Method for synthesizing micro-nano magnesium ammonium phosphate based on micro-channel reaction, material and application

Abstract

The application discloses a method for synthesizing micro-nano scale magnesium ammonium phosphate based on micro-channel reaction, which comprises the following steps: feeding a magnesium-containing solution, a phosphate-containing solution and an ammonia nitrogen-containing solution into a micro-channel reactor through a fluid conveying device to obtain a suspension, wherein the molar ratio of magnesium, nitrogen and phosphorus is 1.0-1.5:1:1; and after post-treatment of the suspension, micro-nano magnesium ammonium phosphate is obtained. The above method can prepare micro-nano scale pure phase magnesium ammonium phosphate hexahydrate. The application also discloses application of the micro-nano magnesium ammonium phosphate in the field of water treatment, which can treat sewage containing Pb 2+ , Cd 2+ . The micro-nano scale pure phase magnesium ammonium phosphate hexahydrate can be obtained at room temperature by virtue of the microcosmic mass transfer mixing capacity in the micro-channel. The micro-nano magnesium ammonium phosphate prepared by the method has a removal rate and adsorption rate which are obviously superior to those of the prior art when used as a heavy metal sewage adsorbent to adsorb Pb 2+ , Cd 2+ .

Description

Technical Field

[0001] This invention belongs to the field of preparation technology of magnesium ammonium phosphate, specifically relating to a method and materials for synthesizing micro-nano magnesium ammonium phosphate via microchannel reaction and its application in heavy metal pollution. Background Technology

[0002] With the rapid development of industry and agriculture, wastewater containing high concentrations of ammonia nitrogen and heavy metal pollution (such as Pb) has become increasingly common. 2+ Cd 2+ The treatment and resource utilization of ammonia nitrogen in wastewater is a major challenge in the field of water environment engineering. Chemical precipitation to convert ammonia nitrogen in wastewater into magnesium ammonium phosphate (MAP, commonly known as struvite) crystals not only removes ammonia nitrogen, but the product, as a crystalline material with abundant surface active sites and ion exchange capacity, also shows great potential in the field of heavy metal adsorption. However, achieving efficient and deep removal of heavy metals using MAP materials places extremely stringent requirements on crystal purity and particle size distribution, and also presents significant challenges to the simplicity of the synthesis process and the industrial scale-up of the equipment.

[0003] Currently, most MAP crystallization synthesis processes rely on traditional stirred-tank reactors. Traditional macroscopic reaction systems suffer from insurmountable defects in rapid mass transfer and uniform mixing: the mixing inside the reactor is extremely uneven, leading to huge local supersaturation gradients within the system. Since this ionic reaction is rapid in aqueous solution, this macroscopic inhomogeneity causes the primary nucleation and crystal growth processes of MAP to overlap and become uncontrolled, ultimately resulting in products with extremely wide particle size distributions, irregular morphologies, and a high tendency to aggregate, while also making it difficult to avoid the growth of accompanying impurity phases. For example, although MAP precipitation was achieved in a magnesium-based desulfurization wastewater co-treatment system (patent publication CN121020895A), it relied on an inefficient ripening process lasting several hours, and the crystal morphology could not be precisely controlled. The macroscopically large particles or severely agglomerated MAP materials produced by this technology are often on the scale of tens to hundreds of micrometers, with their specific surface area significantly compressed, and the internal lattice ion exchange sites not effectively exposed, directly hindering their application value as high-performance heavy metal adsorbents.

[0004] In recent years, microchemical technology has provided a revolutionary means for the controllable synthesis of high-end nano / micro powder materials. Microchannel reactors, with their micrometer-scale characteristics (typically tens to hundreds of micrometers), have fundamentally changed the transport and reaction behavior of fluids. Within the confined space of a microchannel, the fluid diffusion distance is greatly shortened, the phase interface area increases exponentially, and relying on extremely high fluid shear forces, multiple reactants can achieve instantaneous and uniform mixing at the molecular level within milliseconds.

[0005] Although microchannel technology has been applied to organic synthesis and the preparation of some inorganic nanomaterials, its deep integration into the complex "in-situ multiphase crystallization system of ammonia nitrogen wastewater" remains a technological gap. Rapidly and precisely locking the microscopic thermodynamic and kinetic window required for the formation of pure-phase magnesium ammonium phosphate hexahydrate in ammonia nitrogen wastewater multi-component systems is a significant challenge. In recent years, while there have been attempts to introduce microreaction technology into the synthesis of traditional ammonium salts (such as the simple acid-base neutralization to prepare ammonium dihydrogen phosphate) (CN106892413A Method for Direct Crystallization of Ammonium Dihydrogen Phosphate in a Microreactor and CN101993052A A Microreaction System and Application for Ammonium Salt Production), these processes often involve intense exothermic reactions, resulting in extremely complex microreaction systems. These systems require additional series-connected microchannel heat exchangers for forced cooling, or rely on extreme high-temperature vaporization conditions and extremely cumbersome real-time pH feedback control loops. This high complexity and stringent operating window significantly increase production and maintenance costs, severely hindering its industrial-scale application in environmental water treatment. In contrast, exploring a novel process that features a simple device structure, eliminates the need for complex heat exchange and stringent temperature control, and enables convenient and continuous preparation of high-performance micro-nano-scale MAP materials at room temperature not only significantly lowers the threshold for industrial production but also provides a technological advantage for large-scale continuous treatment of ammonia nitrogen wastewater.

[0006] Therefore, there is an urgent need to develop an innovative process based on microchannel reactors to enhance mass transfer, which can not only industrially treat high ammonia nitrogen wastewater, but also generate micro-nano scale MAP materials that can be further used for the deep purification of heavy metal polluted water sources, achieving two goals at once. Summary of the Invention

[0007] To address the shortcomings of traditional batch reactor methods for preparing micro / nano magnesium ammonium phosphate (MAP) materials, such as uneven mixing, large local supersaturation differences leading to uncontrollable crystal growth, large MAP particles (often tens to hundreds of micrometers), and poor adaptability to low-concentration ammonia nitrogen systems, the primary objective of this invention is to provide a continuous synthesis method based on microchannel reaction technology. This method utilizes a minimally sized apparatus, operates stably at room temperature, and efficiently synthesizes pure-phase MAP micro / nano materials using ammonia nitrogen-containing solutions of varying concentrations (simulating ammonia nitrogen wastewater).

[0008] The application of the highly active micron-sized materials prepared by the method of this invention in the treatment of wastewater containing heavy metal ions (especially lead and cadmium) achieves the comprehensive environmental protection goals of resource recycling of waste and "treating waste with waste".

[0009] To achieve the above objectives, the technical solution of the present invention is as follows: A method for synthesizing micro / nano magnesium ammonium phosphate based on microchannel reaction includes the following steps: A magnesium-containing solution, a phosphate-containing solution, and an ammonia nitrogen-containing solution are transported to a microchannel reactor via a fluid transport device to obtain a suspension; the suspension is then post-treated to obtain micro / nano-sized magnesium ammonium phosphate. The molar ratio of magnesium, nitrogen, and phosphorus in the magnesium-containing solution, phosphate-containing solution, and ammonia nitrogen-containing solution is (1.0~1.5):1:1; the reaction temperature in the microchannel reactor is room temperature; and the flow rate of the reaction solution in the microchannel reactor is 5~100 mL / min.

[0010] Preferably, the channel characteristic size of the microchannel reactor is 1~300μm, and the microchannel reactor is one or more of the S-type, F-type, and P-type used in series.

[0011] Preferably, the magnesium-containing solution is one of magnesium chloride aqueous solution and magnesium nitrate aqueous solution, and the concentration of magnesium ions in the magnesium-containing solution is 0.1~0.24 mol / L; the phosphate-containing solution is one of phosphoric acid aqueous solution, disodium hydrogen phosphate aqueous solution, and sodium phosphate aqueous solution, and the concentration of phosphorus ions in the phosphate-containing solution is 0.1~0.2 mol / L; the ammonia nitrogen concentration in the ammonia nitrogen-containing solution is 0.1~0.2 mol / L.

[0012] The magnesium-containing solution of this invention is a magnesium source, specifically a solution prepared from soluble magnesium salts. The phosphate-containing solution is a phosphorus source. The ammonia-nitrogen-containing solution in this invention simulates ammonia-nitrogen wastewater and is prepared from ammonia water or ammonium chloride.

[0013] Preferably, the ammonia nitrogen concentration of the ammonia nitrogen-containing solution is 100 mg / L to 300 mg / L.

[0014] In this invention, an ammonia nitrogen concentration of 0.1~0.2 mol / L simulates high-concentration ammonia nitrogen wastewater, and an ammonia nitrogen concentration of 100 mg / L~300 mg / L simulates low-concentration ammonia nitrogen wastewater. Both can be used to prepare magnesium ammonium phosphate.

[0015] Preferably, the method includes the following steps: preparing 0.1 mol / L magnesium chloride aqueous solution and 0.15 mol / L ammonium chloride aqueous solution respectively, then mixing them to obtain solution A; then preparing 0.1 mol / L sodium phosphate aqueous solution to obtain solution B; the molar ratio of Mg, N, and P is controlled at 1.5:1:1; setting the microchannel size to 1 μm, the reaction conditions to room temperature, and the flow rate to 10 mL / min, pumping solutions A and B into a P-type microchannel reactor to obtain a suspension; and after post-treatment of the suspension, obtaining magnesium ammonium phosphate.

[0016] Another object of the present invention is to provide a magnesium ammonium phosphate micro / nano material prepared by the above method, wherein the material is a pure phase magnesium ammonium phosphate hexahydrate at the micro / nano scale.

[0017] Another object of the present invention is the application of the above-mentioned micro / nano magnesium ammonium phosphate in the field of water treatment, for treating Pb-containing water. 2+ Cd 2+ Sewage.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention overcomes the mass transfer bottleneck caused by macroscopic inhomogeneity in traditional batch reactors by introducing a microchannel reactor with a characteristic size of only 1~300μm. Utilizing the extremely short molecular diffusion distance and high fluid shear force within the confined space, multi-component reactants achieve molecular-level microscopic instantaneous mixing within milliseconds. Compared to traditional synthesis methods that easily generate magnesium phosphate, the extreme mixing environment in the microscale creates an extremely uniform high supersaturation, forcibly inducing explosive pure-phase nucleation of magnesium ammonium phosphate (MAP). This effectively decouples the nucleation and growth processes of crystals, ultimately yielding pure-phase magnesium ammonium phosphate hexahydrate micro / nanomaterials with uniform distribution, regular morphology, and extremely high crystallinity.

[0019] 2. This invention relies on the extreme microscopic mixing capability within the microchannels, exhibiting exceptional tolerance to conditions such as pH, ammonia nitrogen concentration, and temperature. Even when treating wastewater with low ammonia nitrogen concentrations of 100-300 ppm, it can still locally and instantaneously form high supersaturation and successfully induce complete MAP crystallization, overcoming the thermodynamic bottleneck of nucleation difficulties in low-concentration systems. Furthermore, this system eliminates the need for stringent real-time pH feedback adjustment; regardless of whether strongly alkaline sodium phosphate or weakly alkaline disodium hydrogen phosphate is used as the phosphorus source, it can stably synthesize high-purity target products, completely eliminating the interference of macroscopic local pH fluctuations on crystal purity.

[0020] The method of this invention can be carried out stably and continuously at room temperature. The reaction device has an extremely simple structure, and the safety and convenience of operation are fundamentally improved.

[0021] 3. Excellent heavy metal adsorption performance in "waste-to-waste" treatment. This invention transforms ammonia nitrogen wastewater into micro / nano-scale MAP materials for further heavy metal removal, converting heavy metal ions into products with extremely low solubility (hydroxyphosphoric acid lead and amorphous or low-crystallinity Cd–P byproducts). Due to the excellent specific surface area and abundant active sites of the microchannel-synthesized MAP, it exhibits superior adsorption performance for Pb. 2+ and Cd 2+ It exhibits an extremely fast adsorption rate and extremely high removal efficiency (for Pb after 2 minutes of treatment). 2+ The adsorption efficiency reached 98.45%, and the maximum adsorption capacity was 293 mg / g; after 100 min of treatment, the adsorption capacity of Cd was reduced. 2+ Its adsorption efficiency reaches 96.73%. Its deep purification mechanism involves rapid physical adsorption, surface complexation, lattice ion exchange, and dissolution-precipitation transformation mechanism, providing a new path for the comprehensive treatment of ammonia nitrogen and heavy metal wastewater. Attached Figure Description

[0022] Figure 1 The XRD diffraction patterns of intermediate product A and MAP prepared in Example 1 are shown below. Figure 1 a) XRD diffraction pattern of intermediate product A after post-processing and grinding; Figure 1 b) is the XRD diffraction pattern of magnesium ammonium phosphate powder; Figure 2 The XRD diffraction pattern of the MAP prepared in Example 2; Figure 3 The XRD diffraction pattern of the MAP prepared in Example 3; Figure 4 The XRD diffraction pattern of the MAP prepared in Example 4; Figure 4 a) XRD diffraction pattern of MAP prepared for experimental group 1; Figure 4 b) XRD diffraction pattern of MAP prepared in experimental group 2; Figure 5 The XRD diffraction patterns prepared under different ammonia nitrogen concentrations in Example 5 are shown below. Figure 5 a) XRD diffraction pattern of MAP prepared under the condition of ammonia nitrogen concentration of 100 mg / L; Figure 5 b) is the XRD diffraction pattern of MAP prepared under the condition of ammonia nitrogen concentration of 200 mg / L; Figure 5 c) is the XRD diffraction pattern of MAP prepared under the condition of ammonia nitrogen concentration of 300 mg / L; Figure 6 XRD diffraction patterns of MAP1 prepared for Comparative Example 1 and Nano-MAP prepared for Example 6; Figure 6 a) XRD diffraction pattern of MAP1 prepared in Comparative Example 1; Figure 6 b) XRD diffraction pattern of Nano-MAP prepared in Example 6; Figure 7 SEM image of the Nano-MAP prepared in Example 6; Figure 8 SEM image of the MAP prepared in experimental group 1 of Example 4; Figure 9 SEM image of MAP1 prepared for Comparative Example 1; Figure 10 SEM images and elemental distribution maps of the MAP prepared in Experimental Group 1 of Example 4; Figure 11 To apply different adsorbents to the heavy metal Pb in Example 1 2+ Adsorption kinetics curves; Figure 11 a) Curves showing the concentrations of different adsorbents at different times. Figure 11 b) shows the removal rates of different adsorbents at different times. Figure 11 c) Curves of adsorption capacity for different adsorbents at different times; Figure 12 For example 1, MAP adsorption of heavy metal Pb 2+ Subsequent SEM images and element distribution maps; Figure 13 For example 1, MAP adsorption of heavy metal Pb 2+ XRD diffraction pattern of the subsequent product; Figure 14 To apply different adsorbents to the heavy metal Cd in Example 2 2+ Adsorption kinetics curves; Figure 14 a) Curves showing the concentrations of different adsorbents at different times. Figure 14 b) shows the removal rates of different adsorbents at different times. Figure 14 c) Curves of adsorption capacity for different adsorbents at different times; Figure 15 For example 2, MAP adsorption of heavy metal Cd 2+ The subsequent SEM images and element distribution maps. Detailed Implementation

[0023] To more clearly explain the technical solutions of the embodiments of the present invention and the prior art, the invention will be further described below with reference to the figures and examples. The described embodiments are merely some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments in this application are within the scope of protection of this application.

[0024] The microchannel reactors used in this invention are manufactured by Kunshan Fuxi Engineering Technology Co., Ltd., with models DX-S-S6 and DX-F-S6, abbreviated as S-type and F-type; a P-type microchannel reactor manufactured by Jinzhi Micro Chemical Technology Co., Ltd. was also used.

[0025] The microchannels of the microchannel reactor selected in this invention have a mixing function, and the solution is mixed at the millisecond level within the microchannel, so there is no need for additional control of the reaction time.

[0026] The post-processing in this invention consists of: settling, separation, washing, and drying. Specifically, after settling for 30 minutes, the solid precipitate is centrifuged at 10,000 rpm for 3 minutes, washed three times each with deionized water and anhydrous ethanol, and then dried at 80°C for 12 hours.

[0027] The adsorption capacity Qt (mg / g) and removal rate (R, %) in this invention are calculated using the following formulas:

[0028] Among them, C0 and C t , where are the initial concentration and the concentration at time t (mg / L), respectively; V is the solution volume (L); and m is the adsorbent mass (g).

[0029] Example 1 (I) Continuous Synthesis of Micron-sized Magnesium Ammonium Phosphate via Microchannel Multi-step Method

[0030] This embodiment aims to demonstrate the process of synthesizing high-purity micron-sized magnesium ammonium phosphate using a stepwise feeding method in a series-connected S-type microchannel reactor.

[0031] Step 1: Preparation of raw material solution Using analytical grade reagents and deionized water, prepare the following three reaction precursor solutions: 100 mL of 0.24 mol / L magnesium chloride aqueous solution; 100 mL of 0.2 mol / L sodium phosphate aqueous solution; and ammonia nitrogen concentration (in NH4+) diluted with concentrated ammonia water. + 100 mL of an ammonia nitrogen solution with a concentration of 0.2 mol / L was prepared to simulate high-concentration ammonia nitrogen wastewater.

[0032] Step 2: Construction of the microchannel reaction device The fluid delivery system includes three precision metering pumps (Pump1, Pump2, Pump3) and two S-type microchannel reactors in series (Reactor1, Reactor2).

[0033] The outlets of precision metering pumps Pump1 and Pump2 are connected to the two inlets of the first S-type reactor (Reactor1), respectively; the outlet of the first S-type reactor (Reactor1) is connected to one inlet of the second S-type reactor (Reactor2); and the outlet of precision metering pump Pump3 is connected to the other inlet of the second S-type reactor (Reactor2).

[0034] The characteristic channel size of the microchannel reactor was set to 200 μm.

[0035] Step 3: Synthesis Reaction Process Start the precision metering pump and adjust the flow rate to feed the three solutions continuously in stoichiometric ratio. The reaction takes place at room temperature and does not require additional heating or cooling.

[0036] The magnesium-containing solution and the phosphate-containing solution were simultaneously pumped into Reactor 1 through Pump 1 and Pump 2, respectively, with the flow rate adjusted to 20 mL / min, so that the molar ratio of Mg, N, and P was 1.2:1:1. Under the high shear force of the microchannel, the two fluids mix instantaneously and undergo a primary reaction to generate an intermediate product Mg3(PO4)2 suspension (denoted as intermediate product A). Intermediate product A flows directly out and into Reactor2. At the same time, an ammonia nitrogen-containing solution is pumped into Reactor2 via Pump3. The flow rate of the reaction solution in the Reactor2 microchannel reactor is 20 mL / min. In Reactor2, intermediate product A comes into rapid contact with an ammonia nitrogen-containing solution and undergoes phase transformation and crystallization reactions, with the effluent being a magnesium ammonium phosphate suspension.

[0037] Step 4: Post-processing The white suspension flowing out of Reactor2 was collected, and after post-processing, it was ground into powder to obtain magnesium ammonium phosphate powder.

[0038] (II) Product Characterization and Result Analysis

[0039] X-ray powder diffraction (XRD) analysis was performed on intermediate product A (ground into powder after post-processing) and the final product magnesium ammonium phosphate powder prepared in the above steps. The results are as follows: Figure 1 As shown.

[0040] like Figure 1 As shown in a), the diffraction peaks mainly correspond to the standard crystal structure of magnesium phosphate (Mg3(PO4)2) (JCPDS No. 00-035-0329), indicating that before the addition of an ammonia source containing ammonia nitrogen solution, magnesium source and phosphorus source preferentially form magnesium phosphate precipitate.

[0041] like Figure 1 As shown in b), when an ammonia source containing ammonia nitrogen solution is introduced and a secondary reaction is carried out in Reactor 2, the diffraction peaks of the product undergo a complete transformation. The position of its characteristic peak (2θ) is in high agreement with the standard card (JCPDS No. 98-000-0419) of magnesium ammonium phosphate hexahydrate (MgNH4PO4·6H2O).

[0042] Example 2

[0043] This embodiment prepares MAP using a T-type three-way mixer and an F-type microchannel reactor, which is a premixing route for magnesium-containing solutions and phosphate-containing solutions (Mg+P).

[0044] Reaction conditions and procedures: The concentrations of the three precursor solutions were the same as in Example 1, and the molar ratio of Mg, N, and P was 1:1:1. In this example, before entering the microchannel reactor, a T-type three-way mixer was used to premix the magnesium-containing solution and the phosphate-containing solution. The magnesium-containing solution and the phosphate-containing solution entered the T-type three-way mixer through Pump 1 and Pump 2, respectively, and then entered the F-type microchannel reactor together with the ammonia-nitrogen-containing solution delivered by Pump 3 to synthesize MAP. Other conditions were the same as in Example 1.

[0045] like Figure 2 As shown, the XRD diffraction peaks of the final product obtained in Example 2 correspond perfectly to the MAP standard card. This indicates that even with a relatively simple mixer combined with the enhancement effect of a microchannel reactor, pure-phase MAP can still be synthesized stably.

[0046] Example 3

[0047] This embodiment uses a two-stage series S-type microchannel reactor to prepare MAP, which is a premixed route containing ammonia nitrogen solution and phosphate solution (N+P).

[0048] The raw material concentration in this embodiment is the same as in Example 1, except that the molar ratio of Mg, N, and P is 1.5:1:1.

[0049] Both S-shaped microchannel reactors had a microchannel size of 300 μm, the reaction temperature was room temperature, and the flow rate was set at 100 mL / min.

[0050] First, an ammonia nitrogen-containing solution and a sodium phosphate solution containing phosphate ions are pumped into Reactor 1 to form a mixture. Then, this mixture and a magnesium chloride solution are both introduced into Reactor 2 for contact reaction.

[0051] like Figure 3 As shown, even after changing the mixing order of the raw materials, the final product is still high-purity MAP.

[0052] This indicates that the method of the present invention has a wide operating window.

[0053] Example 4

[0054] In this embodiment, sodium phosphate aqueous solution and disodium hydrogen phosphate aqueous solution are used as phosphate-containing solutions to provide phosphorus sources, and a single S-type microchannel reactor is used.

[0055] Reaction conditions and procedures: Prepare aqueous solutions containing 0.1 mol / L magnesium chloride and 0.1 mol / L ammonium chloride, and mix them to obtain mixture A; prepare aqueous solutions containing 0.1 mol / L sodium phosphate (solution B1) and 0.1 mol / L disodium hydrogen phosphate (solution B2) respectively, and set the flow rate to 30 mL / min.

[0056] Experimental Group 1: Mixture A and solution B1 were pumped into an S-type microchannel reactor to obtain magnesium ammonium phosphate suspension, which was then post-processed and ground to obtain magnesium ammonium phosphate powder. Experimental Group 2: Mixture A and solution B2 were pumped into an S-type microchannel reactor to obtain magnesium ammonium phosphate suspension, which was then post-processed and ground to obtain magnesium ammonium phosphate powder.

[0057] Depend on Figure 4 a) and Figure 4 b) It can be seen that MAP materials can be successfully synthesized regardless of whether sodium phosphate aqueous solution or disodium hydrogen phosphate aqueous solution is used as the phosphorus source.

[0058] This embodiment demonstrates the universality of the method of the present invention for different phosphorus sources.

[0059] like Figure 8 The image shown is a SEM image of the MAP prepared in Experimental Group 1 of this embodiment. The pure phase magnesium ammonium phosphate hexahydrate material is uniformly distributed and has a regular morphology. The morphology is rod-shaped with a smooth surface and a clear aspect ratio. The length of the rod-shaped structure is 10-30 μm.

[0060] Example 5

[0061] MAP was synthesized in a low-concentration ammonia nitrogen environment using a P-type single microchannel reactor.

[0062] Reaction conditions and steps: Prepare ammonium chloride solutions with ammonia nitrogen concentrations of 100 mg / L, 200 mg / L, and 300 mg / L, respectively, to simulate low-concentration ammonia nitrogen wastewater. Mix the three concentrations of ammonium chloride solutions with magnesium chloride aqueous solution, controlling the Mg:N molar ratio to be 1.2:1. Then react with sodium phosphate solution through a microchannel reactor, with the Mg:N:P ratio to be 1.2:1:1, to obtain magnesium ammonium phosphate suspension. After post-processing and grinding, magnesium ammonium phosphate powder is obtained.

[0063] like Figure 5 As shown in a), 5b), and 5c), even in the low concentration range of 100 mg / L to 300 mg / L, the enhanced mass transfer within the microchannels still induces the formation of structurally complete MAP crystals.

[0064] Example 6

[0065] Prepare 0.15 mol / L magnesium chloride aqueous solution and 0.1 mol / L ammonium chloride aqueous solution separately, then mix them to obtain solution A. Then prepare 0.1 mol / L sodium phosphate aqueous solution to obtain solution B. The molar ratio of Mg, N and P is controlled at 1.5:1:1.

[0066] A P-type microchannel reactor (microchannel size 1 μm, room temperature) was used, and the flow rate was set to 10 mL / min. Solutions A and B were pumped into the P-type microchannel reactor to obtain a suspension. After post-treatment, magnesium ammonium phosphate was obtained. The material obtained in this embodiment is Nano-MAP.

[0067] like Figure 6 As shown in b), the position of its characteristic peak matches that of the standard card for magnesium ammonium phosphate hexahydrate.

[0068] like Figure 7 As shown, the magnesium ammonium phosphate hexahydrate material is relatively uniformly distributed within the field of view, with a regular morphology. Its microstructure consists of interconnected and stacked nanosheets forming a flower-like morphology. This morphology is beneficial for increasing the specific surface area and enhancing the adsorption / reaction activity of the material.

[0069] Comparative Example 1

[0070] This comparative example shows the synthesis of MAP using the traditional coprecipitation method. The MAP synthesized in this comparative example is labeled as MAP1.

[0071] Reaction conditions and steps: Prepare an aqueous solution containing 0.1 mol / L magnesium chloride and 0.1 mol / L ammonium chloride, and mix them to obtain a mixed solution; prepare an aqueous solution of 0.1 mol / L disodium hydrogen phosphate (first solution) and a 1 mol / L sodium hydroxide solution.

[0072] The first solution was added dropwise to the mixture using a peristaltic pump and stirred until homogeneous. Sodium hydroxide solution was added dropwise to control the pH of the mixture between 8.5 and 9.5, and the product was obtained. The post-processing of the product was the same as in Example 1, and finally, the coprecipitated MAP1 was obtained.

[0073] like Figure 6 As shown in a), the position of its characteristic peaks conforms to the standard card (JCPDS No. 98-000-0419) for magnesium ammonium phosphate hexahydrate (MgNH4PO4·6H2O), and there is a small peak at around 20°, which is identified as a miscellaneous peak.

[0074] Figure 7 , Figure 8 , Figure 9 The comparison shows that the MAP material synthesized by the microchannel method in this invention exhibits better dispersibility, more uniform particle distribution, and no obvious agglomeration phenomenon than MAP1 prepared by the traditional coprecipitation method.

[0075] Application Example 1

[0076] The adsorption and mineralization tests of heavy metal lead were conducted using MAP prepared in Experimental Group 1 of Example 4, MAP1 prepared in Comparative Example 1, and Nano-MAP prepared in Example 6 as adsorbents.

[0077] Adsorption test: 0.04 g of adsorbent was weighed and placed in 200 mL of a prepared heavy metal ion solution of 50-70 ppm, with a solid-liquid ratio controlled at 0.2 g / L. The solution was subjected to constant temperature shaking at 140 rpm at 25℃. Samples were taken at preset time intervals (0-2880 min). After centrifugation and filtration, a clean test solution was obtained, and the concentration of remaining heavy metal ions was measured using inductively coupled atomic emission spectrometry (ICP-OES). The adsorption of lead and cadmium in the experiment was conducted under acidic conditions to simulate the pH of lead- and cadmium-contaminated wastewater under natural conditions.

[0078] like Figure 11 As shown, the reaction time of MAP on Pb is 20 min. 2+ The adsorption reached equilibrium, with a removal rate of 98.58%. In comparison, MAP1 reached adsorption equilibrium in 90 minutes, while Nano-MAP reached adsorption equilibrium in 2 minutes, achieving a removal rate of 98.45% and remaining stable. After normalizing the adsorption capacity, it was shown that Nano-MAP reached a Qt / Qe value of 1 in 2 minutes, while MAP required 20 minutes, and MAP1 required 60-90 minutes, indicating that the nano-sized Nano-MAP had a higher adsorption rate.

[0079] Figure 10 and Figure 12 SEM images and elemental mapping revealed a significant change in the morphology of the material after MAP adsorption. Initially, regular rod-shaped particles were joined by irregular aggregates, and Pb was uniformly distributed. This indicates that the removal mechanism involves not only physical adsorption but also a significant "dissolution-precipitation" mechanism, where MAP crystals partially dissolve to release phosphate ions, which then react with Pb. 2+ Lead phosphate precipitates with smaller solubility products were formed in situ.

[0080] Figure 13 The synthesized new phase was confirmed to be hydroxyphosphoric lead (Pb5(PO4)3OH), with a solubility product Ksp = 10. -80.77 .

[0081] Application Example 2

[0082] The MAP prepared in Experimental Group 1 of Example 4, the MAP1 prepared in Comparative Example 1, and the Nano-MAP prepared in Example 6 were used as adsorbents for the adsorption of heavy metal cadmium (Cd). 2+ Adsorption and mineralization tests of ).

[0083] Adsorption tests: MAP, MAP1 and Nano-MAP for Cd 2+ The adsorption results are as follows Figure 14As shown. The results indicate that when the reaction proceeds for 90 min, MAP has an effect on Cd. 2+ The adsorption reached equilibrium, and the removal rate reached 99.74%. MAP1 reached equilibrium after 30 minutes, but its removal efficiency stabilized at around 95%, and the Cd removal efficiency of MAP... 2+ The concentration decreased rapidly in a short time. Nano-MAP reached equilibrium in 10 min, with a removal rate of 96.76%. After normalization of the adsorption capacity, it was found that Nano-MAP reached a Qt / Qe value of 1 in 10 min, while MAP1 required 40-60 min and MAP required 30 min. The adsorption rate and equilibrium time of Nano-MAP were significantly better than those of MAP and MAP1.

[0084] Figure 15 As shown, a new coating layer appeared on the surface of the MAP material after cadmium adsorption, and the positions of Cd, P, and Mg elements highly overlapped. Based on the kinetic data, the mechanism is presumed to mainly include surface complexation and partial lattice ion exchange (Cd... 2+ Replacement of Mg 2+ This process generates amorphous or low-crystallinity Cd–P byproducts, thereby achieving deep curing of cadmium.

[0085] This invention utilizes an extreme mixing environment within a micron-level channel to completely eliminate local supersaturation differences, reducing the conditions for MAP formation and achieving explosive, uniform nucleation and crystal growth of MAP. This allows for the continuous and stable synthesis of magnesium ammonium phosphate materials with specific microstructures, uniform particle distribution, and extremely high intrinsic adsorption activity within a very short reaction time. Simultaneously, this invention links the in-situ continuous micro-reaction synthesis of ammonia nitrogen wastewater with the deep purification of heavy metal wastewater, producing a highly efficient adsorbent and achieving comprehensive utilization of wastewater resources and "waste-to-waste" treatment.

[0086] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for synthesizing micro / nano magnesium ammonium phosphate based on microchannel reaction, characterized in that, Includes the following steps: A magnesium-containing solution, a phosphate-containing solution, and an ammonia nitrogen-containing solution are transported to a microchannel reactor via a fluid transport device to obtain a suspension; the suspension is then post-treated to obtain micro / nano-sized magnesium ammonium phosphate. The molar ratio of magnesium, nitrogen, and phosphorus in the magnesium-containing solution, phosphate-containing solution, and ammonia nitrogen-containing solution is (1.0~1.5):1:1; the reaction temperature in the microchannel reactor is room temperature; and the flow rate of the reaction solution in the microchannel reactor is 5~100 mL / min.

2. The method for synthesizing micro / nano magnesium ammonium phosphate based on microchannel reaction according to claim 1, characterized in that, The microchannel reactor has a channel characteristic size of 1~300μm, and the microchannel reactor is one or more of the S-type, F-type, and P-type used in series.

3. The method for synthesizing micro / nano magnesium ammonium phosphate based on microchannel reaction according to claim 2, characterized in that, The magnesium-containing solution is one of magnesium chloride aqueous solution and magnesium nitrate aqueous solution, and the concentration of magnesium ions in the magnesium-containing solution is 0.1~0.24 mol / L; the phosphate-containing solution is one of disodium hydrogen phosphate aqueous solution and sodium phosphate aqueous solution; the concentration of phosphorus ions in the phosphate-containing solution is 0.1~0.2 mol / L; the ammonia nitrogen concentration in the ammonia nitrogen-containing solution is 0.1~0.2 mol / L.

4. The method for synthesizing micro / nano magnesium ammonium phosphate based on microchannel reaction according to claim 1, characterized in that, The ammonia nitrogen concentration of the ammonia nitrogen-containing solution is 100 mg / L to 300 mg / L.

5. The method for synthesizing micro / nano magnesium ammonium phosphate based on microchannel reaction according to claim 3, characterized in that, Includes the following steps: Prepare 0.1 mol / L magnesium chloride aqueous solution and 0.15 mol / L ammonium chloride aqueous solution separately, then mix them to obtain solution A. Prepare 0.1 mol / L sodium phosphate aqueous solution to obtain solution B. The molar ratio of Mg, N, and P is controlled at 1.5:1:

1. Use a P-type microchannel reactor with a microchannel size of 1 μm, room temperature reaction conditions, and a flow rate of 10 mL / min. Pump solutions A and B into the P-type microchannel reactor to obtain a suspension. After post-treatment, the suspension yields micro / nano magnesium ammonium phosphate.

6. A micro / nano magnesium ammonium phosphate material prepared by the method of claim 1, characterized in that, The material is pure-phase magnesium ammonium phosphate hexahydrate at the micro-nano scale.

7. An application of the micro / nano magnesium ammonium phosphate as described in claim 6 in the field of water treatment, characterized in that, Treatment of Pb 2+ Cd 2+ Sewage.

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