Production method of low lead-magnesium oxide

Abstract

To provide a production method of low lead-magnesium oxide which can decrease a lead content.SOLUTION: A production method of low lead-magnesium oxide according to the present disclosure includes a step of firing a magnesium compound including at least one selected from the group consisting of magnesium hydroxide, magnesium oxide, and magnesium carbonate at 700°C or more under presence of a halide in low-oxygen atmosphere having an oxygen concentration of 0 to 12 vol.%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing low-lead magnesium oxide. [Background technology]

[0002] Conventionally, a known method for producing magnesium oxide is the technology described in Patent Document 1. Specifically, Patent Document 1 discloses a method for producing magnesium oxide with a reduced lead content, in which magnesium hydroxide containing lead or a lead compound is fired at a temperature in the range of 700 to 1300°C in the presence of a halogen source that is a halide or halogen gas. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-34119 Summary of the Invention [Problem to be solved by the invention]

[0004] In a method for producing magnesium oxide, it is desirable to remove the above-mentioned metals and their oxides contained as impurities to obtain magnesium oxide of higher purity. Examples of such metals include lead, which is known to be harmful to the human body as an enzyme inhibitor. For example, in magnesium oxide produced using the seawater method, slaked lime is produced from natural limestone and used as an alkali source, so the amount of impurities in the magnesium oxide is affected by the quality of the limestone. However, due to the recent depletion of high-quality limestone, there is a demand for a technology for producing low-lead magnesium oxide even when using low-quality limestone with high concentrations of impurities such as lead.

[0005] Therefore, an object of the present disclosure is to provide a method for producing low-lead magnesium oxide that can reduce the lead content. [Means for solving the problem]

[0006] The method for producing low-lead magnesium oxide according to the present disclosure includes a step of firing a magnesium compound containing at least one selected from the group consisting of magnesium hydroxide, magnesium oxide, and magnesium carbonate in the presence of a halide in a low-oxygen atmosphere having an oxygen concentration of 0 to 12% by volume at 700°C or higher. [Effects of the Invention]

[0007] According to the present disclosure, it is possible to provide a method for producing low-lead magnesium oxide that can reduce the lead content. DETAILED DESCRIPTION OF THE INVENTION

[0008] <Embodiment> The embodiments of the present disclosure will be described in detail. Note that the method for producing low-lead magnesium oxide described below is intended to embody the technical concept of the present disclosure, and unless otherwise specified, the present disclosure is not limited to the following.

[0009] <Magnesium compounds> The magnesium compound is a raw material containing at least magnesium, and is a raw material from which magnesium oxide (low-lead magnesium oxide) can be obtained by firing. The magnesium compound includes at least one selected from the group consisting of magnesium hydroxide, magnesium oxide, and magnesium carbonate. The magnesium compound may include only one selected from the group consisting of magnesium hydroxide, magnesium oxide, and magnesium carbonate, or may include magnesium hydroxide and magnesium oxide, or may include magnesium hydroxide and magnesium carbonate, or may include magnesium hydroxide, magnesium oxide, and magnesium carbonate.

[0010] The magnesium compound contains impurity components derived from its raw materials. The impurity components may include one or more of transition metals, alkali metals, alkaline earth metals, other metals, such as lead (Pb), iron (Fe), manganese (Mn), calcium (Ca), aluminum (Al), nickel (Ni), and silicon (Si), as well as ions, oxides, or other compounds containing these metals. The magnesium compound may contain lead at a predetermined content (concentration). The concentration is not particularly limited, but the mass ratio of lead to the entire magnesium compound may be 10 ppm or less, 7 ppm or less, 4 ppm or less, or 2 ppm or less.

[0011] The raw material for the magnesium compound is not particularly limited. For example, magnesium compounds can be obtained by treating seawater or an aqueous magnesium chloride solution (bittern, brine) through a predetermined process. Alternatively, magnesium-containing minerals such as brucite and magnesite can also be used as raw materials. Among magnesium compounds, for example, magnesium hydroxide can be obtained by adding an alkali such as calcium hydroxide or sodium hydroxide to seawater or an aqueous magnesium chloride solution (bittern or brine) to produce a magnesium hydroxide slurry, which is then filtered and dried.

[0012] When magnesium hydroxide is obtained from seawater or magnesium chloride aqueous solution (bittern or brine) and calcium hydroxide, the limestone that is the raw material for calcium hydroxide contains lead (lead or lead compounds) in the limestone as a whole. Therefore, when magnesium hydroxide is produced from seawater and calcium hydroxide, for example, the lead contained in the limestone may be adsorbed onto the magnesium hydroxide as lead ions or mixed into the magnesium hydroxide as lead compounds, resulting in the lead content in the magnesium hydroxide (magnesium compound) being 1.0 ppm or more or 1.5 ppm or more.

[0013] When magnesium oxide is produced by calcining magnesium hydroxide, the properties and uses of the magnesium oxide vary depending on the calcination temperature. For example, magnesium oxide obtained by calcining magnesium hydroxide at high temperatures of 1400°C or higher is called hard-burned (also called heavy-burned or dead-burned) magnesia or magnesia clinker. This magnesium oxide has excellent chemical stability and high-temperature fire resistance, and is used as a refractory material, such as a raw material for basic refractory bricks and monolithic refractories.

[0014] On the other hand, magnesium oxide (also called light-burned magnesia or calcined magnesia) obtained by calcining magnesium hydroxide at temperatures below 1400°C has greater activity than hard-burned magnesia calcined at 1400°C or higher, and is used in a variety of applications. Examples of such applications include fuel cell raw materials, electronic component applications, phosphor raw materials, various target raw materials, raw materials for superconducting thin film substrates, raw materials for tunnel barriers in tunnel magnetoresistance (TMR) devices, toner charge control agents, toner particle size control agents, raw materials for secondary electron multiplier electrodes, raw materials for ultraviolet-emitting semiconductors, raw materials for secondary batteries, additives for fertilizers and foods, raw materials for pharmaceuticals, and raw materials for cosmetics. Among these, magnesium oxide for applications in which it is ingested directly or indirectly by the human body or comes into contact with the human body (e.g., fertilizers, additives for foods, raw materials for pharmaceuticals, raw materials for cosmetics), and the like, is desired to contain fewer heavy metals, such as lead.

[0015] <Method of manufacturing low-lead magnesium oxide> The method for producing low-lead magnesium oxide according to the present disclosure includes a calcination step in which a magnesium compound containing at least one selected from the group consisting of magnesium hydroxide, magnesium oxide, and magnesium carbonate is calcined in the presence of a halide in a low-oxygen atmosphere having an oxygen concentration lower than that of the atmosphere at 700°C or higher. The method for producing magnesium oxide may include other steps in addition to the calcination step. For example, when the magnesium compound contains magnesium hydroxide, the method for producing magnesium oxide may include, prior to the calcination step, a production step of producing a magnesium hydroxide slurry from seawater from which impurities have been removed, a washing step of washing the obtained magnesium hydroxide slurry, and a drying step of dehydrating and drying the washed magnesium hydroxide slurry. Regarding magnesium oxide, magnesium oxide used as a magnesium compound is simply referred to as "magnesium oxide," and magnesium oxide obtained by a calcination step to reduce the lead content is referred to as "low-lead magnesium oxide."

[0016] The halide is not particularly limited, but may be an inorganic halide such as an alkali metal halide or an alkaline earth metal halide, or an organic halide such as ethylene bromide. The halide may be a chloride or bromide, or may be an alkali metal chloride, an alkali metal bromide, an alkaline earth metal chloride, or an alkaline earth metal bromide. Specifically, the halide contains at least one of NaCl, MgCl2, and MgBr2, which are highly safe and produce less harmful decomposition products.

[0017] The amount of halide added may be such that the ratio of halogen contained in the halide to the mass of the magnesium compound (e.g., magnesium hydroxide) converted into magnesium oxide is 0.1% by mass to 5.0% by mass (0.1% to 5.0% by mass), 0.2% by mass to 3.0% by mass, 0.3% by mass to 1.0% by mass, or 0.4% by mass to 0.7% by mass. This range facilitates the removal of impurities such as lead from the magnesium compound during the firing process, thereby improving the purity of the resulting low-lead magnesium oxide. Furthermore, deterioration of the firing furnace due to the halide can be suppressed.

[0018] The gas components other than oxygen that constitute the low-oxygen atmosphere in the firing step are not particularly limited. This low-oxygen atmosphere may contain nitrogen, carbon dioxide, or both. The oxygen concentration in the low-oxygen atmosphere may be 0% by volume or more and 12% by volume or less (0-12% by volume), 10% by volume or less, 5% by volume or less, or 2% by volume or less. The total concentration of nitrogen and carbon dioxide in the low-oxygen atmosphere may be 88% by volume or more, 90% by volume or more, 95% by volume or more, 98% by volume or more, or 100% by volume. Within these ranges, impurities such as lead are easily removed from the magnesium compound in the firing step, thereby improving the purity of the resulting magnesium oxide.

[0019] The firing temperature in the firing step may be 700°C or higher and 1400°C or lower, or 800°C or higher and 1100°C or lower. Within such a range, impurities such as lead are easily removed from the magnesium compound in the firing step, and the purity of the obtained low-lead magnesium oxide can be improved. In addition, low-lead magnesium oxide (light-burned, calcined magnesia) that has relatively high activity and can be used for a variety of applications can be produced. [Example]

[0020] Specific examples of the present disclosure are shown below, but the present disclosure is not limited to these.

[0021] <Magnesium hydroxide cake production (raw material for magnesium compounds)> 1m of seawater 3 To this, 3.0 kg of calcium hydroxide was added to produce magnesium hydroxide, which was then precipitated and concentrated to obtain a magnesium hydroxide slurry with a content of 25.8% converted to magnesium oxide. This was filtered under reduced pressure and washed with water to produce a magnesium hydroxide cake (magnesium compound) with a water content of 40%. The lead content in the obtained magnesium hydroxide cake was quantified by polarized Zeeman atomic absorption spectrometry, and the lead content was found to be 1.5 ppm by mass relative to the magnesium hydroxide solid content (2.18 ppm by mass relative to the magnesium oxide obtained after the calcination step).

[0022] Example 1 Magnesium chloride (MgCl) was added as a halide to the magnesium hydroxide cake and mixed, followed by drying for 12 hours in a dryer set at 105°C to obtain a dried product. The amount of magnesium chloride added was such that the ratio of chlorine in the magnesium chloride to magnesium oxide, calculated as the oxide of the magnesium hydroxide contained in the magnesium hydroxide cake, was 0.5% by mass. Next, 16.4 g of the dried product was placed in an alumina crucible and placed in an alumina tubular furnace. Nitrogen was flowed from one end of the tubular furnace to the other at a flow rate of 200 mL / min so that the nitrogen concentration in the atmosphere inside the tubular furnace was 100% by volume. In this state, the tubular furnace was heated to 900°C, and the dried product was fired for 1 hour to obtain the low-lead magnesium oxide (fired product) of Example 1.

[0023] <Example 2> Low-lead magnesium oxide of Example 2 was obtained in the same manner as Example 1, except that carbon dioxide was flowed from one end of the tubular furnace to the other end so that the carbon dioxide concentration in the atmosphere inside the tubular furnace was 100% by volume (the oxygen concentration in the low-oxygen atmosphere was 0% by volume).

[0024] <Comparative Example 1> Low-lead magnesium oxide of Comparative Example 1 was obtained in the same manner as in Example 1, except that the inside of the tubular furnace was filled with air (oxygen concentration: 21% by volume, nitrogen concentration: 79% by volume).

[0025] <Examples 3 and 4, and Comparative Example 2> Low-lead magnesium oxides of Examples 3, 4, and Comparative Example 2 were obtained in the same manner as in Examples 1 and 2 and Comparative Example 1, respectively, except that the tubular furnace was heated so that the temperature inside the furnace reached 1000°C.

[0026] <Examples 5 to 8 and Comparative Examples 3 and 4> Low-lead magnesium oxides of Examples 5 to 8 and Comparative Examples 3 and 4 were obtained in the same manner as in Examples 1 to 4 and Comparative Examples 1 and 2, respectively, except that magnesium bromide (MgBr2) was added as a halide to the magnesium hydroxide cake.

[0027] <Examples 9 to 12 and Comparative Examples 5 and 6> Low-lead magnesium oxides of Examples 9 to 12 and Comparative Examples 5 and 6 were obtained in the same manner as in Examples 1 to 4 and Comparative Examples 1 and 2, respectively, except that sodium chloride (NaCl) was added to the magnesium hydroxide cake as a halide.

[0028] <Evaluation of lead content> The lead content (mass ratio) of the low-lead magnesium oxide obtained in the above Examples and Comparative Examples was quantified by polarized Zeeman atomic absorption spectrometry (ZA3700 manufactured by Hitachi High-Technologies Corporation). The results are shown in Table 1.

[0029] [Table 1]

[0030] For example, the lead content in each of the Examples, which are produced in a low-oxygen atmosphere, is lower than that in each of the Comparative Examples, which are produced in an air atmosphere, just as the lead content in Examples 1 and 2 is lower than that in Comparative Example 1. In a low-oxygen atmosphere, it is possible to reduce the lead content even when the firing temperature is 1000°C or lower or 900°C or lower.

Claims

1. A method for producing low-lead magnesium oxide, comprising a step of firing a magnesium compound containing at least one selected from the group consisting of magnesium hydroxide, magnesium oxide, and magnesium carbonate in the presence of a halide in a low-oxygen atmosphere having an oxygen concentration of 0 to 12% by volume at 700°C or higher.

2. the low-oxygen atmosphere comprises nitrogen or carbon dioxide; The total concentration of the nitrogen and the carbon dioxide in the low-oxygen atmosphere is 88% by volume or more. The method for producing low-lead magnesium oxide according to claim 1.

3. The halides include NaCl, MgCl ２ , and MgBr ２ at least one of The method for producing low-lead magnesium oxide according to claim 1 or 2.

4. The ratio of the halide to the magnesium compound is 0.1% by mass to 5.0% by mass in terms of a ratio of halogen elements in the halide to magnesium oxide obtained by converting the magnesium compound into an oxide. The method for producing low-lead magnesium oxide according to claim 1 or 2.

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