Production method for magnesium hydroxide

Abstract

To provide a production method for magnesium hydroxide using naturally derived raw materials and in which impurities derived from metals such as heavy metals are reduced.SOLUTION: A production method for magnesium hydroxide comprises a heating step of heat-treating eggshells to prepare calcium oxide, a calcium hydroxide synthesis step of making the calcium oxide react with water to synthesize calcium hydroxide, and a magnesium hydroxide synthesis step of making the calcium hydroxide react with a water-soluble magnesium salt to synthesize magnesium hydroxide.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing magnesium hydroxide. [Background technology]

[0002] As a method for producing magnesium hydroxide, Patent Document 1 describes a method for producing magnesium hydroxide particles by reacting magnesium chloride with an alkaline substance in an aqueous medium.

[0003] Patent Document 2 describes a method for producing highly active magnesium hydroxide, which comprises mixing light-burned magnesia, which is obtained by firing and pulverizing naturally occurring magnesite, containing at least 90% magnesium oxide and 0.5 to 2% by weight of calcium oxide and having a particle size of at most 75 μm, with water, adjusting the pH of the resulting mixture to a range of neutral to less than pH 11.0, and heating to a maximum of 85°C.

[0004] Patent Document 3 describes a method for slaking natural light-burned magnesia, in which light-burned magnesia obtained by firing natural magnesite is pulverized into an ultrafine powder of 5 to 30 microns, a strong alkaline agent is added to water to adjust the pH of the liquid to 11 or higher, the light-burned magnesia is added while stirring, and the mixed liquid is heated to 100°C or higher.

[0005] Non-Patent Document 1 describes the continuous production of magnesium hydroxide using desulfurized bittern and milk of lime as Ca(OH)2 prepared by slaked lime as raw materials. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-200300 [Patent Document 2] Japanese Patent Application Publication No. 08-067515 [Patent Document 3] Japanese Patent Application Publication No. 01-294520 [Non-patent literature]

[0007] [Non-Patent Document 1] Uehara Minoru, Sugiyama Mikio, "On the Production of Magnesium Hydroxide," Journal of the Japanese Society of Saltology, Vol. 10, No. 6 (1956) Summary of the Invention [Problem to be solved by the invention]

[0008] Conventional methods, such as those using sodium hydroxide, require special manufacturing equipment because the pH can become high depending on the manufacturing conditions. When limestone, sandstone, or the like is used as a raw material without using sodium hydroxide, the resulting magnesium hydroxide contains a large amount of metal-derived impurities, such as heavy metals (iron and manganese). When such magnesium hydroxide is added to a resin, these impurities can cause the resin to discolor and can also reduce the thermal stability of the resin. However, removing heavy metals, such as iron and manganese, from magnesium hydroxide requires complicated processes.

[0009] An object of the present disclosure is to provide a method for producing magnesium hydroxide using naturally occurring raw materials and with reduced metal-derived impurities such as heavy metals. [Means for solving the problem]

[0010] A first embodiment of the present disclosure provides a method for producing magnesium hydroxide, which includes a heating step of heat-treating eggshells to prepare calcium oxide, a calcium hydroxide synthesis step of reacting the calcium oxide with water to synthesize calcium hydroxide, and a magnesium hydroxide synthesis step of reacting the calcium hydroxide with a water-soluble magnesium salt to synthesize magnesium hydroxide.

[0011] In the second embodiment of the present disclosure, in the heating step described in the first embodiment, the eggshell may be heated to 900°C or higher and 1,300°C or higher.

[0012] A third embodiment of the present disclosure may be any one of the first and second embodiments, further comprising a preheating step of heating the eggshell at a temperature of 200°C or higher and 300°C or lower before the heating step.

[0013] A fourth embodiment of the present disclosure may further include a crushing step of crushing eggshells in any one of the first to third embodiments.

[0014] In a fifth embodiment of the present disclosure, in any one of the first to fourth embodiments, the water-soluble magnesium salt may include one or more selected from magnesium chloride and magnesium nitrate.

[0015] In a sixth embodiment of the present disclosure, in any one of the first to fifth embodiments, the reaction between the calcium hydroxide and the water-soluble magnesium salt can be carried out by hydrothermal treatment of a mixture containing calcium hydroxide and the magnesium salt.

[0016] In the seventh embodiment of the present disclosure, in the sixth embodiment, the hydrothermal treatment may be carried out at 100°C or higher and 200°C or lower.

[0017] In an eighth embodiment of the present disclosure, in any one of the first to seventh embodiments, the concentration of iron in the magnesium hydroxide may be 50 mass ppm or less.

[0018] In a ninth embodiment of the present disclosure, in any one of the first to eighth embodiments, the concentration of calcium in the magnesium hydroxide can be 0.6 mass % or more in terms of oxide.

[0019] A tenth embodiment of the present disclosure provides magnesium hydroxide having an iron concentration of 50 mass ppm or less and a calcium concentration of 0.6 mass % or more in terms of oxide. [Effects of the Invention]

[0020] According to the present disclosure, a method for producing magnesium hydroxide using naturally occurring raw materials and having reduced metal-derived impurities such as heavy metals can be provided. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present disclosure provides a method for producing magnesium hydroxide, comprising: a heating step of heating the eggshells to prepare calcium oxide; The calcium oxide is reacted with water to synthesize calcium hydroxide. a synthesis step, and and a magnesium hydroxide synthesis step of reacting the calcium hydroxide with a water-soluble magnesium salt to synthesize magnesium hydroxide.

[0022] The manufacturing method disclosed herein uses naturally derived raw materials and can produce magnesium hydroxide with reduced metal-derived impurities such as heavy metals. Furthermore, the present disclosure can use eggshells, which would normally be treated as waste, as a raw material, and can contribute to Goal 12 of the United Nations' Sustainable Development Goals (SDGs), "Ensure sustainable consumption and production patterns."

[0023] The method for producing magnesium hydroxide of the present disclosure preferably further includes a preheating step of heating the eggshells at 200°C or higher and 300°C or lower before the heating step.

[0024] The method for producing magnesium hydroxide according to the present disclosure preferably further comprises a crushing step of crushing the eggshells before the heating step. When a preheating step is performed, the crushing step is preferably performed before the preheating step.

[0025] In the present disclosure, "magnesium hydroxide," "magnesium oxide," and "water-soluble magnesium salt" are not limited to magnesium hydroxide (Mg(OH)2), magnesium oxide (MgO), and water-soluble magnesium salt as compounds (pure substances), respectively, and may contain elements such as Ca, Si, Cl, S, Al, and Fe as impurities. The water-soluble magnesium salt may also be a hydrate thereof.

[0026] In the present disclosure, magnesium hydroxide, magnesium oxide, and water-soluble magnesium salt may preferably be magnesium hydroxide particles, magnesium oxide particles, and water-soluble magnesium salt particles, respectively. In the present disclosure, "particles" refers to an aggregate of particulate materials that are independent of each other. The shape of each particle may be spherical, irregular, or the like. When the particle shape is spherical, "spherical" is not limited to "true spherical."

[0027] The magnesium oxide may be any material containing 80% by mass or more of magnesium oxide (MgO) as a compound. In the magnesium oxide, the content of magnesium oxide (MgO) as a compound is preferably 80% by mass or more and 100% by mass or less, more preferably 85% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, and even more preferably 95% by mass or more and 100% by mass or less, based on 100% by mass of the total amount of magnesium oxide. In the present disclosure, the content of elements in a material can be measured by wavelength dispersive X-ray fluorescence spectroscopy.

[0028] (Crushing process) In the method for producing magnesium hydroxide according to the present disclosure, a pulverization step is preferably carried out before the heating step. In the pulverization step, the eggshells are pulverized. This allows the eggshells to be adjusted to a size suitable for the synthesis of calcium hydroxide and magnesium hydroxide.

[0029] The eggshells may be, typically, available eggshells from terrestrial oviparous animals, such as chicken, quail, turkey, wild goose, duck, goose, ostrich, guinea fowl, cockroach, bantam, pigeon, mute swan, emu, and pheasant, with chicken eggs being particularly preferred.

[0030] The eggshells can be pulverized so that the particle size of the powder after pulverization is preferably 1 mm or more and 10 mm or less, more preferably 1 mm or more and 5 mm or less. In the present disclosure, the particle size of the powder after pulverization can be measured by a sieving method.

[0031] The method for crushing the eggshells is not particularly limited, and examples thereof include crushing using a blender, mixer, mill, or crusher.

[0032] The eggshells are preferably washed with water before being subjected to the heating step, which allows the cuticle layer and other substances adhering to the eggshell surface to be removed.

[0033] Washing may be carried out before or after crushing the eggshells. Washing can be carried out by bringing the eggshells into contact with water, and may be carried out by immersing the eggshells in water before or after crushing, or by spraying water on the eggshells before or after crushing, for example.

[0034] (Preheating process) In the magnesium hydroxide production method of the present disclosure, a preheating step is preferably carried out after the optional crushing step and before the heating step. In the preheating step, the optionally crushed eggshells are preferably heated at 200°C or higher and 300°C or lower. This can more effectively reduce the sulfur odor derived from the eggshell membrane and impurities derived from the eggshell, thereby producing magnesium hydroxide with high purity. Furthermore, by carrying out the preheating step, the crushed eggshells can be stored in a more stable state, which can be advantageous in terms of raw material management.

[0035] The heating temperature in the preheating step may be preferably 200° C. or higher and 300° C. or lower, more preferably 220° C. or higher and 300° C. or lower, and even more preferably 250° C. or higher and 300° C. or lower. When the heating temperature in the preheating step is within this range, impurities can be reduced more efficiently.

[0036] The heating time in the preheating step, i.e., the time for which the heating temperature is maintained, is preferably from 30 minutes to 10 hours, more preferably from 45 minutes to 5 hours, and even more preferably from 1 hour to 3 hours. By keeping the heating time in the preheating step within this range, impurities can be reduced more efficiently.

[0037] The rate of temperature rise to the heating temperature in the preheating step may be preferably 0.1° C. / min to 50° C. / min, more preferably 0.5° C. / min to 30° C. / min, and even more preferably 1° C. / min to 20° C. / min. When the rate of temperature rise in the preheating step is within this range, impurities can be reduced more efficiently.

[0038] The heating atmosphere when the preheating step is carried out is not particularly limited, and the preheating step may be carried out in an air atmosphere, a nitrogen atmosphere, a rare gas atmosphere, or the like.

[0039] When the preheating step is carried out, the preheated eggshells may be subjected to the heating step as they are, or the preheated eggshells may be cooled to room temperature and stored for a certain period of time before being subjected to the heating step. When the preheated eggshells are cooled to room temperature, they may be cooled by natural cooling.

[0040] (Heating process) In the heating step, eggshells are heated to prepare calcium oxide. Preferably, such eggshells are the pulverized eggshells described above. When the pulverization step and / or preheating step are performed, the term "eggshells" can be interpreted as "pulverized eggshells" and / or "preheated eggshells." Calcium oxide can be obtained by performing the heating step.

[0041] The heating temperature in the heating step may be preferably 900° C. or higher and 1,300° C. or lower, more preferably 950° C. or higher and 1,250° C. or lower, and even more preferably 1,000° C. or higher and 1,200° C. or lower. A high heating temperature makes it easy to suppress the by-production of impurities such as calcium carbonate and to obtain calcium oxide with high purity, while a low heating temperature makes it easy to suppress costs.

[0042] The heating time in the heating step, i.e., the time for which the heating temperature is maintained, is preferably from 30 minutes to 12 hours, more preferably from 45 minutes to 6 hours, and even more preferably from 1 hour to 3 hours. By keeping the heating time in the heating step within this range, impurities can be reduced more effectively.

[0043] The rate of temperature rise up to the heating temperature in the heating step may be preferably 0.1° C. / min to 50° C. / min, more preferably 0.5° C. / min to 30° C. / min, and even more preferably 1° C. / min to 20° C. / min. When the rate of temperature rise in the heating step is within this range, impurities can be reduced more effectively.

[0044] The heating atmosphere when carrying out the heating step is not particularly limited, and the heating step may be carried out in an air atmosphere, a nitrogen atmosphere, a rare gas atmosphere, or the like.

[0045] After heating, the eggshells may be cooled by natural cooling or the like.

[0046] (Calcium hydroxide synthesis process) In the calcium hydroxide synthesis step, the calcium oxide is reacted with water to synthesize calcium hydroxide.

[0047] The reaction between calcium hydroxide and water can be carried out by contacting calcium oxide with water, specifically by preparing a first mixed solution by mixing calcium oxide with water and maintaining the first mixed solution at a constant temperature.

[0048] In the first mixed solution, the concentration of calcium oxide may be preferably 50 g / L or more and 500 g / L or less, more preferably 80 g / L or more and 300 g / L or less, and even more preferably 100 g / L or more and 200 g / L or less. The higher the concentration of calcium oxide in the first mixed solution, the greater the amount of magnesium oxide that can be produced per unit volume of the first mixed solution, thereby improving productivity. The lower the concentration of calcium oxide in the first mixed solution, the more the viscosity of the first mixed solution can be maintained within an appropriate range, allowing the calcium hydroxide production reaction to proceed uniformly.

[0049] The first mixed solution can be prepared by mixing calcium oxide and water. When preparing the first mixed solution, wet grinding may be carried out.

[0050] The temperature at which the first mixed liquid is maintained may be preferably from 0° C. to 90° C., more preferably from 20° C. to 90° C., and even more preferably from 50° C. to 90° C. The higher the maintained temperature, the more effectively the first mixed liquid is prevented from freezing and the more effectively the production of calcium hydroxide is promoted, and the lower the maintained temperature, the more effectively the production cost is reduced.

[0051] The calcium hydroxide may be subjected to the magnesium hydroxide synthesis step in the form of a mixed liquid, typically a slurry.

[0052] In the calcium hydroxide, the content of metal-derived impurities such as heavy metals is reduced.

[0053] The iron concentration in the calcium hydroxide of the present disclosure is preferably 40 ppm by mass or less, more preferably 30 ppm by mass or less, and even more preferably 20 ppm by mass or less, and although there is no lower limit, it may be typically 0.01 ppm by mass or more. When the iron concentration in the calcium hydroxide is within this range, when magnesium hydroxide obtained using the calcium hydroxide is added to a resin, coloration of the resin and deterioration of the resin can be suppressed.

[0054] The silicon concentration in the calcium hydroxide of the present disclosure is preferably 50 mass ppm or less, more preferably 45 mass ppm or less, and even more preferably 40 mass ppm or less, calculated as oxide. The lower limit is not limited, but may typically be 1 mass ppm or more. When the silicon concentration in the calcium hydroxide is within this range, the crystal growth of magnesium hydroxide can be promoted.

[0055] In the present disclosure, the content of a specific element in a material in terms of its oxide means the value obtained by dividing the weight-based content of a compound containing the specific element by the molecular weight of the compound containing the specific element, when the total weight of the material is taken as 100 wt %, and then multiplying the result by the molecular weight of the oxide of the specific element.

[0056] The manganese concentration in the calcium hydroxide of the present disclosure is preferably 10 ppm by mass or less, more preferably 8 ppm by mass or less, and even more preferably 5 ppm by mass or less. There is no lower limit, but it may be typically 0.01 ppm by mass or more. When the manganese concentration in the calcium hydroxide is within this range, when magnesium hydroxide obtained using the calcium hydroxide is added to a resin, coloration of the resin and deterioration of the resin can be suppressed.

[0057] The amounts of iron, silicon, and manganese in the calcium hydroxide can be measured by fluorescent X-ray analysis.

[0058] The cadmium concentration in the calcium hydroxide of the present disclosure is preferably 0.5 mass ppm or less, more preferably 0.3 mass ppm or less, and even more preferably 0.1 mass ppm or less, and although there is no lower limit, it may typically be 0.01 mass ppm or more. When the cadmium concentration in the calcium hydroxide is within this range, the biocompatibility of the magnesium hydroxide obtained using the calcium hydroxide can be improved.

[0059] The amount of cadmium in the calcium hydroxide can be measured by polarized Zeeman atomic absorption spectrometry.

[0060] (Magnesium hydroxide synthesis process) In the magnesium hydroxide synthesis step, the calcium hydroxide is reacted with a water-soluble magnesium salt to synthesize magnesium hydroxide. By allowing the water-soluble magnesium salt and calcium hydroxide to coexist, magnesium ions and hydroxide ions combine to produce magnesium hydroxide.

[0061] In the present disclosure, water-soluble may mean that the solubility in water at 25° C. is preferably 0.03 g / mL or more, more preferably 0.1 g / mL or more, and even more preferably 1 g / mL. The upper limit of the solubility in water at 25° C. is not limited, but may generally be 90 g / mL or less.

[0062] The water-soluble magnesium salt preferably contains one or more selected from magnesium chloride and magnesium nitrate, and more preferably contains magnesium chloride.

[0063] The content of the magnesium chloride and magnesium nitrate in the water-soluble magnesium salt may be preferably 80% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, and even more preferably 95% by mass or more and 100% by mass or less.

[0064] The reaction between calcium hydroxide and the water-soluble magnesium salt may be carried out in a second mixture containing calcium hydroxide, the water-soluble magnesium salt, and water.

[0065] The concentration of the water-soluble magnesium salt in the second mixed solution may be preferably 0.1 mol / L or more and 5 mol / L or less, more preferably 0.5 mol / L or more and 4 mol / L or less, and even more preferably 1 mol / L or more and 3 mol / L or less. The higher the concentration of the water-soluble magnesium salt, the higher the productivity can be, and the lower the concentration of the water-soluble magnesium salt, the better the viscosity of the second mixed solution can be maintained within an appropriate range, and the more uniform the production of magnesium hydroxide can be.

[0066] The amount of calcium hydroxide in the second mixed solution may be preferably 50 mol% or more and 99 mol% or less, more preferably 60 mol% or more and 95 mol% or less, and even more preferably 70 mol% or more and 90 mol% or less, relative to 1 mol of the water-soluble magnesium salt. The greater the amount of calcium hydroxide, the higher the yield of magnesium hydroxide and the more improved the productivity. The smaller the amount of calcium hydroxide, the more effectively the magnesium hydroxide powder is prevented from being contaminated with unreacted calcium hydroxide as an impurity.

[0067] The temperature at which the second mixed liquid is prepared may be preferably from 0° C. to 80° C., more preferably from 10° C. to 60° C., and even more preferably from 20° C. to 40° C. By preparing the slurry within this temperature range, freezing of the second mixed liquid is suppressed, and aggregation of magnesium hydroxide is prevented, while the production cost can be kept within an appropriate range.

[0068] The reaction between the calcium hydroxide and the water-soluble magnesium salt can be carried out by a hydrothermal reaction. In a preferred embodiment, the hydrothermal reaction can be carried out by subjecting a slurry containing calcium hydroxide, a water-soluble magnesium salt, and water to a hydrothermal reaction.

[0069] The hydrothermal reaction can typically be carried out by maintaining the second mixed liquid at 100° C. or higher under pressure.

[0070] The temperature during the hydrothermal treatment may be preferably 100° C. or higher and 200° C. or lower, more preferably 140° C. or higher and 200° C. or lower, and even more preferably 150° C. or higher and 180° C. The higher the hydrothermal treatment temperature, the more likely it is that crystal growth of magnesium hydroxide will be promoted, and the lower the hydrothermal treatment temperature, the easier it will be to reduce costs.

[0071] The hydrothermal treatment time may be preferably 0.5 hours to 8 hours, more preferably 1 hour to 6 hours, and even more preferably 2 hours to 4 hours. The longer the hydrothermal treatment time, the more sustained the crystal growth of magnesium hydroxide can be, and the shorter the hydrothermal treatment time, the easier it is to reduce costs.

[0072] The pH of the second mixed solution after the hydrothermal treatment may be preferably 8 or more and 10.5 or less, more preferably 8.5 or more and 10 or less, and even more preferably 8.5 or more and 9.5 or less. The lower the pH, the easier it is to promote the crystal growth of magnesium hydroxide, and the higher the pH, the easier it is to suppress costs.

[0073] The second mixed liquid after the hydrothermal treatment may be subjected to treatments such as solid-liquid separation, washing, drying, etc. In this way, a dried magnesium hydroxide can be obtained.

[0074] The method for the solid-liquid separation is not particularly limited and may be, for example, filtration. The filtration may be carried out under normal pressure, elevated pressure, or reduced pressure. The temperature during the filtration may be preferably 5°C or higher and 50°C or lower, more preferably 10°C or higher and 40°C or lower, and even more preferably 10°C or higher and 35°C or lower.

[0075] The washing can be carried out using a washing solvent such as water. In one embodiment, the washing can be carried out by contacting the filtered magnesium hydroxide with a washing solvent and performing solid-liquid separation. The amount of washing solvent can be preferably 5 parts by mass or more and 100 parts by mass or less, more preferably 5 parts by mass or more and 50 parts by mass or less, and even more preferably 10 parts by mass or more and 30 parts by mass or less, per part by mass of the obtained magnesium hydroxide. The solid-liquid separation can be carried out by the same method as the solid-liquid separation of the mixed liquid after the hydrothermal treatment. The more washing solvent is used, the easier it is to remove impurities, and the less washing solvent is used, the easier it is to reduce production costs.

[0076] The number of times of washing is not particularly limited, and may be preferably from 1 to 10 times, more preferably from 1 to 5 times, and even more preferably from 1 to 3 times. The more times of washing, the higher the washing efficiency.

[0077] The drying can typically be carried out after solid-liquid separation of the mixed solution or the washed mixture. The drying temperature can be preferably 60°C or higher and 300°C or lower, more preferably 80°C or higher and 200°C or lower, and even more preferably 100°C or higher and 150°C or lower. The drying time can be preferably 1 hour or higher and 100 hours or lower, more preferably 2 hours or higher and 50 hours or lower, and even more preferably 8 hours or higher and 24 hours or lower.

[0078] The dried product may be further pulverized. This pulverization can facilitate control of the particle size of the magnesium hydroxide. The pulverization is typically carried out by dry pulverization.

[0079] The magnesium hydroxide obtained by the manufacturing method of the present disclosure uses biologically derived materials as raw materials, and the magnesium hydroxide obtained by the manufacturing method of the present disclosure has reduced metal-derived impurities such as heavy metals.

[0080] The iron concentration in the magnesium hydroxide of the present disclosure is preferably 50 ppm by mass or less, more preferably 40 ppm by mass or less, and even more preferably 20 ppm by mass or less, and although there is no lower limit, it may typically be 0.01 ppm by mass or more. When the iron concentration in the magnesium hydroxide is within this range, when the magnesium hydroxide is added to a resin, coloration of the resin and deterioration of the resin can be suppressed.

[0081] The silicon concentration in the magnesium hydroxide of the present disclosure is, in terms of oxide, preferably 80 ppm by mass or less, more preferably 70 ppm by mass or less, and even more preferably 50 ppm by mass or less, and although there is no lower limit, it may typically be 0.01 ppm by mass or more. When the silicon concentration in the magnesium hydroxide is within this range, crystal growth of the magnesium hydroxide can be promoted, and it is easy to obtain magnesium hydroxide with a regular shape.

[0082] The amounts of iron and silicon in the magnesium hydroxide can be measured by fluorescent X-ray analysis.

[0083] The manganese concentration in the magnesium hydroxide of the present disclosure is preferably 10 ppm by mass or less, more preferably 5 ppm by mass or less, and even more preferably 3 ppm by mass or less, and although there is no lower limit, it may typically be 0.01 ppm by mass or more. When the manganese concentration in the magnesium hydroxide is within this range, when the magnesium hydroxide is added to a resin, coloration of the resin and deterioration of the resin can be suppressed.

[0084] The amount of manganese in the magnesium hydroxide can be measured by ICP emission spectroscopy.

[0085] The cadmium concentration in the magnesium hydroxide of the present disclosure is preferably 0.3 mass ppm or less, more preferably 0.1 mass ppm or less, and even more preferably 0.05 mass ppm or less, and although there is no lower limit, it may typically be 0.001 mass ppm or more. When the cadmium concentration in the magnesium hydroxide is within this range, the biocompatibility of the magnesium hydroxide can be improved.

[0086] The amount of cadmium in the magnesium hydroxide can be measured by polarized Zeeman atomic absorption spectrometry.

[0087] The magnesium hydroxide of the present disclosure may contain calcium. The calcium concentration in the magnesium hydroxide, calculated as oxide, may be preferably 0.6% by mass or more and 2% by mass or less, more preferably 0.7% by mass or more and 1.5% by mass or less, and even more preferably 0.8% by mass or more and 1% by mass or less. When the calcium concentration is within this range, even when the magnesium hydroxide is added to a resin, coloration of the resin and deterioration of the resin can be easily suppressed.

[0088] The amount of calcium in the magnesium hydroxide can be measured by fluorescent X-ray analysis.

[0089] The average particle size of the magnesium hydroxide may be preferably 0.1 μm or more and 5 μm or less, more preferably 0.3 μm or more and 3 μm or less, and even more preferably 0.5 μm or more and 2 μm or less.

[0090] In the present disclosure, the average particle size can be measured by a laser diffraction / scattering method in accordance with JIS Z 8825, and can be the volume-based median size (D50).

[0091] The BET specific surface area of ​​the magnesium hydroxide is preferably 0.1 m 2 / g or more 100m 2 / g or less, more preferably 1m 2 / g or more 20m 2 / g or less, more preferably 3m 2 / g or more 10m 2 / g or less.

[0092] In the present disclosure, the BET specific surface area can be measured by the BET method in accordance with JIS Z 8830.

[0093] The magnesium hydroxide obtained by the production method of the present disclosure can be preferably used as a flame retardant, a neutralizing agent, a food additive (anti-caking agent, magnesium fortifying agent, etc.), an antacid, a laxative, a rubber reinforcing agent, a foam adjusting agent, a pigment, an anti-slip agent, etc.

[0094] In a preferred embodiment, the magnesium hydroxide used in the manufacturing method of the present disclosure has good dispersibility in resins and can be used as a flame retardant. When heated, magnesium hydroxide can release desorbed water through the following endothermic reaction, which is thought to result in the flame retardant effect. Mg(OH)2 → MgO + H2O Therefore, it is believed that if the crystallinity of magnesium hydroxide is good, it will have good dispersibility in the resin and the above reaction will proceed evenly in the resin, resulting in a good flame retardant effect.

[0095] A method for producing a resin composition, which includes mixing the magnesium hydroxide with a resin to obtain a resin composition, is also included within the technical scope of the present disclosure.

[0096] Examples of such resins include thermoplastic resins such as polyolefin resins, polyamide resins, and polyphenylene sulfide resins, and thermosetting resins such as epoxy resins, phenolic resins, silicone resins, urea resins, melamine resins, and unsaturated polyesters.

[0097] The magnesium hydroxide and the resin can be mixed as appropriate depending on the type of resin.

[0098] The present disclosure can provide a new method for producing magnesium hydroxide. In a preferred embodiment, the method can easily produce magnesium hydroxide, and the magnesium hydroxide obtained by the method has good dispersibility in resins, making it suitable for use as a flame retardant, neutralizing agent, food additive (anti-caking agent, magnesium fortifying agent, etc.), antacid, laxative, rubber reinforcing agent, foam adjusting agent, pigment, anti-slip agent, etc. [Example]

[0099] The present invention will be explained in more detail with reference to the following examples, but the present invention is not limited to these examples.

[0100] [Example 1] 500 g of eggshells manufactured by Kewpie Corporation were crushed into powder with a particle size of 1 to 5 mm, and then washed with 10 L of ion-exchanged water.

[0101] The washed eggshells were preheated by heating them and maintaining the temperature at 200-300°C for 2 hours. 300g of the preheated eggshells were then heated at 1,200°C for 2 hours using a KBF624N thermometer manufactured by JTEKT Thermosystems Corporation, to obtain calcium oxide powder.

[0102] Next, 100 g of the obtained calcium oxide was added to 1 L of ion-exchanged water at 50° C. and stirred for 30 minutes to obtain a calcium hydroxide slurry.

[0103] 307 mL of the obtained calcium hydroxide slurry and 293 mL of a 1.8 mol / L aqueous magnesium chloride solution were mixed at temperatures adjusted to 35°C, and then 500 mL of the obtained magnesium hydroxide slurry was subjected to hydrothermal treatment at 170°C for 4 hours.

[0104] Subsequently, the mixture was filtered under reduced pressure and washed with ion-exchanged water in an amount 20 times the mass of the magnesium hydroxide to obtain a cake of magnesium hydroxide. The cake of magnesium hydroxide was dried at 105°C for 24 hours (Yamato Scientific Co., Ltd. constant temperature and blower incubator DKN602) to obtain magnesium hydroxide powder.

[0105] [Example 2] Magnesium hydroxide powder was obtained in the same manner as in Example 1, except that eggshells manufactured by Kagoya Co., Ltd. were used instead of eggshells manufactured by Kewpie Corporation, the amount of calcium hydroxide slurry was 341 mL, and the amount of magnesium chloride aqueous solution was 359 mL.

[0106] [Comparative Example 1] Magnesium hydroxide powder was obtained in the same manner as in Example 1, except that natural limestone was used instead of eggshells, the amount of calcium hydroxide slurry was 269 mL, and the amount of magnesium chloride aqueous solution was 231 mL.

[0107] [Analysis method] Impurity content (calcium hydroxide) In the examples and comparative examples, calcium hydroxide slurry was filtered under reduced pressure and then dried at 105°C to obtain calcium hydroxide powder. The amounts of impurities (Fe, SiO2, Mn, Cd) in the obtained powder were analyzed. Depending on the type of impurity, the analysis was performed by the following method. Fe, SiO2, Mn: Measured using a scanning X-ray fluorescence analyzer ZSX Primus IV manufactured by Rigaku Corporation. Cd: Measured using a polarized Zeeman atomic absorption spectrophotometer ZA3000 manufactured by Hitachi High-Tech Science Corporation.

[0108] Impurity content (magnesium hydroxide) The amounts of impurities (Fe, SiO2, Mn, Cd, and Ca) in the magnesium hydroxides obtained in the examples and comparative examples were analyzed. Depending on the type of impurity, the analysis was carried out by the following methods. Fe, SiO2, CaO: Measured using a scanning X-ray fluorescence analyzer ZSX Primus IV manufactured by Rigaku Corporation. Mn: Measured using Hitachi High-Tech Science Corporation's ICP optical emission spectrometer PS3500. Cd: Measured using a polarized Zeeman atomic absorption spectrophotometer ZA3000 manufactured by Hitachi High-Tech Science Corporation.

[0109] Table 1 shows the measurement results of the amount of impurities in calcium hydroxide.

[0110] [Table 1]

[0111] Table 2 shows the analytical results of magnesium hydroxide.

[0112] [Table 2]

[0113] Examples 1 and 2 are examples of the present disclosure, in which magnesium hydroxide was produced using eggshells, which are components derived from living organisms, and it was confirmed that the content of components derived from heavy metals was reduced. Comparative Example 1 is an example in which limestone was used as the raw material for calcium hydroxide, and it was confirmed that the calcium hydroxide contained a large amount of heavy metals. [Industrial Applicability]

[0114] The method for producing magnesium hydroxide of the present invention can be suitably used as a flame retardant, desulfurizing agent, neutralizing agent, food additive, pharmaceuticals, fertilizer, etc. Considering that the magnesium hydroxide is derived from eggshell raw materials that are also used in foods, etc., it is thought that it may be particularly suitable for use as a food additive or pharmaceutical.

Claims

1. A method for producing magnesium hydroxide, comprising the steps of: a heating step of heat-treating eggshells to prepare calcium oxide; a calcium hydroxide synthesis step of reacting the calcium oxide with water to synthesize calcium hydroxide; and a magnesium hydroxide synthesis step of reacting the calcium hydroxide with a water-soluble magnesium salt to synthesize magnesium hydroxide.

2. The method for producing magnesium hydroxide according to claim 1, wherein the eggshells are heated at a temperature of 900°C or higher and 1,300°C or higher in the heating step.

3. Before the heating step, The method for producing magnesium hydroxide according to claim 1, further comprising a preheating step of heating the eggshells at 200°C or higher and 300°C or lower.

4. Before the heating step, The method for producing magnesium hydroxide according to any one of claims 1 to 3, further comprising a crushing step of crushing eggshells.

5. The method for producing magnesium hydroxide according to any one of claims 1 to 3, wherein the water-soluble magnesium salt comprises one or more selected from magnesium chloride and magnesium nitrate.

6. The method for producing magnesium hydroxide according to any one of claims 1 to 3, wherein the reaction between the calcium hydroxide and the water-soluble magnesium salt is carried out by hydrothermal treatment of a mixture containing the calcium hydroxide and the magnesium salt.

7. The method according to claim 6 , wherein the hydrothermal treatment is carried out at a temperature of 100° C. or higher and 200° C. or lower.

8. The method for producing magnesium hydroxide according to any one of claims 1 to 3, wherein the concentration of iron in the magnesium hydroxide is 50 ppm by mass or less.

9. The method for producing magnesium hydroxide according to any one of claims 1 to 3, wherein the concentration of calcium in the magnesium hydroxide is 0.6 mass% or more in terms of oxide.

10. The iron concentration is 50 ppm by mass or less, Magnesium hydroxide having a calcium concentration of 0.6% by mass or more in terms of oxide.

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