Calcination and atmospheric leaching of lithium minerals

Abstract

According to the present invention, there is provided a method for processing lithium-containing minerals into fractions, the method including a calcination with additives, followed by an atmospheric leaching at an elevated temperature in an alkaline leaching solution.

Description

CALCINATION AND ATMOSPHERIC LEACHING OF LITHIUM MINERALSFIELD

[0001] The present invention relates to a method for processing lithium-containing minerals into fractions, the method including a calcination with additives, followed by an atmospheric leaching in an alkaline leaching solution.BACKGROUND

[0002] Lithium is included in compounds used in several industrial applications. The lithium 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 some form of a leaching step, such as an acid leaching, a water leaching, or a high-pressure alkali leaching.

[0003] All of these alternatives for the leaching step have been developed further to provide a more efficient extraction of lithium and other components of the mineral contained in the ore or the brine. However, less effort has been spent on developing the calcination. Some options exist also for this calcination step, such as shown in CN 101974678 A, which suggests carrying out the calcination of a lepidolite material in the presence of an additive that may include a calcium salt. However, this publication describes an overall process, with a mildly alkaline leaching solution, that will result in fractions from which the lithium and other metals are difficult to separate from the impurities.

[0004] One of the issues of existing calcination and leaching processes is that the silicon (Si) included in most lithium-containing minerals, and the fluoride (F) of some lithium-containing minerals is volatilized in the calcination, causing challenges in off-gas treatments, while both fluorides and silicon (Si) of these minerals are released from the minerals in high amounts, causing further challenges in the separations and purifications that typically follow the leaching step of the process. Therefore, there is a need for newprocesses, wherein lithium can be effectively separated from by-products and impurities, such as from fluoride and silicon compounds.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 processing lithium-containing mineral raw-materials in a calcination step and a leaching step.

[0007] According to a second aspect, there is provided a method, wherein a calcination is carried out with additives intended for limiting the volatilization of the mineral components.

[0008] According to a third aspect, there is provided a method, wherein a leaching is carried out in conditions that will provide an advantageous separation of components into dissolved and solid components.

[0009] The present invention thus relates to a method for processing lithium- containing minerals into fractions, the method comprising the steps of calcining the lithium-containing mineral in the presence of one or more calcium salts, carrying out an atmospheric leaching of the obtained calcine at a pH of 11.5 or higher, and separating the leached slurry into fractions.

[0010] The invention is based on the discovery that the calcination of a lithium mineral in the presence of one or more calcination additives will reduce the amount of fluoride that is volatilized during the calcination, and reduce the amount of silicon and fluoride carried to the filtrate after the leaching. This will further facilitate the separation of the lithium from the fluorides and silicon compounds.

[0011] Significant advantages are achieved using the invention. Among others, excellent extraction rates are achieved for lithium, with almost 100% of the lithium ending up in the solid fraction after the leaching step has been carried out, whereafter the solid fraction can be further separated into sub-fractions, e.g. to provide pure metal products.Likewise, smaller amounts of fluorides and silicon end up in the leaching slurry, thus facilitating an efficient separation of these via the leach solution.BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIGURE 1 illustrates the process configuration in accordance with at least some embodiments of the present invention, with block 1 representing the calcination step of the process, and block 2 representing the leaching step.

[0013] FIGURE 2 illustrates a process configuration of an advantageous embodiment, with additional blocks 3 and 4 representing optional further steps of the process of the invention, providing further separations of mineral components into smaller fractions. The dotted arrows represent the possible recycling options.

[0014] FIGURE 3 illustrates a process configuration of a further advantageous embodiment, with additional block 2a representing an optional pulping step, blocks 2’ and 3’ representing solid / liquid separation steps, block 3a representing one preferred alternative sub-step of the further separation step 3, and blocks 4a and 4b representing carbonation and crystallization steps, respectively, forming alternative sub-steps of the further separation step 4.EMBODIMENTS

[0015] 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. The “leaching” is, in turn, used to dissolve certain components of the calcined mineral, some known processes aiming for leached (or solubilized) lithium salts, whereas some processes aim at “extracting” the lithium from the leach slurry into the solids.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. Some of the above minerals contain fluoride, which also needs to be separated as an impurity, for example in the same desilication.

[0016] The present invention relates to a method for processing lithium-containing minerals into fractions (see Fig. 1), the method comprising the steps of:- subjecting a lithium-containing mineral to a calcination step 1 in the presence of one or more calcination additive(s) selected from calcium salts,- subjecting the thus obtained calcine to an atmospheric leaching step2 at an elevated temperature in a leaching solution having analkaline pH of 11.5 or higher, measured at room temperature, before increasing the temperature, and- obtaining two or more separate fractions from the obtained leach slurry, such as a liquid fraction, containing by-products that can be recovered as separate recovered fractions, and a solid fraction, containing lithium and metals that can be further recovered as separate product fractions.

[0017] Some alternative process configurations are shown in the Figures, with Fig. 1 illustrating one general embodiment, and Figs 2 and 3 illustrating preferred embodiments.

[0018] The lithium-containing starting material is preferably obtained from a lithium-containing ore, concentrate or recycled material, preferably being a concentrate, and is typically in the form of a lithium-containing mineral, such as the ones mentioned above in Table 1, or it can be one of the separately listed clay minerals, but is preferably selected from spodumene, petalite, lepidolite, or zinnwaldite, more preferably being spodumene, lepidolite or zinnwaldite.

[0019] Before or during the calcination step 1, preferably before, the minerals of the starting material(s) are mixed with one or more calcination additive(s) including calcium salt(s). These one or more calcium salts are preferably selected from calcium carbonate (CaCCh), calcium hydroxide (Ca(OH)2), calcium oxide (CaO), calcium sulphate (CaSC ) or calcium chloride (CaCh), preferably being one or more of calcium carbonate, calcium hydroxide, or calcium oxide, and most suitably containing at least calcium carbonate or calcium hydroxide. These calcium salt(s) are preferably added to the lithium-containing mineral, in a ratio of 1: 1 - 10:1 of mineral concentrate : calcium salt, more preferably in a ratio of 3: 1 - 10: 1, and most suitably in a ratio of 3.5:1 - 6: 1. These additives, among others, lead to less agglomeration and less hard smelting. Further, they lead to a reduced volatilization of the fluoride during the calcination, whereby the dosage of the calcium salt(s) can in another alternative be determined as a ratio of calcium ion (Ca) to fluoride ion (F) in the lithium-containing mineral (i.e. a Ca / F ratio) of 0.5-3 mol / mol, preferably 0.7-1.5 mol / mol.

[0020] In an embodiment, the calcination step of the method (see step 1 of Figs. 1, 2 and 3) is carried out at a temperature of 850 - 1200 °C, more preferably 900 - 1200 °C,and most suitably at 900 - 1100 °C. The duration of the calcination step 1 may be, for example 1 min - 5 h, or preferably 30 min - 3 h.

[0021] The material obtained from the calcination, i.e. the calcine, may be carried directly to the leaching step (see step 2 of Figs. 1, 2 and 3). Alternatively, a separate pulping step (step 2a of Fig. 3) may be carried out before the leaching step 2, wherein the calcined mineral material containing lithium, i.e. the calcine, is mixed into an aqueous solution, optionally in the presence of one or more alkali metal reagents, typically used in excess, for producing a slurry containing lithium, preferred alkali metal reagents being a carbonate, such as sodium carbonate, or a hydroxide, such as sodium hydroxide, or a mixture of these, most suitably being a hydroxide. However, the slurry can also be formed as a part of the leaching step 2, and any additions of leaching chemicals can take place in either the optional pulping step 2a or in the leaching step 2.

[0022] The material led to the leaching step 2 typically contains a mineral calcine of varying particle size, as the material does not need to be subjected to a grinding step.

[0023] In one alternative, a mixture of the calcined mineral and an additional uncalcined mineral fraction is processed in the leaching step 2. The uncalcined mineral can be, for example petalite or a different crystallographic structure of spodumene, such as alpha-spodumene.

[0024] As indicated above, the leaching step 2 is carried out as an atmospheric leaching. In such an atmospheric leaching of lithium-containing minerals, it is sufficient for the leaching temperatures to be below the boiling point of the leach solution. Thus, the leaching step 2 may be carried out at a temperature of 80 - 100 °C, a preferred temperature being 90-95 °C.

[0025] For the pressure during the leaching step 2, atmospheric pressure is sufficient. However, the pressure typically adjusts upwards with a raised temperature. Hence, the pressure might adjust to a level slightly above atmospheric pressure (e.g. to 1.1 - 3 bar) at higher leaching temperatures (e.g. at ~100°C).

[0026] The used leaching solution is an alkaline leaching solution having a pH of 11.5 or higher, preferably a leaching solution containing an alkali metal hydroxide.

[0027] In an embodiment, the pH level required in the leaching step 2 is achieved by adjusting the pH using a hydroxide reagent, such as an alkali metal hydroxide or an alkaline earth metal hydroxide, which preferably is selected from sodium hydroxide (NaOH), potassium hydroxide (KOH), lithium hydroxide (LiOH), calcium oxide (CaO), or calcium hydroxide (Ca(OH)2), or a mixture thereof, preferably being sodium hydroxide (NaOH) or potassium hydroxide (KOH). This hydroxide can be added directly into the leaching solution or into the slurry formed in the optional pulping step 2a, and preferably thus forming a leaching solution having a hydroxide content of 0.1 - 250 g / L, preferably 1 - 200 g / L, more preferably 30 - 80 g / L, and even more preferably 40 - 50 g / L, or 0.006 - 14 mol / L. This will give the solution the required high pH, typically being adjusted using said alkali metal hydroxide to a level of 11.5 - 14, preferably to 12 - 14. However, at such levels, contents of alkali reagents are more reliable factors to measure than pH levels. Preferably, the hydroxide content may be in the range of 0.6 - 9 mol / L, more preferably 1 -6 mol / L

[0028] With the above conditions, the leaching step 2 can be carried out for a period of 1 - 48 h, preferably 1 - 36 h, most suitably for a period of 10 - 24 h. Thus, in some embodiments, the leaching time is from 1 h, 5 h, or 10 h, up to 24 h, 30 h, 36 h, 40 h or 48 h.

[0029] Although alkaline leaching in some commonly known 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, before carrying out the leaching step 2, the fresh leaching solution can in one alternative be combined with a recycled solution from a subsequent step of the process, whereby some carbonate might be carried to the leaching step 2 even without separate carbonate addition.

[0030] In a specific embodiment, a calcined lithium-containing mineral selected from the herein mentioned minerals, is in the leaching step 2 extracted from the mineral using an alkaline leaching solution in the presence of carbonate. The carbonate is typically added as a suitable carbonate reagent, such as an alkali metal carbonate, preferably sodium carbonate (Na2COa) or potassium carbonate (K2CO3), or a mixture thereof, most suitably being at least partly composed of sodium carbonate. Further, this carbonate may be added in a stoichiometry of >0-3.5 in relation to lithium content in the mineral of thisembodiment, preferably in a stoichiometry of >0-2.5 in relation to the lithium content in the mineral, and most suitably in a stoichiometry of 1.5 - 2.5.

[0031] In the leaching step 2, the lithium of a lithium-containing mineral, such as lithium oxides or lithium aluminium silicates of the mineral (e.g. the LiKAhF2Si3O9 for lepidolite) are converted in the presence of the hydroxide ions (OH ) of the leaching solution, e.g. into lithium metasilicate (I^SiCh), leaving analcime as a by-product.

[0032] After the leaching step 2, a leach slurry is obtained, which contains lithium in converted form, such as the form of its silicate, as an extract. Thus, within the context of the present disclosure, the lithium extract is referring to lithium that has been converted to such form (i.e. a slurry, or a solid or liquid fraction separated therefrom), wherein lithium is liberated from the structure of the initial mineral of the starting material, i.e. feed material.

[0033] Since this lithium silicate is only sparingly soluble in the leaching solution, it is initially obtained in the form of a slurry. The slurry does not contain significant amount of unreacted mineral, since this mineral 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 2 is 90 to 99 weight-%, calculated from the initial amount of lithium in the mineral.

[0034] The leach slurry obtained from the leaching step 2 can be used as such, and thus be conducted directly to any subsequent reaction, e.g. to achieve further solubilisation.

[0035] In a preferred embodiment, however, the leach slurry is conducted to a postleaching solid / liquid separation step 2’ (a first solid / liquid separation step) to provide a lithium-containing solid, and a liquid that contains among others undesired compounds, such as sodium silicates and other impurities, such as fluorides, but also further lithium compounds in solubilized form.

[0036] Any solid / liquid separation steps mentioned herein can be carried out, for example, using filtration, or by routing the slurry or solution to a thickener.

[0037] In another embodiment, the obtained slurry containing lithium, or a solid or liquid fraction separated therefrom, is processed further (see steps 3 or 4 of Fig. 3) to remove one or more impurities therefrom. Preferably, a liquid fraction obtained from thepost-leaching solid / liquid separation 2’ is used in a liquid-side further processing step 3 (a first further processing step 3), typically followed by a further solid / liquid separation step 3’ (or a second solid-liquid separation step). This further processing step 3 can be carried out for example as a desilication step 3a, 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 therein, such as the fluoride or the silicon, which can then be removed in said further solid / liquid separation step, or a post-desilication solid / liquid separation step 3’ or 3a’ (or said second solid-liquid separation step).

[0038] A further alternative is to separately remove fluorides and silicon from the leach slurry, or from a liquid fraction separated therefrom, by reacting with a calcium reagent, such as calcium hydroxide or calcium oxide, in two stages, whereby the fluoride reacts into calcium fluoride in a first reagent addition stage, which fluoride can be separated from the remaining solution in a solid / liquid separation step (not shown in the Figs.), whereafter the desilication step 3a mentioned above can be carried out, and, again, be followed by said post-desilication solid / liquid separation step 3a’.

[0039] To maintain these separate stages, and obtain separate fluoride and silicon fractions, a preferred option is to analyze the fluoride content of the leach slurry before fluoride removal, or of a liquid fraction separated from the leach slurry, and add about an equivalent amount of calcium reagent to achieve the expected fluoride separation, whereafter further calcium reagent may be added to separately obtain a silicate fraction.

[0040] A desilicated solution obtained after this further processing step(s) 3, can either be recycled to the leaching step 2 or the optional pulping step 2a, or be combined with any stream used in subsequent further processing steps 4, such as a slurry or solid fraction carried to an optional carbonization step 4a (see options shown by the dotted lines and arrows of Figs. 2 and 3), or it can be carried to a impurity removal or be discarded.

[0041] The calcium reagent is preferably added to the desilication step 3 or 3a in a stoichiometry of 1 - 2 in relation to the silicon (Si) content of the slurry or solution. The temperature during this desilication 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 3’ may be recycled, particularly to be reused in the leaching step 2, or in the preceding optional pulping step 2a, or it may be combined with the leach slurry, or preferably with the leach residue (solids fraction) obtained from a post-leachingsolid / liquid separation step 2’, and carried to subsequent processing step 4, such as a carbonization step 4a, which will provide solubilized lithium salt, while other metals remain in solid form.

[0042] In a further embodiment, the leaching step 2 is followed, either directly or after the separation step 2’ described above, by a further processing step 4 (see Figs. 2 or 3), which most suitably includes a carbonization step 4a, also called a bicarbonization step due to the reaction taking place. In the optional carbonization step 4a, the obtained leach slurry or a leach residue separated therefrom, optionally combined with a desilicated solution obtained from solid / liquid separation step 3’, is reacted with carbon dioxide (CO2), preferably carbon dioxide in an excess amount. The yet unsolubilized lithium compounds obtained from the leaching step 2 are thus transformed to solubilized lithium hydrogen carbonate, and are thus capable of essentially complete separation from undesirable, undissolved materials.

[0043] This optional carbonization step 4a 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 will also cause an increased risk for 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.

[0044] The lithium-containing slurry or solution obtained from the processing step 4 may be carried further to subsequent recovery steps (not shown in Figs) for converting the lithium in the slurry or solution into an insoluble compound, i.e. precipitating or crystallizing it.

[0045] Such a precipitation or crystallization may be preceded by a further step of separating any insoluble agents from the slurry or solution obtained from the processing step 4, typically performed by filtering, whereafter a precipitation step 4b is carried out on a liquid fraction.

[0046] Also, a purification (not shown in the Figures) can be carried out before the precipitation step 4b 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,from which a liquid fraction is recovered. 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 4b 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 4b 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, 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 4b involves reacting the slurry or solution containing lithium, obtained from the previous steps, 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 theformation of lithium hydroxide, with the carbonate of the alkaline earth metal forming as a by-product. After an optional solid / liquid separation, 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.

[0051] In an embodiment, the lithium hydroxide -containing slurry or solution can be purified before crystallization.

[0052] This optional purification step (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, carried out before the precipitation step 4b. 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.

[0053] 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.

[0054] In preferred embodiments, 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.

[0055] In further embodiments, the crystallization mother liquor remaining after the crystals have been recovered in a solid / liquid separation, or a fraction thereof, can be recycled to one or more preceding steps of the herein described method, or to 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 leaching step 2, or the optional preceding pulping step 2a, 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 of the preparation of lithium hydroxide. In a further alternative, the mother liquor is recycled back to the crystallization of the precipitation step 4b. Also, the carbon dioxide used in the optional carbonization step 4a can be separated from the crystallization mother liquor, and be recycled back to the carbonization step 4a.

[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 ontheir 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 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.

[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 - Calcination of lithium-containing materials

[0062] A zinnwaldite material was calcined using the parameters of the followingTable 2. Table 2. Calcination parameters

[0063] The conditions of the calcination for the Calcine 1 sample resulted in heavy melting and hard agglomeration, posing a risk in a commercial rotary kiln. Calcine 2 and Calcine 3 were still powder-like and soft after the calcinations.

[0064] The results of a chemical analysis are shown in the following Table 3.Table 3. Chemical analysisLi Al K Ca Fe Zn Rb SiO2F% % % % % % % % %B fore. 1.13 9.64 6.18 0.23 6.01 0.08 0.91 52.7 5.84 calcinationCalcine 1 1.12 10.3 6.37 6.19 0.850 54.3 4.04Calcine 2 0.99 8.9 5.7 8.1 0.49 5.3 0.77 44.6 4.69Calcine 3 0.97 9.1 5.6 7.2 0.53 5.4 0.75 46.7 4.52

[0065] As the results show, the fluoride content in calcines 2 and 3 is still high, which suggests that the fluoride does not volatilize if a Ca reagent is added.Example 2 - Atmospheric alkaline leaching of lithium-containing materials

[0066] The above prepared calcined samples were leached using the conditions shown in the following Table 4, the results of analyses of the leaching solution and leaching solids of the AAL1 sample are shown in the following Tables 5-6, for the AAL2 sample in Tables 7-8, and for the AAL3 sample in Tables 9-10.Table 4. Parameters of atmospheric alkaline leachingable 5. Leaching solution results for AAL1 ample Li Na Mg Al Si K Ca Mn Fe Rb F OH mg / 1 mg / 1 mg / 1 mg / 1 mg / 1 mg / 1 mg / 1 mg / 1 mg / 1 m / I mg / 1 g / Lnitial 31 59500 <2 100 109 81 3 <2 4 <50 176 45.9I h 430 50900 <2 1130 4470 2700 <2 9 15 292 2395 41.9 h 732 54800 <2 492 5790 4240 2 9 6 499 3844 42.0 h 1580 50100 <2 187 9240 7150 2 8 3 652 6089 38.6 h 1600 46400 <2 134 10500 8060 2 6 4 732 6254 37.0 h 1650 48200 <2 131 11000 9090 2 5 4 724 6451 38.010 h 1390 44000 <2 112 9810 8670 2 2 2 703 6084 35.512 h 758 44900 <2 88 8160 8590 2 <2 <2 679 5792 33.314 h 455 43200 <2 57 7310 8110 2 <2 <2 602 5910 32.616 h 378 42200 <2 47 6630 7440 2 <2 <2 507 6303 30.218 h 346 44300 <2 49 6830 8550 2 <2 <2 658 7160 31.4 0 h 296 43700 <2 48 6630 8660 2 <2 <2 678 7168 30.1 2 h 258 43800 <2 49 6670 9090 2 <2 <2 732 7328 31.2 inal filtrate (24h) 265 39200 <2 36 6140 8840 <2 <2 <2 683 6708 29.9 ash filtrate 190 24300 <2 20 3430 4690 <2 <2 <2 363 4091 16.8able 6. Leaching solid results for AAL1. . . . . . . . .. .. Acid-soluble Water Li ample Li Na Mg Al K Ca Mn Fe Rb S1O2 F’T. . . .T.Li soluble Li extraction% % % % % % % % % % % % % %nitial 1.12 10.21 h 0.972 10.4 0.169 29.7 h 0.817 10.5 0.153 42.4 h 0.436 10.4 0.093 70.0 h 0.364 10.3 0.224 0.093 87.68 h 0.466 10.2 0.353 89.910 h 0.503 10.1 0.455 95.712 h 0.696 10.0 0.616 0.399 92.714 h 0.764 10.0 0.787 10016 h 0.819 9.87 0.826 0.531 10018 h 0.847 10.3 0.862 0.565 100 0 h 0.873 10.2 0.883 0.587 100 2 h 0.82 10.3 0.86 100 inal filtrate 0.923 6.63 0.035 10.3 1.89 0.218 0.624 6.04 0.501 41.6 0.4 0.881 0.638 96.3able 7. Leaching solution results for AAL2 ample Li Na Mg Al Si K Ca Mn Fe Rb F OH mg / 1 mg / 1 mg / 1 mg / 1 mg / 1 mg / 1 mg / 1 mg / 1 mg / 1 m / I nig / l g / Lnitial 12 58500 <2 83 73 47 13 <2 <2 <50 90 43.51 h 430 61700 <2 553 2750 2050 2 <2 20 184 683 46.1 h 700 62300 <2 357 3840 2900 2 <2 17 256 936 46.9 h 1080 62000 <2 249 5910 4680 <2 <2 13 409 1290 48.2 h 1160 57700 <2 205 6870 5820 <2 <2 11 541 1430 47.0 h 1210 56000 <2 184 7630 7000 <2 <2 11 673 1540 46.510 h 1200 55600 <2 170 8160 7920 2 <2 9 764 1590 46.312 h 1190 57300 <2 168 8780 9100 3 <2 7 913 1710 46.414 h 969 55400 <2 156 8640 9640 2 <2 3 1030 1740 45.816 h 638 58300 <2 148 8590 10700 2 <2 3 1120 1640 47.418 h 473 56400 <2 141 8280 11000 2 <2 4 1190 1770 47.0 0 h 387 55900 <2 133 8280 11100 2 <2 5 1230 1770 46.2 2 h 371 58100 <2 141 8780 12300 2 <2 6 1390 1890 47.5 inal filtrate (24h) 347 57000 <2 123 8610 12000 <2 <2 6 1310 1710 46.8 ash filtrate 148 13800 <2 31 2100 1400 <2 <2 3 291 394 11.4able 8. Leaching solid results for AAL2Acid- Water Li ample Li Na Mg Al K Ca Mn Fe Rb SiO2F . . .T. , , ,T. soluble Li soluble Li extraction% % % % % % % % % % % % % %nitial 1.03 9.061 h 0.798 9.0 0.470 67.9 h 0.633 9.2 0.396 77.3 h 0.542 9.2 0.317 78.5 h 0.470 9.11 0.285 82.18 h 0.448 9.3 0.308 86.810 h 0.441 9.6 0.312 88.212 h 0.449 9.6 0.337 0.096 89.714 h 0.482 10.2 0.394 92.416 h 0.706 9.15 0.636 93.318 h 0.773 9.2 0.696 0.320 92.6 0 h 0.793 9.5 0.728 0.333 94.0 2 h 0.828 9.00 0.778 95.1 inal filtrate 0.820 5.80 0.082 8.92 1.12 8.67 0.602 5.55 0.315 40.4 4.08 0.757 0.366 93.8able 9. Leaching solution results for AAL3 ample Li Na Mg Al Si K Ca Mn Fe Rb F OH mg / 1 mg / 1 mg / 1 mg / 1 mg / 1 mg / 1 mg / 1 mg / 1 mg / 1 m / I nig / l g / Lnitial 14 55400 <2 51 59 45 17 <2 <2 <50 78.1 43.1I h 471 62200 <2 684 3110 2040 2 <2 13 177 764 47.5 h 789 58800 <2 301 3970 2760 2 <2 7 233 1036 47.6 h 1240 57000 <2 19 6240 4670 2 <2 6 415 1499 46.1 h 1340 54300 <2 159 7420 6340 2 <2 7 598 1749 45.8 h 1360 56300 <2 155 8580 7710 2 <2 6 783 1941 48.310 h 1050 56100 <2 137 8640 8620 2 <2 <2 901 1966 45.812 h 543 55300 <2 118 7910 9360 2 <2 2 1010 1922 44.114 h 400 52900 <2 109 7480 9290 2 <2 3 1020 1867 42.616 h 373 56800 <2 119 8170 10300 4 <2 4 1130 2073 44.918 h 328 57800 <2 108 8290 10400 2 <2 3 1140 2099 18.5 0 h 303 56900 <2 108 8140 10600 2 <2 4 1170 2011 44.5 2 h 282 56600 <2 105 8160 10900 2 <2 3 1210 2104 44.9 inal filtrate (24h) 288 57300 <2 94 8190 10800 <2 <2 3 1200 2119 44.4 ash filtrate 145 14500 <2 26 2190 2710 <2 <2 3 281 522 11.522 able 10. Leaching solid results for AAL3Acid- Water Li ample Li Na Mg Al K Ca Mn Fe Rb SiO2F . . .T. , , ,T. soluble Li soluble Li extraction% % % % % % % % % % % % % %nitial 1.02 9.011 h 0.768 8.92 0.440 67.5 h 0.588 9.12 0.323 74.3 h 0.362 9.54 0.162 81.5 h 0.355 9.18 0.190 84.18 h 0.362 9.37 0.211 85.810 h 0.467 9.37 0.334 87.512 h 0.700 9.60 0.626 0.345 93.214 h 0.748 9.12 0.652 90.716 h 0.727 9.20 0.657 93.318 h 0.803 9.21 0.735 0.425 93.5 0 h 0.833 9.4 0.765 0.515 93.6 2 h 0.800 9.2 0.743 94.5 inal filtrate 0.768 5.24 0.346 8.68 1.27 7.60 0.633 5.85 0.306 41.5 3.72 0.683 0.368 91.3

[0067] Lithium extraction was calculated as:Li extraction %

[0068] As the results show, compared to AA 1, the AAL2 and AAL3 samples (with Ca additives used in the calcinations) showed much lower fluoride and silicon concentrations in the filtrate, as well as smaller OH consumption. Further, the reaction was very fast, with high Li extractions achieved already at short leaching times (with > 80% lithium extracted to the solids at 4-6h, and > 90% at 12-14h).Example 3 - Bicarbonation

[0069] The filter cakes of the AAL1 and AAL3 samples obtained from the leachings ofExample 2 were bicarbonate as shown in Table 7.Table 11. Parameters of bicarbonation test

[0070] The results of the carbonization are shown in the following Tables 12 and 13.Table 12. Bicarbonation solution sample resultsTest Sample Li Na Al Si K Ca Rb F mg / 1 mg / 1 mg / 1 mg / 1 mg / 1 mg / 1 mg / 1 mg / 1Carbl Initial 280 1430 <10 643 293 <2 <50 37210-min 2000 2250 <10 184 394 11 <50 54230-min 2170 2710 16 439 443 21 <50 4631-h 2380 3020 14 380 511 22 <50 5342-h 2410 3050 13 333 515 22 <50 5213-h 2530 3210 11 320 536 21 <50 516Final filtrate 2580 3260 12 273 529 19 <50 493Carb3 Initial 184 406 <20 325 71 5 <30 27.010-min 1230 2070 <20 342 160 165 <30 75.930-min 1350 2700 <20 310 190 106 <30 59.61-h 1320 2790 20 313 199 70 <30 57.82-h 1330 2960 <20 253 196 55 <30 58.13-h 1330 3000 <20 189 199 51 <30 56.0Final filtrate 1300 2960 <20 84 183 46 <30 51.1Table 13. Bicarbonation solid sample resultsTest Sample Li Al F' Acid-soluble Li Li extraction% % % %Carbl Initial 0.738 10.310-min 0.220 10.6 0.164 81.130-min 0.192 10.5 0.136 83.31-h 0.192 10.5 0.136 83.32-h 0.188 10.4 0.132 83.53-h 0.193 10.6 0.127 83.4Final precipitate 0.184 10.9 0.26 0.131 84.6Carb3 Initial 0.72 9.310-min 0.23 9.8 0.110 79.330-min 0.20 9.8 0.079 82.01-h 0.19 9.6 0.073 82.52-h 0.19 9.5 0.068 82.33-h 0.19 9.3 0.066 82.0Final precipitate 0.150 10.1 3.41 0.048 86.9

[0071] As can be seen from the results of this example, a very efficient extraction of the lithium was achieved using the above procedure.INDUSTRIAL APPLICABILITY

[0072] 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.

[0073] Particularly, the herein described new combination of calcination with additives and alkaline leaching makes it possible to obtain pure lithium products without the challenges typically faced caused by silicates and fluorides in the lithium minerals.CITATION LIST Patent LiteratureCN 101974678 AFI 121 785

Claims

CLAIMS:

1. Method for processing lithium-containing minerals into fractions, the method comprising the steps of:- subjecting a lithium-containing mineral to a calcination step (1) in the presence of one or more calcination additive(s) selected from calcium salts, in order to obtain a calcine,- subjecting the thus obtained calcine to an atmospheric leaching step (2) at an elevated temperature in a leaching solution having an alkaline pH of 11.5 or higher, and- obtaining two or more separate fractions from the obtained leach slurry.

2. The method of claim 1, wherein the lithium-containing mineral subjected to calcination is one or more of spodumene, lepidolite, amblygonite, triphylite, petalite, bikitaite, eucryptite, montebrasite, or zinnwaldite, preferably being spodumene, zinnwaldite or lepidolite, more preferably wherein said minerals are obtained from ores of spodumene, zinnwaldite or lepidolite, and most suitably wherein said minerals are in the form of mineral concentrates.

3. The method of claim 1 or 2, wherein the calcination additive(s) are selected from calcium carbonate, calcium hydroxide, calcium oxide, calcium sulphate or calcium chloride, preferably being one or more of calcium carbonate, calcium hydroxide, or calcium oxide, and most suitably containing at least calcium carbonate or calcium hydroxide.

4. The method of any preceding claim, wherein the calcium salts(s) are added to the lithium-containing mineral in a ratio of 1 : 1 - 10: 1 of mineral concentrate : calcium salt, preferably in a ratio of 3: 1 - 10: 1, and more preferably 3.5:1 - 6: 1.

5. The method of any preceding claim, wherein the calcination step (1) is carried out on a lithium-containing mineral further containing fluoride, and the dosage of the calcium salt(s) is selected to achieve a ratio of calcium ion (Ca) to fluoride ion (F) in the lithium- containing mineral of 0.5-3 mol / mol, preferably 0.7-1.5 mol / mol.

6. The method of any preceding claim, wherein the calcination step (1) is carried out at a temperature of 850-1200°C, preferably 900-1200°C, or particularly a temperature of 1000-1100°C.

7. The method of any preceding claim, wherein the alkaline conditions in the leaching solution used in the leaching step (2) are achieved by adjusting the pH using a hydroxide reagent, such as an alkali metal hydroxide or an alkaline earth metal hydroxide, which preferably is selected from sodium hydroxide (NaOH), potassium hydroxide (KOH), lithium hydroxide (LiOH), calcium oxide (CaO), or calcium hydroxide (Ca(OH)2), or a mixture thereof, preferably being sodium hydroxide (NaOH) or potassium hydroxide (KOH).

8. The method of any preceding claim, wherein the alkaline conditions in the leaching solution used in the leaching step (2) are achieved by adding alkali metal hydroxide into the leaching solution into a hydroxide content of 0.1 - 250 g / L, preferably 1 - 200 g / L, more preferably 30 - 80 g / L, and even more preferably 40 - 50 g / L.

9. The process of any preceding claim, wherein the leaching solution used in the leaching step (2) is provided with a hydroxide content of 0.6 - 9 mol / L, preferably 1 -6 mol / L.

10. The method of any preceding claim, wherein the leaching step (2) is carried out at a temperature of 80 - 100 °C, preferably 90 - 95 °C.

11. The method of any preceding claim, wherein the leaching step (2) is carried out for a period of 1- 48 h, preferably 1 - 36 h, most suitably for a period of 10 - 24 h.

12. The method of any preceding claim, wherein a solid / liquid separation step (2’) is carried out after the leaching step (2) to separate a solids fraction and a liquid fraction from the leach slurry.

13. The process of any preceding claim, wherein at least a fraction of the leach slurry or of a solution separated therefrom is processed in a desilication step (3a), preferably carried out by adding a calcium reagent to the leach slurry or the solution separated therefrom, the calcium reagent more preferably being calcium oxide (CaO) or calcium hydroxide (Ca(OH)2), and separating the formed solid silicate from a liquid fraction.

14. The method of any preceding claim, wherein fluorides and silicon are separately removed from the leach slurry, or from a liquid fraction separated therefrom, by reacting with a calcium reagent, such as calcium hydroxide or calcium oxide, in two stages, whereby the fluoride reacts into calcium fluoride in a first reagent addition stage, whereafter the desilication step 3a is carried out.

15. The process of any preceding claims, wherein a liquid fraction is separated from the leach slurry obtained in the leaching step (2), or from a desilicated solution of the leach slurry, and is recycled back to the leaching step (2) and combined with the leaching solution.

16. The process of any preceding claim, wherein at least a fraction of the leach slurry obtained from the leaching step (2), or of solids separated therefrom, is processed further to separate metal salts from said fraction, preferably in processing steps (4) beginning with a carbonization, which will provide solubilized lithium salts, while other metals remain in solid form.

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