Production method for magnesium oxide

Abstract

The present invention provides a novel production method that makes it possible to obtain higher-purity magnesium oxide.　The present disclosure is a production method for magnesium oxide. This production method for magnesium oxide includes the following carbonization step, separation step, crystallization step, and calcination step.　The carbonization step is a step for blowing carbon dioxide gas into a magnesium hydroxide suspension to obtain a magnesium bicarbonate aqueous solution.　The separation step is a step for performing a solid / liquid separation on the magnesium bicarbonate aqueous solution.　The crystallization step is a step for crystallizing magnesium carbonate from an aqueous solution obtained at the separation step.　The calcination step is a step for calcinating the magnesium carbonate to obtain magnesium oxide.　The present disclosure is characterized in that the pH of the magnesium hydroxide suspension is adjusted to at the carbonization step.

Description

Magnesium oxide manufacturing method

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

[0002] Magnesium oxide is used in various industrial fields as an industrial raw material and a pharmaceutical raw material. For example, magnesium oxide is known to exhibit excellent effects in various applications such as medicines, 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, bittern, etc. as a magnesium raw material. Among these methods, for example, as disclosed in Patent Document 1, a method is known in which magnesium oxide is produced by using magnesium oxide, magnesium hydroxide, magnesium carbonate, etc. as a magnesium oxide precursor and calcining the magnesium oxide precursor.

[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 method proposes 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 of 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] International Publication No. 2017 / 195686 Japanese Patent Application Laid-Open No. 2010-132504 Japanese Patent Application Laid-Open No. 63-40722

[0007] Depending on the application, magnesium oxide may be required to have an extremely high purity with impurities removed as much as possible. However, even if the methods of Patent Document 1 or Patent Document 2 are used as part of a method for producing magnesium oxide, it remains unclear whether impurities in magnesium oxide can be sufficiently removed.

[0008] Therefore, an object of the present invention is to provide a novel production method that can obtain magnesium oxide with higher purity.

[0009] The present disclosure includes the following aspects.

[0010] (First Disclosure) The first disclosure is 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 of blowing carbon dioxide gas into a magnesium hydroxide suspension to obtain an aqueous magnesium bicarbonate solution. The separation step is a step of performing solid-liquid separation of the aqueous magnesium bicarbonate 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. The first disclosure is characterized in that the pH of the magnesium hydroxide suspension is adjusted in the carbonation step.

[0011] (Second Disclosure) A second disclosure is the production method according to the first disclosure, characterized in that in the carbonation step, the pH of the magnesium hydroxide suspension is adjusted to within a range of 7.0 or more and less than 7.5.

[0012] (Third Disclosure) The third disclosure is the manufacturing method according to the first disclosure or the second disclosure, characterized in that in the carbonation step, the magnesium hydroxide suspension is heated to a temperature of 0°C or higher and 50°C or lower, and carbon dioxide gas is blown in.

[0013] (Fourth Disclosure) A fourth disclosure is the production method according to any one of the first to third disclosures, wherein in the carbonation step, the aqueous magnesium hydrogen carbonate solution after blowing in the carbon dioxide gas contains undissolved magnesium carbonate.

[0014] (Fifth Disclosure) The fifth disclosure is the production method according to any one of the first to fourth disclosures, characterized in that the crystallization step further includes a heating step in which the crystallized magnesium carbonate is heated.

[0015] (Sixth Disclosure) A sixth disclosure is the manufacturing method according to the fifth disclosure, characterized in that in the heating step, the magnesium carbonate is heated at a temperature of 50°C or higher and 250°C or lower.

[0016] (Seventh Disclosure) A seventh disclosure is the manufacturing method according to the fifth or sixth disclosure, characterized in that in the heating step, the magnesium carbonate is heated for a heating time of 1 hour or more and 72 hours or less.

[0017] According to the present invention, a novel production method can be provided that can obtain magnesium oxide with higher purity.

[0018] Fig. 1 is a scanning electron micrograph of the magnesium carbonate of Reference Example 1. The white lines in the figure indicate 1 µm. Fig. 2 is a scanning electron micrograph of the magnesium carbonate of Reference Example 2. The white lines in the figure indicate 1 µm. Fig. 3 is a scanning electron micrograph of the magnesium carbonate of Reference Example 3. The white lines in the figure indicate 1 µm.

[0019] A preferred embodiment of the method for producing magnesium oxide of the present invention will be described in detail below.

[0020] [Method for producing magnesium oxide] One embodiment of the present invention is a method for producing magnesium oxide, comprising the following carbonation step, separation step, crystallization step, and calcination step. In the carbonation step, carbon dioxide gas is blown into a magnesium hydroxide suspension to obtain an aqueous magnesium hydrogen carbonate solution. In the separation step, the aqueous magnesium hydrogen carbonate 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.

[0021] In the manufacturing method of this embodiment, the pH of the magnesium hydroxide suspension is adjusted in the carbonation step.

[0022] By adjusting the pH of the magnesium hydroxide suspension in the carbonation step, it is possible to precipitate impurities contained in the suspension as solids while leaving the magnesium bicarbonate, which is a magnesium component, dissolved. In other words, the degree of dissolution of impurities can be determined by the pH of the suspension. Examples of impurities include Fe, Al, Si, As, and Pb. The pH of the magnesium hydroxide suspension can be adjusted depending on the types of impurities contained in the suspension or the types of impurities that are to be preferentially removed, so that impurity components with a relatively low tendency to ionize precipitate as solids.

[0023] The impurities precipitated as a solid by adjusting the pH of the suspension can be removed by solid-liquid separation in the subsequent separation step. That is, the impurities contained in the magnesium hydrogen carbonate after the carbonation step can be sufficiently reduced. By sufficiently removing the impurities in this 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.

[0024] In the separation step, it is believed that the impurity components can be precipitated as a solid by adjusting the pH depending on the type of impurity to be removed. In this embodiment, the carbonation step and the separation step are considered to be one set, and these steps may be repeated multiple times. In this case, the pH of the magnesium hydroxide suspension may be adjusted to be different for each set. Alternatively, the pH of the magnesium hydroxide suspension may be adjusted to be the same for each set.

[0025] As described above, the manufacturing method of this embodiment has an extremely low impurity content and produces magnesium oxide with higher purity, which has the advantage of contributing to the achievement of the SDGs (Sustainable Development Goals) adopted at the United Nations Summit.

[0026] The magnesium hydroxide suspension that can be used in the production method of this embodiment is not particularly limited. For example, the magnesium hydroxide suspension can be obtained by the following 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 the following magnesium hydroxide suspension production step before the carbonation step.

[0027] The magnesium hydroxide suspension may be produced by mixing a magnesium source with an alkali source and reacting them together, or by suspending magnesium hydroxide, which is produced as a mineral, in water.

[0028] When the former method is employed for the step of producing a magnesium hydroxide suspension, the magnesium source can be, for example, seawater or an aqueous magnesium chloride solution, with seawater being preferred.

[0029] On the other hand, the alkali source to be reacted with the magnesium source is not particularly limited, and calcium hydroxide can be used, for example. 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 magnesium hydroxide suspension obtained by the above-described production process is subjected to the next carbonation process.

[0031] Hereinafter, each step that may be included in the method for producing magnesium oxide of this embodiment will be described in detail.

[0032] <Carbonation Step> The carbonation step is a step in which carbon dioxide gas is blown into a magnesium hydroxide suspension to obtain an aqueous magnesium hydrogencarbonate solution. The carbon dioxide gas that can be used in the carbonation step may contain other gases as long as the carbonation of magnesium hydroxide is not inhibited. Furthermore, when blowing carbon dioxide gas into the magnesium hydroxide suspension, it is preferable to blow the carbon dioxide gas while stirring the magnesium hydroxide suspension.

[0033] In this carbonation step, the pH of the magnesium hydroxide suspension is adjusted as described above. At this time, the pH of the magnesium hydroxide suspension may be adjusted appropriately depending on the type and content of impurities contained in the suspension. For example, the pH of the magnesium hydroxide suspension in the carbonation step may be adjusted to less than 7.5 or less than 7.4. For example, the pH of the magnesium hydroxide suspension in the carbonation step may be adjusted to 7.0 or more or 7.1 or more.

[0034] In the carbonation step, it is preferable to adjust the pH of the magnesium hydroxide suspension to a range of 7.0 or more and less than 7.5. Adjusting the pH of the magnesium hydroxide suspension to within this range makes it possible to more reliably precipitate multiple types of impurities contained in the suspension. As a result, magnesium oxide of even higher purity can be obtained. Note that if the pH of the magnesium hydroxide suspension is 7.5 or more, the amount of dissolved magnesium component decreases, which may result in a reduced yield.

[0035] In the carbonation step, the pH of the magnesium hydroxide suspension can be adjusted by blowing carbon dioxide gas in. Therefore, in the carbonation step, it is preferable to blow carbon dioxide gas in while continuously or intermittently measuring the pH of the magnesium hydroxide suspension.

[0036] In the carbonation step, the supply rate of carbon dioxide gas when blowing the carbon dioxide gas into the magnesium hydroxide suspension 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.

[0037] If the supply rate of carbon dioxide gas is more than 5.0 L / min per 1 L of the magnesium hydroxide suspension, the supplied carbon dioxide gas will not dissolve completely in the magnesium hydroxide suspension. If the supply rate of carbon dioxide gas is less than 0.1 L / min per 1 L of the magnesium hydroxide suspension, productivity will decrease.

[0038] In the carbonation step, the concentration of the magnesium hydroxide suspension is not particularly limited. For example, the concentration of the magnesium hydroxide suspension is 30 g / L or less. For example, the concentration of the magnesium hydroxide suspension is 1 g / L or more. The concentration of the magnesium hydroxide suspension is preferably 28 g / L or less. Furthermore, the concentration of the magnesium hydroxide suspension is preferably 3 g / L or more. The concentration of the magnesium hydroxide suspension can be calculated using the following formula: Concentration of suspension (g / L) = Weight of magnesium hydroxide (g) / Volume of suspension (L)

[0039] If the concentration of the magnesium hydroxide suspension is higher than 30 g / L, the magnesium hydroxide will not dissolve completely, resulting in a decrease in yield, whereas if the concentration of the magnesium hydroxide suspension is lower than 1 g / L, productivity will decrease.

[0040] In the carbonation step, the temperature of the magnesium hydroxide suspension when blowing in carbon dioxide gas is not particularly limited, but it is preferable to blow in carbon dioxide gas while keeping the temperature of the magnesium hydroxide suspension at 0° C. or higher and 50° C. or lower. When the temperature of the magnesium hydroxide suspension is within this range, it is possible to more reliably precipitate multiple types of impurities contained in the suspension. As a result, it is possible to obtain magnesium oxide of even higher purity.

[0041] A more preferable upper limit of the temperature of the magnesium hydroxide suspension in the carbonation step is 40° C. A still more preferable upper limit of the temperature of the magnesium hydroxide suspension in the carbonation step is 30° C. A more preferable lower limit of the temperature of the magnesium hydroxide suspension in the carbonation step is 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] Furthermore, in the carbonation step, carbon dioxide gas may be blown into the magnesium hydroxide suspension, followed by air. By first blowing carbon dioxide gas into the magnesium hydroxide suspension, the magnesium component can be dissolved while the impurity Fe can be precipitated. Next, air can be blown into the suspension to precipitate the still-dissolved Fe as FeO. This makes it possible to obtain magnesium oxide of even higher purity, with the impurity Fe further reduced.

[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 step> The separation step is a step of subjecting the aqueous magnesium hydrogen carbonate solution after the carbonation step to solid-liquid separation. More specifically, the separation step is a step of separating the aqueous magnesium hydrogen carbonate solution, which is a liquid component, from impurities, which are solid components. This step removes the impurities from the aqueous magnesium hydrogen carbonate solution, thereby obtaining a highly pure aqueous magnesium hydrogen carbonate solution.

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

[0050] <Crystallization Step> The crystallization step is a step of crystallizing magnesium carbonate from the aqueous solution obtained in the separation step. The means for crystallizing magnesium carbonate from the aqueous solution after the separation step is not particularly limited, and examples thereof include heating means. That is, in the crystallization step, magnesium carbonate can be crystallized by heating the aqueous solution after the separation step.

[0051] The heating temperature when crystallizing magnesium carbonate is not particularly limited, and examples thereof include temperatures of 30°C or higher. A preferred lower limit of the heating temperature is 50°C. A preferred upper limit of the heating temperature when crystallizing magnesium carbonate is not particularly limited, and is, for example, 100°C. A preferred upper limit of the heating temperature is 95°C. In this specification, the "heating temperature when crystallizing magnesium carbonate" may be referred to as the "crystallization temperature" to distinguish it from the heating temperature in the heating step described below. By setting the crystallization temperature to a temperature within the above preferred range, the precipitated needle-like crystals of magnesium carbonate become plate-like crystals. This reduces the bulk of magnesium carbonate, improving the handleability of magnesium carbonate.

[0052] The shape of magnesium carbonate crystals is inherited by the shape of magnesium oxide crystals obtained by calcining the magnesium carbonate. In other words, by improving the handling properties of magnesium carbonate, the handling properties of the magnesium oxide finally obtained can be improved.

[0053] The heating time when crystallizing magnesium carbonate is not particularly limited, and can be, for example, 1 minute or more. A preferred lower limit of the heating time when crystallizing magnesium carbonate is 15 minutes. The preferred upper limit of the heating time when crystallizing magnesium carbonate is not particularly limited, but from the viewpoint of productivity, it is, for example, 600 minutes, and more preferably 180 minutes. In this specification, the "heating time when crystallizing magnesium carbonate" may be referred to as the "crystallization time" to distinguish it from the heating time in the heating step described below. This crystallization time refers to the time from when the aqueous solution after the separation step is heated to the crystallization temperature and the temperature is maintained. By setting the crystallization time within the above preferred range, the precipitated needle-like crystals of magnesium carbonate become plate-like crystals. This reduces the bulk of magnesium carbonate, improving the handleability of magnesium carbonate.

[0054] (Heating Step) In the present embodiment, the crystallization step may further include a heating step of heating the crystallized magnesium carbonate. By heating the crystallized magnesium carbonate, the needle-like crystals of magnesium carbonate become plate-like crystals. This reduces the bulk of the magnesium carbonate, improving the handleability of the magnesium carbonate.

[0055] (Heating temperature) In the heating step, the heating temperature of magnesium carbonate is not particularly limited, and examples thereof include a temperature of 50° C. or higher and 250° C. or lower. From the viewpoint of the handleability of magnesium carbonate, the lower limit of the heating temperature is preferably 60° C. Furthermore, from the viewpoint of the handleability or productivity of magnesium carbonate, the upper limit of the heating temperature is preferably 150° C.

[0056] (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 the handling property of magnesium carbonate, the lower limit of the heating time is preferably 3 hours. Furthermore, from the viewpoint of the handling property or productivity of magnesium carbonate, the upper limit of the heating time is preferably 48 hours.

[0057] Since the magnesium carbonate crystallized by the above-described crystallization step is obtained as a solid content in an aqueous solution, the magnesium carbonate can be obtained as a solid by subjecting the aqueous solution containing the crystallized magnesium carbonate to solid-liquid separation. 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.

[0058] 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.

[0059] In the crystallization step, a washing step of the crystallized magnesium carbonate may be carried out as necessary.

[0060] The magnesium carbonate obtained by the above crystallization step is subjected to the next calcination step.

[0061] <Caking Step> The baking step is a step in which magnesium oxide is obtained by baking the magnesium carbonate obtained in the crystallization step.

[0062] 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 a calcination furnace or a microwave.

[0063] 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 500°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.

[0064] 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.

[0065] The magnesium oxide obtained by the above firing step may be subjected to additional treatment steps as necessary, 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.

[0066] According to the manufacturing method of this embodiment as described above, magnesium oxide with an extremely low impurity content and higher purity can be obtained.

[0067] 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.

[0068] 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.

[0069] Example 1 A 1 L reaction vessel was prepared and a 15 g / L magnesium hydroxide suspension was placed in it. Carbon dioxide gas was blown into the reaction vessel at a rate of 500 mL / min while stirring the magnesium hydroxide suspension until the pH of the suspension reached 7.3, thereby obtaining an aqueous magnesium hydrogen carbonate solution.

[0070] 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 90°C and maintained at that temperature for 60 minutes to precipitate magnesium carbonate. The solution was then filtered to obtain a solid magnesium carbonate. The obtained solid was heated at 105°C for 24 hours to obtain a powder of basic magnesium carbonate.

[0071] 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 fired magnesium oxide product. The resulting fired product was sieved through a 150-micron filter to obtain the magnesium oxide powder of Example 1.

[0072] Comparative Example 1 Magnesium oxide powder of Comparative Example 1 was obtained in the same manner as in Example 1, except that carbon dioxide gas was blown into the magnesium hydroxide suspension until the pH reached 6.8.

[0073] Comparative Example 2 Magnesium oxide powder of Comparative Example 2 was obtained in the same manner as in Example 1, except that carbon dioxide gas was blown into the magnesium hydroxide suspension until the pH reached 8.0.

[0074] The magnesium carbonate that was the intermediate product of Example 1 was designated as the magnesium carbonate of Reference Example 1, and its crystal structure was observed with a scanning electron microscope. Furthermore, magnesium carbonate obtained in the same manner as in Example 1, except that the crystallization temperature when precipitating magnesium carbonate was 60°C, was designated as the magnesium carbonate of Reference Example 2, and its crystal structure was observed with a scanning electron microscope. Furthermore, magnesium carbonate obtained in the same manner as in Example 1, except that the crystallization temperature when precipitating magnesium carbonate was 20°C, was designated as the magnesium carbonate of Reference Example 3, and its crystal structure was observed with a scanning electron microscope. Scanning electron microscope photographs of the magnesium carbonates of Reference Examples 1, 2, and 3 are shown in FIGS. 1, 2, and 3, respectively.

[0075] (Quantitative Analysis) The magnesium hydroxide used as the raw material for producing magnesium oxide in Example 1, Comparative Example 1, and Comparative Example 2 was quantitatively analyzed using a scanning X-ray fluorescence analyzer "ZSX Primus IV" manufactured by Rigaku Corporation. The results are shown in Table 1 below.

[0076]

[0077] The intermediate products, basic magnesium carbonate and magnesium oxide, of Example 1, Comparative Example 1, and Comparative Example 2 were quantitatively analyzed using a scanning X-ray fluorescence analyzer "ZSX Primus IV" manufactured by Rigaku Corporation. The results are shown in Tables 2 and 3 below.

[0078] (Calculation of Yield of Magnesium Carbonate) The yield of magnesium carbonate, which is an intermediate product in Example 1, Comparative Example 1, and Comparative Example 2, was calculated according to the following formula: Yield (mass %) = 100 × (A × W2) / (W1 × 24.31 / 58.33) In the above formula, A is the proportion of Mg in magnesium carbonate, W1 is the mass of magnesium hydroxide used in the reaction, and W2 is the mass of magnesium carbonate.

[0079] The calculated yields of magnesium carbonate in Example 1, Comparative Example 1 and Comparative Example 2 are shown in Table 2 below.

[0080] (Al, Fe and SiO ２ In order to evaluate the extent to which impurities contained in the raw magnesium hydroxide were removed in the magnesium oxides of Example 1, Comparative Example 1, and Comparative Example 2, the impurities Al, Fe, and SiO were removed. ２ The removal rate was calculated according to the following formula: Removal rate (%) = (B - C × 40.31 / 58.33) / B. In the above formula, B represents the percentage of Al, Fe, and SiO in the raw material magnesium hydroxide. ２ C is the ratio of Al, Fe and SiO in magnesium oxide. ２ is the percentage.

[0081] Calculated Al, Fe and SiO in Example 1, Comparative Example 1 and Comparative Example 2 ２ The removal rates are shown in Table 3 below.

[0082]

[0083]

[0084] In Comparative Example 2, the amounts of basic magnesium carbonate and magnesium oxide necessary for quantitative analysis were not obtained. ２ and the concentration of Fe could not be measured.

[0085] As described above, it was found that the magnesium oxide manufacturing method of Example 1 can produce magnesium oxide with few impurities.

[0086] 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 the magnesium hydroxide suspension 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, In the carbonation step, the pH of the magnesium hydroxide suspension is adjusted, The crystallization step further includes a heating step of heating the crystallized magnesium carbonate, A method for producing magnesium oxide, characterized in that in the heating step, the magnesium carbonate is heated at a temperature of 50°C or higher and 250°C or lower.

2. The method according to claim 1, wherein the pH of the magnesium hydroxide suspension is adjusted to within a range of 7.0 or more and less than 7.5 in the carbonation step.

3. 2. The method according to claim 1, wherein in the carbonation step, the magnesium hydroxide suspension is heated to a temperature of 0° C. or more and 50° C. or less, and the carbon dioxide gas is blown into the suspension.

4. 2. The method according to claim 1, wherein the aqueous magnesium hydrogen carbonate solution after the carbon dioxide gas is blown into the carbonation step contains undissolved magnesium carbonate.

5. The method according to any one of claims 1 to 4, wherein in the heating step, the magnesium carbonate is heated for a heating time of 1 hour or more and 72 hours or less.