WO2024026982A1

WO2024026982A1 - Treatment method for wastewater

Info

Publication number: WO2024026982A1
Application number: PCT/CN2022/118776
Authority: WO
Inventors: 谭明亮; 李长东; 阮丁山; 周游; 李强; 王娇萍
Original assignee: 广东邦普循环科技有限公司; 湖南邦普循环科技有限公司
Priority date: 2022-08-05
Filing date: 2022-09-14
Publication date: 2024-02-08
Also published as: CN115259316B; CN115259316A

Abstract

A treatment method for wastewater. The treatment method comprises the following steps: step 1, taking wastewater, adding a salt thereto, and carrying out salting out to obtain an organic phase and a first water phase; step 2, taking the first water phase, adding a seed crystal of the salt thereto, and carrying out primary freezing crystallization to obtain a second water phase and a crystal of the salt; and step 3, taking the second water phase, adding an ice crystal seed thereto, and carrying out secondary freezing crystallization to obtain a third water phase and ice crystals. The treatment method at least has the following beneficial effects: firstly, organic matters contained in the wastewater are preliminarily separated out by means of salting out, such that COD of the water phase is reduced, and by means of a two-step freezing crystallization method, the concentration of the salt therein is then reduced by means of freezing crystallization in the first step; and in the second step of freezing crystallization, ice crystals are effectively precipitated under the low-salt and low-COD conditions, so as to obtain high-purity ice crystal water and a concentrated high-COD third water phase. The process is simple, the treatment efficiency is high, and the treatment cost is low.

Description

A kind of wastewater treatment method

Technical field

The present application relates to the technical field of wastewater treatment, and in particular to a method of treating wastewater.

Background technique

In the recycling and regeneration industry of used lithium batteries, dry crushing is usually used in the crushing and sorting stage. However, dry crushing has problems such as flammability, explosion, dust pollution and electrolyte leakage. Therefore, practitioners try to protect the charged battery through water rupture to avoid the occurrence of heat and fire. However, during this process, organic wastewater containing electrolyte with high COD content (can reach 50000-150000mg/L) will also be produced. For this type of wastewater, researchers first tried to use aluminum salts as adsorbents to absorb organic matter in electrolyte wastewater to reduce COD, and then combined biodegradation and reverse osmosis treatment methods to obtain purified water. However, this process requires the use of a large amount of solids Aluminum salt adsorbs organic matter, producing a large amount of hazardous waste, and the biodegradation and reverse osmosis treatment processes of the adsorbed wastewater are complex and costly. In addition, there are also three-stage methods to treat electrolyte wastewater, including ferrous chloride + hydrogen peroxide Fenton oxidation treatment of organic matter, membrane biological oxidizer to further treat wastewater, and reverse osmosis membrane for the third step of wastewater treatment, so as to obtain recyclable wastewater. Recycled or discharged water. However, it is obvious that this process is still cumbersome and has high processing costs. Therefore, it is necessary to provide a wastewater treatment method with simple process, high efficiency and low cost.

Contents of the invention

This application aims to solve at least one of the technical problems existing in the prior art. To this end, this application proposes a wastewater treatment method. The processing method has a simple processing flow, high processing efficiency and low processing cost.

The first aspect of this application provides a processing method for detecting wastewater. The processing method includes the following steps:

Step 1: Take the wastewater, add salt to salt out, and obtain the organic phase and the first aqueous phase;

Step 2: Take the first water phase, add salt crystal seeds and perform a freeze crystallization to obtain the second water phase and salt crystals;

Step 3: Take the second water phase, add ice crystal seeds and perform secondary freezing crystallization to obtain the third water phase and ice crystals.

The processing method according to the embodiment of the present application has at least the following beneficial effects:

The present invention first precipitates the organic matter contained in the wastewater through salting out to reduce the COD in the water phase, and then uses a two-step freezing crystallization method. The first step of freezing crystallization reduces the salt concentration in the wastewater, and the second step of freezing crystallization reduces the salt concentration at low temperature. Ice crystals are effectively precipitated under salt and low COD conditions to obtain high-purity ice crystal water and concentrated high-COD third water phase. The process is simple, the processing efficiency is high, and the processing cost is low.

In some embodiments of the present application, in step 1, salt is added according to the mass ratio of wastewater:salt to (2-10):1 to perform salting out.

In some embodiments of the present application, the salt in step 1 is a soluble alkali metal salt.

In some embodiments of the present application, the salt in step 1 is a soluble sulfate salt.

In some embodiments of the present application, the salt in step 1 is at least one of a soluble sodium salt and a soluble potassium salt.

In some embodiments of the present application, the salt in step 1 is at least one of sodium sulfate and potassium sulfate.

In some embodiments of the present application, the salt seeded in step 2 is the same as the salt in step 1.

In some embodiments of the present application, the mass of the salt seed crystal is 0.001 to 0.01 times the mass of the salt in the first aqueous phase.

In some embodiments of the present application, the salt seed crystal is sodium sulfate decahydrate seed crystal.

In some embodiments of the present application, the temperature of freeze crystallization in step 2 is -5°C to 5°C.

In some embodiments of the present application, the temperature for continuing freeze crystallization in step 3 is -10°C to 0°C.

In some embodiments of the present application, the mass of the ice crystal seeds in step 3 is 0.0001 to 0.01 times the mass of the second water phase.

In some embodiments of the present application, the salt crystals generated in step 2 are recycled to step 1 for salting out.

In some embodiments of the present application, the organic phase in step 1 is recovered as electrolyte.

In some embodiments of the present application, the wastewater is electrolyte-containing wastewater.

In some embodiments of the present application, the electrolyte-containing wastewater is selected from at least one of hydrolysis wastewater, electrolyte production wastewater, battery production wastewater, and battery discharge wastewater.

In some embodiments of the present application, the COD of wastewater is 50,000 to 150,000 mg/L.

In some embodiments of the present application, the COD of the first aqueous phase is 12,000 to 30,000 mg/L.

In some embodiments of the present application, the COD of the second aqueous phase is 15,000 to 30,000 mg/L.

In some embodiments of the present application, the COD of the third aqueous phase is 100,000 to 200,000 mg/L.

Additional aspects and advantages of the application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the application.

Description of the drawings

Figure 1 is a schematic diagram of a wastewater treatment method in an embodiment of the present application.

Detailed ways

The concept of the present application and the technical effects produced will be clearly and completely described below in conjunction with the embodiments to fully understand the purpose, features and effects of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all of the embodiments. Based on the embodiments of the present application, other embodiments obtained by those skilled in the art without exerting creative efforts are all The scope of protection of this application.

The embodiments of the present application are described in detail below. The described embodiments are exemplary and are only used to explain the present application and cannot be understood as limiting the present application.

In the description of this application, several means one or more, plural means two or more, greater than, less than, exceeding, etc. are understood to exclude the original number, and above, below, within, etc. are understood to include the original number. If there is a description of first and second, it is only for the purpose of distinguishing technical features, and cannot be understood as indicating or implying the relative importance or implicitly indicating the number of indicated technical features or implicitly indicating the order of indicated technical features. relation. In the following description, although a logical order is shown in the flowcharts, in some cases, the steps shown or described may be performed in a different order than in the flowcharts.

Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by a person skilled in the technical field belonging to this application. The terms used herein are only for the purpose of describing the embodiments of the present application and are not intended to limit the present application.

In the description of this application, reference to the description of the terms "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" is intended to be in conjunction with the description of the embodiment. or examples describe specific features, structures, materials, or characteristics that are included in at least one embodiment or example of the present application. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

Referring to Figure 1, a wastewater treatment method according to an embodiment of the present application is shown. The method includes the following steps:

Step 1: Take the wastewater, add salt for salting out, and obtain the organic phase and the first aqueous phase; Step 2: Take the first aqueous phase, add salt crystal seeds, and perform a freeze crystallization to obtain the second aqueous phase and salt crystals. ; Step 3: Take the second water phase, add ice crystal seeds and perform secondary freezing crystallization to obtain the third water phase and ice crystals.

Among them, wastewater refers to the wastewater to be treated produced by industrial and agricultural production and urban residents using water, including but not limited to wastewater containing inorganic salts and organic matter. In some specific embodiments, wastewater refers to wastewater with a certain chemical oxygen demand (COD). Furthermore, it can refer to wastewater generated during the production, processing, testing, regeneration and recycling of batteries and their raw materials. wastewater. Specifically, depending on its composition, it is, for example, wastewater containing an electrolyte component.

Electrolyte refers to the liquid electrolyte that conducts current inside the battery, including at least two types such as electrolyte solution and ionic liquid. The applicable objects of the electrolyte usually refer to lithium batteries, such as lithium secondary batteries. It is understood that batteries of other battery types can also be included in this range. Electrolyte solutions generally include organic solvents, lithium salts and additives. The organic solvent can be at least one of ethers and esters. Taking esters as an example, it can usually be carbonate, including but not limited to chain carbonates (such as dimethyl carbonate DMC, diethyl carbonate DEC, Ethyl methyl carbonate (EMC), cyclic carbonates (such as ethylene carbonate EC, propylene carbonate PC), etc. The lithium salt can be LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li(CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiAlO ₄ , LiAlCl ₄ , LiFSI, etc. Additives can be, for example, film-forming additives, flame retardant additives, etc. according to different purposes and needs. Therefore, in this application, wastewater containing electrolyte components generally refers to wastewater containing at least one component of the above-mentioned electrolyte solution. Among them, the concentration of lithium salt is usually less than 3 mol/L, and the mass percentage of additives in the electrolyte is usually less than 5%. Therefore, the COD in wastewater is mainly the organic solvent in the electrolyte. Therefore, wastewater containing electrolyte components further refers to wastewater containing at least the organic solvent of the electrolyte.

Considering the source of wastewater, wastewater containing electrolyte includes but is not limited to wastewater generated from the production process and recycling process. For the production process, it includes but is not limited to wastewater generated during the electrolyte production process, battery production and/or discharge process (such as wastewater generated during the electrolyte injection process, wastewater generated during the formation process, etc.). For the recycling process, it includes but is not limited to hydrobreaking wastewater, that is, the wastewater generated when lithium batteries are recycled through crushing using water as a medium, such as when the lithium batteries to be recycled are cut by a waterjet mechanism or other mechanisms with similar functions. Wastewater is produced when batteries are broken into small pieces, causing the electrolyte in them to mix into the water. The COD value in the wastewater can be specifically higher than 10,000mg/L, higher than 20,000mg/L, higher than 30,000mg/L, higher than 40,000mg/L, higher than 50,000mg/L. Furthermore, the range of the COD value can be, for example, 10,000 to 300,000mg. /L, 20000～250000mg/L, 30000～200000mg/L, 50000～150000mg/L. Furthermore, the wastewater is hydrolysis wastewater, with a COD value of 50,000 to 150,000 mg/L. It should be noted that at least wastewater with a COD value within any of the above ranges can be regarded as high COD wastewater.

Salting out refers to adding soluble salts to wastewater, thereby increasing the interfacial energy between water and organic matter, thereby reducing the dispersion of organic matter in water, and finally forming a separate first aqueous phase and organic phase. The COD value in the water phase is greatly reduced. In some specific embodiments, the organic phase is mainly the organic solvent of the electrolyte, so the organic phase can be used as the electrolyte for further recycling. Specifically, in the actual preparation process, considering various reasons such as operating temperature, lithium salt solubility, chemical properties, electrochemical properties, etc., the organic solvent of the electrolyte usually includes two or more organic solvents, so Recycling the organic phase as an electrolyte can at least separate different types of organic solvents in the organic phase by means including but not limited to physical methods. For example, separation and purification are based on the volatility and solubility of different organic solvents to obtain two or More single organic solvents. It can be understood that recycling the organic phase as electrolyte is not limited to the above method, and any other treatment methods known in the art can also be used. For example, after detecting and confirming the components of the organic phase, directly adding lithium salt, The electrolyte with a set concentration of lithium salt and additives is reformed by using additives and organic solvents. During the salting out process, the selected soluble salt may be a soluble alkali metal salt, such as at least one of soluble sodium salts or potassium salts, specifically NaCl, Na ₂ SO ₄ , NaNO ₃ , KCl, K ₂ One of SO ₄ , KNO ₃ , etc. It can be understood that other substances that can separate organic matter from water in wastewater through salting out can also be used as alternatives, such as alkaline earth metals, soluble salts of other main group metals or sub-group metals such as halide salts, sulfates, nitrates, etc. In some specific embodiments, in order to allow COD to generate an organic phase faster and better, the mass ratio of wastewater and added salt is (2-10):1, for example, it can be 2:1, 3: 1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1. Further, the mass ratio of wastewater and added salt is (3～10):1, (5～10):1. Of course, after adding soluble salts to wastewater, it is usually necessary to mix them evenly and fully dissolve them by stirring, etc., so that salting out can be completed. After the dissolution is completed, methods such as standing can be used to form a stratified first aqueous phase and an organic phase during the salting out process, so that separation can be completed. The standing time may be 0.1 to 5 hours, such as 0.1 hour, 0.2 hour, 0.5 hour, 1 hour, 2 hour, 5 hour, or further 0.5 to 2 hours. Depending on the relative contents of wastewater and salt, as well as its specific composition and other conditions, the standing time can be adjusted adaptively. In the first aqueous phase obtained after standing and layering, the COD value can be below 50,000 mg/L, below 40,000 mg/L, below 30,000 mg/L, or below 20,000 mg/L. Taking hydrolysis wastewater as an example, the COD value of the first aqueous phase The value can be between 12,000 and 30,000 mg/L.

After completing the salting out, the obtained first aqueous phase still needs to undergo two steps of freezing and crystallization. The first step of primary freezing crystallization re-precipitates the salt added to the first aqueous phase during the salting out process, thereby obtaining salt crystals and a low-salt, low-COD second aqueous phase. Then the second step of secondary freezing crystallization will The water in the second aqueous phase analyzes out, thereby obtaining ice crystals and a concentrated, high COD third aqueous phase. Depending on the composition of the salt in the first aqueous phase and the COD value, different freezing crystallization temperatures are required. The higher the COD value, the higher the salt content, and the lower the temperature required to precipitate ice crystals, so in this treatment method The steps of salting out and one-time freezing crystallization are arranged successively to reduce the temperature requirements for the precipitation of ice crystals. At the same time, it can also ensure that the ice crystals can be separated out separately through freezing crystallization in step 3 to achieve concentration of the water phase. The purpose of the first step of freeze crystallization is to precipitate the salt in the first aqueous phase as much as possible. Therefore, for better nucleation and crystal growth, consider adding seed crystals for freeze crystallization. Depending on the composition of the salt in the wastewater and the first water phase, corresponding salt seed crystals can be added. Since a large amount of salt is added to the first aqueous phase during the salting out process, the seed crystals added in the primary freezing crystallization can be the seed crystals of the salt added in step 1. Here, since the temperatures required for freezing crystallization of different salts are also more different, from the perspective of energy conservation and environmental protection, a salt with a higher required temperature is selected as the salt used for salting out in step 1. Similarly, the salt concentration remaining in the second aqueous phase after the primary freeze crystallization also affects the degree of ice crystal precipitation in the secondary freeze crystallization, so it is preferable to use a salt with a lower salt concentration remaining after the freeze crystallization as the seed crystal in step 2 and the step 2. 1. Salt used for salting out. Taking several commonly used salts as an example, sulfate, such as sodium sulfate solution, begins to salt out at about 5°C, and the residual salt concentration in the solution after freezing and crystallization is about 3%; while sodium chloride, calcium chloride, etc. salt out. The temperature must reach about -20°C, and the residual salt concentration in the solution after freeze crystallization is also much higher than 3%. Therefore, the salt is preferably sodium sulfate. In this case, the temperature of primary freezing crystallization can be -5 to 5°C, for example, it can be -5°C, -4°C, -3°C, -2°C, -1°C, 0°C, 1℃, 2℃, 3℃, 4℃, 5℃. In some specific embodiments, the mass ratio of the added salt seeds to the salt in the first aqueous phase is (0.001~0.01):1, for example, it can be 0.001:1, 0.002:1, 0.005:1, 0.01 :1. Here, the salt in the first aqueous phase mainly includes the salt added to the wastewater in step 1, and all of it is transferred to the first aqueous phase after salting out.

After the salt crystals are precipitated by primary freezing and crystallization, the COD value in the second water phase can be below 50,000 mg/L, below 40,000 mg/L, below 30,000 mg/L, or below 20,000 mg/L. Taking hydrolysis wastewater as an example, the second water phase The COD value can be between 15,000 and 30,000 mg/L. It can be understood that since there may still be a certain amount of crystallization water and free water in the salt crystals, the COD value in the second aqueous phase may also change to a certain extent and is therefore not exactly the same as the COD value in the first aqueous phase. At the same time, frozen crystallization cannot completely analyze the salt, so there may still be 1 to 6% mass percent salt in the second aqueous phase, such as 1% salt, 2% salt, 3% salt, 4 % salt, 5% salt, 6% salt, for example, when sodium sulfate is used as the salt for salting out and primary freezing crystallization, the second aqueous phase also contains 1 to 6% sodium sulfate. At the same time, when sodium sulfate is used as the salt crystal seed, the specific form of the sodium sulfate seed crystal may be sodium sulfate decahydrate seed crystal. In order to recycle the generated salt, the salt crystals produced by primary freezing crystallization can be recycled to step 1 to participate in salting out.

After the salt crystals are precipitated by primary freezing crystallization, ice crystal seeds are added to the second water phase and then secondary freezing crystallization is performed, thereby precipitating a large amount of ice crystals and obtaining a highly concentrated third water phase with high COD. In the same way, it is also impossible for ice crystals as crystal seeds to completely precipitate water. Therefore, in some specific embodiments, the crystallization rate of ice crystals in the second water phase is 60 to 90%. Due to a large reduction in water content, the COD value in the concentrated third aqueous phase is above 100,000 mg/L, above 150,000 mg/L, above 200,000 mg/L, above 250,000 mg/L, and above 300,000 mg/L. Further, the COD value in the third aqueous phase is between 100,000 and 200,000 mg/L. In some specific embodiments, the mass ratio of the added ice crystal seeds to the second water phase is (0.0001~0.01):1, for example, it can be 0.0001:1, 0.0002:1, 0.0005:1, 0.001:1, 0.002:1, 0.005:1, 0.01:1. Further, the mass ratio of the added ice crystal seeds to the second water phase is (0.001~0.01):1. In some specific embodiments, the temperature of secondary freezing crystallization can be -10~0°C. At this temperature, the second water phase is in a supercooled state, and a small amount of pure water ice crystals are added as seeds to precipitate. Lots of sandy ice crystals. At the same time, in order to prevent the supercooled second water phase from directly forming a large number of ice cubes doped with other substances without precipitating ice crystals with higher purity, stirring is required during the secondary freezing and crystallization process, and the stirring speed can be 200 to 500 rad/ min. The higher purity water formed by melting the precipitated ice crystals can be used as protective water during the battery crushing process. It is understandable that the precipitated ice crystals do not guarantee extremely high purity, so there may be lower salt and COD in them. In some examples, the COD content of the water finally obtained after melting of the ice crystals precipitated by the frozen crystallization is 400 to 2000 mg/L, and the mass concentration of salt is less than 1%.

It can be understood that since the electrolyte usually contains a relatively low concentration of lithium salt, it is usually difficult to directly precipitate it by adding lithium salt seed crystals in the aforementioned primary freezing crystallization or secondary freezing crystallization. Afterwards, the lithium salt will remain in the third aqueous phase. When the third aqueous phase is recycled back to step 1 for salting out to separate organic matter and repeating the other steps above, the lithium salt in it will continue to be enriched. When the lithium salt concentration reaches the set The value, for example, reaches 5-15g/L or even higher, and the lithium resources can be recovered by methods including but not limited to precipitation, such as adding sodium carbonate to generate lithium carbonate for precipitation recovery.

In some embodiments, adding salt seeds and performing primary freezing crystallization includes, but is not limited to, performing primary freezing while adding salt seeds for crystallization, or starting to freeze for crystallization after adding salt seeds. . Similarly, adding ice crystal seeds and performing secondary freezing and crystallization includes but is not limited to adding ice crystal seeds for crystallization while performing secondary freezing, or starting to freeze for crystallization after adding ice crystal seeds.

In summary, it can be seen that during the conventional wet battery recycling process, the electrolyte is easily discharged into the water to form high COD wastewater. However, it is difficult to achieve effective treatment using traditional Fenton oxidation, biodegradation, and membrane dialysis, and often requires a lot of Only the combined treatment of multiple methods can reduce COD to reusable industrial water standards. However, the process of the combined treatment process of multiple methods is more cumbersome and the treatment cost is higher. The wastewater treatment process provided in this application initially separates organic matter through salting out, and then The two-step freezing crystallization method treats high COD wastewater to achieve high concentration, with simple process, high treatment efficiency and low treatment cost. The three steps are related to each other and complement each other.

In the above treatment method, the crystallized salt produced in the primary freezing crystallization process can be recycled as the salt used in the salting out to separate organic matter in step 1. The organic phase separated by salting out in the first step can be recycled as an electrolyte. The high-COD third aqueous phase concentrated by secondary freezing crystallization can be returned to step 1 for salting out to separate organic matter, truly achieving 100% complete treatment and recycling of wastewater.

In addition, the treatment process provided by the embodiments of the present application has a wide range of application. It can not only be applied to the treatment of hydrolysis wastewater from battery recycling, but is also applicable to various high-quality electrolyte-containing wastewater generated during electrolyte production, battery production and battery discharge. Treatment of COD wastewater.

The following is explained with specific examples. It involves a kind of high COD wastewater containing electrolyte, which comes from the following sources:

Submerge the crushing hob of the twin-shaft crusher with water, and put the lithium battery to be recycled into it. When the hob crushes the lithium battery, it will generate heat rapidly, and the water submerging the hob is used as protective water to provide cooling protection. role. At the same time, during the crushing process of lithium batteries, the electrolyte in them enters the protective water, generating high COD wastewater containing electrolyte.

Example 1

This embodiment provides a wastewater treatment method, including the following steps:

Step 1: Take 2L of high COD wastewater containing electrolyte (COD content is 80000mg/L), add 400g of sodium sulfate to the wastewater (the mass ratio of wastewater to sodium sulfate is about 5:1), stir and dissolve, and then pour it into the water after it is completely dissolved. In the separatory funnel, let stand for 30 minutes to separate the salt solution and the organic phase. After the separation is completed, separate the first aqueous phase with high salt and low COD and the organic phase.

Among them, the organic phase is collected and used as electrolyte for further recycling treatment, and different organic solvents in the electrolyte are separated. The COD content in the first aqueous phase with high salt and low COD is 22000mg/L.

Step 2: Put the high-salt and low-COD first aqueous phase into a freezing tank and freeze it to 4°C. Add 0.5g Na ₂ SO ₄ ·10H ₂ O crystals for one-time freezing crystallization to precipitate Glauber's salt. Filter to obtain 1.6L of low-salt and low-COD aqueous phase. Second aqueous phase of COD and 770g Na ₂ SO ₄ ·10H ₂ O crystals.

Step 3: Put the low-salt and low-COD second aqueous phase into the freezing tank and continue to lower the temperature to -6°C. Stir with a stirring paddle (stirring rate is 400rad/min) and add 1g of pure water ice crystals for secondary freezing. Crystallize to precipitate sand-like ice crystals. After stirring for 5 minutes, the precipitation of ice crystals is basically completed. 1400g of ice crystals and 200 mL of high-salt and high-COD third water phase are separated by suction filtration.

Among them, 1400g of ice crystals are placed at room temperature and melted to obtain reusable industrial water. The COD content of the reusable industrial water is 1000mg/L and the mass percentage of sodium sulfate is 0.5%. It can be used as protective water when lithium batteries are broken; The mass percentage of the salt content of the concentrated high-salt and high-COD third aqueous phase is 28%, and the COD content is 160,000 mg/L.

Table 1. Parameters of water in different processes of Example 1

	体积(mL)Volume (mL)	COD(mg/L)COD(mg/L)	盐含量(％)Salt content (%)
水破碎电池废水Water broken battery wastewater	20002000	8000080000	00
第一水相first aqueous phase	20002000	2200022000	1717
第二水相second aqueous phase	16001600	2500025000	33
冰晶水ice crystal water	14001400	10001000	0.50.5
第三水相third aqueous phase	200200	160000160000	2828

Example 2

Step 1: Take 1.4L of electrolyte-containing wastewater, mix it with 200ml of the concentrated third water in step 3 of Example 1, and then add 770g of Na ₂ SO ₄ ·10H ₂ O frozen in step 2 of Example 1 (mix The mass ratio of wastewater and sodium sulfate decahydrate is 2.8: 1) Stir and dissolve, pour into a separatory funnel after dissolution, and let stand for 30 minutes to separate the salt solution and the organic phase. After the layering is completed, separate the high-salt and low-COD solutions. First aqueous phase and organic phase.

Among them, the organic phase is collected and used as electrolyte for further recycling treatment, and different organic solvents in the electrolyte are separated. The COD content in the first aqueous phase with high salt and low COD is approximately 20,000 mg/L.

Step 2: Put the high-salt and low-COD first aqueous phase into a freezing tank and freeze it to 4°C. Add 0.5g Na ₂ SO ₄ ·10H ₂ O crystals for one-time freezing crystallization to precipitate Glauber's salt. Filter to obtain 1.5L of low-salt and low-COD aqueous phase. Second aqueous phase of COD and 740g Na ₂ SO ₄ ·10H ₂ O crystals.

Step 3: Put the low-salt and low-COD second aqueous phase into the freezing tank and continue to lower the temperature to -5°C. Stir with a stirring paddle (stirring rate is 400rad/min) and add 1g of pure water ice crystals for secondary freezing. Crystallize to precipitate sand-like ice crystals. After stirring for 5 minutes, the precipitation of ice crystals is basically completed. 1300g of ice crystals and 200 mL of high-salt and high-COD third water phase are separated by suction filtration.

Among them, 1,300g of ice crystals are placed at room temperature and melted to obtain reusable industrial water. The COD content of the reusable industrial water is 800mg/L, and the mass percentage of sodium sulfate is 0.5%; while the concentrated high-salt and high-COD The salt content of the three-aqueous phase is 26% by mass, and the COD content is 150,000 mg/L.

Table 2. Parameters of water in different processes of Example 2

Comparative Example 1: Comparison without seed crystal

This comparative example provides a wastewater treatment method. The difference from Example 1 includes not adding seed crystals in step 2. The specific steps are as follows:

Step 1: Take 2L of high COD wastewater containing electrolyte (COD content is 80000mg/L), add 400g of sodium sulfate to the wastewater, stir and dissolve, pour into a separatory funnel after complete dissolution, and let stand for 30 minutes to allow the salt solution to mix with the organic matter. The phases are separated into layers. After the layering is completed, the first aqueous phase with high salt and low COD and the organic phase are separated.

Step 2: Put the first aqueous phase with high salt and low COD into a freezing tank and freeze it to 0°C. Add 0.5g Na ₂ SO ₄ ·10H ₂ O crystals and keep it at 0°C for 30 minutes to precipitate the Glauber's salt. Filter to obtain 1.4L low salt. Second aqueous phase with low COD and 770g Na ₂ SO ₄ ·10H ₂ O crystals.

Step 3: Put the low-salt and low-COD second aqueous phase into the freezing tank and continue to lower the temperature and freeze it to -15°C. Stir with a stirring paddle (stirring rate is 400rad/min) for 15 minutes. As the precipitation of ice increases, it cannot be frozen. Continue to stir, and after freezing for 30 minutes, it will basically become block ice. The ice crystals and concentrated third water phase cannot be separated by suction filtration, and only a whole ice cube can be obtained. After the ice cube melts, the treated water is obtained.

Table 3. Parameters of water in different processes of Comparative Example 1

	水量water volume	COD(mg/L)COD(mg/L)	盐含量(％)Salt content (%)
水破碎电池废水Water broken battery wastewater	20002000	8000080000	00
第一水相first aqueous phase	20002000	2000020000	1818
第二水相second aqueous phase	14001400	2500025000	33
冰ice	14001400	2500025000	33

Comparing this example with Example 1, it can be seen that no seed crystal is added in step 3. Since the COD and salt content in the second water phase still have a certain concentration at this time, the water in it is in a supercooled state, resulting in In the end, the ice crystals cannot be separated out separately, so that the amount of COD in them is still at a high level. Therefore, COD cannot be further separated after the first step of salting out, and the treatment effect of wastewater is poor.

In the same way, since sodium sulfate seed crystals were added in step 2 in this comparative example, Glauber's salt can be precipitated. During the experiment, it was found that if sodium sulfate seed crystals were not added in this step, no sodium sulfate decahydrate would appear if kept at 0°C for 30 minutes. In the case of crystal precipitation, this will further cause the salt content in the second water phase to be too high, making it difficult to separate ice crystals, and the treatment effect of wastewater will still be poor.

Comparative Example 2: Comparison of Salts

This comparative example provides a wastewater treatment method. The difference from Example 1 includes the use of sodium chloride instead of sodium sulfate as the salt used for salting out and the seed crystal used for primary freezing crystallization. The details are as follows:

Step 1: Take 2L of high COD wastewater containing electrolyte (COD content is 80000mg/L), add 500g of sodium chloride to the wastewater, stir and dissolve, pour into a separating funnel after complete dissolution, and let stand for 30 minutes to allow the salt solution to mix with The organic phase is separated into layers. After the layering is completed, the first aqueous phase with high salt and low COD and the organic phase are separated.

Among them, the organic phase is collected and used as electrolyte for further recycling treatment, and different organic solvents in the electrolyte are separated. The COD content in the first aqueous phase with high salt and low COD is 38000mg/L.

Step 2: Put the first aqueous phase with high salt and low COD into a freezing tank and freeze it to -20°C. Keep the temperature for 30 minutes to precipitate 300g of sodium chloride and 1.9L of the second aqueous phase with low salt and low COD.

Step 3: Put the low-salt and low-COD second aqueous phase into the freezing tank and continue to lower the temperature and freeze it to -25°C. Stir with a stirring paddle (stirring rate is 400rad/min) for 15 minutes. As the precipitation of ice increases, it cannot Continue to stir, and after freezing for 30 minutes, it will basically become block ice. The ice crystals and concentrated third water phase cannot be separated by suction filtration. Only a whole block of ice can be obtained. After the ice cube melts, treated water can be obtained.

Table 4. Parameters of water in different processes of Comparative Example 2

	水量water volume	COD(mg/L)COD(mg/L)	盐含量(％)Salt content (%)
水破碎电池废水Water broken battery wastewater	20002000	8000080000	00
第一水相first aqueous phase	20002000	3800038000	2020
第二水相second aqueous phase	19001900	3800038000	99
冷冻出冰Freeze and ice	19001900	3800038000	99

Combining Comparative Example 2 and Example 1, it can be seen that since sodium chloride is used as an alternative to sodium sulfate, the temperature at which crystallization occurs is relatively low, reaching about -20°C. The temperature is too low and the energy consumption required for refrigeration is very high. high. Moreover, the residual salt concentration in the second aqueous phase after primary freeze crystallization is as high as 9%, making it difficult to effectively separate ice crystals during subsequent secondary freeze crystallization. Ultimately, the treatment effect of COD in wastewater is poor and the cost is high.

Example 3

This embodiment provides a wastewater treatment method. The difference from Example 1 is that potassium sulfate is used instead of sodium sulfate, which specifically includes the following steps:

Step 1: Take 2L of high COD wastewater containing electrolyte (COD content is 150000mg/L), add 230g of potassium sulfate to the wastewater (the mass ratio of wastewater to potassium sulfate is 10:1), stir and dissolve, and pour it after complete dissolution. In the separatory funnel, let stand for 30 minutes to separate the salt solution and the organic phase. After the separation is completed, separate the first aqueous phase with high salt and low COD and the organic phase.

Step 2: Put the first water phase with high salt and low COD into a freezing tank and freeze it to -5°C. Add 2.3g K ₂ SO ₄ crystals for primary freezing crystallization to precipitate Glauber's salt. Filter to obtain the second water with low salt and low COD. phase and K ₂ SO ₄ crystals.

Step 3: Put the low-salt and low-COD second water phase into the freezing tank and continue to lower the temperature to -10°C. Stir with a stirring paddle (stirring rate is 400rad/min) and add 1g of pure water ice crystals for secondary freezing. Crystallize to precipitate sand-like ice crystals. After stirring for 5 minutes, the ice crystals are basically precipitated. The ice crystals and the third water phase with high salt and high COD are separated by suction filtration.

Example 4

Step 2: Put the first aqueous phase with high salt and low COD into a freezing tank and freeze it to 0°C. Add 2.3g K ₂ SO ₄ crystals for primary freezing crystallization to precipitate Glauber's salt. Filter to obtain the second aqueous phase with low salt and low COD. and K ₂ SO ₄ crystals.

Step 3: Put the low-salt and low-COD second aqueous phase into a freezing tank and maintain it at 0°C to continue freezing. Stir with a stirring paddle (stirring rate is 200rad/min) and add 10g of pure water ice crystals, and perform secondary freezing and crystallization to precipitate. Sand-like ice crystals are basically precipitated after stirring for 5 minutes. The ice crystals and the third water phase with high salt and high COD are separated by suction filtration.

Example 5

The treatment effect of Examples 3 to 5 on electrolyte wastewater is close to that of Example 1 and Example 2, and will not be described again here.

The present application has been described in detail above with reference to the embodiments. However, the present application is not limited to the above-mentioned embodiments. Various changes can be made within the knowledge scope of those of ordinary skill in the art without departing from the purpose of the present application. In addition, the embodiments of the present application and the features in the embodiments may be combined with each other without conflict.

Claims

The wastewater treatment method is characterized by including the following steps:

Step 1: Take the wastewater, add salt to salt out, and obtain the organic phase and the first aqueous phase;

Step 2: Take the first aqueous phase, add the salt crystal seeds and perform a freeze crystallization to obtain the second aqueous phase and the salt crystals;

Step 3: Take the second water phase, add ice crystal seeds and perform secondary freezing crystallization to obtain the third water phase and ice crystals.
The treatment method according to claim 1, characterized in that, in the step 1, the salt is added according to the mass ratio of the wastewater: the salt to (2-10): 1 for salting out;

Preferably, the salt is a soluble alkali metal salt;

Preferably, the salt is a soluble sulfate;

Preferably, the salt is at least one of a soluble sodium salt and a soluble potassium salt;

Preferably, the salt is at least one of sodium sulfate and potassium sulfate.
The treatment method according to claim 1, characterized in that the mass of the salt seed crystal is 0.001 to 0.01 times the mass of the salt in the first aqueous phase;

Preferably, the seed crystal of the salt is sodium sulfate decahydrate seed crystal.
The processing method according to claim 3, characterized in that the temperature of the primary freezing crystallization in step 2 is -5 to 5°C.
The processing method according to claim 1, characterized in that the temperature of the secondary freezing crystallization in step 3 is -10 to 0°C.
The treatment method according to any one of claims 1 to 5, characterized in that the mass of the ice crystal seeds in step 3 is 0.0001 to 0.01 times the mass of the second water phase.
The treatment method according to any one of claims 1 to 5, characterized in that the salt crystals generated in step 2 are recycled to step 1 to perform the salting out.
The treatment method according to any one of claims 1 to 5, characterized in that the organic phase in step 1 is recovered as an electrolyte.
The treatment method according to any one of claims 1 to 5, characterized in that the wastewater is wastewater containing electrolyte;

Preferably, the electrolyte-containing wastewater is selected from at least one of hydrolysis wastewater, electrolyte production wastewater, battery production wastewater, and battery discharge wastewater.
The treatment method according to claim 9, characterized in that the COD of the wastewater is 50000-150000mg/L;

Preferably, the COD of the first aqueous phase is 12,000 to 30,000 mg/L;

Preferably, the COD of the second aqueous phase is 15,000 to 30,000 mg/L;

Preferably, the COD of the third aqueous phase is 100,000 to 200,000 mg/L.