Process and reaction device for preparing hydroxy calcium phosphate from phosphoric acid waste liquid

Abstract

The invention relates to the technical field of wastewater treatment and resource utilization, in particular to a process and a reaction device for preparing hydroxy calcium phosphate from phosphoric acid waste liquid. Under the condition of continuous stirring, a neutralizing reagent is conveyed into the crystallization reactor, and the conveying rate of the neutralizing reagent is regulated and controlled through a pH real-time monitoring feedback control system; after the pH value of the reaction system is stabilized at 9.0-11.0 and is continuously stabilized for several minutes, stopping conveying the neutralizing reagent into the crystallization reactor, and continuously stirring; and after the crystallization reaction is completed, carrying out solid-liquid separation treatment to obtain a filter cake and filtrate, discharging or recycling the filtrate, and carrying out post-treatment on the filter cake to obtain hydroxy calcium phosphate crystal powder. According to the process, the strong acidity of phosphoric acid and the strong alkalinity of lime are utilized to carry out a neutralization crystallization reaction, and the high-pollution phosphoric acid waste liquid is successfully converted into a hydroxy calcium phosphate product with a high added value, so that the hydroxy calcium phosphate product can be applied to the high-added-value fields such as biomedical materials and high-end fertilizers.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment and resource utilization technology, and in particular to a process and reaction apparatus for preparing hydroxyapatite from phosphoric acid waste liquid. Background Technology

[0002] Phosphoric acid wastewater (hereinafter referred to as phosphoric acid waste liquid) generated in industries such as phosphoric acid chemical industry and metal surface treatment has two significant characteristics: First, the wastewater is strongly acidic and has a high phosphate concentration; second, it has a complex composition and is often accompanied by fluoride ions (F). - ), sulfate (SO4 2- ) and heavy metal ions (such as Pb) 2+ Cd 2+ The presence of impurities such as eutrophication, soil acidification, and heavy metal pollution will lead to complex environmental problems if discharged directly without effective treatment.

[0003] Currently, the mainstream treatment method for phosphoric acid waste liquid is chemical precipitation. The essence of this technology is to add lime (calcium hydroxide) or caustic soda (sodium hydroxide) to the phosphoric acid waste liquid for neutralization, causing phosphate ions to convert into calcium phosphate salt precipitates. Phosphorus resource recovery and water purification are then achieved through solid-liquid separation. This method has the advantages of simple process flow and low equipment investment cost. However, chemical precipitation has the following significant drawbacks: (1) The process control is rough and the value of the calcium phosphate products obtained is low: The chemical precipitation method is simple to operate, but it lacks precise control of reaction parameters, such as dynamic pH regulation, Ca / P molar ratio, crystal nucleation rate, etc. This results in the crystallization product being a low-value calcium phosphate mixture with complex composition and uncertain crystal form, commonly known as "phosphogypsum" or "phosphogypsum mud", which cannot be utilized as a resource.

[0004] (2) The contradiction between the economy of raw materials and the stability of the process is prominent: Although the reaction speed is fast and the processing efficiency is high when using strong alkalis such as caustic soda for neutralization, the price of strong alkalis such as caustic soda is high and not economical; while when using inexpensive lime, although the raw material cost can be reduced by 40%, problems such as reactor scaling and pipeline blockage are very likely to occur, resulting in poor process stability. In addition, the purity of the calcium phosphate salt product formed by crystallization is difficult to guarantee.

[0005] (3) Serious interference from coexisting impurities: Impurities such as fluoride ions, sulfate ions, and heavy metal ions in phosphoric acid waste liquid are prone to co-precipitate with the target product, resulting in excessive impurity content in the crystallized calcium phosphate salt product, which limits its application in high-value-added fields such as biomedical materials and high-end fertilizers.

[0006] This invention provides a process and reaction apparatus for preparing hydroxycalcium phosphate from phosphoric acid waste liquid, which solves the problems of the existing chemical precipitation method for treating phosphoric acid waste liquid, such as the contradiction between treatment cost and process stability, low value of the crystallized calcium phosphate salt product, and excessive impurity content. Summary of the Invention

[0007] The purpose of this invention is to provide a process and reaction apparatus for preparing hydroxycalcium phosphate from phosphoric acid waste liquid, so as to solve the problems of the contradiction between treatment cost and process stability in the existing chemical precipitation method for treating phosphoric acid waste liquid, and the low value and excessive impurity content of the crystallized calcium phosphate salt product.

[0008] The technical solution of the present invention is: a process for preparing hydroxyapatite using phosphoric acid waste liquid, comprising: transporting phosphoric acid waste liquid to a crystallization reactor and monitoring the crystallization pH value in real time; Under continuous stirring, the neutralizing agent is delivered to the crystallization reactor, and the delivery rate of the neutralizing agent is adjusted based on the real-time monitoring of the pH value. When the pH value of the reaction system is less than 7, rapid delivery is performed to quickly deliver the neutralizing agent to the crystallization reactor to rapidly neutralize the acidic substances in the reaction system. When the pH value of the reaction system rises to 7.0, slow titration is performed to gradually increase the pH value of the reaction system in order to provide a stable and homogeneous crystallization reaction environment. Once the pH of the reaction system stabilizes at 9.0-11.0 and remains stable, stop feeding the neutralizing reagent into the crystallization reactor and continue stirring to continue the crystallization reaction. After the crystallization reaction is complete, solid-liquid separation is performed to obtain filter cake and filtrate. The filtrate is discharged or reused, and the filter cake is post-processed to form hydroxycalcium phosphate crystal powder.

[0009] Preferably, the delivery rate of the rapid delivery is 3-10 times the titration rate of the slow titration; The conveying rate of the rapid conveyor is 1-10 L / min.

[0010] Preferably, the neutralizing agent is lime milk with a concentration of 5%-15% (w / v).

[0011] Preferably, when the crystallization reaction is complete, the pH value of the reaction system is controlled within the range of 9.0-11.0; The total calcium to phosphorus molar ratio in the reaction system was controlled within the range of 1.67-2.0.

[0012] Preferably, the reaction temperature of the crystallization reaction is 20℃-60℃; during the crystallization reaction, the transport time for rapid transport is controlled within 20 minutes, and the titration time for slow titration is controlled within the range of 30-120 minutes.

[0013] Preferably, the post-processing includes washing and drying. The cleaning process involves using deionized water as a cleaning agent to wash the filter cake. The drying process is carried out at a temperature of 80℃-120℃.

[0014] The present invention also provides a reaction apparatus for preparing hydroxyapatite from phosphoric acid waste liquid. The above-mentioned process for preparing hydroxyapatite from phosphoric acid waste liquid uses this reaction apparatus for crystallization reaction; it includes a neutralizing reagent preparation system, a crystallization reactor with a stirring device, and a solid-liquid separation system; The crystallization reactor is connected to the phosphoric acid waste liquid storage area and is used to transport the phosphoric acid waste liquid to the crystallization reactor; The output of the neutralizing reagent preparation system is connected to the crystallization reactor via a neutralizing reagent delivery pump; the bottom of the crystallization reactor is connected to the solid-liquid separation system; and the output of the solid-liquid separation system is connected to the wastewater discharge area. The crystallization reactor is equipped with a real-time pH monitoring and feedback control system; one end of the real-time pH monitoring and feedback control system extends into the crystallization reactor to monitor the pH value of the reaction system inside the crystallization reactor. The real-time pH monitoring and feedback control system is electrically connected to the neutralizing reagent delivery pump, and adjusts the working state of the neutralizing reagent delivery pump based on the real-time monitored pH value of the reaction system. The main reactor is also equipped with an outlet at the top, which is used to discharge the supernatant in the reaction system to the wastewater discharge area.

[0015] Preferably, the neutralizing reagent delivery pump includes a first neutralizing reagent delivery pump and a second neutralizing reagent delivery pump; The input ends of the first neutralizing reagent delivery pump and the second neutralizing reagent delivery pump are both connected to the output end of the neutralizing reagent preparation system, and the output ends of the first neutralizing reagent delivery pump and the second neutralizing reagent delivery pump are both connected to the upper end of the crystallization reactor; the real-time pH monitoring and feedback control system is electrically connected to the first neutralizing reagent delivery pump and the second neutralizing reagent delivery pump respectively, and adjusts the start and stop of the first neutralizing reagent delivery pump and the second neutralizing reagent delivery pump based on the pH value of the reaction system, so that when one starts, the other immediately stops.

[0016] Preferably, the neutralizing reagent preparation system includes a raw material silo and a neutralizing reagent preparation device connected to the raw material silo via a conveying auger; the bottom of the neutralizing reagent preparation device is connected to the input end of the neutralizing reagent delivery pump. The neutralizing reagent preparation device is equipped with a stirrer and is connected to the output end of a tap water source to supply tap water required for preparing lime slurry.

[0017] Preferably, the solid-liquid separation system includes a classifying hydrocyclone and a filtration device; the bottom of the main reactor is connected to the upper end of the classifying hydrocyclone via a classifying feed pump; the bottom of the classifying hydrocyclone is connected to the filtration device; the upper end of the classifying hydrocyclone is also connected to the main reactor and the wastewater discharge area respectively; the filtration device is connected to the wastewater discharge area.

[0018] Compared with the prior art, the advantages of the present invention are: (1) The present invention discloses a process and reaction apparatus for preparing hydroxyapatite from phosphoric acid waste liquid. The process utilizes the strong acidity of phosphoric acid and the strong alkalinity of the neutralizing agent to carry out a neutralization crystallization reaction, thereby achieving the one-step preparation of high-purity hydroxyapatite crystal powder from acidic waste liquid and transforming pollutants into high-value-added products. During the crystallization reaction, the pH value of the reaction system is precisely controlled by means of rapid conveying and slow titration to create a good reaction environment for the crystallization reaction. Combined with the precise control of parameters such as the rapid conveying and slow titration rate and the total calcium-phosphorus molar ratio, the occurrence of explosive reactions is effectively avoided, ensuring the stability and uniformity of the crystallization process. This allows the generation of hydroxyapatite crystal powder with a defined crystal form and a single composition, enabling its application in high-value-added fields such as biomedical materials and high-end fertilizers. This realizes the resource utilization of phosphoric acid wastewater and has significant economic benefits.

[0019] (2) This process optimizes the crystallization environment by precisely controlling the pH value of the reaction system and the reaction endpoint, and constructs a separation mechanism in the crystallization reactor so that most of the impurities such as chloride, sodium salt, fluoride ions, sulfate ions and most heavy metal complexes in the phosphoric acid waste liquid remain in a dissolved state and will not enter the crystal lattice of calcium hydroxyphosphate. This effectively avoids the co-precipitation of these impurities with the target product, reduces the impurity content in the calcium hydroxyphosphate crystal powder, and improves the purity of the calcium hydroxyphosphate crystal powder.

[0020] (3) The process uses lime milk as a neutralizing agent, which has low raw material cost and greatly reduces the treatment cost. At the same time, by optimizing the process and reaction device, the problems of reactor scaling and pipeline blockage are effectively avoided, ensuring the stability of the process and solving the contradiction between raw material economy and process stability. In addition, the process has good adaptability to phosphoric acid waste liquid of different concentrations and components. The whole process is simple and easy to achieve automated control and industrial promotion. Attached Figure Description

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1 This is a schematic diagram of the reaction apparatus used in the process of preparing hydroxyapatite from phosphoric acid waste liquid according to the present invention; Figure 2 The image shows the X-ray diffraction (XRD) analysis of the calcium hydroxyphosphate crystals prepared in Example 1 of this invention. The system includes: 1. Neutralization reagent preparation system; 11. Raw material silo; 12. Conveying auger; 13. Neutralization reagent preparation device; 14. Stirrer; 2. Stirring device; 3. Crystallization reactor; 4. Solid-liquid separation system; 41. Grading hydrocyclone; 42. Filtration device; 43. Grading feed pump; 44. Filter cake; 5. Neutralization reagent delivery pump; 51. First neutralization reagent delivery pump; 52. Second neutralization reagent delivery pump; 6. Phosphoric acid waste liquid storage area; 61. Phosphoric acid waste liquid delivery pump; 7. Real-time pH monitoring and feedback control system; 8. Tap water source; 9. Wastewater discharge area. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to specific embodiments: A process for preparing hydroxyapatite using phosphoric acid waste liquid, the process specifically includes the following steps: First, the phosphoric acid waste liquid stored in the phosphoric acid waste liquid storage area is transported to the crystallization reactor by a phosphoric acid waste liquid transfer pump. Then, the pH value of the reaction system in the crystallization reactor is monitored in real time by a pH real-time monitoring and feedback control system installed on the crystallization reactor.

[0023] Next, under continuous stirring, the neutralizing reagent is delivered to the crystallization reactor via a neutralizing reagent delivery pump. During the delivery process, the delivery rate of the neutralizing reagent is automatically adjusted based on a real-time pH monitoring feedback control system. When the pH value of the reaction system is less than 7, rapid delivery is performed, meaning the neutralizing reagent is delivered to the crystallization reactor at a relatively fast rate to quickly neutralize most of the acidic substances in the reaction system. When the pH value of the reaction system rises to 7.0, the pH real-time monitoring feedback control system automatically switches the operating state of the neutralizing reagent delivery pump to slow titration mode for slow titration. This means the neutralizing reagent is delivered to the crystallization reactor at a relatively slow titration rate, allowing the pH value of the reaction system to rise gradually and steadily, thus creating a stable and homogeneous reaction environment for the crystallization reaction. The neutralizing agent is a lime slurry prepared from industrial-grade lime and / or slaked lime and tap water, with the concentration controlled within the range of 5%-15% (w / v). The chemical equation for the crystallization reaction is: 5Ca(OH)₂ + 3H₃PO₄ → Ca₅(PO₄)₃(OH) + 9H₂O. Throughout the process of supplying the neutralizing agent to the crystallization reactor, the rapid delivery rate is relative to the slow titration rate; preferably, the rapid delivery rate is 3-10 times that of the slow titration rate; the rapid delivery rate is preferably 1-10 L / min. Furthermore, during the slow titration process, it is preferable to maintain the pH value of the reaction system at a near-neutral plateau of 7.0-9.0. This range not only provides a stable environment and sufficient time for the crystallization reaction, ensuring the crystallization process proceeds fully, but also effectively avoids excessively high supersaturation in local areas, preventing the formation of amorphous precipitates. Throughout the neutralizing reagent delivery process, the real-time pH monitoring and feedback control system operates continuously. Once the pH value of the reaction system is detected to be lower than 7.0, the real-time pH monitoring and feedback control system will respond immediately and automatically adjust the neutralizing reagent delivery pump to quickly switch it from a slow titration state to a fast delivery state, ensuring that the pH value of the reaction system is always within a controllable range.

[0024] Continue the slow titration operation while closely monitoring the pH change of the reaction system. Once the pH of the reaction system stabilizes at 9.0-11.0 and remains stable for several minutes, stop adding the neutralizing reagent to the crystallization reactor. Subsequently, keep the stirring device running continuously to promote the crystallization reaction. The crystallization reaction can be carried out at room temperature without additional heating; however, during the crystallization process, the acid-base neutralization reaction will release a certain amount of heat, which will naturally raise the temperature of the reaction system, thus maintaining the actual reaction temperature within a suitable range of 20℃-60℃. The entire crystallization reaction process is divided into a rapid transport process in the early stage, a slow titration process in the middle stage, and a reaction process after the neutralizing agent is stopped being transported into the crystallization reactor in the later stage. The total reaction time of the crystallization reaction includes the rapid transport time, the slow titration time, and the reaction time after the neutralizing agent is stopped being transported into the crystallization reactor. In order to ensure that the crystallization reaction achieves the ideal reaction effect and product quality, the rapid transport time needs to be controlled within 20 minutes, the slow titration time needs to be controlled within the range of 30-120 minutes, and the total reaction time of the crystallization reaction needs to be precisely controlled within the range of 60-200 minutes.

[0025] After the crystallization reaction is completed, the reaction system inside the crystallization reactor is transported from the bottom to the solid-liquid separation device at the back end, where solid-liquid separation is performed to obtain filter cake and filtrate. Afterward, the filtrate is discharged to the wastewater discharge area or returned to the crystallization reactor for further treatment, and the filter cake is post-treated to obtain hydroxycalcium phosphate crystal powder. pH control is crucial during the crystallization reaction. The optimal pH range for forming stable calcium hydroxyphosphate crystals is 9.0-11.0. Furthermore, common impurities in phosphoric acid waste liquid, such as most chlorides, sodium salts, and some heavy metal complexes, remain dissolved under this pH condition and do not enter the calcium hydroxyphosphate crystal lattice. Therefore, the pH of the reaction system must be strictly controlled within the range of 9.0-11.0 when the crystallization reaction is complete. If the pH is below this range, unstable products such as dicalcium phosphate may be generated, affecting the quality and performance of the product. If the pH is above this range, it will not only waste lime slurry and increase production costs, but may also introduce other impurities into the calcium hydroxyphosphate crystal lattice, interfering with the normal progress of the crystallization reaction and reducing the purity of the calcium hydroxyphosphate. Meanwhile, since a slight excess of calcium helps the reaction proceed fully and effectively inhibits the formation of other acidic calcium phosphates, the total calcium to phosphorus molar ratio in the reaction system needs to be controlled within the range of 1.67-2.0 when the crystallization reaction is complete. In actual operation, the total calcium to phosphorus molar ratio in the reaction system can be precisely controlled by estimating the phosphorus content in the waste liquid and combining it with precise delivery of lime slurry. During the solid-liquid separation process, due to the different sources of phosphoric acid waste liquid, a certain amount of phosphate rock will be generated in the reaction system during the crystallization reaction. Phosphate rock is an insoluble inert substance and can be separated together with hydroxyapatite in the subsequent preliminary solid-liquid separation process. However, since its density and morphology are different from the hydroxyapatite product formed by crystallization, the hydroxyapatite product formed by crystallization can be further purified by hydrocyclone or fine screening to remove the phosphate rock. When post-processing the obtained filter cake, the first step is to use deionized water as a cleaning agent to clean the filter cake to remove soluble impurities adsorbed on its surface. Usually, it is washed with deionized water 2-3 times to ensure that the impurities are completely removed. Then, the cleaned filter cake is placed in a drying device and dried at 80℃-120℃ to finally obtain high-purity white calcium hydroxyphosphate crystal powder.

[0026] This invention also provides a reaction apparatus for preparing calcium hydroxyphosphate from phosphoric acid waste liquid, and the aforementioned process for preparing calcium hydroxyphosphate from phosphoric acid waste liquid is carried out using this reaction apparatus; as shown Figure 1As shown, the reaction apparatus includes a neutralizing reagent preparation system 1, a crystallization reactor 3 with a stirring device 2, and a solid-liquid separation system 4. The crystallization reactor 3 is connected to a phosphoric acid waste storage area 6, used to transport phosphoric acid waste to the crystallization reactor 3. The output of the neutralizing reagent preparation system 1 is connected to the crystallization reactor 3 via a neutralizing reagent delivery pump 5. The bottom of the crystallization reactor 3 is connected to the solid-liquid separation system 4. The output of the solid-liquid separation system 4 is connected to a wastewater discharge area 9. A real-time pH monitoring and feedback control system 7 is installed on the crystallization reactor 3. One end of the real-time pH monitoring and feedback control system extends into the crystallization reactor to monitor the pH value of the reaction system inside the crystallization reactor 3. The other end of the real-time pH monitoring and feedback control system 7 is electrically connected to the neutralizing reagent delivery pump 5, and the operating state of the neutralizing reagent delivery pump 5 is adjusted based on the real-time monitored pH value of the reaction system. Specifically, the neutralizing reagent delivery pump 5 is automatically switched between a fast delivery state and a slow titration state by adjusting the rotation speed, valve opening, or start / stop of the neutralizing reagent delivery pump 5. An outlet is also provided at the top of the main reactor; when the supernatant in the reaction system reaches the discharge standard, it can be discharged to the wastewater discharge area 9 through the outlet to ensure the stability of the reaction system in the main reactor and to ensure the smooth progress of subsequent reactions.

[0027] In the actual crystallization reaction process, to more precisely control the rate at which the neutralizing reagent is delivered into the crystallization reactor 3, the neutralizing reagent delivery pump 5 includes a first neutralizing reagent delivery pump 5 and a second neutralizing reagent delivery pump 5. Furthermore, the input ends of both the first and second neutralizing reagent delivery pumps 5 are connected to the output end of the neutralizing reagent preparation system 1, and the output ends of both pumps 5 are connected to the upper end of the crystallization reactor 3, ensuring that the neutralizing reagent can be stably and continuously and precisely delivered from the neutralizing reagent preparation system 1 to the crystallization reactor 3 to participate in the reaction. The real-time pH monitoring and feedback control system 7 is connected to the first neutralizing reagent delivery system 1 and the second neutralizing reagent delivery pump 5. Electrically connected to the first neutralizing reagent delivery pump 5 and the second neutralizing reagent delivery pump 5, the system is used to precisely control the start and stop of these two pumps. Specifically, when phosphoric acid waste liquid is delivered to the crystallization reactor 3, because the waste liquid is highly acidic, the real-time pH monitoring and feedback control system 7 will detect that the pH value of the reaction system is less than 7. At this time, the system automatically starts the first neutralizing reagent delivery pump 5 for rapid delivery, allowing it to deliver neutralizing reagent into the crystallization reactor 3 at a relatively fast rate to meet the need for rapid neutralization of the acidic waste liquid. Simultaneously, the second neutralizing reagent delivery pump 5 is turned off. As the neutralization reaction proceeds, when the pH value of the reaction system rises to 7, the real-time pH monitoring and feedback control system 7 will react promptly, turning off the first neutralizing reagent delivery pump 5 and simultaneously starting the second neutralizing reagent delivery pump 5 to deliver neutralizing reagent at a slower rate, achieving slow titration to ensure that the pH value of the reaction system remains stable within a suitable range. During the slow titration process, if the real-time pH monitoring and feedback control system 7 detects that the pH value of the reaction system is less than 7 again, the real-time pH monitoring and feedback control system 7 will restart the first neutralizing reagent delivery pump 5 and simultaneously shut down the second neutralizing reagent delivery pump 5 to quickly adjust the pH value of the reaction system and ensure the smooth progress of the crystallization reaction.

[0028] In this reaction apparatus, the neutralizing reagent preparation system 1 includes a raw material silo 11 and a neutralizing reagent preparation device 13. The raw material silo 11 is connected to the neutralizing reagent preparation device 13 via a conveying auger 12, which is used to transport the raw materials in the raw material silo 11 to the neutralizing reagent preparation device 13. The neutralizing reagent preparation device 13 is equipped with a stirrer 14 and is connected to the output end of a tap water source 8, which is used to supply tap water required for preparing lime slurry into the neutralizing reagent preparation device 13. The bottom of the neutralizing reagent preparation device 13 is connected to the input end of a neutralizing reagent delivery pump 5, which is used to transport the neutralizing reagent prepared in the neutralizing reagent preparation device 13 to the crystallization reactor 3 via the neutralizing reagent delivery pump 5.

[0029] The solid-liquid separation system 4 includes a classifying hydrocyclone 41 and a filtration device 42. The bottom of the main reactor is connected to the upper end of the classifying hydrocyclone 41 via a classifying feed pump 43, which is used to stably and continuously transport the reaction system in the main reactor to the classifying hydrocyclone 41 for preliminary solid-liquid separation. The bottom of the classifying hydrocyclone 41 is connected to the filtration device 42, which smoothly transports the solids initially separated by the classifying hydrocyclone 41 to the filtration device 42 for deep dehydration. The upper end of the classifying hydrocyclone 41 is also connected to the main reactor and the wastewater discharge area 9. When the phosphorus content in the wastewater does not meet the discharge standard or hydroxyapatite crystals are detected, the system can be activated. When the particle size is small, this design can fully utilize its reflux function, returning the separated liquid and some of the lighter, smaller hydroxyapatite particles to the main reactor for recrystallization. This helps improve the growth quality of hydroxyapatite crystals and the overall efficiency of the reaction system, ensuring that phosphorus can be more fully converted into the required crystalline product. When the phosphorus content in the wastewater meets the discharge standards, the separated liquid is discharged to wastewater discharge area 9. This operation not only achieves preliminary solid-liquid separation but also reduces the burden on subsequent wastewater treatment stages, improving the efficiency and reliability of the entire reaction device. The filtration device 42 is connected to the wastewater discharge area 9. The filtrate produced after treatment by the filtration device 42 is discharged to the wastewater discharge area 9 for further treatment; while the dehydrated filter cake 44 undergoes subsequent treatment such as washing and drying. The classifying hydrocyclone 41 can be replaced by a settling tank or other device capable of gravity settling; the filtration device 42 can be a centrifuge or filter press.

[0030] Example 1

[0031] One m³ of phosphoric acid passivation waste liquid from a chemical plant was taken as the phosphoric acid waste liquid to be treated for experimentation. The concentration of phosphoric acid (H3PO4) in the waste liquid was approximately 0.97 mol / L, and the waste liquid contained a small amount of Fe. 3+ Zn 2+ Plasma.

[0032] A 1 m³ phosphoric acid waste liquid (containing approximately 30 kg of phosphorus or 980 mol P) stored in the phosphoric acid waste liquid storage area is transported to the crystallization reactor via a phosphoric acid waste liquid transfer pump; and the pH value of the reaction system in the crystallization reactor is monitored in real time by a pH real-time monitoring and feedback control system installed on the crystallization reactor.

[0033] Industrial-grade quicklime (Ca(OH)2) stored in the raw material silo is conveyed to the neutralizing reagent preparation device via a conveying auger. Simultaneously, tap water is supplied to the neutralizing reagent preparation device. Under ambient temperature and stirring conditions, a lime slurry with a concentration of approximately 10% (w / v) is prepared. Then, under continuous stirring, the lime slurry is conveyed to the crystallization reactor via a neutralizing reagent delivery pump, and the delivery rate of the neutralizing reagent is regulated by a real-time pH monitoring feedback control system. When the pH value of the reaction system is less than 7, the real-time pH monitoring feedback control system activates the first neutralizing reagent delivery pump, delivering the neutralizing reagent to the crystallization reactor at a delivery rate of 5 L / min. When the pH value of the reaction system rises to 7.0, the real-time pH monitoring feedback control system automatically shuts down the first neutralizing reagent delivery pump and simultaneously activates the second neutralizing reagent delivery pump, switching the delivery rate of the neutralizing reagent to a slow titration mode, i.e., a slow titration at a titration rate of 1 L / min, allowing the pH value of the reaction system to gradually increase, providing a stable and homogeneous reaction environment for the crystallization reaction.

[0034] Continue slow titration until the pH of the reaction system stabilizes at 10.0±0.1 and remains stable for 15 minutes. Then stop feeding lime slurry into the crystallization reactor. Continue stirring for 30 minutes to promote the crystallization reaction. This process consumes a total of about 850L of lime slurry, which is equivalent to about 126kg of slaked lime (containing about 1.71kmol Ca). The final Ca / P molar ratio is about 1.77.

[0035] After the crystallization reaction is completed, the reaction system inside the crystallization reactor is transported from the bottom to the solid-liquid separation device at the back end, where solid-liquid separation is performed to obtain filter cake and filtrate. The filtrate is tested and the total phosphorus concentration is less than 0.5 mg / L, which meets the emission standards. The filtrate is then directly discharged into the wastewater discharge area. After the filter cake is washed twice with deionized water, it is dried at 105℃ for 8 hours to finally obtain a white powder.

[0036] X-ray diffraction (XRD) analysis, such as Figure 2 As shown in the figure, the data is compared in an upper and lower partition format: the upper region is the absorption peak characterization spectrum of the white powder obtained in Example 1, and the lower region is the absorption peak characterization spectrum of standard calcium hydroxyphosphate; the comparison shows that the main crystalline phase of the white powder is calcium hydroxyphosphate (Ca5(PO4)3(OH)), with a purity greater than 95%, which fully demonstrates that the white powder has high component uniformity and stable crystal form; in addition, the content of impurities such as iron and zinc in the white powder is far below the relevant standard limits.

[0037] The above embodiments are merely illustrative of the technical concept and features of the present invention, intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and should not be construed as limiting the scope of protection of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects. The scope of the present invention is defined by the appended claims rather than the foregoing description, and thus all changes falling within the meaning and scope of the equivalents of the claims are intended to be included within the present invention.

Claims

1. A process for preparing hydroxyapatite from phosphoric acid waste liquid, characterized in that, include: The phosphoric acid waste liquid is transported to a crystallization reactor, and the pH value is monitored in real time; Under continuous stirring, the neutralizing agent is delivered to the crystallization reactor. The delivery rate of the neutralizing agent is adjusted based on real-time pH monitoring. When the pH of the reaction system is less than 7, rapid delivery is used to quickly neutralize the acidic substances in the reaction system. When the pH of the reaction system rises to... After 7.0, slow titration is performed to gradually increase the pH of the reaction system in order to provide a stable and homogeneous crystallization reaction environment; Once the pH of the reaction system stabilizes at 9.0-11.0 and remains stable, stop feeding the neutralizing reagent into the crystallization reactor and continue stirring to continue the crystallization reaction. After the crystallization reaction is complete, solid-liquid separation is performed to obtain filter cake and filtrate. The filtrate is discharged or reused, and the filter cake is post-processed to form hydroxycalcium phosphate crystal powder.

2. The process for preparing hydroxyapatite from phosphoric acid waste liquid according to claim 1, characterized in that: The delivery rate of the rapid delivery is 3-10 times the titration rate of the slow titration; The conveying rate of the rapid conveyor is 1-10 L / min.

3. The process for preparing hydroxyapatite from phosphoric acid waste liquid according to claim 2, characterized in that: The neutralizing agent is lime milk with a concentration of 5%-15% (w / v).

4. The process for preparing hydroxyapatite from phosphoric acid waste liquid according to claim 2, characterized in that: When the crystallization reaction is complete, the pH value of the reaction system is controlled within the range of 9.0-11.0; The total calcium to phosphorus molar ratio in the reaction system was controlled within the range of 1.67-2.

0.

5. The process for preparing hydroxyapatite from phosphoric acid waste liquid according to claim 2, characterized in that: The reaction temperature of the crystallization reaction is 20℃-60℃; during the crystallization reaction, the transport time for rapid transport is controlled within 20 minutes, and the titration time for slow titration is controlled within the range of 30-120 minutes.

6. The process for preparing hydroxyapatite from phosphoric acid waste liquid according to claim 2, characterized in that: The post-processing includes cleaning and drying. The cleaning process involves using deionized water as a cleaning agent to wash the filter cake. The drying process is carried out at a temperature of 80℃-120℃.

7. A reaction apparatus for preparing hydroxyapatite from phosphoric acid waste liquid, wherein the process for preparing hydroxyapatite from phosphoric acid waste liquid according to any one of claims 1-6 uses this reaction apparatus for crystallization reaction, characterized in that, Includes a neutralizing reagent preparation system, a crystallization reactor with a stirring device, and a solid-liquid separation system; The crystallization reactor is connected to the phosphoric acid waste liquid storage area and is used to transport the phosphoric acid waste liquid to the crystallization reactor; The output of the neutralizing reagent preparation system is connected to the crystallization reactor via a neutralizing reagent delivery pump; the bottom of the crystallization reactor is connected to the solid-liquid separation system; and the output of the solid-liquid separation system is connected to the wastewater discharge area. The crystallization reactor is equipped with a real-time pH monitoring and feedback control system; one end of the real-time pH monitoring and feedback control system extends into the crystallization reactor to monitor the pH value of the reaction system inside the crystallization reactor. The real-time pH monitoring and feedback control system is electrically connected to the neutralizing reagent delivery pump, and adjusts the working state of the neutralizing reagent delivery pump based on the real-time monitored pH value of the reaction system. The main reactor is also equipped with an outlet at the top, which is used to discharge the supernatant in the reaction system to the wastewater discharge area.

8. The apparatus used in the process of preparing hydroxyapatite from phosphoric acid waste liquid according to claim 7, characterized in that: The neutralizing reagent delivery pump includes a first neutralizing reagent delivery pump and a second neutralizing reagent delivery pump; The input ends of the first neutralizing reagent delivery pump and the second neutralizing reagent delivery pump are both connected to the output end of the neutralizing reagent preparation system, and the output ends of the first neutralizing reagent delivery pump and the second neutralizing reagent delivery pump are both connected to the upper end of the crystallization reactor; the real-time pH monitoring and feedback control system is electrically connected to the first neutralizing reagent delivery pump and the second neutralizing reagent delivery pump respectively, and adjusts the start and stop of the first neutralizing reagent delivery pump and the second neutralizing reagent delivery pump based on the pH value of the reaction system, so that when one starts, the other immediately stops.

9. The apparatus for preparing hydroxyapatite from phosphoric acid waste liquid according to claim 7, characterized in that: The neutralizing reagent preparation system includes a raw material silo and a neutralizing reagent preparation device connected to the raw material silo via a conveying auger; the bottom of the neutralizing reagent preparation device is connected to the input end of the neutralizing reagent delivery pump. The neutralizing reagent preparation device is equipped with a stirrer and is connected to the output end of a tap water source to supply tap water required for preparing lime slurry.

10. The apparatus for preparing hydroxyapatite from phosphoric acid waste liquid according to claim 7, characterized in that: The solid-liquid separation system includes a classifying hydrocyclone and a filtration device; the bottom of the main reactor is connected to the upper end of the classifying hydrocyclone via a classifying feed pump; the bottom of the classifying hydrocyclone is connected to the filtration device; the upper end of the classifying hydrocyclone is also connected to the main reactor and the wastewater discharge area respectively; the filtration device is connected to the wastewater discharge area.

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