Magnesium modified straw biochar, and preparation method and application thereof

Abstract

The application discloses magnesium modified straw biochar as well as a preparation method and application thereof, and belongs to the technical field of bio-adsorption materials. The preparation method of the magnesium modified straw biochar comprises the following steps: after straw is immersed in a magnesium salt solution (the concentration of the magnesium salt solution is 0.05-0.5 mol / L) and carbonized, the magnesium modified straw biochar is obtained. The magnesium modified straw biochar prepared by the application has a high specific surface area and rich surface functional groups, can effectively adsorb phosphorus in sewage, and realizes effective removal of phosphorus in eutrophic water bodies.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of biosorption material preparation, in particular to a magnesium modified straw biochar and a preparation method and application thereof. BACKGROUND

[0002] Phosphorus can cause damage to aquatic ecosystems, leading to eutrophication, and excess phosphorus can cause algal blooms, consuming a large amount of oxygen during the decomposition process. In addition, water eutrophication can lead to an increase in blood phosphorus levels in humans, affecting calcium absorption and leading to diseases such as osteoporosis. Water quality deterioration caused by eutrophication has also affected the development of fisheries, agriculture and tourism. The removal of phosphorus from wastewater can be achieved by chemical precipitation, biological treatment, ion exchange, adsorption or a combination of ion exchange and adsorption. Chemical phosphorus removal usually uses iron and aluminum coagulants or calcium hydroxide for treatment, and the resulting solid residues are removed by gravity settling or filtration. Although the precipitate obtained by this method is rich in P, the P is difficult to separate due to chemical bonding, and the effective recovery of P is difficult, limiting the further use of P. Compared with other methods, adsorption is considered to be a simple, efficient, quick and low-cost treatment technology.

[0003] Biochar is an excellent environmental adsorbent, widely available, simple to prepare and structurally stable. Due to its good microporous structure, large specific surface area, high charge density and ion exchange capacity, and its ability to release a large amount of carbon source, it can effectively adsorb organic pollutants, heavy metals and nitrogen and phosphorus in water, and the biochar treated wastewater can be further recycled and added to the soil to provide nutrients and carbon sources, making it an excellent soil conditioner. However, the preparation cost of activated carbon with high adsorption performance is high, and the specific surface area of ordinary biochar on the market is small, and its adsorption capacity for P in wastewater is not ideal. SUMMARY

[0004] The purpose of the present application is to provide a magnesium modified straw biochar and a preparation method and application thereof to solve the problems existing in the prior art. The magnesium modified straw biochar of the present application can effectively adsorb PO4 3- exhibits high adsorption efficiency, and the preparation process is simple, the raw materials are inexpensive, and the preparation cost is low, which can well meet the needs of industrial production and use.

[0005] To achieve the above-mentioned purpose, the present application provides the following solutions:

[0006] One of the technical solutions of the present application is a preparation method of a magnesium modified straw biochar, comprising the following steps:

[0007] immersing the straw in a magnesium salt solution and then carbonizing, crushing and passing through a 20-100 mesh sieve to obtain the magnesium modified straw biochar;

[0008] The concentration of the magnesium salt solution is 0.05-0.5 mol / L.

[0009] Further, the straw includes sunflower straw.

[0010] Further, the mass / volume ratio of the straw and the magnesium salt solution is 50-100 g:1 L.

[0011] Further, the impregnation is stirring impregnation; the stirring impregnation has a rotation speed of 400-800 rpm and a time of 12 h.

[0012] Further, the carbonization has a temperature rising rate of 10℃ / min, a temperature of 500-900℃, and a time of 1-2 h.

[0013] Further, the carbonization is carried out under a nitrogen protective atmosphere, and the nitrogen has a flow rate of 0.3-1 L / min.

[0014] The second technical solution of the present application is a magnesium modified straw biochar prepared by the above preparation method.

[0015] The third technical solution of the present application is an application of the above magnesium modified straw biochar to the adsorption and removal of phosphorus in eutrophic water.

[0016] The present application discloses the following technical effects:

[0017] (1) The magnesium modified straw biochar adsorption material prepared by the present application has a good pore structure, and a large amount of magnesium oxide, an oxidation affinity functional group, exists on the surface, and has excellent adsorption capacity for phosphorus.

[0018] (2) The preparation process of the present application is simple, the raw materials are cheap and easy to obtain, and the preparation cost is low, which can meet the needs of industrial production and use.

[0019] (3) The present application uses agricultural waste sunflower straw as raw material to prepare Mg modified straw biochar as adsorbent, which provides an effective way for the resource utilization of a large amount of agricultural waste, and has significant economic and environmental benefits. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0021] Figure 1 SEM image of the original biochar prepared in Comparative Example 2 of the present application;

[0022] Figure 2 SEM image of the magnesium-modified straw biochar prepared in Example 1 of the present application;

[0023] Figure 3 EDS spectrum of the original biochar prepared in Comparative Example 2 of the present application;

[0024] Figure 4 EDS spectrum of the magnesium-modified straw biochar prepared in Example 1 of the present application;

[0025] Figure 5 Phosphorus adsorption performance of different original biochars prepared in Comparative Example 3, Comparative Examples 6 to 8 of the present application;

[0026] Figure 6 Phosphorus adsorption performance of the original biochars prepared in Comparative Examples 2 to 5 of the present application and the magnesium-modified straw biochars prepared in Example 1, Examples 6 to 8 of the present application;

[0027] Figure 7 Phosphorus adsorption performance of the straw biochar prepared in Comparative Example 1 of the present application and the magnesium-modified straw biochars prepared in Examples 1 to 5 of the present application;

[0028] Figure 8 Isotherm adsorption line of phosphorus by the magnesium-modified straw biochar prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0029] Various illustrative embodiments of the present application are described in detail herein below with reference to the attached drawings. These embodiments are listed by way of example only, and should not be construed as limiting the present application. It should be understood that the detailed description and specific examples, while indicating certain embodiments of the application, are intended for the purposes of illustration only and are not intended to limit the scope of the application.

[0030] It should be understood that the terms used herein are merely for the purpose of describing particular embodiments and are not intended to limit the present application. In addition, for numerical ranges recited in the present application, it should be understood that every intervening value, between the upper and lower limits, is also specifically disclosed. Each smaller range that falls between the upper and lower limits is also specifically disclosed. The upper and lower limits of these smaller ranges can independently be included or excluded in the range.

[0031] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, the preferred methods and materials are described. All patents, patent applications, publications, and descriptions mentioned herein are incorporated by reference for the disclosure and

[0032] Many modifications and variations of the present application described in the specification are possible without departing from the scope or spirit of the application. Other implementations of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. The specification and examples given are exemplary only.

[0033] As used herein, the terms "comprises", "comprising", "includes", "including", "has", "having", "contains", "containing", or variations thereof, are intended to be open-ended terms that mean inclusion, but not limited to, the listed material or list of materials.

[0034] Example 1

[0035] A method for preparing a magnesium-modified straw biochar:

[0036] (1) Pretreatment: The sunflower straw was washed and naturally dried, ground into powder, and washed with deionized water for 10 times. The pretreated sunflower straw powder was obtained by drying at 80°C.

[0037] (2) Impregnation: 10 g of the pretreated sunflower straw powder was added with 200 mL of Mg(NO3)2 solution with a concentration of 0.2 mol / L. After mixing, the slurry was placed on a magnetic stirrer and stirred at a speed of 700 rpm for 12 h. Then the slurry was dried in a forced air drying oven at 80°C for 24 h to obtain the impregnated sunflower straw powder.

[0038] (3) Carbonization: The impregnated sunflower straw powder was placed in a tube furnace and heated to 700°C at a heating rate of 10°C / min. High-purity nitrogen was used as the protective gas with a flow rate of 0.3 L / min. After carbonization for 2 h, the sample was naturally cooled to room temperature and then removed. After crushing and passing through a 20-mesh sieve, the magnesium-modified straw biochar was obtained.

[0039] Example 2

[0040] The same as Example 1, except that the concentration of the Mg(NO3)2 solution in step (2) was 0.05 mol / L.

[0041] Example 3

[0042] The same as Example 1, except that the concentration of the Mg(NO3)2 solution in step (2) was 0.1 mol / L.

[0043] Example 4

[0044] The same as Example 1, except that the concentration of the Mg(NO3)2 solution in step (2) was 0.4 mol / L.

[0045] Example 5

[0046] The same as example 1, except that the concentration of Mg(NO3)2 solution in step (2) is 0.5 mol / L.

[0047] Comparative example 1

[0048] The same as example 1, except that the Mg(NO3)2 solution in step (2) is replaced by water (i.e. the concentration of Mg(NO3)2 solution is 0 mol / L), to obtain straw biochar.

[0049] Example 6

[0050] The same as example 3, except that the carbonization temperature in step (3) is 500℃.

[0051] Example 7

[0052] The same as example 3, except that the carbonization temperature in step (3) is 600℃.

[0053] Example 8

[0054] The same as example 3, except that the carbonization temperature in step (3) is 900℃.

[0055] Comparative example 2

[0056] Preparation of raw biochar (SB):

[0057] (1) Pretreatment: The sunflower straw was washed and naturally dried, ground into powder, washed with deionized water for 10 times, and dried at 80℃ to obtain pretreated sunflower straw powder.

[0058] (2) Carbonization: The pretreated sunflower straw powder was placed in a tube furnace, and the temperature was raised to 700℃ at a rate of 10℃ / min, carbonized for 2h, with high-purity nitrogen as protective gas, nitrogen flow rate was 0.3L / min, after carbonization, it was naturally cooled to room temperature, then taken out, crushed and passed through a 20 mesh sieve to obtain raw biochar.

[0059] Comparative example 3

[0060] The same as comparative example 2, except that the carbonization temperature is 500℃.

[0061] Comparative example 4

[0062] The same as comparative example 2, except that the carbonization temperature is 600℃.

[0063] Comparative example 5

[0064] The same as comparative example 2, except that the carbonization temperature is 900℃.

[0065] Comparative example 6

[0066] The same as Comparative Example 3, except that the sunflower straw is replaced by corn straw.

[0067] Comparative Example 7

[0068] The same as Comparative Example 3, except that the sunflower straw is replaced by wheat straw.

[0069] Comparative Example 8

[0070] The same as Comparative Example 3, except that the sunflower straw is replaced by rice straw.

[0071] Effect Example 1

[0072] A high-resolution field emission scanning electron microscope (SEM) (SUB8020) was used to observe the morphology changes of the original biochar prepared in Comparative Example 2 and the magnesium modified straw biochar prepared in Example 1, and the changes in the surface element content were characterized by energy spectrum.

[0073] Figure 1 is the image of the original biochar (SB) observed by scanning electron microscope at 2000 times magnification; Figure 2 is the image of the magnesium modified straw biochar (0.2MSB) prepared by modifying the magnesium nitrate solution with a concentration of 0.2 mol / L in Example 1 at 2000 times magnification; Figure 3 is the energy spectrum of the original biochar (SB) (main element content); Figure 4 is the energy spectrum of the magnesium modified straw biochar (main element content).

[0074] As can be seen from Figure 1 , the surface of the original biochar is relatively smooth; Figure 2 The magnesium modified straw biochar prepared in Example 1 shown in Figures 3-4 It can be seen that the porous structure covering the surface of the biochar is fluffy magnesium compound, and the magnesium element content on the surface of the magnesium modified straw biochar prepared in Example 1 is significantly improved.

[0075] Effect Example 2

[0076] The adsorption experiment was used to determine the adsorption capacity of different straw biochars for phosphorus, and the specific method was as follows:

[0077] 0.5 g of the original biochar prepared in Comparative Example 3, Comparative Example 6-8 was weighed into a 50 mL conical flask, 30 mL of domestic sewage (TP of domestic sewage = 3.53 mg / L) was added, and after mixing, it was oscillated at 150 rpm and 25°C for 2 h. Sampling, using ammonium molybdate spectrophotometry to determine the TP of the water sample, the results are shown in Figure 5 .

[0078] As can be seen from Figure 5As can be seen from the data, the sunflower straw biochar obtained at a preparation temperature of 500℃ has the best removal effect on TP.

[0079] Example 3

[0080] The adsorption capacity of magnesium-modified straw biochar prepared at different temperatures for phosphorus was determined by adsorption experiments. The specific methods are as follows:

[0081] Weigh 0.1 g of the raw biochar (SB) prepared in Comparative Examples 2-5, and the magnesium-modified straw biochar (MSB) prepared in Examples 3 and 6-8 into 50 mL Erlenmeyer flasks. Add 30 mL of domestic sewage (TP = 6.98 mg / L) to each flask, mix, and shake at 150 rpm and 25 °C for 15 min. Take samples, and determine the TP of the water samples using the ammonium molybdate spectrophotometric method. The results are shown in the figure. Figure 6 .

[0082] from Figure 6 It can be seen that when the preparation temperature is 700℃, the magnesium-modified straw biochar has the best phosphorus removal effect, and the magnesium-modified straw biochar prepared at different temperatures has a significantly better TP removal effect than the original biochar.

[0083] Example of effect 4

[0084] The adsorption capacity of magnesium-modified straw biochar obtained by impregnation with magnesium nitrate solutions of different concentrations for phosphorus was determined by the following method:

[0085] Weigh 0.1 g of the magnesium-modified straw biochar prepared in Examples 1-5 and the straw biochar prepared in Comparative Example 1 into 50 mL Erlenmeyer flasks, respectively. Add 30 mL of domestic sewage (TP = 6.98 mg / L) to each flask, mix, and shake at 150 rpm and 25 °C for 15 min. Take samples, and determine the TP of the water samples using the ammonium molybdate spectrophotometric method. The results are shown in the figure. Figure 7 .

[0086] from Figure 7 It can be seen that when the concentration of the modifier (magnesium nitrate solution) is 0.2, 0.4, and 0.5 mol / L, the magnesium-modified straw biochar has the best phosphorus removal effect, reaching 99%.

[0087] Example 5

[0088] The maximum phosphorus adsorption capacity of magnesium-modified straw biochar was determined using the following method:

[0089] PO4 3-The initial concentration of P solution was set to 5, 10, 20, 30, 50, 100, 200, 300, 400, 600, 800, 1000 mg / L, respectively. 0.1 g of the magnesium modified straw biochar (0.2MSB) prepared in Example 1 was weighed in a 50 mL conical flask, and 30 mL of the above P solution was added, respectively. After mixing, the mixture was shaken at 150 rpm and 25℃ for 2 h. After filtration through a 0.45 μm filter membrane, the concentration of P in the filtrate was determined by the ammonium molybdate spectrophotometric method. 3- The initial concentration of P solution was set to 5, 10, 20, 30, 50, 100, 200, 300, 400, 600, 800, 1000 mg / L, respectively. 0.1 g of the magnesium modified straw biochar (0.2MSB) prepared in Example 1 was weighed in a 50 mL conical flask, and 30 mL of the above P solution was added, respectively. After mixing, the mixture was shaken at 150 rpm and 25℃ for 2 h. After filtration through a 0.45 μm filter membrane, the concentration of P in the filtrate was determined by the ammonium molybdate spectrophotometric method. 3 The initial concentration of P solution was set to 5, 10, 20, 30, 50, 100, 200, 300, 400, 600, 800, 1000 mg / L, respectively. 0.1 g of the magnesium modified straw biochar (0.2MSB) prepared in Example 1 was weighed in a 50 mL conical flask, and 30 mL of the above P solution was added, respectively. After mixing, the mixture was shaken at 150 rpm and 25℃ for 2 h. After filtration through a 0.45 μm filter membrane, the concentration of P in the filtrate was determined by the ammonium molybdate spectrophotometric method. Figure 8 .

[0090] As can be seen from Figure 8 , with the increase of P concentration in the solution, the adsorption capacity of 0.2MSB also gradually increased. When the equilibrium concentration was 0-100 mg / L, the adsorption capacity of 0.2MSB increased rapidly; when the equilibrium concentration was 100-600 mg / L, the adsorption capacity increased slowly, and finally tended to be balanced. The adsorption data was fitted by Langmuir equation, and the R 2 was 0.9706; at the same time, the adsorption data was fitted by Freundlich equation, and the R 2 was 0.9623. It showed that the Langmuir model could better describe the adsorption of P by magnesium modified straw biochar, and the adsorption process was approximately monolayer adsorption. The theoretical maximum adsorption capacity calculated by the Langmuir equation was as high as 179.8 mg / g.

[0091] Effect Example 6

[0092] The specific surface area of the biochar prepared in Comparative Examples 2-8 and Example 1 was determined by using a full-automatic specific surface area analyzer (TriStar II 3020), and the results are shown in Table 1.

[0093] Table 1 Specific surface area of biochar

[0094] Grouping Specific surface area (m 2 / g) Comparative Example 2 194.1311 Comparative Example 3 4.1031 Comparative Example 4 176.9036 Comparative Example 5 193.8779 Comparative Example 6 0.4915 Comparative Example 7 2.0182 Comparative Example 8 18.1837 Example 1 267.9633

[0095] As can be seen from Table 1, the specific surface area of the biochar modified by magnesium nitrate was greatly improved compared with the original biochar, and had obvious advantages compared with other types of biochar.

[0096] The above-described examples only describe the preferred modes of the present application, and do not limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements to the technical solutions of the present application made by those skilled in the art shall fall within the protection scope determined by the claims of the present application.

Claims

1. Application of magnesium modified straw biochar in adsorbing and removing phosphorus in eutrophic water, characterized in that, the adsorption step is as follows: 0.1 g of magnesium modified straw biochar is weighed in a 50 mL conical flask, 30 mL of domestic sewage with TP = 6.98 mg / L is added, and after mixing, it is oscillated at 150 rpm and 25°C for 15 min; the preparation method of the magnesium modified straw biochar is as follows: (1) Pretreatment: The sunflower straw is washed and naturally dried, ground into powder, washed with deionized water for 10 times, and dried at 80°C to obtain pretreated sunflower straw powder; (2) Immersion: 10 g of pretreated sunflower straw powder is added to 200 mL of Mg(NO3)2 solution with a concentration of 0.2 mol / L, mixed, and then placed on a magnetic stirrer for stirring at a speed of 700 rpm for 12 h, and then the slurry is dried in a forced air drying oven at 80°C for 24 h to obtain immersed sunflower straw powder; (3) Carbonization: The immersed sunflower straw powder is placed in a tube furnace, heated to 700°C at a heating rate of 10°C / min, carbonized for 2 h, and high-purity nitrogen is used as the protective gas with a flow rate of 0.3 L / min. After carbonization, it is naturally cooled to room temperature, taken out, crushed, and sieved through a 20-mesh sieve to obtain magnesium modified straw biochar.

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