Calcium phosphate crystal phosphorus recovery method and system suitable for high-phosphorus and low-phosphorus wastewater

Abstract

The invention discloses a calcium phosphate crystal phosphorus recovery method and system suitable for high-phosphorus and low-phosphorus wastewater. The phosphorus recovery method comprises the following steps: firstly adjusting the pH value of phosphorus-containing wastewater to 9.0-10.0, and then adding calcium salt into the phosphorus-containing wastewater, or firstly adding aluminum salt hydrolysate and then adding the calcium salt to obtain wastewater containing calcium phosphate microcrystals; adding aluminum salt into the wastewater, stirring and mixing, carrying out solid-liquid separation to obtain a phosphorus recovery product and clarified wastewater, and discharging the clarified wastewater after reaching the standard; then adding a NaOH solution into the phosphorus recovery product for dissolving and purifying, and carrying out solid-liquid separation on the obtained product to obtain hydroxyl calcium phosphate and a metaaluminate solution; and finally, adding strong acid into the meta-aluminate solution to carry out neutralization reaction, and regenerating into aluminum salt for reutilization. The phosphorus recovery method disclosed by the invention is high in recovery efficiency, can simultaneously realize purification of a phosphorus recovery product and repeated utilization of aluminum salt, and is remarkable in economic benefit and social benefit.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of phosphorus recovery from phosphorus-containing wastewater, and particularly relates to a calcium phosphate crystallization phosphorus recovery method and system suitable for high and low phosphorus-containing wastewater. BACKGROUND

[0002] Phosphorus-containing wastewater is the main source of phosphorus, a nutrient pollutant in water environment. Carrying out phosphorus recovery from phosphorus-containing wastewater can not only effectively curb water eutrophication and other water environmental problems caused by phosphorus loss, but also effectively alleviate the shortage of phosphorus resources in China.

[0003] There are many methods for phosphorus recovery from phosphorus-containing wastewater, including chemical crystallization represented by crystallization of insoluble salt, ion exchange, adsorption, electrodeposition and membrane filtration. However, only chemical crystallization is truly meaningful in the essence, and other methods are only phosphorus separation. Chemical crystallization of phosphorus recovery includes calcium phosphate crystallization, struvite crystallization and blue vitriol crystallization, etc., among which calcium phosphate crystallization is widely used because of its low price, wide source and strong adaptability to phosphorus concentration change.

[0004] However, the change of phosphorus concentration in phosphorus-containing wastewater will seriously impact the operation stability of calcium phosphate crystallization for phosphorus recovery. When the phosphorus concentration in wastewater is too high, calcium phosphate crystallization has the significant feature of explosive nucleation, generating calcium phosphate microcrystals with poor settling performance, which needs to be assisted by polyaluminum chloride (PAC) to improve the phosphorus recovery rate, which brings two adverse effects: one is that the cost of PAC reagent increases significantly, and the other is that PAC and its hydrolysis products enter the phosphorus recovery product, reducing the purity and recovery value of the recovery product; while when the phosphorus concentration in wastewater is too low, it will lead to insufficient crystallization driving force of calcium phosphate, which needs to add a large amount of Ca(OH)2 to increase the crystallization pH value, but even so, the phosphorus recovery rate is still low, and Ca(OH)2 is mixed into the recovery product, reducing the purity and recovery value of the recovery product. Therefore, it is of great significance to develop a calcium phosphate crystallization phosphorus recovery process that can adapt to high and low phosphorus-containing wastewater and can guarantee the purity of the recovery product. 2+ SUMMARY

[0005] The present application aims to at least partially solve one of the problems in the related art.

[0006] To this end, the present application provides a calcium phosphate crystallization phosphorus recovery method and system suitable for high and low phosphorus-containing wastewater, which adjusts the calcium phosphate crystallization process according to the change of phosphorus concentration in phosphorus-containing wastewater, improves the phosphorus recovery efficiency, and realizes the purification of the phosphorus recovery product and the reuse of aluminum salt by means of strong alkali alkalization, thus having good economic and social benefits.

[0007] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:​ In a first aspect, embodiments of the present invention propose a method for recovering crystalline phosphorus from calcium phosphate that is suitable for high- and low-phosphorus wastewater, comprising the following steps: (1) Adjust the pH of the phosphorus-containing wastewater to 9.0-10.0, and then add calcium salt to the phosphorus-containing wastewater, or add aluminum salt hydrolysate first and then add calcium salt to obtain wastewater containing calcium phosphate microcrystals; (2) Add aluminum salt to the wastewater containing calcium phosphate microcrystals, stir and mix, and then separate the solid and liquid to obtain phosphorus recovery product and clarified wastewater; the clarified wastewater meets the discharge standards. (3) Add NaOH solution to the phosphorus recovery product for dissolution and purification, and then perform solid-liquid separation on the obtained product to obtain hydroxycalcium phosphate and aluminic acid solution; (4) Add a strong acid to the aluminic acid solution to carry out a neutralization reaction, regenerate it into aluminum salt, and reuse it.

[0008] In this invention, the hydrolysis products of commonly used coagulant aluminum salts are used as seed crystals. By adding or not adding the hydrolysis products of aluminum salts, the calcium phosphate crystallization process can be switched between induced crystallization and homogeneous crystallization modes, thus making it suitable for the recovery of calcium phosphate crystals from wastewater with high and low phosphorus concentrations.

[0009] In some embodiments, in step (1), when the phosphorus concentration of the phosphorus-containing wastewater is ≥60 mg / L, the specific process of step (1) is as follows: adjust the pH of the phosphorus-containing wastewater to 9.0-10.0, and then add calcium salt to the phosphorus-containing wastewater to obtain wastewater containing calcium phosphate microcrystals; And / or, when the phosphorus concentration of the phosphorus-containing wastewater is <60 mg / L, the specific process of step (1) is as follows: adjust the pH of the phosphorus-containing wastewater to 9.0-10.0, then add aluminum salt hydrolysate to the phosphorus-containing wastewater first, and then add calcium salt to obtain wastewater containing calcium phosphate microcrystals.

[0010] In some embodiments, in step (1), the calcium salt is one or a mixture of two of calcium chloride or calcium nitrate; And / or, the Ca in the calcium salt 2+ With the PO4 in the phosphorus-containing wastewater 3- The molar ratio is (1.67-2.0):1.

[0011] In some embodiments, in step (1), the aluminum salt hydrolysate is prepared by mixing aluminum salt with alkaline solution and then performing a pre-hydrolysis reaction; Optionally, the aluminum salt is one or a mixture of two of aluminum chloride or aluminum nitrate; Optionally, the alkaline solution is a NaOH solution; Optionally, the reaction time of the pre-hydrolysis reaction is 2-3 min; And / or, the concentration of the aluminum salt hydrolysate is 50 mmol / L.

[0012] In some embodiments, in step (2), the aluminum salt is one or a mixture of two of aluminum chloride or aluminum nitrate; And / or, when the phosphorus concentration of the phosphorus-containing wastewater is ≥60 mg / L, the dosage of the aluminum salt is ≥0.1 mmol / L; And / or, when the phosphorus concentration of the phosphorus-containing wastewater is <60 mg / L, the dosage of the aluminum salt is ≤0.01 mmol / L.

[0013] In some embodiments, in step (3), the solid-liquid volume ratio of the phosphorus recovery product to the NaOH solution is 1:(3-5); And / or, the pH value during the dissolution and purification is ≥13, and the dissolution and purification time is 6 h; And / or, the solid-liquid separation is performed using a 100-mesh vibrating screen.

[0014] In some embodiments, in step (4), the strong acid is one or a mixture of two of hydrochloric acid or nitric acid; And / or, the pH of the neutralization reaction is 7-8, and the reaction time is 10 min.

[0015] Secondly, embodiments of the present invention also propose a calcium phosphate crystallization phosphorus recovery system adapted to high- and low-phosphorus wastewater. The phosphorus recovery system is used to implement the phosphorus recovery method described in the first aspect, and includes a crystallization tank, a coagulation tank, a sedimentation tank, a purification tank, a separation tank, a regeneration tank, an alkali storage tank, a calcium salt storage tank, an aluminum salt storage tank, and an acid storage tank. The crystallization tank, the coagulation tank, the sedimentation tank, the purification tank, the separation tank, and the regeneration tank are connected sequentially. The first outlet of the alkali storage tank is connected to the inlet of the crystallization tank, the second outlet of the alkali storage tank is connected to the inlet of the purification tank, the outlet of the calcium salt storage tank is connected to the inlet of the crystallization tank, the outlet of the aluminum salt storage tank is connected to the inlet of the coagulation tank, the inlet of the aluminum salt storage tank is connected to the outlet of the regeneration tank, and the outlet of the acid storage tank is connected to the inlet of the regeneration tank. It also includes a pre-hydrolysis tank, the outlet of which is connected to the inlet of the crystallization tank, the first inlet of which is connected to the third outlet of the alkali storage tank, and the second inlet of which is connected to the outlet of the aluminum salt storage tank.

[0016] In some embodiments, the hydraulic retention time of the crystallization tank is 20-30 min; And / or, the hydraulic retention time of the coagulation tank is 20-30 min. And / or, the sedimentation tank adopts an inclined plate sedimentation method, with a hydraulic retention time of 30 min and a surface loading of ≤0.8 m³. 3 / m 2 ·h.

[0017] In some embodiments, the crystallization tank, the coagulation tank, the purification tank, and the regeneration tank are all equipped with a stirring device; Optionally, when the phosphorus concentration of the phosphorus-containing wastewater is ≥60 mg / L, the stirring speed in the crystallization tank is controlled at 100-150 rpm; when the phosphorus concentration of the phosphorus-containing wastewater is <60 mg / L, the stirring speed in the crystallization tank is controlled at 200-300 rpm. Optionally, the stirring speed of the coagulation tank is 100-150 rpm; Optionally, the stirring speed of the purification tank is 100 rpm; Optionally, the stirring speed of the regeneration tank is 100 rpm.

[0018] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a calcium phosphate crystallization phosphorus recovery system adapted to high and low phosphorus wastewater according to an embodiment of the present invention.

[0020] Attached reference numerals: 1-Alkali storage tank, 101-First inlet of alkali storage tank, 102-Second inlet of alkali storage tank, 103-Third inlet of alkali storage tank, 2-Calcium salt storage tank, 3-Aluminum salt storage tank, 4-Pre-hydrolysis tank, 401-First inlet of pre-hydrolysis tank, 402-Second inlet of pre-hydrolysis tank, 5-Crystallization tank, 6-Coagulation tank, 7-Sedimentation tank, 8-Purification tank, 9-Separation tank, 10-Acid storage tank, 11-Regeneration tank, 12-First solenoid valve, 13-Second solenoid valve. Detailed Implementation

[0021] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0022] In this invention, when a value is described as a range, it should be understood that such disclosure includes disclosure of all possible subranges within that range, as well as specific numerical values ​​falling within that range, regardless of whether specific numerical values ​​or specific subranges are explicitly specified.

[0023] In this invention, the terms “comprising” and “including” and their various variations mean that other elements or wholes may be included but are not specifically described.

[0024] In this invention, the term "and / or" is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone.

[0025] This invention is based on the inventor's discoveries and understanding of the following facts and problems: Traditional methods for recovering phosphorus from wastewater using calcium phosphate crystallization employ either homogeneous crystallization or induced crystallization. Homogeneous crystallization is suitable for wastewater with high phosphorus concentrations, while induced crystallization is better suited for wastewater with low phosphorus concentrations. Therefore, fluctuations in phosphorus concentration in wastewater pose a challenge to the stable operation of the calcium phosphate crystallization phosphorus recovery process. Furthermore, to improve phosphorus recovery rates, large amounts of coagulants such as aluminum salts are required, which not only increases recovery costs but also reduces the purity and reuse value of the recovered products.

[0026] Based on this, to solve the problem of stable operation of the calcium phosphate crystallization phosphorus recovery process under different phosphorus concentrations in wastewater, this invention improves the adaptability of the phosphorus recovery process to changes in wastewater phosphorus concentration by controlling the crystallization mode. The specific principle is as follows: When the phosphorus concentration in the wastewater is ≥60 mg / L, no aluminum salt is added during the crystallization reaction. The process is mainly completed through explosive nucleation of homogeneous crystallization to generate calcium phosphate microcrystals. Then, aluminum salt coagulation is performed on the calcium phosphate microcrystals to obtain a high phosphorus recovery rate. The recovered product is a homogeneous crystallization product agglomerate. When the phosphorus concentration in the wastewater is <60 mg / L, pre-hydrolyzed aluminum salt is added to the wastewater first. The amorphous aluminum hydroxide, a product of aluminum salt hydrolysis, is used to control the crystallization reaction mode to be mainly induced crystallization with amorphous aluminum hydroxide particles as seed crystals. This reduces the activation energy of the crystallization reaction and increases the scale of phosphorus crystallization under low phosphorus conditions. Then, aluminum salt coagulation is performed on the heterogeneous crystallization product to obtain a high phosphorus recovery rate. The recovered product is an induced crystallization product agglomerate.

[0027] Furthermore, to further improve the purity of the phosphorus recovery products from wastewater, this invention utilizes the amphoteric characteristics of the main impurity, aluminum salt hydrolysis products, in the recovered products by alkalizing them with a strong alkaline solution. After alkalization, the calcium phosphate crystals are converted into HAP (hydroxyapatite), which has lower solubility, is thermodynamically stable, and has the highest value. The aluminum salt dissolves into the liquid phase as aluminic acid. After solid-liquid separation, high-purity HAP and a high-concentration aluminic acid solution are obtained. The aluminic acid solution can be further reduced to a weakly alkaline pH using a strong acid solution and then reused as aluminum salt.

[0028] In a first aspect, embodiments of the present invention propose a method for recovering crystalline phosphorus from calcium phosphate that is suitable for high- and low-phosphorus wastewater, comprising the following steps: (1) Adjust the pH of the phosphorus-containing wastewater to 9.0-10.0, and then add calcium salt to the phosphorus-containing wastewater, or add aluminum salt hydrolysate first and then add calcium salt to obtain wastewater containing calcium phosphate microcrystals; (2) Add aluminum salt to the wastewater containing calcium phosphate microcrystals, stir and mix, and then separate the solid and liquid to obtain phosphorus recovery product and clarified wastewater; the clarified wastewater meets the discharge standards. (3) Add NaOH solution to the phosphorus recovery product for dissolution and purification, and then perform solid-liquid separation on the obtained product to obtain hydroxycalcium phosphate and aluminic acid solution; (4) Add a strong acid to the aluminic acid solution to carry out a neutralization reaction, regenerate it into aluminum salt, and reuse it.

[0029] In some embodiments, in step (1), when the phosphorus concentration of the phosphorus-containing wastewater is ≥60 mg / L, the specific process of step (1) is as follows: adjust the pH of the phosphorus-containing wastewater to 9.0-10.0, and then add calcium salt to the phosphorus-containing wastewater to obtain wastewater containing calcium phosphate microcrystals; And / or, when the phosphorus concentration of the phosphorus-containing wastewater is <60 mg / L, the specific process of step (1) is as follows: adjust the pH of the phosphorus-containing wastewater to 9.0-10.0, then add aluminum salt hydrolysate to the phosphorus-containing wastewater first, and then add calcium salt to obtain wastewater containing calcium phosphate microcrystals.

[0030] In some embodiments, in step (1), the calcium salt is one or a mixture of two of calcium chloride or calcium nitrate; And / or, the Ca in the calcium salt 2+ With the PO4 in the phosphorus-containing wastewater 3- The molar ratio is (1.67-2.0):1.

[0031] In some embodiments, in step (1), the aluminum salt hydrolysate is prepared by mixing aluminum salt with alkaline solution and then performing a pre-hydrolysis reaction; Optionally, the aluminum salt is one or a mixture of two of aluminum chloride or aluminum nitrate; Optionally, the alkaline solution is a NaOH solution; Optionally, the reaction time of the pre-hydrolysis reaction is 2-3 min; And / or, the concentration of the aluminum salt hydrolysate is 50 mmol / L, and the aluminum salt (calculated as aluminum) in the aluminum salt hydrolysate accounts for 0.2-0.4 mmol / L of the phosphorus-containing wastewater.

[0032] In some embodiments, in step (2), the aluminum salt is one or a mixture of two of aluminum chloride or aluminum nitrate; And / or, when the phosphorus concentration of the phosphorus-containing wastewater is ≥60 mg / L, the dosage of the aluminum salt is ≥0.1 mmol / L; And / or, when the phosphorus concentration of the phosphorus-containing wastewater is <60 mg / L, the dosage of the aluminum salt is ≤0.01 mmol / L.

[0033] In some embodiments, in step (3), the solid-liquid volume ratio of the phosphorus recovery product to the NaOH solution is 1:(3-5); And / or, the pH value during the dissolution and purification is ≥13, and the dissolution and purification time is 6 h; And / or, the solid-liquid separation is performed using a 100-mesh vibrating screen.

[0034] During the recovery of phosphorus from calcium phosphate crystals, the impurities in the recovered product mainly consist of coagulants added to improve the settling performance of calcium phosphate microcrystals in homogeneous crystallization mode, and seed crystals added during induced crystallization. In this embodiment of the invention, the phosphorus recovery product at high phosphorus concentrations is an agglomerate formed by the adsorption and bridging of calcium phosphate microcrystals by aluminum salt hydrolysis products, and at low phosphorus concentrations, it is a surface crystallization product of calcium phosphate with amorphous aluminum hydroxide as the crystal nucleus and its agglomerates. The main impurities are aluminum salt hydrolysis products. Based on the amphoteric characteristics of aluminum salt hydrolysis products and the characteristic that the crystal form of calcium phosphate crystals will transform into HAP (hydroxyapatite) under high pH conditions, this invention innovatively uses strong alkali NaOH to simultaneously improve the purity and quality of calcium phosphate crystallization products. On the one hand, strong alkali alkalization can dissolve impurities in the form of aluminic acid; on the other hand, calcium phosphate crystal particles can complete the transformation into HAP under the action of strong alkali.

[0035] In some embodiments, in step (4), the strong acid is one or a mixture of two of hydrochloric acid or nitric acid; And / or, the pH of the neutralization reaction is 7-8, and the reaction time is 10 min.

[0036] The phosphorus recovery method of this invention, based on the amphoteric characteristics of aluminum salts and their hydrolysis products, proposes a method of first alkalizing and then acidifying to reuse aluminum salt coagulants: First, the aluminum salt-containing crystallization products are strongly alkalized to obtain a high-concentration aluminic acid solution. Then, the solution is acidified to a pH of 7-8, converting the aluminic acid into soluble aluminum salts, which are then returned to the system's aluminum salt dosing device, thus achieving the reuse of aluminum salts. Therefore, after the phosphorus recovery process is started and running stably, the phosphorus recovery method of this invention only requires the addition of a small amount of aluminum salt when switching from the homogeneous crystallization mode of calcium phosphate under high phosphorus conditions to the calcium phosphate-induced crystallization mode under low phosphorus conditions. No additional aluminum salt coagulant is required during other periods, saving costs.

[0037] Secondly, such as Figure 1As shown in the figure, this embodiment of the invention also proposes a calcium phosphate crystallization phosphorus recovery system adapted to high and low phosphorus wastewater. The phosphorus recovery system is used to implement the phosphorus recovery method described in the first aspect, including a crystallization tank 5, a coagulation tank 6, a sedimentation tank 7, a purification tank 8, a separation tank 9, a regeneration tank 11, an alkali storage tank 1, a calcium salt storage tank 2, an aluminum salt storage tank 3, and an acid storage tank 10. The crystallization tank 5, the coagulation tank 6, the sedimentation tank 7, the purification tank 8, the separation tank 9, and the regeneration tank 11 are connected in sequence. The first outlet 101 of the alkali storage tank 1 is connected to the inlet of the crystallization tank 5, the second outlet 102 of the alkali storage tank 1 is connected to the inlet of the purification tank 8, the outlet of the calcium salt storage tank 2 is connected to the inlet of the crystallization tank 5, the outlet of the aluminum salt storage tank 3 is connected to the inlet of the coagulation tank 6, the inlet of the aluminum salt storage tank 3 is connected to the outlet of the regeneration tank 11, and the outlet of the acid storage tank 10 is connected to the inlet of the regeneration tank 11. It also includes a pre-hydrolysis tank 4, the outlet of which is connected to the inlet of the crystallization tank 5, the first inlet 401 of the pre-hydrolysis tank 4 is connected to the third outlet 103 of the alkali storage tank 1, and the second inlet 402 of the pre-hydrolysis tank 4 is connected to the outlet of the aluminum salt storage tank 3.

[0038] It should be noted that the outlet of the aforementioned aluminum salt storage tank 3 can be connected to the coagulation tank 6 via a separate pipeline, or it can be connected first to the connecting pipeline between the crystallization tank 5 and the coagulation tank 6, and then connected to the inlet of the coagulation tank 6. Understandably, the latter requires the installation of a three-way valve on the connecting pipeline between the crystallization tank 5 and the coagulation tank 6.

[0039] It should also be noted that the pre-hydrolysis tank 4 is designed for phosphorus recovery when the phosphorus concentration in the phosphorus-containing wastewater is <60 mg / L. Furthermore, it can be understood that when the phosphorus concentration in the phosphorus-containing wastewater is <60 mg / L, the outlet of the aluminum salt storage tank 3 is divided into two branches. The first branch connects the outlet of the aluminum salt storage tank 3 to the inlet of the coagulation tank 6, and a first solenoid valve 12 is installed on the first branch. The second branch connects the outlet of the aluminum salt storage tank 3 to the second inlet 402 of the pre-hydrolysis tank 4, and a second solenoid valve 13 is installed on the second branch.

[0040] When the phosphorus concentration in the phosphorus-containing wastewater is <60 mg / L, firstly, the NaOH solution in alkaline storage tank 1 and the aluminum salt in aluminum salt storage tank 3 are separately transported to pre-hydrolysis tank 4 for pre-hydrolysis reaction to obtain aluminum salt hydrolysate (amorphous aluminum hydroxide); then, the pH value of the phosphorus-containing wastewater is adjusted using the NaOH solution in alkaline storage tank 1, and it is mixed with the aluminum salt hydrolysate in pre-hydrolysis tank 4 and the calcium salt in calcium salt storage tank 2 and transported to crystallization tank 5. In crystallization tank 5, the Ca in the calcium salt... 2+ With PO4 in wastewater 3-Crystallization occurs on the surface of amorphous aluminum hydroxide, generating calcium phosphate microcrystals, an induced crystallization product with amorphous aluminum hydroxide as the crystal nucleus. The wastewater containing these calcium phosphate microcrystals is then mixed with aluminum salt from aluminum salt storage tank 3 and transported to coagulation tank 6 for coagulation of the induced crystallization product, resulting in wastewater containing agglomerates of the induced crystallization product. This wastewater is then transported to sedimentation tank 7, where gravity solid-liquid separation occurs. The clarified wastewater is discharged from the bottom outlet of sedimentation tank 7, while the agglomerates of the induced crystallization product are mixed with NaOH solution from alkaline storage tank 1 and enter purification tank 8. Within step 8, the crystal form of calcium phosphate crystals is transformed into HAP (hydroxyapatite), and aluminum salts and their hydrolysis products dissolve into aluminic acid, which enters the liquid phase. The reaction system becomes a high-concentration aluminic acid solution containing HAP, and is then transported to separation tank 9. Under the action of a vibrating screen in separation tank 9, the intercepted HAP solids are discharged through the slag outlet of separation tank 9 as the final phosphorus recovery product. The aluminic acid solution passing through the screen is mixed with the acid solution from acid storage tank 10 and enters regeneration tank 11 to regenerate aluminum salts. The regenerated aluminum salt solution is then transported to aluminum salt storage tank 3 for reuse.

[0041] When the phosphorus concentration in the phosphorus-containing wastewater is ≥60 mg / L, firstly, the pH value of the wastewater is adjusted using NaOH solution in alkaline storage tank 1. Then, it is mixed with calcium salt in calcium salt storage tank 2 and transported to crystallization tank 5. In crystallization tank 5, the calcium salt... 2+ With PO4 in wastewater 3- A calcium phosphate crystallization reaction characterized by explosive nucleation will occur, yielding wastewater containing calcium phosphate microcrystals. This wastewater containing calcium phosphate microcrystals will then be mixed with aluminum salt from aluminum salt storage tank 3 and transported to coagulation tank 6 for coagulation of the calcium phosphate microcrystals, resulting in wastewater containing homogeneous crystallization product agglomerates. This wastewater will then be transported to sedimentation tank 7, where gravity solid-liquid separation will occur. The clarified wastewater will be discharged from the bottom outlet of sedimentation tank 7, while the homogeneous crystallization product agglomerates will be mixed with NaOH solution from alkaline storage tank 1 and enter purification tank 8. In purification tank 8, calcium phosphate crystals will... The crystal form of the crystalline product is transformed into HAP (hydroxyapatite), and the aluminum salt and its hydrolysis products dissolve into aluminic acid and enter the liquid phase. The reaction system becomes a high-concentration aluminic acid solution containing HAP, which is then transported to separation tank 9. Under the action of the vibrating screen in separation tank 9, the intercepted HAP solids are discharged through the slag discharge port of separation tank 9 as the final phosphorus recovery product. The aluminic acid solution that passes through the screen is mixed with the acid solution from acid storage tank 10 and enters regeneration tank 11 to regenerate the aluminum salt. The regenerated aluminum salt solution is then transported to aluminum salt storage tank 3 for reuse.

[0042] In some embodiments, the hydraulic retention time of the crystallization tank 5 is 20-30 min; And / or, the hydraulic retention time of the coagulation tank 6 is 20-30 min. And / or, the sedimentation tank 7 adopts an inclined plate sedimentation method, with a hydraulic retention time of 30 min and a surface loading of ≤0.8 m³. 3 / m 2 ·h.

[0043] In some embodiments, the crystallization tank 5, the coagulation tank 6, the purification tank 8, and the regeneration tank 11 are all equipped with stirring devices. Figure 1 (not shown in the image) Optionally, when the phosphorus concentration of the phosphorus-containing wastewater is ≥60 mg / L, the stirring speed in the crystallization tank 5 is controlled at 100-150 rpm; when the phosphorus concentration of the phosphorus-containing wastewater is <60 mg / L, the stirring speed in the crystallization tank 5 is controlled at 200-300 rpm. Optionally, the stirring speed of the coagulation tank 6 is 100-150 rpm; Optionally, the stirring speed of the purification tank 8 is 100 rpm; Optionally, the stirring speed of the regeneration tank 11 is 100 rpm.

[0044] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. Unless otherwise stated, the experimental methods not specified in the embodiments are conventional methods and conditions well known in the art.

[0045] Example 1 In this embodiment, the total phosphorus concentration in the phosphorus-containing wastewater to be treated is between 15-22 mg / L, of which PO4 3- The content is above 90%, the pH value is around 6.4, and the average influent flow rate is 2 m³. 3 / h. The phosphorus recovery method for this phosphorus-containing wastewater includes the following steps: (1) The pH of the wastewater was adjusted to 10.0 using 1 mol / L NaOH solution. Then, aluminum salt hydrolysate (50 mmol / L aluminum salt hydrolysate was prepared by pre-hydrolysis of AlCl3 and NaOH solution for 2.5 min, of which the amount of AlCl3 added was 0.4 mmol / L) was added to the wastewater. The hydrolysis products of AlCl3 were used to induce crystallization and recover phosphorus. Then, CaCl2 was added and the mixture was transported to a crystallization tank (the Ca / P molar ratio in the crystallization tank was 1.8:1 and the stirring speed was 300 rpm) for induced crystallization. After crystallization for 30 min, wastewater containing calcium phosphate microcrystals was obtained. (2) Add 0.01 mmol / L AlCl3 to the wastewater containing calcium phosphate microcrystals, and stir and mix it in a coagulation tank at a stirring speed of 100 rpm for 30 min for AlCl3 coagulation. The resulting solid-liquid mixture is then transferred to a sedimentation tank, where solid-liquid separation is performed using inclined plate sedimentation. The sedimentation time is controlled at 30 min, and the surface loading is 0.8 m. 3 / m 2 •h, phosphorus recovery products and clarified wastewater are obtained; the clarified wastewater meets the discharge standards. (3) Add 1 mol / L NaOH solution to the phosphorus recovery product obtained in step (2) at a solid-liquid volume ratio of 1:3, and dissolve and purify it in a purification tank. Control the pH value in the purification tank to be ≥13, and the stirring speed to be 100 rpm. After purification for 6 h, use a 100-mesh vibrating screen to separate the obtained suspension product into solid and liquid. The obtained solid is high-purity hydroxyapatite (HAP), which is recovered as the phosphorus recovery product. The obtained separation liquid is aluminic acid solution. (4) In the regeneration tank, the aluminic acid solution obtained in step (3) is regenerated with hydrochloric acid. The stirring speed in the regeneration tank is controlled at 100 rpm, the regeneration time is 10 min, and the pH value after regeneration is controlled at 8.0. The regenerated aluminum salt solution can be obtained and transported to the aluminum salt storage tank for storage and reuse.

[0046] Experimental results show that after treatment using the phosphorus recovery method described in this embodiment, the phosphorus concentration in the effluent is consistently below 1 mg / L, and the phosphorus recovery rate is consistently above 90%. The average particle size of the recovered HAP crystals is 800 μm, the water content is less than 40%, and the purity can reach over 70%.

[0047] Example 2 In this embodiment, the total phosphorus concentration in the phosphorus-containing wastewater to be treated is between 110-145 mg / L, of which PO4 3- The content is above 90%, the pH value is around 6.6, and the average influent flow rate is 2 m³. 3 / h.

[0048] The phosphorus recovery method for phosphorus-containing wastewater in this embodiment is basically the same as that in embodiment 1, except that: the process in this embodiment (1) is as follows: the pH value of the wastewater is adjusted to 9.0 using 1 mol / L NaOH solution, and then CaCl2 is added to the wastewater. The mixture is then transported to a crystallization tank (the Ca / P molar ratio in the crystallization tank is 1.67:1, and the stirring speed is 300 rpm) for homogeneous crystallization. After crystallization for 30 min, wastewater containing calcium phosphate microcrystals is obtained; and in step (2), the amount of AlCl3 added is 0.3 mmol / L. Experimental results show that after treatment using the phosphorus recovery method described in this embodiment, the phosphorus concentration in the effluent is consistently below 5 mg / L, and the phosphorus recovery rate is consistently above 95%. The average particle size of the recovered HAP crystals is 600 μm, the water content is less than 40%, and the purity can reach over 70%.

[0049] Example 3 In this embodiment, the total phosphorus concentration in the phosphorus-containing wastewater to be treated is between 30-45 mg / L, of which PO4 3- The content is above 90%, the pH value is around 6.6, and the average influent flow rate is 2 m³. 3 / h.

[0050] The phosphorus recovery method for phosphorus-containing wastewater in this embodiment is basically the same as that in embodiment 1, except that: in this embodiment (1), the pH value of the wastewater is adjusted to 9.0, the dosage of AlCl3 in the aluminum salt hydrolysate is 0.3 mmol, and the Ca / P molar ratio in the crystallization tank is 1.67:1. Experimental results show that after treatment using the phosphorus recovery method described in this embodiment, the phosphorus concentration in the effluent is stabilized below 2 mg / L, and the phosphorus recovery rate is consistently above 90%. The average particle size of the recovered HAP crystals is 800 μm, the water content is less than 40%, and the purity can reach over 70%.

[0051] Example 4 In this embodiment, the total phosphorus concentration in the phosphorus-containing wastewater to be treated is between 160-188 mg / L, of which PO4 3- The content is above 90%, the pH value is around 6.9, and the average influent flow rate is 2 m³. 3 / h.

[0052] The phosphorus recovery method for phosphorus-containing wastewater in this embodiment is basically the same as that in embodiment 2, except that in step (2) of this embodiment, the dosage of AlCl3 is 0.5 mmol / L.

[0053] Experimental results show that after treatment using the phosphorus recovery method described in this embodiment, the phosphorus concentration in the effluent is consistently below 5 mg / L, and the phosphorus recovery rate is consistently above 95%. The average particle size of the recovered HAP crystals is 600 μm, the water content is less than 40%, and the purity can reach over 70%.

[0054] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0055] Furthermore, 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. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0056] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0057] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0058] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0059] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for recovering crystalline phosphorus from calcium phosphate adapted to high- and low-phosphorus wastewater, characterized in that, Includes the following steps: (1) Adjust the pH of the phosphorus-containing wastewater to 9.0-10.0, and then add calcium salt to the phosphorus-containing wastewater, or add aluminum salt hydrolysate first and then add calcium salt to obtain wastewater containing calcium phosphate microcrystals; (2) Add aluminum salt to the wastewater containing calcium phosphate microcrystals, stir and mix, and then separate the solid and liquid to obtain phosphorus recovery product and clarified wastewater; the clarified wastewater meets the discharge standards. (3) Add NaOH solution to the phosphorus recovery product for dissolution and purification, and then perform solid-liquid separation on the obtained product to obtain hydroxycalcium phosphate and aluminic acid solution; (4) Add a strong acid to the aluminic acid solution to carry out a neutralization reaction, regenerate it into aluminum salt, and reuse it.

2. The method for recovering crystalline phosphorus from calcium phosphate adapted to high- and low-phosphorus wastewater according to claim 1, characterized in that, In step (1), when the phosphorus concentration of the phosphorus-containing wastewater is ≥60 mg / L, the specific process of step (1) is as follows: adjust the pH of the phosphorus-containing wastewater to 9.0-10.0, and then add calcium salt to the phosphorus-containing wastewater to obtain wastewater containing calcium phosphate microcrystals; And / or, when the phosphorus concentration of the phosphorus-containing wastewater is <60 mg / L, the specific process of step (1) is as follows: adjust the pH of the phosphorus-containing wastewater to 9.0-10.0, then add aluminum salt hydrolysate to the phosphorus-containing wastewater first, and then add calcium salt to obtain wastewater containing calcium phosphate microcrystals.

3. The method for recovering crystalline phosphorus from calcium phosphate in high- and low-phosphorus wastewater according to claim 1 or 2, characterized in that, In step (1), the calcium salt is one or a mixture of two of calcium chloride or calcium nitrate; And / or, the Ca in the calcium salt 2+ With the PO4 in the phosphorus-containing wastewater 3- The molar ratio is (1.67-2.0):

1.

4. The method for recovering crystalline phosphorus from calcium phosphate in high- and low-phosphorus wastewater according to claim 1 or 2, characterized in that, In step (1), the aluminum salt hydrolysate is prepared by mixing aluminum salt with alkaline solution and then performing a pre-hydrolysis reaction; Optionally, the aluminum salt is one or a mixture of two of aluminum chloride or aluminum nitrate; Optionally, the alkaline solution is a NaOH solution; Optionally, the reaction time of the pre-hydrolysis reaction is 2-3 min; And / or, the concentration of the aluminum salt hydrolysate is 50 mmol / L.

5. The method for recovering crystalline phosphorus from calcium phosphate adapted to high- and low-phosphorus wastewater according to claim 1, characterized in that, In step (2), the aluminum salt is one or a mixture of two of aluminum chloride or aluminum nitrate; And / or, when the phosphorus concentration of the phosphorus-containing wastewater is ≥60 mg / L, the dosage of the aluminum salt is ≥0.1 mmol / L; And / or, when the phosphorus concentration of the phosphorus-containing wastewater is <60 mg / L, the dosage of the aluminum salt is ≤0.01 mmol / L.

6. The method for recovering crystalline phosphorus from calcium phosphate adapted to high- and low-phosphorus wastewater according to claim 1, characterized in that, In step (3), the solid-liquid volume ratio of the phosphorus recovery product to the NaOH solution is 1:(3-5); And / or, the pH value during the dissolution and purification is ≥13, and the dissolution and purification time is 6 h; And / or, the solid-liquid separation is performed using a 100-mesh vibrating screen.

7. The method for recovering crystalline phosphorus from calcium phosphate adapted to high- and low-phosphorus wastewater according to claim 1, characterized in that, In step (4), the strong acid is one or a mixture of two of hydrochloric acid or nitric acid; And / or, the pH of the neutralization reaction is 7-8, and the reaction time is 10 min.

8. A calcium phosphate crystallization phosphorus recovery system adapted to high- and low-phosphorus wastewater, characterized in that, The phosphorus recovery system is used to implement the phosphorus recovery method according to any one of claims 1-7, comprising a crystallization tank, a coagulation tank, a sedimentation tank, a purification tank, a separation tank, a regeneration tank, an alkali storage tank, a calcium salt storage tank, an aluminum salt storage tank, and an acid storage tank; the crystallization tank, the coagulation tank, the sedimentation tank, the purification tank, the separation tank, and the regeneration tank are connected in sequence; the first outlet of the alkali storage tank is connected to the inlet of the crystallization tank; the second outlet of the alkali storage tank is connected to the inlet of the purification tank; the outlet of the calcium salt storage tank is connected to the inlet of the crystallization tank; the outlet of the aluminum salt storage tank is connected to the inlet of the coagulation tank; the inlet of the aluminum salt storage tank is connected to the outlet of the regeneration tank; and the outlet of the acid storage tank is connected to the inlet of the regeneration tank. It also includes a pre-hydrolysis tank, the outlet of which is connected to the inlet of the crystallization tank, the first inlet of which is connected to the third outlet of the alkali storage tank, and the second inlet of which is connected to the outlet of the aluminum salt storage tank.

9. The calcium phosphate crystallization phosphorus recovery system adapted to high- and low-phosphorus wastewater according to claim 8, characterized in that, The hydraulic retention time of the crystallization tank is 20-30 min; And / or, the hydraulic retention time of the coagulation tank is 20-30 min. And / or, the sedimentation tank adopts an inclined plate sedimentation method, with a hydraulic retention time of 30 min and a surface loading rate ≤0.8 m³. 3 / m 2 ·h.

10. The calcium phosphate crystallization phosphorus recovery system adapted to high- and low-phosphorus wastewater according to claim 8, characterized in that, The crystallization tank, the coagulation tank, the purification tank, and the regeneration tank are all equipped with stirring devices; Optionally, when the phosphorus concentration of the phosphorus-containing wastewater is ≥60 mg / L, the stirring speed in the crystallization tank is controlled at 100-150 rpm; when the phosphorus concentration of the phosphorus-containing wastewater is <60 mg / L, the stirring speed in the crystallization tank is controlled at 200-300 rpm. Optionally, the stirring speed of the coagulation tank is 100-150 rpm; Optionally, the stirring speed of the purification tank is 100 rpm; Optionally, the stirring speed of the regeneration tank is 100 rpm.

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