JP2673443B2 - Method for producing high-purity amorphous calcium phosphate from phosphoric acid solution containing impurities - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing highly pure amorphous calcium phosphate from a phosphoric acid solution containing impurities.

(Prior Art) Conventionally, in order to obtain a high-purity phosphoric acid compound from a phosphoric acid solution containing impurities, the impurities are removed by an ion exchange method using a cation or anion exchange resin, a precipitation removal method, a solvent extraction method, activated carbon, or the like. It had to be synthesized after being removed by an adsorption removal method or the like, which was costly and laborious. Therefore, in practice, such a method is not used, and a metal salt is directly added to a phosphoric acid solution containing impurities to obtain a phosphoric acid compound.
This is because the impurities in the solution are easily taken in as they are, the purity is low, and the applications are limited.

In addition, as a method for treating a phosphoric acid solution containing impurities, in many cases, impurities including phosphoric acid are taken into the precipitate to clean the waste liquid after the treatment (for example, Japanese Patent Publication No.
No. 33314, JP-A-53-46496, etc.), there is no such thing as making the precipitate obtained according to the present invention highly pure.

(Object of the Invention) The present invention provides a method for producing high-purity amorphous calcium phosphate by a method much easier than a phosphoric acid solution containing impurities such as SO ₄ ²⁻ , Cl ⁻ , Fe.

(Structure of the Invention) As a result of intensive studies conducted by the present inventors to obtain a high-purity phosphoric acid compound from a phosphoric acid solution containing impurities, SO ₄ ²⁻ , Cl ⁻ ,
PH of phosphate ion in phosphate solution containing impurities such as Fe
It has been found that the above-mentioned impurities-free high-purity amorphous calcium phosphate can be produced by an extremely easy method of reacting with calcium ions in 6 to 8.

That is, ammonia water is added to a phosphoric acid solution containing impurities to adjust the pH to 2 to 4, and disodium ethylenediaminetetraacetate (hereinafter abbreviated as EDTA) is added. This is because the metal ion as an impurity is made into a chelate by EDTA and the incorporation into the crystal is prevented. Next, a calcium solution was added to this solution, and this solution was added dropwise to the solution kept at pH 6 to 8, preferably pH 7, to obtain high-purity calcium alumofus phosphate. At this time, diammonium hydrogen phosphate and aqueous ammonia were used as buffer solutions to reduce fluctuations in pH. Cl ⁻ forms soluble ammonium chloride with the added ammonium ion, dissolves in the solution, and is not incorporated in the precipitate.

If the pH during the reaction is 6 or less, calcium hydrogen phosphate dihydrate is likely to be produced. SO ₄ ²⁻ is easily replaced with HPO ₄ ²⁻ of calcium hydrogen phosphate dihydrate, and is incorporated into the crystal as calcium sulfate, which does not result in high-purity quality. On the other hand, when the pH is 8 or more, amorphous calcium phosphate can be obtained, but the state of precipitation is very high in water content and the filtration property is poor, so that impurities are likely to remain and high-purity quality cannot be obtained.

The calcium solution used in the present invention is an aqueous solution of calcium chloride or a solution of calcium hydroxide and calcium carbonate dissolved in hydrochloric acid or nitric acid.

Further, if the treatment temperature is 40 ° C. or higher, anhydrous calcium hydrogen phosphate is produced, so it is necessary to perform the treatment at 40 ° C. or lower.

Example 1 9.0% phosphoric ^{_{acid, SO 4 2- 0.5%, Cl}} - 3.28%, Fe10ppm, added 0.01M-EDTA5ml solution 200ml of gravity 1.072, to which an aqueous solution of calcium chloride 28g addition, phosphate dibasic this A precipitate was obtained by dropping into a solution kept at pH 7 with ammonium and aqueous ammonia. The reaction was performed at 25 ° C. As shown in FIG. 1 (a), the precipitate had a broad X-ray diffraction pattern and was amorphous calcium phosphate. Yield 30g,
PO ₄ ^3--based yield was 90%. Table 1 shows the content of impurities in the stock solution, the content of impurities in amorphous calcium phosphate, and the removal rate of impurities. The removal rate was obtained from the change in the absolute amount of impurities.

Example 2 9.0% phosphoric ^{_{acid, SO 4 2- 0.5%, Cl}} - 3.28%, Fe10ppm, in addition to 0.01M-EDTA5ml solution 200ml of gravity 1.072, hydrochloric acid solution of calcium hydroxide 20g addition, this The solution was added dropwise to a solution of which pH was kept at 7 with diammonium hydrogen phosphate and aqueous ammonia to obtain a precipitate. The reaction was performed at 25 ° C. As shown in FIG. 1 (b), this precipitate had a broad X-ray diffraction pattern and was amorphous calcium phosphate. The yield was 28 g, and the yield based on PO ₄ ³⁻ was 85%. Table 2 shows the content of impurities in the stock solution, the content of impurities in the amorphous calcium phosphate, and the removal rate of impurities.

Cl ^- is almost 100%, SO ₄ ^2-, Fe amorphous calcium phosphate obtained are removed 87,86% became a high purity.

Comparative Example 1 9.0% phosphoric ^{_{acid, SO 4 2- 0.5%, Cl}} - 3.28%, Fe10ppm specific gravity
To 200 ml of the 1.072 solution, 5 ml of 0.01 M EDTA was added, and an aqueous solution of 28 g of calcium chloride was added to the solution, which was added dropwise to a solution of which the pH was maintained at 5 with ammonium dihydrogen phosphate and aqueous ammonia to obtain a precipitate. The reaction was performed at 25 ° C. This precipitate was calcium hydrogen phosphate dihydrate as shown in (c) of FIG. The yield was 33 g, and the yield based on PO ₄ ³⁻ was 95%. Table 3 shows the content of impurities in the stock solution, the content of impurities in the obtained precipitate, and the removal rate of impurities.

Fe was removed by 86%. However, Cl ^- removal rate of 99
%, But the content was large at 0.1%. S
Only about half of O ₄ ²⁻ was removed, and a high-purity product could not be obtained.

Comparative Example 2 9.0% phosphoric ^{_{acid, SO 4 2- 0.5%, Cl}} - 3.28%, Fe10ppm specific gravity
To 200 ml of the 1.072 solution, 5 ml of 0.01 M-EDTA was added, and an aqueous solution of 28 g of calcium chloride was added thereto, which was added dropwise to a solution of which the pH was maintained at 9 with diammonium hydrogen phosphate and aqueous ammonia to obtain a precipitate. The reaction was performed at 25 ° C.

The precipitate was amorphous calcium phosphate as shown in (d) of FIG. Yield 29 g, PO ₄ ^3- based yield 8
7%. Table 4 shows the content of impurities in the stock solution, the content of impurities in the amorphous calcium phosphate, and the removal rate of impurities.

(Effects of the Invention) As described above, according to the present invention, highly pure amorphous calcium phosphate can be synthesized by an extremely easy operation of adjusting the pH of a phosphoric acid solution containing impurities to 6 to 8, preferably pH 7. Therefore, it is possible to give a high added value to the phosphoric acid waste liquid and the like.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction diagram, which is arranged in parallel for comparison. The X-ray diffraction patterns (a) are those of Example 1 and (b) are those of the amorphous calcium phosphate obtained in Example 2. (C) is that of calcium hydrogen phosphate dihydrate obtained in Comparative Example 1, and (d) is that of amorphous calcium phosphate obtained in Comparative Example 2.

Claims (3)

(57) [Claims] 1. A phosphoric acid solution containing impurities is treated with aqueous ammonia.
After adjusting the pH to 2-4 and adding ethylenediaminetetraacetic acid disodium, a calcium solution was added, and this solution was adjusted to pH 6-
8. A method for producing high-purity amorphous calcium phosphate, characterized in that the solution is added dropwise to a solution maintained at pH 7, preferably, to carry out the reaction, and that all treatment temperatures are performed at 40 ° C. or lower. 2. The method according to claim 1, wherein an aqueous solution of calcium chloride or an acid solution of calcium carbonate or calcium hydroxide is used as the calcium solution. 3. The method according to claim 1, wherein the pH is adjusted during the reaction with a phosphate buffer or aqueous ammonia.