A method for recycling and reusing a phosphoric acid iron production mother liquor

Abstract

The application discloses a resource recycling and reuse method for a production mother liquor of iron phosphate, and has the advantages of simplicity, high efficiency, economy, low energy consumption and environmental protection, etc. By adopting a bipolar membrane technology, ammonium sulfate / ammonium phosphate in the production mother liquor is directly decomposed into ammonia and acid, ammonia and acid are recycled and reused in the whole preparation process of the iron phosphate, the industrial by-products such as ammonium sulfate and ammonium phosphate are solved from the source, and the market problem of the product is avoided. In addition, the recycling and reuse of iron slag in the process flow is realized.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment technology, specifically to a method for the resource recycling and reuse of mother liquor from ferric phosphate production. Background Technology

[0002] Iron phosphate is a primary cathode material for lithium-ion batteries. Currently, iron phosphate is prepared using various processes, including co-precipitation, hydrothermal synthesis, sol-gel method, oxidation precipitation, ultrasonic chemical method, and the industrial ammonium method. Among these, the industrial ammonium method is a mature and widely used industrial process, offering advantages such as simple reaction, convenient operation, low cost, and high product purity. However, the industrial ammonium method for producing iron phosphate generates a large amount of mother liquor and washing wastewater. Based on industrial production experience, approximately 15 ml of mother liquor and washing wastewater are generated for every ton of iron phosphate produced. 3 Mother liquor from production. The mother liquor is a high-salt wastewater containing a large amount of high-concentration sulfate (SO4) ions. 2- ), ammonia nitrogen (NH4-N) and low concentrations of phosphate (PO4) 3- This is quite difficult to handle.

[0003] Currently, the treatment methods for mother liquor from ferric phosphate production typically combine pretreatment with subsequent advanced treatment and recovery. These methods mainly include chemical precipitation followed by evaporation and crystallization, ion exchange followed by evaporation and crystallization, and ion exchange followed by membrane concentration. These methods all suffer from complex processes, large reagent / resin consumption, high operating and maintenance costs, and waste of valuable metal resources in the mother liquor. While they do yield some industrial byproducts such as ammonium sulfate and ammonium phosphate, subsequent market promotion and sales challenges remain. Therefore, there is an urgent need to develop an effective method for the resource-based recycling and reuse of ferric phosphate production wastewater. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention aims to provide a method for the resource-based recycling and reuse of mother liquor from ferric phosphate production.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for recycling and reusing mother liquor from ferric phosphate production includes the following steps:

[0007] S1. Collect the mother liquor from the production of ferric phosphate and adjust its pH. Remove metal ions from the mother liquor through hydrolysis to achieve deep purification.

[0008] S2. After the reaction in step S1 is completed, the obtained material is precisely filtered. The filter residue contains ferric hydroxide, and the filtrate enters step S3.

[0009] S3. The filtrate obtained in step S2 enters the bipolar membrane system to prepare a mixed acid solution of sulfuric acid and phosphoric acid and ammonia water. The mixed acid solution of sulfuric acid and phosphoric acid enters step S5, and the ammonia water enters step S4.

[0010] S4. A portion of the ammonia water obtained in step S3 is heated, evaporated, and stripped. The other portion of the ammonia water is used to absorb the stripped ammonia gas to obtain concentrated ammonia water. The remaining distilled water after heating, evaporation, and stripping is recycled as an acid-base receiving liquid for use in the bipolar membrane system.

[0011] S5. The mixed acid solution of sulfuric acid and phosphoric acid obtained in step S3 is concentrated by multi-effect evaporation to obtain concentrated mixed acid. The distilled water obtained by multi-effect evaporation is recycled as acid-base receiving liquid for bipolar membrane system.

[0012] S6. The concentrated mixed acid obtained in step S5 and the filter residue obtained in step S2 are mixed with industrial iron powder, heated and stirred to carry out a reduction reaction, and a mixed solution of ferrous sulfate and ferrous phosphate is obtained.

[0013] S7. Add hydrogen peroxide and phosphoric acid to the mixed solution of ferrous sulfate and ferrous phosphate obtained in step S6, adjust the pH of the reaction, and heat to oxidize and synthesize ferric phosphate; after the reaction is completed, perform solid-liquid separation to obtain ferric phosphate slag and production mother liquor, and return the production mother liquor to step S1.

[0014] Further, in step S1, the pH of the iron phosphate production mother liquor is adjusted to 5-8.

[0015] Further, in step S3, the concentration of ammonium sulfate in the filtrate is 100-300 g / L, and the bipolar membrane system employs constant current electrolysis with a current density of 300-800 A / m. 2 The concentration of the ammonia solution obtained is 1.5-2.5 mol / L, and the concentration of the mixed acid of sulfuric acid and phosphoric acid is 0.8-1.2 mol / L.

[0016] Furthermore, in step S4, the concentrated ammonia solution obtained has a mass concentration of 20-25%, and the concentrated ammonia solution is recycled back to steps S1 and S7 to adjust the pH.

[0017] Furthermore, in step S5, the mass concentration of sulfuric acid in the obtained concentrated mixed acid is 40-50%.

[0018] Furthermore, in step S6, the reduction reaction temperature is 30-60℃ and the time is 0.5-2.5h.

[0019] Further, in step S6, the Fe in the ferrous sulfate and ferrous phosphate mixed solution... 2+ The concentration is 50-300 g / L.

[0020] Further, in step S7, hydrogen peroxide and phosphoric acid are added to the mixed solution of ferrous sulfate and ferrous phosphate obtained in step S6 according to the molar ratio of Fe:P:H2O2 of 1:(0.95-1.05):(0.55-0.65).

[0021] Furthermore, in step S7, the heating temperature is 95°C and the pH of the reaction is 1.8-2.0.

[0022] The beneficial effects of this invention are as follows:

[0023] 1) This invention provides a process route and technical method for the resource recycling of mother liquor in the production of ferric phosphate. By adopting bipolar membrane technology, the acid-base separation and recycling of the mother liquor are realized, which solves the problem of reuse and sale of industrial by-products such as ammonium sulfate and ammonium phosphate from the source, realizes the recycling of ammonia and acid, and eliminates the market problem of the products.

[0024] 2) This invention reduces the environmental protection pressure and acid and alkali reagent costs for enterprises, improves the recycling and utilization of resources, and has significant environmental and economic benefits.

[0025] 3) The process flow of this invention is simple, the equipment structure is simple, and the investment is low.

[0026] 4) This invention is also applicable to other chemical industries that produce waste liquid containing ammonium sulfate and ammonium phosphate. Attached Figure Description

[0027] Figure 1 This is a flowchart illustrating the methods of various embodiments of the present invention. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings. It should be noted that this embodiment is based on the present technical solution and provides detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to this embodiment.

[0029] Example 1

[0030] The main components of the mother liquor produced by a certain ferric phosphate manufacturer include NH4. + (As N) 17.5 g / L, SO4 2- 75.6 g / L, PO4 3- 748.9mg / L, TFe380mg / L, pH=1.6.

[0031] like Figure 1 As shown, the specific steps of the resource recycling method for the above-mentioned iron phosphate production mother liquor provided in this embodiment include:

[0032] (1) Take 1L of iron phosphate production mother liquor, perform deep impurity removal on the iron phosphate production mother liquor, add ammonia water, adjust the pH to 8, and remove iron and other metal ions in the production mother liquor through hydrolysis reaction.

[0033] (2) After the reaction is completed, a precision filter is performed. The filter residue obtained is mainly iron hydroxide residue. The iron residue can be used as an iron source in the subsequent reduction reaction. The ammonium sulfate concentration in the filtrate obtained is 300 g / L.

[0034] (3) The filtrate enters a bipolar membrane system, which employs constant current electrolysis at a current density of 800 A / m³. 2 A mixed acid solution of 2.5 mol / L ammonia water, 1.2 mol / L sulfuric acid and phosphoric acid was prepared.

[0035] (4) Part of the ammonia water prepared in step (3) is heated and evaporated to remove the ammonia gas, and the other part of the ammonia water absorbs the ammonia gas that has been removed to prepare concentrated ammonia water with a mass concentration of 25%. The distilled water after heating and evaporating to remove the ammonia gas is used as an acid-base receiving liquid and recycled to the bipolar membrane system. The concentrated ammonia water is recycled back to steps (1) and (7) as a pH adjuster.

[0036] (5) The sulfuric acid and phosphoric acid mixture prepared in step (4) is concentrated by multi-effect evaporation to obtain a concentrated mixed acid with a sulfuric acid mass concentration of 50%. The distilled water obtained by multi-effect evaporation is used as an acid-base receiving liquid and recycled to the bipolar membrane system.

[0037] (6) The concentrated mixed acid and the ferric hydroxide slag produced in step (2) are reacted with 112 g / L of industrial iron powder to undergo a reduction reaction. The mixture is heated to 60 °C and stirred for 2.5 h to obtain Fe. 2+ A mixed solution of ferrous sulfate and ferrous phosphate with a concentration of 300 g / L;

[0038] (7) Add hydrogen peroxide and phosphoric acid to the mixed solution of ferrous sulfate and ferrous phosphate obtained in step (6) and heat to 95°C to oxidize and synthesize ferric phosphate. The molar ratio of Fe:P:H2O2 is 1:1.05:0.65. Add concentrated ammonia produced in step (4) to adjust the pH of the reaction to 2.0. After the reaction is completed, perform solid-liquid separation to obtain ferric phosphate slag and production mother liquor. The production mother liquor is returned to step (1) for further processing.

[0039] Example 2

[0040] The components of the iron phosphate production mother liquor in this embodiment are the same as those in Example 1.

[0041] like Figure 1 As shown, the specific steps of the resource recycling method for the mother liquor of ferric phosphate production provided in this embodiment include:

[0042] (1) Take 1L of iron phosphate production mother liquor, perform deep purification of iron phosphate production mother liquor, add ammonia water, adjust pH=5, and remove iron and other metal ions in the production mother liquor through hydrolysis reaction.

[0043] (2) After the reaction is completed, a fine filtration is performed. The filter residue obtained is mainly iron hydroxide residue. The iron residue can be used as an iron source in the subsequent reduction reaction. The concentration of ammonium sulfate in the filtrate obtained is 100 g / L.

[0044] (3) The filtrate enters a bipolar membrane system, which employs constant current electrolysis at a current density of 300 A / m³. 2 A mixed acid solution of 1.5 mol / L ammonia water, 0.8 mol / L sulfuric acid and phosphoric acid was prepared.

[0045] (4) Part of the ammonia water prepared in step (3) is heated and evaporated to remove the ammonia gas, and the other part of the ammonia water absorbs the ammonia gas that has been removed to prepare concentrated ammonia water with a mass concentration of 20%. The remaining distilled water after heating and evaporating to remove the ammonia gas is used as an acid-base receiving liquid and recycled to the bipolar membrane system. The concentrated ammonia water is recycled back to steps (1) and (7) as a pH adjuster.

[0046] (5) The sulfuric acid and phosphoric acid mixture prepared in step (4) is concentrated by multi-effect evaporation to obtain a concentrated mixed acid with a sulfuric acid mass concentration of 40%. The distilled water from the multi-effect evaporation is used as an acid-base receiving liquid and recycled to the bipolar membrane system.

[0047] (6) The concentrated mixed acid and the ferric hydroxide slag produced in step (2) are reacted with 56 g / L of industrial iron powder to undergo a reduction reaction. The mixture is heated to 30°C and stirred for 0.5 h to obtain Fe. 2+ A mixed solution of ferrous sulfate and ferrous phosphate with a concentration of 50 g / L;

[0048] (7) Add hydrogen peroxide and phosphoric acid to the mixed solution of ferrous sulfate and ferrous phosphate obtained in step (6), heat to 95°C to oxidize and synthesize ferric phosphate. The molar ratio of Fe:P:H2O2 is 1:0.95:0.55. Add concentrated ammonia produced in step (4) to adjust the pH of the reaction to 1.8. After the reaction is completed, perform solid-liquid separation to obtain ferric phosphate slag and production mother liquor. The production mother liquor is returned to step (1) for further processing.

[0049] For those skilled in the art, various corresponding changes and modifications can be made based on the above technical solutions and concepts, and all such changes and modifications should be included within the protection scope of the claims of this invention.

Claims

1. A method for the resource-based recycling and reuse of mother liquor from ferric phosphate production, characterized in that, Includes the following steps: S1. Collect the mother liquor from the production of ferric phosphate and adjust its pH. Remove metal ions from the mother liquor through hydrolysis to achieve deep purification. S2. After the reaction in step S1 is completed, the obtained material is precisely filtered. The filter residue contains ferric hydroxide, and the filtrate enters step S3. S3. The filtrate obtained in step S2 enters the bipolar membrane system to prepare a mixed acid solution of sulfuric acid and phosphoric acid and ammonia water. The mixed acid solution of sulfuric acid and phosphoric acid enters step S5, and the ammonia water enters step S4. S4. A portion of the ammonia water obtained in step S3 is heated, evaporated, and stripped. The other portion of the ammonia water is used to absorb the stripped ammonia gas to obtain concentrated ammonia water. The remaining distilled water after heating, evaporation, and stripping is recycled as an acid-base receiving liquid for use in the bipolar membrane system. S5. The mixed acid solution of sulfuric acid and phosphoric acid obtained in step S3 is concentrated by multi-effect evaporation to obtain concentrated mixed acid. The distilled water obtained by multi-effect evaporation is recycled as acid-base receiving liquid for bipolar membrane system. S6. The concentrated mixed acid obtained in step S5 and the filter residue obtained in step S2 are mixed with industrial iron powder, heated and stirred to carry out a reduction reaction, and a mixed solution of ferrous sulfate and ferrous phosphate is obtained. S7. Add hydrogen peroxide and phosphoric acid to the mixed solution of ferrous sulfate and ferrous phosphate obtained in step S6, adjust the pH of the reaction, and heat to oxidize and synthesize ferric phosphate; after the reaction is completed, perform solid-liquid separation to obtain ferric phosphate slag and production mother liquor, and return the production mother liquor to step S1.

2. The method according to claim 1, characterized in that, In step S1, the pH of the iron phosphate production mother liquor is adjusted to 5-8.

3. The method according to claim 1, characterized in that, In step S3, the concentration of ammonium sulfate in the filtrate is 100-300 g / L, and the bipolar membrane system uses constant current electrolysis with a current density of 300-800 A / m. 2 The concentration of the ammonia solution obtained is 1.5-2.5 mol / L, and the concentration of the mixed acid of sulfuric acid and phosphoric acid is 0.8-1.2 mol / L.

4. The method according to claim 1, characterized in that, In step S4, the concentrated ammonia solution obtained has a mass concentration of 20-25%, and the concentrated ammonia solution is recycled back to steps S1 and S7 to adjust the pH.

5. The method according to claim 1, characterized in that, In step S5, the mass concentration of sulfuric acid in the concentrated mixed acid is 40-50%.

6. The method according to claim 1, characterized in that, In step S6, the reduction reaction temperature is 30-60℃ and the time is 0.5-2.5h.

7. The method according to claim 1, characterized in that, In step S6, the Fe in the ferrous sulfate and ferrous phosphate mixed solution... 2+ The concentration is 50-300 g / L.

8. The method according to claim 1, characterized in that, In step S7, hydrogen peroxide and phosphoric acid are added to the mixed solution of ferrous sulfate and ferrous phosphate obtained in step S6 according to the molar ratio of Fe:P:H2O2 of 1:(0.95-1.05):(0.55-0.65).

9. The method according to claim 1, characterized in that, In step S7, the heating temperature is 95℃ and the pH of the reaction is 1.8-2.0.

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