JPS5811362B2 - Production method of anhydrous dicalcium phosphate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing anhydrous dicalcium phosphate suitable as a raw material for a phosphor.

The particle size, purity, and shape of a phosphate phosphor, such as a calcium halophosphate phosphor, have a close relationship with the essential performance of the phosphor, such as its brightness and workability in forming a phosphor film.

These phosphors have the general formula Ca5(PO4)3(C1・F
): Sb, Mn, and CaHPO4, CaCO3, CaF2, NH4Cl to constitute the required ratio.
, Sb2O3, MnCO3 and other powder raw materials are mixed at 110
It is manufactured by heating and firing at about 0 to 1200°C.

The main component in the production of such fluorescent materials is anhydrous dicalcium phosphate, so in order to determine the physical properties of the fluorescent material, the purity, particle size, and particle shape of the anhydrous dicalcium phosphate must be determined in order to determine the physical properties of the fluorescent material. It needs to be suitable.

Regarding the purity and physical properties of this anhydrous dicalcium phosphate, the specs required by phosphor manufacturers vary;
4. It is common that impurities such as Na, Fe, C1, Mg, and Pb are required to be as low as possible, but grain shape, grain size, Ca/
Regarding the P molar ratio, etc., it is up to each company.

Conventionally, anhydrous dicalcium phosphate, which is a raw material for phosphors, is produced by dehydrating dicalcium phosphate trihydrate, which is produced by reacting purified calcium salt with pure, therefore expensive, purified phosphoric acid. It has been.

That is, the dicalcium phosphate trihydrate produced in the reaction at around room temperature is either mixed with the mother liquor, or after the mother liquor is separated and removed, water is added to form a slurry and heated to 70-100°C, or the precipitate from which the mother liquor has been separated and removed is heated to 100°C or 100°C. It is manufactured by drying at higher temperatures.

Alternatively, it is produced by heating and dehydrating a slurry of dicalcium phosphate trihydrate produced by the reaction of diammonium phosphate and calcium chloride by holding it for a sufficient predetermined period of time. Dicalcium phosphate does not fully satisfy the required purity, crystal shape, and particle size distribution, and has many disadvantages economically.

The present inventors have already proposed a manufacturing method that eliminates the drawbacks of these known methods in Japanese Patent Application No. 50-11424 (%
No. 7198), ammonium hydrogen phosphate tetrahydrate and calcium chloride were reacted to obtain a trihydrate, and the resulting trihydrate was slurried at a slurry concentration of 5 to 20% by weight at a pH of 4.5-
5.5, and rapidly heated and dehydrated at 85-97°C to produce anhydrous dicalcium phosphate with high purity and suitable square particle size. However, this method also eliminates impurities such as Na and Fe. As a result of intensive research on these points, as a result of intensive research, we have determined that the removal of the phosphor is not complete and that it cannot satisfy the phosphor manufacturers who require a rhombus or parallelogram shape and a Ca/P molar ratio of 1.01 or less. We have developed a method for producing anhydrous dicalcium phosphate that solves this problem and allows the shape, Ca/P molar ratio, average particle size, etc. to be freely changed.

That is, the present invention provides suitable purity for the phosphate phosphor raw material,
The purpose of the present invention is to provide a method for producing anhydrous dicalcium phosphate having an average particle size and a Ca/P molar ratio in the form of a rhombus or a parallelogram. dicalcium phosphate trihydrate is produced, and the resulting dicalcium phosphate trihydrate is generally adjusted to pH after adding the dicalcium phosphate trihydrate by adding an inorganic acid.
This is achieved by a method for producing anhydrous dicalcium phosphate, which is characterized in that it is added all at once to hot water of 80° C. or higher adjusted to have a temperature of 4.4 or less, and dehydrated while stirring in a slurry form.

The above method will be explained in more detail below using a specific example.

First, in order to increase the purity, it is desirable to perform the following operation.

That is, after purifying sodium ammonium hydrogen phosphate tetrahydrate obtained from wet phosphoric acid by filtration, recrystallization, etc., it is made into an approximately 20% by weight aqueous solution (hereinafter, unless otherwise specified, % represents weight%), and phosphoric acid A soluble calcium salt solution with a Ca/P molar ratio of 0.03 or more is added to sodium ammonium hydrogen or tetrahydrate to form a calcium phosphate precipitate, and iron is removed by encroachment into the crystals or adsorption and co-precipitation.

The amount of iron dissolved in the raw material sodium ammonium hydrogen phosphate, which is about 1.5 ppm on a crystal basis as Fe, is 0 after treatment.
．． It decreases to 2 ppm or less.

Similarly, calcium chloride, a by-product in the soda ash manufacturing process, is
Add 0% water-soluble phosphate to calcium chloride at a P/Ca molar ratio of 0.005 or more to generate calcium phosphate and remove iron and sulfate roots in calcium chloride by adsorption or entrainment and coprecipitation. As a result, Fe, which was approximately 30 ppm on a crystal basis in calcium chloride, was reduced to 0.0 ppm after treatment. About 300 ppm of S existed below 1 ppm.
04 decreased to 30 ppm or less.

As a method for removing iron from calcium chloride, it is possible to add soda ash to form calcium carbonate and remove it by adsorption, but this is not preferable because the loss of calcium chloride is large.

Sodium ammonium hydrogen phosphate tetrahydrate solution and calcium chloride solution from which iron and sulfate radicals were removed and calcium chloride solution were each mixed with P2O5 of about 5% and CaCl2 of about 10%.
% and precipitate dicalcium phosphate trihydrate crystals by avoiding the reaction according to the following formula so that Ca/P=1.1 (molar ratio) at room temperature.

NaNH4HPO4+CaCl2+2H2O→CaHP
O4.2H20 + NH4Cl + NaCl After separating and removing the mother liquor from the dicalcium phosphate trihydrate crystals, water is added to the crystals to make a slurry concentration of approximately 10%, and inorganic acids such as phosphoric acid, hydrochloric acid, and nitric acid are added to phosphorus. Adjust the pH to 4.4 or less after adding acid dicalcium trihydrate.

The pH adjustment carried out here has the effect of determining the shape and Ca/P molar ratio of anhydrous dicalcium phosphate; when the pH exceeds 4.4, the anhydrous state is dehydrated through a gelation process, and the crystal shape becomes square or rectangular. , at pH 4.4 or lower, it does not undergo the gelation process and tends to be dehydrated to form a rhombus or parallelogram shape.

Furthermore, by increasing the pH to 3.4, the Ca/P molar ratio of the anhydrous salt becomes 1.01, and as the pH decreases, the Ca/P molar ratio also decreases; however, below pH 3.4, the diamond-shaped anhydrous salt becomes It forms a parallelogram at pH 3.4 to 4.4.

In this way, the Ca/P molar ratio is lowered by lowering the pH, and the anhydrous salt crystal shape can be freely adjusted.

This relationship is summarized in Table 1.

As can be seen from this table, if the slurry is dehydrated at a pH of 4.4 or lower (acid concentration of 11/2 or higher), it will not go through a gel state at all during the dehydration process, and the crystal shape will be a diamond, which is suitable as a raw material for phosphor. The Ca/P molar ratio can be adjusted to 1.025 or less.

On the other hand, it is possible to reduce the Ca/P ratio in calcium phosphate by adding EDTA or the like to elute the Ca chelate, but this is impractical as it requires a large amount of EDTA to make Ca, IP<1.01.

On the other hand, there are three possible dehydration methods for dicalcium phosphate trihydrate: (1) continuous method, (2) temperature-rising batch method, and (3)
) A one-time batch method is mentioned.

Method (1) is a method in which dicalcium phosphate trihydrate is produced and then continuously supplied to a dewatering device for dehydration; (2)
(3) is a method in which dicalcium phosphate trihydrate is first produced, separated, and the trihydrate is slurried in water to which a predetermined amount of acid has been added in a batch dehydration tank, and then heated and dehydrated. Add
This refers to a method in which dicalcium phosphate trihydrate is added all at once to hot water maintained at a dehydration temperature to form a slurry and then dehydrated.

Although particle size control differs depending on each method, the present inventors conducted research on each method.

The particle size of the phosphor raw material is preferably 10μ or more,
Furthermore, it is desirable to be able to select an appropriate particle size range depending on the situation.

First, in method (1), the stirring time and anhydration temperature in the trihydrate slurry affect the size of the particle size, and the shorter the stirring time and the lower the anhydration temperature, the larger the particle size of the anhydrous salt obtained ( 1st
Fig. 2).

The higher the acid concentration, the closer the shape becomes to a rhombus or parallelogram, but when the anhydration temperature becomes 80° C. or lower, the shape becomes a rectangle regardless of the acid concentration.

In other words, in order to obtain a diamond-shaped or parallelogram-shaped product, it is sufficient to perform anhydration at a pH of 4.4 or lower (as determined by the acid concentration study above) and a temperature of 85°C or higher during dehydration. Particle size control range is narrow, at most 11μ
However, the batch method is superior in terms of ease of particle size control.

In Figures 1 and 2, the x mark indicates that the phosphoric acid content of the trihydrate slurry is 1.4 as P2O5? /, in the case of l, the Δ mark is P2O53,5? /, In the case of l, ○ mark is P2O57S
The case of i'/A is shown here.

In method (2), the particle size varies greatly depending on the heating time (heating rate), anhydration temperature, and acid concentration, and it is necessary to maintain a constant acid concentration to produce a constant Ca/P molar ratio. Since the acid concentration cannot be changed by the value, the acid concentration is determined by that value.

For this reason, only the heating time and reaction temperature are factors that take part in particle size control, and it takes 3 to 4 minutes to raise the temperature to obtain anhydrous dicalcium phosphate of 10μ, so the heating rate is too high and the temperature rises from room temperature to 90. It is not practical due to the uneconomical and non-industrial nature of repeatedly raising the temperature rapidly to the reaction temperature around ℃ (
(See Figure 3).

In Figure 3, the circle mark indicates a temperature of 82 to 82 with a heating time of 2 to 3 minutes.
In the case of 83℃, the Δ mark is 82 to 83℃ with a heating time of 4 to 5 minutes.
In the case of , the x mark indicates a case where the temperature is 82 to 83°C with a heating time of 6 to 8 minutes, and the φ mark indicates a case where the temperature is 95°C with a heating time of 3 minutes.

Particle size can be controlled by method (3) by stirring time and anhydration temperature; the longer the stirring time or the higher the anhydration temperature, the smaller the particle size of the anhydrous dicalcium phosphate obtained. Become.

On the other hand, as mentioned above, the crystal shape changes depending on the pH; at a pH of 4.4 or above, which undergoes a gelation process, it becomes a square or rectangle, and at a pH below 4.4, which does not undergo a gelation process, it becomes a rhombus or parallelogram.

Figure 4 shows the relationship between stirring time (minutes) and average particle size (μ).
Stirring at 350 rpm, 95°C) is dehydrated through the gelation process, and water with HNO325g/l, pH 2,8 (○, stirring at 240 rpm, 83°C; stirring at 350 rpm, 83°C) is dehydrated without going through the gelation process.

FIG. 5 shows the relationship between anhydration temperature (° C.) and average particle size (μ), and it can be seen that the higher the anhydration temperature, the smaller the average particle size.

The conditions under which the experiment was conducted were a HNO3 concentration of 18.5 g/
1, pH 3, 0, 1, 5 minutes stirring at 350 rpm.

From these results, it can be said that the average particle size of anhydrous dicalcium phosphate can be freely adjusted from 10 to 50 μm by adjusting the anhydration temperature and stirring time.

As detailed above, when considering the production of diamond-shaped anhydrous dicalcium phosphate, the one-time batch method allows the anhydration temperature to be set from the beginning, making it easy to obtain the desired particle size by simply changing the stirring time. By changing the acid concentration during anhydration, the crystal shape can be freely changed. For example, it can be made into a rhombus or parallelogram shape at pH 4.4 or lower, which is extremely superior to the other two methods. It can be said that it is a method.

In the method of the present invention, an inorganic acid is added to dicalcium phosphate trihydrate obtained by reacting sodium ammonium hydrogen phosphate tetrahydrate with calcium chloride so that the pH after adding the trihydrate is 44 or less. [Dicalcium phosphate trihydrate (
The pH itself can be adjusted to a set value of 4.4 or less by adding it to hot water (pH about 3 or less) to which an acid has been added so that the pH is set according to the input amount (about 5.4) (Example Reference)] It is characterized in that it is poured into hot water of 80°C or higher at once and stirred in a slurry form (preferably 50% by weight or less from the viewpoint of workability), and then dehydrated by varying the stirring time, and the suitable average particle size is This is a method for producing anhydrous dicalcium phosphate, which has uniform thickness, thick crystals, and is strong and strong (derived from an average particle size of 10μ or more), which is required for the phosphor raw material, and the shape can be changed by adding acid. This is an industrially excellent method in which the amount can be freely selected along with the Ca/P molar ratio.

Next, the illegality will be explained in further detail by giving examples.

Example Sodium ammonium hydrogen phosphate tetrahydrate produced from wet phosphoric acid was purified by a recrystallization method, and then calcium chloride was added to it as a 20% solution at a ratio of 1 g CaCl2/100 g sodium ammonium hydrogen phosphate tetrahydrate solution. The produced dicalcium phosphate trihydrate is removed to remove iron.

1.5p in sodium ammonium hydrogen phosphate tetrasalt
Iron, which was pm, was reduced to 0.2 ppm after refining.

Similarly, calcium chloride produced in the Tsudani industry was made into a 40% solution, and sodium ammonium hydrogen phosphate tetrahydrate was added to 0% solution.
．． 5gNaNH4HPO4・4H2O/100gCaC
Iron is removed by removing dicalcium phosphate trihydrate which is added at a ratio of 12 solution.

Fe, which was present at 0.65 ppm in calcium chloride, was 0.65 ppm. l
It decreased to ppm.

Dicalcium phosphate trihydrate was produced by reacting the purified sodium ammonium hydrogen phosphate tetrahydrate with a calcium chloride solution.

That is, a calcium chloride solution was placed in a 1001 stainless steel container at a concentration of 250 g/l of CaCl, and sodium ammonium hydrogen phosphate tetrahydrate was added at a concentration of 1.5 g/l of P2O until the molar ratio Ca/P=1.10 was reached.
The reaction was carried out at 0° C. while being poured in a shower and stirring, and the reaction was completed in 70 minutes.

The generated dicalcium phosphate trihydrate was separated using a lacrimal filter, and 900 g of this trihydrate was added to 1,500 g of hot water at 95°C, pH 2.8, containing 25 g/l of HNO3 in a stainless steel container of 31. The slurry was then dehydrated using a stirrer for varying stirring times from 25 seconds to 4 minutes.

The temperature of the slurry liquid at this time was 83°C and the pH was 31.
It changed to

FIG. 4 shows plots of data obtained by varying the stirring speed.

In this method, anhydration was performed without going through a gelation process during dehydration, and the crystal shape was a diamond as shown in FIG. 6, and the Ca/P molar ratio was 1.008.

On the other hand, in the conventional method that involves a gelation process, HNO3 concentration is 0.
．． In the same manner, trihydrate was added to hot water having a pH of 4.5 at a concentration of 9 g/l, and the stirring time was varied to examine the effect on the particle size, which is shown in the x plots in Figure 4.

The shape in this case was a square or parallelogram as shown in FIG. 7, and the Ca/P molar ratio was 1.019.

Comparative Example Dicalcium phosphate trihydrate produced in the same manner as in Example 1.7
kg was put into a 301 polyethylene container filled with 151 kg of warm water and a solution of nitric acid adjusted to 325 g/l of HNO, stirred for several minutes, and charged into a temperature riser to instantaneously raise the temperature to 85°C to perform dehydration.

The obtained anhydrous dicalcium phosphate has a Ca/P molar ratio of 1.00.
8, the shape is rhombic and the average particle size is 7μ, and under the conditions of obtaining a diamond-shaped Ca/P molar ratio of 1.025 or less,
It was difficult to produce anhydrous dicalcium phosphate with a diameter of 0 μ or more (No. 8
(see figure).

[Brief explanation of the drawing]

Of the accompanying drawings, Figures 1 and 2 are graphs showing the relationship between the average particle size, stirring time, and anhydration temperature, respectively, when dicalcium phosphate trihydrate is dehydrated by a continuous method. Figure 3 is a graph showing the relationship between the average particle size and HNO3 concentration when dicalcium phosphate trihydrate is dehydrated by the heating method, and Figures 4 and 5 are FIG. 6 is a graph showing the relationship between the average particle diameter, stirring time, and dehydration temperature when dehydrating aqueous salt by a one-time batch method; FIG. A micrograph (magnification: 650 times) showing crystals of dicalcium phosphate, and FIGS. 7 and 8 are also micrographs of those obtained in a comparative example.

Claims (1)

[Claims] reacting sodium ammonium hydrogen monophosphate tetrahydrate with calcium chloride to produce dicalcium phosphate trihydrate;
An anhydrous method characterized by adding the obtained dicalcium phosphate trihydrate at once to hot water of 80°C or higher adjusted so that the pH after addition is 44 or less, and dehydrating it in the form of a slurry while stirring. Method for producing dicalcium phosphate.