JP3435495B2 - First magnesium phosphate crystal and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a novel magnesium bis (dihydrogen orthophosphate) (Mg (H ₂ PO ₄ )) used for fertilizers, binders for refractories, flame retardants, raw materials for ceramics, etc.
₂ 4H 2 _O) crystals, and to a novel process for producing bis (dihydrogen orthophosphate) crystalline magnesium.

[0002]

2. Description of the Related Art Conventionally, crystals of primary magnesium phosphate, that is, magnesium bis (dihydrogen orthophosphate) cannot be produced by directly reacting a magnesium compound such as magnesium hydroxide with a phosphoric acid compound such as phosphoric acid. There wasn't. The P ₂ O ₅ concentration in the solution was raised to 49%, which is the same as the concentration in the bis (dihydrogen orthophosphate) magnesium tetrahydrate crystal, and the MgO concentration was further increased to bis (dihydrogen orthophosphate) magnesium tetrahydrate crystal. Even if it is raised to 11%, which is about 80% of the medium concentration, bis (dihydrogen orthophosphate)
The crystals did not precipitate at all, probably because of the high solubility of magnesium. In addition, the MgO concentration is further increased to increase the MgO / P
_{When the 2} O ₅ molar ratio exceeds 0.95, dibasic magnesium phosphate, that is, magnesium monohydrogen orthophosphate is precipitated.

Therefore, conventionally, for crystals of magnesium bis (dihydrogen orthophosphate), magnesium carbonate or magnesium oxide was added little by little to phosphoric acid having a specific gravity of 1.6 heated to 80 to 90 ° C., and after cooling. It was produced by a complicated method in which ethyl acetate was added, the mixture was allowed to stand for 12 to 15 hours, and the formed precipitate was filtered. The bis (dihydrogen orthophosphate) magnesium tetrahydrate crystals obtained by such a method were very fine with an average diameter of about 30 μm.

It is also well known that when a crystal is deposited, if a third substance called a habit modifier is coexistent, the growth rate of various crystal planes is different, and a crystal having a specific shape can be obtained. Has been. However, it has not been known to precipitate crystals by coexisting a third substance under the condition that crystals do not precipitate at all.

[0005]

As described above, since the bis (dihydrogen orthophosphate) magnesium crystals produced by the conventional method are very fine, if they are used as fertilizers, they will be immediately melted and washed away. In addition, when mixed with other materials having different particle sizes such as a binder for refractory, there is a problem that it becomes difficult to uniformly mix them by accumulating at the bottom.
Also, conventional bis (dihydrogen orthophosphate) as described above
The manufacturing method of magnesium crystals is a method that requires a complicated operation using an organic solvent and a long crystal formation time, so that the manufacturing cost becomes very high and it is not possible to use it for industrial production as it is. It was very difficult.

[0006]

In order to solve the above-mentioned problems, the inventors of the present invention have conducted extensive research and as a result, have developed a novel manufacturing method, and the average diameter of a crystal which has never existed until now is 1.
It was the first successful production of magnesium bis (dihydrogen orthophosphate) magnesium crystals as large as 00 μm to 200 μm. The invention according to the present application includes, as novel substances, bis (dihydrogen orthophosphate) magnesium crystals (hereinafter referred to as “first invention”) having an average crystal diameter of 100 μm to 200 μm, a phosphoric acid aqueous solution, and Mg.
O _/ P 2 _{0 5} molar ratio is not more than 0.95, and a magnesium compound 8-11 wt% in terms of magnesium oxide, 0.05 to 2.0 wt% in terms of oxide 1
It comprises a method for producing magnesium bis (dihydrogen orthophosphate) crystals (hereinafter referred to as the "second invention"), which comprises reacting in the presence of one or more alkaline earth metal compounds.

The bis (dihydrogen orthophosphate) magnesium crystal according to the first aspect of the invention can be easily produced by the method for producing bis (dihydrogen orthophosphate) magnesium crystal according to the second aspect. In this production method, the magnesium compound used may be any compound as long as it reacts with phosphoric acid.
In order to prevent unnecessary foreign substances such as acid radicals from remaining in the product, it is preferable to use magnesium hydroxide, magnesium oxide or the like. Also, the alkaline earth metal compound used is calcium, in order to react with phosphoric acid and to prevent foreign substances such as unnecessary acid radicals from remaining in the product,
It is preferable to use a hydroxide or oxide such as strontium or barium.

In the method for producing bis (dihydrogen orthophosphate) magnesium crystals according to the present invention, the concentration of the magnesium compound is set to a MgO / P ₂ O ₅ molar ratio of 0.95.
The following is to prevent the production of magnesium monohydrogen orthophosphate, and at the same time, the concentration of the magnesium compound is 8 to 11% by weight in terms of magnesium oxide. This is because if it is less than 10% by weight, crystals of magnesium bis (dihydrogen orthophosphate) do not precipitate even if an alkaline earth metal compound is added, while if it exceeds 11% by weight, the reaction becomes difficult. In addition, the concentration of the alkaline earth metal compound is 0.05
The reason why the content is made to be 2.0% by weight is that if it is less than 0.05% by weight, crystals do not precipitate even if the concentration of the magnesium compound is 11% by weight.
This is because crystals of a phosphate of an alkaline earth metal will also be precipitated if it exceeds.

[0009]

In the production method according to the present invention, it is unclear in what kind of action the large crystals of bis (dihydrogen orthophosphate) magnesium are formed, but the following actions are considered to be involved. Conceivable. That is, the phosphoric acid, there is 0.95 or less MgO _/ P 2 _{O 5} molar ratio, the addition of converted to 8-11% by weight of the magnesium compound to the magnesium oxide, bis (dihydrogen orthophosphate) Magnesium four Concentration as water salt is 57-80%
That is a high concentration. Therefore, it can be said that crystals can be generated if there is any opportunity. In such a state, the alkali metal compound acts as a habit modifier and promotes the growth of specific crystal planes, and as a result,
It is believed that magnesium bis (dihydrogen orthophosphate) crystals grow.

[0010]

【Example】

[Example 1] A 1 L glass beaker containing 85% phosphoric acid 664.4 g and ion-exchanged water 204.4 g was placed in a constant temperature bath set at 80 ° C, and 1.0 g of calcium oxide and magnesium hydroxide with stirring. 130.2 g was added portionwise over 2 hours. While the beaker was gradually cooled at room temperature, stirring was continued, and after 16 hours, filtration was performed using a Nutsche filter to obtain crystals (hereinafter referred to as “crystal I”). The yield was 62.8%.

[Example 2] 584.8 g of 85% phosphoric acid,
A 1 liter glass beaker containing 289.4 g of ion-exchanged water was placed in a constant temperature bath set at 80 ° C., while stirring, 10.0 g of calcium oxide and 115.
8 g was added portionwise over 2 hours. While the beaker was gradually cooled at room temperature, stirring was continued, and after 16 hours, filtration was performed using a Nutsche filter to obtain crystals (hereinafter referred to as “crystal II”). The yield was 27.5%.

[Example 3] 726.2 g of 85% phosphoric acid,
A 1-liter glass beaker containing 125.7 g of ion-exchanged water was placed in a constant temperature bath set at 80 ° C., and while stirring, barium hydroxide 3.4 g and magnesium hydroxide 144.7.
g was added portionwise over 2 hours. While the beaker was gradually cooled at room temperature, stirring was continued, and after 16 hours, filtration was performed using a Nutsche filter to obtain crystals (hereinafter, referred to as “crystal III”. The yield was 36.6%.

Comparative Example 1 85% phosphoric acid 649.8 g,
A 1-liter glass beaker containing 220.1 g of ion-exchanged water was placed in a thermostat set at 80 ° C., and 0.4 g of calcium oxide and 129.7 of magnesium hydroxide with stirring.
g was added portionwise over 2 hours. Stirring was continued while gradually cooling the beaker at room temperature, but no crystal precipitation was observed even after 16 hours.

[Comparative Example 2] 659.6 g of 85% phosphoric acid,
A 1 liter glass beaker containing 185.3 g of ion-exchanged water was placed in a constant temperature bath set at 80 ° C., with stirring, 22.0 g of calcium oxide and 133.
1 g was added portionwise over 2 hours. When the beaker was gradually cooled at room temperature and stirring was continued, the entire solution was crystallized. The crystals were taken out to obtain crystals (hereinafter referred to as “crystal IV”).

[Comparative Example 3] 487.4 g of 85% phosphoric acid,
A 1-liter glass beaker containing 399.1 g of ion-exchanged water was placed in a constant temperature bath set at 80 ° C., 5.0 g of calcium oxide and 108.5 of magnesium hydroxide with stirring.
g was added portionwise over 2 hours. Stirring was continued while gradually cooling the beaker at room temperature, but no crystal precipitation was observed even after 16 hours.

[Comparative Example 4] 450.0 g of 85% phosphoric acid,
A 1 liter glass beaker containing 50.0 g of ion-exchanged water was placed in a constant temperature bath set at 80 ° C., and 72.0 g of magnesium oxide was added little by little over 2 hours while stirring, and then 100.0 g of ion-exchanged water was added. Was added, and then 50.0 g of ethyl acetate was added, and stirring was continued while gradually cooling the beaker at room temperature. After one day and one night, it was filtered, washed with acetone, and air-dried to obtain crystals (hereinafter referred to as "crystal V").
The yield was 32.1%.

Table 1 shows the experimental conditions and crystal formation conditions of Examples 1 to 3 and Comparative Examples 1 to 4 described above.

[Table 1]

The X-ray diffraction patterns of the crystals 1 to V obtained in the above Examples 1 to 3, Comparative Example 2 and Comparative Example 4 are shown in FIGS.
It was the street. These X-ray diffractions are based on Cu tube and N
Using i-filter, electromotive force 35KV and tube current 15m
A was measured at 8000 cps. These X-ray diffractograms were obtained from bis (dihydrogen orthophosphate) magnesium anhydride,
Compared with X-ray diffractograms of magnesium bis (dihydrogen orthophosphate) dihydrate and magnesium polyphosphate, bis (dihydrogen orthophosphate) magnesium tetrahydrate described in Gypsum Lime Magazine No. 205, page 380. From the results of FIGS. 1 to 3 and 5, it is inferred that all of the crystals I to III and V are bis (dihydrogen orthophosphate) magnesium tetrahydrate when compared with the X-ray diffraction pattern of FIG. On the other hand, in FIG. 4, a peak specific to bis (dihydrogen orthophosphate) magnesium tetrahydrate indicated by a circle and a bis (dihydrogen orthophosphate) indicated by a ▽ mark.
Crystal IV is presumed to be a mixture of these salts, since a peak specific to calcium-hydrate is seen. Further, when comparing FIGS. 1 to 3 with FIG. 5, the peaks in FIGS. 1 to 3 are sharper, and thus the crystals I to III have better crystallinity than the crystal V. Is recognized. Furthermore, in FIGS. 1 to 3, 15.3 °, 23.3 °
°, 28.6 °, 35.1 °, 35.6 °, 36.6 °
Since the peak of is particularly high, crystals I to II
In I, it is presumed that a specific crystal plane is particularly grown.

As shown in FIG. 6, when the crystal I was observed under an electron microscope at a magnification of 200 times, large rectangular plate-like crystals having a relatively uniform grain size were observed. And, the characteristic of the shape of these crystals is not only that they are rectangular, but that slopes are formed at the ends of the short sides on both sides of the rectangle, and the side that is in contact with the long side is the side of the long side and the side of the slope. Was to form an elongated hexagon or a trapezoid. Crystals II and III were initially in the same manner. On the other hand, the crystal IV had a mixture of about 150 μm and a finer one. Further, the crystals V were continuously present from very fine particles of less than 1 μm to those of about 50 μm.

Table 2 shows the chemical composition, grain size, and crystal structure of the crystals I to V determined from the above X-ray diffraction pattern.

[Table 2]

[0021]

Since the first magnesium phosphate crystal according to the present invention has the above-mentioned constitution, it does not melt and flow away immediately even when it is used as a fertilizer or the like, and a binder for a refractory material or the like. As a result, even if it is mixed with other materials having different particle sizes, it is not accumulated in the bottom portion and becomes non-uniform. Further, the method for producing the first magnesium phosphate crystal according to the present invention is performed with an expensive organic solvent. Since it is a method that can be manufactured in a short time with simple operation without using
For the first time, it brings about excellent effects such as enabling industrial production of crystals of monobasic magnesium phosphate.

[Brief description of drawings]

FIG. 1 is an X-ray diffraction diagram of crystal I according to the present invention.

FIG. 2 is an X-ray diffraction diagram of crystal II according to the present invention.

FIG. 3 is an X-ray diffraction diagram of crystal III according to the present invention.

FIG. 4 is an X-ray diffraction diagram of crystal IV according to a comparative example of the present invention.

FIG. 5 is an X-ray diffraction diagram of crystal V according to a comparative example of the present invention.

FIG. 6 is a view showing a mode when the crystal I according to the present invention is magnified 200 times with an electron microscope.

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Claims (2)

(57) [Claims] 1. A crystal having an average diameter of 100 μm to 20.
Bis (dihydrogen orthophosphate) magnesium crystal of 0 μm 2. A phosphoric acid aqueous solution and a magnesium compound having a MgO / P ₂ O ₅ molar ratio of 0.95 or less and 8 to 11% by weight in terms of magnesium oxide are converted into oxides. A method for producing bis (dihydrogen orthophosphate) magnesium crystals, which comprises reacting in the presence of 0.05 to 2.0% by weight of one or more alkaline earth metal compounds.