Process and reaction system for synthesizing spherical hydroxyl calcium phosphate by utilizing phosphorus-containing wastewater

Abstract

The invention relates to the technical field of phosphorus-containing wastewater treatment and recycling, in particular to a process and reaction system for synthesizing spherical hydroxyl calcium phosphate by using phosphorus-containing wastewater, and the process comprises the following steps: S1, continuously conveying phosphorus-containing wastewater into a main reaction device, and synchronously dropwise adding alkali liquor into the main reaction device under a continuous stirring condition to construct an initial environment; s2, continuously conveying the calcium salt solution into the main reaction device, forming a reaction zone in the middle of the main reaction device, and carrying out a crystallization reaction; s3, draining crystal mush formed by the crystallization reaction from the bottom of the main reaction device and refluxing to the reaction zone to promote crystal particles in the crystal mush to continuously participate in the crystallization reaction; and S4, discharging crystal particles formed by crystallization from the bottom of the main reaction device, and carrying out separation treatment to obtain spherical hydroxyl calcium phosphate particles. By accurately controlling crystallization reaction conditions, spherical hydroxyl calcium phosphate particles with uniform particle morphology are obtained, and the recovery efficiency of phosphorus resources in wastewater is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of phosphorus-containing wastewater treatment and resource utilization, and particularly relates to a process and a reaction system for synthesizing spherical hydroxyapatite from phosphorus-containing wastewater. BACKGROUND

[0002] With the wide application of phosphorus resources in various fields, the discharge of phosphorus-containing wastewater continues to rise, and the enrichment of phosphorus in the environment is becoming more and more serious. Among them, orthophosphate (PO4 3- ) commonly exists in urban sewage and industrial phosphorus-containing wastewater. If it is not properly treated, it can easily cause water eutrophication and even trigger a series of ecological crises such as large-scale outbreak of blue-green algae. Under this background, developing a phosphorus recovery process that can not only efficiently treat but also realize resource utilization has become a key research direction that needs to be broken through in the field of phosphorus-containing wastewater treatment. Hydroxyapatite (HAP) has attracted much attention in the field of phosphorus crystallization recovery in recent years due to its good chemical stability, excellent biocompatibility and high phosphorus content. In the environment with neutral to weak alkaline conditions, PO4 3- in the solution can react with Ca 2+ to form stable HAP crystals, thereby realizing the migration of phosphorus from the liquid phase to the solid phase.

[0003] However, when the existing hydroxyapatite crystallization process is applied to the actual phosphorus-containing wastewater system, there are still a series of key technical problems to be solved; specifically, (1) it is difficult to control the pH value of the phosphorus-containing wastewater system, and it is difficult to achieve precise and stable regulation; the fluctuation of the pH value will interfere with the uniformity of the crystallization process, and then adversely affect the normal growth of the crystals, resulting in uneven quality of the final product. (2) There is a lack of effective means to adjust the supersaturation of the reaction system; unreasonable control of the supersaturation can easily lead to the generation of non-crystalline substances or the occurrence of particle agglomeration; this not only reduces the phosphorus recovery efficiency, but also increases the complexity and difficulty of the subsequent treatment process.

[0004] The present application provides a process and a reaction system for synthesizing spherical hydroxyapatite from phosphorus-containing wastewater, to solve the problems of difficulty in controlling the pH value of the phosphorus-containing wastewater system, inability to effectively adjust the supersaturation of the reaction system, poor quality of the hydroxyapatite crystals formed by crystallization, and low phosphorus recovery efficiency when the existing hydroxyapatite crystallization process is directly applied to the actual phosphorus-containing wastewater system. SUMMARY

[0005] The application aims to provide a process and a reaction system for synthesizing spherical hydroxyapatite by using phosphorus-containing wastewater, so as to solve the problems of difficulty in controlling the pH value of the phosphorus-containing wastewater system, inability to effectively adjust the supersaturation of the reaction system, poor quality of the hydroxyapatite crystals formed by crystallization, and low phosphorus recovery efficiency when the existing hydroxyapatite crystallization process is directly applied to the actual phosphorus-containing wastewater system.

[0006] The technical scheme of the application is a process and a reaction system for synthesizing spherical hydroxyapatite by using phosphorus-containing wastewater, comprising the following steps: S1. Under continuous stirring, the diluted phosphorus-containing wastewater and the lye are synchronously delivered to a main reaction device to form a reaction system with a stable pH value in the near-neutral range, thereby constructing an initial environment for the crystallization reaction; S2. The calcium salt solution is continuously delivered to the main reaction device, the pH value of the reaction system is accurately controlled to the range of 6.5-7.5 by using the high solubility and the continuous release characteristics of the calcium ions of the calcium salt solution, and a reaction zone is formed in the main reaction device to perform the crystallization reaction; S3. During the crystallization reaction, the crystal slurry formed by the crystallization reaction is introduced and refluxed to the reaction zone to promote the crystal particles in the crystal slurry to continuously participate in the crystallization reaction; S4. After the crystallization reaction is completed, the upper clarified liquid is discharged from the upper part of the main reaction device, and the crystal particles formed by crystallization are discharged from the bottom of the main reaction device, and after separation treatment, the spherical hydroxyapatite particles are obtained.

[0007] Preferably, the delivery rate of the phosphorus-containing wastewater is controlled in the range of 0.5-10 L / min. The delivery rate of the lye gradually decreases as the pH value of the reaction system increases.

[0008] Preferably, the delivery rate of the calcium salt solution is 5%-20% of the delivery rate of the phosphorus-containing wastewater.

[0009] Preferably, the lye is a basic solution containing calcium ions, the calcium salt solution is a neutral solution containing calcium ions, the calcium salt solution serves as the main calcium source, and the lye serves as the supplementary calcium source, which together provide calcium elements, so that the molar ratio of the total calcium elements to phosphorus elements in the reaction system is controlled in the range of 1.6-2.0.

[0010] Preferably, the lye is lime milk, and the calcium salt solution is a calcium chloride solution.

[0011] Preferably, in the reaction system, the concentration of the crystal slurry is controlled in the range of 10-30 g / L. In the reflux process, the reflux ratio is controlled in the range of 3-10:1.

[0012] Preferably, the calcium hydroxyl phosphate particles are in a mixed state and have a particle size of no less than 40 microns.

[0013] The application also provides a reaction system for synthesizing spherical calcium hydroxyl phosphate by using phosphorus-containing wastewater, wherein the reaction system is used in the process for synthesizing spherical calcium hydroxyl phosphate by using phosphorus-containing wastewater; the reaction system comprises a main reaction device, a calcium source preparation module, a phosphorus source preparation module and an alkali liquor preparation module which are connected to the main reaction device through conveying pipelines respectively; The upper part of the main reaction device is provided with a reflux water inlet, the bottom part is provided with a reflux water outlet, and a reflux valve is arranged at the reflux water outlet; the reflux water outlet and the reflux water inlet are connected through a conveying pipeline to form a reflux system. The main reaction device is further provided with a pH detection device and a stirring device; the upper part of the main reaction device is further provided with a water outlet, and the bottom part is further provided with a crystal discharge outlet.

[0014] Preferably, the conveying pipelines through which the phosphorus source preparation module, the calcium source preparation module and the alkali liquor preparation module are connected to the main reaction device are all provided with metering pumps, which are a first metering pump, a second metering pump and a third metering pump respectively.

[0015] Preferably, the calcium source preparation module comprises a calcium source preparation device; the bottom part of the calcium source preparation device is connected to the middle part of the main reaction device; the top part of the calcium source preparation device is provided with a raw material inlet and a water source inlet. The phosphorus source preparation module comprises a phosphorus source preparation device; the bottom part of the phosphorus source preparation device is connected to the bottom part of the main reaction device through a conveying pipeline; the top part of the phosphorus source preparation device is provided with a phosphorus-containing wastewater inlet and a dilution water source inlet; the phosphorus source preparation device is further provided with a pH detector. The alkali liquor preparation module comprises an alkali liquor preparation device which is designed in an open form; the bottom part of the alkali liquor preparation device is provided with a water inlet and an alkali liquor outlet on the opposite sides respectively; the alkali liquor outlet is connected to the top part of the main reaction device.

[0016] The calcium source preparation device, the alkali liquor preparation device and the phosphorus source preparation device are provided with stirrers inside.

[0017] Compared with the prior art, the application has the following advantages: (1) The process and reaction system for synthesizing spherical hydroxyapatite by using phosphorus-containing wastewater provided by the application can improve the regulation precision of the pH value of the reaction system and reduce the regulation difficulty by using alkali and calcium salt solution to cooperatively regulate the pH value of the reaction system; the supersaturation and crystal slurry concentration of the reaction system can be effectively adjusted by diluting the phosphorus-containing wastewater and recycling the crystal slurry, so that the generation of crystal particle agglomeration and non-crystal substances is avoided, and the formation of spherical hydroxyapatite particles with compact structure and uniform particle size is facilitated; that is, the process can finally obtain hydroxyapatite particle products with uniform particle morphology and spherical shape by accurately regulating the pH value, supersaturation and crystal slurry concentration of the reaction system and optimizing the crystallization reaction conditions; the recovery efficiency of phosphorus resources in wastewater is significantly improved, the application performance of the crystallization product is improved, and the process exhibits significant advantages in economic and environmental benefits; at the same time, the process flow is simple, the raw materials are easy to obtain, the operation process is stable and reliable, and no complex automatic control device is needed, so the process is suitable for large-scale industrial application; the problems of the existing hydroxyapatite crystallization process, such as difficulty in controlling the pH value of the phosphorus-containing wastewater system, inability to effectively adjust the supersaturation of the reaction system, poor quality of the hydroxyapatite crystals formed by crystallization, and low recovery efficiency of phosphorus in the phosphorus-containing wastewater system, are solved.

[0018] (2) The pH value of the reaction system can be accurately regulated by the synergistic effect of alkali and calcium salt solution, so that the hydroxyapatite is preferentially deposited under neutral to slightly alkaline conditions, the directional crystallization of the hydroxyapatite is promoted, the crystallization efficiency is effectively improved, and the recovery efficiency of phosphorus in the phosphorus-containing wastewater is significantly improved; specifically, the alkali is directly and separately delivered to the main reaction device, which can not only effectively adjust the pH value of the reaction system, but also avoid the premature reaction of the alkali with the phosphorus source or the calcium source, so as to ensure that the process of adjusting the pH value of the reaction system is controllable and the pH value of the reaction system is more stable; the alkali can also be used as a supplementary calcium source together with the calcium salt solution as the main calcium source to provide the required calcium ions for crystallization, thereby realizing the composite addition of the calcium source.

[0019] (3) The phosphorus source preparation module is used to dilute the phosphorus-containing wastewater, and the crystal slurry recycling system is used to significantly reduce the local supersaturation of the reaction system, inhibit the disordered nucleation in the reaction system, and promote the ordered epitaxial growth of the crystal on the basis of the existing crystal seeds, so as to form spherical hydroxyapatite crystal particles with concentrated particle size and excellent settling performance. BRIEF DESCRIPTION OF DRAWINGS

[0020] The application will be further described below in combination with the drawings and examples: Figure 1 The structure diagram of the reaction system for synthesizing spherical hydroxyapatite by using phosphorus-containing wastewater according to the application is shown in the figure; Figure 2 The morphology of the hydroxyapatite synthesized in Example 1 under a microscope is shown in the figure; Figure 3 The morphology of the calcium hydroxyl phosphate obtained by synthesis of the present application comparative example 1 under microscope; Wherein: 1, main reaction device; 11, reflux water inlet; 12, reflux water outlet; 13, reflux valve; 14, water outlet; 15, crystal discharge port; 16, pH detection device; 17, stirring device; 21, first metering pump; 22, second metering pump; 23, third metering pump; 3, calcium source preparation device; 31, raw material inlet; 32, water source inlet; 4, phosphorus source preparation device; 41, phosphorus-containing wastewater inlet; 42, dilution water source inlet; 43, pH detector; 5, lye preparation device; 51, water inlet; 52, lye outlet; 6, stirrer. DETAILED DESCRIPTION

[0021] The content of the present application will be further described in detail in combination with specific examples: A process for synthesizing spherical calcium hydroxyl phosphate using phosphorus-containing wastewater, comprising the following steps: S1, continuously conveying the diluted phosphorus-containing wastewater into the main reaction device, and simultaneously conveying the lye into the main reaction device under continuous stirring conditions, by accurately controlling the conveying speed and amount of lye, the pH value of the reaction system in the main reaction device is stabilized in the near neutral range, to build a suitable initial environment for the subsequent crystallization reaction. Because the content of phosphorus element in the phosphorus-containing wastewater is high, in order to prevent the high concentration of phosphorus from having an adverse effect on the subsequent crystallization reaction, such as high concentration of phosphorus causing excessive agglomeration between crystals due to high concentration of crystal slurry in the reaction system, before conveying the phosphorus-containing wastewater into the main reaction, it needs to be diluted to adjust the content of phosphorus element in the phosphorus-containing wastewater to a suitable range to meet the requirements of the subsequent crystallization reaction; the conveying rate of the phosphorus-containing wastewater is controlled in the range of 0.5-10 L / min; the conveying rate of the lye depends on the acidity and alkalinity of the reaction system in the main reaction device, and the conveying rate of the lye gradually decreases as the pH value of the reaction system increases; that is, when the pH value of the reaction system is relatively low, the lye is conveyed into the main reaction device at a relatively fast conveying rate, as the pH value of the reaction system increases, the conveying speed of the lye gradually decreases, and when the acidity and alkalinity of the reaction system approaches neutral, the conveying rate of the lye is relatively minimum; stabilizing the pH value of the reaction system in the near neutral range means continuously stabilizing the pH value of the reaction system in the range of 6-8. Under the condition of continuous and stable stirring, it can ensure the rapid transmission and sufficient and uniform mixing of the materials in the reaction system, thereby promoting the progress of the crystallization reaction and preventing particle settling and caking.

[0022] S2, continuously conveying the calcium salt solution from the middle of the main reaction device into the main reaction device by a constant and controllable conveying mode, further finely controlling the pH value of the reaction system by using the high solubility and calcium ion continuous release characteristics of the calcium salt solution, so that the pH value of the reaction system is accurately stabilized in the range of 6.5-7.5; under this accurate pH condition, a specific reaction zone is formed in the middle of the main reaction device, and the crystallization reaction is started to promote the hydroxyapatite to start crystallization. The conveying rate of the calcium salt solution into the main reaction device should be 5%-20% of the conveying rate of the phosphorus-containing wastewater; the lye is an alkaline solution containing calcium ions, and the lye is preferably lime milk, and the concentration of the lime milk is preferably controlled in the range of 5%-25% (w / v); the calcium salt solution is a neutral solution containing calcium ions, and is preferably a calcium chloride solution. In the reaction system, the calcium salt solution serves as the main calcium source to react with the phosphorus elements in the phosphorus-containing wastewater, and the lye can serve as a supplementary calcium source to supplement calcium ions into the reaction system while controlling the pH value of the reaction system, thereby promoting the reaction. In the reaction system, the ratio of the total moles of calcium elements provided by the calcium salt solution and the lye to the moles of phosphorus elements in the reaction system should be controlled in the range of 1.6-2.0.

[0023] S3, during the crystallization reaction process, the crystal slurry reflux system is started to guide the crystal slurry formed during the crystallization reaction process from the bottom of the main reaction device and backflow to the reaction zone, so that the crystal particles in the reaction system can continuously participate in the crystallization reaction, promote the further growth and perfection of the crystals, and improve the completeness and uniformity of the crystallization reaction. During the crystal slurry reflux process, the ratio of the backflow water amount to the total water amount in the main reaction device is 3-10:1, i.e. the reflux ratio is 3-10:1; through the circulation reflux mechanism, the instantaneous supersaturation peak value can be effectively reduced, the crystal growth time is prolonged, and it is more helpful to form spherical hydroxyapatite particles with dense structure and uniform particle size. During the entire crystallization reaction process, the concentration of the crystal slurry in the reaction system needs to be controlled in the range of 10-30 g / L to prevent excessive agglomeration between the crystals, improve the crystallization efficiency, and ensure the product quality. Before the crystallization reaction is carried out, crystal seeds can be pre-added to the main reaction device to provide nucleation sites for the crystallization reaction to promote the start and progress of the crystallization reaction; and during the crystallization reaction process, the pre-added crystal seeds can be circulated and reused in the reaction system through the reflux system; compared with the traditional process, the introduction of the reflux system in the present process significantly reduces the dependence on external introduction of crystal seeds, which not only directly reduces the crystal seed addition cost in the phosphorus recovery process, but also avoids the influence of factors such as quality fluctuation or unstable supply of external crystal seeds on the reaction, thereby greatly improving the stability and continuity of the process.

[0024] S4. After the crystallization reaction is complete, the clarified liquid in the upper part of the main reaction device is discharged from the top, and the crystal particles formed by crystallization are discharged from the bottom. The discharged crystal particles then undergo a series of treatments, including separation, to finally obtain spherical hydroxyapatite particles. This spherical particle morphology not only improves the flowability and dispersibility of the crystallized hydroxyapatite particles, making them easier to handle and more uniformly distributed during processing and use, but also enhances the mechanical strength of the hydroxyapatite particles, reducing damage caused by collisions and compression during storage and transportation, thus significantly improving storage and transportation stability. These excellent characteristics make the hydroxyapatite particles widely applicable to various downstream applications. The particle size of the hydroxyapatite particles is not less than 40 micrometers; and the hydroxyapatite particles are in a mixed state, containing calcium ions and phosphate ions. This process achieves efficient recovery of phosphorus resources from wastewater while precisely controlling the morphology of the product, enhancing its usability. This makes this process highly applicable and promising in multiple fields such as phosphorus-containing wastewater resource treatment and the preparation of phosphorus-based functional materials.

[0025] This application also provides a reaction system for synthesizing spherical calcium hydroxyphosphate using phosphorus-containing wastewater, such as... Figure 1 As shown, the reaction system mainly consists of a main reaction device 1, a calcium source preparation module, a phosphorus source preparation module, and an alkali solution preparation module. Furthermore, the main reaction device 1 is equipped with a stirring device 17, and the calcium source preparation module, phosphorus source preparation module, and alkali solution preparation module are connected to the main reaction device 1 through conveying pipelines. The main reaction device 1 is also equipped with a pH detection device 16 for real-time monitoring of the pH value of the reaction system within the main reaction device 1. Simultaneously, to effectively control the supersaturation of the seed crystals in the reaction system and promote uniform crystal nucleus formation, the main reaction device 1 is equipped with a reflux water inlet 11 at the top and a reflux water outlet 12 at the bottom. A reflux valve 13 is installed at the reflux water outlet 12, which is connected to the reflux water inlet 11 via a pipeline to form a reflux circulation system. The main reaction device 1 is also equipped with a water outlet 14 at the top for discharging the clarified liquid from the top of the main reaction device 1. The main reaction device 1 is also equipped with a crystal outlet 15 at the bottom for easy discharge and collection of the synthesized spherical hydroxyapatite crystals.

[0026] Further, the alkali solution preparation module is connected to the top of the main reaction device 1 through a conveying pipeline, and is used to add the alkali solution into the main reaction device 1 from the top of the main reaction device 1 in a dropwise manner, so as to accurately control the addition amount of the alkali solution, and effectively control the progress of the whole reaction, so as to ensure that the reaction is stably carried out under the predetermined conditions. The calcium source preparation module is connected to the middle part of the main reaction device 1 through a conveying pipeline, and is used to stably and continuously convey the prepared calcium source into the main reaction device 1 from the middle part of the main reaction device 1, so as to provide sufficient calcium source material for the subsequent reaction. The phosphorus source preparation module is connected to the bottom of the main reaction device 1 through a conveying pipeline, and is used to convey the diluted phosphorus-containing waste liquid into the main reaction device 1 from the bottom of the main reaction device 1. When the phosphorus-containing waste liquid enters the main reaction device 1 from the bottom, the water level in the device will gradually rise with the continuous injection of the waste liquid. In the process of the water level rising, the phosphorus-containing waste liquid will contact and fully mix with the calcium salt solution flowing from top to bottom in the middle part of the main reaction device 1, thereby triggering the crystallization reaction, and forming a relatively stable reaction zone in the middle part of the main reaction device 1. At this time, the calcium source and the phosphate in the reaction system form a certain concentration gradient in the reaction zone. And, from the top to the bottom of the main reaction device 1, the concentration of the calcium source gradually decreases, while the concentration of the phosphate gradually increases. This concentration gradient can increase the area of the supersaturated region in the reaction zone, effectively promote the uniform distribution of the reactants and the generation of the crystallization nucleus, and promote the smooth progress of the crystallization reaction.

[0027] The calcium source preparation module includes a core component of a calcium source preparation device 3. The bottom of the calcium source preparation device 3 is connected to the middle of the main reaction device 1 through a conveying pipeline. In order to ensure that the calcium salt solution can be accurately and stably conveyed to the main reaction device 1, a second metering pump 22 is also arranged on the conveying pipeline. A raw material inlet 31 and a water source inlet 32 are arranged at the top of the calcium source preparation device 3, which are respectively used for adding calcium source raw materials and introducing water sources to meet the raw material requirements for the preparation of calcium salt solution. In addition, a stirrer 6 is also arranged in the calcium source preparation device 3. Through the continuous operation of the stirrer 6, the calcium source raw materials and water can be fully mixed, ensuring that the concentration of the prepared calcium salt solution is uniform and stable in nature, and providing high-quality calcium source for subsequent reactions. The phosphorus source preparation module includes a phosphorus source preparation device 4. The bottom of the phosphorus source preparation device 4 is connected to the bottom of the main reaction device 1 through a conveying pipeline. Similarly, in order to ensure that the phosphorus-containing wastewater can be continuously and stably conveyed, a first metering pump 21 is also arranged on the conveying pipeline. A phosphorus-containing wastewater inlet 41 for conveying phosphorus-containing wastewater into the phosphorus source preparation device 4 and a dilution water source inlet 42 for introducing dilution water source into the phosphorus source preparation device 4 are arranged at the top of the phosphorus source preparation device 4. A stirrer 6 is arranged in the phosphorus source preparation device 4, which fully mixes the phosphorus-containing wastewater and the dilution water source under the action of stirring force to form a uniform and stable solution. A pH detector 43 is also arranged on the phosphorus source preparation device 4 for detecting the pH value of the diluted phosphorus-containing wastewater. The lye preparation module includes a lye preparation device 5. The lye preparation device 5 is designed to be open at the top. A water inlet 51 and a lye outlet 52 are arranged at the bottom of the lye preparation device 5, and preferably arranged on the opposite sides of the bottom of the lye preparation device 5. The lye outlet 52 is connected to the top of the main reaction device 1 through a conveying pipeline, so that the lye is added dropwise into the main reaction device 1 from the top of the main reaction device 1. By accurately controlling the amount of lye added, the reaction process is more stable and controllable, providing ideal conditions for subsequent reactions. The reaction device can quantitatively convey the diluted phosphorus-containing wastewater, calcium source liquid and alkali to the main reaction device 1 through the metering pump, and realize the stable adjustment of the reaction system without an automatic pH control system, simplify the operation process and improve the on-site adaptability.

[0028] The reaction system has compact structure and flexible operation, and is suitable for continuous or semi-continuous phosphorus recovery process and other application scenarios with control requirements for crystal morphology and particle size. In actual operation, by adjusting the conveying flow of phosphorus-containing wastewater, calcium salt solution and lye, adjusting the reflux ratio and other reaction conditions, the supersaturation of the reaction system can be effectively controlled, the crystal slurry concentration and crystal particle size can be adjusted, and finally the uniform and stable calcium hydroxyl phosphate product can be obtained.

[0029] Take 1 m³ of phosphorus-containing wastewater generated by a chemical plant as a sample to be treated; the concentration of phosphate in the phosphorus-containing wastewater is above 3000 ppm.

[0030] Example 1

[0031] S1, the phosphorus-containing wastewater is transported to the phosphorus source preparation device for dilution, the concentration of phosphate in the phosphorus-containing wastewater is adjusted to within 2000 ppm, then the diluted phosphorus-containing wastewater is continuously transported to the inside of the main reaction device at a transport rate of 10 L / min from the bottom of the main reaction device, and under the condition of continuous stirring at a speed of 400 rpm, 10% (w / v) lime milk is simultaneously added to the main reaction device, and the addition rate gradually decreases as the pH value of the reaction system increases, so that the pH value of the reaction system in the main reaction device is stabilized at about 7, and the initial environment for the crystallization reaction is constructed; S2, the saturated calcium salt solution is continuously transported to the inside of the main reaction device at a transport rate of 1 L / min from the middle position of the main reaction device, the pH value of the reaction system is accurately controlled to the range of 6.5-7.5 by using the high solubility and calcium ion continuous release characteristics of the calcium salt solution, and a reaction zone is formed in the middle of the main reaction device for the crystallization reaction; S3, during the crystallization reaction, the reflux system is started, the crystal slurry formed by the crystallization reaction is introduced and refluxed from the bottom of the main reaction device 1 to the reaction zone, and the reflux ratio is controlled to be 5:1, so as to promote the crystal particles in the crystal slurry to continuously participate in the crystallization reaction; S4, after the crystallization reaction is completed, the upper clarified liquid is discharged from the water outlet at the upper part of the main reaction device, the crystal particles formed by crystallization are discharged from the crystal discharge port at the bottom of the main reaction device and collected, and after separation treatment, as shown in Figure 2 , the spherical calcium hydroxyl phosphate particles are obtained.

[0032] Comparative Example 1 S1, the phosphorus-containing wastewater is transported to the phosphorus source preparation device for dilution, the concentration of phosphate in the phosphorus-containing wastewater is adjusted to within 2000 ppm, then the diluted phosphorus-containing wastewater is continuously transported to the inside of the main reaction device at a transport rate of 10 L / min from the bottom of the main reaction device, and under the condition of stirring at a speed of 100 rpm, 10% (w / v) lime milk is simultaneously added to the main reaction device, and the addition rate gradually decreases as the pH value of the reaction system increases, so that the pH value of the reaction system in the main reaction device is stabilized at about 7, and the initial environment for the crystallization reaction is constructed; S2, continuously conveying the saturated calcium salt solution into the main reaction device from the middle position of the main reaction device at a conveying rate of 1 L / min, using the high solubility and continuous release characteristics of the calcium salt solution to accurately control the pH value of the reaction system to the range of 6.5-7.5, and forming a reaction zone in the middle of the main reaction device to carry out the crystallization reaction; S3, after the crystallization reaction is completed, the upper clear liquid is discharged from the upper part of the main reaction device, the crystal particles formed by the crystallization are discharged from the bottom of the main reaction device, and after separation treatment, as shown in the figure, the calcium hydroxyl phosphate particles with a sheet-like morphology are obtained. Figure 3

[0033] As can be seen from the comparison between Comparative Example 1 and Example 1, the difference in the synthesis process directly leads to a significant difference in the morphology of the calcium hydroxyl phosphate particles; in Example 1, the dynamic reflux process is adopted to obtain calcium hydroxyl phosphate particles with a spherical morphology, while in Comparative Example 1, the calcium hydroxyl phosphate particles obtained are sheet-shaped. In Example 1, through the synergistic effect of mechanical stirring and external circulation reflux, a turbulent state is formed in the reaction system inside the main reaction device; this dynamic reflux process and the turbulent state of the reaction system enable the initially formed metastable crystal nuclei to be continuously transported to the reaction zone to collide and adsorb with calcium and phosphorus precursors, and then the crystal nuclei undergo a cycle of evolution of "formation-growth-crushing-regrowth", and finally form a spherical structure with the lowest surface energy; at the same time, in the reflux process, the crystal particles rub against the inner wall of the main reaction device, the inner wall of the conveying pipeline and the stirring device, etc., resulting in the formation of local defects on the surface of the particles; these defects can act as active sites to preferentially adsorb calcium ions and phosphate ions in the solution, and then form a calcium and phosphorus coating layer, so that the calcium hydroxyl phosphate particles formed by crystallization are in a mixed state; by controlling the time length of the crystallization reaction, calcium hydroxyl phosphate particles with a particle size of not less than 40 microns are finally obtained. In Comparative Example 1, after the crystal nuclei are formed, they rely on the slow stirring effect and diffusion growth driven by the concentration gradient to grow along the c-axis direction to form a sheet-shaped structure; at the same time, due to the fluctuation of the local supersaturation degree of the solution, secondary nucleation occurs, and finally a sheet-shaped or multi-level sheet layer stacking morphology is formed.

[0034] The above examples are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and implement it, and cannot limit the protection scope of the present application. It is obvious for those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or basic characteristics of the present application, therefore, from any point of view, the examples should be regarded as exemplary and non-limiting, the scope of the present application is defined by the appended claims rather than the above description, therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present application.​

Claims

1. A process for synthesizing spherical hydroxyapatite using phosphorus-containing wastewater, characterized in that, Includes the following steps: S1. Under continuous stirring, the diluted phosphorus-containing wastewater and alkaline solution are simultaneously transported to the main reaction device to form a reaction system with a stable pH value in the near-neutral range, thus creating the initial environment for the crystallization reaction. S2. Calcium salt solution is continuously supplied to the main reaction device. Utilizing the high solubility of calcium salt solution and the continuous release of calcium ions, the pH value of the reaction system is precisely controlled within the range of 6.5-7.5, and a reaction zone is formed in the main reaction device to carry out the crystallization reaction. S3. During the crystallization reaction, the crystal slurry formed by the crystallization reaction is diverted and refluxed back to the reaction zone, so as to promote the continuous participation of crystal particles in the crystal slurry in the crystallization reaction. S4. After the crystallization reaction is completed, the clear liquid in the upper part is discharged from the top of the main reaction device, and the crystal particles formed by crystallization are discharged from the bottom of the main reaction device. After separation, spherical hydroxyapatite particles are obtained.

2. The process for synthesizing spherical hydroxyapatite using phosphorus-containing wastewater according to claim 1, characterized in that: The transport rate of the phosphorus-containing wastewater is controlled within the range of 0.5-10 L / min; The delivery rate of the alkali solution gradually decreases as the pH value of the reaction system increases.

3. The process for synthesizing spherical hydroxyapatite using phosphorus-containing wastewater according to claim 2, characterized in that: The transport rate of the calcium salt solution is 5%-20% of the transport rate of the phosphorus-containing wastewater.

4. The process for synthesizing spherical hydroxyapatite using phosphorus-containing wastewater according to claim 2, characterized in that: The alkaline solution is an alkaline solution containing calcium ions; the calcium salt solution is a neutral solution containing calcium ions; the calcium salt solution serves as the main calcium source, and the alkaline solution serves as a supplementary calcium source, together providing calcium elements, so that the total molar ratio of calcium to phosphorus elements in the reaction system is controlled within the range of 1.6-2.

0.

5. The process for synthesizing spherical hydroxyapatite using phosphorus-containing wastewater according to claim 4, characterized in that: The alkaline solution is lime milk; the calcium salt solution is calcium chloride solution.

6. The process for synthesizing spherical hydroxyapatite using phosphorus-containing wastewater according to claim 2, characterized in that: In the reaction system, the concentration of the crystal slurry is controlled within the range of 10-30 g / L; During the reflux process, the reflux ratio is controlled within the range of 3-10:

1.

7. The process for synthesizing spherical hydroxyapatite using phosphorus-containing wastewater according to claim 1, characterized in that: The hydroxyapatite particles are in a mixed state and have a particle size of not less than 40 micrometers.

8. A reaction system for synthesizing spherical hydroxyapatite from phosphorus-containing wastewater, wherein the process for synthesizing spherical hydroxyapatite from phosphorus-containing wastewater according to any one of claims 1-7 employs this reaction system; characterized in that: It includes a main reaction device, and a calcium source preparation module, a phosphorus source preparation module, and an alkali solution preparation module that are respectively connected to the main reaction device through delivery pipelines; The main reaction device is provided with a reflux water inlet at the top and a reflux water outlet at the bottom, and a reflux valve is provided at the reflux water outlet; the reflux water outlet and the reflux water inlet are connected by a conveying pipeline to form a reflux system; The main reaction device is also equipped with a pH detection device and a stirring device; the upper part of the main reaction device is also equipped with a water outlet, and the bottom part is also equipped with a crystal discharge outlet.

9. The reaction system for synthesizing spherical hydroxyapatite using phosphorus-containing wastewater according to claim 8, characterized in that: Metering pumps are installed on the delivery pipelines connecting the phosphorus source preparation module, the calcium source preparation module, and the alkali solution preparation module to the main reaction device, namely, a first metering pump, a second metering pump, and a third metering pump.

10. The reaction system for synthesizing spherical hydroxyapatite using phosphorus-containing wastewater according to claim 8, characterized in that: The calcium source preparation module includes a calcium source preparation device; the bottom of the calcium source preparation device is connected to the middle of the main reaction device; the top of the calcium source preparation device is provided with a raw material inlet and a water inlet; The phosphorus source preparation module includes a phosphorus source preparation device; the bottom of the phosphorus source preparation device is connected to the bottom of the main reaction device through a delivery pipeline; the top of the phosphorus source preparation device is provided with a phosphorus-containing wastewater inlet and a dilution water inlet; the phosphorus source preparation device is also equipped with a pH meter. The alkali solution preparation module includes an open-type alkali solution preparation device; the bottom of the alkali solution preparation device is provided with a water inlet and an alkali solution outlet on opposite sides; the alkali solution outlet is connected to the top of the main reaction device; The calcium source preparation device, the alkali solution preparation device, and the phosphorus source preparation device are equipped with stirrers inside.

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