A method and device for treating heavy metal wastewater by coupling carbonate with biochar composite adsorbent

Abstract

The present invention relates to a method and device for treating heavy metal wastewater by coupling carbonate with biochar composite adsorbent. The method is: treating heavy metal wastewater by coupling carbonate with biochar composite adsorbent; the preparation of biochar composite adsorbent includes: oxygen activating biochar in a gas containing oxygen at 400-500°C for 30-60 minutes to obtain oxygen-activated biochar; the volume percentage of oxygen contained in the gas is 10-50%; the oxygen-activated biochar and magnesium salt are mixed evenly with water to obtain a mixture, which is then dried and pyrolyzed; the obtained magnesium oxide / oxygen-activated biochar is immersed in an amino acid solution and ultrasonically treated, and then subjected to oscillation treatment and drying to obtain a biochar composite adsorbent. The treatment method and device of the present invention can efficiently and quickly treat low-concentration heavy metal wastewater, and can effectively reduce the dosage of auxiliary agents such as flocculants, thereby reducing the amount of sludge produced, which is beneficial to subsequent treatment.

Description

Technical Field

[0001] The present invention relates to the technical field of heavy metal wastewater treatment, and in particular to a method and a device for treating heavy metal wastewater by utilizing a biochar composite adsorbent coupled with carbonate. Background Art

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

[0003] Chemical precipitation 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. In order to make the effluent concentration meet the standard, it is necessary to increase the dosage to adjust the pH value to a higher level, which leads to a large dosage and a large amount of reagents, which in turn leads to the generation of a large amount of heavy metal sludge. In addition, the precipitate particles produced by the traditional precipitation method (including CaO and sulfide) for treating 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, and subsequent harmless treatment is difficult. Due to the different precipitation ranges of different heavy metals, such as Cu, Ni and Zn precipitation requires a higher pH, which may lead to the dissolution of other heavy metal precipitates, which are sensitive to OH. - The competitive effect of sulfide and sulfur-containing heavy metal capture agents interferes with the removal of other heavy metal ions, resulting in cumbersome and complicated heavy metal wastewater treatment procedures. Sulfide and sulfur-containing heavy metal capture agents also have the problem of producing particles that are too fine and rely on flocculants. At the same time, pollutants are easily generated during the production process and subsequent treatment.

[0004] MgO, a relatively green and environmentally friendly adsorbent commonly used in adsorption methods, can fix heavy metals through ion exchange and precipitation. Due to its low solubility, the release rate of hydroxide is slower, which can avoid the precipitation and dissolution of heavy metal bases caused by excessively high pH. However, the slow reaction rate causes the use of MgO to treat heavy metal wastewater to take longer and requires a larger dosage. In order to increase the adsorption activity of MgO, it is often necessary to adopt a certain activation process to increase its specific surface area in order to obtain a higher adsorption efficiency. However, the general activation method has high cost and energy consumption, is difficult to prepare, and the preparation process is relatively complicated. The activation process of MgO usually faces problems such as high energy consumption, complex and expensive preparation process. The activated MgO adsorbent also has problems such as too small precipitation particles, high dependence on auxiliary agents such as flocculants, high sludge production, and easy failure due to coagulation during use, resulting in a decrease in adsorption efficiency and a decrease in treatment effect. In addition, when dealing with heavy metal ions with smaller molecular weight and more active properties such as Ni, Cu and Zn, the pH often needs to be adjusted to a higher level. Traditional heavy metal adsorbents such as MgO and CaO (quicklime) have poor adsorption effects when dealing with heavy metal ions with lower molecular weight and more active properties (Cu, Ni, Zn, etc.), and it is difficult to achieve the treatment standards.

[0005] Therefore, achieving a fast, efficient, convenient and low-cost treatment method for heavy metal wastewater through the coupling of multiple methods and the improvement of adsorbents remains one of the major needs of the current market. Summary of the invention

[0006] In order to solve one or more technical problems existing in the prior art, the present invention provides a method and a device for treating heavy metal wastewater by coupling a biochar composite adsorbent with carbonate.

[0007] In a first aspect, the present invention provides a method for treating heavy metal wastewater by using a biochar composite adsorbent coupled with carbonate, the method comprising: treating heavy metal wastewater by using a biochar composite adsorbent coupled with carbonate;

[0008] The preparation of the biochar composite adsorbent comprises the following steps:

[0009] (1) activating 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%;

[0010] (2) mixing the oxygen-activated biochar and the magnesium salt with water to obtain a mixture, and then drying and pyrolyzing the mixture to obtain magnesium oxide / oxygen-activated biochar;

[0011] (3) The magnesium oxide / oxygen activated biochar is immersed in an amino acid solution and subjected to ultrasonic treatment, followed by oscillation treatment and drying to obtain a biochar composite adsorbent.

[0012] In a second aspect, the present invention provides a device for treating heavy metal wastewater by utilizing a biochar composite adsorbent coupled with carbonates. The device is an intermittent adsorption treatment device, and the intermittent adsorption device comprises a tank body for accommodating heavy metal wastewater and the biochar composite adsorbent and a stirring device for stirring the heavy metal wastewater and the biochar composite adsorbent. The top of the tank body is provided with a water inlet for the heavy metal wastewater to enter the tank body and a carbonate solution filling device for injecting carbonates into the tank body. The bottom of the tank body is provided with a sampling port and a water outlet with an intercepting filter. Preferably, the carbonate filling device has a flow rate control valve.

[0013] In a third aspect, the present invention provides a device for treating heavy metal wastewater by utilizing a biochar composite adsorbent coupled with carbonate, wherein the device is a filter tank type continuous flow treatment device, and the filter tank type continuous flow treatment device comprises a heavy metal wastewater introduction device, a continuous flow reactor and a carbonate filling device; the heavy metal wastewater introduction device comprises an inlet pipe and a water distributor connected to the inlet pipe, the water distributor is located at the top of the continuous flow reactor, and the heavy metal wastewater is introduced into the continuous flow reactor through the water distributor, preferably, a water inlet control valve is provided on the inlet pipe; a filter is provided inside the continuous flow reactor, and the left and right ends of the filter are connected to the inner wall of the continuous flow reactor, and a biochar composite adsorbent is provided above the filter. Filling area, preferably, the distance between the filter and the top of the continuous flow reactor is 2 to 5 times the distance between the filter and the bottom of the continuous flow reactor; the bottom of the continuous flow reactor is connected with a water outlet pipe; the carbonate filling device comprises a carbonate solution storage tank, a water pump and a carbonate solution injection pipe connected to the carbonate solution storage tank via the water pump, and the carbonate solution injection pipe extends into the biochar composite adsorbent filling area inside the continuous flow reactor; preferably, a carbonate solution control valve is provided between the water pump and the carbonate solution injection pipe, and the carbonate solution control valve is located outside the continuous flow reactor; preferably, a plurality of openings for injecting carbonate solution are provided on the side wall of the carbonate solution injection pipe.

[0014] The present invention provides a device for treating heavy metal wastewater by coupling biochar composite adsorbent with carbonate in a fourth aspect. The device is a continuous flow semi-fluidized bed treatment device, which includes a stirring and mixing device, a semi-fluidized bed reaction device and a liquid storage tank from left to right; an agitator is arranged inside the stirring and mixing device, the upper end of the stirring and mixing device is connected to a heavy metal wastewater inlet pipe, and the lower end of the stirring and mixing device is connected to a carbonate solution inlet pipe; a rectifier plate is arranged near the bottom of the semi-fluidized bed reaction device, an interception filter is arranged above the semi-fluidized bed reaction device, and the rectifier plate is arranged near the bottom of the semi-fluidized bed reaction device. The semi-fluidized bed reaction zone containing biochar composite adsorbent is between the plate and the intercepting filter; the stirring and mixing device is connected to the semi-fluidized bed reaction device via an injection pump, and the stirring and mixing device mixes heavy metal wastewater and carbonate solution and then enters the semi-fluidized bed reaction zone via the injection pump and the rectifier plate of the semi-fluidized bed reaction device; the semi-fluidized bed reaction device and the liquid storage tank are connected through a filtering device; a sampling port and a water outlet are provided at the bottom of the liquid storage tank; preferably, a reflux pipe connected to the stirring and mixing device is also provided at the bottom of the liquid storage tank, and more preferably, a reflux pump is provided on the pipeline of the reflux pipe.

[0015] Compared with the prior art, the present invention has at least the following beneficial effects:

[0016] (1) The present invention develops a treatment method and treatment device for heavy metal wastewater (lead, cadmium, copper, nickel, zinc, etc.). The treatment method and treatment device utilize biochar composite adsorbent coupled with carbonate to treat heavy metal wastewater, that is, through the combination of the use of biochar composite adsorbent and carbonate precipitation process, the heavy metal ions are efficiently and quickly removed, and a corresponding treatment device is designed according to the usage scenario. The biochar composite adsorbent used in the present invention is an amino-modified magnesium oxide / oxygen activated biochar adsorbent material. After the amino-modified magnesium oxide / oxygen activated biochar adsorbent is in contact with heavy metal wastewater, carbonate is simultaneously added to the wastewater. The heavy metal ions such as lead, cadmium, copper, zinc and nickel in the solution are quickly converted into carbonate precipitation by utilizing the adsorption effect of the amino-modified magnesium oxide / oxygen activated biochar adsorbent on heavy metals and the precipitation promotion effect of carbonate. The oxygen-activated biochar substrate is used to capture and adsorb the precipitation particles, so that the fine precipitation particles are attached to the surface of the adsorbent to obtain larger particle products, thereby reducing the difficulty of recovery and separation. The treatment method and treatment equipment in the present invention can efficiently and quickly treat low-concentration heavy metal wastewater, and can obtain larger-sized precipitation particles, effectively reducing the amount of auxiliary agents such as flocculants, thereby reducing the amount of sludge produced, which is beneficial to subsequent treatment.

[0017] (2) The preparation of the biochar composite adsorbent used in the method of the present invention is as follows: first, the biochar is activated by oxygen activation to obtain a higher specific surface area and a better surface pore structure, and further, by loading magnesium oxide and modifying the amino group, an efficient carbon-based composite adsorption material is obtained. The biochar composite adsorbent used is used for the rapid and efficient removal of heavy metal ions such as lead and cadmium in heavy metal wastewater; in the preparation of the biochar composite adsorbent described in the present invention, carbon-based materials such as biochar are used as raw materials, and a limited oxygen activation method is performed under appropriate conditions to effectively increase the pores and oxygen-containing functional groups on the surface of the biochar, and further By using the impregnation-pyrolysis method, magnesium oxide is uniformly and dispersedly loaded on the surface of biochar, and magnesium oxide is used as a linker. Through its reaction with amino acids such as glutamic acid, the biochar composite adsorbent material is finally obtained. The material can use the complexation of amino groups to quickly capture and concentrate heavy metal ions, so that they react with magnesium oxide to produce precipitation in situ, and the precipitation is captured by a porous carbon matrix. The biochar composite adsorbent material obtained by the present invention can efficiently and quickly treat low-concentration heavy metal wastewater, has a fast treatment rate, reduces the use of precipitants, flocculants and other agents, has low sludge production, and can optimize the separation of heavy metal precipitation and the reuse of heavy metals.

[0018] (3) Compared with the fine particles produced by traditional adsorbents, the heavy metal precipitation particles produced by the method of the present invention are significantly increased in size and attached to the adsorbent substrate, thereby obtaining larger particle products, which can effectively reduce the difficulty of recovery and reduce or avoid the use of auxiliary agents, which is conducive to reducing costs, energy consumption and secondary pollution. Compared with traditional heavy metal treatment agents such as CaO and MgO, the method of the present invention treats heavy metal wastewater so that the heavy metal ion concentration can reach the emission standard. The dosage of the biochar composite adsorbent required is much lower than that of CaO and MgO, and since the large-scale use of auxiliary agents such as flocculants is avoided, the amount of sludge produced can be significantly reduced. Since carbonate (generally derived from CO 2 ) participates in the precipitation and removal of lead and cadmium ions. When CO is lacking in the adsorption process, 2 Therefore, the method of the present invention can significantly improve the removal effect and rate of heavy metals while avoiding this situation by using the biochar composite adsorbent and adding carbonate ions exogenously.

[0019] (4) By using the amino-modified magnesium oxide / oxygen-activated biochar adsorbent (biochar composite adsorbent), the effective support and substrate template effect of biochar on MgO after oxygen activation can be utilized to simplify the MgO activation process, reduce the energy consumption of MgO activation, and provide better adsorption effect; its adsorption effect is significantly improved compared with magnesium oxide and magnesium oxide / biochar materials; and the support and dispersion of the biochar substrate after oxygen activation in the present invention on the MgO structure can effectively reduce the decrease in the adsorption efficiency of MgO due to condensation during the adsorption process; heavy metal ions that are difficult to treat using traditional precipitation methods and adsorbents such as CaO and MgO (such as Cu, Ni, Zn, etc., which have a smaller molecular weight, are more active in nature, require a higher pH value for precipitation formation, and have a narrower precipitation pH range) can be effectively treated by the method of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a physical picture of the biochar composite adsorbent product in Example 1 of the present invention;

[0021] Figure 2 1 are SEM images of biochar before oxygen activation and biochar after oxygen activation in Example 1 of the present invention; (a) is a SEM image of biochar before oxygen activation, and (b) is a SEM image of biochar after oxygen activation;

[0022] Figure 3 FT-IR spectra of biochar without oxygen activation (original biochar) and biochar after oxygen activation (oxygen-activated biochar) in Example 1 of the present invention;

[0023] Figure 4 1 is a SEM image of the magnesium oxide / biochar in Comparative Example 1 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;

[0024] Figure 5 are SEM images of the biochar composite adsorbent in Example 1 of the present invention at different magnifications;

[0025] Figure 6 is the XRD spectra of the magnesium oxide / oxygen activated biochar in Example 1 of the present invention and the biochar composite adsorbent (amino-modified magnesium oxide / oxygen activated biochar) in Example 1;

[0026] Figure 7 FT-IR spectra of the magnesium oxide / oxygen activated biochar in Example 1 of the present invention and the biochar composite adsorbent (amino-modified magnesium oxide / oxygen activated biochar) in Example 1;

[0027] Figure 8 1-1: electric stirring device; 1-2: water inlet; 1-3: sampling port; 1-4: carbonate solution filling device; 1-5: flow rate control valve; 1-6: tank body; 1-7: water outlet with interception filter;

[0028] Fig. 9 2-1: water inlet pipe; 2-2: water inlet control valve; 2-3: water distributor; 2-4: carbonate solution storage tank; 2-5: water pump; 2-6: carbonate solution control valve; 2-7: biochar composite adsorbent filler area; 2-8: carbonate solution injection pipeline; 2-9: filter; 2-10: water outlet pipe;

[0029] Fig.10 3-1: heavy metal wastewater inlet pipe; 3-2: stirring and mixing device; 3-3: stirrer; 3-4: semi-fluidized bed reaction zone; 3-5: carbonate solution inlet pipe; 3-6: sample feed pump; 3-7: rectifier plate; 3-8: interception filter; 3-9: filtering device; 3-10: liquid storage tank; 3-11: reflux pipe; 3-12: reflux pump; 3-13: sampling port of liquid storage tank; 3-14: water outlet;

[0030] Fig.11 The removal rate results of heavy metal wastewater treatment using MgO, carbonate, the biochar composite adsorbent in Example 1 (abbreviated as adsorbent in the figure), and the biochar composite adsorbent coupled with carbonate in the present invention are shown in FIG.

[0031] Fig.12 The figures are SEM images of lead and cadmium adsorbed directly using magnesium oxide as adsorbent and coupled with carbonate using the biochar composite adsorbent in Example 1; in the figures, (a) is a SEM image of lead adsorbed directly using magnesium oxide as adsorbent, (b) is a SEM image of cadmium adsorbed directly using magnesium oxide as adsorbent, (c) is a SEM image of lead adsorbed by the biochar composite adsorbent in Example 1 coupled with carbonate, and (d) is a SEM image of cadmium adsorbed by the biochar composite adsorbent in Example 1 coupled with carbonate. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0033] In a first aspect, the present invention provides a method for treating heavy metal wastewater by coupling a biochar composite adsorbent with a carbonate (abbreviated as a method for treating heavy metal wastewater), the method comprising: treating heavy metal wastewater by coupling a biochar composite adsorbent with a carbonate; specifically, for example, when treating heavy metal wastewater by using a biochar composite adsorbent, carbonate is also added to the system; in the present invention, the method is to couple the adsorption of the biochar composite adsorbent with the carbonate-promoted precipitation, and to provide carbonate ions to a solution adjacent to the biochar composite adsorbent in a directional manner, so as to achieve a method for treating heavy metal wastewater (e.g., low-concentration heavy metal wastewater) by rapid precipitation and in-situ capture of the precipitation; the preparation of the biochar composite adsorbent comprises the following steps:

[0034] (1) Activating biochar with oxygen in a gas containing oxygen at 400-500° C. (e.g., 400° C., 450° C., or 500° C.) for 30-60 min (e.g., 30, 35, 40, 45, 50, 55, or 60 min) to obtain oxygen-activated biochar; the volume percentage of oxygen contained in the gas is 10-50% (e.g., 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%); in the present invention, the gas containing oxygen uses an inert gas as a carrier gas, and the inert gas is, for example, nitrogen. Preferably, the gas containing oxygen consists of oxygen and nitrogen;

[0035] (2) mixing the oxygen-activated biochar and the magnesium salt with water to obtain a mixture, and then drying and pyrolyzing the mixture to obtain magnesium oxide / oxygen-activated biochar;

[0036] (3) The magnesium oxide / oxygen activated biochar is immersed in an amino acid solution and subjected to ultrasonic treatment, followed by oscillation treatment and drying to obtain a biochar composite adsorbent (also referred to as amino-modified magnesium oxide / oxygen activated biochar); in the present invention, the amino acid solution uses water as a solvent and is an amino acid aqueous solution; compared to the magnesium oxide adsorbent, the biochar composite adsorbent in the present invention loads magnesium oxide on the surface of the oxygen-activated biochar, and the precipitation of heavy metals such as lead and cadmium on the adsorbent is faster, and the adsorption rate is effectively improved. 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; the present invention performs oxygen activation under appropriate conditions, which can increase the porosity of the biochar surface and form a large number of oxygen-containing functional groups on the surface, thereby During the loading process, the magnesium oxide structure has better dispersion on the biochar surface and stronger adsorption activity, and can provide more reaction sites during the subsequent amination, so that the amino group can be grafted on the material surface; compared with the traditional magnesium oxide activation method, this method does not need to use too high activation temperature and has low energy consumption; compared with other amino grafting methods, when the biochar composite adsorbent of the present invention is used, thanks to the good dispersion of magnesium oxide on the biochar surface, amino modification is simpler, there is less pollution in the preparation process, and the process is simpler; compared with the existing biochar activation method, the present invention uses an oxygen activation method to activate the 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 holes on the flat surface, which is beneficial to the subsequent magnesium oxide loading and makes it more dispersed.

[0037] The present invention adopts a three-step preparation method when preparing the biochar composite adsorbent. First, the biochar surface is activated with oxygen using appropriate oxygen conditions. Subsequently, an impregnation-pyrolysis method is used to uniformly load magnesium oxide on the oxygen-activated biochar surface by utilizing the surface with improved porosity after being activated by oxygen and the oxygen-containing functional groups contained in the surface after oxidation. Subsequently, glutamic acid and other amino acids are used for impregnation. Preferably, the amino acids are connected to magnesium oxide by controlling the impregnation ratio and the impregnation time (ultrasound and oscillation time). The reaction between the metal hydroxyl groups on the surface of the hydrated magnesium oxide and the acidic functional groups contained in the amino acids is used to connect the amino acids to the magnesium oxide, thereby loading the amino groups on the surface of the magnesium oxide. The biochar composite adsorbent in the present invention can utilize the complexation of the amino acids fixed on the surface of the magnesium oxide to concentrate the heavy metal ions near the magnesium oxide on the surface of the biochar. Under the action of ion exchange and precipitation promotion provided by the magnesium oxide, the heavy metal ions are converted into solid precipitation particles, and the precipitation is captured by the surface of the biochar containing a certain number of oxygen-containing functional groups, thereby reducing the difficulty of recovery.

[0038] In the preparation of the biochar composite adsorbent of the present invention, in order to ensure the effect of oxygen activation of biochar, it is necessary to activate it at an 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%, which can increase the porosity of 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 dispersibility on the biochar surface and stronger adsorption activity, and can provide more reaction sites during subsequent amination, so that amino groups can be grafted on 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 of porosity cannot be fully achieved, and if the volume percentage of oxygen is too high and / or the oxygen activation temperature is too high, it will lead to the occurrence of peroxidation, so that the biochar surface is over-oxidized or burned, instead of selectively forming oxygen-containing functional groups, which will damage the structure of the biochar. The porosity is reduced and a large amount of biochar is incinerated, which ultimately affects the adsorption performance of the material. The present invention finds that the adsorption performance of materials with poor magnesium oxide dispersibility is not effectively improved after amination without oxygen activation treatment. The failure of amino groups to be effectively grafted and the loss of magnesium oxide during the grafting process are important reasons. The process of loading amino groups after loading magnesium oxide may cause magnesium oxide to fall off or fail to achieve effective loading of amino acids. The present invention controls the degree of reaction between magnesium oxide and amino acids during grafting. If the magnesium oxide is not sufficiently dispersible, larger particles will be formed in the pores of biochar, which are easier to fall off when reacting with acidic amino grafting agents. 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 reduction in the number of grafted amino groups and a reduction in the amount of grafting. The present invention is precisely because the biochar is properly activated with oxygen, so that magnesium oxide can be evenly dispersed and amino modification can be effectively introduced, so that the adsorbent can retain the loading of magnesium oxide and amino groups at the same time.

[0039] The present invention prepares a biochar composite adsorbent and promotes the generation of carbonate or basic carbonate precipitation on the adsorbent surface and nearby areas by quantitatively adding carbonate during the adsorption process, and captures the precipitated particles by the adsorbent, thereby achieving the effect of reducing the use of subsequent treatment agents such as flocculants. The method of the present invention can quickly remove low-concentration heavy metal wastewater, reduce the use of precipitants, flocculants and other agents, and optimize the separation of heavy metal precipitation and the reuse of heavy metals.

[0040] According to some preferred embodiments, the method further includes a step of pre-treating the heavy metal wastewater before treating the heavy metal wastewater with a biochar composite adsorbent coupled with carbonate, wherein the pre-treatment is: adjusting the pH of the heavy metal wastewater to not less than 3 after sedimentation and filtration.

[0041] According to some specific implementation methods, the pretreatment of heavy metal wastewater is: removing larger precipitated particles in the heavy metal wastewater through preliminary sedimentation, filtration and other means, and preliminarily adjusting the pH to remove some heavy metal ions; wherein, the pH adjustment method is mainly to add one or more of magnesium oxide, calcium oxide and sodium hydroxide, and by controlling the addition amount, the pH value is adjusted to above 3, at which time the heavy metal concentration is generally below 50 mg / L.

[0042] According to some specific embodiments, the method further includes a step of recovering heavy metal precipitates after the heavy metal wastewater treatment; the recovery step may, for example, be: after the heavy metal wastewater treatment, the precipitates are mainly attached to the surface of the biochar composite adsorbent, and can be separated from the water body together with the biochar composite adsorbent by a simpler filtration method, thereby effectively reducing the difficulty of separation, avoiding excessive use of flocculants, and reducing the amount of heavy metal sludge generated; after the biochar composite adsorbent with the precipitates is filtered and recovered, the heavy metals on the surface can be recovered by acid washing or the like, or the biochar composite adsorbent and the surface heavy metals can be smelted and reused together; in the present invention, the acid washing may, for example, be selected from dilute hydrochloric acid, dilute nitric acid or carbon dioxide gas.

[0043] According to some preferred embodiments, the method is carried out using an intermittent adsorption treatment device or a filter pool continuous flow treatment device or a continuous flow semi-fluidized bed treatment device; the carbonate is one or more of sodium carbonate, sodium bicarbonate, potassium carbonate and potassium bicarbonate, and when treating heavy metal wastewater, the carbonate is added to the heavy metal wastewater in the form of a carbonate solution, and the concentration of the carbonate solution is 10-100mmol / L; when treating heavy metal wastewater, the amount of the biochar composite adsorbent is such that the concentration of the biochar composite adsorbent in the heavy metal wastewater is 50-1000ppm; and / or when treating heavy metal wastewater, the amount of the carbonate is such that the molar ratio of the carbonate ions contained in the carbonate to the heavy metal ions contained in the heavy metal wastewater is (1-2):1.

[0044] According to some preferred embodiments, in step (1): the flow rate of the gas (gas containing oxygen) does not exceed 10L / h, preferably 5-10L / h (e.g. 5, 6, 7, 8, 9 or 10L / h). After a large number of creative experiments, the present invention has obtained a suitable gas flow rate for oxygen activation of the present invention. The present invention has found that a suitable gas flow rate can ensure that oxygen is evenly distributed during the oxygen activation process, so that the oxygen activation reaction on the surface of the biochar is carried out evenly, avoiding that some parts of the biochar fail to fully contact oxygen due to insufficient gas flow rate, and at a suitable flow rate, a suitable reaction rate can be achieved, so that the activation reaction can be fully carried out without being too fast or too slow; in addition, a suitable 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 cause uneven 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 pretreatment and carbonization of biomass materials; preferably, the biomass materials are lignocellulosic biomass materials; more preferably, the lignocellulosic biomass materials are 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 materials are cleaned to remove excess sediment and other attachments on the surface, then the biomass materials are cut into small pieces, dried to remove most of the water, and then crushed with a pulverizer, and the biomass materials with a size (particle size) not greater than 18 mesh are selected by sieving, and naturally 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. (eg, 250° C., 300° C. or 350° C.), and the time of the carbonization treatment does not exceed 2 hours.

[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 of plant origin, including straw, grass leaves and wood materials; after selecting the material, first clean the biomass material to remove excess mud and other attachments on the surface, then cut the biomass material into small pieces, dry and remove most of the moisture, use a pulverizer to crush it, screen and select materials with a size (particle size) less than 18 mesh, obtain pretreated biomass materials, and naturally air-dry them for use; place the pretreated biomass material in an inert protective gas (such as nitrogen), raise the temperature to about 300°C, and undergo a carbonization treatment (pyrolysis) of no more than 2 hours, and during the carbonization treatment, use a higher carrier gas flow rate (for example, nitrogen or argon with a flow rate of 30 to 50 L / h) to blow away the volatiles produced by pyrolysis to obtain biochar.

[0048] According to some specific embodiments, step (1) is: placing the biochar in a gas containing oxygen (containing 10 to 50% oxygen by volume), the flow rate of the oxygen-containing gas does not exceed 1 L / h, and the temperature is controlled at 400-500°C, the reaction time is controlled at 30-60 minutes, and the surface of the biochar is oxidized by oxygen; then, the ventilation and heating are stopped, and the biochar is cooled 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) (e.g., 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,

[0050] Preferably, the mass ratio of the oxygen activated biochar to the magnesium contained in the magnesium salt is 1:(0.02-0.3),

[0051] The present invention finds that if the amount of magnesium is too low, the magnesium oxide loading is insufficient, the adsorption capacity is too low, the required dosage is too large, and the amino grafting is prone to overreaction and complete removal of magnesium oxide; and if the amount of magnesium is too high and the loading 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 dried at 60 to 80°C (for example, 60°C, 65°C, 70°C, 75°C or 80°C) for 6 to 12h (for example, 6, 7, 8 , 9, 10, 11 or 12h), and then dried at 120-150°C (e.g., 120°C, 125°C, 130°C, 135°C, 140°C or 150°C) for 1-2h (e.g., 1, 1.5 or 2h); and / or the pyrolysis temperature is 400-600°C (e.g., 400°C, 450°C, 500°C, 550°C or 600°C), and the pyrolysis time is 1-2h (e.g., 1, 1.5 or 2h).

[0052] According to some preferred embodiments, in step (2): the pyrolysis is carried out in a mixed gas containing oxygen and an inert gas, the volume percentage of oxygen in the mixed gas is 5-12% (e.g., 5%, 6%, 7%, 8%, 9%, 10%, 11% or 12%), and preferably, the flow rate of the mixed gas is 5-10 L / h. Different from the conventional pyrolysis under pure inert atmosphere conditions, in the preparation of magnesium oxide / oxygen activated biochar, the present invention preferably contains a suitable concentration of oxygen in the inert atmosphere. Compared with a pure inert atmosphere (e.g., nitrogen), that is, compared with pyrolysis under oxygen isolation conditions, the present invention finds that the presence of a suitable concentration of oxygen helps to promote the formation and surface activation of magnesium oxide, can better control the reaction, make the formation of magnesium oxide more complete and uniform, help to enhance the interaction between oxygen-activated biochar and magnesium oxide, and make magnesium oxide more dispersed on the surface of biochar, more activated, and more adsorbed, thereby helping to improve the adsorption performance of the material.

[0053] According to some specific embodiments, step (2) is: mixing the oxygen-activated biochar with a magnesium salt (magnesium chloride and / or magnesium sulfate) in a mixing ratio of 1:(0.02-0.3) by mass ratio of the oxygen-activated biochar to the magnesium contained in the magnesium salt, adding a certain amount of water to the mixture, the amount of water used being such that the mass volume ratio of the oxygen-activated biochar to the water is 1 g:(10-20) mL, mixing them uniformly by stirring or ultrasound or other means, slowly drying them at 60-80° C. to a slurry state, heating and drying the slurry state mixture at a temperature of 120-150° C. for 1-2 h, and then pyrolyzing it under oxygen-limited conditions, i.e., raising the temperature to 400-600° C. for 1-2 h, to complete the magnesium oxide loading, and rinsing the obtained material with clean water, drying it, and storing it for standby use, to obtain magnesium oxide / oxygen-activated biochar.

[0054] 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) (for example, 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) (for example, 1:0.01, 1:0.02, 1:0.03, 1:0.04 or 1:0.05).

[0055] According to some preferred embodiments, the amino acids contained in the amino acid solution are glutamic acid and / or glycine; in the present invention, the amino acids can be selected from small molecule agents having both amino and carboxyl groups, and relatively simple and cheap amino acids such as glycine and glutamic acid are usually selected.

[0056] According to some preferred embodiments, in step (3): the ultrasonic treatment time is 3 to 6 minutes (e.g., 3, 4, 5 or 6 minutes); the oscillation treatment temperature is 30 to 50°C (e.g., 30°C, 35°C, 40°C, 45°C or 50°C), and the oscillation treatment time is 5 to 10 minutes (e.g., 5, 6, 7, 8, 9 or 10 minutes); in the present invention, the ultrasonic treatment frequency is, for example, 28kHz to 40kHz, and the oscillation treatment rate is, for example, 120 to 200rpm; 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 to 0.05), The ultrasonic treatment time is 3 to 6 minutes, and the oscillation treatment temperature is 5 to 10 minutes. That is, by reasonably controlling the impregnation ratio and the impregnation time, it is beneficial to make the magnesium oxide and the amino acid react effectively, so that the amino acid and the magnesium oxide are effectively connected, so that the amino group is effectively loaded on the surface of the magnesium oxide (the amino group is grafted to the surface of the magnesium oxide), and amino-modified magnesium oxide / oxygen-activated biochar is obtained, which is beneficial to improve the performance of the heavy metal adsorbent; the present invention finds that too little amino acid, too short ultrasound and oscillation time will lead to insufficient amino grafting, and vice versa, it will lead to excessive consumption of magnesium oxide; and / or the drying temperature is 85 to 105°C (for example, 85°C, 90°C, 95°C, 100°C or 105°C).

[0057] According to some specific embodiments, step (3) is: immersing magnesium oxide / oxygen activated biochar in an amino acid solution such as glutamic acid at a solid-liquid mass ratio of 1:10, and the mass ratio of magnesium oxide / oxygen activated biochar to amino acid is 1:0.01-0.05, dispersing by ultrasound for about 5 minutes, oscillating at 30-50°C for 5-10 minutes, and then drying the mixed solution at 85-105°C, rinsing with clean water and drying to obtain the biochar composite adsorbent.

[0058] In a second aspect, the present invention provides a device for treating heavy metal wastewater by coupling a biochar composite adsorbent with a carbonate (abbreviated as a device for treating heavy metal wastewater), for example Figure 8 As shown; the device is an intermittent adsorption treatment device, which includes a tank body 1-6 for accommodating heavy metal wastewater and biochar composite adsorbent and a stirring device (preferably an electric stirring device 1-1) for stirring the heavy metal wastewater and the biochar composite adsorbent, the top of the tank body 1-1 is provided with a water inlet 1-2 for the heavy metal wastewater to enter the tank body and a carbonate solution filling device 1-4 for injecting carbonate into the tank body 1-1, and the bottom of the tank body 1-1 is provided with a sampling port 1-3 and a water outlet 1-7 with an intercepting filter; preferably, the carbonate filling device 1-4 has a flow rate control valve 1-5.

[0059] When the present invention uses an intermittent adsorption treatment device to treat heavy metal wastewater, the treatment device is a single reactor with a stirring device; the treatment method is: first, the heavy metal wastewater is placed in a tank body, and a certain amount of biochar composite adsorbent is added to the bottom of the tank body, and an electric stirring device is used for stirring; after about 5-30 minutes of stirring, a carbonate solution filling device is used, and under the control of a flow rate control valve, a certain concentration of reagent B (i.e., carbonate solution) is introduced at a certain speed, and after stirring for a certain period of time, it is detected through a sampling port whether it meets the standard, and then discharged through a water outlet with an intercepting filter. In this process, the biochar composite adsorbent with precipitation is filtered out by the intercepting filter. In the present invention, unless otherwise specified, the biochar composite adsorbent is prepared by steps (1) to (3) described in the present invention; when the concentration of heavy metal ions in the heavy metal wastewater is low (<50 mg / L) and the pH value is higher than 3, the intermittent adsorption treatment device is preferably used directly for treatment; when the heavy metal concentration is high (≥50 mg / L) or the pH value is lower than 3, it is preferably treated after pre-treatment. In the intermittent adsorption treatment device, the dosage of the biochar composite adsorbent is adjusted according to the total content of magnesium oxide, and is controlled within the range of 50-1000ppm; the carbonate in the reagent B (carbonate solution) introduced is a mixture of one or more of sodium carbonate, sodium bicarbonate, potassium carbonate and potassium bicarbonate, with a concentration of 10-100mmol / L, and the total amount of carbonate and / or bicarbonate is 1-2 times the total molar amount of heavy metal ions introduced into the heavy metal wastewater in the tank body, which can be injected into the tank body together with the incoming water, or injected into the tank body near the biochar composite adsorbent within 10 minutes of the start of the operation of the intermittent adsorption treatment device. After the carbonate is injected, it is stirred for 20 minutes, and the biochar composite adsorbent with heavy metal precipitation is filtered to remove; the intermittent adsorption treatment device is particularly suitable for the rapid treatment of heavy metal wastewater with small treatment demand and unstable output.

[0060] In a third aspect, the present invention provides a device for treating heavy metal wastewater by coupling a biochar composite adsorbent with a carbonate (abbreviated as a device for treating heavy metal wastewater), for example Fig. 9As shown; the device is a filter pool type continuous flow treatment device, and the filter pool type continuous flow treatment device includes a heavy metal wastewater introduction device, a continuous flow reactor and a carbonate filling device; the heavy metal wastewater introduction device includes an inlet pipe 2-1 and a water distributor 2-3 connected to the inlet pipe 2-1, the water distributor 2-3 is located at the top of the continuous flow reactor, and the heavy metal wastewater is introduced into the continuous flow reactor through the water distributor 2-3. Preferably, a water inlet control valve 2-2 is provided on the pipeline of the inlet pipe 2-1; the continuous flow reactor is provided with a filter 2-9 inside, the left and right ends of the filter 2-9 are connected to the inner wall of the continuous flow reactor, and a biochar composite adsorbent filler area 2-7 is provided above the filter 2-9. Preferably, the filter 2-9 is 200 meters away from the continuous flow reactor. The distance from the top of the reactor is 2 to 5 times the distance from the filter 2-9 to the bottom of the continuous flow reactor; the bottom of the continuous flow reactor is connected with a water outlet pipe 2-10; the carbonate filling device includes a carbonate solution storage tank 2-4, a water pump 2-5 and a carbonate solution injection pipe 2-8 connected to the carbonate solution storage tank 2-4 via the water pump 2-5, and the carbonate solution injection pipe 2-8 extends into the biochar composite adsorbent filler area 2-7 inside the continuous flow reactor; preferably, a carbonate solution control valve 2-6 is provided between the water pump 2-5 and the carbonate solution injection pipe 2-8, and the carbonate solution control valve 2-6 is located outside the continuous flow reactor; preferably, a plurality of openings for injecting carbonate solution are opened on the side wall of the carbonate solution injection pipe 2-8.

[0061] When the present invention adopts a filter tank type continuous flow treatment device for treatment, the continuous flow reactor can be a fixed bed or a filter tank; the treatment method is, for example: placing a biochar composite adsorbent in a biochar composite adsorbent filler area, opening a water inlet control valve, and introducing heavy metal wastewater that has undergone preliminary filtration / sand filtration and other pre-treatments through a water inlet pipe, and evenly entering the continuous flow reactor through a water distributor; at this time, opening a carbonate solution control valve, and injecting a certain concentration of reagent B (carbonate solution) stored in a carbonate solution storage tank into the continuous flow reactor through a carbonate solution injection pipeline; intercepting the biochar composite adsorbent with precipitation through a filter screen, a filter membrane and other structures in the filter, and conducting a comparison of the effluent pH value and the heavy metal concentration. After the monitoring meets the standard, it is discharged through the outlet pipe; the pretreatment is pH adjustment, preliminary precipitation and filtration, the pH is adjusted to above 3, and the heavy metal ion concentration is controlled below 50 mg / L; the concentration of reagent B (carbonate solution) is 10-100 mmol / L, the injection rate matches the molar content of heavy metal ions in the influent, the total amount of carbonate and bicarbonate is 2-5 times that of the influent, and can enter the continuous flow reactor together with the influent, or be injected near the position of the biochar composite adsorbent in the continuous flow reactor, and the effluent intercepts and removes the biochar composite adsorbent with precipitation through a filter screen or a filter membrane; the filter pool type continuous flow treatment device is suitable for the treatment of heavy metal wastewater with large treatment demand and relatively stable production.

[0062] In a fourth aspect, the present invention provides a device for treating heavy metal wastewater by using a biochar composite adsorbent coupled with carbonate (abbreviated as a device for treating heavy metal wastewater), for example, Fig.10As shown; the device is a continuous flow semi-fluidized bed treatment device, which includes a stirring and mixing device 3-2, a semi-fluidized bed reaction device and a liquid storage tank 3-10 from left to right; a stirrer 3-3 is arranged inside the stirring and mixing device 3-2, the upper end of the stirring and mixing device 3-2 is connected to a heavy metal wastewater inlet pipe 3-1, and the lower end of the stirring and mixing device 3-2 is connected to a carbonate solution inlet pipe 3-5; a rectifier plate 3-7 is arranged near the bottom of the semi-fluidized bed reaction device, an interception filter 3-8 is arranged above the semi-fluidized bed reaction device, and a semi-fluidized bed reaction zone 3-1 containing a biochar composite adsorbent is provided between the rectifier plate 3-7 and the interception filter 3-8. 4; the stirring and mixing device 3-2 is connected to the semi-fluidized bed reaction device via an injection pump 3-6, and the stirring and mixing device 3-2 mixes the heavy metal wastewater and the carbonate solution and then enters the semi-fluidized bed reaction zone 3-4 via the injection pump 3-6 and the rectifier plate 3-7 of the semi-fluidized bed reaction device; the semi-fluidized bed reaction device and the liquid storage tank 3-10 are connected via a filtering device 3-9; a sampling port 3-13 and a water outlet 3-14 of the liquid storage tank are provided at the bottom of the liquid storage tank 3-10; preferably, a reflux pipe 3-11 connected to the stirring and mixing device 3-2 is also provided at the bottom of the liquid storage tank 3-10, and more preferably, a reflux pump 3-12 is provided on the pipeline of the reflux pipe 3-11.

[0063] When the present invention uses a continuous flow semi-fluidized bed treatment device to treat heavy metal wastewater, a biochar composite adsorbent is placed in a semi-fluidized bed reaction zone, and the heavy metal wastewater that has been pre-treated by preliminary filtration / sand filtration is passed into a stirring and mixing device through a heavy metal wastewater inlet pipe, and is pre-mixed with a reagent B (carbonate solution) entering the carbonate solution inlet pipe under stirring by a stirrer, and is pumped by a sampling pump and enters the semi-fluidized bed reaction zone after passing through a rectifying plate, and after being fully mixed and reacted with the biochar composite adsorbent therein, it is intercepted and filtered by an interception filter and a filtering device, and enters a liquid In the storage tank, sampling is carried out through the sampling port of the liquid storage tank for testing. If the standard is met, the wastewater is discharged through the outlet. If the standard is not met, the reflux pipe is opened and the reflux pump is started to return the wastewater to the stirring and mixing device and then treated again until the treatment meets the standard. The concentration of reagent B (carbonate solution) is 10-100mmol / L, and the injection rate matches the molar content of heavy metal ions in the influent water, and the total amount of carbonate and bicarbonate is 1-2 times of that. The continuous flow semi-fluidized bed treatment device is suitable for the treatment of heavy metal wastewater with large treatment demand, low heavy metal concentration and stable production.

[0064] In the process of adsorption treatment, the present invention selects a corresponding treatment device according to the scale and characteristics of the heavy metal wastewater to be treated, adds a carbonate solution to the solution around the adsorbent at a fixed point, utilizes the characteristics of carbonate to reduce the pH value and solubility required for heavy metal precipitation, promotes the concentrated heavy metal ions and magnesium oxide to release hydroxide ions to produce precipitation, thereby accelerating the precipitation rate and improving the adsorption efficiency; at the same time, utilizes the adsorption capacity of the biochar composite adsorbent material to capture the generated precipitation particles, fixes the generated carbonate and basic carbonate precipitation on the carbon-based surface of the adsorbent, thereby increasing the size of the heavy metal solid particles, which is beneficial to subsequent recovery and separation, and reduces the use of auxiliary agents such as flocculants, and reduces the amount of sludge produced; the device for treating heavy metal wastewater in the present invention is matched with the treatment method, and is used to realize the provision of carbonate ions to the solution in the vicinity of the biochar composite adsorbent, and can separate the precipitated heavy metal precipitation from the water body together with the biochar composite adsorbent.

[0065] The technical scheme in the embodiment of the present invention will be clearly and completely described below. Obviously, the described embodiment is only a part of the embodiment of the present invention, rather than all the 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.

[0066] The preparation methods of biochar used in the following embodiments and comparative examples are the same, specifically:

[0067] 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 pieces, dried to remove most of the moisture, and then crushed using a pulverizer. The material with a size (particle size) less than 18 mesh is sieved and selected to obtain the pretreated biomass material, which is naturally air-dried for use; the pretreated biomass material is placed in a nitrogen atmosphere, the temperature is raised to 300°C, and carbonized for 1.5 hours. During the carbonization process, a higher carrier gas flow rate (nitrogen flow rate of 35 L / h) is used to blow away the volatiles generated in the carbonization process to obtain biochar.

[0068] Example 1

[0069] This embodiment provides a method for preparing a biochar composite adsorbent and a method for treating heavy metal wastewater by coupling the biochar composite adsorbent with carbonate.

[0070] The preparation of the biochar composite adsorbent is as follows:

[0071] ① Place the biochar in a gas containing oxygen at a flow rate of 8 L / h, control the temperature at 450°C, and control the reaction (oxygen activation) time at 40 minutes; then, stop ventilation and heating, cool, and obtain oxygen-activated biochar; the oxygen-containing gas is a mixture of oxygen and nitrogen, and the oxygen-containing gas contains 25% oxygen by volume and 75% nitrogen by volume.

[0072] ② The oxygen-activated biochar obtained in step ① is mixed with magnesium chloride in a mixing ratio of 1:0.1 in mass ratio of oxygen-activated biochar to magnesium contained in magnesium chloride, a certain amount of water is added to the mixture (the mass volume ratio of oxygen-activated biochar to water is 1 g:15 mL), and after mixing them evenly by stirring, they are dried at 70°C for 8 hours to a slurry state, and the slurry-like mixture is heated and dried at a temperature of 130°C for 1.5 hours, and then pyrolyzed at a temperature of 500°C for 1.5 hours in a mixed gas (flow rate of 8 L / h) composed of oxygen and nitrogen to complete the magnesium oxide loading, and the obtained material is rinsed with clean water and dried to obtain magnesium oxide / oxygen-activated biochar; wherein the volume percentage of oxygen contained in the mixed gas is 8%, and the volume percentage of nitrogen contained in the mixed gas is 92%.

[0073] ③ The magnesium oxide / oxygen activated biochar obtained in step ② is immersed in a glutamate solution (glutamate aqueous solution) and ultrasonicated for 5 minutes, then oscillated at 40°C for 8 minutes, and then the obtained mixed solution is dried at 95°C, rinsed with clean water and dried to obtain a biochar composite adsorbent; wherein the mass ratio of the magnesium oxide / oxygen activated biochar to the glutamate solution is 1:10, and the mass ratio of the magnesium oxide / oxygen activated biochar to the glutamate contained in the glutamate solution is 1:0.03.

[0074] The method for treating heavy metal wastewater is: using the prepared biochar composite adsorbent coupled with carbonate to treat heavy metal wastewater, specifically: using Figure 8 The device shown in the figure is carried out; first, the heavy metal wastewater is placed in a tank body, and a biochar composite adsorbent is added to the bottom of the tank body, and an electric stirring device is used for stirring; after 20 minutes of stirring, a carbonate solution with a concentration of 50mmol / L to 100mmol / L is introduced at a uniform speed through a carbonate solution filling device under the control of a flow rate control valve, and the stirring treatment is carried out for 240 to 360 minutes; when treating the heavy metal wastewater, the amount of the biochar composite adsorbent is such that the concentration of the biochar composite adsorbent in the heavy metal wastewater is 100 to 200ppm; when treating the heavy metal wastewater, the amount of the carbonate is such that the molar ratio of the carbonate ions contained in the carbonate to the heavy metal ions contained in the heavy metal wastewater is 1.2:1.

[0075] Example 2

[0076] Embodiment 2 is substantially the same as Embodiment 1, except that:

[0077] ① Place the biochar in a gas containing oxygen at a flow rate of 2 L / h, control the temperature at 450°C, and control the reaction (oxygen activation) time at 40 minutes; then, stop ventilation and heating, cool, and obtain oxygen-activated biochar; the oxygen-containing gas is a mixture of oxygen and nitrogen, and the oxygen-containing gas contains 25% oxygen by volume and 75% nitrogen by volume.

[0078] Example 3

[0079] Embodiment 3 is substantially the same as Embodiment 1, except that:

[0080] ① Place the biochar in a gas containing oxygen at a flow rate of 20 L / h, control the temperature at 450°C, and control the reaction (oxygen activation) time at 40 minutes; then, stop ventilation and heating, cool, and obtain oxygen-activated biochar; the oxygen-containing gas is a mixture of oxygen and nitrogen, and the oxygen-containing gas contains 25% oxygen by volume and 75% nitrogen by volume.

[0081] Example 4

[0082] Embodiment 4 is substantially the same as Embodiment 1, except that:

[0083] ② The oxygen-activated biochar obtained in step ① is mixed with magnesium chloride in a mixing ratio of 1:0.1 in terms of the mass ratio of oxygen-activated biochar to magnesium contained in magnesium chloride. A certain amount of water is added to the mixture (the mass volume ratio of oxygen-activated biochar to water is 1 g:15 mL). After mixing evenly by stirring, the mixture is dried at 70°C for 8 h to a slurry state. The slurry state mixture is then heated and dried at 130°C for 1.5 h, and then pyrolyzed at 500°C in a nitrogen atmosphere (flow rate of 8 L / h) for 1.5 h. The obtained material is rinsed with clean water and dried to obtain magnesium oxide / oxygen-activated biochar.

[0084] Example 5

[0085] Example 5 is substantially the same as Example 1, except that:

[0086] ③ The magnesium oxide / oxygen activated biochar obtained in step ② is immersed in a glutamate solution (glutamate aqueous solution) and ultrasonicated for 5 minutes, then oscillated at 40°C for 8 minutes, and then the obtained mixed solution is dried at 95°C, rinsed with clean water and dried to obtain a biochar composite adsorbent; wherein the mass ratio of the magnesium oxide / oxygen activated biochar to the glutamate solution is 1:10, and the mass ratio of the magnesium oxide / oxygen activated biochar to the glutamate contained in the glutamate solution is 1:0.005.

[0087] Example 6

[0088] Embodiment 6 is substantially the same as Embodiment 1, except that:

[0089] ③ The magnesium oxide / oxygen activated biochar obtained in step ② is immersed in a glutamate solution (glutamate aqueous solution) and ultrasonicated for 5 minutes, then oscillated at 40°C for 8 minutes, and then the obtained mixed solution is dried at 95°C, rinsed with clean water and dried to obtain a biochar composite adsorbent; wherein the mass ratio of the magnesium oxide / oxygen activated biochar to the glutamate solution is 1:10, and the mass ratio of the magnesium oxide / oxygen activated biochar to the glutamate contained in the glutamate solution is 1:0.08.

[0090] Example 7

[0091] Example 7 is substantially the same as Example 1, except that:

[0092] ③ The magnesium oxide / oxygen activated biochar obtained in step ② is immersed in a glutamate solution (glutamate aqueous solution) and ultrasonicated for 10 minutes, then oscillated at 40°C for 20 minutes, and then the obtained mixed solution is dried at 95°C, rinsed with clean water and dried to obtain a biochar composite adsorbent; wherein the mass ratio of the magnesium oxide / oxygen activated biochar to the glutamate solution is 1:10, and the mass ratio of the magnesium oxide / oxygen activated biochar to the glutamate contained in the glutamate solution is 1:0.03.

[0093] Comparative Example 1

[0094] Biochar was mixed with magnesium chloride in a mixing ratio of 1:0.1 between the mass ratio of biochar and magnesium contained in magnesium chloride, a certain amount of water was added to the mixture (the mass volume ratio of biochar to water was 1 g:15 mL), and after being mixed evenly by stirring, the mixture was dried at 70°C for 8 h to a slurry state, and the slurry state mixture was heated and dried at 130°C for 1.5 h, and then pyrolyzed at 500°C in a nitrogen atmosphere for 1.5 h to complete the magnesium oxide loading, and the obtained material was rinsed with clean water and dried to obtain magnesium oxide / biochar.

[0095] Comparative Example 2

[0096] Comparative Example 2 is substantially the same as Example 1, except that:

[0097] ① Placing the biochar in a static oxygen-containing gas, and controlling the temperature at 900°C, and the reaction (oxygen activation) time at 120 minutes; then, stopping ventilation and heating, cooling, and obtaining oxygen-activated biochar; the oxygen-containing gas is a mixture of oxygen and nitrogen, and the oxygen-containing gas contains 5% by volume of oxygen and 95% by volume of nitrogen.

[0098] Comparative Example 3

[0099] Comparative Example 3 is substantially the same as Example 1, except that:

[0100] ① Place the biochar in a gas containing oxygen, the flow rate of the oxygen-containing gas is 8 L / h, and the temperature is controlled at 600°C, and the reaction (oxygen activation) time is controlled at 120 minutes; then, stop ventilation and heating, cool, and obtain oxygen-activated biochar; the oxygen-containing gas is a mixture of oxygen and nitrogen, and the oxygen-containing gas contains 5% by volume of oxygen and 95% by volume of nitrogen.

[0101] Comparative Example 4

[0102] Comparative Example 4 is substantially the same as Example 1, except that:

[0103] ① Place the biochar in a gas containing oxygen at a flow rate of 8 L / h, control the temperature at 300°C, and control the reaction (oxygen activation) time at 40 minutes; then, stop ventilation and heating, cool, and obtain oxygen-activated biochar; the oxygen-containing gas is a mixture of oxygen and nitrogen, and the oxygen-containing gas contains 60% oxygen by volume and 40% nitrogen by volume.

[0104] Comparative Example 5

[0105] Comparative Example 5 is substantially the same as Example 1, except that the heavy metal adsorbent in this comparative example is prepared as follows:

[0106] ① Place the biochar in a gas containing oxygen at a flow rate of 8 L / h, control the temperature at 450°C, and control the reaction (oxygen activation) time at 40 minutes; then, stop ventilation and heating, cool, and obtain oxygen-activated biochar; the oxygen-containing gas is a mixture of oxygen and nitrogen, and the oxygen-containing gas contains 25% oxygen by volume and 75% nitrogen by volume.

[0107] ② The oxygen activated biochar obtained in step ① is mixed 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, and a certain amount of water is added to the mixture (the mass volume ratio of oxygen activated biochar to water is 1g:15mL), and after stirring to mix it evenly, glutamic acid solution (glutamic acid aqueous solution) is added and ultrasonicated for 5 minutes, and then oscillated at 40°C for 8 minutes, and then dried at 70°C for 8 hours until it is slurry, and the slurry mixture is then heated at a temperature of 130°C. After heating and drying for 1.5 hours, the material is pyrolyzed in a mixed gas of oxygen and nitrogen (flow rate of 8 L / h) at a temperature of 500°C for 1.5 hours, and the obtained 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 oxygen-activated biochar to glutamate solution is 1:10, and the mass ratio of the oxygen-activated biochar to glutamate contained in the glutamate solution is 1:0.03.

[0108] A physical picture of the biochar composite adsorbent product in Example 1 of the present invention, such as Figure 1 As shown; SEM images of biochar without oxygen activation and biochar after oxygen activation in Example 1 of the present invention, as shown Figure 2 shown; from Figure 2 The results show 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 follows Figure 3 shown; from Figure 3 It can be seen that there are more oxygen-containing functional groups on the surface of oxygen-activated biochar; the SEM images of the magnesium oxide / biochar in Comparative Example 1 of the present invention and the magnesium oxide / oxygen-activated biochar in Example 1 are as follows: Figure 4 shown; from Figure 4 It can be seen that compared with the magnesium oxide loading structure on the original biochar surface, the magnesium oxide loaded on the biochar surface after oxygen activation in the present invention has better dispersibility; Figures 2 to 4 The results show that the oxygen activation method used 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, so that the magnesium oxide can be evenly dispersed on the surface, the adsorption activity is stronger, and more reaction sites can be provided during the subsequent amination, so that the amino group can be grafted on the material surface; SEM images of the biochar composite adsorbent in Example 1 of the present invention at different magnifications, such as Figure 5 shown; from Figure 5 It can be seen that after amino modification, the magnesium oxide support is still well dispersed on the surface of the biochar composite adsorbent; the XRD spectra of the magnesium oxide / oxygen activated biochar in Example 1 of the present invention and the biochar composite adsorbent (amino modified magnesium oxide / oxygen activated biochar) in Example 1 are as follows: Figure 6 shown; from Figure 6 The XRD results also show that magnesium oxide is successfully loaded onto the surface of oxygen-activated biochar. After amino modification, magnesium oxide on the surface of the biochar composite adsorbent is still retained. The FT-IR spectra of magnesium oxide / oxygen-activated biochar in Example 1 of the present invention and the biochar composite adsorbent (amino-modified magnesium oxide / oxygen-activated biochar) in Example 1 are as follows: Figure 7 shown; from Figure 7 The FT-IR spectrum showed that the amino group was successfully modified on the surface of magnesium oxide / oxygen activated biochar. These results indicate that the biochar composite adsorbent material of the present invention uses magnesium oxide as a connecting material, and the amino group is modified on the magnesium oxide material on the surface of the biochar material through the limited reaction of magnesium oxide and amino acids. The composite modified adsorbent material can achieve a more efficient heavy metal removal effect by coupling the complexation of amino groups with heavy metals with the precipitation of magnesium oxide, ion exchange and the like.

[0109] The present invention uses the adsorbents finally prepared in each embodiment and each comparative example to treat heavy metal wastewater. The method for treating heavy metal wastewater is: using each adsorbent coupled with carbonate to treat heavy metal wastewater, specifically: using Figure 8The device shown in the figure is carried out; first, the heavy metal wastewater is placed in a tank body, and an adsorbent is added to the bottom of the tank body, and an electric stirring device is used for stirring; after 20 minutes of stirring, a carbonate solution (sodium carbonate aqueous solution) with a concentration of 50mmol / L is introduced at a uniform speed through a carbonate solution filling device under the control of a flow rate control valve, and the stirring treatment is carried out for 300 minutes; when treating the heavy metal wastewater, the amount of the sodium carbonate is such that the molar ratio of the carbonate ions contained in the sodium carbonate to the heavy metal ions (such as Pb, Cd, Cu, Ni or Zn) contained in the heavy metal wastewater is 1.2:1; the heavy metal ions (such as Pb, Cd, Cu, Ni or Zn) contained in the heavy metal wastewater ) is 100mmol / L; when treating Pb heavy metal wastewater, the amount of the adsorbent is such that the concentration of the adsorbent in the heavy metal wastewater is 100ppm; when treating Cd heavy metal wastewater, the amount of the adsorbent is such that the concentration of the adsorbent in the heavy metal wastewater is 200ppm; when treating Cu heavy metal wastewater, the amount of the adsorbent is such that the concentration of the adsorbent in the heavy metal wastewater is 100ppm. The removal rates of heavy metal wastewater treated by coupling carbonate in each embodiment and each comparative example are shown in Table 1. The dosage and treatment time required for the adsorbent in each embodiment and each comparative example to meet the standard effluent concentration are shown in Table 1.

[0110] Table 1

[0111]

[0112]

[0113] In Table 1, the method of pumping 5% carbon dioxide in "using the biochar composite adsorbent in Example 1 + pumping 5% carbon dioxide" is carried out with reference to the method in CN 113087065 A, and the dosage of other adsorbents and the concentration of heavy metal ions are the same as those in other embodiments; when CO is introduced 2 When CO 2 It is acidic, requiring a larger amount of adsorbent to be added, and the time required for the gas to pass through the liquid membrane into the solution and take effect may also be reduced.

[0114] The removal rate results of heavy metal wastewater treatment using MgO, carbonate, the biochar composite adsorbent in Example 1 (abbreviated as adsorbent in the figure), and the biochar composite adsorbent coupled with carbonate are shown in the figure. Fig.11 shown; from Fig.11The results show that, by comparing the treatment effects of using biochar composite adsorbent alone, carbonate solution alone and the coupling of the two on low-concentration heavy metal wastewater, the biochar composite adsorbent used in the method of the present invention is better than the unsupported MgO adsorbent, and after being combined with the addition of carbonate, the treatment effect and rate are significantly improved; the method of the present invention can effectively improve the removal capacity and rate of heavy metal ions, and after coupling the addition of biochar composite adsorbent and carbonate precipitation, the removal rate and removal rate of heavy metal ions are significantly improved, and heavy metal ions (such as Cu, Ni and Zn ions) that cannot be treated by a single method are also effectively treated; when the dosage of biochar composite adsorbent is 100ppm / 200ppm / 100ppm, and the molar ratio of carbonate to heavy metal ions is 1.2:1, the treated Pb and Cu both meet the emission standards, and the removal rate of Cd is also effectively improved; Fig.11 When the results were tested, the initial concentrations of different heavy metal ions were all 100mmol / L, the amount of MgO added was equal to the MgO contained in the biochar composite adsorbent, the dosage of the biochar composite adsorbent added to treat Pb / Cd / Cu / Ni / Zn wastewater was 100ppm / 200ppm / 100ppm / 200ppm / 200ppm, respectively, the molar ratio of carbonate to heavy metal ions was 1.2:1, and when the biochar composite adsorbent was coupled with carbonate to treat heavy metal wastewater, the dosage of the biochar composite adsorbent and carbonate was halved (when the method of the present invention is used to treat heavy metal wastewater, compared with a single method, the dosage of the biochar composite adsorbent is halved to 50ppm / 100ppm / 50ppm / 100ppm / 100ppm, respectively, and the molar ratio of carbonate to heavy metal ions in carbonate is halved to 0.6:1). The present invention directly uses magnesium oxide adsorbent and uses the biochar composite adsorbent in Example 1 to couple carbonate to adsorb lead and cadmium. The SEM picture is as follows, Fig.12 shown; from Fig.12 The results show that after adsorption, compared with the direct use of magnesium oxide adsorbent, the lead and cadmium precipitates attached to the surface of the biochar composite adsorbent after the method of the present invention is used to remove lead and cadmium, and the solid size is significantly increased, making it easier to remove from the water body; in particular, Figure 6 , Fig.11 and Fig.12 The preparation of the magnesium oxide adsorbent used in the process is as follows: magnesium chloride is added to water (the mass volume ratio of magnesium chloride to water is 1 g:15 mL), and after mixing them evenly by stirring, the mixture is dried at 70°C for 8 hours to a slurry state, and the slurry state mixture is heated and dried at a temperature of 130°C for 1.5 hours, and then pyrolyzed at a temperature of 500°C in an air atmosphere for 1.5 hours. The obtained material is rinsed with clean water and dried to obtain magnesium oxide.

[0115] Parts of the present invention that are not described in detail are well known to those skilled in the art.

[0116] 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 embodiments of the present invention.

Claims

1. A method for treating heavy metal wastewater using a biochar composite adsorbent coupled with carbonate, characterized in that: The method comprises: treating heavy metal wastewater by coupling carbonate with biochar composite adsorbent; The preparation of the biochar composite adsorbent comprises the following steps: (1) activating 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) mixing the oxygen-activated biochar and the magnesium salt uniformly with water to obtain a mixture, and then drying and pyrolyzing the mixture to obtain magnesium oxide / oxygen-activated biochar; the mass ratio of the oxygen-activated biochar to the magnesium contained in the magnesium salt is 1:(0.02-0.3); (3) The magnesium oxide / oxygen activated biochar is immersed in an amino acid solution and subjected to ultrasonic treatment, and then subjected to oscillation treatment and drying to obtain a biochar composite adsorbent; the mass ratio of the magnesium oxide / oxygen activated biochar to the amino acid solution is 1:(5-15); 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).

2. The method according to claim 1, characterized in that: The method further comprises a step of pre-treating the heavy metal wastewater before treating the heavy metal wastewater with the biochar composite adsorbent coupled with carbonate, wherein the pre-treatment comprises: adjusting the pH value of the heavy metal wastewater to not less than 3 after sedimentation and filtration.

3. The method according to claim 1, characterized in that: The method is carried out using an intermittent adsorption treatment device or a filter tank continuous flow treatment device or a continuous flow semi-fluidized bed treatment device; The carbonate is one or more of sodium carbonate, sodium bicarbonate, potassium carbonate and potassium bicarbonate. When treating heavy metal wastewater, the carbonate is added to the heavy metal wastewater in the form of a carbonate solution, and the concentration of the carbonate solution is 10-100 mmol / L; When treating heavy metal wastewater, the amount of the biochar composite adsorbent used is such that the concentration of the biochar composite adsorbent in the heavy metal wastewater is 50-1000 ppm.

4. The method according to claim 1, characterized in that: When treating heavy metal wastewater, the amount of the carbonate used is such that the molar ratio of carbonate ions contained in the carbonate to heavy metal ions contained in the heavy metal wastewater is (1-2):

1.

5. The method according to any one of claims 1 to 3, characterized in that: In step (1): the flow rate of the gas does not exceed 10 L / h.

6. The method according to any one of claims 1 to 3, characterized in that: The biochar is obtained by pre-treating and carbonizing biomass materials.

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

8. The method according to claim 6, characterized in that: The biomass material is a lignocellulose biomass material.

9. The method according to claim 8, characterized in that: The lignocellulosic biomass material is one or more of straw, grass leaves and wood materials, and the straw is corn straw.

10. The method according to claim 6, 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 hours.

11. The method according to any one of claims 1 to 3, characterized in that In step (2): The magnesium salt is magnesium chloride and / or magnesium sulfate; The drying is firstly drying at 60-80° C. for 6-12 hours, and then drying at 120-150° C. for 1-2 hours.

12. The method according to any one of claims 1 to 3, characterized in that In step (2): The pyrolysis temperature is 400-600° C., and the pyrolysis time is 1-2 hours.

13. The method according to any one of claims 1 to 3, characterized in that In step (2): The pyrolysis is carried out in a mixed gas containing oxygen and an inert gas, wherein the volume percentage of oxygen in the mixed gas is 5-12%.

14. The method according to any one of claims 1 to 3, characterized in that In step (3): The mass ratio of the magnesium oxide / oxygen activated biochar to the amino acid solution is 1:

10.

15. The method according to any one of claims 1 to 3, characterized in that In step (3): The amino acids contained in the amino acid solution are glutamic acid and / or glycine; The ultrasonic treatment time is 3 to 6 minutes; The temperature of the shaking treatment is 30-50° C., and the time of the shaking treatment is 5-10 min.

16. The method according to any one of claims 1 to 3, characterized in that In step (3): The drying temperature is 85-105°C.

17. A device for treating heavy metal wastewater using a biochar composite adsorbent coupled with carbonate, characterized in that: The device is a filter tank type continuous flow treatment device, which includes a heavy metal wastewater introduction device, a continuous flow reactor and a carbonate filling device; The heavy metal wastewater introduction device comprises a water inlet pipe and a water distributor connected to the water inlet pipe, the water distributor is located at the top of the continuous flow reactor, the heavy metal wastewater is introduced into the continuous flow reactor through the water distributor, and a water inlet control valve is arranged on the water inlet pipe; The continuous flow reactor has a filter inside, the left and right ends of the filter are connected to the inner wall of the continuous flow reactor, and a biochar composite adsorbent filling area is arranged above the filter, and the biochar composite adsorbent is the biochar composite adsorbent according to claim 1; The carbonate filling device comprises a carbonate solution storage tank, a water pump and a carbonate solution injection pipeline connected to the carbonate solution storage tank via the water pump, and the carbonate solution injection pipeline extends into the biochar composite adsorbent filling area inside the continuous flow reactor.

18. The device according to claim 17, characterized in that: The distance between the filter and the top of the continuous flow reactor is 2 to 5 times the distance between the filter and the bottom of the continuous flow reactor; the bottom of the continuous flow reactor is connected with a water outlet pipe.

19. The device according to claim 17, characterized in that: A carbonate solution control valve is arranged between the water pump and the carbonate solution injection pipeline, and the carbonate solution control valve is located outside the continuous flow reactor.

20. The device according to claim 17, characterized in that: The side wall of the carbonate solution injection pipe is provided with a plurality of openings for injecting carbonate solution.

21. A device for treating heavy metal wastewater using a biochar composite adsorbent coupled with carbonate, characterized in that: The device is a continuous flow semi-fluidized bed treatment device, which includes a stirring and mixing device, a semi-fluidized bed reaction device and a liquid storage tank from left to right; a stirrer is arranged inside the stirring and mixing device, the upper end of the stirring and mixing device is connected to a heavy metal wastewater inlet pipe, and the lower end of the stirring and mixing device is connected to a carbonate solution inlet pipe; A rectifying plate is provided near the bottom of the semi-fluidized bed reaction device, an intercepting filter is provided above the semi-fluidized bed reaction device, and a semi-fluidized bed reaction zone containing a biochar composite adsorbent is provided between the rectifying plate and the intercepting filter; the biochar composite adsorbent is the biochar composite adsorbent according to claim 1; The stirring and mixing device is connected to the semi-fluidized bed reaction device via a sampling pump, and the stirring and mixing device mixes the heavy metal wastewater and the carbonate solution and then enters the semi-fluidized bed reaction zone via the sampling pump and the rectifying plate of the semi-fluidized bed reaction device; The semi-fluidized bed reaction device and the liquid storage tank are connected via a filtering device; The bottom of the liquid storage tank is provided with a sampling port and a water outlet.

22. The device according to claim 21, characterized in that: The bottom of the liquid storage tank is also provided with a reflux pipe connected to the stirring and mixing device.

23. The device according to claim 22, characterized in that: A reflux pump is arranged on the pipeline of the reflux pipe.

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