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

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 waste refractory crucibles. Specifically, the present invention relates to a method for producing high-purity lithium phosphate with a purity of 99.9% or more by pulverizing and dissolving waste refractory crucibles of the present invention, followed by solid-liquid separation, anion exchange, wet magnetic separation, carbonation, and lithium phosphate precipitation reaction.

Background Art

[0002] The positive electrode active material of a lithium secondary battery is produced by firing at a high temperature in a refractory crucible (also called a sagger, also known as a firing sleeve) made of oxidation ceramics mainly composed of SiO2, Al2O3, and MgO. Since the refractory crucible is repeatedly used for high-temperature firing of a lithium-containing composite oxide, which is a raw material of the positive electrode active material, its surface is eroded over time, and lithium hydroxide, lithium carbonate, and the positive electrode active material are deposited on the eroded part. Finally, the refractory crucible whose surface has been eroded by the lithium hydroxide, lithium carbonate, etc. has a reduced thermal durability and is discarded.

[0003] It is said that the annual generation amount of waste refractory crucibles in Korea is about 9,000 tons, but in conjunction with the spread of mobile devices and electric vehicles, the recent rapid increase in the demand for lithium-ion secondary batteries is remarkable, and accordingly, the generation amount of waste refractory crucibles is expected to increase rapidly.

[0004] As described above, the refractory crucible is used in the production of the positive electrode active material and is eroded by the lithium-containing composite oxide during the high-temperature firing process, losing its function. Therefore, if the lithium-containing composite oxide deposited on the eroded part can be recovered in the form of high-purity lithium sulfate, lithium carbonate, or lithium phosphate from the waste refractory crucible that is discarded due to the reduction in thermal durability caused by repeated high-temperature firing of the lithium-containing composite oxide, it is expected that it can be reused in the production of lithium-ion secondary batteries to reduce production costs. However, there is no known method for recovering high-purity lithium compounds from waste refractory crucibles.

[0005] All references, including publications, patent applications, and patents cited in this specification, are incorporated herein by reference to the same extent as if each individual reference were specifically and individually indicated and incorporated by reference, and as if all of the content thereof were set forth herein.

Summary of the Invention

Problems to be Solved by the Invention

[0006] An object of the present invention is to maximize the recovery rate of lithium by recovering trace amounts of lithium contained in the wastewater generated in the process of recovering lithium compounds from waste refractory crucibles discarded after being used in high-temperature firing during the production of positive electrode active materials for lithium secondary batteries as sparingly soluble lithium phosphate.

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

Means for Solving the Problems

[0008] The present invention provides a method for producing high-purity lithium phosphate from waste refractory crucibles, comprising: a first step of pulverizing waste refractory crucibles to produce pulverized waste refractory crucibles; a second step of adding an alkaline leaching agent and water to the pulverized waste refractory crucibles and reacting them to produce a slurry of dissolved pulverized waste refractory crucibles; a third step of performing primary solid-liquid separation on the slurry of dissolved pulverized waste refractory crucibles; a fourth step of passing the filtrate obtained as the liquid phase using the primary solid-liquid separation through an anion exchange resin to perform an anion exchange reaction; a fifth step of performing a carbonation reaction on the permeate of the anion exchange reaction to produce a carbonation reaction solution; a sixth step of performing secondary solid-liquid separation on the carbonation reaction solution; a seventh step of performing reverse osmosis concentration on the filtrate obtained as the liquid phase using the secondary solid-liquid separation; an eighth step of performing a heat fractionation precipitation reaction on the concentrated solution obtained using the reverse osmosis concentration; a ninth step of performing tertiary solid-liquid separation on the reaction solution of the heat fractionation precipitation reaction; a tenth step of performing a lithium phosphate precipitation reaction on the filtrate obtained as the liquid phase using the tertiary solid-liquid separation; and an eleventh step of performing quaternary solid-liquid separation on the reaction solution of the lithium phosphate precipitation reaction to obtain high-purity lithium phosphate as the solid phase.

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

[0010] The carbonation reaction is carried out 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 hydrogen carbonate into the permeate, reacting until the pH reaches 7, and then allowing it to stay under temperature conditions of 80 to 100 °C for 20 minutes or more to terminate the reaction. The reverse osmosis pressure concentration is carried out using a batch reverse osmosis pressure facility, and the upper limit of the operating pressure of the pump is set to 20 kg / cm 2 and concentrated until the lithium concentration in the filtrate obtained as the liquid phase using the secondary solid-liquid separation reaches 10,000 to 20,000 mg / L.

[0011] The heat fractionation precipitation reaction is characterized by heating the concentrated liquid obtained using the reverse osmosis pressure concentration under temperature conditions of 80 to 100 °C for 20 minutes or more to precipitate lithium carbonate. The lithium phosphate precipitation reaction is carried out by adding an aqueous solution of soluble phosphate corresponding to 1 to 1.1 times the equivalent of the lithium ions dissolved in the filtrate obtained as the liquid phase using the tertiary solid-liquid separation, adjusting the pH to 12 or more, and then allowing it to stay under temperature conditions of 80 to 100 °C for 20 minutes or more to precipitate lithium phosphate.

[0012] Lithium phosphate produced by the production method of the present invention is characterized in that its purity is 99.9% or more.

Advantages of the Invention

[0013] The present invention provides an optimized method for recovering lithium contained in wastewater generated in the process of recovering lithium from a lithium-containing composite oxide deposited on the eroded surface of a waste refractory crucible as hardly soluble lithium phosphate. Therefore, it is expected that if the method for producing high-purity lithium phosphate from a waste refractory crucible of the present invention is used, the recovery rate of lithium can be maximized in the process of recovering lithium from the waste refractory crucible to be discarded.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0015] The present invention relates to a method for producing high-purity lithium phosphate from waste refractory crucibles. As the refractory crucibles are repeatedly used, they are eroded and destroyed by lithium hydroxide, lithium carbonate, etc. The present invention aims to recover high-purity lithium carbonate, which is a lithium compound with high added value, from waste refractory crucibles that are discarded without being recycled. The waste refractory crucibles are ceramic containers used for firing the positive electrode active material for secondary batteries, and mainly composed of SiO2, Al2O3, and MgO. Table 1 shows the composition of the waste refractory crucibles used for sintering NCA (sample name: SG1) and NCM (sample name: SG2), which are the positive electrode materials.

[0016]

Table 1

[0017] As a result of the analysis, it was confirmed that the lithium (Li) contents of SG1 and SG2 were 2.1% and 0.88% respectively, and the higher one, and when converted to the lithium carbonate content, it was confirmed that it corresponded to SG1 = 11.17% and SG2 = 4.68%. Also, it was confirmed that the nickel and cobalt contents were 0.13 to 0.16% and 0.01 to 0.02% respectively, and it was confirmed that the value to be recovered was sufficiently high.

[0018] The waste refractory box furnace is composed of mullite, cordierite, alumina, quartz, magnesium aluminate, lithium silicate, lithium aluminum oxide, lithium aluminum silicate, etc. Among the constituent components of the waste refractory box furnace, the substances causing the destruction of the refractory box furnace are lithium silicate, lithium aluminum oxide, lithium aluminum silicate, etc.

[0019] The present invention provides a method for producing high-purity lithium phosphate from waste refractory crucibles, which includes: a first step of pulverizing waste refractory crucibles to produce pulverized waste refractory crucibles; a second step of adding an alkali leaching agent and water to the pulverized waste refractory crucibles and then reacting them to produce a slurry of dissolved pulverized waste refractory crucibles; a third step of performing primary solid-liquid separation on the slurry of dissolved pulverized waste refractory crucibles; a fourth step of passing the filtrate obtained as the liquid phase through an anion exchange resin using the primary solid-liquid separation to perform an anion exchange reaction; a fifth step of performing a carbonation reaction on the passing liquid of the anion exchange reaction to produce a carbonation reaction liquid; a sixth step of performing secondary solid-liquid separation on the carbonation reaction liquid; a seventh step of performing reverse osmosis concentration on the filtrate obtained as the liquid phase using the secondary solid-liquid separation; an eighth step of performing a heat fractionation precipitation reaction on the concentrated liquid obtained using the reverse osmosis concentration; a ninth step of performing tertiary solid-liquid separation on the reaction liquid of the heat fractionation precipitation reaction; a tenth step of performing a lithium phosphate precipitation reaction on the filtrate obtained as the liquid phase using the tertiary solid-liquid separation; and an eleventh step of performing quaternary solid-liquid separation on the reaction liquid of the lithium phosphate precipitation reaction to obtain high-purity lithium phosphate as the solid phase.

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

[0021] The carbonation reaction is carried out by introducing the passing solution 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 lithium hydrogen carbonate solution into the passing solution, reacting until the pH reaches 7, and then allowing it to stay for 20 minutes or more under a temperature condition of 80 to 100 °C to terminate the reaction. The reverse osmosis pressure concentration is carried out using a batch reverse osmosis pressure facility, and the upper limit of the operating pressure of the pump is set to 20 kg / cm 2 and concentrated until the lithium concentration in the filtrate obtained as the liquid phase using the secondary solid-liquid separation reaches 10,000 to 20,000 mg / L.

[0022] The heat fractionation precipitation reaction is characterized by heating the concentrated solution obtained using the reverse osmosis pressure concentration for 20 minutes or more under a temperature condition of 80 to 100 °C to precipitate lithium carbonate. The lithium phosphate precipitation reaction is carried out by adding an aqueous solution of soluble phosphate corresponding to 1 to 1.1 times the equivalent of the lithium ions dissolved in the filtrate obtained as the liquid phase using the tertiary solid-liquid separation, adjusting the pH to 12 or more, and then allowing it to stay for 20 minutes or more under a temperature condition of 80 to 100 °C 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 crucibles of the present invention will be described in detail step by step.

[0025] (1) The first step: Waste refractory crucible pulverization step The waste refractory crucible is crushed into powder with a particle size of 200# or less. When pulverizing the waste refractory crucible all at once, there is a problem that the pulverization efficiency is too low. Therefore, it is preferable to first coarsely crush it to 1 mm or less using primary crushing with a jaw crusher, and then pulverize it to 200# (mesh) or less using secondary crushing with a ball mill. Although the waste refractory crucible has high compressive strength, it is characterized by being vulnerable to impact. For crushing the waste refractory crucible, an impact crusher can be applied, but there is a problem that crushing particles with sharp surfaces of high hardness are generated, increasing the wear of the crusher parts and driving up the cost. Therefore, in the present invention, a jaw crusher that is easy to replace parts and has a low cost is used in the primary crushing process, and a ball mill is used in the secondary crushing process. Preferably, in order to improve the pulverization efficiency, an intermediate crusher such as an impact crusher may be arranged before the secondary crushing process.

[0026] (2) Second step: Dissolution step of waste refractory crucible powder The pulverized waste refractory crucible obtained by micronization using the first step contains lithium-containing substances such as lithium hydroxide, lithium carbonate, lithium silicate, lithium aluminum oxide, or lithium aluminum silicate. Most of the lithium-containing substances are water-soluble, but some substances containing lithium aluminum silicate have a problem that their solubility in water is low and it is difficult to dissolve them only with water. In order to solve the above problem, in the present invention, a waste refractory crucible pulverized material dissolution step is applied in which the waste refractory crucible pulverized material is mixed with an alkali leaching agent in which any one or two or more selected from the group consisting of alkali metal hydroxides, alkali metal carbonates, or alkaline earth metal hydroxides are mixed and water, and then heated. Since the waste refractory crucible pulverized material dissolution step of the present invention is heated and dissolved together with the alkali leaching agent, lithium aluminum silicate having a low solubility in water can be decomposed and dissolved, so that there is an advantage that the recovery rate of lithium is increased. The decomposition and dissolution reaction of the lithium-containing substance having a low solubility tends to have higher reactivity in proportion to the concentration and temperature of the alkali. For this reason, when an alkali leaching agent containing an alkali metal salt is used, the concentrations of silicon and aluminum increase, so that a separate step for removing them is required. On the contrary, when a leaching agent produced by an alkaline earth metal oxide or hydroxide and water is used, soluble silicon and aluminum form hardly soluble salts, which promotes the decomposition of lithium aluminum silicate and helps to keep the concentrations of silicon and aluminum in the solution low. It reacts with lithium carbonate having a relatively low solubility to produce lithium hydroxide having a high solubility and hardly soluble carbonate, so that there is an advantage of improving the leaching rate of lithium. Therefore, in the waste refractory crucible pulverized material dissolution step of the present invention, calcium hydroxide, calcium oxide, or magnesium hydroxide is used as a leaching agent for promoting lithium extraction, and the addition amount thereof is preferably 5 to 50 parts by weight based on 100 parts by weight of the waste refractory crucible.In the step of dissolving the crushed waste refractory crucible, when the temperature is 20°C or lower, it takes 6 hours or more to complete the reaction, while under the temperature condition of 50°C, the reaction is completed within 2 hours, and under the temperature condition of 80°C, it is confirmed that the reaction is completed within 30 minutes. Also, when the temperature is near 100°C, the reaction is completed within 10 minutes, but there is a problem that a great deal of energy loss occurs due to the evaporation of water. Therefore, in the preferred step of dissolving the crushed waste refractory crucible of the present invention, the reaction is carried out at a temperature of 50 to 80°C for 30 to 120 minutes.

[0027] In short, the preferred step of dissolving the crushed waste refractory crucible of the present invention is to heat a slurry of crushed waste refractory crucible containing 5 to 50 parts by weight of calcium hydroxide, calcium oxide, or magnesium hydroxide as a leaching agent with respect to 100 parts by weight of the crushed waste refractory crucible pulverized to 200# (mesh) or less to a temperature of 50 to 80°C and react for 30 to 120 minutes. For reference, if an aqueous alkali metal hydroxide corresponding to 5 to 50% of its usage amount is further added together with an alkaline earth metal hydroxide (or oxide) under the same conditions, an effect that the leaching rate and leaching ratio of lithium increase by about 5% can be obtained. The above method is a suitable method when the increase in process cost can be tolerated.

[0028] (3) The third step: the primary solid-liquid separation step The dissolution reaction solution of the crushed waste refractory crucible is subjected to solid-liquid separation (primary solid-liquid separation). For the primary solid-liquid separation, a sedimentation tank, a filter press, a screw filter, a centrifuge, etc. can be used, and the efficiency can be enhanced by combining two or more of these. The solid phase obtained by the primary solid-liquid separation contains a positive electrode active material and a refractory composition, and the liquid phase (filtrate) contains lithium (Li + ), aluminum (Al(OH)4 - ), silicon (H2SiO4 2-It includes

[0029] (4) The fourth step: Anion exchange step The filtrate obtained in the primary solid-liquid separation step is a strongly alkaline lithium hydroxide aqueous solution with a pH of 12 or higher. The lithium hydroxide aqueous solution contains impurities such as Al(OH)4 - , H2SiO4 2- and Ca 2+ etc. In the present invention, in order to remove the impurities, an anion exchange step of passing through an anion exchange resin is performed. The anion exchange resin may be a resin that can be used in the strong base region. Preferably, trimethyl ammonium or dimethyl ethanolamine is adsorbed on a styrene-based resin having a gel structure to contain an OH - functional group. The anion exchange step can be performed in an ion exchange tower where the height of the anion exchange resin layer is 80 cm or more, and can be performed while flowing the lithium hydroxide aqueous solution at a flow rate of 0.1 to 1 m / sec under normal temperature conditions. It is preferable to use a continuous ion exchange tower designed such that the resin used for a certain period of time is regenerated and input by contacting the treatment solution in a countercurrent manner. When the filtrate (lithium hydroxide aqueous solution) obtained in the primary solid-liquid separation step is injected into the ion exchange tower, the impurities bind to the anion exchange resin and remain, and the lithium hydroxide aqueous solution is obtained as a flow-through, so the purity is increased.

[0030] The anion exchange resin used for a certain period of time desorbs and regenerates the adsorbed anions. At this time, the backwash solution generated is sent to the waste refractory crucible pulverized material dissolution process, which is the second step, for reuse. The regenerated anion exchange resin is sent to the anion exchange tower for reuse. At this time, water and slaked lime may be further added to the backwash solution and put into the waste refractory crucible pulverized material dissolution process.

[0031] In addition, the anion exchange process may be further carried out with the filtrate from the seventh solid-liquid separation process performed after the lithium leaching process in the lithium carbonate production process or the lithium sulfate production process.

[0032] (5) The fifth step: the primary carbonation reaction step The passing solution that has passed through the ion exchange tower is an aqueous lithium hydroxide 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 includes a first carbonation method of injecting carbon dioxide (CO2) gas into the aqueous lithium hydroxide solution (see Chemical Formula 1), a second carbonation method of mixing the aqueous lithium hydroxide solution and carbonated water (see Chemical Formula 2), a third carbonation method of mixing the aqueous lithium hydroxide solution and an aqueous lithium hydrogen carbonate solution (see Chemical Formula 3), a fourth carbonation method of mixing the aqueous lithium hydroxide solution and an aqueous sodium carbonate solution (see Chemical Formula 4), or a fifth carbonation method of mixing the aqueous lithium hydroxide solution and an aqueous potassium carbonate solution (see Chemical Formula 5) is applicable.

[0033]

Chemical formula

[0034]

Chemical formula

[0035]

Chemical formula

[0036] [Chemical formula]

[0037] [Chemical formula]

[0038] Among the carbonation methods described above, the fourth and fifth carbonation methods may produce impurities such as sodium and potassium, respectively, and thus there is a problem that these impurities must be removed using additional processes. Therefore, in the present invention, the first, second, or third carbonation method, which does not raise concerns about the generation of such impurities, is preferably used, and more preferably, the first carbonation method in which carbon dioxide gas is injected is used.

[0039] According to an embodiment of the present invention, in the first carbonation method, 1 L of an aqueous lithium hydroxide solution concentrated to a concentration of 2 mol / L is introduced into a pressure reactor with a capacity of 1.5 L (liters), and while stirring, carbon dioxide gas is blown in at a flow rate of 1 L / min, and the lithium carbonate formation reaction is completed in about 22 minutes. The concentration of the aqueous lithium hydroxide solution in this reaction is preferably 0.5 to 5 mol / L. If the concentration of the aqueous lithium hydroxide solution is lower than 0.5 mol / L, the amount of lithium carbonate produced is too small and the process efficiency decreases, and if the concentration is higher than 5 mol / L, there is a problem that the viscosity of the aqueous solution is too high and impurities cannot be removed. 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 is about 35°C. Therefore, no separate heating operation is required during the reaction period, but when the temperature rises, not only does the solubility of lithium carbonate decrease and the yield rate of lithium carbonate increase, but also the crystal growth rate increases and the effect of increasing the purity by recrystallization is obtained. Therefore, it is preferable to perform the reaction so that the temperature of the final reaction solution becomes 80 to 100°C.

[0040] The carbonation reaction solution of the present invention is in a strong alkaline state with a pH of 12 or more at the initial stage of the reaction, and gradually decreases as the reaction proceeds and converges to pH 7. The production of lithium carbonate ends at around pH 9, and lithium carbonate is redissolved as lithium bicarbonate in a pH state lower than pH 9. Therefore, it is preferable that the carbonation reaction ends when the pH is in the range of 8 to 10. However, even if the reaction proceeds until the pH of the reaction solution reaches 7, since the produced lithium bicarbonate is recovered in the subsequent process, the yield rate does not decrease. Rather, since there is an advantage of suppressing damage to the membrane as much as possible in the subsequent reverse osmosis concentration process, it is more preferable to react until the pH of the reaction solution reaches 7.

[0041] In short, in the primary carbonation reaction step of the present invention, an aqueous lithium hydroxide solution having a concentration of 0.5 to 5 mol / L is introduced into a pressure reaction vessel (or a sealed vessel), carbon dioxide gas is injected therein, and the reaction is carried out until the pH reaches 7. Then, the temperature of the reaction solution is heated to 80 to 100°C, and the reaction solution is retained at that temperature for 20 minutes or more to terminate the carbonation reaction.

[0042] According to the second carbonation method of the present invention, 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 lower can be used. Preferably, carbonated water produced by injecting carbon dioxide gas at a pressure of 10 bar at a temperature of 5°C or lower is used. About 0.68 mol of carbon dioxide is dissolved in the carbonated water produced by injecting carbon dioxide gas at a pressure of 10 bar at 5°C or lower.

[0043] According to an embodiment of the present invention, if 1 L of the carbonated water and 500 mL of an aqueous lithium hydroxide solution of 2.72 mol are mixed and reacted for 30 minutes under a temperature condition of 20°C, then heated to 100°C and aged for 10 minutes and then filtered, about 39 g of high-purity lithium carbonate can be obtained. It is also preferable that the pH of the aqueous solution is about 7 at the end of this reaction.

[0044] The third carbonation method of the present invention is a method using an aqueous solution of lithium hydrogen carbonate (LiHCO3), and an aqueous solution of lithium hydrogen carbonate produced by reacting lithium carbonate with carbonic acid water or an aqueous solution of lithium hydrogen carbonate produced by reacting lithium carbonate with carbon dioxide in a pressure vessel can be used. It is preferable to use an aqueous solution of lithium hydrogen carbonate produced by reacting lithium carbonate with carbon dioxide in a pressure vessel, because when lithium carbonate reacts with carbon dioxide in a pressure vessel, the concentration of lithium bicarbonate in the aqueous solution can be rapidly increased.

[0045] (6) Sixth step: Secondary solid-liquid separation step Solid-liquid separation is performed on the carbonation reaction solution to obtain solid-phase lithium carbonate and liquid-phase filtrate. The filtrate contains about 1,500 to 2,000 mg / L of lithium ions, which are introduced into the production process of lithium phosphate and produced as high-purity lithium phosphate.

[0046] (7) Seventh step: Primary reverse osmosis pressure 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 state of lithium hydrogen carbonate. In the present invention, the aqueous solution of lithium hydrogen carbonate is concentrated using a reverse osmosis membrane for the filtrate.

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

[0048] The final concentration of the aqueous lithium bicarbonate solution produced using the reverse osmotic pressure concentration process may be 10,000 to 20,000 mg / L. If the concentration of the aqueous lithium bicarbonate solution is concentrated to a concentration lower than 10,000 mg / L, there is a drawback that the energy consumption becomes relatively high compared to the amount of lithium carbonate obtained in the subsequent heating and fractional precipitation process, which is a subsequent step. If the concentration of the aqueous lithium bicarbonate solution is concentrated beyond 20,000 mg / L, there is a problem 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 primary reverse osmotic pressure concentration process may be carried out by further adding the filtrate obtained as the liquid phase of the sixth solid-liquid separation step after the pressurized carbonic acid dissolution step, the fifth solid-liquid separation step, and the secondary heating and fractionation step in the process of producing the solid phase separated by secondary solid-liquid separation after the anion exchange step as high-purity lithium carbonate.

[0050] (8) The eighth step: the primary heating and fractional precipitation step Heat the aqueous lithium bicarbonate solution, which is the concentrated solution of the primary reverse osmotic pressure concentration process, to precipitate only lithium carbonate. The precipitation process is represented by Chemical Formula 6.

[0051]

Chemical formula

[0052] When the reaction temperature is low and the pressure is high, the dissolution reaction of lithium carbonate proceeds to produce lithium bicarbonate. When the reaction temperature is high and the pressure is low, lithium bicarbonate precipitates as lithium carbonate. In the said reaction, lithium carbonate precipitates even with just intense stirring or aeration, but there is a drawback that the rate is very slow. Therefore, the most economical and simple method of precipitating lithium bicarbonate as lithium carbonate in the said reaction is to heat the reaction solution to 80 - 100°C while stirring. The precipitation reaction rate of lithium carbonate varies according to temperature and pressure. The higher the temperature and the lower the pressure, the faster the reaction. According to the embodiment, when an aqueous solution with a concentration of 2 mol / L of lithium carbonate (LiHCO3) is heated to 100°C, the precipitation reaction of lithium carbonate is completed within 20 minutes.

[0053] (9) The ninth step: the third solid-liquid separation step Solid-liquid separation is performed on the precipitation reaction solution of the primary heating and separation precipitation step. The solid phase obtained by using the said solid-liquid separation contains a trace amount of aluminum silicon, which is an impurity, together with the lithium carbonate compound. The said solid phase is put into the pressurized carbonic acid dissolution step for the production of high-purity lithium carbonate. The liquid phase obtained by using the said solid-liquid separation contains lithium, sodium, and potassium at a concentration of several hundred to several thousand mg / L. The said liquid phase is put into the lithium phosphate precipitation step for the production of high-purity lithium phosphate.

[0054] (10) The tenth step: the lithium phosphate precipitation step If sodium phosphate is added to the filtrate obtained in the third solid-liquid separation step, lithium ions contained in the filtrate are precipitated as lithium phosphate and recovered. For this purpose, a soluble phosphate aqueous solution corresponding to 1 to 1.1 times the equivalent amount necessary to precipitate all of the lithium aqueous solution, which is the filtrate obtained by the third solid-liquid separation, and the lithium dissolved in the aqueous solution, as lithium phosphate, is introduced into a reaction tank. After adding an alkali so that the pH of the aqueous solution becomes 12 or higher, the reaction solution is allowed to stay for 20 minutes or more under temperature conditions of 80 to 100 °C to complete the precipitation reaction of lithium phosphate. The lithium phosphate precipitation step may be carried out further including a filtrate having impurities exceeding 5,000 mg / L as the filtrate of the eighth solid-liquid separation step for the production of lithium carbonate, or may be carried out further including a filtrate having impurities exceeding 5,000 mg / L as the filtrate of the ninth solid-liquid separation step for the production of high-purity lithium sulfate.

[0055] (11) The 11th step: the fourth solid-liquid separation step The lithium phosphate precipitate produced by the lithium phosphate precipitation step is obtained as a solid phase using the fourth solid-liquid separation step, and the lithium phosphate is produced as high-purity lithium phosphate having a purity of 99.9% or more using post-treatment such as drying. The liquid phase obtained using the solid-liquid separation is discharged after removing phosphoric acid by contacting with slaked lime.

[0056] The specific embodiments described in this specification are merely meant to represent preferred modes or exemplifications of the present invention, and thereby do not limit the scope of the present invention. It is obvious to those skilled in the art that modifications and other uses of the present invention do not depart from the scope of the invention described in the claims of this specification.

Industrial Applicability

[0057] By using the method for producing high-purity lithium phosphate from waste refractory crucibles of the present invention, not only can the discarded waste refractory crucibles be recycled to produce high-purity lithium phosphate that can be used in the manufacture 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 manufacturing process can be recycled.

Claims

1. A first step of pulverizing waste refractory crucibles to produce pulverized waste refractory crucibles; A second step of adding an alkali leaching agent and water to the pulverized waste refractory crucibles and then reacting them to produce a pulverized waste refractory crucible dissolution reaction slurry; A third step of performing primary solid-liquid separation on the pulverized waste refractory crucible dissolution reaction slurry; A fourth step of passing the filtrate obtained as the liquid phase using the primary solid-liquid separation through an anion exchange resin to perform an anion exchange reaction; A fifth step of performing a carbonation reaction on the permeate of the anion exchange reaction to produce a carbonation reaction solution; A sixth step of performing secondary solid-liquid separation on the carbonation reaction solution; A seventh step of performing reverse osmosis concentration on the filtrate obtained as the liquid phase using the secondary solid-liquid separation; An eighth step of performing a heat fractionation precipitation reaction on the concentrated solution obtained using the reverse osmosis concentration; A ninth step of performing tertiary solid-liquid separation on the reaction solution of the heat fractionation precipitation reaction; A tenth step of performing a lithium phosphate precipitation reaction on the filtrate obtained as the liquid phase using the tertiary solid-liquid separation; An eleventh step of performing quaternary solid-liquid separation on the reaction solution of the lithium phosphate precipitation reaction to obtain high-purity lithium phosphate as the solid phase; A method for producing high-purity lithium phosphate from waste refractory crucibles, comprising the above steps.

2. The pulverized waste refractory crucible dissolution reaction slurry is prepared by adding 5 to 50 parts by weight of calcium hydroxide, calcium oxide, or magnesium hydroxide, which is an alkali leaching agent, to 100 parts by weight of pulverized waste refractory crucibles pulverized to 200# (mesh) or less, mixing 350 parts by weight of water, and reacting this at a temperature condition of 50 to 80°C for 30 to 120 minutes. The method for producing high-purity lithium phosphate from waste refractory crucibles according to Claim 1, characterized in that.

3. The anion exchange resin is an anion exchange resin produced by adsorbing trimethyl ammonium or dimethyl ethanolamine onto a styrene resin having a gel structure. The anion exchange reaction is carried out by passing the filtrate obtained as a liquid phase using the primary solid-liquid separation through an anion exchange column filled with the anion exchange resin at a flow rate of 0.1 to 1 m / sec. A method for producing high-purity lithium phosphate from waste refractory crucibles according to claim 1.

4. The carbonation reaction is carried out by charging the passing liquid of the anion exchange reaction into a pressure reaction vessel (or a closed vessel), injecting one selected from carbon dioxide, carbonated water, and an aqueous solution of lithium hydrogen carbonate into the passing liquid, reacting until the pH reaches 7, and then allowing the reaction to terminate by retaining it for 20 minutes or more under a temperature condition of 80 to 100 °C. A method for producing high-purity lithium phosphate from waste refractory crucibles according to claim 1.

5. The reverse osmosis pressure concentration is carried out using a batch reverse osmosis pressure equipment, and the upper limit of the operating pressure of the pump is set to 20 kg / cm ２ and concentrated until the lithium concentration in the filtrate obtained as a liquid phase using the secondary solid-liquid separation reaches 10,000 to 20,000 mg / L. A method for producing high-purity lithium phosphate from waste refractory crucibles according to claim 1.

6. The heat separation precipitation reaction is characterized by heating the concentrated liquid obtained using the reverse osmosis pressure concentration at a temperature condition of 80 to 100 °C for 20 minutes or more to precipitate lithium carbonate. A method for producing high-purity lithium phosphate from waste refractory crucibles according to claim 1.

7. The lithium phosphate precipitation reaction is carried out by adding an aqueous solution of soluble phosphate corresponding to 1 to 1.1 times the equivalent of lithium ions dissolved in the filtrate obtained as the liquid phase using the above-mentioned three-stage solid-liquid separation, adjusting the pH to 12 or higher, and then allowing it to stay at a temperature of 80 to 100 °C for 20 minutes or more to precipitate lithium phosphate. The method for producing high-purity lithium phosphate from waste refractory crucibles according to claim 1, characterized in that.

8. The high-purity lithium phosphate has a purity of 99.0% or higher. The method for producing high-purity lithium phosphate from waste refractory crucibles according to claim 1, characterized in that.

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