Preparation process of agroforestry waste-based biochar composite filter material

Abstract

The application discloses a preparation process of a biochar composite filter material based on agricultural and forestry wastes, and comprises the following steps: ingredient preparation: 70 parts of high alumina bauxite, 30 parts of blast furnace slag, 20-25 parts of biochar based on agricultural and forestry wastes, 15-20 parts of calcium carbonate whiskers, 2-3 parts of sodium silicate and 10-15 parts of a reinforcing agent; the sodium silicate is configured into a solution by adding water, and is mixed with the high alumina bauxite, the blast furnace slag, the biochar based on agricultural and forestry wastes, the calcium carbonate whiskers and the reinforcing agent to granulate, the particle size is 6-8 mm, and the mixture is dried at 100 DEG C; the temperature is raised to 400 DEG C and kept for 15 min, then the temperature is raised to 1150 DEG C at a speed of 1-2 DEG C / min, and calcination is carried out for 20 min, so that the product is obtained. The composite filter material prepared by the process has high strength and is convenient for recycling; moreover, the composite filter material is fast in membrane formation and has a strong adsorption effect on ammonia nitrogen, COD and P.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of environment-friendly adsorption filter material, in particular to a kind of agroforestry waste-based biochar composite filter material and its preparation process. BACKGROUND

[0002] Agroforestry waste is the byproduct generated in the process of agricultural and forestry production and processing, mainly including tree bark, shell, sawdust, straw, bagasse, etc., which is huge in quantity, renewable, short in regeneration cycle, biodegradable, and environment-friendly. Direct landfill or incineration of agroforestry waste not only pollutes the environment, but also wastes resources. At present, agroforestry waste is treated and reused, such as preparing cultivation medium, soil conditioner, organic fertilizer and biochar after fermentation, among which the application of agroforestry waste biochar in sewage purification is very wide.

[0003] The common method of agroforestry waste biochar in the prior art is to modify the biochar, such as using citric acid to activate the biochar, silicon to modify the biochar, and magnesium to modify the biochar, so as to increase the adsorption performance. In addition, the biochar is compounded with other components such as attapulgite and chitosan to prepare a composite adsorption material.

[0004] The current problems of biochar-based adsorption material are: 1. Low strength of adsorption material, not easy to recycle; 2. Slow or difficult to form biofilm, and the adsorption performance of ammonia nitrogen needs to be further enhanced. SUMMARY

[0005] Therefore, the present application aims at the deficiencies of the prior art, and provides a preparation process of agroforestry waste-based biochar composite filter material. The prepared composite filter material has high strength and is easy to recycle. Moreover, it has fast biofilm formation and strong adsorption effect on ammonia nitrogen, COD and P.

[0006] To achieve the above-mentioned purposes, the present application adopts the following technical solutions:

[0007] A preparation process of agroforestry waste-based biochar composite filter material, comprising the following steps:

[0008] (1) After the agroforestry waste is crushed and dried, it is heated to 600℃ at a rate of 10℃ / min under N2 atmosphere for 2h to obtain agroforestry waste-based biochar;

[0009] (2) Ingredients: 70 parts of high alumina bauxite, 30 parts of blast furnace slag, 20-25 parts of agroforestry waste-based biochar, 15-20 parts of calcium carbonate whisker, 2-3 parts of sodium silicate, and 10-15 parts of reinforcing agent;

[0010] (3) The sodium silicate is configured into a solution, and mixed with high alumina bauxite, blast furnace slag, agroforestry waste-based biochar, calcium carbonate whisker and reinforcing agent to granulate, with a particle size of 6-8mm, and then dried.

[0011] (4) heating to 400 DEG C and keeping for 15 min, then heating to 1150 DEG C at 1-2 DEG C / min, calcining for 20 min, and obtaining the product.

[0012] Further, the bauxite contains 75-76wt% of Al2O3, 18-18.5wt% of SiO2 and 1-1.1wt% of Fe2O3.

[0013] Further, the blast furnace slag contains 14-15wt% of Al2O3, 35.01-36wt% of SiO2 and 39-40wt% of CaO.

[0014] Further, the reinforcing agent is prepared by the following steps:

[0015] polyvinyl alcohol is dissolved in hot water to prepare a 3-4wt% polyvinyl alcohol solution, 2.3-3wt% polyethylene glycol of the total amount of the polyvinyl alcohol solution is added, then the silica and aluminum fluoride are stirred uniformly, and the mixture is frozen at -20 DEG C for 12h, placed at room temperature for 12h, and the cycle is repeated for 4 times, and the product is obtained by drying and crushing;

[0016] the molar ratio of the silica to the aluminum fluoride is 2:3, and the total amount of the silica and the aluminum fluoride added is 20% of the total amount of the polyvinyl alcohol solution.

[0017] Further, the agricultural and forestry waste powder is one or two of sawdust, shell, rice husk, straw and sugarcane residue after drying and crushing.

[0018] Further, the product prepared in step (4) is immersed in 3-5wt% lye, activated at 85 DEG C for 40 min, washed and dried to obtain the composite filter material.

[0019] The application has the following beneficial effects:

[0020] 1. The application discloses a preparation process of an agricultural and forestry waste-based bio-carbon composite filter material, wherein the composite filter material is prepared from bauxite, blast furnace slag and agricultural and forestry waste as main raw materials through calcination, the prepared filter material has a porosity of 51.4-53.6%, high strength and is not easy to break, and is convenient for recycling; and the composite filter material has fast membrane formation and strong adsorption effect on heavy metals, N, P and COD in sewage.

[0021] 2、The raw materials for preparing the composite filter material in the application are high alumina bauxite and blast furnace slag, wherein the main components of the high alumina bauxite and the blast furnace slag are Al2O3 and SiO2, after adjusting the composition of the raw materials, after high-temperature calcination, the components such as Al2O3 and SiO2 in the raw materials react, and finally the phase composition is mainly mullite phase, which has very high strength and can be used as a skeleton component. The agricultural and forestry waste-based biochar and calcium carbonate whiskers are used as pore-forming agents, and the moisture, organic matter and the like in the filter material decompose during preheating to generate gas inside and outside the filter material; as the temperature rises, organic matter, amorphous carbon and the like become gas sources, continuously generating gas inside the filter material, and the internal pores are partially connected and escape from the surface; as the temperature continues to rise, the calcium carbonate whiskers decompose to further generate gas, and a large number of connected pores appear inside; therefore, the pores of the application are uniformly distributed, the specific surface area is large, and the overall structural strength is high.

[0022] 3、The application also adds a reinforcing agent, the main components of the reinforcing agent are aluminum fluoride and silicon dioxide, the aluminum fluoride and the silicon dioxide are dispersed in a polyvinyl alcohol gel system, as the calcination temperature rises, the polyvinyl alcohol gradually decomposes at high temperature, the aluminum fluoride and the silicon dioxide undergo gas phase reactions under high-temperature conditions, AlF3+H2O=AlOF+2HF, SiO2+4HF=SiF4+2H2O, as the temperature rises and the influence of gas phase transmission, the AlOF and the SiF4 continue to react, and finally convert into mullite whiskers, which are grown in a one-dimensional direction on the surface of the mullite of the composite filter material and filled in the gaps of the skeleton, which has the effects of structural reinforcement and helps microbial biofilm formation, thereby increasing the adsorption and water purification effects. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 It is a dynamic adsorption test simulation device diagram;

[0024] Figure 2 It is an ammonia nitrogen removal rate curve diagram;

[0025] Figure 3 It is a COD removal rate curve diagram. EMBODIMENT

[0026] The application will be further described below in combination with the drawings and examples. Example 1

[0027] A preparation process of an agricultural and forestry waste-based biochar composite filter material, comprising the following steps:

[0028] (1) After the agricultural and forestry waste is crushed and dried, it is burned at 10℃ / min to 600℃ under N2 atmosphere for 2h to obtain agricultural and forestry waste-based biochar; in this embodiment, the agricultural and forestry waste powder is sawdust.

[0029] (2) ingredients: 70 parts of high alumina bauxite, 30 parts of blast furnace slag, 20 parts of agroforestry waste-based biochar, 20 parts of calcium carbonate whisker, 2 parts of sodium silicate, 10 parts of reinforcing agent;

[0030] (3) The sodium silicate is stirred with water to form a solution (water amount is 30% of the weight of the ingredients), and is mixed with the high alumina bauxite, blast furnace slag, agroforestry waste-based biochar, calcium carbonate whisker and reinforcing agent to form granules with a particle size of 8 mm, which are dried at 100℃;

[0031] (4) The temperature is raised to 400℃ and maintained for 15 min, and then raised to 1150℃ at a rate of 1℃ / min, and calcined for 20 min;

[0032] (5) The product prepared in step (4) is immersed in a 3wt% sodium hydroxide solution, activated at 85℃ for 40 min, washed and dried to obtain the composite filter material.

[0033] The high alumina bauxite contains 75-76wt% of Al2O3, 18-18.5wt% of SiO2 and 1-1.1wt% of Fe2O3; the blast furnace slag contains 14-15wt% of Al2O3, 35.01-36wt% of SiO2 and 39-40wt% of CaO. The agroforestry waste-based biochar used in step (2) has a particle size of 70-150μm, the calcium carbonate whisker has a diameter of 1-2μm and a length of 50-80μm.

[0034] The reinforcing agent is prepared by the following steps:

[0035] Polyvinyl alcohol is dissolved in hot water to form a 3wt% polyvinyl alcohol solution, 2.3wt% of the total amount of polyvinyl alcohol solution is added to polyethylene glycol (PEG-600), and then silica and aluminum fluoride are stirred uniformly, frozen at -20℃ for 12h, placed at room temperature for 12h, and the cycle is repeated 4 times, dried and crushed to obtain the product.

[0036] The molar ratio of silica to aluminum fluoride is 2:3, and the total amount of silica and aluminum fluoride added is 20% of the total amount of polyvinyl alcohol solution. Example 2

[0037] A preparation process of an agroforestry waste-based biochar composite filter material, comprising the following steps:

[0038] (1) After the agroforestry waste is crushed and dried, it is heated to 600℃ at a rate of 10℃ / min under N2 atmosphere, and fired for 2h to obtain agroforestry waste-based biochar;

[0039] (2) ingredients: 70 parts of high alumina bauxite, 30 parts of blast furnace slag, 20 parts of agroforestry waste-based biochar, 20 parts of calcium carbonate whisker, 2 parts of sodium silicate, 10 parts of reinforcing agent;

[0040] (3) The sodium silicate is configured into a solution with water, mixed with high alumina bauxite, blast furnace slag, agricultural and forestry waste-based biochar, calcium carbonate whisker and reinforcing agent to granulate, with a particle size of 8 mm, and dried at 100°C;

[0041] (4) The temperature is raised to 400°C and kept for 15 min, then raised to 1150°C at a rate of 1.5°C / min, and calcined for 20 min;

[0042] (5) The product prepared in step (4) is immersed in 4wt% lye, activated at 85°C for 40 min, washed and dried to obtain the composite filter material.

[0043] The high alumina bauxite contains 75-76wt% Al2O3, 18-18.5wt% SiO2 and 1-1.1wt% Fe2O3; the blast furnace slag contains 14-15wt% Al2O3, 35.01-36wt% SiO2 and 39-40wt% CaO. The particle size of the agricultural and forestry waste-based biochar is 70-150μm, the diameter of the calcium carbonate whisker is 1-2μm, and the length is 50-80μm.

[0044] The reinforcing agent is prepared by the following steps:

[0045] The polyvinyl alcohol is dissolved in hot water to configure a 3.5wt% polyvinyl alcohol solution, 2.5wt% polyethylene glycol (PEG-600) of the total amount of polyvinyl alcohol solution is added, then the silica and aluminum fluoride are stirred uniformly, frozen at -20°C for 12h, placed at room temperature for 12h, and the cycle is repeated 4 times, dried and crushed to obtain the product;

[0046] The molar ratio of the silica to the aluminum fluoride is 2:3, and the addition amount of the silica and the aluminum fluoride is 20% of the total amount of the polyvinyl alcohol solution.

[0047] The agricultural and forestry waste powder is dried and crushed from sugarcane residue. Example 3

[0048] A preparation process of an agricultural and forestry waste-based biochar composite filter material, comprising the following steps:

[0049] (1) The agricultural and forestry waste is crushed and dried, then heated to 600°C at a rate of 10°C / min under N2 atmosphere for 2h to obtain agricultural and forestry waste-based biochar;

[0050] (2) Ingredients: high alumina bauxite 70 parts, blast furnace slag 30 parts, agricultural and forestry waste-based biochar 24 parts, calcium carbonate whisker 16 parts, sodium silicate 2.5 parts, and reinforcing agent 14 parts;

[0051] (3) The sodium silicate is configured into a solution with water, mixed with high alumina bauxite, blast furnace slag, agricultural and forestry waste-based biochar, calcium carbonate whisker and reinforcing agent to granulate, the particle size is 8 mm, and dried at 100°C;

[0052] (4) The temperature is increased to 400°C and kept for 15 min, then increased to 1150°C at 2°C / min, and calcined for 20 min;

[0053] (5) The product prepared in step (4) is immersed in 5wt% lye, activated at 85°C for 40 min, washed and dried to obtain the composite filter material.

[0054] The high alumina bauxite contains 75-76wt% Al2O3, 18-18.5wt% SiO2 and 1-1.1wt% Fe2O3; the blast furnace slag contains 14-15wt% Al2O3, 35.01-36wt% SiO2 and 39-40wt% CaO. The particle size of the agricultural and forestry waste-based biochar is 70-150μm, the diameter of the calcium carbonate whisker is 1-2μm, and the length is 50-80μm.

[0055] The reinforcing agent is prepared by the following steps:

[0056] The polyvinyl alcohol is dissolved in hot water to configure a 3.5wt% polyvinyl alcohol solution, 2.8wt% polyethylene glycol (PEG-600) of the total amount of polyvinyl alcohol solution is added, then the silicon dioxide and aluminum fluoride are stirred uniformly, frozen at -20°C for 12h, placed at room temperature for 12h, and the cycle is repeated for 4 times, dried and crushed to obtain the product.

[0057] The molar ratio of the silicon dioxide to the aluminum fluoride is 2:3, and the addition amount of the silicon dioxide and the aluminum fluoride is 20% of the total amount of the polyvinyl alcohol solution.

[0058] The agricultural and forestry waste powder is sawdust dried and crushed. Example 4

[0059] A preparation process of an agricultural and forestry waste-based biochar composite filter material, comprising the following steps:

[0060] (1) The agricultural and forestry waste is crushed and dried, then heated to 600°C at 10°C / min under N2 atmosphere, and fired for 2h to obtain the agricultural and forestry waste-based biochar;

[0061] (2) Ingredients: 70 parts of high alumina bauxite, 30 parts of blast furnace slag, 25 parts of agricultural and forestry waste-based biochar, 15 parts of calcium carbonate whisker, 3 parts of sodium silicate and 15 parts of reinforcing agent;

[0062] (3) The sodium silicate is configured into a solution with water, mixed with high alumina bauxite, blast furnace slag, agricultural and forestry waste-based biochar, calcium carbonate whisker and reinforcing agent to granulate, the particle size is 8 mm, and dried at 100°C;

[0063] (4) heating to 400℃ for 15 min, then heating to 1150℃ at a rate of 2℃ / min, calcining for 20 min;

[0064] (5) immersing the product prepared in step (3) in 5wt% lye, activating at 85℃ for 40 min, washing and drying to obtain the composite filter material.

[0065] The high bauxite has Al2O3 75-76wt%, SiO2 18-18.5wt%, Fe2O3 1-1.1wt%; the blast furnace slag has Al2O3 14-15wt%, SiO2 35.01-36wt%, CaO 39-40wt%. The particle size of the biochar based on agricultural and forestry waste is 70-150μm, the diameter of the calcium carbonate whisker is 1-2μm, and the length is 50-80μm.

[0066] The reinforcing agent is prepared by the following steps:

[0067] Dissolve polyvinyl alcohol in hot water to prepare a 4wt% polyvinyl alcohol solution, add 3wt% of the total amount of polyvinyl alcohol solution of polyethylene glycol (PEG-600), then add silica and aluminum fluoride and stir until uniform, freeze at -20℃ for 12h, place at room temperature for 12h, repeat the cycle 4 times, dry and crush to obtain the product.

[0068] The molar ratio of silica to aluminum fluoride is 2:3, and the addition amount of silica and aluminum fluoride is 20% of the total amount of polyvinyl alcohol solution.

[0069] The agricultural and forestry waste powder is sawdust dried and crushed.

[0070] Comparative Example 1

[0071] Comparative Example 1 is a comparative example of Example 4, and the difference between Example 4 and Comparative Example 1 is that the calcium carbonate whisker is replaced by biochar based on agricultural and forestry waste.

[0072] Comparative Example 2

[0073] Comparative Example 2 is a comparative example of Example 4, and the difference between Example 4 and Comparative Example 2 is that no reinforcing agent is added.

[0074] Performance test:

[0075] 1. The compressive strength and porosity of the filter material prepared in Examples 1-4 and Comparative Examples 1-2 are detected, wherein 15 filter materials are randomly taken, the compressive strength of each is measured, and then the average value of the compressive strength of 15 filter materials is taken; the porosity is measured according to the test method of GJ / T299-2008 "Artificial ceramsite filter material for water treatment".

[0076] 2. Adsorption test:

[0077] (1) Test water is artificially configured simulated wastewater: COD 300 mg / L, total nitrogen 25 mg / L, ammonia nitrogen (NH4 + -N) 15 mg / L.

[0078] The dynamic adsorption test simulation device is shown in Figure 1 , the adsorption column 1 has an inner diameter of 5 cm and a total height of 100 cm, the middle part is filled with filter material 2, water flows into the adsorption column 1 from bottom to top by a water pump, water is discharged from the water outlet above the adsorption column 1, the water outlet is provided with a sampling port, and air is pumped into the adsorption column 1 by an air compressor through an aeration head. A grid support plate is fixed at a height of 10 cm of the adsorption column, the support plate is filled with filter material with a particle size of 8 mm, the filter material layer has a height of 70 cm, and water is discharged from the top of the filter material.

[0079] The membrane hanging and detection test: after the activated sludge (purchased from Shandong Luxing Environmental Protection Technology Co., Ltd.) is uniformly mixed with artificial wastewater at a volume ratio of 1:1, the mixture is poured into the filter column from the top end of the reactor until the mixture is above the surface of the filter material, and then the mixture is allowed to be covered and exposed, the air inlet amount is 10 L / h, and after each continuous covered and exposed for 8 h, the mixture is stopped for 1 h, which is beneficial to the deposition and adhesion of microorganisms on the surface of the filter material. Every 24 h, half of the mixture is discharged and artificial wastewater is supplemented; after the mixture is covered and exposed for 3 days, the reactor is emptied. Then, the experimental wastewater is pumped in, the air-water ratio is 3:1, and the hydraulic retention time is 6 h. Every 7 days, air-water combined backwashing is performed (air washing strength is 9 L / h, water washing strength is 5 L / h, and time is 2 min); the concentrations of COD and ammonia nitrogen in the inlet and outlet water are detected every certain period of time, the removal rate is calculated, and detailed curves are shown in Figure 2 and Figure 3 , wherein the removal rate after the system is stabilized is shown in Table 1.

[0080] (2) The P removal rate is obtained by static adsorption test, 50 g of filter material is added in 50 L of simulated wastewater, and stirring adsorption is performed for 24 h, the P concentration before and after adsorption is detected, and the removal rate is calculated.

[0081] Table 1: Performance detection data

[0082]

[0083] As shown in Table 1, the porosity of the filter material prepared in the application is 51.4-53.6%, the compressive strength is 5.25-5.71 MPa, the strength is high, the filter material is not easy to break, and the filter material is convenient for recycling; and the static removal rate of P can reach 96.5-98.3%, and the adsorption performance is excellent.

[0084] In addition, as shown in Figure 2 and Figure 3 , the filter material prepared in Examples 1-4 of the application has high removal rates of NH4 +The -N removal rate is 18.3-20.1%, and with the extension of the biofilm formation time, the removal rate of NH4 + The -N removal rate is 88.6-89.8% and tends to be stable, and the removal rate of NH4 4+ The -N removal rate is 92.1-93.8%, which shows that the filter material prepared in the application has fast biofilm formation, and the removal rate of NH4 + The -N removal rate is 92.1-93.8%, which shows that the filter material prepared in the application has fast biofilm formation, and the removal rate of NH4

[0085] Compared with Example 4, in Comparative Example 1, calcium carbonate whiskers are replaced by biochar based on agricultural and forestry waste, and in Comparative Example 2, no reinforcing agent is added. The compressive strength of the filter material prepared in Comparative Example 2 is obviously lower than that of Example 4, which shows that the reinforcing agent added in the application has the effect of structural reinforcement. Combined with the above analysis, it can be seen that the filter material prepared in Example 4 has the effects of structural reinforcement and adsorption performance increase. Figure 2 It can be seen that the removal rate of NH 4+ The removal rate of -N tends to be stable, while the removal rate of NH 4+ The removal rate of -N tends to be stable, while the removal rate of NH 4+ The removal rate of -N is obviously lower than that of Example 4, and the biofilm formation speed is slow, which shows that the reinforcing agent added in the application indeed helps the biofilm formation and increases the adsorption performance; and calcium carbonate whiskers can also increase the adsorption performance. Combined with the above analysis, it can be seen that the filter material prepared in Example 4 has the effects of structural reinforcement and adsorption performance increase. Figure 3 It can be seen that the removal rate of COD of the filter material prepared in Comparative Example 1 and Comparative Example 2 is lower than that of Example 4, which shows that the reinforcing agent in the application not only has the effect of structural reinforcement, but also helps to increase the adsorption rate of COD; and the addition of calcium carbonate whiskers as a pore-forming agent can also synergistically increase the adsorption performance and water purification effect.

[0086] Finally, it should be pointed out that the above examples are only used to illustrate the technical solutions of the application and not to limit it. Other modifications or equivalent replacements of the technical solutions of the application made by those skilled in the art should be covered in the scope of the claims of the application, as long as they do not deviate from the spirit and scope of the technical solutions of the application.

Claims

1. A process for the preparation of an agroforestry waste based biochar composite filter media, characterized by: The method comprises the following steps: (1) crushing and drying the agricultural and forestry waste, and then calcining the agricultural and forestry waste at 10 ℃ / min to 600 ℃ under N2 atmosphere for 2 h to obtain the agricultural and forestry waste-based biochar; (2) ingredients: 70 parts of high-alumina bauxite, 30 parts of blast furnace slag, 20-25 parts of agricultural and forestry waste-based biochar, 15-20 parts of calcium carbonate whisker, 2-3 parts of sodium silicate, and 10-15 parts of reinforcing agent; (3) uniformly stirring the sodium silicate with water, and mixing and granulating the high-alumina bauxite, blast furnace slag, agricultural and forestry waste-based biochar, calcium carbonate whisker, and reinforcing agent to obtain granules with a particle size of 6-8 mm, and then drying the granules; (4) heating to 400 ℃ and keeping for 15 min, then heating to 1150 ℃ at 1-2 ℃ / min, and calcining for 20 min to obtain the product; The reinforcing agent is prepared by the following steps: dissolving polyvinyl alcohol in hot water to prepare a 3-4 wt% polyvinyl alcohol solution, adding 2.3-3 wt% of the total amount of the polyvinyl alcohol solution of polyethylene glycol, then uniformly stirring the silica and aluminum fluoride, freezing at -20 ℃ for 12 h, placing at room temperature for 12 h, and repeating the cycle for 4 times, and then drying and crushing to obtain the product; the molar ratio of the silica to the aluminum fluoride is 2:3, and the total amount of the silica and the aluminum fluoride added is 20% of the total amount of the polyvinyl alcohol solution.

2. The process for preparing the agroforestry waste based biochar composite filter media as claimed in claim 1, wherein: The high-alumina bauxite contains 75-76 wt% of Al2O3, 18-18.5 wt% of SiO2, and 1-1.1 wt% of Fe2O3.

3. The process for preparing the agroforestry waste based biochar composite filter media as claimed in claim 1, wherein the process comprises of: The blast furnace slag contains 14-15 wt% of Al2O3, 35.01-36 wt% of SiO2, and 39-40 wt% of CaO.

4. The process for preparing a biochar composite filter media from agroforestry waste as claimed in claim 1, wherein: The agricultural and forestry waste is one or two of sawdust, fruit shell, rice husk, straw, and sugarcane residue.

5. The process for preparing a biochar composite filter material based on agricultural and forestry waste according to claim 1, characterized in that: immersing the product prepared in step (4) in 3-5 wt% lye, activating at 85 ℃ for 40 min, washing and drying to obtain the composite filter material.

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