A method for chemical remediation of heavy metal contaminated soil

Abstract

This invention discloses a chemical remediation method for heavy metal contaminated soil. The method involves passivating the soil by adding magnesite powder and phosphate rock powder to laundry wastewater. Then, a mixture of modified wheat bran biochar (using fly ash as a proppant) and modified tea residue biochar (modified with mercaptopropionic acid) is added for further treatment. Finally, hyperaccumulating plants are planted to adsorb the heavy metals from the soil, resulting in clean, regenerated soil. This invention significantly improves ion exchange and adsorption complexation performance by selecting laundry wastewater as a soil pH enhancer and anionic surfactant provider, controlling the mass ratio of magnesite powder to phosphate rock powder, adjusting the ratio of modified wheat bran biochar and modified tea residue biochar, and modifying the synthesis conditions during biochar modification. This significantly enhances the solidification and adsorption effects on heavy metals. The chemical remediation method for heavy metal contaminated soil described in this invention is environmentally friendly and can promote ecological agricultural development.

Description

Technical Field

[0001] This invention relates to a chemical remediation method for heavy metal contaminated soil, belonging to the field of soil heavy metal pollution treatment technology. Background Technology

[0002] Heavy metals in soil pollution are characterized by their insidious, long-term, non-degradable, and irreversible nature. They easily cause groundwater pollution and can enter the human body through the food chain, harming human health. Current technologies for heavy metal remediation in soil rely on adding various exogenous fixatives to contaminated soil. These fixatives immobilize heavy metals in the soil through adsorption, precipitation, ion exchange, and redox reactions, reducing their mobility and bioavailability in the environment. This reduces their toxicity to soil microorganisms and plants, showing promising application prospects for the remediation of large-scale heavy metal-contaminated soils.

[0003] CN115945511A discloses a method for remediating heavy metal-contaminated agricultural soil. Adding soil conditioners, biomass pellets, and livestock waste to plowed contaminated soil can effectively passivate and fix heavy metal ions in the soil, improving soil fertility. However, relying solely on the adsorption capacity of biochar without modification leaves unadsorbed heavy metal ions in the soil. CN108046955A discloses a soil conditioner for remediating cadmium-contaminated soil and its preparation method. This is achieved by grinding urea, superphosphate, potassium chloride, lime, biochar, and fly ash, mixing them with wood acetic acid solution, and granulating the mixture. This method can increase soil pH, reduce the content of available heavy metals in the soil, and improve soil fertility. However, its effective range for heavy metals is limited, showing excellent results only for cadmium. Therefore, there is a need to develop a green and environmentally friendly chemical remediation method for heavy metal-contaminated soil with high heavy metal fixation and adsorption capabilities. Summary of the Invention

[0004] Purpose of the invention: This invention aims to provide a chemical remediation method for heavy metal contaminated soil.

[0005] Technical solution: The present invention provides a chemical remediation method for heavy metal contaminated soil, characterized by comprising the following steps:

[0006] (1) Till the soil contaminated with heavy metals, air dry it, and weigh it;

[0007] (2) Add magnesite powder and phosphate rock powder to the laundry wastewater, mix evenly, pour into the soil surface dried in step (1), plow, and air dry to obtain passivated soil.

[0008] (3) Mix the modified wheat bran biochar with fly ash as a proppant and the modified tea residue biochar modified with mercaptopropionic acid evenly, spread it on the passivated soil surface, and then plow it.

[0009] (4) Plant hyperaccumulating plants in the soil treated in step (3) to adsorb heavy metals in the soil and obtain clean and regenerated soil.

[0010] Furthermore, in step (2), the pH value of the laundry wastewater is 8 to 10, and the content of anionic surfactant in the laundry wastewater is 15% to 40%.

[0011] Further, in step (2), the total amount of magnesite powder and phosphate rock powder used is 3 to 5 wt% of the heavy metal contaminated soil to be treated.

[0012] Further, in step (2), the mass ratio of magnesite powder to phosphate rock powder is 1:0.7 to 1.

[0013] Furthermore, in step (2), the solid-liquid ratio of the magnesite powder, phosphate rock powder, and laundry wastewater is 1:0.7 to 1:4.3 to 5 g / g / mL.

[0014] Further, in step (3), the total amount of modified wheat bran biochar and modified tea residue biochar is 20-30 wt% of the heavy metal contaminated soil to be treated.

[0015] Further, in step (3), the mass ratio of the modified wheat bran biochar to the modified tea residue biochar is 1:0.7-1.

[0016] Further, in step (3), the preparation of the modified wheat bran biochar includes the following steps:

[0017] Wheat bran is crushed and sieved to obtain wheat bran powder. The wheat bran powder is then mixed evenly with fly ash and aluminum dihydrogen phosphate adhesive, and calcined to obtain the final product.

[0018] Furthermore, the sieving is performed through a 100-mesh sieve.

[0019] Furthermore, the mass ratio of wheat bran powder, fly ash and aluminum dihydrogen phosphate adhesive is 1:0.7 to 1:0.5 to 0.7.

[0020] Furthermore, the calcination temperature is 600–800°C, and the calcination time is 3–6 hours.

[0021] Furthermore, in step (3), the preparation of the modified tea residue biochar includes the following steps:

[0022] Tea residue is crushed, sieved, and then soaked in anhydrous ethanol, followed by soaking in mercaptopropionic acid. The mixture is then subjected to hydrothermal reaction under constant temperature and nitrogen purging, dried, ground, and sieved again to obtain modified tea residue biochar.

[0023] Furthermore, the sieving is performed through a 20-mesh sieve.

[0024] Furthermore, the mass ratio of the tea residue powder, anhydrous ethanol, and mercaptopropionic acid is 1:0.7 to 1:0.7 to 1.

[0025] Furthermore, the soaking time with anhydrous ethanol is 12–24 hours.

[0026] Furthermore, the soaking time with added mercaptopropionic acid is 12–24 hours.

[0027] Furthermore, the temperature of the hydrothermal reaction is 300–600°C, and the time of the hydrothermal reaction is 5–10 hours.

[0028] Furthermore, the material is sieved through a 60-mesh sieve.

[0029] Furthermore, in step (4), the hyperaccumulating plant is Sedum aizoon, and the planting time is more than one year.

[0030] Repair mechanism:

[0031] First, this invention uses laundry wastewater to reduce the concentration of hydrogen ions in the soil, increase the negative charge on the surface of soil particles, promote the adsorption of heavy metal ions on the soil colloid surface, and realize the resource utilization of laundry wastewater. Furthermore, the magnesium ions in magnesite powder can undergo ion exchange with heavy metal ions in the soil, forming carbonate-bound salt precipitates, achieving a passivation effect on heavy metals in the soil. Meanwhile, phosphate rock powder not only provides nutrients for plant absorption but also releases phosphate ions. Metal cations are directly adsorbed onto the phosphate surface and undergo a displacement reaction with cations in the amorphous phosphate lattice to form stable phosphates. The synergistic effect of these two mechanisms increases the passivation and fixation of heavy metal ions while providing nutrients to promote plant growth, achieving a preliminary soil remediation effect.

[0032] Secondly, in this invention, wheat bran powder and fly ash are bonded together with aluminum dihydrogen phosphate adhesive and sintered to form a porous biochar structure, which facilitates the adsorption of heavy metal ions. Furthermore, the SiO2, Al2O3, CaO, and TiO2 in the fly ash act as proppants during sintering and carbonization, preventing carbon collapse. The porous structure formed after sintering also contributes to the adsorption of heavy metals. Tea residue powder contains polyphenols rich in oxygen-containing functional groups such as hydroxyl and phenolic hydroxyl groups, which are the main functional groups for heavy metal adsorption on biochar. Tea residue powder modified with mercaptopropionic acid introduces thiol groups with strong nucleophilicity, which can also form stable complexes with heavy metals. When thiol groups form complexes with heavy metals, they are usually bound together by coordinate bonds, eliminating the free state of the heavy metals. After the sulfur and nitrogen atoms in the thiol groups combine with the cations in the heavy metals, the heavy metal ions are captured in the chemical bonds on the thiol group surface, thus achieving adsorption. Furthermore, biochar has a high organic content and contains various trace elements needed for plant growth, such as nitrogen, phosphorus, and potassium, which can improve soil properties.

[0033] Finally, phytoremediation is one of the most promising in-situ remediation technologies for purifying soil contaminated with heavy metals. Selecting appropriate phytoremediation materials based on local conditions is crucial for successful implementation. This invention selects *Sedum aizoon*, which grows rapidly. Using *Sedum aizoon* leaves as explants can induce callus tissue and regenerate intact plants. *Sedum aizoon* is a hyperaccumulator of cadmium and lead, capable of absorbing significant amounts of cadmium and lead into the aboveground parts of the plant, effectively reducing heavy metal pollution in the soil. This invention features a diverse formulation, combining organic, inorganic, and bioremediation methods, encompassing multiple mechanisms of action such as adsorption, precipitation, complexation, and ion exchange, with synergistic effects among the components.

[0034] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0035] (1) This invention uses laundry wastewater to increase the pH value of the soil and provides anionic surfactants, which can significantly improve ion exchange and adsorption complexation performance. The addition of magnesite powder and phosphate rock powder further significantly improves the solidification effect on heavy metals. When used for the solidification of heavy metals in the soil, it can effectively adsorb heavy metals such as cadmium, mercury, lead, and arsenic in the soil. The use of laundry wastewater realizes the resource utilization and harmless treatment of domestic sewage, which is environmentally friendly and promotes the ecological development of agriculture.

[0036] (2) The modified wheat bran biochar formed by using wheat bran and fly ash as a proppant in this invention can improve the adsorption performance and stability of heavy metals in soil, effectively achieving the remediation of heavy metal pollution in soil. The modified tea residue biochar modified with mercaptopropionic acid in this invention can form stable complexes with heavy metals, thus adsorbing them. Furthermore, the biochar has a high organic content, realizing the resource-based reuse of agricultural waste and turning waste into treasure.

[0037] (3) This invention selects Sedum aizoon as a hyperaccumulator to adsorb heavy metals in the soil, which can effectively adsorb heavy metals such as cadmium and lead in the soil, reducing cadmium and lead in the soil by 7.5% and 5.4% respectively. It effectively reduces heavy metal pollution in the soil and obtains clean and regenerated soil. Detailed Implementation

[0038] The technical solution of the present invention will be further described below.

[0039] The composition of laundry wastewater includes: 15%–40% anionic surfactants, 5%–10% nonionic surfactants, 3%–5% antibacterial agents, 3%–5% fragrances, and other additives, with a pH value of 8–10.

[0040] Example 1

[0041] (1) Take 1000g of heavy metal contaminated soil to be treated, plow and air dry it. Weigh 29.4g of magnesite powder and 20.6g of phosphate rock powder and add them to 500mL of laundry wastewater. Mix them evenly and pour them onto the surface of the air-dried heavy metal contaminated soil. Plow and stir until they are evenly mixed with the heavy metal contaminated soil and continue to air dry to obtain the passivated soil.

[0042] (2) After crushing the wheat bran, pass it through a 100-mesh sieve to obtain wheat bran powder. Weigh 53.5g of wheat bran powder, 37.5g of fly ash, and 26.6g of aluminum dihydrogen phosphate adhesive, mix them evenly, and calcine them in a muffle furnace at 600℃ for 3h to obtain modified wheat bran biochar.

[0043] (3) After drying and crushing Lipton tea residue, the residue was passed through a 20-mesh sieve to obtain tea residue powder. 82.4g of tea residue powder was weighed into a 200mL beaker, 104.3mL of anhydrous ethanol was added and the mixture was soaked for 24h, followed by the addition of 0.8mL of mercaptopropionic acid and soaking for another 24h. The mixture was then transferred to a reaction vessel, purged with nitrogen, and the temperature was set to 300℃ for 5h. After the reaction vessel cooled to room temperature, it was removed, dried, ground, and passed through a 60-mesh sieve to obtain modified tea residue biochar.

[0044] (4) Weigh 117.6g of modified wheat bran biochar and 82.4g of modified tea residue biochar, mix them evenly, and spread them on the surface of the passivated soil. Turn over and stir until they are evenly mixed with the soil. Plant Sedum aizoon in the passivated and adsorption-treated soil for 1 year or more to adsorb heavy metals in the soil and obtain clean and regenerated soil.

[0045] Example 2

[0046] Same as Example 1, except that the mass ratio of magnesite powder to phosphate rock powder is 1:1, that is, 25.0g of magnesite powder and 25.0g of phosphate rock powder.

[0047] Example 3

[0048] Same as Example 1, except that the mass ratio of magnesite powder to phosphate rock powder is 2:1, that is, magnesite powder is 33.4g and phosphate rock powder is 16.7g.

[0049] Comparative Example 1

[0050] Same as Example 1, except that there is no magnesite powder and the amount of phosphate rock powder is 50g.

[0051] Comparative Example 2

[0052] Same as Example 1, except that there is no phosphate rock powder, and the amount of magnesite powder is 50g.

[0053] Evaluation criteria: The effective contents of cadmium, mercury, lead, and arsenic in the untreated soil (original soil), soils from Examples 1-3, and Comparative Examples 1-2 were determined by inductively coupled plasma mass spectrometry. The results are shown in Table 1.

[0054] Table 1 shows the test results of heavy metal content in the soil of untreated soil, Example 1, and Comparative Examples 1-4.

[0055] Cadmium (mg / kg) Mercury (mg / kg) Lead (mg / kg) Arsenic (mg / kg) Untreated soil 5.46 2.75 127.67 65.92 Example 1 3.75 1.97 86.65 50.82 Example 2 4.02 2.06 87.43 53.77 Example 3 4.52 2.46 90.62 55.86 Comparative Example 1 4.93 2.89 94.73 58.24 Comparative Example 2 5.02 3.12 98.85 59.49

[0056] The results in Table 1 show that the combined use of magnesite powder and phosphate rock powder in the untreated soil and the soils of Examples 1-3 is significantly better than the use of phosphate rock powder alone in Comparative Example 1 and the use of magnesite powder alone in Comparative Example 2. Furthermore, by changing the mass ratio of magnesite powder to phosphate rock powder, the soil cleaning effect is better when the mass ratio of magnesite powder to phosphate rock powder is in the range of 1:0.7 to 1, which is reflected in the lower effective content of cadmium, mercury, lead and arsenic in the soil.

[0057] Example 4

[0058] (1) Take 1000g of heavy metal contaminated soil to be treated, plow and air dry it. Weigh 29.4g of magnesite powder and 20.6g of phosphate rock powder and add them to 500mL of laundry wastewater. Mix them evenly and pour them onto the surface of the air-dried heavy metal contaminated soil. Plow and stir until they are evenly mixed with the soil and continue to air dry to obtain the passivated soil.

[0059] (2) After crushing the wheat bran, pass it through a 100-mesh sieve to obtain wheat bran powder. Weigh 53.5g of wheat bran powder, 37.5g of fly ash, and 26.6g of aluminum dihydrogen phosphate adhesive, mix them evenly, and calcine them in a muffle furnace at 600℃ for 3h to obtain modified wheat bran biochar.

[0060] (3) After drying and crushing the tea residue, pass it through a 20-mesh sieve to obtain tea residue powder. Weigh 82.4g of tea residue powder into a 200mL beaker, add 73.0mL of anhydrous ethanol and soak for 24h, then add 0.5mL of mercaptopropionic acid and soak for another 24h. Transfer it to a reaction vessel, purge with nitrogen and set the temperature to 300℃ for 5h. After the reaction vessel cools to room temperature, remove it, dry it, grind it, and pass it through a 60-mesh sieve to obtain modified tea residue biochar.

[0061] (4) Weigh 117.6g of modified wheat bran biochar and 82.4g of modified tea residue biochar, mix them evenly, and then spread them on the surface of the passivated soil. Turn over and stir until they are evenly mixed with the soil. Plant Sedum aizoon in the passivated and adsorption-treated soil for one year or more to adsorb heavy metals in the soil and obtain clean and regenerated soil.

[0062] Example 5

[0063] Similar to Example 2, except that: 45.5g of wheat bran powder, 31.8g of fly ash, and 22.7g of aluminum dihydrogen phosphate adhesive were calcined to obtain modified wheat bran biochar. 100.0g of tea residue powder, 88.6mL of anhydrous ethanol, and 0.6mL of mercaptopropionic acid were reacted hydrothermally to obtain modified tea residue biochar. The mass ratio of modified wheat bran biochar to modified tea residue biochar was 1:1, i.e., 100.0g of modified wheat bran biochar and 100.0g of modified tea residue biochar.

[0064] Example 6

[0065] Similar to Example 2, except that: 55.0g of wheat bran powder, 38.5g of fly ash, and 27.5g of aluminum dihydrogen phosphate adhesive were calcined to obtain modified wheat bran biochar. 79.0g of tea residue powder, 70.0mL of anhydrous ethanol, and 0.48mL of mercaptopropionic acid were reacted hydrothermally to obtain modified tea residue biochar. The mass ratio of modified wheat bran biochar to modified tea residue biochar was approximately 1.5:1, i.e., 121.0g of modified wheat bran biochar and 79.0g of modified tea residue biochar.

[0066] Comparative Example 3

[0067] Same as Example 2, except that: no modified wheat bran biochar was added, the modified tea residue biochar was obtained by hydrothermal reaction with 200.0g of tea residue powder, 177.2mL of anhydrous ethanol, and 1.2mL of mercaptopropionic acid, and the amount of modified tea residue biochar used was 200.0g.

[0068] Comparative Example 4

[0069] Same as Example 2, except that: no modified tea residue biochar was added, and the modified wheat bran biochar was obtained by calcination with 90.9g of wheat bran powder, 63.6g of fly ash, and 45.5g of aluminum dihydrogen phosphate adhesive, with a total amount of 200g of modified wheat bran biochar.

[0070] Evaluation criteria: The effective contents of cadmium, mercury, lead, and arsenic in the untreated soil, soil samples from Examples 4-6, and Comparative Examples 3-4 were determined by inductively coupled plasma mass spectrometry. The results are shown in Table 2.

[0071] Table 2 shows the test results of heavy metal content in the soil of untreated soil, Example 2, and Comparative Examples 5-8:

[0072] Cadmium (mg / kg) Mercury (mg / kg) Lead (mg / kg) Arsenic (mg / kg) Untreated soil 5.46 2.75 127.67 65.92 Example 4 3.32 1.49 75.27 45.41 Example 5 3.45 1.53 76.32 46.32 Example 6 3.97 2.01 85.37 50.42 Comparative Example 3 4.47 2.46 93.29 58.31 Comparative Example 4 4.87 2.41 95.63 56.92

[0073] The results in Table 2 show that the combined use of modified wheat bran biochar and modified tea residue biochar in Examples 4-6 is significantly better than that in Comparative Example 3 and Comparative Example 4. Furthermore, by changing the mass ratio of modified wheat bran biochar to modified tea residue biochar, the adsorption effect of modified wheat bran biochar to modified tea residue biochar in the soil is better when the mass ratio is in the range of 1:(0.7-1), which is reflected in the lower effective content of cadmium, mercury, lead, and arsenic in the soil.

[0074] Example 7

[0075] Same as Example 4, except that the mass ratio of wheat bran powder, fly ash and aluminum dihydrogen phosphate adhesive is 1:1:1, that is, wheat bran powder is 39.2g, fly ash is 39.2g and aluminum dihydrogen phosphate adhesive is 39.2g.

[0076] Example 8

[0077] Same as Example 4, except that the mass ratio of wheat bran powder, fly ash and aluminum dihydrogen phosphate adhesive is 1:2:2, that is, wheat bran powder is 23.6g, fly ash is 47.0g and aluminum dihydrogen phosphate adhesive is 47.0g.

[0078] Comparative Example 5

[0079] Same as Example 4, except that there is no fly ash and aluminum dihydrogen phosphate binder, and the amount of wheat bran powder is 117.6g.

[0080] Evaluation criteria: The effective contents of cadmium, mercury, lead, and arsenic in the untreated soil (original soil), soils from Examples 4, 7-8, and Comparative Example 5 were determined by inductively coupled plasma mass spectrometry. The results are shown in Table 3.

[0081] Table 3 shows the test results of heavy metal content in the soil of untreated soil, Examples 4, 7-8, and Comparative Example 5:

[0082] Cadmium (mg / kg) Mercury (mg / kg) Lead (mg / kg) Arsenic (mg / kg) Untreated soil 5.46 2.75 127.67 65.92 Example 4 3.32 1.49 75.27 45.41 Example 7 3.54 1.57 77.52 48.34 Example 8 4.67 2.21 83.78 51.02 Comparative Example 5 5.17 2.63 93.29 58.13

[0083] The results in Table 3 show that the combined use of wheat bran powder, fly ash, and aluminum dihydrogen phosphate adhesive in untreated soil, Examples 4, and Examples 7-8 is significantly better than the use of wheat bran powder alone in Comparative Example 5. Furthermore, by changing the mass ratio of wheat bran powder, fly ash, and aluminum dihydrogen phosphate adhesive, the soil cleaning effect is better when the mass ratio of wheat bran powder, fly ash, and aluminum dihydrogen phosphate adhesive is in the range of 1:0.7 to 1:0.7 to 1, which is reflected in the lower effective content of cadmium, mercury, lead, and arsenic in the soil.

[0084] Example 9

[0085] Same as Example 4, except that the calcination temperature of the muffle furnace is 800°C.

[0086] Example 10

[0087] Same as Example 4, except that the calcination temperature of the muffle furnace is 1000℃.

[0088] Example 11

[0089] Same as Example 4, except for the muffle furnace calcination time, which is 6 hours.

[0090] Example 12

[0091] Same as Example 4, except for the muffle furnace calcination time, which is 9 hours.

[0092] Evaluation criteria: The effective contents of cadmium, mercury, lead, and arsenic in the untreated soil (original soil) and the soils from Examples 4 and 9-12 were determined by inductively coupled plasma mass spectrometry. The results are shown in Table 4.

[0093] Table 4 shows the test results of heavy metal content in untreated soil and soil samples from Examples 4, 9-12:

[0094] Cadmium (mg / kg) Mercury (mg / kg) Lead (mg / kg) Arsenic (mg / kg) Untreated soil 5.46 2.75 127.67 65.92 Example 4 3.32 1.49 75.27 45.41 Example 9 3.67 1.73 78.42 47.34 Example 10 4.54 2.61 85.66 52.23 Example 11 3.75 1.89 78.21 47.86 Example 12 4.79 2.44 83.31 53.58

[0095] The results in Table 4 show that, compared with the heavy metal content in untreated soil and soils from Examples 4 and 9-12, modified wheat bran biochar obtained by changing the calcination temperature and time of wheat bran powder in a muffle furnace has a better soil cleaning effect when the calcination temperature is in the range of 600-800℃ and the calcination time is in the range of 3-6h. This is reflected in the lower effective content of cadmium, mercury, lead and arsenic in the soil.

[0096] Example 13

[0097] Same as Example 4, except that the mass ratio of tea residue powder, anhydrous ethanol, and mercaptopropionic acid is 1:1:1, that is, tea residue powder is 82.4g, anhydrous ethanol is 104.3mL, and mercaptopropionic acid is 0.7mL g.

[0098] Example 14

[0099] Same as Example 4, except that the mass ratio of tea residue powder, anhydrous ethanol, and mercaptopropionic acid is 1:2:2, that is, the tea residue powder is 82.4g, the anhydrous ethanol is 208.6mL, and the mercaptopropionic acid is 1.4mL.

[0100] Comparative Example 6

[0101] Same as Example 4, except that it was not soaked in anhydrous ethanol and mercaptopropionic acid, and the amount of tea residue powder was 82.4g.

[0102] Evaluation criteria: The effective contents of cadmium, mercury, lead, and arsenic in the untreated soil (original soil), soils from Examples 4, 13-14, and Comparative Example 6 were determined by inductively coupled plasma mass spectrometry. The results are shown in Table 5.

[0103] Table 5 shows the test results of heavy metal content in the soil of untreated soil, Examples 4, 13-14, and Comparative Example 6.

[0104] Cadmium (mg / kg) Mercury (mg / kg) Lead (mg / kg) Arsenic (mg / kg) Untreated soil 5.46 2.75 127.67 65.92 Example 4 3.32 1.49 75.27 45.41 Example 13 3.46 1.56 76.32 47.52 Example 14 4.38 2.15 85.57 53.23 Comparative Example 6 5.47 2.67 94.53 59.31

[0105] The results in Table 5 show that the combined use of tea residue powder, anhydrous ethanol, and mercaptopropionic acid in untreated soil, Examples 4, 13-14, and Comparative Example 6 is significantly better than the use of tea residue powder alone in Comparative Example 6. Furthermore, by changing the mass ratio of tea residue powder, anhydrous ethanol, and mercaptopropionic acid, the soil cleaning effect is better when the mass ratio of tea residue powder, anhydrous ethanol, and mercaptopropionic acid is in the range of 1:0.7 to 1:0.7 to 1, which is reflected in the lower effective content of cadmium, mercury, lead, and arsenic in the soil.

[0106] Example 15

[0107] Similar to Example 4, except that the soaking time of the tea leaves in anhydrous ethanol is 12 hours.

[0108] Example 16

[0109] Same as Example 4, except that the soaking time of the tea leaves in anhydrous ethanol is 48 hours.

[0110] Example 17

[0111] Similar to Example 4, except that the tea leaves are soaked in mercaptopropionic acid for 12 hours.

[0112] Example 18

[0113] Same as Example 4, except that the soaking time of the tea leaves in mercaptopropionic acid is 48 hours.

[0114] Example 19

[0115] Same as Example 4, except that the hydrothermal reaction temperature is 600°C.

[0116] Example 20

[0117] Same as Example 4, except that the hydrothermal reaction temperature is 900°C.

[0118] Example 21

[0119] Same as Example 4, except for the hydrothermal reaction time, which is 10 hours.

[0120] Example 22

[0121] Same as Example 4, except for the hydrothermal reaction time, which is 15 hours.

[0122] Evaluation criteria: The effective contents of cadmium, mercury, lead, and arsenic in the untreated soil (original soil) and the soils from Examples 4 and 15-22 were determined by inductively coupled plasma mass spectrometry. The results are shown in Table 6.

[0123] Table 6 shows the test results of heavy metal content in untreated soil and soil samples from Examples 4, 12-22:

[0124] Cadmium (mg / kg) Mercury (mg / kg) Lead (mg / kg) Arsenic (mg / kg) Untreated soil 5.46 2.75 127.67 65.92 Example 4 3.32 1.49 75.27 45.41 Example 15 3.74 1.72 78.21 48.92 Example 16 4.83 2.37 80.12 52.46 Example 17 3.78 1.92 77.48 47.65 Example 18 4.73 2.53 82.31 54.87 Example 19 3.37 1.82 79.32 49.45 Example 20 4.89 2.42 82.53 51.24 Example 21 3.57 1.74 78.63 48.34 Example 22 4.95 2.56 82.35 50.57

[0125] The results in Table 6 show that, comparing the heavy metal content in untreated soil with that in Examples 4 and 15-22, the modified tea residue biochar obtained by changing the soaking time of tea residue in anhydrous ethanol and mercaptopropionic acid, as well as the hydrothermal temperature and time in the reactor, showed better soil cleaning effects when the soaking time of tea residue in anhydrous ethanol was in the range of 12-24 h, the soaking time of tea residue in mercaptopropionic acid was in the range of 12-24 h, the hydrothermal temperature in the reactor was in the range of 300-600℃, and the calcination time was in the range of 5-10 h. This was reflected in the lower effective content of cadmium, mercury, lead, and arsenic in the soil.

Claims

1. A chemical remediation method for heavy metal contaminated soil, characterized in that, Includes the following steps: (1) Till the soil contaminated with heavy metals, air dry it, and weigh it; (2) Add magnesite powder and phosphate rock powder to the laundry wastewater, mix evenly, pour into the soil surface dried in step (1), plow, and air dry to obtain passivated soil. (3) Mix the modified wheat bran biochar with fly ash as a proppant and the modified tea residue biochar modified with mercaptopropionic acid evenly, spread it on the passivated soil surface, and then plow it. (4) Plant hyperaccumulating plants in the soil treated in step (3) to adsorb heavy metals in the soil and obtain clean and regenerated soil; In step (3), The preparation of the modified wheat bran biochar includes the following steps: Wheat bran is crushed and sieved to obtain wheat bran powder. The wheat bran powder is then mixed evenly with fly ash and aluminum dihydrogen phosphate adhesive, and calcined to obtain the final product. The mass ratio of the wheat bran powder, fly ash and aluminum dihydrogen phosphate adhesive is 1:0.7~1:0.5~0.7, the calcination temperature is 600~800℃, and the calcination time is 3~6 h. The preparation of the modified tea residue biochar includes the following steps: Tea residue is crushed, sieved, and then soaked in anhydrous ethanol, followed by soaking in mercaptopropionic acid. The mixture is then subjected to a hydrothermal reaction under constant temperature and nitrogen purging. After drying, grinding, and further sieving, modified tea residue biochar is obtained. The mass ratio of tea residue powder, anhydrous ethanol, and mercaptopropionic acid is 1:0.7~1:0.7~1. The soaking time in anhydrous ethanol is 12~24 h, the soaking time in mercaptopropionic acid is 12~24 h, the hydrothermal reaction temperature is 300~600℃, and the hydrothermal reaction time is 5~10 h.

2. The chemical remediation method for heavy metal contaminated soil according to claim 1, characterized in that, In step (2), the pH value of the laundry wastewater is 8 to 10, and the content of anionic surfactant in the laundry wastewater is 15% to 40%.

3. The chemical remediation method for heavy metal contaminated soil according to claim 1, characterized in that, In step (2), the total amount of magnesite powder and phosphate rock powder used is 3-5 wt% of the heavy metal contaminated soil to be treated.

4. The chemical remediation method for heavy metal contaminated soil according to claim 1, characterized in that, In step (2), the mass ratio of magnesite powder to phosphate rock powder is 1:0.7~1, and the solid-liquid ratio of magnesite powder, phosphate rock powder and laundry wastewater is 1:0.7~1:4.3~5 g / g / mL.

5. The chemical remediation method for heavy metal contaminated soil according to claim 1, characterized in that, In step (3), the total amount of modified wheat bran biochar and modified tea residue biochar is 20-30 wt% of the heavy metal contaminated soil to be treated, and the mass ratio of modified wheat bran biochar to modified tea residue biochar is 1:0.7-1.

6. The chemical remediation method for heavy metal contaminated soil according to claim 1, characterized in that, The crushed wheat bran is sieved through a 100-mesh sieve.

7. The chemical remediation method for heavy metal contaminated soil according to claim 1, characterized in that, The crushed tea leaves are sieved through a 20-mesh sieve, and then sieved again through a 60-mesh sieve.

8. The chemical remediation method for heavy metal contaminated soil according to claim 1, characterized in that, In step (4), the hyperaccumulating plant is Sedum aizoon, and the planting time is more than 1 year.