Process and system for preparing lithium carbonate

Abstract

A process and system for preparing high-purity (e.g., battery-grade) lithium carbonate from a lithium-containing brine. Lithium carbonate seed crystals are first mixed with the lithium-containing brine to produce a first slurry. The first slurry reacts with a sodium carbonate solution to produce a second slurry. Lithium carbonate solids are separated from the second slurry and washed with pure water using a suitable process such as centrifugation. A portion of the washed lithium carbonate may be recycled as the seed lithium carbonate crystals.

Description

PROCESS AND SYSTEM FOR PREPARING LITHIUM CARBONATECROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to United States provisional patent application no. 63 / 620,467, filed on January 12, 2024, and entitled “Process and System for Lithium Carbonate”, the entirety of which is hereby incorporated by reference herein.TECHNICAL FIELD

[0002] The present disclosure relates to systems, processes, and techniques for preparing lithium carbonate (TUCCL). More particularly, the present disclosure relates to preparing high- purity (e.g., battery-grade) lithium carbonate from a lithium-containing brine through a reaction that does not require a carbon dioxide carbonization-decomposition process.BACKGROUND

[0003] Lithium carbonate is a core raw ingredient for making cathode active materials of lithium-ion batteries, which have strict purity requirements for materials used in their manufacture. Impurities in the lithium carbonate used in lithium-ion batteries may lead to poor charging performance of the batteries and poor long-term battery health. An example specification for battery-grade lithium carbonate is shown in Table 1.Table 1: Specification for battery-grade lithium carbonateSUMMARY

[0004] According to a first aspect, there is provided a process for preparing lithium carbonate from a lithium-containing brine, the process comprising: mixing the lithium-containing brine with lithium carbonate seed crystals to produce a first slurry; reacting the first slurry with a sodium carbonate solution to produce a second slurry; separating lithium carbonate solids from the second slurry; and washing the separated lithium carbonate solids with a pure water to produce washed lithium carbonate solids, wherein the pure water has a total dissolved solids concentration of less than 10 mg / L.

[0005] A concentration of the lithium carbonate seed crystals in the lithium-containing brine may be at least 50 g / L.

[0006] The process may further comprise recycling a portion of the washed lithium carbonate solids as the lithium carbonate seed crystals.

[0007] The process may further comprise controlling lithium concentration to be within 10 - 25 g / L in the lithium-containing brine by adjusting an amount of water in the lithium-containing brine before the lithium-containing brine is mixed with the lithium carbonate seed crystals.

[0008] The separating and the washing of lithium carbonate solids may use either a peeler centrifuge or a pusher centrifuge.

[0009] The reacting of the first slurry with the sodium carbonate solution may be performed by directing the first slurry and the sodium carbonate solution into a first reactor through a slurry inlet of the first reactor and a solution inlet of the first reactor that is below the slurry inlet, respectively.

[0010] The reacting of the first slurry with the sodium carbonate solution may comprise: mixing 60% to 80% of a total of the first slurry and the sodium carbonate solution in the first reactor; mixing 20% to 40% of the total of the first slurry and the sodium carbonate solution in a second reactor fluidly coupled to, and downstream of, the first reactor; and transferring the second slurry resulting from the mixing in the first reactor to the second reactor, wherein the separating is performed on the second slurry transferred to the second reactor from the first reactor and on the second slurry resulting from the mixing in the second reactor.

[0011] The reacting may occur within a temperature range of approximately 80 °C to approximately 95 °C.

[0012] According to another aspect, there is provided a system for preparing lithium carbonate from a lithium-containing brine, the system comprising: a mixing container configured to receive and mix the lithium-containing brine and lithium carbonate seed crystals to produce a first slurry; a reactor unit fluidly coupled to the mixing container, wherein the reactor unit is configured to receive the first slurry from the mixing container and a sodium carbonate solution, and to react the first slurry and the sodium carbonate solution together to produce a second slurry; and a solids-liquid separator fluidly coupled to the reactor unit, wherein the solids-liquid separator is configured to receive the second slurry and to separate lithium carbonate solids from the second slurry, and to receive a pure water after the separating of the lithium carbonate solids to wash the separated lithium carbonate solids to produce washed lithium carbonate solids, wherein the pure water has a total dissolved solids concentration of less than 10 mg / L.

[0013] The system may further comprise a return conduit fluidly coupling the solids-liquid separator to the mixing container to permit recycling of a portion of the washed lithium carbonate solids as the lithium carbonate seed crystals.

[0014] The solids-liquid separator may be either a peeler centrifuge or a pusher centrifuge.

[0015] The reactor unit may comprise a slurry inlet for the first slurry and a solution inlet for the sodium carbonate solution, and the solution inlet may be positioned below the slurry inlet.

[0016] The reactor unit may comprise a first reactor and a second reactor that is fluidly coupled to and positioned downstream of the first reactor, wherein the slurry inlet and the solution inlet comprise part of the first reactor, and wherein the second reactor is fluidly coupled to the mixing container to receive a portion of the first slurry therefrom without the portion of the first slurry having passed through the first reactor.

[0017] The reactor unit may be configured to be maintained at a temperature range of approximately 80 °C to approximately 95 °C when the first slurry and the sodium carbonate solution are being reacted to produce the second slurry.

[0018] This summary does not necessarily describe the entire scope of all aspects. Other aspects, features and advantages will be apparent to those of ordinary skill in the art upon review of the following description of specific embodiments.BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In the accompanying drawings, which illustrate one or more example embodiments:

[0020] FIGS. 1 and 2 are schematic diagrams illustrating systems for preparing lithium carbonate, according to example embodiments.

[0021] For the sake of clarity, not every component is labeled, nor is every component of each embodiment shown where illustration is unnecessary to allow those of ordinary skill in the art to understand the embodiments described herein.DETAILED DESCRIPTION

[0022] Lithium is generally first recovered as a lithium-containing brine either from brine lakers (e.g., Salar) or mineral deposits (e.g., Spodumene ore) for producing lithium products such as lithium carbonate and lithium hydroxide monohydrate. The lithium-containing brine has other impurities such as calcium, magnesium, sodium, chloride, and sulfate ions. When lithium carbonate is prepared through reacting a lithium-containing brine with sodium carbonate solution, impurity ions may become entrapped in crude lithium carbonate solids through physical adsorption onto lithium carbonate particles or incorporation into lithium carbonate crystal lattices, leading to a crude product containing the entrapped impurities. High-purity (e.g., battery-grade) lithium carbonate is generally prepared through further purifying the crude lithium carbonate solids through a carbon dioxide carbonization-decomposition process that includes 1) reacting the crude lithium carbonate with carbon dioxide and water to produce a lithium bicarbonate solution, 2) removing calcium and magnesium impurities in the lithium bicarbonate solution through filtration and chelating ion exchange, and 3) decomposing the lithium bicarbonate under an increased solution temperature to produce a high-purity lithium carbonate product. This existing preparation process for high-purity lithium carbonate involves too many purification steps and has disadvantages of low yield and high production cost. At least some example embodiments disclosed herein provide systems and methods to prepare high-purity (e.g., battery-grade) lithiumcarbonate from a lithium-containing brine through a reaction that does not require a carbon dioxide carbonization-decomposition process, which is a primary driver of the yield and production cost issues.

[0023] FIG. 1 illustrates, according to one example embodiment, a system 100 for preparing lithium carbonate from a lithium-containing brine. The system 100 comprises: i) a mixing container 110 configured to receive and mix the lithium-containing brine and lithium carbonate seed crystals to produce a first slurry; ii) a reactor unit 120, fluidly coupled to the mixing container 110, configured to receive and react the first slurry and a sodium carbonate solution to produce a second slurry; and iii) a solids-liquid separator 130 configured to receive the second slurry and to separate lithium carbonate solids from the second slurry, and to receive a pure water after the separating of lithium carbonate solids to wash the separated lithium carbonate solids to produce washed lithium carbonate solids. As used herein, a “pure water” refers to any water with a total dissolved solids concentration of less than 10 mg / L.

[0024] The system 100 may further comprise a return conduit 133 to recycle a portion of the washed lithium carbonate solids as the lithium carbonate seed crystals, and one or more pretreatment units (not shown in FIG. 1) to purify and concentrate the lithium-containing brine. The one or more pretreatment units may comprise, for example, one or more reverse osmosis, evaporator and ion exchange units.

[0025] The mixing container 110 may comprise, for example, a tank with a stirrer and / or a pipe capable of providing in-line slurry mixing. For example, the lithium-containing brine and the lithium carbonate seed crystals may both be fed into a pipe in which the fluid therein experiences sufficient turbulent flow to mix the lithium-containing brine and lithium carbonate seed crystals to result in the second slurry.

[0026] As shown in FIG. 1, the reactor unit 120 comprises at least a first reactor 120a comprising a slurry inlet 121 for receiving the first slurry and a solution inlet 123 for receiving the sodium carbonate solution. The solution inlet 123 in FIG. 1 is positioned below the slurry inlet 121. Positioning the solution inlet 123 below the slurry inlet 121 enhances the growth of lithium carbonate solids from the lithium carbonate seed crystals while the first slurry and the sodiumcarbonate solution are reacting, as compared to positioning them at the same level or positioning the solution inlet 123 above the slurry inlet 121.

[0027] The solids-liquid separator 130 may comprise any suitable type of centrifuge, such as any one or more of a peeler centrifuge, a pusher centrifuge, or a decanter centrifuge. For example, when considering the same amount of pure water for use in lithium carbonate washing, each of the peeler and pusher centrifuges does a better job of lithium carbonate washing than the decanter centrifuge. More particularly, in comparison to a decanter centrifuge, lithium carbonate washed using the peeler / pusher centrifuge may have 80% fewer sodium chloride impurities than lithium carbonate washed with a decanter centrifuge. This can make lithium carbonate washed using a peeler or pusher centrifuge better suited for use as recycled lithium carbonate seed crystals and as a final lithium carbonate product.

[0028] According to at least some embodiments and with reference to FIG. 1, a process for preparing lithium carbonate from a lithium-containing brine comprises: i) mixing the lithium-containing brine with lithium carbonate seed crystals to produce a first slurry; ii) reacting the first slurry with a sodium carbonate solution to produce a second slurry; iii) separating lithium carbonate solids from the second slurry; and iv) washing the separated lithium carbonate solids with pure water to produce washed lithium carbonate solids.

[0029] According to at least some embodiments, the process further comprises recycling a portion of the washed lithium carbonate solids as the lithium carbonate seed crystals. The concentration of the lithium carbonate seed crystals in the first slurry may be at least 50 g / L.

[0030] According to at least some embodiments, the process further comprises controlling lithium content to be within a range of 10 - 25 g / L (inclusive of 10 and 25 g / L) in the lithium- containing brine through either of removing water from, or adding water to, the lithium-containing brine prior to being mixed with the lithium carbonate seed crystals. For example, at a reaction temperature of 80 - 90 °C, lithium carbonate conversion yield is less than 80% when the lithium content in the lithium-containing brine is less than 10 g / L, and the final lithium carbonate product does not qualify as battery -grade even after extensive washing. Analogously, the lithium carbonateproduct requires additional purification through carbon dioxide carbonization-decomposition to qualify as battery-grade when the lithium content in the lithium-containing brine is more than 25g / L. More generally, in at least some embodiments maintaining a reaction temperature of between approximately 80 °C - 95 °C helps to result in high yield given the solubility of lithium carbonate tends to decrease with temperature. Reactor temperature may be controlled by heating the reactor using a heater or other kind of heat exchanger to the desired temperature setpoint, and maintaining the reactor at that temperature using, for example, insulation.

[0031] When operating the system 100 to prepare lithium carbonate, a lithium-containing brine is fed via conduit 101 to the system 100 and the mixing container 110. The lithium-containing brine may be produced from brine lakes (e.g., Salar), geothermal brines, produced waters resulting from oil / gas production, or produced using mineral deposits (e.g., Spodumene ore). For example, Spodumene ore may be crushed and roasted, and the lithium therein may be leached into an acidic solution to produce a lithium brine. The lithium concentration in the lithium-containing brine is measured and controlled to be within the range of 10 - 25 g / L (inclusive of endpoints) by removing water from and / or adding water to the lithium-containing brine prior to the brine reaching the mixing container 110. The lithium-containing brine is mixed with lithium carbonate seed crystals within the mixing container 110 to produce the first slurry. The first slurry is directed via conduit 102 to the reaction unit 120, and enters the reaction unit 120 via the slurry inlet 121; in FIG. 1, the reaction unit 120 comprises the first reactor 120a.

[0032] The sodium carbonate solution is directed via conduit 122 to the first reactor 120a and enters the first reactor 120a via its solution inlet 123. A portion of lithium from the lithium- containing brine in the first slurry is converted into lithium carbonate by reacting the dissolved lithium in the brine with the sodium carbonate delivered via the sodium carbonate solution. During this reaction, the lithium carbonate seed crystals act as nucleates for the second slurry. Mixing the lithium carbonate seed crystals with the lithium-containing brine to form the first slurry in the mixing container 110 and prior to the reaction that generates the second slurry in the first reactor 120a forces the lithium ions from the lithium-containing brine and the lithium carbonate seed crystals to contact each other, and promotes the growth of lithium carbonate solids on to the lithium carbonate seed crystals. The lithium carbonate seed crystals accordingly act as a preferential site on which lithium carbonate may precipitate, in contrast to on tank walls, for example. The secondslurry from the first reactor 120a is directed via conduit 126 to the solids-liquid separator 130. Either a peeler centrifuge or a pusher centrifuge is used to separate the lithium carbonate solids from the second slurry. Removing the lithium carbonate solids from the second slurry produces a mother liquor, which is discharged via conduit 132 out of the solids-liquid separator 130. A pure water is directed via conduit 131 to the separator 130 to wash the separated lithium carbonate solids, producing washed lithium carbonate solids and a used water. The used water is also discharged via conduit 132, and may be recycled (not shown in FIG. 1) for making the sodium carbonate solution or producing the lithium-containing brine. A portion of the washed lithium carbonate solids is recycled via conduit 133 as the lithium carbonate seed crystals for depositing into the mixing container 110 to generate the first slurry. The residual portion of the washed lithium carbonate is directed via conduit 134 to another washing process (not shown in FIG. 1) that is downstream of the system 100 to result in production of battery-grade lithium products. This additional washing process may comprise, for example, any one or more of a slurry wash where the solids are suspended in a tank of clean water to wash out the impurities within the lithium carbonate solids, then are transferred to another pusher or peeler centrifuge for separation of solids and liquids, and then a final in-situ wash of the lithium carbonate solids may be performed in the centrifuge.

[0033] FIG. 2 illustrates, according to another example embodiment, a system 200 for preparing lithium carbonate from a lithium-containing brine. The system 200 of FIG. 2 has the same configuration as the system 100 of FIG. 1, except that the reaction unit 120 further comprises a second reactor 120b fluidly coupled to, and downstream of, the first reactor 120a. The second reactor 120b is fluidly coupled between the first reactor 120a and the solids-liquid separator 130 such that the second slurry exiting the second reactor 120b is delivered to the solids-liquid separator 130. During operation of the system 200, 60% - 80% of the first slurry exiting the mixing container 110 and sodium carbonate solution are directed to the first reactor 120a via conduits 102 and 122, respectively, and the remainder (20% - 40%) is directed to the second reactor 120b via conduits 103 and 125, respectively. Conduit 124 fluidly coupling the first and second reactors 120a, b together is used to deliver the second slurry from the first reactor 120a to the second reactor 120b, for eventual delivery to the solids-liquid separator 130.

[0034] Using multiple reactors can be beneficial by increasing reaction time (i.e., multiple reactors facilitate increased residence time of the reactants) and by permitting a slower dosing regimen that gives lithium carbonate crystals the opportunity to grow more slowly to achieve a certain size. In at least some embodiments, the increased residence time may permit larger crystals to be grown than when a single reactor is used despite the slower crystal growth rate. A slower crystal growth rate may also decrease the likelihood that impurities will become entrapped in the crystal.

[0035] Certain embodiments are further illustrated in the following examples. It is however to be understood that these examples are for illustrative purposes only and are not to be used to limit the scope of the present disclosure in any manner.EXAMPLESExample 1 : Preparation of Lithium Carbonate

[0036] 50 L of a synthetic lithium-containing brine comprising 18 g / L lithium, 60 g / L Na, and 183.8 g / L Cl is prepared from lithium chloride and sodium chloride. The lithium-containing brine was mixed with 2.5 kg of lithium carbonate seed crystals to form the first slurry. The first slurry was fed to a reactor through an upper level inlet of the reactor and was heated to 80 °C. 29.7 L of 280 g / L sodium carbonate solution at 40°C was fed to the reactor through a lower level inlet. The first slurry reacted with sodium carbonate in the reactor at around 80 °C with a residence time of 2 hr to form the second slurry. The second slurry was separated into lithium carbonate solids and a mother liquor using a peeler centrifuge acting as the solids-liquid separator 130. The mother liquor was discharged from the peeler centrifuge. The lithium carbonate solids were then washed within the peeler centrifuge by rinsing the centrifuged cake using 2 L of hot (around 80 °C) pure water to produce washed lithium carbonate solids. A portion of the washed lithium carbonate was saved as seeds for further production of the first slurry and lithium carbonate solids. The residual portion of the washed lithium carbonate was further washed using hot pure water through a process comprising resuspending the washed lithium carbonate in hot pure water, then centrifugation, then rinsing, then centrifugation, then rinsing, and then centrifugation. The final washed lithium carbonate solids were dried at 150 °C. The dried lithium carbonate final product (Li2COs) wasabout 99.72% pure by weight, and had a concentration of Na of about 80 ppm and of Cl of about 15 ppm.Example 2: Preparation of Lithium Carbonate

[0037] Lithium carbonate was prepared in a process similar to Example 1 except that a synthetic lithium-containing brine, the seed crystals and the sodium carbonate solution were mixed directly to prepare a lithium carbonate slurry without pre-mixing the synthetic lithium-containing brine and the seed crystals for a first slurry. The dried lithium carbonate final product (L^CCL) was about 99.29% pure by weight, and had a concentration of Na of about 4,500 ppm and of Cl of about 320 ppm.Example 3: Preparation of Lithium Carbonate

[0038] Lithium carbonate was prepared in a process similar to Example 1 except that 1.0 kg of lithium carbonate seed crystals was used mixed with 50 L of synthetic lithium-containing brine to form the first slurry. The dried lithium carbonate final product (T^CCL) was about 99.68% pure by weight, and had a concentration of Na of about 550 ppm and of Cl of about 80 ppm.Example 4: Preparation of Lithium Carbonate

[0039] A lithium-containing brine was recovered from a Salar and comprised 60.5 g / L lithium, 0.85 g / L Na, 0.21 g / L Ca, and 312.5 g / L Cl. The lithium-containing brine was purified using a chelating ion exchange process to reduce Ca to a concentration of about 15 mg / L. 50 L of the purified lithium-containing brine was then mixed with 2.5 kg of lithium carbonate seed crystals to form the first slurry. The first slurry was fed to a reactor through an upper level inlet of the reactor and was heated to 80 °C. 85.2 L of 280 g / L sodium carbonate solution at 40 °C was fed to the reactor through a lower level inlet. The first slurry reacted with sodium carbonate in the reactor at around 80 °C with a residence time of 2 hr to form the second slurry. The second slurry was separated into lithium carbonate solids and a mother liquor using a peeler centrifuge. The mother liquor was discharged out of the peeler centrifuge. The lithium carbonate solids were then washed within the peeler centrifuge by rinsing the centrifuged cake using 5 L of hot (around 80 °C) pure water to produce washed lithium carbonate solids. The washed lithium carbonate was further washed using hot pure water through a process of resuspending in hot pure water, thencentrifugation, then rinsing, then centrifugation, then rinsing, and then centrifugation. The final washed lithium carbonate solids were dried at 150 °C. The dried lithium carbonate final product (Li2COs) was about 98.2% pure by weight, and had a concentration of Na of about 8,500 ppm and of Cl of about 2,100 ppm.Example 5: Preparation of Lithium Carbonate

[0040] Lithium carbonate was prepared in a process similar to Example 4 except that the purified lithium-containing brine was diluted by adding pure water to form a diluted lithium- containing brine comprising 24.5 g / L lithium. 50 L of the diluted lithium-containing brine was mixed with 2.5 kg of lithium carbonate seed crystals to form the first slurry. The first slurry was fed to a reactor through an upper level inlet of the reactor and was heated to 80 °C. 35.6 L of 280 g / L sodium carbonate solution at 40 °C was fed to the reactor through a lower level inlet. The first slurry reacted with sodium carbonate in the reactor at around 80 °C with a residence time of 2 hr to form the second slurry. The second slurry was separated into lithium carbonate solids and a mother liquor using a peeler centrifuge. The mother liquor was discharged out of the peeler centrifuge. The lithium carbonate solids were then washed within the peeler centrifuge by rinsing the centrifuged cake using 2.5 L of hot (around 80 °C) pure water to produce washed lithium carbonate solids. The washed lithium carbonate was further washed using hot pure water through a process of resuspending in hot pure water, then centrifugation, then rinsing, then centrifugation, then rinsing, and then centrifugation. The final washed lithium carbonate solids were dried at 150 °C. The dried lithium carbonate final product (Li2COs) was about 99.65% pure by weight, and had a concentration of Na of about 150 ppm and of Cl of about 25 ppm.

[0041] The terminology used herein is only for the purpose of describing particular embodiments and is not intended to be limiting. Accordingly, as used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and “comprising”, when used in this specification, specify the presence of one or more stated features, integers, steps, operations, elements, and components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and groups. Directional terms such as “top”, “bottom”, “upwards”, “downwards”, “vertically”, and “laterally” are used in thefollowing description for the purpose of providing relative reference only, and are not intended to suggest any limitations on how any article is to be positioned during use, or to be mounted in an assembly or relative to an environment. Additionally, the term “couple” and variants of it such as “coupled”, “couples”, and “coupling” as used in this description are intended to include indirect and direct connections unless otherwise indicated. For example, if a first device is coupled to a second device, that coupling may be through a direct connection or through an indirect connection via other devices and connections.

[0042] Use of language such as "at least one of X, Y, and Z," "at least one of X, Y, or Z," "at least one or more of X, Y, and Z," "at least one or more of X, Y, and / or Z," or "at least one of X, Y, and / or Z," is intended to be inclusive of both a single item (e.g., just X, or just Y, or just Z) and multiple items (e.g., {X and Y}, {X and Z}, {Y and Z}, or {X, Y, and Z}). The phrase "at least one of' and similar phrases are not intended to convey a requirement that each possible item must be present, although each possible item may be present. The term "or" is generally employed in its sense including "and / or" unless the content clearly dictates otherwise.

[0043] As used herein, unless the context indicates otherwise a reference to a parameter being “about” or “approximately” a particular value means that parameter is within 10% of that value.

[0044] It is contemplated that any part of any aspect or embodiment discussed in this specification can be implemented or combined with any part of any other aspect or embodiment discussed in this specification, so long as such implementation or combination is not performed using mutually exclusive parts.

[0045] One or more example embodiments have been described by way of illustration only. This description is presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the form disclosed. It will be apparent to persons skilled in the art that a number of variations and modifications can be made without departing from the scope of the claims.

Claims

CLAIMS1. A process for preparing lithium carbonate from a lithium-containing brine, the process comprising: i) mixing the lithium-containing brine with lithium carbonate seed crystals to produce a first slurry; ii) reacting the first slurry with a sodium carbonate solution to produce a second slurry; iii) separating lithium carbonate solids from the second slurry; and iv) washing the separated lithium carbonate solids with a pure water to produce washed lithium carbonate solids, wherein the pure water has a total dissolved solids concentration of less than 10 mg / L.

2. The process of claim 1, wherein a concentration of the lithium carbonate seed crystals in the lithium-containing brine is at least 50 g / L.

3. The process of claim 1 or 2, further comprising recycling a portion of the washed lithium carbonate solids as the lithium carbonate seed crystals.

4. The process of any one of claims 1 to 3, further comprising controlling lithium concentration to be within 10 - 25 g / L in the lithium-containing brine by adjusting an amount of water in the lithium-containing brine before the lithium-containing brine is mixed with the lithium carbonate seed crystals.

5. The process of any one of claims 1 to 4, wherein the separating and the washing of lithium carbonate solids uses either a peeler centrifuge or a pusher centrifuge.

6. The process of any one of claims 1 to 5, wherein the reacting of the first slurry with the sodium carbonate solution is performed by directing the first slurry and the sodium carbonate solution into a first reactor through a slurry inlet of the first reactor and a solution inlet of the first reactor that is below the slurry inlet, respectively.

7. The process of claim 6, wherein the reacting of the first slurry with the sodium carbonate solution comprises:i) mixing 60% to 80% of a total of the first slurry and the sodium carbonate solution in the first reactor; ii) mixing 20% to 40% of the total of the first slurry and the sodium carbonate solution in a second reactor fluidly coupled to, and downstream of, the first reactor; and iii) transferring the second slurry resulting from the mixing in the first reactor to the second reactor, wherein the separating is performed on the second slurry transferred to the second reactor from the first reactor and on the second slurry resulting from the mixing in the second reactor.

8. The process of any one of claims 1 to 7, wherein the reacting occurs within a temperature range of approximately 80 °C to approximately 95 °C.

9. A system for preparing lithium carbonate from a lithium-containing brine, the system comprising: i) a mixing container configured to receive and mix the lithium-containing brine and lithium carbonate seed crystals to produce a first slurry; ii) a reactor unit fluidly coupled to the mixing container, wherein the reactor unit is configured to receive the first slurry from the mixing container and a sodium carbonate solution, and to react the first slurry and the sodium carbonate solution together to produce a second slurry; and iii) a solids-liquid separator fluidly coupled to the reactor unit, wherein the solids-liquid separator is configured to receive the second slurry and to separate lithium carbonate solids from the second slurry, and to receive pure water after the separating of the lithium carbonate solids to wash the separated lithium carbonate solids to produce washed lithium carbonate solids, wherein the pure water has a total dissolved solids concentration of less than 10 mg / L.

10. The system of claim 9, further comprising a return conduit fluidly coupling the solids-liquid separator to the mixing container to permit recycling of a portion of the washed lithium carbonate solids as the lithium carbonate seed crystals.

11. The system of claim 9 or 10, wherein the solids-liquid separator is either a peeler centrifuge or a pusher centrifuge.

12. The system of any one of claims 9 to 11, wherein the reactor unit comprises comprising a slurry inlet for the first slurry and a solution inlet for the sodium carbonate solution, and wherein the solution inlet is positioned below the slurry inlet.

13. The system of claim 12, wherein the reactor unit comprises a first reactor and a second reactor that is fluidly coupled to and positioned downstream of the first reactor, wherein the slurry inlet and the solution inlet comprise part of the first reactor, and wherein the second reactor is fluidly coupled to the mixing container to receive a portion of the first slurry therefrom without the portion of the first slurry having passed through the first reactor.

14. The system of any one of claims 9 to 13, wherein the reactor unit is configured to be maintained at a temperature range of approximately 80 °C to approximately 95 °C when the first slurry and the sodium carbonate solution are being reacted to produce the second slurry.

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