Fractional precipitation and resource recycling process and system for wastewater containing phosphorus and aluminum

Abstract

The invention discloses a process and a system for fractional precipitation and resource recovery of wastewater containing phosphorus and aluminum, which are characterized in that the wastewater containing phosphorus and aluminum collected in a wastewater collection tank and a lime solution in a lime agent tank are respectively pumped into a pretreatment reaction tank, aluminum in the wastewater forms an aluminum phosphate precipitate under the condition that the pH is 5-6, and the aluminum phosphate precipitate enters a precipitation tank for mud-water separation; water is fed into a phosphorus recovery crystallization reactor, a calcium chloride agent pool and a lime agent pool are combined to add agents into the phosphorus recovery crystallization reactor, a crystallization reaction is carried out under the condition that the pH value is 7-8 to obtain hydroxyapatite crystals, and sludge separated from a sedimentation tank and the hydroxyapatite crystals are subjected to cleaning and dewatering treatment through a first cleaning and dewatering system and a second cleaning and dewatering system respectively; according to the method, efficient recovery of phosphorus and aluminum is achieved, the landfill problem of phosphorus-containing and aluminum-containing chemical sludge is avoided, and the pressure of natural resources is relieved.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to a graded sedimentation and resource recovery process for phosphorus-aluminum-containing wastewater and a greywater reuse system. Background Technology

[0002] In the production process of electronic aluminum foil, aluminum-containing phosphoric acid wastewater is generated. Its typical characteristics include a low pH value and high concentrations of phosphate (phosphorus concentration can reach over 10,000 mg / L) and aluminum ions (aluminum ion concentration can reach hundreds to thousands of mg / L). Direct discharge of this wastewater will cause serious environmental pollution. Large amounts of phosphorus can easily lead to eutrophication of the receiving water bodies, while the long-term accumulation of aluminum ions will damage the aquatic ecosystem and affect human health through the food chain. Currently, this type of wastewater is mainly treated by direct alkali neutralization, which involves adding alkaline agents such as lime to the water to control the pH to a slightly alkaline level. This neutralizes the acidity and, through the calcium in the lime, converts the aluminum and phosphorus in the water into precipitates that are separated from the water. This treatment method is simple and has a significant effect on removing aluminum and phosphorus, but it also has obvious drawbacks: the sludge production is large, and the sludge contains a mixture of aluminum and phosphorus components, making it difficult to separate and utilize as resources, requiring outsourced solid waste treatment.

[0003] Due to the scarcity of phosphorus resources, the industry is gradually exploring phosphorus resource recovery technologies. A common approach is to recover phosphorus in the form of hydroxyapatite using a fluidized bed crystallization method, with lime being a frequently used chemical reagent. However, the presence of aluminum in the wastewater causes aluminum precipitates during phosphorus recovery crystallization, affecting the purity of the product and failing to solve the phosphorus-aluminum separation problem. This significantly reduces the purity and resource value of the phosphorus product. Furthermore, existing hydroxyapatite crystallization processes often rely on a single calcium source (such as lime). Lime is strongly alkaline; if multiple substances are recovered simultaneously, the pH and reagent ratios during the reaction become highly restrictive. Excessive lime addition can lead to a pH > 12, causing aluminum re-dissolution (forming [Al(OH)4]). - The presence of hydroxyapatite and competing precipitates (such as Ca(OH)2) can induce the formation of byproducts, reducing the purity of hydroxyapatite. Summary of the Invention

[0004] To overcome the above-mentioned defects, the present invention provides a graded sedimentation and resource recovery process and system for phosphorus-containing aluminum wastewater. This graded sedimentation and resource recovery process and system can remove phosphorus and aluminum from phosphorus-containing aluminum wastewater to meet safe discharge standards, and can achieve high-purity recovery of aluminum phosphate products and hydroxyapatite products.

[0005] The technical solution adopted by this invention to solve its technical problem is a graded sedimentation and resource recovery process for phosphorus-aluminum-containing wastewater, comprising the following steps:

[0006] Step 1: The phosphorus- and aluminum-containing wastewater is continuously pumped into the pretreatment reaction tank. Simultaneously, a calcium-containing agent is continuously added to the pretreatment reaction tank via a transfer pump. The pH of the reaction mixture in the pretreatment reaction tank is controlled at 5-6. Aluminum in the wastewater forms aluminum phosphate precipitate. The chemical reaction formula is as follows:

[0007] 2Al 3+ +3H2PO4 - +3Ca 2+ +6H2O=2AlPO4↓3Ca(H2PO4)2·2H2O;

[0008] Step 2: Separate the mud and water from the mixture obtained after the reaction in Step 1;

[0009] Step 3: The water separated in Step 2 is sent to the phosphorus recovery crystallization reactor. Simultaneously, a calcium-containing reagent is added to the reactor, and the pH of the wastewater is adjusted to 7-8 to carry out a crystallization reaction to obtain hydroxyapatite. The phosphorus content in the effluent from the phosphorus recovery crystallization reactor is reduced to below 5 mg / L. The chemical reaction formula for the crystallization reaction is as follows:

[0010] 10Ca 2+ +6HPO4 2- +2OH - =Ca 10 (PO4)6(OH)2↓;

[0011] Step 4: Dehydrate and recover the sludge sediment separated in Step 2 and the crystals discharged from the phosphorus recovery crystallization reactor in Step 3 to obtain aluminum phosphate and hydroxyapatite products, respectively.

[0012] The phosphorus-containing aluminum wastewater generated by aluminum foil manufacturing enterprises mainly contains phosphorus and aluminum, with phosphorus content reaching 15,000 to 25,000 mg / L and aluminum content reaching 2,500 to 4,000 mg / L.

[0013] By controlling the pH of the wastewater through staged dosing, the wastewater is first adjusted to a weakly acidic state. Under acidic conditions, aluminum preferentially forms aluminum phosphate precipitate, thus removing aluminum from the wastewater. After aluminum removal, the aluminum content in the effluent is significantly reduced. Then, the wastewater is adjusted to a weakly alkaline state. Under weakly alkaline conditions, phosphorus forms hydroxyapatite crystals, thus removing phosphorus.

[0014] This invention achieves a directional reaction between aluminum phosphate and hydroxyapatite through staged dosing and pH control, overcoming the bottleneck of co-precipitation in traditional technologies. The aluminum pretreatment effectively avoids the influence of aluminum hydroxide seed crystals in subsequent phosphorus recovery, ensuring the quality and crystallization effect of the recovered phosphorus product and solving the problem of low purity caused by phosphorus-aluminum competition during crystallization. The recovered aluminum phosphate precipitate, after simple washing and dehydration, can be used to produce fire-retardant coatings, flame-retardant plastics, and other fire-resistant materials, as well as industrial additives such as glass fluxes and ceramic binders. The recovered phosphorus crystals, after washing and simple dehydration, form a high-purity hydroxyapatite product, which can be used as a raw material for phosphorus chemical production, thus achieving the goal of phosphorus resource recovery.

[0015] As a further improvement of the present invention, the calcium-containing agent in step one is a 2%-5% lime solution; the calcium-containing agent in step three is a 10%-30% calcium chloride solution and a 2%-5% lime solution, wherein the amount of calcium chloride solution and lime solution added in step three is such that the Ca / P ratio is 1.6-2.0 and the pH of the mixed solution in the phosphorus recovery crystallization reactor is maintained at 7-8.

[0016] In step three, calcium chloride provides the main calcium source required for crystallization, and lime solution is added to fine-tune the pH. By adding calcium chloride solution and lime solution in a coordinated manner, the coupling contradiction between Ca / P and pH is resolved, and high-purity hydroxyapatite crystals are formed.

[0017] As a further improvement of the present invention, in step three, the effluent from the phosphorus recovery crystallization reactor enters the integrated treatment system for standard treatment. After phosphorus and aluminum are removed from the wastewater, it enters the integrated treatment system for conventional standard treatment.

[0018] As a further improvement of the present invention, the phosphorus recovery crystallization reactor in step three is equipped with an effluent reflux device, with a reflux ratio of 3:1 to 10:1. By refluxing the effluent to dilute the influent, excessive supersaturation within the crystallization reactor can be prevented, thus avoiding crystal bursting and ensuring the particle size of the crystallized product.

[0019] As a further improvement of the present invention, the sludge sediment separated in step two and the crystals discharged from the phosphorus recovery crystallization reactor in step three are respectively washed and dehydrated to form aluminum phosphate product and hydroxyapatite product. The washing and dehydration steps can be washing and dehydration, or dehydration, washing and dehydration. Dehydration can be carried out by pressure filtration or other dehydration methods.

[0020] As a further improvement of the present invention, in step two, mud-water separation is achieved through a sedimentation tank. Besides using a sedimentation tank, mud-water separation can also be achieved through centrifugal cyclone separation or filtration.

[0021] As a further improvement of the present invention, in step one, the mixture is continuously stirred in the pretreatment reaction tank by a stirrer at a speed of 20-60 r / min and a hydraulic retention time of 15-45 min. After the reaction, the aluminum removal rate in the water reaches more than 95%.

[0022] As a further improvement of the present invention, the phosphorus- and aluminum-containing wastewater generated during the production process is first collected in a wastewater collection tank and homogenized before being sent to a pretreatment reaction tank.

[0023] A graded sedimentation and resource recovery system for phosphorus-aluminum-containing wastewater includes a wastewater collection tank, a pretreatment reaction tank, a sedimentation tank, a calcium chloride reagent tank, a lime reagent tank, a phosphorus recovery crystallization reactor, a comprehensive treatment system, a first wastewater lift pump, a second wastewater lift pump, a first dosing pump, a second dosing pump, a third dosing pump, a first cleaning and dewatering system, a second cleaning and dewatering system, a first pH meter, a second pH meter, and a control system. The wastewater collection tank is used to collect phosphorus- and aluminum-containing wastewater generated during the production process. The calcium chloride reagent tank and the lime reagent tank are used to prepare calcium chloride and lime solutions. The first wastewater lift pump... The pumps can pump phosphorus- and aluminum-containing wastewater collected in the wastewater collection tank into the pretreatment reaction tank. The first dosing pump can pump lime solution from the lime reagent tank into the pretreatment reaction tank. The pretreatment reaction tank is equipped with a stirrer, which can mix the phosphorus- and aluminum-containing wastewater and lime solution entering the pretreatment reaction tank. The second wastewater lift pump can pump the mixed liquid after reaction in the pretreatment reaction tank into the sedimentation tank. The outlet of the sedimentation tank is connected to the inlet of the phosphorus recovery crystallization reactor through a pipeline. The effluent from the sedimentation tank flows by gravity into the phosphorus recovery crystallization reactor. The second and third dosing pumps can respectively dispense calcium chloride reagent. Calcium chloride solution in the reagent tank and lime solution in the lime reagent tank are pumped into the phosphorus recovery crystallization reactor. The outlet of the phosphorus recovery crystallization reactor is connected to the inlet of the integrated treatment system via a pipeline. The effluent from the phosphorus recovery crystallization reactor flows by gravity into the integrated treatment system, which can treat the effluent from the phosphorus recovery crystallization reactor to meet standards. The sludge discharge port of the sedimentation tank is connected to the first cleaning and dewatering system via a pipeline to supply sludge for sedimentation. The crystal discharge port at the lower end of the phosphorus recovery crystallization reactor is connected to the second cleaning and dewatering system via a pipeline to supply crystal particles. The first cleaning and dewatering system can process the sludge discharged from the sedimentation tank. The first and second pH meters are used to clean and dehydrate the crystal particles discharged from the phosphorus recovery crystallization reactor to form aluminum phosphate product. The second cleaning and dehydration system can clean and dehydrate the crystal particles discharged from the phosphorus recovery crystallization reactor to form hydroxyapatite product. The first and second pH meters can detect the pH of the mixed solution in the pretreatment reaction tank and the phosphorus recovery crystallization reactor, respectively. The first and second pH meters communicate with the control system. The control system can control the start and stop and the flow rate ratio of the first wastewater lift pump, the second wastewater lift pump, the first dosing pump, the second dosing pump and the third dosing pump according to the pH of the mixed solution in the pretreatment reaction tank and the phosphorus recovery crystallization reactor.

[0024] As a further improvement of the present invention, the phosphorus recovery crystallization reactor is provided with a crystal discharge zone, an inlet zone, a reaction zone, and an outlet zone from bottom to top. The lower section of the phosphorus recovery crystallization reactor forms a crystal discharge port that communicates with the crystal discharge zone. The inlet zone of the phosphorus recovery crystallization reactor is provided with a reflux inlet and a wastewater inlet from bottom to top. The wastewater inlet is connected to the outlet of the sedimentation tank through a pipe. The side wall of the inlet zone of the phosphorus recovery crystallization reactor is also provided with a calcium chloride inlet and a lime inlet. The calcium chloride solution and the lime solution enter the inlet zone of the phosphorus recovery crystallization reactor through the calcium chloride inlet and the lime inlet, respectively. The side wall of the outlet zone of the phosphorus recovery crystallization reactor is provided with a reflux outlet and a crystallization reaction outlet from bottom to top. The reflux outlet is connected to the reflux inlet through a reflux pipe. A reflux pump is also provided, which can pump the water from the reflux outlet of the phosphorus recovery crystallization reactor into the reflux inlet.

[0025] The beneficial effects of this invention are as follows: This invention uses wastewater itself as a resource source, and through graded adjustment of the pH of phosphorus- and aluminum-containing wastewater, preferential aluminum removal is achieved under acidic conditions, and phosphorus removal is achieved under weakly alkaline conditions. This realizes the directional reaction of aluminum phosphate and hydroxyapatite, breaking through the bottleneck of easy co-precipitation in traditional technologies, and solving the problem of low purity of phosphorus recovery products due to phosphorus-aluminum competition during crystallization. It achieves high-value recovery of aluminum phosphate and hydroxyapatite, with a total phosphorus recovery rate >99% and an aluminum recovery rate >95%. The purity of the recovered aluminum phosphate is ≥95%, which can meet the requirements of the construction, glass manufacturing, and ceramics industries. High-purity hydroxyapatite particles are obtained. The purity is not less than 85%, and the P2O5 content is >36%, which meets the national standards for phosphate rock. This invention solves the coupling contradiction between Ca / P and pH by using calcium chloride as the main calcium source for crystallization and lime milk to finely adjust the pH. This results in the formation of high-purity hydroxyapatite crystals. Furthermore, by replacing part of the lime with calcium chloride, the calcium consumption is reduced by 30%, and the added value of the sludge can cover more than 60% of the reagent cost. This invention achieves efficient recovery of phosphorus and aluminum, avoids the landfill problem of phosphorus- and aluminum-containing chemical sludge, and at the same time, the recovered phosphorus resources can replace the consumption of phosphate rock, alleviating the pressure on natural resources. Attached Figure Description

[0026] Figure 1 This is a system schematic diagram of the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Therefore, the detailed description of the embodiments of the present invention provided below is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Example: A graded sedimentation and resource recovery system for phosphorus-aluminum wastewater includes a wastewater collection tank 1, a pretreatment reaction tank 2, a sedimentation tank 3, a calcium chloride reagent tank 4, a lime reagent tank 5, a phosphorus recovery crystallization reactor 6, a comprehensive treatment system 7, a first wastewater lift pump 8, a second wastewater lift pump 9, a first dosing pump 10, a second dosing pump 11, a third dosing pump 12, a first cleaning and dewatering system 13, a second cleaning and dewatering system 14, a first pH meter, a second pH meter, and a control system. The wastewater collection tank 1 is used to collect phosphorus- and aluminum-containing wastewater generated during the production process. The calcium chloride reagent tank 4 and the lime reagent tank 5 are used to prepare calcium chloride and lime solutions. The first wastewater lift pump 8 can pump the phosphorus- and aluminum-containing wastewater collected in the wastewater collection tank 1 into the pretreatment reaction tank 2. The first dosing pump 10 can pump the lime solution in the lime reagent tank 5 into the pretreatment reaction tank 2. The pretreatment reaction tank 2 is equipped with a stirrer, which can stir and mix the phosphorus- and aluminum-containing wastewater and lime solution entering the pretreatment reaction tank 2. The second wastewater lift pump 9 can pump the mixed liquid after reaction in the pretreatment reaction tank 2 into the sedimentation tank 3. The outlet of the sedimentation tank 3 is connected to the inlet of the phosphorus recovery crystallization reactor 6 through a pipeline. The effluent from the sedimentation tank 3 flows by gravity into the phosphorus recovery crystallization reactor 6. The second dosing pump 11 and the third dosing pump 12 can respectively... The calcium chloride solution in the calcium chloride reagent tank 4 and the lime solution in the lime reagent tank 5 are pumped into the phosphorus recovery crystallization reactor 6. The outlet of the phosphorus recovery crystallization reactor 6 is connected to the inlet of the integrated treatment system 7 via a pipeline. The effluent from the phosphorus recovery crystallization reactor 6 flows by gravity into the integrated treatment system 7, which can treat the effluent from the phosphorus recovery crystallization reactor 6 to meet standards. The sludge discharge port of the sedimentation tank 3 is connected to the first cleaning and dewatering system 13 via a pipeline to supply sludge for sedimentation. The crystal discharge port at the lower end of the phosphorus recovery crystallization reactor 6 is connected to the second cleaning and dewatering system 14 via a pipeline to supply crystal particles. The first cleaning and dewatering system 13 can process the sludge discharged from the sedimentation tank 3. The sludge is settled, cleaned, and dewatered to form aluminum phosphate product. The second cleaning and dewatering system 14 can clean and dewater the crystal particles discharged from the phosphorus recovery crystallization reactor 6 to form hydroxyapatite product. The first pH meter and the second pH meter can detect the pH of the mixed liquid in the pretreatment reaction tank 2 and the phosphorus recovery crystallization reactor 6, respectively. The first pH meter and the second pH meter communicate with the control system. The control system can control the start-up, shutdown, and flow rate ratio of the first wastewater lift pump 8, the second wastewater lift pump 9, the first dosing pump 10, the second dosing pump 11, and the third dosing pump 12 according to the pH of the mixed liquid in the pretreatment reaction tank 2 and the phosphorus recovery crystallization reactor 6.

[0029] The control system controls the first dosing pump 10, the second dosing pump 11, the third dosing pump 12, and the wastewater booster pump based on the detection data from the first pH meter and the second pH meter. By setting the linkage control of the second dosing pump 11 and the third dosing pump 12, the pH inside the crystallization reactor is maintained at 7-8, while the Ca / P ratio is stabilized at 1.6-2.0.

[0030] The phosphorus recovery crystallization reactor 6 is divided into a crystal discharge zone, an inlet zone, a reaction zone, and an outlet zone from bottom to top. The lower section of the reactor 6 forms a crystal discharge port 61 connected to the crystal discharge zone. The inlet zone of the reactor 6 is provided with a reflux inlet 62 and a wastewater inlet 63 from bottom to top. The wastewater inlet 63 is connected to the outlet of the sedimentation tank 3 via a pipe. The side wall of the inlet zone of the reactor 6 is also provided with a calcium chloride inlet 64 and a lime inlet 65. Calcium chloride solution and lime solution enter through the calcium chloride inlet 64 and lime inlet 65, respectively. The phosphorus recovery crystallization reactor 6 has an inlet water zone and an outlet water zone. The outlet water zone of the phosphorus recovery crystallization reactor 6 is provided with a reflux outlet 66 and a crystallization reaction outlet 67 from bottom to top on the side wall. The reflux outlet 66 is connected to the reflux inlet 62 through a reflux pipe. A reflux pump 68 is also provided. The reflux pump 68 can pump the water effluent from the reflux outlet 66 of the phosphorus recovery crystallization reactor 6 into the reflux inlet 62. The reflux of the water effluent from the phosphorus recovery crystallization reactor 6 dilutes the water effluent from the phosphorus recovery crystallization reactor 6, prevents excessive supersaturation in the crystallization reactor from causing crystal bursting, and ensures the particle size of the crystallized product.

[0031] A certain electronic aluminum foil manufacturing company generates phosphorus-containing and aluminum-containing wastewater with a phosphorus content of 22,400 mg / L and an aluminum content of 2,690 mg / L. The company collects and treats this wastewater separately.

[0032] The company currently uses lime precipitation pretreatment to remove high concentrations of phosphorus and aluminum from the water, but phosphorus and aluminum are not recovered. Calculations show that 230 kg of wet sludge is generated per ton of water, which is outsourced for treatment.

[0033] The company uses the graded sedimentation and resource recovery process for phosphorus- and aluminum-containing wastewater of the present invention to treat the above-mentioned wastewater. The specific steps are as follows:

[0034] First, the wastewater is discharged into a pretreatment reaction tank, and the pH is adjusted to 5.3–5.8 by adding 3% lime solution for pretreatment, with a HRT of 30 min. After sufficient reaction, it enters a sedimentation tank, where the aluminum content in the supernatant is 8 mg / L. This supernatant is pumped to a phosphorus recovery crystallization reactor, where 10% calcium chloride and 3% lime solution are continuously added via separate dosing pumps, controlling the Ca / P ratio at 1.67 and maintaining the reaction pH at 7.2–7.8. The effluent reflux ratio is set to 5:1. The residual phosphorus content in the phosphorus recovery crystallization effluent is 1.6 mg / L. This effluent is then sent to a comprehensive wastewater treatment system for centralized treatment and discharge in compliance with standards.

[0035] The aluminum phosphate sludge recovered from the sedimentation tank, after washing and dewatering by pressure filtration, can achieve a purity of over 95% and can be used as a glass flux. The hydroxyapatite crystals in the phosphorus recovery crystallization reactor are discharged through the crystal outlet; after washing and dewatering, the obtained hydroxyapatite can achieve a purity of up to 88% and can be used as a raw material for phosphorus chemical production. Calculations show that 12.1 kg of oven-dry aluminum phosphate and 119 kg of oven-dry hydroxyapatite crystals can be recovered per ton of water. This process avoids sludge generation while producing resource products, resulting in significant environmental and economic benefits.

Claims

1. A graded sedimentation and resource recovery process for phosphorus-aluminum-containing wastewater, characterized in that: Includes the following steps: Step 1: The phosphorus- and aluminum-containing wastewater is continuously pumped into the pretreatment reaction tank. Simultaneously, a calcium-containing agent is continuously added to the pretreatment reaction tank via a transfer pump. The pH of the reaction mixture in the pretreatment reaction tank is controlled at 5-6. Aluminum in the wastewater forms aluminum phosphate precipitate. The chemical reaction formula is as follows: 2Al 3+ +3H2PO4 - +3Ca 2+ 6H2O=2AlPO4↓+3Ca(H2PO4)2·2H2O; Step 2: Separate the mud and water from the mixture obtained after the reaction in Step 1; Step 3: The water separated in Step 2 is sent to the phosphorus recovery crystallization reactor. Simultaneously, a calcium-containing reagent is added to the reactor, and the pH of the wastewater is adjusted to 7-8 to carry out a crystallization reaction to obtain hydroxyapatite. The phosphorus content in the effluent from the phosphorus recovery crystallization reactor is reduced to below 5 mg / L. The chemical reaction formula for the crystallization reaction is as follows: 10Ca 2+ +6HPO4 2- +2OH-=Ca 10 (PO4)6(OH)2↓; Step 4: Dehydrate and recover the sludge sediment separated in Step 2 and the crystals discharged from the phosphorus recovery crystallization reactor in Step 3 to obtain aluminum phosphate and hydroxyapatite products, respectively.

2. The graded sedimentation and resource recovery process for phosphorus-aluminum-containing wastewater according to claim 1, characterized in that: In step one, the calcium-containing agent is a 2%-5% lime solution; in step three, the calcium-containing agent is a 10%-30% calcium chloride solution and a 2%-5% lime solution. In step three, the amount of calcium chloride solution and lime solution added is such that the Ca / P ratio is 1.6-2.0 and the pH of the mixed solution in the phosphorus recovery crystallization reactor is maintained at 7-8.

3. The graded sedimentation and resource recovery process for phosphorus-aluminum-containing wastewater according to claim 1, characterized in that: In step three, the effluent from the phosphorus recovery crystallization reactor enters the integrated treatment system for treatment to meet standards.

4. The graded sedimentation and resource recovery process for phosphorus-aluminum-containing wastewater according to claim 1, characterized in that: In step three, the phosphorus recovery crystallization reactor is equipped with an effluent reflux device with a reflux ratio of 3:1 to 10:

1.

5. The graded sedimentation and resource recovery process for phosphorus-containing aluminum wastewater according to claim 1, characterized in that: The sludge sediment separated in step two and the crystals discharged from the phosphorus recovery crystallization reactor in step three are washed and dehydrated to form aluminum phosphate and hydroxyapatite products, respectively.

6. The graded sedimentation and resource recovery process for phosphorus-aluminum-containing wastewater according to claim 1, characterized in that: In step two, mud and water are separated by a sedimentation tank.

7. The graded sedimentation and resource recovery process for phosphorus-aluminum-containing wastewater according to claim 1, characterized in that: In step one, the mixture in the pretreatment reaction tank is continuously stirred by a stirrer at a speed of 20-60 r / min and a hydraulic retention time of 15-45 min. After the reaction, the aluminum removal rate in the water reaches more than 95%.

8. The graded sedimentation and resource recovery process for phosphorus-aluminum-containing wastewater according to claim 1, characterized in that: The phosphorus- and aluminum-containing wastewater generated during the production process is first collected in a wastewater collection tank and homogenized before being sent to a pretreatment reaction tank.

9. A system for graded sedimentation and resource recovery of phosphorus-containing aluminum wastewater used in the graded sedimentation and resource recovery process of phosphorus-containing aluminum wastewater according to any one of claims 1-8, characterized in that: The system includes a wastewater collection tank (1), a pretreatment reaction tank (2), a sedimentation tank (3), a calcium chloride reagent tank (4), a lime reagent tank (5), a phosphorus recovery crystallization reactor (6), a comprehensive treatment system (7), a first wastewater lift pump (8), a second wastewater lift pump (9), a first dosing pump (10), a second dosing pump (11), a third dosing pump (12), a first cleaning and dewatering system (13), a second cleaning and dewatering system (14), a first pH meter, a second pH meter, and a control system. The wastewater collection tank is used to collect phosphorus- and aluminum-containing wastewater generated during the production process. The calcium chloride reagent tank and the lime reagent tank are used for... The process involves preparing calcium chloride and lime solutions. A first wastewater lift pump pumps phosphorus- and aluminum-containing wastewater collected in a wastewater collection tank into a pretreatment reaction tank. A first dosing pump pumps lime solution from a lime reagent tank into the pretreatment reaction tank. The pretreatment reaction tank is equipped with a mixer to thoroughly mix the phosphorus- and aluminum-containing wastewater and lime solution entering the tank. A second wastewater lift pump pumps the reacted mixture from the pretreatment reaction tank into a sedimentation tank. The outlet of the sedimentation tank is connected to the inlet of a phosphorus recovery crystallization reactor via a pipeline. The effluent from the sedimentation tank flows by gravity into the phosphorus recovery crystallization reactor. The second dosing pump and the first... The three-pronged pump can pump the calcium chloride solution from the calcium chloride tank and the lime solution from the lime tank into the phosphorus recovery crystallization reactor. The outlet of the phosphorus recovery crystallization reactor is connected to the inlet of the integrated treatment system via a pipeline. The effluent from the phosphorus recovery crystallization reactor flows by gravity into the integrated treatment system, which can treat the effluent from the phosphorus recovery crystallization reactor to meet standards. The sludge discharge port of the sedimentation tank is connected to the first cleaning and dewatering system via a pipeline to supply sludge for sedimentation. The crystal discharge port at the lower end of the phosphorus recovery crystallization reactor is connected to the second cleaning and dewatering system via a pipeline to supply crystal particles. The first cleaning and dewatering system can discharge sludge from the sedimentation tank. The sludge sediment is washed and dewatered to form aluminum phosphate product. The second washing and dewatering system can wash and dewater the crystal particles discharged from the phosphorus recovery crystallization reactor to form hydroxyapatite product. The first pH meter and the second pH meter can detect the pH of the mixed liquid in the pretreatment reaction tank and the phosphorus recovery crystallization reactor, respectively. The first pH meter and the second pH meter communicate with the control system. The control system can control the start and stop and the flow rate ratio of the first wastewater lift pump, the second wastewater lift pump, the first dosing pump, the second dosing pump and the third dosing pump according to the pH of the mixed liquid in the pretreatment reaction tank and the phosphorus recovery crystallization reactor.

10. The graded sedimentation and resource recovery system for phosphorus-aluminum-containing wastewater according to claim 9, characterized in that: The phosphorus recovery crystallization reactor is divided into a crystal discharge zone, an inlet zone, a reaction zone, and an outlet zone from bottom to top. The lower section of the phosphorus recovery crystallization reactor forms a crystal discharge port (61) that communicates with the crystal discharge zone. The inlet zone of the phosphorus recovery crystallization reactor is provided with a reflux inlet (62) and a wastewater inlet (63) from bottom to top. The wastewater inlet is connected to the outlet of the sedimentation tank through a pipe. The side wall of the inlet zone of the phosphorus recovery crystallization reactor is also provided with a calcium chloride inlet (64) and a lime inlet. (65) Calcium chloride solution and lime solution enter the inlet area of ​​the phosphorus recovery crystallization reactor through the calcium chloride inlet and lime inlet, respectively. The side wall of the outlet area of ​​the phosphorus recovery crystallization reactor is provided with a reflux outlet (66) and a crystallization reaction outlet (67) from bottom to top. The reflux outlet is connected to the reflux inlet through a reflux pipe. A reflux pump (68) is also provided. The reflux pump can pump the water from the reflux outlet of the phosphorus recovery crystallization reactor into the reflux inlet.

Images