JP2787974B2 - Method for producing hydrocalumite - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing hydrocalumite, and more particularly to CaO-A.
The present invention relates to a method for industrially advantageously producing hydrocalumite by reacting an l ₂ O ₃ -based compound with a soluble calcium salt and / or slaked lime in a liquid as a starting material and then crystallizing the same. .

[0002]

2. Description of the Related Art Conventionally, hydrocalumite has a general formula

Embedded image 3CaO · Al ₂ O ₃ · CaX _{2 / m} · nH ₂ O (where X is a monovalent or divalent anion, m represents the valency of the anion, and n represents 20 or less. ), Which is a layered crystal compound in the form of a divalent / trivalent metal composite hydroxide, and is known to have anion-exchange properties. Hydrotalcite, which is an Mg-Al-based composite hydroxide, belongs to the same category as such a compound, and is typically used as a resin additive, for example.

[0003] Hydrocalumite has been proposed as a chloride ion scavenger effective for suppressing corrosion of reinforcing bars due to salt damage in concrete structures, for example (Japanese Patent Laid-Open No. 4-154648). As a manufacturing method, for example, X in the general formula NO ₂ ^- For a is nitrite type hydrocalumite, by adding calcium nitrite solution to a solution of sodium aluminate to precipitate a gel, is crystallized Methods are known.

[0004]

In the above, in particular,
Nitrite-type hydrocalumite is expected as a concrete additive because of its excellent chlorine ion trapping ability and metal rust prevention ability. However, sodium aluminate,
When a soluble calcium salt such as calcium nitrite is used, the reaction proceeds relatively smoothly, but the production cost becomes relatively expensive, and the anion exchange capacity of the obtained hydrocalumite is not sufficient. For example, when it is used as a chlorine ion trapping agent for concrete structures, it may not be preferable.

Accordingly, an object of the present invention is to provide a method for producing hydrocalumite which is inexpensive and has high anion exchange capacity.

[0006]

The present inventors have SUMMARY OF THE INVENTION In view of the ordination problems, were intensively studied, using the CaO-Al ₂ O ₃ based compound in place of the sodium aluminate as the starting material, soluble The present inventors have found a method for producing hydrocalumite which is less expensive and has a higher anion exchange capacity by reacting a calcium salt and / or slaked lime and then crystallization.

That is, the method for producing hydrocalumite provided by the present invention is a method for preparing a CaO—Al ₂ O ₃ compound, a soluble calcium salt and / or slaked lime in a liquid.
The reaction is carried out in a temperature range of 60 ° C. or less,
Crystallized in the temperature range

Embedded image 3CaO · Al ₂ O ₃ · CaX _{2 / m} · nH ₂ O (wherein X is a monovalent or divalent anion, m represents the valency of the anion, and n represents 20 or less. ) Is characterized by producing hydrocalumite represented by the formula (1).

Hereinafter, the present invention will be described. The raw material used in the present invention may be any material as long as it can be obtained industrially. Examples of the CaO—Al ₂ O ₃ -based compound include CaO · Al ₂ O ₃ and 5CaO as chemical formulas.
_{· 3Al 2 O 3, 2CaO ·} Al 2 O 3, 3CaO · 5Al
Fine powders having a mineral composition such as ₂ O ₃ , 12CaO · 7Al ₂ O ₃ , and 3CaO · Al ₂ O ₃ are mentioned. In the present invention, in particular, CaO.Al ₂ O ₃ , 5CaO.3Al
Alumina cement composed of a mineral composition such as ₂ O ₃ , 2CaO.Al ₂ O ₃ is preferable.

As soluble calcium salts, inorganic salts such as chlorides, nitrates and nitrites are economically advantageous, but organic acid salts can be used if necessary.
Further, the concentration is not limited.

[0010] The production method according to the present invention is characterized in that the above CaO-A
One of the features is that the l ₂ O ₃ compound is reacted with a soluble calcium salt and / or slaked lime in a liquid.

In the above reaction, if necessary, the reaction may be carried out in the presence of an alkali metal salt. Examples of the alkali metal salt include sodium chloride, sodium nitrite, sodium nitrate and the like, and the concentration thereof is not particularly limited.

The mixing operation of the raw materials in this reaction is carried out by C
aO-Al ₂ O ₃ -based compound, soluble calcium salt and / or
Alternatively, slaked lime only needs to be present in the liquid, and the method of adding it is not particularly limited.

However, in this reaction, CaO / Al ₂
The molar ratio of O ₃ is preferably set in the range of 3.3 to 4.2. The reason is that when this molar ratio is, for example, less than 3.3, not only the yield of the target product becomes extremely low, but also the ratio of amorphous becomes large even after ripening in crystallization. , Lower the crystallinity. In addition, the molar ratio is 4.2
Is exceeded, hydrocalumite is not generated and Ca (O
H) ₂ or 3CaO.Al ₂ O ₃ (hereinafter, referred to as “C ₃ A”).

The slurry concentration of the reaction system is industrially appropriate in the range of 5 to 30% by weight. For example, when the slurry concentration exceeds 30% by weight, the viscosity of the reaction system becomes high and stirring becomes difficult. If it is less than 5% by weight, the productivity is poor.
Therefore, the concentration may be set within the above range for economic reasons.

In the present invention, when a soluble calcium salt and slaked lime are used, their ratio cannot be limited by the production conditions and the type of anion.
aO / Ins-CaO (s-CaO is the amount of soluble calcium salt converted to CaO, Ins-CaO is lime
(Representing the amount in terms of O) in the range of 0 to 3, preferably 0.1 to 2.

The reaction temperature may be 60 ° C. or lower, preferably 30 ° C. or lower. The reaction time is not particularly limited as long as it is 0.5 hours or more. By this reaction, a gel-like precipitate is formed, and it is preferable to carry out the reaction under the above conditions, including homogenization of the system and aging of the product.

Next, after the completion of the reaction, crystallization is performed so as to generate crystal particles of hydrocalumite. At this time, the crystallization temperature is at most 70 ° C, preferably 40 to 65 ° C.
It is important to set in the range. The crystallization temperature,
When the reaction is carried out at a temperature higher than 70 ° C., hydrocalumite is generated, but the anion exchange capacity is low. In addition, Ca (OH) ₂ and C ₃ A are not preferred because side reactions tend to occur.

Further, in the production method of the present invention, the crystallization reaction may be carried out under normal pressure, but may be carried out by crystallization under reduced pressure for crystallization while partially removing water under reduced pressure. This is because in this method, the concentration of the reaction system is concentrated, and the amount of anions incorporated in the hydrocalumite is increased, which tends to significantly increase the anion exchange capacity. The crystallization time may be 2 hours or more.

After completion of the crystallization, the precipitate is filtered, washed and dried by a conventional method. After drying, pulverization and classification can be performed if necessary.

The white crystals obtained by the production method of the present invention have the general formula

Embedded image 3CaO · Al ₂ O ₃ · CaX _{2 / m} · nH ₂ O (where X is a monovalent or divalent anion, m represents the valency of the anion, and n represents 20 or less) ), Whose crystals are fine powder having a layered structure and have high anion exchange capacity.

Accordingly, the hydrocalumite according to the present invention is expected to be used as a rust preventive pigment for concrete and as a resin additive, especially for nitrite type hydrocalumite.

[0022]

EXAMPLES The present invention will be described below more specifically with reference to Examples. Example 1: Production of nitrite-type hydrocalumite Al ₂ O ₃ : 54.89% by weight, CaO: 34.59% by weight
, Calcium nitrite monohydrate 4.04 kg, slaked lime 3.69 kg, water 40 kg
Was added and the reaction was carried out at 25 ° C. for 24 hours. As a result, a gel-like precipitate was formed. Next, the slurry was heated to 60 ° C. and crystallized while continuing stirring at normal pressure for 4 hours. The obtained precipitate was filtered and washed by a conventional method, and then dried to obtain 17 kg of a white solid. The obtained white solid was pulverized to obtain a white powder of 150 mesh or less.
The white powder was analyzed by X-ray diffraction, chemical analysis, infrared absorption spectrum, and electron micrograph. As a result, layered nitrite-type hydrocalumite containing a small amount of Ca (OH) ₂ and C ₃ A.6H ₂ O as impurities was used. Confirmed that there is.

Example 2 Production of Nitrite-Type Hydrocalumite After completion of the reaction, about 5% by weight of water was removed by distillation under reduced pressure, and crystallization was performed under reduced pressure. As a result of the same operation as in Example 1, 18 kg of a white solid was obtained. The obtained white solid was pulverized to obtain a white powder of 150 mesh or less. As a result of analyzing the white powder in the same manner as in Example 1,
It was confirmed that a layered nitrite type hydrocalumite containing a small amount of Ca (OH) ₂ and C ₃ A · 6H ₂ O as impurities.

Example 3: Production of nitrite-type hydrocalumite Al ₂ O ₃ : 54.89% by weight, CaO: 34.59% by weight
Was added to 5 kg of alumina cement containing sodium nitrite, 3.71 kg of sodium nitrite, 5.68 kg of slaked lime, and 40 kg of water, and reacted at 25 ° C. for 24 hours. A solid was obtained. The obtained white solid was pulverized to obtain a white powder of 150 mesh or less. As a result of analyzing the white powder in the same manner as in Example 1, it was confirmed that the white powder was a layered nitrite-type hydrocalmite containing a small amount of Ca (OH) ₂ and C ₃ A.6H ₂ O as impurities.

Example 4: Production of nitrite-type hydrocalumite 5 kg of the alumina cement used in Example 1, 11.51 kg of calcium nitrite monohydrate and 40 kg of water were added and reacted at 25 ° C for 24 hours. The same operation as in Example 1 was performed to obtain 17.2 kg of a white solid. The obtained white solid was pulverized to obtain a white powder of 150 mesh or less. As a result of analyzing the white powder in the same manner as in Example 1, it was confirmed that the powder was layered nitrite-type hydrocalumite.

Example 5: Production of nitrite-type hydrocalumite 5 kg of the alumina cement used in Example 1, 5.68 kg of slaked lime, 3.71 kg of sodium nitrite and 40 kg of water were added and reacted at 25 ° C. for 24 hours. Then, the same operation as in Example 1 was performed to obtain 17.2 kg of a white solid. The obtained white solid was pulverized to obtain a white powder of 150 mesh or less. As a result of analyzing the white powder in the same manner as in Example 1,
It was confirmed that a layered nitrite type hydrocalumite containing a small amount of Ca (OH) ₂ and C ₃ A · 6H ₂ O as impurities.

Example 6: Production of nitric acid type hydrocalumite In place of the sodium nitrite of Example 5, sodium nitrate 4.57
The same procedure as in Example 5 was carried out except that kg was used.
7.2 kg of a white solid were obtained. The obtained white solid was pulverized to obtain a white powder of 150 mesh or less. As a result of analyzing the white powder in the same manner as in Example 1, a small amount of C was found as an impurity.
It was confirmed that it was a layered nitric acid type hydrocalumite containing a (OH) ₂ and C ₃ A.6H ₂ O.

Comparative Example 1 A white powder was recovered in the same manner as in Example 1 except that the reaction temperature was 65 ° C. and the crystallization was performed at 75 ° C. When the white powder was analyzed in the same manner as in Example 1, no nitrite-type hydrocalumite was formed, and it was found that the mixture was a mixture of Ca (OH) ₂ and C ₃ A.6H ₂ O.

Measurement of anion exchange capacity The anion exchange capacity of the hydrocalumite obtained in Examples 1 to 5 was measured by the following method, and the results shown in Table 1 were obtained. Measurement method 10 g of the hydrocalumite sample powder obtained in the example was added to 100 ml of 0.1 N NaCl solution, and the mixture was stirred for 4 hours. Then, the amount of anions released into the solution was measured. For example, in the case of nitrite-type hydrocalumite, the amount (mg) of released nitrite is calculated as (mg-eq / g) and expressed as anion exchange capacity.

[0030]

Table 1 Example 1 Anion exchange capacity (mg-eq / g) 1 1.555 1.70 3 1.35 4 2.75 5 1.30 6 1.27

[0031]

As described above, the production method according to the present invention comprises:
The method is characterized by reacting a CaO-Al ₂ O ₃ -based compound with a soluble calcium salt and / or slaked lime in a liquid and then crystallizing it. Hydrocalumite having high ion exchange ability can be obtained.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hidenobu Tatematsu 2-8-8 Hikaricho, Kokubunji-shi, Tokyo 38 Within the Railway Technical Research Institute (72) Inventor Jun Takada 2--8 Hikaricho, Kokubunji-shi, Tokyo 38 Within the Railway Technical Research Institute (56) References JP-A-5-43282 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C01F 7/00

Claims (6)

(57) [Claims] 1. A method in which a CaO—Al ₂ O ₃ compound and a soluble calcium salt and / or slaked lime are mixed at a temperature of 60 ° C. or lower in a liquid .
At a temperature range, binding <br/> formula by crystallization embedded image _{3CaO · Al 2 O 3 · CaX} 2 / m · nH 2 O ( wherein in the temperature range of then 70 ° C. or less, X is A monovalent or divalent anion, m represents the valence of the anion, and n represents 20 or less). 2. The method for producing hydrocalumite according to claim 1, wherein the reaction in the liquid is performed in the presence of an alkali metal salt. 3. The method for producing hydrocalumite according to claim 1, wherein the crystallization is performed under reduced pressure. 4. The method for producing hydrocalumite according to claim 1, wherein the CaO—Al ₂ O ₃ compound is an alumina cement. 5. The method according to claim 1, wherein the molar ratio of CaO / Al ₂ O _{3 in} the liquid is 3.
The method for producing hydrocalumite according to any one of claims 1 to 4, wherein the method is within a range of 3 to 4.2. 6. X is _{^{OH -, Cl -, NO 3}} - and NO ₂ ^- at least one member selected from the group consisting of claim 1
6. The method for producing hydrocalumite according to any one of items 5 to 5.