JPH0360772B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a method for producing high purity lithium carbonate powder. More specifically, the present invention relates to a method for producing high-purity lithium carbonate powder with a small amount of components that lose weight on heating. The recent development of the electronics industry is remarkable, and functional devices based on new principles, such as new ceramics, are being developed one after another. Along with this, the materials used as raw materials are required to be of even higher purity and quality. In recent years, lithium carbonate has been attracting attention as a raw material for single crystals or thin films such as lithium tantalate and lithium niobate, which are components of surface acoustic wave filters, temperature and humidity sensors, optoelectronic devices, etc. High purity and high quality are desired. It is important that the lithium carbonate used for this purpose has a low content of metal impurities such as alkali metals, alkaline earth metals, and transition metals, anionic impurities such as chlorine and sulfuric acid radicals, and has a low content of components lost on heating. . In other words, when producing single crystals of lithium tantalate, lithium niobate, etc. using lithium carbonate and tantalum pentoxide or niobium pentoxide as raw materials using a platinum crucible using the Czyochralski method, the weight of lithium carbonate and other components is The ratio must be strictly controlled to a specific ratio known as the congruent melt composition; any deviation from this ratio will result in variations in the properties of the resulting product and a decrease in yield due to the occurrence of crystal cracks. Lithium carbonate with fewer components is desired. However, conventional lithium carbonate contains components other than lithium carbonate that disappear and lose weight at temperatures below the melting point of lithium carbonate, for example in the temperature range of 300 to 550°C.
It exists from 0.5% to several percent, and its amount varies between raw material lots and depending on the part of the raw material used, causing errors in the amount of lithium carbonate charged, making it difficult to control the composition ratio mentioned above, and reducing performance and yield. was causing a decline in <Prior art and problems to be solved by the invention> Recrystallization methods, reprecipitation methods, diaphragm electrolysis methods, etc. are known as methods for obtaining crude lithium compounds, generally lithium carbonate with higher purity than crude lithium carbonate. . As an example of a recrystallization method, a method is known in which an aqueous lithium carbonate solution is evaporated and concentrated to precipitate lithium carbonate and remove impurities. As an example of the reprecipitation method, a method is known in which an aqueous lithium carbonate solution and milk of lime are reacted to form lithium hydroxide, impurities are removed as carbonate, and then reacted with carbon dioxide to precipitate lithium carbonate (US Pat. No. 4,207,297). . Further, as an example of the diaphragm electrolysis method, a method is known in which a lithium sulfate aqueous solution is electrolyzed through a diaphragm to obtain high-purity lithium hydroxide, which is then reacted with carbon dioxide to precipitate lithium carbonate (Japanese Patent Application Laid-open No. 43174/1983). However, all of these methods are related to methods for removing metal impurities and anion impurities in lithium carbonate, and until now, when producing single crystals of lithium niobate, lithium tantalate, etc. using the Czyochralski method described above, However, considering the composition of the reaction product, no effective proposal has been made regarding a method for producing high-purity lithium carbonate with few components that lose heat on heating and have a negative effect on performance and yield. Unavoidably, 500~
The reality is that lithium carbonate is fired at a temperature of 600°C to remove components that lose weight on heating. For this reason, the amount of components lost by heating is small, at least
It is desired to provide high purity lithium carbonate of 0.1% by weight or less. <Means and effects for solving the problems> As a result of intensive studies by the present inventors to solve the above-mentioned problems and develop an economical method for producing high-purity lithium carbonate with a small amount of heat loss components, It was found that the heating loss component is generated during the crystallization operation of precipitating lithium carbonate crystals from an aqueous lithium compound solution, and its main component is water. Furthermore, the components lost on heating cannot be reduced by extending the crystallization time, strengthening the stirring in the crystallization tank, increasing or decreasing pressure during crystallization, etc., but recrystallization of the aqueous lithium compound solution, reprecipitation, etc. When crystals of lithium carbonate are precipitated by heating the aqueous solution to a temperature of 90°C or higher and crystallizing, the components lost on heating in the lithium carbonate are removed.
It has been found that the amount can be reduced to 0.1% by weight or less.
(Hereinafter referred to as the first method) Furthermore, 5 to 100 parts by weight of lithium carbonate powder is added to the lithium compound aqueous solution in advance during crystallization per 100 parts by weight of lithium carbonate newly produced by crystallization, and It has been found that by heating the liquid temperature to 70°C or higher and crystallizing it, it is possible to reduce the amount of components lost on heating in lithium carbonate to 0.1% by weight or less, particularly 0.02% by weight or less. (Hereinafter referred to as the second method) It is conventionally known that by this method, high purity lithium carbonate with a small amount of components lost on heating can be obtained by simple means such as crystallization at a high liquid temperature and addition of lithium carbonate. It's something that didn't exist before. The lithium carbonate powder obtained by crystallization does not require any treatment such as calcination, and only simple drying is required, and the yield of lithium carbonate during crystallization is significantly improved. The configurations of these methods will be explained below. Examples of aqueous solutions containing lithium compounds include crude lithium compounds, generally aqueous lithium carbonate solutions made from crude lithium carbonate, or aqueous solutions containing lithium compounds solubilized with well-known inorganic acids, milk of lime, etc. A purified lithium compound aqueous solution treated by a well-known recrystallization method, reprecipitation method, ion exchange method, etc. is used. The type of lithium compound in the aqueous solution containing the lithium compound is not limited to any type as long as it changes to lithium carbonate and precipitates crystals through the reaction during crystallization, but lithium hydroxide, lithium carbonate below the saturated concentration, Lithium hydrogen carbonate and the like are preferred. In the case of lithium hydroxide, in the first method, a lithium hydroxide aqueous solution with a concentration of 5 to 10% by weight is placed in a pressure-resistant crystallization tank equipped with a stirrer, a heating jacket, a carbon dioxide inlet, and a lithium carbonate slurry outlet. The aqueous solution is heated until the temperature reaches 90°C or higher, and then, while maintaining the liquid temperature at 90°C or higher, carbon dioxide equivalent to 1/2 or more of lithium hydroxide is continuously blown into the crystallization tank. Converts lithium oxide to lithium carbonate and precipitates it as crystals. Lithium carbonate is separated and recovered from the obtained lithium carbonate slurry by a known separation means, washed and then dried at 60°C to 120°C by a well-known drying method. The amount of components lost on heating in the obtained lithium carbonate varies depending on the temperature of the lithium hydroxide aqueous solution at the time of crystallization, and the higher the liquid temperature, the smaller the amount. In other words, when the liquid temperature is 90°C or higher, the components lose weight on heating.
High purity lithium carbonate can be obtained with a heating loss component of 0.1% by weight or less and 0.05% by weight or less when the liquid temperature is 120°C or higher. In the crystallization tank, the lithium carbonate powder precipitated as crystals is dispersed by means such as stirring so that it is sufficiently suspended and dispersed without being deposited at the bottom of the tank. If the lithium carbonate powder is deposited due to insufficient dispersion, the amount of components lost on heating in the obtained lithium carbonate increases. Carbon dioxide is supplied continuously so that the crystallization time is at least 1 hour, preferably 3 hours or more. When carbon dioxide is rapidly supplied to precipitate lithium carbonate crystals so that the crystallization is completed within one hour, the amount of loss on heating of the resulting lithium carbonate powder increases. In the case of lithium hydroxide, in the second method, when crystals of lithium carbonate are precipitated from a 5 to 10% by weight aqueous solution of lithium hydroxide and carbon dioxide using the same crystallization tank, the crystallization of lithium carbonate is performed in the aqueous solution prior to the start of crystallization. Lithium carbonate powder is added to the solution, stirred and dispersed, and the temperature of the aqueous solution is heated to 70°C or higher, and carbon dioxide equivalent to one-half or more of the lithium hydroxide in the aqueous solution is blown into the solution to form crystals of lithium carbonate. Let it precipitate. With this method, it is possible to obtain lithium carbonate powder containing less than 0.1% by weight of components that lose weight on heating at a lower liquid temperature than with the first method, and at a liquid temperature of 100°C or higher, the components that lose weight on heating can be obtained.
It is possible to obtain lithium carbonate powder with extremely low heating loss components of 0.02% by weight or less. In this method as well, stirring and dispersion of the lithium carbonate powder in the crystallization tank and crystallization time are carried out in the same manner as in the first method. The lithium carbonate added prior to crystallization may be in the form of powder, but the average particle size is preferably 80 μm or less, more preferably 50 μm or less. The amount added is lithium carbonate, which is newly precipitated as crystals by crystallization.
5 to 100 parts by weight per 100 parts by weight, preferably 10 to 100 parts by weight
50 parts by weight. When the amount is less than 5 parts by weight, the effect of adding lithium carbonate powder prior to crystallization is small, and even when 100 parts by weight or more is added, no significant reduction in the component lost on heating is observed. The lithium carbonate powder to be added is lithium carbonate powder crystallized by the first method, lithium carbonate powder obtained by calcining commercially available high-purity lithium carbonate at a temperature of 550°C for 1 hour, or lithium carbonate powder separately crystallized by the second method. Use a material with a small amount of components that lose weight on heating, such as In these two methods, even if the lithium compound in the aqueous solution used for crystallization is lithium carbonate or lithium hydrogen carbonate, the component lost on heating depends on the precipitation behavior of lithium carbonate, so the same effect as in the case of lithium hydroxide can be obtained. . For example, in the case of a lithium carbonate aqueous solution with a saturated concentration or less, the aqueous solution is placed in a crystallization tank and the water is removed under reduced pressure to concentrate the lithium carbonate concentration to a saturated concentration or higher. Crystallize by heating above ℃. In the second method, prior to crystallization, lithium carbonate powder is added to the aqueous solution and the temperature of the aqueous solution is heated to 70° C. or higher to perform crystallization. By either method, lithium carbonate powder having a heating loss component of 0.1% by weight or less can be obtained. In the case of lithium hydrogen carbonate, the concentration is 5 to 8.
In the first method, a lithium hydrogen carbonate aqueous solution of 1% by weight is placed in a crystallization tank and carbon dioxide is desorbed by reduced pressure or nitrogen gas feed to convert it into lithium carbonate and precipitate lithium carbonate crystals. Decompose under reduced pressure and crystallize while maintaining the temperature. In the second method, prior to crystallization, lithium carbonate powder is added to the aqueous solution in the same manner as in the case of lithium hydroxide, and the temperature of the aqueous solution is heated to 70°C or higher to decompose the lithium hydrogen carbonate and crystallize lithium carbonate. is precipitated. By either method, lithium carbonate powder having a heating loss component of 0.1% by weight or less can be obtained. <Effects of the Present Invention> The present invention is the second method of the above two methods, and has the effects described below. By a simple and economical method of controlling the temperature of the crystallization solution and adding lithium carbonate powder, high-purity lithium carbonate with a heating loss component of 0.1% by weight or less, and even 0.02% by weight or less can be obtained. Since the solubility of lithium carbonate in water decreases as the temperature increases, the yield of lithium carbonate in the crystallization operation is greatly improved. No special firing equipment is required, there is no lithium carbonate contamination associated with the firing operation, and high-purity lithium carbonate with high product value can be obtained. Reference example 1 Crystallization tank with internal volume equipped with a stirrer, heating steam jacket, lithium compound aqueous solution feed port, lithium carbonate powder addition port, gas inlet, exhaust port, lithium carbonate slurry outlet, pressure gauge, etc. 30 pressure autoclave was used. The purified aqueous lithium hydroxide solution having a concentration of 5.2% by weight was poured into a crystallization tank through the aqueous solution feed port, and the liquid temperature was raised to 90°C over about 30 minutes while thoroughly stirring at a rotation speed of 600 rpm. While thoroughly stirring and maintaining the liquid temperature at 90℃, carbon dioxide gas was continuously supplied into the tank from the gas inlet at a flow rate of 2.2 per minute for 4 hours.
Lithium carbonate crystals were crystallized by reacting with lithium hydroxide. After the crystallization was completed, the lithium carbonate slurry was extracted from the crystallization tank and separated from water using a centrifuge, and the lithium carbonate cake was washed with 10 portions of 80°C warm water, and the lithium carbonate cake was vacuum-dried at 60°C for 12 hours. The weight change on heating of dry lithium carbonate was measured using a thermobalance, and the proportion of the weight loss on heating up to 550°C was taken as the weight loss component on heating. The yield of the obtained lithium carbonate powder was 74.4%, the average particle size was 47 μm, and the component lost on heating was 0.092%. Example 1 Using the same crystallization tank as used in Reference Example 1, purified lithium hydroxide aqueous solution with a concentration of 5.2% by weight was mixed with 20%
was poured into the crystallization tank through the aqueous solution feed port and the liquid temperature was raised to 80°C while stirring. 165 g of lithium carbonate powder having an average particle size of 43 μm and a heating loss component of 0.073% was added from the lithium carbonate powder inlet and thoroughly stirred to disperse it in the aqueous solution. While maintaining the liquid temperature at 80°C and stirring thoroughly, carbon dioxide gas was continuously supplied into the tank at a flow rate of 2.2 per minute for 4 hours to crystallize lithium carbonate crystals. Dry lithium carbonate powder was obtained in the same manner as in Reference Example 1. The recovery rate of the lithium carbonate powder was 70.2%, the average particle size was 52 μm, and the component lost on heating was 0.052%. Reference Example 2, Example 2 Crystallization and recovery were performed in the same manner as Reference Example 1 and Example 1, except that the same crystallization tank as in Reference Example 1 was used, and the liquid temperature and the amount of lithium carbonate powder added were changed. Ta.

[Table] Reference Example 3 Using the same crystallization tank as that used in Reference Example 1, the concentration
20 g of a 1.1% by weight aqueous lithium carbonate solution was put into the crystallization tank from the aqueous solution feed port, 63 g of the same lithium carbonate powder as used in Example 1 was added, and the liquid temperature was raised to 90° C. with thorough stirring. While thoroughly stirring and maintaining the liquid temperature at 90°C, the mixture was evacuated from the exhaust port and water was evaporated over 4 hours until the liquid volume became about 10%, thereby precipitating lithium carbonate. The obtained lithium carbonate slurry was soaked in 80℃ hot water 4
Separation and drying was carried out in the same manner as in Reference Example 1 except for washing with. The yield of lithium carbonate powder is 67.7%, the average particle size is
The diameter was 66 μm, and the weight loss component on heating was 0.071%. Reference Example 4 The same crystallization tank as used in Reference Example 1 was used. Twenty grams of purified lithium hydrogen carbonate aqueous solution having a concentration of 8.0% by weight was placed in a crystallization tank, 89 g of the same lithium carbonate powder as used in Example 1 was added, and the liquid temperature was raised to 90° C. with thorough stirring. While maintaining the liquid temperature at 90°C, argon gas was introduced through the gas inlet at a rate of 0.8 times per minute, and lithium carbonate was crystallized while expelling carbon dioxide gas generated by decomposition of lithium hydrogen carbonate. Crystallization time is approx.
It was hot for 2.5 hours. The obtained lithium carbonate slurry was separated, washed and dried in the same manner as in Reference Example 1. Lithium carbonate powder with an average particle size of 51 μm and a heating loss component of 0.058% was obtained in a yield of 77.0%. Comparative Example 1, Reference Examples 5 to 7 Same as the example except that the same crystallization tank as used in the reference example was used, lithium carbonate powder was not added, and the temperature of the lithium compound aqueous solution was set as follows. lithium carbonate was crystallized.

[Table] Um aqueous solution
Yield, average particle size, of the obtained lithium carbonate powder,
The components that lost weight on heating were as follows.

【table】

Claims (1)

[Claims] 1. When obtaining lithium carbonate powder by crystallization from an aqueous lithium hydroxide solution, a 5 to 10% by weight lithium hydroxide aqueous solution is added to the lithium hydroxide aqueous solution prior to the start of crystallization. 10 to 50 parts by weight of lithium carbonate powder is added to 100 parts by weight of lithium carbonate produced by crystallization, stirred and dispersed, and the lithium hydroxide aqueous solution is heated to 70°C or higher, and then crystallized while blowing carbon dioxide. 1. A method for producing lithium carbonate powder, the method comprising analyzing lithium carbonate powder. 2. The method for producing lithium carbonate powder according to claim 1, wherein the lithium carbonate powder added prior to the start of crystallization has an average particle size of 80 μm or less.