2024 Volume 7 Issues 4–5

Open Access

INEOS OPEN, 2024, 7 (4–5), 110–116  Journal of Nesmeyanov Institute of Organoelement Compounds of the Russian Academy of Sciences Download PDF DOI: 10.32931/io2444r

Recovery of Lithium from Natural Raw Materials. Minireview

Abstract

This review briefly discusses acidic, basic, and saline methods of lithium salt recovery from mineral spodumene, methods of processing natural chloride brines by alternative removal of attendant elements of the first and second groups as well as the recovery of lithium salts by using DALH-Cl based on Al(OH)₃. A suggested hypothesis provides the explanation for some unusual properties of the material by the influence of hydrogen bonds and dissociation of Al(OH)₃ in an aqueous medium.

Key words: spodumen, brine, aluminum hydroxide, DALH-Cl.

 

Introduction

The following reactions occur during the process [4]:

18(Ca(OH)2S + 10MgCl2S + 0.5H2OL → Mg10(OH)18Cl2∙0.5H2OL+18CaClOHS

(4)

The precipitation of alkaline earth metals can also be carried out using quicklime:

18CaOS + 10MgCl2S + 9.5H2O → 18CaClOHS∙Mg10(OH)18Cl2∙0.5H2OS

(5)

In both cases, filtering the liquid phase from gel-like precipitates is very difficult. The use of quicklime and cooling the mixture make filtering somewhat easier, but in the latter case the probability of precipitation of LiCl∙H₂O increases, so that lithium losses are significant. Calcium cations can be removed from the brine with oxalic acid [4] or by converting Ca²⁺ into insoluble gypsum, and vice versa, if there is a need to remove sulfate anions, an equivalent of calcium ions is added. It was also suggested to use barium instead of calcium to remove SO₄^2– [9].

Some brines contain admixtures of organic compounds, which were suggested to be removed by heating the dry residue formed after separation of solid by-products of brine processing and evaporation of the liquid fraction at about 300 °C. Organic compounds either evaporate or undergo pyrolysis and then evaporate. When heated, boric acid salts are converted into the products insoluble in isopropanol, which is used to finally extract lithium chloride [6, 10].

Boric acid was suggested to be removed from a 40% brine concentrate by vigorously stirring it with a solution of octanol in kerosene [11]. It is known that lithium cations interact with alcohols, forming solvates. However, in the brine with such a high concentration there is no free water, but only water that has gone into the hydration of salts. In other words, lithium chloride is not dissociated in the concentrated solution, and, therefore, boric acid can be removed from this brine without affecting lithium chloride. Sometimes boron is also removed as CaO·3B₂O₃·3H₂O [12].

From the analysis of the above patent literature, it is clear that the separation of lithium from the impurities of other elements using simple chemical reactions is a multi-step process. Typically, the industrial processes end with the reactions listed below [11]. Sometimes LiOH·H₂O is purified by recrystallization, and its conversion to lithium carbonate is carried out by passing carbon dioxide through the solution. Lithium carbonate can also be further purified by dissolving it in cold water and then heating the solution almost to boiling. Lithium carbonate precipitates from the solution, while the solubility of other salts only increases.

2 LiCl+Na2CO3 →2 NaCl + Li2CO3	(6)
Li2CO3 + Ca(OH)2+2H2O → 2LiOH·H2O + CaCO3↓	(7)
LiOH·H2O + HCl →LiСl+2H2O	(8)
2 LiOH·H2O +CO2 → Li2CO3 + 3H2O	(9)

The stepwise extraction of lithium salts from brine allows for obtaining both technical products and pure LiCl, Li₂CO₃, and LiOH of the reagent and high purity grades. If lithium carbonate is produced for obtaining a power source, its purity should be no lower than 99.5% (chemical grade) and preferably 99.95% (high purity grade) [4]. It is obvious that the preparation of such products requires a large consumption of reagents and time, which cannot but affect the yield and cost of the final product. In this respect, new approaches to the extraction and purification of lithium salts have recently begun to develop. The method for isolating pure lithium carbonate from the original brine was described in the Russian patent [13]. First, the brine is treated with a group reagent, most likely sodium carbonate, which precipitates all alkaline earth carbonates that poorly dissolve in water, while lithium carbonate remains in the solution. After removing the precipitate, the selective crystallization of lithium carbonate from the liquid phase is carried out, slightly increasing its temperature and filtering out the precipitated lithium carbonate at the first stage of crystallization, and then repeating the procedure of a gradual increase of the mother liquor temperature twice and removing the salt. As a result, Li₂CO₃ with a purity of 99.5% is obtained.

Ryabtsev et al. [14] suggested the application of membrane electrolysis of aqueous solutions of LiCl, Li₂SO₄, and Li₂CO₃ of any origin to obtain very pure lithium hydroxide monohydrate. To accomplish the process, the authors proposed using cation-exchange membranes that separate the cathode and anode circuits of electromagnetic cells. During electrolysis, solutions constantly circulate through the cathode and anode circuits, and due to the presence of the cation-exchange membrane, the solution in the anode circuit is depleted of lithium salt. Lithium hydroxide accumulates in the solution circulating through the cathode circuit, from which a portion of the lithium hydroxide solution is periodically withdrawn for its purification mainly from calcium and magnesium using standard methods. The cathode solution is supplemented with a fresh portion of the initial solution. As a result, the authors obtained chemically pure lithium hydroxide monohydrate.

3.2. Sorbents for the lithium salt recovery from brines

As follows from the previous section, the technology of stepwise purification of brines from lithium-associated components is well developed; the chemical reactions in use are simple and are utilized in a sequence that depends on the source composition. However, the multi-stage processes not only complicate the isolation of the target component, but also increase the cost of the final product. The use of sorption processes can, if not completely, then at least partially reduce a number of stages of separate precipitation of the components. The use of ion-exchange resins for this purpose could be an obvious solution. Indeed, a complex industrial technology for the purification of polluted waters of different origins, including brines, from alkaline earth elements, heavy metals, oil products, and organic impurities was suggested in the recent patent [15]. The brine processing includes the precipitation of the main amount of calcium and magnesium, and to remove their traces, the process scheme implies the use of a carboxyl cationite and a chelate resin containing iminodiacetate groups. When such a resin in lithium form comes into contact with MgCl₂, the cation coordinates with two carboxy groups, displacing two lithium chloride molecules into the solution. Such a resin was also used in other cases, for example, when working with the DALH-Cl sorbent.

An interesting inorganic ion exchange material Li₄Mn₅O₁₂ is described in the patent [16]. The ion exchanger particles with a diameter of 1 μm are covered with ZrO₂. The coating thickness is 2 nm. This material is washed with dilute hydrochloric acid, during which lithium cations in the ion exchanger are replaced by protons and lithium chloride passes into the solution. A chloride brine is passed through the ion exchanger in the H⁺ form, during which only lithium cations are extracted from the brine. After saturation of the cation exchanger with lithium, the material is rinsed with hydrochloric acid, and the process is repeated again. The exceptional selectivity of crystalline Li₄Mn₅O₁₂ is apparently associated with the structure of the ion exchanger, which contains cavities, the sizes and spatial configuration of which are complementary to the sizes and spatial configuration of lithium cations. In other words, the ion exchanger can be attributed to the sorbent with a molecular recognition effect; it operates through the key-and-lock principle [17]. Coating the ion exchanger particles with zirconium oxide does not interfere with the interdiffusion of exchanging ions, but creates a barrier that prevents the material dissolution.

The above-mentioned patent also describes the principle of obtaining spherical particles of porous polyvinylidene difluoride (fluoroplast-2), the outer surface of these particles and the inner surface of the pores are coated with Li₄Mn₅O₁₂, which in turn is coated with ZrO₂. The spherical particles of the composite have an average diameter of 2 mm, which allows them to be used under dynamic conditions.

Gavlina and Ivanov [18] developed a two-temperature reagent-free method for ion-exchange purification of lithium chloride from impurities of metals of the first and second groups. A column filled with methacrylate ion-exchange resin KB-4P2 in a lithium form was brought into equilibrium with a solution of 0.98 N LiCl + 0.02 N KCl + 0.01 N CaCl₂ with pH = 8.9 at 22 °C, passing the excess of this solution from top to bottom, after which the column was heated to 90 °C and the initial solution was again passed through it from top to bottom at the same temperature. Since at this stage calcium actively displaced lithium from the ion exchanger, the volume of solution, after which CaCl₂ breakthrough began, was determined and which should be taken for subsequent separation of the mixture using parametric pumping (this term means that the chromatographic front does not extend beyond the sorbent layer.) Then the column was cooled to 22 °C and the entire volume of the solution collected at 90 °C was passed through the column from the bottom up at 22 °C. The eluate was collected and passed through the ion exchanger from the bottom up at 90 °C. The separation at room and elevated temperatures was repeated several times, the process was stopped at 90 °C. As a result, it was found that at high temperatures the concentration of calcium in the eluate gradually decreased due to its selective extraction by the sorbent from the solution in about nine times. On the contrary, at 22 °C the concentration of calcium in the filtrate gradually increased due to the regeneration of the ion exchange resin.

Unlike the polymer ion exchanger, purification of a 1.03 N LiCl + 0.020 N KCl + 0.0012 N CaCl₂ solution from potassium on zeolite A using a similar technique proceeds effectively at 20 °C. After several runs of parametric pumping, the concentration of potassium in the solution was reduced by 45 times. A thermodynamic description of two-temperature reagent-free separation of salts is given in the review [19]. We would like to believe that a non-trivial approach to purifying lithium chloride from impurities of alkali and alkaline earth metal salts will be in demand in the processing of brines.

All the above-described methods of processing natural hydromineral raw materials involve the extraction of a certain volume of brine, whereas natural sources continuously supply brine, for example, the daily volume of the Berikey deposit (Dagestan, Russia) reaches 1500 m³. The concentration of lithium cations in this source, according to various analyses, composes 39–44 mg/L. Simple calculations show that about 360 kg of lithium chloride are lost per day. It is clear that only adsorption of lithium chloride on a solid sorbent in the simulating moving bed mode can solve the problem of continuous extraction of LiCl.

At the end of the 20th century, the Institute of Solid-State Chemistry and Mechanochemistry of the Siberian Branch of the Russian Academy of Sciences began active development of a sorbent based on the composite of aluminum hydroxide and lithium chloride: The material was called DALH-Cl (double aluminum lithium hydroxide) [19]. This was an important step towards solving the problem of continuous processing of brines. In this respect, the results obtained deserve a more detailed consideration.

It was originally synthesized by mixing aqueous solutions of aluminum chloride, lithium chloride, and sodium hydroxide:

LiCl + AlCl3 + 2NaOH + mH2O → [LiAl2(OH)6]Cl mH2O↓ + 2NaCl

(10)

The co-precipitation of the lithium salt and amorphous aluminum hydroxide, which rather quickly acquires a crystalline form, apparently leads to the formation of an inclusion compound with an ordered structure (the authors of numerous works in this area call DALH-Cl an intercalation compound [20]).

In order to understand the crystal structure of DALH-Cl, hydrargillite particles (one of the crystalline forms of Al(OH)₃) were placed in a 20 M LiCl solution at 90 °C. In several days, the crystals changed the appearance, and their chemical composition corresponded to the formula given in equation 10. Interestingly, even if DALH-Cl is obtained by dissolving Al in LiOH, it has the same composition. In principle, it is possible to increase the content of aluminum in DALH-Cl synthetically, but it is impossible to increase the content of LiCl. The investigation showed that the structure of DALH-Cl is a set of layered packets, each of which is formed by three layers: two layers of closely packed aluminum hydroxide and a third layer containing lithium and chlorine ions, as well as water molecules. No signs of starting hydrargillite were found.

It should be noted that during investigation of DALH-Cl, the main focus was on the structural studies using modern physicochemical methods, while its properties, which are important for the extraction of lithium salts from brine, were relegated to the background, most likely because these properties are not easy to explain.

The composite with the composition exactly corresponding to the above formula (11) appeared to poorly extract lithium chloride from brine.

Later, Ryabtsev [21] proposed two other ways of obtaining DALH-Cl, the preferred option being the one that implies the use of cheaper lithium carbonate:

2AlCl3 + 6LiOH + mH2O → [LiAl2(OH)6]Cl mH2O↓ + 5LiCl

(11)

2AlCl3 + 3Li2CO3 + (3+n)H2O → [LiAl2(OH)6]Cl·mH2O↓ + 5LiCl +3CO2↑

(12)

Both routes yield DALH-Cl with a defective, poorly crystallized, disordered, and single-phase structure. Apparently, a large excess of LiCl prevents complete crystallization of the product. The composition of a large batch of DALH-Cl (30 kg), obtained by reaction (12) with LiOH, corresponded to the formula LiCl∙2.6Al(OH)₃∙4H₂O [22]. Finely ground powder of the resulting dry DALH-Cl was mixed with polyvinyl chloride and methylene chloride, the resulting paste was extruded, and the product was obtained in the form of tablets with 2×2 mm sizes. 92% of the binding polymer was then removed from the tablets by extraction with methylene chloride [23]. In tablets, between the particles of the original sorbent in the form of powder, there remains free space (gigapores) with a diameter of 1000 nm and a small proportion of large mesopores with a diameter of more than 20 nm, while smaller pores are absent according to argon adsorption data in the granulated product [21].

The structure and properties of the initial DALH-Cl and granulated material based on it were studied in detail and presented in a generalized form in the book [24]. Three unusual properties of this double aluminum lithium hydroxide are noteworthy, which, unfortunately, remained unexplained.

Firstly, the equilibrium of lithium chloride absorption from an aqueous solution at 25 °C is reached only after 24 h (Fig. 2), whereas the removal of absorbed LiCl by washing with water at 50 °C occurs so rapidly that this difference cannot be explained by the influence of temperature alone.

Figure 2. Kinetic curves of LiCl removal from DALH-Cl, obtained by reaction (11), by washing with water (a) at 50 °С
and LiCl absorption from brine at 2 g/L salt concentration, 25 °С, and total salts of 450 g/L (b) [22].

Secondly, if DALH-Cl with a defective structure is washed with water, it easily releases only 30–40% of lithium being present in the material, and upon subsequent contact with chloride brine, it restores its composition.

Thirdly, the performed investigations showed that, if the molar ratio Al(OH)₃:LiCl in DALH-Cl with a defective structure exceeds 3 and in the material with a crystalline form—2.5, then the amount of lithium chloride removed during washing with water begins to exceed the amount of salt absorbed from the chloride solution [24].

Finally, a very important property of DALH-Cl is its selectivity for extracting lithium chloride from brines containing salts of alkali and alkaline earth metals.

We took the liberty of expressing our hypothesis that explains the above non-trivial properties of DALH-Cl.

The incomplete extraction of lithium can be understood by turning again to reaction (11). The large amount of unreacted LiCl suggests that, after the reaction completion, it not only remains in the solution, but also precipitated DALH-Cl can mechanically capture LiCl, which remains in it after drying. Thus, the so-called molecularly imprinted material is formed. Menzheres et al. [22] rightly assumed that during rinsing, pure water simply washes out some of LiCl from defective DALH-Cl, and upon contact with brine after equilibrium establishing, lithium chloride again occupies the vacated place. It is possible that it completely corresponds to the size and structure of the hydrated lithium chloride molecule (unfortunately, it is impossible to verify this assumption experimentally). In this case, the selectivity of the salt absorption can only be explained by the fact that "the place of lithium in this compound cannot be occupied by any other element" [22]. It can also be assumed that 60–70% of LiCl is included into the crystalline fraction of DALH-Cl and is not available to water.

However, it is also important to note that the absorption of LiCl from water and its removal with water at close temperatures is not an adsorption process, and DALH-Cl cannot be called an adsorbent. Indeed, adsorption is the process of concentrating the sorbate at the interface of two phases, caused by interactions such as dispersion, hydrophobic, ionic, etc. [25]. In our case, one phase is the solid material DALH-Cl or simply aluminum hydroxide, and the other is an aqueous solution. Water plays an important role in understanding the processes occurring during the extraction of lithium using aluminum hydroxide.

In the Al(OH)₃–H₂O system, there are multiple hydrogen bonds that compact the structure of DALH-Cl. Water and LiCl dissolved in it slowly diffuse between the small particles of this granular material, while lithium chloride, being a strong chaotropic agent, destroys the hydrogen bonds and thereby loosens the structure of DALH-Cl (presumably, even causing some swelling). The removal of lithium chloride by water occurs rapidly from the loose and more accessible structure, but after this, the hydrogen bonds are restored again.

In an aqueous medium, Al(OH)₃ exhibits amphoteric properties and is therefore a weak electrolyte, up to 3% of its completely dissociated molecules dissolve in water. The remaining aluminum hydroxide molecules retain a tendency to dissociate, due to which a δ⁺ charge appears on the Al cation and a δ^– charge on the OH group.

When LiCl comes into contact with Al(OH)₃, the formation of the ionic Li–O bond is natural. It is this interaction that is responsible for the adsorption of lithium chloride on amorphous freshly precipitated Al(OH)₃ [26–29] and on its crystalline analog [30]. Compared to other alkali metals, the Li–O bond is the shortest and strongest one [31, 32], and therefore LiCl is sorbed preferentially over other cations of the first group metals.

We performed two experiments confirming our ideas about the reason for the extraction of lithium chloride with aluminum hydroxide. In the first case, a macroporous chloromethylated copolymer of styrene with divinylbenzene was taken and molecules of tris(hydroxymethyl)aminomethane NH₂C(CH₂OH)₃ were attached to the inner surface of the macropores via C–N bonds. A considerable number of OH groups on the surface of the macropores are accessible to LiCl, but no sorption from a 0.1 N aqueous solution was observed. In another experiment, we took polyvinyl alcohol of the general formula -{СН₂СН(ОН)}- with a molecular weight of 86 kDa, it swells well in water, but also does not absorb the salt. A charge on the hydroxy group is really needed to implement the absorption of the lithium salt. The formation of ionic bonds is also confirmed by the fact that the desorption of lithium by water from amorphous Al(OH)₃ is possible only at elevated temperatures [24] (DALH-Cl turned out to be a hydrolytically unstable material and at 70 °C decomposes into LiCl and Al(OH)₃).

The propensity of Al(OH)₃ for dissociation can explain another unusual property of DALH-Cl at first glance. The greater the molar ratio of aluminum hydroxide to lithium chloride, the greater the absolute amount of Al(OH)₃ that dissolves in water, which is inevitably accompanied by the release of an additional portion of LiCl due to its leaching with water.

DALH-Cl appeared to be a complex object for studying and understanding its properties. The combination of the latter determines the practical significance of the material. The advantages of DALH-Cl include, first of all, the possibility of concentrating a brine without significant energy costs when the hydromineral source is located in a region with a boreal climate. Secondly, the brine passed through DALH-Cl is largely purified from the impurity components accompanying lithium chloride, although remaining MgCl₂ and CaCl₂ must be additionally extracted, for example, using a chelating resin taken in the Li form.

Over the past years, a technology for the production of DALH-Cl and a technology for the continuous production of the lithium chloride concentrate from chloride brines using a simulating moving bed system have been developed. The license for both technologies was sold to China, where a plant for the production of aluminum hydroxide and lithium composite was built in the city of Hoi Zhou, which has been used for several years for practical purposes. In Russia, a pilot plant for the production of lithium carbonate from associated waters of oil production was created in the Irkutsk Oblast. At the end of the discussion of the problems of DALH-Cl, it should still be noted that this material is short-lived; being constantly in dynamic contact with water, Al(OH)₃ will gradually dissolve. However, only practice will show how important this problem is. For the future, however, it is more important to know what volume of brine of the known lithium concentration can be passed through one volume (or unit weight) of DALH-Cl under optimal conditions before lithium breakthrough and what capacity of the material is achieved in this case.

To replace the irregularly shaped particles of DALH-Cl, the authors of patents [33–35] suggested its analog in the form of spherical particles of macroporous anionite based on a copolymer of styrene with divinylbenzene. The authors filled the pores of the sorbent with a saturated solution of AlCl₃, dried the granules, and treated them first with ammonia water to precipitate Al(OH)₃ and then with a solution of LiCl or LiOH. The resulting composite withstood 60 cycles of lithium chloride absorption from chloride brine and subsequent removal of the lithium salt with water. However, the capacity of the sorbent subsequently began to gradually decrease due to the loss of aluminum hydroxide.

4. Conclusions

In this review, we briefly described the current state-of-the-art of the problem of lithium salt extraction from natural raw materials. We touched only on the scientific aspects of the problem and the chemical processes underlying the treatment of raw materials, leaving the problems of technology as such beyond the scope of this work.

In the world, lithium is concentrated, firstly, in lithium-bearing ores, and secondly, in hydromineral and geothermal sources. The processing of mineral ores, in particular spodumene, is actually the only method capable of meeting the state's need for valuable material.

At the same time, we cannot discount the processing of hydromineral raw materials, including sources, associated waters of oil production, and existing lakes. The processing of aqueous brines includes two directions: the sequential separation of each of the lithium associated components and the sorption processes.

The chemical methods for the stepwise separation of impurities have been studied for a long time, the optimal approaches have been developed, and currently the efforts of researchers are aimed primarily at improving the technology and using more modern equipment.

The sorption selective extraction of lithium salts from complex mixtures of elements of the first and second groups is attractive because all non-sorbed impurities leave with the flow of intergranular liquid, so the lithium salt desorbed afterwards should be practically free of contaminants.

Currently, only in Russia the method and technology for producing the lithium-selective sorbent DALH-Cl was developed, which represents a composite of lithium chloride and aluminum hydroxide. In addition, freshly precipitated Al(OH)₃ exhibits good sorption properties. Aluminum hydroxide, although a disposable sorbent, is currently being actively introduced in Dagestan for processing the Berikey deposit. The authors of the process not only demonstrated the production of lithium carbonate in a short time, but also developed the method for converting spent Al(OH)₃ into AlCl₃, from which Al(OH)₃ can be obtained again.

We also included two analytical papers that we found interesting, one devoted to the two-temperature reagent-free extraction of lithium chloride from its mixture with calcium and potassium chlorides on a carboxy-containing cationite and zeolite. The second paper is devoted to the synthesis and investigations of the sorption properties of the exclusively selective spinel sorbent Li₄Mn₅O₁₂, which is currently used as a cathode material in lithium-ion batteries [36].

Acknowledgements

This work was performed with financial support from the Ministry of Science and Higher Education of the Russian Federation (agreement no. 075-00277-24-00).

Conflict of interests

The authors have no conflicts of interest to declare.

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