A method for treating LiFSI wastewater

Abstract

This application relates to a method for treating LiFSI wastewater. A method for treating LiFSI wastewater includes the following steps: Adsorption: Adsorb LiFSI wastewater with resin to obtain resin adsorbed with LiFSI; Desorption: Rinse the resin adsorbed with LiFSI with an alkali solution to obtain a LiFSI desorption solution; Concentration: Heat and concentrate the LiFSI desorption solution to obtain a lithium-containing concentrated solution; Neutralization: Add acid to the lithium-containing concentrated solution for neutralization to obtain a neutralized solution; Lithium precipitation: React with carbonate and / or carbon dioxide in the neutralized solution to obtain a carbonate precipitate. This application solves the problem that FSI ‑ cannot be decomposed in large quantities in the existing wastewater treatment process, while fully recovering lithium resources, being more environmentally friendly and having high economic benefits.

Description

Technical Field

[0001] This application relates to the field of wastewater treatment, and specifically relates to a method for treating LiFSI wastewater. Background Art

[0002] Lithium, as an important metallic element, is a new type of energy and strategic resource with great prospects, and is widely used in industries such as electronics, metallurgy, medicine, glass, ceramics, batteries, and new energy. In recent years, with the rapid development of the new energy industry, the demand for lithium has increased sharply.

[0003] As a new type of lithium battery electrolyte, LiFSI (lithium bis(fluorosulfonyl)imide) has the advantages of high stability, excellent low-temperature performance, and good hydrolysis stability, and is gradually replacing LiPF6 (lithium hexafluorophosphate). With the increasingly mature production process of LiFSI and the continuous reduction of costs, in recent years, the number of newly built, renovated, and expanded LiFSI manufacturers has increased, and the output has also increased rapidly. In addition, the amount of recycled and disassembled waste lithium batteries is also increasing. Whether it is a large amount of LiFSI-containing wastewater (LiFSI content is 1000 - 20000 ppm) generated during the production process (such as cleaning LiFSI filter residues, cleaning production equipment, and cleaning packaging barrels) or LiFSI-containing wastewater generated from the recycling and disassembly of waste lithium batteries, if LiFSI is not extracted and recovered, the existing sewage treatment process cannot decompose FSI in LiFSI - resulting in FSI- remaining in the water, and FSI - (bis(fluorosulfonyl)imide acid ion) remaining in the water seriously affects the LAS (anionic surfactant, the national first-class water quality requirement is lower than 0.5 ppm) of the water quality, and at the same time wastes a large amount of lithium resources.

[0004] Therefore, the present invention is proposed. Summary of the Invention

[0005] The main purpose of the present invention is to provide a method for treating LiFSI wastewater, which solves the problem that FSI - cannot be decomposed in large quantities in the existing wastewater treatment process, and at the same time fully recovers lithium resources, is more environmentally friendly and has high economic benefits.

[0006] To achieve the above objectives, the present invention provides the following technical solutions.

[0007] A method for treating LiFSI wastewater, comprising the following steps:

[0008] Adsorption: Adsorbing LiFSI wastewater with resin to obtain resin adsorbed with LiFSI;

[0009] Desorption: Flushing the resin adsorbed with LiFSI with an alkali solution to obtain a LiFSI desorption solution;

[0010] Concentration: Heat and concentrate the LiFSI analytical solution to obtain a lithium-containing concentrated solution;

[0011] Neutralization: Add acid to the lithium-containing concentrated solution for neutralization to obtain a neutralized solution;

[0012] Lithium precipitation: Add carbonate and / or react with carbon dioxide to the neutralized solution to obtain a carbonate precipitate.

[0013] In the above method of the present invention, LiFSI in the wastewater is first enriched by adsorption and analysis methods, and then the alkali solution therein is heated to react with LiFSI, so as to decompose FSI - into FSO 3- , SO4 2- and F - , thus fundamentally solving the problem of high FSI - content in the wastewater; finally, after neutralization, lithium precipitants such as carbonate and carbon dioxide are added to convert the lithium ions therein into lithium carbonate precipitate, so as to recover lithium in the wastewater.

[0014] It can be seen that the treatment method of the present invention not only fundamentally removes FSI - , but also recovers metallic lithium, improving the economic benefits of wastewater treatment.

[0015] Through experimental detection, using the treatment method of the present invention, the decomposition rate of FSI - is at least 99.6%, and the lithium recovery rate is at least 93%.

[0016] The operating conditions and raw material types in the five main steps of the above treatment method can be further optimized to improve the decomposition rate, improve the lithium recovery rate, shorten the reaction time or reduce the cost, etc., as listed below.

[0017] In some embodiments, the alkali solution is an inorganic strong base solution, preferably at least one or a combination of sodium hydroxide, potassium hydroxide, lithium hydroxide, magnesium hydroxide, calcium hydroxide, and aluminum hydroxide aqueous solutions.

[0018] On the one hand, inorganic strong bases do not introduce exogenous impurities or impurities that are difficult to remove, and on the other hand, they have strong alkalinity and can quickly analyze and decompose FSI - .

[0019] In some embodiments, the alkali solution is at least one of potassium hydroxide solution or sodium hydroxide solution. Since the ionic strengths of different salt ions are different, and the influence on the chemical equilibrium of the decomposition reaction and the lithium precipitation reaction is different, similar to potassium hydroxide solution or sodium hydroxide solution, it is more conducive to the rapid and complete progress of the decomposition reaction and the lithium precipitation reaction. Therefore, potassium hydroxide solution or sodium hydroxide solution is preferred, and potassium hydroxide is better.

[0020] In some embodiments, the concentration of the lye is 3% to 10%. Considering comprehensive factors such as reaction rate and cost, a lye concentration of 3% to 10% is preferred, such as 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc., and a more preferred range includes 5% to 8%, etc.

[0021] In some embodiments, the temperature of the heating and concentration is 80 to 100 °C, preferably 95 - 100 °C. When heated to 80 to 100 °C, the decomposition rate of FSI - basically reaches the highest, and no other by-products are generated. Among them, a more preferred temperature range is 95 - 100 °C.

[0022] In some embodiments, the equipment for heating and concentration is one or several of a double-effect evaporator, a triple-effect evaporator, a falling-film evaporator, a thin-film evaporator, and a distillation column, used in series or in parallel.

[0023] These evaporators all have the advantages of high evaporation efficiency and fast heat transfer rate. Using them in the heating and concentration process of the present invention can improve the reaction rate and reduce energy consumption at the same time.

[0024] In some embodiments, the resin is a neutral resin or a weakly basic resin, preferably PD201 resin.

[0025] The neutral resin or the weakly basic resin has a high adsorption coefficient for LiFSI in the LiFSI wastewater, and among them, PD201 resin is preferred.

[0026] In some embodiments, after the adsorption, the content of LiFSI in the LiFSI wastewater reaches below 0.2 ppm.

[0027] When the adsorption reaches that the content of LiFSI reaches below 0.2 ppm, on the one hand, the FSI in the resin effluent - already meets the national standard requirements, and on the other hand, it can ensure that LiFSI is almost completely enriched.

[0028] In some embodiments, the end point pH value of the neutralization reaches 6.5 to 7.0.

[0029] When the neutralization reaches pH = 6.5 to 7.0, lithium carbonate precipitate can be quickly formed after adding a lithium precipitation agent. In the actual treatment process, the end point pH value cannot be completely controlled to be a constant specific value, and usually a certain fluctuation range is allowed, such as 6.5 to 6.8, 6.8 to 7.0, etc. Even for the treatment of a large amount of wastewater, the end point pH value can be allowed to fluctuate within a relatively wide range of 6.5 to 7.0.

[0030] In some embodiments, the acid added for neutralization is one or a combination of sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, oxalic acid, acetic acid, hypochlorous acid, and formic acid.

[0031] Similar to the lye, when adding acid for neutralization, multiple factors such as introducing no impurities or fewer impurities and having a fast reaction rate need to be considered simultaneously. Sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, oxalic acid, acetic acid, hypochlorous acid, and formic acid can all meet the above requirements, and sulfuric acid is preferred. Additionally, during the treatment process, these acids can be added in the form of a solution or by introducing an acidic gas.

[0032] In some embodiments, the carbonate is at least one of sodium carbonate and potassium carbonate.

[0033] Both of these salts can react with lithium ions quickly to form lithium carbonate precipitation. The addition amount of the carbonate is usually determined according to the lithium content in the solution, and an appropriate excess is added.

[0034] In some embodiments, in the lithium precipitation step, after the reaction, filtration is also carried out. The filtration equipment preferably includes one or a combination of a plate and frame filter, a bag filter, a candle filter, a scraper centrifuge, a horizontal centrifuge, a belt centrifuge, a siphon centrifuge, and a pusher centrifuge.

[0035] The precipitate is filtered out by filtration, and the effluent water can be used as industrial water or for other sewage treatment. The plate and frame filter, bag filter, candle filter, scraper centrifuge, horizontal centrifuge, belt centrifuge, siphon centrifuge, and pusher centrifuge used for filtration can all be used for large-flow sewage treatment.

[0036] In summary, compared with the prior art, the present invention has at least achieved the following technical effects:

[0037] (1) Fundamentally removed FSI in the wastewater through a decomposition reaction - ;

[0038] (2) Recovered metallic lithium in the wastewater, improving the economic benefits of sewage treatment;

[0039] (3) Only common safe and non-toxic chemical reagents such as inorganic bases, inorganic acids, and carbonates are used during the treatment process, improving the safety of sewage treatment volume and reducing the raw material cost;

[0040] (4) Optimized the operating conditions in each step, providing a prerequisite for further improving the efficiency and economic benefits of wastewater treatment.

[0041] The above description is only an overview of the technical solution of this application. In order to understand the technical means of this application more clearly, it can be implemented according to the content of the specification. And in order to make the above and other purposes, features and advantages of this application more obvious and understandable, the specific implementation manners of this application are given below. Specific implementation manners

[0042] The embodiments of the technical solution of this application will be described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, so they are only examples and cannot be used to limit the protection scope of this application.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above description are intended to cover non-exclusive inclusion.

[0044] In the description of the embodiments of this application, technical terms such as "first" and "second" are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity, specific order or primary-secondary relationship of the indicated technical features. In the description of the embodiments of this application, "a plurality of" means two or more, unless otherwise specifically defined.

[0045] Referring to "embodiments" herein means that a particular feature, structure or characteristic described in connection with the embodiments can be included in at least one embodiment of this application. The phrase appears in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0046] In the description of the embodiments of this application, the term "and / or" is only a description of the association relationship of associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this article generally represents an "or" relationship between the associated objects before and after.

[0047] In the description of the embodiments of this application, the term "a plurality of" refers to two or more (including two). Similarly, "a plurality of groups" refers to two or more groups (including two groups), and "a plurality of pieces" refers to two or more pieces (including two pieces).

[0048] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installation", "connection", "connection", "fixation" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can also be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific circumstances.

[0049] As described in the background art, existing LiFSI wastewater treatment methods have problems such as non-compliance of FSI - content. For this reason, the present invention provides a safe and highly cost-effective treatment method. This method mainly involves five key steps of adsorption, desorption, concentration, neutralization, and lithium precipitation in sequence. Some embodiments are listed in this article to illustrate the treatment effect of the present invention, as follows (it should be noted that after a certain condition before lithium precipitation in the present invention changes, the ion content participating in the lithium precipitation reaction may be different. To ensure an excess of the lithium precipitating agent, the dosage of the lithium precipitating agent also has corresponding differences).

[0050] Example 1

[0051] Take 4.5 m of PD201 resin 3 and fill it into the resin column. At a flow rate of 3 m 3 / h, LiFSI wastewater with a content of 2500 ppm (referring to the content of LiFSI, the same applies hereinafter) is introduced from the top of the resin column, discharged from the bottom and circulated back to the original water tank. Samples are taken to detect the LiFSI content of the bottom effluent and online monitor LAS ≤ 0.2 ppm. When the LiFSI content is less than 0.2 ppm, the water is discharged; when the LiFSI content of the bottom effluent is greater than 0.2 ppm or the online monitored LAS is greater than 0.2 ppm, the water inlet is stopped, and the water pressure in the resin column is drained with air, and the treatment is repeated until the LiFSI content of the bottom effluent ≤ 0.2 ppm.

[0052] A potassium hydroxide solution with a mass fraction of 5% is introduced into the resin column and soaked for 2 h. After 2 h, the alkali solution is continuously pumped in at a flow rate of 2 m 3 / h and discharged from the bottom at a flow rate of 2 m 3 / h. After continuously introducing the alkali solution for 2 h, the introduction of the alkali solution is stopped, and the alkali solution in the resin column is drained to obtain an alkali solution with a Li 3 content of 1-2%, and at this time, the resin column can be desorbed and used for the next LiFSI adsorption. +

[0053] ​When the lye is concentrated to 50% of the original volume at 92 - 95 °C, stop concentration, filter and transfer it to the neutralization kettle for stirring. Slowly add hydrochloric acid with a mass fraction of 3% for neutralization. After adjusting the pH value to 6.5 - 7, add deionized water and adjust the Li + concentration in the solution to 2%; pump it into a 5 m 3 solution with a 2% Li + concentration to the alkalization kettle, then pour in 760 kg of sodium carbonate and stir for 3 - 4 h to obtain a lithium carbonate turbid liquid. Finally, centrifuge and dehydrate the lithium carbonate turbid liquid with a scraper centrifuge to obtain 548 kg of lithium carbonate powder. The lithium carbonate content in the lithium carbonate powder is 90.2%, the water content is 8.3%, and the impurity content is 1.5%.

[0054] Example 2

[0055] The main difference from Example 1 is that the lye is replaced with sodium hydroxide, and correspondingly, the amount of sodium carbonate added during lithium precipitation is different, as follows.

[0056] Take 4.5 m 3 of PD201 resin and fill it into the resin column. Feed 2500 ppm LiFSI wastewater into the top of the resin column at a flow rate of 3 m 3 / h, discharge it from the bottom and recycle it back to the original water tank. Sample and detect the LiFSI content in the bottom effluent and online monitor LAS less than 0.2 ppm. When the LiFSI content is less than 0.2 ppm, discharge the water; when the LiFSI content in the bottom effluent is greater than 0.2 ppm or the online monitored LAS is greater than 0.2 ppm, stop feeding water, press the water in the resin column dry with air, and repeat the treatment until the LiFSI content in the bottom effluent ≤ 0.2 ppm.

[0057] Feed a sodium hydroxide solution with a mass fraction of 5% into the resin column and soak it for 2 h. After 2 h, continue to pump the lye into the column at a flow rate of 2 m 3 / h and discharge the lye from the bottom at a flow rate of 2 m 3 / h. Stop feeding the lye after continuously feeding the lye for 2 h, and press the lye in the resin column dry to obtain about 6 m3 of lye with a Li + content of 1 - 2%. At this time, after desorbing the resin column, it can be used for the next LiFSI adsorption.

[0058] When the lye is concentrated to 50% of the original volume at 92 - 95 °C, stop concentration, filter and transfer it to the neutralization kettle for stirring. Slowly add hydrochloric acid with a mass fraction of 3% for neutralization. After adjusting the pH value to 6.5 - 7, add deionized water and adjust the Li + concentration in the solution to 2%; pump it into a 5 m 3 solution with a 2% Li +A solution with a certain concentration is added to the alkalization kettle, and then 760 kg of sodium carbonate is poured in and stirred for 3 - 4 hours to obtain a lithium carbonate suspension. Finally, the lithium carbonate suspension is centrifugally dehydrated by a scraper centrifuge to obtain 603 kg of lithium carbonate powder, with a lithium carbonate content of 78.7%, a water content of 10.5%, and an impurity content of 10.8%.

[0059] Example 3

[0060] The main difference from Example 1 is that the acid added during neutralization is replaced with sulfuric acid, and correspondingly, there is a difference in the amount of sodium carbonate added during lithium precipitation, as follows.

[0061] Take 4.5 m of PD201 resin 3 and fill it into the resin column. At a flow rate of 3 m 3 / h, 2500 ppm of LiFSI wastewater enters from the top of the resin column, exits from the bottom and is recycled back to the original water tank. Samples are taken to detect the LiFSI content in the bottom effluent and online monitor that LAS is less than 0.2 ppm. When the LiFSI content is less than 0.2 ppm, the water is discharged; when the LiFSI content in the bottom effluent is greater than 0.2 ppm or the online monitored LAS is greater than 0.2 ppm, the water inlet is stopped, and the water pressure in the resin column is pressed dry with air, and the treatment is repeated until the LiFSI content in the bottom effluent ≤ 0.2 ppm.

[0062] A potassium hydroxide solution with a mass fraction of 5% is introduced into the resin column and soaked for 2 hours. After 2 hours, continue to pump in the alkali solution at a flow rate of 2 m 3 / h and discharge the alkali solution from the bottom at a flow rate of 2 m 3 / h. After continuously pumping in the alkali solution for 2 hours, stop pumping in the alkali solution, and press dry the alkali solution in the resin column to obtain about 6 m3 of alkali solution with a Li + content of 1 - 2%. At this time, after the resin column is desorbed, it can be used for the next LiFSI adsorption. The treatment is repeated until the LiFSI content in the bottom effluent ≤ 0.2 ppm.

[0063] When the alkali solution is concentrated to 50% of the original volume at 92 - 95 °C, stop concentrating, filter and transfer it to the neutralization kettle for stirring. Slowly add sulfuric acid with a mass fraction of 4% for neutralization, adjust the pH value to 6.5 - 7, then add deionized water and adjust the Li + concentration in the solution to 2%; pump in 5 m 3 of the solution with a well - adjusted 2% Li + concentration to the alkalization kettle, then pour in 760 kg of sodium carbonate and stir for 3 - 4 hours to obtain a lithium carbonate suspension. Finally, the lithium carbonate suspension is centrifugally dehydrated by a scraper centrifuge to obtain 551 kg of lithium carbonate powder, with a lithium carbonate content of 91.2%, a water content of 6.7%, and an impurity content of 2.1%. The treatment is repeated until the LiFSI content in the bottom effluent ≤ 0.2 ppm.

[0064] Example 4

[0065] The main difference from Example 1 is that the concentration of the lye is increased to 10%, and correspondingly, the amount of sodium carbonate added during lithium precipitation is different, as follows.

[0066] Take 4.5 m of PD201 resin 3 and pack it into the resin column. Feed 2500 ppm LiFSI wastewater into the top of the resin column at a flow rate of 3 m 3 / h, discharge it from the bottom and recycle it back to the original water tank. Sample and detect the LiFSI content in the bottom effluent and online monitor that LAS is less than 0.2 ppm. When the LiFSI content is less than 0.2 ppm, discharge the water; when the LiFSI content in the bottom effluent is greater than 0.2 ppm or the online monitored LAS is greater than 0.2 ppm, stop feeding water, press the water in the resin column dry with air, and repeat the treatment until the LiFSI content in the bottom effluent ≤ 0.2 ppm.

[0067] Pass a potassium hydroxide solution with a mass fraction of 10% into the resin column and soak it for 2 h. After 2 h, continue to pump the lye into the column at a flow rate of 2 m 3 / h and discharge the lye from the bottom at a flow rate of 2 m 3 / h. Stop feeding the lye after continuously feeding the lye for 2 h, and press the lye in the resin column dry to obtain about 6 m 3 Li + lye with a content of 1 - 2%. At this time, the resin column can be desorbed and used for the next LiFSI adsorption after desorption.

[0068] When the lye is concentrated to 50% of the original lye volume at 92 - 95 °C, stop the concentration, filter and transfer it to the neutralization kettle for stirring. Slowly add hydrochloric acid with a mass fraction of 3% for neutralization. After adjusting the pH value to 6.5 - 7, add deionized water and adjust the Li + concentration in the solution to 1%; pump 5 m3 of the solution with a 1% Li + concentration into the alkalization kettle, then pour in 380 kg of sodium carbonate and stir for 3 - 4 h to obtain a lithium carbonate turbid liquid. Finally, centrifuge and dehydrate the lithium carbonate turbid liquid through a scraper centrifuge to obtain 270 kg of lithium carbonate powder, with a lithium carbonate content of 85.3%, a water content of 7.8%, and an impurity content of 6.9%.

[0069] Example 5

[0070] The main difference from Example 1 is that the lithium precipitation agent is replaced by carbon dioxide, as follows.

[0071] Take 4.5 m of PD201 resin 3 and pack it into the resin column. Feed at a flow rate of 3 m 3The flow rate of 2500 ppm LiFSI wastewater enters from the top of the resin column at a rate of / h, exits from the bottom and is recycled back to the original water tank. Samples are taken to detect the LiFSI content in the bottom effluent and online monitor that LAS is less than 0.2 ppm. When the LiFSI content is less than 0.2 ppm, the water is discharged; when the LiFSI content in the bottom effluent is greater than 0.2 ppm or the online monitored LAS is greater than 0.2 ppm, the water inlet is stopped, and the water pressure in the resin column is dried with air, and the treatment is repeated until the LiFSI content in the bottom effluent ≤ 0.2 ppm.

[0072] A potassium hydroxide solution with a mass fraction of 5% is introduced into the resin column and soaked for 2 h. After 2 h, the alkali solution is continuously pumped in at a flow rate of 2 m 3 / h and discharged from the bottom at a flow rate of 2 m 3 / h. After continuously feeding the alkali solution for 2 h, the feeding of the alkali solution is stopped, and the alkali solution in the resin column is dried to obtain about 6 m 3 Li + alkali solution with a content of 1 - 2%. At this time, after the resin column is desorbed, it can be used for the next LiFSI adsorption.

[0073] When the alkali solution is concentrated to 50% of the original volume at 92 - 95 °C, the concentration is stopped, filtered and transferred to a neutralization kettle for stirring. A hydrochloric acid with a mass fraction of 3% is slowly added for neutralization. After adjusting the pH value to 6.5 - 7, deionized water is added and the Li + concentration in the solution is adjusted to 2%; 5 m 3 of the solution with a 2% Li+ concentration is pumped into the alkalization kettle, and then 350 kg of carbon dioxide is slowly introduced into the kettle. After the feeding is completed, it continues for 2 h to obtain a lithium carbonate turbid liquid. Finally, the lithium carbonate turbid liquid is centrifugally dehydrated through a scraper centrifuge to obtain 606 kg of lithium carbonate powder. The lithium carbonate content in the lithium carbonate powder is 85.8%, the water content is 13.8%, and the impurity content is 0.4%.

[0074] Example 6

[0075] The difference from Example 1 is only that the alkali solution - potassium hydroxide is replaced by magnesium hydroxide, and the rest of the operations and conditions remain unchanged.

[0076] This example obtains 545 kg of lithium carbonate powder. The lithium carbonate content in the lithium carbonate powder is 86.3%, the water content is 8.5%, and the impurity content is 5.2%.

[0077] Examples 7 - 10

[0078] The difference from Example 1 is only the concentration of the potassium hydroxide solution, which is 2%, 3%, 8%, and 12% respectively, and the rest of the operations and conditions remain unchanged. It is found that the analytical effect of Examples 7-8 with decreasing concentration becomes worse, resulting in the resin reaching saturation quickly during repeated use, so the total analysis time is extended; while the analytical effect of Examples 9-10 with increasing concentration is better, and it can be analyzed completely quickly, and the adsorption capacity of the resin also increases during repeated use. In addition, since the lithium ion concentration is quantified to 2% during lithium precipitation in all examples, there is no significant difference in the amount of lithium carbonate obtained and the impurity content.

[0079] Examples 11-14

[0080] The difference from Example 1 is only the temperature during heating and concentration, which is controlled at 70-73°C, 80-85°C, 97-100°C, and 105-110°C respectively, and the rest of the operations and conditions remain unchanged. It is found that the decomposition effect of FSI in Examples 11-12 with decreasing temperature becomes worse, resulting in an increase in the amount of acid used during neutralization; while the decomposition effect of Examples 13-14 with increasing temperature is better, and the amount of acid used during neutralization is reduced. In addition, since the lithium ion concentration is quantified to 2% during lithium precipitation in all examples, there is no significant difference in the amount of lithium carbonate obtained and the impurity content. - The difference from Example 1 is only the temperature during heating and concentration, which is controlled at 70-73°C, 80-85°C, 97-100°C, and 105-110°C respectively, and the rest of the operations and conditions remain unchanged. It is found that the decomposition effect of FSI in Examples 11-12 with decreasing temperature becomes worse, resulting in an increase in the amount of acid used during neutralization; while the decomposition effect of Examples 13-14 with increasing temperature is better, and the amount of acid used during neutralization is reduced. In addition, since the lithium ion concentration is quantified to 2% during lithium precipitation in all examples, there is no significant difference in the amount of lithium carbonate obtained and the impurity content.

[0081] Example 15

[0082] The difference from Example 1 is only the type of resin used for adsorption, which is as follows.

[0083] Take 4.5 m of LX-363 resin 3 and fill it into the resin column. At a flow rate of 3 m 3 / h, the LiFSI wastewater with a content of 2500 ppm (referring to the content of LiFSI, the same applies hereinafter) enters from the top of the resin column, is discharged from the bottom and recycled back to the original water tank. Samples are taken to detect the LiFSI content of the bottom effluent and online monitor LAS ≤ 0.2 ppm. When the LiFSI content is less than 0.2 ppm, the water is discharged; when the LiFSI content of the bottom effluent is greater than 0.2 ppm or the online monitored LAS is greater than 0.2 ppm, the water inlet is stopped, and the water pressure in the resin column is drained with air, and the treatment is repeated until the LiFSI content of the bottom effluent ≤ 0.2 ppm.

[0084] Pass a potassium hydroxide solution with a mass fraction of 5% into the resin column and soak it for 2 h. After 2 h, continue to pump the alkali solution into the column at a flow rate of 2 m 3 / h and discharge the alkali solution from the bottom at a flow rate of 2 m 3 / h. After continuously feeding the alkali solution for 2 h, stop feeding the alkali solution, and drain the alkali solution in the resin column to obtain about 6 m 3 Li +The lye with a content of 0.02-0.05% can be used for the next LiFSI adsorption after the resin column is desorbed.

[0085] Concentrate the lye at 92-95 °C until the Li + concentration is 2.3%-2.5%; stop concentration, filter and transfer it to a neutralization kettle for stirring, slowly add hydrochloric acid with a mass fraction of 3% for neutralization, adjust the pH value to 6.5-7, and then adjust the Li + to 2% with deionized water; pump 5 m 3 The solution with a 2% Li + concentration is transferred to an alkalization kettle, then 760 kg of sodium carbonate is poured in and stirred for 3-4 h to obtain a lithium carbonate turbid liquid. Finally, the lithium carbonate turbid liquid is centrifugally dehydrated by a scraper centrifuge to obtain 548 kg of lithium carbonate powder. The lithium carbonate content in the lithium carbonate powder is 65.2%, the water content is 12.3%, and the impurity content is 22.5%.

[0086] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should all be covered by the scope of the claims and the description of the present application. In particular, as long as there is no structural conflict, the technical features mentioned in each embodiment can be combined in any way. The present application is not limited to the specific embodiments disclosed in the text, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for treating LiFSI wastewater, characterized in that, It includes the following steps: Adsorption: Adsorb the LiFSI wastewater with resin to obtain the resin adsorbed with LiFSI; Desorption: Rinse the resin adsorbed with LiFSI with an alkali solution to obtain a LiFSI desorption solution; Concentration: Heat and concentrate the LiFSI desorption solution to obtain a lithium-containing concentrated solution; Neutralization: Add acid to the lithium-containing concentrated solution for neutralization to obtain a neutralized solution; Lithium precipitation: React with carbonate and / or carbon dioxide in the neutralized solution to obtain a carbonate precipitate; The alkali solution is at least one of potassium hydroxide solution and sodium hydroxide solution; The concentration of the alkali solution is 5%-8%; 2. The treatment method of LiFSI wastewater according to claim 1, characterized in that The temperature for the heat concentration is 80-100°C; 3. The treatment method of LiFSI wastewater according to claim 2, wherein, The temperature for the heat concentration is 95-100°C; 4. The treatment method of LiFSI wastewater according to claim 1 or 2, characterized in that, The equipment for the heat concentration is one or several of a double-effect evaporator, a triple-effect evaporator, a falling-film evaporator, a thin-film evaporator, and a distillation column used in series or in parallel; 5. The treatment method of LiFSI wastewater according to claim 1, wherein The resin is a neutral resin or a weakly basic resin; 6. The treatment method of LiFSI wastewater according to claim 5, characterized in that, The resin is PD201 resin; 7. The treatment method of LiFSI wastewater according to claim 1 or 5, characterized in that, After the adsorption, the LiFSI content in the LiFSI wastewater reaches below 0.2 ppm; 8. The treatment method of LiFSI wastewater according to claim 1, characterized in that, The end-point pH value of the neutralization reaches 6.5-7.0; 9. The treatment method of LiFSI wastewater according to claim 1 or 8, characterized in that, The acid added in the neutralization is one or a combination of sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, oxalic acid, acetic acid, hypochlorous acid, and formic acid; 10. The treatment method of LiFSI wastewater according to claim 1, characterized in that, The carbonate is at least one of sodium carbonate and potassium carbonate; 11. The treatment method of LiFSI wastewater according to claim 1, wherein In the lithium precipitation step, filtration is also carried out after the reaction; 12. The treatment method of LiFSI wastewater according to claim 11, characterized in that, The equipment used for the filtration is one or a combination of a plate-and-frame filter, a bag filter, a candle filter, a scraper centrifuge, a horizontal centrifuge, a belt centrifuge, a siphon centrifuge, and a pusher centrifuge.