Method for recovering graphite

Abstract

A method for recovering graphite according to the present invention comprises the steps of: preparing recycled graphite; acid-leaching the recycled graphite; first washing the acid-leached recycled graphite with first washing water containing alcohol; second washing the first-washed recycled graphite with second washing water at 20°C to 90°C; and third washing the second-washed recycled graphite with third washing water at room temperature.

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. 10-2024-0189843, 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 the graphite is intended to be reused for secondary batteries, the low degree of graphitization leads 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 without the risk of fire or explosion, and for easily recovering high-purity graphite with low impurity content through a simple process.

[0013] The present invention provides a method for recovering graphite, comprising the steps of: preparing recycled graphite; acid leaching the recycled graphite; first washing the acid-leached recycled graphite with a first washing water containing alcohol; second washing the first washed recycled graphite with a second washing water at 20 to 90°C; and third washing the second washed recycled graphite with a third washing water at room temperature.

[0014] The method for recovering graphite according to the present invention has the advantage of eliminating the risk of fire and explosion during the process of recovering graphite from waste batteries and enabling the easy recovery of high-purity graphite through a simple process.

[0015] 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.

[0016] 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.

[0017]

[0018] One aspect of the present invention relates to a method for recovering graphite, comprising the steps of: preparing regenerated graphite; acid-leaching the regenerated graphite; acid-leaching the regenerated graphite and washing it first with a first washing water containing alcohol; washing the first-washed regenerated graphite second with a second washing water at 20 to 90°C; and washing the second-washed regenerated graphite third with a third washing water at room temperature.

[0019] The method for recovering graphite according to the present invention has the advantage of improving the efficiency of the high-purity process by performing first to third washes during the washing process after acid leaching of the regenerated graphite.

[0020]

[0021] Step of preparing recycled graphite

[0022] A method for recovering graphite according to the present invention includes the step of preparing recycled graphite.

[0023] In one embodiment of the present invention, the recycled graphite may be derived from waste batteries or process scrap.

[0024] The above recycled graphite may be in a state where organic carbon has been removed.

[0025]

[0026] In another embodiment of the present invention, the step of preparing the regenerated graphite comprises: the step of preparing a graphite source; and the step of mixing the graphite source with an acidic compound to remove organic carbon contained in the graphite source; wherein the acidic compound may comprise one or more selected from the group consisting of ammonium persulfate, citric acid, boric acid, and ammonium fluoride.

[0027] Using the regenerated graphite from which the organic carbon has been removed is desirable because it can reduce process time and the amount of washing water used, and also improve the cleaning effect.

[0028]

[0029] In the present invention, the term “graphite source” may refer to waste batteries or scrap generated during the process of manufacturing secondary batteries.

[0030] 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.

[0031]

[0032] The step of preparing the graphite source may include the step of magnetically separating the crushed material recovered from the waste battery or scrap.

[0033] In another 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.

[0034]

[0035] The step of preparing the shredded material recovered from the above waste battery or scrap is not specifically limited in the present invention.

[0036] 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.

[0037] 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.

[0038]

[0039] 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.

[0040] Specifically, the battery may be a lithium secondary battery. More specifically, the battery may be a spent lithium secondary battery.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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%.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] The above flotation separation may apply the contents described below.

[0063]

[0064] 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.

[0065] 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.

[0066]

[0067] The above product, in short, the graphite source may have a carbon (C) content of 70 weight% or more, preferably 75 weight% or more.

[0068] It is desirable that high-purity graphite can be recovered when the carbon content satisfies the above range.

[0069]

[0070] 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.

[0071] 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.

[0072] 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.

[0073] Conversely, the contact angle of the cathode material is less than 20°, indicating a very hydrophilic characteristic.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] This offers the advantage of not only increasing the yield of graphite but also raising its purity.

[0078] 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.

[0079]

[0080] 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.

[0081] 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.

[0082]

[0083] In another embodiment of the present invention, the acidic compound may not contain hydrofluoric acid.

[0084]

[0085] 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.

[0086] The present invention has the advantage of excellent organic carbon removal performance while not containing the above-mentioned hydrofluoric acid.

[0087]

[0088] 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.

[0089]

[0090] In another embodiment of the present invention, the concentration of the acidic compound may be 0.5 to 2.5 M.

[0091] The concentration of the acidic compound may preferably be 0.7 to 2.3 M, and more preferably 1.3 to 2.0 M.

[0092] 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.

[0093]

[0094] 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.

[0095] 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.

[0096] 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.

[0097]

[0098] In another embodiment of the present invention, the step of removing the organic carbon may be performed for 0.1 to 4 hours.

[0099] Preferably, it can be performed for 0.3 to 3 hours, more preferably for 0.5 to 2 hours.

[0100] 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.

[0101]

[0102] In another embodiment of the present invention, the step of removing the organic carbon may be performed at 60 to 80°C.

[0103] The step of removing the organic carbon can preferably be performed at 65 to 80°C, more preferably at 70 to 80°C.

[0104] 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.

[0105]

[0106] 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.

[0107] 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.

[0108]

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114]

[0115] 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.

[0116] At this time, solid-liquid separation can be performed by a method conventionally performed, and the present invention is not limited thereto.

[0117]

[0118] 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.

[0119] The above flotation separation may be performed using a flotation separator, but is not limited thereto.

[0120] In the above-mentioned flotation separation step, the solvent may be a hydrophilic solvent, such as water.

[0121] 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.

[0122]

[0123] 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.

[0124] 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.

[0125]

[0126] 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.

[0127] 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.

[0128]

[0129] 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.

[0130] 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.

[0131]

[0132] 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.

[0133] Specifically, in the above-mentioned floating screening step, the foaming agent and the collector may be further added.

[0134] 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.

[0135] 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.

[0136] The above foaming agent may be added in an amount of 150 to 250 g / t, but is not limited thereto.

[0137]

[0138] 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.

[0139] The above-mentioned saturating agent may use, for example, koresene, xanthochlor, fatty acids, etc., but is not limited thereto.

[0140] The above-mentioned collector may be added in an amount of 150 to 250 g / t, but is not limited thereto.

[0141]

[0142] By recovering the graphite source from which the organic carbon has been removed, in other words, the regenerated graphite, through the above-mentioned floating separation step, high-purity graphite can be recovered.

[0143] 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.

[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]

[0147] 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.

[0148] [Equation 1]

[0149] Organic C Content = Total C Content - Elemental C Content

[0150]

[0151] 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, namely recycled graphite, is removed in advance.

[0152]

[0153] Acid leaching step of regenerated graphite

[0154] A method for recovering graphite according to the present invention comprises the step of acid leaching the regenerated graphite.

[0155] By acid leaching the above-mentioned recycled graphite, other impurities, specifically cathode material components, and more specifically valuable metals such as nickel, cobalt, manganese, and lithium can be removed.

[0156]

[0157] The acid used in the above acid leaching may be any acid commonly used in the art, provided that it does not impede the purpose of the present invention. For example, the above acid leaching may be performed using inorganic acids such as sulfuric acid, nitric acid, phosphoric acid, and perchloric acid, or organic acids such as phosphoric acid and acetic acid, but is not limited thereto.

[0158] Specifically, the above acid leaching can be performed using sulfuric acid.

[0159] It is desirable that the above acid leaching is performed using the above sulfuric acid, as this can further increase the purity of the recovered graphite.

[0160]

[0161] The above acid may have a concentration of 1.5 to 3 M, preferably 1.5 to 2 M.

[0162] If the concentration of the acid satisfies the above range, it is desirable to maximize the acid leaching effect while reducing process costs.

[0163]

[0164] The above acid leaching can be performed by adding the regenerated graphite to the acidic solution to lower the pH to 3 or lower, specifically to 1 or lower. When the pH of the acidic solution satisfies the above range, a leaching solution containing valuable metals such as nickel, cobalt, manganese, and lithium can be easily obtained.

[0165]

[0166] The above acid leaching can be performed such that the solid-liquid ratio of the regenerated graphite and the acidic solution satisfies 10 to 40 weight%, preferably 10 to 30 weight%, more preferably 15 to 30 weight%.

[0167] If the above high-to-liquid ratio satisfies the above range, it is desirable to be able to increase the acid leaching effect while minimizing the amount of acid used.

[0168]

[0169] In another embodiment of the present invention, the step of acid leaching the regenerated graphite may be performed by immersing the regenerated graphite in acid and then applying ultrasound.

[0170] Specifically, when acid leaching the above-mentioned regenerated graphite, it is desirable to apply ultrasound to maximize the acid leaching effect.

[0171] More specifically, if the carbon content of the regenerated graphite does not reach the battery level, the purity of the recovered graphite can be increased by acid leaching while applying the ultrasound.

[0172]

[0173] The above ultrasound can be applied at 35 to 45 W, preferably 38 to 45 W, and more preferably 40 to 45 W, based on 2 L of solvent.

[0174] When the above-mentioned ultrasound satisfying the above range is applied, it is desirable to maximize the acid leaching effect while reducing the acid leaching time.

[0175] The above acid leaching step can be performed for 0.5 to 8 hours, preferably 1 to 4 hours, more preferably 2 to 4 hours.

[0176] If the above acid leaching step is performed within the above time range, it is desirable to minimize the acid leaching time while ensuring a sufficient acid leaching effect.

[0177]

[0178] The above acid leaching step can be performed at a temperature of 80°C or lower at room temperature, preferably 25°C to 80°C, and more preferably 40°C to 80°C.

[0179] If the acid leaching step is performed within the above temperature range, it is desirable to maximize the acid leaching effect while suppressing the phenomenon of the acid boiling over.

[0180]

[0181] In another embodiment of the present invention, the method may further include the step of acid-leaching the regenerated graphite; and the step of separating the acid-leached regenerated graphite into solid and liquid phases.

[0182] The above solid-liquid separation can be performed using a filter press, vacuum filter, centrifuge, tecanter, etc., but is not limited thereto, and methods commonly performed in the industry may be used.

[0183]

[0184] In another embodiment of the present invention, the method may further include the step of separating solids and liquids; and subsequently, the step of drying the regenerated graphite.

[0185] The above drying may be performed at a temperature of 110 to 180°C, preferably 120 to 150°C, more preferably 140 to 1150°C for 0.5 to 3 hours, preferably 1 to 3 hours, more preferably 2 to 3 hours, but is not limited thereto.

[0186] However, if the above drying is performed to satisfy the above range, it is desirable to be able to minimize the drying time while reducing the energy required for the drying.

[0187]

[0188] The method may further include a step of drying the regenerated graphite; and subsequently, a step of acid-leaching the regenerated graphite.

[0189] In another embodiment of the present invention, the step of acid-leaching the regenerated graphite may be performed two or more times.

[0190] In short, the step of acid-leaching the regenerated graphite may be performed two or more times.

[0191] Specifically, by not undergoing the step of washing after solid-liquid separation of the regenerated graphite, thereby including residual sulfuric acid in the regenerated graphite, and then drying the regenerated graphite; by undergoing the step of finely expanding the interlayer spacing of the regenerated graphite by the residual sulfuric acid contained in the regenerated graphite, and then performing a second acid leaching, the leaching effect of the second acid leaching can be maximized.

[0192]

[0193] In another embodiment of the present invention, the step of acid leaching the regenerated graphite; prior to this, the step of leaching the regenerated graphite with one or more selected from the group consisting of ammonium persulfate, hydrogen peroxide, potassium permanganate, sodium chlorate, chloric acid, and sodium hypochlorite may be further included.

[0194] Specifically, if the organic carbon is not sufficiently removed, the method may further include the step of leaching the regenerated graphite with one or more selected from the group consisting of ammonium persulfate, hydrogen peroxide, potassium permanganate, sodium chlorate, chloric acid, and sodium hypochlorite.

[0195] The amount of solution and the pre-leaching time used in the step of pre-leaching the regenerated graphite can be applied to the amount of solution and the leaching time used in the acid leaching step.

[0196]

[0197] The method may further include, but is not limited to, a step of pre-leaching the regenerated graphite and then separating the regenerated graphite from solid to liquid; and / or a step of drying.

[0198] The conditions for the above-mentioned high-liquid separation step and the above-mentioned drying step may be applied to the aforementioned contents.

[0199]

[0200] First washing step

[0201] The method for recovering graphite according to the present invention comprises the step of washing the acid-leached regenerated graphite with a first washing water containing alcohol.

[0202] Although it is not desired to be limited by theory, after impurities contained in the regenerated graphite are leached by an acid such as sulfuric acid, gelation may occur depending on ion concentration, temperature, etc., and solid-liquid separation into the filtrate may not be effective. In particular, since Co gels into sulfates and is not easily separated into the filtrate, by washing the acid-leached regenerated graphite with the first washing water containing the alcohol, not only is the acid remaining in the regenerated graphite removed, but the gelled salts can also be dissolved and removed into the filtrate using an alcohol-based washing solution.

[0203] In another embodiment of the present invention, the first washing water may comprise one or more selected from the group consisting of methanol, ethanol, isopropanol, n-propanol, butanol, and isobutanol. Specifically, the first washing water may comprise a diluted solution of alcohol.

[0204] In another embodiment of the present invention, the first washing water may contain methanol. Specifically, the first washing water may be methanol.

[0205] When the first washing water is methanol, it is desirable because it not only effectively removes residual acid on the regenerated graphite due to its strong cleaning power, but also suppresses the phenomenon of residual matter remaining on the surface of the regenerated graphite after the first washing due to its high volatility. In particular, as mentioned above, it is desirable because it facilitates the removal of gelled substances, and it is also desirable in terms of reducing process costs because it is cheaper than other alcohols.

[0206]

[0207] The first washing water may be used in an amount of 1 to 2 times, preferably 1 to 1.5 times, relative to the total weight of the recycled graphite. The first washing water may further include distilled water, wherein the distilled water may be used in an amount of 1 to 10 times, preferably 2 to 5 times, relative to the total weight of the recycled graphite.

[0208] If the amount of the first washing water used satisfies the above range, it is desirable that not only is the amount of the first washing water minimized, but the amounts of the second washing water and the third washing water to be described later can also be minimized.

[0209] The first washing described above may be performed by an immersion method, but is not limited thereto. For example, the first washing may be performed by repeating solid-liquid separation after immersion, but is not limited thereto, and a conventionally performed method may be used.

[0210] For example, the first washing may be performed two or more times, but is not limited thereto.

[0211]

[0212] Second washing step

[0213] The graphite recovery method according to the present invention comprises the step of washing the first washed regenerated graphite a second time with a second washing water at 20 to 90°C.

[0214] Specifically, the second washing water may have a temperature of 25 to 90°C, more specifically 50 to 90°C, and most specifically 50 to 80°C.

[0215] By washing the first washed regenerated graphite with the second washing water, impurities remaining in the form of complexes can be dissolved.

[0216] Specifically, since carbonate-based impurities have high solubility at relatively low temperatures, specifically below 50°C, and more specifically at room temperature of about 23 to 25°C, it is easy to use a second washing water at a relatively low temperature.

[0217] When the second washing water is at a high temperature, specifically 50 to 90°C, there is an advantage in that the gelled salts can be easily removed.

[0218] The second washing water can be used in an amount of 1 to 2 times, preferably 1 to 1.5 times, the total weight of the recycled graphite.

[0219] If the amount of the second washing water used satisfies the above range, it is desirable that not only is the amount of the second washing water minimized, but the amount of the first washing water and the third washing water to be described later can also be minimized.

[0220]

[0221] The second washing water may be water or NaOH. Specifically, the second washing water may be water.

[0222] Specifically, the second washing water may be high-temperature water of 50°C or higher, and thus, even if water is used, the solubility of salts remaining in the solid graphite is increased so that they can be easily removed.

[0223] However, since carbonate-based impurities have high solubility in relatively low-temperature water, it is desirable to appropriately adjust the temperature of the second washing water according to the type of residual impurities.

[0224]

[0225] 3rd washing step

[0226] A method for recovering graphite according to the present invention comprises the step of washing the regenerated graphite that has been washed a third time with a third washing water at room temperature.

[0227] The third washing water may be room temperature water, for example, 30°C or lower.

[0228] Specifically, if the second washing water is at a high temperature, specifically 50°C or higher, it is preferable to use low-temperature water of 30°C or lower for the third washing water to increase the solubility of carbonate-based impurities and remove them.

[0229] The above third washing water may be water.

[0230] The third washing water can be used in an amount of 1 to 2 times, preferably 1 to 1.5 times, the total weight of the recycled graphite.

[0231] If the amount of the third washing water used satisfies the above range, it is desirable that not only is the amount of the third washing water minimized, but the amounts of the first washing water and the second washing water can also be minimized.

[0232]

[0233] In another embodiment of the present invention, the method may further include the step of washing the second washed regenerated graphite a third time with a third washing water at room temperature; and the step of leaching the third washed regenerated graphite with a base.

[0234] Specifically, if the carbon content of the regenerated graphite washed in the third step is less than the desired carbon content, more specifically, if the carbon content is less than 99.96% and Al-based impurities and other oxide-based impurities remain, the purity of the obtained graphite can be increased by further including a step of leaching with a base.

[0235] The above base may include one or more selected from the group consisting of NaOH, KOH, and Na2CO3, but is not limited thereto, and bases commonly used in the industry may be used.

[0236] Specifically, the base may be NaOH.

[0237] If the above base is NaOH, it is desirable as it offers the advantage of minimizing leaching time while reducing process costs.

[0238] The above base may have a concentration of 1 to 10 M, preferably 2 to 7 M, and more preferably 2 to 5 M.

[0239] If the concentration of the above base satisfies the above range, it is desirable to maximize the base leaching effect while reducing process costs.

[0240] The above base may be used in an amount of 1 to 5 times, preferably 2 to 5 times, the total weight of the regenerated graphite.

[0241] If the amount of the above base used satisfies the above range, it is desirable because the removal of residual impurities is effective while minimizing the amount of the above base used.

[0242]

[0243] The above base leaching can be performed for 1 to 4 hours, preferably 1.5 to 4 hours, and more preferably 2 to 4 hours.

[0244] It is desirable that the above base leaching be performed within the above time range, as this allows residual impurities to be sufficiently dissolved while minimizing process time.

[0245]

[0246] In another embodiment of the present invention, the method may further include the step of washing the second washed regenerated graphite a third time with a third washing water at room temperature; and then mixing the third washed regenerated graphite with one or more fluorine compounds selected from the group consisting of NH4F, NaF, KF, and BF3 to decompose residual organic matter.

[0247] Specifically, if the initial sample of the regenerated graphite has high Cu and organic carbon content, the acid leaching effect may be somewhat reduced because the NCM component dissolves after all the Cu is dissolved during the aforementioned acid leaching. Therefore, high-purity graphite can be recovered by performing a preliminary acid leaching step, followed by sulfuric acid leaching and the first to third washes, and then mixing with the fluorine-based compound to decompose the residual organic matter.

[0248] In summary, if the Cu content and organic carbon content of the initial sample of the regenerated graphite are somewhat high, for example, if the Cu content exceeds 2% and the organic carbon content exceeds 2%, it is preferable to further perform the step of acid leaching the regenerated graphite; prior to that, the step of leaching the regenerated graphite with one or more selected from the group consisting of ammonium persulfate, hydrogen peroxide, potassium permanganate, sodium chlorate, chloric acid, and sodium hypochlorite; and the step of decomposing residual organic matter by mixing the third washed regenerated graphite with one or more fluorine-based compounds selected from the group consisting of NH4F, NaF, KF, and BF3.

[0249] The above fluorine-based compound may be included in an amount of 5 to 30 parts by weight, preferably 5 to 20 parts by weight, and more preferably 5 to 10 parts by weight, based on 100 parts by weight of the total recycled graphite.

[0250] When the above-mentioned fluorine-based compound is mixed within the above range, it is desirable to maximize the desired effect while minimizing the amount of the fluorine compound used.

[0251]

[0252] In another embodiment of the present invention, the method may further include the step of decomposing the residual organic matter; or the step of leaching the base from the third washed regenerated graphite; and subsequently, the step of washing the regenerated graphite a fourth time with a fourth washing water.

[0253] Between the step of decomposing the residual organic matter and the fourth washing step, a step of drying the regenerated graphite may be further included, but is not limited thereto.

[0254] At this time, the above drying may be applied to the aforementioned contents.

[0255] Between the step of leaching the regenerated graphite with a base and the step of washing the fourth, a step of separating the regenerated graphite from solid to liquid may be further included, but is not limited thereto.

[0256] At this time, the above-mentioned high-value separation can be applied to the aforementioned details.

[0257]

[0258] Except that the above-mentioned fourth washing water may be room temperature water and the above-mentioned fourth washing water may be used in a ratio of 3 to 5 times the total weight of the regenerated graphite, the contents of the above-mentioned third washing water may be applied.

[0259] High-purity graphite can be recovered by washing the base or the fluorine-based compound together with residual impurities with the above-mentioned fourth washing water.

[0260]

[0261] The above-mentioned fourth washing step; thereafter, a drying step may be further included as needed, but is not limited thereto.

[0262]

[0263] The graphite recovered by the method of recovering graphite according to the present invention has the advantage of high purity and a very low impurity content.

[0264] Specifically, the graphite recovered by the method of recovering graphite according to the present invention may have a C content of 99.96% or more, specifically 99.98% or more.

[0265] Therefore, the graphite recovered by the method of recovering graphite according to the present invention can be usefully used as a negative electrode material for a secondary battery.

[0266]

[0267] 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.

[0268]

[0269] <Experimental Example 1>

[0270] Manufacturing of graphite sources

[0271] 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.

[0272] 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.

[0273] Afterwards, the magnetic material was separated and removed from the reduced heat-treated product using a magnetic separator with a magnetic force of 3,000 Gauss, thereby recovering the non-magnetic graphite source.

[0274] After measuring the elemental C content and organic C content of the recovered graphite source, the results are shown in Table 1 below.

[0275]

[0276] Sample 1

[0277] 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.

[0278]

[0279] Sample 2

[0280] A slurry was prepared by mixing 300g of 2M ammonium persulfate with 100g of a graphite source obtained according to the preparation example, and the process was carried out in the same manner as Sample 1, except that the mixture was stirred at 80°C for 2 hours, and the results are shown in Table 1 below.

[0281]

[0282] Sample 3

[0283] The graphite recovered from Sample 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.

[0284]

[0285] Sample 4

[0286] 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.

[0287]

[0288] Elemental C Content (wg%) Organic C Content (wg%) Graphite Source (Preparation Example, Initial Cathode Material Sample) 75.0 5.69 Graphite recovered according to Sample 1 84.3 0.6 Graphite recovered according to Sample 2 85.1 0.0 Graphite recovered according to Sample 3 94.5 0.0 Graphite recovered according to Sample 4 80.2 5.2

[0289] Referring to Table 1 above, the graphite recovered according to Sample 4 showed a slight increase in the content of elemental 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 elemental C compared to graphite obtained through the process of recovering graphite extracted from mines by flotation.

[0290] 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.

[0291]

[0292] On the other hand, referring to samples 1 and 2, it was found 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.

[0293] It can be seen that Sample 3 showed an improvement of 14.3 wt% in 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 organic carbon was removed first to restore the hydrophobicity of graphite to strong hydrophobicity, and impurities were hydrophilized to their original properties.

[0294] In order to use the graphite obtained through the method of Sample 2 or Sample 3 as a negative electrode material for a secondary battery, the elemental C content must be 99.96% or higher, so it is necessary to remove trace amounts of impurities again.

[0295]

[0296] <Experimental Example 2>

[0297] Regenerated graphite (Sample 4) was obtained using the same method as Sample 3 of Experimental Example 1. The composition of the regenerated graphite was confirmed through ICP analysis, and the results are shown in Table 2 below.

[0298] After that, graphite was recovered from the recycled graphite (sample 4) using the methods according to the examples and comparative examples, respectively, and the components of the recovered graphite were confirmed through ICP analysis, and the results are shown in Table 2 below.

[0299]

[0300] (wt%) C Grade Ni Grade Co Grade Mn Grade Li Grade Al Grade Cu Grade Starting material (regenerated graphite, sample 4) 8 1.8 2.1 0.6 0.7 0.9 3.4 2.5 Example 1 9 6.6 20.06 9 0.01 9 0.01 30.4 2 6 22.01 Example 2 9 9.8 50.007 0.002 0.003 0.007 0.015 0.027 Example 3 9 9.99 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 Example 4 9 9.98 <0.0001 <0.0001 <0.0001 0.001 50.003 3 <0.0001

[0301] Example 1

[0302] (Primary leaching with sulfuric acid) Regenerated graphite was subjected to primary acid leaching using 2M sulfuric acid. At this time, the solid-to-liquid ratio was 20 wt%, the leaching temperature was 60℃, and the leaching time was 4 hours.

[0303] (Solid-liquid separation and room temperature water washing) After separating the solid and liquid of the regenerated graphite that had undergone primary leaching with sulfuric acid, it was washed with room temperature water (distilled water). At this time, the washing solution was used in a ratio of 2 times the total weight of the regenerated graphite.

[0304] (Secondary leaching with sulfuric acid) Regenerated graphite washed with room temperature water was subjected to secondary acid leaching. Specifically, the regenerated graphite was subjected to secondary acid leaching using 3M sulfuric acid. At this time, the solid-to-liquid ratio was 30 wt%, the leaching temperature was 80℃, and the leaching time was 8 hours.

[0305] (Solid-liquid separation and room temperature water washing) After separating the solid and liquid of the regenerated graphite that had undergone secondary leaching with sulfuric acid, it was washed with room temperature water (distilled water). At this time, the washing solution was used in a ratio of 2 times the total weight of the regenerated graphite.

[0306] (NaOH leaching) Washed recycled graphite was leached with 2M NaOH. At this time, the amount of NaOH used was 5 times the total weight of the recycled graphite, the leaching temperature was 60℃, and the leaching time was 8 hours.

[0307] (Solid-liquid separation and room temperature water washing) After NaOH leaching, the regenerated graphite was separated into solid and liquid phases and then washed with room temperature water (distilled water). At this time, the washing solution was used in a ratio of 5 times the total weight of the regenerated graphite.

[0308]

[0309] Example 2

[0310] (Primary sulfuric acid leaching) Regenerated graphite was subjected to primary acid leaching using 2M sulfuric acid. At this time, the solid-to-liquid ratio was 20 wt%, the leaching temperature was 80℃, and the leaching time was 4 hours. In addition, ultrasound was applied at 45W during the acid leaching process.

[0311] (First wash) Recycled graphite was washed using methanol (concentration: 25%). At this time, the washing solution was used in a ratio of 1.5 times the total weight of the recycled graphite.

[0312] (Second Wash) The recycled graphite was washed using distilled water at 60°C. At this time, the washing solution was used in a ratio of 1.5 to the total weight of the recycled graphite.

[0313] (Third Wash) The recycled graphite was washed using distilled water at room temperature. At this time, the washing solution was used in a ratio of 1.5 times the total weight of the recycled graphite.

[0314] (NaOH leaching) Washed recycled graphite was leached with 2M NaOH. At this time, the amount of NaOH used was 5 times the total weight of the recycled graphite, the leaching temperature was 80℃, and the leaching time was 4 hours.

[0315] (Solid-liquid separation and room temperature water washing) After NaOH leaching, the regenerated graphite was separated into solid and liquid phases and then washed with room temperature water (distilled water). At this time, the washing solution was used in a ratio of 5 times the total weight of the regenerated graphite.

[0316]

[0317] Example 3

[0318] (Primary leaching with sulfuric acid) Regenerated graphite was subjected to primary acid leaching using 2M sulfuric acid. At this time, the solid-to-liquid ratio was 20 wt%, the leaching temperature was 60℃, and the leaching time was 2 hours.

[0319] (Solid-liquid separation and drying) The recycled graphite obtained from the first acid leaching was separated into solid and liquid phases and then dried at a temperature of 140°C for 2 hours.

[0320] (Secondary leaching of sulfuric acid)

[0321] Regenerated graphite was subjected to secondary acid leaching using 2M sulfuric acid. At this time, the solid-to-liquid ratio was 20 wt%, the leaching temperature was 60℃, and the leaching time was 2 hours.

[0322] (Solid-liquid separation) Regenerated graphite leached by secondary acid separation was separated into solid and liquid.

[0323] (First wash) Recycled graphite was washed using methanol (concentration: 25%). At this time, the washing solution was used in a ratio of 1.5 times the total weight of the recycled graphite.

[0324] (Second Wash) The recycled graphite was washed using distilled water at 60°C. At this time, the washing solution was used in a ratio of 1.5 to the total weight of the recycled graphite.

[0325] (Third Wash) The recycled graphite was washed using distilled water at room temperature. At this time, the washing solution was used in a ratio of 1.5 times the total weight of the recycled graphite.

[0326] (NaOH leaching) Washed recycled graphite was leached with 2M NaOH. At this time, the amount of NaOH used was 4 times the total weight of the recycled graphite, the leaching temperature was 60℃, and the leaching time was 2 hours.

[0327] (Solid-liquid separation and room temperature water washing) After NaOH leaching, the regenerated graphite was separated into solid and liquid phases and then washed with room temperature water (distilled water). At this time, the washing solution was used in a ratio of 3 times the total weight of the regenerated graphite.

[0328]

[0329] Example 4

[0330] (Pre-leaching with ammonium persulfate) Regenerated graphite was pre-leached using 2M ammonium persulfate. At this time, the amount of ammonium persulfate used was 4 times the total weight of the regenerated graphite, the leaching temperature was 40℃, and the leaching time was 1 hour.

[0331] (Solid-liquid separation and room temperature water washing) Regenerated graphite that had undergone ammonium persulfate pre-leaching was separated into solid and liquid phases and then washed with room temperature water (distilled water). At this time, the washing solution was used in a ratio of 2 times the total weight of the regenerated graphite.

[0332] (Primary leaching with sulfuric acid) Regenerated graphite was subjected to primary acid leaching using 2M sulfuric acid. At this time, the solid-to-liquid ratio was 25 wt%, the leaching temperature was 60℃, and the leaching time was 2 hours.

[0333] (Solid-liquid separation and drying) The recycled graphite obtained from the first acid leaching was separated into solid and liquid phases and then dried at a temperature of 140°C for 2 hours.

[0334] (Secondary leaching of sulfuric acid)

[0335] Regenerated graphite was subjected to secondary acid leaching using 2M sulfuric acid. At this time, the solid-liquid ratio was 25 wt%, the leaching temperature was 60℃, and the leaching time was 2 hours.

[0336] (Solid-liquid separation) Regenerated graphite leached by secondary acid separation was separated into solid and liquid.

[0337] (First Wash) Recycled graphite was washed using methanol (concentration: 25%). At this time, the washing solution was used in a ratio of 1 to the total weight of the recycled graphite.

[0338] (Second Wash) The recycled graphite was washed using distilled water at 60°C. At this time, the washing solution was used in a ratio of 1 to the total weight of the recycled graphite.

[0339] (Third Wash) The recycled graphite was washed using distilled water at room temperature. At this time, the washing solution was used in a ratio of 1 to the total weight of the recycled graphite.

[0340] (NH4F mixing and drying)

[0341] 5 parts by weight of NH4F were mixed with 100 parts by weight of the total washed recycled graphite and then dried at a temperature of 80°C.

[0342] (Washing with room temperature water) Regenerated graphite mixed with NH4F was washed with room temperature water (distilled water). At this time, the washing solution was used in a ratio of 5 times the total weight of the regenerated graphite.

[0343]

[0344] Referring to Table 2 above, Example 1 is a case where room temperature water was used throughout the washing process, and Example 2 is a method of Example 1 in which methanol was used during the washing process, followed by a second washing with high-temperature water at 80°C and a third washing with room temperature water, thereby dissolving and discharging the substance remaining as a complex in the graphite solid in the form of sulfates into the filtrate, so that the purity of the graphite is slightly improved.

[0345] Example 3 is a method that maximizes the effect of the second leaching by performing only solid-liquid separation after the first sulfuric acid leaching and not washing, thereby leaving residual sulfuric acid in the regenerated graphite, drying at 140°C to slightly expand the interlayer spacing of the graphite due to the residual sulfuric acid, and then performing a second sulfuric acid leaching. Subsequently, as in Example 2, it was washed with methanol, high-temperature water, and room-temperature water; at this time, since the C content was less than 99.96%, base leaching with NaOH was performed again to improve the C quality.

[0346] In Example 4, high-purity graphite was recovered by performing pre-leaching using ammonium persulfate, which is effective for leaching Cu, followed by solid-liquid separation and washing, then performing primary leaching and solid-liquid separation with sulfuric acid, washing with methanol, high-temperature water, and room-temperature water, decomposing organic matter using ammonium NH4F fluoride to dissolve organic C and residual impurities, and then performing immersion treatment followed by solid-liquid separation and washing.

[0347] That is, referring to Table 2, it can be seen that the graphite recovered according to the example has high C purity and low impurity content.

[0348]

[0349] 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. Step of preparing recycled graphite; A step of acid leaching the above-mentioned regenerated graphite; A step of first washing the acid-leached regenerated graphite with a first washing water containing alcohol; A step of washing the first washed regenerated graphite a second time with a second washing water at 20 to 90°C; and A step of washing the regenerated graphite that has been washed a second time with a third washing water at room temperature; including, Method for recovering graphite.

2. In Paragraph 1, The step of acid leaching the regenerated graphite is performed by immersing the regenerated graphite in acid and then applying ultrasound. Method for recovering graphite.

3. In Paragraph 1, A method for recovering graphite in which the temperature of the second washing water is 50 to 90°C.

4. In Paragraph 1, A method for recovering graphite in which the first washing water comprises one or more selected from the group consisting of methanol, ethanol, isopropanol, n-propanol, butanol, and isobutanol.

5. In Paragraph 4, A method for recovering graphite in which the first washing water above contains methanol.

6. In Paragraph 1, A step of washing the regenerated graphite washed a third time with a third washing water at room temperature; thereafter, A method for recovering graphite, further comprising the step of leaching the base from the third washed regenerated graphite.

7. In Paragraph 1, A step of washing the regenerated graphite washed a third time with a third washing water at room temperature; thereafter, A method for recovering graphite, further comprising the step of mixing the third washed regenerated graphite with one or more fluorine-based compounds selected from the group consisting of NH4F, NaF, KF, and BF3 to decompose residual organic matter.

8. In Paragraph 6 or 7, A step of decomposing the above residual organic matter; or a step of leaching the base from the third washed regenerated graphite; thereafter, A method for recovering graphite, further comprising the step of washing the above-mentioned regenerated graphite with a fourth washing water.

9. In Paragraph 1, A method for recovering graphite in which the step of acid leaching the above-mentioned regenerated graphite is performed two or more times.

10. In Paragraph 1, The step of acid leaching the above-mentioned regenerated graphite; thereafter, A method for recovering graphite, further comprising the step of separating solids and liquids from the acid-leached regenerated graphite.

11. In Paragraph 10, A method for recovering graphite, further comprising the above-mentioned step of separating solids and liquids; and subsequently, the step of drying the regenerated graphite.

12. In Paragraph 1, The step of acid leaching the above-mentioned regenerated graphite; prior to, A method for recovering graphite, further comprising the step of leaching the regenerated graphite with one or more selected from the group consisting of ammonium persulfate, hydrogen peroxide, potassium permanganate, sodium chlorate, chloric acid, and sodium hypochlorite.

13. In Paragraph 1, The above-mentioned recycled graphite is a method for recovering graphite derived from waste batteries or process scrap.

14. In Paragraph 1, The step of preparing the above-mentioned regenerated graphite; is, 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.

15. In Paragraph 14, 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; The method comprises the step of magnetically separating the heat-treated product into a magnetic material and a non-magnetic material; and the step of floatingly separating the non-magnetic material. Method for recovering graphite.