RU2223142C2 - Method of preparing sorbent for recovering lithium from brines - Google Patents

Abstract

FIELD: sorbents. SUBSTANCE: invention relates to aluminum hydroxide-based inorganic sorbents selectively recovering lithium from naturally occurring lithium-containing brines. For that end, concentrated aluminum chloride and lithium hydroxide solutions or solid reagents in presence of water at liquid-to-solids ratio 1.1-4.4 are brought into direct contact and resulting compound is treated with water so desorbing a part of lithium. EFFECT: simplified sorbent preparation method. 3 dwg, 2 tbl, 7 ex

Description

 The invention relates to chemical materials science, in particular to methods for producing inorganic sorbents based on aluminum hydroxide, selectively extracting lithium from natural brines and technological chloride salt solutions containing lithium.

State of the art
A known method of producing a chlorine-containing variety of double hydroxide of aluminum and lithium composition LiCl • 2Al (OH) ₃ • nH ₂ O, used as a selective sorbent for the extraction of lithium from lithium-containing brines. The sorbent is synthesized by solid-phase interaction of aluminum hydroxide with crystalline lithium chloride in the presence of a small amount of water, followed by activation of the obtained LiCl • 2Al (OH) ₃ • nH ₂ O powder in an activator mill to give it sorption properties [1].

 The disadvantages of the method are the two-stage process, high energy consumption and the inability to scale the process due to the lack of industrial type activators.

A known method of producing microcrystalline hydrated selective sorbent LiCl • 2Al (OH) ₃ suspended in the pores of an anion exchange resin [2]. The method includes:
a) introducing freshly precipitated aluminum hydroxide into the pores of the resin, for which the resin is soaked in a saturated AlCl ₃ solution, and then treated with ammonium hydroxide;
b) washing the resin to remove excess ammonium hydroxide, residues of aluminum chloride and ammonium chloride resulting from the reaction;
c) treating the resin with precipitate Al (OH) ₃ with a LiOH solution at elevated temperature to convert the precipitate into a hydrated compound LiOH • 2Al (OH) ₃ ;
d) processing the resin with a precipitate of LiOH • 2Al (OH) ₃ , which does not have sorption properties with respect to lithium ions, hydrochloric acid or a solution of lithium chloride to convert the precipitate into a hydrated compound LiCl • 2Al (OH) ₃ (or LiCl • 2Al ( OH) ₃ • nН ₂ O), which is the sorbent.

 The disadvantages of this method are the complexity and multi-stage process, the need to wash the sorbent from the reagents before each operation, as well as the need to use a resin to improve the filtering properties of the precipitate.

A known method of producing a hydrated composite material based on Al (OH) ₃ composition LiCl / Al (OH) ₃ , designed to extract lithium from brines [3]. The method involves reacting commercial crystalline Al (OH) ₃ in the form of gibbsite, bayerite or norstrandite with lithium hydroxide in the presence of water at W: T = 0.67 to form a LiOH / Al (OH) ₃ composite, in which the molar fraction of LiOH ranges from 0.2 to 0.33. At 25 ^o With this process requires from 24 to 48 hours. The resulting composite is then treated with a hydrochloric acid solution to convert it to the sorption form LiCl / Al (OH) ₃ . This operation is carried out at a pH of 5-7 (preferably in the presence of NaHCO ₃ as a buffer) for 1-2 hours. As a result of this operation, in addition to the sorbent, a waste solution with a concentration of 10 g / l LiCl is also formed. Disposal of this solution by evaporation and crystallization of LiCl • H ₂ O from it will require large energy costs.

The sorbent thus obtained is then prepared for the sorption process, for which it is brought into contact with H ₂ O to remove the necessary amount of LiCl, which is then restored in the structure during subsequent processing of the sorbent with lithium-containing brine. Sorption and desorption of lithium is carried out at a temperature of 80 ^o C.

 According to the technical nature and the achieved result, this method is the closest to the claimed one and is selected as a prototype.

The disadvantages of the method are two-stage and the duration of the synthesis process of the sorbent. In addition, the sorbent obtained in this way can remove lithium from brines only at a temperature of 80 ^o C and above, due to its crystalline structure.

SUMMARY OF THE INVENTION
The technical result of the claimed invention is to simplify the method of synthesis of the sorbent and obtain on this basis such a sorbent that can adsorb lithium from brines at ambient temperature.

The technical result is achieved by the fact that they directly interact with a mixture of crystalline aluminum chloride and lithium hydroxide in the presence of a small amount of water (W: T is 1.1-4.4 in terms of anhydrous reagents) or their concentrated solutions. In this case, the interaction proceeds according to the reaction:
2AlCl ₃ + 6LiOH + nH ₂ O -> LiCl • 2Al (OH) ₃ • nH ₂ O + 5LiCl (1).

Therefore, the ratio of the components is taken in accordance with the stoichiometric reaction coefficients (1). Along with the formation of the sorbent according to reaction (1), a LiCl solution with a concentration of ~ 100-280 g / l is also obtained depending on the state of aggregation of the reagents and the amount of water introduced into the system. The formation of a lithium chloride background solution with such a high concentration prevents the formation of the LiOH • 2Al (OH) ₃ • nH ₂ O compound, which is not adsorbed with respect to lithium ions, in this system.

Reaction (1) is exothermic, that is, the interaction proceeds with the release of heat, which contributes to a very fast process. When using reagents in the solid state, the process is completed in 15 minutes. When using concentrated solutions of AlCl ₃ and LiOH, the process proceeds much faster within 5 minutes. An increase in the reaction time of more than 30 min is undesirable, since the amount of LiCl entering the sorbent structure, i.e. chemically bound to Al (OH) ₃ , decreases, as can be seen from the data of the table (figure 1, experiment 7). The speed of the exothermal reaction AlCl ₃ + LiOH allows filtering the pulp in the heated state, which helps to increase the speed of its filtration.

The use of reagents in the solid state simplifies the process, since there is no need for preliminary preparation of AlCl ₃ and LiOH solutions with a given concentration and, therefore, the hardware design of the technological process of sorbent synthesis is simplified. The use of solid reagents minimizes the amount of water in the reaction mixture. In this case, less waterlogged precipitates are formed and their moisture content decreases by about 20% compared with precipitates obtained by draining concentrated aqueous solutions (about 52 instead of 66 wt.%). In addition, the use of solid reagents can significantly reduce the volume of the mother liquor and increase its concentration to about 276 g / l LiCl. This concentration is achieved with L: T equal to 1.1 (in terms of anhydrous reagents), that is, this is the lower limit of the amount of water that can be introduced into the mixture of solid reagents AlCl ₃ and LiOH. Below this limit, the interaction is inhibited (at least an hour is required to complete the process), the pulp thickens strongly, it loses fluidity, and difficulties arise in quantitatively transferring it to the filter, that is, there are technological difficulties, although the sorption properties of the sorbent obtained under these conditions do not are getting worse. The upper limit of the amount of added water to solid reagents is limited by the feasibility of achieving in the mother liquor concentrations of LiCl not lower than 105-110 g / l. The ratio of the amount of water to the total amount of solid reagents should not exceed 4.4. Exceeding this value leads to dilution of the mother liquor according to the LiCl content, to an increase in the water content in the composition of the sorbent and to a deterioration in its filtering properties.

The use of concentrated AlCl ₃ and LiOH solutions prepared from the corresponding solid compounds can significantly accelerate the sorbent synthesis process, but in this case additional time is required for preparing the solutions and determining their concentration.

Obtained by the proposed method, the sorbent has a defective structure (Fig. 2), which subsequently allows sorption of lithium from brines at ambient temperature, without pre-heating the brine to 80 ^o C and above.

Thus, the main distinguishing features of the claimed invention are:
1) the use of LiOH powder or its solution for direct synthesis of a sorbent - a chlorine-containing variety of double lithium aluminum hydroxide - LiCl • 2Al (OH) ₃ • nH ₂ O, and not for the formation of an intermediate phase of the non-sorption-capable compound LiOH • 2Al (OH) ₃ • nH ₂ O;
2) the use of aluminum chloride as an aluminum-containing compound as a simultaneous supplier of chlorine ions necessary for the formation of the LiCl • 2Al (ОН) ₃ • nН ₂ O phase;
3) elimination of the need to use hydrochloric acid;
4) the implementation of the synthesis of the sorbent in one stage;
5) a decrease in the duration of the synthesis by about two orders of magnitude;
6) non-waste method;
7) the possibility of carrying out the sorption process on the sorbent obtained by this method without pre-heating the brine.

These features in combination can significantly simplify the process (Fig. 3), reduce the time of sorbent synthesis and open up the possibility of creating a simple waste-free technological process for producing the sorbent, since LiCl • H ₂ can be precipitated from the concentrated lithium chloride solution, which is formed in the course of sorbent synthesis after additional evaporation O and implemented as a commercial product.

The invention is novel, since for the first time a direct interaction of AlCl ₃ and LiOH is proposed for the synthesis of the sorbent LiCl • 2Al (OH) ₃ • nH ₂ O, which is not available in available sources of information.

List of figures, drawings and tables
FIG. 1. The dependence of the composition of precipitation and mother liquors on the time of interaction of aluminum chloride and lithium hydroxide, taken in the form of solids or solutions.

FIG. 2. A typical diffraction pattern of the obtained sorbent, which according to chemical analysis and in accordance with the data of the ASTM card index corresponds to the compound LiCl • 2Al (OH) ₃ • nH ₂ O.

 FIG. 3. The table, which shows comparative data on the claimed method and the prototype method.

 Information confirming the possibility of carrying out the invention is set forth in the examples.

 Example 1

To a mixture of 40 g of solid AlCl ₃ • 6H ₂ O and 11.92 g of solid LiOH was added 36.5 ml of distilled water (W: T = 1.1 in terms of anhydrous reagents) and the pulp was stirred for 15 minutes. The precipitate is filtered off, washed twice with distilled water on a filter and dried in air. The composition of sediment and mother liquor is given in the table (figure 1, 1). Then 10 g of the precipitate is treated with water until about 40% of lithium chloride is removed from the sorbent structure, which is controlled by the lithium content in the liquid phase. Thus, approximately 8 mg of lithium per 1 g of dry sorbent was removed. To establish a complete statistical exchange capacity (PSOE), natural chloride brine of the following composition is used, g / l: LiCl 5.80; KCl 2.0; NaCl 3.7; MgCl ₂ 427; CaCl ₂ 12 (sum of salts ~ 450 g / l); pH 5.20. After desorption of LiCl, 200 ml of brine are poured to a weighed portion of the sorbent and stirred for a day. The sorption capacity of the sorbent (PSOE) at a temperature of 20 ^o C was 8.0 mg / g

 Example 2

 The same as in example 1, but the amount of water added to the mixture of solid reagents is 80.8 ml (W: T is 2.4), and lithium is desorbed from the wet cake after filtration until about 40% of lithium is removed from the sorbent structure, which corresponds to a capacity of 7.9 mg / g in terms of dry sorbent. When using a brine, the composition of which is shown in example 1, PSOE is 8.0 mg / g (figure 1, experiment 2).

 Example 3

The same as in example 1, but the amount of added water is 149 ml (W: T is 4.4). The composition of the dry sediment is given in the table (figure 1, 3). The precipitate is treated with water and about 35% LiCl is removed from the precipitate structure, which corresponds to an exchange capacity of 7 mg / g. Full static capacity using a natural sorbent having a pH of 4.6 and containing, g / l: CaCl ₂ 324.8; MgCl ₂ 113.5; NaCl 12.7; KCl 5.3; LiCl 1.9 (total salt 460 g / l) was 7 mg / g. The sorption temperature of 25 ^o C.

 Example 4

40 ml of AlCl ₃ solution containing 383 g / l AlCl _{3 is} mixed with 88 ml of lithium hydroxide solution containing 94.6 g / l LiOH and stirring of the pulp is continued for 5 minutes. The precipitate is filtered off and washed twice with distilled water. The compositions of the air-dry sediment and the filtrate are shown in the table (figures 1, 4). To determine the sorption capacity of the sorbent, an air-dry sample of 5 g is treated with distilled water at W: T ~ 50 to remove ~ 35% of lithium chloride included in the structure of the compound LiCl • 2Al (OH) ₃ • nH ₂ O. Thus, 7.0 mg of lithium per 1 g of dry material. The full static exchange capacity of the sorbent is set on natural chloride brine, the composition of which is shown in Example 1. The total sorption capacity of the sorbent was 6.9 mg / g.

 Example 5

100 ml of a solution of AlCl ₃ with a concentration of 380 g / l is mixed with 171.5 ml of a LiOH solution with a concentration of 117.0 g / l and stirred for 15 minutes. The precipitate is filtered off, washed and lithium stripped from the wet cake until ~ 30% lithium chloride is removed from its structure, which is ~ 6 mg / g in terms of the dried sorbent. The composition of the air-dry sorbent is presented in the table (Fig. 1, 5). To determine the total static exchange capacity using natural brine with a content of, g / l: CaCl ₂ 324.8; MgCl ₂ 113.5; NaCl 12.7; KCl 5.3; LiCl 1.9; the amount of salts ~ 460 g / l; pH 4.6. The total exchange capacity of the sorbent was 6.0 mg / g.

 Example 6

 The same as in example 4, but the mixing time of the pulp during the synthesis of the sorbent is 30 minutes The composition of the air dry sediment is indicated in the table (figure 1, 6). The total exchange capacity of the sorbent when using a brine, the composition of which is shown in example 1, was 7.5 mg / g

 Example 7

40 g of the AlCl ₃ • 6H ₂ O solid salt is mixed with 100 ml of LiOH with a content of 94.3 g / l and the pulp is stirred for 15 minutes. The precipitate is filtered off, washed on a filter and dried in air. The composition of sediment and mother liquor is given in the table (Fig. 1 to 8). 10 g of the precipitate is treated with water until ~ 40% lithium chloride, which is part of the sorbent structure, is removed, which corresponds to a capacity of 7.3 mg / g. To establish a complete sorption exchange capacity, a brine is used, the composition of which is given in Example 1. PSOE is 7.0 mg / g.

 Examples for W: T <1.6 and W: T> 4.9 (negative) are presented in the table (Fig. 1, experiments 9 and 10).

Industrial applicability
The proposed method in comparison with the prototype method allows you to:
- significantly simplify the process by replacing two operations with one;
- significantly reduce the time of synthesis of the sorbent;
- exclude the use of hydrochloric acid solution;
- to carry out the process of sorption of lithium from brines without heating them;
- significantly increase the service life of the sorbent, making it virtually unlimited, since the sorbent is easily regenerated by a weakly concentrated LiCl solution, while the crystalline sorbent in the prototype method during each sorption-desorption cycle experiences deformation shifts and gradually breaks down. In this case, it is impossible to regenerate the sorbent. The authors of the prototype method note the need for a complete replacement of the sorbent, although they do not indicate its duration;
- implement the creation of a closed, waste-free technology for producing sorbent. For this purpose, the concentrated lithium chloride solution formed during the interaction of AlCl ₃ with LiOH can be disposed of in two ways: either by membrane electrolysis, converted into a LiOH solution and returned to the process head, which will allow the closure of the technological scheme and reduce the reagent costs of sorbent production, or evaporated to anhydrous LiCl (or LiCl • Н ₂ О) and is sold as a commercial product.

The proposed method is the simplest of all existing methods for producing the sorbent LiCl • 2Al (OH) ₃ • nH ₂ O and is planned for use in the extraction of lithium from highly mineralized lithium-containing brines of the Irkutsk platform and other deposits.

Sources of information
1. RF patent 2113405, C 01 D 15/00, C 01 F 7/04 07/09/97, publ. 10.10.98, BI 28. N.P. Kotsupalo, L.T. Menzherez, V.I. Titarenko, A.D. Ryabtsev.

 2. Patent US 4347327, C 08 D 5/20, B 01 J 20/00, decl. 11/19/79, publ. 08/31/82. J.M. Lee, W.C. Bauman.

 3. Patent US 6280693, C 01 D 15/00, B 01 J 20/00, C 09 K 003/00, claimed. 09/20/96, publ. 08/28/2001. W.S. Bauman, J.L. Burba (prototype).

Claims (1)

A method of producing a sorbent for the extraction of lithium from brine, comprising reacting an aluminum-containing reagent with lithium hydroxide in the presence of water, obtaining the compound LiCl · 2Al (OH) ₃ · nH ₂ O and treating it with water with desorption of a part of lithium from the structure, characterized in that for the interaction aluminum chloride and lithium hydroxide are supplied, while the reagents are supplied in solid form with the addition of water to a ratio of W: T = (1.1-4.4): 1 in terms of anhydrous reagents or in the form of their concentrated solutions, and treatment with water compounds LiCl · 2AL (OH) ₃ · nH ₂ O is carried out until reaching its exchange capacity for lithium 6-8 mg / L.

Images