Wastewater recovery of phosphorus-containing products and its recovery methods and equipment

Abstract

This application relates to a method and apparatus for recovering phosphorus-containing products from wastewater, comprising seed crystals and crystalline products formed on the surface of the seed crystals, wherein the crystalline products include calcium hydroxyphosphate; wherein the density of the seed crystals is a, and a ≥ 3.0 g / cm³. 3 The above technical solution improves the phosphorus recovery efficiency in wastewater treatment, promotes the crystal growth of calcium hydroxyphosphate through high-density seed crystals, enhances the stability and separation performance of the crystallized products, reduces the difficulty of subsequent treatment, and improves the purity and recovery rate of recovered phosphorus-containing products, thus achieving the technical effect of efficient resource utilization.

Description

Technical Field

[0001] This application relates to the field of electronic technology, and in particular to a wastewater recovery method and apparatus for phosphorus-containing products. Background Technology

[0002] The principle of fluidized bed induced crystallization for phosphorus removal is that ions that can form precipitates undergo heterogeneous crystallization in a supersaturated solution containing seed crystals, causing the ions to precipitate and crystallize on the surface of the seed crystals. This method is often used in wastewater treatment, and the recovered phosphate products have high purity and low water content, which can be directly applied to industrial and agricultural production.

[0003] Existing technologies typically use quartz sand as seed crystals to promote the crystallization of hydroxyapatite. However, quartz sand has a low surface energy and limited adsorption capacity for phosphate ions, resulting in low crystallization efficiency. Summary of the Invention

[0004] This application provides a wastewater recovery method for phosphorus-containing products, which improves crystallization efficiency and at least partially solves the above-mentioned technical problems.

[0005] To achieve the above objectives, according to a first aspect of this application, a wastewater recovery phosphorus-containing product is provided, comprising seed crystals and a crystalline product formed on the surface of the seed crystals, wherein the crystalline product comprises calcium hydroxyphosphate; wherein,

[0006] The density of the seed crystal is a, where a ≥ 3.0 g / cm³. 3 .

[0007] Alternatively, the crystalline product may also include fluorapatite.

[0008] Optionally, calcium hydroxyphosphate accounts for ≥95% of the mass fraction of the crystalline product.

[0009] Optionally, the seed crystals may include garnet and / or zircon sand.

[0010] Optionally, the seed crystals have a particle size of 0.15 mm to 0.3 mm.

[0011] Optionally, the density range of the seed crystals is b, 5.0 g / cm³. 3 ≥b≥3.0g / cm 3 .

[0012] Optionally, the particle size of phosphorus-containing products recovered from wastewater is 0.5mm-1mm.

[0013] According to a second aspect of this application, a method for recovering phosphorus-containing products from wastewater includes the following steps:

[0014] An acidic phosphorus-containing solution and seed crystals are provided. The acidic phosphorus-containing solution is then introduced into the seed crystals to obtain a first intermediate solution. The acidic phosphorus-containing solution contains calcium ions.

[0015] An alkaline solution is provided and added to the first intermediate solution to obtain a phosphorus-containing product;

[0016] Phosphorus-containing products include seed crystals and crystalline products formed on the surface of the seed crystals, the crystalline products including calcium hydroxyphosphate; among which,

[0017] The density of the seed crystal is a, where a ≥ 3.0 g / cm³. 3 .

[0018] Optionally, the amount of seed crystals added to the first intermediate solution is 50 g / L to 200 g / L.

[0019] Optionally, the preparation method of the acidic phosphorus-containing solution includes:

[0020] Phosphorus-containing wastewater, an acidic solution, and calcium salts are provided. The acidic solution is added to the phosphorus-containing wastewater to obtain a second intermediate solution. The second intermediate solution is mixed with the calcium salts to obtain an acidic phosphorus-containing solution.

[0021] Optionally, the acidic solution includes at least one of hydrochloric acid and nitric acid.

[0022] Optionally, the calcium salt includes at least one of calcium chloride and calcium nitrate.

[0023] Optionally, in the second intermediate solution, the molar ratio of calcium ions to phosphate ions is greater than or equal to 3.

[0024] Optionally, phosphorus-containing wastewater includes orthophosphate and fluoride ions.

[0025] Optionally, the concentration of phosphate in the orthophosphate is 1 mg / L to 50 mg / L.

[0026] Optionally, an alkaline solution is provided and added to a first intermediate solution to generate a crystalline product on the seed crystal surface, yielding a phosphorus-containing product, comprising:

[0027] Provide an alkaline solution and add it to the first intermediate solution to adjust the pH to 9.5-11.

[0028] Optionally, the alkaline solution includes at least one of sodium hydroxide and potassium hydroxide.

[0029] Optionally, the concentration of the alkaline solution is less than or equal to 0.1 mol / L.

[0030] Optionally, an acidic phosphorus-containing solution is provided, to which seed crystals are added to obtain a first intermediate solution, comprising:

[0031] Seed crystals are introduced into a fluidized bed, and an acidic phosphorus-containing solution is fed into the bottom of the fluidized bed to obtain the first intermediate solution.

[0032] Optionally, the rising rate of the acidic phosphorus-containing solution in the fluidized bed is 2 m / h-10 m / h.

[0033] Optionally, an alkaline solution is provided and added to the first intermediate solution to obtain a phosphorus-containing product, comprising:

[0034] An alkaline solution is added to the inlet of the acidic phosphorus-containing solution in the fluidized bed. When the phosphorus-containing product particle size grows to 0.5 mm-1 mm, it is discharged from the fluidized bed.

[0035] According to a third aspect of this application, an apparatus for recovering phosphorus-containing products from wastewater is also provided, including a fluidized bed, a first inlet, a second inlet, a crystal discharge port, and a drain outlet. The drain outlet is located above the crystal discharge port, and the first inlet and the second inlet are arranged opposite to each other and are located between the drain outlet and the crystal discharge port.

[0036] Optionally, the wastewater recycling device also includes a mixing pipe, which has at least two inlets and one outlet, with the outlet connected to the first inlet.

[0037] Optionally, the wastewater recycling device also includes a control device, which includes an electrically connected pH detector, a controller, and a pump body. The pump body is located outside the fluidized bed and is connected to the second inlet. The pH detector is located inside the fluidized bed to detect the pH value inside the fluidized bed and generate a digital signal that is transmitted to the controller. The controller controls the operation of the pump body according to the digital signal.

[0038] The wastewater recovery of phosphorus-containing products in this application embodiment includes seed crystals and crystalline products formed on the surface of the seed crystals, wherein the crystalline products include calcium hydroxyphosphate; wherein the density of the seed crystals is a, and a ≥ 3.0 g / cm³. 3 The proposed technical solution improves the phosphorus recovery efficiency during wastewater treatment. By promoting the crystal growth of hydroxyapatite through high-density seed crystals, it enhances the stability and separation performance of the crystallized products, reduces the difficulty of subsequent processing, and improves the purity and recovery rate of recovered phosphorus-containing products, thus achieving the technical effect of efficient resource utilization.

[0039] Other features and advantages of this application will be described in detail in the following detailed description section. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0041] To gain a more complete understanding of this application and its beneficial effects, the following description will be provided in conjunction with the accompanying drawings, wherein the same reference numerals in the following description denote the same parts.

[0042] Figure 1 This is a schematic diagram of the overall structure of the wastewater recycling device for phosphorus-containing products provided in an exemplary embodiment of this disclosure.

[0043] Figure 2 This is a diagram of the crystallized product provided in an exemplary embodiment of this disclosure.

[0044] Figure 3 This is a pre-reaction seed crystal SEM-EDS image provided in an exemplary embodiment of this disclosure.

[0045] Figure 4 This is a SEM-EDS image of the post-reaction crystallization product provided in an exemplary embodiment of this disclosure.

[0046] Figure 5 These are XRD patterns of the seed crystals before the reaction and the products after the reaction provided in the exemplary embodiments of this disclosure.

[0047] Figure 6 This is a schematic diagram showing the results of phosphorus concentration and turbidity detection in Comparative Example 1 provided in an exemplary embodiment of this disclosure.

[0048] Figure 7 This is a schematic diagram showing the results of phosphorus concentration and turbidity detection in Example 1 provided in the exemplary embodiments of this disclosure.

[0049] Explanation of reference numerals in the attached figures:

[0050] 10. Fluidized bed; 11. First inlet; 12. Second inlet; 13. Crystal discharge port; 14. Drain port; 15. Mixing pipe; 16. pH detector; 17. Controller; 18. Pump body. Detailed Implementation

[0051] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the protection scope of this application.

[0052] According to a first aspect of this application, this disclosure provides a phosphorus-containing product for wastewater recovery, comprising seed crystals and a crystalline product formed on the surface of the seed crystals, the crystalline product comprising calcium hydroxyphosphate; wherein the density of the seed crystals is a, and a ≥ 3.0 g / cm³. 3 .

[0053] The above-mentioned technical solution, through its proprietary technical features, addresses the problem that existing technologies typically use quartz sand as seed crystals to promote the crystallization of calcium hydroxyphosphate. However, quartz sand has a low surface energy and limited adsorption capacity for phosphate ions, resulting in low crystallization efficiency. This solution improves phosphorus recovery efficiency in wastewater treatment by promoting calcium hydroxyphosphate crystal growth through high-density seed crystals, enhancing the stability and separation performance of the crystallized products, reducing the difficulty of subsequent treatment, and simultaneously improving the purity and recovery rate of recovered phosphorus-containing products, thus achieving efficient resource utilization.

[0054] In some embodiments, the calcium hydroxyphosphate constitutes ≥95% of the mass fraction of the crystalline product. It is understood that the mass fraction of the calcium hydroxyphosphate in the crystalline product is not particularly limited herein, for example, 96%, 98%, or 99%.

[0055] In some embodiments, the seed crystal comprises garnet and / or zircon sand. This arrangement, using garnet and zircon sand, is inexpensive, readily available, and chemically stable, significantly improving the uniformity and crystallinity of crystal growth. This achieves optimized control of the crystal growth process, reduces production costs, and ensures the quality of the crystalline product. Furthermore, during this process, PO4... 3- Ca 2+ and OH - The resulting supersaturated solution was induced to crystallize by garnet seeds, and the product grew on the seed surface. PO4 3- Ca 2+ and OH - First, the hydroxyapatite precursor is generated. Due to the high density of garnet (3.9 g / cm³),... 3 The hydroxyapatite precursor attached to it cannot be dispersed by the water flow. During fluidized bed operation, the fluidized seed crystals collide with each other, providing interaction forces, while the water flow provides water pressure. The continuously introduced wastewater increases PO4. 3- Ca 2+ OH - Under the combined effects of concentration and other factors, the hydroxyapatite precursor overcomes the reaction energy barrier to transform into calcium hydroxyapatite. The reaction process is rapid; during the experiment, a white product was observed to gradually grow on the surface of the red seed crystals, with no seed or product loss, and the product particle size gradually increased.

[0056] It is understandable that the garnet grain size can vary. When the garnet grain size is too small, garnet may be lost, and when the garnet grain size is too large, the induced crystallization effect is poor.

[0057] In view of this, in some embodiments, the garnet grain size is 0.15mm-0.3mm. This setting effectively improves the utilization rate of garnet as a crystal nucleation inducer through this grain size control technology, making the crystallization process more controllable and stable, thereby achieving a balance between crystallization efficiency and material loss in industrial production.

[0058] It is understandable that seed crystals are micro-particles, and their particle size distribution and surface characteristics directly affect the uniformity of crystal growth and product performance.

[0059] In some embodiments, the density range of the seed crystals is b, wherein 4.0 g / cm³ 3 ≥b≥3.0g / cm 3 This setup controls the seed crystal density within a range of 4.0 g / cm³. 3 With 3.0g / cm 3 This ensures that the seed crystals have a suitable settling rate in the growth solution, reducing the risk of excessively rapid settling due to excessively high density or unstable suspension due to excessively low density, thereby improving the uniformity of crystal growth and the yield.

[0060] It is understandable that the crystallized product will continue to grow on the seed crystal, eventually forming crystal particles with specific morphology and size.

[0061] In some embodiments, the particle size of the phosphorus-containing product recovered from the wastewater is 0.5mm-1mm. This setting controls the particle size of the phosphorus-containing product within the range of 0.5mm-1mm, reducing dust pollution caused by excessively fine powder, and overcoming the defect of large particles easily causing stratification.

[0062] According to a second aspect of this application, a method for recovering phosphorus-containing products from wastewater includes the following steps:

[0063] An acidic phosphorus-containing solution and seed crystals are provided. The acidic phosphorus-containing solution is then introduced into the seed crystals to obtain a first intermediate solution. The acidic phosphorus-containing solution contains calcium ions.

[0064] An alkaline solution is provided and added to the first intermediate solution to obtain a phosphorus-containing product;

[0065] The phosphorus-containing product includes seed crystals and a crystalline product formed on the surface of the seed crystals, wherein the crystalline product includes calcium hydroxyphosphate; wherein the density of the seed crystals is a, and a ≥ 3.0 g / cm³. 3 .

[0066] This technical solution employs a three-step method to achieve efficient crystallization and separation of phosphorus: First, an acidic phosphorus-containing solution is used to allow phosphorus to exist in the form of soluble phosphate, facilitating subsequent crystallization control; second, the characteristics of high-density seed crystals (a≥3.0g / cm3) are utilized to achieve rapid sedimentation separation; finally, an alkaline solution is added to promote the efficient precipitation of phosphorus as phosphate crystals. This method effectively recovers phosphorus from wastewater, significantly shortening the crystallization induction time and improving crystallization quality.

[0067] It is understood that the acidic phosphorus-containing solution may originate from phosphate fertilizer residues in industrial wastewater or agricultural runoff. These sources typically contain high concentrations of phosphate.

[0068] In some embodiments, the method for preparing the acidic phosphorus-containing solution includes:

[0069] Phosphorus-containing wastewater, an acidic solution, and a calcium salt are provided. The acidic solution is added to the phosphorus-containing wastewater to obtain a second intermediate solution. The second intermediate solution is mixed with the calcium salt to obtain an acidic phosphorus-containing solution.

[0070] This setup, by mixing phosphorus-containing wastewater with acidic solutions and calcium salts, can effectively promote the precipitation reaction of phosphates, improve phosphorus recovery efficiency, and achieve efficient phosphorus recovery and resource utilization.

[0071] It is understood that the acidic solution is one that does not react with calcium ions to form a precipitate. Furthermore, the acidic solution can also remove carbonate ions from phosphorus-containing wastewater.

[0072] In some embodiments, the acidic solution includes at least one of hydrochloric acid and nitric acid. This arrangement allows for the selection of a suitable acidic solution based on the needs of different application scenarios. Hydrochloric acid and sulfuric acid are highly corrosive and acidic, suitable for applications requiring rapid reactions or high acidity conditions. By providing a variety of acidic solution options, different process requirements and environmental constraints can be flexibly addressed, improving the applicability and efficiency of the solution.

[0073] Understandably, the calcium salt should be a water-soluble calcium salt, providing excess calcium ions to facilitate subsequent phosphorus precipitation. This is because water-soluble calcium salts dissolve rapidly and release calcium ions, resulting in a high calcium ion concentration in the solution. Excess calcium ions can combine with phosphate ions to form calcium phosphate precipitate. Furthermore, a higher calcium ion concentration is more conducive to promoting the precipitation reaction towards calcium phosphate formation, thereby improving phosphorus removal efficiency. Simultaneously, the selection of a water-soluble calcium salt also reduces the problem of insufficient calcium ion supply due to low calcium salt solubility.

[0074] In some embodiments, the calcium salt includes at least one of calcium chloride and calcium nitrate. This configuration effectively provides calcium ions to meet the needs of different application scenarios.

[0075] It is understandable that changing reaction conditions (such as temperature, pressure, or concentration) can affect the equilibrium position, but will not change the value of the equilibrium constant. This is because the equilibrium constant is only related to temperature and is an inherent characteristic of the reaction at a specific temperature. When the temperature remains constant, even if other conditions are adjusted to shift the equilibrium in a certain direction, the equilibrium constant remains unchanged.

[0076] In some embodiments, the molar ratio of calcium ions to phosphate ions in the second intermediate solution is greater than or equal to 3. This setting ensures an excess of calcium ions in the reaction system, thereby promoting the formation of calcium phosphate precipitate. This is because a higher calcium-to-phosphorus molar ratio favors the formation of a more stable calcium phosphate compound, while reducing the concentration of free phosphate ions in the solution, driving the reaction toward precipitation, and allowing the phosphorus concentration in the effluent to drop below 0.3 mg / L.

[0077] It is understood that the phosphorus-containing wastewater contains various forms of phosphate, such as orthophosphate, pyrophosphate, and organophosphate compounds. These different forms of phosphate exhibit different chemical behaviors and reactivity during wastewater treatment, leading to increased treatment difficulty.

[0078] In some embodiments, the phosphorus-containing wastewater includes orthophosphate and fluoride ions. This is because orthophosphate is common in phosphorus-containing wastewater and is chemically stable, making it easy to remove using conventional chemical precipitation methods. Orthophosphate can form insoluble phosphate precipitates with various metal ions (such as calcium, iron, and aluminum), thereby achieving efficient phosphorus removal. Fluoride ions can further generate fluorapatite.

[0079] In some embodiments, the concentration of phosphate in the orthophosphate is 1-50 mg / L. This setting results in a high crystallization rate and good crystallization effect when the supersaturation in the water distribution zone is low.

[0080] In some embodiments, the step of providing an alkaline solution and adding it to the first intermediate solution to obtain a phosphorus-containing product specifically includes:

[0081] An alkaline solution is provided and added to the first intermediate solution to adjust its pH to 9.5-11. This setting ensures that phosphorus is fully precipitated under alkaline conditions, improving the purity and yield of phosphorus-containing products. This is because within the pH range of 9.5-11, phosphate ions (PO43-) can form stable phosphate precipitates with metal ions in the solution, effectively separating and enriching phosphorus. Furthermore, this pH range also inhibits the co-precipitation of other impurity ions, reducing contamination of phosphorus-containing products. Simultaneously, the alkaline environment helps neutralize any acidic byproducts that may be generated during the reaction, maintaining the stability of the reaction system and further optimizing the process conditions.

[0082] Understandably, alkaline solutions can be common alkaline solutions such as sodium hydroxide, potassium hydroxide, or ammonia. These solutions are chosen because they can quickly and effectively provide hydroxide ions (OH-), thereby rapidly raising the pH of the solution to the target range.

[0083] In some embodiments, the alkaline solution includes at least one of sodium hydroxide and potassium hydroxide. This configuration allows for precise pH control due to the strong alkalinity and high solubility of sodium hydroxide and potassium hydroxide, reducing uneven precipitation caused by localized over-alkalinity.

[0084] In some embodiments, the concentration of the alkaline solution is less than or equal to 0.1 mol / L. This setting, by limiting the total amount of OH- ions, ensures reaction efficiency while reducing the corrosive effects of strong alkali on experimental equipment and lowering the risk of side reactions caused by a sudden increase in pH.

[0085] It is understood that the above-mentioned reactions can be carried out in different reaction vessels, including but not limited to continuous flow reactors, batch reactors or microchannel reactors. By optimizing the selection and design of reaction vessels, reaction efficiency can be significantly improved, byproduct formation can be reduced and precise control of reaction conditions can be achieved.

[0086] In some embodiments, providing an acidic phosphorus-containing solution, to which seed crystals are added to obtain a first intermediate solution, includes:

[0087] Seed crystals are introduced into a fluidized bed, and an acidic phosphorus-containing solution is fed into the bottom of the fluidized bed to obtain the first intermediate solution.

[0088] This configuration ensures sufficient contact between the seed crystals and the acidic phosphorus-containing solution, improving the crystal growth rate and uniformity. The bottom-inlet design of the fluidized bed ensures that the solution flows from bottom to top, forming a countercurrent contact with the suspended seed crystals, further enhancing mass transfer efficiency.

[0089] In some embodiments, the rising rate of the acidic phosphorus-containing solution in the fluidized bed is 2 m / h-10 m / h.

[0090] This setting reduces the local concentration drop of reactants caused by excessively low flow rates, while preventing premature particle loss due to excessively high flow rates, thus achieving a balance between reaction efficiency and material residence time.

[0091] It is understood that the amount of seed crystals added should exceed the height of the water distribution zone in the fluidized bed to ensure uniform distribution and sufficient contact of the reactants within the fluidized bed. The water distribution zone is an area at the bottom of the fluidized bed used for uniform fluid distribution.

[0092] In some embodiments, the amount of seed crystals added is 50 g / L to 200 g / L. This setting ensures that the seed crystals form a sufficient concentration gradient in the fluidized bed to promote full contact between the reactants and the catalyst, while also reducing the risk of increased bed pressure drop or localized accumulation due to excessive seed crystals.

[0093] In some embodiments, providing an alkaline solution and adding it to the first intermediate solution to obtain a phosphorus-containing product includes:

[0094] An alkaline solution is added to the inlet of an acidic phosphorus-containing solution in a fluidized bed, and the phosphorus-containing product is discharged from the fluidized bed when the particle size grows to 0.5 mm-1 mm.

[0095] This setup, by adding an alkaline solution to the inlet of the acidic phosphorus-containing solution in the fluidized bed, promotes phosphorus precipitation, improves phosphorus recovery efficiency, and neutralizes the acidic environment, reducing solution corrosivity. The phosphorus-containing product is discharged from the fluidized bed when its particle size reaches 0.5mm-1mm. This reduces side reactions and improves purity.

[0096] According to the third aspect of this application, such as Figure 1 As shown, an apparatus for recovering phosphorus-containing products from wastewater is also provided, including a fluidized bed 10, which includes a first inlet 11, a second inlet 12, a crystal discharge port 13, and a drain port 14. The drain port 14 is located above the crystal discharge port 13. The first inlet 11 and the second inlet 12 are arranged opposite to each other and are located between the drain port 14 and the crystal discharge port 13.

[0097] In this technical solution, an acidic phosphorus-containing solution is introduced through the first inlet 11, and an alkaline solution is introduced through the second inlet 12, thereby forming a neutralization reaction zone at the bottom of the fluidized bed 10. This design allows the acidic phosphorus-containing solution and the alkaline solution to mix and react fully at the bottom of the fluidized bed 10, generating phosphate precipitates. The structure of the drain outlet 14 located above the crystal discharge outlet 13 facilitates solid-liquid separation: the lighter liquid is discharged through the upper drain outlet 14, while the denser crystalline product settles at the bottom and is collected through the crystal discharge outlet 13. The opposing inlet design generates countercurrent flow, enhancing the mixing efficiency of the reactants. This device structure effectively solves the problems of insufficient reaction and uneven crystal growth in traditional phosphorus recovery processes.

[0098] In some embodiments, the wastewater recycling device further includes a mixing pipe 15, which includes at least two inlets and one outlet, the outlet being connected to the first inlet 11.

[0099] With this setup, the second intermediate solution is input through one inlet and the calcium salt is input through the other inlet. After mixing in the mixed calcium salt, the solution is input into the fluidized bed 10 through the outlet. The dual-inlet structure can reduce the premature contact between the two solutions before they enter the mixed calcium salt, thus reducing precipitation problems caused by excessively high local concentrations. Secondly, the extended path set in the mixing pipe 15 increases the residence time of the solution, giving the two substances more opportunities for convection and diffusion, thereby improving the uniformity of mixing.

[0100] Understandably, a fixed amount of alkaline solution can be added directly to the fluidized bed 10 to meet the requirements for the reaction. However, due to the complexity of the reaction system, the pH value within the fluidized bed 10 cannot be known in real time, which will reduce the quality of the crystallized product.

[0101] In view of this, in some embodiments, the wastewater recycling device further includes a control device, which includes an electrically connected pH detector 16, a controller 17, and a pump body 18. The pump body 18 is located outside the fluidized bed 10 and is connected to the second inlet 12. The pH detector 16 is disposed inside the fluidized bed 10 to detect the pH value inside the fluidized bed 10 and generate a digital signal that is transmitted to the controller 17. The controller 17 controls the working state of the pump body 18 according to the digital signal.

[0102] This setup allows for real-time monitoring of pH changes within the fluidized bed 10, enabling precise adjustment of the alkaline solution addition rate based on actual needs. The pH detector 16 converts the detected pH value into a digital signal, which is transmitted to the controller 17. The controller 17 analyzes the deviation between the current pH value and the target value using a preset algorithm, thereby adjusting the operating state of the pump 18 and controlling the alkaline solution addition rate. This closed-loop control system effectively avoids instability in the quality of the crystallized product caused by pH fluctuations, improving the stability of the reaction system and the consistency of the product. Furthermore, automated control reduces human error, improving process repeatability and production efficiency.

[0103] The following specific examples illustrate this:

[0104] Example 1

[0105] Acidic phosphorus-containing wastewater (pH 5.5) was obtained by mixing phosphorus-containing wastewater (phosphate concentration 1 mg / L, fluoride ion concentration 1 mg / L) with hydrochloric acid and calcium chloride (calcium ion concentration 200 mg / L). Garnet (particle size 0.15 mm-0.3 mm, dosage 50 g / L) was mixed with the acidic phosphorus-containing solution to obtain the first intermediate solution. The upward flow rate of the acidic phosphorus-containing wastewater was 10 m / h. Sodium hydroxide (concentration 0.1 mol / L) was mixed with the first intermediate solution, and the pH was controlled at 9.5-11. The seed crystals gradually grew to about 1 mm and were discharged to obtain the crystallized product.

[0106] Example 2

[0107] Phosphorus-containing wastewater (phosphate concentration 20 mg / L, fluoride ion concentration 1.2 mg / L) was mixed with nitric acid and calcium nitrate (calcium ion concentration 200 mg / L) to obtain acidic phosphorus-containing wastewater (pH 5.7). Garnet (particle size 0.15 mm-0.3 mm, dosage 100 g / L) was mixed with the acidic phosphorus-containing solution to obtain the first intermediate solution. The upward flow rate of the acidic phosphorus-containing wastewater was 10 m / h. Sodium hydroxide (concentration 0.1 mol / L) was mixed with the first intermediate solution, and the pH was controlled at 9.5-11. The seed crystals gradually grew to about 1 mm and were discharged to obtain the crystallized product.

[0108] Example 3

[0109] Acidic phosphorus-containing wastewater (phosphate concentration 20 mg / L, fluoride ion concentration 1.1 mg / L) was obtained by mixing phosphoric acid and calcium chloride (calcium ion concentration 200 mg / L). Garnet (particle size 0.15 mm-0.3 mm, dosage 100 g / L) was mixed with the acidic phosphorus-containing solution to obtain the first intermediate solution. The upward flow rate of the acidic phosphorus-containing wastewater was 8 m / h. Potassium hydroxide (concentration 0.1 mol / L) was mixed with the first intermediate solution, and the pH was controlled at 9.5-11. The seed crystals gradually grew to about 1 mm and were discharged to obtain the crystallized product.

[0110] Example 4

[0111] Phosphorus-containing wastewater (phosphate concentration 20 mg / L, fluoride ion concentration 0.5 mg / L) was mixed with hydrochloric acid and calcium nitrate (calcium ion concentration 200 mg / L) to obtain acidic phosphorus-containing wastewater (pH 6). Garnet (particle size 0.15 mm-0.3 mm, dosage 150 g / L) was mixed with the acidic phosphorus-containing solution to obtain the first intermediate solution. The upward flow rate of the acidic phosphorus-containing wastewater was 4 m / h. Sodium hydroxide (concentration 0.01 mol / L) was mixed with the first intermediate solution, and the pH was controlled at 9.5-11. The seed crystals gradually grew to about 1 mm and were discharged to obtain the crystallized product.

[0112] Example 5

[0113] Phosphorus-containing wastewater (phosphate concentration 50 mg / L, fluoride ion concentration 0.5 mg / L) was mixed with hydrochloric acid and calcium chloride (calcium ion concentration 200 mg / L) to obtain acidic phosphorus-containing wastewater (pH 4.5). Garnet (particle size 0.15 mm-0.3 mm, dosage 200 g / L) was mixed with the acidic phosphorus-containing solution to obtain the first intermediate solution. The upward flow rate of the acidic phosphorus-containing wastewater was 2 m / h. Potassium hydroxide (concentration 0.01 mol / L) was mixed with the first intermediate solution, and the pH was controlled at 9.5-11. The seed crystals gradually grew to about 1 mm in size and were discharged to obtain the crystallized product.

[0114] Comparative Example 1:

[0115] Acidic phosphorus-containing wastewater (pH 5.8) was prepared by mixing phosphorus-containing wastewater (phosphate concentration 10 mg / L, fluoride ion concentration 1 mg / L) with hydrochloric acid and calcium chloride (calcium ion concentration 200 mg / L). Quartz sand (particle size 0.15 mm-0.3 mm, dosage 100 g / L) was then mixed with the acidic phosphorus-containing solution to obtain an intermediate solution. The upward flow velocity of the acidic phosphorus-containing wastewater was 2 m / h. Sodium hydroxide (concentration 0.01 mol / L) was then mixed with the intermediate solution, and the pH was controlled at 9.5-11 for crystallization.

[0116] Comparative Example 2:

[0117] Acidic phosphorus-containing wastewater (phosphate concentration 100 mg / L, fluoride ion concentration 0.5 mg / L) was obtained by mixing phosphoric acid and calcium nitrate (calcium ion concentration 200 mg / L). Quartz sand (particle size 0.15 mm-0.3 mm, dosage 200 g / L) was mixed with the acidic phosphorus-containing solution to obtain an intermediate solution. The upward flow rate of the acidic phosphorus-containing wastewater was 10 m / h. Potassium hydroxide (concentration 0.1 mol / L) was mixed with the intermediate solution, and the pH was controlled at 9.5-11 for crystallization.

[0118] Testing standards:

[0119] SEM-EDS Testing: 《JY / T0584-2020 General Rules for Scanning Electron Microscopy Analysis》

[0120] XRD Testing: 《JY / T0587-2020 General Rules for Polycrystalline X-ray Diffraction Methods》

[0121] XRF Testing: 《JY / T0569-2020 General Rules for X-ray Fluorescence Spectroscopy》

[0122] Phosphorus concentration testing method: 《HJ670-2013 Determination of Phosphate and Total Phosphorus in Water - Continuous Flow-Ammonium Molybdate Spectrophotometric Method》

[0123] Turbidity testing method: 《HJ1075-2019 Water Quality - Determination of Turbidity - Turbidity Meter Method》

[0124] Test results:

[0125] from Figure 2 As can be seen, Figure (a) shows the product during the experiment of Comparative Example 1, and Figure (b) shows the product during the experiment of Example 1. The product in Figure (a) is a transparent flocculent substance that is severely lost with the water and disintegrates after discharge, making it impossible to recover. The crystalline product in Figure (b) is solid, with no product loss or seed crystal loss, and the product can be recovered.

[0126] from Figure 3 and Figure 4 It can be seen that: Figure 3 SEM-EDS of the seed crystals before the reaction in Example 1. Figure 4 This is a SEM-EDS analysis of the crystallized product after the reaction in Example 1. Before the reaction, the seed crystals were blocky, regularly shaped, with clearly visible edges and corners. The main elements were Mg, Al, Si, Ca, Te, O, and F, with a particle size of approximately 200 μm, and were 80-100 mesh garnet. After the reaction, the crystallized product was irregularly spherical, with the main elements being Ca, P, O, and F, and a particle size of approximately 1 mm. The main component was hydroxyapatite, accompanied by trace amounts of amorphous calcium phosphate.

[0127] from Figure 5 It can be seen that: Figure 5 The XRD patterns of the seed crystals before and after the reaction in Examples 1-5 are shown. The seed crystals before the reaction were garnets. The diffraction peaks of the products after the reaction were mainly hydroxyapatite. However, the (300) peak at 32.9 degrees overlapped with the (202) peak at 32.2 degrees, indicating that there was distortion or defects in the crystals. Fluoride ions partially replaced the hydroxyl groups, causing the peak at 32.9 degrees to shift to a lower angle. Therefore, the dephosphorized products were hydroxyapatite and trace amounts of amorphous calcium phosphate. In addition, the XRD patterns of the crystal products also contained diffraction peaks of the garnet seed crystals, indicating that the phosphorus-containing products were attached to the garnet seed crystals.

[0128] from Figure 6 and Figure 7 It can be seen that: these are respectively Comparative Example 1 ( Figure 6 ) and Example 1 ( Figure 7 The diagram shows the results of phosphorus concentration and turbidity testing. After 50 hours of continuous operation, the phosphorus concentration in the effluent of Comparative Example 1 exceeded 0.3 mg / L and the turbidity exceeded 20 NTU, reaching 300-400 NTU, which did not meet the integrated wastewater discharge standard. In Example 1, the phosphorus concentration in the effluent was ≤0.3 mg / L and the turbidity was ≤20 NTU, which met the wastewater discharge standard and could meet the Class IV surface water standard.

[0129] Table 1 shows the XRF of the seed crystals before the reaction and the crystallized products after the reaction.

[0130]

[0131]

[0132] As can be seen from Table 1, the Ca and P content of the product after the reaction increased significantly, accounting for more than 95%, indicating that the purity of the product is higher than 95%.

[0133] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more features. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0134] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0135] The embodiments, implementation methods, and related technical features of this application can be combined and substituted for each other without conflict.

[0136] The above are merely preferred embodiments of this application and are not intended to limit this application in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of this application without departing from the scope of the technical solution of this application shall still fall within the scope of the technical solution of this application.

Claims

1. A phosphorus-containing wastewater recovery product, characterized in that, It includes seed crystals and crystalline products formed on the surface of the seed crystals, wherein the crystalline products include calcium hydroxyphosphate; wherein, The density of the seed crystal is a, where a ≥ 3.0 g / cm³. 3 .

2. The wastewater recovery phosphorus-containing product according to claim 1, characterized in that, The crystallized products also include fluorapatite.

3. The wastewater recovery phosphorus-containing product according to claim 1, characterized in that, The hydroxyphosphate accounts for ≥95% of the mass fraction of the crystalline product.

4. The wastewater recovery phosphorus-containing product according to claim 1, characterized in that, The seed crystals include garnet and / or zircon sand.

5. The wastewater recovery phosphorus-containing product according to claim 1, characterized in that, The seed crystals have a particle size of 0.15mm-0.3mm.

6. The wastewater recovery phosphorus-containing product according to claim 1, characterized in that, The density range of the seed crystal is b, and the density of the seed crystal is 5.0 g / cm³. 3 ≥b≥3.0g / cm 3 .

7. The wastewater recovery phosphorus-containing product according to claim 1, characterized in that, The particle size of the phosphorus-containing products recovered from the wastewater is 0.5mm-1mm.

8. A method for recovering phosphorus-containing products from wastewater, characterized in that, Includes the following steps: An acidic phosphorus-containing solution and seed crystals are provided. The acidic phosphorus-containing solution is then introduced into the seed crystals to obtain a first intermediate solution. The acidic phosphorus-containing solution contains calcium ions. An alkaline solution is provided and added to the first intermediate solution to generate a crystallized product on the surface of the seed crystals, thereby obtaining a waste-recovered phosphorus-containing product; The recycled phosphorus-containing waste products include seed crystals and crystalline products formed on the surface of the seed crystals, wherein the crystalline products include calcium hydroxyphosphate; wherein, The density of the seed crystal is a, where a ≥ 3.0 g / cm³. 3 .

9. The method for recovering phosphorus-containing products from wastewater according to claim 8, characterized in that, The amount of seed crystals added to the first intermediate solution is 50 g / L-200 g / L.

10. The method for recovering phosphorus-containing products from wastewater according to claim 8, characterized in that, The method for preparing the acidic phosphorus-containing solution includes: A phosphorus-containing wastewater, an acidic solution, and a calcium salt are provided. The acidic solution is added to the phosphorus-containing wastewater to obtain a second intermediate solution. The second intermediate solution is mixed with the calcium salt to obtain the acidic phosphorus-containing solution.

11. The method for recovering phosphorus-containing products from wastewater according to claim 10, characterized in that, The acidic solution includes at least one of hydrochloric acid and nitric acid.

12. The method for recovering phosphorus-containing products from wastewater according to claim 10, characterized in that, The calcium salt includes at least one of calcium chloride and calcium nitrate.

13. The method for recovering phosphorus-containing products from wastewater according to claim 10, characterized in that, In the second intermediate solution, the molar ratio of calcium ions to phosphate ions is greater than or equal to 3.

14. The method for recovering phosphorus-containing products from wastewater according to claim 10, characterized in that, The phosphorus-containing wastewater includes orthophosphate and fluoride ions.

15. The method for recovering phosphorus-containing products from wastewater according to claim 14, characterized in that, In the phosphorus-containing wastewater, the concentration of phosphate in the orthophosphate is 1 mg / L-50 mg / L.

16. The method for recovering phosphorus-containing products from wastewater according to claim 8, characterized in that, The provision of an alkaline solution, which is added to the first intermediate solution to generate a crystalline product on the surface of the seed crystals, yielding a phosphorus-containing product, includes: An alkaline solution is provided and added to the first intermediate solution to adjust the pH to 9.5-11, so as to generate a crystallized product on the surface of the seed crystals, thereby obtaining the phosphorus-containing product recovered from the wastewater.

17. The method for recovering phosphorus-containing products from wastewater according to claim 16, characterized in that, The alkaline solution includes at least one of sodium hydroxide solution and potassium hydroxide solution.

18. The method for recovering phosphorus-containing products from wastewater according to claim 17, characterized in that, The concentration of the alkaline solution is less than or equal to 0.1 mol / L.

19. The method for recovering phosphorus-containing products from wastewater according to claim 8, characterized in that, The provision of an acidic phosphorus-containing solution, into which seed crystals are added to obtain a first intermediate solution, includes: Seed crystals are added into the fluidized bed (10), and an acidic phosphorus-containing solution is fed into the bottom of the fluidized bed (10) to obtain the first intermediate solution.

20. The method for recovering phosphorus-containing products from wastewater according to claim 19, characterized in that, The rising rate of the acidic phosphorus-containing solution in the fluidized bed (10) is 2 m / h-10 m / h.

21. The method for recovering phosphorus-containing products from wastewater according to claim 19, characterized in that, The provision of an alkaline solution, which is added to the first intermediate solution, yields a phosphorus-containing product, comprising: An alkaline solution is added to the inlet of an acidic phosphorus-containing solution in a fluidized bed (10), and the phosphorus-containing product is discharged from the fluidized bed (10) when the particle size grows to 0.5 mm-1 mm.

22. An apparatus for recovering phosphorus-containing products from wastewater, used to prepare the phosphorus-containing products recovered from wastewater as described in any one of claims 1-7, characterized in that, The fluidized bed (10) includes a first liquid inlet (11), a second liquid inlet (12), a crystal discharge port (13), and a drain port (14). The drain port (14) is located above the crystal discharge port (13). The first liquid inlet (11) and the second liquid inlet (12) are arranged opposite to each other and are located between the drain port (14) and the crystal discharge port (13).

23. The apparatus for recovering phosphorus-containing products from wastewater according to claim 22, characterized in that, The wastewater recycling device also includes a mixing pipe (15), which includes at least two inlets and one outlet, the outlet being connected to the first liquid inlet (11).

24. The apparatus for recovering phosphorus-containing products from wastewater according to claim 22, characterized in that, The wastewater recycling device also includes a control device, which includes an electrically connected pH detector (16), a controller (17), and a pump (18). The pump (18) is located outside the fluidized bed (10) and is connected to the second inlet (12). The pH detector (16) is located inside the fluidized bed (10) to detect the pH value inside the fluidized bed (10) and generate a digital signal to be transmitted to the controller (17). The controller (17) controls the working state of the pump (18) according to the digital signal.

Images