A method for chemically cleaning lithium carbonate scale from the surface of an instrument.

Abstract

This invention relates to a method for removing lithium carbonate scale from the surface of equipment such as crystallization apparatus and evaporation apparatus. A non-acidic cleaning solution, such as water, is introduced into the apparatus. Once inside the apparatus, CO2 is injected and mixed with the cleaning solution. This converts the lithium carbonate scale into lithium bicarbonate, which dissolves in the cleaning solution. Subsequently, the cleaning solution containing the dissolved lithium bicarbonate is discharged from the apparatus.

Description

Technical Field

[0001] The present invention relates to a method for removing lithium carbonate scale from the surface of an apparatus used, for example, in the production of lithium hydroxide monohydrate.

Background Art

[0002] Lithium hydroxide is an important component of rechargeable batteries and other devices. In systems and methods used for the production of lithium hydroxide, evaporation and crystallization systems are utilized to concentrate lithium hydroxide and ultimately crystallize lithium hydroxide monohydrate. In many cases, lithium hydroxide is produced from brine containing carbonate. Since the solubility of lithium carbonate decreases with increasing temperature and / or removal of moisture during the evaporation process, lithium carbonate often precipitates during the evaporation of brine of lithium hydroxide. Therefore, in evaporation systems and other related apparatuses, scaling of lithium carbonate occurs on the apparatus and heat transfer surfaces. As a result, it is necessary to regularly clean the apparatus to remove the scaling of lithium carbonate, which limits the operating time of the lithium hydroxide production apparatus.

[0003] Due to the low solubility of lithium carbonate, it is difficult to timely remove the scale of lithium carbonate by simple water washing that may be effective for removing other scales with high solubility. Therefore, common methods for removing the scale of lithium carbonate include high-pressure water washing (hydroblast) or chemical washing using an acidic solution to react with and dissolve the scale of lithium carbonate. Various acids are effective, and common acids used for washing include nitric acid, hydrochloric acid, sulfuric acid, acetic acid, or citric acid.

[0004] While hydroblasting can remove lithium carbonate scale, it is difficult to completely remove the scale as with chemical cleaning. This is especially true when scale forms not only on the heat transfer surfaces of these systems but also on the walls of the vessels and piping. Furthermore, hydroblasting is typically a contract service and requires external resources that are subject to delays and availability. Finally, cleaning by hydroblasting is a lengthy process that can take several days to complete.

[0005] Chemical cleaning may be a faster method for removing lithium carbonate scale. However, using acidic solutions raises concerns about the increased potential for equipment corrosion, as well as safety concerns regarding the handling of acidic solutions, which are typically at high temperatures. Disposing of used acidic solutions can also be difficult and costly. Furthermore, residual acidic solutions that are not completely drained after cleaning can contaminate the product during restart.

[0006] Therefore, there is a real need for a method that overcomes the shortcomings and disadvantages of hydroblasting and acid-based chemical cleaning, and effectively removes lithium carbonate scale from the surface of equipment. [Overview of the Initiative]

[0007] This invention relates to a method for removing lithium carbonate scale from the surface of a device. A cleaning solution in the form of water or an aqueous solution is introduced into the device and comes into contact with the lithium carbonate scale. If lithium carbonate is present in the device, the pH of the cleaning solution will be greater than 9, usually above 12. CO2 is mixed with the cleaning solution in the device and converted the lithium carbonate scale into lithium bicarbonate. Lithium bicarbonate is more soluble than lithium carbonate and subsequently dissolves in the cleaning solution. As the conversion continues and the scale dissolves, the pH of the cleaning solution will drop to about 7 to 9 near the end of the cleaning method. The cleaning solution containing lithium bicarbonate is then discharged from the device. This cleaning method is usually carried out in the range of 10 to 50°C.

[0008] The method for removing lithium carbonate scale from equipment services can be carried out in a batch or continuous manner. In a continuous manner, the cleaning solution can be continuously circulated through the equipment. After circulation within the equipment for a certain period, the used cleaning solution can be purged from the equipment. If necessary, the method can be continued by supplying cleaning solution to the equipment, adding CO2 continuously for a period, and then purging the used cleaning solution.

[0009] In one embodiment, the present invention includes the following: A method for removing lithium carbonate scale from the surface of an apparatus, a. Introduce a cleaning solution in the form of water or an aqueous solution into the apparatus and bring it into contact with the lithium carbonate scale formed on the surface of the apparatus, thereby increasing the pH of the cleaning solution to more than 9. b. Mixing CO2 with the washing solution to lower the pH of the washing solution from approximately 7 to 9 converts lithium carbonate scale to lithium bicarbonate. Converting lithium carbonate scale to lithium bicarbonate means that lithium bicarbonate will dissolve in the cleaning solution, and converting lithium carbonate scale to lithium bicarbonate is... c. A method comprising discharging a cleaning solution containing dissolved lithium bicarbonate from the apparatus.

[0010] In another embodiment, the present invention includes the following: A method for removing lithium carbonate scale from the surface of an apparatus, a. Introducing a non-acidic cleaning solution with a temperature of less than 50°C into the apparatus and bringing it into contact with the lithium carbonate scale formed on the surface of the apparatus, b. The cleaning solution must be water or an aqueous solution. c. Circulating the cleaning solution within the device, d. By mixing CO2 with the cleaning solution, lithium carbonate scale is converted to lithium bicarbonate, e. Converting lithium carbonate scale to lithium bicarbonate means that lithium carbonate will dissolve in the cleaning solution. f. A method comprising discharging a cleaning solution containing dissolved lithium carbonate from the apparatus.

[0011] In yet another embodiment, the present invention includes the following: A method for removing lithium carbonate scale from the internal surface of a crystallization apparatus or evaporator, wherein the crystallization apparatus or evaporator includes a steam body, a heat exchanger, and associated piping, and the method is: a. Introducing a cleaning solution in the form of water or aqueous solution into the crystallization or evaporation apparatus to fill the steam body, heat exchanger, and associated piping of the crystallization or evaporation apparatus with the cleaning solution. b. After the washing solution is introduced into the crystallization or evaporation apparatus, CO2 from a CO2 source is introduced into the crystallization or evaporation apparatus and mixed with the washing solution within the crystallization or evaporation apparatus. c. After CO2 is mixed with the cleaning solution, the cleaning solution is circulated over the surfaces of the steam body, heat exchanger, and associated piping to convert lithium carbonate scale on the surfaces of the steam body, heat exchanger, and associated piping into lithium bicarbonate. d. Dissolving lithium bicarbonate in the washing solution, e. A method comprising discharging a washing solution containing dissolved lithium carbonate from a crystallizer or evaporator.

[0012] Other objects and advantages of the present invention will become apparent by examining the following description and accompanying drawings, which merely illustrate the invention. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic diagram of a forced-circulation crystallization apparatus, illustrating an example of a method for removing lithium carbonate scale from the internal surface of the crystallization apparatus. [Modes for carrying out the invention]

[0014] As described above, lithium carbonate scaling tends to accumulate on the surfaces of equipment used in lithium production. The present invention relates to a cleaning method for removing lithium carbonate scale from equipment surfaces without using acid. Instead, as described below, the pH of the cleaning solution in the equipment is adjusted to a generally neutral range of approximately 7 to 9, resulting in the conversion of lithium carbonate scale to lithium bicarbonate, which is more soluble than lithium carbonate. The converted lithium bicarbonate dissolves in the cleaning solution, and the cleaning solution can then be discharged or purged from the equipment.

[0015] Chemical cleaning methods can be used to remove lithium carbonate scaling from any other equipment, including evaporators, crystallizers, tanks or containers, piping, and liquid carbonate scale. Furthermore, the described chemical cleaning methods can be implemented as batch methods or as continuous cleaning methods. In the batch method, the cleaning solution circulates and remains in the equipment for a selected period. Upon entering the equipment, some lithium carbonate dissolves, initially causing the pH to be high, around 12. During the batch method, CO2 is continuously added until the lithium carbonate is converted to lithium bicarbonate and sufficient scale is removed, at which point the pH of the cleaning solution becomes approximately 7 to 9. Once it is determined that the lithium carbonate scale has been adequately removed from the equipment surface by this method, the cleaning solution containing the dissolved lithium bicarbonate is discharged or purged from the equipment. In many cases, a single batch method will successfully complete the cleaning operation, especially if started at the appropriate time. In some cases, a large amount of lithium carbonate scale may be present on the equipment surface, requiring multiple batch cleaning methods.

[0016] In the continuous method, the cleaning solution is introduced into the apparatus and continuously circulated within it. In one example, the cleaning solution is continuously circulated over a selected period. During this period, additional cleaning solution can be continuously added while CO2 is continuously added, allowing for the continuous removal of used cleaning solution. After that, the circulation is stopped, and the used cleaning solution containing dissolved lithium bicarbonate is purged from the apparatus.

[0017] Figure 1 is a schematic diagram of a forced-circulation crystallization apparatus, schematically shown by the number 10, and this is an example of a crystallization system that may be used in a lithium production method. The design and operation of the forced-circulation crystallization apparatus 10 are well known and understood by those skilled in the art. However, it may be helpful to briefly describe the main components of the crystallization apparatus 10. It includes a steam body 12, which includes a feed inlet 14. During the crystallization method, the concentrate or liquid is held at the bottom of the steam body. A concentrate line 16 extends from the bottom of the steam body 12 to a recirculation pump 18. The recirculation pump 18 sends the liquid or concentrate through line 28 to a heat exchanger, schematically shown by the number 20. The heat exchanger 20 includes several tubes arranged within a housing. The heat exchanger housing includes a steam inlet 24 and a condensate outlet 26. During the crystallization method, the recirculation pump 18 sends the liquid or concentrate from the steam body 12 to a heat transfer tube 22 and from the heat transfer tube to line 32 and back to the steam body 12. During the crystallization process, the concentrate passing through the heat exchanger 20 is heated by injecting steam into the steam inlet 24, and then the concentrate or liquid passing through the heat transfer tube 22 is heated. The resulting condensate is discharged from the condensate outlet 26. During the crystallization process, a portion of the concentrate, also called the product, is discharged from an outlet 30 formed in line 28. The steam generated in the crystallization apparatus 10 is discharged from a steam outlet 34 formed at the top of the steam body 12.

[0018] The forced-circulation crystallization apparatus 10 and similar evaporators and crystallizers can be used in various ways in lithium production methods. For example, consider the case where the forced-circulation crystallization apparatus 10 is used to concentrate and crystallize a brine solution of lithium hydroxide containing carbonate. In this method, lithium carbonate will form scale on the internal surface of the crystallizer, at least partially, because it has a solubility inverse to temperature. Therefore, during the concentration and crystallization of the brine solution of lithium hydroxide, tubes of lithium carbonate will form on the internal surface of the crystallizer 10.

[0019] As described above, the cleaning method can be carried out either as a batch method or a continuous method. For illustrative purposes, the continuous method will be described. A cleaning solution, such as water or an aqueous solution, is supplied to the crystallizer 10 via the supply inlet 14. The entire crystallizer 10, including the steam body 12, the heat exchanger 20, and the associated piping, is filled with the cleaning solution. Various outlets are closed to maintain the cleaning solution within the crystallizer 10. Since carbonates are already present in the crystallizer, the pH of the cleaning solution entering the crystallizer usually rises to 9 or higher, and in some cases to 12 or higher. As shown in Figure 1, there is a CO2 source operationally connected to the crystallizer 10. In this example, the CO2 source is designed to inject CO2 into the cleaning solution at a point just upstream of the recirculation pump 18. Once the cleaning solution is contained throughout the crystallizer 10, the recirculation pump 18 circulates the cleaning solution through the heat exchanger 20 and through the steam body 12 back to the recirculation pump. This continues, with CO2 being injected and mixed into the cleaning solution while it is circulating. A sufficient amount of CO2 is injected into the cleaning solution to lower its pH to approximately neutral, around 7 to 9. By monitoring the pH of the cleaning solution, the amount of CO2 injected can be controlled to maintain the pH within the range of 7 to 9. Within this pH range, all or at least most of the lithium carbonate scale will be effectively converted to lithium bicarbonate, which is more soluble than lithium carbonate. The converted lithium bicarbonate dissolves in the cleaning solution as it circulates through the crystallizer 10. Once it is confirmed that the lithium carbonate scale has been completely removed from the internal surface of the crystallizer, the cleaning solution is discharged or purged from one of the outlets of the crystallizer 10. In some cases, this is sufficient to remove the target amount of lithium carbonate scale. In other cases, as described above, it may be necessary to refill the crystallizer 10 with cleaning solution and circulate the solution through the crystallizer. In fact, in some cases, the method may involve repeated cycles of supply and purging. In some cases, it may be desirable to pressurize the cleaning solution within the crystallizer or other apparatus. Pressurizing a system containing a cleaning solution increases the solubility of CO2 in water or aqueous solution, which helps to lower the pH of the cleaning solution to near neutral.

[0020] The present invention has many advantages. One advantage is that the present invention enables chemical cleaning near neutral pH (in the range of 7 to 9). This makes the handling of the used cleaning solution safer and at the same time minimizes the risk of corrosion. This method, unlike other conventional chemical cleaning techniques, has a high potential for recovering lithium from the used cleaning solution by heat treatment or increasing the pH. Although lithium recovery is possible with conventional chemical cleaning, due to the low pH of the cleaning solution, the acids used usually require additional chemicals to raise the pH. Furthermore, the acids used tend to contaminate the recovered lithium with nitrates, chlorides, sulfates, acetates, or citrates depending on the acid used. Using carbon dioxide adds no additional contaminants to the process and there is no risk of contamination by cleaning chemicals during lithium recovery.

[0021] Also, it should be noted that the used cleaning solution from conventional chemical cleaning can only be used after neutralization and may need to be discarded through an approved waste disposal operator, resulting in the loss of the lithium content that should have been recovered as a product. Finally, the carbon dioxide used in this method is usually available at the relevant factory and there is no need to procure external expertise or chemicals that are not usually available on-site. In fact, the use of carbon dioxide is a low-cost chemical and does not require other additional chemicals such as corrosion inhibitors.

[0022] In the above description, the scaling of lithium carbonate and the production of lithium hydroxide monohydrate have been described in the context of the crystallization apparatus. However, the scaling of lithium carbonate may occur in various apparatuses and systems used in the processes of other various lithium production methods. The method for removing the scale of lithium carbonate described here is applicable to all lithium production methods and the apparatuses used. The term "apparatus" used here is broadly defined to include crystallization apparatuses, evaporation apparatuses, pipes, containers, tanks, systems, and other structures and surfaces found in lithium production methods where scaling of lithium carbonate may occur.

[0023] Of course, the present invention can also be implemented by specific methods other than those described herein without departing from the scope and essential features of the present invention. Therefore, the embodiments disclosed herein should be construed as illustrative in all respects and not limiting, and all modifications that fall within the meaning and equivalent scope of the appended claims are intended to be included therein.

Claims

1. A method for removing lithium carbonate scale from the surface of an apparatus, A non-acidic cleaning solution having a temperature of less than 50°C is introduced into the apparatus and brought into contact with the lithium carbonate scale formed on the surface of the apparatus. The cleaning solution is water or an aqueous solution, The cleaning solution is circulated within the apparatus, CO ２ By mixing it with the cleaning solution, the lithium carbonate scale is converted to lithium bicarbonate, Converting the lithium carbonate scale to lithium bicarbonate means that the lithium carbonate dissolves in the cleaning solution, A method comprising: discharging the cleaning solution containing the dissolved lithium carbonate from the apparatus.

2. The cleaning solution, after contact with the lithium carbonate scale, initially has a pH greater than 9, and CO ２ The method according to claim 1, wherein mixing the cleaning solution with the lithium carbonate scale to convert the lithium carbonate scale to lithium bicarbonate reduces the pH of the cleaning solution from approximately 7 to 9.

3. A sufficient amount of CO2 is used to lower the pH of the washing solution from approximately 7 to 9. ２ The method according to claim 1, comprising mixing with the cleaning solution.

4. Sufficient CO2 to convert all or at least most of the lithium carbonate scale into lithium bicarbonate. ２ The method according to claim 1, comprising mixing with the cleaning solution.

5. A method for removing lithium carbonate scale from the internal surface of a crystallization apparatus or evaporator, wherein the crystallization apparatus or evaporator includes a steam body, a heat exchanger, and associated piping, and the method is: A cleaning solution in the form of water or aqueous solution is introduced into the crystallization apparatus or evaporator, thereby filling the steam body, heat exchanger, and associated piping of the crystallization apparatus or evaporator with the cleaning solution. After the cleaning solution is introduced into the crystallization apparatus or evaporation apparatus, CO ２ CO from the source ２ The CO is introduced into the crystallization apparatus or evaporation apparatus, and the CO is stored in the crystallization apparatus or evaporation apparatus. ２ Mixing with the cleaning solution, The aforementioned CO ２ After being mixed with the cleaning solution, the cleaning solution is circulated over the surfaces of the steam body, heat exchanger, and associated piping to convert the lithium carbonate scale on the surfaces of the steam body, heat exchanger, and associated piping into lithium bicarbonate. Dissolving the lithium bicarbonate in the cleaning solution, A method comprising discharging the washing solution containing the dissolved lithium carbonate from the crystallizer or evaporator.

6. the CO ２ Before mixing the CO with the cleaning liquid, the pH of the cleaning liquid in the crystallization device or the evaporation device is greater than 7, and after mixing the CO ２ with the cleaning liquid to convert the scale of lithium carbonate to lithium bicarbonate, the pH of the cleaning liquid drops from about 7 to 9. The method according to claim 5.

7. A method for removing lithium carbonate scale from the surface of an apparatus, A cleaning solution in the form of water or an aqueous solution is introduced into the apparatus and brought into contact with the lithium carbonate scale formed on the surface of the apparatus, thereby increasing the pH of the cleaning solution to more than 9. CO ２ By mixing it with the cleaning solution, the pH of the cleaning solution is lowered from approximately 7 to 9, thereby converting the lithium carbonate scale into lithium bicarbonate. Converting the lithium carbonate scale to lithium bicarbonate means that the lithium bicarbonate dissolves in the cleaning solution, A method comprising discharging the cleaning solution containing the dissolved lithium bicarbonate from the apparatus.

8. The method according to claim 7, wherein the removal of lithium carbonate scale from the surface of the apparatus is carried out without using an acid.

9. The method according to claim 7, wherein the temperature of the cleaning solution is maintained below 50°C during the method for removing lithium carbonate scale from the surface of the apparatus.

10. The method according to claim 7, wherein the cleaning solution is continuously circulated through the apparatus.

11. The method according to claim 10, wherein the cleaning solution containing the dissolved lithium bicarbonate is discharged from the apparatus while the cleaning solution is circulating through the apparatus or after it has been circulated.

12. The method according to claim 7, further comprising enhancing the removal of lithium carbonate scale by pressurizing the cleaning solution in the apparatus during the removal of lithium carbonate scale.

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