WO2025120253A1

WO2025120253A1 - Leaching of lithium concentrates

Info

Publication number: WO2025120253A1
Application number: PCT/FI2024/050653
Authority: WO
Inventors: Tian Zhang; Eero KOLEHMAINEN
Original assignee: Metso Finland Oy
Current assignee: Metso Finland Oy
Priority date: 2023-12-08
Filing date: 2024-12-04
Publication date: 2025-06-12
Anticipated expiration: 2026-06-08
Also published as: CN120119115A

Abstract

According to the present invention, there is provided a process for converting the lithium of a lithium-containing mineral into soluble form, as well as the use of the lithium-containing slurry or solution obtained from said process in the preparation of crystals of a solid lithium compound.

Description

LEACHING OF LITHIUM CONCENTRATES

FIELD

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

BACKGROUND

[0002] Lithium is an element forming compounds with several industrial applications. The lithium for these purposes is mainly obtained from lithium brines and ores using a hydrometallurgical extraction process. The conventional lithium processing from ores contains a calcination or roasting process at high temperatures, followed by hydrometallurgical treatment such as pressure leaching.

[0003] For example, US 9255012 B2 and US 11292725 B2 describe the leaching of calcined lithium-containing mineral materials in leach solutions containing a carbonate. In US 9255012 B2, the solution obtained from the leaching step is bicarbonate, followed by crystallization of a lithium carbonate product. In US 11292725 B2, the lithium in the leach slurry is reacted further into the hydroxide. However, both publications describe processes, wherein a calcination of the raw material, combined with a carbonate-based leach solution, has been used to provide the desired lithium extraction rates.

[0004] One of the main issues of the calcination or roasting process is high energy consumption, and this is becoming more significant with rising energy costs. Therefore, there is a need for new processes, wherein lithium, also in uncalcined form, can be effectively leached from mineral raw materials. SUMMARY OF THE INVENTION

[0005] The 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 the lithium in raw-materials based on uncalcined lithium-containing mineral into at least partially soluble form.

[0007] According to a second aspect of the invention, there is provided a process for leaching lithium out of lithium-containing mineral raw-materials, using leaching conditions that are capable of solubilising even uncalcined minerals.

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

[0009] According to yet a further aspect, there is provided a method that utilizes a desilicated solution in the recycled feeds.

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

[0011] The invention is based on the discovery that lithium can be leached from lithium-containing minerals even without the calcination of the mineral, which previously has been considered an essential step of the process, if the conditions of the pressureleaching are optimized in a suitable manner.

[0012] Thus, the mineral-based lithium raw materials used in the invention can be directly leached without calcination or roasting pretreatments.

[0013] Significant advantages are achieved using the invention. Among others, the invention makes it possible to leach lithium concentrates without calcination pretreatment and without the related expensive equipment, whereby significant savings can be achieved in both cost and energy, the emissions of gases, such as CO2, can be reduced, and more sustainable and environmentally friendly lithium products can be obtained. [0014] Further, it has been surprisingly discovered that at least for some lithium- containing minerals, also better extraction rates can be achieved for lithium, when using concentrates of uncalcined mineral in the leaching step of the process.

[0015] When further utilizing a desilication step in the process, a further advantage is achieved in that the recycling options in the process are improved, as the silicates carried to the process with the uncalcined raw material are still present in high contents in the leach solution and would benefit from a silicon removal before recycling.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIGURE 1 illustrates the process configuration in accordance with at least some embodiments of the present invention, with block 1 representing the leaching step of the process, block 2 representing an optional carbonization step, and block 3 representing an optional conversion step for converting the lithium hydrogen carbonate obtained in the carbonization step into an insoluble compound, whereby the dotted line separates the optional steps of the process from the essential leaching step.

[0017] FIGURE 2 illustrates a process configuration of an advantageous embodiment, with additional block 0 representing an optional pulping step, block 1’ representing an optional solid/liquid separation step, block 4 representing an optional desilication (or silicon removal) step, and block 4’ representing an optional further solid/liquid separation step, from which the solution can be recycled back to the pulping step 0 or carried further to the carbonization step 2 (as shown with the dotted arrows).

EMBODIMENTS

[0018] DEFINITIONS

Lithium-containing minerals can be found in many different forms, such as the ones listed in the following Table 1, spodumene being the most commonly used due to its availability. Table 1.

Further, it can exist as clay minerals, such as masutomilite, swinefordite, hectorite, cookeite and jadarite.

“Calcination” of lithium-containing minerals is a thermal step typically carried out to provide a changed structure that is more susceptible to leaching, by changing the crystal structure of the mineral. Thus, the “calcined” form is commonly selected for use in leaching, whereas the “uncalcined” form has been considered too stable in the past. [0019] The present invention relates to a process for converting the lithium in a concentrate of an uncalcined lithium-containing mineral into soluble form by pressure leaching (see step 1 of Fig. 1) the mineral concentrate in a leach solution having a hydroxide (OH-) content of 0.6 - 9 mol/L, more preferably 1 - 6mol/L, at a temperature of 120 - 240 °C, preferably 150-220 °C. [0020] The used lithium-containing mineral can be the uncalcined form of any of the above mentioned minerals of Table 1, or the separately listed clay minerals, but is preferably selected from spodumene, petalite, lepidolite and zinnwaldite, more preferably being petalite. [0021] The hydroxide content used in the process is preferably achieved by adding a hydroxide-containing alkaline reagent, for example selected from the alkali metal hydroxides sodium hydroxide (NaOH), potassium hydroxide (KOH) and lithium hydroxide (LiOH), or a mixture thereof, preferably being sodium hydroxide. This hydroxide is used mainly to adjust the pH of the leach solution to a sufficiently high level, preferably being a level of >11.5, more preferably 11.5 - 14. However, at such levels, contents of alkaline reagents are more reliable factors to measure than pH levels.

[0022] Pressure leaching steps of lithium-containing mineral raw materials are commonly carried out at temperatures as high as 300 °C, but in the present process, lower temperatures of < 240 °C are sufficient. The pressure during the leaching 1 is preferably 3- 10 bar, more preferably 5-30 bar, even more preferably 5-25 bar. The pressure may not necessarily require separate adjustment, as it adjusts upwards with a raised temperature. With these conditions, a relatively short time for the raw material in the leaching reactor is sufficient, such as a leaching time of 30 min - 4 h.

[0023] Due to the used high temperature and high pressure, the leaching 1 is typically performed in a suitable autoclave or series of autoclaves.

[0024] In an embodiment of the process described herein, the leaching solution further contains a carbonate reagent, such as an alkali metal carbonate, preferably sodium carbonate (Na2COs) or potassium carbonate (K2CO3), or a mixture thereof, most suitably being at least partly composed of sodium carbonate. Typically, this carbonate is added in a stoichiometry of 0-3 related to lithium content in the mineral, most suitably in a stoichiometry of >0-2.5 related to the lithium content in the mineral. Thus, the content can also be 0, whereby in a specific embodiment of the process, the leaching step is carried out without carbonate reagent, i.e. with no carbonate added to the leaching solution.

[0025] In another embodiment, a recycled solution from a subsequent step of the process can be added to the leaching solution, in addition to the feed based on mineral concentrate.

[0026] In a further embodiment of the process described herein, a separate pulping step 0 is carried out before the pressure leaching step, wherein the mineral concentrate containing lithium is mixed into an aqueous solution, optionally in the presence of an alkali metal carbonate, for producing a slurry containing lithium. However, the slurry can also be formed as a part of the pressure-leaching step 1. A preferred alkali metal carbonate is sodium carbonate, and is typically used in excess.

[0027] Thus, in the leaching step 1, the lithium aluminium silicates of the mineral (e.g. the LiAlSi40io for petalite) are converted to the solubilized or partially solubilized form of e.g. lithium carbonate (I^CCh) or lithium metasilicate (I^SiCh). For example, in the presence of sodium hydroxide and using a petalite-based raw material, in the main reaction, the lithium-containing mineral reacts with the hydroxide ions (OH ) and Li2SiO3 and analcime are produced.

[0028] After the leaching step 1, a leach slurry is obtained, which contains lithium in the form of its carbonate or silicate, depending on whether a carbonate has been present in the leaching step 1. Since these intermediate products are only sparingly soluble in the leaching solution, with particularly the carbonate being only partially solubilized, they are obtained in the form of a slurry. The slurry does not contain significant amount of unreacted mineral, since it has transformed, e.g. to sodium aluminium silicate. In other words, lithium contained in the mineral has been liberated. Typically, the yield of liberated lithium from the leaching step is 90 to 95 weight-%, calculated from the mineral. The obtained slurry can be used as such, and thus be conducted directly to any subsequent reaction, e.g. to achieve further solubilisation

[0029] Depending on the intended further use of the leach slurry, it may alternatively be conducted to a solid/liquid separation step 1 ’ to provide a liquid that contains a smaller amount of undesired compounds, such as sodium silicates and other impurities. According to this alternative, the solution separated from the solids in the optional separation step 1 ’ may be recycled, e.g. to be reused in the same leaching step 1, or it may be used in intermediate separation or conversion steps 4 to provide a modified solution for recycling. In a further alternative, a dilution of the obtained slurry or the solution with water can be carried out.

[0030] Thus, in a further embodiment (see Fig. 2), the leach slurry is conducted to a solid/liquid separation step 1 ’ that is followed by a silicon removal step 4, also called a desilication step, wherein a calcium reagent, such as calcium oxide (CaO) or calcium hydroxide (Ca(OH)2) is added to the solution to cause the formation of calcium silicates, 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 and produces calcium silicate.

[0031] The calcium reagent is preferably added in a stoichiometry of 1 - 2 related to the silicon (Si) content of the solution. The temperature during this reaction is preferably 80 - 100 °C, and a duration of 1 - 10 hours is typically sufficient, preferably 1 - 8 hours. The solution separated from the solids in the further separation step 4’ may be recycled, particularly to be reused in the leaching step 1, or preferably in the preceding optional pulping step 0, or it may be combined with the leach slurry, or preferably with the leach residue obtained from the previous solid/liquid separation step 1’, and carried to subsequent processing, such as the carbonization step 2 described below.

[0032] In a further embodiment, the leaching 1 is followed, either directly or with the intermediate separation 1 ’ and desilication 4 steps described above, by a carbonization step (see step 2 of Fig. 1 or Fig. 2), also called a bicarbonization step due to the reaction taking place. In this carbonization 2, the obtained leach slurry or a leach residue separated therefrom is reacted with carbon dioxide (CO2), preferably carbon dioxide in an excess amount. The yet unsolubilized lithium compounds obtained from the leaching step are thus transformed to solubilized lithium hydrogen carbonate, and are thus capable of essentially complete separation from undesirable, undissolved materials.

[0033] This optional carbonization step 2 may be performed at a temperature between 0 to 50 °C, preferably between 15 to 40 °C, and typically at a pressure of 1 - 15 bar, more typically 1 - 10 bar, preferably atmospheric pressure. Higher pressure improves the solubilisation of carbon dioxide into the aqueous solution, but increasing the pressure too much will cause the increased formation of by-products and impurities. Mixing is preferably provided, e.g. using any suitable mixer which provides mixing for dispersing gas, liquid and solids very efficiently.

[0034] The lithium-containing slurry or solution obtained from the process described herein may also be used further in a method for the preparation of crystals of a solid lithium compound by carrying out the further step (see step 3 of Fig. 1) of converting the lithium hydrogen carbonate in the slurry or solution into an insoluble compound, and crystallizing it. [0035] Said conversion 3 may be preceded by a further step of separating any insoluble agents from the slurry or solution in a solid/liquid separation step 2’ (not shown in the Figures), typically performed by filtering, whereafter the conversion step 3 is carried out on a liquid fraction. The separation step 2’ can be carried out, for example, using filtration, or by routing the slurry or solution to a thickener, from where the overflow can be carried to the conversion step 3, and the underflow can be discarded, recovered or filtered further in order to recover all lithium remaining therein.

[0036] Also, a purification 2” (not shown in the Figures) can be carried out before the conversion step 3 to remove impurities, such as trivalent and/or divalent metal ions, e.g. calcium, magnesium, aluminium and iron ions, preferably after a solid/liquid separation step, from which a liquid fraction is recovered. Preferably, ion exchange is used for the purification 2”. The ion exchange can be performed for example by using a method disclosed in Finnish patent 121 785. Typically, the purifying by ion exchange is performed 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 commercial names Amberlite IRC 748 (IDA) and Amberlite IRC 7476 (APA). Typically, the cation exchange resin is a resin which has a polystyrenic matrix crosslinked with divinylbenzene containing aminophosphonic groups.

[0037] The above mentioned conversion step 3 results in the formation of a solid lithium compound or precipitate that can be crystallized into pure crystals that preferably are either lithium carbonate or lithium hydroxide.

[0038] If preparing lithium carbonate, the conversion step 3 a involves heating the slurry or solution containing lithium hydrogen carbonate, preferably to a temperature in the range of 70-100 °C, to decompose the bicarbonate and crystallize lithium carbonate.

[0039] In this reaction, a slurry containing water and lithium carbonate precipitate is formed. The solid lithium carbonate is separated from the obtained slurry in a solid/liquid separation step 3’ (not shown in the Figures), and thus a battery-grade lithium carbonate is obtained. Standard battery grade lithium carbonate contains lithium carbonate at least 99.5%. However, using the process described herein, it is possible to produce superior battery grade lithium carbonate containing at least 99.99% of lithium carbonate. [0040] If preparing lithium hydroxide, the conversion step 3b involves reacting the slurry or solution containing lithium, obtained from the solubilisation process, or optionally pretreated, using a hydroxide reagent, i.e. an alkaline earth metal hydroxide, to produce a slurry containing lithium hydroxide in soluble form. The used alkali earth metal hydroxide is preferably selected from calcium and barium hydroxide, more preferably being calcium hydroxide, optionally prepared by reaction of calcium oxide (CaO) in the aqueous solution. The alkali earth metal hydroxide may also be mixed with water or an aqueous solution prior to use in the reaction. Also in this reaction, a recycled mother liquor obtained from the subsequent crystallization can be used. The hydroxide conversion is typically carried out at a temperature of 10-100°C, preferably 20-60°C, and most suitably 20-40°C. Typically, the hydroxide conversion 3b is carried out at atmospheric pressure. The presence of alkaline earth metal hydroxide and the above mentioned process conditions result in the formation of lithium hydroxide, and an alkaline earth metal carbonate as a by-product.

[0041] After an optional solid/liquid separation step 3’ (not shown in the Figures), preferably carried out using filtration, or by routing the slurry or solution to a thickener, a lithium hydroxide -containing solution of relatively high purity is obtained.

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

[0043] This optional purification step 3” (not shown in the Figures) is preferably based on purification of dissolved ions and components, and more preferably includes an ion exchange or a membrane separation, or both, most suitably by using a cation exchange resin, particularly a selective cation exchange resin. The ion exchange can be performed for example as described above for the preceding optional purification step 2”, carried out before the conversion step 3. The membrane separation can be carried out using a semi- permeable membrane, which separates ionic or other dissolved compounds from aqueous solutions. More precisely, the membrane separation can be used to fractionate the dissolved ions and compounds by their size (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 repelling action for multivalent cations) and attracts anions, and vice versa. These phenomena will enable the purification of, for example, multivalent metal cations, complexed species (such as aluminium hydroxide complexes), polymeric species (such as dissolved silica) and larger anions (e.g. sulfate and carbonate ions) from lithium hydroxide solutions. Based on the above, it is particularly preferred to combine a membrane separation with an ion exchange, most suitably by first carrying out a membrane separation, and then an ion exchange for polishing removal of multivalent metal cations.

[0044] Crystals of lithium hydroxide monohydrate can be recovered from the lithium hydroxide -containing solution by crystallizing. The crystallizing is typically performed by heating the solution to a temperature of approximately the boiling point of the solution, to evaporate the liquid, or by recrystallizing the monohydrate from a suitable solvent. The method described herein enables production of pure lithium hydroxide monohydrate with excellent yield and purity in a continuous and simple process, typically providing battery grade lithium hydroxide monohydrate crystals.

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

[0046] In further embodiments, the crystallization mother liquor remaining after the crystals have been recovered in a solid/liquid separation step, or a fraction thereof, can be recycled to one or more preceding steps of either the solubilisation process, or the preparation of crystals of a solid lithium compound, thus allowing the recovery of any uncrystallised lithium. In one alternative, the mother liquor is recycled to the pressure leaching step 1, or the optional preceding pulping step 0, to take part in the pH adjustment therein, thus reducing the need for further added sodium hydroxide. In another alternative, related to the hydroxide route, the mother liquor is recycled to the hydroxide conversion step 3b of the preparation of lithium hydroxide. In a further alternative, the mother liquor is recycled back to the crystallization. Also, the carbon dioxide used in the optional carbonization step 2 of the solubilisation can be separated from the crystallization mother liquor, and be recycled back to the carbonization step 2.

[0047] The advantage achieved by recycling to the early steps with lower alkalinity, such as the pressure-leaching 1 or the lithium conversion steps 3, is that some impurities in the crystallization mother liquor (e.g. aluminium and silicon) have a solubility that increases with increasing alkalinity (e.g. caused by increasing lithium hydroxide concentration), whereby these alkali-soluble impurities can be removed by recycling them in solution to a step of lower alkalinity. For example in the hydroxide conversion step 3b, these impurities form sparingly soluble compounds (e.g. aluminium hydroxide), and can be discarded with the solids after a subsequent separation step. Without these recycling options, the impurities are typically concentrated in the crystallization, and contaminate the product.

[0048] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[0049] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment.

[0050] As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, 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 their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous 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 lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can 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 invention.

[0052] While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0053] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also unrecited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", i.e. a singular form, throughout this document does not exclude a plurality.

EXAMPLES

Reference Example

[0054] Petalite samples obtained from mines in North America (A) and Europe (B) were calcined at temperatures ranging from 1100 °C to 1190 °C, and then leached at 220 °C in a leaching solution containing sodium carbonate (Na2COs) and sodium hydroxide (NaOH). The calcination conditions, leaching conditions and achieved lithium extraction rates are shown in the following Table 2.

[0055] As the below results indicate, high extraction rates for the extraction of lithium from calcined petalite requires maintaining a sufficiently high pH during the entire leaching step as well as a sufficiently high sodium carbonate content, and the end result is easily affected by e.g. a pH reduction. The pH reduction can be avoided by using high amounts of alkali, but the process is still highly susceptible to detrimental changes. able 2.

NaOH (500 g/L) addition (mL) / material (g)

Example 1 - Leaching of uncalcined lithium-containing materials

[0056] Uncalcined petalite samples (lithium content in the mineral 1.42 wt.% for Tests 1-15 and 1.91 wt.% for Test 16) were leached in a leaching solution containing sodium hydroxide (NaOH), and in some samples also sodium carbonate (Na2CCh). The raw material content in the slurry was 200 g/L.

[0057] The raw material and the sodium carbonate were typically mixed before the leaching was started, but the sodium hydroxide was added either as a single dosage in the beginning of the leaching, or as a continuous dosage (see Test 11).

[0058] The leaching conditions were varied to show the effect of the variations on the lithium extraction rates. The leaching temperature was maintained within the range of

150 - 200 °C, the duration of the leaching within the range of 1 - 4 hours, the sodium carbonate dosage within the stoichiometry of 0 - 2.5 related to lithium content in the mineral, and the pH within the range of 11.5 - 14. The different leaching conditions and the achieved lithium extraction rates are shown in the following Table 3.

able 3.

* NaOH solution added continuously

** NaOH (500 g/L) addition (mL) / feed material (g)

[0059] As these results indicate, the process of the invention, using a pressure leaching step on uncalcined lithium-containing mineral, is more versatile than the known process, and high extraction rates can be achieved using broad reaction conditions. It can be seen from the results that a sufficient alkali dosage leads to a high lithium extraction rate with very little negative impact from the other conditions (see particularly Test 1, as compared to Tests 8, 3 and 4). As shown when comparing e.g. Tests 1, 10, 13 and 14, changes in temperature have a smaller impact on the extraction rates than changes in the pH. Likewise, as seen when comparing Tests 1, 7 and 10, changes in leaching time have very little impact on the extraction rates. Finally, as shown when comparing Tests 1, 5, 6 and 9, changes in Na2CO; dosage have no impact on the extraction rates when the pH has been effectively maintained at a sufficiently high level using a sufficient alkali dosage, and even reactions without any Na2CO; dosage can be effective.

Example 2 - Carbonization

[0060] The slurry obtained from Test 16 of Example 1, having a solid concentration of 200 g/L, was conducted to a separate carbonization step, with a CO2 gas feed of 1000 mL/min. The carbonization was carried out at a temperature of 30 °C, and with a duration of 8 hours, followed by a separation of the final lithium-containing filtrate from a final precipitate. Samples were also obtained from the reaction mixture at various points during the reaction, analysed and filtered, to show the contents of the mixture at various points of the carbonization. The contents of the obtained various filtrates and precipitates are shown in the following Table 4. As demonstrated by these results, a lithium extraction of 96.2 % can be achieved, and no calcination is required.

Table 4.

Table 4 (continued).

Example 3 - Desilication

[0061] The leach slurry obtained from Test 1 of Example 1 was conducted to a solid/liquid separation step from which the separated solution was conducted to a silicon removal step, wherein calcium oxide (CaO) was added to the solution to cause the formation of calcium silicates. [0062] Test conditions

- CaO addition: 1.2 stoich. to Si

- Temperature: 90 °C

- Duration time: 8 hours

[0063] After the reaction, the formed solid silicates were separated from the remaining desilicated solution. Solution samples were also obtained after Ih and 4h of reaction. The silicon and hydroxide contents of the solutions were analyzed and the results shown in the following Table 5.

Table 5.

[0064] As can be seen from the results of Table 5, the silicon content of the leach solution was reduced from 38200 mg/L to 47 mg/L in 8h of desilication.

Example 4 - Alkaline leaching using recycled desilicated solution

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

Table 6.

* NaOH (500 g/L) addition (mL) / feed material (g)

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

[0067] The leached slurry obtained from Example 4 was carried to a solid/liquid separation, and the separated leach residue was mixed with the desilicated filtrate obtained from Example 3, and used in a carbonization step: Temperature: 30 °C

Duration time: 8 hours

Solid concentration: 300 g/L

CO2 gas feed: 1000 mL/min [0068] The carbonization was followed by a separation of the final lithium-containing filtrate from a final precipitate. Samples were also obtained from the reaction mixture at various points during the reaction, analysed and filtered, to show the contents of the mixture at various points of the carbonization. The contents of the obtained various filtrates and precipitates are shown in the following Table 7. Table 7.

[0069] As shown in the results of Table 7, mixing the leach residue with the recycled solution from a desilication can still result in an excellent separation of Al species, as well as an excellent Li extraction. 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 cause an improvement of the process.

[0071] Particularly, the herein described new leaching step makes it possible to leach lithium concentrates without a calcination pretreatment and without the need for expensive calcination equipment. Thus, significant savings can be achieved in both cost and energy, the emissions of gases, such as CO2, can be reduced, and more sustainable and environmentally friendly lithium products can be obtained. CITATION LIST

Patent Literature

US 9255012 B2

US 11292725 B2

Claims

CLAIMS:

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

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

3. The process of claim 1 or 2, wherein the pH level of the leaching solution is adjusted to > 11.5, preferably 11.5 - 14.

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

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

6. The process of any preceding claim, 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 of any preceding claim, wherein the leaching is carried out for a period of 30 min - 4 h.

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

9. The process of any preceding claim, wherein the leaching solution further contains a carbonate reagent, such as sodium carbonate (Na2COs) or potassium carbonate (K2CO3), preferably in a stoichiometry of up to 3 related to the lithium content in the mineral, most suitably in a stoichiometry of >0 - 2.5 related to the lithium content in the mineral.

10. The process of any of claims 1-8, wherein the leaching is carried out without carbonate reagent, in a leaching solution containing no added carbonate.

11. The process of any preceding claim, wherein the leaching is followed by a carbonization step, wherein the obtained leach slurry is reacted with a carbon dioxide (CO2), preferably the carbon dioxide is used in an excess amount.

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

13. The process of claim 12, wherein the filtrate obtained from the desilication step is recycled, either to be reused in the leaching step 1 , or preferably in the preceding optional pulping step, or it may be carried to a subsequent processing step, such as a bicarbonization step.

14. Use of the lithium-containing slurry or solution obtained from the process of any preceding claim in the preparation of crystals of a solid lithium compound by carrying out the further step of

- converting the lithium hydrogen carbonate in the slurry or solution into an insoluble compound, by crystallizing it.

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

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