Salvia miltiorrhiza residue modified charcoal as well as preparation method and application thereof

Abstract

The embodiment of the invention discloses salvia miltiorrhiza residue modified charcoal as well as a preparation method and application thereof. The preparation method of the salvia miltiorrhiza residue modified biochar comprises the following steps: soaking salvia miltiorrhiza residue in a tripotassium phosphate aqueous solution, washing with ultrapure water, drying, pyrolyzing, grinding and sieving to obtain the salvia miltiorrhiza residue modified biochar. Salvia miltiorrhiza dregs are used as raw materials, and the phosphorus modified biochar material (3K-BC) is prepared through phosphate modification. Researches show that 3K-BC has good adsorption performance on heavy metals (Cd and Pb). The 3K-BC is added into the soil, so that the migration of Pb and Cd in the soil can be reduced; the 3K-BC has dual functions of fixing heavy metal Pb / Cd and improving soil fertility in the growth process of ligusticum wallichii. The research provides a simple and feasible solution for scientifically synthesizing the phosphorus-modified biochar from the traditional Chinese medicine residues and repairing the Pb and Cd polluted water / soil.

Description

Technical Field

[0001] The embodiments of the present invention relate to the technical field of environmental heavy metal remediation and treatment, and specifically to a biochar modified with salvia miltiorrhiza residue, and a preparation method and application thereof. Background Art

[0002] Heavy metal contamination of soil and wastewater is a very serious environmental problem because it has adverse effects on human health and ecosystems. For wastewater, common heavy metal treatment methods include chemical precipitation, ion exchange, membrane separation, electrochemical method, adsorption method and biological method. For soil, common treatment methods include physical method, chemical method, bioremediation, etc. Among them, chemical adsorption method represented by biochar has low remediation cost, high efficiency and low technical requirements. The application of biochar has become a very promising solution. In particular, biochar after chemical modification has a richer specific surface area and surface functional groups, showing excellent performance in heavy metal adsorption.

[0003] Therefore, based on the traditional adsorption method, the development of modified multifunctional biochar with strong selectivity, large adsorption capacity, high detection sensitivity and good stability has good practical application prospects. Summary of the Invention

[0004] To this end, the embodiments of the present invention provide a biochar modified with Danshen medicinal residues, and a preparation method and application thereof.

[0005] In order to achieve the above objectives, the embodiments of the present invention provide the following technical solutions:

[0006] According to a first aspect of an embodiment of the present invention, the present invention provides a method for preparing biochar modified with Danshen medicinal residues, comprising soaking the Danshen medicinal residues in a tripotassium phosphate aqueous solution, washing with ultrapure water, drying, pyrolyzing, grinding and sieving to obtain the Danshen medicinal residue modified biochar.

[0007] Furthermore, the preparation method of the salvia miltiorrhiza residue comprises: first crushing the salvia miltiorrhiza residue to less than 2 mm, soaking it in a saturated potassium phosphate aqueous solution for 24 hours, washing the excess phosphate on the surface of the residue with ultrapure water, and then drying it in an oven (80°C). Using a vacuum tube furnace, heating the temperature to 600°C at a heating rate of 10°C / min, and continuing the pyrolysis time for 2 hours. After the pyrolysis is completed, naturally cooling to room temperature, washing with ultrapure water, vacuum drying, and storing in a brown bottle for future use.

[0008] Furthermore, the concentration of the tripotassium phosphate aqueous solution is 1.8-2.40 mol / L.

[0009] Furthermore, the soaking is carried out under stirring conditions, the soaking temperature is 10-35° C., and the soaking time is 18-36 hours.

[0010] Furthermore, the drying conditions are: 70-85° C., 3-6 hours.

[0011] Furthermore, the pyrolysis conditions are: 550-650° C., 1.5-2.5 hours under anoxic conditions.

[0012] Furthermore, the particle size of the ground and sieved sieve is 1-2 mm.

[0013] Furthermore, the preparation method of the biochar modified with Danshen medicinal residues includes:

[0014] The salvia miltiorrhiza residue was crushed to <2 mm, soaked in a saturated potassium phosphate aqueous solution for 24 h, and the excess phosphate on the surface of the residue was washed with ultrapure water. Then, it was dried in an 80°C oven for 3 h, and heated to 600°C at a heating rate of 10°C / min in a vacuum tube furnace. The pyrolysis time was continued for 2 h. After the pyrolysis was completed, it was naturally cooled to room temperature, washed with ultrapure water, and vacuum-dried. It was stored in a brown bottle for later use.

[0015] According to a second aspect of the embodiments of the present invention, the present invention provides a biochar modified from Danshen medicinal residue, which is prepared by the method described in any one of the above items.

[0016] According to a third aspect of the embodiments of the present invention, the present invention provides the use of the biochar modified with the Danshen medicinal residue as described above in the remediation of lead and cadmium contaminated water bodies / soils.

[0017] According to a fourth aspect of the embodiments of the present invention, the present invention provides the use of the biochar modified with the Danshen residue as described above in the cultivation of Ligusticum chuanxiong.

[0018] The embodiments of the present invention have the following advantages:

[0019] This study uses Salvia miltiorrhiza residue as raw material and prepares phosphorus-modified biochar material (3K-BC) through phosphate modification. Studies have shown that 3K-BC has good adsorption properties for heavy metals (Cd and Pb). Adding 3K-BC to soil helps reduce the migration of Pb and Cd in the soil; 3K-BC has the dual functions of fixing heavy metals Pb / Cd and improving soil fertility during the growth of Chuanxiong. This study provides a simple and feasible solution for the scientific use of traditional Chinese medicine residues to synthesize phosphorus-modified biochar and remediate Pb and Cd-contaminated water and soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments or the description of the prior art. Obviously, the drawings described below are merely exemplary, and those skilled in the art can derive other implementation drawings based on the provided drawings without inventive effort.

[0021] Figure 1 The NaOH-EDTA extracts of BC and 3K-BC provided by the present invention 31 P NMR spectra, Or-P: orthophosphate, Py-P: pyrophosphate.

[0022] Figure 2 The effect of the initial pH value provided by the present invention on the removal of Pb and Cd by 3K-BC.

[0023] Figure 3 The experimental results of the adsorption of Pb and Cd by 3K-BC provided by the present invention, A: adsorption kinetics; B: pseudo-first-order kinetic model; C: pseudo-second-order kinetic model; D: intraparticle diffusion model; E: Elovich model; F: Bangham model.

[0024] Figure 4 The adsorption isotherms of heavy metals on 3K-BC provided by the present invention are: A: Pb; B: Cd.

[0025] Figure 5 Scanning electron microscope-energy dispersive spectrometer (SEM-EDS) spectra of BC and 3K-BC provided by the present invention before and after heavy metal adsorption.

[0026] Figure 6 The Fourier transform infrared spectra (A) and X-ray photoelectron spectra (BG) of BC, 3K-BC, 3K-BC-Pb and 3K-BC-Cd provided by the present invention.

[0027] Figure 7 The present invention provides the mechanism of 3K-BC adsorption of Pb / Cd in solution.

[0028] Figure 8 Effects of the 3K-BC provided by the present invention on soil enzyme activity, available phosphorus, and water retention: A: urease; B: neutral phosphatase; C: available phosphorus; D: water retention.

[0029] Figure 9 This is the scanning electron microscope-energy dispersive spectrum (SEM-EDS) spectrum before and after 3K-BC adsorption in the soil experiment provided by the present invention.

[0030] Figure 10 X-ray diffraction spectrum (A), Fourier transform infrared spectrum (B) and X-ray photoelectron spectrum (CF) before and after 3K-BC adsorption in the soil experiment provided by the present invention.

[0031] Figure 11 The present invention provides the form distribution of Pb (A) and Cd (B) in the soil after adding 0%, 1% and 3% 3K-BC to improve the soil.

[0032] Figure 12 Heavy metal fixation analysis provided by the present invention, A: bioavailability by CaCl2 extraction; B, C: leaching toxicity by TCLP extraction.

[0033] Figure 13 Effects of the 3K-BC provided by the present invention on the growth of Chuanxiong Rhizoma. A: dry weight of different plant parts; B: content of ferulic acid, ligustilide A and ligustilide in the plant. DETAILED DESCRIPTION

[0034] The following describes the implementation of the present invention using specific embodiments. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. Obviously, the embodiments described are only a portion of the present invention, not all of it. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are intended to fall within the scope of protection of the present invention.

[0035] Potassium phosphate trihydrate (molecular weight 266.31, 99%) was purchased from Aladdin Reagent Company (China) and used without further purification. All other chemical reagents used in this study were of at least analytical grade. Chuanxiong and Lingzi were provided by the Meishan Traditional Chinese Medicine Cooperative (Sichuan, China). All aqueous solutions were prepared using ultrapure water produced by a laboratory pure water system (18.25 MΩ / cm, WBZ1001-UP).

[0036] Example 1 Preparation of biochar and phosphorus-modified biochar

[0037] The experiment selected Salvia miltiorrhiza residue (the residue after being extracted with water or ethanol and then dried) as the raw material, which was collected from Chengdu Xinfuyuan Chinese Medicine Pieces Co., Ltd.

[0038] Preparation of phosphorus-modified biochar: Salvia miltiorrhiza residue (particle size <2 mm) was immersed in a saturated K₃PO₄ solution and magnetically stirred at room temperature (25°C) for 24 hours. Excess phosphate on the surface of the residue was washed with ultrapure water and dried at 80°C for 3 hours. The modified residue was placed in a tube furnace and pyrolyzed at 600°C at a heating rate of 10°C / min for 2 hours. After cooling, the biochar was ground and sieved (1-2 mm) and sealed in a brown container for further use, designated as 3K-BC.

[0039] The pH and EC of the two biochars were measured using a pH meter (pHS-3C+, Ark Technology, China) and a conductivity meter (CT-20, Lichen Technology, China). 1 g of biochar powder was weighed, added to 20 mL of deionized water at a ratio of 1:20 (g:mL), mixed, and shaken thoroughly for 30 minutes. After standing for 1 minute, the pH value was measured using a pH meter, and the EC value was measured using a conductivity meter. Ash content was determined by heating the mixture at 815°C in a muffle furnace for 2 hours. The carbon (C), hydrogen (H), nitrogen (N), and sulfur (S) contents were determined using an elemental analyzer (EA, Elementar UNICUBE, Germany). Oxygen content was calculated by subtraction (O% = 100% - (Ash% + C% + H% + N% + S%)). The contents of heavy metals lead (Pb) and cadmium (Cd) in biochar were determined by microwave digestion instrument (NAI-WB40, Shanghai Naai, China) and inductively coupled plasma mass spectrometry (ICP-MS, Agilent 7700, USA). The specific surface area of ​​the material was determined by BET method using physical adsorption instrument (JW-BK100, JWGB, China), and the pore size and total pore volume of the material were calculated by BJH method. 31 P NMR nuclear magnetic resonance spectroscopy (600 MHz, Bruker, Germany) was used to measure the two biochars before and after modification to determine the type of phosphate loaded.

[0040] The basic physical and chemical properties of BC and 3K-BC are shown in Table 1. Both the original biochar and the modified biochar are alkaline. After modification, the conductivity is significantly enhanced from 0.42mS / cm to 1.52mS / cm. The specific surface area is also increased from 1.55m 2 / g increased to 4.60m 2 / g, which may be due to the pore-forming effect of K ions. The ash content and organic element content of biochar before and after modification are shown in Table 2. The prepared biochar and modified biochar have good stability because the H / C and O / C ratios of the prepared materials are <0.6 and <0.4, respectively. The H / C ratio is a parameter of carbonization degree and can be used to characterize the aromaticity of biochar. Phosphate modification increases the O / C ratio of biochar, thereby increasing the hydrophilicity of biochar. The (O+N) / C ratio of 3K-BC is 0.31, which is greater than that of the original biochar at 0.18, indicating that modification can improve the polarity of biochar, thereby increasing its adsorption capacity for polar compounds. In order to ensure that the heavy metals in the added materials did not exceed the standard, this experiment used microwave digestion to determine the full amount of heavy metals Pb and Cd in the biochar before and after modification. Both types of biochar before and after modification did not exceed the national requirements for biochar technical indicators (Pb is 50ppm, Cd is 0.3ppm) (NY / T 4159-2022), proving the feasibility of applying the material to the environment.

[0041] like Figure 1 As shown, the spectrum of the original biochar is dominated by the Or-P signal (5.4 to 5.7 ppm), with a very small Py-P signal also detected (-4.1 to -5.3 ppm). However, in the spectrum of the modified biochar, only the Or-P signal was detected, and its intensity was 8-9 times that of the original biochar, confirming the successful loading of orthophosphate. Furthermore, the disappearance of the Py-P signal after modification is presumably due to the loss of potassium pyrophosphate during the modification process due to its high solubility.

[0042] Table 1 Basic physicochemical properties of BC and 3K-BC

[0043]

[0044] SSA: specific surface area; PD: pore diameter; PV: pore volume.

[0045] Table 2 Determination results of organic elements in BC and 3K-BC

[0046]

[0047] Example 2 Evaluation of the adsorption performance of modified biochar for Pb / Cd

[0048] 1. Effect of initial pH on Cd / Pb adsorption by modified biochar

[0049] 10 mg of modified biochar was weighed into a centrifuge tube. Then, 25 mL of a 300 mg / L solution of Pb(NO₃)₂ and a 50 mg / L solution of Cd(NO₃)₂ were added. The pH values ​​were adjusted to 2.00, 3.00, 4.00, 5.00, and 6.00, respectively, using a small amount of 1 M HNO₃ or NaOH solution. The mixture was shaken at 220 rpm at 25°C for 12 h and then filtered through a nylon membrane filter with a pore size of 0.45 μm. The concentrations of Pb and Cd in the samples were determined using an inductively coupled plasma atomic emission spectrometer (ICP-OES, Agilent 720ES, USA).

[0050] like Figure 2 As shown, the removal rate of both heavy metals by 3K-BC continuously increases with increasing pH. At low solution pH, H ions enter the modified material, protonating activated groups such as -COOH and -OH on the surface, thereby preventing the binding of heavy metal ions to surface functional groups. As the pH increases, the H ion concentration decreases, and the functional groups in the modified material gradually deprotonate. The electrostatic repulsion between the pores increases, making it easier for heavy metal ions to enter the modified material, resulting in an increase in adsorption capacity. At pH 5, the adsorption rates of both heavy metals reach a plateau. At this point, the biochar adsorption rates for lead (Pb) reach 59.42% and for cadmium (Cd) reach 71.89%. When the pH increases from 5 to 6, although the adsorption rates increase to 63.51% and 75.25%, respectively, a white turbidity appears in the Pb experiment. At this point, the white precipitate has not yet been added to the biochar. This is presumably because the high Pb concentration causes a reaction with NaOH, resulting in the formation of Pb(OH)2 precipitate. Therefore, the initial pH value in the subsequent experiments was determined to be pH=5.

[0051] 2. Adsorption characteristics of modified biochar for Pb / Cd

[0052] 2.1 Adsorption kinetics experiments

[0053] Batch adsorption experiments were conducted to investigate the adsorption performance of modified biochar for lead and cadmium. First, adsorption kinetics were measured using the following steps: 10 mg of modified biochar was weighed and mixed with 25 mL of 0.01 mol / L NaNO₃ solution in a 50 mL centrifuge tube. This solution contained either a 300 mg / L Pb(NO₃)₂ solution or a 50 mg / L Cd(NO₃)₂ solution. The solution was adjusted to its optimal adsorption pH (pH = 5) by dropwise addition of a small amount of 1 M HNO₃ or NaOH solution. The centrifuge tube was placed in a 25°C incubator and shaken at 220 rpm. Simultaneously, samples were taken at intervals of 0-60 h, filtered through a 0.45 μm microporous membrane, and the Pb and Cd concentrations in the filtrate were analyzed using ICP-MS. The adsorption capacity of Pb and Cd by biochar at different times was determined. The results were fitted using five kinetic models: pseudo-first-order, pseudo-second-order, intraparticle diffusion, Elovich, and Bangham.

[0054] The adsorption kinetics of Pb and Cd by 3K-BC are shown in the following table: Figure 3 As shown in Table 3. In general, for Pb, 3K-BC reaches adsorption equilibrium at around 600 min; for Cd, 3K-BC reaches adsorption equilibrium at around 400 min. This indicates that Cd is adsorbed faster than Pb. Compared with the pseudo-first-order kinetic fitting parameters, the pseudo-second-order kinetic model R 2 The values ​​are higher, at 0.9926 and 0.9606, respectively. Furthermore, the equilibrium adsorption capacities of 352.73 mg / g (Pb) and 128.95 mg / g (Cd) calculated by the pseudo-second-order model are closer to the experimental adsorption capacities. Therefore, the adsorption process in this experiment conforms to the pseudo-second-order kinetic model, indicating that the adsorption rates of Pb and Cd on 3K-BC are controlled by the number of active sites on the material surface, with chemical adsorption being the primary mechanism.

[0055] The intraparticle diffusion model describes the diffusion process of heterogeneous adsorbents. Figure 3 (D) and Table 4 show that the adsorption process of Pb on 3K-BC can be roughly divided into three dynamic stages: external diffusion, internal diffusion, and adsorption equilibrium. First, the heavy metal diffuses from the solution to the outer surface of the adsorbent, mainly due to the electrostatic attraction between the adsorbent surface and the heavy metal; the second stage is intraparticle diffusion, where the heavy metal enters the active sites inside the pores from the outer surface of the adsorbent and binds, thereby playing an adsorption role; finally, the adsorption rate decreases until it reaches equilibrium. R of each stage 2 It is proved that Pb is consistent with the intra-particle diffusion model. In addition, the third segment R 2The value of the diffusion rate K in each stage gradually decreases (K1>K2>K3), indicating that the reaction is getting slower and slower, and finally the rate is close to 0, and the adsorption amount no longer changes with time. Figure 3 (D) shows that the removal processes of the two heavy metals are multilinearly correlated, and the intercepts C1, C2, and C3 of the fitting lines are not 0, indicating that internal diffusion is not the only rate-limiting step controlling the heavy metal removal process, and the adsorption rate should be controlled by both external and internal diffusion.

[0056] The Elovich kinetic model describes the propagation and diffusion speed of a substance in a medium. It is widely used in various environments, especially for the adsorption of pollutants from aqueous solutions. As shown in Table 4, the correlation coefficients R for Pb and Cd are 2 The values ​​of 0.9640 and 0.9622 are both greater than 0.95, indicating that this model is consistent with the adsorption process of the two heavy metals by 3K-BC, that is, the adsorption process involves heterogeneous diffusion and chemical reaction. The Bangham model is often used to describe the pore diffusion model. Figure 3 (F) is the linear diagram of the Bangham pore diffusion model, and the correlation coefficient R between Pb and Cd 2 The values ​​are 0.9192 and 0.9400, respectively, indicating that pore diffusion exists in the adsorption process, but this diffusion is not the only factor that determines the adsorption rate.

[0057] Table 33 Fitting parameters of the adsorption kinetic model of lead and cadmium by K-BC

[0058]

[0059] Table 43 K-BC intraparticle diffusion model parameters for lead and cadmium

[0060]

[0061] 2.2 Adsorption isotherm experiment

[0062] For the adsorption isotherm experiment, the Pb concentration range was 200-1000 mg / L, with a gradient of 200, 300, 400, 600, 800, and 1000 mg / L. The Cd concentration range was 5-50 mg / L, with a gradient of 5, 10, 15, 25, 35, and 50 mg / L. Other steps were identical to those for the kinetic experiment, resulting in adsorption isotherm results. The results were fitted using the Langmuir, Freundlich, and Sips isotherm models.

[0063] The adsorption capacity (Q, mg / L) of the adsorbent was calculated using the following formula:

[0064]

[0065] In the formula, C o and C t are the initial and equilibrium heavy metal concentrations (mg / L), v is the volume of the solution (L), and m is the mass of the added biochar (g).

[0066] The adsorption isotherm is the curve of the dependence between the adsorption amount of pollutants on the solid phase and their concentration in the liquid phase. The adsorption isotherms of Pb and Cd on 3K-BC are as follows: Figure 4 As shown. This study found that the adsorption isotherm data of the two heavy metals were L-shaped, first increasing and then tending to stabilize. That is, the adsorption capacity of modified biochar for heavy metals increased with the increase of equilibrium concentration and gradually reached saturation. At the same time, the adsorption capacity of 3K-BC for Pb was much greater than that for Cd. In order to explore the adsorption process of biochar for heavy metals, the Langmuir, Freundlich and Sips models were used to analyze the adsorption isotherm experimental results, and the fitting results were shown as follows: Figure 4 As shown in Table 5, compared with the Freundlich model, the Langmuir model is more suitable for describing the adsorption process of 3K-BC on Pb and Cd, and the fitting correlation coefficient R 2 They are 0.9743 and 0.9516 respectively. This shows that the adsorption process of the material for Pb and Cd is the same, both are monolayer adsorption. The maximum adsorption capacity of 3K-BC for Pb and Cd was calculated by Langmuir model fitting, which is 361.82 mg / g and 123.03 mg / g respectively. The constants 1 / n of the Freundlich model for the two heavy metals are both less than 0.5, indicating that 3K-BC has a strong adsorption effect on Pb and Cd, and the adsorption process is easy. The Sips isotherm model is considered to be a combination of the Langmuir and Freundlich models, avoiding the limitations of both. The fitting parameters R for Pb and Cd calculated based on the Sips isotherm model are: 2 The values ​​are 0.9287 and 0.9473, respectively, both less than 0.95. Furthermore, the theoretical maximum adsorption capacity of 3K-BC for Pb is 456.38 mg / g, significantly different from the actual Pb adsorption capacity (355.15 mg / g). Therefore, Sips is not suitable for describing the adsorption process of heavy metals by this experimental material.

[0067] Table 6 lists the theoretical maximum adsorption capacity of modified biochar for Pb or Cd removal reported in other literature. By comparison, the adsorption capacity of Pb and Cd by the present experimental material is greater than that of most reported biochars. The results show that the prepared 3K-BC has high potential for the removal of heavy metals Pb and Cd.

[0068] Table 53 Fitting parameters of the adsorption isotherm model of K-BC for lead and cadmium

[0069]

[0070] Table 6 Comparison of removal adsorption characteristics of lead and cadmium by different phosphorus-modified biochars

[0071]

[0072]

[0073] 3. Characterization of biochar before and after Cd / Pb adsorption

[0074] In order to investigate the mechanism of Cd / Pb removal by phosphate-loaded biochar, the characterization characteristics of 3K-BC before and after heavy metal adsorption were examined. The surface morphology images of the biochar samples before and after adsorption were observed using a scanning electron microscope combined with an energy dispersive X-ray detector (SEM-EDS, ZEISS AxioImagerM2 EVO10, Germany). X-ray photoelectron spectroscopy (XRD, Rigaku Ultma IV, Japan) was used to analyze the crystalline characteristics of the samples. The biochar was qualitatively analyzed at 400-4000 cm with the help of a Fourier transform infrared spectrometer (FT-IR, PerkinElmer Frontier, China). -1 The surface elemental composition and relative percentages of the materials were obtained by X-ray photoelectron spectroscopy (XPS, Thermo Scientific K-Alpha, USA).

[0075] 3.1 SEM-EDS

[0076] The SEM-EDS results of biochar are as follows Figure 5 As shown. The surface of the original biochar (BC) is rough and porous. After modification, there is no significant difference in its surface. Due to the existence of its porous structure, it is speculated that its surface can undergo physical adsorption with heavy metals. The semi-quantitative results of EDS showed that after modification with potassium phosphate, the potassium content increased from the original 4.21% to 18.85%, and the phosphorus content increased from the original 0.23% to 3.63%, indicating the successful modification of potassium phosphate. After adsorption of both heavy metals, precipitated compounds were present on its surface, especially after adsorption of Pb, the particle phenomenon on its surface was more obvious. The semi-quantitative EDS results after adsorption showed that the content of K and P elements on the surface of the modified biochar decreased significantly, while the content of heavy metals Pb and Cd increased. The above proves the contribution of potassium and phosphorus to the adsorption of heavy metals, and it is speculated that the adsorption mechanism includes precipitation between phosphate and heavy metal ions and cation exchange involving potassium ions.

[0077] 3.2 FT-IR

[0078] The different surface functional groups of four biochars (BC, 3K-BC, 3K-BC-Pb, and 3K-BC-Cd) were determined by FT-IR spectroscopy in the detection range of 400–4000 cm -1 ,like Figure 6 (A) shows the 1689cm before adsorption. -1 After adsorption, the wave number shifted to 1658 cm -1 , which is attributed to the vibration of the C=O group. It is speculated that the C=O functional group is involved in the precipitation of metal ions, thus causing the shift of the wave number. -1 The peak at 1390 cm is attributed to -COOH. -1 Attributed to CO3 2- Stretching vibration. 874cm -1 The peak at 1043 cm is attributed to the out-of-plane bending vibration absorption peak of the C-H bond. In addition, for the modified biochar, the peak at 1043 cm -1 belongs to PO4 3- The peaks of phosphate ions were confirmed, which is consistent with the results of SEM-EDS. By comparing the BC before modification, the infrared spectrum of 3K-BC showed more peaks, proving that the surface of the modified material has more functional groups. After adsorption of heavy metals, PO4 3- A decrease in peak intensity or shift in peak position indicates that phosphorus-containing functional groups participate in heavy metal interactions. Similar phenomena were observed for other functional groups. In summary, these different oxygen-containing functional groups on the biochar surface may play an important role in the adsorption and immobilization of heavy metals.

[0079] 3.3XPS

[0080] XPS images before and after adsorption Figure 6 (B-G) The full spectrum shows that for the biochar after Pb adsorption, new peaks at 138.32 eV and 143.05 eV are detected, attributed to Pb 4f; for the biochar after Cd adsorption, new peaks at 405.72 eV and 412.04 eV are detected, attributed to Cd 3d. This indicates that both heavy metals were successfully adsorbed onto the 3K-BC surface. Figure 6(C) shows the C1s spectrum of biochar. After modification, the peaks at binding energies of 284.75 (61.65%), 285.60 (36.34%), and 288.65 eV (2.00%) correspond to C–C / C–H, C–O / C–N, and COOH functional groups, respectively. The position and intensity of the characteristic peaks of these groups shifted after Pb / Cd adsorption. C–O can form Pb / Cd-O complexes with heavy metals, resulting in a decrease in the relative CO content. This is presumably due to precipitation or complexation with Pb / Cd, leading to the loss or gain of these groups. It has been reported that the aromatic structure of biochar can provide π electrons for ion exchange with heavy metals during the adsorption process and form metal-π complexes with them. After Pb adsorption, the COOH content increased from 2.00% to 10.42%, indicating the formation of a Pb-COOH complex. After Cd adsorption, the COOH content decreased, suggesting that the adsorption mechanism may involve ion exchange. like Figure 6 As shown in (D), in the fine spectrum of O1s, the three peaks at 530.97eV (24.90%), 531.94eV (53.23%) and 533.47eV (21.85%) on 3K-BC are attributed to C=O / P=O, CO / PO and -OH / OC=O groups, respectively. After adsorption, the ratio of C=O / P=O increased from 24.90% to 32.09% and 31.17%, respectively, indicating the formation of lead phosphate or cadmium phosphate precipitates. At the same time, other oxygen-containing functional groups can also undergo complexation with heavy metals. After phosphate modification, a peak belonging to P 2p was observed on 3K-BC, confirming the successful loading of phosphate during co-pyrolysis, which is consistent with the SEM-EDS and FT-IR results. As shown Figure 6 As shown in (E), the peaks at 133.21 (44.22%) and 134.08 eV (57.78%) of 3K-BC correspond to P=O and P–O, respectively. After adsorption of Pb / Cd, the P=O content increases to 49.99% and 55.68%, respectively, while the P–O content decreases to 50.01% and 44.32%, respectively, indicating the involvement of P=O and P–O in the adsorption process. Figure 6 The peaks at 138.32 eV and 143.05 eV in (F) can be attributed to Pb 4f 7 / 2 and Pb 4f 5 / 2 The difference between the double peaks is 4.8eV, proving the existence of Pb-O structure. 5 / 2 represents the chemical state corresponding to electrostatic attraction, porosity, or electronic interaction, while Pb 4f 7 / 2 represents the chemical state associated with precipitation, ion exchange or complexation. 7 / 2 The peak area of ​​Pb 4f 5 / 2The peak area of ​​​​the adsorption process is shown to be dominated by chemical adsorption. Figure 6 The two peaks at 405.07 eV and 412.00 eVd in (G) are attributed to Cd 2+ The two peaks at 405.73eV and 412.51eV are attributed to Cd-O, which is adsorbed on the surface of the material as a precipitate through metal-π electron bonds.

[0081] based on 31 The results of PNMR showed that ( Figure 1 ), the surface of phosphorus-modified biochar is mainly composed of orthophosphate. Therefore, Cd-orthophosphate is the main co-precipitation form between P and heavy metal Cd in the material. These results indicate that physical adsorption, precipitation, complexation of oxygen-containing functional groups and cation exchange occurred during the adsorption process of Pb and Cd. Adsorption mechanism is as follows Figure 7 shown.

[0082] Example 3 Soil experiment

[0083] 1. Preparation and Incubation of Contaminated Soil Samples

[0084] Experimental soil was collected from Pengzhou, Sichuan Province, the authentic production area of ​​the traditional Chinese medicine Chuanxiong. Soil was collected from the topsoil layer at a depth of 0–20 cm, dried (room temperature 24–26°C), and passed through a 2 mm mesh to remove impurities. After microwave digestion with HF-HNO₃-HCl (2:6:3), background levels of lead and cadmium in the soil were determined by inductively coupled plasma mass spectrometry (ICP-MS). Soil pH was measured using a pH meter, with a soil-to-water ratio of 1:2.5 (w / v). Soil cation exchange capacity (CEC) was determined by ultrasonic extraction-spectrophotometry (HJ 889-2017 standard, China), and soil organic matter (TOC) was determined by H₂SO₄-K₂Cr₂Oₐ oxidation (HJ 615-2011 standard, China). Soil total nitrogen, available potassium, and available phosphorus were determined according to soil analysis methods (NYT 1848–2010 standard, China).

[0085] Standard solutions of two heavy metals, Cd and Pb (purchased from Henan R&D Center for certified reference material), were added to the soil and incubated at room temperature at 45% of its saturated water holding capacity for 50 days. These solutions were then prepared as standard heavy metal mixed soils with high and low concentrations, which were then used as standby. Incubation experiments were conducted in 500 mL plastic conical flasks with lids to evaluate the adsorption of heavy metals from the contaminated soil by modified biochar. Different doses (1% and 3%) of modified biochar were thoroughly mixed with 200 g of contaminated soil samples, with detailed groupings shown in Table 7. Each treatment was replicated three times. The soil samples were then incubated at room temperature at a constant humidity (45% of its water holding capacity) for 60 days. The low heavy metal concentration refers to 200 mg / kg Pd (0.8 times the national secondary standard) and 0.5 mg / kg Cd (1.7 times the national secondary standard); the high heavy metal concentration refers to 500 mg / kg Pd (the national tertiary standard) and 3 mg / kg Cd (three times the national tertiary standard). After incubation, the soil samples were air-dried, and approximately 100 g of soil was ground through 2 mm and 0.15 mm sieves and stored for further physical and chemical analysis. To better investigate the adsorption of heavy metals between the materials, the HHM3 group was used as an example. The adsorbed biochar was collected using sieves and tweezers for characterization and analysis, primarily using SEM-EDS, XRD, FT-IR, and XPS techniques.

[0086] Table 7 Grouping conditions in soil experiments

[0087]

[0088]

[0089] Note: LowHMs (low heavy metal concentration) refers to the concentration containing 200mg / kg lead and 0.5mg / kg cadmium, and HighHMs (high heavy metal concentration) refers to the concentration containing 500mg / kg lead and 3mg / kg cadmium.

[0090] 2. Analysis of changes in soil properties

[0091] To investigate the effects of biochar addition on soil properties, the experiment focused on enzyme activity, available phosphorus, and water retention. Enzyme activity is closely related to environmental conditions and serves not only as an important biomarker for detecting soil changes but also as evidence of heavy metal sequestration in soil. Urease plays a crucial role in regulating nitrogen mobility in soil ecosystems. Phosphatases, including acidic, neutral, and alkaline phosphatases, facilitate the conversion of organic phosphorus in the soil into inorganic phosphorus that can be absorbed and utilized by plants. Based on the neutral soil pH, neutral phosphatase activity in the soil was measured using a citrate buffer colorimetric method. Urease activity was measured using a sodium phenolate-sodium hypochlorite colorimetric method. To investigate the potential of phosphorus-modified biochar as a phosphate fertilizer substitute, the available phosphorus content of different groups was determined using sodium bicarbonate extraction followed by molybdenum antimony spectrophotometry. The available phosphorus content obtained from multiple extractions was used to evaluate the slow-release effect of the experimental materials on phosphorus. To investigate the impact of the materials on soil water retention, water retention was tested. The specific method is as follows: 1.0g of BC / 3K-BC was mixed with 150g of dry soil, 50mL of ultrapure water was added, and the mixture was weighed (W0). The mixture was stored at room temperature and weighed regularly (W t ). At the same time, a blank group without biochar was set up as a control to observe the effect of the added material on the water retention of the soil. The calculation formula is as follows:

[0092]

[0093] The results of the soil enzyme activity, available phosphorus, and water retention are as follows:

[0094] 2.1 Enzyme activity assay

[0095] The urease and phosphatase contents in soils with different ratios of 3K-BC were as follows: Figure 8 (A, B) Phosphatase and urease are hydrolases. Phosphatase activity is positively correlated with total phosphorus, while urease activity is positively correlated with nitrogen, reflecting soil fertility and the biotoxicity of HMs. Compared to CK, both high and low concentrations of HMs inhibited the levels of both enzymes, with higher concentrations of heavy metals leading to a more pronounced inhibitory effect. Application of 1% 3K-BC significantly reduced the activities of both enzymes, with urease and phosphatase levels in the LHM1 group even higher than in the CK group. This demonstrates the biochar's stimulatory effect on both enzymes. It is speculated that the alkaline biochar directly alters the pH of acidic soil, thereby increasing urease and phosphatase levels. Furthermore, the active substances released by BC in the soil can enhance the activities of urease, phosphatase, and other enzymes. When the biochar application rate was increased to 3%, both LHM3 and HHM3 showed a relatively weaker stimulatory effect on urease activity compared to the group without 3K-BC. Regarding phosphatase, 3% 3K-BC exhibited an inhibitory effect. Therefore, the material with a 1% application rate had a better effect on soil enzyme activity, and it was not recommended to increase the dosage to 3%.

[0096] 2.2 Available phosphorus content

[0097] Effect of 3K-BC on the available phosphorus content in different treatment groups Figure 8 (C) shows that the content of available phosphorus increases with the increase in the amount of biochar applied. The available phosphorus content of the three groups without biochar addition (CK, LHM0, HHM0) was almost gone after the first extraction. For LHM1 and HHM1 with an application rate of 1%, the remaining available phosphorus content after four extractions was 56% and 45% of the first extraction, respectively. A similar phenomenon was observed in the group with an application rate of 3%. This shows that the material has a slow-release effect on the release of available phosphorus. To a certain extent, the experimentally prepared material 3K-BC can partially replace traditional phosphate fertilizers.

[0098] 2.3 Water retention test

[0099] Biochar has been shown to improve soil fertility by increasing soil porosity, water retention, and promoting aggregate stability. Figure 8 (D) Overall, the water retention of the biochar-added experimental group was similar to that of the CK, reaching equilibrium around day 14. However, during the first ten days, the water retention between the groups was in the order: 3K-BC > BC > CK. This demonstrates that short-term biochar application can improve soil water retention.

[0100] 3. Potential adsorption mechanisms in soil

[0101] 3.1 SEM-EDS

[0102] In order to study the potential adsorption mechanism of modified biochar on Pb / Cd under soil conditions. This experiment took the HHM3 group as an example to characterize the biochar before and after adsorption in soil. Among them, four common characterization techniques are mainly included: SEM-EDS, XRD, FT-IR, and XPS. SEM-EDS was used to observe the changes in the morphological structure and surface element content of biochar before and after modification and before and after adsorption. Figure 9 As shown. In this study, the surface of 3K-BC exhibited a rich porous structure. After 50 days of incubation in soil, the biochar surface was covered with some particulate compounds, the pores were mostly blocked by particulate compounds, and some of the pore structure collapsed. According to semi-quantitative EDS analysis results, compared with the pre-adsorption state, the P and K content of the biochar surface decreased, while the Pb and Cd content increased, demonstrating the material's effective adsorption of the two heavy metals through precipitation and ion exchange mechanisms.

[0103] 3.2XRD

[0104] The XRD patterns of 3K-BC before and after incubation are as follows: Figure 10 (A) shows broad and strong diffraction peaks near 22° and 42°, representing typical characteristic peaks of amorphous carbon. For 3K-BC, typical characteristic peaks corresponding to Ca3(PO4)2 were found at 2θ = 22.275°, 24.180°, 24.392°, 28.677°, and 30.847°. Peaks corresponding to K2HPO4 were found at 2θ = 20.794°, 24.074°, 27.884°, 30.000°, 53.069°, and 57.989°. After the adsorption of heavy metals, the intensities of some original peaks were significantly reduced or even disappeared. At the same time, some peaks related to Pb and Cd compounds appeared on the biochar surface. For Pb, characteristic peaks of PbHPO4 appeared at 2θ = 26.561°, 30.899°, and 32.963°. For Cd, the peaks at 2θ = 17.884, 27.619, and 31.587 correspond to Cd(OH)2; the peaks at 2θ = 11.111, 20.688, and 23.386 correspond to Cd3(PO4)2; and the peaks at 2θ = 14.603, 16.878, 24.127, and 36.508 correspond to CdH4(PO4)2·2H2O. Anions released from biochar (such as PO4 3- OH - ) can react with heavy metal ions (Pb and Cd) to form mineral precipitation compounds. The results show that the fixation mechanism of 3K-BC on Pb and Cd in soil may include the reaction of heavy metal ions with PO4 3- and OH - coprecipitation effect.

[0105] 3.3 FT-IR

[0106] FT-IR is used to qualitatively identify the characteristic functional groups on the surface of biochar materials. The FT-IR spectra of phosphorus-modified biochar before and after incubation are as follows: Figure 10 (B) 3730cm -1 The peaks at 2977 and 2890 cm-1 are assigned to the stretching vibration of OH. -1 The peak at 2358 cm is assigned to the stretching vibration of aliphatic CH. -1 The peak at 1570 cm is attributed to the stretching vibration of C≡C. -1 The characteristic peak at 1538 cm was attributed to COOH. After 15 days of incubation, the peak position of the characteristic peak shifted and became 1538 cm -1 Stretching vibration. 1043 and 873 cm -1 The peak at is assigned to PO4 3- Biochar is formed by OH, C≡C, COOH and PO4 3-Various functional groups such as PO4 can increase the binding sites for specific adsorption of heavy metals. These characteristic peaks were greatly weakened or even disappeared completely after 50 days of incubation. This phenomenon indicates that PO4 3- , OH, COOH and C≡C and other functional groups may be involved in the immobilization process of heavy metals. 3- It can directly participate in the surface complexation and precipitation of Pb and Cd. At the same time, only the characteristic peak of orthophosphate was found on the surface of 3K-BC, which is consistent with the XRD and 31 The results of PNMR remained consistent.

[0107] 3.4XPS

[0108] To further clarify the role of modified biochar in the adsorption process in soil, this experiment measured the XPS spectra of 3K-BC before and after incubation. The results are shown in Figure 10(CF). The characteristic peaks of two heavy metals can be observed from the full spectrum of biochar after adsorption, proving the successful loading of heavy metals. For the fine spectrum of C1s, Figure 10 The peaks at 285.69eV, 284.70eV, and 289.20eV in (D) are attributed to C–C / C–H, C–O / C–N, and COOH functional groups, respectively. The relative contents before the adsorption of heavy metals were 33.42%, 63.38%, and 3.19%, respectively, while the relative contents after the adsorption of Pb and Cd were 40.05%, 55.25%, and 4.70%, respectively. The results show that after the adsorption of heavy metals, the relative contents of C–C / C–H and COOH functional groups increased, indicating that heavy metal complexes were formed on the surface of the material after the adsorption of heavy metals. At the same time, the content of C–O decreased, which may be attributed to the deprotonation of the C–O(H) group, resulting in the separation of heavy metal ions and H + For the fine spectrum of O1s, Figure 10The peaks at 530.96 eV (35.74%), 532.22 eV (44.70%), and 533.58 eV (19.56%) in (E) are attributed to C=O / P=O, C–O / P–O, and -OH / O–C=O groups, respectively. Before heavy metal adsorption, their relative contents were 35.74%, 44.70%, and 19.56%, respectively. After HM adsorption, their contents increased to 26.13%, 34.29%, and 39.58%, respectively. The decrease in the content of C=O / P=O and C–O / P–O groups, coupled with an increase in their binding energies, confirms their involvement in the heavy metal adsorption process. This is consistent with the XRD results, indicating the formation of a phosphate-heavy metal precipitate. The peaks at 132.98 eV and 133.71 eV in the P 2p fine spectrum are attributed to P=O and P–O, respectively. Their relative contents before HM adsorption were 53.59% and 46.41%, respectively, but after HM adsorption, they increased to 39.48% and 60.53%. Simultaneously, the binding energies of both peaks increased to 133.70 eV and 134.58 eV, respectively, likely due to the binding of functional groups to heavy metals, demonstrating their involvement in the adsorption process.

[0109] In summary, the adsorption mechanism of 3K-BC on Pb and Cd in soil is mainly composed of precipitation, cation exchange and complexation.

[0110] 4. Speciation analysis of heavy metals in soil

[0111] The presence of Cd and Pb in the amended soil was investigated using the European Community Bureau of Reference (BCR) sequential extraction procedure. Briefly, 1.000 g of the biochar-soil mixture was placed in a 50 mL polytetrafluoroethylene tube and extracted with 0.11 M acetic acid (40 mL), 0.5 M NH₂OH·HCl (40 mL; pH = 2), 8.8 M H₂O₂ (10 mL; pH = 2), 1 M NH₄OAc (20 mL; pH = 2), and aqua regia (HCl / HNO₃, 3:1, 8 mL), respectively, to obtain the acid-soluble, reducible, oxidizable, and residual fractions of HMs. The heavy metal contents of each fraction were determined by ICP-OES.

[0112] The experiment used the modified BCR sequential extraction method to study the forms of heavy metals, in order to explore the changes in the forms of Pb and Cd in the soil when adding different amounts of biochar. In this method, heavy metal ions are divided into four forms, namely acid-soluble, reducible, oxidizable and residual. Among them, the acid-soluble form can be directly absorbed and utilized by plants and is the easiest to absorb and accumulate in organisms; while the residual form is the most stable form and is also the most difficult for plants and animals to absorb and utilize. Figure 11As shown, in the experiment without biochar addition, the distribution of Pb species was acid-soluble > residual > oxidizable > reducible; while the distribution of Cd species was acid-soluble > reducible > residual > oxidizable. Compared with the experiment without biochar addition, the addition of 1% and 3% 3K-BC effectively reduced the acid-soluble content of both heavy metals, Pb and Cd, with the 3% addition being more effective than the 1% addition. The acid-soluble content of both heavy metals decreased significantly with increasing biochar addition. At a 3% addition, the acid-soluble content of Pb and Cd decreased by 15% and 20%, respectively, in the low-concentration heavy metal group, while the residual content increased by 15% and 14%, respectively, in the corresponding experiment group. At this same time, the acid-soluble content of Pb and Cd decreased by 14% and 27%, respectively, in the high-concentration heavy metal group, while the residual content increased by 6% and 25%, respectively. This indicates that 3K-BC has a better fixation effect on Pb in low-pollution soils, while 3K-BC has a stronger fixation effect on Cd in highly polluted environments. In summary, different amounts of modified biochar treatment can convert Pb and Cd into more stable forms, and the effect is more pronounced with increasing amounts, demonstrating the potential of phosphorus-modified biochar to immobilize heavy metals in soils.

[0113] 5. Bioavailability and potential ecological risk assessment

[0114] The availability of HMs to soil bioavailability was analyzed using CaCl₂ extraction. Briefly, soil was extracted with 0.01 M CaCl₂ at 20°C for 2 hours using a soil extraction ratio of 1:5 (w / v). The mixture was shaken and centrifuged at 3000 rpm for 15 minutes. The supernatant was then filtered through a 0.45 μm microporous filter and analyzed for Pb and Cd concentrations in the extract by ICP-MS.

[0115] The Toxicity Characteristic Leaching Procedure (TCLP) was used to assess changes in leaching toxicity in modified soils. Generally, 5 g of soil sample was mixed with 100 mL of 0.5 M glacial acetic acid solution (pH = 2.88), shaken continuously for 16 h, and then centrifuged to obtain the supernatant. Samples were prepared through a 0.45 μm microporous filter membrane, and after dilution, the concentrations of Cd and Pb were analyzed using ICP-MS. All tests were performed in triplicate. This study used the Nemerow index (NI) and potential ecological risk index (RI) methods to assess the ecological risks of heavy metals in soils.

[0116] (1) Nemerow index calculation method

[0117]

[0118] Among them, P i is a single pollution index, C i is the concentration of heavy metals extracted by TCLP in the soil after the pot experiment, Si is the TCLP international standard (the concentrations of Pb and Cd are 5 and 0.5 mg / kg respectively), NPI is the Nemerow comprehensive pollution index, P max is the maximum value of the pollution index, P avr It is the average value of the individual pollution indices.

[0119] (2) Calculation method of potential risk index

[0120] E i =T i ×P i (5)

[0121]

[0122] Where E i is a single potential ecological risk index; T i is the toxicity reaction coefficient of a single heavy metal (Pb is 5, Cd is 30), P i is a single pollution index; PI is a comprehensive potential ecological risk index of multiple metals.

[0123] The CaCl2 and TCLP extraction methods were used to assess the bioavailability and leaching toxicity of HMs in contaminated soils, respectively. Increased mobility and bioavailability of heavy metals in soils make them more accessible to plants and other organisms. The content of bioavailable heavy metals in soil was studied, and the results were as follows: Figure 12 (A) For the untreated biochar-added test groups, LHM0 and HHM0 exhibited the highest heavy metal extraction yields, at 3.53 μg / kg and 20.95 μg / kg for Pb, respectively; for Cd, LHM0 and HHM0 exhibited 11.25 μg / kg and 62.88 μg / kg, respectively. This indicates that the soil medium itself has a higher immobilization effect on Pb. Furthermore, for both high and low heavy metal concentration test groups, the immobilization of heavy metals in the modified soil significantly increased with increasing 3K-BC application rates. Furthermore, the percentage reduction of different heavy metal contents was calculated by comparing the values ​​measured in the untreated biochar-added test group. At a 3% application rate, the reduction rates for Pb and Cd were 86% and 91%, respectively, at the low concentration, and 86% and 93%, respectively, at the high concentration. Therefore, 3K-BC has a greater immobilization efficiency for Cd than for Pb.

[0124] TCLP extraction content Figure 12(B, C). For Pb, the extractable contents of LHM0 and HHM0 were 112.45 mg / kg and 219.00 mg / kg, respectively; for Cd, the extractable contents of LHM0 and HHM0 were 0.68 mg / kg and 2.22 mg / kg, respectively. With the introduction of 3K-BC, the leached heavy metal content decreased significantly when the application rate increased from 1% to 3%. Compared with no biochar addition, the TCLP-extracted Pb content decreased by 24% and 37% at low biochar concentrations (1%) and 3% treatments, respectively, and by 21% and 39% at high biochar concentrations. Similarly, for Cd, the content decreased by 38% and 44% at low biochar concentrations (1%) and 3% treatments, respectively, and by 10% and 18% at high biochar concentrations. Risk assessment of the incubated soils was performed using the Nemerow Index (NPI) and Potential Ecological Risk Index (PI), and the results are shown in Table 8. For Cd, under low-concentration heavy metal conditions, the Pi value decreased from 1.36 to 0.83 and 0.77 with the increase in application amount. This indicates that the degree of soil pollution has changed from light pollution to non-pollution level. Similarly, after treatment with 3K-BC, the Pi values ​​in the soil decreased significantly with the increase in application amount, especially for Pb at high concentrations, which decreased from 43.80 (HHM0) to 34.61 (HHM1) and 26.67 (HHM3), which confirms the effectiveness of 3K-BC in improving the heavy metal environment in the soil. In addition, for other groups, the experimental results did not reduce the degree of pollution, which may be because the initial concentration of heavy metals in the experimental setting was too high, so that the soil could not be improved to a non-pollution level with a limited amount of 3K-BC. The NPI value reflects the comprehensive pollution status of heavy metals in the soil. Under low heavy metal concentration conditions, for Cd, the NPI value decreased from 0.96 (LHM0) to 0.35 (LHM1) and 0.31 (LHM3), indicating that the soil has fallen from the warning level to a safe level. For the other experimental groups, whether under low or high heavy metal concentration conditions, the NPI value decreased with increasing application amount, similar to the trend of the Pi value.

[0125] The potential ecological risk index (EI) can be used to assess the ecological risk level of a single or multiple heavy metals based on their properties and environmental behavior. Table 8 shows that the Ei values ​​for heavy metals in soil are higher for Pb than for Cd, indicating that Pb is the most hazardous element in the experimental soils. Adding modified biochar to the soils decreased the Ei values ​​for all experimental groups. For example, for Cd at low concentrations, the Ei value decreased from 40.87 (LHM0) to 24.94 (LHM1) and 23.05 (LHM3), indicating that the environmental risk in the experimental groups decreased from medium to low risk. For the other groups, the Ei values ​​showed a similar trend to the Nemerow index. This means that the addition of 3K-BC can reduce the ecological risk of heavy metals in soil at both high and low concentrations. For the high-concentration contamination group, although the addition of 3% of the material reduced the ecological risk of Pb and Cd, the index remained high. Furthermore, the comprehensive assessment index (PI) values ​​in the low-concentration group were 153.32, 110.23, and 94.16, respectively—all below 150, indicating a low risk level. In the high-concentration group, the addition of 3K-BC shifted the soil risk from high to medium. In summary, 3K-BC is an effective immobilization material for reducing the ecological risks of Pb and Cd.

[0126] Table 8 Nemerow index and potential ecological risk index of heavy metals in soil

[0127]

[0128]

[0129] Example 4 Potted experiment

[0130] The Chinese medicinal herb Chuanxiong (Ligusticum chuanxiong) was cultivated in pots and used as an experimental design material to investigate its effects on plant growth. Contaminated soil was prepared by adding standard heavy metal stock solutions. The lead concentration was set at 200 ppm, and the cadmium concentration was set at 3 ppm. The treatments and design were as follows: BK (normal soil), 1% BC-BK (1% 3K-BC + normal soil), 0% BC-HM (0% 3K-BC + contaminated soil), and 1% BC-HM (1% 3K-BC + contaminated soil), totaling four groups, with six replicates per group. After seven months of cultivation in a natural environment, the roots, stems, and leaves of Ligusticum chuanxiong were harvested and washed with deionized water. The main indicators measured for Ligusticum chuanxiong included yield, heavy metal distribution, and medicinal efficacy evaluation. The distribution of heavy metals in different plant parts was determined using microwave digestion and ICP-MS using samples from different plant parts. Medicinal efficacy refers to the analysis of the heavy metal distribution using a high-performance liquid chromatograph (HPLC, Agilent 1260, USA) and a chromatographic column (Thermo BDS C 18, 4.6mm×250mm, 5μm) to determine the specific contents of its main components (ferulic acid, ligustilide A, and ligustilide).

[0131] Metal accumulation and pollution index calculation:

[0132] The bioconcentration factor (BCF) and transfer factor (TF) were calculated as:

[0133]

[0134] Where M plant is the Pb / Cd concentration in plant biomass, M soil is the total heavy metal concentration in the soil, in mg / kg. aboveground is the heavy metal concentration in the aboveground part of plant tissue, and M root Indicates the concentration of heavy metals in roots.

[0135] 1. Impact of biochar application on yield

[0136] Effect of modified biochar on the yield during the growth of Chuanxiong Figure 13 (A). For the blank soil (BK) and 1% BC-BK, the addition of 1% 3K-BC increased the weight of the roots and leaves of Chuanxiong by approximately 10% and 3%, respectively, while the weight of the stem remained unchanged. Comparisons between the BK and 0% BC-HM groups revealed that the addition of heavy metals inhibited the growth of all parts of the Chuanxiong plant. Pb and Cd in the soil-plant system impair root nutrient absorption and photosynthesis, thereby inhibiting plant growth. Compared to BK, the root and leaf weights of the 1% BC-HM soil increased by approximately 28% and 18%, respectively, while the stem weight decreased by approximately 17%. It has been reported that the application of biochar can promote better plant growth. Experimental results indicate that 3K-BC promotes the growth of Chuanxiong, particularly the roots, the medicinal part. This is presumably because the biochar is rich in phosphorus and potassium, essential for plants, thus acting as a fertilizer to promote growth. The use of biochar as an organic alternative to synthetic waste for soil improvement has been a key focus of agricultural scientists in recent years.

[0137] 2. Impact of biochar application on medicinal effectiveness

[0138] The contents of the medicinal components of the roots of the traditional medicinal parts of different groups were determined. The contents of ferulic acid, ligustilide A and ligustilide were as follows: Figure 13(B) In the blank soil, 1% 3K-BC had a moderately stimulating effect on ferulic acid and ligustilide A, but had no significant effect on the content of ligustilide. With the addition of heavy metals to the soil, all three active ingredients showed an inhibitory effect. The contents of ferulic acid, ligustilide A, and ligustilide decreased to 0.34 mg / g, 2.38 mg / g, and 24.24 mg / g, respectively. The inhibitory effect of heavy metals on ligustilide was particularly pronounced. The results indicate that the heavy metals Pb and Cd inhibit the production of active ingredients in Chuanxiong, possibly due to the accumulation of heavy metals in Chuanxiong, thereby inhibiting its normal physiological and biochemical processes. Adding 1% 3K-BC or 1% BC-HM to the heavy metal-contaminated soil mitigated the inhibitory effects on the three active ingredients, as evidenced by an increase in their contents. For example, the content of ligustilide increased from 24.24 mg / g to 29.63 mg / g. The experiment proved that 3K-BC has a positive effect on the active ingredients of Chuanxiong and can, to a certain extent, offset the negative effects of heavy metals in the soil. In summary, 3K-BC has the potential to alleviate heavy metal stress during the growth of Chuanxiong.

[0139] 3. Effect of biochar application on the distribution of heavy metals in organisms

[0140] The distribution of heavy metals in different parts of Ligusticum chuanxiong is shown in Table 9. For the 0% BC-HM and 1% BC-HM groups, the distribution of Pb in the stem showed a significant decrease, while the distribution of Cd in all three parts showed a significant decrease (P < 0.05), demonstrating that Ligusticum chuanxiong is more sensitive to the heavy metal Cd. Among the four groups, the highest accumulation of heavy metals was found in the 0% BC-HM group. The BCF values ​​for Cd in each group were greater than 1, indicating that Cd is relatively enriched in Ligusticum chuanxiong. Ligusticum chuanxiong has a certain enrichment effect on all heavy metals, and most of them are enriched in the rhizomes. For Pb, the BCF values ​​were all less than 1, indicating that it has not reached the level of enrichment in Ligusticum chuanxiong. There were no significant differences in the TF values ​​for Pb and Cd between the 0% BC-HM and 1% BC-HM heavy metal contaminated plants. This is likely due to the tendency of Chuanxiong roots to accumulate heavy metals and their low translocation capacity, which weakens the biochar's transport function. In summary, the application of 3K-BC reduced the Pb and Cd contents in the roots, stems, and leaves of Chuanxiong to a certain extent, providing a reference for heavy metal removal cultivation techniques in Chuanxiong.

[0141] Table 9 Concentrations of lead and cadmium in different plant parts

[0142]

[0143]

[0144] Different letters indicate statistically significant differences between treatments (mean ± SD, N = 3). Abbreviations: BCF, bioconcentration factor; TF, transport factor.

[0145] Summary:

[0146] In this study, biochar was applied to heavy metal contaminated solution or soil to investigate its adsorption mechanism and effect on Pb and Cd. The results of kinetic and isotherm experiments showed that the adsorption process of Pb and Cd on 3K-BC could be well described by the pseudo-second-order kinetic model and Langmuir isotherm model, indicating that the adsorption was chemical adsorption and monolayer adsorption. At the same time, the maximum adsorption capacity of 3K-BC for Pb and Cd was calculated to be 361.82 mg / g and 123.03 mg / g, respectively, by fitting the Langmuir model. The adsorption capacity of the experimental material was high, indicating that the adsorption performance of the prepared material was ideal. The adsorption mechanism mainly included physical adsorption, precipitation, complexation of oxygen-containing functional groups, and cation exchange. The enzyme activity and available phosphorus in the remediated soil were studied. The results showed that 1% of 3K-BC showed a promoting effect on urease and phosphatase in the soil. When the application amount increased to 3%, the material showed an inhibitory effect on phosphatase. Modified BCR extraction experiments were conducted on the distribution of heavy metals in the improved soil, and the bioavailability and potential ecological risk of the soil were evaluated. 3K-BC showed good immobilization ability for Pb and Cd in the contaminated soil by converting unstable acid-soluble fractions into stable components. The bioavailability and potential ecological risk assessment showed that the application of the material could reduce the availability of heavy metals Pb and Cd. In addition, the yield, medicinal effectiveness, and heavy metal distribution of Chuanxiong in the pot experiment showed that 3K-BC had a positive promoting effect on the growth of Chuanxiong, and had the dual functions of immobilizing heavy metals Pb / Cd and improving soil fertility. This study provides a simple and feasible solution for the scientific use of Chinese herbal residue to synthesize phosphorus-modified biochar and remediate Pb and Cd-contaminated water bodies / soil.

[0147] Although the present application has been described in detail with general description and specific embodiments above, it is obvious to those skilled in the art that some modifications or improvements can be made on the basis of the present application. Therefore, these modifications or improvements made without departing from the spirit of the present application are within the scope of the present application.

Claims

1. A method for preparing biochar modified with Danshen medicinal residue, characterized in that: The salvia miltiorrhiza residue is soaked in a potassium phosphate aqueous solution, washed with ultrapure water, dried, pyrolyzed, ground and sieved to obtain the salvia miltiorrhiza residue modified biochar.

2. The method for preparing biochar modified with Danshen medicinal residue according to claim 1, characterized in that: The concentration of the tripotassium phosphate aqueous solution is 1.8-2.40 mol / L.

3. The method for preparing biochar modified with Danshen medicinal residue according to claim 1, characterized in that: The soaking is carried out under stirring conditions, the soaking temperature is 10-35° C., and the soaking time is 18-36 hours.

4. The method for preparing biochar modified with Danshen residue according to claim 1, characterized in that: The drying conditions are: 70-85° C., 3-6 hours.

5. The method for preparing biochar modified with Danshen residue according to claim 1, characterized in that: The pyrolysis conditions are: 550-650° C., 1.5-2.5 hours under anoxic conditions.

6. The method for preparing biochar modified with Danshen residue according to claim 1, characterized in that: The particle size of the ground and sieved mesh is 1-2 mm.

7. The method for preparing biochar modified with Danshen residue according to claim 1, characterized in that: The preparation method of the salvia miltiorrhiza residue modified biochar comprises: The salvia miltiorrhiza residue was crushed to <2 mm, soaked in a saturated potassium phosphate aqueous solution for 24 h, and the excess phosphate on the surface of the residue was washed with ultrapure water. Then, it was dried in an 80°C oven for 3 h, and heated to 600°C at a heating rate of 10°C / min in a vacuum tube furnace. The pyrolysis time was continued for 2 h. After the pyrolysis was completed, it was naturally cooled to room temperature, washed with ultrapure water, and vacuum-dried. It was stored in a brown bottle for later use.

8. A biochar modified with Danshen residue, characterized in that: It is made by the method according to any one of claims 1 to 7.

9. Use of the biochar modified with Danshen residue according to claim 8 in remediation of lead and cadmium contaminated water / soil.

10. Use of the biochar modified with Danshen residue according to claim 8 in the cultivation of Chuanxiong.

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