Calcination and pressure 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 a pressure leaching in an alkaline leaching solution.

Description

CALCINATION AND PRESSURE 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 a pressure 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, an alkali leaching or a high- pressure 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 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 new processes, 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, pressure leaching 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.

[0012] It was further discovered that the excellent extraction rates can be achieved also with short leaching times, as around 90% of the lithium will be transferred to the solid phase at the beginning of the leaching. Thus, smaller and less expensive equipment can be used to carry out the present method, as compared to existing pressure leaching equipment.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] 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.

[0014] 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.

[0015] 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

[0016] 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.

[0017] The present invention relates to a 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,- subjecting the thus obtained calcine to a pressure leaching step 2 in a leaching solution having an alkaline 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 further recovered as separate recovered sub-fractions, and a solid fraction, containing lithium and metals that can be further recovered as separate product sub-fractions.

[0018] Some alternative process configurations are shown in the Figs, with Fig. 1 illustrating one general embodiment, and Figs 2 and 3 illustrating preferred embodiments.

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

[0020] 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 calciumsalt(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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] As indicated above, the leaching step 2 is carried out as a pressure leaching. In such a pressure leaching of lithium-containing minerals, the leaching temperatures can be as high as 300 °C, although also lower temperatures of < 280 °C, or temperatures of < 240 °C may be sufficient.

[0026] In an embodiment, the temperature during the leaching step 2 is thus preferably 120 - 300 °C, more preferably 120-280 °C, such as 120-260 °C or 120-240 °C, even more preferably 150-220 °C. Thus, in some embodiments, the temperature of theleaching step 2 may range from 120 °C or 150 °C up to 220 °C, 240 °C, 260 °C, 280 °C or 300 °C.

[0027] The pressure during the leaching step 2 is preferably 3 - 85 bar, more preferably 3 - 65 bar, even more preferably 3-30 bar, or 5-30 bar, and most suitably 5-25 bar or 10-25 bar. Thus, in some embodiments, the pressure during the leaching step 2 may range from 3 bar, 5 bar or 10 bar up to 25 bar, 30 bar, 50 bar, 65 bar or 85 bar. The pressure may not necessarily require separate adjustment, as it adjusts upwards with a raised temperature. Hence, the pressure is typically higher at higher leaching temperatures.

[0028] 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.

[0029] 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 10 - 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

[0030] With the above conditions, even a short leaching time is sufficient. It was discovered that by pressure leaching at the temperatures set forth herein, the leaching step 2 may be carried out for a period of 1 min - 4 h, preferably 5 min - 3 h, most suitably for a period of 1 - 2 h. Thus, in some embodiments, the leaching time is from 1 min, 2 min, 3 min, 4 min or 5 min, up to 2 h, 3 h, 4 h, or 5 h.

[0031] Due to the preferred high temperature and high pressure, the leaching step 2 is typically performed in a suitable autoclave or series of autoclaves. When a leaching time of less than 5 h is employed, the volume of the equipment can be reduced fromconventional volumes without a decreased process efficiency. The temperature of the leaching step 2 may, in turn, be slightly increased, such as by using a temperature in the upper end of the temperature ranges disclosed herein (e.g. a temperature of 220 - 300 °C), without significant negative impact on the equipment, e.g. the autoclave. The type of mineral raw material may also be taken into account when selecting the leaching conditions, as for example lepidolite, zinnwaldite and amblygonite contain fluorine, which therefore may be leached at lower temperatures to increase the equipment service length.

[0032] Although pressure 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.

[0033] 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 this embodiment, 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.

[0034] 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 LiKA12F2Si3O9 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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 the post-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).

[0041] 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 theFigs.), whereafter the desilication step 3a mentioned above can be carried out, and, again, be followed by said post-desilication solid / liquid separation step 3a’.

[0042] 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.

[0043] 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 an impurity removal or be discarded.

[0044] 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-leaching solid / 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.

[0045] 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.

[0046] 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 too much will cause the increased formation of by-products and impurities. Mixing is preferably provided, e.g. using any suitable mixer which provides mixing for dispersing gas, liquid and solids very efficiently.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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 the formation 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.

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

[0055] 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 beforethe 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.

[0056] Crystals of lithium hydroxide monohydrate can be recovered from the lithium hydroxide -containing solution by crystallizing. The crystallizing is typically performed by heating the solution to a temperature of approximately the boiling point of the solution, to evaporate the liquid, or by recrystallizing the monohydrate from a suitable solvent. The method described herein enables production of pure lithium hydroxide monohydrate with excellent yield and purity in a continuous and simple process, typically providing battery grade lithium hydroxide monohydrate crystals.

[0057] In preferred embodiments, either one of the crystallizations, for producing carbonate or hydroxide crystals, is typically followed by another solid-liquid separation step, preferably carried out using filtration, or by routing the slurry or solution to a thickener.

[0058] In further embodiments, the crystallization mother liquor remaining after the crystals have been recovered in a solid / liquid separation, 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 pressure 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 precipitationof 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.

[0059] 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.

[0060] 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.

[0061] As used herein, a plurality of items, structural elements, compositional elements, and / or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

[0062] 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.

[0063] 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.

[0064] 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

[0065] A zinnwaldite material was calcined using the parameters of the following Table 2.Table 2. Calcination parameters

[0066] 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.

[0067] The results of a chemical analysis are shown in the following Table 3.Table 3. Chemical analysisLi Al K Ca Fe Zn Rb SiO2F% % % % % % % % %Rpfnrp, . 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

[0068] 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 - Pressure alkaline leaching of lithium-containing materials

[0069] The above prepared calcined samples were leached using the conditions shown in the following Table 4, the results of an analysis of the leaching solution are shown in the following Table 5, and the results of an analysis of the leaching solids are shown in Table 6.Table 4. Parameters of pressure alkaline leachingable 5. Pressure alkaline leaching solution results est Sample Li Na 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 mg / 1 g / LALI Initial 21 30000 50 59 54 3 <2 <3 <50 110 22.90-min 211 19800 18 2510 11200 <3 <2 <3 701 9130 12.430-min 144 17700 <10 5770 12300 <3 <2 <3 731 9180 11.160-min 139 17300 <10 7680 12700 <3 <2 <3 753 9190 11.090-min 143 16900 <10 8780 13100 <3 <2 <3 793 9220 11.0Final filtrate 162 14500 <10 8070 11200 <3 <2 <3 633 7980 9.59AL2 Initial 8 29300 50 33 38 15 <2 <2 <50 60 20.50-min 185 25400 95 2560 6370 2 <2 2 357 1900 19.430-min 99 20100 39 3910 10300 2 <2 2 631 2150 17.460-min 84 19500 30 4690 10700 2 <2 2 688 2265 17.090-min 79 20000 27 5270 11100 2 <2 2 706 2195 16.6Final filtrate 103 19000 20 5190 10000 <2 <2 <2 580 2115 15.4AL3 Initial 13 30300 42 28 38 26 <2 <2 <50 60 22.70-min 173 22100 86 2320 6690 2 <2 <2 323 1985 18.230-min 104 18500 41 3360 9750 2 <2 <2 591 2130 16.860-min 82 17200 29 4080 9330 2 <2 <2 628 2100 15.390-min 76 17800 26 4700 9840 15 <2 <2 652 2225 15.6Final filtrate 105 17700 <20 5060 9410 <2 <2 <2 580 2255 15.3able 6. Pressure alkaline leaching solid resultsTest Sample Li Na Al K Ca Mn Fe Rb SiO2FT. soluble Li extraction% % % % % % % % % % % %PALI Initial 1.15 10.40-min 0.99 9.5 0.94 95.230-min 1.02 10.0 0.96 94.260-min 1.04 9.8 1.01 97.090-min 1.07 10.2 1.02 95.4Filter cake 1.03 7.3 10.4 1.3 0.22 0.65 6.3 0.59 46.5 0.30 1.02 99.1PAL2 Initial 0.97 8.99 8.170-min 0.83 8.83 7.90 0.748 91.430-min 0.87 8.89 7.96 0.697 82.060-min 0.86 8.96 8.08 0.817 95.690-min 0.94 9.13 8.17 0.812 87.0Filter cake 0.976 5.54 9.10 1.19 8.30 0.551 5.21 0.512 39.5 3.63 0.901 92.4PAL3 Initial 0.979 9.20 6.910-min 0.824 9.05 7.27 0.74 91.330-min 0.869 8.91 7.13 0.75 87.460-min 0.862 9.18 7.19 0.63 76.390-min 0.903 9.06 7.29 0.83 92.4Filter cake 0.906 5.62 9.12 1.28 7.20 0.537 5.34 0.509 40.3 3.37 0.84 93.2

[0070] Lithium extraction was calculated as:Li extraction %

[0071] As the results show, compared to PALI, PAL2 and PAL3 (with calcium additives) showed much lower fluoride and silicon concentrations in the filtrate, as well as smaller hydroxide (OH) consumption. Further, the reaction was very fast, with high Li extractions achieved already at 0 min.Example 3 - Bicarbonation

[0072] The filter cakes obtained from the leachings of Example 2 were bicarbonate as shown in Table 7.Table 7. Parameters of bicarbonation test

[0073] The results of the carbonization are shown in the following Tables 8 and 9.Table 8. 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 274 214 <5 799 156 20 <5010-min 3110 398 <5 404 275 46 <50 9830-min 2970 417 <5 309 279 71 <50 971-h 3060 430 <5 201 294 72 <50 992-h 3150 457 <5 140 316 84 <50 1013-h 3350 495 <5 114 348 90 <50 104Final filtrate 3320 516 <5 98 352 61 <50 105Carb2 Initial 84 250 <10 300 145 8 <50 7.510-min 2330 602 <10 201 342 95 <50 11830-min 2510 692 <10 169 361 33 <50 82.31-h 2420 716 <10 111 375 25 <50 74.82-h 2500 766 <10 92 375 25 <50 65.63-h 2340 78 <5 84 382 28 <50 58.5Final filtrate 2430 817 <5 75 388 18 <50 62.5Carb3 Initial 87 239 <5 283 109 7 <50 10.210-min 2280 577 <5 189 294 75 <50 98.630-min 2370 686 <5 203 321 39 <50 90.91-h 2340 695 <5 155 320 32 <50 75.82-h 2360 746 8 151 329 41 <50 70.33-h 2370 771 <5 125 369 32 <50 64.4Final filtrate 2420 802 <5 128 379 31 <50 67.3Table 9. Bicarbonation solid sample resultsTest Sample Li Al F' Acid-soluble Li Li extraction% % % %Carbl Initial 0.80310-min 0.156 10.7 0.083 86.830-min 0.152 10.8 0.079 87.31-h 0.147 10.7 0.079 87.62-h 0.147 10.5 0.075 87.33-h 0.143 10.5 0.074 87.7Final precipitate 0.139 10.8 0.29 0.06 88.4Carb2 Initial 0.931 9.2510-min 0.238 9.18 0.133 76.030-min 0.204 9.14 0.101 79.31-h 0.194 9.19 0.100 80.42-h 0.192 9.13 0.103 80.53-h 0.194 9.21 0.105 80.5Final precipitate 0.161 9.27 3.46 0.072 83.9Carb3 Initial 0.91 9.2110-min 0.235 9.04 0.084 76.630-min 0.208 9.23 0.087 79.71-h 0.202 9.21 0.081 80.22-h 0.202 9.16 0.086 80.13-h 0.198 9.18 0.075 80.6Final precipitate 0.205 9.00 3.26 0.086 79.5

[0074] 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

[0075] 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.

[0076] Particularly, the herein described new combination of calcination with additives and pressure 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 LISTPatent LiteratureCN 101974678 A FI 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,- subjecting the thus obtained calcine to a pressure leaching step (2) 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 salt(s) are added to the lithium-containing mineral in a ratio of 1 : 1 - 10: 1 of mineral material : calcium salt, preferably in a ratio of 3 : 1 - 10: 1, 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 10 - 50 g / L.

9. The method 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 120 - 300 °C, preferably 120 - 280 °C, more preferably 150 - 220 °C.

11. The method of any preceding claim, wherein the leaching step (2) is carried out at a pressure of 3 - 85 bar, preferably 3 - 65 bar, more preferably 5 - 30 bar, most suitably 10 - 25 bar.

12. The method of any preceding claim, wherein the leaching step (2) is carried out for a period of 1 min- 4 h, preferably 5 min - 3 h, most suitably for a period of 1 - 2 h.

13. 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.

14. The method 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.

15. 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.

16. The method 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.

17. The method 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 salt, while other metals remain in solid form.

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