Struvite composite material, method for producing the same, and use thereof

Abstract

The present application relates to a kind of struvite composite material and its preparation method and application, the struvite composite material can convert the large amount of struvite sludge formed when sewage treatment plant is urgently recycled and utilized to composite nanomaterial of core-shell structure, then utilize the product as adsorbent after high temperature calcination of this material, such as landfill leachate and other high ammonia nitrogen, high COD wastewater is adsorbed and handled, realize the effect of efficient removal of ammonia nitrogen and organic matter in wastewater, purify water quality;Simultaneously, the composite material has unique memory effect in structure, after high temperature calcination after adsorbing wastewater, can have adsorption function, realize renewable cyclic use.Further, the preparation method and process of the composite material are simple, raw material cost is low, supply is large, environmental friendly, wide applicability, reaction condition is mild, can greatly reduce production and input cost, suitable for popularization and application.

Description

Technical Field

[0001] This invention relates to the field of new materials technology, and in particular to a guano composite material, its preparation method, and its application. Background Technology

[0002] High-concentration wastewater, such as landfill leachate, typically has high levels of ammonia nitrogen and chemical oxygen demand (COD), reaching concentrations of several thousand milligrams per liter. The main form of nitrogen is ammonia nitrogen, accounting for approximately 80% to 90% of the total nitrogen. Free ammonia in ammonia nitrogen is highly toxic, and high ammonia nitrogen levels can alter the biochemical properties of water bodies, reducing their biodegradability and making removal difficult. Simultaneously, the wastewater contains large amounts of high-molecular-weight organic matter and easily soluble humic substances, resulting in high COD and difficulty in degradation, easily causing serious pollution. Traditional wastewater treatment methods, such as biofilm technology, cannot directly treat this type of wastewater. Therefore, wastewater with high ammonia nitrogen and high COD cannot be directly discharged into mixed wastewater treatment plants and must undergo pretreatment on-site.

[0003] Since commonly used biochemical treatment methods often fail to achieve satisfactory pollutant removal, effectively reducing high ammonia nitrogen and high COD during wastewater pretreatment is a key research topic in the environmental field. Magnesium ammonium phosphate (MAP, struvite) crystallization precipitation, also known as struvite (MgNH4PO4·6H2O) crystallization precipitation, involves adding magnesium and orthophosphate to ammonia-rich wastewater to form struvite precipitate, thereby achieving wastewater denitrification. This method is currently widely used worldwide, with relatively mature technology and large-scale production. However, it requires a large amount of chemical reagents, resulting in high input costs, and generates a large amount of struvite sludge during the treatment process. How to effectively recycle and utilize this struvite sludge is an urgent problem to be solved.

[0004] Furthermore, adsorption is a commonly used physical method in wastewater treatment, offering advantages such as simple process, reliable operation, low cost, and wide adaptability. However, selecting a high-efficiency and economical adsorbent is one of the key issues in wastewater treatment using adsorption. In summary, effectively recycling struvite sludge to produce a high-efficiency, environmentally friendly, and economical adsorbent for treating high-ammonia nitrogen and high-COD wastewater has significant practical implications and application value for addressing current wastewater treatment challenges. Summary of the Invention

[0005] Therefore, it is necessary to provide a struvite composite material, its preparation method and application. By effectively recycling the large amount of struvite sludge generated in sewage treatment, a renewable, environmentally friendly, efficient and economical struvite composite material can be made, which can be used as an adsorbent to treat wastewater with high ammonia nitrogen and high COD.

[0006] In a first aspect, the present invention provides a method for preparing a struvite composite material, comprising the following steps:

[0007] A core-shell material is provided, wherein the core of the core-shell material is struvite and the shell is hydrotalcite nanosheets;

[0008] The core-shell material is calcined to prepare the struvite composite material, wherein the calcination temperature is 200℃~300℃.

[0009] In some embodiments, the calcination time is 1 hour to 5 hours.

[0010] In some embodiments, the method for preparing the core-shell material includes the following steps:

[0011] Mix struvite crystals with water, add alkali to adjust the pH of the system to 9-12, stir, and prepare a mixture.

[0012] An aluminum salt solution is added to the mixture to carry out the reaction. The resulting reaction solution is subjected to solid-liquid separation, the solid phase is collected, the solid phase is washed until neutral, and dried to prepare the core-shell material.

[0013] In some embodiments, the preparation step of the mixture satisfies at least one of the following conditions:

[0014] (1) The alkali includes one or more of sodium hydroxide, potassium hydroxide, ammonium bicarbonate, sodium oxide and sodium carbonate;

[0015] (2) The stirring time is 0.5h~2h;

[0016] (3) The raw materials for preparing the struvite crystals include struvite sludge produced by wastewater treatment plants.

[0017] In some embodiments, the step of adding the aluminum salt solution satisfies at least one of the following conditions:

[0018] (1) The aluminum salt in the aluminum salt solution includes one or more of aluminum nitrate, aluminum sulfate and aluminum chloride;

[0019] (2) The concentration of the aluminum salt solution is 0.05 mol / L to 0.5 mol / L;

[0020] (3) The aluminum salt solution is added at a rate of 0.1 mL / min to 3 mL / min.

[0021] In some embodiments, the reaction satisfies at least one of the following conditions:

[0022] (1) The molar ratio of magnesium in the struvite crystals to aluminum in the aluminum salt solution is (4-20):1;

[0023] (2) The reaction temperature is 20℃~50℃;

[0024] (3) The reaction time is 1h~120h.

[0025] In a second aspect, the present invention provides a struvite composite material prepared by the preparation method described above.

[0026] A third aspect of the invention provides the application of the struvite composite material described above in wastewater treatment.

[0027] In some embodiments, the wastewater includes one or more of landfill leachate, anaerobic process supernatant, and ammonia industrial wastewater.

[0028] In a fourth aspect, the present invention provides a wastewater adsorbent comprising the struvite composite material as described above.

[0029] The present invention has the following beneficial effects:

[0030] This invention utilizes a core-shell structured composite nanomaterial with a struvite core and a hydrotalcite nanosheet shell. The product of this material, after high-temperature calcination, is used as an adsorbent to treat wastewater with high ammonia nitrogen and high COD, such as landfill leachate, achieving efficient removal of ammonia nitrogen and organic matter and water purification. The struvite can be obtained from the large amount of struvite sludge generated during wastewater treatment in sewage plants, thus transforming the urgently needed struvite sludge resource into an environmentally friendly, efficient, and economical wastewater adsorbent capable of adsorbing high ammonia nitrogen and high COD. This provides a feasible way for the effective resource recycling of struvite sludge.

[0031] The principle behind the wastewater adsorption effect of the struvite composite material prepared by high-temperature calcination of the above-mentioned core-shell material is as follows:

[0032] In core-shell materials, the core struvite, specifically magnesium ammonium phosphate, undergoes thermal decomposition under high-temperature calcination. This decomposition destroys its crystal structure, resulting in the loss of ammonium ions as ammonia or ammonium ions. The resulting struvite pyrolysis products can combine with ammonia nitrogen in solution to regenerate magnesium ammonium phosphate compounds. Different pyrolysis temperatures lead to varying degrees of crystal structure decomposition in struvite, and consequently, different adsorption capacities for ammonia nitrogen. After high-temperature calcination, the CO32- content between the core and shell layers increases. 2－ The decomposition of CO2 escapes from the interlayer, disrupting the interlayer structure of the hydrotalcite nanosheets and causing a certain degree of structural change in magnesium aluminum hydrotalcite, resulting in an amorphous structure with a larger specific surface area. Magnesium aluminum hydrotalcite possesses a unique memory effect; when the calcined modified hydrotalcite is added to wastewater, a large number of anions enter the interlayer, causing the hydrotalcite interlayer structure to recombine, achieving efficient removal of ammonia nitrogen and organic matter from wastewater and purifying the water quality.

[0033] Furthermore, the struvite composite material has a unique memory effect in its structure. When the material is put into wastewater with high ammonia nitrogen and high COD, its structure can be restored to the structure before high-temperature calcination after adsorbing pollutants. After high-temperature calcination again, it can still have adsorption function. Experiments have verified that it can repeatedly adsorb wastewater at least 3 times, which has the advantage of being regenerable and recyclable.

[0034] In addition, the preparation method and process of the guano composite material provided by this invention are simple, the raw material cost is low, the supply is large, it is environmentally friendly, widely applicable, the reaction conditions are mild, and it can be recycled, which can greatly reduce production and input costs and is suitable for promotion and application. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0036] Figure 1 The X-ray diffraction characteristic peak patterns of the struvite used in Example 1 and Comparative Example 2 are shown.

[0037] Figure 2 This is a flowchart illustrating the preparation process of the core-shell material in Example 1.

[0038] Figure 3 The image shows the characteristic peaks of the X-ray diffraction pattern of the core-shell material used in Example 1.

[0039] Figure 4 The X-ray diffraction characteristic peak patterns of the magnesium aluminum hydrotalcite used in Comparative Examples 1 and 2 are shown.

[0040] Figure 5 The images shown are scanning electron microscope (SEM) images of the materials prepared in Example 1 and Comparative Examples 1 and 2. In the examples, a is an SEM image of the adsorbent obtained by calcining struvite at 300°C, b is an SEM image of the adsorbent obtained by calcining hydrotalcite at 300°C, c is an SEM image of the struvite composite material obtained by calcining at 300°C, and d is an SEM image of the struvite composite material obtained by calcining at 300°C after adsorbing landfill leachate.

[0041] Figure 6 The images show the X-ray diffraction characteristic peaks of the adsorbent obtained after calcining the core-shell material used in Example 1 at 300°C and after adsorbing the leachate.

[0042] Figure 7The adsorption capacity and removal rate of COD, ammonia nitrogen, total nitrogen and total phosphorus in the adsorbent obtained after calcining the core-shell material used in Example 1 at 300°C are shown. It should be noted that the scale between 40mg / L and 900mg / L on the vertical axis has been compressed for a more intuitive display of the results.

[0043] Figure 8 To examine the X-ray diffraction characteristic peak spectra of the adsorbent obtained after calcining the struvite used in Example 1 at different temperatures (100℃, 200℃, 300℃, 400℃, 500℃) and the adsorbent obtained after calcining at different temperatures (200℃, 300℃, 400℃, 500℃) after adsorbing leachate.

[0044] Figure 9 To investigate the adsorption capacity and removal rate of ammonia nitrogen and total nitrogen in the leachate after the core-shell material used in Example 1 was calcined at 200℃.

[0045] Figure 10 To examine the X-ray diffraction characteristic peak patterns of the core-shell material used in Example 2 after calcination at 300℃ and after regeneration and cyclic adsorption of the same leachate three times.

[0046] Figure 11 To verify the adsorption capacity of the core-shell material used in Example 2 after calcination and regeneration at 300℃ and repeated adsorption of the same leachate three times, it should be noted that the scale between 40mg / L and 900mg / L on the vertical axis has been compressed for a more intuitive display of the results.

[0047] Figure 12 To investigate the removal rates of COD, ammonia nitrogen, total nitrogen, and total phosphorus of the core-shell material used in Example 2 after calcination and regeneration at 300°C and repeated adsorption of the same leachate three times.

[0048] Figure 13 To examine the X-ray diffraction characteristic peak patterns of the core-shell material used in Example 2 after calcination at 300℃ and subsequent regeneration and cyclic adsorption of three equal portions of leachate three times.

[0049] Figure 14 To examine the adsorption capacity of the core-shell material used in Example 2 after calcination at 300℃ and sequential regeneration and cyclic adsorption of three equal portions of leachate three times, it should be noted that the scale between 40 mg / L and 900 mg / L on the vertical axis was compressed for a more intuitive presentation of the results.

[0050] Figure 15To investigate the removal rates of COD, ammonia nitrogen, total nitrogen, and total phosphorus of the core-shell material used in Example 2 after calcination at 300°C and subsequent regeneration and cyclic adsorption of three equal portions of leachate three times.

[0051] Figure 16 The X-ray diffraction characteristic peak spectra of the adsorbent obtained by calcining the magnesium aluminum hydrotalcite used in Comparative Example 1 at 300℃ and the adsorbent after adsorbing the leachate are shown.

[0052] Figure 17 The adsorption capacity and removal rate of COD, ammonia nitrogen, total nitrogen and total phosphorus in the leachate after the magnesium aluminum hydrotalcite used in Comparative Example 1 was calcined at 300℃ are shown. It should be noted that the scale between 40mg / L and 900mg / L on the vertical axis was compressed for a more intuitive display of the results. Figure 18 The X-ray diffraction characteristic peak spectra of the adsorbents obtained by calcining struvite and magnesium aluminum hydrotalcite at 300℃ and by physical mixing, after simultaneously adsorbing leachate.

[0053] Figure 19 The adsorption capacity and removal rate of COD, ammonia nitrogen and total nitrogen in the leachate after the struvite used in each comparative example was calcined at 300℃.

[0054] Figure 20 The adsorbent obtained by physically mixing struvite and magnesium aluminum hydrotalcite at 300℃ in Comparative Example 2 simultaneously adsorbs COD, ammonia nitrogen, and total nitrogen from the leachate, and the adsorption capacity and removal rate are compared. Detailed Implementation

[0055] The following detailed description, in conjunction with specific embodiments, illustrates the guano composite material of the present invention, its preparation method, and its applications. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0056] Unless otherwise defined, 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 invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0057] Unless otherwise stated or in case of contradiction, the terms or phrases used herein shall have the following meanings:

[0058] In this article, "one or more" refers to any one, two or more of the listed items.

[0059] In this document, the optional range of "and / or", "or / and", and "and / or" includes any one of two or more of the related listed items, as well as any and all combinations of the related listed items, including any two related listed items, any more related listed items, or a combination of all the related listed items.

[0060] In this document, terms such as "further," "even further," and "particularly" are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of this invention.

[0061] In this document, terms such as "first aspect," "second aspect," "third aspect," and "fourth aspect" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly specifying the importance or quantity of the indicated technical features. Furthermore, "first," "second," "third," and "fourth" serve only as a non-exhaustive enumeration and should be understood as not constituting a closed limitation on quantity. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of the invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified. In the description of the present invention, "several" means at least one, such as one, two, etc., unless otherwise explicitly specified.

[0062] In this invention, numerical ranges are involved. Unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe features or characteristics, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are included.

[0063] Unless otherwise specified, the percentage content involved in this invention refers to mass percentage for solid-liquid mixtures and solid-phase-solid mixtures, and volume percentage for liquid-phase-liquid mixtures.

[0064] Unless otherwise specified, all percentage concentrations mentioned in this invention refer to the final concentration. The final concentration refers to the proportion of the added component in the system after the addition of that component.

[0065] Unless otherwise specified, the temperature parameters in this invention allow for both isothermal treatment and treatment within a certain temperature range. The isothermal treatment allows temperature fluctuations within the precision range controlled by the instrument. Fluctuations are permitted within ranges such as ±5°C, ±2°C, ±1°C, ±0.5°C, ±0.4°C, ±0.3°C, ±0.2°C, and ±0.1°C. In this invention, "room temperature" refers to the absence of temperature control operations, generally 4°C to 35°C, preferably 20±5°C.

[0066] The aluminum salts in this invention may contain water of crystallization or not. For example, "aluminum nitrate" can be understood as aluminum nitrate without water of crystallization, or it can be Al(NO3)2·3H2O with nine molecules of water of crystallization. Similarly, "aluminum chloride" can be understood as anhydrous aluminum chloride without water of crystallization, or it can be AlCl3 6H2 O with six molecules of water of crystallization.

[0067] In this invention, the technical features described in an open-ended manner include both closed-ended technical solutions composed of the listed features and open-ended technical solutions that include the listed features.

[0068] Struvite, a type of mineral, is composed of magnesium ammonium phosphate (MAP) with the molecular formula Mg(NH4)PO4·6H2O, and can be used as a nitrogen and phosphorus fertilizer. The high-temperature pyrolysis product of struvite, MgHPO4 (MHP), has an adsorption and removal rate of over 95% for ammonia nitrogen in wastewater. After pyrolysis, struvite can not only treat wastewater with high ammonia nitrogen content but also convert MAP into MHP. MHP adsorbs ammonia nitrogen, restores the MAP structure, and then undergoes further high-temperature pyrolysis to retain its adsorption function, thus achieving the recycling of struvite. However, the COD removal efficiency of struvite pyrolysis products in wastewater is not high, and the adsorption of ammonia nitrogen by MHP leads to an increase in phosphorus concentration in the effluent. Excessive phosphorus content in wastewater can cause eutrophication and black and odorous water bodies. Therefore, after using struvite pyrolysis products for wastewater denitrification, further removal of COD and phosphorus from the wastewater is crucial.

[0069] Hydrotalcite (Mg4Al2(OH)) 12 Hydrotalcite (CO3·4H2O), a natural layered anionic clay, possesses unique anionic layered structure that endows it with properties such as alkalinity, tunable cation distribution on the layers, and exchangeable anions between layers. Modified hydrotalcite after high-temperature calcination exhibits high COD removal efficiency and excellent phosphorus adsorption performance. After adsorbing anions from wastewater, the interlayer structure of the modified hydrotalcite is restored, allowing it to be calcined again at high temperatures to produce a product with adsorption capabilities, enabling repeated recycling.

[0070] Using the large amount of struvite sludge generated during wastewater treatment as a precursor, and under alkaline conditions, the thermal decomposition products of struvite are used as sources of magnesium and phosphate. An aluminum source is added, and through struvite recrystallization, a struvite@hydrotalcite core-shell structured composite nanomaterial (Mg3Al-CO3SLDH) can be generated, in which carbonate anion intercalated hydrotalcite shells coat the struvite. During the experiment, the technicians of this application unexpectedly discovered that this material can be calcined at high temperature to obtain struvite composite materials. The product of high-temperature calcination (Mg3Al-CO3SLDO) can be used as an adsorbent to treat wastewater with high ammonia nitrogen and high COD, such as landfill leachate, to efficiently remove ammonia nitrogen and organic matter from the wastewater and achieve the purpose of purifying the water quality.

[0071] In a first aspect, the present invention provides a method for preparing a struvite composite material, comprising the following steps:

[0072] A core-shell material is provided, wherein the core of the core-shell material is struvite and the shell is hydrotalcite nanosheets;

[0073] The core-shell material is calcined to prepare the struvite composite material, wherein the calcination temperature is 200℃~300℃.

[0074] Understandably, the calcination temperature includes, but is not limited to: 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃, 290℃, and 300℃.

[0075] In one specific example, the calcination time is 1 hour to 5 hours. It is understood that the calcination time includes, but is not limited to, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, and 5 hours.

[0076] In one specific example, the method for preparing the core-shell material includes the following steps:

[0077] Mix struvite crystals with water, add alkali to adjust the pH of the system to 9-12, stir, and prepare a mixture.

[0078] An aluminum salt solution is added to the mixture to carry out the reaction. The resulting reaction solution is subjected to solid-liquid separation, the solid phase is collected, the solid phase is washed until neutral, and dried to prepare the core-shell material.

[0079] In one specific example, in the preparation step of the mixture, the alkali includes one or more of sodium hydroxide, potassium hydroxide, ammonium bicarbonate, sodium oxide, and sodium carbonate. Understandably, in the step of adding alkali to adjust the pH of the system, the pH of the system includes, but is not limited to, 9, 9.5, 10, 10.5, 11, 11.5, and 12.

[0080] In one specific example, the stirring time in the preparation step of the mixture is 0.5h to 2h. It is understood that the stirring time includes, but is not limited to, 0.5h, 1h, 1.5h, and 2h.

[0081] In one specific example, in the preparation step of the mixture, the raw material for preparing the struvite crystals includes struvite sludge produced from wastewater treatment at a sewage treatment plant.

[0082] In one specific example, the aluminum salt in the aluminum salt solution includes one or more of aluminum nitrate, aluminum sulfate, and aluminum chloride.

[0083] In one specific example, the concentration of the aluminum salt solution is 0.05 mol / L to 0.5 mol / L. It is understood that the concentration of the aluminum salt solution includes, but is not limited to: 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, 0.45 mol / L, and 0.5 mol / L.

[0084] In one specific example, the solvent for the aluminum salt solution in the reaction includes water.

[0085] In one specific example, the aluminum salt solution is added at a rate of 0.1 mL / min to 3 mL / min. It is understood that the addition rate of the aluminum salt solution includes, but is not limited to, 0.1 mL / min, 0.5 mL / min, 1 mL / min, 1.5 mL / min, 2 mL / min, 2.5 mL / min, and 3 mL / min.

[0086] In one specific example, the molar ratio of magnesium in the struvite crystals to aluminum in the aluminum salt solution is (4-20):1. Understandably, the molar ratio of magnesium in the struvite crystals to aluminum in the aluminum salt solution includes, but is not limited to: 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 19:1, and 20:1.

[0087] In one specific example, the reaction temperature is 20℃~50℃. It is understood that the reaction temperature includes, but is not limited to: 20℃, 21℃, 22℃, 23℃, 24℃, 25℃, 26℃, 27℃, 28℃, 29℃, 30℃, 31℃, 32℃, 33℃, 34℃, 35℃, 36℃, 37℃, 38℃, 39℃, 40℃, 41℃, 42℃, 43℃, 44℃, 45℃, 46℃, 47℃, 48℃, 49℃, and 50℃.

[0088] In one specific example, the reaction time is 1 hour to 120 hours. It is understood that the reaction time includes, but is not limited to: 1 hour, 5 hours, 10 hours, 15 hours, 20 hours, 25 hours, 30 hours, 35 hours, 40 hours, 45 hours, 50 hours, 55 hours, 60 hours, 65 hours, 70 hours, 75 hours, 80 hours, 85 hours, 90 hours, 95 hours, 100 hours, 105 hours, 110 hours, 115 hours, and 120 hours.

[0089] In a second aspect, the present invention provides a struvite composite material prepared by the preparation method described above.

[0090] A third aspect of the invention provides the application of the struvite composite material described above in wastewater treatment.

[0091] In one specific example, the wastewater includes at least one of the following characteristics:

[0092] (1) Ammonia nitrogen content is 10 mg / L to 7000 mg / L;

[0093] (2) Chemical oxygen demand is 10 mg / L to 8000 mg / L;

[0094] (3) Total phosphorus content is 1 mg / L to 100 mg / L;

[0095] (4) The total nitrogen content is 10 mg / L to 8000 mg / L.

[0096] In one specific example, the wastewater includes one or more of landfill leachate, anaerobic process supernatant, and ammonia industrial wastewater.

[0097] In a fourth aspect, the present invention provides a wastewater adsorbent comprising the struvite composite material as described above.

[0098] Specifically, this invention utilizes the product of struvite that is slightly soluble when heated under certain alkaline conditions as a magnesium source, phosphorus source, and ammonia source, and adds an appropriate amount of aluminum source to grow hydrotalcite nanosheets in situ in an alkaline environment to coat the unreacted and completely dissolved struvite, forming a core-shell structured composite nanomaterial. The product of this material after high-temperature calcination is used to prepare an environmentally friendly adsorbent that can adsorb high ammonia nitrogen and high COD, which is then applied to wastewater treatment systems such as landfill leachate.

[0099] The present invention will be further described in detail below with reference to specific embodiments. Experimental parameters not specified in the following embodiments should first be referred to the guidelines given in this application, and may also be referred to experimental manuals or other experimental methods known in the art, or the experimental conditions recommended by the manufacturer. It is understood that the instruments and materials used in the following embodiments are relatively specific, and may not be limited to these in other embodiments.

[0100] Experimental materials and methods:

[0101] The struvite crystals used in Example 1 and Comparative Example 2 were purchased from Shanghai Bisheng Environmental Protection Technology Co., Ltd. They can also be obtained from struvite sludge generated during wastewater treatment at sewage treatment plants through a sedimentation method. Their X-ray diffraction characteristic peak patterns are shown below. Figure 1 As shown. Understandably, struvite crystals can also be prepared using methods found in existing literature.

[0102] The preparation steps of the core-shell material (Mg3Al-CO3 SLDH) used in Example 1 are as follows, and the flowchart is shown below. Figure 2 As shown: 5.5g of struvite crystals were ground into powder and placed in a 500mL three-necked flask; 200mL of deionized water was added. The pH was maintained at 11.5 by adding 4M sodium hydroxide solution dropwise. After stirring vigorously at 35°C for 1 hour, 50mL of 0.14mol Al(NO3)3·9H2O deionized water was added dropwise at a rate of 2mL / min. The mixture was stirred at 35°C for 24 hours. After the reaction was completed, the precipitate was separated by vacuum filtration. The filter cake was repeatedly washed with deionized water until the pH was neutral. Then, the filter cake was dried overnight in a vacuum oven at 40°C. The dried lumps were carefully ground to obtain 6g of white powder. Its X-ray diffraction characteristic peak pattern is shown below. Figure 3 As shown. Understandably, core-shell materials can also be prepared by means of commercially available materials or by referring to methods in existing literature.

[0103] The preparation steps (coprecipitation method) of magnesium aluminum hydrotalcite (Mg3Al-CO3 LDH) used in Comparative Examples 1 and 2 are as follows: 50 mL of a solution containing 0.75 M Mg(NO3)2·6H2O and 0.25 M Al(NO3)3·9H2O was added dropwise to 50 mL of 0.5 M Na2CO3 aqueous solution. The pH was maintained at 10.0 by adding 4 M sodium hydroxide aqueous solution. The mixture was stirred and crystallized at room temperature for 17 hours. After washing with deionized water until neutral, the mixture was filtered and separated, then placed in a drying oven at room temperature overnight. After grinding, 6 g of white powder was obtained. Its X-ray diffraction characteristic peak pattern is shown below. Figure 4 As shown. Understandably, magnesium aluminum hydrotalcite can also be prepared by means of commercially available materials or by referring to methods in existing literature.

[0104] Preparation of wastewater simulation solution: The landfill leachate used in the examples and comparative examples were all from a landfill in a certain city. The specific test results are shown in Table 1.

[0105] Table 1

[0106]

[0107] Scanning Electron Microscopy (SEM): The morphology, structure, and elemental composition of the prepared samples are characterized using a scanning electron microscope (SEM). First, the sample to be tested is fixed on the sample stage of the scanning electron microscope with conductive adhesive. A conductive metal film (gold or platinum film) is deposited on the sample using a gold sputtering system (small ion sputtering instrument). Then, the gold-plated sample stage is sent into the instrument for adjustment, focusing, imaging, and elemental analysis.

[0108] X-ray diffraction (XRD) analysis: Powder X-ray diffraction (XRD) spectra were acquired using Cu Kα radiation (α1 = 1.540598 Å, α2 = 1.54426 Å, weighted average = 1.541847 Å) in scanning mode on a PANAnalytical X 'Pert Pro diffractometer. The scanning range was 2θ = 5.0100–80.9760º with a step size of 0.0170º and a scan step size of 55.8800 s. The sample was mounted on a stainless steel holder and produced peaks at 43.36, 44.29, and 50.51 degrees, none of which interfered with the analysis.

[0109] Example 1

[0110] Example 1 describes a core-shell adsorbent obtained by calcining synthesized core-shell materials at 300°C.

[0111] The core-shell material was placed in a ceramic crucible and then placed in a muffle furnace. The calcination temperature was set to 300℃ and the calcination time to 3 hours to prepare struvite composite material, i.e., struvite core-shell type adsorbent. Electron microscopy and X-ray diffraction analysis were performed, and the results are as follows: Figure 5 and Figure 6 As shown, an adsorption test of landfill leachate was then conducted.

[0112] The specific steps for the adsorption test of landfill leachate by adsorbent (adsorption experiment) are as follows: The obtained adsorbent is added to the landfill leachate in excess at a concentration of 1.1 times the ammonia nitrogen concentration. The pH of the landfill leachate is maintained at 7.5~8.0. The mixture is stirred evenly and allowed to react for 1.5 hours. After solid-liquid separation by filtration through filter paper, the supernatant is taken and diluted. The concentrations of COD, ammonia nitrogen, total nitrogen, and total phosphorus in the landfill leachate after adsorption are tested respectively. The solid part is collected directly and dried in an oven at 40℃ for 12 hours before being analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD).

[0113] The COD concentration of the leachate was determined using a 50 mL transparent acid burette (HDHJ / YQ-B-009) according to HJ 828-2017 "Determination of Chemical Oxygen Demand in Water - Dichromate Method", with a detection limit of 4 mg / L.

[0114] The ammonia nitrogen concentration in the leachate was determined using a V-5100 visible spectrophotometer (HDHJ / YQ-J-007) according to HJ 536-2009 "Determination of Ammonia Nitrogen in Water - Salicylic Acid Spectrophotometric Method". The detection limit was 0.01 mg / L.

[0115] The total nitrogen concentration of the leachate was determined using the standard HJ 636-2012 "Determination of Total Nitrogen in Water by Alkaline Potassium Persulfate Digestion Ultraviolet Spectrophotometric Method" with a UV-8000 UV-Vis spectrophotometer (HDHJ / YQ-J-005), and the detection limit was 0.05 mg / L.

[0116] The total phosphorus concentration of the leachate was determined using GB 11893-89 "Determination of Total Phosphorus in Water - Ammonium Molybdate Spectrophotometric Method" with a V-5100 visible spectrophotometer (HDHJ / YQ-J-006), and the detection limit was 0.01 mg / L.

[0117] For details of the adsorption experiment results, please refer to Figure 6 and Figure 7 The removal rates of COD, ammonia nitrogen, total nitrogen, and total phosphorus after adsorbing landfill leachate by the struvite composite material were 26%, 41%, 47%, and 27%, respectively, indicating that the struvite composite material has a good effect on wastewater treatment and can efficiently remove ammonia nitrogen and organic matter from wastewater, thus purifying the water quality.

[0118] Example 1

[0119] This study investigates the adsorption effect of struvite composite materials at different calcination temperatures.

[0120] The core-shell material was placed in a ceramic crucible within a muffle furnace, and calcined at temperatures of 100℃, 200℃, 300℃, 400℃, and 500℃ for 3 hours. The struvite composite materials calcined at different temperatures were analyzed by scanning electron microscopy and X-ray diffraction. Subsequently, the struvite composite materials calcined at 200℃ and 300℃ were tested for adsorption of landfill leachate (testing method as in Example 1). The experimental results are as follows: Figures 5-9 As shown in Table 2.

[0121] The analysis results show that adsorption tests were conducted under different calcination conditions, from... Figure 8 The XRD results showed that only struvite composites calcined at 200℃ and 300℃ could restore their structure after adsorbing wastewater; under calcination conditions of 100℃, 400℃ and 500℃, struvite composites could not be regenerated. Finally, by comparing the adsorption effects of the struvite composite material after calcination at 200℃ and 300℃, 300℃ was determined to be the optimal calcination temperature: After calcination at 200℃, the COD content of the adsorbent adsorbed from the landfill leachate was 5400 mg / L, an increase of 1000 mg / L compared to the original leachate; while the total phosphorus content after adsorption was 168.4 mg / L, an increase of approximately 3.56 times compared to the original leachate, and the removal rates of ammonia nitrogen and total nitrogen reached 31.41% and 43.70%, respectively. After calcination at 300℃, the total phosphorus content of the adsorbent adsorbed from the landfill leachate was 10.08 mg / L, a decrease of 27.33% compared to the original leachate, and the removal rates of COD, ammonia nitrogen, and total nitrogen reached 26.18%, 41.18%, and 47.59%, respectively.

[0122] Table 2 Adsorption experimental results of the adsorbent obtained after calcining the core-shell material at 200℃

[0123]

[0124] Examining Example 2

[0125] This case study verifies the recyclability of struvite composite materials:

[0126] 1. Core-shell struvite composite material regenerates and recycles the same landfill leachate three times.

[0127] Take a sample of landfill leachate, place the struvite composite material obtained in Example 1 into the leachate, and after adsorption, separate the solid and liquid components by filtration with filter paper. Collect the adsorbed leachate, collect and dry the solid portion, and then perform X-ray diffraction analysis and adsorption result detection. Subsequently, recover the sample after the adsorption experiment, place it in a ceramic crucible in a muffle furnace, set the calcination temperature to 300 °C, and the calcination time to 3 h. Perform X-ray diffraction analysis on the pyrolysis products of the core-shell material, and then reintroduce it into the landfill leachate for adsorption result detection. Repeat the above steps 3 times. The experimental results are as follows: Figure 10 , Figure 11 and Figure 12 As shown, the results indicate that the ammonia nitrogen removal rate of the same landfill leachate was as high as 70% or more after being adsorbed three times by the core-shell regenerated adsorbent material, demonstrating strong regenerability and good adsorption performance.

[0128] 2. Core-shell struvite composite material undergoes three regeneration cycles to adsorb an equal amount of landfill leachate.

[0129] Three equal portions of landfill leachate were taken. The struvite composite material obtained in Example 1 was placed in the first portion of the leachate. After adsorption, solid-liquid separation was achieved by filtration with filter paper. The adsorbed leachate was collected, and the solid portion was collected, dried, and subjected to X-ray diffraction analysis and adsorption result detection. Subsequently, the sample after the adsorption experiment was recovered, placed in a ceramic crucible in a muffle furnace, and calcined at 300 °C for 3 h. After X-ray diffraction analysis of the pyrolysis products of the core-shell material, it was added to the second portion of landfill leachate for adsorption result detection and calcination again. The above steps were repeated, that is, the struvite composite material that had adsorbed the second portion of landfill leachate was calcined again and then added to the third portion of landfill leachate for adsorption result detection and calcination again. The experimental results are as follows. Figure 13 , Figure 14 and Figure 15 As shown, the results indicate that the struvite composite material has good regeneration performance, stable removal performance for pollutants such as ammonia nitrogen, and good adsorption performance.

[0130] Comparative Example 1

[0131] Comparative Example 1: The adsorbent obtained by calcining carbonate-intercalated magnesium aluminum hydrotalcite prepared by co-precipitation method was as follows:

[0132] Magnesium-aluminum hydrotalcite was placed in a ceramic crucible within a muffle furnace and calcined at 300°C for 3 hours. The pyrolysis products of the calcined hydrotalcite were analyzed by scanning electron microscopy and X-ray diffraction, followed by tests on the adsorption of landfill leachate (using the same method as in Example 1). The experimental results are as follows: Figure 5 , Figure 16 , Figure 17 and Figure 18 As shown.

[0133] like Figure 17 As shown, the adsorbent prepared in Comparative Example 1 achieved removal rates of 13% for COD, 19.18% for ammonia nitrogen, 28.98% for total nitrogen, and 29.24% for total phosphorus after adsorbing landfill leachate. It is evident that the struvite composite material provided in Example 1, when used as an adsorbent to treat wastewater with high ammonia nitrogen and high COD, exhibits significantly higher removal rates for COD, ammonia nitrogen, total nitrogen, and total phosphorus than the adsorbent prepared in Comparative Example 1, demonstrating superior adsorption performance and better adsorption effect.

[0134] Comparative Example 2

[0135] Comparative Example 2 uses an adsorbent obtained by calcining guanoite as the raw material. The specific steps are as follows:

[0136] Struvite was placed in a ceramic crucible and then placed in a muffle furnace. The calcination temperature was set to 300℃, and the calcination time was 3 hours. The pyrolysis products of the calcined struvite were analyzed by scanning electron microscopy and X-ray diffraction, followed by tests on the adsorption of landfill leachate (testing method as in Example 1). The experimental results are as follows: Figure 18 and Figure 19 As shown in the figure. The results show that the removal rates of COD, ammonia nitrogen, and total nitrogen of the adsorbent prepared in Comparative Example 2 after adsorbing landfill leachate were 17%, 20.9%, and 35.37%, respectively. It can be seen that when the struvite composite material provided in Example 1 is used as an adsorbent to treat wastewater with high ammonia nitrogen and high COD, the removal rates of COD, ammonia nitrogen, and total nitrogen are significantly higher than those of the adsorbent prepared in Comparative Example 2, indicating superior adsorption performance and better adsorption effect.

[0137] Comparative Example 3

[0138] Comparative Example 3 was an adsorbent obtained by physically mixing struvite and hydrotalcite after calcination, specifically:

[0139] The white powder obtained by grinding struvite crystals and the white powder obtained by drying and grinding magnesium aluminum hydrotalcite were placed in separate ceramic crucibles and placed in a muffle furnace. The calcination temperature was set to 300℃ and the calcination time was 3 hours. X-ray diffraction analysis was performed on the pyrolysis products after calcination. Subsequently, the products were physically mixed in a mortar and pestle at a 1:1 mass ratio and used as adsorbents for landfill leachate adsorption tests (test method same as in Example 1). The results are as follows: Figure 18 , Figure 20 As shown in Table 3.

[0140] The results show that the total phosphorus content of the adsorbent prepared in Comparative Example 3 after adsorbing landfill leachate was 162.8 mg / L, which was about 3.4 times higher than that in the original solution. The removal rates of COD, ammonia nitrogen, and total nitrogen were 24%, 26%, and 40%, respectively. It is evident that the struvite composite material provided in Example 1, when used as an adsorbent to treat wastewater with high ammonia nitrogen and high COD, also exhibited significantly higher removal rates of COD, ammonia nitrogen, total nitrogen, and total phosphorus than the adsorbent prepared in Comparative Example 3, demonstrating superior adsorption performance and better adsorption effect.

[0141] Table 3 Adsorption experimental results of the adsorbent obtained in Comparative Example 3

[0142]

[0143] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0144] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. An application of a struvite composite material in the adsorption and removal of ammonia nitrogen, total phosphorus, and COD from wastewater, characterized in that, The preparation method of the guano composite material includes the following steps: A core-shell material is provided, wherein the core of the core-shell material is struvite and the shell is a hydrotalcite nanosheet with carbonate anion intercalation. The core-shell material is calcined to prepare the struvite composite material. The calcination temperature is 300°C and the calcination time is 3 hours. The preparation method of the core-shell material includes the following steps: Mix struvite crystals with water, add alkali to adjust the pH of the system to 9-12, stir, and prepare a mixture. An aluminum salt solution is added to the mixture to carry out the reaction. The resulting reaction solution is subjected to solid-liquid separation, the solid phase is collected, the solid phase is washed until neutral, and dried to prepare the core-shell material.

2. The application according to claim 1, characterized in that, The preparation steps of the mixture satisfy at least one of the following conditions: (1) The alkali includes one or more of sodium hydroxide, potassium hydroxide, ammonium bicarbonate and sodium carbonate; (2) The stirring time is 0.5h~2h; (3) The raw materials for preparing the struvite crystals include struvite sludge produced by wastewater treatment plants.

3. The application according to claim 1, characterized in that, The step of adding the aluminum salt solution satisfies at least one of the following conditions: (1) The aluminum salt in the aluminum salt solution includes one or more of aluminum nitrate, aluminum sulfate and aluminum chloride; (2) The concentration of the aluminum salt solution is 0.05 mol / L to 0.5 mol / L; (3) The aluminum salt solution is added at a rate of 0.1 mL / min to 3 mL / min.

4. The application according to claim 1, characterized in that, The reaction satisfies at least one of the following conditions: (1) The molar ratio of magnesium in the struvite crystals to aluminum in the aluminum salt solution is (4-20):1; (2) The reaction temperature is 20℃~50℃; (3) The reaction time is 1h to 120h.

5. The application according to any one of claims 1 to 4, characterized in that, The wastewater includes one or more of the following: landfill leachate, anaerobic process supernatant, and ammonia industrial wastewater.

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