Graphite refining method

Abstract

To purify high-purity graphite from a graphite-containing raw material without performing acid treatment or alkaline solution treatment.SOLUTION: A graphite purification method includes performing one or more times a purification step (x) composed of a cycle of aggregation and separation promotion treatment performed as a treatment of strongly stirring a suspension of a graphite-containing raw material to cause graphite components to aggregate in liquid while separating impurities from the resultant aggregate so as to move the impurities into the liquid and then flotation treatment of separating and collecting the graphite component aggregate produced in the aggregation and separation promotion treatment. The method further includes, if necessary, wet-grinding the graphite-containing raw material before the aggregation and separation promotion treatment (wherein, when the purification step (x) is performed two times or more, it corresponds to the aggregation and separation promotion treatment in at least one cycle of the purification step (x)). Performing the aggregation and separation promotion treatment of strongly stirring the suspension of the graphite-containing raw material to promote graphite aggregation and impurities separation before the flotation treatment enables the impurities to be easily separated and removed and high-purity graphite to be obtained.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for purifying high-purity graphite from graphite-containing raw materials such as graphite-containing ores and graphite-containing refractories. [Background technology]

[0002] Generally, when graphite-containing ore is refined to obtain high-purity graphite, the raw graphite ore contains graphite crystals. After crushing the ore, it is refined by repeatedly flotation and grinding. Because graphite is a hydrophobic substance, flotation uses kerosene or other collectors to promote the aggregation of graphite in water and its adhesion to air bubbles. However, once the graphite concentration reaches a certain level, the aggregates become strong, making it difficult to remove impurities (gangue components) trapped in the aggregates, and further increasing the purity. Therefore, by repeatedly flotation and grinding, the graphite is refined to a graphite purity of approximately 95% by mass, and then immersed in acid or alkali to dissolve and remove the impurities, resulting in high-purity graphite with a purity of 95% by mass or more (see, for example, Patent Document 1). Specifically, the raw material is immersed in acid to remove basic impurities, and then immersed in an alkaline solution to remove acidic impurities, thereby achieving high purity.

[0003] Other methods proposed for purifying graphite from graphite-containing raw materials include, for example, a method in which graphite-containing dust generated at steel mills and the like is subjected to repeated flotation and grinding, and then sulfuric acid is added to highly purify the graphite (Patent Document 2), and a method in which used magnesia carbon bricks are crushed and graphite is recovered by flotation or acid treatment (Patent Document 3). However, these methods also involve treatment with acid. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 57-88017 [Patent Document 2] Japanese Patent Application Publication No. 58-223610 [Patent Document 3] Japanese Patent Application Laid-Open No. 2013-1606 Summary of the Invention [Problem to be solved by the invention]

[0005] The acid and alkaline solutions used to refine graphite in the above-mentioned conventional technologies have a significant environmental impact if discharged as is, so it is usually necessary to install dedicated equipment and neutralize the solution before discharging it, which results in extremely high production costs. In contrast, when graphite is refined using only flotation without using chemicals such as acid or alkaline solutions, only graphite with a purity of less than 95% by mass is obtained. Graphite for graphite products, such as graphite for batteries, requires a purity of 95% by mass or more, and conventional technologies require treatment with acid or alkaline solutions, which is one of the reasons for the rise in graphite prices.

[0006] Therefore, an object of the present invention is to solve the above-mentioned problems of the conventional art and to provide a method for purifying high-purity graphite from a graphite-containing raw material without treatment with an acid or alkaline solution. [Means for solving the problem]

[0007] In order to solve the above problems, the present inventors have conducted extensive research into a method for purifying graphite without relying on acid treatment or alkaline solution treatment, and as a result have developed the following purification method, which has a low environmental impact and allows high-purity graphite to be easily obtained. The present inventors initially began research to develop a method for recovering graphite from used magnesia-carbon bricks. While investigating methods for purifying graphite through repeated flotation processes, they noticed that graphite, a refractory raw material, has three characteristics that distinguish it from common amorphous carbons such as soot and carbon black: (i) a large primary particle size, (ii) high hydrophobicity due to advanced crystallization, and (iii) cleavability. These characteristics are believed to be advantageous for high-purity graphite production by stirring, in that (1) it facilitates disintegration and impurity separation by stirring, (2) it facilitates separation and aggregation in water, and (3) it facilitates the removal of firmly adhered impurities. They then came up with the idea that optimizing the stirring conditions for a suspension of graphite-containing raw materials might enable high-purity graphite production without the need for costly and environmentally burdensome processes such as the dissolution and separation of impurities using acids or alkalis. Based on this idea, they tried to use strong stirring in the stirring adjustment process between flotation treatments, and found that strong stirring of graphite-containing powder in water effectively promoted the aggregation of graphite and the separation of impurities, resulting in the production of graphite of extremely high purity.

[0008] The present invention was made based on these findings and has the following gist. [1] A method for purifying a graphite component from a graphite-containing raw material, comprising: A method for purifying graphite, characterized by carrying out a purification process (x) once or twice or more times, which comprises one cycle of a flocculation / separation promotion process in which a suspension of graphite-containing raw material is vigorously stirred to flocculate the graphite components in the liquid, while separating impurities from the flocculates and transferring them into the liquid, and a flotation process in which the graphite component flocculates produced by the flocculation / separation promotion process are separated and recovered.

[0009] [2] A method for purifying graphite according to the above-mentioned [1], characterized in that the graphite-containing raw material is wet-pulverized before the aggregation / separation promotion treatment (however, when the purification step (x) is carried out twice or more times, the aggregation / separation promotion treatment is carried out in at least one purification step (x)). [3] A method for purifying graphite according to the above-mentioned [2], characterized in that the purification step (x) is carried out two or more times, and at least the graphite-containing raw material before the aggregation / separation promotion treatment in the final purification step (x) and / or the intermediate purification step (x) is wet-pulverized. [4] A method for purifying graphite according to any one of the methods [1] to [3] above, characterized in that the entire amount of the graphite-containing raw material that has been subjected to the aggregation and separation promotion treatment is subjected to flotation treatment.

[0010] [5] A method for purifying graphite according to any one of the methods [1] to [3] above, characterized in that the graphite-containing raw material that has been subjected to the aggregation and separation promotion treatment is sieved and the residue on the sieve is subjected to a flotation treatment. [6] A method for purifying graphite according to any one of the methods [1] to [5] above, wherein the graphite-containing raw material to be purified is a pre-treated one. [7] A method for purifying graphite according to any one of the above [1] to [6], characterized in that the aggregation and separation promotion treatment is carried out in water to which an oil-based binder has been added. [8] A method for purifying graphite according to any one of the methods [1] to [7] above, wherein the treatment for dissolving impurities with an acid and the treatment for dissolving impurities with an alkali are not carried out.

[0011] [9] A method for purifying graphite, in any one of the methods [1] to [8] above, characterized in that the graphite-containing raw material is one or more selected from the group consisting of graphite-containing ore, graphite-containing refractories, intermediate refined products thereof, and low- and medium-purity graphite.

[10] A method for purifying graphite according to any one of the above-mentioned [1] to [9], characterized in that in the aggregation and separation promotion treatment, the suspension of the graphite-containing raw material is vigorously stirred at a stirring power density of 80 W / kg or more.

[11] A method for producing graphite, characterized in that graphite is produced by purifying a graphite-containing raw material by any one of the purification methods [1] to

[10] above. [Effects of the Invention]

[0012] According to the present invention, high-purity graphite can be refined from a graphite-containing raw material without dissolving impurities with an acid or alkaline solution. This allows graphite refinement with low environmental impact, and also reduces the processing costs and equipment costs for refinement, making it possible to obtain high-purity graphite at low cost. [Brief explanation of the drawings]

[0013] [Figure 1] An explanatory diagram schematically illustrating the principle of graphite purification in the method of the present invention. [Figure 2] FIG. 1 is an explanatory diagram showing a processing flow of one embodiment of the purification method of the present invention. [Figure 3] FIG. 1 is an explanatory diagram showing a processing flow of another embodiment of the purification method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] The graphite purification method of the present invention involves carrying out once or twice or more purification steps (x) in which a suspension of the graphite-containing raw material is vigorously stirred to aggregate the graphite component in the liquid, while separating impurities from the aggregates and transferring them into the liquid, and a flotation process is carried out to separate and recover the aggregates of the graphite component produced by the aggregation and separation promotion process. As previously mentioned, in the present invention, we have investigated methods for removing impurities (gangue components) trapped in strong agglomerates, which are a problem when refining graphite-containing raw materials by flotation. As a result, we have found that by vigorously stirring the suspension of the graphite-containing raw material prior to flotation to promote the agglomeration of graphite and the separation of impurities (agglomeration / separation promotion treatment), it is possible to easily separate and remove impurities and obtain high-purity graphite. For this reason, in the present invention, step (x), which forms one cycle of the agglomeration / separation promotion treatment and the flotation treatment as described above, is carried out once or twice or more times.

[0015] In the present invention, the graphite-containing raw material (graphite-containing material) to be refined is not particularly limited and may be any material containing graphite. Examples include graphite-containing ores (e.g., natural flake graphite), graphite-containing refractories (e.g., magnesia carbon bricks), intermediate refinements thereof, and low- or medium-purity graphite, and one or more of these may be the target. Here, the graphite-containing refractories are generally used refractories, but are not limited thereto and may include, for example, defective refractory bricks. Graphite-containing ores and intermediate refinements of graphite-containing refractories are semi-finished products with low graphite purity. Low- or medium-purity graphite is a graphite product with a relatively low purity, such as a graphite product refined solely by flotation of natural flake graphite.

[0016] The graphite-containing raw material subjected to a series of processes in the refining step (x) of the present invention may be pretreated, if necessary, to obtain a powder suitable for graphite purification. When the graphite-containing raw material is a recycled material such as a graphite-containing refractory, pretreatments such as (i) pulverization using hydration expansion or (ii) mechanical pulverization can be used. The pretreatment (i) described above involves, for example, pulverizing magnesia carbon bricks by crushing the graphite and magnesia using the hydration expansion of the magnesia. The powder is typically obtained through a series of processes: "crushing → magnetic separation (removal of iron derived from slag) → sieving → hydrothermal treatment of the under-sieve material (pulverization treatment)." On the other hand, the pretreatment (ii) described above typically involves a series of processes: "crushing → magnetic separation (removal of iron derived from slag) → sieving → pulverization of the under-sieve material." Furthermore, when the graphite-containing raw material is graphite-containing ore, the powder is typically obtained through crushing → pulverization. On the other hand, for example, when the graphite-containing raw material is low- or medium-purity graphite (graphite product), pre-treatment to make it into powder may not be necessary.

[0017] FIG. 1 shows a schematic diagram of the principle of refining graphite in the refining step (x) of the present invention. The aggregation and separation promotion treatment carried out in the refining step (x) of the present invention is a treatment for promoting separation of the graphite component and the impurities (gangue components) by vigorously stirring a suspension of the graphite-containing raw material (powder) and taking advantage of the difference in hydrophilicity between the two. Because graphite components are hydrophobic and lipophilic, and most impurities are hydrophilic, the aggregation and separation promotion process is preferably carried out in water with the addition of a liquid binder (crosslinking liquid). This binder bonds the graphite particles together, facilitating the formation of aggregates. Oil-based binders are preferred, such as kerosene, light oil, diesel fuel (including those containing bio-based oils), and heavy oil. One or more of these can be used. However, heavy oil has a high viscosity, which makes it effective for promoting aggregation in liquid, but difficult to separate from the recovered graphite. Therefore, light oils such as kerosene, light oil, and diesel fuel are preferred as binders. This binder acts to bind and aggregate the graphite components in liquid. There are no particular restrictions on the amount of binder added, but if the amount added is too small, the binder effect of binding the graphite particles together will not be sufficient, while if the amount added is too large, the binding will be weak; therefore, an amount (weight) of about 0.5 to 1.0 times the amount (weight) of the graphite-containing raw material added is appropriate.

[0018] In this aggregation and separation promotion process, a suspension of graphite-containing raw material (powder) is vigorously stirred to aggregate the graphite components in the liquid, while separating impurities from the aggregates and transferring them into the liquid, thereby promoting the separation of the graphite components from the impurities. More specifically, the strong agitation of the suspension initially aggregates the graphite components, containing the liquid and impurities. However, collisions between graphite particles and the inner wall of the treatment vessel due to the strong agitation, as well as rotation on the wall, gradually push out the liquid and impurities (hydrophilic substances) from the aggregates, resulting in a dense aggregation of the graphite components. Meanwhile, hydrophilic impurities attached to or exposed on the surface of the graphite aggregates are separated from the graphite aggregates and transferred into the liquid due to the crushing of some of the graphite aggregates by the agitator (e.g., impeller) and the impact during agglomeration formation. In other words, the impurities are separated by being pushed out of the graphite aggregates into the liquid. Through this series of actions, the graphite components aggregate, and the aggregates are gradually purified.

[0019] The means (mixer) for performing the aggregation and separation promotion process is not particularly limited as long as it can vigorously stir the suspension of the graphite-containing raw material (powder), and examples that can be used include (i) a mixer equipped with a stirrer (stirring blade) that rotates at high speed inside a container to vigorously stir the liquid, and (ii) a so-called static mixer in which a stirrer is fixed inside a container and the pressure-fed liquid is forced to collide with the stirrer, resulting in vigorous stirring. Of these, in the case of mixer (i), stirring by rotation of the stirrer (stirring blade) allows for flexible adjustment of the stirring intensity and time, making it suitable for cases where the properties of the suspension to be stirred are not constant. In addition, stirring by a static mixer (ii) is less likely to emulsify, making it suitable for cases where it is desired to shorten the time required for subsequent flotation. The selection of a stirring means can be made based on the characteristics of each of these.

[0020] In the aggregation / separation promotion treatment, in order to vigorously stir the suspension of the graphite-containing raw material, the stirring power density of the mixer is preferably 50 W / kg or more, and particularly preferably 80 W / kg or more. Here, the stirring power density (W / kg) is the value obtained by multiplying the power consumption of the mixer (electricity measured with a power consumption meter) by the nominal efficiency of the power machine, and dividing this stirring power (W) by the mass of the suspension. If the stirring power density of the mixer is less than 50 W / kg, there is a risk that the strong stirring required to achieve the above-mentioned effects aimed at by the present invention will not be obtained. In the flocculation / separation promotion treatment of the present invention, there is no particular need to adjust the pH of the treatment liquid (suspension). In this flocculation / separation promotion treatment, the graphite-containing raw material is often alkaline, and since no acid is used, the treatment liquid (suspension) has a pH higher than 5. For example, if the graphite-containing raw material is a refractory material containing magnesia, the pH will be 8 or higher.

[0021] The graphite-containing raw material after the flocculation and separation promotion treatment described above is subjected to flotation. In this case, either (i) the flocculated and separation promotion treated graphite-containing raw material is sieved and only the sieve-surface material is flotation treated, or (ii) the flocculated and separation promotion treated graphite-containing raw material is entirely flotation treated without sieving. In method (i), a sieve with openings smaller than the size of the graphite aggregates is used, and many graphite aggregates are contained on the sieve-surface, so high-purity graphite can be efficiently obtained. However, since graphite is also contained on the sieve-surface, the yield of recovered graphite (carbon recovery rate) is lower than in method (ii). In this method, depending on the openings of the sieve, large impurities may remain on the sieve, but these impurities are removed in the subsequent flotation treatment. Furthermore, because the interstitial water between the particles of graphite agglomerates that pass through the sieve is suspended water, washing with clean water (for example, by showering the sieve with washing water) while recovering the graphite is effective for achieving high purity. On the other hand, in the above method (ii), both graphite agglomerates and impurities are subjected to the flotation process regardless of their size, so the yield of recovered graphite (carbon recovery rate) is high, and washing can achieve the same high purification effect as in (i). Note that when the refining step (x) is performed two or more times, the above method (i) or (ii) can be selected for each refining step (x), so that (i) can be performed in one or more refining steps (x) and (ii) can be performed in other refining steps (x).

[0022] Flotation may be performed according to conventional methods. For example, graphite-containing raw materials are added to water containing a collecting agent such as kerosene or diesel, and optionally a foaming agent. The mixture is stirred with a stirring device to form a suspension, and air (air bubbles) is then supplied from below (although air may be supplied in other ways). This causes the air bubbles to selectively adhere to graphite (graphite aggregates), a hydrophobic substance, and the buoyancy of the air bubbles causes the graphite to rise to the surface. On the other hand, the impurities, which are hydrophilic substances, do not adhere to the air bubbles, and the impurities sink (precipitate) under their own weight. The floating matter (floating matter) is recovered as high-purity graphite or as an intermediate product with a high graphite concentration to be processed in the next refining step (x). The specific method and conditions of the flotation process may be other than those described above, as long as the process allows graphite (graphite aggregates), a hydrophobic substance, to float and separate from the impurities.

[0023] If the refining step (x) is to be repeated, the float separated in the flotation treatment in the refining step (x) is subjected to the flocculation / separation promotion treatment in the next refining step (x) or to the wet grinding treatment performed before that (this wet grinding treatment will be described later). Furthermore, the float separated in the flotation treatment when the refining step (x) is performed only once, or the float separated in the flotation treatment in the final refining step (x) when the refining step (x) is performed two or more times, is recovered as high-purity graphite, washed with water as needed, and then subjected to a water removal treatment (such as suction filtration) and a drying treatment to produce a high-purity graphite product. Furthermore, if the refining step (x) is performed two or more times, the removed material (sediment) in the flotation treatment in the second or subsequent refining steps (x) may be returned to the previous refining step (x) to recover unrecovered graphite. Furthermore, the removed material (sediment) from the flotation treatment in the first refining step (x), or the removed material (sediment) from the flotation treatment when the refining step (x) is performed only once, may be subjected to another flotation treatment to recover unrecovered graphite, and the removed material (sediment) may then be used for other purposes, such as a converter slag forming agent or environmental magnesium hydroxide when the graphite-containing raw material is a graphite-containing refractory.

[0024] In the present invention, the flocculation / separation promotion treatment and the flotation treatment are usually carried out in separate facilities (treatment tanks), but the flocculation / separation promotion treatment and the flotation treatment may be carried out sequentially in one tank, or in one tank and a pipe connected to the tank. In the present invention, the refining step (x), which is a cycle of the above-described flocculation / separation promotion treatment and flotation treatment, is carried out once or twice or more times, but whether the refining step (x) is carried out only once or twice or more times can be determined depending on the type of graphite-containing raw material to be treated and the target purified purity of graphite, etc. For example, when the graphite-containing raw material is low- or medium-purity graphite (graphite product), the refining step may be carried out only once, but it is generally preferable to carry out the refining step (x) twice or more times.

[0025] In the present invention, wet pulverization is carried out on the graphite-containing raw material before the aggregation / separation promotion treatment in the purification step (x), as necessary. Here, when the purification step (x) is carried out two or more times, the wet pulverization is carried out before the aggregation / separation promotion treatment in at least one purification step (x). The graphite-containing raw material processed in the refining process (x) may contain single-edged particles, which are impurities with graphite adhering to their surfaces (especially in graphite-containing refractories). When a large number of these single-edged particles are present, their inclusion in the recovered product reduces the graphite purity of the recovered product, while their inclusion in the rejected product reduces the graphite yield. Separating graphite from these single-edged particles using the aforementioned flocculation and separation promotion process and flotation alone is difficult; obtaining high-purity graphite requires a process to separate the graphite from the single-edged particles. Single-edged particles are generally processed using a fine-grinding device that crushes and grinds them. However, because graphite is softer than the impurities, dry processing (crushing) can cause the impurities that make up the single-edged particles to be pushed into the graphite, making it difficult to eliminate the single-edged state. In contrast, it has been found that wet-pulverizing single-edged particles can properly peel off graphite adhering to the surface of impurities, thereby more effectively preventing impurities from being mixed into the graphite aggregates in the aggregation / separation promotion treatment and promoting the high purity of the graphite aggregates. For this reason, in the present invention, wet-pulverization is performed, as necessary, on the graphite-containing raw material before the aggregation / separation promotion treatment in the refining step (x) (however, if the refining step (x) is performed two or more times, the aggregation / separation promotion treatment in at least one refining step (x) is performed).

[0026] Wet milling is a milling method in which powder is mixed with a solvent, i.e., milled in a slurried state. In an embodiment in which the refining step (x) is performed two or more times, when wet pulverization is introduced, the graphite-containing raw material may be wet-pulverized before the aggregation / separation promotion treatment in any one or more of the refining steps (x), or the graphite-containing raw material may be wet-pulverized before the aggregation / separation promotion treatment in each of the refining steps (x). However, in order to promote separation of fine particles, it is preferable to wet-pulverize at least the graphite-containing raw material before the aggregation / separation promotion treatment in the final refining step (x) and / or intermediate refining steps (x).

[0027] As mentioned above, single-edged particles are particularly abundant in graphite-containing refractories, so wet milling is particularly effective for purifying graphite from graphite-containing refractories. On the other hand, when the graphite-containing raw material is graphite-containing ore (such as natural flake graphite) or low- or medium-purity graphite (graphite products), single-edged particles are generally not contained in large quantities, so wet milling may not be necessary. In the present invention, the refining step (x), which involves a flocculation / separation promotion treatment and a flotation treatment, is carried out once or twice or more times, and if necessary, wet pulverization is carried out before the flocculation / separation promotion treatment, thereby enabling the refined graphite to be sufficiently purified, and therefore treatment with an acid or alkaline solution, as has been conventionally carried out, is not carried out.

[0028] 2 shows a process flow of one embodiment of the purification method of the present invention, in which the purification step (x) is performed only once. In this embodiment, the graphite-containing raw material before the aggregation / separation promoting treatment is subjected to wet pulverization. 3 shows a process flow of another embodiment of the purification method of the present invention, in which the purification step (x) is performed four times (purification steps (x1) to (x4)), and the graphite-containing raw material is subjected to wet pulverization before the aggregation / separation promotion treatment in the final purification step (x4). As described above, wet pulverization may be performed before the aggregation / separation promotion treatment in any one or more of the purification steps (x1) to (x4), or may be performed before the aggregation / separation promotion treatment in each purification step (x).

[0029] The purity of graphite obtained by the refining method of the present invention is not particularly limited. As mentioned above, a purity of 95% by mass or more is required for graphite for graphite products, such as graphite for batteries, and therefore, graphite with a high purity of 95% by mass or more is refined for such applications. However, as in the example described below (Example 1 of Invention Example 1), for example, a graphite-containing refractory material may be refined to graphite with a purity of 80% by mass or more. According to the graphite refining method of the present invention as described above, high-purity graphite can be produced efficiently and at low cost. [Example]

[0030] [Example 1] Graphite was refined using crushed magnesia carbon bricks used in steelworks as a graphite-containing raw material. 100 g of crushed used magnesia carbon bricks (sample) that passed through a 1 mm sieve were used as the graphite-containing raw material. The flocculation and separation promotion treatment was carried out using a mixer equipped with a stirring blade and rotating at 10,000 rpm in a 1,000 mL glass container. The sample and distilled water were placed in this mixer to a total volume of 750 mL, and 7.5 mL of kerosene was added as a binder. The treatment was then carried out by rotating the stirring blade at the specified stirring power density for 10 minutes.

[0031] The flotation process was carried out by placing the sample and distilled water in a 2000 mL glass measuring cylinder, adding 0.5 mL of kerosene as a collector and 0.1 mL of pine oil as a foaming agent, and supplying air (bubbles) from the bottom while stirring. The floating matter from this flotation process was collected, and excess water was removed by suction filtration before being used in the next process. Wet grinding was carried out using a grinder with an outer diameter of 120 mm and a capacity of 1000 mL, containing 5 mm diameter ceramic balls at 40% of the pot's capacity. After sealing the pot containing the sample and 120 mL of distilled water, the wet grinding process was carried out at 120 rpm for 6 hours. After grinding, the sample was washed with distilled water and collected. After removing excess water by suction filtration, the sample was used for the next step.

[0032] In each of the invention examples and comparative examples, the samples were purified as follows. Invention Examples 1 and 2 The refining process (x), which consists of a cycle of flocculation and separation promotion treatment followed by flotation treatment, was carried out four times. In each refining process (x), the entire amount of the sample that had undergone flocculation and separation promotion treatment was subjected to flotation treatment. Invention Example 3 As in Examples 1 and 2, the refining process (x), which consists of a cycle of flocculation / separation promotion treatment → flotation treatment, was carried out four times, and wet grinding treatment was carried out before the flocculation / separation promotion treatment in each refining process (x). Comparison Example 1 The flotation treatment alone was carried out four times. Comparative Example 2 The flocculation and separation promotion treatment alone was carried out four times, and in each flocculation and separation promotion treatment, the treated sample was passed through a sieve with 75 μm mesh and then collected by pouring water over the sieve.

[0033] The final recovered material after the required purification process was filtered with suction, air-dried, and then dried in a dryer at 110°C for 24 hours. After drying, the mass of each sample was measured and then subjected to TG-DTA. Carbon was burned in air, and the carbon concentration was calculated from the mass loss rate to determine the free carbon content. The mass and carbon content of the removed material were also determined in the same way, and the carbon recovery rate was calculated as a percentage by dividing the carbon-containing mass of the recovered material by the total carbon weight of the recovered and removed materials. These results, along with the purification conditions, are shown in Table 1.

[0034] Comparing Comparative Example 1 and Comparative Example 2, Comparative Example 2, in which only flocculation and separation promotion treatment was carried out, had a slightly higher free carbon concentration in the recovered material than Comparative Example 1, in which only flotation treatment was carried out. Also, the carbon recovery rate was significantly higher at 54 mass% compared to 12 mass% in Comparative Example 1, but the free carbon in the recovered material was a relatively low value of 77 mass%. In contrast, in Example 1 of the present invention, the carbon recovery rate was lower than that of Comparative Example 2, but was about 24% by mass higher than that of Comparative Example 1. In particular, the free carbon concentration of the recovered material was 81% by mass, which is the same level as that of commercially available graphite, and high-purity graphite was obtained. In addition, Example 2 of the present invention is an example in which the stirring power density in the aggregation / separation promotion treatment is lower than that of Example 1. In Example 2 of the present invention, the purity of the separated graphite is equivalent to that of Example 1, but the graphite recovery rate tends to be lower. However, compared to Comparative Example 1, a sufficiently high graphite recovery rate is obtained.

[0035] Observation of the recovered material from Example 1 using a scanning electron microscope revealed the presence of numerous single-edged particles with graphite covering the impurity surface. Compared to Example 1, Example 3, which underwent wet pulverization (other conditions were the same as Example 1), showed a dramatic improvement in the free carbon concentration of the recovered material and an improvement in the carbon recovery rate. This is thought to be due to the graphite being separated from the single-edged particles by the wet pulverization. As described above, the method of the present invention, which performs refining step (x) by combining flocculation / separation promotion treatment and flotation treatment, makes it possible to recover graphite of higher purity than refining methods that perform flotation alone. Furthermore, by combining this with wet grinding treatment, it is possible to purify graphite of a purity comparable to that obtained by graphite refining methods that use treatment with acid or alkaline solutions.

[0036] [Table 1]

[0037] [Example 2] High-purity graphite was produced by using commercially available medium-purity graphite as a graphite-containing raw material. The medium-purity graphite (sample) used as the graphite-containing raw material was 89% pure graphite by mass, which was obtained by flotation of natural flake graphite. 100 g of this graphite was used. The flocculation / separation promotion treatment and the flotation treatment were carried out under the same conditions as in Example 1. In each of the invention examples and comparative examples, the samples were purified as follows. Invention examples The refining process (x), which consists of a cycle of flocculation and separation promotion treatment followed by flotation treatment, was carried out four times. In each refining process (x), the entire amount of the sample that had undergone flocculation and separation promotion treatment was subjected to flotation treatment. Comparison Example 1 The flotation treatment alone was carried out four times. Comparative Example 2 After four rounds of flotation, the ore was subjected to acid and alkali treatments. The acid treatment involved using 6N hydrochloric acid and stirring for two hours at 60°C to dissolve impurities. The ore was then placed in a sodium hydroxide solution and stirred for two hours at 60°C.

[0038] The final recovered material after the required purification process was filtered under suction, air-dried, and then dried in a dryer at 110°C for 24 hours. After drying, the mass of each sample was measured and then subjected to TG-DTA. Carbon was burned in air, and the carbon concentration was calculated from the mass loss rate, giving the free carbon content. The mass and carbon content of the removed material were also determined in the same way, and the carbon recovery rate was calculated as a percentage by dividing the carbon-containing mass of the recovered material by the total carbon weight of the recovered and removed materials. These results, along with the purification conditions, are shown in Table 2.

[0039] In Comparative Example 1, in which only flotation treatment was carried out, rapid floating of aggregates was observed even after repeated flotation treatment, the water remained clean, and there was almost no increase in the carbon concentration of the recovered material relative to the raw material. In contrast, in the inventive example, water suspension was observed during the flocculation and separation promotion treatment, and the free carbon concentration of the recovered material was significantly improved to over 98% by mass. Meanwhile, the carbon recovery rate was approximately 99% by mass in both the inventive example and the comparative example. These results demonstrate that the method of the present invention is effective in refining natural flake graphite to achieve high purity. In Comparative Example 2, acid-alkali treatment was carried out after flotation treatment, but in the present invention example, high-purity graphite was obtained that was almost equivalent to that of Comparative Example 2. As such, it is clear that the present invention makes it possible to purify high-purity graphite that is comparable to that obtained by the conventional refining method that involves acid-alkali treatment.

[0040] [Table 2]

Claims

1. A method for purifying a graphite component from a graphite-containing raw material, comprising: a purification step (x) in which one cycle is performed once or twice or more times, the purification step (x) comprising a flocculation / separation promotion treatment in which a suspension of a graphite-containing raw material is vigorously stirred to flocculate the graphite component in the liquid, while separating impurities from the flocculation and transferring them into the liquid, and a flotation treatment in which the graphite component flocculation produced by the flocculation / separation promotion treatment is separated and collected; A method for purifying graphite, comprising wet-pulverizing a graphite-containing raw material prior to the aggregation / separation promotion treatment (provided that, when the purification step (x) is performed two or more times, the aggregation / separation promotion treatment is performed in at least one purification step (x)).

2. The method for purifying graphite according to claim 1, characterized in that the refining step (x) is carried out two or more times, and at least the graphite-containing raw material is wet-pulverized before the aggregation / separation promoting treatment in the final refining step (x) and / or the intermediate refining step (x).

3. 2. The method for purifying graphite according to claim 1, wherein the entire amount of the graphite-containing raw material that has been subjected to the aggregation and separation promotion treatment is subjected to flotation treatment.

4. 2. The method for purifying graphite according to claim 1, wherein the graphite-containing raw material subjected to the aggregation and separation promotion treatment is sieved, and the remaining material on the sieve is subjected to a flotation treatment.

5. 2. The method for purifying graphite according to claim 1, wherein the graphite-containing raw material to be purified is pre-treated.

6. 2. The method for purifying graphite according to claim 1, wherein the aggregation and separation promotion treatment is carried out in water to which an oil-based binder has been added.

7. 2. The method for purifying graphite according to claim 1, wherein the method does not involve a treatment for dissolving impurities with an acid or an alkali.

8. 2. The method for refining graphite according to claim 1, wherein the graphite-containing raw material is at least one selected from the group consisting of graphite-containing ore, graphite-containing refractories, intermediate refined products thereof, and low- or medium-purity graphite.

9. 2. The method for purifying graphite according to claim 1, wherein the aggregation and separation promotion treatment involves vigorously stirring the suspension of the graphite-containing raw material at a stirring power density of 80 W / kg or more.

10. A method for producing graphite, comprising purifying a graphite-containing raw material by the refining method according to any one of claims 1 to 9.

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