Magnesium modified crab shell biochar as well as preparation method and application thereof

Abstract

The invention provides magnesium modified crab shell biochar as well as a preparation method and application thereof, and the preparation method comprises the following steps: A) sequentially carrying out water washing, drying, crushing, sieving, acid leaching, washing and drying on crab shells to obtain crab shell powder; b) mixing the crab shell powder, magnesium salt and water, heating and stirring, and performing solid-liquid separation to obtain an intermediate product; c) roasting the intermediate product in a protective atmosphere to obtain a roasted product; and D) mixing the roasted product, alkali and water, and carrying out a heating reaction to obtain the magnesium modified crab shell biochar. The modified crab shell biochar in the invention meets the dual requirements of physical and chemical adsorption; and in cooperation with magnesium salt modification, the developed material has certain adsorption capacity on nitrogen and phosphorus, and the adsorbed material can also be used for a slow-release fertilizer after being treated. The biochar material disclosed by the invention is excellent in adsorption efficiency, and particularly, the biochar material still keeps relatively high adsorption capacity under high-acidity and high-alkalinity conditions.

Description

Technical Field

[0001] The present invention belongs to the technical field of adsorption materials, and in particular relates to magnesium-modified crab shell biochar, a preparation method and application thereof. Background Art

[0002] Phosphorus, a vital natural resource, plays a key role in industrial and agricultural production. However, excessive phosphorus discharge into water bodies can pose a range of hazards, including eutrophication, agricultural soil contamination, human health impacts, increased water treatment costs, and environmental risks. Phosphorus removal from wastewater can be achieved through chemical precipitation, biological treatment, ion exchange, adsorption, or a combination of ion exchange and adsorption. Adsorption is particularly effective, and biochar is readily available and inexpensive, making it a popular choice.

[0003] Biochar is a product obtained by heating biomass raw materials from 300°C to 1000°C in an oxygen-deficient or oxygen-free environment and then calcining them for a specified period of time. Commonly used biochar materials include straw biochar (corn straw, corn cob, and reed), shell biochar (peanut and walnut shells), wood biochar (bamboo and pine wood), and manure biochar (cow dung and sludge). Biochar produced from biomass materials has a large surface area and abundant pores. While effectively removing phosphorus from phosphorus-containing wastewater, it also enables the secondary utilization of various crop wastes and other solid wastes. Its high efficiency and economical nature make it a current research hotspot. However, the production of biomass materials such as straw is seasonal, the production of wood biomass is relatively low, and shell and manure biomass require pretreatment. This results in limited biochar usage and increased treatment costs when used for wastewater treatment. In addition, biochar is not ideal for adsorbing phosphorus because it is negatively charged. At the same time, the adsorption performance of biochar is limited by many factors. A large amount of biochar is required for sewage treatment to meet the treatment requirements. Therefore, it is necessary to select a suitable modifier to improve the adsorption capacity of biochar. When a small amount of modified biochar material is added, a better effluent effect can be achieved and the treatment cost can be reduced. Summary of the Invention

[0004] The purpose of the present invention is to provide a magnesium-modified crab shell biochar, a preparation method and application thereof. The magnesium-modified crab shell biochar in the present invention has excellent adsorption efficiency for phosphorus in sewage, especially maintaining a high phosphorus adsorption capacity under highly acidic and highly alkaline conditions.

[0005] The present invention provides a method for preparing magnesium-modified crab shell biochar, comprising the following steps:

[0006] A) washing, primary drying, crushing, sieving, acid leaching, washing and secondary drying the crab shells in sequence to obtain crab shell powder;

[0007] B) mixing the crab shell powder, magnesium salt and water, heating and stirring, and obtaining an intermediate product after solid-liquid separation;

[0008] C) calcining the intermediate product under a protective atmosphere to obtain a calcined product;

[0009] D) mixing the roasted product, alkali and water, and heating the mixture for reaction to obtain magnesium-modified crab shell biochar.

[0010] Preferably, in step A), hydrochloric acid is used for acid leaching, the concentration of the hydrochloric acid is 0.1 to 1 mol / L, and the time of the acid leaching is 30 to 60 minutes.

[0011] Preferably, in step A), the crab shells are crushed and sieved to a mesh size of 60 to 90.

[0012] Preferably, the step B) is specifically:

[0013] The crab shell powder and the magnesium salt solution are mixed, heated and stirred, and solid-liquid separation is performed to obtain an intermediate product;

[0014] The concentration of the magnesium salt solution is 0.04-0.4 mol / L, and the solid-liquid ratio of the crab shell powder to the magnesium salt solution is 1 g: (15-25) mL.

[0015] Preferably, the heating temperature in step B) is 60-100° C., and the heating and stirring time is 2-4 hours.

[0016] Preferably, the calcination temperature in step C) is 400-800° C. and the calcination time is 2-3 hours;

[0017] The protective atmosphere includes argon and / or nitrogen.

[0018] Preferably, in the step D), the roasted product is mixed with an alkaline solution and heated to react to obtain magnesium-modified crab shell biochar;

[0019] The alkaline solution is a sodium hydroxide solution, and the concentration of the alkaline solution is 0.1-1 mol / L.

[0020] Preferably, the temperature of the heating reaction in step D) is 55-85° C., and the heating reaction time is 0.5-2 h.

[0021] The present invention provides a magnesium-modified crab shell biochar, which is prepared according to the preparation method described above.

[0022] The application provides application of the magnesium modified crab shell biochar as described above in adsorbing phosphorus-containing substances in a water body.

[0023] The pH value of the water body is 2-9.

[0024] The application provides a preparation method of magnesium modified crab shell biochar, which comprises the following steps: A) sequentially performing water washing, drying, crushing, sieving, acid immersion, washing and drying on crab shells to obtain crab shell powder; B) mixing the crab shell powder, a magnesium salt and water, heating and stirring, and performing solid-liquid separation to obtain an intermediate product; C) performing calcination on the intermediate product in a protective atmosphere to obtain a calcination product; and D) mixing the calcination product, an alkali and water, heating and reacting to obtain the magnesium modified crab shell biochar. In the application, the porosity of the crab shell pretreated through acid immersion is increased, the surface is rougher, the specific surface area is larger, and the physical adsorption performance of the biochar material is improved; after the carbonized material is treated with an alkali, hydroxyl groups, carboxyl groups and other oxygen-containing functional groups are loaded on the biochar material, which is beneficial to the complexation, ion bridge bonding and other effects of the biochar and phosphate, and can effectively improve the adsorption capacity of the biochar for phosphate, so that the modified crab shell biochar meets the dual requirements of physical and chemical adsorption; in combination with the modification of the magnesium salt, the developed material has a certain adsorption capacity for nitrogen and phosphorus, and the material after adsorption can be used for slow-release fertilizer. The biochar material in the application has excellent adsorption efficiency, especially under high-acidity and high-alkalinity conditions. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only the embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of the provided drawings.

[0026] Figure 1 is a SEM image of untreated crab shell, the crab shell biochar has a grid structure and many impurities;

[0027] Figure 2 is a SEM image of crab shell treated with hydrochloric acid, the surface impurities are removed and the grid structure is damaged;

[0028] Figure 3 is a SEM image of crab shell treated with magnesium chloride, the crab shell has a clear fiber network and a smooth gap structure;

[0029] Figure 4 is a SEM image of crab shell treated with magnesium chloride and then treated with sodium hydroxide, the magnesium salt reacts with the functional groups on the surface of the crab shell biochar to form new adsorption sites. DETAILED DESCRIPTION

[0030] The present invention provides a method for preparing magnesium-modified crab shell biochar, comprising the following steps:

[0031] A) washing, drying, crushing, sieving, acid-leaching, washing and drying the crab shells in sequence to obtain crab shell powder;

[0032] B) mixing the crab shell powder, magnesium salt and water, heating and stirring, and obtaining an intermediate product after solid-liquid separation;

[0033] C) calcining the intermediate product under a protective atmosphere to obtain a calcined product;

[0034] D) mixing the roasted product, alkali and water, and heating the mixture for reaction to obtain magnesium-modified crab shell biochar.

[0035] Compared with other biochar materials, the crab shell biochar material used in the present invention contains a special chitin structure with a high specific surface area, rich functional groups, and a special pore structure, which produces an efficient synergistic effect when combined with magnesium salts, so that the modified crab shell biochar maintains high adsorption performance in a wider range of pH values ​​and ionic strengths, and can achieve selective adsorption of specific pollutants.

[0036] In the present invention, washing the crab shells with water is a conventional operation in the art, and the present invention will not go into details here.

[0037] In the present invention, the primary drying temperature is preferably 60 to 80° C., more preferably 65 to 75° C., and the primary drying time is preferably 10 to 20 hours, more preferably 12 to 18 hours.

[0038] In the present invention, the washed crab shells are crushed and sieved to a mesh size of preferably 60 to 90 meshes, more preferably 70 to 80 meshes.

[0039] In the present invention, the sieved crab shells are preferably acid-leached using a hydrochloric acid solution, and the concentration of the hydrochloric acid solution is preferably 0.1-1 mol / L, more preferably 0.3-0.8 mol / L, such as 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, preferably a range value with any of the above values ​​as the upper or lower limit; the acid leaching time is preferably 30-60 min, more preferably 40-50 min, and the acid leaching is preferably carried out at room temperature, such as 25-35°C.

[0040] After the acid leaching is completed, the acid-leached crab shells are washed and dried for a second time. The washing is preferably water washing. The temperature of the second drying is preferably 60-80°C, more preferably 65-75°C. The time of the first drying is preferably 10-20 hours, more preferably 12-18 hours.

[0041] After obtaining the crab shell powder, the present invention uses magnesium salt to modify the crab shell powder. Specifically, the crab shell powder is mixed with a magnesium salt solution, heated and stirred, and then subjected to solid-liquid separation, washing, drying, grinding and screening to obtain an intermediate product.

[0042] In the present invention, the magnesium salt is preferably an inorganic salt of magnesium, more preferably one or more of magnesium sulfate, magnesium halide and magnesium nitrate. Specifically, in an embodiment of the present invention, magnesium chloride can be used; the concentration of the magnesium salt solution is preferably 0.04 to 0.4 mol / L, more preferably 0.1 to 0.3 mol / L, such as 0.04 mol / L, 0.05 mol / L, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L , 0.4 mol / L, preferably a range value with any of the above numerical values ​​as the upper or lower limit; the solid-liquid ratio of the crab shell powder to the magnesium salt solution is preferably 1g: (15-25) mL, more preferably 1g: (18-22) mL, such as 1g: 15mL, 1g: 16mL, 1g: 17mL, 1g: 18mL, 1g: 19mL, 1g: 20mL, 1g: 21mL, 1g: 22mL, 1g: 23mL, 1g: 24mL, 1g: 25mL, preferably a range value with any of the above numerical values ​​as the upper or lower limit.

[0043] In the present invention, after the crab shell powder is mixed with the magnesium salt solution, the heating temperature is preferably 60-100°C, more preferably 70-90°C, such as 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, preferably a range value with any of the above values ​​as the upper or lower limit; the heating time is preferably 2-4 hours, more preferably 3-4 hours; the heating process is accompanied by stirring, and the stirring speed is preferably 400-800 rpm, more preferably 500-700 rpm.

[0044] After the modification of the magnesium salt is completed, the heated modified mixture is subjected to solid-liquid separation, and the obtained solid is washed with water 5 to 8 times, dried, ground and sieved to obtain an intermediate product. The drying temperature is preferably 45 to 65° C., more preferably 50 to 55° C., and the mesh size of the grinding and sieving is preferably 120 to 200 meshes.

[0045] After obtaining the intermediate product, the present invention roasts the intermediate product under a protective atmosphere to obtain a roasted product.

[0046] In the present invention, the protective atmosphere preferably includes argon and / or nitrogen; the calcination temperature is preferably 400-800°C, more preferably 500-700°C, such as 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, preferably a range value with any of the above values ​​as the upper or lower limit; the calcination time is preferably 2-3 hours, and the calcination heating rate is preferably 3-8°C / min, more preferably 5-6°C / min.

[0047] After obtaining the roasted product, the present invention mixes the roasted product with an alkaline solution, heats and stirs, and reacts. After the reaction is completed, the solid and liquid are separated, and the product is dried to obtain magnesium-modified crab shell biochar.

[0048] In the present invention, the alkaline solution is preferably a sodium hydroxide solution, and the concentration of the alkaline solution is preferably 0.1 to 1 mol / L, more preferably 0.3 to 0.8 mol / L, such as 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, preferably any of the above values ​​as the upper or lower limit The ratio of the mass of the calcined product to the volume of the alkaline solution is preferably 1g: (10-20)mL, more preferably 1g: (12-18)mL, such as 1g: 10mL, 1g: 11mL, 1g: 12mL, 1g: 13mL, 1g: 14mL, 1g: 15mL, 1g: 16mL, 1g: 17mL, 1g: 18mL, 1g: 19mL, 1g: 20mL, preferably with any of the above values ​​as the upper or lower limit of the range value.

[0049] In the present invention, the heating temperature is preferably 55-85°C, more preferably 60-80°C, such as 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, preferably a range value with any of the above values ​​as the upper or lower limit; the heating time is preferably 0.5-2h, more preferably 1-1.5h.

[0050] In the present invention, the drying temperature is preferably 45 to 65° C., more preferably 50 to 55° C., and the drying time is preferably 10 to 20 hours, more preferably 12 to 18 hours.

[0051] The present invention provides a magnesium-modified crab shell biochar, which is prepared according to the preparation method described above.

[0052] The present invention also provides an application of the magnesium-modified crab shell biochar described above in adsorbing phosphorus-containing substances in water bodies. The magnesium-modified crab shell biochar in the present invention still maintains a high phosphorus adsorption capacity under highly acidic and highly alkaline conditions, and the pH value in the water body can be extended to 2 to 9.

[0053] The invention provides a preparation method of magnesium-modified crab shell biochar, comprising the following steps: A) sequentially washing, drying, crushing, sieving, acid leaching, washing and drying crab shells to obtain crab shell powder; B) mixing the crab shell powder, magnesium salt and water, heating and stirring, and performing solid-liquid separation to obtain an intermediate product; C) roasting the intermediate product under a protective atmosphere to obtain a roasted product; and D) mixing the roasted product, alkali and water, heating for reaction, and obtaining magnesium-modified crab shell biochar. In the present invention, the porosity of the crab shells pretreated with acid leaching increases, the surface becomes rougher, and the specific surface area is larger, thereby improving the physical adsorption performance of the biochar material. The carbonized material is then treated with alkali to load oxygen-containing functional groups such as hydroxyl and carboxyl groups onto the biochar material, which is beneficial to the complexation and ionic bridging between the biochar and phosphate, effectively improving the adsorption capacity of phosphate, allowing the modified crab shell biochar to meet the dual needs of physical and chemical adsorption. Combined with magnesium salt modification, the developed material has a certain adsorption capacity for both nitrogen and phosphorus. The adsorbed material can also be used as a slow-release fertilizer after treatment. The biochar material of the present invention performs well in adsorption efficiency, especially maintaining a high adsorption capacity under highly acidic and alkaline conditions.

[0054] In order to further illustrate the present invention, the magnesium-modified crab shell biochar provided by the present invention, its preparation method and application are described in detail below in combination with the examples, but it should not be understood as limiting the scope of protection of the present invention.

[0055] The adsorption capacity and adsorption efficiency in the examples and comparative examples were calculated according to the following method:

[0056] Calculation of adsorption capacity

[0057] The calculation method for the adsorption capacity and adsorption efficiency of modified biochar materials for phosphorus in simulated wastewater is as follows:

[0058]

[0059] Where:

[0060] C0——initial concentration of phosphate (mg / L);

[0061] C t ——Residual concentration of phosphate at time t (mg / L);

[0062] V——volume of solution (L);

[0063] m——weight of biochar (g);

[0064] q t ——phosphate adsorption capacity at time t (mg / g);

[0065] R——phosphate removal rate at time t (%).

[0066] Example 1

[0067] (1) Preparation of acid-leached magnesium-modified biochar

[0068] The crab shell material was placed in a beaker, washed with distilled water, and then dried in a vacuum oven at 65°C. The material was then crushed and passed through a 60-mesh sieve. The sieved sample was acid-soaked in 0.5 mol / L hydrochloric acid for 45 minutes, washed, and dried in a vacuum oven at 65°C to obtain biomass powder.

[0069] The obtained biomass powder was mixed with 0.04 mol / LMgCl2 solution (solid-liquid ratio 1 g: 25 mL), placed in a reactor, stirred at a speed of 800 rpm / min, the stirring temperature was 80 ° C, heated for 2 h, filtered, washed with water 6 times, dried in a vacuum drying oven at 65 ° C, ground, and passed through a 120 mesh sieve to obtain an intermediate product.

[0070] The intermediate product was placed in a tube furnace and calcined at 600°C for 2 h in an argon environment at a heating rate of 6°C / min to obtain magnesium-modified biochar.

[0071] (2) Alkali-leached biochar powder

[0072] The magnesium-modified biochar in 1) was mixed with 0.1 mol / L NaOH (solid-liquid ratio 1 g: 15 mL), placed in a reactor, heated and stirred at 85°C and dried at 65°C, and the final product was modified crab shell biochar.

[0073] (3) Application

[0074] The obtained modified crab shell biochar was used to simulate phosphogypsum leachate (total phosphorus: 2000 mg / L, F-: 1000 mg / L, sulfate: 200 mg / L) to adsorb soluble phosphorus with an adsorption efficiency of 95.39%.

[0075] Comparative Example 1

[0076] (1) Preparation of acid-leached magnesium-modified biochar

[0077] The crab shell material was placed in a beaker, washed with distilled water, and then dried in a vacuum oven at 65°C. The material was then crushed and passed through a 60-mesh sieve. The sieved sample was acid-soaked in 0.5 mol / L hydrochloric acid for 45 minutes, washed, and dried in a vacuum oven at 65°C to obtain biomass powder.

[0078] The biomass powder was placed in a tube furnace and calcined at 600°C for 2 h in an argon environment at a heating rate of 6°C / min to obtain magnesium-modified biochar.

[0079] (2) Alkali-leached biochar powder

[0080] The magnesium-modified biochar in 1) was mixed with 0.1 mol / L NaOH (solid-liquid ratio 1 g: 15 mL), placed in a reactor, heated and stirred at 85°C and dried at 65°C, and the final product was modified crab shell biochar.

[0081] (3) Application

[0082] The obtained modified crab shell biochar was used to simulate phosphogypsum leachate (total phosphorus: 2000 mg / L, F-: 1000 mg / L, sulfate: 200 mg / L) to adsorb soluble phosphorus with an adsorption rate of 78.65%.

[0083] Comparative Example 2

[0084] (1) Preparation of acid-leached magnesium-modified biochar

[0085] The crab shell material was placed in a beaker, washed with distilled water, and then dried in a vacuum oven at 65°C. The material was then crushed and passed through a 60-mesh sieve. The sieved sample was acid-soaked in 0.5 mol / L hydrochloric acid for 45 minutes, washed, and dried in a vacuum oven at 65°C to obtain biomass powder.

[0086] The obtained biomass powder was mixed with 0.04 mol / LMgCl2 solution (solid-liquid ratio 1 g: 25 mL), placed in a reactor, stirred at a speed of 800 rpm / min, the stirring temperature was 80 ° C, heated for 2 h, filtered, washed with water 6 times, dried in a vacuum drying oven at 65 ° C, ground, and passed through a 120 mesh sieve to obtain an intermediate product.

[0087] The intermediate product was placed in a tube furnace and calcined at 600°C for 2 h in an argon environment at a heating rate of 6°C / min to obtain magnesium-modified biochar.

[0088] (2) Application

[0089] The obtained magnesium-modified biochar was used to simulate phosphogypsum leachate (total phosphorus: 2000 mg / L, F-: 1000 mg / L, sulfate: 200 mg / L) to adsorb soluble phosphorus with an adsorption rate of 72.98%.

[0090] Comparative Example 3

[0091] (1) Preparation of acid-leached magnesium-modified biochar

[0092] The crab shell material was placed in a beaker, washed with distilled water, and then dried in a vacuum oven at 65°C. The material was then crushed and passed through a 60-mesh sieve. The sieved sample was acid-soaked in 0.5 mol / L hydrochloric acid for 45 minutes, washed, and dried in a vacuum oven at 65°C to obtain biomass powder.

[0093] The biomass powder was placed in a tube furnace and calcined at 600°C for 2 h in an argon environment at a heating rate of 6°C / min to obtain magnesium-modified biochar.

[0094] (2) Application

[0095] The obtained magnesium-modified biochar was used to simulate phosphogypsum leachate (total phosphorus: 2000 mg / L, F-: 1000 mg / L, sulfate: 200 mg / L) to adsorb soluble phosphorus with an adsorption rate of 54.25%.

[0096] in conclusion:

[0097] The test data shows that the crab shell biochar material treated with acid leaching, mixed magnesium salt roasting and mixed alkali heating showed the best adsorption rate. The advantage of this synergistic treatment method is that acid leaching can effectively remove some impurities, creating good conditions for subsequent treatment. Mixed magnesium salt roasting can further adjust the structure and pore distribution of biochar and enhance its adsorption capacity. Mixed alkali heating can promote the transformation of functional groups on the surface of biochar in an alkaline environment and enhance the adsorption affinity for specific pollutants. This three-in-one treatment method can more comprehensively optimize the performance of biochar materials, thereby showing a better adsorption effect, compared with single or combined methods such as only acid leaching and mixed magnesium salt roasting, only acid leaching and mixed alkali heating, and only acid leaching.

[0098] Example 2

[0099] (1) Preparation of acid-leached magnesium-modified biochar

[0100] The crab shell material was placed in a beaker, washed with distilled water, and then dried in a vacuum oven at 65°C. The material was then crushed and passed through a 60-mesh sieve. The sieved sample was acid-soaked in 0.5 mol / L hydrochloric acid for 45 minutes, washed, and dried in a vacuum oven at 65°C to obtain biomass powder.

[0101] The obtained biomass powder was mixed with 0.1 mol / LMgCl2 solution (solid-liquid ratio 1 g: 25 mL), placed in a reactor, stirred at a speed of 800 rpm / min, the stirring temperature was 80 ° C, heated for 2 h, filtered, washed with water 6 times, dried in a vacuum drying oven at 65 ° C, ground, and passed through a 120 mesh sieve to obtain an intermediate product.

[0102] The intermediate product was placed in a tube furnace and calcined at 600°C for 2h under argon atmosphere at a heating rate of 6°C / min to obtain magnesium modified biochar

[0103] (2) Alkaline leaching of biochar powder

[0104] The product in 1) was mixed with 0.1 mol / L NaOH (solid-liquid ratio 1 g: 15 mL), which was placed in a reaction kettle for heating and stirring, the temperature was 85°C, the drying temperature was 65°C, and the final product was modified crab shell biochar.

[0105] (3) Application

[0106] The modified crab shell biochar obtained was used for adsorbing soluble phosphorus in simulated phosphogypsum leachate (total phosphorus: 2000 mg / L, F-: 1000 mg / L, sulfate: 200 mg / L), and the adsorption rate was 96.41%.

[0107] Example 3

[0108] (1) Preparation of magnesium modified biochar by acid leaching

[0109] The crab shell material was placed in a beaker, washed with distilled water, dried in a vacuum drying oven at 65°C, and then crushed and sieved through a 60 mesh sieve. The sieved sample was placed in 0.5 mol / L hydrochloric acid for acid leaching for 45 min, washed, dried in a vacuum drying oven at 65°C, to obtain biomass powder.

[0110] The obtained biomass powder was mixed with 0.3 mol / L MgCl2 solution (solid-liquid ratio 1 g: 25 mL), which was placed in a reaction kettle and stirred at a speed of 800 rpm / min, the stirring temperature was 80°C, heated for 2h, filtered, washed with water for 6 times, dried in a vacuum drying oven at 65°C, ground and sieved through a 120 mesh sieve to obtain an intermediate product.

[0111] The intermediate product was placed in a tube furnace and calcined at 600°C for 2h under argon atmosphere at a heating rate of 6°C / min to obtain magnesium modified biochar.

[0112] (2) Alkaline leaching of biochar powder

[0113] The product in 1) was mixed with 0.1 mol / L NaOH (solid-liquid ratio 1 g: 15 mL), which was placed in a reaction kettle for heating and stirring, the temperature was 85°C, the drying temperature was 65°C, and the final product was modified crab shell biochar.

[0114] (3) Application

[0115] The modified crab shell biochar obtained was used for adsorbing soluble phosphorus in simulated phosphogypsum leachate (total phosphorus: 2000 mg / L, F-: 1000 mg / L, sulfate: 200 mg / L), and the adsorption rate was 97.62%.

[0116] Example 4

[0117] (1) Preparation of acid-leached magnesium-modified biochar

[0118] The crab shell material was placed in a beaker, washed with distilled water, and then dried in a vacuum oven at 65°C. The material was then crushed and passed through a 60-mesh sieve. The sieved sample was acid-soaked in 0.5 mol / L hydrochloric acid for 45 minutes, washed, and dried in a vacuum oven at 65°C to obtain biomass powder.

[0119] The obtained biomass powder was mixed with 0.4 mol / LMgCl2 solution (solid-liquid ratio 1 g: 25 mL), placed in a reactor, stirred at a speed of 800 rpm / min, the stirring temperature was 80 ° C, heated for 2 h, filtered, washed with water 6 times, dried in a vacuum drying oven at 65 ° C, ground, and passed through a 120 mesh sieve to obtain an intermediate product.

[0120] The intermediate product was placed in a tube furnace and calcined at 600°C for 2 hours under an argon environment at a heating rate of 3-8°C / min to obtain magnesium-modified biochar.

[0121] (2) Alkali-leached biochar powder

[0122] The product in 3) was mixed with 0.1 mol / L NaOH (solid-liquid ratio 1 g: 15 mL), placed in a reactor and heated with stirring at 85° C. and a drying temperature of 65° C., and the final product was modified crab shell biochar.

[0123] (3) Application

[0124] The obtained modified crab shell biochar was used to simulate phosphogypsum leachate (total phosphorus: 2000 mg / L, F-: 1000 mg / L, sulfate: 200 mg / L) to adsorb soluble phosphorus with an adsorption rate of 95.32%.

[0125] in conclusion:

[0126] The magnesium in the modifier, loaded onto the biochar material, facilitates complexation and ionic bridging between the biochar and phosphate, thereby improving the biochar's chemical adsorption properties. However, varying MgCl₂ solution concentrations also altered the biochar's adsorption properties. The adsorption efficiency was highest at a 0.mol / L MgCl₂ solution concentration, but it began to decline as the MgCl₂ solution concentration continued to increase. This may be because, after reaching a certain magnesium modification concentration, the adsorption sites on the biochar surface may become saturated. Further increasing the magnesium modification concentration did not significantly improve the adsorption efficiency; instead, the protonation effect may have reduced the adsorption rate.

[0127] Example 5

[0128] (1) Preparation of acid-leached magnesium-modified biochar

[0129] The crab shell material was placed in a beaker, washed with distilled water, and then dried in a vacuum oven at 65°C. The material was then crushed and passed through a 60-mesh sieve. The sieved sample was acid-soaked in 0.5 mol / L hydrochloric acid for 45 minutes, washed, and dried in a vacuum oven at 65°C to obtain biomass powder.

[0130] The obtained biomass powder was mixed with 0.3 mol / LMgCl2 solution (solid-liquid ratio 1 g: 25 mL), placed in a reactor, stirred at a speed of 800 rpm / min, the stirring temperature was 80 ° C, heated for 2 h, filtered, washed with water 6 times, dried in a vacuum drying oven at 65 ° C, ground, and passed through a 120 mesh sieve to obtain an intermediate product.

[0131] The intermediate product was placed in a tube furnace and calcined at 600°C for 2 hours under an argon environment at a heating rate of 3-8°C / min to obtain magnesium-modified biochar.

[0132] (2) Alkali-leached biochar powder

[0133] The product in 1) was mixed with 0.5 mol / L NaOH (solid-liquid ratio 1 g: 15 mL), placed in a reactor and heated with stirring at 85° C. and a drying temperature of 65° C., and the final product was modified crab shell biochar.

[0134] (3) Application

[0135] The obtained modified crab shell biochar was used to simulate phosphogypsum leachate (total phosphorus: 2000 mg / L, F-: 1000 mg / L, sulfate: 200 mg / L) to adsorb soluble phosphorus with an adsorption rate of 98.81%.

[0136] Example 6

[0137] (1) Preparation of acid-leached magnesium-modified biochar

[0138] The crab shell material was placed in a beaker, washed with distilled water, and then dried in a vacuum oven at 65°C. The material was then crushed and passed through a 60-mesh sieve. The sieved sample was acid-soaked in 0.5 mol / L hydrochloric acid for 45 minutes, washed, and dried in a vacuum oven at 65°C to obtain biomass powder.

[0139] The obtained biomass powder was mixed with 0.3 mol / LMgCl2 solution (solid-liquid ratio 1 g: 25 mL), placed in a reactor, stirred at a speed of 800 rpm / min, the stirring temperature was 80 ° C, heated for 2 h, filtered, washed with water 6 times, dried in a vacuum drying oven at 65 ° C, ground, and passed through a 120 mesh sieve to obtain an intermediate product.

[0140] The product was placed in a tube furnace and calcined at 600°C for 2 h in an argon environment at a heating rate of 6°C / min to obtain magnesium-modified biochar.

[0141] (2) Alkali-leached biochar powder

[0142] The product in 3) was mixed with 0.6 mol / L NaOH (solid-liquid ratio 1 g: 15 mL), placed in a reactor and heated with stirring at 85° C. and a drying temperature of 65° C., and the final product was modified crab shell biochar.

[0143] (3) Application

[0144] The obtained modified crab shell biochar was used to simulate phosphogypsum leachate (total phosphorus: 2000 mg / L, F-: 1000 mg / L, sulfate: 200 mg / L) to adsorb soluble phosphorus with an adsorption rate of 97.62%.

[0145] Example 7

[0146] (1) Preparation of acid-leached magnesium-modified biochar

[0147] The crab shell material was placed in a beaker, washed with distilled water, and then dried in a vacuum oven at 65°C. The material was then crushed and passed through a 60-mesh sieve. The sieved sample was acid-soaked in 0.5 mol / L hydrochloric acid for 45 minutes, washed, and dried in a vacuum oven at 65°C to obtain biomass powder.

[0148] The obtained biomass powder was mixed with 0.3 mol / LMgCl2 solution (solid-liquid ratio 1 g: 25 mL), placed in a reactor, stirred at a speed of 800 rpm / min, the stirring temperature was 80 ° C, heated for 2 h, filtered, washed with water 6 times, dried in a vacuum drying oven at 65 ° C, ground, and passed through a 120 mesh sieve to obtain an intermediate product.

[0149] The intermediate product was placed in a tube furnace and calcined at 600°C for 2 hours under an argon environment at a heating rate of 3-8°C / min to obtain magnesium-modified biochar.

[0150] (2) Alkali-leached biochar powder

[0151] The product in 1) was mixed with 1 mol / L NaOH (solid-liquid ratio 1 g: 15 mL), placed in a reactor and heated with stirring at 85° C. and a drying temperature of 65° C., and the final product was modified crab shell biochar.

[0152] (3) Application

[0153] The obtained modified crab shell biochar was used to simulate phosphogypsum leachate (total phosphorus: 2000 mg / L, F-: 1000 mg / L, sulfate: 200 mg / L) to adsorb soluble phosphorus with an adsorption rate of 94.32%.

[0154] Conclusion: Because sodium hydroxide deposits oxygen-containing functional groups such as hydroxyl and carboxyl groups on biochar, the biochar's porosity increases, its surface becomes rougher, and its specific surface area increases. However, different sodium hydroxide concentrations also alter the biochar's adsorption properties. Adsorption efficiency is highest at a sodium hydroxide concentration of 0.5 mol / L, but begins to decline as the base concentration continues to increase. This may be because the biochar's surface functional groups exhibit different charge states at different pH values. Under highly alkaline conditions, the functional groups on the biochar surface may deprotonate, changing their charge characteristics and thus affecting their adsorption capacity for pollutants such as phosphorus.

[0155] Example 8

[0156] (1) Preparation of acid-leached magnesium-modified biochar

[0157] The crab shell material was placed in a beaker, washed with distilled water, and then dried in a vacuum oven at 65°C. The material was then crushed and passed through a 60-mesh sieve. The sieved sample was acid-soaked in 0.5 mol / L hydrochloric acid for 45 minutes, washed, and dried in a vacuum oven at 65°C to obtain biomass powder.

[0158] The obtained biomass powder was mixed with 0.3 mol / LMgCl2 solution (solid-liquid ratio 1 g: 25 mL), placed in a reactor, stirred at a speed of 800 rpm / min, the stirring temperature was 80 ° C, heated for 2 h, filtered, washed with water 6 times, dried in a vacuum drying oven at 65 ° C, ground, and passed through a 120 mesh sieve to obtain an intermediate product.

[0159] The intermediate product was placed in a tube furnace and calcined at 600°C for 2 hours under an argon environment at a heating rate of 3-8°C / min to obtain magnesium-modified biochar.

[0160] (2) Alkali-leached biochar powder

[0161] The product in 3) was mixed with 1 mol / L NaOH (solid-liquid ratio 1 g: 15 mL), placed in a reactor and heated with stirring at 85°C and a drying temperature of 65°C to obtain modified crab shell biochar.

[0162] (3) Application

[0163] The modified crab shell biochar was used to simulate phosphogypsum leachate (total phosphorus: 2000 mg / L, F-: 1000 mg / L, sulfate: 200 mg / L) to adsorb soluble phosphorus with an adsorption rate of 99.64%.

[0164] Example 9

[0165] (1) Preparation of acid-leached magnesium-modified biochar

[0166] The crab shell material was placed in a beaker, washed with distilled water, and then dried in a vacuum oven at 65°C. The material was then crushed and passed through a 60-mesh sieve. The sieved sample was acid-soaked in 0.5 mol / L hydrochloric acid for 45 minutes, washed, and dried in a vacuum oven at 65°C to obtain biomass powder.

[0167] The obtained biomass powder was mixed with 0.3 mol / LMgCl2 solution (solid-liquid ratio 1 g: 25 mL), placed in a reactor, stirred at a speed of 800 rpm / min, the stirring temperature was 80 ° C, heated for 2 h, filtered, washed with water 6 times, dried in a vacuum drying oven at 65 ° C, ground, and passed through a 120 mesh sieve to obtain an intermediate product.

[0168] The intermediate product was placed in a tube furnace and calcined at 600°C for 2 hours under an argon environment at a heating rate of 3-8°C / min to obtain magnesium-modified biochar.

[0169] (2) Alkali-leached biochar powder

[0170] The product in 1) was mixed with 1 mol / L NaOH (solid-liquid ratio 1 g: 15 mL), placed in a reactor and heated with stirring at 85° C. and a drying temperature of 65° C., and the final product was modified crab shell biochar.

[0171] (3) Application

[0172] The obtained modified crab shell biochar was used to simulate phosphogypsum leachate (total phosphorus: 2000 mg / L, F-: 1000 mg / L, sulfate: 200 mg / L) to adsorb soluble phosphorus with an adsorption rate of 97.54%.

[0173] In summary: The solid-to-liquid ratio affects the concentration of MgCl₂ in the solution, which in turn influences the degree of magnesium ion binding to biochar. Magnesium ions can form complexes or ionic bridges with functional groups on the biochar surface, enhancing the biochar's phosphorus adsorption capacity. A smaller solid-to-liquid ratio means more biomass powder in a fixed volume of solution. This increases the contact area between the biochar and the phosphorus in the solution, which improves adsorption efficiency. Adsorption efficiency is highest when the solid-to-liquid ratio is 4:1. As the solid-to-liquid ratio increases, the adsorption rate decreases. This may be because a higher solid-to-liquid ratio increases the viscosity of the solution, affecting stirring efficiency and mass transfer. Insufficient stirring results in uneven contact between the biochar and the phosphorus in the solution, potentially reducing adsorption efficiency.

[0174] Example 10

[0175] (1) Preparation of acid-leached magnesium-modified biochar

[0176] The crab shell material was placed in a beaker, washed with distilled water, and then dried in a vacuum oven at 65°C. The material was then crushed and passed through a 60-mesh sieve. The sieved sample was acid-soaked in 0.5 mol / L hydrochloric acid for 45 minutes, washed, and dried in a vacuum oven at 65°C to obtain biomass powder.

[0177] The obtained biomass powder was mixed with 0.3 mol / LMgCl2 solution (solid-liquid ratio 1 g: 25 mL), placed in a reactor, stirred at a speed of 800 rpm / min, the stirring temperature was 80 ° C, heated for 2 h, filtered, washed with water 6 times, dried in a vacuum drying oven at 65 ° C, ground, and passed through a 120 mesh sieve to obtain an intermediate product.

[0178] The intermediate product was placed in a tube furnace and calcined at 400°C for 2 h in an argon environment at a heating rate of 6°C / min to obtain magnesium-modified biochar.

[0179] (2) Alkali-leached biochar powder

[0180] The product in 1) was mixed with 1 mol / L NaOH (solid-liquid ratio 1 g: 15 mL), placed in a reactor and heated with stirring at 85° C. and a drying temperature of 65° C., and the final product was modified crab shell biochar.

[0181] (3) Application

[0182] The obtained modified crab shell biochar was used to simulate phosphogypsum leachate (total phosphorus: 2000 mg / L, F-: 1000 mg / L, sulfate: 200 mg / L) to adsorb soluble phosphorus with an adsorption rate of 97.76%.

[0183] Example 11

[0184] (1) Preparation of acid-leached magnesium-modified biochar

[0185] The crab shell material was placed in a beaker, washed with distilled water, and then dried in a vacuum oven at 65°C. The material was then crushed and passed through a 60-mesh sieve. The sieved sample was acid-soaked in 0.5 mol / L hydrochloric acid for 45 minutes, washed, and dried in a vacuum oven at 65°C to obtain biomass powder.

[0186] The obtained biomass powder was mixed with 0.3 mol / LMgCl2 solution (solid-liquid ratio 1 g: 25 mL), placed in a reactor, stirred at a speed of 800 rpm / min, the stirring temperature was 80 ° C, heated for 2 h, filtered, washed with water 6 times, dried in a vacuum drying oven at 65 ° C, ground, and passed through a 120 mesh sieve to obtain an intermediate product.

[0187] The intermediate product was placed in a tube furnace and calcined at 400°C for 2 h in an argon environment at a heating rate of 6°C / min to obtain magnesium-modified biochar.

[0188] (2) Alkaline leaching of biochar powder

[0189] The product in 1) was mixed with 1 mol / L NaOH (solid-liquid ratio 1 g: 15 mL), which was placed in a reaction kettle for heating and stirring, the temperature was 85°C, the drying temperature was 65°C, and the final product was modified crab shell biochar.

[0190] (3) Application

[0191] The obtained modified crab shell biochar was used for adsorption of soluble phosphorus in simulated phosphogypsum leachate (total phosphorus: 2000 mg / L, F-: 1000 mg / L, sulfate: 200 mg / L), and the adsorption rate was 95.87%.

[0192] Summary: Carbonization temperature is one of the important factors affecting the adsorption performance of biochar, which affects the pore structure, specific surface area, chemical composition, surface functional groups, etc. of biochar. However, different carbonization temperatures also affect the adsorption performance of biochar materials. When the carbonization temperature is 600°C, the adsorption performance of biochar is the highest, but when the temperature continues to rise, the adsorption performance begins to decrease. This may be because higher temperatures cause the release of volatile substances in biochar, which may cause the collapse of the pore structure of biochar or excessive sintering, thereby reducing the porosity and specific surface area. As the carbonization temperature increases, the pore size of biochar may increase, resulting in a decrease in the number of micropores and an increase in the proportion of macropores and mesopores. Micropores are particularly effective for adsorbing small molecular pollutants, so changes in pore size may reduce the adsorption capacity for certain pollutants, etc.

[0193] Example 12

[0194] (1) Preparation of acid leaching magnesium modified biochar

[0195] The crab shell material was placed in a beaker, washed with distilled water, then dried in a vacuum drying oven at 65°C, then crushed and sieved through a 60 mesh sieve. The sieved sample was placed in 0.1 mol / L hydrochloric acid for acid leaching for 45 min, washed, dried in a vacuum drying oven at 65°C, and the biomass powder was obtained.

[0196] The obtained biomass powder was mixed with 0.04 mol / L MgCl2 solution (solid-liquid ratio 1 g: 25 mL), which was placed in a reaction kettle and stirred at a speed of 800 rpm / min, the stirring temperature was 80°C, heated for 2h, filtered, washed with water for 6 times, dried in a vacuum drying oven at 65°C, ground and sieved through a 120 mesh sieve to obtain the intermediate product.

[0197] The intermediate product was placed in a tube furnace and calcined at 600°C for 2h in an argon environment in the tube furnace at a heating rate of 6°C / min to obtain magnesium modified biochar.

[0198] (2) Alkali-leached biochar powder

[0199] The product in 1) was mixed with 0.1 mol / L NaOH (solid-liquid ratio 1 g: 15 mL), placed in a reactor and heated with stirring at 85° C. and a drying temperature of 65° C., and the final product was modified crab shell biochar.

[0200] (3) Application

[0201] The obtained modified crab shell biochar was used to simulate phosphogypsum leachate (total phosphorus: 2000 mg / L, F-: 1000 mg / L, sulfate: 200 mg / L) to adsorb soluble phosphorus with an adsorption rate of 75.29%.

[0202] Example 13

[0203] (1) Preparation of acid-leached magnesium-modified biochar

[0204] The crab shell material was placed in a beaker, washed with distilled water, and then dried in a vacuum oven at 65°C. The material was then pulverized and passed through a 60-mesh sieve. The sieved sample was acid-soaked in 0.6 mol / L hydrochloric acid for 45 minutes, washed, and dried in a vacuum oven at 65°C to obtain biomass powder.

[0205] The obtained biomass powder was mixed with 0.04 mol / LMgCl2 solution (solid-liquid ratio 1 g: 25 mL), placed in a reactor, stirred at a speed of 800 rpm / min, the stirring temperature was 80 ° C, heated for 2 h, filtered, washed with water 6 times, dried in a vacuum drying oven at 65 ° C, ground, and passed through a 120 mesh sieve to obtain an intermediate product.

[0206] The intermediate product was placed in a tube furnace and calcined at 600°C for 2 h in an argon environment at a heating rate of 6°C / min to obtain magnesium-modified biochar.

[0207] (2) Alkali-leached biochar powder

[0208] The product in 1) was mixed with 0.1 mol / L NaOH (solid-liquid ratio 1 g: 15 mL), placed in a reactor and heated with stirring at 85° C. and a drying temperature of 65° C., and the final product was modified crab shell biochar.

[0209] (3) Application

[0210] The obtained modified crab shell biochar was used to simulate phosphogypsum leachate (total phosphorus: 2000 mg / L, F-: 1000 mg / L, sulfate: 200 mg / L) to adsorb soluble phosphorus with an adsorption rate of 90.11%.

[0211] Example 14

[0212] (1) Preparation of acid-leached magnesium-modified biochar

[0213] The crab shell material was placed in a beaker, washed with distilled water, and then dried in a vacuum oven at 65°C. The material was then pulverized and passed through a 60-mesh sieve. The sieved sample was acid-soaked in 1 mol / L hydrochloric acid for 45 minutes, washed, and dried in a vacuum oven at 65°C to obtain biomass powder.

[0214] The obtained biomass powder was mixed with 0.04 mol / LMgCl2 solution (solid-liquid ratio 1 g: 25 mL), placed in a reactor, stirred at a speed of 800 rpm / min, the stirring temperature was 80 ° C, heated for 2 h, filtered, washed with water 6 times, dried in a vacuum drying oven at 65 ° C, ground, and passed through a 120 mesh sieve to obtain an intermediate product.

[0215] The intermediate product was placed in a tube furnace and calcined at 600°C for 2 h in an argon environment at a heating rate of 6°C / min to obtain magnesium-modified biochar.

[0216] (2) Alkali-leached biochar powder

[0217] The product in 1) was mixed with 0.1 mol / L NaOH (solid-liquid ratio 1 g: 15 mL), placed in a reactor and heated with stirring at 85° C. and a drying temperature of 65° C., and the final product was modified crab shell biochar.

[0218] (3) Application

[0219] The obtained modified crab shell biochar was used to simulate phosphogypsum leachate (total phosphorus: 2000 mg / L, F-: 1000 mg / L, sulfate: 200 mg / L) to adsorb soluble phosphorus with an adsorption rate of 84.66%.

[0220] Conclusion: Hydrochloric acid increases the porosity of biochar, making its surface rougher and its specific surface area larger. However, different hydrochloric acid concentrations also affect the adsorption properties of biochar. Adsorption efficiency is highest at 0.5 mol / L, but decreases as the acid concentration increases. This may be because the surface functional groups of biochar exhibit different charge states at different pH values. Under highly acidic conditions, the functional groups on the biochar surface may become protonated, changing their charge properties and thus affecting their adsorption capacity for pollutants such as phosphorus.

[0221] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing magnesium-modified crab shell biochar, comprising the following steps: A) washing, primary drying, crushing, sieving, acid leaching, washing and secondary drying the crab shells in sequence to obtain crab shell powder; B) mixing the crab shell powder, magnesium salt and water, heating and stirring, and obtaining an intermediate product after solid-liquid separation; C) calcining the intermediate product under a protective atmosphere to obtain a calcined product; D) mixing the roasted product, alkali and water, and heating the mixture for reaction to obtain magnesium-modified crab shell biochar.

2. The preparation method according to claim 1, characterized in that In step A), hydrochloric acid is used for acid leaching, the concentration of the hydrochloric acid is 0.1 to 1 mol / L, and the time of the acid leaching is 30 to 60 minutes.

3. The preparation method according to claim 1, characterized in that In the step A), the crab shells are crushed and sieved with a mesh size of 60 to 90 meshes.

4. The preparation method according to claim 1, characterized in that The step B) is specifically as follows: The crab shell powder and the magnesium salt solution are mixed, heated and stirred, and solid-liquid separation is performed to obtain an intermediate product; The concentration of the magnesium salt solution is 0.04-0.4 mol / L, and the solid-liquid ratio of the crab shell powder to the magnesium salt solution is 1 g: (15-25) mL.

5. The preparation method according to claim 1, characterized in that The heating temperature in step B) is 60-100° C., and the heating and stirring time is 2-4 hours.

6. The preparation method according to claim 1, characterized in that The calcination temperature in step C) is 400-800°C and the calcination time is 2-3 hours; The protective atmosphere includes argon and / or nitrogen.

7. The preparation method according to claim 1, characterized in that In the step D), the roasted product is mixed with an alkaline solution and heated for reaction to obtain magnesium-modified crab shell biochar; The alkaline solution is a sodium hydroxide solution, and the concentration of the alkaline solution is 0.1-1 mol / L.

8. The preparation method according to claim 1, characterized in that The heating reaction temperature in step D) is 55-85° C., and the heating reaction time is 0.5-2 h.

9. A magnesium-modified crab shell biochar prepared according to the preparation method according to any one of claims 1 to 8.

10. Use of the magnesium-modified crab shell biochar according to claim 9 in adsorbing phosphorus-containing substances in water; The pH value of the water body is 2-9.

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