JP2600562B2 - Manufacturing method of hematite fine particles - 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 hematite fine particles, which is a pigment powder for paints, a colorant for rubber and plastics, a pigment for cosmetics, and an ultraviolet absorber utilizing the ultraviolet absorbing ability of hematite. Is useful as

[0002]

2. Description of the Related Art Hematite has a red color, has no toxicity, is thermally stable and is extremely inexpensive, and is therefore widely used as a red coloring pigment. In addition, since it is chemically stable, it is widely used as a non-polluting rust-preventive and anti-corrosive pigment. In particular, hematite fine particles of 0.2 μm to 0.4 μm have the highest hiding power and have been actively studied recently. When red is not clear, an organic red pigment is used when sharpness is required. Organic red pigments are expensive, are thermally unstable, are difficult to add to resins having a high melting point, are easily degraded, and have many problems such as toxicity. Hematite ultrafine particles having a particle size of 0.1 μm or less have the property of transmitting visible light but absorbing ultraviolet light when dispersed uniformly when mixed with a resin, and are also used as a transparent pigment powder as an ultraviolet absorber. Further, an organic red pigment can be used as the transparent red color.

[0003] As a method for producing hematite fine particles, a method of pulverizing and purifying bengal powder is known. However, it is industrially impossible to obtain hematite fine particles having a uniform particle size of 1 µm or less by this method. Accordingly, currently, generally, methods for obtaining hematite fine particles include (1) a method for obtaining hematite fine particles by heating a hydrous iron hydroxide (mainly α-FeOOH, β-FeOOH) or ferric hydroxide in an autoclave ( JP-B-45-18372, JP-A-58
-20733, 62-216919, 63-16253
5), (2) A method of synthesizing fine particles of hydrous iron oxide or magnetite by wet synthesis, washing with water, filtering, drying, and heat-treating at 250 ° C. or more to obtain hematite fine particles (Japanese Patent Publication No.
1-2640, JP-B 52-13528, JP-B 54
-7280, JP-B-62-40293, JP-A-61-1
63121, JP-A-61-232225).
Another method for producing hematite particles from an aqueous solution at a temperature of 100 ° C. or lower is disclosed in JP-A-51-819.
There are three methods described in the publications. That is, JP-A-51-8
According to the method described in JP-A-193-193, an alkali hydrogen carbonate alone is added to an aqueous ferrous salt solution, or both an alkali hydrogen carbonate, an alkali carbonate and an alkali hydroxide are added, and the pH is adjusted.
The oxidation reaction is carried out at a temperature of 7 to 11 and a temperature of 65 to 100 ° C. In this method, particles of other types other than hematite particles are mixed.

[0004]

In the above-mentioned method for producing hematite fine particles, the method using an autoclave requires a large-scale facility, which is economically and industrially disadvantageous. In addition, a temperature of 250 ° C. or more is required to obtain hematite fine particles by heating and dehydrating hydrous iron oxide, and to obtain hematite fine particles by heat-treating magnetite, 400 ° C.
C. or more is required, and in such a production method having a baking step at 250 ° C. or more, agglomeration occurs during baking, and it is difficult to disperse the particles in a vehicle such as a paint or a plastic while maintaining the particle size of the primary particles. Currently commercially available ultrafine hematite particles having a diameter of 0.1 μm or less are obtained by subjecting a fine hydrous iron oxide to a sintering prevention treatment and dehydrating by heating to obtain hematite fine particles. Since they are needle-shaped, they can easily form flocs other than agglomeration during firing, and it is extremely difficult to disperse them in vehicles such as paints and plastics. From such a point of view, there is a strong demand for a method for inexpensively obtaining fine particles of hematite having good dispersibility and no aggregation.

[0005]

Means for Solving the Problems As a result of studying a method of inexpensively producing hematite fine particles having a narrow particle size distribution and extremely excellent dispersibility, the present invention has been achieved. That is, in the presence of ions of at least one compound selected from the group consisting of a water-soluble halogen compound, a water-soluble sulfate compound, and a water-soluble nitrate compound, an aqueous suspension of hydrated iron hydroxide is adjusted to a pH value of 3 to 11 6
A method for producing hematite microparticles, which comprises heating to 0 to 100 ° C. to produce hematite microparticles, further comprising reacting an aqueous ferrous salt solution with an aqueous alkali solution to form a first hydroxide.
Hydrogen peroxide water in an amount required to produce iron and oxidize all divalent iron ions to trivalent iron ions with respect to Fe in the aqueous suspension (hereinafter referred to as “equivalent”) And using the obtained iron oxide hydroxide, the aqueous suspension thereof in the presence of ions of at least one compound selected from a water-soluble halogen compound, a water-soluble sulfate compound, and a water-acid nitrate compound,
A production method for producing hematite fine particles in the above-mentioned pH value and temperature range was also found.

In order to obtain hematite fine particles by heating and dehydrating hydrous iron oxide, a temperature of 250 ° C. or higher is required. However, in the present invention, it is possible to dehydrate the hydrous iron oxide at a temperature of 100 ° C. or less in the presence of the above-mentioned ions, and to obtain hematite fine particles having extremely excellent dispersibility and a narrow particle size distribution. X-ray analysis did not show any mixture of particles other than hematite particles.

A method for obtaining an aqueous suspension containing iron oxide hydroxide and at least one of the above-mentioned water-soluble three compounds includes:
An aqueous alkaline solution is added to the aqueous ferrous salt solution to form a precipitate of ferrous hydroxide, which is oxidized with an oxygen-containing gas or an oxidizing agent such as a hydrogen peroxide solution, and the obtained iron oxide hydroxide is washed with water.・ A water suspension is obtained by dissolving at least one of the above-mentioned compounds, which have been filtered and dried and a suitable water-soluble compound, in water or by using a by-product salt generated by neutralizing excess alkali. There are ways. When using hydrogen peroxide as an oxidizing agent,
An amount necessary to oxidize all divalent iron ions to trivalent iron ions, that is, an equivalent or more is necessary, but if it is less than the equivalent,
Other types of particles other than hematite particles are mixed in the product after heating.

[0008] In the present invention, a method for obtaining an aqueous suspension containing iron oxide hydroxide and at least one of the above-mentioned water-soluble three compounds is described by adding an excess alkali to an aqueous ferric salt solution. A method in which a precipitate is formed, and a method of dissolving at least one of the above-mentioned compounds containing water-soluble iron hydroxide and a suitable water-soluble compound obtained by washing, filtering and drying in water, and neutralizing the excess alkali. There is a method of directly obtaining an aqueous suspension using a by-product salt. There are various types of hydrous iron oxide produced from the aqueous ferrous salt solution as a starting material, and any of them can be used depending on the production conditions. The hydrous iron hydroxide produced from the aqueous ferric salt solution as a starting material is an amorphous one described as Fe (OH) _3, and the behavior of hematite formation is represented by α-, β-, γ-, δ-FeOOH. Same as case. Since the obtained hematite fine particles have different particle diameters, the raw materials may be properly used depending on the purpose.

When Fe (OH) ₃ is used as the iron oxide hydroxide, the particle diameter is 0.03 to 0.2 μm, α- or γ-Fe
In the case of OOH, a particle size of about 0.1 μm, δ- or β-
In the case of FeOOH, hematite fine particles having a particle size of 0.01 to 0.03 μm can be produced. In particular, δ-FeOOH is preferably used for producing hematite fine particles having a fine particle diameter. Therefore, as described above, an aqueous alkali solution is added to the aqueous ferrous salt solution to produce ferrous hydroxide, and an equivalent amount or more of hydrogen peroxide solution is added thereto to add iron oxide hydroxide, that is, δ-F
Although eOOH can be obtained, reaction conditions and the like other than the condition using an equivalent amount or more of hydrogen peroxide as an oxidizing agent will be described in detail below. (1) As a ferrous salt which is a raw material for producing ferrous hydroxide, ferrous chloride, ferrous nitrate, ferrous sulfate and the like are preferable. The concentration of the aqueous solution is not limited to the solubility limit. (2) As alkali (aqueous solution), KOH, NaO
H, Na ₂ CO ₃ , NaHCO ₃ , K ₂ CO ₃ , KHC
O ₃ or NH ₃ water is used. The addition of the alkali is desirably at least equivalent to the ferrous salt. The concentration of the aqueous solution is not limited to the solubility limit. (3) Concentration of aqueous hydrogen peroxide Generally, a commercially available product is about 35% H ₂ O ₂ water, but it may be diluted or used as it is.

(4) The temperature at the time of synthesizing δ-FeOOH is not limited, but it is 0 in relation to H ₂ O ₂ water.
The range of -40C is preferred. In addition, the pH value at the time of the synthesis needs to be a pH at which ferrous hydroxide Fe (OH) ₂ can be present, and is preferably pH> 3. Δ-FeOOH is Fe
Since rapid oxidation of (OH) ₂ is necessary, blowing in air is not preferable because goethite α-FeOOH can be formed.
In particular, the atmosphere during the reaction is not limited. Furthermore, δ
The solvent used for the synthesis of -FeOOH is generally water, but the reaction can be carried out in a solvent such as an alcohol or an organic acid in which iron ions can be present.

Next, the production of hematite fine particles from iron oxide hydroxide will be described in detail. Among the water-soluble halogen compounds, water-soluble sulfate compounds and water-soluble nitrate compounds to be added, alkali metals, particularly chlorides and sulfates of Na and K, are easy to handle. A mixture of two or more compounds may be used.
In the present invention, these compounds, especially neutral salts (p
In addition to the addition of H = 3 to 11), the above-mentioned compound may be added when producing hydrous iron oxide. In the case of using a salt produced as a by-product by neutralizing excess alkali after the production of hydrous iron oxide, the type of the compound mixed with the iron compound as the raw material and the type of alkali are determined. For example, when iron (I) chloride is reacted with sodium hydroxide to obtain Fe (OH) ₂ and oxidized to obtain iron oxide hydroxide, neutralize the alkali with hydrochloric acid to obtain iron oxide hydroxide and sodium chloride. Can be obtained. When ferric nitrate and potassium hydroxide are reacted with each other to obtain iron hydroxide, and when the excess alkali is neutralized with sulfuric acid, a mixture of iron hydroxide and potassium nitrate and potassium chloride is obtained. PH of water suspension is pH 3 or higher 11
The pH may be as low as possible, but pH 4 to 9 is preferable for prompt termination of hematite. When the pH exceeds 11, hematite fine particles in the present invention cannot be obtained, and α-FeO
OH growth is seen. When the pH is less than 3, the content of the iron oxide hydroxide does not change at all.

When the heating temperature is 90 ° C. or lower, it takes a long time to produce hematite, and preferably 90 ° C. or higher. As for the heating method, the reaction vessel may be placed in a thermostat in which the iron oxide hydroxide slurry containing the ion of the compound is kept at 60 ° C. or higher, or the vessel may be directly heated by a heater, a burner, steam, or the like. It may be heated by throwing in a throw-in heater. Alternatively, the solution may be heated by directly introducing steam. The heating time is 20 to 1000 hours at 60 ° C., 8
0 ° C for 2 to 100 hours, 90 ° C for 1 to 30 hours, 1
At 00 ° C., a range of about 1 to 300 minutes is suitable. Further, the concentration of the salt present during heating must be 0.5 wt% or more with respect to the solution regardless of the slurry concentration, and the upper limit concentration is up to the saturation value.

[0013]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples. Example 1 A ferrous hydroxide slurry was prepared by adding an aqueous solution in which 0.2 mol of ferrous chloride was dissolved in 500 ml of distilled water to an aqueous solution in which 0.8 mol of sodium hydroxide was dissolved in 500 ml of distilled water. Was. H ₂ O ₂ (0.4 mol
l / l) 1000 ml (4 equivalents) was added and δ-FeO
An OH slurry was obtained. Hydrochloric acid (1N) was added to the slurry to adjust the pH to 3.5, and the slurry was heated with a mantle heater and maintained at 95 ° C. for 1 hour. Thereafter, decantation was repeated, and sodium chloride was removed by washing with water, followed by filtration and drying. As a result of X-ray diffraction of the obtained powder, a diffraction peak of hematite was obtained. As a result of observation with a transmission electron microscope, it was confirmed that the particles were spherical hematite fine particles of 0.01 μm to 0.02 μm.

Example 2 An aqueous solution in which 0.2 mol of ferrous sulfate was dissolved in 500 ml of distilled water was added to an aqueous solution in which 0.8 mol of potassium hydroxide was dissolved in 500 ml of distilled water. A slurry was made. This slurry is mixed with H ₂ O ₂ (0.4 mol
/ L) 1000 ml (4 times the equivalent) was added and δ-FeOO was added.
H slurry was obtained. Hydrochloric acid (1N) was added to this slurry to adjust the pH to 9.5, and the slurry of hydrous iron oxide and potassium sulfate was heated with a mantle heater and maintained at 95 ° C. for 1 hour. Thereafter, decantation was repeated, potassium sulfate was removed by washing with water, and then filtered and dried.
As a result of X-ray diffraction of the obtained powder, a diffraction peak of hematite was obtained. As a result of observation with a transmission electron microscope, 0.03
It was confirmed that the particles were spherical hematite fine particles of μm to 0.06 μm.

Example 3 An aqueous solution in which 0.2 mol of ferric nitrate was dissolved in 500 ml of distilled water was added to an aqueous solution in which 0.6 mol of sodium hydroxide was dissolved in 500 ml of distilled water, and iron-containing hydroxide (hydroxide) was added. A ferric slurry was made. At this time, the pH was 5.8. Put the heater into the slurry
C. for 30 minutes. Thereafter, decantation was repeated, and sodium nitrate was removed by washing with water, followed by filtration and drying. As a result of X-ray diffraction of the obtained powder, a diffraction peak of hematite was obtained. As a result of observation with a transmission electron microscope, it was confirmed that the particles were spherical hematite fine particles of 0.06 μm to 0.08 μm.

EXAMPLE 4 An aqueous solution in which 25 mol of ferric chloride was dissolved in 25 l of distilled water was added to an aqueous solution of 41.2 mol of sodium carbonate dissolved in 25 l of distilled water to obtain an aqueous solution of ferric hydroxide (ferric hydroxide). )
Made a slurry. At this time, the pH was 6.0.
Steam was directly blown into the slurry and the boiling state was maintained for 2 hours. Thereafter, the sodium chloride was washed with water using a fine powder washing device using a ceramic filter to remove it, and then the slurry was dried using a spray drier. As a result of X-ray diffraction of the obtained powder, a diffraction peak of hematite was obtained. As a result of observation with a transmission electron microscope, 0.06 μm to 0.
It was confirmed that the particles were spherical hematite fine particles of 08 μm.

Example 5 In the same manner as in Example 2, the iron compound and the alkali as raw materials were used in the following combinations. Ferrous chloride-potassium hydroxide, ferrous chloride-sodium hydroxide, ferrous chloride-ammonia water, ferrous nitrate-potassium hydroxide, ferrous nitrate-sodium hydroxide, nitric acid
Iron-ammonia water, ferrous sulfate-sodium hydroxide, ferrous sulfate-ammonia water The X-ray diffraction of the obtained powder showed a diffraction peak of hematite. As a result of observation with a transmission electron microscope, 0.02
It was confirmed that the particles were spherical hematite fine particles of μm to 0.1 μm.

Example 6 In the same manner as in Example 3, the raw material iron compound and alkali were used in the following combinations. Ferric chloride-potassium hydroxide, ferric chloride-sodium hydroxide, ferric chloride-ammonia water, ferric nitrate-potassium hydroxide, ferric nitrate-ammonia water, ferric nitrate-
Potassium hydroxide, ferric sulfate-sodium hydroxide, and ferric sulfate-aqueous ammonia The obtained powder was subjected to X-ray diffraction. As a result, a diffraction peak of hematite was obtained. As a result of observation with a transmission electron microscope, 0.02
It was confirmed that the particles were spherical hematite fine particles of μm to 0.1 μm.

Example 7 Dry powder 100 of 0.2 μm goethite α-FeOOH
g of NaCl and 20 g of NaCl are introduced into 1000 l of distilled water.
A slurry of hydrous iron oxide containing aCl as an ion was obtained. This slurry is heated while stirring with a mantle heater,
Maintained at 98 ° C. for 2 hours. Wash this slurry with water,
As a result of X-ray diffraction of the powder obtained by drying, only a peak of hematite was found. Observation with a transmission electron microscope confirmed that the particles were spherical particles having a particle size of 0.2 to 0.4 μm.

Example 8 An aqueous solution in which 0.5 mol of ferrous chloride was dissolved in 500 ml of distilled water was added to an aqueous solution in which 1.5 mol of sodium hydroxide was dissolved in 500 ml of distilled water. A slurry was made. At room temperature, the slurry is mixed with H ₂ O ₂ (0.5 mol
l / l) 1000 ml (2 times the equivalent) and add δ-FeO
An OH slurry was obtained. Hydrochloric acid (1N) was added to the slurry to adjust the pH to 7.0, and the slurry was heated with a mantle heater and maintained at 95 ° C. for 1 hour. Thereafter, decantation washing was repeated to remove sodium chloride by washing with water, followed by filtration and drying. X-ray diffraction of the obtained powder showed a diffraction peak of hematite. As a result of observation with a transmission electron microscope, it was confirmed that the particles were spherical hematite fine particles of 0.01 to 0.03 μm.

Example 9 An aqueous solution obtained by dissolving 0.1 mol of ferrous chloride in 500 ml of distilled water was added to an aqueous solution obtained by dissolving 0.4 mol of sodium hydroxide in 500 ml of distilled water. A slurry was made. This slurry is mixed with H ₂ O ₂ (0.2mo.
l / l) 1000 ml (4 equivalents) was added and δ-FeO
An OH slurry was obtained. Hydrochloric acid (1N) was added to the slurry to adjust the pH to 7.0, and the slurry was heated with a mantle heater and maintained at 95 ° C. for 1 hour. Thereafter, decantation washing was repeated to remove sodium chloride by washing with water, followed by filtration and drying. X-ray diffraction of the obtained powder showed a diffraction peak of hematite. As a result of observation with a transmission electron microscope, it was confirmed that the particles were spherical hematite fine particles of 0.01 to 0.03 μm.

Comparative Example 1 An aqueous solution in which 0.2 mol of ferrous chloride was dissolved in 500 ml of distilled water was added to an aqueous solution in which 0.8 mol of sodium hydroxide was dissolved in 500 ml of distilled water. A slurry was made. H ₂ O ₂ (0.4 mol
l / l) to obtain a slurry of δ-FeOOH. The slurry was washed with water to remove sodium chloride, and heated at 95 ° C. for 1 hour with a mantle heater in the absence of compounds such as salts. As a result of X-ray diffraction of the powder obtained by filtration and drying, the diffraction peak was δ-FeOOH.
Did not change.

Comparative Example 2 An aqueous solution in which 0.2 mol of ferrous chloride was dissolved in 500 ml of distilled water was added to an aqueous solution in which 0.8 mol of sodium hydroxide was dissolved in 500 ml of distilled water. A slurry was made. H ₂ O ₂ (0.4 mol
l / l) to obtain a slurry of δ-FeOOH. The pH of the slurry at this time was pH 13.5. This slurry was heated at 95 ° C. for 1 hour with a mantle heater while maintaining the pH at 13.5. The obtained precipitate was washed with water to remove sodium chloride and sodium hydroxide. As a result of X-ray diffraction of the obtained powder, the diffraction peak was δ-FeO
Remained OH.

Comparative Example 3 An aqueous solution obtained by dissolving 0.2 mol of ferric nitrate in 500 ml of distilled water was added to an aqueous solution obtained by dissolving 0.5 mol of sodium hydroxide in 500 ml of distilled water. A ferric slurry was made. At this time, the pH was 2.5. Put the heater into the slurry
C. for 30 minutes. Thereafter, decantation washing was repeated to remove sodium nitrate by washing with water, followed by filtration and drying. The resulting powder was amorphous by X-ray diffraction, and no peak was observed.

Comparative Example 4 An aqueous solution in which 0.2 mol of ferrous chloride was dissolved in 500 ml of distilled water was added to an aqueous solution in which 0.8 mol of sodium hydroxide was dissolved in 500 ml of distilled water. A slurry was made. H ₂ O ₂ (0.4 mol
l / l) 1000 ml (4 equivalents) was added and δ-FeO
An OH slurry was obtained. Hydrochloric acid (1N) was added to the slurry to adjust the pH to 2.0, and the slurry was heated with a mantle heater and maintained at 95 ° C. for 1 hour. Thereafter, decantation washing was repeated to remove sodium chloride by washing with water, followed by filtration and drying. As a result of observation with a transmission electron microscope, the sample was amorphous and no diffraction peak was observed.

Comparative Example 5 An aqueous solution in which 0.2 mol of ferrous chloride was dissolved in 500 ml of distilled water was added to an aqueous solution in which 0.8 mol of sodium hydroxide was dissolved in 500 ml of distilled water. A slurry was made. This slurry is mixed with H ₂ O ₂ (0.2mo.
(l / l) 400 ml (0.8 equivalents) was added. Hydrochloric acid (1N) was added to the slurry to adjust the pH to 8.5, and the slurry was heated with a mantle heater and maintained at 95 ° C. for 1 hour. Thereafter, decantation washing was repeated to remove sodium chloride by washing with water, followed by filtration and drying. X-ray diffraction of the obtained powder showed diffraction peaks of hematite and magnetite.

[0027]

According to the present invention, hematite fine particles having a narrow particle size distribution and extremely excellent dispersibility can be produced at low temperature and without the need for complicated equipment and operation, and therefore can be produced at low cost. The obtained hematite has excellent dispersibility in vehicles such as paints and plastics.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-226740 (JP, A) JP-A-51-8193 (JP, A) JP-B 2-47410 (JP, B2) JP-B-57- 44608 (JP, B2)

Claims (2)

(57) [Claims] 1. An aqueous suspension of iron oxide hydroxide in the presence of ions of at least one compound selected from the group consisting of a water-soluble halogen compound, a water-soluble sulfate compound, and a water-soluble nitrate compound, and a pH value of 3 A method for producing fine particles of hematite, characterized in that the fine particles are heated to 60 to 100 ° C. to produce fine particles of hematite. 2. A ferrous hydroxide solution is produced by reacting an aqueous solution of a ferrous salt with an aqueous alkali solution to oxidize all divalent iron ions to trivalent iron ions with respect to Fe in the aqueous suspension. 2. The method for producing hematite fine particles according to claim 1, wherein an aqueous solution of hydrogen peroxide in an amount necessary for the above is added, and the obtained hydrous iron oxide is used.