JP2009046390A - Production method of high purity lithium carbonate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a production method obtaining high purity lithium carbonate with the content of each element, Na, K, Ca, Al, and Si, of not higher than 1 ppm and an ignition loss at 500°C of not higher than 0.1 wt.% even if using a lithium hydroxide with a high impurity content as a reaction raw material. <P>SOLUTION: In this manufacturing method of high purity lithium carbonate, an aqueous solution containing a raw lithium hydroxide is precision filtered, then crystallized, and the resultant refined lithium hydroxide and carbon dioxide are reacted in an aqueous solvent and lithium carbonate (a) is recovered. In slurry containing the lithium carbonate (a), carbon dioxide is introduced and an aqueous solution containing lithium hydrogen carbonate is obtained, then the aqueous solution containing lithium hydrogen carbonate is thermally decomposed, and the resultant lithium carbonate (b) is heat-treated at 350-600°C to obtain lithium carbonate (c). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  In particular, the present invention relates to the production of high-purity lithium carbonate useful as a raw material for electronic materials, optical industrial materials, particularly lithium tantalate single crystals, lithium potassium tantalate single crystals, lithium niobate single crystals and lithium potassium niobate single crystals. It is about the method.

  Lithium carbonate is a compounding agent such as heat-resistant glass and optical glass, ceramic materials, lithium secondary battery materials used in batteries for mobile phones and laptop computers, electrolyte materials, lithium niobate used in semiconductor lasers, etc. It is used in various applications such as raw materials for 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-mentioned electronic material or optical industrial material, if there are many impurities, the electrical characteristics and optical characteristics deteriorate, so that it is required to have a high purity with few impurities.

  In addition, recently, lithium niobate single crystals, lithium potassium niobate single crystals, lithium tantalate single crystals and lithium potassium tantalate single crystals obtained using lithium carbonate as a raw material are, for example, blue light crystals for semiconductor lasers. It has attracted attention as being useful for second harmonic generation (SHG) devices. Since these single crystals generate light having a short wavelength of about 390 nm in the ultraviolet region, they can be applied to a wide range of uses such as optical disk memory, medical use, photochemistry use, and various optical measurement uses. In addition, since these single crystals have a large electro-optic effect, they can also be used as an optical storage element using the photorefractive effect.

  However, when the single crystal is used, for example, for a second harmonic generation element, if the composition of the single crystal varies even slightly, the wavelength of the second harmonic oscillated from the element is not preferable. The cause of the fluctuation of the composition of the single crystal is usually due to the magnitude of ignition loss of the raw material. That is, if the ignition loss of the raw material is large, the blending ratio of the raw material tends to deviate from the theoretical amount. Here, the loss on ignition refers to a value obtained by dividing the weight loss of the substance generated by removing the volatile component from the substance by heat-treating the substance at 500 ° C. for a predetermined time by the mass before the heat treatment. . When the raw material is lithium carbonate, this volatile component is usually water, an organic substance, unreacted hydrated lithium hydroxide, or the like.

  As described above, when lithium carbonate is used as a raw material for a single crystal, in addition to being highly pure as described above, it is required to further reduce ignition loss.

  Specifically, when lithium carbonate is used as an electronic material or an optical industrial material, it is desired that the content of dissimilar metals and other impurities is several ppm level in lithium carbonate. Further, when lithium carbonate is used as a raw material for producing lithium niobate single crystal, lithium potassium niobate single crystal, lithium tantalate single crystal, lithium potassium tantalate single crystal, etc., the content of these impurities in lithium carbonate Is 1 ppm or less and the loss on ignition is less than 0.1% by weight.

  Conventionally, as a method for producing such high-purity lithium carbonate, for example, an aqueous solution containing lithium bicarbonate obtained by reacting crude lithium carbonate and carbon dioxide is subjected to microfiltration, and then the lithium bicarbonate is contained. Heat treatment of an aqueous solution to be deposited to deposit lithium carbonate (Japanese Patent Laid-Open No. 62-252315), treatment of an aqueous solution containing lithium bicarbonate obtained by reacting crude lithium carbonate and carbon dioxide with an ion exchange module After that, a method (Japanese Patent Publication No. 2002-505248) or the like in which an aqueous solution containing the lithium bicarbonate is heated to precipitate lithium carbonate has been proposed. According to these methods, lithium carbonate having a certain degree of purity can be obtained.

  However, in the invention described in the above document, the raw lithium carbonate, which is a raw material, is manufactured using lithium hydroxide or the like that contains a large amount of impurities such as Si, Al, Na, K, and Ca. There are many. For this reason, even if high purity lithium carbonate is produced from crude lithium carbonate containing a large amount of such impurities, there is a problem that the impurity content of the obtained lithium carbonate cannot be sufficiently reduced. Further, the lithium carbonate thus produced has a problem that it is difficult to reduce the content of these impurities to 1 ppm or less even if purification is performed later. Further, even if the impurity content of lithium carbonate can be reduced to 1 ppm or less, there is a problem that the ignition loss is high because the ignition loss at 500 ° C. is 0.4% by weight or more.

JP 62-252315 A JP-T-2002-505248

  Therefore, the object of the present invention is to reduce ignition at 500 ° C. when the content of each element of Na, K, Ca, Al and Si is 1 ppm or less even when lithium hydroxide having a high impurity content is used as a reaction raw material. Another object of the present invention is to provide a method for producing a high-purity lithium carbonate having an amount of 0.1% by weight or less.

  In the present invention, as a result of intensive studies in view of such circumstances, lithium hydrogen carbonate is produced using lithium carbonate obtained by reacting purified lithium hydroxide and carbon dioxide that have undergone a specific purification step, and then the hydrogen carbonate. When lithium is pyrolyzed, high purity lithium carbonate in which the content of each element of at least Na, K, Ca, Al, and Si is reduced to 1 ppm or less is obtained. As a result, it was found that high purity lithium carbonate with reduced content was obtained, and the present invention was completed.

  That is, the present invention is a first step in which an aqueous solution containing crude lithium hydroxide is microfiltered and then crystallized to obtain purified lithium hydroxide. The purified lithium hydroxide and carbon dioxide are reacted in an aqueous solvent. A second step of recovering the precipitated lithium carbonate (a), a third step of preparing a slurry containing the lithium carbonate (a), and introducing an aqueous solution containing lithium hydrogen carbonate by introducing carbon dioxide into the slurry; A fourth step of thermally decomposing the aqueous solution containing lithium hydrogen carbonate to obtain lithium carbonate (b), and a fifth step of obtaining lithium carbonate (c) by heat-treating the lithium carbonate (b) at 350 to 600 ° C. It provides the manufacturing method of the high purity lithium carbonate characterized by including this.

  According to the method for producing high-purity lithium carbonate according to the present invention, even when lithium hydroxide having a large impurity content is used as a reaction raw material, the content of at least each element of Na, K, Ca, Al and Si is 1 ppm or less. In addition, high-purity lithium carbonate with a loss on ignition of 0.05% by weight or less can be produced. This high-purity lithium carbonate is a raw material for electronic materials and optical industrial materials, particularly lithium niobate single crystals. It is useful as a raw material for producing lithium potassium niobate, lithium tantalate and lithium potassium tantalate.

  Hereinafter, the present invention will be described in detail.

(First step)
In the first step of the present invention, an aqueous solution containing crude lithium hydroxide is finely filtered and then crystallized to reduce the content of at least Na, K, Ca, Al, and Si elements to several ppm or less. This is a step for obtaining purified lithium hydroxide.

  In the first step, first, an aqueous solution containing crude lithium hydroxide is prepared. The aqueous solution can be prepared, for example, by dissolving crude lithium hydroxide in water. In the present invention, crude lithium hydroxide refers to lithium hydroxide in which the content of each element of Na, K, Ca, Al, and Si exceeds 10 ppm. The crude lithium hydroxide used in the first step may be obtained by any production method, for example, crude lithium hydroxide obtained by reaction of lithium carbonate and calcium hydroxide, and lithium sulfate and hydroxide. Examples include crude lithium hydroxide obtained by reaction with barium.

The water for dissolving the crude lithium hydroxide is not particularly limited, but water having as low an impurity concentration as possible is used. Among these, when pure water from which ionic impurities such as Na, K, Ca, Cl, and SO ₄ are removed through at least a reverse osmosis membrane, an ultrafiltration membrane, an ion exchange membrane, etc., crude lithium hydroxide is used. This is particularly preferable because it is possible to prevent contamination from impurities derived from water that dissolves. As treated water to be passed through reverse osmosis membranes, ultrafiltration membranes or ion exchange resins, for example, raw water such as industrial water, city water, river water, etc. is treated with a pretreatment device made of a coagulation filtration device, activated carbon, etc. In addition, those obtained by removing most of the suspended matter and organic matter in the raw water, or those treated with a pure water apparatus using an ion exchange resin are used.

  A commercially available membrane module can be used as the reverse osmosis membrane. In addition, there are no particular limitations on the operating conditions for the production of pure water using the module, and any conventional method may be followed. For example, as a reverse osmosis membrane, a molecular weight cut off is usually 400 to 100,000, preferably 1000 to 10,000. Specific examples of the membrane include cellulose acetate polymer and polyamide polymer. , Crosslinked polyamine polymers, crosslinked polyether polymers, polysulfone, sulfonated polysulfone, polyvinyl alcohol, and the like. These may be appropriately selected and used. Further, the shape of the membrane may be any of flat plate type, spiral type, hollow fiber type, tubular type, pleated type and the like.

  A commercially available membrane module can be used as the ultrafiltration membrane. Moreover, there is no restriction | limiting in particular in the operating conditions of pure water manufacture using this module, What is necessary is just to follow a conventional method. For example, examples of the ultrafiltration membrane include those having a fractional molecular weight of usually 400 to 100,000, preferably 1000 to 10,000. Specific examples of the material of the membrane include regenerated cellulose, polyethersulfone, and polysulfone. Polyacrylonitrile, polyvinyl alcohol, sintered metal, ceramic, carbon and the like are appropriately used. The shape of the membrane may be any of flat plate type, spiral type, tubular type, hollow fiber type, pleated type and the like.

  The concentration of the crude lithium hydroxide in the aqueous solution containing the crude lithium hydroxide is not particularly limited as long as it is not higher than the saturation solubility of lithium hydroxide. However, since the solubility of lithium hydroxide strongly depends on the temperature at which it is dissolved, for example, to dissolve at 80 ° C., the concentration in terms of LiOH is usually 1 to 12% by weight, preferably 9 to 12% by weight.

  In the first step, next, an aqueous solution containing crude lithium hydroxide is microfiltered to remove insolubles containing impurity components such as Si and Al.

  Microfiltration can be performed using a filtering material such as a microfiltration membrane. Examples of the microfiltration membrane that can be used in the first step include a screen filter having a surface filtration action, a depth filter having an internal filtration action, etc., but a screen filter having a surface filtration action efficiently removes insolubles. It is preferable in that it can be performed. The nominal pore size of the microfiltration membrane is usually 1 μm or less, preferably 0.2 to 0.5 μm. The material of the microfiltration membrane is not particularly limited. For example, a membrane of an organic substance such as collodion, cellophane, acetylcellulose, polyacrylonitrile, polysulfone, polyolefin, polyamide, polyimide, polyvinylidene fluoride, or the like Examples thereof include films of inorganic substances such as graphite, ceramics, and porous glass. Moreover, when performing microfiltration on a laboratory scale, a filtering material such as a PTFE membrane filter can be used. The type of the screen filter is not particularly limited, but the cartridge type is preferable because it is easy to operate.

  Examples of the method for performing microfiltration include a method of introducing the above-described crude lithium hydroxide aqueous solution into a commercially available microfiltration device. The pressure condition for the microfiltration operation is not particularly limited, and can be performed under reduced pressure or under pressure, but the temperature of the crude lithium hydroxide aqueous solution is usually 0 to 100 using a feed pump. And introduced into a microfiltration device at a flow rate of usually 1 to 30 ml / min, preferably 5 to 15 ml / min, usually 0.1 to 0.5 MPa, preferably 0.2 to 0. It is preferable to filter at a pressure of 3 MPa. The microfiltration is preferably performed at a temperature at which lithium hydroxide does not precipitate from the aqueous solution.

  In the first step, after performing the above-mentioned microfiltration, a crystallization operation is performed on an aqueous solution containing crude lithium hydroxide to obtain purified lithium hydroxide. In the present invention, by performing further crystallization operation after performing microfiltration, Si, Al, Na, Ca, K, Fe, Zn, Mg, Sr, etc. are further compared with the state after performing microfiltration. Impurities can be reduced.

  Examples of the crystallization operation used in the first step include a method of precipitating lithium hydroxide by cooling an aqueous solution containing the crude lithium hydroxide after the fine filtration, or the crude lithium hydroxide after the fine filtration. There is a method in which an aqueous solution is heated to evaporate water in the aqueous solution to precipitate lithium hydroxide. Of these, the latter heating method is preferred because of the high recovery efficiency of purified lithium hydroxide.

  In the latter heating method, for example, an aqueous solution containing the crude lithium hydroxide subjected to the above-described microfiltration is usually heated to 80 ° C. or higher, preferably 90 to 100 ° C., and then the water in the aqueous solution is usually 10 to 70 ° C. It can be carried out by evaporating and removing 30% by weight, preferably 30 to 60% by weight, and then cooling to room temperature. Thus, when water is removed from the aqueous solution containing crude lithium hydroxide within the above range, purified lithium hydroxide from which impurities are efficiently removed is obtained. The crystallization operation by heating may be performed under reduced pressure.

  Before the crystallization operation, if necessary, the concentration of the aqueous solution of crude lithium hydroxide is adjusted so that LiOH is usually 1 to 13% by weight, preferably 9 to 11% by weight. This is preferable because the lithium recovery efficiency is good.

  In addition, in the first step, in addition to the above microfiltration operation and crystallization operation, when lithium hydroxide purification operation using a chelate resin is performed, further lithium hydroxide such as Ca, Zn, Mg and Sr It is preferable because impurities can be reduced. The refining operation using the chelate resin is preferable because it is efficient in operation because it can be sent to the next step as it is in the liquid state and subsequently operated after the crystallization operation, particularly after the microfiltration and before the crystallization operation. .

  The type of chelate resin that can be used for the purification operation using the chelate resin is not particularly limited, and examples thereof include iminodiacetic acid type and aminophosphate type chelate resins.

  The purification operation using a chelate resin is, for example, a concentration obtained by converting an aqueous solution containing lithium hydroxide in the filtrate after the microfiltration and before the crystallization operation, or an aqueous solution containing lithium hydroxide after the crystallization operation into LiOH. Is usually 1 to 13% by weight, preferably 9 to 11% by weight, and then the aqueous solution is contacted with a chelate resin.

In the purification operation using the chelate resin, the space velocity (SV) of the aqueous solution containing lithium hydroxide passing through the chelate resin is usually ^{1 to} 20 hr ⁻¹ , preferably 3 to 8 hr ⁻¹ . When the purification operation using the chelate resin is performed as described above, impurities such as Ca, Zn, Mg, and Sr in the purified lithium hydroxide can be reduced to the ppb level.

  The first step can be repeated as many times as necessary until the amount of impurities contained in the lithium hydroxide falls below the desired amount.

(Second step)
The second step is a step of recovering the precipitated lithium carbonate (a) by reacting the purified lithium hydroxide obtained in the first step with carbon dioxide in an aqueous solvent.

  In the second step, first, purified lithium hydroxide and carbon dioxide are allowed to react in an aqueous solvent. Specifically, for example, a method of preparing an aqueous solution containing purified lithium hydroxide by dissolving the purified lithium hydroxide in water can be mentioned. When the aqueous solution is prepared in this manner, purified lithium hydroxide and carbon dioxide can be reacted in an aqueous solvent by introducing carbon dioxide into the aqueous solution.

The water for dissolving the purified lithium hydroxide can be the same as the water for dissolving the crude lithium hydroxide. However, ionic impurities such as Na, K, Ca, Cl, and SO ₄ were removed by passing a reverse osmosis membrane, an ultrafiltration membrane, ion-exchanged water, and the like in the same manner as water for dissolving crude lithium hydroxide. The use of pure water is particularly preferable because it can prevent contamination of impurities derived from water that dissolves purified lithium hydroxide.

  The concentration of purified lithium hydroxide in the aqueous solution containing purified lithium hydroxide is not particularly limited as long as it is less than the saturated solubility of lithium hydroxide. However, since the solubility of lithium hydroxide strongly depends on the temperature as described above, for example, when it is dissolved at 25 ° C., the concentration of purified lithium hydroxide in the aqueous solution in terms of LiOH is usually 1 to 10% by weight, Preferably, it is 5 to 10% by weight in that the purified lithium hydroxide can be dissolved and the reaction efficiency with carbon dioxide is good.

  In the second step, next, for example, by introducing carbon dioxide into the aqueous solution containing the purified lithium hydroxide, the purified lithium hydroxide and carbon dioxide are reacted in an aqueous solvent to obtain lithium carbonate (a). To precipitate. The carbon dioxide used in the second step is not particularly limited, but use carbon dioxide from which an acid solution such as sulfuric acid and nitric acid is passed in advance to remove impurities mixed in from storage tanks, pressure regulating valves, piping, etc. Is preferable because high-purity lithium carbonate (a) is easily obtained.

  When the amount of carbon dioxide introduced is usually 0.5 to 2.5, preferably 0.5 to 0.8, in terms of molar ratio to purified lithium hydroxide, there is no side reaction to lithium hydrogen carbonate and high purity lithium carbonate (A) is preferable because it can be obtained in high yield.

  In addition, when carbon dioxide is introduced into an aqueous solution containing purified lithium hydroxide, the pH decreases as carbon dioxide is introduced. However, when the pH is 8.35 or less, lithium hydrogen carbonate is generated. The amount of carbon dioxide introduced is desirably until the pH of the reaction meter is usually 10 or more, preferably 8.5 or more.

  The reaction temperature is usually 0 to 100 ° C, preferably 60 to 80 ° C. It is preferable for the reaction temperature to be within this range because high purity lithium carbonate (a) can be obtained in high yield. The temperature of the reaction system usually rises as carbon dioxide is introduced, but is preferably kept within the above temperature range. In addition, the reaction time is not particularly limited because the reaction is rapidly performed by contact of lithium hydroxide and carbon dioxide. The second step can be performed at normal pressure or under pressure.

  The second step can be performed by either a batch or continuous method. When the reaction is carried out batchwise, the precipitated lithium carbonate (a) usually becomes a massive primary particle aggregate in which fine primary particles are weakly bonded to each other. Moreover, when it reacts by a continuous type, the lithium carbonate (a) which precipitates will become a fine primary particle normally.

  After completion of the reaction, the precipitated lithium carbonate (a) is filtered and washed by a conventional method, and dried as desired to obtain lithium carbonate (a). In addition, it is preferable to use pure water as the water used for cleaning because it is easy to prevent the impurities derived from the cleaning water from being mixed and to easily obtain lithium carbonate (a). Moreover, drying is preferably performed in a closed system in order to avoid contamination of impurities from the air. Specifically, a method of drying under reduced pressure is preferable at the laboratory level, and a method of using a drying device such as a paddle dryer is preferable at the industrial level.

  The lithium carbonate (a) thus obtained, when reacted in a batch system, is a massive primary particle aggregate in which fine primary particles are weakly bonded to each other, and the average primary particle size is usually 1 to 20 μm. The average particle size of the primary particle aggregate is usually 10 to 150 μm, preferably 30 to 100 μm. On the other hand, when it is made to react continuously, the obtained lithium carbonate (a) is fine primary particles, and the average particle size of the primary particles is usually 1 to 100 μm, preferably 10 to 60 μm.

  Moreover, lithium carbonate (a) has a purity of usually 99.00% or more, preferably 99.99% or more, and is highly pure.

  Further, the lithium carbonate (a) has a high purity because each impurity content of Na, Ca, Al, Si and K is 10 ppm or less, preferably 5 ppm or less. Further, the lithium carbonate (a) has an impurity content of Na, Ca, Al, Si and K within the above range, and further has an impurity content of Mg, Sr, Fe and Zn of 10 ppm. Hereinafter, it is preferably 5 ppm or less, and has high purity.

(Third process)
The third step is a step of preparing an aqueous slurry containing lithium carbonate (a) obtained in the second step, and preparing an aqueous solution containing lithium hydrogen carbonate by introducing carbon dioxide into the slurry.

  In the third step, first, lithium carbonate (a) obtained in the second step is dispersed in water to prepare an aqueous slurry containing lithium carbonate (a).

The water in which lithium carbonate (a) is dispersed can be the same as the water in which crude lithium hydroxide is dissolved. However, ionic impurities such as Na, K, Ca, Cl, and SO ₄ were removed by passing through a reverse osmosis membrane, an ultrafiltration membrane, an ion exchange membrane, and the like in the same manner as water for dissolving crude lithium hydroxide. The use of pure water is particularly preferable because it can prevent contamination of water-derived impurities in which lithium carbonate (a) is dispersed.

  The concentration of lithium carbonate (a) in the slurry containing lithium carbonate (a) is preferably set to a concentration equivalent to or higher than the solubility of lithium hydrogen carbonate produced by the introduction of carbon dioxide. This is because, when an aqueous solution containing a high concentration of lithium hydrogen carbonate is used, lithium carbonate (b) can be obtained in a high yield, so that the solubility of the generated lithium hydrogen carbonate is much higher than the solubility of lithium carbonate. It is because it is possible to obtain lithium carbonate (b) in a high yield when excess lithium carbonate (a) is dispersed in consideration of the high cost. Specifically, the concentration of lithium carbonate (a) in the slurry containing lithium carbonate (a) is usually 1 to 12% by weight, preferably 4 to 8% by weight.

Next, carbon dioxide is introduced into the slurry containing lithium carbonate (a), and the following reaction formula (1)
(Chemical formula 1)
Li ₂ CO ₃ + CO ₂ + H ₂ O → 2LiHCO ₃ (1)
To produce lithium hydrogen carbonate to obtain an aqueous solution containing the lithium hydrogen carbonate.

  The carbon dioxide used in the third step is not particularly limited, but in the same way as in the second step, an acid solution such as sulfuric acid or nitric acid is passed in advance, and impurities mixed in from a storage tank, pressure regulating valve, piping, etc. It is preferable to use removed carbon dioxide because high purity lithium carbonate is easily obtained.

  The amount of carbon dioxide introduced is usually 1 or more, preferably 1 to 5, in terms of molar ratio to lithium carbonate (a). The end point of this reaction is the solubilization reaction of lithium carbonate (a) by the introduction of carbon dioxide, that is, the formation reaction of lithium hydrogen carbonate is an equilibrium reaction as shown in the above formula (1). Since the change in the consumption of lithium carbonate (a) with respect to the change in the amount introduced is small, it is efficient to determine the calculated amount of carbon dioxide by controlling the flow rate with respect to a preset lithium concentration.

  The reaction temperature is usually −40 to 50 ° C., preferably 0 to 30 ° C., so that carbon dioxide in the solution can be maintained at a high concentration, and the produced lithium hydrogen carbonate is not decomposed, which is preferable. Moreover, since this reaction is rapidly performed by contact of lithium carbonate (a) and carbon dioxide, the reaction time is not particularly limited.

  The above reaction is preferable when carbon dioxide and lithium carbonate (a) are dispersed and contacted using an efficient gas-liquid contact facility such as high-speed stirring because these contact efficiency is high and the production efficiency of lithium hydrogen carbonate is high. . The said reaction in a 3rd process can be performed under a normal pressure or pressurization.

  After completion of the above reaction, the obtained aqueous solution containing lithium hydrogen carbonate is usually a transparent one having almost no suspension. However, when the aqueous solution is cloudy, it is preferable to perform microfiltration in order to remove insoluble matters. It is preferable to perform microfiltration in this way and use the obtained filtrate in the fourth step of the next step because it is easy to obtain high purity lithium carbonate (b) in the fourth step. In addition, the method of performing microfiltration should just follow the microfiltration method of said 1st process.

(Fourth process)
In the fourth step, the aqueous solution containing lithium hydrogen carbonate obtained in the third step is decomposed by heating, and the following reaction formula (2)
(Chemical formula 2)
2LiHCO ₃ → Li ₂ CO ₃ + CO ₂ + H ₂ O (2)
To obtain lithium carbonate (b).

  In the fourth step, first, the aqueous solution containing lithium hydrogen carbonate is heated at 40 ° C. or higher, preferably 50 ° C. or higher, particularly preferably 70 to 95 ° C. with stirring. Along with this heating, decomposition of lithium hydrogen carbonate in the aqueous solution is promoted. Since the decomposition amount of lithium hydrogen carbonate increases as the temperature increases, the yield of lithium carbonate (b) also increases with increasing temperature. In addition, the time required for decomposition is not particularly limited. That is, when the temperature of the aqueous solution is raised, lithium carbonate (b) is substantially thermally decomposed even when the temperature is not raised to the above temperature range, and lithium carbonate (b) is generated. . At this time, the particle diameter of lithium carbonate (b) can be controlled by appropriately changing the stirring conditions and other decomposition conditions. In addition, the carbon dioxide gas generated by this reaction can be recovered and reused as the carbon dioxide of the raw material in the third step.

In the fourth step, after completion of the reaction, the produced lithium carbonate (b) is solid-liquid separated, washed, dried, pulverized and classified as desired to obtain lithium carbonate (b). The water used for washing can be the same as the water for dissolving the crude lithium hydroxide. However, ionic impurities such as Na, K, Ca, Cl, and SO ₄ were removed by passing through a reverse osmosis membrane, an ultrafiltration membrane, an ion exchange membrane, and the like in the same manner as water for dissolving crude lithium hydroxide. Use of pure water is particularly preferable because it can prevent contamination of impurities derived from cleaning water.

  The lithium carbonate (b) thus obtained is a columnar crystal lithium carbonate (b) having no aggregation, and the average particle size determined by a scanning electron micrograph (SEM) is usually 1 to 150 μm, preferably 20 to 100 μm. is there.

  Further, the lithium carbonate (b) has a purity of usually 99.900% or more, preferably 99.999% or more, and is highly pure.

  Furthermore, the lithium carbonate (b) has an impurity content of Na, Ca, Al, Si, and K of 1 ppm or less, preferably 0.8 ppm or less, and is more pure than lithium carbonate (a). . Further, the lithium carbonate (b) has an impurity content of Na, Ca, Al, Si and K within the above range, and further has an impurity content of Mg, Sr, Fe and Zn of 1 ppm. Hereinafter, it is preferably 0.8 ppm or less, and has a higher purity than lithium carbonate (a).

(Fifth process)
In the fifth step, the lithium carbonate (b) obtained in the fourth step is heat-treated at a predetermined temperature to obtain high-purity lithium carbonate (c) with little loss on ignition.

  The heat treatment temperature is 350 to 600 ° C, preferably 450 to 550 ° C. In this step, high-purity lithium carbonate (c) with little ignition loss can be obtained by performing the heat treatment within this range. On the other hand, if the heat treatment temperature is less than 350 ° C., the ignition loss component cannot be sufficiently removed, and if it exceeds 600 ° C., decomposition of lithium carbonate (c) is accompanied.

In the present invention, the loss on ignition is a value obtained by obtaining a weight W ₄ which is decreased when 2 g of a lithium carbonate sample having a weight W ₀ is heat-treated at 500 ° C. for 2 hours in a heating furnace, and dividing W ₄ by W _0. Is expressed in% by weight.

  The heat treatment time is not particularly limited, but is usually 1 to 8 hours, preferably 3 to 6 hours. The heat treatment may be performed in the air or in an oxygen atmosphere, and is not particularly limited. After completion of the heat treatment, the product is appropriately cooled and pulverized and classified as desired to obtain a lithium carbonate (c) product.

  The lithium carbonate (c) thus obtained is a columnar crystal, and the average particle size determined by a scanning electron micrograph (SEM) is usually 1 to 150 μm, preferably 20 to 100 μm.

  Further, the lithium carbonate (c) has a purity of usually 99.900% or more, preferably 99.999% or more, and is highly pure.

  Furthermore, the lithium carbonate (c) has an impurity content of Na, Ca, Al, Si, and K of 1 ppm or less, preferably 0.8 ppm or less, and is higher in purity than lithium carbonate (a). . The lithium carbonate (c) has an impurity content of Na, Ca, Al, Si and K within the above range, and further has an impurity content of Mg, Sr, Fe and Zn of 1 ppm. Hereinafter, it is preferably 0.8 ppm or less, and has a higher purity than lithium carbonate (a).

  Further, the lithium carbonate (c) has a loss on ignition of usually 0.1% by weight or less, preferably 0.05% by weight or less.

  The first to fifth steps are not particularly limited, and may be performed in a normal atmosphere or in a clean room.

  High-purity lithium carbonate (c) obtained by the production method according to the present invention can be suitably used as a raw material for electronic materials and optical industrial materials, and includes lithium niobate single crystal, lithium potassium niobate single crystal, tantalate It can be suitably used as a raw material for producing lithium single crystal, lithium potassium tantalate single crystal, etc., and in particular, can be suitably used as a raw material for producing lithium niobate single crystal or lithium tantalate single crystal.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these.

  In the following Examples and Comparative Examples, commercially available lithium hydroxide monohydrate was used as crude lithium hydroxide. The impurity content in this lithium hydroxide sample is shown in Table 1. The amount of impurities is a value determined by ICP emission analysis, ICP mass spectrometry, and turbidimetry.

Example 1 and Comparative Example 1
<First step>
An aqueous solution was prepared by dissolving 1062 g of the above crude lithium hydroxide monohydrate in 50 g of pure water at 50 ° C. Pure water was obtained by treating water treated with a pure water production apparatus equipped with an ion exchange resin with an ultrafiltration module (manufactured by Asahi Chemical Industry Co., Ltd., molecular weight cut off 6000), and was used in the following examples. Pure water is also subjected to the same treatment as the pure water. Next, the aqueous solution in which the crude lithium hydroxide prepared above was dissolved was filtered at 40 ° C. using a PTFE membrane filter having a pore size of 0.5 μm. Table 2 shows impurity contents in a lithium hydroxide sample obtained by partially collecting the filtrate after filtration and drying under reduced pressure.

  Next, the mixture was heated to 95 ° C. and crystallized for 4 hours while retaining moisture under reduced pressure. The recovered water was 3300 g. After cooling, the precipitated lithium hydroxide was recovered by solid-liquid separation by a conventional method to obtain purified lithium hydroxide. Table 3 shows the impurity content in a lithium hydroxide sample obtained by partially collecting the recovered material and drying it under reduced pressure.

<Second step>
As a LiOH containing purified lithium hydroxide obtained in the first step, 2000 g of a 10% aqueous solution was charged into a reaction vessel (temperature 40 ° C., pH 12). Next, a washing bottle capacity of 500 ml containing 300 ml of 30% sulfuric acid aqueous solution, size; carbon dioxide passed through 7 cm × 7 cm wide × 15 cm high was introduced into the reaction system at a flow rate of 1500 ml / min at normal pressure. It was introduced over 5 hours, and immediately after the introduction of carbon dioxide, the reaction was terminated (temperature 75 ° C., pH 9.5). Next, after standing, the reaction solution was removed, and 300 g of pure water was further added for washing treatment. Next, after filtration by a conventional method, the product was further washed with 300 g of pure water, dried under reduced pressure at 120 ° C. for 12 hours, and then pulverized lightly to obtain 220 g of lithium carbonate (yield 71.3%). Table 4 shows the main physical properties of the obtained lithium carbonate. The impurity content was measured by ICP emission spectrometry, ICP mass spectrometry, and turbidimetry. The particle size was determined by scanning electron micrograph (SEM). Further, a weight W ₄ decreased when a lithium carbonate sample having a weight W ₀ was heat-treated at 500 ° C. for 2 hours in a heating furnace, and a value obtained by dividing W ₄ by W ₀ was defined as an ignition loss. Moreover, the TG curve of the lithium carbonate obtained in the second step is shown in FIG.

<Third step>
A slurry containing lithium carbonate obtained by adding 150 g of lithium carbonate obtained in the second step to 3000 g of pure water at 10 ° C. was prepared. Next, carbon dioxide which passed through a washing bottle (capacity: 500 ml, size: length 7 cm × width 7 cm × height 15 cm) in which 300 ml of 30% sulfuric acid aqueous solution was put into the slurry under normal pressure and high speed stirring was reacted. The reaction system was introduced at a flow rate of 1000 ml / min for 3 hours while maintaining the temperature in the reaction system at 10 ° C. The reaction liquid after introduction was transparent.

<Fourth process>
Next, the transparent liquid obtained in the third step was heated to 95 ° C. and thermally decomposed with stirring for 1 hour to precipitate lithium carbonate. After cooling, lithium carbonate was solid-liquid separated by a conventional method to recover lithium carbonate, dried under reduced pressure at 120 ° C. for 12 hours, and pulverized lightly to obtain 103 g of lithium carbonate (yield 68.7%). Table 5 shows the main physical properties of the obtained lithium carbonate. The impurity content was measured by ICP emission spectrometry, ICP mass spectrometry, and turbidimetry. The particle diameter was determined by scanning electron micrograph (SEM), and the ignition loss was measured in the same manner as described above. Moreover, the TG curve of the lithium carbonate obtained at the 4th process is shown in FIG.

<Fifth process>
30 g of each of the lithium carbonate obtained in the fourth step was collected, and each sample was heat-treated in an electric furnace for 5 hours at 500 ° C. (Example 1) and 200 ° C. (Comparative Example 1), and then cooled to high purity. Lithium carbonate was obtained. Table 6 shows the main physical properties of the obtained high purity lithium carbonate. The impurity content was measured by ICP emission spectrometry, ICP mass spectrometry, and turbidimetry. Further, the ignition loss was measured in the same manner as described above. FIG. 3 shows a TG curve of the lithium carbonate obtained in Example 1, and FIG. 4 shows a TG curve of the lithium carbonate obtained in Comparative Example 1.

Comparative Example 2
The first step to the second step were performed in the same manner as in Example 1, and then the obtained lithium carbonate was heat-treated at 500 ° C. for 5 hours to obtain lithium carbonate. Table 6 shows the main physical properties of the obtained lithium carbonate. The impurity content was measured by ICP emission spectrometry, ICP mass spectrometry, and turbidimetry. Further, the particle diameter was determined by an electron micrograph (SEM), and the ignition loss was measured in the same manner as described above.

Example 2
<First step>
After performing microfiltration and crystallization under the same conditions as in Example 1, 3000 g of a 10% aqueous solution was prepared as LiOH containing the obtained lithium hydroxide (temperature 25 ° C.). Further, 500 ml of iminodiacetic acid type chelate resin (Amberlite IRC748, manufactured by Organo Corporation) was packed in a glass column (cylindrical size; inner diameter 40 mm, length 640 mm) to prepare a column filled with the chelate resin. The aqueous solution containing lithium hydroxide prepared above was fed to a column packed with the chelate resin prepared above at a space velocity (SV) = 4 hr ⁻¹ . Table 7 shows the impurity content in a lithium hydroxide sample obtained by collecting a part of the solution after the chelate resin treatment and drying under reduced pressure.

<Second step>
As a LiOH containing purified lithium hydroxide obtained in the first step, 2500 g of a 10% aqueous solution was charged into a reaction vessel (temperature 40 ° C., pH 12.1). Next, carbon dioxide passed through a washing bottle (capacity: 500 ml, size: length 7 cm × width 7 cm × height 15 cm) containing 300 ml of 30% sulfuric acid aqueous solution into the reaction system at a flow rate of 1500 ml / min at normal pressure. The reaction was introduced over 2 hours, and the reaction was terminated immediately after the introduction of carbon dioxide (temperature 75 ° C., pH 9.3). Next, after standing, the reaction solution is removed, and 300 g of pure water is further added to perform washing treatment. After filtration by a conventional method, further washing with 300 g of pure water, and drying under reduced pressure at 120 ° C. for 12 hours, It was pulverized lightly to obtain 283 g of lithium carbonate (yield 73.4%). Table 8 shows the main physical properties of the obtained lithium carbonate. The amount of impurities was measured by ICP emission spectrometry, ICP mass spectrometry, and turbidimetry. Moreover, the particle diameter of the primary particle and the particle diameter of the secondary particle were determined by a scanning electron micrograph (SEM).

<Third step>
A slurry containing lithium carbonate obtained by adding 200 g of lithium carbonate obtained in the second step to 4000 g of pure water at 10 ° C. was prepared. Next, carbon dioxide which passed through a washing bottle (capacity: 500 ml, size: length 7 cm × width 7 cm × height 15 cm) in which 300 ml of 30% sulfuric acid aqueous solution was put into the slurry under normal pressure and high speed stirring was reacted. It was introduced at a flow rate of 1000 ml / min while maintaining the temperature at 15 ° C. over 3.5 hours. The reaction liquid after introduction was transparent.

<Fourth process>
Next, the transparent liquid obtained in the third step was heated to 95 ° C. and thermally decomposed with stirring for 1.5 hours to precipitate lithium carbonate. After cooling, lithium carbonate is solid-liquid separated by a conventional method to recover lithium carbonate, further washed with 100 g of pure water, dried under reduced pressure at 120 ° C. for 12 hours, and pulverized lightly to give 142 g of lithium carbonate (yield 71 0.0%). Table 9 shows the main physical properties of the obtained lithium carbonate. The impurity content was measured by ICP emission spectrometry, ICP mass spectrometry, and turbidimetry. Further, the particle diameter was determined by scanning electron micrograph (SEM), and the ignition loss was measured in the same manner as described above.

<Fifth process>
30 g of lithium carbonate obtained in the fourth step was heat-treated in an electric furnace at 500 ° C. for 5 hours, then cooled and pulverized to obtain high purity lithium carbonate. Table 10 shows the main physical properties of the obtained high purity lithium carbonate. The impurity content was measured by ICP emission spectrometry, ICP mass spectrometry, and turbidimetry. Further, the particle diameter was determined by scanning electron micrograph (SEM), and the ignition loss was measured in the same manner as described above.

2 is a graph showing a TG curve of lithium carbonate obtained in the second step of Example 1. FIG. 4 is a graph showing a TG curve of lithium carbonate obtained in the fourth step of Example 1. FIG. 2 is a graph showing a TG curve of lithium carbonate obtained in Example 1. FIG. 2 is a graph showing a TG curve of lithium carbonate obtained in Comparative Example 1. FIG.

Claims (6)

  A first step in which an aqueous solution containing crude lithium hydroxide is precisely filtered and then crystallized to obtain purified lithium hydroxide. Lithium carbonate precipitated by reacting the purified lithium hydroxide with carbon dioxide in an aqueous solvent A second step of recovering (a), a third step of preparing a slurry containing the lithium carbonate (a) and introducing carbon dioxide into the slurry to obtain an aqueous solution containing lithium hydrogen carbonate, including the lithium hydrogen carbonate Including a fourth step of obtaining lithium carbonate (b) by thermally decomposing an aqueous solution, and a fifth step of obtaining lithium carbonate (c) by heat-treating the lithium carbonate (b) at 350 to 600 ° C. To produce high purity lithium carbonate.   The method for producing high-purity lithium carbonate according to claim 1, wherein the microfiltration in the first step is performed using a filter medium having a pore diameter of 1 µm or less.   The crystallization in the first step is characterized in that lithium hydroxide is precipitated by heating an aqueous solution containing crude lithium hydroxide after the microfiltration to evaporate water in the aqueous solution. Item 3. A method for producing high purity lithium carbonate according to Item 1 or 2.   In the first step, the aqueous solution containing lithium hydroxide after the microfiltration and before the crystallization operation or the aqueous solution containing lithium hydroxide after the crystallization operation is further purified using a chelate resin. The method for producing high-purity lithium carbonate according to any one of claims 1 to 3.   A method for producing high-purity lithium carbonate, comprising a fifth step of heat treating the lithium carbonate (b) at 350 to 600 ° C. to obtain lithium carbonate (c).   6. The lithium carbonate (b) is lithium carbonate having an average particle diameter of 1 to 150 [mu] m, a purity of 99.900% or more, and each of Na, Ca, Al, Si and K is 1 ppm or less. Of producing high purity lithium carbonate.

Images