CN120119115A

CN120119115A - Leaching of lithium concentrate

Info

Publication number: CN120119115A
Application number: CN202311682884.9A
Authority: CN
Inventors: 张天; 埃罗·寇罗麦内恩
Original assignee: Metso Finland Oy
Current assignee: Metso Finland Oy
Priority date: 2023-12-08
Filing date: 2023-12-08
Publication date: 2025-06-10
Also published as: WO2025120253A1

Abstract

According to the present invention, there is provided a process for converting lithium in a lithium-containing mineral into a soluble form, and a method for preparing solid lithium compound crystals using a lithium-containing slurry or solution obtained by the process.

Description

Leaching of lithium concentrate

Technical Field

The present invention relates to a process for converting lithium in a lithium-containing mineral into at least partially soluble form, and to the use of a lithium-containing slurry or solution obtained from said process for the preparation of solid lithium compound crystals.

Background

Lithium is an element forming a compound and has a variety of industrial applications. Lithium used for these purposes is obtained mainly from lithium brine and ores by hydrometallurgical extraction processes. Traditional processes for extracting lithium from ores include high temperature calcination or roasting processes followed by hydrometallurgical treatment such as pressure leaching.

For example, US 9255012 B2 and US11292725 B2 describe leaching of calcined lithium-containing minerals in a carbonate-containing leach solution. In US 9255012 B2, the solution obtained in the leaching step is bicarbonate, and then the lithium carbonate product is crystallized. In US 11292725B 2, the lithium in the leached slurry is further reacted to a hydroxide. However, both publications describe processes in which the raw materials are calcined, in combination with a carbonate-based leach solution, to provide the desired lithium extraction rate.

One of the main problems of the calcination or roasting process is high energy consumption, and this problem becomes more important as the energy costs rise. Thus, there is a need for new processes in which lithium in uncalcined form can also be efficiently leached from mineral raw materials.

Disclosure of Invention

The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

According to a first aspect of the present invention there is provided a process for converting lithium in a raw material based on uncalcined lithium-containing minerals into at least partially soluble form.

According to a second aspect of the present invention there is provided a process for leaching lithium from a lithium-containing mineral feedstock using leaching conditions that are capable of dissolving even uncalcined minerals.

According to another aspect, a method of using at least partially dissolved lithium in the preparation of solid lithium compound crystals is provided.

According to yet another aspect, a method of utilizing a desilication solution in a recycle feed is provided.

The present invention thus relates to a process for converting lithium in a lithium-containing mineral into at least partially soluble form, and to the use of a lithium-containing slurry or solution obtained from said process for the preparation of solid lithium compound crystals.

The present invention is based on the finding that lithium can be leached from lithium-containing minerals even without calcining the minerals if the conditions of the pressure leaching are optimised in a suitable way.

Thus, the lithium-containing mineral raw material used in the present invention can be leached directly without calcination or roasting pretreatment.

Significant advantages are obtained with the present invention. The invention ensures that the leaching of the lithium concentrate does not need calcination pretreatment or related expensive equipment, thereby remarkably saving cost and energy, reducing the emission of gases such as carbon dioxide and the like and obtaining more sustainable and more environment-friendly lithium products.

Furthermore, it has surprisingly been found that the extraction of lithium is also better for at least some lithium-containing minerals when using uncalcined mineral concentrates in the leaching step of the process.

Another advantage is obtained when a desilication step is further employed in the process, namely that the recycling options in the process are improved, since the silicate brought into the process together with the uncalcined raw material is still present in the leaching solution in high levels, which benefits from the silicon removal prior to recycling.

Drawings

Fig. 1 shows a process configuration according to at least some embodiments of the invention, wherein box 1 represents the leaching step of the process, box 2 represents the optional carbonization step, and box 3 represents the optional conversion step for converting lithium bicarbonate obtained in the carbonization step into insoluble compounds, wherein a dashed line separates the optional steps of the process from the necessary leaching steps.

Fig. 2 shows a process configuration of an advantageous embodiment, with the addition of box 0 representing an optional pulping step, box 1 'representing an optional solid/liquid separation step, box 4 representing an optional desilication (or desilication) step, and box 4' representing an optional further solid/liquid separation step from which the solution may be recycled back to pulping step 0 or carried further to carbonization step 2 (as indicated by the dashed arrow).

Detailed description of the preferred embodiments

Definition of the definition

The lithium-containing minerals may take many different forms, such as those listed in table 1 below, with spodumene (Spodumene) being most commonly used because of its availability.

TABLE 1

In addition, it may exist in the form of clay minerals such as manganese lepidolite (masutomilite), hectorite (swinefordite), hectorite (hectorite), laponite (cookeite) and Gu Daer stones (jadarite).

The "calcination" of lithium-containing minerals is a thermal step, typically by altering the crystal structure of the mineral, so that it is more susceptible to leaching. Thus, during leaching, the "calcined" form is typically selected, whereas the "uncalcined" form was previously considered too stable.

The invention relates to a process for converting lithium in uncalcined lithium-containing concentrates into soluble form by pressure leaching the concentrate in a leach solution having a hydroxyl ion (OH ^-) content of 0.6-9mol/L, more preferably 1-6mol/L, at a temperature of 120-240 ℃, preferably 150-220 ℃ (see step 1 of FIG. 1).

The lithium-containing mineral used may be in the uncalcined form of any one of the minerals in table 1, or may be a clay mineral as otherwise listed, but is preferably selected from spodumene, petalite, lepidolite and petalite, more preferably petalite.

The hydroxide ion content used in the process is preferably achieved by adding a hydroxide ion-containing alkaline agent, such as an alkali metal hydroxide, selected from sodium hydroxide (NaOH), potassium hydroxide (KOH) and lithium hydroxide (LiOH), or mixtures thereof, preferably sodium hydroxide. The hydroxide ions are mainly used to adjust the pH of the leachate to a sufficiently high level, preferably not less than 11.5, more preferably 11.5-14. However, at such pH values, the content of alkaline agent is more reliable in measurement than the pH value.

The pressure leaching step of the lithium-containing mineral feedstock is typically carried out at a temperature of up to 300 ℃, but in the present process, a lower temperature of less than or equal to 240 ℃ is sufficient. The pressure during leaching 1 is preferably 3-10 bar, more preferably 5-30 bar, even more preferably 5-25 bar. The pressure does not necessarily need to be adjusted separately, as it will adjust upwards as the temperature increases. Under these conditions, the time of the feedstock in the leaching reactor is relatively short, for example, 30 minutes to 4 hours.

Because of the use of high temperature and pressure, leaching 1 is typically carried out in a suitable autoclave or series of autoclaves.

In one embodiment of the process described herein, the leach solution further contains a carbonate reagent, such as an alkali metal carbonate, preferably sodium carbonate (Na ₂CO₃) or potassium carbonate (K ₂CO₃), or a mixture thereof, most suitably at least partially composed of sodium carbonate. Typically, the amount of such carbonate added is between 0 and 3 times, most suitably >0 and 2.5 times the lithium content of the mineral on a stoichiometric basis. Therefore, the addition amount may be 0. In a specific embodiment of the process, the leaching step is performed in the absence of a carbonate reagent, i.e. without adding carbonate to the leachate.

In another embodiment, recycled liquor from a subsequent step of the process may be added to the leachate in addition to the concentrate feed.

In another embodiment of the process described herein, a separate pulping step 0 is performed prior to the pressure leaching step, wherein the lithium-containing concentrate is mixed into an aqueous solution, optionally in the presence of alkali metal carbonate, to produce a lithium-containing slurry. However, slurry formation may also be part of the pressure leaching step 1. The preferred alkali metal carbonate is sodium carbonate and is generally used in excess.

Thus, in leaching step 1, the lithium aluminosilicate (e.g., petalite LiAlSi ₄O₁₀) in the mineral is converted into a dissolved or partially dissolved form, such as lithium carbonate (Li ₂CO₃) or lithium metasilicate (Li ₂SiO₃). For example, using petalite raw material in the presence of sodium hydroxide, in the main reaction, the lithium-containing mineral reacts with hydroxide ions (OH ^-) to produce Li ₂SiO₃ and analcite.

After leaching step 1, a leach slurry is obtained containing lithium in the form of carbonate or silicate, depending on whether carbonate is present in leaching step 1. Since these intermediates are only slightly soluble in the leachate, in particular carbonates are only partially soluble, they are obtained in the form of a slurry. The slurry does not contain significant amounts of unreacted minerals because they have been converted to sodium aluminum silicate. In other words, lithium contained in the minerals has been released. Typically, the proportion of lithium released from the leaching step is 90 to 95% by weight, calculated on the mineral basis. The slurry obtained can be used as such and thus be directly subjected to any subsequent reaction, for example to achieve further dissolution.

Depending on the further use of the leach slurry, the solid/liquid separation step 1' may optionally be performed to provide a liquid containing smaller amounts of undesirable compounds (e.g. sodium silicate and other impurities). According to this alternative, the solution separated from the solids in the optional separation step 1' may be recycled, for example reused in the same leaching step 1, or it may be used in an intermediate separation or conversion step 4 to provide a solution for recycling. In another alternative, the slurry or solution obtained may be diluted with water.

Thus, in another embodiment (see fig. 2), the leach slurry is subjected to a solid/liquid separation step 1', followed by a silicon removal step 4, also referred to as a desilication step, wherein a calcium reagent, such as calcium oxide (CaO) or calcium hydroxide (Ca (OH) ₂), is added to the solution to form calcium silicate, which can then be removed in a subsequent further solid/liquid separation step 4'. In the desilication step 4, in the main reaction, silicon reacts with calcium and calcium silicate is produced.

Preferably, the calcium reagent is added in an amount of 1-2 times the silicon (Si) content of the solution in stoichiometric terms. The temperature during the reaction is preferably from 80 to 100℃and a duration of from 1 to 10 hours is generally sufficient, preferably from 1 to 8 hours. The solution separated from the solids in the further separation step 4 'may be recycled, in particular in the leaching step 1 or preferably in the optional pulping step 0 before, or it may be combined with the leaching slurry or preferably with the leaching residue obtained from the solid/liquid separation step 1' before and subjected to a subsequent treatment, such as the carbonization step 2 described below.

In another embodiment, after leaching 1, either directly or together with the intermediate separation 1' and desilication 4 steps described above, a carbonization step (see step 2 of fig. 1 or 2) is carried out, also called a bicarbonate step, due to the reaction taking place. In this carbonization step 2, the obtained leach slurry or leach residue separated therefrom is reacted with carbon dioxide (CO ₂), preferably excess carbon dioxide. Undissolved lithium compounds obtained from the leaching step are thus converted into dissolved lithium bicarbonate and can thus be substantially completely separated from the undesired, undissolved material.

The optional carbonization step 2 may be carried out at a temperature between 0 and 50 ℃, preferably between 15 and 40 ℃, and typically 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 excessive increases in pressure will result in increased formation of byproducts and impurities. The process preferably provides mixing, for example using any suitable mixer, which is very effective for dispersing gases, liquids and solids.

The lithium-containing slurry or solution obtained from the process described herein may also be used in a method for preparing solid lithium compound crystals by performing a further step (see step 3 of fig. 1) of converting lithium bicarbonate in the slurry or solution into insoluble compounds and crystallizing them.

Prior to said conversion step 3, there may be a further step of separating any insoluble reagents from the slurry or solution in a solid/liquid separation step 2' (not shown in the figures), typically by filtration, followed by a conversion step 3 of the liquid fraction. The separation step 2' may be performed, for example, using filtration, or by feeding the slurry or solution into a thickener, from where overflow (overflow) may be fed to the conversion step 3, and the underflow (underflow) may be discarded, recycled or further filtered to recover all the lithium remaining therein.

Alternatively, purification 2 "(not shown in the figures) may be carried out prior to the conversion step 3 to remove impurities, such as trivalent and/or divalent metal ions, e.g. calcium, magnesium, aluminum and iron ions, preferably after a solid/liquid separation step, from which the liquid fraction is recovered. Preferably, ion exchange is used for purification 2". Ion exchange can be performed, for example, by using the method disclosed in finnish patent 121785. Typically, purification by ion exchange is performed by using a cation exchange resin, which may be, for example, iminodiacetic acid (IDA) or aminophosphonic acid (APA). Such resins are manufactured, for example, under the trade names Amberlite IRC 748 (IDA) and Amberlite IRC 7476 (APA). Typically, the cation exchange resin is a resin having a polystyrene matrix crosslinked with divinylbenzene containing aminophosphonic acid groups.

The conversion step 3 described above allows the formation of solid lithium compounds or precipitates which can be crystallized into pure crystals, preferably lithium carbonate or lithium hydroxide.

If lithium carbonate is prepared, the conversion step 3a comprises heating a slurry or solution containing lithium bicarbonate, preferably to a temperature of 70-100 ℃, to decompose the bicarbonate and crystallize the lithium carbonate.

In this reaction, a slurry containing water and lithium carbonate precipitate is formed. In a solid/liquid separation step 3' (not shown in the drawings), solid lithium carbonate is separated from the obtained slurry, thereby obtaining battery grade lithium carbonate. Standard battery grade lithium carbonate contains at least 99.5% lithium carbonate. However, using the methods described herein, high quality battery grade lithium carbonate containing at least 99.99% lithium carbonate can be produced.

If lithium hydroxide is prepared, the conversion step 3b comprises reacting a lithium-containing slurry or solution obtained from a dissolution process or optionally pretreated therewith using a hydroxide reagent, i.e., an alkaline earth metal hydroxide, to produce a slurry containing soluble lithium hydroxide. The alkaline earth metal hydroxide used is preferably selected from calcium hydroxide and barium hydroxide, more preferably calcium hydroxide, optionally prepared by reaction of calcium oxide (CaO) in an aqueous solution. The alkaline earth metal hydroxide may also be mixed with water or an aqueous solution before use in the reaction. Also in this reaction, recycled mother liquor obtained from subsequent crystallization may be used. The conversion step is generally carried out at a temperature of from 10 to 100 ℃, preferably from 20 to 60 ℃, most preferably from 20 to 40 ℃. Typically, the hydroxide conversion step 3b is carried out at atmospheric pressure. The presence of alkaline earth metal hydroxides and the above process conditions lead to the formation of lithium hydroxide and alkaline earth metal carbonates as by-products.

After the optional solid/liquid separation step 3' (not shown in the figures), a relatively high purity lithium hydroxide-containing solution is obtained, preferably using filtration, or by feeding the slurry or solution to a thickener.

In one embodiment, the lithium hydroxide containing slurry or solution may be purified prior to crystallization.

This optional purification step 3 "(not shown in the figures) is preferably based on the purification of dissolved components and ions, more preferably comprising ion exchange or membrane separation, or both, most suitably by using cation exchange resins, in particular selective cation exchange resins. Ion exchange may be performed, for example, as described above for purification step 2 ". Membrane separation may be performed using a semi-permeable membrane that separates ions or other dissolved compounds from an aqueous solution. More precisely, membrane separation can be used to fractionate dissolved ions and compounds according to their size (depending on the pore size of the membrane material) and/or their charge (depending on the surface charge of the membrane material). The positive surface charge repels cations (having a stronger repulsive effect on multivalent cations) and attracts anions, and vice versa. These phenomena will be able to purify, for example, multivalent metal cations, complexing species (e.g., aluminum hydroxide complexes), polymeric species (e.g., dissolved silica), and larger anions (e.g., sulfate and carbonate ions) from lithium hydroxide solutions. Based on the above, it is particularly preferable to combine membrane separation with ion exchange, most suitably by first performing membrane separation and then ion exchange to complete removal of polyvalent metal cations.

Crystals of lithium hydroxide monohydrate can be recovered by crystallization from a solution containing lithium hydroxide. Crystallization is typically performed by heating the solution to a temperature of about the boiling point of the solution to evaporate the liquid, or by recrystallising the monohydrate from a suitable solvent. The methods described herein are capable of producing pure lithium hydroxide monohydrate in excellent yields and purity in a continuous and simple process, typically providing battery grade lithium hydroxide monohydrate crystals.

In a preferred embodiment of the method, the step for producing carbonate or hydroxide crystals is typically followed by another solid-liquid separation step, preferably using filtration or by feeding the slurry or solution to a thickener.

In further embodiments, the crystallization mother liquor, or a portion thereof, remaining after recovery of the crystals in the solid/liquid separation step may be recycled to one or more previous steps of the dissolution process or the preparation of solid lithium compound crystals, thereby allowing recovery of any non-crystallized lithium. In one alternative, the mother liquor is recycled to the pressure leaching step 1, or optionally to the previous pulping step 0, to participate in the pH adjustment therein, thereby reducing the need for further addition of sodium hydroxide. In another alternative related to the hydroxide route, the mother liquor is recycled to the hydroxide conversion step 3b for the preparation of lithium hydroxide. In another alternative, the mother liquor is recycled back to the crystallization step. Furthermore, the carbon dioxide used in the optional carbonization step 2 of the dissolution process may be separated from the crystallization mother liquor and recycled back to the carbonization step 2.

By recycling to an earlier step with a lower alkalinity, such as pressure leaching 1 or lithium conversion step 3, the advantage obtained is that some impurities in the crystallization mother liquor (e.g. aluminum and silicon) have increased solubility with increasing alkalinity (e.g. caused by increasing lithium hydroxide concentration) so that these alkali soluble impurities can be removed by recycling them in solution to the step of lower alkalinity. For example, in hydroxide conversion step 3b, these impurities form sparingly soluble compounds (e.g., aluminum hydroxide) and can be discarded with the solids after a subsequent separation step. Without these recycling options, impurities typically concentrate during crystallization and contaminate the product.

It is to be understood that the disclosed embodiments of the invention are not limited to the specific structures, process steps, or materials disclosed herein, but extend to equivalents thereof as recognized by those of ordinary skill in the relevant arts. It is also to be understood that the terminology employed herein is for the purpose of describing particular embodiments only and is not intended to be limiting.

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 phrase "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment.

As used herein, a plurality of items, structural elements, constituent elements, and/or materials may be presented in a common list for convenience. However, these lists should be understood as though each individual member of the list is individually identified as a separate and unique member. Thus, without being stated to the contrary, any individual member of the list should not be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group. In addition, various embodiments and examples of the invention, along with alternatives to the various components thereof, may be referred to herein. It should be understood that such embodiments, examples and alternatives are not to be construed as actual equivalents of each other, but rather as separate and independent representations of the present invention.

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 may be practiced without one or more of the specific details, or with other methods, components, materials, and so forth. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

While the above examples illustrate the principles of the 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 implementation details can be made without the exercise of inventive faculty, without departing from the principles and concepts of the invention. The invention, therefore, is not to be restricted except in the spirit of the appended claims.

The verbs "to comprise" and "comprise" as used herein are open-ended constraints that neither preclude nor require the presence of unrecited features. The features recited in the claims can be freely combined with each other unless explicitly stated otherwise. Furthermore, it should be understood that the use of "a" or "an" herein, i.e., the singular, does not exclude the plural.

Examples

Reference example

Petalite samples obtained from north american (a) and european (B) mines were calcined at a temperature of 1100 ℃ to 1190 ℃ and then leached in a leaching solution containing sodium carbonate (Na ₂CO₃) and sodium hydroxide (NaOH) at 220 ℃. Calcination conditions, leaching conditions and lithium extraction achieved are shown in table 2 below.

As shown in the following results, a high extraction rate of lithium from calcined petalite requires to maintain a sufficiently high pH value and a sufficiently high sodium carbonate content throughout the leaching step, and the final result is easily affected by e.g. pH decrease. The lowering of the pH can be avoided by using a large amount of base, but the process is still very susceptible to detrimental changes.

EXAMPLE 1 Leaching of uncalcined lithium-containing Material

Samples of uncalcined petalite (1.42 wt.% lithium in the minerals of test 1-15, 1.91wt.% lithium in the minerals of test 16) were leached in a leachate containing sodium hydroxide (NaOH), and in some samples also sodium carbonate (Na ₂CO₃). The raw material content in the slurry was 200g/L.

The raw material and sodium carbonate are typically mixed before the leaching begins, but sodium hydroxide is added in a single dose or in successive doses at the beginning of leaching (see test 11).

The leaching conditions were varied to show the effect of the variation on lithium extraction. The leaching temperature is kept in the range of 150-200 ℃, the leaching time is kept in the range of 1-4 hours, the sodium carbonate dosage is kept in the stoichiometric range of 0-2.5 times the lithium content in the minerals, and the pH value is kept in the range of 11.5-14. The different leaching conditions and the lithium extraction achieved are shown in table 3 below.

As these results indicate, the process of the present invention uses a pressure leaching step on the uncalcined lithium-containing minerals, is more versatile than known processes, and can achieve high extraction rates using a wide range of reaction conditions. From the results, it can be seen that a sufficient amount of base results in a high lithium extraction rate, while the negative effects of other conditions are very small (see in particular test 1, compared to tests 8, 3 and 4). As shown in comparative tests 1, 10, 13 and 14, the effect of temperature change on the extraction rate was smaller than the effect of pH change on the extraction rate. Also, as seen when comparing tests 1, 7 and 10, the change in leaching time had very little effect on extraction yield. Finally, as shown in comparative tests 1, 5, 6 and 9, when the pH is effectively maintained at a sufficiently high level with sufficient amount of base, the change in the amount of Na ₂CO₃ has no effect on the extraction rate, even without any reaction with the amount of Na ₂CO₃.

EXAMPLE 2 carbonization

The slurry obtained from test 16 of example 1, with a solids concentration of 200g/L, was subjected to a separate carbonization step, in which the CO ₂ gas feed was 1000mL/min. Carbonization was performed at a temperature of 30 ℃ for 8 hours, and then the final lithium-containing filtrate was separated from the final precipitate. Samples were taken from the reaction mixture at different time points during the reaction, analyzed and filtered to show the content of the mixture at different time points of carbonization. The contents of the various filtrates and precipitates obtained are shown in Table 4 below. As demonstrated by these results, a lithium extraction of 96.2% can be achieved and calcination is not required.

TABLE 4 Table 4

Filtrate from the filtration	pH	Li
			Reaction time		mg/l
1h	7.41	3720
			2h	7.4	3550
4h	7.4	3640
			6h	7.4	3680
8h	7.4	3670
			Final filtrate	7.39	3770

Table 4 (subsequent)

Precipitate of	Li	Al	Li extraction yield
				Reaction time	%	%	%
1h	0.139	10.4
				2h	0.121	10.2
4h	0.123	10.3
				6h	0.120	10.2
8h	0.113	10.2
				Final precipitate	0.111	10.2	96.2

EXAMPLE 3 desilication

The leached slurry obtained from test 1 of example 1 was subjected to a solid/liquid separation step, and the solution separated therefrom was subjected to a silicon removal step in which calcium oxide (CaO) was added to the solution to form calcium silicate.

Test conditions

CaO addition in a 1.2 times stoichiometric amount relative to the Si content

-Temperature of 90 DEG C

Duration of 8 hours

After the reaction, the solid silicate formed is separated from the remaining desilication solution. After 1h and 4h of reaction, a solution sample was obtained. The silicon and hydroxide content of the solution was analyzed and the results are shown in table 5 below.

TABLE 5

	Leaching filtrate	After 1h	After 4 hours	Desilication filtrate
					Si(mg/L)	38200	255	99	47
OH(mol/L)	0.848	0.796	0.912	0.848

As can be seen from the results in Table 5, the silicon content in the leachate dropped from 38200mg/L to 47mg/L during the 8 hour desilication.

EXAMPLE 4 alkaline Leaching Using recycled desilication solution

The leaching described in example 1 was repeated using the desilication solution obtained from the desilication of example 3, but using as feed an uncalcined petalite concentrate from north america (Li content: 1.91%) with a solids content of 200g/L. The different leaching conditions and the lithium extraction rates achieved are shown in table 6 below.

TABLE 6

* NaOH (500 g/L) addition (mL)/feed (g)

When the recycle solution is used, the addition amount of NaOH can be reduced as compared with the case shown in example 1, because the recycle solution has a high hydroxide content.

The leach slurry obtained from example 4 was subjected to solid/liquid separation, and the separated leach residue was mixed with the desilication filtrate obtained from example 3 and used in the carbonization step:

-temperature of 30 DEG C

Duration of 8 hours

-Solids concentration 300g/L

CO ₂ gas feed 1000mL/min

The final lithium-containing filtrate is separated from the final precipitate after carbonization. Samples were taken from the reaction mixture at different time points during the reaction, analyzed and filtered to show the content of the mixture at different time points of carbonization. The contents of the various filtrates and precipitates obtained are shown in Table 7 below.

TABLE 7

Filtrate from the filtration	pH	Li
			Reaction time		mg/l
0h	13.7	113
			1h	7.8	5840
2h	7.7	5030
			4h	7.7	6180
6h	7.7	6380
			8h	7.8	6510
Final filtrate		6810

Table 7 (subsequent)

Precipitate of	Li	Al	Li extraction yield
				Reaction time	%	%	%
0h	2.4	10.8
				1h	0.19	11.0
2h	0.14	11.2
				4h	0.10	11.2
6h	0.079	11.1
				8h	0.12	11.3
Final precipitate	0.129	10.9	95.2

As shown in the results of table 7, mixing the leaching residue with the recycle solution from desilication still achieves excellent separation of Al, as well as excellent lithium extraction.

Industrial applicability

The process of the present invention may be used as part of any hydrometallurgical process for the recovery of lithium products from lithium-containing minerals and to improve the process.

In particular, the novel leaching step described herein allows leaching of lithium concentrate without the need for calcination pretreatment, nor expensive calcination equipment. Therefore, the cost and energy sources can be greatly saved, the emission of gases such as CO ₂ and the like is reduced, and more sustainable and more environment-friendly lithium products are obtained.

CITATION LIST

Patent literature

US 9255012 B2

US 11292725 B2

Claims

1. A process for converting lithium in a lithium-containing mineral to an at least partially soluble form, characterized in that a non-calcined lithium-containing mineral concentrate is provided and the mineral is pressure leached in a leaching solution having a hydroxide content of 0.6-9mol/L at a temperature of 120-240 ℃.

2. The process according to claim 1, wherein the uncalcined lithium-containing mineral is selected from spodumene, petalite, lepidolite and petalite or any combination thereof, preferably petalite.

3. A process according to claim 1 or 2, wherein the pH of the leach solution is ≡11.5, preferably 11.5-14.

4. A process according to any one of the preceding claims wherein the hydroxide content of the leach solution is preferably 1-6mol/L.

5. A process according to any one of the preceding claims, wherein the leaching is carried out at a temperature of 150-220 ℃.

6. A process according to any one of the preceding claims, wherein the leaching is carried out at a pressure of 3-30 bar, preferably 5-25 bar, more preferably 10-25 bar.

7. A process according to any one of the preceding claims, wherein the leaching is carried out for a period of from 30 minutes to 4 hours.

8. A process according to any one of the preceding claims, wherein the hydroxide content is achieved by adding a hydroxide-containing alkaline reagent, preferably an alkali metal hydroxide, selected from sodium hydroxide (NaOH), potassium hydroxide (KOH) and lithium hydroxide (LiOH) or mixtures thereof, more preferably sodium hydroxide.

9. A process according to any one of the preceding claims, wherein the leach liquor further comprises a carbonate reagent, such as sodium carbonate (Na ₂CO₃) or potassium carbonate (K ₂CO₃), preferably in an amount of up to 3, most suitably >0-2.5, stoichiometric amounts related to the lithium content in the mineral.

10. The process of any one of claims 1-8, wherein the leaching is performed in a carbonate-free leach solution without carbonate reagent.

11. A process according to any one of the preceding claims, wherein the leaching is followed by a carbonization step, wherein the obtained leached slurry is reacted with carbon dioxide (CO ₂), preferably with an excess of carbon dioxide.

12. A process according to any one of the preceding claims, wherein a desilication step is carried out after the leaching step, by adding a calcium reagent, preferably calcium oxide (CaO) or calcium hydroxide (Ca (OH) ₂), to the leaching slurry or to a solution separated therefrom, and separating the formed solid silicate therefrom, resulting in a filtrate.

13. A process according to claim 12, wherein the filtrate obtained from the desilication step is recycled to the leaching step 1 for reuse, or to the previous optional pulping step, or may be sent to a subsequent processing step, such as a carbonic acid hydrogenation step.

14. Use of a lithium-containing slurry or solution obtained from the process according to any one of the preceding claims for the preparation of solid lithium compound crystals by performing the further step of converting lithium bicarbonate in the slurry or solution into insoluble compounds by crystallization.

15. The use according to claim 14, wherein the step of separating any insoluble reagents from the slurry or solution is performed prior to the step of converting.

16. Use according to claim 14 or 15, wherein the lithium precipitate is lithium carbonate or lithium hydroxide.