A magnetic biochar composite material and its preparation method and application

Abstract

The present invention discloses a magnetic biochar composite material, its preparation method, and application. The preparation method of the magnetic biochar composite material comprises the following steps: S1. treating diatomaceous earth with alkali to obtain alkali-leached diatomaceous earth; S2. mixing biochar, alkali-leached diatomaceous earth, ferrous salt, ferric salt, and phosphoric acid, and heating the mixture to obtain the biochar composite material; and S3. pyrolyzing the biochar composite material to obtain the magnetic biochar composite material. The present invention modifies the biochar by using specific amounts of biochar, alkali-leached diatomaceous earth, ferrous salt, ferric salt, and phosphoric acid. The synthesized magnetic biochar composite material has low hydrophilicity, high porosity, and a large number of adsorption sites, and has excellent adsorption effects on oil and suspended solids in wastewater from power transmission and transformation projects.

Description

Technical Field

[0001] The present invention relates to the field of wastewater technology, and more specifically, to a magnetic biochar composite material and a preparation method and application thereof. Background Art

[0002] Wastewater generated during the flushing process of mechanical equipment used in excavation at power transmission and transformation project bases is rich in suspended solids and oil. This wastewater is characterized by complex water composition, high chemical oxygen demand (COD) and biochemical oxygen demand (BOD), poor oil-water separation, and large treatment scales. Direct discharge would negatively impact water quality and, in turn, the ecological environment. To ensure the smooth operation of power transmission and transformation projects, developing economical, efficient, and green wastewater treatment technologies that simultaneously control high concentrations of suspended solids and oil is a top priority for these projects.

[0003] Currently, there are many methods for treating wastewater contaminated by suspended matter and oil. The total amount of oily wastewater and suspended matter generated by mechanical flushing equipment is also greater, and the composition is more complex and difficult to remove. Traditional treatment methods can no longer achieve good treatment results. Adsorption is a relatively mature wastewater treatment method. It can use the pore structure on the surface of the adsorbent to physically and chemically adsorb various pollutants in the water to achieve a separation effect. However, there are many types of adsorbents. When treating wastewater, a single adsorbent cannot remove suspended matter and oil pollution at the same time. For example, biochar has a large amount of charge on its surface, is porous inside, and has rich functional groups on its surface. Therefore, it has good adsorption properties and is widely used in the field of water treatment. However, it is not ideal when used alone to adsorb oil pollution and suspended matter in wastewater from power transmission and transformation projects.

[0004] Therefore, it is of great significance to modify biochar and develop a preparation method for a magnetic biochar composite material that has a good adsorption effect on oil and suspended matter in power transmission and transformation project wastewater. Summary of the Invention

[0005] The purpose of the present invention is to solve the problem in the prior art that biochar has an unsatisfactory adsorption effect on oil and suspended solids in wastewater from power transmission and transformation projects, and to provide a magnetic biochar composite material and its preparation method and application.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] In a first aspect, the present invention provides a method for preparing a magnetic biochar composite material, comprising the following steps:

[0008] S1. treating diatomaceous earth with alkali to obtain alkali-leached diatomaceous earth;

[0009] S2. mixing biochar, alkali-leached diatomaceous earth, ferrous salt, ferric salt, and phosphoric acid, and heating the mixture to react to obtain a biochar composite material;

[0010] S3. Pyrolyzing the biochar composite material to obtain a magnetic biochar composite material;

[0011] Wherein, in step S2, the ratio of the biochar, alkali-leached diatomaceous earth, ferrous salt, ferric salt and phosphoric acid is (5-10) g: (3.0-3.5) g: (1.5-2) mol: (1.5-2) mol: (1.5-2) mol.

[0012] The present invention modifies biochar by using specific amounts of biochar, alkali-leached diatomaceous earth, ferrous salt, ferric salt and phosphoric acid, so that the synthesized magnetic biochar composite material has low hydrophilicity, high porosity and a large number of adsorption sites, and has a good adsorption effect on oil and suspended matter in the wastewater of power transmission and transformation projects.

[0013] Specifically, ferrous salts and ferric salts will synthesize ferric oxide and magnetic ferric oxide, which is not only conducive to the recovery of magnetic biochar composite materials from power transmission and transformation project wastewater, but also can enhance the adsorption effect of magnetic biochar composite materials on oil and suspended matter in power transmission and transformation project wastewater.

[0014] In the biochar, alkali-leached diatomaceous earth, ferrous salt, ferric salt and phosphoric acid system, phosphoric acid can form phosphates with metal ions in biochar and alkali-leached diatomaceous earth, forming a large number of active sites on the surface and inside of biochar and alkali-leached diatomaceous earth, and helping the system to corrode the structure of biochar and alkali-leached diatomaceous earth during pyrolysis treatment, thereby forming pores and increasing the porosity of the magnetic biochar composite material. Therefore, it is beneficial to enhance the adsorption effect of the magnetic biochar composite material on oil and suspended matter in the wastewater of power transmission and transformation projects.

[0015] In addition, the magnetic biochar composite material obtained by pyrolysis treatment of biochar, alkali-leached diatomaceous earth, ferrous salt, ferric salt and phosphoric acid has low hydrophilicity and high lipophilicity, has a good adsorption effect on oil pollution, and the adsorption speed is fast.

[0016] Preferably, in step S1, the base is at least one of NaOH, KOH, and ammonia water.

[0017] Preferably, the step S1 specifically comprises: soaking diatomaceous earth with alkali and stirring to obtain alkali-soaked diatomaceous earth.

[0018] More preferably, the concentration of the base is 0.5-2 mol / L; and the stirring time is 6-12 h.

[0019] Preferably, in step S2, the molar ratio of ferrous salt to ferric salt is 1:1.

[0020] Preferably, in step S2, the method for preparing the biochar is: pyrolyzing a biocalcium carbonate material to obtain the biochar; the biocalcium carbonate material is crab shells and / or shrimp shells.

[0021] More preferably, the temperature of the pyrolysis treatment is 450-600° C. and the time is 2-3 hours.

[0022] More preferably, the pyrolysis treatment is carried out under a protective atmosphere of an inert gas; specifically, the inert gas is at least one of nitrogen and argon.

[0023] The present invention selects crab shells and / or shrimp shells to prepare biochar materials, which can fully utilize biological waste crab shells and / or shrimp shells and make them into resources, and has the advantages of being economical, environmentally friendly, and low-cost.

[0024] Preferably, in step S2, the ferrous salt is at least one of ferrous sulfate, ferrous chloride (ferrous dichloride), ferrous nitrate, and ferrous hydroxide.

[0025] Preferably, in step S2, the iron salt is at least one of ferric sulfate, ferric chloride (ferric chloride), ferric nitrate, and ferric hydroxide.

[0026] Preferably, in step S2, the mixing time of the biochar, alkali-leached diatomaceous earth, ferrous salt, ferric salt and phosphoric acid is 30-60 minutes.

[0027] Preferably, in step S2, after mixing the biochar, alkali-leached diatomaceous earth, ferrous salt, ferric salt and phosphoric acid, the pH of the system is adjusted to 5-9 with alkali.

[0028] More preferably, the pH of the system is adjusted with alkali at 25-50°C.

[0029] Preferably, in step S2, the heating reaction temperature is 80-100° C. and the time is 0.5-1.5 h.

[0030] Preferably, in step S3, the temperature of the pyrolysis treatment is 200-400°C.

[0031] More preferably, in step S3, the temperature of the pyrolysis treatment is 250-350°C.

[0032] The reason why the present invention uses a pyrolysis treatment temperature of 200-400°C is that when the temperature is less than 200°C, it is not conducive to the synthesis of ferrous oxide and magnetic ferric oxide by ferrous salts and ferric salts, and it will also make it difficult for phosphoric acid to play a role and not conducive to the formation of holes, thereby improving the hydrophilicity of the magnetic biochar composite material and reducing the porosity and the number of adsorption sites of the magnetic biochar composite material; while when the temperature is greater than 400°C, it is easy to cause a large amount of decomposition of biochar and serious damage to the structure of alkali-leached diatomaceous earth, thereby improving the hydrophilicity of the magnetic biochar composite material and reducing the porosity and the number of adsorption sites of the magnetic biochar composite material; that is, when the heat treatment temperature is 200-400°C, the adsorption effect of the magnetic biochar composite material on oil and suspended matter in the wastewater of power transmission and transformation projects can be further improved.

[0033] In a second aspect, the present invention provides a magnetic biochar composite material, which is prepared by the above-mentioned preparation method.

[0034] In a third aspect, the present invention provides an application of a magnetic biochar composite material in wastewater treatment.

[0035] In a fourth aspect, the present invention provides a wastewater treatment method, comprising:

[0036] Magnetic biochar composite materials were added to wastewater for adsorption treatment.

[0037] Preferably, the wastewater is wastewater from power transmission and transformation projects, containing oil and suspended matter.

[0038] Preferably, the solid-liquid ratio of the magnetic biochar composite material and wastewater is (0.1-0.5) g:100 mL.

[0039] Preferably, the temperature of the adsorption treatment is 20-45° C., and the time is ≥20 min, specifically 20-180 min.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] The present invention modifies biochar by using specific amounts of biochar, alkali-leached diatomaceous earth, ferrous salt, ferric salt and phosphoric acid, so that the synthesized magnetic biochar composite material has low hydrophilicity, high porosity and a large number of adsorption sites, and has a good adsorption effect on oil and suspended matter in the wastewater of power transmission and transformation projects.

[0042] The present invention can further improve the adsorption effect of the magnetic biochar composite material on oil and suspended matter in power transmission and transformation project wastewater by controlling the heat treatment temperature of biochar, alkali-leached diatomaceous earth, ferrous salt, ferric salt and phosphoric acid to 200-400°C.

[0043] In addition, the magnetic biochar composite material of the present invention can be recycled and can be used multiple times. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a line graph showing the adsorption effect of the magnetic biochar composite material on oil and suspended solids at different addition amounts according to Example 1.

[0045] Figure 2 This is a line graph showing the adsorption effect of the magnetic biochar composite material on oil and suspended solids at different adsorption treatment temperatures in Example 1.

[0046] Figure 3 This is a line graph of the adsorption effect of the magnetic biochar composite material on oil and suspended matter at different adsorption treatment times in Example 1.

[0047] Figure 4 This is a statistical chart of the adsorption effect of the magnetic biochar composite material on oil and suspended matter at different times of use in Example 1. DETAILED DESCRIPTION

[0048] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0049] In the various embodiments and comparative examples of the present invention, the reagents used are as follows:

[0050] The manufacturer of diatomaceous earth is Tianjin Damao Chemical Reagent Factory, CAS number is 61790-53-2, serial number 3714;

[0051] The preparation method of biochar is:

[0052] (1) The crab shells of the biological calcium carbonate material were washed with tap water and deionized water, dried in an oven at 60°C for 24 h, and then crushed with a grinder and passed through a 0.2 mm sieve to obtain crab shell powder;

[0053] (2) The crab shell powder was placed in a tube furnace, heated to 550°C at a rate of 10°C / min under a nitrogen atmosphere, and calcined at 550°C for 2 h for pyrolysis treatment, and then naturally cooled to room temperature to obtain biochar;

[0054] In addition, the present invention uses COD removal rate, oil removal rate, and turbidity removal rate as treatment effect indicators to indicate the adsorption effect of the magnetic biochar composite material on oil and suspended solids in the wastewater of power transmission and transformation projects. The larger the values ​​of COD removal rate, oil removal rate, and turbidity removal rate, the better the adsorption effect of the magnetic biochar composite material on oil and suspended solids in the wastewater of power transmission and transformation projects.

[0055] Example 1

[0056] This embodiment provides a magnetic biochar composite material, the preparation method of which includes the following steps:

[0057] S1. Add 1.5 mol / L sodium hydroxide solution to the diatomaceous earth until it just covers the diatomaceous earth and stir with a magnetic stirrer for 6 h. Filter, rinse with ultrapure water until neutral, and dry to constant weight to obtain alkaline-leached diatomaceous earth.

[0058] S2. 5 g of biochar, 2.5 g of alkali-leached diatomaceous earth, 100 mL of a mixed solution containing 1 mol / L FeSO4 and 1 mol / L FeCl3, and 100 mL of a 1 mol / L H3PO4 solution were stirred using a magnetic stirrer at 500 rpm for 30 min. The pH of the system was adjusted to 9 with 1.5 mol / L sodium hydroxide solution at 45°C. The mixture was then heated at 80°C for 1 h, filtered, washed with ultrapure water until neutral, and dried to constant weight to obtain a biochar composite material.

[0059] S3. The biochar composite material was placed in a muffle furnace and pyrolyzed at 350°C for 6 h, washed to remove ash, and dried to a constant weight to obtain a magnetic biochar composite material;

[0060] Wherein, in step S2, the ratio of the biochar, alkali-leached diatomaceous earth, FeSO4, FeCl3 and H3PO4 is 5g:2.5g:0.1mol:0.1mol:0.1mol.

[0061] Examples 2-11 and Comparative Examples 1-8

[0062] Examples 2-11 and Comparative Examples 1-8 provide different magnetic biochar composite materials. The difference between them and Example 1 is that the amounts of biochar, alkali-leached diatomaceous earth, FeSO4, FeCl3 and H3PO4 are different. The rest are consistent with Example 1, as shown in the following table:

[0063] Table 1 Amounts of biochar, alkali-leached diatomite, FeSO4, FeCl3 and H3PO4 in Examples 1-11 and Comparative Examples 1-8

[0064]

[0065] Examples 12-17

[0066] Examples 12-17 provide different magnetic biochar composite materials, which differ from Example 1 in that the pyrolysis treatment temperature in step S3 is different. The rest is consistent with Example 1, as shown in the following table:

[0067] Table 2 Pyrolysis treatment temperature in step S3 of Examples 1 and 12-17

[0068]

[0069]

[0070] Performance Testing

[0071] 1. The adsorption performance of oil and suspended solids on the magnetic biochar composite materials of each embodiment and comparative example was tested. Specifically:

[0072] 0.4 g of the magnetic biochar composite material prepared in each embodiment or comparative example was added to 100 mL of power transmission and transformation project wastewater containing oil and suspended matter, and the mixture was adsorbed at 30° C. for 120 minutes to obtain the power transmission and transformation project wastewater after adsorption treatment. The COD value, oil content, and turbidity of the power transmission and transformation project wastewater before and after adsorption treatment were tested, and the removal rates of COD, oil, and turbidity were calculated respectively.

[0073] Among them, the suspended solids content in the wastewater of power transmission and transformation projects is about 5000mg / L;

[0074] The COD value test method is as follows: at room temperature, according to the HJ / T 399-2007 standard, use a multi-parameter water quality meter to test the COD value of the power transmission and transformation project wastewater;

[0075] The oil content test method is as follows: at room temperature, according to the HJ 970-2018 standard, the oil content of the power transmission and transformation project wastewater is tested by ultraviolet spectrophotometry;

[0076] The turbidity test method is as follows: at room temperature, according to the turbidity determination - spectrophotometry GB / T15893.1-1995 standard, use a multi-parameter water quality meter to test the turbidity of the power transmission and transformation project wastewater;

[0077] COD removal rate (%) = (COD value of power transmission and transformation project wastewater before adsorption treatment - COD value of power transmission and transformation project wastewater after adsorption treatment) / COD value of power transmission and transformation project wastewater before adsorption treatment × 100%;

[0078] Oil removal rate (%) = (oil content of power transmission and transformation project wastewater before adsorption treatment - oil content of power transmission and transformation project wastewater after adsorption treatment) / oil content of power transmission and transformation project wastewater before adsorption treatment × 100%;

[0079] Turbidity removal rate (%) = (turbidity of power transmission and transformation project wastewater before adsorption treatment - turbidity of power transmission and transformation project wastewater after adsorption treatment) / turbidity of power transmission and transformation project wastewater before adsorption treatment × 100%;

[0080] The present invention uses COD removal rate, oil removal rate, and turbidity removal rate as treatment effect indicators to indicate the adsorption effect of the magnetic biochar composite material on oil and suspended solids in the wastewater of power transmission and transformation projects. The larger the COD removal rate, oil removal rate, and turbidity removal rate, the better the adsorption effect of the magnetic biochar composite material on oil and suspended solids in the wastewater of power transmission and transformation projects.

[0081] The experimental results are shown in the following table:

[0082] Table 3 Performance test results of various embodiments and comparative examples

[0083] COD removal rate / % Oil removal rate / % Turbidity removal rate / % Example 1 81.92 87.14 95.14 Example 2 82.99 89.12 96.54 Example 3 80.99 88.79 94.33 Example 4 80.45 85.54 93.34 Example 5 81.23 86.13 93.56 Example 6 78.46 83.25 91.66 Example 7 77.99 80.77 92.15 Example 8 80.34 83.65 90.46 Example 9 78.28 86.11 93.77 Example 10 81.46 86.56 94.44 Example 11 81.34 86.78 95.10 Example 12 78.56 82.89 92.67 Example 13 76.14 78.98 89.16 Example 14 77.17 78.91 85.68 Example 15 82.79 85.24 92.79 Example 16 60.72 64.98 78.66 Example 17 62.34 65.92 78.56 Comparative Example 1 57.09 60.32 74.89 Comparative Example 2 23.28 14.88 56.09 Comparative Example 3 56.90 59.83 73.67 Comparative Example 4 36.99 34.44 46.10 Comparative Example 5 53.89 60.78 69.45 Comparative Example 6 51.89 53.65 67.91 Comparative Example 7 55.65 57.40 71.45 Comparative Example 8 45.99 32.87 35.98

[0084] As can be seen from Table 3, the present invention modifies biochar by using specific amounts of biochar, alkali-leached diatomaceous earth, ferrous salt, ferric salt and phosphoric acid, so that the synthesized magnetic biochar composite material has low hydrophilicity, high porosity and a large number of adsorption sites, and has a good adsorption effect on oil and suspended matter in the wastewater of power transmission and transformation projects.

[0085] The present invention can further improve the adsorption effect of the magnetic biochar composite material on oil and suspended matter in power transmission and transformation project wastewater by controlling the heat treatment temperature of biochar, alkali-leached diatomaceous earth, ferrous salt, ferric salt and phosphoric acid to 200-400°C.

[0086] 2. The adsorption performance of the magnetic biochar composite material prepared in Example 1 on oil and suspended solids was tested at different dosages. Specifically:

[0087] 0.1 g, 0.2 g, 0.3 g, 0.4 g, and 0.5 g of the magnetic biochar composite material prepared in Example 1 were added to 100 mL of power transmission and transformation project wastewater containing oil and suspended matter, respectively, and adsorption treatment was performed at 30° C. for 120 min to obtain power transmission and transformation project wastewater after adsorption treatment; the COD value, oil content, and turbidity of the power transmission and transformation project wastewater before and after adsorption treatment were tested, and the removal rates of COD, oil, and turbidity were calculated respectively;

[0088] The suspended solids content in the wastewater from power transmission and transformation projects is approximately 5000 mg / L. The test methods for COD value, oil content, and turbidity, as well as the calculation of their respective removal rates, refer to the relevant content of the experiments in Part 1 of the performance test.

[0089] The experimental results are shown in the following table:

[0090] Table 4 Performance test results of magnetic biochar composite material under different addition amounts in Example 1

[0091]

[0092] Figure 1This is a line graph showing the adsorption effect of the magnetic biochar composite material on oil and suspended solids at different addition amounts according to Example 1.

[0093] From Table 4 and Figure 1 It can be seen that with the increase in the dosage of magnetic biochar composite materials, the overall removal efficiency of COD, oil and turbidity in the wastewater of power transmission and transformation projects shows a trend of first increasing and then tending to be stable. When the dosage of magnetic biochar composite materials is 0.4g, the COD removal efficiency, as well as the oil and turbidity removal rates all reach more than 80%.

[0094] 3. The magnetic biochar composite material prepared in Example 1 was subjected to adsorption treatment at different temperatures to test its adsorption performance on oil and suspended solids. Specifically:

[0095] 0.4 g of the magnetic biochar composite material prepared in Example 1 was added to 100 mL of power transmission and transformation project wastewater containing oil and suspended matter, and adsorption treatment was performed at 25° C., 30° C., 35° C., 40° C., and 45° C. for 120 min, respectively, to obtain power transmission and transformation project wastewater after adsorption treatment; the COD value, oil content, and turbidity of the power transmission and transformation project wastewater before and after adsorption treatment were tested, and the removal rates of COD, oil, and turbidity were calculated respectively;

[0096] The suspended solids content in the wastewater from power transmission and transformation projects is approximately 5000 mg / L. The test methods for COD value, oil content, and turbidity, as well as the calculation of their respective removal rates, refer to the relevant content of the experiments in Part 1 of the performance test.

[0097] The experimental results are shown in the following table:

[0098] Table 5 Performance test results of magnetic biochar composite material under different adsorption treatment temperatures in Example 1

[0099] Adsorption treatment temperature / ℃ COD removal rate / % Oil removal rate / % Turbidity removal rate / % 25 77.79 85.32 94.32 30 81.92 87.14 95.14 35 80.52 86.41 94.07 40 78.11 85.29 93.69 45 74.99 84.35 92.35

[0100] Figure 2 This is a line graph of the adsorption effect of the magnetic biochar composite material on oil and suspended matter at different adsorption treatment temperatures in Example 1.

[0101] From Table 5 and Figure 2 It can be seen that with the increase of the adsorption treatment temperature of the magnetic biochar composite material, the overall removal efficiency of COD, oil and turbidity in the wastewater of the power transmission and transformation project shows a trend of first increasing and then decreasing. When the adsorption treatment temperature is 30°C, the COD removal efficiency, as well as the oil and turbidity removal rates all reach more than 80%.

[0102] 4. The adsorption performance of the magnetic biochar composite material prepared in Example 1 on oil and suspended solids was tested at different adsorption treatment times. Specifically:

[0103] 0.4 g of the magnetic biochar composite material prepared in Example 1 was added to 100 mL of power transmission and transformation project wastewater containing oil and suspended matter, and the mixture was adsorbed at 30° C. for 20 min, 40 min, 60 min, 80 min, 100 min, 120 min, 140 min, 160 min, and 180 min to obtain the power transmission and transformation project wastewater after adsorption treatment; the COD value, oil content, and turbidity of the power transmission and transformation project wastewater before and after adsorption treatment were tested, and the removal rates of COD, oil, and turbidity were calculated respectively;

[0104] The suspended solids content in the wastewater from power transmission and transformation projects is approximately 5000 mg / L. The test methods for COD value, oil content, and turbidity, as well as the calculation of their respective removal rates, refer to the relevant content of the experiments in Part 1 of the performance test.

[0105] The experimental results are shown in the following table:

[0106] Table 6 Performance test results of magnetic biochar composite material under different adsorption treatment times in Example 1

[0107] Adsorption treatment time / min COD removal rate / % Oil removal rate / % Turbidity removal rate / % 20 55.09 40.41 59.78 40 66.51 55.84 73.94 60 68.19 57.41 77.01 80 77.87 67.67 89.28 100 79.91 76.72 93.52 120 81.92 87.14 95.14 140 89.75 91.04 94.46 160 88.56 90.95 92.40 180 86.35 88.92 96.70

[0108] Figure 3 This is a line graph of the adsorption effect of the magnetic biochar composite material on oil and suspended matter at different adsorption treatment times in Example 1.

[0109] From Table 6 and Figure 3 It can be seen that as the adsorption treatment time of the magnetic biochar composite material increases, the overall removal efficiency of the COD, oil, and turbidity removal rates in the power transmission and transformation project wastewater shows a gradually increasing trend, especially a rapid increase within 0-120 minutes. This shows that the magnetic biochar composite material of the present invention has a good adsorption effect on oil and suspended matter in the power transmission and transformation project wastewater. As the adsorption treatment reaction proceeds, the large oil droplets in the power transmission and transformation project wastewater gradually decompose into small oil droplets, which are more easily absorbed by the magnetic biochar composite material. The adsorption rate is relatively fast, and the removal rate of pollutants such as oil and suspended matter increases relatively quickly. In addition, as the adsorption treatment reaction continues, the amount of pollutants such as oil and suspended matter is significantly reduced, and the content of pollutants such as residual oil and suspended matter is not much. At the same time, the adsorbed oil and grease will partially desorb, resulting in a slow increase in the subsequent removal rate.

[0110] 5. The magnetic biochar composite material prepared in Example 1 was subjected to a recycling and reuse experiment. Specifically:

[0111] (1) 0.4 g of the magnetic biochar composite material prepared in Example 1 was added to 100 mL of power transmission and transformation project wastewater containing oil and suspended matter, and adsorption treatment was carried out at 30°C for 120 min to obtain the power transmission and transformation project wastewater after adsorption treatment; the COD value, oil content and turbidity of the power transmission and transformation project wastewater before and after adsorption treatment were tested, and the removal rates of COD, oil and turbidity were calculated respectively;

[0112] The suspended solids content in the wastewater from power transmission and transformation projects is approximately 5000 mg / L. The test methods for COD value, oil content, and turbidity, as well as the calculation of their respective removal rates, refer to the relevant content of the experiments in Part 1 of the performance test.

[0113] (2) After conducting the experiment in part (1), the magnetic biochar composite material in the power transmission and transformation project wastewater was recovered by using a magnet and subjected to desorption treatment to obtain the first recovered magnetic biochar composite material, and the experiment in part (1) was conducted again;

[0114] (3) Repeat the experiment in part (2);

[0115] The experimental results are shown in the following table:

[0116] Table 7 Performance test results of repeated use of magnetic biochar composite materials in Example 1

[0117]

[0118] In the table, the performance test results of “the first time” refer to the performance test results obtained by performing the experiment of part (1) on the magnetic biochar composite material prepared in Example 1, i.e., the first use of the magnetic biochar composite material;

[0119] The performance test results of the “second time” refer to the performance test results obtained by performing the experiments (1)-(2) on the magnetic biochar composite material prepared in Example 1, i.e., the magnetic biochar composite material was recycled for the first time;

[0120] The performance test results of the “third time” refer to the performance test results obtained by performing the experiments of parts (1) to (3) on the magnetic biochar composite material prepared in Example 1, that is, the magnetic biochar composite material was recycled for the second time.

[0121] Figure 4 This is a statistical chart of the adsorption effect of the magnetic biochar composite material on oil and suspended matter at different times of use in Example 1.

[0122] From Table 7 and Figure 4It can be seen that after the second recycling of the magnetic biochar composite material, its removal rate of COD, oil and turbidity in the power transmission and transformation project wastewater can still reach more than 80% of the initial use of the magnetic biochar composite material, and the power transmission and transformation project wastewater still meets the discharge standards.

[0123] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a magnetic biochar composite material, characterized in that: The steps include: S1. Treating diatomaceous earth with alkali to obtain alkali-leached diatomaceous earth; S2. mixing biochar, alkali-leached diatomaceous earth, ferrous salt, ferric salt, and phosphoric acid, and heating the mixture to react to obtain a biochar composite material; S3. Pyrolyzing the biochar composite material to obtain a magnetic biochar composite material; Wherein, in step S2, the ratio of the biochar, alkali-leached diatomaceous earth, ferrous salt, ferric salt and phosphoric acid is (5-10) g: (3.0-3.5) g: (1.5-2) mol: (1.5-2) mol: (1.5-2) mol; In step S2, the method for preparing biochar is: pyrolyzing a biocalcium carbonate material to obtain biochar; the biocalcium carbonate material is crab shell and / or shrimp shell.

2. The method for preparing the magnetic biochar composite material according to claim 1, wherein: In step S3, the temperature of the pyrolysis treatment is 200-400°C.

3. The method for preparing the magnetic biochar composite material according to claim 2, wherein: In step S3, the temperature of the pyrolysis treatment is 250-350°C.

4. The method for preparing the magnetic biochar composite material according to claim 1, wherein: The step S1 specifically comprises: soaking diatomaceous earth with alkali and stirring to obtain alkali-soaked diatomaceous earth.

5. The method for preparing the magnetic biochar composite material according to claim 1, wherein: In the biochar preparation method, the temperature of the pyrolysis treatment is 450-600° C. and the time is 2-3 hours.

6. The method for preparing the magnetic biochar composite material according to claim 1, wherein: At least one of the following (1)-(4): (1) In step S1, the base is at least one of NaOH, KOH, and ammonia water; (2) In step S2, the ferrous salt is at least one of ferrous sulfate, ferrous chloride, ferrous nitrate, and ferrous hydroxide; (3) In step S2, the iron salt is at least one of ferric sulfate, ferric chloride, ferric nitrate, and ferric hydroxide; (4) In step S2, after mixing the biochar, alkali-leached diatomaceous earth, ferrous salt, ferric salt and phosphoric acid, the pH of the system is adjusted to 5-9 with alkali.

7. A magnetic biochar composite material, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the magnetic biochar composite material according to claim 7 in wastewater treatment.

9. A wastewater treatment method, characterized in that: include: The magnetic biochar composite material according to claim 7 is added to the wastewater for adsorption treatment.

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