A method for treating iron phosphate production wastewater

Abstract

The present application relates to the technical field of lithium ion battery cathode material, in particular to a kind of phosphorus acid iron production wastewater treatment method.The present application includes the following steps:S1.pH is adjusted to 10.6-11.5 by adding zirconium industry waste lye to phosphorus acid iron production wastewater, after reaction, solid-liquid separation is carried out, and the precipitate is removed, to obtain solution A;S2.carbonate is added to solution A, after reaction, solid-liquid separation is carried out, and the precipitate is removed, to obtain solution B;S3.solution B is reused to crude phosphoric acid for producing phosphorus acid iron;And / or, solution B is treated by membrane.The present application uses zirconium industry waste lye for the pretreatment of phosphorus acid iron production wastewater, not only can reduce the pretreatment cost, and the phosphorus acid root retention rate in pretreated wastewater is relatively high, can be directly reused to crude phosphoric acid, reduce phosphorus loss;While effectively reducing the hardness of phosphorus acid iron, when carrying out the later stage membrane treatment, it can significantly reduce the risk of fouling and membrane blocking.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery cathode material technology, and more specifically, to a method for treating wastewater from the production of iron phosphate. Background Technology

[0002] With the rapid development of new energy storage technologies and the booming rise of electric vehicles, lithium iron phosphate (LFP) batteries hold an absolute dominant position in the market. As a crucial cathode material for lithium-ion batteries, LFP has seen significant advancements in research and application, further driving up demand. The LFP production process, involving synthesis and washing, generates a large amount of acidic wastewater. Currently, this wastewater is mainly treated using ultrafiltration, nanofiltration, and reverse osmosis technologies. However, scaling and membrane clogging are prone to occur during treatment, affecting stable production operations. Therefore, effective pretreatment is essential to remove scale-forming ions.

[0003] A common pretreatment method is chemical precipitation, which involves adding sodium hydroxide and sodium carbonate to the wastewater to reduce its total hardness. However, this method is costly. Furthermore, reusing this pretreated water in the upstream ferric phosphate production process would further reduce production costs and improve efficiency. However, current pretreatment methods result in phosphorus loss and low phosphorus recovery rates. Direct reuse of untreated wastewater leads to high levels of impurities such as Ca and Mg, negatively impacting ferric phosphate quality. Therefore, further optimization of the ferric phosphate wastewater pretreatment process is needed to reduce production costs and phosphorus loss, while also minimizing the risk of scaling and membrane clogging from incompletely reused wastewater in the downstream membrane treatment stage.

[0004] The production of zirconium oxychloride generates a large amount of waste alkaline solution with high alkali concentration and high silicate content, posing a significant challenge in its treatment. Using this waste alkaline solution for the pretreatment of ferric phosphate wastewater would be crucial for reducing the treatment costs of both ferric phosphate wastewater and zirconium industry waste alkaline solution.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a method for treating ferric phosphate wastewater, thereby solving the technical problems of high pretreatment costs and significant phosphorus loss in the pretreated water, which prevents effective reuse of ferric phosphate production wastewater in the prior art. This invention uses zirconium waste alkaline solution in the pretreatment of ferric phosphate production wastewater, which not only reduces pretreatment costs but also results in a high phosphate retention rate in the pretreated water, allowing it to be directly reused in crude phosphoric acid, thus reducing phosphorus loss. At the same time, it effectively reduces the hardness of ferric phosphate, significantly reducing the risk of scaling and membrane clogging during subsequent membrane treatment.

[0007] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0008] A method for treating ferric phosphate wastewater includes the following steps:

[0009] S1. Add zirconium waste alkaline solution to the ferric phosphate production wastewater to adjust the pH to 10.6-11.5. After the reaction, separate the solid and liquid, remove the precipitate, and obtain solution A.

[0010] S2. Add carbonate to solution A, react and separate solid and liquid phases, remove the precipitate to obtain solution B;

[0011] S3. Recycle the solution B into crude phosphoric acid for the production of ferric phosphate; and / or, perform membrane treatment on the solution B.

[0012] Preferably, in step S1, the concentration of NaOH in the zirconium waste alkaline solution is 10wt%-15wt%, and the Si content is 0.5wt%-1.5wt%.

[0013] Preferably, in step S2, the carbonate includes sodium carbonate and / or potassium carbonate.

[0014] Preferably, in step S3, a portion of the solution B is recycled to the crude phosphoric acid for the production of the ferric phosphate, and the remaining solution B is subjected to the membrane treatment.

[0015] Preferably, in step S3, the method for producing the iron phosphate includes the following steps:

[0016] (1) Add the solution B to the crude phosphoric acid, wherein the mass ratio of the crude phosphoric acid to the solution B is 1:1.2-1.5, then add alkali to adjust the pH to 4.3-4.5, after the reaction, the solid and liquid are separated, and then add the solution B to adjust the pH to 6-8 to obtain phosphate salt;

[0017] (2) The phosphate salt, iron salt and hydrogen peroxide are used for precipitation reaction, and after solid-liquid separation and washing, a first-wash filter cake is obtained.

[0018] (3) The first-washed filter cake is pulped to obtain a slurry. Phosphoric acid is added to the slurry, the slurry is heated and aged, and after solid-liquid separation, it is washed to obtain a second-washed filter cake. The second-washed filter cake is calcined to obtain anhydrous ferric phosphate.

[0019] Preferably, in step (1), the alkali includes at least one of sodium hydroxide, potassium hydroxide, and ammonia.

[0020] Preferably, in step (1), the mass concentration of phosphorus in the phosphate salt is 19%-20%.

[0021] Preferably, in step (2), the molar ratio of Fe, P, and H2O2 in the iron salt, the phosphate salt, and the hydrogen peroxide is 1-1.3:1:0.5-1.

[0022] Preferably, in step (3), after adding the phosphoric acid, the pH of the slurry is 1.45-1.50.

[0023] Preferably, in step (3), the temperature of the aged slurry is 85-95℃, and the aging time is 1-3h.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] (1) The present invention utilizes zirconium waste alkaline solution to treat ferric phosphate wastewater, which can effectively reduce the hardness of ferric phosphate wastewater, and at the same time reduce the pretreatment cost of ferric phosphate wastewater and the treatment cost of zirconium waste alkaline solution.

[0026] (2) The wastewater from the production of ferric phosphate contains elements such as Ca, Mg, Mn, P, and Fe, while the alkaline waste liquid from the zirconium industry contains a large amount of silicon. During the process of mixing the alkaline waste liquid from the zirconium industry with the ferric phosphate wastewater to pH = 10.6 to 11.5, Ca, Mg and other ions form precipitates with silicate ions, which not only reduces the hardness of the ferric phosphate wastewater, but also removes Si from the alkaline waste liquid from the zirconium industry. The method of the present invention simultaneously achieves effective pretreatment of ferric phosphate wastewater and treatment of alkaline waste liquid from the zirconium industry.

[0027] (3) In the process of treating iron phosphate wastewater with zirconium waste alkaline solution, the concentration of silicate ions is high and calcium silicate precipitates preferentially. The retention rate of phosphate in the solution is higher than that of phosphate treated with conventional alkali (such as sodium hydroxide). The solution pretreated with zirconium waste alkaline solution can effectively reduce P loss. Attached Figure Description

[0028] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0029] Figure 1 A flow chart of wastewater treatment process in the production of ferric phosphate provided in an embodiment of the present invention. Detailed Implementation

[0030] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0031] like Figure 1 As shown, the present invention provides a method for treating ferric phosphate wastewater, comprising the following steps:

[0032] S1. Add zirconium waste alkaline solution to the ferric phosphate production wastewater to adjust the pH to 10.6-11.5. After the reaction, separate the solid and liquid, remove the precipitate, and obtain solution A.

[0033] S2. Add carbonate to solution A, react and separate the solid and liquid phases, remove the precipitate, and obtain solution B;

[0034] S3. Recycle solution B into crude phosphoric acid for the production of ferric phosphate; and / or, subject solution B to membrane treatment (post-wastewater treatment).

[0035] Among them, the zirconium waste alkaline solution is silicon-containing waste alkaline solution generated during the production of zirconium oxychloride.

[0036] Ferric phosphate wastewater contains elements such as Ca, Mg, Mn, P, and Fe, while zirconium waste alkaline solution contains a large amount of silicon. The method of this invention adds zirconium waste alkaline solution to ferric phosphate wastewater, utilizing the reaction of Ca and Mg ions with silicate ions to form precipitates, thereby reducing the hardness of ferric phosphate wastewater and removing Si from zirconium waste alkaline solution. This achieves effective pretreatment of ferric phosphate wastewater and treatment of zirconium waste alkaline solution simultaneously, effectively reducing the pretreatment cost of ferric phosphate wastewater and solving the treatment problem of zirconium waste alkaline solution.

[0037] In the pretreatment of ferric phosphate, this invention first uses zirconium waste alkaline solution to remove magnesium ions and most of the calcium, controlling the amount of zirconium waste alkaline solution to be slightly insufficient to avoid excessive silicon pollution. The remaining small amount of calcium ions is removed using carbonates. To balance pretreatment costs and product quality, the amount of zirconium waste alkaline solution used needs to be reasonably controlled. This invention controls the amount of zirconium waste alkaline solution by controlling the pH (10.6-11.5). If the pH after adding zirconium waste alkaline solution is too low, the amount of zirconium waste alkaline solution used will be small, the amount of carbonate used will be large, the pretreatment cost of ferric phosphate wastewater will be high, and the treatment capacity of zirconium waste alkaline solution will be reduced. If the pH after adding zirconium waste alkaline solution is too high, it will easily cause excessive silicon and lead to silicon pollution.

[0038] In the treatment method of this invention, during the process of mixing zirconium waste alkaline solution and ferric phosphate wastewater to pH=10.6-11.5, the concentration of silicate ions is high, calcium silicate preferentially precipitates, and the retention rate of phosphate ions in the solution is higher than that of conventional alkaline treatment. The solution pretreated by the method of this invention can also effectively reduce phosphorus loss when preparing phosphate salts.

[0039] In some implementations, for example, in step S1, after adding zirconium waste alkaline solution, the pH of the solution can be any one value or a range of any two values ​​from 10.6, 10.8, 11, 11.2, 11.4, 11.5.

[0040] In some specific embodiments of the present invention, in step S1, the concentration of NaOH in the zirconium waste alkaline solution is 10wt%-15wt%, for example, it can be any one value or a range of any two values ​​from 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, and 15wt%; the Si content is 0.5wt%-1.5wt%, for example, it can be any one value or a range of any two values ​​from 0.5wt%, 0.7wt%, 0.9wt%, 1.1wt%, 1.3wt%, and 1.5wt%.

[0041] In some specific embodiments of the present invention, in step S2, the carbonate includes sodium carbonate and / or potassium carbonate, for example, it can be a sodium carbonate solution or a potassium carbonate solution.

[0042] In some specific embodiments of the present invention, in step S2, the mass concentration of carbonate in the solution after the reaction is 0.02% to 0.05%, with a slight excess of carbonate to ensure that calcium ions can be completely precipitated.

[0043] In some specific embodiments of the present invention, in step S3, a portion of solution B is recycled to crude phosphoric acid for the production of ferric phosphate, and the remaining solution B undergoes downstream membrane treatment. Recycling solution B to crude phosphoric acid to prepare phosphate salts enables the reuse of phosphorus elements, reduces P resource waste, and lowers the cost of further downstream membrane treatment of wastewater. However, the wastewater volume during ferric phosphate production is large, making it difficult to recycle all of it. Excessive recycling would lead to excessively low phosphorus concentration in the phosphate salts. Therefore, solution B is partially recycled and partially treated by downstream membrane treatment. Since the pretreatment method of the present invention can effectively reduce the hardness of wastewater, it can effectively slow down scaling tendencies and avoid membrane fouling during downstream treatment, allowing it to enter a high-pressure reverse osmosis system for further treatment.

[0044] In some specific embodiments of the present invention, step S3, the method for producing iron phosphate includes the following steps:

[0045] (1) Add solution B to crude phosphoric acid. The mass ratio of crude phosphoric acid to solution B is 1:1.2-1.5. Then add alkali to adjust the pH to 4.3-4.5. After the reaction, the solid and liquid are separated to remove impurity ions such as Al and Ti. Then add solution B to adjust the pH to 6-8 to obtain phosphate salt.

[0046] (2) A precipitation reaction was carried out using phosphate salts, iron salts and hydrogen peroxide. After solid-liquid separation and washing, a first-wash filter cake was obtained.

[0047] (3) The first-washed filter cake is pulped to obtain a slurry. Phosphoric acid is added to the slurry, the slurry is heated and aged, and after solid-liquid separation, it is washed to obtain a second-washed filter cake. The second-washed filter cake is calcined to obtain anhydrous iron phosphate.

[0048] In step (1), since the pH of crude phosphoric acid is low, if all the pH of crude phosphoric acid is adjusted by solution B, a large amount of solution B will be needed, which will lead to the phosphate salt concentration being too low. Therefore, the present invention uses solution B in combination with conventional alkali to adjust the pH of crude phosphoric acid, which can not only realize the reuse of ferric phosphate wastewater and reduce production costs, but also avoid the phosphate salt concentration being too low.

[0049] In some embodiments, typically but not limitingly, for example, the mass ratio of crude phosphoric acid to the first added solution B can be any one of 1:1.2, 1:1.3, 1:1.4, 1:1.5 or a range of any two of these values; the pH of the solution after adding alkali can be any one of 4.3, 4.4, 4.5 or a range of any two of these values; and after the second addition of solution B, the pH of the phosphate solution can be any one of 6, 6.5, 7, 7.5, 8 or a range of any two of these values.

[0050] In some specific embodiments of the present invention, in step (1), the alkali used includes at least one of sodium hydroxide, potassium hydroxide, and ammonia water.

[0051] In some specific embodiments of the present invention, in step (1), the mass concentration of P element in the obtained phosphate salt is 19% to 20%, for example, it can be any one value or a range of any two values ​​among 19%, 19.10%, 19.23%, 19.30%, 19.50%, 19.70%, and 20%.

[0052] In some specific embodiments of the present invention, in step (2), the molar ratio of Fe, P, and H2O2 in iron salt, phosphate salt, and hydrogen peroxide is 1-1.3:1:0.5-1. For example, it can be any one value or a range of any two values ​​from 1:1:0.5, 1:1:0.8, 1:1:1, 1.2:1:0.5, 1.2:1:0.8, 1.2:1:1, 1.3:1:0.5, 1.3:1:0.8, 1.3:1:1.

[0053] In some specific embodiments of the present invention, in step (3), after adding phosphoric acid, the pH of the slurry is 1.45-1.50. For example, it can be any one value or a range of any two values ​​among 1.45, 1.46, 1.47, 1.48, 1.49, and 1.50.

[0054] In some specific embodiments of the present invention, in step (3), the temperature of the aging slurry is 85-95°C, for example, it can be any one value or a range of any two values ​​among 85°C, 88°C, 90°C, 92°C, and 95°C; the aging time of the slurry is 1-3 hours, for example, it can be any one value or a range of any two values ​​among 1 hour, 1.5 hours, 2 hours, 2.5 hours, and 3 hours.

[0055] The following detailed description of some embodiments of the present invention is provided in conjunction with specific examples. Unless otherwise specified, the raw materials used in the embodiments can be obtained commercially available.

[0056] Example 1

[0057] Step S1: Add zirconium waste alkaline solution with NaOH concentration of 15wt% and Si content of 1.5wt% to the ferric phosphate production wastewater to adjust the pH to 11. After stirring for 15 minutes, separate the solid and liquid, remove the precipitate, and obtain solution A.

[0058] Step S2: Add a 10 wt% sodium carbonate solution to solution A (the sodium carbonate concentration in the solution after the reaction is 0.02 wt%), stir for 10 min, separate the solid and liquid, remove the precipitate, and obtain solution B;

[0059] Step S3: Add solution B to the crude acid, with a mass ratio of crude phosphoric acid to solution B of 1:1.3. Then add 32wt% NaOH solution to adjust the pH to 4.3. Stir for a period of time, and after solid-liquid separation, add solution B again to adjust the pH of the filtrate to 6.5 to obtain phosphate salt; the phosphorus content in the obtained phosphate salt is 19.30%.

[0060] Step S4: Mix iron salt, phosphate salt, and hydrogen peroxide at a molar ratio of Fe, P, and H2O2 of 1:1:0.8, react for 2 hours, filter under pressure, and wash repeatedly to obtain a first-wash filter cake;

[0061] Step S5: Pulverize the first-wash filter cake at 60℃ to obtain a slurry. Add phosphoric acid to the slurry to adjust the pH to 1.50. Heat to 90℃. After the slurry turns white, keep it at that temperature for 60 minutes. After pressure filtration and washing, obtain the second-wash filter cake. Calcine the second-wash filter cake to obtain anhydrous ferric phosphate.

[0062] Example 2

[0063] S1: Add zirconium waste alkaline solution with a NaOH concentration of 10wt% and a Si content of 1wt% to the ferric phosphate production wastewater to adjust the pH to 10.6. After stirring for 15 minutes, separate the solid and liquid, remove the precipitate, and obtain solution A.

[0064] S2: Add a 10wt% sodium carbonate solution to solution A (the sodium carbonate concentration in the solution after the reaction is 0.03wt%), stir for 10 min, then separate the solid and liquid phases, remove the precipitate, and obtain solution B;

[0065] S3: Add solution B to crude acid, with a mass ratio of crude phosphoric acid to solution B of 1:1.2. Then add 32wt% NaOH solution to adjust the pH to 4.4. Stir for a period of time, and after solid-liquid separation, add solution B again to adjust the pH of the filtrate to 6 to obtain phosphate salt. The phosphorus content in the obtained phosphate salt is 19.23%.

[0066] S4: Iron salt, phosphate salt and hydrogen peroxide are mixed in a Fe:P:H2O2 molar ratio of 1:1:0.5. After reacting for 2 hours, the mixture is filtered under pressure and washed repeatedly to obtain a first-wash filter cake.

[0067] S5: The first-wash filter cake is pulped at 60℃ to obtain a slurry. Phosphoric acid is added to the slurry to adjust the pH to 1.45. The temperature is raised to 85℃. After the slurry turns white, it is kept at this temperature for 3 hours. After pressure filtration and washing, a second-wash filter cake is obtained. The second-wash filter cake is calcined to obtain anhydrous ferric phosphate.

[0068] Example 3

[0069] S1: Add zirconium waste alkaline solution with a NaOH concentration of 12wt% and a Si content of 1.2wt% to the ferric phosphate production wastewater to adjust the pH to 11.5. After stirring for 15 minutes, separate the solid and liquid, remove the precipitate, and obtain solution A.

[0070] S2: Add a 10wt% sodium carbonate solution to solution A (the sodium carbonate concentration in the solution after the reaction is 0.05wt%), stir for 10 min, then separate the solid and liquid phases, remove the precipitate, and obtain solution B;

[0071] S3: Add solution B to crude acid, with a mass ratio of crude phosphoric acid to solution B of 1:1.5. Then add 32wt% NaOH solution to adjust the pH to 4.5. Stir for a period of time, and after solid-liquid separation, add solution B again to adjust the pH of the filtrate to 8 to obtain phosphate salt. The phosphorus content in the obtained phosphate salt is 19.27%.

[0072] S4: Iron salt, phosphate salt and hydrogen peroxide are mixed in a Fe, P and H2O2 molar ratio of 1:1:1. After reacting for 2 hours, the mixture is filtered under pressure and washed repeatedly to obtain a first-wash filter cake.

[0073] S5: The first-wash filter cake is pulped at 60℃ to obtain a slurry. Phosphoric acid is added to the slurry to adjust the pH to 1.48. The temperature is raised to 95℃. After the slurry turns white, it is kept at this temperature for 1 hour. After pressure filtration and washing, a second-wash filter cake is obtained. The second-wash filter cake is calcined to obtain anhydrous ferric phosphate.

[0074] Comparative Example 1

[0075] The difference between Comparative Example 1 and Example 1 is that the alkali used in the pretreatment process of ferric phosphate production wastewater is sodium hydroxide solution. The specific steps are as follows:

[0076] S1: Add a 15wt% NaOH solution to the ferric phosphate production wastewater to adjust the pH to 11. After stirring for 15 minutes, separate the solid and liquid phases, remove the precipitate, and obtain solution A.

[0077] S2: Add a 10wt% sodium carbonate solution (same amount as in Example 1) to solution A, stir for 10 min, then separate the solid and liquid, remove the precipitate, and obtain solution B;

[0078] S3: Add solution B (the crude phosphoric acid used and the mass ratio of crude phosphoric acid to solution B are the same as in Example 1) to the crude acid, add 32wt% NaOH solution to adjust the pH to 4.3, stir for a period of time, and after solid-liquid separation, add solution B again to adjust the pH of the filtrate to 6.5 to obtain phosphate salt; the phosphorus content in the obtained phosphate salt is 18.93%;

[0079] S4: Iron salt, phosphate salt and hydrogen peroxide are mixed in a Fe:P:H2O2 molar ratio of 1:1:0.8. After reacting for 2 hours, the mixture is filtered under pressure and washed repeatedly to obtain a first-wash filter cake.

[0080] Step S5: Pulverize the first-washed filter cake at 60℃ to obtain a slurry. Add phosphoric acid to the slurry to adjust the pH to 1.50. Heat to 90℃. After the slurry turns white, keep it at that temperature for 60 minutes. After pressure filtration and washing, calcine the filter cake to obtain anhydrous ferric phosphate.

[0081] Comparative Example 2

[0082] Comparative Example 2 is similar to Example 1, except that the ferric phosphate production wastewater was not pretreated. Instead, an equal amount of untreated ferric phosphate production wastewater was used to replace solution B in Example 1 and reused in crude phosphoric acid. All other conditions were the same as in Example 1.

[0083] Test case

[0084] The impurity element content of the ferric phosphate production wastewater, the solution B obtained in each example and Comparative Example 1, and the impurity content, Fe / P (molar ratio) and specific surface area of ​​the ferric phosphate prepared in each example and Comparative Example were tested respectively; the test results are shown in Table 1.

[0085] Table 1

[0086]

[0087]

[0088] The data above show that the wastewater pretreated by the embodiment of the present invention has lower calcium and magnesium ion content and higher phosphorus content compared to Comparative Example 1. The method of the present invention has a relatively high phosphorus recovery rate and reduces phosphorus loss compared to sodium hydroxide solution pretreatment. The ferric phosphate prepared by the embodiment of the present invention has lower levels of impurities compared to the comparative example. In Comparative Example 2, the ferric phosphate wastewater was directly reused, resulting in high impurity content. Furthermore, because the untreated ferric phosphate wastewater is acidic, direct reuse in crude phosphoric acid production leads to increased alkali usage and production costs, and the zirconium industry waste alkaline solution cannot be effectively utilized. Therefore, the method of the present invention significantly reduces the hardness of ferric phosphate wastewater and reduces phosphorus loss, while simultaneously achieving effective pretreatment of ferric phosphate wastewater and treatment of zirconium industry waste alkaline solution.

[0089] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A method for treating ferric phosphate wastewater, characterized in that, Includes the following steps: S1. Add zirconium waste alkaline solution to the ferric phosphate production wastewater to adjust the pH to 10.6-11.

5. After the reaction, separate the solid and liquid phases, remove the precipitate, and obtain solution A. The zirconium waste alkaline solution contains 10wt%-15wt% NaOH and 0.5wt%-1.5wt% Si. S2. Add carbonate to solution A, react, separate solid and liquid, remove the precipitate, and obtain solution B; S3. Recycle the solution B into crude phosphoric acid for the production of ferric phosphate; and / or, perform membrane treatment on the solution B.

2. The method for treating ferric phosphate wastewater according to claim 1, characterized in that, In step S2, the carbonate includes sodium carbonate and / or potassium carbonate.

3. The method for treating ferric phosphate wastewater according to claim 1, characterized in that, In step S3, a portion of the solution B is recycled into the crude phosphoric acid to produce the ferric phosphate, and the remaining solution B is subjected to the membrane treatment.

4. The method for treating ferric phosphate wastewater according to claim 1, characterized in that, In step S3, the method for producing the iron phosphate includes the following steps: (1) Add the solution B to the crude phosphoric acid so that the mass ratio of the crude phosphoric acid to the solution B is 1:1.2-1.

5. Then add alkali to adjust the pH to 4.3-4.

5. After the reaction, the solid and liquid are separated. Then add the solution B to adjust the pH to 6-8 to obtain phosphate salt. (2) The phosphate salt, iron salt and hydrogen peroxide are used for precipitation reaction, and after solid-liquid separation and washing, a first-wash filter cake is obtained; (3) The first-washed filter cake is pulped to obtain a slurry. Phosphoric acid is added to the slurry, the slurry is aged by heating, and after solid-liquid separation, it is washed to obtain a second-washed filter cake. The second-washed filter cake is calcined to obtain anhydrous ferric phosphate.

5. The method for treating ferric phosphate wastewater according to claim 4, characterized in that, In step (1), the alkali includes at least one of sodium hydroxide, potassium hydroxide, and ammonia water.

6. The method for treating ferric phosphate wastewater according to claim 4, characterized in that, In step (1), the mass concentration of phosphorus in the phosphate salt is 19%-20%.

7. The method for treating ferric phosphate wastewater according to claim 4, characterized in that, In step (2), the molar ratio of Fe, P and H2O2 in the iron salt, the phosphate salt and the hydrogen peroxide is 1-1.3:1:0.5-1.

8. The method for treating ferric phosphate wastewater according to claim 4, characterized in that, In step (3), after adding the phosphoric acid, the pH of the slurry is 1.45-1.

50.

9. The method for treating ferric phosphate wastewater according to claim 4, characterized in that, In step (3), the temperature of the aged slurry is 85-95℃, and the aging time is 1-3h.

Images