An oxygen-activated biochar-based heavy metal adsorbent modified by the composite of amino group and magnesium oxide and its preparation method

Abstract

The present invention relates to an oxygen-activated biochar-based heavy metal adsorbent modified by the composite of amino group and magnesium oxide and a preparation method thereof. The method includes: subjecting biochar to oxygen activation at 400-500 °C for 30-60 min in a gas containing oxygen to obtain oxygen-activated biochar; the volume percentage of oxygen contained in the gas is 10-50%; mixing the oxygen-activated biochar and a magnesium salt evenly with water to obtain a mixture, and then drying and pyrolyzing to obtain magnesium oxide / oxygen-activated biochar; impregnating the magnesium oxide / oxygen-activated biochar in an amino acid solution, performing ultrasonic treatment, then performing oscillation treatment and drying to prepare the oxygen-activated biochar-based heavy metal adsorbent modified by the composite of amino group and magnesium oxide. The heavy metal adsorbent obtained by the present invention can rapidly treat low-concentration heavy metal wastewater, has excellent adsorption performance, low sludge production, and can optimize the separation of heavy metal precipitation and the reuse of heavy metals.

Description

Technical Field

[0001] The present invention relates to the technical field of heavy metal adsorbent materials, and particularly to an oxygen-activated biochar-based heavy metal adsorbent modified by composite modification of amino groups and magnesium oxide and a preparation method thereof. Background Art

[0002] At present, heavy metal wastewater is mainly treated by chemical precipitation methods (represented by lime neutralization precipitation method), heavy metal scavengers, membrane separation and related derivative methods.

[0003] The chemical precipitation method is the most widely used method at present. When using alkaline precipitants such as CaO (quicklime, slaked lime) to treat heavy metal wastewater, the treatment effect is insufficient and the treatment rate is slow. To make the effluent concentration meet the standard, a high dosage is required, and the dosage of the medicament is large; in addition, the precipitate particles generated by the traditional precipitation method (including CaO and sulfides) for treating wastewater are too fine, and the subsequent treatment is highly dependent on auxiliary medicaments such as flocculants, flotation agents and surfactants, so secondary pollution is caused; in addition, the amount of heavy metal sludge generated by the traditional method is large, resulting in the generation of a large amount of heavy metal sludge, and the subsequent harmless treatment is difficult, and the treatment process is cumbersome and complex.

[0004] MgO, a relatively green and environmentally friendly adsorbent commonly used in the adsorption method, can immobilize heavy metals through ion exchange and precipitation. Due to its low solubility and slower release rate of hydroxide ions, it can avoid the dissolution of heavy metal hydroxide precipitates caused by too high pH. However, the too slow reaction rate results in longer time consumption and larger dosage when using MgO to treat heavy metal wastewater. Traditional MgO-based lead and cadmium adsorbents usually need to be activated to increase the specific surface area during preparation to obtain more reactive magnesium oxide to improve the adsorption efficiency. To improve the adsorption activity of MgO, certain activation processes are often required to increase its specific surface area to achieve higher adsorption efficiency. However, general activation methods have high costs and energy consumption, and the preparation temperature can reach 1000 - 1200 °C. The preparation of activated magnesium oxide usually has problems such as high preparation temperature (about 1000 °C for calcining magnesite) or complex preparation processes (spray drying method, sol-gel method, etc.). For example, when using wet methods such as precipitation method, sol-gel method or spray drying method, the preparation process is complex, the reagent consumption is large, and the cost is high. At the same time, the activated MgO adsorbent also has the problem of too small precipitation particles, high dependence on auxiliary agents such as flocculants, and is prone to failure due to coagulation during use, resulting in a decrease in adsorption efficiency. When using porous carbon materials as the substrate to load magnesium oxide to prepare composite adsorbents, it can bring a certain improvement to the adsorption activity of magnesium oxide. Using biochar to support MgO can improve the adsorption performance, but it has high requirements for the surface properties of biochar materials. The support and dispersion effect of raw biochar on magnesium oxide is insufficient, and activated biochar with a higher specific surface area needs to be used as the support material. If unactivated biochar materials are used for loading, the activation degree of magnesium oxide particles is still low, and the adsorption rate is still insufficient. Moreover, the energy consumption and reagent consumption of traditional activation methods are both high, and the improvement of material properties needs to be enhanced. Amino modification is also an effective means to improve the heavy metal adsorption performance of adsorbents. For example, grafting functional groups with complexing ability such as amino groups on the surface of biochar is an important method to improve the adsorption performance. However, traditional amino grafting methods are usually complex, the difficulty of amino grafting is large, the reagent dosage is large and the pollution risk is high. And usually, the adsorption capacity of amino-modified carbon materials is controlled by the number of amino groups, which is often very limited. When the adsorption amount meets the requirements, the consumption of related reagents is large, resulting in a certain cost pressure.

[0005] In addition, after treating heavy metal wastewater with current heavy metal treatment agents such as precipitants and heavy metal scavengers, there are generally problems such as too small precipitation particles, high dependence on agents such as flocculants and flotation agents, further increase in the production of heavy metal sludge, and difficulties in subsequent treatment.

[0006] In summary, to solve one or more of the above existing technical problems, it is highly necessary to provide an oxygen-activated biochar-based heavy metal adsorbent with composite modification of amino and magnesium oxide and its preparation method. SUMMARY OF THE INVENTION

[0007] In order to solve one or more technical problems existing in the prior art, the present invention provides an oxygen-activated biochar-based heavy metal adsorbent modified by composite of amino group and magnesium oxide and a preparation method thereof.

[0008] In a first aspect, the present invention provides a preparation method of an oxygen-activated biochar-based heavy metal adsorbent modified by composite of amino group and magnesium oxide, and the method comprises the following steps:

[0009] (1) Oxygen-activate biochar in a gas containing oxygen at 400-500 °C for 30-60 min to obtain oxygen-activated biochar; the volume percentage content of oxygen in the gas is 10-50%;

[0010] (2) Mix oxygen-activated biochar and a magnesium salt evenly with water to obtain a mixture, and then obtain magnesium oxide / oxygen-activated biochar through drying and pyrolysis;

[0011] (3) Immerse magnesium oxide / oxygen-activated biochar in an amino acid solution and perform ultrasonic treatment, and then perform oscillation treatment and drying to prepare an oxygen-activated biochar-based heavy metal adsorbent modified by composite of amino group and magnesium oxide.

[0012] Preferably, in step (1): the flow rate of the gas does not exceed 10 L / h, and preferably is 5-10 L / h.

[0013] Preferably, the biochar is obtained by pretreatment and carbonization of a biomass material; preferably, the biomass material is a lignocellulosic biomass material; more preferably, the lignocellulosic biomass material is one or more of straw, grass leaves and wood materials; further preferably, the straw is corn straw.

[0014] Preferably, the carbonization treatment is carried out under the protection of an inert gas, the temperature of the carbonization treatment is 250-350 °C, and the time of the carbonization treatment does not exceed 2 h.

[0015] Preferably, in step (2): the mass ratio of the oxygen-activated biochar to the magnesium contained in the magnesium salt is 1:(0.02-0.3), preferably, the magnesium salt is magnesium chloride and / or magnesium sulfate; the drying is first drying at 60-80 °C for 6-12 h, and then drying at 120-150 °C for 1-2 h; and / or the temperature of the pyrolysis is 400-600 °C, and the time of the pyrolysis is 1-2 h.

[0016] Preferably, in step (2): the pyrolysis is carried out in a mixed gas containing oxygen and an inert gas, and the volume percentage content of oxygen in the mixed gas is 5-12%.

[0017] Preferably, in step (3): the mass ratio of the magnesium oxide / oxygen-activated biochar to the amino acid solution is 1:(5-15), preferably 1:10; and / or the mass ratio of the magnesium oxide / oxygen-activated biochar to the amino acids contained in the amino acid solution is 1:(0.01-0.05).

[0018] Preferably, the amino acids contained in the amino acid solution are glutamic acid and / or glycine.

[0019] Preferably, in step (3): the time of the ultrasonic treatment is 3-6 min; the temperature of the oscillation treatment is 30-50 °C, and the time of the oscillation treatment is 5-10 min; and / or the temperature of the drying is 85-105 °C.

[0020] In a second aspect, the present invention provides a heavy metal adsorbent based on oxygen-activated biochar modified by the composite of amino groups and magnesium oxide prepared by the preparation method described in the first aspect of the present invention.

[0021] Compared with the prior art, the present invention has at least the following beneficial effects:

[0022] (1) The present invention develops a method for obtaining a higher specific surface area and a better surface pore structure by activating biochar through oxygen activation, and further obtaining an efficient carbon-based composite adsorption material through the loading of magnesium oxide and the modification of amino groups, which is used for the rapid and efficient removal of heavy metal ions such as lead and cadmium in heavy metal wastewater. The method of the present invention uses carbon-based materials such as biochar as raw materials, and effectively increases the pores and oxygen-containing functional groups on the surface of biochar by carrying out limited oxygen activation under suitable conditions. Further, the impregnation-pyrolysis method is adopted to uniformly and dispersedly load magnesium oxide on the surface of biochar, and taking magnesium oxide as a linker, through its reaction with amino acids such as glutamic acid, a heavy metal adsorbent material based on oxygen-activated biochar modified by the composite of amino groups and magnesium oxide is finally obtained. This material can rapidly capture and concentrate heavy metal ions by the complexation of amino groups, cause in-situ precipitation by reacting with magnesium oxide, and capture the precipitate through a porous carbon matrix. The heavy metal adsorbent material obtained by the present invention can treat low-concentration heavy metal wastewater, has a fast treatment rate, reduces the use of chemicals such as precipitants and flocculants, has a low sludge production, and can optimize the separation of heavy metal precipitates and the recycling of heavy metals.

[0023] (2) Compared with the magnesium oxide adsorbent, after loading magnesium oxide on the surface of biochar activated by oxygen, the speed of heavy metal precipitation such as lead and cadmium in the adsorbent is faster, the adsorption rate is effectively improved, and both the adsorption capacity and adsorption rate are higher than those of unloaded magnesium oxide and directly loaded magnesium oxide. After amino grafting, the adsorption capacity and adsorption rate can be further improved; in the present invention, when the dosage of the amino and magnesium oxide composite modified oxygen-activated biochar-based heavy metal adsorbent is 400 ppm and treating 200 mg / L lead wastewater, the removal rate exceeds 99.9%, the effluent concentration is lower than 0.1 mg / L, and the equilibrium time is significantly shorter than that of magnesium oxide loaded biochar, and the initial adsorption rate is faster.

[0024] (3) Under suitable conditions, the present invention conducts oxygen activation on biochar, which can increase the porosity of the biochar surface and form a large number of oxygen-containing functional groups on the surface. Therefore, during the process of loading magnesium oxide, the magnesium oxide structure has better dispersion on the biochar surface and stronger adsorption activity. And during subsequent amination, more reaction sites can be provided, enabling the amino group to be grafted on the material surface; however, for materials with poor magnesium oxide dispersion without oxygen activation treatment, the adsorption performance is not effectively improved after amination, and the important reasons are that the amino group fails to be effectively grafted and the loss of magnesium oxide during the grafting process; compared with traditional magnesium oxide activation methods, this method does not require too high activation temperature and has lower energy consumption; compared with other amino grafting methods, when using the method of the present invention, due to the good dispersion of magnesium oxide on the biochar surface, amino modification is simpler, less pollution is generated during the preparation process, and the process is simpler; compared with existing biochar activation methods, the method of the present invention uses oxygen activation to activate biochar, and during oxygen activation, the concentration and temperature used in the present invention are more conducive to uniformly increasing oxygen-containing functional groups on the biochar surface and shaping pores on the flat surface, which is beneficial to subsequent magnesium oxide loading and makes its dispersion better.

[0025] (4) After adsorption with the heavy metal adsorbent prepared by the present invention, the particle size of heavy metal precipitation particles increases significantly and adheres to the adsorbent substrate, so that larger particle products can be obtained, the recovery difficulty is reduced, and the cost and energy consumption are reduced. Description of the Drawings

[0026] Figure 1 It is a graph showing the adsorption results of lead and cadmium ions by the amino and magnesium oxide composite modified oxygen-activated biochar-based heavy metal adsorbent prepared in Example 1 of the present invention and the heavy metal adsorbents prepared in Comparative Examples 1-4;

[0027] Figure 2 It is a physical picture of the amino and magnesium oxide composite modified oxygen-activated biochar-based heavy metal adsorbent product prepared in Example 1 of the present invention;

[0028] Figure 3 SEM images of the biochar without oxygen activation and the biochar after oxygen activation in Example 1 of the present invention; (a) is the SEM image of the biochar without oxygen activation, and (b) is the SEM image of the biochar after oxygen activation;

[0029] Figure 4 FT-IR spectra of the biochar without oxygen activation (raw biochar) and the biochar after oxygen activation (oxygen-activated biochar) in Example 1 of the present invention;

[0030] Figure 5 SEM images of the magnesium oxide / biochar heavy metal adsorbent obtained in Comparative Example 2 of the present invention and the magnesium oxide / oxygen-activated biochar in Example 1; In the figure, (a) and (b) correspond to the SEM images of the magnesium oxide / biochar sample at different magnifications, and (c) and (d) correspond to the SEM images of the magnesium oxide / oxygen-activated biochar sample at different magnifications;

[0031] Figure 6 SEM images of the oxygen-activated biochar-based heavy metal adsorbent modified by the composite of amino group and magnesium oxide prepared in Example 1 of the present invention at different magnifications;

[0032] Figure 7 XRD spectra of the magnesium oxide / oxygen-activated biochar in Example 1 of the present invention and the oxygen-activated biochar-based heavy metal adsorbent modified by the composite of amino group and magnesium oxide prepared in Example 1 (amino group-modified magnesium oxide / oxygen-activated biochar);

[0033] Figure 8 FT-IR spectra of the magnesium oxide / oxygen-activated biochar in Example 1 of the present invention and the oxygen-activated biochar-based heavy metal adsorbent modified by the composite of amino group and magnesium oxide prepared in Example 1 (amino group-modified magnesium oxide / oxygen-activated biochar);

[0034] Figure 9 SEM images of directly using the magnesium oxide adsorbent and using the oxygen-activated biochar-based heavy metal adsorbent modified by the composite of amino group and magnesium oxide prepared in Example 1 after adsorbing lead and cadmium;

[0035] In the figure, (a) is the SEM image of directly using the magnesium oxide adsorbent after adsorbing lead, (b) is the SEM image of directly using the magnesium oxide adsorbent after adsorbing cadmium, (c) is the SEM image of using the oxygen-activated biochar-based heavy metal adsorbent modified by the composite of amino group and magnesium oxide prepared in Example 1 after adsorbing lead, and (d) is the SEM image of using the oxygen-activated biochar-based heavy metal adsorbent modified by the composite of amino group and magnesium oxide prepared in Example 1 after adsorbing cadmium. Detailed implementation mode

[0036] To make the objectives, technical solutions and advantages of the present invention more clear, the following will, in combination with the embodiments of the present invention, clearly and completely describe the technical solutions of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0037] The present invention provides, in a first aspect, a method for preparing an oxygen-activated biochar-based heavy metal adsorbent modified by amino groups and magnesium oxide. The method comprises the following steps:

[0038] (1) Oxygen-activate biochar in a gas containing oxygen at 400 - 500 °C (such as 400 °C, 450 °C or 500 °C) for 30 - 60 min (such as 30, 35, 40, 45, 50, 55 or 60 min) to obtain oxygen-activated biochar; the volume percentage content of oxygen in the gas is 10 - 50% (such as 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50%); in the present invention, the gas containing oxygen uses an inert gas as the carrier gas, and the inert gas is, for example, nitrogen. Preferably, the gas containing oxygen is composed of oxygen and nitrogen;

[0039] (2) Mix oxygen-activated biochar and a magnesium salt evenly with water to obtain a mixture, and then obtain magnesium oxide / oxygen-activated biochar through drying and pyrolysis;

[0040] (3) Immerse magnesium oxide / oxygen-activated biochar in an amino acid solution and perform ultrasonic treatment, and then perform oscillation treatment and drying to prepare an oxygen-activated biochar-based heavy metal adsorbent modified by amino groups and magnesium oxide (abbreviated as heavy metal adsorbent or amino-modified magnesium oxide / oxygen-activated biochar); in the present invention, the amino acid solution uses water as the solvent and is an aqueous amino acid solution.

[0041] The present invention adopts a three-step preparation method. First, the surface of biochar is oxygen-activated under appropriate oxygen conditions. Subsequently, an impregnation-pyrolysis method is used. By utilizing the surface with increased porosity after oxygen activation and the oxygen-containing functional groups on the surface after oxidation, magnesium oxide is uniformly loaded on the surface of the oxygen-activated biochar. Then, amino acids such as glutamic acid are used for impregnation. Preferably, by controlling the impregnation ratio and impregnation time (ultrasonic and oscillation time), the reaction between the metal hydroxyl groups on the surface of hydrated magnesium oxide and the acidic functional groups contained in the amino acids is utilized to connect the amino acids with magnesium oxide, thereby loading amino groups on the surface of magnesium oxide. The heavy metal adsorbent based on oxygen-activated biochar modified by the composite of amino groups and magnesium oxide in the present invention can utilize the complexation of the amino acids fixed on the surface of magnesium oxide to concentrate heavy metal ions near the magnesium oxide on the biochar surface. Under the action of ion exchange and precipitation promotion provided by magnesium oxide, the heavy metal ions are converted into solid precipitate particles, and the precipitate is captured by the biochar surface containing a certain number of oxygen-containing functional groups, reducing the recovery difficulty.

[0042] Compared with magnesium oxide adsorbents, after loading magnesium oxide on the surface of oxygen-activated biochar in the present invention, the precipitation rate of heavy metals such as lead and cadmium in the adsorbent is faster, the adsorption rate is effectively improved, and both the adsorption capacity and adsorption rate are higher than those of unloaded magnesium oxide and directly loaded magnesium oxide. After amino grafting, the adsorption capacity and adsorption rate can be further improved. After adsorption with the heavy metal adsorbent prepared by the present invention, the size of the heavy metal precipitate particles increases significantly and adheres to the adsorbent substrate, so that larger particle products can be obtained, the recovery difficulty is reduced, and the cost and energy consumption are decreased.

[0043] In order to ensure the effect of oxygen-activated biochar, activation needs to be carried out under appropriate oxygen content and temperature, that is, oxygen activation is carried out at 400-500 °C under the condition that the volume percentage of oxygen is 10-50%. This can increase the porosity of the biochar surface and form a large number of oxygen-containing functional groups on the surface. Thus, during the magnesium oxide loading process, the magnesium oxide structure has better dispersion on the biochar surface and stronger adsorption activity. And during subsequent amination, more reaction sites can be provided, enabling amino groups to be grafted onto the material surface. The present invention finds that if the volume percentage of oxygen is too low and / or the oxygen activation temperature is too low, the formation of oxygen-containing functional groups on the biochar surface and the increase in porosity cannot be fully achieved. If the volume percentage of oxygen is too high and / or the oxygen activation temperature is too high, peroxidation reactions will occur, resulting in over-oxidation or combustion of the biochar, rather than selectively forming oxygen-containing functional groups. This will damage the biochar structure, reduce its porosity, and cause a large amount of biochar to ash, ultimately affecting the adsorption performance of the material. The present invention finds that for materials with poor dispersion of magnesium oxide without oxygen activation treatment, the adsorption performance is not effectively improved after amination. The important reasons for the ineffective grafting of amino groups and the loss of magnesium oxide during the grafting process are that during the process of loading amino groups after loading magnesium oxide, magnesium oxide may be removed or effective loading of amino acids cannot be achieved. When grafting is carried out in the present invention, it is achieved by controlling the reaction degree of magnesium oxide and amino acids. If the dispersion of magnesium oxide is insufficient, larger particles will be formed in the biochar pores. When reacting with acidic amino acid grafting agents, they are more likely to fall off. When the particles are larger, the specific surface area is also smaller, and the contact surface with the amino acid grafting agent is too small, resulting in a decrease in the number of grafted amino groups and the grafting amount. Due to the appropriate oxygen activation of the biochar in the present invention, magnesium oxide can be evenly dispersed while amino group modification can be effectively introduced, enabling the heavy metal adsorbent to retain the loading of both magnesium oxide and amino groups. Compared with traditional magnesium oxide activation methods, this method does not require too high an activation temperature and has lower energy consumption. Compared with other amino grafting methods, when using the method of the present invention, due to the good dispersion of magnesium oxide on the biochar surface, amino group modification is simpler, with less pollution and a simpler process during preparation. Compared with existing biochar activation methods, the method of the present invention uses oxygen activation to activate biochar. And during oxygen activation, the present invention finds that the concentration and temperature used are more conducive to evenly increasing oxygen-containing functional groups on the biochar surface and shaping pores on the flat surface, which is beneficial to subsequent magnesium oxide loading and makes its dispersion better.

[0044] According to some preferred embodiments, in step (1): the flow rate of the gas (gas containing oxygen) does not exceed 10 L / h, preferably 5-10 L / h (such as 5, 6, 7, 8, 9 or 10 L / h); through a large number of creative experiments in the present invention, the appropriate gas flow rate for oxygen activation in the present invention is obtained. The present invention finds that an appropriate gas flow rate can ensure the uniform distribution of oxygen during the oxygen activation process, so that the oxygen activation reaction on the surface of the biochar proceeds uniformly, avoiding the situation that some parts of the biochar fail to fully contact oxygen due to insufficient gas flow rate. And at an appropriate flow rate, an appropriate reaction rate can be achieved, enabling the activation reaction to proceed sufficiently without being too fast or too slow; in addition, an appropriate gas flow rate can ensure the uniform fluidity of the gas in the reactor and to a certain extent improve the production capacity of oxygen-activated biochar, thereby increasing production efficiency; if the gas flow rate is too large, it may lead to non-uniform distribution of the gas during the oxygen activation process, affecting the uniformity of the reaction.

[0045] According to some preferred embodiments, the biochar is obtained by pretreating and carbonizing a biomass material; preferably, the biomass material is a lignocellulosic biomass material; more preferably, the lignocellulosic biomass material is one or more of straw, grass leaves and wood materials; further preferably, the straw is corn straw; in the present invention, the pretreatment is, for example: first, the biomass material is washed to remove excess attachments such as sediment on the surface, then the biomass material is cut into small pieces, dried to remove most of the moisture, and then pulverized using a pulverizer, and the biomass material with a size (particle size) not greater than 18 mesh is selected by screening and air-dried for use.

[0046] According to some preferred embodiments, the carbonization treatment is carried out under the protection of an inert gas, the temperature of the carbonization treatment is 250-350 °C (such as 250 °C, 300 °C or 350 °C), and the time of the carbonization treatment does not exceed 2 h.

[0047] According to some specific embodiments, the preparation of the biochar is as follows: the source of the biomass material is a lignocellulosic biomass material mainly from plant sources, including straw, grass leaves and wood materials, etc.; after selecting the materials, first, the biomass material is washed to remove excess attachments such as sediment on the surface, then the biomass material is cut into small pieces, dried to remove most of the moisture, and then pulverized using a pulverizer, and the material with a size (particle size) less than 18 mesh is selected by screening to obtain the pretreated biomass material, which is air-dried for use; the pretreated biomass material is placed in an inert protective gas (such as nitrogen), the temperature is raised to about 300 °C, and after carbonization treatment (pyrolysis) for no more than 2 h, and during this carbonization treatment process, the volatiles generated by pyrolysis are blown away using a higher carrier gas flow rate (such as nitrogen or argon with a flow rate of 30-50 L / h) to obtain the biochar.

[0048] According to some specific embodiments, step (1) is as follows: putting the biochar into a gas containing oxygen (the volume percentage of oxygen is 10-50%), the feeding flow rate of the gas containing oxygen does not exceed 10 L / h, controlling the temperature at 400-500 °C, controlling the reaction time at 30-60 minutes, and oxidizing its surface with oxygen; then, stopping ventilation and heating, and cooling to obtain oxygen-activated biochar.

[0049] According to some preferred embodiments, in step (2): the mass ratio of the oxygen-activated biochar to the magnesium contained in the magnesium salt is 1:(0.02-0.3) (for example, 1:0.02, 1:0.05, 1:0.08, 1:0.1, 1:0.15, 1:0.2, 1:0.25 or 1:0.3). Preferably, the magnesium salt is magnesium chloride and / or magnesium sulfate; in the present invention, preferably, the mass ratio of the oxygen-activated biochar to the magnesium contained in the magnesium salt is 1:(0.02-0.3). It is found in the present invention that if the amount of magnesium is too low, the loading amount of magnesium oxide is insufficient, the adsorption capacity is too low, and the dosage required is too large, and it is easy to overreact during amino grafting to completely remove magnesium oxide; if the amount of magnesium is too high, the loading amount is too large, it is easy to form agglomerated magnesium oxide particles, which is not conducive to its dispersion on the biochar substrate; the drying is first drying at 60-80 °C (for example, 60 °C, 65 °C, 70 °C, 75 °C or 80 °C) for 6-12 h (for example, 6, 7, 8, 9, 10, 11 or 12 h), and then drying at 120-150 °C (for example, 120 °C, 125 °C, 130 °C, 135 °C, 140 °C or 150 °C) for 1-2 h (for example, 1, 1.5 or 2 h); and / or the temperature of the pyrolysis is 400-600 °C (for example, 400 °C, 450 °C, 500 °C, 550 °C or 600 °C), and the time of the pyrolysis is 1-2 h (for example, 1, 1.5 or 2 h).

[0050] According to some preferred embodiments, in step (2): the pyrolysis is carried out in a mixed gas containing oxygen and an inert gas, and the volume percentage of oxygen in the mixed gas is 5-12% (such as 5%, 6%, 7%, 8%, 9%, 10%, 11% or 12%). Preferably, the flow rate of the mixed gas is 5-10 L / h. Different from the pyrolysis under conventional pure inert atmosphere conditions, in the preparation of magnesium oxide / oxygen-activated biochar in the present invention, it is preferably to contain an appropriate concentration of oxygen in the inert atmosphere. Compared with a pure inert atmosphere (such as nitrogen), that is, compared with pyrolysis under oxygen-insulated conditions, the present invention finds that the presence of an appropriate concentration of oxygen helps to promote the formation and surface activation of magnesium oxide, can better control the progress of the reaction, make the formation of magnesium oxide more complete and uniform, helps to enhance the interaction between oxygen-activated biochar and magnesium oxide, can make the dispersion of magnesium oxide on the biochar surface better, the activation higher, and the adsorption activity stronger, thus being beneficial to improving the adsorption performance of the material.

[0051] According to some specific embodiments, step (2) is: mixing the oxygen-activated biochar with a magnesium salt (magnesium chloride and / or magnesium sulfate), and the mixing ratio is that the mass ratio of magnesium contained in the oxygen-activated biochar to the magnesium salt is 1:(0.02 - 0.3). Adding a certain amount of water to the mixture, and the dosage of the water is such that the mass-volume ratio of the oxygen-activated biochar to water is 1 g:(10 - 20) mL. After mixing evenly by means such as stirring or ultrasonic treatment, it is slowly dried to a slurry state at 60 - 80 °C, and then the slurry-like mixture is heated and dried at 120 - 150 °C for 1 - 2 h, and then pyrolyzed under oxygen-limited conditions, that is, the temperature is raised to 400 - 600 °C for pyrolysis for 1 - 2 h to complete the loading of magnesium oxide. The prepared material is rinsed with clear water and dried for storage for later use to obtain magnesium oxide / oxygen-activated biochar.

[0052] According to some preferred embodiments, in step (3): the mass ratio of the magnesium oxide / oxygen-activated biochar to the amino acid solution is 1:(5 - 15) (such as 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14 or 1:15), preferably 1:10; and / or the mass ratio of the magnesium oxide / oxygen-activated biochar to the amino acid contained in the amino acid solution is 1:(0.01 - 0.05) (such as 1:0.01, 1:0.02, 1:0.03, 1:0.04 or 1:0.05).

[0053] According to some preferred embodiments, the amino acid contained in the amino acid solution is glutamic acid and / or glycine; in the present invention, the amino acid can be selected as a small molecule agent having both an amino group and a carboxyl group, and usually relatively simple and inexpensive amino acids such as glycine and glutamic acid are selected.

[0054] According to some preferred embodiments, in step (3): the time of the ultrasonic treatment is 3 - 6 min (such as 3, 4, 5 or 6 min); the temperature of the oscillation treatment is 30 - 50 °C (such as 30 °C, 35 °C, 40 °C, 45 °C or 50 °C), and the time of the oscillation treatment is 5 - 10 min (such as 5, 6, 7, 8, 9 or 10 min); in the present invention, the frequency of the ultrasonic treatment is, for example, 28 kHz - 40 kHz, and the rate of the oscillation treatment is, for example, 120 - 200 rpm; in the present invention, by controlling the mass ratio of the magnesium oxide / oxygen-activated biochar to the amino acid contained in the amino acid solution to be 1:(0.01 - 0.05), the time of the ultrasonic treatment is 3 - 6 min, and the temperature of the oscillation treatment is 5 - 10 min, that is, by reasonably controlling the impregnation ratio and the impregnation time, it is beneficial to make magnesium oxide and amino acid react effectively, effectively connect the amino acid with magnesium oxide, thereby effectively loading the amino group on the surface of magnesium oxide (grafting the amino group onto the surface of magnesium oxide), obtaining amino-modified magnesium oxide / oxygen-activated biochar, which is beneficial to improving the performance of the heavy metal adsorbent; the present invention finds that too little amino acid, too short ultrasonic and oscillation time will all lead to insufficient amino group grafting amount, and vice versa will lead to excessive consumption of magnesium oxide; and / or the drying temperature is 85 - 105 °C (such as 85 °C, 90 °C, 95 °C, 100 °C or 105 °C).

[0055] According to some specific embodiments, step (3) is: impregnating the magnesium oxide / oxygen-activated biochar in an amino acid solution such as glutamic acid at a solid-liquid mass ratio of 1:10, the mass ratio of the magnesium oxide / oxygen-activated biochar to the amino acid is 1:0.01 - 0.05, dispersing by ultrasonic treatment for about 5 minutes, oscillating at 30 - 50 °C for 5 - 10 minutes, then drying the mixed solution at 85 - 105 °C, rinsing with water and drying to obtain an oxygen-activated biochar-based heavy metal adsorbent with amino and magnesium oxide composite modification.

[0056] In the second aspect of the present invention, there is provided an oxygen-activated biochar-based heavy metal adsorbent with amino and magnesium oxide composite modification prepared by the preparation method described in the first aspect of the present invention. The present invention provides an oxygen-activated biochar-based heavy metal adsorbent with amino and magnesium oxide composite modification, which captures and concentrates heavy metal ions by using the complexing action of the amino group on them, converts the ions into solid precipitate particles by using the ion exchange and precipitation-promoting action of magnesium oxide, and captures the precipitate particles by the carbon-based surface rich in functional groups due to oxygen activation; the oxygen-activated biochar-based heavy metal adsorbent with amino and magnesium oxide composite modification in the present invention can rapidly treat low-concentration heavy metal wastewater, reduce the use of agents such as precipitants and flocculants, and optimize the separation of heavy metal precipitation and the reuse of heavy metals.

[0057] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the protection scope of the present invention. Without special instructions, each raw material used in the embodiments of the present invention and the comparative examples can be obtained through commercial purchase or synthesized by existing methods.

[0058] The preparation methods of the biochar used in the following embodiments and comparative examples are the same, specifically as follows:

[0059] First, the biomass material (corn straw) is washed to remove the attached substances such as excess sediment on the surface, and then the corn straw is cut into small pieces. After drying to remove most of the moisture, it is pulverized using a pulverizer, and the materials with a size (particle size) less than 18 mesh are selected by screening to obtain the pretreated biomass material, which is naturally air-dried for later use; the pretreated biomass material is placed in a nitrogen atmosphere, the temperature is raised to 300 °C, and carbonization treatment is carried out for 1.5 h. During this carbonization process, a relatively high carrier gas flow rate (nitrogen with a flow rate of 35 L / h) is used to blow away the volatile substances generated during the carbonization process to obtain biochar.

[0060] Example 1

[0061] ① The biochar is placed in a gas containing oxygen, the flow rate of the gas containing oxygen is 8 L / h, and the temperature is controlled at 450 °C, and the reaction (oxygen activation) time is controlled at 40 minutes; then, the ventilation and heating are stopped, and it is cooled to obtain oxygen-activated biochar; the gas containing oxygen is composed of a mixture of oxygen and nitrogen, and the volume percentage of oxygen in the gas containing oxygen is 25%, and the volume percentage of nitrogen is 75%.

[0062] ② The oxygen-activated biochar obtained in step ① is mixed with magnesium chloride, and the mixing ratio is that the mass ratio of magnesium contained in the oxygen-activated biochar to magnesium chloride is 1:0.1. A certain amount of water (the mass-volume ratio of the oxygen-activated biochar to water is 1 g:15 mL) is added to the mixture, and it is mixed evenly by stirring. After drying at 70 °C for 8 h to a slurry state, the slurry-like mixture is heated and dried at 130 °C for 1.5 h, and then pyrolyzed at 500 °C for 1.5 h in a mixed gas composed of oxygen and nitrogen (flow rate of 8 L / h) to complete the loading of magnesium oxide. The prepared material is rinsed with clean water and dried to obtain magnesium oxide / oxygen-activated biochar; wherein, the volume percentage of oxygen in the mixed gas is 8%, and the volume percentage of nitrogen is 92%.

[0063] ③ Immerse the magnesium oxide / oxygen-activated biochar obtained in step ② in a glutamic acid solution (aqueous glutamic acid solution) and ultrasonicate for 5 min, then oscillate at 40 °C for 8 min. Subsequently, dry the resulting mixed solution at 95 °C, then rinse with water and dry to obtain a heavy metal adsorbent based on oxygen-activated biochar modified by the composite of amino group and magnesium oxide; wherein, the mass ratio of magnesium oxide / oxygen-activated biochar to the glutamic acid solution is 1:10, and the mass ratio of magnesium oxide / oxygen-activated biochar to glutamic acid contained in the glutamic acid solution is 1:0.03.

[0064] Example 2

[0065] ① Place the biochar in a gas containing oxygen, with the flow rate of the gas containing oxygen being 5 L / h, control the temperature at 500 °C, and control the reaction (oxygen activation) time at 30 minutes; subsequently, stop ventilation and heating, cool to obtain oxygen-activated biochar; the gas containing oxygen is composed of a mixture of oxygen and nitrogen, and the volume percentage of oxygen contained in the gas containing oxygen is 10%, and the volume percentage of nitrogen contained is 90%.

[0066] ② Mix the oxygen-activated biochar obtained in step ① with magnesium chloride, and the mixing ratio is that the mass ratio of oxygen-activated biochar to magnesium contained in magnesium chloride is 1:0.1. Add a certain amount of water (the mass-volume ratio of oxygen-activated biochar to water is 1 g:15 mL) to the mixture, mix it evenly by stirring, dry it to a slurry state at 70 °C for 8 h, then heat and dry the slurry-like mixture at 130 °C for 1.5 h, and then pyrolyze it at 500 °C in a mixed gas composed of oxygen and nitrogen (flow rate of 5 L / h) for 1.5 h to complete the loading of magnesium oxide. The obtained material is rinsed with water and dried to obtain magnesium oxide / oxygen-activated biochar; wherein, the volume percentage of oxygen contained in the mixed gas is 5%, and the volume percentage of nitrogen contained is 95%.

[0067] ③ Immerse the magnesium oxide / oxygen-activated biochar obtained in step ② in a glutamic acid solution (aqueous glutamic acid solution) and ultrasonicate for 5 min, then oscillate at 40 °C for 8 min. Subsequently, dry the resulting mixed solution at 95 °C, then rinse with water and dry to obtain a heavy metal adsorbent based on oxygen-activated biochar modified by the composite of amino group and magnesium oxide; wherein, the mass ratio of magnesium oxide / oxygen-activated biochar to the glutamic acid solution is 1:10, and the mass ratio of magnesium oxide / oxygen-activated biochar to glutamic acid contained in the glutamic acid solution is 1:0.01.

[0068] Example 3

[0069] ① Place the biochar in a gas containing oxygen. The flow rate of the gas containing oxygen is 10 L / h, and the temperature is controlled at 400 °C. The reaction (oxygen activation) time is controlled at 60 minutes. Subsequently, stop ventilation and heating, and cool to obtain oxygen-activated biochar. The gas containing oxygen is composed of oxygen and nitrogen, and the volume percentage of oxygen in the gas containing oxygen is 50%, and the volume percentage of nitrogen is 50%.

[0070] ② Mix the oxygen-activated biochar obtained in step ① with magnesium chloride. The mixing ratio is that the mass ratio of magnesium in the oxygen-activated biochar to magnesium chloride is 1:0.1. Add a certain amount of water to the mixture (the mass-volume ratio of the oxygen-activated biochar to water is 1 g:15 mL). After mixing evenly by stirring, dry it at 70 °C for 8 h until it becomes slurry. Then heat and dry the slurry mixture at 130 °C for 1.5 h, and then pyrolyze it at 500 °C for 1.5 h in a mixed gas composed of oxygen and nitrogen (flow rate: 10 L / h) to complete the loading of magnesium oxide. The prepared material is rinsed with clean water and dried to obtain magnesium oxide / oxygen-activated biochar. Among them, the volume percentage of oxygen in the mixed gas is 12%, and the volume percentage of nitrogen is 88%.

[0071] ③ Immerse the magnesium oxide / oxygen-activated biochar obtained in step ② in a glutamic acid solution (aqueous glutamic acid solution) and ultrasonicate for 5 min, then oscillate at 40 °C for 8 min. Subsequently, dry the obtained mixed solution at 95 °C, rinse with clean water and dry to obtain a heavy metal adsorbent based on oxygen-activated biochar with amino and magnesium oxide composite modification. The mass ratio of magnesium oxide / oxygen-activated biochar to the glutamic acid solution is 1:10, and the mass ratio of magnesium oxide / oxygen-activated biochar to glutamic acid in the glutamic acid solution is 1:0.05.

[0072] Example 4

[0073] Example 4 is basically the same as Example 1, except that:

[0074] ① Place the biochar in a gas containing oxygen. The flow rate of the gas containing oxygen is 2 L / h, and the temperature is controlled at 450 °C. The reaction (oxygen activation) time is controlled at 40 minutes. Subsequently, stop ventilation and heating, and cool to obtain oxygen-activated biochar. The gas containing oxygen is composed of oxygen and nitrogen, and the volume percentage of oxygen in the gas containing oxygen is 25%, and the volume percentage of nitrogen is 75%.

[0075] Example 5

[0076] Example 5 is basically the same as Example 1, except that:

[0077] ① Place the biochar in a gas containing oxygen. The flow rate of the gas containing oxygen is 20 L / h, and the temperature is controlled at 450 °C. The reaction (oxygen activation) time is controlled at 40 minutes. Subsequently, stop ventilation and heating, and cool to obtain oxygen-activated biochar. The gas containing oxygen is composed of a mixture of oxygen and nitrogen. The volume percentage of oxygen in the gas containing oxygen is 25%, and the volume percentage of nitrogen is 75%.

[0078] Example 6

[0079] Example 6 is basically the same as Example 1, except that:

[0080] ② Mix the oxygen-activated biochar obtained in step ① with magnesium chloride. The mixing ratio is such that the mass ratio of magnesium contained in the oxygen-activated biochar to magnesium chloride is 1:0.1. Add a certain amount of water to the mixture (the mass-volume ratio of the oxygen-activated biochar to water is 1 g:15 mL). After mixing evenly by stirring, dry it at 70 °C for 8 h until it becomes a slurry. Then, heat and dry the slurry mixture at 130 °C for 1.5 h, and then pyrolyze it at 500 °C in a nitrogen atmosphere (flow rate: 8 L / h) for 1.5 h. The prepared material is rinsed with clean water and dried to obtain magnesium oxide / oxygen-activated biochar.

[0081] Example 7

[0082] Example 7 is basically the same as Example 1, except that:

[0083] ③ Immerse the magnesium oxide / oxygen-activated biochar obtained in step ② in a glutamic acid solution (aqueous glutamic acid solution) and ultrasonicate for 5 min, then oscillate at 40 °C for 8 min. Subsequently, dry the obtained mixed solution at 95 °C, rinse with clean water and dry to obtain an oxygen-activated biochar-based heavy metal adsorbent with amino and magnesium oxide composite modification. Among them, the mass ratio of the magnesium oxide / oxygen-activated biochar to the glutamic acid solution is 1:10, and the mass ratio of the magnesium oxide / oxygen-activated biochar to the glutamic acid contained in the glutamic acid solution is 1:0.005.

[0084] Example 8

[0085] Example 8 is basically the same as Example 1, except that:

[0086] ③ The magnesium oxide / oxygen-activated biochar obtained in step ② was impregnated in a glutamic acid solution (aqueous glutamic acid solution) and ultrasonicated for 5 min, then oscillated at 40 °C for 8 min. Subsequently, the obtained mixed solution was dried at 95 °C, rinsed with water and dried to obtain a heavy metal adsorbent based on oxygen-activated biochar with amino groups and magnesium oxide composite modification; wherein, the mass ratio of magnesium oxide / oxygen-activated biochar to the glutamic acid solution is 1:10, and the mass ratio of magnesium oxide / oxygen-activated biochar to the glutamic acid contained in the glutamic acid solution is 1:0.08.

[0087] Example 9

[0088] Example 9 is basically the same as Example 1, except that:

[0089] ③ The magnesium oxide / oxygen-activated biochar obtained in step ② was impregnated in a glutamic acid solution (aqueous glutamic acid solution) and ultrasonicated for 10 min, then oscillated at 40 °C for 20 min. Subsequently, the obtained mixed solution was dried at 95 °C, rinsed with water and dried to obtain a heavy metal adsorbent based on oxygen-activated biochar with amino groups and magnesium oxide composite modification; wherein, the mass ratio of magnesium oxide / oxygen-activated biochar to the glutamic acid solution is 1:10, and the mass ratio of magnesium oxide / oxygen-activated biochar to the glutamic acid contained in the glutamic acid solution is 1:0.03.

[0090] Comparative Example 1

[0091] Magnesium chloride was added to water (the mass-volume ratio of magnesium chloride to water is 1 g:15 mL), and it was mixed evenly by stirring. Then it was dried at 70 °C for 8 h until it became a slurry. The slurry-like mixture was further dried by heating at 130 °C for 1.5 h, and then pyrolyzed at 500 °C for 1.5 h in an air atmosphere. The obtained material was rinsed with water and dried to obtain magnesium oxide.

[0092] Comparative Example 2

[0093] Biochar and magnesium chloride were mixed, and the mixing ratio was that the mass ratio of magnesium contained in biochar to magnesium chloride is 1:0.1. A certain amount of water was added to the mixture (the mass-volume ratio of biochar to water is 1 g:15 mL), and it was mixed evenly by stirring. Then it was dried at 70 °C for 8 h until it became a slurry. The slurry-like mixture was further dried by heating at 130 °C for 1.5 h, and then pyrolyzed at 500 °C for 1.5 h in a nitrogen atmosphere to complete the loading of magnesium oxide. The obtained material was rinsed with water and dried to obtain magnesium oxide / biochar.

[0094] Comparative Example 3

[0095] ① Mix biochar with magnesium chloride at a mixing ratio of 1:0.1 in terms of the mass ratio of magnesium contained in biochar to magnesium chloride. Add a certain amount of water to the mixture (the mass-volume ratio of biochar to water is 1 g:15 mL). After mixing evenly by stirring, dry it at 70 °C for 8 h until it becomes a slurry. Then, heat and dry the slurry mixture at 130 °C for 1.5 h, and then pyrolyze it in a nitrogen atmosphere at 500 °C for 1.5 h to complete the loading of magnesium oxide. The prepared material is rinsed with clean water and dried to obtain magnesium oxide / biochar.

[0096] ② Immerse the magnesium oxide / biochar obtained in step ① in a glutamic acid solution (aqueous glutamic acid solution) and ultrasonicate for 5 min, then oscillate at 40 °C for 8 min. Subsequently, dry the obtained mixed solution at 95 °C, rinse it with clean water and dry it to obtain amino-modified magnesium oxide / biochar; wherein, the mass ratio of the magnesium oxide / biochar to the glutamic acid solution is 1:10, and the mass ratio of the magnesium oxide / biochar to glutamic acid contained in the glutamic acid solution is 1:0.03.

[0097] Comparative Example 4

[0098] ① Place biochar in a gas containing oxygen. The flow rate of the gas containing oxygen is 8 L / h, and the temperature is controlled at 450 °C. The reaction (oxygen activation) time is controlled at 40 minutes; subsequently, stop ventilation and heating, and cool to obtain oxygen-activated biochar; the gas containing oxygen is composed of a mixture of oxygen and nitrogen, and the volume percentage of oxygen contained in the gas containing oxygen is 25%, and the volume percentage of nitrogen contained is 75%.

[0099] ② Mix the oxygen-activated biochar obtained in step ① with magnesium chloride at a mixing ratio of 1:0.1 in terms of the mass ratio of magnesium contained in oxygen-activated biochar to magnesium chloride. Add a certain amount of water to the mixture (the mass-volume ratio of oxygen-activated biochar to water is 1 g:15 mL). After mixing evenly by stirring, dry it at 70 °C for 8 h until it becomes a slurry. Then, heat and dry the slurry mixture at 130 °C for 1.5 h, and then pyrolyze it in a nitrogen atmosphere at 500 °C for 1.5 h to complete the loading of magnesium oxide. The prepared material is rinsed with clean water and dried to obtain magnesium oxide / oxygen-activated biochar.

[0100] Comparative Example 5

[0101] Comparative Example 5 is basically the same as Example 1, except that:

[0102] ① Place the biochar in a static oxygen-containing gas, control the temperature at 900 °C, and control the reaction (oxygen activation) time at 120 minutes; subsequently, stop ventilation and heating, and cool to obtain oxygen-activated biochar; the oxygen-containing gas is composed of oxygen and nitrogen, and the oxygen-containing gas contains 5% by volume of oxygen and 95% by volume of nitrogen.

[0103] Comparative Example 6

[0104] Comparative Example 6 is basically the same as Example 1, except that:

[0105] ① Place the biochar in an oxygen-containing gas, the flow rate of the oxygen-containing gas is 8 L / h, control the temperature at 600 °C, and control the reaction (oxygen activation) time at 120 minutes; subsequently, stop ventilation and heating, and cool to obtain oxygen-activated biochar; the oxygen-containing gas is composed of oxygen and nitrogen, and the oxygen-containing gas contains 5% by volume of oxygen and 95% by volume of nitrogen.

[0106] Comparative Example 7

[0107] Comparative Example 7 is basically the same as Example 1, except that:

[0108] ① Place the biochar in an oxygen-containing gas, the flow rate of the oxygen-containing gas is 8 L / h, control the temperature at 300 °C, and control the reaction (oxygen activation) time at 40 minutes; subsequently, stop ventilation and heating, and cool to obtain oxygen-activated biochar; the oxygen-containing gas is composed of oxygen and nitrogen, and the oxygen-containing gas contains 60% by volume of oxygen and 40% by volume of nitrogen.

[0109] Comparative Example 8

[0110] ① Place the biochar in an oxygen-containing gas, the flow rate of the oxygen-containing gas is 8 L / h, control the temperature at 450 °C, and control the reaction (oxygen activation) time at 40 minutes; subsequently, stop ventilation and heating, and cool to obtain oxygen-activated biochar; the oxygen-containing gas is composed of oxygen and nitrogen, and the oxygen-containing gas contains 25% by volume of oxygen and 75% by volume of nitrogen.

[0111] ②Mix the oxygen-activated biochar obtained in step ① with magnesium chloride. The mixing ratio is that the mass ratio of magnesium contained in the oxygen-activated biochar to magnesium chloride is 1:0.1. Add a certain amount of water to the mixture (the mass-volume ratio of the oxygen-activated biochar to water is 1 g:15 mL). After mixing evenly by stirring, then add a glutamic acid solution (aqueous glutamic acid solution) and ultrasonicate for 5 min, then oscillate at 40 °C for 8 min, and then dry at 70 °C for 8 h until it becomes a slurry. Then heat and dry the slurry mixture at 130 °C for 1.5 h, and then pyrolyze in a mixed gas composed of oxygen and nitrogen (flow rate: 8 L / h) at 500 °C for 1.5 h. The prepared material is rinsed with clean water and dried to obtain a heavy metal adsorbent; wherein, the volume percentage of oxygen in the mixed gas is 8%, and the volume percentage of nitrogen is 92%; the mass ratio of the oxygen-activated biochar to the glutamic acid solution is 1:10, and the mass ratio of the oxygen-activated biochar to glutamic acid contained in the glutamic acid solution is 1:0.03.

[0112] In the present invention, the adsorption performance of the heavy metal adsorbents finally prepared in each example and each comparative example was tested. The test method is as follows: Treat lead wastewater and cadmium wastewater with a concentration of 500 mg / L at 25 °C. The dosage of the heavy metal adsorbent is 200 ppm. After adsorption equilibrium, the measured adsorption capacity (maximum adsorption capacity) results are shown in Table 1; Treat lead wastewater and cadmium wastewater with a concentration of 200 mg / L at 25 °C. After adsorption for 360 min, the dosage of the heavy metal adsorbent required to meet the effluent concentration standard is measured, and the results are shown in Table 1.

[0113] Table 1

[0114]

[0115]

[0116] The adsorption results of lead and cadmium ions by the amino- and magnesium oxide-composite modified oxygen-activated biochar-based heavy metal adsorbent prepared in Example 1 of the present invention and the heavy metal adsorbents prepared in Comparative Examples 1-4 are shown in Figure 1 as shown. In Figure 1 , the test conditions for the adsorption results of lead ions are as follows: Treat 200 mg / L lead wastewater at 25 °C. The dosage of the heavy metal adsorbent is 400 ppm, and the treatment time is 360 min. The test conditions for the adsorption results of cadmium ions are as follows: Treat 200 mg / L cadmium wastewater at 25 °C. The dosage of the heavy metal adsorbent is 400 ppm, and the treatment time is 360 min; From Figure 1As can be seen from the results in Table 1, compared with the magnesium oxide heavy metal adsorbent, after loading magnesium oxide on the surface of biochar activated by oxygen, the precipitation rate of heavy metals such as lead and cadmium in the adsorbent is faster, the adsorption rate is effectively improved, and both the adsorption capacity and adsorption rate are higher than those of unloaded magnesium oxide and directly loaded magnesium oxide. After amino grafting, the adsorption capacity and adsorption rate can be further improved; when the dosage of the adsorbent modified by the composite of amino and magnesium oxide is 400 ppm and treating 200 mg / L lead wastewater, the removal rate exceeds 99.9%, and the effluent concentration is lower than 0.1 mg / L; the physical picture of the heavy metal adsorbent based on oxygen-activated biochar modified by the composite of amino and magnesium oxide prepared in Example 1 of the present invention is as Figure 2 shown; the SEM diagrams of the biochar without oxygen activation and the biochar after oxygen activation in Example 1 of the present invention are as Figure 3 shown; from Figure 3 the results, it can be seen that compared with the original biochar, the surface roughness and microporous structure of the biochar after oxygen activation are significantly improved, which is more conducive to the improvement of its specific surface area; the FT-IR spectra of the biochar without oxygen activation (original biochar) and the biochar after oxygen activation (oxygen-activated biochar) in Example 1 of the present invention are as Figure 4 shown, and from Figure 4 it can be seen that there are more oxygen-containing functional groups on the surface of the oxygen-activated biochar; the SEM diagrams of the magnesium oxide / biochar heavy metal adsorbent obtained in Comparative Example 2 of the present invention and the magnesium oxide / oxygen-activated biochar in Example 1 are as Figure 5 shown, and from Figure 5 it can be seen that compared with the magnesium oxide loading structure on the surface of the original biochar, the magnesium oxide loaded on the surface of the biochar after oxygen activation in the present invention has better dispersion; from Figures 3 to 5 the results, it can be known that the oxygen activation method adopted in the present invention can increase the porosity of the biochar surface, increase the pore structure on the biochar surface, and form a large number of oxygen-containing functional groups on the surface, so that during the magnesium oxide loading process, the magnesium oxide structure has better dispersion on the biochar surface, enabling the magnesium oxide to be evenly dispersed and loaded on the surface with stronger adsorption activity, and during the subsequent amination, it can provide more reaction sites, enabling the amino group to be grafted on the material surface; the SEM diagrams of the heavy metal adsorbent based on oxygen-activated biochar modified by the composite of amino and magnesium oxide prepared in Example 1 of the present invention at different magnification are as Figure 6 shown, and from Figure 6It can be seen that after amino modification, the magnesium oxide support is still well-dispersed on the surface of the oxygen-activated biochar-based heavy metal adsorbent modified by the composite of amino and magnesium oxide; the XRD patterns of magnesium oxide / oxygen-activated biochar (magnesium oxide / oxygen-activated biochar) in Example 1 of the present invention and the oxygen-activated biochar-based heavy metal adsorbent modified by the composite of amino and magnesium oxide (amino-modified magnesium oxide / oxygen-activated biochar) prepared in Example 1 are as shown in Figure 7 shown. The XRD results from Figure 7 also indicate that magnesium oxide is successfully loaded onto the surface of the oxygen-activated biochar. After amino modification, magnesium oxide on the surface of the oxygen-activated biochar-based heavy metal adsorbent modified by the composite of amino and magnesium oxide is still retained; the FT-IR spectra of magnesium oxide / oxygen-activated biochar in Example 1 of the present invention and the oxygen-activated biochar-based heavy metal adsorbent modified by the composite of amino and magnesium oxide (amino-modified magnesium oxide / oxygen-activated biochar) prepared in Example 1 are as shown in Figure 8 shown. The FT-IR spectra from Figure 8 show that amino groups are successfully modified on the surface of magnesium oxide / oxygen-activated biochar. These results show that the oxygen-activated biochar-based heavy metal adsorbent material modified by the composite of amino and magnesium oxide in the present invention uses magnesium oxide as a connecting material. Through the limited reaction of magnesium oxide with amino acids, amino groups are modified on the magnesium oxide material on the surface of the biochar material. The heavy metal adsorbent material after composite modification can couple the complexation of amino groups with heavy metals with the precipitation and ion exchange of magnesium oxide, etc., so as to achieve a more efficient heavy metal removal effect; the SEM images of the magnesium oxide adsorbent directly used in the present invention and the oxygen-activated biochar-based heavy metal adsorbent modified by the composite of amino and magnesium oxide prepared in Example 1 after adsorbing lead and cadmium are as shown in Figure 9 shown. From the results of Figure 9 , it can be known that after the adsorption is completed, compared with directly using the magnesium oxide adsorbent, when using the heavy metal adsorbent in the present invention to remove lead and cadmium, the precipitates of lead and cadmium can be evenly dispersed and attached to the surface of the heavy metal adsorbent, and the solid size increases significantly, and the separation and removal are more simple.

[0117] The parts not detailed in the present invention are well-known technologies to those skilled in the art.

[0118] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A preparation method of an oxygen-activated biochar-based heavy metal adsorbent modified by the composite of amino and magnesium oxide, characterized in that, The method includes the following steps: (1) Oxygen-activate biochar in a gas containing oxygen at 400-500 °C for 30-60 min to obtain oxygen-activated biochar; the volume percentage of oxygen contained in the gas is 10-50%; (2) Mix the oxygen-activated biochar and magnesium salt evenly with water to obtain a mixture, and then obtain magnesium oxide / oxygen-activated biochar through drying and pyrolysis; (3) Immerse the magnesium oxide / oxygen-activated biochar in an amino acid solution and perform ultrasonic treatment, and then perform oscillation treatment and drying to prepare a heavy metal adsorbent based on oxygen-activated biochar with amino groups and magnesium oxide composite modification.

2. The preparation method according to claim 1, characterized in that, In step (1): The flow rate of the gas does not exceed 10 L / h.

3. The preparation method according to claim 2, characterized in that, In step (1): The flow rate of the gas is 5-10 L / h.

4. According to the preparation method described in claim 1, it is characterized in that: The biochar is obtained by pretreating and carbonizing biomass materials.

5. According to the preparation method described in claim 4, it is characterized in that: The biomass material is a lignocellulosic biomass material.

6. According to the preparation method described in claim 5, it is characterized in that: The lignocellulosic biomass material is one or more of straw, grass leaves, and wood materials.

7. According to the preparation method described in claim 6, it is characterized in that: The straw is corn straw.

8. According to the preparation method described in claim 4, it is characterized in that: The carbonization treatment is carried out under the protection of an inert gas, the temperature of the carbonization treatment is 250-350 °C, and the time of the carbonization treatment does not exceed 2 h.

9. The preparation method according to claim 1, characterized in that, In step (2): The mass ratio of the oxygen-activated biochar to the magnesium contained in the magnesium salt is 1:(0.02-0.3); The drying is first carried out at 60-80 °C for 6-12 h, and then at 120-150 °C for 1-2 h; and / or The temperature of the pyrolysis is 400-600 °C, and the time of the pyrolysis is 1-2 h.

10. According to the preparation method described in claim 9, it is characterized in that: The magnesium salt is magnesium chloride and / or magnesium sulfate.

11. The preparation method according to claim 1, characterized in that, In step (2): The pyrolysis is carried out in a mixed gas containing oxygen and an inert gas, and the volume percentage of oxygen contained in the mixed gas is 5-12%.

12. The preparation method according to claim 1, characterized in that, In step (3): The mass ratio of the magnesium oxide / oxygen-activated biochar to the amino acid solution is 1:(5-15); and / or The mass ratio of the magnesium oxide / oxygen-activated biochar to the amino acid contained in the amino acid solution is 1:(0.01-0.05).

13. The preparation method according to claim 12, characterized in that, In step (3): The mass ratio of the magnesium oxide / oxygen-activated biochar to the amino acid solution is 1:

10.

14. According to the preparation method described in claim 1, it is characterized in that: The amino acid contained in the amino acid solution is glutamic acid and / or glycine.

15. The preparation method according to claim 1, characterized in that, In step (3): The time of the ultrasonic treatment is 3-6 min; The temperature of the oscillation treatment is 30-50 °C, and the time of the oscillation treatment is 5-10 min; and / or The temperature of the drying is 85-105 °C.

16. An amino and magnesium oxide composite modified oxygen-activated biochar-based heavy metal adsorbent prepared by the preparation method according to any one of claims 1 to 15.

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