JPH052611B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing high purity magnesium hydroxide. As steel manufacturing technology advances, the physical properties required for refractories are becoming increasingly strict. Historically, when looking at magnesia clinker used as steelmaking furnace material, it was first desired to develop magnesia clinker with increased purity, in other words, a high content of magnesium oxide, and then development of magnesia clinker with high bulk density, in other words, low porosity. Magnesia clinker is desired, and recently there has been a desire to develop magnesia clinker with even larger periclase crystal grains. Magnesium hydroxide that originates from seawater, bittern, or brine (hereinafter referred to as seawater-derived magnesium hydroxide) inevitably contains various impurities that exist in these sources, and therefore the amount of impurities remains unchanged in the final product. Magnesia clinker (hereinafter referred to as seawater-derived magnesia clinker)
affect the quality of the product. Such impurities are contained in magnesia clinker of seawater origin, for example as boron oxide (B ₂ O ₃ ), calcium oxide (CaO) or silicon dioxide (SiO ₂ ). After the development of magnesia clinker with a low impurity content reached a certain level, it gradually became clear that improving the purity alone could not impart the desired and sufficient properties to refractories, especially when B ₂ O ₃ as an impurity.
It has become clear that magnesia clinker greatly affects the properties of refractories, such as hot physical properties, spalling resistance, and _slag resistance, using _magnesia clinker. Various methods of providing high density magnesia clinker have been proposed in recent years. There are broadly two methods for producing magnesia clinker with a low B ₂ O ₃ content (hereinafter referred to as low boron magnesia clinker). One method is to reduce the boron content of magnesium hydroxide, which is a raw material, and the second method is to reduce the boron content of magnesium hydroxide, which is the raw material.
This method attempts to volatilize boron when magnesium hydroxide is fired. The former method involves, for example, adding Mg(OH) ₂ to seawater and removing boron compounds in the seawater by adsorbing them to Mg(OH) ₂ (see Japanese Patent Publication No. 45-53);
Add Zr(OH) ₄ to remove boron compounds in seawater from Zr
(OH) ₄ is similarly adsorbed and removed (see Japanese Patent Publication No. 51-5839). Tokuko Showa 51-5839
According to the description in the issue, Zr(OH) ₄ seems to have a higher boron adsorption ability than Mg(OH) ₂ , but Zr(OH)
Even when using ₄ , e.g. boron content
It is stated that in order to obtain seawater with a boron content as low as 3ppm (as B ₂ O ₃ ), it is necessary to use approximately 300 times the amount of boron present in raw seawater. In particular, in the method of using Zr(OH) ₄ as an adsorbent, magnesium hydroxide containing Zr(OH) ₄ is given because Zr(OH) ₄ remains in seawater, albeit in a small amount. There is also a method in which when seawater and lime are reacted, an excess of lime is used to raise the pH to 11 or higher to prevent boron from being adsorbed by the resulting magnesium hydroxide. This method, however, reduces _B2O3 to 0.10% by weight on a scorching basis _.
Just as CaO increases to 2.49% by weight and B ₂ O ₃ decreases to 0.04% by weight, CaO increases to 5.06% by weight, reducing boron only produces magnesium hydroxide with an increased amount of calcium hydroxide. (See Table 1 of Japanese Patent Publication No. 57-31547). For this reason, in the invention of Japanese Patent Publication No. 57-31547, purified magnesium hydroxide is light-fired at 700 to 1100°C as described above, and the resulting light-fired product is poured into a large amount of seawater to be rehydrated. Purified magnesium hydroxide with low calcium oxide content is produced, and this purified magnesium hydroxide is calcined to produce 99.6% by weight of MgO, 0.10% by weight of CaO and _0.011 % by weight of _B2O3 as the lowest content of _{B2O3 .} A high-purity, high-density magnesia clinker having a chemical composition of 3.47 g/cm ³ and a high density of 3.47 g/cm 3 was obtained. The method disclosed in Japanese Patent Publication No. 57-31547 not only uses an excessive amount of lime but also requires a refining step, resulting in large energy losses, so it cannot necessarily be said to be an industrially advantageous method. The second method of firing, especially to volatilize boron, is
This is a method in which a sodium salt such as sodium carbonate is added to magnesium hydroxide, and boron is volatilized as Na ₂ B ₄ O ₇ during firing (U.S. Patent No.
3275461). This method tends to increase the porosity of the resulting magnesia clinker. Yamamoto et al. also found that if the calcium hydroxide impurity content in magnesium hydroxide is reduced, boron will easily volatilize as B ₂ O ₃ when it is fired, resulting in high-purity, high-density magnesia with a low B ₂ O ₃ content. It was revealed that clinker could be obtained, and the magnesium hydroxide obtained by adding lime to decarbonated seawater was separated and lightly calcined, and then put into seawater or water again to rehydrate it, and the impurities were removed from the magnesium hydroxide. Calcium hydroxide is removed to produce magnesium hydroxide with low calcium hydroxide content, and this is calcined to produce the lowest B ₂ O ₃ content: MgO 99.63%, CaO 0.24%, SiO ₂ 0.14%,
_{Fe2O3 0.04} %, _{Al2O3 0.05} % and _{B2O3 0.008} %
A high-purity, high-density magnesia clinker having a composition of 3.42 g/cm 3 and a bulk density of 3.42 g/cm ³ was obtained (see Refractories Vol. 25, p. 548, 1973, especially Table 8). According to this document, the above-mentioned high-purity high-density magnesia clinker is obtained by firing magnesium hydroxide having a B ₂ O ₃ content of 0.139% by weight on a scorching heat basis. On the other hand, demand for magnesia carbon bricks has recently increased rapidly. Magnesia carbon brick is an unfired brick made by pressure-molding a mixture of magnesia clinker and graphite.It has much better spalling resistance and slag resistance than magnesia brick, which has been used in large quantities in the past. have. The reason for this is thought to be that graphite acts as a cushioning material for magnesia clinker and has poor wettability with slag. It is therefore believed that the mechanism of wear of magnesia carbon bricks is not that the graphite part is eroded by slag, but that the magnesia clinker part is gradually eroded by slag. Recently, a magnesia clinker with large periclase crystal grains has been required as a suitable magnesia clinker for use in magnesia carbon bricks, and in fact, magnesia carbon bricks using such magnesia clinker with large periclase crystal grains have become even more superior. It has also been demonstrated that it has spalling resistance. However, the above-mentioned refractories Vol. 25, p. 547, 1973
As shown in Figure 16 of 2012, there have been no reports of magnesia clinker derived from seawater with a periclase crystal grain size exceeding 50 microns. Therefore, an object of the present invention is to provide a method for producing high-purity magnesium hydroxide, which has an extremely low content of calcium and boron, and is suitable for providing magnesia clinker with high purity, high bulk density, and coarse grains. Further objects and advantages of the present invention will become apparent from the description below. According to the present invention, the above objects and advantages of the present invention are, expressed in weight percent, on a scorching basis: MgO not more than 99.3% CaO not more than 0.3% SiO ₂ not more than 0.2% B ₂ O ₃ not more than 0.03 Fe ₂ O ₃ and Al ₂ Total amount of O ₃ 0.15% or less MgO, CaO, SiO ₂ , B ₂ O ₃ , Fe ₂ O ₃ and Al ₂
High-purity water with the following composition, where the total amount of O ₃ is 100% by weight, and is produced by the reaction of seawater, bittern or bittern water with dolomite or lime or their hydrates. A method for producing magnesium oxide is provided. The above-mentioned high-purity magnesium hydroxide can be produced according to the method of the present invention described below. The method of the present invention will be explained below. That is, according to the present invention, the high-purity magnesium hydroxide of the present invention can be obtained by treating a decarboxylated liquid of seawater, bittern, or can water with an acid addition type ion exchange resin capable of capturing boron-containing anions. Depending on the ion exchange resin treatment, decarboxylation or removal of insoluble carbonates is performed before or after the ion exchange resin treatment, and this is reacted with calcined dolomite or lime or their hydrates to obtain a
Expressed as, based on scorching heat, MgO 99.3% or more CaO 0.3% or less SiO ₂ 0.2% or less B ₂ O ₃ 0.05% or less (preferably 0.03% or less) Total amount of Fe ₂ O ₃ and Al ₂ O ₃ 0.15% or less However, it is manufactured by producing high purity magnesium hydroxide having the following composition, where the total amount of MgO, CaO, SiO ₂ , B ₂ O ₃ , Fe ₂ O ₃ and Al ₂ O ₃ is 100%. be able to. The magnesium-containing aqueous solution used in the method of the present invention is a decarboxylated solution of seawater, bittern or brine. The decarboxylated solution can be obtained by adding an alkaline compound such as calcium hydroxide or a strong acid such as sulfuric acid to seawater, bittern or brine according to a known method. The ion exchange resin used in the method of the invention is one that is capable of trapping boron-containing anions. As such an ion exchange resin, one having, for example, a polyhydric alcohol residue as a pendant group as a trapping group for boron-containing anions is preferably used. For example, as a pendant group, the following formula _-CnH2n -N(R)-Z where n is an integer of 1 to 4, R is a monovalent hydrocarbon group, and Z is a pentahydroxyhexyl group or An example is an ion exchange resin containing a group represented by a tetrahydroxypentyl group. In the above formula, R is a monovalent hydrocarbon group such as methyl, ethyl, propyl, butyl, hexyl, octyl, lauryl, cyclohexyl, phenyl, benzyl. The pentahydroxyhexyl group representing Z has the formula -
It can be represented by C ₆ H ₈ (OH) ₅ , such as sorbityl, mannityl, galactityl, etc. The tetrahydroxypentyl group has the formula -C ₅ H ₆ (OH) ₄
For example, arabicyl, ribicyl, etc. As such an ion exchange resin, for example, the following formula Those having an N-methylglucamine group represented by the following are preferably used. The above-mentioned ion exchange resin used in the present invention is disclosed, for example, in US Pat. No. 2,813,838. This US patent is incorporated herein by reference. Previously, it has been suggested that boron may be removed from seawater or concentrated bittern using such boron-selective ion exchange resins [Interceram, NR, 3, 1973, p.
212-218], there are no known examples of producing high-purity magnesium hydroxide for producing magnesia clinker from seawater treated with such ion-exchange resins, and therefore it is difficult to use such ion-exchange resins. In particular, it is not known at all what boron content magnesium hydroxide can be obtained. According to the method of the present invention, a magnesium-containing aqueous solution (preferably pH 8 to 10) such as seawater is preferably treated by passing it through a column filled with the above-mentioned ion exchange resin. The processing rate of the magnesium-containing aqueous solution is suitably about 0.1 to 0.6 m ³ per minute per 1 m ³ of ion exchange resin. Ion exchange resins are usually commercially available as acid addition salts, and it is generally recommended that they be converted into free form with an alkali such as caustic soda or ammonia before use. However, according to the present invention, ion exchange resins are commercially available as acid addition salts. For example, it has been shown that it can be used in its hydrochloride or sulfate form, and that it is preferable to use it in its free form in order to obtain magnesium hydroxide with an extremely low CaO content. Ion exchange resins can be regenerated by treatment with strong acids such as sulfuric or hydrochloric acid; therefore, according to the present invention, used ion exchange resins saturated with boron-containing anions, such as borate anions, are treated with strong acids. It has the advantage that after being regenerated, it can be reused as is for treating magnesium-containing aqueous solutions such as seawater without treatment with alkali. According to the invention, the magnesium-containing aqueous solution comprises:
Decarboxylation and removal of insoluble carbonates before treatment with ion exchange resin. Decarboxylation can be carried out by adding a strong acid such as sulfuric acid or hydrochloric acid to the magnesium-containing aqueous solution while blowing air, and removal of insoluble carbonates can be carried out by filtration, for example sand filtration. According to the present invention, preferably by filtering the decarboxylated liquid of seawater, bittern or camphor water to remove carbonate ions or insoluble carbonates from the decarboxylated liquid, and then subjecting it to ion exchange resin treatment, B. Not only ₂ O ₃ but also magnesium hydroxide with low CaO content can be obtained. Treated water treated with ion _exchange resins contains _boron at very low concentrations, e.g.
A decarboxylation treatment solution containing 13 ppm of boron can be treated with an ion exchange resin to produce a treatment solution containing 1 ppm or less in terms of B ₂ O ₃ . According to the invention, this treated water is then reacted with dolomite calcined material or lime or their hydrates according to methods known per se, and has the following composition, expressed in weight percent, on a burning basis: not less than 99.3% MgO CaO 0.3% or less SiO ₂ 0.2% or less B ₂ O ₃ 0.05% or less (preferably 0.03% or less) High purity magnesium hydroxide of the present invention having a total amount of Fe ₂ O ₃ and Al ₂ O ₃ of 0.15% or less is produced. do. This high-purity magnesium hydroxide is especially compatible with CaO.
It is characterized by containing B ₂ O ₃ at a very low level, and provides magnesia clinker having high density and coarse crystal grains, as will be detailed later. As magnesium hydroxide derived from seawater, high-purity magnesium hydroxide containing extremely few impurities as described above has not been known so far. According to the method of the present invention, the high-purity magnesium hydroxide of the present invention having the above composition containing very low levels of CaO and B ₂ O ₃ is pressed and then fired to produce high-density, coarse-grained magnesia. Clinker can be produced. Pressure molding is usually 2 to 3 tons/
Preferably, the molding is carried out under a pressure of 1 cm ² to give a compact having a density of about 1.5 to 1.7 g/cm ³ . Further, the firing is usually carried out at a temperature of 1900 to 2100°C for about 15 minutes to 1 hour. Thus, expressed as oxides, MgO 99.3% or more CaO 0.3% or less SiO ₂ 0.2% or less B ₂ O ₃ Less than 0.01% Total amount of Fe ₂ O ₃ and Al ₂ O ₃ 0.15% or less However, MgO, CaO , the total amount of SiO ₂ , B ₂ O ₃ , Fe ₂ O ₃ and Al ₂ O ₃ is 100% by weight, and has a bulk density of 3.40 g/cm ³ or more, as defined later. The average particle size of magnesia periclase crystals is 60 microns or more, as measured by the method
A high density coarse grained magnesia clinker, preferably 80 microns or greater, is provided. One of the excellent features of the above method of the present invention is that seawater,
Treatment of bittern or bittern water decarboxylation with an acid-added ion exchange resin capable of capturing boron-containing anions produces highly pure magnesium hydroxide containing only very low levels of CaO and B ₂ O ₃ There is a point in doing it. Another feature of the present invention is that by firing such high-purity magnesium hydroxide, not only the bulk density is 3.40 g/cm ³ or more as described above, but also the average particle size of periclase crystals is extremely large, 60 microns or more. It also has the ability to produce magnesia clinker. Based on scorching heat standards, CaO is less than 0.3% by weight and B ₂ O ₃
By firing high-purity magnesium hydroxide, which has an extremely low content of CaO and _{B2O3 of} 0.05% by weight, a magnesium clinker having coarse crystal grains as described above can be produced. It is a fact revealed for the first time by the present inventor that this can be obtained. The above-mentioned high purity coarse grained magnesia clinker preferably has a diameter of 70 microns or more, more preferably
It has periclase crystals of magnesia with an average grain size of 80 microns or more, particularly preferably 90 microns or more. The above-mentioned high purity coarse grained magnesia clinker is preferably 3.42 g/cm ³ or more, more preferably
It has a bulk density of 3.43 g/cm ³ or more. Further, the above-mentioned high purity coarse grained magnesia clinker preferably contains, expressed in weight percent, as an oxide, MgO 99.4% or more CaO 0.25% or less SiO ₂ 0.2% or less B ₂ O ₃ less than 0.01% Fe ₂ O ₃ The composition has a total amount of Al ₂ O ₃ of 0.15% or less. EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited in any way by the Examples. In addition, various physical property values in this specification were measured by the following methods. Chemical composition “Gakushin Method 1 Chemical analysis method of magnesia clinker” determined by the Test Methods Subcommittee of the 124th Committee of the Japan Society for the Promotion of Science (see 1981 edition refractory notebook)
Measured according to. In particular, the analysis of B ₂ O ₃ was carried out using curcumin (absorption photometry), which was adopted as the Gakushin method under consideration by the same committee. Bulk Density (Bulk Specific Gravity) “JSPS Method 2 Measuring Method of Apparent Porosity, Apparent Specific Gravity and Bulk Specific Gravity of Magnesia Clinker” (1981 Edition Refractory Notebook) determined by the Test Methods Subcommittee of the 124th Committee of the Japan Society for the Promotion of Science (Reference), it was calculated using the following calculation method. Bulk specific gravity = W ₁ / W ₃ − W ₂ ×S W ₁ : Dry weight of clinker (g) W ₂ : Weight of sample saturated with white kerosene in white kerosene (g) W ₃ : Sample saturated with white kerosene Weight (g) S: Specific gravity of white kerosene at measurement temperature (g/cm ³ ) Average particle size of periclase crystals Considering the particle size distribution of clinker, pieces of about 5 to 10 mm are taken out at random. This is cut and polished and the polished surface is observed using a reflection microscope. Photographs were taken at 20x magnification of three areas considered to be representative.
Enlarge these three times and print them on photographic paper. Among the periclase particles in the three photographs, select 50 of the largest particles, measure the maximum particle size, and use the average value as the average particle size of the periclase crystals. Example 1 Carbonate ions dissolved in seawater (CO ₂ equivalent value: 80 ppm) were reduced to CO ₂ equivalent value: 10 ppm by adding milk of lime, and then filtered using a sand filter. This decarboxylation treatment solution contained approximately 12 ppm of boron as H ₃ BO ₃ . Furthermore, this solution was passed through an adsorption tower packed with 100 ion exchange resins (N-methylglucamine group-containing, sulfate type) capable of capturing boron-containing anions at a rate of 40/min to remove H ₃ BO ₃ . adsorbed to the resin,
A low boron content seawater with a H ₃ BO ₃ content of 0.70 ppm was produced. This seawater and milk of lime were reacted at a reaction rate of 92%, and the resulting magnesium hydroxide precipitate was filtered and washed with decarboxylated tap water to produce high purity magnesium hydroxide as shown in Table 1. . The numbers shown in Table 1 represent weight %, and Ig
Loss represents the amount lost during scorching heat.

[Table] Reference Example 1 The magnesium hydroxide produced in Example 1 was dried in a dryer to a water content of 8% by weight. Furthermore, after pressure molding at a molding pressure of 3t/ ^cm3 , oxygen and
It was fired at a high temperature of 2000℃ in a propane gas furnace. The chemical composition, bulk density, and average particle size of periclase crystals of this magnesia clinker are shown in Table 2. Furthermore, a photograph showing the periclase crystal is shown in FIG.

[Table] Example 2 The method of Example 1 was repeated except that the passing rate of the decarboxylated liquid through the adsorption tower was changed to 30/min.
A low boron seawater with a H ₃ BO ₃ content of 0.45 ppm was produced. This seawater and milk of lime are reacted at a reaction rate of 92%, and the resulting magnesium hydroxide precipitate is filtered and washed with decarbonated water to produce high-purity magnesium hydroxide as shown in Table 3. generated.

[Table] Reference Example 2 The chemical composition, bulk density, and average particle size of periclase crystals of magnesia clinker obtained by sintering the magnesium hydroxide produced in Example 2 in exactly the same manner as described in Reference Example 1 are shown below. It is shown in Table-4. Furthermore, a photograph of the periclase crystal is shown in Fig. 2.

[Table] Comparative Example 1 Boron in the seawater was removed by adding 2.7 kg of magnesium hydroxide cake (in terms of dry matter) to seawater 100 which had been decarboxylated by the same method as described in Example 1 and thoroughly stirring and mixing. Let it adsorb,
_The content was reduced to _5.75ppmH3BO3 . This seawater and milk of lime are reacted at a reaction rate of 92%, and the produced magnesium hydroxide is washed with decarboxylated tap water.
Purified magnesium hydroxide as shown in Table 5 was produced.

[Table] This purified magnesium hydroxide was sintered in the same manner as described in Reference Example 1. The chemical composition, bulk density and periclase grain size of the obtained clinker are shown in Table 6. Furthermore, a photograph of the periclase crystal is shown in Fig. 3.

【table】 [Brief explanation of drawings]

Figures 1 and 2 of the accompanying drawings are micrographs (magnification approximately 150 times) showing the structure of periclase crystals of magnesia clinker obtained from high-purity magnesium hydroxide according to the production method of the present invention. FIG. 3 is a micrograph (approximately 150x magnification) showing the structure of periclase crystals of a comparative magnesia clinker obtained from comparative magnesium hydroxide. 1st
In the figure, the minimum graduation of the scale shown in the photograph represents 10μ.

Claims (1)

[Claims] 1. (1) Decarboxylation treatment of seawater, bittern or can water, (2) removal of insoluble carbonates from the treated liquid, and (3) acid addition capable of capturing boron-containing anions. (4) React the obtained treatment liquid with burnt dolomite or lime or their hydrates to obtain MgO of 99.3% or more on a sintering basis expressed in weight percent. CaO 0.3% or less SiO ₂ 0.2% or less B ₂ O ₃ 0.05% or less Total amount of Fe ₂ O ₃ and Al ₂ O ₃
A method for producing high purity magnesium hydroxide having a composition of 0.15% or less. 2 Expressed in weight%, on a scorching heat basis, has a composition of MgO 99.3% or more CaO 0.3% or less SiO ₂ 0.2% or less B ₂ O ₃ 0.03% or less Total amount of Fe ₂ O ₃ and Al ₂ O ₃ 0.15% or less A method according to claim 1, characterized in that high purity magnesium hydroxide is produced. 3. The method according to claim 1 or 2, wherein the removal of the insoluble carbonate in step (2) is carried out by filtration. 4. The ion exchange resin has a polyhydric alcohol residue as a pendant group as a boron-containing anion trapping group.
The method described in any one of paragraphs. 5 The ion exchange resin has the following formula as a boron-containing anion trapping group: Any one of claims 1 to 3 containing an N-methylglucamine group represented by
The method described in section.