Precipitate recovery method

Abstract

The present invention provides a precipitate recovery method, with which it is possible to efficiently recover a precipitate containing lithium from lithium that is contained in a composite oxide when lithium contained in a lithium ion battery is recovered.　Disclosed is a precipitate recovery method for recovering lithium that is contained in a composite oxide as a precipitate containing lithium. This precipitate recovery method includes: a first step for heating the composite oxide and chlorine or a chlorine compound and bringing the composite oxide and the chlorine or chlorine compound into contact with each other; a second step for adding deionized water to the composite oxide and the chlorine or chlorine compound that have been heated and brought into contact with each other in the first step, and recovering a primary filtrate by filtering the deionized water; a third step for adding an alkaline substance to the primary filtrate that is recovered in the second step so as to adjust the pH value, and recovering a secondary filtrate by filtering the primary filtrate after adding a carbonation substance to the primary filtrate; and a fourth step for recovering a precipitate, which is precipitated by performing a dehydration treatment and filtration of the secondary filtrate that is recovered in the third step, as a precipitate containing lithium.

Description

Precipitate recovery method

[0001] The present invention relates to a precipitate recovery method for recovering lithium contained in a composite oxide obtained by dissolving a lithium ion battery as a precipitate.

[0002] In recent years, the spread of electric vehicles has led to a rapid increase in demand for batteries that use lithium (hereinafter referred to as "lithium-ion batteries"). Furthermore, in light of the recent trend toward reducing carbon dioxide emissions, the demand for electric vehicles that do not use fossil fuels is expected to continue to expand, and as a result, the demand for lithium-ion batteries is also expected to increase further.

[0003] Lithium-ion batteries are formed using an exterior material made of a metal such as iron or aluminum. The interior of the exterior material contains a positive electrode material, which is aluminum foil with a positive electrode active material such as lithium nickel oxide, lithium cobalt oxide, or lithium manganese oxide adhered to it, and a negative electrode material, which is copper foil with a negative electrode active material such as graphite adhered to its surface. A separator, such as a porous polypropylene resin film, is provided between the positive electrode material and the negative electrode material, and the interior of the exterior material is filled with and sealed with an electrolyte solution such as lithium hexafluorophosphate.

[0004] Lithium-ion batteries are disposed of as waste lithium-ion batteries due to performance degradation caused by repeated charging and discharging, or due to the disposal of equipment. They are also disposed of as waste lithium-ion batteries when defective products are discovered during the manufacturing process. Therefore, with the increase in the number of electric vehicles manufactured in recent years, the number of disposed lithium-ion batteries (the number of waste lithium-ion batteries) manufactured for electric vehicles is expected to increase.

[0005] Waste lithium-ion batteries contain valuable metals such as copper, nickel, cobalt, and lithium. Therefore, technologies for recovering and recycling valuable metals from waste lithium-ion batteries are being developed as a measure to conserve resources and prevent environmental pollution.

[0006] For example, Patent Documents 1 and 2 disclose a method for recovering lithium carbonate from cathode materials of waste lithium-ion batteries, in which valuable metals such as nickel and cobalt are recovered by performing acid leaching and solvent extraction multiple times as hydrometallurgy, and then carbon dioxide gas is blown into the resulting solution. The method also discloses that the use of expensive hydrogen peroxide can be reduced, and the number of steps required for solvent extraction of manganese can be reduced.

[0007] Patent No. 6352846 Patent No. 6334450

[0008] However, in the inventions disclosed in Patent Documents 1 and 2, various valuable metals must be recovered individually and sequentially by hydrometallurgy until lithium is recovered from waste lithium-ion batteries, which poses a problem of low lithium recovery efficiency.

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a precipitate recovery method for recovering lithium contained in a lithium ion battery, which can efficiently recover lithium from lithium contained in a composite oxide as a lithium-containing precipitate.

[0010] [1] A method for recovering lithium contained in a composite oxide as a lithium-containing precipitate, the method comprising: a first step of heating and contacting the composite oxide with chlorine or a chlorine compound; a second step of adding deionized water to the heated and contacted composite oxide and chlorine or a chlorine compound in the first step and filtering the deionized water to recover a primary filtrate; a third step of adding an alkaline substance to the primary filtrate recovered in the second step to adjust the pH and adding a carbonated substance to the primary filtrate, and then filtering the primary filtrate to recover a secondary filtrate; and a fourth step of dehydrating and filtering the secondary filtrate recovered in the third step to recover the precipitate as a lithium-containing precipitate. [2] The method for recovering a precipitate according to [1], wherein the chlorine compound includes at least one of an alkali metal chloride and an alkaline earth metal chloride. [3] The precipitate recovery method according to [1] or [2], wherein the composite oxide is slag remaining after recovery of metals containing one or two elements selected from cobalt and nickel from molten metal obtained by dissolving lithium-ion batteries. [4] The precipitate recovery method according to any one of [1] to [3], further comprising a step of crushing the heated and contacted composite oxide and the chlorine or chlorine compound in the first step. [5] The precipitate recovery method according to any one of [1] to [4], wherein the chlorine or chlorine compound in the first step is adjusted so that the mass ratio of chloride to lithium contained in the composite oxide is 1.0 or more and 3.0 or less. [6] The precipitate recovery method according to any one of [1] to [5], further comprising a step of adding deionized water to the heated and contacted composite oxide and the chlorine or chlorine compound in the second step, and then stirring the deionized water. [7] The method for recovering a precipitate according to any one of [1] to [6], wherein in the second step, the temperature of the deionized water is 65° C. or higher. [8] The method for recovering a precipitate according to any one of [1] to [7], wherein in the third step, the pH value of the primary filtrate is adjusted to 10 or higher. [9] The method for recovering a precipitate according to any one of [1] to [8], wherein in the third step, the carbonated substance is carbon dioxide gas.

[10] The method for recovering a precipitate according to any one of [1] to [9], wherein in the third step, the steps of adjusting the pH value by adding the alkaline substance, adding the carbonated substance, and recovering the secondary filtrate are repeated multiple times.

[11] The method for recovering a precipitate according to any one of [1] to

[10] , wherein in the fourth step, the dehydration treatment is performed by adding an alcohol to the secondary filtrate.

[0011] According to the present invention, lithium contained in a lithium ion battery can be efficiently recovered as a precipitate containing lithium from the lithium contained in the composite oxide.

[0012] FIG. 1 is a diagram showing the verification results of the molten state of each valuable metal in pyrometallurgy. FIG. 2 is a schematic diagram showing an example of a precipitate recovery method in this embodiment. FIG. 3 is a diagram showing the form (abundance rate) of carbonate ions based on the pH value in the primary filtrate. FIG. 4 is a diagram showing the process flow of the precipitate recovery method in the example. FIG. 5 is a diagram showing the extraction rate of lithium into deionized water depending on whether or not the first step is performed. FIG. 6 is a diagram showing the proportion (distribution rate) of lithium contained in the precipitate etc. generated in the fourth step.

[0013] When recovering valuable metals from lithium-ion batteries, first, the lithium-ion batteries are subjected to pretreatment such as disassembly, removal of the electrolyte, and pulverization. Then, the pretreated lithium-ion batteries are subjected to dry refining or hydrometallurgy to recover the valuable metals.

[0014] Pyrometallurgy is a method of recovering valuable metals by applying heat to lithium-ion batteries and adding a reducing agent to promote an oxidation-reduction reaction, while hydrometallurgy is a method of recovering valuable metals by solvent extraction, which adds a solvent to lithium-ion batteries to extract valuable metals, or by electrochemical methods, which apply an electric potential to separate valuable metals.

[0015] The present inventors have focused on recovering valuable metals from the cathode material of lithium-ion batteries, particularly for the purpose of recovering lithium, in relation to a method for recovering valuable metals from the cathode material of lithium-ion batteries. First, when the cathode material of a lithium-ion battery is subjected to pyrometallurgy, the molten states of the metals nickel, cobalt, manganese, and lithium contained in the cathode material were examined. The molten state was examined by investigating the proportion (distribution ratio) of each metal contained in the molten alloy (metal), slag, etc. produced by pyrometallurgy. The results of the examination of the molten state of each valuable metal contained in the cathode material are shown in Figure 1.

[0016] As shown in Figure 1, it was confirmed that 100% of the lithium contained in the cathode material of a lithium-ion battery is incorporated into the molten slag produced by pyrometallurgy. It was also confirmed that most of the nickel and cobalt contained in the cathode material are incorporated into the molten metal (crude metal). Furthermore, it was also confirmed that most of the manganese contained in the cathode material is incorporated into the molten slag.

[0017] The present inventors have focused on a conventional method for recovering lithium from lithium ore (hydrometallurgy). The recovery of lithium from lithium ore involves first extracting lithium ore (mainly LiAl(SiO ３ ) ２ ) with an alkali metal (e.g., CaCl ２ , Na ２ SO ４ The lithium carbonate is then precipitated by adding sodium carbonate to the molten salt (see formula (2) below). ２ +2LiAl(SiO ３ ) ２ → CaAl ２ Si ２ O ８ +2LiCl...(1) 2LiCl+Na ２ CO ３ →2NaCl+LiCO ３ ...(2)

[0018] Based on these findings, the present inventors have discovered a method for efficiently recovering lithium from lithium-ion batteries. Specifically, they have conceived of combining pyrometallurgy of a cathode material with a method for recovering lithium from lithium ore (hydrometallurgy) using the slag that has absorbed all of the lithium produced by pyrometallurgy.

[0019] More specifically, by first subjecting the cathode material of a lithium-ion battery to pyrometallurgy, it is possible to separate it into a metal (crude metal) containing most of the nickel and cobalt and slag containing all of the lithium. In other words, it is possible to separate all of the lithium from most of the nickel and cobalt. It was then thought that by subjecting the slag containing all of the lithium to hydrometallurgy, it would be possible to recover most of the lithium as a precipitate. This would enable the final recovery rate of lithium used in the cathode material of a lithium-ion battery to be improved. Furthermore, hydrometallurgy of the slag makes it possible to selectively separate the manganese and lithium contained in the slag.

[0020] Next, an embodiment of the present invention will be described with reference to Fig. 2. Fig. 2 is a schematic diagram showing an example of a precipitate recovery method according to this embodiment. As shown in Fig. 2, the precipitate recovery method according to this embodiment includes first to fourth steps. The precipitate recovery method according to this embodiment is a method for recovering lithium contained in a composite oxide as a lithium-containing precipitate.

[0021] As the composite oxide, it is preferable to use slag remaining after metals containing one or two elements of cobalt and nickel are recovered from molten metal obtained by dissolving lithium ion batteries using a pyrometallurgical process.

[0022] This embodiment includes a first step of heating and contacting a composite oxide with chlorine or a chlorine compound. By heating and contacting a lithium-containing composite oxide with chlorine or a chlorine compound, the chlorination reaction of lithium can be promoted. In this case, for example, the composite oxide and chlorine or a chlorine compound may be charged into an electric furnace or an arc furnace, and contacted and heated to form a molten salt, thereby promoting the chlorination reaction of lithium.

[0023] In the first step, it is preferable to adjust the amount of chlorine or a chlorine compound so that the molar ratio of chloride to lithium contained in the composite oxide (Cl / Li) is 1.0 or more and 3.0 or less. By setting the molar ratio to 1.0 or more, the chlorination reaction of lithium can be promoted. Furthermore, by setting the molar ratio to 3.0 or less, a decrease in yield can be suppressed.

[0024] Here, the chlorine or chlorine compound may be adjusted by calculating the mass of lithium contained in the composite oxide before contacting it with the composite oxide, and adjusting the mass ratio of chloride to lithium to be 1.0 or more and 3.0 or less based on the calculated mass of lithium. The method for calculating the mass of lithium is not particularly limited as long as it allows for calculation of the mass of lithium contained in the composite oxide. For example, a portion of the composite oxide may be dissolved in acid, and measurement and calculation may be performed using inductively coupled plasma atomic emission spectroscopy (ICP-AES). Furthermore, in the process of producing the composite oxide, the mass concentration of lithium may be calculated based on the mass concentration of lithium contained in each raw material and the weight ratio of each raw material to the total raw materials.

[0025] The contact of the composite oxide with chlorine or a chlorine compound is preferably carried out at a temperature of 800°C or higher and 950°C or lower. This is because contact at a temperature lower than 800°C does not promote the chlorination reaction between lithium contained in the composite oxide and chloride. The contact of the composite oxide with chlorine or a chlorine compound is preferably carried out at a temperature of 800°C or higher, because the chlorination reaction between lithium and chloride is promoted at a higher temperature. Furthermore, contact at a temperature of 950°C or lower can promote the dissolution of lithium chloride into deionized water while suppressing volatilization, thereby suppressing a decrease in the lithium recovery rate.

[0026] Chlorine gas may be used as the chlorine. A metal chloride may be used as the chlorine compound. Specifically, the chlorine compound preferably includes at least one of an alkali metal chloride and an alkaline earth metal chloride. Alkaline earth metals also include beryllium and magnesium. These chlorine compounds and chlorine have higher boiling points than compounds of heavy metals and chlorine. Therefore, by setting the temperature during contact between the composite oxide and chlorine or the chlorine compound to 800°C or higher and 950°C or lower, volatilization of the chlorine compound and chlorine can be suppressed, and the production of lithium contained in the composite oxide as lithium chloride can be promoted.

[0027] The temperature during contact between the composite oxide and chlorine or the chlorine compound may be controlled as the temperature of the composite oxide, or may be controlled as the temperature of the atmosphere in a reaction vessel into which the composite oxide and chlorine or the chlorine compound are charged.

[0028] Preferably, the first step further includes a step of crushing the heated and contacted composite oxide and chlorine or a chlorine compound. Crushing the composite oxide and chlorine or a chlorine compound can further promote the dissolution of valuable metals such as lithium in deionized water in the subsequent second step. Various crushing devices, such as a jaw crusher, a vibration mill, or a ball mill, may be used as long as they can crush the oxide to a particle size (size) sufficient to promote the dissolution of valuable metals such as lithium in the subsequent step. From the viewpoint of improving the efficiency of the dissolution treatment in the subsequent step, the particle size after crushing is preferably 1.000 mm or less. Furthermore, from the viewpoint of reducing the scattering loss of the composite oxide and chlorine or a chlorine compound during crushing, a particle size of 0.050 mm or more is preferred.

[0029] This embodiment includes a second step of adding deionized water to the composite oxide and chlorine or a chlorine compound that have been heated and contacted in the first step, and filtering the deionized water to recover a primary filtrate. By adding deionized water to the composite oxide and chlorine or a chlorine compound in which the lithium chloride reaction has been promoted and filtering the mixture, it is possible to promote the dissolution of valuable metals such as lithium into the deionized water and the recovery of lithium as a filtrate.

[0030] In the second step, the temperature of the deionized water is preferably 65°C or higher. This is because if the temperature of the deionized water is lower than 65°C, dissolution of lithium chloride produced by the chlorination reaction in the first step is not promoted. Moreover, from the viewpoint of promoting dissolution of lithium chloride, the upper limit of the temperature of the deionized water is preferably 100°C or lower, more preferably 90°C or lower, and even more preferably 85°C or lower. From the viewpoint of promoting dissolution of lithium chloride, the temperature of the deionized water is most preferably 70°C or higher and 80°C or lower.

[0031] The second step preferably further includes a step of stirring the deionized water after adding the deionized water to the heated and contacted composite oxide and chlorine or chlorine compound, because stirring the deionized water can further promote the dissolution of lithium chloride in the deionized water.

[0032] In this embodiment, there is provided a third step of adding an alkaline substance to the primary filtrate recovered in the second step to adjust the pH value, and adding a carbonated substance to the primary filtrate, and then filtering the primary filtrate to recover a secondary filtrate. That is, by adjusting the pH value of the primary filtrate to fall within a predetermined range prior to the addition of the carbonated substance to the primary filtrate, the recovery efficiency of the precipitate as lithium carbonate in the fourth step can be improved.

[0033] In the third step, it is preferable to adjust the pH value of the primary filtrate to 10 or more. Here, the form (abundance rate) of carbonate ions based on the pH value in the primary filtrate will be explained using FIG. 3. FIG. 3 is a diagram showing the form (abundance rate) of carbonate ions based on the pH value in the primary filtrate. As shown in FIG. 3, when the pH value is less than 10, carbonate ions (CO ３２－ ) compared to bicarbonate ions (HCO ３ － ) becomes stable, making it difficult to recover lithium as carbonate in a subsequent step. The upper limit of the pH value is also preferably 14 or less, more preferably 13 or less, and most preferably about 12, from the viewpoint of recovering lithium as carbonate.

[0034] In the third step, the addition of a carbonating substance is sodium carbonate (Na ２ CO ３ In the third step, the carbonation substance is preferably carbon dioxide gas in order to prevent excess alkali metal ions from being mixed into the primary filtrate.

[0035] Regarding the addition of carbonation substances, sodium carbonate (Na ２ CO ３ When the addition of sodium carbonate is employed, it is preferable to add an amount of sodium carbonate (lithium equivalent) that enables the carbonation treatment of the amount of lithium contained in the primary filtrate recovered in the second step, taking into account the amount of lithium contained in the primary filtrate. In this case, the amount of lithium contained in the primary filtrate may first be measured by ICP atomic emission spectroscopy. Then, it is preferable to add an amount of sodium carbonate of "a / 2 moles" as a "lithium equivalent" relative to the measured amount of lithium "a moles." By adjusting the amount of sodium carbonate to be added to the "lithium equivalent" based on the amount of lithium contained in the primary filtrate, it is possible to promote the carbonation of lithium and avoid excessive addition (use) of sodium carbonate.

[0036] When adding the carbonated substance by blowing carbon dioxide gas, it is preferable to blow carbon dioxide gas at a rate of 2 NL per minute for a predetermined time (60 minutes) into the primary filtrate recovered in Step 2. Blowing carbon dioxide gas at a rate of 2 NL per minute for 60 minutes promotes the carbonation of lithium and also allows the supply of carbon dioxide gas to be just enough to accommodate the amount of lithium contained in the primary filtrate.

[0037] From the viewpoint of improving the recovery rate of lithium, it is preferable to perform the steps of adjusting the pH value by adding an alkaline substance, adding a carbonated substance, and recovering the secondary filtrate multiple times in the third step. More specifically, it is preferable to adjust the pH value of the primary filtrate and add a carbonated substance to recover the secondary filtrate, and then adjust the pH value of the recovered secondary filtrate again, add a carbonated substance, and recover the filtrate by filtration. In the third step, due to the addition of the carbonated substance, carbonation of calcium occurs simultaneously with the carbonation of lithium. Therefore, when the number of filtration steps is small (for example, about once), the amount of calcium carbonate precipitated increases.

[0038] The third step preferably includes a step of stirring the primary filtrate when adjusting the pH value by adding an alkaline substance and adding a carbonated substance, as shown in Fig. 2. That is, by stirring the primary filtrate, the pH value can be adjusted more efficiently, and the recovery efficiency of lithium as carbonate in the subsequent fourth step can be improved.

[0039] This embodiment includes a fourth step of recovering, as a precipitate containing lithium, a precipitate formed by dehydrating and filtering the secondary filtrate recovered in the third step. The secondary filtrate that has been subjected to the third step has had its pH adjusted and has had a carbonation substance added thereto. Therefore, during the treatment in the fourth step, it is possible to improve the recovery efficiency of the precipitate as lithium carbonate.

[0040] In the fourth step, the dehydration treatment may be carried out by adding alcohol, boiling, or the like. From the viewpoint of improving the recovery efficiency of the precipitate, it is preferable to carry out the dehydration treatment by adding alcohol to the secondary filtrate, and it is more preferable to carry out the dehydration treatment by adding ethanol. That is, by adding ethanol to the secondary filtrate, the recovery efficiency of the precipitate as lithium carbonate can be further improved. Furthermore, when the secondary filtrate is boiled, lithium contained in the secondary filtrate can be concentrated above its solubility and precipitated.

[0041] The fourth step preferably includes a step of stirring the secondary filtrate when carrying out the dehydration treatment, as shown in Fig. 2. By stirring the secondary filtrate, the recovery efficiency of the precipitate as lithium carbonate can be further improved.

[0042] As described above, according to the present invention, lithium contained in a lithium-ion battery can be efficiently recovered as a lithium-containing precipitate from the lithium contained in the composite oxide. In particular, in the first step, the composite oxide containing all of the lithium produced by pyrometallurgy is heated and brought into contact with chlorine or a chlorine compound, thereby promoting the chlorination reaction of all of the lithium contained in the cathode material. Then, by adjusting the pH value in the third step and performing a dehydration treatment in the fourth step, the recovery efficiency of the precipitate as lithium carbonate can be improved.

[0043] Next, an example in which the deposit recovery method of the present invention was implemented will be described. First, prior to implementing the present invention, used lithium ion batteries (waste lithium ion batteries) were subjected to pyrometallurgy. Specifically, the waste lithium ion batteries were subjected to pretreatments such as disassembly, discharge, and removal of the electrolyte. Thereafter, the cathode material of the waste lithium ion batteries was placed in an electric furnace together with a reducing agent and a flux, and subjected to a heat treatment in an inert gas atmosphere (Ar gas atmosphere) for a predetermined time, thereby performing a metal reduction treatment from the cathode material. Thereafter, the metal and slag produced by the pyrometallurgy were separated, and metals (nickel and cobalt) were recovered from the metal. The flux used was calcium oxide (CaO) and silicon dioxide (SiO ２ The reducing agent and flux were added to the cathode material of the waste lithium ion battery in a mass percentage ratio of CaO / SiO ２ The experiment was carried out under the condition that ρ=0.5.

[0044] A portion of the chemical composition of the cathode material after pretreatment is shown in Table 1. The chemical composition of the slag produced by pyrometallurgy is shown in Table 2, and the mineral phases of the slag are shown in Table 3. The mineral phases shown in Table 3 were measured by X-ray diffraction.

[0045]

[0046]

[0047]

[0048] Next, the precipitate recovery method of the present invention was carried out on slag (complex oxide) produced by pyrometallurgy. The process flow of the precipitate recovery method carried out in the examples is shown in Figure 4. As shown in Figure 4, in Examples 1 to 6 described below, a first step was carried out in which slag as a composite oxide produced by pyrometallurgy and a chlorine compound (calcium chloride) were heated and brought into contact with each other to form a molten salt. When carrying out the first step, a step of crushing the heated and contacted slag and calcium chloride was also carried out.

[0049] In addition, a second step was performed in which deionized water was added to the crushed object and stirred to cause water leaching, and the deionized water was filtered (primary filtration) to recover the primary filtrate. Furthermore, an alkaline substance (sodium hydroxide) was added to the primary filtrate to adjust the pH value, and a carbonated substance was added (addition of sodium carbonate or blowing in carbon dioxide gas) to perform a carbonation treatment. A third step was performed in which the primary filtrate was filtered (secondary filtration) to recover the secondary filtrate, and this process was repeated once or multiple times. The secondary filtrate was then dehydrated (by boiling or addition of ethanol) and filtered to recover a precipitate containing lithium. Table 4 shows the specific treatment details for each example performed for the purpose of recovering lithium.

[0050]

[0051] As shown in Table 4, in the first step of Example 1, calcium chloride (chlorine compound) was adjusted so that the mass ratio (Cl / Li) of chloride to lithium contained in the slag (composite oxide) was 1.5, and the slag was brought into contact with the composite oxide and roasted at a temperature of 800°C. In the first step, crushing was also performed using a jaw crusher to a crushed particle size of 0.500 mm. In the second step, the slag was immersed in deionized water at 70°C for a predetermined time (90 minutes) while stirring, and then filtered (primary filtration) to recover the primary filtrate. In the third step, an alkaline substance (sodium hydroxide: NaOH) was added so that the pH value of the primary filtrate became 12.0, and a carbonated substance (sodium carbonate: NaOH) equivalent to the lithium was added. ２ CO ３ ) was added, and filtration (secondary filtration) was performed to recover a secondary filtrate. In the third step, the filtration was repeated once. In the fourth step, the secondary filtrate was subjected to dehydration (boiling) and filtration, and a precipitate containing lithium was recovered.

[0052] In Example 2, in the first step, calcium chloride (chlorine compound) was adjusted so that the mass ratio (Cl / Li) of chloride to lithium contained in the slag (composite oxide) was 2.0, and the slag was brought into contact with the slag and roasted at a temperature of 900°C. In the first step, crushing was also performed using a jaw crusher, and the crushed particle size was 0.250 mm. In the second step, the slag was immersed in deionized water at 75°C for a predetermined time (80 minutes) while being stirred, and then filtered (primary filtration) to recover the primary filtrate. In the third step, an alkaline substance (sodium hydroxide: NaOH) was added so that the pH value of the primary filtrate became 11.0, and a carbonated substance (sodium carbonate: NaOH) equivalent to the lithium was added. ２ CO ３ ) was added, and filtration (secondary filtration) was performed to recover a secondary filtrate. In the third step, the filtration was repeated once. In the fourth step, the secondary filtrate was subjected to dehydration (boiling) and filtration, and a precipitate containing lithium was recovered.

[0053] In Example 3, in the first step, calcium chloride (chlorine compound) was adjusted so that the mass ratio (Cl / Li) of chloride to lithium contained in the slag (composite oxide) was 1.8, and the mixture was brought into contact with the slag and roasted at a temperature of 850°C. In the first step, crushing was also performed using a vibration mill to achieve a particle size of 0.100 mm after crushing. In the second step, the mixture was immersed in deionized water at 80°C for a predetermined time (90 minutes) while stirring, and then filtered (primary filtration) to recover the primary filtrate. In the third step, an alkaline substance (sodium hydroxide: NaOH) was added so that the pH value of the primary filtrate became 12.0, and carbon dioxide gas (CO ) was introduced at a rate of 2 NL per minute. ２ ) was added for a predetermined time (60 minutes), followed by filtration (secondary filtration) to recover a secondary filtrate. In the third step, the filtration was repeated three times. In the fourth step, the secondary filtrate was dehydrated (by adding ethanol) and filtered, and a precipitate containing lithium was recovered.

[0054] In Example 4, in the first step, calcium chloride (chlorine compound) was adjusted so that the mass ratio of chloride to lithium (Cl / Li) contained in the slag (composite oxide) was 1.3, and the mixture was brought into contact with the slag and roasted at a temperature of 950°C. In the first step, crushing was also performed using a vibration mill to achieve a particle size of 0.080 mm after crushing. In the second step, the mixture was immersed in deionized water at 80°C for a predetermined time (85 minutes) while stirring, and then filtered (primary filtration) to recover the primary filtrate. In the third step, an alkaline substance (sodium hydroxide: NaOH) was added so that the pH value of the primary filtrate became 11.5, and carbon dioxide gas (CO ) was introduced at a rate of 2 NL per minute. ２ ) was added for a predetermined time (60 minutes), followed by filtration (secondary filtration) to recover a secondary filtrate. In the third step, the filtration was repeated three times. In the fourth step, the secondary filtrate was dehydrated (by adding ethanol) and filtered, and a precipitate containing lithium was recovered.

[0055] In Example 5, in the first step, calcium chloride (chlorine compound) was adjusted so that the mass ratio (Cl / Li) of chloride to lithium contained in the slag (composite oxide) was 1.1, and the slag was brought into contact with the lithium slag and roasted at a temperature of 800°C. In the first step, the slag was also crushed using a vibration mill to a particle size of 0.075 mm after crushing. In the second step, the slag was immersed in deionized water at 80°C for a predetermined time (90 minutes) while stirring, and then filtered (primary filtration) to recover the primary filtrate. In the third step, an alkaline substance (sodium hydroxide: NaOH) was added so that the pH value of the primary filtrate became 12.0, and carbon dioxide gas (CO ) was introduced at a rate of 2 NL per minute. ２ ) was added for a predetermined time (60 minutes), followed by filtration (secondary filtration) to recover a secondary filtrate. In the third step, the filtration was repeated three times. In the fourth step, the secondary filtrate was dehydrated (by adding ethanol) and filtered, and a precipitate containing lithium was recovered.

[0056] In Example 6, in the first step, calcium chloride (chlorine compound) was adjusted so that the mass ratio (Cl / Li) of chloride to lithium contained in the slag (composite oxide) was 3.0, and the slag was brought into contact with the lithium slag and roasted at a temperature of 800°C. In the first step, the slag was also crushed using a vibration mill to a particle size of 0.050 mm after crushing. In the second step, the slag was immersed in deionized water at 80°C for a predetermined time (90 minutes) while stirring, and then filtered (primary filtration) to recover the primary filtrate. In the third step, an alkaline substance (sodium hydroxide: NaOH) was added so that the pH value of the primary filtrate became 12.0, and carbon dioxide gas (CO ) was introduced at a rate of 2 NL per minute. ２ ) was added for a predetermined time (60 minutes), followed by filtration (secondary filtration) to recover a secondary filtrate. In the third step, the filtration was repeated four times. In the fourth step, the secondary filtrate was dehydrated (by addition of ethanol) and filtered, and a precipitate containing lithium was recovered.

[0057] The comparative example was based on the inventions described in Patent Documents 1 and 2 as prior art, and targeted cathode material for waste lithium-ion batteries. The solution obtained after solvent extraction of nickel and cobalt by hydrometallurgy was subjected to the addition of an alkaline agent and subsequent injection of carbon dioxide gas to recover lithium. Specifically, the cathode material for waste lithium-ion batteries was first leached for a predetermined time (90 minutes) at a temperature of 20°C with the addition of hydrogen peroxide and sulfuric acid, and solvent extraction with an organic acid was then performed multiple times. Next, an alkaline substance (sodium hydroxide: NaOH) was added to the residual solution after solvent extraction so that the pH value was 12.0, and carbon dioxide gas (CO ) was injected at a rate of 2 NL per minute. ２ ) was added over a predetermined time (60 minutes). Thereafter, the residual liquid was filtered once to recover lithium.

[0058] Then, for Examples 1 to 6 and the Comparative Example, the "lithium recovery rate (%)" was calculated using the following formula (3). The calculated "lithium recovery rate (%)" means the ratio (%) of the amount of lithium (mass%) contained in the precipitate recovered in the final step of each Example to the amount of lithium (mass%) contained in the slag (composite oxide) produced by pyrometallurgy. The results of calculating the "lithium recovery rate (%)" for each Example are shown in Table 5. Lithium recovery rate (%) = Amount of lithium contained in final precipitate (mass%) / Amount of lithium contained in slag after pyrometallurgy (mass%) ... (3)

[0059]

[0060] As shown in Table 5, it was confirmed that the "lithium recovery rate (%)" was 50% or more in all of the inventive examples. On the other hand, it was also confirmed that the "lithium recovery rate (%)" was only about 40% in the comparative examples.

[0061] Next, the inventors investigated the state of dissolution of lithium in deionized water (extraction rate) in the second step and the proportion (distribution rate) of lithium contained in the precipitates and the like formed at the end of the fourth step, which are affected by the presence or absence of the first step in which the slag (composite oxide) is brought into contact with calcium chloride (chlorine compound) and heated.

[0062] Specifically, in the implementation of Example 3, the state of dissolution of lithium in deionized water (extraction rate) was calculated for the primary filtrate recovered in Step 2. Next, the proportion of lithium contained in the precipitates and the like generated in Step 4 (distribution rate) was calculated. The results of the verification are shown in Figures 5 and 6.

[0063] As shown in Figure 5, by contacting and heating the slag (composite oxide) with calcium chloride (chlorine compound) in the first step, it was confirmed that the extraction rate of lithium into deionized water in the second step was 80% or more in the present invention (with first step), compared to the extraction rate (6.8%) in the conventional method (without first step). Furthermore, based on this result, as shown in Figure 6, it was also confirmed that approximately 50% or more of lithium was incorporated into the precipitate generated in the fourth step.

Claims

1. A precipitate recovery method for recovering lithium contained in a complex oxide as a lithium-containing precipitate, comprising: a first step of heating and contacting the complex oxide with chlorine or a chlorine compound; a second step of adding deionized water to the complex oxide and chlorine or a chlorine compound that have been heated and contacted in the first step and filtering the deionized water to recover a primary filtrate; a third step of adding an alkaline substance to the primary filtrate recovered in the second step to adjust the pH value, and adding a carbonated substance to the primary filtrate, and then filtering the primary filtrate to recover a secondary filtrate; and a fourth step of dehydrating and filtering the secondary filtrate recovered in the third step to recover the precipitate as a lithium-containing precipitate.

2. The method for recovering precipitate according to claim 1, wherein the chlorine compound includes at least one of an alkali metal chloride and an alkaline earth metal chloride.

3. A method for recovering precipitates according to claim 1 or 2, wherein the composite oxide is slag remaining after metals containing one or two of cobalt and nickel are recovered from molten metal obtained by dissolving lithium-ion batteries in a process for recovering the metals.

4. A method for recovering precipitate according to any one of claims 1 to 3, further comprising a step of crushing the composite oxide and the chlorine or chlorine compound that have been heated and contacted in the first step.

5. A method for recovering precipitates according to any one of claims 1 to 4, wherein in the first step, the chlorine or chlorine compound is adjusted so that the ratio of chloride to lithium contained in the composite oxide is 1.0 or more and 3.0 or less.

6. The precipitate recovery method according to any one of claims 1 to 5, further comprising the step of adding deionized water to the heated and contacted composite oxide and the chlorine or chlorine compound in the second step, and then stirring the deionized water.

7. A method for recovering precipitate according to any one of claims 1 to 6, wherein in the second step, the temperature of the deionized water is 65°C or higher.

8. A method for recovering precipitate according to any one of claims 1 to 7, wherein in the third step, the pH value of the primary filtrate is adjusted to 10 or higher.

9. A method for recovering precipitate according to any one of claims 1 to 8, wherein in the third step, the carbonated substance is carbon dioxide gas.

10. A precipitate recovery method according to any one of claims 1 to 9, wherein in the third step, the steps of adjusting the pH value by adding the alkaline substance, adding the carbonated substance, and recovering the secondary filtrate are carried out multiple times.

11. A method for recovering precipitate according to any one of claims 1 to 10, wherein in the fourth step, the dehydration treatment is carried out by adding an alcohol to the secondary filtrate.

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