Method for preparing high-purity lithium sulfate from waste saggar

Abstract

The invention provides an optimized method for recovering high-purity lithium sulfate from a lithium-containing composite oxide deposited on an erosion surface of a waste sagger. Therefore, it is expected that by means of the method for preparing the high-purity lithium sulfate from the waste saggar, the high-purity lithium sulfate capable of being used for preparing the lithium secondary battery can be prepared by recycling the waste saggar; and moreover, positive active materials, iron oxide, aluminum oxide, silicate and calcium carbonate which are additionally obtained in the preparation process can be recycled.

Description

Technical Field

[0001] The present invention relates to a method for preparing high-purity lithium sulfate from waste saggers. Specifically, the present invention relates to a method for preparing high-purity lithium sulfate with a purity of 99.9% or more by crushing and dissolving the waste saggers, and then performing solid-liquid separation, magnetic separation, lithium leaching and concentration. Background Art

[0002] The positive electrode active material of the lithium secondary battery is made by high-temperature firing in a sagger made of oxide ceramics with SiO2, Al2O3, and MgO as the main components. The above-mentioned sagger is used for repeated high-temperature firing of lithium-containing composite oxides (as raw materials for positive electrode active materials). Therefore, its surface is eroded over time, and lithium hydroxide, lithium carbonate and positive electrode active materials are deposited in the above-mentioned eroded parts. The sagger whose surface is corroded by the above-mentioned lithium hydroxide, lithium carbonate, etc. is eventually discarded due to reduced heat resistance. It is understood that South Korea produces about 9,000 tons of waste saggers each year, but with the rapid increase in demand for lithium secondary batteries due to the popularity of mobile devices and electric vehicles, the generation of waste saggers is expected to increase rapidly.

[0003] As mentioned above, the sagger is used to prepare the positive electrode active material. During the high-temperature sintering process, it is corroded by the lithium-containing composite oxide, resulting in the loss of its function. Therefore, if the lithium-containing composite oxide deposited in the eroded part of the waste sagger that has been discarded due to the repeated high-temperature sintering of the lithium-containing composite oxide and the reduced heat resistance can be recovered into the form of high-purity lithium sulfate, lithium carbonate, or lithium phosphate, it is expected to be reused in the production of lithium-ion secondary batteries, thereby saving production costs. However, a method for recovering high-purity lithium compounds from waste saggers has not yet been disclosed.

[0004] Patent documents and reference documents mentioned in the present specification are hereby incorporated by reference into the present specification to the same extent as if the respective documents were expressly designated individually by reference.

[0005] Patent documents and reference documents mentioned in the present specification are hereby incorporated by reference into the present specification to the same extent as if the respective documents were expressly designated individually by reference. Summary of the invention

[0006] Problems to be solved by the invention

[0007] The 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 saggers discarded after high-temperature sintering when preparing positive electrode active materials for lithium secondary batteries.

[0008] Other objects and technical features of the present invention will be more specifically presented through the detailed description of the invention, the claims and the accompanying drawings.

[0009] Solutions for solving problems

[0010] The present invention provides a method for preparing high-purity lithium sulfate from waste saggers, comprising: a first step of preparing a waste sagger crushed material by crushing the waste sagger; a second step of adding an alkali leaching agent and water to the waste sagger crushed material and reacting to prepare a dissolution reaction slurry of the waste sagger crushed material; a third step of performing a first solid-liquid separation on the dissolution reaction slurry of the waste sagger crushed material; a fourth step of preparing a solid phase obtained by the first solid-liquid separation into a suspension, performing a first wet magnetic separation process, and obtaining a first magnetic adsorbent and a first non-magnetic adsorbent; a fourth step of preparing the first non-magnetic adsorbent into a suspension, performing a second wet magnetic separation process, and obtaining a second magnetic adsorbent and a second non-magnetic adsorbent. The fifth step; the sixth step of adding water and a leaching agent into the second non-magnetic adsorbent and reacting them to prepare a lithium leaching reaction solution; the seventh step of performing a second solid-liquid separation on the lithium leaching reaction solution; the eighth step of adjusting the pH of the liquid filtrate obtained by the second solid-liquid separation to 6 to 8 to prepare a neutralization reaction solution; the ninth step of performing a third solid-liquid separation on the neutralization reaction solution; the tenth step of performing reverse osmosis concentration on the liquid filtrate obtained by the third solid-liquid separation; the eleventh step of performing evaporation concentration on the concentrated solution obtained by the reverse osmosis concentration process; and the twelfth step of performing a fourth solid-liquid separation on the concentrated solution obtained by the evaporation concentration to obtain a solid phase of high-purity lithium sulfate.

[0011] The above-mentioned waste sagger crushed material dissolution reaction slurry is characterized in that it is prepared by adding 5 to 50 parts by weight of calcium hydroxide, calcium oxide, or magnesium hydroxide as an alkaline leaching agent to 100 parts by weight of waste sagger crushed material with a size of less than 200# (mesh), mixing with 350 parts by weight of water, and reacting at 50°C to 80°C for 30 to 120 minutes. The leaching agent used to leach the above-mentioned second non-magnetic adsorbent is characterized in that it is selected from any one or a mixture of two or more of the group consisting of sulfuric acid, sulfurous acid, sulfur dioxide, and sulfur trioxide.

[0012] The present invention is characterized in that an alkali neutralizer is added to the liquid phase filtrate obtained by the second solid-liquid separation, and after the pH is adjusted to 6 to 8, the third solid-liquid separation is performed to remove silicon and aluminum in the solid phase as impurities. The reverse osmosis concentration process is characterized in that a batch reverse osmosis device is used, and the upper limit of the working pressure of the pump is set to 50 kg / cm 2 , concentrated until the lithium concentration of the liquid filtrate obtained by the third solid-liquid separation reaches 10000 mg / l to 70000 mg / l.

[0013] The lithium sulfate prepared by the preparation method of the present invention is characterized in that the purity is above 99.9%.

[0014] Effects of the Invention

[0015] The present invention provides an optimized method for recovering high-purity lithium sulfate from lithium-containing composite oxides deposited on the eroded surface of discarded old saggers. Therefore, it is expected that the method for preparing high-purity lithium sulfate from waste saggers of the present invention can not only prepare high-purity lithium sulfate that can be used to prepare lithium secondary batteries by recycling the discarded old saggers, but also recycle the positive electrode active material, iron oxide, aluminum oxide, silicate and calcium carbonate obtained in the preparation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The method for preparing high-purity lithium sulfate from waste saggers of the present invention is schematically shown in FIG.

[0017] Figure 2 2 shows the XRD analysis results of the constituent minerals of the waste sagger of the present invention.

[0018] Figure 3 This is a scanning electron microscope (SEM) photograph of the crushed waste sagger, showing the overall particle size distribution and the structure of the particle surface. DETAILED DESCRIPTION

[0019] The present invention relates to a method for preparing high-purity lithium sulfate from waste saggers. With repeated use of the saggers, the saggers will be damaged by erosion by lithium hydroxide or lithium carbonate. The purpose of the present invention is to recover high-purity lithium sulfate as a high-value-added lithium compound from waste saggers that are discarded without recycling. The above-mentioned waste saggers are used as sintered ceramic containers for positive electrode active materials for secondary batteries, and their main components are SiO2, Al2O3, and MgO. Table 1 shows the composition of sintered waste saggers used as NCA (sample name: SG1) and NCM (sample name: SG2) as positive electrode materials.

[0020]

Table 1

[0021] composition SG1(NCA) SG2(NCM) <![CDATA[Li2O(as Li)]]> 4.52(2.1)％ 1.89(0.88)％ NiO 0.13％ 0.16％ <![CDATA[Co3O4]]> 0.01％ 0.02％ <![CDATA[SiO2]]> 49.38％ 30.73％ <![CDATA[Al2O3]]> 38.25％ 51.38％ CaO 0.48％ 0.52％ MgO 5.37％ 13.63％ <![CDATA[Fe2O3]]> 0.33％ 0.54％ <![CDATA[Na2O]]> 0.32％ 0.12％ <![CDATA[K2O]]> 0.30％ 0.19％ Others 0.91％ 0.82％

[0022] The analysis results confirmed that the lithium (Li) content of SG1 and SG2 was high, 2.1% and 0.88% respectively. When converted into lithium carbonate content, it was confirmed that SG1 = 11.17% and SG2 = 4.68%. In addition, the nickel and cobalt contents were confirmed to be 0.13% to 0.16% and 0.01% to 0.02% respectively, which have sufficient recovery value.

[0023] The above-mentioned waste sagger is composed of mullite, cordierite, alumina, quartz, magnesium aluminate, lithium silicate, lithium aluminum oxide, lithium aluminum silicate, etc. Among the components of the above-mentioned waste sagger, the substances causing the sagger to be destroyed are lithium silicate, lithium aluminum oxide, lithium aluminum silicate, etc.

[0024] The present invention provides a method for preparing high-purity lithium sulfate from waste saggers, comprising: a first step of preparing a waste sagger crushed material by crushing the waste sagger; a second step of adding an alkali leaching agent and water to the waste sagger crushed material and reacting to prepare a dissolution reaction slurry of the waste sagger crushed material; a third step of performing a first solid-liquid separation on the dissolution reaction slurry of the waste sagger crushed material; a fourth step of preparing a solid phase obtained by the first solid-liquid separation into a suspension, performing a first wet magnetic separation process, and obtaining a first magnetic adsorbent and a first non-magnetic adsorbent; a fourth step of preparing the first non-magnetic adsorbent into a suspension, performing a second wet magnetic separation process, and obtaining a second magnetic adsorbent and a second non-magnetic adsorbent. The fifth step; the sixth step of adding water and a leaching agent into the second non-magnetic adsorbent and reacting them to prepare a lithium leaching reaction solution; the seventh step of performing a second solid-liquid separation on the lithium leaching reaction solution; the eighth step of adjusting the pH of the liquid filtrate obtained by the second solid-liquid separation to 6 to 8 to prepare a neutralization reaction solution; the ninth step of performing a third solid-liquid separation on the neutralization reaction solution; the tenth step of performing reverse osmosis concentration on the liquid filtrate obtained by the third solid-liquid separation; the eleventh step of performing evaporation concentration on the concentrated solution obtained by the reverse osmosis concentration process; and the twelfth step of performing a fourth solid-liquid separation on the concentrated solution obtained by the evaporation concentration to obtain a solid phase of high-purity lithium sulfate.

[0025] The above-mentioned waste sagger crushed material dissolution reaction slurry is characterized in that it is prepared by adding 5 to 50 parts by weight of calcium hydroxide, calcium oxide, or magnesium hydroxide as an alkaline leaching agent to 100 parts by weight of the waste sagger crushed material with a mesh size of less than 200#, mixing with 350 parts by weight of water, and reacting at 50°C to 80°C for 30 to 120 minutes. The leaching agent used to leach the above-mentioned second non-magnetic adsorbent is characterized in that it is selected from any one or a mixture of two or more of the group consisting of sulfuric acid, sulfurous acid, sulfur dioxide, and sulfur trioxide.

[0026] After adding an alkali neutralizer to the liquid filtrate obtained by the second solid-liquid separation, the pH is adjusted to 6 to 8, and then the third solid-liquid separation is performed to remove silicon and aluminum in the solid phase as impurities. The reverse osmosis concentration process is characterized in that a batch reverse osmosis device is used and the upper limit of the working pressure of the pump is set to 50 kg / cm 2 , concentrated until the lithium concentration of the liquid filtrate obtained by the third solid-liquid separation reaches 10000 mg / l to 70000 mg / l.

[0027] The high-purity lithium sulfate prepared by the preparation method of the present invention is characterized in that the purity is above 99.9%.

[0028] Best Mode for Carrying Out the Invention

[0029] Hereinafter, the method for preparing high-purity lithium sulfate from waste saggers of the present invention is described in detail according to different processes.

[0030] (1) The first process: waste sagger crushing process

[0031] The waste sagger is crushed into powder of less than 200#. When the above-mentioned waste sagger is micronized at one time, there is a problem of too low crushing efficiency. Therefore, preferably, after the coarse crushing is less than 1mm by the first crushing using a jaw crusher, it is crushed to less than 200# (mesh) by the second crushing using a ball mill. The above-mentioned waste sagger has a high compression strength, but weak impact resistance. An impact crusher can be used to crush the above-mentioned waste sagger, but since crushed particles with high hardness and sharp surface will be produced, there is a problem of increased wear of the crusher parts and increased costs. Therefore, in the present invention, in the first crushing process, a jaw crusher with easy replacement of parts and low cost is used, and in the second crushing process, a ball mill is used. Preferably, in order to improve the crushing efficiency, a medium crusher such as an impact crusher can be configured before the second crushing process.

[0032] (2) Second process: Dissolution process of crushed waste saggers

[0033] The waste sagger pulverized by the first process includes lithium-containing substances such as lithium hydroxide, lithium carbonate, lithium silicate, lithium aluminum oxide, or lithium aluminum silicate. For the above-mentioned lithium-containing substances, although most of the lithium-containing substances are water-soluble, some substances including lithium aluminum silicate have low solubility in water and are difficult to dissolve with water alone. In order to solve the above-mentioned problem, the present invention applies a waste sagger pulverized material dissolution process in which the above-mentioned waste sagger pulverized material is mixed with an alkali leaching agent selected from any one or more of the group consisting of alkali metal hydroxides, alkali metal carbonates, or alkaline earth metal hydroxides and water and then heated. The waste sagger pulverized material dissolution process of the present invention is dissolved by heating with the above-mentioned alkali leaching agent, and lithium aluminum silicate with low solubility in water can also be decomposed and dissolved, thereby having the advantage of increasing the recovery rate of lithium. The decomposition and dissolution reaction of the above-mentioned lithium-containing substances with low solubility has a tendency to increase in reactivity in proportion to the concentration and temperature of the alkali. For this reason, if an alkaline leaching agent containing an alkali metal salt is used, the concentration of silicon and aluminum will increase, so a separate process for removing them is required. In contrast, if a leaching agent prepared from an alkaline earth metal oxide or hydroxide and water is used, soluble silicon or aluminum and insoluble salts are formed, so that it helps to promote the decomposition of lithium aluminum silicate while maintaining a lower concentration of silicon and aluminum in the solution, and reacts with lithium carbonate with lower solubility to generate lithium hydroxide and insoluble carbonate with higher solubility, thereby having the advantage of increasing the leaching rate of lithium. Therefore, in the waste sagger crushing material dissolution process of the present invention, calcium hydroxide, calcium oxide, or magnesium hydroxide is used as a leaching agent to promote lithium extraction, and the addition amount is 5 to 50 parts by weight based on 100 parts by weight of the waste sagger. It was confirmed that the above-mentioned waste sagger crushing material dissolution process takes more than 6 hours to terminate the reaction at a temperature below 20°C; the reaction is terminated within 2 hours at a temperature of 50°C; and the reaction is terminated within 30 minutes at a temperature of 80°C. Moreover, at about 100°C, the reaction is terminated within 10 minutes, but there is a problem of large energy loss due to evaporation of water. Therefore, the preferred waste sagger crushing material dissolution process of the present invention is to react at a temperature of 50°C to 80°C for 30 minutes to 120 minutes.

[0034] In summary, in the preferred waste sagger crushing material dissolution process of the present invention, the waste sagger crushing material slurry is heated at a temperature of 50°C to 80°C and reacted for 30 minutes to 120 minutes, wherein the waste sagger crushing material slurry contains 5 to 50 parts by weight of calcium hydroxide, calcium oxide, or magnesium hydroxide as a leaching agent relative to 100 parts by weight of the waste sagger crushing material crushed to 200# (mesh) or less. For reference, under the same conditions, if an alkali metal hydroxide equivalent to 5% to 50% of its usage amount is further added together with the alkaline earth metal hydroxide (or oxide), the leaching rate and leaching rate of lithium will increase by about 5%. If the increase in process costs can be accepted, the above method can become a preferred method.

[0035] (3) The third process: the first solid-liquid separation process

[0036] The dissolving reaction liquid of the above-mentioned waste sagger crushed material is subjected to solid-liquid separation (first solid-liquid separation). The above-mentioned first solid-liquid separation can use a sedimentation tank, a filter press, a spiral filter, a centrifuge, etc., or a combination of two or more thereof to improve its efficiency. The solid phase obtained by the above-mentioned first 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- ).

[0037] (4) The fourth process: the first wet magnetic separation process

[0038] The solid phase obtained by the first solid-liquid separation is subjected to the first wet magnetic separation. Preferably, the first wet magnetic separation process is carried out after adding water to the solid phase to prepare a slurry. It is sufficient as long as the water quality of the water reaches that of industrial water. If the water quality is the same, the water used in the process can also be reused. The purpose of the first wet magnetic separation is to remove iron flakes (iron oxide) or iron scales mixed in due to wear when crushing waste saggers. Since the iron flakes or iron scales have very strong magnetization capabilities, they can be removed as magnetic adsorbents at a magnetic flux density of 100 to 500 gauss. When the density is below 200 gauss, most of the iron flakes and iron scales are removed as magnetic adsorbents, but when the density exceeds 200 gauss, the mixing rate of the positive active material mixed in the iron flakes and iron scales as magnetic adsorbents will increase. Therefore, when wet magnetic separation is carried out under conditions exceeding 200 gauss, separate magnetic separation of the mixed positive active material may be required. The magnetically adsorbed materials separated by the first wet magnetic separation process include iron flakes and iron scales, and the non-magnetically adsorbed materials include positive electrode active materials, aluminum oxide, silicon dioxide, magnesium aluminate, aluminum silicate and lithium aluminum silicate.

[0039] (5) Fifth process: Second wet magnetic separation process

[0040] The purpose of the second wet magnetic separation process of the present invention is to separate positive electrode active materials including nickel oxide and cobalt oxide, etc. and aluminum oxide, silicon dioxide, magnesium aluminate, aluminum silicate and lithium aluminum silicate from the non-magnetic adsorbents of the first wet magnetic separation process. The positive electrode active materials contained in the above non-magnetic adsorbents have weak magnetism or paramagnetism. Therefore, in order to recover the above positive electrode active materials as magnetic adsorbents, a magnet with a high magnetic flux density is required. The second wet magnetic separation process of the present invention can use a high gradient magnetic separator with a magnetic flux density of more than 10,000 Gauss, and preferably, a high gradient magnetic separator with a magnetic flux density of more than 30,000 Gauss can be used. And, preferably, the above high gradient magnetic separator has a structure for flowing the slurry containing the particles to be separated between the magnetized magnetic media. The solid concentration of the above slurry can be 1% to 10%. If the concentration of the above solids is lower than 1%, unnecessary storage tanks will increase with the increase in water consumption, and there is a problem of increased energy costs. If the concentration of the above solids exceeds 10%, there is a problem of significantly reduced sorting efficiency. Through the above-mentioned second wet magnetic sorting process, the positive electrode active material is sorted as a magnetic adsorbent, and the composition of the remaining waste saggers without water-soluble lithium, that is, alumina, silicon dioxide, magnesium aluminate, aluminum silicate and lithium aluminum silicate, etc. are sorted as non-magnetic adsorbents. For every 1 kg of waste sagger crushed material, the amount of lithium contained in lithium aluminum silicate is about 1000 mg to 6000 mg, wherein lithium aluminum silicate is a sparingly soluble lithium compound remaining in the solid phase of the first solid-liquid separation process after water leaching.

[0041] (6) Sixth process: lithium leaching process

[0042] When the sparingly soluble lithium compound (lithium aluminum silicate) contained in the non-magnetic adsorbent of the above-mentioned second wet magnetic separation process is reacted with a leaching agent, a lithium eluting leachate and a leaching residue are obtained. When lithium sulfate is to be obtained from the lithium eluting leachate, 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 an acid leaching agent. When lithium is leached from the sparingly soluble lithium compound using the above-mentioned leaching agent, if the temperature of the reaction solution is lower than 100°C, there is a problem that it is difficult to increase the leaching rate to more than 95%. In order to solve the above-mentioned problem, in the present invention, the reaction temperature is set to 100°C to 200°C, and the lithium is recovered by sufficient stirring for more than 1 hour, at which time the leaching rate is more than 95%.

[0043] According to an embodiment of the present invention, the amount of acid leaching agent added is preferably added in an amount 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 relative to 100 parts by weight of the above-mentioned non-magnetic adsorbent. Preferably, if 50 parts by weight of sulfuric acid is added relative to 100 parts by weight of the above-mentioned non-magnetic adsorbent, and the slurry mixed with 350 parts by weight of water is put into a sealed reaction container, and the leaching reaction is carried out at a temperature of 150° C. for 3 hours, more than 97% of lithium will be leached. When using acid, most of the insoluble matter is oxides containing silicon or aluminum.

[0044] (7) The seventh process: the second solid-liquid separation process

[0045] The leaching reaction slurry (which has been subjected to the above-mentioned lithium leaching process) is subjected to solid-liquid separation, and the leaching solution containing the eluted lithium is separated into a liquid phase, and the leaching residue is separated into a solid phase. The above-mentioned leaching residue contains silicon dioxide, aluminum oxide, and magnesium as main components. The above-mentioned solid-liquid separation can use a solid-liquid separation device such as a filter press.

[0046] (8) The eighth process: neutralization reaction process

[0047] The liquid phase leachate obtained from the second solid-liquid separation process contains impurities such as aluminum and silicon in addition to lithium, which are removed by a neutralization reaction process. The aluminum and silicon components exist in the form of Al(OH)3 and SiO2·H2O in the neutral pH region. The Al(OH)3 and SiO2·H2O have low solubility and are leached. Therefore, if the pH of the leachate is adjusted to the neutral region (pH 6 to 8), the impurities are separated and removed as precipitates, thereby obtaining 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 neutralizers. If the neutralizer is added, heat is generated, so no separate heating process is required, but if the temperature of the reaction solution is high, the growth and aggregation of impurity particles are promoted, and solid-liquid separation is easily achieved. Therefore, it is preferred to heat the reaction solution to 70°C to 100°C for neutralization reaction.

[0048] (9) Ninth process: the third solid-liquid separation process

[0049] The lithium aqueous solution and the precipitate generated by the neutralization reaction process are separated by performing a third solid-liquid separation on the neutralization reaction solution. If the neutralization reaction solution is subjected to solid-liquid separation, liquid lithium and solid impurities are obtained. The impurities include silicon dioxide and aluminum hydroxide.

[0050] (10) The tenth process: the first reverse osmosis concentration process

[0051] The concentration of lithium contained in the neutral pH liquid lithium aqueous solution obtained by the third solid-liquid separation is 300 mg / l to 3000 mg / l. If lithium is directly recovered without concentration, there is a problem of low concentration. Therefore, in the present invention, the above lithium aqueous solution is concentrated to increase the lithium concentration, and then lithium is recovered. Preferably, a reverse osmosis filter with low energy cost is used as the above concentration method. Preferably, for the reverse osmosis filter of the present invention, a cheaper batch reverse osmosis device is used instead of the expensive multi-stage countercurrent reverse osmosis device used in the large-capacity desalination process. The above lithium aqueous solution can be concentrated to a lithium concentration of 10000 mg / l to 70000 mg / l. If it is concentrated to a concentration lower than 10000 mg / l, the energy cost of the evaporation concentration process as a subsequent process becomes too high, and if the lithium is concentrated to a concentration higher than 70000 mg / l, the energy cost required to apply a high reverse osmotic pressure is too high, which is no different from the evaporation method. Preferably, the lithium aqueous solution can be concentrated to a lithium concentration of 50,000 mg / l. In order to concentrate the lithium concentration to 50,000 mg / l, a water level adjustment sensor can be used to set the upper limit of the pump working pressure to 50 kg / cm 2 The filtrate (water) obtained in the above reverse osmosis concentration process can be used for the above first wet magnetic separation process.

[0052] (11) Eleventh process: evaporation concentration process

[0053] If the concentrated solution obtained by the above-mentioned reverse osmosis concentration process is continued to be heated and concentrated, lithium sulfate will be precipitated, and lithium sulfate can be obtained when solid-liquid separation is performed on it. For the above-mentioned concentration, a method of heating to 100°C for concentration under normal pressure and a method of evaporation concentration at a temperature below 100°C under reduced pressure can be used. In the present invention, the above-mentioned evaporation concentration method is used, preferably until the lithium sulfate concentration in the concentrated solution reaches 50% to 70%. The concentrated solution obtained in the above-mentioned evaporation concentration process is put into solid-liquid separation, and the filtrate (water) can be used for the above-mentioned first wet magnetic separation process.

[0054] (12) Process 12: Fourth solid-liquid separation process

[0055] The concentrated liquid obtained by the above evaporation concentration process is subjected to solid-liquid separation to obtain high-purity lithium sulfate in the solid phase and impurity aqueous solution (filtrate) in the liquid phase. The above filtrate is treated by different processes according to the concentration of impurities. When the impurity concentration of the above filtrate is below 5000 mg / l, it is re-entered into the above evaporation concentration process for re-concentration. When the impurity concentration exceeds 5000 mg / l, it is put into the lithium phosphate precipitation process for treatment. The solid phase obtained from the above fourth solid-liquid separation process is lithium sulfate, and the above lithium sulfate is high-purity lithium sulfate of more than 99.0%.

[0056] The specific embodiments described in this specification represent preferred embodiments or examples of the present invention, and the scope of the present invention is not limited thereto. It is obvious to those skilled in the art that modifications and other uses of the present invention will not exceed the scope of the invention described in the claims herein.

[0057] Industrial Applicability

[0058] By using the method for preparing high-purity lithium sulfate from waste saggers of the present invention, not only can high-purity lithium sulfate for preparing lithium secondary batteries be prepared by recycling the discarded waste saggers, but also positive electrode active materials, iron oxide, aluminum oxide, silicate and calcium carbonate obtained in the preparation process can be recycled.

Claims

1. A method for preparing high-purity lithium sulfate from waste saggers, comprising: The first step of preparing the waste sagger crushed material by crushing the waste sagger; A second step of adding an alkali leaching agent and water to the crushed waste sagger and reacting them to prepare a dissolution reaction slurry of the crushed waste sagger; A third step of performing a first solid-liquid separation on the dissolution reaction slurry of the waste sagger crushed material; After the solid phase obtained by the first solid-liquid separation is prepared into a suspension, a first wet magnetic separation process is performed to obtain a first magnetically adsorbed substance and a first non-magnetic adsorbed substance; a fourth step; After preparing the first non-magnetic adsorbent into a suspension, performing a second wet magnetic separation process to obtain a second magnetic adsorbent and a second non-magnetic adsorbent; a fifth step; A sixth step of adding water and a leaching agent into the second non-magnetic adsorbent and reacting them to prepare a lithium leaching reaction solution; A seventh step of performing a second solid-liquid separation on the lithium leaching reaction solution; An eighth step of adjusting the pH of the liquid filtrate obtained by the second solid-liquid separation to 6 to 8 to prepare a neutralization reaction solution; A ninth step of performing a third solid-liquid separation on the neutralization reaction liquid; a tenth step of performing reverse osmosis concentration on the liquid filtrate obtained by the third solid-liquid separation; An eleventh step of evaporating and concentrating the concentrated liquid obtained by the reverse osmosis concentration process; as well as The twelfth step is to perform a fourth solid-liquid separation on the concentrated solution obtained by the evaporation concentration to obtain high-purity lithium sulfate in a solid phase.

2. The method for preparing high-purity lithium sulfate from waste sagger according to claim 1, wherein: The waste sagger crushed material dissolution reaction slurry is prepared by adding 5 to 50 parts by weight of calcium hydroxide, calcium oxide, or magnesium hydroxide as an alkaline leaching agent to 100 parts by weight of the waste sagger crushed material with a size of less than 200 meshes, mixing with 350 parts by weight of water, and reacting at 50° C. to 80° C. for 30 to 120 minutes.

3. The method for preparing high-purity lithium sulfate from waste sagger according to claim 1, wherein: The leaching agent used for leaching the second non-magnetic adsorbent is any one selected from the group consisting of sulfuric acid, sulfurous acid, sulfur dioxide, and sulfur trioxide, or a mixture of two or more thereof.

4. The method for preparing high-purity lithium sulfate from waste sagger according to claim 1, wherein: An alkali neutralizer is added to the liquid phase filtrate obtained by the second solid-liquid separation to adjust the pH to 6 to 8, and then the third solid-liquid separation is performed to remove silicon and aluminum in the solid phase as impurities.

5. The method for preparing high-purity lithium sulfate from waste sagger according to claim 1, wherein: The reverse osmosis concentration process uses a batch reverse osmosis device and sets the upper limit of the pump working pressure to 50kg / cm 2 , and concentrated until the lithium concentration of the liquid filtrate obtained by the third solid-liquid separation reaches 10000 mg / l to 70000 mg / l.

6. The method for preparing high-purity lithium sulfate from waste saggers according to claim 1, wherein: The purity of the high-purity lithium sulfate is above 99.9%.

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