Method for recovering lithium from lithium-ion secondary batteries

Abstract

To provide a method for recovering lithium from a lithium ion secondary battery, enabling suppression of lithium loss occurring when concentrating lithium leachate obtained by leaching the lithium ion secondary battery with water thereby enabling recovery of high purity lithium at a high recovery rate.SOLUTION: A method for recovering lithium from a lithium ion secondary battery is provided, including: a heat treatment step of heating a lithium ion secondary battery including at least one of cobalt, nickel and manganese at 700°C or higher; a crushing step of crushing the heat treated object of the lithium ion secondary battery obtained in the heat treatment step; a classification step of classifying the crushed object obtained in the crushing step, at a classification point of 0.6 mm or more and 2.4 mm or less to obtain a coarse grain product and a fine grain product; a lithium leaching step of leaching lithium included in the recovered fine grain product into water to obtain a lithium leachate having a lithium concentration of less than 1,500 mg / L; and a membrane separation step of forming the lithium leachate as a first lithium concentrate using a nano filtration (NF) membrane or a reverse osmosis (RO) membrane.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for recovering lithium from a lithium ion secondary battery. [Background technology]

[0002] Lithium-ion secondary batteries are lightweight, have a high capacity, and have a high electromotive force compared to conventional lead-acid batteries and nickel-cadmium secondary batteries, and are used as secondary batteries for personal computers, electric vehicles, mobile devices, etc. The positive electrode of a lithium-ion secondary battery contains valuable materials such as cobalt and nickel, and is made of lithium cobalt oxide (LiCoO2), ternary positive electrode materials (LiNi x Co y Mn z O2(x+y+z=1)) and so on.

[0003] As the use of lithium-ion secondary batteries is expected to continue to expand, from the perspective of resource recycling, it is desirable to recover valuable materials such as lithium from lithium-ion secondary batteries that are discarded due to defective products generated during the manufacturing process or due to the end of the lifespan of the devices they are used in or the batteries. When recovering valuable materials such as lithium from lithium-ion secondary batteries, it is important to separate and recover the various metals and impurities used in the lithium-ion secondary batteries in order to increase the value of the recovered materials. In particular, when lithium carbonate recovered from discarded lithium-ion secondary batteries is used as a battery material, lithium carbonate with a high impurity content is required, because the electrical properties of the lithium carbonate deteriorate if it contains a large amount of impurities.

[0004] As a technique for recovering lithium carbonate from lithium ion secondary batteries while suppressing the incorporation of impurities, for example, a method has been proposed in which used lithium ion secondary batteries are calcined and lithium is leached into water to produce lithium carbonate from the resulting solution (see, for example, Patent Document 1). In this proposed technique, for example, used lithium ion secondary batteries are calcined, and the resulting solution, obtained by leaching lithium into water, is stored in a crystallization tank containing an anode and a cathode, and an electric current is passed through the solution containing lithium ions and carbonate ions to precipitate lithium carbonate at and near the cathode, and lithium is recovered as lithium carbonate salt. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5872788 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the conventional technology described in Patent Document 1 has a problem in that the recovery rate of lithium carbonate is insufficient due to insufficient concentration of lithium near the cathode.

[0007] The present invention aims to solve the problems of the prior art and achieve the following object: That is, the present invention aims to provide a method for recovering lithium from a lithium ion secondary battery, which can suppress lithium loss when concentrating a lithium leachate obtained by leaching a lithium ion secondary battery with water, and recover high-purity lithium at a high recovery rate. [Means for solving the problem]

[0008] The means for solving the above problems are as follows: <1> a heat treatment step of heating a lithium ion secondary battery containing at least one of cobalt, nickel, and manganese at 700°C or higher; a crushing step of crushing the heat-treated lithium ion secondary battery obtained in the heat treatment step; a classification step of classifying the crushed material obtained in the crushing step at a classification point of 0.6 mm or more and 2.4 mm or less to obtain a coarse product and a fine product; a lithium leaching step in which lithium contained in the fine granule product recovered in the classification step is leached into water to obtain a lithium leachate having a lithium concentration of less than 1,500 mg / L; a membrane separation step of subjecting the lithium leachate to a first lithium concentrate using a nanofiltration (NF) membrane or a reverse osmosis (RO) membrane; The present invention relates to a method for recovering lithium from a lithium ion secondary battery, the method comprising the steps of: <2> The lithium leaching solution has a fluorine concentration of 20 mg / L or more and a pH of 10.5 or more. <1> This is a method for recovering lithium from the lithium ion secondary battery described in 1. <3> The first lithium concentrated solution has a lithium concentration of 1,500 mg / L or more and less than 4,000 mg / L, and a liquid temperature of 50°C or less. <1> or <2> This is a method for recovering lithium from the lithium ion secondary battery described in 1. <4> a fluorine removal step of adding calcium hydroxide to the first lithium concentrated solution and removing solidified fluorine by solid-liquid separation to obtain a fluorine-removed solution, <1> from <3> 1. A method for recovering lithium from the lithium ion secondary battery according to any one of the above. <5> a calcium removal step of removing calcium ions in the first lithium concentrated solution with a cation exchange resin to obtain a calcium-removed solution having a calcium concentration of 10 mg / L or less. <4> This is a method for recovering lithium from the lithium ion secondary battery described in 1. <6> The method further comprises the step of performing electrodialysis either before or after the calcium removal step, or both before and after the calcium removal step, to obtain a second lithium concentrate having a lithium concentration of 4,000 mg / L or more. <5> This is a method for recovering lithium from the lithium ion secondary battery described in 1. <7> a lithium carbonate recovery step of heating the calcium-removed solution or the second lithium concentrated solution and adding carbon dioxide at 60°C or higher to recover lithium carbonate, <5> or <6> This is a method for recovering lithium from the lithium ion secondary battery described in 1. <8> the fluorine content in the leaching residue after the lithium leaching step is 3% or less; <1> from <7> 1. A method for recovering lithium from the lithium ion secondary battery according to any one of the above. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a method for recovering lithium from a lithium ion secondary battery, which can suppress lithium loss when concentrating a lithium leachate obtained by leaching a lithium ion secondary battery with water, and can recover high-purity lithium at a high recovery rate. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a flow diagram showing an example of the method of recovering lithium from a lithium ion secondary battery according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] (Lithium recovery method) The method for recovering lithium from a lithium ion secondary battery of the present invention includes a heat treatment step, a crushing step, a classification step, a lithium leaching step, and a membrane separation step, and preferably includes a fluorine removal step, a calcium removal step, an electrodialysis step, and a lithium carbonate recovery step, and may further include other steps as necessary.

[0012] In the prior art disclosed in the above Patent Document 1 (Japanese Patent No. 5872788), electrophoresis is used as a method for concentrating lithium and removing impurities such as fluorine, but electrophoresis not only requires complicated steps to carry out, but also has the problem of high implementation costs, since lithium is concentrated near the cathode. Furthermore, when the present inventors conducted follow-up tests on the technology disclosed in the above Patent Document 1, they found that it was difficult to achieve a lithium recovery rate of 50% or more, as shown in Comparative Example 2 described below.

[0013] As described above, the present inventors have found that the conventional techniques have a problem in that the recovery rate of lithium may be low when concentrating lithium in the lithium leachate. Therefore, the present inventors have further intensively investigated a lithium recovery method capable of recovering lithium from a lithium leachate at a high recovery rate. As a result, they have found that a method for recovering lithium from a lithium ion secondary battery, which includes: a heat treatment step of heating a lithium ion secondary battery containing at least one of cobalt, nickel, and manganese at 700°C or higher; a crushing step of crushing the heat-treated lithium ion secondary battery obtained in the heat treatment step; a classification step of classifying the crushed product obtained in the crushing step at a classification point of 0.6 mm or more and 2.4 mm or less to obtain a coarse particle product and a fine particle product; a lithium leaching step of leaching lithium contained in the fine particle product recovered in the classification step into water to obtain a lithium leachate having a lithium concentration of less than 1,500 mg / L; and a membrane separation step of converting the lithium leachate into a first lithium concentrate using a nanofiltration (NF) membrane or a reverse osmosis (RO) membrane, can suppress lithium loss during concentration and recover a high-purity lithium salt from the lithium concentrate, which led to the present invention.

[0014] <Heat treatment process> The heat treatment step is a step of heat treating (roasting) a lithium ion secondary battery containing at least one of cobalt, nickel, and manganese at 700° C. or higher.

[0015] -Lithium-ion secondary battery- The lithium ion secondary battery is not particularly limited and can be appropriately selected depending on the purpose. Examples include defective lithium ion secondary batteries generated during the manufacturing process of lithium ion secondary batteries, lithium ion secondary batteries discarded due to a defect in the equipment used or the end of the life of the equipment used, and used lithium ion secondary batteries discarded due to the end of the life of the equipment.

[0016] The shape, structure, size and material of the lithium ion secondary battery are not particularly limited and can be appropriately selected depending on the purpose. The shape of the lithium ion secondary battery is not particularly limited and can be appropriately selected depending on the purpose. Examples include laminate type, cylindrical type, button type, coin type, square type, and flat type. Examples of lithium-ion secondary batteries include those including a positive electrode, a negative electrode, a separator, an electrolytic solution containing an electrolyte and an organic solvent, and an outer container that is a battery case that houses the positive electrode, the negative electrode, the separator, and the electrolytic solution. When the secondary battery is covered with the outer container, the inside of the secondary battery is likely to be reduced by carbon derived from the negative electrode active material during heat treatment. Note that the lithium-ion secondary battery may be in a state in which the positive electrode, the negative electrode, etc. have fallen off. The form of the lithium-ion secondary battery is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include a battery cell, a battery module, and a battery pack. Here, a battery module refers to a battery in which a plurality of battery cells, which are unit batteries, are connected and assembled into a single housing, and a battery pack refers to a battery in which a plurality of battery modules are assembled into a single housing. The battery pack may also include a controller and a cooling device.

[0017] --Positive electrode-- The positive electrode is not particularly limited as long as it has a positive electrode active material, and can be appropriately selected depending on the purpose. The shape of the positive electrode is not particularly limited and can be appropriately selected depending on the purpose. Examples include a flat plate shape and a sheet shape.

[0018] ---Positive electrode current collector--- The shape, structure, size, material, etc. of the positive electrode current collector are not particularly limited and can be appropriately selected depending on the purpose. The positive electrode current collector may be in the form of, for example, a foil. Examples of materials for the positive electrode current collector include stainless steel, nickel, aluminum, copper, titanium, tantalum, etc. Among these, aluminum is preferred.

[0019] The positive electrode material is not particularly limited and can be appropriately selected depending on the purpose. For example, it preferably contains at least a positive electrode active material containing lithium, a conductive agent, and a binder resin, and further contains other components as necessary. Examples of the positive electrode active material include lithium manganese oxide (LiMn2O4), lithium cobalt oxide (LiCoO2), and lithium cobalt nickel oxide (LiCo 1 / 2 Ni 1 / 2 O2), ternary and NCM systems, etc. x Co y Mn z O2(x+y+z=1), LiNi, also known as NCA system x Co y Al z (x+y+z=1), lithium iron phosphate (LiFePO4), lithium titanate (Li2TiO3), etc. Among these, lithium manganese oxide, lithium cobalt oxide, lithium cobalt nickel oxide (LiCo 1 / 2 Ni 1 / 2 O2), ternary systems, NCM systems, etc. x Co y Mn z O2(x+y+z=1), LiNi, also known as NCA system x Co y Al z (x+y+z=1) is preferred because it allows lithium to be easily converted into a water-soluble form by heat treatment. The conductive agent is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include carbon black, graphite, carbon fiber, and metal carbides. The binder resin is not particularly limited and can be appropriately selected depending on the purpose. Examples include homopolymers or copolymers of vinylidene fluoride, tetrafluoroethylene, acrylonitrile, ethylene oxide, and the like, and styrene-butadiene rubber.

[0020] --Negative electrode-- The negative electrode is not particularly limited as long as it has a negative electrode active material, and can be appropriately selected depending on the purpose. The shape of the negative electrode is not particularly limited and can be appropriately selected depending on the purpose. Examples include a flat plate shape and a sheet shape.

[0021] ---Negative electrode current collector--- The shape, structure, size, material, etc. of the negative electrode current collector are not particularly limited and can be appropriately selected depending on the purpose. The negative electrode current collector may be in the form of, for example, a foil. Examples of materials for the negative electrode current collector include stainless steel, nickel, aluminum, copper, titanium, and tantalum, with copper being preferred among these.

[0022] The negative electrode material is not particularly limited and can be appropriately selected depending on the purpose. Examples include carbon materials such as graphite and hard carbon, and titanates.

[0023] The temperature in the heat treatment (heat treatment temperature) is 700°C or higher, preferably 750°C or higher and 1,080°C or lower, and more preferably 750°C or higher and 900°C or lower. By setting the heat treatment temperature to 700°C or higher, the lithium in Li(Ni / Co / Mn)O2 in the positive electrode active material and LiPF6 in the electrolyte can be converted into substances in a form in which lithium is soluble in aqueous solution, such as lithium fluoride (LiF), lithium carbonate (Li2CO3), and lithium oxide (Li2O), and impurities other than fluorine can be separated during lithium leaching. The heat treatment temperature refers to the temperature of the lithium ion secondary battery during the heat treatment. The heat treatment temperature can be measured by inserting a thermometer such as a couple or thermistor into the lithium ion secondary battery at the heat treatment temperature.

[0024] The time for heat treating a lithium-ion secondary battery (heat treatment time) is not particularly limited and can be selected appropriately depending on the purpose, but is preferably from 1 minute to 5 hours, and more preferably from 1 minute to 2 hours. The heat treatment time may be any time that allows the lithium-containing compound to reach the desired temperature, and by slowing the rate of temperature increase, the formation of insoluble lithium oxides can be suppressed and the lithium leaching rate can be improved. Furthermore, the time for maintaining the temperature after heating may be short. The heat treatment time is preferably within the above range, which is advantageous in terms of the cost required for the heat treatment and the productivity in producing the lithium solution.

[0025] The heat treatment method is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include a method using a roasting furnace. The roasting furnace is not particularly limited and can be appropriately selected depending on the purpose. Examples include batch furnaces such as rotary kilns, fluidized bed furnaces, tunnel furnaces and muffle furnaces, cupola furnaces and stoker furnaces.

[0026] <Crushing process> The crushing step is not particularly limited as long as it is a step of crushing the lithium ion secondary battery (roasted product) that has been heat-treated in the heat treatment step to obtain crushed products, and can be appropriately selected depending on the purpose. The crushing step is preferably, for example, a step of crushing the roasted product by impact to obtain crushed products. If the outer container of the lithium ion secondary battery does not melt during the heat treatment, it is more preferable to perform pre-crushing by cutting the roasted product with a cutter before applying an impact to the roasted product.

[0027] Examples of methods for crushing by impact include a method in which the roasted material is thrown by a rotating striking plate and struck against a collision plate, and a method in which the roasted material is hit by a rotating striker (beater). Specifically, this can be done using a hammer crusher or the like. An example of a method for crushing by impact is a method in which the roasted material is hit with ceramic or other balls, which can be performed using a ball mill, etc. Crushing by impact can also be performed using, for example, a biaxial crusher with a short blade width and length for crushing by compression.

[0028] The crushing time in the crushing step is not particularly limited and can be selected appropriately depending on the purpose, but the crushing time per 1 kg of lithium ion secondary batteries is preferably from 1 second to 30 minutes, more preferably from 2 seconds to 10 minutes, and particularly preferably from 3 seconds to 5 minutes.

[0029] <Classification process> The classification step is not particularly limited as long as it is a step of classifying the crushed material into a coarse product and a fine product and obtaining recovered products from each of them, and can be appropriately selected depending on the purpose.

[0030] The classification method is not particularly limited and can be appropriately selected depending on the purpose, and can be carried out using, for example, a vibrating sieve, a multistage vibrating sieve, a cyclone, a standard sieve according to JIS Z8801, etc. By classification, copper, iron, aluminum, etc. can be separated into a coarse product, and lithium can be concentrated in a fine product. The classification point in the classification is preferably 0.6 mm or more and 2.4 mm or less, and more preferably 0.85 mm or more and 1.7 mm or less. When the classification point in the classification is 2.4 mm or less, the incorporation of impurities such as copper, iron, and aluminum into the fine-grained product can be suppressed, and the amount of lithium recovered per unit weight when the fine-grained product is leached can be improved. Furthermore, when the classification point in the classification is 0.6 mm or more, the recovery of lithium in the coarse-grained product can be suppressed, and the amount of lithium recovered when the fine-grained product is leached can be improved. The classification into coarse and fine products may be repeated several times, and this reclassification can further reduce the impurity content of each product.

[0031] <Lithium leaching process> The lithium leaching step is a step in which lithium contained in the fine granule product recovered in the classification step is leached into water to obtain a lithium leachate having a lithium concentration of less than 1,500 mg / L. The lithium concentration of the obtained lithium leachate is less than 1,500 mg / L, although it depends on the heat treatment conditions of the lithium ion secondary battery and the solid-liquid ratio during leaching. The inventors have found that the lithium in the fine granule product exists mainly as lithium carbonate, lithium fluoride, or lithium oxide. They have also found that the leaching rate of lithium salts into water can be improved by making the lithium concentration of the lithium leachate less than 1,500 mg / L. The lithium in the lithium leachate is dissolved mainly as lithium carbonate and lithium fluoride. In other words, the amount of CO3, which is approximately equal to the amount of lithium, is 2- ions and F - On the other hand, if the lithium leachate is concentrated by some method to a lithium concentration of 1,500 mg / L or more and then heated to 60°C or more (reducing the solubility of lithium carbonate), lithium carbonate will precipitate. Here, the lithium concentration can be measured by ICP-AES analysis using, for example, ICAP 6300DuO (manufactured by Thermo Fisher Scientific Co., Ltd.).

[0032] By leaching lithium into water in the lithium leaching step, it is possible to recover almost all (100%) of impurities such as nickel (Ni), cobalt (Co), and manganese (Mn) as residue. Therefore, when leaching lithium into water, it is preferable to perform solid-liquid separation of the slurry water from which lithium has been leached using filter paper or a solid-liquid separator in order to recover residues such as nickel, cobalt, and manganese. In other words, in the lithium leaching step of the lithium recovery method, it is preferable to remove residues such as nickel, cobalt, and manganese by solid-liquid separation.

[0033] The water used in the lithium leaching step is not particularly limited and can be appropriately selected depending on the purpose. Examples include pure water such as industrial water, tap water, ion-exchanged water, ultrafiltered water, reverse osmosis water, and distilled water, and ultrapure water.

[0034] The pH (hydrogen ion exponent) of the lithium leaching solution is preferably 10.5 or higher, more preferably 10.5 or higher and 12.5 or lower, and particularly preferably 10.5 or higher and 12.0 or lower. By adjusting the pH of the lithium leaching solution to 10.5 or higher, the amount of calcium hydroxide or other additives used to increase the pH can be reduced. The amount of dissolved calcium ions provided by the added calcium hydroxide or other additives can also be reduced. Furthermore, when the calcium removal step is performed in a later stage, the amount of remover (e.g., cation exchange resin or carbonate) used can be reduced. On the other hand, when the pH of the lithium leaching solution is 12.5 or lower, the added components are more easily dissolved, improving the efficiency of fluorine removal.

[0035] The leaching residue contains valuable materials such as cobalt, nickel, and carbon. Fluorine can be removed from the leaching residue by the lithium leaching process. It is preferable that the fluorine content in the leaching residue after the lithium leaching process is 3% or less. Since the amount of fluorine removed is inversely proportional to the solid-liquid ratio during leaching, leaching at a low solid-liquid ratio is preferable to remove fluorine from the leaching residue, but the lower the solid-liquid ratio, the lower the lithium / fluorine ratio that is obtained as a low-concentration lithium leachate. By applying reverse osmosis membrane separation to this low-concentration lithium leachate, a liquid with an increased lithium concentration (first lithium concentrated liquid) can be recovered, enabling more efficient lithium purification (for example, recovery of lithium carbonate).

[0036] The fluorine concentration of the lithium leaching solution is preferably 20 mg / L or more, because when a fluorine removal step described later is carried out, the fluorine can be solidified and separated, and the fluorine concentration can be reduced to less than 20 mg / L. The fluorine concentration can be measured, for example, using an apparatus in which an F-2021 fluoride ion electrode (manufactured by DKK-TOA Corporation) is connected to an IM-32P glass electrode type hydrogen ion concentration indicator (manufactured by DKK-TOA Corporation).

[0037] The lithium leaching method in the lithium leaching step is not particularly limited and can be selected appropriately depending on the purpose. For example, the fine granular product of the lithium ion secondary battery recovered in the classification step can be added to a liquid (water) and stirred to leach lithium into the liquid. The stirring speed of the liquid in the lithium leaching step is not particularly limited and can be selected appropriately depending on the purpose, and can be, for example, 200 rpm. The leaching time in the lithium leaching step is not particularly limited and can be appropriately selected depending on the purpose, and can be, for example, 1 hour.

[0038] <Membrane separation process> The membrane separation step is a step of concentrating the lithium leachate obtained in the lithium leaching step using a nanofiltration (NF) membrane or a reverse osmosis (RO) membrane to obtain a first lithium concentrate. The concentration treatment in the membrane separation step is preferably carried out at a temperature of the lithium leachate of 50°C or less. By carrying out the membrane separation step at a temperature of the lithium leachate of 50°C or less, it is possible to prevent lithium carbonate from crystallizing and blocking the membrane surface, and lithium and carbonate ions can be concentrated in the resulting first lithium concentrated solution at low cost. Note that fluorine is also concentrated in the first lithium concentrated solution, but this fluorine is efficiently removed in the fluorine removal step described below. Furthermore, the lithium concentration of the first lithium concentrate can be 1,500 mg / L or more and less than 4,000 mg / L. By setting the lithium concentration of the first lithium concentrate to less than 4,000 mg / L, it is possible to prevent lithium carbonate from crystallizing and clogging the membrane surface during membrane separation, enabling continuous, stable membrane separation over a long period of time (with reduced increase in operating pressure). When an NF membrane is used, fluorine can be removed from the permeate side. In the present invention, a lithium leachate having a lithium concentration of less than 1,500 mg / L is subjected to membrane separation (membrane concentration), and therefore the lithium concentration can be adjusted to 1,500 mg / L or more and less than 4,000 mg / L more cheaply than other concentration methods (e.g., evaporation concentration or electrodialysis).

[0039] As described above, in the present invention, a first lithium concentrate solution having a lithium concentration of 1,500 mg / L or more can be produced by treating a lithium ion secondary battery through the heat treatment step, crushing step, classification step, lithium leaching step, and membrane separation step.

[0040] <Fluorine removal process> The fluorine removal step is a step of adding calcium hydroxide to the first lithium concentrated solution and removing the solidified fluorine by solid-liquid separation to obtain a fluorine-removed solution. In other words, while both lithium and fluorine can be concentrated in the first lithium concentrated solution by the membrane separation step, the solidified fluorine can be removed by adding calcium hydroxide, which solidifies the fluorine contained in the first lithium concentrated solution, to the first lithium concentrated solution. The fluorine removal step can reduce the fluorine concentration in the post-fluoride removal solution to about 5 mg / L to 20 mg / L. Even if the fluorine removal step is performed on the lithium leaching solution without performing the concentration treatment using the membrane separation step, the fluorine concentration in the resulting post-fluoride removal solution is at a similar level of 5 mg / L to 20 mg / L. Therefore, performing fluorine removal on the first lithium concentrated solution can reduce the ratio of the fluorine concentration to the lithium concentration compared to the case where the membrane separation step is not performed, and can reduce the fluorine content of the finally obtained recovered lithium product.

[0041] The calcium hydroxide may be added in the form of a solid calcium hydroxide to the first lithium concentrate, or in the form of a solution or slurry in which calcium hydroxide is dissolved. Here, an example of a preferred form for adding calcium hydroxide will be described. As described above, in the lithium leaching step, the pH of the lithium leaching solution can be adjusted to 10.5 or higher by adjusting the lithium concentration when leaching lithium into water. This is thought to be because the lithium leaching solution becomes a lithium hydroxide solution. By increasing the pH during leaching, the amount of alkali added to raise the pH to 12 or higher after the addition of calcium hydroxide can be reduced. Furthermore, if the pH of the first lithium concentrated solution after the addition of calcium hydroxide is less than 12, it is preferable to add additional alkali to adjust the pH to 12 or higher. Under these conditions, in view of the solubility product of calcium, the calcium ions (Ca 2+ ) dissolved in the water can be suppressed to 1,000 mg / L or less. 2+ The amount of cation exchange resin used to remove HCl can be reduced. By using calcium hydroxide for fluoride solidification, the addition of calcium and the adjustment of pH can be carried out simultaneously by simply adding calcium hydroxide (slaked lime). On the other hand, calcium ions (Ca 2+) is dissolved in a small amount, fluorine can be sufficiently removed. For example, when the fluorine concentration in the first lithium concentrated solution before fluorine removal is 2,000 mg / L, the fluorine concentration in the lithium leaching solution can be reduced to about 20 mg / L by performing the fluorine removal step.

[0042] Here, in the fluorine removal step, solidifying fluorine means solidifying fluorine so that it can be removed from the lithium leachate. Therefore, for example, when removing fluorine from the lithium leachate by solid-liquid separation, the fluorine may be solidified so that it can be separated into solid and liquid. In this case, for example, the solidified fluorine may be in the form of fine particles or may be in the form of a precipitate (sediment) having a certain size.

[0043] The method for removing solidified fluorine in the fluorine removal step is not particularly limited and can be appropriately selected depending on the purpose. For example, a method using solid-liquid separation, a method for removing a precipitate (sediment) formed by solidified fluorine, etc. are mentioned. Among these, a method using solid-liquid separation is preferred. In other words, in the fluorine removal step, it is preferred to remove solidified fluorine by solid-liquid separation. By removing solidified fluorine by solid-liquid separation, fluorine can be removed from the lithium leachate with higher accuracy.

[0044] The solidified fluorine can be removed by solid-liquid separation, for example, by filtering the lithium leachate (which may be in the form of a slurry) using filter paper or a solid-liquid separator. The filter paper used to remove solidified fluorine by solid-liquid separation is not particularly limited and can be selected appropriately depending on the purpose. However, it is preferable to use quantitative filter paper, and it is more preferable to use filter paper classified as Type 5C in JIS P3801. The solid-liquid separator used for removing solidified fluorine by solid-liquid separation is not particularly limited and can be appropriately selected depending on the purpose. Examples include a screw press, a roller press, a belt screen, a vibrating sieve, a multi-plate wave filter, a vacuum dehydrator, a pressure dehydrator (filter press), a belt press, a screw press, a centrifugal concentration dehydrator (screw decanter), and a multi-disk dehydrator.

[0045] Furthermore, by using an aluminum compound such as aluminum sulfate, calcium aluminate, or aluminum chloride as a second additive component in addition to calcium hydroxide, the fluoride concentration can be further reduced than when a calcium compound is used alone, and the fluoride concentration in the post-fluoride removal solution can be reduced to, for example, 10 mg / L or less. Furthermore, aluminum leached during lithium leaching can be coprecipitated during fluoride solidification, and the aluminum can be used as a fluoride remover along with the removal of aluminum.

[0046] The amount of the additive component added relative to the total amount of the first lithium concentrate is not particularly limited and can be appropriately selected depending on the purpose. When the first lithium concentrate contains carbonate ions, the additive component reacts with the carbonate ions and is consumed, so it is preferable to increase the amount of the additive component added. From the viewpoint of stably solidifying and separating fluorine, the amount of the additive component added is preferably an amount that allows the additive component to react with both the fluorine and the carbonate ions contained in the first lithium concentrate when the total amounts of fluorine and carbonate ions contained in the first lithium concentrate are X moles (mol) of fluorine and Y moles (mol) of carbonate ions. The amount of the additive component added relative to the X moles (mol) of fluorine and Y moles (mol) of carbonate ions in the first lithium concentrated solution may be, for example, 0.5 × (X + 2Y) mol or more and 10 × (X + 2Y) mol or less when the valence of the additive component ions is divalent. More preferably, the amount of the additive component added relative to the X moles (mol) of fluorine and Y moles (mol) of carbonate ions in the first lithium concentrated solution may be, for example, 0.75 (X + 2Y) mol or more and 5 (X + 2Y) mol or less. For example, when calcium hydroxide (where the valence of calcium ions is divalent) is used as the compound containing the additive component, the amount of calcium hydroxide added relative to X moles (mol) of fluorine and Y moles (mol) of carbonate ions in the first lithium concentrated solution is preferably 0.5 × (X + 2Y) mol or more and 10 × (X + 2Y) mol or less, and more preferably 0.75 × (X + 2Y) mol or more and 5 × (X + 2Y) mol or less.

[0047] In the fluorine removal step, it is preferable to stir the first lithium concentrated solution after adding calcium hydroxide. The stirring speed of the first lithium concentrate is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 20 rpm or more and 2,000 rpm or less, and more preferably 50 rpm or more and 1,000 rpm or less, for example. The stirring time for the first lithium concentrated solution is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 5 minutes or more and 240 minutes or less, and more preferably 15 minutes or more and 120 minutes or less. By setting the stirring time (reaction time) to 240 minutes or less, re-dissolution of solidified fluorine can be prevented.

[0048] The fluorine concentration in the post-fluoride removal solution can be determined by, for example, measuring the fluorine concentration by an ion electrode method or ion chromatography.

[0049] <Calcium removal process> The calcium removal step is a step of removing calcium ions from the first lithium concentrated solution using a cation exchange resin to obtain a calcium-removed solution having a calcium concentration of 10 mg / L or less. For the adsorption and removal of calcium ions using a cation exchange resin, multiple types of ion adsorption resins or ion adsorption resin towers can be used. By contacting the cation exchange resin with the first lithium concentrate, calcium ions can be adsorbed onto the cation exchange resin and removed while leaving lithium dissolved. This allows the calcium content in the lithium carbonate to be further reduced. In addition, cation exchange resin adsorption reduces CO32- Ca without supplying ions 2+ ions (to obtain calcium-removed solution), CO3 2- The ions do not dissolve in the calcium-removed solution. As a result, it is possible to concentrate the calcium-removed solution without precipitating lithium carbonate. Lithium ions (cations) are not adsorbed to the cation exchange resin. It is preferable to carry out electrodialysis either before or after the calcium removal step, or both, to concentrate the solution after calcium removal.

[0050] In the above-mentioned fluoride removal process, calcium hydroxide is used to remove fluoride, and the calcium concentration in the post-fluoride removal solution can be suppressed to 1,000 mg / L or less. Therefore, the amount of cation exchange resin used per unit amount of post-fluoride removal solution is small, and calcium removal using a cation exchange resin can be carried out at low cost (economically). Addition of carbonates and addition of the resulting calcium carbonate are also conceivable as methods for removing calcium ions, but the calcium removal process using a cation exchange resin is preferred because it is more accurate and can produce Li carbonate with a lower Ca content. Furthermore, the calcium removal process using a cation exchange resin does not use CO3 during calcium removal. 2- Since no calcium ions are supplied, only calcium ions can be selectively removed without causing lithium carbonate precipitation or loss.

[0051] <Electrodialysis process> The electrodialysis step is a step of performing electrodialysis either before or after the calcium removal step, or both, to obtain a second lithium-enriched solution having a lithium concentration of 4,000 mg / L or more. Note that the electrodialysis step may be performed by multi-stage treatment to concentrate the solution to a predetermined concentration. The fluoride removal process and calcium removal process reduce the CO3 2- Since most of the ions are removed as calcium carbonate, the solution after calcium removal contains CO3 2-ions are hardly contained. Therefore, even if the lithium ions are concentrated to 4,000 mg / L or more, crystallization of lithium carbonate does not occur in the lithium carbonate recovery step described below. In addition, since the ion exchange membrane used in electrodialysis has higher resistance to alkali than the nanofiltration (NF) membrane or reverse osmosis (RO) membrane used in membrane concentration, it is preferable to concentrate the post-fluoride removal solution (pH 12 or higher) after fluoride removal by electrodialysis. The concentration ratio for concentrating the post-fluoride removal solution is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 1.5 to 100 times, more preferably 3 to 50 times, and particularly preferably 5 to 10 times. If the concentration ratio exceeds 100 times, lithium fluoride may precipitate inside the device during electrodialysis. Furthermore, if the concentration ratio is 10 times or less, concentration may be completed with only one stage of electrodialysis rather than multistage treatment, which is particularly preferred from the perspective of equipment installation costs. Note that concentration by electrodialysis can increase the lithium carbonate production rate by 5 times or more compared to evaporation concentration with equipment of the same scale.

[0052] <Lithium carbonate recovery process> The lithium carbonate recovery step is a step of heating the calcium-removed solution or the second lithium-concentrated solution and adding carbon dioxide at 60° C. or higher to recover lithium carbonate. That is, lithium carbonate can be selectively crystallized by utilizing the difference in solubility between lithium carbonate and other lithium salts (e.g., lithium sulfate, lithium fluoride), and lithium carbonate can be recovered at a high concentration. The heating temperature of the second lithium concentrate is preferably 60°C or higher, more preferably 80°C or higher, and particularly preferably 95°C or higher. The higher the heating temperature, the more the solubility of lithium carbonate can be reduced, and the more the amount of lithium carbonate crystallized can be increased. Examples of heating methods include heating with an electric heater or a pipe made of copper, stainless steel, Teflon (registered trademark), or the like through which heated steam passes.

[0053] The method for adding carbon dioxide to the calcium-removed solution or the second lithium-enriched solution is not particularly limited and can be appropriately selected depending on the purpose, but is preferably carried out by blowing in a gas containing carbon dioxide or adding a carbonate. Examples of the carbon dioxide-containing gas include air and carbon dioxide gas. Examples of the carbonate include sodium carbonate and potassium carbonate. The carbonate ion concentration of the lithium-containing solution after carbon dioxide is supplied is preferably 2 or more relative to the lithium concentration of 1, more preferably 3 or more relative to the lithium concentration of 1, and particularly preferably 4 to 32.3 relative to the lithium concentration of 1. If the carbonate ion concentration is less than 2 relative to the lithium concentration of 1, the amount of lithium sulfate precipitated increases in addition to lithium carbonate, and industrial-grade lithium carbonate (lithium carbonate purity of 99.0% or more) may not be crystallized. On the other hand, if the carbonate ion concentration exceeds 32.3 relative to the lithium concentration of 1, the lithium carbonate may absorb water from the solution containing dissolved metals derived from carbonates added to dissolve the carbonate ions, and the metal purity derived from carbonates in the lithium carbonate may become excessive.

[0054] It is preferable to continue stirring the liquid during the recovery of lithium carbonate. Stirring can make the concentrations of carbonate ions and impurity ions (e.g., fluorine ions) in the liquid uniform, and also make the particle size of the lithium carbonate precipitate uniform, thereby reducing the generation of impurity crystals or the entrainment of the liquid into the lithium carbonate precipitate, and therefore reducing the impurity quality in the recovered lithium carbonate. When recovering lithium carbonate, crystallization may be started or continued with lithium carbonate crystals added beforehand or during crystallization. The addition of these crystals (seed crystals) can improve and homogenize the particle size of the lithium carbonate recovered by crystallization, thereby reducing the water content of the crystals and further reducing the quality of impurities derived from water-containing components. In the lithium carbonate recovery step, lithium carbonate can also be crystallized by heating the liquid to a temperature equal to or higher than the temperature at which the liquid evaporates during crystallization and evaporating and concentrating the liquid.

[0055] The precipitated lithium (lithium carbonate) can be recovered using known tools such as a spoon, a rake, a scraper, etc. The slurry containing the precipitated lithium carbonate has low viscosity, so it does not clog pipes and can be recovered by supplying the slurry to a solid-liquid separator (for example, a filter press) with a pump while stirring.

[0056] As described above, lithium leachate obtained by treating lithium ion secondary batteries is subjected to a membrane separation process to concentrate lithium and fluorine, and lithium is recovered as lithium carbonate from the concentrated lithium solution after concentration, whereby lithium carbonate with a low fluorine content and high purity (grade) can be easily obtained.

[0057] <Other processes> The other steps are not particularly limited and can be appropriately selected depending on the purpose.

[0058] Here, an example of an embodiment of the method for recovering lithium from a lithium ion secondary battery of the present invention will be described with reference to the drawings.

[0059] First Embodiment FIG. 1 is a flow chart showing an example of a method for recovering lithium from a lithium ion secondary battery according to the first embodiment. 1, a lithium ion secondary battery (LIB) is first subjected to a heat treatment (heat treatment step) to obtain a heat-treated LIB. This process converts, for example, lithium in Li(Ni / Co / Mn)O2 in the positive electrode active material of the LIB or LiPF6 in the electrolyte into substances in which lithium is soluble in aqueous solutions, such as lithium fluoride (LiF), lithium carbonate (Li2CO3), and lithium oxide (Li2O), making it possible to separate nickel, cobalt, manganese, etc., and also melting and separating aluminum (Al) in the LIB. Next, in the first embodiment, the LIB heat-treated product is crushed and classified (crushing step and classification step) to obtain a coarse-grained product and a fine-grained product. Here, impurities such as copper (Cu), iron (Fe), and aluminum (Al) can be separated and removed from the coarse-grained product.

[0060] In the first embodiment, lithium is then leached from the fine product into water, and a residue containing impurities such as nickel (Ni), cobalt (Co), and manganese (Mn) is formed in the lithium leaching solution. Then, residues containing nickel (Ni), cobalt (Co), and manganese (Mn) are removed from the lithium-leached solution by solid-liquid separation to produce a lithium leachate. The obtained lithium leachate is subjected to membrane separation by passing it through a nanofiltration (NF) membrane or a reverse osmosis (RO) membrane to obtain a first lithium concentrated solution.

[0061] Next, calcium hydroxide, which solidifies the fluorine contained in the first lithium concentrate, is added to the lithium solution to remove the solidified fluorine, thereby obtaining a fluorine-removed liquid (fluorine removal step). The fluorine-removed liquid from which the solidified fluorine has been removed is passed through a cation exchange resin to adsorb and remove calcium ions to a concentration of 10 mg / L or less (calcium removal step). The obtained calcium-removed liquid is subjected to electrodialysis (electrodialysis step) to obtain a second lithium concentrate with a lithium concentration of 4,000 mg / L or more. The obtained second lithium concentrate is heated to 60°C or higher, and carbon dioxide (gas) is added to crystallize and recover lithium carbonate (lithium carbonate recovery step). [Example]

[0062] Examples of the present invention will be described below, but the present invention is not limited to these examples in any way.

[0063] Example 1 <Preparation of lithium solution> A lithium-ion secondary battery (approximately 10 kg) containing cobalt, nickel, and manganese as the positive electrode active material was heat-treated using a muffle furnace (KBF66812-S, manufactured by Koyo Thermo Systems Co., Ltd.) at a heat treatment temperature of 800°C (heated over 1 hour and then maintained for 2 hours) with an air supply rate of 5 L / min. Next, the heat-treated lithium ion secondary batteries (heat-treated lithium ion secondary batteries) were crushed using a hammer crusher (Makino-type swing hammer crusher HC-20-3.7, manufactured by Makino Sangyo Co., Ltd.) as a crushing device under conditions of 50 Hz (hammer peripheral speed 38 m / s) and a hole diameter of 10 mm in the punched metal at the outlet, thereby obtaining crushed lithium ion secondary batteries.

[0064] Next, the crushed lithium-ion secondary battery material was sieved using a sieve with 1.2 mm mesh (diameter 200 mm, manufactured by Tokyo Screen Co., Ltd.). After sieving, the 1.2 mm sieve (coarse product) and the sieve (fine product) were collected. The resulting fine product (fluorine content: 5.5%) was used to leach lithium into water using a leachate volume of 100 L, a solid-liquid ratio of 10%, a stirring speed of 200 rpm, and a leach time of 1 hour. The lithium-leached water (slurry) was then subjected to solid-liquid separation using Class 5C filter paper (manufactured by Toyo Roshi Kaisha, Ltd.), and the residue containing nickel (Ni), cobalt (Co), and manganese (Mn) was removed to produce a lithium leachate. The fluorine content of the residue was 2.0%, and fluorine was successfully removed from the valuables in the residue and transferred to the lithium leachate.

[0065] The lithium concentration of the prepared lithium leachate was measured by high-frequency inductively coupled plasma atomic emission spectroscopy (ICP-AES analysis) using an ICAP 6300DuO (manufactured by Thermo Fisher Scientific Co., Ltd.), and was found to be 772 mg / L. The fluoride ion concentration was measured using an apparatus consisting of an IM-32P glass electrode hydrogen ion concentration indicator (manufactured by DKK Toa Corporation) connected to an F-2021 fluoride ion electrode (manufactured by DKK Toa Corporation), and the fluoride concentration was found to be 372 mg / L. The pH of the prepared lithium leaching solution was measured using a pH meter (HM-25R, manufactured by DKK-TOA Corporation) and found to be 11.1.

[0066] Next, a reverse osmosis (RO) membrane separation test was performed using a flat membrane testing device at an operating pressure of 1.5 MPa on 13,290 mL of lithium leachate (liquid temperature 20°C) using a reverse osmosis (RO) membrane (product name: ESPA2-LD, manufactured by Nitto Denko Corporation), yielding 4,500 mL of a first lithium concentrate and 8,790 mL of permeate (membrane separation process). Next, 4,500 mL of the first lithium concentrate was added to a 10 L glass beaker and stirred at 150 rpm using a stirrer with a rotor blade diameter of 150 mm. 21 g / L of slaked lime powder was added from the top of the beaker, and stirring was continued for 1 hour, after which the stirring was stopped and the solution was subjected to suction filtration with 5C filter paper to separate the filtrate (liquid after fluoride removal) and the residue (CaF2, etc.), followed by the fluoride removal step. A calcium removal step was carried out by passing 4,380 mL of the fluoride-removed solution through a cation exchange resin tower (product name: Duolite C20SC, manufactured by Sumika Chemtex Co., Ltd.) at a space velocity (SV) of 1 to obtain a calcium-adsorbed and removed solution (4,370 mL). The entire amount of this solution was subjected to electrodialysis using an electrodialysis apparatus (Acilyzer EX-3B, manufactured by Astom Co., Ltd.) (electrodialysis step), and the solution was concentrated four-fold to obtain 1,100 mL of a second lithium concentrate. 1,000 mL of the obtained second lithium concentrated solution was heated to a liquid temperature of 90°C and stirred with a hot magnetic stirrer, while CO2 gas was diffused into the solution until the pH of the solution decreased to 11.0. After the gas diffusion, the slurry in which lithium carbonate had crystallized was subjected to suction filtration with 5C filter paper, and lithium carbonate was recovered (lithium carbonate recovery step).

[0067] <Evaluation of quality, recovery rate, and burning weight loss> The mass of the lithium carbonate was measured using an electromagnetic balance (product name: GX-8K, manufactured by A&D Corporation) after drying at 100°C for 1 hour using a dryer (product name: DRM620DD, manufactured by Advantec Toyo Co., Ltd.). The impurity quality of the lithium carbonate was analyzed by heating and dissolving the recovered lithium carbonate in aqua regia (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and analyzing the solution using a high-frequency inductively coupled plasma optical emission spectrometer (iCaP6300, manufactured by Thermo Fisher Scientific K.K.) to determine the content ratio (quality) of various impurities other than fluorine and ignition loss. For the fluorine and chlorine contents, lithium carbonate was burned at 1,000°C using an automatic sample combustion device (product name: AQF-100·ICS-1500, manufactured by Dia Instruments Co., Ltd.) to volatilize the fluorine and chlorine, which were then absorbed into an absorption liquid, which was then analyzed by ion chromatography. The sulfate radicals were analyzed by the gravimetric method (lithium carbonate was dissolved in hydrochloric acid, filtered, and barium hydroxide was added to the filtrate to make barium sulfate, which was then incinerated in a muffle furnace and measured as barium sulfate weight, and the sulfuric acid content was calculated from this weight). Regarding the loss on ignition, the lithium carbonate after drying was dried at 550°C for 3 hours, and then the loss in weight was measured.

[0068] Next, the results of the reverse osmosis membrane test are shown in Table 1, the composition of the lithium solution after each step and the amount of lithium (%) in each solution when the amount of lithium in the lithium leaching solution is taken as 100% are shown in Table 2, and the quality of the recovered lithium carbonate is shown in Table 3.

[0069] Example 2 The same operation as in Example 1 was carried out, except that an NF membrane (product name: NANO-SW, manufactured by Nitto Denko Corporation) was used instead of the RO membrane in Example 1, and reverse osmosis membrane separation was performed on 14,500 mL of lithium leachate (liquid temperature: 20°C) using a flat membrane testing apparatus at an operating pressure of 1.0 MPa, thereby obtaining 4,500 mL of a first lithium concentrate and 10,000 mL of a permeate. The results of the reverse osmosis membrane test are shown in Table 1, and the quality of the recovered lithium carbonate is shown in Table 3.

[0070] Example 3 Lithium carbonate was recovered in the same manner as in Example 1, except that the fluorine removal step was not performed. The quality of the recovered lithium carbonate is shown in Table 3.

[0071] Example 4 Lithium carbonate was recovered in the same manner as in Example 1, except that the calcium removal step was not performed. The quality of the recovered lithium carbonate is shown in Table 3.

[0072] Example 5 In Example 1, the electrodialysis step was not performed, and the entire amount (4,000 mL) of the post-crystallization liquid after lithium carbonate recovery (first time) was mixed with fresh lithium leaching solution (9,290 mL), and the mixture was again concentrated by RO membrane concentration until the lithium concentration reached 2,255 mg / L. This concentrated liquid was again subjected to the steps from the fluorine removal step onwards, excluding the electrodialysis step, to recover lithium carbonate (second time) (i.e., the post-crystallization liquid was repeatedly subjected to the membrane concentration step, thereby performing two-stage treatment). Except for this, lithium carbonate was recovered in the same manner as in Example 1. The quality of the recovered lithium carbonate is shown in Table 3.

[0073] (Comparative Example 1) Lithium carbonate was recovered by the same operation as in Example 1, except that a reverse osmosis membrane test using an RO membrane was performed on a lithium leachate (lithium concentration: 2,559 mg / L) obtained by setting the solid-liquid ratio when leaching lithium into water to 40% in Example 1. In Comparative Example 1, the lithium concentration of the first lithium concentrate was 7,000 mg / L or more, but the test was interrupted because lithium carbonate precipitated on the RO membrane surface, causing an increase in operating pressure. In addition, in Comparative Example 1, the recovery rate of lithium in the first lithium concentrate at the time the test was interrupted was 33%.

[0074] (Comparative Example 2) The aqueous leachate of the lithium ion secondary battery obtained in Example 3 was subjected to recovery of lithium carbonate by the method described in Example 1 of Patent Document 1 (Japanese Patent No. 5872788). In Comparative Example 2, the recovery rate of lithium from the lithium solution after electrophoresis was about 50%, and the remaining 50% was distributed to the impurity concentrated solution side containing a high concentration of fluorine. However, recovering lithium from this solution by electrophoresis again would be more costly, making it difficult to recover lithium, and it was therefore difficult to improve the lithium recovery rate to 50% or more in Comparative Example 2.

[0075] (Comparative Example 3) Lithium carbonate was recovered in the same manner as in Example 1, except that the membrane separation step (membrane concentration) was not performed in Example 1. The fluorine content in the recovered lithium carbonate was 600 ppm (the fluorine content was high because the solution was purified without concentration by membrane separation). In Comparative Example 3, concentration by electrodialysis alone was insufficient, and the recovery rate of lithium in the recovered lithium carbonate was only 45%, assuming that the lithium in the lithium leaching solution was 100%.

[0076] [Table 1]

[0077] [Table 2]

[0078] [Table 3]

[0079] From the results of Tables 1 to 3, it is clear that in Example 1, 99% of lithium was recovered in the first lithium concentrated solution. The lithium concentration was able to be concentrated to 2,255 mg / L. In Example 1, no lithium crystallization occurred. In Example 1, when the lithium in the lithium leaching solution was taken as 100%, 70% of the lithium was recovered in the recovered lithium carbonate. Furthermore, in Example 1, high-purity lithium carbonate with a calcium content of 51 ppm and a fluorine content of 200 ppm could be produced.

[0080] In Example 2, 88% of lithium was recovered in the first lithium concentrated solution, and the lithium concentration was concentrated to 2,208 mg / L. No lithium crystallization occurred in Example 2. Furthermore, in Example 2, 29% of the fluorine was removed into the permeate side. In Example 2, when the lithium in the lithium leaching solution was taken as 100%, 60% of the lithium was recovered in the recovered lithium carbonate. In addition, in Example 2, high-purity lithium carbonate with a calcium content of 61 ppm and a fluorine content of 100 ppm was obtained.

[0081] In Example 3, lithium carbonate having a fluorine content of 113,300 ppm and a lithium carbonate content of 88.2% was obtained. In Example 3, when the lithium in the lithium leaching solution was taken as 100%, 70% of lithium was recovered in the recovered lithium carbonate.

[0082] In Example 4, lithium carbonate having a calcium content of 24,460 ppm and a lithium carbonate content of 95% or more was obtained. In addition, in Example 4, when the lithium in the lithium leaching solution was taken as 100%, 70% of lithium was recovered in the recovered lithium carbonate.

[0083] In Example 5, high-purity lithium carbonate with a calcium content of 64 ppm and a fluorine content of 100 ppm could be purified. Furthermore, in Example 5, when the lithium content in the lithium leaching solution was taken as 100%, 51% of lithium was recovered in the recovered lithium carbonate. Furthermore, in Example 5, by repeatedly performing the membrane concentration step on the post-crystallization solution, it was possible to further improve the lithium recovery rate.

Claims

1. a heat treatment step of heating a lithium ion secondary battery containing at least one of cobalt, nickel, and manganese at 700°C or higher; a crushing step of crushing the heat-treated lithium ion secondary battery obtained in the heat treatment step; a classification step of classifying the crushed material obtained in the crushing step at a classification point of 0.6 mm or more and 2.4 mm or less to obtain a coarse product and a fine product; a lithium leaching step in which lithium contained in the fine granule product recovered in the classification step is leached into water to obtain a lithium leachate having a lithium concentration of less than 1,500 mg / L; a membrane separation step of separating the lithium leachate into a first lithium concentrate using a nanofiltration (NF) membrane or a reverse osmosis (RO) membrane; A method for recovering lithium from a lithium ion secondary battery, comprising:

2. 2. The method for recovering lithium from a lithium ion secondary battery according to claim 1, wherein the lithium leaching solution has a fluorine concentration of 20 mg / L or more and a pH of 10.5 or more.

3. 3. The method for recovering lithium from a lithium ion secondary battery according to claim 1, wherein the first lithium concentrated solution has a lithium concentration of 1,500 mg / L or more and less than 4,000 mg / L, and a solution temperature of 50°C or less.

4. 4. The method for recovering lithium from a lithium ion secondary battery according to claim 1, further comprising a fluorine removal step of adding calcium hydroxide to the first lithium concentrated solution and removing solidified fluorine by solid-liquid separation to obtain a fluorine-removed solution.

5. 5. The method for recovering lithium from a lithium ion secondary battery according to claim 4, further comprising a calcium removal step of removing calcium ions in the first lithium concentrated solution with a cation exchange resin to obtain a calcium-removed solution having a calcium concentration of 10 mg / L or less.

6. 6. The method for recovering lithium from a lithium ion secondary battery according to claim 5, further comprising an electrodialysis step of performing electrodialysis either before or after the calcium removal step, or both before and after the calcium removal step, to obtain a second lithium concentrate solution having a lithium concentration of 4,000 mg / L or more.

7. 7. The method for recovering lithium from a lithium ion secondary battery according to claim 5, further comprising a lithium carbonate recovery step of heating the calcium-removed solution or the second lithium concentrated solution and adding carbon dioxide at 60°C or higher to recover lithium carbonate.

8. 8. The method for recovering lithium from a lithium ion secondary battery according to claim 1, wherein the fluorine content in the leaching residue after the lithium leaching step is 3% or less.

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