Preparation method of functional biochar with hydrotalcite-like structure

Abstract

The invention belongs to a practical technology in the field of environmental engineering, develops a preparation method of functional biochar with a hydrotalcite-like structure, and mainly utilizes amino, silicon-based and calcium-based structures in waste animal shell biomass raw materials (shrimp shells are taken as an embodiment) rich in chitin and a calcium-silicon-based hard structure to prepare the functional biochar with the hydrotalcite-like structure. On one hand, a mild aging photo-thermal alkali soaking method is adopted, and on the basis of retaining an amino functional group, the material is induced to be modified to form a hydrotalcite structure; on the other hand, a mild carbonization and activation strategy is adopted, the loss of nitrogen is reduced, and finally the functional charcoal which has a hydrotalcite-like structure, is rich in nitrogen-containing functional groups on the surface and is capable of efficiently removing heavy metal ions is prepared. When the functional biochar is used for treating simulated wastewater containing divalent cadmium, divalent cadmium ions in the wastewater can be efficiently adsorbed.

Description

Technical Field

[0001] The present invention relates to the development of a preparation method of functional biochar with a hydrotalcite-like structure. The surface of this functional biochar is rich in nitrogen-containing functional groups and can be used for the efficient treatment of wastewater containing cations (cadmium ions are taken as an example in this embodiment). It is involved in the field of water treatment in engineering and the field of material synthesis in technology. Background Art

[0002] There are some cadmium plating enterprises distributed in Baotou City, mainly plating a layer of cadmium coat on rare earth permanent magnets for waterproofing, anti-corrosion and beauty. However, cadmium ions (Cd 2+ , which can also be marked as Cd(II)) are highly toxic, so the control of the emission concentration of cadmium ions is very strict. The conventional treatment methods are the combination of precipitation method and reverse osmosis method to ensure that the cadmium ion concentration in the discharged wastewater meets the requirements of the discharge standard. However, in the event of an accident, if the wastewater containing Cd 2+ leaks, the toxic sulfide precipitant cannot be put into the external water body, and technologies such as ion exchange and reverse osmosis filtration cannot be used in the external water body. The adsorption method, with its advantages of low technical threshold, simplicity, high efficiency and strong adaptability, is one of the most widely used emergency treatment technologies. In recent years, biochar has been extensively studied due to its low cost and wide raw material sources. Especially with the continuous in-depth research on the adsorption mechanism, it shows that through modification design, the adsorption efficiency and adsorption capacity of biochar for specific target pollutants can be improved. It was previously found that the adsorption ability of biochar for heavy metal ions is affected by surface functional groups such as nitrogen-containing / sulfur-containing functional groups. Therefore, some people add a modification process in the preparation process of biochar and use nitrogen-containing or sulfur-containing modifiers to increase the density of functional groups such as mercapto and amino groups on the material surface, thereby improving the efficiency of the material to adsorb heavy metal ions. However, there is a dynamic adsorption and desorption process in the adsorption process. Therefore, inhibiting the desorption of heavy metal ions and removing trace heavy metal ions are the main directions for the functional upgrade of modified biochar. The present invention uses waste shrimp shells as raw materials and prepares a functional biochar material doped with a hydrotalcite-like structure through an alkali solution soaking and aging method, which can quickly and efficiently remove cadmium ions through ion exchange. At the same time, a structure with a large number of nitrogen-containing functional groups on the surface is prepared by using the high content of chitin in the material, and the adsorption of cadmium ions is strengthened by improving the adsorption ability. The preparation process utilizes solar energy, effectively reducing energy and material consumption. Summary of the Invention

[0003] The present invention develops an alkali solution soaking and aging method to prepare a functional biochar material doped with a hydrotalcite-like structure and rich in nitrogen-containing functional groups on the surface, and is used for the selective and efficient treatment of cadmium-containing wastewater. The specific technical solutions of the present invention are as follows: ① Raw material preparation: Waste animal shells rich in both chitin and calcium-silicon-based hard structures are selected. Taking waste shrimp shells as an example, they are washed with deionized water and dried in an oven at 90 °C. 25.0 g of the dried waste shrimp shells are placed in a 0.4 L liquid nitrogen ball-milling tank and pulverized into shrimp shell powder by liquid nitrogen ball-milling. The ball-milling temperature is the liquid nitrogen temperature (-196 °C), and the rotation speed is 500 revolutions per minute; ② Impregnation (modification): Take 5.0 g of shrimp shell powder and put it into a 250 mL beaker with a blackened surface. Add 100 mL of 2.0 mol / L potassium hydroxide solution, seal it with a sealing film, and place it in the sun for light heat treatment for 2 days. After the soaking is completed, quickly filter out the shrimp shell powder using a Buchner funnel and medium-speed qualitative filter paper, wash it to neutrality, then dry it in the sun for 1 day, and transfer the powder to a corundum boat; ③ Carbonization activation: Put the above corundum boat into a tubular furnace, heat it to 450 °C (heating rate is 10 °C / min) in a nitrogen atmosphere and hold for 1 h. After the reaction is completed, let it cool naturally to room temperature. Grind the carbonized sample into powder in an agate mortar and weigh it. Add KOH solid in a ratio of 1:1, add 5 mL of deionized water and 1 mL of ethanol in portions, stir evenly and then put it into the tubular furnace again. Heat it to 800 °C (heating rate is 10 °C / min) in a nitrogen atmosphere and hold for 1 h, then cool naturally to room temperature. Put the solid in the corundum boat into a 250 mL beaker, add 0.2 mol / L dilute HCl to it and stir slowly, then filter it with a Buchner funnel and a microporous filter membrane (aqueous system), wash it with deionized water, and use a pH test paper to detect the pH of the filtrate until the filtrate pH is washed to neutrality. Grind the biochar with an agate mortar and pass it through a 200-mesh fine sieve to obtain modified shrimp shell biochar (SCK). Description of the drawings

[0004] Figure 1 It is a formation mechanism diagram of functional biochar (FB), the abstract drawing.

[0005] Figure 2 It is the N 2 adsorption and desorption isotherm of modified shrimp shell biochar (SCK). According to the classification standard of the International Union of Pure and Applied Chemistry (IUPAC), the N 2 isotherm of FB conforms to the type-IV isotherm, indicating that there are a large number of microporous structures on the material surface. Calculated by the BJH (Barret, Joyner, and Halenda) method, the specific surface area of SCK is 36 m 2 / g.

[0006] Figure 3 It is the SEM image of modified shrimp shell biochar (SCK). The surface of SCK is rough, and a large number of macroporous structures and mineral crystal structures can be seen.

[0007] Figure 4 It is the full-spectrum XPS scan of the modified shrimp shell biochar (SCK). The corresponding Ca, S, Si, O, N, and C signals are all obvious, indicating that there are indeed a large number of oxygen-containing, sulfur-containing, and nitrogen-containing functional groups on the surface of the material, and there may also be minerals such as calcium carbonate and calcium silicate.

[0008] Figure 5 It is the comparison result diagram of the removal rate of Cd(II) adsorbed by the modified shrimp shell biochar (SCK) in the simulated Cd(II) wastewater environment with different coexisting Ca(II) and Na(I) ion concentrations.

[0009] Figure 6 It is the result diagram of the removal rate of Cd(II) in the simulated Cd(II) wastewater with different pH values by the modified shrimp shell biochar (SCK). Specific implementation mode

[0010] The present invention will be further described below in conjunction with embodiments.

[0011] Example 1: Add 0.01 g of SCK to a conical flask containing 100 mL of 30 mg / L Cd(II) simulated wastewater, place it in an oscillator, and shake it at a rate of 200 revolutions per minute at 25 °C for 60 minutes. Use a 1 mL pipette to extract the sample and filter it into a 2 mL centrifuge tube, and number it. Detect the remaining Cd(II) concentration in it. The experiment shows that the removal rate of Cd(II) by SCK is as high as over 99.85%. The removal situation is shown in Figure 6 (pH = 7).

[0012] Example 2: Add 100 mL of 30 mg / L Cd(II) simulated wastewater to 6 conical flasks. Weigh 0.6, 1.2, and 1.8 g of NaCl and CaCl 2 solids and put them into the conical flask and stir until completely dissolved. Weigh 0.01 g of SCK and add it to the conical flask. Place it in a constant temperature oscillator and shake it at a rate of 200 revolutions per minute at 25 °C for 60 minutes. Use a 1 mL pipette to extract the sample and filter it into a 2 mL centrifuge tube, and detect the remaining Cd(II) concentration in it. The removal situation is shown in Figure 5 .

[0013] Example 3: Take 5 conical flasks and add 100 mL of 30 mg / L Cd(II) simulated wastewater. Use 0.1 mol / L NaOH and HCl solutions to adjust the pH of the solution to 1, 3, 5, 7, and 9. Take 0.01 g of SCK and add it to the conical flask. Place it in a constant temperature oscillator and shake it at a rate of 200 revolutions per minute at 25 °C for 60 minutes. Use a 1 mL pipette to extract the sample and filter it into a 2 mL centrifuge tube, and detect the remaining Cd(II) concentration in it. The removal situation is shown inFigure 6 。

Claims

1. A method for preparing functional biochar with a hydrotalcite-like structure is developed. The surface of the functional biochar is rich in nitrogen-containing functional groups and can be used to efficiently treat wastewater containing heavy metal cations (in this embodiment, cadmium ions are used as an example). The method is characterized in that: The preparation process includes but is not limited to the following steps: Step 1: Select waste biomass raw materials rich in chitin and calcium-silicon-based hard structures (including but not limited to shrimp shells, crab shells, beetle shells, turtle shells, etc.). Take shrimp shells as an example, wash them with deionized water (including but not limited to common solvents or detergents such as water and ethanol), and place them in an oven at 90°C for drying; take 25.0 g of the dried waste shrimp shells and place them in a 0.4L liquid nitrogen ball milling tank, and use liquid nitrogen ball milling to crush them into shrimp shell powder (liquid nitrogen ball milling is used to accelerate grinding, and it also includes the method of not using liquid nitrogen but simply extending the ball milling time), the ball milling temperature is the liquid nitrogen temperature, and the rotation speed is 500r / min; Step 2: Take 5.0 g of shrimp shell powder and put it into a 250 mL beaker with a black surface, add 100 mL of 2.0 mol / L potassium hydroxide solution (including other alkaline substances but not limited to KOH), seal it with a sealing film, expose it to sunlight, and perform photothermal treatment for 2 days. After soaking, use a Buchner funnel and medium-speed qualitative filter paper to quickly filter out the shrimp shell powder, wash it to neutrality, and then use sunlight to dry it for 1 day, and transfer the powder to a corundum boat; Step 3: Place the above corundum boat in a tube furnace, heat it to 450 °C (heating rate of 10 °C / min) under a nitrogen atmosphere, and keep it for 1 hour; after the reaction is completed, wait for it to cool naturally to room temperature, place the carbonized sample in an agate mortar, grind it into powder and weigh it, add potassium hydroxide solid in a weight ratio of 1:1, add 5 mL of deionized water and 1 mL of ethanol respectively, stir evenly and place it in a tube furnace again, heat it to 800 °C (heating rate of 10 °C / min) under a nitrogen atmosphere and keep it for 1 hour, cool it naturally to room temperature, place the solid in the corundum boat in a 250 mL beaker, add 0.2 mol / L dilute hydrochloric acid and stir slowly, then filter it with a Buchner funnel and a microporous filter membrane (water system), wash it with deionized water, and regularly detect the pH of the filtrate with pH test paper until the pH of the filtrate is washed to neutral. Use an agate mortar to grind the biochar and pass it through a 200-mesh fine sieve to obtain modified shrimp shell biochar (SCK).

2. The modified shrimp shell biochar (SCK) according to claim 1, characterized in that The above-mentioned biomass raw materials are all environmental wastes. The cadmium nitrate, potassium hydroxide (KOH), concentrated hydrochloric acid (HCl, 36%), sodium chloride (NaCl) and calcium chloride (CaCl2) used in the previous and subsequent examples are all analytically pure, and the solvents used in the experiments are all deionized water; 2 mol / L and 0.2 mol / L KOH solutions are prepared as modified impregnating agents and pH regulators, 2.0 mol / L and 0.2 mol / L HCl solutions are prepared as detergents and pH regulators, and a cadmium nitrate solution with a concentration of 30 mg / L is prepared as a simulated divalent cadmium-containing wastewater. 100 mL of cadmium nitrate solution containing 30 mg / L is added with 0.6, 1.2, and 1.8 g of NaCl and CaCl2 solids to configure cationic environments of different concentrations; 100 mL of cadmium nitrate solution containing 30 mg / L is added with different proportions of 0.2 mol / L KOH solution, 2.0 mol / L, and 0.2 mol / L HCl solution to adjust the pH of the solution, and pH = Cadmium nitrate solutions with concentrations of 1.0, 3.0, 5.0, 7.0, 9.0 and 30 mg / L were used as the simulated solutions containing divalent cadmium ions (Cd 2+ , which can also be labeled as Cd(Ⅱ) wastewater.

3. The preparation process according to claim 1, characterized in that: The waste biomass materials rich in chitin and calcium-silicon hard structure (including but not limited to shrimp shells, crab shells, beetle shells, turtle shells, etc.) contain chitin ((C8H 13 O5N) n ) and calcium-silicon-based hard structures (CaSO4, CaSiO3, SiO2 or CaCO3); chitin has amino functional groups on the surface, which is conducive to the adsorption of heavy metal ions; and thermal aging under alkaline conditions can induce calcium-based salts and silicon-based salts, and even calcium-silicon-based structures to form hydrotalcite-like structures, using the calcium ions in the hydrotalcite to exchange heavy metal ions, thereby synergistically removing heavy metal ions from the water.

4. The preparation technology of functional biochar having a hydrotalcite-like structure and rich in nitrogen-containing functional groups on the surface and having high efficiency in removing heavy metal ions according to claim 1, characterized in that: Considering the energy saving of actual operation, the hot soaking process adopted in the embodiment is heated by solar energy, and the drying process adopted is solar energy drying.

5. The method for preparing functional biochar having a hydrotalcite-like structure and rich in nitrogen-containing functional groups on the surface and having high efficiency in removing heavy metal ions according to claim 1, characterized in that: Similar functional biochar materials can be prepared by adjusting the carbonization temperature (350-600℃) and the activation temperature (600-1000℃). The optimal temperature combination required for the preparation process of different raw materials is different.

6. The method for preparing functional biochar having a hydrotalcite-like structure and rich in nitrogen-containing functional groups on the surface and having high efficiency in removing heavy metal ions according to claim 1, characterized in that: The surface area of ​​the prepared functional biochar material is greater than 36 cm 2 / g, when the dosage of functional biochar was 0.1 g / L, Cd 2+ (Also marked as Cd(Ⅱ)) When the initial concentration was 30 mg / L, the adsorption removal rate of Cd(Ⅱ) reached 99.85% after oscillation at 200 rpm for 60 minutes at 25°C; the adsorption process was significantly affected by the acidic environment. When the pH dropped from 7.0 to 1.0, the removal rate of Cd(Ⅱ) by SCK dropped from 99.85% to 51.47%.

7. The method for preparing functional biochar having a hydrotalcite-like structure and rich in nitrogen-containing functional groups on the surface and having high efficiency in removing heavy metal ions according to claim 1, characterized in that: The prepared functional biochar material has poor cation tolerance; when the functional biochar dosage is 0.1 g / L and Na + In the case of simulated coexisting wastewater with initial concentrations of 6, 8, and 12 g / L and an initial Cd(Ⅱ) concentration of 30 mg / L, the Cd(Ⅱ) adsorption removal rate decreased to 93.6% after oscillation at 200 rpm for 60 minutes at 25°C. 2+ The initial concentrations were 6, 8, and 12 g / L, and the initial concentration of Cd(Ⅱ) was 30 mg / L. After oscillating at 200 rpm for 60 min at 25°C, the Cd(Ⅱ) adsorption removal rate decreased to 93.6%.

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