Method for producing lithium carbonate and apparatus for producing lithium carbonate

Abstract

Provided is a method for producing lithium carbonate, the method comprising: an introduction step for introducing ultrafine bubbles containing carbon dioxide into a lithium-containing solution to prepare a bubble-containing lithium solution; a heating step for heating the bubble-containing lithium solution to 60°C or higher to precipitate lithium carbonate; and a recovery step for recovering the lithium carbonate from the bubble-containing lithium solution after the heating step. The pH value of the lithium-containing solution is 10.0 or higher.

Description

Method for producing lithium carbonate, apparatus for producing lithium carbonate 【0001】 The present invention relates to a method for producing lithium carbonate and an apparatus for producing lithium carbonate. 【0002】 In recent years, lithium compounds have been used as raw materials for various ceramic materials, catalysts, pigments, etc. (see, for example, Patent Document 1), and the demand for them is also increasing. 【0003】 Known lithium compounds include lithium oxide, lithium hydroxide, lithium carbonate, etc. Among lithium compounds, lithium carbonate is particularly used as a raw material for various applications in view of its reactivity, handling properties, etc., and the supply and demand of it is tight. 【0004】 Therefore, there has been a demand for a new method for producing lithium carbonate that can produce lithium carbonate from various lithium-containing solutions such as waste liquids containing lithium. 【0005】 Japanese Patent Application Laid-Open No. 2024-143413 【0006】 One aspect of the present invention aims to provide a method for producing lithium carbonate that can produce lithium carbonate from a lithium-containing solution. 【0007】 According to one embodiment of the present invention to solve the above problems, an introduction step of introducing ultra-fine bubbles containing carbon dioxide into a lithium-containing solution to obtain a bubble-containing lithium solution, a heating step of heating the bubble-containing lithium solution to 60°C or higher to precipitate lithium carbonate, a recovery step of recovering the lithium carbonate from the bubble-containing lithium solution after the heating step, and the pH value of the lithium-containing solution is 10.0 or higher, a method for producing lithium carbonate is provided. 【0008】 According to one embodiment of the present invention, a method for producing lithium carbonate that can produce lithium carbonate from a lithium-containing solution can be provided. 【0009】 FIG. 1 is a schematic diagram of an apparatus for producing lithium carbonate according to one embodiment of the present disclosure. 【0010】The following describes embodiments for carrying out the present invention, but the present invention is not limited to the embodiments described below, and various modifications and substitutions can be made to the embodiments described below without departing from the scope of the present invention. [Method for producing lithium carbonate] The inventors of the present invention have investigated a method for producing lithium carbonate from a lithium-containing solution. 【0011】 During our investigation, we attempted to crystallize lithium carbonate by blowing carbon dioxide into a lithium-containing solution. However, simply blowing in carbon dioxide and heating resulted in a low yield of lithium carbonate, and there was a problem that the purity of the lithium carbonate also decreased if the purity of the lithium component in the lithium-containing solution was not high. 【0012】 Therefore, the inventors of the present invention conducted further investigations. As a result, they discovered that by introducing carbon dioxide as extremely small bubbles called ultrafine bubbles (registered trademark) into a lithium-containing solution, lithium carbonate can be easily produced in high yield and high purity, unlike when simply blowing in carbon dioxide, thus completing the present invention. 【0013】 The lithium carbonate production method of this embodiment may include an introduction step, a heating step, and a recovery step. 【0014】 The following describes each process. (1) Introduction process In the introduction process, ultrafine bubbles containing carbon dioxide are introduced into a lithium-containing solution to create a bubble-containing lithium solution. (1-1) About ultrafine bubbles (About ultrafine bubbles) Bubbles called fine bubbles (registered trademark) are bubbles with a diameter smaller than 100 μm, and fine bubbles are divided into microbubbles and ultrafine bubbles depending on their diameter. 【0015】 Microbubbles refer to bubbles with a diameter of 1 μm or more but less than 100 μm, while ultrafine bubbles refer to bubbles with a diameter of less than 1 μm. 【0016】The carbon dioxide-containing bubbles introduced into the lithium-containing solution during the introduction process only need to contain ultrafine bubbles; in addition to ultrafine bubbles, they may also contain microbubbles or other bubbles that are not sufficiently small in diameter. 【0017】 According to the inventors' research, using ultrafine bubbles allows for significantly higher yields and purity of lithium carbonate compared to simply blowing carbon dioxide into a lithium-containing solution to attempt lithium carbonate deposition. In other words, ultrafine bubbles exhibit different properties from ordinary, visible bubbles, and can produce advantageous effects beyond simply reducing the bubble size. 【0018】 When introduced into various solutions, ultrafine bubbles are less likely to burst compared to visible bubbles and can remain in the solution for several days to several months. 【0019】 The presence, diameter, and average diameter of ultrafine bubbles can be evaluated using methods such as laser diffraction / scattering or nanoparticle tracking analysis (NTA analysis). 【0020】 Examples of evaluation devices using laser diffraction and scattering methods include the nanoparticle size distribution analyzer (model: SALD-7500nano) manufactured by Shimadzu Corporation. Examples of evaluation devices using nanoparticle tracking analysis include the nanoparticle analysis system (model: Nano Sight300) manufactured by Nippon Quantum Design Co., Ltd. and the nanoparticle imaging analyzer (model: VIDEO DROP) manufactured by Meiwa Forsis Co., Ltd. 【0021】 If the lithium solution containing bubbles contains foreign matter other than ultrafine bubbles, such as precipitates, the evaluation may be performed after removing the foreign matter by filtration or other means. 【0022】In the introduction step, the average diameter of the ultrafine bubbles introduced into the lithium-containing solution is not particularly limited, but may be, for example, 50 nm to 500 nm, or 80 nm to 300 nm. In this specification, the average diameter of the ultrafine bubbles means the median diameter (D50) in the volume-based particle size distribution. 【0023】 By reducing the average diameter of ultrafine bubbles to 500 nm or less, it is believed that it will be possible to stabilize ultrafine bubbles in lithium-containing solutions and allow them to exist at high concentrations. 【0024】 By making the average diameter of ultrafine bubbles 50 nm or more, ultrafine bubbles can be easily generated and introduced. (Method for generating ultrafine bubbles) The method for generating ultrafine bubbles is not particularly limited. Methods for generating ultrafine bubbles include using microbubbles as raw materials and directly generating ultrafine bubbles. 【0025】 Methods for generating ultrafine bubbles using microfine bubbles as a raw material include high-speed swirling liquid flow methods, pressurized dissolution methods, and Venturi methods. 【0026】 For example, ultrafine bubbles can be generated by introducing carbon dioxide into a lithium-containing solution while stirring it in an environment with a higher pressure than atmospheric pressure (i.e., an increased partial pressure of carbon dioxide), and then reducing the pressure to atmospheric pressure. When a lithium-containing solution with dissolved carbon dioxide is reduced in pressure, the supersaturated carbon dioxide in the lithium-containing solution is generated as ultrafine bubbles as described above. It should be noted that ultrafine bubbles can be generated by increasing the relative pressure of the carbon dioxide when introducing it and then reducing the pressure, so the above operation may also be performed using a pressure other than atmospheric pressure as a reference. 【0027】Furthermore, by applying ultrasound while rapidly stirring a solution containing carbon dioxide and lithium in an environment with a higher pressure than atmospheric pressure (where the partial pressure of carbon dioxide is increased), ultrafine bubbles containing carbon dioxide can be generated in a lithium-containing solution. 【0028】 Methods for directly generating ultrafine bubbles include surfactant-added micropore methods and ultrasonic cavitation methods. 【0029】 From the perspective of generating a large amount of ultrafine bubbles, it is also possible to use a combination of multiple generation methods. 【0030】 In the introduction process, a lithium-containing lithium solution may be generated by passing a lithium-containing solution and carbon dioxide through an ultrafine bubble generator. 【0031】 The method for generating ultrafine bubbles in an ultrafine bubble generator is not particularly limited; for example, it is sufficient if a lithium-containing solution can generate fine bubbles containing carbon dioxide within the lithium-containing solution as it passes through the ultrafine bubble generator. 【0032】 Examples of ultrafine bubble generators include self-priming nozzles that, when a lithium-containing solution passes through the ultrafine bubble generator, self-prime carbon dioxide is drawn in by the Venturi effect and then crushed, generating fine bubbles. 【0033】 The ultrafine bubble generator may have a high-velocity section, such as a throttling, on the flow path inside the ultrafine bubble generator, and may be a generator that can atomize carbon dioxide-containing bubbles by the intense turbulence generated when a lithium-containing solution or carbon dioxide passes through the high-velocity section. 【0034】 The carbon dioxide supply pressure, which is the pressure of the carbon dioxide supplied to the ultrafine bubble generator, is preferably higher than the solution supply pressure, which is the pressure of the lithium-containing solution supplied to the ultrafine bubble generator. The solution supply pressure is not particularly limited, but may be, for example, 0.1 MPa or more and 1.0 MPa or less. 【0035】 The difference between the carbon dioxide supply pressure and the solution supply pressure is not particularly limited, but may be, for example, 0.1 MPa or more, or 0.2 MPa or more. The upper limit of the difference between the carbon dioxide supply pressure and the solution supply pressure may be, for example, 6 MPa or less, or 1 MPa or less. The difference between the carbon dioxide supply pressure and the solution supply pressure may be, for example, 0.1 MPa or more and 6 MPa or less, or 0.2 MPa or more and 1 MPa or less. 【0036】 For example, an ultrafine bubble generating nozzle can be used as an ultrafine bubble generator. 【0037】 Ultrafine bubble generating nozzles are commercially available, and by using an ultrafine bubble generating nozzle, it is particularly easy to introduce carbon dioxide-containing ultrafine bubbles into a lithium-containing solution. 【0038】 When using an ultrafine bubble generating nozzle (hereinafter also referred to as "nozzle"), the pressure of the carbon dioxide supplied to the nozzle can be selected and is not particularly limited. For example, the pressure of the carbon dioxide supplied to the nozzle may be 0.2 MPa or higher, 0.25 MPa or higher, or 0.3 MPa or higher. The upper limit of the carbon dioxide pressure is also not particularly limited and can be selected according to the pressure resistance performance of the nozzle, for example, it may be 15 MPa or lower. The pressure of the carbon dioxide supplied to the nozzle may be 0.2 MPa or higher and 15 MPa or lower, 0.25 MPa or higher and 15 MPa or lower, or 0.3 MPa or higher and 15 MPa or lower. (1-2) Regarding solutions containing lithium (solutions containing lithium) Solutions containing lithium are not particularly limited and include lithium alone and various solutions containing lithium-containing compounds. 【0039】 The solvent in the lithium-containing solution is not particularly limited and may include one or more organic solvents selected from water and alcohols. 【0040】According to the method for producing lithium carbonate of the present embodiment, lithium carbonate can also be produced from various lithium-containing solutions such as waste liquid containing lithium, which has hardly been used as a raw material for lithium carbonate in the past. Further, according to the method for producing lithium carbonate of the present embodiment, lithium carbonate can be easily produced from a lithium-containing solution with high yield and high purity. Therefore, as the lithium-containing solution, for example, from the viewpoint of the method for producing lithium carbonate of the present embodiment, it may contain elements other than lithium and compounds not containing lithium, which are impurities. 【0041】 The lithium-containing solution used in the method for producing lithium carbonate of the present embodiment may be, for example, a solution containing one or more selected from lithium and lithium compounds. The lithium-containing solution may also be various solutions containing lithium such as waste liquid generated during the production of lithium compounds and seawater. (Concentration of lithium) The concentration of lithium contained in the lithium-containing solution is not particularly limited, but it is preferably high from the viewpoint of promoting the reaction with ultrafine bubbles containing carbon dioxide and particularly increasing the yield. Therefore, the concentration of lithium contained in the lithium-containing solution may be, for example, 0.5 g / L or more, 2.0 g / L or more, or 4.0 g / L or more. 【0042】The upper limit of the lithium concentration in the lithium-containing solution is not particularly limited, but from the viewpoint of reducing the precipitation of lithium compounds other than lithium carbonate that are not intended to be precipitated in the solution, it may be, for example, 50 g / L or less, or 40 g / L or less. The lithium concentration in the lithium-containing solution may be, for example, 0.5 g / L or more and 50 g / L or less, 2.0 g / L or more and 50 g / L or less, or 4.0 g / L or more and 40 g / L or less. (Concentration of cations other than lithium) From the viewpoint of increasing the purity of the lithium carbonate to be produced and reducing the inclusion of impurities, it is usually preferable that the concentration of cations other than lithium in the lithium-containing solution is low. However, according to the lithium carbonate production method of this embodiment, high-purity lithium carbonate can be produced even if the concentration of cations other than lithium in the lithium-containing solution is high. For this reason, according to the lithium carbonate production method of this embodiment, a higher concentration of cations other than lithium in the lithium-containing solution is particularly effective compared to other lithium carbonate production methods. Therefore, the total concentration of cations other than lithium in the lithium-containing solution used in the lithium carbonate production method of this embodiment may be 50 mg / L or more, or 100 mg / L or more. 【0043】 However, if the concentration of cations other than lithium in the lithium-containing solution becomes too high, the amount of lithium carbonate that can be produced will also decrease. For this reason, from the viewpoint of productivity, the total concentration of cations other than lithium in the lithium-containing solution may be 4000 mg / L or less, or 2000 mg / L or less. The total concentration of cations other than lithium in the lithium-containing solution used in the lithium carbonate production method of this embodiment may be 50 mg / L or more and 4000 mg / L or less, or 100 mg / L or more and 2000 mg / L or less. 【0044】The concentration of each component in the solution containing lithium can be evaluated by ICP (Inductively Coupled Plasma) or the like. (pH value) The pH value of the solution containing lithium is not particularly limited, but from the viewpoint of promoting the reaction with carbon dioxide, it may be, for example, an alkaline solution. 【0045】 Therefore, the pH value of the solution containing lithium may be, for example, 10.0 or more based on 25°C. 【0046】 By setting the pH value of the solution containing lithium to 10.0 or more, ultrafine bubbles containing carbon dioxide can be easily dissolved in the solution containing lithium, and the yield of lithium carbonate can be particularly increased. Further, by setting the pH value of the solution containing lithium to 10.0 or more, the purity of the obtained lithium carbonate can be particularly increased. 【0047】 The upper limit of the pH value of the solution containing lithium is not particularly limited, but it may be, for example, 14.0 or less, 13.5 or less, or 13.0 or less. 【0048】 Therefore, the pH value of the solution containing lithium may be, for example, 10.0 or more and 14.0 or less, 10.0 or more and 13.5 or less, or 10.0 or more and 13.0 or less. (Temperature of the solution containing lithium) From the viewpoint of increasing the solubility and stabilizing the ultrafine bubbles containing carbon dioxide when introducing them, the temperature of the solution containing lithium into which the ultrafine bubbles are introduced is preferably lower. Also, from the viewpoint of preventing the reaction between lithium in the solution containing lithium and carbon dioxide contained in the ultrafine bubbles from proceeding during the introduction process, the temperature of the solution containing lithium is preferably lower. 【0049】 In the introduction process, the temperature of the solution containing lithium when introducing the ultrafine bubbles containing carbon dioxide is preferably, for example, 30°C or less, more preferably 25°C or less, and even more preferably 20°C or less. 【0050】However, if the temperature of the lithium-containing solution becomes excessively low, it may solidify depending on the solvent, and a lot of energy will be required for cooling. For this reason, the temperature of the lithium-containing solution when introducing ultrafine bubbles containing carbon dioxide in the introduction step is preferably -5°C or higher, more preferably 0°C or higher, even more preferably above 0°C, and particularly preferably 5°C or higher. 【0051】 Therefore, in the introduction step, the temperature of the lithium-containing solution when introducing carbon dioxide-containing ultrafine bubbles is preferably -5°C to 30°C, more preferably 0°C to 25°C, even more preferably above 0°C and 20°C, and particularly preferably 5°C to 20°C. (1-3) Time to carry out the introduction step The introduction step can be carried out continuously, and the introduction step is not particularly limited as it depends on the amount of lithium-containing solution to be treated, but the introduction step may be carried out for, for example, 10 minutes to 120 minutes. (1-4) Amount of carbon dioxide to be introduced In the introduction step, the amount of carbon dioxide-containing ultrafine bubbles to be introduced into the lithium-containing solution is not particularly limited and can be selected, for example, according to the lithium concentration contained in the lithium-containing solution. 【0052】 The amount of carbon dioxide introduced into a lithium-containing solution can be evaluated, for example, by the total carbon content of the bubble-containing lithium solution obtained after the introduction. In the introduction step, ultrafine bubbles containing carbon dioxide can be introduced into the lithium-containing solution such that, for example, the total carbon content of the bubble-containing lithium solution is 1000 mg / L or more. The total carbon content of the bubble-containing lithium solution may be, for example, 1200 mg / L or more. Preferably, the total carbon content of the bubble-containing lithium solution is 1500 mg / L or more, and more preferably 2000 mg / L or more. 【0053】 By introducing carbon dioxide into a bubble-containing lithium solution so that the total carbon content is 1000 g / mL or more, lithium carbonate can be obtained in particularly high yield. 【0054】 There is no particular upper limit to the total carbon content of the bubble-containing lithium solution. However, introducing excessive amounts of carbon dioxide would require time and cost, so the total carbon content of the bubble-containing lithium solution may be, for example, 4000 mg / L or less. Therefore, in the introduction process, the ultrafine bubbles containing carbon dioxide may be introduced so that the total carbon content of the bubble-containing lithium solution is 1000 mg / L or more and 4000 mg / L or less, 1200 mg / L or more and 4000 mg / L or less, 1500 mg / L or more and 4000 mg / L or less, or 2000 mg / L or more and 4000 mg / L or less. 【0055】 Furthermore, in the introduction process, for example, the number of ultrafine bubbles contained in a unit volume of the bubble-containing lithium solution is 1 × 10⁻⁶ ７ Ultrafine bubbles may be introduced to achieve a concentration of 1 x 10¹⁶ bubbles / mL or higher. ７ By introducing ultrafine bubbles to a concentration of 1 / mL or higher, a sufficient amount of ultrafine bubbles can be present in the bubble-containing lithium solution. This allows for the acquisition of lithium carbonate in particularly high yields. 【0056】 There is no particular upper limit to the number of ultrafine bubbles contained in a unit volume of a bubble-containing lithium solution, but for example, 1 × 10⁻⁶ １１ The number of particles / mL or less may be used. Therefore, in the introduction process, the number of ultrafine bubbles containing carbon dioxide in a unit volume of the bubble-containing lithium solution is 1 × 10⁻¹⁶. ７ pieces / mL or more 1×10 １１ The number of particles / mL or less may be introduced. (2) Heating step In the heating step, the lithium solution containing bubbles obtained in the introduction step can be heated to precipitate lithium carbonate. 【0057】By performing a heating process, a reaction proceeds in the bubble-containing lithium solution in which the lithium component reacts with the carbon dioxide contained in the ultrafine bubbles to produce lithium carbonate. 【0058】 In the heating process, the bubble-containing lithium solution can be heated to 60°C or higher, 80°C or higher, or 90°C or higher. 【0059】 In the heating process, there is no particular upper limit to the temperature at which the bubble-containing lithium solution is heated. It is preferable to set the temperature below the boiling point of the solvent contained in the bubble-containing lithium solution, but it may be, for example, 105°C or below, or 100°C or below. 【0060】 Therefore, in the heating process, the temperature at which the bubble-containing lithium solution is heated may be, for example, 60°C to 105°C, 80°C to 105°C, or 90°C to 100°C. 【0061】 The method for heating the bubble-containing lithium solution in the heating process is not particularly limited and may be a batch method or a continuous method. 【0062】 When heating is performed continuously, for example, the area around the pipe through which the bubble-containing lithium solution passes may be locally heated by a heater or the like, and the system may be configured so that the bubble-containing lithium solution reaches a predetermined temperature as it passes through the heated area. Alternatively, the heating means may include various heaters using electric heating wires, oil baths, water baths, etc. Microwaves can also be used as the heating means. 【0063】It is preferable to clearly distinguish between the introduction step and the heating step. In other words, it is preferable not to perform the operation of introducing carbon dioxide-containing ultrafine bubbles into a lithium-containing solution and the operation of heating the bubble-containing lithium solution simultaneously. If carbon dioxide introduction and heating are performed simultaneously, the pH value of the lithium-containing solution and the bubble-containing lithium solution will drop rapidly, and it is thought that ions other than lithium will also precipitate at the same time, making it easier for impurities to be introduced. Furthermore, if the introduction step and heating step are performed simultaneously, the yield of lithium carbonate will decrease significantly, and if the lithium concentration in the lithium-containing solution is low, almost no lithium carbonate will be obtained. 【0064】 In the lithium carbonate production method of this embodiment, the introduction step and the heating step can be carried out as separate steps, so that carbon dioxide reacts selectively with lithium and lithium carbonate with reduced impurity contamination can be produced in high yield. (3) Recovery step In the recovery step, lithium carbonate can be recovered from the bubble-containing lithium solution after the heating step. 【0065】 During the heating process, lithium in the bubble-containing lithium solution reacts with carbon dioxide contained in the ultrafine bubbles, causing lithium carbonate to precipitate. 【0066】 Therefore, in the recovery process, lithium carbonate precipitated in the bubble-containing lithium solution can be recovered by solid-liquid separation. 【0067】 While there are no particular limitations on the specific method of solid-liquid separation in the recovery process, the lithium carbonate obtained by the lithium carbonate production method of this embodiment tends to have a large particle size and very high filterability, so various solid-liquid separation methods can be used. Specifically, for example, one or more methods selected from centrifugal separation, pressure filtration, vacuum filtration, etc., can be used. Furthermore, solid-liquid separation may be carried out by a batch method or a continuous method. 【0068】In the recovery process, the temperature (liquid temperature) of the bubble-containing lithium solution when recovering lithium carbonate is not particularly limited and may be at room temperature without heating. Furthermore, in the recovery process, the temperature (liquid temperature) of the bubble-containing lithium solution when recovering lithium carbonate may be, for example, 60°C or higher, 80°C or higher, 90°C or higher, or 95°C or higher. 【0069】 By raising the temperature of the bubble-containing lithium solution to 60°C or higher, the solubility of lithium carbonate can be reduced, thereby increasing the yield. 【0070】 In the recovery process, there is no particular upper limit to the temperature of the bubble-containing lithium solution when recovering lithium carbonate; for example, it may be below the boiling point of the solvent contained in the bubble-containing lithium solution. 【0071】 The lithium carbonate recovered in the recovery process can be used directly as a raw material for lithium compound production, but it can also be used as a raw material for lithium compound production after, for example, drying to remove solvents. 【0072】 Therefore, the lithium carbonate production method of this embodiment may further include a drying step. Furthermore, the lithium carbonate production method of this embodiment may include any steps other than the drying step. The following describes any optional steps, such as the drying step, that the lithium carbonate production method of this embodiment may include. (4) Drying step In the drying step, the lithium carbonate recovered in the recovery step is dried to reduce and remove solvents and other substances. 【0073】 In the drying process, the means for drying lithium carbonate are not particularly limited, but one or more drying methods selected from, for example, stationary drying, airflow drying, rotary kiln, roller hearth kiln, microwave heating, vacuum drying, etc., may be used. 【0074】When heating lithium carbonate in the drying process, the drying temperature is not particularly limited and can be selected according to the solvent of the lithium-containing solution. For example, the heating temperature when drying lithium carbonate in the drying process may be 100°C or higher. (5) Grinding process The lithium carbonate particles obtained in the recovery process or after the drying process may form coarse particles due to weak sintering or aggregation. 【0075】 Therefore, the lithium carbonate production method of this embodiment may also include a grinding step. In the grinding step, the lithium carbonate obtained after the recovery step and the drying step is ground to obtain particles consisting of primary particles or secondary particles formed by the aggregation of multiple primary particles. The secondary particles may be ground in such a way that the number of primary particles they contain is reduced. 【0076】 In the grinding process, the equipment used for grinding and the grinding conditions can be selected to achieve the required degree of aggregation and particle size for lithium carbonate. 【0077】 Grinding can be carried out using grinding equipment such as a jet mill, ball mill, or wet ball mill. 【0078】 Furthermore, the grinding process can be carried out in multiple stages using multiple grinding devices. 【0079】 After crushing, sieving, classification, etc. can be performed as needed, and particle size characteristics such as particle size distribution can be further adjusted and selected. (6) Washing step The lithium carbonate production method of this embodiment may further include a washing step to wash the lithium carbonate obtained in the recovery step, if necessary. By performing the washing step, impurity components remaining on the surface of the lithium carbonate particles can be removed. 【0080】 The washing process can be carried out by mixing lithium carbonate with a washing liquid to form a slurry, stirring it for a predetermined time, and then performing solid-liquid separation. After solid-liquid separation, drying can also be performed. In the washing process, water can be used as the washing liquid, for example. 【0081】In the washing process, if water is used as the liquid for washing, it is preferable that the water be pure water. (7) Preparation process According to the lithium carbonate manufacturing method of this embodiment, it is possible to produce lithium carbonate from a lithium-containing solution regardless of the lithium content, etc. 【0082】 However, in lithium-containing solutions, if the lithium content is low, the productivity of lithium carbonate may decrease. 【0083】 Furthermore, in solutions containing lithium, if the lithium content is excessively high, the yield of lithium carbonate may decrease. 【0084】 Therefore, the lithium carbonate production method of this embodiment may also include a preparation step in which the lithium concentration in a lithium-containing solution (precursor solution) is adjusted to produce a lithium-containing solution that is supplied to the introduction step. 【0085】 In the preparation process, the method for adjusting the lithium concentration in a lithium-containing solution is not particularly limited, as it depends on the properties of the lithium-containing solution and the presence or absence of impurity ions. For example, one or more methods selected from heating concentration, vacuum concentration, evaporation concentration, freeze concentration, separation membranes (nanofiltration membrane NF, reverse osmosis membrane RO), reverse-phase chromatography, electrodialysis, adsorption, and high-pressure liquid extraction can be used to increase the lithium concentration in the lithium-containing solution. The preparation process can also be carried out in multiple stages, and in this case, multiple concentration methods can be combined. 【0086】 The method for diluting a lithium-containing solution to lower the lithium concentration is not particularly limited, but one example is to add the solvent contained in the lithium-containing solution. 【0087】In the preparation process, in addition to the lithium concentration, or instead of adjusting the lithium concentration, the pH value or temperature of the lithium-containing solution can also be adjusted. The pH value of the lithium-containing solution can be adjusted, for example, by adding acid or alkali, or by concentrating or diluting it. The temperature (liquid temperature) of the lithium-containing solution can be adjusted by heating or cooling it. 【0088】 The pH value and temperature of the lithium-containing solution may be adjusted in a separate process from the process for adjusting the lithium concentration. In this case, the lithium carbonate manufacturing method of this embodiment may include a temperature adjustment step or a pH adjustment step in addition to, or instead of, the concentration adjustment step. [Lithium Carbonate Manufacturing Apparatus] According to the lithium carbonate manufacturing apparatus of this embodiment, lithium carbonate can be manufactured by carrying out a lithium carbonate manufacturing method according to one aspect of this disclosure. For this reason, some of the matters already described will be omitted. 【0089】 For example, as shown in Figure 1, the lithium carbonate production apparatus 10 of this embodiment may include an ultrafine bubble generator 11, a storage tank 12, a heating device 13, and a recovery device 14. (1) Ultrafine bubble generator In the ultrafine bubble generator 11, ultrafine bubbles containing carbon dioxide can be introduced into the lithium-containing solution by circulating a lithium-containing solution and carbon dioxide. 【0090】 The ultrafine bubble generator 11 can also be connected by piping to a tank 15 containing a lithium-containing solution, a cylinder 16 for supplying carbon dioxide, etc., in order to supply a lithium-containing solution. 【0091】 Since the ultrafine bubble generator has already been explained, I will omit the explanation here. 【0092】The lithium carbonate production apparatus 10 of this embodiment may further include a control device for controlling the supply conditions of the lithium-containing solution and carbon dioxide supplied to the ultrafine bubble generator 11, as needed. The control device can control the supply amount and supply pressure of the lithium-containing solution and carbon dioxide according to, for example, the total amount of carbon in the bubble-containing lithium solution produced by the ultrafine bubble generator 11, the average diameter of the ultrafine bubbles, etc. The control device may, for example, control the supply conditions of the lithium-containing solution and carbon dioxide so that the average diameter of the carbon dioxide-containing ultrafine bubbles in the bubble-containing lithium solution is within a predetermined range. 【0093】 The control device may include a CPU, which is an arithmetic processing unit for performing calculations necessary for control, RAM or ROM as main memory, auxiliary storage, an input / output interface, and a display device as an output device. The CPU, main memory, auxiliary storage, input / output interface, and output device of the control device can be interconnected by a bus. All of the above components of the control device do not need to be housed in the same enclosure; for example, the auxiliary storage and display device may be provided externally. The auxiliary storage can be an SSD or HDD. 【0094】 CPU stands for Central Processing Unit, RAM stands for Random Access Memory, and ROM stands for Read Only Memory. SSD stands for Solid State Drive, and HDD stands for Hard Disk Drive. 【0095】 Input / output interfaces include wired or wireless interfaces for exchanging control values ​​and other data. 【0096】 Furthermore, input / output interfaces include user interfaces such as touch panels, keyboards, and operation buttons for selecting control conditions. 【0097】The control device can be made up of a personal computer (PC) or the like. For this reason, each of the above parts of the control device may be realized through the cooperation of software and hardware, with the CPU executing a program that has been pre-stored in the personal computer or other information processing device. (2) Storage tank The storage tank 12 can store a bubble-containing lithium solution produced by circulating a lithium-containing solution and carbon dioxide through the ultrafine bubble generator 11. 【0098】 Therefore, the storage tank 12 can be any tank capable of storing the bubble-containing lithium solution, and its shape and material are not particularly limited. The storage tank 12 may also have a cooling device to control the temperature of the bubble-containing lithium solution, for example, by keeping it cool. The cooling device can be configured to maintain the temperature of the bubble-containing lithium solution stored in the storage tank 12 at a desired low temperature, and may include, for example, a water bath or a thermoelectric conversion material such as a Peltier element. 【0099】 The storage tank may be equipped with measuring devices for measuring the total amount of carbon in the bubble-containing lithium solution and the average diameter of the ultrafine bubbles, if necessary. The measuring devices may transmit the measurement results to the control device. (3) Heating device The heating device 13 can heat the bubble-containing lithium solution. The heating device 13 only needs to be positioned so as to heat the bubble-containing lithium solution, and may be installed in the storage tank 12 as shown in Figure 1, or it may be installed in a location other than the storage tank 12. 【0100】 The heating device 13 may be various heaters using electric heating wires, an oil bath, a water bath, etc. The heating device 13 may also be a microwave heating device. The heating device may be formed by combining multiple heating means, such as a heater and a microwave heating device. (4) Recovery device The recovery device 14 can recover the precipitated lithium carbonate by heating the bubble-containing lithium solution. 【0101】The recovery device 14 can be any device capable of separating and recovering lithium carbonate from the bubble-containing lithium solution by performing solid-liquid separation. The recovery device 14 may be a device that uses one or more methods selected from centrifugal separation, pressure filtration, vacuum filtration, etc. The solid-liquid separation by the recovery device 14 may be carried out by a batch type (processing type) or a continuous type. (5) In addition, the lithium carbonate production apparatus of this embodiment may also have a drying device, a grinding device, a washing device, a conditioning device, etc., as needed. 【0102】 The drying apparatus can dry the lithium carbonate recovered in the recovery process and remove the solvent contained in the bubble-containing lithium solution. The drying process can be carried out using the drying apparatus, and since examples of drying methods used in the drying apparatus have already been explained in the description of the drying process, the explanation will be omitted here. 【0103】 The pulverization process can be carried out using a pulverizing device, which can pulverize or crush the lithium carbonate particles obtained by the recovery device and drying device to select a particle size within a desired range. 【0104】 A washing apparatus is used to wash lithium carbonate obtained by a drying apparatus or a grinding apparatus. The washing apparatus can be configured to mix lithium carbonate with a washing liquid and then separate the solid and liquid components. For example, the washing apparatus may include a washing tank for storing a mixture of lithium carbonate and the washing liquid, a stirrer for mixing and stirring the mixture in the washing tank, and a solid-liquid separator for separating the lithium carbonate into solid and liquid components after washing. If the washing liquid is water, the washing tank may also be referred to as a water washing tank. 【0105】 The adjustment device can perform adjustment processes. The adjustment device can adjust, for example, the lithium concentration, pH, temperature, etc., of a lithium-containing solution. The adjustment device can concentrate or dilute, for example, a lithium-containing solution. The tank 15 in which the lithium-containing solution is stored may also serve as the adjustment device, and the lithium carbonate production apparatus of this embodiment may also have an adjustment device separate from the tank 15. 【0106】The method for adjusting the lithium concentration in the adjustment device has already been explained, so the explanation will be omitted here. 【0107】 In the lithium carbonate production apparatus of this embodiment, the lithium-containing solution supplied to the ultrafine bubble generator preferably has a pH value of 10.0 or higher. For this reason, the lithium carbonate production apparatus of this embodiment may further have an adjustment device, and the adjustment device may adjust the pH value of the lithium-containing solution so that the pH value falls within the above range. 【0108】 Furthermore, the pH value and temperature of the lithium-containing solution may be adjusted using a separate device from the lithium concentration adjustment device. In this case, the lithium carbonate production apparatus of this embodiment may also have a temperature adjustment device or a pH adjustment device in addition to the concentration adjustment device, or in addition to the concentration adjustment device. 【0109】 According to the lithium carbonate production apparatus of this embodiment described above, lithium carbonate can be easily produced from a lithium-containing solution. 【0110】 The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way by these examples. [Example 1] Lithium carbonate was produced by the following procedure. (1) Introduction step A lithium-containing waste liquid was prepared as a lithium-containing solution. 【0111】 The solvent in the lithium-containing solution was water, and the pH value was 10.2 at 25°C. Analysis of ions present at concentrations of 50 mg / L or higher, as determined by an ICP emission spectrometer (VARIAN 725ES), showed Li: 4.3 g / L, and the total concentration of cations other than lithium was 400 mg / L. 【0112】 A lithium-containing solution was supplied at high pressure to an ultrafine bubble generating nozzle (manufactured by Shibata Corporation, model number U20H), while high-purity carbon dioxide was simultaneously supplied at a flow rate of 1 L / min. The supply was continued for 20 minutes. The supply pressure of carbon dioxide was set to 0.35 MPa. 【0113】Through the above procedure, ultrafine bubbles containing carbon dioxide were introduced into a lithium-containing solution to obtain a bubble-containing lithium solution. 【0114】 The average diameter of ultrafine bubbles in a bubble-containing lithium solution is 110 nm, and the number of ultrafine bubbles per unit volume of the bubble-containing lithium solution is 2.5 × 10⁻¹⁶. ８ The value was 1 unit / mL. The same was observed in Example 2 and Reference Example 1 below. The average diameter of the ultrafine bubbles was measured using a nanoparticle size distribution analyzer (Shimadzu Corporation, model: SALD-7500nano) that employs laser diffraction and scattering. The average diameter of the ultrafine bubbles refers to the median diameter (D50) in the volume-based particle size distribution. 【0115】 When evaluated using a total organic carbon analyzer (Shimadzu Corporation, model: TOC-VCPH), the total carbon content in the bubble-containing lithium solution was 3300 mg / L. (2) Heating process The obtained bubble-containing lithium solution was placed in a stainless steel tank which served as a storage tank. 【0116】 The solution was heated to 95°C while being stirred and rotated in a disk turbine at 500 rpm, and held therefore for 30 minutes. As a result of the above operations, precipitates were observed in the bubble-containing lithium solution. (3) Recovery process The bubble-containing lithium solution after the heating process was subjected to continuous solid-liquid separation using a vacuum filter at room temperature (25°C) to recover a white powder containing water. (4) Drying process The white powder recovered in the recovery process was dried at 120°C for 10 hours in an atmospheric environment to obtain a dried powder. 【0117】 X-ray diffraction measurements of the obtained dried powder confirmed that it was a single-phase lithium carbonate. ICP measurements of the dried powder showed a Li grade of 18.7% by mass. Non-lithium cations present in the lithium-containing waste liquid at concentrations of 50 mg / L or higher were below the detection limit, and were confirmed to be less than 0.01% by mass. The Li grade of the dried powder refers to the mass percentage of lithium contained in the dried powder. 【0118】The average particle size of the recovered lithium carbonate was 73 μm. 【0119】 To evaluate the average particle size, a laser diffraction dry particle size distribution analyzer (Sympatec, HELOS & RODOS) was used to obtain a volume-based particle size distribution using the laser diffraction and scattering method. From the obtained volume-based particle size distribution, the volume-average particle size MV was calculated and used as the average particle size. 【0120】 The lithium recovery rate in this process was 37.0% by mass. [Example 2] Lithium carbonate was produced under the same conditions and procedures as in Example 1, except that the pH value of the lithium-containing solution used in the introduction step was set to 11.5. The total carbon content in the bubble-containing lithium solution obtained in the introduction step was 3300 mg / L. 【0121】 X-ray diffraction measurements of the dried powder obtained after the drying process confirmed that the dried powder was a single phase of lithium carbonate. ICP measurements of the dried powder showed a Li content of 18.7% by mass. Non-lithium cations present in the lithium-containing waste liquid at concentrations of 50 mg / L or higher were below the detection limit, and were confirmed to be less than 0.01% by mass. 【0122】 The average particle size of the recovered lithium carbonate was 72 μm. 【0123】 The lithium recovery rate in this process was 38.0% by mass. [Reference Example 1] Lithium carbonate was produced under the same conditions and procedures as in Example 1, except that the pH value of the lithium-containing solution used in the introduction step was set to 9.7. The total carbon content in the bubble-containing lithium solution obtained in the introduction step was 2800 mg / L. 【0124】 X-ray diffraction measurements of the dried powder obtained after the drying process confirmed that the dried powder was a single phase of lithium carbonate. ICP measurements of the dried powder showed a Li content of 18.4% by mass. The powder contained 0.5% by mass of cations other than lithium, which were present in the lithium-containing waste liquid at concentrations of 50 mg / L or higher. 【0125】The average particle size of the recovered lithium carbonate was 72 μm. 【0126】 The lithium recovery rate in this process was 29.4% by mass. [Comparative Example 1] The same lithium-containing solution as in Example 2 was transferred to a stainless steel tank reactor. 【0127】 Then, while stirring with a disk turbine rotating at 500 rpm, high-purity carbon dioxide was flowed in at 1 L / min, bubbling into the lithium-containing solution. Simultaneously, the lithium-containing solution was heated to 95°C and the heating was continued for 30 minutes. During the heating, the carbon dioxide bubbling and stirring by the disk turbine were continued. 【0128】 After heating, the resulting slurry was continuously subjected to solid-liquid separation using a vacuum filter to obtain a white powder containing water. 【0129】 The recovered white powder was dried at 120°C for 10 hours under an atmospheric environment to obtain a dried powder. 【0130】 X-ray diffraction measurements of the obtained dried powder confirmed that it was a single-phase lithium carbonate. ICP measurements of the dried powder showed a Li content of 13.0% by mass. It also contained 9.0% by mass of cations other than lithium, which were present in the lithium-containing waste liquid at concentrations of 50 mg / L or higher. 【0131】 SEM observation of the recovered lithium carbonate revealed that the obtained lithium carbonate was amorphous and that fine particles were present on the particle surface. EDS measurement confirmed that the fine particles on the particle surface were foreign matter derived from cations other than lithium that were present in the lithium-containing waste liquid. The average particle size was 30 μm. 【0132】The lithium recovery rate in this process was 10.8% by mass. [Note] Embodiments of the present disclosure are, for example, as follows: <1> A method for producing lithium carbonate, comprising: an introduction step of introducing ultrafine bubbles containing carbon dioxide into a lithium-containing solution to form a bubble-containing lithium solution; a heating step of heating the bubble-containing lithium solution to 60°C or higher to precipitate lithium carbonate; and a recovery step of recovering the lithium carbonate from the bubble-containing lithium solution after the heating step, wherein the pH value of the lithium-containing solution is 10.0 or higher. <2> The method for producing lithium carbonate according to <1>, wherein in the introduction step, the lithium-containing lithium solution and carbon dioxide are passed through an ultrafine bubble generator to produce the bubble-containing lithium solution. <3> The method for producing lithium carbonate according to <2>, wherein the ultrafine bubble generator is an ultrafine bubble generating nozzle. <4> The method for producing lithium carbonate according to any one of <1> to <3>, wherein the introduction step is carried out for 10 minutes or more and 120 minutes or less. <5> The method for producing lithium carbonate according to any one of <1> to <4>, wherein the temperature of the lithium-containing solution is greater than 0°C and 20°C or less. <6> The method for producing lithium carbonate according to any one of <1> to <5>, wherein the temperature of the bubble-containing lithium solution when recovering the lithium carbonate in the recovery step is 60°C or higher. <7> The method for producing lithium carbonate according to any one of <1> to <6>, wherein the concentration of lithium contained in the lithium-containing solution is 0.5 g / L or more. <8> The method for producing lithium carbonate according to any one of <1> to <7>, wherein the total carbon content of the bubble-containing lithium solution is 1000 mg / L or more. <9> The method for producing lithium carbonate according to any one of <1> to <8>, wherein the average diameter of the ultrafine bubbles is 50 nm or more and 500 nm or less. <10> In the introduction step, the number of ultrafine bubbles contained in a unit volume of the bubble-containing lithium solution is 1 × 10 ７A method for producing lithium carbonate according to any one of <1> to <9>, wherein the ultrafine bubbles are introduced so that the concentration is 50 mg / L or more. <11> A method for producing lithium carbonate according to any one of <1> to <10>, wherein the total concentration of cations other than lithium in the lithium-containing solution is 50 mg / L or more. <12> A lithium carbonate production apparatus comprising: an ultrafine bubble generator; a storage tank for storing a bubble-containing lithium solution produced by passing a lithium-containing solution and carbon dioxide through the ultrafine bubble generator; a heating device for heating the bubble-containing lithium solution; and a recovery device for recovering lithium carbonate precipitated by heating the bubble-containing lithium solution, wherein the pH value of the lithium-containing solution is 10.0 or higher. <13> A lithium carbonate production apparatus according to <12>, further comprising an adjustment device, wherein the pH value of the lithium-containing solution is made 10.0 or higher by the adjustment device. 【0133】 This application claims priority based on Japanese Patent Application No. 2024-214009, filed with the Japan Patent Office on December 6, 2024, and the entire contents of Japanese Patent Application No. 2024-214009 are incorporated herein by reference. 【0134】 10. Lithium carbonate production equipment 11. Ultrafine bubble generator 12. Storage tank 13. Heating device 14. Recovery device 15. Tank 16. Cylinder

Claims

1. A method for producing lithium carbonate, comprising: an introduction step of introducing ultrafine bubbles containing carbon dioxide into a lithium-containing solution to form a bubble-containing lithium solution; a heating step of heating the bubble-containing lithium solution to 60°C or higher to precipitate lithium carbonate; and a recovery step of recovering the lithium carbonate from the bubble-containing lithium solution after the heating step, wherein the pH value of the lithium-containing solution is 10.0 or higher.

2. The method for producing lithium carbonate according to claim 1, wherein in the introduction step, the lithium-containing solution and carbon dioxide are passed through an ultrafine bubble generator to produce the bubble-containing lithium solution.

3. The method for producing lithium carbonate according to claim 2, wherein the ultrafine bubble generator is an ultrafine bubble generating nozzle.

4. A method for producing lithium carbonate according to any one of claims 1 to 3, wherein the introduction step is carried out for 10 minutes or more and 120 minutes or less.

5. A method for producing lithium carbonate according to any one of claims 1 to 4, wherein the temperature of the lithium-containing solution is greater than 0°C and 20°C or less.

6. The method for producing lithium carbonate according to any one of claims 1 to 5, wherein the temperature of the bubble-containing lithium solution when recovering the lithium carbonate in the recovery step is 60°C or higher.

7. A method for producing lithium carbonate according to any one of claims 1 to 6, wherein the lithium concentration in the lithium-containing solution is 0.5 g / L or more.

8. A method for producing lithium carbonate according to any one of claims 1 to 7, wherein the total carbon content of the bubble-containing lithium solution is 1,000 mg / L or more.

9. The method for producing lithium carbonate according to any one of claims 1 to 8, wherein the average diameter of the ultrafine bubbles is 50 nm or more and 500 nm or less.

10. In the introduction step, the number of ultrafine bubbles contained in a unit volume of the bubble-containing lithium solution is 1 × 10 ７ A method for producing lithium carbonate according to any one of claims 1 to 9, wherein the ultrafine bubbles are introduced in such a quantity as 1 / mL or more.

11. A method for producing lithium carbonate according to any one of claims 1 to 10, wherein the total concentration of cations other than lithium in the lithium-containing solution is 50 mg / L or more.

12. A lithium carbonate production apparatus comprising: an ultrafine bubble generator; a storage tank for storing a bubble-containing lithium solution produced by passing a lithium-containing solution and carbon dioxide through the ultrafine bubble generator; a heating device for heating the bubble-containing lithium solution; and a recovery device for recovering lithium carbonate precipitated by heating the bubble-containing lithium solution, wherein the pH value of the lithium-containing solution is 10.0 or higher.

13. The lithium carbonate production apparatus according to claim 12, further comprising an adjustment device, wherein the adjustment device adjusts the pH value of the lithium-containing solution to 10.0 or higher.

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