A rare earth element-nitrogen and phosphorus co-doped biochar, its preparation method and application

Abstract

The present invention belongs to the field of environmental pollution treatment, and relates to a method for removing heavy metals by using element-doped modified biochar, specifically a rare earth element-nitrogen and phosphorus co-doped biomass carbon and its preparation method and application; the present invention discloses a biochar modification method, that is, doping rare earth elements and nitrogen and phosphorus elements on the surface of biochar. The selected rare earth elements include one or more of lanthanum, cerium, praseodymium, and neodymium, and are mixed evenly with diammonium hydrogen phosphate according to a certain mass ratio and subjected to hydrothermal reaction at a certain temperature. Utilize the electron transfer ability of rare earth elements to form pyridine nitrogen, pyrrole nitrogen, and graphene nitrogen on the surface of biochar, improve the adsorption ability of biochar to heavy metals, the phosphorus element has a certain pore-forming effect on the surface of biochar, and makes biochar rich in phosphate groups, thereby realizing the efficient removal and passivation of heavy metals.

Description

Technical Field

[0001] The present invention belongs to the field of environmental pollution control, and relates to a method for removing heavy metals by using element-doped modified biochar, specifically a rare earth element-nitrogen and phosphorus co-doped biochar and its preparation method and application. Background Art

[0002] With the rapid progress of urbanization and industrialization, a large amount of heavy metals are discharged by industrial and mining enterprises and enter the environment such as the atmosphere, water bodies, and soil, causing a huge impact on the ecological environment system. Since heavy metals are cumulative and hidden, and are generally present in the environment, they can enter the human body through the food chain and food web, posing a great threat to human health. Therefore, the treatment and restoration of heavy metals have become a key issue in current environmental pollution control.

[0003] The remediation methods of heavy metals in soil can be divided into physical methods, chemical methods, biological methods, and combined remediation technologies. Physical methods are highly efficient, suitable for small-scale remediation but costly, and can damage soil organic matter and structure; chemical methods have low cost, relatively high efficiency, and are suitable for large-scale remediation, but are prone to damage soil structure and cause secondary pollution; biological methods, as an environmentally friendly remediation method, do not damage soil organic matter and structure and have low cost, but have a long remediation cycle and are not suitable for the remediation of highly contaminated soil. The adsorption method, as a combined remediation method of physical and chemical methods, overcomes the defects of using a single method. Biochar (BC), as a widely used adsorbent, is a carbonaceous residue obtained by pyrolysis of biomass under low temperature and oxygen-limited conditions. Due to its developed pore structure, large specific surface area, high surface activity, and rich functional groups, it has the advantages of low cost, wide source, and high efficiency, and is an environmentally friendly and promising environmental functional adsorption material.

[0004] Under normal conditions, biochar itself has certain pores, specific surface area, and functional groups, so it has a strong ability to adsorb and remove heavy metals. However, since the pores, specific surface area, and functional groups of biochar cannot meet the removal efficiency and removal amount of target pollutants, it is necessary to modify it. Currently, the commonly used biochar modification technology is to improve the porosity, specific surface area, functional groups, or more of its properties on the basis of the original biochar, so as to exert more performance. Element doping modification is a commonly used biochar modification method. By introducing some element functional groups on the surface of the carbon material, the specific surface area and active sites of biochar are increased, thus providing more defect sites, which is conducive to more adsorption of pollutants on the material surface; or using the redox reaction of element functional groups to reduce the toxicity of heavy metals. Summary of the Invention

[0005] The purpose of the present invention is to provide a rare earth element nitrogen and phosphorus co-doped porous biochar and its preparation method and application, mainly through different element doping processes, to obtain a porous biochar material that can be used for heavy metal remediation. The porous biochar material takes advantage of the rare earth element's ability to transfer electrons, nitrogen's provision of active sites, and phosphorus's pore-forming properties, and has the characteristics of simple preparation process, high heavy metal removal efficiency, and less secondary pollution.

[0006] Nitrogen doping is the process of introducing pyrrolic nitrogen, pyridinic nitrogen and graphitic nitrogen into the biochar surface to increase the surface adsorption sites for heavy metals (such as Cb 2+ , Pb 2+ ). Phosphorus doping can help dehydration, aromatization, and cross-linking of biomass during the carbonization process, and ultimately play a pore-forming role. At present, biochar modified with common rare earth elements is often used to remove phosphate pollution. Some studies have found that the La-modified biochar surface introduces functional group structures such as hydroxyl, ketone, ester, and carbonyl, which have a certain adsorption effect on Cd and As. In order to explore the effect of metal and non-metal co-doped carbon materials on their performance, this patent attempts to introduce rare earth elements, nitrogen, and phosphorus elements on the surface of biochar to provide more defects and adsorption sites, and improve the ability to remove heavy metals, in the hope of further expanding and deepening the research on element-doped modified biochar.

[0007] To achieve the above objectives, the first aspect of the present invention discloses a rare earth element-nitrogen-phosphorus co-doped biochar, which is made of biochar composite rare earth elements and inorganic elements nitrogen and phosphorus.

[0008] The rare earth element includes one or more of lanthanum, cerium, praseodymium and neodymium.

[0009] Preferably, the biochar can be prepared from hyperaccumulator plants in rare earth mining areas, and the hyperaccumulator plants include Dicranopteris dichotoma, Pinus massoniana, and Cunninghamia lanceolata.

[0010] The second aspect of the present invention discloses a method for preparing the above-mentioned rare earth element-nitrogen and phosphorus co-doped biochar, comprising the following steps:

[0011] S1: adding biomass powder and rare earth salt into a mixed aqueous solution of anhydrous ethanol, and then adding diammonium hydrogen phosphate into the reaction system to fully react to obtain a suspension;

[0012] S2: Pour the suspension obtained in S1 into a hydrothermal reactor and react at a temperature of 100-200°C for 12-24 hours. After the hydrothermal reaction is completed, wash, centrifuge and dry to obtain rare earth element-nitrogen and phosphorus co-doped biochar.

[0013] The diammonium hydrogen phosphate reagent used in the present invention can not only play the role of nitrogen and phosphorus co-doping, but also phosphorus can act as an activator to increase the porosity and introduce phosphate PO4 on the surface of biochar.3- , it forms precipitates such as lead phosphate (Pb3(PO4)2) with heavy metal lead; nitrogen introduces pyridine nitrogen, pyrrole nitrogen and graphene nitrogen on the surface of biochar; moreover, the presence of rare earth elements improves the electron transfer efficiency.

[0014] The introduction of non-metallic elements such as nitrogen and phosphorus mainly changes the existing biochar structure, provides channels and active centers, and can restore the pH of the soil by increasing the alkalinity. The introduction of metal elements such as rare earth elements is a method to effectively adjust the surface chemistry and electronic properties of biomass carbon materials.

[0015] In S1, by mass ratio, the biomass powder: diammonium hydrogen phosphate: rare earth element is 1:1:0.003 - 0.03. Preferably, the mass ratio of the biomass powder: diammonium hydrogen phosphate: rare earth element can be 1:1:0.003, 1:1:0.01, 1:1:0.03; preferably 1:1:0.03.

[0016] The biochar powder described in S1 is obtained by passing through a 40 - 80 mesh sieve. Preferably, it is a 60 mesh sieve.

[0017] The rare earth salts described in S1 include carbonates, nitrates, fluorides, phosphates, oxides or silicates of lanthanum, cerium, praseodymium and neodymium.

[0018] In S2, the centrifugal speed is 7000 - 8000 r / min; in S2, it is dried at 60 - 80 °C for 24 h.

[0019] The third aspect of the present invention discloses the application of the above rare earth element - nitrogen and phosphorus co - doped biochar in heavy metal pollution remediation.

[0020] The heavy metals include one or a combination of more of lead, chromium and cadmium.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The present invention uses agricultural and forestry waste such as Dicranopteris dichotoma and Pinus massoniana that naturally grow in ionic rare earth ore areas as carbon precursors for carbonization to produce new biomass carbon products in the form of stable biochar, which has important significance for promoting the sustainable development of the agricultural and forestry industries.

[0023] 2. The rare earth element - nitrogen and phosphorus co - doped biochar prepared by the present invention significantly improves the removal ability of heavy metals such as lead; the presence of rare earth elements, nitrogen and phosphorus enhances the adsorption performance and passivation ability of the modified biochar towards heavy metals. Description of the Drawings

[0024] Figure 1 It is the SEM - EDS diagram of the rare earth element - nitrogen and phosphorus co - doped biochar material

[0025] Figure 2 XRD comparison chart of biochar co-doped with rare earth elements-nitrogen and phosphorus and other biochars

[0026] Figure 3 Comparison chart of the Pb adsorption effects of biochar co-doped with rare earth elements-nitrogen and phosphorus and other biochars Specific implementation manners

[0027] The present invention will be further described below by way of examples, but the present invention is not limited to the scope of the described examples. For the experimental methods without specific conditions in the following examples, they are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0028] Comparative Example 1

[0029] S1: Dissolve 10 g of Dicranopteris dichotoma biomass powder passing through 60 mesh and 0.9352 g of lanthanum nitrate hexahydrate in 150 mL of a mixed solution of absolute ethanol (the concentration of absolute ethanol is 9.38 mol / L), stir for 30 min until completely dissolved to form a suspension.

[0030] S2: Pour the above suspension into a 100 mL hydrothermal reaction kettle, control the temperature at 180 °C, take out the reaction kettle after 12 h, cool it to room temperature, then wash it three times each with deionized water and absolute ethanol, and dry it at 60 °C for 24 h to obtain lanthanum-doped biochar La-BC.

[0031] Comparative Example 2

[0032] S1: Dissolve 10 g of Dicranopteris dichotoma biomass powder passing through 60 mesh and 10 g of diammonium hydrogen phosphate in 150 mL of a mixed solution of absolute ethanol (the concentration of absolute ethanol is 9.38 mol / L), stir for 30 min until completely dissolved to form a suspension.

[0033] S2: Pour the above suspension into a 100 mL hydrothermal reaction kettle, control the temperature at 180 °C, take out the reaction kettle after 12 h, cool it to room temperature, then wash it three times each with deionized water and absolute ethanol, and dry it at 60 °C for 24 h to obtain nitrogen and phosphorus co-doped biochar NP-BC.

[0034] Example 1

[0035] S1: Dissolve 10 g of Dicranopteris dichotoma biomass powder passing through 60 mesh and 0.9352 g of lanthanum nitrate hexahydrate in 150 mL of a mixed solution of absolute ethanol (the concentration of absolute ethanol is 9.38 mol / L), stir for 30 min; then add 10 g of diammonium hydrogen phosphate and stir until completely dissolved to form a suspension.

[0036] S2: Pour the above suspension into a 100 mL hydrothermal reactor, control the temperature at 180 °C, take out the reactor after 12 h, cool it to room temperature, then wash it three times with deionized water and anhydrous ethanol respectively, and dry it at 60 °C for 24 h to obtain lanthanum, nitrogen and phosphorus co-doped biochar LaNP-BC.

[0037] Application of Biochar Prepared in Example 2 in Adsorbing Heavy Metals

[0038] Respectively take 0.4 g of biomass powder prepared from Dicranopteris dichotoma, La-BC in Comparative Example 1, NP-BC in Comparative Example 2 and LaNP-BC in Example 1 and put them into a 250 mL conical flask, add 200 mL of 400 mg / L lead solution (pH = 5), place it on a shaker at 25 °C and 200 rpm for reaction for 24 h until the adsorption reaches equilibrium. Take the supernatant and filter it through a 0.45 μm filter membrane, then dilute the filtrate by an appropriate multiple, and use ICP-OES to measure the concentration of the remaining lead ions; obtain the data in Table 1.

[0039] Table 1 Comparison of the Pb Adsorption Capabilities of Biochars Doped with Three Elements and the Original Biochar

[0040]

[0041]

[0042] Combined with the data in Table 1, compared with La-BC and NP-BC obtained by separately doping rare earth elements or nitrogen and phosphorus elements with biochar, the diammonium hydrogen phosphate reagent used in the present invention can not only play the role of co-doping nitrogen and phosphorus elements, in which phosphorus element can be used as an activator to increase the porosity, and introduce phosphate groups PO4 3- on the biochar surface, and form precipitates such as lead phosphate (Pb3(PO4)2) with heavy metal lead; nitrogen element introduces pyridine nitrogen, pyrrole nitrogen and graphene nitrogen on the biochar surface; moreover, the presence of rare earth elements improves the electron transfer efficiency, and the presence of rare earth elements, nitrogen and phosphorus greatly enhances the adsorption performance and passivation ability of the modified biochar to heavy metals. The LaNP-BC obtained in the examples of the present invention has a removal rate of up to 83.94% for heavy metal lead, compared with the removal rates of 8.01%, 12.56% and 20.71% for heavy metal lead by BC, La-BC and NP-BC in Comparative Examples 1 and 2; significantly improves the effect of removing heavy metal Pb and achieves unexpected technical effects.

[0043] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and all should be covered within the protection scope of the present invention.

Claims

1. A preparation method of rare earth element-nitrogen and phosphorus co-doped biochar, characterized in that, It is made of biochar compounded with rare earth elements and inorganic elements nitrogen and phosphorus; The biochar is prepared from hyperaccumulator plants existing in rare earth mining areas, and the hyperaccumulator plants include Dicranopteris dichotoma, Pinus massoniana, and Cunninghamia lanceolata; The rare earth element is lanthanum; The preparation method of the rare earth element-nitrogen-phosphorus co-doped biochar includes the following steps: S1: Add biomass powder and rare earth salt into the mixed aqueous solution of absolute ethanol, and then add diammonium hydrogen phosphate to the reaction system, and fully react to obtain a suspension; S2: Pour the suspension obtained in S1 into a hydrothermal reaction kettle, react at a temperature of 100-200 °C for 12-24 h. After hydrothermal reaction, wash, centrifuge, and dry to obtain rare earth element-nitrogen-phosphorus co-doped biochar; In S1, by mass ratio, the biomass powder: diammonium hydrogen phosphate: rare earth element is 1:1:0.003~0.03; The biochar is used for heavy metal pollution remediation.

2. The preparation method of rare earth element-nitrogen and phosphorus co-doped biochar according to claim 1, characterized in that, The biomass powder in S1 is obtained by passing through a 40-80 mesh sieve.

3. The preparation method of rare earth element-nitrogen and phosphorus co-doped biochar according to claim 1, characterized in that, The rare earth salts in S1 include carbonates, nitrates, fluorides, phosphates, or silicates of lanthanum, cerium, praseodymium, and neodymium.

4. The preparation method of rare earth element-nitrogen and phosphorus co-doped biochar according to claim 1, characterized in that, The centrifugation speed in S2 is 7000-8000 r / min; in S2, it is dried at 60 °C for 24 h.

5. Application of the rare earth element-nitrogen and phosphorus co-doped biochar obtained by the preparation method according to claim 1 in heavy metal pollution remediation.

6. The application according to claim 5, characterized in that, The heavy metals include one or more combinations of lead, chromium, and cadmium.

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