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

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 waste refractory saggers. Specifically, the present invention relates to a method for producing high-purity lithium sulfate with a purity of 99.9% or more by pulverizing and dissolving waste refractory saggers of the present invention, followed by solid-liquid separation, magnetic separation, lithium leaching, and concentration.

Background Art

[0002] The positive electrode active material of a lithium secondary battery is produced by firing at a high temperature in a refractory sagger (also known as a firing sleeve, alias) made of an oxide ceramic mainly composed of SiO2, Al2O3, and MgO. Since the refractory sagger 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 sagger whose surface has been eroded by the lithium hydroxide, lithium carbonate, etc. has reduced thermal durability and is discarded.

[0003] It is said that the annual generation amount of waste refractory saggers in Korea is about 9,000 tons. However, combined 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 saggers is expected to increase rapidly.

[0004] As described above, the refractory sagger is used in the production of the positive electrode active material and is eroded by the lithium-containing composite oxide in 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 sagger whose thermal durability has decreased due to repeated high-temperature firing with respect to the lithium-containing composite oxide, it is expected to be reused in the production of lithium-ion secondary batteries to reduce the production cost. However, a method for recovering high-purity lithium compounds from waste refractory saggers is not known at all.

[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 set forth in full herein.

[0006] 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 set forth in full herein.

Summary of the Invention

Problems to be Solved by the Invention

[0007] An object of the present invention is to provide a method for recovering high-purity lithium sulfate with a purity of 99.9% or more from waste refractory crucibles that are discarded after being used for high-temperature firing in the production of a cathode active material for a lithium secondary battery.

[0008] 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

[0009] The present invention provides a method for producing high-purity lithium sulfate from waste refractory crucibles, comprising: a first step of pulverizing waste refractory crucibles to produce waste refractory crucible pulverized matter; a second step of adding an alkali leaching agent and water to the waste refractory crucible pulverized matter and then reacting to produce a waste refractory crucible pulverized matter dissolution reaction slurry; a third step of performing primary solid-liquid separation on the waste refractory crucible pulverized matter dissolution reaction slurry; a fourth step of manufacturing the solid phase obtained by the primary solid-liquid separation as a suspension and then performing a primary wet magnetic separation process to obtain a first magnetic adherent and a first non-magnetic adherent; a fifth step of manufacturing the first non-magnetic adherent as a suspension and then performing a secondary wet magnetic separation process to obtain a second magnetic adherent and a second non-magnetic adherent; a sixth step of adding water and a leaching agent to the second non-magnetic adherent and then reacting to produce a lithium leaching reaction solution; a seventh step of performing secondary solid-liquid separation on the lithium leaching reaction solution; an eighth step of adjusting the pH of the filtrate obtained as the liquid phase by the secondary solid-liquid separation to 6-8 to produce a neutralization reaction solution; a ninth step of performing tertiary solid-liquid separation on the neutralization reaction solution; a tenth step of performing reverse osmosis pressure concentration on the filtrate obtained as the liquid phase by the tertiary solid-liquid separation; an eleventh step of performing evaporation concentration on the concentrated solution obtained by the reverse osmosis pressure concentration process; and a twelfth step of performing quaternary solid-liquid separation on the concentrated solution obtained by the evaporation concentration to obtain high-purity lithium sulfate as the solid phase.

[0010] The waste refractory crucible pulverized matter dissolution reaction slurry is produced by adding 5-50 parts by weight of calcium hydroxide, calcium oxide, or magnesium hydroxide, which is an alkali leaching agent, to 100 parts by weight of waste refractory crucible pulverized matter pulverized to 200# (mesh) or less, mixing 350 parts by weight of water, and reacting this at a temperature condition of 50-80°C for 30-120 minutes. The leaching agent used for leaching the second non-magnetic adherent 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.

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

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

Effect 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 erosion 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 waste refractory crucible to be discarded 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.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0015] The present invention relates to a method for producing high-purity lithium sulfate from waste refractory crucibles. As the refractory crucibles are repeatedly used, they are eroded and destroyed by lithium hydroxide, lithium carbonate, etc. The purpose of the present invention is to recover high-purity lithium sulfate, 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 of 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, which were relatively high. When converted to the lithium carbonate content, it was confirmed that SG1 corresponded to 11.17% and SG2 corresponded to 4.68%. Also, it was confirmed that the nickel and cobalt contents were 0.13 - 0.16% and 0.01 - 0.02% respectively, indicating that the value to be recovered was sufficiently high.

[0018] The waste refractory crucibles are 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 crucibles, the substances causing the destruction of the refractory crucibles are lithium silicate, lithium aluminum oxide, lithium aluminum silicate, etc.

[0019] The present invention provides a method for producing high-purity lithium sulfate 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 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 producing a solid phase obtained by the primary solid-liquid separation as a suspension and then performing a primary wet magnetic separation process to obtain a first magnetic attachment and a first non-magnetic attachment; a fifth step of producing the first non-magnetic attachment as a suspension and then performing a secondary wet magnetic separation process to obtain a second magnetic attachment and a second non-magnetic attachment; a sixth step of adding water and a leaching agent to the second non-magnetic attachment and then reacting them to produce a lithium leaching reaction solution; a seventh step of performing secondary solid-liquid separation on the lithium leaching reaction solution; an eighth step of adjusting the pH of the filtrate obtained as a liquid phase by the secondary solid-liquid separation to 6-8 to produce a neutralization reaction solution; a ninth step of performing tertiary solid-liquid separation on the neutralization reaction solution; a tenth step of performing reverse osmosis pressure concentration on the filtrate obtained as a liquid phase by the tertiary solid-liquid separation; an eleventh step of performing evaporation concentration on the concentrated solution obtained by the reverse osmosis pressure concentration process; and a twelfth step of performing quaternary solid-liquid separation on the concentrated solution obtained by the evaporation concentration to obtain high-purity lithium sulfate as a solid phase.

[0020] The slurry of dissolved pulverized waste refractory crucibles is produced by adding 5-50 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 50-80°C for 30-120 minutes. The leaching agent used for leaching the second non-magnetic attachment is characterized by being any one or a mixture of two or more selected from the group consisting of sulfuric acid, sulfurous acid, sulfur dioxide, and sulfur trioxide.

[0021] After adding an alkali neutralizing agent to the filtrate obtained as the liquid phase using the secondary solid-liquid separation to adjust the pH to 6 to 8, the tertiary solid-liquid separation is performed to remove silicon and aluminum, which are impurities, as the solid phase. The reverse osmosis pressure concentration step is performed using a batch reverse osmosis pressure facility, and the upper limit of the operating pressure of the pump is set to 50 kg / cm 2 and the filtrate obtained as the liquid phase using the tertiary solid-liquid separation is concentrated until the lithium concentration becomes 10,000 to 70,000 mg / L.

[0022] The high-purity lithium sulfate produced by the production method of the present invention is characterized in that the purity is 99.9% or more.

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

[0024] (1) First step: Waste refractory crucible crushing step The waste refractory crucible is crushed into powder of 200# or less. If the waste refractory crucible is pulverized 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 having sharp surfaces with high hardness are generated, increasing the wear of the parts of the crusher and raising 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 step, and a ball mill is used in the secondary crushing step. Preferably, in order to improve the pulverization efficiency, an intermediate crusher such as an impact crusher may be arranged before the secondary crushing step.

[0025] (2) Second step: Dissolution step of waste refractory crucible crushed material 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 problems, 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 with 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 with 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, so that it 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 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 more than 6 hours 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.

[0026] In short, in the preferred step of dissolving the crushed waste refractory crucible of the present invention, 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 is heated to a temperature of 50 to 80°C and reacted for 30 to 120 minutes. For reference, if, under the same conditions, an aqueous alkali metal hydroxide corresponding to 5 to 50% of its usage amount is further added together with the alkaline earth metal hydroxide (or oxide), 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.

[0027] (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 - ), and silicon (H2SiO4 2- ).

[0028] (4) The fourth step: the primary wet magnetic separation step Wet magnetic separation is performed on the solid phase obtained by using the primary solid-liquid separation. The primary wet magnetic separation step is preferably performed after adding water to the solid phase to produce a slurry. The water may have a water quality similar to that of industrial water, and if the water quality is the same, the water used during the process can be reused. The purpose of the primary wet magnetic separation is to remove iron pieces (iron oxide) and iron scale mixed in during the crushing of waste refractory crucibles due to abrasion. Since the iron pieces and iron scale have a very strong magnetization ability, they can be removed as magnetic attachments at a magnetic flux density of about 100 to 500 gauss. When the magnetic flux density is 200 gauss or less, almost all of the iron pieces and iron scale as magnetic attachments are removed. However, when it exceeds 200 gauss, the mixing rate of the positive electrode active material increases together with the iron pieces and iron scale as magnetic attachments. Therefore, when wet magnetic separation is performed above 200 gauss, separate magnetic separation for the mixed positive electrode active material may be required. The magnetic attachments separated using the primary wet magnetic separation step include iron pieces and iron scale, and the non-magnetic attachments include positive electrode active material, alumina, silica, magnesium aluminate, aluminum silicate, and lithium aluminum silicate.

[0029] (5) Fifth step: Secondary wet magnetic separation step The secondary wet magnetic separation process of the present invention aims to separate a positive electrode active material containing nickel oxide, cobalt oxide, etc., alumina, silica, magnesium aluminate, aluminum silicate, and lithium aluminum silicate from the non-magnetic substances in the primary wet magnetic separation process. The positive electrode active material contained in the non-magnetic substances has weak magnetism or paramagnetism. Therefore, in order to recover the positive electrode active material as a magnetic substance, a magnet having a high magnetic flux density is required. In the secondary wet magnetic separation process of the present invention, a high-gradient magnetic separator having a magnetic flux density of 10,000 gauss or more can be used, preferably, a high-gradient magnetic separator having a magnetic flux density of 30,000 gauss or more can be used. Further, the high-gradient magnetic separator preferably has a structure in which a slurry containing particles to be separated flows between magnetic media magnetized. The concentration of the solid matter in the slurry may be 1 to 10%. If the concentration of the solid matter is less than 1%, as the amount of water used increases, there is a problem that the number of unnecessary storage tanks increases and the energy cost rises. If the concentration of the solid matter exceeds 10%, there is a problem that the separation efficiency is significantly reduced. By using the secondary wet magnetic separation process, the positive electrode active material is separated as a magnetic substance, and alumina, silica, magnesium aluminate, aluminum silicate, and lithium aluminum silicate, which are the compositions of the remaining waste refractory crucibles from which water-soluble lithium has been removed, are separated as non-magnetic substances. The amount of lithium contained in lithium aluminum silicate, which is a poorly soluble lithium compound remaining in the solid phase of the primary solid-liquid separation process after water leaching, is about 1,000 to 6,000 mg per 1 kg of the waste refractory crucible pulverized product.

[0030] (6) Step 6: Lithium Leaching Step When the sparingly soluble lithium compound (lithium aluminum silicate) contained in the non-magnetically attached matter in the secondary wet magnetic separation step is reacted with a leaching agent, a leachate in which lithium is eluted and a leach residue are obtained. When attempting to obtain lithium sulfate from the leachate in which lithium has been eluted, any one or a mixture of two or more selected from the group consisting of sulfuric acid, sulfurous acid, sulfur dioxide, and sulfur trioxide can be used as the acid leaching agent. When leaching lithium from the sparingly soluble lithium compound using the leaching agent, if the temperature of the reaction solution is less than 100°C, there is a problem that it is difficult to raise the leaching rate to 95% or more. To solve this problem, in the present invention, the reaction temperature is set to 100 to 200°C, and sufficient stirring is carried out for 1 hour or more to recover lithium at a leaching rate of 95% or more.

[0031] According to an embodiment of the present invention, the addition amount of the acid leaching agent is preferably added in an amount such that the pH of the reaction solution becomes 1 to 2 after the leaching reaction. When using sulfuric acid, it can be used in an amount of 5 to 50 parts by weight with respect to 100 parts by weight of the non-magnetically attached matter. Preferably, when 50 parts by weight of sulfuric acid is added to 100 parts by weight of the non-magnetically attached matter and the slurry mixed with 350 parts by weight of water is put into a sealed reaction vessel and the leaching reaction is carried out under the temperature condition of 150°C for 3 hours, 97% or more of lithium is leached. When using an acid, most of the insoluble matter is an oxide containing silicon or aluminum.

[0032] (7) The seventh step: The secondary solid-liquid separation step The leaching reaction slurry that has undergone the lithium leaching step is subjected to solid-liquid separation to separate the leachate containing the eluted lithium as the liquid phase and the leach residue as the solid phase. The leach residue has silica, alumina, and magnesium as the main components, and the solid-liquid separation can be carried out using a solid-liquid separation device such as a filter press.

[0033] (8) The eighth step: The neutralization reaction step The leachate obtained as the liquid phase in the second solid-liquid separation step contains impurities such as aluminum and silicon in addition to lithium. In order to remove these, a neutralization reaction step was carried out. The aluminum and silicon components exist as Al(OH)3 and SiO2·H2O, etc. in the neutral pH range, and since the solubility of Al(OH)3 and SiO2·H2O, etc. is low, they are leached out. Therefore, if the pH of the leachate is adjusted to the neutral range (pH 6 - 8), the impurities are separated and removed as precipitates, making it possible to obtain lithium in an aqueous solution state. When an acid leaching agent is used, alkali metal hydroxides, calcium hydroxide, calcium oxide, magnesium hydroxide, etc. can be used as neutralizing agents. When the neutralizing agent is added, heat is generated, so a separate heating step is not necessary. However, if the temperature of the reaction solution is high, it promotes the growth and aggregation of impurity particles, making it easier to perform solid-liquid separation. Therefore, it is preferable to heat the reaction solution to 70 - 100 °C to carry out the neutralization reaction.

[0034] (9) The ninth step: Tertiary solid-liquid separation step Tertiary solid-liquid separation is performed on the neutralization reaction solution to separate the lithium aqueous solution and the precipitate generated using the neutralization reaction step. When solid-liquid separation is performed on the neutralization reaction solution, lithium is obtained as the liquid phase and the impurities are obtained as the solid phase. The impurities include silica and aluminum hydroxide, etc.

[0035] (10) The tenth step: Primary reverse osmosis concentration step The lithium contained in the neutral pH lithium aqueous solution obtained as the liquid phase of the tertiary solid-liquid separation is 300 to 3,000 mg / L. There is a problem that the concentration is slightly low for directly recovering lithium without concentration. Therefore, in the present invention, the lithium aqueous solution is concentrated to increase the lithium concentration, and then lithium is recovered. As the concentration method, a method using a reverse osmosis filter with low energy cost is preferably used. The reverse osmosis filter of the present invention preferably uses a more inexpensive batch-type reverse osmosis facility, rather than an expensive multi-stage countercurrent reverse osmosis facility used in a large-capacity desalination process. The concentration of the lithium aqueous solution can be carried out so that the lithium concentration becomes 10,000 to 70,000 mg / L. If it is concentrated to a concentration lower than 10,000 mg / L, the energy cost of the subsequent evaporation concentration process is too high. If lithium is concentrated to a concentration higher than 70,000 mg / L, the energy cost required to apply a high reverse osmotic pressure is too high and the difference from the evaporation method disappears. Preferably, it can be carried out so as to reach 50,000 mg / L. In order to concentrate until the concentration of the lithium reaches 50,000 mg / L, a water level adjustment sensor can be used, and the upper limit of the operating pressure of the pump can be set to 50 kg / cm 2 and the operation can be carried out. The filtrate (water) obtained in the reverse osmosis concentration process can be used in the primary wet sorting process.

[0036] (11) The 11th step: Evaporation concentration step If the concentrated liquid obtained using the reverse osmosis concentration step is continuously heated and concentrated, lithium sulfate will precipitate. If this is subjected to solid-liquid separation, lithium sulfate can be obtained. The concentration can be carried out using a method of heating and concentrating at 100°C under normal pressure and a method of evaporating and concentrating at a temperature of 100°C or lower under reduced pressure. In the present invention, the evaporation concentration method is used, and it is preferable to proceed until the concentration of lithium sulfate in the concentrated liquid reaches the 50 to 70% level. The concentrated liquid obtained in the evaporation concentration step is put into solid-liquid separation, and the filtrate (water) can be used in the primary wet sorting process.

[0037] (12) Twelfth step: Fourth solid-liquid separation step Solid-liquid separation is performed on the concentrated liquid obtained using the evaporation and concentration step to obtain high-purity lithium sulfate as a solid phase and an impurity aqueous solution (filtrate) as a liquid phase. The filtrate is processed by different steps according to the concentration of impurities. When the concentration of impurities in the filtrate is 5,000 mg / L or less, it is re-introduced into the evaporation and concentration step for re-concentration. When the concentration of impurities exceeds 5,000 mg / L, it is introduced into the lithium phosphate precipitation step for treatment. The solid phase obtained by the fourth solid-liquid separation step is lithium sulfate, and the lithium sulfate is high-purity lithium sulfate of 99.0% or more.

[0038] The specific embodiments described in this specification are merely meant to represent preferred modes or exemplifications of the present invention, and thereby the scope of the present invention is not limited. 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

[0039] By using the method for producing high-purity lithium sulfate from waste refractory crucibles of the present invention, not only can the discarded waste refractory crucibles be recycled to produce high-purity lithium sulfate that can be used in the manufacture of lithium secondary batteries, but also the positive electrode 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 waste refractory crucible pulverized matter; A second step of adding an alkali leaching agent and water to the waste refractory crucible pulverized matter and then reacting to produce a waste refractory crucible pulverized matter dissolution reaction slurry; A third step of performing primary solid-liquid separation on the waste refractory crucible pulverized matter dissolution reaction slurry; A fourth step of manufacturing the solid phase obtained by using the primary solid-liquid separation as a suspension and then performing a primary wet magnetic separation process to obtain a first magnetic adherent and a first non-magnetic adherent; A fifth step of manufacturing the first non-magnetic adherent as a suspension and then performing a secondary wet magnetic separation process to obtain a second magnetic adherent and a second non-magnetic adherent; A sixth step of adding water and a leaching agent to the second non-magnetic adherent and then reacting to produce a lithium leaching reaction solution; A seventh step of performing secondary solid-liquid separation on the lithium leaching reaction solution; An eighth step of adjusting the pH of the filtrate obtained as the liquid phase by using the secondary solid-liquid separation to 6 to 8 to produce a neutralization reaction solution; A ninth step of performing tertiary solid-liquid separation on the neutralization reaction solution; A tenth step of performing reverse osmosis pressure concentration on the filtrate obtained as the liquid phase by using the tertiary solid-liquid separation; An eleventh step of performing evaporation concentration on the concentrated solution obtained by using the reverse osmosis pressure concentration process; A twelfth step of performing quaternary solid-liquid separation on the concentrated solution obtained by using the evaporation concentration to obtain high-purity lithium sulfate as the solid phase; A method for producing high-purity lithium sulfate from waste refractory crucibles, including the above steps.

2. The waste refractory crucible pulverized material 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 the waste refractory crucible pulverized material pulverized to 200# (mesh) or less, mixing 350 parts by weight of water, and reacting this mixture at a temperature of 50 to 80 °C for 30 to 120 minutes. A method for producing high-purity lithium sulfate from the waste refractory crucible according to claim 1, characterized in that it is manufactured in this way.

3. The leaching agent used for leaching the second non-magnetically attached 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. A method for producing high-purity lithium sulfate from the waste refractory crucible according to claim 1, characterized in that it is so.

4. An alkali neutralizing agent is added to the filtrate obtained as the liquid phase using the secondary solid-liquid separation to adjust the pH to 6 to 8, and then the tertiary solid-liquid separation is performed to remove silicon and aluminum, which are impurities, as the solid phase. A method for producing high-purity lithium sulfate from the waste refractory crucible according to claim 1, characterized in that it is so.

5. The reverse osmotic pressure concentration step is carried out using a batch reverse osmotic pressure equipment, and the upper limit of the operating pressure of the pump is set to 50 kg / cm ２ and concentrated until the lithium concentration of the filtrate obtained as the liquid phase using the tertiary solid-liquid separation reaches 10,000 to 70,000 mg / L. A method for producing high-purity lithium sulfate from the waste refractory crucible according to claim 1, characterized in that it is manufactured in this way.

6. The high-purity lithium sulfate has a purity of 99.9% or more. A method for producing high-purity lithium sulfate from the waste refractory crucible according to claim 1, characterized in that it is so.

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