Mineral modified biochar material as well as preparation method and application thereof

Abstract

The invention provides a mineral modified biochar material and a preparation method and application thereof.The preparation method comprises the following steps that A, phosphate tailings are ground, sieved and then calcined, the calcined phosphate tailings and activated carbon are mixed and stirred in water, then solid-liquid separation is conducted, and calcium-magnesium-rich filtrate is obtained; b) mixing the calcium-magnesium-rich filtrate, a surfactant and biomass powder, and reacting to obtain an intermediate product; and C) calcining the intermediate product in an atmosphere containing water vapor to obtain the mineral modified biochar material. The mineral modified biochar material can keep efficient adsorption capacity within a wide pH range (3-13), meanwhile, the number of times of cyclic adsorption is increased, the mineral modified biochar material can be recycled as a slow-release fertilizer after adsorption, and the mineral modified biochar material has wider application in practical application.

Description

Technical Field

[0001] The present invention belongs to the technical field of sewage treatment, and in particular relates to a mineral-modified biochar material, a preparation method thereof, and an application thereof. Background Art

[0002] With the rapid development of phosphorus chemical enterprises in my country, the phosphorus concentration in the wastewater discharged by them is getting higher and higher, which leads to serious eutrophication pollution of water bodies and the damage to the water ecosystem is becoming more and more serious, becoming a typical water pollution problem. As a popular phosphorus pollution treatment method today, adsorption phosphorus removal technology is relatively simple to operate during the treatment process, uses relatively simple equipment, has high purification efficiency for wastewater, can be used for deep treatment of wastewater, and will not cause secondary pollution. The adsorption method can be used to treat phosphorus in phosphorus-containing wastewater to recover phosphorus in the wastewater and make it into economical by-products such as organic fertilizers, thereby realizing the recycling of phosphorus. In addition, adsorption phosphorus removal is also suitable for treating low-concentration phosphorus-containing wastewater. Therefore, it can be considered that adsorption phosphorus removal has a relatively broad development prospect.

[0003] Due to its porous structure and large specific surface area, biochar can adsorb phosphate ions through intermolecular attraction (van der Waals force), so biochar has strong physical adsorption properties. In addition, the surface of biochar contains oxygen-containing functional groups and metal ions, so biochar can remove phosphorus from wastewater by forming stable chemical bonds through electrostatic interactions and adsorption bridging with phosphate ions. Other methods include pore filling, hydrogen bonding, π-π interactions, hydrophobic interactions, catalytic degradation, and complexation. The modified biochar increases the number of adsorption active sites on its surface. The phosphate ions in the wastewater combine with the active sites on the surface of the modified biochar through chemical bonds or physical adsorption and precipitate, thereby completing the removal of phosphorus.

[0004] Existing patent CN 106140087 A, "A Sludge Activated Carbon Adsorbent for Wastewater Phosphorus Removal and Its Preparation Method," consists of 0.1%-5.0% pyrolusite powder and 95%-99.9% sludge activated carbon. The sludge activated carbon adsorbent is prepared by mixing, ultrasonically activating with a ZnCl2 solution and dilute sulfuric acid solution, calcining at 450-650°C, cooling, and then washing to neutrality. Sludge contains a large amount of heavy metals, posing a risk of secondary pollution. The adsorbent is in powder form, making solid-liquid separation difficult after adsorption, resulting in high filtration resistance, easy clogging of equipment, and difficulty in recycling. Manganese ions in the pyrolusite may dissolve after adsorption, causing secondary water pollution. Summary of the Invention

[0005] The purpose of the present invention is to provide a mineral-modified biochar material, a preparation method and application thereof. The mineral-modified biochar material in the present invention can effectively reduce the phosphorus content in wastewater and has excellent reusability.

[0006] The present invention provides a method for preparing a mineral-modified biochar material, comprising the following steps:

[0007] A) grinding and sieving the phosphate tailings and then calcining them, mixing the calcined phosphate tailings and activated carbon in water, stirring and then separating the solid and liquid to obtain a calcium-magnesium-rich filtrate;

[0008] B) mixing the calcium-magnesium-rich filtrate, a surfactant, and biomass powder, and reacting to obtain an intermediate product;

[0009] C) calcining the intermediate product in an atmosphere containing water vapor to obtain a mineral-modified biochar material.

[0010] Preferably, in step A), the phosphate tailings are screened to a mesh size of 200 to 300 meshes;

[0011] The calcination temperature in the step A) is 950-1050° C., and the calcination time in the step A) is 2-3 hours.

[0012] Preferably, in step A), the mass ratio of activated carbon to phosphate tailings is 1:(10-30).

[0013] Preferably, the concentration of calcium ions in the calcium-magnesium-rich filtrate is 10.75-1.5 mol / L, and the concentration of magnesium ions is 0.5-1.25 mol / L.

[0014] Preferably, the biomass powder is grapefruit peel powder, and the mass ratio of the biomass powder to the calcium-magnesium-rich filtrate is 1:(25-100);

[0015] The mass of the surfactant is 0.5-2% of the mass of the biomass powder.

[0016] Preferably, the reaction temperature in step B) is 50-80° C., and the reaction time in step B) is 2-5 hours.

[0017] Preferably, the water vapor-containing atmosphere comprises water vapor and a protective gas, and the protective gas comprises nitrogen and / or argon;

[0018] The flow rate of the water vapor is 1 to 5% of the flow rate of the protective gas.

[0019] Preferably, the calcination temperature in step C) is 300-900° C., and the calcination time in step C) is 1-5 hours.

[0020] The present invention provides a mineral-modified biochar material, which is prepared according to the above-mentioned method for preparing the mineral-modified biochar material.

[0021] The present invention provides a use of the mineral-modified biochar material as described above as an adsorbent in removing phosphorus from wastewater.

[0022] The present invention provides a method for preparing a mineral-modified biochar material, comprising the following steps: A) grinding and screening phosphate tailings and then calcining them, mixing the calcined phosphate tailings and activated carbon in water, stirring, and then performing solid-liquid separation to obtain a calcium-magnesium-rich filtrate; B) mixing the calcium-magnesium-rich filtrate, a surfactant, and biomass powder, reacting to obtain an intermediate product; and C) calcining the intermediate product under a steam-containing atmosphere to obtain a mineral-modified biochar material. The present invention utilizes calcium and magnesium resources in phosphate tailings, pretreating the phosphate tailings, reacting with biomass powder in the presence of a surfactant, and finally calcining under a steam atmosphere, so that the effective components in the phosphate tailings can be better combined with the biomass powder, optimizing the material structure, and improving the adsorption efficiency and stability of the mineral-modified biochar material; and the mineral-modified biochar material can maintain efficient adsorption capacity in a wide pH range (3 to 13), while also increasing the number of cyclic adsorption cycles. After adsorption, the mineral-modified biochar material can be recycled as a slow-release fertilizer, having a wider range of applications in practical applications. DETAILED DESCRIPTION

[0023] The present invention provides a method for preparing a mineral-modified biochar material, comprising the following steps:

[0024] A) grinding and sieving the phosphate tailings and then calcining them, mixing the calcined phosphate tailings and activated carbon in water, stirring and then separating the solid and liquid to obtain a calcium-magnesium-rich filtrate;

[0025] B) mixing the calcium-magnesium-rich filtrate, a surfactant, and biomass powder, and reacting to obtain an intermediate product;

[0026] C) calcining the intermediate product in an atmosphere containing water vapor to obtain a mineral-modified biochar material.

[0027] In the present invention, the phosphate tailings are raw phosphate tailings from Yunnan Phosphate Chemical Group. The phosphate tailings are complex in composition and contain a variety of metal ions and organic impurities, which can affect the subsequent modification of biomass powder and the adsorption properties of the material. The present invention preferably pre-treats the phosphate tailings to remove the complex impurities in the phosphate tailings. The present invention preferably grinds and sieves the phosphate tailings, calcines them, dissolves them in water, adds activated carbon, and stirs them before solid-liquid separation to obtain a calcium-magnesium-rich filtrate.

[0028] In the present invention, the mesh size of the grinding and sieving is preferably 200-300 mesh, the calcination temperature is preferably 950-1050°C, more preferably 1000-1020°C, such as 950°C, 960°C, 970°C, 980°C, 990°C, 1000°C, 1010°C, 1020°C, 1030°C, 1040°C, 1050°C, preferably with any of the above values as the upper or lower limit; the calcination time is preferably 2-3 hours.

[0029] In this invention, the addition of activated carbon effectively adsorbs and removes impurities from the phosphate tailings solution, resulting in a pure, calcium-magnesium-rich filtrate. This purified filtrate can better combine with the biomass powder, optimizing the material structure and improving the Pta-GCX's phosphate adsorption performance, ensuring its high efficiency and stability in adsorption applications.

[0030] In the present invention, the mass ratio of the calcined phosphate tailings to water is preferably 1: (15-30), more preferably 1: (20-25), the mass ratio of the activated carbon to the phosphate tailings is preferably 1: (10-30), more preferably 1: (15-25), such as 1: 10, 1: 15, 1: 20, 1: 25, 1: 30, preferably a range value with any of the above values as the upper or lower limit; the concentration of calcium ions in the calcium-magnesium-rich filtrate is 0.75-1.5 mol / L, more preferably 0.9-1.2 mol / L, such as 0.75 mol / L, 0.8 mol / L, 0.85 mol / L, 0.9 mol / L, 0.95 mol / L, 1.0 mol / L, 1.05 mol / L, 1.1 mol / L, 1.15 mol / L, 1.2 mol / L, 1.25 mol l / L, 1.3mol / L, 1.35mol / L, 1.4mol / L, 1.45mol / L, 1.5mol / L, preferably a range value with the above arbitrary numerical value as the upper or lower limit, the concentration of magnesium ions is preferably 0.5-1.25mol / L, more preferably 0.8-1mol / L, such as 0.5mol / L, 0.55mol / L, 0.6mol / L, 0.65mol / L, 0.7mol / L, 0.75mol / L, 0.8mol / L, 0.85mol / L, 0.9mol / L, 0.95mol / L, 1.0mol / L, 1.05mol / L, 1.1mol / L, 1.15mol / L, 1.2mol / L, 1.25mol / L, preferably a range value with the above arbitrary numerical value as the upper or lower limit.

[0031] In the present invention, the biomass material is preferably crushed, sieved and dried to a constant weight to obtain biomass powder, which is then mixed with a calcium-magnesium-rich filtrate and a surfactant to react.

[0032] In the present invention, the biomass material is preferably grapefruit peel, the sieve mesh of the biomass material is preferably 60-90 mesh, and the drying temperature is preferably 55-85°C, more preferably 60-80°C.

[0033] In the present invention, the mass ratio of the biomass fine powder to the calcium-magnesium-rich filtrate is preferably 1:(25-100), more preferably 1:(30-90), such as 1:25, 1:30, 1:35, 1:40, 1:45, 1:50, 1:55, 1:60, 1:65, 1:70, 1:75, 1:80, 1:85, 1:90, 1:95, 1:100, preferably a range value with any of the above values as the upper or lower limit.

[0034] In the present invention, the surfactant significantly reduces the surface tension of the liquid, ensuring more complete contact between the biomass powder and the calcium-magnesium-rich filtrate, thereby forming a more uniform mixing system. The addition of the surfactant allows the formation of tiny bubbles or micelles during mixing, which can be converted into pores within the material during subsequent freeze-drying and calcination. The surfactant forms a protective film around the biomass powder and calcium and magnesium ions during mixing, preventing particle agglomeration during calcination. The surfactant also introduces polar or non-polar groups, enhancing the material's electrostatic or hydrophobic adsorption of phosphate. These improvements result in Pta-GCX exhibiting significantly improved phosphate adsorption performance, particularly maintaining high adsorption capacity across a wide pH range (3-13). Furthermore, the addition of the surfactant enhances the material's stability and mechanical strength, making it more suitable for practical applications. The surfactant is preferably one or more of polyethylene glycol, sodium lauryl sulfate, and cetyltrimethylammonium bromide, with the mass of the surfactant preferably ranging from 0.5 to 2%, and more preferably from 1 to 1.5%, of the biomass powder mass.

[0035] After obtaining a mixed solution of biomass powder, calcium-magnesium-rich filtrate and surfactant, the present invention stirs and heats it to react, and after the reaction is completed, solid-liquid separation is performed, and the obtained filter residue is washed with water, freeze-dried, crushed and sieved to obtain an intermediate product.

[0036] In the present invention, the reaction temperature is preferably 50-80°C, more preferably 60-70°C, such as 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, preferably a range value with any of the above values as the upper or lower limit; the reaction time is preferably 2-5 hours, more preferably 3-4 hours, and the stirring speed during the reaction is preferably 600-1200 rpm, more preferably 800-1000 rpm.

[0037] In the present invention, the freeze-drying includes two stages: freezing and freeze-drying. In the freezing stage, the freezing temperature is preferably -18 to -20°C, and the freezing time is preferably 12 to 24 hours. In the freeze-drying stage, the freeze-drying temperature is preferably -90 to -60°C, more preferably -80 to -70°C, such as -90°C, -80°C, -70°C, and -60°C, preferably a range value with any of the above values as the upper or lower limit.

[0038] After obtaining the intermediate product, the present invention places the intermediate product in an atmosphere containing water vapor for calcination. After the calcination is completed, the calcined product is naturally cooled, washed and dried to obtain the final product, a mineral-modified biochar material (Pta-GCX).

[0039] In the present invention, the water vapor-containing atmosphere preferably comprises water vapor and a protective atmosphere. The protective atmosphere is preferably nitrogen and / or argon. The water vapor flow rate is preferably 1-5% of the protective atmosphere flow rate, more preferably 2-4%, such as 1%, 2%, 3%, 4%, or 5%, preferably within a range with any of the above values as upper or lower limits. The present invention utilizes the high thermal conductivity and good diffusivity of water vapor to enable it to quickly penetrate the material interior, forming a microporous structure during the calcination process. These microporous structures not only increase the specific surface area of the material but also provide more adsorption sites for adsorbates. The presence of water vapor can reduce the concentration of carbon dioxide in the calcination atmosphere, thereby reducing the thermal resistance during calcination. Calcination in a water vapor atmosphere can achieve the same decomposition effect as traditional calcination methods at lower temperatures, which not only reduces energy consumption but also reduces the problems of material sintering and performance degradation that may be caused by high-temperature calcination. Water vapor can react with active sites on the material surface to produce intermediates, which can provide more active sites in the subsequent adsorption process. The addition of water vapor can remove some impurities and volatile byproducts generated during calcination.

[0040] In the present invention, the calcination temperature is preferably 300-900°C, more preferably 400-800°C, such as 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, preferably a range value with any of the above numerical values as the upper or lower limit; the calcination heating rate is preferably 3-10°C / min, more preferably 5-8°C / min, and the calcination time is preferably 1-5 hours, more preferably 2-3 hours.

[0041] The present invention also provides a mineral-modified biochar material, which is prepared according to the preparation method described above.

[0042] The present invention also provides the use of the mineral-modified biochar material described above as an adsorbent for removing phosphorus-containing substances from wastewater. The mineral-modified biochar material Pta-GCX in this invention exhibits significant advantages in cyclic adsorption performance and material recycling, making it particularly innovative and practical compared to traditional adsorbent materials and carbon materials described in other patents. The adsorption efficiency of many traditional adsorbent materials decreases significantly with the number of cycles, typically falling below 60% after three to four cycles. In contrast, the Pta-GCX material utilizes a unique preparation process, such as the introduction of water vapor during calcination, to optimize its pore structure and enhance its adsorption performance while also enhancing its stability and reusability. It can be recycled for more than five times while maintaining an adsorption rate above 80%. Furthermore, the Pta-GCX material's post-adsorption recycling value further enhances its practicality. Most traditional adsorbent materials are difficult to dispose of after adsorption, often requiring complex regeneration processes or direct disposal, which not only increases costs but also potentially causes secondary environmental pollution. The Pta-GCX material can be recycled as a slow-release fertilizer after adsorption.

[0043] In order to further illustrate the present invention, a mineral-modified biochar material, a preparation method and an application thereof provided by the present invention are described in detail below in combination with examples, but they should not be construed as limiting the scope of protection of the present invention.

[0044] The adsorption efficiency of phosphate adsorption in the following examples was calculated according to the following formula:

[0045] η=(C0-C t ) / C0×100%;

[0046] Where η is the adsorption rate, C0 is the initial concentration, C t is the concentration after a fixed reaction time.

[0047] Example 1

[0048] The dried pomelo peel was crushed into 60 mesh and dried to constant weight (temperature 60° C.) to obtain pomelo peel powder.

[0049] The phosphate tailings were ground to 200 mesh, calcined at 950°C for 2 hours, dissolved in water at a mass ratio of 1:25, activated carbon (mass ratio to phosphate tailings 1:20) was added, stirred for 30 minutes, and then solid-liquid separation was performed to obtain a calcium-magnesium-rich filtrate.

[0050] Grapefruit peel powder and calcium-magnesium-rich filtrate were mixed in a mass ratio of 1:100. Polyethylene glycol (1% by mass of the biomass powder) was added as a surfactant and stirred at 60°C at 800 rpm / min for 3 hours. After solid-liquid separation, the filter residue was frozen at -18°C for 12 hours and then freeze-dried at -60°C for 24 hours to obtain an intermediate product. The intermediate product was calcined at 400°C at a heating rate of 5°C / min for 2 hours in an argon protective gas atmosphere containing 2% water vapor. After natural cooling, it was washed and dried to obtain Pta-GCX.

[0051] The prepared Pta-GCX was used to adsorb phosphate, and its adsorption performance for phosphate in wastewater with pH=7 was tested.

[0052] The results show that the adsorption capacity of Pta-GCX for phosphate in wastewater with pH = 7 reaches 215 mg / g, and the adsorption efficiency is 99.8%. After 5 cycles of adsorption, the adsorption efficiency still remains above 90%.

[0053] Example 2

[0054] The dried pomelo peel was crushed into 75 mesh and dried to constant weight (temperature 70° C.) to obtain pomelo peel powder.

[0055] The phosphate tailings were ground to 250 mesh, calcined at 1000°C for 2.5 hours, dissolved in water at a mass ratio of 1:25, and activated carbon (with a mass ratio of 1:20 to the phosphate tailings) was added. After stirring for 30 minutes, the solid and liquid were separated to obtain a calcium-magnesium-rich filtrate.

[0056] Grapefruit peel powder and calcium-magnesium-rich filtrate were mixed in a mass ratio of 1:100. Sodium lauryl sulfate (1.5% by mass of the biomass powder) was added as a surfactant and stirred at 70°C at 1000 rpm / min for 4 hours. After solid-liquid separation, the filter residue was frozen at -20°C for 18 hours and then freeze-dried at -70°C for 36 hours to obtain an intermediate product. The intermediate product was calcined at 500°C at a heating rate of 8°C / min for 3 hours in an argon protective gas atmosphere containing 3% water vapor. After natural cooling, it was washed and dried to obtain Pta-GCX.

[0057] The prepared Pta-GCX was used to adsorb phosphate, and its adsorption performance for phosphate in wastewater with pH = 10 was tested.

[0058] The results show that the adsorption capacity of Pta-GCX for phosphate in wastewater with pH = 10 reaches 201 mg / g, and the adsorption efficiency is 98.7%. After 5 cycles of adsorption, the adsorption efficiency still remains above 90%.

[0059] Example 3

[0060] The dried pomelo peel was crushed into 90 meshes and dried to constant weight (temperature 80° C.) to obtain pomelo peel powder.

[0061] The phosphate tailings were ground to 300 mesh, calcined at 1050°C for 3 hours, dissolved in water at a mass ratio of 1:25, activated carbon (mass ratio to phosphate tailings 1:20) was added, stirred for 30 minutes, and then solid-liquid separation was performed to obtain a calcium-magnesium-rich filtrate.

[0062] Grapefruit peel powder and calcium-magnesium-rich filtrate were mixed in a mass ratio of 1:100. Hexadecyltrimethylammonium bromide (2% by mass of the biomass powder) was added as a surfactant and stirred at 80°C at 1200 rpm / min for 5 hours. After solid-liquid separation, the filter residue was frozen at -20°C for 24 hours and then freeze-dried at -90°C for 48 hours to obtain an intermediate product. The intermediate product was calcined at 900°C at a heating rate of 10°C / min for 4 hours in an argon atmosphere containing 5% water vapor. After natural cooling, it was washed and dried to obtain Pta-GCX.

[0063] The prepared Pta-GCX was used to adsorb phosphate, and its adsorption performance for phosphate in wastewater with pH = 13 was tested.

[0064] The results showed that Pta-GCX achieved an adsorption capacity of 188 mg / g of phosphate in wastewater at a pH of 13, with an adsorption efficiency of 96.6%. Even after five cycles of adsorption, the adsorption efficiency remained above 90%. These three examples demonstrate that pH does affect the material's phosphorus adsorption to some extent, but the impact is minimal.

[0065] Comparative Example 1

[0066] The dried pomelo peel was crushed into 60 mesh and dried to constant weight (temperature 60° C.) to obtain pomelo peel powder.

[0067] The phosphate tailings were ground to 200 mesh, calcined at 950 °C for 2 hours, dissolved in water at a mass ratio of 1:25 without adding activated carbon, stirred for 30 minutes, and then solid-liquid separation was performed to obtain a calcium-magnesium-rich filtrate.

[0068] Grapefruit peel powder and calcium-magnesium-rich filtrate were mixed in a mass ratio of 1:100 without adding a surfactant and stirred at 800 rpm / min at 60°C for 3 hours. After solid-liquid separation, the filter residue was frozen at -18°C for 12 hours and then freeze-dried at -60°C for 24 hours to obtain an intermediate product. The intermediate product was calcined at 400°C at a heating rate of 5°C / min for 2 hours under an argon protective gas atmosphere (without water vapor), naturally cooled, washed, and dried to obtain Pta-GCX.

[0069] The prepared Pta-GCX was used to adsorb phosphate, and its adsorption performance for phosphate in wastewater with pH=7 was tested.

[0070] The results showed that the adsorption capacity of Pta-GCX for phosphate in wastewater at pH 7 was 169 mg / g, with an adsorption efficiency of 83.4%. Compared with Example 1, the adsorption performance was significantly reduced, indicating that the addition of activated carbon and surfactants, as well as the steam calcination environment, are crucial for improving adsorption performance.

[0071] Comparative Example 2

[0072] The dried pomelo peel was crushed into 75 mesh and dried to constant weight (temperature 70° C.) to obtain pomelo peel powder.

[0073] The phosphate tailings were ground to 250 mesh, calcined at 1000°C for 2.5 hours, dissolved in water at a mass ratio of 1:25, and activated carbon (with a mass ratio of 1:20 to the phosphate tailings) was added. After stirring for 30 minutes, the solid and liquid were separated to obtain a calcium-magnesium-rich filtrate.

[0074] Grapefruit peel powder and calcium-magnesium-rich filtrate were mixed in a mass ratio of 1:100, and sodium lauryl sulfate (1.5% by mass of the biomass powder) was added as a surfactant. The mixture was stirred at 70°C at 1000 rpm / min for 4 hours. After solid-liquid separation, the filter residue was frozen at -20°C for 18 hours and then freeze-dried at -70°C for 36 hours to obtain an intermediate product. The intermediate product was calcined at 500°C at a heating rate of 8°C / min for 3 hours under an argon protective gas environment (without water vapor), naturally cooled, washed, and dried to obtain Pta-GCX.

[0075] The prepared Pta-GCX was used to adsorb phosphate, and its adsorption performance for phosphate in wastewater with pH = 10 was tested.

[0076] The results showed that the adsorption capacity of Pta-GCX for phosphate in wastewater with a pH of 10 was 153 mg / g, and the adsorption efficiency was 81.8%. Compared with Example 2, the adsorption performance decreased, indicating that the steam calcination environment plays an important role in improving the adsorption performance.

[0077] Comparative Example 3

[0078] The dried pomelo peel was crushed into 90 meshes and dried to constant weight (temperature 80° C.) to obtain pomelo peel powder.

[0079] The phosphate tailings were ground to 300 mesh, calcined at 1050°C for 3 hours, dissolved in water at a mass ratio of 1:25, activated carbon (mass ratio to phosphate tailings 1:20) was added, stirred for 30 minutes, and then solid-liquid separation was performed to obtain a calcium-magnesium-rich filtrate.

[0080] Grapefruit peel powder and calcium-magnesium-rich filtrate were mixed in a mass ratio of 1:100 without the addition of surfactant and stirred at 80°C at 1200 rpm / min for 5 hours. After solid-liquid separation, the residue was frozen at -20°C for 24 hours and then freeze-dried at -90°C for 48 hours to obtain an intermediate product. The intermediate product was calcined at 900°C at a heating rate of 10°C / min for 4 hours in an argon atmosphere containing 5% water vapor. After natural cooling, it was washed and dried to obtain Pta-GCX. The prepared Pta-GCX was used to adsorb phosphate, and its adsorption performance was tested in wastewater with a pH of 13.

[0081] The results showed that the adsorption capacity of Pta-GCX for phosphate in wastewater with a pH of 13 was 149 mg / g, and the adsorption efficiency was 85.4%. Compared with Example 3, the adsorption performance decreased, indicating that the addition of surfactant plays an important role in improving the adsorption performance.

[0082] Comparative Example 4

[0083] The dried pomelo peel was crushed into 60 mesh and dried to constant weight (temperature 60° C.) to obtain pomelo peel powder.

[0084] CaO and MgO were mixed in a mass ratio of 1:1 to obtain a mixed powder. The mixed powder was calcined at 950°C for 2 hours, dissolved in water in a mass ratio of 1:25, and activated carbon (with a mass ratio of 1:20 to CaO and MgO) was added. After stirring for 30 minutes, solid-liquid separation was performed to obtain a calcium-magnesium-rich filtrate.

[0085] Grapefruit peel powder and calcium-magnesium-rich filtrate were mixed in a mass ratio of 1:100. Polyethylene glycol (1% by mass of the biomass powder) was added as a surfactant and stirred at 60°C at 800 rpm / min for 3 hours. After solid-liquid separation, the filter residue was frozen at -18°C for 12 hours and then freeze-dried at -60°C for 24 hours to obtain an intermediate product. The intermediate product was calcined at 400°C at a heating rate of 5°C / min for 2 hours in an argon protective gas atmosphere containing 2% water vapor. After natural cooling, it was washed and dried to obtain CaO / MgO-GCX.

[0086] The prepared CaO / MgO-GCX was used to adsorb phosphate, and its adsorption performance for phosphate in wastewater with pH=7 was tested.

[0087] Results showed that the CaO / MgO-GCX achieved an adsorption capacity of 193 mg / g of phosphate in wastewater at a pH of 7, with an adsorption efficiency of 95.2%. After five cycles of adsorption, the adsorption efficiency dropped significantly, falling below 80%. This decrease in adsorption performance compared to Example 1 suggests that the presence of other components in the phosphate tailings promotes phosphorus adsorption. The decrease in adsorption performance with increasing cycles suggests that phosphate tailings, as a modifier, can effectively extend the material's service life.

[0088] 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 a mineral-modified biochar material, comprising the following steps: A) grinding and sieving the phosphate tailings and then calcining them, mixing the calcined phosphate tailings and activated carbon in water, stirring and then separating the solid and liquid to obtain a calcium-magnesium-rich filtrate; B) mixing the calcium-magnesium-rich filtrate, a surfactant, and biomass powder, and reacting to obtain an intermediate product; C) calcining the intermediate product in an atmosphere containing water vapor to obtain a mineral-modified biochar material.

2. The preparation method according to claim 1, characterized in that In the step A), the phosphate tailings are screened to a mesh size of 200 to 300 meshes; The calcination temperature in the step A) is 950-1050° C., and the calcination time in the step A) is 2-3 hours.

3. The preparation method according to claim 1, characterized in that In the step A), the mass ratio of activated carbon to phosphate tailings is 1:(10-30).

4. The preparation method according to claim 1, characterized in that The calcium ion concentration in the calcium-magnesium-rich filtrate is 10.75-1.5 mol / L, and the magnesium ion concentration is 0.5-1.25 mol / L.

5. The preparation method according to claim 4, characterized in that The biomass powder is grapefruit peel powder, and the mass ratio of the biomass powder to the calcium-magnesium-rich filtrate is 1:(25-100); The mass of the surfactant is 0.5-2% of the mass of the biomass powder.

6. The preparation method according to claim 1, characterized in that The reaction temperature in step B) is 50-80° C., and the reaction time in step B) is 2-5 hours.

7. The preparation method according to claim 1, characterized in that The water vapor-containing atmosphere comprises water vapor and a protective gas, wherein the protective gas comprises nitrogen and / or argon; The flow rate of the water vapor is 1 to 5% of the flow rate of the protective gas.

8. The preparation method according to claim 1, characterized in that The calcination temperature in the step C) is 300 to 900° C., and the calcination time in the step C) is 1 to 5 hours.

9. A mineral-modified biochar material, characterized in that: The biochar is prepared according to the method for preparing the mineral-modified biochar material according to any one of claims 1 to 8.

10. Use of the mineral-modified biochar material according to claim 1 as an adsorbent in removing phosphorus from wastewater.