Magnesium oxide manufacturing method

Abstract

To provide a novel method for producing magnesium oxide with superior handleability.SOLUTION: Disclosed is a method for producing magnesium oxide. The method of the present disclosure for producing magnesium oxide comprises a carbonation step, a separation step, a crystallization step, and a calcination step. The carbonation step is a step of blowing carbon dioxide gas into a suspension of a magnesium compound to obtain an aqueous magnesium hydrogen carbonate solution. The separation step is a step for solid-liquid separation of the aqueous magnesium hydrogen carbonate solution. The crystallization step is a step of crystallizing magnesium carbonate from the aqueous solution obtained in the separation step. The calcination step is a step of calcining the magnesium carbonate to obtain magnesium oxide. In the present disclosure, the crystallization step is performed under crystallization conditions in which the crystallization temperature is 50°C or more and less than 80°C. Furthermore, the crystallization step is performed under crystallization conditions in which the product of the crystallization temperature and crystallization time is 60°C h or more and less than 210°C h.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a novel method for producing magnesium oxide. [Background technology]

[0002] Magnesium oxide is used in various industrial fields as an industrial and pharmaceutical raw material, and is known to exhibit excellent properties in various applications, such as pharmaceuticals, foods, vulcanization accelerators, pigments, chemical heat storage materials, battery materials, ceramic materials, adsorbents, abrasives, and catalysts.

[0003] Magnesium oxide is industrially produced by various methods using seawater, flooding water, bittern, etc. as a magnesium raw material. Among these methods, a method is known, as disclosed in Patent Document 1, in which a magnesium compound such as magnesium oxide, magnesium hydroxide, or magnesium carbonate is used as a magnesium oxide precursor and the magnesium oxide precursor is calcined to produce magnesium oxide.

[0004] As a method for producing magnesium carbonate, for example, Patent Document 2 proposes a method for producing high-purity magnesium carbonate, particularly magnesium carbonate with a low iron content, from low-grade magnesium hydroxide produced as an ore. Specifically, the proposed method involves blowing an oxygen-containing gas together with carbon dioxide into a suspension of low-grade magnesium hydroxide to form a solution containing magnesium bicarbonate, and heating the liquid after solid-liquid separation to produce and precipitate magnesium carbonate. The production method in Patent Document 2 is said to enable high-purity magnesium carbonate to be produced easily.

[0005] Furthermore, Patent Document 3 proposes a method for removing impurities in a method for producing magnesium carbonate by reacting magnesium hydroxide slurry with carbon dioxide gas. Specifically, the proposed impurity removal method involves maintaining the pH, which decreases during the carbonation process, at a pH value of 7.6 to 8.0 at which magnesium carbonate does not dissolve 100%, and filtering the reaction liquid after carbonation using undissolved magnesium produced at the end of carbonation as a precoat agent.

[0006] When the methods described in these patent documents are employed as part of a method for producing magnesium oxide, it is expected that high-purity magnesium oxide can be obtained. Such high-purity magnesium oxide is then used, for example, in tablets for pharmaceuticals or foods. As an example of such tablets, Patent Document 4 discloses tablets containing magnesium oxide particles as a main component. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2017 / 195686 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-132504 [Patent Document 3] Japanese Patent Application Publication No. 63-40722 [Patent Document 4] International Publication No. 2011 / 030659 Summary of the Invention [Problem to be solved by the invention]

[0008] Such tablets are produced by molding a composition containing magnesium oxide as a main component into a predetermined shape by compression molding known as tableting. However, when the methods described in Patent Documents 1 to 3 are used, bulky magnesium oxide may be obtained, which may make it difficult to handle when molding the tablets.

[0009] When magnesium oxide that is easier to handle is required, the magnesium oxide formed by the methods of Patent Documents 1 to 3 described above is not sufficient, and further improvements are required.

[0010] Therefore, an object of the present invention is to provide a novel method for producing magnesium oxide that is easier to handle. [Means for solving the problem]

[0011] The present disclosure includes the following aspects.

[0012] (First Disclosure) The first disclosure relates to a method for producing magnesium oxide. The method for producing magnesium oxide of the first disclosure includes the following carbonation step, separation step, crystallization step, and calcination step. The carbonation step is a step in which carbon dioxide gas is blown into a suspension of a magnesium compound to obtain an aqueous solution of magnesium hydrogen carbonate. The separation step is a step of subjecting the aqueous magnesium hydrogen carbonate solution to solid-liquid separation. The crystallization step is a step of crystallizing magnesium carbonate from the aqueous solution obtained in the separation step. The calcination step is a step of calcining the magnesium carbonate to obtain magnesium oxide. In the first disclosure, the crystallization step is carried out under crystallization conditions in which the crystallization temperature is equal to or higher than 50° C. and lower than 80° C. Furthermore, the crystallization step is carried out under crystallization conditions in which the product of the crystallization temperature and the crystallization time is equal to or higher than 60° C. h and lower than 210° C. h.

[0013] (Second Disclosure) A second disclosure is the production method according to the first disclosure, characterized in that the crystallization temperature is 60°C or higher and 70°C or lower.

[0014] (Third Disclosure) A third disclosure is the production method according to the first or second disclosure, characterized in that the product of the crystallization temperature and the crystallization time is 120°C·h or more and 140°C·h or less.

[0015] (Fourth Disclosure) A fourth disclosure is the production method according to any one of the first to third disclosures, wherein the crystallization step further includes a heating step of heating the crystallized magnesium carbonate.

[0016] (Fifth Disclosure) A fifth disclosure is the manufacturing method according to the fourth disclosure, wherein the heating step heats the magnesium carbonate at a temperature of 50°C or higher and 250°C or lower.

[0017] (Sixth Disclosure) A sixth disclosure is the manufacturing method according to the fourth or fifth disclosure, wherein the heating step heats the magnesium carbonate for a heating time of 1 hour or more and 72 hours or less.

[0018] (7th Disclosure) A seventh disclosure is the manufacturing method according to any one of the fourth to sixth disclosures, wherein the calcination step calcines the magnesium carbonate heated in the heating step at a temperature of 600°C or higher and 1500°C or lower. [Effects of the Invention]

[0019] According to the production method of the present invention, magnesium oxide that is easier to handle can be obtained. [Brief explanation of the drawings]

[0020] [Figure 1] 1 shows scanning electron microscope photographs of magnesium carbonate (a), which is an intermediate product of Example 1, and magnesium oxide (b), which is the final product after firing, and magnesium carbonate (c), which is an intermediate product of Comparative Example 5, and magnesium oxide (d), which is the final product after firing. The white lines in the figures indicate a length of 1 μm. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, preferred embodiments of the method for producing magnesium oxide of the present invention will be described in detail. In this specification, various numerical ranges mean ranges including the upper and lower limit values ​​unless otherwise specified.

[0022] [Magnesium oxide manufacturing method] One embodiment of the present invention is a method for producing magnesium oxide, which includes the following carbonation step, separation step, crystallization step, and calcination step. In the carbonation step, carbon dioxide gas is blown into a suspension of a magnesium compound to obtain an aqueous magnesium bicarbonate solution. In the separation step, the aqueous magnesium bicarbonate solution is subjected to solid-liquid separation. In the crystallization step, magnesium carbonate is crystallized from the aqueous solution obtained in the separation step. In the calcination step, magnesium carbonate is calcined to obtain magnesium oxide.

[0023] In this embodiment, the crystallization step is carried out under crystallization conditions in which the crystallization temperature is 50° C. or higher and lower than 80° C. Furthermore, the crystallization step is carried out under crystallization conditions in which the product of the crystallization temperature and the crystallization time is 60° C. h or higher and lower than 210° C. h.

[0024] By carrying out the crystallization step under such specific crystallization conditions, the crystal form of the crystallized magnesium carbonate tends to be needle-like crystals or plate-like crystals. This reduces the bulk of the magnesium carbonate, improving the handling of the magnesium carbonate. Furthermore, since the crystal form of the magnesium carbonate is inherited by the crystal form of the magnesium oxide obtained after calcination, the crystal form of the magnesium oxide after calcination also tends to be needle-like crystals or plate-like crystals. This also reduces the bulk of the magnesium oxide after calcination, improving the handling of the magnesium oxide during molding. Therefore, according to the manufacturing method of this embodiment, magnesium oxide that is easier to handle can be obtained.

[0025] If the manufacturing method of this embodiment can produce magnesium oxide that is easy to handle, it will be possible to improve the productivity of products containing the magnesium oxide, which has the advantage of contributing to the achievement of the SDGs (Sustainable Development Goals) adopted at the United Nations Summit.

[0026] The magnesium compound suspension that can be used in the production method of this embodiment is not particularly limited, and examples thereof include suspensions containing magnesium hydroxide, magnesium silicate, magnesium oxide, magnesium carbonate, or a mixture of two or more of these.

[0027] For example, when a magnesium hydroxide suspension is used as the magnesium compound suspension, the magnesium hydroxide suspension can be obtained by a magnesium hydroxide suspension production step using seawater or an aqueous magnesium chloride solution as a raw material. That is, the production method of this embodiment may include such a magnesium hydroxide suspension production step before the carbonation step.

[0028] The magnesium hydroxide suspension production step may be a method of mixing a magnesium source and an alkali source and reacting them. Alternatively, the magnesium hydroxide suspension production step may be a method of suspending magnesium hydroxide produced as a mineral in water. When the former method is employed for the magnesium hydroxide suspension production step, the magnesium source may be, for example, seawater or an aqueous magnesium chloride solution. It is preferable to use seawater as the magnesium source.

[0029] On the other hand, the alkali source to be reacted with the magnesium source is not particularly limited, and for example, calcium hydroxide can be used. An example of calcium hydroxide is slaked lime. Slaked lime can be obtained by slaked lime, which is calcium oxide. Slaked lime may be in the form of milk of lime, for example.

[0030] The above-described production process is an example of a production process for a magnesium hydroxide suspension, but when a suspension of a magnesium compound other than magnesium hydroxide is used, a production process appropriate for the type of magnesium compound may be adopted. Note that if a magnesium compound suspension can be obtained without such a production process, it is not necessary to have such a production process.

[0031] The magnesium compound suspension obtained by the above-described production process is then subjected to the subsequent carbonation process.

[0032] Hereinafter, various steps that may be included in the method for producing magnesium oxide of this embodiment will be described in detail.

[0033] <Carbonation process> The carbonation step is a step of blowing carbon dioxide gas into a suspension of a magnesium compound to obtain an aqueous magnesium hydrogencarbonate solution. The carbon dioxide gas that can be used in the carbonation step may contain other gases within a range that does not inhibit the carbonation of the magnesium compound. When blowing carbon dioxide gas into a suspension of a magnesium compound, it is preferable to blow the carbon dioxide gas while stirring the suspension.

[0034] Furthermore, in the carbonation step, it is preferable to adjust the pH of the magnesium compound suspension. In this case, the pH of the magnesium compound suspension may be adjusted depending on the type of impurities contained in the suspension or the type of impurities to be preferentially removed so that impurity components with relatively low ionization tendency precipitate as solids. Examples of impurities include Fe, Al, Si, As, and Pb.

[0035] For example, the pH of the magnesium compound suspension is preferably adjusted to less than 7.5 or less than 7.4. Alternatively, the pH of the magnesium compound suspension is preferably adjusted to 7.0 or greater or 7.1 or greater. In the carbonation step, adjusting the pH of the magnesium compound suspension within this range allows impurities contained in the suspension to be sufficiently precipitated as solids while leaving the magnesium component, magnesium bicarbonate, dissolved. As a result, magnesium oxide of higher purity can be obtained. Note that if the pH of the magnesium compound suspension is 7.5 or greater, the amount of dissolved magnesium component will be reduced, which may result in an insufficient yield.

[0036] Incidentally, impurities precipitated as a solid by adjusting the pH of the suspension can be removed by solid-liquid separation in the subsequent separation step. By sufficiently reducing impurities in this way in the carbonation step or separation step, the magnesium oxide obtained through the subsequent crystallization step and calcination step will have an extremely low impurity content, resulting in magnesium oxide with a higher purity.

[0037] In the carbonation step, the pH of the magnesium compound suspension may be adjusted by blowing carbon dioxide gas into the suspension. In this case, the carbonation step is preferably carried out while continuously or intermittently measuring the pH of the magnesium compound suspension.

[0038] In the carbonation step, the supply rate of carbon dioxide gas when blowing the carbon dioxide gas into the suspension of the magnesium compound is not particularly limited. For example, the supply rate of carbon dioxide gas is 5.0 L / min or less. For example, the supply rate of carbon dioxide gas is 0.1 L / min or more. A preferred upper limit of the supply rate of carbon dioxide gas is 3.0 L / min or less. A preferred lower limit of the supply rate of carbon dioxide gas is 0.2 L / min or more.

[0039] In the carbonation step, the concentration of the magnesium compound suspension is not particularly limited. For example, the concentration of the magnesium compound suspension is 30 g / L or less. For example, the concentration of the magnesium compound suspension is 1 g / L or more. The concentration of the magnesium compound suspension is preferably 28 g / L or less. Furthermore, the concentration of the magnesium compound suspension is preferably 3 g / L or more. The concentration of the magnesium compound suspension can be calculated using the following formula. Concentration of suspension (g / L) = Weight of magnesium compound (g) / Volume of suspension (L)

[0040] In the carbonation step, the temperature of the suspension when carbon dioxide gas is blown in is not particularly limited, but it is preferable to blow carbon dioxide gas into the suspension of the magnesium compound at a temperature of 0°C or higher and 50°C or lower. When the temperature of the suspension is within this range, multiple types of impurities contained in the suspension can be more reliably precipitated. As a result, magnesium oxide with even higher purity can be obtained.

[0041] In the carbonation step, the upper limit temperature of the suspension of the magnesium compound is more preferably 40°C. In the carbonation step, the upper limit temperature of the suspension of the magnesium compound is even more preferably 30°C. In the carbonation step, the lower limit temperature of the suspension of the magnesium compound is more preferably 20°C.

[0042] In the carbonation step, it is preferable that the aqueous magnesium hydrogen carbonate solution after the carbon dioxide gas is blown into contains undissolved magnesium carbonate. If the aqueous magnesium hydrogen carbonate solution after the carbon dioxide gas is blown into contains such undissolved magnesium carbonate, solid-liquid separation after the carbonation step becomes easy. As a result, magnesium oxide of higher purity can be obtained.

[0043] In the carbonation step, carbon dioxide gas may be blown into the suspension of the magnesium compound, followed by air. By first blowing carbon dioxide gas into the suspension of the magnesium compound, the magnesium component can be dissolved while the impurity Fe can be precipitated. Next, by blowing air into the suspension, the still-dissolved Fe can be precipitated as FeO. This allows for the production of even higher purity magnesium oxide with even less Fe as an impurity.

[0044] The impurities precipitated as a solid in the carbonation step as described above can be removed by solid-liquid separation in the subsequent separation step. That is, the aqueous magnesium hydrogen carbonate solution obtained in the carbonation step is subjected to the subsequent separation step.

[0045] <Separation process> The separation step is a step of subjecting the aqueous magnesium bicarbonate solution after the carbonation step to solid-liquid separation. More specifically, the separation step is a step of separating the aqueous magnesium bicarbonate solution, which is a liquid component, from impurities, which are solid components. This step removes the impurities from the aqueous magnesium bicarbonate solution, thereby obtaining an aqueous magnesium bicarbonate solution with high purity.

[0046] In this specification, "separation" includes not only the case where the solid content and the liquid content are completely separated, but also the case where a small amount of water is unavoidably contained in the solid content.

[0047] The separation means that can be used in the separation step is not particularly limited, and examples thereof include filtration means, membrane separation means, centrifugation means, solid-liquid separation means, and natural settling means.

[0048] In the separation step, the aqueous magnesium bicarbonate solution obtained after the carbonation step may be used as is, but is not limited to this. For example, the separation step may be performed in advance by adding water to the aqueous magnesium bicarbonate solution to adjust the concentration. Examples of the water used in this step include ion-exchanged water. The separation step may be performed once, or may be performed in two or more separate steps.

[0049] In the separation step, the pH may also be adjusted depending on the type of impurities to be removed. Furthermore, the carbonation step and the separation step may be considered as one set, and these steps may be repeated multiple times. In this case, the pH of the suspension may be adjusted to be different for each set. Alternatively, the pH of the suspension may be adjusted to be the same for each set.

[0050] The aqueous magnesium hydrogen carbonate solution from which impurities have been removed by the above separation steps is subjected to the next crystallization step.

[0051] <Crystallization process> The crystallization step is a step of crystallizing magnesium carbonate from the aqueous solution obtained in the separation step. In the crystallization step, magnesium carbonate can be crystallized by heating the aqueous solution after the separation step at a predetermined temperature for a predetermined time. In this specification, the "heating temperature when crystallizing magnesium carbonate" is referred to as the "crystallization temperature" to distinguish it from the heating temperature in the heating step described below. Similarly, the "heating time when crystallizing magnesium carbonate" is referred to as the "crystallization time."

[0052] (crystallization temperature) In this embodiment, the crystallization temperature when crystallizing magnesium carbonate is 50° C. or higher and lower than 80° C. Furthermore, the crystallization temperature is preferably 60° C. or higher and 70° C. or lower. If the crystallization temperature is 80° C. or higher, the crystal form of the obtained magnesium carbonate will be petal-like crystals, and the bulk will tend to be large.

[0053] Furthermore, in this embodiment, the crystallization step is performed under crystallization conditions such that the product of the crystallization temperature and the crystallization time is 60°C·h or more and less than 210°C·h. By performing the crystallization step under specific crystallization conditions, where the crystallization temperature is 50°C or more and less than 80°C, and the product of the crystallization temperature and the crystallization time is 60°C·h or more and less than 210°C·h, needle-shaped or plate-shaped magnesium carbonate crystals can be crystallized. When the crystallized magnesium carbonate has a needle-shaped or plate-shaped crystal form, the magnesium oxide after calcination also tends to have a needle-shaped or plate-shaped crystal form. This reduces the bulk of the magnesium oxide, resulting in magnesium oxide that is easier to handle. Note that when the product of the crystallization temperature and the crystallization time is 210°C·h or more, the resulting magnesium carbonate tends to have a petal-shaped crystal form, which tends to be bulky.

[0054] The crystallization conditions are preferably such that the crystallization temperature is 60°C or higher and 70°C or lower, and the product of the crystallization temperature and the crystallization time is 60°C·h or higher and lower than 210°C·h. When the crystallization step is carried out under such crystallization conditions, magnesium carbonate can be more reliably crystallized as needle-like or plate-like crystals.

[0055] Furthermore, the crystallization conditions are preferably such that the crystallization temperature is 50°C or higher and lower than 80°C, and the product of the crystallization temperature and the crystallization time is 120°C·h or higher and 140°C·h or lower. When the crystallization step is carried out under such crystallization conditions, needle-like or plate-like magnesium carbonate crystals can be more reliably crystallized.

[0056] Furthermore, the crystallization conditions are particularly preferably such that the crystallization temperature is 60°C or higher and 70°C or lower, and the product of the crystallization temperature and the crystallization time is 120°C·h or higher and 140°C·h or lower. When the crystallization step is carried out under such crystallization conditions, magnesium carbonate can be more reliably crystallized in the form of needle-like or plate-like crystals.

[0057] (crystallization time) In this embodiment, the crystallization time for crystallizing magnesium carbonate is not particularly limited as long as the product of the crystallization temperature and the crystallization time is 60°C·h or more and less than 210°C·h. That is, the crystallization time may be in the range of 0.75 hours or more and less than 4.2 hours. In this specification, the crystallization time refers to the time during which the aqueous solution after the separation step is heated to the crystallization temperature and then maintained at that temperature.

[0058] (Heating process) In this embodiment, the crystallization step may further include a heating step of heating the crystallized magnesium carbonate. Heating the crystallized magnesium carbonate makes it more likely that the crystal form of the magnesium carbonate will become needle-like crystals or plate-like crystals. As a result, the bulk of the magnesium carbonate tends to be lower, and the handling of the magnesium carbonate can be more reliably improved.

[0059] (Heating temperature) In the heating step, the heating temperature of magnesium carbonate is not particularly limited, but may be, for example, a temperature of 50° C. or higher and 250° C. or lower. From the viewpoint of handling magnesium carbonate, the lower limit of the heating temperature is preferably 60° C. Furthermore, from the viewpoint of ease of handling magnesium carbonate and productivity, the upper limit of the heating temperature is preferably 150° C.

[0060] (Heating time) In the heating step, the heating time of magnesium carbonate is not particularly limited, but may be, for example, 1 hour or more and 72 hours or less. From the viewpoint of handling magnesium carbonate, the lower limit of the heating time is preferably 3 hours. Furthermore, from the viewpoint of ease of handling magnesium carbonate and productivity, the upper limit of the heating time is preferably 48 hours.

[0061] The magnesium carbonate crystallized by the above-described crystallization step is obtained as a solid content in an aqueous solution. Therefore, the aqueous solution containing the crystallized magnesium carbonate can be subjected to solid-liquid separation to obtain magnesium carbonate as a solid. That is, the crystallization step may further include a step of subjecting the aqueous solution containing the crystallized magnesium carbonate to solid-liquid separation to obtain magnesium carbonate as a solid.

[0062] The means for performing solid-liquid separation of the aqueous solution containing the crystallized magnesium carbonate is not particularly limited, and for example, the same separation means as in the above-mentioned separation step can be used.

[0063] In the crystallization step, a washing step of the crystallized magnesium carbonate may be carried out as necessary.

[0064] The magnesium carbonate obtained by the above crystallization step is subjected to the next calcination step.

[0065] <Firing process> The calcination step is a step in which the magnesium carbonate obtained in the crystallization step is calcined to obtain magnesium oxide.

[0066] The calcination means for calcining magnesium carbonate is not particularly limited as long as it can produce magnesium oxide. Examples of such calcination means include those using a calcination furnace or microwaves.

[0067] The calcination temperature when calcining magnesium carbonate is not particularly limited as long as it is a temperature at which magnesium oxide can be produced. Examples of such a calcination temperature include temperatures of 600°C or higher. The upper limit of the calcination temperature is not particularly limited, but is, for example, 1500°C from the viewpoint of the quality or productivity of magnesium oxide. The calcination temperature is preferably 700°C or higher. Furthermore, the calcination temperature is preferably 1200°C or lower.

[0068] The calcination time when calcining magnesium carbonate is not particularly limited as long as it is a time that can produce magnesium oxide. Examples of such a calcination time include a time of 1 minute or more. The upper limit of the calcination time is not particularly limited, but from the viewpoint of productivity, it is, for example, 24 hours. The calcination time is preferably 30 minutes or more. Furthermore, the calcination time is preferably 6 hours or less.

[0069] The magnesium oxide obtained by the above firing step may be subjected to additional treatment steps as needed, such as a surface treatment step in which the surface of magnesium oxide particles is treated with various surface treatment agents, a crushing step in which the magnesium oxide is crushed into powder, a classification step in which the magnesium oxide is classified by particle size, or a molding step in which the magnesium oxide is molded into a predetermined shape.

[0070] According to the manufacturing method of this embodiment as described above, magnesium oxide that is easier to handle can be obtained.

[0071] The manufacturing method of the present invention is not limited to the above-described embodiments or the examples described below, and appropriate combinations, substitutions, modifications, etc. are possible within the scope that does not deviate from the object and intent of the present invention. [Example]

[0072] EXAMPLES The present invention will be explained in more detail below by way of examples and comparative examples, but the present invention is not limited to these examples.

[0073] Example 1 A 15 g / L magnesium hydroxide suspension was placed in a reaction vessel. Carbon dioxide gas was blown into the magnesium hydroxide suspension at a rate of 500 mL / min while stirring until the pH of the suspension reached a predetermined value, thereby obtaining an aqueous magnesium hydrogen carbonate solution.

[0074] The obtained aqueous magnesium hydrogen carbonate solution was subjected to solid-liquid separation using a Nutsche separator to remove solid impurities. The solution was then heated to 70°C and maintained at that temperature for 1 hour to precipitate magnesium carbonate. The solution was then filtered to obtain a solid magnesium carbonate. The obtained solid was then heated at 105°C for 24 hours to obtain a powder of basic magnesium carbonate.

[0075] A crucible for firing was prepared and basic magnesium carbonate was placed in it. This crucible was then placed in a firing furnace that had been preheated to 900°C. After being placed in the crucible, firing was carried out at 900°C for 2 hours under atmospheric pressure to obtain a magnesium oxide fired product. The resulting fired product was sieved through a 150-micron filter to obtain the magnesium oxide powder of Example 1.

[0076] Example 2 Magnesium oxide powder of Example 2 was obtained in the same manner as in Example 1, except that the crystallization time was changed to 2 hours.

[0077] Example 3 Magnesium oxide powder of Example 3 was obtained in the same manner as in Example 1, except that the crystallization temperature was changed to 60°C.

[0078] Example 4 Magnesium oxide powder of Example 4 was obtained in the same manner as in Example 1, except that the crystallization temperature and crystallization time were changed to 60° C. and 2 hours, respectively.

[0079] Example 5 Magnesium oxide powder of Example 5 was obtained in the same manner as in Example 1, except that the crystallization temperature and crystallization time were changed to 60° C. and 3 hours, respectively.

[0080] Example 6 Magnesium oxide powder of Example 6 was obtained in the same manner as in Example 1, except that the firing temperature was changed to 800°C.

[0081] Comparative Example 1 Magnesium oxide powder of Comparative Example 1 was obtained in the same manner as in Example 1, except that the crystallization time was changed to 3 hours.

[0082] Comparative Example 2 Magnesium oxide powder of Comparative Example 2 was obtained in the same manner as in Example 1, except that the crystallization temperature was changed to 80°C.

[0083] Comparative Example 3 Magnesium oxide powder of Comparative Example 3 was obtained in the same manner as in Example 1, except that the crystallization temperature and crystallization time were changed to 90° C. and 0.5 hours, respectively.

[0084] Comparative Example 4 Magnesium oxide powder of Comparative Example 4 was obtained in the same manner as in Example 1, except that the crystallization temperature was changed to 90°C.

[0085] Comparative Example 5 Magnesium oxide powder of Comparative Example 5 was obtained in the same manner as in Example 1, except that the crystallization temperature and crystallization time were changed to 95° C. and 3 hours, respectively.

[0086] Comparative Example 6 Magnesium oxide powder of Comparative Example 6 was obtained in the same manner as in Example 1, except that the crystallization temperature and crystallization time were changed to 95° C. and 6 hours, respectively.

[0087] The bulk (mL / 10 g) of each of the magnesium carbonate intermediate products and magnesium oxide final products obtained in Examples 1 to 6 and Comparative Examples 1 to 6 was measured according to the following measurement method. The measurement results are shown in Table 1 below.

[0088] (Method of measuring bulk) Weigh out 5g of the magnesium carbonate or magnesium oxide sample to be measured, place it in a 100mL measuring cylinder, and measure the volume (mL) of the sample. Convert the obtained volume (mL) per 5g of sample to the volume (mL) per 10g, and use this as the volume (mL / 10g).

[0089] [Table 1]

[0090] The magnesium carbonate intermediate product of Example 1 and the magnesium oxide final product after firing were observed under a scanning electron microscope to confirm their respective crystal morphologies. Similarly, the magnesium carbonate intermediate product of Comparative Example 5 and the magnesium oxide final product after firing were observed under a scanning electron microscope to confirm their respective crystal morphologies. These scanning electron microscope photographs are shown in Figure 1.

[0091] (Tableting test) Using a manual tabletop tablet press HAND-TAB (Ichihashi Seiki Co., Ltd., HANDTAB-100R), magnesium oxide samples (250 mg, φ10 flat punch) of Examples 1 to 6 were compressed under a pressure of 10 kN to form tablets. The thickness (mm) and hardness (N) of the obtained tablets were measured for tablet evaluation. Tablet hardness was measured using a load cell type tabletop hardness tester (Okada Seiko Co., Ltd., DC-50). The measured value of tablet hardness was the average of three measurements. The results of tablet evaluation are shown in Table 2 below.

[0092] [Table 2]

[0093] As shown in Table 1, it was found that the magnesium oxides of Examples 1 to 6 produced by the production method of the present invention all had low bulk and could be handled easily during molding. It was also found that the magnesium carbonates, which were intermediate products of Examples 1 to 6, also had low bulk and were easy to handle. On the other hand, it was found that the magnesium oxides of Comparative Examples 1 to 6, which were produced by production methods with different crystallization conditions, were all bulky and difficult to handle during molding.In addition, it was found that the magnesium carbonates, which were intermediate products of Comparative Examples 1 to 6, were also bulky and difficult to handle.

[0094] Furthermore, as shown in Figure 1, both the magnesium carbonate intermediate product of Example 1 and the magnesium oxide final product after firing had needle-like crystal morphology. On the other hand, both the magnesium carbonate intermediate product of Comparative Example 5 and the magnesium oxide final product after firing had bulky petal-like crystal morphology. The difference in bulk between the above-mentioned Examples and Comparative Examples is presumed to be due to the difference in crystal morphology.

[0095] Furthermore, as shown in Table 2, it was found that the magnesium oxides of Examples 1 to 6 also had excellent tabletability. [Industrial Applicability]

[0096] The method for producing magnesium oxide of the present invention can be suitably used for producing magnesium oxide that can be used for various applications such as pharmaceuticals, foods, vulcanization accelerators, pigments, chemical heat storage materials, battery materials, ceramic materials, adsorbents, abrasives, and catalysts.

Claims

1. a carbonation step of blowing carbon dioxide gas into a suspension of a magnesium compound to obtain an aqueous magnesium hydrogen carbonate solution; a separation step of subjecting the aqueous magnesium hydrogen carbonate solution to solid-liquid separation; a crystallization step of crystallizing magnesium carbonate from the aqueous solution obtained in the separation step; a calcination step of calcining the magnesium carbonate to obtain magnesium oxide, The method for producing magnesium oxide is characterized in that the crystallization step is carried out under crystallization conditions in which the crystallization temperature is 60°C or higher and 70°C or lower, and the product of the crystallization temperature and the crystallization time is 60°C·h or higher and 180°C·h or lower.

2. The manufacturing method described in claim 1, characterized in that the carbonation process adjusts the pH to 7.0 or higher and less than 7.

5.

3. 2. The method according to claim 1, wherein the product of the crystallization temperature and the crystallization time is 120°C·h or more and 140°C·h or less.

4. 2. The method according to claim 1, wherein the crystallization step further comprises a heating step of heating the crystallized magnesium carbonate.

5. The method according to claim 4, wherein the heating step heats the magnesium carbonate at a temperature of 50°C or higher and 250°C or lower.

6. The method according to claim 4, wherein the heating step heats the magnesium carbonate for a heating time of 1 hour to 72 hours.

7. 6. The method according to claim 5, wherein the calcination step calcines the magnesium carbonate heated in the heating step at a temperature of 600° C. or higher and 1500° C. or lower.

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