A novel atmospheric leaching process of lithium concentrates

Abstract

According to the present invention, there is provided a method for processing a lithium-containing concentrate by leaching at atmospheric pressure. Typically, the leaching takes place at a temperature below the boiling point of the leach solution and during a time of 4 – 48 hours, and is a mild leaching process that can be carried out without using an autoclave.

Description

A NOVEL ATMOSPHERIC LEACHING PROCESS OF LITHIUM CONCENTRATESFIELD

[0001] The present invention relates to a method for processing a lithium-containing concentrate in an atmospheric 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 including pressure leaching.

[0003] For example, US 9255012 B2 and US 11292725 B2 describe the leaching of calcined lithium-containing mineral materials by pressure leaching with leach solutions containing carbonate. In US 9255012 B2, the slurry obtained from the leaching step contains lithium carbonate, which is then converted to lithium bicarbonate and 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 pressure leaching using carbonate-based leach solution, has been used to provide the desired lithium extraction rates.

[0004] One of the issues of existing processes using known leaching conditions is that they require the use of autoclaves due to the high-pressure and high-temperature conditions used for the leaching step. Therefore, there is a need for new processes, wherein lithium can be effectively leached in mild conditions, in more simple equipment. 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 method for recovering lithium from lithium-containing concentrates, using leaching at atmospheric pressure.

[0007] According to a second aspect, there is provided a process for leaching lithium-containing concentrates without carbonates.

[0008] According to a third aspect, there is provided a method, which allows the further processing of the slurry obtained from the leaching step to recover lithium therefrom. Optionally, this further processing can include one or more steps for decreasing the content of impurities in the slurry or fractions separated therefrom.

[0009] The present invention thus relates to a method for processing a lithium- containing concentrate by leaching at atmospheric pressure at a temperature below the boiling point of the solution during a time of 4 - 48 hours to obtain a slurry containing extractable lithium.

[0010] The invention is based on the discovery that lithium can be recovered from lithium-containing mineral concentrates without utilizing high pressure. Further, the typically used leaching chemicals, such as carbonate reagents, can be avoided.

[0011] Significant advantages are achieved using the invention. Among others, the invention makes it possible to leach lithium concentrates without an autoclave, in an atmospheric leaching, whereby significant savings can be achieved in both cost and energy, and more sustainable and environmentally friendly lithium products can be obtained.

[0012] An advantage of the optional impurity removal steps in the method is that the recycling options are improved.DRAWINGS

[0013] FIGURE 1 illustrates the process configuration in accordance with some embodiments of the present invention, with block 1 representing the leaching step of the invention, block 2 representing one or more optional reaction steps for separating impurities or by-products from a leach slurry or solution, and blocks 3 and 4 representing one or more optional steps of converting 3 the lithium in a slurry or solids fraction into a form that can easily be precipitated, and / or one or more optional steps 4 for recovering lithium. The dotted arrows represent some possible recycling options.

[0014] FIGURE 2 illustrates a process configuration of an advantageous embodiment, with additional block 0 representing optional pretreatments, typically including calcination (0a) and / or pulping steps (0b), block 1’ representing an optional solid / liquid separation step, and block 2’ representing optional further solid / liquid separation step(s) following the reaction step(s) of block 2. Thus, in case there are more than one steps 2, a single step 2’ can follow the final step 2, or preferably each step 2 can be followed by a separate separation step 2’. Further, block 3 herein represents a carbonization step, from which a slurry or solution can be carried to a block 4, which represents a lithium recovery step. The solution obtained from the final 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).

[0015] FIGURE 3 illustrates a process configuration of another advantageous embodiment, 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. Eikewise, further steps 3’ and 4’ are shown, representing optional solid / liquid separations.EMBODIMENTS

[0016] DEFINITIONSLithium-containing minerals can be found in many different forms, such as the ones listed in the following Table 1. Table 1.Spodumene, lepidolite, petalite and zinnwaldite are of particular interest due to their availability and their advantageous structures. Further, the lithium can can be found in clay minerals, such as masutomilite, swinefordite, hectorite, cookeite and j adarite .Leaching at high pressure has typically been considered necessary to provide an efficient leaching of the valuable metals of these minerals, but the “atmospheric leaching” described herein refers to a leaching step carried out at atmospheric pressure, thus making it possible to avoid the use of expensive autoclaves.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 method.

[0017] The present invention relates to a method for processing a lithium-containing concentrate by leaching at atmospheric pressure at a temperature below the boiling point of the leach solution during a time of 4 - 48 hours to obtain a slurry containing extractable lithium (see step 1 of Figs. 1-3). Preferred temperatures are 20-96 °C, more preferably 70- 95 °C. Likewise, preferred leaching times are 4 - 24h, more preferably 4 - 20 h, and even more preferably 4 - 14h.

[0018] Typically, the leaching 1 is followed by one or more steps for recovering lithium, or converting the lithium in a slurry or solids fraction into a form that can easily be precipitated (see steps 3 and 4 of Figs. 1-3), and possibly one or more steps for separating impurities or by-products from a leach slurry or solution (see step 2 of Figs. 1 and 2).

[0019] The lithium-containing concentrate used as starting material is preferably obtained from 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, jadarite, and zinnwaldite, or any combination thereof. The starting material of the leaching step contains no excess chemicals and contains a feed material of varying particle size, as the material has not been subjected to a grinding step.

[0020] 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. 2) 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, LiAIShOs and Li2A12Si30io.

[0021] In an embodiment, a separate pulping step (see step 0b of Fig. 2) may be carried out before the leaching step, wherein the mineral concentrate containing lithium is mixed into an aqueous solution, for producing the slurry containing lithium. However, it is also possible to form the slurry as a part of the leaching step 1.

[0022] The leaching step 1 is carried out as an atmospheric leaching, and can be carried out as a water leaching, acid leaching or alkaline leaching. In general, the usedleaching conditions are mild, with the atmospheric pressure combined with a low temperature.

[0023] In an embodiment, the leaching step 1 is carried out as an alkaline leaching, preferably in a leaching solution containing an alkali metal hydroxide.

[0024] The alkali metal hydroxide 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 / 1, 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.

[0025] In another embodiment, the leaching step 1 is carried out as an acid leaching, preferably in 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.

[0026] In the leaching step 1, the lithium-containing concentrate will be mixed into the leaching solution to form a slurry. The solids content of this slurry will have an impact on the efficiency of the leaching. In the method described herein, a preferred solids content during the leaching step 1 is 100 - 500 g / L, a more preferred content being 150 - 350 g / L, and a particularly suitable content being 200 - 300 g / L.

[0027] Pressure leaching processes designed for lithium-containing mineral raw materials are commonly carried out at temperatures as high as 300 °C, and in some cases even as low as 150 °C, but in the present process, even lower temperatures of < 100 °C are sufficient, or even < 95 °C.

[0028] In an embodiment, the temperature during leaching is 20-96 °C, preferably 70-95 °C. As stated above, atmospheric pressure is sufficient for the purposes of the method described herein.

[0029] Despite the above mild leaching conditions, a relatively short residence time for the raw material in the leaching reactor is sufficient, such as by continuing the leachingfor a period of up to 48h, preferably 4 - 24h, more preferably 4 - 14h, even more preferably 5 - 10 h, and most suitably 5 - 9 h.

[0030] Although pressure leaching in many common processes is carried out in the presence of a carbonate reagent, the present method may be carried out without such carbonate reagent, i.e. with no carbonate added to the leaching solution. However, the fresh leaching solution can be combined with a recycled solution from a subsequent step of the process before carrying out the leaching step 1, whereby some carbonate might be transferred to the solution.

[0031] In embodiments, where the leaching step 1 is carried out with carbonate addition, the 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 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.

[0032] After the leaching step 1, a leach slurry is obtained, which contains lithium mainly 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.

[0033] With the above leaching conditions, the leach slurry obtained after the leaching step 1 will still contain lithium in the solids. Thus, further processing steps with the aim of recovering lithium may be carried out on said slurry, or preferably on a solids fraction separated from the slurry, particularly following an alkaline leaching. Thus, a solid / liquid separation step (see step 1 ’ of Figs. 2 to 3) may be carried out on the slurry, to obtain a lithium-containing solid fraction and a liquid fraction that contains among others undesired compounds, such as silicates, fluorides, and other impurities, but also further lithium compounds in solubilized form. This separation step may 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 a further processing step, and the underflow can be discarded, recovered or filtered further in order to recover all lithium remaining therein.

[0034] Since also the liquid fraction obtained from the separation step will contain some lithium, it is preferred to utilize also the liquid fraction further in the process. A suitable alternative is to separate the liquid fraction from the leach slurry and recycle it back to the leaching step 1, or an optional pulping step 0b, to be added into the leaching solution before the leaching step.

[0035] As indicated above, the leaching step 1 may be followed by further processing steps, mainly with the aim of recovering lithium, but also with the aim of reducing the amount of impurities in the leach slurry, or the fractions separated therefrom.

[0036] In an embodiment, applied particularly if the lithium fails to precipitate during the leaching step (not shown in the Figures), the leaching step may be followed by a step of adding carbonate or phosphate to a liquid fraction separated from the leach slurry, to cause the precipitation of the lithium therein as a lithium carbonate or phosphate. This lithium carbonate or phosphate can then be processed further as described below, or combined with a lithium-containing solids fraction previously separated from the leach slurry.

[0037] In another embodiment (not shown in the Figures) relating to the acid leaching option, the leaching step may be followed by a step of adding an alkali metal hydroxide, e.g. as sodium hydroxide (NaOH) to a liquid fraction separated from the leach slurry to precipitate and remove solid impurities, such as iron (Fe), aluminium (Al), magnesium (Mg) and calcium (Ca) as their hydroxides. The remaining purified lithium- rich solution may then be carried to the above mentioned carbonate addition step or to a further processing step, as described below.

[0038] In yet a further embodiment, the leaching step may be followed by a carbonization step (see step 3 of Figs. 1-3), wherein the obtained leach slurry containing lithium, or a solids fraction separated therefrom, is reacted with carbon dioxide (CO2) to form a lithium bicarbonate. Preferably, the carbon dioxide is used in an excess amount. In this step, the yet unsolubilized lithium compounds obtained from the leaching step 1 are transformed to solubilized lithium hydrogen carbonate, and are thus capable of essentially complete separation from undesirable, undissolved materials.

[0039] 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.

[0040] The leach slurry, or solid or liquid fractions obtained from the leach slurry, can also be processed further to reduce the amount of undesired components or impurities therein (see step 2 of Figs. 1 and 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 is 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 canthen 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.

[0045] Thus, in an embodiment, a lithium-containing solution obtained in the present method, such as the solubilized fraction obtained from a carbonization step 3, optionally separated from a residue in a solid / liquid separation step 3’, may be subjected to a precipitation or crystallization step (see step 4 of Figs. 1-3) for recovering lithium in crystallized form, preferably in the form of its carbonate or its hydroxide.

[0046] Also, a purification (not shown in the Figures) can be carried out on the lithium-containing solution before a precipitation step 4, to remove impurities, such as trivalent and / or divalent metal ions, e.g. calcium, magnesium, aluminium and iron ions. Preferably, ion exchange is used for the purification. 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.

[0047] 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.

[0048] If preparing lithium carbonate, the precipitation step 4 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.

[0049] In this carbonate precipitation 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, 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.

[0050] If preparing lithium hydroxide, the precipitation step 4 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 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 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.

[0051] After an optional solid / liquid separation step 4’, 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. However, this lithium hydroxide - containing slurry or solution can also be purified before crystallization, preferably using a technique based on purification of dissolved ions and components, and more preferably including 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. 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 repellingaction 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.

[0052] 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.

[0053] 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.

[0054] 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, such as the optional carbonization step 3, or the optional precipitation step 4. In one alternative, the mother liquor is recycled to the leaching step 1, or the optional preceding pulping step 0b, to take part in any pH adjustment therein, thus reducing the need for further added hydroxide reagent. In another alternative, related to the hydroxide precipitation route, the mother liquor is recycled to the hydroxide precipitation step of the preparation of lithium hydroxide. Also, the carbon dioxide used in the optional carbonization step 3 can be separated from the crystallization mother liquor, and be recycled back to the carbonization step 3.

[0055] The advantage achieved by recycling to the early steps with lower alkalinity, such as 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 thesealkali-soluble impurities can be removed by recycling them in solution to a step of lower alkalinity. For example in the hydroxide precipitation step, 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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 practicedwithout 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.

[0060] 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.

[0061] 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 spodumene

[0062] Calcined spodumene samples were subjected to leaching in the conditions shown in the following Table 2.Table 2.Test 1 :

[0063] The sample from Test 1 was calcined at 1075 °C, and then leached as shown above. During the leaching a number of samples were drawn from both the solution and the solids, which samples were analyzed. The results are shown in the following Table 3.Table 3.

[0064] The final filter cake of the Test 1 sample was also carbonated at a temperature of 40 °C for 8h at a solid content of 200 g / L, and using a CO2 gas feed of 1000 ml / min. The results are shown in the following Table 4.Table 4.Test 2:

[0065] The sample from Test 2 was calcined at 1075 °C, and then leached as shown above in Table 2. During the leaching a number of samples were drawn from both the solution and the solids, which samples were analyzed. The results are shown in the following Table 5.Table 5.Test 3 :

[0066] The sample from Test 3 was calcined at 1075 °C, and then leached as shown above in Table 2. During the leaching a number of samples were drawn from both the solution and the solids, which samples were analyzed. The results are shown in the following Table 6.Table 6.Test 4:

[0067] The sample from Test 4 was calcined at 1075 °C, and then leached as shown above in Table 2. During the leaching a number of samples were drawn from both the solution and the solids, which samples were analyzed. The results are shown in the following Table 7.Table 7.Test 5 :

[0068] The sample from Test 5 was calcined at 1075 °C, and then leached as shown above in Table 2. During the leaching a number of samples were drawn from both the solution and the solids, which samples were analyzed. The results are shown in the following Table 8.Table 8.Test 6:

[0069] The sample from Test 6 was calcined at 1075 °C, and then leached as shown above in Table 2. During the leaching a number of samples were drawn from both the solution and the solids, which samples were analyzed. The results are shown in the following Table 9.Table 9.Test 7 :

[0070] The sample from Test 7 was calcined at 1075 °C, and then leached as shown above in Table 2. During the leaching a number of samples were drawn from both the solution and the solids, which samples were analyzed. The results are shown in the following Table 10.Table 10.Test 8:

[0071] The sample from Test 8 was calcined, and then leached as shown above inTable 2. During the leaching a number of samples were drawn from both the solution and the solids, which samples were analyzed. The results are shown in the following Table 11.Table 11.Example 2 - Leaching of calcined zinnwaldite

[0072] Zinnwaldite samples were subjected to calcination and leaching in the conditions shown in the following Table 12.Table 12.Test 9:

[0073] The zinnwaldite sample from Test 9 was calcined and leached as shown above in Table 12. During the leaching a number of samples were drawn from both the solution and the solids, which samples were analyzed. The results are shown in the following Table 13.Table 13.Test 10:

[0074] The zinnwaldite sample from Test 10 was calcined and leached as shown above in Table 12. During the leaching a number of samples were drawn from both the solution and the solids, which samples were analyzed. The results are shown in the following Table 14. Table 14.Example 3 - Leaching of calcined lepidolite

[0075] Lepidolite samples were subjected to calcination and leaching in the conditions shown in the following Table 15.Table 15.Test 11 :

[0076] The lepidolite sample from Test 11 was calcined and leached as shown above in Table 15. During the leaching a number of samples were drawn from both the solution and the solids, which samples were analyzed. The results are shown in the following Table 16.Table 16.Test 12:

[0077] The lepidolite sample from Test 12 was calcined and leached as shown above in Table 15. During the leaching a number of samples were drawn from both the solution and the solids, which samples were analyzed. The results are shown in the following Table 17.Table 17.Test 13:

[0078] The lepidolite sample from Test 13 was calcined and leached as shown above in Table 15. During the leaching a number of samples were drawn from both the solution and the solids, which samples were analyzed. The results are shown in the following Table 18.Table 18.Test 14:

[0079] The lepidolite sample from Test 14 was calcined and leached as shown above in Table 15. During the leaching a number of samples were drawn from both the solution and the solids, which samples were analyzed. The results are shown in the following Table 19.Table 19.Example 4 - Leaching of calcined petalite

[0080] Petalite samples were subjected to calcination and leaching in the conditions shown in the following Table 20.Table 20.Test 15:

[0081] The petalite sample from Test 15 was calcined and leached as shown above in Table 20. During the leaching a number of samples were drawn from both the solution and the solids, which samples were analyzed. The results are shown in the following Table 21.Table 21.Example 5 - Acid leaching of calcined zinnwaldite

[0082] Zinnwaldite samples were subjected to calcination and leaching in the conditions shown in the following Table 22.Table 22.Test 16:

[0083] The zinnwaldite sample from Test 16 was calcined and leached as shown above in Table 22. During the leaching a number of samples were drawn from both the solution and the solids, which samples were analyzed. The results are shown in the following Table 23.Table 23.Test 17:

[0084] The zinnwaldite sample from Test 17 was calcined and leached as shown above in Table 22. During the leaching a number of samples were drawn from both the solution and the solids, which samples were analyzed. The results are shown in the following Table 24.Table 24.Example 6 - Acid leaching of calcined lepidolite

[0085] Lepidolite samples were subjected to calcination and leaching in the conditions shown in the following Table 25.Table 25.Test 18:

[0086] The lepidolite sample from Test 18 was calcined and leached as shown above in Table 25. During the leaching a number of samples were drawn from both the solution and the solids, which samples were analyzed. The results are shown in the following Table 26.Table 26.Test 19:

[0087] The lepidolite sample from Test 19 was calcined and leached as shown above in Table 25. During the leaching a number of samples were drawn from both the solution and the solids, which samples were analyzed. The results are shown in the following Table 27.Table 27.

[0088] As these results indicate, the method of the invention, using an atmospheric leaching step and low temperatures, is more versatile than the known processes, and provides comparable extraction rates despite the mild conditions.INDUSTRIAL APPLICABILITY

[0089] The method 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.

[0090] Particularly, the herein described new leaching step makes it possible to leach lithium concentrates without the use of an expensive autoclave. Further, the leaching temperatures can be kept lower than in prior art processes.REFERENCE SIGNS LIST

[0091] The method of the invention involves a leaching step 1 carried out at atmospheric pressure at a temperature below the boiling point of the leach solution. Thus, the method of the invention comprises the following step:1 Atmospheric leaching

[0092] In various embodiments, some further steps can be included in the method, as shown in Figs. 1-3. Based on the Figures, any single one of the following optional steps may also be included in the method, or a combination of two or more such additional steps:0a calcination step0b pulping step1 ’ solid / liquid separation following the leaching step 12 Separation of impurities or by-products from a leach slurry or solution, optionally in the form of:2a fluoride removal2a’ solid / liquid separation following fluoride removal2b silicon removal2b’ solid / liquid separation following silicon reoval3,4 convertion of the lithium in a slurry or solids fraction into a form that can easily be precipitated, typically in the form of:3 carbonization3 ’ optional solid / liquid separation following carbonization4 lithium precipitation / crystallization4’ optional solid / liquid separation following Li precipitation / crystallizationCITATION LIST Patent LiteratureFI 121785 BUS 9255012 B2US 11292725 B2

Claims

CLAIMS:

1. A method for processing a lithium-containing concentrate by leaching in a leaching solution at atmospheric pressure at a temperature below the boiling point of the leach solution during a time of 4 - 48 hours to obtain a slurry containing lithium.

2. The method of claim 1, wherein the lithium-containing concentrate is obtained from a lithium-containing mineral, which preferably is selected from spodumene, petalite, lepidolite, jadarite and zinnwaldite, or any combination thereof.

3. The method of claim 1 or 2, wherein the lithium-containing concentrate contains one or more lithium-containing minerals in calcined form, whereby the calcination has preferably been carried out at a temperature of 800 - 1200 °C, more preferably at a temperature of 900 - 1150 °C, even more preferably at 900 - 1100 °C.

4. The method of any preceding claim, wherein the leaching step is carried out as a water leaching, acid leaching or alkaline leaching.

5. The method of any preceding claim, wherein the leaching step is carried out as an alkaline leaching, preferably in a leaching solution containing an alkali metal hydroxide.

6. The method of any preceding claim, wherein the leaching step is carried out in a leaching solution containing an alkali metal hydroxide, which is selected from sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH)2) and lithium hydroxide (LiOH), or a mixture thereof, preferably being sodium hydroxide.

7. The method of claim 5 or 6, wherein the alkali metal hydroxide is added into the leaching solution in 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.

8. The method of any preceding claim, wherein the pH level of the leaching solution is adjusted to 11.5 - 14, preferably to 12 - 14.

9. The method of any of claims 1 to 4, wherein the leaching step is carried out as an acid leaching, preferably in a leaching solution containing sulphuric acid.

10. The method of any preceding claim, wherein the leaching step is carried out in a slurry formed by the lithium-containing concentrate and the leaching solution, the slurry having a solid content of 100 - 500 g / L, preferably 150 - 350 g / L, more preferably 200 - 300 g / L.

11. The method of any preceding claim, wherein the leaching step is carried out at a temperature from 20 to less than 100 °C, preferably 20 - 95 °C.

12. The method of any preceding claim, wherein the leaching step is carried out for a period of 4 - 24h, preferably 4 - 14h, more preferably 4 - 10 h, even more preferably 5 - 9 h.

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

14. The method of any of claims 1 to 12, wherein the leaching solution further contains a carbonate reagent, such as sodium carbonate (Na2CCh) 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.

15. The method 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.

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

17. The method 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.

18. The method of any preceding claim, wherein the obtained slurry containing lithium, or a solids fraction separated therefrom, is solubilized, e.g. in a carbonization step, and a solubilized fraction is subsequently subjected to a crystallization step for recovering lithium in crystallized form, preferably in the form of its carbonate or its hydroxide.

19. The method 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.

20. The method of claim 19, 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.

21. The method of claim 19 or 20, wherein silicon of the slurry or a solids or liquid fraction is removed therefrom by reacting with a calcium reagent, such as calcium hydroxide or calcium oxide, whereby the silicon separates as a solid calcium silicate.