Method for recovering nickel, cobalt and lithium from waste saggar

Abstract

The method has the advantages that after the waste saggars are crushed, nickel oxide and cobalt oxide serving as positive active substances are recovered through wet magnetic separation, and impurities are removed through Al and Si precipitation reaction and evaporation concentration, so that high-purity lithium hydroxide is recovered. Therefore, by utilizing the method for recovering the positive active material and the lithium hydroxide from the waste saggar, the lithium and the positive active material with high additional value can be recovered from the waste saggar abandoned in the manufacturing process of the lithium secondary battery and reused, so that the manufacturing cost of the lithium secondary battery is expected to be reduced.

Description

Technical Field

[0001] The invention relates to a method for recovering positive electrode active material and lithium hydroxide from waste sagger. Background Art

[0002] The positive electrode active material of the lithium ion secondary battery is synthesized by a method of high temperature calcination of a lithium-containing composite oxide. During the high temperature calcination process, if the lithium-containing composite oxide is in direct contact with sparks, smoke, etc., the quality of the synthesized positive electrode active material will decrease. Therefore, the lithium-containing composite oxide is placed in a sagger, which is a refractory container with excellent thermal conductivity, and then prepared by a high temperature calcination method.

[0003] The sagger for preparing the positive electrode active material is made of oxide ceramics with SiO2, Al2O3, MgO and the like as main components. For the sagger for preparing the positive electrode active material, when the lithium-containing composite oxide is repeatedly sintered at high temperature, its surface will be corroded by lithium hydroxide or lithium carbonate produced during the high temperature sintering process, and the positive electrode active material synthesized with lithium hydroxide and lithium carbonate will be deposited in the eroded part. Finally, the heat resistance of the sagger corroded by the lithium hydroxide or lithium carbonate will decrease, and it will eventually be discarded as a waste sagger.

[0004] It is reported that the amount of waste saggers generated in South Korea is about 30,000 tons per year, but with the popularization of mobile devices and electric vehicles, the demand for lithium-ion secondary batteries has increased dramatically, and the amount of waste saggers 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 and lithium deposited in the eroded parts from the waste saggers discarded due to the decrease in heat resistance caused by repeated high-temperature sintering of lithium-containing composite oxides, it is expected to be reused in the production of lithium-ion secondary batteries, thereby saving production costs.

[0006] 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

[0007] Problems to be solved by the invention

[0008] The object of the present invention is to provide an economical and effective method for recovering high value-added lithium, nickel, cobalt and other compounds from waste saggers for preparing positive electrode active materials which have been discarded due to corrosion caused by lithium hydroxide or lithium carbonate etc. during repeated use.

[0009] 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.

[0010] Solutions for solving problems

[0011] The present invention provides a method for recovering positive electrode active material and lithium hydroxide from waste saggers, comprising: a first step of wet-crushing the waste saggers and performing solid-liquid separation; a second step of applying wet magnetic separation to the solid obtained by the solid-liquid separation to recover the positive electrode active material; and

[0012] The third step is to carry out Al and Si precipitation reaction and evaporation concentration on the filtrate obtained by the above solid-liquid separation to recover lithium hydroxide.

[0013] The wet pulverizing is characterized in that the waste sagger is dried and pulverized and then wet ball milled to perform fine pulverization so that the particle size is less than 200 meshes.

[0014] The characteristic of the above wet magnetic separation is that after preparing iron oxide and iron scale as magnetic adsorbents through a primary wet magnetic separation, the non-magnetic adsorbents of the primary wet magnetic separation are subjected to a secondary wet magnetic separation, thereby recovering the positive electrode active material as the magnetic adsorbent; the characteristic of the above Al and Si precipitation reaction is that alkaline earth metal hydroxides and additives are mixed in the filtrate obtained through the above solid-liquid separation to precipitate water-soluble aluminum compounds (such as aluminates) into insoluble substances, such as hydrated calcium aluminosilicate or ettringite, and water-soluble silicon-containing compounds are precipitated into insoluble substances such as hydrated calcium silicate.

[0015] The above evaporation and concentration is characterized in that the filtrate obtained by the above solid-liquid separation is subjected to the above Al and Si precipitation reaction, and after solid-liquid separation, the obtained filtrate is evaporated and concentrated to recover lithium hydroxide; in order to prevent the reaction with carbon dioxide gas in the air to generate lithium carbonate and reduce the purity, the atmosphere is adjusted with inert gas such as nitrogen.

[0016] Effects of the Invention

[0017] The advantages of the present invention are that the discarded old saggers can be crushed, and then the nickel oxide and cobalt oxide as positive electrode active materials can be recovered by wet magnetic separation, and impurities can be removed by Al and Si precipitation reaction and evaporation concentration to recover high-purity lithium hydroxide. Therefore, by utilizing the method of recovering positive electrode active materials and lithium hydroxide from the waste saggers of the present invention, high-value-added lithium and positive electrode active materials can be recovered from the waste saggers discarded in the manufacturing process of lithium secondary batteries and reused, thereby hopefully reducing the manufacturing cost of lithium secondary batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The diagram shows a method for recovering positive electrode active material and lithium hydroxide from waste saggers of the present invention.

[0019] Figure 2 As an analysis of the present invention NCA (LiNi 0.8 Co 0.15 Al 0.05 ) shows the mineral phase of the etched layer of the waste sagger used for sintering, showing that the etched layer is mainly composed of Li4SiO4, LiAlO2, LiAlSi2O6 and Li2CO3.

[0020] Figure 3 As an analysis of the present invention NCA (LiNi 0.8 Co 0.15 Al 0.05 ) is a diagram of the mineral phase of the crushed waste sagger used for sintering, showing that the waste sagger is mainly composed of Al2O3 and also includes Li 0.6 Al 0.6 Si 2.4 O6、Al6Si2O 13 、SiO2、MgAl2O4 and Mg2Al4Si5O 18 The results of mineral phases etc.

[0021] Figure 4 The scanning electron microscope images of the sagger ground material and the etched layer of the present invention are shown. DETAILED DESCRIPTION

[0022] The present invention provides a method for recovering positive electrode active material and lithium hydroxide from waste saggers, comprising: a first step of wet-crushing the waste saggers and performing solid-liquid separation; a second step of applying wet magnetic separation to the solid obtained by the solid-liquid separation to recover the positive electrode active material; and

[0023] The third step is to carry out Al and Si precipitation reaction and evaporation concentration on the filtrate obtained by the above solid-liquid separation to recover lithium hydroxide.

[0024] The above-mentioned waste sagger is used as a sagger for sintering and synthesizing positive electrode active materials, and is a ceramic with SiO2, Al2O3 and MgO as main components.

[0025] The wet pulverization is characterized in that it is performed using a ball mill. Preferably, the wet pulverization is performed after the sagger is coarsely pulverized to a size of 0.5 to 10 mm by dry pulverization. The wet pulverization is characterized in that the sagger is finely pulverized into a fine powder state of less than 200 mesh by a ball mill, and the pulverized product after the wet pulverization is separated into solid and liquid by solid-liquid separation.

[0026] The solid obtained by the above solid-liquid separation is used to recover the positive electrode active material by wet magnetic separation. The above positive electrode active material includes lithium-nickel-cobalt oxide. The above wet magnetic separation includes a primary wet magnetic separation and a secondary wet magnetic separation. The above primary wet magnetic separation has a magnetic flux density of 100 to 500 Gauss, and removes iron, iron oxide, iron scale, etc. as magnetic adsorbents. Preferably, the above primary wet magnetic separation has a magnetic flux density of 100 to 200 Gauss, and removes iron, iron oxide, and iron scale as magnetic adsorbents. The above secondary wet magnetic separation is characterized by having a magnetic density of 25,000 to 30,000 Gauss, recovering the positive electrode active material as a magnetic adsorbent, and recovering alumina and aluminosilicate as non-magnetic adsorbents. Preferably, the above second wet magnetic separation is characterized by using a separator with a magnetic density of more than 20,000 Gauss.

[0027] The present invention performs Al and Si precipitation reaction and evaporation concentration on the filtrate obtained by the above solid-liquid separation to recover lithium hydroxide. The above Al and Si precipitation reaction is characterized in that alkaline earth metal hydroxide and gypsum are mixed in the filtrate obtained by the above solid-liquid separation to separate water-soluble Al(OH)4 - It precipitates as insoluble hydrated calcium aluminosilicate or ettringite, and converts water-soluble SiO4 2- The precipitate is insoluble calcium silicate hydrate.

[0028] The evaporation and concentration of the present invention is characterized in that the filtrate obtained by the solid-liquid separation is subjected to Al and Si precipitation reaction, and after the solid-liquid separation, the filtrate obtained is evaporated and concentrated to recover lithium hydroxide.

[0029] The above evaporation concentration includes primary, secondary and tertiary evaporation concentration. First, the primary evaporation concentration is a process of removing impurities containing calcium hydroxide, calcium carbonate, aluminum hydroxide and silicon dioxide, which may contain some lithium hydroxide and lithium carbonate. Preferably, the above primary evaporation concentration is carried out until 0.5% to 5% of lithium hydroxide is precipitated.

[0030] The secondary evaporation and concentration is a process for precipitating lithium hydroxide, and the liquid obtained by solid-liquid separation of the concentrated liquid prepared by the primary evaporation and concentration is preferably carried out until the lithium hydroxide is precipitated by 50% to 80%. The characteristic of the precipitated lithium hydroxide is that the purity of the lithium hydroxide recovered after washing, filtration and drying is above 99.9%.

[0031] The above-mentioned three-time evaporation and concentration is a process in which the lithium hydroxide that has not been precipitated in the above-mentioned two-time evaporation and concentration process is re-entered into the one-time evaporation and concentration process to improve the recovery rate of lithium hydroxide. The above-mentioned three-time evaporation and concentration adopts the liquid obtained by solid-liquid separation of the concentrated liquid prepared by the above-mentioned two-time evaporation and concentration, and is preferably carried out until the above-mentioned lithium hydroxide is precipitated by 90% to 95%. Since the solid obtained by solid-liquid separation after the above-mentioned two-time evaporation and concentration, that is, lithium hydroxide, contains impurities and may have a low purity, it should be redissolved in the filtrate used for the one-time evaporation and concentration, and precipitated as high-purity lithium hydroxide in the two-time evaporation and concentration process. In addition, the liquid obtained by solid-liquid separation after washing the high-purity lithium hydroxide obtained after the above-mentioned two-time evaporation and concentration, that is, the filtrate will be put into the Al, Si precipitation reaction liquid and used again in the lithium hydroxide recovery process.

[0032] Best Mode for Carrying Out the Invention

[0033] The method for recovering positive electrode active material and lithium hydroxide from waste sagger of the present invention will be described in detail below.

[0034] 1) Analysis of waste saggers

[0035] The sagger of the present invention can be a sagger discarded after the positive electrode active material for secondary batteries is fired. The container used for firing the positive electrode active material can be a ceramic with SiO2, Al2O3, and MgO as main components.

[0036] Table 1 shows the X-ray fluorescence analysis (XRF) and atomic absorption spectrophotometry analysis of NCA (LiNi 0.8 Co 0.15 Al 0.05 ) The result of the composition of the waste sagger used for sintering.

[0037]

Table 1

[0038]

[0039] The analysis results show that the lithium (Li) content is relatively high, at 1.5%, which is about 8.0% when converted into lithium carbonate. In addition, the cobalt content is also around 0.2%, which can be considered to have sufficient recycling value.

[0040] Figure 2 and Figure 3 The results show that NCA (LiNi 0.8 Co 0.15 Al 0.05 ) Results of X-ray diffraction analysis of the mineral phase of the waste sagger used for sintering. Figure 2This is the analysis result of the surface part of the sagger, that is, the part that has been in contact with the positive electrode active material. The diffraction lines of lithium silicate, lithium aluminum oxide, lithium aluminum silicate, lithium carbonate, etc. can be well observed. However, the amount of positive electrode active material is small and the crystallinity is poor, so no obvious diffraction lines are observed.

[0041] Figure 3 This is an X-ray diffraction pattern that analyzes the mineral phase of the entire used sagger, which is a sample that is completely crushed and mixed. The interior of the sagger is composed of the following raw materials of the sagger: mullite, cordierite, alumina, quartz, spinel, and diffraction lines such as lithium aluminum silicate that are considered to be generated by the reaction with lithium impregnated from the surface can also be observed.

[0042] 2) Processing technology of waste sagger

[0043] Figure 1 The invention shows a process for separating iron oxide, iron scale, positive electrode active material, aluminum silicate and lithium hydroxide from the waste sagger of the invention. In particular, when the waste sagger treatment process of the invention is used, it has the advantage of obtaining high-purity lithium hydroxide monohydrate with a purity of more than 99.9%.

[0044] (1) Crushing process of waste sagger

[0045] First, the waste sagger (S1) is crushed into powders of less than 200#. Since the one-time micronization of the waste sagger has the problem of reduced crushing efficiency, preferably, in step 1, coarse crushing to less than 1 mm is performed by dry crushing (S2), and then in step 2, fine crushing to less than 200# is performed by wet crushing (S3). In a batch processing process that attaches more importance to crushing efficiency than initial investment cost, preferably, a jaw crusher and an impact mill (or hammer mill) are placed in series, and the particle size of the crushed product is less than 1 mm.

[0046] The above-mentioned waste sagger has the characteristics of strong compression strength but weak impact resistance. If only the crushing efficiency is considered, it is also possible to use only an impact crusher such as an impact crusher without going through multiple steps. However, the above-mentioned impact crusher has the problem that the crushed particles have a high hardness and sharp side, and the crushing easily causes the parts to wear, thereby increasing the crushing cost.

[0047] Therefore, in the present invention, after dry pulverizing (S2) using a jaw crusher with easy replacement of parts and low cost in step 1, fine pulverizing is performed using a wet ball mill in step 2. In particular, the wet ball mill has the advantage of being able to extract lithium during the fine pulverization process of the waste sagger.

[0048] Preferably, the ball mill used for the wet pulverization (S3) has the following structure: a waste sagger coarse pulverization slurry mixed with waste sagger coarse pulverization material and water is fed from one end, and an overflow slurry containing particles finely pulverized by ball milling flows out from the other end. In addition, preferably, the overflow slurry is passed through a 200# sieve and particles with a size of 200# or more are transported to the input port.

[0049] Preferably, for the above-mentioned waste sagger coarse grinding slurry, 100 to 1000 parts by weight of water is mixed with 100 parts by weight of the waste sagger coarse grinding material to prepare it. When the amount of water contained in the above-mentioned waste sagger coarse grinding slurry is less than 100 parts by weight, the viscosity of the slurry is too high, which will not only reduce the efficiency of fine grinding by ball milling, but also reduce the leaching rate of lithium. If the amount of water contained in the above-mentioned waste sagger coarse grinding slurry exceeds 1000 parts by weight, the energy cost of the subsequent concentration process will be increased. Preferably, for the above-mentioned waste sagger coarse grinding slurry, 200 to 500 parts by weight of water is mixed with 100 parts by weight of the waste sagger coarse grinding material to prepare it. Preferably, the residence time of the above-mentioned waste sagger coarse grinding slurry in the ball mill is 10 minutes to 120 minutes. If the residence time is less than 10 minutes, there are problems that the lithium leaching rate is reduced and the fine pulverization efficiency is reduced, while if the residence time exceeds 120 minutes, unnecessary increase in energy cost is caused.

[0050] (2) Solid-liquid separation process of micro-crushed slurry from waste sagger

[0051] The finely pulverized waste sagger finely pulverized slurry is subjected to solid-liquid separation (S4) to be separated into solid (S5) and filtrate (S6). The solid (S5) contains positive electrode active material and a refractory composition containing iron oxide, iron scale, aluminum silicate, aluminum oxide, etc., and the filtrate (S6) is equivalent to a lithium leachate in which lithium, aluminum and silicon are dissolved. The solid-liquid separation can use a sedimentation tank, a filter press, a screw filter, a centrifuge, etc., or two or more of them can be combined to improve its efficiency. Some lithium may be leached from the solid (S5). Therefore, the solid (S5) will be washed with clean water to minimize the loss of lithium, and the water (washing water) used in the washing will be used as the ball milling water for the wet pulverization (S3) and reused.

[0052] (3) Wet magnetic separation process

[0053] The solid (S5) contains a positive electrode active material (S13) and a refractory composition (S11, S14), and in the filtrate, lithium and aluminum silicon are present in the form of Li + OH - 、Al(OH)4 - 、SiO4 2- The solid (S5) is subjected to magnetic separation (S8 and S12) to recover iron oxide, iron scale, and positive electrode active material, and the alumina and aluminosilicate as the composition of the sagger will remain as residues. The filtrate (S6) is subjected to an Al and Si precipitation removal step (S15) to recover lithium hydroxide.

[0054] The magnetic separation is composed of a primary wet separation process (S8) and a secondary wet magnetic separation process (S12). It is sufficient for the water used in the wet magnetic separation process to reach the water quality of industrial water, and the water used in the process can also be reused. The solid (S5) obtained from the solid-liquid separation process (S4) is prepared into a solid slurry by adding water so that the concentration of the solid reaches 1%-10%, and is put into the primary wet magnetic separation process (S8).

[0055] The purpose of the single wet magnetic separation process (S8) is to remove iron oxide, iron flakes, iron scales, etc. that are mixed in due to the wear of the crusher. The magnetic adsorbents (S9) of the single wet magnetic separation process (S8) are iron oxide and iron scales. Because they are strongly attracted to magnets, they can be fully removed by a magnet with a magnetic flux density of 100 gauss to 500 gauss. At this time, most of the magnetic adsorbents (S9) recovered below 200 gauss are iron oxide and iron scales, but if the magnetic flux density exceeds 200 gauss, the proportion of positive electrode active material (S13) mixed in the magnetic adsorbent (S9) may increase. The iron oxide and iron scales (S11) recovered by the above-mentioned single wet magnetic separation process (S8) are stored in a separate place after dehydration.

[0056] The purpose of the secondary wet magnetic separation process (S12) of the present invention is to recover positive electrode active materials (S13) containing nickel oxide and cobalt oxide, etc. from the non-magnetic adsorbent (S10) of the primary wet magnetic separation process (S8). Since the above-mentioned positive electrode active materials (S13) are equivalent to weak magnetic or paramagnetic bodies, in order to recover them as magnetic adsorbents, a magnet with a high magnetic flux density is required. In the secondary wet magnetic separation process (S12) of the present invention, the recovery of the positive electrode active materials (S13) is preferably carried out using a magnetic medium with a magnetic flux density of 10,000 to 30,000 gauss. However, since some positive electrode active materials such as lithium cobalt oxide (LCO) and nickel-cobalt-manganese (NCM) have the property of being strongly attracted by magnets, if only these positive electrode active materials are to be recovered, a magnet with a magnetic flux density of about 2,000 gauss is sufficient.

[0057] Preferably, the magnetic separator used in the above-mentioned secondary wet magnetic separation process (S12) has a structure for flowing the slurry containing the particles to be separated between the magnetized magnetic media. At this time, preferably, the solid (S5) and the non-magnetic adsorbent (S10) are made into a slurry with a concentration of 1%-10% for use. If the solid concentration of the above-mentioned slurry is lower than 1%, additional storage tanks need to be added as the amount of water used increases, and there is a problem of increased energy costs, and if the above-mentioned concentration exceeds 10%, there is a problem of a significant decrease in sorting efficiency.

[0058] 4)Al(OH)4 - and SiO4 2- Precipitation process

[0059] The filtrate (S6) obtained by subjecting the pulverized sagger to solid-liquid separation (S4) contains Li + OH - 、Al(OH)4 - 、SiO4 2- Therefore, if an alkaline earth metal hydroxide such as calcium hydroxide or magnesium hydroxide and gypsum are mixed in the above filtrate (S6), the water-soluble Al(OH)4 - and SiO4 2-It will be precipitated into insoluble calcium silicate hydrate (CSH), calcium aluminum silicate hydrate (CASH) and ettringite through pozzolanic reaction and the like. The preferred temperature of the above-mentioned Al and Si precipitation reaction (S15) is 50°C to 80°C, and the time is 30 minutes to 120 minutes. The above-mentioned Al and Si precipitation reaction (S15) is very sensitive to the reaction temperature. The higher the temperature, the faster the reaction rate. As an example, if the above-mentioned Al and Si precipitation reaction (S15) is carried out at a temperature below 20°C, it takes more than 6 hours to complete, and the particle size of the product is also very small, which makes it difficult to separate the solid and the liquid. At 50°C, the Al and Si precipitation reaction (S15) ends within 2 hours, and at 80°C, the reaction ends within 30 minutes. When the Al and Si precipitation reaction (S15) is carried out at about 100°C, the reaction will be completed within 10 minutes, but energy loss will occur due to the evaporation of water.

[0060] As the precipitation agent (S16) used in the precipitation reaction of the Al and Si precipitation reaction (S15), an alkaline earth metal hydroxide is used, preferably calcium hydroxide. The amount of the precipitation agent (S16) added depends on the amount of Al(OH)4 present in the solution. - and SiO4 2- Preferably, calcium hydroxide is added in an amount equivalent to 1 to 2 times the equivalent 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 unremoved Al(OH)4 - and SiO4 2- The amount of gypsum added will increase. If more than 2 times the equivalent is used, the process cost will increase. The amount of gypsum added is preferably 0.5 to 1 times the amount of calcium hydroxide added.

[0061] Additives such as calcium hydroxide and gypsum can be added in the wet ball milling process. In this case, the advantages are that the lithium leaching rate will increase and the process will become simpler, but the magnetic separation efficiency will decrease, the slurry will harden, and handling will become difficult.

[0062] (5) Solid-liquid separation process for Al and Si precipitation reaction products

[0063] The reactants of the Al and Si precipitation reaction (S15) are subjected to solid-liquid separation (S17) to separate the solid (S18) and the filtrate (S19). The solid (S18) contains poorly soluble CSH and CASH, ettringite as reaction products of the Al and Si precipitation reaction (S15), and the filtrate (S19) is a lithium leaching solution containing lithium. The solid-liquid separation (S17) 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 (S18) can be washed with clean water to minimize the loss of lithium contained therein, and then the washing water is mixed in the filtrate (S6) used for the Al and Si precipitation reaction (S15) and reused.

[0064] The filtrate (S19) separated by the solid-liquid separation (S17) is mostly water and lithium hydroxide, and contains less than 100 ppm of calcium (Ca 2+ ), aluminum (Al(OH)4 - ), silicon (SiO4 2- ). Carbon dioxide is injected (S20) to remove impurities in the filtrate (S19). When the carbon dioxide (S20) is injected into the filtrate (S19), the calcium is precipitated as calcium carbonate. The precipitated calcium carbonate can be further prepared by solid-liquid separation, but since it can be separated into solid by solid-liquid separation (S22) in the following evaporation and concentration process, it can be omitted.

[0065] (6) Evaporation concentration process

[0066] The filtrate (S19) from which the above impurities are precipitated is subjected to an evaporation concentration process (S21, S24, S26). The evaporation concentration process (S21, S24, S26) is a process for increasing the lithium concentration in the filtrate (S19) and removing residual impurities such as magnesium hydroxide and calcium carbonate by precipitation. Preferably, the evaporation concentration process (S21), the second evaporation concentration process (S24) and the third evaporation concentration process (S26) are composed of a first evaporation concentration process (S21), a second evaporation concentration process (S24) and a third evaporation concentration process (S26).

[0067] The primary evaporation concentration process (S21) refers to evaporating the filtrate (S19) under reduced pressure at 70° C. to 95° C. The primary evaporation concentration process (S21) can also be carried out under atmospheric pressure at 100° C., but in this case, it is important to purge nitrogen or argon to prevent carbon dioxide from contacting the evaporated concentrate.

[0068] Preferably, the primary evaporation and concentration process (S21) is performed from the moment when lithium hydroxide begins to precipitate until about 0.5% to 5% of the entire lithium hydroxide is precipitated. If the primary evaporation and concentration process (S21) is terminated before the amount of lithium hydroxide precipitated reaches 0.5%, the removal rate of impurities containing magnesium hydroxide, calcium carbonate, etc. will decrease, and if the concentration is concentrated to a precipitation amount greater than 5%, lithium hydroxide will be excessively precipitated and return to step S6) together with the impurities, so the process efficiency will decrease.

[0069] The lithium hydroxide concentrate prepared by the above-mentioned one-time evaporation concentration process (S21) is subjected to solid-liquid separation (S22). The above-mentioned solid-liquid separation (S22) is a process of separating magnesium hydroxide, calcium carbonate and the like, which are impurities precipitated in the above-mentioned one-time evaporation concentration process (S21), from the concentrate, and part of the lithium hydroxide may be precipitated together with the above-mentioned impurities. The above-mentioned solid-liquid separation (S22) can use a sedimentation tank, a filter press, a spiral filter, a centrifuge and the like, or a combination of two or more thereof to improve its efficiency.

[0070] The solid (S23) obtained from the solid-liquid separation (S22) is mixed with the filtrate (S6) obtained from the solid-liquid separation (S4) of the finely pulverized waste sagger and reused, thereby further recovering lithium hydroxide contained in the impurities.

[0071] The secondary evaporation concentration process (S24) is carried out on the filtrate obtained from the primary evaporation concentration process (S21) and its solid-liquid separation (S22) under the same conditions as the primary evaporation concentration process until 50% to 80% of the lithium hydroxide in the filtrate is precipitated. If the concentration is terminated before the lithium hydroxide precipitation reaches 50%, the recovery rate of lithium hydroxide will decrease and the process cost will increase. If the concentration is carried out so that the lithium hydroxide precipitation exceeds 80%, the purity of the recovered lithium hydroxide will decrease. The concentrated solution subjected to the secondary evaporation concentration process (S24) is subjected to solid-liquid separation (S25) to separate the lithium hydroxide with the solid (28). The solid-liquid separation (S25) 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.

[0072] The third evaporation and concentration process (S26) is a process in which the filtrate of the second evaporation and concentration process (S24) and the solid-liquid separation (S25) is further concentrated and then put into the evaporation and concentration process again to maximize the recovery rate of lithium hydroxide. The third evaporation and concentration process (S26) is carried out in the same method as the first and second evaporation and concentration processes (S21, S24) until 90% to 95% of the lithium hydroxide in the concentrated solution is precipitated. The solid generated by the third evaporation and concentration process (S26) is lithium hydroxide containing a small amount of the above impurities, which is mixed into the filtrate (S19) obtained by solid-liquid separation (S17) after the Al and Si precipitation reaction (S15) to dissolve, and then re-enter the first evaporation and concentration process. The liquid generated by the third evaporation and concentration process (S26) includes trace amounts of aluminum and silicon, which are put into the Al and Si precipitation reaction (S15) to remove them. If the concentration is terminated before the lithium hydroxide precipitation amount reaches 90%, the process cost of the Al, Si precipitation reaction (S15) will increase, and if the concentration is performed so that the lithium hydroxide precipitation amount exceeds 95%, the purity of the lithium hydroxide dissolved in the filtrate (S19) obtained by solid-liquid separation (S17) after the Al, Si precipitation reaction (S15) will be excessively reduced. Solid-liquid separation (S27) is a process for separating the lithium hydroxide generated in the three evaporation concentration processes (S26) from the aqueous solution. Generally, a sedimentation tank, a filter press, a spiral filter, a centrifuge, etc. can be used, or two or more of them can be combined to improve their efficiency. A series of concentration processes performed successively once, twice, and three times can be carried out in a separate concentration tank or in sequence in one concentration tank.

[0073] (7) Obtaining high-purity lithium hydroxide

[0074] The high-purity lithium hydroxide of the present invention is lithium hydroxide monohydrate with a purity of more than 99.9%, which is prepared by the following method: the solid (S28) obtained in the solid-liquid separation (S25) after the above-mentioned secondary evaporation concentration process (S24) is washed and filtered (S29), and the obtained solid is dried at 80°C to 100°C (S30) until the attached moisture content is less than 1%. The above-mentioned washing and filtering (S29) is washed with a high-purity lithium hydroxide saturated solution and then filtered, and the above-mentioned process is repeated about 3 times. The filtrate obtained in the above-mentioned three washing and filtering (S29) processes will be mixed with the filtrate (S19) obtained by solid-liquid separation (S17) after the above-mentioned Al and Si precipitation reaction (S15), and then put into the above-mentioned primary, secondary and tertiary evaporation concentration processes (S21, S24, S26) again.

[0075] 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 of this specification.

[0076] Industrial Applicability

[0077] By using the method for recovering positive electrode active material and lithium hydroxide from waste saggers of the present invention, high value-added lithium and positive electrode active material can be recovered from waste saggers discarded in the process of manufacturing lithium secondary batteries and reused.

Claims

1. A method for recovering positive electrode active material and lithium hydroxide from waste saggers, comprising: The first step is to wet-crush the waste sagger and perform solid-liquid separation; The second step is to apply wet magnetic separation to the solid obtained by the solid-liquid separation to recover the positive electrode active material; as well as The third step is to carry out Al and Si precipitation reaction and evaporation concentration on the filtrate obtained by the solid-liquid separation to recover lithium hydroxide.

2. The method for recovering positive electrode active material and lithium hydroxide from waste sagger according to claim 1, wherein: The wet pulverizing is to dry and pulverize the waste sagger and then perform wet ball milling to perform fine pulverization so that the particle size is less than 200 meshes.

3. The method for recovering positive electrode active material and lithium hydroxide from waste sagger according to claim 1, wherein: The wet magnetic separation is to remove iron oxide and iron scale as magnetically adsorbed products through a primary wet magnetic separation, and then perform a secondary wet magnetic separation on the non-magnetically adsorbed products of the primary wet magnetic separation, thereby recovering the positive electrode active material as the magnetically adsorbed product.

4. The method for recovering positive electrode active material and lithium hydroxide from waste sagger according to claim 1, wherein: The Al and Si precipitation reaction is to mix the hydroxide of alkaline earth metal and gypsum in the filtrate obtained by the solid-liquid separation to separate the water-soluble Al(OH)4 - The precipitation is insoluble calcium sulfonate and hydrated calcium aluminosilicate, and the water-soluble SiO4 2- The precipitate is insoluble calcium silicate hydrate.

5. The method for recovering positive electrode active material and lithium hydroxide from waste sagger according to claim 1, wherein: The evaporation concentration is to carry out the Al and Si precipitation reaction on the filtrate obtained by the solid-liquid separation, and then evaporate and concentrate the obtained filtrate after solid-liquid separation, so as to recover lithium hydroxide.

6. The method for recovering positive electrode active material and lithium hydroxide from waste sagger according to claim 5, wherein: The purity of the lithium hydroxide is above 99.9%.

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