JP5431019B2 - Method for producing high purity lithium carbonate - Google Patents

Description

  The present invention relates to high-purity lithium carbonate obtained from crude lithium carbonate and a method for producing the same, and more particularly to high-purity lithium carbonate useful as a raw material for electronic materials, battery materials, optical materials, and the like, and a method for producing the same.

  Lithium carbonate is a compounding agent such as heat-resistant glass and optical glass, ceramic materials, lithium ion secondary battery materials used in batteries for mobile phones and laptop computers, electrolyte materials, lithium niobate used in semiconductor lasers, etc. It is used for various applications such as raw materials such as single crystals and lithium tantalate single crystals.

  The properties required for lithium carbonate are diverse and depend on the application. For example, when lithium carbonate is used as the above-described electronic material, battery material, or optical material, if there are many impurities, the electrical characteristics and optical characteristics deteriorate, so it is required to have high purity with few impurities. . Specifically, high-purity lithium carbonate having a content of dissimilar metals and other impurities of several ppm level, and further 1 ppm or less is demanded.

  Conventionally, as a method for producing such high-purity lithium carbonate, carbon dioxide is blown into a lithium hydroxide aqueous solution, or carbon dioxide is blown into a re-dissolved aqueous solution after recrystallizing lithium hydroxide from the aqueous solution. A method, and a method of reacting the aqueous solution with a water-soluble carbonate such as sodium carbonate are also known.

  However, in these methods, since the element in which the reaction proceeds locally rapidly is strong, the generated lithium carbonate is likely to be fine particles, and further, they are secondarily aggregated, and thus contain reaction system impurities therein. As a result, there is a drawback that the purity is lowered. Moreover, repeating recrystallization of lithium hydroxide lengthens the process and causes an increase in manufacturing cost.

  For these methods, methods in which rapid local reactions are suppressed have been proposed, and several methods for producing high-purity lithium carbonate from crude lithium carbonate have been proposed. For example, after microfiltration of an aqueous solution containing lithium bicarbonate obtained by reacting crude lithium carbonate and carbon dioxide, the lithium bicarbonate aqueous solution is heat treated to deposit lithium carbonate (Patent Document 1), An aqueous solution containing lithium bicarbonate obtained by reacting crude lithium carbonate and carbon dioxide is treated with an ion exchange module or an ion-selective medium, and then the aqueous solution containing lithium bicarbonate is heated to treat lithium carbonate. Method of precipitating (Patent Document 2, Patent Document 3), Method of introducing carbon dioxide into a crude lithium carbonate aqueous slurry, adding a water-soluble organic solvent to an aqueous solution in which lithium carbonate and carbon dioxide are dissolved, and precipitating lithium carbonate ( Patent Document 4) and the like have been proposed.

  However, in the invention described in the above document, different materials such as Na, K, Mg, Ca, Fe, Pb, Al, Si, Cu, Cr, Ni, and Sr derived from raw raw lithium carbonate and other impurities are used. There was a problem that the removal was insufficient, or it took too much time to remove the industrial production level.

  Moreover, about the lithium carbonate obtained by the said invention, the method of refine | purifying in post-processing can be considered. For example, in Patent Document 5, a lithium compound is dissolved in an acid, a coprecipitation agent is added to the solution, an alkali is added to shift the pH of the solution to an alkaline region, and the precipitate is separated by filtration. A method for obtaining a high-purity lithium compound has been proposed.

  However, in this method, indium, bismuth or lanthanum is used as a coprecipitation agent, and these may remain as impurities. Furthermore, even after obtaining lithium carbonate from crude lithium carbonate and purifying high-purity lithium carbonate by this method, the process becomes complicated, which is industrially disadvantageous.

JP 62-252315 A JP-T-2002-505248 Special table 2001-525313 gazette JP-A-11-310414 JP-A-4-193711

  An object of the present invention is to provide high-purity lithium carbonate by eliminating the above-mentioned drawbacks of the prior art.

Specifically, an object of the present invention is to provide a production method for obtaining high-purity lithium carbonate by a simple method even when crude lithium carbonate having a high impurity content is used as a starting material.

  As a result of intensive studies in view of such circumstances, the present inventors have used crude lithium carbonate as a starting material, and obtained an aqueous solution obtained by reacting the crude lithium carbonate and carbon dioxide in an aqueous solvent. It was found that high-purity lithium carbonate in which the content of dissimilar metals and other impurities is extremely reduced can be obtained by heat treatment after adjusting to chelate and completing the present invention.

The present invention is also a method for producing high-purity lithium carbonate (A) from crude lithium carbonate (a), wherein carbon dioxide is introduced into an aqueous slurry containing crude lithium carbonate (a) to form an aqueous lithium hydrogen carbonate solution. A first step to obtain, a second step of adding a chelating agent after adjusting the pH to 8.0 or more by adding an alkaline compound to the lithium hydrogen carbonate aqueous solution, and a lithium hydrogen carbonate aqueous solution obtained by the second step. Provided is a method for producing high-purity lithium carbonate, comprising a third step of obtaining lithium carbonate (A) by solid-liquid separation after obtaining an aqueous solution containing lithium carbonate (A) by heat treatment. Is.

High purity lithium carbonate to the present invention thus obtained, impurities, particularly dissimilar metals such as Ca and Mg are reduced, in particular, useful electronic materials, battery materials, as a raw material for an optical material. Further, according to the method for producing high purity lithium carbonate according to the present invention, even if crude lithium carbonate having a large impurity content is used as a starting material, impurities can be reduced by a simple method, which is industrially advantageous. High purity lithium carbonate can be produced by a simple method.

(Method for producing high-purity lithium carbonate)
A method for producing high-purity lithium carbonate according to the present invention will be described.
The high purity lithium carbonate (A) production method of the present invention includes a first step of obtaining a lithium hydrogen carbonate aqueous solution by introducing carbon dioxide into an aqueous slurry containing crude lithium carbonate (a), and the lithium hydrogen carbonate aqueous solution. After adjusting the pH to an alkaline region of 8.0 or higher by adding an alkaline compound, the lithium hydrogen carbonate aqueous solution obtained by thermally decomposing the lithium hydrogen carbonate aqueous solution obtained in the second step of adding a chelating agent and the second step (A And a third step of obtaining lithium carbonate (A) by solid-liquid separation.

(First step)
The first step of the present invention is a step of obtaining an aqueous lithium hydrogen carbonate solution by introducing carbon dioxide into an aqueous slurry containing crude lithium carbonate (a).

  The lithium carbonate (a) used in the first step contains a foreign metal and other impurities, and may be obtained from any production method or may be a commercially available product. As a manufacturing method of lithium carbonate (a), what is obtained by reaction of the solution which evaporated and concentrated lithium-containing brine and soda ash is mentioned, for example.

  Examples of the different metal contained in lithium carbonate (a) include one or more elements selected from Na, K, Mg, Ca, Fe, Pb, Al, Si, Cu, Cr, Ni, Sr, and the like. . The content of the different metal is preferably 0.1% by mass or more, more preferably 0.5 to 1.5% by mass. Among the dissimilar metals, in particular, the Ca content is preferably 50 ppm or more, more preferably 50 to 200 ppm, and the Mg content is preferably 20 ppm or more, more preferably 20 to 100 ppm.

  Other impurities include sulfate radicals, halogen elements, metal oxides, and the like. The total content of these impurities is preferably 0.1 to 1.5% by mass.

  The lithium carbonate (a) in the present invention containing these different metals, impurities, etc., preferably has a purity of 98% or more and less than 99.9% by the difference method. Lithium carbonate (a) obtained by the above-described production method and lithium carbonate (a) available as an inexpensive commercial product usually satisfy these physical properties.

The water for dissolving lithium carbonate (a) in the first step is not particularly limited, but it is preferable to use water having a low impurity concentration. For example, when pure water from which ionic impurities such as Na ⁺ , K ⁺ , Ca ²⁺ , Cl ⁻ , SO ₄ ²⁻ are passed through a reverse osmosis membrane, an ultrafiltration membrane, an ion exchanger, etc. is used, This is particularly preferable because it can prevent impurities derived from water dissolving lithium carbonate (a). Examples of water to be passed through reverse osmosis membranes, ultrafiltration membranes, ion exchangers, etc. include raw water such as industrial water, city water, river water, etc. Those treated to remove most of the suspended matter and organic matter in the raw water, or those treated with a pure apparatus using an ion exchanger are used.

  The aqueous slurry containing lithium carbonate (a) in the first step is adjusted by dispersing it in water at a concentration equal to or higher than the saturation solubility of lithium carbonate. Lithium carbonate (a) and water are preferably made into an aqueous slurry in a mass ratio of 2:98 to 8:92, more preferably 3:97 to 7:93. By setting it as the aqueous slurry of this ratio, since it can be more than the solubility with respect to the water of the lithium hydrogencarbonate produced | generated by reaction with the carbon dioxide mentioned later, reaction efficiency becomes good.

  In the first step, carbon dioxide is introduced into the aqueous slurry containing lithium carbonate (a). This carbon dioxide may be generally commercially available. The purity of the carbon dioxide is preferably 99% or more, and the upper limit may be determined in consideration of economy.

Reaction with lithium carbonate (a) by introducing carbon dioxide is represented by the following reaction formula (2)
Li ₂ CO ₃ + CO ₂ + H ₂ O → 2LiHCO ₃ (2)
Is done. In order to proceed with this reaction suitably, it is preferable to carry out by an efficient gas-liquid contact facility such as high-speed stirring.

  Moreover, since the solubility of lithium carbonate (a) is so large that the reaction conditions in a 1st process are low temperature and high pressure, a melt | dissolution rate becomes quick. However, when the operation is performed at a lower temperature and a higher pressure, it is preferable to perform the device under practical conditions such as room temperature and atmospheric pressure in consideration of economy, considering the equipment and considering the equipment load. Specifically, the reaction is preferably performed at a temperature of 40 ° C. or lower, more preferably 30 ° C. or lower, and a pressure of atmospheric pressure or higher.

  The amount of carbon dioxide introduced into the aqueous slurry in the first step is preferably determined from the viewpoint of carbon dioxide utilization efficiency because the reaction system for hydrogenation of lithium carbonate (a) is an equilibrium reaction. Specifically, it is preferably introduced in an amount of 1 to 1.5 mol with respect to 1 mol of lithium carbonate (a) to be used.

  By performing the first step under the above conditions, lithium carbonate (a) and carbon dioxide react efficiently, and the generated lithium hydrogen carbonate can be stably present in the aqueous solution.

(Second step)
The second step of the present invention is a step of adding a chelating agent after adding an alkaline compound to the lithium hydrogen carbonate aqueous solution obtained in the first step and adjusting the pH to the alkaline region.

  In the second step, the pH of the aqueous lithium hydrogen carbonate solution obtained in the first step is adjusted to the alkaline region, but the aqueous lithium hydrogen carbonate solution before adjustment is usually near neutrality. Specifically, the pH is preferably 7.0 to 8.0, and more preferably pH 7.2 to 7.8. From this pH, an alkaline compound is added to the lithium hydrogen carbonate aqueous solution to obtain a pH in the alkaline region. The pH value after adjustment is preferably 8.0 or more, more preferably 8.0 to 12.0. By being in this range, the stability when the impurity metal element is chelated is improved.

  Examples of the alkaline compound used in the second step include alkali metal hydroxides. Specifically, as the alkali metal hydroxide, lithium hydroxide, sodium hydroxide, potassium hydroxide and the like are preferable, and among these, the lithium hydrogen carbonate aqueous solution is effectively transferred to the alkaline region, and other than Li Lithium hydroxide is particularly preferable from the viewpoint of preventing alkali metal contamination.

  The alkaline compound may be added by any method as long as the pH of the aqueous lithium hydrogen carbonate solution can be adjusted efficiently. For example, the method of preparing the aqueous solution of an alkaline compound and adding this aqueous solution is mentioned.

  In the second step, by adding a chelating agent to the lithium hydrogen carbonate aqueous solution adjusted to the alkaline region, Na, K, Mg, Ca, Fe, Pb, Al, Si, Cu in the lithium hydrogen carbonate aqueous solution are further added. , Cr, Ni and Sr can be reduced. The reason for performing the purification operation by adding a chelating agent after adjusting to the alkaline region is that metals such as Ca, Mg, and Fe among different metals form more stable metal chelates in the alkaline region than in the neutral region. And is also a feature of the present invention.

  The chelating agent used in the second step is not particularly limited as long as it can reduce dissimilar metals such as Na, K, Mg, Ca, Fe, Pb, Al, Si, Cu, Cr, Ni and Sr. . For example, aminodiamine-based ethylenediaminetetraacetic acid (EDTA) or its amine salt, nitrilotriacetic acid (NTA), diethylenetriaminepentaacetic acid (DTPA), cyclohexanediaminetetraacetic acid (CyDTA), phosphonic acid-based hydroxyethylidene diphosphones An acid (HEDP) etc. are mentioned. Among these, aminocarboxylic acid-based chelating agents are preferably used because they are standard, and more specifically, EDTA, CyDTA, and the like are particularly preferable.

  The addition amount of the chelating agent is preferably determined from the amount of the different metal contained in the above-described lithium carbonate (a), using as a guide the equivalent or more of the impurities to be removed contained in the raw material.

  In the second step, it is preferable to filter the aqueous lithium hydrogen carbonate solution to remove impure components, for example, water-insoluble components such as foreign metal hydroxides. This filtration can be performed after the first step, after pH adjustment, or after addition of a chelating agent. However, if there is no impure component during the purification operation with the chelating agent, the efficiency of purification can be increased. , Preferably after the pH adjustment.

  The filtration method may be any method as long as an impure component such as a water-insoluble component in the lithium hydrogen carbonate aqueous solution can be removed. For example, methods such as microfiltration, filter press, cartridge filter and the like can be exemplified.

(Third process)
The third step of the present invention is a step of obtaining high-purity lithium carbonate (lithium carbonate (A)) by subjecting the lithium hydrogen carbonate aqueous solution obtained in the second step to heat treatment and then solid-liquid separation.

The decarboxylation reaction of lithium hydrogen carbonate by heat treatment is represented by the following reaction formula (3)
2LiHCO ₃ → Li ₂ CO ₃ + CO ₂ + H ₂ O (3)
Is done. In order to proceed this reaction suitably, it is preferable to heat the lithium hydrogen carbonate aqueous solution with stirring at 40 ° C. or higher, more preferably 50 ° C. or higher, particularly 70 to 95 ° C. This heating promotes the decarboxylation reaction of lithium hydrogen carbonate in the aqueous solution. Since the amount of decarboxylation of lithium hydrogen carbonate increases as the temperature increases, the yield of lithium carbonate (A) also improves.

  The time required for decarboxylation is not particularly limited. That is, when the temperature of the aqueous solution is increased, lithium carbonate (A) is substantially generated by decarboxylation even when the temperature is not fully increased to the above temperature range, so that the time required for decarboxylation may be determined appropriately. is there. In the heat treatment, the particle size of lithium carbonate (A) can be controlled by appropriately changing the stirring conditions and other conditions.

  The carbon dioxide generated by the heat treatment in the third step can be recovered and reused as the raw material carbon dioxide in the first step.

  In the third step, after completion of the heat treatment, the produced lithium carbonate (A) is subjected to solid-liquid separation, washed and dried as desired to obtain lithium carbonate (A). Solid-liquid separation can be performed by a conventional method. For example, the solid content is separated by a centrifuge, a filter press or the like to obtain a solid (cake). This solid usually contains 5 to 20% by mass of water, but since this water contains foreign metals and other impurities, the solid should be washed with clean water. Is preferred.

  For washing, the same water as that used for dissolving lithium carbonate (a) can be used. This washing may be performed to such an extent that the water contained in the solid can be replaced. For example, 1 to 10 times the amount of water with respect to the weight of the solid is brought into contact with the solid once or a plurality of times. be able to. The contact between the water and the solid material may be performed to such an extent that the water in the solid material can be replaced and the lithium carbonate (A) in the solid material is not washed away. For example, the method of exposing the solid material to running water, The method of immersing an object is mentioned.

  The drying is not particularly limited as long as contamination by external impurities can be prevented. For example, a vacuum dryer or a shelf heating dryer is suitable. What is necessary is just to implement this drying on the conditions which lithium carbonate (A) does not change in quality, It is preferable that temperature is 100-150 degreeC and time is about 1 to 5 hours.

  The mother liquor obtained by solid-liquid separation can be circulated for use in preparing an aqueous slurry containing lithium carbonate (a) in the first step. This mother liquor contains lithium carbonate corresponding to the saturation solubility, and the raw material yield can be further increased by recovering and using this. This is possible because the reaction of the present invention does not contain different salts for lithium carbonate other than impurities from the raw material.

  Lithium carbonate (A) obtained by the third step can be pulverized and classified as necessary to obtain high-purity lithium carbonate having a large temporary particle size and not agglomerated. This lithium carbonate (A) has a remarkably small amount of impurities compared to conventional lithium carbonate. Specifically, Na, K, Mg, Ca, Fe, Pb, Al, Si, Cu, Cr, Ni, Sr, etc. In particular, the Ca content is 5 ppm or less, and the Mg content is 4 ppm or less. The purity is 99.99% by mass or more, and the high-purity lithium carbonate produced using crude lithium carbonate as a starting material has unprecedented physical properties.

  The high-purity lithium carbonate in the present invention can be suitably used as a raw material for electronic materials, battery materials, and optical materials. Also, lithium niobate used as a raw material for lithium ion secondary batteries, electrolyte materials, semiconductor lasers, etc. It can also be suitably used as a raw material for crystals and lithium tantalate single crystals.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples.
(1) Dissimilar metals Using an ICP emission spectroscopic analyzer (Varianty Series II, LibertySeries II), measurement was performed by ICP emission spectroscopic analysis to determine the content of dissimilar metals.
(2) Purity of lithium carbonate It calculated | required by the difference method using the following Formula.
Lithium carbonate (%) = 100− (sum of impurities)
The impurities in this example and the comparative example are different metals (Ca, Fe, Si, Mg, Al) described in Table 1.
(3) pH
The pH was measured with a pH meter (D-51 manufactured by Horiba, Ltd.).

[Example 1]
<First step>
50 parts by mass of crude lithium carbonate (lithium carbonate (a)) containing impurities shown in Table 1 was added to 950 parts by mass of pure water to prepare a slurry. Next, carbon dioxide was introduced under normal pressure while stirring until the slurry became transparent, to obtain an aqueous lithium hydrogen carbonate solution.
<Second step>
To this aqueous lithium hydrogen carbonate solution, 10 parts by mass of lithium hydroxide as an alkaline compound was added to make an aqueous lithium hydrogen carbonate solution having a pH of 8.6, followed by filtration under reduced pressure, and ethylenediaminetetraacetic acid (as a chelating agent) was added to the resulting filtrate. EDTA) was added in an amount of 0.2 parts by mass to obtain an aqueous lithium hydrogen carbonate solution in the second step.
<Third step>
The aqueous lithium hydrogen carbonate solution obtained in the second step was heated to 95 ° C. with stirring, dehydrated by heat treatment at this temperature for 1 hour, and a slurry containing high-purity lithium carbonate (lithium carbonate (A1)) It was. This slurry was subjected to solid-liquid separation by filtration under reduced pressure to obtain a solid and a mother liquor. The obtained solid was dried for 2 hours in a constant temperature dryer (Yamato Kagaku Co., Ltd., wind constant temperature high temperature device DKN402) maintained at 120 ° C., to obtain 41 parts by mass of lithium carbonate (A1). The analysis results of lithium carbonate (A1) are shown in Table 1.

[Example 2]
<First step>
33 parts by weight of lithium carbonate (a) shown in Table 1 was added to 967 parts by weight of the mother liquor (17 parts by weight of lithium carbonate dissolved) obtained by the method in the third step of Example 1 to prepare a slurry. Except for this, the same method as in Example 1 was used.
<Second step>
The same method as in Example 1 was used. The pH of the aqueous lithium hydrogen carbonate solution after addition of lithium hydroxide was 8.6.
<Third step>
The same method as in Example 1 was used. The obtained lithium carbonate (A2) was 37 parts by mass. The analysis results of lithium carbonate (A2) are shown in Table 1.

Example 3
<First step>
The same method as in Example 1 was used.
<Second step>
The same procedure as in Example 1 was performed except that 10 parts by mass of lithium hydroxide as an alkaline compound and 0.2 parts by mass of CyDTA as a chelating agent were added. The pH of the aqueous lithium hydrogen carbonate solution after addition of lithium hydroxide was 8.6.
<Third step>
The same method as in Example 1 was used. The obtained lithium carbonate (A3) was 40 parts by mass. The analysis results of lithium carbonate (A3) are shown in Table 1.

Example 4
<First step>
The same method as in Example 1 was used.
<Second step>
The same procedure as in Example 1 was carried out except that 10 parts by mass of lithium hydroxide as an alkaline compound and 1 part by mass of an amine salt of EDTA (manufactured by Kirest Co., Ltd., Kirest M-50) as a chelating agent were added. The pH of the aqueous lithium hydrogen carbonate solution after addition of lithium hydroxide was 8.6.
<Third step>
The same method as in Example 1 was used. The obtained lithium carbonate (A4) was 40 parts by mass. The analysis results of lithium carbonate (A4) are shown in Table 1.

[Comparative Example 1]
<First step>
The same method as in Example 1 was used.
<Second step>
The same procedure as in Example 1 was carried out except that no alkaline compound was added. In addition, pH before filtering lithium hydrogencarbonate aqueous solution was 7.5.
<Third step>
The same method as in Example 1 was used. The obtained lithium carbonate (B1) was 32 parts by mass. The analysis results of lithium carbonate (B1) are shown in Table 1.

[Comparative Example 2]
<First step>
The same method as in Example 1 was used.
<Second step>
The same procedure as in Example 1 was performed except that the alkaline compound and the chelating agent were not added. In addition, pH before filtering lithium hydrogencarbonate aqueous solution was 7.5.
<Third step>
The same method as in Example 1 was used. The obtained lithium carbonate (B2) was 32 parts by mass. The analysis results of lithium carbonate (B2) are shown in Table 1.

[Comparative Example 3]
<First step>
The same method as in Example 1 was used.
<Second step>
The same procedure as in Example 1 was performed except that no chelating agent was added. The pH of the aqueous lithium hydrogen carbonate solution after addition of lithium hydroxide was 8.6.
<Third step>
The same method as in Example 1 was used. The obtained lithium carbonate (B3) was 40 parts by mass. The analysis results of lithium carbonate (B3) are shown in Table 1.

  As is clear from the results shown in Table 1, the lithium carbonate obtained in Examples 1 to 4 has a reduced impurity content and is highly purified compared to the lithium carbonate obtained in Comparative Examples 1 to 3. I understand that.

Claims (6)

A method for producing high purity lithium carbonate (A) from crude lithium carbonate (a), comprising:
A first step of obtaining an aqueous lithium hydrogen carbonate solution by introducing carbon dioxide into an aqueous slurry containing crude lithium carbonate (a);
A second step of adding a chelating agent after adjusting the pH to 8.0 or more by adding an alkaline compound to the lithium hydrogen carbonate aqueous solution; and
The third step of obtaining lithium carbonate (A) by solid-liquid separation after heat treatment of the aqueous lithium hydrogen carbonate solution obtained in the second step to obtain an aqueous solution containing lithium carbonate (A),
A method for producing high-purity lithium carbonate, comprising: The method for producing high-purity lithium carbonate according to claim 2 , wherein the alkaline compound in the second step is lithium hydroxide. Process for producing a high purity lithium carbonate according to any one of claims 1 or 2 chelating agent is ethylene diamine tetraacetic acid in the second step. The manufacturing method of the high purity lithium carbonate as described in any one of Claims 1-3 which uses the mother liquid obtained by solid-liquid separation in a 3rd process as a solvent of the aqueous slurry in a 1st process. The method for producing high-purity lithium carbonate according to any one of claims 1 to 4 , wherein the high-purity lithium carbonate has a Ca content of 5 ppm or less and an Mg content of 4 ppm or less. The method for producing high purity lithium carbonate according to any one of claims 1 to 5 , wherein the purity of the high purity lithium carbonate is 99.99% or more.