RU2795224C1 - Process and method for lithium carbonate purification based on a lithium chloride solution with impurities - Google Patents

Abstract

FIELD: inorganic chemistry.

SUBSTANCE: recovery of high purity lithium from crude lithium chloride brine. Crude brine is loaded into a feed tank maintained at temperature T₁ and containing a source of carbonate sufficient to precipitate all of the carbonate-forming solids in the crude brine to form a precipitated mixture and a crystal-free supernatant. The supernatant is fed from the feed tank to the first crystallization reactor, which is maintained at temperature T₂, crystallizing lithium carbonate therefrom. Temperature T₁ is less than temperature T₂. The flow rate is controlled by maintaining an equilibrium concentration of lithium carbonate in the dissolved phase of the crystallization reactor.

EFFECT: method allows continuous work on selective crystallization with a significant reduction in the size of the equipment used.

8 cl, 7 dwg, 2 tbl, 1 ex

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This ordinary application claims priority under 35 U.S.C. § 119(e) U.S. Provisional Application No. 62/946767, filed December 11, 2019, which is directly incorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Scope of the present invention:

The present invention generally relates to methods for recovering high purity lithium carbonate from crude brine. More specifically, the present invention relates to methods for purifying high purity lithium carbonate from lithium chloride brine, using lithium carbonate as an intermediate.

2. Description of the prior art:

The global lithium mining industry has struggled to meet the rapidly growing demand for raw materials for battery grade lithium carbonate, which is used to make cathodes and electrolytes in the lithium-ion battery industry. Demand is driven by the rapid adoption of battery, electric and hybrid electric vehicles to reduce vehicle emissions, as well as the introduction of large lithium-ion batteries to balance power supply with electricity demand for renewable energy generation systems, including solar, wind and tidal power.

"Battery grade" lithium carbonate is a general term, but is commonly used to refer to a purity of lithium carbonate greater than 99.5%. The properties of lithium make it one of the most attractive battery materials of all elements. Worldwide, rechargeable lithium-ion batteries power most cell phones and laptop computers, as well as most powerful power tools, and automakers are applying and developing improvements to lithium-ion batteries for electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs). ). Rechargeable lithium-ion batteries are also used in energy storage systems.

Although lithium is a ubiquitous element, the vast majority of the world's chemical supply of lithium comes from two main areas: lithium-rich continental salt deposits in Chile and Argentina; and hard rock deposits of spodumene pegmatite in western Australia. Typically, salt deposits are processed domestically to produce lithium carbonate chemicals, while spodumene hard rock deposits are mined and concentrated domestically, and then the concentrate is sent to China, where it is further processed and converted into lithium hydroxide monohydrate.

In particular, for salt deposits in Chile and Argentina, they are typically pumped to the surface and cycle through a series of evaporation ponds over a period of 12-24 months. Three main processes take place in these ponds: evaporation of water into the atmosphere and subsequent concentration; precipitation of various types of salts as saturation limits are reached; and forced precipitation of various types of salts as chemicals are added to the ponds. Typically, the resulting lithium chloride-rich solutions are then further purified by various industrial processes and then converted to the final product, lithium carbonate. The classical process commonly used to produce lithium carbonate is difficult to control and often produces a relatively dirty form of lithium carbonate, referred to as the "technical grade" form. This commercial grade lithium carbonate is suitable for several industrial applications of lithium, but is generally not suitable for modern lithium-ion battery applications.

Typically in the industry commercial lithium carbonate is enriched using CO ₂ or a bicarbonate process, which leads to additional technical and operational complexity, as well as additional operating costs. At all stages of the production of lithium carbonate using industry standard methods of periodic crystallization, the formation of pure crystals of lithium carbonate (without inclusions of other salts) is difficult.

While conventional processing of brines to produce lithium rich salts or solutions eliminates most of the interfering ions, there remains a need for simplified removal of interfering ions from raw solid lithium salts for the production of battery grade lithium carbonate. Existing methods are inefficient in terms of the energy, time and materials required to process raw (technical) lithium carbonate to a level of purity sufficient for modern batteries.

The production of acceptable quality lithium carbonate from brines requires the use of methods to remove the specific cations and anions that accompany lithium in solution and then to concentrate the lithium for extraction.

It is accepted, although not proven, that a lithium chloride crystal containing greater than or equal to 0.07% by weight of Mg may have too high a magnesium content to be useful in the production of lithium metal and subsequent use in the production of organolithium metal compounds. Thus, the industry requires that organolithium catalysts in polymerization reactions contain little magnesium. Lithium chloride with a high magnesium content can also adversely affect the operation of the lithium cell in the production of lithium metal.

Similarly, sodium impurity in lithium chloride crystal is reported in the production of lithium metal. Thus, low sodium lithium salts are desirable. Sodium in lithium chloride crystals above 0.6% by weight produces a metal containing 1% by weight of sodium or more. A sodium concentration of approximately 1% by weight in lithium metal or higher makes the lithium metal more reactive towards natural air constituents, making the metal more difficult and dangerous to handle. Table 1 provides data regarding the limits and allowable amounts of sodium in various sources of lithium:

TABLE 1

Sodium content of lithium chloride

Maximum Na content in LiCl Chemical purity Battery cleanliness metallic purity % lithium chloride 99.2 99.2 99.8 % Na** 0.17 0.04 0.0006

**% by weight in lithium chloride.

Commercial processes used to produce low sodium lithium carbonate and lithium chloride on an industrial scale include the recovery of lithium compounds from mineral deposits such as spodumene ore and natural brines. A number of processes have been described and some have been commercialized for the production of lithium carbonate from these sources.

One of these commercial methods involves the extraction of lithium from an ore or brine containing lithium, obtaining a solution of pure lithium sulfate, as described in US patent No. 2516109, or a solution of lithium chloride, such as described in US patent No. 5219550. After purification of the solutions, add sodium carbonate in the form of a solid or solution for the precipitation of lithium carbonate crystals. Then, the lithium carbonate is filtered from the waste solution (mother liquor), and the lithium carbonate is washed, dried, sorted and packaged.

Lithium carbonate is often used as a raw material to produce other lithium compounds, such as lithium chloride, lithium hydroxide monohydrate, lithium bromide, lithium nitrate, lithium sulfate, lithium niobate, various lithium-containing cathode materials, electrolyte salts, etc. Lithium carbonate itself is used as an additive in the electrolytic production of aluminum to increase the efficiency of galvanic cells and as a source of lithium oxide in the production of glass, enamels and ceramics. High purity lithium carbonate is used in medicine and modern batteries.

For example, the current commercial method for producing chemical grade lithium chloride is to react a lithium base such as lithium carbonate monohydrate or lithium hydroxide with concentrated hydrochloric acid to produce a pure lithium chloride brine. The resulting lithium chloride brine is evaporated in a vacuum crystallizer at a temperature of 101°C or higher to obtain a product, crystalline anhydrous lithium chloride. This method produces a product that meets most commercial specifications for chemical grade lithium chloride, but not for low sodium lithium chloride.

Chemical grade lithium chloride is suitable for air drying, fluxes, intermediate compound in the production of mixed ion exchange zeolites, and also as raw materials for electrolysis cell for the production of chemical grade lithium metal.

Chemically pure lithium metal is used, among other things, for the production of organolithium metal compounds. These compounds are used as a catalyst in the polymerization and pharmaceutical industries.

Chemical grade anhydrous lithium chloride must contain less than 0.16% sodium to produce a metal containing less than 1% sodium. The importance of minimizing the sodium content of the metal and the associated costs are the principal reasons for the use of lithium hydroxide monohydrate or lithium carbonate as a feedstock for the production of lithium chloride and then lithium metal. With this in mind, low sodium lithium chloride typically contains less than 0.0008% sodium by weight and is commercially produced to produce low sodium lithium metal suitable for battery and alloy applications.

On an industrial scale, low sodium lithium chloride is produced indirectly from chemical grade lithium carbonate. Lithium carbonate is converted to lithium hydroxide monohydrate by reaction with slaked lime. The resulting suspension contains precipitated calcium carbonate and a solution of lithium hydroxide with a concentration of 2-4% by weight, which are separated by filtration.

The lithium hydroxide solution is concentrated in a vacuum evaporator crystallizer in which lithium hydroxide monohydrate crystallizes, leaving soluble sodium in the mother liquor.

Crystalline lithium hydroxide monohydrate is separated from the mother liquor and dried. This salt typically contains 0.02 to 0.04% sodium. To further reduce the sodium content, lithium hydroxide monohydrate must be dissolved in pure water and recrystallized, and then reacted with pure hydrochloric acid to form a concentrated lithium chloride solution containing less than 10 ppm sodium. The resulting lithium solution is then evaporated to dryness to provide anhydrous lithium chloride suitable for the production of battery grade lithium metal containing less than 100 ppm sodium. The above method requires seven main processing steps, described below:

1) Recovery and purification of low boron aqueous solution containing 6% by weight or less Li from lithium-containing ores and natural brines;

2) Purification of brine from magnesium and calcium and filtration;

3) Precipitation of lithium carbonate from the purified brine by adding Na ₂ CO ₃ , and then filtering and drying the lithium carbonate;

4) Reaction of slaked lime and lithium carbonate to obtain LiOH solution and filtration;

5) crystallization of LiOH⋅H ₂ O in a vacuum crystallizer;

6) dissolution of LiOH⋅H ₂ O crystals and recrystallization of LiOH⋅H ₂ O from solution; And

7) Reaction of high purity HCl with recrystallized LiOH⋅H ₂ O to obtain high purity lithium chloride brine from which low sodium lithium chloride is crystallized and drying of lithium chloride.

Low sodium lithium carbonate can be obtained from recrystallized LiOH⋅H ₂ O using the first part of the process described above. Recrystallized LiOH⋅H ₂ O is then mixed with water and reacts with CO ₂ to precipitate lithium carbonate. The steps of the method are shown below:

1) Recovery and purification of low boron aqueous solution containing 6% by weight or less Li from lithium-containing ores and natural brines;

2) Purification of brine from magnesium and calcium and filtration;

3) Precipitation of Li ₂ CO ₃ f from the purified brine by adding Na ₂ CO ₃ , filtering and drying.

4) The reaction of slaked lime and Li ₂ CO ₃ to obtain a solution of LiOH and filtration.

5) Crystallization of LiOH⋅H ₂ O in a vacuum crystallizer.

6) Dissolution and recrystallization of LiOH⋅H ₂ O from solution.

7) Reaction of CO ₂ gas with slurry containing recrystallized LiOH⋅H ₂ O, crystallizing high purity low sodium lithium carbonate crystals, filtration and drying.

Getting lithium carbonate

A common method for producing a precipitate of lithium carbonate from a solution of lithium chloride is to mix sodium carbonate (Na ₂ CO ₃ ) or a suspension of sodium carbonate with a solution of lithium chloride in a reaction vessel and heat the mixture to about 85-100°C, which causes periodic precipitation of lithium carbonate. To improve lithium carbonate separation, a "heel" or residual slurry from a similar reaction is included as part of the sodium carbonate addition. The residual slurry acts as a set of nucleation nuclei, aiding intermittent crystallization resulting in a lithium carbonate precipitate with good settling, filtration and washing properties. The addition of sodium carbonate is controlled by reacting the sodium carbonate solution with sodium carbonate to form sodium carbonate and dissolved sodium chloride (NaCl). In other words, the concentrations are controlled so that the process is carried out within the solubility range of NaCl to prevent co-precipitation of sodium chloride with lithium carbonate.

The reaction with sodium carbonate precipitates lithium carbonate according to the equation:

2LiCl + Na ₂ CO ₃ => Li ₂ CO ₃ + 2NaCl

The use of direct addition of sodium carbonate (dry) to a lithium salt solution in this manner results in lithium carbonate of very low purity, in which significant amounts of other ions, in particular sodium, are present. A significant portion of lithium carbonate is recovered from brines, which also contain high amounts of sodium, making the production of low sodium lithium salts difficult and expensive.

The evaporated concentrated lithium chloride solution used to precipitate lithium carbonate typically has a lithium ion concentration in the solution in the range of 0.6 to 7.3% by weight and a concentration of sodium carbonate in the solution in the range of 25 to 56%, the higher ranges of the latter are suspensions of hydrated sodium carbonate (Na ₂ CO ₃ ⋅H ₂ O)).

The reactants are mixed at temperatures ranging from room temperature to about 100°C, and the resulting mixture is heated. The lithium carbonate formed is then separated by centrifugation at a temperature in the vicinity of 100° C., at which the lithium carbonate precipitate has the least solubility in water.

The solution of the product after centrifugation contains a noticeable amount of soluble Li ₂ CO ₃ . The presence of a large amount of sodium chloride makes further recovery of unprecipitated Li ₂ CO ₃ difficult, and even subsequent cooling of the remaining solution after removal of solid particles of lithium carbonate to 0°C removes only a small amount of sodium chloride by precipitation.

Reuse of the mother liquor early in the brine treatment is often done to improve lithium recovery efficiency and to achieve the highest possible economic recovery from the initial precipitation, whether the mother liquor is discarded or recycled.

Currently, the most common and inexpensive method for producing battery-grade, low-sodium lithium carbonate directly from natural brines containing lithium involves some pre-treatment to produce technical-grade lithium carbonate, which is purified by a chemical conversion cycle, whereby the lithium carbonate is reacted with carbon dioxide and water to form a soluble lithium bicarbonate solution.

Li ₂ CO ₃ + CO ₂ + H ₂ O \u003d\u003e 2LiHCO ₃

The fully solubilized lithium bicarbonate is separated from insoluble impurities. The lithium bicarbonate is then converted back to lithium carbonate by heating by adjusting the pH to release carbon dioxide. Unfortunately, this method requires equipment for carrying out gas-liquid reactions, while the reaction rate is proportional to the pressure and concentration of dissolved CO ₂ . Thus, pressurized reaction equipment is needed for the most efficient operation, which greatly increases the complexity, energy requirement, hazard, and maintenance costs of the plant and method.

Direct recrystallization of dirty lithium carbonate (without chemical interconversion) offers a potential purification method. However, this method is not used for two main reasons.

First, lithium carbonate has a very low "reverse solubility" which, unlike sodium chloride and most other salts, results in a decrease in water solubility as the temperature of the solution rises. Increasing the solution temperature increases the precipitation and recovery of lithium carbonate while minimizing co-precipitation and sodium chloride contamination. Although this property is advantageous in terms of selective solubility (least soluble in temperature regions where other salts are more soluble), saturated solutions can only contain 18 mg lithium carbonate per ml of simulated brine (at 20°C). Thus, the processing of the material (complete solubility of the crude product) requires a large volume of solvent.

Secondly, the recrystallization of commercial grade lithium carbonate cannot be effectively carried out from the mother liquor (containing large amounts of dissolved sodium salts) since a net reduction in the content of sodium impurities is not achieved. This disadvantage is associated with the formation of crystalline agglomerates - trapping sodium-containing amorphous or crystalline impurities. This particular type of crystalline impurities cannot be effectively removed by washing since they are inclusion bodies and are trapped within the lithium carbonate crystalline matrix. Thus, purification requires separating the crude lithium carbonate from the mother liquor, washing, and then resuspension and recrystallization from pure water.

Examples of lithium carbonate agglomerates, as shown by optical microscopy, are shown in FIG. 1A and 1B. Examples of lithium carbonate single crystals without agglomerates are shown in FIG. 2A and 2B.

For the reasons outlined above, there is still a need to improve the process for purifying lithium from the intermediate lithium carbonate in order to overcome the shortcomings of conventional methods.

SUMMARY OF THE INVENTION

In a first embodiment, the present invention relates to a method for recovering lithium from crude brine, comprising:

loading the crude brine into a feed tank maintained at T ₁ and containing a sufficient source of carbonate to precipitate all of the carbonate-forming solids in the crude brine, forming a precipitated mixture and a crystal-free supernatant; And

supplying the crystal-free supernatant from the feed tank to the first crystallization reactor, which is maintained at a temperature T ₂ , crystallizing the lithium carbonate salt from the crystal-free supernatant;

where the temperature T ₁ is less than the temperature T _2; And

controlling the flow rate by maintaining an equilibrium concentration of lithium carbonate in the liquid phase of the crystallization reactors.

The method may also include feeding the liquid phase from the first crystallization reactor back to the feed tank. The method may also include feeding the liquid phase from the first crystallization reactor to a second crystallization reactor which is maintained at a temperature T ₃ ; where the temperature T ₃ is greater than the temperature T ₂ . Similarly, the method may include feeding the liquid phase from the first crystallization reactor to the second crystallization reactor, which is maintained at a temperature T ₃ ; where the temperature T ₃ is greater than the temperature T ₂ ; and continuing the method of supplying the liquid phase from the “n” crystallization reactor to the “n+1” crystallization reactor, where the “n+1” crystallization reactor is maintained at a temperature greater than the temperature of the “n” crystallization reactor; where "n" is an integer greater than or equal to 2.

High quality lithium carbonate nuclei can be added to the first crystallization reactor. The carbonate source may be sodium carbonate, potassium carbonate or carbon dioxide. The flow rate may be sufficient to maintain an equilibrium concentration of dissolved lithium carbonate in the dissolved phase such that the total crystallization mass flow rate is greater than the maximum flow rate employed. The flow rate can be adjusted to provide a solution addition rate to achieve 50-250 g Li ₂ CO ₃ per hour, as required by the process and as the equipment allows.

An additional scope of applicability of the present invention will become apparent from the detailed description below. However, it should be understood that the detailed description and specific examples, while indicating the preferred mode of carrying out the present invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to a person skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more apparent from the detailed description below and the accompanying drawings, which are given by way of illustration only and thus do not limit the present invention. In the drawings, like reference numerals are used to refer to like elements in different views.

Fig. 1A and 1B show examples of lithium carbonate agglomerates as seen by optical microscopy.

Fig. 2A and 2B show examples of single crystals of lithium carbonate without aggregates according to optical microscopy.

Fig. 3A and 3B show graphs showing variations in the solubility of Li ₂ CO ₃ .

Fig. 4 is a graph showing the solubility values of Li ₂ CO ₃ at 95° C. as a function of Na ₂ CO ₃ concentration for three NaCl concentrations.

Fig. 5 is a diagram showing an exemplary system of the present invention.

Fig. 6 is a graph showing fluctuations in the solubility of lithium carbonate at different temperatures.

Fig. 7 is a graph showing the theoretical purity of solids samples from both the feed tank (solvent) and the crystallization reactor (crystallizer) over time in ICPOES analysis.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The present invention is a novel process that uses selective crystallization to produce battery-grade or other high-purity lithium carbonate greater than 99.5% lithium carbonate (Li ₂ CO ₃ ). While other exemplary methods use lithium carbonate crystallization as a purification method, the method of the present invention provides a greatly simplified and direct method to high purity lithium carbonate from raw groundwater brines containing many dissolved salts.

The present invention provides an integrated and novel method, which reduces the number of major processing steps, for the production of high purity lithium carbonate with a sodium content of 0.01 to 0.002% by weight directly from natural brines containing lithium, concentrated to 0.2-10.0% by weight Li. The method of the present invention avoids:

1) Single and double stages of recrystallization of lithium hydroxide monohydrate.

2) Double recrystallization of lithium carbonate to lithium bicarbonate and back to carbonate.

3) Thorough titration of carbonate addition (solubility based selective precipitation) to initially precipitate unwanted cations (eg Mg and Ca).

Eliminating the carbon dioxide/bicarbonate cycle (which is used in conventional processes) entails a dramatic simplification in terms of required equipment (e.g. no pressurized oxygen dioxide for chemical interconversion plus associated industrial infrastructure), reduced materials needed ( water and lost sample), as well as reduced energy requirements for post-processing. With regard to the physical plant, the reduction in the necessary process steps, the simplification of the processing method, and continuous operational design significantly reduce the physical burden on the pilot plant. As such, the present invention provides significant improvements in operability and usability, allowing small site operations to be considered and brought online with lower capital and infrastructure investments.

Experimental precipitation of Li ₂ CO ₃ from LiCl shows that it is generally difficult to obtain Li ₂ CO ₃ with good precipitation, filtration and washing characteristics. The following observations and conclusions refer to the precipitation of Li ₂ CO ₃ from LiCl solutions.

(1) Effect of NaCl concentration on the solubility of Li ₂ CO ₃

Ions in solution have "cross effects" affecting ion solubility and precipitation. A study of the effect on solubility of Li ₂ CO ₃ is shown in FIG. 3A and 3B. At 95°C, when the concentration of NaCl increases to about 9%, the solubility of Li ₂ CO ₃ increases from 7.5 g/l in pure water to about 9.3 g/l. As the concentration of NaCl increases further, the solubility of Li ₂ CO ₃ decreases so that at 25 weight percent NaCl it is only about 6.5 g/l, which is less than the solubility in water. KCl has a similar effect on the solubility of Li ₂ CO ₃ to about the same extent.

(2a) Reagent concentration

Taking into account the above data on the effect of NaCl concentration on the solubility of Li ₂ CO ₃ , it is desirable to work with such concentrations of reagents that provide a high concentration of NaCl in the mother liquor. Precipitation of NaCl should be avoided due to exceeding its maximum solubility. When working with aqueous solutions of LiCl and Na ₂ CO ₃ NaCl precipitation is not possible. However, when using Na ₂ CO ₃ in the form of a suspension of solid Na ₂ CO ₃ ⋅H ₂ O in its saturated solution, it is necessary to ensure that the concentrations of the reagents do not lead to precipitation of NaCl. Also in these cases it is necessary to take into account the influence of an excess of Na ₂ CO ₃ , which moderately reduces the solubility of NaCl in the mother liquor, as well as the presence of NaCl in the LiCl solution (see 2b below).

(2b) Lithium chloride solutions

When extracting lithium from natural chloride brines, the recovered LiCl solution obtained by solar evaporation, after appropriate purification, usually contains a moderate amount of NaCl and KCl. Through simple solar evaporation, the concentration of both of the latter (especially NaCl) can be reduced to fairly low levels. Table 2 shows the solubility of NaCl in solutions with different contents of LiCl at 25°C and 100°C.

TABLE 2

Solubility of NaCl in sun-evaporated brine with moderate to high concentrations of lithium chloride

Weight percent LiCl Weight percent NaCl at 25°C Weight percent NaCl at 100°C 12 12.3 15.0 18 6.5 9.3 20 5.3 8.0 25 2.6 5.0 thirty 1.0 2.6 40 0.2 1.1 45 0.2 0.8

Under properly controlled process conditions, precipitated lithium carbonate with good physical properties can be obtained in the LiCl concentration range indicated above. However, recovery will vary greatly, increasing as LiCl concentration increases. Achieving higher LiCl concentrations requires increased solar evaporation and increased residence time in the evaporation tanks.

(2c) Sodium carbonate solution

In addition to carrying out the precipitation of Li ₂ CO ₃ with concentrated Na ₂ CO ₃ solutions (from 26 to 33 weight percent Na ₂ CO ₃ ), it is also possible to use suspensions of soda ash and water with a total content of Na ₂ CO ₃ above 33 weight percent. These slurries include a mixture of solid hydrated sodium carbonate (Na ₂ CO ₃ ⋅H ₂ O) in saturated sodium carbonate solution. Successfully used suspensions containing up to 56 weight percent of the total Na ₂ CO ₃ that can be easily pumped. The use of these suspensions makes it possible to achieve the highest possible concentration of NaCl in the mother liquor in combination with a LiCl solution of the appropriate concentration. Therefore, the Li ₂ CO ₃ recovery rate is high. However, one of the disadvantages of using suspensions is the impossibility of removing some insoluble impurities from soda ash by filtration.

(3) Order of mixing reagents

In LiCl solutions, well settling and filterable precipitates can be obtained by using dilute lithium carbonate solutions containing 0.5 to 5 wt % Li ⁺ by adding the solution cold (25°C) to a cold sodium carbonate solution, followed by heating to about -100°C before centrifugation. This method was carried out successfully only when a LiCl solution with a concentration of no more than 20 weight percent LiCl was used.

The preferred method of mixing the reactants is to simultaneously add the lithium chloride solution and the sodium carbonate solution (or slurry) to the medium sized heel of the unfiltered slurry (or mother liquor) from the previous precipitation. Typically, each solution is added at a flow rate approximately proportional to its volume, so that the total addition time is approximately 1 hour. Good shaking is maintained throughout. This method resulted in precipitates with excellent physical properties and is applicable to LiCl solutions at a concentration of 45 weight percent LiCl.

(4) Deposition temperature

It was previously stated that the solubility of lithium carbonate in both water and sodium chloride solution is retrograde (i.e., an increase in temperature leads to a decrease in solubility), which contradicts the usual effect of temperature on the solubility of salt. Therefore, it must be centrifuged and filtered at an elevated temperature in order to improve lithium recovery. When using the simultaneous method described above, the reactants can be mixed at room temperature and at some intermediate temperature, such as 50°C, instead of 95°C. Thereafter, the temperature is raised to about 95° C. before centrifugation in order to obtain a pellet with excellent properties. This method provides a distinct advantage over using an addition temperature near 95°C, since this method eliminates unwanted evaporation and heat loss that can occur when maintaining a temperature near 95°C during a relatively long addition step.

(5) Application of excess NaCO ₃

It is desirable to use approximately 10% excess of Na ₂ CO ₃ over the equivalent of LiCl, thereby reducing the solubility of Li ₂ CO ₃ in the mother liquor by increasing the concentration of carbonate ions. The decrease in the solubility of Li ₂ CO ₃ with increasing concentration of Na ₂ CO ₃ is not linear (i.e., the degree of decrease decreases with increasing Na ₂ CO ₃ ). Therefore, the cost of the applied excess Na ₂ CO ₃ must be balanced against the increase in recovery of Li ₂ CO ₃ to ensure that the excess is justified. Generally, an excess of 5 to 10% Na ₂ CO ₃ over the stoichiometric amount is preferred.

The three curves of Fig. 4 give the experimentally determined values of the solubility of Li ₂ CO ₃ at 95°C as a function of the concentration of Na ₂ CO ₃ for three concentrations of NaCl. These curves graphically illustrate the effect of the concentration of Na ₂ CO ₃ and NaCl on the solubility of Li ₂ CO ₃ . These curves can be used to calculate the expected loss of Li ₂ CO ₃ with the mother liquor for any given set of compositions and concentrations of reagents.

Currently, there are several methods for removing lithium from lithium chloride-enriched brine and other liquids containing lithium. However, the methods are not currently used to produce low magnesium and lithium carbonate fluids. Traditional methods of using spodumene or lithium aluminosilicate ore (LiAlSi ₂ O ₆ ) to extract lithium carbonate from mineral sources also produce materials of insufficient purity. Accordingly, it is necessary to recover lithium from a lithium-containing brine with a purity sufficient to obtain high purity lithium metal as a lithium salt, such as lithium chloride or lithium carbonate.

In this regard, the most important advantage of the method of the present invention lies in the ability to control the growth rate of lithium carbonate crystals in the presence of native (high in sodium salt) mother brine. This advantage can be achieved by understanding the relationship between the crystal growth rate as a function of solution temperature and the concentration of dissolved lithium carbonate. By controlling the crystallization method, the size, shape and quality of the lithium carbonate crystals can be controlled, and the formation of unwanted agglomerates can be prevented.

One embodiment of the entire method of the present invention may be generally described using a schematic representation of the exemplary system shown in FIG. 5.

First, crude brine 1 is obtained. Preferably, crude brine 1 is primarily lithium chloride. The composition of the crude chloride brine 1 is not limited, but will typically contain 0.1-6 wt% Li, 0.1-3 wt% Na, 0.001-0.4 wt% K, 0.01-2.6% by weight Ca, 0.01-0.5% by weight Mg, 0.1-0.22% by weight B and 0.1-0.3% by weight Si. The approximate composition of crude chloride brine 1 is 1 wt% Li, 2.5 wt% Na, 0.01 wt% K, 0.01 wt% Mg, 0.01 wt% Ca, 0.12% by weight B and 0.26% by weight Si.

The crude brine 1 is fed into the feed tank 4 via line 2 and treated with enough sodium carbonate to precipitate all of the carbonate-forming solids 5 (Mg, Ca and Li). This precipitated mixture will be of lower quality than commercial lithium carbonate produced by other processes, since this precipitated mixture will contain all of the carbonate forms of the relevant cations. The feed tank 4 contains a mixer 6. The mixer 6 mixes the contents of the feed tank 4 to keep the solids in solution and promote mass transfer. Mixer 6 need not be a physical mixer; the mixer 6 can simply mix with the liquid flow.

The purpose of this first stage is to displace both Li ₂ CO ₃ and CaCO ₃ /MgCO ₃ etc. as a crude solid. In factory tests, only Ca/Mg (possibly boron and Si) is deposited first, producing a Li ₂ CO ₃ solution that is metastable and supersaturated. On standing, the solution eventually precipitates Li ₂ CO ₃ , but this is not controlled. Measurements using ion chromatography allow you to know the exact content of [Li+] in the input brine. For example, approximately 3000 mg Li+ supplied as LiCl yields approximately 16 g Li ₂ CO ₃ /l, but the saturation limit at 10° C. is only approximately 12-14 g/l. Thus, after softening, supersaturation occurs. This kinetically stable state will eventually lead to spontaneous crystallization of Li ₂ CO ₃ in a cold reactor. The method of the present invention can utilize this metastable state for more efficient recovery, both in terms of energy consumption and process time. While conventional methods would involve simply heating a given batch to induce crystallization, the already high supersaturation combined with the lack of control afforded by temperature variation does not allow for control of the crystallization process. In the present invention, the supersaturated solution is added in a controlled manner using continuous crystallization principles in a well stirred seeded crystallization reactor (at a temperature of approximately 70°C). This protocol provides consistent, reproducible crystal growth that can be maintained to avoid agglomeration, resulting in a cleaner material that is easier to process. Thus, the process of the present invention is not adversely affected by high supersaturation, which would complicate conventional methods using periodic recrystallization of supersaturated lithium carbonate using thermal or chemical supersaturation. These prior methods using batch crystallization would not be able to control the process, resulting in equipment failure and impure product. The method of the present invention can also use chemical supersaturation to increase mass throughput. This feature is likely responsible for the unusually broad chemical resistance.

Secondly, the supply tank 4 is maintained at a low temperature T ₁ . The lower temperature T ₁ may be -10°C to 40°C, preferably 5°C to 25°C, more preferably 10°C to 20°C. At a given temperature, lithium carbonate will have its highest solubility. Specifically, the solubility may be 10 mg/ml to 30 mg/ml, more preferably 15 mg/ml to 21 mg/ml. The feed tank 4 further includes a solid waste line 8 which will remove any solid material (most likely MgX and CaX) from the waste material. MgX may be magnesium hydroxide, magnesium silicate, magnesium borate or magnesium carbonate. CaX may be calcium hydroxide, calcium silicate, calcium borate or calcium carbonate.

The crystal-free supernatant in feed tank 4 is then fed to the first crystallization reactor 14 via feed line 10. This crystal-free supernatant can be obtained using standard filtration or precipitation methods suitable for the pilot plant, including, but not limited to, any standard means. separation of solid and liquid phases, including filtration using a membrane or sintered material, centrifugal settling and gravitational settling. The first crystallization reactor 14 is maintained at a high temperature T ₂ . High temperature T ₂ may be from 40°C to 100°C, preferably from 55°C to 85°C, more preferably from 65°C to 75°C. This temperature provides lower solubility conditions for the lithium carbonate salt. In particular, the solubility may be from 2 mg/ml to 20 mg/ml, preferably from 5 mg/ml to 10 mg/ml. The first crystallization reactor 14 is further seeded with high purity lithium carbonate to provide a growth medium for lithium carbonate crystals. This seeding may involve the spontaneous formation of Li ₂ CO ₃ (primary nucleation) by heating the liquid phase to form a supersaturated solution, or the seeding may be by adding commercially available high purity (greater than 99.95%) Li ₂ CO ₃ . An example of this solubility variation is shown in FIG. 6 which is a solubility chart of lithium carbonate in water.

In principle, the temperature difference between the two containers can be as little as 1°C, however, a minimum temperature of 30°C is the most reasonable to provide a time and energy efficient method. In this regard, a higher temperature difference between T ₁ and T ₂ leads to less control over the crystallization of the lithium carbonate salt, but more lithium carbonate salt is formed. On the other hand, a lower temperature difference between T ₁ and T ₂ results in greater control of crystallization, but less lithium carbonate salt is formed. Regardless of this, the method of the claimed invention will work at any temperature difference between T ₁ and T ₂ , where the crystallization rate is controlled by controlling a combination of (i) the flow rate at the inlet and outlet of each of the tanks and (ii) the temperature difference between the reactors.

By controlling the crystallization rate, the present invention makes it possible to control the size, morphology and agglomeration of the crystals. The present invention also has the advantage of being able to control (i) the flow rate to and from each of the vessels and (ii) the temperature difference between the reactors as the process progresses so that changes in the crystallization rate can be made as needed. The inclusion of high purity lithium carbonate seeds further provides a means of reducing the degree of supersaturation and controlling the crystallization rate and morphology of the precipitated crystals.

For FIG. 6, the samples were processed using the general method above. Solubility measurements allow prediction of mass transfer efficiency on a volume basis. Samples were determined using a three-fold gravimetric analysis, determining the total mass of lithium carbonate in solution.

The first crystallization reactor 14 may include a mechanical agitator 16 which is used to effectively agitate and mix the reactor while maintaining a uniform distribution of concentration throughout the reactor. This mixing, in turn, ensures a uniform crystal growth rate and prevents clumping and agglomeration of the purified Li ₂ CO ₃ .

As an example of the method of the present invention, the feed tank 4 can be maintained at 20°C while the first crystallization reactor 14 is maintained at 90°C. This temperature difference of 70°C provides a theoretical mass throughput of 7 mg of lithium carbonate per ml of brine circulating between the two conditions. Since the brine enters the crystallization reactor 14 first at a higher temperature T ₂ , the brine becomes supersaturated with respect to the new temperature. This temperature difference causes crystallization, which displaces the lithium carbonate from the solution, thereby reducing the content of lithium carbonate in the solution.

The purified lithium carbonate 15 is collected at the bottom of the first crystallization reactor 14 and filtered through a filter 18 (e.g., a bag filter or filter press, or other filtration or sedimentation method suitable for the pilot plant, including, but not limited to, any standard separation media solids/liquids, including filtration using a membrane or sintered media, centrifugal settling and gravity settling) to collect purified, solid lithium carbonate.

In the simplest method of the present invention, the crystal-free liquid phase from the first crystallization reactor 14 is pumped back to the feed tank 4 via the return line 21, which is cooled in the line as it is returned. Thus, the liquid phase is now undersaturated compared to the lower temperature, allowing the lithium carbonate (dirty) from the solid phase to dissolve and return to the liquid phase at its equilibrium concentration. Impurities (such as Ca or MgCO ₃ ) remain in the solid phase since they will have the lowest solubility in the feed tank 4 (lower temperature T ₁ ) and will not further contaminate the liquid phase.

Then, the liquid phase cycling process is continued from the feed tank 4 (where lithium carbonate has a high solubility) to the first crystallization reactor 14 (where the solubility of lithium carbonate is low). This method creates a net mass transfer of lithium carbonate moving from the feed tank 4 to the first crystallization reactor 14. The liquid phase thus acts as a conveyor belt.

If the purity of the lithium carbonate in the first crystallization reactor 14 is insufficient, a second crystallization reactor 24 can be added along the flow path. The crystal-free supernatant containing lithium carbonate from the first crystallization reactor 14 will be fed to the second crystallization reactor 24 via a transfer line 20. Three temperatures will be used in this embodiment. The temperature T ₁ of the feed tank 4 will be the lowest temperature, the temperature T ₃ of the second crystallization reactor 24 will be the highest, and the temperature T ₂ of the first crystallization reactor 14 will be between the temperatures T ₁ and T ₃ . As before, the method will function if the temperature difference between T ₃ , T ₂ and T ₁ is only 1°C, however, a temperature difference of at least 10-20°C is preferred (T ₃ -T ₂ and T ₂ -T ₁ ), to ensure operation with acceptable efficiency. The second crystallization reactor is actually a clone of the first one with identical equipment (filtration, mixers, temperature control).

The second crystallization reactor 24 includes a mixer 26. The mixer 26 mixes the contents of the second crystallization reactor 24 to maintain a constant concentration (ie, to prevent gradients from occurring). Mixer 26 is not necessarily a physical mixer; the mixer 26 may simply be agitation by a liquid flow. However, in the preferred embodiment, mixer 26 is a physical mixer.

The purified lithium carbonate 25 is collected at the bottom of the second crystallization reactor 24 and filtered through a filter 28 (eg baghouse or filter press) to collect the purified solid lithium carbonate. The final recovered lithium carbonate is further subjected to a 50% clean water (reverse osmosis or distilled) wash in the filtration step before drying and final packaging.

The crystal-free liquid phase in the second crystallization reactor 24 is pumped back to the feed tank 4 via the transfer line 32, which is cooled in the line as it is returned. Thus, the liquid phase is now undersaturated compared to the concentration at the lower temperature, allowing the lithium carbonate (dirty) from the solid phase to dissolve and return to the liquid phase at its equilibrium concentration. Impurities (such as Ca or MgCO ₃ ) remain in the solid phase since they will have the lowest solubility in the feed tank 4 (lower temperature T ₁ ) and will not further contaminate the liquid phase.

The input selection valve 31 allows the operator to select (i) whether to recycle material from the first crystallization reactor 14 and/or the second crystallization reactor 24, or (ii) whether to direct the fresh brine 1 to be processed into the supply tank 4. Thus, the valve input selection 31 can choose whether to add new fresh material containing more Li ⁺ to enter the process or spent brine to dissolve the remaining dirty Li ₂ CO ₃ .

The addition of a second crystallization reactor 24 adds a fractional crystallization sequence in which the high impurity solids from the feed tank 4 are dissolved, crystallized once, yielding a purer solid in the first crystallization reactor 14, which is constantly in dynamic motion (dissolution and buildup). ) with a final crystallization event in the second crystallization reactor 24 to produce high purity material. Either gradually (continuous mode) or stepwise (batch mode), the purified crystals will be isolated by filtration or some other method of separating the solid and liquid phases. They will be removed from the reactor and isolated as the final purified product.

In another embodiment, multiple steps can be added as needed to adapt to virtually any brine chemistry, making the entire process modular, flexible, and highly adaptable, greatly increasing the variety of brines that can be processed with the process without the need for significant reconstructions of the entire design. In other words, more crystallization reactors (N+1) can be added as needed.

Each of the N+1 crystallization reactors contains a mixer 36. The mixer 36 mixes the contents of the N+1 crystallization reactor while maintaining a constant concentration (ie, prevents the formation of gradients). Mixer 36 is not necessarily a physical mixer; the mixer 36 can simply mix with the liquid flow.

Purified lithium carbonate 35 is collected at the bottom of the N+1 reactor for crystallization and filtered through a filter 38 (eg baghouse or filter press) to collect purified solid lithium carbonate. The finally recovered lithium carbonate is further washed 50 with pure water (reverse osmosis or distilled) in the filtration step, before drying and final packaging.

The crystal-free liquid phase from the N+1 crystallization reactor is pumped back to the feed tank 4 via the transfer line 40, which is cooled in the lines as it is returned. Thus, the liquid phase is now undersaturated compared to the concentration at the lower temperature, allowing the lithium carbonate (dirty) from the solid phase to dissolve and return to the liquid phase at its equilibrium concentration. Impurities (such as Ca or MgCO ₃ ) remain in the solid phase since they will have the lowest solubility in the feed tank 4 (lower temperature T ₁ ) and will not further contaminate the liquid phase.

Waste stream 55, after washing with pure crystalline solids, can be reused to recover Li using conventional means such as, but not limited to, solvent extraction.

After separation of the crystalline product in the filter, two separate spent waste streams are formed. The first waste stream is the spent supernatant from the hot reactor. The second waste stream is a wash, which is pure reverse osmosis water or deionized water at 70°C used to wash the filter cake. Wash water washes away the adhering supernatant and dissolves the outer layer of crystals. These waste streams are quite pure, the only other component being [Na+] or [K+]. Combining waste streams with a Li-selective solvent extract will make it possible to expediently recover any Li from wastewater, dramatically increasing efficiency. The solvent extract can then be used as a raw material for a recrystallization process.

After washing, the separated lithium carbonate is fed through line 60 to the dryer and then removed from the dryer through line 65.

As an additional method, dirty Li ₂ CO ₃ (crystalline material less than 99.5% pure) can be charged via line 19 to the first crystallization reactor 14. The crude crystalline material can be dissolved and then recrystallized (processed) to obtain pure crystalline material 15. This now pure crystalline material will be isolated by filtration or some other solid-liquid separation process as the final purified product. Again, several steps can be added to adapt to any purity of Li ₂ CO ₃ loaded through line 19.

During recrystallization, a suspension is obtained (dry batch and pure water or a thickened suspension from a hot crystallizer) and kept in a cold tank. A cold reservoir will provide non-diluting dissolution. The supernatant (filtered) from the cold reservoir is passed into the hot crystallizer at a controlled flow rate as before. The ability to use pure water with lower [Na] allows a purer product to be isolated. The supernatant from the hot tank (after filtration) is returned to the cold tank to re-dissolve the less pure crystals. This recrystallization can be carried out as a cascaded MSMPR (sequential temperature rise) step or by intermittent isolation, solvent washing and reloading of the dry crystals into pure water. In this last case, the solvent extracted material can be reintroduced into the system. With enough customization, continuous re-introduction of samples can be added to make the whole process run in a completely continuous fashion.

The present invention has a number of advantages over conventional methods.

First, less working solvent is required. Since the liquid phase is used primarily as a stock transporter from the feeder to the crystallizer, the process can potentially use a small working volume of brine, which greatly reduces the size of the processing reactor and the physical space required for the plant without compromising potential stock recovery capability. As such, the present method is more flexible and can be deployed in a wide variety of locations. With the addition of some form of built-in evaporation to the return loop, three other benefits could be realized. That is, (i) the process will become fully continuous as feedstock can be added as raw brine, (ii) purified solids/waste can be collected from the crystallizer or feeder, and (iii) spent brine can be concentrated and recycled to maximize lithium recovery. at even lower initial loads Li. Thus, the present invention may be a continuous process rather than a batch process.

Secondly, the rate of crystallization can be tightly controlled by the temperature difference between the reactors and the flow rate in and out of the tanks. In all other processes, the crystallization of lithium carbonate occurs at the expense of a high degree of supersaturation in order to maximize the recovery of the desired salt. While this promotes fast cleanup, it also results in less control of the crystallization rate and causes agglomerates to form. In the present invention, the overall degree of supersaturation is maintained at a relatively low level because the over-concentrated solution dosed into the larger reactor is a relatively small fraction (1% to 25% by volume) of the total retained medium. While the net mass recovered per unit time is thus smaller, a degree of crystal control (size, morphology and agglomeration) is easily achieved.

Thirdly, the method of the present invention is highly adaptable. Due to the ability of the present invention to change the flow, the rate of crystallization can be controlled even if the chemical composition of the input raw material suddenly changes. In one embodiment, this benefit is achieved by incorporating embedded analytics technology. In another embodiment, a microscopic probe of the crystallization process can be used to continuously monitor size, shape and quality (single crystal versus agglomerate) in a stream. Another embodiment may include an in-line ion chromatography system to track cation composition and concentration over time. These tools allow process conditions (eg, flow rate and temperature) to be adapted and continually modified to ensure optimal plant operation and can respond to changes in feed brine composition or other feedstock changes.

With regard to inline analytical technology, the concentration of other ions greatly affects the solubility of the target Li ₂ CO ₃ . The built-in analytical technology works to isolate pure material despite the salt-rich environment. Inline analytical technology (eg ion chromatography) can be used to adapt to variable input streams (eg adding too much or too little Na ₂ CO ₃ will cause fluctuations in solubility or crystallization behavior).

For example, turbidity tracking with the Blaze tool (Blaze 900 from Blaze Metrics) prevents system crashes, evaluates crystallization rates, and applies values to fix flow rate and temperature ranges. In general, turbidity monitoring is an important process metric to ensure that the system is operating within normal limits and that crystallization is proceeding properly. The Blaze tool allows you to track turbidity over time, which gives you the change in mass of crystals per unit time to confidently control crystallization (temperature and flow addition rates). In general, too rapid crystallization will result in agglomeration of the crystals. The Blaze tool also visualizes the crystals as they pass through the filter press to correlate the shape of the crystals with purity. The Blaze microscope reports the length of the cord, which gives a measurement of the size and shape of the crystals over time during the crystallization process. Thus, it is possible to (1) trigger changes in temperature, flow rate, or filtration time (setting operation) based on the Blaze data and (2) change dwell time and possibly make purity decisions based on crystal image data.

As another example, the composition of a brine can be monitored using ion chromatography. In particular, the concentration and composition of the brine can be monitored and quantified at several key control points. For example, inlet monitoring allows you to specify the exact amount of sodium carbonate needed to properly soften the inlet brine and check the initial state. In this regard, too much carbonate will also mean too high [Na+], causing an increase in the solubility of the product Li ₂ CO ₃ . Monitoring of the softened filtered supernatant gives [Li+] as it exits the cold tank and to confirm that only CaCO ₃ and other minor impurities are removed as solids from the cold tank (i.e. that chemical supersaturation is maintained without loss of Li ₂ CO ₃ in the cold tank). Monitoring of the hot filtered supernatant gives [Li+] after crystallization, which proves that the hot tank was hot enough to trigger crystallization.

Fourth, given the effect of NaCl concentration on the solubility of Li ₂ CO ₃ , very high brine concentrations can be used to increase recovery in the crystallization process. The maximum total mass of recovered Li ₂ CO ₃ is determined by the difference in solubility between two different temperatures in the reactors. With pure Li ₂ CO ₃ at 95°C the solubility is about 10 mg/ml. However, if the NaCl content exceeds 25% by weight, the solubility of Li ₂ CO ₃ falls below about 6 mg/ml. Thus, the use of a high concentration of NaCl to displace more Li ₂ CO ₃ from the solution and increase the recovery yield has its advantages. In contrast, in conventional crystallization processes, operation at high concentrations of NaCl results in a high degree of contamination and a decrease in the purity of the final Li ₂ CO ₃ . The continuous crystallization of the present invention exploits this combined solubility behavior while achieving high purity Li ₂ CO ₃ in this process.

With these advantages, the present invention provides a reduction in the final cost of production by reducing the energy requirement for material processing and additionally offers advantages in terms of greenhouse gas equivalents released during processing.

EXAMPLES

Solids samples from both the feed tank (dissolver) and the crystallization reactor (crystallizer) were isolated and analyzed by ICPOES. The results are shown in FIG. 7. It has been found that the solids samples from the dissolvers gradually decrease in purity as Li ₂ CO ₃ is recovered, leaving behind mostly CaCO ₃ . Samples from the crystallizer retained high purity. The current triplicate error rates in the ICPOES data confirm that the sample is >99% pure (i.e., greater than 99.5% pure).

References in the present invention to terms such as "vertical", "horizontal", etc., are given by way of example, and not by way of limitation, in order to set the scope. It is clear that various other scopes of consideration can be applied to describe the invention without deviating from the essence and scope of the invention. It is also clear that features of the invention are not necessarily shown in the drawings to scale. Furthermore, to the extent that the terms "consists of", "includes", "having", "has", "with", or variations thereof are used in either the detailed description or the claims, these terms are intended to be inclusive and open, like the term "inclusive".

References in the present invention to terms modified by the approximation expression, such as "about", "approximately" and "substantially", should not be limited to the exact meaning indicated. The approximation expression may correspond to the accuracy of the instrument used to measure the value and, unless otherwise dependent on the accuracy of the instrument, may indicate +/-10% of the set value(s).

An element "connected" or "connected" to another element may be directly connected to or associated with another element, or, instead, one or more intermediate elements may be present. An element can be "directly connected" or "directly connected" to another element if there are no intermediate elements. An element may be "indirectly connected" or "indirectly connected" to another element if at least one intermediate element is present. An element "on" or "in contact" with another element may be directly on or in direct contact with another element, or one or more intermediate elements may be present instead. An element may be "directly on" or in "direct contact" with another element if there are no intermediate elements. An element may be "indirectly on" or in "indirect contact" with another element if at least one intermediate element is present.

The terminology used in the present invention is only intended to describe specific embodiments and is not intended to limit the invention. As used in the present invention, the singular forms "a", "an" and "the" are also intended to include plural forms, unless the context clearly indicates otherwise. In addition, it should be understood that the terms "comprises" and/or "comprising" when used in the present invention determine the presence of the claimed features, integers, steps, operations, elements and/or components, but does not exclude the presence or addition of one or more other signs, integers, stages, operations, elements, components and/or their groups.

Although the invention has been illustrated by the description of various embodiments, and although these embodiments are described in sufficient detail, it is not the applicant's intention to limit the scope of the appended claims in any way to these details. Additional advantages and modifications will be apparent to those skilled in the art. Thus, the present invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and the illustrative example shown and described. In the interest of fully enabling those of ordinary skill in the art to make and use the claimed invention, Applicant has provided information on both the advantages and disadvantages of various detailed embodiments. It will be appreciated by those skilled in the art that in some applications the disadvantages of the particular embodiment detailed above can be completely avoided and are outweighed by the overall benefits provided by the claimed invention. Accordingly, departures from the above detailed descriptions may be made without departing from the spirit or scope of Applicant's general inventive concept.

Claims (18)

1. A method for extracting lithium from a crude brine, including: loading the crude brine (1) into a feed tank (4) maintained at T ₁ and containing a carbonate source sufficient to precipitate all of the carbonate-forming solids in the crude brine (1) to form a precipitated mixture and a crystal-free supernatant, and supplying the crystal-free supernatant from the feed tank (4) to the first crystallization reactor (14), which is maintained at a temperature T ₂ , crystallizing the lithium carbonate salt from the crystal-free supernatant, where the temperature value T₁ less than the temperature value T₂, And controlling the flow rate by maintaining an equilibrium concentration of lithium carbonate in the dissolved phase of the crystallization reactor (14). 2. The method of claim 1, further comprising: feeding the liquid phase from the first crystallization reactor (14) back to the feed tank (4). 3. Process according to claim 1 or 2, wherein high purity lithium carbonate nuclei are introduced into the first crystallization reactor (14). 4. The method according to any one of paragraphs. 1-3, further comprising: feeding the liquid phase from the first crystallization reactor (14) to the second crystallization reactor (24), which is maintained at a temperature T ₃ , where the temperature value T ₃ is greater than the temperature value T ₂ . 5. The method according to any one of paragraphs. 1-4, wherein the carbonate source is sodium carbonate, potassium carbonate, or carbon dioxide. 6. The method according to any one of paragraphs. 1-5, further comprising: feeding the liquid phase from the first crystallization reactor (14) to the second crystallization reactor (24), which is maintained at a temperature T ₃ , where the value of the temperature T ₃ is greater than the value of the temperature T ₂ , and continuation of the method of supplying the liquid phase from the "n" crystallization reactor to the "n+1" crystallization reactor, where the "n+1" crystallization reactor is maintained at a temperature greater than the temperature of the "n" crystallization reactor, where "n" is an integer greater than or equal to 2. 7. The method according to any one of paragraphs. 1-6, in which the flow rate is sufficient to maintain an equilibrium concentration of dissolved lithium carbonate in the dissolved phase, so that the total mass flow rate of crystallization is greater than the maximum applied flow rate. 8. The method according to any one of paragraphs. 1-7, in which the flow rate is adjusted to ensure the rate of addition of the solution to achieve 50-250 g Li ₂ CO ₃ per hour.

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