A method for treating wastewater produced in the production of a sodium-ion battery cathode material, prussian blue

Abstract

The present application relates to a kind of wastewater comprehensive treatment method, specifically to treat a kind of sodium ion battery positive material prussian blue production process wastewater comprehensive treatment method.In the production process, two kinds of wastewater of high concentration salt and low concentration salt need to be discharged.This method is concentrated by evaporation high concentration salt wastewater, after cooling, sodium sulfate salt is precipitated, filtrate is obtained by filtration, and sodium citrate salt is crystallized.In order to save energy, low concentration salt wastewater is treated by different scheme, mixed with precipitant, so that citric acid and sulfuric acid insoluble salt solid are precipitated, to purify wastewater.The method comprehensively treats sodium ion battery material prussian blue production process wastewater, through appropriate crystallization and precipitation process, separates and recovers economic salt in high concentration salt wastewater, reduces the environmental problems caused by low concentration salt wastewater direct discharge, has economic and environmental benefits.

Description

TECHNICAL FIELD

[0001] The application relates to a comprehensive wastewater treatment method, in particular to a comprehensive treatment method for wastewater generated in a production process of a sodium-ion battery cathode material, namely Prussian blue. BACKGROUND

[0002] With the increasing demand for energy storage and the emergence of the problem of lithium resource supply shortage, it is essential to develop new electrochemical energy storage systems. Sodium-ion batteries, as a kind of energy storage technology with similar performance and working principle to lithium-ion batteries, have a good development prospect. Prussian blue, as a kind of sodium-ion battery cathode material, has an open three-dimensional framework structure, can realize fast reversible sodium ion intercalation and deintercalation, and has a theoretical mass specific capacity of 170 mAh / g. The mass specific energy density is comparable to that of lithium iron phosphate cathode material used in lithium-ion batteries. In addition, its synthesis method is simple and economical, and it is a very promising sodium-ion battery cathode material.

[0003] Prussian blue is usually produced by coprecipitation. Compared with the solid-phase method commonly used for the production of layered oxides and polyanion compounds, the coprecipitation method has the advantage of not needing a sintering process, directly obtaining the desired product, thereby avoiding the disadvantages of long reaction period and high energy consumption. The system for synthesizing Prussian blue by coprecipitation generally includes transition metal salt, sodium ferrocyanide salt and complexing agent. Among them, high-concentration complexing agent is a key control factor, which can adjust the reaction rate and affect the crystallinity of the product. However, Prussian blue is not composed of complexing agent, i.e. the desired product does not contain complexing agent. After the reaction, a large amount of complexing agent is added and mixed with the remaining ion salt, etc., forming high-concentration salt wastewater. Secondly, the product needs to be washed in the subsequent process, which forms low-concentration salt wastewater with similar composition to high-concentration salt wastewater. If these wastewaters are not properly treated, not only will it be a waste of resources, but also will cause environmental pollution.

[0004] Therefore, it is of great economic and environmental benefits to develop a production process for Prussian blue, a sodium-ion battery cathode material, to separate and recover economic salts from high-concentration salt wastewater. SUMMARY

[0005] In view of the problem that the existing sodium ion battery positive material Prussian blue production process wastewater is difficult to treat, the process wastewater is divided into high-concentration salt wastewater and low-concentration salt wastewater, and a comprehensive treatment method combining physical and chemical methods is provided according to their physical and chemical properties. The high-concentration salt wastewater is concentrated to a certain multiple, then cooled to precipitate a large amount of sodium sulfate, filtered to separate the solid, and then the filtrate is allowed to stand to crystallize sodium citrate; the low-concentration salt wastewater is treated by adding a precipitant such as calcium chloride to form calcium salts with citrate and sulfate ions, then filtered to remove a large amount of environmentally unfriendly salts in the wastewater. This method divides the Prussian blue sodium ion battery positive material production process wastewater into high and low concentration salt types, and uses energy-saving and reasonable and effective process methods according to their physical and chemical properties. It can effectively recover economic salts in wastewater and reduce emissions, and has considerable economic and environmental benefits.

[0006] The technical scheme adopted by the present application is: the treatment of high-concentration salt wastewater generated in the co-precipitation process and low-concentration salt wastewater generated in the washing process, the specific process is as follows:

[0007] I. Treatment of high-concentration salt wastewater:

[0008] (1) Collect the high-concentration salt wastewater, add a certain amount of alkali to adjust the pH value, heat to 50-80 DEG C, and evaporate and concentrate to a certain multiple;

[0009] (2) The concentrated wastewater is cooled to 15-30 DEG C, at which time a large amount of powdery solid precipitates, and sodium sulfate solid and concentrated filtrate are obtained by filtration;

[0010] (3) The concentrated filtrate is transferred into a crystallization barrel, and the crystallization barrel is allowed to stand for 0.5-2 days to crystallize blocky crystals, and the residual waste liquid is poured out to obtain crystalline sodium citrate solid;

[0011] II. Treatment of low-concentration salt wastewater:

[0012] (4) Collect the low-concentration salt wastewater generated in the Prussian blue washing process and the residual waste liquid of step (3), add a certain amount of iron salt, stir for 0.5-1 h, and slowly stir until the waste liquid is slightly suspended;

[0013] (5) The wastewater after step (4) is neutralized to neutral by adding a certain amount of alkali, and then a certain amount of calcium salt precipitant is added, stirred and allowed to stand for 0.5-3 h, until the generated precipitate can be separated from the supernatant, and then all the precipitate is filtered out.

[0014] In the present application, the sodium ion battery positive material Prussian blue production process wastewater is two batches of wastewater discharged in the production process of Prussian blue, and its composition contains one or more of sodium citrate, sodium sulfate, citric acid, sodium ferrocyanide and sodium chloride.

[0015] In the application, the high-concentration salt wastewater is wastewater discharged in the Prussian blue co-precipitation process, wherein the concentration of sodium citrate is 0.1-0.5 mol / L, the concentration of sodium sulfate is 0.1-0.3 mol / L, the concentration of citric acid is 0.005-0.02 mol / L, and the content of other components such as sodium ferrocyanide is less than 0.001 mol / L (sodium chloride is a salt that does not need to be treated).

[0016] In the application, the low-concentration salt wastewater is wastewater discharged in the Prussian blue washing process, wherein the content of sodium citrate, sodium sulfate, citric acid and sodium ferrocyanide is less than 0.005 mol / L.

[0017] In the application, the sodium ion battery positive electrode material Prussian blue production process wastewater comprehensive treatment method is characterized in that, in step (1), the certain multiple is 5-10 times, and the wastewater is concentrated by a certain multiple, so as to make the sodium citrate salt and sodium sulfate salt close to the saturation concentration. In step (2), the temperature is lowered to 15-30 DEG C. Concentration and temperature reduction can precipitate sodium sulfate, while sodium citrate with large solubility cannot be precipitated. The liquid cooling after concentration is a process developed according to the difference between the solubility-temperature curves of sodium citrate salt and sodium sulfate salt. Because the solubility of sodium citrate is very large, and the solubility of sodium sulfate decreases sharply with the decrease of temperature. Therefore, by using the concentration and cooling process, a large amount of sodium sulfate can be precipitated.

[0018] In the application, the sodium ion battery positive electrode material Prussian blue production process wastewater comprehensive treatment method is characterized in that, in step (1) and step (5), the alkali is one of sodium hydroxide, sodium carbonate, sodium bicarbonate and the like.

[0019] In the application, the iron salt in step (4) is one of ferrous sulfate, ferric sulfate, ferric chloride and polymeric ferric sulfate, and the calcium salt precipitant in step (5) is one of calcium chloride, calcium hydroxide and calcium oxide.

[0020] The process in step (1) is similar, and the PH value of the wastewater is adjusted to neutral by adding alkali in step (5), so that the discharged wastewater is in a neutral state. In step (1), the PH value is adjusted to be slightly alkaline by adding alkali, so that the sodium citrate is reacted with citric acid, and the subsequent crystallized sodium citrate is more pure. In step (5), calcium chloride is added to make the citrate and sulfate ions in the wastewater form a difficult-to-dissolve salt precipitate, so as to remove the environmentally unfriendly ions in the wastewater.

[0021] In summary, the beneficial effects of the present application are: after the wastewater produced in the prussian blue production process is treated by the method provided by the present application, most of the sodium sulfate and sodium citrate are effectively recovered, and the discharge is reduced, which has considerable economic and environmental benefits. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 A treatment flow chart of high-concentration salt wastewater.

[0023] Figure 2 A treatment flow chart of low-concentration salt wastewater. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical scheme and advantages of the present application more clearly embodied, the present application will be further described in detail below.

[0025] Example 1

[0026] About 500 L of high-concentration salt wastewater of batch 1 is collected and 100 g of sodium hydroxide is added to adjust the pH value to 8, and then the waste liquid is introduced into an evaporator. The temperature is raised to 60 DEG C to evaporate water, and when the wastewater is concentrated to 1 / 5 of the volume, the concentrated wastewater is discharged, stirred and cooled to 20 DEG C, and a large amount of sodium sulfate solid powder is precipitated in the concentrated wastewater during cooling, the stirring is stopped and then the solid powder is filtered out;

[0027] The filtrate after concentration and filtration is introduced into a crystallization barrel and left for 1 day, and then about 60 L of residual waste liquid is poured into a waste liquid barrel, and the blocky sodium citrate crystals in the crystallization barrel are recovered;

[0028] The low-concentration wastewater of the prussian blue washing process of batch 1 is collected into a waste liquid barrel, mixed with the residual waste liquid after concentration and crystallization, and then 20 g of ferrous sulfate is added and stirred for 0.5 h until the wastewater is in a suspended state. 10 g of sodium hydroxide is added again to adjust the pH of the wastewater to neutral, and then 500 g of calcium chloride is added, stirred for 0.5 h and then left to precipitate, and the solid precipitate is filtered out.

[0029] The sodium sulfate is precipitated and filtered out from the high-concentration salt wastewater after concentration and cooling treatment, and the filtrate is then crystallized to obtain sodium citrate, and the results are shown in Table 1.

[0030] The 60 L of residual waste liquid obtained after concentration and crystallization is mixed with 100 L of low-concentration wastewater produced in the washing process, and the addition of ferrous salt removes sodium ferrocyanide, adjusts the pH value, and adds calcium chloride precipitator to remove most of the sulfate and citrate in the wastewater, and the results are shown in Table 2.

[0031] Example 2

[0032] About 500 L of high-concentration salt wastewater of Batch 2 was collected and 100 g of sodium hydroxide was added to adjust the pH value to 8, and then the wastewater was introduced into an evaporator. The temperature was raised to 60°C to evaporate water, and when the wastewater was concentrated to 1 / 6 of the volume, the concentrated wastewater was discharged, stirred and cooled to 20°C. As the concentrated wastewater cooled, a large amount of sodium sulfate solid powder precipitated out, stirring was stopped and the solid powder was filtered out;

[0033] The filtered filtrate was introduced into a crystallization barrel and left to stand for 1 day, and when large crystals slowly grew in the barrel, about 40 L of residual wastewater was poured into a wastewater barrel, and the sodium citrate block crystals in the crystallization barrel were recovered;

[0034] The low-concentration wastewater of the Prussian blue washing process of Batch 1 was collected into a wastewater barrel, mixed with the residual wastewater after concentration and crystallization, and then 20 g of ferrous sulfate was added and stirred for 0.5 h until the wastewater became suspended. 10 g of sodium hydroxide was added again to adjust the pH of the wastewater to neutral, and then 400 g of calcium chloride was added, stirred for 0.5 h and then left to precipitate, and the solid precipitate was filtered out.

[0035] The high-concentration salt wastewater was concentrated and treated by cooling to precipitate and filter out sodium sulfate, and the filtrate was then crystallized to obtain sodium citrate, and the results are shown in Table 1.

[0036] The 40 L of residual wastewater obtained after concentration and crystallization was mixed with 100 L of low-concentration wastewater generated in the washing process, and the ferrous cyanide was removed by adding ferrous salt, adjusting the pH value, and adding calcium chloride precipitant, which can remove most of the sulfate and citrate in the wastewater, and the results are shown in Table 2.

[0037] Example 3

[0038] About 500 L of high-concentration salt wastewater of Batch 3 was collected and 100 g of sodium hydroxide was added to adjust the pH value to 8, and then the wastewater was introduced into an evaporator. The temperature was raised to 60°C to evaporate water, and when the wastewater was concentrated to 1 / 7 of the volume, the concentrated wastewater was discharged, stirred and cooled to 20°C. As the concentrated wastewater cooled, a large amount of sodium sulfate solid powder precipitated out, stirring was stopped and the solid powder was filtered out;

[0039] The filtered filtrate was introduced into a crystallization barrel and left to stand for 1 day, and when large crystals slowly grew in the barrel, about 15 L of residual wastewater was poured into a wastewater barrel, and the sodium citrate block crystals in the crystallization barrel were recovered;

[0040] The low-concentration wastewater of the Prussian blue washing process of Batch 1 was collected into a wastewater barrel, mixed with the residual wastewater after concentration and crystallization, and then 20 g of ferrous sulfate was added and stirred for 0.5 h until the wastewater became suspended. 10 g of sodium hydroxide was added again to adjust the pH of the wastewater to neutral, and then 400 g of calcium chloride was added, stirred for 0.5 h and then left to precipitate, and the solid precipitate was filtered out.

[0041] The high concentration salt wastewater was treated by concentration and cooling to precipitate and filter sodium sulfate, and the filtrate was then crystallized to obtain sodium citrate, and the results are shown in Table 1.

[0042] The 15 L residual wastewater obtained after concentration and crystallization was mixed with 100 L low concentration wastewater generated in the washing process, and the sodium ferrocyanide was removed by adding ferrous salt, adjusting the pH value, and adding calcium chloride precipitant, so that most of the sulfate and citrate in the wastewater can be removed, and the results are shown in Table 2.

[0043] Table 1 Treatment results of high concentration salt wastewater

[0044]

[0045] Table 2 Treatment results of low concentration salt wastewater

[0046]

[0047] According to the above examples, it can be known that each batch of Prussian blue production process wastewater contains about 65 kg of sodium citrate and sodium sulfate salt. After treatment by the method of the present application, most of the economic salts of sodium sulfate and sodium citrate can be effectively recovered and separated, and the pollution of discharge can be reduced.

Claims

1. A method for treating wastewater produced in the production of Prussian blue, a sodium-ion battery cathode material, the method comprising the treatment of high-concentration salt wastewater produced in a co-precipitation process and low-concentration salt wastewater produced in a washing process, and the specific process being as follows: I. Treatment of high-concentration salt wastewater: Step (1) Collect the high-concentration salt wastewater, add a certain amount of alkali to adjust the pH value, and heat to 50-80 ℃, and then evaporate and concentrate to a certain multiple; Step (2) Cool the concentrated wastewater to 15-30 ℃, at which time a large amount of powdery solid precipitates, and sodium sulfate solid and concentrated filtrate are obtained by filtration; Step (3) Transfer the concentrated filtrate into a crystallization barrel, and let it stand for 0.5-2 days, during which blocky crystalline sodium citrate is crystallized out, and residual waste liquid is poured out to obtain crystalline sodium citrate solid; II. Treatment of low-concentration salt wastewater: Step (4) Collect the low-concentration salt wastewater produced in the Prussian blue washing process and the residual waste liquid of Step (3), add a certain amount of iron salt, and stir for 0.5-1 h until the waste liquid slowly becomes a state of slight suspension; Step (5) Add a certain amount of alkali to neutralize the acid-base degree of the wastewater to neutral, and then add a certain amount of calcium salt precipitant, stir and stand for 0.5-3 h until the generated precipitate slowly settles and can be separated from the supernatant, and then filter out all the precipitate solid.

2. The method for treating wastewater produced in the production of a sodium-ion battery cathode material, Prussian blue, according to claim 1, characterized in that, The wastewater produced in the production of Prussian blue, a sodium-ion battery cathode material, is two batches of wastewater discharged in the production process of Prussian blue, and the components thereof include one or more of sodium citrate, sodium sulfate, citric acid, sodium ferrocyanide, and sodium chloride.

3. The method for treating wastewater produced in the production of a sodium-ion battery cathode material, Prussian blue, according to claim 1, characterized in that, The high-concentration salt wastewater is wastewater discharged in the co-precipitation process of Prussian blue, wherein the concentration of sodium citrate is 0.1-0.5 mol / L, the concentration of sodium sulfate is 0.1-0.3 mol / L, the concentration of citric acid is 0.005-0.02 mol / L, and the content of sodium ferrocyanide is less than 0.001 mol / L.

4. The method for treating wastewater produced in the production of a sodium-ion battery cathode material, Prussian blue, according to claim 1, characterized in that, The low-concentration salt wastewater is wastewater discharged in the washing process of Prussian blue, wherein the content of sodium citrate, sodium sulfate, citric acid, and sodium ferrocyanide is all less than 0.005 mol / L.

5. The method for treating wastewater produced in the production of a sodium-ion battery cathode material, Prussian blue, according to claim 1, characterized in that, In Step (1), the certain multiple is 5-10 times, and in Step (2), the cooling is to 15-30 ℃, and the concentration and cooling cause sodium sulfate to precipitate, while the sodium citrate with high solubility does not precipitate.

6. The method for treating wastewater produced in the production of a sodium-ion battery cathode material, Prussian blue, according to claim 1, characterized in that, In Step (1) and Step (5), the alkali is one of sodium hydroxide, sodium carbonate, and sodium bicarbonate.

7. The method for treating wastewater produced in the production of a sodium-ion battery cathode material, Prussian blue, according to claim 1, characterized in that, In Step (4), the iron salt is one of ferrous sulfate, ferric sulfate, ferric chloride, and polymeric ferric sulfate, and in Step (5), the calcium salt precipitant is one of calcium chloride, calcium hydroxide, and calcium oxide.

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