A thiol-modified biochar, a preparation method, a regeneration method and an application thereof

Abstract

This invention discloses a thiol-modified biochar, its preparation method, regeneration method, and applications. This invention utilizes the thiol group to modify Hg... 2+ Pb 2+ Cd 2+ Highly selective adsorption is achieved through strong coordination and complexation of heavy metals; biochar prepared from agricultural waste costs only 10%–20% of commercial activated carbon, the amount of thiolizing agent is controllable, and the overall material cost is low; the strong coordination of thiol groups to soft acid heavy metals is unaffected by Ca²⁺. + Mg² + It eliminates interference from a large number of coexisting ions; the acidic thiourea solution can be efficiently regenerated at room temperature without damaging the thiol structure, allowing for multiple cycles and reduced operating costs; and the heavy metals in the eluent can be recovered and utilized, achieving resource utilization.

Description

Technical Field

[0001] This invention relates to the field of urea ammonia production wastewater treatment technology, and in particular to a mercapto-modified biochar, its preparation method, regeneration method and application. Background Technology

[0002] During the ammonia production process from urea hydrolysis in coal-fired power plants, wastewater often contains trace amounts of highly toxic heavy metal ions, such as Hg, due to impurities in the urea raw materials, corrosion of equipment and pipelines, and introduction of these substances by process water. 2+ Pb 2+ Cd 2+ Cu 2+ Zn 2+ Ni 2+ Although the volume of this type of wastewater is small (0.5-1 ton per week), the long-term accumulation of heavy metal ions can still cause serious pollution to the receiving water bodies or soil. Conventional chemical precipitation methods (such as hydroxide precipitation and sulfide precipitation), while simple to operate, have limited treatment precision, especially for Hg. 2+ Amphoteric metals are prone to redissolution when pH fluctuates; ion exchange methods offer good selectivity, but the resin is easily contaminated by organic matter in wastewater, and the regeneration wastewater is difficult to treat; activated carbon, commonly used in adsorption methods, has no selectivity for heavy metals and can tolerate coexisting ions (such as Na+). + Ca 2+ They will strongly compete for adsorption sites, leading to a significant decrease in the removal rate of heavy metals.

[0003] Therefore, there is an urgent need to develop a highly efficient treatment material and technology that is highly selective, renewable, and widely applicable for treating low concentrations of heavy metals (<10 mg / L) in urea-to-ammonia wastewater. Summary of the Invention

[0004] The present invention aims to at least partially solve one of the technical problems in the related art.

[0005] Therefore, embodiments of the present invention propose a thiol-modified biochar, its preparation method, regeneration method, and applications. The present invention utilizes the thiol group to modify Hg... 2+ Pb 2+ Cd 2+ The strong coordination complexation of heavy metals enables highly selective adsorption, and the adsorbent is gently regenerated and the heavy metals are recycled through acidic thiourea solution.

[0006] In a first aspect, the present invention provides a method for preparing thiol-modified biochar, comprising the following steps:

[0007] (1) After removing impurities, washing, drying and pulverizing the biochar raw material, the pulverized biochar raw material is obtained; (2) The pulverized biochar raw material is pyrolyzed to obtain biochar, which is then washed, impurities removed, and dried for later use. (3) Add the coupling agent to the biochar dispersion to adjust the pH to acidic, and stir and reflux the reaction under water bath conditions; (4) After the reaction is complete, the thiol-modified biochar is obtained by filtration, washing and drying.

[0008] Furthermore, the biochar raw material includes at least one of agricultural waste, forestry waste, and urban sludge.

[0009] Furthermore, in step (1), the pulverization process involves first pulverizing the biochar raw material to 2-5 cm, then pulverizing it using a high-speed pulverizer and passing it through a 60-mesh sieve.

[0010] Furthermore, in step (2), the pyrolysis process involves raising the temperature from room temperature to 500-700°C at a rate of 5-10°C / min under inert gas protection and holding it at that temperature for 1-3 hours.

[0011] Furthermore, the biochar dispersion is obtained by dispersing biochar in a mixed solvent of anhydrous ethanol and water with a volume ratio of 1:1 to 4:1, and the solid-liquid ratio of the biochar dispersion is 1:5 to 1:20.

[0012] Furthermore, the amount of the coupling agent added is 20% to 60% of the biochar mass, and the coupling agent includes at least one of 3-mercaptopropyltrimethoxysilane and 3-mercaptopropyltriethoxysilane.

[0013] Furthermore, in step (3), adjusting the pH to acidity involves using glacial acetic acid or dilute hydrochloric acid to adjust the pH to 4-5.

[0014] Furthermore, the stirring and reflux reaction in step (3) is a mechanical stirring and reflux reaction in a water bath at 60~80℃ for 4~8h.

[0015] Secondly, the present invention provides a thiol-modified biochar prepared by the method proposed in the first aspect above, wherein the thiol-modified biochar has a thiol grafting amount of 0.5~1.5 mmol / g.

[0016] Thirdly, the present invention provides a method for regenerating thiol-modified biochar prepared by the method proposed in the first aspect above, or a method for regenerating thiol-modified biochar proposed in the second aspect above, comprising the following steps: A regenerant comprising thiourea and hydrochloric acid is prepared, wherein the concentration of thiourea in the regenerant is 0.1~0.5 mol / L and the concentration of hydrochloric acid is 0.05~0.2 mol / L; The regenerated adsorbent and eluent are obtained by eluting the saturated thiol-modified biochar with the regenerator. The regenerated adsorbent is washed and recycled, and the eluent is subjected to heavy metal recovery treatment.

[0017] Fourthly, this invention proposes the application of thiol-modified biochar prepared by the method proposed in the first aspect above, or thiol-modified biochar proposed in the second aspect above, as a heavy metal adsorbent in the treatment of urea-to-ammonia wastewater.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention utilizes the thiol group to target Hg 2+ Pb 2+ Cd 2+ Highly selective adsorption is achieved through strong coordination and complexation of heavy metals; biochar prepared from agricultural waste costs only 10%–20% of commercial activated carbon, the amount of thiolizing agent is controllable, and the overall material cost is low; the strong coordination of thiol groups to soft acid heavy metals is unaffected by Ca²⁺. + Mg² + It eliminates interference from a large number of coexisting ions; the acidic thiourea solution can be efficiently regenerated at room temperature without damaging the thiol structure, allowing for multiple cycles and reduced operating costs; and the heavy metals in the eluent can be recovered and utilized, achieving resource utilization. Attached Figure Description

[0019] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein: Figure 1 This is a flowchart of the preparation method of the mercapto-modified biochar of the present invention; Figure 2 This is a schematic diagram of the adsorption, regeneration, and heavy metal recovery process of the thiol-modified biochar of the present invention. Detailed Implementation

[0020] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0021] The following description, in conjunction with the accompanying drawings, describes the thiol-modified biochar proposed in this invention, its preparation method, regeneration method, and applications.

[0022] like Figure 1 As shown, the method for preparing thiol-modified biochar of the present invention includes the following steps: (1) After removing impurities, washing, drying and pulverizing the biochar raw material, the pulverized biochar raw material is obtained; (2) The pulverized biochar raw material is pyrolyzed to obtain biochar, which is then washed, impurities removed, and dried for later use; (3) Add the coupling agent to the biochar dispersion to adjust the pH to acidic, and stir and reflux the reaction under water bath conditions; (4) After the reaction is complete, the thiol-modified biochar is obtained by filtration, washing and drying.

[0023] Step (1) is the pretreatment process of biochar raw materials, in which the biochar raw materials are removed of impurities, washed, dried and then crushed to obtain crushed biochar raw materials. The biochar raw materials include at least one of agricultural waste, forestry waste and urban sludge. Agricultural waste includes rice straw, corn straw, wheat straw and peanut shells, etc., and forestry waste includes sawdust and fruit shells, etc. Rice straw is preferred as the biochar raw material because it has low silicon content, high volatile matter and is easy to form a porous structure.

[0024] The impurity removal process involves manually picking or air-classifying to remove inert impurities such as stones, metals, and plastics mixed in with the raw materials, preventing these impurities from contaminating the biochar or damaging the pyrolysis equipment during the pyrolysis process. The washing process involves repeatedly rinsing the biochar raw materials 2-3 times with tap water or deionized water, soaking for 10-15 minutes each time before draining. The purpose of washing is to remove dirt, dust, soluble salts, etc., adhering to the surface of the raw materials, avoiding excessive ash content that could affect the pore structure and adsorption performance of the biochar. The drying process involves drying at 105±5℃ for 12-24 hours until constant weight is achieved (the difference in mass between two adjacent weighings is less than 0.5%).

[0025] The crushing process involves first crushing the biochar raw material into small pieces of 2-5cm, then further crushing it using a high-speed crusher and passing it through a 60-mesh sieve.

[0026] Step (2) is the pyrolysis process of biochar. The crushed biochar raw material is pyrolyzed to obtain biochar, which is then washed, impurities removed, and dried for later use.

[0027] The equipment for pyrolysis is a tubular resistance furnace or a rotary pyrolysis furnace. The pyrolysis process involves raising the temperature from room temperature to 500-700℃ at a rate of 5-10℃ / min under inert gas protection and holding it at that temperature for 1-3 hours. After pyrolysis, the temperature is naturally cooled to room temperature in an inert gas atmosphere, wherein the inert gas is nitrogen or argon and the flow rate of the inert gas is 100-300 mL / min.

[0028] After cooling to room temperature, the biochar was removed and washed with 0.1 mol / L hydrochloric acid for 30-40 min to remove ash and soluble impurities. It was then washed with deionized water until neutral and dried at 105±5℃ for 6-12 h for later use. The specific surface area of ​​the prepared biochar can reach 200-500 m² / g, and the total pore volume is 0.1-0.3 cm³ / g.

[0029] Steps (3) and (4) are the process of thiol grafting modification. The coupling agent is added to the dispersion of biochar to adjust the pH to acidic. The reaction is carried out by stirring and reflux under water bath conditions. After the reaction is completed, the biochar is obtained by filtration, washing and drying.

[0030] First, a biochar dispersion was prepared by dispersing biochar in a mixed solvent of anhydrous ethanol and water at a volume ratio of 1:1 to 4:1, with a solid-liquid ratio of 1:5 to 1:20. Then, a coupling agent was added, and the pH was adjusted to 4 to 5 using glacial acetic acid or dilute hydrochloric acid to promote silane hydrolysis. The reaction was carried out under reflux with mechanical stirring in a water bath at 60 to 80°C for 4 to 8 hours. The amount of coupling agent added was 20% to 60% of the biochar mass, and the coupling agent included at least one of 3-mercaptopropyltrimethoxysilane and 3-mercaptopropyltriethoxysilane. After the reaction was completed, the mixture was separated by filtration and washed 3 to 4 times each with anhydrous ethanol and deionized water, with each wash volume being 5 to 10 times the solid mass. Finally, the mixture was vacuum dried at 60±5°C for 12 to 24 hours to obtain thiol-modified biochar.

[0031] The thiol-modified biochar of the present invention is prepared by the method of the present invention, and the thiol grafting amount of the thiol-modified biochar is 0.5~1.5 mmol / g.

[0032] In the treatment of urea-to-ammonia wastewater, the thiol-modified biochar of this invention is used as a heavy metal adsorbent, utilizing the thiol groups to adsorb Hg. 2+ Pb 2+ Cd 2+ The strong coordination complexation of heavy metals enables highly selective adsorption.

[0033] When thiol-modified biochar is used as an adsorbent, it can be operated in either a fixed-bed adsorption or a stirred-tank adsorption mode. Fixed-bed adsorption is suitable for continuous treatment. The thiol-modified biochar is packed into a vertical glass or plexiglass column with a packing height of 10–50 cm and an empty bed contact time (EBCT) of 5–30 min. Wastewater flows through the packing layer from top to bottom or bottom to top. The concentration of heavy metals in the effluent is monitored online. When the effluent concentration approaches the discharge standard limit, the influent is stopped, and the process begins regeneration. Stirred-tank adsorption is suitable for intermittent treatment. A calculated amount of modified biochar and wastewater is added to the reactor, the reaction is stirred until equilibrium is reached, and the adsorbent is separated by settling or filtration. The effluent is then discharged or proceeds to the next process.

[0034] After adsorption saturation, thiol-modified biochar can be regenerated and recycled. The regeneration process includes the following steps: (a) Prepare a regenerant comprising thiourea and hydrochloric acid, wherein the concentration of thiourea in the regenerant is 0.1~0.5 mol / L and the concentration of hydrochloric acid is 0.05~0.2 mol / L; (b) The regenerated adsorbent and eluent are obtained by eluting the saturated thiol-modified biochar with a regenerator. The regenerated adsorbent is washed and recycled, and the eluent is treated for heavy metal recovery.

[0035] Step (a) involves preparing the regenerant. First, the required amounts of thiourea and hydrochloric acid are calculated. Water is then added to bring the volume to the desired level to obtain the regenerant. The concentration of thiourea in the regenerant is 0.1–0.5 mol / L, and the concentration of hydrochloric acid is 0.05–0.2 mol / L. Thiourea can react with Hg... 2+ Pb 2+ They form stable, soluble complexes, such as [Hg(SC(NH2)2)2] 2+ This displaces heavy metals from their adsorption sites; hydrochloric acid provides H+. + This allows partially protonated thiol groups to release heavy metals while preventing metal hydrolysis and precipitation.

[0036] In some embodiments, the regenerant further comprises NaCl and ascorbic acid, wherein the concentration of NaCl is 0.1~0.5 mol / L, and NaCl can increase the ionic strength of the eluent and promote mass transfer; the concentration of ascorbic acid is 0.01~0.05 mol / L, and ascorbic acid acts as a reducing agent to prevent Hg²⁺ from oxidizing. + Reduced to Hg 0 .

[0037] Step (b) is the regeneration process, in which the thiol-modified biochar after adsorption saturation is eluted with a regenerating agent to obtain a regenerated adsorbent and an eluent. The regenerated adsorbent is washed and recycled, and the eluent is treated for heavy metal recovery.

[0038] The sulfur atom in the thiourea molecule pairs with Hg 2+ Soft acid heavy metal ions have extremely strong affinity (soft-soft interaction) and can competitively remove heavy metals already complexed on thiol groups, forming a more stable [Hg(SC(NH2)2)2] 2+ Complex ions, and H + To induce thiolization (-SH→-SH2) + This process further weakens the adsorbent's binding with heavy metals, thereby regenerating the adsorbent. The regenerated adsorbent is then washed and reused. Regular sampling is performed to test the adsorbent's saturated adsorption capacity and its post-regeneration adsorption capacity. When the regeneration efficiency falls below 70%, the adsorbent is replaced, and the elution wastewater is treated for heavy metal recovery.

[0039] After multiple regenerations, the concentration of heavy metals in the eluent accumulates and increases, reaching a level that can be recovered (e.g., Hg). 2+(>500 mg / L). Heavy metals can be recovered using electrodeposition, precipitation, or sulfide precipitation-calcination methods. In the electrodeposition method, the eluent is placed in an electrolytic cell, with a stainless steel plate as the cathode and a titanium-coated ruthenium plate as the anode, at a current density of 50~200 A / m. 2 Electrolysis lasts 2-4 hours. Heavy metals such as mercury and lead are reduced to elemental metals at the cathode, which can be stripped and recycled as valuable products, generating economic benefits. After electrodeposition, the concentration of heavy metals in the solution can be reduced to <10 mg / L, which can be reused to prepare new regenerants or diluted before discharge. In the precipitation method, sulfides (such as Na2S) are added to the eluent to form extremely insoluble sulfide precipitates of heavy metals. Filtering separates the sludge rich in heavy metals, which can be sold to metal smelters. In the sulfide precipitation-calcination method, sulfide precipitates are added first. After washing and drying, the precipitates are calcined at 600-800℃ to convert them into metal oxides with high purity.

[0040] In addition, the clarified liquid after electrodeposition or precipitation can be reused as a regenerant after replenishing with thiourea and hydrochloric acid, achieving regenerant recycling and reducing chemical consumption and wastewater discharge. If the concentration of heavy metals in the final elution is extremely low and has no recovery value, it can be introduced into the plant's wastewater treatment system for treatment and discharge after meeting standards.

[0041] In the regeneration process of saturated thiol-modified biochar, the fixed-bed adsorption operation involves the following steps: After adsorption saturation, the wastewater in the adsorption column is drained, and the column is rinsed with deionized water at a volume of 1-2 times the bed size. Then, a regenerant volume of 1-5 times the bed size is passed counter-currently through the bed at a flow rate of 0.5-2 BV / h, with a residence time of 0.5-2 h. The eluent is collected, and the bed is then washed with deionized water until the pH is neutral, at which point it can be reused for adsorption. The regeneration efficiency can reach 90%-95%, and the adsorption capacity remains above 80% of the initial value after five reuses. Figure 2 As shown, the wastewater in the wastewater storage tank is treated by adsorption with thiol-modified biochar and then discharged as treated water. The heavy metal concentration in the treated water effluent is lower than the Class I standard of the "Integrated Wastewater Discharge Standard" (GB 8978-1996) (e.g., Hg≤0.05 mg / L, Pb≤1.0 mg / L, Cd≤0.1 mg / L). After adsorption saturation, acidic thiourea regenerator is introduced in situ into the fixed bed column (flowing counterclockwise through the bed) to regenerate the adsorbent within the column. The eluent containing heavy metals flows out from the bottom of the column and enters the heavy metal recovery unit. The eluent is used for heavy metal recovery by electrodeposition. After replenishing with thiourea and hydrochloric acid, the regenerated solution after electrodeposition is stored in the regenerator storage tank for reuse as a regenerator.

[0042] In the stirred tank adsorption operation, the saturated adsorbent and regenerator are mixed in a stirred tank at a solid-liquid mass ratio of 1:10 to 1:30, stirred for 30 to 60 minutes, and then filtered and separated. The adsorbent is washed with water and reused.

[0043] The present invention will now be described in detail with reference to specific embodiments.

[0044] Example 1 After removing impurities, washing, and drying rice straw, it is pulverized into small pieces of 2-5 cm. Then, it is further pulverized using a high-speed pulverizer and passed through a 60-mesh sieve to obtain pulverized rice straw. 500 g of pulverized rice straw is placed in a tubular resistance furnace and heated from room temperature to 600°C at a rate of 5°C / min under nitrogen protection at 300 mL / min, and held at this temperature for 2 hours. After pyrolysis, it is naturally cooled to room temperature under a nitrogen atmosphere. The resulting biochar is removed, washed with 0.1 mol / L hydrochloric acid for 30 minutes to remove ash and soluble impurities, then washed with deionized water until neutral, and dried at 105°C for 10 hours for later use.

[0045] Biochar was dispersed in a 1:1 volume ratio of anhydrous ethanol and water to obtain a biochar dispersion with a solid-liquid ratio of 1:10. Then, a coupling agent, 3-mercaptopropyltrimethoxysilane, was added, and the pH was adjusted to 4.5 using glacial acetic acid to promote silane hydrolysis. The reaction was carried out under reflux with mechanical stirring in a 70°C water bath for 6 hours. The amount of coupling agent added was 40% of the biochar mass. After the reaction was complete, the mixture was separated by filtration and washed three times each with anhydrous ethanol and deionized water, with each wash volume being 7 times the solid mass. The mixture was then vacuum dried at 60°C for 20 hours to obtain thiol-modified biochar. Elemental analysis showed that the thiol grafting amount was 0.85 mmol / g. FTIR spectra showed that the modified biochar exhibited a high thiol content at 2570 cm⁻¹. -1 The presence of a characteristic SH absorption peak at the point indicates that the thiol modification is complete.

[0046] Prepare 100 mL of simulated wastewater to mimic the actual water quality characteristics of urea-to-ammonia production wastewater, including Hg. 2+ The concentration was 5.0 mg / L, Pb 2+ The concentration was 10.0 mg / L, Cd 2+ The concentration was 5.0 mg / L, and Ca was added simultaneously. 2+ Concentration of 100 mg / L, Mg 2+ A concentration of 50 mg / L was used as a coexisting interfering ion, and the pH was adjusted to 6.0. 0.1 g of mercapto-modified biochar was added, and adsorption was carried out by shaking at 25 °C for 2 h.

[0047] After filtration, the concentrations of each metal ion were measured, and the adsorption capacity and removal rate were calculated. Among them, Hg... 2+ The removal rate was 99.2%, and the adsorption capacity was 4.96 mg / g; Pb 2+ The removal rate was 98.6%, and the adsorption capacity was 9.86 mg / g; Cd 2+ The removal rate was 97.2%, and the adsorption capacity was 4.86 mg / g. (The text abruptly ends here, seemingly mid-sentence.)2+ (100 mg / L), Mg 2+ Under conditions of (50 mg / L), thiol-modified biochar's effect on Hg 2 + Pb 2+ Cd 2+ The removal rates remained above 97%, indicating that the coexisting alkaline earth metal ions had minimal interference with thiol coordination adsorption. The removal rates of the three heavy metals were in the following order: Hg 2+ (99.2%) > Pb 2+ (98.6%) > Cd 2+ (97.2%), and the order of complexation stability constants of thiol groups with soft Lewis acids and heavy metals (Hg) 2+ >Pb 2+ >Cd 2+ (Consistent)

[0048] The partition coefficient (Kd) was calculated based on the adsorption data: for Hg 2+ The Kd is 124,000 mL / g, which is significant for Pb. 2+ The Kd value was 70,429 mL / g, which is significant for Cd. 2+ The Kd value is 34,714 mL / g, which is significant for Ca. 2+ The Kd is approximately 1,523 mL / g. (Hg) 2+ Kd is approximately Ca 2+ 81 times (nearly two orders of magnitude higher) demonstrates that thiol-modified biochar has a significant effect on Hg. 2+ It exhibits extremely high selectivity. This stems from the fact that the thiol group (-SH) acts as a soft base, reacting with Hg... 2+ Strong soft-soft interactions between (soft Lewis acids), while Ca 2+ Mg 2+ It belongs to the class of hard Lewis acids and has extremely weak binding ability with thiol groups.

[0049] Isothermal adsorption experiments showed that the Langmuir model fit R²>0.99, and the maximum adsorption capacity of mercury reached 125 mg / g, indicating that the adsorption of heavy metals by thiol-modified biochar is monolayer chemisorption (Langmuir model) rather than physisorption.

[0050] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms may refer to different embodiments or examples. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0051] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0052] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for preparing thiol-modified biochar, characterized in that, Includes the following steps: (1) After removing impurities, washing, drying and pulverizing the biochar raw material, the pulverized biochar raw material is obtained; (2) The pulverized biochar raw material is pyrolyzed to obtain biochar, which is then washed, impurities removed, and dried for later use. (3) Add the coupling agent to the biochar dispersion to adjust the pH to acidic, and stir and reflux the reaction under water bath conditions; (4) After the reaction is complete, the thiol-modified biochar is obtained by filtration, washing and drying.

2. The method as described in claim 1, characterized in that, The biochar raw materials include at least one of agricultural waste, forestry waste, and urban sludge.

3. The method as described in claim 1, characterized in that, The pulverization process in step (1) involves first pulverizing the biochar raw material to 2-5 cm, then pulverizing it using a high-speed pulverizer and passing it through a 60-mesh sieve.

4. The method as described in claim 1, characterized in that, In step (2), the pyrolysis process involves raising the temperature from room temperature to 500-700°C at a rate of 5-10°C / min under the protection of an inert gas, and holding the temperature for 1-3 hours.

5. The method as described in claim 1, characterized in that, The biochar dispersion is obtained by dispersing biochar in a mixed solvent of anhydrous ethanol and water with a volume ratio of 1:1 to 4:1, and the solid-liquid ratio of the biochar dispersion is 1:5 to 1:

20.

6. The method as described in claim 1, characterized in that, The amount of the coupling agent added is 20% to 60% of the biochar mass, and the coupling agent includes at least one of 3-mercaptopropyltrimethoxysilane and 3-mercaptopropyltriethoxysilane.

7. The method as described in claim 1, characterized in that, In step (3), adjusting the pH to acidity involves using glacial acetic acid or dilute hydrochloric acid to adjust the pH to 4-5. And / or, the stirring and reflux reaction in step (3) under water bath conditions is a mechanical stirring and reflux reaction in a water bath at 60~80℃ for 4~8h.

8. A thiol-modified biochar, characterized in that, The thiol-modified biochar is prepared by the method described in any one of claims 1 to 7, wherein the thiol grafting amount is 0.5 to 1.5 mmol / g.

9. A method for regenerating thiol-modified biochar, characterized in that, The regeneration process of the thiol-modified biochar prepared by the method of any one of claims 1 to 7 or the thiol-modified biochar of claim 8 includes the following steps: A regenerant comprising thiourea and hydrochloric acid is prepared, wherein the concentration of thiourea in the regenerant is 0.1~0.5 mol / L and the concentration of hydrochloric acid is 0.05~0.2 mol / L; The regenerated adsorbent and eluent are obtained by eluting the saturated thiol-modified biochar with the regenerator. The regenerated adsorbent is washed and recycled, and the eluent is subjected to heavy metal recovery treatment.

10. The application of the thiol-modified biochar prepared by the method according to any one of claims 1 to 7 or the thiol-modified biochar according to claim 8 as a heavy metal adsorbent in the treatment of urea-to-ammonia wastewater.

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