Method for repairing heavy metal contaminated soil through iron phosphate residues obtained after lithium extraction of retired batteries

Abstract

The invention belongs to the field of solid waste treatment of decommissioned power batteries, and particularly relates to a method for repairing heavy metal contaminated soil through iron phosphate residues obtained after lithium extraction of decommissioned batteries, in particular to a method for resource utilization of the residual iron phosphate residues obtained after lithium extraction of decommissioned lithium iron phosphate batteries. Residual solid substances of the waste lithium iron phosphate power battery are treated to obtain iron phosphate residue powder, then the iron phosphate residue powder is input into the soil, in a special biochemical system of the soil, the material can slowly release phosphate ions and iron ions, the nutrient content of the soil is higher, and the heavy metal contaminated soil can be stably repaired. According to the method, a reasonable and feasible treatment method is provided for the special low-value solid waste, meanwhile, high-value utilization of the special low-value solid waste is achieved, an economical and efficient soil remediation material is obtained, and an innovative solution is provided for the field of solid waste and soil remediation in the new energy industry.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid waste treatment of retired power batteries, and specifically relates to a method for repairing heavy metal contaminated soil with iron phosphate residues after lithium extraction from retired batteries. Background Art

[0002] With the rapid development of the new energy vehicle industry, the installed capacity of power batteries has exploded, and the problem of disposing of retired batteries has become an important challenge restricting the green transformation of the industry. These retired batteries contain precious metals such as lithium (1.5-3.5wt%), as well as environmental risk substances such as electrolyte residues (carbonates), heavy metals (Ni, Co, etc.) and fluorides. Improper treatment and disposal methods are a waste of resources and may cause environmental pollution. The current mainstream treatment paths in this industry are divided into three major directions: cascade utilization, pyrometallurgy and wet recovery. Among them, the wet recovery process uses a mixed system composed of sulfuric acid and hydrogen peroxide to react at 80℃-95℃ for 4-6 hours to convert lithium into Li 2 SO 4 The lithium phosphate enters the solution in the form of ions, and battery-grade lithium carbonate can be obtained through evaporation and crystallization. This treatment method has a lithium selective leaching efficiency of over 95%, which can achieve the recovery of precious metals, and the reaction process does not require extreme temperature or pressure conditions, so it is widely used. Each ton of retired batteries treated by the wet method will produce about one ton of ferrophosphorus slag (dry basis). These ferrophosphate residues have low utilization value and have not yet found a good place to go, becoming solid waste.

[0003] In recent years, heavy metal contaminated soil must be repaired before it can be reused. Conventional remediation technologies mainly include physical remediation, chemical remediation and biological remediation. The traditional remediation method uses leaching technology. Although it can remove heavy metals, it can only be used for ex situ remediation. There are problems such as complex operation and high cost, which makes it difficult to apply to large-scale contaminated soil. Stabilization technology is the mainstream technology for the remediation of heavy metal contaminated soil. By adding materials to the soil to react with heavy metals, such as adsorption, precipitation and complexation, heavy metals are fixed, their mobility and bioavailability are reduced, and the harm to plants, microorganisms and soil animals is reduced to negligible. This technology has advantages in terms of economy and operability. The key to stabilization remediation technology is to select suitable stabilization materials. Traditional commonly used stabilization materials include lime, clay minerals, etc. Although the unit price is not high, the amount of soil remediation is large, and the accumulated material cost cannot be underestimated. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for repairing heavy metal contaminated soil with iron phosphate residues after lithium extraction from retired batteries. The phosphate ions of the iron phosphate residues are released to react with heavy metals in the soil to form a chemical precipitation process, thereby achieving stabilization of heavy metals such as Pb and Cd, and stabilizing and repairing heavy metal contaminated soil; and the material can slowly release soil-friendly phosphate ions and iron ions, thereby increasing the nutrient content of the soil.

[0005] In order to achieve the above object, the present invention provides the following technical solutions: A method for remediating heavy metal contaminated soil using iron phosphate residues after lithium extraction from retired batteries comprises the following steps: S1. Pretreatment: Collect the residual solid matter of the discarded lithium iron phosphate power battery after wet leaching treatment, air-dry, grind, and pass through a 60-100 mesh sieve to obtain a sieved dry powder, which is the iron phosphate residue powder; S2. Soil analysis: Analyze the properties of the soil in the area to be repaired, analyze the content and occurrence form of heavy metals in the soil of the area; clarify the level and distribution of heavy metal pollution in order to confirm the amount of repair materials to be added and the repair depth; S3. Soil remediation: Select the in-situ or ex-situ remediation mode, select the remediation depth according to the depth of soil pollution, apply the iron phosphate residue powder to the soil of the plot to be remediated in proportion, and mix it thoroughly through a stirring device, while maintaining the moisture of the soil, and covering it with a protective layer for cultivation to allow for a full reaction; S4. Effect verification: After 2-3 months of maintenance and repair, collect soil samples after the reaction to test the soil nutrient status and the effect of heavy metal stabilization.

[0006] Furthermore, in step S2, 50g-100g of soil samples are collected from different locations of the land to be restored for analysis, and samples of different soil depths are collected from each location for heavy metal determination to confirm the concentration and distribution of heavy metal pollution; the sampling depths below the soil surface are: 0 meter, 0.5 meter, 1 meter, 1.5 meters, 2 meters, 2.5 meters, and 3 meters.

[0007] Furthermore, after obtaining the iron phosphate residue powder in step S1, the iron phosphate residue powder is subjected to a component analysis; if after the component analysis, the concentration of metal elements contained in the iron phosphate residue powder is still higher than the soil background value, it is necessary to further remove the precious metals by wet extraction again until the final iron phosphate residue powder has impurity elements that are no higher than the soil environmental background value.

[0008] Furthermore, in step S1, the content of the composition analysis of the iron phosphate residue powder includes the content and form of each element; the elements to be analyzed include: lithium, cobalt, nickel, aluminum, phosphorus, and iron.

[0009] Furthermore, in step S3, the addition ratio of the iron phosphate residue powder is 1%-10% of the soil mass of the land to be restored.

[0010] Furthermore, in step S3, during the soil remediation process, the soil moisture content is maintained at 10%-15%.

[0011] Furthermore, the ferric phosphate residue powder has an appearance of dark gray powder, irregular particle morphology, small particles aggregated into agglomerates, and a particle size distribution in the micron range; its molecular structure is isophosphate iron manganese ore, containing the following elements in weight ratios: 18%-25% Fe, 20%-30% P, 0.05%-0.12% Ti, 0.04%-0.10% Mn, 0.01%-0.03% Ni and 0.01%-0.02% Cu.

[0012] Furthermore, in step S4, after 2-3 months of curing and repair, the effect of stabilization of heavy metals in the soil is detected; 50g-100g of the repaired soil sample is collected, air-dried, and the heavy metal leaching concentration is measured and compared with the standard value. If the test result still does not meet the standard, continue to increase the material and curing time until the heavy metal leaching rate is lower than the limit specified in the standard.

[0013] Furthermore, in step S4, the standard limit of heavy metal leaching concentration refers to the groundwater quality standard, or is compared with the background value of local groundwater; the specific method for detecting the stabilization of soil heavy metals is selected according to the subsequent planned use of the soil: (1) If the soil is subsequently used as farmland, the bioavailability assessment is performed using the simulated plant root leaching procedure (DTPA method); (2) If the soil is subsequently used as construction land, the synthetic precipitation leaching procedure (SPLP) is used to evaluate the restoration effect; (3) If the soil is subsequently used as a landfill, the leaching of heavy metals in the soil will be evaluated using the Toxicity Characteristic Leaching Procedure (TCLP) using a small molecule acid solution that simulates a landfill.

[0014] The present invention focuses on the background of large-scale generation of solid waste from retired power batteries and soil remediation, and proposes a method for resource utilization of the remaining iron phosphate residue after lithium extraction from retired lithium iron phosphate batteries. The iron phosphate residue is used for the remediation of heavy metal-contaminated soil, which finds a valuable way out for this solid waste. Phosphorus (P) and iron (Fe) in the iron phosphate residue are both soil-friendly elements. In the special biochemical system of the soil, the material can slowly release phosphate ions and iron ions, which not only makes the soil more nutritious, but also stabilizes and remediates heavy metal-contaminated soil; it not only solves the problem of iron phosphate residue disposal in the prior art, but also provides a new idea and resource for soil pollution remediation.

[0015] The working principle of the present invention is that the main component of the iron phosphate residue after lithium extraction from retired power batteries is P 2 O 5 and Fe 2 O 3 After being mixed into the soil, it can slowly release phosphate ions and iron ions. Through the process of phosphate ion release and reaction with soil heavy metals to form chemical precipitation, heavy metals such as Pb and Cd can be stabilized. At the same time, phosphorus and iron supplement nutrients for the soil. The iron phosphate residue releases phosphate in the soil and forms precipitation with Pb and Cd. The main reaction equation is as follows: 5Pb 2+ + 3H 2 PO 4 - + H 2 O = Pb 5 (PO 4 ) 3 OH↓+ 7H + ; 3Pb 2+ +2PO 4 3- = Pb 3 (PO 4 ) 2 ↓; 3C 2+ +2PO 4 3- = Cd 3 (PO 4 ) 2 ↓; Pb and Cd combine with phosphate to form insoluble precipitate Pb 5 (PO 4 ) 3 OH, Pb 3 (PO 4 ) 2 、Cd 3 (PO 4 ) 2, the solubility product constant K of the three sp 10 respectively -62.79 , 10 -43.53 , 10 -32.6 Therefore, adding iron phosphate residues to heavy metal contaminated soil can effectively reduce the dissolution of heavy metals such as Pb and Cd, and can effectively stabilize heavy metals Pb and Cd in the soil.

[0016] The beneficial effects of the present invention are: (1) The present invention proposes an innovative technology for synergistically enhancing the utilization of ferrophosphorus slag and soil remediation, which innovatively transforms industrial solid waste ferrophosphorus slag into an environmental remediation functional material for the treatment of heavy metal compound-contaminated soil. The concentration of heavy metal leaching in the remediated soil is significantly reduced, which can achieve the dual ecological benefits of pollution control and solid waste resource utilization. (2) Different from traditional chemical remediation technology, the present invention adopts an in-situ precipitation mechanism under near-neutral conditions, without the need to add strong acid / alkali and other chemical agents, thus avoiding the environmental risk of heavy metal redissolution and release in traditional processes. The present invention is environmentally friendly, economically feasible and engineering accessible, and provides a model for cross-domain resource utilization of retired batteries in the field of new energy vehicles. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. Among them: Figure 1 The figure is the XRD spectrum of the iron phosphate residue powder according to the embodiment of the present invention.

[0018] Figure 2 These are the results of extracting Pb and Cd using the DTPA method in the verification example of the present invention; wherein (a) is the result of extracting Pb using the DTPA method, and (b) is the result of extracting Cd using the DTPA method.

[0019] Figure 3 These are the results of extracting Pb and Cd by the TCLP extraction method in the verification example of the present invention; wherein (a) is the result of extracting Pb by the TCLP extraction method, and (b) is the result of extracting Cd by the TCLP extraction method. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field belong to the scope of protection of the present invention.

[0021] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0022] A method for remediating heavy metal contaminated soil using iron phosphate residues after lithium extraction from retired batteries comprises the following steps: S1. Pretreatment: Collect the residual solid matter of the discarded lithium iron phosphate power battery after wet leaching treatment, air-dry, grind, and pass through a 60-100 mesh sieve to obtain a sieved dry powder, which is the iron phosphate residue powder; the iron phosphate residue powder is ground and sieved to become a dry powder material with a particle size below the micron level to ensure a better reaction effect; The pH of the iron phosphate residue powder is tested and adjusted as appropriate to a pH of 5-9 to ensure that the pH is within the acceptable pH range for the soil and that materials with this pH will not have a significant impact on the soil when entering the soil (since the soil itself has a large pH buffer range, the pH range of this material can also be wider).

[0023] The iron phosphate residue powder is subjected to component analysis, including full element analysis and property characterization; the full element analysis includes at least the content and form of lithium, cobalt, nickel, aluminum, phosphorus and iron. Lithium, cobalt, nickel, aluminum and iron are heavy metal materials commonly used in positive electrode materials of power batteries, and their content must be ensured to be no higher than the soil environmental background value; the property characterization includes at least the pH and particle size analysis of the iron phosphate residue powder; if after component analysis, the concentration of metal elements contained in the iron phosphate residue powder is still higher than the soil background value, it is necessary to further remove the precious metals by wet extraction again, until the final iron phosphate residue powder has impurities whose elements are no higher than the soil environmental background value.

[0024] S2. Soil analysis: Analyze the properties of the soil in the area to be repaired, analyze the heavy metal content and occurrence form of the soil, and determine the iron and phosphorus content; clarify its nutrient status and heavy metal pollution level and distribution; Soil analysis requires a full understanding of the soil properties, especially the heavy metal pollution status, in order to confirm the amount of repair material to be added and the repair depth.

[0025] S3. Soil remediation: Select in-situ or ex-situ remediation mode, select the remediation depth according to the soil pollution depth, and the remediation depth should be at least consistent with the soil pollution depth; apply the iron phosphate residue powder to the soil of the plot to be remediated at a weight ratio of 1%-10%, and mix it thoroughly through a stirring device, while maintaining the moisture of the soil, and cover it with a protective layer for cultivation to achieve sufficient reaction. Preferably, the amount of iron phosphate residue powder added is 5% of the weight of the soil.

[0026] S4. Effect verification: After 2-3 months of maintenance and repair, collect soil samples after the reaction to test the soil nutrient status and the effect of heavy metal stabilization.

[0027] Furthermore, in step S2, soil samples from different locations of the land to be restored are collected for analysis, and 50g-100g of samples of different soil depths are collected at each location for heavy metal determination to confirm the concentration and distribution of heavy metal pollution; the sampling depths below the soil surface are: 0 meter, 0.5 meter, 1 meter, 1.5 meters, 2 meters, 2.5 meters, and 3 meters.

[0028] Furthermore, the proportion and depth of adding the iron phosphate residue powder to the soil are determined based on the iron and phosphorus content of the iron phosphate residue powder itself and the iron and phosphorus content and depth of the soil of the land to be restored.

[0029] Furthermore, in step S3, since the iron phosphate residue powder is relatively stable, the soil moisture content needs to be maintained at 10%-15% during the soil remediation process, so that phosphate ions will be slowly released under the special biochemical environment of the soil with moisture.

[0030] Furthermore, the ferric phosphate residue powder has a dark gray powder appearance, irregular particle morphology, small particles aggregated into agglomerates, and a particle size distribution in the micrometer range. Its molecular structure is isophosphite; at the same time, the XRD characteristic peak also shows that CaSO 4 、Al 2 (SO 4 ) 3 and MnSO 4 The coexistence of phases is generated by the delithiation of retired lithium-ion batteries. It contains the following elements: 18%-25% Fe, 20%-30% P, 0.05%-0.12% Ti, 0.04%-0.10% Mn, 0.01%-0.03% Ni and 0.01%-0.02% Cu (by weight); the main component of the iron phosphate residue is Fe 2 O 3 , P 2 O 5 , the rest is Al 2 O 3 、TiO 2 , CaO, AgO, MnO.

[0031] Furthermore, in step S4, after 2-3 months of curing and repair, the method for detecting the effect of stabilization of heavy metals in the soil is as follows: 50g-100g of the repaired soil sample is collected, air-dried, and the heavy metal leaching concentration is measured and compared with the standard value. If the test result still does not meet the standard, continue to increase the material and curing time until the leaching rate is lower than the limit specified in the standard.

[0032] Furthermore, in step S4, the standard limit of heavy metal leaching concentration refers to the groundwater quality standard (GB14848-2017), or is compared with the background value of local groundwater; the specific method for detecting the stabilization of soil heavy metals is selected according to the subsequent planned use of the soil: (1) If the soil is subsequently used as agricultural land, the simulated plant root leaching procedure (DTPA) is used to evaluate the bioavailability; (2) If the soil is subsequently used for construction, the simulated acid rain leaching procedure (SPLP) is used to evaluate the restoration effect; (3) If the soil is subsequently used as a landfill, the toxicity leaching procedure (TCLP) simulating the small molecule acid environment of a landfill will be used to evaluate the leaching of heavy metals in the soil.

[0033] Verification Example The main components and contents of the iron phosphate residue powder in this verification example are shown in Table 1. Figure 1 As shown in the figure, the phase composition of ferrophosphorus slag was detected by X-ray diffractometer (XRD-6100) at a scanning speed of 2° / min in the range of 10°-80° to obtain the XRD spectrum of ferrophosphorus slag. The XRD spectrum shows that the ferrophosphorus residue and the isophosphorus iron manganese ore (Fe, Mn)PO 4 The results are highly consistent, and its space group is Pmnb (62), the unit cell parameters are a=5.824Å, b=9.823Å, c=4.786Å, and Z=4. This result confirms that the ferrophosphorus slag comes from the de-lithiated waste lithium iron phosphate (LiFePO 4 )Battery.

[0034] Table 1 Main components and contents of iron phosphate residue

[0035] The soil condition of the land to be restored is as follows: the soil is contaminated with lead (Pb) and cadmium (Cd) in a mining area in Jiyuan, Henan Province. The contents of effective Pb and Cd extractable by DTPA in the original contaminated soil are 386.50 mg / kg and 4.22 mg / kg respectively; the contents of effective Pb and Cd extractable by TCLP are 76 mg / kg and 3.77 mg / kg respectively.

[0036] Soil remediation process: According to the soil conditions of the plot to be remediated, the amount of iron phosphate residue powder added is determined to be 5% of the soil mass; the remediation method is in-situ remediation, and the iron phosphate residue powder is mixed with the soil evenly by stirring; the soil moisture content is always maintained at 70% of the maximum field water holding capacity, and covered with a protective layer; the remediation cycle is 180 days; after the iron phosphate residue powder is added, continuous maintenance is carried out, and soil samples are taken at 28 days and 180 days of remediation. The remediation group is the group remediated by the iron phosphate residue powder, and a control group is also set up without the iron phosphate residue powder treatment.

[0037] Effect verification: The DTPA method and TCLP extraction method were used to evaluate the stabilization effect of Pb and Cd after soil remediation.

[0038] (I) DTPA method (bioavailability assessment): The DTPA solution contains 28 mol / L nitric acid, 6 mol / L hydrochloric acid, 0.005 mol / L diethyltriaminepentaacetic acid (DTPA), 0.1 mol / L triethanolamine (TEA) and 0.01 mol / L CaCl 2 , the pH value needs to be strictly controlled, pH is 7.30±0.05.

[0039] Take 1.00±0.05g of freeze-dried soil sample and place it in a 50mL centrifuge tube, add 30mL of DTPA extract, and oscillate on an air bath constant temperature oscillator at 25±2℃ (temperature must be strictly controlled) and 180rpm / min for 2h. Then remove it, centrifuge it, pass it through a 0.45μm polyethersulfone filter membrane, transfer it to a 5mL centrifuge tube, and centrifuge it. Use inductively coupled plasma emission spectrometer (ICP) to determine the concentration of effective heavy metals.

[0040] The results are shown in Table 2. Figure 2 As shown in the figure, after 180 days of remediation, the remediation effect of the remediation group using iron phosphate residue was evaluated by bioavailability assessment (DTPA) method. The DTPA-extractable effective Pb content decreased from 386.50 mg / kg to 158.71 mg / kg, and the DTPA-extractable effective Cd content decreased from 4.22 mg / kg to 1.65 mg / kg; that is, after the contaminated soil was remediated by iron phosphate residue, the stabilization remediation rates of Pb and Cd could reach 58.94% and 60.81% respectively. This shows that the addition of iron phosphate residue enhances the stability of Pb and Cd, and the stabilization remediation rate gradually increases with the increase in the number of remediation days, indicating that this material can slowly release phosphate ions, and after soil chemical reactions, form stable compounds with heavy metals, significantly inhibit their mobility, and reduce their biological toxicity. The calculation formula for the remediation rate is as follows: R(%)=(C 0 -C n ) / C 0 ×100%; In the above formula, R represents the stabilization repair rate (%); C 0 represents the heavy metal leaching concentration of the original soil (mg / kg); C n It represents the heavy metal leaching concentration of the soil after restoration (mg / kg); n is the number of days.

[0041] Figure 2The remediation-0d, remediation-14d, remediation-28d, and remediation-180d in the remediation group represent the Pb ( Figure 2 (a) 、Cd( Figure 2 (b) The concentration of DTPA extractable effective state. Control-0d, Control-14d, Control-28d, Control-180d represent the Pb ( Figure 2 (a) 、Cd( Figure 2 (b) DTPA extractable effective state concentration.

[0042] Table 2 Results of extraction of Pb and Cd by DTPA method (mg / kg)

[0043] (II) TCLP Extraction Method (Toxicity Leaching Procedure Assessment) Preparation of TCLP solution: Add 5.7 mL of glacial acetic acid (analytical grade) and 64.3 mL of 1 mol / L sodium hydroxide solution to 500 mL of deionized water, and make up to 1 L. The pH of the solution is 4.93±0.05.

[0044] Take 1.00±0.05g of freeze-dried soil sample in a 50mL centrifuge tube, add 30mL TCLP extract, and oscillate on an air bath constant temperature oscillator at 25±2℃ (temperature strictly controlled) and 180rpm / min for 18h. After removal, centrifuge, pass through a 0.45μm polyethersulfone filter membrane, transfer to a 5ml centrifuge tube, and centrifuge, and use ICP to determine the concentration of the effective state of heavy metals.

[0045] The results are shown in Table 3. Figure 3 As shown in the figure, after 180 days of restoration, the toxic leaching procedure (TCLP) was used to evaluate the restoration effect of the soil restoration group using iron phosphate residues. The TCLP extractable effective Pb content decreased from 76.00 mg / kg to 11.03 mg / kg, and the TCLP extractable effective Cd content decreased from 3.77 mg / kg to 1.97 mg / kg; that is, the stabilization effect on Pb and Cd can reach 85.49% and 47.22% respectively. It can be seen that iron phosphate residues have a significant stabilization effect on both Pb and Cd in the soil, especially for Pb.

[0046] Figure 3 The remediation-0d, remediation-14d, remediation-28d, and remediation-180d in the remediation group represent the Pb ( Figure 3 (a) 、Cd( Figure 3(b) The concentration of TCLP extractable effective state. Control-0d, Control-14d, Control-28d, Control-180d represent the Pb concentration of the control group contaminated soil at 0d, 14d, 28d, and 180d, respectively. Figure 3 (a) 、Cd( Figure 3 (b) TCLP can extract the concentration of the effective state.

[0047] Table 3 Results of extracting Pb and Cd by TCLP extraction method (unit: mg / kg)

[0048] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are within the scope of protection of the pending claims of the present invention.

Claims

1. A method for repairing heavy metal contaminated soil using iron phosphate residues after lithium extraction from retired batteries, characterized in that: The steps include: S1. Pretreatment: Collect the residual solid matter of the discarded lithium iron phosphate power battery after wet leaching treatment, air-dry, grind, and pass through a 60-100 mesh sieve to obtain a sieved dry powder, which is the iron phosphate residue powder; S2. Soil analysis: Analyze the properties of the soil in the area to be repaired, analyze the content and occurrence form of heavy metals in the soil of the area; clarify the level and distribution of heavy metal pollution in order to confirm the amount of repair materials to be added and the repair depth; S3. Soil remediation: Select the in-situ or ex-situ remediation mode, select the remediation depth according to the depth of soil pollution, apply the iron phosphate residue powder to the soil of the plot to be remediated in proportion, and mix it thoroughly through a stirring device, while maintaining the moisture of the soil, and covering it with a protective layer for cultivation to allow for a full reaction; S4. Effect verification: After 2-3 months of maintenance and repair, collect soil samples after the reaction to test the soil nutrient status and the effect of heavy metal stabilization.

2. The method for repairing heavy metal contaminated soil with iron phosphate residues after lithium extraction from retired batteries according to claim 1, characterized in that: In step S2, 50g-100g of soil samples are collected from different locations of the land to be restored for analysis, and samples of different soil depths are collected from each location for heavy metal determination to confirm the concentration and distribution of heavy metal pollution; the sampling depths below the soil surface are: 0 meter, 0.5 meter, 1 meter, 1.5 meters, 2 meters, 2.5 meters, and 3 meters.

3. The method for repairing heavy metal contaminated soil with iron phosphate residues after lithium extraction from retired batteries according to claim 1, characterized in that: After obtaining the iron phosphate residue powder in step S1, the iron phosphate residue powder is subjected to a component analysis; if after the component analysis, the concentration of metal elements contained in the iron phosphate residue powder is still higher than the soil background value, it is necessary to further remove the precious metals by wet extraction again until the final iron phosphate residue powder has impurity elements that are no higher than the soil environmental background value.

4. The method for repairing heavy metal contaminated soil with iron phosphate residues after lithium extraction from retired batteries according to claim 3, characterized in that: In step S1, the content of the composition analysis of the iron phosphate residue powder includes the content and form of each element; The elements to be analyzed include: lithium, cobalt, nickel, aluminum, phosphorus, and iron.

5. The method for repairing heavy metal contaminated soil with iron phosphate residues after lithium extraction from retired batteries according to claim 1, characterized in that: In step S3, the addition ratio of the iron phosphate residue powder is 1%-10% of the soil mass of the land to be restored.

6. The method for repairing heavy metal contaminated soil with iron phosphate residues after lithium extraction from retired batteries according to claim 1, characterized in that: In step S3, during the soil remediation process, the soil moisture content is maintained at 10%-15%.

7. The method for remediating heavy metal contaminated soil with iron phosphate residues after lithium extraction from retired batteries according to claim 1, characterized in that: The ferric phosphate residue powder has a dark grey powder appearance, irregular particle shape, small particles aggregated into agglomerates, and a particle size distribution in the micrometer range; its molecular structure is isophosphorus iron manganese ore, containing the following elements in weight ratios: 18%-25% Fe, 20%-30% P, 0.05%-0.12% Ti, 0.04%-0.10% Mn, 0.01%-0.03% Ni and 0.01%-0.02% Cu.

8. The method for repairing heavy metal contaminated soil with iron phosphate residues after lithium extraction from retired batteries according to claim 1, characterized in that: In step S4, after 2-3 months of curing and repair, the stabilization effect of heavy metals in the soil is detected; 50g-100g of the repaired soil sample is collected, air-dried, and the heavy metal leaching concentration is measured and compared with the standard value. If the test result still does not meet the standard, continue to increase the material and curing time until the heavy metal leaching rate is lower than the limit specified in the standard.

9. The method for remediating heavy metal contaminated soil with iron phosphate residues after lithium extraction from retired batteries according to claim 8, characterized in that: In step S4, the standard limit of heavy metal leaching concentration refers to the groundwater quality standard, or is compared with the background value of local groundwater; the specific method for detecting the stabilization of soil heavy metals is selected according to the subsequent planned use of the soil: (1) If the soil is subsequently used as agricultural land, the simulated plant root leaching procedure (DTPA) is used to evaluate the bioavailability; (2) If the soil is subsequently used for construction, the simulated acid rain leaching procedure (SPLP) is used to evaluate the restoration effect; (3) If the soil is subsequently used as a landfill, the toxicity leaching procedure (TCLP) simulating the small molecule acid environment of a landfill will be used to evaluate the leaching of heavy metals in the soil.

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