them to remove most of the moisture, crush them with a pulverizer, and screen them to select materials with a size (particle size) of less than 18 mesh to obtain pre-treated biomass material. Let it air dry naturally for later use.

[0081] ② The pretreated biomass material obtained in step ① is transferred to a heating device, and the temperature is raised to 400℃ for pre-carbonization for 2 hours under the condition of introducing inert gas to obtain biochar; wherein, the inert gas is nitrogen, and the flow rate is 8L / h.

[0082] ③ Add the biochar obtained in step ② to a gallic acid hot solution at a temperature of 90℃ and a concentration of 60g / L. Stir and impregnate for 12 hours while maintaining the solution temperature at 90℃ to obtain an impregnation solution. The ratio of biochar to gallic acid hot solution is 30g:1L, that is, the amount of biochar added is 30g per liter of gallic acid hot solution. While still hot, pour the obtained impregnation solution (at 90℃ before filtration) into a filtration device (vacuum filtration device) equipped with an aqueous filter membrane (pore size 0.45μm). Filter at room temperature of 25℃, controlling the filtration time to not exceed 5min, separate the solid, and then dry it at 70℃ to constant weight to obtain biochar coated with a gallic acid layer (surface-strengthened biochar), which can be used as a biochar adsorbent material.

[0083] Comparative Example 4

[0084] ① First, wash the biomass material (corn stalks) to remove excess mud and sand from the surface. Then, cut the corn stalks into small pieces, dry them to remove most of the moisture, crush them with a pulverizer, and screen them to select materials with a size (particle size) of less than 18 mesh to obtain pre-treated biomass material. Let it air dry naturally for later use.

[0085] ② The pretreated biomass material obtained in step ① is transferred to a heating device, and the temperature is raised to 400℃ for pre-carbonization for 2 hours under the condition of introducing inert gas to obtain biochar; wherein, the inert gas is nitrogen, and the flow rate is 8L / h.

[0086] ③ Add the biochar obtained in step ② and magnesium chloride hexahydrate to a gallic acid hot solution at a temperature of 90℃ and a concentration of 60g / L. Stir and impregnate for 12 hours while maintaining the solution temperature at 90℃ to obtain an impregnation solution. The ratio of biochar to gallic acid hot solution is 30g:1L, that is, the amount of biochar added is 30g per liter of gallic acid hot solution. While still hot, pour the obtained impregnation solution (at 90℃ before filtration) into a filtration device (vacuum filtration device) equipped with an aqueous filter membrane (pore size 0.45μm). Filter at room temperature of 25℃, controlling the filtration time to not exceed 5min, and separate the solid to obtain a mixture. The amount of magnesium salt used is 1 times the mass of the added biochar.

[0087] ④ The mixture obtained in step ③ is transferred to a heating device and heated under the condition of passing an inert gas. First, the temperature is raised to 135℃ at a rate of 3℃ / min and heated for 1.5h. Then, the inert gas is continued to be passed through and the temperature is raised to 600℃ at a rate of 3℃ / min for pyrolysis for 1.5h. Finally, the obtained material is rinsed with water and dried at 70℃ to constant weight to obtain magnesium oxide modified biochar adsorbent material. The inert gas is nitrogen and the flow rate is 8L / h.

[0088] Comparative Example 5

[0089] ① First, wash the biomass material (corn stalks) to remove excess mud and sand from the surface. Then, cut the corn stalks into small pieces, dry them to remove most of the moisture, crush them with a pulverizer, and screen them to select materials with a size (particle size) of less than 18 mesh to obtain pre-treated biomass material. Let it air dry naturally for later use.

[0090] ② The pretreated biomass material obtained in step ① is transferred to a heating device, and the temperature is raised to 400℃ for pre-carbonization for 2 hours under the condition of introducing inert gas to obtain biochar; wherein, the inert gas is nitrogen, and the flow rate is 8L / h.

[0091] ③ The biochar obtained in step ② is stirred and impregnated (mixed) in a magnesium salt solution (temperature 20℃) for 1 hour, and then dried at 70℃ to obtain a mud-like mixture with a water content of 25%; wherein, the magnesium salt in the magnesium salt solution is magnesium chloride hexahydrate, the concentration of magnesium chloride hexahydrate is 200g / L, and the amount of magnesium salt used is 1 times the mass of the added biochar.

[0092] ④ The slurry mixture obtained in step ③ is transferred to a heating device and heated under the condition of passing an inert gas. First, the temperature is raised to 135°C at a rate of 3°C / min and heated for 1.5 hours. Then, the inert gas is continued to be passed through, and the temperature is raised to 600°C at a rate of 3°C / min for pyrolysis for 1.5 hours. Finally, the obtained material is rinsed with clean water and dried at 70°C to constant weight to obtain magnesium oxide modified biochar. The inert gas is nitrogen, and the flow rate is 8 L / h.

[0093] ⑤ Add the magnesium oxide-modified biochar obtained in step ④ to a gallic acid hot solution at 90℃ and a concentration of 60 g / L. Stir and impregnate for 12 hours while maintaining the solution temperature at 90℃ to obtain an impregnation solution. The ratio of the gallic acid hot solution to the biochar added in step ② is 1 L: 30 g. While still hot, pour the obtained impregnation solution (at 90℃ before filtration) into a filtration device (vacuum filtration device) equipped with an aqueous filter membrane (pore size 0.45 μm). Filter at room temperature of 25℃, controlling the filtration time to not exceed 5 min, separate the solid, and then dry it at 70℃ to constant weight to obtain the surface-strengthened oxidized magnesium oxide-supported biochar material.

[0094] Comparative Example 6

[0095] Comparative Example 6 is basically the same as Example 1, except that:

[0096] In step ③, a hot gallic acid solution with a concentration of 25 g / L is used.

[0097] Comparative Example 7

[0098] Comparative Example 7 is basically the same as Example 1, except that:

[0099] In step ③, a hot gallic acid solution with a concentration of 200 g / L is used.

[0100] Comparative Example 8

[0101] Comparative Example 8 is basically the same as Example 1, except that:

[0102] In step ③, the filter device is preheated to 55°C before filtration, and filtration is carried out in an environment of 55°C.

[0103] Comparative Example 9

[0104] Comparative Example 9 is basically the same as Example 1, except that:

[0105] In step ④, the mixture is dried to obtain a mud-like mixture with a moisture content of 5%.

[0106] Comparative Example 10

[0107] Comparative Example 10 is basically the same as Example 1, except that:

[0108] In step ④, drying yields a mud-like mixture with a moisture content of 50%.

[0109] Comparative Example 11

[0110] Comparative Example 11 is basically the same as Example 1, except that:

[0111] ④ The gallic acid-coated biochar obtained in step ③ is stirred and impregnated in a magnesium salt solution (temperature 70℃) for 1 hour, and then dried at 70℃ to obtain a slurry-like mixture with a water content of 25%; wherein, the magnesium salt in the magnesium salt solution is magnesium chloride hexahydrate, the concentration of magnesium chloride hexahydrate is 200g / L, and the amount of magnesium salt used is 1 times the mass of the biochar added in step ③.

[0112] Comparative Example 12

[0113] Comparative Example 12 is basically the same as Example 1, except that:

[0114] In step ③, the obtained impregnation solution is cooled to 25°C and then poured into a filtration device (vacuum filtration device) equipped with an aqueous filter membrane (pore size 0.45μm). The solution is filtered at room temperature of 25°C, and the filtration time is controlled to not exceed 5 minutes. The solid is separated to obtain biochar coated with gallic acid.

[0115] Comparative Example 13

[0116] Comparative Example 13 is basically the same as Example 1, except that:

[0117] ③ Add the biochar obtained in step ② to a gallic acid solution with a concentration of 1 g / L (the temperature of the gallic acid solution is room temperature 25℃), and stir and impregnate for 18 hours at room temperature 25℃ to obtain an impregnation solution. The ratio of biochar to gallic acid solution is 2 g: 1 L, that is, the amount of biochar added is 2 g per liter of gallic acid solution. Pour the obtained impregnation solution (before filtration, the temperature is 25℃) into a filtration device (vacuum filtration device) equipped with an aqueous filter membrane (pore size 0.45 μm), filter at room temperature 25℃, and control the filtration time to not exceed 5 min to separate the solid and obtain gallic acid-coated biochar.

[0118] ④ The gallic acid-coated biochar obtained in step ③ is stirred and impregnated in a magnesium salt solution (temperature 25℃) for 1 hour, and then dried at 70℃ to obtain a mud-like mixture with a water content of 25%; wherein, the magnesium salt in the magnesium salt solution is magnesium chloride hexahydrate, the concentration of magnesium chloride hexahydrate is 200g / L, and the amount of magnesium salt used is 1 times the mass of the biochar added in step ③.

[0119] Comparative Example 14

[0120] ① First, clean the biomass material (corn cob) to remove excess mud and sand from the surface. Then, cut the corn cob into small pieces, dry them to remove most of the moisture, crush them with a pulverizer, and screen them to select materials with a size (particle size) of less than 18 mesh to obtain pretreated biomass material. Let it air dry naturally for later use.

[0121] ② The pretreated biomass material obtained in step ① is transferred to a heating device, and the temperature is raised to 400℃ for pre-carbonization for 2 hours under the condition of introducing inert gas to obtain biochar; wherein, the inert gas is nitrogen, and the flow rate is 8L / h.

[0122] ③ At room temperature (25℃), gallic acid was prepared into a 1.0 g / L aqueous solution, and the pH was adjusted to 5.0 using 0.1 mol / L hydrochloric acid and 0.1 mol / L sodium hydroxide.

[0123] ④ Add the biochar obtained in step ② to the gallic acid aqueous solution to obtain a mixed solution with a biochar mass concentration of 2 g / L. Stir the mixed solution at room temperature (25°C) for 7 days.

[0124] ⑤ After stirring, the liquid phase is removed by filtration at 25°C, and the remaining solid is freeze-dried in a freeze dryer to obtain gallic acid impregnated biochar.

[0125] ⑥ The gallic acid-impregnated biochar obtained in step ⑤ is stirred and impregnated (mixed) in a magnesium salt solution (temperature 25℃) for 1 hour, and then dried at 70℃ to obtain a mud-like mixture with a water content of 25%; wherein, the magnesium salt in the magnesium salt solution is magnesium chloride hexahydrate, the concentration of magnesium chloride hexahydrate is 200g / L, and the amount of magnesium salt used is 1 times the mass of the biochar added in step ④.

[0126] ⑦ The slurry mixture obtained in step ⑥ is transferred to a heating device and heated under the condition of passing an inert gas. First, the temperature is raised to 135°C at a rate of 3°C / min and heated for 1.5 hours. Then, the inert gas is continued to be passed through, and the temperature is raised to 600°C at a rate of 3°C / min for pyrolysis for 1.5 hours. Finally, the obtained material is rinsed with water and dried at 70°C to constant weight to obtain magnesium oxide modified biochar. The inert gas is nitrogen, and the flow rate is 8 L / h.

[0127] The adsorption performance of the biochar adsorbents finally prepared in each embodiment and comparative example was tested. The test method was as follows: lead wastewater with a concentration of 500 mg / L (dosage 200 ppm), cadmium wastewater with a concentration of 500 mg / L (dosage 600 ppm), NH3-N wastewater with a concentration of 100 mg / L (dosage 500 ppm), and PO4-P wastewater with a concentration of 200 mg / L (dosage 500 ppm) were treated at 25℃. After adsorption equilibrium was reached, the adsorption capacity (maximum adsorption capacity) was measured and the results are shown in Table 1.

[0128] Table 1

[0129]

[0130]

[0131] A physical image of the magnesium oxide-modified surface-reinforced biochar adsorbent material prepared in Example 1 of this invention is shown below. Figure 1 As shown; SEM images of the magnesium oxide-modified surface-strengthened biochar adsorbent material prepared in Example 1 of this invention at different magnifications, as shown. Figure 2 As shown; from Figure 2 The results show that surface functional group enhancement followed by magnesium salt impregnation effectively improves the activation degree and loading dispersibility of magnesium oxide; the XRD pattern of the magnesium oxide-modified surface-strengthened biochar adsorbent material prepared in Example 1 of this invention is shown below. Figure 3 As shown, the XRD pattern demonstrates that the surface of the magnesium oxide-modified surface-reinforced biochar adsorbent material is loaded with magnesium oxide; the SEM images of the adsorption of lead and cadmium by the magnesium oxide adsorbent directly used in this invention and by the magnesium oxide-modified surface-reinforced biochar adsorbent material prepared in Example 1 are shown below. Figure 4 As shown; from Figure 4 The results show that after adsorption, compared with the direct use of magnesium oxide adsorbent, the magnesium oxide-modified surface-strengthened biochar adsorbent used in the method of this invention can adhere to the surface of the magnesium oxide-modified surface-strengthened biochar adsorbent after lead and cadmium removal, and the solid size is significantly increased, making separation and removal simpler. Figure 3 and Figure 4The preparation of magnesium oxide is as follows: magnesium nitrate (mass-volume ratio of magnesium nitrate to water is 1g:15mL) is added to water and mixed evenly by stirring. The mixture is then dried at 70℃ for 8h to a slurry state. The slurry mixture is then heated in a nitrogen atmosphere (flow rate of 8L / h) at 135℃ for 1.5h, and then pyrolyzed in a nitrogen atmosphere (flow rate of 8L / h) at 600℃ for 1.5h. The obtained material is rinsed with water and dried to constant weight to obtain magnesium oxide.

[0132] The parts of this invention not described in detail are techniques known to those skilled in the art.

[0133] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a magnesium oxide-modified surface-strengthened biochar adsorbent material, characterized in that, The method includes the following steps: (1) Pre-carbonize biomass materials to obtain biochar; (2) The biochar is stirred and impregnated in a gallic acid hot solution to obtain an impregnation solution, and then the impregnation solution is filtered to obtain biochar coated with a gallic acid layer; in step (2), the gallic acid concentration of the gallic acid hot solution is 50~150g / L, and the temperature of the gallic acid hot solution is 70~90℃; the ratio of the amount of biochar to the amount of gallic acid hot solution is (25~75)g:1L; before the impregnation solution is filtered, the temperature is not lower than 70℃, and the filtration time is not more than 5min; (3) The biochar coated with gallic acid layer is stirred and impregnated in magnesium salt solution, and then dried to obtain a mixture; in step (3), the temperature of the magnesium salt solution does not exceed 30°C; the concentration of the magnesium salt solution is 200~500g / L; and it is dried to obtain a mud-like mixture with a water content of 20~40%; (4) The mixture is subjected to heating treatment at 120~150℃ and pyrolysis treatment at 400~600℃ in an inert gas to obtain magnesium oxide modified surface-strengthened biochar adsorbent material.

2. The preparation method according to claim 1, characterized in that, In step (1): The biomass material is a lignocellulose-based biomass material.

3. The preparation method according to claim 2, characterized in that: The lignocellulosic biomass material is one or more of agricultural and forestry waste and wood materials.

4. The preparation method according to claim 2, characterized in that: The lignocellulosic biomass material is one or more of the following: corn cob, straw, grass leaves, fruit shells, and wood materials.

5. The preparation method according to claim 1, characterized in that, In step (1): Before pre-carbonization, the biomass material is pretreated by washing and cutting it into blocks, then drying, crushing and sieving to obtain biomass material with a particle size of less than 18 mesh.

6. The preparation method according to claim 1, characterized in that, In step (1): The pre-carbonization is carried out in a nitrogen atmosphere, or the pre-carbonization is carried out in a confined space after oxygen has been removed by limited combustion; and / or The pre-carbonization temperature is 300~600℃, and the time is 1~3h.

7. The preparation method according to claim 6, characterized in that, In step (1): The pre-carbonization temperature is 400℃ and the time is 2 hours.

8. The preparation method according to claim 1, characterized in that, In step (2): The temperature of the gallic acid hot solution is 80~90℃; The mass ratio of the biochar to the gallic acid in the gallic acid hot solution is 1:(1~3); and / or The stirring and impregnation time is 12-24 hours.

9. The preparation method according to claim 1, characterized in that, In step (2): The filtered liquid is recycled and reused until it is cooled to 40°C and no solids precipitate.

10. The preparation method according to claim 1, characterized in that, In step (3): The magnesium salt in the magnesium salt solution is one or more of magnesium nitrate, magnesium sulfate, and magnesium chloride. The temperature of the magnesium salt solution shall not exceed 20°C; The magnesium in the magnesium salt solution contains a magnesium to biochar mass ratio of (0.1~0.3):1 (in step (2)); and / or The stirring and soaking time is 1 to 2 hours.

11. The preparation method according to claim 1, characterized in that, In step (3): The drying temperature is 60~75℃.

12. The preparation method according to claim 1, characterized in that, In step (4): Heat treatment at 120~150℃ for 1~2 hours; and / or Pyrolysis treatment at 400~600℃ for 1~2 hours.

13. A magnesium oxide-modified surface-strengthened biochar adsorbent material prepared by any one of claims 1 to 12.

Images