Novel atmospheric pressure leaching method of lithium concentrate

Abstract

According to the invention, a method is provided for treating a lithium-containing concentrate by leaching at atmospheric pressure. Generally, the leaching is carried out at a temperature lower than the boiling point of the leaching solution for 4-48 hours, which is a mild leaching process and can be carried out without using an autoclave.

Description

Technical Field

[0001] The present invention relates to a method for treating lithium-containing concentrate in an atmospheric pressure leaching step. Background Art

[0002] Lithium is an element that forms compounds with a variety of industrial applications. The lithium used for these purposes is primarily obtained from lithium brines and ores using hydrometallurgical extraction processes. Conventional processes for extracting lithium from ores involve high-temperature calcination or roasting, followed by hydrometallurgical treatments, including pressure leaching.

[0003] For example, US 9255012 B2 and US 11292725 B2 describe leaching of calcined lithium-containing mineral materials by pressure leaching with a leaching solution containing carbonates. In US 9255012 B2, the slurry obtained from the leaching step contains lithium carbonate, which is then converted into lithium bicarbonate and crystallized into a lithium carbonate product. In US 11292725 B2, the lithium in the leached slurry is further reacted into hydroxide. However, both publications describe methods in which pressure leaching using a carbonate-based leaching solution has been used to provide the desired lithium extraction rate.

[0004] One of the problems with existing processes using known leaching conditions is that they require the use of autoclaves due to the high pressure and temperature conditions used for the leaching step. Therefore, new processes are needed in which lithium can be efficiently leached under milder conditions and in simpler equipment. Similarly, leaching in the presence of carbonates is not optimal from an extraction yield perspective. Summary of the Invention

[0005] The invention is defined by the features of the independent claims. Particular embodiments are defined in the dependent claims.

[0006] According to a first aspect of the present invention, there is provided a method for recovering lithium from a lithium-containing concentrate by leaching at atmospheric pressure.

[0007] According to a second aspect, there is provided a method for leaching a lithium-containing concentrate in the absence of carbonates.

[0008] According to a third aspect, a method is provided which allows the slurry obtained from the leaching step to be further processed to recover lithium therefrom. Optionally, the further processing may include one or more steps for reducing the content of impurities in the slurry or a fraction separated therefrom.

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

[0010] The present invention is based on the discovery that lithium can be recovered from lithium-containing mineral concentrates without the use of high pressure. In addition, commonly used leaching chemicals, such as carbonate reagents, can be avoided.

[0011] Significant advantages are achieved using the present invention. Among other things, the present invention makes it possible to leach lithium concentrate in atmospheric pressure leaching without an autoclave, thereby achieving significant savings in cost and energy and making it possible to obtain a more sustainable and environmentally friendly lithium product.

[0012] An advantage of the optional impurity removal step in the process is improved recycling options. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 A process configuration according to some embodiments of the present invention is shown, wherein box 1 represents the leaching step of the present invention, box 2 represents one or more optional reaction steps for separating impurities or by-products from the leached slurry or solution, and boxes 3 and 4 represent one or more optional steps 3 of converting lithium in the slurry or solid fraction to a readily precipitable form, and / or one or more optional steps 4 of recovering lithium. Dashed arrows represent some possible recycling options.

[0014] Figure 2 A process configuration of an advantageous embodiment is shown, wherein a further block 0 represents an optional pretreatment, typically comprising a calcination (0a) and / or a slurrying step (0b), a block 1' represents an optional solid / liquid separation step, and a block 2' represents an optional further solid / liquid separation step after the reaction step of block 2. Thus, in the case of more than one step 2, a single step 2' may be after the last step 2, or preferably each step 2 may be followed by a separate separation step 2'. Furthermore, block 3 here represents a carbonization step, from which the slurry or solution can be conveyed to block 4, which represents a lithium recovery step. The solution obtained from the last separation step 2' can be recycled back to the slurrying step 0 or further conveyed to a carbonization step 3 (as indicated by the dotted arrow).

[0015] Figure 3 Another advantageous embodiment of the process configuration is shown, wherein block 2 is divided into blocks 2a and 2a', which respectively represent the fluoride reaction and separation from the solution carried over from the solid / liquid separation 1' following the leaching step 1; and blocks 2b and 2b', which respectively represent the silicate reaction and separation. Similarly, further blocks 3' and 4' are shown, representing the optional solid / liquid separation. DETAILED DESCRIPTION

[0016] definition

[0017] Lithium-containing minerals can exist in a variety of different forms, such as those listed in Table 1 below.

[0018] Table 1

[0019]

[0020] Spodumene, lepidolite, petalite and lepidolite are of particular interest due to their availability and their favorable structures. Additionally, lithium can be present in clay minerals such as masutomilite, swinefordite, hectorite, cookeite and jadarite.

[0021] High pressure leaching is generally considered necessary to provide efficient leaching of the valuable metals of these minerals, but "atmospheric pressure leaching" as used herein refers to a leaching step carried out at atmospheric pressure, thereby avoiding the use of expensive autoclaves.

[0022] Most of the above-mentioned minerals contain silicon, which is produced as a by-product after the minerals are processed to recover valuable metals therefrom. "Desilication", also known as silicon removal, refers to the removal of silicon from the leach stream obtained from the process.

[0023] The present invention relates to a method for treating lithium-containing concentrates by leaching at a temperature below the boiling point of the leaching solution at atmospheric pressure for 4 to 48 hours to obtain a slurry containing extractable lithium (see Figure 1-3 In step 1), the preferred temperature is 20-96° C., more preferably 70-95° C. Similarly, the preferred leaching time is 4-24 hours, more preferably 4-20 hours, even more preferably 4-14 hours.

[0024] Typically, leaching 1 is followed by one or more steps to recover the lithium, or to convert the lithium in the slurry or solid fraction into a form that is readily precipitated (see Figure 1-3 3 and 4), and possibly one or more steps of separating impurities or by-products from the leach slurry or leach solution (see Figure 1 and 2 Step 2).

[0025] The lithium-containing concentrate used as starting material is preferably obtained from a lithium-containing mineral such as those mentioned in Table 1 above, or it may be one of the clay minerals listed individually, but preferably selected from spodumene, petalite, lepidolite, jaddarite and lepidolite, or any combination thereof. The starting material for the leaching step does not contain excess chemicals and contains feed of varying particle sizes, as the material has not been subjected to a grinding step.

[0026] Typically, the mineral starting material fed to the leaching step 1 is used in calcined form, so the calcination (see Figure 2 Step 0a) is preferably carried out at a temperature of 800-1200°C, more preferably 900-1150°C, even more preferably 900-1100°C. Optionally, a mixture of calcined and uncalcined minerals is used in the concentrate fed to the leaching step. The calcined lithium mineral may have a different crystal structure than the uncalcined mineral, for example β-spodumene, γ-spodumene, LiAlSi3O8 and Li2Al2Si3O 10 .

[0027] In one embodiment, a separate pulping step may be performed before the leaching step (see Figure 2 Step 0b) of the present invention, wherein a mineral concentrate containing lithium is mixed with an aqueous solution for producing a slurry containing lithium. However, the slurry can also be formed as part of the leaching step 1.

[0028] The leaching step 1 is carried out as atmospheric pressure leaching and can be carried out as water leaching, acid leaching or alkaline leaching. Typically, the leaching conditions used are mild, wherein atmospheric pressure is combined with low temperature.

[0029] In one embodiment, the leaching step 1 is performed as alkaline leaching, preferably in a leaching solution containing an alkali metal hydroxide.

[0030] The alkali metal hydroxide can be, for example, selected from sodium hydroxide (NaOH), potassium hydroxide (KOH) and lithium hydroxide (LiOH), or mixtures thereof, preferably sodium hydroxide. It is typically added to the leach solution to a hydroxide ion 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 results in a particularly high pH value for the solution, which is typically adjusted to 11.5-14, preferably 12-14, using the alkali metal hydroxide. However, at such pH values, the content of the alkaline agent is a more reliable measurement factor than the pH value.

[0031] In another embodiment, the leaching step 1 is carried out in the form of acid leaching, preferably in a leaching solution containing sulfuric acid (H2SO4), phosphoric acid (H3PO4) or carbonic acid (H2CO3). The acid is usually added to the leaching solution at a concentration of 1-10 mol / L.

[0032] In leaching step 1, the lithium-containing concentrate is mixed with a leach solution to form a slurry. The solids content of this slurry will affect the efficiency of leaching. In the method described herein, the preferred solids content during leaching step 1 is 100-500 g / L, more preferably 150-350 g / L, and particularly preferably 200-300 g / L.

[0033] Pressure leaching processes designed for lithium-containing mineral raw materials are usually carried out at temperatures up to 300°C, 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.

[0034] In one embodiment, the temperature during leaching is from 20 to 96° C., preferably from 70 to 95° C. As mentioned above, atmospheric pressure is sufficient for the purposes of the methods described herein.

[0035] Despite the mild leaching conditions described above, a relatively short residence time of the raw material in the leaching reactor is sufficient, for example by continuing the leaching for a period of up to 48 hours, preferably 4-24 hours, more preferably 4-14 hours, even more preferably 5-10 hours, most preferably 5-9 hours.

[0036] While pressure leaching in many common processes is carried out in the presence of a carbonate reagent, the present method can be carried out in the absence of such a carbonate reagent, i.e. without adding carbonate to the leach solution. However, the fresh leach solution can be combined with a recycled solution from a subsequent step of the method before carrying out the leach step 1, whereby some carbonate may be transferred into the solution.

[0037] In some embodiments, the leaching step 1 is carried out with the addition of a carbonate, typically by adding a suitable carbonate reagent, such as an alkali metal carbonate, preferably sodium carbonate (Na2CO3) or potassium carbonate (K2CO3), or a mixture thereof, most suitably consisting at least in part of sodium carbonate. Typically, the carbonate is added in a stoichiometric amount of >0-3 relative to the lithium content of the mineral of this embodiment, most suitably in a stoichiometric amount of >0-2.5 relative to the lithium content of the mineral.

[0038] After leaching step 1, a leach slurry is obtained, which contains lithium primarily in the form of its silicate salt. Since this intermediate product is only slightly soluble in the leach solution, it is obtained in the form of a slurry. The slurry does not contain a large amount of unreacted minerals because it has been converted into, for example, sodium aluminum silicate.

[0039] Under the above leaching conditions, the leached slurry obtained after leaching step 1 will still contain lithium in the solids. Therefore, further processing steps with the purpose of recovering lithium can be carried out on the slurry or, preferably, on the solid fraction separated from the slurry, in particular after alkaline leaching. Therefore, the slurry can be subjected to a solid / liquid separation step (see Figures 2 to 3 In another embodiment, the present invention provides a method for separating the lithium ion battery from the lithium ion battery by using a lithium ion battery as the raw material of the lithium ion battery. The method further comprises the steps of: (a) separating the lithium ion battery from the lithium ion battery; (b) separating the lithium ion battery from the lithium ion battery; and (c) separating the lithium ion battery from ... and (b) separating the lithium ion battery from the lithium ion battery. The method further comprises the steps of: (a) separating the lithium ion battery from the lithium ion battery; and (b) separating the lithium ion battery from the lithium ion battery. The method further comprises the steps of: (a) separating the lithium ion battery from the lithium ion battery; and (b) separating the lithium ion battery from the lithium ion battery.

[0040] Since the liquid fraction obtained from the separation step will also contain some lithium, it is preferred to further utilize the liquid fraction 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 the optional slurrying step 0b to be added to the leach solution before the leaching step.

[0041] As mentioned above, the leaching step 1 may be followed by further treatment steps, primarily with the aim of recovering the lithium, but also with the aim of reducing the amount of impurities in the leach slurry or fractions separated therefrom.

[0042] In one embodiment, particularly if lithium fails to precipitate during the leaching step (not shown), the leaching step may be followed by a step of adding a carbonate or phosphate to the liquid fraction separated from the leach slurry to precipitate the lithium therein as lithium carbonate or lithium phosphate. This lithium carbonate or lithium phosphate may then be further processed as described below or combined with the lithium-containing solid fraction previously separated from the leach slurry.

[0043] In another embodiment (not shown) involving an acid leaching option, the leaching step may be followed by a step in which an alkali metal hydroxide, such as sodium hydroxide (NaOH), is added to the liquid fraction separated from the leach slurry to precipitate and remove solid impurities, such as iron (Fe), aluminum (Al), magnesium (Mg), and calcium (Ca) in the form of hydroxides. The remaining purified lithium-rich solution may then be sent to the carbonate addition step described above or to further processing steps, as described below.

[0044] In a further embodiment, the leaching step may be followed by a carbonization step (see Figure 1-3The present invention also provides a step 3) in which the obtained lithium-containing leached slurry or the solid fraction separated therefrom is reacted with carbon dioxide (CO2) to form lithium bicarbonate. Preferably, the carbon dioxide is used in excess. In this step, the undissolved lithium compounds obtained from the leaching step 1 are converted into soluble lithium bicarbonate and can thus be separated substantially completely from the undesired, undissolved materials.

[0045] The optional carbonization step 3 can be carried out at a temperature of 0 to 50° C., preferably 15 to 40° C., and is typically carried out at a pressure of 1 to 15 bar, more typically 1 to 10 bar, preferably atmospheric pressure. Higher pressures increase the solubility of carbon dioxide in aqueous solutions, but increasing the pressure too much will lead to increased formation of by-products and impurities. Mixing is preferably provided, for example, using any suitable mixer that is very effective in providing mixing for dispersed gases, liquids, and solids.

[0046] The leach slurry or the solid or liquid fractions obtained therefrom may also be further treated to reduce the amount of undesirable components or impurities therein (see Figure 1 and Figure 2 Step 2).

[0047] An alternative is to remove fluoride from the leach slurry or the liquid fraction separated therefrom by reaction with a calcium reagent such as calcium hydroxide or calcium oxide (see Figure 3 In step 2a), the fluoride is reacted to form calcium fluoride, which can be separated from the remaining solution in the solid / liquid separation step 2a'. The reagent dosage is selected to cause only precipitation of fluoride. Therefore, a preferred option is to analyze the fluoride content of the leachate slurry or the liquid fraction separated therefrom before fluoride removal and add approximately the same amount of calcium reagent.

[0048] Another alternative is to provide a silicon removal step, also called a desiliconization step (see Figure 3 Preferably, both fluoride removal and silicon removal are performed, whereby the silicon removal step is performed after the fluoride removal step.

[0049] Preferably, desilication 2b is performed on the liquid fraction separated from the leach slurry, or on a purified form of the leach slurry (e.g. subjected to fluoride removal), and the desilication solution obtained after this step can be recycled to the leaching step 1, or combined with any stream used in further processing steps (e.g. the slurry or solid fraction sent to the optional carbonization step 3), or sent to further impurity removal.

[0050] In the desiliconization step 2b, a calcium reagent, such as calcium oxide (CaO) or calcium hydroxide (Ca(OH)2), can be added to the silicon-containing solution to be treated, so that the silicon reacts with the calcium to form calcium silicate, which is then removed in the subsequent further solid / liquid separation step 2b'. The calcium reagent is preferably added in a stoichiometric amount of 1-2 relative to the silicon (Si) content in the solution. The temperature during this reaction is preferably 80-100°C, and a duration of 1-10 hours is generally sufficient, for example 1-8 hours. The solution separated from the solids in the further separation step 2b' can be recycled, in particular in the leaching step 1, or reused in the preceding optional pulping step 0b, or it can be combined with the leach slurry, or preferably with the leach residue (solid fraction) obtained from the solid / liquid separation step 1' after the leaching step 1, and conveyed to a subsequent treatment, such as the carbonization step 3.

[0051] Thus, in one embodiment, the lithium-containing solution obtained in the present process, such as the solubilized fraction obtained from the carbonization step 3, optionally separated from the residue in the solid / liquid separation step 3', may be subjected to a precipitation or crystallization step (see Figure 1-3 step 4) to recover the lithium in crystalline form, preferably in the form of its carbonate or its hydroxide.

[0052] In addition, before the precipitation step 4, the lithium-containing solution can also be purified (not shown) to remove impurities, such as trivalent and / or divalent metal ions, such as calcium, magnesium, aluminum and iron ions. Preferably, ion exchange is used for purification. Ion exchange can be carried out, for example, by using the method disclosed in Finnish Patent 121785. Typically, the purification of ion exchange is carried out by using a cation exchange resin, which can be, for example, iminodiacetic acid (IDA) or aminophosphonic acid (APA). Such resins are, for example, manufactured under the trade names Amberlite IRC 748 (IDA) and Amberlite IRC 7476 (APA). Typically, a cation exchange resin is a resin having a polystyrene matrix cross-linked with divinylbenzene containing aminophosphine groups.

[0053] The above-mentioned precipitation step 4 results in the formation of a solid lithium compound or precipitate, which can be crystallized into pure crystals, preferably pure crystals of lithium carbonate or lithium hydroxide.

[0054] If lithium carbonate is produced, the precipitation step 4 comprises heating the slurry or solution containing lithium bicarbonate, preferably to a temperature of 70-100° C., to decompose the bicarbonate and crystallize out the lithium carbonate.

[0055] During this carbonate precipitation reaction, a slurry containing water and precipitated lithium carbonate is formed. In a solid / liquid separation step, the solid lithium carbonate is separated from the resulting slurry, yielding battery-grade lithium carbonate. Standard battery-grade lithium carbonate contains at least 99.5% lithium carbonate. However, using the methods described herein, it is possible to produce high-quality battery-grade lithium carbonate containing at least 99.99% lithium carbonate.

[0056] If lithium hydroxide is prepared, the precipitation step 4 comprises reacting a slurry or solution containing lithium obtained from the dissolution process or optionally pretreated with a hydroxide reagent, i.e. an alkaline earth metal hydroxide, to produce a slurry containing lithium hydroxide in soluble form. The alkaline earth metal hydroxide used is preferably selected from calcium hydroxide and barium hydroxide, more preferably calcium hydroxide, which is optionally prepared by reacting calcium oxide (CaO) in an aqueous solution. The alkaline earth metal hydroxide may also be mixed with water or an aqueous solution before being used in the reaction. Also in this reaction, a recycled mother liquor obtained from a subsequent crystallization may be used. The hydroxide precipitation is typically carried out at a temperature of 10-100°C, preferably 20-60°C, and most preferably 20-40°C. Typically, the hydroxide precipitation is carried out at atmospheric pressure. The presence of the alkaline earth metal hydroxide and the above-mentioned process conditions result in the formation of lithium hydroxide, with carbonates of alkaline earth metals formed as by-products.

[0057] After the optional solid / liquid separation step 4' (preferably using filtration or by conveying the slurry or solution to a thickener), a relatively high purity lithium hydroxide-containing solution is obtained. However, this lithium hydroxide-containing slurry or solution can also be purified before crystallization, preferably using a purification technology based on dissolved ions and components, more preferably including ion exchange or membrane separation, or both, most preferably by using a cation exchange resin, particularly a selective cation exchange resin. Ion exchange can be carried out, for example, as described above. Membrane separation can be carried out using a semi-permeable membrane that separates ions or other dissolved compounds from an aqueous solution. More precisely, membrane separation can be used to classify the size of dissolved ions and compounds (depending on the pore size of the membrane material) and / or their charge (depending on the surface charge of the membrane material). Positive surface charge repels cations (having a stronger repulsive effect on multivalent cations) and attracts anions, and vice versa. These phenomena will enable purification of, for example, multivalent metal cations, complexed substances (such as aluminum hydroxide complexes), polymeric substances (such as dissolved silica) and larger anions (such as sulfate and carbonate ions) from lithium hydroxide solution. Based on the above, it is particularly preferred to combine membrane separation with ion exchange, and it is most appropriate to improve the removal of polyvalent metal cations by first performing membrane separation and then performing ion exchange.

[0058] Crystals of lithium hydroxide monohydrate can be recovered from a solution containing lithium hydroxide by crystallization. Crystallization is typically performed by heating the solution to a temperature approximately at the boiling point of the solution to evaporate the liquid, or by recrystallizing the monohydrate from a suitable solvent. The methods described herein enable the production of pure lithium hydroxide monohydrate in excellent yield and purity in a continuous and simple process, typically providing battery-grade lithium hydroxide monohydrate crystals.

[0059] In a preferred embodiment of the process, crystallization, either for the production of carbonate or hydroxide crystals, is typically followed by another solid-liquid separation step, preferably using filtration, or by passing the slurry or solution to a thickener.

[0060] In a further embodiment, the crystallization mother liquor or a portion thereof remaining after recovering the crystals in the solid / liquid separation step can be recycled to one or more previous steps, such as the optional carbonization step 3 or the optional precipitation step 4. In an alternative, the mother liquor is recycled to the leaching step 1, or the optional previous pulping step 0b, to participate in any pH adjustment therein, thereby reducing the need for further addition of hydroxide reagents. In another alternative, in connection with the hydroxide precipitation route, the mother liquor is recycled to the hydroxide precipitation step for preparing lithium hydroxide. In addition, the carbon dioxide used in the optional carbonization step 3 can be separated from the crystallization mother liquor and recycled back to the carbonization step 3.

[0061] The advantage achieved by recycling to a previous step with lower alkalinity (e.g., lithium precipitation step 4) is that some impurities in the crystallization mother liquor (e.g., aluminum and silicon) have an increasing solubility with increasing alkalinity (e.g., caused by an increase in lithium hydroxide concentration), so that these alkali-soluble impurities can be removed by recycling them in solution to a step with lower alkalinity. For example, in the hydroxide precipitation step, these impurities form sparingly soluble compounds (e.g., aluminum hydroxide) and can be discarded with the solids after the subsequent separation step. Without these recycling options, impurities would typically concentrate in the crystallization and contaminate the product.

[0062] It should be understood that the embodiments of the present invention disclosed herein are not limited to the specific structures, process steps or materials disclosed herein, but extend to equivalents thereof that will be recognized by those skilled in the relevant art. It should also be understood that the terminology used herein is for the purpose of describing specific embodiments and is not intended to be limiting.

[0063] 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, the 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.

[0064] As used herein, for convenience, multiple items, structural elements, constituent elements and / or materials can be listed in a general column. However, these lists should be understood as each member in the list being individually identified as a separate and unique member. Therefore, in the absence of an opposite indication, any single member in the list should not be interpreted as being in fact equivalent to any other member in the same list simply based on its presentation in a common group. In addition, various embodiments and examples of the present invention can be mentioned herein together with alternatives to its various parts. It should be understood that such embodiments, embodiments and alternatives should not be interpreted as being in fact equivalent to each other, but should be regarded as independent and separate presentations of the present invention.

[0065] In addition, the described features, structures or characteristics can be combined in any suitable manner in one or more embodiments. In the following description, many specific details, such as examples of lengths, widths, shapes, etc., are provided to provide a thorough understanding of the embodiments of the present invention. However, those skilled in the relevant art will recognize that the present invention can be implemented without one or more of the specific details, or using other methods, components, materials, etc. to implement. In other cases, well-known structures, materials or operations are not shown or described in detail to avoid confusing various aspects of the present invention.

[0066] Although the above examples illustrate the principles of the present invention in one or more specific applications, it will be apparent to those skilled in the art that many modifications may be made in form, usage, and implementation details without exercising inventive power and without departing from the principles and concepts of the present invention. Therefore, it is not intended that the present invention be limited except by the following claims.

[0067] As used herein, the verbs "to comprise" and "to include" are open limitations that neither exclude nor require the presence of unrecited features. The features recited in the appended claims are mutually freely combinable unless expressly stated otherwise. Furthermore, it should be understood that the use of "a" or "an" throughout this document, i.e., in the singular, does not exclude a plural reference.

[0068] Example

[0069] Example 1 - Leaching of calcined spodumene

[0070] The calcined spodumene samples were leached under the conditions shown in Table 2 below.

[0071] Table 2.

[0072]

[0073]

[0074] Test 1:

[0075] The sample from Test 1 was calcined at 1075°C and then leached as described above. During the leaching process, multiple samples were extracted from the solution and solids and analyzed. The results are shown in Table 3 below.

[0076] Table 3.

[0077]

[0078] The final filter cake of the Test 1 sample was also carbonated at a temperature of 40° C. with a solid content of 200 g / L for 8 h using a CO2 gas feed of 1000 ml / min. The results are shown in Table 4 below.

[0079] Table 4.

[0080]

[0081]

[0082] Test 2:

[0083] The sample from Test 2 was calcined at 1075°C and then leached as shown in Table 2 above. During the leaching process, multiple samples were taken from the solution and solids and analyzed. The results are shown in Table 5 below.

[0084] Table 5.

[0085]

[0086] Test 3:

[0087] The sample from Test 3 was calcined at 1075°C and then leached as shown in Table 2 above. During the leaching process, multiple samples were taken from the solution and solids and analyzed. The results are shown in Table 6 below.

[0088] Table 6.

[0089]

[0090]

[0091] Test 4:

[0092] The sample from Test 4 was calcined at 1075°C and then leached as shown in Table 2 above. During the leaching process, multiple samples were extracted from the solution and solids and analyzed. The results are shown in Table 7 below.

[0093] Table 7.

[0094]

[0095]

[0096] Test 5:

[0097] The sample from Test 5 was calcined at 1075°C and then leached as shown in Table 2 above. During the leaching process, multiple samples were taken from the solution and solids and analyzed. The results are shown in Table 8 below.

[0098] Table 8.

[0099]

[0100] Test 6:

[0101] The sample from Test 6 was calcined at 1075°C and then leached as shown in Table 2 above. During the leaching process, multiple samples were taken from the solution and solids and analyzed. The results are shown in Table 9 below.

[0102] Table 9.

[0103]

[0104]

[0105] Test 7:

[0106] The sample from Test 7 was calcined at 1075°C and then leached as shown in Table 2 above. During the leaching process, multiple samples were taken from the solution and solids and analyzed. The results are shown in Table 10 below.

[0107] Table 10.

[0108]

[0109]

[0110] Test 8:

[0111] The sample from Test 8 was calcined and then leached as shown in Table 2 above. During the leaching process, multiple samples were taken from the solution and solids and analyzed. The results are shown in Table 11 below.

[0112] Table 11.

[0113]

[0114]

[0115] Example 2 - Leaching of calcined ferrolithite

[0116] The lithophile mica samples were calcined and leached under the conditions shown in Table 12 below.

[0117] Table 12.

[0118] unit Test 9 Test 10 Calcination temperature ℃ 900 950 Leaching temperature ℃ 95 95 Leaching time h 5 10 Solid content g / L 200 250 Add 500g / L NaOH mL / g 2.0 2.0

[0119] Test 9:

[0120] The lepidolite sample from Test 9 was calcined and leached as shown in Table 12 above. During the leaching process, multiple samples were extracted from the solution and solids and analyzed. The results are shown in Table 13 below.

[0121] Table 13.

[0122]

[0123] Test 10:

[0124] The lepidolite sample from Test 10 was calcined and leached as shown in Table 12 above. During the leaching process, multiple samples were extracted from the solution and solids and analyzed. The results are shown in Table 14 below.

[0125] Table 14.

[0126]

[0127] Example 3 - Leaching of calcined lepidolite

[0128] The lepidolite samples were calcined and leached under the conditions shown in Table 15 below.

[0129] Table 15.

[0130]

[0131] Test 11:

[0132] The lepidolite sample from Test 11 was calcined and leached as shown in Table 15 above. During the leaching process, multiple samples were extracted from the solution and solids and analyzed. The results are shown in Table 16 below.

[0133] Table 16.

[0134]

[0135] Test 12:

[0136] The lepidolite sample from Test 12 was calcined and leached as shown in Table 15 above. During the leaching process, multiple samples were extracted from the solution and solids and analyzed. The results are shown in Table 17 below.

[0137] Table 17.

[0138]

[0139]

[0140] Test 13:

[0141] The lepidolite sample from Test 13 was calcined and leached as shown in Table 15 above. During the leaching process, multiple samples were extracted from the solution and solids and analyzed. The results are shown in Table 18 below.

[0142] Table 18.

[0143]

[0144] Test 14:

[0145] The lepidolite sample from Test 14 was calcined and leached as shown in Table 15 above. During the leaching process, multiple samples were extracted from the solution and solids and analyzed. The results are shown in Table 19 below.

[0146] Table 19.

[0147]

[0148] Example 4 - Leaching of calcined petalite

[0149] The petalite samples were calcined and leached under the conditions shown in Table 20 below.

[0150] Table 20.

[0151] unit Test 15 Calcination temperature ℃ 1180 Leaching temperature ℃ 95 Leaching time h 12 Solid content g / L 250 Add 500g / L NaOH mL / g 2.0

[0152] Test 15:

[0153] The petalite sample from Test 15 was calcined and leached as shown in Table 20 above. During the leaching process, multiple samples were extracted from the solution and solids and analyzed. The results are shown in Table 21 below.

[0154] Table 21.

[0155]

[0156] Example 5 - Acid Leaching of Calcined Lithops

[0157] The lithophile mica samples were calcined and leached under the conditions shown in Table 22 below.

[0158] Table 22.

[0159] unit Test 16 Test 17 Calcination temperature ℃ 950 950 Leaching temperature ℃ 30 70-75 Leaching time h 12 12 Solid content g / L 200 180 <![CDATA[H2SO4 solution]]> mol / L 5 5

[0160] Test 16:

[0161] The lepidolite sample from Test 16 was calcined and leached as shown in Table 22 above. During the leaching process, multiple samples were extracted from the solution and solids and analyzed. The results are shown in Table 23 below.

[0162] Table 23.

[0163] sample Li Al Si K <![CDATA[F - ]]> mg / l mg / l mg / l mg / l mg / l initial 180 924 32 384 347 1h 798 6840 24 4810 2690 2h 1060 9180 22 6670 3700 4h 1290 11600 36 8160 4690 6h 1470 13000 21 9380 5290 8h 1620 13900 20 10300 5690 10h 1690 14700 20 10700 6030 Final filtrate (12h) 1730 15200 19 11000 6240

[0164] Test 17:

[0165] The lepidolite sample from Test 17 was calcined and leached as shown in Table 22 above. During the leaching process, multiple samples were extracted from the solution and solids and analyzed. The results are shown in Table 24 below.

[0166] Table 24.

[0167] sample Li Al Si K <![CDATA[F - ]]> mg / l mg / l mg / l mg / l mg / l initial 275 1670 119 981 536 1h 1740 15700 28 11500 6640 2h 1740 15800 27 11800 6760 4h 1900 17300 25 13100 7300 6h 2000 17800 24 13900 7490 8h 2030 17900 22 13900 7450 Final filtrate (12h) 2100 18600 14 14600 7730

[0168] Example 6 - Acid Leaching of Calcined Lepidolite

[0169] The lepidolite samples were calcined and leached under the conditions shown in Table 25 below.

[0170] Table 25.

[0171] unit Test 18 Test 19 Calcination temperature 920 920 Leaching temperature ℃ 30 70-75 Leaching time h 12 12 Solid content g / L 200 200 <![CDATA[H2SO4 solution]]> mol / L 5 5

[0172] Test 18:

[0173] The lepidolite sample from Test 18 was calcined and leached as shown in Table 25 above. During the leaching process, multiple samples were extracted from the solution and solids and analyzed. The results are shown in Table 26 below.

[0174] Table 26.

[0175] sample Li Al Si K mg / l mg / l mg / l mg / l initial 1150 7600 75 4290 1h 1770 13600 28 8610 2h 1820 14700 24 9130 4h 2030 14700 24 9390 6h 2280 15600 25 10000 8h 2420 15800 21 10200 10h 2490 16300 19 10300 Final filtrate (12h) 2630 16600 60 10300

[0176] Test 19:

[0177] The lepidolite sample from Test 19 was calcined and leached as shown in Table 25 above. During the leaching process, multiple samples were extracted from the solution and solids and analyzed. The results are shown in Table 27 below.

[0178] Table 27.

[0179] sample Li Al Si K mg / l mg / l mg / l mg / l initial 819 4410 108 2410 1h 2880 20400 27 13100 2h 2990 20500 21 13200 4h 3360 22500 21 14500 6h 3490 23300 22 14600 8h 3740 23900 19 15100 10h 3920 24600 13 15800 Final filtrate (12h) 3950 24900 12 15800

[0180] As these results demonstrate, the process of the present invention using an atmospheric pressure leaching step and low temperatures is more versatile than known processes and provides comparable extraction yields despite the mild conditions.

[0181] Industrial Applicability

[0182] The method of the present invention may be used as part of, and improve upon, any hydrometallurgical process for recovering lithium products from lithium-containing minerals.

[0183] In particular, the novel leaching step described herein can leach lithium concentrate without the use of expensive autoclaves. Furthermore, the leaching temperature can be kept lower than in prior art processes.

[0184] Reference Signs List

[0185] The method of the present invention comprises a leaching step 1 carried out at atmospheric pressure at a temperature below the boiling point of the leaching solution. Thus, the method of the present invention comprises the following steps:

[0186] 1 atmosphere leaching

[0187] In various embodiments, the method may further include some further steps, such as Figure 1-3 Based on the accompanying drawings, any one of the following optional steps may also be included in the method, or a combination of two or more such additional steps:

[0188] 0a Calcination step

[0189] 0b Pulping step

[0190] 1' Solid / liquid separation after leaching step 1

[0191] 2. Separation of impurities or by-products from the leach slurry or solution, optionally in the form of:

[0192] 2a Fluoride Removal

[0193] 2a' Solid / liquid separation after fluoride removal

[0194] 2b Silicon Removal

[0195] 2b' Solid / liquid separation after silicon removal

[0196] 3,4 Convert the lithium in the slurry or solid fraction into a readily precipitable form, typically the following:

[0197] 3 Carbonization

[0198] 3' Optional solid / liquid separation after carbonization

[0199] 4 Lithium precipitation / crystallization

[0200] Optional solid / liquid separation after 4'Li precipitation / crystallization

[0201] Reference List

[0202] Patent Literature

[0203] FI 121785 B

[0204] US 9255012 B2

[0205] US11292725 B2

Claims

1. A method for treating lithium-containing concentrate, the method comprising leaching in a leaching solution at a temperature below the boiling point of the leaching solution and at atmospheric pressure for 4 to 48 hours to obtain a lithium-containing slurry.

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

3. A process as claimed in claim 1 or 2, wherein the lithium-containing concentrate comprises one or more lithium-containing minerals in calcined form, and thus preferably has been calcined at a temperature of 800-1200°C, more preferably 900-1150°C, even more preferably 900-1100°C.

4. A method as claimed in any one of the preceding claims, wherein the leaching step is carried out as water leaching, acid leaching or alkaline leaching.

5. A method according to any one of the preceding claims, wherein the leaching step is carried out as alkaline leaching, preferably in a leaching solution containing an alkali metal hydroxide.

6. The method according to any one of the preceding claims, wherein the leaching step is carried out in a leaching solution containing an alkali metal hydroxide selected from the group consisting of sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH)2) and lithium hydroxide (LiOH), or mixtures thereof, preferably sodium hydroxide.

7. The process according to claim 5 or 6, wherein the alkali metal hydroxide is added to the leaching solution at a hydroxide ion content of 0.1-250 g / l, preferably 1-200 g / l, more preferably 30-150 g / l, even more preferably 50-120 g / l.

8. The method according to any one of the preceding claims, wherein the pH level of the leach solution is adjusted to 11.5-14, preferably 12-14.

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

10. A method according to any one of the preceding claims, wherein the leaching step is carried out in a slurry formed from the lithium-containing concentrate and the leach solution, the slurry having a solids content of 100-500 g / L, preferably 150-350 g / L, more preferably 200-300 g / L.

11. A method as claimed in any one of the preceding claims, wherein the leaching step is carried out at a temperature of from 20°C to below 100°C, preferably from 20°C to 95°C.

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

13. A method as claimed in any one of the preceding claims, wherein the leaching step is carried out in the absence of a carbonate reagent in a leach solution to which no carbonate is added.

14. The method of any one of claims 1 to 12, wherein the leaching solution further contains a carbonate reagent, such as sodium carbonate (Na2CO3) or potassium carbonate (K2CO3), preferably the stoichiometric amount of the carbonate reagent relative to the lithium content of the mineral is at most 3, most suitably >0-2.5 relative to the lithium content of the mineral.

15. A method as claimed in any one of the preceding claims, wherein a solid / liquid separation step is performed to separate a solid fraction and a liquid fraction from the leachate slurry.

16. A process as claimed in any one of the preceding claims, wherein the liquid fraction is separated from the leach slurry and recycled back to the leaching step and combined with the leach solution.

17. The method as claimed in any one of the preceding claims, wherein the lithium-containing slurry obtained or the solid fraction separated therefrom is further treated in a carbonization step by reacting it with carbon dioxide (CO2), preferably in excess.

18. A process as claimed in any one of the preceding claims, wherein the lithium-containing slurry obtained or the solid fraction separated therefrom is solubilised in a carbonisation step and the solubilised fraction is subsequently subjected to a crystallisation step to recover the lithium in crystalline form, preferably in the form of its carbonate or its hydroxide.

19. A method as claimed in any one of the preceding claims, wherein the obtained lithium-containing slurry or a solid or liquid fraction separated therefrom is further treated before or after carbonising the lithium in the slurry to remove one or more impurities therefrom.

20. A process as claimed in claim 19, wherein fluoride is removed from the slurry or solid fraction by reacting it with a calcium reagent such as calcium hydroxide or calcium oxide, whereby the fluoride is separated as calcium fluoride.

21. A process as claimed in claim 19 or 20, wherein silicon is removed from the slurry or solid or liquid fraction by reaction with a calcium reagent such as calcium hydroxide or calcium oxide, whereby the silicon is separated as solid calcium silicate.

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