Wastewater treatment method and treatment system

Abstract

The invention discloses a wastewater treatment method and system, and the treatment method comprises the following steps: carrying out first concentration crystallization treatment on wastewater to obtain a concentrated treatment solution, carrying out solid-liquid separation treatment on the concentrated treatment solution to obtain ammonium sulfate and a first mother solution, and monitoring the specific gravity of the first mother solution and the mass content of phosphorus in the first mother solution, the wastewater comprises NH4 < + >, SO4 < 2-> and PO4 < 3->; when the specific gravity of the first mother liquor and the mass content of the phosphorus element meet first preset values, carrying out second concentration and crystallization treatment on the first mother liquor to obtain ammonium dihydrogen phosphate and second mother liquor; when the specific gravity of the first mother liquor and the mass content of the phosphorus element do not meet the first preset value, mixing the first mother liquor with the wastewater, and then carrying out first concentration crystallization treatment. According to the treatment method, the impurity content in ammonium sulfate can be reduced, the added value of byproducts is improved, and the economic benefit of wastewater treatment is improved.

Description

Technical Field

[0001] This application belongs to the field of wastewater treatment technology, and in particular relates to a wastewater treatment method and system. Background Technology

[0002] Currently, regarding NH4 + SO4 2- and PO4 3- The main methods for recovering inorganic salts from wastewater are pretreatment followed by evaporation and crystallization to produce ammonium sulfate as a byproduct, or further cooling and crystallization to produce ammonium dihydrogen phosphate as a byproduct. However, current wastewater treatment methods suffer from poor quality of the produced ammonium sulfate and low economic efficiency. Summary of the Invention

[0003] This application provides a wastewater treatment method and system. The treatment method of this application can reduce the impurity content in ammonium sulfate and improve the economic benefits of wastewater treatment.

[0004] In a first aspect, embodiments of this application provide a wastewater treatment method, the method comprising: performing a first concentration and crystallization treatment on the wastewater to obtain a concentrated treatment liquid; performing a solid-liquid separation treatment on the concentrated treatment liquid to obtain ammonium sulfate and a first mother liquor; and monitoring the specific gravity of the first mother liquor and the mass content of phosphorus in the first mother liquor, wherein the wastewater includes NH4. + SO4 2- and PO4 3- When the specific gravity and phosphorus content of the first mother liquor meet the first preset value, the first mother liquor is subjected to a second concentration and crystallization treatment to obtain ammonium dihydrogen phosphate and a second mother liquor; when the specific gravity and phosphorus content of the first mother liquor do not meet the first preset value, the first mother liquor is mixed with wastewater and / or the liquid phase after wastewater concentration and then subjected to a first concentration and crystallization treatment.

[0005] In this embodiment of the application, by controlling the first preset value of the first mother liquor and performing post-treatment on the first mother liquor according to the first preset value, the amount of phosphorus entrained in ammonium sulfate can be effectively reduced, and ammonium sulfate and ammonium dihydrogen phosphate can be better separated to achieve a better salt separation effect, thereby improving the quality of ammonium sulfate products produced by wastewater treatment, thereby increasing the added value of products in the wastewater treatment process, reducing the cost of wastewater treatment, and improving economic benefits.

[0006] In some possible implementations, when the specific gravity and phosphorus content of the first mother liquor meet the first preset values, the step of performing a second concentration and crystallization treatment on the first mother liquor to obtain ammonium dihydrogen phosphate and a second mother liquor includes: the first preset values ​​include a specific gravity of 1.41 to 1.43 for the first mother liquor and a phosphorus content of 80 g / L to 100 g / L for the first mother liquor.

[0007] In the above possible implementations, the processing method provided in this application embodiment can further control the phosphorus content in ammonium sulfate by controlling the specific gravity of the first mother liquor to 1.41 to 1.43 and controlling the mass content of phosphorus in the first mother liquor to 80 g / L to 100 g / L, thereby achieving a better salt separation effect, reducing the impurity content in ammonium sulfate, further improving the grade of ammonium sulfate, and increasing product revenue.

[0008] In some possible implementations, when the specific gravity and phosphorus content of the first mother liquor meet the first preset values, in the step of performing a second concentration and crystallization treatment on the first mother liquor to obtain ammonium dihydrogen phosphate and a second mother liquor, the second mother liquor is mixed with wastewater and / or the liquid phase after wastewater concentration and then subjected to the first concentration and crystallization treatment; and / or, the time of the second concentration and crystallization treatment is 5h to 7h.

[0009] In the above possible implementation methods, mixing the second mother liquor with wastewater and then performing a first concentration and crystallization treatment can further improve the enrichment of elements and increase the element recovery rate. A second concentration and crystallization treatment time of 5-7 hours can improve the grade of ammonium dihydrogen phosphate and also increase product yield.

[0010] In some possible implementations, the steps of performing a first concentration and crystallization treatment on the wastewater to obtain a concentrated treatment liquid, performing solid-liquid separation treatment on the concentrated treatment liquid to obtain ammonium sulfate and a first mother liquor, and monitoring the specific gravity and phosphorus content of the first mother liquor include: adjusting the pH value of the wastewater to a first value to precipitate magnesium ammonium phosphate solid phase, separating pretreated wastewater and magnesium ammonium phosphate, wherein the wastewater includes NH4+. + Mg 2+ SO4 2- and PO4 3- The pH value is the second value, which is less than the first value. Optionally, the first value is 5-7 and the second value is 1.5-3. The mass content of magnesium in the pretreated wastewater is ≤150mg / L. The pretreated wastewater is subjected to a first concentration and crystallization treatment to obtain a concentrated treatment liquid. The concentrated treatment liquid is subjected to solid-liquid separation treatment to obtain ammonium sulfate and a first mother liquor. The specific gravity of the first mother liquor and the mass content of phosphorus in the first mother liquor are monitored.

[0011] In the above possible implementations, the embodiments of this application improve the economic efficiency of the wastewater treatment process by pretreating the wastewater and increasing the byproduct magnesium ammonium phosphate, and reduce the impact of magnesium on the product quality of ammonium sulfate and ammonium dihydrogen phosphate.

[0012] In some possible implementations, the treatment method may further include: monitoring the mass content of magnesium in the first mother liquor, and when the mass content of magnesium in the first mother liquor meets a second preset value, the first mother liquor is diluted and mixed with wastewater. Optionally, the treatment method satisfies at least one of the following: (1) the second preset value includes a mass content of magnesium in the first mother liquor ≥ 1.5 g / L; (2) the first concentration and crystallization treatment includes at least one liquid phase concentration treatment and one concentration and crystallization treatment, the wastewater is concentrated to obtain a first concentrated liquid phase, the first concentrated liquid phase is concentrated and crystallized to obtain a concentrated treatment liquid, and optionally, the first concentrated liquid phase is used to dilute the first mother liquor.

[0013] In the above possible implementations, the processing method of this application embodiment, by monitoring the mass content of magnesium in the first mother liquor, performs dynamic monitoring and scenario-specific processing, achieving stable separation effects and product quality, improving the recovery and utilization rate of phosphorus and magnesium, and reducing the interference of magnesium impurities on the purity of the main product and equipment scaling. Furthermore, by using a first concentrate to dilute the first mother liquor, this application embodiment can effectively reduce equipment scaling problems during the reuse of the first mother liquor, while also reducing water consumption and providing overall economic benefits for the treatment method.

[0014] In the above possible implementations, the embodiments of this application reduce the risk of pipeline blockage by controlling the dilution ratio of the first mother liquor and / or the mass content of magnesium in the first mother liquor, control the magnesium concentration within the optimal range, promote the precipitation of magnesium ammonium phosphate in the form of high purity and large particles, and improve separation efficiency.

[0015] Secondly, embodiments of this application provide a wastewater treatment system, comprising: an ammonium sulfate concentration and crystallization unit, which performs a first concentration and crystallization treatment on wastewater to obtain a concentrated treatment liquid; an ammonium sulfate separation unit, which separates the concentrated treatment liquid to obtain ammonium sulfate and a first mother liquor, wherein the inlet of the ammonium sulfate separation unit is connected to the outlet of the ammonium sulfate concentration and crystallization unit; and a first mother liquor post-treatment unit, comprising a first mother liquor storage tank and an ammonium dihydrogen phosphate concentration and separation module, wherein the outlet of the first mother liquor storage tank is connected to a hydrometer and a sampling port, and the ammonium dihydrogen phosphate concentration and separation module performs a second concentration and crystallization treatment on the first mother liquor to obtain ammonium dihydrogen phosphate and a second mother liquor, wherein the inlet of the first mother liquor storage tank is connected to the outlet of the ammonium sulfate separation unit, and the outlet of the first mother liquor storage tank is connected to the inlet of the ammonium sulfate concentration and crystallization unit and the inlet of the ammonium dihydrogen phosphate concentration and separation module, respectively.

[0016] In some possible implementations, the ammonium dihydrogen phosphate concentration and separation module includes a first mother liquor concentration and crystallization sub-module, an ammonium dihydrogen phosphate separation sub-module, and a second mother liquor storage tank. The outlet of the first mother liquor storage tank is connected to the inlet of the ammonium sulfate concentration and crystallization unit and the inlet of the first mother liquor concentration and crystallization sub-module, respectively. The outlet of the first mother liquor concentration and crystallization sub-module is connected to the inlet of the ammonium dihydrogen phosphate separation sub-module. The outlet of the ammonium dihydrogen phosphate separation sub-module is connected to the inlet of the second mother liquor storage tank. The outlet of the second mother liquor storage tank is connected to the inlet of the ammonium sulfate concentration and crystallization unit.

[0017] In some possible implementations, the processing system may also include a pretreatment unit for separating magnesium from the processing system to obtain magnesium ammonium phosphate, with the outlet of the pretreatment unit connected to the inlet of the ammonium sulfate concentration and crystallization unit.

[0018] In some possible implementations, the first mother liquor post-processing unit may further include a first mother liquor dilution tank, the outlet of which is connected to the inlet of the first mother liquor dilution tank; and / or, the sampling port is connected to a phosphorus content detection module and a magnesium content detection module.

[0019] In some possible implementations, the ammonium sulfate concentration and crystallization unit includes a liquid phase concentration module and a concentration and crystallization module connected in sequence, with the outlet of the first mother liquor storage tank connected to the inlet of the concentration and crystallization module, and the outlet of the liquid phase concentration module connected to the inlet of the first mother liquor dilution storage tank. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic process flow diagram of a wastewater treatment method according to an embodiment of this application.

[0022] Figure 2 This is a schematic process flow diagram of a wastewater treatment method according to another embodiment of this application.

[0023] The accompanying drawings are not necessarily drawn to scale. Detailed Implementation

[0024] The embodiments of this application will be described in detail below. These embodiments should not be construed as limiting the scope of this application.

[0025] As used in this application, the terms “comprising,” “containing,” and “including” are used in their open, non-restrictive sense.

[0026] Additionally, quantities, ratios, and other numerical values ​​are sometimes presented in range format in this document. It should be understood that such range format is for convenience and brevity and should be interpreted flexibly to include not only the numerical values ​​explicitly specified as range limits, but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly specified.

[0027] In the detailed description and claims, a list of items connected by the terms "one or more of," "one or more of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A or B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, or C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0028] Currently, regarding NH4 + SO4 2- and PO4 3- The main methods for recovering inorganic salts from wastewater are pretreatment followed by evaporation and crystallization to produce ammonium sulfate as a byproduct, or further cooling and crystallization to produce ammonium dihydrogen phosphate as a byproduct. However, current wastewater treatment methods suffer from poor quality of the produced ammonium sulfate, resulting in poor economic benefits. This is particularly problematic for wastewater from ferric phosphate production.

[0029] With the increasing global demand for renewable energy and electric vehicles, lithium iron phosphate (LFP) batteries are gaining an increasingly larger share of the battery market due to their advantages such as high safety, environmental friendliness, stable cycle life, and economical cost. Iron phosphate, as a precursor material for LFP batteries, is also in growing demand. The wastewater from LFP production, hereinafter referred to as LFP wastewater, is characterized by high concentrations of ammonia nitrogen, sulfate, magnesium ions, and total phosphorus, and a low pH. The current main process involves pretreatment + evaporation crystallization + membrane treatment for pure water reuse in a zero-discharge treatment manner. Specifically, the pretreated LFP wastewater undergoes evaporation crystallization to produce ammonium sulfate as a byproduct, or further cooling crystallization to produce ammonium dihydrogen phosphate as a byproduct. However, the quality of both byproducts produced by this process is currently poor, resulting in limited economic value. Therefore, improving the quality of byproducts, thereby increasing their profitability and even reusing them as raw materials for LFP production, ultimately reducing the operating costs of LFP wastewater treatment, has become a significant challenge in LFP wastewater treatment.

[0030] In view of the above problems, this application provides a wastewater treatment method and system. The treatment method can reduce the impurity content in ammonium sulfate, increase the added value of by-products, and improve the economic benefits of wastewater treatment.

[0031] The embodiments of this application will be described in detail below.

[0032] Wastewater treatment methods

[0033] A wastewater treatment method, such as Figure 1 As shown, the processing method includes:

[0034] S100 involves a first concentration and crystallization treatment of the wastewater to obtain a concentrated solution. This concentrated solution is then subjected to solid-liquid separation to obtain ammonium sulfate and a first mother liquor. The specific gravity and phosphorus content of the first mother liquor are monitored. The wastewater contains NH4+. + SO4 2- and PO4 3- .

[0035] S200, when the specific gravity and phosphorus content of the first mother liquor meet the first preset value, the first mother liquor is subjected to a second concentration and crystallization treatment to obtain ammonium dihydrogen phosphate and a second mother liquor.

[0036] S300, when the specific gravity and phosphorus content of the first mother liquor do not meet the first preset value, the first mother liquor is mixed with wastewater and / or the liquid phase after wastewater concentration and then subjected to the first concentration and crystallization treatment.

[0037] As an example, the specific gravity of the first mother liquor can be measured using a hydrometer after sampling and calculated based on the temperature of the first mother liquor. Alternatively, the specific gravity of the first mother liquor can be measured online in real time using a hydrometer. Furthermore, in this application, the specific gravity of the first mother liquor is the specific gravity corresponding to the real-time temperature of the first mother liquor, which can be between 80℃ and 95℃. The mass content of phosphorus in the first mother liquor can be detected by sampling and using a quinoline phosphomolybdate titration method, or it can be monitored online using an ion-selective electrode method.

[0038] In this embodiment, the treatment method controls a first preset value for the first mother liquor and performs post-treatment on the first mother liquor according to the first preset value. This controls the process of enriching phosphorus in the first mother liquor from a low concentration to a higher concentration, further controlling the mass content of phosphorus in the first mother liquor within the concentration of the co-crystallization point of ammonium sulfate and ammonium dihydrogen phosphate. This can effectively reduce the amount of phosphorus entrained in ammonium sulfate, further enabling better separation of ammonium sulfate and ammonium dihydrogen phosphate to achieve a better salt separation effect, improving the quality of ammonium sulfate products produced from wastewater treatment, and also improving the production efficiency of ammonium dihydrogen phosphate. This increases the added value of products in the wastewater treatment process, reduces the cost of wastewater treatment, and improves economic benefits.

[0039] In some embodiments, the wastewater may be selected from ferric phosphate production wastewater, desulfurization wastewater and phosphating wastewater, wherein the ferric phosphate production wastewater may be ferric phosphate production wastewater produced using the ammonium process, the desulfurization wastewater may be desulfurization wastewater treated by the ammonium magnesium sulfate process, and the phosphating wastewater may be phosphating wastewater generated during the metal surface treatment process.

[0040] In some embodiments, in step S200, when the specific gravity and phosphorus content of the first mother liquor meet the first preset values, the first mother liquor is subjected to a second concentration and crystallization treatment to obtain ammonium dihydrogen phosphate and the second mother liquor. The first preset value includes a specific gravity of the first mother liquor of 1.41 to 1.43, for example, the specific gravity of the first mother liquor can be 1.41, 1.412, 1.415, 1.418, 1.42, 1.422, 1.425, 1.428, 1.43, or any of the above values. The phosphorus content in the first mother liquor is 80 g / L to 100 g / L, for example, the phosphorus content in the first mother liquor can be 80 g / L, 82 g / L, 85 g / L, 88 g / L, 90 g / L, 92 g / L, 95 g / L, 98 g / L, 100 g / L, or any of the above values.

[0041] As an example, the specific gravity and phosphorus content of the first mother liquor can be controlled by controlling the transfer flow rate of the first mother liquor, so that the first mother liquor meets the first preset value.

[0042] In the above embodiments, the processing method provided in this application can further control the phosphorus content in ammonium sulfate by controlling the specific gravity of the first mother liquor to 1.41 to 1.43 and controlling the mass content of phosphorus in the first mother liquor to 80 g / L to 100 g / L, thereby achieving a better salt separation effect, reducing the impurity content in ammonium sulfate, further improving the grade of ammonium sulfate, and increasing product revenue.

[0043] In some embodiments, in step S200, when the specific gravity and phosphorus content of the first mother liquor meet the first preset value, the first mother liquor is subjected to a second concentration and crystallization treatment to obtain ammonium dihydrogen phosphate and the second mother liquor. The second mother liquor is mixed with wastewater and / or the liquid phase after wastewater concentration and then subjected to the first concentration and crystallization treatment.

[0044] In the above embodiments, the first concentration and crystallization treatment after mixing the second mother liquor with wastewater can further improve the enrichment of elements and increase the element recovery rate.

[0045] In some embodiments, in step S200, when the specific gravity and phosphorus content of the first mother liquor meet the first preset value, the first mother liquor is subjected to a second concentration and crystallization treatment to obtain ammonium dihydrogen phosphate and the second mother liquor. The time for the second concentration and crystallization treatment is 5h to 7h. For example, the time for the second evaporation and crystallization treatment can be 5h, 5.2h, 5.5h, 5.8h, 6h, 6.2h, 6.5h, 6.8h, 7h, or any range of the above values.

[0046] In the above embodiments, the second concentration and crystallization treatment time of 5h to 7h can improve the grade of ammonium dihydrogen phosphate and also increase product yield.

[0047] In some embodiments, the second concentration and crystallization process can utilize a flash crystallizer. This contrasts with the indirect heat exchange cooling of conventional circulating water-cooled crystallizers, which involves removing heat via a circulating cooling tower, consuming cooling water and wasting material heat energy. Flash crystallization, on the other hand, utilizes the residual heat of the material to further concentrate its volume, increasing evaporation rates, reducing cooling water consumption, and improving ammonium dihydrogen phosphate salt production. Furthermore, it enhances overall system stability, reduces steam consumption, and lowers operating costs.

[0048] In some embodiments, step S100, which involves subjecting the wastewater to a first concentration and crystallization treatment to obtain a concentrated treatment liquid, and then subjecting the concentrated treatment liquid to a solid-liquid separation treatment to obtain ammonium sulfate and a first mother liquor, and monitoring the specific gravity of the first mother liquor and the mass content of phosphorus in the first mother liquor, includes:

[0049] S110 adjusts the pH of the wastewater to the first value to precipitate magnesium ammonium phosphate solids, separating pretreated wastewater and magnesium ammonium phosphate. The wastewater contains NH4+. + Mg 2+ SO4 2- and PO4 3- Furthermore, the pH value is the second value, which is less than the first value.

[0050] S120, the pretreated wastewater is subjected to a first concentration and crystallization treatment to obtain a concentrated treatment liquid, and the concentrated treatment liquid is subjected to solid-liquid separation treatment to obtain ammonium sulfate and a first mother liquor, and the specific gravity of the first mother liquor and the mass content of phosphorus in the first mother liquor are monitored.

[0051] In the above embodiments, this application embodiment improves the economic efficiency of the wastewater treatment process by pretreating the wastewater and increasing the byproduct magnesium ammonium phosphate, and reduces the impact of magnesium on the product quality of ammonium sulfate and ammonium dihydrogen phosphate.

[0052] In some embodiments, the first value can be 5 to 7, for example, the first value can be 5, 5.2, 5.5, 5.8, 6, 6.2, 6.5, 6.8, 7, or any range of the above values.

[0053] In some embodiments, the second value can be 1.5 to 3, for example, the second value can be 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, or any range of the above values.

[0054] In some embodiments, the mass content of magnesium in the pretreated wastewater is ≤150 mg / L. For example, the mass content of magnesium in the pretreated wastewater can be 10 mg / L, 20 mg / L, 50 mg / L, 80 mg / L, 100 mg / L, 120 mg / L, 150 mg / L, or any range of the above values.

[0055] In some embodiments, the treatment method may further include: S400, monitoring the mass content of magnesium in the first mother liquor, and when the magnesium content of the first mother liquor meets a second preset value, diluting the first mother liquor and mixing it with wastewater.

[0056] In the above embodiments, the processing method of this application monitors the mass content of magnesium in the first mother liquor, performs dynamic monitoring and scene-specific processing, which can achieve stable separation effect and product quality, improve the recovery rate of phosphorus and magnesium, and reduce the interference of magnesium impurities on the purity of the main product and equipment scaling.

[0057] In some embodiments, the first concentration and crystallization treatment includes at least one liquid phase concentration treatment and one concentration and crystallization treatment. After the wastewater is concentrated by the liquid phase treatment, a first concentrated liquid phase is obtained. After the first concentrated liquid phase is concentrated and crystallized, a concentrated treatment liquid is obtained.

[0058] It is understandable that the liquid phase after wastewater concentration includes the first concentrated liquid phase, which can be the liquid phase after wastewater has been concentrated by membrane or evaporation.

[0059] In some embodiments, the dilution factor of the first mother liquor is 2 to 40 times.

[0060] In some embodiments, the first mother liquor can be diluted with wastewater stock solution or water. When the first mother liquor is diluted with wastewater stock solution, the dilution ratio of the first mother liquor is 30 to 40 times.

[0061] In some embodiments, a first concentrate may be used to dilute the first mother liquor, and when the first concentrate is used to dilute the first mother liquor, the dilution factor of the first mother liquor is 2 to 3 times.

[0062] In the above embodiments, the present application embodiments can effectively reduce the equipment scaling problem during the reuse of the first mother liquor by using the first concentrated liquid phase and / or wastewater raw liquid to dilute the first mother liquor, while reducing water consumption and providing economic benefits for the overall treatment method.

[0063] In some embodiments, the second preset value includes a magnesium content in the first mother liquor of ≥1.5 g / L.

[0064] In the above embodiments, this application embodiment reduces the risk of pipeline blockage by controlling the dilution ratio of the first mother liquor and / or the mass content of magnesium in the first mother liquor, controls the magnesium concentration in the optimal range, promotes the precipitation of magnesium ammonium phosphate in the form of high purity and large particles, and improves the separation efficiency.

[0065] In some embodiments, the pH of the first concentrated liquid phase is 3 to 4. For example, the pH of the first concentrated liquid phase can be 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, or any range of the above values.

[0066] In some embodiments, the mass content of magnesium in the first concentrated liquid phase is ≤350 mg / L. For example, the mass content of magnesium in the first concentrated liquid phase can be 50 mg / L, 100 mg / L, 150 mg / L, 200 mg / L, 250 mg / L, 300 mg / L, 350 mg / L, or any range of the above values.

[0067] In some embodiments, the monitoring frequency of the mass content of phosphorus in the first mother liquor is 1 to 2 times per hour.

[0068] In some embodiments, the monitoring frequency of the magnesium content in the first mother liquor is 1 to 2 times per hour.

[0069] In the above embodiments, by monitoring the phosphorus and magnesium content at a high frequency of 1-2 times per hour, fluctuations in the mother liquor composition (such as changes in upstream process parameters and variations in phosphorus and magnesium concentrations caused by batch differences in raw materials) can be captured in real time, reducing the mismatch between the processing technology and the actual composition of the mother liquor due to monitoring lag. This reduces the amount of magnesium entering the ammonium dihydrogen phosphate crystallization stage, ensuring the purity of the ammonium dihydrogen phosphate product. In addition, it can further balance testing costs and process requirements, significantly reduce the duration of abnormal composition, reduce raw material waste and defective product rates, and also reduce equipment wear and tear and increased labor costs caused by excessive testing, extend equipment operating cycles, and reduce maintenance costs.

[0070] Wastewater treatment system

[0071] A wastewater treatment system includes: an ammonium sulfate concentration and crystallization unit, which is used to perform a first concentration and crystallization treatment on the wastewater to obtain a concentrated treatment liquid.

[0072] The ammonium sulfate separation unit is used to separate and concentrate the treatment liquid to obtain ammonium sulfate and the first mother liquor. The inlet of the ammonium sulfate separation unit is connected to the outlet of the concentration and crystallization unit.

[0073] The first mother liquor post-processing unit includes a first mother liquor storage tank and an ammonium dihydrogen phosphate concentration and separation module. The outlet of the first mother liquor storage tank is connected to a hydrometer and a sampling port. The ammonium dihydrogen phosphate concentration and separation module is used to perform a second concentration and crystallization treatment on the first mother liquor to obtain ammonium dihydrogen phosphate and a second mother liquor. The inlet of the first mother liquor storage tank is connected to the outlet of the ammonium sulfate separation unit. The outlet of the first mother liquor storage tank is connected to the inlet of the ammonium sulfate concentration and crystallization unit and the inlet of the ammonium dihydrogen phosphate concentration and separation module, respectively.

[0074] As an example, the ammonium sulfate separation unit may include a thickener, a first centrifuge, and a first fluidized bed. The inlet of the thickener is connected to the outlet of the ammonium sulfate concentration and crystallization unit. The underflow outlet of the thickener (also known as the crystal slurry outlet) is connected to the inlet of the first centrifuge. The outlet of the first centrifuge is connected to the first fluidized bed. The inlet of the first mother liquor storage tank is connected to the overflow outlet of the thickener and the outlet of the first centrifuge, respectively.

[0075] Furthermore, the first mother liquor can be processed using either a sequential batch transfer or a continuous transfer. The sequential batch transfer involves processing the first mother liquor in batches based on its total volume and the equipment's predetermined processing capacity. The specific transfer method can be selected based on the system equipment and the capacity of the system's heavy storage tank.

[0076] In some embodiments, the ammonium dihydrogen phosphate concentration and separation module includes a first mother liquor concentration and crystallization sub-module, an ammonium dihydrogen phosphate separation sub-module, and a second mother liquor storage tank. The outlet of the first mother liquor storage tank is connected to the inlet of the ammonium sulfate concentration and crystallization unit and the inlet of the first mother liquor concentration and crystallization sub-module, respectively. The outlet of the first mother liquor concentration and crystallization sub-module is connected to the inlet of the ammonium dihydrogen phosphate separation sub-module. The outlet of the ammonium dihydrogen phosphate separation sub-module is connected to the inlet of the second mother liquor storage tank. The outlet of the second mother liquor storage tank is connected to the ammonium sulfate concentration and crystallization unit.

[0077] As an example, the ammonium dihydrogen phosphate concentration and separation module may include a flash crystallizer (a first mother liquor concentration and crystallization sub-module), a second centrifuge (an ammonium dihydrogen phosphate separation sub-module), a second mother liquor storage tank, and a second fluidized bed. The outlet of the first mother liquor storage tank is connected to the inlet of the ammonium sulfate concentration and crystallization unit and the inlet of the flash crystallizer, respectively. The outlet of the flash crystallizer is connected to the inlet of the second centrifuge. The solid phase outlet of the second centrifuge is connected to the second fluidized bed, and the liquid phase outlet of the second centrifuge is connected to the second mother liquor storage tank.

[0078] In some embodiments, the processing system may further include a pretreatment unit for separating magnesium from the processing system to obtain magnesium ammonium phosphate, wherein the outlet of the pretreatment unit is connected to the inlet of the ammonium sulfate concentration and crystallization unit.

[0079] As an example, the pretreatment unit can be an integrated purification system. Specifically, the integrated purification system may include a pipeline mixer or mixing tank for pH adjustment. The outlet of the pipeline mixer or mixing tank is connected to a sedimentation tank. Additives can be added to promote the precipitation or crystal growth of magnesium ammonium phosphate. The solid phase outlet of the sedimentation tank is connected to the inlet of a plate and frame filter, and the liquid phase outlet of the sedimentation tank is connected to the inlet of an ammonium sulfate separation unit. A pipeline mixer is further preferred to reduce the equipment footprint.

[0080] In some embodiments, the first mother liquor post-processing unit may further include a first mother liquor dilution tank, the outlet of which is connected to the inlet of the first mother liquor dilution tank.

[0081] As an example, a stirring device may be installed in the first mother liquor dilution tank to accelerate the dilution rate of the first mother liquor.

[0082] In some embodiments, the sampling port may also be connected to a phosphorus content detection module and / or a magnesium content detection module.

[0083] In some embodiments, the ammonium sulfate concentration and crystallization unit includes a liquid phase concentration module and a concentration and crystallization module connected in sequence, the outlet of the first mother liquor storage tank is connected to the inlet of the concentration and crystallization module, and the outlet of the liquid phase concentration module is connected to the inlet of the first mother liquor dilution storage tank.

[0084] As an example, the liquid phase concentration module can be a membrane concentration device, and the concentration and crystallization module can be a multi-effect evaporator that includes at least three evaporators connected in series. The outlet of the first mother liquor storage tank and the outlet of the second mother liquor storage tank are both connected to the inlet of the last evaporator in the multi-effect evaporator.

[0085] In some embodiments, the processing system may further include a control unit, which is used to monitor at least one of the pretreatment unit, the ammonium sulfate concentration and crystallization unit, the ammonium sulfate separation unit, and the first mother liquor post-treatment unit to obtain monitoring results, and to regulate at least one of the pretreatment unit, the ammonium sulfate concentration and crystallization unit, the ammonium sulfate separation unit, and the first mother liquor post-treatment unit based on the monitoring results.

[0086] As an example, the treatment method and system of this application can be combined to treat ferric phosphate wastewater, such as... Figure 2 As shown, the specific processing procedure is as follows:

[0087] After the ferric phosphate wastewater, membrane concentration wastewater and the first mother liquor are diluted and mixed, Mg and P are precipitated in the form of magnesium ammonium phosphate as a byproduct, resulting in pretreated ferric phosphate wastewater.

[0088] Pretreated ferric phosphate wastewater undergoes reverse osmosis membrane concentration in a membrane concentrator to obtain a first concentrated liquid phase. This first concentrated liquid phase then enters a mechanical vapor recompression (MVR) system for evaporation and crystallization. The MVR system includes a first evaporator, a second evaporator, and a third evaporator. The first concentrated liquid phase undergoes a first evaporation and concentration in the first evaporator to obtain a second concentrated liquid phase. This second concentrated liquid phase undergoes a second evaporation and concentration in the second evaporator to obtain a third concentrated liquid phase. The third concentrated liquid phase undergoes further evaporation and concentration in the third evaporator to obtain a concentrated treated liquid. The solid-liquid mixture in the salt leg at the bottom of the third evaporator is transferred to a first thickener via a crystallization pump. The supernatant in the first thickener overflows into a first mother liquor tank, while the bottom material is sent to a first centrifuge for solid-liquid separation. The solid salt is conveyed by belt to a first fluidized bed, where it is dried to obtain the final ammonium sulfate product. A first thermometer is installed in the liquid phase of the third evaporator, and its data is remotely transmitted to the central control system. A first flow meter is installed in the evaporation and crystallization steam condensate of the MVR system, and its data is also remotely transmitted to the central control system.

[0089] The liquid material from the first centrifuge flows by gravity to the first mother liquor tank, whose outlet is connected to a transfer pump. The transfer pump outlet is equipped with an online hydrometer and a sampling port. Data from the online hydrometer is remotely transmitted to the central control system. Samples of the first mother liquor are taken through the sampling port, and the mass percentages of phosphorus and magnesium in the samples are measured. The transfer pump outlet is connected to the third evaporator crystallizer, the flash crystallizer, and the first mother liquor dilution tank, with transfer controlled remotely via valves.

[0090] The first mother liquor meets the following conditions: specific gravity of 1.41–1.43, phosphorus content of 80–100 g / L, and magnesium content <1.5 g / L. The mother liquor is then transferred to the flash crystallizer. A second flow meter is installed on the transfer pipeline to the flash crystallizer, and its data is remotely transmitted to the central control system. A second thermometer is installed on the liquid phase of the flash crystallizer, and its data is also remotely transmitted to the central control system. A third flow meter is installed on the condensate tank transfer pipeline of the flash crystallizer, and its data is also remotely transmitted to the central control system. An online negative pressure gauge is installed in the flash crystallizer, and its data is remotely transmitted to the central control system. A propeller is installed at the bottom of the flash crystallizer to mix the materials within the crystallizer, promoting crystal growth and continuously increasing particle size. The top of the flash crystallizer is connected to a surface condenser, which in turn is connected to a vacuum pump to create negative pressure. Secondary steam, under negative pressure, passes through the surface condenser and cools to obtain condensate. The condensate is collected in a flash condensate tank via a gas-liquid separator. Non-condensable gases are pumped to a tail gas treatment system for purification before being discharged. After the first mother liquor undergoes flash crystallization in the flash crystallizer, the solid-liquid mixture at the bottom of the flash crystallizer is transferred to the second thickener. The supernatant overflows into the second mother liquor storage tank and is then transferred to the third evaporator concentrator to mix with the third concentrated liquid for further processing. The bottom material enters the second centrifuge for centrifugal separation, and the solid salt is conveyed by a belt conveyor to the second fluidized bed for drying into ammonium dihydrogen phosphate.

[0091] If the first mother liquor does not meet the following requirements: specific gravity of 1.41-1.43, phosphorus content of 80g / L-100g / L, and magnesium content of <1.5g / L, the first mother liquor is transferred to the third evaporator crystallizer and mixed with the third concentrate for evaporation and crystallization.

[0092] When the magnesium content in the first mother liquor is ≥1.5g / L, the first mother liquor is transferred to the first mother liquor dilution storage tank. The first mother liquor dilution storage tank is equipped with a fourth flow meter, and the data from the fourth flow meter is remotely transmitted to the central control system. The first concentrated liquid phase is used for dilution to avoid pipe blockage caused by high salt concentration. After dilution, the material is transferred and mixed with the iron phosphate wastewater raw solution for treatment.

[0093] In the above example, the settings of the flow meter and thermometer in the processing system can be adjusted according to the actual situation and are not limited to the settings in the example.

[0094] Example

[0095] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0096] In this embodiment, the quality testing of ammonium sulfate is performed using the testing method disclosed in GB / T 535-2020, the quality testing of ammonium dihydrogen phosphate is performed using the testing method disclosed in GB / T 10209, and the quality testing of magnesium ammonium phosphate is performed using the testing method disclosed in T / SXAS 005-2020.

[0097] Example 1

[0098] In this embodiment, the main components of the wastewater include Mg. 2+ PO4 3- NH4 + SO4 2- The wastewater also contained relatively low levels of other metal ions and chloride ions, with a total salt concentration of 9.10% and a pH value of 1.66. The phosphorus and magnesium content in the wastewater was as follows: Mg: 405.33 mg / L, P: 4440.27 mg / L.

[0099] A wastewater treatment method includes the following steps:

[0100] The wastewater is pretreated by an integrated purification device to obtain pretreated wastewater and magnesium ammonium phosphate.

[0101] The pretreated wastewater was subjected to membrane concentration treatment to obtain the first concentrated liquid phase. The water quality of the first concentrated liquid phase was as follows: Mg: 188.11 mg / L, P: 4668.38 mg / L, total salt concentration: 15.25%, pH value: 3.88.

[0102] The first concentrated liquid phase was subjected to triple-effect evaporation and crystallization using an MVR system. After triple-effect concentration, the first mother liquor and solid product were separated. At this point, the initial specific gravity of the first mother liquor was 1.37. The solid product was dried in a fluidized bed to obtain ammonium sulfate. The first mother liquor was transferred to the third evaporator and mixed with the third concentrated liquid phase for further evaporation and crystallization. The material temperature in the third evaporator was controlled at approximately 101°C.

[0103] After continuous salt extraction, the phosphorus content in the first mother liquor becomes enriched, with its concentration rising to 80 g / L. The specific gravity of the first mother liquor increases from 1.37 to 1.420. A portion of the first mother liquor is then continuously transferred to the flash crystallizer. The flow rate of the triple-effect crystallizer is controlled by adjusting the valve for this transfer. The residence time in the flash crystallizer is controlled at 6 hours, and the temperature is 50°C. After flash crystallization, solid-liquid separation is performed to obtain ammonium dihydrogen phosphate product and a second mother liquor. The second mother liquor is then mixed with the third concentrate and subjected to further evaporation and crystallization.

[0104] After continuous evaporation, the magnesium content in the first mother liquor is enriched, and the magnesium element concentration rises to 1.5 g / L. The first mother liquor is then transferred to the mother liquor dilution storage tank in a sequential batch process. The first concentrated liquid phase is used for dilution. The material in the mother liquor dilution tank is transferred to the integrated purification device for pretreatment, producing magnesium ammonium phosphate as a by-product. The first mother liquor is diluted by 2 times. The mother liquor dilution storage tank is equipped with a mixing and stirring system.

[0105] In this embodiment, the product data for ammonium sulfate is detailed in Table 1, the product data for ammonium dihydrogen phosphate is detailed in Table 2, and the product data for magnesium ammonium phosphate is detailed in Table 3.

[0106] Example 2

[0107] The only difference between Example 2 and Example 1 is the wastewater, which includes Mg. 2+ PO4 3- NH4 + SO4 2- The wastewater also contained relatively low levels of other metal ions and chloride ions, with a total salt concentration of 6.26% and a pH of 2.29. The phosphorus and magnesium content in the wastewater was as follows: Mg: 364.31 mg / L, P: 1635.26 mg / L. For detailed data on ammonium sulfate, ammonium dihydrogen phosphate, and magnesium ammonium phosphate in this example, please refer to Table 1.

[0108] Example 3

[0109] The difference between Example 3 and Example 1 lies only in that the first mother liquor was transferred to initiate flash crystallization treatment when its specific gravity was controlled at 1.410 and its phosphorus content at 81.18 g / L. For detailed product data of ammonium sulfate, ammonium dihydrogen phosphate, and magnesium ammonium phosphate in this example, please refer to Table 1.

[0110] Example 4

[0111] The difference between Example 4 and Example 1 lies only in that the first mother liquor was transferred to initiate flash crystallization when its specific gravity was 1.430 and its phosphorus content was 99.83 g / L. For detailed product data of ammonium sulfate, ammonium dihydrogen phosphate, and magnesium ammonium phosphate in this example, please refer to Table 1.

[0112] Example 5

[0113] The difference between Example 5 and Example 1 lies only in that, when the specific gravity of the first mother liquor was 1.432 and the phosphorus content was 112.05 g / L, the first mother liquor was transferred to initiate flash crystallization treatment. After the magnesium concentration increased to 2.2 g / L, the first mother liquor was diluted. For detailed product data of ammonium sulfate, ammonium dihydrogen phosphate, and magnesium ammonium phosphate in this example, please refer to Table 1; for detailed product data of ammonium dihydrogen phosphate, please refer to Table 2; and for detailed product data of magnesium ammonium phosphate, please refer to Table 3.

[0114] Example 6

[0115] The only difference between Example 6 and Example 1 is that the specific gravity of the first mother liquor is 1.406 and the phosphorus content is 62.70 g / L. For detailed product data of ammonium sulfate, ammonium dihydrogen phosphate, and magnesium ammonium phosphate in this example, please refer to Table 1.

[0116] Comparative Example 1

[0117] The difference between Comparative Example 1 and Example 1 is that the specific gravity is not monitored in real time, the specific gravity of the first mother liquor is 1.44 during salt separation, the magnesium content in the first mother liquor is not monitored, and the magnesium is not diluted back to the pretreatment.

[0118] More specifically, the raw material wastewater in Example 1 is pretreated to obtain pretreated wastewater and magnesium ammonium phosphate; the pretreated wastewater is concentrated by MVR evaporation to obtain ammonium sulfate product and evaporation residue. The evaporation temperature is 105°C. When the evaporation rate is significantly reduced, the evaporation residue is flashed at 50°C to obtain ammonium dihydrogen phosphate.

[0119] For detailed data on ammonium sulfate, ammonium dihydrogen phosphate, and magnesium ammonium phosphate in this comparative example, please refer to Table 1; for detailed data on ammonium dihydrogen phosphate, please refer to Table 2; and for detailed data on magnesium ammonium phosphate, please refer to Table 3.

[0120] Table 1. Parameters of ammonium sulfate obtained in Examples 1-8 and Comparative Example 1

[0121] element S / ％ N / ％ Moisture / % Free acid / % Water-insoluble matter / % Cl / ％ P / ％ Level I Standard ≥24 ≥20.5 ≤0.5 ≤0.05 ≤0.5 ≤1 / Example 1 24.64 20.59 0.28 0.0011 0.0115 0.0037 0.0763 Example 2 24.19 20.71 0.3 0.0011 0.0523 0.0079 0.1147 Example 3 24.52 20.55 0.43 0.0012 0.011 0.0047 0.0918 Example 4 24.16 20.69 0.41 0.0011 0.0265 0.0054 0.3081 Example 5 24.38 20.24 0.27 0.0012 0.0335 0.0032 0.4920 Example 6 24.15 20.56 0.4 0.0013 0.0084 0.0033 0.1300 Comparative Example 1 20.53 18.21 0.47 0.0013 0.003 0.0034 1.8331

[0122] Table 2. Parameters of ammonium dihydrogen phosphate obtained in Examples 1-8 and Comparative Example 1.

[0123]

[0124]

[0125] Note: In Table 2, Mi represents the total content of Fe, Cr, and Zn elements.

[0126] Table 3. Parameters of magnesium ammonium phosphate obtained in Examples 1-8 and Comparative Example 1.

[0127]

[0128] According to Example 1, the ammonium sulfate product produced meets the Grade I standard of GBT535-2020 "Fertilizer Grade Ammonium Sulfate". Its selling price is double that of the inferior Grade II product standard, and the recovery benefit is increased by 142%. The produced ammonium dihydrogen phosphate product meets the iron phosphate recycling standard, and the recovery benefit is increased by 200%. The recovery value of the magnesium ammonium phosphate product is also improved, achieving resource utilization. As can be seen from the data of Examples 1 and 5, this application can further regulate the quality of ammonium dihydrogen phosphate product by controlling the magnesium content in the first mother liquor. As can be seen from the data of Examples 1, 3 to 6, this application can further regulate the quality of ammonium sulfate and ammonium dihydrogen phosphate by controlling the specific gravity and phosphorus content of the first mother liquor. In particular, when the specific gravity of the first mother liquor is controlled at 1.41 to 1.43 and the phosphorus content is controlled at 80 g / L to 100 g / L, the main content of ammonium dihydrogen phosphate product is ≥55%, which can be directly applied in the production process of iron phosphate, further improving the product value.

[0129] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for treating wastewater, characterized in that, The processing method includes: The wastewater undergoes a first concentration and crystallization treatment to obtain a concentrated liquid. This concentrated liquid is then subjected to solid-liquid separation to obtain ammonium sulfate and a first mother liquor. The specific gravity and phosphorus content of the first mother liquor are monitored. The wastewater contains NH4+. + SO4 2- and PO4 3- ; When the specific gravity and phosphorus content of the first mother liquor meet the first preset value, the first mother liquor is subjected to a second concentration and crystallization treatment to obtain ammonium dihydrogen phosphate and a second mother liquor. When the specific gravity and phosphorus content of the first mother liquor do not meet the first preset value, the first mother liquor is mixed with the wastewater and / or the concentrated liquid phase of the wastewater and then subjected to a first concentration and crystallization treatment.

2. The processing method according to claim 1, characterized in that, In the step of performing a second concentration and crystallization treatment on the first mother liquor to obtain ammonium dihydrogen phosphate and a second mother liquor when the specific gravity and phosphorus content of the first mother liquor meet the first preset value: The first preset value includes a specific gravity of 1.41 to 1.43 for the first mother liquor and a phosphorus content of 80 g / L to 100 g / L for the first mother liquor.

3. The processing method according to claim 1, characterized in that, In the step of obtaining ammonium dihydrogen phosphate and a second mother liquor by performing a second concentration and crystallization treatment on the first mother liquor when the specific gravity and phosphorus content of the first mother liquor meet the first preset value, the second mother liquor is mixed with the wastewater and / or the liquid phase after wastewater concentration and then subjected to the first concentration and crystallization treatment. And / or, the second concentration and crystallization treatment takes 5 to 7 hours.

4. The processing method according to claim 1, characterized in that, The steps of performing a first concentration and crystallization treatment on the wastewater to obtain a concentrated treatment liquid, performing solid-liquid separation treatment on the concentrated treatment liquid to obtain ammonium sulfate and a first mother liquor, and monitoring the specific gravity and the mass content of phosphorus in the first mother liquor include: The pH of the wastewater is adjusted to a first value to precipitate magnesium ammonium phosphate solids, and pretreated wastewater and magnesium ammonium phosphate are separated. The wastewater includes NH4+. + Mg 2+ SO4 2- and PO4 3- Furthermore, the pH value is a second value, which is less than the first value. Optionally, the first value is 5 to 7, the second value is 1.5 to 3, and the mass content of magnesium in the pretreated wastewater is ≤150 mg / L. The pretreated wastewater is subjected to a first concentration and crystallization treatment to obtain a concentrated treatment liquid. The concentrated treatment liquid is then subjected to solid-liquid separation treatment to obtain ammonium sulfate and a first mother liquor. The specific gravity of the first mother liquor and the mass content of phosphorus in the first mother liquor are monitored.

5. The processing method according to claim 1, characterized in that, The processing method further includes: Monitor the mass content of magnesium in the first mother liquor. When the mass content of magnesium in the first mother liquor meets the second preset value, the first mother liquor is diluted and mixed with the wastewater. Optionally, the processing method satisfies at least one of the following: (1) The second preset value includes a magnesium content in the first mother liquor of ≥1.5 g / L; (2) The first concentration and crystallization treatment includes at least one liquid phase concentration treatment and one concentration and crystallization treatment. The wastewater is concentrated to obtain a first concentrated liquid phase, and the first concentrated liquid phase is concentrated and crystallized to obtain the concentrated treatment liquid. Optionally, the first concentrated liquid phase is used to dilute the first mother liquor.

6. A wastewater treatment system, characterized in that, include: An ammonium sulfate concentration and crystallization unit is used to perform a first concentration and crystallization treatment on the wastewater to obtain a concentrated treatment solution. An ammonium sulfate separation unit is used to separate and concentrate the treatment liquid to obtain ammonium sulfate and a first mother liquor. The inlet of the ammonium sulfate separation unit is connected to the outlet of the ammonium sulfate concentration and crystallization unit. The first mother liquor post-processing unit includes a first mother liquor storage tank and an ammonium dihydrogen phosphate concentration and separation module. The outlet of the first mother liquor storage tank is connected to a hydrometer and a sampling port. The ammonium dihydrogen phosphate concentration and separation module is used to perform a second concentration and crystallization treatment on the first mother liquor to obtain ammonium dihydrogen phosphate and a second mother liquor. The inlet of the first mother liquor storage tank is connected to the outlet of the ammonium sulfate separation unit. The outlet of the first mother liquor storage tank is connected to the inlet of the ammonium sulfate concentration and crystallization unit and the inlet of the ammonium dihydrogen phosphate concentration and separation module, respectively.

7. The processing system according to claim 6, characterized in that, The ammonium dihydrogen phosphate concentration and separation module includes a first mother liquor concentration and crystallization sub-module, an ammonium dihydrogen phosphate separation sub-module, and a second mother liquor storage tank. The outlet of the first mother liquor storage tank is connected to the inlet of the ammonium sulfate concentration and crystallization unit and the inlet of the first mother liquor concentration and crystallization sub-module, respectively. The outlet of the first mother liquor concentration and crystallization sub-module is connected to the inlet of the ammonium dihydrogen phosphate separation sub-module. The outlet of the ammonium dihydrogen phosphate separation sub-module is connected to the inlet of the second mother liquor storage tank. The outlet of the second mother liquor storage tank is connected to the inlet of the ammonium sulfate concentration and crystallization unit.

8. The processing system according to claim 6, characterized in that, The processing system further includes a pretreatment unit for separating magnesium from the processing system to obtain magnesium ammonium phosphate. The outlet of the pretreatment unit is connected to the inlet of the ammonium sulfate concentration and crystallization unit.

9. The processing system according to claim 6, characterized in that, The first mother liquor post-processing unit further includes a first mother liquor dilution storage tank, the outlet of which is connected to the inlet of the first mother liquor dilution storage tank. And / or, the sampling port is connected to a phosphorus content detection module and / or a magnesium content detection module.

10. The processing system according to claim 9, characterized in that, The ammonium sulfate concentration and crystallization unit includes a liquid phase concentration module and a concentration and crystallization module connected in sequence. The outlet of the first mother liquor storage tank is connected to the inlet of the concentration and crystallization module, and the outlet of the liquid phase concentration module is connected to the inlet of the first mother liquor dilution storage tank.

Images