Modified biochar for repairing heavy metal polluted water and soil and preparation method of modified biochar

Abstract

The invention relates to the technical field of pollution remediation materials, and discloses modified biochar for heavy metal polluted water and soil remediation and a preparation method thereof.The modified biochar takes a biochar matrix as a carrier, and a ferrous functional component, a polyphenol-calcium fixation component, a weakly soluble calcium magnesium phosphorus component and a magnesium aluminum exchange buffer component are introduced; the preparation method comprises the following steps: preparing basic biochar through biomass pyrolysis, pre-embedding ferrous iron, fixing polyphenol-calcium, forming weakly soluble calcium-magnesium-phosphorus components in situ, constructing magnesium-aluminum exchange buffer components and drying and preparing. The material has the functions of valence state regulation and control, interface fixation, precipitation fixation and exchange buffer, can be used for heavy metal polluted water and soil remediation, and is suitable for a multi-heavy metal coexistence system.

Description

Technical Field

[0001] This invention relates to the field of pollution remediation materials technology, specifically to a modified biochar for the remediation of heavy metal-polluted soil and water and its preparation method. Background Technology

[0002] With the continued existence of activities such as mining, smelting, electroplating, chemical processing, discharge of heavy metal-containing wastewater, and improper storage of metal-containing solid waste, the accumulation of heavy metals such as lead, cadmium, copper, zinc, nickel, and chromium in water bodies and soil is becoming increasingly prominent. Once in the environmental media, heavy metals are characterized by their slow degradation, complex migration pathways, and long environmental residence time. They not only affect the physicochemical properties of water and soil but also exert a lasting impact on ecosystems and human health through the food chain. Therefore, developing materials and application technologies suitable for the remediation of polluted water and soil is of practical significance.

[0003] Biochar has been widely used in the remediation of heavy metal pollution in recent years due to its wide availability, low cost, large specific surface area, rich pore structure, and the presence of a certain number of oxygen-containing functional groups on its surface. In existing technologies, biochar is typically modified through acid-base activation, metal salt loading, mineral composites, or enhancement with oxygen- and nitrogen-containing groups to improve its adsorption, complexation, ion exchange, or precipitation fixation capabilities for heavy metal ions. Modified biochar has already demonstrated certain application value in single-metal pollution systems.

[0004] However, most existing modified biochars for heavy metal remediation are designed around a single mechanism of action, typically focusing on increasing adsorption capacity, expanding the number of surface functional groups, or introducing a specific inorganic active component. When faced with real-world polluted environments containing multiple heavy metals, this approach is prone to problems such as competition for adsorption sites, a single immobilization pathway, and inconsistent control effects for different heavy metals. For systems containing both high-valence and divalent heavy metals, existing materials often struggle to simultaneously achieve both initial valence regulation and subsequent stable immobilization, thus limiting their applicability in complex systems.

[0005] Meanwhile, while some modified biochars in existing technologies exhibit a certain heavy metal removal capacity in the initial experimental stages, the introduced active components are prone to desorption, migration, or activity decay during continuous contact, water-soil cycles, or changes in pH conditions, thus affecting long-term stability. Especially in contaminated soil remediation, materials not only need initial fixation capabilities but also need to maintain low heavy metal activity and leaching risk over a longer period. If the modified components are not stably bonded to the biochar carrier, or if there is mutual interference between different functional components within the material, its sustained remediation capacity will be weakened.

[0006] Furthermore, there are significant differences in remediation requirements between polluted water and polluted soil. Water remediation typically requires materials with rapid interfacial reaction rates and high initial removal efficiencies, while soil remediation focuses more on long-term passivation, leaching control, and stability under fluctuating environmental conditions. In existing technologies, materials designed for water bodies may not maintain stability in soil, while materials designed for soil passivation may have insufficient reaction rates in water. Therefore, how to construct a modified biochar material suitable for both polluted water and polluted soil, capable of phased regulation and stable fixation under conditions of multiple heavy metal coexistence, remains a technical problem that needs to be solved in this field. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a modified biochar for the remediation of heavy metal-contaminated water and soil and its preparation method. It solves the problems of existing modified biochar mainly relying on a single mechanism of action, making it difficult to simultaneously achieve the conversion of high-valence heavy metals and the stable fixation of multiple divalent heavy metals, as well as the insufficient applicability of existing materials in both water and soil media, the easy migration of active components, and insufficient long-term remediation stability.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a modified biochar for the remediation of water and soil contaminated with heavy metals, characterized in that the modified biochar comprises the following components:

[0009] Ferrous functional component, calculated as iron, in the form of 0.3 to 3.0 parts by weight;

[0010] A polyphenol-calcium immobilized component, wherein the polyphenol is 0.5 to 4.0 parts by weight and the calcium is 0.2 to 2.0 parts by weight;

[0011] The weakly soluble calcium, magnesium and phosphorus components, wherein phosphorus is 1.0 to 6.0 parts by weight, calcium is 0.8 to 6.0 parts by weight, and magnesium is 0.1 to 2.0 parts by weight;

[0012] The magnesium-aluminum exchange buffer component contains 1.0 to 5.0 parts by weight of magnesium and 0.3 to 2.5 parts by weight of aluminum.

[0013] Preferably, the biochar matrix is ​​derived from one or more of corn stalks, rice stalks, peanut shells, sawdust, and fungal residue; the polyphenols in the polyphenol-calcium immobilization component are selected from one or more of tannic acid, tea polyphenols, and tannins; and the calcium in the polyphenol-calcium immobilization component is derived from one or more of calcium hydroxide, calcium acetate, and calcium chloride.

[0014] Preferably, the weakly soluble calcium magnesium phosphate component comprises one or more of dicalcium phosphate, octacalcium phosphate, hydroxyapatite, magnesium-containing calcium phosphate, and magnesium ammonium phosphate, wherein the Ca / P molar ratio of the weakly soluble calcium magnesium phosphate component is 1.0 to 1.8, and the Mg / P molar ratio is 0.05 to 0.60.

[0015] Preferably, the Mg / Al molar ratio in the magnesium-aluminum exchange buffer component is 2.0 to 4.0, the particle size of the modified biochar is 0.074 to 2.0 mm, and the pH of the aqueous extract is 7.0 to 10.5.

[0016] A method for preparing modified biochar for the remediation of water and soil contaminated with heavy metals includes the following steps:

[0017] S1. Pyrolyze the biomass raw material at 450-650℃ for 1-3 hours under limited oxygen conditions to obtain basic biochar;

[0018] S2. The basic biochar is added to a deoxygenated aqueous solution of ferrous salt for impregnation treatment. The pH of the impregnation system is controlled at 4.5-6.0. After treatment, the biochar is separated and dried to obtain ferrous pre-embedded biochar.

[0019] S3. The ferrous pre-embedded biochar is added to a polyphenol solution for treatment, and then a calcium source is added and the pH of the system is controlled at 6.5-8.0 to perform polyphenol-calcium immobilization treatment to obtain an immobilization activation intermediate.

[0020] S4. The immobilized activation intermediate is contacted with a phosphorus source, a calcium source, and a magnesium source, and the pH of the system is controlled to be 7.5-9.0 to allow the weakly soluble calcium, magnesium and phosphorus components to form in situ, thereby obtaining a weakly soluble calcium, magnesium and phosphorus supported intermediate.

[0021] S5. The weakly soluble calcium magnesium phosphorus supported intermediate is contacted with magnesium salt and aluminum salt, and the magnesium aluminum exchange buffer component is formed in situ under alkaline conditions, followed by aging treatment.

[0022] S6. Filter, wash and dry the material obtained in step S5 at 80-120°C to obtain the modified biochar.

[0023] Preferably, before step S1, the following pretreatment is further included: the biomass raw material is washed and dried at 60-105°C for 8-24 hours, and then pulverized to 0.5-5 mm, and the moisture content of the biomass raw material is controlled below 15 wt%.

[0024] Preferably, in step S2, the ferrous salt is one of ferrous sulfate heptahydrate and ferrous chloride tetrahydrate, the concentration of the ferrous salt solution is 0.02-0.30 mol / L, the liquid-to-solid ratio is 5:1-20:1 mL / g, the impregnation temperature is 20-40℃, and the impregnation time is 1-4 h; in step S3, the concentration of the polyphenol solution is 0.5-5.0 wt%, and the reaction continues for 0.5-3 h after the calcium source is added.

[0025] Preferably, in step S4, the phosphorus source is one or more of potassium dihydrogen phosphate, ammonium dihydrogen phosphate, disodium hydrogen phosphate, calcium hydrogen phosphate dihydrate, bone meal ash, and defluorinated phosphate rock powder, and the Ca / P molar ratio is 1.0-1.8, and the Mg / P molar ratio is 0.05-0.60; in step S5, the Mg / Al molar ratio of the magnesium salt to the aluminum salt is 2.0-4.0, the pH of the system is 8.5-10.0, the aging temperature is 25-60℃, and the aging time is 4-12h.

[0026] Preferably, steps S2 to S5 are performed sequentially; the material obtained in step S4 is not subjected to heat treatment at a temperature higher than 120°C before entering step S5; in step S6, the washing frequency is 1 to 5 times, the drying time is 6 to 24 hours, and the dried material is crushed and passed through a 40 to 100 mesh sieve.

[0027] This invention provides modified biochar for the remediation of water and soil contaminated with heavy metals and its preparation method. It has the following beneficial effects:

[0028] 1. This invention introduces a ferrous functional component, a polyphenol-calcium immobilization component, a weakly soluble calcium-magnesium-phosphorus component, and a magnesium-aluminum exchange buffer component onto the same carrier in modified biochar, enabling the material to simultaneously possess valence state regulation, interfacial immobilization, precipitation fixation, and exchange buffering functions. Specifically, the ferrous functional component facilitates the early conversion of high-valence heavy metals, the weakly soluble calcium-magnesium-phosphorus component promotes the conversion of heavy metals such as Pb and Cu to lower-solubility forms, the magnesium-aluminum exchange buffer component facilitates the continuous immobilization of divalent heavy metals such as Cd, Zn, and Ni, and the polyphenol-calcium immobilization component improves the adhesion stability of each inorganic active component on the biochar surface. Therefore, this invention is applicable to pollution systems where multiple heavy metals coexist.

[0029] 2. The preparation method of this invention employs a stepwise process involving ferrous pre-intercalation, polyphenol-calcium fixation, in-situ formation of weakly soluble calcium, magnesium, and phosphorus components, and construction of a magnesium-aluminum exchange buffer component. This allows different functional components to be introduced onto the biochar surface in a predetermined order. This technical route helps reduce disordered reactions and mutual interference among the precursor components during the preparation process, ensuring that the ferrous component preferentially distributes at the biochar interface, and the polyphenol-calcium component first forms a fixation base before further supporting the phosphorus and magnesium-aluminum components. This results in a more clearly defined functional configuration of the obtained material and makes the preparation process easier to control.

[0030] 3. This invention employs a two-step process: first, initial contact under low-oxygen, slightly acidic conditions in the treatment of polluted water, followed by subsequent contact under neutral or weakly alkaline conditions; second, pre-wetting and pre-contact are performed in the treatment of polluted soil, followed by comprehensive mixing and curing. This application method aligns with the sequence of action of the functional components in the material, facilitating the initial activation of the ferrous functional component for the conversion of high-valence heavy metals, followed by the activation of the phosphorus and magnesium-aluminum components for the fixation of divalent heavy metals. This enhances the applicability of this invention to both polluted water and polluted soil. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the method steps of the present invention;

[0032] Figure 2 This is a flowchart illustrating the phased application of the modified biochar of the present invention for the remediation of polluted water bodies. Detailed Implementation

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Please see the appendix Figure 1 - Appendix Figure 2 A modified biochar for the remediation of water and soil contaminated with heavy metals, comprising the following components:

[0035] Ferrous functional component, calculated as iron, in the form of 0.3 to 3.0 parts by weight;

[0036] A polyphenol-calcium immobilized component, wherein the polyphenol is 0.5 to 4.0 parts by weight and the calcium is 0.2 to 2.0 parts by weight;

[0037] The weakly soluble calcium, magnesium and phosphorus components, wherein phosphorus is 1.0 to 6.0 parts by weight, calcium is 0.8 to 6.0 parts by weight, and magnesium is 0.1 to 2.0 parts by weight;

[0038] The magnesium-aluminum exchange buffer component contains 1.0 to 5.0 parts by weight of magnesium and 0.3 to 2.5 parts by weight of aluminum.

[0039] Weigh 500g of cleaned, dried, and pulverized corn stalks, controlling the particle size to 1-3mm, and place them in a tube furnace. Under nitrogen protection, heat the furnace to 550℃ at a rate of 10℃ / min, hold for 2 hours, and then cool to room temperature to obtain basic biochar. Crush the obtained basic biochar and pass it through a 40-mesh sieve, then weigh 100g for later use.

[0040] Deoxygenated water was prepared by purging deionized water with nitrogen for 30 minutes. 8.30 g of ferrous sulfate heptahydrate was weighed and dissolved in 1000 mL of deoxygenated water to prepare a ferrous impregnation solution, and the pH was adjusted to 5.2 with dilute hydrochloric acid. 100 g of basic biochar was added to this ferrous impregnation solution, and the mixture was stirred and impregnated for 2 hours at 25°C and 200 rpm under nitrogen protection. After impregnation, the mixture was filtered, quickly rinsed once with 100 mL of deoxygenated water, and then vacuum dried at 60°C for 8 hours to obtain a ferrous pre-intercalated biochar intermediate.

[0041] Weigh 2.00 g of tannic acid and dissolve it in 400 mL of deionized water to prepare a polyphenol solution. Add the above-mentioned ferrous pre-intercalated biochar intermediate to the polyphenol solution and stir at 25 °C and 200 rpm for 1 h. Separately weigh 2.20 g of calcium acetate, dissolve it in 100 mL of deionized water, and slowly add it dropwise to the above system. Adjust the pH of the system to 7.2 with 0.1 mol / L sodium hydroxide solution, and continue stirring for 1 h. After the reaction is complete, filter and, without complete drying, obtain the polyphenol-calcium immobilized activated intermediate.

[0042] 6.80 g of potassium dihydrogen phosphate was weighed and dissolved in 200 mL of deionized water to prepare a phosphorus source solution. 4.40 g of calcium chloride and 2.00 g of magnesium chloride hexahydrate were weighed and dissolved in 200 mL of deionized water to prepare a calcium-magnesium mixed solution. The above polyphenol-calcium immobilization activation intermediate was dispersed in 500 mL of deionized water and stirred at 30 °C and 250 rpm. The calcium-magnesium mixed solution was added first, followed by the phosphorus source solution added dropwise over 60 min, with the pH of the system controlled at 8.2 using 0.5 mol / L sodium hydroxide solution. After the addition was complete, the reaction was continued with stirring for 1.5 h. The mixture was then filtered to obtain a weakly soluble calcium-magnesium-phosphorus supported intermediate wet material.

[0043] 12.20 g of magnesium chloride hexahydrate and 6.00 g of aluminum chloride hexahydrate were weighed and dissolved in 300 mL of deionized water to prepare a magnesium-aluminum mixed salt solution with a Mg / Al molar ratio of 3.0. The above weakly soluble calcium-magnesium-phosphorus supported intermediate wet material was dispersed in 600 mL of deionized water and stirred at 30 °C and 250 rpm. Simultaneously, the magnesium-aluminum mixed salt solution and a 1.0 mol / L sodium hydroxide solution were added dropwise, maintaining the pH at 9.2 for 60 min. After the addition was complete, stirring continued for 1 h, followed by aging at 40 °C for 6 h. After aging, the mixture was filtered, washed three times with deionized water, dried at 100 °C for 12 h, pulverized, and passed through a 60-mesh sieve to obtain the modified biochar product.

[0044] The modified biochar obtained, based on 100 parts by weight of base biochar, includes the following functional components: approximately 1.1 parts by weight of ferrous functional component (calculated as Fe), 2.0 parts by weight of polyphenolic component (calculated as tannic acid), approximately 0.6 parts by weight of polyphenol-calcium immobilization component (calculated as Ca), approximately 1.5 parts by weight of weakly soluble calcium, magnesium, and phosphorus component (calculated as P), approximately 1.6 parts by weight of phosphorus immobilization component (calculated as Ca), approximately 2.4 parts by weight of magnesium-aluminum exchange buffer component (calculated as Mg), and approximately 0.8 parts by weight of magnesium-aluminum exchange buffer component (calculated as Al).

[0045] A method for preparing modified biochar for the remediation of water and soil contaminated with heavy metals includes the following steps:

[0046] S1. Preparation of basic biochar.

[0047] Biomass raw materials are selected as the carbon source, including one or more of corn stalks, rice stalks, peanut shells, sawdust, and fungal residue. Preferably, the biomass raw materials are first washed, dried, and pulverized to reduce the impact of surface sediment, soluble impurities, and raw material moisture content on the pyrolysis process. The treated biomass raw materials are then subjected to pyrolysis under limited oxygen conditions, with the pyrolysis temperature controlled at 450–650℃ and the holding time at 1–3 hours. After cooling, basic biochar is obtained. If necessary, the obtained basic biochar is pulverized and sieved to obtain basic biochar within a predetermined particle size range. The basic biochar obtained in this step serves as a carrier for subsequent functional component loading.

[0048] S2, ferri pre-embedding treatment.

[0049] The basic biochar obtained in step S1 is impregnated in a deoxygenated aqueous solution of ferrous salt, which is one of ferrous sulfate, ferrous chloride, or their hydrates. The pH of the impregnation system is controlled at 4.5–6.0. ​​Preferably, the impregnation is carried out in a low-oxygen environment to reduce ferrous ion oxidation. After impregnation, the ferrous component enters the surface and near-surface region of the basic biochar and undergoes adsorption, coordination, or ion exchange with the oxygen-containing functional groups on the biochar surface. After impregnation, the system is subjected to solid-liquid separation, and the resulting solid is dried to obtain ferrous pre-embedded biochar. This step is used to pre-construct active sites with reducing properties on the biochar surface.

[0050] S3, polyphenol-calcium fixation treatment.

[0051] The ferrous pre-intercalated biochar obtained in step S2 was added to a polyphenol solution for treatment. The polyphenols were one or more selected from tannins, tea polyphenols, and tannins. After polyphenol treatment, a calcium source was added to the system, and the pH of the system was controlled to 6.5–8.0 for polyphenol-calcium immobilization treatment to obtain an immobilization activation intermediate. The calcium source was one or more selected from calcium hydroxide, calcium acetate, and calcium chloride. In this step, the polyphenol components first adhered to the surface of the ferrous pre-intercalated biochar, and then calcium ions formed bridging interactions with polyphenol molecules and oxygen-containing groups on the biochar surface, thereby forming a relatively stable immobilization layer at the biochar interface. This step was used to improve the adhesion stability of subsequent inorganic active components on the biochar surface.

[0052] S4, in-situ construction of weakly soluble calcium, magnesium and phosphorus components.

[0053] The immobilization and activation intermediate obtained in step S3 is contacted with a phosphorus source, a calcium source, and a magnesium source, and the pH of the system is controlled at 7.5–9.0 to allow the weakly soluble calcium, magnesium, and phosphorus components to form in situ, resulting in a weakly soluble calcium, magnesium, and phosphorus-loaded intermediate. The phosphorus source is one or more of potassium dihydrogen phosphate, ammonium dihydrogen phosphate, disodium hydrogen phosphate, calcium hydrogen phosphate, bone meal ash, and defluorinated phosphate rock powder; the calcium and magnesium sources are one or more of soluble or weakly soluble calcium and magnesium salts. In this step, phosphorus, calcium, and magnesium are deposited and transformed near the surface of the immobilization and activation intermediate, forming a weakly soluble calcium, magnesium, and phosphorus immobilization component. This step is used to introduce a phosphorus immobilization environment on the biochar surface that is conducive to the precipitation and immobilization of heavy metals.

[0054] In-situ construction of S5, magnesium-aluminum exchange buffer component.

[0055] The weakly soluble calcium-magnesium-phosphorus loaded intermediate obtained in step S4 is contacted with magnesium and aluminum salts, and a magnesium-aluminum exchange buffer component is formed in situ under alkaline conditions, followed by aging treatment. The magnesium salt is one of magnesium chloride, magnesium nitrate, or their hydrates, and the aluminum salt is one of aluminum chloride, aluminum nitrate, or their hydrates; the alkaline conditions are achieved by adding sodium hydroxide solution, ammonia, or other alkaline regulators. In this step, magnesium and aluminum ions undergo hydrolysis and deposition on the material surface, forming a magnesium-aluminum exchange buffer component with exchange sites and buffering capacity. The aging treatment is used to stabilize the binding state of this component on the material surface. This step is used to improve the material's ability to exchange and fix divalent heavy metals and improve the interfacial stability of the material in different water and soil environments.

[0056] S6, Post-processing.

[0057] The material obtained in step S5 is filtered, washed, and dried at 80–120°C to obtain modified biochar. Washing is used to remove unbound soluble salts and free precursors, while drying is used to reduce the moisture content of the material and stabilize its state. If necessary, the dried material is crushed and sieved to obtain a particle size range suitable for addition to polluted water bodies or mixing with polluted soil.

[0058] Preferably, steps S1 to S6 are performed sequentially. By first pre-intercalating ferrous iron, then immobilizing polyphenols with calcium, and subsequently constructing a weakly soluble calcium-magnesium-phosphorus component and a magnesium-aluminum exchange buffer component, different functional components can be introduced into the biochar surface in a sequential manner, reducing disordered reactions and mutual interference between the precursor components, thereby improving the rationality of the distribution and binding stability of each functional component on the material surface. The modified biochar prepared by the above steps can be applied to the remediation of heavy metal-contaminated water bodies and contaminated soils.

[0059] Example

[0060] Example 1:

[0061] This embodiment provides a modified biochar for the remediation of water and soil contaminated with heavy metals. As the main embodiment, it is used to illustrate the complete technical solution of the present invention, including the complete formula, the complete preparation process, and the staged application method for contaminated water bodies, specifically including the following steps:

[0062] S1. Preparation of basic biochar. Weigh 500g of washed corn stalks, dry them at 80℃ for 12h, crush them to 1-3mm, place them in a tube furnace, heat them to 550℃ at 10℃ / min under nitrogen protection, keep them at that temperature for 2h, cool them naturally to room temperature, crush them and pass them through a 40-mesh sieve, weigh 100g, and obtain basic biochar.

[0063] S2. Ferrous pre-intercalation treatment. Deionized water was purged with nitrogen for 30 min to obtain deoxygenated water. 8.30 g of ferrous sulfate heptahydrate was weighed and dissolved in 1000 mL of deoxygenated water. The pH of the solution was adjusted to 5.2 with 0.1 mol / L hydrochloric acid. 100 g of basic biochar was added, and the mixture was stirred and impregnated for 2 h at 25 °C and 200 rpm under nitrogen protection. After impregnation, the mixture was filtered, quickly rinsed once with 100 mL of deoxygenated water, and vacuum dried at 60 °C for 8 h to obtain ferrous pre-intercalated biochar.

[0064] S3. Polyphenol-calcium immobilization treatment. Weigh 2.00 g of tannic acid and dissolve it in 400 mL of deionized water. Add the ferrous pre-intercalated biochar obtained in step S2 to this solution and stir for 1 h at 25 °C and 200 rpm. Separately, dissolve 2.20 g of calcium acetate in 100 mL of deionized water and slowly add it dropwise to the above system. Adjust the pH of the system to 7.2 with 0.1 mol / L sodium hydroxide solution and continue stirring for 1 h. Filter to obtain the immobilized and activated intermediate.

[0065] S4. Construction of the weakly soluble calcium-magnesium-phosphorus component. 6.80 g of potassium dihydrogen phosphate was dissolved in 200 mL of deionized water as the phosphorus source solution; 4.40 g of calcium chloride and 2.00 g of magnesium chloride hexahydrate were dissolved in 200 mL of deionized water as the calcium-magnesium mixed solution. The immobilized and activated intermediate obtained in step S3 was dispersed in 500 mL of deionized water. The calcium-magnesium mixed solution was added first at 30 °C and 250 rpm, followed by the phosphorus source solution added dropwise over 60 min. The pH of the system was controlled at 8.2 using 0.5 mol / L sodium hydroxide solution. After the addition was complete, stirring was continued for 1.5 h. The mixture was then filtered to obtain the weakly soluble calcium-magnesium-phosphorus supported intermediate.

[0066] S5. Construction of the magnesium-aluminum exchange buffer component. 12.20 g of magnesium chloride hexahydrate and 6.00 g of aluminum chloride hexahydrate were dissolved in 300 mL of deionized water to prepare a magnesium-aluminum mixed salt solution. The intermediate obtained in step S4 was dispersed in 600 mL of deionized water. The magnesium-aluminum mixed salt solution and 1.0 mol / L sodium hydroxide solution were simultaneously added dropwise at 30 °C and 250 rpm, maintaining the pH at 9.2 for 60 min. After the addition was complete, stirring was continued for 1 h, followed by aging at 40 °C for 6 h.

[0067] S6. Post-processing. Filter the material obtained in step S5, wash it three times with deionized water, dry it at 100℃ for 12 hours, pulverize it and pass it through a 60-mesh sieve to obtain the modified biochar product.

[0068] When the obtained modified biochar is used for the treatment of polluted water, a Pb-containing formulation is prepared. 2+ 50mg / L, Cd 2+ 10 mg / L, Cr(VI) 20 mg / L and Cu 2+ 1000 mL of simulated contaminated water with a concentration of 25 mg / L was mixed with 2.50 g of modified biochar. In the first stage, the mixture was stirred at 25°C and 150 rpm, with slow bubbling of nitrogen to maintain a low dissolved oxygen environment. The pH of the system was adjusted to 5.5 with 0.1 mol / L hydrochloric acid, and the mixture was allowed to react for 30 min. In the second stage, nitrogen flow was stopped, and the pH of the system was adjusted to 7.5 with 0.1 mol / L sodium bicarbonate solution. The mixture was stirred for another 120 min, followed by filtration and sample collection for analysis.

[0069] Example 2:

[0070] This embodiment provides a modified biochar with low side parameters to illustrate that the present invention can still be implemented under conditions where the amount of some components added and some process parameters are close to the lower limit. Specifically, it includes the following steps:

[0071] S1. Preparation of basic biochar. Weigh 500g of washed rice straw, dry it at 85℃ for 10h, crush it to 1-2mm, place it in a tube furnace, heat it to 500℃ at 8℃ / min under nitrogen protection, keep it at that temperature for 1.5h, cool it, crush it and pass it through a 40-mesh sieve, weigh 100g to obtain basic biochar.

[0072] S2. Ferrous pre-intercalation treatment. 4.15 g of ferrous sulfate heptahydrate was dissolved in 1000 mL of deoxygenated water, and the pH was adjusted to 5.5 with dilute hydrochloric acid. 100 g of basic biochar was added, and the mixture was stirred and impregnated for 1.5 h at 25 °C, 180 rpm, and under nitrogen protection. After impregnation, the mixture was filtered and dried under vacuum at 55 °C for 6 h to obtain ferrous pre-intercalated biochar.

[0073] S3. Polyphenol-calcium immobilization treatment. Dissolve 1.00 g of tannic acid in 300 mL of deionized water, add the ferrous pre-intercalated biochar obtained in step S2, and stir at 25 °C and 180 rpm for 0.8 h. Then dissolve 1.10 g of calcium acetate in 80 mL of deionized water and add it dropwise to the system. Adjust the pH to 6.8 with 0.1 mol / L sodium hydroxide, continue stirring for 0.8 h, filter, and obtain the immobilized and activated intermediate.

[0074] S4. Construction of the weakly soluble calcium-magnesium-phosphorus component. 4.60 g of ammonium dihydrogen phosphate was dissolved in 180 mL of deionized water as the phosphorus source solution; 2.75 g of calcium chloride and 1.20 g of magnesium chloride hexahydrate were dissolved in 180 mL of deionized water as the calcium-magnesium mixed solution. The immobilized and activated intermediate obtained in step S3 was dispersed in 450 mL of deionized water. The calcium-magnesium mixed solution was added first at 28 °C and 220 rpm, followed by the phosphorus source solution added dropwise over 45 min. The pH of the system was controlled at 8.0 with 0.5 mol / L sodium hydroxide solution, and the reaction was continued for 1 h. After filtration, the weakly soluble calcium-magnesium-phosphorus supported intermediate was obtained.

[0075] S5. Construction of the magnesium-aluminum exchange buffer component. 9.00 g of magnesium nitrate hexahydrate and 4.80 g of aluminum nitrate nonahydrate were dissolved in 280 mL of deionized water to prepare the magnesium-aluminum precursor solution. The intermediate obtained in step S4 was dispersed in 550 mL of deionized water. The magnesium-aluminum precursor solution and 1.0 mol / L ammonia were added dropwise simultaneously at 25 °C, maintaining the pH at 9.0 for 50 min. After the addition was complete, stirring was continued for 0.8 h, followed by aging at 35 °C for 4 h.

[0076] S6. Post-processing. Filter the material obtained in step S5, wash it 3 times, dry it at 90℃ for 10 hours, pulverize it and pass it through a 60-mesh sieve to obtain the modified biochar product.

[0077] When the obtained modified biochar is used for the treatment of polluted water, a Pb-containing formulation is prepared. 2+ 30mg / L, Cd2+ 5 mg / L, Cr(VI) 10 mg / L and Cu 2+ 1000 mL of simulated contaminated water with a concentration of 20 mg / L was mixed with 1.50 g of modified biochar. In the first stage, the mixture was stirred at 25 °C and 120 rpm, and the pH was adjusted to 6.0 with 0.1 mol / L hydrochloric acid for 20 min. In the second stage, the pH was adjusted to 7.0 with 0.1 mol / L sodium bicarbonate solution, and stirring continued for 90 min. The mixture was then filtered and sampled for analysis.

[0078] Example 3:

[0079] This embodiment provides a modified biochar with high side parameters to illustrate the implementation of the present invention under conditions where the amount of some components added and some process parameters are close to the upper limit. Specifically, it includes the following steps:

[0080] S1. Preparation of basic biochar. Weigh 500g of washed corn stalks, dry them at 90℃ for 12h, crush them to 1-3mm, place them in a tube furnace, heat them to 620℃ at 10℃ / min under nitrogen protection, keep them at that temperature for 3h, cool them, crush them and pass them through a 40-mesh sieve, weigh 100g, and obtain basic biochar.

[0081] S2. Ferrous pre-intercalation treatment. 13.80 g of ferrous sulfate heptahydrate was dissolved in 1000 mL of deoxygenated water. The pH was adjusted to 4.8 with dilute hydrochloric acid, and 100 g of basic biochar was added. The mixture was stirred and impregnated for 3 h at 25 °C, 220 rpm, and under nitrogen protection. After impregnation, the mixture was filtered, rinsed once with a small amount of deoxygenated water, and dried under vacuum at 55 °C for 8 h to obtain ferrous pre-intercalated biochar.

[0082] S3. Polyphenol-calcium immobilization treatment. Dissolve 3.50 g of tannic acid in 450 mL of deionized water, add the ferrous pre-intercalated biochar obtained in step S2, and stir at 25 °C and 200 rpm for 1.2 h. Dissolve 4.20 g of calcium acetate in 120 mL of deionized water and add it dropwise to the system. Adjust the pH of the system to 7.8 with 0.5 mol / L sodium hydroxide solution, continue stirring for 1.5 h, filter, and obtain the immobilized activation intermediate.

[0083] S4. Construction of the weakly soluble calcium-magnesium-phosphorus component. 17.50 g of potassium dihydrogen phosphate was dissolved in 260 mL of deionized water as the phosphorus source solution; 11.00 g of calcium chloride and 4.80 g of magnesium chloride hexahydrate were dissolved in 240 mL of deionized water as the calcium-magnesium mixed solution. The immobilized and activated intermediate obtained in step S3 was dispersed in 550 mL of deionized water. The calcium-magnesium mixed solution was added first at 35 °C and 260 rpm, followed by the phosphorus source solution added dropwise over 70 min. The pH of the system was controlled at 8.8 with 1.0 mol / L sodium hydroxide solution. After the addition was complete, stirring was continued for 2 h, followed by filtration to obtain the weakly soluble calcium-magnesium-phosphorus supported intermediate.

[0084] S5. Construction of the magnesium-aluminum exchange buffer component. 20.50 g of magnesium chloride hexahydrate and 9.60 g of aluminum chloride hexahydrate were dissolved in 350 mL of deionized water to prepare a magnesium-aluminum mixed salt solution. The intermediate obtained in step S4 was dispersed in 700 mL of deionized water. The magnesium-aluminum mixed salt solution and 1.0 mol / L sodium hydroxide solution were simultaneously added dropwise at 30 °C, maintaining the pH at 9.8 for 70 min. After the addition was complete, stirring was continued for 1.5 h, followed by aging at 50 °C for 12 h.

[0085] S6. Post-processing. Filter the material obtained in step S5, wash it 4 times with deionized water, dry it at 110℃ for 16 hours, pulverize it and pass it through a 60-mesh sieve to obtain the modified biochar product.

[0086] When the obtained modified biochar is used for the treatment of polluted water, a Pb-containing formulation is prepared. 2+ 80mg / L, Cd 2+ 20 mg / L, Cr(VI) 40 mg / L and Cu 2+ 1000 mL of simulated contaminated water with a concentration of 40 mg / L was mixed with 4.00 g of modified biochar. In the first stage, the mixture was stirred at 25°C and 180 rpm, with slow bubbling of nitrogen to maintain a low dissolved oxygen environment. The pH of the system was adjusted to 5.0 with 0.1 mol / L hydrochloric acid, and the mixture was allowed to react for 45 min. In the second stage, nitrogen flow was stopped, and the pH of the system was adjusted to 8.2 with 0.1 mol / L sodium bicarbonate solution. The mixture was stirred for another 180 min, followed by filtration and sample collection for analysis.

[0087] Example 4:

[0088] This embodiment provides a modified biochar for phased application in soil remediation, illustrating the implementation of the invention in a contaminated soil scenario, and describing the complete process of pre-wetting, pre-reduction contact, thorough mixing, and curing stabilization, specifically including the following steps:

[0089] S1. Preparation of basic biochar. Weigh 500g of washed corn stalks, dry them at 80℃ for 12h, crush them to 1-3mm, place them in a tube furnace, heat them to 560℃ at 10℃ / min under nitrogen protection, keep them at that temperature for 2h, cool them, crush them and pass them through a 40-mesh sieve, weigh 100g, and obtain basic biochar.

[0090] S2. Ferrous pre-intercalation treatment. 7.50 g of ferrous sulfate heptahydrate was dissolved in 1000 mL of deoxygenated water, the pH was adjusted to 5.2 with dilute hydrochloric acid, 100 g of basic biochar was added, and the mixture was stirred and impregnated for 2 h at 25 °C, 200 rpm and nitrogen protection. After filtration, it was vacuum dried at 60 °C for 8 h to obtain ferrous pre-intercalated biochar.

[0091] S3. Polyphenol-calcium immobilization treatment. Dissolve 2.20 g of tannic acid in 380 mL of deionized water, add the ferrous pre-intercalated biochar obtained in step S2, and stir for 1 h at 25 °C and 200 rpm. Dissolve 2.00 g of calcium acetate in 100 mL of deionized water and add it dropwise to the system. Adjust the pH to 7.1 with 0.1 mol / L sodium hydroxide solution, continue stirring for 1 h, filter, and obtain the immobilized activation intermediate.

[0092] S4. Construction of the weakly soluble calcium magnesium phosphate component. 15.00 g of calcium hydrogen phosphate dihydrate was added to 300 mL of deionized water to form a slurry. Then, 1.50 g of magnesium chloride hexahydrate and 1.20 g of calcium chloride were added, and the pH of the slurry was adjusted to 7.6. The immobilized and activated intermediate obtained in step S3 was added to this slurry, and the mixture was stirred at 30 °C and 250 rpm for 3 h. After filtration, the weakly soluble calcium magnesium phosphate supported intermediate was obtained.

[0093] S5. Construction of the magnesium-aluminum exchange buffer component. 12.00 g of magnesium chloride hexahydrate and 5.80 g of aluminum chloride hexahydrate were dissolved in 300 mL of deionized water to prepare the magnesium-aluminum precursor solution. The intermediate obtained in step S4 was dispersed in 600 mL of deionized water. The magnesium-aluminum precursor solution and 1.0 mol / L sodium hydroxide solution were simultaneously added dropwise at 30 °C, maintaining the pH at 9.1 for 60 min. After the addition was complete, stirring was continued for 1 h, followed by aging at 40 °C for 6 h.

[0094] S6. Post-processing. Filter the material obtained in step S5, wash it 3 times, dry it at 100℃ for 12 hours, pulverize it and pass it through a 40-mesh sieve to obtain the modified biochar product.

[0095] When the modified biochar was used to treat contaminated soil, 10 kg of artificially prepared contaminated soil was used. The total Pb content in the contaminated soil was 420 mg / kg, the total Cd content was 9.0 mg / kg, and the total Cr(VI) content was 42 mg / kg. Modified biochar was added at 4.0 wt% of the dry weight of the soil, for a total dosage of 400 g, of which 120 g was used for the first stage and 280 g for the second stage. In the first stage, 120 g of modified biochar was pre-wetted in 96 mL of deionized water, allowed to stand for 2 h, and then thoroughly mixed with the contaminated soil for 15 min. The soil moisture content was then adjusted to 60% of field capacity, and the soil was covered and allowed to stand at 25 °C for 12 h to allow the ferrous functional components to preferentially contact the high-valence heavy metals in the soil. In the second stage, the remaining 280g of modified biochar was added to 220mL of deionized water to form moist granules, which were then added to the aforementioned soil and mixed for another 20 minutes. The soil moisture content was adjusted to 65% of field capacity, and the soil was covered and cured at 25℃ for 30 days, with the soil being turned over once every 7 days. After the curing period, samples were taken to analyze the content of available and leached heavy metals in the soil.

[0096] Comparative Example

[0097] Comparative Example 1:

[0098] Compared with Example 1, the difference is that the ferrous pre-intercalation treatment is not performed, and the basic biochar is directly used in the polyphenol-calcium immobilization step, while the rest are the same.

[0099] Comparative Example 2:

[0100] Compared with Example 1, the difference is that the polyphenol-calcium immobilization treatment is not performed. After the ferrous pre-embedding, the weakly soluble calcium, magnesium and phosphorus components are deposited directly and the magnesium-aluminum exchange buffer components are constructed. All other aspects are the same.

[0101] Comparative Example 3:

[0102] Compared with Example 1, the difference is that the deposition of weakly soluble calcium, magnesium and phosphorus components is not performed, but only the pre-intercalation of ferrous iron, polyphenol-calcium fixation and the construction of magnesium-aluminum exchange buffer components are performed, while the rest are the same.

[0103] Comparative Example 4:

[0104] Compared with Example 1, the difference is that the magnesium-aluminum exchange buffer component is not constructed, and only the ferrous pre-intercalation, polyphenol-calcium fixation and weakly soluble calcium-magnesium-phosphorus component deposition are performed, while the rest are the same.

[0105] Comparative Example 5:

[0106] Compared with Example 1, the difference is that ferrous salt, polyphenol, calcium source, phosphorus source, magnesium source and aluminum source are added to the basic biochar dispersion system at one time for a one-step blending reaction, instead of proceeding in the order of ferrous pre-intercalation, polyphenol-calcium immobilization, deposition of weakly soluble calcium, magnesium and phosphorus components and construction of magnesium-aluminum exchange buffer components. All other steps are the same.

[0107] Comparative Example 6:

[0108] Compared with Example 1, the difference is that instead of a staged application / contact method, all the modified biochar was added to the polluted water at once during the treatment process, and the mixture was continuously stirred under the same pH conditions until the treatment was completed. All other aspects were the same.

[0109] Comparative Example 7:

[0110] Compared with Example 4, the difference is that no pre-wetting and pre-reduction contact treatment is performed in the process of remediating contaminated soil. All the modified biochar is directly mixed with the contaminated soil in one go. Everything else is the same.

[0111] Comparative Example 8:

[0112] Compared with Example 1, the difference is that no calcium source is added in the polyphenol-calcium immobilization treatment, and only tannic acid is used to pre-intercalate ferrous biochar. All other aspects are the same.

[0113] Test example:

[0114] This test case is used to evaluate the feasibility and differences of application of each embodiment and comparative sample in heavy metal polluted water and polluted soil, and to examine the effects of the ferrous functional component, polyphenol-calcium immobilization component, weakly soluble calcium magnesium phosphate component, magnesium aluminum exchange buffer component and staged application method on the overall treatment behavior in the technical solution of this invention.

[0115] The samples prepared according to Examples 1-4 and Comparative Examples 1-8 were numbered respectively, with Example 1 designated as E1, Example 2 as E2, Example 3 as E3, and Example 4 as E4; and Comparative Examples 1-8 as C1-C8 respectively. Each sample was placed in a desiccator for 24 hours before testing to allow it to reach a relatively stable state before use.

[0116] In water body testing, simulated polluted water containing multiple heavy metals was prepared. A stock solution was prepared using Pb(NO3)2, CdCl2·2.5H2O, K2Cr2O7, and CuSO4·5H2O, which was then diluted with deionized water to obtain the polluted water for testing. The polluted water contained Pb... 2+ The initial concentration was controlled at 50.0 mg / L, Cd 2+ The initial concentration was controlled at 10.0 mg / L, the initial concentration of Cr(VI) was controlled at 20.0 mg / L, and the initial concentration of Cu... 2+The initial concentration was controlled at 25.0 mg / L, the background electrolyte was 1.0 mmol / L NaNO3, and the initial pH was adjusted to 5.7 ± 0.1. For each experiment, 1000 mL of contaminated water was placed in a 1500 mL Erlenmeyer flask, and 2.50 g of the corresponding sample was added.

[0117] For E1, E2, E3 and C1 to C5, C8, the same staged treatment method as in Example 1 was adopted: In the first stage, the mixture was stirred at 150 rpm at 25°C, and the low dissolved oxygen condition was controlled by slow bubbling of nitrogen gas, maintaining the pH at 5.4 to 5.8 for 30 min; in the second stage, nitrogen gas was stopped, and the pH was adjusted to 7.4 to 7.8 with 0.1 mol / L NaHCO3 solution, and stirring was continued for 120 min.

[0118] For C6, a one-time continuous contact method was adopted, without stage transition, and the mixture was continuously stirred at 25°C and 150 rpm for 150 min while maintaining the initial pH near the standard conditions.

[0119] After treatment, all samples were filtered through a 0.45 μm filter membrane, and the concentrations of Pb, Cd, Cr, and Cu in the filtrate were determined. The endpoint pH, total iron concentration, and total phosphorus concentration in the filtrate were also measured. Pb, Cd, and Cu were determined using inductively coupled plasma atomic emission spectrometry (ICP-AES), Cr(VI) was determined using diphenylcarbazide spectrophotometry, total iron was determined using o-phenanthroline spectrophotometry, and total phosphorus was determined using ammonium molybdate spectrophotometry.

[0120] In soil testing, artificially contaminated soil was used for evaluation. Air-dried loam that had passed through a 20-mesh sieve was taken, and after adjusting the moisture content, Pb(NO3)2, CdCl2·2.5H2O, and K2Cr2O7 solutions were added to bring the total Pb content to 420 mg / kg, the total Cd content to 9.0 mg / kg, and the total Cr(VI) content to 42 mg / kg. After mixing, the mixture was allowed to stand for 7 days to mature, yielding the contaminated soil for testing. 10.0 kg of the contaminated soil was taken and applied to samples E4 and C7 according to the methods described in Example 4 and Comparative Example 7, respectively. E4 was applied in stages: first, 30% of the total amount of modified biochar was added and pre-wetted for 12 hours of pre-contact; then the remaining 70% was added and mixed, maintaining 65% of field capacity for 30 days of curing. C7 did not undergo pre-wetting or pre-reduction stages; all samples were directly mixed with the soil at once, and the curing conditions were the same as for E4. After the curing period, the soil pH, DTPA-extractable Pb and Cd, and Cr(VI) content in the alkaline extract were measured, and the concentrations of Pb, Cd, and total Cr in the leachate were determined according to the HJ / T299 method.

[0121] To reduce random errors, each experiment was conducted in parallel three times, and the data in the table are the average values.

[0122] Table 1. Endpoint concentrations and related indicators of each example and comparative sample in water contaminated with multiple heavy metals:

[0123] sample endpoint Pb concentration (mg / L) endpoint Cd concentration (mg / L) endpoint Cr(VI) concentration (mg / L) endpoint Cu concentration (mg / L) endpoint pH Total iron in filtrate (mg / L) Total phosphorus in filtrate (mg / L) E1 1.82 0.61 0.46 1.37 7.62 0.31 0.58 E2 3.44 1.18 0.93 2.86 7.33 0.27 0.41 E3 0.96 0.39 0.18 0.92 7.88 0.48 0.84 C1 4.78 1.42 6.85 3.51 7.49 0.09 0.55 C2 3.95 1.26 1.34 3.02 7.18 0.42 1.36 C3 8.64 1.87 0.69 5.11 7.44 0.34 0.19 C4 2.91 1.74 0.73 2.58 7.05 0.36 0.64 C5 10.72 3.46 2.91 7.84 6.41 1.28 0.07 C6 5.26 1.68 2.43 4.29 6.18 0.44 0.62 C8 4.62 1.31 0.82 3.43 7.36 0.39 1.12

[0124] Table 2. Removal rates of various examples and comparative samples in water contaminated with multiple heavy metals:

[0125] sample Pb removal rate (%) Cd removal rate (%) Cr(VI) removal rate (%) Cu removal rate (%) E1 96.36 93.9 97.7 94.52 E2 93.12 88.2 95.35 88.56 E3 98.08 96.1 99.1 96.32 C1 90.44 85.8 65.75 85.96 C2 92.1 87.4 93.3 87.92 C3 82.72 81.3 96.55 79.56 C4 94.18 82.6 96.35 89.68 C5 78.56 65.4 85.45 68.64 C6 89.48 83.2 87.85 82.84 C8 90.76 86.9 95.9 86.28

[0126] Table 3. Physicochemical indicators and available heavy metal content of contaminated soil after treatment in Example 4 and Comparative Example 7:

[0127] sample Soil pH DTPA-Pb (mg / kg) DTPA-Cd (mg / kg) Cr(VI) (mg / kg) HJ / T299 Leaching of Pb (mg / L) HJ / T299 Leaching Cd (mg / L) HJ / T299 Leaching Total Cr (mg / L) Blank contaminated soil 5.63 118.4 3.71 11.6 1.94 0.186 0.93 E4 6.92 32.7 0.84 1.9 0.42 0.031 0.18 C7 6.36 58.9 1.47 4.8 0.88 0.072 0.39

[0128] As can be seen from Tables 1 and 2, Examples 1-3 all achieved low endpoint concentrations in the composite heavy metal system, and also showed good results for Pb. 2+ Cd 2+ Cr(VI) and Cu 2+ The system demonstrated simultaneous control capability. E3 showed superior performance across various indicators, indicating that the reduction and precipitation fixation processes were more complete under higher ferrous and phosphorus content. Example 2 still achieved simultaneous removal of multiple heavy metals, demonstrating the feasibility of this technique even at lower functional component dosage levels. The data distribution of Example 1 falls between that of Examples 2 and 3, reflecting a stable treatment level under moderate parameter conditions.

[0129] In the comparative examples, Comparative Example 1, lacking the ferrous pre-intercalation step, showed a significantly higher Cr(VI) endpoint concentration than Example 1, indicating that the ferrous functional component has a direct effect on the preferential conversion of high-valence heavy metals. Comparative Example 3, lacking the weakly soluble calcium, magnesium, and phosphorus components, showed a more significant increase in the endpoint concentrations of Pb and Cu, indicating that the phosphorus component plays a major role in the subsequent fixation of divalent heavy metals. Comparative Example 4, lacking the magnesium-aluminum exchange buffer component, showed a higher Cd endpoint concentration, reflecting the significant effect of the exchange buffer site on moderately affinistic divalent ions. Comparative Example 2, lacking the polyphenol-calcium immobilization component, showed a significant increase in the total phosphorus concentration in the filtrate, indicating that this component inhibits the migration of inorganic active components at the interface. Comparative Example 8, containing only tannic acid and no calcium source, showed higher total phosphorus and heavy metal endpoint concentrations than Example 1, indicating that simple organic polyphenol treatment is insufficient to replace the polyphenol-calcium complex effect. The one-step blend sample of Comparative Example 5 performed worse overall than Example 1, and the total iron in the filtrate increased, indicating that a stepwise construction path is beneficial for the effective immobilization of functional components on the biochar surface. When Comparative Example 6 did not use a staged application method, the final concentrations of Cr(VI), Pb, and Cu were all higher than those in Example 1, while the final pH was lower, indicating that the staged contact conditions promoted the preferential conversion of high-valence heavy metals and subsequent precipitation fixation.

[0130] Table 3 shows that after treatment in contaminated soil in Example 4, the levels of DTPA-extractable Pb, DTPA-extractable Cd, alkali-extracted Cr(VI), as well as leached Pb, Cd, and total Cr, were significantly lower than in the blank contaminated soil and also lower than in Comparative Example 7. Compared with Example 4, Comparative Example 7, due to the absence of pre-wetting and pre-reduction contact stages, had higher levels of both available and leached heavy metal residues in its soil. This indicates that performing local pre-contact in the soil system before comprehensive mixing is beneficial for the ferrous functional components to react with higher valence heavy metals first, while providing a more stable reaction environment for subsequent phosphorus fixation and exchange buffering.

[0131] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A modified biochar for the remediation of heavy metal-contaminated water and soil, characterized in that, The modified biochar comprises the following components: Ferrous functional component, calculated as iron, in the form of 0.3 to 3.0 parts by weight; A polyphenol-calcium immobilized component, wherein the polyphenol is 0.5 to 4.0 parts by weight and the calcium is 0.2 to 2.0 parts by weight; The weakly soluble calcium, magnesium and phosphorus components, wherein phosphorus is 1.0 to 6.0 parts by weight, calcium is 0.8 to 6.0 parts by weight, and magnesium is 0.1 to 2.0 parts by weight; The magnesium-aluminum exchange buffer component contains 1.0 to 5.0 parts by weight of magnesium (Mg) and 0.3 to 2.5 parts by weight of aluminum.

2. The modified biochar for remediation of heavy metal-contaminated soil and water according to claim 1, characterized in that, The biochar matrix is ​​derived from one or more of corn stalks, rice stalks, peanut shells, sawdust, and fungal residue; the polyphenols in the polyphenol-calcium immobilization component are selected from one or more of tannic acid, tea polyphenols, and tannins; and the calcium in the polyphenol-calcium immobilization component is derived from one or more of calcium hydroxide, calcium acetate, and calcium chloride.

3. The modified biochar for remediation of heavy metal-contaminated soil and water according to claim 1, characterized in that, The weakly soluble calcium magnesium phosphate component comprises one or more of the following: dicalcium phosphate, octacalcium phosphate, hydroxyapatite, magnesium-containing calcium phosphate, and magnesium ammonium phosphate, wherein the Ca / P molar ratio of the weakly soluble calcium magnesium phosphate component is 1.0 to 1.8, and the Mg / P molar ratio is 0.05 to 0.

60.

4. The modified biochar for remediation of heavy metal-contaminated soil and water according to claim 1, characterized in that, The Mg / Al molar ratio in the magnesium-aluminum exchange buffer component is 2.0–4.0, the particle size of the modified biochar is 0.074–2.0 mm, and the pH of the aqueous extract is 7.0–10.

5.

5. A method for preparing modified biochar for the remediation of heavy metal-contaminated water and soil, as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Pyrolyze the biomass raw material at 450-650℃ for 1-3 hours under limited oxygen conditions to obtain basic biochar; S2. The basic biochar is added to a deoxygenated aqueous solution of ferrous salt for impregnation treatment. The pH of the impregnation system is controlled at 4.5-6.

0. After treatment, the biochar is separated and dried to obtain ferrous pre-embedded biochar. S3. The ferrous pre-embedded biochar is added to a polyphenol solution for treatment, and then a calcium source is added and the pH of the system is controlled at 6.5-8.0 to perform polyphenol-calcium immobilization treatment to obtain an immobilization activation intermediate. S4. The immobilized activation intermediate is contacted with a phosphorus source, a calcium source, and a magnesium source, and the pH of the system is controlled to be 7.5-9.0 to allow the weakly soluble calcium, magnesium and phosphorus components to form in situ, thereby obtaining a weakly soluble calcium, magnesium and phosphorus supported intermediate. S5. The weakly soluble calcium magnesium phosphorus supported intermediate is contacted with magnesium salt and aluminum salt, and the magnesium aluminum exchange buffer component is formed in situ under alkaline conditions, followed by aging treatment. S6. Filter, wash and dry the material obtained in step S5 at 80-120°C to obtain the modified biochar.

6. The method for preparing modified biochar for remediation of heavy metal-contaminated water and soil according to claim 5, characterized in that, Before step S1, the following pretreatment is also included: the biomass raw material is washed and dried at 60-105℃ for 8-24 hours, and then crushed to 0.5-5mm, and the moisture content of the biomass raw material is controlled below 15wt%.

7. The method for preparing modified biochar for remediation of heavy metal-contaminated water and soil according to claim 5, characterized in that, In step S2, the ferrous salt is one of ferrous sulfate heptahydrate and ferrous chloride tetrahydrate, the concentration of the ferrous salt solution is 0.02-0.30 mol / L, the liquid-to-solid ratio is 5:1-20:1 mL / g, the impregnation temperature is 20-40℃, and the impregnation time is 1-4 h; in step S3, the concentration of the polyphenol solution is 0.5-5.0 wt%, and the reaction continues for 0.5-3 h after the calcium source is added.

8. The method for preparing modified biochar for remediation of heavy metal-contaminated water and soil according to claim 5, characterized in that, In step S4, the phosphorus source is one or more of potassium dihydrogen phosphate, ammonium dihydrogen phosphate, disodium hydrogen phosphate, calcium hydrogen phosphate dihydrate, bone meal ash, and defluorinated phosphate rock powder, and the Ca / P molar ratio is 1.0-1.8 and the Mg / P molar ratio is 0.05-0.60; in step S5, the Mg / Al molar ratio of the magnesium salt to the aluminum salt is 2.0-4.0, the pH of the system is 8.5-10.0, the aging temperature is 25-60℃, and the aging time is 4-12h.

9. A method for preparing modified biochar for remediation of heavy metal-contaminated soil and water according to claim 5, characterized in that, Steps S2 to S5 are performed sequentially; the material obtained in step S4 is not subjected to heat treatment at a temperature higher than 120°C before entering step S5; in step S6, the washing is performed 1 to 5 times, the drying time is 6 to 24 hours, and the dried material is crushed and passed through a 40 to 100 mesh sieve.

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