Method for recovering graphite

Abstract

A method for recovering graphite according to the present invention comprises the steps of: preparing a graphite supply source; and mixing the graphite supply source with an acidic compound to remove organic carbon contained in the graphite supply source, wherein the acidic compound includes at least one selected from the group consisting of ammonium persulfate, citric acid, boric acid, and ammonium fluoride.

Description

Method for recovering graphite

[0001] The present invention relates to a method for recovering graphite, specifically a method for recovering graphite from waste batteries or process scrap.

[0002] This application claims priority to Korean Patent Application No. 10-2024-0189842 filed on December 18, 2024, the entire contents of which are incorporated herein by reference.

[0003]

[0004] With the recent increase in demand for electric vehicles, the production of secondary batteries for EVs is surging, and technological development regarding methods to recover valuable resources from scrap and waste batteries generated during the production process is also becoming very active.

[0005] In particular, recycling technologies for recovering cathode materials such as Ni, Co, and Mn, as well as Li, are being actively developed, and many technologies have been commercialized and are being used industrially.

[0006] However, in the case of graphite, the cathode material, it is only recovered as residue and waste carbon powder during the process of recovering the anode material and Li through sulfuric acid leaching.

[0007] Specifically, conventional processes for recovering graphite, which serves as a negative electrode material, from waste batteries and waste scrap basically utilize a process of separating graphite from graphite mines, purifying it, and producing it as a material for secondary batteries.

[0008] However, in such cases, large quantities of sulfuric acid, hydrochloric acid, and NaOH are used, and hydrofluoric acid (HF) is also frequently used to remove oxide-based minerals. Consequently, this induces oxidation and defects in the surface and crystal structure of the graphite; when reused for secondary batteries, this results in a low degree of graphitization, leading to limitations in recycling.

[0009] In order to restore the degree of graphitization, high-temperature heat treatment must be performed in an inert atmosphere at a high temperature of 2,000 to 3,000°C, but in this case, the problem arises that the recycling process costs increase rapidly.

[0010] In addition, when recycling the cathode material, there is a problem in that the graphite particles are partially coated by organic carbon such as electrolyte, binders such as PVDF, other plastic components, and tar-based materials mixed in with the graphite, which reduces the effect of acid and base leaching.

[0011] Therefore, there is a need to develop a method for easily recovering graphite, which is the cathode material.

[0012] The present invention aims to provide a method for recovering graphite from waste batteries that eliminates the risk of fire and explosion during the recovery process and enables the easy removal of organic carbon through a simple process.

[0013] In addition, the present invention aims to provide a method for recovering graphite from waste batteries that has a low organic carbon content and excellent purity.

[0014] The present invention provides a method for recovering graphite, comprising the steps of: preparing a graphite source; and mixing the graphite source with an acidic compound to remove organic carbon contained in the graphite source, wherein the acidic compound comprises one or more selected from the group consisting of ammonium persulfate, citric acid, boric acid, and ammonium fluoride.

[0015] The method for recovering graphite according to the present invention has the advantage that there is no risk of fire or explosion during the process of recovering graphite from waste batteries, and organic carbon can be easily removed through a simple process.

[0016] In addition, there is the advantage of being able to easily recover graphite with a low organic carbon content and excellent purity.

[0017] Figure 1 is a diagram showing the LC-MS results of a graphite source.

[0018] Hereinafter, embodiments of the present invention will be described in detail. However, these are presented as examples and are not intended to limit the present invention, and the present invention is defined only by the scope of the claims set forth below.

[0019] In the present invention, when it is stated that a certain member is located "on" another member, this includes not only cases where a certain member is in direct contact with another member, but also cases where another member is interposed between the two members.

[0020] In the present invention, when a part is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0021]

[0022] One aspect of the present invention relates to a method for recovering graphite, comprising the steps of: preparing a graphite source; and mixing the graphite source with an acidic compound to remove organic carbon contained in the graphite source, wherein the acidic compound comprises one or more selected from the group consisting of ammonium persulfate, citric acid, boric acid, and ammonium fluoride.

[0023] Conventionally, to remove organic carbon, methods were used such as using hydrofluoric acid or heat treatment at temperatures above 500°C, which is the temperature at which PVDF, a binder for secondary batteries, decomposes. However, hydrofluoric acid is a highly toxic substance to the environment and the human body, making it difficult to use in large quantities industrially. Furthermore, the method of thermal decomposition at temperatures above 500°C poses risks such as fire and explosion, and it is difficult to configure the equipment industrially because the influx of oxygen must be completely blocked during the thermal decomposition process.

[0024] In the present invention, the risk to workers can be reduced by removing organic carbon in advance using an acidic compound comprising one or more selected from the group consisting of ammonium persulfate, citric acid, boric acid, and ammonium fluoride as a graphite source.

[0025]

[0026] A method for recovering graphite according to the present invention includes the step of preparing a graphite source.

[0027] In the present invention, the term “graphite source” may refer to waste batteries or scrap generated during the process of manufacturing secondary batteries.

[0028] For example, it can refer to black mass, reduction reactants, cathode materials recovered through a sorting process from reduction reactants, NCM ternary batteries, scrap generated during the manufacturing process of LFP batteries, etc.

[0029]

[0030] The step of preparing the graphite source may include the step of magnetically separating the crushed material recovered from the waste battery or scrap.

[0031] In one embodiment of the present invention, the step of preparing the graphite source may include: a step of preparing a product obtained by reducing a crushed material recovered from a waste battery at a high temperature; a step of magnetically separating the heat-treated product into a magnetic material and a non-magnetic material; and a step of floating and separating the non-magnetic material.

[0032] The step of preparing the shredded material recovered from the above waste battery or scrap is not specifically limited in the present invention.

[0033] For example, a waste battery disposal method may include the steps of preparing a product by reducing and heat-treating a crushed material recovered from a waste battery at a high temperature, separating the product by magnetic force, and crushing a product having magnetism among the magnetically separated products to separate magnetic and non-magnetic materials.

[0034] The step of preparing a product obtained by reducing and heat-treating the crushed material recovered from a waste battery at a high temperature may include the step of preparing a battery, the step of crushing the battery into a battery crush, and the step of heat-treating the crushed battery crush at a high temperature.

[0035]

[0036] The step of preparing the battery may be a step of processing various types of batteries including lithium ions, and the battery may be, for example, a lithium secondary battery separated from a car, a secondary battery separated from an electronic device such as a mobile phone, camera, or laptop, but is not limited thereto.

[0037] Specifically, the battery may be a lithium secondary battery. More specifically, the battery may be a spent lithium secondary battery.

[0038] The step of crushing the battery may refer to a process of applying impact or pressure to the battery so that a part of the battery detaches from the battery.

[0039] The step of crushing the battery may refer to a process of grinding the battery, a process of cutting the battery, a process of compressing the battery, and any combination thereof. Specifically, the crushing step may include any process that destroys the battery to obtain small-sized crushed material.

[0040] The step of crushing the battery may include all processes of compressing the prepared battery or destroying the battery by applying external forces such as shear force or tensile force. For example, the step of crushing the battery may be carried out using a crusher.

[0041] The step of crushing the battery can be performed at least once. Specifically, the step of crushing can be performed at least once, either continuously or discontinuously.

[0042] The step of crushing the battery may be carried out under conditions of supplying an inert gas, carbon dioxide, nitrogen, water, or a combination thereof, or under vacuum conditions of 100 torr or less. When carried out under the aforementioned conditions, the supply of oxygen is suppressed to prevent the electrolyte from reacting with oxygen, thereby preventing an explosion caused by this, and the vaporization of the electrolyte is suppressed so as not to generate flammable gases such as ethylene, propylene, or hydrogen.

[0043] The step of high-temperature heat treatment of the crushed battery material may include the step of introducing the battery material into a furnace capable of raising the temperature to a high temperature and raising the battery material to a temperature above its melting point.

[0044] The above battery crushed material may include valuable metals such as Ni, Co, Mn, and Li, and graphite-based raw materials. The above high-temperature heat treatment may involve heat treatment conditions that perform a high-temperature reduction reaction without undergoing a melting step of the battery.

[0045] The step of high-temperature heat treatment of the battery crushed material can be performed in a gas atmosphere of at least one of an inert gas, carbon dioxide, carbon monoxide, hydrocarbon gas, and oxygen. In the case of the inert gas, it may include, for example, at least one of argon and nitrogen. By performing a reduction reaction of the crushed material in the gas atmosphere, there is an advantage of increasing the recovery rate of graphite-based raw materials contained in the battery crushed material.

[0046] Specifically, the step of high-temperature heat treatment of the battery crushed material can be performed in a gas atmosphere where the oxygen concentration is 1.0 vol% or less. Specifically, the oxygen concentration can be performed in a gas atmosphere in the range of 0.1 vol%.

[0047] If the above oxygen concentration satisfies the above range, it is desirable as it has the advantage of suppressing the problem of lithium loss and the generation of large amounts of carbon dioxide and carbon monoxide under localized high-temperature conditions.

[0048] The step of high-temperature heat treatment of the battery crushed material can be performed in a range of 600 to 1,500°C. Specifically, the step of high-temperature heat treatment can be performed in a range of 900 to 1,500°C, more specifically in a range of 1,100 to 1,500°C, and even more specifically in a range of 1,300 to 1,500°C.

[0049] If the step of high-temperature heat treatment of the above-mentioned battery crushed material is performed within the above-mentioned temperature range, the rate at which organic carbon is thermally decomposed and removed increases, and it is desirable as this has the advantage of suppressing problems such as increased equipment and operating costs due to heat treatment costs and refractory materials capable of withstanding high temperatures.

[0050] The step of magnetically separating the above-mentioned high-temperature heat-treated product can separate the product by magnetically separating it to separate the magnetic material having magnetism from the non-magnetic material having non-magnetism. Magnetic separation can utilize the magnetic material to separate particles through contact with the magnetic material, and various types of magnetic separation methods can be applied.

[0051] The magnetic material may be a composition comprising valuable metals such as Ni, Co, and Mn, for example, a composition comprising a core portion and a shell portion disposed on said core portion. The core portion may include a valuable metal recovery alloy. The core portion of the composition for recovering valuable metals may be recovered from the cathode material component within a waste battery.

[0052] The above non-magnetic material may include a graphite-based material containing carbon that is not bonded to a valuable metal in the magnetic separation step, and may further include a compound containing Li.

[0053] Specifically, the method for recovering graphite according to the present invention may involve separation to prevent the recovery of valuable metals such as NCM and lithium together with the graphite. Specifically, since the valuable metal is relatively expensive, if the valuable metal is recovered together with the graphite, economic feasibility may actually deteriorate; therefore, the present invention efficiently separates the graphite from the valuable metal.

[0054] The above magnetic separation step can be performed in a magnetic strength range of 1,000 to 5,000 Gauss. Specifically, the magnetic separation step can be performed in a magnetic strength range of 2,000 to 3,000 Gauss.

[0055] Since the magnetic separation step is performed within the above magnetic strength range, there is an advantage in that graphite-based raw materials can be efficiently separated.

[0056] Subsequently, the method may include a step of floating the magnetically separated non-magnetic material. The non-magnetic material having non-magnetism separated in the magnetic separation step may be separated, which includes graphite.

[0057] The above flotation separation step may be a step of separating a floating material containing graphite and a precipitate containing valuable metals. Specifically, the above flotation separation step may be a step of separating hydrophobic graphite from the non-magnetic material and precipitating a lithium-containing compound and fine particles of a valuable metal alloy.

[0058] Subsequently, the process may include a step of drying the output, namely, the graphite source recovered through the above-mentioned flotation separation. By undergoing the drying step, a graphite source in powder form can be obtained.

[0059] The above flotation separation may apply the contents described below.

[0060]

[0061] The step of drying the above product can be performed in a range of 80 to 200°C. Specifically, the step of drying the above product can be performed in a range of 100 to 150°C.

[0062] If drying is performed outside the upper limit of the above temperature range, there is a problem that some of the graphite may be oxidized during the drying process and a fire may occur due to combustion. If drying is performed outside the lower limit of the above temperature range, the moisture in the particles in the powder state of the output is not completely dried, and a product with a high moisture content is discharged, which increases the amount of acid used in the leaching process of the wet smelting process downstream.

[0063]

[0064] The above product, in short, the graphite source may have a carbon (C) content of 70 weight% or more, preferably 75 weight% or more.

[0065] It is desirable that high-purity graphite can be recovered when the carbon content satisfies the above range.

[0066] A method for recovering graphite according to the present invention comprises the step of mixing the graphite source with an acidic compound to remove organic carbon contained in the graphite source.

[0067] The method for recovering graphite according to the present invention has the advantage of reducing the amount of acid and base used and significantly reducing the acid and base leaching process recovery compared to conventional cathode material recycling methods by mixing the graphite source with an acidic compound to remove organic carbon contained in the graphite source in advance.

[0068] Generally, the degree of hydrophobicity and hydrophilicity of a material can be determined by measuring the contact angle, and natural graphite has a contact angle of 120° or more, indicating strong hydrophobicity.

[0069] Conversely, the contact angle of the cathode material is 20° or less, and it has very hydrophilic characteristics.

[0070] Since the contact angle of graphite in the state where organic carbon is not removed ranges from 70 to 90° and that of the cathode material ranges from 60 to 80°, the difference in contact angle between the two materials is not large. Therefore, when only graphite is selectively floated and recovered by flotation separation, the effect of increasing the elemental C content is insufficient, and the recovery rate of graphite also becomes very low.

[0071] The organic carbon contained in the above graphite source may be in the form of carbon black or a low molecular weight state, in which polymers such as plastic components PP (Polypropylene), PS (Polystyrene), PC (Polycarbonate), HDPE (High Density Polyethylene), LDPE (Low Density Polyethylene), and binder PVDF (Polypropylidene Fluoride) are not completely thermally decomposed during a high-temperature reduction reaction.

[0072] In this invention, an acidic compound that has strong oxidizing properties but is less harmful to the human body and environmentally safe compared to conventionally used HF (Hydrofulric acid), benzene-based compounds, and toluene-based compounds can be used to break the chain of the organic carbon polymer and decompose it into low-molecular-weight substances, thereby making it easy to remove.

[0073] This offers the advantage of not only increasing the yield of graphite but also raising its purity.

[0074] The above “organic carbon” may include aliphatic compounds, aromatic compounds, ester compounds, etc., and may be interpreted as a term commonly interpreted in the art.

[0075]

[0076] In the present invention, the acidic compound comprises one or more selected from the group consisting of ammonium persulfate, citric acid, boric acid, and ammonium fluoride.

[0077] When the above acidic compound comprises one or more selected from the group consisting of ammonium persulfate, citric acid, boric acid, and ammonium fluoride, it is desirable because it has lower toxicity and lower environmental burden compared to conventionally used reagents, specifically hydrofluoric acid, benzene, toluene, xylene-based compounds, etc., and residual reagents can be recovered and recycled, and water treatment is easy when discharged as wastewater.

[0078]

[0079] In another embodiment of the present invention, the acidic compound may not contain hydrofluoric acid.

[0080] The aforementioned hydrofluoric acid is a highly toxic substance to the environment and the human body, making it difficult to use in large quantities industrially.

[0081] The present invention has the advantage of excellent organic carbon removal performance while not containing the above-mentioned hydrofluoric acid.

[0082]

[0083] The above acidic compound may be in the form of an aqueous solution, but is not limited thereto. However, if the above acidic compound is in the form of an aqueous solution, it is preferable because it facilitates mixing with the graphite source and facilitates the removal of the organic carbon.

[0084]

[0085] In another embodiment of the present invention, the concentration of the acidic compound may be 0.5 to 2.5 M.

[0086] The concentration of the acidic compound may preferably be 0.7 to 2.3 M, and more preferably 1.3 to 2.0 M.

[0087] When the concentration of the acidic compound satisfies the above range, it is desirable to maximize the removal effect of the organic carbon while minimizing the amount of the acidic compound added.

[0088]

[0089] In another embodiment of the present invention, the graphite source to the acidic compound may be mixed in a weight ratio of 1:1 to 1:7.

[0090] The graphite source to the acidic compound can be mixed in a weight ratio preferably 1:1.5 to 1:6, more preferably 1:3 to 1:5.

[0091] When the graphite source and the acidic compound are mixed to satisfy the above weight ratio, it is desirable that the content of the acidic compound is minimized, the mixing of the graphite source and the acidic compound is easy, and the organic carbon contained in the graphite source can be sufficiently dissolved in the acidic compound.

[0092]

[0093] In another embodiment of the present invention, the step of removing the organic carbon may be performed for 0.1 to 4 hours.

[0094] The step of removing the organic carbon above can preferably be performed for 0.3 to 3 hours, more preferably for 0.5 to 2 hours.

[0095] When the step of removing the organic carbon is performed during the above time range, it is desirable that the mixing of the graphite source and the acidic compound is sufficient while minimizing the process time of the step of removing the organic carbon, so that the organic carbon contained in the graphite source can be sufficiently dissolved in the acidic compound.

[0096]

[0097] In another embodiment of the present invention, the step of removing the organic carbon may be performed at 60 to 80°C.

[0098] The step of removing the organic carbon can preferably be performed at 65 to 80°C, more preferably at 70 to 80°C.

[0099] If the step of removing the organic carbon is performed within the above temperature range, it is desirable to suppress the phenomenon of the acidic compound boiling over rapidly while increasing the reactivity between the acidic compound and the carbon source.

[0100]

[0101] The step of removing the organic carbon can be performed under stirring. The stirring is not limited to an RPM as long as the level at which the solids do not settle is maintained. For example, the step of removing the organic carbon can be performed with stirring at 10 to 300 RPM, preferably 50 to 250 RPM, and more preferably 100 to 200 RPM.

[0102] If the above stirring speed satisfies the above range, it is desirable to be able to shorten the process time of the step of removing the organic carbon.

[0103]

[0104] A step of removing the above organic carbon; subsequently, high-purity graphite can be recovered by separating the liquid containing dissolved organic carbon through filtering and washing processes and recovering the residue.

[0105] The above filtering method is not specifically limited in the present invention.

[0106] The above washing can be performed at room temperature and may be done using distilled water, but is not limited thereto.

[0107]

[0108] In another embodiment of the present invention, the method may further include the step of removing the organic carbon; and subsequently, the step of removing impurities by flotation separation of the graphite source from which the organic carbon has been removed.

[0109] Preferably, a method for recovering graphite according to the present invention may include the steps of: preparing a graphite source; mixing the graphite source with an acidic compound to remove organic carbon contained in the graphite source; and removing impurities by flotation separation of the graphite source from which the organic carbon has been removed.

[0110] If the method further includes the step of removing impurities by flotation screening of the graphite source from which the organic carbon has been removed, it is desirable as it has the advantage of increasing the carbon content.

[0111] Although not intended to be limited by theory, by pre-removing the organic carbon from the graphite source, the graphite source is restored to its hydrophobic state, and impurities such as Li compounds, valuable metals such as Ni, Co, Mn, alloys or oxides, FeP, LP, and Cu are hydrophilized to their original characteristics and removed through flotation, thereby increasing the carbon content.

[0112] Specifically, all of the above impurities are hydrophilic and have a low contact angle of 50° or less; however, if organic carbon is adsorbed or coated on the surface, the hydrophilicity may be weakened by the hydrophobic organic carbon. By removing such organic carbon in advance and separating it through flotation, the graphite recovers high hydrophobicity and the above impurities recover high hydrophilicity, allowing the graphite and the impurities to be easily separated.

[0113]

[0114] Specifically, the graphite source and the acidic compound are mixed to remove organic carbon contained in the graphite source, and then the solid-liquid separation is performed. After the solid is separated, a solvent, specifically water, is added to the solid to adjust the concentration of the solid to 5 to 50%, and then flotation separation is performed.

[0115] At this time, solid-liquid separation can be performed by a method conventionally performed, and the present invention is not limited thereto.

[0116]

[0117] The above flotation separation is a method for separating particles by considering the difference in specific gravity of each substance, for example, by utilizing a specific solvent, particles can be separated based on the large or small specific gravity of the particles corresponding to the specific solvent.

[0118] The above flotation separation may be performed using a flotation separator, but is not limited thereto.

[0119] In the above-mentioned flotation separation step, the solvent may be a hydrophilic solvent, such as water.

[0120] Through the above flotation separation, the graphite source from which the hydrophobic organic carbon has been removed is floated, and the hydrophilic impurities can be easily removed by dissolving in the solvent, specifically in water.

[0121]

[0122] Specifically, the solvent may be mixed in a weight ratio of 1:3 to 1:5 with respect to the total weight of the graphite source from which the organic carbon has been removed.

[0123] It is desirable that the solvent is added to satisfy the above range relative to the total weight of the graphite source from which the organic carbon has been removed, so as to maximize the flotation separation efficiency.

[0124]

[0125] In the above floating separation step, the stirring speed of the floating separator may be 100 to 800 RPM, preferably 200 to 700 RPM, and more preferably 300 to 500 RPM.

[0126] When the above stirring speed satisfies the above range, it is desirable to increase the recovery rate of the graphite source from which the organic carbon has been removed as the hydrophobic graphite source is sufficiently suspended.

[0127]

[0128] In the above floating screening step, the floating screening may be performed for 1 to 10 minutes, preferably 2 to 8 minutes, more preferably 2 to 5 minutes.

[0129] If the above flotation separation time satisfies the above time range, it is desirable to increase the recovery rate of the graphite source from which the organic carbon has been removed while minimizing the process time.

[0130]

[0131] In the above-mentioned floating screening step, one or more selected from the group consisting of a foaming agent and a collector may be further added.

[0132] Specifically, in the above-mentioned floating screening step, the foaming agent and the collector may be further added.

[0133] When the above foaming agent is further added, the graphite source from which the organic carbon has been removed rises to the top of the flotation separator along with the bubbles, making recovery easier, which is desirable.

[0134] The above foaming agent is not limited to those commonly used in the industry, and for example, MIBC (Methyl Isobutyl Carbinol), PPG (Polypropylene Glycol), Aero Froth 70, etc. may be used, but are not limited thereto.

[0135] The above foaming agent may be added in an amount of 150 to 250 g / t, but is not limited thereto.

[0136]

[0137] It is desirable to include the above-mentioned collector in addition to the graphite source from which the organic carbon has been removed, as this makes floating easier and can improve processability.

[0138] The above-mentioned saturating agent may use, for example, koresene, xanthochlor, fatty acids, etc., but is not limited thereto.

[0139] The above-mentioned collector may be added in an amount of 150 to 250 g / t, but is not limited thereto.

[0140]

[0141] By recovering the graphite source from which the organic carbon has been removed through the above-mentioned floating separation step, high-purity graphite can be recovered.

[0142] The graphite recovered through the above-mentioned floating separation step may further undergo a drying step, but is not limited thereto, and the drying may be appropriately performed within a range that does not impede the purpose of the present invention.

[0143]

[0144] In another embodiment of the present invention, the recovered graphite may have a content of C element of 82% or more by weight, specifically 84% or more by weight, and more specifically 94% or more by weight, based on the total weight.

[0145] In another embodiment of the present invention, the recovered graphite may have an organic carbon content of 5 weight% or less, specifically 3 weight% or less, more specifically 0.6 weight% or less with respect to the total weight.

[0146] In the present invention, the “organic carbon content” can be obtained by quantitatively analyzing the spectrum of CO2 gas generated by oxidizing all carbon by heating the total graphite content to 1,200°C in an oxygen atmosphere, and by quantifying the CO2 gas generated by oxidizing the un-thermally decomposed element C by oxidizing the same sample by heating it to 750°C in an Ar gas atmosphere for at least 5 minutes. Through this, the organic carbon content is calculated arithmetically as follows. This measurement method is specified in DIN EN 15936 solids TOC method.

[0147] [Equation 1]

[0148] Organic C Content = Total C Content - Elemental C Content

[0149]

[0150] The graphite recovered according to the method for recovering graphite according to the present invention has the advantage of having a high content of C element and a minimized content of organic carbon, as organic carbon contained in the graphite source is removed in advance.

[0151]

[0152] Preferred embodiments and comparative examples of the present invention are described below. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited to the following examples.

[0153]

[0154] Preparation Example: Preparation of a graphite source

[0155] Cells, modules, or packs of electric vehicle waste batteries containing a lithium-ion cathode material, a graphite anode material, an aluminum current collector, a separator, an electrolyte, and a copper current collector were prepared. After freezing the waste batteries at -30°C and crushing them, the waste batteries were shredded using a shredder under atmospheric or inert gas conditions so that the longest length between the width and length was 100 mm or less.

[0156] Afterwards, the crushed battery material was heat-treated at 1,300°C under conditions of 0.5% oxygen partial pressure to perform a reduction process and obtain a reduced heat-treated product.

[0157] Afterwards, the magnetic material was separated and removed from the reduced heat-treated product using a magnetic separator with a magnetic strength of 3,000 Gauss, thereby recovering the non-magnetic graphite source.

[0158] After measuring the elemental C content and organic C content of the recovered graphite source, the results are shown in Table 1 below.

[0159] In addition, the results of LC-MS analysis to qualitatively analyze the organic carbon contained in the recovered graphite source are shown in Figure 1.

[0160] Referring to Figure 1, a typical polymeric pattern is observed, confirming the presence of organic carbon in the sample.

[0161]

[0162] Example 1

[0163] 300g of 2M ammonium persulfate was mixed with 100g of a graphite source obtained according to the preparation example to prepare a slurry, stirred at 25℃ for 2 hours, filtered, and washed with distilled water at room temperature to separate the dissolved organic carbon into a filtrate, and the elemental C content and organic C content of the graphite recovered as residue were measured, and the results are shown in Table 1 below.

[0164]

[0165] Example 2

[0166] A slurry was prepared by mixing 300g of 2M ammonium persulfate with 100g of a graphite source obtained according to the preparation example, and then stirred at 80°C for 2 hours. Except for this, the procedure was carried out in the same manner as Example 1, and the results are shown in Table 1 below.

[0167]

[0168] Example 3

[0169] The graphite recovered through Example 2 was flotated using a Denver Sub A type 2L Cell flotation separator. At this time, 250 g / t of the foaming agent MIBC and 250 g / ton of the collector kerosene were added together. The process was carried out for 5 minutes at a slurry concentration of 30% and an impeller rotation speed of 500 rpm, after which the graphite floating to the top of the equipment was recovered. The elemental C content and organic C content of the recovered graphite were measured, and the results are shown in Table 1 below.

[0170]

[0171] Comparative example

[0172] The graphite obtained according to the preparation example was flotated using a Denver Sub A type 2L Cell flotation separator. At this time, 250 g / t of the foaming agent MIBC and 250 g / ton of the collector kerosene were added together. The process was carried out for 5 minutes at a slurry concentration of 30% and an impeller rotation speed of 500 rpm, after which the graphite floating to the top of the equipment was recovered. The elemental C content and organic C content of the recovered graphite were measured, and the results are shown in Table 1 below.

[0173]

[0174] Elemental C content (wg%) Organic C content (wg%) Graphite source (Preparation example, initial cathode material sample) 75.0 5.69 Graphite recovered according to Comparative Example 80.2 5.2 Graphite recovered according to Example 1 84.3 0.6 Graphite recovered according to Example 2 85.1 0.0 Graphite recovered according to Example 3 94.5 0.0

[0175] Referring to Table 1 above, the graphite recovered according to the comparative example showed a slight increase in the content of element C from 75.0% to 80.2%, which is about 5.2%, compared to the graphite source. However, since graphite has very strong hydrophobic properties, this can be said to be a very low rate of increase in the content of element C compared to graphite obtained through a process of recovering graphite extracted from mines by flotation.

[0176] This is because organic carbon, which is less hydrophobic than graphite, coats the surface of graphite particles to reduce their hydrophobicity, and organic carbon also coats the surfaces of other impurities, such as hydrophilic cathode particles and Li compound particles, thereby imparting hydrophobicity. As a result, the hydrophobic and hydrophilic properties of the two types of particles become similar, which reduces the effect of floating graphite and precipitating impurities.

[0177]

[0178] On the other hand, referring to Examples 1 and 2, it can be seen that the elemental C content increased from 75 wt% of the graphite source sample to 84.3 wt% and 85.1 wt%, respectively, and the organic C content decreased from 5.69 wt% to 0.6 wt% and 0.0 wt%, respectively.

[0179] It can be seen that Example 3 shows an improvement of 14.3 wt% in the elemental C content from 80.2 wt% to 94.5 wt% compared to the comparative example in which organic carbon was not removed. This can be attributed to the fact that the hydrophobicity of the graphite was restored to strong hydrophobicity by first removing the organic carbon, and the impurities were hydrophilized according to their original properties.

[0180]

[0181] The present invention is not limited to the above embodiments and can be manufactured in various different forms, and those skilled in the art will understand that the invention can be implemented in other specific forms without changing the technical concept or essential features of the invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. A step of preparing a graphite source; and A step of mixing the graphite source with an acidic compound to remove organic carbon contained in the graphite source; Includes, The above acidic compound comprises one or more selected from the group consisting of ammonium persulfate, citric acid, boric acid, and ammonium fluoride, Method for recovering graphite.

2. In Paragraph 1, A method for recovering graphite in which the above acidic compound does not contain hydrofluoric acid.

3. In Paragraph 1, A method for recovering graphite in which the graphite source and the acidic compound are mixed in a weight ratio of 1:1 to 1:

7.

4. In Paragraph 1, A method for recovering graphite in which the concentration of the above acidic compound is 0.5 to 2.5 M.

5. In Paragraph 1, A method for recovering graphite in which the step of removing the organic carbon is performed for 0.1 to 4 hours.

6. In Paragraph 1, A method for recovering graphite in which the step of removing the organic carbon is performed at 60 to 80°C.

7. In Paragraph 1, The step of preparing the above graphite source; is, A step of preparing a product obtained by reducing and heat-treating the crushed material recovered from waste batteries at a high temperature; A step of magnetically separating the heat-treated product into magnetic and non-magnetic materials; and Step of separating the above-mentioned non-magnetic material by floating; A method for recovering graphite that includes 8. In Paragraph 1, The step of removing the above organic carbon; thereafter, A step of removing impurities by flotation separation of the graphite source from which the organic carbon has been removed; A method for recovering graphite that further includes 9. In Paragraph 1, A method for recovering graphite in which the recovered graphite has a content of C element of 82% or more based on the total weight.

10. In Paragraph 1, A method for recovering graphite in which the recovered graphite has an organic carbon content of 5% by weight or less relative to the total weight.

11. In Paragraph 10, A method for recovering graphite in which the recovered graphite has an organic carbon content of 0.6 weight% or less relative to the total weight.

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