Recycling treatment method of lithium iron phosphate cleaning wastewater

Abstract

The invention relates to the field of wastewater treatment, in particular to a recovery treatment method of lithium iron phosphate cleaning wastewater. The invention relates to a method for recycling lithium iron phosphate cleaning wastewater. Comprising a phosphorus, iron and manganese removal unit, a first sedimentation tank, a coagulation unit, a second sedimentation tank, a chemical softening unit, a third sedimentation tank, a pH regulating tank, an immersed ultrafiltration membrane unit, an ultrafiltration water producing tank, a primary reverse osmosis unit, a concentrated water reverse osmosis unit, a primary reverse osmosis water producing tank, a secondary reverse osmosis unit and a secondary reverse osmosis water producing tank.

Description

Technical Field

[0001] The invention relates to the field of wastewater treatment, and in particular to a method for recycling lithium iron phosphate cleaning wastewater. Background Art

[0002] With the development of science and technology, the application of electronic devices is becoming more and more extensive, especially the application scenarios of mobile electronic devices are becoming more and more abundant. Almost all mobile electronic devices are inseparable from batteries, and the research and development of battery technology has received more and more attention, among which battery manufacturing technology is the core of the industry.

[0003] Lithium iron phosphate (LiFePO4) is a widely used cathode material for lithium-ion batteries, and is favored for its high energy density, long cycle life, and good thermal stability. The main wastewater in the production process of lithium iron phosphate is lithium iron phosphate cleaning wastewater, which contains a variety of chemical substances, such as phosphates, heavy metal ions, organic solvents, etc. If it is directly discharged without proper treatment, it will cause serious pollution to the environment. The current treatment method for lithium iron phosphate cleaning wastewater is due to the requirements of GB31573-2015 "Inorganic Chemical Industry Pollutant Emission Standards", resulting in a lack of better methods for the large-scale recycling and treatment of lithium iron phosphate cleaning wastewater, and an improvement plan is urgently needed. Summary of the invention

[0004] The present invention hopes to provide a method for recycling and treating lithium iron phosphate cleaning wastewater, and the specific scheme is as follows: A method for recycling lithium iron phosphate cleaning wastewater comprises the following steps: (1) Adjust the pH of lithium iron phosphate cleaning wastewater to 9.5-11; (2) The mixed liquid after treatment in step (1) enters the first sedimentation tank to separate the generated sediment into mud and water; (3) The intermediate liquid after treatment in step (2) enters the coagulation unit, and coagulant polyferric and flocculant are added for coagulation and sedimentation; (4) The treated mixed liquid after step (3) enters the second sedimentation tank to separate the generated sediment into mud and water; (5) The coagulated liquid after treatment in step (4) enters the chemical softening unit; (6) The softened mixed liquid after treatment in step (5) enters the third sedimentation tank to separate the generated sediment into mud and water; (7) The softening liquid after treatment in step (6) enters the pH adjustment tank and adjusts the pH to 7-8; (8) The conditioned liquid after treatment in step (7) enters the submerged ultrafiltration membrane unit and is filtered through the submerged ultrafiltration membrane unit to obtain ultrafiltration product water; (9) The ultrafiltration water produced after the treatment in step (8) enters the ultrafiltration water production pool, and the secondary reverse osmosis concentrated water enters the ultrafiltration water production pool, together forming the primary reverse osmosis treated liquid; (10) The first-stage reverse osmosis treated liquid after the treatment in step (9) enters the first-stage reverse osmosis unit for desalination treatment to obtain first-stage reverse osmosis product water and first-stage reverse osmosis concentrated water; the first-stage reverse osmosis recovery rate is between 50% and 80%; (11) The primary reverse osmosis concentrated water after the treatment in step (10) enters the concentrated water reverse osmosis unit for desalination treatment to obtain concentrated water reverse osmosis product water and concentrated water reverse osmosis concentrated water; the concentrated water reverse osmosis recovery rate is between 50% and 75%; (12) The produced water from the primary reverse osmosis unit and the concentrated water reverse osmosis unit enters the primary reverse osmosis produced water pool and together constitutes the secondary reverse osmosis treated liquid; (13) The secondary reverse osmosis treated liquid of the primary reverse osmosis water production pool obtained in step (12) enters the secondary reverse osmosis unit and undergoes desalination treatment to obtain secondary reverse osmosis produced water and secondary reverse osmosis concentrated water, and the secondary reverse osmosis produced water is reused; the secondary reverse osmosis recovery rate is between 70% and 90%.

[0005] In the step (1), Ca(OH)2 solid or Ca(OH)2 dilution is used to adjust the pH, and Na2CO3 is added in the step (5).

[0006] In the step (3), the coagulant is one of polyaluminum and polyiron, and the coagulant addition concentration is 0.5-100 mg / L.

[0007] In the step (3), the flocculant is any one of cationic PAM, anionic PAM and non-ionic PAM, and the flocculant addition concentration is 0.5-10 mg / L.

[0008] In step (7), the pH is adjusted using one of sulfuric acid, hydrochloric acid and citric acid.

[0009] In the wastewater treated by the recycling treatment method of lithium iron phosphate cleaning wastewater of the present invention, the phosphate radical in the wastewater reacts to produce calcium phosphate precipitation, and reacts with iron and manganese ions to produce iron hydroxide and manganese hydroxide precipitation. The total phosphorus in the wastewater can be reduced to below 0.1 mg / L, and the iron and manganese ions can be reduced to below 0.2 mg / L.

[0010] During the coagulation and sedimentation process, polyferric sulfate is hydrolyzed to produce a large number of multinuclear complexes such as [Fe4(H2O)6], [Fe2(H2O)6], and [Fe(OH)2]. Through adsorption, bridging, and cross-linking, the colloidal particles in the water can be condensed together. At the same time, a series of physical and chemical changes have occurred, making them have a strong electrical neutralization ability, thereby reducing the potential of the micelles, breaking the stability of the micelles, and promoting the rapid coagulation and precipitation of the micelles. Through the coagulation and sedimentation process, the COD in the wastewater can be reduced to below 20mg / L.

[0011] In the chemical softening process, sodium carbonate reacts with calcium and magnesium ions in water to form insoluble precipitates, thereby achieving the purpose of softening water. 2+ ) and magnesium (Mg 2 + ) ions. During the reaction, calcium and magnesium ions react with carbonate ions (CO3 2- ) to form calcium carbonate (CaCO3) and magnesium carbonate (MgCO3) precipitation which are insoluble in water. The resulting precipitate can be separated from the water by filtration or sedimentation, thus removing the calcium and magnesium ions that cause water hardness. Through the chemical softening process, the total hardness in the wastewater can be reduced to less than 1 mg / L.

[0012] During the pH condition process, the pH is adjusted to 7-8 by adding acid solution. The purpose of adjusting the pH is to make the wastewater meet the operating requirements of the membrane system.

[0013] The submerged ultrafiltration membrane filtration system is a negative pressure suction filtration system. The effluent from the upstream process flows into the membrane pool by gravity. Under the action of the water level pressure difference and the suction pump, it penetrates through the outer wall of the hollow fiber membrane into the interior of the membrane; the pollutants are trapped on the surface of the membrane. Through the submerged ultrafiltration membrane filtration system, the turbidity of wastewater can be reduced to below 1NTU.

[0014] Reverse osmosis is a membrane separation technology powered by pressure gradient. Like a molecular filter, it can effectively remove dissolved salts, colloids, bacteria and organic matter from water. The reverse osmosis system can concentrate the treated water several times to increase the amount of recycled water. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The present invention is a process flow chart of a method for recycling and treating lithium iron phosphate cleaning wastewater. DETAILED DESCRIPTION Example

[0016] See Figure 1As shown, a method for recycling and treating lithium iron phosphate cleaning wastewater of the present invention includes phosphorus, iron, and manganese removal units, a first sedimentation tank, a coagulation unit, a second sedimentation tank, a chemical softening unit, a third sedimentation tank, a pH adjustment tank, an immersed ultrafiltration membrane unit, an ultrafiltration water production tank, a primary reverse osmosis unit, a concentrated water reverse osmosis unit, a primary reverse osmosis water production tank, a secondary reverse osmosis unit, and a secondary reverse osmosis water production tank.

[0017] See Figure 1 As shown, the phosphorus, iron and manganese removal unit of the present invention adds lime Ca(OH)2 to adjust the pH of the lithium iron phosphate cleaning wastewater to 9.5-11, reacts the phosphate radicals in the wastewater to produce calcium phosphate precipitation, and reacts with iron and manganese ions to produce water iron hydroxide and manganese hydroxide precipitation. The present invention can use Ca(OH)2 solid or Ca(OH)2 diluent to adjust the pH.

[0018] The treated mixed liquid from the phosphorus, iron and manganese removal units enters the first sedimentation tank to separate the mud and water from the produced sediment, and the sediment is transported out after passing through the mud discharge system and filter press.

[0019] The treated intermediate liquid of the first sedimentation tank B enters the coagulation unit, and coagulation and sedimentation are carried out by adding coagulant polyferric and flocculant PAM to remove suspended solids in the wastewater and reduce the turbidity, COD, etc. of the wastewater. Among them, the coagulant of the present invention can be one of polyaluminum and polyferric, and the coagulant addition concentration is 0.5-100 mg / L, and the flocculant is any one of cationic PAM, anionic PAM, and non-ionic PAM, and the flocculant addition concentration is 0.5-10 mg / L.

[0020] The coagulation treatment mixed liquid of the coagulation unit enters the second sedimentation tank to separate the mud and water from the generated sediment, and the sediment is transported out after passing through the mud discharge system and filter press.

[0021] The coagulated liquid from the second sedimentation tank enters the chemical softening unit. By adding Na2CO3, the calcium ions in the coagulated liquid react to produce calcium carbonate precipitates to remove the Ca(OH)2 calcium ions brought in.

[0022] The softened mixed liquid from the chemical softening unit enters the third sedimentation tank to separate the mud and water from the produced sediment, and the sediment is transported out after passing through the mud discharge system and filter press.

[0023] The softened liquid in the third sedimentation tank enters the pH adjustment tank, and H2SO4 is added to adjust the pH to 7-8. The purpose of adjusting the pH is to make the wastewater meet the operation requirements of the membrane system. Among them, the pH adjustment of the present invention can use one of sulfuric acid, hydrochloric acid and citric acid.

[0024] The regulating liquid in the pH regulating tank enters the submerged ultrafiltration membrane unit H and is filtered through the ultrafiltration membrane to obtain ultrafiltration water product. The ultrafiltration membrane used in the present invention can be either a submerged ultrafiltration membrane or a column ultrafiltration membrane.

[0025] The ultrafiltration water produced by the submerged ultrafiltration membrane unit enters the ultrafiltration water production pool, and at the same time, the secondary reverse osmosis concentrated water enters the ultrafiltration water production pool, together forming the primary reverse osmosis treated liquid.

[0026] The first-stage reverse osmosis treated liquid of the ultrafiltration water production pool enters the first-stage reverse osmosis unit for desalination treatment to obtain first-stage reverse osmosis produced water and first-stage reverse osmosis concentrated water. The first-stage reverse osmosis recovery rate of the present invention is between 50% and 80%.

[0027] The primary reverse osmosis concentrated water of the primary reverse osmosis unit enters the concentrated water reverse osmosis unit K for desalination treatment to obtain concentrated water reverse osmosis product water and concentrated water reverse osmosis concentrated water, and the concentrated water reverse osmosis concentrated water meets the discharge standards. Among them, the concentrated water reverse osmosis recovery rate of the present invention is between 50% and 75%.

[0028] The produced water from the primary reverse osmosis unit and the concentrated water reverse osmosis unit K enters the primary reverse osmosis produced water pool and together constitutes the secondary reverse osmosis treated liquid; The secondary reverse osmosis treated liquid of the primary reverse osmosis water production pool enters the secondary reverse osmosis and undergoes desalination treatment to obtain secondary reverse osmosis produced water and secondary reverse osmosis concentrated water, and the secondary reverse osmosis produced water is reused. The secondary reverse osmosis recovery rate of the present invention is between 70% and 90%.

[0029] Application Example 1 The total phosphorus content of the experimental influent was 1500mg / L and the manganese ion content was 306mg / L. The total phosphorus, iron, manganese, etc. in the cleaning wastewater were removed by adding lime to adjust the pH to 10.5. The total phosphorus content in the wastewater after treatment was 0.13mg / L and the manganese ion content was 0.17mg / L. After subsequent concentration by the membrane system for 6 times, it still met the requirements of the discharge standard.

[0030] The COD content of the experimental influent was 334 mg / L. After coagulation and sedimentation treatment, the COD content was 7.5 mg / L. After subsequent concentration by the membrane system for 6 times, it still met the requirements of the discharge standard.

[0031] The treatment effects of the experimental water samples are shown in Table 1 below: Table 1 Serial number project Water Intake Recycled water External drainage 1 COD / (mg / L) 360 / 45 2 Conductivity (us / cm) 5020 10 8000 3 Manganese (mg / L) 306 / 1.02 4 Total phosphorus (mg / L) 1500 / 0.78 5 Total nitrogen (mg / L) 3 / 18 So far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent replacements or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

Claims

1. A method for recycling lithium iron phosphate cleaning wastewater, characterized in that: The steps include: Adjust the pH of lithium iron phosphate cleaning wastewater to 9.5-11; The mixed liquid after the treatment in step (1) enters the first sedimentation tank to separate the generated sediment into mud and water; The intermediate liquid after the treatment in step (2) enters the coagulation unit, and the coagulant polyferric and flocculant are added for coagulation and sedimentation; The treated mixed liquid after step (3) enters the second sedimentation tank to separate the generated sediment into mud and water; The coagulated liquid after treatment in step (4) enters the chemical softening unit; The softened mixed liquid after the treatment in step (5) enters the third sedimentation tank to separate the generated sediment into mud and water; The softened liquid after the treatment in step (6) enters the pH adjustment tank to adjust the pH to 7-8; The conditioned liquid after the treatment in step (7) enters the submerged ultrafiltration membrane unit and is filtered through the submerged ultrafiltration membrane unit to obtain ultrafiltration product water; The ultrafiltration water produced after the treatment in step (8) enters the ultrafiltration water production pool, and the secondary reverse osmosis concentrated water enters the ultrafiltration water production pool, together forming the primary reverse osmosis treated liquid; The first-stage reverse osmosis treated liquid after step (9) enters the first-stage reverse osmosis unit for desalination treatment to obtain first-stage reverse osmosis product water and first-stage reverse osmosis concentrated water; the first-stage reverse osmosis recovery rate is between 50% and 80%; The primary reverse osmosis concentrated water after the treatment in step (10) enters the concentrated water reverse osmosis unit for desalination treatment to obtain concentrated water reverse osmosis product water and concentrated water reverse osmosis concentrated water; the concentrated water reverse osmosis recovery rate is between 50% and 75%; The produced water from the primary reverse osmosis unit and the concentrated water reverse osmosis unit enters the primary reverse osmosis produced water pool and together constitutes the secondary reverse osmosis treated liquid; The secondary reverse osmosis treated liquid of the primary reverse osmosis water production pool obtained in step (12) enters the secondary reverse osmosis unit and undergoes desalination treatment to obtain secondary reverse osmosis produced water and secondary reverse osmosis concentrated water, and the secondary reverse osmosis produced water is reused; the secondary reverse osmosis recovery rate is between 70% and 90%.

2. A method for recycling lithium iron phosphate cleaning wastewater as claimed in claim 1, characterized in that: In the step (1), Ca(OH)2 solid or Ca(OH)2 dilution is used to adjust the pH, and Na2CO3 is added in the step (5).

3. A method for recycling lithium iron phosphate cleaning wastewater as claimed in claim 1, characterized in that: In the step (3), the coagulant is one of polyaluminum and polyiron, and the coagulant addition concentration is 0.5-100 mg / L.

4. A method for recycling lithium iron phosphate cleaning wastewater as claimed in claim 1, characterized in that: In the step (3), the flocculant is any one of cationic PAM, anionic PAM and non-ionic PAM, and the flocculant addition concentration is 0.5-10 mg / L.

5. A method for recycling lithium iron phosphate cleaning wastewater as claimed in claim 1, characterized in that: In step (7), the pH is adjusted using one of sulfuric acid, hydrochloric acid and citric acid.

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