Treatment method for terminal salt-splitting mother liquor of zero-discharge treatment system for iron phosphate wastewater

Abstract

The present invention relates to a treatment method for the terminal salt-splitting mother liquor of a zero-discharge treatment system for iron phosphate wastewater. Among them, the treatment method for the terminal salt-splitting mother liquor includes: S1. Precipitating heavy metal ions in the salt-splitting mother liquor to obtain a clear liquid; S2. Mixing the clear liquid with a ferrous salt solution and hydrogen peroxide to obtain a mixed slurry; S3. Performing pressure filtration on the mixed slurry to obtain a first filter cake and a pressure filtration mother liquor. Subsequently, washing the first filter cake to obtain a first washing liquid and a second filter cake; S4. Aging, washing, and pressure filtering the second filter cake to obtain a third filter cake and a second washing liquid; S5. Sintering and dehydrating the third filter cake to obtain battery-grade anhydrous iron phosphate; wherein, the pressure filtration mother liquor and the first washing liquid are low-concentration ammonium sulfate solutions, and the pressure filtration mother liquor and the washing liquid are used for refluxing to the iron phosphate wastewater treatment system to prepare ammonium sulfate products; the second washing liquid is used for preparing the ferrous salt solution in step S2.

Description

Technical Field

[0001] The present invention belongs to the technical field of industrial wastewater treatment, and relates to a treatment method for the terminal salt-separating mother liquor of a zero-discharge treatment system for iron phosphate wastewater. Background Art

[0002] In the existing zero-discharge treatment system for iron phosphate wastewater, the main steps include pretreatment, membrane concentration + high-efficiency evaporation concentration, and crystallization and salt separation to achieve the purpose of zero discharge. However, in this treatment system, the mother liquor and the rinsing water are collected separately. Among them, the rinsing water has a large volume and a relatively low TDS (Total Dissolved Solids) content compared to the mother liquor. The mother liquor has a high TDS content and a smaller volume than the rinsing water. Therefore, the mother liquor and the rinsing water are pretreated separately according to their characteristics. First, the suspended solids content in the water is reduced, and then RO (Reverse Osmosis) membrane concentration is carried out. The produced pure water is recycled, and the concentrated water is subjected to high-efficiency evaporation concentration and crystallization separation. The products are ammonium sulfate and ammonium phosphate. Specifically, the primary crystallization and salt separation product is ammonium sulfate, and the secondary cooling crystallization and salt separation product is ammonium phosphate.

[0003] In the existing treatment method, the mother liquor from which the by-products are separated mainly flows back to the front end of the system for treatment. However, for the salt-separating mother liquor at the back end of crystallization and salt separation flowing back to the front end of membrane treatment and being treated by the system circulation method, there are the following defects: The content of impurity ions in the mother liquor after salt separation is high: calcium ions are 300 - 600 mg / L, magnesium ions are 800 - 2000 mg / L, manganese ions are 600 - 1200 mg / L, and iron ions are 200 - 50 mg / L, and the TDS is high (generally 150 - 220 g / L). When directly flowing back to the front end, the pretreatment load at the front end increases, the salt content of the water entering the membrane equipment rises, the operating pressure increases, the water production flow rate decreases, and the equipment and pipelines are prone to scale and fouling. At the same time, when the salt-separating mother liquor at the back end of crystallization and salt separation is flowed back to the evaporation system, the defect of this method is that after evaporation and crystallization separation, the remaining salt-separating mother liquor water contains a large amount of sodium ions and other metal ions. During the evaporation system circulation and concentration process, the concentration increases, and miscellaneous salts such as magnesium ammonium sulfate and sodium / magnesium / manganese sulfate are generated and separated together with the ammonium sulfate crystals, affecting the nitrogen content of the product ammonium sulfate. The ammonium sulfate has been below the coking grade (nitrogen content ≥ 20.5%) for a long time, reducing the economic value.

[0004] In view of the above, it is necessary to further improve and perfect the treatment method for the terminal salt-separating mother liquor of the zero-discharge treatment system for iron phosphate wastewater to effectively treat the iron phosphate wastewater and carry out resource recovery. Summary of the Invention

[0005] In order to solve the problem that the mother liquor of salt separation is difficult to treat, the present invention provides a method for treating the terminal mother liquor of salt separation in a zero-discharge treatment system for iron phosphate wastewater, so as to effectively reduce the TDS and the content of other metal ions in the water quality and recover the phosphorus element in the high-salt wastewater, and realize the zero-discharge treatment system for iron phosphate wastewater with resource recovery of the terminal mother liquor of salt separation.

[0006] The present application provides a method for treating the terminal mother liquor of iron phosphate wastewater, comprising the steps of:

[0007] S1. Precipitating heavy metal ions in the mother liquor of salt separation to obtain a clear liquid;

[0008] S2. Mixing the clear liquid with a ferrous salt solution and hydrogen peroxide to obtain a mixed slurry;

[0009] S3. Performing pressure filtration on the mixed slurry to obtain a first filter cake and a pressure filtration mother liquor. Thereafter, washing the first filter cake to obtain a first washing liquid and a second filter cake;

[0010] S4. Performing aging, pressure filtration and washing on the second filter cake to obtain a third filter cake and a second washing liquid;

[0011] S5. Sintering and dehydrating the third filter cake to obtain battery-grade anhydrous iron phosphate;

[0012] Wherein, the pressure filtration mother liquor and the first washing liquid are ammonium sulfate solutions with low concentrations, and the pressure filtration mother liquor and the washing liquid are used for refluxing to the iron phosphate wastewater treatment system to prepare ammonium sulfate products; the second washing liquid is used for preparing the ferrous salt solution in step S2.

[0013] In some embodiments, the phosphorus content in the mother liquor of salt separation is 3%-8%, the calcium ion content is 300-600 mg / L, the magnesium ion content is 800-2000 mg / L, the manganese ion content is 600-1200 mg / L, the iron ion content is 200-500 mg / L, and the sodium ion content is 15000-30000 mg / L.

[0014] In some embodiments, step S1 includes:

[0015] Collecting the mother liquor of salt separation, and thereafter, adjusting the pH value of the mother liquor of salt separation to 7.0-7.5 to obtain a mixed slurry;

[0016] Performing pressure filtration on the mixed slurry to obtain the clear liquid and a filter cake;

[0017] Wherein, the contents of iron ions, calcium ions, magnesium ions and manganese ions in the clear liquid are all lower than 50 ppm, and the filter cake includes magnesium ammonium phosphate, manganese ammonium phosphate and calcium phosphate.

[0018] In some embodiments, step S2 includes:

[0019] Providing the ferrous salt solution;

[0020] Mixing the supernatant with the ferrous salt solution and hydrogen peroxide, stirring and reacting for 20 - 40 min, and then heating to 60 - 80 °C and stirring and reacting for 30 - 60 min to obtain a mixed slurry;

[0021] Wherein, the molar ratio of ferrous ions in the ferrous salt solution to phosphorus in the supernatant is 1:1.2 - 0.95, and the molar ratio of hydrogen peroxide in hydrogen peroxide to ferrous ions in the ferrous salt solution is 0.5 - 0.75:1.

[0022] In some embodiments, the ferrous salt solution is a saturated ferrous sulfate solution.

[0023] In some embodiments, step S3 includes:

[0024] Performing pressure filtration on the mixed slurry using a filter press to obtain a first filter cake and a pressure filtration mother liquor;

[0025] Washing the first filter cake with water having a conductivity less than or equal to 20 us / cm after membrane concentration treatment to obtain a first washing solution and a second filter cake;

[0026] Wherein, the conductivity of the first washing solution is 3000 - 5000 us / cm.

[0027] In some embodiments, step S4 includes:

[0028] Adding water to the second filter cake and stirring to obtain a slurry-like mixture;

[0029] Adding phosphoric acid to the slurry-like mixture, stirring and then heating to 90 - 100 °C and maintaining the temperature and stirring for 60 - 80 min to obtain an intermediate product;

[0030] Performing pressure filtration and washing on the intermediate product to obtain a third filter cake and a second washing solution.

[0031] In some embodiments, the slurry-like mixture and the phosphoric acid are mixed in a ratio of a molar ratio of ferrous ions to phosphoric acid of 1:1.5 - 2.0.

[0032] In some embodiments, step S5 includes:

[0033] Performing drying treatment on the third filter cake so that the moisture content of the third filter cake ≤ 5%;

[0034] Performing high-temperature sintering on the dried third filter cake to obtain battery-grade anhydrous iron phosphate.

[0035] In some embodiments, the high-temperature sintering includes a first sintering stage, a second sintering stage, and a third sintering stage. Among them, the first sintering stage is a temperature rising stage, that is, the temperature is raised to 550-650 °C, and the temperature rising time is 60-90 min. The second sintering stage is a temperature maintaining stage, that is, the temperature is 550-650 °C, and the maintaining time is 100-150 min. The third sintering stage is a temperature dropping stage, that is, the temperature is dropped to room temperature, and the temperature dropping time is 100-150 min. Beneficial effects:

[0036] (1) Compared with the existing treatment methods, after the mother liquor for salt separation is treated by this method, the TDS and the contents of other metal ions in the water quality are effectively reduced, thereby reducing the impact on the front end of the zero-discharge system for iron phosphate wastewater;

[0037] (2) Compared with the existing treatment methods, the present invention effectively reduces the impact on the purity of ammonium salt by-products, and fully utilizes the phosphorus element in the water quality to produce high-purity anhydrous iron phosphate;

[0038] (3) In the treatment method of this application, the content of impurity elements in the low-concentration ammonium sulfate wastewater generated is low, and it is recycled to the front end of the system for treatment. The process additives phosphoric acid, ammonia water, ferrous, and hydrogen peroxide are converted into ammonium by-products after passing through the system cycle, and no other impurity elements are introduced, and at the same time, resource recovery is realized. Description of the Drawings

[0039] Figure 1 It is a schematic flow chart of the conventional treatment method for the zero-discharge system of iron phosphate wastewater in the prior art;

[0040] Figure 2 It is a schematic flow chart of the treatment method for the terminal mother liquor for salt separation of the zero-discharge treatment system for iron phosphate wastewater in this application;

[0041] Figure 3 It is a schematic flow chart of step S1 in the treatment method for the terminal mother liquor for salt separation of the zero-discharge treatment system for iron phosphate wastewater in this application;

[0042] Figure 4 It is a process flow chart of the treatment method for the terminal mother liquor for salt separation of a zero-discharge treatment system for iron phosphate wastewater in this application;

[0043] Figure 5 It is a process flow chart of another treatment method for the terminal mother liquor for salt separation of the zero-discharge treatment system for iron phosphate wastewater in this application. Detailed Embodiments

[0044] The embodiments of the technical solution of the present application will be described in detail below with reference to the accompanying drawings. The following embodiments are only used to illustrate the technical solution of the present application more clearly, so they are only examples and cannot be used to limit the protection scope of the present application.

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above accompanying drawings are intended to cover non-exclusive inclusion.

[0046] Referring to "embodiments" herein means that the specific features, structures, or characteristics described in connection with the embodiments can be included in at least one embodiment of this application. The phrase appears in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0047] As Figure 1 shown, Figure 1 as shown in the content, it is the conventional treatment process of the zero-discharge system for iron phosphate wastewater: the mother liquor and the rinsing water are collected separately. Considering the characteristics that the amount of rinsing water is large and the TDS content is relatively low compared with the mother liquor, while the TDS content of the mother liquor water is high and the amount of water is smaller than that of the rinsing water, they are pretreated separately to reduce the suspended solid content in the water, and the pretreated water is concentrated by an RO membrane to produce pure water for reuse, and the concentrated water is subjected to high-efficiency evaporation concentration and crystallization separation. The products are ammonium sulfate and ammonium phosphate, among which the first crystallization and salt separation product is ammonium sulfate, and the second cooling crystallization and salt separation product is ammonium phosphate; in the conventional treatment method, the mother liquor for separating by-products mainly flows back to the front end of the system for treatment. The defect of this method: after evaporation crystallization separation, the remaining salt separation mother liquor contains a large amount of sodium ions and other metal ions. During the circulating concentration process of the evaporation system, the concentration increases, and miscellaneous salts such as magnesium ammonium sulfate, sodium sulfate / magnesium / manganese are generated and separated together with the ammonium sulfate crystals, affecting the nitrogen content of the product ammonium sulfate. The ammonium sulfate has been below the coking grade (nitrogen content ≥ 20.5%) for a long time, and the economic value has decreased.

[0048] To solve the problems existing in the aforementioned prior art, as Figure 2 shown, this application proposes a method for treating the terminal salt separation mother liquor of a zero-discharge treatment system for iron phosphate wastewater, including the steps of:

[0049] S1. Precipitate heavy metal ions in the salt separation mother liquor to obtain a clear liquid;

[0050] S2. Mix the clear liquid with a ferrous salt solution and hydrogen peroxide to obtain a mixed slurry;

[0051] S3. Filter press the mixed slurry to obtain a first filter cake and a filtrate mother liquor. Subsequently, wash the first filter cake to obtain a first washing liquid and a second filter cake;

[0052] S4. Age, filter press, and wash the second filter cake to obtain a third filter cake and a second washing liquid;

[0053] S5. Sinter and dehydrate the third filter cake to obtain battery-grade anhydrous ferric phosphate;

[0054] Among them, the filtrate mother liquor and the first washing liquid are ammonium sulfate solutions with low concentrations. The filtrate mother liquor and the washing liquid are used to be refluxed to the ferric phosphate wastewater treatment system to prepare ammonium sulfate products; the second washing liquid is used for the preparation of the ferrous salt solution in step S2.

[0055] It should be noted that in this application, the salt-separated mother liquor to be treated is a waste liquid with a phosphorus content of 3%-8%, a calcium ion content of 300-600 mg / L, a magnesium ion content of 800-2000 mg / L, a manganese ion content of 600-1200 mg / L, an iron ion content of 200-500 mg / L, and a sodium ion content of 15000-30000 mg / L.

[0056] Among them, step S1 includes:

[0057] S10. Collect the salt-separated mother liquor. Subsequently, adjust the pH value of the salt-separated mother liquor to 7.0-7.5 to obtain a mixed slurry;

[0058] S11. Filter press the mixed slurry to obtain the clear liquid and the filter cake;

[0059] Among them, the contents of iron ions, calcium ions, magnesium ions, and manganese ions in the clear liquid are all lower than 50 ppm, and the filter cake includes magnesium ammonium phosphate, manganese ammonium phosphate, and calcium phosphate.

[0060] Specifically, as Figure 3 shown, in this application, first collect the salt-separated mother liquor into the mother liquor tank. There is a stirring device in the mother liquor tank. Through continuous stirring, homogenize and avoid crystallization and precipitation of the mother liquor. Subsequently, add ammonia water to the mother liquor tank to adjust the pH value of the salt-separated mother liquor to 7.0-7.5, and stir and react for 30-60 min. Rely on the enriched phosphorus element in the salt-separated mother liquor to form a high-phosphate ionic environment, and destroy the precipitation-dissolution equilibrium of calcium phosphate, magnesium ammonium phosphate, and manganese ammonium phosphate under neutral or weakly alkaline conditions to precipitate calcium, magnesium, and manganese elements to obtain a mixed slurry.

[0061] Furthermore, the bottom of the mother liquor tank is connected to a plate and frame feed pump, and the mixed slurry in the mother liquor tank is pumped into a plate and frame filter press. The plate and frame filter cloth is made of polyester, with an air permeability of 1 - 3 L / ㎡ / s. Clear liquid and filter cake are obtained through filtration. The clear liquid is sampled and tested. After treatment, the iron, calcium, magnesium, and manganese ions in the clear liquid are all below 50 ppm. The main components of the filter cake are magnesium ammonium phosphate, manganese ammonium phosphate, calcium phosphate, etc. After the filter cake is sludge-dried, the mass fraction of available phosphorus pentoxide is ≥40%, the moisture content is ≤5%, and the nitrogen content is ≥11%, and it can be sold as citric acid-soluble phosphate fertilizer.

[0062] Among them, step S2 includes:

[0063] S20: Provide a ferrous salt solution;

[0064] S21: Mix the clear liquid with the ferrous salt solution and hydrogen peroxide, stir and react for 20 - 40 min. Then, raise the temperature to 60 - 80 °C and stir and react for 30 - 60 min to obtain a mixed slurry;

[0065] Among them, the molar ratio of ferrous ions in the ferrous salt solution to phosphorus in the clear liquid is 1:1.2 - 0.95, and the molar ratio of hydrogen peroxide in hydrogen peroxide to ferrous ions in the ferrous salt solution is 0.5 - 0.75:1.

[0066] Among them, the provided ferrous salt solution is a saturated ferrous sulfate solution, and the raw material can be selected from one of ferrous sulfate or ferrous sulfate heptahydrate. When preparing the ferrous sulfate solution, the preparation temperature needs to be controlled at 50 - 60 °C, stirred until dissolved and saturated, and the iron ion content in the prepared ferrous sulfate solution is sampled and tested; then, the prepared ferrous sulfate solution is mixed with the clear liquid prepared in step S1, and hydrogen peroxide is added for oxidation at the same time, stirred and reacted for 20 - 40 min. When the color presents light yellow, the liquid temperature is raised to 60 - 80 °C and stirred continuously for 30 - 60 min to obtain a mixed slurry. Through the control of temperature, stirring rate, and pH, the iron element content in each batch of saturated solution is similar, which is easy for production control. At the same time, all saturated ferrous sulfate solutions are used, which can effectively increase the volume efficiency of subsequent synthesis of iron phosphate.

[0067] In this application, the hydrogen peroxide used is 27% - 30% industrial-grade hydrogen peroxide. The addition ratio of ferrous ions to phosphorus is 1:0.95 - 1.20, and the molar ratio of hydrogen peroxide to ferrous ions is 0.5 - 0.75:1. At this ratio, the content of iron phosphate in the obtained mixed slurry is relatively high.

[0068] Among them, step S3 includes:

[0069] S30: Use a filter press to filter the mixed slurry to obtain a first filter cake and a filter press mother liquor;

[0070] S31. Wash the first filter cake with water having a conductivity less than or equal to 20 us / cm after membrane concentration treatment to obtain a first cleaning solution and a second filter cake;

[0071] Among them, the conductivity of the first cleaning solution is 3000 - 5000 us / cm.

[0072] Specifically, in this application, after the reaction for synthesizing iron phosphate is completed, the mixed slurry is subjected to pressure filtration treatment. Preferably, a plate and frame filter press can be used for pressure filtration treatment to obtain a first filter cake and a pressure filtration mother liquor. Among them, the separated pressure filtration mother liquor is mainly a low-concentration ammonium sulfate solution, which is refluxed to the front-end water tank of the zero-discharge treatment system for iron phosphate wastewater. Through the zero-discharge treatment system for iron phosphate wastewater, it is concentrated and evaporated to produce ammonium sulfate products. The separated first filter cake is washed with water. The water used for washing the first filter cake is pure water (conductivity ≤ 20 μs / cm) treated by membrane concentration. Wash until the conductivity of the first cleaning solution is 3000 - 5000 us / cm, stop washing, and collect the second filter cake obtained after washing.

[0073] Among them, step S4 includes:

[0074] S40. Add water to the second filter cake and stir to obtain a slurry-like mixture;

[0075] S41. Add phosphoric acid to the slurry-like mixture, stir and heat up to 90 - 100 °C, and keep stirring for 60 - 80 min to obtain an intermediate product;

[0076] S42. Perform pressure filtration and cleaning treatment on the intermediate product to obtain a third filter cake and a second cleaning solution.

[0077] In this application, water is added to the second filter cake and stirred until it is broken up into a slurry-like state to obtain a slurry-like mixture. Then, according to the molar ratio of ferrous ions to phosphoric acid of 1:1.5 - 2.0, phosphoric acid is added to the slurry-like mixture for mixing and stirring, and the temperature is raised to 90 - 100 °C at a gentle boil. Preferably, the temperature is raised to 95 - 99 °C, and the stirring speed is 400 - 500 r / min. By increasing the stirring speed, the phenomenon of violent boiling can be avoided. During the stirring and heating process, the color will change from light yellow to milky white. Taking this as a time node, keep stirring for 60 - 80 min; since the content of iron, arsenic, and heavy metal elements is limited in national standard industrial phosphoric acid, it can avoid affecting the iron-phosphorus ratio of the iron phosphate slurry and the purity of the terminal iron phosphate product. Therefore, industrial-grade phosphoric acid is preferably involved in phosphoric acid.

[0078] Furthermore, after the insulation is completed, the intermediate product is subjected to filter pressure treatment to obtain a third filter cake and a second cleaning liquid. The filter pressure treatment can be performed using a plate and frame filter press. The separated filter press mother liquor has a low salt content, TDS10000-25000 mg / L, pH value 2-3, and temperature 40-60°C. It can be refluxed to the S2 stage and used as pre-dissolved water for the ferrous salt solution. The separated filter cake is washed with water treated with membrane concentration (conductivity ≤20μs / cm, pH6-7). The second cleaning liquid is washed until the conductivity is 300-500μs / cm, then the washing is stopped and the washed filter cake, i.e., the third filter cake, is collected. The second cleaning liquid has low salt and impurity element content and contains some phosphate, which can be refluxed to the S2 stage and used as pre-dissolved water for the ferrous salt solution.

[0079] Wherein, step S5 includes:

[0080] S50, drying the third filter cake so that the moisture content of the third filter cake is ≤5%;

[0081] S51, sintering the third filter cake after the drying process at high temperature to obtain battery-grade anhydrous iron phosphate.

[0082] In the present application, the third filter cake is dried, for example, by a rotary drum dryer or spray drying, so that the moisture content of the third filter cake is ≤5%. Thereafter, the dried third filter cake is sintered at high temperature to obtain battery-grade anhydrous iron phosphate. The indicators of the prepared battery-grade anhydrous iron phosphate meet the industry standard HG / T4701-2021 for iron phosphate for batteries. The specific requirements are as follows: Fe% 35.7-36.7, P% 20.0-21.1, Fe / P = 0.96-1.0, specific surface area 3-16m2 / g, particle size D501-9μm, and XRD impurity peak ratio <5%.

[0083] Further, in the present application, high temperature sintering includes a first sintering stage, a second sintering stage and a third sintering stage, wherein the first sintering stage is a temperature rising stage, i.e., the temperature is raised to 550-650°C, and the heating time is 60-90 minutes, the second sintering stage is a temperature maintaining stage, i.e., the temperature is 550-650°C, and the maintenance time is 100-150 minutes, and the third sintering stage is a temperature decreasing stage, i.e., the temperature is lowered to room temperature, and the cooling time is 100-150 minutes. In the present application, the purity of the anhydrous ferric phosphate product is ensured by controlling the three temperature stages.

[0084] Specifically, Figure 4 and Figure 5As shown in the content, the treatment method of the terminal salt-splitting mother liquor of the zero-discharge treatment system for iron phosphate wastewater proposed in this application operates stably, reduces the problem of high impurity content of by-products caused by the reflux of salt-splitting mother liquor and the decline in economic value, and the produced battery-grade anhydrous iron phosphate has high economic value, and realizes the system closed-loop and the resource utilization of high-salt wastewater.

[0085] Next, the treatment method of the terminal salt-splitting mother liquor of the iron phosphate wastewater zero-discharge treatment system of this application will be further explained with specific examples.

[0086] Example 1

[0087] S1: The phosphorus content in the salt-splitting mother liquor is 5%, calcium ion is 450 mg / L, magnesium ion is 1500 mg / L, manganese ion is 1000 mg / L, iron ion is 400 mg / L, and sodium ion is 20000 mg / L; collect the salt-splitting mother liquor, continuously stir, homogenize and avoid crystallization and precipitation of the mother liquor. Then, add ammonia water to adjust the pH value to 7.5, stir and react for 50 min. The bottom of the mother liquor tank is connected to the plate-frame feed pump, and the mixed slurry in the mother liquor tank is pumped into the plate-frame filter press. The clear liquid is collected into the phosphorus salt collection tank, and the phosphorus content is detected by sampling to be 4.613%, in which the iron ion is 49 ppm, the calcium ion is 49.4 ppm, the magnesium ion is 48.9 ppm, and the manganese ion is 49.1 ppm; the filter cake is subjected to sludge drying, and the main components are magnesium ammonium phosphate, manganese ammonium phosphate, calcium phosphate, etc., in which the mass fraction of available phosphorus pentoxide is 40%, the moisture is 4.9%, and the nitrogen content is 11.9%, which can be sold as citric-soluble phosphate fertilizer.

[0088] S2: First, prepare ferrous sulfate solution, control the preparation temperature at 60 °C, stir until dissolved and saturated, and sample to detect the iron content in the solution; then mix the ferrous sulfate solution with the phosphorus salt solution (the clear liquid after impurity removal of the salt-splitting mother liquor described in S1 - the clear liquid of the plate-frame filtration), and at the same time add hydrogen peroxide for oxidation, stir and react for 30 min. When the mixed liquid turns light yellow, raise the liquid temperature to 78 °C and continue to stir for 56 min to obtain a mixed slurry. Among them, the hydrogen peroxide is 28% industrial-grade hydrogen peroxide, and the addition ratio is that the molar ratio of ferrous ion to phosphorus is 1:1, and the molar ratio of hydrogen peroxide to ferrous ion is 0.6:1.

[0089] S3: Carry out solid-liquid separation of the mixed slurry by using a plate-frame filter press. The separated filter-press mother liquor is mainly a low-concentration ammonium sulfate solution, which is refluxed to the front-end water tank of the iron phosphate wastewater treatment system, and ammonium sulfate products are prepared by concentration and evaporation through the iron phosphate wastewater treatment system; the separated first filter cake is washed, and the washing water is the water treated by membrane concentration (conductivity 20 μs / cm), and the washing is stopped until the conductivity of the first washing liquid is 4000 μs / cm, and the second filter cake obtained after washing is collected.

[0090] S4: Add water to the second filter cake and stir to break it up into a slurry. Add phosphoric acid to it. The phosphoric acid involved is industrial-grade phosphoric acid. The addition ratio is that the molar ratio of ferrous ions to phosphoric acid is 1:1.5. Mix and stir, and heat the mixture to a gentle boil at 95°C. Increase the stirring speed to avoid the mixture boiling over. During the process of stirring and heating, the color changes from light yellow to milky white. Take this as the time node, keep warm and stir for 68 minutes. After the reaction is over, use a plate and frame filter press for separation. The separated mother liquor from the filter press has a low salt content, with a TDS of 20000 mg / L, a pH value of 2, and a temperature of 50°C. It is refluxed to the S2 stage as the pre-dissolving water for the ferrous solution. The separated filter cake is washed. The washing water is the water treated by membrane concentration (conductivity 19 μs / cm). Wash until the conductivity of the second washing liquid reaches 300 μs / cm, then stop washing and collect the third filter cake obtained after washing.

[0091] S5: Dry the third filter cake using a rotary drum dryer to reduce the moisture content of the filter cake to 5%. Then, conduct high-temperature sintering and control three temperature stages to ensure the purity of the anhydrous iron phosphate product. Specifically, in the temperature rising stage from 0°C to 550°C, the time is controlled for 90 minutes. In the temperature maintaining stage at 550°C, the time is maintained for 150 minutes. In the temperature dropping stage from 550°C to 24 (the description here seems incorrect, assuming it should be a proper value), the time is controlled for 140 minutes. The finished product after sintering is anhydrous iron phosphate. After testing the anhydrous iron phosphate, all indicators meet the industry standard HG / T 4701-2021 for iron phosphate for batteries: Fe% 36.1, P% 20.0, Fe / P = 1.0, specific surface area 12 m 2 / g, particle size D50 7 μm, and the proportion of XRD miscellaneous peaks is 4.9%.

[0092] Example 2

[0093] S1: The phosphorus content in the mother liquor for salt separation is 8%, calcium ions 520 mg / L, magnesium ions 1300 mg / L, manganese ions 800 mg / L, ferrous ions 350 mg / L, and sodium ions 30000 mg / L. Collect the mother liquor for salt separation, continuously stir, homogenize and avoid crystallization and precipitation of the mother liquor. Then, add ammonia water to adjust the pH value to 7.0 and stir and react for 40 minutes. Filter the mixed slurry, collect the clear liquid and take a sample to detect the phosphorus content, which is 7.652%. Among them, ferrous ions are 49.1 ppm, calcium ions are 49.6 ppm, magnesium ions are 49 ppm, and manganese ions are 48.9 ppm. The filter cake is subjected to sludge drying. The mass fraction of available phosphorus pentoxide is 41.2%, the moisture content is 4.99%, and the nitrogen content is 11.8%. It is sold as citrate-soluble phosphate fertilizer.

[0094] S2: First, prepare a ferrous sulfate heptahydrate solution, control the preparation temperature at 50 °C, stir until it is dissolved to saturation, and take a sample to detect the iron content in the solution. Then, mix the ferrous sulfate solution with the phosphate solution (the clarified liquid after impurity removal from the salt separation mother liquor described in S1 - the plate - frame filtration clarified liquid), and at the same time add hydrogen peroxide for oxidation, stir and react for 40 min. When the mixed liquid turns light yellow, raise the liquid temperature to 70 °C and continue to stir for 38 min. Among them, the hydrogen peroxide is 29% industrial - grade hydrogen peroxide, and the addition ratio is that the molar ratio of ferrous ion to phosphorus is 1:0.95, and the molar ratio of hydrogen peroxide to ferrous ion is 0.55:1.

[0095] S3: Use a plate - frame filter press to separate the solid and liquid of the mixed slurry. The separated filter - press mother liquor is mainly a low - concentration ammonium sulfate solution, which is refluxed to the front - end water tank of the iron phosphate wastewater treatment system and concentrated and evaporated through the iron phosphate wastewater treatment system to produce ammonium sulfate products. The first filter cake after separation is washed, and the washing water is the water treated by membrane concentration (conductivity 19.9 μs / cm). Wash until the conductivity of the first washing liquid is 3000 μs / cm, then stop washing, and collect the second filter cake obtained after washing.

[0096] S4: Add water to the second filter cake and stir to break it up into a slurry state. Add phosphoric acid to it, and the addition ratio is that the molar ratio of ferrous ion to phosphoric acid is 1:1.8. Mix and stir, and heat the mixed liquid to a gentle boil at 99 °C. Increase the stirring speed to avoid the mixed liquid from boiling over. During the stirring and heating process, the color changes from light yellow to milky white. Take this as the time node, keep warm and stir for 70 min. After the reaction ends, a plate - frame filter press can be used for separation. The separated filter - press mother liquor has a low salt content, with TDS 25000 mg / L, pH value 3, and temperature 60 °C, and is refluxed to the S2 stage as the pre - dissolution water for the ferrous solution. The filter cake after separation is washed, and the washing water is the water treated by membrane concentration (conductivity 19.3 μs / cm). Wash until the conductivity of the second washing liquid is 330 μs / cm, then stop washing, and collect the third filter cake obtained after washing.

[0097] S5: Dry the third filter cake by spray drying to reduce the moisture content of the filter cake to 5%. Then, carry out high - temperature sintering, control three temperature stages to ensure the purity of the anhydrous iron phosphate product. Specifically, in the temperature - rising stage from 0 °C to 650 °C, the time is controlled at 80 min; in the temperature - maintaining stage at 650 °C, the time is maintained for 100 min; in the temperature - dropping stage from 650 °C to 25 °C, the time is controlled at 110 min. The product after sintering is anhydrous iron phosphate. After testing, the anhydrous iron phosphate meets the industry standard HG / T4701 - 2021 for iron phosphate for batteries: Fe% 35.7, P% 21.0, Fe / P = 0.99, specific surface area 8 m 2 / g, particle size D50 3 μm, and the XRD miscellaneous peak ratio is 4.8%.

[0098] Example 3

[0099] S1: The phosphorus content in the mother liquor for salt separation is 6%, calcium ions 400 mg / L, magnesium ions 800 mg / L, manganese ions 1100 mg / L, iron ions 200 mg / L, and sodium ions 15000 mg / L; collect the mother liquor for salt separation, continuously stir, homogenize and avoid crystallization and precipitation of the mother liquor. Then, add ammonia water to adjust the pH value to 7.1, stir and react for 30 min. Connect the bottom of the mother liquor tank to the plate-frame feed pump, pump the mixed slurry in the mother liquor tank into the plate-frame filter press, collect the clear liquid into the phosphorus salt collection tank, and take a sample to detect that the phosphorus content is 5.616%, in which iron ions are 49.2 ppm, calcium ions are 49.1 ppm, magnesium ions are 49.3 ppm, and manganese ions are 49 ppm; the filter cake is subjected to sludge drying, and the main components are magnesium ammonium phosphate, manganese ammonium phosphate, calcium phosphate, etc., in which the mass fraction of available phosphorus pentoxide is 40.8%, the moisture content is 4.7%, and the nitrogen content is 11%, which can be sold as citric acid-soluble phosphate fertilizer.

[0100] S2: First, prepare a ferrous sulfate solution, control the preparation temperature at 53 °C, stir until dissolved and saturated, and take a sample to detect the iron content in the solution; then mix the ferrous sulfate solution with the phosphorus salt solution (the clear liquid after impurity removal of the mother liquor for salt separation described in S1 - the clear liquid of the plate-frame filtration), and at the same time add hydrogen peroxide for oxidation, stir and react for 28 min. When the mixed liquid turns light yellow, raise the liquid temperature to 60 °C and continue to stir for 60 min to obtain a mixed slurry. Among them, the hydrogen peroxide is 27% industrial-grade hydrogen peroxide, and the addition ratio is that the molar ratio of ferrous ions to phosphorus is 1:1.10, and the molar ratio of hydrogen peroxide to ferrous ions is 0.7:1.

[0101] S3: Perform solid-liquid separation on the mixed slurry using a plate-frame filter press. The separated filter press mother liquor is mainly a low-concentration ammonium sulfate solution, which is refluxed to the front-end water tank of the iron phosphate wastewater treatment system and concentrated and evaporated through the iron phosphate wastewater treatment system to produce ammonium sulfate products; the separated first filter cake is washed, and the washing water is the water treated by membrane concentration (conductivity 19.7 μs / cm), and the washing is stopped until the conductivity of the first washing liquid is 5000 μs / cm, and the second filter cake obtained after washing is collected.

[0102] S4: Add the second filter cake to water and stir to break it up into a slurry. Add phosphoric acid to it, with the molar ratio of ferrous ions to phosphoric acid being 1:1.9. Mix and stir, and heat the mixture to a gentle boil at 96 °C. Increase the stirring speed to avoid the mixture boiling over. During the stirring and heating process, the color changes from light yellow to milky white. Take this as the time point, keep warm and stir for 75 min. After the reaction ends, use a plate and frame filter press for separation. The separated mother liquor from the filter press has a low salt content (TDS 10000 mg / L, pH value 2.5, temperature 52 °C), and is refluxed to the S2 stage as the pre-dissolution water for the ferrous sulfate solution. The separated filter cake is washed with water treated by membrane concentration (conductivity 19.9 μs / cm) until the conductivity of the second washing liquid reaches 400 μs / cm, then stop washing and collect the washed third filter cake.

[0103] S5: Dry the third filter cake to reduce the moisture content of the filter cake to 4.5%. Then, carry out high-temperature sintering, controlling three temperature stages to ensure the purity of the anhydrous iron phosphate product. Specifically, the temperature rising stage is 0 °C to 580 °C, and the time is controlled for 70 min. The temperature maintaining stage is 580 °C, and the time is maintained for 120 min. The temperature dropping stage is 580 °C to 23, and the time is controlled for 130 min. The finished product after sintering is anhydrous iron phosphate. After testing the anhydrous iron phosphate, all indicators meet the industry standard HG / T 4701-2021 for iron phosphate for batteries: Fe% 36.2, P% 20.3, Fe / P = 0.96, specific surface area 16 m 2 / g, particle size D50 1 μm, and the proportion of XRD miscellaneous peaks 4.8%.

[0104] Example 4

[0105] S1: The phosphorus content in the mother liquor for salt separation is 3%, calcium ions 600 mg / L, magnesium ions 1000 mg / L, manganese ions 600 mg / L, ferrous ions 450 mg / L, and sodium ions 25000 mg / L. Collect the mother liquor for salt separation, continuously stir, homogenize and avoid crystallization and precipitation of the mother liquor. Then, add ammonia water to adjust the pH value to 7.2 and stir and react for 60 min. The bottom of the mother liquor tank is connected to a plate and frame feed pump, and the mixed slurry in the mother liquor tank is pumped into a plate and frame filter press. The clear liquid is collected into a phosphorus salt collection tank, and the phosphorus content is sampled and detected to be 2.523%, among which ferrous ions are 48.9 ppm, calcium ions are 49.4 ppm, magnesium ions are 49.5 ppm, and manganese ions are 49.2 ppm. The filter cake is subjected to sludge drying, and the main components are magnesium ammonium phosphate, manganese ammonium phosphate, calcium phosphate, etc. The mass fraction of available phosphorus pentoxide is 42%, the moisture is 4.7%, and the nitrogen content is 12%. It can be sold as citric acid-soluble phosphate fertilizer.

[0106] S2: First, prepare a ferrous salt solution. The preparation temperature needs to be controlled at 58°C, and stir until it is dissolved to saturation. Then, take a sample to detect the iron content in the solution. Next, mix the ferric salt solution with the phosphate solution (the clarified liquid after impurity removal from the salt separation mother liquor described in S1 - the plate - frame filtration clarified liquid), and simultaneously add hydrogen peroxide for oxidation. Stir and react for 25 minutes. When the mixed liquid turns light yellow, raise the liquid temperature to 80°C, and continue to stir for 30 minutes to obtain a mixed slurry. Among them, the hydrogen peroxide is 30% industrial - grade hydrogen peroxide, and the addition ratio is that the molar ratio of ferrous ion to phosphorus is 1:1.20, and the molar ratio of hydrogen peroxide to ferrous ion is 0.5:1.

[0107] S3: Use a plate - frame filter press to separate the solid and liquid of the mixed slurry. The separated filter - press mother liquor is mainly a low - concentration ammonium sulfate solution, which is refluxed to the front - end water tank of the iron phosphate wastewater treatment system, and ammonium sulfate products are prepared through concentration and evaporation by the iron phosphate wastewater treatment system. The first filter cake after separation is washed, and the washing water is the water treated by membrane concentration (conductivity 19.3 μs / cm). Rinse until the conductivity of the first washing liquid reaches 3500 μs / cm, then stop washing, and collect the second filter cake obtained after washing.

[0108] S4: Add pure water to the second filter cake and stir to break it up into a slurry state. Add phosphoric acid to it, and the addition ratio is that the molar ratio of ferrous ion to phosphoric acid is 1:2.0. Mix and stir, and heat the mixed liquid to a gentle boil at 98°C. Increase the stirring speed to avoid the mixed liquid from boiling over. During the process of stirring and heating, the mixed liquid changes from light yellow to milky white. Take this as a time node, keep it warm and stir for 60 minutes. Then, carry out solid - liquid separation. The separated filter - press mother liquor has low salt content: TDS 15000 mg / L, pH value 2.8, temperature 40°C, and it is refluxed to the S2 stage as the pre - dissolution water for the ferrous solution. The filter cake after separation is washed, and the washing water is the water treated by membrane concentration (conductivity 18 μs / cm). Wash until the conductivity of the second washing liquid reaches 450 μs / cm, then stop washing, and collect the third filter cake obtained after washing.

[0109] S6: Dry the third filter cake to reduce the moisture content of the filter cake to 5%. Then, carry out high - temperature sintering, and control three temperature stages to ensure the purity of the anhydrous iron phosphate product. Specifically, in the temperature - rising stage from 0°C to 600°C, the time is controlled at 60 minutes; in the temperature - maintaining stage at 600°C, the time is maintained for 140 minutes; in the temperature - dropping stage from 600°C to 22 (the unit here seems incorrect, assuming it should be a temperature value), control the time at 150 minutes. The product after sintering is anhydrous iron phosphate. After testing, the anhydrous iron phosphate meets the industry standard HG / T4701 - 2021 for iron phosphate used in batteries: Fe% 35.9, P% 20.7, Fe / P = 0.97, specific surface area 13 m 2 / g, particle size D50 9 μm, and the proportion of XRD miscellaneous peaks 4.9%.

[0110] Example 5

[0111] S1: The phosphorus content in the mother liquor for salt separation is 7%, calcium ion is 300 mg / L, magnesium ion is 2000 mg / L, manganese ion is 1200 mg / L, iron ion is 500 mg / L, and sodium ion is 19000 mg / L. Collect the mother liquor for salt separation, continuously stir, homogenize and avoid crystallization and precipitation of the mother liquor. Then add ammonia water to adjust the pH value to 7.3, stir and react for 45 min, filter press, collect the filtered clear liquid into the phosphorus salt collection tank, and take a sample to detect that the phosphorus content is 6.431%, in which the iron ion is 49 ppm, calcium ion is 49.4 ppm, magnesium ion is 48.9 ppm, and manganese ion is 49.1 ppm. The filter cake is subjected to sludge drying. The main components are magnesium ammonium phosphate, manganese ammonium phosphate, calcium phosphate, etc. The mass fraction of available phosphorus pentoxide is 41%, the moisture content is 4.5%, and the nitrogen content is 11.6%. It can be sold as citric acid-soluble phosphate fertilizer.

[0112] S2: First, prepare a ferrous sulfate heptahydrate ferrous salt solution, control the preparation temperature at 56 °C, stir until dissolved and saturated, and take a sample to detect the iron content in the solution. Then mix the ferrous sulfate solution with the phosphorus salt solution (the clear liquid after impurity removal of the mother liquor for salt separation described in S1 - the clear liquid after plate and frame filter press), and at the same time add hydrogen peroxide for oxidation, stir and react for 35 min. When the mixed liquid turns light yellow, raise the liquid temperature to 66 °C and continue to stir for 45 min to obtain a mixed slurry. Among them, the hydrogen peroxide is 28% industrial - grade hydrogen peroxide, and the addition ratio is that the molar ratio of ferrous ion to phosphorus is 1:0.98, and the molar ratio of hydrogen peroxide to ferrous ion is 0.75:1.

[0113] S3: The mixed slurry can be subjected to solid - liquid separation using a plate and frame filter press. The separated filter - press mother liquor is mainly a low - concentration ammonium sulfate solution, which is refluxed to the front - end water tank of the iron phosphate wastewater treatment system and concentrated and evaporated through the iron phosphate wastewater treatment system to produce ammonium sulfate products. The first filter cake after separation is washed, and the washing water is the water treated by membrane concentration (conductivity 20 μs / cm). Wash until the conductivity of the first washing liquid is 4500 μs / cm, stop washing, and collect the second filter cake obtained after washing.

[0114] S4: Add the second filter cake to water and stir to break it up into a slurry. Add phosphoric acid to it, with the molar ratio of ferrous ions to phosphoric acid being 1:1.6. Mix and stir, and heat the mixture to a gentle boil at 97 °C. Increase the stirring speed to avoid the mixture boiling over. During the stirring and heating process, the color changes from light yellow to milky white. Take this as the time node, keep warm and stir for 80 min. After the reaction is completed, use a plate and frame filter press for separation. The separated mother liquor from the filter press has a low salt content: TDS 18000 mg / L, pH value 3, and temperature 46 °C. It is refluxed to the S2 stage as the pre-dissolving water for the ferrous sulfate solution. The separated filter cake is washed, and the washing water is the water treated by membrane concentration (conductivity 19 μs / cm). Wash until the conductivity of the second washing liquid is 500 μs / cm, then stop washing and collect the obtained third filter cake.

[0115] S6: Dry the third filter cake using a rotary drum dryer to reduce the moisture content of the filter cake to 4.9%. Then, conduct high-temperature sintering, controlling three temperature stages to ensure the purity of the anhydrous iron phosphate product. Specifically, the temperature rising stage is 0 °C to 620 °C, with the time controlled at 75 min; the temperature maintaining stage is 620 °C, with the time maintained for 130 min; the temperature dropping stage is 620 °C to 21, with the time controlled at 100 min. The finished product after sintering is anhydrous iron phosphate. After testing the anhydrous iron phosphate, all indicators meet the industry standard HG / T 4701-2021 for iron phosphate for batteries: Fe% 36.7, P% 21.1, Fe / P = 0.98, specific surface area 5 m 2 / g, particle size D50 6 μm, and the XRD peak ratio of impurities is 4.7%.

[0116] As can be seen from the above embodiments, the anhydrous iron phosphate prepared by the method of the present invention meets all the indicators of the industry standard HG / T 4701-2021 for iron phosphate for batteries: Fe% 35.7 - 36.7, P% 20.0 - 21.1, Fe / P = 0.96 - 1.0, specific surface area 3 - 16 m 2 / g, particle size D50 1 - 9 μm, and the XRD peak ratio of impurities < 5%. It reduces the problem of high impurity content in by-products and decreased economic value caused by the reflux of the mother liquor for salt separation, realizes a system closed-loop, and enables the resource utilization of high-salt wastewater.

[0117] It should be noted that this application is not limited to the above embodiments. The above embodiments are only examples, and embodiments with the same composition and the same function and effect as the technical idea within the technical solution scope of this application are all included in the technical scope of this application. In addition, within the scope not departing from the gist of this application, various modifications that those skilled in the art can think of and other ways constructed by combining some constituent elements in the embodiments are also included in the scope of this application.

Claims

1. A method for treating the terminal salt-splitting mother liquor of a zero-discharge treatment system for iron phosphate wastewater, characterized in that, it includes the steps: S1. Precipitate heavy metal ions in the salt-splitting mother liquor to obtain a clear liquid; S2. Mix the clear liquid with a ferrous salt solution and hydrogen peroxide to obtain a mixed slurry; S3. Perform pressure filtration on the mixed slurry to obtain a first filter cake and a pressure filtration mother liquor. Thereafter, wash the first filter cake to obtain a first washing liquid and a second filter cake; S4. Age, pressure filter, and wash the second filter cake to obtain a third filter cake and a second washing liquid, and the conductivity of the second washing liquid is 300-500 μs / cm; S5. Sinter and dehydrate the third filter cake to obtain battery-grade anhydrous iron phosphate; wherein, the pressure filtration mother liquor and the first washing liquid are low-concentration ammonium sulfate solutions, and the pressure filtration mother liquor and the washing liquid are used to be refluxed to the iron phosphate wastewater treatment system to prepare ammonium sulfate products; the second washing liquid is used for the preparation of the ferrous salt solution in step S2; wherein, the phosphorus content in the salt-splitting mother liquor is 3%-8%, the calcium ion content is 300-600 mg / L, the magnesium ion content is 800-2000 mg / L, the manganese ion content is 600-1200 mg / L, the iron ion content is 200-500 mg / L, and the sodium ion content is 15000-30000 mg / L; wherein, the treatment of the iron phosphate wastewater by the zero-discharge treatment system for iron phosphate wastewater includes pretreatment, membrane concentration, evaporation concentration, and crystallization and salt splitting. The crystallization and salt splitting include primary crystallization and salt splitting and secondary cooling crystallization and salt splitting. The product of the primary crystallization and salt splitting is ammonium sulfate, and the product of the secondary cooling crystallization and salt splitting is ammonium phosphate. The salt-splitting mother liquor is the mother liquor obtained after the crystallization and salt splitting treatment.

2. The treatment method according to claim 1, characterized in that, step S1 includes: Collect the salt-splitting mother liquor. Thereafter, adjust the pH value of the salt-splitting mother liquor to 7.0-7.5 to obtain a mixed slurry; Perform pressure filtration on the mixed slurry to obtain the clear liquid and the filter cake; wherein, the contents of iron ions, calcium ions, magnesium ions, and manganese ions in the clear liquid are all lower than 50 ppm, and the filter cake includes magnesium ammonium phosphate, manganese ammonium phosphate, and calcium phosphate.

3. The treatment method according to claim 1, characterized in that, step S2 includes: Provide the ferrous salt solution; Mix the clear liquid with the ferrous salt solution and hydrogen peroxide, stir and react for 20-40 min. Thereafter, raise the temperature to 60-80 °C and stir and react for 30-60 min to obtain a mixed slurry; wherein, the molar ratio of ferrous ions in the ferrous salt solution to phosphorus in the clear liquid is 1:1.2~0.95, and the molar ratio of hydrogen peroxide in hydrogen peroxide to ferrous ions in the ferrous salt solution is 0.5~0.75:

1.

4. The treatment method according to claim 3, characterized in that, the ferrous salt solution is a saturated ferrous sulfate solution.

5. The treatment method according to claim 1, characterized in that, step S3 includes: The mixed slurry is subjected to pressure filtration using a filter press to obtain a first filter cake and a pressure filtration mother liquor; The first filter cake is washed with water having a conductivity less than or equal to 20 us / cm after membrane concentration treatment to obtain a first cleaning solution and a second filter cake; Among them, the conductivity of the first cleaning solution is 3000 - 5000 us / cm.

6. The treatment method according to claim 1, characterized in that, the step S4 includes: Adding water to the second filter cake and stirring to obtain a slurry-like mixture; Adding phosphoric acid to the slurry-like mixture, stirring and then heating to 90 - 100 °C, and maintaining the stirring for 60 - 80 min to obtain an intermediate product; Performing pressure filtration and cleaning treatment on the intermediate product to obtain a third filter cake and a second cleaning solution.

7. The treatment method according to claim 6, characterized in that, The slurry-like mixture and the phosphoric acid are mixed in a molar ratio of ferrous ions to phosphoric acid of 1:1.5 - 2.

0.

8. The treatment method according to claim 1, characterized in that, the step S5 includes: Performing drying treatment on the third filter cake so that the moisture content of the third filter cake ≤ 5%; Performing high-temperature sintering on the dried third filter cake to obtain battery-grade anhydrous iron phosphate.

9. The treatment method according to claim 8, characterized in that: The high-temperature sintering includes a first sintering stage, a second sintering stage and a third sintering stage. Among them, the first sintering stage is a temperature rising stage, that is, heating to 550 - 650 °C, and the heating time is 60 - 90 min. The second sintering stage is a temperature maintaining stage, that is, the temperature is 550 - 650 °C, and the maintaining time is 100 - 150 min. The third sintering stage is a temperature dropping stage, that is, cooling to room temperature, and the cooling time is 100 - 150 min.

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