Process for generating a zero liquid discharge waste and improving lithium recovery in lithium production plants

Abstract

The present invention entails a process for converting a lithium hydroxide brine to lithium carbonate in a manner that results in a zero liquid discharge. Essentially, the process entails a closed loop that includes a carbonation reactor and an evaporative crystallizer. Through a carbonation process, the lithium hydroxide brine yields lithium carbonate leaving a liquid stream that includes lithium and carbonate. After pH adjustments, the liquid stream is directed into the evaporative crystallizer that concentrates the liquid stream. The concentrate is directed to a solids-liquid separator that produces a wet cake and a lithium-rich stream that is mixed with the lithium hydroxide brine to yield additional lithium carbonate that can be introduced into a lithium recovery plant.

Description

[0001] PROCESS FOR GENERATING A ZERO LIQUID DISCHARGE WASTE AND IMPROVING LITHIUM RECOVERY IN LITHIUM PRODUCTION PLANTS

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to systems and processes for recovering lithium from lithium sources, and more particularly to systems and processes for minimizing or reducing the production of liquid waste in the course of lithium recovery.

[0004] BACKGROUND OF THE INVENTION

[0005] Some lithium recovery processes entail converting a lithium carbonate brine to lithium hydroxide crystals. In the course of this process, a lithium hydroxide brine concentrated in impurities is typically produced. To recover lithium from the lithium hydroxide brine, some processes subject the lithium hydroxide brine to a carbonation process which converts some of the lithium of the lithium hydroxide brine to lithium carbonate that can be directed back into the lithium recovery plant to produce the lithium hydroxide crystals. However, a typical carbonation process produces significant liquid waste. Liquid discharge during the process for recovering lithium from lithium hydroxide brine presents several environmental and operational challenges. When large volumes of liquid containing brine are processed, the liquid discharge typically contains various contaminants, such as heavy metals, salts and other chemicals. If not properly treated, these contaminants can pollute nearby water sources, harming aquatic ecosystems and additionally discharging untreated or inadequately treated liquid can lead to regulatory violations, resulting in fines or delays. From an operational perspective, managing and disposing of wastewater is costly, requiring complex treatment systems and processes to meet environmental standards. This not only increases the overall cost of the lithium recovery process, but also diminishes the sustainability of the operation. Moreover, the disposal of liquid effluent can contribute to water depletion, particularly in water scarce regions.

[0006] SUMMARY OF THE INVENTION

[0007] The present invention relates to a lithium recovery system and process that entails converting a lithium hydroxide brine to lithium carbonate and doing so while minimizing or limiting a liquid discharge. Lithium hydroxide brine is mixed with carbon dioxide in a carbonation reactor to form a solution containing lithium and carbonate. Lithium carbonate is precipitated from the solution and removed from the solution through a solids-liquid separator, leaving a liquid stream containing lithium and carbonate. The lithium carbonate can then be re-introduced into the lithium recovery plant. Carbonate in the liquid stream is then converted to carbon dioxide through a pH adjustment. Resulting carbon dioxide is stripped from the liquid stream. Thereafter, the pH of the liquid stream is adjusted upwardly and subjected to an evaporative crystallization process. This produces a concentrate containing solids (such as salts) and a lithium-rich solution. Concentrate is purged from the evaporative crystallizer and the solids therein are separated from the lithium-rich solution to form wet cake. The lithium-rich solution is directed into the carbonation reactor or another carbonation reactor where it is mixed with the lithium hydroxide brine and the carbon dioxide. Hence, the mixing of the lithium hydroxide brine, lithium-rich solution and carbon dioxide results in the production of the lithium carbonate that can be separated and re-introduced to the lithium recovery plant. Thus, impurities in the lithium hydroxide brine are removed as wet cake through a closed loop process including at least one carbonation reactor and the evaporative crystallizer while maintaining a zero or near zero liquid discharge.

[0008] In another embodiment of the present invention, the above discussed carbonation- evaporative crystallizer process with zero liquid discharge is incorporated into a lithium recovery plant. Here, a lithium hydroxide brine is produced from a lithium source. Impurities are removed from the lithium hydroxide brine. Thereafter, the lithium hydroxide brine is directed into a lithium hydroxide crystallizer (for example, a lithium hydroxide monohydrate (LIOH.H2O) crystallizer that yields lithium hydroxide crystals and a lithium hydroxide brine. To recover residual lithium from the lithium hydroxide brine, the process entails subjecting the lithium hydroxide brine to the closed loop carbonation process discussed above which ultimately converts some of the lithium in the lithium hydroxide brine to lithium carbonate which is introduced into the lithium recovery plant while the process of converting the lithium hydroxide brine to lithium carbonate yields a zero or near zero liquid discharge.

[0009] Other objects and advantages of the present invention will become apparent and obvious from a study of the following description and the accompanying drawings which are merely illustrative of the invention.

[0010] DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a schematic illustration of a process for recovering lithium carbonate from a lithium hydroxide brine while yielding a zero or near zero liquid discharge.

[0012] Figure 2 is a schematic illustration of an alternate process for recovering lithium carbonate from a lithium hydroxide brine while yielding a zero or near zero liquid discharge.

[0013] Figure 3 is a schematic illustration of a lithium recovery plant incorporating the process of Figure 1. DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0014] The present invention relates to a zero or near zero liquid discharge process employed in a lithium recovery plant for recovering lithium carbonate from a lithium hydroxide brine produced in a lithium hydroxide monohydrate crystallizer. Once recovered, the lithium carbonate is re-introduced into a lithium recovery plant.

[0015] Figure 1 depicts a lithium hydroxide brine being directed into a carbonation reactor 10. Carbon dioxide (CO2) gas is reacted with the lithium hydroxide brine in the carbonation reactor 10. Lithium carbonate (LI2CO3) is precipitated from the lithium hydroxide brine. The lithium hydroxide brine and precipitated lithium carbonate are directed to a solids-liquid separator 12 which separates the lithium carbonate (solids) and yields a liquid stream 14 containing lithium and carbonate.

[0016] Liquid stream 14 is directed into a mixing tank 16. Here, the pH of the liquid stream is reduced, in one example to 4.5 or below, by mixing an acidic reagent such as hydrogen chloride (HCI) with the liquid stream. As indicated in Figure 1 , the hydrogen chloride can be provided from a hydrogen chloride source or provided from spent ion exchange waste which may contain lithium. By lowering the pH of the liquid stream 14, carbonate in solution is converted to carbon dioxide. Liquid stream 14 now containing carbon dioxide is directed from the mixing tank 16 through line 18 and through a heat exchanger 20 which pre-heats the liquid stream. From the heat exchanger 20, the liquid stream containing carbon dioxide is directed to a decarbonator 22 which strips the carbon dioxide from the liquid stream.

[0017] From the decarbonator 22, the liquid stream 14 is directed into an evaporative crystallizer 24. An alkaline reagent is reacted with the liquid stream 14 in the evaporative crystallizer 24. In the example shown in Figure 1 , sodium hydroxide (NaOH) is directed through line 28 into the evaporative crystallizer 24 and mixed with the liquid stream. Sodium hydroxide can be provided from a sodium hydroxide source or could be provided as spent sodium hydroxide from an ion exchange regeneration process. By adding sodium hydroxide to the liquid stream, this adds a sodium source and at the same time raises the pH of the liquid stream. In one example, sufficient sodium hydroxide is added to raise the pH of the liquid stream to 10 or higher.

[0018] In the evaporative crystallizer 24, water is evaporated and recovered and the recovered water is directed through line 30 and through the heat exchanger 20 which as pointed out above pre-heats the liquid stream 14 prior to entering the evaporative crystallizer. As noted above, the sodium hydroxide elevates the pH of the liquid stream in the evaporative crystallizer 24 and at the same time provides a sodium source that facilitates the crystallization of salts. As the liquid stream is concentrated, salts (for example, sodium chloride, sodium sulfate, glaserite, etc.) crystallize. The majority of the lithium remains in solution. Concentration is limited to prevent high lithium loss due to significant co- precipitation of lithium salts. This can be implemented in various ways. For example, once the solids are separated from the concentrated liquid stream, a portion or all of that liquid stream can be purged from the crystallizer to the carbonation reactor. The boiling point rise and laboratory analysis can be monitored to determine the proper rate at which to purge.

[0019] Concentrate in the evaporative crystallizer 24 is purged and directed to a solids-liquid separator 32. While various types of solids-liquid separators can be employed, in the example discussed here the crystallized salts are separated by a centrifuge. Separated salts are typically in the form of waste cake and represent the discharge of a “zero liquid discharge” (ZLD) facility. The filtrate or liquid produced by the solids-liquid separator 32 is a lithium-rich stream. This lithium-rich stream is directed through line 34 into the carbonation reactor 10 where it is mixed with the lithium hydroxide brine and carbon dioxide to yield the lithium carbonate that is separated and removed from the process as a solid in the solids- liquid separator 12.

[0020] Thus, it is seen that the carbonation reactor 10 and the evaporative crystallizer 24 function in a closed loop process to convert the lithium hydroxide brine to lithium carbonate which can introduce or re-introduced into a lithium recovery plant. By employing the evaporative crystallizer 24 with a carbonation reactor 10, all or substantially all of the waste produced in the course of converting the lithium hydroxide brine to lithium carbonate is removed from the process in the form of waste cake (crystallized salts). This gives rise to a zero or near zero liquid discharge process.

[0021] While the process described above and illustrated in Figure 1 includes a single carbonation reactor 10, it should be understood that a second carbonation reactor could be incorporated into the process. For example, the lithium-rich stream in line 34 could be directed to a second carbonation reactor where it is mixed with carbon dioxide to produce lithium carbonate, which again could be re-introduced into the lithium recovery plant. This means that the lithium-rich stream does not necessarily have to be returned to the carbonation reactor 10, but could be returned to another carbonation reactor. This is illustrated in Figure 2 of the alternate embodiment. As seen in Figure 2, the lithium-rich stream in line 34 is directed to a second carbonation reactor 10A where it is mixed with carbon dioxide. This produces lithium carbonate that is precipitated and separated by the solids-liquid separator 12A. This produces a second liquid stream that is directed through line 14A to the mixing tank 16 where it is mixed with the liquid stream passing in line 14 to the mixing tank 16.

[0022] Figure 3 shows an exemplary process where the process of Figure 1 and described above is integrated with a lithium recovery plant indicated generally by the numeral 40. Detailed discussions of an overall lithium recovery process is unnecessary, but a general discussion of exemplary processes carried out in a lithium recovery process and how the process of Figure 1 integrates into an overall lithium recovery process may be helpful. It is understood and appreciated by those skilled in the art that the process shown in Figure 1 and described above can be integrated into various lithium recovery processes found in lithium recovery plants.

[0023] In one exemplary lithium recovery process, a lithium-containing brine is recovered from a lithium source and through various chemical and physical processes, the lithium- containing brine is converted to a lithium carbonate (solids). Lithium carbonate and lime are mixed in a lithium conversion unit as depicted in Figure 2 and the effluent from the lithium conversion unit is directed to a lithium hydroxide brine purification unit where certain impurities, such as calcium and magnesium, are precipitated from the lithium hydroxide brine.

[0024] The lithium hydroxide brine is then directed into a lithium hydroxide monohydrate crystallizer which concentrates the lithium hydroxide brine to form a concentrate that includes lithium hydroxide monohydrate (LiOH«H2O) crystals. The lithium hydroxide monohydrate crystals are separated from the concentrate and subjected to a drying and packaging process, as indicated in Figure 2, which produces lithium hydroxide monohydrate crystals.

[0025] A portion of the concentrate produced by the lithium hydroxide monohydrate crystallizer is purged. The purge includes lithium and various salts and impurities and is generally referred to as a lithium hydroxide brine. This lithium hydroxide brine is directed from the lithium hydroxide monohydrate crystallizer in the lithium recovery plant to the carbonation reactor 10. As discussed above, lithium hydroxide brine is mixed with carbon dioxide in the carbonation reactor 10 which results in the precipitation of lithium carbonate which is separated from the resulting liquid stream 14 by the solids-liquid separator 12. The separated lithium carbonate (solids) is then re-introduced into the lithium recovery plant by directing the lithium carbonate into the lithium conversion unit shown in Figure 2. The liquid stream resulting from the separation that occurred with the solids-liquid separator 12 is treated in the mixing tank 16 and the evaporative crystallizer 24 as described above with respect to the system and process shown in Figure 1 .

[0026] Here, the present invention presents a zero liquid discharge process for recovering lithium carbonate from a lithium hydroxide brine. Without the process depicted in Figure 1 , conventional processes for recovering lithium carbonate from a lithium hydroxide brine typically produces a significant liquid discharge. The present process recovers lithium that would be lost in other conventional processes that convert lithium hydroxide brine to lithium carbonate. In addition, the acid (HCI) and caustic (NaOH) serve as potential outlets for waste generated by ion exchange regeneration within the lithium recovery plant. Finally, the evaporative crystallizer 24 recovers water that can be reused in the lithium recovery plant. This provides for the efficient use of water and reduces or minimizes the need for an external water source. This is especially important in areas where there is a scarce amount of water available.

[0027] The present invention may, of course, be carried out in other specific ways than those herein set forth without departing from the scope and the essential characteristics of the invention. The present embodiments disclosed herein are therefore to be construed in all respects as illustrative and not restrictive and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.

Claims

CLAIMSWhat is claimed is:1 . A process for recovering lithium from a lithium source in a lithium recovery plant, comprising: a. producing a lithium hydroxide brine from the lithium source; b. removing impurities from the lithium hydroxide brine; c. concentrating and crystallizing the lithium hydroxide brine to form lithium hydroxide crystals and a concentrated lithium hydroxide brine; d. drying the lithium hydroxide crystals; e. recovering lithium carbonate from the concentrated lithium hydroxide brine while limiting liquid discharge by: i. mixing carbon dioxide with the concentrated lithium hydroxide brine in a carbonation reactor to form the lithium carbonate; ii. precipitating the lithium carbonate from the concentrated lithium hydroxide brine in the carbonation reactor; iii. separating the lithium carbonate from the concentrated lithium hydroxide brine which yields a liquid stream containing lithium and carbonate; iv. introducing the separated lithium carbonate into the lithium recovery plant; v. reducing the pH of the liquid stream, converting at least some of the carbonate in the liquid stream to carbon dioxide, and stripping the carbon dioxide from the liquid stream; vi. raising the pH of the liquid stream; vii. directing the liquid stream containing the lithium to an evaporative crystallizer; viii. concentrating the liquid stream in the evaporative crystallizer to form a concentrate containing solids and lithium; ix. subjecting the concentrate to a solids-liquid separator and producing a wet cake and a lithium-rich stream and in the process producing a zero liquid discharge in the course of converting the lithium hydroxide brine to lithium carbonate; and x. directing the lithium-rich stream to the lithium carbonation reactor or other carbonation reactor and recovering additional lithium carbonate.

2. The process of claim 1 wherein the carbonation reactor or the other carbonation reactor and the evaporative crystallizer are disposed in a process loop that continuouslyreceives the lithium hydroxide brine and produces lithium carbonate while the liquid stream flows in one part of the process loop and the lithium-rich stream flows in another part of the process loop.

3. The process of claim 1 wherein reducing the pH of the liquid stream includes mixing an acidic reagent with the liquid stream at a point downstream from the carbonation reactor, and wherein raising the pH of the liquid stream occurs downstream of a point where the carbon dioxide is stripped from the liquid stream.

4. The method of claim 3 wherein the pH of the liquid stream is raised in the evaporative crystallizer or upstream of the evaporative crystallizer by mixing an alkaline reagent with the liquid stream.

5. The process of claim 1 wherein reducing the pH of the liquid stream includes reducing the pH to 4.5 or less, and wherein increasing the pH of the liquid stream includes increasing the pH to 8 or higher.

6. A process for recovering lithium from a lithium hydroxide brine while limiting the discharge of liquid from the process, the process comprising: mixing carbon dioxide with the lithium hydroxide brine in a carbonation reactor; precipitating lithium carbonate from the lithium hydroxide brine; subjecting the lithium hydroxide brine to a solids-liquid separator and separating the lithium carbonate from the lithium hydroxide brine and yielding a liquid stream containing lithium and carbonate; reducing the pH of the liquid stream, converting at least some carbonate in the liquid stream to carbon dioxide, and stripping the carbon dioxide from the liquid stream; raising the pH of the liquid stream; directing the liquid stream containing the lithium to an evaporative crystallizer; concentrating the liquid stream in the evaporative crystallizer to form a concentrate containing solids and lithium; subjecting the concentrate to a solids-liquid separator and producing a wet cake and a lithium-rich stream; and mixing the lithium-rich stream with the lithium hydroxide brine and carbon dioxide in the carbonation reactor to form lithium carbonate, or mixing the lithium-rich stream with carbon dioxide in a second carbonation reactor.

7. The process of claim 6 wherein the pH of the liquid stream is raised in the evaporative crystallizer or upstream of the evaporative crystallizer.

8. The process of claim 6 including mixing sodium hydroxide with the liquid stream upstream of the evaporative crystallizer and / or mixing sodium hydroxide with the liquid stream in the evaporative crystallizer.

9. The process of claim 6 wherein reducing the pH of the liquid stream includes reducing the pH to 4.5 or less, and wherein increasing the pH of the liquid stream includes increasing the pH of the liquid stream to 8 or higher.

10. The process of claim 6 wherein the lithium carbonate produced by the process is directed into a lithium processing plant.11 . The process of claim 6 wherein the evaporative crystallizer acts as a water recovery device.

12. The process of claim 6 wherein the concentration of lithium in the evaporative crystallizer is limited to prevent lithium loss due to co-precipitation of lithium salts.

13. The process of claim 6 including a mixing tank connected between the carbonation reactor and the evaporative crystallizer, and wherein an acid reagent is mixed with the liquid stream in the mixing tank to reduce the pH of the liquid stream and to convert carbonate in the liquid stream to carbon dioxide.

14. The process of claim 6 wherein the carbonation reactor and evaporative crystallizer are disposed in a process loop that continuously receives the lithium hydroxide brine and yields lithium carbonate while the liquid stream flows in one part of the process loop and the lithium-rich stream flows in another part of the process loop.

15. The process of claim 6 wherein the carbonation reactor is a primary outlet for the lithium carbonate while the evaporative crystallizer concentrates lithium upstream of the carbonation reactor and acts as a water recovery device and the outlet of a waste in the form of the wet cake.

16. The process of claim 6 wherein the lithium-rich stream is mixed with carbon dioxide in the second carbonation reactor, and wherein the process includes precipitating lithium carbonate in the second carbonation reactor and separating the precipitated lithium carbonate and producing a second liquid stream that is mixed with the liquid stream.

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