A method for preparing a biochar metal adsorbent based on zizania straw and blue-green algae

Abstract

The application discloses a method for preparing a biochar metal adsorbent based on wild rice straw and blue-green algae, and belongs to the technical field of environmental engineering. The method comprises the following steps: (1) drying the wild rice straw and the blue-green algae, then mixing and drying, and then crushing to obtain a raw material of biochar; (2) carbonizing the raw material of biochar prepared in the step (1) under an inert gas atmosphere to obtain biochar; (3) dispersing the biochar prepared in the step (2) in an alkali solution, stirring, and then drying; (4) pyrolyzing the dried biochar in the step (4) under an inert gas atmosphere, removing, using an acid solution to perform acid pickling, then washing with water until neutral, and drying to obtain wild rice straw-blue-green algae biochar.

Description

Technical Field

[0001] This invention relates to a method for preparing biochar metal adsorbents based on water chestnut straw and cyanobacteria, belonging to the field of environmental engineering technology. Technical Background The wastewater from nuclear power plants contains radioactive elements, with tritium being the most abundant, followed by iodine-129, ruthenium-106, carbon-14, cobalt-60, copper-66, strontium-90, cesium-134, cesium-137, and other substances. The threat to human health and sustainable development will last for hundreds or even tens of thousands of years, causing unpredictable damage and harm.

[0002] Radioactive elements in the ocean can be removed by adsorption; however, traditional adsorbents such as activated carbon are expensive, increasing the cost of use. Meanwhile, the preparation process of novel adsorbents is complex, resulting in very high production and time costs, making them unsuitable for large-scale industrial applications. Therefore, finding highly efficient, cost-effective adsorbent materials without secondary pollution has become a research hotspot. In recent years, biochar has attracted much attention due to its low cost and environmental friendliness, playing a significant role in environmental, chemical, and agricultural fields. Summary of the Invention

[0003] To address the problems and shortcomings of existing technologies, the present invention aims to provide a method for efficiently preparing biochar metal adsorbents based on water chestnut straw and cyanobacteria. This invention is based on the fundamental principles of solid waste treatment and disposal—reduction, harmlessness, stabilization, and resource recovery—and utilizes biochar obtained from waste processing to treat metal elements in water.

[0004] As aquatic plants, water chestnuts and cyanobacteria have a certain adsorption capacity for metal ions in water. Therefore, this invention produces biochar from water chestnut stalks and cyanobacteria, realizing their adsorption function for metal elements in nuclear wastewater, while simultaneously utilizing both water chestnut stalks and cyanobacteria as resources.

[0005] This invention aims to provide a method for preparing water chestnut straw-cyanobacteria biochar, comprising the following steps: (1) Dry the water chestnut stalks and blue-green algae, then mix them and dry them, and then crush them to obtain the raw material for biochar; (2) Take the raw material of biochar prepared in step (1) and carbonize it in an inert gas atmosphere to obtain biochar; (3) Disperse the biochar prepared in step (2) in an alkaline solution, stir, and then dry; (4) The dried biochar in step (4) is subjected to high-temperature pyrolysis in an inert gas atmosphere, then removed, acid washed with acid solution, then washed with water until neutral, and dried to obtain water chestnut straw-blue algae biochar.

[0006] Furthermore, in step (1), the mass ratio of the water chestnut straw and the blue-green algae is 0.7~1.3:1.

[0007] Preferably, the mass ratio of the water chestnut straw and the blue-green algae in step (1) is 1:1.

[0008] Furthermore, the drying conditions in step (1) are drying at 70~90℃ for 50~100h.

[0009] Furthermore, in step (2), the carbonization temperature is 600~700℃ and the time is 50~90min.

[0010] Furthermore, the alkaline solution in step (3) is a KOH solution.

[0011] Furthermore, the concentration of the alkaline solution in step (3) is 2~5 mol / L. Furthermore, the stirring time in step (3) is 15~20h.

[0012] Furthermore, in step (4), the high-temperature pyrolysis temperature is 800~850℃ and the time is 100~150min.

[0013] Furthermore, the acid solution in step (4) is an HCl solution.

[0014] Furthermore, the concentration of the acid solution in step (4) is 0.5~1.5 mol / L.

[0015] This invention provides a water chestnut straw-cyanobacteria biochar prepared according to the above method.

[0016] The present invention relates to the application of water chestnut straw-cyanobacteria biochar in the environmental, chemical, and agricultural fields.

[0017] Furthermore, in the environmental and chemical fields, the application involves using water chestnut straw-cyanobacteria biochar as an adsorbent.

[0018] Furthermore, the agricultural application is the use of water chestnut straw and cyanobacteria to prepare biochar-based fertilizers.

[0019] The beneficial effects of this invention are: 1. The water chestnut straw-cyanobacteria biochar prepared by this invention is alkaline and has a negatively charged surface, which is beneficial for the adsorption of metal elements.

[0020] 2. The water chestnut straw-cyanobacteria biochar prepared by this invention has a high specific surface area, small pore volume, and high optimal pH, making it suitable for application in wastewater treatment containing metal ions. 3. The present invention uses a combination of cyanobacteria and water chestnut straw to prepare the product, which can significantly recover resources and improve the utilization rate of waste. Attached Figure Description

[0021] Figure 1 The relationship between the adsorption capacity of water chestnut straw-cyanobacterial biochar and time.

[0022] Figure 2 The relationship between the adsorption capacity of water chestnut straw-cyanobacteria biochar and pH.

[0023] Figure 3 The relationship between the adsorption capacity of rice straw-cyanobacteria biochar and pH.

[0024] Figure 4 The relationship between the adsorption capacity of reed straw-cyanobacteria biochar and pH. Detailed Implementation

[0025] Example 1 The preparation steps of water chestnut straw-cyanobacteria biochar are as follows: (1) Raw material pretreatment: Water chestnut stalks and cyanobacteria were naturally sun-dried for three days under ventilated conditions. The dried stalks and cyanobacteria were collected, the water chestnut stalks were cut into 2-3 cm long segments, and the cyanobacteria were flattened. The water chestnut stalks and cyanobacteria were mixed at a mass ratio of 1:1 and transferred to a forced-air drying oven, where they were dried at 70°C for 72 hours. Finally, the dried material was pulverized using a pulverizer, passed through a 30-mesh sieve, packed into a plastic bag, and placed in a desiccator as raw material for the preparation of biochar.

[0026] (2) Carbonization treatment: Weigh the pretreated powder and place it in a tube furnace. Then, continuously introduce nitrogen gas at a flow rate of 200 mL / min for 60 min. After exhausting the air, start the tube furnace and heat it to 700℃ at a heating rate of 20 ℃ / min. After carbonization for 60 min, cool it to room temperature to obtain biochar.

[0027] (3) Impregnation treatment: The biochar obtained in step (2) was dispersed in a 4 mol / L KOH solution and stirred at 300 rpm at room temperature for 20 h. After impregnation, it was transferred to a 105℃ oven and dried for 240 min before being taken out for the next step of processing.

[0028] (4) Activation treatment: The impregnated biochar was transferred to a tube furnace for high-temperature pyrolysis. Nitrogen gas was continuously introduced at a flow rate of 200 mL / min for 60 min to make the working area of ​​the quartz tube of the tube furnace oxygen-free. The temperature was then increased to 850℃ at a heating rate of 20 ℃ / min and held at that temperature for 120 min. After cooling to room temperature, the sample was taken out.

[0029] 5) Post-washing treatment: Use 1 mol / L HCl solution to acid wash the activated sample in step (4) to remove the potassium salt formed on the surface of biochar during the pyrolysis process, then wash repeatedly with deionized water until the solution is neutral and the pH is 7, and then put it into an oven at 105℃ to dry to constant weight.

[0030] Example 2 Metal Adsorption 1. Adsorption experiments were conducted on cobalt-containing wastewater samples using the prepared biochar. The specific steps are as follows: (1) Accurately weigh 1.25 g of Co(NO3)2 and put it into a beaker. Add water to dissolve it completely. Complex cobalt(II) with NH4SCN solution and mask Fe in the solution with saturated NaF solution. 3+ Eliminate interference. Transfer the entire solution to a 250 mL volumetric flask and dilute to volume to obtain a 5 g / L cobalt(II) stock solution for later use.

[0031] (2) Transfer 0, 4 mL, 8 mL, 12 mL, 16 mL, 20 mL and 24 mL of cobalt(II) stock solution to a 100 mL volumetric flask, add water to make up to volume, and obtain a series of cobalt(II) standard solutions with concentrations of 0, 0.2 g / L, 0.4 g / L, 0.6 g / L, 0.8 g / L, 1.0 g / L and 1.2 g / L, respectively.

[0032] (3) According to the existing technology, the absorbance of the cobalt (II) standard solution is the largest at a wavelength of 618 nm. Therefore, the absorbance of the standard solution is measured at a wavelength of 618 nm, and an absorbance standard curve is plotted.

[0033] (4) Take the cobalt (II) stock solution and dilute it to 50 mL of 0.5 g / L wastewater sample. Add 0.3 g of the water chestnut straw-cyanobacterial biochar (adsorbent) prepared in Example 1 for adsorption. Take samples at adsorption times of 1 min, 5 min, 10 min, 20 min, 40 min, 60 min, 120 min and 180 min respectively to measure the absorbance. Find the corresponding concentration on the standard curve and compare it with the initial concentration.

[0034] (5) Take the cobalt (II) stock solution and dilute it to 50 mL of 0.5 g / L wastewater sample. Add 0.3 g of the water chestnut straw-cyanobacterial biochar (adsorbent) prepared in Example 1 for adsorption. Adjust the pH of the sample and set 6 different pH groups of 6.5, 7, 7.5, 8.5, 9.5 and 10.5. Measure the absorbance after 60 min under different pH conditions. Find the corresponding concentration on the standard curve and compare it with the initial concentration.

[0035] 2. Adsorption experiments were conducted on nickel-containing wastewater samples using the prepared biochar. The specific steps are as follows: (1) Transfer 0, 4 mL, 8 mL, 12 mL, 16 mL, 20 mL and 24 mL of 5 g / L nickel (II) standard working solution into a 100 mL volumetric flask and dilute to the mark with deionized water. The concentrations of this standard series are 0, 0.2 g / L, 0.4 g / L, 0.6 g / L, 0.8 g / L, 1.0 g / L and 1.2 g / L.

[0036] (2) Flame atomic absorption spectrophotometry was used. Deionized water and nickel national standard solution were used as blank solutions for zeroing. The flame type was set to air-acetylene oxidizing type, the acetylene flow rate was 1700 L / min, and the air pressure was 0.3 MPa. Under the instrument operating conditions, atomic absorption tests were performed according to the low concentration instrument operating conditions. The concentration was used to perform linear regression on the measured absorbance to obtain the linear regression equation.

[0037] (3) Take the nickel (II) standard working solution and dilute it into 50 mL of 0.5 g / L wastewater sample. Add 0.3 g of the water chestnut straw-cyanobacterial biochar (adsorbent) prepared in Example 1 for adsorption. Take samples at adsorption times of 1 min, 5 min, 10 min, 20 min, 40 min, 60 min, 120 min and 180 min respectively to measure its absorbance. Find the corresponding concentration on the standard curve and compare it with the initial concentration.

[0038] (5) Take the nickel (II) standard working solution and dilute it to 50 mL of 0.5 g / L wastewater sample. Add 0.3 g of the water chestnut straw-cyanobacterial biochar (adsorbent) prepared in Example 1 for adsorption. Adjust the pH of the sample and set 6 different pH groups of 6.5, 7, 7.5, 8.5, 9.5 and 10.5. Measure the absorbance after 60 min under different pH conditions. Find the corresponding concentration on the standard curve and compare it with the initial concentration.

[0039] 3. Use the prepared biochar to conduct adsorption experiments on copper-containing wastewater samples. The specific steps are the same as those for adsorption experiments on cobalt-containing wastewater samples.

[0040] (1) Prepare a copper ion stock solution with a mass concentration of 5 g / L. Dilute the copper ion stock solution with deionized water to prepare copper ion standard solutions with mass concentrations of 0, 0.2 g / L, 0.4 g / L, 0.6 g / L, 0.8 g / L, 1.0 g / L, and 1.2 g / L.

[0041] (2) The copper ion detection reagent contains 0.10 g / L 2-(5-bromo-2-pyridiniazo)-5-diethylaminophenol, 0.08 mL / L Tween-80, 10 mL / L H2O2, 25 g / L NaF, 30 mL / L ethylene glycol, and 60 mmol / L of acetate-sodium acetate buffer solution at pH 3.5.

[0042] (3) Take a 10 mL colorimetric tube, add an appropriate amount of copper ion standard solution or water sample, dilute with deionized water to the 5 mL mark, add 200 μL of copper ion detection reagent, shake well, place at room temperature (25 °C) for 10 min, use deionized water as a reference, measure the absorbance at a wavelength of 545 nm, and find the content of copper ions in the water sample by plotting a standard curve.

[0043] (4) Take copper ion stock solution and dilute it to 50 mL of wastewater sample with a concentration of 0.5 g / L. Add 0.3 g of the water chestnut straw-cyanobacterial biochar (adsorbent) prepared in Example 1 for adsorption. Take samples at adsorption times of 1 min, 5 min, 10 min, 20 min, 40 min, 60 min, 120 min and 180 min respectively to measure the absorbance. Find the corresponding concentration on the standard curve and compare it with the initial concentration.

[0044] (5) Take copper ion stock solution and dilute it to 50 mL of wastewater sample with a concentration of 0.5 g / L. Add 0.3 g of the water chestnut straw-cyanobacterial biochar (adsorbent) prepared in Example 1 for adsorption. Adjust the pH of the sample and set 6 different pH groups of 6.5, 7, 7.5, 8.5, 9.5 and 10.5. Measure the absorbance after 60 min under different pH conditions. Find the corresponding concentration on the standard curve and compare it with the initial concentration.

[0045] The experimental data are shown in Table 1 below and appendix. Figure 1 , 2 It was found that the water chestnut straw-cyanobacterial biochar had a good adsorption capacity for trace metals in water. The adsorption capacity first increased and then decreased with increasing pH, and the adsorption capacity was stronger in a slightly alkaline environment at room temperature. The adsorption capacity initially increased with time and then tended to stabilize.

[0046] Table 1. Saturation removal rate of metal ions by water chestnut straw-cyanobacteria (1:1) biochar

[0047] Example 3 The steps of Example 1 were followed, except that the mass ratio of water chestnut straw to cyanobacteria was adjusted to 0.7:1 to prepare water chestnut straw-cyanobacteria biochar. Then, the steps of Example 2 were followed to perform the test. The saturation removal rates of cobalt (II), nickel (II), and copper (II) are shown in the table below.

[0048] Table 2. Saturation removal rate of metal ions by water chestnut straw-cyanobacteria biochar (0.7:1)

[0049] Example 4 The steps of Example 1 were followed, except that the mass ratio of water chestnut straw to cyanobacteria was adjusted to 1.3:1 to prepare water chestnut straw-cyanobacteria biochar. Then, the steps of Example 2 were followed to perform the test. The saturation removal rates of the three metal elements, cobalt (II), nickel (II), and copper (II), are shown in the table below.

[0050] Table 3. Saturation removal rate of metal ions by water chestnut straw-cyanobacteria (1.3:1) biochar

[0051] Comparative Example 1 The steps in Example 1 were followed, except that no cyanobacteria were added and biochar was prepared entirely from water chestnut straw. The biochar was then tested according to the steps in Example 2. The adsorption effects of water chestnut straw biochar on cobalt (II), nickel (II), and copper (II) in water are shown in the table below.

[0052] Table 4. Saturation removal rate of metal ions by water chestnut straw biochar

[0053] By comparing Examples 1-3 and Comparative Example 1, it can be found that the adsorption effect of water chestnut straw-cyanobacterial biochar prepared by adding cyanobacteria is improved compared with that of water chestnut straw biochar for cobalt(II), nickel(II), and copper(II). Furthermore, the comparison of Examples 1-3 also shows that the mixing ratio of cyanobacteria and water chestnut straw also affects the adsorption effect of water chestnut straw-cyanobacterial biochar, with the optimal adsorption effect obtained when water chestnut straw and cyanobacteria are mixed at a mass ratio of 1:1.

[0054] Comparative Example 2 Rice straw was collected and processed according to the steps in Example 1 to prepare rice straw + cyanobacterial biochar. Simultaneously, the adsorption effect of rice straw + cyanobacterial biochar was investigated, referring to the adsorption experiment in Example 2, as shown in Tables 5, 6, and 7 and Appendix. Figure 3 As shown.

[0055] Comparative Example 3 Following the steps in Example 1, reed straw was used to prepare reed straw + cyanobacterial biochar. Simultaneously, referring to the adsorption experiment in Example 2, the adsorption effect of reed straw + cyanobacterial biochar was investigated, as shown in Tables 5, 6, and 7 and Appendix. Figure 4 As shown.

[0056] Comparative Example 4 The adsorption performance of water chestnut straw and cyanobacteria biochar was compared with that of commercially available reed straw and rice straw biochar. When the adsorption saturation points were similar and the adsorption time was sufficiently long, the adsorption capacity mainly depended on the pore filling mechanism, electrostatic interactions, and the number of functional groups.

[0057] Taking the adsorption of cobalt(II) as an example, biochar made from water chestnut straw and cyanobacteria has a honeycomb-like microporous structure and is rich in various functional groups such as CO, -OH, aromatic C=C and C=O, which can complex with cobalt(II). It contains alkaline metal ions (K... + Ca2 + Na + Mg 2+ Biochar, etc., undergoes ion exchange with cobalt(II) in the solution, thereby reducing the cobalt(II) content in the water. The larger the specific surface area and porosity, the stronger the adsorption capacity for heavy metals. The higher the [(N+O) / C] atomic ratio, the more polar functional groups are on the biochar surface, the weaker the hydrophobicity of the biochar surface, and the stronger the adsorption capacity for metal ions in the water. The higher pH of biochar can promote the adsorption and precipitation of cobalt(II). The various properties in Table 2 show that biochar made from water chestnut straw and cyanobacteria has a good adsorption effect on cobalt(II) in water.

[0058] Table 5 Properties of Three Types of Biochar

[0059] At room temperature, 0.3 g of reed straw + cyanobacterial biochar, rice straw + cyanobacterial biochar, and water chestnut straw + cyanobacterial biochar were respectively used to treat 50 mL of 0.5 g / L wastewater solutions of cobalt, nickel, and copper. The pH of the solutions was adjusted to 8, and the solutions were stirred at 25 °C and 180 rpm for 24 h. After adsorption, the solutions were allowed to stand for 24 h, and the absorbance of the supernatant was measured at the corresponding wavelength and converted into adsorption capacity.

[0060] Table 6. Adsorption capacity of three types of biochar at the same pH.

[0061] We also compared the adsorption effects of three types of biochar on three metal ions in water under the optimal pH conditions.

[0062] Table 7 Adsorption rates of three types of biochar at optimal pH

[0063] As can be seen from the data in Tables 5-7, the adsorption effect of water chestnut straw-cyanobacteria biochar is better than that of reed straw + cyanobacteria biochar and rice straw + cyanobacteria biochar, both at the same pH and at their respective optimal pH. Furthermore, water chestnut straw-cyanobacteria biochar has a higher optimal pH, making it more suitable for application in the treatment of wastewater containing metal ions.

[0064] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. An application of water chestnut straw-cyanobacteria biochar as an adsorbent, characterized in that, The adsorbent is used in the treatment of wastewater containing metal ions, wherein the metal ion is one of cobalt(II), nickel(II), or copper(II); the preparation method of the wild rice straw-cyanobacteria biochar includes the following steps: (1) Dry the water chestnut stalks and cyanobacteria, then mix them and dry them, and then crush them to obtain the raw material for biochar; the mass ratio of water chestnut stalks and cyanobacteria is 0.7~1.3:1; (2) Take the raw material of biochar prepared in step (1) and carbonize it in an inert gas atmosphere to obtain biochar; the carbonization temperature is 600~700℃ and the time is 50~90min; (3) Disperse the biochar prepared in step (2) in an alkaline solution, stir, and then dry; (4) The dried biochar in step (3) is subjected to high-temperature pyrolysis in an inert gas atmosphere, then removed, acid washed with acid solution, then washed with water until neutral, and dried to obtain water chestnut straw-blue algae biochar; the high-temperature pyrolysis temperature is 800~850℃ and the time is 100~150min.

2. The application according to claim 1, characterized in that, In step (1), the mass ratio of the water chestnut straw and the blue-green algae is 1:

1.

3. The application according to claim 1, characterized in that, The concentration of the alkaline solution in step (3) is 2~5 mol / L.

4. The application according to claim 1, characterized in that, The stirring time in step (3) is 15~20h.

5. The application according to claim 1, characterized in that, The concentration of the acid solution in step (4) is 0.5~1.5 mol / L.

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