Leaching of lithium concentrate

Abstract

According to the present invention, there is provided a process for converting lithium in a lithium-containing mineral into a soluble form, and a method for preparing a solid lithium compound crystal using a lithium-containing slurry or solution obtained by the process.

Description

Technical Field

[0001] The present invention relates to a process for converting lithium in a lithium-containing mineral into at least a partially soluble form, and to the use of a lithium-containing slurry or solution obtained by said process in the preparation of solid lithium compound crystals. Background Art

[0002] Lithium is an element that forms compounds and has various industrial applications. Lithium for these purposes is mainly obtained from lithium brines and ores by hydrometallurgical extraction processes. Traditional processes for extracting lithium from ores include high-temperature calcination or roasting processes, followed by hydrometallurgical treatment such as pressure leaching.

[0003] For example, US 9255012 B2 and US11292725 B2 describe the leaching of calcined lithium-containing minerals in a leaching solution containing carbonate. In US 9255012 B2, the solution obtained from the leaching step is bicarbonate, and then a lithium carbonate product is crystallized. In US11292725 B2, the lithium in the leaching slurry further reacts to form hydroxide. However, the processes described in these two publications, which involve calcining the raw materials and combining them with a carbonate-based leaching solution, are used to provide the required lithium extraction rate.

[0004] One of the main problems with the calcination or roasting process is the high energy consumption, and this problem has become more important with the rising energy costs. Therefore, new processes are needed in which lithium in an uncalcined form can also be effectively leached from mineral raw materials. Summary of the Invention

[0005] The present 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, there is provided a process for converting lithium in a raw material based on an uncalcined lithium-containing mineral into at least a partially soluble form.

[0007] According to a second aspect of the present invention, there is provided a process for leaching lithium from a lithium-containing mineral raw material using leaching conditions that can even dissolve uncalcined minerals.

[0008] According to another aspect, there is provided a method of using at least partially dissolved lithium in the preparation of solid lithium compound crystals.

[0009] According to yet another aspect, there is provided a method of utilizing a desilication solution in a recycle feed.

[0010] Therefore, the present invention relates to a process for converting lithium in a lithium-containing mineral into at least a partially soluble form, and to the use of a lithium-containing slurry or solution obtained by said process in the preparation of solid lithium compound crystals.

[0011] The present invention is based on the discovery that lithium can be leached from lithium-containing minerals without calcining the minerals, provided that the conditions of pressure leaching are optimized in a suitable manner.

[0012] Therefore, the lithium-containing mineral raw materials used in the present invention can be directly leached without calcination or roasting pretreatment.

[0013] Significant advantages can be obtained by using the present invention. Among them, the present invention enables the leaching of lithium concentrate without calcination pretreatment and without the associated expensive equipment, thereby significantly saving costs and energy, reducing the emissions of gases such as carbon dioxide, and obtaining a more sustainable and environmentally friendly lithium product.

[0014] In addition, it has surprisingly been found that when using uncalcined mineral concentrate in the leaching step of the process, the lithium extraction rate is also better, at least for some lithium-containing minerals.

[0015] When a desilication step is further adopted in the process, another advantage can be obtained, that is, the recycling options in the process are improved, because the silicate brought into the process together with the uncalcined raw material still exists in the leaching solution in a high content, and it will benefit from silicon removal before recycling. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Shows a process configuration according to at least some embodiments of the present invention, wherein box 1 represents the leaching step of the process, box 2 represents an optional carbonation step, and box 3 represents an optional conversion step for converting lithium bicarbonate obtained in the carbonation step into an insoluble compound, wherein the dashed line separates the optional steps of the process from the necessary leaching step.

[0017] Figure 2 Shows a process configuration of an advantageous embodiment, with additional box 0 representing an optional pulping step, box 1' representing an optional solid / liquid separation step, box 4 representing an optional desilication (or silicon removal) step, and box 4' representing an optional further solid / liquid separation step, and the solution can be recycled back to the pulping step 0 or further carried to the carbonation step 2 (as shown by the dashed arrow). DETAILED EMBODIMENTS

[0018] DEFINITIONS Lithium-containing minerals can have many different forms, such as those listed in Table 1 below, and spodumene is the most commonly used among them due to its availability. Table 1 In addition, it can exist in the form of clay minerals such as masutomilite, swinefordite, hectorite, cookeite, and jadarite. "Calcination" of lithium-containing minerals is a thermal step, usually by changing the crystal structure of the minerals to make their structure change, thus making them more easily leached. Therefore, in the leaching process, the "calcined" form is usually selected, while the "uncalcined" form was considered too stable in the past.

[0019] The present invention relates to a process for converting lithium in uncalcined lithium-containing concentrate into a soluble form: by subjecting the concentrate in the leaching solution to pressure leaching at a temperature of 120 - 240 °C, preferably 150 - 220 °C, wherein the content of hydroxide ions (OH - ) in the leaching solution is 0.6 - 9 mol / L, more preferably 1 - 6 mol / L (see Figure 1 step 1).

[0020] The lithium-containing minerals used can be the uncalcined form of any of the minerals in Table 1, or the clay minerals listed separately, but are preferably selected from spodumene, petalite, lepidolite, and triphylite, more preferably petalite.

[0021] The content of hydroxide ions used in the process is preferably achieved by adding a hydroxide ion-containing alkaline reagent, such as an alkali metal hydroxide, selected from sodium hydroxide (NaOH), potassium hydroxide (KOH), and lithium hydroxide (LiOH), or a mixture thereof, preferably sodium hydroxide. Hydroxide ions are mainly used to adjust the pH value of the leaching solution to a sufficiently high level, preferably ≥ 11.5, more preferably 11.5 - 14. However, at such a pH value, the content of the alkaline reagent is more reliable than the pH value in terms of measurement.

[0022] The pressure leaching step of the lithium-containing mineral raw material is usually carried out at a temperature up to 300 °C, but in this process, a lower temperature of ≤ 240 °C is sufficient. The pressure during the first leaching is preferably 3 - 10 bar, more preferably 5 - 30 bar, even more preferably 5 - 25 bar. The pressure does not necessarily need to be adjusted separately because it will be adjusted upward as the temperature increases. Under these conditions, the residence time of the raw material in the leaching reactor can be relatively short, for example, the leaching time is 30 minutes to 4 hours.

[0023] Due to the use of high temperature and high pressure, the first leaching is usually carried out in a suitable autoclave or a series of autoclaves.

[0024] In one embodiment of the process described herein, the leaching solution further contains a carbonate reagent, such as an alkali metal carbonate, preferably sodium carbonate (Na 2 CO3 ) or potassium carbonate (K 2 CO 3 ), or a mixture thereof, most preferably consisting at least in part of sodium carbonate. Usually, the addition amount of such carbonate is 0 - 3 times, most preferably >0 - 2.5 times, of the lithium content in the mineral on a stoichiometric basis. Therefore, the addition amount can also be 0. In a specific embodiment of this process, the leaching step is carried out without a carbonate reagent, i.e., no carbonate is added to the leaching solution.

[0025] In another embodiment, in addition to the concentrate feed, a recycle liquid from a subsequent step of the process can also be added to the leaching solution.

[0026] In another embodiment of the process described herein, a separate pulping step 0 is carried out before the pressure leaching step, in which the lithium-containing concentrate is mixed into an aqueous solution, optionally in the presence of an alkali metal carbonate, to produce a lithium-containing slurry. However, the formation of the slurry can also be part of the pressure leaching step 1. The preferred alkali metal carbonate is sodium carbonate, and it is usually used in excess.

[0027] Thus, in the leaching step 1, the lithium aluminosilicate in the mineral (e.g., petalite LiAlSi 4 O 10 ) is converted into a dissolved or partially dissolved form, such as lithium carbonate (Li 2 CO 3 ) or lithium metasilicate (Li 2 SiO 3 ). For example, in the presence of sodium hydroxide, using petalite raw material, in the main reaction, the lithium-containing mineral reacts with hydroxide ions (OH - ) to produce Li 2 SiO 3 and analcime.

[0028] After the leaching step 1, a leaching slurry is obtained, which contains lithium in the form of carbonate or silicate, depending on whether carbonate is present in the leaching step 1. Since these intermediate products are only slightly soluble in the leaching solution, especially the carbonate can only be partially dissolved, they are obtained in the form of a slurry. The slurry will not contain a large amount of unreacted minerals because they have been converted into sodium aluminosilicate. In other words, the lithium contained in the mineral has been released. Usually, based on the mineral calculation, the ratio of lithium released from the leaching step is 90 to 95 wt%. The obtained slurry can be used as it is and thus directly undergo any subsequent reaction, such as to achieve further dissolution.

[0029] Depending on the further use of the leaching slurry, a solid / liquid separation step 1' may be optionally carried out to provide a liquid containing a smaller amount of undesired compounds (such as sodium silicate and other impurities). According to this alternative, the solution separated from the solid in the optional separation step 1' can be recycled, for example, reused in the same leaching step 1, or it can be used in an intermediate separation or conversion step 4 to provide a solution for recycling. In another alternative, the obtained slurry or solution can be diluted with water.

[0030] Thus, in another embodiment (see Figure 2 ), the leaching slurry is subjected to a solid / liquid separation step 1', followed by a silicon removal step 4, also known as a desilication step, in which a calcium reagent such as calcium oxide (CaO) or calcium hydroxide (Ca(OH) 2 ) is added to the solution to form calcium silicate, which can then be removed in a subsequent further solid / liquid separation step 4'. In the desilication step 4, in the main reaction, silicon reacts with calcium to produce calcium silicate.

[0031] Preferably, the amount of calcium reagent added is 1-2 times the silicon (Si) content in the solution on a stoichiometric basis. The temperature during this reaction process is preferably 80-100 °C, and a duration of 1-10 hours is usually sufficient, preferably 1-8 hours. The solution separated from the solid in the further separation step 4' can be recycled, especially reused in the leaching step 1 or preferably in the optional pulping step 0 in front, or it can be combined with the leaching slurry or preferably with the leaching residue obtained from the previous solid / liquid separation step 1' and subjected to subsequent treatment such as the carbonation step 2 described below.

[0032] In another embodiment, after leaching 1, directly or together with the above intermediate separation 1' and desilication 4 steps, a carbonation step (see Figure 1 or Figure 2 step 2) is carried out, which is also called a bicarbonation step due to the reaction occurring. In this carbonation step 2, the obtained leaching slurry or the leaching residue separated therefrom reacts with carbon dioxide (CO 2 ), preferably an excess of carbon dioxide. The undissolved lithium compounds obtained from the leaching step are thus converted into dissolved lithium bicarbonate and can therefore be separated from the undesired, undissolved materials almost completely.

[0033] The optional carbonation step 2 can be carried out at a temperature between 0 and 50 °C, preferably between 15 and 40 °C, and generally at a pressure of 1 to 15 bar, more typically 1 to 10 bar, preferably atmospheric pressure. Higher pressures increase the solubility of carbon dioxide in the aqueous solution, but excessive increase in pressure will lead to an increase in the formation of by-products and impurities. Mixing is preferably provided in the process, for example using any suitable mixer which is very effective for dispersing gases, liquids and solids.

[0034] The lithium-containing slurry or solution obtained from the process described herein can also be used in a method for preparing solid lithium compound crystals by carrying out the following further steps (see Figure 1 step 3): converting lithium bicarbonate in the slurry or solution into an insoluble compound and crystallizing it.

[0035] Before the conversion step 3, there can be a further step of separating any insoluble reagents from the slurry or solution in a solid / liquid separation step 2’ (not shown in the figure), typically by filtration, and then carrying out the conversion step 3 on the liquid part. The separation step 2’ can be carried out, for example, using filtration or by feeding the slurry or solution into a thickener from where the overflow can be fed to the conversion step 3 and the underflow can be discarded, recycled or further filtered to recover all the lithium remaining therein.

[0036] Alternatively, purification 2” (not shown in the figure) can be carried out before the conversion step 3 to remove impurities such as trivalent and / or divalent metal ions, such as calcium, magnesium, aluminum and iron ions, preferably after the solid / liquid separation step, from which the liquid part is recovered. Preferably, ion exchange is used for purification 2”. Ion exchange can be carried out, for example, by using the method disclosed in Finnish Patent 121785. Generally, purification by ion exchange is carried out by 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). Generally, the cation exchange resin is a resin having a polystyrene matrix crosslinked with divinylbenzene containing aminophosphonic acid groups.

[0037] The above conversion step 3 causes the formation of a solid lithium compound or precipitate which can be crystallized into pure crystals, preferably lithium carbonate or lithium hydroxide.

[0038] If lithium carbonate is prepared, the conversion step 3a 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.

[0039] In this reaction, a slurry containing water and lithium carbonate precipitate is formed. In the solid / liquid separation step 3' (not shown in the figure), solid lithium carbonate is separated from the obtained slurry, thereby obtaining battery-grade lithium carbonate. Standard battery-grade lithium carbonate contains at least 99.5% lithium carbonate. However, using the method described herein, high-quality battery-grade lithium carbonate containing at least 99.99% lithium carbonate can be produced.

[0040] If lithium hydroxide is prepared, the conversion step 3b involves reacting the lithium-containing slurry or solution obtained from the dissolution process or optionally pretreated with a hydroxide reagent, i.e., an alkaline earth metal hydroxide, to produce a slurry containing soluble lithium hydroxide. The alkaline earth metal hydroxide used is preferably selected from calcium hydroxide and barium hydroxide, more preferably calcium hydroxide, and 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 being used for the reaction. Also in this reaction, the recycled mother liquor obtained from the subsequent crystallization can be used. This conversion step is typically carried out at a temperature of 10 - 100 °C, preferably 20 - 60 °C, most suitably 20 - 40 °C. Generally, the conversion step 3b of the hydroxide is carried out at atmospheric pressure. The presence of the alkaline earth metal hydroxide and the above process conditions result in the formation of lithium hydroxide and alkaline earth metal carbonate as a by-product.

[0041] After the optional solid / liquid separation step 3' (not shown in the figure), preferably carried out by filtration or by feeding the slurry or solution to a thickener, a solution containing lithium hydroxide with relatively high purity is obtained.

[0042] In one embodiment, the slurry or solution containing lithium hydroxide can be purified before crystallization.

[0043] This optional purification step 3” (not shown in the figure) is preferably based on the purification of dissolved components and ions, more preferably includes ion exchange or membrane separation, or both, and most suitably by using a cation exchange resin, particularly a selective cation exchange resin. Ion exchange can be carried out, for example, in the manner described above for purification step 2”. Membrane separation can be carried out using a semi-permeable membrane that separates ions or other dissolved compounds from an aqueous solution. More precisely, membrane separation can be used to fractionate them according to the size of the dissolved ions and compounds (depending on the pore size of the membrane material) and / or their charge (depending on the surface charge of the membrane material). A positive surface charge repels cations (with a stronger repulsion for polyvalent cations) and attracts anions, and vice versa. These phenomena will enable the purification of, for example, polyvalent metal cations, complex substances (such as aluminum hydroxide complexes), polymeric substances (such as dissolved silica), and larger anions (such as sulfate and carbonate ions) from a lithium hydroxide solution. Based on the above, it is particularly preferred to combine membrane separation with ion exchange, most suitably by first performing membrane separation and then ion exchange to complete the removal of polyvalent metal cations.

[0044] Crystals of lithium hydroxide monohydrate can be recovered by crystallization from a solution containing lithium hydroxide. Crystallization is typically carried out by heating the solution to a temperature around the boiling point of the solution to evaporate the liquid, or by recrystallizing the monohydrate from a suitable solvent. The methods described herein are capable of producing pure lithium hydroxide monohydrate in a continuous and simple process with excellent yield and purity, typically providing battery-grade lithium hydroxide monohydrate crystals.

[0045] In a preferred embodiment of the method, the step of producing carbonate or hydroxide crystals is typically followed by another solid-liquid separation step, preferably carried out using filtration or by conveying the slurry or solution to a thickener.

[0046] In a further embodiment, the crystallization mother liquor remaining after the recovery of crystals in the solid / liquid separation step or a portion thereof can be recycled to the dissolution process or one or more previous steps in the preparation of solid lithium compound crystals, thereby allowing the recovery of any uncrystallized lithium. In one alternative, the mother liquor is recycled to the pressure leaching step 1, or an optional previous pulping step 0, to participate in the pH adjustment therein, thereby reducing the need for further addition of sodium hydroxide. In another alternative related to the hydroxide route, the mother liquor is recycled to the hydroxide conversion step 3b for preparing lithium hydroxide. In another alternative, the mother liquor is recycled back to the crystallization step. Additionally, the carbon dioxide used in the optional carbonation step 2 of the dissolution process can be separated from the crystallization mother liquor and recycled back to the carbonation step 2.

[0047] By recycling to earlier steps with lower alkalinity, such as pressure leaching step 1 or lithium conversion step 3, the advantage obtained is that some impurities in the crystallization mother liquor (such as aluminum and silicon) have increased solubility with the increase in alkalinity (such as caused by the increase in lithium hydroxide concentration), so that these alkali-soluble impurities can be removed by recycling them in solution to steps with lower alkalinity. For example, in hydroxide conversion step 3b, these impurities form slightly soluble compounds (such as aluminum hydroxide), and can be discarded together with the solids after the subsequent separation step. Without these recycling options, impurities would typically concentrate during the crystallization process and contaminate the product.

[0048] It should be understood that the disclosed embodiments of the present invention are not limited to the specific structures, process steps or materials disclosed herein, but extend to their equivalents recognized by those of ordinary skill in the relevant art. It should also be understood that the terms used herein are for the purpose of describing specific embodiments only and are not intended to be limiting.

[0049] References to "an embodiment" or "embodiments" throughout the specification mean that the specific features, structures or characteristics described in connection with that embodiment are included in at least one embodiment of the present invention. Thus, the phrases "in an embodiment" or "in embodiments" appearing throughout the specification do not necessarily all refer to the same embodiment.

[0050] As used herein, for convenience, a plurality of items, structural elements, compositional elements and / or materials may be presented in a common list. However, these lists should be understood to mean that each individual member in the list is identified as a separate and unique member. Thus, without contrary indication, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on its presentation in the common group. Additionally, various embodiments and examples of the present invention, along with alternatives for its various components, may be mentioned herein. It should be understood that such embodiments, examples and alternatives are not to be construed as de facto equivalents of each other, but rather as separate and independent representations of the present invention.

[0051] Furthermore, the described features, structures or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of length, width, shape, etc., to provide a thorough understanding of the embodiments of the present invention. However, those skilled in the relevant art will recognize that the present invention may be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials or operations are not shown or described in detail to avoid obscuring aspects of the present invention.

[0052] While the above examples illustrate the principles of the present invention in one or more specific applications, it will be apparent to those of ordinary skill in the art that many modifications in form, usage, and details of implementation can be made without exercising creativity and without departing from the principles and concepts of the present invention. Accordingly, the present invention is not limited except as defined by the appended claims.

[0053] As used herein, the verbs "comprise" and "include" are open-ended limitations that neither exclude nor require the presence of features not recited. Unless otherwise expressly stated, the features recited in the claims may be freely combined with one another. Further, it should be understood that the use of "a" or "an", i.e., the singular form, herein does not exclude the plural form. Examples Reference Examples

[0054] Spodumene samples obtained from mines in North America (A) and Europe (B) were calcined at temperatures between 1100 °C and 1190 °C and then leached in a leaching solution containing sodium carbonate (Na 2 CO 3 ) and sodium hydroxide (NaOH) at 220 °C. The calcination conditions, leaching conditions, and the lithium extraction rates achieved are shown in Table 2 below.

[0055] As shown by the following results, a high extraction rate of lithium from calcined spodumene requires maintaining a sufficiently high pH value and a sufficiently high sodium carbonate content throughout the leaching step, and the final result is easily affected by, for example, a decrease in pH. A decrease in pH can be avoided by using a large amount of base, but the process remains highly susceptible to detrimental variations. Example 1 - Leaching of Uncalcined Lithium-Containing Material

[0056] Uncalcined spodumene samples (lithium content in the minerals of Tests 1 - 15 was 1.42 wt.%, and lithium content in the mineral of Test 16 was 1.91 wt.%) were leached in a leaching solution containing sodium hydroxide (NaOH), and in some samples, sodium carbonate (Na 2 CO 3 ) was also present. The raw material content in the slurry was 200 g / L.

[0057] The raw material and sodium carbonate were generally mixed before the start of leaching, but sodium hydroxide was added in a single dose or continuously at the start of leaching (see Test 11).

[0058] The leaching conditions were changed to show the effect of the changes on the lithium extraction rate. The leaching temperature was maintained in the range of 150 - 200 °C, the leaching time was maintained in the range of 1 - 4 hours, the sodium carbonate dosage was maintained in the stoichiometric range of 0 - 2.5 times the lithium content in the mineral, and the pH value was maintained in the range of 11.5 - 14. The different leaching conditions and the achieved lithium extraction rates are shown in Table 3 below.

[0059] As these results show, the process of the present invention uses a pressure leaching step for uncalcined lithium-containing minerals, is more versatile than known processes, and high extraction rates can be achieved using a wide range of reaction conditions. As can be seen from the results, sufficient alkali dosage leads to high lithium extraction rates, while the negative impact of other conditions is very small (see especially Test 1, compared with Tests 8, 3, and 4). As shown when comparing Tests 1, 10, 13, and 14, the effect of temperature change on the extraction rate is less than the effect of pH change on the extraction rate. Similarly, as seen when comparing Tests 1, 7, and 10, the change in leaching time has a very small effect on the extraction rate. Finally, as shown when comparing Tests 1, 5, 6, and 9, when sufficient alkali dosage is used to effectively maintain the pH at a sufficiently high level, the change in Na 2 CO 3 dosage has no effect on the extraction rate, and even the reaction without using any Na 2 CO 3 dosage is effective. Example 2 - Carbonation

[0060] The slurry with a solid concentration of 200 g / L obtained from Test 16 of Example 1 was subjected to a separate carbonation step, where the CO 2 gas feed was 1000 mL / min. The carbonation was carried out at a temperature of 30 °C for 8 hours, and then the final lithium-containing filtrate was separated from the final precipitate. Samples were taken from the reaction mixture at different time points during the reaction, analyzed and filtered to show the content of the mixture at different time points of carbonation. The content of the various filtrates and precipitates obtained is shown in Table 4 below. As proven by these results, a lithium extraction rate of 96.2% can be achieved and no calcination is required. Table 4 filtrate pH Li reaction time mg / l 1h 7.41 3720 2h 7.4 3550 4h 7.4 3640 6h 7.4 3680 8h 7.4 3670 final filtrate 7.39 3770 Table 4 (continued) precipitate Li Al Li extraction rate reaction time ％ ％ ％ 1h 0.139 10.4 2h 0.121 10.2 4h 0.123 10.3 6h 0.120 10.2 8h 0.113 10.2 final precipitate 0.111 10.2 96.2 Example 3 - Desilication

[0061] The leaching slurry obtained from Test 1 of Example 1 was subjected to a solid / liquid separation step, and the separated solution was subjected to a silicon removal step, where calcium oxide (CaO) was added to the solution to form calcium silicate.

[0062] test conditions - CaO addition amount: stoichiometry of 1.2 times related to the Si content - Temperature: 90 °C - Duration: 8 hours

[0063] After the reaction, the formed solid silicate is separated from the remaining desilication solution. Solution samples are obtained after 1 h and 4 h of reaction. The silicon and hydroxide contents in the solution are analyzed, and the results are shown in Table 5 below. Table 5 leaching filtrate after 1 h after 4 h desilication filtrate Si (mg / L) 38200 255 99 47 OH (mol / L) 0.848 0.796 0.912 0.848

[0064] As can be seen from the results in Table 5, during the 8-hour desilication process, the silicon content in the leaching solution decreased from 38200 mg / L to 47 mg / L. Example 4 - Alkaline leaching using recycled desilication solution

[0065] The leaching described in Example 1 was repeated using the desilication solution obtained from the desilication in Example 3, but using uncalcined petalite concentrate from North America (Li content: 1.91%) as the feed, with a solid content of 200 g / L. The different leaching conditions and the achieved lithium extraction rates are shown in Table 6 below. Table 6 * NaOH (500 g / L) addition amount (mL) / feed (g)

[0066] Compared with the situation shown in Example 1, when using the recycled solution, the addition amount of NaOH can be reduced because the recycled solution has a high hydroxide content.

[0067] The leaching slurry obtained from Example 4 was subjected to solid / liquid separation, and the separated leaching residue was mixed with the desilication filtrate obtained from Example 3 and used for the carbonization step: - Temperature: 30 °C - Duration: 8 hours - Solid concentration: 300 g / L - CO 2 Gas feed: 1000 mL / min

[0068] After carbonization, the final lithium-containing filtrate was separated from the final precipitate. Samples were taken from the reaction mixture at different time points during the reaction, analyzed and filtered to show the contents of the mixture at different time points of carbonization. The contents of the various filtrates and precipitates obtained are shown in Table 7 below. Table 7 filtrate pH Li reaction time mg / l 0h 13.7 113 1h 7.8 5840 2h 7.7 5030 4h 7.7 6180 6h 7.7 6380 8h 7.8 6510 final filtrate 6810 Table 7 (continued) precipitate Li Al Li extraction rate reaction time ％ ％ ％ 0h 2.4 10.8 1h 0.19 11.0 2h 0.14 11.2 4h 0.10 11.2 6h 0.079 11.1 8h 0.12 11.3 final precipitate 0.129 10.9 95.2

[0069] As shown in the results of Table 7, mixing the leaching residue with the recycled solution from desilication can still achieve excellent separation of Al and an excellent lithium extraction rate. Industrial applicability

[0070] The process of the present invention can be used as part of any hydrometallurgical process for recovering lithium products from lithium-containing minerals and can improve the process.

[0071] In particular, the new leaching step described herein enables leaching of lithium concentrate without calcination pretreatment or expensive calcination equipment. Therefore, costs and energy can be greatly saved, emissions of gases such as CO 2 can be reduced, and more sustainable and environmentally friendly lithium products can be obtained. Citation list Patent documents US 9255012 B2 US 11292725 B2

Claims

1. A process for converting lithium in a lithium-containing mineral into at least a partially soluble form, characterized in that an uncalcined lithium-containing mineral concentrate is provided and the mineral is subjected to pressure leaching in a leaching solution having a hydroxide content of 0.6 - 9 mol / L at a temperature of 120 - 240 °C.

2. The process according to claim 1, wherein the uncalcined lithium-containing mineral is selected from spodumene, petalite, lepidolite and triphylite or any combination thereof, preferably petalite.

3. The process according to claim 1 or 2, wherein the pH value of the leaching solution is ≥ 11.5, preferably 11.5 - 14.

4. The process according to any one of the preceding claims, wherein the hydroxide content of the leaching solution is preferably 1 - 6 mol / L.

5. The process according to any one of the preceding claims, wherein the leaching is carried out at a temperature of 150 - 220 °C.

6. The process according to any one of the preceding claims, wherein the leaching is carried out at a pressure of 3 - 30 bar, preferably 5 - 25 bar, more preferably 10 - 25 bar.

7. The process according to any one of the preceding claims, wherein the leaching is carried out for a time of 30 minutes to 4 hours.

8. The process according to any one of the preceding claims, wherein the hydroxide content is achieved by adding a hydroxide-containing basic reagent, and the reagent is preferably an alkali metal hydroxide selected from sodium hydroxide (NaOH), potassium hydroxide (KOH) and lithium hydroxide (LiOH) or a mixture thereof, more preferably sodium hydroxide.

9. The process according to any one of the preceding claims, wherein the leachate further comprises a carbonate reagent, such as sodium carbonate (Na 2 CO 3 ) or potassium carbonate (K 2 CO 3 ), preferably in a stoichiometry related to the lithium content in the mineral, with a maximum of 3, most suitably >0 - 2.

5.

10. The process according to any one of claims 1 - 8, wherein the leaching is carried out in a leaching solution without adding carbonate and in the absence of a carbonate reagent.

11. The process according to any one of the preceding claims, wherein after the leaching is a carbonization step, in which the obtained leaching slurry reacts with carbon dioxide (CO 2 ), preferably using an excess of carbon dioxide.

12. The process according to any one of the preceding claims, wherein a desilication step is carried out after the leaching step by adding a calcium reagent to the leaching slurry or the solution separated therefrom, the calcium reagent preferably being calcium oxide (CaO) or calcium hydroxide (Ca(OH) 2 ), and separating the formed solid silicate therefrom to obtain a filtrate.

13. The process according to claim 12, wherein the filtrate obtained from the desilication step is recycled to the leaching step 1 for reuse, or recycled to the optional previous pulping step for reuse, or it can be sent to a subsequent processing step, such as a bicarbonation step.

14. Use of a lithium-containing slurry or solution obtained by the process according to any one of the preceding claims in the preparation of solid lithium compound crystals by performing the following further steps: converting lithium bicarbonate in the slurry or solution into an insoluble compound by crystallization.

15. The use according to claim 14, wherein before the conversion step, a step of separating any insoluble reagent from the slurry or solution is carried out.

16. The use according to claim 14 or 15, wherein the lithium precipitate is lithium carbonate or lithium hydroxide.

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