Method for producing recycled magnesia refractory raw materials and recycled magnesia refractory raw materials

Abstract

This method uses carbon-containing refractories, including magnesia, as a starting material to produce recycled magnesia refractory raw materials in which aluminum carbide is removed while suppressing the formation of brucite, and graphite is removed while reducing energy consumption compared to conventional technologies. [Solution] A method for producing recycled magnesia refractory raw material, comprising a heating and pressurizing step of heating and pressurizing a carbon-containing refractory material containing magnesia in a steam atmosphere to obtain a treated material, and a graphite removal step of removing at least graphite particles from the treated material.

Description

Technical Field

[0001] The present invention relates to a method for producing recycled magnesia refractory raw materials and recycled magnesia refractory raw materials.

Background Art

[0002] For the purpose of effective utilization of resources, the recycling of magnesia-carbon refractories is being promoted. For example, a method of removing aluminum carbide contained in used magnesia-carbon refractories and recovering recycled refractory raw materials is known.

[0003] For example, Patent Document 1 includes a granulation step of granulating carbon-containing refractory bricks such as magnesia-carbon to obtain granulated bricks, and a heat treatment step of heating the granulated bricks in an externally heated rotary kiln in the presence of an oxidizing gas to obtain recycled refractory raw materials. The heat treatment step discloses a method for producing recycled refractory raw materials in which the heating temperature is 850°C or higher and 1000°C or lower, and the heating time in the heat treatment step is 4 hours or longer.

[0004] Further, Patent Document 2 discloses a method for treating magnesia-carbon products, which includes the following steps A to F. A. A step of using a magnesia-carbon product, wherein the magnesia-carbon product has the following characteristics: mainly composed of magnesia and carbon, and containing Al4C3. B. A step of using water. C. A step of using a gas, wherein the gas has the following characteristics: containing carbon dioxide, and the proportion of carbon dioxide in the gas is higher than the proportion of carbon dioxide in the air. D. A step of using a container surrounding a chamber. E. A step of preparing the magnesia-carbon product in the chamber. F. A step of applying temperature and pressure to the chamber while simultaneously preparing the water and the gas in the chamber.

Prior Art Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2024-013030 [Patent Document 2] Special Publication No. 2022-543756 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The manufacturing method described in Patent Document 1 is useful in that it can produce recycled magnesia raw material with a reduced carbon content of 1% by mass or less from magnesia carbonized refractory bricks. However, it requires a heat treatment process at high temperatures of 850°C or higher, which requires a great deal of energy, and there are also issues with CO2 emissions associated with energy consumption.

[0007] Furthermore, the method described in Patent Document 2 removes aluminum carbide from magnesia-carbon products without generating brucite. However, it requires a step (step F) in which water and a gas containing carbon dioxide are simultaneously prepared and added to a chamber where temperature and pressure are applied, thus requiring the preparation of carbon dioxide gas. Moreover, since the processed material obtained by the method in Patent Document 2 still contains residual graphite (carbon), it is intended for reuse as a magnesia-carbon product. Therefore, when it is reused as a recycled magnesia refractory material in bricks, etc., its use is limited to magnesia-carbon products, and consequently, the amount used is also limited.

[0008] Therefore, the present invention aims to produce a recycled magnesia refractory material using a carbon-containing refractory material containing magnesia as a starting material, in which aluminum carbide is removed while suppressing the formation of brucite, and graphite is removed while further reducing energy consumption compared to conventional technology. [Means for solving the problem]

[0009] The present invention relates to a method for producing recycled magnesia refractory raw materials, characterized by comprising a heating and pressurizing step of heating and pressurizing a carbon-containing refractory material containing magnesia in a steam atmosphere to obtain a treated product, and a graphite removal step of removing at least graphite particles from the treated product.

[0010] Furthermore, the recycled magnesia refractory raw material according to the present invention is characterized by being obtained by a manufacturing method that includes a heating and pressurizing step of heating and pressurizing a carbon-containing refractory material containing magnesia in a steam atmosphere to obtain a treated product, and a graphite removal step of removing at least graphite particles from the treated product.

[0011] According to these configurations, a recycled magnesia refractory material can be obtained by using a carbon-containing refractory material containing magnesia as a starting material, while suppressing the formation of brusite, removing aluminum carbide, and further removing graphite particles. In addition, since the process can be carried out at a significantly lower temperature than that of conventional technologies, energy consumption can be reduced, and CO2 emissions associated with energy consumption can also be reduced.

[0012] Preferred embodiments of the present invention will be described below. However, the scope of the present invention is not limited by the examples of preferred embodiments described below.

[0013] In one embodiment of the method for producing recycled magnesia refractory raw material according to the present invention, it is preferable that the processing pressure in the heating and pressurizing step is an absolute pressure of 0.5 MPa or more and 0.7 MPa or less.

[0014] This configuration makes it easier to remove aluminum carbide while suppressing the formation of brusite, and also makes it easier to remove graphite particles in the graphite removal process.

[0015] In one embodiment of the method for producing recycled magnesia refractory raw material according to the present invention, it is preferable that the processing time in the heating and pressurizing step is 6 hours or more and 13 hours or less.

[0016] According to this configuration, it is easy to remove aluminum carbide while suppressing the generation of blue sites, and it is easy to remove graphite particles in the graphite removal step.

[0017] As one aspect, the method for producing a regenerated magnesia refractory raw material according to the present invention preferably further includes a granulation step of granulating the carbon-containing refractory containing magnesia before the heat and pressure treatment step.

[0018] According to this configuration, since the carbon-containing refractory containing magnesia is granulated before the heat and pressure treatment, it is easy to remove graphite particles.

[0019] As one aspect, the method for producing a regenerated magnesia refractory raw material according to the present invention preferably includes sieving the processed material using a sieve with a mesh size of 0.3 mm or less in the graphite removal step.

[0020] According to this configuration, it is easy to remove graphite particles in a simple process.

[0021] As one aspect, the method for producing a regenerated magnesia refractory raw material according to the present invention preferably has a carbon content of 1.0% by mass or less in the obtained regenerated magnesia refractory raw material.

[0022] According to this configuration, a regenerated magnesia refractory raw material that can be used as a raw material for refractories for a wide range of applications can be obtained.

[0023] Further features and advantages of the present invention will become more apparent from the following illustrative and non-limiting description of embodiments, with reference to the drawings.

Embodiments for Carrying Out the Invention

[0024] The method for producing a regenerated magnesia refractory raw material and embodiments of the regenerated magnesia refractory raw material according to the present invention will be described in detail.

[0025] <Method for Producing Regenerated Magnesia Refractory Raw Material> The method for producing recycled magnesia refractory material according to this embodiment is a method for producing recycled magnesia refractory material using a carbon-containing refractory brick containing magnesia (hereinafter referred to as a magnesia-carbon refractory brick), which is a carbon-containing refractory material containing magnesia, as a starting material, and includes a heating and pressurizing step of heating and pressurizing the magnesia-carbon refractory brick in a steam atmosphere to obtain a treated product, and a graphite removal step of removing at least graphite particles from the treated product. The production method according to this embodiment yields recycled magnesia refractory material in which the aluminum carbide content and carbon content are reduced compared to the magnesia-carbon refractory brick used as the starting material.

[0026] Based on the above-mentioned prior art, the inventors diligently investigated the following points (A) and (B) as a method for producing recycled magnesia refractory raw materials from magnesia-carbon refractory bricks. (A) To remove aluminum carbide while suppressing the formation of brusite, without actively introducing carbon dioxide gas in a heating and pressurizing device such as an autoclave. (B) To produce recycled magnesia refractory material that has been separated from graphite. As a result, we found that by heating and pressurizing magnesia-carbon refractory bricks in a steam atmosphere, aluminum carbide can be removed while suppressing the formation of brusite, and the material can also be made more easily separable from graphite. According to the present invention, the carbon content can be reduced simply by separating the easily separable graphite in a graphite separation process. Furthermore, according to the present invention, the process proceeds even at a significantly lower processing temperature compared to the processing temperature described in Patent Document 1. Therefore, recycled magnesia refractory raw materials can be obtained using a manufacturing method that reduces energy consumption and CO2 emissions compared to conventional methods. In addition, since it is not necessary to introduce carbon dioxide gas in the heating and pressurizing process as described in Patent Document 2, the process can be simplified.

[0027] The magnesia-carbon refractory brick in this embodiment contains at least magnesia and carbon. Examples of magnesia-carbon refractory bricks include magnesia carbon and magnesia spinel carbon. In the method for producing recycled magnesia refractory raw materials according to this embodiment, any magnesia-carbon refractory brick, including those exemplified above, can be used as the starting material.

[0028] The definition of "refractory brick" follows JIS R2001-1985. That is, "refractory brick" is "refractory material in various shapes suitable for constructing kilns, furnaces, and other structures used at high temperatures."

[0029] Magnesia-carbon refractory bricks are typically obtained by molding a compound formed from a mixture of a magnesia-containing raw material, a carbon-containing raw material, and other optional additives (such as binders and additives), and then heat-treating the mixture. The type of magnesia-carbon refractory brick obtained corresponds to the metal oxide (i.e., magnesia) contained in the selected refractory raw material. The refractory and carbon raw materials are commonly, but not limited to, supplied in powder form. The resulting magnesia-carbon refractory bricks are widely used, for example, in areas that come into contact with molten metal in steelmaking processes, and the appropriate type of magnesia-carbon refractory brick is selected depending on the application.

[0030] In the method for producing recycled magnesia refractory material according to this embodiment, used magnesia-carbon refractory bricks can be used as the starting material. Here, used magnesia-carbon refractory bricks refer to magnesia-carbon refractory bricks that have a history of being used in processes such as steel manufacturing. Obtaining recycled magnesia refractory material using used magnesia-carbon refractory bricks as a starting material has significance as a method for reusing used magnesia-carbon refractory bricks.

[0031] As described above, in the method for producing recycled magnesia refractory raw materials according to this embodiment, the type of magnesia-carbon refractory brick used as the starting material is arbitrary, but it is preferable to use a single type of magnesia-carbon refractory brick (magnesia carbonaceous refractory brick). In this case, the recycled magnesia refractory raw material can be obtained as a single type of refractory material, making it easier to use the recycled magnesia refractory raw material as a brick material. Therefore, the method for producing recycled refractory raw materials according to this embodiment may include a classification step of classifying magnesia-carbon refractory bricks by type.

[0032] Here, magnesia-carbon refractory bricks are used as the starting material in order to obtain recycled magnesia refractory material, and to reduce the amount of naturally derived magnesia material used. In particular, Japan relies heavily on imports for much of its magnesia material, so it is desirable to reduce the amount of naturally derived magnesia material used. Furthermore, when magnesia-carbon refractory bricks are recycled using conventional technology, the proportion of magnesia contained in the resulting recycled refractory material is sometimes lower than that of the starting material (low magnesia yield). However, according to the method for producing recycled refractory material in this embodiment, magnesia can be recycled with a relatively high yield.

[0033] The carbon content of used magnesia-carbon refractory bricks is preferably 50% by mass or less, and more preferably 25% by mass or less. The lower limit of the carbon content is not particularly limited, but for example, the carbon content of used magnesia-carbon refractory bricks is generally 15% by mass or more.

[0034] Used magnesia-carbon refractory bricks, recovered from steel mills and other facilities, may contain aluminum carbide. Aluminum carbide is produced when magnesia-carbon refractory bricks, which have added metallic aluminum, are used in the steel manufacturing process, and the reaction between metallic aluminum and carbon proceeds due to heating. A lower aluminum carbide content in refractory bricks helps suppress cracking and other damage after molding and shipment, and tends to result in higher strength.

[0035] Furthermore, used magnesia-carbon refractory bricks may have metals, slag, etc., attached to them, originating from the process and location of use. Therefore, in the manufacturing method of recycled magnesia refractory raw materials according to this embodiment, a removal step (scaling treatment) to remove metals and slag attached to the magnesia-carbon refractory bricks may be performed before the granulation step or the heating and pressurizing step described later.

[0036] Next, each step of the manufacturing method for recycled magnesia refractory material according to this embodiment will be described. In the present invention, the granulation step is not necessarily required, and recycled magnesia refractory material can be manufactured without going through the granulation step. However, a manufacturing method including the granulation step will be described below as an example.

[0037] [Refining process] The granulation process is a process of granulating magnesia-carbon refractory bricks to obtain granulated bricks. Any method can be used to carry out the granulation process, as long as it is a method that can granulate magnesia-carbon refractory bricks. The granulation process is preferably carried out before the heating and pressurizing process. The granulation process includes, for example, crushing the magnesia-carbon refractory bricks, and the magnesia-carbon refractory bricks are crushed using a known crushing device such as a jaw crusher.

[0038] If the magnesia-carbon refractory bricks subjected to the granulation process contain aluminum carbide, the granulation process may include contacting the magnesia-carbon refractory bricks with water. When aluminum carbide comes into contact with water, it expands due to hydration, causing the structure of the magnesia-carbon refractory bricks to break down from the inside. In this case, if the magnesia-carbon refractory bricks are left exposed to the elements after contact with water, they will naturally disintegrate. Thus, by contacting the magnesia-carbon refractory bricks with water, they can be granulated. In this case, the energy consumed in the granulation process can be reduced compared to using machinery such as a crushing device.

[0039] Furthermore, the microstructure of finely granulated magnesia-carbon refractory bricks mainly consists of magnesia particles, composite particle aggregates formed by the complex intermingling of magnesia and graphite particles, and also includes individual graphite particles. These "composite particle aggregates" are present in the microstructure of used magnesia-carbon bricks as a result of the high-temperature processes involved in steelmaking.

[0040] The maximum particle size of the granulated bricks obtained in the granulation process is more preferably 35 mm or less, and even more preferably 10 mm or less. Within this range, the removal of aluminum carbide is facilitated in the heating and pressurizing process, and the graphite particles are more easily separated from the composite particle aggregates. There is no particular lower limit to the maximum particle size of the granulated bricks obtained in the granulation process, but it is, for example, 1 mm or more.

[0041] [Heating and pressurizing process] The heating and pressing process involves heating and pressing magnesia-carbon refractory bricks under a steam atmosphere to obtain a processed product. The processing apparatus used in the heating and pressing process is not particularly limited as long as it is a heating and pressing apparatus capable of heating and pressing the inside of the apparatus, but an autoclave is preferably used. By using an autoclave, a processed product obtained by heating and pressing magnesia-carbon refractory bricks under a steam atmosphere in a relatively short time can be obtained. Conventional industrial autoclaves can be used as autoclaves. The size of the apparatus used in the heating and pressing process is arbitrary, and the size of the sample to be pressed depends on the size of the apparatus. Examples of heating and pressing apparatuses other than autoclaves include high-pressure reactors.

[0042] In the heating and pressurizing process according to this embodiment, it is preferable that the atmospheric gas in the processing apparatus consists of 50 mol% or more water vapor. More preferably, it is preferable that the atmospheric gas in the processing apparatus consists of 90 mol% or more water vapor, and even more preferably 95 mol% or more. In order to fill the processing container in the processing apparatus with water vapor, it is preferable that the heating and pressurizing device releases the air inside the processing container in the initial stages of heating and then seals it when the temperature exceeds, for example, 90°C. By having a high water vapor ratio in the atmospheric gas in the processing apparatus in this way, it is possible not only to remove aluminum carbide while suppressing the formation of brusite, but also to remove graphite particles from composite particle aggregates. In the pressurizing and heating process according to this embodiment, it is not necessary to introduce carbon dioxide gas.

[0043] The processing pressure (absolute pressure) in the heating and pressurizing process is preferably 0.5 MPa or more and 0.7 MPa or less. Pressurizing at an absolute pressure of 0.5 MPa or more and 0.7 MPa or less makes it easier to remove aluminum carbide while further suppressing the formation of brusite, and makes it easier to separate graphite particles from composite particle aggregates. The processing pressure (absolute pressure) in the heating and pressurizing process is more preferably 0.5 MPa or more and 0.6 MPa or less.

[0044] When heating and pressurizing treatment is performed under the above-described steam atmosphere and processing pressure (absolute pressure), the processing temperature (theoretical value) can be set within the range of approximately 150°C to 170°C. When the atmospheric gas inside the processing apparatus is mostly filled with steam, the absolute pressure inside the processing apparatus can be set to 0.5 MPa or more and 0.7 MPa or less by setting the temperature based on the saturated steam curve. It is more preferable that the processing temperature in the heating and pressurizing process be set to 151°C to 165°C.

[0045] The processing time in the heating and pressurizing process is not limited to this, but is preferably 6 hours or more and 13 hours or less. A processing time of 6 hours or more and 13 hours or less makes it easier to remove aluminum carbide while further suppressing the formation of brusite, and makes it easier to separate graphite particles from the composite particle aggregates. The processing time in the heating and pressurizing process is more preferably 7 hours or more and 9 hours or less, and even more preferably 7 hours or more and 8 hours or less. However, the optimal processing time in the heating and pressurizing process varies depending on various conditions such as the particle size of the magnesia-carbon refractory brick, the atmosphere inside the heating and pressurizing apparatus, and the type of apparatus, so it should be set appropriately according to the actual processing conditions.

[0046] [Graphite removal process] The graphite removal process is a process of removing graphite particles from the processed material obtained by the heating and pressurizing process. Preferably, the graphite removal process is a process of removing graphite particles by applying a physical action to the graphite particles, which have become easier to separate from the composite particle aggregates by the heating and pressurizing process. In this embodiment, the graphite removal process is preferably a process of sieving the graphite particles from the processed material using a sieve. The mesh size of the sieve should be such that the graphite particles can pass through the sieve and be separated from the recycled magnesia refractory material, and a mesh size of 0.3 mm or less is preferable, for example, a mesh size of 0.3 mm.

[0047] The method for producing recycled magnesia refractory material according to this embodiment may optionally include at least one of the following steps: a particle size adjustment step for adjusting the particle size of the recycled magnesia refractory material obtained in the above step, and a classification step for classifying the recycled magnesia refractory material. Known particle size adjustment methods and classification methods can be used for these steps.

[0048] In the classification process, the recycled magnesia refractory material may be classified into multiple particle size categories. In this case, recycled magnesia refractory material classified into predetermined particle size categories can be obtained, making it easier to select the appropriate recycled magnesia refractory material for use as a refractory material depending on the purpose.

[0049] <Recycled Magnesia Refractory Material> The recycled magnesia refractory raw material obtained by the above manufacturing method has reduced brucite formation, reduced aluminum carbide content, and further reduced carbon content. Therefore, the purity of the recycled magnesia refractory raw material can be increased. The recycled magnesia refractory raw material obtained by the above manufacturing method is not particularly limited in terms of its composition and content, as long as brucite formation is suppressed and the aluminum carbide content and carbon content are reduced compared to the untreated magnesia-carbon refractory brick used as the starting material. However, the carbon content, aluminum carbide content, and brucite content of the recycled magnesia refractory raw material are preferably as described below.

[0050] The carbon content of the recycled magnesia refractory material is preferably 1.0% by mass or less. If the carbon content of the recycled magnesia refractory material is 1.0% by mass or less, it has high purity and is easy to use as a recycled magnesia refractory material. The carbon content of the recycled magnesia refractory material is more preferably 0.7% by mass or less. There is no particular lower limit to the carbon content of the resulting recycled refractory material, but for example, 0.1% by mass or more may remain. Furthermore, it is preferable that the recycled magnesia refractory material substantially does not contain composite particle aggregates of magnesia particles and graphite particles.

[0051] Furthermore, the aluminum carbide content of the recycled magnesia refractory material is preferably 0.3% by mass or less. If the aluminum carbide content of the recycled magnesia refractory material is 0.3% by mass or less, it has high purity and is easy to use as a recycled magnesia refractory material. It is more preferable that the aluminum carbide content of the recycled magnesia refractory material is 0.05% by mass or less. There is no particular lower limit to the aluminum carbide content of the obtained recycled refractory material.

[0052] It is preferable that the recycled magnesia refractory material is substantially free of brucite. For example, it is preferable not to detect a brucite peak using an X-ray diffractometer.

[0053] Furthermore, the recycled magnesia refractory material obtained by the above manufacturing method is a recycled material, and the starting material, magnesia-carbon refractory brick, also exists in various compositions and states. In addition, the composition and state may differ further depending on the process using the magnesia-carbon refractory brick, so the specific form of the structure or properties of the manufactured product will also vary in diverse ways. Thus, it is practically impossible to disclose all the structures and properties of the recycled magnesia refractory material according to this embodiment in the application. Therefore, at the time of filing, it is impossible or impractical to directly identify the recycled magnesia refractory material obtained by the above manufacturing method by its structure or properties other than what is described herein.

[0054] [Other embodiments] The method for producing recycled magnesia refractory material and other embodiments of the recycled magnesia refractory material according to the present invention will be described below. Note that the configurations disclosed in each of the following embodiments can be applied in combination with configurations disclosed in other embodiments, as long as no inconsistencies arise.

[0055] In the manufacturing method described in the above embodiment, the graphite removal step was described as a step of sieving graphite particles from the processed material using a sieve. However, the method of the graphite removal step in the present invention is not particularly limited as long as graphite particles can be removed. For example, a dry specific gravity separation device such as an air table separator or a fluidized bed separator may be used, or graphite particles may be removed by physically washing them away using a wet washing device or the like.

[0056] In the above embodiment, a configuration in which the obtained recycled magnesia refractory material substantially does not contain brucite was described as an example. However, the recycled magnesia refractory material in the present invention may contain a small amount of brucite.

[0057] With regard to other configurations, the embodiments disclosed herein are illustrative in all respects, and it should be understood that the scope of the present invention is not limited thereto. Those skilled in the art will readily understand that modifications can be made as appropriate without departing from the spirit of the invention. Therefore, other embodiments modified without departing from the spirit of the invention are naturally included within the scope of the present invention.

[0058] The method for producing the recycled magnesia refractory raw material of this embodiment and the recycled magnesia refractory raw material will be described in more detail below with reference to examples. However, the scope of the present invention is not limited by the following test examples. [Examples]

[0059] (Example 1) The starting material was used as a magnesia carbon brick, and recycled magnesia refractory material was produced by going through the following processes: granulation, heating and pressurization, and graphite removal.

[0060] [Refining process] Used magnesia carbon bricks were crushed to approximately 10 mm using a jaw crusher. The amount of aluminum carbide and free carbon in the crushed used magnesia carbon bricks (starting material) was measured using the method described later, and the amount of aluminum carbide was 5.0% by mass, and the amount of free carbon was 15% by mass.

[0061] [Heating and pressurizing process] The resulting 4 kg of pulverized material was placed in a stainless steel container and set in the processing container inside an autoclave (autoclave unit manufactured by Toyo Koatsu Co., Ltd.). Water was pre-filled into the bottom of the autoclave's processing container.

[0062] Next, the temperature was set based on the saturated water vapor curve to ensure that the absolute pressure inside the processing apparatus was 0.5 MPa. Since the temperature at which the saturated water vapor pressure of water reaches 0.5 MPa is 151.84°C, the temperature inside the processing vessel was set to 151.84°C and the autoclave was started. During the initial heating phase, a valve attached to the autoclave's processing vessel was opened to release internal air. When the temperature exceeded 90°C, the valve was closed to seal the processing vessel, filling the atmosphere inside with water vapor. Afterward, the heating and pressurizing treatment was carried out for 6 hours after the temperature inside the autoclave reached 151.84°C. After the heating and pressurizing treatment, the treated material was removed from the autoclave. The resulting pressurized and heated material had finer particles than the material before treatment.

[0063] [Graphite removal process] Next, graphite particles were separated from the obtained heat-pressurized material by sieving. The sieving was performed for 5 minutes using a vibrating sieve with a mesh size of 0.3 mm. The material remaining on the sieve was used as the recycled magnesia refractory material for Example 1.

[0064] (Examples 2-9) Recycled magnesia refractory raw material was produced in the same manner as in Example 1, except that the processing pressure and processing time were changed to the conditions shown in Table 1.

[0065] The following evaluations were performed using the recycled magnesia refractory materials from Examples 1 to 9.

[0066] [Amount of residual aluminum carbide] The amount of aluminum carbide remaining in the recycled magnesia refractory material was measured using gas chromatography. The obtained recycled magnesia refractory material was further ground into fine powder, weighed a predetermined amount, and placed in a container. A predetermined concentration and amount of hydrochloric acid was added to the container, and the amount of CH4 generated was quantified. Since the reaction between aluminum carbide and hydrochloric acid proceeds according to the following reaction equation (1), the amount of aluminum carbide contained in the recycled magnesia refractory material was calculated. Al4C 3(s) +12HCl (aq) →3CH 4(g) +4AlCl 3(s) ...(1)

[0067] The residual amount of aluminum carbide in recycled magnesia refractory raw materials was evaluated according to the following criteria. A: Aluminum carbide content is less than 0.05% by mass. B: Aluminum carbide content is 0.05% by mass or more and less than 0.3% by mass. C: Aluminum carbide content of 0.3% by mass or more

[0068] [Residual amount of free carbon] The amount of free carbon remaining in the recycled magnesia refractory material was measured in accordance with JIS R2011:2007, and it was evaluated whether or not carbon (graphite particles) could be separated from the recycled magnesia refractory material.

[0069] The amount of free carbon in recycled magnesia refractory material was evaluated according to the following criteria. A: Free carbon content is less than 0.1% by mass. B: Free carbon content is 0.1% by mass or more and less than 2.0% by mass. C: Free carbon content of 2.0% by mass or more

[0070] [Bluesite generation] The presence or absence of brucite (Mg(OH)2) in recycled magnesia refractory material was confirmed by X-ray diffraction using an X-ray diffractometer (BULKER D8 ADVANCE).

[0071] Blue site formation was visually evaluated by detecting the Mg(OH)2 peak using X-ray diffraction, according to the following criteria. A: No brucite (Mg(OH)2) detected. B: Brusite (Mg(OH)2) detected at a minute level. C: Clear detection of brucite (Mg(OH)2)

[0072] The overall evaluation was based on the following criteria: if all three items—residual aluminum carbide, residual free carbon, and brusite formation—received an "A" rating; if all items received a "B" rating or higher, and at least one item received a "B" rating, it was classified as a "B" rating; and if any one item received a "C" rating, it was classified as a "C" rating.

[0073] Table 1 shows the evaluation results for Examples 1 to 9, along with the manufacturing conditions. [Table 1]

[0074] As shown in Table 1, the recycled magnesia refractory raw materials of Examples 1 to 9, which underwent a heating and pressurizing process and a graphite removal process, showed suppressed brucite formation and reduced aluminum carbide and free carbon content.

[0075] Among Examples 1 to 9, Examples 1 to 4, in which the processing pressure (absolute pressure) in the heating and pressurizing process was 0.5 to 0.7 MPa and the processing time was 6 to 13 hours, showed particularly good results compared to Examples 5 to 9, as they suppressed the formation of brucite while removing aluminum carbide and left less free carbon residue.

Claims

1. A heating and pressurizing process to obtain a treated product by heating and pressurizing a carbon-containing refractory material containing magnesia in a steam atmosphere, A graphite removal step, which removes at least graphite particles from the processed material, A method for producing recycled magnesia refractory raw materials containing this material.

2. The method for producing recycled magnesia refractory raw material according to claim 1, wherein the processing pressure in the heating and pressurizing step is an absolute pressure of 0.5 MPa or more and 0.7 MPa or less.

3. A method for producing recycled magnesia refractory raw material according to claim 1 or 2, wherein the processing time in the heating and pressurizing step is 6 hours or more and 13 hours or less.

4. A method for producing recycled magnesia refractory raw material according to claim 1, further comprising a granulation step of granulating the carbon-containing refractory material containing the magnesia before the heating and pressurizing step.

5. A method for producing recycled magnesia refractory raw material according to claim 1 or 4, wherein the graphite removal step includes sieving the treated material using a sieve with a mesh opening of 0.3 mm or less.

6. A method for producing recycled magnesia refractory raw material according to claim 1, wherein the carbon content of the obtained recycled magnesia refractory raw material is 1.0% by mass or less.

7. A recycled magnesia refractory raw material obtained by a manufacturing method comprising a heating and pressurizing step of heating and pressurizing a carbon-containing refractory material containing magnesia in a steam atmosphere to obtain a treated material, and a graphite removal step of removing at least graphite particles from the treated material.

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