Process

Abstract

A method of extracting lithium hydroxide from a lithium-containing solid, such as a lithium ore or lithium battery. The problem addressed by the present invention is to provide an extraction method in which non-lithium components are removed in sequence rather than simultaneously. The method of the invention comprises the consecutive steps of dissolving a lithium-containing solid in an acid, precipitating a non-lithium metal product using a first base, precipitating the conjugate base of the acid using a second base, and separating lithium hydroxide from the resulting solution.

Description

Technical Field

[0001] The present invention relates to a method for processing metal-containing materials to extract or recover metals and other compounds suitable for further utilization. More particularly, the present invention provides a method for extracting lithium from lithium-containing solids, such as black matter recovered by battery recycling. Background Art

[0002] With the increasing use of electric vehicles, global demand for batteries, particularly lithium-ion batteries, is increasing. Lithium, therefore, is a valuable resource that can be obtained from the environment through mining lithium ore or extracting mineral-rich salt lake brines. Both methods have environmental impacts: brine extraction is considered to risk soil salinization and place demands on local ecological structures and landscapes, while mining requires large tracts of land and often damages the landscape over generations. Lithium mining and processing also involve significant water consumption, and byproduct seepage can have considerable impacts on local water sources and aquaculture.

[0003] Lithium hydroxide (specifically, lithium hydroxide monohydrate) is one of the two main forms of lithium used in lithium-ion batteries, the other being lithium carbonate. Typically, the production of lithium hydroxide requires energy-intensive electrolysis or an additional precipitation step compared to lithium carbonate.

[0004] Therefore, there is strong interest in improved lithium extraction methods as well as lithium recovery and reuse.

[0005] Black matter is a waste product generated during the recycling of lithium-ion batteries. During the battery recycling process, lithium-ion batteries are disassembled and the lithium-rich parts are shredded, producing the so-called "black matter." This lithium-rich material comes from the battery electrodes and contains various other elements, such as nickel, manganese, and cobalt. Therefore, these elements need to be processed and separated before they can be reused in battery production.

[0006] A well-known method for recovering elements from nitric oxide is leaching precipitation. This involves dissolving the nitric oxide in an acid, such as sulfuric acid, and then adding a reagent, such as sodium hydroxide, to raise the pH. This first step introduces metals (potentially lithium, nickel, manganese, or cobalt) into solution. A second step precipitates most of the metals, while soluble elements, such as lithium, remain in solution and can be subsequently recovered. However, when sodium hydroxide is used, the sodium remains in solution along with the lithium and must subsequently be removed.

[0007] Others have suggested using metal hydroxides such as barium hydroxide and calcium hydroxide. Due to the low solubility of barium sulfate or calcium sulfate, when sufficient hydroxide is added to dissolved black matter, the barium sulfate or calcium sulfate precipitates out all at once along with other insoluble metals, leaving only lithium hydroxide. It has been reported that a solid lithium hydroxide product can be produced with only a drying step (KR101975468B1).

[0008] Similar techniques could be applied to other solid lithium sources, such as lithium-based anodes or lithium-containing ores like spodumene, mica, or lepidolite. Summary of the Invention

[0009] The present inventors sought to provide an improved, more environmentally friendly method for extracting lithium hydroxide from lithium-rich materials, such as shredded lithium battery electrodes or the like (so-called black matter). To this end, the inventors proposed a multi-step precipitation method involving precipitation from a solution formed by treating the lithium-rich material with an acid, such as sulfuric acid. In the first precipitation step, the so-called insoluble metals are recovered in a mixed metal product (if present in the raw material, these metals may include nickel, cobalt, and manganese, as well as other elements / compounds present in the raw material, such as late transition metals, such as aluminum). In the second precipitation step, the conjugate base of the acid, for example, if sulfuric acid is used, is precipitated, and the sulfate compound is recovered. The resulting lithium hydroxide solution can be dried or further precipitated to recover the lithium hydroxide solution.

[0010] The lithium-rich material may suitably be a lithium-containing solid. For example, it may be a natural (mined) material such as spodumene, mica or lepidolite, or it may be an artificial material such as black matter or a lithium-containing anode.

[0011] Therefore, in a first aspect, the present invention may provide a method for extracting lithium hydroxide from a lithium-containing solid, the method comprising:

[0012] (i) a dissolving step comprising treating the lithium-containing solid with an acid to obtain a dissolving step solution;

[0013] (ii) a first precipitation step comprising adding a first base to the dissolving step solution to precipitate the metal product as a first precipitate, and then separating the first precipitate to obtain a first precipitation step solution;

[0014] (iii) a second precipitation step comprising adding a second base to the first precipitation step solution to precipitate a compound containing the conjugate base of the acid as a second precipitate, and then separating the second precipitate to obtain a second precipitation step solution;

[0015] (iv) separating lithium hydroxide from the second precipitation step solution.

[0016] Suitably, the second base is a metal hydroxide (such as an alkaline earth metal hydroxide) or a metal oxide (such as an alkaline earth metal oxide which reacts to form an alkaline earth metal hydroxide when added to water). Most preferably, an alkaline earth metal hydroxide is used.

[0017] The first base and the second base may be the same or different. Preferably they are different.

[0018] The present inventors have observed that the use of a multi-step precipitation process may have the following advantages: (1) the mixed metal product (the first precipitate, which may be referred to as reprecipitated nigrescence when the lithium-containing solid is nigrescence) may contain fewer contaminants, such as barium, and therefore be more useful and / or have a higher value; (2) reagent costs may be lower; and / or (3) in addition to the mixed metal product and lithium hydroxide, a third stream may be recovered, namely the precipitate recovered in the second precipitation step. This stream may itself be utilized or further processed; in other words, it may be recycled.

[0019] Conventionally, the treatment of lithium-containing solids begins by adding an acid to dissolve the lithium-containing solids, thereby producing a dissolution step solution. In the art, this may be referred to as "dissolving" or "leaching" the black matter, where the lithium-containing solid is the black matter.

[0020] The acid may, for example, be selected from sulfuric acid, phosphoric acid, hydrochloric acid, citric acid and oxalic acid. In some embodiments, it is sulfuric acid.

[0021] Typically, concentrated sulfuric acid (e.g., 98 wt %, 18 M) is used. Other acids that may be used include inorganic acids such as concentrated phosphoric acid (e.g., 85 wt %, 15 M) and concentrated hydrochloric acid (e.g., 37 wt %, 12 M), and organic acids such as citric acid and oxalic acid.

[0022] When using acids that are solid at room temperature, such as citric acid and oxalic acid, concentrated solutions of these acids can be used. For example, a 55-65 wt% (e.g., 59.2 wt%) citric acid solution or a 9 wt% oxalic acid solution can be used at room temperature. Even more concentrated acid solutions can be formed by heating, for example, a 76.2 wt% citric acid solution can be used at 70°C.

[0023] The ratio of acid to lithium-containing material used is not particularly limited, as it depends on the lithium-containing material and acid used. For example, a larger number of moles of monoprotic acid, such as hydrochloric acid, is required compared to a diprotic acid, such as sulfuric acid. The ratio of acid to lithium-containing material can be 5 to 100 moles of acid per kg of lithium-containing material.

[0024] Concentrated sulfuric acid (e.g., 96%, 18 M) is suitably used. The ratio of sulfuric acid to lithium-containing material can be, for example, 10 to 40 moles of sulfuric acid to 1 kg of lithium-containing solid, suitably 15 to 30 or 20 to 25 moles of sulfuric acid to 1 kg of lithium-containing solid. A suitable example is 1 kg of black matter to about 23 moles of sulfuric acid.

[0025] Concentrated hydrochloric acid (e.g., 37 wt %, 12 M) is suitably used. The ratio of hydrochloric acid to lithium-containing material can be, for example, 20 to 80 moles of hydrochloric acid to 1 kg of lithium-containing solid, suitably 30 to 60 or 40 to 50 moles of hydrochloric acid to 1 kg of lithium-containing solid. A suitable example is about 46 moles of hydrochloric acid to 1 kg of black matter.

[0026] The dissolution step can be carried out at room temperature or at a temperature above room temperature, for example at 40° C. to 80° C., suitably at 60° C. to 65° C., for example about 70° C. This is advantageous because elevated temperatures can accelerate the dissolution rate and increase the solubility of the metal salt.

[0027] Optionally, an additional step of heating the lithium-containing solid is performed before the dissolution step. The purpose of this heating step is to remove volatile and / or organic components. For example, heating can be continued until no mass change is observed. Preferably, the heating step is performed at 50°C to 100°C, optionally 60°C to 80°C, optionally 65°C to 75°C, and in some embodiments, at about 70°C.

[0028] Optionally, an additional step of filtering the solution from the dissolution step is performed after the dissolution step and before the first precipitation step. This removes insoluble components, such as carbon (in the form of graphite) and metals resistant to acid dissolution, such as gold and copper. This allows for the recovery of these metals and improves the purity of the precipitate produced in the first precipitation step.

[0029] In some embodiments, the dissolution step solution is diluted prior to the first precipitation step; however, more conveniently, it is not diluted prior to the first precipitation step.

[0030] In the first precipitation step, a base (the so-called first base) is added to the solution from the dissolution step to raise the pH. The base can be provided as a solid, a solution, or an aqueous solution. Preferably, the base is water-soluble (a base that dissolves in water) because homogeneous solutions react faster than heterogeneous mixtures.

[0031] The pH of the solution is increased to precipitate the so-called insoluble metals in the solution from the dissolution step as a first precipitate. The term "insoluble metals" is understood in the art to refer to metals whose associated salts (e.g., hydroxides if the first base is a hydroxide ion source, or sulfides if the first base is a sulfide ion source) are insoluble (<1 mg / mL, preferably <0.5 mg / mL, and more preferably <0.1 mg / mL) in the solution produced by adding the first base to the solution from the dissolution step. The composition of the first precipitate depends on the composition of the initial lithium-containing solid and the base used in the first precipitation step. Typically, the precipitate will contain hydroxides of the insoluble metals (particularly when the first base is a hydroxide ion source). The precipitate may also include sulfides, oxides, or carbonates of the insoluble metals. The first precipitate may also contain the base used in the first precipitation step. Typically, the first precipitate will contain insoluble nickel, cobalt, and manganese compounds. Suitable bases for the first precipitation step may include ammonium persulfate, ammonium carbonate, ammonia, barium hydroxide, and calcium hydroxide.

[0032] In some embodiments, the first base is not an alkali metal-containing base; the use of an alkali metal-containing base may be undesirable because the introduction of alkali metal anions can contaminate the lithium hydroxide product.

[0033] In some preferred embodiments, the first base is ammonium persulfate, ammonium carbonate, or aqueous ammonia, with ammonium persulfate being particularly suitable. Using an ammonium base is advantageous because ammonium cations can be easily removed from the first precipitate (e.g., reprecipitated nigra) by heating. Generally speaking, fewer impurities in the first precipitate (reprecipitated nigra) indicate that it is more likely to be suitable for reuse and / or have a higher resale value, requiring less processing.

[0034] The amount of first base required to precipitate the transition metal depends on the amount of acid used and the composition of the lithium-containing solid. Preferably, the base is used in an amount at least equimolar to the acid. For diprotic acids, such as sulfuric acid, at least 2 moles of base are used per mole of acid. For triprotic acids, such as phosphoric acid, at least 3 moles of base are used per mole of acid.

[0035] The solubility of transition metal hydroxides depends on the metal and the pH of the solution. Generally, metal hydroxides are soluble at low pH (around pH 0) and high pH (around pH 14), with lower solubility at intermediate pH values. For example, the minimum solubility of aluminum is approximately pH 6-7; the minimum solubility of iron is approximately pH 7-9; the minimum solubility of nickel is approximately pH 10-10.5; the minimum solubility of cobalt is approximately pH 10-12; and the minimum solubility of manganese is approximately pH 11-12. However, some metals, such as iron, begin to precipitate at around pH 3.

[0036] Therefore, the optimal pH value of the first precipitation step depends on the composition of the lithium-containing solid.In the first precipitation step, the first base may preferably be added in an amount sufficient to raise the pH of the solution to pH 3-12.

[0037] After adding the first base in the first precipitation step, the precipitated metal product can be separated by any suitable means to provide a first precipitate and a first precipitation solution. This includes, but is not limited to, gravity settling, filtration, centrifugation, and hydrocyclone separation.

[0038] The liquid obtained after the first precipitation (first precipitation solution) is then treated with a metal base (the so-called second base).

[0039] Suitable second bases are alkaline earth metal hydroxides, such as barium hydroxide or calcium hydroxide, or alkaline earth metal oxides, such as barium oxide or calcium oxide (which react with water to form the corresponding hydroxide), preferably barium hydroxide. Barium hydroxide is preferred due to its high water solubility, while the resulting barium salts generally have low water solubility.

[0040] Suitably, when sulfuric acid is used as the acid in the dissolution step, the second base is barium hydroxide or calcium hydroxide. Barium hydroxide is preferred because barium sulfate has very low water solubility (0.24 mg / L at 20°C), while calcium sulfate has a higher solubility (2.6 g / L at 25°C).

[0041] When phosphoric acid is used as the acid in the dissolution step, the second base is preferably barium hydroxide or calcium hydroxide. Barium phosphate is insoluble in water, while calcium phosphate has a solubility of 0.002 g / L at 20°C.

[0042] When hydrochloric acid is used as the acid in the dissolving step, the second base is preferably barium hydroxide. The solubility of barium chloride at 20°C is 358g / L.

[0043] When citric acid is used as the acid in the dissolving step, the second base is preferably barium hydroxide or calcium hydroxide. At 18°C, the solubility of barium citrate is 0.406 g / L and the solubility of calcium citrate is 0.85 g / L.

[0044] When oxalic acid is used as the acid in the dissolution step, the second base is preferably barium hydroxide or calcium hydroxide. At 20°C, the solubility of barium oxalate is 0.003 g / L and the solubility of calcium oxalate is 6.7 mg / L.

[0045] The base used in the first and second precipitation steps can be the same, for example both the first and second bases can be barium hydroxide. However, it is preferred to use different bases because a cheaper and less toxic first base can be used, such as ammonium persulfate.

[0046] The first precipitation solution contains a lithium salt formed when the lithium-rich material is treated with an acid. By adding an alkaline earth metal hydroxide base (or forming the alkaline earth metal hydroxide base in situ by adding the corresponding oxide), a double displacement reaction occurs to form lithium hydroxide (which remains in solution) and an alkaline earth compound containing the conjugate base of the acid (which precipitates from solution and can be separated from the liquid by any suitable method). This includes, but is not limited to, gravity settling, filtration, centrifugation, or hydrocyclone separation.

[0047] The amount of second base required to precipitate the acid conjugate base ion depends on the amount of acid and base used in the first precipitation step. For example, the amount of the second base can be calculated by measuring the concentration of the acid conjugate base ion (e.g., sulfate ion when sulfuric acid is used) in the first precipitation solution and adding an equimolar amount of the second base. The concentration of the acid conjugate base ion in the first precipitation solution can be determined using methods such as titration. Methods for titrating sulfates, phosphates, chlorides, citrates, and oxalates are known in the art.

[0048] Alternatively, the second base can be added in portions until precipitation is no longer observed. For example, precipitation can be observed using an online camera.

[0049] Because most impurities have already been separated in the first precipitation step, the inventors have observed that the precipitate separated in the second precipitation step may be sufficiently pure for further use. This reduces waste and / or makes the process more cost-effective. When the barium compound is used as the second base, further uses include recycling to produce barium hydroxide and selling the barium salt.

[0050] After adding the base in the second precipitation step, the precipitated compound comprising the conjugate base of the acid can be separated by any suitable means to provide a second precipitate and a second precipitation solution. This includes, but is not limited to, gravity settling, filtration, centrifugation, or hydrocyclone separation.

[0051] After the second precipitation step is complete, a lithium hydroxide solution (second precipitation step solution) is obtained. This can be evaporated to obtain lithium hydroxide, or the lithium hydroxide can be precipitated, for example, using an antisolvent precipitation / recrystallization. Suitable lithium hydroxide precipitation methods will be apparent to those skilled in the art.

[0052] The claimed process offers advantages over prior art leaching methods, which are expensive due to the type and quantity of reagents used. This can negatively impact process economics. Furthermore, to completely remove all impurities from the solution in prior art methods, large amounts of metal hydroxide are required. This ultimately forms a primary precipitate (e.g., reprecipitated nigra), which can be perceived as an impurity, thereby reducing the quality of the precipitate (reprecipitated nigra) and, consequently, its market value.

[0053] The present invention includes any combination of the described aspects and preferred features unless such a combination is expressly impermissible or explicitly avoided. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Embodiments and experiments illustrating the principles of the present invention will now be discussed with reference to the accompanying drawings, in which:

[0055] Figure 1 A flow chart of a process described in the prior art is shown.

[0056] Figure 2 A flow chart showing the process of the present invention is shown. DETAILED DESCRIPTION

[0057] Various aspects and embodiments of the present invention will now be discussed with reference to the accompanying drawings. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned herein are incorporated herein by reference.

[0058] Lithium-containing solid

[0059] The lithium-containing solid used in the dissolution step of the present invention is not particularly limited. Any suitable material may be used. This includes both natural (mined) and man-made materials. Natural (mined) lithium-containing solids include ores such as spodumene, mica, and lepidolite. Man-made lithium-containing solids include recycled waste streams, such as black matter and lithium-containing anodes.

[0060] Recycled materials typically have significantly higher lithium contents than natural (mined) materials. For example, niobium contains approximately 5% lithium by weight, while lithium ore (i.e., spodumene) typically contains only 3% by weight. However, these man-made sources also contain significant amounts of transition metals, which can complicate lithium separation. These transition metals can also be valuable byproducts.

[0061] This invention describes a process for obtaining useful products, particularly lithium hydroxide, from lithium-containing solids. The inventors believe that this process is efficient and potentially more economical and / or environmentally friendly than prior art methods for this purpose. It can be used to extract lithium from so-called natural sources, such as ores, or from recycled materials, such as spent batteries (by processing black matter or lithium-containing anode material).

[0062] substantia nigra

[0063] Black matter is a well-known term in the art. It is typically formed from recycled lithium-ion batteries, but other lithium-based batteries can also be used. In the first stage of battery recycling, lithium-rich electrode materials (which can be cathodes, anodes, or both) are shredded, crushed, and / or ground in a mechanical process.

[0064] Depending on the source battery type (lithium-ion, lithium polymer, lithium cobalt oxide, lithium iron phosphate, etc.), black matter can have different elemental compositions. Typically, black matter is primarily composed of carbon (in the form of graphite), nickel, lithium, and cobalt. Black matter typically contains: lithium, carbon, fluorine, sodium, magnesium, aluminum, manganese, iron, cobalt, nickel, copper, zinc, and phosphorus.

[0065] The source of the black mass is not particularly limited; any lithium-containing battery material can be used in the process of the present invention. For example, the black mass can be formed from one or more battery types selected from the group consisting of lithium nickel manganese cobalt oxide (NMC), lithium nickel cobalt aluminum oxide (NCA), lithium iron phosphate (LFP), lithium manganese oxide (LMO), and lithium cobalt oxide (LCO).

[0066] In some embodiments, the black mass is derived from NMC or LFP batteries. In some embodiments, the black mass is derived from NMC batteries.

[0067] Method according to the invention

[0068] Figure 2 The process of the method according to the present invention comprising two steps of precipitation is schematically shown. Figure 1 This is in contrast to the prior art method with a single precipitation step shown schematically in .

[0069] Dissolution step

[0070] When the lithium-containing solid is niobium, this step can be called "niobium dissolution" or "leaching" and is used as the first step in the chemical treatment of lithium-ion battery waste in existing methods. Acids react with the metals, metal oxides, and other metal compounds in the niobium, converting them into salts that can be dissolved in solution.

[0071] In one embodiment, sulfuric acid is added to the lithium-containing solid, in this case, the black matter, during the dissolution step. In some embodiments, 1 to 50 moles of sulfuric acid are used per kilogram of the black matter, optionally 10 to 40 moles, optionally 20 to 30 moles, optionally 20 to 25 moles, optionally 22 to 24 moles, and optionally 23 moles. In some embodiments, the ratio of lithium-containing solid (e.g., black matter) to sulfuric acid is 100 g / L to 10,000 g / L, optionally 200 g / L to 5,000 g / L, optionally 400 g / L to 2000 g / L, optionally 600 g / L to 1200 g / L, optionally 700 g / L to 900 g / L, and optionally 800 g / L.

[0072] Sulfuric acid may be used as a 90% to 100% concentrated solution (by weight in water).

[0073] In other embodiments, phosphoric acid may be used. Phosphoric acid may be used in the form of a 75% to 100% concentrated solution (by weight in water).

[0074] In other embodiments, hydrochloric acid may be used. Hydrochloric acid may be used in the form of a 30% to 40% concentrated solution (by weight in water).

[0075] In other embodiments, citric acid can be used. Citric acid can be used in the form of a 40% to 85% solution (by weight in water).

[0076] In other embodiments, oxalic acid may be used. Oxalic acid may be used in the form of a 5% to 15% solution (by weight in water).

[0077] In some embodiments, the dissolving step is performed at room temperature. In some embodiments, the dissolving step is performed above room temperature, e.g., 50°C to 100°C, optionally 60°C to 90°C, optionally 70°C to 80°C.

[0078] In some embodiments, an additional step of heating the lithium-containing solid is performed prior to the dissolving step. In some embodiments, this is performed at a temperature of 50°C to 100°C, optionally 60°C to 80°C, optionally 65°C to 75°C, and in some embodiments at about 70°C.

[0079] In some embodiments, the dissolving step is followed by an additional step of removing solids from the solution in the dissolving step. For example, the mixture can be separated by gravity separation, filtration, centrifugation, or hydrocyclone separation.

[0080] First precipitation step

[0081] The solution of the dissolving step is treated with a first base ( Figure 2 The solution is treated with barium hydroxide (in the above scheme) to raise the pH. This causes the insoluble metals to precipitate (the so-called first precipitate described herein).

[0082] This precipitate typically contains nickel, cobalt, and manganese. It may also contain magnesium, aluminum, iron, copper, and zinc. It may also include metals from the first base used, such as barium. Obviously, the amount depends on the composition of the lithium-containing solid and the first base.

[0083] As an alternative to the first base, calcium hydroxide or ammonium persulfate, ammonium carbonate, or ammonia can be used. These may be less expensive than barium hydroxide. Other bases suitable for the first precipitation step may include alkaline earth metal hydroxides, such as Mg(OH)2, Ca(OH)2, Sr(OH)2, or Ba(OH)2, alkaline earth metal oxides (which hydrate to provide alkaline earth metal hydroxides), such as MgO, CaO, SrO, or BaO, alkaline earth metal carbonates, such as MgCO3, CaCO3, SrCO3, or BaCO3, alkaline earth metal sulfides, such as MgS, CaS, SrS, or BaS, ammonia, ammonium hydroxide, ammonium carbonate, ammonium persulfate, and organic amines.

[0084] In some embodiments, upon addition of the first base, the pH is raised to 3 or higher, optionally 4 or higher, optionally 5 or higher, optionally 6 or higher, optionally 7 or higher, optionally 8 or higher, optionally 9 or higher, optionally 10 or higher, or optionally 11 or higher. Suitably, upon addition of the first base, the pH is raised to 12 or lower, optionally 11 or lower, optionally 10 or lower, optionally 9 or lower, optionally 8 or lower, optionally 7 or lower, optionally 6 or lower, optionally 5 or lower, or optionally 4 or lower. Suitable pH values after addition of the first base are in the range of 3-12.

[0085] The precipitated metal product (i.e., the first precipitate) is separated from the first precipitation solution. For example, the mixture can be separated by gravity separation, filtration, centrifugation, or hydrocyclone separation. This provides a mixed metal product as the first precipitate, also referred to as reprecipitated nigrescence when the lithium-containing solid is nigrescence. By using only the amount of base required to precipitate the metal while leaving the conjugate base of the acid in solution, the first precipitate has a higher purity and, therefore, a higher practical / economic value than precipitates formed by prior art methods.

[0086] Second precipitation step

[0087] The liquid remaining after separation of the first precipitate, referred to herein as the first precipitation step solution, is then treated with a second base.

[0088] This is suitably a metal hydroxide, such as barium hydroxide or calcium hydroxide ( Figure 2 Suitably, it is not sodium hydroxide, as the sodium remains in solution and must be separated from the lithium hydroxide product.

[0089] For example, when sulfuric acid is used as the dissolution step acid, this step precipitates barium sulfate (or other sulfate salts, depending on the second base used), removing impurities from the solution while recovering the sulfate salts for use, further processing, or resale, making the process more environmentally friendly. The resulting lithium hydroxide solution is low in sulfate; the resulting sulfate precipitate is essentially free of impurities in the form of insoluble metals (or their sulfates / hydroxides) removed by the first precipitation step.

[0090] Similarly, when phosphoric acid or hydrochloric acid is used, the precipitate contains phosphate anions or chloride anions, respectively, and likewise for oxalic acid and citric acid, the precipitate contains oxalate and citrate anions, respectively.

[0091] The second base is suitably an alkaline earth metal hydroxide, such as Mg(OH)2, Ca(OH)2, Sr(OH)2 or Ba(OH)2, or an alkaline earth metal oxide (the hydrate of which provides the corresponding alkaline earth metal hydroxide), such as MgO, CaO, SrO or BaO. Preferably, the second base is soluble in water, and is therefore preferably Ca(OH)2 or Ba(OH)2.

[0092] After the second is added, the second precipitate is separated from the second precipitation solution. For example, the mixture can be separated by gravity separation, filtration, centrifugation, and hydrocyclone separation.

[0093] Lithium hydroxide separation steps

[0094] The second precipitation step solution is a lithium hydroxide solution. Lithium hydroxide can be separated into its monohydrate (LiOH·H2O) or anhydrate (LiOH) by liquid evaporation or crystallization. Suitable crystallization techniques include antisolvent crystallization, in which lithium hydroxide is precipitated from solution upon addition of a suitable organic solvent, such as acetone. The antisolvent can then be recovered, for example, by distillation, after separation of the solid lithium hydroxide.

[0095] ***

[0096] The features disclosed in the foregoing description, the appended claims or the drawings, appropriately expressed in their specific form or in the form of means for performing the disclosed functions, or methods or processes for obtaining the disclosed results, may be used alone or in any combination of these features to realize different forms of the invention.

[0097] Although the present invention has been described in conjunction with the above exemplary embodiments, many equivalent modifications and variations will be apparent to those skilled in the art upon consideration of this disclosure. Therefore, the exemplary embodiments of the present invention described above are intended to be illustrative rather than restrictive. Various changes may be made to the described embodiments without departing from the spirit and scope of the present invention.

[0098] For the avoidance of doubt, any theoretical explanations provided herein are intended to enhance the reader's understanding, and the inventors do not wish to be bound by any theoretical explanations.

[0099] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0100] Throughout this specification, including the claims that follow, unless the context requires otherwise, the words “comprise” and “include” and variations such as “comprises”, “comprising” and “including”, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0101] It must be noted that, as used in the specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from "about" one particular value, and / or to "about" another particular value. When such a range is expressed, another embodiment includes from the from particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent "about," it can be understood that the particular value forms another embodiment. The term "about" in connection with a numerical value is optional and means, for example, + / - 10%.

[0102] References

[0103] Some publications are cited above in order to more fully describe and disclose the present invention and the prior art in the field to which the present invention belongs. The full citations of these references are as follows. The entire contents of these references are incorporated herein.

[0104] KR101975468B1.

Claims

1. A method for extracting lithium hydroxide from a lithium-containing solid, the method comprising: (i) a dissolving step comprising treating the lithium-containing solid with an acid to obtain a dissolving step solution; (ii) a first precipitation step comprising adding a first base to the dissolving step solution to precipitate the metal product as a first precipitate, and then separating the first precipitate to obtain a first precipitation step solution; (iii) a second precipitation step comprising adding a second base to the first precipitation step solution to precipitate a compound containing the conjugate base of the acid as a second precipitate, and then separating the second precipitate to obtain a second precipitation step solution; (iv) separating lithium hydroxide from the second precipitation step solution.

2. The method of claim 1, wherein the lithium-containing solid is black matter.

3. The method of claim 1 or 2, wherein the first base and the second base are different.

4. A process according to any preceding claim, wherein the acid is sulphuric acid, phosphoric acid, hydrochloric acid, citric acid or oxalic acid.

5. A process according to any preceding claim, wherein the acid is sulphuric acid.

6. A process according to any preceding claim, wherein the second base is a metal hydroxide, preferably barium hydroxide.

7. A process according to any preceding claim, wherein the first base is ammonium sulfate.

8. A method according to any preceding claim, wherein the lithium-containing solid is heated to a temperature of 50°C to 100°C prior to the dissolving step (i).

9. A process according to any preceding claim, wherein solids are removed from the dissolution step solution after the dissolution step (i) and before the first precipitation step (ii).

10. The method according to any one of the preceding claims, wherein in the first precipitation step, the amount of the first base is sufficient to raise the pH of the solution to pH 3-12.

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