CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 371 of PCT Application No. PCT/RU2018/050073 filed on Jul. 3, 2018, which claims priority to Russian Application No. RU 2017123383 filed on Sep. 25, 2017, the contents of which are hereby incorporated by reference as if recited in their entirety.

FIELD OF THE INVENTION

The present invention relates to chemical material science, in particular to methods of producing an inorganic aluminum hydroxide sorbent for selective lithium recovery from natural brines or technogenic lithium-containing chloride salt solutions.

BACKGROUND OF THE INVENTION

An inorganic sorbent based on a hydrated composite material LiCl/Al(OH)3was applied for the selective lithium recovery from brines worldwide [1]. The sorbent is produced by reacting of commercial crystalline Al(OH)3(crystal size 140 μm or more) as gibbsite, bayerite or nordstrandite with lithium hydroxide in the presence of water at L: S=0.69 to form a composite material LiOH/Al(OH)3. The resulting composite is further treated with a 20% solution of hydrochloric acid to obtain the sorption form of LiOH/Al(OH)3. After separation of the solid phase from the mother liquor, the sorbent is rinsed with water to remove a part of LiCl from the structure.

When subsequent contacting of the sorbent with lithium-containing chloride brine, the deficiency of LiCl is filled. The lithium recovered from the brine is further desorbed with water. The sorption and desorption of lithium is carried out at 80° C. The disadvantages of the method include two-stage process and long duration of the synthesis of the sorbent, application of a strong hydrochloric acid solution and a high process temperature (80° C.) for sorption and desorption of lithium chloride. However, the major disadvantage of this sorbent is a mechanical destruction of its crystals during operation which makes its practical application impossible.

There is known a method of synthesis of a microcrystalline hydrated selective sorbent of formula LiCl.2Al(OH)3suspended directly within the macropores of the anion-exchange resin [2].

The method comprises the following stages:

a) Incorporating a freshly formed Al(OH)3into the pores of a resin by soaking the resin within saturated solution of AlCl3followed by treating with aqueous ammonia solution;

b) Washing the resin to remove excessive reagents;

c) Treating the resin containing Al(OH)3with a LiOH solution to obtain the intermediate compound LiOH.2Al(OH)3;

d) treating of the resin containing intermediate compound with hydrochloric acid solution or lithium chloride solution to convert the intermediate compound into the compound LiCl.2Al(OH)3.

The disadvantages of the method include, firstly, the complexity and the multiplicity of the synthesis process stages, secondly, rapid “washing out” of compound LiCl.2Al(OH)3(for 7 to 10 days from the beginning of sorbent application) from resin macropores during sorption-desorption cycles.

There is known a method of producing a granular selective sorbent for lithium recovery from brines by electrochemical dissolution of metallic aluminum in a concentrated solution of lithium chloride to form the compound LiCl.2Al(OH)3.m H2O, separating a sorbent phase from the solution phase, drying and granulating the dry sorbent powder with a binder (fluoroplastic powder) dissolved in acetone [3]. The disadvantages of this method of sorbent synthesis include: high power consumption of the electrochemical synthesis process, low productivity of the process and high explosion- and fire hazard of the granulation process, due to the use of acetone as a solvent.

PCT/DE2001/004062 discloses a method of producing a granular sorbent for lithium recovery from brines and a plant for its embodiment [4] that comprises a production of LiCl.2Al(OH)3.nH2O powder by mixing an aluminum hydroxide with lithium chloride in the presence of a calculated amount water in a high-speed mixer for bulk materials with a stirrer and a treatment of the resulting mixture in a centrifugal activating mill to obtain a LiCl.2Al(OH)3.nH2O powder with a particle size of 0.16 mm or less.

A granulation of the produced powder is carried out by extruding a paste obtained by mixing the sorbent powder with the PVC resin (binder) dissolved in methylene chloride. After distilling off methylene chloride vapors, the extrudate is crushed and classified to obtain product with granule size of 1.0 to 1.5 mm. The vapors of methylene chloride distilled during granulation are absorbed by Freon oil (grade XF-22c-16) from the carrier gas stream (air) to obtain a 20% solution of methylene chloride in oil, which is fed for thermal desorption of methylene chloride followed by condensation of its vapors and recycling the condensed phase of methylene chloride to sorbent production. The disadvantages of this method include a high power consumption of the LiCl.2Al(OH)3.nH2O powder synthesis, low stability of the obtained compound and absence of reliable mechanical activation equipment. The above-mentioned disadvantages make it impossible to implement the method on an industrial scale.

RU Pat. 2223142 discloses a method of producing a sorbent for lithium recovery from brines [5] to eliminate the disadvantages of the previous method [4]. The technical result is achieved by a direct interaction of a mixture of crystalline aluminum chloride and lithium hydroxide in the presence of a small amount of water or their concentrated solutions to form LiCl.2Al(OH)3.mH2O. The interaction proceeds according to the reaction:
2AlCl3+6LiOH+nH2O→LiCl.2Al(OH)3.nH2O+5LiCl  (1)

Despite the high quality of the product, its high stability and reproducibility, the significant disadvantage of this method is a high consumption of the most expensive commercial lithium product, lithium hydroxide. One mole of the resulting compound requires 6 moles of LiOH. In addition, the method is characterized by the presence of a large amount of lithium-containing waste products in the form of LiCl solution, which requires additional costs for lithium regeneration.

Later the same authors proposed a method of producing a sorbent for lithium recovery from brines, which is based on application of cheaper and less deficit Li2CO3instead of LiOH for synthesis of LiCl.2Al(OH)3.nH2O [6]. The solid phase of the product is formed according to the following reaction:
2AlCl3+3Li2CO3+(3+n)H2O→LiCl.2Al(OH)3.nH2O+5LiCl+3CO2(2)

At the same time, the byproduct of the reaction is easily converted to lithium carbonate by precipitation from the solution by soda according to the following reaction:
2LiCl+Na2CO3→Li2CO3↓+2NaCl  (3)

The regenerated lithium carbonate is recycled to the production of the sorbent. Thus, only 0.5 mole of Li2CO3is required to obtain 1 mole of LiCl.2Al(OH)3.nH2O compound. However, this method has significant disadvantage, namely, a low rate of reaction (2) and consequently a long duration of sorbent synthesis, which takes several hours. In addition, the synthesis process is often accompanied by the formation of LiCl.2Al(OH)3.nH2O in gel state, which makes it difficult to separate the solid phase from the mother liquor. The process also does not provide granulation of the sorbent powder obtained.

RU Pat. 2455063 discloses a method of producing a granular sorbent for lithium recovery from brines [7] which is capable to eliminate the disadvantages of the above-described method. The method comprises producing a chlorine-containing species of double aluminum lithium hydroxide (LiCl.2Al(OH)3.nH2O) from an aluminum chloride solution by preliminarily mixing with a lithium hydroxide or lithium carbonate at atomic ratio Al:Li of 2.0 to 2.3 and adding NaOH to the mixed solution to set pH value of 6 to 7. The LiCl.2Al(OH)3.nH2O precipitate is separated from the solution, dried, ground and granulated by adding of polyvinyl chloride and methylene chloride as solvent. The methylene chloride evaporated during granulation is regenerated and recycled to production process.

In terms of its technical essence and achieved result this method is considered to be the closest analogue of present invention and is chosen as the prototype of the present invention. However, in addition to the undoubted advantages, this method has the following disadvantages:

the application of filtration to separate the synthesized DHAL-Cl from the mother liquor leads to the formation of a very dense cake, which has to be crushed before proceeding to the next operation;

excessive content of lithium chloride in the finished product caused by unreasonably increased consumption of expensive lithium reagents when producing DHAL-Cl sorbent;

unreasonably long duration of a single-stage drying of DHAL-Cl powder;

high residual organic solvent content in the extrudate, which leads to increased consumption of the solvent, on the one hand, and deterioration of sanitary-hygienic labor conditions, on the other hand;

the unreasonably low value of the mechanical strength of the original DHAL-Cl particles obtained by crushing the degassed extrudate due to their irregular shape;

the methylene chloride regeneration system based on vapor absorption-desorption by oil with subsequent condensation into the liquid phase is not only bulky and difficult to operate, but also fire hazardous due to presence of a large volume of combustible vacuum oil;

high vapor pressure of methylene chloride due to its low boiling point (40° C.) leads to large losses of the solvent during extrusion;

use for the production of lithium-containing aqueous solution of AlCl3only expensive commercial lithium products, namely, Li2CO3and LiOH.H2O, whereas there are a whole number of lithium-containing by-products and waste-products which could be used successfully for preparing aluminium-lithium solution at a lithium production plant.

The proposed method of obtaining a granular sorbent for lithium recovery from lithium-containing brines as in-line process at a plant for fabrication of commercial lithium products retains all the advantages of the prototype and eliminates the above disadvantages.

SUMMARY OF THE INVENTION

The technical result that eliminates the above-mentioned disadvantages is achieved using the following techniques and operations.The dispersed phase (powder) of double aluminum and lithium hydroxide (DHAL-Cl) is synthesized from a lithium-containing solution of aluminum chloride with a concentration of AlCl3of 45 to 220 kg/m3. The lithium-containing aluminum chloride solution is prepared by dissolving aluminum chloride hexahydrate in an aqueous solution containing the calculated amount of lithium which was introduced both in the form of individual (commercial) lithium compounds LiCl, Li2CO3, LiOH.H2O, and in the form of mixtures of these compounds as well in the form of lithium-containing solutions and mixtures of lithium-containing solutions or in forms of mixtures of individual lithium compounds with lithium-containing solutions coming from the corresponding regeneration stages at a plant for fabrication of commercial lithium products LiCl, Li2CO3, LiOH.H2O from natural lithium-containing brines. Separation of DHAL-Cl dispersed phase from the mother liquor (aqueous NaCl solution) is carried out by centrifugation, and the obtained fugate is applied for the production of a disinfection solution of sodium hypochlorite. The separated DHAL-Cl dispersed phase is repulped in the calculated volume of water to remove excess of LiCl from DHAL-Cl by desorption into the liquid phase while stirring the pulp for 20 to 30 minutes. The pulp is centrifuged, the obtained fugate (aqueous LiCl solution) is recycled to the operation of preparing a lithium-containing solution of aluminum chloride, and DHAL-Cl dispersed phase is subjected to a two-stage drying, wherein DHAL-Cl is first dried by heated air in fluidized bed at temperature 70 to 75° C. until the residual moisture content is 9.5 wt. %, then DHAL-Cl is subjected to the vacuum drying with stirring at temperature 60 to 65° C. until the residual moisture content is 1.5-2.0 wt. 0%.The dried and ground DHAL-Cl powder is mixed with a previously prepared solution of chlorinated polyvinyl chloride (CPVC resin) in organochlorine solvent which could be not only methylene chloride, but also trichloroethylene, tetrachlorethylene or mixtures thereof, to form a paste. The prepared paste is extruded through a drawing nozzle with orifice diameter of 5 mm. The extrudate is brought into countercurrent contact with the air stream heated to 120-130° C. to evaporate the organochlorine solvent. After air degassing stage, the extrudate is fed to the vacuum degassing stage under a pressure of 0.4-0.6 atm. After degassing, the extrudate is subjected to crushing and classification by feeding the recycle (fine fraction of granulated DHAL-Cl) to the paste preparation operation. DHAL-Cl granules with a size of at least 1.0 mm and not more than 2.0 mm are pelletized to obtain the sorbent granules of a rounded shape, thereby to increase their mechanical strength and to recycle the screening product to the paste preparation operation.The air stream cooled during the degassing of the extrudate and saturated with vapors of an organochlorine solvent or a mixture of their vapors is fed to compression under pressure of 6 atm which is accompanied by cooling the air-vapor stream to −3° C. and condensation of vapors of an organochlorine solvent or a vapor mixture of organochlorine solvents and water. The separation of the condensed phase from the gas phase is carried out by mist elimination, and the separation of an organochlorine solvent or a mixture of organochlorine solvents from water is carried out by decantating.After separation the condensed phase, the compressed air-vapor stream is fed to deep cooling to −15° C. which is accompanied by deep condensation of the vapors of an organochlorine solvent or a vapor mixture of organochlorine solvents into the liquid phase and water vapor into the ice crystals, followed by separation of the condensed phases from the air flow and separation of the condensed phases into solid (ice) phase and liquid (organochlorine solvent or a mixture of organochlorine solvents) phase. Decompression of the air stream separated from the condensed phases is carried out by heating to 0° C. Thereafter the purified and dried air stream is heated to 120-130° C. and recycled to the extrudate degassing operation.After combining liquid condensed phases of an organochlorine solvent or a mixture of organochlorine solvents obtained during compression and deep cooling of the air-vapor stream, the liquid solvent is recycled to dissolve the chlorinated polyvinyl chloride. The combined phase of ice crystals and a liquid condensed phase from the air-vapor compression operation is fed to the operation of preparing a lithium-containing solution of AlCl3.

In comparison with the prototype the proposed solutions have the following advantages:

1. Reducing a production price of granular DHAL-Cl due to reducing the consumption of lithium-containing reagent, when synthesis of the dispersed phase of DHAL-Cl, replacing expensive commercial lithium products with lithium-containing by-products and waste products obtained, for example, from natural lithium brines or the excess LiCl contained in the synthesized DHAL-Cl, simplification of a system for recovery of organochlorine solvent;

2. Increasing the mechanical strength of the granulated sorbent DHAL-Cl;

3. Reducing the fire hazard of a production;

4. Reducing the emission of an organochlorine solvent vapors into the air of the working area and the environment.

The reality of achieving the technical result is confirmed by the description of the technological scheme for production of granular DHAL-Cl sorbent.

