Graphite refining method

Abstract

The graphite purification method according to the present invention includes an acid washing step of acid washing graphite with an acid mixture, an acid mixture recovery step of recovering the acid mixture after washing in the acid washing step, a washing step of washing the graphite separated from the acid mixture in the acid mixture recovery step, and a dehydration step of dehydrating the graphite after washing in the washing step.

Description

Technical Field

[0001] The present invention relates to a method for purifying graphite, and more particularly, to a method for purifying low-purity graphite using an acid mixture to obtain high-purity graphite with a purity of 99% or more, and minimizing environmental pollution and post-treatment costs by recovering and reusing the acid mixture used for purification.

Background Art

[0002] Ordinary graphite mined in nature exhibits a purity of only 70% to 80% even under optimal conditions. However, by beneficiating these natural graphite, graphite with a carbon content of about 95% to 97% can be obtained.

[0003] However, with the development of industries in recent years, there is a growing demand for more highly purified graphite in applications such as friction materials, electrodes, batteries, fuel cells, and graphene.

[0004] In particular, in recent years, due to the explosive demand caused by industrial development and its wide use as the negative electrode material of lithium-ion batteries, there is currently a demand for graphite purified to a carbon content of 99% or more.

[0005] Since the purity of graphite after ordinary mining and beneficiation processes is relatively low, in order to obtain high-purity graphite, it is necessary to purify the graphite to further increase its carbon content.

[0006] Graphite concentrate contains mainly metal impurities such as iron sulfide and quartz in addition to the carbon component. A method is known for increasing the purity of graphite by treating the graphite concentrate with an acid to dissolve the impurities.

[0007] Conventional processes for producing high-purity graphite are roughly classified into a wet smelting method and a dry smelting method.

[0008] Wet smelting methods include flotation, alkali fusion, and acid-based refining, while dry smelting methods include chlorine roasting and high-temperature processing.

[0009] These conventional processes for refining high-purity graphite often involve the use of toxic gases or generate large amounts of wastewater, resulting in high post-treatment costs and posing problems from both an economic and environmental standpoint.

[0010] Therefore, there is a strong need for graphite refining methods that can minimize environmental pollution and reduce post-processing costs. [Overview of the project] [Problems that the invention aims to solve]

[0011] This invention aims to solve the problems of the conventional method and to provide a graphite refining method that can refine low-purity graphite using an acid mixture to produce high-purity graphite with a purity of 99% or more, while minimizing environmental pollution and post-treatment costs by recovering and reusing the acid mixture used in the refining process.

[0012] The objects of the present invention are not limited to those stated above, and other objects not explicitly stated will be clearly understood by those skilled in the art from the following description. [Means for solving the problem]

[0013] A graphite refining method for achieving the above-described object of the present invention comprises: an acid washing step of acid washing graphite with an acid mixture; an acid mixture recovery step of recovering the acid mixture after washing in the acid washing step; and a washing step of washing the graphite separated from the acid mixture in the acid mixture recovery step. The process includes a dewatering step of dewatering the graphite that has been cleaned in the cleaning step.

[0014] In this case, the acid mixture may be a mixture of hydrochloric acid and hydrofluoric acid.

[0015] Furthermore, the weight ratio of graphite:hydrochloric acid:hydrofluoric acid can be 1:0.5 to 1:0.5 to 1.

[0016] Furthermore, in the acid washing step, the graphite and the acid mixture may be added to the reactor and the washing process may be carried out for 10 to 30 hours.

[0017] Furthermore, the cleaning process may be repeated one to five times.

[0018] Furthermore, the cleaning process may be carried out using water equivalent to 40% to 50% of the volume of the graphite.

[0019] Furthermore, in the washing process, the graphite can be washed using ultrapure water.

[0020] Furthermore, the acid mixture recovery step or dehydration step may be performed in a vacuum belt filter.

[0021] Furthermore, the acid mixture recovery step may include a solid-liquid separation step for separating the acid mixture from the graphite, and a foreign matter removal step for removing foreign matter from the acid mixture separated in the solid-liquid separation step.

[0022] Furthermore, the foreign matter removal step may include a first foreign matter removal step for temporarily removing foreign matter from the acid mixture separated in the solid-liquid separation step, and a second foreign matter removal step for removing relatively minute foreign matter remaining after the first foreign matter removal step.

[0023] Furthermore, in the first foreign matter removal process, a Teflon filter is used to remove foreign matter. In the second foreign matter removal step, foreign matter can be removed using an ion exchange resin filter.

[0024] Furthermore, the acid mixture obtained through the first foreign matter removal step and the second foreign matter removal step can be reused in the acid washing step.

[0025] In addition, in order to adjust the ratio of the recycled acid mixture, a predetermined amount of additional acid mixture can be introduced.

Advantages of the Invention

[0026] According to the graphite purification method of the present invention, the following effects can be achieved.

[0027] First, by purifying low-purity graphite using an acid mixture, high-purity graphite with a purity of 99% or more can be obtained.

[0028] Second, by using a reactor for acid washing and a vacuum belt filter, a continuous process becomes possible, and high-purity graphite with high purity can be continuously obtained.

[0029] Third, by using an acid mixture obtained by mixing hydrofluoric acid and hydrochloric acid, the acid washing efficiency of graphite is improved, and the production efficiency can be improved.

[0030] Fourth, instead of using the acid mixture only once and then discarding it, after separating and recovering the acid mixture after the acid washing is completed by solid-liquid separation, removing foreign substances mixed in the acid mixture, and recycling it more than 10 times, environmental pollution can be minimized and the purification cost can be reduced.

[0031] Fifth, by washing the solid-liquid separated graphite with ultrapure water, and at this time, using only the minimum amount of washing water, environmental pollution and purification cost can be minimized, and the washing efficiency can be maximized.

[0032] The effects of the present invention are not limited to the effects exemplified above, and other effects not mentioned will also be clearly understood by those skilled in the art from the description of the claims.

Brief Description of the Drawings

[0033] The following drawings accompanying this specification illustrate preferred embodiments of the present invention and, together with the detailed description of the invention, serve to further illustrate the technical idea of ​​the invention. Therefore, the present invention is not to be construed as being limited solely to what is shown in these drawings.

[0034] [Figure 1] This is a flowchart illustrating the graphite refining method according to the present invention. [Modes for carrying out the invention]

[0035] The advantages and features of the present invention, as well as methods for achieving them, will become clearer by referring to the embodiments described in detail below, together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below and can be carried out in a variety of different forms, and these embodiments are provided only to complete the disclosure of the present invention and to allow those skilled in the art to fully understand the scope of the present invention, and the present invention is defined solely by the claims.

[0036] The terms used herein are for illustrative purposes only and are not intended to limit the invention. In this specification, the singular form includes the plural form unless otherwise specified in the context. The terms “comprises” and / or “comprising” as used herein do not exclude the existence or addition of one or more other components in addition to those described. Throughout this specification, identical reference numerals refer to the same component, and “and / or” includes each of the described components and all one or more combinations thereof. Furthermore, terms such as “first,” “second,” etc., are used to describe various components, but these components are not limited by these terms; they are simply used to distinguish one component from others. Therefore, it goes without saying that the first component referred to below may be the second component within the scope of the technical idea of ​​the invention.

[0037] Unless otherwise defined, all terms used herein (including technical and scientific terms) shall be used in the sense generally understood by those skilled in the art in the field to which this invention pertains. Furthermore, terms defined in general dictionaries shall not be interpreted ideally or excessively unless explicitly given a specific definition.

[0038] Preferred embodiments of the present invention will be described in detail below with reference to the attached drawings.

[0039] Graphite refining method Figure 1 is a flowchart showing the graphite purification method according to the present invention in sequence. As shown in Figure 1, the graphite purification method according to the present invention first involves washing the graphite with an acid mixture to remove impurities such as metal impurities contained in the graphite (S100). In this acid washing step S100, the graphite and the acid mixture are simultaneously put into a reactor and leaching is performed for 10 to 30 hours, preferably about 20 hours. At this time, the acid mixture used for acid washing can be a mixture of various acidic liquids in various ratios, but it is preferable to use an acid mixture of hydrochloric acid (HCl) and hydrofluoric acid (HF). Here, hydrochloric acid diluted to 30% to 40%, preferably about 35%, is used, and hydrofluoric acid diluted to 40% to 60%, preferably about 50%, is used.

[0040] Furthermore, the acid mixture used in the acid washing process S100 is a mixture of graphite, hydrochloric acid, and hydrofluoric acid in a weight ratio of 1:0.5 to 1:0.5 to 1, preferably 1:0.75:0.75. That is, the hydrochloric acid and hydrofluoric acid constituting the acid mixture are mixed in a weight ratio of 1:1, and the acid washing can be carried out by adding the acid mixture thus mixed to the reactor in a weight ratio of graphite and acid mixture of 1:1 to 1:2, preferably 1:1.5. If the ratio of the acid mixture is less than 1, the leaching effect of graphite by acid washing will be insufficient, while if the ratio of the acid mixture exceeds 2, there will be no significant difference in the leaching effect. Therefore, from the viewpoint of preventing the wasteful use of the acid mixture, it is preferable to select the ratio of graphite to the acid mixture from the weight ratio range of 1:1 to 1:2.

[0041] In the aforementioned acid washing process S100, the graphite is leached with an acid mixture in the reactor for a predetermined time, and foreign substances such as metal impurities contained in the graphite are removed.

[0042] Next, the graphite and acid mixture leached out in the reactor for a predetermined time is subjected to solid-liquid separation, and the separated acid mixture is recovered (S200). More specifically, this acid mixture recovery step (S200) may include a solid-liquid separation step (S210), a first foreign matter removal step (S220), and a second foreign matter removal step (S230). Each step is described in detail below.

[0043] First, the solid-liquid separation step S210 is a step in which the solid graphite and the liquid acid mixture supplied from the reactor are separated. Such a solid-liquid separation step (S210) can be carried out using any apparatus that can easily separate the solid graphite and the liquid acid mixture, but in the present invention, it is preferable to carry out the steps from the acid mixture recovery step (S200) to the dewatering step (S400) described later using a vacuum belt filter. Since vacuum belt filters are well known, a detailed explanation of their configuration and usage will be omitted. To ensure that subsequent steps can be carried out more smoothly, the graphite separated by the vacuum belt filter may be further fed into a vacuum belt filter to spread the graphite widely on the vacuum belt filter to a predetermined thickness before the washing step (S300).

[0044] A vacuum belt filter is a device that filters and dewaters sludge generated in desulfurization equipment or various chemical processes, and is applicable to various chemical processes. In such a vacuum belt filter, sludge that has passed through the sedimentation and classification equipment is uniformly distributed at the top of the filter, and after the water contained in the sludge is removed by vacuum, it is finally discharged. Furthermore, by washing the filter cloth at the same time as dewatering the cake, the vacuum belt filter maintains consistency in dewatering conditions and enables continuous processing. Due to these characteristics, it is preferable to use a vacuum belt filter in the graphite refining method according to the present invention. That is, in the solid-liquid separation step (S210) according to the present invention, when the graphite and acid mixture are introduced into the vacuum belt filter from the reactor, the solid graphite remains at the top of the vacuum belt filter, and the liquid acid mixture flows downward through the vacuum belt filter, thereby performing solid-liquid separation.

[0045] The first foreign matter removal step (S220) is a step to remove foreign matter contained in the acid mixture separated from graphite in the solid-liquid separation step (S210). This first foreign matter removal step (S220) is a step to remove residual sludge, such as some graphite, that remains after the solid-liquid separation step (S210). In this case, the first foreign matter removal step (S220) may use any apparatus and process that can smoothly remove residual solid foreign matter such as sludge, but preferably a filter is used, and more preferably a Teflon filter is used to remove foreign matter such as sludge.

[0046] The second foreign matter removal step (S230) is a step to remove foreign matter that is relatively smaller than the foreign matter temporarily removed in the first foreign matter removal step (S220), more preferably foreign matter such as metal ions. The purpose of this second foreign matter removal step (S230) is to finally remove residual foreign matter in order to reuse the acid mixture separated in the solid-liquid separation step (S210) in the acid washing step (S100). Any step and apparatus can be used as long as they can remove the foreign matter mixed in the acid mixture to the greatest extent possible, but preferably an ion exchange resin is used to remove metal ions remaining in the separated acid mixture, and more preferably an anionic ion exchange resin is used.

[0047] In this invention, the foreign matter removal process is mainly described in a configuration in which the foreign matter removal process is carried out in two stages: a first foreign matter removal process (S220) and a second foreign matter removal process (S230). However, it is obvious that, depending on the usage, the foreign matter removal process may be carried out only once, or in three or more stages.

[0048] The acid mixture obtained after the acid mixture recovery process (S200), which includes the solid-liquid separation process (S210), the first foreign matter removal process (S220), and the second foreign matter removal process (S230) described above, can be reused in the acid washing process (S100). In this process, a predetermined volume loss occurs in the acid mixture during the acid mixture recovery process (S200). Therefore, an amount of new acid mixture equivalent to the volume lost is added to the recovered acid mixture, and the acid washing process (S100) is carried out. The loss rate of the acid mixture in the acid mixture recovery process (S200) is approximately 15% to 20%, and new acid mixture equivalent to the volume lost is added and used, taking into account the ratio with graphite in the acid washing process S100. At this time, as described above, the new acid mixture used is a mixture of hydrochloric acid and hydrofluoric acid in a 1:1 ratio. Thus, in the process of adding a predetermined amount of new acid mixture to the recovered acid mixture and using it, considering the acid washing efficiency, it is preferable to discard all of the recovered acid mixture and use 100% new acid mixture after repeating the acid washing process (S100) 10 to 20 times.

[0049] In the acid mixture recovery step (S200), the graphite separated from the acid mixture moves along the vacuum belt filter, and a washing step (S300) is performed to wash away any remaining acid mixture from the graphite. In this washing step (S300), it is preferable to use pure water or ultrapure water to prevent foreign substances such as ions from contaminating the graphite during washing. Pure water or ultrapure water refers to water from which primary treated raw water (feed water) has been reduced to extremely low levels by advanced water purification methods such as ion exchange resin, reverse osmosis (R / O), and sterilization. Pure water and ultrapure water are distinguished according to the degree of ion removal in the aforementioned treatment steps. In this washing step (S300), the graphite is washed by spraying washing water equivalent to 40% to 50% of the graphite's volume onto the graphite as it moves along the vacuum belt filter.

[0050] The aforementioned cleaning process (S300) can be repeated 1 to 5 times, preferably about 3 times, on the graphite moving along the vacuum belt filter, thereby completely cleaning any remaining acid mixture from the graphite.

[0051] Although the washing process (S300) is described after each step of the acid mixture recovery process (S200) for the sake of explanation, it is obvious that preferably the foreign matter removal process and the washing process (S300) can be carried out simultaneously after the solid-liquid separation process (S210) in the acid mixture recovery process (S200).

[0052] Finally, the purification process for high-purity graphite can be completed by dewatering the washed graphite (S400). The vacuum belt filter is vacuumed by a built-in compressor that continuously draws in air, and this vacuum is used to dewater the water from the graphite. Once dewatering is complete, the graphite adhering to the vacuum belt filter can be separated from the belt by appropriate negative pressure and recovered in a recovery tank.

[0053] According to the present invention, ultra-high-purity graphite with impurities of 1 ppm or less can be obtained as refined graphite through the process described above.

[0054] Usage in graphite refining methods The graphite refining method having the steps described above will be described in more detail sequentially based on one embodiment.

[0055] To remove foreign substances such as metal ions present in the graphite by leaching it with an acid mixture, graphite and the acid mixture are simultaneously introduced into the leaching reactor (S100). Here, the graphite introduced into the reactor is low-purity graphite obtained by ore-dressing graphite mined naturally or in its natural state, and its purity may be around 95% to 97%. In addition, as a pretreatment step before introducing it into the reactor, the graphite may be crushed to maximize the leaching efficiency by acid washing.

[0056] In this case, the acid mixture is a mixture of hydrochloric acid and hydrofluoric acid, mixed in a 1:1 ratio. The resulting mixture of graphite and acid can then be added to the reactor in a weight ratio of 1:1.5, i.e., graphite:hydrochloric acid:hydrofluoric acid is 1:0.75:0.75.

[0057] The graphite introduced into the reactor in this manner is then thoroughly washed with an acid mixture by carrying out an acid washing process for 10 to 30 hours, preferably about 20 hours.

[0058] The graphite and acid mixture, which have been acid-washed in the reactor for a predetermined period of time, are fed into a vacuum belt filter for the subsequent process.

[0059] The graphite and acid mixture introduced into the vacuum belt filter through the inlet is supplied while being uniformly spread to match the width of the filter belt via the input box. The sludge-like graphite remains on the top of the belt filter, while the liquid acid mixture passes through the filter belt. In other words, solid-liquid separation of the solid graphite and the liquid acid mixture is performed (S210). At this time, the acid mixture that has passed through the filter belt is not discarded but is recovered separately (S200).

[0060] The graphite and acid mixture, separated in this way, proceed to the next process individually and simultaneously. However, for the sake of explanation, the subsequent process for the acid mixture will be described first.

[0061] The acid mixture, which is fed into the vacuum belt filter and recovered after being separated from the graphite, may contain various foreign substances that were introduced during the graphite washing process. To remove these foreign substances, at least one foreign substance removal step can be performed. In this invention, a configuration in which foreign substance removal is performed in two stages is described as a standard, but this is only one embodiment, and the foreign substance removal step may be performed in only one stage, or in three or more stages.

[0062] First, foreign matter contained in the acid mixture filtered by the vacuum belt filter is temporarily removed using a Teflon filter as foreign matter having a predetermined volume, such as graphite residue (S220).

[0063] Next, metal ions and other substances present in the acid mixture from which foreign matter has been temporarily removed are removed using an ion exchange resin filter or the like (S230).

[0064] The acid mixture, from which foreign matter has been removed in two stages, is sufficiently free of foreign matter to be reusable in the acid washing process (S100). However, during the solid-liquid separation process (S210), the first foreign matter removal process (S220), and the second foreign matter removal process (S230), a volume loss of approximately 15% to 20% of the initial input volume occurs.

[0065] The acid mixture recovered in the aforementioned acid mixture recovery step (S200) is reused in the acid washing step (S100) to wash new low-purity graphite in the reactor. For a loss of 15% to 20%, a new acid mixture of hydrochloric acid and hydrofluoric acid in a 1:1 ratio is used to replenish the lost volume.

[0066] Thus, for acid mixtures that have been recovered and washed approximately 10 to 20 times, the leaching effect by acid washing may decrease. Therefore, it is preferable to completely discard the acid mixture and then perform the acid washing process (S100) using a new acid mixture. The number of times the acid mixture is recovered and reused may be selectively determined by the user, taking into consideration the amount of impurities contained in the graphite or various surrounding environmental factors.

[0067] This concludes the explanation regarding the recovery and reuse of the acid mixture. Next, we will explain in detail the treatment process for the graphite sludge separated by the solid-liquid separation process (S210).

[0068] The sludge-like graphite, separated from the acid mixture after being introduced into the vacuum belt filter, can be introduced while being sufficiently spread to cover the area of ​​the belt filter due to the structure of the inlet of the vacuum belt filter. However, depending on the application, a feeding process using a feeding device may be carried out to spread the sludge-like graphite more uniformly or to adjust the thickness of the sludge-like graphite.

[0069] As mentioned above, the sludge-like graphite spread on the vacuum belt filter at a thickness selected by the user is transported along the vacuum belt filter as the filter is driven.

[0070] The sludge-like graphite being transported in this manner is cleaned by spraying cleaning water using a cleaning device to remove any remaining acid mixture from the sludge-like graphite (S300). This cleaning process (S300) can be repeated one to five times depending on the usage, but in this invention, we will mainly describe a configuration in which the cleaning process is performed three times.

[0071] In each washing process (S300), sludge-like graphite is washed using ultrapure water equivalent to 40% to 50% of the graphite volume. During this process, washing and filtration are performed simultaneously due to the characteristics of the belt filter.

[0072] As mentioned above, the moisture contained in the graphite, which is thoroughly washed as it moves along the vacuum belt filter, decreases in moisture content during transport due to the characteristics of the belt filter, and a partial vacuum is generated by the action of the built-in compressor, which is configured to continuously suck in air. By utilizing this vacuum, residual moisture is dehydrated (S400).

[0073] Completely dewatered graphite may adhere to the upper surface of the filter belt. In such cases, it can be separated from the filter belt and recovered into a recovery tank or similar by using a predetermined negative pressure.

[0074] After the graphite is separated, the belt filter is cleaned by a brush roller and a high-pressure cleaning device before returning to the input port. Therefore, even when a continuous process is performed, the contamination of newly introduced graphite and acid mixture with foreign matter is minimized, enabling a stable continuous process.

[0075] The graphite obtained through the aforementioned process is high-purity graphite with an impurity content of 1 ppm or less, and can be used in various industrial fields.

[0076] As described above, those skilled in the art in which the present invention pertains will understand that the present invention can be implemented in other specific forms without departing from its technical idea or essential features. Therefore, the embodiments described above should be understood to be illustrative and not restrictive in all respects. The scope of the present invention is indicated not by the detailed description but by the claims set forth below, and all modifications or variations derived from the meaning and scope of the claims and the concept of equivalents thereto should be interpreted as being included within the scope of the present invention.

Claims

1. An acid washing process in which graphite is acid washed using an acid mixture, An acid mixture recovery step is performed to recover the acid mixture after the acid washing process is complete. A washing step for washing the graphite separated from the acid mixture in the acid mixture recovery step, A dewatering step is performed to dewater the graphite that has been cleaned in the washing step, Includes, The acid mixture recovery step is, A solid-liquid separation step for separating the acid mixture from the graphite, A foreign matter removal step is performed to remove foreign matter from the acid mixture separated in the solid-liquid separation step, Includes, The aforementioned foreign matter removal process is: A first foreign matter removal step is performed to temporarily remove foreign matter from the acid mixture separated in the solid-liquid separation step, In order to make the acid mixture from which foreign matter has been temporarily removed through the first foreign matter removal step reusable in the acid washing step, a second foreign matter removal step is performed to remove relatively minute foreign matter remaining after the first foreign matter removal step, A graphite refining method, including the following.

2. The graphite purification method according to claim 1, wherein the acid mixture is a mixture of hydrochloric acid and hydrofluoric acid.

3. The graphite purification method according to claim 2, wherein the weight ratio of graphite:hydrochloric acid:hydrofluoric acid is 1:0.5 to 1:0.5 to 1.

4. The graphite purification method according to claim 1, wherein in the acid washing step, the graphite and the acid mixture are introduced into a reactor and the washing process is carried out for 10 to 30 hours.

5. The graphite refining method according to claim 1, wherein the washing step is repeated one to five times.

6. The graphite purification method according to claim 1, wherein the washing step is performed using water equivalent to 40% to 50% of the volume of the graphite.

7. The graphite purification method according to claim 1, wherein the washing step involves washing the graphite with ultrapure water.

8. The graphite purification method according to claim 1, wherein the acid mixture recovery step or dehydration step is performed in a vacuum belt filter.

9. In the first foreign matter removal process, a Teflon filter is used to remove foreign matter. The graphite purification method according to claim 1, wherein the second foreign matter removal step involves removing foreign matter using an ion exchange resin filter.

10. The graphite refining method according to claim 9, wherein the acid mixture obtained through the first foreign matter removal step and the second foreign matter removal step is reused in the acid washing step.

11. The graphite refining method according to claim 10, further comprising adding a predetermined amount of additional acid mixture to adjust the proportion of the reused acid mixture.

Images