A method for treating wastewater from a process for preparing iron phosphate by mixing phosphorus and sulfur

Abstract

The application provides a wastewater treatment method for a phosphorus-sulfur mixed preparation process of iron phosphate, in which cleaning wastewater and mother liquor are pretreated through an electro-catalytic oxidation technology and a polytetrafluoroethylene tubular membrane, concentrated to the highest degree through a high-multiple-concentration membrane, and finally evaporated and crystallized to obtain a sodium sulfate product. The treatment method has a small occupied area, can not only recover the sodium sulfate product, but also realize water reuse in the whole process, reduces the operation cost of an enterprise, and reduces the total amount of pollutant emissions.

Description

Technical Field

[0001] This invention belongs to the technical field of wastewater treatment, specifically relating to a wastewater treatment method for the process of preparing iron phosphate from phosphorus and sulfur mixtures. Background Technology

[0002] Ferric phosphate is a widely used chemical raw material. It can be used as an iron supplement in food, as well as in pigments, catalysts for organic synthesis, and ceramic and metal glazes. Its main application at present is in the preparation of battery materials.

[0003] Iron phosphate (FeFe) is used as a precursor in the preparation of lithium iron phosphate (LFP) and sodium iron phosphate (SOF). Compared to other lithium battery cathode materials, this type of battery using LFP or SOF as the cathode is highly regarded for its superior safety, long lifespan, high energy density, fast charging capability, environmental friendliness, and excellent high-temperature performance. Its thermal stability under high temperature or overcharge conditions, and its resistance to thermal runaway or combustion, make it stand out in terms of safety. Furthermore, their cycle life far exceeds that of traditional lead-acid batteries, reaching over 2000 cycles, meaning a theoretical lifespan of 7 to 8 years under standard charging conditions. Because they do not contain heavy metals or rare metals, LFP and SOF batteries are environmentally friendly and meet the requirements of green energy and sustainable development.

[0004] However, the production of ferric phosphate inevitably generates industrial wastewater. In particular, the wastewater generated in the mixed phosphorus-sulfur ferric phosphate production process is more complex in composition than that from conventional ferric phosphate production. This process produces two streams of wastewater: the filtrate from the plate and frame filter press, known as the mother liquor, and the washing wastewater from the ferric phosphate process. Both streams contain large amounts of ammonia nitrogen, heavy metal ions (such as iron and manganese ions), hardness ions (such as calcium and magnesium ions), and a large amount of organic matter, resulting in high COD values. Therefore, it is necessary to implement zero-discharge treatment for this type of industrial wastewater to avoid environmental pollution.

[0005] Currently, the common method for treating industrial wastewater from ferric phosphate production is coagulation and sedimentation to remove impurities such as calcium, magnesium, and iron ions. This method not only has poor sedimentation efficiency and requires a large area, but also introduces substances like PAC and PAM, affecting the effectiveness of subsequent membrane treatment. Furthermore, current membrane concentration technology can only concentrate the TDS of the brine to 100,000–120,000 mg / L, leading to high loads on subsequent evaporation systems, poor treatment efficiency, and low reclaimed water reuse rates. Summary of the Invention

[0006] The purpose of this invention is to solve the technical problems in the prior art of treating industrial wastewater after the preparation of ferric phosphate, which involves a large footprint, high load on the subsequent evaporation system, poor treatment effect, and low water reuse rate. Therefore, this invention provides a wastewater treatment method for the ferric phosphate preparation process using a phosphorus-sulfur mixture, which has a small footprint and can not only recover sodium sulfate products but also achieve water reuse throughout the entire process, thereby reducing enterprise operating costs and reducing the total amount of pollutant emissions.

[0007] To solve the above problems, the present invention is implemented according to the following technical solution:

[0008] This invention provides a wastewater treatment method for the preparation of iron phosphate from phosphorus and sulfur mixtures, the method comprising the following wastewater treatment steps:

[0009] The cleaning wastewater is transported to the first electrocatalytic oxidation unit for reaction, and the reacted cleaning wastewater is transported to the first polytetrafluoroethylene tubular membrane unit for reaction, wherein sodium hydroxide and sodium carbonate are added to the first polytetrafluoroethylene tubular membrane unit.

[0010] The cleaning wastewater after the reaction in the first polytetrafluoroethylene tubular membrane device is fed into the first-stage RO system; the concentrate produced by the first-stage RO system is fed into the second-stage RO system.

[0011] The concentrate produced by the secondary RO system is fed into the first high-concentration membrane device, the concentrate produced by the first high-concentration membrane device is fed into the brine tank, and the desalinated water produced by the first high-concentration membrane device is returned to the secondary RO system for further treatment.

[0012] In a preferred embodiment, the freshwater produced by the primary RO system is fed into the permeate RO system for treatment; the freshwater produced by the secondary RO system is fed into the permeate RO system for treatment; and the concentrate produced by the permeate RO system is returned to the primary RO system for further treatment.

[0013] In a preferred embodiment, the membrane of the primary RO system is a brackish water reverse osmosis membrane, and the membrane of the secondary RO system is a seawater desalination membrane.

[0014] In a preferred embodiment, the method further includes the following mother liquor treatment steps: the mother liquor is transported to a second electrocatalytic oxidation device for reaction; the reacted mother liquor is transported to a second polytetrafluoroethylene tubular membrane device for reaction, wherein sodium hydroxide and sodium carbonate are added to the second polytetrafluoroethylene tubular membrane device; the mother liquor after reaction in the second polytetrafluoroethylene tubular membrane device is input into a second high-concentration membrane device; and the mother liquor after treatment in the second high-concentration membrane device is input into a concentrated brine tank.

[0015] In a preferred embodiment, the concentrated water and mother liquor from the brine tank are transported to an evaporator to obtain a concentrated liquid and condensate; the concentrated liquid is fed into a centrifuge to separate precipitate and liquid; the condensate is fed into a heat exchanger for cooling and then fed into the product water RO system for further treatment; the precipitate is fed into a dryer for treatment to obtain sodium sulfate; and the liquid is dried to obtain mixed salts.

[0016] In a preferred embodiment, the first electrocatalytic oxidation device and the second electrocatalytic oxidation device are electrocatalytic oxidation devices with porous anodes; or, the first electrocatalytic oxidation device and the second electrocatalytic oxidation device are three-dimensional electrocatalytic oxidation devices.

[0017] In a preferred embodiment, both the first PTFE tubular membrane device and the second PTFE tubular membrane device have a concentrate circulation system and an exhaust system; the first high-concentration membrane device and the second high-concentration membrane device are high-pressure nanofiltration devices or medium-low pressure reverse osmosis devices with a certain salt permeability.

[0018] In a preferred embodiment, the evaporation device is an MVR evaporation device or a multi-effect evaporation device; the centrifuge is a two-stage pusher centrifuge; and the dryer is a vibrating fluidized bed dryer.

[0019] As a preferred embodiment, the method for obtaining mixed salts by drying the liquid is as follows: the liquid is dried using a low-temperature scraper or drum dryer.

[0020] In a preferred embodiment, the pH range of the effluent from the first and second PTFE tubular membrane devices is 10-11; the TDS of the concentrate produced by the secondary RO system is 100,000-120,000 mg / L; the conductivity of the desalinated water produced by the permeate RO system is less than 10 μS / cm; and the TDS of the concentrate produced by the first and second high-concentration membrane devices is 200,000 mg / L.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] This invention provides a wastewater treatment method for the preparation of iron phosphate from phosphorus and sulfur. The method involves pretreating the washing wastewater and mother liquor using electrocatalytic oxidation and a polytetrafluoroethylene (PTFE) tubular membrane, followed by high-concentration using a high-concentration membrane, and finally obtaining sodium sulfate product through evaporation and crystallization. This treatment method requires a small footprint and not only recovers sodium sulfate product but also enables water reuse throughout the entire process, reducing operating costs and overall pollutant emissions.

[0023] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0024] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings, wherein:

[0025] Figure 1 This is a technical structural diagram of a wastewater treatment method for a phosphorus-sulfur mixed process for preparing ferric phosphate according to the present invention.

[0026] Figure 2 This is an example diagram of a preferred embodiment of the present invention;

[0027] In the picture:

[0028] 11-Wastewater cleaning tank; 12-First electrocatalytic oxidation device; 13-First polytetrafluoroethylene tubular membrane device;

[0029] 21- Primary RO system, 22- Secondary RO system, 23- Permeate RO system, 24- Reclaimed water tank;

[0030] 31-Mother liquor tank, 32-Second electrocatalytic oxidation device, 33-Second polytetrafluoroethylene tubular membrane device;

[0031] 41-First high-concentration membrane unit, 42-Second high-concentration membrane unit, 43-Concentrated brine tank;

[0032] 51-Evaporation device, 52-Heat exchanger, 53-Centrifuge, 54-Dryer, 55-Sodium sulfate collection tank, 56-Liquid drying device, 57-Miscellaneous salt collection tank;

[0033] 60 - Sludge collection tank. Detailed Implementation

[0034] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0035] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. Unless otherwise defined, the technical or scientific terms used in this specification should have the ordinary meaning understood by one of ordinary skill in the art to which this application pertains. The terms "first," "second," and similar words used in this specification and claims do not indicate any order, quantity, or importance, but are merely used to distinguish different technical features.

[0036] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0037] To address the technical problems of existing technologies for treating industrial wastewater from the preparation of ferric phosphate, which involve large land area requirements, high load on subsequent evaporation systems, poor treatment efficiency, and low water reuse rates, this invention provides a wastewater treatment method for the phosphorus-sulfur mixed process of ferric phosphate preparation. This method not only requires a small land area but also recovers sodium sulfate products and enables water reuse throughout the entire process, reducing enterprise operating costs and total pollutant emissions. It offers high economic, social, and environmental benefits and has promising application prospects.

[0038] Specifically, this invention provides a wastewater treatment method for the process of preparing iron phosphate from phosphorus and sulfur mixtures, the method comprising the following wastewater treatment steps:

[0039] (1) The cleaning wastewater is transported to the first electrocatalytic oxidation device for reaction, and the reacted cleaning wastewater is transported to the first polytetrafluoroethylene tubular membrane device for reaction, wherein sodium hydroxide and sodium carbonate are added to the first polytetrafluoroethylene tubular membrane device.

[0040] It is understandable that the cleaning wastewater generated in the process of preparing iron phosphate from phosphorus and sulfur contains high concentrations of organic matter and ammonia nitrogen. Direct discharge of these pollutants without treatment would have a serious impact on the environment. Electrocatalytic oxidation is a highly efficient wastewater treatment technology capable of removing chemical oxygen demand (COD) and ammonia nitrogen from wastewater. Specifically, the cleaning wastewater is fed into the first electrocatalytic oxidation unit. During the electrocatalytic oxidation process, a voltage is applied to generate highly oxidizing hydroxyl radicals. These hydroxyl radicals can react non-selectively with the organic matter in the wastewater, mineralizing it into carbon dioxide and water, thereby reducing the COD value. During electrocatalysis, the electric field promotes the migration and mass transfer of pollutants, increasing the contact efficiency between pollutants and the catalytic surface, thus increasing the oxidation reaction rate. Furthermore, the ammonia nitrogen in the cleaning wastewater can be oxidized into nitrogen gas during electrocatalytic oxidation, thereby reducing the ammonia nitrogen content in the wastewater.

[0041] Understandably, polytetrafluoroethylene (PTFE, commonly known as Teflon) tubular membranes possess excellent chemical stability and hydrophobicity. Feeding cleaning wastewater into the first PTFE tubular membrane unit allows for the physical removal of suspended solids, colloidal particles, and larger molecules through membrane filtration, reducing the load on subsequent treatment steps. Adding sodium hydroxide adjusts the pH of the wastewater, further promoting the precipitation of metal ions. Sodium hydroxide dissolves in water to produce hydroxide ions (OH-). - Hydroxide ions can react with metal ions in wastewater to form water-insoluble metal hydroxide precipitates, such as Fe. 2+ Fe 3+ and Mg 2+ Can react with OH - The reaction produces Fe(OH)₂, Fe(OH)₃, and Mg(OH)₂ precipitates, and Mn 2+ It can generate precipitates such as Mn(OH)2, thereby removing iron, magnesium, and manganese ions from wastewater. Sodium carbonate, upon dissolving in water, produces carbonate ions (CO3-). 2- Carbonate ions can form carbonate precipitates with metal ions, for example, Ca... 2+ With CO3 2- The reaction produces CaCO3 precipitate, thereby removing calcium ions from the wastewater. These precipitates are then filtered out through a membrane in the first polytetrafluoroethylene tubular membrane unit.

[0042] (2) The cleaning wastewater after the reaction of the first polytetrafluoroethylene tubular membrane device is fed into the first-stage RO system, and the concentrate produced by the first-stage RO system is fed into the second-stage RO system.

[0043] It should be noted that RO system, or reverse osmosis system, is a membrane separation technology that uses a semi-permeable membrane to separate solutes and solvents in a solution under pressure. Wastewater is fed into an RO system, and by applying pressure higher than the osmotic pressure of the solution, water molecules are forced through the semi-permeable membrane, while dissolved solids and other impurities are retained. This effectively removes impurities from the water, including salts, minerals, bacteria, viruses, and certain chemicals, thus providing highly purified water.

[0044] (3) The concentrated water generated by the secondary RO system is fed into the first high-concentration membrane device, the concentrated water generated by the first high-concentration membrane device is fed into the concentrated brine tank, and the fresh water generated by the first high-concentration membrane device is returned to the secondary RO system for further treatment.

[0045] It should be noted that high-concentration membranes are a type of membrane technology used to achieve high concentration of solutes in high-salinity wastewater. High-concentration membrane technology can significantly reduce the processing capacity and investment costs of subsequent evaporation and crystallization equipment, reduce operating costs, and simplify the operation process. It features high concentration capacity and low energy consumption.

[0046] It should be noted that the fresh water mentioned in this invention refers to water that has been filtered through a membrane, in which most of the dissolved solids, minerals, microorganisms and other impurities are retained by the membrane. Concentrated water, on the other hand, refers to the portion of water that fails to pass through the membrane, which contains a higher concentration of dissolved solids and impurities because these substances are blocked and concentrated by the membrane.

[0047] Specifically, the TDS of the concentrate produced by the secondary RO system is 100,000-120,000 mg / L.

[0048] Specifically, the freshwater produced by the primary RO system is fed into the permeate RO system for treatment, the freshwater produced by the secondary RO system is fed into the permeate RO system for treatment, and the concentrate produced by the permeate RO system is returned to the primary RO system for further treatment.

[0049] Specifically, the conductivity of the freshwater produced by the RO system is less than 10 μS / cm.

[0050] It should be noted that electrical conductivity is an important parameter for measuring the content of dissolved salts and other ionic substances in water; it represents the water's ability to conduct electricity. The lower the conductivity, the higher the purity of the water.

[0051] Preferably, the membrane in the primary RO system is a brackish water reverse osmosis membrane, and the membrane in the secondary RO system is a seawater desalination membrane.

[0052] It should be noted that using brackish water reverse osmosis membranes as the membrane in a primary RO system has many advantages, such as high desalination rate, high water production, strong fouling resistance, low energy consumption, and long lifespan. Using seawater desalination membranes as the membrane in a secondary RO system, on the other hand, offers advantages such as high desalination rate, low energy consumption, ease of operation, and environmental friendliness.

[0053] The wastewater treatment method for the phosphorus-sulfur mixed preparation process of ferric phosphate according to the present invention further includes the following mother liquor treatment step:

[0054] (1) The mother liquor is transported to the second electrocatalytic oxidation device for reaction, and the mother liquor after reaction is transported to the second polytetrafluoroethylene tubular membrane device for reaction, wherein sodium hydroxide and sodium carbonate are added to the second polytetrafluoroethylene tubular membrane device.

[0055] Understandably, the mother liquor produced in the phosphorus-sulfur mixed process for preparing iron phosphate contains high concentrations of organic matter and ammonia nitrogen. Electrocatalytic oxidation technology can remove the chemical oxygen demand (COD) and ammonia nitrogen from the mother liquor. The electrocatalytically oxidized mother liquor is then transported to a second polytetrafluoroethylene tubular membrane device, where sodium hydroxide and sodium carbonate are added to remove metal ions such as calcium, magnesium, iron, and manganese ions.

[0056] (2) The mother liquor after the reaction in the second polytetrafluoroethylene tubular membrane device is fed into the second high-concentration membrane device.

[0057] (3) Input the mother liquor after it has been treated by the second high-concentration membrane device into the concentrated brine tank.

[0058] Specifically, the effluent pH range in the first and second polytetrafluoroethylene (PTFE) tubular membrane units is 10-11.

[0059] Specifically, the TDS of the concentrate produced by the first and second high-concentration membrane units is 200,000 mg / L.

[0060] Specifically, the concentrated water and mother liquor fed into the concentrated brine tank are transported to the evaporation unit to obtain concentrated liquid and condensate.

[0061] Preferably, the evaporation device is an MVR evaporation device or a multi-effect evaporation device. MVR evaporation devices are characterized by high energy efficiency, low operating costs, high automation, environmental friendliness, and the ability to operate at relatively low temperatures. Multi-effect evaporation devices are characterized by low energy consumption, high thermal efficiency, high operational flexibility, and low chemical consumption.

[0062] Specifically, the concentrate is fed into a centrifuge to separate the precipitate and liquid; the condensate is fed into a heat exchanger for cooling and then fed into the product water RO system for further treatment.

[0063] Preferably, the centrifuge is a two-stage pusher centrifuge. Two-stage pusher centrifuges feature high automation, high rotational speed and separation factor, low maintenance costs, and the ability to effectively wash solid products, with washing liquid and mother liquor discharged separately, ensuring solid purity.

[0064] Specifically, the precipitate obtained by centrifuging the concentrate is fed into a dryer for further processing to obtain sodium sulfate; the liquid obtained by centrifuging the concentrate is dried to obtain mixed salts.

[0065] Preferably, the dryer is a vibrating fluidized bed dryer. Vibrating fluidized bed dryers are characterized by high efficiency, uniform drying, energy saving, simple operation, low dust emission during the drying process, clean working environment, and compliance with environmental protection requirements.

[0066] Preferably, the liquid is dried using a low-temperature scraper or drum dryer to obtain mixed salts. Mixed salts refer to various inorganic salts present in the mother liquor, which can be recycled or disposed of as waste. Preferably, the present invention outsources the disposal of the mixed salts.

[0067] In a preferred embodiment, the first and second electrocatalytic oxidation devices are electrocatalytic oxidation devices with porous anodes. Electrocatalytic oxidation devices with porous anodes exhibit high catalytic activity, stable electrode dimensions, long service life, and strong corrosion resistance during the electrocatalytic oxidation process. Furthermore, the porous anode electrode does not produce dissolution contamination and can operate at lower voltages, saving energy consumption.

[0068] In another preferred embodiment, the first and second electrocatalytic oxidation devices are three-dimensional electrocatalytic oxidation devices. Three-dimensional electrocatalytic oxidation devices have high processing capacity, low cost, and are easy to operate. Compared with traditional two-dimensional electrocatalytic oxidation technology, the three-dimensional technology increases the number of catalytic active sites on the electrode surface, thereby improving the efficiency of the catalytic oxidation reaction.

[0069] In a preferred embodiment, both the first PTFE tubular membrane device and the second PTFE tubular membrane device have a concentrate circulation system and an exhaust system.

[0070] In a preferred embodiment, the first high-concentration membrane device and the second high-concentration membrane device are high-pressure nanofiltration devices or medium-to-low-pressure reverse osmosis devices with a certain salt permeability. High-pressure nanofiltration devices have the characteristics of high treatment efficiency, low energy consumption, low operating costs, and long service life. Medium-to-low-pressure reverse osmosis devices with a certain salt permeability have the characteristics of high desalination rate, energy saving, low operating costs, and environmental friendliness.

[0071] In summary, the wastewater treatment method for the preparation of ferric phosphate from a mixed phosphorus and sulfur acid process provided by this invention organically combines electrocatalytic oxidation technology with a polytetrafluoroethylene tubular membrane. This method can remove impurities from the wastewater in the process of preparing ferric phosphate from a mixed phosphorus and sulfur acid. After treatment, the wastewater is concentrated by RO membrane and high-concentration membrane to achieve the lowest possible evaporation. Then, it is passed through an evaporation crystallization device to achieve zero wastewater discharge and obtain sodium sulfate product. This treatment method has a small footprint and can not only recover sodium sulfate product but also achieve water reuse throughout the entire process, reducing enterprise operating costs and the total amount of pollutants discharged.

[0072] The present invention discloses a wastewater treatment method for a phosphorus-sulfur mixed process for preparing ferric phosphate, which is based on a wastewater treatment system for the same process. This system includes: a cleaning wastewater tank 11, a first electrocatalytic oxidation device 12, a first polytetrafluoroethylene tubular membrane device 13, a primary RO system 21, a secondary RO system 22, a product water RO system 23, a recycled water tank 24, a mother liquor tank 31, a second electrocatalytic oxidation device 32, a second polytetrafluoroethylene tubular membrane device 33, a first high-concentration membrane device 41, a second high-concentration membrane device 42, a concentrated brine tank 43, an evaporator 51, a heat exchanger 52, a centrifuge 53, a dryer 54, a sodium sulfate collection tank 55, a liquid drying device 56, a miscellaneous salt collection tank 57, and a sludge collection tank 60.

[0073] like Figure 1 As shown, in a preferred embodiment of the present invention, in a first aspect, cleaning wastewater is transported from cleaning wastewater tank 11 to a first electrocatalytic oxidation device 12. After reducing the organic matter and ammonia nitrogen content in the water using electrocatalytic oxidation technology, the cleaning wastewater is then transported to a first polytetrafluoroethylene tubular membrane device 13, where sodium hydroxide and sodium carbonate are added. After reacting to generate precipitates, the precipitates are separated from the liquid using membrane filtration to remove metal ions such as iron and magnesium ions from the wastewater. The effluent from the first polytetrafluoroethylene tubular membrane device 13 is then input into a primary RO system 21. On one hand, the concentrated water produced by the primary RO system 21 enters a secondary RO system 22, and the concentrated water produced by the secondary RO system 22 is input into a first high-concentration membrane device 41. The concentrated water produced by the first high-concentration membrane device 41 is then transported to a concentrated brine tank 43. On the other hand, the desalinated water produced by the primary RO system 21 enters a permeate RO system 23, the desalinated water produced by the secondary RO system 22 enters a permeate RO system 23, and the desalinated water produced by the first high-concentration membrane device 41 flows back to the secondary RO system 22 for further treatment. The fresh water produced by the permeate RO system 23 is transported to the recycled water tank 24, while the concentrated water produced by the permeate RO system 23 flows back to the primary RO system 21 for further treatment.

[0074] Secondly, the mother liquor is transported from the mother liquor tank 31 to the second electrocatalytic oxidation device 32. After reducing the organic matter and ammonia nitrogen content in the water using electrocatalytic oxidation technology, the mother liquor is then transported to the second polytetrafluoroethylene tubular membrane device 33, where sodium hydroxide and sodium carbonate are added. After the reaction produces precipitate, the precipitate is separated from the liquid using membrane filtration to remove metal ions such as iron and magnesium ions from the mother liquor. The effluent from the second polytetrafluoroethylene tubular membrane device 33 is then fed into the second high-concentration membrane device 42. The mother liquor treated by the second high-concentration membrane device 42 is then transported to the second high-concentration membrane device 43.

[0075] Thirdly, the sludge produced after being processed by the first polytetrafluoroethylene tubular membrane device 13 and the second polytetrafluoroethylene tubular membrane device 33 is transported to the sludge collection tank 60.

[0076] Fourthly, the concentrated water and mother liquor input into the concentrated brine tank 43 are transported to the evaporator 51. After evaporation, the resulting condensate enters the heat exchanger 52 for cooling. The cooled condensate is then transported to the product water RO system 23 for further treatment. The concentrated liquid obtained after evaporation is input into the centrifuge 53, where it is processed to obtain precipitate and liquid. The precipitate is transported to the dryer 54 for drying to obtain sodium sulfate, which is collected in the sodium sulfate collection tank 55. The liquid is transported to the liquid drying device 56 for drying to obtain mixed salts, which are collected in the mixed salt collection tank 57.

[0077] In one specific embodiment, the cleaning wastewater to be treated has a flow rate of 10,000 m³ / d, with an influent pH of 2.3, total phosphorus of 200 mg / L, TDS of 20,000 mg / L, ammonia nitrogen of 50 mg / L, COD of 500 mg / L, total iron of 100 mg / L, calcium ions of 30 mg / L, and manganese ions of 10 mg / L. The mother liquor to be treated has a flow rate of 2,400 m³ / d, with a pH of 2, total phosphorus of 1,000 mg / L, TDS of 150,000 mg / L, ammonia nitrogen of 20 mg / L, COD of 500 mg / L, total iron of 500 mg / L, calcium ions of 100 mg / L, and manganese ions of 300 mg / L. After treatment by the wastewater treatment method for the phosphorus-sulfur mixed process for preparing iron phosphate provided by this invention, zero discharge of cleaning wastewater and mother liquor is achieved, the reclaimed water is returned to the original system for reuse, and the sodium sulfate meets the industrial standard for anhydrous sodium sulfate.

[0078] Other technologies for the wastewater treatment method of the phosphorus-sulfur mixed preparation process for iron phosphate described in this embodiment are found in the prior art.

[0079] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Therefore, any modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A wastewater treatment method for a process for the preparation of iron phosphate from phosphosulphuric acid, characterized in that, The method comprises the following cleaning wastewater treatment steps: The cleaning wastewater is sent to the first electro-catalytic oxidation device for reaction, and the reacted cleaning wastewater is sent to the first polytetrafluoroethylene tubular membrane device for reaction, wherein the first polytetrafluoroethylene tubular membrane device is added with sodium hydroxide and sodium carbonate; The cleaning wastewater reacted by the first polytetrafluoroethylene tubular membrane device is input into the primary RO system; the concentrated water generated by the primary RO system is input into the secondary RO system; The concentrated water generated by the secondary RO system is input into the first high-concentration membrane device, the concentrated water generated by the first high-concentration membrane device is input into the concentrated brine tank, and the fresh water generated by the first high-concentration membrane device is backflowed to the secondary RO system for reprocessing; The fresh water generated by the primary RO system is input into the water production RO system for processing; The fresh water generated by the secondary RO system is input into the water production RO system for processing; The concentrated water generated by the water production RO system is backflowed to the primary RO system for reprocessing; The method further comprises the following mother liquor treatment steps: The mother liquor is sent to the second electro-catalytic oxidation device for reaction, and the reacted mother liquor is sent to the second polytetrafluoroethylene tubular membrane device for reaction, wherein the second polytetrafluoroethylene tubular membrane device is added with sodium hydroxide and sodium carbonate; The mother liquor reacted by the second polytetrafluoroethylene tubular membrane device is input into the second high-concentration membrane device; The mother liquor processed by the second high-concentration membrane device is input into the concentrated brine tank; The concentrated water and the mother liquor input into the concentrated brine tank are sent to the evaporation device to obtain concentrated liquid and condensed water; The concentrated liquid is input into the centrifuge to separate to obtain precipitate and liquid; the condensed water is input into the heat exchanger for cooling and then input into the water production RO system for reprocessing; The precipitate is input into the dryer for processing to obtain sodium sulfate; and the liquid is dried to obtain miscellaneous salt.

2. The wastewater treatment method of the phosphorus-sulfur mixed preparation process of the iron phosphate according to claim 1, characterized in that: The membrane of the primary RO system is a brackish water reverse osmosis membrane, and the membrane of the secondary RO system is a seawater desalination membrane.

3. The wastewater treatment method of the phosphorus-sulfur mixed preparation process of the iron phosphate according to claim 1, characterized in that: The first electro-catalytic oxidation device and the second electro-catalytic oxidation device are electro-catalytic oxidation devices with porous anodes; or the first electro-catalytic oxidation device and the second electro-catalytic oxidation device are three-dimensional electro-catalytic oxidation devices.

4. The wastewater treatment method of the phosphorus-sulfur mixed preparation process of the iron phosphate according to claim 1, characterized in that: The first polytetrafluoroethylene tubular membrane device and the second polytetrafluoroethylene tubular membrane device both have concentrated water circulation systems and exhaust systems; The first high-concentration membrane device and the second high-concentration membrane device are high-pressure nanofiltration devices or medium-low pressure reverse osmosis devices with a certain salt permeation rate.

5. The wastewater treatment method of the phosphorus-sulfur mixed preparation process of the iron phosphate according to claim 1, characterized in that: The evaporation device is an MVR evaporation device or a multi-effect evaporation device; The centrifuge is a double-stage pusher centrifuge. The dryer is a vibrating fluidized bed dryer.

6. The method of claim 1, wherein the method is characterized by, The method for drying the liquid to obtain the mixed salt is: The liquid is dried by using a low-temperature scraper or roller drying equipment.

7. The wastewater treatment method of a phosphorus-sulfur mixed process for preparing iron phosphate according to any one of claims 1-6, characterized in that: The pH value of the effluent from the first and second polytetrafluoroethylene tubular membrane devices ranges from 10 to 11; The TDS of the concentrated water produced by the secondary RO system is 10-12 million mg / L; The water producing RO system produces fresh water with a conductivity of less than 10 ; The TDS of the concentrated water produced by the first and second high-concentration membrane devices is 20 million mg / L.

Images