Method for producing high-purity lithium phosphate from waste refractory saggers

Abstract

The present invention provides an optimized method for recovering high-purity lithium phosphate from a lithium-containing composite oxide deposited on the eroded surface of a waste refractory crucible to be discarded. Therefore, by using the method for producing high-purity lithium phosphate from the waste refractory crucible of the present invention, not only can the discarded waste refractory crucible be recycled to produce high-purity lithium phosphate that can be used in the production of lithium secondary batteries, but it is also expected that the cathode active material, iron oxide, alumina, silicate, and calcium carbonate obtained incidentally in the production process can be recycled.

Description

[Technical Field]

[0001] The present invention relates to a method for producing high-purity lithium phosphate from used refractory saggers, and more particularly to a method for producing high-purity lithium phosphate having a purity of 99.9% or more by crushing and dissolving the used refractory saggers of the present invention, followed by solid-liquid separation, anion exchange, wet magnetic separation, carbonation, and lithium phosphate precipitation reaction. [Background technology]

[0002] The positive electrode active material of a lithium secondary battery is produced by firing at high temperatures in a fireproof sagger (also known as a firing sagger) made of ceramic oxides primarily composed of SiO2, Al2O3, and MgO. The fireproof sagger is repeatedly used for high-temperature firing of the lithium-containing composite oxide, the raw material for the positive electrode active material. Over time, the surface of the fireproof sagger is eroded, and lithium hydroxide, lithium carbonate, and the positive electrode active material are deposited in the eroded areas. Eventually, the fireproof sagger, whose surface has been eroded by the lithium hydroxide, lithium carbonate, etc., loses its thermal durability and is discarded.

[0003] It is said that the amount of waste fireproof sacks generated in Korea is about 9,000 tons per year, but the recent rapid increase in demand for lithium-ion secondary batteries, coupled with the increasing popularity of mobile devices and electric vehicles, is remarkable, and it is expected that the amount of waste fireproof sacks generated will also increase sharply.

[0004] As described above, refractory saggers are used in the production of positive electrode active materials, but they lose their functionality due to corrosion by lithium-containing composite oxides during the high-temperature firing process. Therefore, if the lithium-containing composite oxide deposited at the corrosion site can be recovered in the form of high-purity lithium sulfate, lithium carbonate, or lithium phosphate from used refractory saggers, which are discarded due to a decrease in thermal durability caused by repeated high-temperature firing of the lithium-containing composite oxide, it is expected that the lithium-containing composite oxide can be reused in the production of lithium-ion secondary batteries, thereby reducing production costs. However, no method for recovering high-purity lithium compounds from used refractory saggers is known.

[0005] All references cited herein, including publications, patent applications, and patents, are hereby incorporated by reference to the same extent as if each individual reference was specifically and individually indicated to be incorporated by reference and set forth in its entirety herein. Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a method for maximizing the recovery rate of lithium by recovering trace amounts of lithium contained in wastewater generated in a process for recovering lithium compounds from used refractory saggers that are discarded after being used in high-temperature calcination in the manufacture of positive electrode active materials for lithium secondary batteries, by recovering the lithium as sparingly soluble lithium phosphate.

[0007] Other objects and technical features of the present invention will be more specifically presented in the following detailed description of the invention, claims and drawings. [Means for solving the problem]

[0008] The present invention includes a first step of crushing used refractory saggers to produce a crushed used refractory sagger; a second step of adding an alkali leaching agent and water to the crushed used refractory saggers and then reacting them to produce a crushed used refractory sagger dissolution reaction slurry; a third step of subjecting the crushed used refractory sagger dissolution reaction slurry to primary solid-liquid separation; a fourth step of passing the filtrate obtained as a liquid phase from the primary solid-liquid separation through an anion exchange resin to perform an anion exchange reaction; a fifth step of carbonating the filtrate from the anion exchange reaction to produce a carbonation reaction liquid; and a sixth step of subjecting the carbonation reaction liquid to secondary solid-liquid separation. a seventh step of subjecting the filtrate obtained as a liquid phase by the secondary solid-liquid separation to reverse osmosis concentration; an eighth step of subjecting the concentrated liquid obtained by the reverse osmosis concentration to a thermal fractional precipitation reaction; a ninth step of subjecting the reaction liquid of the thermal fractional precipitation reaction to tertiary solid-liquid separation; a tenth step of subjecting the filtrate obtained as a liquid phase by the tertiary solid-liquid separation to lithium phosphate precipitation; and an eleventh step of subjecting the reaction liquid of the lithium phosphate precipitation reaction to quaternary solid-liquid separation to obtain high-purity lithium phosphate as a solid phase.

[0009] The waste refractory sagger crushed material dissolution reaction slurry is produced by adding 5 to 50 parts by weight of an alkaline leaching agent, such as calcium hydroxide, calcium oxide, or magnesium hydroxide, to 100 parts by weight of waste refractory sagger crushed to 200# (mesh) or less, mixing with 350 parts by weight of water, and reacting the mixture at a temperature of 50 to 80°C for 30 to 120 minutes. The anion exchange resin is produced by adsorbing trimethyl ammonium or dimethyl ethanolamine to a styrene-based resin having a gel structure, and the anion exchange reaction is carried out by passing the filtrate obtained as a liquid phase by the primary solid-liquid separation through an anion exchange tower packed with the anion exchange resin at a flow rate of 0.1 to 1 m / sec.

[0010] The carbonation reaction is characterized by introducing the permeate of the anion exchange reaction into a pressure reaction vessel (or a sealed vessel), injecting one selected from carbon dioxide, carbonated water, and an aqueous solution of lithium bicarbonate into the permeate, and reacting until the pH reaches 7, and then retaining the permeate at a temperature of 80 to 100°C for 20 minutes or more to terminate the reaction. The reverse osmosis concentration is performed using a batch-type reverse osmosis equipment, and the upper limit of the pump operating pressure is 20 kg / cm. 2 and concentrating the filtrate obtained as a liquid phase by the secondary solid-liquid separation until the lithium concentration in the filtrate becomes 10,000 to 20,000 mg / L.

[0011] The thermal fractional precipitation reaction is characterized by heating the concentrate obtained by the reverse osmosis concentration at a temperature of 80 to 100°C for 20 minutes or more to precipitate lithium carbonate, and the lithium phosphate precipitation reaction is characterized by adding a soluble phosphate aqueous solution in an amount corresponding to 1 to 1.1 times the equivalent of the lithium ions dissolved in the filtrate obtained as a liquid phase by the tertiary solid-liquid separation, adjusting the pH to 12 or more, and allowing the solution to remain at a temperature of 80 to 100°C for 20 minutes or more to precipitate lithium phosphate.

[0012] The lithium phosphate produced by the production method of the present invention is characterized by having a purity of 99.9% or more. [Effects of the Invention]

[0013] The present invention provides an optimized method for recovering, as sparingly soluble lithium phosphate, lithium contained in wastewater generated in a process for recovering lithium from lithium-containing composite oxides deposited on the eroded surfaces of discarded refractory saggers. Therefore, it is expected that the method for producing high-purity lithium phosphate from discarded refractory saggers of the present invention can maximize the lithium recovery rate in the process for recovering lithium from discarded refractory saggers. [Brief explanation of the drawings]

[0014] [Figure 1]The method for producing high-purity lithium phosphate from waste refractory saggers of the present invention is shown schematically in Fig. 1. The production method includes wet magnetic separation, lithium leaching, and a neutralization reaction, followed by solid-liquid separation, and then introducing the liquid phase obtained into an anion exchange step. [Figure 2] The method for producing high-purity lithium phosphate from used refractory saggers of the present invention is shown in Fig. 2. The production method includes wet magnetic separation, lithium leaching, neutralization, and solid-liquid separation, followed by introducing the liquid phase into an anion exchange step. [Figure 3] 1 shows the results of X-ray diffraction (XRD) analysis of the constituent minerals of the waste refractory sagger of the present invention. [Figure 4] 1 is a scanning electron microscope (SEM) photograph of crushed waste refractory saggers, showing the overall particle size distribution and particle surface structure. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention relates to a method for producing high-purity lithium phosphate from used refractory saggers. With repeated use, refractory saggers are corroded and destroyed by lithium hydroxide, lithium carbonate, and the like. The present invention aims to recover high-purity lithium carbonate, a high-value-added lithium compound, from used refractory saggers that are discarded without being reused. The used refractory saggers are ceramic containers used to sinter positive electrode active materials for secondary batteries, and are primarily composed of SiO2, Al2O3, and MgO. Table 1 shows the compositions of the used refractory saggers used to sinter the positive electrode materials NCA (sample name: SG1) and NCM (sample name: SG2).

[0016] [Table 1]

[0017] Analysis revealed that the lithium (Li) contents of SG1 and SG2 were high at 2.1% and 0.88%, respectively, which, when converted to lithium carbonate, corresponded to SG1 = 11.17% and SG2 = 4.68%. Furthermore, the nickel and cobalt contents were also confirmed to be 0.13-0.16% and 0.01-0.02%, respectively, confirming that the value to be recovered was sufficiently high.

[0018] The waste refractory saggers are made of mullite, cordierite, alumina, quartz, magnesium aluminate, lithium silicate, lithium aluminum oxide, lithium aluminum silicate, etc. Among the components of the waste refractory saggers, the substances that cause the refractory saggers to break are lithium silicate, lithium aluminum oxide, lithium aluminum silicate, etc.

[0019] The present invention includes a first step of crushing used refractory saggers to produce a crushed used refractory sagger; a second step of adding an alkali leaching agent and water to the crushed used refractory saggers and then reacting them to produce a crushed used refractory sagger dissolution reaction slurry; a third step of subjecting the crushed used refractory sagger dissolution reaction slurry to primary solid-liquid separation; a fourth step of passing the filtrate obtained as a liquid phase from the primary solid-liquid separation through an anion exchange resin to perform an anion exchange reaction; a fifth step of carbonating the filtrate from the anion exchange reaction to produce a carbonation reaction liquid; and a sixth step of subjecting the carbonation reaction liquid to secondary solid-liquid separation. a seventh step of subjecting the filtrate obtained as a liquid phase by the secondary solid-liquid separation to reverse osmosis concentration; an eighth step of subjecting the concentrated liquid obtained by the reverse osmosis concentration to a thermal fractional precipitation reaction; a ninth step of subjecting the reaction liquid of the thermal fractional precipitation reaction to tertiary solid-liquid separation; a tenth step of subjecting the filtrate obtained as a liquid phase by the tertiary solid-liquid separation to lithium phosphate precipitation; and an eleventh step of subjecting the reaction liquid of the lithium phosphate precipitation reaction to quaternary solid-liquid separation to obtain high-purity lithium phosphate as a solid phase.

[0020] The waste refractory sagger crushed material dissolution reaction slurry is produced by adding 5 to 50 parts by weight of an alkaline leaching agent, such as calcium hydroxide, calcium oxide, or magnesium hydroxide, to 100 parts by weight of waste refractory sagger crushed to 200# (mesh) or less, mixing with 350 parts by weight of water, and reacting the mixture at a temperature of 50 to 80°C for 30 to 120 minutes. The anion exchange resin is produced by adsorbing trimethyl ammonium or dimethyl ethanolamine to a styrene-based resin having a gel structure, and the anion exchange reaction is carried out by passing the filtrate obtained as a liquid phase by the primary solid-liquid separation through an anion exchange tower packed with the anion exchange resin at a flow rate of 0.1 to 1 m / sec.

[0021] The carbonation reaction is characterized by introducing the permeate of the anion exchange reaction into a pressure reaction vessel (or a sealed vessel), injecting one selected from carbon dioxide, carbonated water, and an aqueous solution of lithium bicarbonate into the permeate, and reacting until the pH reaches 7, and then retaining the permeate at a temperature of 80 to 100°C for 20 minutes or more to terminate the reaction. The reverse osmosis concentration is performed using a batch-type reverse osmosis equipment, and the upper limit of the pump operating pressure is 20 kg / cm. 2 and concentrating the filtrate obtained as a liquid phase by the secondary solid-liquid separation until the lithium concentration in the filtrate becomes 10,000 to 20,000 mg / L.

[0022] The thermal fractional precipitation reaction is characterized by heating the concentrate obtained by the reverse osmosis concentration at a temperature of 80 to 100°C for 20 minutes or more to precipitate lithium carbonate, and the lithium phosphate precipitation reaction is characterized by adding a soluble phosphate aqueous solution in an amount corresponding to 1 to 1.1 times the equivalent of the lithium ions dissolved in the filtrate obtained as a liquid phase by the tertiary solid-liquid separation, adjusting the pH to 12 or more, and allowing the solution to remain at a temperature of 80 to 100°C for 20 minutes or more to precipitate lithium phosphate.

[0023] The lithium phosphate produced by the production method of the present invention is characterized by having a purity of 99.9% or more.

[0024] Hereinafter, the method for producing high-purity lithium phosphate from waste refractory saggers according to the present invention will be described in detail step by step.

[0025] (1) First process: Crushing of used fireproof saggers The used refractory saggers are crushed to a powder of 200# or less. The crushing efficiency of the used refractory saggers is too low to crush them all at once. Therefore, it is preferable to crush them to 1 mm or less using a jaw crusher as a primary crusher, and then crush them to 200# (mesh) or less using a ball mill as a secondary crusher. The used refractory saggers have high compressive strength but are vulnerable to impact. While an impact crusher can be used to crush the used refractory saggers, it generates crushed particles with sharp, high-hardness surfaces, which increases wear on the crusher parts and increases costs. Therefore, in the present invention, a jaw crusher, which is easy to replace and inexpensive, is used in the primary crushing process, and a ball mill is used in the secondary crushing process. Preferably, an intermediate crusher such as an impact crusher may be installed before the secondary crushing process to improve crushing efficiency.

[0026] (2) Second process: Dissolving crushed waste refractory saggers The pulverized waste refractory saggers obtained through the first process contain lithium-containing materials, such as lithium hydroxide, lithium carbonate, lithium silicate, lithium aluminum oxide, or lithium aluminum silicate. While most lithium-containing materials are water-soluble, some, including lithium aluminum silicate, have low solubility in water and are difficult to dissolve with water alone. To address this issue, the present invention employs a process for dissolving the pulverized waste refractory saggers, in which the pulverized waste refractory saggers are mixed with water and an alkaline leaching agent containing at least one selected from the group consisting of alkali metal hydroxides, alkali metal carbonates, and alkaline earth metal hydroxides, followed by heating. The process for dissolving the pulverized waste refractory saggers of the present invention involves heating and dissolving the pulverized waste refractory saggers with the alkaline leaching agent, which can decompose and dissolve materials such as lithium aluminum silicate, which has low solubility in water, thereby increasing the lithium recovery rate. The decomposition and dissolution reactions of the low-solubility lithium-containing material tend to increase in reactivity in proportion to the alkali concentration and temperature. Therefore, using an alkaline leaching agent containing an alkali metal salt results in high concentrations of silicon and aluminum, necessitating a separate process for their removal. In contrast, using a leaching agent prepared from an alkaline earth metal oxide or hydroxide and water promotes the decomposition of lithium aluminum silicate and helps maintain low concentrations of silicon and aluminum in the solution by forming sparingly soluble salts with soluble silicon and aluminum. This reacts with lithium carbonate, which has a relatively low solubility, to produce highly soluble lithium hydroxide and sparingly soluble carbonates, thereby improving the lithium leaching rate. Therefore, in the process for dissolving the crushed used refractory saggers of the present invention, calcium hydroxide, calcium oxide, or magnesium hydroxide is used as a leaching agent to promote lithium extraction, and the amount of calcium hydroxide added is preferably 5 to 50 parts by weight per 100 parts by weight of the used refractory saggers.It has been confirmed that the dissolving process of the crushed used refractory saggers takes more than 6 hours to complete the reaction at temperatures below 20°C, within 2 hours at 50°C, and within 30 minutes at 80°C. At temperatures close to 100°C, the reaction is completed within 10 minutes, but there is a problem in that significant energy loss occurs due to evaporation of water. Therefore, the preferred dissolving process of the crushed used refractory saggers of the present invention involves carrying out the reaction for 30 to 120 minutes at temperatures of 50 to 80°C.

[0027] In summary, the preferred process for dissolving crushed used refractory saggers of the present invention involves heating a slurry of crushed used refractory saggers containing 100 parts by weight of crushed used refractory saggers (crushed to 200# mesh or less) and 5-50 parts by weight of a leaching agent, calcium hydroxide, calcium oxide, or magnesium hydroxide, to a temperature of 50-80°C and allowing it to react for 30-120 minutes. For reference, under the same conditions, adding an additional amount of alkali metal hydroxide water equivalent to 5-50% of the alkaline earth metal hydroxide (or oxide) used can increase the lithium leaching rate and yield by approximately 5%. This method is suitable when higher process costs can be tolerated.

[0028] (3) Third step: Primary solid-liquid separation step The dissolved reaction solution of the pulverized waste refractory saggers is subjected to solid-liquid separation (primary solid-liquid separation). For the primary solid-liquid separation, a settling tank, a filter press, a screw filter, a centrifuge, or the like can be used, and the efficiency can be increased by combining two or more of these. The solid phase obtained by the primary solid-liquid separation contains the positive electrode active material and the refractory composition, and the liquid phase (filtrate) contains lithium (Li + ), aluminum (Al(OH)4 - ), silicon (H2SiO4 2-The filtrate is input into an anion exchange process and a carbonation process to produce high-purity lithium carbonate, and the solid phase is input into a multi-stage magnetic separation process, a lithium leaching process and a carbonation reaction process to recover the lithium contained therein as lithium carbonate, and the recovered lithium carbonate is input into a pressurized carbon dioxide dissolution process performed after the anion exchange process and carbonation process of the filtrate to produce high-purity lithium carbonate. Hereinafter, first, a process for producing high-purity lithium carbonate using the filtrate will be described, and then a process for producing high-purity lithium carbonate using the solid phase will be described.

[0029] (4) Fourth step: anion exchange step The filtrate obtained in the primary solid-liquid separation step is a strongly alkaline lithium hydroxide aqueous solution having a pH of 12 or higher. The lithium hydroxide aqueous solution contains Al(OH)4 - , H2SiO4 2- and Ca 2+ In the present invention, in order to remove the impurities, an anion exchange process is carried out in which the solution is passed through an anion exchange resin. The anion exchange resin may be a resin that can be used in a strong base range, and preferably is a styrene-based resin having a gel structure, which is used to adsorb trimethyl ammonium or dimethyl ethanolamine to form OH groups. - It is preferable that the anion exchange resin contains a functional group. The anion exchange step can be carried out in an ion exchange tower in which the height of the anion exchange resin bed is 80 cm or more, and can be carried out while flowing the lithium hydroxide aqueous solution at a flow rate of 0.1 to 1 m / sec under room temperature conditions. The ion exchange tower is preferably a continuous ion exchange tower that comes into contact with the treatment solution in a countercurrent manner and is designed so that the resin used for a certain period of time is regenerated and introduced. When the filtrate (lithium hydroxide aqueous solution) obtained in the primary solid-liquid separation step is injected into the ion exchange tower, the impurities remain by binding to the anion exchange resin, and the lithium hydroxide aqueous solution is obtained as a flow-through liquid, resulting in a high purity.

[0030] After being used for a certain period of time, the anion exchange resin is regenerated by desorbing the adsorbed anions, and the backwash solution generated in this process is sent to the second process, the process of dissolving crushed used refractory saggers, for reuse. The regenerated anion exchange resin is sent to the anion exchange tower for reuse. In this case, water and slaked lime may be further added to the backwash solution and then fed to the process of dissolving crushed used refractory saggers.

[0031] The anion exchange step may further include a filtrate from a seventh solid-liquid separation step performed after a lithium leaching step in a lithium carbonate production step or a lithium sulfate production step.

[0032] (5) Fifth step: Primary carbonation reaction step The liquid that has passed through the ion exchange column is a lithium hydroxide aqueous solution from which impurities have been removed. In the present invention, a primary carbonation reaction step is performed to obtain lithium carbonate (Li2CO3) from the lithium hydroxide. The primary carbonation reaction step can be performed using a first carbonation method (see Chemical Formula 1) in which carbon dioxide (CO2) gas is injected into a lithium hydroxide aqueous solution, a second carbonation method (see Chemical Formula 2) in which a lithium hydroxide aqueous solution is mixed with carbonated water, a third carbonation method (see Chemical Formula 3) in which a lithium hydroxide aqueous solution is mixed with a lithium bicarbonate aqueous solution, a fourth carbonation method (see Chemical Formula 4) in which a lithium hydroxide aqueous solution is mixed with a sodium carbonate aqueous solution, or a fifth carbonation method (see Chemical Formula 5) in which a lithium hydroxide aqueous solution is mixed with a potassium carbonate aqueous solution.

[0033] [ka]

[0034] [ka]

[0035] [ka]

[0036] [ka]

[0037] [ka]

[0038] Among the carbonation methods, the fourth and fifth carbonation methods have the problem that they may produce impurities such as sodium and potassium, and therefore require additional steps to remove the impurities. Therefore, the present invention uses the first, second, or third carbonation method, which does not involve the risk of producing the impurities, and preferably uses the first carbonation method, which involves injecting carbon dioxide gas.

[0039] According to an embodiment of the present invention, in the first carbonation method, 1 L of a lithium hydroxide aqueous solution concentrated to a concentration of 2 mol / L is charged into a 1.5 L (liter) pressure reactor and stirred while blowing carbon dioxide gas at a flow rate of 1 L / min, and the lithium carbonate production reaction is completed in approximately 22 minutes. The concentration of the lithium hydroxide aqueous solution in this reaction is preferably 0.5 to 5 mol / L. If the concentration of the lithium hydroxide aqueous solution is lower than 0.5 mol / L, the amount of lithium carbonate produced is too small, resulting in reduced process efficiency. If the concentration is higher than 5 mol / L, the viscosity of the aqueous solution is too high, making it difficult to remove impurities. The first carbonation method of the present invention is an exothermic reaction, and when an aqueous solution at 20°C is reacted, the temperature at the end of the reaction will be approximately 35°C. Therefore, no separate heating operation is required during the reaction period. However, as the temperature increases, the solubility of lithium carbonate decreases, resulting in an increase in the yield rate of lithium carbonate, and the crystal growth rate also increases, resulting in an effect of increasing the purity through recrystallization. Therefore, it is preferable to carry out the reaction so that the final temperature of the reaction solution is 80 to 100°C.

[0040] The carbonation reaction solution of the present invention is in a strongly alkaline state with a pH of 12 or higher at the beginning of the reaction, and as the reaction proceeds, the pH gradually decreases and converges to pH 7. The production of lithium carbonate ends at a pH of approximately 9, and at a pH lower than 9, lithium carbonate is redissolved as lithium bicarbonate. Therefore, it is preferable to terminate the carbonation reaction when the pH is in the range of 8 to 10. However, even if the reaction is allowed to proceed until the pH of the reaction solution reaches 7, the produced lithium bicarbonate is recovered in a subsequent step, so the yield is not reduced. In fact, it is more preferable to continue the reaction until the pH of the reaction solution reaches 7, as this has the advantage of minimizing membrane damage in the subsequent reverse osmosis concentration step.

[0041] In short, the primary carbonation reaction step of the present invention involves introducing an aqueous lithium hydroxide solution having a concentration of 0.5 to 5 mol / L into a pressure reaction vessel (or a sealed vessel), injecting carbon dioxide gas into the vessel and allowing the reaction to proceed until the pH reaches 7, then heating the reaction solution to a temperature of 80 to 100°C and retaining the solution at that temperature for 20 minutes or more to terminate the carbonation reaction.

[0042] The second carbonation method of the present invention can use carbonated water produced by injecting carbon dioxide gas at a pressure of 5 to 20 bar at a temperature of 5 to 10° C. or less, and preferably uses carbonated water produced by injecting carbon dioxide gas at a pressure of 10 bar at a temperature of 5° C. or less. Carbonated water produced by injecting carbon dioxide gas at a pressure of 10 bar at a temperature of 5° C. or less has about 0.68 mol of carbon dioxide dissolved therein.

[0043] According to an embodiment of the present invention, 1 L of the carbonated water is mixed with 500 mL of a 2.72 mol lithium hydroxide aqueous solution, and the mixture is reacted at 20°C for 30 minutes, then heated to 100°C, aged for 10 minutes, and filtered to obtain about 39 g of high-purity lithium carbonate. In this reaction, it is also preferable to adjust the pH of the aqueous solution to about 7 at the end of the reaction.

[0044] The third carbonation method of the present invention is a method using an aqueous solution of lithium bicarbonate (LiHCO3), and can use an aqueous solution of lithium bicarbonate produced by reacting lithium carbonate with carbonated water or an aqueous solution of lithium bicarbonate produced by reacting lithium carbonate with carbon dioxide in a pressure vessel. The aqueous solution of lithium bicarbonate is preferably an aqueous solution of lithium bicarbonate produced by reacting lithium carbonate with carbon dioxide in a pressure vessel, because the reaction of lithium carbonate with carbon dioxide in a pressure vessel can quickly increase the concentration of lithium bicarbonate in the aqueous solution.

[0045] (6) Sixth step: Secondary solid-liquid separation step The carbonation reaction solution is subjected to solid-liquid separation to obtain solid-phase lithium carbonate and liquid-phase filtrate. The filtrate contains approximately 1,500 to 2,000 mg / L of lithium ions and is then input into a lithium phosphate production process to produce high-purity lithium phosphate.

[0046] (7) Seventh step: Primary reverse osmosis concentration step The filtrate obtained in the secondary solid-liquid separation step has a pH of 6 to 8 and contains 1,500 to 2,000 mg / L of lithium in the form of lithium bicarbonate. In the present invention, the filtrate is subjected to a reverse osmosis membrane to concentrate an aqueous lithium bicarbonate solution.

[0047] When a reverse osmosis filter is used in the reverse osmosis concentration step, it is advantageous to use a multistage countercurrent reverse osmosis facility, which has low energy costs, in a large-capacity desalination step, although the initial equipment cost is high. However, in a facility with a work throughput of less than 1,000 tons, as in the present invention, a method using a batch-type reverse osmosis facility and continuing to pass the treatment solution through the filter until a certain concentration is reached is preferably adopted. When using the batch-type reverse osmosis facility, in order to concentrate the solution until the lithium concentration reaches 20,000 mg / L, a water level adjustment sensor is used, and the upper limit of the pump operating pressure is set to 20 kg / cm. 2 You can set it to and drive it.

[0048] The final concentration of the lithium bicarbonate aqueous solution produced using the reverse osmosis concentration process may be 10,000 to 20,000 mg / L. If the concentration of the lithium bicarbonate aqueous solution is lower than 10,000 mg / L, there is a drawback in that the amount of energy consumed is relatively large compared to the amount of lithium carbonate obtained in the subsequent thermal fractional precipitation process. If the concentration of the lithium bicarbonate aqueous solution is higher than 20,000 mg / L, there is a drawback in that lithium carbonate is generated and deposited on the surface of the reverse osmosis membrane, causing damage to the membrane.

[0049] In addition to these, the first reverse osmosis concentration step may be performed by further adding a filtrate obtained as a liquid phase in the sixth solid-liquid separation step after the pressurized carbon dioxide dissolution step, the fifth solid-liquid separation step, and the second thermal fractionation step in the process of producing high-purity lithium carbonate from the solid phase separated by the secondary solid-liquid separation step after the anion exchange step.

[0050] (8) Eighth step: Primary heating fractionation precipitation step The lithium bicarbonate aqueous solution, which is the concentrate from the first reverse osmosis concentration step, is heated to precipitate only lithium carbonate. The precipitation process is represented by Chemical Formula 6.

[0051] [ka]

[0052] When the reaction temperature is low and the pressure is high, the dissolution reaction of lithium carbonate progresses to produce lithium bicarbonate, while when the reaction temperature is high and the pressure is low, lithium bicarbonate precipitates as lithium carbonate. In this reaction, lithium carbonate can be precipitated simply by vigorous stirring or aeration, but the precipitation rate is extremely slow. Therefore, the most economical and simplest method for precipitating lithium bicarbonate as lithium carbonate in this reaction is to heat the reaction solution to 80 to 100°C while stirring. The precipitation reaction rate of lithium carbonate varies depending on the temperature and pressure, and the higher the temperature and the lower the pressure, the faster the reaction. According to an embodiment, when an aqueous solution of lithium carbonate (LiHCO3) with a concentration of 2 mol / L is heated to 100°C, the precipitation reaction of lithium carbonate is completed within 20 minutes.

[0053] (9) Ninth step: Tertiary solid-liquid separation step The precipitation reaction liquid from the primary heating fractional precipitation step is subjected to solid-liquid separation. The solid phase obtained by the solid-liquid separation contains a lithium carbonate compound as well as a trace amount of aluminum silicon as an impurity. The solid phase is then introduced into a pressurized carbon dioxide dissolution step for producing high-purity lithium carbonate. The liquid phase obtained by the solid-liquid separation contains lithium, sodium, and potassium at concentrations of several hundred to several thousand mg / L. The liquid phase is then introduced into a lithium phosphate precipitation step for producing high-purity lithium phosphate.

[0054] (10) Tenth step: Lithium phosphate precipitation step By adding sodium phosphate to the filtrate obtained in the tertiary solid-liquid separation step, lithium ions contained in the filtrate are precipitated and recovered as lithium phosphate. To this end, the lithium aqueous solution obtained by the tertiary solid-liquid separation and a soluble phosphate aqueous solution corresponding to 1 to 1.1 times the equivalent amount required to precipitate all of the lithium dissolved in the aqueous solution as lithium phosphate are charged into a reaction vessel, and an alkali is added to adjust the pH of the aqueous solution to 12 or higher. The reaction solution is then allowed to stand at a temperature of 80 to 100°C for 20 minutes or longer to complete the precipitation reaction of lithium phosphate. The lithium phosphate precipitation step may be performed using the filtrate from the eighth solid-liquid separation step for producing lithium carbonate, which further includes a filtrate having an impurity content of more than 5,000 mg / L. Alternatively, the filtrate from the ninth solid-liquid separation step for producing high-purity lithium sulfate, which further includes a filtrate having an impurity content of more than 5,000 mg / L.

[0055] (11) Eleventh step: Quaternary solid-liquid separation step The lithium phosphate precipitate produced by the lithium phosphate precipitation process is obtained as a solid phase by a fourth solid-liquid separation process, and the lithium phosphate is then subjected to post-treatments such as drying to produce high-purity lithium phosphate with a purity of 99.9% or higher. The liquid phase obtained by the solid-liquid separation is contacted with slaked lime to remove phosphoric acid and then discharged.

[0056] The specific embodiments described herein are meant merely to represent preferred aspects or examples of the invention, and are not intended to limit the scope of the invention. Modifications and other uses of the invention will be apparent to those skilled in the art without departing from the scope of the invention as set forth in the claims herein. [Industrial Applicability]

[0057] By utilizing the method for producing high-purity lithium phosphate from used refractory saggers of the present invention, it is expected that not only can discarded used refractory saggers be reused to produce high-purity lithium phosphate that can be used in the production of lithium secondary batteries, but also the positive electrode active material, iron oxide, alumina, silicate, and calcium carbonate incidentally obtained in the production process can be reused.

Claims

1. A first step of crushing the waste refractory saggers to produce crushed waste refractory saggers; A second step of adding an alkali leaching agent and water to the pulverized waste refractory saggers and then reacting them to prepare a pulverized waste refractory saggers dissolution reaction slurry; A third step of performing primary solid-liquid separation of the waste refractory sagger pulverized material dissolution reaction slurry; a fourth step of passing the filtrate obtained as a liquid phase by the primary solid-liquid separation through an anion exchange resin to perform an anion exchange reaction; a fifth step of carrying out a carbonation reaction on the permeate of the anion exchange reaction to produce a carbonation reaction solution; A sixth step of subjecting the carbonation reaction liquid to secondary solid-liquid separation; a seventh step of concentrating the filtrate obtained as a liquid phase by the secondary solid-liquid separation under reverse osmosis pressure; an eighth step of subjecting the concentrate obtained by the reverse osmosis concentration to a thermal fractional precipitation reaction; a ninth step of subjecting the reaction solution of the thermal fractional precipitation reaction to tertiary solid-liquid separation; a tenth step of subjecting the filtrate obtained as a liquid phase by the tertiary solid-liquid separation to a lithium phosphate precipitation reaction; an eleventh step of subjecting the reaction solution of the lithium phosphate precipitation reaction to a quaternary solid-liquid separation to obtain high-purity lithium phosphate as a solid phase; 1. A method for producing high purity lithium phosphate from waste refractory saggers, comprising:

2. 2. The method for producing high-purity lithium phosphate from used refractory saggers according to claim 1, wherein the waste refractory saggers crushed to 200# (mesh) or less are dissolved and reacted by adding 5 to 50 parts by weight of an alkaline leaching agent, such as calcium hydroxide, calcium oxide, or magnesium hydroxide, to 100 parts by weight of the waste refractory saggers crushed to 200# (mesh) or less, mixing with 350 parts by weight of water, and reacting the mixture at a temperature of 50 to 80° C. for 30 to 120 minutes.

3. 2. The method for producing high-purity lithium phosphate from used refractory saggers according to claim 1, wherein the anion exchange resin is prepared by adsorbing trimethyl ammonium or dimethyl ethanolamine onto a styrene-based resin having a gel structure, and the anion exchange reaction is performed by passing a filtrate obtained as a liquid phase by the primary solid-liquid separation through an anion exchange tower packed with the anion exchange resin at a flow rate of 0.1 to 1 m / sec.

4. 2. The method for producing high-purity lithium phosphate from used refractory saggers according to claim 1, wherein the carbonation reaction is carried out by introducing a filtrate from the anion exchange reaction into a pressure reaction vessel (or a sealed vessel), injecting one selected from carbon dioxide, carbonated water, and an aqueous lithium bicarbonate solution into the filtrate, and reacting until the filtrate reaches pH 7, and then retaining the filtrate at a temperature of 80 to 100° C. for 20 minutes or more to terminate the reaction.

5. The reverse osmosis concentration is carried out using a batch reverse osmosis equipment, and the upper limit of the pump operating pressure is set to 20 kg / cm ２ and concentrating the filtrate obtained as a liquid phase by the secondary solid-liquid separation until the lithium concentration in the filtrate is 10,000 to 20,000 mg / L.

6. 2. The method for producing high-purity lithium phosphate from used refractory saggers according to claim 1, wherein the thermal fractionation precipitation reaction involves heating the concentrate obtained by the reverse osmosis concentration at a temperature of 80 to 100°C for 20 minutes or more to precipitate lithium carbonate.

7. 2. The method for producing high-purity lithium phosphate from used refractory saggers according to claim 1, wherein the lithium phosphate precipitation reaction is carried out by adding a soluble phosphate aqueous solution in an amount corresponding to 1 to 1.1 times the equivalent of lithium ions dissolved in the filtrate obtained as a liquid phase by the tertiary solid-liquid separation, adjusting the pH to 12 or more, and allowing the solution to remain at a temperature of 80 to 100° C. for 20 minutes or more to precipitate lithium phosphate.

8. 2. The method for producing high-purity lithium phosphate from waste refractory saggers according to claim 1, wherein the high-purity lithium phosphate has a purity of 99.0% or more.

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