A nitrogen-sulfur-magnesium composite-modified biochar adsorbent material and preparation method thereof

Abstract

The present invention relates to a biochar adsorbent material compositely modified with nitrogen, sulfur and magnesium and a preparation method thereof. The method comprises: pre-treating a biomass material to obtain a pre-treated biomass material; uniformly mixing the pre-treated biomass material, a magnesium source and a nitrogen and sulfur source with water to obtain a first mixture, and then drying the first mixture to obtain a second mixture; sequentially subjecting the second mixture to a heating treatment at 120 to 150°C, a pyrolysis treatment at 300 to 350°C and a pyrolysis treatment at 500 to 700°C in a mixed gas containing oxygen and an inert gas to obtain a biochar adsorbent material compositely modified with nitrogen, sulfur and magnesium; the volume percentage of oxygen contained in the mixed gas is 10 to 30%. The biochar adsorbent obtained by the present invention can efficiently and quickly treat low-concentration heavy metal wastewater, has excellent adsorption performance, reduces the use of auxiliary reagents such as flocculants, has low sludge production, and can optimize the separation of heavy metal precipitates and the reuse of heavy metals.

Description

Technical Field

[0001] The invention relates to the technical field of adsorbent materials, in particular to a nitrogen-sulfur-magnesium composite-modified biochar adsorbent material and a preparation method thereof. Background Art

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

[0003] Chemical precipitation is currently the most widely used method. 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. In order to make the effluent concentration meet the standard, a higher dosage is required, and the dosage of the reagents is large. In addition, the precipitate particles produced by traditional precipitation methods (including CaO and sulfide) to treat wastewater are too fine, and the subsequent treatment is highly dependent on auxiliary agents such as flocculants, flotation agents and surfactants, thus causing secondary pollution. In addition, the traditional method produces a large amount of heavy metal sludge, resulting in the production of a large amount of heavy metal sludge, making subsequent harmless treatment difficult and the treatment process cumbersome and complicated.

[0004] MgO, a relatively environmentally friendly adsorbent commonly used in adsorption methods, can immobilize heavy metals through ion exchange and precipitation. Due to its low solubility, hydroxide release is slower, preventing heavy metal alkaline precipitation and dissolution caused by excessively high pH. However, the slow reaction rate results in a longer treatment time and a higher dosage of MgO for heavy metal wastewater treatment. Traditional MgO-based lead and cadmium adsorbents typically require activation during preparation to increase the specific surface area, producing more reactive activated magnesium oxide to improve adsorption efficiency. To enhance the adsorption activity of MgO, a specific activation process is often required to increase its specific surface area and achieve higher adsorption efficiency. However, typical activation methods are costly and energy-intensive, with preparation temperatures reaching 1000-1200°C. The preparation of activated magnesium oxide often faces challenges such as high temperatures (calcination of magnesite requires around 1000°C) or complex processes (such as spray drying and sol-gel methods). For example, wet preparation methods such as precipitation and sol-gel methods, or spray drying methods, are complex, require high reagent consumption, and are costly. At the same time, the activated MgO adsorbent also has the problem of the precipitation particles produced being too small, and it is highly dependent on auxiliary agents such as flocculants and flotation agents. The amount of heavy metal sludge produced further increases, making subsequent treatment difficult, and it is easy to become ineffective due to coagulation during use, resulting in a decrease in adsorption efficiency. When porous carbon materials are used as a substrate to load magnesium oxide to prepare composite adsorbents, the adsorption activity of magnesium oxide can be improved to a certain extent. However, when unactivated substrate materials are used for loading, the activation degree of magnesium oxide particles is low, and the adsorption rate is still insufficient. When biochar is used as a supporting material to load MgO to reduce coagulation, and the biochar substrate is used to capture precipitation particles, high requirements are placed on the surface properties of the biochar material. The original biochar has insufficient support and dispersion effects on magnesium oxide, and the activation degree of magnesium oxide is also low. It is usually necessary to use higher temperatures to prepare biochar and composite materials, and the reagent consumption or energy consumption is large.

[0005] In summary, in order to solve one or more of the above-mentioned technical problems, it is very necessary to provide a nitrogen-sulfur-magnesium composite modified biochar adsorbent material and a preparation method thereof. Summary of the Invention

[0006] In order to solve one or more technical problems existing in the prior art, the present invention provides a nitrogen-sulfur-magnesium composite modified biochar adsorbent material and a preparation method thereof.

[0007] In a first aspect, the present invention provides a method for preparing a nitrogen-sulfur-magnesium composite-modified biochar adsorbent material, the method comprising the following steps:

[0008] (1) pretreating the biomass material to obtain a pretreated biomass material;

[0009] (2) mixing the pretreated biomass material, the magnesium source, and the nitrogen and sulfur sources with water to obtain a first mixture, and then drying the first mixture to obtain a second mixture;

[0010] (3) The second mixture is subjected to a heating treatment at 120-150° C., a pyrolysis treatment at 300-350° C., and a pyrolysis treatment at 500-700° C. in a mixed gas containing oxygen and an inert gas, to obtain a nitrogen-sulfur-magnesium composite modified biochar adsorbent material; the volume percentage of oxygen contained in the mixed gas is 10-30%.

[0011] Preferably, the biomass material is a lignocellulosic biomass material; preferably, the lignocellulosic biomass material is one or more of straw, grass leaves and wood materials; more preferably, the straw is corn straw.

[0012] Preferably, the magnesium source is one or more of magnesium nitrate, magnesium sulfate and magnesium chloride; the nitrogen and sulfur source is thiourea, or the nitrogen and sulfur source is a mixture of thiourea and urea, or the nitrogen and sulfur source is a mixture of thiourea and melamine.

[0013] Preferably, the mass ratio of the pretreated biomass material, the magnesium contained in the magnesium source and the nitrogen and sulfur source is 1:(0.1-0.5):(0.05-0.2).

[0014] Preferably, the mass ratio of the magnesium contained in the magnesium source to the nitrogen and sulfur source is (3-8):1.

[0015] Preferably, in step (2), the drying temperature is 60 to 80° C., and the drying time is 6 to 18 hours.

[0016] Preferably, the heating time at 120-150° C. is 1-2 hours; the pyrolysis time at 300-350° C. is 1-2 hours; and / or the pyrolysis time at 500-700° C. is 1-2 hours.

[0017] Preferably, in step (3): the flow rate of the mixed gas comprising oxygen and inert gas does not exceed 10 L / h, preferably 5 to 10 L / h.

[0018] Preferably, the pretreatment of the biomass material is as follows: the biomass material is washed and cut into blocks, and then dried, crushed and sieved to obtain a pretreated biomass material with a particle size of less than 18 mesh.

[0019] In a second aspect, the present invention provides a nitrogen-sulfur-magnesium composite-modified 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) The present invention provides a method for preparing a biochar adsorbent material that combines magnesium oxide loading with nitrogen and sulfur modification, which is used for the rapid and efficient removal of lead and cadmium ions in heavy metal wastewater. The method of the present invention uses biomass material as raw material, adopts an impregnation method to disperse magnesium source and nitrogen and sulfur source thiourea on the surface of the biomass material, and then uses a one-step oxygen-limited pyrolysis method under a certain concentration of oxygen atmosphere to simultaneously carry out biomass carbonization, biochar activation, magnesium oxide loading and activation, and nitrogen / sulfur doping, and finally obtain the nitrogen-sulfur-magnesium composite modified biochar adsorbent material; when the nitrogen-sulfur-magnesium composite modified biochar adsorbent of the present invention is used to adsorb lead and cadmium ions, the free electrons provided by the nitrogen and sulfur doped into the carbon surface and the chelation effect are used to concentrate the heavy metal ions, so that the heavy metal ions react with the active magnesium oxide dispersed on the adsorbent surface to produce precipitation, and the precipitation is captured by the porous carbon matrix, thereby obtaining large-sized heavy metal precipitation particles that are easy to separate; the biochar adsorbent material obtained by the present invention can efficiently and quickly treat low-concentration heavy metal wastewater, can reduce the amount of auxiliary reagents such as flocculants, and has low sludge production.

[0022] (2) Compared with the traditional method for preparing activated magnesium oxide, the method of the present invention requires a lower heating temperature (for example, the heating temperature required for the preparation from calcined magnesite is reduced from about 1000°C to about 500-700°C), and the energy consumption is less. At the same time, compared with other activation methods such as precipitation, sol-gel and spray drying, the one-step oxygen-limited pyrolysis method of the present invention under a certain concentration of oxygen atmosphere is simpler and has fewer steps. The present invention provides a highly efficient and fast biochar adsorbent material prepared by a relatively simple and low-energy method, which has a wide application market.

[0023] (3) Compared with magnesium oxide adsorbent, the nitrogen-sulfur-magnesium composite modified biochar adsorbent material in the present invention is faster in precipitating heavy metals such as lead and cadmium when treating wastewater, and the adsorption rate is significantly improved. Under the joint action of the nitrogen-sulfur-magnesium surface and the active magnesium oxide, the adsorption amount of the nitrogen-sulfur-magnesium composite modified biochar adsorbent exceeds the sum of the magnesium oxide-loaded biochar and the nitrogen-sulfur doped biochar, indicating that the doping of nitrogen and sulfur and the magnesium oxide modification have achieved effective coupling and played a good synergistic role. When the addition amount of the nitrogen-sulfur-magnesium composite modified biochar adsorbent material is 400 ppm, when treating 200 mg / L of lead wastewater, the removal rate exceeds 99.9%, and the effluent concentration is lower than 0.1 mg / L.

[0024] (4) The present invention found that the adsorption performance of the biochar material that was successively doped with nitrogen and sulfur and loaded with magnesium oxide was not effectively improved compared with the biochar loaded with magnesium oxide, while the adsorption performance of the biochar adsorbent material modified with nitrogen, sulfur and magnesium simultaneously in the present invention was better, and the coupling effect of nitrogen, sulfur and magnesium loading in the present invention was better.

[0025] (5) Compared with the materials prepared under oxygen-isolating conditions in the prior art, the nitrogen-sulfur-magnesium composite modified biochar adsorbent material prepared in the present invention under the participation of appropriate oxygen concentration can make the activation degree of the biochar substrate and the magnesium oxide carrier higher, the dispersion of the magnesium oxide particles is also better, and its adsorption effect is significantly better.

[0026] (6) After adsorption using the biochar adsorbent material prepared by the present invention, the size of heavy metal precipitation particles increases significantly and adheres to the adsorbent substrate, thereby obtaining larger particle products, reducing the difficulty of recovery, and reducing costs and energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a graph showing the adsorption results of lead and cadmium ions by the nitrogen-sulfur-magnesium composite modified biochar adsorbent material prepared in Example 1 of the present invention and the adsorbents prepared in Comparative Examples 1 to 3;

[0028] Figure 2 This is a graph showing the adsorption results of lead and cadmium ions by the nitrogen-sulfur-magnesium composite modified biochar adsorbent material prepared in Example 1 of the present invention and the adsorbents prepared in Comparative Examples 4 to 6;

[0029] Figure 3 This is a physical picture of the nitrogen-sulfur-magnesium composite-modified biochar adsorbent material product prepared in Example 1 of the present invention;

[0030] Figure 4 These are SEM images of the nitrogen-sulfur-magnesium composite-modified biochar adsorbent material prepared in Example 1 of the present invention at different magnifications;

[0031] Figure 5 This is the XRD spectrum of the nitrogen-sulfur-magnesium composite-modified biochar adsorbent material (also referred to as nitrogen-sulfur-magnesium composite-modified porous biochar) prepared in Example 1 of the present invention;

[0032] Figure 6 These are SEM images of lead and cadmium adsorbed directly using magnesium oxide as an adsorbent and using the nitrogen-sulfur-magnesium composite modified biochar adsorbent material prepared in Example 1; in the figure, (a) is an SEM image of lead adsorbed directly using magnesium oxide as an adsorbent, (b) is an SEM image of cadmium adsorbed directly using magnesium oxide as an adsorbent, (c) is an SEM image of lead adsorbed by the nitrogen-sulfur-magnesium composite modified biochar adsorbent material prepared in Example 1, and (d) is an SEM image of cadmium adsorbed by the nitrogen-sulfur-magnesium composite modified biochar adsorbent material prepared in Example 1. DETAILED DESCRIPTION

[0033] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the embodiments described are part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0034] In a first aspect, the present invention provides a method for preparing a nitrogen-sulfur-magnesium composite-modified biochar adsorbent material, the method comprising the following steps:

[0035] (1) pretreating the biomass material to obtain a pretreated biomass material;

[0036] (2) mixing the pretreated biomass material, the magnesium source, and the nitrogen and sulfur sources with water to obtain a first mixture, and then drying the first mixture to obtain a second mixture;

[0037] (3) the second mixture is sequentially subjected to a heating treatment at 120-150°C (e.g., 120°C, 130°C, 140°C, or 150°C), a pyrolysis treatment at 300-350°C (e.g., 300°C, 310°C, 320°C, 330°C, 340°C, or 350°C), and a pyrolysis treatment at 500-700°C (e.g., 500°C, 550°C, 600°C, 650°C, or 700°C) in a mixed gas containing oxygen and an inert gas to obtain a nitrogen-sulfur-magnesium composite modified biochar adsorbent material (abbreviated as biochar adsorbent material or nitrogen-sulfur-magnesium composite modified porous biochar); the volume percentage of oxygen contained in the mixed gas is 1 0-30% (e.g., 10%, 15%, 25% or 30%); in the present invention, the 120-150°C heating treatment, the 300-350°C pyrolysis treatment and the 500-700°C pyrolysis treatment are all carried out in a mixed gas containing oxygen and an inert gas; in the present invention, under the condition of passing a mixed gas containing oxygen with a concentration of 10%-30%, the temperature is raised to 300-350°C for pyrolysis, which can simultaneously complete preliminary carbonization, oxygen activation and doping, and the temperature is raised to 500-700°C for pyrolysis, which can simultaneously complete subsequent activation and magnesium oxide loading; in the present invention, the inert gas can be, for example, nitrogen and / or argon.

[0038] Different from the prior art which usually prepares adsorbent materials under oxygen-isolating conditions, the present invention selects a certain concentration of oxygen as an oxidant and activator, uses thiourea as a modifying agent for simultaneous nitrogen doping and sulfur doping, and magnesium salt as a precursor of magnesium oxide. After the magnesium source (such as magnesium nitrate) and thiourea are evenly dispersed on the surface of the biomass by an impregnation method, a one-step pyrolysis method is adopted under mixed gas conditions containing a certain concentration of oxygen to achieve the preparation and simultaneous activation of biochar and magnesium oxide composite materials at a relatively low temperature. The present invention finds that during the pyrolysis process, the oxidizing properties of oxygen can be utilized to oxidize and activate the biochar surface to obtain surface-activated biochar. At the same time, the redox reactions of thiourea and the functional groups on the surface of biochar under high temperature conditions are utilized to dope nitrogen and sulfur elements into the aromatic structure on the biochar surface, thereby improving its surface properties and facilitating the adsorption and concentration of heavy metal ions. In addition, through the decomposition reaction of magnesium salt at high temperature, the biochar surface area can be activated. The domain is loaded with magnesium oxide, and the template effect of the biochar substrate activated in the process is utilized to increase the specific surface area of ​​magnesium oxide, thereby obtaining a highly active magnesium oxide structure, and finally obtaining a nitrogen-sulfur-magnesium composite-modified biochar adsorption material in which the biochar substrate and the magnesium oxide support are synchronously activated and coupled with nitrogen and sulfur doping; in the process of adsorbing heavy metal ions, the nitrogen-sulfur-magnesium composite-modified biochar adsorbent material prepared by the present invention has the ability to provide free electrons on the surface of biochar doped with nitrogen and sulfur, and can chelate with heavy metal ions, and can form delocalized π bonds, and produce conjugated effects with heavy metal ions, thereby achieving the effect of rapid adsorption of heavy metal ions; after the heavy metal ions are concentrated near the surface of biochar by doping the surface, the heavy metal ions are converted into solid precipitation particles under the action of ion exchange and precipitation promotion provided by the magnesium oxide on the surface of the biochar, and are captured by the carbon-based surface after oxygen activation, thereby increasing the particle size, reducing the difficulty of recovery, reducing the use of auxiliary reagents such as flocculants, and reducing the amount of sludge produced.

[0039] Compared with magnesium oxide adsorbent, the nitrogen-sulfur-magnesium composite modified biochar adsorbent material in the present invention is faster in precipitating heavy metals such as lead and cadmium when treating wastewater, and the adsorption rate is significantly improved. Under the joint action of the nitrogen-sulfur-magnesium surface and the active magnesium oxide, the adsorption amount of the nitrogen-sulfur-magnesium composite modified biochar adsorbent exceeds the sum of the magnesium oxide-loaded biochar and the nitrogen-sulfur doped biochar, indicating that the nitrogen and sulfur doping and the magnesium oxide modification have achieved effective coupling and played a good synergistic role. When the addition amount of the nitrogen-sulfur-magnesium composite modified biochar adsorbent material is 400ppm, when treating 200mg / L lead wastewater, the removal rate exceeds 99.9%, and the effluent concentration is 100%. The concentration is lower than 0.1 mg / L; the present invention finds that the adsorption performance of the biochar material that is successively doped with nitrogen and sulfur and loaded with magnesium oxide is not effectively improved compared with the biochar loaded with magnesium oxide, while the adsorption performance of the biochar adsorbent material that is simultaneously modified with nitrogen, sulfur and magnesium in the present invention is better, and the coupling effect of the nitrogen, sulfur and magnesium loading in the present invention is better; compared with the materials prepared under oxygen-isolating conditions in the prior art, the biochar adsorbent material compositely modified with nitrogen, sulfur and magnesium prepared in the presence of oxygen at an appropriate concentration in the present invention can make the activation degree of the biochar substrate and the magnesium oxide support higher, the dispersion of the magnesium oxide particles is also better, and the adsorption effect is significantly better.

[0040] In order to ensure the effect of oxygen activation, the present invention performs the pyrolysis at an appropriate oxygen content and temperature, that is, the pyrolysis treatment at 300-350°C and the pyrolysis treatment at 500-700°C are carried out in sequence under the condition that the volume percentage of oxygen is 10-30%, which can increase the porosity of the biochar surface and form a large number of oxygen-containing functional groups on the surface, thereby making the magnesium oxide structure more dispersed on the biochar surface during the magnesium oxide loading process, and making the activation degree of the biochar substrate and the magnesium oxide support higher and the adsorption activity stronger; the present invention finds that if the volume percentage of oxygen is too low and / or the pyrolysis treatment is too high, the biochar surface porosity can be increased. If the temperature of the treatment is too low, the formation of oxygen-containing functional groups on the surface of biochar and the increase of porosity cannot be fully achieved, the dispersion of magnesium oxide structure on the surface of biochar cannot be guaranteed, and the activity of magnesium oxide structure cannot be affected. If the volume percentage of oxygen is too high and / or the pyrolysis treatment temperature is too high, it will lead to the occurrence of overoxidation, thereby causing excessive oxidation or combustion of biochar, rather than selectively forming oxygen-containing functional groups. This will damage the structure of biochar, reduce its porosity, and cause a large amount of biochar to ash, which will also affect the activation of magnesium oxide structure and its dispersion on the surface of biochar, and ultimately affect the adsorption performance of the material. Compared with the traditional method for preparing activated magnesium oxide, the heating temperature required by the method of the present invention is lower (for example, the preparation required from calcining magnesite is reduced from about 1000°C to about 500-700°C), and the energy consumption is less; and during oxygen activation, the present invention found that the concentration and temperature used are more conducive to uniformly increasing oxygen-containing functional groups on the surface of biochar and shaping pores on the flat surface, which is beneficial to the loading of magnesium oxide and makes its dispersion better.

[0041] According to some preferred embodiments, the biomass material is a lignocellulosic biomass material; preferably, the lignocellulosic biomass material is one or more of straw, grass leaves and wood materials; more preferably, the straw is corn straw.

[0042] According to some preferred embodiments, the magnesium source is one or more of magnesium nitrate, magnesium sulfate and magnesium chloride; in the present invention, the magnesium source can be magnesium salts such as magnesium nitrate, magnesium sulfate and magnesium chloride, and can be a mixture of multiple magnesium salts; for example, the molar proportion of magnesium in the mixed salt cations is not less than 60%, and if non-magnesium ion cations are contained, the non-magnesium ion cations are one or more of sodium, potassium and calcium; for example, the proportion of nitrate in the anions in the mixed salt should not be higher than 40%, and the non-nitrate anions are preferably one or more of sulfate and chloride to ensure that the mixed salt is more conducive to forming stable magnesium oxide particles at high temperature; the nitrogen and sulfur source is thiourea, or the nitrogen and sulfur source is a mixture of thiourea and urea, or the nitrogen and sulfur source is a mixture of thiourea and melamine; in the present invention, for example, a small amount of urea or melamine can be added to thiourea to adjust the nitrogen and sulfur ratio.

[0043] According to some preferred embodiments, the mass ratio of the pretreated biomass material, the magnesium contained in the magnesium source, and the nitrogen and sulfur source is 1:(0.1-0.5):(0.05-0.2).

[0044] According to some preferred embodiments, the mass ratio of the magnesium contained in the magnesium source to the nitrogen and sulfur sources is (3-8):1 (e.g., 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, or 8:1), preferably (3-5:1). In the present invention, preferably, the mass ratio of the magnesium contained in the magnesium source to the nitrogen and sulfur sources is (3-8):1. The present invention has found that if the nitrogen and sulfur sources are too much, they easily cover the magnesium oxide, reducing the adsorption effect; if too little, the doped nitrogen and sulfur cannot achieve sufficient effect.

[0045] According to some preferred embodiments, in step (2): the drying temperature is 60-80°C (e.g., 60°C, 65°C, 70°C, 75°C or 80°C), and the drying time is 6-18h (e.g., 6, 8, 10, 12, 14, 16 or 18h).

[0046] According to some specific embodiments, step (2) is: mixing the pretreated biomass material with a magnesium source and a nitrogen and sulfur source, and the mixing mass ratio is pretreated biomass material: magnesium in the magnesium source: thiourea = 1: (0.1-0.5): (0.05-0.2), preferably 1: (0.15-0.45): (0.05-0.15), adding a certain amount of water, and mixing them uniformly by stirring or ultrasonic means to obtain a first mixture, and then slowly drying the first mixture at 60-80°C (drying time, for example, 6-18 hours) to a slurry state to obtain a second mixture; this step (2) is the impregnation mixing step of the material.

[0047] According to some preferred embodiments, the heating time at 120-150° C. is 1-2 hours; the pyrolysis time at 300-350° C. is 1-2 hours; and / or the pyrolysis time at 500-700° C. is 1-2 hours.

[0048] According to some preferred embodiments, in step (3): the flow rate of the mixed gas containing oxygen and inert gas does not exceed 10 L / h, preferably 5 to 10 L / h (for example, 5, 6, 7, 8, 9 or 10 L / h); the present invention has obtained a suitable gas flow rate of the present invention through a large number of creative experiments. The present invention has found that an appropriate gas flow rate can ensure that oxygen is uniformly distributed during the initial carbonization, oxygen activation, doping and loading processes, so that the initial carbonization, oxygen activation, doping and loading reactions of the biochar are carried out uniformly, avoiding that some parts fail to fully contact oxygen due to insufficient gas flow rate, and at an appropriate flow rate, an appropriate reaction rate can be achieved, so that the activation reaction can be fully carried out without being too fast or too slow; in addition, an appropriate gas flow rate can ensure uniform fluidity of the gas in the reactor and improve production capacity to a certain extent, thereby increasing production efficiency; if the gas flow rate is too large, it may cause uneven distribution of the gas, affecting the uniformity of the reaction.

[0049] According to some specific embodiments, step (3) is: moving the second mixture in a slurry state into a heating device, heating it under the condition of passing a certain concentration of oxygen (a concentration of 10%-30% oxygen), first raising the temperature to 120-150 ° C, heating and drying for 1-2 hours, while passing oxygen with a concentration of 10%-30%, raising the temperature to 300-350 ° C for pyrolysis for 1-2 hours, completing preliminary carbonization, oxygen activation and doping, and then raising the temperature to 500-700 ° C, pyrolysis for 1-2 hours, completing subsequent activation and magnesium oxide loading; the prepared material is used for water It can be used after rinsing and drying; in the present invention, it is preferred that the added mass ratio of magnesium and thiourea in the magnesium salt is controlled at 8:1 to 3:1. Within this range, when the concentration of heavy metal ions in the heavy metal wastewater to be treated is high, for example, a higher amount of magnesium salt can be selected to load more magnesium oxide; in the present invention, when the magnesium source is a mixed salt, and when the mixed salt contains more nitrate ions, for example, it is preferred to select a lower oxygen concentration within the range of 10 to 30%; this step (3) is a one-step pyrolysis carbonization-activation-loading-doping step performed simultaneously.

[0050] According to some preferred embodiments, the pretreatment of the biomass material is as follows: the biomass material is washed and cut into blocks, and then dried, crushed and sieved to obtain a pretreated biomass material with a particle size of less than 18 mesh.

[0051] According to some specific embodiments, step (1) is as follows: the source of the biomass material is a lignocellulosic biomass material mainly of plant origin, including straw, grass leaves and wood materials; after selecting the material, the biomass material is first cleaned to remove excess sediment and other attachments on the surface, and then the biomass material is cut into small blocks, dried to remove most of the moisture, and then crushed using a grinder, and sieved to select materials with a size (particle size) less than 18 mesh to obtain pretreated biomass materials, which are naturally air-dried for use.

[0052] The second aspect of the present invention provides a nitrogen-sulfur-magnesium composite-modified biochar adsorbent material prepared by the preparation method described in the first aspect of the present invention; the present invention provides a nitrogen-sulfur-magnesium composite-modified biochar-based porous carbon heavy metal adsorbent, which utilizes the free electrons and delocalized π bonds provided by the doping of nitrogen and sulfur on the surface of biochar to provide chelation and conjugation effects to concentrate heavy metal ions, and utilizes the ion exchange and precipitation-promoting effects of magnesium oxide to convert the ions into solid precipitation particles, and the precipitation particles are captured by the carbon matrix of the activated biochar. The material can quickly treat low-concentration heavy metal wastewater, reduce the use of auxiliary agents such as flocculants, and optimize the separation of heavy metal precipitates and the reuse of heavy metals.

[0053] 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 embodiments of the present invention, rather than all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. Unless otherwise specified, each raw material used in the embodiments of the present invention and the comparative examples can be obtained by commercial purchase or synthesized by existing methods.

[0054] Example 1

[0055] ① First, the biomass material (corn stalks) is cleaned to remove excess sediment and other attachments on the surface, and then the corn stalks are cut into small blocks. After drying to remove most of the moisture, they are crushed using a grinder, and the materials with a size (particle size) less than 18 mesh are screened to obtain pretreated biomass materials, which are then naturally air-dried for use.

[0056] ② The pretreated biomass material obtained in step ① is mixed with a magnesium source (magnesium nitrate) and a nitrogen and sulfur source (thiourea) in a mixing mass ratio of pretreated biomass material: magnesium in magnesium nitrate: thiourea = 1:0.4:0.08, and a certain amount of water is added (the mass volume ratio of the pretreated biomass material to water is 1 g:15 mL). After stirring and mixing evenly, a first mixture is obtained, and then the first mixture is dried at 70°C for 8 hours to a slurry to obtain a second mixture.

[0057] ③ The second mixture obtained in step ② is moved to a heating device and heat-treated under the condition of passing a mixed gas containing oxygen and an inert gas. First, the temperature is raised to 135°C and heated to dry for 1.5 hours. Then, the temperature is raised to 320°C for pyrolysis for 1.5 hours under the condition of passing a mixed gas containing oxygen and an inert gas. After completing preliminary carbonization, oxygen activation and doping, the temperature is raised to 600°C for pyrolysis for 1.5 hours under the condition of passing a mixed gas containing oxygen and an inert gas. Activation and magnesium oxide loading are completed, and the obtained material is rinsed with clean water and dried to obtain a nitrogen-sulfur-magnesium composite modified biochar adsorbent material; wherein the mixed gas containing oxygen and an inert gas (nitrogen) is a mixture of oxygen and nitrogen, the volume percentage of oxygen in the mixed gas containing oxygen and an inert gas is 15%, and the volume percentage of nitrogen is 85%, and the flow rate of the mixed gas containing oxygen and an inert gas is 8L / h.

[0058] Example 2

[0059] ① First, the biomass material (corn stalks) is cleaned to remove excess sediment and other attachments on the surface, and then the corn stalks are cut into small blocks. After drying to remove most of the moisture, they are crushed using a grinder, and the materials with a size (particle size) less than 18 mesh are screened to obtain pretreated biomass materials, which are then naturally air-dried for use.

[0060] ② The pretreated biomass material obtained in step ① is mixed with a magnesium source (magnesium nitrate) and a nitrogen and sulfur source (thiourea) in a mixing mass ratio of pretreated biomass material: magnesium in magnesium nitrate: thiourea = 1:0.15:0.05, and a certain amount of water is added (the mass volume ratio of the pretreated biomass material to water is 1 g:15 mL). After stirring and mixing evenly, a first mixture is obtained, and then the first mixture is dried at 70°C for 8 hours to a slurry to obtain a second mixture.

[0061] ③ The second mixture obtained in step ② is moved to a heating device and heated under the condition of passing a mixed gas containing oxygen and an inert gas. First, the temperature is raised to 135°C and heated to dry for 1.5 hours. Then, the temperature is raised to 320°C for pyrolysis for 1.5 hours under the condition of passing a mixed gas containing oxygen and an inert gas. After completing preliminary carbonization, oxygen activation and doping, the temperature is raised to 600°C for pyrolysis for 1.5 hours under the condition of passing a mixed gas containing oxygen and an inert gas. Activation and magnesium oxide loading are completed, and the obtained material is rinsed with clean water and dried to obtain a nitrogen-sulfur-magnesium composite modified biochar adsorbent material; wherein the mixed gas containing oxygen and an inert gas is a mixture of oxygen and nitrogen, the volume percentage of oxygen in the mixed gas containing oxygen and an inert gas is 30%, and the volume percentage of nitrogen is 70%, and the introduction flow rate of the mixed gas containing oxygen and an inert gas is 10L / h.

[0062] Example 3

[0063] ① First, the biomass material (corn stalks) is cleaned to remove excess sediment and other attachments on the surface, and then the corn stalks are cut into small blocks. After drying to remove most of the moisture, they are crushed using a grinder, and the materials with a size (particle size) less than 18 mesh are screened to obtain pretreated biomass materials, which are then naturally air-dried for use.

[0064] ② The pretreated biomass material obtained in step ① is mixed with a magnesium source (magnesium nitrate) and a nitrogen and sulfur source (thiourea) in a mixing mass ratio of pretreated biomass material: magnesium in magnesium nitrate: thiourea = 1:0.45:0.15, and a certain amount of water is added (the mass volume ratio of the pretreated biomass material to water is 1 g:15 mL). After stirring and mixing evenly, a first mixture is obtained, and then the first mixture is dried at 70°C for 8 hours to a slurry to obtain a second mixture.

[0065] ③ The second mixture obtained in step ② is moved to a heating device and heated under the condition of passing a mixed gas containing oxygen and an inert gas. First, the temperature is raised to 135°C and heated to dry for 1.5 hours. Then, the temperature is raised to 320°C for pyrolysis for 1.5 hours under the condition of passing a mixed gas containing oxygen and an inert gas. After completing preliminary carbonization, oxygen activation and doping, the temperature is raised to 600°C for pyrolysis for 1.5 hours under the condition of passing a mixed gas containing oxygen and an inert gas. Activation and magnesium oxide loading are completed, and the obtained material is rinsed with clean water and dried to obtain a nitrogen-sulfur-magnesium composite modified biochar adsorbent material; wherein the mixed gas containing oxygen and an inert gas is a mixture of oxygen and nitrogen, the volume percentage of oxygen in the mixed gas containing oxygen and an inert gas is 10%, and the volume percentage of nitrogen is 90%, and the introduction flow rate of the mixed gas containing oxygen and an inert gas is 5L / h.

[0066] Example 4

[0067] Example 4 is basically the same as Example 1, except that:

[0068] ② Mix the pretreated biomass material obtained in step ① with a magnesium source (magnesium nitrate) and a nitrogen and sulfur source (thiourea) in a mixing mass ratio of pretreated biomass material: magnesium in magnesium nitrate: thiourea = 1:0.4:0.2, add a certain amount of water (the mass volume ratio of the pretreated biomass material to water is 1 g:15 mL), stir and mix evenly to obtain a first mixture, and then dry the first mixture at 70°C for 8 h to a slurry to obtain a second mixture.

[0069] Example 5

[0070] Example 5 is basically the same as Example 1, except that:

[0071] ② Mix the pretreated biomass material obtained in step ① with a magnesium source (magnesium nitrate) and a nitrogen and sulfur source (thiourea) in a mixing mass ratio of pretreated biomass material: magnesium in magnesium nitrate: thiourea = 1:0.5:0.05, add a certain amount of water (the mass volume ratio of the pretreated biomass material to water is 1 g:15 mL), stir and mix evenly to obtain a first mixture, and then dry the first mixture at 70°C for 8 h to a slurry to obtain a second mixture.

[0072] Example 6

[0073] Example 6 is substantially the same as Example 1, except that:

[0074] ③ The second mixture obtained in step ② is moved to a heating device and heated under the condition of passing a mixed gas containing oxygen and an inert gas. First, the temperature is raised to 135°C and heated to dry for 1.5 hours. Then, the temperature is raised to 320°C for pyrolysis for 1.5 hours under the condition of passing a mixed gas containing oxygen and an inert gas. After completing preliminary carbonization, oxygen activation and doping, the temperature is raised to 600°C for pyrolysis for 1.5 hours under the condition of passing a mixed gas containing oxygen and an inert gas to complete activation and magnesium oxide loading. The obtained material is rinsed with clean water and dried to obtain a nitrogen-sulfur-magnesium composite modified biochar adsorbent material; wherein the mixed gas containing oxygen and an inert gas is a mixture of oxygen and nitrogen, the volume percentage of oxygen in the mixed gas containing oxygen and an inert gas is 15%, and the volume percentage of nitrogen is 85%, and the introduction flow rate of the mixed gas containing oxygen and an inert gas is 2L / h.

[0075] Example 7

[0076] Example 7 is basically the same as Example 1, except that:

[0077] ③ The second mixture obtained in step ② is moved to a heating device and heated under the condition of passing a mixed gas containing oxygen and an inert gas. First, the temperature is raised to 135°C and heated to dry for 1.5 hours. Then, the temperature is raised to 320°C for pyrolysis for 1.5 hours under the condition of passing a mixed gas containing oxygen and an inert gas. After completing preliminary carbonization, oxygen activation and doping, the temperature is raised to 600°C for pyrolysis for 1.5 hours under the condition of passing a mixed gas containing oxygen and an inert gas. Activation and magnesium oxide loading are completed, and the obtained material is rinsed with clean water and dried to obtain a nitrogen-sulfur-magnesium composite modified biochar adsorbent material; wherein the mixed gas containing oxygen and an inert gas is a mixture of oxygen and nitrogen, the volume percentage of oxygen in the mixed gas containing oxygen and an inert gas is 15%, and the volume percentage of nitrogen is 85%, and the flow rate of the mixed gas containing oxygen and an inert gas is 20L / h.

[0078] Comparative Example 1

[0079] ① First, the biomass material (corn stalks) is cleaned to remove excess sediment and other attachments on the surface, and then the corn stalks are cut into small blocks. After drying to remove most of the moisture, they are crushed using a grinder, and the materials with a size (particle size) less than 18 mesh are screened to obtain pretreated biomass materials, which are then naturally air-dried for use.

[0080] ② The pretreated biomass material obtained in step ① is moved to a heating device, and the temperature is raised to 320° C. for pyrolysis for 1.5 hours under the condition of passing a mixed gas containing oxygen and an inert gas to complete carbonization and obtain a biochar adsorbent; wherein the mixed gas containing oxygen and an inert gas is formed by a mixture of oxygen and nitrogen, and the volume percentage of oxygen in the mixed gas containing oxygen and an inert gas is 15%, and the volume percentage of nitrogen in the mixed gas containing oxygen and an inert gas is 85%, and the introduction flow rate of the mixed gas containing oxygen and an inert gas is 8 L / h.

[0081] Comparative Example 2

[0082] ① First, the biomass material (corn stalks) is cleaned to remove excess sediment and other attachments on the surface, and then the corn stalks are cut into small blocks. After drying to remove most of the moisture, they are crushed using a grinder, and the materials with a size (particle size) less than 18 mesh are screened to obtain pretreated biomass materials, which are then naturally air-dried for use.

[0083] ② The pretreated biomass material obtained in step ① is mixed with a magnesium source (magnesium nitrate) in a mixing mass ratio of pretreated biomass material: magnesium in magnesium nitrate = 1:0.4, and a certain amount of water is added (the mass volume ratio of the pretreated biomass material to water is 1 g:15 mL). After stirring and mixing evenly, a first mixture is obtained, and then the first mixture is dried at 70°C for 8 hours to a slurry to obtain a second mixture.

[0084] ③ The second mixture obtained in step ② is moved to a heating device and subjected to heat treatment under the condition of passing a mixed gas containing oxygen and inert gas. First, the temperature is raised to 135°C and heated to dry for 1.5 hours. Then, the temperature is raised to 320°C for pyrolysis for 1.5 hours under the condition of passing a mixed gas containing oxygen and inert gas. The temperature is raised to 600°C for pyrolysis for 1.5 hours under the condition of passing a mixed gas containing oxygen and inert gas. The obtained material is rinsed with clean water and dried to obtain a magnesium oxide-loaded biochar adsorbent; wherein the mixed gas containing oxygen and inert gas is a mixture of oxygen and nitrogen, the volume percentage of oxygen in the mixed gas containing oxygen and inert gas is 15%, and the volume percentage of nitrogen in the mixed gas containing oxygen and inert gas is 85%. The introduction flow rate of the mixed gas containing oxygen and inert gas is 8L / h.

[0085] Comparative Example 3

[0086] ① First, the biomass material (corn stalks) is cleaned to remove excess sediment and other attachments on the surface, and then the corn stalks are cut into small blocks. After drying to remove most of the moisture, they are crushed using a grinder, and the materials with a size (particle size) less than 18 mesh are screened to obtain pretreated biomass materials, which are then naturally air-dried for use.

[0087] ② The pretreated biomass material obtained in step ① is mixed with a nitrogen and sulfur source (thiourea) in a mixing mass ratio of pretreated biomass material: thiourea = 1:0.2, and a certain amount of water is added (the mass volume ratio of the pretreated biomass material to water is 1 g:15 mL). After stirring and mixing evenly, a first mixture is obtained, and then the first mixture is dried at 70°C for 8 hours to a slurry to obtain a second mixture.

[0088] ③ The second mixture obtained in step ② is moved to a heating device and subjected to heat treatment under the condition of passing a mixed gas containing oxygen and an inert gas. First, the temperature is raised to 135°C and heated to dry for 1.5 hours. Then, the temperature is raised to 320°C for pyrolysis for 1.5 hours under the condition of passing a mixed gas containing oxygen and an inert gas. The temperature is raised to 600°C for pyrolysis for 1.5 hours under the condition of passing a mixed gas containing oxygen and an inert gas. The obtained material is rinsed with clean water and dried to obtain a nitrogen-sulfur doped biochar adsorbent; wherein the mixed gas containing oxygen and an inert gas is a mixture of oxygen and nitrogen, and the volume percentage of oxygen in the mixed gas containing oxygen and an inert gas is 15%, and the volume percentage of nitrogen is 85%. The flow rate of the mixed gas containing oxygen and an inert gas is 8 L / h.

[0089] Comparative Example 4

[0090] ① First, the biomass material (corn stalks) is cleaned to remove excess sediment and other attachments on the surface, and then the corn stalks are cut into small blocks. After drying to remove most of the moisture, they are crushed using a grinder, and the materials with a size (particle size) less than 18 mesh are screened to obtain pretreated biomass materials, which are then naturally air-dried for use.

[0091] ② The pretreated biomass material obtained in step ① is mixed with a magnesium source (magnesium nitrate) in a mixing mass ratio of pretreated biomass material: magnesium in magnesium nitrate = 1:0.4, and a certain amount of water is added (the mass volume ratio of the pretreated biomass material to water is 1 g:15 mL). After stirring and mixing evenly, a first mixture is obtained, and then the first mixture is dried at 70°C for 8 hours to a slurry to obtain a second mixture.

[0092] ③ The second mixture obtained in step ② is moved to a heating device and heat-treated under the condition of passing a mixed gas comprising oxygen and an inert gas. First, the temperature is raised to 135°C and heated to dry for 1.5 hours. Then, the temperature is raised to 320°C for pyrolysis for 1.5 hours under the condition of passing a mixed gas comprising oxygen and an inert gas. The temperature is raised to 600°C for pyrolysis for 1.5 hours under the condition of passing a mixed gas comprising oxygen and an inert gas. The obtained material is rinsed with clean water and dried to obtain magnesium oxide-loaded biochar for standby use; wherein the mixed gas comprising oxygen and an inert gas is a mixture of oxygen and nitrogen, the volume percentage of oxygen in the mixed gas comprising oxygen and an inert gas is 15%, and the volume percentage of nitrogen is 85%, and the flow rate of the mixed gas comprising oxygen and an inert gas is 8 L / h.

[0093] ④ Mix the magnesium oxide-loaded biochar obtained in step ③ with a nitrogen and sulfur source (thiourea), the mass amount of thiourea being 8% of the mass of the pretreated biomass material in step ②, add a certain amount of water (the mass volume ratio of magnesium oxide-loaded biochar to water is 1 g: 15 mL), stir and mix evenly to obtain a third mixture, and then dry the third mixture at 70°C for 8 hours to a slurry to obtain a fourth mixture.

[0094] ⑤ The fourth mixture obtained in step ④ is moved to a heating device and heated under the condition of passing a mixed gas containing oxygen and an inert gas. First, the temperature is raised to 135°C and heated and dried for 1.5 hours. Then, the temperature is raised to 320°C for pyrolysis for 1.5 hours under the condition of passing a mixed gas containing oxygen and an inert gas. The temperature is raised to 600°C for pyrolysis for 1.5 hours under the condition of passing a mixed gas containing oxygen and an inert gas. The obtained material is rinsed with clean water and dried to obtain a biochar adsorbent that is first loaded with magnesium and then doped with nitrogen and sulfur; wherein the mixed gas containing oxygen and an inert gas is a mixture of oxygen and nitrogen, the volume percentage of oxygen in the mixed gas containing oxygen and an inert gas is 15%, and the volume percentage of nitrogen is 85%. The flow rate of the mixed gas containing oxygen and an inert gas is 8 L / h.

[0095] Comparative Example 5

[0096] ① First, the biomass material (corn stalks) is cleaned to remove excess sediment and other attachments on the surface, and then the corn stalks are cut into small blocks. After drying to remove most of the moisture, they are crushed using a grinder, and the materials with a size (particle size) less than 18 mesh are screened to obtain pretreated biomass materials, which are then naturally air-dried for use.

[0097] ② The pretreated biomass material obtained in step ① is mixed with a nitrogen and sulfur source (thiourea), the mass amount of thiourea is 8% of the mass of the pretreated biomass material, and a certain amount of water is added (the mass volume ratio of the pretreated biomass material to water is 1g:15mL). After stirring and mixing evenly, a first mixture is obtained, and then the first mixture is dried at 70°C for 8h to a slurry to obtain a second mixture.

[0098] ③ The second mixture obtained in step ② is moved to a heating device and heat-treated under the condition of passing a mixed gas containing oxygen and an inert gas. First, the temperature is raised to 135°C and heated to dry for 1.5 hours. Then, the temperature is raised to 320°C for pyrolysis for 1.5 hours under the condition of passing a mixed gas containing oxygen and an inert gas. The temperature is raised to 600°C for pyrolysis for 1.5 hours under the condition of passing a mixed gas containing oxygen and an inert gas. The obtained material is rinsed with clean water and dried to obtain nitrogen-sulfur-doped biochar; wherein the mixed gas containing oxygen and an inert gas is a mixture of oxygen and nitrogen, and the volume percentage of oxygen in the mixed gas containing oxygen and an inert gas is 15%, and the volume percentage of nitrogen is 85%. The flow rate of the mixed gas containing oxygen and an inert gas is 8 L / h.

[0099] ④ Mix the nitrogen-sulfur doped biochar obtained in step ③ with a magnesium source (magnesium nitrate), and the amount of magnesium nitrate is such that the magnesium content in the magnesium nitrate is 40% of the mass of the pretreated biomass material in step ②. Add a certain amount of water (the mass volume ratio of nitrogen-sulfur doped biochar to water is 1 g: 15 mL), stir and mix evenly to obtain a third mixture, and then dry the third mixture at 70°C for 8 hours to a slurry to obtain a fourth mixture.

[0100] ③ The fourth mixture obtained in step ④ is moved to a heating device and subjected to heat treatment under the condition of passing a mixed gas containing oxygen and an inert gas. First, the temperature is raised to 135°C and heated to dry for 1.5 hours. Then, the temperature is raised to 320°C for pyrolysis for 1.5 hours under the condition of passing a mixed gas containing oxygen and an inert gas. The temperature is raised to 600°C for pyrolysis for 1.5 hours under the condition of passing a mixed gas containing oxygen and an inert gas. The obtained material is rinsed with clean water and dried to obtain a biochar adsorbent first doped with nitrogen and sulfur and then loaded with magnesium; wherein the mixed gas containing oxygen and an inert gas is a mixture of oxygen and nitrogen, the volume percentage of oxygen in the mixed gas containing oxygen and an inert gas is 15%, and the volume percentage of nitrogen is 85%. The flow rate of the mixed gas containing oxygen and an inert gas is 8 L / h.

[0101] Comparative Example 6

[0102] Comparative Example 6 is substantially the same as Example 1, except that:

[0103] ③ The second mixture obtained in step ② was transferred to a heating device and heated under the introduction of pure nitrogen gas. First, the temperature was raised to 135°C and heated to dry for 1.5 hours. Then, the temperature was raised to 320°C for pyrolysis for 1.5 hours under the introduction of pure nitrogen gas. The temperature was raised to 600°C for pyrolysis for 1.5 hours under the introduction of pure nitrogen gas. The obtained material was rinsed with clean water and dried to obtain a modified biochar adsorbent. The introduction flow rate of the pure nitrogen gas was 8 L / h.

[0104] Comparative Example 7

[0105] Comparative Example 7 is substantially the same as Example 1, except that:

[0106] ③ The second mixture obtained in step ② is moved to a heating device and heated under the condition of passing a mixed gas containing oxygen and inert gas. First, the temperature is raised to 135°C and heated to dry for 1.5 hours. Then, the temperature is raised to 320°C for pyrolysis for 1.5 hours under the condition of passing a mixed gas containing oxygen and inert gas. The temperature is raised to 600°C for pyrolysis for 1.5 hours under the condition of passing a mixed gas containing oxygen and inert gas. The obtained material is rinsed with clean water and dried to obtain a modified biochar adsorbent material; wherein the mixed gas containing oxygen and inert gas is a mixture of oxygen and nitrogen, and the volume percentage of oxygen in the mixed gas containing oxygen and inert gas is 5%, and the volume percentage of nitrogen is 95%, and the introduction flow rate of the mixed gas containing oxygen and inert gas is 8L / h.

[0107] Comparative Example 8

[0108] Comparative Example 8 is substantially the same as Example 1, except that:

[0109] ③ The second mixture obtained in step ② is moved to a heating device and heated under the condition of passing a mixed gas containing oxygen and inert gas. First, the temperature is raised to 135°C and heated to dry for 1.5 hours. Then, the temperature is raised to 320°C for pyrolysis for 1.5 hours under the condition of passing a mixed gas containing oxygen and inert gas. The temperature is raised to 600°C for pyrolysis for 1.5 hours under the condition of passing a mixed gas containing oxygen and inert gas. The obtained material is rinsed with clean water and dried to obtain a modified biochar adsorbent material; wherein the mixed gas containing oxygen and inert gas is a mixture of oxygen and nitrogen, and the volume percentage of nitrogen is 45%, the volume percentage of oxygen in the mixed gas containing oxygen and inert gas is 55%, and the introduction flow rate of the mixed gas containing oxygen and inert gas is 8L / h.

[0110] Comparative Example 9

[0111] Comparative Example 9 is substantially the same as Example 1, except that:

[0112] ③ The second mixture obtained in step ② is moved to a heating device and heated under the condition of passing a mixed gas containing oxygen and an inert gas. First, the temperature is raised to 135°C and heated and dried for 1.5 hours. Then, the temperature is raised to 320°C for pyrolysis for 1.5 hours under the condition of passing a mixed gas containing oxygen and an inert gas. When pure nitrogen gas (flow rate of 8 L / h) is passed, the temperature is raised to 600°C for pyrolysis for 1.5 hours. The obtained material is rinsed with clean water and dried to obtain a modified biochar adsorbent material; wherein the mixed gas containing oxygen and an inert gas is a mixture of oxygen and nitrogen, and the volume percentage of oxygen in the mixed gas containing oxygen and an inert gas is 15%, and the volume percentage of nitrogen is 85%. The flow rate of the mixed gas containing oxygen and an inert gas is 8 L / h.

[0113] The present invention tested the adsorption performance of the biochar adsorbents finally prepared in each embodiment and each comparative example. The test method is as follows: treating lead wastewater and cadmium wastewater with a concentration of 500 mg / L at 25°C, the adsorbent dosage is 200 ppm, and after adsorption equilibrium, the adsorption amount (maximum adsorption amount) is measured as shown in Table 1; treating lead wastewater and cadmium wastewater with a concentration of 200 mg / L at 25°C, and after adsorption for 360 minutes, the adsorbent dosage required to make the effluent concentration meet the standard is measured as shown in Table 1.

[0114] Table 1

[0115]

[0116] The adsorption results of lead and cadmium ions by the nitrogen-sulfur-magnesium composite modified biochar adsorbent material prepared in Example 1 of the present invention and the adsorbents prepared in Comparative Examples 1 to 3 are shown in FIG. Figure 1 As shown; the adsorption results of lead and cadmium ions by the biochar adsorbent material modified by nitrogen, sulfur and magnesium prepared in Example 1 of the present invention and the adsorbent prepared in Comparative Examples 4 to 6 are shown in FIG. Figure 2 shown; in Figure 1 and Figure 2 The test conditions for the adsorption of lead ions are: treating 200 mg / L lead wastewater at 25°C, the dosage of the adsorbent is 400 ppm, and the treatment time is 360 min. The test conditions for the adsorption of cadmium ions are: treating 200 mg / L cadmium wastewater at 25°C, the dosage of the adsorbent is 400 ppm, and the treatment time is 360 min. Figures 1 to 2 As shown, when the biochar adsorbent modified with nitrogen, sulfur and magnesium in the present invention treats wastewater, the precipitation of heavy metals such as lead and cadmium is produced faster, and the adsorption rate is significantly improved. Under the joint action of the surface containing nitrogen and sulfur and the active magnesium oxide, the adsorption amount of the biochar modified with nitrogen, sulfur and magnesium exceeds the sum of the biochar loaded with magnesium oxide and the biochar doped with nitrogen and sulfur, indicating that the doping of nitrogen and sulfur and the modification with magnesium oxide have achieved effective coupling; when the dosage is 400ppm, when treating 200mg / L of lead and cadmium wastewater, the removal rate exceeds 99.9%, and the effluent concentration is lower than 0.1mg / L; the biochar material that is successively doped with nitrogen and sulfur and loaded with magnesium oxide has not been effectively improved compared with the biochar loaded with magnesium oxide. Improved, and the adsorption performance of the biochar material modified simultaneously with nitrogen, sulfur and magnesium is more excellent, and the coupling effect of nitrogen, sulfur and magnesium loading is better; compared with the material prepared under oxygen isolation conditions, the nitrogen, sulfur and magnesium composite modified biochar adsorbent material prepared under the participation of oxygen in the present invention has a higher degree of activation of the biochar substrate and the magnesium oxide carrier, and the dispersion of the magnesium oxide particles is also better, and its adsorption effect is better. The present invention utilizes the concentration effect of nitrogen and sulfur doped biochar on heavy metals coupled with the ion exchange and precipitation effect of magnesium oxide to obtain a nitrogen, sulfur and magnesium modified porous carbon-based adsorption material with efficient removal of heavy metal ions; the actual picture of the nitrogen, sulfur and magnesium composite modified biochar adsorbent material product prepared in Example 1 of the present invention, as shown Figure 3 As shown; SEM images of the nitrogen-sulfur-magnesium composite modified biochar adsorbent material prepared in Example 1 of the present invention at different magnifications, as shown Figure 4 shown; from Figure 4 The results show that magnesium oxide loading, nitrogen and sulfur doping and biochar oxidation activation are carried out simultaneously in a one-step method. The reaction of oxygen with the carbon substrate and nitrogen / sulfur reagents can enable the material to achieve a high surface activation effect. The nitrogen-sulfur-magnesium composite modified biochar adsorbent prepared by the present invention has a highly active surface, such as Figure 4(b) shows the XRD spectrum of the nitrogen-sulfur-magnesium composite modified biochar adsorbent material (also referred to as nitrogen-sulfur-magnesium composite modified porous biochar) prepared in Example 1 of the present invention, as shown in FIG. Figure 5 As shown in FIG, the XRD pattern proves that magnesium oxide is loaded on the surface of the nitrogen-sulfur-magnesium composite modified porous biochar; the present invention directly uses magnesium oxide adsorbent and the nitrogen-sulfur-magnesium composite modified biochar adsorbent material prepared in Example 1 to adsorb lead and cadmium. Figure 6 shown; from Figure 6 The results show that after adsorption, compared with the direct use of magnesium oxide adsorbent, the lead and cadmium precipitates can be attached to the surface of the biochar adsorbent modified with nitrogen, sulfur and magnesium in the method of the present invention after lead and cadmium removal, and the solid size is significantly increased, making separation and removal easier. In particular, Figure 5 and Figure 6 The preparation of magnesium oxide in the method is as follows: magnesium nitrate is added to water (the mass volume ratio of magnesium nitrate to water is 1g:15mL), the mixture is mixed evenly by stirring, and then dried at 70°C for 8h to a slurry. The slurry mixture is then heated and dried at 135°C under a nitrogen atmosphere for 1.5h, and then pyrolyzed at 600°C in a nitrogen atmosphere for 1.5h. The obtained material is rinsed with clean water and dried to obtain magnesium oxide.

[0117] Parts of the present invention that are not described in detail are well known 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, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. Application of a nitrogen-sulfur-magnesium composite modified biochar adsorbent material in adsorbing lead and cadmium in heavy metal wastewater, characterized in that: The preparation of the nitrogen-sulfur-magnesium composite modified biochar adsorbent material comprises the following steps: (1) pre-treating the biomass material to obtain a pre-treated biomass material; (2) uniformly mixing the pretreated biomass material, the magnesium source, and the nitrogen and sulfur source with water to obtain a first mixture, and then drying the first mixture to obtain a second mixture; the mass ratio of the pretreated biomass material, the magnesium contained in the magnesium source, and the nitrogen and sulfur source is 1:(0.1-0.5):(0.05-0.2), and the mass ratio of the magnesium contained in the magnesium source to the nitrogen and sulfur source is (3-8):1; (3) The second mixture is subjected to heating treatment at 120-150°C for 1-2 h, pyrolysis treatment at 300-350°C for 1-2 h, and pyrolysis treatment at 500-700°C for 1-2 h in a mixed gas containing oxygen and an inert gas, to obtain a nitrogen-sulfur-magnesium composite modified biochar adsorbent material; the volume percentage of oxygen contained in the mixed gas is 10-30%; and the flow rate of the mixed gas containing oxygen and an inert gas is 5-10 L / h.

2. The use according to claim 1, characterized in that: The biomass material is a lignocellulose biomass material.

3. The use according to claim 2, characterized in that: The lignocellulosic biomass material is one or more of straw, grass leaves and wood materials.

4. The use according to claim 3, characterized in that: The straw is corn straw.

5. The use according to claim 1, characterized in that: The magnesium source is one or more of magnesium nitrate, magnesium sulfate and magnesium chloride; The nitrogen and sulfur source is thiourea, or the nitrogen and sulfur source is a mixture of thiourea and urea, or the nitrogen and sulfur source is a mixture of thiourea and melamine.

6. The use according to claim 1, characterized in that In step (2): The drying temperature is 60-80° C., and the drying time is 6-18 hours.

7. The use according to claim 1, characterized in that: The pretreatment of the biomass material comprises the following steps: washing the biomass material, cutting the biomass material into blocks, drying, crushing and screening the blocks to obtain pretreated biomass material with a particle size of less than 18 mesh.

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