Use of high-boiling organic solvents for lithium carbonate extraction from silicates

Abstract

Admixtures and processes for extracting lithium from lithium-bearing silicates are disclosed In one example, the process includes reacting a lithium-bearing silicate with a sodium carbonate in a protic high-boiling (PHB) solvent thereby producing a mixture containing solid lithium carbonate and a sodium aluminosilicate. (Figure 1)

Description

USE OF HIGH-BOILING ORGANIC SOLVENTS FOR LITHIUM CARBONATE EXTRACTION FROM SILICATESRelated Applications

[0001] The present application claims convention priority from Australian provisional patent applications 2024902926 (13 September 2024) and 2024903068 (24 September 2024). The content of AU’926 and AU’ 068 is incorporated herein by reference in its entirety.Field of the Invention

[0002] The herein described invention relates to processes for the extraction and recovery of lithium carbonate from lithium containing aluminosilicate materials in organic solvents.Background of the Invention

[0003] Any discussion of the publications throughout the specification should in no way be considered as an admission that such publications are widely known or forms part of common general knowledge in the field.

[0004] At an industrial level, lithium is assuming ever-increasing popularity given its many uses: ceramics, glasses, batteries, electronics, lubricating greases, metallurgy, pyrotechnics, air purification, optics, polymer chemistry, military applications and medicine — to name but a few. One of the principal uses of lithium is in batteries — and demand has grown significantly since all-electric vehicles assumed a foothold in the market. Lithium is especially amenable to use in batteries owing to its high electrode potential; and because of its low atomic mass, lithium batteries have high charge-to-weight and power-to-weight ratios. Depending on the design, lithium batteries can produce from 1.5 V (comparable to a zinc-carbon or alkaline battery) to about 3.7 V.

[0005] Lithium carbonate is an important commodity chemical notably useful for the production of lithium-ion batteries. Standard grades for lithium carbonate include: “Industrial Grade” which comprises <99% Li2CO3 on a molar basis; “Technical Grade” which comprises 99% Li2CO3; “Battery Grade” which comprises 99.5% Li2CO3 and accounts for about 75% of the global battery market (2022); “EV Grade” which comprises 99.9% Li2CO3 and accounts for 15% of the worldwide battery market; andfinally, “EV-Plus Grade” lithium carbonate which is 99.99% pure and accounts for the remaining 10% of the market. Notably, the battery grade (battery, EV, and EV+) specifications continue to evolve and become more stringent, not just in purity but in allowable concentrations of specific impurities and in crystal size, shape, and morphology.

[0006] Naturally, lithium occurs in a number of pegmatites, in ocean water, brine wells, and phyllosilicates. It is from the pegmatites and brine waters that lithium is obtained on a commercial basis.

[0007] Of the pegmatites, spodumene is the most common commercially exploited lithium mineral. It is a pyroxene mineral comprising lithium aluminosilicate, LiAl(SiO3)2. The normal low-temperature form, a-spodumene, is monoclinic whereas the high-temperature forms, y- and P-spodumene are hexagonal and tetragonal system, respectively. The thermal activation of a-spodumene can produce a mixture of y- and P- spodumene at temperatures above 900 °C.

[0008] Methods of extracting lithium from spodumene can be classified according to three broad categories: acidic, caustic, and “green”. Typically, all extraction methods require calcination of the a-spodumene (thermal conversion to the P-form), as less than 1% of the lithium contained in a-spodumene is extractable due to the monoclinic crystal structure being largely impenetrable to extraction media and ion mobility being extremely low.

[0009] Acid leaching of lithium from P-spodumene is typically characterised by harsh conditions. In general, a first step is mixing the P-spodumene with concentrated sulfuric acid (96%) at about 250 °C in a sulfating kiln. Therein, the lithium aluminosilicates react to form lithium sulfate which is highly soluble in water.Hydrometallurgical steps follow this acid roasting and leaching, and after crystallisation with soda ash, a Li2CO3 product with a purity of about 98-99 % is precipitated in excellent yields.

[0010] It will be appreciated that the industrial-scale use of strong, concentrated acids, soda ash and other reagents in relation to spodumene extraction can be expensive, inconvenient and environmentally-damaging. Further, the sequence of extraction steps before a commercially saleable technical grade lithium carbonate is obtained can be somewhat labour-intensive.

[0011] International Patent Publication WO 2018 / 157203, now assigned to the present Applicant, proposed for the first time a “green” method for the extraction oflithium carbonate from spodumene using relatively mild conditions (temperature, pressure, time) and most significantly, using carbonic acid as the extraction medium. Commercialisation of this technology is ongoing.

[0012] Other methods of extracting lithium from its constituent ores involve the use of caustic sodium. For instance, when sodium carbonate and an excess of water are applied under specific conditions, the sodium displaces the lithium, and the resultant lithium carbonate then leaches into the aqueous solvent. The lithium carbonate is then removed from the aqueous solution using CO2 to acidify the solution and facilitate precipitation. An example of such a process is US Patent No. 3,112,172, dated 5 December 1960, and assigned to the Department of Natural Resources of the Province of Quebec, Canada.

[0013] Previous publications include: Grasso, M.L. et al., “Lithium extraction from P-LiAlSi20e using NazCOs through thermal reaction” Minerals Engineering 176 (2022) 107349; Xiong Lu et al., “Extraction of Lithium and Synthesis of Kaolinite from a-Spodumene via Alkali Calcination” Chemistry Select 4 January 2024, 9, e202304480; Chen, Y. et al., “Preparation of lithium carbonate from spodumene by a sodium carbonate autoclave process”, 2011, Hydrometallurgy, vol 109, no. 1, pp 43-46; US 2015 / 0044124; US 3,112,172; US 4,124,684; US 2020 / 0071794; WO 2021 / 148403; WO 2018 / 157203; WO 2019 / 204707 and US 2024 / 0102126.

[0014] Other representative publications include US Patent Nos. 11,292,725; and 9,255,012 to Outotec (Metso); and US Pat. Nos. 4,124,684; 3,380,802; 3,310,368; 3,131,022; 3,112,171; 3,112,170; and 3,017,243 to Quebec, commonly known as the Quebec Process.

[0015] It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

[0016] It is an object of an especially preferred form of the present invention to provide an improved process for extracting lithium carbonate from lithium-bearing silicates that overcomes the disadvantages of conventional methods. Traditional extraction techniques often rely on harsh acids or caustic reagents, which can be costly, environmentally damaging, and operationally complex.Summary of the Invention

[0017] The present invention relates to an improved process for extracting lithium carbonate from lithium-bearing silicate minerals, such as spodumene, usingprotic high-boiling (PHB) organic solvents. Unlike traditional methods that rely on harsh acids or caustic reagents, the disclosed process employs a PHB solvent — such as ethylene glycol or glycerol — in which sodium carbonate is dissolved. When the lithium-bearing silicate is mixed with sodium carbonate in this solvent and heated, a sodium-for-lithium exchange reaction occurs, resulting in the formation of solid lithium carbonate and a sodium aluminosilicate by-product. The process is designed to maximise lithium recovery while minimising the use of water and aggressive chemicals. The invention has a cyclic and continuous process design, which emphasises the recycling of reagents and solvents.

[0018] The invention aims to simplify the extraction process, reduce the need for aggressive chemicals, and achieve high yields of lithium carbonate with greater purity. This approach not only streamlines the overall process but also enhances safety and sustainability, making it more suitable for modem industrial applications. The provides a process that is both economically and environmentally advantageous through the recycling of key reagents and solvents. The cyclic and continuous embodiments of the process are designed to minimise waste, reduce raw material consumption, and lower operational costs. This closed-loop approach not only lessens the environmental footprint of lithium production but also supports scalability and adaptability for large-scale industrial operations, addressing the growing global demand for battery -grade lithium carbonate in a responsible and efficient manner.

[0019] Overall, the invention provides a more sustainable and economically viable approach to lithium extraction, particularly suited to the growing demand for battery-grade lithium carbonate. By avoiding the use of strong acids and minimising waste generation, the process offers significant advantages in terms of safety, efficiency, and environmental responsibility. Its adaptability to both batch and continuous industrial operations makes it highly relevant for modem lithium supply chains, supporting the transition to cleaner energy technologies and the expanding electric vehicle market.

[0020] According to a first aspect of the present invention there is provided a process for extracting lithium from a lithium-bearing silicate, the process comprising:

[0021] reacting an admixture of the lithium-bearing silicate with a sodium carbonate in a protic high-boiling (PHB) solvent thereby producing a mixture containing solid lithium carbonate and a sodium aluminosilicate,

[0022] wherein the admixture includes the sodium carbonate in a total amount sufficient to provide a molar ratio of sodium to lithium of at least 1 : 1; and

[0023] separating the lithium carbonate from the sodium aluminosilicate.

[0024] In an embodiment, the admixture is reacted to the point where substantially all of the lithium in the silicate has been converted to a lithium carbonate.

[0025] In one embodiment, the process is carried out under conditions that ensure the reaction proceeds to completion, such that substantially all of the lithium originally present in the lithium-bearing silicate is converted into lithium carbonate. This is achieved by carefully controlling the amount of sodium carbonate added, the reaction temperature, and the duration of the process, as well as by maintaining optimal mixing and solvent conditions. By driving the reaction to this extent, the process maximises lithium recovery, resulting in a highly efficient extraction method that leaves only trace amounts of lithium in the spent silicate residue. This approach is particularly advantageous for industrial applications where high yield and resource efficiency are critical.

[0026] In an embodiment, a mass ratio of the PHB solvent to the silicate is less than about 5: 1.

[0027] In an embodiment, the reaction is at a temperature of about 110 °C to about 350 °C.

[0028] In an embodiment, the reaction is in an oxygen-free environment.

[0029] In an embodiment, the admixture is free of water.

[0030] In an embodiment, the lithium-bearing silicate is a P-spodumene.

[0031] In an embodiment, the PHB solvent has a boiling point greater than about180 °C.

[0032] In an embodiment, the PHB solvent includes ethylene glycol, propylene glycol, methoxyethanol, ethoxyethanol, methoxypropanol, ethoxypropanol, diethylene glycol, dipropylene glycol, glycerol, 3 -m ethoxy- 1,2-propane diol, 2-methyl-l,3- propanediol, and / or trimethylolmethane.

[0033] In an embodiment, the process further comprises the steps of:

[0034] admixing P-spodumene with a sodium carbonate, such that an atomic ratio of Na from the sodium carbonate:Li in the P-spodumene is greater than 1, in a protic high-boiling (PHB) solvent such that a liquid: solids ratio is about 5: 1 to about 1 :1 by weight; and

[0035] maintaining the admixture at a reaction temperature of about 120 °C to about 350 °C thereby providing crystalline lithium carbonate.

[0036] In an embodiment, the process further comprises the step of:

[0037] heating the admixture to the temperature and then maintaining the admixture at the temperature; wherein heating the admixture includes distilling water therefrom and thereby providing an anhydrous admixture.

[0038] In an embodiment, the PHB solvent includes ethylene glycol, propylene glycol, methoxyethanol, ethoxyethanol, methoxypropanol, ethoxypropanol, diethylene glycol, dipropylene glycol, glycerol, 3 -m ethoxy- 1,2-propane diol, 2-methyl-l,3- propanediol, and / or trimethylolmethane.

[0039] In an embodiment, a solubility of the sodium carbonate in the PHB solvent at the reaction temperature is at least ten times (lOx) greater than the solubility of lithium carbonate in the PHB solvent at the reaction temperature.

[0040] In an embodiment, the admixture is free of water or substantially free of water.

[0041] In an embodiment, the process further comprises the steps of:

[0042] separating the PHB solvent from the mixture that includes the solid lithium carbonate and sodium aluminosilicate;

[0043] recycling the PHB solvent and any unreacted sodium carbonate to the reacting step;

[0044] leaching lithium from the solid residue by admixing the solid residue with water and carbon dioxide to form a slurry of a lithium bicarbonate solution and a solid sodium aluminosilicate residue;

[0045] separating the lithium bicarbonate solution from the solid sodium aluminosilicate residue;

[0046] crystallising lithium carbonate from the lithium bicarbonate solution;

[0047] separating the crystalised lithium carbonate from a mother liquor; and

[0048] recycling the mother liquor to the leaching step.

[0049] In an embodiment, the lithium-bearing silicate is a P-spodumene.

[0050] In an embodiment, the PHB solvent is separated from the solid residue without cooling the slurry.

[0051] In an embodiment, crystallising the lithium carbonate includes removing carbon dioxide from the lithium bicarbonate solution; and wherein the carbon dioxide is recycled to the leaching step.

[0052] In an embodiment, the lithium carbonate produced has a purity of at least 99.5%.

[0053] In an embodiment, the lithium-bearing silicate is selected from the groupconsisting of P-spodumene, lepidolite, petalite, lithium clays, and mixtures thereof.

[0054] In an embodiment, the PHB solvent comprises a mixture of ethylene glycol and glycerol.

[0055] According to a second aspect of the present invention there is provided an apparatus for extracting lithium carbonate from a lithium-bearing silicate, comprising:

[0056] (a) a reactor for reacting an admixture of the lithium-bearing silicate, sodium carbonate, and a PHB solvent;

[0057] (b) a separation unit for isolating solid lithium carbonate from sodium aluminosilicate;

[0058] (c) a recycling system for the PHB solvent and unreacted sodium carbonate; and

[0059] (d) a crystallisation unit for recovering crystallised lithium carbonate from a lithium bicarbonate solution.

[0060] According to a third aspect of the present invention there is provided a slurry for use in the extraction of lithium carbonate, the slurry comprising a lithium- bearing silicate, sodium carbonate, and a protic high-boiling solvent, wherein the slurry is anhydrous or substantially anhydrous.

[0061] According to a fourth aspect of the present invention there is provided lithium carbonate when produced by the process of the first aspect of the invention, wherein the lithium carbonate is suitable for use in battery manufacturing.

[0062] In a further aspect, the present invention provides a process for extracting lithium from a lithium-bearing silicate, the process comprising:

[0063] reacting an admixture of the lithium-bearing silicate with a sodium carbonate in a protic high-boiling (PHB) solvent thereby producing a mixture containing solid lithium carbonate and a sodium aluminosilicate, wherein the admixture includes the sodium carbonate in a total amount sufficient to provide a molar ratio of sodium to lithium of at least 1 : 1;

[0064] separating the lithium carbonate from the sodium aluminosilicate.

[0065] In an embodiment, the admixture is reacted to the point where substantially all of the lithium in the silicate has been converted to a lithium carbonate.

[0066] In an embodiment, a mass ratio of the PHB solvent to the silicate is less than 5: 1.

[0067] In an embodiment, the reaction is at a temperature of about 110 °C to the boiling point of the PHB solvent at standard pressure.

[0068] In an embodiment, the reaction is at a temperature of about 110 °C to about 350 °C.

[0069] In an embodiment, the reaction is in an oxygen-free environment.

[0070] In an embodiment, the reaction is oxygen (O2)-free.

[0071] In an embodiment, the admixture is reacted in an inert-gas environment thereby preventing the oxidation or degradation of the PHB solvent.

[0072] In an embodiment, the admixture is free of water.

[0073] In an embodiment, the lithium-bearing silicate is a spodumene, lepidolite, petalite, amblygonite, zinnwaldite, lithium-clay, or admixture thereof.

[0074] In an embodiment, the lithium-bearing silicate is a calcined lithium- bearing silicate.

[0075] In an embodiment, the calcined lithium-bearing silicate is a P-spodumene.

[0076] In an embodiment, the admixture is reacted for a time of about 1 minute to about 180 minutes.

[0077] In an embodiment, the PHB solvent has a boiling point greater than about 180 °C.

[0078] In an embodiment, the PHB solvent has a melting point in a range of about 10 °C to about 150 °C.

[0079] In an embodiment, the PHB solvent includes ethylene glycol, propylene glycol, methoxyethanol, ethoxyethanol, methoxypropanol, ethoxypropanol, diethylene glycol, dipropylene glycol, glycerol, 3 -m ethoxy- 1,2-propane diol, 2-methyl-l,3- propanediol, and / or trimethylolmethane.

[0080] In a further aspect, the present invention provides a process for producing lithium carbonate comprising:

[0081] admixing P-spodumene with a sodium carbonate, such that an atomic ratio of Na from the sodium carbonate:Li in the P-spodumene is greater than 1, in a protic high-boiling (PHB) solvent such that a liquid: solids ratio is about 5: 1 to about 1 :1 by weight; and

[0082] maintaining the admixture at a reaction temperature of about 120 °C to the boiling point of the PHB solvent at a pressure of about 0.8 to about 2 bar for about 1 minute to about 180 minutes.

[0083] In an embodiment, a sodium carbonate includes anhydrous sodium carbonate, sodium carbonate monohydrate, sodium carbonate heptahydrate, sodium carbonate decahydrate, sodium sesquicarbonate, sodium bicarbonate, or mixtures thereof.

[0084] In an embodiment, a sodium carbonate is anhydrous sodium carbonate.

[0085] In an embodiment, the process further includes heating the admixture to the temperature and then maintaining the admixture at the temperature; wherein heating the admixture includes distilling water therefrom and thereby providing an anhydrous admixture.

[0086] In an embodiment, the the PHB solvent includes ethylene glycol, propylene glycol, methoxyethanol, ethoxyethanol, methoxypropanol, ethoxypropanol, di ethylene glycol, dipropylene glycol, glycerol, 3 -methoxy- 1,2-propane diol, 2-methyl- 1,3 -propanediol, and / or trimethylolmethane.

[0087] In an embodiment, a solubility of the sodium carbonate in the PHB solvent at the reaction temperature is at least ten times (lOx) greater than the solubility of lithium carbonate in the PHB solvent at the reaction temperature.

[0088] In an embodiment, the admixture is free of water.

[0089] In a further aspect, the present invention provides a cyclic process for producing lithium carbonate and sodium aluminosilicate from a lithium-bearing silicate comprising:

[0090] admixing, in a protic high-boiling (PHB) solvent, the lithium-bearing silicate and sodium carbonate, such that a Li:Na atomic ratio is about 1 : 1 to about 1 :2, at a temperature of about 120 °C to about 300 °C, thereby forming a slurry containing solid lithium carbonate and sodium aluminosilicate;

[0091] separating the PHB solvent from a solid residue that includes the solid lithium carbonate and sodium aluminosilicate;

[0092] recycling the PHB solvent and any unreacted sodium carbonate to the admixing step;

[0093] leaching lithium from the solid residue by admixing the solid residue with water and carbon dioxide to form a slurry of a lithium bicarbonate solution and a solid sodium aluminosilicate residue;

[0094] separating the lithium bicarbonate solution from the solid sodium aluminosilicate residue;

[0095] crystallising lithium carbonate from the lithium bicarbonate solution;

[0096] separating the crystalised lithium carbonate from a mother liquor; and

[0097] recycling the mother liquor to the leaching step.

[0098] In an embodiment, the lithium-bearing silicate is a P-spodumene.

[0099] In an embodiment, the PHB solvent is separated from the solid residuewithout cooling the slurry.

[0100] In an embodiment, crystallising the lithium carbonate includes removing carbon dioxide from the lithium bicarbonate solution; and wherein the carbon dioxide is recycled to the leaching step.

[0101] In a further aspect, the present invention provides a continuous process for producing lithium carbonate and sodium aluminosilicate from a lithium-bearing silicate, the process comprising:

[0102] passing an admixture of a protic high-boiling (PHB) solvent, the lithium- bearing silicate, and anhydrous sodium carbonate through a reactor at a temperature below the standard pressure boiling point of the PHB solvent, thereby producing a slurry of lithium carbonate and sodium aluminosilicate in the PHB solvent;

[0103] separating the PHB solvent from a commixture of lithium carbonate and sodium aluminosilicate, and recycling the PHB solvent to the reactor;

[0104] admixing, in a leach tank, water and carbon dioxide with the commixture thereby leaching lithium bicarbonate into the water;

[0105] separating the lithium bicarbonate in water from the sodium aluminosilicate;

[0106] crystallising lithium carbonate from the lithium bicarbonate in water by heating and removing carbon dioxide;

[0107] recycling the carbon dioxide to the leach tank; and

[0108] separating the crystallised lithium carbonate from the water and recycling the water to the leach tank.

[0109] In an embodiment, the residence time in the reactor is about 1 minute to about 180 minutes.

[0110] In an embodiment, the reactor is a stirred-tank reactor.

[0111] In an embodiment, the reactor is a pipe.

[0112] In an embodiment, the separated PHB solvent includes unreacted sodium carbonate.

[0113] In a further aspect, the present invention provides a slurry comprising: an admixture of a lithium-bearing silicate carried in a fluid that includes sodium carbonate and a protic high-boiling (PHB) solvent.

[0114] In an embodiment, the lithium bearing silicate is a P-spodumene.

[0115] In an embodiment, the slurry is anhydrous.

[0116] Although the invention will be described with reference to specificexamples it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.Brief Description of the Figures

[0117] For a more complete understanding of the disclosure, reference should be made to the following detailed description and accompanying drawings wherein:

[0118] Figure 7 is a process flow diagram of one embodiment described herein.

[0119] Figure 2 is a process flow diagram of another embodiment described herein.

[0120] While specific embodiments are illustrated in the drawings, with the understanding that the disclosure is intended to be illustrative, these embodiments are not intended to limit the invention described and illustrated herein.Definitions and Nomenclature

[0121] Objects, features, and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating specific embodiments of the 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 those skilled in the art from this detailed description.

[0122] Herein, the use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims and / or the specification may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.”

[0123] The term “about” means, in general, the stated value plus or minus 5%.

[0124] The use of the term “or” in the claims is used to mean “and / or” unless explicitly indicated to refer to alternatives only or the alternative are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and “and / or.”

[0125] Unless the context clearly requires otherwise, the words “comprise”, “comprising”, “include”, “including” and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”. As used herein, the phrase “consisting of’ excludes any element, step, or ingredient not expressly presented. When the phrase “consists of’ (or variations thereof) appears in a clause of the body of a claim, rather than immediatelyfollowing the preamble, it limits only the element set forth in that clause; other elements are not excluded from the claim as a whole. As used herein, the phrase “consisting essentially of’ limits the scope of a claim to the specified elements or method steps, plus those that do not materially affect the basis and novel characteristic(s) of the claimed subject matter.

[0126] The transitional phrase “consisting of’ excludes any element, step, or ingredient not specified. If in the claim, such would close the claim to the inclusion of materials other than those recited except for impurities ordinarily associated therewith. When the phrase “consisting of’ appears in a clause of the body of a claim, rather than immediately following the preamble, it limits only the element set forth in that clause; other elements are not excluded from the claim as a whole.

[0127] The transitional phrase “consisting essentially of’ is used to define a composition, process or method that includes materials, steps, features, components, or elements, in addition to those literally disclosed, provided that these additional materials, steps, features, components, or elements do not materially affect the basic and novel characteristic(s) of the claimed invention. The term “consisting essentially of’ occupies a middle ground between "comprising" and “consisting of’.

[0128] The recitation of a numerical range using endpoints includes all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.).

[0129] The terms “preferred” and “preferably” refer to embodiments of the invention that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances.Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful and is not intended to exclude other embodiments from the scope of the invention.

[0130] Percentages in general are on a weight / weight basis (i.e., % w / w; wt.%).

[0131] This specification is prepared having regard to the principles of general application. As such, where the specification discloses a principle of general application, the claims may be drafted in correspondingly general terms (Biogen vMedeva

[1997] RPC 1 at 48). A “principle of general application” is a general principle that can be practically applied in making a class of products, or in working a process, including where the claims define the products or processes in terms of the result to be achieved.Detailed Description

[0132] In order to achieve a satisfactory yield of lithium, the decomposition of silicates with alkali metal salts involves specific conditions, depending upon the particular alkali metal salt employed. The commercial processes for producing lithium salts generally do not act on the silicates directly with alkali metal salts, but employ relatively drastic preliminary steps, for example, decomposition with sulfuric acid to form lithium sulfate and a discardable residue. The lithium sulfate is then converted to the carbonate, and then, if desired, to further end salts.

[0133] Herein, the direct exchange of an alkali metal cation (e.g., sodium or potassium) for the lithium cation in the silicate (or aluminosilicate) delivers excellent recovery of the lithium without the inhibition often occurring in aqueous reaction conditions. Accordingly, a first embodiment is a process for extracting lithium from a lithium-bearing silicate, that is preferably run anhydrous. In one example, the process can include reacting an admixture of the lithium-bearing silicate with a sodium carbonate in a protic high-boiling (PHB) solvent thereby producing a mixture containing solid lithium carbonate and a sodium aluminosilicate. Preferably, the admixture includes the sodium carbonate in a total amount sufficient to provide a molar ratio of sodium to lithium (the lithium present in the lithium-bearing silicate) of at least 1, preferably at least 1.05, 1.1, 1.15, 1.2, or 1.25. That is, the sodium is preferably not a limiting reagent in a sodium-for- lithium exchange reaction. The process further can include separating the lithium carbonate from the sodium aluminosilicate.

[0134] Notably and throughout, the reaction of a sodium carbonate with the lithium-bearing silicate occurs in a protic high-boiling (PHB) solvent. Preferably, these PHB solvents are organic solvents with at least one hydroxyl group, more preferably multiple hydroxyl groups. Importantly, sodium carbonate has an appreciable solubility in the PHB solvents. That is, sodium carbonate can dissolve at concentrations of at least Ig / L in the PHB solvent. Preferably, sodium carbonate has a solubility in the PHB solvent of at least about 1 g / L, 5 g / L, 10 g / L, 20 g / L, 50 g / L, 75 g / L, or 100 g / L; more preferably the sodium carbonate solubility at the reaction temperature is at least about 100 g / L, 250 g / L, or 500 g / L. The reactions described here and throughout this disclosure are preferably two-phase reactions (liquid / solid) based on a sodium carbonate solution (in the PHB solvent) acting on a lithium-bearing silicate solid; and thereby producing a two- phase product (slurry) that includes a liquid phased of the PHB solvent and any unreacted sodium carbonate and a solid phase (commixture) of lithium carbonate and the spentsilicate.

[0135] Notably, the reactants and reaction conditions are preferably predetermined such that the admixture is reacted to the point where substantially all of the lithium in the silicate has been converted to lithium carbonate (U2CO3). That is, the extraction efficiency of the exchange reaction is in excess of 90%, 95%, or 98% and the spent silicate retains less than about 10%, 5%, or 2% of its original concentration of lithium.

[0136] The PHB solvents may be specifically chosen to promote the dissolution of sodium carbonate while maintaining very low solubility for lithium carbonate, which facilitates efficient precipitation and separation of the lithium product. This approach enables a sodium-for-lithium exchange reaction under controlled conditions, allowing for high yields of lithium carbonate with minimal contamination from other phases.

[0137] The PHB solvent preferably dissolves all of the sodium carbonate in the reaction admixture. In alternative examples, the PHB solvent dissolves a sufficient proportion of the sodium carbonate to facilitate a facile sodium for lithium exchange. In still other examples, the PHB solvent dissolves sodium carbonate to an extent that the solution (solvent plus dissolved sodium carbonate) includes at least one sodium to lithium present in the silicate, that is the solution and silicate have a sodium to lithium molar ratio of at least 1 : 1. Notably, the reaction mixture, can further include undissolved sodium carbonate that dissolves during the exchange reaction of sodium for lithium thereby facilitating the completion of the sodium for lithium exchange.

[0138] In view of the dissolution of the sodium carbonate, the process, preferably, includes a mass ratio of the PHB solvent to the silicate (liquid: solid) having a value less than about 10, 9, 8, 7, or 6; more preferably, less than about 5, 4, 3, or 2. Notably, the PHB solvent weight precent (or L:S ratio value) is limited primarily by the solubility of the sodium carbonate and any required pumping / mixing viscosities; wherein, preferably, the sodium carbonate is fully soluble in the solvent at the reaction temperature and the viscosity of the slurry (starting slurry and product slurry) are sufficiently low to allow for facile manipulation with industrial pumps, mixers, and other systems.

[0139] The sodium for lithium exchange reaction may occur at room temperature but for the facile exchange of sodium for lithium, the reaction is preferably run at elevated temperatures. In one example, the reaction is at a temperature of about 110 °C to the boiling point of the PHB solvent at standard pressure. Preferably, the reaction is at atemperature of about 110 °C to about 350 °C, about 120 °C to about 300 °C, about 150 °C to about 250 °C. In a preferable instance, the reaction temperature is about 125 °C, 150 °C, 175 °C, 200 °C, 225 °C, 250 °C, 275 °C, 300 °C, or a temperature therebetween.

[0140] Due, in part, to the high temperatures of the reaction, the process is preferably run in an air-free or oxygen-free environment; thereby preventing the oxidation or combustion of the PHB solvent. Notably, this would prolong the usability of the solvent and reduce the need for future solvent purification processes. In one example, the reaction is run oxygen (O2)-free; in another example, the admixture is reacted in an inert-gas environment (e.g., nitrogen or argon) thereby preventing the oxidation or degradation of the PHB solvent. Still further, as the reaction is run at high temperature with reagents and / or products that can react with or be affected by water; the admixture is preferably free of water.

[0141] While the application of the herein described process may be applicable to a plurality of lithium bearing materials, the process is particularly relevant to the liberation of lithium from lithium -bearing silicates; preferably lithium-bearing ores and minerals. In one instance, the lithium-bearing silicate can be a spodumene, lepidolite, petalite, amblygonite, zinnwaldite, lithium-clay, or admixture thereof. Notably, the process is particularly relevant to lithium-bearing hard rock, for example, spodumene and petalite. In another instance, the process can be applied to the recovery of lithium from layered or soft minerals, for example lepidolite and lithium-clays (particularly those found in and around the McDermitt Caldera). In a particularly preferable instance, the lithium-bearing silicate is a spodumene.

[0142] In another particularly preferably instance, the lithium-bearing silicate is a calcined lithium-bearing silicate. That is, a lithium-bearing silicate that has been heated to or above a transition temperature whereby the crystal structure of the lithium-bearing silicate is affected. One example of a calcined lithium-bearing silicate is P-spodumene which can be prepared by the calcination of a-spodumene or petalite and may be available from the calcination of other lithium-bearing silicates. In another instance, the lithium-bearing silicate can be a-spodumene, P-spodumene, and / or y-spodumene.

[0143] The reaction time can be dependent on the lithium-bearing silicate employed in the process, but preferably, the process has a reaction time (wherein the admixture is reacted for a time) of about 1 minute to about 180 minutes, about 1 min to about 150 min, about 1 min to about 10 min, about 1 min to about 90 min, preferably, about 1 minute to about 60 minutes, or about 1 minute to about 30 minutes. The precisereaction time will vary depending on the lithium-bearing silicate, the reaction temperature, the ratio of sodium to lithium; and the PHB solvent. Under preferable reaction conditions, the reaction time can be less than 30 min, 25 min, 20 min, 15 min, 10 min, 5 min, or 2 min. When the reaction is completed in very short periods of time, the reaction time may be longer than necessary due to process limitations on moving the material to any subsequent step. For example, in instances where the reaction is completed in less than 5 minutes, the reaction time may be 10 min or greater due to limitations on pumping, filtering, or separating products and reagents.

[0144] Another important feature of the process is the utilisation of a protic, high boiling-point (PHB) solvent. Preferably, the PHB solvent has a boiling point greater than about 150 °C, 180 °C, 200 °C, 220 °C, 240 °C, 260 °C, 280 °C, or 300 °C. In certain instances, the PHB solvent can be solid at room temperature. Accordingly, the PHB solvent can have a melting point in a range of about 40 °C to about 150 °C, about 40 °C to about 125 °C, or about 40 °C to about 100 °C. Another important feature of the PHB solvent is a pH in the range of about 4 to about 10, preferably about 5 to about 9, or about 6 to about 8; more preferably, the PHB solvent has a near neutral pH, and even more preferably is not acidic. Still more preferably, the PHB solvent does not react with sodium carbonate. Accordingly, organic acids and inorganic acids are not PHB solvents. In one example, the PHB solvent can be ethylene glycol, propylene glycol, methoxyethanol, ethoxy ethanol, methoxypropanol, ethoxypropanol, diethylene glycol, dipropylene glycol, glycerol, 3 -m ethoxy- 1,2-propane diol, 2-methyl-l,3-propanediol, trimethylolmethane, or mixtures thereof. In another example, the solvent includes a diol and / or triol, for example, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, ethyl ene-propylene glycol, glycerol, or mixtures thereof. In still other instances, the PHB solvent is a low VOC solvent. In particularly preferable instances, the PHB solvent includes, consists essentially of, or consists of ethylene glycol, propylene glycol, glycerol, or mixtures thereof.

[0145] Notably, the process further includes separating the lithium carbonate from the sodium aluminosilicate; herewith physical or chemical separations are applicable. In a preferable instance, the lithium carbonate is dissolved into a compatible solvent and separated from the solid sodium aluminosilicate. The lithium can then be recovered as a carbonate, hydroxide, or other salt as desired. Direct physical separation can be by size or floatation.

[0146] Another embodiment of the herein described invention, is a process forproducing lithium carbonate from P-spodumene. The process includes admixing P- spodumene with a sodium carbonate in a protic high-boiling (PHB) solvent; and maintaining this admixture at a reaction temperature of about 120 °C to the boiling point of the PHB solvent at a pressure of about 0.8 to about 2 bar for about 1 minute to about 180 minutes. The process further includes an atomic ratio of Na (from the sodium carbonate):Li (in the P-spodumene) that is greater than 1; preferably, the ratio is about 1, about 1.05, about 1.1, about 1.15, about 1.2, about 1.25, about 1.3, about 1.35, about 1.4, about 1.45, about 1.5, about 1.6, about 1.7, about 1.8, about 1.9, or about 2. The process still further includes a liquid: solids (w / w) ratio that is about 5: 1 to about 1 : 1, preferably about 2.5: 1 to about 1 : 1; the L:S ratio can be about 10, about 9, about 8, about 7, about 6, about 5, about 4, about 3, about 2, or about 1.

[0147] The sodium carbonate can include anhydrous sodium carbonate, sodium carbonate monohydrate, sodium carbonate heptahydrate, sodium carbonate decahydrate, sodium sesquicarbonate, sodium bicarbonate, or mixtures thereof. Preferably, the sodium carbonate includes anhydrous sodium carbonate. More preferably, the sodium carbonate consists essentially of, or consists of anhydrous sodium carbonate.

[0148] Herewith, the process can further include heating the admixture to the reaction temperature. The heating can further include distilling water from the admixture therefrom and thereby providing an anhydrous admixture.

[0149] As described above, the PHB solvent can be ethylene glycol, propylene glycol, methoxyethanol, ethoxyethanol, methoxypropanol, ethoxypropanol, diethylene glycol, dipropylene glycol, glycerol, 3 -m ethoxy- 1,2-propane diol, 2-methyl-l,3- propanediol, trimethylolmethane, or mixtures thereof. In one example, the solvent includes a diol or triol, for example, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, ethyl ene-propylene glycol, and glycerol. In another example, the PHB solvent is a low VOC solvent. In a particularly preferable example, the PHB solvent includes, consists essentially of, or consists of ethylene glycol, propylene glycol, glycerol, or mixtures thereof. More preferably, heating the admixture distils any residual water therefrom that may be included in the solvent. Even more preferably, the solvent is anhydrous or dry, e.g., with water concentrations less than 0.1%, 0.01%, or 0.001% by weight. In a still more preferable instance, the admixture (inclusive of the solvent and reagents) is free of water; notably, the process can include distilling water from the admixture, thereby providing an admixture that is free of water.

[0150] An important aspect of the herein described process is the solubility of thesodium carbonate in the PHB solvent and the insolubility of the lithium carbonate in the solvent. In a preferable instance, the solubility of the sodium carbonate in the PHB solvent at the reaction temperature is at least 5x, lOx, 15x, or 20x greater than the solubility (g / L) of lithium carbonate in the PHB solvent at the reaction temperature.

[0151] Turning to Figure 7, yet another embodiment is a cyclic process for producing lithium carbonate and sodium aluminosilicate from a lithium-bearing silicate. Herewith, cyclic means that reagents (e.g., CO2, sodium carbonate) and / or solvents (e.g., water and PHB solvents) are recycled in the process thereby reducing the requirements for continuous or semi -continuous processing of the lithium-bearing silicate (preferably P-spodumene) into the lithium carbonate and the sodium aluminosilicate. In one instance, the cyclic process includes admixing, in a PHB solvent, the lithium-bearing silicate and sodium carbonate, such that a Li:Na atomic ratio is about 1 : 1 to about 1 :2, at a temperature of about 120 °C to about 300 °C, for about 1 minute to about 120 minutes, thereby facilitating an exchange reaction and forming a slurry containing solid lithium carbonate and sodium aluminosilicate. After the completion of, preferably, the exchange reaction, the process includes separating the PHB solvent from a solid residue that includes the solid lithium carbonate and sodium aluminosilicate and recycling the PHB solvent and any unreacted sodium carbonate to the admixing step. Notably, in instances wherein the sodium carbonate is in excess (on a Na:Li molar basis), the excess sodium carbonate preferably remains dissolved in the PHB solvent and is recycled for further use in exchange reactions.

[0152] The process thereafter includes leaching lithium from the solid residue by admixing the solid residue with water and carbon dioxide to form a slurry of a lithium bicarbonate solution and a solid sodium aluminosilicate residue. Then, the process includes separating the lithium bicarbonate solution from the solid sodium aluminosilicate residue. The solid sodium aluminosilicate, preferably, contains less than 10%, 5%, or 1% of the lithium contained in the lithium-bearing silicate from which it is derived. Herewith, the sodium aluminosilicate is a waste product of the reaction and is not recycled for further processing in the process.

[0153] The separated lithium bicarbonate solution is preferably heated and reduced thereby facilitating the crystallisation of the lithium carbonate therefrom. Notably, one aspect of crystallising lithium carbonate from a lithium bicarbonate solution is the removal of excess CO2 which can be recovered and recycled to the extraction step. The process, accordingly, includes crystallising lithium carbonate from the lithiumbicarbonate solution; separating the crystalised lithium carbonate from a mother liquor; and recycling the mother liquor to the leaching step. Crystallising the lithium carbonate can further include removing carbon dioxide from the lithium bicarbonate solution; and wherein the carbon dioxide is recycled to the leaching step. The mother liquor is primarily water (from the extraction step) but may include a low concentration of lithium. As any concentration of lithium in the mother liquor reduces the isolated yield of lithium carbonate from the lithium -bearing silicate, the concentration of lithium in the mother liquor is, preferably, less than 5000 ppm, 2500 ppm, 2000 ppm, 1500 ppm, 1000 ppm, or 500 ppm.

[0154] In a preferable instance, after the completion of the exchange reaction, the process includes separating the PHB solvent from the solid residue at or within about 10, 20, 30, 40, or 50 °C of the reaction temperature. Herein, the PHB solvent can be separated from the solid residue by filtration, centrifugation, or other processes that can operate at the filtration temperature. In one preferable example, the filtration is accomplished with a Nutzche filter wherein after the removal of the PHB solvent, the washing of the filter cake (solid residue) can be carried out. In another instance, the PHB solvent is separated from the solid residue without cooling the slurry. In still another instance, PHB solvent is separated from the solid residue without cooling and the PHB solvent-filtrate is recycled for further exchange reactions without cooling.

[0155] Still another embodiment is a continuous process for producing lithium carbonate and sodium aluminosilicate from a lithium-bearing silicate. As used herein, the term “continuous” refers to the concurrent performance of one or more process steps as well as the recirculation and / or recycling of reagents or materials in the same, previous, or later process steps. In particular, the term “continuous” refers to the addition of reagents and removal or products without the termination of a particular step or process. In a preferable instance, the term “continuous” refers to the consistent production of a product without discrete termination of the production rate. Herewith, the continuous process can include a plurality of steps, preferably, operating concurrently or semi- concurrently. These steps include passing an admixture of a PHB solvent, the lithium- bearing silicate, and anhydrous sodium carbonate through a reactor at a temperature below the standard pressure boiling point of the PHB solvent, thereby producing a slurry of lithium carbonate and sodium aluminosilicate in the PHB solvent; separating the PHB solvent from a commixture of lithium carbonate and sodium aluminosilicate, and recycling the PHB solvent to the reactor, preferably the separated PHB solvent includesunreacted sodium carbonate; admixing, in a leach tank, water and carbon dioxide with the commixture thereby leaching lithium bicarbonate into the water; separating the lithium bicarbonate in water from the sodium aluminosilicate; crystallising lithium carbonate from the lithium bicarbonate in water by heating and removing carbon dioxide; recycling the carbon dioxide to the leach tank; and separating the crystallised lithium carbonate from the water and recycling the water to the leach tank.

[0156] In a preferable instance, the residence time in the reactor is about 1 minute to about 180 minutes. Notably, the residence time in the reactor can be determined based on an average turnover time or a flow-rate vs flow-path (wherein the residence time is the time the admixture takes to travel at the flow-rate through the flow-path).

[0157] In another instance, the reactor can be a stirred-tank reactor operating as a batch reactor or a continuous reactor. In examples wherein the reactor is a batch reactor, the process preferably includes a plurality of batch reactors operating in parallel or contemporaneously to provide consistent operation; while one reactor is undergoing loading / unloading a second reactor is producing the slurry of lithium carbonate and sodium aluminosilicate in the PHB solvent. In another example the reactor is a continuous stirred tank reactor (CSTR) wherein portions of the admixture are fed to the CSTR while the slurry is removed. In still another instance, the reactor can be a pipe or a tubular flow reactor. Therein, the admixture is pumped or fed into a proximal end of the pipe or tubular flow reactor and the slurry is removed from a distal end of the pipe or tubular flow reactor.

[0158] Still another embodiment is a slurry or heterogeneous fluid useful in the preparation of lithium carbonate by the above-described processes. In one instance, the slurry includes, consists essentially of, or consists of an admixture of a lithium-bearing silicate carried in a fluid that includes sodium carbonate and a protic high-boiling (PHB) solvent. The lithium bearing silicate is preferably P-spodumene. In a preferable instance, the slurry is anhydrous.Industrial Applicability

[0159] The process described herein has significant industrial applicability, particularly for the large-scale extraction and production of high -purity lithium carbonate from lithium-bearing silicate minerals such as spodumene. By utilising a protic high- boiling organic solvent and enabling efficient recycling of reagents and solvents, the process reduces both operational costs and environmental impact compared toconventional acid or caustic extraction methods. Its cyclic and continuous embodiments are well-suited for integration into existing industrial operations, supporting the growing demand for battery -grade lithium carbonate in the energy storage, electric vehicle, and electronics sectors. The adaptability, efficiency, and sustainability of the process make it highly relevant for modern lithium supply chains and industrial chemical manufacturing.Economic and Environmental Considerations

[0160] The process described in this invention offers notable economic and environmental advantages over conventional lithium extraction methods. By employing a protic high-boiling organic solvent and enabling the recycling of key reagents, the process significantly reduces the consumption of raw materials and minimises waste generation. This not only lowers operational costs but also decreases the environmental footprint associated with lithium production, particularly by avoiding the use of harsh acids and minimising effluent streams. The ability to operate under relatively mild conditions further reduces energy requirements and the risk of hazardous emissions, making the process both economically attractive and environmentally responsible for large-scale industrial adoption.

[0161] While the compositions and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the compositions and / or methods in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit and scope of the invention. More specifically, it will be apparent that certain agents that are both chemically and physically related may be substituted for the agents described herein while the same or similar results would be achieved. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:-1. A process for extracting lithium from a lithium -bearing silicate, the process comprising: reacting an admixture of the lithium-bearing silicate with a sodium carbonate in a protic high-boiling (PHB) solvent thereby producing a mixture containing solid lithium carbonate and a sodium aluminosilicate, wherein the admixture includes the sodium carbonate in a total amount sufficient to provide a molar ratio of sodium to lithium of at least 1 : 1; separating the lithium carbonate from the sodium aluminosilicate.

2. A process according to claim 1, wherein the admixture is reacted to the point where substantially all of the lithium in the silicate has been converted to a lithium carbonate.

3. A process according to claim 1 or claim 2, wherein a mass ratio of the PHB solvent to the silicate is less than 5: 1.

4. A process according to any one of the preceding claims, wherein the reaction is at a temperature of about 110 °C to about 350 °C.

5. A process according to claim 4, wherein the reaction is in an oxygen-free environment.

6. A process according to any one of the preceding claims, wherein the admixture is free of water.

7. A process according to any one of the preceding claims, wherein the lithium- bearing silicate is a P-spodumene.

8. A process according to any one of the preceding claims, wherein the PHB solvent has a boiling point greater than about 180 °C.

9. A process according to any one of the preceding claims, wherein the PHB solventincludes ethylene glycol, propylene glycol, methoxyethanol, ethoxy ethanol, methoxypropanol, ethoxypropanol, diethylene glycol, dipropylene glycol, glycerol, 3 -methoxy- 1,2-propane diol, 2-methyl-l,3-propanediol, and / or trimethylolmethane.

10. A process according to any one of the preceding claims, further comprising: admixing P-spodumene with a sodium carbonate, such that an atomic ratio of Na from the sodium carbonate:Li in the P-spodumene is greater than 1, in a protic high-boiling (PHB) solvent such that a liquid: solids ratio is about 5: 1 to about 1 : 1 by weight; and maintaining the admixture at a reaction temperature of about 120 °C to about 350 °C thereby providing crystalline lithium carbonate.

11. A process according to claim 10, further including heating the admixture to the temperature and then maintaining the admixture at the temperature; wherein heating the admixture includes distilling water therefrom and thereby providing an anhydrous admixture.

12. A process according to claim 10 or claim 11, wherein the PHB solvent includes ethylene glycol, propylene glycol, methoxy ethanol, ethoxyethanol, methoxypropanol, ethoxypropanol, diethylene glycol, dipropylene glycol, glycerol, 3 -methoxy- 1,2-propane diol, 2-methyl-l,3-propanediol, and / or trimethylolmethane.

13. A process according to any one of claims 10 to 12, wherein a solubility of the sodium carbonate in the PHB solvent at the reaction temperature is at least ten times (lOx) greater than the solubility of lithium carbonate in the PHB solvent at the reaction temperature.

14. A process according to any one of claims 10 to 13, wherein the admixture is free of water.

15. A process according to any one of the preceding claims, further comprising: separating the PHB solvent from the mixture that includes the solidlithium carbonate and sodium aluminosilicate; recycling the PHB solvent and any unreacted sodium carbonate to the reacting step; leaching lithium from the solid residue by admixing the solid residue with water and carbon dioxide to form a slurry of a lithium bicarbonate solution and a solid sodium aluminosilicate residue; separating the lithium bicarbonate solution from the solid sodium aluminosilicate residue; crystallising lithium carbonate from the lithium bicarbonate solution; separating the crystalised lithium carbonate from a mother liquor; and recycling the mother liquor to the leaching step.

16. A process according to claim 15, wherein the lithium-bearing silicate is a P- spodumene.

17. A process according to claim 15 or claim 16, wherein the PHB solvent is separated from the solid residue without cooling the slurry.

18. A process according to any one of claims 15 to 17, wherein crystallising the lithium carbonate includes removing carbon dioxide from the lithium bicarbonate solution; and wherein the carbon dioxide is recycled to the leaching step.

19. A process according to any one of the preceding claims, wherein the lithium carbonate produced has a purity of at least 99.5%.

20. A process according to any one of the preceding claims, wherein the lithium- bearing silicate is selected from the group consisting of P-spodumene, lepidolite, petalite, lithium clays, and mixtures thereof.

21. A process according to any one of the preceding claims, wherein the PHB solvent comprises a mixture of ethylene glycol and glycerol.

22. An apparatus for extracting lithium carbonate from a lithium-bearing silicate, comprising:(a) a reactor for reacting an admixture of the lithium-bearing silicate, sodium carbonate, and a PHB solvent;(b) a separation unit for isolating solid lithium carbonate from sodium aluminosilicate;(c) a recycling system for the PHB solvent and unreacted sodium carbonate; and(d) a crystallisation unit for recovering crystallised lithium carbonate from a lithium bicarbonate solution.

23. A slurry for use in the extraction of lithium carbonate, the slurry comprising a lithium-bearing silicate, sodium carbonate, and a protic high-boiling solvent, wherein the slurry is anhydrous.

24. Lithium carbonate when produced by a process as defined according to any one of claims 1 to 21, wherein the lithium carbonate is suitable for use in battery manufacturing.

25. A process for extracting lithium from a lithium -bearing silicate, the process comprising: reacting an admixture of the lithium-bearing silicate with a sodium carbonate in a protic high-boiling (PHB) solvent thereby producing a mixture containing solid lithium carbonate and a sodium aluminosilicate, wherein the admixture includes the sodium carbonate in a total amount sufficient to provide a molar ratio of sodium to lithium of at least 1 : 1; separating the lithium carbonate from the sodium aluminosilicate.

26. The process of claim 25, wherein the admixture is reacted to the point where substantially all of the lithium in the silicate has been converted to a lithium carbonate.

27. The process of claim 25 or claim 26, wherein a mass ratio of the PHB solvent to the silicate is less than 5: 1.

28. The process of any one of claims 25 to 27, wherein the reaction is at atemperature of about 110 °C to the boiling point of the PHB solvent at standard pressure.

29. The process of claim 28, wherein the reaction is at a temperature of about 110 °C to about 350 °C.

30. The process of any one of claims 25 to 29, wherein the reaction is in an oxygen- free environment.

31. The process of any one of claims 25 to 30, wherein the reaction is oxygen (O2)- firee.

32. The process of any one of claims 25 to 31, wherein the admixture is reacted in an inert-gas environment thereby preventing the oxidation or degradation of the PHB solvent.

33. The process of any one of claims 25 to 32, wherein the admixture is free of water.

34. The process of any one of claims 25 to 33, wherein the lithium-bearing silicate is a spodumene, lepidolite, petalite, amblygonite, zinnwaldite, lithium-clay, or admixture thereof.

35. The process of any one of claims 25 to 34, wherein the lithium-bearing silicate is a calcined lithium-bearing silicate.

36. The process of claim 36, wherein the calcined lithium-bearing silicate is a P- spodumene.

37. The process of any one of claim 25 to 36, wherein the admixture is reacted for a time of about 1 minute to about 180 minutes.

38. The process of any one of claims 25 to 37, wherein the PHB solvent has a boiling point greater than about 180 °C.

39. The process of any one of claims 25 to 38, wherein the PHB solvent has a melting point in a range of about 10 °C to about 150 °C.

40. The process of any one of claims 25 to 39, wherein the PHB solvent includes ethylene glycol, propylene glycol, methoxy ethanol, ethoxyethanol, methoxypropanol, ethoxypropanol, diethylene glycol, dipropylene glycol, glycerol, 3 -methoxy- 1,2-propane diol, 2-methyl-l,3-propanediol, and / or trimethylolmethane.

41. A process for producing lithium carbonate comprising: admixing P-spodumene with a sodium carbonate, such that an atomic ratio of Na from the sodium carbonate:Li in the P-spodumene is greater than 1, in a protic high-boiling (PHB) solvent such that a liquid: solids ratio is about 5: 1 to about 1 : 1 by weight; and maintaining the admixture at a reaction temperature of about 120 °C to the boiling point of the PHB solvent at a pressure of about 0.8 to about 2 bar for about 1 minute to about 180 minutes.

42. The process of claim 41, wherein a sodium carbonate includes anhydrous sodium carbonate, sodium carbonate monohydrate, sodium carbonate heptahydrate, sodium carbonate decahydrate, sodium sesquicarbonate, sodium bicarbonate, or mixtures thereof.

43. The process of claim 42, wherein a sodium carbonate is anhydrous sodium carbonate.

44. The process of claim 41 or 42 further including heating the admixture to the temperature and then maintaining the admixture at the temperature; wherein heating the admixture includes distilling water therefrom and thereby providing an anhydrous admixture.

45. The process of any one of claims 41 to 44, wherein the PHB solvent includes ethylene glycol, propylene glycol, methoxy ethanol, ethoxyethanol, methoxypropanol, ethoxypropanol, diethylene glycol, dipropylene glycol,glycerol, 3 -methoxy- 1,2-propane diol, 2-methyl-l,3-propanediol, and / or trimethylolmethane.

46. The process of any one of claims 41 to 45, wherein a solubility of the sodium carbonate in the PHB solvent at the reaction temperature is at least ten times (lOx) greater than the solubility of lithium carbonate in the PHB solvent at the reaction temperature.

47. The process of any one of claims 41 to 46, wherein the admixture is free of water.

48. A cyclic process for producing lithium carbonate and sodium aluminosilicate from a lithium-bearing silicate comprising: admixing, in a protic high-boiling (PHB) solvent, the lithium-bearing silicate and sodium carbonate, such that a Li:Na atomic ratio is about 1 : 1 to about 1 :2, at a temperature of about 120 °C to about 300 °C, thereby forming a slurry containing solid lithium carbonate and sodium aluminosilicate; separating the PHB solvent from a solid residue that includes the solid lithium carbonate and sodium aluminosilicate; recycling the PHB solvent and any unreacted sodium carbonate to the admixing step; leaching lithium from the solid residue by admixing the solid residue with water and carbon dioxide to form a slurry of a lithium bicarbonate solution and a solid sodium aluminosilicate residue; separating the lithium bicarbonate solution from the solid sodium aluminosilicate residue; crystallising lithium carbonate from the lithium bicarbonate solution; separating the crystalised lithium carbonate from a mother liquor; and recycling the mother liquor to the leaching step.

49. The process of claim 48, wherein the lithium-bearing silicate is a P-spodumene.

50. The process of claim 48 or 49, wherein the PHB solvent is separated from the solid residue without cooling the slurry.

51. The process of any one of claims 48 to 50, wherein crystallising the lithium carbonate includes removing carbon dioxide from the lithium bicarbonate solution; and wherein the carbon dioxide is recycled to the leaching step.

52. A continuous process for producing lithium carbonate and sodium aluminosilicate from a lithium-bearing silicate, the process comprising: passing an admixture of a protic high-boiling (PHB) solvent, the lithium- bearing silicate, and anhydrous sodium carbonate through a reactor at a temperature below the standard pressure boiling point of the PHB solvent, thereby producing a slurry of lithium carbonate and sodium aluminosilicate in the PHB solvent; separating the PHB solvent from a commixture of lithium carbonate and sodium aluminosilicate, and recycling the PHB solvent to the reactor; admixing, in a leach tank, water and carbon dioxide with the commixture thereby leaching lithium bicarbonate into the water; separating the lithium bicarbonate in water from the sodium aluminosilicate; crystallising lithium carbonate from the lithium bicarbonate in water by heating and removing carbon dioxide; recycling the carbon dioxide to the leach tank; and separating the crystallised lithium carbonate from the water and recycling the water to the leach tank.

53. The process of claim 52, wherein the residence time in the reactor is about 1 minute to about 180 minutes.

54. The process of claim 52 or 53, wherein the reactor is a stirred-tank reactor.

55. The process of any one of claims 52 to 54, wherein the reactor is a pipe.

56. The process of any one of claims 52 to 55, wherein the separated PHB solvent includes unreacted sodium carbonate.

57. A slurry comprising:an admixture of a lithium-bearing silicate carried in a fluid that includes sodium carbonate and a protic high-boiling (PHB) solvent.

58. The slurry of claim 57, wherein the lithium bearing silicate is a P-spodumene.

59. The slurry of claim 57 or claim 58, wherein the slurry is anhydrous.

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