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

Abstract

The present invention provides an optimized method for recovering high-purity lithium sulfate 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 sulfate from the waste refractory crucible of the present invention, not only can the discarded waste refractory crucible be reused to produce high-purity lithium sulfate that can be used in the production of lithium secondary batteries, but it is also expected that the positive electrode active material, iron oxide, alumina, silicate, and calcium carbonate obtained incidentally in the production process can be reused.

Description

[Technical Field]

[0001] The present invention relates to a method for producing high-purity lithium sulfate from used refractory saggers, and more particularly to a method for producing high-purity lithium sulfate 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, magnetic separation, lithium leaching, and concentration. [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.

[0006] 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]

[0007] An object of the present invention is to provide a method for recovering high-purity lithium sulfate having a purity of 99.9% or more from used refractory saggers that are discarded after being used in high-temperature firing in the production of positive electrode active materials for lithium secondary batteries.

[0008] 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]

[0009] The present invention includes a first step of crushing used refractory saggers to produce crushed used refractory saggers; 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 performing primary solid-liquid separation on the crushed used refractory sagger dissolution reaction slurry; a fourth step of producing a suspension from the solid phase obtained by the primary solid-liquid separation and then performing a primary wet magnetic separation process to obtain first magnetized particles and first non-magnetized particles; a fifth step of producing a suspension from the first non-magnetized particles and then performing a secondary wet magnetic separation process to obtain second magnetized particles and second non-magnetized particles; and a fifth step of adding water and a leaching agent to the second non-magnetized particles and then reacting them to produce lithium leaching. The present invention provides a method for producing high-purity lithium sulfate from a waste refractory sagger, the method comprising: a sixth step of producing a reaction solution; a seventh step of performing secondary solid-liquid separation on the lithium leaching reaction solution; an eighth step of producing a neutralized reaction solution by adjusting the pH of the filtrate obtained as a liquid phase by the secondary solid-liquid separation to 6 to 8; a ninth step of performing tertiary solid-liquid separation on the neutralized reaction solution; a tenth step of performing reverse osmosis concentration on the filtrate obtained as a liquid phase by the tertiary solid-liquid separation; an eleventh step of performing evaporation concentration on the concentrate obtained by the reverse osmosis concentration step; and a twelfth step of performing quaternary solid-liquid separation on the concentrate obtained by the evaporation concentration to obtain high-purity lithium sulfate in a solid phase.

[0010] 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 for 30 to 120 minutes at a temperature of 50 to 80°C. The leaching agent used to leach the second non-magnetic material is one or a mixture of two or more selected from the group consisting of sulfuric acid, sulfurous acid, sulfur dioxide, and sulfur trioxide.

[0011] The present invention is characterized in that an alkaline neutralizing agent is added to the filtrate obtained as a liquid phase by the secondary solid-liquid separation to adjust the pH to 6 to 8, and then the tertiary solid-liquid separation is carried out to remove silicon and aluminum, which are impurities, as a solid phase. The reverse osmosis concentration step is carried out using a batch-type reverse osmosis equipment, and the upper limit of the pump operating pressure is set to 50 kg / cm. 2 and concentrating the filtrate obtained as a liquid phase by the tertiary solid-liquid separation until the lithium concentration is 10,000 to 70,000 mg / L.

[0012] The lithium sulfate 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 high-purity lithium sulfate from a lithium-containing composite oxide deposited on the eroded surface of a discarded refractory sagger. Therefore, by utilizing the method for producing high-purity lithium sulfate from a discarded refractory sagger of the present invention, it is expected that not only can the discarded refractory saggers be reused to produce high-purity lithium sulfate 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. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic diagram illustrating a method for producing high-purity lithium sulfate from waste refractory saggers according to the present invention. [Figure 2] 1 shows the results of X-ray diffraction (XRD) analysis of the constituent minerals of the waste refractory sagger of the present invention. [Figure 3] 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 sulfate from used refractory saggers. With repeated use, refractory saggers are corroded by lithium hydroxide, lithium carbonate, and the like and destroyed. The present invention aims to recover high-purity lithium sulfate, a high-value-added lithium compound, from used refractory saggers that are discarded without being reused. The used refractory saggers are ceramic containers used for firing 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 for sintering 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 crushed used refractory saggers; 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 performing primary solid-liquid separation on the crushed used refractory sagger dissolution reaction slurry; a fourth step of producing a suspension from the solid phase obtained by the primary solid-liquid separation and then performing a primary wet magnetic separation process to obtain first magnetized particles and first non-magnetized particles; a fifth step of producing a suspension from the first non-magnetized particles and then performing a secondary wet magnetic separation process to obtain second magnetized particles and second non-magnetized particles; and a fifth step of adding water and a leaching agent to the second non-magnetized particles and then reacting them to produce lithium leaching. The present invention provides a method for producing high-purity lithium sulfate from a waste refractory sagger, the method comprising: a sixth step of producing a reaction solution; a seventh step of performing secondary solid-liquid separation on the lithium leaching reaction solution; an eighth step of producing a neutralized reaction solution by adjusting the pH of the filtrate obtained as a liquid phase by the secondary solid-liquid separation to 6 to 8; a ninth step of performing tertiary solid-liquid separation on the neutralized reaction solution; a tenth step of performing reverse osmosis concentration on the filtrate obtained as a liquid phase by the tertiary solid-liquid separation; an eleventh step of performing evaporation concentration on the concentrate obtained by the reverse osmosis concentration step; and a twelfth step of performing quaternary solid-liquid separation on the concentrate obtained by the evaporation concentration to obtain high-purity lithium sulfate in 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 for 30 to 120 minutes at a temperature of 50 to 80°C. The leaching agent used to leach the second non-magnetic material is one or a mixture of two or more selected from the group consisting of sulfuric acid, sulfurous acid, sulfur dioxide, and sulfur trioxide.

[0021] The filtrate obtained as a liquid phase by the secondary solid-liquid separation is adjusted to a pH of 6 to 8 by adding an alkaline neutralizer, and then the tertiary solid-liquid separation is carried out to remove impurities such as silicon and aluminum as a solid phase. The reverse osmosis concentration step is carried out using a batch-type reverse osmosis equipment, and the upper limit of the pump operating pressure is set to 50 kg / cm. 2 and concentrating the filtrate obtained as a liquid phase by the tertiary solid-liquid separation until the lithium concentration is 10,000 to 70,000 mg / L.

[0022] High-purity lithium sulfate produced by the production method of the present invention is characterized by a purity of 99.9% or more.

[0023] Hereinafter, the method for producing high-purity lithium sulfate from waste refractory saggers according to the present invention will be described in detail step by step.

[0024] (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.

[0025] (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.

[0026] 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.

[0027] (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- ) is included.

[0028] (4) Fourth process: Primary wet magnetic separation process The solid phase obtained by the primary solid-liquid separation is subjected to wet magnetic separation. The primary wet magnetic separation process is preferably performed after adding water to the solid phase to produce a slurry. The water may be of industrial water quality, and the water used in the process may be reused if it has the same quality. The primary wet magnetic separation is intended to remove iron particles (iron oxide) and iron scale that are mixed in due to wear during the crushing of the used refractory saggers. The iron particles and iron scale have very strong magnetization properties and can be removed as magnetized matter at a magnetic flux density of approximately 100 to 500 gauss. At a magnetic flux density of 200 gauss or less, most of the iron particles and iron scale are removed as magnetized matter. However, at a magnetic flux density exceeding 200 gauss, the rate of contamination of the positive electrode active material along with the iron particles and iron scale as magnetized matter increases. Therefore, when wet magnetic separation is performed at a magnetic flux density exceeding 200 gauss, a separate magnetic separation for the mixed positive electrode active material may be required. The magnetically attracted materials separated using the primary wet magnetic separation process include iron pieces and iron scale, and the non-magnetically attracted materials include the positive electrode active material, alumina, silica, magnesium aluminate, aluminum silicate, and lithium aluminum silicate.

[0029] (5) Fifth process: Secondary wet magnetic separation process The secondary wet magnetic separation process of the present invention aims to separate a positive electrode active material containing nickel oxide and cobalt oxide, and alumina, silica, magnesium aluminate, aluminum silicate, and lithium aluminum silicate from the non-magnetic material of the primary wet magnetic separation process. The positive electrode active material contained in the non-magnetic material is weakly magnetic or paramagnetic. Therefore, a magnet with a high magnetic flux density is required to recover the positive electrode active material as a magnetic material. The secondary wet magnetic separation process of the present invention can use a high-gradient magnetic separator with a magnetic flux density of 10,000 gauss or more, preferably a high-gradient magnetic separator with a magnetic flux density of 30,000 gauss or more. Furthermore, the high-gradient magnetic separator preferably has a structure in which a slurry containing particles to be separated is poured between magnetized magnetic media. The solid concentration of the slurry can be 1 to 10%. If the solids concentration is less than 1%, the amount of water used increases, resulting in the need for unnecessary storage tanks and increased energy costs. If the solids concentration exceeds 10%, the separation efficiency drops significantly. The secondary wet magnetic separation process separates the positive electrode active material as a magnetic material, while the remaining components of the used refractory saggers after the water-soluble lithium has been removed, such as alumina, silica, magnesium aluminate, aluminum silicate, and lithium aluminum silicate, are separated as non-magnetic materials. The amount of lithium contained in lithium aluminum silicate, a sparingly soluble lithium compound remaining in the solid phase of the primary solid-liquid separation process after water leaching, is approximately 1,000 to 6,000 mg per kg of crushed used refractory saggers.

[0030] (6) Sixth step: Lithium leaching step The poorly soluble lithium compound (lithium aluminum silicate) contained in the non-magnetic material from the secondary wet magnetic separation process is reacted with a leaching agent to obtain a leachate containing eluted lithium and a leach residue. To obtain lithium sulfate from the leachate containing eluted lithium, an acid leaching agent can be used, which may be any one or a mixture of two or more selected from the group consisting of sulfuric acid, sulfurous acid, sulfur dioxide, and sulfur oxide. When leaching lithium from poorly soluble lithium compounds using the leaching agent, if the reaction solution temperature is below 100°C, it is difficult to achieve a leaching rate of 95% or higher. To solve this problem, in the present invention, the reaction temperature is set to 100 to 200°C, and the mixture is thoroughly stirred for at least one hour to recover lithium at a leaching rate of 95% or higher.

[0031] According to an embodiment of the present invention, the amount of acid leaching agent added is preferably such that the pH of the reaction solution after the leaching reaction is 1 to 2. When sulfuric acid is used, 5 to 50 parts by weight can be used per 100 parts by weight of the non-magnetized material. Preferably, 50 parts by weight of sulfuric acid is added per 100 parts by weight of the non-magnetized material, and the mixture is mixed with 350 parts by weight of water. The resulting slurry is then poured into a sealed reaction vessel and subjected to a leaching reaction at a temperature of 150°C for 3 hours, at which point 97% or more of the lithium is leached. When acid is used, the insoluble matter is mostly oxides containing silicon or aluminum.

[0032] (7) Seventh step: Secondary solid-liquid separation step The leaching reaction slurry after the lithium leaching step is subjected to solid-liquid separation to separate a leachate containing eluted lithium as a liquid phase and a leach residue as a solid phase. The leach residue is mainly composed of silica, alumina, and magnesium, and the solid-liquid separation can be performed using a solid-liquid separator such as a filter press.

[0033] (8) Eighth step: Neutralization reaction step The leachate obtained as a liquid phase in the second solid-liquid separation step contains impurities such as aluminum and silicon in addition to lithium, and a neutralization step was performed to remove these impurities. The aluminum and silicon components exist as Al(OH)3 and SiO2·H2O in the neutral pH range, and Al(OH)3 and SiO2·H2O are leached due to their low solubility. Therefore, by adjusting the pH of the leachate to the neutral range (pH 6-8), the impurities are separated and removed as precipitates, allowing lithium to be obtained in the form of an aqueous solution. When using an acid leaching agent, alkali metal hydroxides, calcium hydroxide, calcium oxide, magnesium hydroxide, etc. can be used as neutralizing agents. The addition of the neutralizing agent generates heat, eliminating the need for a separate heating step. However, a higher temperature in the reaction solution promotes the growth and aggregation of impurity particles, facilitating solid-liquid separation. Therefore, it is preferable to perform the neutralization reaction by heating the reaction solution to 70-100°C.

[0034] (9) Ninth step: Tertiary solid-liquid separation step The neutralization reaction solution is subjected to a tertiary solid-liquid separation to separate the lithium aqueous solution produced by the neutralization reaction process from the precipitate. When the neutralization reaction solution is subjected to solid-liquid separation, lithium is obtained as a liquid phase and impurities are obtained as a solid phase. The impurities include silica and aluminum hydroxide.

[0035] (10) Tenth step: Primary reverse osmosis concentration step The lithium concentration of the neutral pH lithium aqueous solution obtained as the liquid phase of the tertiary solid-liquid separation is 300 to 3,000 mg / L, which is too low for direct lithium recovery without concentration. Therefore, in the present invention, the lithium aqueous solution is concentrated to increase the lithium concentration, and then lithium is recovered. A method using a reverse osmosis filter, which requires low energy costs, is preferably used as the concentration method. The reverse osmosis filter of the present invention is preferably a batch-type reverse osmosis system, which is less expensive than the expensive multistage countercurrent reverse osmosis system used in large-capacity desalination processes. The lithium aqueous solution can be concentrated to a lithium concentration of 10,000 to 70,000 mg / L. Concentrating to a concentration lower than 10,000 mg / L requires too high an energy cost for the subsequent evaporation concentration process, while concentrating to a concentration higher than 70,000 mg / L requires too high an energy cost for applying high reverse osmosis pressure, making this method indistinguishable from evaporation methods. Preferably, the concentration can be increased to 50,000 mg / L. To increase the concentration of lithium to 50,000 mg / L, a water level adjustment sensor can be used, and the upper limit of the pump operating pressure can be set to 50 kg / cm. 2 The filtrate (water) obtained in the reverse osmosis concentration step can be used in the primary wet separation step.

[0036] (11) 11th step: Evaporation and concentration step When the concentrate obtained using the reverse osmosis concentration step is heated and concentrated, lithium sulfate precipitates, and lithium sulfate is obtained by solid-liquid separation. The concentration can be carried out by heating to 100°C under normal pressure or by evaporating to a temperature of 100°C or less under reduced pressure. In the present invention, the evaporative concentration method is used, and it is preferable to proceed until the lithium sulfate concentration in the concentrate reaches a level of 50 to 70%. The concentrate obtained in the evaporative concentration step is introduced into solid-liquid separation, and the filtrate (water) can be used in the primary wet separation step.

[0037] (12) 12th step: Quaternary solid-liquid separation step The concentrated liquid obtained using the evaporation and concentration process is subjected to solid-liquid separation to obtain high-purity lithium sulfate as a solid phase and an impurity aqueous solution (filtrate) as a liquid phase. The filtrate is treated through different processes depending on the impurity concentration. If the impurity concentration of the filtrate is 5,000 mg / L or less, it is re-introduced into the evaporation and concentration process for re-concentration, and if the impurity concentration exceeds 5,000 mg / L, it is treated by being input into the lithium phosphate precipitation process. The solid phase obtained by the fourth solid-liquid separation process is lithium sulfate, and the lithium sulfate is high-purity lithium sulfate of 99.0% or more.

[0038] 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]

[0039] By utilizing the method for producing high-purity lithium sulfate from used refractory saggers of the present invention, it is possible not only to recycle discarded used refractory saggers to produce high-purity lithium sulfate that can be used in the production of lithium secondary batteries, but also to recycle the positive electrode active material, iron oxide, alumina, silicate, and calcium carbonate that are incidentally obtained in the production process.

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 producing the solid phase obtained by the primary solid-liquid separation as a suspension and then performing a primary wet magnetic separation process to obtain first magnetized objects and first non-magnetized objects; a fifth step of preparing the first non-magnetic material as a suspension and then performing a secondary wet magnetic separation process to obtain second magnetic material and second non-magnetic material; a sixth step of adding water and a leaching agent to the second non-magnetic material and then reacting them to produce a lithium leaching reaction solution; a seventh step of subjecting the lithium leaching reaction solution to secondary solid-liquid separation; an eighth step of adjusting the pH of the filtrate obtained as a liquid phase by the secondary solid-liquid separation to 6 to 8 to produce a neutralized reaction liquid; a ninth step of subjecting the neutralization reaction solution to tertiary solid-liquid separation; a tenth step of concentrating the filtrate obtained as a liquid phase by the tertiary solid-liquid separation under reverse osmosis pressure; an eleventh step of evaporating and concentrating the concentrate obtained using the reverse osmosis concentration step; a twelfth step of subjecting the concentrate obtained by the evaporation concentration to a quaternary solid-liquid separation to obtain high-purity lithium sulfate in a solid phase; 1. A method for producing high purity lithium sulfate from waste refractory saggers, comprising:

2. 2. The method for producing high-purity lithium sulfate from used refractory saggers according to claim 1, wherein the waste refractory saggers crushed material dissolution reaction slurry is produced by adding 5 to 50 parts by weight of an alkaline leaching agent, calcium hydroxide, calcium oxide, or magnesium hydroxide, to 100 parts by weight of crushed 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 sulfate from waste refractory saggers according to claim 1, wherein a leaching agent used in leaching the second non-magnetic material is any one or a mixture of two or more selected from the group consisting of sulfuric acid, sulfurous acid, sulfur dioxide, and sulfur trioxide.

4. 2. The method for producing high-purity lithium sulfate from waste refractory saggers according to claim 1, wherein an alkali neutralizing agent is added to a filtrate obtained as a liquid phase by the secondary solid-liquid separation to adjust the pH to 6 to 8, and then the tertiary solid-liquid separation is carried out to remove silicon and aluminum as impurities as a solid phase.

5. The reverse osmosis concentration step is carried out using a batch reverse osmosis equipment, and the upper limit of the pump operating pressure is set to 50 kg / cm. ２ and concentrating the filtrate obtained as a liquid phase by the tertiary solid-liquid separation until the lithium concentration in the filtrate is 10,000 to 70,000 mg / L.

6. 2. The method for producing high-purity lithium sulfate from waste refractory saggers according to claim 1, wherein the high-purity lithium sulfate has a purity of 99.9% or more.

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