A novel leaching process of lithium concentrates

Abstract

According to the present invention, there is provided a process for extracting lithium from a lithium-containing mineral, preferably in calcined form, in a process utilizing a particularly short leaching step.

Description

A NOVEL 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 short leaching step.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 long leaching times have been used, the processes being based on an essentially full dissolution of the lithium.

[0004] One of the main issues of existing processes is that they require harsh leaching conditions to be maintained for a long time, thus also requiring large and expensive equipment. Therefore, there is a need for new processes, wherein lithium can be effectively extracted using simpler procedures. 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 extracting lithium from lithium-containing mineral raw-materials.

[0007] According to a second aspect, there is provided a process for extracting lithium from lithium-containing mineral raw-materials using short leaching times.

[0008] According to a third aspect, there is provided a process, wherein at least one of the solid and solution phase 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] The present invention thus relates to a process for extracting lithium from a lithium-containing mineral, by providing a concentrate of lithium-containing mineral, and pressure leaching the mineral concentrate in a leaching solution for a period of less than 30 min to obtain a slurry containing extracted lithium.

[0010] The invention is based on the discovery that lithium can be recovered from lithium-containing minerals at short leaching times 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.

[0011] Significant advantages are achieved using the invention.

[0012] Since there is no requirement to cause complete dissolution of all the lithium in the starting material, high extraction rates were achieved at very short leaching times, such as a few minutes. In addition to shorter processing times, this has the advantage of smaller equipment needed for the leaching step and lower costs.

[0013] It was a surprising discovery that at least for some lithium-containing minerals, these better extraction rates can be achieved also with very short leaching times. Thus, smaller and less expensive equipment can be used.

[0014] An advantage of the optional impurity removal step in the process is that the recycling options in the process are improved, and the impurities 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, 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, block 2 representing an impurity removal 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).

[0017] FIGURE 3 illustrates a process configuration of another advantageous embodiment, with block 0 separated into different pretreatments, typically including calcination (0a) and / or pulping steps (0), further with block 2 separated into 2a and 2a’ representing fluoride reaction and separation, respectively, from the solution carried from the solid / liquid separation 1’ following the leaching step 1, and 2b and 2b’ representing silicate reaction and separation, respectively. Likewise, further steps 3’ and 4’ are shown, representing optional solid / liquid separations.EMBODIMENTS

[0018] 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 1Further, 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.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.

[0019] The present invention relates to a process for recovering lithium from a lithium-containing mineral, by providing a concentrate of lithium-containing mineral, and pressure leaching the mineral concentrate in a leaching solution for a period of less than 30 min to obtain a slurry containing extracted lithium.

[0020] 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 mentionedabove 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 with structures similar to the structures of petalite (LiAlSi40io) and spodumene (LiAlSi2Oe), e.g. LiAIShOg and I^AhSisOio, more preferably being spodumene or petalite. The mineral is preferably used in calcined form, a particularly preferred alternative being calcined spodumene.

[0021] The starting material typically contains no excess chemicals and contains a mineral concentrate of varying particle size, as the material has not been subjected to a grinding step.

[0022] Typically, the minerals of the starting materials carried to the leaching step 1 are used in calcined form, whereby a calcination (see step 0a of Fig. 3) has preferably been carried out at a temperature of 800 - 1200 °C, more preferably at 900 - 1150 °C, and even more preferably at 900 - 1100 °C. Optionally, a mixture of calcined and uncalcined minerals are used in the concentrate carried to the leaching step. The lithium minerals after the calcination can have different crystallographic structures as compared to uncalcined minerals, such as beta-spodumene, gamma-spodumene, LiAIShOg and ^AbSisOio.

[0023] In an embodiment, a separate pulping step (see step 0 of Figs. 2 and 3) may be 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 and / or a hydroxide, for producing the slurry containing lithium. However, the slurry can also be formed as a part of the pressure-leaching step 1, and any chemical additions can take place in either the optional pulping step 0 or in the leaching step 1. A preferred alkali metal carbonate is sodium carbonate, and is typically used in excess.

[0024] The leaching step (see step 1 of Fig. 1) is preferably carried out as a pressure leaching.

[0025] Pressure leaching of lithium-containing mineral raw materials can be carried out at temperatures as high as 300 °C, although also lower temperatures of < 280 °C, or temperatures of < 240 °C may be sufficient.

[0026] In an embodiment of the present process, the temperature during leaching is thus preferably 120 - 300 °C, more preferably 120-280 °C, such as 120-260 °C or 120— 240 °C, even more preferably 150-220 °C. Thus, in some embodiments, the temperatureof the leaching step may range from 120 °C or 150 °C up to 220 °C, 240 °C, 260 °C, 280 °C or 300 °C.

[0027] The pressure during the leaching 1 is preferably 3 - 85 bar, more preferably 3 - 65 bar, even more preferably 3-30 bar, or 5-30 bar, and most suitably 5-25 bar or 10-25 bar. Thus, in some embodiments, the pressure during the leaching step 1 may range from 3 bar, 5 bar or 10 bar up to 25 bar, 30 bar, 50 bar, 65 bar or 85 bar. The pressure may not necessarily require separate adjustment, as it adjusts upwards with a raised temperature. Hence, the pressure is typically higher at higher leaching temperatures.

[0028] In an embodiment, the used leaching solution is an alkaline leaching solution, preferably a leaching solution containing an alkali metal hydroxide.

[0029] The alkali metal hydroxide of this embodiment can, for example, be selected from sodium hydroxide (NaOH), potassium hydroxide (KOH) and lithium hydroxide (LiOH), or a mixture thereof, preferably being sodium hydroxide. It is typically added into the leaching solution into a hydroxide content of 0.1 - 250 g / L, preferably 1 - 200 g / L, more preferably 30 - 150 g / L, and even more preferably 50 - 120 g / L. This will give the solution a particularly high pH, typically being adjusted using the alkali metal hydroxide to 11.5 - 14, preferably to 12 - 14. However, at such levels, contents of alkali reagents are more reliable factors to measure than pH levels.

[0030] In one embodiment, the hydroxide content is in the range of 0.6 - 9 mol / L, preferably 1 -6 mol / L

[0031] In another embodiment, the leaching solution is an acid leaching solution, preferably a leaching solution containing sulphuric acid (H2SO4), phosphoric acid (H3PO4) or carbonic acid (H2CO3). The acid is typically added into the leaching solution into a concentration of 1 - 10 mol / L.

[0032] With the above conditions, a short leaching time is sufficient. It was discovered that by pressure leaching at the temperatures set forth herein, the leaching time can be less than 30 min, such as 1 min - 25 min or 3 min - 15 min. Thus, in some embodiments, the leaching time is from 0.5 min, 1 min or 3 min up to 5 min, 10 min, 15 min, 20 min, 25 min or 30 min.

[0033] Due to the preferred high temperature and high pressure, the leaching 1 is typically performed in a suitable autoclave or series of autoclaves. When a leaching time of less than 30 min is employed, the volume of the equipment can be significantly reduced without a decreased process efficiency. The temperature of the leaching step may, in turn, be slightly increased, such as by using a temperature in the upper end of the temperature ranges disclosed herein (e.g. a temperature of 220 - 300 °C), without significant negative impact on the equipment, e.g. the autoclave. The type of mineral raw material may also be taken into account when selecting the leaching conditions, as for example lepidolite, zinnwaldite and amblygonite contain fluorine, which therefore may be leached at lower temperatures to increase the equipment service length.

[0034] 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 leach solution can in one alternative be combined with a recycled solution from a subsequent step of the process before carrying out the leaching step, whereby some carbonate might be carried to the leaching step even without separate carbonate addition.

[0035] In a specific embodiment, a calcined lithium-containing mineral selected from the above mentioned minerals, is extracted in an alkaline leaching solution with carbonate addition. The carbonate addition typically takes place by adding a suitable 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 >0-3.5 related to lithium content in the mineral of this embodiment, preferably in a stoichiometry of >0-2.5 related to the lithium content in the mineral, and most suitably in a stoichiometry of 1.5 - 2.5.

[0036] In another embodiment of the process described herein, a separate pulping step 0 (see Figs. 2 and 3) 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 pressureleaching step 1.

[0037] Thus, in the leaching step 1, the lithium of a lithium-containing mineral, such as lithium oxides or lithium aluminium silicates of the mineral (e.g. the LiAlSi40io forpetalite) are converted to the solubilized or partially solubilized form of e.g. lithium metasilicate (I^SiCh). 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.

[0038] After the leaching step 1 , a leach slurry is obtained, which contains lithium in converted form, such as the form of its silicate, as an extract. 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. Thus, within the context of the present disclosure, the lithium extract is referring to lithium that has been converted to such solubilized or partially solubilized form (i.e. a slurry), wherein lithium is liberated from the structure of the initial mineral of the starting material, i.e. feed material.

[0039] 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.

[0040] The obtained slurry containing lithium, or a solid or liquid fraction separated therefrom, may be processed further (see step 2 of Fig. 2) to remove one or more impurities therefrom, before or after a carbonization of the lithium in the slurry. This can be carried out for example by adding a calcium reagent, such as calcium oxide (CaO) or calcium hydroxide (Ca(OH)2) to the slurry or solution to cause a reaction with the impurities, such as fluoride or silicon, which can then be removed in a subsequent further solid / liquid separation step 2’.

[0041] One alternative is to remove fluorides from the leach slurry, or from a liquid fraction separated therefrom, (see step 2a of Fig. 3) by reacting with a calcium reagent, such as calcium hydroxide or calcium oxide, whereby the fluoride reacts into calcium fluoride, which can be separated from the remaining solution in a solid / liquid separation step 2a’. The reagent dosages are selected to cause only precipitation of the fluorides.Therefore, a preferred option is to analyze the fluoride content of the leach slurry before fluoride removal, or of a liquid fraction separated therefrom, and add about an equivalent amount of calcium reagent.

[0042] Another alternative is to provide a silicon removal step, also called a desilication step (see step 2b of Fig. 3). Preferably, both a fluoride removal and a silicon removal are carried out, whereby this silicon removal step is carried out after the fluoride removal step.

[0043] Preferably, the desilication 2b is carried out on a liquid fraction separated from the leach slurry, or a purified version of the leach slurry (e.g. subjected to a fluoride removal), and a desilicated solution obtained after this step can either be recycled to the leaching step 1, or be combined with any stream used in further processing steps, such as the slurry or solid fraction carried to the optional carbonization step 3, or be carried to a further impurity removal.

[0044] In the desilication step 2b, a calcium reagent, such as calcium oxide (CaO) or calcium hydroxide (Ca(OH)2) may be added to the solution containing the silicon to be treated, to cause the silicon to react with the calcium and form calcium silicates, which can then be removed in a subsequent further solid / liquid separation step 2b’. 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 2b’ may be recycled, particularly to be reused in the leaching step 1, or in the preceding optional pulping step 0b, or it may be combined with the leach slurry, or preferably with the leach residue (solids fraction) obtained from a solid / liquid separation step 1 ’ following the leaching step 1, and carried to subsequent processing, such as a carbonization step 3. 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 tosolubilized lithium hydrogen carbonate, and are thus capable of essentially complete separation from undesirable, undissolved materials.

[0045] 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.

[0046] 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.

[0047] 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’ (see Fig. 3), 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.

[0048] Also, a purification 3” (not shown in the Figures) can be carried out before the precipitation step 4 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 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.

[0049] 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.

[0050] 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.

[0051] 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’ (see Fig. 3), 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.

[0052] 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.

[0053] After an optional solid / liquid separation step 4’ (see Fig. 3), 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.

[0054] In an embodiment, the lithium hydroxide -containing slurry or solution can be purified before crystallization.

[0055] 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 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] The advantage achieved by recycling to an earlier step with lower alkalinity, such as the pressure-leaching 1 of certain embodiments or the lithium precipitation steps 4, 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 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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 - Rapid leaching of lithium-containing materials

[0066] Calcined spodumene concentrate (lithium content in the mineral 2.66 wt.%) and uncalcined petalite samples (lithium content in the mineral 1.90 wt.%) were leached in a leaching solution containing sodium hydroxide (NaOH). The alkalinity of each leach solution was adjusted by adding NaOH solution in a concentration of 500 g / L. The dosage of added NaOH solution was 1.25 mL / g raw material for the spodumene sample and 1.5 mL / g raw material for the petalite sample. The temperature during the leaching was maintained at around 220 °C.

[0067] The leach solution was heated to a temperature of 220 °C, whereafter samples were taken at 0 min, 3 min, 5 min, 10 min and 15 min (final cake). The results for the spodumene sample are presented in Table 2 and the results for the petalite sample are presented in Table 3. Table 2Table 3

[0068] From the results it can be seen that the lithium extraction was very high already at the beginning of the leach step and reached 100 % of the theoretical value at the latest after five minutes. For the calcined spodumene sample, an extraction rate of 100 % was reached already at the initiation of the leaching process, i.e., upon reaching a temperature of 220 °C.

[0069] In order to verify the influence of leaching during the heating time in Example 2, a reference tests were carried out with a slightly different setup. In the reference tests, a second sample of calcined spodumene concentrate and uncalcined petalite concentrate was independently subjected to a leaching step with preheating prior to addition of alkaline solution. The leaching was considered initiated when the total amount of alkaline solution had been mixed with the raw material.

[0070] The leaching was carried out at a temperature of 220 °C. The calcined spodumene feed material (560 g) and the uncalcined petalite feed material (560 g) were heated in respective test to the leaching temperature of 220 °C, at which point a NaOH solution with a concentration of 762 g / L was added to respective leach solution. The amount of added NaOH solution was 560 mL for the spodumene sample and 650 mL for the petalite sample.

[0071] The results as presented in Table 4 and Table 5 below showed similar results for the lithium extraction as in the first test, the results of which are presented in Table 2 andTable 3.Table 4Table 5INDUSTRIAL 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 in shorter processing times and without the need for large expensive equipment. Despite this, excellent lithium extraction rates can be achieved.CITATION LISTPatent LiteratureUS 9255012 B2US 11292725 B2

Claims

CLAIMS:

1. A process for extracting lithium from a lithium-containing mineral, characterized by providing a concentrate of lithium-containing mineral, and pressure leaching the mineral concentrate in a leaching solution for a period of less than 30 min to obtain a slurry containing extracted lithium.

2. The process of claim 1, wherein the lithium-containing mineral is provided in calcined form, preferably the lithium-containing mineral is selected from calcined spodumene, petalite, lepidolite and zinnwaldite or any combination thereof, preferably being at least partly selected from calcined minerals, more preferably selected at least partly from calcined spodumene.

3. The process of claim 1 or 2, 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.

4. 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.

5. The process of any preceding claim, wherein alkali metal hydroxide is added into the leaching solution into a hydroxide content of 0.1 - 250 g / L, preferably 1 - 200 g / L, more preferably 30 - 150 g / L, and even more preferably 50 - 120 g / L.

6. The process of any one of claims 1-3, wherein the leaching solution is an acid leaching solution, preferably a leaching solution containing sulphuric acid (H2SO4), phosphoric acid (H3PO4) or carbonic acid (H2CO3).

7. The process of claim 6, wherein the acid is added into the leaching solution into a concentration of 1 - 10 mol / L.

8. The process of any preceding claim, wherein the leaching step is carried out at a temperature of at a temperature of 120 - 300 °C, preferably 120 - 280 °C, more preferably 150 - 220 °C.

9. The process of any preceding claim, wherein the leaching step is carried out at a pressure of 3 - 85 bar, preferably 3 - 65 bar, more preferably 5 - 30 bar, most suitably 10 - 25 bar.

10. The process of any preceding claim, wherein the leaching step is carried out for a period of 1 min - 25 min, preferably 3 min - 15 min.

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

12. The process of any of claims 1 to 5 or 8 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 3.5 related to the lithium content in the mineral, more preferably in a stoichiometry of >0 - 2.5 related to the lithium content in the mineral, and most suitably in a stoichiometry of 1.5 - 2.5.

13. The process of any preceding claim, wherein a solid / liquid separation step is carried out to separate a solids fraction and a liquid fraction from the leach slurry.

14. The process of any preceding claim, wherein the liquid fraction is separated from the leach slurry and is recycled back to the leaching step and combined with the leaching solution.

15. The process of any preceding claim, wherein the obtained slurry containing lithium, or a solids fraction separated therefrom, is processed further in a carbonization step, wherein it is reacted with carbon dioxide (CO2), preferably used in an excess amount.

16. The process of any preceding claim, wherein the obtained slurry containing lithium, or a solid or liquid fraction separated therefrom, is processed further to remove one or more impurities therefrom, before or after a carbonization of the lithium in the slurry.

17. The process of claim 16, wherein fluoride of the slurry or the solids fraction is removed therefrom by reacting with a calcium reagent, such as calcium hydroxide or calcium oxide, whereby the fluoride separates as calcium fluoride.

18. The process of claim 16 or 17, wherein silicon of the slurry, or a solids or liquid fraction separated therefrom, is removed by reacting with a calcium reagent, such as calcium hydroxide or calcium oxide, whereby the silicon separates as a solid calcium silicate.

19. The process of any preceding claim, which includes a precipitation to obtain a solid lithium compound.

20. The process of claim 19, wherein the solid lithium compound is lithium carbonate or lithium hydroxide.

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