Wastewater treatment and recovery process in production process of layered oxide positive electrode material of sodium-ion battery

Abstract

The invention discloses a wastewater treatment and recovery process in the production process of a layered oxide positive electrode material of a sodium-ion battery, and belongs to the field of environmental protection, the wastewater treatment and recovery process comprises the following steps: S1, respectively carrying out pH regulation on mother liquor and washing water, and respectively carrying out MF microporous filtration on the mother liquor and the washing water after pH regulation; s2, the filtered mother liquor and washing water are subjected to pH adjustment respectively, and the mother liquor and washing water subjected to pH adjustment are subjected to UF ultrafiltration respectively; s3, carrying out first-stage RO membrane treatment on the washing water UF produced water subjected to UF ultrafiltration; carrying out second-stage RO membrane treatment on mother liquor UF produced water and first-stage RO concentrated water after UF ultrafiltration; s4, carrying out resin defluorination on the concentrated water treated by the second-stage RO membrane; the produced water after the second-stage RO membrane treatment is returned to the first-stage RO membrane treatment in the step S3; and S5, treating the wastewater subjected to resin defluorination through a bipolar membrane, and recovering to obtain sodium hydroxide and sulfuric acid, so that the problem that sodium ions and sulfate ions cannot be recovered in the prior art is solved.

Description

Technical Field

[0001] The present invention relates to the field of environmental protection, and in particular to a wastewater treatment and recycling process in the production process of layered oxide positive electrode materials for sodium ion batteries. Background Art

[0002] There are three main types of positive electrode materials for sodium-ion batteries: layered oxides, Prussian blue compounds, and polyanion compounds. Layered oxides have been widely studied for their high specific capacity advantage, but they are prone to structural changes or phase transitions during the sodium ion extraction process, resulting in a decrease in battery cycle performance. In order to improve the stability of the material, it is usually necessary to dope electrochemically active elements such as Mn, Fe, and Ni. Prussian blue compounds and polyanion compounds are also hot topics of research. They each have unique structural and performance advantages. For example, Prussian blue compounds have open three-dimensional channels, which allow Na+ to migrate quickly in the channels and have good structural stability and rate performance; most polyanion positive electrode materials have an open three-dimensional skeleton, good rate performance and good cycle performance, but generally poor conductivity. As the most mature route, layered oxide materials have a conventional preparation process, are easy to scale up, and are more smoothly transmitted from the technical end to the industrial end. At present, the industrialization of layered metal oxide processes for sodium ion batteries mainly includes two-step liquid phase method and one-step solid phase method. Except for raw materials and specific process parameters, the two-step liquid phase method is highly consistent with the preparation process of lithium battery ternary positive electrode materials, with high reuse rate of lithium battery equipment, and is easy to industrialize sodium ion batteries rapidly. Compared with the liquid phase method, the one-step solid phase method does not require the precursor preparation step, but the sintering temperature is higher, and the consistency and stability of the product are lower than that of the liquid phase method, but the cost advantage is very obvious.

[0003] The production process of liquid phase sodium layered oxide positive electrode material includes the following steps: dissolving and mixing manganese sulfate, iron sulfate and nickel sulfate, filtering and adding sodium hydroxide to react at -50°C, aging, removing the supernatant, centrifugation and washing, and drying and mixing to obtain a precursor; grinding and mixing sodium carbonate and nickel hydroxide iron manganese precursors, sintering at 750-850°C, and then coarsely crushing and finely crushing to obtain layered oxide positive electrode material. The water quality of the mother liquor in the aging process and the washing water in the centrifugal washing process is mainly as follows: pH value range: 6-9; main solute: Na2SO4, Fe2+<100mg / L, TDS: 5000-6000mg / L. If it is directly discharged, it will cause environmental pollution and waste of sodium ions, so it needs to be treated; and the existing wastewater treatment process cannot achieve the recycling of sodium ions and sulfate ions. Summary of the invention

[0004] The invention provides a wastewater treatment and recovery process in the production process of layered oxide positive electrode materials for sodium ion batteries, which solves the problem in the prior art that sodium ions and sulfate ions cannot be recovered.

[0005] In order to solve this technical problem, the present invention provides the following technical solution:

[0006] The wastewater treatment and recycling process of the sodium ion battery layered oxide positive electrode material production process includes the following steps:

[0007] S1, the mother liquor and the washing water are respectively subjected to pH adjustment, and the mother liquor and the washing water after pH adjustment are respectively subjected to MF microfiltration;

[0008] S2, the mother liquor and washing water after filtration are respectively subjected to pH adjustment, and the mother liquor and washing water after pH adjustment are respectively subjected to UF ultrafiltration;

[0009] S3, the washing water and UF produced water after UF ultrafiltration are treated by a first stage RO membrane; the mother liquor and UF produced water after UF ultrafiltration and a first stage RO concentrated water are treated by a second stage RO membrane;

[0010] S4, the concentrated water after the second-stage RO membrane treatment is subjected to resin defluorination; the produced water after the second-stage RO membrane treatment is returned to the first-stage RO membrane treatment in step S3;

[0011] S5. The wastewater after defluorination by resin is treated by bipolar membrane to recover sodium hydroxide and sulfuric acid.

[0012] Preferably, the pH adjustment in step S1 uses sodium hydroxide with a mass fraction of 32%.

[0013] Preferably, the pH of the mother liquor and the washing water after pH adjustment in step S1 is 12.

[0014] The pH of the mother liquor and the washing water is adjusted to 12 using sodium hydroxide, which can remove the iron ions in the mother liquor and the washing water.

[0015] Preferably, after the MF microfiltration in step S1, the filter residue enters plate and frame filtration for further dehydration, and the moisture content of the sludge after dehydration is less than 70%.

[0016] Preferably, the pH adjustment in step S2 uses sulfuric acid with a mass fraction of 30%.

[0017] Preferably, the pH adjustment in step S2 is to adjust the pH of the mother liquor and the washing water to pH 6.

[0018] Preferably, the ratio of the mother liquor UF product water after UF ultrafiltration in step S3 to the first stage RO concentrated water is 50:36-38.

[0019] Preferably, the ratio of the mother liquor UF product water after UF ultrafiltration in step S3 to the first stage RO concentrated water is 50:37.

[0020] Preferably, the fluorine removal rate of the resin defluorination in step S4 is ≥98%.

[0021] Preferably, the bipolar membrane treatment in step S5 obtains 8% by mass sodium hydroxide and 10% by mass sulfuric acid, the 10% by mass sulfuric acid is concentrated by acid evaporation to obtain 50% by mass sulfuric acid, and the 8% by mass sodium hydroxide is concentrated by alkali evaporation to obtain 32% by mass sodium hydroxide; the condensed water obtained by acid evaporation and alkali evaporation is reused as reclaimed water; the generated sodium hydroxide can be reused in the layered metal oxide production process, avoiding external purchase, treating wastewater and reducing the front-end production and operation costs; in addition, high-purity sulfuric acid can be obtained at the same time, which can be sold externally or reused in the aforementioned pH adjustment step.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] The overall process achieves zero emissions and produces no by-product pollutants;

[0024] The production process of layered metal oxides requires the introduction of elements such as manganese, iron, nickel, and sodium. The wastewater generated in the production process can achieve sodium ion balance through this wastewater treatment process, that is, the sodium hydroxide generated in this wastewater treatment process can be reused in the layered metal oxide production process, avoiding external purchase, and treating wastewater while reducing the front-end production and operation costs; in addition, high-purity sulfuric acid can be obtained at the same time and can be sold externally, increasing corporate benefits and realizing the coupling of wastewater treatment and material production technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0026] Figure 1 It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments. The illustrative embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0028] Example

[0029] like Figure 1 As shown, the wastewater treatment and recycling process of the layered oxide sodium ion positive electrode material production process includes the following steps:

[0030] The mother liquor and washing water were adjusted to pH 12 with 32% sodium hydroxide by mass, and the mother liquor and washing water after pH adjustment were subjected to MF microfiltration, and the residue after MF microfiltration was further dehydrated by plate and frame filtration, and the moisture content of the sludge after dehydration was less than 70%;

[0031] The mother liquor and washing water after filtration were adjusted to pH 6 using 30% sulfuric acid by mass, and the mother liquor and washing water after pH adjustment were subjected to UF ultrafiltration respectively;

[0032] The wash water and UF produced water after UF ultrafiltration are treated by a first-stage RO membrane; the mother liquor and UF produced water after UF ultrafiltration and the first-stage RO concentrated water are treated by a second-stage RO membrane at an inlet ratio of 50:37;

[0033] The concentrated water after the second-stage RO membrane treatment is subjected to resin defluorination, and the fluorine removal rate of the resin defluorination is ≥98%. The produced water after the second-stage RO membrane treatment is returned to the first-stage RO membrane treatment; the water quality analysis of the wash water treatment process is shown in Table 1, and the water quality analysis of the mother liquor treatment process is shown in Table 2.

[0034] The wastewater after defluorination by resin is treated by bipolar membrane, and the bipolar membrane treatment obtains 8% by mass of sodium hydroxide and 10% by mass of sulfuric acid. The 10% by mass of sulfuric acid is concentrated by acid evaporation to obtain 50% by mass of sulfuric acid, and the 8% by mass of sodium hydroxide is concentrated by alkali evaporation to obtain 32% by mass of sodium hydroxide (as shown in Table 3); the condensed water obtained by acid evaporation and alkali evaporation is reused as reclaimed water.

[0035] Table 1

[0036]

[0037] Table 2

[0038]

[0039] Table 3

[0040]

[0041] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A process for treating and recovering wastewater from the production of layered oxide cathode materials for sodium ion batteries, characterized in that: The steps include: S1, the mother liquor and the washing water are respectively subjected to pH adjustment, and the mother liquor and the washing water after pH adjustment are respectively subjected to MF microfiltration; S2, the mother liquor and washing water after filtration are respectively subjected to pH adjustment, and the mother liquor and washing water after pH adjustment are respectively subjected to UF ultrafiltration; S3, the washing water and UF produced water after UF ultrafiltration are treated by a first stage RO membrane; the mother liquor and UF produced water after UF ultrafiltration and a first stage RO concentrated water are treated by a second stage RO membrane; S4, the concentrated water after the second-stage RO membrane treatment is subjected to resin defluorination; the produced water after the second-stage RO membrane treatment is returned to the first-stage RO membrane treatment in step S3; S5. The wastewater after defluorination by resin is treated by bipolar membrane to recover sodium hydroxide and sulfuric acid.

2. The process for treating and recovering wastewater from the production process of layered oxide positive electrode materials for sodium ion batteries according to claim 1, characterized in that: The pH in step S1 is adjusted by using sodium hydroxide with a mass fraction of 32%.

3. The process for treating and recovering wastewater from the production process of layered oxide positive electrode materials for sodium ion batteries according to claim 1, characterized in that: The pH of the mother liquor and the washing water after pH adjustment in step S1 was 12.

4. The process for treating and recovering wastewater from the production process of layered oxide positive electrode materials for sodium ion batteries according to claim 1, characterized in that: After the MF microporous filtration in step S1, the filter residue enters the plate and frame filtration for further dehydration, and the moisture content of the sludge after dehydration is less than 70%.

5. The process for treating and recovering wastewater from the production process of layered oxide positive electrode materials for sodium ion batteries according to claim 1, characterized in that: The pH adjustment in step S2 uses sulfuric acid with a mass fraction of 30%.

6. The process for treating and recovering wastewater from the production process of layered oxide positive electrode materials for sodium ion batteries according to claim 1, characterized in that: The pH adjustment in step S2 is to adjust the pH of the mother liquor and the washing water to pH 6.

7. The process for treating and recovering wastewater from the production process of layered oxide positive electrode materials for sodium ion batteries according to claim 1, characterized in that: The ratio of the mother liquor UF produced water and the first stage RO concentrated water after UF ultrafiltration in step S3 is 50:36-38.

8. The process for treating and recovering wastewater from the production process of layered oxide positive electrode materials for sodium ion batteries according to claim 7, characterized in that: The ratio of the mother liquor UF product water and the first stage RO concentrated water after UF ultrafiltration in step S3 is 50:

37.

9. The process for treating and recovering wastewater from the production process of layered oxide positive electrode materials for sodium ion batteries according to claim 1, characterized in that: The fluorine removal rate of the resin defluorination in step S4 is ≥98%.

10. The process for treating and recovering wastewater from the production process of layered oxide positive electrode materials for sodium ion batteries according to claim 1, characterized in that: The bipolar membrane treatment in step S5 obtains 8% by mass sodium hydroxide and 10% by mass sulfuric acid, the 10% by mass sulfuric acid is concentrated by acid evaporation to obtain 50% by mass sulfuric acid, and the 8% by mass sodium hydroxide is concentrated by alkali evaporation to obtain 32% by mass sodium hydroxide; the condensed water obtained by acid evaporation and alkali evaporation is reused as reclaimed water.

Images