Prussian blue wastewater zero discharge treatment process

Abstract

The invention discloses a zero-discharge treatment process for Prussian blue wastewater, and relates to the field of battery materials. The wastewater comprises wash water and mother liquor, and the process comprises the following steps: S1, filtering the wash water, adjusting the pH value of the filtrate to ≤6, and performing membrane concentration treatment after heat exchange and cooling to obtain wash water concentrate; S2, mixing the wash water concentrate with the mother liquor, adjusting the pH value of the filtrate to ≤6 after filtering, and performing resin adsorption treatment on the wastewater after the pH adjustment; S3, oxidizing the wastewater after the resin adsorption treatment; S4, evaporating, centrifuging and drying the oxidized wastewater to obtain a sodium sulfate product, and the problem that ferrocyanide cannot be recovered in the prior art is solved.

Description

Technical Field

[0001] The invention relates to the field of battery materials, and in particular to a zero-discharge treatment process for Prussian blue wastewater. Background Art

[0002] Prussian sodium-ion battery materials have the advantages of low cost, good cycle performance, high actual specific capacity and voltage platform, and the production process is generally obtained by reacting sodium ferrocyanide with transition metal salts. However, incompletely reacted ferrocyanide will be produced during battery production, and this wastewater contains a high concentration of ferrocyanide.

[0003] The existing method for treating Prussian sodium-ion batteries generally adopts the method of adding salt and complexing agents to destroy ferrocyanide, thereby removing ferrocyanide in wastewater. On the one hand, this method will introduce new impurities. On the other hand, the residual ferrocyanide in the wastewater is easily heated to produce volatile cyanide, which is not conducive to zero-emission salt distillation. The removal effect of ferrocyanide is not ideal, and the recovery and reuse of ferrocyanide cannot be achieved. Summary of the invention

[0004] The invention provides a zero-discharge treatment process for Prussian blue wastewater, which solves the problem in the prior art that ferrocyanide cannot be recovered.

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

[0006] The zero-discharge treatment process of Prussian blue wastewater, wherein the wastewater includes wash water and mother liquor, comprises the following steps:

[0007] S1, filtering the wash water, adjusting the pH value of the filtrate to ≤6, and performing membrane concentration treatment after heat exchange and cooling to obtain wash water concentrate;

[0008] S2, the wash water concentrate and the mother liquor are mixed, the filtrate pH is adjusted to ≤ 6 after filtration, the pH adjusted wastewater resin adsorption treatment;

[0009] S3, oxidizing the wastewater after resin adsorption treatment;

[0010] S4. The oxidized wastewater is evaporated, centrifuged and dried to obtain a sodium sulfate product.

[0011] After removing suspended solids in the sewage by filtration and concentrating it with a membrane, ferrocyanide is adsorbed and recovered by resin, COD is removed by ozone oxidation, and finally high-purity sodium sulfate is obtained by MVR evaporation and crystallization, which can be made into sodium sulphate.

[0012] Preferably, step S1 uses 30% by mass sulfuric acid to adjust the pH value; after heat exchange and cooling in step S1, the washing water temperature is controlled not to exceed 35°C.

[0013] The PH value of the fine filtered water is adjusted and heat exchanged to meet the membrane operating temperature requirements.

[0014] The membrane concentration treatment in step S1 includes: sequentially passing through a UF membrane and a first-stage RO membrane, a second-stage RO membrane, and a third-stage RO membrane concentration treatment.

[0015] Preferably, in step S1: the UF membrane produced water enters a stage of RO membrane treatment, and the UF membrane concentrated water returns for filtration;

[0016] The concentrated water from the first stage RO membrane enters the second stage RO membrane for treatment, and the concentrated water from the second stage RO membrane enters the third stage RO membrane for treatment. The concentrated water from the third stage RO membrane is the obtained washing concentrated water;

[0017] The water produced by the first stage RO membrane, the second stage RO membrane and the third stage RO membrane enters the secondary RO membrane for concentration and then returns to the first stage RO membrane for treatment.

[0018] The clarification and filtration function of the UF membrane is used to clarify and filter the wastewater after pH adjustment and heat exchange. The first stage RO membrane uses the interception function of the RO membrane to concentrate the ultrafiltration membrane water and the second stage RO concentrated water. The second stage RO membrane uses the interception function of the RO membrane to conduct a second concentration of the first stage RO concentrated water. The third stage RO membrane uses the interception function of the RO membrane to conduct a third concentration of the second stage RO membrane concentrated water.

[0019] Preferably, in step S2, the temperature of the mother liquor and the concentrated washing water after filtration is controlled not to exceed 35° C.; and step S2 uses 30% by mass sulfuric acid for pH adjustment.

[0020] Adjust the pH of the water produced by precision filtration to meet the pH requirements of resin adsorption operation.

[0021] Preferably, the resin adsorption treatment in step S2 is: firstly transform the weakly basic anion resin with a sulfuric acid solution having a mass fraction of 8%, and then utilize the adsorption function of the transformed weakly basic anion resin to adsorb ferrocyanate on the wastewater after pH adjustment.

[0022] The ferrocyanide ions adsorbed by the resin can be regenerated into sodium ferrocyanide through alkali and can be reused in production as raw materials, which indirectly reduces the cost of purchasing raw materials for production. It is more cost-effective and more stable in operation than the traditional oxidation method.

[0023] The alkali-regenerated resin can be recycled after being treated with sulfuric acid.

[0024] Preferably, the oxidation in step S3 is ozone oxidation.

[0025] The ascorbic acid of the wastewater produced by ozone oxidation is used to achieve a lower COD level and reduce the amount of mother liquor in the evaporator.

[0026] Preferably, the evaporation in step S4 is MVR evaporation crystallization; and the evaporation temperature is ≥110°C.

[0027] Preferably, in step S4, wet salt and centrifuge liquid are separated after centrifugation; the wet salt is dried in a fluidized bed to obtain sodium sulfate; and the centrifuge liquid is dried by steam to obtain sodium sulfate.

[0028] Preferably, the water content of sodium sulfate is 0.5-1.5%, and the purity of sodium sulfate is ≥97.0%.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] After removing suspended solids from the sewage by filtration and concentrating it with a membrane, the ferrocyanide is adsorbed and recovered by resin, COD is removed by ozone oxidation, and finally high-purity alum is obtained by MVR evaporation and crystallization.

[0031] The treatment method of this scheme can effectively remove COD and cyanide from wastewater; the water in the recycling process can be made into pure water and ultrapure water to achieve zero discharge.

[0032] The ferrocyanide ions adsorbed by the resin can be regenerated into sodium ferrocyanide through alkali and can be reused in production as raw materials, which indirectly reduces the cost of purchasing raw materials for production. It is more cost-effective and more stable in operation than the traditional oxidation method.

[0033] The alkali-regenerated resin can be recycled after being treated with sulfuric acid. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] 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:

[0035] Figure 1 This is a schematic diagram of the zero-discharge treatment process for Prussian blue wastewater according to the present invention;

[0036] Figure 2 It is a schematic diagram of the MVR evaporation and crystallization section of the zero-discharge treatment process for Prussian blue wastewater of the present invention. DETAILED DESCRIPTION

[0037] 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.

[0038] Example

[0039] like Figure 1-2The zero-discharge treatment process for Prussian blue wastewater of the present invention comprises wash water and mother liquor, which are divided into three sections, a wash water membrane concentration section, a mother liquor wastewater treatment section, and an MVR evaporation crystallization section; the wash water inlet water quality is shown in Table 1, and the mother liquor inlet water quality is shown in Table 2.

[0040] Table 1

[0041] Water volume Water volume SS Ni Fe Mn <![CDATA[Na + ]]> <![CDATA[m 3 / d]]> <![CDATA[m 3 / h]]> mg / L mg / L mg / L mg / L mg / L 2000.00 83.33 100.0 10.0 46.9 5.0 1703.7 <![CDATA[Fe(CN)6 4- ]]> <![CDATA[SO4 2- ]]> <![CDATA[OH - / H + ]]> TDS COD T PH mg / L mg / L mg / L mg / L mg / L ℃ - 178.0 3380.3 14.0 5291.0 250.0 50-60 8.5-9.5

[0042] Table 2

[0043] Water volume Water volume SS Ni Fe Mn <![CDATA[Na + ]]> <![CDATA[m 3 / d]]> <![CDATA[m 3 / h]]> mg / L mg / L mg / L mg / L mg / L 1000.00 41.67 1000.0 120.0 558.5 60.0 35506.0 <![CDATA[Fe(CN)6]]> <![CDATA[SO4 2- ]]> <![CDATA[OH - ]]> TDS COD T PH mg / L mg / L mg / L mg / L mg / L ℃ - 2118.5 72000.0 170.0 109974.5 3000.0 75.0 10-12

[0044] The processing process includes the following steps:

[0045] Wash water membrane concentration section: select PE / PA filter element to filter the wash water, use 30% mass fraction sulfuric acid to adjust the pH value of the filtrate to ≤6, and control the wash water temperature not to exceed 35℃ after heat exchange and cooling. Then, the wash water is concentrated by UF membrane and first-stage RO membrane, second-stage RO membrane, and third-stage RO membrane in sequence. The UF membrane produced water enters the first-stage RO membrane for treatment, and the UF membrane concentrated water is returned for filtration;

[0046] UF membrane is designed with hollow fiber membrane, membrane area: 75 / 77㎡. RO membrane is designed with anti-pollution brackish water reverse osmosis membrane, membrane area: 37.2㎡.

[0047] The second stage RO membrane is designed with seawater desalination reverse osmosis membrane, with a membrane area of ​​37.2㎡. The third stage RO membrane is designed with high pressure reverse osmosis membrane, with a membrane area of ​​37.0 / 30.7 / 34.8㎡

[0048] The concentrated water from the first stage RO membrane enters the second stage RO membrane for treatment, and the concentrated water from the second stage RO membrane enters the third stage RO membrane for treatment to obtain the concentrated water from the third stage RO membrane;

[0049] The water produced by the first stage RO membrane, the second stage RO membrane and the third stage RO membrane enters the secondary RO membrane for concentration and then returns to the first stage RO membrane for treatment.

[0050] The quality of the three-stage RO concentrated water after the three-stage RO membrane concentration treatment is shown in Table 3:

[0051] Table 3

[0052] Water volume Water volume SS Ni Fe Mn <![CDATA[Na + ]]> <![CDATA[m 3 / d]]> <![CDATA[m 3 / h]]> mg / L mg / L mg / L mg / L mg / L 109.66 4.57 / 9.81 918.14 9.79 33343.07 <![CDATA[Fe(CN)6 4- ]]> <![CDATA[SO4 2- ]]> <![CDATA[OH - / H + ]]> TDS COD T PH mg / L mg / L mg / L mg / L mg / L ℃ - 3482.70 66444.01 0.00 103289.4 4892.69 35.0 6

[0053] It can be seen that after filtration and membrane concentration treatment, not only the suspended solids are removed, but the ions therein are also concentrated.

[0054] In addition, the sludge pool after filtration is filtered by a filter press to separate the filtrate and filter cake. Selection of filter press: 1250 / 50 square high-pressure diaphragm, electric hydraulic automatic pressure maintenance, automatic plate filter press, underflow effluent, liquid accumulation plate glass fiber reinforced plastic material, simple mud bucket, 1 use, frame carbon steel anti-corrosion, maximize the reduction of sludge moisture content. Daily sludge processing volume: about 0.51t / d, moisture content: about 60%.

[0055] Mother liquor wastewater treatment section: the wash water concentrate is mixed with the mother liquor, and the temperature is controlled not to exceed 35°C after filtering;

[0056] After heat exchange of the mother liquor, clarify the flow, select PE / PA filter element for filtration to ensure turbidity < 5NTU.

[0057] Heat exchanger parameters: spiral tube heat exchanger: heat exchange area 80㎡, inlet water 32℃, outlet water 39℃, circulation volume 110m³ / h, reducing the mother liquid water temperature from 75℃ to 35℃; material, tube side 316L / shell side 304.

[0058] The pH of the filtrate was adjusted to ≤6 with 30% sulfuric acid, and the weakly alkaline anion resin was first transformed with 8% sulfuric acid solution (the flow rate of the sulfuric acid solution was 36.74 m 3 / d), using the adsorption function of the transformed weakly alkaline anion resin, the wastewater after pH adjustment was adsorbed with ferrocyanate, and the wastewater after pH adjustment was adsorbed with ferrocyanate. The water quality of the effluent after adsorption is shown in Table 4:

[0059] Table 4

[0060] Water volume Water volume SS Ni Fe Mn <![CDATA[Na + ]]> <![CDATA[m 3 / d]]> <![CDATA[m 3 / h]]> mg / L mg / L mg / L mg / L mg / L 1102.85 45.95 1.00 0.50 0.5 0.50 35484.11 <![CDATA[Fe(CN)6 4- ]]> <![CDATA[SO4 2- ]]> <![CDATA[OH - / H + ]]> TDS COD T PH mg / L mg / L mg / L mg / L mg / L ℃ - 8.10 74055.62 0.00 109548.8 3185.08 35.00 7-8

[0061] It can be seen that after resin treatment, the recovery rate of Fe(CN)6 is as high as 99.6%.

[0062] The ferrocyanide adsorbed by the resin was passed through an 8% alkali solution (flow rate of 36.74 m 3 / d) The regenerated sodium ferrocyanide can be reused in production as raw material, which indirectly reduces the cost of purchasing raw materials for production. It is more cost-effective and more stable in operation than the traditional oxidation method.

[0063] The alkali-regenerated resin was converted into an 8% aqueous solution of sulfuric acid.

[0064] Next, the wastewater treated by resin adsorption was oxidized by ozone. The water quality after oxidation is shown in Table 5:

[0065] Table 5

[0066] Water volume Water volume SS Ni Fe Mn <![CDATA[Na + ]]> <![CDATA[m 3 / d]]> <![CDATA[m 3 / h]]> mg / L mg / L mg / L mg / L mg / L 1102.85 45.95 1.00 0.50 0.50 0.50 35484.11 <![CDATA[Fe(CN)6 4- ]]> <![CDATA[SO4 2- ]]> <![CDATA[OH - / H + ]]> TDS COD T PH mg / L mg / L mg / L mg / L mg / L ℃ - 8.10 74055.62 0.00 109548.8 50.00 35.00 /

[0067] It can be seen that after ozone oxidation, the COD removal rate is as high as 98.4%.

[0068] MVR evaporation and crystallization section: the oxidized wastewater is evaporated at a temperature of ≥110°C; wet salt and centrifuge are separated after centrifugation; the wet salt is dried in a fluidized bed to obtain sodium sulfate; the centrifuge is dried by steam to obtain sodium sulfate, the water content of the sodium sulfate is 0.5-1.5%, and the purity of sulfuric acid is ≥97.0%.

[0069] 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 zero-discharge treatment process for Prussian blue wastewater, wherein the wastewater includes wash water and mother liquor, characterized in that: It consists of the following steps: S1, filtering the wash water, adjusting the pH value of the filtrate to ≤6, and performing membrane concentration treatment after heat exchange and cooling to obtain wash water concentrate; S2, the wash water concentrate and the mother liquor are mixed, the filtrate pH is adjusted to ≤ 6 after filtration, the pH adjusted wastewater resin adsorption treatment; S3, oxidizing the wastewater after resin adsorption treatment; S4, evaporating, centrifuging and drying the oxidized wastewater to obtain a sodium sulfate product; In step S1, 30% by mass sulfuric acid is used to adjust the pH value; after heat exchange and cooling in step S1, the washing water temperature is controlled not to exceed 35°C; The membrane concentration treatment in step S1 includes: sequentially passing through a UF membrane and a first-stage RO membrane, a second-stage RO membrane, and a third-stage RO membrane concentration treatment; The UF membrane produced water enters a stage of RO membrane treatment, and the UF membrane concentrated water returns to filtration; The concentrated water from the first stage RO membrane enters the second stage RO membrane for treatment, and the concentrated water from the second stage RO membrane enters the third stage RO membrane for treatment. The concentrated water from the third stage RO membrane is the obtained washing concentrated water; The water produced by the first stage RO membrane, the second stage RO membrane, and the third stage RO membrane enters the secondary RO membrane for concentration and then returns to the first stage RO membrane for treatment; The resin adsorption treatment in step S2 is as follows: firstly, a weakly basic anion resin is transformed with a sulfuric acid solution having a mass fraction of 8%, and then the adsorption function of the transformed weakly basic anion resin is utilized to adsorb ferrocyanate on the wastewater after pH adjustment; The ferrocyanide ions adsorbed by the resin are regenerated into sodium ferrocyanide through alkali and reused in production as raw material.

2. The zero-discharge treatment process for Prussian blue wastewater according to claim 1, characterized in that: In step S2, the temperature of the mother liquor and the concentrated washing water after filtration is controlled not to exceed 35° C.; in step S2, 30% by mass sulfuric acid is used for pH adjustment.

3. The zero-discharge treatment process for Prussian blue wastewater according to claim 1, characterized in that: The oxidation in step S3 is ozone oxidation.

4. The zero-discharge treatment process for Prussian blue wastewater according to claim 1, characterized in that: The evaporation in step S4 is MVR evaporation crystallization; the evaporation temperature is ≥110°C.

5. The zero-discharge treatment process for Prussian blue wastewater according to claim 1, characterized in that: In step S4, the wet salt and the centrifuge liquid are separated after centrifugation; the wet salt is dried in a fluidized bed to obtain sodium sulfate; and the centrifuge liquid is dried by steam to obtain sodium sulfate.

6. The zero-discharge treatment process for Prussian blue wastewater according to claim 5, characterized in that: The water content of sodium sulfate is 0.5-1.5%, and the purity of sodium sulfate is ≥97.0%.

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