Calcination and atmospheric leaching of lithium minerals

Abstract

According to the present invention there is provided a process for the staged treatment of a lithium-containing mineral, the process comprising calcination under an additive followed by atmospheric pressure leaching at elevated temperature in an alkaline leach solution.

Description

Technical Field

[0001] This invention relates to a method for classifying lithium-containing minerals, the method comprising calcination with additives, followed by atmospheric pressure leaching in an alkaline leaching solution. Background Technology

[0002] Lithium is a component of compounds used in a variety of industrial applications. It is primarily obtained from lithium brines and ores through hydrometallurgical extraction methods. Traditional methods of processing lithium from ores involve calcination or roasting at high temperatures, followed by hydrometallurgical treatment, including some form of leaching step, such as acid leaching, aqueous leaching, or high-pressure alkaline leaching.

[0003] All these options for the leaching step have been further developed to more efficiently extract lithium and other components from minerals contained in ore or brine. However, less effort has been devoted to the development of calcination. Several options exist for this calcination step, such as those shown in CN 101974678A, which suggests calcining lepidolite materials in the presence of additives that may include calcium salts. However, this publication describes a general method using a moderately alkaline leaching solution that produces fractions from which lithium and other metals are difficult to separate from impurities.

[0004] One problem with existing calcination and leaching methods is that silicon (Si) contained in most lithium-containing minerals and fluorides (F) in some lithium-containing minerals volatilize during calcination, posing a challenge to waste gas treatment. Simultaneously, significant amounts of fluorides and silicon (Si) are released from the minerals, further challenging the separation and purification typically performed after the leaching step. Therefore, new methods are needed where lithium can be effectively separated from byproducts and impurities, such as fluorides and silicon compounds. Summary of the Invention

[0005] This invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0006] According to a first aspect of the present invention, a method for processing lithium-containing mineral raw materials is provided, the method comprising a calcination step and a leaching step.

[0007] According to the second aspect, a method is provided in which calcination is carried out with additives to limit the volatilization of mineral components.

[0008] According to a third aspect, a method is provided in which leaching is carried out under conditions that advantageously separate the components into dissolved components and solid components.

[0009] Therefore, the present invention relates to a method for classifying lithium-containing minerals, the method comprising the following steps: calcining the lithium-containing minerals in the presence of one or more calcium salts, leaching the obtained calcined material under atmospheric pressure at a pH of 11.5 or higher, and separating the leaching slurry into different fractions.

[0010] This invention is based on the discovery that calcining lithium minerals in the presence of one or more calcination additives reduces the amount of fluorides volatilized during calcination and reduces the amount of silicon and fluorides carried into the filtrate after leaching. This will further facilitate the separation of lithium from fluorides and silicon compounds.

[0011] Significant advantages are achieved using this invention. Among these advantages, excellent lithium extraction rates are achieved, with nearly 100% of the lithium ultimately remaining in the solid fraction after the leaching step. This solid fraction can then be further separated into sub-fractions, for example, to provide a pure metal product. Similarly, smaller amounts of fluoride and silicon are ultimately present in the leaching slurry, thereby facilitating their efficient separation through the leaching solution. Attached Figure Description

[0012] Figure 1 A method configuration according to at least some embodiments of the present invention is shown, wherein block 1 represents the calcination step of the method and block 2 represents the leaching step.

[0013] Figure 2 A method configuration of an advantageous embodiment is shown, wherein additional boxes 3 and 4 indicate optional further steps of the method of the invention, which provide for further separation of the mineral components into smaller fractions. Dashed arrows indicate possible recovery options.

[0014] Figure 3 Another advantageous embodiment of the method configuration is shown, wherein additional box 2a represents an optional pulping step, boxes 2' and 3' represent solid / liquid separation steps, box 3a represents a preferred optional sub-step of further separation step 3, and boxes 4a and 4b represent carbonation and crystallization steps, respectively, which form optional sub-steps of further separation step 4. Detailed Implementation

[0015] definition

[0016] Lithium-bearing minerals can exist in many different forms, such as those listed in Table 1 below, with spodumene being the most commonly used due to its availability.

[0017] Table 1.

[0018]

[0019] In addition, it can also exist in the form of clay minerals, such as: masutomilite, swinefordite, hectorite, cookeite and jadarite.

[0020] The “calcination” of lithium-containing minerals is a thermal step that typically alters the mineral’s crystal structure to provide structural changes that facilitate leaching. In turn, “leaching” is used to dissolve certain components of the calcined minerals. Some known processes are designed to leach (or dissolve) lithium salts, while others are designed to “extract” lithium from the leaching slurry into the solid.

[0021] Most of the aforementioned minerals contain silicon, which becomes a byproduct after the minerals are processed to recover valuable metals. "Desilication," also known as silicon removal, refers to the removal of silicon from the leaching stream obtained by the method of this invention. Some of the aforementioned minerals contain fluorides, which also need to be separated as impurities, for example, in the same desilication process.

[0022] This invention relates to a method for classifying lithium-containing minerals (see...). Figure 1 The method includes the following steps:

[0023] - The lithium-containing minerals are calcined in the presence of one or more calcination additives selected from calcium salts in step 1.

[0024] - In a leaching solution with an alkaline pH of 11.5 or higher, the resulting calcined product is subjected to atmospheric pressure leaching step 2 at an elevated temperature, wherein the pH value is measured at room temperature, and then the temperature is increased, and

[0025] - Obtain two or more separate fractions from the obtained leachate slurry, such as a liquid fraction and a solid fraction, wherein the liquid fraction contains byproducts that can be recovered as separate recovery fractions, and the solid fraction contains lithium and metals that can be further recovered as separate product fractions.

[0026] The attached figures show some optional method configurations, in which... Figure 1 A general implementation scheme is shown. Figure 2 and Figure 3 A preferred embodiment is shown.

[0027] The lithium-containing starting material is preferably obtained from lithium-containing ore, concentrate or recycled material, preferably concentrate, and is generally in the form of lithium-containing minerals, such as those mentioned above in Table 1, or it may be one of the clay minerals listed separately, but is preferably selected from spodumene, lepidolite, lepidolite or lepidolite, more preferably spodumene, lepidolite or lepidolite.

[0028] Before or during calcination step 1, preferably before calcination step 1, the starting material minerals are mixed with one or more calcination additives comprising calcium salts. These one or more calcium salts are preferably selected from calcium carbonate (CaCO3), calcium hydroxide (Ca(OH)2), calcium oxide (CaO), calcium sulfate (CaSO4), or calcium chloride (CaCl2), preferably one or more of calcium carbonate, calcium hydroxide, or calcium oxide, and most preferably contain at least calcium carbonate or calcium hydroxide. These calcium salts are preferably added to the lithium-containing minerals at a mineral concentrate:calcium salt ratio of 1:1 to 10:1, more preferably at a ratio of 3:1 to 10:1, and most preferably at a ratio of 3.5:1 to 6:1. These additives particularly reduce agglomeration and hard melts. Furthermore, they lead to a reduction in fluoride volatilization during calcination; therefore, in another alternative, the dosage of the calcium salt can be determined as a molar ratio of calcium ions (Ca) to fluoride ions (F) in the lithium-containing minerals (i.e., the Ca / F ratio) of 0.5-3 mol / mol, preferably 0.7-1.5 mol / mol.

[0029] In one embodiment, the calcination step of the method (see...) Figure 1 , 2 Step 1) of step 3 is carried out at a temperature of 850-1200°C, more preferably at 900-1200°C, and most preferably at 900-1100°C. The duration of calcination step 1 can be, for example, 1 minute to 5 hours, or preferably 30 minutes to 3 hours.

[0030] The material obtained from calcination, i.e., the calcined product, can be directly sent to the leaching step (see...). Figure 1 , 2 And step 2 of step 3). Alternatively, a separate pulping step can be performed before leaching step 2 (and step 3). Figure 3 Step 2a) involves mixing lithium-containing calcined mineral material (i.e., the calcined product) into an aqueous solution, optionally in the presence of one or more alkali metal reagents (usually in excess), to produce a lithium-containing slurry. Preferred alkali metal reagents are carbonates such as sodium carbonate, or hydroxides such as sodium hydroxide, or mixtures of these reagents, most preferably hydroxides. However, the slurry can also be formed as part of leaching step 2, and any addition of leaching chemicals can be carried out in optional pulping step 2a or in leaching step 2.

[0031] The material entering leaching step 2 typically contains calcined minerals of varying particle sizes because it does not require a grinding step.

[0032] In an alternative, a mixture of calcined minerals and additional uncalcined mineral fractions is treated in leaching step 2. The uncalcined minerals can be, for example, different crystal structures of spodumene or pyroxene, such as α-spodumene.

[0033] As described above, leaching step 2 is carried out in the form of atmospheric pressure leaching. In this atmospheric pressure leaching of lithium-containing minerals, a leaching temperature below the boiling point of the leaching solution is sufficient. Therefore, leaching step 2 can be carried out at a temperature of 80–100°C, preferably 90–95°C.

[0034] Atmospheric pressure is sufficient for the pressure during leaching step 2. However, the pressure is typically adjusted upwards as the temperature increases. Therefore, at higher leaching temperatures (e.g., ~100°C), the pressure may be adjusted to a level slightly above atmospheric pressure (e.g., 1.1–3 bar).

[0035] The leaching solution used is an alkaline leaching solution with a pH of 11.5 or higher, preferably a leaching solution containing alkali metal hydroxides.

[0036] In one embodiment, the pH level required in leaching step 2 is achieved by adjusting the pH using a hydroxide reagent, such as an alkali metal hydroxide or alkaline earth metal hydroxide, preferably selected from sodium hydroxide (NaOH), potassium hydroxide (KOH), lithium hydroxide (LiOH), calcium oxide (CaO), or calcium hydroxide (Ca(OH)2), or mixtures thereof, preferably sodium hydroxide (NaOH) or potassium hydroxide (KOH). The hydroxide can be added directly to the leaching solution or to the slurry formed in optional pulping step 2a, and preferably thus forms a leaching solution with a hydroxide content of 0.1-250 g / L, preferably 1-200 g / L, more preferably 30-80 g / L, even more preferably 40-50 g / L or 0.006-14 mol / L. This will give the solution the desired high pH, ​​typically adjusted to 11.5-14, preferably 12-14, using the alkali metal hydroxide. However, at such levels, the content of the alkaline reagent is a more reliable measurement factor than the pH level. Preferably, the hydroxide content can be in the range of 0.6-9 mol / L, more preferably 1-6 mol / L.

[0037] Under the above conditions, leaching step 2 can be carried out for 1-48 hours, preferably 1-36 hours, and most suitablely 10-24 hours. Therefore, in some embodiments, the leaching time is 1 hour, 5 hours or 10 hours to 24 hours, 30 hours, 36 hours, 40 hours or 48 hours.

[0038] While alkaline leaching is carried out in the presence of a carbonate reagent in some known methods, this method can be carried out without a carbonate reagent, i.e., without adding carbonate to the leaching solution. However, in an alternative embodiment, the fresh leaching solution can be combined with the recycled solution from subsequent steps of the method before leaching step 2, so that some carbonate may be carried into leaching step 2 even without separate carbonate addition.

[0039] In one specific embodiment, in leaching step 2, an alkaline leaching solution is used to extract calcined lithium-containing minerals selected from those mentioned herein, in the presence of carbonates. Carbonates are typically added as suitable carbonate reagents, such as alkali metal carbonates, preferably sodium carbonate (Na₂CO₃) or potassium carbonate (K₂CO₃), or mixtures thereof, most preferably consisting at least partially of sodium carbonate. Furthermore, the carbonate may be added in a stoichiometric ratio of >0-3.5 relative to the lithium content in the mineral of this embodiment, preferably in a stoichiometric ratio of >0-2.5 relative to the lithium content in the mineral, and most preferably in a stoichiometric ratio of 1.5-2.5.

[0040] In leaching step 2, the hydroxide ions (OH-) in the leaching solution - In the presence of lithium, lithium in lithium-containing minerals, such as lithium oxides or lithium aluminum silicates (e.g., LiKAl2F2Si3O9 of lepidolite), is converted into, for example, lithium metasilicate (Li2SiO3), leaving analcime as a byproduct.

[0041] Following leaching step 2, a leaching slurry is obtained containing lithium in a converted form, such as lithium in its silicate form, as an extract. Therefore, in the context of this disclosure, lithium extract refers to lithium that has been converted to this form (i.e., the slurry or the solid or liquid fraction separated from it), wherein lithium is released from the structure of the initial minerals in the starting material (i.e., the feed).

[0042] Since this lithium silicate is only slightly soluble in the leaching solution, it is initially obtained in the form of a slurry. The slurry does not contain a significant amount of unreacted mineral, as the mineral has been converted to, for example, sodium aluminum silicate. In other words, the lithium contained in the mineral has been released. Typically, the yield of lithium released from leaching step 2 is 90 to 99% by weight, calculated from the initial amount of lithium in the mineral.

[0043] The leachate obtained from leaching step 2 can be used as is and therefore directly fed into any subsequent reaction, such as to achieve further dissolution.

[0044] However, in a preferred embodiment, the leached slurry is sent to a post-leaching solid / liquid separation step 2' (first solid / liquid separation step) to provide lithium-containing solids and liquids, the liquids containing, in particular, unwanted compounds such as sodium silicate and other impurities such as fluorides, but also containing lithium compounds in dissolved form.

[0045] Any solid / liquid separation steps mentioned in this article can be performed, for example, by filtration or by feeding the slurry or solution to a thickener.

[0046] In another embodiment, the resulting lithium-containing slurry or the solid or liquid fraction separated therefrom is further processed (see...). Figure 3 Step 3 or 4) is performed to remove one or more impurities. Preferably, the liquid fraction obtained from the solid / liquid separation 2' after leaching is used on the liquid side for further processing step 3 (first further processing step 3), typically followed by a further solid / liquid separation step 3' (or a second solid / liquid separation step). This further processing step 3 can be carried out, for example, in the form of a desilication step 3a, in which a calcium reagent such as calcium oxide (CaO) or calcium hydroxide (Ca(OH)2) is added to the slurry or solution to cause a reaction with impurities therein such as fluorides or silicon, which can then be removed in the further solid / liquid separation step, or in the solid / liquid separation step 3' or 3a' (or the second solid / liquid separation step) after desilication.

[0047] Another alternative is to remove fluoride and silicon from the leaching slurry or the liquid fraction separated therefrom in two stages by reacting with a calcium reagent such as calcium hydroxide or calcium oxide. The fluoride reacts to form calcium fluoride in the first reagent addition stage, which can be separated from the remaining solution in a solid / liquid separation step (not shown in the figure). After that, the above-described desilication step 3a can be performed, followed by the desilication-following solid / liquid separation step 3a'.

[0048] To maintain these separate stages and obtain separate fluoride and silica fractions, a preferred option is to analyze the fluoride content of the leaching slurry before fluoride removal, or to analyze the fluoride content of the liquid fraction separated from the leaching slurry, and add approximately equal amounts of calcium reagent to achieve the desired fluoride separation. Additional calcium reagent may then be added to obtain the silicate fraction separately.

[0049] The desilication solution obtained after this further processing step 3 can be recycled to leaching step 2 or optional pulping step 2a, or combined with any stream used in subsequent further processing step 4 (e.g., slurry or solid fraction sent to optional carbonation step 4a) (see by Figure 1 and 2 (The options are shown by the dashed lines and arrows), or you can remove impurities or discard it.

[0050] The calcium reagent is preferably added to the desilication step 3 or 3a in a stoichiometric ratio of 1-2 relative to the silicon (Si) content in the slurry or solution. The temperature during the desilication reaction is preferably 80-100°C, and a duration of 1-10 hours, for example 1-8 hours, is generally sufficient. The solution separated from the solids in the further separation step 3' can be recycled, particularly in the leaching step 2 or in the preceding optional pulping step 2a, or it can be combined with the leaching slurry, or preferably with the leaching residue (solid fraction) obtained from the solid / liquid separation step 2' after leaching, and sent to the subsequent processing step 4, such as the carbonation step 4a, which will provide dissolved lithium salts while other metals remain in solid form.

[0051] In another embodiment, a further processing step 4 is performed either directly after leaching step 2 or after the separation step 2' described above (see [link to embodiment]). Figure 2 Alternatively, step 3) most preferably includes a carbonation step 4a (also known as a hydrocarbonation step due to the reaction that occurs). In the optional carbonation step 4a, the resulting leaching slurry or the leaching residue separated therefrom (optionally combined with the desilication solution obtained from the solid / liquid separation step 3') is reacted with carbon dioxide (CO2), preferably with an excess of carbon dioxide. The undissolved lithium compound obtained from leaching step 2 is thus converted into dissolved lithium bicarbonate and is therefore able to be separated substantially completely from the undesirable undissolved material.

[0052] The optional carbonation step 4a can be carried out at a temperature of 0-50°C, preferably 15-40°C, and typically at a pressure of 1-15 bar, more typically 1-10 bar, preferably at atmospheric pressure. Higher pressure improves the solubility of carbon dioxide in aqueous solution, but increased pressure also increases the risk of formation of byproducts and impurities. It is preferable to use, for example, any suitable mixer to provide mixing that effectively disperses the gas, liquid, and solid components.

[0053] The lithium-containing slurry or solution obtained from processing step 4 can be further transported to a subsequent recovery step (not shown in the figure) to convert the lithium in the slurry or solution into an insoluble compound, i.e., to precipitate or crystallize it.

[0054] Prior to this precipitation or crystallization, another step may be performed to separate any insoluble reagents from the slurry or solution obtained from processing step 4, typically by filtration, followed by precipitation step 4b of the liquid fraction.

[0055] Furthermore, purification (not shown in the figure) can be performed before precipitation step 4b to remove impurities, such as trivalent and / or divalent metal ions, such as calcium, magnesium, aluminum, and iron ions, preferably after solid / liquid separation (from which the liquid fraction is recovered). Preferably, purification is performed using ion exchange. Ion exchange can be performed, for example, by using the method disclosed in Finnish Patent 121785. Typically, purification by ion exchange is performed using a cation exchange resin, which can be, for example, iminodiacetic acid (IDA) or aminophosphonic acid (APA). Such resins are manufactured, for example, under the trade names Amberlite IRC 748 (IDA) and Amberlite IRC 7476 (APA). Typically, the cation exchange resin is a resin having a polystyrene matrix crosslinked with divinylbenzene containing aminophosphonic acid groups.

[0056] The precipitation step 4b described above results in the formation of a solid lithium compound or precipitate, which can crystallize into pure crystals, preferably lithium carbonate or lithium hydroxide.

[0057] If lithium carbonate is to be prepared, precipitation step 4b includes heating the slurry or solution containing lithium bicarbonate, preferably to a temperature of 70-100°C, to decompose the bicarbonate and crystallize the lithium carbonate.

[0058] In this carbonate precipitation reaction, a slurry containing water and lithium carbonate precipitate is formed. Solid lithium carbonate is separated from the obtained slurry in a solid / liquid separation process, thereby obtaining battery-grade lithium carbonate. Standard battery-grade lithium carbonate contains at least 99.5% lithium carbonate. However, using the method described herein, superior battery-grade lithium carbonate containing at least 99.99% lithium carbonate can be produced.

[0059] If preparing lithium hydroxide, precipitation step 4b involves reacting a hydroxide reagent (i.e., an alkaline earth metal hydroxide) with a lithium-containing slurry or solution obtained from a previous step (or optionally pretreated) to produce a slurry containing lithium hydroxide in a soluble form. The alkaline earth metal hydroxide used is preferably selected from calcium hydroxide and barium hydroxide, more preferably calcium hydroxide, which is optionally prepared by the reaction of calcium oxide (CaO) in an aqueous solution. The alkaline earth metal hydroxide can also be mixed with water or an aqueous solution before use in the reaction. Also in this reaction, recycled mother liquor obtained from subsequent crystallization can be used. Hydroxide precipitation is typically carried out at a temperature of 10-100°C, preferably 20-60°C, most suitable 20-40°C. Typically, hydroxide precipitation is carried out at atmospheric pressure. The presence of the alkaline earth metal hydroxide and the above-described method conditions lead to the formation of lithium hydroxide, with alkaline earth metal carbonates forming as byproducts. After optional solid / liquid separation (preferably using filtration), or by feeding the slurry or solution to a thickener, a lithium hydroxide-containing solution with relatively high purity is obtained.

[0060] In one embodiment, the lithium hydroxide-containing slurry or solution can be purified prior to crystallization.

[0061] This optional purification step (not shown in the figure) is preferably based on the purification of dissolved ions and components, and more preferably includes ion exchange or membrane separation or both, most suitably using cation exchange resins, particularly selective cation exchange resins. Ion exchange can be performed, for example, as described above for the optional purification prior to precipitation step 4b. Membrane separation can be performed using a semi-permeable membrane, which separates ions or other dissolved compounds from the aqueous solution. More precisely, membrane separation can be used to fractionate dissolved ions and compounds by the size (depending on the pore size of the membrane material) and / or their charge (depending on the surface charge of the membrane material). Positive surface charges repel cations (with a stronger repulsion for polyvalent cations) and attract anions, and vice versa. These phenomena will enable the purification from lithium hydroxide solutions of, for example, polyvalent metal cations, complexes (e.g., aluminum hydroxide complexes), polymers (e.g., dissolved silica), and larger anions (e.g., sulfate and carbonate ions). Based on the above, it is particularly preferred to combine membrane separation with ion exchange, most suitably performing membrane separation first, followed by ion exchange to optimize the removal of polyvalent metal cations.

[0062] Lithium hydroxide monohydrate crystals can be recovered from lithium hydroxide-containing solutions by crystallization. Crystallization is typically carried out by heating the solution to approximately its boiling point to evaporate the liquid or by recrystallizing the monohydrate from a suitable solvent. The method described herein enables the production of pure lithium hydroxide monohydrate in excellent yield and purity in a continuous and simple process, typically providing battery-grade lithium hydroxide monohydrate crystals.

[0063] In a preferred embodiment, after any crystallization for the production of carbonate or hydroxide crystals, there is usually another solid / liquid separation step, preferably performed by filtration or by feeding the slurry or solution to a thickener.

[0064] In a further embodiment, the remaining mother liquor or a portion thereof after recovering the crystals in the solid / liquid separation can be recycled to one or more prior steps of the method described herein, or to the preparation of crystals of solid lithium compounds, thereby allowing the recovery of any uncrystallized lithium. In one alternative, the mother liquor is recycled to leaching step 2 or optionally to the preceding pulping step 2a for pH adjustment, thereby reducing the need for further addition of hydroxide reagents. In another alternative related to the hydroxide route, the mother liquor is recycled to the hydroxide precipitation for the preparation of lithium hydroxide. In yet another alternative, the mother liquor is recycled back to the crystallization in precipitation step 4b. Furthermore, the carbon dioxide used in the optional carbonation step 4a can be separated from the mother liquor and recycled back to carbonation step 4a.

[0065] It should be understood that the embodiments of the invention disclosed herein are not limited to the specific structures, method steps, or materials disclosed herein, but extend to their equivalents that will be recognized by those skilled in the art. It should also be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.

[0066] Throughout this specification, references to "one embodiment" or "implementation" mean that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment of the invention. Therefore, the phrases "in one embodiment" or "in an embodiment" appearing in various places throughout this specification do not necessarily refer to the same embodiment.

[0067] As used herein, for convenience, multiple items, structural elements, constituent elements, and / or materials may be presented in the same list. However, these lists should be interpreted as if each member of the list were individually identified as a separate and unique member. Therefore, without indication to the contrary, no single member of such a list should be construed as a de facto equivalent of any other member in the same list merely based on their presentation in the same group. Furthermore, various embodiments and examples of the invention may be mentioned herein along with alternatives to their various components. It should be understood that these embodiments, examples, and alternatives should not be construed as de facto equivalents of each other, but should be considered as separate and autonomous representations of the invention.

[0068] Furthermore, the described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Numerous specific details, such as examples of length, width, shape, etc., are provided in the following description to provide a thorough understanding of embodiments of the invention. However, those skilled in the art will recognize that the invention can be practiced without one or more specific details or using other methods, components, materials, etc. In other instances, well-known structures, materials, or operations have not been shown or described in detail to avoid obscuring aspects of the invention.

[0069] While the foregoing examples illustrate the principles of the invention in one or more specific applications, it will be apparent to those skilled in the art that many modifications can be made in the form, use, and details of the implementation without inventive effort and without departing from the principles and concepts of the invention. Therefore, the invention is not intended to be limited except by the claims set forth below.

[0070] The verbs “comprising” and “including” are used herein as open-ended restrictions, neither excluding nor requiring the presence of any unlisted features. Unless otherwise expressly stated, the features recited in the dependent claims may be freely combined with each other. Furthermore, it should be understood that the use of “a” or “an” (i.e., the singular form) throughout this document does not exclude the plural.

[0071] Example

[0072] Example 1 - Calcination of Lithium-Containing Materials

[0073] The lithium iron phosphate mica material was calcined using the parameters in Table 2 below.

[0074] Table 2. Calcination parameters

[0075]

[0076]

[0077] The calcination conditions of calcined sample 1 resulted in severe melting and hard agglomeration, posing a risk in commercial rotary kilns. Calcined samples 2 and 3 remained powdery and soft after calcination.

[0078] The results of the chemical analysis are shown in Table 3 below.

[0079] Table 3. Chemical Analysis

[0080]

[0081] As the results show, the fluoride content in calcined products 2 and 3 remains high, indicating that the fluoride will not volatilize if Ca reagent is added.

[0082] Example 2 - Atmospheric Pressure Alkaline Leaching of Lithium-Containing Materials

[0083] The calcined samples prepared above were leached using the conditions shown in Table 4 below. The analytical results of the leaching solution and leaching solids of sample AAL1 are shown in Tables 5-6 below, the analytical results of the leaching solution and leaching solids of sample AAL2 are shown in Tables 7-8 below, and the analytical results of the leaching solution and leaching solids of sample AAL3 are shown in Tables 9-10 below.

[0084] Table 4. Atmospheric Pressure Alkaline Leaching (AAL) Parameters

[0085]

[0086]

[0087]

[0088]

[0089]

[0090]

[0091]

[0092]

[0093] The lithium extraction rate is calculated as follows:

[0094]

[0095] The results showed that, compared with AAL1, samples AAL2 and AAL3 (containing Ca additives during calcination) exhibited significantly lower concentrations of fluoride and silicon in the filtrate, and OH... - The consumption is also relatively small. In addition, the reaction is very fast, and high Li extraction rates have been achieved in a very short leaching time (>80% of lithium is extracted into the solid in 4-6 hours, and >90% in 12-14 hours).

[0096] Example 3 - Hydrocarbonation

[0097] The filter cakes of AAL1 and AAL3 samples obtained from the leaching of Example 2 were bicarbonates, as shown in Table 11.

[0098] Table 11. Hydrocarbonation (Carb) Test Parameters

[0099] unit Carb1 Carb3 Filter cake AAL1 AAL3 temperature ℃ 30 30 pressure atm. atm. Duration h 4 4 Solid content g / L 300 300 <![CDATA[CO2 gas supply]]> mL / min 1000 1000 Li extraction rate (AAL+Carb) ％ 84.6 86.9

[0100] The carbonation results are shown in Tables 12 and 13 below.

[0101] Table 12. Results of hydrocarbonated solution samples

[0102]

[0103] Table 13. Results of hydrocarbonated solid samples

[0104]

[0105] The results of this embodiment show that the above procedure achieves very efficient lithium extraction.

[0106] Industrial applicability

[0107] The method of the present invention can be used as part of any hydrometallurgical method for recovering lithium products from lithium-containing minerals, and can be improved upon.

[0108] In particular, the novel combination of calcination with additives and alkaline leaching described herein enables the production of pure lithium products without the challenges typically caused by silicates and fluorides in lithium minerals.

[0109] Reference List

[0110] Patent documents

[0111] CN 101974678 A

[0112] FI 121 785

Claims

1. A method for classifying lithium-containing minerals, the method comprising the following steps: - In the presence of one or more calcination additives selected from calcium salts, lithium-containing minerals are calcined in step (1) to obtain the calcined product. - In a leaching solution with an alkaline pH of 11.5 or higher, the resulting calcined product is subjected to atmospheric pressure leaching step (2) at an elevated temperature, and - Obtain two or more individual fractions from the obtained leachate.

2. The method according to claim 1, wherein the lithium-containing mineral subjected to calcination is one or more of spodumene, lepidolite, lepidolite, lithium iron phosphate, spodumene, lepidolite, hydroxyapatite, or lepidolite, preferably spodumene, lepidolite, or lepidolite, more preferably wherein the mineral is obtained from ore containing spodumene, lepidolite, or lepidolite, and most preferably wherein the mineral is in the form of a concentrate.

3. The method according to claim 1 or 2, wherein the calcining additive is selected from calcium carbonate, calcium hydroxide, calcium oxide, calcium sulfate or calcium chloride, preferably one or more of calcium carbonate, calcium hydroxide or calcium oxide, and most preferably contains at least calcium carbonate or calcium hydroxide.

4. The method according to any one of the preceding claims, wherein the calcium salt is added to the lithium-containing mineral at a concentrate:calcium salt ratio of 1:1 to 10:1, preferably at a ratio of 3:1 to 10:1, more preferably at a ratio of 3.5:1 to 6:

1.

5. The method according to any one of the preceding claims, wherein the calcination step (1) is performed on lithium-containing minerals that also contain fluorides, and the dosage of the calcium salt is selected to achieve a ratio of calcium ions (Ca) to fluoride ions (F) in the lithium-containing minerals of 0.5-3 mol / mol, preferably 0.7-1.5 mol / mol.

6. The method according to any one of the preceding claims, wherein the calcination step (1) is carried out at a temperature of 850-1200°C, preferably 900-1200°C, or particularly 1000-1100°C.

7. The method according to any one of the preceding claims, wherein the alkaline condition in the leaching solution used in the leaching step (2) is achieved by adjusting the pH using a hydroxide reagent, such as an alkali metal hydroxide or an alkaline earth metal hydroxide, preferably selected from sodium hydroxide (NaOH), potassium hydroxide (KOH), lithium hydroxide (LiOH), calcium oxide (CaO) or calcium hydroxide (Ca(OH)2), or mixtures thereof, preferably sodium hydroxide (NaOH) or potassium hydroxide (KOH).

8. The method according to any one of the preceding claims, wherein the alkaline conditions in the leaching solution used in the leaching step (2) are achieved by adding an alkali metal hydroxide to the leaching solution to a hydroxide content of 0.1-250 g / L, preferably 1-200 g / L, more preferably 30-80 g / L, and even more preferably 40-50 g / L.

9. The method according to any one of the preceding claims, wherein the leaching solution used in the leaching step (2) has a hydroxide content of 0.6-9 mol / L, preferably 1-6 mol / L.

10. The method according to any one of the preceding claims, wherein the leaching step (2) is carried out at a temperature of 80-100°C, preferably 90-95°C.

11. The method according to any one of the preceding claims, wherein the leaching step (2) is performed for 1-48 hours, preferably 1-36 hours, most preferably 10-24 hours.

12. The method according to any one of the preceding claims, wherein a solid / liquid separation step (2') is performed after the leaching step (2) to separate solid fractions and liquid fractions from the leaching slurry.

13. The method according to any one of the preceding claims, wherein at least one fraction of the leach slurry or the solution separated therefrom is treated in the desilication step (3a), preferably by adding a calcium reagent to the leach slurry or the solution separated therefrom, the calcium reagent being more preferably calcium oxide (CaO) or calcium hydroxide (Ca(OH)2), and separating the formed solid silicate from the liquid fraction.

14. The method according to any one of the preceding claims, wherein fluoride and silicon are removed from the leaching slurry or the liquid fraction separated therefrom in two stages by reacting with a calcium reagent such as calcium hydroxide or calcium oxide, whereby the fluoride reacts to calcium fluoride in a first reagent addition stage, followed by the desilication step 3a.

15. The method according to any one of the preceding claims, wherein the leaching slurry obtained from the leaching step (2) or the liquid fraction from the desilication solution of the leaching slurry is separated and recycled back to the leaching step (2) and combined with the leaching solution.

16. The method according to any one of the preceding claims, wherein at least one fraction of the leaching slurry obtained from the leaching step (2) or at least one fraction of the solids separated therefrom is further processed to separate metal salts from the fractions, preferably in a processing step (4) beginning with carbonation, which provides dissolved lithium salts while other metals remain in solid form.

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