RU2196735C1 - Process of extracting monohydrate of high-purity lithium hydroxide from materials containing lithium carbonate - Google Patents

Abstract

FIELD: chemical technology of production of inorganic compounds. SUBSTANCE: invention refers to processes of extraction of monohydrate of high-purity lithium hydroxide from materials containing lithium carbonate or technical lithium. Lithium carbonate is solved in sulfuric acid formed in anode chamber of membrane electrolyzer with obtainment of solution of lithium sulfate. Solution of lithium sulfate with concentration 180-200 kg/cu.m (3.3-3.6 kg eq/cu.m) displays high conduction and allows process of conversion of lithium sulfate to hydroxide to be conducted in electrolyzer with current density 5.0-15.0 A/dm and voltage drop across cell 4.7-5.1 V. Under conditions of membrane electrolysis formed solution of lithium hydroxide (catolyte) includes impurities of bivalent and trivalent metals contained in technical lithium carbonate or waste carrying Li₂CO₃. Solution of lithium hydroxide and lithium carbonate won within scope of technological process is utilized to purify anolyte from impurities. Concentration of lithium hydroxide in catolyte is kept at level 35.0-45.0 kg/cu.m. It is achieved when concentration of acid in anolyte equals 0.6-1.0 kg eq/cu.m. Keeping concentration of LiOH at level of 35.0-45.0 kg/cu.m is determined by least summary expenses on process of electrolysis and evaporation of solutions of LiOH. Content of impurities Na⁺ and K⁺ is maintained at level of 0.35-1.2 relative per cent in solutions of lithium hydroxide by extraction of portion of mother liquor. Monohydrate of lithium hydroxide formed in this case contains ≤0,060 mas.% of sodium (potassium) which can be washed out under conditions of counterflush prior to winning high-purity LiOH.H₂O. Carbon dioxide at stage of neutralization of sulfuric acid by lithium carbonate is used for reclamation of lithium from mother liquors with production of lithium carbonate which is utilized in technological circuit to purify anolyte or is returned for operation of neutralization of sulfuric acid. EFFECT: potential for entrainment of technical lithium carbonate and waste containing lithium carbonate in process of extraction of high-purity monohydrate of lithium hydroxide. 4 cl, 6 dwg, 4 tbl

Description

 The invention relates to the field of chemical technology for the production of inorganic compounds, and in particular to methods for producing lithium hydroxide monohydrate of high purity from materials containing lithium carbonate or technical lithium carbonate.

 A known method of obtaining a solution of lithium hydroxide from solid carbonate-containing lithium waste by contacting them with water, settling the resulting pulp, decanting the clarified liquid phase, followed by its filtration and recirculation of the obtained lithium-containing solution through the central chamber of the electrodialyzer to obtain a lithium hydroxide solution in the cathode chamber, in the anode chamber solution of a mixture of acids, in the central chamber - desalted liquid returned to the contact operation of solid lithium carbonate waste with water (RU 2071819, publ. 20.01.97).

The disadvantages of this method are the low concentration of lithium hydroxide in the resulting alkaline solution (not more than 25 kg / m ³ ), the low productivity of the process due to the low current density (up to 2 A / dm ² ), high specific energy consumption due to the insufficient concentration of lithium in the recycle solution due to the low solubility of lithium carbonate, on the one hand, and the use of a three-chamber electrodialysis cell, on the other hand.

A known method of producing a solution of lithium hydroxide from materials containing lithium compounds, in particular from waste lithium batteries / patent (New Zealand) WO 9859385, 1998 /, including the extraction of lithium in the form of its highly soluble salt to obtain a solution of lithium sulfate, electrolysis of lithium sulfate in an electrochemical cell having a cathode and anode space separated cation exchange membrane Nafion 350. lithium sulfate electrolysis is carried out at a current density of 20 A / dm ² and the voltage drop across the cell is 5.3 V. in this case, output is carried out to the todnogo space lithium hydroxide solution (catholyte) and the anode of the space - lithium sulfate solution into the product mixture with the anode process - sulfuric acid (anolyte). The lithium hydroxide solution removed from the cathode space is subjected to ultrafiltration for purification from impurities.

 The disadvantages of this method include the need to use scarce and expensive highly selective Nation 350 cation-exchange membranes to obtain a pure product, the limited type of raw materials — lithium batteries, and the need to use ultrafiltration method, which requires unique equipment (special high-pressure pumps), to clean impurities of the obtained lithium hydroxide solution and special membranes). In addition, this process is limited to obtaining only a LiOH solution and does not contain any redistributions that allow producing high-purity lithium hydroxide monohydrate as a final product.

A known method of producing lithium hydroxide of high purity from natural brines containing halides (chlorides and bromides) of lithium, potassium, calcium and magnesium, including sorption of lithium from brine to obtain a solution of lithium chloride, its concentration and electrochemical conversion by membrane electrolysis to obtain a hydroxide solution lithium containing LiOH up to 14.0 wt.%, crystallization of lithium hydroxide monohydrate, carbonization of a portion of LiOH solution to produce lithium carbonate and utilization of chlorine and hydrogen (RU 2157338, publ. 10.10.20 00). A mixture of a solution of lithium chloride with lithium carbonate is subjected to electrochemical conversion, moreover, lithium chloride is obtained by passing brine through a layer of inorganic sorbent, followed by elution with water, obtaining a solution of lithium chloride and its purification from impurities on cation exchange resin, and electrolysis is carried out in the presence of a reducing agent at a current density of 3- 30 A / dm ² . The waste anode chlorine is captured by bromine-containing brine, the cathode hydrogen is burned, and the heat generated is used to evaporate 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, which is sent after thickening to the operation of obtaining a mixture of lithium carbonate with a solution of lithium chloride.

The disadvantages of this method are the low concentration of lithium chloride solutions obtained by selective sorption of lithium from brines on an inorganic sorbent (eluates), which are used to obtain a solution of lithium hydroxide, the need for ion exchange purification of the entire volume of the eluate from Ca ²⁺ and Mg ^{2+ ions} , increased toxicity of the process of electrochemical conversion of LiCl to LiOH due to the release of chlorine gas as a by-product, which requires special protection of the membranes due to their extremely low stability in ag active media containing active chlorine, and the need to use a reducing agent to prevent the formation of oxychlorides.

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

 The proposed method allows to eliminate these drawbacks, namely, to refuse to use only natural brines as raw materials to obtain lithium chloride solutions that require concentration and ion-exchange purification of impurities, in addition, the proposed method allows to exclude the formation of anode chlorine in the process of electrochemical conversion, thereby ensuring long membrane life.

(на аноде) (1)
2Н₂O+2е-->2ОН^-+Н₂

(на катоде) (2)
В результате анодного процесса генерируются Н⁺ - ионы, а перенос ионов лития в катодную камеру обеспечивает наличие свободных ионов SO₄ ^2-, которые задерживаются катионообменной мембраной в анодной камере, поэтому в анолите всегда присутствует серная кислота. При контакте анолита с карбонатом лития в результате реакции нейтрализации образуется сульфат лития по реакции:
H₂SO₄+Li₂CO₃=Li₂SO₄+H₂O+CO₂

(3)
И таким образом, осуществляется воспроизводство раствора сульфата лития, при этом обеспечивается его концентрация 180-200 г/л (3,3-3,6 г-экв/л). Растворы с указанной концентрацией Li₂SO₄ имеют наиболее высокую электропроводимость, снижение концентрации ниже 180 г/л приводит к снижению электропроводимости раствора, повышение концентрации выше 200 г/л вызывает увеличение вязкости раствора. Конверсию таких растворов сульфата лития проводили при плотностях тока от 5 до 15 А/дм². При указанных плотностях тока процесс протекает стабильно и не наблюдается поляризации мембран.SUMMARY OF THE INVENTION
The technical result is achieved by the fact that a material containing lithium carbonate, or technical lithium carbonate is dissolved in the acid formed in the anode chamber of the electrolyzer, with the formation of lithium sulfate. A solution of lithium sulfate has a high electrical conductivity, therefore, its use for conversion to lithium hydroxide is accompanied by a decrease in ohmic losses in the electrolyte and a decrease in voltage during electrolysis in general. In addition, lead anodes can be used in the electrolysis of sulfate solutions, which significantly reduces the cost of the electrolyzer case is stainless steel). Oxygen released at the anode does not create problems with its utilization, and the resulting acid makes it easy to reproduce lithium sulfate from its carbonate. Electrode processes are described by the following reactions:
H ₂ O-2e -> 2H ⁺ + ¹ / 2O ₂

(on the anode) (1)
2Н ₂ O + 2е ^- > 2ОН ^- + Н ₂

(at the cathode) (2)
As a result of the anode process, H ⁺ ions are generated, and the transfer of lithium ions to the cathode chamber ensures the presence of free SO ₄ ^2- ions, which are retained by the cation exchange membrane in the anode chamber, therefore sulfuric acid is always present in the anolyte. Upon contact of the anolyte with lithium carbonate as a result of the neutralization reaction, lithium sulfate is formed by the reaction:
H ₂ SO ₄ + Li ₂ CO ₃ = Li ₂ SO ₄ + H ₂ O + CO ₂

(3)
And thus, the reproduction of the lithium sulfate solution is carried out, while ensuring its concentration of 180-200 g / l (3.3-3.6 g-equiv / l). Solutions with the indicated concentration of Li ₂ SO ₄ have the highest electrical conductivity, a decrease in the concentration below 180 g / l leads to a decrease in the electrical conductivity of the solution, an increase in the concentration above 200 g / l causes an increase in the viscosity of the solution. The conversion of such lithium sulfate solutions was carried out at current densities from 5 to 15 A / dm ² . At the indicated current densities, the process proceeds stably and membrane polarization is not observed.

The cation-exchange membrane provides the transfer of cations from the anode to the cathode under the action of an electric field with the formation of a lithium hydroxide solution in which cations - impurities contained in the initial lithium carbonate (Na ⁺ , K ⁺ , Ca ²⁺ Mg ²⁺ , Fe ³⁺⁾ will be present Al ³⁺ ), which may contaminate the final product LiOH • H ₂ O.

+2Li⁺ (4)
Mg²⁺+2LiOH=Mg(OH)₂

+2Li⁺(5)
Fe³⁺+3LiOH=Fe(OH)₃

+3Li⁺ (6)
Al³⁺+3LiOH=Аl(ОН)₃

+3Li⁺ (7)
4Аl(ОН)₃+Li₂СО₃+nН₂O=Li₂CO₃•4Аl(ОН)₃•nН₂O(ДГАЛ-СО₃)

(8)
карбонатсодержащая разновидность двойного гидроксида алюминия и лития.The technical result is also achieved by the fact that the method involves the chemical purification of a part of the anolyte from Ca ²⁺ Mg ²⁺ , Fe ³⁺ and Al ³⁺ impurities by converting them into insoluble salts by adding carbonate and lithium hydroxide obtained as part of the technological scheme:
Ca ²⁺ + Li ₂ CO ₃ = CaCO ₃

+ 2Li ⁺ (4)
Mg ²⁺ + ² LiOH = Mg (OH) ₂

+ 2Li ⁺ (5)
Fe ³⁺ + ³ LiOH = Fe (OH) ₃

+ 3Li ⁺ (6)
Al ³⁺ + 3LiOH = Al (OH) ₃

+ 3Li ⁺ (7)
4Al (OH) ₃ + Li ₂ CO ₃ + nH ₂ O = Li ₂ CO ₃ • 4Al (OH) ₃ • nH ₂ O (DGAL-CO ₃ )

(8)
carbonate-containing variety of double hydroxide of aluminum and lithium.

 The purification of the anolyte from these impurities allows you to get the final product of a high degree of purity.

The technical result is also achieved by the fact that the concentration of the LiOH solution in the cathode chamber is maintained at 35-45 kg / m ³ , the LiOH solution is evaporated to a content of 170-180 kg / m ³ , the evaporated solution is cooled to 30-40 ^o C. The resulting LiOH crystals • H ₂ O is separated by centrifugation, and the mother liquor is returned to evaporation, while providing conditions for crystallization of lithium hydroxide monohydrate of the required purity. This is achieved by removing part of the mother liquor containing Na ⁺ and K ⁺ ions, which avoids their accumulation and maintains the concentration of these ions in the LiOH solution supplied for evaporation at the level of 0.35-1.20 rel.%, Thereby ensuring the content impurities of sodium in crystals of LiOH • H ₂ O≤0.06 wt.%. Then, LiOH • H ₂ O crystals are subjected to countercurrent washing, as a result of which the content of these impurities in the crystals decreases to 0.002 wt.%.

The value of LiOH concentration in catholyte at the level of 35-45 kg / m ³ is due to the lowest total energy consumption for the electrolysis and evaporation of LiOH solutions.

The technical result is also achieved by the fact that to create a concentration of LiOH in catholyte at the level of 35-45 kg / m ³ it is necessary to maintain the concentration of acid in the anolyte at the level of 0.6-1.0 kg-equiv / m ³ , since when the acid concentration is lower 0.6 kg-equiv / m ³ there is a danger of incomplete dissolution of lithium carbonate and its deposition in membranes, an increase in acid concentration above 1 kg-equivalent / m ³ reduces the transfer of lithium ions.

+Н₂О (9)
Полученная пульпа карбоната лития фильтруется, твердая фаза карбоната лития отделяется и после промывки подается на операцию очистки анолита или нейтрализации серной кислоты, а фаза раствора, содержащая карбонаты и гидроксиды щелочных металлов, выводится из технологического цикла.The technical result is also achieved by the fact that carbon dioxide from the stage of neutralization of sulfuric acid is used for the disposal of lithium from alkaline mother liquors in the form of carbonate:
2LiOH _(p) + CO _{2 (T)} = Li ₂ CO _{3 (t)}

+ H ₂ O (9)
The resulting lithium carbonate pulp is filtered, the solid lithium carbonate phase is separated and, after washing, it is sent to the anolyte purification or sulfuric acid neutralization operation, and the solution phase containing alkali metal carbonates and hydroxides is removed from the technological cycle.

The proposed method for producing lithium hydroxide monohydrate, made according to the invention, allows to obtain the final product of high purity from materials containing lithium carbonate, contaminated with impurities and representing poorly soluble lithium compounds, with a minimum energy consumption and high yield of LiOH • H ₂ O.

List of drawings
In the future, the invention is illustrated by specific examples of its implementation, graphs and drawings, where
figure 1 shows a process flow diagram for producing lithium hydroxide monohydrate from industrial carbonate by membrane electrolysis of lithium sulfate;
figure 2 is a schematic diagram of a laboratory setup for producing a LiOH solution from lithium carbonate by membrane electrolysis of lithium sulfate:
1 - membrane electrolyzer; 2 - a reactor for converting Li ₂ CO ₃ to lithium sulfate; 3 - capacity for catholyte; 4 - pump; 5 - U-shaped manometer; 6.7 - water dispensers in anolyte and catholyte; 8 - water seal; 9.10 - filters; 11 - receiving capacity of the LiOH solution;
in FIG. 3 - dependence of dynamic viscosity - η, MPa • s (1) and electrical conductivity - γ, cm • cm ^-1 - (2) on the concentration of lithium sulfate in solution;
in FIG. 4 - dependence of the transfer of lithium ions on the acid content in the anolyte when the LiOH content in catholyte is 45 g / l (j = 10.2 A / dm ² );
in FIG. 5 is a graph of the change in the cost of energy for producing 1 t of LiOH • H ₂ O from Chilean lithium carbonate versus the concentration of LiOH solution obtained by electrochemical conversion of lithium sulfate by membrane electrolysis:
1) the cost of energy for membrane electrolysis;
2) the cost of energy for evaporation of the solution;
3) the total cost of the combined method;
figure 6 - dependence of the residual content of sodium impurities in LiOH • H ₂ About after triple washing of the samples (C _con. ) from the initial sodium content in the crystals (C _ref. ).

Information confirming the possibility of implementing the invention
The technology for producing LiOH • H ₂ About a high degree of purity from materials containing Li ₂ CO ₃ , or technical lithium carbon, includes the following operations:
- translation of lithium carbonate into a solution of lithium sulfate;
- purification of a solution of lithium sulfate from impurities of Ca, Mg, Fe, Al carbonate-alkaline method;
- obtaining conversion solutions of alkali (catholyte) by the method of membrane electrolysis;
- obtaining crystals of LiOH • H ₂ O conversion of the alkali evaporation and crystallization, separating the solid phase LiOH • H ₂ O from the mother liquor by centrifugation;
- countercurrent washing with condensate (demineralized water) of squeezed LiOH • Н ₂ О from the remains of the mother liquor with the return of the washing water to evaporation;
- carbonization of alkaline mother liquors to obtain Li ₂ CO ₃ pulp, separation of the solid phase by filtration, countercurrent washing with condensate and return of Li ₂ CO ₃ to the process.

 Figure 1 presents the proposed process flow diagram for producing lithium hydroxide monohydrate.

The technological chain has the following order of operations. An acidic solution of lithium sulfate obtained by neutralizing H ₂ SO ₄ with lithium carbonate is fed to the operation of electrochemical conversion of Li ₂ SO ₄ to LiOH, after which the mixture of sulfate solution and anode-forming sulfuric acid obtained as a result of the electrochemical reaction is returned to the stage of producing lithium sulfate (reaction 3) to make up for the lithium-containing material and neutralize the excess acid with lithium carbonate. In this case, the anolyte is constantly purified from Ca ²⁺ , Mg ²⁺ , Fe ³⁺ Al ³⁺ impurities that have passed into the solution. The cleaning is carried out by the carbonate-alkaline method by removing part of the sulfate solution, neutralizing acidity with solid lithium carbonate and additional alkalization with a concentrated LiOH solution, filtering to separate the precipitate (CaCO ₃ , Mg (OH) ₂ , Fe (OH) ₃ , Al (OH) ₃ and DGAL-CO ₃ (reactions 4-8), followed by the return of the purified lithium sulfate solution to the anode space of the cell.The pH of the sulfate solution is regulated by the flow rate of Li ₂ CO ₃ and the concentration of SO ₄ ^2- by introducing H ₂ O, the amount of which sulfate solution e decreases during the electrochemical conversion. Gaseous products are removed from the cathodic (hydrogen) and anode (oxygen) chambers through gas separators. The alkali solution formed in the conversion plant, the concentration of which is maintained by supplying water, is partially removed from the process and sent to the evaporation stage. evaporation, cooling crystallization and evaporated solution the pulp LiOH • H ₂ O is centrifuged, the resulting crystals are directed to the washing and the mother liquor is returned to evaporation tion, wherein a portion of the mother liquor removed from the process and supplied to the carbonization step for recycling a lithium Li ₂ CO _3. The wash water formed at the stage of washing the crystals of LiOH • H ₂ O, which is a highly concentrated LiOH solution, is returned to the evaporation operation and is partially used in the anolyte purification operation. The washed crystals after dehydration and drying are a commercial product.

The lithium carbonate formed as a result of carbonization of the mother liquor LiOH is washed from the residues of the alkaline mother liquor and returns to the production cycle. Wash water after washing with Li ₂ CO _{3 is} returned to the stage of carbonization, and alkaline mother liquors containing some amounts of Li, Na, K are removed as waste or used for production needs.

 The developed technological scheme is characterized by a comprehensive approach to solving the problem of using materials containing lithium carbonate or technical carbonate as lithium raw materials and allows to obtain high purity lithium hydroxide monohydrate using a minimum amount of reagents, and also eliminates the formation of waste, including harmful ones.

 The following are specific examples confirming the implementation of the method.

Example 1. The conversion of a solution of lithium sulfate to hydroxide was carried out on the installation (figure 2), the main part of which is a membrane electrolyzer (1) having a stainless steel cathode and a lead anode. The interelectrode space of the electrolyzer is divided by a MK-40 cation-exchange membrane, forming the anode and cathode chambers, perforated corrugated grids are placed in the chambers. The thickness of the chambers was varied from 2 to 16 mm. The working area of the membranes and electrodes was 0.78 DM ² . The installation worked in a flow-circulation mode, the circulation of the anolyte and catholyte using a peristaltic pump (4) was carried out along individual paths through the cells of the electrolyzer.

 The pressure in the chambers was monitored using a U - shaped pressure gauge (5). The concentration of LiOH in the catholyte was maintained by dosing water into a container with conversion alkali. The replenishment of Li ions and maintaining the required pH in the anolyte was carried out by supplying solid lithium carbonate to the tank (2). Water was also supplied there to replenish its consumption for electrochemical reactions (see reactions 1 and 2).

 The gaseous products of electrode reactions were removed from the tanks of anolyte and catholyte; moreover, a water trap was installed for the latter (8), which excludes carbonization of alkali with carbon dioxide.

 The electrolyzer was powered from a stabilized DC power supply equipped with instruments for monitoring the magnitude of the current and voltage.

 Monitoring the progress of the process was carried out by measuring the concentrations in the corresponding solutions and volumes of working solutions.

Studies of the electrochemical conversion of lithium carbonate through lithium sulfate were carried out in the galvanostatic mode. The concentration of lithium sulfate was 180-200 g / l (3.3-3.6 g-eq / l), which corresponds to the highest electrical conductivity of the Li ₂ SO ₄ solution. With increasing concentration of Li ₂ SO ₄ above the specified increases the viscosity of the solution (figure 3). The volumetric flow rate of the solutions was 0.15 L / min. The current density was varied in the range of 5-15 A / dm ² (I = 6-12 A). At the indicated current densities, there is a linear dependence of the voltage on the current load, which confirms the absence of polarization of the membranes. The temperature of the process depending on the current load varied in the range of 30-40 ^o C.

 During the experiments, the main parameters of the electrolysis process were determined (transfer of lithium ions through the membrane to the cathode chamber, voltage on the cell, energy consumption per unit of the obtained product), as well as the composition of the conversion alkali (catholyte) and the effect of the composition of the anolyte on it.

The rate of transfer of lithium ions to the cathode chamber (ΔР _Li ⁺ , gLi / h • dm ² ) was determined by changing the concentration of OH ^- ions in catholyte and changing its volume per unit time. For electrochemical conversion, technical lithium carbonate was used, the composition of which is given in Table 1.

 The experimental results obtained in various modes are shown in table 2.

As follows from the table. 2, in the range of current loads of 4-12 A (j = 5-15 A / dm ² ), the conversion process of Li ₂ SO ₄ -> LiOH proceeds stably, the voltage varies between 4.1-5.3 V. The concentration of LiOH in catholyte received from 44 to 82 g / l. However, an increase in LiOH concentration led to a slight decrease in lithium transfer (Example 4). The content of H ₂ SO ₄ in the anolyte in the range of 0.6-1.0 g-eq / l (kg-eq / m ³ ) does not affect the conversion process. However, increasing the concentration of H ₂ SO ₄ to 1.4 g-eq / L dramatically reduces the transfer of lithium into the cathode chamber (Fig. 4).

Example 5. The LiOH solution obtained in Examples 1-3 and having a LiOH concentration of ~ 45 g / L was evaporated to a pulp with a LiOH content of ~ 180 g / L. Calculation of the total cost of the processes of conversion and evaporation to obtain LiOH • H ₂ O shows that the concentration of LiOH in the solution for evaporation of 35-45 kg / m ³ is optimal (figure 5). The content of Na and K impurities was determined in solutions prior to evaporation and then in LiOH • H ₂ O samples isolated from the corresponding solutions. The results of the analysis of solutions and samples of LiOH • H ₂ O are given in table.3. It follows from the table that with an increase in the concentration of Na ⁺ in the solution from 0.35 to 2.97 rel.%, Its content in LiOH • H ₂ O crystals increases from 0.008 to 0.145 wt.%.

Example 6. Samples of lithium hydroxide monohydrate obtained in experiment 5 were subjected to a three-stage washing. A saturated liquid of grade H.Ch. grade was used as a washing liquid. in distilled water, the ratio of V _TV . : V _W = 1: 1 at each washing stage. From table 4 it follows that samples 1-4, containing up to 0.06 wt.% Na, it was possible to wash to a sodium content of up to 0.0024%, i.e. get a product of commercial quality. With an increase in the Na content in the sample above 0.06 wt.%, In particular up to 0.092 wt. %, the residual Na content in the washed sample increases sharply and amounts to 0.0103 wt.%, which does not correspond to the required quality.

From examples 5.6 it follows that the Na content in the washed crystals of LiOH • H ₂ O should not exceed 0.06 wt.%, Which is ensured while maintaining the concentration of Na in the evaporated solution not higher than 1.2 rel.%. After a three-stage washing of such crystals, a marketable LiOH • Н ₂ О containing Na (K) at the level of 0.002 wt.% Was obtained, which is clearly seen in the graph - Fig.6.

 Thus, the method allows the use of materials containing lithium carbonate, or commercial lithium carbonate to obtain lithium hydroxide monohydrate of high purity.

 Industrial applicability.

 The proposed method allows to involve in the production of industrial lithium carbonate, as well as waste containing lithium carbonate, to obtain lithium hydroxide monohydrate of high purity. At present, cheap Chilean lithium carbonate is supplied to Russia, which contains impurities of monovalent and multivalent metals, but can be processed into high-purity lithium hydroxide by the proposed method. Since the production of lithium hydroxide from solid aluminosilicate raw materials is currently not functioning in Russia, the proposed method is very promising and can provide the country with a valuable strategic product. This will not require the construction of a plant for its receipt, because the available space in plants that previously processed spodumene will allow the proposed process to be implemented on existing equipment with minimal costs for the purchase of industrial membrane-type electrolyzers.

Claims (5)

1. A method of producing lithium hydroxide monohydrate of high purity from materials containing lithium carbonate, comprising electrochemical conversion of a readily soluble lithium salt to lithium hydroxide by membrane electrolysis, evaporation of the solution and crystallization of lithium hydroxide monohydrate, carbonization of a portion of the lithium hydroxide solution (mother liquor) to obtain carbonate lithium and its use in the technological process, separation and utilization of hydrogen, characterized in that as a soluble lithium salt is used lithium sulfate, which is obtained by direct contact of a material containing lithium carbonate, or technical lithium carbonate with the acid formed in the anode chamber, and the concentration of sulfuric acid in the anolyte is maintained at the level of 0.6-1.0 kg-equiv / m ³ required for the reproduction of a solution of lithium sulfate with a content of 3.3-3.6 kg-equiv / m ³ , while part of the obtained solution of lithium sulfate after purification from impurities of divalent and trivalent metals is filtered and returned to the anode space of the electrolyzer, and the concentration of lithium oxide in catholyte is maintained equal to 35-45 kg / m ³ , crystallization of lithium hydroxide monohydrate from one stripped off solution is carried out at a concentration of impurity sodium (potassium) ions of 0.35-1.2 rel. %, which is maintained due to the constant withdrawal of part of the mother liquor, the obtained crystals of lithium hydroxide monohydrate are subjected to countercurrent washing to a sodium (potassium) content of ≤ 0.002 wt. %  2. The method according to p. 1, characterized in that the mother liquor after separation of lithium hydroxide monohydrate is fed to carbonization by carbon dioxide formed during the neutralization of sulfuric acid by lithium carbonate.  3. The method according to p. 1, characterized in that the purification of the anolyte from impurities of two and trivalent metals is carried out by removing part of the anolyte and adding carbonate and lithium hydroxide to it, followed by separation of the precipitate.  4. The method according to p. 1, characterized in that the alkali diffusing from the cathode chamber through the membrane neutralizes the acid in the membrane layer from the anode side, thereby providing conditions for the stability of MK-40 membranes.  5. The method according to p. 1, characterized in that the lead plate is used as the anode of the electrolyzer, and stainless steel is used as the cathode.

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