Treatment method of iron phosphate production wastewater

Abstract

The invention relates to the technical field of lithium ion battery positive electrode materials, in particular to a treatment method of iron phosphate production wastewater. Comprising the following steps: S1, adding zirconium industry waste alkali liquor into iron phosphate production wastewater to adjust the pH value to 10.6-11.5, carrying out solid-liquid separation after reaction, and removing precipitate to obtain a solution A; s2, adding carbonate into the solution A, carrying out solid-liquid separation after reaction, and removing precipitate to obtain a solution B; s3, recycling the solution B into crude phosphoric acid for producing iron phosphate; and / or performing membrane treatment on the solution B. The waste alkali liquor in the zirconium industry is used for pretreatment of the iron phosphate production wastewater, so that the pretreatment cost can be reduced, the phosphate radical retention rate in the pretreated wastewater is relatively high, the pretreated wastewater can be directly reused in crude phosphoric acid, and the phosphorus loss is reduced; and meanwhile, the hardness of iron phosphate can be effectively reduced, and the risk of scaling and membrane blocking can be remarkably reduced during later-section membrane treatment.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion battery positive electrode materials, and in particular to a method for treating iron phosphate production wastewater. Background Art

[0002] With the rapid development of new energy storage technologies and the booming of electric vehicles, lithium iron phosphate batteries have an absolute dominant position in the market. Among them, lithium iron phosphate, as an important positive electrode material for lithium-ion batteries, has also made significant progress in its research and development and application, further driving the demand for iron phosphate. In the process of iron phosphate production, a large amount of acidic wastewater is generated through synthesis, washing and other steps. At present, this wastewater is mainly treated by ultrafiltration, nanofiltration, reverse osmosis and other technologies. During the treatment process, scaling and membrane clogging are prone to occur, which affects the stable operation of production. Effective pretreatment must be carried out to remove ions that are prone to scaling.

[0003] A more common pretreatment method is to use chemical precipitation to add sodium hydroxide and sodium carbonate to the wastewater to reduce the total hardness of the wastewater, and the pretreatment cost is relatively high. In addition, if this part of the pretreated water can be reused in the front-end iron phosphate preparation, it will further reduce the production cost of iron phosphate and improve the production efficiency of the enterprise. However, the current pretreatment method will cause phosphorus loss in the wastewater, and the recycling rate of phosphorus is low. If the production wastewater is directly reused without pretreatment, it will lead to high content of impurities such as Ca and Mg, affecting the quality of iron phosphate. Therefore, the pretreatment process of iron phosphate wastewater needs to be further optimized to reduce production costs and phosphorus losses, while reducing the risk of scaling and membrane blockage of wastewater that is not fully reused during the subsequent membrane treatment.

[0004] In the process of producing zirconium oxychloride, a large amount of waste alkali liquid is generated, which has a high alkali concentration and contains a large amount of silicate. How to deal with it is a big problem. If this part of waste alkali liquid can be used for the pretreatment of iron phosphate wastewater, it will be of great significance to reduce the treatment cost of iron phosphate wastewater and zirconium industry waste alkali liquid.

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

[0006] The purpose of the present invention is to provide a method for treating ferric phosphate wastewater to solve the technical problems in the prior art that the pretreatment cost of ferric phosphate production wastewater is high, the phosphorus loss in the water after pretreatment is large, and it cannot be effectively reused; the present invention uses zirconium industry waste alkali liquor in the pretreatment of ferric phosphate production wastewater, which not only reduces the pretreatment cost, but also has a relatively high phosphate retention rate in the water after pretreatment, which can be directly reused in crude phosphoric acid to reduce phosphorus loss; at the same time, it can effectively reduce the hardness of ferric phosphate, and can significantly reduce the risk of scaling and membrane clogging during the subsequent membrane treatment.

[0007] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0008] A method for treating iron phosphate wastewater comprises the following steps:

[0009] S1. Add zirconium industry waste alkali solution to the iron phosphate production wastewater to adjust the pH to 10.6-11.5, separate the solid and liquid after the reaction, remove the precipitate, and obtain solution A;

[0010] S2. adding carbonate to the solution A, separating the solid and liquid after the reaction, removing the precipitate, and obtaining a solution B;

[0011] S3. recycling the solution B into crude phosphoric acid for producing iron phosphate; and / or, subjecting the solution B to membrane treatment.

[0012] Preferably, in step S1, the concentration of NaOH in the zirconium industry waste alkali 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, part of the solution B is recycled into the crude phosphoric acid for producing the iron phosphate, and the rest of the solution B is subjected to the membrane treatment.

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

[0016] (1) adding 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 adding alkali to adjust the pH to 4.3-4.5, separating the solid and the liquid after the reaction, and then adding the solution B to adjust the pH to 6-8 to obtain a phosphate salt;

[0017] (2) using the phosphate salt, iron salt and hydrogen peroxide to carry out precipitation reaction, and washing after solid-liquid separation to obtain a washed filter cake;

[0018] (3) beating the first-wash filter cake to obtain a slurry, adding phosphoric acid to the slurry, heating the slurry to age it, washing it after solid-liquid separation to obtain a second-wash filter cake, and calcining the second-wash filter cake to obtain anhydrous iron phosphate.

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

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

[0021] Preferably, in step (2), Fe, P, H 2 O2 The molar ratio 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° C., and the time of the aged slurry is 1-3 h.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

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

[0026] (2) The ferric phosphate production wastewater contains elements such as Ca, Mg, Mn, P, and Fe, and the zirconium industry waste alkali liquor contains a large amount of silicon. In the process of mixing the zirconium industry waste alkali liquor and the ferric phosphate wastewater to pH = 10.6-11.5, Ca, Mg ions and silicate ions form precipitation, which not only reduces the hardness of the ferric phosphate wastewater, but also removes Si in the zirconium industry waste alkali liquor. The method of the present invention simultaneously realizes the effective pretreatment of the ferric phosphate wastewater and the treatment of the zirconium industry waste alkali liquor.

[0027] (3) In the process of using zirconium industry waste alkali liquid to treat iron phosphate wastewater in the present invention, the silicate ion concentration is relatively high, calcium silicate is precipitated preferentially, and the retention rate of phosphate in the solution is higher than that of phosphate treated only with conventional alkali (such as sodium hydroxide). The phosphate salt is prepared by using the solution pretreated with zirconium industry waste alkali liquid, which can effectively reduce P loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1 A process flow chart of wastewater treatment in the iron phosphate production process provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0030] The technical scheme of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not specified in the reagents or instruments used, they are all conventional products that can be purchased commercially.

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

[0032] S1. Add zirconium industry waste alkali solution to the iron phosphate production wastewater to adjust the pH to 10.6-11.5, separate the solid and liquid after the reaction, remove the precipitate, and obtain solution A;

[0033] S2. adding carbonate to solution A, separating the solid and liquid after the reaction, removing the precipitate, and obtaining solution B;

[0034] S3. Reusing solution B into crude phosphoric acid for producing iron phosphate; and / or, subjecting solution B to membrane treatment (post-wastewater treatment).

[0035] Among them, zirconium industry waste alkali liquid is silicon-containing waste alkali liquid generated in the production process of zirconium oxychloride.

[0036] Ferric phosphate wastewater contains elements such as Ca, Mg, Mn, P, and Fe, and zirconium industry waste alkali liquor contains a large amount of silicon. The method of the present invention adds zirconium industry waste alkali liquor into ferric phosphate wastewater, utilizes Ca, Mg and other ions to react with silicate to form precipitation, reduces the hardness of ferric phosphate wastewater, and removes Si in zirconium industry waste alkali liquor, thereby achieving effective pretreatment of ferric phosphate wastewater and treatment of zirconium industry waste alkali liquor, which can not only effectively reduce the pretreatment cost of ferric phosphate wastewater, but also solve the problem of treating zirconium industry waste alkali liquor.

[0037] When pretreating ferric phosphate, the present invention first uses zirconium industry waste alkali liquid to remove magnesium ions and most of the calcium, controls the amount of zirconium industry waste alkali liquid to be slightly insufficient, avoids pollution caused by excessive silicon, and removes the remaining small amount of calcium ions using carbonate; in order to balance the pretreatment cost and product quality, it is necessary to reasonably control the amount of zirconium industry waste alkali liquid. The present invention controls the amount of zirconium industry waste alkali liquid by controlling pH (10.6-11.5). If the pH after adding the zirconium industry waste alkali liquid is too small, the amount of zirconium industry waste alkali liquid is small, the amount of carbonate is large, the pretreatment cost of ferric phosphate wastewater is high, and the treatment amount of zirconium industry waste alkali liquid is reduced; if the pH after adding the zirconium industry waste alkali liquid is too large, it is easy to cause excessive silicon and silicon pollution.

[0038] In the treatment method of the present invention, during the process of mixing zirconium industry waste alkali liquid and iron phosphate wastewater to pH = 10.6-11.5, the silicate ion concentration is relatively high, calcium silicate is preferentially precipitated, and the retention rate of phosphate in the solution is higher than that of conventional alkali treatment. The solution pretreated by the method of the present invention is used to prepare phosphate salts, which can also effectively reduce phosphorus loss.

[0039] In some embodiments, for example, in step S1, after adding zirconium industry waste alkali solution, the pH of the solution can be any point value among 10.6, 10.8, 11, 11.2, 11.4, 11.5 or a range value consisting of any two point values.

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

[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%, and the carbonate is slightly excessive to ensure that the calcium ions can be completely precipitated.

[0043] In some specific embodiments of the present invention, in step S3, part of solution B is recycled into crude phosphoric acid for the production of ferric phosphate, and the remaining solution B is subjected to post-stage membrane treatment; recycling solution B into crude phosphoric acid to prepare phosphate salts can achieve the reuse of phosphorus elements, reduce P resource waste, and reduce the cost of further post-stage membrane treatment of wastewater. However, the amount of wastewater in the production process of ferric phosphate is large, and it is difficult to fully reuse it. Excessive recycling will lead to too low phosphorus concentration in phosphate salts. Therefore, solution B adopts a treatment method of partially recycling and partially undergoing post-stage membrane treatment. Since the pretreatment method of the present invention can effectively reduce the hardness of wastewater, it can effectively slow down the scaling tendency and avoid membrane pollution during post-stage treatment, and can enter a high-pressure reverse osmosis system for subsequent treatment.

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

[0045] (1) adding solution B to crude phosphoric acid, wherein the mass ratio of crude phosphoric acid to solution B is 1:1.2-1.5, then adding alkali to adjust the pH to 4.3-4.5, performing solid-liquid separation after the reaction, removing impurity ions such as Al and Ti, and then adding solution B to adjust the pH to 6-8 to obtain a phosphate salt;

[0046] (2) using phosphate, iron salt and hydrogen peroxide to carry out precipitation reaction, and washing after solid-liquid separation to obtain a washed filter cake;

[0047] (3) beating the first-wash filter cake to obtain a slurry, adding phosphoric acid to the slurry, heating the slurry to age it, washing it after solid-liquid separation to obtain a second-wash filter cake, and calcining the second-wash filter cake to obtain anhydrous iron phosphate.

[0048] In step (1), since the pH of crude phosphoric acid is low, if solution B is used entirely to adjust the pH of crude phosphoric acid, a large amount of solution B needs to be used, which will result in too low a phosphate concentration. Therefore, the present invention uses solution B in combination with conventional alkali to adjust the pH of crude phosphoric acid, which can not only achieve the reuse of iron phosphate wastewater and reduce production costs, but also avoid too low a phosphate concentration.

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

[0050] In some specific embodiments of the present invention, in step (1), the base 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 the P element in the obtained phosphate salt is 19% to 20%, for example, it can be any point value among 19%, 19.10%, 19.23%, 19.30%, 19.50%, 19.70%, 20% or a range value consisting of any two point values.

[0052] In some specific embodiments of the present invention, in step (2), Fe, P, H 2 O 2The molar ratio is 1-1.3:1:0.5-1, for example, it can be any point value among 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, or a range value consisting of any two point values.

[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 point value among 1.45, 1.46, 1.47, 1.48, 1.49, 1.50 or a range value consisting of any two point values.

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

[0055] The following is a detailed description of some embodiments of the present invention in conjunction with specific examples. The raw materials in the examples can be purchased from the market unless otherwise specified.

[0056] Example 1

[0057] Step S1: adding waste alkali solution from zirconium industry with a NaOH concentration of 15 wt% and a Si content of 1.5 wt% to the wastewater from iron phosphate production to adjust the pH to 11, stirring for 15 min, separating the solid and the liquid, removing the precipitate, and obtaining solution A;

[0058] Step S2: adding a sodium carbonate solution with a mass concentration of 10 wt% to solution A (the sodium carbonate concentration in the solution after the reaction is 0.02 wt%), stirring for 10 min, separating the solid and the liquid, removing the precipitate, and obtaining solution B;

[0059] Step S3: adding solution B to the crude acid, the mass ratio of crude phosphoric acid to solution B being 1:1.3, then adding a NaOH solution having a mass concentration of 32 wt% to adjust the pH to 4.3, stirring for a period of time, and after solid-liquid separation, adding solution B to adjust the pH of the filtrate to 6.5 to obtain a phosphate salt; the phosphorus content of the obtained phosphate salt is 19.30%;

[0060] Step S4: Mix the iron salt, phosphate salt and hydrogen peroxide according to the concentration of Fe, P and H 2 O 2 The mixture was mixed at a molar ratio of 1:1:0.8, reacted for 2 hours, filtered, and washed repeatedly to obtain a washed filter cake;

[0061] Step S5: The first-wash filter cake is beaten at 60° C. to obtain a slurry, phosphoric acid is added to the slurry, the pH is adjusted to 1.50, the temperature is raised to 90° C., the slurry is kept warm for 60 minutes after turning white, and a second-wash filter cake is obtained by filter pressing and washing, and the second-wash filter cake is calcined to obtain anhydrous iron phosphate.

[0062] Example 2

[0063] S1: Adding zirconium industry waste alkali solution with a NaOH concentration of 10 wt% and a Si content of 1 wt% to the iron phosphate production wastewater to adjust the pH to 10.6, stirring for 15 minutes, separating the solid and liquid, removing the precipitate, and obtaining solution A;

[0064] S2: adding a sodium carbonate solution with a mass concentration of 10 wt% to solution A (the sodium carbonate concentration in the solution after the reaction is 0.03 wt%), stirring for 10 min, separating the solid and the liquid, removing the precipitate, and obtaining solution B;

[0065] S3: adding solution B to the crude acid, the mass ratio of crude phosphoric acid to solution B being 1:1.2, then adding a NaOH solution having a mass concentration of 32 wt% to adjust the pH to 4.4, stirring for a period of time, and after solid-liquid separation, adding solution B to adjust the pH of the filtrate to 6 to obtain a phosphate salt; the phosphorus content of the obtained phosphate salt is 19.23%;

[0066] S4: Mix iron salt, phosphate salt and hydrogen peroxide according to Fe, P, H 2 O 2 The mixture was mixed at a molar ratio of 1:1:0.5, reacted for 2 hours, filtered, and washed repeatedly to obtain a washed filter cake;

[0067] S5: The first-wash filter cake is beaten at 60°C to obtain a slurry, phosphoric acid is added to the slurry, the pH value is adjusted to 1.45, the temperature is raised to 85°C, the slurry turns white and is kept warm for 3 hours, a second-wash filter cake is obtained by filter pressing and washing, and the second-wash filter cake is calcined to obtain anhydrous iron phosphate.

[0068] Example 3

[0069] S1: Adding zirconium industry waste alkali solution with a NaOH concentration of 12 wt% and a Si content of 1.2 wt% to the iron phosphate production wastewater to adjust the pH to 11.5, stirring for 15 minutes, separating the solid and liquid, removing the precipitate, and obtaining solution A;

[0070] S2: adding a sodium carbonate solution with a mass concentration of 10 wt% to solution A (the sodium carbonate concentration in the solution after the reaction is 0.05 wt%), stirring for 10 min, separating the solid and the liquid, removing the precipitate, and obtaining solution B;

[0071] S3: adding solution B to the crude acid, the mass ratio of crude phosphoric acid to solution B is 1:1.5, then adding a NaOH solution with a mass concentration of 32wt% to adjust the pH to 4.5, stirring for a period of time, and after solid-liquid separation, adding solution B to adjust the pH of the filtrate to 8 to obtain a phosphate salt; the phosphorus content of the obtained phosphate salt is 19.27%;

[0072] S4: Mix iron salt, phosphate salt and hydrogen peroxide according to Fe, P, H 2 O 2 The mixture was mixed at a molar ratio of 1:1:1, reacted for 2 hours, filtered, and washed repeatedly to obtain a washed filter cake;

[0073] S5: The first-wash filter cake is beaten at 60°C to obtain a slurry, phosphoric acid is added to the slurry, the pH value is adjusted to 1.48, the temperature is raised to 95°C, the slurry turns white and is kept warm for 1 hour, a second-wash filter cake is obtained by filter pressing and washing, and the second-wash filter cake is calcined to obtain anhydrous iron 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, and the specific steps are as follows:

[0076] S1: Adding a 15 wt% NaOH solution to the ferric phosphate production wastewater to adjust the pH to 11, stirring for 15 min, separating the solid and the liquid, removing the precipitate, and obtaining solution A;

[0077] S2: adding a sodium carbonate solution with a mass concentration of 10 wt % (the amount is the same as in Example 1) to solution A, stirring for 10 min, separating the solid and the liquid, removing the precipitate, and obtaining solution B;

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

[0079] S4: Mix iron salt, phosphate salt and hydrogen peroxide according to Fe, P, H 2 O 2 The mixture was mixed at a molar ratio of 1:1:0.8, reacted for 2 hours, filtered, and washed repeatedly to obtain a washed filter cake;

[0080] Step S5: Beat the washed filter cake at 60°C to obtain a slurry, add phosphoric acid to the slurry, adjust the pH to 1.50, raise the temperature to 90°C, keep the slurry warm for 60 minutes after it turns white, filter press and wash, and calcine the filter cake to obtain anhydrous iron phosphate.

[0081] Comparative Example 2

[0082] Comparative Example 2 is similar to Example 1, except that the ferric phosphate production wastewater is not pretreated, and an equal amount of ferric phosphate production wastewater that has not been pretreated is directly used to replace Solution B in Example 1 and reused in crude phosphoric acid, and the other conditions are the same as Example 1.

[0083] Test example

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

[0085] Table 1

[0086]

[0087]

[0088] It can be seen from the above data that the calcium and magnesium ion content in the wastewater after pretreatment in the embodiment of the present invention is lower, and the P content is higher than that in Comparative Example 1. The recovery rate of phosphorus in the method of the present invention is relatively high, and the P loss can be reduced compared with the pretreatment with sodium hydroxide solution. The iron phosphate prepared by the embodiment of the present invention has lower impurity elements than the comparative example; in Comparative Example 2, the iron phosphate wastewater is directly reused, which not only has a high impurity content, but also because the unpretreated iron phosphate wastewater is acidic, directly reused in crude phosphoric acid will lead to an increase in the amount of alkali, increase production costs, and zirconium industry waste alkali liquor cannot be effectively utilized. Therefore, the method of the present invention greatly reduces the hardness of iron phosphate wastewater, reduces phosphorus loss, and can simultaneously achieve effective pretreatment of iron phosphate wastewater and treatment of zirconium industry waste alkali liquor.

[0089] Although the present invention has been illustrated and described with specific embodiments, it should be appreciated that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents without departing from the spirit and scope of the present invention. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention. Therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A method for treating iron phosphate wastewater, characterized in that: The following steps are involved: S1. Add zirconium industry waste alkali solution to the iron phosphate production wastewater to adjust the pH to 10.6-11.5, separate the solid and liquid after the reaction, remove the precipitate, and obtain solution A; S2. adding carbonate to the solution A, separating the solid and liquid after the reaction, removing the precipitate, and obtaining a solution B; S3. recycling the solution B into crude phosphoric acid for producing iron phosphate; and / or, subjecting the solution B to membrane treatment.

2. The method for treating ferric phosphate wastewater according to claim 1, characterized in that: In step S1, in the zirconium industry waste alkali solution, the concentration of NaOH is 10wt%-15wt%, and the content of Si is 0.5wt%-1.5wt%.

3. 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.

4. The method for treating ferric phosphate wastewater according to claim 1, characterized in that: In step S3, part of the solution B is recycled into the crude phosphoric acid for producing the ferric phosphate, and the rest of the solution B is subjected to the membrane treatment.

5. The method for treating ferric phosphate wastewater according to claim 1, characterized in that: In step S3, the method for producing the ferric phosphate comprises the following steps: (1) adding 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 adding alkali to adjust the pH to 4.3-4.5, separating the solid and the liquid after the reaction, and then adding the solution B to adjust the pH to 6-8 to obtain a phosphate salt; (2) using the phosphate salt, iron salt and hydrogen peroxide to carry out precipitation reaction, and washing after solid-liquid separation to obtain a washed filter cake; (3) beating the first-wash filter cake to obtain a slurry, adding phosphoric acid to the slurry, heating the slurry to age it, washing it after solid-liquid separation to obtain a second-wash filter cake, and calcining the second-wash filter cake to obtain anhydrous iron phosphate.

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

7. The method for treating ferric phosphate wastewater according to claim 5, characterized in that: In step (1), the mass concentration of P element in the phosphate salt is 19%-20%.

8. The method for treating ferric phosphate wastewater according to claim 5, 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.

9. The method for treating ferric phosphate wastewater according to claim 5, characterized in that: In step (3), after adding the phosphoric acid, the pH of the slurry is 1.45-1.

50.

10. The method for treating ferric phosphate wastewater according to claim 5, characterized in that: In step (3), the temperature of the aged slurry is 85-95°C, and the time of the aged slurry is 1-3h.

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