Preparation and Application of a Hydrothermal Biochar / Geopolymer Composite

Abstract

The present invention discloses a method for preparing a hydrothermal biochar / geopolymer composite material. Wheat straw is crushed and mixed evenly with fly ash. Potassium hydroxide solution is added and stirred in a stirring device. Curing produces a biochar / geopolymer composite precursor, which is then subjected to a hydrothermal carbonization process to obtain the hydrothermal biochar / geopolymer composite material. The straw powder, potassium hydroxide, and distilled water content are 5% to 35%, 65% to 85%, and 30% to 90% of the fly ash mass, respectively. The hydrothermal temperature is 220°C to 260°C, the hydrothermal time is 4 hours, and the hydrothermal medium is a 0-2 mol / L potassium hydroxide solution. The resulting hydrothermal biochar / geopolymer composite material exhibits excellent results when used for the adsorption and removal of lead ions in water and in-situ deactivation of lead in soil. This method has the advantages of simple process, low cost, low energy consumption, resource utilization of solid waste, and environmental friendliness. It has broad application prospects in heavy metal-contaminated water and soil.

Description

Technical Field

[0001] The present invention belongs to the field of solid waste resource utilization and heavy metal contaminated water and soil remediation, and specifically relates to a method for preparing a hydrothermal biochar / geopolymer composite material, and the use of the prepared hydrothermal biochar / geopolymer composite material for adsorbing lead ions in water and in-situ passivating lead in soil. Background Art

[0002] Biochar is a stable, highly aromatic solid substance mainly composed of carbon, produced by thermochemical conversion of biomass raw materials such as straw, wood, livestock and poultry manure, and sludge under oxygen-free (limited) conditions. It also contains hydrogen (H), oxygen (O), nitrogen (N), sulfur (S), ash, and some trace elements. Currently, the preparation methods of biochar mainly include pyrolysis, gasification, and hydrothermal carbonization [1-3]. Due to its large specific surface area, rich oxygen-containing functional groups, loose and porous microstructure, high pH and CEC, and strong stability, biochar can adsorb and passivate heavy metals through surface complexation, precipitation, physical adsorption, and cation exchange. Therefore, it has broad application prospects in the adsorption and removal of heavy metals in water bodies and the passivation of heavy metals in soils [4-6]. However, the adsorption and passivation performance of raw biochar for heavy metals is not ideal, and it needs to be modified or combined with other materials [7].

[0003] Geopolymers, referred to as geopolymers, are a type of amorphous to semi-crystalline inorganic polymerized aluminosilicates produced by dissolution and polycondensation of siliceous and aluminous raw materials such as calcined clay minerals or fly ash under the action of a strong alkaline activator. 4- Tetrahedron and [AlO4] 5- The tetrahedrons are connected by covalent bonds formed by shared vertex oxygen atoms to form a zeolite-like porous anionic skeleton structure. The molecular structure can be abbreviated as R2O-Al2O3-SiO2-H2O (R = Na, K) [8]. The unique zeolite-like structure of geopolymers gives them ion exchange and adsorption properties similar to zeolites, and they also have good application potential in the treatment of heavy metal pollution in water and soil. Darmayanti et al. [9] reported that the structural order of sodium-type geopolymers is higher than that of potassium-type geopolymers, and therefore has higher Cu 2+ The adsorption capacity can reach 40 mg / g, and the adsorption process conforms to the Langmuir isotherm and pseudo-second-order kinetics. In addition, recent studies have found that geopolymers are converted into zeolites with higher structural order under certain hydrothermal reaction conditions, thereby improving their pore structure and adsorption performance [10,11]. The simultaneous preparation of hydrothermal biochar and hydrothermal conversion of geopolymers can not only utilize the alkaline environment of geopolymers to modify biochar, but also save energy, achieving two goals at one stroke.

[0004] Through a systematic review of a large number of domestic and foreign patents and literature, no relevant reports were found on hydrothermal biochar / geopolymer composites and their adsorption and removal of lead in water and in situ passivation of soil lead.

[0005] The following are the references given by the inventor:

[0006] 【1】Zhang Changhe, Wang Jianlong, Li Hongxin, Su Huihui, Sun Zheng, Wang Xueting. Research progress on biochar remediation of polycyclic aromatic hydrocarbons contaminated soil [J / OL]. Applied Chemical Industry: 1-7 [2023-03-13].

[0007] 【2】Zhang Xiaoying, Chen Su, Liu Ying, Feng Tianzhen, Chao Lei. Research progress on biochar aging and its effects on heavy metal adsorption and fixation[J / OL]. Journal of Agricultural Resources and Environment: 1-15[2023-03-13].

[0008] 【3】Jiang Jing, Wu Yi, Sheng Guangyao. Research progress on biochar modification and its removal of pollutants in water[J]. Functional Materials, 2022, 53(12): 12073-12084.

[0009] 【4】Guo Dandan, Zhai Xiaowei. Study on the adsorption performance and mechanism of modified biochar for Pb~(2+) and Cd~(2+)[J / OL]. Applied Chemical Industry: 1-8[2023-03-14].

[0010] 【5】Song Shaohua, Xu Jinlan, Song Xiaoqiao, Yu Yuan. Research progress on remediation of heavy metal polluted water bodies with magnetic biochar[J]. Functional Materials, 2023, 54(01): 1058-1069.

[0011] 【6】Zong Dapeng, Tian Wen, Li Weiyu, Zhang Mengyan, Xu Wumei, Xiang Ping. Research progress on the mechanism of passivation of heavy metals in typical soils by biochar from agricultural and forestry wastes [J / OL]. Journal of Ecotoxicology: 1-18 [2023-03-14].

[0012] 【7】Huang Shiyuan, Lin Senhuan, Deng Jian, Wang Guohua, Li Yingjie. Research progress of clay mineral / biochar composites in water treatment[J]. Applied Chemical Industry, 2022, 51(11): 3362-3368.

[0013] 【8】Davidovits J. Geopolymers: inorganic polymeric new materials [J]. Journal of Thermal Analysis and Calorimetry, 1991, 37(8): 1633-1656.

[0014] 【9】Darmayanti L, Kadja GT, Notodarmojo S, Damanhuri E, MuktiRR. Structural alteration within fly ash-based geopolymers governing theadsorption of Cu 2+ from aqueous environment: Effect of alkali activation[J]. Journal of Hazardous Materials, 2019, 377: 305-314.

[0015]

[10] He PY, Zhang YJ, Zhang XM, Chen H. Diverse zeolites derived from acirculating fluidized bed fly ash based geopolymer for the adsorption of leadions from wastewater. Journal of Cleaner Production, 2021, 312, 127769.

[0016]

[11] Zhang Yaojun, Zhang Ye, Han Zhichao, He Panyang, Chen Hao. Research progress of in situ conversion of geopolymers into zeolite molecular sieves[J]. Materials Review, 2020, 34(23): 23033-23041. Summary of the Invention

[0017] The purpose of the present invention is to provide a method for preparing a hydrothermal biochar / geopolymer composite material, and to apply the prepared composite material to improve water environment or soil environment.

[0018] In order to achieve the above tasks, the present invention adopts the following technical solutions:

[0019] A method for preparing a hydrothermal biochar / geopolymer composite material is characterized in that fly ash, straw powder and an aqueous solution of potassium hydroxide are placed in a stirring device for mixing to form a uniformly mixed slurry, and the slurry is formed and cured to obtain a biochar / fly ash geopolymer precursor. The amount of straw powder, potassium hydroxide and water is based on the mass of the fly ash; the amount of straw powder is 5% to 35% of the mass of the fly ash, the amount of potassium hydroxide is 65% to 85% of the mass of the fly ash, and the amount of water is 30% to 90% of the mass of the fly ash. The hydrothermal temperature is set at 220° C. to 260° C., and the hydrothermal time is set at 4 hours.

[0020] The specific steps include:

[0021] (1) Weigh fly ash according to the formula and place it in an automatic mixer with a set program;

[0022] (2) Weigh the straw according to the formula, dry it, crush it with a grinder, pass it through a 100-mesh sieve, add it to the automatic mixer described in step (1), and dry-mix it evenly;

[0023] (3) Weighing solid potassium hydroxide according to the formula;

[0024] (4) Weigh water according to the formula and dissolve solid potassium hydroxide in water;

[0025] (5) After the potassium hydroxide solution is cooled to room temperature, it is added to the mixer described in step (2) and stirred for 10 minutes to obtain a uniform slurry;

[0026] (6) The slurry was placed in a plastic film sealed bag, placed in a constant temperature box at 80°C for 8 hours, then taken out and cured at room temperature for 48 hours to obtain a biochar / geopolymer composite material precursor;

[0027] (7) The precursor of step (6) is placed in a hydrothermal reactor, potassium hydroxide solution is measured at a solid-liquid ratio of 1:10, added to the reactor, and hydrothermal carbonization is performed at a temperature of 220°C to 260°C for 4 hours;

[0028] (8) The product obtained in step (7) was rinsed alternately with distilled water and anhydrous ethanol, filtered until the filtrate was neutral, placed in a constant temperature drying oven at 105° C. and dried for 12 h, and granulated to obtain particles with a particle size of 0.250 mm to 0.600 mm, which is the hydrothermal biochar / geopolymer composite material.

[0029] Experiments conducted by the applicant have shown that the prepared hydrothermal biochar / geopolymer composite material can be used for the adsorption and removal of lead ions in water and the in-situ passivation of lead in soil.

[0030] The specific implementation is as follows:

[0031] (1) A certain amount of hydrothermal biochar / geopolymer composite material is placed in a container with a certain volume and a concentration of C o The Pb(NO3)2 solution was shaken in a water bath constant temperature shaker for 24 hours, centrifuged, and the Pb content in the supernatant was detected by ICP. 2+ concentration, and calculated the removal rate and adsorption amount of lead ions in water by hydrothermal biochar / geopolymer composites;

[0032] (2) A certain amount of hydrothermal biochar / geopolymer composite material particles were added to simulated lead-contaminated soil, mixed evenly, and then distilled water was added to maintain 50% of the field water holding capacity. After 7 days, the particles were taken out and air-dried. The available lead in the soil was then extracted with diethyltriaminepentaacetic acid. The lead ion concentration in the extract was detected by ICP, and the passivation rate of the hydrothermal biochar / geopolymer composite material on soil lead was calculated.

[0033] The innovation of the present invention lies in the ingenious modification of biochar by the alkaline environment of geopolymer, while simultaneously combining the hydrothermal preparation of biochar with the promotion of geopolymer structural transformation to obtain a hydrothermal biochar-fly ash geopolymer composite material for removing or passivating heavy metals. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is the process flow for the preparation and application of hydrothermal biochar / geopolymer composite materials;

[0035] Figure 2 is a scanning electron microscope photograph of the hydrothermal biochar / geopolymer composite material prepared in Preparation Example 2;

[0036] Figure 3 Hydrothermal biochar / geopolymer composites passivate Pb in soil 2+ 's effect diagram.

[0037] Figure 4 It is the adsorption removal rate and adsorption amount of lead ions in water by the hydrothermal biochar / geopolymer composite material in Example 1-3.

[0038] The present invention is further described in detail below with reference to the accompanying drawings and embodiments. DETAILED DESCRIPTION

[0039] In the following examples, the applicant provides examples of the preparation of hydrothermal biochar / geopolymer composite materials and their application in the adsorption and removal of lead ions in water or in-situ passivation of soil lead.

[0040] It should be noted that the following embodiments are only provided for the inventor to better explain the present invention, and the present invention is not limited to these embodiments.

[0041] The main raw materials used in the preparation of hydrothermal biochar / geopolymer composite materials are industrial solid waste fly ash, agricultural solid waste straw powder and potassium hydroxide. Among them, the dosage of straw powder, potassium hydroxide and water is based on the mass of fly ash; the dosage of straw powder is 5% to 35% of the mass of fly ash, the dosage of potassium hydroxide is 65% to 85% of the mass of fly ash, and the dosage of water is 30% to 90% of the mass of fly ash. The hydrothermal temperature is set at 220℃ to 260℃, the hydrothermal time is set at 4h, and the hydrothermal medium is set to distilled water or potassium hydroxide aqueous solution.

[0042] The specific preparation is as follows:

[0043] (1) Wheat straw was collected from local farmland, dried, crushed and then passed through a 100-mesh sieve for later use.

[0044] (2) Fly ash: Grade I fly ash from the Sanmenxia Power Plant in Henan Province was used. The fly ash was dried in an oven at 105°C for 10 h. The main oxide composition (mass percentage) of the fly ash is shown in Table 1.

[0045] Table 1: Oxide composition of fly ash (wt%)

[0046] oxides <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> CaO <![CDATA[Na2O]]> MgO <![CDATA[K2O]]> <![CDATA[SO3]]> <![CDATA[TiO2]]> Loss impurities wt% 52.77 29.14 5.81 4.49 0.48 0.98 2.53 0.81 1.44 0.84 margin

[0047] (3) Potassium hydroxide was purchased from Sinopharm Chemical Reagent Co., Ltd., analytical grade.

[0048] Preparation Example 1:

[0049] Accurately weigh 200g of fly ash raw material and use it as the measurement basis (100%). Using the external blending method, the mass of straw powder is 20% of the mass of fly ash, the amount of potassium hydroxide is 75% of the mass of fly ash, and the mass of water is 50% of the mass of fly ash.

[0050] Before preparation, potassium hydroxide solution is prepared with water and potassium hydroxide.

[0051] The fly ash and straw powder were placed in an automatic mixer, and the prepared potassium hydroxide solution was poured in, mixed and stirred evenly, and a uniform slurry was formed through reaction. The slurry was then placed in a plastic film sealed bag and sealed, placed in a constant temperature box and cured at 80°C for 8 hours, and then taken out and cured at room temperature for 48 hours to obtain a biochar / geopolymer composite material precursor.

[0052] 12 g of the precursor was weighed and placed in a hydrothermal reactor. 120 mL of distilled water was added, and the reaction was carried out at 220°C for 4 h. After the hydrothermal reaction was completed, the precursor was removed and rinsed alternately with distilled water and anhydrous ethanol. The filtrate was filtered until it was neutral. After drying at 105°C for 12 h, it was crushed and passed through a 30-60 mesh standard sieve to obtain particles with a particle size of 0.25 mm to 0.60 mm, which was the hydrothermal biochar / geopolymer composite material (labeled as 30HBCGC-220-0).

[0053] Preparation Example 2:

[0054] Accurately weigh 200g of fly ash raw material and use it as the measurement basis (100%). Using the external blending method, the mass of straw powder is 20% of the mass of fly ash, the amount of solid potassium hydroxide is 75% of the mass of fly ash, and the mass of water is 50% of the mass of fly ash.

[0055] Before preparation, potassium hydroxide solution is prepared with water and potassium hydroxide.

[0056] The fly ash and straw powder were placed in an automatic mixer, and the prepared potassium hydroxide solution was poured in, mixed and stirred evenly, and a uniform slurry was formed through reaction. The slurry was then placed in a plastic film sealed bag and sealed, placed in a constant temperature box and cured at 80°C for 8 hours, and then taken out and cured at room temperature for 48 hours to obtain a biochar / geopolymer composite material precursor.

[0057] 12 g of the precursor was weighed and placed in a hydrothermal reactor. 120 mL of distilled water was added and the reaction was carried out at 240°C for 4 h. After the hydrothermal reaction was completed, the precursor was removed and rinsed alternately with distilled water and anhydrous ethanol. The filtrate was filtered until it was neutral. After drying at 105°C for 12 h, it was crushed and passed through a 30-60 mesh standard sieve to obtain particles with a particle size of 0.25 mm to 0.60 mm, which was the hydrothermal biochar / geopolymer composite material (labeled as 30HBCGC-240-0). Figure 2 This is a scanning electron microscope photograph of the sample prepared in Example 2. Preparation Example 3:

[0058] Accurately weigh 200g of fly ash raw material and use it as the measurement basis (100%). Using the external blending method, the mass of straw powder is 20% of the mass of fly ash, the amount of solid potassium hydroxide is 75% of the mass of fly ash, and the mass of water is 50% of the mass of fly ash.

[0059] Before preparation, potassium hydroxide solution is prepared with water and potassium hydroxide.

[0060] The fly ash and straw powder were placed in an automatic mixer, and the prepared potassium hydroxide solution was poured in, mixed and stirred evenly, and a uniform slurry was formed through reaction. The slurry was then placed in a plastic film sealed bag and sealed, placed in a constant temperature box and cured at 80°C for 8 hours, and then taken out and cured at room temperature for 48 hours to obtain a biochar / geopolymer composite material precursor.

[0061] 12 g of the precursor was weighed and placed in a hydrothermal reactor. 120 mL of distilled water was added and the reaction was carried out at 260°C for 4 h. After the hydrothermal reaction was completed, the precursor was removed and rinsed alternately with distilled water and anhydrous ethanol. The filtrate was filtered until it was neutral. After drying at 105°C for 12 h, it was crushed and passed through a 30-60 mesh standard sieve to obtain particles with a particle size of 0.25 mm to 0.60 mm, which was the hydrothermal biochar / geopolymer composite material (labeled as 30HBCGC-260-0).

[0062] The inventors have experimentally proved that the hydrothermal biochar / geopolymer composite material prepared in the embodiment can efficiently adsorb and remove Pb in water. 2+ and in situ passivation of Pb(II) in soil.

[0063] The specific implementation is as follows:

[0064] (1) A certain amount of hydrothermal biochar / geopolymer composite material is placed in a container with a certain volume and a concentration of C o The Pb(NO3)2 solution was shaken in a water bath constant temperature shaker for 24 hours, centrifuged, and the supernatant was removed and the Pb in it was detected by ICP. 2 + The concentration is C t , and calculate the removal rate and adsorption amount of lead ions in water by hydrothermal biochar / geopolymer composites;

[0065] (2) A certain amount of hydrothermal biochar / geopolymer composite material particles were added to simulated lead-contaminated soil, mixed evenly, and then distilled water was added to maintain 50% of the field water holding capacity. After 7 days, the particles were taken out and air-dried. The available lead in the soil was then extracted with diethyltriaminepentaacetic acid. The lead ion concentration in the extract was detected by ICP, and the passivation rate of the hydrothermal biochar / geopolymer composite material on soil lead was calculated.

[0066] Application Experiment Example 1:

[0067] (1) Adsorption: 0.05 g of the hydrothermal biochar / geopolymer composite material sample (30HBCGC-220-0) prepared in Preparation Example 1 was accurately weighed and added to 100 mL of a 100 mg / L lead nitrate solution. The mixture was shaken in a water bath constant temperature shaker for 24 h and then centrifuged. The Pb content in the supernatant was detected by ICP. 2+ The removal rate and adsorption capacity of lead ions were calculated to be 81.85% and 163.71 mg / g ( Figure 4 );

[0068] (2) In situ passivation: 3.6 g of the hydrothermal biochar / geopolymer composite material sample (30HBCGC-220-0) prepared in Preparation Example 1 was accurately weighed, added to 40 g of simulated lead-contaminated soil, mixed evenly, and then distilled water was added to maintain 50% of the field water holding capacity. After 7 days, the sample was taken out and air-dried. The available lead in the soil was then leached with diethyltriamine pentaacetic acid. The lead ion concentration in the extract was detected by ICP, and the passivation rate for soil lead was calculated to be 45.33% ( Figure 3 ).

[0069] Application Experiment Example 2:

[0070] (1) Adsorption: 0.05 g of the hydrothermal biochar / geopolymer composite material sample (30HBCGC-240-0) prepared in Preparation Example 2 was accurately weighed and added to 100 mL of a 100 mg / L lead nitrate solution. The mixture was shaken in a water bath constant temperature shaker for 24 h and then centrifuged. The Pb content in the supernatant was detected by ICP. 2+The removal rate and adsorption capacity of lead ions were calculated to be 93.88% and 187.76 mg / g respectively. Figure 4 );

[0071] (2) In situ passivation: 3.6 g of the hydrothermal biochar / geopolymer composite material sample (30HBCGC-240-0) prepared in Preparation Example 2 was accurately weighed, added to 40 g of simulated lead-contaminated soil, mixed evenly, and then distilled water was added to maintain 50% of the field water holding capacity. After 7 days, the sample was taken out and air-dried. The available lead in the soil was then leached with diethylenetriaminepentaacetic acid. The lead ion concentration in the extract was detected by ICP, and the passivation rate for soil lead was calculated to be 72.86% ( Figure 3 ).

[0072] Application Experiment Example 3:

[0073] (1) Adsorption: 0.05 g of the hydrothermal biochar / geopolymer composite material sample (30HBCGC-260-0) prepared in Preparation Example 3 was accurately weighed and added to 100 mL of a 100 mg / L lead nitrate solution. The mixture was shaken in a water bath constant temperature shaker for 24 h and then centrifuged. The Pb content in the supernatant was detected by ICP. 2+ The removal rate and adsorption capacity of lead ions were calculated to be 76.06% and 152.12 mg / g respectively. Figure 4 );

[0074] (2) In situ passivation: 3.6 g of the hydrothermal biochar / geopolymer composite material sample (30HBCGC-260-0) prepared in Preparation Example 3 was accurately weighed, added to 40 g of simulated lead-contaminated soil, mixed evenly, and then distilled water was added to maintain 50% of the field water holding capacity. After 7 days, the sample was taken out and air-dried. The available lead in the soil was then leached with diethyltriamine pentaacetic acid. The lead ion concentration in the extract was detected by ICP, and the passivation rate for soil lead was calculated to be 48.71% ( Figure 3 ).

Claims

1. A method for preparing a hydrothermal biochar / geopolymer composite material, characterized in that: The fly ash, straw powder and potassium hydroxide aqueous solution are placed in a stirring device and mixed to form a uniform slurry, which is then cured to obtain a biochar / geopolymer precursor, which is then subjected to a hydrothermal reaction, washed, dried and granulated to obtain a hydrothermal biochar / geopolymer composite material; The dosage of straw powder, potassium hydroxide and distilled water is 20%, 75% and 50% of the fly ash mass respectively, the hydrothermal temperature is 220℃~260℃, the hydrothermal time is 4h, and the hydrothermal medium is 0~2mol / L potassium hydroxide solution; The specific steps include: (1) Weigh fly ash according to the formula and place it in an automatic mixer with a set program; (2) Weigh the straw according to the formula, dry it, crush it with a grinder, pass it through a 100-mesh sieve, add it to the automatic mixer described in step (1), and dry-mix it evenly; (3) Weighing solid potassium hydroxide according to the formula; (4) Weigh water according to the formula and dissolve solid potassium hydroxide in water; (5) After the potassium hydroxide solution is cooled to room temperature, it is added to the mixer described in step (2) and stirred for 10 minutes to obtain a uniform slurry; (6) The slurry was placed in a plastic film sealed bag, placed in a constant temperature box at 80°C for 8 hours, then taken out and cured at room temperature for 48 hours to obtain a biochar / geopolymer composite material precursor; (7) The biochar / geopolymer composite material precursor described in step (6) is placed in a hydrothermal reactor, potassium hydroxide solution is measured at a solid-liquid ratio of 1:10, added to the reactor, and hydrothermal carbonization is performed at a temperature of 220° C. to 260° C. The hydrothermal reaction time is 4 hours to obtain a product; (8) The product obtained in step (7) was rinsed alternately with distilled water and anhydrous ethanol, filtered until the filtrate was neutral, placed in a constant temperature drying oven at 105° C. for 12 h, and granulated to obtain particles with a particle size of 0.250 mm to 0.600 mm, which is the hydrothermal biochar / geopolymer composite material; The oxide mass percentages of the fly ash are as follows: SiO2: 52.77%, Al2O3: 29.14%, Fe2O3: 5.81%, CaO: 4.49%, Na2O: 0.48%, MgO: 0.98%, K2O: 2.53%, SO3: 0.81%, TiO2: 1.44%, Loss: 0.84%, and the remainder is unavoidable impurities.

2. Use of the hydrothermal biochar / geopolymer composite material prepared by the method of claim 1 for adsorption and removal of lead ions in water and in-situ passivation of lead in soil; The specific implementation is as follows: (1) A certain amount of hydrothermal biochar / geopolymer composite material is placed in a container with a certain volume and a concentration of C o The Pb(NO3)2 solution was shaken in a water bath constant temperature shaker for 24 hours, centrifuged, and the Pb content in the supernatant was detected by ICP. 2+ concentration, and calculated the removal rate and adsorption amount of lead ions in water by hydrothermal biochar / geopolymer composites; (2) A certain amount of hydrothermal biochar / geopolymer composite material particles were added to simulated lead-contaminated soil, mixed evenly, and then distilled water was added to maintain 50% of the field water holding capacity. After 7 days, the particles were taken out and air-dried. The available lead in the soil was then extracted with diethyltriaminepentaacetic acid. The lead ion concentration in the extract was detected by ICP, and the passivation rate of the hydrothermal biochar / geopolymer composite material on soil lead was calculated.

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