JP2012211078A - Highly pure magnesium oxide powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide magnesium oxide powder having a sufficiently low content of lead as an impurity.SOLUTION: The magnesium oxide powder having 99.9 mass% or more of purity and a content of Pb of less than 0.1 ppm, wherein a half-value width of a peak of surfaces (111), (200), and (220) in powder X-ray diffraction measurement using Cu-Kα-ray is 0.20° or less, respectively and Dis 0.1-10 μm.

Description

  The present invention relates to high purity magnesium oxide powder.

  Magnesium hydroxide powder and magnesium oxide powder are used in various fields, such as various additives such as food additives, fuel cell raw materials, electronic component applications, phosphor raw materials, various target material raw materials, raw materials for superconducting thin films, tunnel magnetism. Tunnel barrier material for resistance element (TMR), protective film material for PDP, crystalline magnesium oxide layer material for PDP, toner charge modifier, toner particle size modifier, secondary electron multiplier electrode material, ultraviolet light emitting semiconductor material, It is used as a raw material for secondary batteries, a pharmaceutical raw material, a cosmetic raw material, and the like, and has attracted attention as an inorganic material having an extremely wide range of uses.

  These powders are required to have a higher purity. Among impurities, lead (Pb) is an element harmful to the human body and an element that adversely affects various uses. It is desired to reduce the content.

  Conventionally, in producing high-purity magnesium hydroxide powder, a purification method or the like is performed, and as a method for producing high-purity magnesium oxide powder, firing in a chlorine atmosphere or the like is performed. The following patent documents 1-3 are mentioned as literature which described content of lead.

  Patent Document 1 describes that magnesium oxide powder having a lead content of 7 ppm or less is obtained by firing magnesium hydroxide at a temperature of 700 to 1300 ° C. In Table 1, 0.3 ppm is described as the minimum value of the lead content.

  In Patent Document 2, a magnesium raw material obtained by refining seawater to remove heavy metals and an alkali raw material such as caustic soda and calcium hydroxide are reacted to obtain magnesium hydroxide having a lead content of 0.6 ppm. It is described that magnesium oxide having a lead content of about 0.1 to 1.2 ppm is produced by firing.

Patent Document 3 describes that magnesium oxide having a lead content of 2 × 10 ⁻⁷ mol / mol or less can be produced by firing magnesium hydroxide in the presence of a halogen source. In the Examples, the lead content is described as 1.9 to 7.4 × 10 ⁻⁸ mol / mol, that is, about 0.1 to 1.0 ppm.

  Moreover, although content of lead is not described, the following patent documents 4-5 are mentioned as literature which described high purity magnesium hydroxide powder or magnesium oxide powder.

  Patent Document 4 describes a method for producing high-purity magnesium oxide powder by firing magnesium oxalate at 1200 to 1400 ° C.

  In Patent Document 5, an aqueous alkali solution is mixed with an aqueous solution obtained by mixing high-purity magnesium chloride and purified water to obtain a magnesium hydroxide slurry, and then a flocculant is added to the slurry to precipitate magnesium hydroxide. Furthermore, a method for producing high-purity magnesium hydroxide by hydrothermally treating the obtained magnesium hydroxide is described.

JP 2003-33159 A JP 2004-345912 A JP 2004-244313 A JP 2007-91525 A JP 2007-254250 A

  According to the methods disclosed in the above documents, although the lead content in magnesium hydroxide and magnesium oxide can be reduced, a high-purity product with a lower lead content cannot be produced. That is, in the method of baking magnesium hydroxide described in Patent Documents 1 and 3 in the presence of a halogen source, there is a limit to the reduction of lead, and a lead content of at least about 0.1 ppm can be achieved. According to the methods described in Patent Documents 2 and 5, lead is re-eluted into the raw material solution in the raw material purification step of magnesium hydroxide, so that a lead content of less than 0.1 ppm cannot be achieved. Patent Document 4 does not describe any special process that can reduce the lead content. Therefore, the method described in this document cannot sufficiently reduce the lead content.

  Therefore, an object of the present invention is to provide a magnesium hydroxide powder and a magnesium oxide powder having a sufficiently low content of lead as an impurity.

  As a result of repeated studies to solve the above-mentioned problems, the inventors of the present invention have, as a method for producing high-purity magnesium hydroxide described in Patent Document 5, a purification step for holding a magnesium hydroxide slurry at high temperature and high agitation. Unexpectedly, it has been found that the lead content of the obtained magnesium hydroxide powder is reduced, and the present invention has been achieved.

  That is, the present invention relates to a magnesium hydroxide powder having a purity of 99.9% by mass or more and a Pb content of less than 0.1 ppm. Here, the content of Pb is preferably 0.01 ppm or less.

The present invention also relates to a magnesium oxide powder having a purity of 99.9% by mass or more and a Pb content of less than 0.1 ppm. Here, the content of Pb is preferably 0.01 ppm or less. Moreover, it is preferable that the half widths of the peaks of the (111) plane, the (200) plane, and the (220) plane in the powder X-ray diffraction method using Cu—Kα rays are each 0.20 degrees or less, and laser diffraction The cumulative 50% particle diameter (D ₅₀ ) determined by the scattering particle size distribution measurement is preferably 0.1 to 10 μm.

  The magnesium hydroxide powder and magnesium oxide powder of the present invention have a sufficiently low content of lead as an impurity.

  The magnesium hydroxide powder or magnesium oxide powder of the present invention has an extremely high purity of magnesium hydroxide of 99.9% or more and a Pb content of less than 0.1 ppm. The Pb content can be further 0.05 ppm or less, or 0.01 ppm or less. Further, the lower limit of the Pb content may be 0.001 ppm or more, or 0.005 ppm or more. Thus, the magnesium hydroxide powder or the magnesium oxide powder having a low lead content is obtained for the first time in the present invention, and the significance of the low content of lead that adversely affects various applications is extremely great. Magnesium hydroxide and magnesium oxide have a strong tendency to adsorb lead, and it has been extremely difficult to sufficiently reduce the content by simple washing.

  Since the magnesium oxide powder of the present invention has good crystallinity, the crystal distortion is extremely small, and there are few lattice defects in the crystal. Specifically, the half widths of the peaks of the (111) plane, (200) plane, and (220) plane in the powder X-ray diffraction method using Cu-Kα rays are each 0.20 degrees or less. . Although the minimum of the said half value width is not specifically limited, For example, it is 0.070 degree | times or more, or 0.090 degree | times or more is possible.

The average particle size of the magnesium oxide powder of the present invention is preferably in the range of 0.1 to 10 μm with a cumulative 50% particle size (D ₅₀ ) by laser diffraction scattering type particle size distribution measurement. D ₅₀ may be 1.0 μm or more, or less than 1.0 μm. The lower limit of the numerical range is more preferably 0.3 μm or more. The upper limit is more preferably 8 μm or less, and further preferably 6 μm or less. Note that D ₅₀ is a median diameter, which is a particle diameter (μm) corresponding to 50% by volume in a cumulative particle size graph. When a powder is divided into two by a certain particle diameter, it is smaller on the larger side. It is the particle size where the sides are equal.

  Next, a method for producing the magnesium hydroxide powder or magnesium oxide powder of the present invention will be described.

  The magnesium hydroxide powder of the present invention is obtained by reacting an aqueous alkaline solution with an aqueous solution obtained by mixing magnesium chloride and water to obtain a magnesium hydroxide slurry, and then holding the magnesium hydroxide slurry for a certain period of time under high temperature and high agitation. Then, a flocculant is added to the slurry to precipitate magnesium hydroxide, and the supernatant is recovered to obtain a purified magnesium chloride aqueous solution. Then, the resulting purified magnesium chloride solution is reacted with an alkaline aqueous solution to produce water. It is obtained by obtaining a magnesium oxide slurry and hydrothermally treating the obtained magnesium hydroxide slurry.

  The magnesium hydroxide powder of the present invention can be obtained by firing the magnesium hydroxide powder thus obtained in, for example, a firing furnace.

  As said magnesium chloride, it is preferable to use high purity anhydrous magnesium chloride.

  Water is mixed with the magnesium chloride raw material to obtain a magnesium chloride aqueous solution. The amount of water added is preferably 2 to 5 times the mass of anhydrous magnesium chloride. At this time, ion-exchanged ultrapure water is used as the water. In particular, in order to reduce the amount of impurities contained in water, it is preferable to use ultrapure water that has been refined to an electric conductivity of 0.1 μS / cm or less through an ion exchange resin.

  Next, in order to purify and remove Pb contained in the magnesium chloride aqueous solution, an alkali source was added so that the reaction rate was 20 mol% with respect to magnesium ions, and after maintaining for a certain period of time, this magnesium hydroxide was further added. The slurry is held for a certain time under high temperature and high agitation. Specifically, the temperature is maintained at a temperature of about 80 ° C. to less than the boiling point for about 10 to 100 hours under high agitation of about 15,000 to 30,000 rpm. By removing the magnesium hydroxide precipitate adsorbing the impurities thus obtained, a highly purified purified raw material solution having a very low Pb amount is obtained. Although the reason why the Pb content is reduced by such a holding step is not clear, crystallization of magnesium hydroxide particles is promoted by holding at high temperature under high agitation, and Pb adsorbed on the surface of the magnesium hydroxide particles is in the crystal. This is presumed to be caused by the fact that the re-elution into the solvent is suppressed. Sodium hydroxide is preferable in terms of low impurity contamination, but ammonia water can also be used. Sodium hydroxide is preferably an aqueous solution in which an alkali having an alkali content of 20 to 50% by mass is dissolved. In addition, in order to purify and remove Pb contained in NaOH itself, before using sodium hydroxide in this reaction, a magnesium chloride solution is used so that the reaction rate becomes 10 mol% with respect to hydroxide ions. To increase the purity. By the above reaction, 10 mol% of hydroxide ions in the aqueous sodium hydroxide solution react with magnesium ions and precipitate as magnesium hydroxide, and impurities are precipitated and removed. Reduce.

Next, the resulting purified MgCl ₂ solution is subjected to a secondary reaction with an alkali source such as NaOH to obtain a magnesium hydroxide slurry. By subjecting the obtained magnesium hydroxide slurry to hydrothermal treatment (temperature: 100 to 150 ° C., time: 0 to 60 minutes) in an autoclave, the high purity magnesium hydroxide powder of the present invention is obtained. By performing autoclaving, it is considered that crystal grains can be prepared and impurities incorporated in the crystals can be leached into the solution, and as a result, the amount of impurities can be reduced.

  The high-purity magnesium oxide powder of the present invention can be obtained by firing the high-purity magnesium hydroxide powder of the present invention obtained as described above at approximately 1000 to 1500 ° C.

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

  In the following examples, various physical properties and the like were measured according to the following procedure.

(1) Method for measuring purity of magnesium hydroxide and magnesium oxide The purity of magnesium hydroxide and magnesium oxide was calculated as a value obtained by subtracting the total amount of impurities measured from 100% by mass.

(2) Impurity amount and Pb amount measuring method of magnesium hydroxide and magnesium oxide Impurity amount of magnesium hydroxide and magnesium oxide (Si, Al, Ca, Fe, V, Cr, Mn, Ni, Zn, B, Zr, Cu , Na, K, Cl) and Pb amounts were measured after dissolving the sample in acid using an ICP mass spectrometer (4500 manufactured by Agilent).
(3) Powder X-ray diffraction method Using an X-ray diffractometer (trade name: RINT-UltimaIII, manufactured by Rigaku), a magnesium oxide powder sample is measured and analyzed by a powder X-ray diffraction method using Cu-Kα rays. Using software (trade name: Jade 6, manufactured by Rigaku), the peak near 2θ = 36.9 deg is the (111) plane, the peak near 2θ = 42.9 deg is the (200) plane, and the peak near 2θ = 62.3 deg Was the (220) plane, and the half width of each peak was calculated.
(4) Laser diffraction / scattering particle size distribution measuring method Using a laser diffraction / scattering particle size distribution measuring device (trade name: HIRA, Nikkiso Co., Ltd.), a cumulative 50% particle size (D ₅₀ ) was measured.

Example 1
Anhydrous magnesium chloride (MgCl ₂ ) was dissolved in ion-exchanged water to prepare an about 3.5 mol / l magnesium chloride aqueous solution. As the MgCl ₂ in the reaction rate of 20 mol%, MgCl ₂ solution and 25% NaOH solution each fed to the reactor at a metering pump, was continuously reacted. The reaction slurry was overflowed from the reactor in a residence time of 30 minutes. Next, the slurry recovered by overflow was held at 40 ° C. for 3 hours, and then the temperature rising rate was adjusted to a range of 2 ° C. ± 0.5 ° C. per minute and the temperature was raised to 90 ° C. Then, a homogenizer (Hiscotron NS- 50, manufactured by Microtech Nichion Co., Ltd.) and kept at high speed stirring at 19,000 rpm for 48 hours, after which 500 ppm of flocculant is added to the produced magnesium hydroxide, allowed to settle, and the supernatant (purified) Magnesium chloride aqueous solution) was recovered.

While stirring the recovered purified magnesium chloride solution, a 25% NaOH solution was added so that the reaction rate of MgCl ₂ was 90 mol%, and the mixture was stirred for 30 minutes. The obtained magnesium hydroxide slurry was hydrothermally treated at 130 ° C. for 1 hour in an autoclave. The hydrothermally treated magnesium hydroxide slurry was filtered, washed with water and dried to obtain magnesium hydroxide powder.

  The obtained magnesium hydroxide powder was baked in an electric furnace at 1300 ° C. for 60 minutes to obtain a magnesium oxide powder.

  Table 1 shows the results of measuring the lead content and purity of these magnesium hydroxide powder and magnesium oxide powder. Table 2 shows the measurement result of the magnesium oxide powder in the powder X-ray diffraction method and the measurement result of the cumulative 50% particle diameter.

(Comparative Example 1)
Anhydrous magnesium chloride (MgCl ₂ ) was dissolved in ion-exchanged water to prepare an about 3.5 mol / l magnesium chloride aqueous solution. As the MgCl ₂ in the reaction rate of 20 mol%, MgCl ₂ solution and 25% NaOH solution each fed to the reactor at a metering pump, was continuously reacted. The reaction slurry was overflowed from the reactor in a residence time of 30 minutes. Next, while stirring the slurry recovered by the overflow, 500 ppm of a flocculant was added to the produced magnesium hydroxide and allowed to settle, and the supernatant (purified magnesium chloride aqueous solution) was recovered.

While stirring the recovered purified magnesium chloride solution, a 25% NaOH solution was added so that the reaction rate of MgCl ₂ was 90 mol%, and the mixture was stirred for 30 minutes. The obtained magnesium hydroxide slurry was hydrothermally treated at 130 ° C. for 1 hour in an autoclave. The hydrothermally treated magnesium hydroxide slurry was filtered, washed with water and dried to obtain magnesium hydroxide powder. The steps of Comparative Example 1 described above are in accordance with the method described in Patent Document 5.

  The obtained magnesium hydroxide powder was baked in an electric furnace at 1300 ° C. for 60 minutes to obtain a magnesium oxide powder.

  Table 1 shows the results of measuring the lead content and purity of these magnesium hydroxide powder and magnesium oxide powder. Table 2 shows the measurement result of the magnesium oxide powder in the powder X-ray diffraction method and the measurement result of the cumulative 50% particle diameter.

(Comparative Example 2)
The calcium hydroxide slurry was added to the magnesium chloride solution having a concentration of 2.0 mol / l so that the obtained magnesium oxide concentration was 1.2 mol / l. This mixed solution was reacted at 70 ° C. for 2 hours, filtered, washed with water, and dried to obtain magnesium hydroxide.

  Furthermore, this magnesium hydroxide was baked and crushed at 1000 ° C. for 20 minutes in a rotary kiln to obtain a magnesium oxide powder.

  Table 1 shows the results of measuring the lead content and purity of these magnesium hydroxide powder and magnesium oxide powder. Table 2 shows the measurement result of the magnesium oxide powder in the powder X-ray diffraction method and the measurement result of the cumulative 50% particle diameter.

(Comparative Example 3)
Dissolve 225 g of hexahydrate magnesium chloride in 500 mL of distilled water, add a solution prepared by dissolving 80 g of sodium hydroxide in 500 mL of distilled water while stirring at 800 rpm, stop stirring after 10 minutes, leave it for 1.5 hr, and filter , Washed with water and dried to obtain magnesium hydroxide powder.

  Furthermore, it baked at 1100 degreeC for 60 minutes with the electric furnace, and obtained the magnesium oxide powder.

  Table 1 shows the results of measuring the lead content and purity of these magnesium hydroxide powder and magnesium oxide powder. Table 2 shows the measurement result of the magnesium oxide powder in the powder X-ray diffraction method and the measurement result of the cumulative 50% particle diameter.

  From Table 1, the magnesium hydroxide powder and the magnesium oxide powder produced in Example 1 had extremely low lead content as compared with those in Comparative Examples 1 to 3.

  The high-purity magnesium hydroxide powder and high-purity magnesium oxide powder of the present invention are used in various fields, such as various additives such as food additives, fuel cell raw materials, electronic component applications, phosphor raw materials, various target material raw materials, superconductivity. Thin film base material, tunnel barrier material for tunnel magnetoresistive element (TMR), protective film material for PDP, crystalline magnesium oxide layer material for PDP, toner charge adjusting agent, toner particle size adjusting agent, secondary electron multiplying electrode raw material It can be used as a raw material for ultraviolet light emitting semiconductors, a raw material for secondary batteries, a pharmaceutical raw material, a cosmetic raw material, and the like.

Claims (4)

  Magnesium oxide powder having a purity of 99.9% by mass or more and a Pb content of less than 0.1 ppm.   The magnesium oxide powder according to claim 1, wherein the Pb content is 0.01 ppm or less.   3. The half width of peaks of (111) plane, (200) plane, and (220) plane in powder X-ray diffraction using Cu—Kα rays is 0.20 degrees or less, respectively. Magnesium oxide powder. Cumulative 50% particle diameter measured by a laser diffraction scattering particle size distribution measurement _{(D 50)} is 0.1 to 10 [mu] m, magnesium oxide powder according to claim 1.