Method for recovering nickel, cobalt, and lithium from waste refractory saggers

Abstract

The present invention has an advantage in that after crushing the discarded refractory sacks, nickel oxide and cobalt oxide, which are positive active materials, are recovered using wet magnetic separation, and impurities are removed through Al, Si precipitation reaction and evaporation concentration to recover high purity lithium hydroxide. Therefore, by using the method for recovering positive active materials and lithium hydroxide from the discarded refractory sacks of the present invention, it is possible to recover and reuse high value-added lithium and positive active materials from the discarded refractory sacks discarded in the manufacturing process of lithium secondary batteries, and therefore it is expected that the manufacturing cost of lithium secondary batteries can be reduced.

Description

[Technical Field]

[0001] The present invention relates to a method for recovering positive electrode active material and lithium hydroxide from discarded saggers. [Background technology]

[0002] The positive electrode active material of a lithium ion secondary battery is synthesized by a method of calcining a lithium-containing composite oxide at a high temperature. If the lithium-containing composite oxide comes into direct contact with flames, ash smoke, or the like during the high-temperature calcination process, the quality of the synthesized positive electrode active material will be reduced. Therefore, the lithium-containing composite oxide is produced by a method of placing it in a fireproof sagger, which is a fireproof container with excellent thermal conductivity, and then calcining it at a high temperature.

[0003] The refractory sagger for producing the positive electrode active material is made of ceramic oxide containing SiO2, Al2O3, MgO, etc. as its main components. When the refractory sagger for producing the positive electrode active material is repeatedly subjected to high-temperature firing of the lithium-containing composite oxide, its surface is corroded by lithium hydroxide or lithium carbonate, etc., produced during the high-temperature firing process, and the positive electrode active material synthesized together with the lithium hydroxide and lithium carbonate is deposited at the eroded site. As a result, the heat durability of the refractory sagger corroded by the lithium hydroxide or lithium carbonate is reduced, and the refractory sagger is eventually discarded as a waste refractory sagger.

[0004] It is said that the amount of waste fireproof sacks generated in Korea is about 30,000 tons per year, but the recent rapid increase in demand for lithium-ion secondary batteries, coupled with the popularization of mobile devices and electric vehicles, is remarkable, and the amount of waste fireproof sacks generated is expected to increase sharply.

[0005] Therefore, if it is possible to recover high-value-added positive electrode active materials such as nickel and cobalt deposited in eroded areas from used refractory saggers that are discarded due to reduced thermal durability caused by repeated high-temperature firing of lithium-containing composite oxides, as well as lithium, it is expected that the recovered materials can be recycled for the production of lithium-ion secondary batteries, thereby reducing production costs.

[0006] The patents and references mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication was individually and specifically indicated by reference. Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide an economical and effective method for recovering high-value compounds such as lithium, nickel, and cobalt from discarded fireproof saggers used in the manufacture of positive electrode active materials, which are discarded due to corrosion caused by lithium hydroxide, lithium carbonate, etc. with repeated use.

[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 provides a method for recovering positive electrode active material and lithium hydroxide from used refractory saggers, the method comprising: a first step of wet-pulverizing the used refractory saggers to perform solid-liquid separation; a second step of applying wet magnetic separation to the solid obtained by the solid-liquid separation to recover positive electrode active material; and a third step of subjecting the filtrate obtained by the solid-liquid separation to a precipitation reaction of Al and Si and evaporation and concentration to recover lithium hydroxide.

[0010] The wet pulverization is characterized in that the waste refractory saggers are dry-pulverized (dry pulverized) and then wet ball milled (wet ball mill pulverized) to finely pulverize them to a particle size of 200 mesh or less.

[0011] The wet magnetic separation is characterized in that iron oxide and iron scale as magnetized matter are removed using primary wet magnetic separation, and then secondary wet magnetic separation is carried out on the non-magnetized matter from the primary wet magnetic separation, thereby recovering the positive electrode active material as a magnetized matter. The precipitation reaction of Al and Si is characterized in that an alkaline earth metal hydroxide and an additive are mixed with the filtrate obtained using the solid-liquid separation, thereby precipitating water-soluble aluminum compounds such as aluminates as sparingly soluble substances such as calcium aluminum silicate hydrate or ettringite, and precipitating water-soluble silicon-containing compounds as sparingly soluble substances such as calcium silicate hydrate.

[0012] The evaporation concentration is characterized in that the filtrate obtained by the solid-liquid separation is subjected to a precipitation reaction of Al and Si, and the filtrate is then subjected to solid-liquid separation, and the filtrate is then subjected to evaporation concentration to recover lithium hydroxide, and is characterized in that the atmosphere is adjusted with an inert gas such as nitrogen to prevent lithium hydroxide from reacting with carbon dioxide gas in the air to produce lithium carbonate, which would result in a decrease in purity. [Effects of the Invention]

[0013] The present invention has the advantage of recovering high-purity lithium hydroxide by crushing discarded refractory saggers, recovering nickel oxide and cobalt oxide, which are cathode active materials, using wet magnetic separation, and removing impurities through a precipitation reaction of Al and Si and evaporation and concentration. Therefore, by using the method for recovering cathode active material and lithium hydroxide from discarded refractory saggers of the present invention, high-value-added lithium and cathode active material can be recovered and reused from discarded refractory saggers discarded in the manufacturing process of lithium secondary batteries, which is expected to reduce the manufacturing costs of lithium secondary batteries. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic diagram showing a method for recovering a positive electrode active material and lithium hydroxide from a used refractory sagger according to the present invention. [Figure 2] The mineral phase analysis of the erosion layer of the waste refractory sagger used in the sintering of the NCA (LiNi0.8Co0.15Al0.05) of the present invention shows that the erosion layer is mainly composed of Li4SiO4, LiAlO2, LiAlSi2O6 and Li2CO3. [Figure 3] The mineral phases of the crushed waste refractory saggers used in the sintering of the NCA (LiNiCoAl) of the present invention were analyzed, and the results showed that the waste refractory saggers were mainly composed of AlO, and also contained mineral phases such as LiAlSiO, AlSiO, SiO, MgAlO, and MgAlSiO. [Figure 4] 1 shows scanning electron micrographs of the refractory sagger crushed and eroded layers of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention provides a method for recovering a positive electrode active material and lithium hydroxide from a used refractory saggers, the method comprising: a first step of wet-pulverizing the used refractory saggers to perform solid-liquid separation; a second step of recovering a positive electrode active material by applying wet magnetic separation to the solid obtained by the solid-liquid separation; and a third step of recovering lithium hydroxide from the filtrate obtained by the solid-liquid separation by subjecting Al and Si to a precipitation reaction and evaporative concentration.

[0016] The waste refractory sagger is a refractory sagger for firing and synthesizing a positive electrode active material, and is made of ceramics containing SiO2, Al2O3, and MgO as main components.

[0017] The wet pulverization is preferably carried out after coarsely pulverizing the refractory sagger to a level of 0.5 to 10 mm using dry pulverization. The wet pulverization is preferably carried out by pulverizing the refractory sagger to a level of 0.5 to 10 mm using ball milling to finely pulverize the refractory sagger to a fine powder of 200 mesh or less using ball milling, and the wet-pulverized material is separated into a solid and a liquid using solid-liquid separation.

[0018] The solid obtained by the solid-liquid separation is subjected to wet magnetic separation to recover a positive electrode active material. The positive electrode active material includes lithium-nickel-cobalt oxide. The wet magnetic separation includes primary wet magnetic separation and secondary wet magnetic separation. The primary wet magnetic separation has a magnetic flux density of 100 to 500 gauss to remove iron, iron oxide, iron scale, and other magnetically attached materials. Preferably, the primary wet magnetic separation has a magnetic flux density of 100 to 200 gauss to remove iron, iron oxide, and iron scale. The secondary wet magnetic separation has a magnetic density of 25,000 to 30,000 gauss to recover the positive electrode active material as a magnetically attached material and alumina, aluminosilicate, and other magnetically attached materials. Preferably, the secondary wet magnetic separation is performed using a separator with a magnetic density of 20,000 gauss or more.

[0019] In the present invention, the filtrate obtained by the solid-liquid separation is subjected to a precipitation reaction of Al and Si and evaporation and concentration to recover lithium hydroxide. The Al and Si precipitation reaction is carried out by mixing the filtrate obtained by the solid-liquid separation with an alkaline earth metal hydroxide, gypsum, etc., to recover water-soluble Al(OH)4 - is precipitated as sparingly soluble calcium aluminum silicate hydrate or ettringite, and water-soluble SiO4 2- is precipitated as poorly soluble calcium silicate hydrate.

[0020] The evaporation concentration of the present invention is characterized in that the filtrate obtained by the solid-liquid separation is subjected to a precipitation reaction of Al and Si, and the filtrate obtained by the solid-liquid separation is subjected to evaporation concentration to recover lithium hydroxide.

[0021] The evaporation concentration includes primary, secondary, and tertiary evaporation concentration. First, the primary evaporation concentration is a process for removing impurities including calcium hydroxide, calcium carbonate, aluminum hydroxide, and silicon dioxide, and may also contain some lithium hydroxide and lithium carbonate. The primary evaporation concentration is preferably carried out until 0.5 to 5% of lithium hydroxide is precipitated.

[0022] The secondary evaporation concentration is a process for precipitating lithium hydroxide, and is preferably carried out using a liquid obtained by solid-liquid separation of the concentrated liquid produced by the primary evaporation concentration until 50 to 80% of the lithium hydroxide is precipitated. The precipitated lithium hydroxide is washed, filtered, and dried, and the lithium hydroxide recovered using this has a purity of 99.9% or more.

[0023] The tertiary evaporation and concentration is a process for improving the recovery rate of lithium hydroxide by reintroducing lithium hydroxide that was not precipitated in the secondary evaporation and concentration process into the primary evaporation and concentration process. The tertiary evaporation and concentration is preferably carried out using a liquid obtained by solid-liquid separation of the concentrate produced by the secondary evaporation and concentration, and is continued until 90 to 95% of the lithium hydroxide is precipitated. Since the lithium hydroxide obtained as a solid by solid-liquid separation after the secondary evaporation and concentration may contain impurities and have a low purity, it is re-dissolved in the filtrate from the primary evaporation and concentration process to be precipitated as high-purity lithium hydroxide in the secondary evaporation and concentration process. Furthermore, the filtrate obtained as a liquid by solid-liquid separation after being used to wash the high-purity lithium hydroxide obtained after the secondary evaporation and concentration is introduced into the Al and Si precipitation reaction solution and reused in the lithium hydroxide recovery process.

[0024] <Mode for carrying out the invention> The method of recovering the positive electrode active material and lithium hydroxide from the waste refractory saggers of the present invention will be described in detail below.

[0025] 1) Analysis of used fireproof sacks The fireproof sagger of the present invention may be a fireproof sagger that is discarded after being used to sinter a positive electrode active material for a secondary battery, or may be a container for sintering a positive electrode active material and may be a ceramic mainly composed of SiO2, Al2O3, and MgO.

[0026] Table 1 shows the NCA (LiNi 0.8 Co 0.15 Al 0.05 The composition of the waste refractory saggers used in the sintering of the sintered porcelain was analyzed by X-ray fluorescence spectroscopy (XRF) and atomic absorption spectroscopy.

[0027] [Table 1]

[0028] Analysis revealed that the lithium (Li) content was on the high side at 1.5%, which is equivalent to about 8.0% lithium carbonate. The cobalt content was also about 0.2%, making it deemed to be well worth recovering.

[0029] Figures 2 and 3 show the NCA (LiNi 0.8 Co 0.15 Al 0.05 The results of X-ray diffraction analysis of the mineral phase of a used refractory sagger used in sintering the cathode active material are shown in Figure 2. Figure 2 shows the analysis results for the surface of the refractory sagger, i.e., the portion that had been in contact with the cathode active material. While diffraction lines for lithium silicate, lithium aluminum oxide, lithium aluminum silicate, and lithium carbonate are clearly visible, no clear diffraction lines are observed for the cathode active material due to its low abundance and poor crystallinity.

[0030] Figure 3 shows an X-ray diffraction pattern of a sample of a completely crushed and mixed used fireproof sagger, i.e., an analysis of the entire mineral phase of the used fireproof sagger. The interior of the fireproof sagger is composed of the raw materials of the fireproof sagger: mullite, cordierite, alumina, quartz, and spinel. Diffraction lines of lithium aluminum silicate, which is thought to have been produced by a reaction with lithium that had seeped in from the surface, were also observed.

[0031] 2) Waste refractory sagger processing process 1 shows a process for separating iron oxide, iron scale, positive electrode active material, aluminosilicate, and lithium hydroxide from used refractory saggers according to the present invention. In particular, the use of the process for treating used refractory saggers according to the present invention has the advantage of being able to obtain high-purity lithium hydroxide monohydrate with a purity of 99.9% or more.

[0032] (1) Crushing process of used fireproof saggers First, the waste refractory saggers (S1) are crushed to a powder of 200# or less. Since pulverizing the waste refractory saggers all at once has the problem of low crushing efficiency, it is preferable to perform dry crushing (S2) to roughly crush the waste refractory saggers to 1mm or less in Step 1, and then wet crushing (S3) to finely crush the waste refractory saggers to 200# or less in Step 2. In a mass processing process where crushing efficiency is more important than initial investment cost, it is preferable to arrange a jaw crusher and an impact mill (or hammer mill) in series and crush the crushed product to a particle size of 1mm or less.

[0033] The waste refractory saggers have a relatively high compressive strength but are weak to impact. If only the crushing efficiency is taken into consideration, it is possible to use only an impact crusher such as an impact crusher without going through the various steps. However, the crushed particles of the impact crusher have sharp surfaces with high hardness, so the parts are easily worn during crushing, which can result in a problem of high crushing costs.

[0034] Therefore, in the present invention, dry crushing (S2) is performed using a jaw crusher, which is easy to replace parts and inexpensive, in Step 1, and then finely crushing is performed using wet ball milling in Step 2. In particular, the wet ball milling has the advantage of being able to extract lithium during the finely crushing process of the waste refractory saggers.

[0035] The ball mill used in the wet grinding (S3) is preferably configured such that a coarsely ground slurry of used refractory saggers, which is a mixture of coarsely ground used refractory saggers and water, is fed into one end, and overflow water containing particles finely ground using ball milling flows out from the other end. Furthermore, the overflowed slurry is preferably passed through a 200# sieve, and particles with a particle size of 200# or more are conveyed to the feed port.

[0036] The coarsely pulverized waste refractory saggers slurry is preferably produced by mixing 100 parts by weight of coarsely pulverized waste refractory saggers with 100 to 1,000 parts by weight of water. If the amount of water contained in the coarsely pulverized waste refractory saggers slurry is less than 100 parts by weight, the viscosity of the slurry will be too high, resulting in low fine pulverization efficiency using ball milling and a low lithium leaching rate. If the amount of water contained in the coarsely pulverized waste refractory saggers slurry exceeds 1,000 parts by weight, there is a problem of high energy costs for the subsequent concentration process. Preferably, the coarsely pulverized waste refractory saggers slurry is produced by mixing 200 to 500 parts by weight of water with 100 parts by weight of coarsely pulverized waste refractory saggers. The residence time of the coarsely pulverized waste refractory saggers slurry in the ball mill is preferably 10 to 120 minutes. If the residence time is less than 10 minutes, the lithium leaching rate will be low and the pulverization efficiency will also be reduced, while if the residence time is more than 120 minutes, this will result in an unnecessary increase in energy costs.

[0037] (2) Solid-liquid separation process of the finely ground slurry from used refractory saggers The finely pulverized waste refractory sagger slurry is subjected to solid-liquid separation (S4) to separate it into a solid (S5) and a filtrate (S6). The solid (S5) contains a refractory composition containing the cathode active material, iron oxide, iron scale, aluminosilicate, alumina, etc., while the filtrate (S6) corresponds to a lithium leachate containing dissolved lithium, aluminum, and silicon. A settling tank, filter press, screw filter, centrifuge, etc. can be used for the solid-liquid separation, and two or more of these can be combined to increase efficiency. Some lithium may have been leached into the solid (S5). Therefore, the solid (S5) is washed with clean water to minimize lithium loss, and the water used for washing (washing water) is reused as the water for ball milling in the wet grinding (S3).

[0038] (3) Wet magnetic separation process The solid (S5) contains a positive electrode active material (S13) and a refractory composition (S11) (S14), and the filtrate contains lithium and aluminum silicon as Li + , O.H. - , Al(OH)4 - , SiO4 2- From the solid (S5), iron oxide, iron scale, and positive electrode active material are recovered through magnetic separation (S8 and S12), and alumina and aluminosilicate, which are the components of the refractory sagger, are left behind as residue, and the filtrate (S6) is subjected to an Al and Si precipitation removal step (S15) to recover lithium hydroxide.

[0039] The magnetic separation is comprised of a primary wet separation step (S8) and a secondary wet magnetic separation step (S12). The water used in the wet magnetic separation step may be of industrial water quality, and the water used in the process may be reused. The solid (S5) obtained in the solid-liquid separation step (S4) is added with water to a solid concentration of 1 to 10%, to produce a solid slurry, which is then introduced into the primary wet magnetic separation step (S8).

[0040] The purpose of the primary wet magnetic separation process (S8) is to remove iron oxide, iron chips, and iron scale that have become mixed in due to wear on the crusher. The magnetically attracted materials (S9) in the primary wet magnetic separation process (S8) are iron oxide and iron scale. These materials are highly attracted to magnets and can be sufficiently removed using a magnet with a magnetic flux density of approximately 100 to 500 gauss. While the magnetically attracted materials (S9) recovered at a flux density of 200 gauss or less are mostly iron oxide and iron scale, magnetic flux densities above 200 gauss can increase the proportion of positive electrode active material (S13) mixed in the magnetically attracted materials (S9). The iron oxide and iron scale (S11) recovered using the primary wet magnetic separation process (S8) are dehydrated and stored in a separate location.

[0041] The purpose of the secondary wet magnetic separation step (S12) of the present invention is to recover a positive electrode active material (S13) containing nickel oxide, cobalt oxide, and the like from the non-magnetic material (S10) of the primary wet magnetic separation step (S8). Because the positive electrode active material (S13) corresponds to a weakly magnetic or paramagnetic material, a magnet with a high magnetic flux density is required to recover it as a magnetic material. The recovery of the positive electrode active material (S13) in the secondary wet magnetic separation step (S12) of the present invention is preferably carried out using a magnetic medium with a magnetic flux density of 10,000 to 30,000 gauss. However, some positive electrode active materials, such as lithium cobalt dioxide (LCO) and nickel cobalt manganese oxide (NCM), are strongly attracted to magnets. Therefore, when attempting to recover only these materials, a magnet with a magnetic flux density of approximately 2,000 gauss may be sufficient for recovery.

[0042] The magnetic separator used in the secondary wet magnetic separation step (S12) preferably has a structure that allows a slurry containing particles to be separated to flow between magnetized magnetic media. In this case, the solids (S5) and non-magnetized materials (S10) are preferably produced as a slurry with a concentration of 1 to 10%. If the solids concentration of the slurry is less than 1%, the amount of water used increases, requiring additional storage tanks, which increases energy costs. However, if the concentration exceeds 10%, the separation efficiency drops significantly.

[0043] (4)Al(OH)4 - and SiO4 2- Precipitation process The filtrate (S6) obtained by solid-liquid separation (S4) of the crushed refractory sagger crushed material contains Li + , O.H. - , Al(OH)4 - , SiO4 2- Therefore, if the filtrate (S6) is mixed with alkaline earth metal hydroxides such as calcium hydroxide and magnesium hydroxide and gypsum, water-soluble Al(OH)4 - and SiO42- However, the Al,Si precipitates as poorly soluble calcium silicate hydrate (CSH), calcium aluminum silicate hydrate (CASH), ettringite, etc. The Al,Si precipitation reaction (S15) is preferably carried out at a temperature of 50 to 80°C for a reaction time of 30 to 120 minutes. The Al,Si precipitation reaction (S15) is very sensitive to the reaction temperature, and the higher the temperature, the higher the reaction rate. For example, if the Al,Si precipitation reaction (S15) is carried out at a temperature of 20°C or less, it takes more than 6 hours to complete, and the product particle size is very fine, making solid-liquid separation difficult. At 50°C, the Al,Si precipitation reaction (S15) is completed within 2 hours, and at 80°C, the reaction is completed within 30 minutes. If the Al, Si precipitation reaction (S15) is carried out at a temperature close to 100°C, the reaction will be completed within 10 minutes, but energy loss will occur due to evaporation of water.

[0044] The precipitant (S16) used in the Al and Si precipitation reaction (S15) is an alkaline earth metal hydroxide, preferably calcium hydroxide. The amount of precipitant (S16) added is determined based on the amount of Al(OH)4 present in the solution. - and SiO4 2- The amount of calcium hydroxide added is determined by the amount of calcium silicate hydrate (CSH) and calcium aluminum silicate hydrate (CASH), and it is preferable to add calcium hydroxide in an amount equivalent to 1 to 2 times the amount required to produce calcium silicate hydrate (CSH) and calcium aluminum silicate hydrate (CASH). If the amount of calcium hydroxide added is less than the equivalent amount, the amount of unremoved Al(OH)4 in the solution will increase. - and SiO4 2- If the amount of gypsum used exceeds 2 equivalents, the process cost will increase. The amount of gypsum added is preferably 0.5 to 1 times the amount of calcium hydroxide added.

[0045] Addition of additives such as calcium hydroxide and gypsum can be performed in the wet ball milling process, which has the advantage of increasing the lithium leaching rate and simplifying the process, but can also reduce the efficiency of magnetic separation and lead to hardened sludge, which can make processing difficult.

[0046] (5) Solid-liquid separation process for Al and Si precipitates The reaction product of the Al, Si precipitation reaction (S15) is subjected to solid-liquid separation (S17) to separate a solid (S18) and a filtrate (S19). The solid (S18) contains the reaction products of the Al, Si precipitation reaction (S15), namely, sparingly soluble calcium silicate hydrate (CSH), calcium aluminum silicate hydrate (CASH), and ettringite. The filtrate (S19) is a lithium leachate containing lithium. A settling tank, filter press, screw filter, centrifuge, or the like can be used for the solid-liquid separation (S17), and two or more of these can be combined to increase efficiency. The solid (S18) is washed with clean water to minimize the loss of lithium contained therein. The wash water can be mixed with the filtrate (S6) used in the Al, Si precipitation reaction (S15) for reuse.

[0047] The filtrate (S19) separated using the solid-liquid separation (S17) is mostly water and lithium hydroxide, and contains 100 ppm or less of calcium (Ca 2+ ), aluminum (Al(OH)4 - ), silicon (SiO4 2- ) is contained in the filtrate (S19). Carbon dioxide (S20) is injected to remove impurities from the filtrate (S19). When the carbon dioxide (S20) (S20) is injected into the filtrate (S19), the calcium is precipitated as calcium carbonate. The precipitated calcium carbonate can be further produced by solid-liquid separation, but this can be omitted because it can be separated as a solid using solid-liquid separation (S22) in the evaporation and concentration process described below.

[0048] (6) Evaporation and concentration process The filtrate (S19) from which the impurities have been precipitated is subjected to evaporation and concentration steps (S21), (S24), and (S26). The evaporation and concentration steps (S21), (S24), and (S26) are steps for increasing the lithium concentration of the filtrate (S19) and removing remaining impurities such as magnesium hydroxide and calcium carbonate by precipitating them, and preferably comprise a first evaporation and concentration step (S21), a second evaporation and concentration step (S24), and a third evaporation and concentration step (S26).

[0049] The primary evaporation and concentration step (S21) involves subjecting the filtrate (S19) to reduced pressure evaporation at 70 to 95° C. The primary evaporation and concentration step (S21) can also be performed under atmospheric pressure at 100° C. In this case, it is essential to purge with nitrogen or argon gas to prevent contact between the carbon dioxide (S20) and the evaporated and concentrated liquid.

[0050] The primary evaporation concentration step (S21) is preferably carried out from the point at which lithium hydroxide begins to precipitate until approximately 0.5 to 5% of the total lithium hydroxide is precipitated. If the primary evaporation concentration step (S21) is terminated before the amount of lithium hydroxide precipitated reaches 0.5%, the removal rate of impurities including magnesium hydroxide, calcium carbonate, etc. will decrease. If the concentration is continued until an amount higher than 5% is precipitated, lithium hydroxide will be excessively precipitated, and the lithium hydroxide will be returned to step (S6) together with the impurities, reducing the process efficiency.

[0051] The lithium hydroxide concentrate produced in the primary evaporation concentration step (S21) is subjected to solid-liquid separation (S22). The solid-liquid separation (S22) is a step of separating impurities such as magnesium hydroxide and calcium carbonate precipitated in the primary evaporation concentration step (S21) from the concentrate, and some lithium hydroxide may precipitate together with the impurities. The solid-liquid separation (S22) can be performed using a settling tank, filter press, screw filter, centrifuge, or the like, and two or more of these can be combined to increase efficiency.

[0052] The solid (S23) obtained by the solid-liquid separation (S22) is mixed with the filtrate (S6) obtained by the solid-liquid separation (S4) of the pulverized waste refractory saggers and reused, thereby making it possible to recover a larger amount of lithium hydroxide contained in the impurities.

[0053] The secondary evaporation concentration step (S24) is performed on the filtrate obtained from the primary evaporation concentration step (S21) and the solid-liquid separation (S22) under the same conditions as the primary evaporation concentration step. The secondary evaporation concentration step (S24) is performed until 50 to 80% of the lithium hydroxide in the filtrate is precipitated. If the concentration is terminated before the amount of precipitated lithium hydroxide reaches 50%, the lithium hydroxide recovery rate decreases, resulting in increased process costs. Concentration performed so that the amount of precipitated lithium hydroxide exceeds 80%, results in a decrease in the purity of the recovered lithium hydroxide. The concentrate from the secondary evaporation concentration step (S24) is subjected to solid-liquid separation (S25) to separate lithium hydroxide as a solid phase (S28). A settling tank, filter press, screw filter, centrifuge, or the like can be used for the solid-liquid separation (S25), and the efficiency can be enhanced by combining two or more of these.

[0054] The tertiary evaporation concentration step (S26) is a step for maximizing the recovery rate of lithium hydroxide by further concentrating the filtrate from the secondary evaporation concentration step (S24) and solid-liquid separation (S25) and then reintroducing it into the evaporation concentration process. The tertiary evaporation concentration step (S26) is carried out in the same manner as the primary and secondary evaporation concentration steps (S21) and (S24), but is continued until 90-95% of the lithium hydroxide in the concentrated solution is precipitated. The solid produced using the tertiary evaporation concentration step (S26) is lithium hydroxide containing trace amounts of the impurities. After the Al, Si precipitation reaction (S15), the solid is mixed and dissolved in the filtrate (S19) obtained by solid-liquid separation (S17), and then reintroduced into the primary evaporation concentration step. The liquid produced using the tertiary evaporation concentration step (S26) contains trace amounts of aluminum and silicon, but is fed into the Al, Si precipitation reaction (S15) to remove these elements. Terminating the concentration before the lithium hydroxide precipitation amount reaches 90% would increase the cost of the Al / Si precipitation reaction (S15). Concentrating the lithium hydroxide precipitation amount beyond 95% would result in excessively low purity of the lithium hydroxide that should be mixed and dissolved in the filtrate (S19) obtained by solid-liquid separation (S17) after the Al / Si precipitation reaction (S15). The solid-liquid separation (S27) is a process for separating the lithium hydroxide produced in the tertiary evaporation concentration step (S26) from the aqueous solution. Typically, a settling tank, a filter press, a screw filter, a centrifuge, or the like can be used, and two or more of these can be combined to increase efficiency. The primary, secondary, and tertiary concentration steps may be performed in separate concentration tanks or sequentially in a single concentration tank.

[0055] (7) Obtaining high-purity lithium hydroxide The high-purity lithium hydroxide of the present invention is lithium hydroxide monohydrate having a purity of 99.9% or more, and is produced by washing the solid (S28) obtained by solid-liquid separation (S25) performed after the second evaporation concentration step (S24), filtering the solid (S29), and drying the solid at 80-100°C until the content of attached moisture is 1% or less (S30). The washing and filtration (S29) involves washing with a saturated solution of high-purity lithium hydroxide and then filtering, and this process is repeated about three times. The filtrate obtained from the three washing and filtration steps (S29) is mixed with the filtrate (S19) obtained by solid-liquid separation (S17) after the Al and Si precipitation reaction (S15), and is then re-introduced into the first, second, and third evaporation concentration steps (S21), (S24), and (S26).

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

[0057] By utilizing the method of the present invention for recovering positive electrode active material and lithium hydroxide from used refractory saggers, it is possible to recover and reuse high-value added lithium and positive electrode active material from used refractory saggers discarded in the manufacturing process of lithium secondary batteries.

Claims

1. A first step of wet-crushing waste refractory saggers and separating them into solid and liquid; a second step of recovering a positive electrode active material by applying wet magnetic separation to the solid obtained by the solid-liquid separation; a third step of recovering lithium hydroxide by subjecting the filtrate obtained by the solid-liquid separation to an Al and Si precipitation reaction and evaporation and concentration; A method for recovering a positive electrode active material and lithium hydroxide from a waste refractory sagger, comprising:

2. 2. The method for recovering a positive electrode active material and lithium hydroxide from a used refractory sagger as set forth in claim 1, wherein the wet pulverization comprises dry-pulverizing the used refractory sagger and then wet ball milling the pulverized material to a particle size of 200 mesh or less.

3. 2. The method for recovering positive electrode active material and lithium hydroxide from waste refractory saggers according to claim 1, wherein the wet magnetic separation is performed by first wet magnetic separation to remove iron oxide and iron scale as magnetized matter, and then by performing second wet magnetic separation on the non-magnetized matter from the first wet magnetic separation to recover positive electrode active material as magnetized matter.

4. The Al and Si precipitation reaction is carried out by mixing the filtrate obtained by the solid-liquid separation with an alkaline earth metal hydroxide and gypsum to form a water-soluble Al(OH) ４ － is precipitated as sparingly soluble ettringite and calcium aluminum silicate hydrate, and water-soluble SiO ４ ２－ 2. The method for recovering a positive electrode active material and lithium hydroxide from waste refractory saggers according to claim 1, characterized in that the above-mentioned is precipitated as sparingly soluble calcium silicate hydrate.

5. 2. The method for recovering positive electrode active material and lithium hydroxide from waste refractory saggers according to claim 1, wherein the evaporation and concentration comprises subjecting a filtrate obtained by the solid-liquid separation to the Al and Si precipitation reaction, and then subjecting the filtrate obtained by solid-liquid separation to evaporation and concentration, thereby recovering lithium hydroxide.

6. 6. The method for recovering positive electrode active material and lithium hydroxide from waste refractory saggers according to claim 5, wherein the lithium hydroxide has a purity of 99.9% or more.

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