Phosphate / iron composite modified spartina alterniflora biochar as well as preparation method and application thereof
Patent Information
- Application Number
- CN202511564651.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-30
- Publication Date
- 2026-01-13
AI Technical Summary
Existing biochar has poor remediation capacity in heavy metal contaminated soil, and existing technologies do not fully utilize the invasive plant Spartina alterniflora resource, and there is insufficient research on preparation process optimization and modification.
Phosphate/iron composite modification was used to treat Spartina alterniflora straw, and phosphate/iron composite modified Spartina alterniflora biochar was prepared by mixing, drying and pyrolysis. The iron oxide and phosphate mineral precipitation on its surface enhanced the fixation of heavy metals, thereby increasing the adsorption capacity and plant tolerance.
It effectively reduces the mobility of heavy metals in the soil, reduces plant absorption, enhances the fixation effect of heavy metals, improves plant tolerance and growth capacity to heavy metals, and promotes the soil remediation process.
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Figure CN121314541A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of heavy metal contaminated soil remediation technology, and in particular to a phosphate / iron composite modified Spartina alterniflora biochar, its preparation method, and its application. Background Technology
[0002] Biochar, a carbon-rich material obtained through the thermochemical conversion of biomass under oxygen-limited conditions, is characterized by its well-developed pore structure, large specific surface area, and abundant surface functional groups. These properties endow it with excellent adsorption capacity, ion exchange performance, and chemical stability. Therefore, biochar shows significant potential in the fields of environmental pollution control and ecological restoration. Its core applications include: improving soil properties, efficiently adsorbing and fixing various pollutants (including heavy metals and organic matter) in the environment (such as soil and water bodies), and achieving carbon sequestration and emission reduction through stable carbon forms. Its application value is being widely explored and verified.
[0003] In the remediation of heavy metal-contaminated soil, existing soil remediation technologies have many shortcomings: physical remediation is costly and damages soil structure; chemical remediation is prone to secondary pollution; and bioremediation has a long cycle. Biochar plays a positive role in the remediation of heavy metal-contaminated soil by adsorbing heavy metals and improving soil physicochemical indicators. Metals on the surface of biochar can undergo cation exchange with protons or alkali metals; electrostatic interactions can occur between the biochar surface and metals; functional groups on the aromatic structure of biochar can form π-metal complexes with electron-rich domains; ash and other substances on biochar can precipitate heavy metals; and reducing substances carried by biochar can reduce heavy metals and achieve adsorption. However, the adsorption effect of biochar is affected by preparation conditions, raw material characteristics, and application methods. To improve the efficiency of biochar in the remediation of heavy metal-contaminated soil, its modification research is receiving increasing attention. The core objective of modification is to optimize the physicochemical properties of biochar, such as increasing specific surface area and porosity (often achieved through acid-base activation), adjusting pH value, or introducing specific functional groups. Among these, metal-based modification (such as the addition of Fe, S, P and their compounds) and phosphate modification are particularly crucial.
[0004] Biochar, as an emerging soil conditioner, has been applied to soil remediation, but its raw materials are mostly agricultural and forestry waste, resulting in insufficient resource utilization of invasive plants. Furthermore, there is a lack of systematic research on specialized biochar preparation and application technologies for different degraded soils (such as saline-alkali land and heavy metal-affected soils). Spartina alterniflora, as an invasive plant, has rapidly expanded in coastal areas, and its high biomass offers potential for biomass utilization; however, current technologies have not fully explored its application in biochar preparation.
[0005] In the research and development of materials for modifying heavy metal contaminated soil, the iterative optimization of biochar preparation technology and the improvement of its application efficiency have always been the focus of research. Current technical approaches focus on developing more efficient and lower-cost preparation processes, while also striving to enhance the effectiveness of biochar in environmental remediation scenarios. Although there have been some breakthroughs, significant technological gaps remain in areas such as refined control of the preparation process, overcoming cost thresholds, and strengthening the core functions of modified biochar in remediating heavy metal contaminated soil.
[0006] Therefore, it is of great significance to study a phosphate / iron composite modified Spartina alterniflora biochar that can remediate heavy metal contaminated soil, as well as its preparation method and application. Summary of the Invention
[0007] The purpose of this invention is to provide a phosphate / iron composite modified Spartina alterniflora biochar, its preparation method and application, so as to solve the problem that the existing modified biochar has poor ability to remediate heavy metal contaminated soil.
[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing phosphate / iron composite modified Spartina alterniflora biochar, comprising the following steps: 1) After mixing Fe2(SO4)3 and K2HPO4 solution with Spartina alterniflora straw, the mixture was filtered and dried sequentially to obtain phosphate / iron composite treated Spartina alterniflora straw. 2) Phosphate / iron composite treatment of Spartina alterniflora straw followed by pyrolysis yields phosphate / iron composite modified Spartina alterniflora biochar.
[0009] Preferably, in step 1), the concentration of Fe2(SO4)3 in the mixed solution of Fe2(SO4)3 is 200~250 g / L, the concentration of K2HPO4 is 100~150 g / L, and the solvent is water.
[0010] Preferably, in step 1), the volume-to-mass ratio of the mixed solution of Fe2(SO4)3 and K2HPO4 to Spartina alterniflora straw is 8-12 mL: 0.8-1.2 g.
[0011] Preferably, in step 1), the mixing speed is 150~250 rpm and the mixing time is 2~3 h; the drying temperature is 80~120℃ and the drying time is 8~16 h.
[0012] Preferably, in step 2), the pyrolysis heating rate is 4~6℃ / min, the pyrolysis temperature is 600~700℃, and the pyrolysis time is 3~5h; The pyrolysis was carried out under a nitrogen atmosphere at a rate of 0.08~0.12 L / min.
[0013] The present invention also provides the phosphate / iron composite modified Spartina alterniflora biochar prepared by the aforementioned method.
[0014] This invention also provides the application of the phosphate / iron composite modified Spartina alterniflora biochar in the remediation of soils contaminated with chromium and cadmium.
[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention uses biochar prepared from the biomass resources of the invasive coastal plant Spartina alterniflora as raw material and applies it to the treatment of heavy metal contaminated soil, effectively achieving the dual goals of waste resource utilization and heavy metal contaminated soil treatment.
[0016] The phosphate / iron composite modified Spartina alterniflora biochar prepared by this invention can release phosphates to form stable phosphate mineral precipitates with heavy metals, thereby reducing bioavailability, decreasing the mobility of heavy metals in the soil, and reducing the absorption of heavy metals by plants.
[0017] The iron oxides on the surface of the phosphate / iron composite modified biochar can enhance the fixation of heavy metal ions through electrostatic adsorption, ion exchange and complexation reaction, which helps to form iron film on the crop root surface, block or reduce the migration of heavy metals to crop roots and grains, and reduce health risks.
[0018] Furthermore, the combined effect of iron and phosphorus in phosphate / iron modified biochar can enhance the adsorption capacity of biochar and significantly improve the fixation effect on heavy metals. Simultaneously, it can improve plant tolerance to heavy metals and growth capacity, increase net photosynthesis and biomass, and accelerate the soil remediation process. Attached Figure Description
[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.
[0020] Figure 1 Scanning electron microscope and elemental distribution diagram of S, Fe and P of phosphate / iron composite modified Spartina alterniflora biochar obtained in Example 3; Figure 2 A graph showing the changes in soil pH in different treatment groups; Figure 3 This graph shows the changes in available phosphorus content in soil under different treatment groups. Figure 4 A graph showing the changes in available potassium content in soil under different treatment groups; Figure 5 The graph shows the changes in soil organic carbon content in different treatment groups; Figure 6 Figure showing the changes in the distribution of heavy metal speciation in soils under different treatment groups; Figure 7 Figure 1 shows the changes in soil microbial community structure in different treatment groups; Figure 8 This figure shows the changes in net photosynthetic rate, biomass, and heavy metal distribution in different parts of rice in different treatment groups. Detailed Implementation
[0021] This invention provides a method for preparing phosphate / iron composite modified Spartina alterniflora biochar, comprising the following steps: 1) After mixing Fe2(SO4)3 and K2HPO4 solution with Spartina alterniflora straw, the mixture was filtered and dried sequentially to obtain phosphate / iron composite treated Spartina alterniflora straw. 2) Phosphate / iron composite treatment of Spartina alterniflora straw followed by pyrolysis yields phosphate / iron composite modified Spartina alterniflora biochar.
[0022] In this invention, in step 1), the Spartina alterniflora straw is preferably washed, dried, and crushed before mixing; The washing reagent is preferably water; the drying temperature is preferably 90~110℃, more preferably 95~105℃, and even more preferably 98~100℃; the drying time is preferably 9~12h, more preferably 9.5~11h, and even more preferably 10~10.5h; the particle size of the pulverized material is preferably ≤2mm, more preferably ≤1.8mm, and even more preferably ≤1.5mm. In this invention, in step 1), the concentration of Fe2(SO4)3 in the mixed solution of Fe2(SO4)3 and K2HPO4 is preferably 200-250 g / L, more preferably 210-240 g / L, and even more preferably 220-230 g / L; the concentration of K2HPO4 is preferably 100-150 g / L, more preferably 110-140 g / L, and even more preferably 120-130 g / L; and the solvent is preferably water.
[0023] In this invention, in step 1), the volume-to-mass ratio of the mixed solution of Fe2(SO4)3 and K2HPO4 to Spartina alterniflora straw is preferably 8-12 mL: 0.8-1.2 g, more preferably 9-11 mL: 0.9-1.1 g, and even more preferably 10 mL: 1-1.05 g.
[0024] In this invention, in step 1), the mixing speed is preferably 150~250 rpm, more preferably 170~240 rpm, and even more preferably 200~220 rpm; the mixing time is preferably 2~3 h, and even more preferably 2.5 h; the mixing is preferably done using a cantilever stirrer; the drying temperature is preferably 80~120℃, more preferably 90~110℃, and even more preferably 95~100 rpm; the drying time is preferably 8~16 h, more preferably 9~15 h, and even more preferably 10~12 h.
[0025] In this invention, in step 1), the filtration is preferably vacuum filtration, and the vacuum degree of the vacuum filtration is preferably 50~70kPa, more preferably 55~65kPa, and even more preferably 60~62kPa.
[0026] In this invention, in step 1), after filtration, it is preferable to wash the product. The washing reagent is preferably water, and the number of washings is preferably 3 to 8 times, more preferably 4 to 7 times, and even more preferably 5 to 6 times.
[0027] In this invention, in step 2), the heating rate of pyrolysis is preferably 4~6℃ / min, more preferably 4.5~5.5℃ / min, and even more preferably 5~5.2℃ / min; the pyrolysis temperature is preferably 600~700℃, more preferably 620~680℃, and even more preferably 650~660℃; and the pyrolysis time is preferably 3~5h, more preferably 3.5~4.5h, and even more preferably 4h. The pyrolysis is preferably carried out under a nitrogen atmosphere, and the nitrogen flow rate is preferably 0.08~0.12 L / min, more preferably 0.09~1.1 L / min, and even more preferably 1 L / min.
[0028] In this invention, nitrogen is used as a protective gas.
[0029] In this invention, in step 2), cooling is performed after pyrolysis; the cooling temperature is preferably 20~30℃, more preferably 22~28℃, and even more preferably 25~26℃.
[0030] The present invention also provides the phosphate / iron composite modified Spartina alterniflora biochar prepared by the aforementioned method.
[0031] This invention also provides the application of the phosphate / iron composite modified Spartina alterniflora biochar in the remediation of soils contaminated with chromium and cadmium.
[0032] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.
[0033] Example 1
[0034] Large pieces of Spartina alterniflora straw were washed with water, dried at 100℃ for 10 hours, and then crushed to obtain Spartina alterniflora straw with a particle size of 1.8 mm. A mixed solution of Fe2(SO4)3 with a concentration of 200 g / L and K2HPO4 with a concentration of 100 g / L was prepared using water as a solvent. The mixed solution was then mixed with Spartina alterniflora straw at a volume-mass ratio of 8 mL: 1 g. The mixture was stirred at 150 rpm for 2 h using a cantilever stirrer. The filtrate was then removed by vacuum filtration at a vacuum degree of 60 kPa. The solid part was washed 5 times with deionized water and dried in an oven at 80 °C for 8 h to obtain phosphate / iron composite treated Spartina alterniflora straw. Phosphate / iron composite-treated Spartina alterniflora straw was placed in a tube furnace, nitrogen gas was introduced at a rate of 0.08 L / min, and the temperature was raised to 600℃ at a rate of 4℃ / min. After pyrolysis for 3 hours, it was cooled to room temperature to obtain phosphate / iron composite-modified Spartina alterniflora biochar.
[0035] Example 2
[0036] Large pieces of Spartina alterniflora straw were washed with water, dried at 100℃ for 10 hours, and then crushed to obtain Spartina alterniflora straw with a particle size of 1.8 mm. A mixed solution of Fe2(SO4)3 with a concentration of 250 g / L and K2HPO4 with a concentration of 150 g / L was prepared using water as a solvent. The mixed solution was then mixed with Spartina alterniflora straw at a volume-mass ratio of 12 mL: 1 g. The mixture was stirred at 250 rpm for 2 h using a cantilever stirrer. The solution was then vacuum filtered at a vacuum degree of 55 kPa to remove the filtrate. The solid part was washed with deionized water and dried in an oven at 120 °C for 8 h to obtain phosphate / iron composite treated Spartina alterniflora straw. Phosphate / iron composite-treated Spartina alterniflora straw was placed in a tube furnace, nitrogen gas was introduced at a rate of 0.12 L / min, and the temperature was raised to 700℃ at a rate of 6℃ / min. After pyrolysis for 5 hours, it was cooled to room temperature to obtain phosphate / iron composite-modified Spartina alterniflora biochar.
[0037] Example 3
[0038] Large pieces of Spartina alterniflora straw were washed with water, dried at 105℃ for 10 hours, and then crushed to obtain Spartina alterniflora straw with a particle size of 1.8 mm. A mixed solution of Fe2(SO4)3 with a concentration of 220 g / L and K2HPO4 with a concentration of 110 g / L was prepared using water as a solvent. The mixed solution was then mixed with Spartina alterniflora straw at a volume-mass ratio of 10 mL: 1 g. The mixture was stirred at 200 rpm for 2.5 h using a cantilever stirrer. The mixture was then vacuum filtered at a vacuum degree of 60 kPa to remove the filtrate. The solid part was washed with deionized water and dried in an oven at 105 °C for 12 h to obtain phosphate / iron composite treated Spartina alterniflora straw. Phosphate / iron composite-treated Spartina alterniflora straw was placed in a tube furnace, nitrogen gas was introduced at a rate of 0.1 L / min, and the temperature was raised to 650℃ at a rate of 5℃ / min. After pyrolysis for 4 hours, it was cooled to room temperature to obtain phosphate / iron composite-modified Spartina alterniflora biochar, denoted as "PFBC".
[0039] Comparative Example 1
[0040] Large pieces of Spartina alterniflora straw were washed with water, dried at 105℃ for 10 hours, and then crushed to obtain Spartina alterniflora straw with a particle size of 1.8 mm. Spartina alterniflora straw was placed in a tube furnace, and nitrogen gas was introduced at a rate of 0.1 L / min as a protective gas. The temperature was increased to 650℃ at a rate of 5℃ / min for pyrolysis for 4 hours. After cooling, the straw was removed to obtain Spartina alterniflora biochar, denoted as "BC".
[0041] Comparative Example 2
[0042] Large pieces of Spartina alterniflora straw were washed with water, dried at 105℃ for 10 hours, and then crushed to obtain Spartina alterniflora straw with a particle size of 1.8 mm. Spartina alterniflora straw was uniformly mixed with a 250 g / L Fe2(SO4)3 aqueous solution at a mass-volume ratio of 1 g: 10 mL and stirred at 200 rpm for 2.5 h. The mixture was then vacuum filtered and washed several times to remove excess iron salts. The resulting mixture was dried at 105°C for 12 h and then heated to 650°C in a tube furnace at a rate of 5°C / min using nitrogen as a protective gas for 4 h. After cooling, the mixture was removed to obtain iron-modified Spartina alterniflora biochar, denoted as "FBC".
[0043] The following performance tests were conducted on the phosphate / iron composite modified Spartina alterniflora biochar obtained in Examples 1-3, the Spartina alterniflora biochar obtained in Comparative Example 1, and the iron-modified Spartina alterniflora biochar obtained in Comparative Example 2: Scanning electron microscopy analysis: Scanning electron microscopy was performed on the phosphate / iron composite modified Spartina alterniflora biochar prepared in Example 3, and the results are as follows: Figure 1 As shown.
[0044] Scanning electron microscopy and elemental distribution diagrams of S, Fe, and P of the phosphate / iron composite modified Spartina alterniflora biochar obtained in Example 3 are shown below. Figure 1 As shown. By Figure 1 As can be seen, in addition to Fe and P, the phosphate / iron composite modified Spartina alterniflora biochar obtained in Example 3 also contains a certain amount of S. Moreover, the distribution of the elements shows that Fe and P are evenly distributed, indicating that the phosphate / iron composite modified Spartina alterniflora biochar successfully introduced Fe and P and they adhered well to the surface of the biochar.
[0045] Heavy metal contaminated soil remediation experiment: The materials obtained from Example 3, Comparative Example 1, and Comparative Example 2 were used in heavy metal contaminated soil remediation experiments. The specific steps are as follows: The mass of rice potting soil (air-dried and sieved through a 5mm sieve) was 1.5 kg / pot. Five treatment groups and one blank control group (CK) were set up, with three replicates in each group. The treatment groups were respectively treated with 0.5% (BC1), 1% (BC2), and 2% (BC3) of the rice potting soil obtained from Comparative Example 1 (Spartina alterniflora biochar), 1% (FBC2) of the iron-modified Spartina alterniflora biochar obtained from Comparative Example 2 (Spartina alterniflora biochar), and 1% (PFBC2) of the phosphate / iron composite modified Spartina alterniflora biochar. Rice seeds were sourced from farmers in Yancheng City, Jiangsu Province. Plump rice seeds were selected and soaked in 30wt% hydrogen peroxide for 15 minutes, then thoroughly washed several times with deionized water. Rice seedlings were grown to approximately 10 cm in plastic seedling trays in a 25°C constant temperature incubator before transplanting. The pot experiment was conducted in a greenhouse and lasted for 5 months. The cultivated rice seedlings were transplanted into pots, with 2 plants in each pot. During the growth period, the plants were watered in a timely manner to keep the amount of water covering the rice relatively constant.
[0046] The physicochemical properties of heavy metal-contaminated soil from rice pots are shown in Table 1. Among them, soil cation exchange capacity (CEC) was determined by hexaamminecobalt trichloride extraction-spectrophotometry, available phosphorus (AP) in soil was determined by sodium bicarbonate extraction-molybdenum antimony spectrophotometry, available potassium (AK) in soil was determined by ammonium acetate-inductively coupled plasma mass spectrometry, soil organic carbon (SOC) was determined by low-temperature external heating potassium dichromate oxidation-colorimetric method, and chromium (Cr) and cadmium (Cd) were determined by inductively coupled plasma mass spectrometry.
[0047] Table 1. Physicochemical properties of heavy metal contaminated soil from rice pot experiments
[0048] The following graph shows the changes in soil pH, available phosphorus (AP), available potassium (AK), soil organic carbon (SOC), heavy metal speciation, and microbial community structure in different treatment groups. Figures 2-7As shown. By Figures 2-7 It is evident that, compared to the control (CK), the biochar treatment groups all affected soil pH, AP, AK, SOC, and pH. The pH of BC2, FBC2, and PFBC2 significantly increased from 7.23 in CK to 8.01, 8.01, and 7.94, respectively, but there were no significant differences among different biochar addition amounts and types. The AP of PFBC2 increased by 9.32%, 13.10%, and 14.13% compared to CK, BC2, and FBC2, respectively; the AK of PFBC2 increased by 26.75%, 21.92%, and 29.37% compared to CK, BC2, and FBC2, respectively; and the SOC content of CK was 21.79 g·kg⁻¹. -1 Different biochar treatment groups all significantly increased the SOC content in the soil, with increases ranging from 6.33% to 11.38%; from the Actinobacteria phylum ( Actinobacteriota From the perspective of biochar treatment, the levels of PFBC2 and FBC2 were significantly improved compared to the control (CK), with increases of 26.12% and 17.43%, respectively, indicating that biochar application enhanced the tolerance of soil microorganisms to Cd pollution. The proportion of heavy metal residues in all biochar treatment groups showed an upward trend. The Cr residue in the PFBC2 treatment increased by 137.51%, 21.73%, and 47.40% compared to CK, BC2, and FBC2, respectively, while the corresponding Cd residue increases were 35.82%, 39.54%, and -5.66%, respectively. Compared with CK, BC2, and FBC2, the Cr iron-manganese oxide state of FBC2 treatment decreased by 33.88%, 10.24%, and 20.82%, respectively, while the Cd iron-manganese oxide state decreased by 25.74%, 22.37%, and 1.38%, respectively. Compared with CK, BC2, and FBC2, the Cr exchangeable state of FBC2 treatment decreased by 11.04%, -23.90%, and 13.16%, respectively, while the Cd exchangeable state decreased by 38.17%, 29.81%, and 15.47%, respectively, indicating a significant reduction in the availability of heavy metals.
[0049] The changes in net photosynthetic rate, biomass, and heavy metal distribution in different parts of rice in different treatment groups are shown in the figure below. Figure 8 As shown. By Figure 8It is evident that biochar significantly improved the net photosynthetic rate (Pn) and biomass of rice. Compared to the control (CK), BC2, and FBC2 groups, the Pn of the PFBC2 treatment group increased by 34.23%, 15.64%, and 2.87%, respectively, corresponding to increases in total biomass of 37.64%, 14.68%, and 5.68%. Particularly, the biochar treatment groups showed a significant increase in root and cereal biomass compared to the control group. Furthermore, the biochar treatment groups significantly reduced the heavy metal content in rice. Compared with CK, BC2, and FBC2, the Cr content in the roots of the two treatment groups decreased by 36.29%, 14.04%, and 18.28%, respectively, corresponding to a decrease of 37.61%, 0.15%, and 3.62% in the Cr content of the grains. In contrast, the Cd content in the roots of the PFBC2 treatment group decreased by 49.86%, 14.51%, and 28.70% compared with CK, BC2, and FBC2, respectively, corresponding to a decrease of 54.34%, -35.70%, and 4.04% in the Cd content of the grains, effectively reducing health risks.
[0050] It is evident that the phosphate / iron composite modified Spartina alterniflora biochar prepared by this invention has good application effects in the remediation of heavy metal contaminated soil and has broad application prospects.
[0051] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A method for preparing phosphate / iron composite modified Spartina alterniflora biochar, characterized in that, Includes the following steps: 1) After mixing Fe2(SO4)3 and K2HPO4 solution with Spartina alterniflora straw, the mixture was filtered and dried sequentially to obtain phosphate / iron composite treated Spartina alterniflora straw. 2) Phosphate / iron composite treatment of Spartina alterniflora straw followed by pyrolysis yields phosphate / iron composite modified Spartina alterniflora biochar.
2. The method for preparing phosphate / iron composite modified Spartina alterniflora biochar according to claim 1, characterized in that, In step 1), the concentration of Fe2(SO4)3 in the mixed solution of Fe2(SO4)3 is 200~250 g / L, the concentration of K2HPO4 is 100~150 g / L, and the solvent is water.
3. The method for preparing phosphate / iron composite modified Spartina alterniflora biochar according to claim 2, characterized in that, In step 1), the volume-to-mass ratio of the mixed solution of Fe2(SO4)3 and K2HPO4 to Spartina alterniflora straw is 8-12 mL: 0.8-1.2 g.
4. The method for preparing phosphate / iron composite modified Spartina alterniflora biochar according to claim 2 or 3, characterized in that, In step 1), the mixing speed is 150~250 rpm and the mixing time is 2~3 h; the drying temperature is 80~120℃ and the drying time is 8~16 h.
5. The method for preparing phosphate / iron composite modified Spartina alterniflora biochar according to claim 1, characterized in that, In step 2), the pyrolysis heating rate is 4~6℃ / min, the pyrolysis temperature is 600~700℃, and the pyrolysis time is 3~5h. The pyrolysis was carried out under a nitrogen atmosphere at a rate of 0.08~0.12 L / min.
6. The phosphate / iron composite modified Spartina alterniflora biochar prepared by the method for preparing phosphate / iron composite modified Spartina alterniflora biochar according to any one of claims 1 to 5.
7. The application of the phosphate / iron composite modified Spartina alterniflora biochar according to claim 6 in the remediation of soil contaminated with chromium and cadmium.