A biochar composite material for heavy metal wastewater treatment, its preparation method and application

Abstract

The present invention discloses a biochar composite material for heavy metal wastewater treatment, its preparation method and application. The method includes modifying biochar with ethylenediamine to obtain ethylenediamine-modified biochar; acidifying and magnetizing the ethylenediamine-modified biochar to obtain magnetically modified biochar; loading nano-manganese dioxide onto the magnetically modified biochar to obtain a biochar composite material. The present invention improves the adsorption capacity and the potential for recycling and application.

Description

Technical Field

[0001] The present invention relates to a biochar composite material for treating heavy metal wastewater, a preparation method thereof, and an application thereof, belonging to the technical field of water treatment. Background Art

[0002] Heavy metals contained in water bodies are common inorganic pollutants in the environment. They often cannot be degraded by microorganisms in nature and are very likely to be transmitted and transferred in the environment through food chains and various ecological cycles, ultimately bringing continuous and irreversible harm to the human body. Heavy metals in the water environment are extremely difficult to degrade due to the enrichment effect and will combine with other chemical substances in the environment to form more toxic inorganic or organic heavy metal pollutants.

[0003] At present, the main methods for treating heavy metal wastewater include chemical precipitation method, solvent extraction method, electrodialysis method, membrane separation method, biological treatment method, ion exchange method, adsorption method, reverse osmosis method, etc. Some traditional methods and emerging technologies such as membrane separation are limited to a certain extent in their wide application in the field of heavy metal wastewater treatment due to their respective disadvantages and cost problems. In recent years, the adsorption method is considered a recyclable, eco-friendly and sustainable treatment technology with broad application prospects because of its advantages such as low cost, high efficiency, easy operation, good treatment effect, and renewable use of adsorbents.

[0004] Biochar is a solid product generated by the high-temperature pyrolysis of bio-organic materials (biomass) in an anoxic or oxygen-free environment. Biochar has a low cost and has the advantage of a large adsorption capacity for pollutants in water. However, it still has the following disadvantages: limited adsorption capacity, and the difficulty of solid-liquid separation of non-magnetic biochar leads to low potential for recovery and reuse. Summary of the Invention

[0005] The purpose of the present invention is to provide a biochar composite material for treating heavy metal wastewater, a preparation method thereof, and an application thereof, so as to solve the problems of limited adsorption capacity and difficulty in recovery existing in the prior art.

[0006] To achieve the above purpose, the present invention is implemented by adopting the following technical solutions:

[0007] In the first aspect, the present invention provides a preparation method of a biochar composite material for treating heavy metal wastewater, including:

[0008] Modifying biochar with ethylenediamine to obtain ethylenediamine-modified biochar;

[0009] Acidifying and magnetizing the ethylenediamine-modified biochar to obtain magnetically modified biochar;

[0010] Loading nano-manganese dioxide onto the magnetically modified biochar to obtain a biochar composite material.

[0011] In combination with the first aspect, further, the biochar is prepared by the following method:

[0012] Select moso bamboo and crush it;

[0013] Heat the crushed moso bamboo under anoxic conditions at 380 - 420 °C until it is completely carbonized to obtain biochar made of moso bamboo.

[0014] In combination with the first aspect, further, modifying the biochar with ethylenediamine to obtain ethylenediamine-modified biochar includes:

[0015] Put 10 - 30 parts by mass of biochar into a mixed solution of epichlorohydrin and N, N-dimethylformamide, stir and heat for 50 - 70 min;

[0016] After adding 899 - 2697 parts by mass of ethylenediamine, continue to stir and heat for 50 - 70 min;

[0017] After adding 728 - 1092 parts by mass of triethylamine solution, continue to stir and heat for 110 - 130 min;

[0018] Purify the synthesized product to obtain ethylenediamine-modified biochar.

[0019] In combination with the first aspect, further, the mass concentration of the triethylamine solution is 99%;

[0020] The purification includes: washing the unreacted organic matter on the surface of the synthesized product with absolute ethanol, filtering with a vacuum filter and drying in an oven.

[0021] In combination with the first aspect, further, acidifying and magnetizing the ethylenediamine-modified biochar to obtain magnetically modified biochar includes:

[0022] Mix a 1.5 - 2.5 mol / L nitric acid solution and ethylenediamine-modified biochar in a container according to a liquid-solid ratio of (9 - 11):1, place a reflux device at the container mouth, continuously soak at 100 - 120 °C for 1.5 - 2.5 h, monitor the pH value in real time during the soaking process to make the supernatant neutral, wash after cooling, and then dry the solution to obtain acid-modified biochar;

[0023] A Fe3O4 colloidal solution is prepared using a soluble salt of trivalent iron or its hydrate and a soluble salt of divalent iron or its hydrate with a molar ratio of 1.5 - 2.5:1. 1000 - 2000 parts by mass of the Fe3O4 colloidal solution and 360 - 400 parts by mass of acid-modified biochar are added to an ammonia water solution together. After stirring for 25 - 35 min, solid-liquid separation and washing are carried out. Then, the biochar concentration is maintained at 23.0 - 23.4 mg / L in a container. After adding a n-propanol solution according to a volume ratio of 1:(9 - 11), ultrasonic treatment is carried out for 15 - 25 min. Then, polyethylene glycol is added to the container to maintain the biochar concentration at 26.6 - 27.0 mg / L, and it is placed in a stirrer and continuously stirred for 23 - 25 h. After stirring is completed, it is recovered with a magnet, washed with ultrapure water, and dried to obtain magnetically modified biochar;

[0024] The soluble salt of trivalent iron or its hydrate is preferably FeCl3·6H2O, and the soluble salt of divalent iron or its hydrate is preferably FeCl2·4H2O.

[0025] In combination with the first aspect, further, the nano manganese dioxide is prepared by the following method:

[0026] 1 - 1.5 g of KMnO4 is added to 70 - 100 mL of a dilute H2SO4 solution with a mass fraction of 70%. (NH4)2S2O8 is added to the dilute H2SO4 solution, and the concentration of (NH4)2S2O8 in the dilute H2SO4 solution is 7.3 - 7.8 mmol / L. It is ultrasonically stirred until dissolved to obtain a nano manganese dioxide solution.

[0027] In combination with the first aspect, further, the loading of the nano manganese dioxide onto the magnetically modified biochar to obtain a biochar composite material includes:

[0028] The nano manganese dioxide solution and the magnetically modified biochar are added to a container, sealed, and hydrothermally reacted at 170 - 190 °C in an oven for 23 - 25 h. It is naturally cooled to room temperature, the supernatant is removed, and the obtained precipitate is purified to obtain the biochar composite material.

[0029] In combination with the first aspect, further, the purification includes: centrifugally washing with deionized water until neutral, and drying at 55 - 65 °C for 23 - 25 h.

[0030] In a second aspect, the present invention also provides a biochar composite material for treating heavy metal wastewater, prepared by the method according to any one of the first aspect.

[0031] In a third aspect, the present invention also provides an application of the biochar composite material for treating heavy metal wastewater described in the second aspect, using the biochar composite material to adsorb heavy metal ions in wastewater.

[0032] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0033] The present invention provides a biochar composite material for heavy metal wastewater treatment, its preparation method and application. Ethylenediamine and manganese dioxide are used to modify the existing biochar to prepare a biochar composite material. Ethylenediamine can improve the adsorption capacity of biochar by expanding the pores of biochar and adding functional groups on the surface of biochar. Manganese dioxide is selected as the composite material. According to the analysis of the physical properties of manganese dioxide, it can be concluded that manganese dioxide has good effects in adsorption performance. Combining the characteristics of manganese dioxide and biochar can enhance the adsorption capacity of biochar for heavy metal ions in water. After magnetic modification, the specific surface area of biochar increases significantly, and the number of micropores is small. When combined with heavy metal ions, it can reach the adsorption equilibrium relatively quickly. Moreover, after magnetic modification, a magnet can be used to recover the biochar, solving the problem of difficult recovery. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a flowchart of a preparation method of a biochar composite material for heavy metal wastewater treatment provided by an embodiment of the present invention;

[0035] Figure 2 is a scanning electron microscope image of ordinary biochar provided by an embodiment of the present invention;

[0036] Figure 3 is a scanning electron microscope image of a biochar composite material for heavy metal wastewater treatment provided by an embodiment of the present invention.

[0037] Figure 4 is an FTIR infrared spectrum diagram of biochar provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and cannot be used to limit the protection scope of the present invention.

[0039] As Figure 1 shown, an embodiment of the present invention provides a preparation method of a biochar composite material for heavy metal wastewater treatment, including the following steps:

[0040] S1. Preparation, modification and negative magnetization of biochar (including: modifying biochar with ethylenediamine to obtain ethylenediamine-modified biochar; acidifying and magnetizing the ethylenediamine-modified biochar to obtain magnetically modified biochar).

[0041] 1) Selection of biochar materials. Purchase high-quality moso bamboo from merchants and chop it up.

[0042] 2) Preparation of bamboo-based biochar. The processed moso bamboo was heated at 400 °C under the same anoxic conditions for 4 h to carbonize it. After grinding, it was filtered through a 100-mesh sieve to obtain the biochar prepared from moso bamboo.

[0043] 3) Preparation of ethylenediamine-modified biochar. Take 0.2 g of biochar and place it in a three-necked round-bottom flask. After adding 5 mL of epichlorohydrin and 45 mL of N,N-dimethylformamide, stir and heat for 1 h; after adding 20 mL of ethylenediamine, continue to stir and heat for 1 h; after adding 12.5 mL of triethylamine (99%) solution, then stir and heat for 2 h. Wash the unreacted organic matter on the surface of the synthesis product with absolute ethanol, filter it with a vacuum filter and put it into a drying oven. Take it out after drying and store it in a sealed manner to prepare the ethylenediamine-modified biochar.

[0044] 4) Take the ethylenediamine-modified biochar and mix it with a 2 mol / L nitric acid solution at a liquid-solid ratio of 10:1 (mL:g) in a 250 mL conical flask. Place a bent-neck funnel at the mouth of the flask and continuously soak it on an electric hot plate at 110 °C for 2 h. After waiting for the solution to cool, wash it with ultrapure water and monitor the pH value in real time to make the supernatant neutral. Then dry the solution to obtain the acid-modified biochar. Prepare a Fe3O4 colloidal solution with a molar ratio of 2:1 of FeCl3·6H2O and FeCl2·4H2O, and add it together with 3.8 g of the acid-modified biochar to an ammonia water solution of a certain concentration. After stirring for 30 min, separate and wash it, and at the same time keep the biochar concentration at 23.2 mg / L. After adding a n-propanol solution according to a volume ratio of 1:10, ultrasonically treat it for 20 min to eliminate the influence of － Cl + -, NH4

[0045] plasma. Then add polyethylene glycol to the beaker to keep its concentration at about 26.8 mg / L, and put it into a stirrer and continuously stir for 24 h to prevent the magnetic powder from aggregating. After the above process is completed, recover the biochar with a magnet, wash it 3 times with ultrapure water and then dry it to obtain the magnetic-modified biochar.

[0046] Preparation of nano-manganese dioxide: Weigh 1.25 g of KMnO4 and add it to 70 - 100 mL of dilute H2SO4 solution. 7.5 mmol / L of (NH4)2S2O8 is added to the dilute H2SO4 solution, and the concentration of (NH4)2S2O8 in the dilute H2SO4 solution is 7.5 mmol / L. Stir it ultrasonically until it dissolves; transfer the obtained solution to a polytetrafluoroethylene-lined autoclave, add the previously prepared magnetic modified biochar, seal it, and carry out hydrothermal reaction at 180 °C for 24 h in an oven; cool it naturally to room temperature; remove the supernatant, and wash the obtained precipitate with deionized water by centrifugation until it is neutral; dry it at 60 °C for 1 day to obtain the biochar composite material.

[0047] S3. In the embodiments of the present invention, the prepared biochar composite material is also used for the treatment experiment of heavy metal wastewater and compared with ordinary biochar.

[0048] Compare the morphology of the biochar composite material prepared in this example with that of ordinary biochar; the scanning electron microscope image of the biochar composite material prepared in this example is as Figure 2 and Figure 3 shown. Among them, Figure 2 a1 is the scanning electron microscope image of ordinary biochar at 20 μm, b1 is the scanning electron microscope image of acid-modified biochar at 20 μm, and c1 is the scanning electron microscope image of magnetic-modified biochar at 20 μm; Figure 3 a2 is the scanning electron microscope image of ordinary biochar at 50 μm, b2 is the scanning electron microscope image of acid-modified biochar at 50 μm, and c2 is the scanning electron microscope image of magnetic-modified biochar at 50 μm.

[0049] Analyze its functional groups with a Fourier transform infrared spectrometer, and study the structure and morphology of the composite material with SEM, XRD and TG. Among them, Figure 4 is the FTIR infrared spectrum image of biochar, and Table 1 is the comparison of the surface characteristics of the three kinds of biochar.

[0050] Table 1 Comparison of the surface characteristics of the three kinds of biochar

[0051]

[0052] Design experiments: 1. The optimal manganese dioxide loading amount required for the biochar composite to reach the maximum adsorption capacity; 2. Based on 1, the optimal temperature required for the biochar composite to reach the maximum adsorption capacity; 3. Based on 1, the concentration of copper sulfate solution when the biochar composite reaches the maximum adsorption capacity. The experimental method is as follows: Prepare copper sulfate solutions with the same concentration (mass concentration of 12%), add the biochar composite respectively, place them in a constant temperature shaking incubator with controlled temperature, and conduct adsorption experiments. After the experiment is completed, let the solutions of each group stand for 10 minutes, sample the upper layer solution with a 10 mL syringe with a needle hole, filter it with a 0.45 μm aqueous phase needle filter, measure the copper sulfate concentration in the filtrate respectively, record the experimental data, and analyze the data. Subsequently, a comparative experiment on the adsorption performance of the biochar composite and ordinary biochar under the same conditions was carried out, and the method was as above. Table 2 shows the comparison of the adsorption capacities of different adsorbents for Cu 2+ comparison of adsorption capacities

[0053] Table 2 Comparison of the adsorption capacities of different adsorbents for Cu 2+ comparison of adsorption capacities

[0054]

[0055]

[0056] As shown in Table 2, the adsorption capacity of the biochar composite prepared by the present invention is significantly higher than that of ordinary biochar.

[0057] After the adsorption experiment, the recovery of biochar was carried out, and the recovery rate data is shown in Table 3:

[0058] Table 3 Comparison of the recovery rates of different adsorbents

[0059]

[0060] Among them, the recovery methods of ordinary biochar and acid-modified biochar are to filter the adsorbed copper sulfate solution, dry the filtered product, weigh it, and divide the obtained weight by the added amount to obtain the recovery rate; the recovery method of the biochar composite is to put a magnet into the adsorbed copper sulfate solution, stir slowly until no solid particles can be seen in the solution, scrape off the recovered material, dry it, weigh it, and divide the obtained weight by the added amount to obtain the recovery rate.

[0061] From the data in Table 3, it can be seen that the recovery rate of the biochar composite prepared by the present invention has been greatly improved.

[0062] Different initial concentrations of heavy metal ions also have different effects on the adsorption effect of biochar. Fix the pH value of the solution, add 1 g of the biochar composite (with a ratio of 7.9 g), set the adsorption time to 4 h, and the initial concentration of heavy metal ions on Cu 2+The influence of the adsorption capacity is shown in Table 4.

[0063] Table 4 Adsorption effect of 7.9 g ratio magnetic modified biochar on Cu with different initial concentrations 2+

[0064]

[0065] As shown in Table 4, the higher the initial concentration of heavy metal ions, the better the adsorption effect of the biochar composite. In this invention, ethylenediamine and manganese dioxide are mainly used to modify biochar to prepare biochar composites. The preparation method of biochar composites is determined through research experiments, and SEM, XRD, and TG infrared spectrum analyses are carried out on the prepared products. From the comprehensive analysis results, because manganese dioxide itself has good adsorption properties, after manganese dioxide is negatively magnetized, the physical properties of biochar are enhanced. Therefore, the specific surface area of magnetic modified biochar increases significantly, and the number of micropores is small. When combined with heavy metal ions, it can reach the adsorption equilibrium relatively quickly; the modified biochar has the advantage of having more surface functional groups, which can provide more adsorption sites for coordination reactions to enhance the adsorption effect.

[0066] An experimental study on treating heavy metal wastewater with the biochar composite prepared in this invention is carried out to obtain its treatment effect. It can be analyzed that the adsorption effect of the biochar composite prepared in this invention on heavy metal ions is significantly better than that of ordinary biochar. This invention provides high convenience for the adsorption of heavy metal ions, alleviates the limitations of the biochar treatment method, and also provides a scientific theoretical basis for the application of biochar in water pollution treatment. Moreover, this technical solution is easy to operate, has high efficiency, low cost, less secondary pollution, and good adsorption effect.

[0067] The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and deformations can be made, and these improvements and deformations should also be regarded as the protection scope of the present invention.​

Claims

1. A preparation method of a biochar composite material for heavy metal wastewater treatment, characterized in that, Comprising: Put 10 - 30 parts by mass of biochar into a mixed solution of epichlorohydrin and N,N - dimethylformamide, stir and heat for 50 - 70 min; After adding 899 - 2697 parts by mass of ethylenediamine, continue to stir and heat for 50 - 70 min; After adding 728 - 1092 parts by mass of triethylamine solution, continue to stir and heat for 110 - 130 min; Purify the composite to obtain ethylenediamine - modified biochar; Mix a 1.5 - 2.5 mol / L nitric acid solution and ethylenediamine - modified biochar according to the liquid - solid ratio of (9 - 11 mL):1 g in a container. Place a reflux device at the container mouth, soak continuously at 100 - 120 °C for 1.5 - 2.5 h. Monitor the pH value in real - time during the soaking process to make the supernatant neutral. After cooling, wash and then dry the solution to obtain acid - modified biochar; Prepare an Fe3O4 colloidal solution with a soluble salt of trivalent iron or its hydrate and a soluble salt of divalent iron or its hydrate. The molar ratio of the soluble salt of trivalent iron or its hydrate to the soluble salt of divalent iron or its hydrate is (1.5 - 2.5):

1. Add 1000 - 2000 parts by mass of the Fe3O4 colloidal solution and 360 - 400 parts by mass of acid - modified biochar into an ammonia water solution. After stirring for 25 - 35 min, perform solid - liquid separation and washing. Then, keep the biochar concentration at 23.0 - 23.4 mg / L in a container. Add a n - propanol solution according to the volume ratio of 1:(9 - 11) and treat with ultrasonic waves for 15 - 25 min. Then, add polyethylene glycol to the container to keep the biochar concentration at 26.6 - 27.0 mg / L, put it into a stirrer and stir continuously for 23 - 25 h. After stirring is completed, recover with a magnet, wash with ultrapure water and then dry to obtain magnetically modified biochar; Load nano - manganese dioxide onto the magnetically modified biochar to obtain a biochar composite material.

2. The preparation method of the biochar composite material for heavy metal wastewater treatment according to claim 1, characterized in that, The biochar is prepared by the following method: Select bamboo, and crush the bamboo; Heat the crushed bamboo under anoxic conditions at 380 - 420 °C until it is completely carbonized to obtain biochar made of bamboo.

3. The preparation method of the biochar composite material for heavy metal wastewater treatment according to claim 1, characterized in that, The mass concentration of the triethylamine solution is 99%; The purification includes: washing the unreacted organic matter on the surface of the composite with absolute ethanol, filtering with a vacuum filter and drying in an oven.

4. The preparation method of the biochar composite material for heavy metal wastewater treatment according to claim 1, characterized in that, The soluble salt hydrate of trivalent iron is FeCl3•6H2O, and the soluble salt hydrate of divalent iron is FeCl2•4H2O.

5. The preparation method of the biochar composite material for heavy metal wastewater treatment according to claim 1, wherein, The nano - manganese dioxide is prepared by the following method: Add 1 - 1.5 g of KMnO4 to 70 - 100 mL of a 70% dilute H2SO4 solution by mass fraction. (NH4)2S2O8 is added to the dilute H2SO4 solution, and the concentration of (NH4)2S2O8 in the dilute H2SO4 solution is 7.3 - 7.8 mmol / L. Stir ultrasonically until it dissolves to obtain a nano - manganese dioxide solution.

6. The preparation method of the biochar composite material for heavy metal wastewater treatment according to claim 1, characterized in that, The loading of nano - manganese dioxide onto the magnetically modified biochar to obtain a biochar composite material includes: Add the nano-manganese dioxide solution and magnetically modified biochar into a container, seal it, and carry out hydrothermal reaction at 170-190 °C in an oven for 23-25 h. Naturally cool it to room temperature, remove the supernatant, and the obtained precipitate is purified to obtain the biochar composite material.

7. The preparation method of the biochar composite material for heavy metal wastewater treatment according to claim 6, wherein The purification includes: centrifugally washing with deionized water until neutral, and drying at 55-65 °C for 23-25 h.

8. A biochar composite material for treating heavy metal wastewater, characterized in that, Prepared by the preparation method according to any one of claims 1-7.

9. Use of the biochar composite material for treating heavy metal wastewater according to claim 8, characterized in that, Use the biochar composite material to adsorb heavy metal ions in wastewater.

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