Iron phosphate wastewater zero discharge and resource treatment system and method

Abstract

The application discloses a kind of iron phosphate wastewater zero discharge and resource processing system and method, belong to industrial wastewater treatment technical field, processing system includes the plate heat exchanger connected in turn, regulating pool, primary flocculation reaction pool, secondary flocculation reaction pool, fluidized bed, ultrafiltration system, two-stage enrichment RO system, multistage water production RO system and pure water reuse pool, and with two-stage enrichment RO system connection MVR evaporator, with MVR evaporator connection centrifugal compressor, with centrifugal compressor connection drying device, primary flocculation reaction pool is provided with stirring scraping wall device, stirring scraping wall device is used to stir primary flocculation reaction pool and when stirring, scrape the inner wall of primary flocculation reaction pool, secondary flocculation reaction pool is provided with lifting stirring device, lifting stirring device is used to stir secondary flocculation reaction pool and when stirring, relatively secondary flocculation reaction pool lifting movement changes stirring position.The application can realize iron phosphate wastewater zero discharge reuse, resource recycling.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment technology, and in particular, to a zero-discharge and resource-based treatment system for ferric phosphate wastewater. Furthermore, this invention also relates to a treatment method comprising the aforementioned ferric phosphate wastewater treatment system. Background Technology

[0002] Driven by the global energy industry transformation and upgrading, and China's "dual-carbon" goals, the new energy vehicle industry, powered by lithium-ion batteries, has experienced explosive growth. Lithium iron phosphate (LFP) cathode materials possess advantages such as low raw material prices, good specific capacity, cycle life, and safety, resulting in LFP batteries holding approximately 80% of the new energy vehicle power battery market share, becoming the mainstream direction with a promising future. However, due to the characteristics of LFP production wastewater—high acidity, high temperature, large treatment volume, high salinity, and numerous and complex impurities—and with the rapid development of the LFP and LFP market and increasingly stringent environmental regulations, manufacturers face challenges such as zero discharge of LFP production wastewater, resource recovery, cost control, and industry barriers. These challenges have become significant bottlenecks restricting the development of battery-grade LFP manufacturers.

[0003] The properties of ferric phosphate wastewater are determined by the production process and raw materials. Due to continuous upgrades in production processes and requirements for water and energy conservation, more and more enterprises are mixing mother liquor and wash water to form mixed mother liquor wastewater. The quality of mixed mother liquor wastewater differs greatly from that of pure mother liquor / wash water. Before treatment, the ferric phosphate mixed wastewater contains: TDS: 69,000–83,000 mg / L, phosphate: 900–2,000 mg / L, ammonium: 11,000–15,600 mg / L, sulfate: 45,000–58,000 mg / L, total iron: 100–300 mg / L, manganese: 100–200 mg / L, calcium: 50–100 mg / L, magnesium: 1,200–2,000 mg / L, fluoride: 20–40 mg / L, etc., which presents a high degree of difficulty in industrial treatment. If not properly treated and disposed of, it will cause serious environmental and safety problems.

[0004] There are many methods for treating ferric phosphate wastewater, such as flocculation sedimentation, lime precipitation, filtration, and membrane treatment, which are widely used in practical engineering. However, each of these technologies has its own defects or shortcomings, and a single process technology unit cannot achieve the requirement of zero wastewater discharge and resource recovery.

[0005] Currently, the most mainstream process route for zero discharge and resource utilization of ferric phosphate wastewater (mother liquor and wash water) is to treat the mother liquor and wash water separately. First, the pH is adjusted to remove iron, manganese, magnesium, calcium, etc. The salt concentration of the wash water is concentrated using a pre-concentrated RO membrane and then mixed with the wastewater after the mother liquor treatment. The mixture is then sent to a primary or secondary membrane concentration system to concentrate the sulfate concentration and perform evaporation concentration. The permeate from the primary or secondary membrane concentration system enters the intermediate RO system for desalination. The pre-concentrated RO permeate is mixed with the evaporated condensate and purified through a multi-stage RO desalination process to meet the permeate reuse standard.

[0006] In reality, most existing engineering cases show that ferric phosphate wastewater treatment systems cannot achieve full-scale zero discharge and resource recovery.

[0007] For example, Chinese patent document CN114716089A discloses a multi-stage membrane concentration process for treating ferric phosphate wastewater. This process uses a series of acid-resistant nanofiltration membrane columns of varying numbers to achieve multi-effect evaporation of concentrated brine to form solid compound fertilizer and to reuse the treated water. While acid-resistant nanofiltration membranes eliminate the need for pH adjustment during pretreatment, ferric phosphate wastewater is complex, highly acidic, concentrated, and contains numerous impurities. Ineffective pretreatment can lead to increased membrane fouling frequency due to poor impurity removal, and the corrosive nature of the strong acid can affect membrane lifespan, increase replacement cycles, and impact the overall system stability. Furthermore, the wastewater contains high concentrations of ammonia nitrogen. Due to the penetrating effect of ammonia molecules, ammonia nitrogen cannot be completely and effectively blocked, often exceeding standards in practical applications and failing to meet the requirements for water reuse. Additionally, the concentrated product is primarily ammonium phosphate compound fertilizer, which contains numerous impurities such as ammonium sulfate and magnesium sulfate, affecting the quality and marketability of the byproducts.

[0008] For example, Chinese patent document CN113354177A discloses a system and method for the full-element resource utilization treatment of iron phosphate wastewater containing ammonia nitrogen. It first uses ammonia water and calcium hydroxide to raise the pH to remove iron and manganese metal ions and precipitate calcium hydrogen phosphate; then it uses sulfuric acid to adjust the pH to precipitate byproducts such as calcium sulfate dihydrate and calcium phosphate; finally, it recovers ammonia nitrogen by stripping to remove nitrogen. Ammonia nitrogen is recovered to a certain extent, but the whole process is very long, requires a lot of acid and alkali, and generates a lot of chemical sludge. Moreover, the precipitated calcium sulfate dihydrate and the sodium sulfate byproduct after evaporation and crystallization have low economic value, and the cost of transporting and disposing of sludge is high, so it does not have a comprehensive cost-effectiveness.

[0009] For example, Chinese patent document CN116462347A discloses a method for treating wastewater from ferric phosphate production. First, nanofiltration is used to intercept various metal ions and sulfate ions. Then, the nanofiltration concentrate is subjected to heavy metal and impurity removal. After that, it is mixed with nanofiltration permeate and fed into reverse osmosis for permeate production and concentration. Finally, sulfuric acid by-product is obtained through evaporation and crystallization. However, the entire process is lengthy and has many steps with large amounts of reagents, large amounts of sludge, and many by-products. In particular, the high concentration of calcium and magnesium ions after evaporation and crystallization has an adverse effect on evaporator fouling and scaling, and also affects the quality of ammonium sulfate by-product.

[0010] For example, Chinese patent document CN115231758A discloses a method for treating ferric phosphate wastewater and a method for preparing fertilizer using ferric phosphate wastewater. It adopts a method of separate treatment of mother liquor and washing liquor to finally obtain magnesium ammonium phosphate, monoammonium phosphate, ammonium phosphate by-products and pure water for reuse. However, the pretreatment of solid-liquid separation by only adjusting the pH in two stages is difficult to meet the requirements of accurate impurity removal and solve the problem of supersaturation in actual engineering. The suspended solids, colloids, particulate matter and other impurities after solid-liquid separation need to be further removed by various filtration methods before they can meet the requirements of the subsequent membrane system.

[0011] The technical problem this invention aims to solve is to improve upon the shortcomings of existing technologies by providing a system and method for the precise removal of impurities from mixed wastewater containing iron phosphate discharged via the ammonia process, optimizing membrane system combinations, and achieving efficient and energy-saving evaporation and crystallization. This system truly achieves stable process operation, good treatment results, zero wastewater discharge and reuse, and resource recovery. Simultaneously, it addresses several problems encountered in the use of multi-stage sedimentation tanks in existing wastewater treatment systems. For example, the primary sedimentation tank, which mainly removes heavy metal ions and suspended solids, is prone to impurity accumulation on its inner wall, even leading to clumping and wall adhesion, requiring frequent shutdowns for cleaning and affecting overall wastewater treatment efficiency. Furthermore, the secondary sedimentation tank suffers from difficulties in uniformly stirring the wastewater at the bottom during pH adjustment, resulting in incomplete reaction of the mixed liquor and frequent need to extend reaction time, thus reducing working efficiency. Summary of the Invention

[0012] The purpose of this invention is to address the above-mentioned problems by providing a zero-discharge and resource-based treatment system and method for ferric phosphate wastewater. This system, used for the comprehensive treatment of mixed ferric phosphate wastewater, comprises three main parts: a pretreatment system, a membrane treatment system, and an evaporation and crystallization system. It achieves zero-discharge wastewater reuse and resource recovery. Furthermore, it specifically improves upon several problems encountered in the use of multi-stage flocculation sedimentation tanks in existing treatment systems, effectively increasing the overall wastewater treatment efficiency and achieving higher economic benefits for the wastewater treatment system of this invention.

[0013] To achieve the above objectives, the technical solution adopted by the present invention is: a zero-discharge and resource-based treatment system for iron phosphate wastewater, comprising a plate heat exchanger, an equalization tank, a primary flocculation reaction tank, a secondary flocculation reaction tank, a fluidized bed, an ultrafiltration system, a two-stage concentration RO system, a multi-stage permeable RO system, and a pure water reuse tank connected in sequence; an MVR evaporator connected to the two-stage concentration RO system; a centrifugal compressor connected to the MVR evaporator; and a drying device connected to the centrifugal compressor. The primary flocculation reaction tank is equipped with a stirring and scraping device, which is used to stir the primary flocculation reaction tank and scrape the inner wall of the primary flocculation reaction tank clean during stirring. The secondary flocculation reaction tank is equipped with a lifting and stirring device, which is used to stir the secondary flocculation reaction tank and moves up and down relative to the secondary flocculation reaction tank to change the stirring position during stirring.

[0014] Furthermore, a first rotating shaft is vertically arranged inside the primary flocculation reaction tank. The first rotating shaft has a second sliding groove extending in the vertical direction. The stirring and scraping device includes a first stirring plate, a second stirring plate, and a scraping assembly. The first end of the first stirring plate and the first end of the second stirring plate are separately disposed in the second sliding groove and are both used to slide along the second sliding groove. The second end of the first stirring plate and the second end of the second stirring plate are both connected to the scraping assembly. The scraping assembly is used to abut against the inner wall of the primary flocculation reaction tank.

[0015] Furthermore, the stirring and scraping device also includes two second sliders respectively disposed in the second chute, and two second springs that abut against the two second sliders in a one-to-one correspondence. The second springs press against the end of the second slider away from the other second slider. The first end of the first stirring plate is hinged to one of the second sliders, and the first end of the second stirring plate is hinged to the other second slider.

[0016] Furthermore, the wall scraping assembly includes a mounting plate and a wall scraping component detachably connected to the mounting plate, as well as a first slider and a first spring disposed within the mounting plate. The mounting plate has a first groove radially formed along the first rotating shaft. The first slider is embedded in the first groove and is used to slide along the first groove. The first spring is spring-loaded at both ends of the first slider along its sliding direction. The first end of the first stirring plate is fixedly connected to the first slider, and the first end of the second stirring plate is hinged to the first slider.

[0017] Furthermore, the secondary flocculation reaction tank is provided with a second rotating shaft and a guide rod located on one side of the second rotating shaft and parallel to the second rotating shaft. The second rotating shaft is provided with an outer filament segment. The lifting and stirring device includes a first mounting plate sleeved on the outer filament segment of the second rotating shaft and used to be driven to lift and lower when the second rotating shaft rotates. A limit ring is provided on the outer ring of the first mounting plate. The guide rod passes through the limit ring. Stirring blades are arranged on the first mounting plate. A roller is provided at the end of the stirring blades away from the first mounting plate. An annular limit groove coaxial with the second rotating shaft is provided in the limit ring. The roller is embedded in the annular limit groove and used to roll along the annular limit groove.

[0018] Furthermore, the lifting and stirring device also includes a second mounting plate sleeved on the outer thread section of the second rotating shaft and used to be driven to lift and lower when the second rotating shaft rotates, a limiting rod connected to the second mounting plate, and a plurality of swing rod assemblies arranged on the outer periphery of the second mounting plate; the guide rod passes through the limiting rod, the swing rod assembly includes a swinging element and a mounting rod arranged in a ring array on the outside of the second mounting plate, the mounting rod has a third sliding groove opened along the radial direction of the second rotating shaft, a third slider is slidably arranged in the third sliding groove, a limiting post is provided on one side of the third slider, the first end of the swinging element is hinged to the inner wall of the secondary flocculation reaction tank, a fourth sliding groove is opened on the swinging element, the limiting post passes through the fourth sliding groove and is used to slide along the fourth sliding groove when the second mounting plate moves up and down, thereby driving the swinging element to swing and achieve the stirring effect.

[0019] Furthermore, the oscillating member has a V-shaped plate structure, and the oscillating member is provided with through holes spaced apart for allowing ferric phosphate wastewater to flow through and form turbulence.

[0020] Furthermore, the fluidized bed includes an outer cylinder and an inner reaction cylinder located inside the outer cylinder, as well as an aeration device located in the inner reaction cylinder. The inner reaction cylinder is a cylindrical structure with an open top, a narrowing middle section, and a sealed bottom. There is a gap between the inner reaction cylinder and the outer cylinder. An air inlet pipe is provided at the top of the outer cylinder, extending into the inner reaction cylinder and connecting to the aeration device. A crystal discharge port is provided at the bottom of the outer cylinder. A water inlet pipe is provided on the lower part of the outer cylinder wall, extending into the inner reaction cylinder. A water outlet pipe is provided at the top of the outer cylinder. A feed pipe for adding seed crystals to the inner reaction cylinder is provided on the outer cylinder wall.

[0021] In addition, the present invention also discloses a treatment method using the above-mentioned zero-discharge and resource-based treatment system for ferric phosphate wastewater, which includes the following steps:

[0022] S100, Pretreatment:

[0023] S101: Heat exchange and cooling treatment of ferric phosphate wastewater;

[0024] S102: The ferric phosphate wastewater after heat exchange and cooling is transported to the equalization tank for homogenization treatment; S103: The wastewater after homogenization treatment enters the primary flocculation reaction tank and ammonia water is added for flocculation reaction. The stirring and scraping device is started to stir the primary flocculation reaction tank and scrape the inner wall of the primary flocculation reaction tank clean during stirring.

[0025] S104: The supernatant of the primary flocculation reaction tank enters the secondary flocculation reaction tank and ammonia water is added to the secondary flocculation reaction tank to carry out flocculation reaction. The lifting and stirring device is started to stir the secondary flocculation reaction tank and moves up and down relative to the secondary flocculation reaction tank to change the stirring position during stirring.

[0026] S200, membrane treatment:

[0027] S201: The permeate from the secondary flocculation reactor enters the ultrafiltration system after being filtered through a fluidized bed.

[0028] S202: Permeate from the ultrafiltration system is pumped into a two-stage RO (reinforcement) system;

[0029] S203: Permeate from the two-stage concentration RO system enters the multi-stage permeate RO system;

[0030] S204: Permeate from the multi-stage RO system flows into the pure water reuse tank;

[0031] S300, Evaporation and Crystallization:

[0032] S301: The concentrate from the two-stage RO system is evaporated, crystallized, and centrifuged to produce byproducts.

[0033] Furthermore, in step S101, the temperature of the ferric phosphate wastewater is reduced to below 35°C via a plate heat exchanger.

[0034] In step S103, ammonia water is added to the primary flocculation reaction tank to adjust the pH to 5-5.5;

[0035] In step S103, the sludge settled in the primary flocculation reaction tank is dewatered by a plate and frame filter press to form sludge cake, and the filtrate after dewatering is returned to the equalization tank.

[0036] In step S104, ammonia water is added to the secondary flocculation reaction tank to adjust the pH to 8.5-9.5.

[0037] Furthermore, in step S201, the fluidized bed uses one or more of the following granular fillers as seed crystals: micro-sand quartz sand with a specification of 0.3-1mm, anthracite, activated carbon, zeolite, volcanic rock, and ceramsite. The fluidized wastewater is further filtered by a multi-media or manganese sand filter to remove iron and manganese substances and fine particulate matter. Before entering the ultrafiltration system, the wastewater is adjusted to a neutral to slightly acidic environment by adding sulfuric acid. A 100-200um security filter is installed before the ultrafiltration system.

[0038] Furthermore, in step S202, the first stage of the two-stage concentration RO system has a water production rate of 50%-60% and a water production rate of 75%-80% after concentration. The TDS after concentration is higher than 150,000 mg / L, and the total concentration of Mg / Ca / Mn / Fe / F is controlled to be <20 ppm.

[0039] In step S204, the total desalination rate of the multi-stage RO system reaches 99.99%, the total water production rate is higher than 95%, and the conductivity of the produced water is ≤10µs / cm.

[0040] Furthermore, step S301 specifically includes: adopting a combined process of preheating + two-stage double-effect falling film evaporation + forced circulation evaporation thermal crystallization + centrifugal drying. In the preheating stage, heat is recovered by setting up a preheater. After preheating, the material concentration of the first-effect falling film evaporator is controlled at 20%-22%, and the design boiling point rises by 2-3℃. The material concentration of the second-effect falling film evaporator is controlled at 38%-40%, and the design boiling point rises by 5-6℃. When entering the forced circulation evaporation, the design boiling point rises by 8-9℃. Subsequently, the centrifugal drying process uses a centrifugal compressor as the evaporation heating device and uses an automatic double centrifuge to achieve solid-liquid separation. The ammonium sulfate crystals after centrifugal separation are transported to a drying system using an ammonium sulfate vibrating fluidized bed or drum dryer for drying. After drying, ammonium sulfate by-products are produced.

[0041] The beneficial effects of this invention are:

[0042] 1. The method of the present invention is an integrated process package or system solution for treating ferric phosphate mixed (mother liquor + washing liquid) wastewater. It is simpler than the traditional process of separating mother liquor and washing liquid, has fewer process units, makes reaction conditions easier to control, has better overall treatment effect, more stable and reliable system operation, and lower investment and operating costs, among other advantages.

[0043] 2. From the perspective of the overall process technology classification treatment route and pollutant removal law, the two-stage classification treatment process of "pretreatment + membrane concentration" adopted in this invention achieves the retention of specific particle size substances in the retention spectrum. This not only ensures technical feasibility, but also ensures the normal operation of each process unit classification treatment, and achieves economic optimization, realizing the reasonable distribution of filtration load of each process.

[0044] 3. The pretreatment stage of this invention plays a crucial role in adjusting pH, cooling, and removing suspended solids (SS), chemical oxygen demand (COD), colloids, and metal ions. This creates favorable influent conditions and ensures optimal performance for the subsequent membrane system and evaporation crystallization. The pretreatment stage primarily removes large particles and highly concentrated pollutants with complex and varied components. The membrane system and evaporation crystallization system are relatively sensitive processes, with stringent requirements for influent water quality and material conditions. Otherwise, substances that clog, corrode, pollute, or damage membrane elements and evaporation crystallization facilities will directly lead to system collapse or even paralysis, resulting in significant costs and losses. The process technology adopted in this invention follows a principle of removing pollutant particles from coarse to fine, and the concentration and composition of pollutants also decrease gradually. The working sequence is scientifically sound, ensuring that each stage at least meets the requirements for stable and reliable operation of the next stage.

[0045] 4. The pretreatment method of this invention innovatively incorporates a fluidized bed filtration process unit, specifically addressing the supersaturation of metal compounds that occurs during the heavy metal removal process of ferric phosphate wastewater. This stage further reduces the concentration of various metals, preventing crystal precipitation in the ultrafiltration and reverse osmosis membrane systems and thus preventing membrane fouling. Simultaneously, it provides excellent protection against fouling in subsequent membrane systems and scaling in the evaporation system, effectively reducing the cleaning frequency of the membrane and evaporation systems and increasing their service life and equipment lifespan.

[0046] 5. The membrane system of this invention features optimized combination and configuration, resulting in high permeate and desalination rates and excellent effluent quality. To address the requirements for TDS enhancement and permeate conductivity, the membrane elements are optimally designed and arranged through permeate grading and concentrate segmentation. Through water volume and material balance calculations and analysis, the concentrate from each stage of RO is returned to the optimal upstream position. This ensures that the TDS enhancement from reverse osmosis reaches 150,000 mg / L, or even higher than 160,000 mg / L, which is 25%–50% higher than the TDS of conventional evaporation systems, significantly reducing evaporation and saving investment and operating costs. Furthermore, the multi-stage RO process achieves high permeate volume and rate; after the removal of water from the dewatered sludge and a small amount of water from the mother liquor after evaporation and crystallization, the remaining water is essentially reused. The process route and method of this invention achieve zero discharge and resource utilization of ferric phosphate wastewater, with good energy-saving advantages, more stable system operation, no need for complex processes and equipment, and easy to apply on a large scale in industrial applications. It is a wastewater comprehensive treatment method with great economic value and very good market promotion value.

[0047] 6. The processing system of this invention addresses the problem that existing primary flocculation reaction tanks easily accumulate impurities on their inner walls during use, and may even clump together and stick to the walls, requiring frequent shutdowns for cleaning. By setting a stirring and scraping device on the first rotating shaft, the stirring and scraping device can stir the tank while scraping the inner wall of the primary flocculation reaction tank when the first rotating shaft rotates, reducing the problem of sedimentation and clumping on the inner wall, preventing the inner wall from being easily corroded, and eliminating the need for frequent shutdowns to clean the inner wall of the reaction tank.

[0048] 7. In order to ensure that the wastewater at the bottom of the secondary flocculation reaction tank of the treatment system of the present invention is fully stirred and mixed evenly during pH adjustment, thereby improving the reaction efficiency, a lifting and stirring device is set on the second rotating shaft. When the second rotating shaft rotates, it can drive the lifting and stirring device to move up and down while stirring, thereby achieving full stirring of wastewater at each level in the secondary flocculation reaction tank and full mixing with the reagent. This effectively solves the problem of low work efficiency caused by simply extending the stirring time to improve the reaction effect in conventional operation.

[0049] Of course, any product implementing this invention does not necessarily need to achieve all the advantages described above simultaneously. In addition to the objectives, features, and advantages described above, this invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0050] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0051] Figure 1 This is a schematic diagram of the process flow of the ferric phosphate wastewater treatment method of the present invention;

[0052] Figure 2 This is a schematic diagram of the overall primary and secondary flocculation reaction tanks of a preferred embodiment of the present invention.

[0053] Figure 3 This is a schematic diagram of the internal structure of the primary flocculation reaction tank in a preferred embodiment of the present invention.

[0054] Figure 4 This is a schematic diagram of the structure of the first stirring plate portion in a preferred embodiment of the present invention.

[0055] Figure 5 This is a schematic diagram of the external appearance of the secondary flocculation reaction tank according to a preferred embodiment of the present invention.

[0056] Figure 6 This is a schematic diagram of the internal structure of the secondary flocculation reaction tank in a preferred embodiment of the present invention.

[0057] Figure 7This is a schematic diagram of the installation of the stirring blades according to a preferred embodiment of the present invention.

[0058] Figure 8 This is a schematic diagram of the installation of the roller at the tail end of the stirring blade in a preferred embodiment of the present invention.

[0059] Figure 9 This is a schematic diagram of the bottom end installation of the second rotating shaft according to a preferred embodiment of the present invention.

[0060] Figure 10 This is a schematic diagram of the installation of the swing component according to a preferred embodiment of the present invention.

[0061] Figure 11 This is a schematic diagram of the internal structure of a fluidized bed according to a preferred embodiment of the present invention.

[0062] Legend: 100, Primary Flocculation Reactor; 200, Secondary Flocculation Reactor; 1, First Inlet; 2, First Top Cover; 3, First Sliding Block; 4, First Slide Groove; 5, Mounting Plate; 6, Scraper; 7, Mounting Base; 8, First Stirring Plate; 9, Second Stirring Plate; 10, Second Slide Groove; 11, Second Sliding Block; 12, Spring; 13, First Rotating Shaft; 14, First Bearing; 15, First Outlet; 16, First Support Rod; 17, First Motor; 18, First Turntable; 19, Second Turntable; 20, ... 21. Second top cover; 22. Second motor; 23. Second inlet; 24. Second outlet; 25. Second rotating shaft; 26. First mounting plate; 27. Stirring blade; 28. Limiting ring; 29. ​​Guide rod; 30. Second mounting plate; 31. Limiting rod; 32. Mounting rod; 33. Third slide groove; 34. Swing rod assembly; 35. Swinging component; 36. Stirring swing rod; 37. Fourth slide groove; 38. Third slider; 39. Second bearing; 40. Second support rod; 41. Connecting plate; 42. Roller; 43. Limiting groove. Detailed Implementation

[0063] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways as defined and covered below.

[0064] Please refer to Figure 2-11This invention discloses a zero-discharge and resource-based treatment system for ferric phosphate wastewater, comprising a plate heat exchanger, an equalization tank, a primary flocculation reaction tank 100, a secondary flocculation reaction tank 200, a fluidized bed, an ultrafiltration system, a two-stage concentration RO system, a multi-stage permeable RO system, and a pure water reuse tank connected in sequence; an MVR evaporator connected to the two-stage concentration RO system; a centrifugal compressor connected to the MVR evaporator; and a drying device connected to the centrifugal compressor. The primary flocculation reaction tank 100 is equipped with a stirring and scraping device for stirring the primary flocculation reaction tank 100 and scraping its inner wall clean during stirring. The secondary flocculation reaction tank 200 is equipped with a lifting and stirring device for stirring the secondary flocculation reaction tank 200 and for moving up and down relative to the secondary flocculation reaction tank 200 to change the stirring position during stirring.

[0065] The process described in this invention operates stably and can achieve zero discharge and reuse of ferric phosphate wastewater, as well as resource recovery. Furthermore, for the primary sedimentation tank 100, which mainly removes heavy metal ions and suspended solids, impurities easily accumulate on its inner wall, even leading to clumping and wall adhesion. A stirring and scraping device is installed for real-time cleaning. Regarding the secondary sedimentation tank 200, where the wastewater at the bottom is difficult to stir evenly during pH adjustment, resulting in incomplete reaction of the mixed liquid, a lifting and stirring device is installed to ensure thorough stirring and uniform mixing of the liquids in each layer.

[0066] For preferred options, please refer to [the provided text]. Figure 3 and Figure 4 A first rotating shaft 13 is vertically arranged inside the primary flocculation reaction tank 100. The first rotating shaft 13 has a second sliding groove 10 extending in the vertical direction. The stirring and scraping device includes a first stirring plate 8, a second stirring plate 9, and a scraping assembly. The first end of the first stirring plate 8 and the first end of the second stirring plate 9 are separately disposed in the second sliding groove 10 and are both used to slide along the second sliding groove 10. The second end of the first stirring plate 8 and the second end of the second stirring plate 9 are both connected to the scraping assembly. The scraping assembly is used to abut against the inner wall of the primary flocculation reaction tank 100.

[0067] In this embodiment, the stirring and scraping device further includes two second sliders 11 respectively disposed in the second groove 10, and two second springs 12 corresponding to and abutting against the two second sliders 11. The second springs 12 are pressed against the ends of the second sliders 11 away from the other second slider 11. The first end of the first stirring plate 8 is hinged to one of the second sliders 11, and the first end of the second stirring plate 9 is hinged to the other second slider 11. The scraping assembly includes a mounting plate 5 and a scraping component 6 detachably connected to the mounting plate 5, as well as a first slider 3 and a first spring disposed in the mounting plate 5. The mounting plate 5 has a first groove 4 radially opened along the first rotating shaft 13. The first slider 3 is embedded in the first groove 4 and is used to slide along the first groove 4. The first spring is pressed against both ends of the first slider 3 along its sliding direction. The first end of the first stirring plate 8 is fixedly connected to the first slider 3, and the first end of the second stirring plate 9 is hinged to the first slider 3.

[0068] It is understood that the first stirring plate 8 and the second stirring plate 9 form a V-shaped stirring assembly. One end of the first stirring plate 8 is fixedly connected to the first slider 3, while one end of the second stirring plate 9 is hinged to the first slider 3. The first stirring plate 8 and the second stirring plate 9 are respectively hinged to two symmetrical second sliders 11 within the second chute 10. The two second sliders 11 are connected to the upper and lower inner walls of the second chute 10 respectively via springs 12. When the first rotating shaft 13 is stationary, the springs 12 pull the two second sliders 11 apart, simultaneously causing one end of the first stirring plate 8 and the second stirring plate 9 to separate at a larger angle. When the first rotating shaft 13 rotates, due to the centrifugal force, the mounting plate 5 tends to move radially outward relative to the first rotating shaft 13, thereby causing the first slider 3 to move outward, and simultaneously causing the first stirring plate 8 and the second stirring plate 9 to close. During the displacement of the mounting plate 5, the wall scraper 6 on its side contacts the inner wall of the primary flocculation reaction tank 100 for wall scraping treatment. Since the first rotating shaft 13 requires a high rotational speed, and the two sides of the first slider 3 are connected to the inner wall of the mounting plate 5 by springs 12, it can provide buffer protection for the mounting plate 5 and the scraper 6.

[0069] In one feasible embodiment, the lower end of the first rotating shaft 13 is connected to the first bearing 14, and the first bearing 14 is fixedly connected to the inner wall of the primary flocculation reaction tank 100 via the first support rod 16. The upper end of the first rotating shaft 13 extends out of the first top cover 2 of the primary flocculation reaction tank 100 and is connected to the second turntable 19. The second turntable 19 can form a gear pair with the first turntable 18. The first turntable 18 is driven by the first motor 17, which is mounted on the outer wall of the primary flocculation reaction tank 100 via a mounting bracket. This driving method can significantly reduce the installation space at the top of the primary flocculation reaction tank 100, thereby avoiding gaps in the transmission pipeline. At the same time, since the primary flocculation reaction tank 100 requires a large stirring force, directly mounting the wall motor on the first top cover 2 can reduce the noise of working vibration and the frictional wear of the first top cover 2.

[0070] For preferred options, please refer to [the provided text]. Figure 6-10 As shown, the secondary flocculation reaction tank 200 is provided with a second rotating shaft 24 and a guide rod 28 located on one side of the second rotating shaft 24 and parallel to the second rotating shaft 24. The second rotating shaft 24 is provided with an outer filament segment. The lifting and stirring device includes a first mounting plate 25 sleeved on the outer filament segment of the second rotating shaft 24 and used to be driven to lift and lower when the second rotating shaft 24 rotates. A limit ring 27 is provided on the outer ring of the first mounting plate 25. The guide rod 28 passes through the limit ring 27. A stirring blade 26 is arranged on the first mounting plate 25. A roller 41 is provided at the end of the stirring blade 26 away from the first mounting plate 25. An annular limit groove 42 coaxial with the second rotating shaft 24 is provided in the limit ring 27. The roller 41 is embedded in the annular limit groove 42 and used to roll along the annular limit groove 42.

[0071] The lifting and stirring device further includes a second mounting plate 29 sleeved on the outer thread section of the second rotating shaft 24 and used to be driven to lift and lower when the second rotating shaft 24 rotates, a limiting rod 30 connected to the second mounting plate 29, and a plurality of swing rod assemblies 33 arranged on the outer periphery of the second mounting plate 29; the guide rod 28 passes through the limiting rod 30, and the swing rod assembly 33 includes a swing member 34 and mounting rods 31 arranged in a ring array on the outside of the second mounting plate 29. The mounting rods 31 have a third sliding groove 32 radially along the second rotating shaft 24, and a third slider 37 is slidably arranged in the third sliding groove 32. A limiting post is provided on one side of the third slider 37. The first end of the swing member 34 is hinged to the inner wall of the secondary flocculation reaction tank 200. A fourth sliding groove 36 is provided on the swing member 34. The limiting post passes through the fourth sliding groove 36 and is used to slide along the fourth sliding groove 36 when the second mounting plate 29 moves up and down, thereby driving the swing member 34 to swing and achieve the stirring effect.

[0072] It is understandable that the first mounting plate 25 and the second mounting plate 29 are connected to the second rotating shaft 24 via a screw and nut lifting connection structure. The guide rod 28, in conjunction with the limiting ring 27 and the limiting rod 30, provides limiting and guiding functions for the first mounting plate 25 and the second mounting plate 29. The second rotating shaft 24 is driven by a second motor 21 mounted on the second top cover 20 of the secondary flocculation reactor 200. The second motor 21 is a stepper motor with pre-set forward and reverse rotation parameters. Since the rotational speed requirement for the second rotating shaft 24 is not high, it can drive the first mounting plate 25 and the second mounting plate 29 to rise and fall at a uniform speed. The bottom end of the second rotating shaft 24 is connected to a second bearing 38, which is fixedly connected to the inner wall of the secondary flocculation reactor 200 via a second support rod 39.

[0073] The working principle of the stirring blade 26 is as follows: The stirring blade 26 is rotatably mounted, which can be achieved through bearings. For example, a bearing is mounted on the first mounting plate 25, and the stirring blade 26 is connected to the outside of the bearing. The upper and lower water-facing surfaces of the stirring blade 26 can be cut. A roller 41 is provided at the outer end of the stirring blade 26, and the roller 41 is located in the limiting groove 42 of the limiting ring 27, realizing the rotatable mounting of the stirring blade 26. When the second rotating shaft 24 drives the first mounting plate 25 to rise and fall, the stirring blade 26 is impacted by the water and rotates, thereby achieving full mixing of the mixture at each level.

[0074] In this preferred embodiment, the swing arm assembly 33 includes a swing member 34 and mounting rods 31 arranged in a ring array on the outside of the second mounting plate 29. A third sliding groove 32 is provided on the mounting rods 31, and a third slider 37 is slidably disposed in the third sliding groove 32. A limiting post is provided on one side of the third slider 37. One end of the swing member 34 is hinged to the inner wall of the secondary flocculation reaction tank 200. A fourth sliding groove 36 is provided on the swing member 34, and the limiting post is disposed through the fourth sliding groove 36.

[0075] Specifically, the swing member 34 has a V-shaped plate structure, and the swing member 34 is provided with through holes spaced apart for allowing ferric phosphate wastewater to flow through and form turbulence.

[0076] The working principle of the swing arm assembly 33 is as follows: A stirring swing arm 35 is provided on one side of the V-shaped swing member 34. One end of the stirring swing arm 35 is hinged to the connecting plate 40, and the connecting plate 40 is fixedly connected to the inner wall of the secondary flocculation reaction tank 200. The fourth sliding groove 36 on the stirring swing arm 35 limits the limiting post on the third slider 37, and the third slider 37 can slide within the horizontal third sliding groove 32. When the second rotating shaft 24 drives the second mounting plate 29 to move up and down, it simultaneously drives the third slider 37 to move. The third slider 37 further drives the stirring swing arm 35 and the swing member 34 to swing around the hinge point of the connecting plate 40, thereby realizing the stirring of each layer of the mixture by the V-shaped swing member 34.

[0077] In this preferred embodiment, both the primary flocculation reaction tank 100 and the secondary flocculation reaction tank 200 can adopt a bottom conical design, and the bottom of the two are respectively provided with a first outlet 15 and a second outlet 23 for convenient centralized discharge.

[0078] Preferred option, please proceed. Figure 11 As shown, the fluidized bed stirring and scraping device includes an outer cylinder stirring and scraping device and an inner reaction cylinder stirring and scraping device located inside the outer cylinder stirring and scraping device, as well as an aeration device located in the inner reaction cylinder stirring and scraping device. The inner reaction cylinder stirring and scraping device is a cylindrical structure with an open top, a narrowing middle section, and a sealed bottom. There is a gap between the inner reaction cylinder stirring and scraping device and the outer cylinder stirring and scraping device. An air inlet stirring and scraping device is provided at the top of the outer cylinder stirring and scraping device, which extends into the inner reaction cylinder stirring and scraping device and is connected to the aeration device. A crystal discharge port is provided at the bottom of the outer cylinder stirring and scraping device. A water inlet pipe is provided on the lower part of the outer cylinder stirring and scraping device and extends into the inner reaction cylinder stirring and scraping device. A water outlet pipe is provided at the top of the outer cylinder stirring and scraping device. A feed pipe for adding seed crystals to the inner reaction cylinder stirring and scraping device is provided on the cylinder wall of the outer cylinder stirring and scraping device.

[0079] In this preferred embodiment, the fluidized bed, through the arrangement of an outer cylinder and an inner reaction cylinder, forms a supernatant zone in the upper part of the outer cylinder (where a baffle can be arranged on the upper part of the inner reaction cylinder 302, and a water outlet weir can be set above the baffle. A gap is left between the baffle and the inner wall of the outer cylinder. The baffle can block, separate and fix impurities so that the clear liquid can flow out from the water outlet at the water outlet weir). The gap between the inner reaction cylinder and the outer cylinder forms a separation zone, and a crystal precipitation zone is formed at the bottom of the inner reaction cylinder. The supersaturated solution in the wastewater enters the inner reaction cylinder for reaction. Simultaneously, compressed air and "seed crystals" (such as micro-sand quartz sand, anthracite, activated carbon, zeolite, volcanic rock, and ceramsite, with micro-sand quartz sand being preferred) are introduced into the inner reaction cylinder. At the bottom of the inner reaction cylinder 302, a large number of bubbles are formed through an aeration device (such as perforated pipes or aeration discs) to form a three-phase suspension fluidized system of "gas-liquid-solid" with the supersaturated wastewater and seed crystals. Under the action of fluid shear force, disturbance, impact, and contact, the supersaturated wastewater becomes unstable and destabilized. Metal ion compounds continuously adhere to and diffuse on the surface of the seed crystals, gradually growing into new "crystal nuclei". As the "crystal nuclei" grow larger and heavier to a certain extent, they form precipitate particles. Finally, the supernatant from the top of the inner reaction cylinder is separated from the seed crystal mixture. The supernatant flows out evenly through the effluent weir plate, and the precipitate particles are collected in the crystal sedimentation zone by gravity sedimentation of the seed crystals. The metal precipitates are further removed by periodic "sludge discharge".

[0080] The fluidized bed structure in this treatment system is simple and practical, with clear and independent zones. It creates conditions for supersaturated wastewater to form crystal nuclei, precipitate, and separate through seed crystal induction, achieving the goal of removing metal precipitates from supersaturated wastewater. The seed crystals are readily available and inexpensive. Using granular fillers such as quartz sand as seed crystal carriers effectively promotes the formation of new crystal nuclei and accelerates precipitation. Compared to traditional precipitation methods, this significantly shortens the reaction and precipitation time and increases the precipitation effect. In the separation zone, where aeration is not disruptive, the separation of mud and water is more thorough. The aeration device at the bottom of the reaction tank generates a large number of bubbles. Its function is to create a three-phase suspension fluidized system of gas, liquid, and solid with the supersaturated wastewater and seed crystals. This allows the metal compounds in the supersaturated wastewater to fully contact, collide, and adsorb with the seed crystals, facilitating the adhesion of more supersaturated metal compounds to the seed crystal surface, accelerating the formation of larger and heavier crystal nuclei, and improving the precipitation effect.

[0081] In addition, this invention also discloses a treatment method using the above-mentioned zero-discharge and resource-based treatment system for ferric phosphate wastewater, comprising pretreatment, membrane treatment, and evaporation crystallization steps, wherein...

[0082] S100, Pretreatment: The ferric phosphate wastewater is cooled by heat exchange through a plate heat exchanger, and then enters the equalization tank for homogenization. The equalized wastewater enters the primary flocculation reaction tank 100 and ammonia water is added for flocculation reaction. The sludge settled in the primary flocculation reaction tank 100 is dewatered by a plate and frame filter press to form sludge cake. The filtrate is returned to the equalization tank. The supernatant of the primary flocculation reaction tank 100 enters the secondary flocculation reaction tank 200 and ammonia water is added again for reaction.

[0083] The purpose of pretreatment is to reduce the content of COD, manganese, iron, magnesium, calcium, and heavy metal ions in wastewater, and to minimize the impact of inorganic salt scaling, biological contamination, organic contamination, and colloidal contamination on the membrane concentration system and evaporation concentration. Because the temperature of ferric phosphate wastewater is relatively high, generally between 40℃ and 60℃, a plate heat exchanger is installed before the wastewater enters the equalization tank for heat exchange and cooling to reduce its temperature to below 35℃, in order to improve the safety factor and ensure the safe and stable operation of system equipment and pipes.

[0084] Considering the fluctuations in the volume and quality of ferric phosphate wastewater, the mixed ferric phosphate wastewater is lowered in temperature before entering an equalization tank for homogenization, facilitating relatively stable operating conditions for subsequent process units. After adjustment, the mixed wastewater enters the primary / secondary flocculation reaction sedimentation tank. Ammonia is added to adjust the pH to 5-5.5 before it enters the primary high-efficiency flocculation reaction sedimentation tank. The sludge from the sedimentation is dewatered using a plate and frame filter press to form a sludge cake, achieving the removal of iron, manganese heavy metal ions and suspended solids. The dewatered filtrate is returned to the preceding equalization tank. The supernatant from the primary reaction sedimentation enters the secondary high-efficiency flocculation sedimentation tank, where ammonia is added again to adjust the pH to approximately 8.5-9.5 for reaction sedimentation, removing calcium and magnesium ions, fluorides, and suspended solids, achieving the purpose of pre-treatment and stepwise precipitation of metal ions.

[0085] Through a two-stage reaction sedimentation process, large suspended solids, metal ions, and fluorides are largely removed. However, in practical engineering, the most easily overlooked issue is the supersaturation phenomenon that can occur with metal ion compounds. This resulting supersaturated solution is unbalanced and unstable. When subjected to vibration or disturbance, excess solute in the wastewater will precipitate crystals, leading to a saturated solution. These crystals can cause membrane fouling in subsequent ultrafiltration and reverse osmosis systems, affecting the normal and stable operation of the entire system. In this invention, a fluidized bed filtration system is installed after the high-efficiency sedimentation tank reaction sedimentation. Particulate packing materials (micro-sand, anthracite, activated carbon, zeolite, volcanic rock, ceramsite, preferably micro-sand) with a size of 0.30-1.0 mm (preferably 0.50-0.75 mm) are used as seed crystals in the fluidized bed system.

[0086] The seed crystals used in this invention are preferably made of quartz sand, which has a much higher density than wastewater. Specifically designed for treating mixed wastewater containing iron phosphate, the purpose is to destabilize and adsorb supersaturated metal compounds in the wastewater, such as Fe(OH)2, Fe(OH)3, MnO2, Mn(OH)2, MgNH4PO4, and CaF2, onto the micro-sand seed crystals. This forms denser and heavier flocs on the micro-sand seed crystals, accelerating the trapping and sedimentation process, significantly shortening the settling time, and improving the removal efficiency of supersaturated metal compounds. By keeping the crystals in a suspended state, the supersaturated solution in the wastewater becomes unstable and destabilized under the vibration and disturbance conditions during the fluidization process. At this time, the metal compounds in the supersaturated solution continuously adhere to the seed crystals under the mutual disturbance, collision, and trapping effects of the water flow and the suspended seed crystals. Because quartz sand has a much higher density than wastewater, after the seed crystals grow larger, become heavier, and stabilize, they are deposited and enriched in the sludge zone below the fluidized bed under their own gravity. Finally, the removal of metal precipitates is achieved through a "sludge discharge" method. Fluidized bed filtration effectively removes metal compounds from wastewater that exceed their normal solubility, achieving a 30%–50% higher metal ion removal rate compared to processes without this technology. The fluidized wastewater then passes through a multi-media / manganese sand filter to further remove iron, manganese, and fine particulate matter, creating favorable conditions for entry into the ultrafiltration membrane system. Before ultrafiltration, sulfuric acid is added to adjust the pH to a slightly acidic-neutral environment (pH 6.0–7.0). A 100–200 μm security filter is installed before the ultrafiltration system. The ultrafiltration system removes fine particulate matter, microorganisms, and colloidal substances, meeting the feed conditions for subsequent reverse osmosis.

[0087] S200, Membrane Treatment: The permeate from the secondary flocculation reactor 200 enters the ultrafiltration system after being filtered by the fluidized bed. The ultrafiltration permeate is pumped into the two-stage concentration RO system. The permeate from the two-stage concentration RO system enters the multi-stage permeate RO system. The permeate from the multi-stage permeate RO system flows into the pure water reuse tank.

[0088] The main function of membrane treatment is to concentrate ferric phosphate wastewater and reuse the permeate. After concentration via reverse osmosis, the TDS meets the requirements for evaporation and crystallization. The conductivity of the permeate from RO is required to be less than 10 μS / cm for reuse. The TDS of the mixed ferric phosphate wastewater after ultrafiltration is approximately 70,000 mg / L. It is then pumped into a primary / secondary RO system via a high-pressure pump in the ultrafiltration permeate tank. The primary RO permeate yield is 50%–60%, and the secondary RO permeate yield is 75%–80%. After concentration, the TDS reaches over 150,000 mg / L, while the total concentration of Mg / Ca / Mn / Fe / F is controlled to be <20 ppm. This significantly reduces the evaporation rate and the risk of fouling and scaling in the subsequent evaporation system, achieving a TDS of 100,000–1200 mg / L higher than conventional methods. The evaporation rate of 00 mg / L entering the evaporation system is reduced by 25% to 50%. After secondary concentration, the permeate is returned to the ultrafiltration permeate tank. After the concentrated RO permeate is treated by the multi-stage RO permeate system, the desalination rate of each stage of RO is over 95%, the total desalination rate of the membrane system reaches 99.99%, the total permeate rate reaches over 95%, and the permeate conductivity is ≤10 μS / cm (TDS is basically below 5), which meets the pure water reuse requirements of the production process section. The concentrated water after the multi-stage RO permeate can be flexibly returned to the ultrafiltration permeate tank / concentrated RO permeate tank / permeate tank after the first stage of RO permeate.

[0089] S300 Evaporation and Crystallization: The concentrated water from the two-stage RO treatment is evaporated, crystallized, and centrifuged to produce a packaged product for sale. The purpose of evaporation and crystallization is to concentrate the solid substance through evaporation, and then obtain a high-quality ammonium sulfate byproduct through crystallization, centrifugation, and drying, thereby generating revenue through external sales. Based on the material analysis of the concentrate and the solubility curve and boiling point (108.2℃) of ammonium sulfate, a high-efficiency and energy-saving MVR evaporator is adopted. At high temperature, ammonium sulfate first reaches saturation, and ammonium sulfate crystals precipitate. After centrifugation, part of the mother liquor is returned to the system for further evaporation, while a small amount of mixed salt is enriched and discharged from the system through the mother liquor for separate drying treatment.

[0090] Considering the system's energy consumption and equipment operational stability, a combined process of preheating + two-stage double-effect falling film evaporation + forced circulation evaporation thermal crystallization + centrifugal drying is adopted. The preheating stage primarily recovers heat through a preheater to improve system energy efficiency. The double-effect falling film + forced circulation evaporation stage is the most critical, with key equipment being the evaporator and compressor. Based on the boiling point elevation curve of ammonium sulfate, the material concentration in the first-effect falling film evaporator after preheating is designed to be controlled at 20%–22%, with a designed boiling point elevation of 2–3°C. The material concentration in the second-effect falling film evaporator is designed to be controlled at 38%–40%, with a designed boiling point elevation of 5–6°C. During forced circulation evaporation, the designed boiling point elevation is 8–9°C. A centrifugal compressor is used as the key equipment for evaporation temperature rise, ensuring heat transfer temperature difference, achieving material evaporation and concentration, and reducing system energy consumption. An automatic double centrifuge with a large adjustable capacity is used for solid-liquid separation. The ammonium sulfate crystals after centrifugal separation are transported to a drying system such as an ammonium sulfate vibrating fluidized bed or drum dryer for drying. After drying, the product is packaged and sold.

[0091] It is understandable that equipping the evaporation system with a preheater to recover heat from the condensate is beneficial for improving system efficiency. Based on the boiling point elevation curve of ammonium sulfate, to reduce equipment investment and energy consumption, the MVR evaporation adopts a "double-effect falling film + forced circulation evaporation process." Falling film evaporation is characterized by low energy consumption and small investment; at low concentrations, falling film evaporation is used, with most of the water evaporating in the low-energy-consumption process section. Forced circulation evaporation is characterized by resistance to salt formation, scaling, and fluctuations; at high concentrations, forced circulation is used, increasing the material flow rate and reducing the residence time of the liquid in the heat exchanger. Furthermore, the material circulates fully within the tubes, making salt formation in the heat exchanger less likely, effectively reducing the probability of salt formation in the evaporator and ensuring system stability. Finally, a large-capacity adjustable automatic dual centrifuge is selected to achieve solid-liquid separation, obtaining high-quality ammonium sulfate byproducts with few impurities, meeting the Type I requirements of "Fertilizer Grade Ammonium Sulfate" (GB / T535-2020), enabling high-profit byproduct sales and revenue generation.

[0092] Using the treatment method of this invention, based on water and material balance calculations, the amount of concentrated liquid to be treated is less than 50% of the total designed influent. The evaporation rate (the ratio of evaporation to the designed concentrated liquid treatment volume) can reach over 85%, the ammonium sulfate output (the ratio of solid ammonium sulfate to the designed concentrated liquid treatment volume) accounts for over 14%, the purity of solid ammonium sulfate is over 99%, and it is basically all evaporated and crystallized. The corresponding mother liquor discharge accounts for less than 1%, and the water content of impurities in the dried ammonium sulfate crystallization mother liquor is less than 5%. In addition, the high-temperature condensate (distilled water) generated during the evaporation process is cooled by heat exchange in the preheater and then returned to the primary concentration RO permeate tank after being cooled by a cooling tower or cooler.

[0093] In summary, the evaporation crystallization process described above not only yields high-value, high-quality ammonium sulfate solids with product quality meeting the Type I standard of "Fertilizer Grade Ammonium Sulfate" (GB / T535-2020), but also ensures that almost all of the system's condensate is recycled back to the RO process section for reuse as production process water, truly achieving full-scale operation and realizing the goals of resource recovery and zero discharge.

[0094] Example

[0095] Take the ferric phosphate mixed wastewater treatment system of a 60,000-ton / year ferric phosphate project as an example.

[0096] (1) Design water volume: 220m³ 3 / h

[0097] (2) Design influent water quality: as shown in Table 1.

[0098] Table 1. Water quality indicators of mixed wastewater containing ferric phosphate

[0099]

[0100]

[0101] (3) Processing requirements

[0102] ① Requirements for recycled water quality and concentrate

[0103] The treated wastewater must meet the following conductivity requirements: <10 μS / cm;

[0104] The requirements for the concentrate after wastewater membrane concentration are: TDS≥150000mg / L.

[0105] ② Requirements for crystallized salts

[0106] The ammonium sulfate product from this project meets the Type I requirements of "Fertilizer Grade Ammonium Sulfate" (GB / T535-2020). Specific technical specifications are shown in the table below:

[0107]

[0108] Note: After drying the mother liquor from ammonium sulfate crystallization, the moisture content of the impurities is less than or equal to 5%.

[0109] (4) Comprehensive comparison of the examples and comparative examples: as shown in Table 2.

[0110] Table 2 Comparison of overall performance between the examples and comparative examples.

[0111]

[0112] Based on the comparative analysis of the proportions and examples in terms of designed feed capacity and the proportion of solid ammonium sulfate, for a processing scale of 220m³, it is found that... 3Under continuous operation conditions of 7200h with influent and operating conditions, the feed throughput and evaporation rate of the embodiment are at least 10t / h higher than those of the two comparative embodiments. Therefore, it saves at least 10% in terms of energy consumption. Moreover, judging from the proportion of solid ammonium sulfate in the feed throughput, the ammonium sulfate by-product of the embodiment has higher purity and better quality.

[0113] In summary, the comprehensive operating cost analysis of the embodiments and comparative examples shows that the annual operating cost of the embodiments is 3,041,280 yuan less than that of comparative example 1 and 6,906,240 yuan less than that of comparative example 2. This demonstrates that the process route and method of the present invention have greater energy-saving advantages on the basis of achieving zero discharge and resource utilization of ferric phosphate wastewater. Moreover, the system operates more stably, does not require complex processes and equipment, and is easy to carry out on a large scale in industrial applications. It is a wastewater comprehensive treatment method with great economic value and has very good market promotion value.

[0114] Although the method of this invention is an industrial wastewater treatment process, it is essentially another auxiliary "production process" for iron phosphate production enterprises. Through this production process, not only can zero wastewater discharge and resource recycling be achieved, creating considerable economic benefits, but also the goals of energy conservation, environmental protection, carbon reduction and emission reduction can be achieved, creating good ecological and environmental benefits.

[0115] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. This fluidized bed device is suitable for large-scale production of various series, offers good results, requires less investment, has low cost, is convenient to transport and install, and is easy to manage.

[0116] This document describes the principles and implementation methods of the present invention. The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A zero-discharge and resource-based treatment system for ferric phosphate wastewater, characterized in that, The system includes, in sequence, a plate heat exchanger, an equalization tank, a primary flocculation reaction tank (100), a secondary flocculation reaction tank (200), a fluidized bed (300), an ultrafiltration system, a two-stage concentration RO system, a multi-stage permeable RO system, and a pure water reuse tank; an MVR evaporator connected to the two-stage concentration RO system; a centrifugal compressor connected to the MVR evaporator; and a drying device connected to the centrifugal compressor. The primary flocculation reaction tank (100) is equipped with a stirring and scraping device for stirring the primary flocculation reaction tank (100) and scraping the inner wall of the primary flocculation reaction tank (100) during stirring. The secondary flocculation reaction tank (200) is equipped with a lifting and stirring device for stirring the secondary flocculation reaction tank (200). The stirring device moves up and down relative to the secondary flocculation reaction tank (200) during stirring to change the stirring position; a first rotating shaft (13) is vertically arranged in the primary flocculation reaction tank (100), and the first rotating shaft (13) has a second sliding groove (10) extending in the vertical direction. The stirring and scraping device includes a first stirring plate (8), a second stirring plate (9) and a scraping assembly. The first end of the first stirring plate (8) and the first end of the second stirring plate (9) are separated from each other and are arranged in the second sliding groove (10) and are both used to slide along the second sliding groove (10). The second end of the first stirring plate (8) and the second end of the second stirring plate (9) are both connected to the scraping assembly. The scraping assembly is used to abut against the inner wall of the primary flocculation reaction tank (100). The stirring and scraping device further includes two second sliders (11) respectively disposed in the second slide groove (10), and two second springs (12) corresponding to and abutting against the two second sliders (11). The second springs (12) press against the end of the second slider (11) away from the other second slider (11). The first end of the first stirring plate (8) is hinged to one of the second sliders (11), and the first end of the second stirring plate (9) is hinged to the other second slider (11). The scraping assembly includes a mounting plate (5) and a device connected to the mounting plate (5). The mounting plate (5) includes a detachable scraper (6), a first slider (3) and a first spring, and a first groove (4) is provided in the mounting plate (5) along the radial direction of the first rotating shaft (13). The first slider (3) is embedded in the first groove (4) and is used to slide along the first groove (4). The first spring is pressed at both ends of the first slider (3) along its sliding direction. The first end of the first stirring plate (8) is fixedly connected to the first slider (3), and the first end of the second stirring plate (9) is hinged to the first slider (3).

2. The zero-discharge and resource-based treatment system for ferric phosphate wastewater according to claim 1, characterized in that, The secondary flocculation reaction tank (200) is provided with a second rotating shaft (24) and a guide rod (28) located on one side of the second rotating shaft (24) and parallel to the second rotating shaft (24). The second rotating shaft (24) is provided with an outer filament segment. The lifting and stirring device includes a first mounting plate (25) sleeved on the outer filament segment of the second rotating shaft (24) and used to be driven to lift and lower when the second rotating shaft (24) rotates. The outer ring of the first mounting plate (25) is provided with a limiting ring (27). The guide rod (28) passes through the limiting ring (27). The first mounting plate (25) is provided with stirring blades (26). The end of the stirring blades (26) away from the first mounting plate (25) is provided with a roller (41). The limiting ring (27) is provided with an annular limiting groove (42) coaxial with the second rotating shaft (24). The roller (41) is embedded in the annular limiting groove (42) and used to roll along the annular limiting groove (42).

3. The zero-discharge and resource-based treatment system for ferric phosphate wastewater according to claim 2, characterized in that, The lifting and stirring device further includes a second mounting plate (29) sleeved on the outer thread section of the second rotating shaft (24) and used to be driven to lift and lower when the second rotating shaft (24) rotates, a limiting rod (30) connected to the second mounting plate (29), and a plurality of swing rod assemblies (33) arranged on the outer periphery of the second mounting plate (29); the guide rod (28) passes through the limiting rod (30), and the swing rod assembly (33) includes a swing member (34) and mounting rods (31) arranged in a ring array on the outside of the second mounting plate (29), and the mounting rods (31) have a third groove (32) opened in the radial direction of the second rotating shaft (24). The third slide (32) is slidably provided with a third slider (37), and a limiting post is provided on one side of the third slider (37). The first end of the swing member (34) is hinged to the inner wall of the secondary flocculation reaction tank (200). A fourth slide (36) is provided on the swing member (34). The limiting post passes through the fourth slide (36) and is used to slide along the fourth slide (36) when the second mounting plate (29) moves up and down, thereby driving the swing member (34) to swing and achieve the stirring effect. The swing member (34) is a V-shaped plate structure, and through holes are provided at intervals on the swing member (34) for allowing ferric phosphate wastewater to flow through to form turbulence.

4. The zero-discharge and resource-based treatment system for ferric phosphate wastewater according to claim 1, characterized in that, The fluidized bed includes an outer cylinder and an inner reaction cylinder located inside the outer cylinder, as well as an aeration device located in the inner reaction cylinder. The inner reaction cylinder is a cylindrical structure with an open top, a narrowing middle section, and a sealed bottom. There is a gap between the inner reaction cylinder and the outer cylinder. An air inlet pipe is provided at the top of the outer cylinder, which extends into the inner reaction cylinder and is connected to the aeration device. A crystal discharge port is provided at the bottom of the outer cylinder. A water inlet pipe is provided on the lower part of the outer cylinder wall, which extends into the inner reaction cylinder. A water outlet pipe is provided at the top of the outer cylinder. A feed pipe for adding seed crystals to the inner reaction cylinder is provided on the outer cylinder wall.

5. A method for zero-discharge and resource-based treatment of ferric phosphate wastewater, employing the zero-discharge and resource-based treatment system for ferric phosphate wastewater as described in any one of claims 1-4, characterized in that, The process includes the following steps: S100, Preprocessing: S101: Heat exchange and cooling treatment of ferric phosphate wastewater; S102: The ferric phosphate wastewater after heat exchange and cooling is transported to the equalization tank for homogenization and mass equalization treatment. S103: The ferric phosphate wastewater that has been treated by equalization and homogenization enters the primary flocculation reaction tank (100) and ammonia water is added to carry out flocculation reaction. The stirring and scraping device is started to stir the primary flocculation reaction tank (100) and scrape the inner wall of the primary flocculation reaction tank (100) clean during stirring. S104: The supernatant of the primary flocculation reaction tank (100) enters the secondary flocculation reaction tank (200) and ammonia water is added to the secondary flocculation reaction tank (200) for flocculation reaction. The lifting and stirring device is started to stir the secondary flocculation reaction tank (200) and moves up and down relative to the secondary flocculation reaction tank (200) to change the stirring position during stirring. S200, membrane treatment: S201: The permeate from the secondary flocculation reactor (200) enters the ultrafiltration system after being filtered through the fluidized bed (300); S202: Permeate from the ultrafiltration system is pumped into a two-stage RO (reinforcement) system; S203: Permeate from the two-stage concentration RO system enters the multi-stage permeate RO system; S204: Permeate from the multi-stage RO system flows into the pure water reuse tank; S300, Evaporation and Crystallization: S301: The concentrate from the two-stage RO system is evaporated, crystallized, and centrifuged to produce byproducts.

6. The method for zero discharge and resource utilization treatment of ferric phosphate wastewater according to claim 5, characterized in that, In step S101, the temperature of the ferric phosphate wastewater is reduced to below 35°C by a plate heat exchanger. In step S103, ammonia water is added to the primary flocculation reaction tank (100) to adjust the pH to 5-5.5; the sludge settled in the primary flocculation reaction tank (100) in step S103 is dewatered by a plate and frame filter press to form sludge cake, and the filtrate after dewatering is returned to the equalization tank. In step S104, ammonia water is added to the secondary flocculation reaction tank (200) to adjust the pH to 8.5-9.5; in step S201, the fluidized bed (300) uses one or more of the following granular fillers as seed crystals: micro-sand quartz sand with a specification of 0.3-1mm, anthracite, activated carbon, zeolite, volcanic rock, and ceramsite. The fluidized wastewater is further filtered by a multi-media or manganese sand filter to remove iron and manganese substances and fine particulate matter. Before entering the ultrafiltration process, sulfuric acid is added to adjust the pH to a neutral to slightly acidic environment. A 100-200µm security filter is installed before the system; in step S202, the first stage of the two-stage concentration RO system has a water production rate of 50%-60% and the second stage has a water production rate of 75%-80%, with the TDS after concentration being higher than 150,000 mg / L, and the total concentration of Mg / Ca / Mn / Fe / F controlled to be <20ppm; in step S204, the total desalination rate of the multi-stage water production RO system reaches 99.99%, the total water production rate is higher than 95%, and the conductivity of the produced water is ≤10µs / cm.

7. The method for zero discharge and resource utilization treatment of ferric phosphate wastewater according to claim 5, characterized in that, Step S301 specifically includes: using a combined process of preheating + two-stage double-effect falling film evaporation + forced circulation evaporation thermal crystallization + centrifugal drying to treat the concentrate from the two-stage concentration RO system. In the preheating stage, heat is recovered by setting up a preheater. After preheating, the material concentration of the first-effect falling film evaporator is controlled at 20%-22%, and the design boiling point is raised by 2-3℃. The material concentration of the second-effect falling film evaporator is controlled at 38%-40%, and the design boiling point is raised by 5-6℃. When entering the forced circulation evaporation, the design boiling point is raised by 8-9℃. Subsequently, the centrifugal drying process uses a centrifugal compressor as the evaporation and heating device, and uses an automatic double centrifuge to achieve solid-liquid separation. The ammonium sulfate crystals after centrifugal separation are transported to a drying system using an ammonium sulfate vibrating fluidized bed or drum dryer for drying. After drying, ammonium sulfate by-product is produced.

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