A novel alkaline leaching process of lithium concentrates

Abstract

According to the present invention, there is provided a process for recovering lithium from a lithium-containing mineral in a process utilizing a leaching step, wherein no carbonates are required, the obtained leach slurry thus containing silicates.

Description

A NOVEL ALKALINE LEACHING PROCESS OF LITHIUM CONCENTRATESFIELD

[0001] The present invention relates to a process for recovering lithium from a lithium-containing mineral in a process utilizing a leaching step, wherein no carbonates are required.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 relatively mild leaching condition with leach solutions containing a carbonate. In US 9255012 B2, the solution obtained from the leaching step contains bicarbonate, which is then crystallized into 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 leaching using carbonate-based leach solution, has been used to provide the desired lithium extraction rates.

[0004] One of the main issues of existing processes using known leaching conditions is that they require the material to have been carried via a calcination with optimum calcination conditions, which are difficult to maintain in an industrial scale. Therefore, there is a need for new processes, wherein lithium can be effectively leached also from uncalcined mineral raw materials and materials calcined under non-optimal conditions. Likewise, the leaching in the presence of carbonates is not optimal in view of extraction rates.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 invention, there is provided a process for separating lithium from lithium-containing mineral raw-materials, using leaching conditions that are capable of solubilising even uncalcined minerals.

[0007] According to a second aspect, there is provided a process for leaching lithium-containing mineral raw-materials, without the need for leaching chemicals, such as carbonates.

[0008] According to a third aspect, there is provided a process, wherein at least one of the solid and solution phases of the leach slurry obtained from the leaching step is treated further to decrease the contents of by-products and impurities in the process streams.

[0009] According to a further aspect, there is provided a process that desilicates a process stream and utilizes the desilicated stream in recycle streams.

[0010] The present invention thus relates to a process for recovering lithium from a lithium-containing mineral, comprising a) a leaching step, carried out in an aqueous leaching solution having a pH of > 11.5, at a temperature of 120 - 240 °C, these leaching conditions providing a silicate product, b) a step for desilicating the leach solution obtained from the leaching step, and recirculating the remaining solution to one or more other steps of the process, and c) one or more steps for recovering lithium as a solid lithium compound from the lithium-containing leach residue obtained from the leaching step.

[0011] The invention is based on the discovery that lithium can be recovered from lithium-containing minerals without utilizing leaching chemicals, particularly carbonate reagents, and even without requiring the calcination of the mineral. These factors have both been considered essential in past processes.

[0012] 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.

[0013] 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.

[0014] An advantage of the desilication step in the process is that the recycling options in the process are improved, and the silicates carried to the process from the mineral, still being present in high contents in the leach solution, can be removed.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] 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 a desilication step, and blocks 3 and 4 representing one or more steps for recovering lithium, or converting the lithium in a slurry or solution into a form that can easily be precipitated. The dotted arrows represent the possible recycling options.

[0016] 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, and block 2’ representing an optional further solid / liquid separation step. Further, block 3 herein represents a carbonization step and block 4 represents a lithium recovery step. The solution obtained from separation step 2’ can be recycled back to the pulping step 0 or carried further to the carbonization step 3 (as shown with the dotted arrows).EMBODIMENTS

[0017] DEFINITIONSLithium-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, whereas it is difficult to maintain the optimum calcination conditions in an industrial scale and also the “uncalcined” form has been considered too stable in the past. Most of the above minerals contain silicon, which becomes a by-product after the mineral has been processed to recover valuable metals therefrom.“Desilication”, also called silicon removal, is the removal of the silicon from leach streams obtained in the present process.

[0018] The present invention relates to a process for recovering lithium from a lithium-containing mineral, comprising a) a leaching step 1 carried out in an aqueous leaching solution having a pH of > 11.5, at a temperature of 120 - 240 °C, these leaching conditions providing a silicate product, b) a step for desilicating 2 the leach solution obtained from the leaching step 1, and recirculating the remaining solution to one or more other steps of the process, and c) one or more steps 3,4 for recovering lithium as a solid lithium compound from the lithium-containing leach residue obtained from the leaching step.

[0019] The lithium-containing starting material is preferably obtained from a lithium-containing ore, concentrate or recycled material, preferably being a concentrate, and is typically in the form of a lithium-containing mineral, such as the ones mentioned above in Table 1, or it can be one of the separately listed clay minerals, but is preferably selected from spodumene, petalite, lepidolite , zinnwaldite and intermediate minerals between petalite and spodumene (e.g. LiAIShCL), more preferably being spodumene or petalite. The mineral can be used in calcined or uncalcined form.

[0020] Any of said minerals can be used in calcined form, although a preferred calcined alternative is calcined spodumene.

[0021] Likewise, any of said minerals can be used in uncalcined form, although preferred uncalcined alternatives are uncalcined spodumene and uncalcined petalite, whereas petalite in either calcined or uncalcined form is particularly preferred.

[0022] The leaching step (see step 1 of Fig. 1) is preferably carried out as a pressure leaching. In general, the used leaching conditions have been selected to allow the leaching of a lithium containing mineral without adding a carbonate leaching reagent.

[0023] Pressure leaching 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.

[0024] In an embodiment of the present process, the temperature during leaching is preferably 120-240 °C, more preferably 150-220 °C. Advantageously, the leaching step is carried out in a leach solution having a hydroxide (OH ) content of 0.6-9 mol / L, more preferably 1 - 6 mol / L.

[0025] 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.

[0026] The mentioned hydroxide content is preferably achieved by addition of an alkali metal hydroxide, such as a hydroxide selected from sodium hydroxide (NaOH), potassium hydroxide (KOH) and lithium hydroxide (LiOH), or a mixture thereof, more preferably being sodium hydroxide. This hydroxide may be used e.g. to adjust the pH of the leach solution to a sufficiently high level, preferably being a level of >11.5, more preferably 12 - 14. However, at such levels, contents of alkali reagents are more reliable factors to measure than pH levels.

[0027] With the above 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.

[0028] Due to the used high temperature and high pressure, the leaching 1 is typically performed in a suitable autoclave or series of autoclaves.

[0029] Although pressure leaching in many common processes is carried out in the presence of a carbonate reagent, the present process may be carried out without carbonate reagent, i.e. with no carbonate added to the leaching solution. However, the fresh alkaline leach solution can be combined with a recycled solution from a subsequent step of the process before carrying out the leaching step.

[0030] In a specific embodiment, a lithium-containing mineral selected from the above mentioned minerals, preferably being a calcined mineral, is converted to Li2SiO3 in a leaching step 1 carried out at a pH of > 11.5 and with carbonate addition. The carbonate addition typically takes place by adding a suitable carbonate reagent, such as an alkalimetal carbonate, preferably sodium carbonate (ISfeCCh) 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 of this embodiment, most suitably in a stoichiometry of >0-2.5 related to the lithium content in the mineral.

[0031] In another embodiment of the process described herein, a separate pulping step 0 (see Fig. 2) is carried out before the pressure leaching step, wherein the mineral concentrate containing lithium is mixed into an aqueous solution, for producing a slurry containing lithium. Optionally, the slurry can be formed as a part of the pressure-leaching step 1.

[0032] 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 metasilicate (Li2SiO3). For example, in the presence of sodium hydroxide and using a petalite-based raw material, in the main reaction, lithium-containing minerals react with OH’ and Li2SiO3 and analcime are produced.

[0033] After the leaching step 1, a leach slurry is obtained, which contains lithium in the form of its silicate. Since this intermediate product is only sparingly soluble in the leaching solution, it is 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.

[0034] In a preferred embodiment, the leach slurry is thus conducted to a solid / liquid separation step 1 ’ to provide a lithium-containing solid, and a liquid that contains among others undesired compounds, such as sodium silicates and other impurities, but also further lithium compounds in solubilized form.

[0035] Thus, the solution obtained from the leach slurry (see Fig. 1) is conducted to a silicon removal step 2, also called a desilication step. In the preferred alternative mentioned above (see Fig. 2), the desilication 2 can be preceded by a solid / liquid separation step 1 ’ from which the solution is carried to the desilication step 2. In thedesilication, a calcium reagent, such as calcium oxide (CaO) or calcium hydroxide (Ca(0H)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 2’. In the desilication step 2, in the main reaction silicon reacts with calcium and calcium silicate is produced.

[0036] 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, e.g. 1 - 8 hours. The solution separated from the solids in the further separation step 2’ 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 optional previous solid / liquid separation step 1’, and carried to subsequent processing, such as a carbonization step 3 described below.

[0037] In a further embodiment, the leaching 1 is followed, either directly or with the intermediate separation 1 ’ step described above, by a recovery step 3,4 (see Fig. 1), which preferably includes a carbonization step (see step 3 of Fig. 2), also called a bicarbonization step due to the reaction taking place. In the optional carbonization 3, the obtained leach slurry or a leach residue separated therefrom, optionally combined with a desilicated solution obtained from solid / liquid separation step 2’, 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.

[0038] This optional carbonization step 3 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.

[0039] The lithium-containing slurry or solution obtained from the previous recovery step 3 may be carried further to a subsequent recovery step 4 (see step 4 of Figs. 1 and 2) for converting the lithium in the slurry or solution into an insoluble compound, i.e.precipitating or crystallizing it. This step thus also forms a part of the recovery steps 3,4 mentioned above.

[0040] Said precipitation or crystallization 4 may be preceded by a further step of separating any insoluble agents from the slurry or solution in a solid / liquid separation step 3’ (not shown in the Figures), typically performed by filtering, whereafter the precipitation step 4 is carried out on a liquid fraction. The separation step 3’ 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 precipitation step 4, and the underflow can be discarded, recovered or filtered further in order to recover all lithium remaining therein.

[0041] Also, a purification 3” (not shown in the Figures) can be carried out before the precipitation step 4 to remove impurities, such as tri valent 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 3”. 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.

[0042] The above mentioned precipitation step 4 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.

[0043] If preparing lithium carbonate, the precipitation step 4a 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.

[0044] In this carbonate precipitation 4a 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 4’ (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, itis possible to produce superior battery grade lithium carbonate containing at least 99.99% of lithium carbonate.

[0045] If preparing lithium hydroxide, the precipitation step 4b 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 precipitation 4b is typically carried out at a temperature of 10-100°C, preferably 20-60°C, and most suitably 20-40°C. Typically, the hydroxide precipitation 4b 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, with the carbonate of the alkaline earth metal forming as a by-product.

[0046] After an optional solid / liquid separation step 4’ (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.

[0047] In an embodiment, the lithium hydroxide -containing slurry or solution can be purified before crystallization.

[0048] This optional purification step 4” (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 3”, carried out before the precipitation step 4. 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 multivalentcations) 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.

[0049] 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.

[0050] 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.

[0051] 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 hydroxide reagent. In another alternative, related to the hydroxide route, the mother liquor is recycled to the hydroxide precipitation step 4b 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 3 of the solubilisation can be separated from the crystallization mother liquor, and be recycled back to the carbonization step 3.

[0052] The advantage achieved by recycling to the early steps with lower alkalinity, such as the pressure-leaching 1 or the lithium precipitation steps 4, is that some impuritiesin 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 precipitation step 4b, 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the followingdescription, 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.

[0057] 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.

[0058] 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.EXAMPLESExample 1 - Leaching of calcined and uncalcined lithium-containing minerals

[0059] Calcined spodumene samples and both calcined and uncalcined petalite samples (lithium content in the spodumene samples were 2.4 wt.% and lithium content in the petalite samples were 1.42-1.97 wt.%.) were subjected to pressure leaching in various conditions shown in the following Table 2. Sodium hydroxide (NaOH) was used for pH adjustment when necessary. The raw material content in the leaching slurries was 200 g / L.

[0060] The sodium carbonate of the existing process and the sodium hydroxide used in the novel process for pH adjustments were both added to the raw material slurry as a single dosage in the beginning of the leaching.

[0061] The leaching conditions were maintained for a duration of 1-3 hours.Table 2.

[0062] As these results indicate, the process of the invention, using a pressure leaching step on either a calcined or uncalcined lithium-containing mineral and carried out without a carbonate reagent, is more versatile than the known process, and provides higher extraction rates.Example 2 - Desilication

[0063] A leach slurry was obtained from the novel alkaline leaching conducted by leaching uncalcined petalite samples (lithium content in the mineral 1.91 wt.%) at 200 °C for 2h in a leaching solution containing no added carbonate, but containing sodium hydroxide (NaOH), the solution having a pH of 13.54 before leaching. The raw material content in the slurry was 200 g / L.

[0064] The leach slurry 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.

[0065] Test conditions- CaO addition: 1.2 stoich. to Si- Temperature: 90 °C- Duration time: 8 hours

[0066] 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 3.Table 3.

[0067] As can be seen from the results of Table 3, the silicon content of the leach solution was reduced from 38200 mg / L to 47 mg / L in 8h of desilication.Example 3 - Alkaline leaching using recycled desilicated solution

[0068] The alkaline leaching described in Example 1 was repeated using a desilicated solution obtained from the desilication of Example 2, but using as feed material uncalcined petalite concentrate from North America (Li content: 1.91 %), and a solid content of 200 g / L. The leaching condition and the achieved lithium extraction rate are shown in the following Table 4.Table 4.* NaOH (500 g / L) addition (mL) / feed material (g)

[0069] The leached slurry obtained from Example 2 was carried to a solid / liquid separation, and the separated leach residue was mixed with the desilicated filtrate obtained from Example 2, and used in a carbonization step:- Temperature: 30 °C- Duration time: 8 hours- Solid concentration: 300 g / L- CO2 gas feed: 1000 mL / min

[0070] 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 5. Table 5.

[0071] As shown in the results of Table 5, 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

[0072] 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.

[0073] 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. Further, carbonate reagents can be avoided, and still excellent lithium extraction rates can be achieved.CITATION LISTPatent LiteratureUS 9255012 B2US 11292725 B2

Claims

CLAIMS:

1. A process for recovering lithium from a lithium-containing mineral, comprising a) a leaching step (1) carried out in an aqueous leaching solution having a pH of > 11.5, at a temperature of 120 - 240 °C, b) a step for desilicating (2) the leach solution obtained from the leaching step (1), and recirculating the remaining solution to one or more other steps of the process, and c) one or more steps (3,4) for recovering lithium as a solid lithium compound from the lithium-containing leach residue obtained from the leaching step.

2. The process of claim 1, wherein the lithium-containing mineral is selected from spodumene, petalite, lepidolite, zinnwaldite and intermediate minerals between petalite and spodumene (e.g. LiAISnOs), or any combination thereof3. The process of claim 1, wherein the lithium-containing mineral is selected from calcined spodumene, petalite, lepidolite and zinnwaldite or any combination thereof, preferably being calcined spodumene.

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

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

6. The process of any preceding claim, wherein the pH level of the leaching solution is adjusted to 12 - 14.

7. The process of any preceding claims, wherein the pH is adjusted before the leaching step using a hydroxide reagent, such as an alkali metal hydroxide, which preferably is selected from sodium hydroxide (NaOH), potassium hydroxide (KOH) and lithium hydroxide (LiOH), or a mixture thereof, preferably being sodium hydroxide.

8. The process of any preceding claim, wherein the leaching step (1) is carried out at the hydroxide content of preferably 1 - 6 mol / L.

9. The process of any preceding claim, wherein the leaching step (1) is carried out at a temperature of at a temperature of 150 - 220 °C.

10. The process of any preceding claim, wherein the leaching step (1) is carried out at a pressure of 3 - 30 bar, preferably 5 - 25 bar, more preferably 10 - 25 bar.

11. The process of any preceding claim, wherein the leaching step (1) is carried out for a period of 30 min - 4 h.

12. The process of any preceding claim, wherein the leaching step (1) is carried out without carbonate reagent, in a leaching solution containing no added carbonate.

13. The process of any of claims 1 to 3 and 5 to 10, 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.

14. The process of any preceding claim, wherein the recovery step(s) (3,4) include a carbonization step (3), wherein the obtained leach slurry is reacted with a carbon dioxide (CO2), preferably the carbon dioxide is used in an excess amount.

15. The process of any preceding claim, wherein the desilication step (2) is carried out 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.

16. The process of any preceding claim, wherein the solution obtained from the desilication step (2) is recycled, either to be reused in the leaching step (1), or preferably in a preceding optional pulping step (0), or it may be carried to a subsequent processing step, such as a bicarbonization step (3).

17. The process of any preceding claim, wherein recovery steps (3,4) includes a precipitation (4) to obtain a solid lithium compound.

18. The process of claim 12, wherein the solid lithium compound is lithium carbonate or lithium hydroxide.

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