Preparation method and application of lanthanum modified knot biochar

Abstract

The application discloses a preparation method and application of lanthanum modified lotus node biochar and belongs to the technical field of in-situ remediation of river and lake water pollution; the lanthanum modified lotus node biochar with in-situ loaded nano lanthanum hydroxide on the surface and in the pore is prepared from waste lotus nodes through pyrolysis carbonization, lanthanum chloride immersion and lye aging, and the material has both hydrophobic and oleophilic physical adsorption performance and phosphate chemical fixation performance; the material is made into a floating adsorption unit and arranged in a polluted water area, so that the oil film on the water surface can be simultaneously adsorbed and the water body phosphate can be fixed, and the vicious cycle of oil film blockage and endogenous phosphorus release is broken; and the saturated material can be used as a slow-release phosphorus fertilizer and recycled. The application realizes integrated and collaborative management of oil-phosphorus composite pollution, realizes waste treatment by waste, is low in cost, environment-friendly and suitable for in-situ remediation of open water areas of rivers and lakes.

Description

Technical Field

[0001] This invention relates to the field of biochar technology, specifically to a method for preparing lanthanum-modified lotus root biochar and its application. Background Technology

[0002] Oil film pollution and eutrophication often coexist in surface water bodies such as rivers and lakes, representing a complex pollution problem that urgently needs to be addressed in the field of water environment management. Oil films mainly originate from industrial oily wastewater discharge, ship fuel spills, urban surface runoff, and atmospheric deposition. The physical barrier they form hinders water reoxygenation, leading to oxygen deprivation and death of aquatic organisms. Furthermore, the toxic components in the oil film can accumulate through the food chain, threatening aquatic ecosystem safety and human health. Eutrophication is caused by excessive input of nitrogen and phosphorus nutrients. Phosphorus is a key limiting factor for eutrophication in freshwater bodies, and the oxygen deprivation exacerbated by oil films further promotes the release of endogenous phosphorus from bottom sediments, forming a vicious cycle of "oil film blockage – oxygen deprivation – phosphorus release – eutrophication exacerbation."

[0003] Existing pollution control systems often treat oil spill removal and phosphorus pollution control as separate projects, employing single methods such as oil-absorbing mats and chemical precipitation. This approach suffers from problems such as dispersed equipment, complex operation, poor synergy, and high treatment costs. Furthermore, existing lanthanum-modified materials are only developed for single phosphorus removal functions, and their porous structure's adsorption potential for oily substances remains untapped. Conventional lanthanum-modified biochar primarily uses rice husks and straw as precursors, with micropores as the main pore structure, limiting its mass transfer and storage capacity for large oil molecules. In addition, the resource utilization rate of agricultural waste such as lotus root nodes is low, and conventional disposal methods easily lead to resource waste and secondary pollution. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing lanthanum-modified lotus root biochar and its application, aiming to solve the problems existing in the prior art.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing lanthanum-modified lotus root biochar includes the following steps: S1. Pretreatment: Collect waste lotus root sections, wash and dry them, and then crush them to the preset particle size; S2. Pyrolysis and carbonization: The pretreated lotus root particles are placed in a tube furnace, heated to the pyrolysis temperature at a preset rate under inert gas protection, and pyrolyzed at a constant temperature. After natural cooling, lotus root biochar is obtained. S3. Impregnation modification: Add lotus root biochar to lanthanum chloride solution according to the preset solid-liquid ratio and impregnate with stirring at room temperature; S4. Aging Loading: Slowly add alkaline solution to the impregnation system to adjust the pH to the alkaline range, and continue stirring for aging, so that lanthanum ions are precipitated and loaded in situ in the form of nano-lanthanum hydroxide; S5. Post-processing: Filter, wash until neutral, and dry to obtain the target product.

[0006] Furthermore, in step S1, the particle size of the crushed waste lotus root sections is 0.5–5 mm; in step S2, the inert gas is nitrogen, the heating rate is 5–10 °C / min, the pyrolysis temperature is 450–550 °C, and the isothermal pyrolysis time is 1.5–2.5 h.

[0007] Furthermore, before step S3, the lotus root biochar is subjected to a hydrophobic pretreatment with a coupling agent. The carbon skeleton surface is chemically grafted with a silane coupling agent to block some of the hydrophilic hydroxyl groups, resulting in a water contact angle greater than 120°, which gives it superhydrophobic properties and enhances its ability to actively capture oil films on the water surface.

[0008] Furthermore, in step S3, the solid-liquid ratio is 1:10 to 1:50 (g / ml), the concentration of the lanthanum chloride solution is 0.1 to 0.3 mol / L, and the stirring and impregnation time is 6 to 12 h.

[0009] Furthermore, in step S4, the alkaline solution is a sodium hydroxide solution with a mass fraction of 10% to 20%, the pH is adjusted to 9 to 10, and the stirring and aging time is 2 to 4 hours; in step S5, the drying temperature is 60 to 80°C, and the drying time is 12 to 24 hours.

[0010] Secondly, the lanthanum-modified lotus root biochar material prepared by the above preparation method includes nano-lanthanum hydroxide particles uniformly loaded in situ within the internal channels of the lotus root biochar.

[0011] Furthermore, the proportion of mesopore volume to total pore volume in the lotus root biochar matrix is ​​≥60%, the particle size of the nano-lanthanum hydroxide particles is 10-50 nm, the saturated adsorption rate of the material for diesel is ≥10 g / g, the saturated adsorption capacity for phosphate ions under pH=6-8 conditions is ≥30 mg / g, and the lanthanum ion leaching concentration in neutral water is ≤0.05 mg / L.

[0012] On the other hand, the lanthanum-modified lotus root biochar is applied to the in-situ treatment of oil film and eutrophication on river and lake surfaces, including the following steps: S1. Preparation of floating adsorption unit: Lanthanum-modified lotus root biochar was filled into a water-permeable bag with a pore size smaller than the material particle size, and then sealed to obtain a floating adsorption unit. S2. In-situ purification: The floating adsorption unit is deployed in the oil film accumulation area on the surface of rivers and lakes. The porous and hydrophobic properties of the material are used to adsorb oily substances. At the same time, nano-lanthanum hydroxide is used to fix phosphate ions through La-OP inner sphere complexation and LaPO precipitation to achieve synergistic in-situ treatment. S3. Saturated material recycling and resource utilization: After the adsorption unit is saturated, it is retrieved, recycled, and utilized as a resource.

[0013] Furthermore, in step S1, the permeable bag is a non-woven bag or a polyethylene mesh bag with a pore size of 0.1-0.3 mm, and each adsorption unit is filled with 100-500 g of lanthanum-modified lotus root biochar.

[0014] Furthermore, in step S2, the deployment density of the floating adsorption units is 1 to 5 units per square meter of water surface, and they are deployed in the downwind area of ​​rivers and lakes and in the water flow convergence area, either deployed individually or integrated into the existing ecological floating bed system.

[0015] Furthermore, in step S3, the saturated adsorption unit is retrieved and recovered by manual or mechanical means. The recovered saturated material is then air-dried and used as a slow-release phosphate fertilizer in gardens or as an additive component in the substrate for cultivating aquatic plants.

[0016] Compared with the prior art, the present invention has the following significant advantages: 1. Synergistic Functions for Integrated Treatment of Oil-Phosphorus Complex Pollution: This invention is the first to utilize a single lanthanum-modified lotus root biochar material to simultaneously achieve physical adsorption of oil film on the water surface and chemical fixation of phosphate in the water, breaking the vicious cycle of "oil film blockage - hypoxia - endogenous phosphorus release - eutrophication aggravation". It also solves the problems of existing technologies that require the separate deployment of two systems for oil pollution removal and phosphorus removal, resulting in poor synergistic effects and high treatment costs. 2. Using waste to treat waste and building a green circular economy model: Functional materials are prepared by using waste lotus root sections generated from lotus root processing as raw materials. This not only solves the problem of resource waste and environmental pollution caused by agricultural waste disposal, but also significantly reduces the cost of treatment materials. The materials after adsorption saturation have a high phosphorus content and can be directly used as slow-release phosphate fertilizer in gardens or as a substrate for cultivating aquatic plants, forming a complete closed loop of "waste → functional materials → pollutant enrichment → fertilizer reuse". 3. In-situ remediation, flexible deployment and easy operation: It adopts the form of floating adsorption units, which do not require power equipment or fixed structures. The deployment density and position can be flexibly adjusted according to the distribution of oil film and the degree of pollution. It prioritizes the coverage of severely polluted areas such as downwind areas and water flow convergence areas. It can also be integrated into existing ecological floating bed systems. It is particularly suitable for in-situ remediation of open water areas of rivers and lakes. 4. Unique structure, excellent and stable adsorption performance: The natural hierarchical porous structure of the lotus root matrix retains a high proportion of mesopores after carbonization, which has excellent capillary adsorption and storage capacity for oil macromolecules, solving the defects of conventional rice husk and straw biochar, which are mainly microporous and have limited oil mass transfer. At the same time, the well-developed pores provide abundant loading sites for nano-lanthanum hydroxide, ensuring that the material has both high phosphorus removal capacity and long-term stability. 5. Synergistic Purification of Oil Absorption and Phosphorus Removal through Hydrophilic-Hydrophobic Heterogeneous Structure: Modification with a silane coupling agent enhances the hydrophobic affinity of the carbon skeleton for oily substances, while the abundant mesoporous-microporous structure within the lotus root biochar and the surface-loaded nano-lanthanum hydroxide particles retain their hydrophilicity and chemical activity. This microscale hydrophilic-hydrophobic heterostructure allows the material to repel the bulk aqueous phase and enrich the oil film (hydrophobic function), while simultaneously allowing dissolved phosphate ions in the water to enter the pores and be chemically fixed (hydrophilic function), thus achieving synergistic purification.

[0017] 6. Environmentally friendly with no risk of secondary pollution: The raw materials used are natural biomass, the modification process is mild, and the lanthanum ion leaching concentration in neutral water is far below the national standard limit, which ensures the safety and controllability of the water ecology; the adsorption unit uses biodegradable non-woven bags or polyethylene mesh bags, and the saturated materials can be recycled, avoiding the secondary pollution problem that traditional polypropylene oil-absorbing felts need to be disposed of as hazardous waste after disposal. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the preparation method of the present invention; Figure 2 This is a schematic diagram of the in-situ treatment method of the present invention. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0020] Example 1: Preparation of Lanthanum-Modified Lotus Root Biochar Step 1: Pretreatment: Collect the waste lotus root sections generated during lotus root processing, rinse them repeatedly with tap water to remove surface mud and impurities, place them in a 60℃ forced-air drying oven to dry for 24 hours until constant weight, take them out and crush them with a pulverizer, and sieve them to obtain lotus root section particles with a particle size of 2-3mm.

[0021] Step 2, Pyrolysis and Carbonization: Weigh 200g of the above-mentioned lotus root granules, spread them evenly in a quartz boat, and place them in a tube furnace. Nitrogen gas is introduced as a protective gas at a flow rate of 100mL / min, and the temperature is increased to 500℃ at a rate of 8℃ / min, and pyrolyzed at this constant temperature for 2 hours. After pyrolysis, the mixture is naturally cooled to room temperature under a nitrogen atmosphere, and the resulting black lotus root biochar is obtained and sealed for later use.

[0022] Step 3, Impregnation Modification: Weigh 50g of lotus root biochar and add it to 1L of 0.2mol / L lanthanum chloride solution at a solid-liquid ratio of 1:20 (g / mL). Stir and impregnate at 250r / min for 8h at room temperature.

[0023] Step 4, Aging and Loading: Slowly add a 15% sodium hydroxide solution to the above impregnation system while stirring. Adjust the pH of the system to 9.5 and continue stirring for 3 hours to allow lanthanum ions to precipitate in situ as nano-lanthanum hydroxide and be loaded into the surface and internal pores of the biochar.

[0024] Step 5, Post-processing: The reaction mixture is separated by filtration, and the solid product is repeatedly washed with deionized water until the pH of the filtrate is neutral. The washed solid is dried in a 70℃ forced-air drying oven for 18 hours, then ground to obtain lanthanum-modified lotus root biochar material.

[0025] Example 2: Preparation of Lanthanum-Modified Lotus Root Biochar Step 1 Pretreatment: Collect waste lotus root sections, wash and dry them, then crush them and sieve them to obtain lotus root section particles with a particle size of 0.5-1mm.

[0026] Step 2: Pyrolysis and carbonization: Place the lotus root particles in a tube furnace, heat them to 450°C at a rate of 5°C / min under nitrogen protection, pyrolyze at a constant temperature for 1.5 hours, and then cool naturally to obtain lotus root biochar.

[0027] Step 3 Impregnation modification: Add lotus root biochar to a 0.1 mol / L lanthanum chloride solution at a solid-liquid ratio of 1:10 (g / mL) and impregnate at room temperature for 6 hours with stirring.

[0028] Step 4: Aging load: Add 10% sodium hydroxide solution to adjust the pH to 9, and continue stirring for aging for 2 hours.

[0029] Step 5 Post-processing: Filter and wash until neutral, then dry at 60℃ for 24h to obtain lanthanum-modified lotus root biochar.

[0030] Example 3: Preparation of Lanthanum-Modified Lotus Root Biochar S1 Pretreatment: Collect waste lotus root sections, wash and dry them, then crush them and sieve them to obtain lotus root section particles with a particle size of 4-5 mm.

[0031] S2 pyrolysis carbonization: Lotus root particles are placed in a tube furnace and heated to 550℃ at a rate of 10℃ / min under nitrogen protection. The mixture is then kept at a constant temperature for 2.5 hours and allowed to cool naturally to obtain lotus root biochar.

[0032] S3 Impregnation Modification: Lotus root biochar was added to a 0.3 mol / L lanthanum chloride solution at a solid-liquid ratio of 1:50 (g / mL), and impregnated at room temperature for 12 h with stirring.

[0033] S4 aging load: Add 20% sodium hydroxide solution to adjust the pH to 10, and continue stirring for aging for 4 hours.

[0034] S5 post-treatment: Filter and wash until neutral, then dry at 80℃ for 12h to obtain lanthanum-modified lotus root biochar.

[0035] Example 4: Preparation of floating adsorption unit Lanthanum-modified lotus root biochar prepared in Example 1 was filled into permeable nonwoven bags with a pore size of 0.2 mm at a rate of 300 g per bag, and sealed with nylon thread to obtain a floating adsorption unit. The nonwoven bag is made of polypropylene nonwoven fabric, which has good water permeability and corrosion resistance, and the pore size is smaller than the material particle size, which can effectively prevent the leakage of biochar particles.

[0036] It should be noted that by performing hydrophobic pretreatment of the lotus root biochar with a coupling agent before lanthanum modification (before S3), and by chemically grafting the carbon skeleton surface with a silane coupling agent to block some hydrophilic hydroxyl groups, the material's water contact angle is greater than 120°, giving it superhydrophobic properties and thus enhancing the material's ability to actively capture oil films on the water surface. The process sequence is coupling agent treatment first, followed by lanthanum modification, to ensure that the two modification steps do not interfere with each other.

[0037] Example 5: Application of in-situ treatment of oil film and eutrophication on river and lake surfaces The synergistic purification principle of hydrophobicity, oleophilicity, and phosphate chemical fixation functions in this invention: 1. Scale separation of action: The hydrophobic and oleophilic functions act on the macroscopic surface and macroporous region of the material, responsible for repelling water and actively capturing and enriching the oil film on the water surface; the chemical fixation of phosphate occurs inside the mesoporous-microporous interior, where dissolved phosphate ions in water diffuse into the pores with the water flow, come into contact with the active sites of nano-lanthanum hydroxide and are chemically fixed.

[0038] 2. Independent active sites: Nano-lanthanum hydroxide is loaded onto the inner surface of the pores via electrostatic adsorption and intrapore precipitation. This physical loading mechanism does not depend on the surface hydroxyl groups blocked by the coupling agent.

[0039] Thus, this biochar material achieves integrated treatment of oil-phosphorus complex pollution through a synergistic mechanism of "physical oil absorption by hydrophobic carbon skeleton" and "chemical phosphorus removal by hydrophilic lanthanum active sites".

[0040] Specifically, an area in a city's landscape lake with oil film accumulation and severe phosphorus pollution was selected as the test water area. The oil film thickness on the water surface of this area was approximately 0.1–0.3 mm, the total phosphorus concentration in the water was 0.12 mg / L, and the dissolved oxygen concentration was 4.2 mg / L.

[0041] The floating adsorption units prepared in Example 4 were deployed in the test water area at a density of 3 units per square meter of water surface, with priority given to their placement at the downwind end of the lake and in areas where water flows converge. The adsorption units float on the water surface and utilize the porous and hydrophobic properties of lotus root biochar to rapidly adsorb oily substances from the oil film on the water surface. Simultaneously, phosphate ions in the water pass through the nonwoven bag and come into contact with the nano-lanthanum hydroxide loaded on the material surface, where they are fixed through La-OP internal spherical complexation and LaPO precipitation.

[0042] After seven consecutive days of operation, the oil film on the surface of the test water area was basically removed, the total phosphorus concentration in the water body dropped to 0.018 mg / L, reaching the Class II standard of the "Surface Water Environmental Quality Standard" (GB3838-2002), and the dissolved oxygen concentration rose to 6.8 mg / L, and the aquatic ecological environment was significantly improved.

[0043] Example 6: Recycling and Resource Utilization of Saturated Materials Once the floating adsorption unit is saturated (determined by periodically monitoring the oil and phosphorus concentrations in the water), it is manually retrieved and recovered. The recovered saturated adsorption material is then placed in a ventilated area to air dry naturally, removing surface moisture.

[0044] The air-dried saturated material contains approximately 2.5% phosphorus (calculated as PO), and can be directly applied to gardens and green spaces as a slow-release phosphate fertilizer at a rate of 500 kg / hm. Alternatively, it can be added to aquatic plant cultivation substrate at a ratio of 10% to 20% to provide continuous phosphorus nutrition for aquatic plant growth.

[0045] Performance testing Oil adsorption performance test: The saturated adsorption rate of the material for diesel oil was tested by gravimetric method. The results showed that the lanthanum-modified lotus root biochar prepared in Example 1 had a saturated adsorption rate of 12.6 g / g for diesel oil, which was much higher than that of traditional polypropylene oil-absorbing felt (about 8 g / g).

[0046] Phosphorus adsorption performance test: Static adsorption tests were conducted at pH=7 and an initial phosphorus concentration of 50 mg / L. The results showed that the material prepared in Example 1 had a saturated adsorption capacity of 36.2 mg / g for phosphate, and its adsorption performance was stable within the pH range of 6 to 8.

[0047] Lanthanum ion leaching test: The material was immersed in neutral deionized water and shaken for 24 hours. The concentration of lanthanum ions in the leachate was then detected by ICP-MS. The results showed that the lanthanum ion leaching concentration was 0.03 mg / L, which is far below the limit requirements for rare earth elements in the "Surface Water Environmental Quality Standard" (GB3838-2002), ensuring the safety of the aquatic ecological environment.

[0048] It should be noted that the above embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing lanthanum-modified lotus root biochar, characterized in that, Includes the following steps: S1. Pretreatment: Collect waste lotus root sections, wash and dry them, and then crush them to the preset particle size; S2. Pyrolysis and carbonization: The pretreated lotus root particles are placed in a tube furnace, heated to the pyrolysis temperature at a preset rate under inert gas protection, and pyrolyzed at a constant temperature. After natural cooling, lotus root biochar is obtained. S3. Impregnation modification: Add lotus root biochar to lanthanum chloride solution according to the preset solid-liquid ratio and impregnate with stirring at room temperature; S4. Aging Loading: Slowly add alkaline solution to the impregnation system to adjust the pH to the alkaline range, and continue stirring for aging, so that lanthanum ions are precipitated and loaded in situ in the form of nano-lanthanum hydroxide; S5. Post-processing: Filter, wash until neutral, and dry to obtain the target product.

2. The preparation method according to claim 1, characterized in that, In step S1, the particle size of the crushed waste lotus root sections is 0.5-5 mm; in step S2, the inert gas is nitrogen, the heating rate is 5-10℃ / min, the pyrolysis temperature is 450-550℃, and the isothermal pyrolysis time is 1.5-2.5 h.

3. The preparation method according to claim 2, characterized in that, Before step S3, the lotus root biochar is subjected to hydrophobic pretreatment with a coupling agent. The carbon skeleton surface is chemically grafted with a silane coupling agent to block some hydrophilic hydroxyl groups, and the water contact angle of the material is greater than 120°, giving it superhydrophobic properties and enhancing the material's ability to actively capture oil films on the water surface.

4. The preparation method according to claim 3, characterized in that, In step S3, the solid-liquid ratio is 1:10 to 1:50 (g / ml), the concentration of lanthanum chloride solution is 0.1 to 0.3 mol / L, and the stirring and impregnation time is 6 to 12 h.

5. The preparation method according to claim 6, characterized in that, In step S4, the alkaline solution is a sodium hydroxide solution with a mass fraction of 10% to 20%, the pH is adjusted to 9 to 10, and the stirring and aging time is 2 to 4 hours; in step S5, the drying temperature is 60 to 80°C, and the drying time is 12 to 24 hours.

6. The lanthanum-modified lotus root biochar material prepared by the preparation method according to any one of claims 1-5, characterized in that, It includes nano-lanthanum hydroxide particles uniformly loaded in situ within the internal pores of the lotus root biochar.

7. The lanthanum-modified lotus root biochar material according to claim 6, characterized in that, The proportion of mesopore volume to total pore volume in the lotus root biochar matrix is ​​≥60%, the particle size of nano-lanthanum hydroxide particles is 10-50 nm, the saturated adsorption rate of the material for diesel is ≥10 g / g, the saturated adsorption capacity for phosphate ions is ≥30 mg / g under pH=6-8 conditions, and the lanthanum ion leaching concentration in neutral water is ≤0.05 mg / L.

8. A method for in-situ remediation of oil film and eutrophication on river and lake surfaces using lanthanum-modified lotus root biochar as described in any one of claims 6-7, characterized in that, Includes the following steps: S1. Preparation of floating adsorption unit: Lanthanum-modified lotus root biochar was filled into a water-permeable bag with a pore size smaller than the material particle size, and then sealed to obtain a floating adsorption unit. S2. In-situ purification: The floating adsorption unit is deployed in the oil film accumulation area on the surface of rivers and lakes. The porous and hydrophobic properties of the material are used to adsorb oily substances. At the same time, nano-lanthanum hydroxide is used to fix phosphate ions through La-OP inner sphere complexation and LaPO precipitation to achieve synergistic in-situ treatment. S3. Saturated material recycling and resource utilization: After the adsorption unit is saturated, it is retrieved, recycled, and utilized as a resource.

9. The in-situ treatment method according to claim 8, characterized in that, In step S1, the permeable bag is a non-woven bag or a polyethylene mesh bag with a pore size of 0.1-0.3 mm, and each adsorption unit is filled with 100-500 g of lanthanum-modified lotus root biochar.

10. The in-situ treatment method according to claim 9, characterized in that, In step S2, the floating adsorption units are deployed at a density of 1 to 5 units per square meter of water surface, located at the downwind end of rivers and lakes and in areas where water flows converge, either individually or integrated into existing ecological floating bed systems. In step S3, saturated adsorption units are retrieved and recovered manually or mechanically. The recovered saturated material is then air-dried and used as a slow-release phosphate fertilizer in gardens or as an additive component in aquatic plant cultivation substrates.

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