Process for removing lithium carbonate scale

Description

/ 11 PROCESS FOR REMOVING LITHIUM CARBONATE SCALE FIELD OF THE INVENTION

[001] The present invention relates to processes for removing lithium carbonate scale from the surfaces of equipment used, for example, in the production of lithium hydroxide monohydrate. BACKGROUND OF THE INVENTION

[002] Lithium hydroxide is an important component in rechargeable batteries and other devices. The systems and processes used in the production of lithium hydroxide employ evaporation and crystallization systems to concentrate the lithium hydroxide and ultimately crystallize lithium hydroxide monohydrate. In many cases, lithium hydroxide is produced from brine that includes carbonate. Because the solubility of lithium carbonate decreases as the temperature increases and / or due to the removal of water during the evaporation process, lithium carbonate often precipitates during the evaporation of lithium hydroxide brine. This results in lithium carbonate fouling on equipment and heat transfer surfaces in the evaporation system and other related equipment.This limits the operating time of lithium hydroxide production equipment, since the equipment must be cleaned regularly to remove lithium carbonate scale.

[003] The low solubility of lithium carbonate makes it difficult to remove lithium carbonate scale in a timely manner by simple water washing, which may be effective for removing other highly soluble scale. Therefore, typical methods for removing lithium carbonate scale include high-pressure water washing (hydroblasting) or chemical cleaning using an acidic solution to react and dissolve the lithium carbonate scale. A wide variety of acids are effective, but the most common acids used for washing include Petition 870250086975, dated 09 / 25 / 2025, page 11 / 30 / 11 nitric acid, hydrochloric acid, sulfuric acid, acetate or citric acid.

[004] Although hydroblasting can remove lithium carbonate scale, it is difficult to remove it completely as effectively as chemical cleaning. This is especially true when scale forms not only on the heat transfer surfaces found in these systems, but also on the walls of the vessels and piping. Furthermore, hydroblasting is typically a contracted service and requires external resources subject to delays and availability. Finally, hydroblasting is a time-consuming process that can take days to complete.

[005] Chemical cleaning can be a faster way to remove lithium carbonate scale. However, the use of acidic solutions raises concerns about the increased potential for corrosion in equipment, as well as safety issues regarding the handling of typically hot acidic solutions. Disposing of used acidic solutions can also be difficult and expensive. In addition, residual acidic solution that is not fully evacuated after cleaning can lead to product contamination upon restart.

[006] Therefore, there is a real need for an effective way to remove lithium carbonate scale from equipment surfaces that overcomes the disadvantages and drawbacks of hydroblasting and chemical cleaning with acids. SUMMARY OF THE INVENTION

[007] The present invention relates to a process for removing lithium carbonate scale from equipment surfaces. A cleaning solution in the form of water or an aqueous solution is directed to the equipment and comes into contact with the lithium carbonate scale. With the presence of lithium carbonate on the equipment, the cleaning solution assumes a pH greater than 9, typically reaching 12 or Petition 870250086975, dated 09 / 25 / 2025, page 12 / 30 / 11 more. CO2 is mixed with the cleaning solution in the equipment, which causes the lithium carbonate scale to be converted 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, there will be a reduction in the pH of the cleaning solution to approximately 7-9 near the end of the cleaning process. The cleaning solution containing lithium bicarbonate is then discharged from the equipment. This cleaning process is normally carried out in the range of 10 to 50°C.

[008] The process of removing lithium carbonate scale from service equipment can be implemented as a batch process or a continuous process. When implemented as a continuous process, the cleaning solution can be continuously circulated through the equipment. After a period of circulation in the equipment, the used cleaning solution can be purged from the equipment. If necessary, the process can continue with periods of feeding cleaning solution into the equipment, along with the continuous addition of CO2, followed by periods of purging the used cleaning solution.

[009] In one embodiment, the present invention involves: A process for removing lithium carbonate scale from equipment surfaces, comprising: a. directing a cleaning solution in the form of water or an aqueous solution into the equipment and into contact with the lithium carbonate deposits formed on the equipment surfaces, resulting in a pH of the cleaning solution greater than 9; b. convert lithium carbonate deposits into lithium bicarbonate by mixing CO2 with the cleaning solution and reducing the pH of the cleaning solution to approximately 7-9; in which the conversion of lithium carbonate scale into Petition 870250086975, dated 09 / 25 / 2025, page 13 / 30 / 11 lithium bicarbonate results in the dissolution of lithium bicarbonate in the cleaning solution; and c. Discharge the cleaning solution containing the dissolved lithium bicarbonate from the equipment.

[0010] In another embodiment, the present invention involves: A process for removing lithium carbonate scale from equipment surfaces, comprising: a. Direct a non-acidic cleaning solution with a temperature below 50°C into the equipment and into contact with the lithium carbonate deposits formed on the equipment surfaces; b. where the cleaning solution is water or an aqueous solution; c. circulate the cleaning solution through the equipment; d. convert lithium carbonate encrustations into lithium bicarbonate by mixing CO2 with the cleaning solution; and in which the conversion of lithium carbonate encrustations into lithium bicarbonate results in the dissolution of lithium carbonate in the cleaning solution; and f. Discharge the cleaning solution containing the dissolved lithium carbonate from the equipment.

[0011] In another embodiment, the present invention involves: A process for removing lithium carbonate scale from the internal surfaces of a crystallizer or evaporator, wherein the crystallizer or evaporator includes a vapor body, heat exchanger and associated piping, the process comprising: a. Direct a cleaning solution in the form of water or an aqueous solution to the crystallizer or evaporator and flood the vapor body, heat exchanger, and associated piping of the crystallizer or evaporator with the cleaning solution; b. after the cleaning solution has been directed to the Petition 870250086975, dated 09 / 25 / 2025, page 14 / 30 / 11 crystallizer or evaporator, direct CO2 from a CO2 source into the crystallizer or evaporator and mix the CO2 with the cleaning solution in the crystallizer or evaporator; c. After the CO2 has been mixed with the cleaning solution, circulate the cleaning solution over the surfaces of the steam body, heat exchanger, and associated piping, and in the process, convert the lithium carbonate scale on the surfaces of the heat exchanger, steam body, and associated piping into lithium bicarbonate; d. Dissolve the lithium bicarbonate in the cleaning solution; and e. Discharge the cleaning solution containing the dissolved lithium carbonate from the crystallizer or evaporator.

[0012] Other objectives and advantages of the present invention will become apparent and obvious from studying the following description and the accompanying drawings, which are merely illustrative of the invention. DESCRIPTION OF THE DRAWING

[0013] Figure 1 is a schematic illustration of a forced circulation crystallizer and illustrates an example of a process for removing lithium carbonate scale from the internal surfaces of the crystallizer. DESCRIPTION OF EXAMPLE MODALITIES

[0014] As discussed above, equipment used in lithium production tends to exhibit lithium carbonate scale on its surfaces. The present invention involves a cleaning process for removing lithium carbonate scale from equipment surfaces without the use of acids. Instead, as explained below, the pH of a cleaning solution in the equipment is adjusted to a generally neutral range of approximately 7-9, which results in the conversion of the lithium carbonate scale into lithium bicarbonate, which is more soluble than lithium carbonate. The converted lithium bicarbonate is Petition 870250086975, dated 09 / 25 / 2025, page 15 / 30 / 11 dissolves in the cleaning solution and the cleaning solution can be discharged or purged from the equipment.

[0015] The chemical cleaning process can be used to remove lithium carbonate scale from evaporators, crystallizers, tanks or vessels, piping, and any other equipment containing liquid carbonate scale. Furthermore, the described chemical cleaning process can be implemented as a batch process or as a continuous cleaning process. In a batch process, the cleaning solution will remain in the equipment for a selected period of time while circulating. After the cleaning solution enters the equipment, it will initially have a high pH, ​​around 12, due to the dissolution of some lithium carbonate. During the batch process, CO2 is continuously added until the lithium carbonate is converted to enough lithium bicarbonate to remove the scale, at which point the cleaning solution will have a pH of approximately 7-9.Once it is determined that the process has successfully cleaned the lithium carbonate scale from the equipment surfaces, the cleaning solution containing dissolved lithium bicarbonate will be discharged or purged from the equipment. In many cases, a single batch process will perform a successful cleaning operation, especially if initiated in a timely manner. In some cases, it may be necessary to perform multiple batch cleaning processes due to the high degree of lithium carbonate scale on the equipment surfaces.

[0016] In a continuous process, the cleaning solution is directed to the equipment and circulates continuously through the equipment. In one example, the cleaning solution is circulated continuously for a selected period of time. During this period, additional cleaning solution can be added continuously, and the used cleaning solution can be removed continuously, continuing to add CO2. After that, the circulation is stopped and the used cleaning solution containing the Petition 870250086975, dated 09 / 25 / 2025, page 16 / 30 / 11 dissolved lithium bicarbonate is purged from the equipment.

[0017] Figure 1 is a schematic illustration of a forced circulation crystallizer, usually indicated by the numeral 10, and which is an example of a crystallization system that can be used in a lithium production process. The design and operation of the forced circulation crystallizer 10 are well known and recognized by those skilled in the art. However, a brief review of the main components of the crystallizer 10 may be useful. It includes a vapor body 12 which includes a feed inlet 14. During the crystallization process, the concentrate or liquor is held in a lower portion of the vapor body. A concentrate line 16 extends from the lower portion of the vapor body 12 to a recirculation pump 18. The recirculation pump 18 pumps the liquor or concentrate through the line 28 to a heat exchanger usually indicated by the numeral 20. The heat exchanger 20 includes a plurality of tubes arranged within a housing.The heat exchanger housing includes a steam inlet 24 and a condensate outlet 26. During a crystallization process, the recirculation pump 18 pumps liquor or concentrate from the steam body 12 into and through the heat transfer tubes 22 and out of the heat transfer tubes in line 32, which leads back to the steam body 12. During the crystallization process, the concentrate passing through the heat exchanger 20 is heated by the injection of steam at the steam inlet 24, which in turn heats the concentrate or liquor passing through the heat transfer tubes 22. The resulting condensate is discharged through the condensate outlet 26. During the crystallization process, a portion of the concentrate, sometimes referred to as the product, is discharged from the outlet 30 formed in line 28. The steam generated in the crystallizer 10 is exhausted through a steam outlet 34 formed in the upper portion of the steam body 12.

[0018] The forced circulation crystallizer 10 and evaporators and Petition 870250086975, dated 09 / 25 / 2025, page 17 / 30 / 11 Similar crystallizers can be employed in various ways in a lithium production process. To give an example, suppose that the forced circulation crystallizer 10 is used to concentrate and crystallize a lithium hydroxide brine containing carbonate. In the process, lithium carbonate will form scale on the internal surfaces of the crystallizer due, at least in part, to its inverse solubility with respect to temperature. Therefore, during the course of concentration and crystallization of the lithium hydroxide brine, the internal surfaces of the crystallizer 10 will suffer lithium carbonate scale formation.

[0019] As discussed above, the cleaning process can be implemented as a batch process or a continuous process. For explanatory purposes, the continuous implementation will be discussed. A cleaning solution, such as water or an aqueous solution, is fed into the crystallizer 10 through the feed inlet 14. The entire crystallizer 10, including the steam body 12, the heat exchanger 20, and the associated piping, is flooded with the cleaning solution. Several outlets are closed in order to keep the cleaning solution in the crystallizer 10. Due to the presence of carbonate already in the crystallizer, the pH of the cleaning solution, once in the crystallizer, will typically rise above 9 and, in some cases, rise to 12 or more. As seen in Figure 1, there is a CO2 source operatively connected to the crystallizer 10. In this example, the CO2 source is designed to inject CO2 into the cleaning solution at a point immediately 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 vapor body 12 and back to the recirculation pump. This is continued and, while the cleaning solution is being circulated, CO2 is injected into the cleaning solution and mixed with it. Sufficient CO2 is injected into the cleaning solution in order to reduce the pH of the cleaning solution to a generally acceptable pH. Petition 870250086975, dated 09 / 25 / 2025, page 18 / 30 / 11 neutral, in the order of approximately 7-9. The pH of the cleaning solution can be monitored, and the amount of CO2 injected into the cleaning solution can be controlled so as to maintain the pH of the cleaning solution in the range of 7 to 9. This pH range will effectively convert all or at least a substantial portion of the lithium carbonate scale into 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 has been determined that the lithium carbonate scale has been successfully removed from the inner surface of the crystallizer, the cleaning solution is discharged or purged through one of the outlets in the crystallizer 10. In some cases, this will be sufficient to remove a specific amount of lithium carbonate scale.In other cases, it may be necessary to refill the crystallizer 10 with the cleaning solution and circulate the solution through the crystallizer as described above. In fact, in some cases, the process may include repeated feeding and purging cycles. In some cases, it may be desirable to pressurize the cleaning solution in the crystallizer or other equipment. By pressurizing the system containing the cleaning solution, the solubility of CO2 in water or aqueous solution is increased, and this, in turn, is useful for reducing the pH of the cleaning solution to a near-neutral pH.

[0020] The present invention offers many advantages. One advantage is that the invention allows chemical cleaning at a near-neutral pH (in the range of 7 to 9). This makes the cleaning solution used safer to handle and, at the same time, minimizes the risk of corrosion. Unlike other conventional chemical cleaning techniques, this method allows for a more probable potential for lithium recovery from the cleaning solution used through heat treatment or pH increase. Although lithium recovery in conventional chemical cleaning is conceivable, the acids used typically require chemicals. Petition 870250086975, dated 09 / 25 / 2025, page 19 / 30 / 11 additional steps to increase the pH due to the low pH of the washing solution. Furthermore, the acid used will tend to contaminate the recovered lithium with nitrate, chloride, sulfate, acetate, or citrate, depending on the acid used. With carbon dioxide, no additional contaminants would be added to the process, and lithium recovery is not at risk of contamination by cleaning chemicals.

[0021] Furthermore, it should be noted that the cleaning solutions used in conventional chemical cleaning can only be made after neutralization and may involve the requirement that disposal be carried out through a licensed waste disposal entity, resulting in a loss of lithium content that could otherwise be recovered as a product. Finally, the carbon dioxide used in the process is usually available at the facilities involved and does not require the acquisition of external knowledge or chemicals that would not normally be available locally. In fact, the use of carbon dioxide represents a lower-cost chemical and does not require other additional chemicals such as corrosion inhibitors.

[0022] The discussion above mentioned lithium carbonate fouling in the context of a crystallizer and the production of lithium hydroxide monohydrate. However, lithium carbonate fouling can occur in various equipment and systems employed in the course of several other lithium production processes. The lithium carbonate fouling removal process discussed here applies to all lithium production processes and the equipment used. The term “equipment,” as used herein, is broadly defined to include crystallizers, evaporators, piping, vessels, tanks, systems, and other structures and surfaces encountered in lithium production processes that may suffer lithium carbonate fouling.

[0023] The present invention can, of course, be carried out in other ways. Petition 870250086975, dated 09 / 25 / 2025, p. 20 / 30 / 11 specific ways beyond those set forth herein, without departing from the scope and essential characteristics of the invention. The present embodiments described herein should therefore be interpreted in all respects as illustrative and not restrictive, and all alterations that fall within the meaning and range of equivalence of the appended claims should be encompassed by them. Petition 870250086975, dated 09 / 25 / 2025, p. 21 / 30

Claims

1 / 3 CLAIMS 1. A process for removing lithium carbonate scale from the internal surfaces of a crystallizer or evaporator, wherein the crystallizer or evaporator includes a steam body, heat exchanger and associated piping, the process characterized in that it comprises: directing a non-acidic cleaning solution in the form of water or an aqueous solution into the crystallizer or evaporator and flooding the steam body, heat exchanger and associated piping of the crystallizer or evaporator with the non-acidic cleaning solution; after the non-acidic cleaning solution has been directed into the crystallizer or evaporator, directing CO2 from a CO2 source into the crystallizer or evaporator and mixing the CO2 with the non-acidic cleaning solution in the crystallizer or evaporator;After the CO2 has been mixed with the non-acidic cleaning solution, circulate the non-acidic cleaning solution over the surfaces of the steam body, heat exchanger, and associated piping, and in the process, convert the lithium carbonate scale on the surfaces of the steam body, heat exchanger, and associated piping into lithium bicarbonate; dissolve the lithium bicarbonate in the non-acidic cleaning solution; and discharge the non-acidic cleaning solution containing the dissolved lithium bicarbonate from the crystallizer or evaporator.

2. Process according to claim 1, characterized in that, before mixing CO2 with the non-acidic cleaning solution, the pH of the non-acidic cleaning solution in the crystallizer or evaporator is greater than 7, and in that, after mixing CO2 with the non-acidic cleaning solution and converting lithium carbonate scale into lithium bicarbonate, the pH of the non-acidic cleaning solution is reduced to approximately 7-9. Petition 870250086975, dated 09 / 25 / 2025, p. 28 / 30 2 / 3 3. Process according to claim 1, characterized in that it is implemented as a batch process, wherein the non-acidic cleaning solution remains in the crystallizer or evaporator for a selected period of time and, during the selected period of time, the non-acidic cleaning solution is circulated through the evaporator or crystallizer; and, during the batch process, CO2 is added continuously until the lithium carbonate scale is converted into lithium bicarbonate.

4. Process according to claim 3, characterized in that the non-acidic cleaning solution initially assumes a pH of approximately 12 in the evaporator or crystallizer.

5. Process for removing lithium carbonate scale from equipment surfaces, characterized in that it comprises: directing a non-acidic cleaning solution having a temperature below 50°C into the equipment and into contact with the lithium carbonate scale formed on the equipment surfaces; wherein the non-acidic cleaning solution is water or an aqueous solution; circulating the non-acidic cleaning solution through the equipment; converting the lithium carbonate scale into lithium bicarbonate by mixing CO2 with the non-acidic cleaning solution; wherein the conversion of the lithium carbonate scale into lithium bicarbonate results in the dissolution of the lithium bicarbonate in the non-acidic cleaning solution; and discharging the non-acidic cleaning solution containing the dissolved lithium bicarbonate from the equipment.

6. Process according to claim 5, characterized in that, initially, the non-acidic cleaning solution after contact with lithium carbonate scale has a pH greater than 9; and in that the conversion of lithium carbonate scale into lithium bicarbonate by mixing CO2 with the non-acidic cleaning solution reduces the pH of the non-acidic cleaning solution to approximately 7-9.

7. Process according to claim 5, characterized in that it includes mixing sufficient CO2 with the non-acidic cleaning solution to reduce the pH of the non-acidic cleaning solution to approximately 7-9.

8. Process for removing lithium carbonate scale from equipment surfaces, characterized in that it comprises: directing a non-acidic cleaning solution in the form of water or an aqueous solution into the equipment and into contact with the lithium carbonate scale formed on the equipment surfaces, resulting in a pH of the non-acidic cleaning solution being greater than 9; converting the lithium carbonate scale into lithium bicarbonate by mixing CO2 with the non-acidic cleaning solution and reducing the pH of the non-acidic cleaning solution to approximately 7-9; wherein the conversion of the lithium carbonate scale into lithium bicarbonate results in the dissolution of the lithium bicarbonate in the non-acidic cleaning solution; and discharging the non-acidic cleaning solution containing the dissolved lithium bicarbonate from the equipment.

9. Process according to claim 8, characterized in that the removal of lithium carbonate scale from equipment surfaces is implemented without the use of acid.

10. Process according to claim 8, characterized in that, during the process of removing lithium carbonate scale from the equipment surfaces, the temperature of the cleaning solution is maintained below 50°C. Petition 870250086975, dated 09 / 25 / 2025, page 30 / 30

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