Systems and methods of leaching lithium using sodium sulfate

Abstract

The present disclosure is directed to systems and methods of leaching lithium sources using sodium sulfate. The process can include mixing a lithium source, a first sodium sulfate, and lithium hydroxide in a reactor and leaching the lithium source in the mixture in the reactor to form residual solids and a lithium sulfate leachate.

Description

SYSTEMS AND METHODS OF LEACHING LITHIUM USING SODIUM SULFATEFIELD

[0001] This disclosure relates to systems and methods for leaching lithium from a lithium source using sodium sulfate. More specifically, this disclosure relates to systems and methods for leaching lithium from a lithium source using sodium sulfate and a base comprising lithium hydroxide.BACKGROUND

[0002] A lithium source such as spodumene is typically converted to lithium hydroxide monohydrate (LHM) via an acid roast of beta-spodumene with sulfuric acid. This process can include roasting the beta-spodumene with sulfuric acid at elevated temperatures followed by leaching with water to form a lithium sulfate solution. The lithium sulfate solution can then be concentrated and causticized to precipitate the sulfate ions as a sodium salt, which is crystallized and filtered out to produce sodium sulfate anhydrous as solid waste. For example, between 1.5 to 2 kg of sodium sulfate anhydrous can be formed for every kilogram of LHM produced during the sulfuric acid leaching of spodumene process.SUMMARY

[0003] It is becoming increasingly difficult to find outlets or customers for sodium sulfate and disposal of sodium sulfate can be difficult and expensive due to its high solubility in water. Applicants have discovered an improved sodium sulfate leaching process that can be retrofitted into an existing lithium hydroxide monohydrate (sulfuric acid leaching) plant.

[0004] Described herein are systems and methods of leaching lithium using sodium sulfate. Leaching using sodium sulfate can eliminate the sulfuric acid mix, acid roast, water leaching, magnesium removal, and / or sodium sulfate purification sections of a typical spodumene sulfuric acid leaching process to recover lithium. In addition, because there may be no sodium sulfate byproduct when leaching using sodium sulfate when compared to sulfuric acid, any sodium sulfate (sodium sulfate decahydrate) produced can be recycled back to the leaching step.

[0005] Applicant discovered that leaching of lithium from a lithium source (e.g.. 0- spodumene) using sodium sulfate can be improved by including lithium hydroxide as a base in the leaching process and by utilizing a leaching reactor that has an internal surfacecomprising a high-nickel (e.g., >50% Ni) alloy. Utilizing the lithium hydroxide and / or the reactor with an internal high-nickel surface can improve or maintain high lithium yield while minimizing corrosion and / or solid deposition within the leaching reactor.

[0006] In some embodiments, a method of producing lithium hydroxide monohydrate includes mixing a lithium source, a first sodium sulfate, and lithium hydroxide in a reactor; leaching the lithium source in the mixture in the reactor at a temperature of 200-275°C and a pressure of 250-600 psig to form residual solids and a leachate comprising lithium sulfate; separating the leachate from the residual solids; reacting a base with the leachate to form a second sodium sulfate and a solution comprising lithium hydroxide; separating the second sodium sulfate from the solution comprising lithium hydroxide; and crystallizing the solution comprising lithium hydroxide to form lithium hydroxide monohydrate. In some embodiments, the lithium source comprises spodumene, lepidolite, petalite, amblygonite, zinnwaldite, triphylite, lithiophilite, or combinations thereof. In some embodiments, the method includes calcining a precursor lithium source to form the lithium source. In some embodiments, the precursor lithium source comprises a-spodumene and the lithium source comprises [3-spodumene. In some embodiments, the method includes recycling the second sodium sulfate to the reactor to be used as at least a portion of the first sodium sulfate in the mixture in the reactor. In some embodiments, the lithium source in the mixture is leached in the reactor for at least one hour. In some embodiments, the reactor has an internal surface comprising a nickel alloy with at least 50% nickel. In some embodiments, the nickel alloy is a nickel-chromium-based alloy. In some embodiments, a mass ratio of the first sodium sulfate to the lithium source in the mixture is 1 :6-1 :2. In some embodiments, a mass ratio of the lithium hydroxide io the lithium source in the mixture is 1 :200- 1:35 In some embodiments, a mass ratio of the first sodium sulfate to the lithium hydroxide m the mixtureIn some embodiments, the mixture has a pH of at least 7, at least 9, or at least 10. In some embodiments, the mixture has a liquid to solid ratio of 3-10 mL / g. In some embodiments, at least 75% of lithium contained in the lithium source is extracted during leaching. In some embodiments, the method includes concentrating the leachate prior to reacting the base with the leachate. In some embodiments, concentrating the leachate comprises evaporating solvent from the leachate. In some embodiments, the base comprises sodium hydroxide.

[0007] It will be appreciated that any of the variations, aspects, features and options described in view of the systems, methods, and / or powders apply equally to the systems,methods, powders, other devices / configurations, and vice versa. It will also be clear that any one or more of the above variations, aspects, features and options can be combined.

[0008] Additional advantages will be readily apparent to those skilled in the art from the following detailed description. The aspects and descriptions herein are to be regarded as illustrative in nature and not restrictive.

[0009] All publications, including patent documents, scientific articles and databases, referred to in this application are incorporated by reference in their entirety for all purposes to the same extent as if each individual publication were individually incorporated by reference. If a definition set forth herein is contrary to or otherwise inconsistent with a definition set forth in the patents, applications, published applications and other publications that are herein incorporated by reference, the definition set forth herein prevails over the definition that is incorporated herein by reference.BRIEF DESCRIPTION OF THE FIGURES

[0010] The disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0011] FIG. 1 illustrates an example flowchart for a lithium hydroxide production process in accordance with some embodiments disclosed herein.

[0012] FIG. 2 is an exemplary image of an interior of a 2L Hastelloy B autoclave after leaching of beta-spodumene in accordance with some embodiments disclosed herein.

[0013] FIG. 3 is a scanning electron microscope image of the dried tailings from run 1 of the Examples in accordance with some embodiments disclosed herein.

[0014] FIG. 4 is a scanning electron microscope image of the dried tailings from run 6 of the Examples in accordance with some embodiments disclosed herein.

[0015] FIG. 5 is a scanning electron microscope image of the dried tailings from a standard sulfuric acid leaching of beta-spodumene in accordance with some embodiments disclosed herein.

[0016] FIG. 6 is a particle size distribution analysis for the tailings from Run 1 of the Examples in accordance with some embodiments disclosed herein.

[0017] FIG. 7 is a particle size distribution analysis for the tailings from Run 2 of the Examples in accordance with some embodiments disclosed herein.DETAILED DESCRIPTION

[0018] Reference will now be made in detail to implementations and embodiments of various aspects and variations of devices, compounds, powders, systems, and methodsdescribed herein. Although several exemplary variations of the devices, compounds, powders, systems, and methods are described herein, other variations of the devices, compounds, powders, systems, and methods may include aspects of the devices, compounds, powders, systems, and methods described herein combined in any suitable manner having combinations of all or some of the aspects described.

[0019] Described herein are systems and methods of leaching lithium sources using sodium sulfate. In addition, disclosed herein are systems and methods of converting lithium sources to lithium hydroxide using sodium sulfate during leaching. Specifically, Applicant discovered that leaching of lithium from a lithium source (e.g., β-spodumene) using sodium sulfate can be improved by including lithium hydroxide as a base in the leaching process and / or by utilizing a leaching reactor that has an internal surface comprising a nickel alloy (e.g., high-nickel alloy). Utilizing the lithium hydroxide and / or the reactor with an internal nickel surface can improve or maintain high lithium yield while minimizing corrosion and / or solid deposition within the leaching reactor. In addition, any sodium sulfate produced in the processes disclosed herein can be reused / recycled in the leaching step. Furthermore, there may be enough residual lithium hydroxide in the recycled sodium sulfate to eliminate or reduce the amount of virgin base used in the leaching step as described herein.

[0020] FIG. 1 illustrates process 100 for producing lithium hydroxide as disclosed herein. In some embodiments, to form the lithium hydroxide disclosed herein, a precursor lithium source can be transformed into a lithium source at step 101. For example, some precursor lithium sources may not be in their best form for leaching. In some embodiments, the precursor lithium source can be spodumene (e.g., LiAlSiiOs), lepidolite, petalite, amblygonite, zinnwaldite, triphylite, lithiophilite, or combinations thereof. In some embodiments, the spodumene can be alpha-spodumene (a-spodumene) In some embodiments, transforming the precursor lithium source to a lithium source can include beating (e.g.. calcining) the precursor lithium source. In some embodiments, the heating can occur at a temperature of at least about 900 °C, at least about 950 °C, at least about 1000 "C, at least about 1050 °C. or at least 1 100 °C In some embodiments, the heating can occur at a temperature of at most about 1200 °C, at most about 1 150 °C, at most about 1100 °C, at most about 1050, or at most about 1000 °C. In some embodiments, the heating can take place for at least about 30 minutes, at least about 1 hour, at least about 1 .5 hours, or at least about 2 hours. In some embodiments, the heating step can take place in a kiln.

[0021] In some embodiments, the precursor lithium source can be a-spodumene which can be transformed into β-spodumene via calcination. The β phase of the spodumene can be more reactive and therefore a better phase for leaching to recover the lithium therein.

[0022] In some embodiments, the lithium source can be a lithium source formed from the transformation of the precursor lithium source. In some embodiments, the lithium source can be spodumene (e.g., LiAlSizOs), lepidolite, petalite, amblygonite, zinnwaldite, triphylite, lithiophilite, or combinations thereof. In some embodiments, the lithium source is β-spodumene. In some embodiments, the lithium source can be milled io desired particle size for leaching. In some embodiments, the lithium source can be milled via a ball mill, jet mill, attrition mill, hammer mill, cryogenic mill, colloid mill, fluid energy mill, and / or ultrasonic mill. In some embodiments, the lithium source can have a panicle size distribution with a D90 of at least about 1 micron, at least about 5 microns, at least about 10 microns, at least about 15 microns, at least about 20 microns, at least about 25 microns, at least about 30 microns, or at least about 35 microns. In some embodiments, the lithium source can have a particle size distribution with a D90 of at most about 200 microns, at most about 150 microns, at most about 100 microns, at most about 75 microns, at most about 50 microns, at most about 45 microns, or at most about 40 microns. The D90 refers to the particle diameter at the 90 vol% undersize point in the distribution. In other words, the D90 signifies the point in the particle diameter distribution, up to and including which, 90% of the total volume of particles in the sample is contained.

[0023] In some embodiments, the lithium hydroxide production process can include a step 102 of leaching a lithium source using sodium sulfate and an additive. In some embodiments, the leaching can include mixing a lithium source, sodium sulfate, and an additive in a reactor and then leaching the lithium source in the mixture. In some embodiments, the mixture can be stirred in the reactor. In some embodiments, the mixture can be stirred throughout the leaching process. In some embodiments, the mixture can be stirred throughout the leaching process with a speed of at least about 100 rpm, at least about 250 rpm, at least about 500 rpm, at least about 700 rpm, or at least about 1000 rpm.

[0024] During leaching, lithium can be extracted from the lithium source. For example, an exemplar}' reaction formula for leaching β-spodumene using sodium sulfate is shown by the following equation:

[0025] In some embodiments, the reactor can be a leaching reactor. In some embodiments, the reactor can be a pressure leaching reactor. In some embodiments, the reactor can be anautoclave. In some embodiments, the reactor can have an internal surface comprising a nickel alloy. In some embodiments, the reactor can have an internal surface comprising a nickel alloy. In some embodiments, the nickel alloy can be a high-nickel alloy. In some embodiments, the high-nickel alloy can have at least about 50%, at least about 55%, at least about 60%, at least about 65%, at least about 70%, at least about 75%, or at least about 80% nickel. In some embodiments, the high-nickel alloy can be pure nickel. In some embodiments, the nickel alloy can be a nickel-chromium-based alloy. In some embodiments, the reactor can have an internal surface comprising carbon steel, stainless steel, an Inconel alloy, a Hastelloy alloy, a Monel alloy, or a combination thereof. In some embodiments, the stainless steel can be 316 or 304 stainless steel. In some embodiments, the Inconel alloy can be Inconel 600. In some embodiments, the Hastelloy alloy can be Hastelloy B or Hastelloy C.

[0026] In some embodiments, the sodium sulfate can be sodium sulfate anhydrous (SSA) and / or sodium sulfate decahydrate (SSD). In some embodiments, the sodium sulfate can be solid and / or aqueous in a solution when added to the reactor for leaching. In some embodiments, the mass ratio of sodium sulfate to lithium source in the mixture can be at least about 1 :6. at least about 1:3, or at least about 1:2. hi some embodiments, the mass ratio of sodium sulfate to lithium source m the mixture can be at most about 2: 1, at most about 1 .5: 1 , at most about 1: 1 , or at most about 1 : 1 3. In some embodiments, the mass ratio of sodium sulfate to lithium source in the mixture can be about 1 :6-2: 1 , about 1 :6-l : I , about 1 :6-1 : 2, or about 1 :6-1 : 1 3

[0027] In some embodiments, an additive can be added to the leaching reactor to enhance the leaching efficiency and / or adjust the pH of the leaching reactor. In some embodiments, the additive can be a base. In some embodiments, the base can be sodium hydroxide (e.g., NaOH), lime (e.g., CaO), lithium hydroxide (e.g., LiOH), barium hydroxide (e.g., Ba(OH)2), other alkali bases (e.g., alkali metal oxides and / or hydroxides), other alkaline earth bases (e.g., alkaline earth metal oxides and / or hydroxides), or combinations thereof. In some embodiments, the additive can be lithium hydroxide. In some embodiments, the lithium hydroxide does not react, but passes through the system to maintain the pH. In some embodiments, using a calcium-based base can lead to the formation of calcium sulfate leading to scaling. In some embodiments, using a sodium-based base can lead to the formation of more sodium sulfate anhydrous. In addition, strong bases such as sodium hydroxide are more reactive which may make it more difficult to control the pH. In some embodiments, using a potassium-based base can make it difficult to remove potassium fromthe overall system and potassium may reach the final lithium hydroxide product. In some embodiments, using an organic base such as an amine can carry through to the final lithium hydroxide product and buildup in the recycle streams leading to potential flammability issues. In some embodiments, the mass ratio of additive to lithium source in the mixture can be at least about 1.200, al least about 1 : 100, or at least about 1'50. In some embodiments, the mass ratio of additive to lithium source in the mixture can be at most about 1: 10. at most about 1:20. at most about 1 :25, or at most about 1:35. In some embodiments, the mass ratio of additive io lithium source in the mixture can be about 1 :200- 1 :35 or about 1 :100-1:20.

[0028] In some embodiments, the mass ratio of sodium sulfate to additive in the mixture can be at least about 1 : 100, at least about 1.75. at least about 1 :50, at least about 1 :30, or at least about 1:25. In some embodiments, the mass ratio of sodium sulfate to additive in the mixture can be at most about 1 : 10. at most about 1 : 15. or at most about 1 :20. In some embodiments, the mass ratio of additive to lithium source in the mixture can be about 1:100- 1 : 10 or about 1 .50-1: 10.

[0029] In some embodiments, a solvent can also be mixed with the lithium source, sodium sulfate, and additive in the reactor. In some embodiments, the solvent can be water, an organic solvent, or combinations thereof. In some embodiments, at least one of the lithium source, sodium sulfate, and additive can be mixed with the solvent (and possibly dissolved in the solvent) before being added to the leaching reactor. For example, in some embodiments, the sodium sulfate can be mixed with the solvent to form an aqueous solution of sodium sulfate, before being added to the leaching reactor.

[0030] In some embodiments, the mixture can have a pH of at least about 6.5, at least about 7, at least about 8, at least about 9, at least about 10, or at least about 11. In some embodiments, the mixture can have a pH of at most about 14, at most about 13, at most about 12, at most about 11, at most about 10, at most about 9, or at most about 8. As explained above, the base can control and / or maintain the pH of the mixture. In some embodiments, a Liquid to Solid ratio (L / S) in mL / g of the mixture can be at least about 3 mL / g. at least about 4 mL / g, at least about 5 mL / g. at least about 6 mL / g, or at least about 7 mL / g. In some embodiments, a L / S ratio of the mixture can be at most about 20 mL / g, at most about 15 mL / g, or at most about 10 mL / g.

[0031] In some embodiments, leaching the lithium source can include heating the mixture. In some embodiments, the temperature during leaching (e.g., temperature in leaching reactor) can be at least about 100 °C. at least about 150 °C, at least about 200 °C, al leastabout 210 °C, at least about 215 °C, at least about 220 °C, or al least about 230 °C. In some embodiments, the temperature during leaching can be at most about 400 °C, at most about 350 °C , at most about 300 °C, at most about 275 °C. at most about 250 °C, or at most about 230 °C. In some embodiments, the temperature during leaching can be about 150-300 °C, about 200-250 °C. or about 210-230 °C.

[0032] In some embodiments, leaching the lithium source can include pressure leaching the lithium source. In some embodiments, the pressure during leaching (e.g., pressure in leaching reactor) can be at least about 200 psig, at least about 250 psig, at least about 300 psig, at least about 350 psig, at least about 400 psig, at least about 450 psig, or at least about 500 psig. In some embodiments, the pressure during leaching can be at most about 600 psig, at most about 550 psig, at most about 500 psig. at most about 450 psig. or at most about 400 psig. In some embodiments, the pressure during leaching can be about 250-500 psig, about 300-450 psig, or about 300-400 psig. In some embodiments, higher pressure (e.g., above 500 psig) can increase capital costs.

[0033] In some embodiments, the leaching of the lithium source in the reactor can be leached for at least about 30 minutes, at least about 1 hour, at least about 1.5 hours, at least about 2 hours, at least about 2.5 hours, at least about 3 hours, at least about 3.5 hours, or at least about 4 hours. In some embodiments, the leaching of the lithium source in the reactor can be leached for at most about 10 hours, at most about 8 hours, at most about 5 hours, or at most about 4 hours. In some embodiments, the longer the time the lower the throughput and higher for potential wear and tear on the reactor.

[0034] Leaching the lithium source can result in a leachate that includes lithium extracted from the lithium source and residual solids or tailings. In some embodiments, the leachate includes dissolved lithium. In some embodiments, the leachate includes lithium sulfate. In some embodiments, the residual solids can be in the form of a slurry. In some embodiments, the residual solids can include those elements from the lithium source (and sodium sulfate and / or additive) that may be insoluble in the leachate. These insoluble elements can include sodium, silicon, aluminum, others, and combinations thereof. For example, in leaching beta-spodumene with sodium sulfate, the residual solids can include sodium analcime (2NaAlShO6.HiO) and the leachate can include lithium sulfate.

[0035] In some embodiments, the extraction efficiency of lithium or lithium yield for the leaching process can be at least about 75%, at least about 80%, at least about 85%, or at least about 90%. The extraction efficiency of lithium or lithium yield for the leaching process can be calculated by techniques know n to those of ordinary skill in the art, includingfor example, by total lithium out over total lithium in (e.g., total lithium in lithium sulfate over total incoming lithium (spodumene and lithium hydroxide present)).

[0036] In some embodiments, the method of forming lithium hydroxide can further include separating the leachate from residual solids of the leaching process at step 103. In some embodiments, this separation step can be a solid / liquid separation step as the leachate can be in liquid or aqueous form and the leaching residues can be solids. In some embodiments, the separation step can include any known separation step in the art such as a multi-stage belt filter and / or a reslurry tank. In some embodiments, the separation can include filtering the leachate (i.e., filtrate) from the residual solids.

[0037] In some embodiments, the leachate can be concentrated at step 104. In some embodiments, concentrating the leachate can include removing impurities and / or evaporating solvent from the leachate. In some embodiments, removing impurities from the leachate can include any known impurity removal step in the art such as adding sodium carbonate to reduce calcium, running the lithium sulfate or lithium hydroxide through an ion exchange column, membrane purification, or combinations thereof.

[0038] In some embodiments, the leachate can be causticized at step 105. In some embodiments, the leachate can be causticized to precipitate the sulfate ions. In some embodiments, a caustic agent can be added to the leachate. In some embodiments, the caustic agent can be a base. In some embodiments, the base can be sodium hydroxide. In some embodiments, reacting the leachate with a base can form sodium sulfate and a lithium solution. In some embodiments, the sodium sulfate can be SSA and / or SSD. In some embodiments, the lithium solution can be a lithium hydroxide solution. For example, an exemplary' reaction formula for causticization of the leachate using sodium hy droxide is shown by the following equation:In some embodiments, the driving force for the formation of lithium hydroxide can be the precipitation of sodium sulfate decahydrate (SSD). SSD has a sharp solubility curve below 33°C. In some embodiments, the causticization process can include cooling the leachate to a temperature of less than or equal to about 33°C. less than or equal to about 30°C. less than or equal to about 20°C, less than or equal to about 10 °C, less than or equal to about 5 °C, less than or equal to about 0 °C, less than or equal to about -5 °C, or less than or equal to about -8 °C. In some embodiments, the causticization process can include cooling the leachate a temperature of greater than or equal to about -I5°C, greater than or equal to about-10°C. greater than or equal to about -8°C. greater than or equal to about -5 °C, or greater than or equal to about 0°C. SSD can have very’ low solubility at -8 °C.

[0039] In some embodiments, the sodium sulfate can be separated from the lithium solution in step 106. In some embodiments, this separation step can be a solid / liquid separation step as the lithium solution can be in aqueous form and the sodium sulfate can be solid. In some embodiments, the separation step can include any known separation step in the art. In some embodiments, the separation can include filtering the lithium solution (i.e.. filtrate) from the sodium sulfate solids. In some embodiments, the sodium sulfate solids can be recycled and used in the lithium source leaching step 102 as the sodium sulfate used for leaching. In some embodiments, at least a portion of the sodium sulfate in the mixture in the leaching reactor can include sodium sulfate from the sodium sulfate separation step. In some embodiments, when the sodium sulfate is recycled to the leaching reactor for leaching the lithium source, the sodium sulfate may also can also provide at least a portion of the additive (e.g., lithium hydroxide) used in the leaching process.

[0040] In some embodiments, lithium from the lithium solution can be crystallized at step 107. In some embodiments, the crystallization step can be any known crystallization process in the art. In some embodiments, crystallizing the lithium solution can include crystallizing a lithium hydroxide solution to form lithium hydroxide monohydrate.

[0041] In some embodiments, the lithium hydroxide monohydrate can then be dried, put into a holding tank, and / or fed into various sized packages.

[0042] In some embodiments, the lithium hydroxide production process can also include a step of soluble salt removal. For example, in some embodiments, potassium or sodium salts (e.g., potassium sulfate and / or sodium sulfate) may be removed from the process.

[0043] In some embodiments, the lithium hydroxide monohydrate can be used to make an electrode active material for an electrode. In some embodiments, the electrode can be used in a battery (e.g., a lithium-ion battery). In some embodiments, the battery can include an anode, a cathode, a separator, and / or an electrolyte. In some embodiments, the battery’ can be a solid-state battery.

[0044] For the purpose of clarity and a concise description, features are described herein as part of the same or separate embodiments; however, it will be appreciated that the scope of the disclosure includes embodiments having combinations of all or some of the features described.EXAMPLES

[0045] The following examples are presented for purposes of illustration, and are not intended to impose limitations on the scope of this disclosure.

[0046] Twenty -four 1-2L autoclave tests were run for high temperature and high pressure leaching of lithium from beta-spodumene using sodium sulfate, with the results summarized in Tables 1-4 below. The first eighteen tests were run in a 2-L Hastelloy B autoclave. As discovered by Applicant, Hastelloy B is not recommended for high temperature basic reactions as moderate corrosion and deposition of very hard solids as shown in FIG. 2 were observed in these runs. The final six tests were run in a 1-L Inconel 600 (high nickel) autoclave. No visible corrosion or deposition of solids was observed in this Inconel autoclave.TABLE 1 - Leaching IngredientsTABLE 2 - Leaching Conditions

[0047] A first beta-Spodumene for Runs 1-18 was used, a second beta-Spodumene for Runs 19-22 was used, a third beta-Spodumene for Run 23 was used, and a fourth beta-Spodumene for Run 24 was used. Extra washing provided additional yield from extra washing of tailings. Revised yield is the max theoretical yield with perfect washing pH for the lithium sulfate filtrate. LiOH in the tables refers to lithium hydroxide monohydrate. Runs 1-18 used a Hastelloy B autoclave. Runs 19-24 used an Inconel autoclave. In the tables, Na2SO4 refers to sodium sulfate and Na2SO3 refers to sodium sulfite. Runs 1-17 used 500 RPM during leaching, run 18 used 1000 RPM during leaching, and runs 19-24 used 700 RPM during leaching.TABLE 3 - Leachate and Solids CompositionsTABLE 4 - ICP Results (ppm) for the Leachate and Dried Reaction Tailings

[0048] An exemplary experimental procedure using run 19 as the representative example is as follows. Sodium sulfate (45.19 g) was dissolved in DI water (500.49 g) in a beaker at ~30 °C with magnetic stirring. The sodium sulfate solution, beta-Spodumene (100.05 g), and lime (2.03 g) were added to a 1-L Inconel autoclave. The autoclave was sealed, put into a heater / stirrer stand, stirred at 700 RPM, and heated to 210 °C (255 psig). After 3 hours, the heating was stopped, the heater was lowered from the autoclave, and air cooling was started through the cooling coils. After 1 hour (37 °C reactor contents), the autoclave was opened, the solids were collected on a filter, and a 100 mL DI water wash of the autoclave was added to the filter. The filtrate (517.08 g, pH 10) was analyzed by ICP. The wetcake (215.87 g) was dried overnight at 110 °C (118.37 g) and analyzed by ICP.

[0049] The first two runs had very good yields (90-92%) observed after additional washing of the tailings to fully extract the lithium sulfate product. With the standard sulfuric acid leaching process, a proton from sulfuric acid can go into the rock matrix and a lithium atom can come out. The excess sulfuric acid is neutralized in the leaching tanks with limestone (CaCO3), leaving considerable amounts (-20% of the total tailings mass) of both limestone and gypsum (CaSO4) in the tailings. In the sodium sulfate leaching process, a sodium ion can go into the rock as a lithium ion can come out. While there is a small increase in mass from the added sodium, with no limestone or gypsum present, the net tailings mass can be lower. The average % sodium in the tailings observed in these tests (8.2%) was in reasonable accordance with the theoretical maximum amount of sodium for full replacement of lithium (9%). Overall, the dried tailings mass is around 110% of the incoming dry Spodumene mass compared to 120-125% for the existing commercial process.

[0050] Run 3 was a test with no base additive present, which resulted in a very low (31%) yield. In Run 4, sodium hydroxide was used in place of lime (CaO), with a lower (81%) yield observed. In Runs 6-8, sodium sulfite was used in place of sodium sulfate to test possibly eliminating using a base additive. The goal of these runs was to hopefully avoidthe corrosion and solids deposition seen in reactions using lime. While the autoclave was much cleaner after the three runs, the yield was consistently lower with sodium sulfite. In addition, utilizing sodium sulfite during leaching would not allow for the potential of recycling the post-causticization sodium sulfate back into the leaching process.

[0051] A variety of standard process development options were tested in the next set of runs. Using half of the lime charge reduced the yield to 80%, while decreasing the reaction time from three hours to one hour greatly lowered the yield (29%). The drop in yield from reducing the lime charge was in doubt because going back to the standard literature conditions (Run 11) resulted in an even lower yield (76%). At this point, it was suspected that the corrosion and deposition of solids observed in all the standard runs (FIG. 2) was resulting in fouling of the autoclave and a general degradation of the yield in all the runs.

[0052] A test of lithium hydroxide in place of lime (Run 12) had a lower yield (80%) but the yield was higher than a comparable standard test (Run 11) immediately preceding it. The use of barium hydroxide (Run 13) as the base did seem to reduce the yield (76%) in a more meaningful way. Runs 14-16 was a set of back-to-back runs with no cleaning of the autoclave to simulate running commercially to see if the solids deposition increased to unacceptable levels, resulting in lower yields. The yield steadily decreased through this series of runs. Run 17 was a test of higher temperature (230 °C in place of 210 °C), with a lower yield (72%), while Run 18 was a standard test (77%), except running at 1000 RPM instead 500 RPM as in Runs 1-17.

[0053] The general conclusion from the original set of testing was that the material of construction (Hastelloy B) resulted in artificially poor results for most of these experiments. After the arrival and setup of the Inconel autoclave, this equipment was used for the final six reactions of the test campaign (Runs 19-24). No visible corrosion or solids deposition was observed in any of the six runs in Inconel. Three tests under the standard literature conditions were completed (Runs 19-21) at both 210 and 220 °C, with acceptable yields (87-88%) when extra washing was done on the tailings to extract all the soluble lithium, comparable to a multi-stage belt filter. A test using lithium hydroxide as the base additive (Run 22) had an excellent yield (91%). Two tests were completed on alternative beta-Spodumene samples, with a poor yield (78%) observed with the beta-Spodumene of Run 23 but a high yield (91%) when using the beta-Spodumene of Run 24.

[0054] Aside from the lithium content used to calculate the yields, other common elements were tested in the lithium sulfate filtrate and the dried tailings. The major elements are summarized in Table 4 above. While the runs based on the standard literatureconditions with lime had generally similar compositions, there were some interesting differences in the ICP results for the other runs. Eliminating lime from the process greatly reduced the calcium levels in both the lithium sulfate and the tailings. More potassium was leached out in the sodium sulfate / spodumene process. This can involve a larger potassium bleed stream and / or reduce yield and throughput. This was more noticeable with Run 24 and Run 23 beta-Spodumene. Run 23 Spodumene has a much higher amount of potassium, resulting in twice the level of potassium in the lithium sulfate.

[0055] There were some other differences in the composition of the streams when using different Spodumenes. There was much lower boron in the lithium sulfate due to the lower levels of boron in these two Spodumene mines. There were higher levels of sodium, iron, calcium, and magnesium in Run 24 tailings due to the higher levels of these elements in Spodumene. For Runs 19-22, a different supply of the beta-Spodumene was used, so the levels of potassium, magnesium, and iron (and other elements) in the tailings were different compared to the amounts observed in Runs 1-18.

[0056] Aside from elimination of the SSA byproduct stream, another difference with a sodium sulfate / Spodumene leach compared to the existing commercial process can be differences in the mass and composition of the tailings. The total mass of the tailings can be lower compared to the existing tailings because there may not be any gypsum or unreacted limestone in the tailings. The composition of the rock portion of the tailings can be different because instead of a proton from sulfuric acid being exchanged for the lithium in the Spodumene, a sodium ion is going into the aluminosilicate matrix, forming sodium analcime. This can impact the potential sale of this stream as a byproduct. 11 may be usable as a Zeolite because it no longer contains calcium sulfate or carbonate. As shown in FIGS. 3 and 4, the new tailings form spherical agglomerates (unlike the jagged rocks in the existing tailings (e.g., LAS tailings) from sulfuric acid leaching process shown in FIG. 5), which look like traditional zeolites.

[0057] The particle size distributions for the tailings from Run 1 and Run 2 are shown in FIGS. 6 and 7, respectively. In some embodiments, the new tailings can have a particle size distribution with a D50 of at least about 15 microns, at least about 20 microns, at least about 25 microns, at least about 30 microns, at least about 35 microns, or at least about 40 microns. In some embodiments, the new tailings can have a particle size distribution with a D50 of at most about 50 microns, at most about 45 microns, at most about 40 microns, at most about 35 microns, at most about 30 microns, or at most about 25 microns. In some embodiments, the new tailings can have a particle size distribution with a D10 of at least about 5 microns,at least about 10 microns, at least about 15 microns, at least about 20 microns, at least about 25 microns, or at least about 30 microns. In some embodiments, the new tailings can have a particle size distribution with a D 10 of at most about 40 microns, at most about 35 microns, at most about 30 microns, at most about 25 microns, at most about 20 microns, or at most about 15 microns. In some embodiments, the new tailings can have a particle size distribution with a D90 of at least about 75 microns, at least about 80 microns, at least about 85 microns, at least about 90 microns, at least about 95 microns, or at least about 100 microns. In some embodiments, the new tailings can have a particle size distribution with a D90 of at most about 110 microns, at most about 105 microns, at most about 100 microns, at most about 95 microns, at most about 90 microns, or at most about 85 microns. The particle size and particle size distributions can be measured by techniques known to those of ordinary skill in the art, including for example, a Malvern Mastersizer 300.

[0058] The sodium sulfate leaching process described herein can provide numerous advantages including: (1) no or minimal formation of a separate isolated sodium sulfate byproduct besides the sodium sulfate that is recycled; (2) elimination of sulfuric acid, lime, and / or limestone from the leaching process; (3) elimination of acid mix, acid roast, magnesium removal and / or sodium sulfate anhydrous isolation and purification sections from the process; (4) lower tailings mass and / or potential sale of tailings (as zeolite); and / or (5) lower scope GHG emissions due to not transporting SSA, less transportation for raw materials and tailings, and / or removal of kilns. In addition, utilizing lithium hydroxide as the base, there may be enough residual base in the recycled sodium sulfate to eliminate or reduce the need for a separate base feed to the leaching reactor. In some embodiments, the concentration of the base can be increased to improve throughput and lower operating costs.DEFINITIONS

[0059] Unless defined otherwise, all terms of art, notations and other technical and scientific terms or terminology used herein are intended to have the same meaning as is commonly understood by one of ordinary skill in the art to which the claimed subject matter pertains. In some cases, terms with commonly understood meanings are defined herein for clarity and / or for ready reference, and the inclusion of such definitions herein should not necessarily be construed to represent a substantial difference over what is generally understood in the art.

[0060] The terms “powders” and “particles” used herein are equivalent, except that a single powder refers to a plurality of particles. This disclosure can apply to a wide range of particles and powders.

[0061] As used herein, the word “layer(s)” and “coating(s)” are equivalent. Specifically, each term “layer(s)” or “coating(s)” as used in relation to a particle(s) indicates that at least a portion of the surface of such particle, substantially all, or all of the surface of such particle(s) is covered by or in contact with the “layer(s)” or “coating(s).” Similarly, the term “coated” in relation to a particle(s) indicates that at least a portion of the surface of the particle, substantially all, or all of the surface of the particle(s) is covered by or in contact with the substance(s) with which the parti cle(s) is said to be “coated.”

[0062] Reference to “about” a value or parameter herein includes (and describes) variations that are directed to that value or parameter per se. For example, description referring to “about X” includes description of “X”. In addition, reference to phrases “less than”, “greater than”, “at most”, “at least”, “less than or equal to”, “greater than or equal to”, or other similar phrases followed by a string of values or parameters is meant to apply the phrase to each value or parameter in the string of values or parameters.

[0063] As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It is also to be understood that the term “and / or” as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. It is further to be understood that the terms “includes, “including,” “comprises,” and / or “comprising,” when used herein, specify the presence of stated features, integers, steps, operations, elements, components, and / or units but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, units, and / or groups thereof.

[0064] This application discloses several numerical ranges in the text and figures. The numerical ranges disclosed inherently support any range or value within the disclosed numerical ranges, including the endpoints, even though a precise range limitation is not stated verbatim in the specification because this disclosure can be practiced throughout the disclosed numerical ranges.

[0065] The above description is presented to enable a person skilled in the art to make and use the disclosure, and is provided in the context of a particular application and its requirements. Various modifications to the preferred embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the disclosure.Thus, this disclosure is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.

Claims

CLAIMS1. A method of producing lithium hydroxide monohydrate comprising: mixing a lithium source, a first sodium sulfate, and lithium hydroxide in a reactor; leaching the lithium source in the mixture in the reactor at a temperature of 200-275°C and a pressure of 250-600 psig to form residual solids and a leachate comprising lithium sulfate; separating the leachate from the residual solids; reacting a base with the leachate to form a second sodium sulfate and a solution comprising lithium hydroxide; separating the second sodium sulfate from the solution comprising lithium hydroxide; and crystallizing the solution comprising lithium hydroxide to form lithium hydroxide monohydrate.

2. The method of claim 1, wherein the lithium source comprises spodumene, lepidolite, petalite, amblygonite, zinnwaldite, triphylite, lithiophilite, or combinations thereof.

3. The method of any one of claims 1-2, further comprising calcining a precursor lithium source to form the lithium source.

4. The method of claim 3, wherein the precursor lithium source comprises α- spodumene and the lithium source comprises -spodumene.

5. The method of any one of claims 1-4, further comprising recycling the second sodium sulfate to the reactor to be used as at least a portion of the first sodium sulfate in the mixture in the reactor.

6. The method of any one of claims 1-5, wherein the lithium source in the mixture is leached in the reactor for at least one hour.

7. The method of any one of claims 1-6, wherein the reactor has an internal surface comprising a nickel alloy with at least 50% nickel.

8. The method of claim 7. wherein the nickel alloy is a nickel-chromium-based alloy.

9. The method of any one of claims 1-8, wherein a mass ratio of the first sodium sulfate to the lithium source in the mixture is 1 -.6-1:

210. The method of any one of claims 1-9, wherein a mass ratio of the lithium hydroxide to the lithium source in the mixture is 1:200-1:

35.

11. The method of any one of claims 1-10, wherein a mass ratio of the first sodium sulfate to the lithium hydroxide in the mixture is 1 : 50-1 : 10.

12. The method of any one of claims 1-11, wherein the mixture has a pH of at least 7.

13. The method of any one of claims 1-12, wherein the mixture has a liquid to solid ratio of 3-10 mL / g.

14. The method of any one of claims 1-13, wherein at least 75% of lithium contained in the lithium source is extracted during leaching.

15. The method of any one of claims 1-14, further comprising concentrating the leachate prior to reacting the base with the leachate.

16. The method of claim 15, wherein concentrating the leachate comprises evaporating solvent from the leachate.

17. The method of any one of claims 1-16, wherein the base comprises sodium hydroxide.

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