A method for preparing a composite material for repairing soil and water bodies and its use

Abstract

The application discloses a preparation method of a composite material for repairing soil and water bodies and application of the composite material, and comprises the following steps: mixing excessive phosphate and calcium hydroxide to obtain a mixed solution, then putting pretreated biochar into the mixed solution for modification treatment, and obtaining modified biochar through cracking and drying; ball-milling the modified biochar and nZVI at a certain proportion to obtain modified biochar material loaded with nZVI; and mixing the modified biochar material and activated bacillus pasteurii at a certain proportion to obtain the composite material. By taking phosphate and a reaction product of phosphate and calcium hydroxide as a modifier, the caking of the biochar can be reduced, the specific surface area and porosity of the biochar are increased, and meanwhile, calcium in calcium phosphate attached to the modified biochar can provide a calcium source for mineralization of microorganisms in the later stage, and the solidification effect of the microorganisms on heavy metals and organic matters is enhanced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of soil and water remediation, and particularly relates to a preparation method of a composite material for remediation of soil and water and application thereof. BACKGROUND

[0002] With the development of society and the progress of science and technology, people enjoy high level of living conditions, and the solid waste generated by industrial activities and urban life also increases year by year, and part of the land and water resources are seriously polluted. The solid waste basically contains heavy metals, which will migrate from the solid waste to the ground surface over time. Influenced by rain erosion, surface runoff scouring and weathering, heavy metals will migrate to the natural environment in large quantities, seriously affecting the quality of soil and groundwater in China, and causing great threat to the ecological environment and human health. At the same time, it will also change the physical and mechanical properties of the soil body and affect the safety of the project.

[0003] The heavy metal pollutants mainly include composite heavy metals such as cadmium (Cd), lead (Pb), chromium (Cr) and zinc (Zn). Among them, Cd as the primary inorganic pollutant has wide pollution range, high intensity, great harm and high point exceeding standard rate of 7.0%. Cd and Pb are not essential elements for human body, and even trace amounts of Cd and Pb will affect the nervous system, kidney system, hematopoietic system, cardiovascular system and male reproductive system of human body, leading to the occurrence of major diseases such as slow brain development of children, male infertility, cancer of important organ cells and the like.

[0004] Common heavy metal remediation technologies mainly include physical remediation technology, chemical remediation technology and biological remediation technology. The traditional physical remediation and chemical remediation have been well developed in China, but they have high resource consumption and often cause secondary pollution. The biological remediation technology mainly includes plant remediation, animal remediation and microbial remediation, but the plant remediation has a long cycle. Therefore, it is urgent to seek a sustainable green remediation technology with low energy consumption and high remediation efficiency.

[0005] In view of this, it is necessary to design a preparation method of a composite material for remediation of soil and water and application thereof to solve the above problems. SUMMARY

[0006] The present application aims to provide a preparation method of a composite material for remediation of soil and water and application thereof with low energy consumption, high remediation efficiency and sustainable green remediation.

[0007] To achieve the above-mentioned application purposes, the present application provides a preparation method of a composite material for remediation of soil and water, which comprises the following steps:

[0008] S1, mixing excess phosphate with calcium hydroxide to obtain a mixed solution, then placing the pretreated biochar in the mixed solution for modification treatment, and obtaining modified biochar through cracking and drying;

[0009] S2, ball milling the modified biochar obtained in step S1 with nano zero-valent iron (nZVI) at a certain proportion to obtain a modified biochar material loaded with nZVI;

[0010] S3, mixing the modified biochar material obtained in step S2 with activated Bacillus pasteurii at a certain proportion to obtain a composite material.

[0011] nZVI has strong adsorption and reduction performance, high reaction activity, large specific surface area and other characteristics, and has a unique core-shell structure, and has been widely studied and applied in soil and water environment remediation. However, nZVI has the disadvantages of easy agglomeration in natural environment, easy oxidation, instability and the like, which reduces its reaction performance and limits its further development in the field of heavy metal and organic matter pollution remediation. Biochar (BC) is an environmentally friendly material, which has high specific surface area, dense microporous structure and strong adsorption, and contains rich oxygen-containing functional groups, and has strong adsorption and complexation effect on heavy metals. Loading nZVI on biochar can reduce the agglomeration of nZVI, play the advantages of both, and improve the effective fixation capacity of both on heavy metals. At the same time, the addition of biochar can provide a suitable environment space for microorganisms, reduce the persecution of heavy metals on microorganisms, and be beneficial to the growth and reproduction of microorganisms, and enhance the remediation capacity of microorganisms on heavy metals. The composite material obtained by loading nZVI and microorganisms on the biochar modified by phosphate and alkali has obviously improved the fixation efficiency of heavy metals, greatly reduces the migration rate of heavy metals, and reduces the toxicity of heavy metals to the surrounding environment.

[0012] As a further improvement of the application, in step S1, the ratio of the amount-of-substance concentration of the phosphate to the calcium hydroxide is greater than or equal to 2:1, preferably, the ratio of the amount-of-substance concentration of the phosphate to the calcium hydroxide is 2:1-5:1; the concentration of the calcium hydroxide is 2-4 mol / L.

[0013] As a further improvement of the application, in step S1, the mass ratio of the phosphate to the biochar is 0.8-1.2:1.

[0014] As a further improvement of the application, in step S1, the pretreatment is: washing, filtering, drying, crushing and sieving the biochar, wherein the drying temperature is 80-100℃, the drying time is 18-24h, and the screen mesh aperture is 0.5-1.0mm.

[0015] As a further improvement of the present application, in step S1, the modification treatment is: placing the biochar in a mixed solution of phosphate and calcium hydroxide, soaking at room temperature for 24-48h, and then drying, wherein the initial temperature of the mixed solution is 50-60℃, the drying temperature is 80-100℃, and the drying time is 18-24h.

[0016] As a further improvement of the present application, in step S1, the phosphate is a mixture of one or both of tri-potassium phosphate and tri-sodium phosphate; and the biochar is any one of rice husk, rice straw, and straw.

[0017] As a further improvement of the present application, in step S1, the pyrolysis operation is: placing the modified biochar in a tube furnace, introducing nitrogen gas into the tube furnace at a flow rate of 0.1-0.3L / min to discharge the air in the furnace, heating at a rate of 5-15℃ / min to 450-600℃, and then holding for 2-3h for pyrolysis, and then naturally cooling to complete the pyrolysis, and then washing the pyrolyzed biochar with deionized water until the pH is neutral.

[0018] As a further improvement of the present application, in step S2, the mass ratio of the modified biochar to nZVI is 20-100:1.

[0019] As a further improvement of the present application, in step S2, the ball milling operation is: placing the modified biochar and nZVI in a ball mill, adding grinding balls at a ball-to-material ratio of 5:1-15:1, mechanically grinding for 1-3h, the rotation speed of the ball mill is 300-450r / min, and the diameter of the grinding balls can be selected according to actual conditions, for example, the diameter of the grinding balls is any one or a combination of 2.4mm, 1.0mm, and 0.6mm.

[0020] As a further improvement of the present application, in step S3, the ratio of the modified biochar material to the Bacillus pasteurii bacterial solution is 1g:(5-6)mL.

[0021] As a further improvement of the present application, in step S3, the Bacillus pasteurii used is purchased from the American Type Culture Collection, and the strain number is ATCC 11859.

[0022] As a further improvement of the present application, in step S3, the activation treatment operation of the Bacillus pasteurii includes the following steps:

[0023] (1) preparing a liquid medium, the components of the liquid medium include: 20g / L yeast extract, 10g / L ammonium sulfate, 15.748g / L Tris, and 5g / L sodium chloride, and the solvent is deionized water;

[0024] (2) the freeze-dried powder of Bacillus pasteurii is inoculated into a liquid culture medium and placed on a shaking table to culture for 24-48 h at 30 DEG C and a rotation speed of 150-200 r / min to activate the strain, and a bacterial liquid with an OD600 of 1.1-1.3 is obtained.

[0025] As a further improvement of the present application, in step S3, the culture operation is as follows: after the modified biochar material is mixed with Bacillus pasteurii, the mixture is placed on a shaking table to culture for 20-30 h at 30 DEG C and a rotation speed of 150-200 r / min.

[0026] The present application also provides a composite material for repairing soil and water, which is prepared according to the preparation method of the composite material for repairing soil and water.

[0027] The present application also provides the application of the composite material in repairing soil and water.

[0028] As a further improvement of the present application, when used for soil repair, the composite material is mixed with soil at a mass ratio of 1:18-1:22 to obtain a treatment product, the treatment product is pressed into a shape, and then a cementation nutrient solution with a concentration of 0.5 mol / L of CaCl2 and urea is used to sufficiently mineralize the soil, and finally, the heavy metals are solidified after standing for 7-28 days.

[0029] As a further improvement of the present application, when used for water repair, the cementation nutrient solution is added to a liquid culture medium to obtain a culture liquid, and then the water to be repaired is mixed with the composite material and the culture liquid to stand and culture to solidify the heavy metals, and the use ratio of the water to be repaired, the composite material and the culture liquid is adjusted according to the pollution degree of the water body.

[0030] The present application has the following advantages:

[0031] 1. In the present application, the biochar is modified by placing it in a mixed solution of phosphate and calcium hydroxide, which can utilize the excess phosphate to modify the biochar, so that the modified biochar can load more phosphorus-containing functional groups, thereby enhancing the solidification effect of heavy metals, and the potassium hydroxide generated by the reaction of phosphate and calcium hydroxide can also modify the biochar, effectively increasing the specific surface area of the biochar and enriching the pore structure of the biochar, thereby realizing the dual modification of the biochar. In addition, during the modification process, the calcium phosphate generated by the reaction of phosphate and calcium hydroxide, which is difficult to dissolve in water, will also adhere to the biochar, and when the composite material is used for soil repair, the slow dissolution of the calcium phosphate in the soil can provide phosphorus elements for plants, which is beneficial to the growth of plants; at the same time, the composite material can increase the pH of the environment, which is beneficial to the mineralization of microorganisms and the solidification of heavy metals.

[0032] 2. The application uses phosphate and the reaction product of phosphate and calcium hydroxide as a modifier to reduce the caking of biochar, increase the specific surface area and porosity, and at the same time, the calcium element in the calcium phosphate attached to the modified biochar can provide a calcium source for the mineralization of microorganisms in the later stage, which is beneficial to the mineralization of microorganisms and enhances the solidification effect of microorganisms on heavy metals and organic matter.

[0033] 3. The application loads nano zero-valent iron on biochar, which can disperse nano zero-valent iron well, reduce the agglomeration of nano zero-valent iron, and at the same time, biochar can be used as a place for microorganisms to attach, which can also reduce the direct contact between nano zero-valent iron and microorganisms, and is beneficial to the growth and reproduction of microorganisms.

[0034] 4. The material involved in the application has a wide source and low price, and does not cause secondary pollution to the environment, which is a green and economical composite material, and the composite material can improve the efficiency of heavy metal fixation, greatly reduce the migration rate of heavy metals, and reduce the toxicity of heavy metals to the surrounding environment. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 Flowchart for the preparation method of the composite material for repairing soil and water.

[0036] Figure 2 Results of the influence of different mass ratios of potassium phosphate and rice husk on the adsorption of heavy metals by the composite material.

[0037] Figure 3 Results of the influence of calcium hydroxide concentration on the adsorption of heavy metals by the composite material.

[0038] Figure 4 Results of the influence of the mass ratio of modified biochar and nZVI on the heavy metal solidification capacity of the composite material. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical scheme and advantages of the application clearer, the application will be described in detail below with reference to the drawings and specific examples.

[0040] It should also be noted that, in order to avoid obscuring the application due to unnecessary details, only structures and / or processing steps closely related to the scheme of the application are shown in the drawings, and other details not closely related to the application are omitted.

[0041] In addition, it should also be noted that the term "comprise", "include" or any other variant thereof is intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or equipment.

[0042] Example 1

[0043] like Figure 1 As shown, this embodiment provides a method for preparing a composite material for soil and water remediation, including the following steps:

[0044] S1. Add 228g of tripotassium phosphate to 200mL of 2.5mol / L calcium hydroxide to form a mixed solution; wash, filter, dry, crush, and pass through a 0.8mm sieve of 285g of rice husks and add them to the mixed solution to soak at room temperature for 36h. The initial temperature of the mixed solution is 50℃. Then, place the soaked rice husks in an 80℃ oven to dry for 24h; then, place the dried rice husks in a tube furnace for pyrolysis, where the nitrogen flow rate is 0.2L / min, and the tube furnace is heated to 500℃ at a rate of 10℃ / min and held at that temperature for 2.5h; finally, place the pyrolyzed rice husks in an oven to dry and obtain modified biochar.

[0045] S2. The modified biochar obtained in step S1 is ball-milled with nZVI at a mass ratio of 40:1 and a ball-to-material ratio of 10:1 for 2 hours at a ball mill speed of 300 r / min to obtain modified biochar material loaded with nZVI.

[0046] S3. The modified biochar material obtained in step S2 is mixed with the activated Bacillus pasteurellium culture at a ratio of 1g:5.5mL and placed on a shaker. The mixture is then cultured at 30°C and 160r / min for 24h to obtain the composite material.

[0047] Soil remediation: Excavate soil contaminated with heavy metals Cd and Pb, crush it using a pulverizer, and pass it through a 2mm sieve to obtain fine-grained soil. Mix the composite material with the soil at a mass ratio of 1:20 (modified biochar material in the composite material to soil) to obtain a treated product. After pressing the treated product into shape, fully immerse it in a cementing nutrient solution, insert an oxygen supply pump, and immerse it in the cementing nutrient solution for 12 hours. Then, remove the treated product and cure it at 26℃ for 12 hours. Repeat the above immersion and curing process twice to fully mineralize the soil. Finally, let it stand for 14 days to solidify the heavy metals.

[0048] Example 2-11

[0049] Examples 2-3 provide a method for preparing composite materials for soil and water remediation, respectively. Compared with Example 1, the amount of rice husk used in Examples 2-3 is adjusted from 285g to 228g and 190g, respectively. The remaining steps are the same as in Example 1 and will not be repeated here.

[0050] Compared with Example 1, in Example 4, the amount of tripotassium phosphate was adjusted from 228g to 424g, and the amount of rice husk was adjusted from 285g to 530g. The remaining steps were the same as in Example 1 and will not be repeated here. Compared with Example 4, in Examples 5-8, the concentration of calcium hydroxide was adjusted from 2.5mol / L to 2, 3, 3.5, and 4mol / L, respectively. The remaining steps were the same as in Example 1 and will not be repeated here.

[0051] Compared with Example 1, the mass ratio of modified biochar to nZVI in Examples 9-11 was adjusted from 40:1 to 20:1, 80:1 and 100:1 respectively. The remaining steps were the same as in Example 1 and will not be repeated here.

[0052] Comparative Examples 1-2

[0053] Comparative Examples 1 and 2 respectively provide a method for preparing composite materials for soil and water remediation. Compared with Example 1, the amount of rice husk used in Comparative Examples 1 and 2 was adjusted from 285g to 456g and 114g, respectively. The remaining steps are the same as in Example 1 and will not be repeated here.

[0054] Examples 2-3 and Comparative Examples 1-2 were subjected to soil remediation in the same manner as in Example 1, and the soil remediation results were tested.

[0055] In Examples 1-3 and Comparative Examples 1-2, the mass ratios of tripotassium phosphate to rice husks were 0.8:1, 1:1, 1.2:1, 0.5:1, and 2:1, respectively. Figure 2 As shown, when the mass ratio of tripotassium phosphate to rice husk is in the range of 0.8-1.2:1, in Examples 1-3, the adsorption capacity of the composite material for Pb is above 80 mg / g and the adsorption capacity for Cd is above 75 mg / g. When the mass ratio of tripotassium phosphate to rice husk is lower than 0.8:1 (Comparative Example 1) or higher than 1.2:1 (Comparative Example 2), the adsorption capacity of the composite material for Pb and Cd decreases significantly.

[0056] Comparative Examples 3-4

[0057] Comparative Examples 3 and 4 respectively provide a method for preparing composite materials for soil and water remediation. Compared with Example 4, the concentration of calcium hydroxide in Comparative Examples 3 and 4 was adjusted from 2.5 mol / L to 1.5 mol / L and 1 mol / L, respectively. The remaining steps are the same as in Example 1 and will not be repeated here.

[0058] Examples 4-8 and Comparative Examples 3-4 were subjected to soil remediation in the same manner as in Example 1, and the soil remediation results were tested.

[0059] like Figure 3As shown, when the concentration of calcium hydroxide is in the range of 2-4 mol / L, the solidification effect of Cd in the soil in Examples 4-8 is above 75%. When the concentration of calcium hydroxide is reduced to 1.5 mol / L and 1 mol / L, the solidification effect of Cd in the soil is significantly reduced (Comparative Examples 3 and 4). When the concentration of calcium hydroxide is greater than 3.5 mol / L, the solidification effect of Cd in the soil gradually decreases with the increase of calcium hydroxide concentration.

[0060] Comparative Examples 5-6

[0061] Comparative Examples 5 and 6 respectively provide a method for preparing composite materials for soil and water remediation. Compared with Example 1, the mass ratio of modified biochar to nZVI in Comparative Examples 5 and 6 is adjusted from 40:1 to 1:1 and 10:1 respectively. The remaining steps are the same as in Example 1 and will not be repeated here.

[0062] Examples 9-11 and Comparative Examples 5-6 were subjected to soil remediation in the same manner as in Example 1, and the soil remediation results were tested.

[0063] like Figure 4 As shown, when the mass ratio of modified biochar to nZVI is in the range of 20:1-100:1, the Cd fixation capacity in the soil in Examples 1 and 9-11 is above 75%. When the mass ratio of modified biochar to nZVI is adjusted from 40:1 to 10:1 and 1:1, the Cd fixation capacity in the soil decreases significantly. This may be because the increased content of nano-zero valent iron affects the growth and reproduction of microorganisms, thereby inhibiting the microorganisms' ability to remediate the soil, resulting in a decrease in the soil remediation capacity of the composite material. When the mass ratio of modified biochar to nZVI exceeds 80:1, the Cd fixation capacity in the soil shows a downward trend.

[0064] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a composite material for soil and water remediation, characterized in that, Includes the following steps: S1. Mix excess phosphate with calcium hydroxide to obtain a mixed solution, then place the pretreated biochar in the mixed solution for modification treatment, and obtain modified biochar by pyrolysis and drying; The molar concentration ratio of the phosphate to calcium hydroxide is greater than or equal to 2:1; the concentration of the calcium hydroxide is 2-4 mol / L; the mass ratio of the phosphate to biochar is 0.8-1.2:

1. S2. The modified biochar obtained in step S1 is ball-milled with nZVI in a certain proportion to obtain modified biochar material loaded with nZVI. The mass ratio of the modified biochar to nZVI is 20-100:1; S3. The modified biochar material obtained in step S2 is mixed with activated Bacillus pasteurellii in a certain proportion to obtain a composite material; the ratio of the modified biochar material to the Bacillus pasteurellii bacterial solution is 1g:(5-6)mL.

2. The method for preparing the composite material for soil and water remediation according to claim 1, characterized in that: In step S1, the modification treatment is as follows: the biochar is soaked in a mixed solution of phosphate and calcium hydroxide at room temperature for 24-48 hours and then dried, wherein the initial temperature of the mixed solution is 50-60℃.

3. The method for preparing the composite material for soil and water remediation according to claim 1, characterized in that: In step S1, the phosphate is one or a mixture of two of tripotassium phosphate and trisodium phosphate.

4. The method for preparing the composite material for soil and water remediation according to claim 1, characterized in that: In step S1, the biochar is any one of rice husks, rice straw, or stalks.

5. A composite material for remediating soil and water bodies, characterized in that, The composite material is prepared by the preparation method according to any one of claims 1-4.

6. An application of the composite material according to claim 5, characterized in that: The composite material is used for soil and water remediation.

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