Iron phosphate wastewater treatment method and system

Abstract

This invention relates to the technical field of ferric phosphate wastewater, specifically to a method and system for treating ferric phosphate wastewater. The treatment method includes the following steps: pretreating ferric phosphate washing wastewater, followed by solid-liquid separation to obtain a first clear liquid and a first precipitate; adding a reducing agent to the first precipitate for dissolution, and adjusting the pH to 1.8-2.0 with acid to obtain a second clear liquid; adjusting the pH of the second clear liquid to 5.2-5.7, and performing solid-liquid separation to obtain a third clear liquid; adjusting the pH of the third clear liquid to 6.8-7.2, and performing solid-liquid separation to obtain a second precipitate; adjusting the pH of the first clear liquid to 8.3-8.5, and performing solid-liquid separation to obtain a third precipitate. This invention, by adjusting the ferric phosphate wastewater to different pH values ​​at different stages, can selectively remove different metal elements under different pH conditions, enabling the classified collection of different metal element precipitates and creating greater economic value.

Description

Technical Field

[0001] This invention relates to the technical field of ferric phosphate wastewater, and specifically to a method and system for treating ferric phosphate wastewater. Background Technology

[0002] In recent years, with the rapid development of the new energy industry, lithium batteries have become increasingly popular due to their advantages such as large energy storage capacity, long lifespan, good economic efficiency, and high safety. Lithium iron phosphate is one of the main commercially available lithium battery cathode materials both domestically and internationally, and its market demand continues to grow. As a precursor for the production of lithium iron phosphate cathode materials, the demand for iron phosphate is also increasing year by year.

[0003] The production of ferric phosphate involves processes such as synthesis, washing, aging, and evaporation drying. The wastewater generated includes washing water. The treatment of ferric phosphate washing water usually involves processes such as precipitation, filtration, and reverse osmosis to produce pure water for reuse at the upstream end. Because ferric phosphate washing water contains a large number of metal element impurities, most of the metal impurities need to be pretreated and precipitated before entering the filtration membrane process.

[0004] Current pretreatment processes typically involve adding ammonia to adjust the pH to 8.5, precipitating elements such as calcium, magnesium, manganese, and iron, ultimately producing phosphate fertilizer. This method precipitates various impurity metals together, creating a mixed phosphate fertilizer. This not only results in low-value fertilizer, but the removal of manganese and iron from the wash water is highly dependent on the phosphorus content and ammonia dosage, leading to unstable removal rates. This can cause manganese and iron to enter subsequent processing stages, causing membrane fouling and damage. Furthermore, this process consumes large amounts of ammonia and sulfuric acid, resulting in high reagent costs and an overall high cost for wastewater treatment. Summary of the Invention

[0005] In view of the technical problems existing in the background art, this application provides a method and system for treating ferric phosphate wastewater, which aims to solve the technical problems of unstable removal rates of manganese and iron elements in the current treatment process, which easily leads to fouling and membrane oxidation in subsequent process links.

[0006] In a first aspect, embodiments of this application provide a method for treating ferric phosphate wastewater, comprising the following steps: The wastewater from washing with ferric phosphate was pretreated and then separated into solid and liquid components to obtain a first clear liquid and a first precipitate. A reducing agent is added to the first precipitate to dissolve it, and acid is added to adjust the pH to 1.8-2.0 to obtain the second clear solution; The pH of the second clear liquid was adjusted to 5.2-5.7, and after solid-liquid separation, a third clear liquid was obtained. The pH of the third supernatant was adjusted to 6.8-7.2, and a second precipitate was obtained by solid-liquid separation. The pH of the first supernatant was adjusted to 8.3-8.5, and a third precipitate was obtained by solid-liquid separation.

[0007] In the technical solution of this application embodiment, the pH value of ferric phosphate wastewater is adjusted to different values ​​at different stages. Different metal elements are removed in a targeted manner under different pH conditions, which effectively improves the removal rate and reduces the treatment cost of ferric phosphate wastewater. Simultaneously, the stepwise precipitation method is less dependent on the phosphorus content in the wastewater, and the removal rate is more stable. This method can better reduce the amount of manganese and ferric elements entering the membrane treatment stage, reducing membrane fouling and oxidative damage, thereby lowering the costs of membrane washing and replacement. Through the technical solution of this application embodiment, different metal elements can be removed in a targeted manner under different pH conditions. After the different metal element precipitates are collected separately, they are then subjected to different recovery treatments, ultimately producing magnesium, manganese, and ferric elements into by-products with higher purity and higher value.

[0008] In some embodiments, the preprocessing step includes: The pH of the ferric phosphate washing wastewater was adjusted to 6.8-7.2 by adding alkaline solution and adding bisulfite solution; The alkaline solution is one or more of ammonia, sodium hydroxide, and potassium hydroxide.

[0009] In this embodiment, by adding alkaline solution and bisulfite solution to adjust the pH to 6.8-7.2, and simultaneously under stirring and aeration conditions, manganese in the water will form a black manganese dioxide precipitate, and iron will form ferric hydroxide precipitate, thereby removing manganese and iron from the water. The principle is as follows: HSO3 - Under weakly acidic to neutral and aerobic conditions, simultaneously subjected to Fe in water 3+ and Mn 2+ Ion catalysis activates and generates sulfate free radicals ( ), sulfite free radicals ( ) and persulfate free radicals ( Various active substances with high oxidation potentials, such as ), react as follows: Fe 3+ +HSO3 - +O2→Fe 2+ +H + + +Mn(Ⅱ)+H + →HSO5 - +Mn(Ⅲ) Mn(Ⅲ) + SO3 2- / HSO3 - →Mn(Ⅱ)+ +HSO3 - →HSO5 - + +SO3 2- → +SO4 2- , and These active substances have strong oxidizing properties; Mn in water... 2+ exist Under the influence of [the substance], an oxidation reaction occurs to form MnO2 precipitate, and the reaction is as follows: 2 +2Mn 2+ +H₂O→MnO₂↓+Mn 2+ +SO4 2- +3H + In addition, there is a small amount of Mn. 2+ They will adsorb onto the MnO2 flocs and precipitate together. Under these conditions, iron ions in the solution will also form ferric hydroxide and manganese dioxide, which will co-precipitate. After this series of reactions, iron and manganese ions in the phosphorus-iron wastewater can be removed simultaneously.

[0010] In some embodiments, the concentration of the bisulfite added is 20-25 ppm; The reaction temperature for adjusting the ferric phosphate washing wastewater is 40~45℃.

[0011] In this embodiment, the concentration of bisulfite added is 20-25 ppm. The removal rate of manganese is ensured by controlling the concentration of bisulfite added. When the concentration of bisulfite added is below 20 ppm, the ideal treatment effect is not achieved, and the manganese removal rate is unsatisfactory. When the concentration of bisulfite added is above 25 ppm, it acts as a reducing agent for the already generated manganese dioxide, dissolving the solid manganese dioxide.

[0012] In some embodiments, the first precipitate includes at least ferric hydroxide and manganese dioxide, and the reducing agent is one or more of sodium sulfite, sodium bisulfite, and sodium thiosulfate. The molar ratio of the reducing agent to manganese dioxide is 1.2:1 to 1.5:1, and the molar ratio of the reducing agent to ferric hydroxide is 0.6:1 to 0.7:1.

[0013] In some embodiments, the acid solution is one or more of sulfuric acid and hydrochloric acid.

[0014] In this embodiment, the reducing agent is selected as one or more of sodium sulfite, sodium bisulfite, and sodium thiosulfate. The pH is adjusted to 1.8-2.0 by adding acid to dissolve manganese dioxide and ferric hydroxide into a solution of divalent manganese and divalent iron. The principle is that manganese dioxide and ferric hydroxide undergo a reduction reaction under the action of the reducing agent and sulfuric acid to generate divalent manganese ions and divalent iron ions. MnO2 + 2HSO3 - +2H + →Mn 2+ +2SO4 2- +2H2O Fe(OH)3+HSO3 - +2H + →Fe 2+ +2SO4 2- +2H2O.

[0015] By using a molar ratio of reducing agent to manganese dioxide of 1.2:1 to 1.5:1 and a molar ratio of reducing agent to ferric hydroxide of 0.6:1 to 0.7:1, the reducing agent is slightly in excess. This ensures complete reduction and reasonable cost control while preventing catalytic oxidation reactions from occurring again in subsequent processing steps.

[0016] In some embodiments, ammonia is added to adjust the pH of the second clear liquid to 5.2-5.7, and ferrous hydroxide precipitate is obtained by solid-liquid separation.

[0017] In this embodiment, the pH of the second clarified solution is adjusted to 5.2-5.7 by adding ammonia. Under these conditions, Fe... 2+ Ferrous hydroxide precipitate is formed, thereby removing iron ions from the water.

[0018] In some embodiments, ammonia is added to adjust the pH of the third supernatant to 6.8-7.2, and a bicarbonate solution is added; The molar ratio of bicarbonate to manganese dioxide is 2.2:1 to 2.5:1, and the bicarbonate is one or more of ammonium bicarbonate and sodium bicarbonate.

[0019] In this embodiment, after removing iron ions, the third supernatant is further treated with ammonia to bring the pH to 6.8-7.2, and bicarbonate is added simultaneously. This bicarbonate reacts with MnSO4 to produce manganese carbonate, which can be directly used as a byproduct. The specific reaction process is as follows: 2NH4HCO3+MnSO4→MnCO3+CO2↑+(NH4)2SO4+H2O.

[0020] By controlling the molar ratio of bicarbonate solution to manganese dioxide to be 2.2:1 to 2.5:1, and ensuring that the bicarbonate content is slightly excessive, all manganese elements can be converted into manganese carbonate.

[0021] In some embodiments, an alkaline solution and phosphorus-containing wastewater are added to adjust the pH value of the first clarified solution to 8.3-8.5, wherein the alkaline solution is one or more of ammonia, sodium hydroxide, and potassium hydroxide.

[0022] In this embodiment, by adding alkaline solution to the iron phosphate wastewater from which manganese and iron have been removed, the pH value of the first clarified liquid is adjusted to 8.3-8.5. Magnesium in the water will be removed by forming magnesium ammonium phosphate precipitate (MgNH4PO4·6H2O).

[0023] Secondly, embodiments of this application provide a ferric phosphate wastewater treatment system, including an iron and manganese recovery section and a magnesium recovery section connected in sequence; The iron and manganese recovery section includes a primary sedimentation tank, a first sludge thickening tank, a first plate and frame filter press, and an iron and manganese recovery treatment unit connected in sequence. The magnesium recovery section includes a secondary sedimentation tank and a second sludge thickening tank connected in sequence. The outlets of the primary sedimentation tank, the first sludge thickening tank, and the first plate and frame filter press are connected to the inlet of the primary product water tank, and the outlet of the primary product water tank is connected to the inlet of the secondary sedimentation tank. The effluent from the secondary sedimentation tank is directly subjected to further treatment.

[0024] In the technical solution of this application embodiment, ferric phosphate wastewater first enters a primary sedimentation tank. Alkali and bisulfite solutions are simultaneously added at the front end of the primary sedimentation tank to adjust the pH to 6.8-7.2, causing iron and manganese ions in the wastewater to form a first precipitate. After settling in the primary sedimentation tank, the supernatant enters a primary permeate tank, while the first precipitate enters a first sludge thickening tank. The thickened precipitated sludge is then dewatered by a first plate and frame filter press. Both the permeate from the plate and frame filter press and the supernatant from the sludge thickening tank are discharged into the primary permeate tank, forming a first clear liquid. The first precipitate then enters an iron and manganese recovery treatment unit for further processing.

[0025] After the manganese and iron removal process, the ferric phosphate wastewater (first clarified liquid) enters the second sedimentation tank after passing through the primary product water tank. Alkali solution is added at the front end of the second sedimentation tank, and RO concentrate (containing a certain amount of phosphorus) is discharged at the same time to adjust the pH to 8.3~8.5. Under these conditions, the magnesium element in the water will form magnesium ammonium phosphate precipitate (MgNH4PO4·6H2O) to form the third precipitate, which enters the second sludge thickening tank and is thus removed.

[0026] In some embodiments, the iron and manganese recovery treatment unit includes a dissolving tank, an iron removal sedimentation tank, a reaction vessel, and a manganese recovery unit connected in sequence; the iron removal sedimentation tank is connected to a second plate and frame filter press, and the outlet of the second plate and frame filter press is connected to the inlet of the reaction vessel. The manganese recovery unit includes a third plate and frame filter press, a rinsing tank, a fourth plate and frame filter press, and a dryer connected in sequence, and the reaction vessel is connected to the third plate and frame filter press.

[0027] In this embodiment, the first precipitate enters a dissolving tank, where excess reducing agent and acid are added to adjust the pH to 1.8-2.0, converting manganese dioxide and ferric hydroxide into a solution of divalent manganese and divalent iron. This mixed solution (the second clear liquid) then enters an iron removal precipitation tank, where ammonia solution is added to adjust the pH to 5.2-5.7. Under these conditions, Fe... 2+ Ferrous hydroxide precipitate is generated, thereby removing iron ions from the water. After filtration by a second plate and frame filter press, the solid precipitate is ferrous hydroxide, and the permeate from the plate and frame filter press enters the subsequent process flow. The solution after iron ion removal (third clear liquid) enters the reaction vessel, and ammonia water is added to bring the pH value to 6.8-7.2. At the same time, bicarbonate is added to react with MnSO4 to generate manganese carbonate. After the reaction is complete, the mixed liquid is dehydrated using a third plate and frame filter press. The dehydrated manganese carbonate is rinsed with pure water in a rinsing tank and dehydrated using a fourth plate and frame filter press. The manganese carbonate after rinsing and dehydration is dried in a paddle dryer, and finally, manganese carbonate (second precipitate) byproduct is packaged.

[0028] Compared with the prior art, the beneficial effects of this application include: The treatment method and system of this application adjust the pH value of ferric phosphate wastewater to different stages, and remove different metal elements under different pH conditions. This allows for the separate collection of different metal element precipitates, followed by different recovery treatments, ultimately producing magnesium, manganese, and iron elements as higher-purity and more valuable byproducts, which can create greater economic value. Simultaneously, the stepwise precipitation method is less dependent on the phosphorus content in the wastewater, has a more stable removal rate, and can better reduce the amount of manganese and iron elements entering the membrane treatment stage, reducing membrane fouling and oxidative damage, thereby lowering membrane washing and replacement costs.

[0029] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0031] Figure 1 This is a flowchart of the processing method in the embodiments of this application; Figure 2 This is a schematic diagram of the processing system in an embodiment of this application; Explanation of reference numerals in the attached drawings: 1. Primary sedimentation tank; 2. First sludge thickening tank; 3. First plate and frame filter press; 4. Primary permeate tank; 5. Secondary sedimentation tank; 6. Second sludge thickening tank; 7. Dissolving tank; 8. Iron removal sedimentation tank; 9. Second plate and frame filter press; 10. Reactor; 11. Third plate and frame filter press; 12. Rinsing tank; 13. Fourth plate and frame filter press; 14. Dryer; 15. Wash water stabilization tank. Detailed Implementation

[0032] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0034] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0035] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0036] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0037] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0038] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0039] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0040] The current treatment process for ferric phosphate wastewater has the following problems: the removal rate of manganese and iron is unstable, which can easily cause fouling and membrane oxidation in subsequent processes; it generates mixed by-product phosphate fertilizer containing a large number of impurities, which is low in price and lacks competitive advantage in the industry; the manganese and iron in the wastewater cannot be effectively recovered, which also causes a certain waste of resources; in addition, the input cost of ammonia and sulfuric acid is high.

[0041] This application optimizes the treatment process for ferric phosphate wastewater to address the above-mentioned problems, thereby improving the removal rate of manganese and iron elements, increasing the purity and value of by-products, and reducing the treatment cost of ferric phosphate wastewater.

[0042] Please refer to Figure 1 In a first aspect, embodiments of this application provide a method for treating ferric phosphate wastewater, comprising the following steps: The wastewater from washing with ferric phosphate was pretreated and then separated into solid and liquid components to obtain a first clear liquid and a first precipitate. A reducing agent is added to the first precipitate to dissolve it, and acid is added to adjust the pH to 1.8-2.0 to obtain the second clear solution; The pH of the second clear liquid was adjusted to 5.2-5.7, and after solid-liquid separation, a third clear liquid was obtained. The pH of the third supernatant was adjusted to 6.8-7.2, and a second precipitate was obtained by solid-liquid separation. The pH of the first supernatant was adjusted to 8.3-8.5, and a third precipitate was obtained by solid-liquid separation.

[0043] In the technical solution of this application embodiment, the pH value of ferric phosphate wastewater is adjusted to different values ​​at different stages. Different metal elements are removed specifically under different pH conditions, effectively improving the removal rate and reducing the treatment cost of ferric phosphate wastewater. Simultaneously, the stepwise precipitation method is less dependent on the phosphorus content in the wastewater, resulting in a more stable removal rate. This method can better reduce the amount of manganese and ferric elements entering the membrane treatment stage, reducing membrane fouling and oxidative damage, thereby lowering the costs of membrane washing and replacement. Through the technical solution of this application embodiment, different metal elements can be removed specifically under different pH conditions. The precipitates of different metal elements are then collected and recycled, ultimately producing higher purity and higher value byproducts from magnesium, manganese, and ferric elements.

[0044] Specifically, the ferric phosphate washing wastewater is pretreated and then separated into solid and liquid components to obtain a first clear liquid and a first precipitate.

[0045] A reducing agent is added to the first precipitate to dissolve it, and acid is added to adjust the pH to 1.8-2.0, or any value within the above range, to obtain a second clear solution.

[0046] Adjust the pH of the second clear liquid to 5.2-5.7, or any value within the above range, and then perform solid-liquid separation to obtain the third clear liquid.

[0047] The pH of the third supernatant is adjusted to 6.8-7.2, or any value within the above range, and then subjected to solid-liquid separation to obtain a second precipitate.

[0048] The pH of the first supernatant is adjusted to 8.3-8.5, or any value within the above range, and a third precipitate is obtained by solid-liquid separation.

[0049] Furthermore, in some embodiments, the preprocessing step includes: The pH of the ferric phosphate washing wastewater was adjusted to 6.8-7.2 by adding alkaline solution and adding bisulfite solution; The alkaline solution is one or more of ammonia, sodium hydroxide, and potassium hydroxide.

[0050] In the technical solution of this application embodiment, by adding alkaline solution and bisulfite solution to adjust the pH to 6.8~7.2, and under the conditions of stirring and aeration, manganese in the water will form a black manganese dioxide precipitate and iron will form ferric hydroxide precipitate, thereby removing manganese and iron from the water.

[0051] The principle is as follows: HSO3 - Under weakly acidic to neutral and aerobic conditions, simultaneously subjected to Fe in water 3+ and Mn 2+ Ion catalysis activates and generates sulfate free radicals ( ), sulfite free radicals ( ) and persulfate free radicals ( Various active substances with high oxidation potentials, such as ), react as follows: Fe 3+ +HSO3 - +O2→Fe 2+ +H + + +Mn(Ⅱ)+H + →HSO5 - +Mn(Ⅲ) Mn(Ⅲ) + SO3 2- / HSO3 - →Mn(Ⅱ)+ +HSO3 - →HSO5 - + +SO3 2- → +SO4 2- , and These active substances have strong oxidizing properties; Mn in water... 2+ exist Under the influence of [the substance], an oxidation reaction occurs to form MnO2 precipitate, and the reaction is as follows: 2 +2Mn 2+ +H₂O→MnO₂↓+Mn 2+ +SO4 2- +3H + In addition, there is a small amount of Mn. 2+ They will adsorb onto the MnO2 flocs and precipitate together. Under these conditions, iron ions in the solution will also form ferric hydroxide and manganese dioxide, which will co-precipitate. After this series of reactions, iron and manganese ions in the phosphorus-iron wastewater can be removed simultaneously.

[0052] Furthermore, in some embodiments, the concentration of the bisulfite added is 20-25 ppm; The reaction temperature for adjusting the ferric phosphate washing wastewater is 40~45℃.

[0053] In the technical solution of this application embodiment, the concentration of bisulfite added is 20-25 ppm. The removal rate of manganese is ensured by controlling the concentration of bisulfite added. When the concentration of bisulfite added is below 20 ppm, the ideal treatment effect is not achieved, and the removal rate of manganese is not ideal. When the concentration of bisulfite added is above 25 ppm, it will act as a reducing agent for the already generated manganese dioxide, dissolving the already generated solid manganese dioxide.

[0054] Specifically, the concentration of the added bisulfite is 20-25 ppm, for example 20, 21, 22, 23, 24, 25 ppm, or any value within the above range.

[0055] Adjust the reaction temperature of the ferric phosphate washing wastewater to 40~45℃, for example 40, 41, 42, 43, 44, 45℃, or any value within the above range.

[0056] Furthermore, in some embodiments, the first precipitate includes at least ferric hydroxide and manganese dioxide, and the reducing agent is one or more of sodium sulfite, sodium bisulfite, and sodium thiosulfate; The molar ratio of the reducing agent to manganese dioxide is 1.2:1 to 1.5:1, and the molar ratio of the reducing agent to ferric hydroxide is 0.6:1 to 0.7:1.

[0057] Specifically, the molar ratio of the reducing agent to manganese dioxide is 1.2:1, 1.3:1, 1.4:1, 1.5:1, or any ratio within the above range.

[0058] The molar ratio of reducing agent to ferric hydroxide is 0.6:1, 0.7:1, or any ratio within the above range.

[0059] Furthermore, in some embodiments, the acid solution is one or more of sulfuric acid and hydrochloric acid.

[0060] In the technical solution of this application embodiment, the reducing agent is selected as one or more of sodium sulfite, sodium bisulfite, and sodium thiosulfate, and the pH is adjusted to 1.8~2.0 by adding acid to dissolve manganese dioxide and ferric hydroxide into a solution containing divalent manganese and divalent iron. The principle is that manganese dioxide and ferric hydroxide undergo a reduction reaction under the action of reducing agent and sulfuric acid to generate divalent manganese ions and divalent iron ions. MnO2 + 2HSO3 - +2H + →Mn 2+ +2SO4 2- +2H2O Fe(OH)3+HSO3 - +2H + →Fe2+ +2SO4 2- +2H2O.

[0061] By controlling the molar ratio of reducing agent to manganese dioxide to 1.2:1~1.5:1 and the molar ratio of reducing agent to ferric hydroxide to 0.6:1~0.7:1, the reducing agent is slightly in excess. This ensures complete reduction and reasonable cost control while preventing the catalytic oxidation reaction from occurring again in subsequent processing.

[0062] Furthermore, in some embodiments, ammonia water is added to adjust the pH of the second supernatant to 5.2-5.7, and ferrous hydroxide precipitate is obtained by solid-liquid separation.

[0063] In the technical solution of this application embodiment, the pH value of the second clear liquid is adjusted to 5.2~5.7 by adding ammonia water. Under this condition, Fe 2+ Ferrous hydroxide precipitate is formed, thereby removing iron ions from the water.

[0064] Furthermore, in some embodiments, ammonia water is added to adjust the pH of the third supernatant to 6.8-7.2, and a bicarbonate solution is added; The molar ratio of bicarbonate to manganese dioxide is 2.2:1 to 2.5:1, and the bicarbonate is one or more of ammonium bicarbonate and sodium bicarbonate.

[0065] In the technical solution of this application embodiment, after removing iron ions, ammonia is added to the third supernatant until the pH value reaches 6.8-7.2, and bicarbonate is added simultaneously. This bicarbonate reacts with MnSO4 to produce manganese carbonate, which can be directly used as a byproduct. The specific reaction process is as follows: 2NH4HCO3+MnSO4→MnCO3+CO2↑+(NH4)2SO4+H2O.

[0066] By controlling the molar ratio of bicarbonate solution to manganese dioxide to be 2.2:1 to 2.5:1, and ensuring that the bicarbonate content is slightly excessive, all manganese elements can be converted into manganese carbonate.

[0067] Specifically, the molar ratio of bicarbonate solution to manganese dioxide is 2.2:1, 2.3:1, 2.4:1, 2.5:1, or any ratio within the above range.

[0068] Furthermore, in some embodiments, an alkaline solution and phosphorus-containing wastewater are added to adjust the pH value of the first clarified solution to 8.3-8.5, wherein the alkaline solution is one or more of ammonia, sodium hydroxide, and potassium hydroxide.

[0069] In the technical solution of this application embodiment, by adding alkaline solution to the iron phosphate wastewater from which manganese and iron elements have been removed, the pH value of the first clear liquid is adjusted to 8.3~8.5, so that magnesium elements in the water precipitate to form magnesium ammonium phosphate (MgNH4PO4·6H2O), thereby being removed.

[0070] Please refer to Figure 2 Secondly, embodiments of this application provide a ferric phosphate wastewater treatment system, including an iron and manganese recovery section and a magnesium recovery section connected in sequence. The iron and manganese recovery section includes a primary sedimentation tank 1, a first sludge thickening tank 2, a first plate and frame filter press 3, and an iron and manganese recovery treatment unit connected in sequence. The magnesium recovery section includes a secondary sedimentation tank 5 and a second sludge thickening tank 6 connected in sequence. The outlets of the primary sedimentation tank 1, the first sludge thickening tank 2 and the first plate and frame filter press 3 are connected to the inlet of the primary product water tank 4, and the outlet of the primary product water tank 4 is connected to the inlet of the secondary sedimentation tank 5. The effluent from the secondary sedimentation tank 5 is directly subjected to further treatment.

[0071] In the technical solution of this application embodiment, the ferric phosphate washing wastewater first enters the primary sedimentation tank 1. Alkali solution and bisulfite solution are simultaneously added at the front end of the primary sedimentation tank 1 to adjust the pH to 6.8-7.2. Iron and manganese ions in the sedimentation wastewater form a first precipitate. After settling in the primary sedimentation tank 1, the supernatant enters the primary permeate tank 4, while the first precipitate enters the first sludge thickening tank 2. The thickened precipitated sludge enters the first plate and frame filter press 3 for dewatering. Both the permeate from the plate and frame filter press and the supernatant from the first sludge thickening tank 2 are discharged into the primary permeate tank 4 to form a first clear liquid. The dewatered first precipitate then enters the iron and manganese recovery treatment unit for further processing.

[0072] After the manganese and iron removal process, the ferric phosphate wastewater (first clarified liquid) enters the secondary sedimentation tank 5 after passing through the primary product water tank 4. Alkali solution is added at the front end of the secondary sedimentation tank 5, and RO concentrate (containing a certain amount of phosphorus) is discharged at the same time to adjust the pH to 8.3~8.5. Under these conditions, the magnesium element in the water will generate magnesium ammonium phosphate (MgNH4PO4·6H2O), forming the third precipitate, which enters the second sludge thickening tank 6, thus being removed.

[0073] Furthermore, in some embodiments, the iron and manganese recovery treatment unit includes a dissolving tank 7, an iron removal sedimentation tank 8, a reaction vessel 10, and a manganese recovery unit connected in sequence; the iron removal sedimentation tank 8 is connected to a second plate and frame filter press 9, and the outlet of the second plate and frame filter press 9 is connected to the inlet of the reaction vessel 10. The manganese recovery unit includes a third plate and frame filter press 11, a rinsing tank 12, a fourth plate and frame filter press 13, and a dryer 14 connected in sequence. The reaction vessel 10 is connected to the third plate and frame filter press 11.

[0074] In the technical solution of this application embodiment, the first precipitate enters the dissolving tank 7. Excess reducing agent and acid are added to the dissolving tank 7 to adjust the pH to 1.8-2.0, dissolving manganese dioxide and ferric hydroxide into a solution containing divalent manganese and divalent iron. This mixed solution (the second clear liquid) then enters the iron removal precipitation tank 8, where ammonia solution is added to adjust the pH to 5.2-5.7. Under these conditions, Fe... 2+ Ferrous hydroxide precipitate is generated, thereby removing iron ions from the water. After filtration by the second plate and frame filter press 9, the solid is ferrous hydroxide, and the permeate from the plate and frame filter press enters the subsequent process flow. The solution after iron ion removal (third clear liquid) enters the reaction vessel 10, where ammonia water is added until the pH value reaches 6.8-7.2. At the same time, bicarbonate is added to react with MnSO4 to generate manganese carbonate. After the reaction is complete, it is dehydrated using the third plate and frame filter press 11. The dehydrated manganese carbonate is rinsed with pure water in the rinsing tank 12 and then dehydrated again using the fourth plate and frame filter press 13. The manganese carbonate after rinsing and dehydration is dried in the paddle dryer 14, finally generating manganese carbonate (second precipitate) as a byproduct. The permeate from the third plate and frame filter press 11 and the fourth plate and frame filter press 13 enters the subsequent process flow for further treatment.

[0075] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0076] Example 1 A method for treating ferric phosphate wastewater includes the following steps: (1) The wastewater from washing iron phosphate is pretreated by adding ammonia to adjust the pH of the wastewater to 7.0 and adding sodium bisulfite solution. After solid-liquid separation, a first clear liquid and a first precipitate are obtained. The first precipitate contains at least iron hydroxide and manganese dioxide. The concentration of sodium bisulfite is 20 ppm. The reaction temperature of the wastewater from washing iron phosphate is 40°C. The reaction is carried out under stirring and aeration conditions. (2) Sodium bisulfite solution was added to the first precipitate to dissolve it, and sulfuric acid was added to adjust the pH to 2.0 to obtain a second clear liquid. The molar ratio of sodium bisulfite to manganese dioxide was 1.2:1, and the molar ratio of sodium bisulfite to iron hydroxide was 0.6:1. (3) Add ammonia to adjust the pH of the second clear liquid to 5.5, and after solid-liquid separation, ferrous hydroxide precipitate and the third clear liquid are obtained; (4) Add ammonia water to adjust the pH of the third clear liquid to 7.0, and add ammonium bicarbonate solution; the molar ratio of ammonium bicarbonate solution to manganese dioxide is 2.2:1. After solid-liquid separation, the second precipitate manganese carbonate is obtained. (5) Add ammonia and phosphorus-containing wastewater to adjust the pH of the first clear liquid to 8.5. After solid-liquid separation, the third precipitate, magnesium ammonium phosphate precipitate (MgNH4PO4·6H2O), is obtained.

[0077] Example 2 (1) The wastewater from washing iron phosphate is pretreated by adding sodium hydroxide to adjust the pH of the wastewater to 7.2 and adding sodium bisulfite solution. After solid-liquid separation, a first clear liquid and a first precipitate are obtained. The first precipitate contains at least iron hydroxide and manganese dioxide. The concentration of sodium bisulfite is 25 ppm, the reaction temperature of the wastewater from washing iron phosphate is 45°C, and the reaction is carried out under stirring and aeration conditions. (2) Sodium sulfite solution was added to the first precipitate to dissolve it, and hydrochloric acid was added to adjust the pH to 1.8 to obtain a second clear liquid. The molar ratio of sodium sulfite to manganese dioxide was 1.5:1, and the molar ratio of sodium sulfite to ferric hydroxide was 0.7:1. (3) Add ammonia water to adjust the pH of the second clear liquid to 5.2, and after solid-liquid separation, ferrous hydroxide precipitate and the third clear liquid are obtained; (4) Add ammonia water to adjust the pH of the third clear liquid to 6.8, and add sodium bicarbonate solution; the molar ratio of sodium bicarbonate solution to manganese dioxide is 2.5:1. After solid-liquid separation, the second precipitate manganese carbonate is obtained. (5) Add potassium hydroxide and phosphorus-containing wastewater to adjust the pH of the first clear liquid to 8.3. After solid-liquid separation, the third precipitate, magnesium ammonium phosphate precipitate (MgNH4PO4·6H2O), is obtained.

[0078] Example 3 (1) The wastewater from washing iron phosphate was pretreated by adding potassium hydroxide to adjust the pH of the wastewater to 6.8 and adding sodium bisulfite solution. After solid-liquid separation, a first clear liquid and a first precipitate were obtained. The first precipitate contained at least iron hydroxide and manganese dioxide. The concentration of sodium bisulfite was 22 ppm. The reaction temperature of the wastewater from washing iron phosphate was 43°C. The reaction was carried out under stirring and aeration conditions. (2) Sodium thiosulfate solution was added to the first precipitate to dissolve it, and hydrochloric acid was added to adjust the pH to 1.9 to obtain a second clear liquid. The molar ratio of sodium thiosulfate to manganese dioxide was 1.4:1, and the molar ratio of sodium thiosulfate to iron hydroxide was 0.6:1. (3) Add ammonia water to adjust the pH of the second clear liquid to 5.7, and after solid-liquid separation, ferrous hydroxide precipitate and the third clear liquid are obtained; (4) Add ammonia water to adjust the pH of the third clear liquid to 7.2, and add ammonium bicarbonate solution; the molar ratio of ammonium bicarbonate solution to manganese dioxide is 2.3:1. After solid-liquid separation, the second precipitate manganese carbonate is obtained. (5) Add sodium hydroxide and phosphorus-containing wastewater to adjust the pH of the first clear liquid to 8.4. After solid-liquid separation, the third precipitate, magnesium ammonium phosphate precipitate (MgNH4PO4·6H2O), is obtained.

[0079] Example 4 (1) The wastewater from washing iron phosphate is pretreated by adding ammonia to adjust the pH of the wastewater to 7.0 and adding sodium bisulfite solution. After solid-liquid separation, a first clear liquid and a first precipitate are obtained. The first precipitate contains at least iron hydroxide and manganese dioxide. The concentration of sodium bisulfite is 24 ppm. The reaction temperature of the wastewater from washing iron phosphate is 42°C. The reaction is carried out under stirring and aeration conditions. (2) Sodium bisulfite solution was added to the first precipitate to dissolve it, and hydrochloric acid was added to adjust the pH to 2.0 to obtain a second clear liquid. The molar ratio of sodium bisulfite to manganese dioxide was 1.3:1, and the molar ratio of sodium bisulfite to iron hydroxide was 0.7:1. (3) Add ammonia water to adjust the pH of the second clear liquid to 5.6, and after solid-liquid separation, ferrous hydroxide precipitate and the third clear liquid are obtained; (4) Add ammonia water to adjust the pH of the third clear liquid to 7.0, and add ammonium bicarbonate solution; the molar ratio of ammonium bicarbonate solution to manganese dioxide is 2.4:1. After solid-liquid separation, the second precipitate manganese carbonate is obtained. (5) Add ammonia and phosphorus-containing wastewater to adjust the pH of the first clear liquid to 8.5. After solid-liquid separation, the third precipitate, magnesium ammonium phosphate precipitate (MgNH4PO4·6H2O), is obtained.

[0080] Comparative Example 1 The only difference between this comparative example and Example 1 is that the concentration of sodium bisulfite added is 18 ppm, while the other steps and conditions are the same as in Example 1.

[0081] Comparative Example 2 The only difference between this comparative example and Example 1 is that the concentration of sodium bisulfite added is 27 ppm, while the other steps and conditions are the same as in Example 1.

[0082] Comparative Example 3 The only difference between this comparative example and Example 1 is that the molar ratio of sodium bisulfite to manganese dioxide is 1.0:1, and the molar ratio of sodium bisulfite to ferric hydroxide is 0.5:1.

[0083] Analysis of test results for each embodiment and comparative example The detection data of iron, manganese and magnesium elements in the effluent of Examples 1-4 and Comparative Examples 1-3 are shown in the following tables. Table 1 shows the detection data of iron, manganese and magnesium elements in the first clear liquid of Examples 1-4 and Comparative Examples 1-2, and Table 2 shows the detection data of iron and manganese elements in the second clear liquid of Examples 1-4 and Comparative Example 3.

[0084] Table 1 Table 2 The data in Table 1 show that the iron and manganese content in the first clear liquid of Examples 1-4 is relatively low, with iron content ranging from 0-0.06% and manganese content from 1.5-1.8%. In contrast, the iron and manganese content in the first clear liquid of Comparative Examples 1-2 is higher than that of Examples 1-4, indicating that the optimal concentration of bisulfite in ferric phosphate washing wastewater is 20-25 ppm. Controlling the concentration of bisulfite ensures the removal rate of manganese. When the concentration of bisulfite is below 20 ppm (Comparative Example 1), the ideal treatment effect is not achieved, and the manganese removal rate is unsatisfactory. When the concentration of bisulfite is above 25 ppm (Comparative Example 2), it acts as a reducing agent for the already generated manganese dioxide, dissolving the solid manganese dioxide and resulting in a higher manganese content.

[0085] As can be seen from the data in Table 2, the contents of iron and manganese in the second clear liquid in Examples 1-4 are higher than the detection data in Comparative Example 3. This indicates that the reducing agent is slightly over-produced in step (2) to avoid the catalytic oxidation reaction in subsequent processing while ensuring complete reduction and reasonable cost control. The reducing agent dosage in Comparative Example 3 is lower than that in Examples 1-4, which is the theoretical calculation ratio. Iron and manganese were not completely reduced during the processing.

[0086] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for treating ferric phosphate wastewater, characterized in that, Includes the following steps: The wastewater from washing with ferric phosphate was pretreated and then separated into solid and liquid components to obtain a first clear liquid and a first precipitate. A reducing agent is added to the first precipitate to dissolve it, and acid is added to adjust the pH to 1.8-2.0 to obtain the second clear solution; The pH of the second clear liquid was adjusted to 5.2-5.7, and after solid-liquid separation, a third clear liquid was obtained. The pH of the third supernatant was adjusted to 6.8-7.2, and a second precipitate was obtained by solid-liquid separation. The pH of the first supernatant was adjusted to 8.3-8.5, and a third precipitate was obtained by solid-liquid separation.

2. The method for treating ferric phosphate wastewater according to claim 1, characterized in that, The preprocessing steps include: The pH of the ferric phosphate washing wastewater was adjusted to 6.8-7.2 by adding alkaline solution and adding bisulfite solution; The alkaline solution is one or more of ammonia, sodium hydroxide, and potassium hydroxide.

3. The method for treating ferric phosphate wastewater according to claim 2, characterized in that, The concentration of the bisulfite added is 20-25 ppm; The reaction temperature for adjusting the ferric phosphate washing wastewater is 40~45℃.

4. The method for treating ferric phosphate wastewater according to claim 1, characterized in that, The first precipitate includes at least ferric hydroxide and manganese dioxide, and the reducing agent is one or more of sodium sulfite, sodium bisulfite, and sodium thiosulfate. The molar ratio of the reducing agent to manganese dioxide is 1.2:1 to 1.5:1, and the molar ratio of the reducing agent to ferric hydroxide is 0.6:1 to 0.7:

1.

5. The method for treating ferric phosphate wastewater according to claim 1, characterized in that, The acid solution is one or more of sulfuric acid and hydrochloric acid.

6. The method for treating ferric phosphate wastewater according to claim 1, characterized in that, Ammonia was added to adjust the pH of the second supernatant to 5.2-5.

7. After solid-liquid separation, ferrous hydroxide precipitate was obtained.

7. The method for treating ferric phosphate wastewater according to claim 4, characterized in that, Add ammonia to adjust the pH of the third supernatant to 6.8-7.2, and add bicarbonate solution; The molar ratio of bicarbonate to manganese dioxide is 2.2:1 to 2.5:1, and the bicarbonate is one or more of ammonium bicarbonate and sodium bicarbonate.

8. The method for treating ferric phosphate wastewater according to claim 1, characterized in that, The pH of the first clear liquid is adjusted to 8.3-8.5 by adding alkaline solution and phosphorus-containing wastewater. The alkaline solution is one or more of ammonia water, sodium hydroxide, and potassium hydroxide.

9. A ferric phosphate wastewater treatment system, characterized in that, It includes iron and manganese recovery sections and magnesium recovery sections connected in sequence; The iron and manganese recovery section includes a primary sedimentation tank, a first sludge thickening tank, a first plate and frame filter press, and an iron and manganese recovery treatment unit connected in sequence. The magnesium recovery section includes a secondary sedimentation tank and a second sludge thickening tank connected in sequence. The outlets of the primary sedimentation tank, the first sludge thickening tank, and the first plate and frame filter press are connected to the inlet of the primary product water tank, and the outlet of the primary product water tank is connected to the inlet of the secondary sedimentation tank. The effluent from the secondary sedimentation tank is directly subjected to further treatment.

10. The ferric phosphate wastewater treatment system according to claim 9, characterized in that, The iron and manganese recovery and treatment unit includes a dissolving tank, an iron removal sedimentation tank, a reaction vessel, and a manganese recovery unit connected in sequence; the iron removal sedimentation tank is connected to a second plate and frame filter press, and the outlet of the second plate and frame filter press is connected to the inlet of the reaction vessel. The manganese recovery unit includes a third plate and frame filter press, a rinsing tank, a fourth plate and frame filter press, and a dryer connected in sequence, and the reaction vessel is connected to the third plate and frame filter press.

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