RU2157338C2 - Method of production of high-purity lithium hydroxide from natural brines - Google Patents

Abstract

FIELD: chemical technology of production of lithium compounds from natural brines containing halides (chlorides and bromides) of lithium, potassium, calcium and magnesium; production of high-purity lithium hydroxide. SUBSTANCE: method includes electrochemical conversion of mixture of lithium chloride with lithium carbonate both in presence of reductant and without it. Lithium chloride is produced by passing the brine through layer of inorganic sorbent followed by elution of lithium with water, thus obtaining solution of lithium chloride and cleaning the eluate from admixtures on cationite. Electrolysis is performed at current density of 3 to 30 A/sq.dm. Crystallization of lithium hydroxide is performed at carbonization of part of LiOH solution, thus obtaining lithium carbonate. Waste chlorine is entrapped by bromine-containing brine. Cathode hydrogen is burnt and heat is used for additional strengthening the solution of lithium hydroxide. EFFECT: enhanced efficiency. 2 cl, 3 dwg, 2 tbl, 7 ex

Description

 Areas of technology.

 The invention relates to chemical technology for producing lithium compounds, in particular to a method for producing lithium hydroxide and its salts from natural brines.

 The prior art.

 A known method of producing lithium hydroxide with a high degree of purity from brines containing lithium halides and other alkali metals (Na, K), as well as magnesium halides and alkaline earth metals (Ca, Sr) [1l. The method includes concentrating the brine in evaporation basins to a content of 2-7% lithium, crystallizing and separating alkali metal salts (Na, K), precipitating magnesium and alkaline earth metals by alkalizing the brine to a pH of 10.5 - 11.5 using lime in the first stage milk, then lithium hydroxide and carbonate, neutralizing the brine and diluting it to a Li content of 4.48%, followed by electrolysis of the brine in an electrolytic cell with an ion-selective membrane Nafion 475, 325, separating the catholyte from the anolyte, and obtaining a solution of hydroxide l itium with a concentration of up to 8-14% in the cathode chamber and the release of gaseous chlorine at the anode.

To obtain high purity lithium hydroxide monohydrate, it is crystallized from a catholyte solution in which the content of impurity cations does not exceed 0.5%. Partial crystallization of LiOH • H ₂ O from such a solution resulted in a product with a chlorine impurity content of not more than 0.03% (usually 0.005%). During carbonization of a lithium hydroxide solution, lithium carbonate with a chloride content of not more than 0.0065% was obtained. Released chlorine and hydrogen, entering into the interaction, form hydrochloric acid, which is used to obtain high-purity lithium chloride, resulting from the exchange reaction with high-purity lithium hydroxide monohydrate [1].

 This method is the closest to the claimed technical solution and we have chosen as a prototype.

The disadvantages of this method are:
- the multi-stage process of LiCl isolation associated with the concentration of brines in a natural way with the separation of Na and K halides, then precipitation of Ca and Mg impurities with lime, filtering the brine from precipitates formed, subsequent concentration of the brine using immersion combustion, further precipitation of Ca, Mg and Fe impurities with LiOH and Li ₂ CO ₃ , again separation of precipitation, acidification of a solution of LiCl;
- additional costs for the purchase of reagents (lime) for the allocation of impurities;
- high energy costs for multiple filtering of brine from precipitation;
- additional costs for obtaining hydrochloric acid from gaseous Cl ₂ and H ₂ ;
- the use of expensive Nafion membranes during electrolysis;
- the use for electrolysis of solutions of only a highly soluble lithium salt (LiCl);
- limited applicability of the method only to sodium chloride type brines (low in calcium ions).

The proposed method allows to eliminate these disadvantages, namely to eliminate the concentration of the entire volume of the brine, reagent cleaning of impurities Mg and Ca, to expand the capabilities of the method by using any type of brines, including calcium chloride type brines, and also to use lithium hydroxide in the electrolysis process only solutions of lithium chloride, but also pulp of lithium carbonate with solutions of readily soluble lithium salts (LiCl, Li ₂ SO ₄ , etc.) or water.

 SUMMARY OF THE INVENTION

 The technical result is achieved by passing the brine through a layer of inorganic sorbent followed by elution of lithium with water to obtain a lithium chloride solution (the concentration of lithium chloride increases 5-10 times against the LiCl content in the initial brine) and purification of the eluate from Ca and Mg impurities using KU ion exchange resin -2 in Li-form, electrolysis of a mixture of the obtained LiCl solution with lithium carbonate in an electrolyzer with a MK-40 cation exchange membrane to obtain a LiOH solution, as well as by using chlorine released on an ode to produce bromine from brine and / or lithium bromide, as well as high purity lithium chloride by trapping chlorine with a hydroxide solution or a pulp of lithium carbonate.

After lithium is extracted from brines in the form of chloride, the eluate with a concentration of LiCl ~ 8-15 g / l is mixed with lithium carbonate powder and the pulp is electrolyzed in a membrane electrolyzer with a MK-40 or MK-41 cation-exchange membrane separating the anode and cathode chambers. In the anode chamber, pulp of lithium carbonate circulates with a solution of LiCl; in the cathode — a LiOH solution, the initial concentration of which should be at least 5 g / l. Concentration of the LiOH solution is due to the transition of Li ⁺ ions from the anode chamber to the cathode and the decomposition of water at the cathode by the reaction of H ₂ O + e ---> 1/2 H ₂ + OH ^- . The resulting solution contains 60-120 g / L LiOH and Cl ≤ 0.3 g / L.

Gaseous chlorine formed on the anode is either captured by brine, which contains Br ^- ion and oxidized to elemental bromine, or captured by a pulp of lithium carbonate to obtain a LiCl solution. After bromine is isolated, it is used to produce lithium bromide by known methods [2], for example, by reacting liquid bromine or its vapors with a LiOH solution or a pulp of lithium carbonate. Chlorine released at the anode can also be captured by a pulp of lithium carbonate with water in the presence of a reducing agent, for example, urea, by the reaction:
3Li ₂ CO ₃ + 3Cl ₂ + (NH ₂ ) ₂ CO = 6LiCl + N ₂ + 4CO ₂ + 2H ₂ O.

 Hydrogen gas formed at the cathode is burned and the resulting coolant is used to evaporate lithium hydroxide solutions.

 For the conversion of lithium chloride salts with carbonate or pulps of lithium carbonate with water into lithium hydroxide, mono - or bipolar electrolyzers were used (Fig. 1). In monopolar electrolyzers, perforated electrodes were used. When using bipolar electrolyzers, current was supplied only to the anode and cathode located in the extreme chambers, and iridized titanium foil with an iridium coating thickness of at least 0.5 μm was used as intermediate electrodes (Fig. 1a). When using monopolar electrolyzers, current was supplied to each cathode and anode (Fig. 1b). In both cases, carbon electrodes or oxide-tungsten titanium anodes (ORTA) modified with silicon oxide or titanium electrodes coated with platinum were used as anodes. Stainless steel was used as the cathode.

Electrolysis was carried out at current densities of 3-30 A / dm ² until a LiOH concentration of 60-120 g / L was reached in the solution. The concentration of impurity ions in the LiOH solution was ≤ 0.3 g / L. The resulting lithium hydroxide solutions were evaporated to crystallize LiOH • H ₂ O using a heat transfer fluid obtained by burning hydrogen. After crystallization of LiOH • H ₂ O, the washed and dried precipitate contained no more than 0.003% chlorine impurity. During the electrolysis of pulps of lithium carbonate and water in the obtained LiOH • H ₂ O, the chlorine content was beyond its detection. During carbonization of the mother liquor of LiOH with an admixture of NaOH and KOH (not more than 10%), lithium carbonate was obtained, which was sent to the electrolysis of pulps of lithium carbonate in a LiCl solution.

 Thus, the main distinguishing features of the proposed method are the use of lithium carbonate for pulp electrolysis with an aqueous solution of lithium chloride (or another soluble lithium salt, for example sulfate) or water; utilization of chlorine released at the anode to produce bromine, lithium bromide or its chloride and hydrogen released at the cathode, to obtain the coolant used in the evaporation of the LiOH solution.

The proposed method is universal, as it allows the use of both soluble lithium salts (LiCl, Li ₂ SO ₄ ) and sparingly soluble lithium carbonate, as well as mixtures of lithium chloride and lithium carbonate, sulfate and lithium carbonate, to produce lithium hydroxide high purity. The method is universal, as it allows the use of brines of any type containing lithium and bromine. To obtain lithium hydroxide, you can use lithium carbonate obtained from natural brines, and commercial lithium carbonate, for example Chilean, which has a low cost in the world market. The use of the eluate of selective sorption of lithium from brines mixed with lithium carbonate can increase the economics of brine processing through the use of chlorine in bromine production, as well as by increasing the range of products. Involving in the process cheap Chilean lithium carbonate mixed with eluate will increase the amount of lithium hydroxide monohydrate obtained. During electrolysis, membranes of domestic production (MK-40, MK-41) can be used without degrading the quality of the products.

 The invention is novel, since comparing it with known solutions in the art shows that the use of lithium carbonate pulp with aqueous solutions of lithium salts or water to obtain lithium hydroxide by membrane electrolysis was not found in available sources of information.

 Enumeration of figures and tables.

 1. Scheme of flows of pulp solutions in electrolytic cells.

 2. Examples for obtaining a solution of lithium hydroxide (table).

 3. An example of the implementation of the method (Technological scheme).

 4. Comparison table according to the claimed method and the prototype method.

 Information confirming the possibility of carrying out the invention.

 Example 1

10 l of brine having the composition (g / l): LiCl - 2.5; CaCl ₂ - 350; MgCl ₂ - 120; Br ^- - 9.3 and a total salinity of ~ 500 g / l, passed through a column filled with an inorganic sorbent (350 g; volume 450 cm ³ ), selective for Li ions and prepared according to the method [3]. The main component of the sorbent is a compound of the composition LiCl • 2Al (OH) ₃ • mH ₂ O, capable of donating part of LiCl during desorption with water to obtain eluates - solutions of lithium chloride with a concentration of 15 g / l LiCl and 0.5 g / l magnesium chloride and calcium . During lithium desorption, the sorbent is washed from brine residues with 2 volumes of water (900 ml), supplying water through the column at a rate of ~ 2 l per hour. After that, lithium is desorbed from the sorbent, passing water through the column at a speed of 0.4 l per hour. The resulting eluate in an amount of ~ 0.9 L is dropped onto an ion-exchange column filled with KU-2 resin in Li-form in order to purify Ca and Mg ions from impurities. After cleaning, the cast chloride solution has a total content of CaCl ₂ and MgCl ₂ impurities of 0.004 g / l.

25 g of Li ₂ CO ₃ are poured into the eluate purified from impurities and the resulting suspension is stirred. The pulp is subjected to electrolysis in a bipolar electrolyzer, consisting of 5 unit cells (Fig. 1A). At the extreme electrodes made of stainless steel (cathode) and carbon graphite (anode), a constant electric current is supplied. A solution of lithium hydroxide circulates in the cathode chambers; in the anode, a suspension of Li ₂ CO ₃ in a LiCl solution. The electrolyzer contains four intermediate electrodes made of titanium foil and coated with iridium on the anode side. The anode and cathode chambers in the unit cell are separated by MK-40 brand cation exchange membranes, and the unit cells are separated by intermediate electrodes. The electrolysis is carried out in galvanostatic mode at a current density of 3 A / DM ² . The initial and final concentration of solutions, the transfer of Li ions to the cathode chamber upon receipt of a final LiOH concentration of ~ 65 g / l, as well as the content of impurities and energy costs for the electrolysis process are presented in the table (Fig. 2).

0.7 L of a 65 g / L LiOH solution was evaporated ~ 2.5 times and cooled to room temperature. The resulting lithium hydroxide monohydrate LiOH • H ₂ O in an amount of 62 g after separation in a centrifuge contained 0.002% Cl.

Chlorine released at the anode was passed through Tishchenko’s flask filled with brine. In this case, the bromide ions contained in the brine were oxidized with chlorine to elemental bromine by the reaction: CaBr ₂ + Cl ₂ ---> Br ₂ + CaCl ₂ .

During the operation of the electrolyzer, 5.0 g of Cl ₂ were obtained and, in accordance with the above reaction, 9 g of Br ₂ (degree of chlorine absorption ~ 80%)
Example 2

 The eluate obtained as described in Example 1 was concentrated to a LiCl content of 100 g / L.

30 g of Li ₂ CO _{3 was} poured into a lithium chloride solution with a concentration of ~ 100 g / L; the resulting suspension after stirring was electrolyzed in a galvanostatic mode at a current density of 15 A / dm ² in a monopolar electrolyzer consisting of a perforated cathode (stainless steel) and anode (platinum titanium), separated by cation exchange membranes of the MK-40 brand (Fig. 16). The initial and final concentration of solutions, the transfer of lithium ions to the cathode chamber upon receipt of lithium hydroxide with a concentration of ~ 80 g / l, the content of impurities and energy costs for the electrolysis process are presented in the table (Fig. 2).

During the electrolysis, 2.5 g of Cl _{2 were released} , which were captured by the brine in Tishchenko’s flask, and 4.5 g of Br _{2 were} discarded. Elemental bromine was blown off from the brine by air, bromine vapor was sent to a flask of pulp 2.07 g of Li ₂ CO ₃ in 200 ml of water containing 0.67 g of urea. With stirring and heating the reaction mass to 45 ^° C, a solution of lily bromide with a concentration of 25 g / L was obtained.

 Example 3

The same as in example 2, but the electrolysis process was carried out at a current density of 20 A / dm ² until the LiOH concentration in the solution reached ~ 75 g / l. The results of the experiment are shown in the table (Fig. 2).

In the course of the experiment, 4.8 g of Cl _{2 were released} , which were captured by the initial bromine-containing brine. As a result of the oxidation of the Br ^- ion, ~ 10.85 g of Br _{2 was} obtained, the vapors of which, while blowing bromine from brine with air, were caught with a mixture of 50 ml of a solution of lithium hydroxide 65.17 g / l and 1.1 g of urea when heated to 50 ^o C. Received a solution of lithium bromide with a concentration of 230 g / l.

 Example 4

The eluate obtained as in example 1 was concentrated to a LiCl content = 250 g / l
28 g of Li ₂ CO ₃ and 7.5 g of urea were added to a 1 L solution of lithium chloride, the resulting suspension was electrolyzed in a monopolar electrolyzer consisting of a perforated cathode (stainless steel) and an anode (ORTA modified with silicon oxide, 10%), separated between themselves cation exchange membrane brand MK-40. In the cathode space there is a LiOH solution, in the anode space there is a suspension of Li ₂ CO ₃ in a LiCl solution and urea. Electrolysis is carried out at a current density of 30 A / DM ² . The initial and final concentration of solutions, the transfer of lithium ions to the cathode chamber upon receipt of a LiOH concentration of ~ 60 g / l, the content of impurities in LiOH, and the energy consumption for carrying out the electrolysis process are presented in the table (Fig. 2).

After evaporation of the LiOH solution (60 g / L) by a factor of ~ 2 and crystallization of the precipitate in the resulting LiOH • H ₂ O, the Cl content was 0.003%.

 Chlorine was captured by starting brine as described in Example 1.

 Example 5

The eluate obtained as in example 1 was concentrated to 300 g / l LiCl. A solution of lithium chloride in water was subjected to electrolysis in a monopolar electrolyzer, as described in example 4. The results of the experiment are shown in table (Fig. 2). The resulting solution contained 121 g / l of LiOH and 0.3 g / l of chlorine impurities. After evaporation of the LiOH solution (121 g / l) and crystallization of the precipitate in the obtained LiOH • H ₂ O, the chlorine content was 0.003%.

 Example 6

The implementation of the method is carried out in accordance with the circuit shown in FIG. 3. The eluate after selective sorption of lithium from natural brine with a concentration of 10-15 g / l LiCl is fed into a container for mixing it with lithium carbonate, from which the pulp enters the membrane-type cell, the anode and cathode chambers of which are separated by a MK-40 cation exchange membrane ( MK-41). The catholyte, after reaching a LiOH concentration of 100-120 g / l, is supplied from the electrolysis cell for evaporation to an apparatus heated by heat from the combustion of hydrogen released at the cathode. After evaporation and cooling of the solution for crystallization of LiOH • H ₂ O, the precipitate is separated by centrifugation, and the mother liquor containing a mixture of hydroxides LiOH, NaOH and KOH (the content of the latter up to 10%) is sent to carbonization. Carbonization is carried out with anode gas after capturing the main quantities of chlorine with the starting brine. The lithium carbonate pulp is thickened, a precipitate of lithium carbonate is separated and sent to a container for mixing with selective lithium sorption eluate. Part of the pulp Li ₂ CO ₃ with water is used to absorb bromine. Air is passed through the brine after absorption of chlorine and oxidation of the Br ^- ion to elemental bromine to blow off Br ₂ and trap it with a pulp of lithium carbonate (LiOH solutions can also be used to trap bromine). The resulting solution of lithium bromide to obtain a marketable product can either be concentrated to ~ 55% LiBr or crystalline lithium bromide LiBr ₂ • H ₂ O can be isolated.

Thus, the implementation of the method is carried out in a closed technological cycle, and the technological scheme is non-waste. The energy consumption for the conversion of pulp Li ₂ CO ₃ and LiCl by the present method and the energy consumption for the conversion of LiCl by the prototype method are almost the same. However, the total energy consumption for the implementation of the method is significantly reduced due to the use of heat from the burning of cathode hydrogen.

 Example 7. (Comparative).

A solution of lithium chloride in water was subjected to electrolysis in a monopolar electrolyzer. The anolyte composition and electrolysis conditions were used as described in the prototype (see Fig. 4). The resulting catholyte contained 80.4 g / L LiOH and 0.95 g / L LiCl. The transfer of Li ⁺ and energy consumption in the experiment were comparable with those obtained in the examples of the present method. However, in catholyte, the content of LiCl impurities increased by ~ 3 times.

After evaporation of the LiOH solution, a precipitate of LiOH • H ₂ O was obtained with a chlorine impurity content of 0.008%.

The process of electrolysis of the pulp Li ₂ CO ₃ in a LiCl solution in the presence of urea allows not only to obtain a high purity product, but also to reduce energy consumption for the electrolysis process.

From the comparison of the proposed method with the prototype method, it should be noted the obvious advantages of the proposed method:
- reducing the multi-stage process of obtaining a solution of lithium chloride from natural multicomponent brines;
- Organization of a completely closed waste-free process;
- ease of disposal of chlorine by trapping it with brine;
- an increase in the range of products due to the production of lithium bromide;
- the use of catholyte with a lower impurity content of lithium chloride, from which lithium hydroxide monohydrate, as well as high-purity lithium carbonate, chloride and bromide;
- reduction of the total energy consumption for the process of obtaining LiOH • H ₂ O due to the use of heat carrier from the combustion of hydrogen.

T. about. The method allows to improve the economic performance of the technology for the simultaneous production of lithium hydroxide, bromide or lithium bromide, as well as through the use of chlorine and hydrogen obtained in the process of electrolysis of pulp Li ₂ CO ₃ , with solutions of lithium chloride, and also by obtaining highly concentrated solutions of lithium hydroxide, which reduces energy costs for the production of lithium hydroxide monohydrate. In addition, the method allows the use of chlorine from electrolysis to produce high purity lithium chloride to produce lithium metal.

 Industrial applicability.

 The proposed method allows to involve lithium enriched bromine splits in production for use as a raw material for obtaining high-purity lithium products: chloride, hydroxide, carbonate, lithium bromide.

 The method allows the use of commercial lithium carbonate, for example Chilean, which has a low cost on the world market, in a mixture with a LiCl solution obtained from brines, to obtain high purity lily hydroxide.

 Sources of information.

 1. The patent of Germany N 2700748, C 01 D 15/02 from 08.09.77. (prototype).

 2. V.I. Ksenzenko, D.S. Stasinevich. "Chemistry and technology of bromine, iodine and their compounds", M. Chemistry, 1995.

 3. Patent N2050184, B 01 J, 02/11/93.

Claims (2)

1. A method of producing lithium hydroxide of high purity from natural brines containing halides (chlorides and bromides) of lithium, potassium, calcium and magnesium, comprising obtaining a solution of lithium chloride, its electrochemical conversion by membrane electrolysis to obtain a lithium hydroxide solution containing LiOH up to 14 , 0%, crystallization of lithium hydroxide monohydrate, carbonization of a part of a LiOH solution to produce lithium carbonate and utilization of chlorine and hydrogen, characterized in that the mixture is subjected to electrochemical conversion solution and lithium chloride with lithium carbonate, moreover, lithium chloride is obtained by passing brine through a layer of inorganic sorbent, followed by elution of lithium with water to obtain a solution of lithium chloride and purification of the eluate from impurities on cation exchange resin, and electrolysis is carried out at a current density of 3-30 A / dm ² ; the outgoing anodic chlorine is captured by the initial bromine-containing brine; cathode hydrogen is burned, and the generated heat is used to supplement the lithium hydroxide solution; the mother liquor after crystallization of LiOH • H ₂ O is subjected to carbonization by direct contact with the anode gas to form lithium carbonate pulp, directed after thickening to the operation of obtaining a mixture of lithium carbonate with a solution of lithium chloride.  2. The method according to p. 1, characterized in that the electrolysis is carried out in the presence of a reducing agent.

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