JPH08119635A - Production of granular fine magnetite particles - Google Patents

Abstract

PURPOSE: To make magnetite particles uniform in particle size by heating an alkaline suspension contg. granular fine goethite particles and colloidal ferrous hydroxide. CONSTITUTION: An alkali hydroxide other than NH4 OH is added to an aq. soln. of an alkali carbonate other than (NH4 )2 CO3 by 0.1-0.3mol per 1mol alkali carbonate to prepare an aq. alkali soln. An aq. ferrous salt soln. is mixed with >=1.0 equiv. of the aq. alkali soln. based on the amt. of Fe<2+> and they are brought into a reaction in a nonoxidizing atmosphere to prepare a suspension of an iron-contg. precipitate having 0.3-0.6mol/l concn. of Fe<2+> . This suspension is stirred at 50-65 deg.C for 30-360min in a nonoxidizing atmosphere, a water-soluble silicate is added to the suspension by 0.5-5.0at.% (expressed in terms of Si) of the amt. of Fe<2+> and they are brought into a reaction at 50-60 deg.C in a flow of oxygen-contg. gas to form granular fine goethite particles. An aq. ferrous salt soln. and an aq. alkali hydroxide soln. are then added to the suspension in a nonoxidizing atmosphere and the resultant alkaline suspension of >=pH11 contg. fine goethite particles and colloidal ferrous hydroxide is stirred under heating at 40-100 deg.C.

Description

Detailed Description of the Invention

[0001]

The present invention has a BET specific surface area value of 4
The present invention relates to a method for producing a granular magnetite fine particle powder having a uniform particle size of 0 to 80 m ² / g.

The main use of the granular magnetite fine particle powder according to the present invention is as a material particle powder for magnetic ink and magnetic toner, and also for adsorption of sulfur oxides, hydrogen sulfide, nitrogen oxides, etc. in air or gas. It is an agent, a deodorant, and a material powder for various catalysts.

[0003]

2. Description of the Related Art In recent years, a printing technique called an ink jet method has attracted attention in a field requiring high speed recording such as a terminal recording device of a computer and a facsimile.

In this ink jet system, an ink manufactured using a highly soluble substance such as a dye has a pore diameter of about several tens.
A pattern is drawn on a recording paper by ejecting it from a very fine nozzle of about μm, charging the ejected ink droplet, and controlling the electric field to arbitrarily deflect the flight direction of the droplet. Is.

Recently, magnetic ink is used in the ink jet method because it is easier to control by a magnetic field than the method of controlling the electric field. By controlling the magnetic field, the flight direction of ink droplets can be arbitrarily deflected. It has been proposed and put into practical use.

Magnetic ink is generally produced by dispersing and mixing granular magnetite particles, which are well known as magnetic particles having a black color, in a vehicle, and the granular magnetite particles are dispersed in the vehicle as solid particles. ,
In addition, it has been pointed out that the content of the ink must be increased to a certain degree in order to impart appropriate magnetism to the ink, so that the nozzle is likely to be clogged, and the granular magnetite particles have a large specific gravity. It has also been pointed out that the ink droplets ejected from the nozzles do not fly and fall.

In order to solve the above problems of magnetic ink,
There is a strong demand for granular magnetite particles having a particle size as fine as possible and a uniform particle size.

As one of the electrostatic latent image developing methods, a so-called one-component magnetic toner is used in which composite particles obtained by mixing and dispersing granular magnetite particle powder in a resin are used as a developer without using a carrier. The developing method is widely known and widely used.

Recently, in order to improve the performance of copying machines, in particular, to reduce the particle size of magnetic toner as a developer in order to increase the resolution, granular magnetite powder particles mixed and dispersed in a resin are also used. Moreover, 0.1 to 0.
With a particle size of about 2 μm, it is difficult to uniformly mix and disperse in each magnetic toner. Therefore, in order to uniformly mix and disperse the granular magnetite particles in the individual magnetic toners, the particle size is finer, in particular, 0.
There is a strong demand for magnetite particles having a uniform particle size of less than 1 μm.

On the other hand, sulfur oxides, hydrogen sulfide, nitrogen oxides, etc. in the atmosphere and gases are the cause of air pollution. Especially, sulfur oxides, hydrogen sulfide, etc. are used not only as a source of air pollution but also with iron. It is directly involved in the atmospheric corrosion of structures and bridges, and nitrogen oxides, etc. are a trigger for photochemical smog. Efforts are being made day and night to remove the.

However, a large amount of exhaust gas is being emitted due to the increase of combustion furnaces and the spread of automobiles with the development of industry, and various measures have been taken, but the present situation is still insufficient. There is a strong demand for the development of adsorbents and deodorants having excellent adsorption ability for oxides, hydrogen sulfide, nitrogen oxides and the like.

[0012] This fact is, for example, that the concentration of nitrogen oxides in the atmosphere in the city in the "Chemical Society of Japan" published by the Chemical Society of Japan (1985), page 2315, decreases even if various measures are taken. Not only that, but also the increasing tendency is seen, and efforts to remove nitrogen oxides are becoming more important.
... "is as described.

Although adsorbents excellent in adsorption capacity for sulfur oxides, hydrogen sulfide, nitrogen oxides, etc. are currently most demanded, known adsorbents such as activated carbon, silica gel, zeolite, etc. are sulfur oxides, It has been pointed out that it is still insufficient as an adsorbent for hydrogen sulfide and nitrogen oxides.

This fact is described, for example, in "Chemical Society of Japan" published by the Chemical Society of Japan (1978), page 665, "... Inorganic compounds such as activated carbon and various metal oxides for adsorbing and removing sulfur dioxide. However, there are still problems with the adsorption capacity, selectivity, regeneration method, etc., and the development of new adsorbents is desired .... "and the above-mentioned" Journal of the Chemical Society of Japan "(1985). Activated carbon is a "‥‥ general adsorbent pp 2315, although silica gel and zeolite are effective for nO _2, ability to adsorb nO is not sufficient. Therefore, the development of high adsorption capacity materials to nO It is desired .... "

It has been found that magnetite powder particles are excellent in adsorption ability for sulfur oxides, hydrogen sulfide, nitrogen oxides and the like, and have been attracting attention. This fact is described in, for example, “... NOx and SO in Japanese Unexamined Patent Publication No. 4-83531”.
Cleans polluted air containing harmful gas such as x and O ₂ gas, nitrogen compound gas such as NH ₃ , carboxyl group gas such as H ₂ S, and carboxylic acid gas such as acetic acid It can be used as an air cleaning material, or as a cleaning material for combustion exhaust gas or harmful gas .. It can also be used as a food freshness preserving agent. "..." is as described.

Since the adsorbent for sulfur oxide, hydrogen sulfide, nitrogen oxide, etc. adsorbs an object on the surface thereof, the larger the specific surface area of the adsorbent, the more the adsorbing ability increases. The adsorbent is required to be as fine as possible. This fact is, for example, the above-mentioned "Journal of the Chemical Society of Japan".
(1980) p. 681, "... In the study of gas molecule adsorption on the solid surface, powders having a large surface area are often used."

Further, the material powders used for various catalysts are required to have a large specific surface area as much as the adsorbent described above. For example, "Industrial catalyst" (1964), published by Nikkan Kogyo Shimbun, page 4, "... The first choice of catalyst is to choose a catalyst with high activity ..." On page 62, "... it is desirable that a solid catalyst has a large effective surface area. Therefore, it is used in a powder or porous state ..." and "Pigment Dispersion Technology" issued by the Technical Information Institute. (1993)
Year) Page 18 "... The smaller the particles ...
The chemical activity of the particles is increased. "..." is as described.

The prior art relating to magnetite particle powder used as an adsorbent or a catalyst is described in the above-mentioned JP-A-4-
For example, Japanese Patent Laid-Open No. 83531, Japanese Patent Laid-Open No. 5-131020, Japanese Patent Laid-Open No. 5-163023, and the like can be given.

As the prior art relating to the magnetite particle powder used as the material powder for the magnetic ink and the magnetic toner, there are JP-A-4-204949 and JP-A-5-49549.
No. 3,390,010 is cited.

[0020]

Conventionally, a method for producing granular magnetite particles has been obtained by mixing an aqueous solution of a ferrous salt such as ferrous sulfate with an alkaline aqueous solution such as sodium hydroxide or sodium carbonate. 60 to 1 in an aqueous solution containing an iron-containing precipitate such as Fe (OH) ₂ or FeCO ₃ .
A method of ventilating an oxidizing gas in the temperature range of 00 ° C. (for example, JP-B-44-668 and JP-B-49-3).
5520), using an aqueous ferrous salt solution such as ferrous sulfate and an aqueous ferric salt solution such as ferric sulfate, Fe ²⁺ : Fe ³⁺
Is adjusted to 1: 2, an alkaline aqueous solution such as NaOH is added to the mixed iron aqueous solution in an amount of 1 equivalent or more, and the mixture is heated and mixed in a temperature range of 50 to 100 ° C., a so-called coprecipitation method, water-containing method. A method of heating an alkaline suspension containing ferric oxide particles or ferric oxide particles and ferrous hydroxide in a ratio of Fe ²⁺ and Fe ³⁺ of about 1: 2 (JP-B-48-27).
No. 200, US Pat. No. 2631085) and the like are known.

That is, in the case of the above-mentioned method, in the case of air-oxidizing a suspension of Fe (OH) ₂ at a proper temperature in Japanese Patent Publication No. 2-36553, ferromagnetic Fe ₃ O
_{Although 4} particles can be obtained, the particle size of the Fe ₃ O ₄ particles obtained by this method is an average particle size, generally 100
As described above, the generated magnetite particles generally have a large particle size of 0.1 μm or more, and it is difficult to obtain fine particles of less than 0.1 μm, and the particle size is uniform. Particles are hard to say.

In the case of the above method, an alkali is added to a mixed aqueous solution of a ferrous salt and a ferric salt described in Japanese Patent Publication No. 2-33655, and Fe ₃ is added according to the following formula.
It is well known to produce O ₄ particles, but the target particle size of Fe ₃ O ₄ particles becomes smaller than 100Å. However, since it is too fine, it becomes difficult to mix and disperse it in a vehicle or a resin, and the particle size is asymmetric.

In the case of the above method, 0.1 μm
It is easy to obtain granular magnetite particles having the above large particle size.

Further, usually, a ferrous salt aqueous solution and an alkaline aqueous solution are reacted to obtain a suspension containing an iron-containing precipitate, and an oxygen-containing gas is passed through the suspension to carry out an oxidation reaction. It is also produced by a method in which iron oxide hydroxide particles are produced, filtered, washed with water and dried to obtain iron oxide hydroxide particle powder, and the iron oxide hydroxide particle powder is dehydrated and reduced to obtain magnetite particle powder.

The iron oxide hydroxide particles obtained by this production method are needle-shaped or spindle-shaped. The particle shape of magnetite particles obtained by dehydrating and reducing acicular or spindle-shaped iron oxide hydroxide particles is also acicular or spindle-shaped. When these needle-shaped or spindle-shaped particles are heat-treated, the particle shape collapses or changes occur due to sintering between particles. For example, "Development of Magnetic Materials and High Dispersion Technology of Magnetic Particles" issued by Sogo Gijutsu Center Co., Ltd. (1982), page 8, "... When heating temperature rises ... Large voids are created by gathering small voids in the.
The strength of the needle-shaped particles is weak due to the holes, and at the same time, sintering occurs between the particles, resulting in agglomerates and poor dispersibility.
"..." is as described.

As a method for producing iron oxide hydroxide particles other than the above, there is a method for producing a spindle-shaped goethite particle powder described in JP-B-63-13941.
This is a suspension of FeCO ₃ obtained by reacting an aqueous solution of ferrous salt with an aqueous solution of alkali carbonate, and adding water-soluble silicate to the oxidation reaction of this suspension, and aerating an oxygen-containing gas into the solution. Is a method for producing spindle-shaped goethite particles by carrying out an oxidation reaction, and in the case of this method, the axial ratio (major axis diameter / minor axis diameter-below, simply “axial ratio”)
Say. Although goethite particles having a particle size of about 1.5 to 1.0 are obtained, the particle size is still about 0.15 μm or more.

The goethite particles described in JP-B-51-12318, JP-B-51-16039, JP-B-51-21639 and JP-B-51-21640 have an axial ratio of 5; The following spindle-shaped particles are obtained, and fine particles having an average particle diameter of 50 to 200Å have been obtained. The spindle-shaped particles having an axial ratio of about 3 are obtained from the respective examples described in the respective publications. It is a particle.

As the granular goethite particle powder, fine granular α-iron oxyhydroxide (Applicant's note: goethite) described in JP-A-60-141625 can be mentioned, which is a water-soluble silica. Granular goethite fine particles of "0.1 μm or less" in "Example 2" and "Example 3" of the same publication by performing an oxidation reaction of a ferrous salt aqueous solution in the presence of acid salt, ammonium carbonate and caustic alkali. Has been obtained. However, as shown in "FIG. 1" of "Example 1" of the same publication, the particle size distribution is asymmetric.

The raw material containing FeO and Fe ₂ O ₃ as the main components described in JP-A-4-83531 mentioned above is dust or scale slag, and it is difficult to obtain a uniform particle size distribution, and it is difficult to obtain an arbitrary particle size distribution. It is also difficult to set the particle size.

Further, the method for producing magnetite particles described in Japanese Patent Laid-Open No. 5-131020 is not described.

The oxygen-defective magnetite particles described in the above-mentioned Japanese Patent Laid-Open No. Hei 5-163023 are obtained by dispersing a spherical polymer as a core in an aqueous solution of a hydrolyzable iron salt, and then forming a spherical polymer-iron oxide. It is obtained by a complicated method of obtaining composite particles and then subjecting the composite particles to heat treatment and reduction.

The above-mentioned Japanese Patent Laid-Open No. 4-204949 discloses that
Although acicular magnetite particles have been obtained by using acicular maghemite particles as the ferric salt raw material, it is good when it is used for the purpose of utilizing the acicular particle shape, but it is problematic because it is acicular in dispersibility. Is.

In the above-mentioned Japanese Patent Laid-Open No. 5-339010,
Hydrous ferric oxide particles or ferric oxide particles is the specific surface area is 50 to 200 m ² / g is used as the ferric salt starting material, when the specific surface area exceeds 200 meters ² / g is
It is described that it is difficult to obtain magnetite fine particles of less than 0.1 μm.

The particle size is as fine as possible,
Granular magnetite particles having a uniform particle size are currently most demanded, but in the case of the above-mentioned method, granular magnetite fine particle powders satisfying these various characteristics have not yet been obtained.

Therefore, in the present invention, the BET specific surface area value is 4
A technical problem is a production method capable of obtaining granular magnetite fine particles having a uniform particle size of 0 to 80 m ² / g.

[0036]

The above technical problems can be achieved by the method of the present invention as follows.

That is, according to the present invention, when a ferrous salt aqueous solution and an alkaline aqueous solution are reacted in a non-oxidizing atmosphere to form a suspension containing an iron-containing precipitate, alkali hydroxide except for aqueous ammonia is carbonated. While being added to an aqueous solution of an alkali carbonate excluding ammonium and any of the suspensions, the amount of the alkali hydroxide added is in the range of 0.1 to 0.3 mol with respect to 1 mol of the alkali carbonate,
The total amount of both the alkalis is Fe in the aqueous solution of the ferrous salt.
An amount exceeding 1.0 equivalent relative ^2+, moreover, 0.3 to Fe ²⁺ in the ferrous salt aqueous solution within the suspension
A suspension containing the iron-containing precipitate was prepared by containing the iron in a concentration range of 0.6 mol / l, and the suspension was mixed in a temperature range of 50 to 65 ° C. under a non-oxidizing atmosphere.
The mixture was maintained and stirred for 0 to 360 minutes, and then a water-soluble silicate was added to the suspension in an amount of 0.5 to 5.0 atomic% in terms of Si in terms of Si with respect to Fe ²⁺ in the ferrous salt aqueous solution. After 50
Oxygen-containing gas is passed through the liquid in the temperature range of 60 ° C. to carry out an oxidation reaction to produce granular goethite fine particles, and then a non-oxidizing atmosphere is created, and an aqueous ferrous salt solution and a hydroxide are added to the liquid. An alkaline aqueous solution is charged and reacted to form an alkaline suspension containing the particulate goethite fine particles and colloidal ferrous hydroxide having a pH value of more than 11, and the suspension is 40 to 100 ° C. in a non-oxidizing atmosphere. Is a method for producing granular magnetite fine particles, which comprises producing granular magnetite fine particles by heating and stirring in the temperature range.

The structure of the present invention will be described in more detail as follows.

First, the production of granular goethite fine particles as precursor particles of the granular magnetite fine particles according to the present invention will be described.

Examples of the ferrous salt aqueous solution used in the present invention include ferrous sulfate aqueous solution and ferrous chloride aqueous solution.

The amount of the aqueous ferrous salt solution is in the range of 0.3 to 0.6 mol / l as the reaction concentration. 0.3
When it is less than mol / l, the reaction concentration is not thin and industrial. When it exceeds 0.6 mol / l, the particle size distribution of the obtained granular goethite fine particles becomes wide. It is preferably 0.4 to 0.5 mol / l.

In the present invention, when a ferrous salt aqueous solution and an alkaline aqueous solution are reacted to obtain a suspension containing an iron-containing precipitate, it is carried out under a non-oxidizing atmosphere. The reason is that it is necessary to avoid the occurrence of goethite particles due to the initiation of an oxidation reaction in an oxidizing atmosphere before the growth of the generated goethite particles is suppressed in the short axis direction.

To create a non-oxidizing atmosphere, an inert gas (N ₂ gas or the like) or a reducing gas (H ₂ gas or the like) may be ventilated in the reaction vessel.

Examples of the alkali carbonate used in the present invention include sodium carbonate, potassium carbonate and the like. Further, it is preferable to dissolve the alkali carbonate in water in advance and use it as an aqueous solution because it reacts with the aqueous ferrous salt solution. It should be noted that ammonium carbonate is discharged out of the reaction system when the suspension containing the iron-containing precipitate is maintained and stirred in a non-oxidizing atmosphere, the ammonium carbonate is reactively decomposed and the ammonium salt becomes NH ₃ gas. So it cannot be used.

Further, since the pH value of the reaction solution is in the alkaline region, NH ₃ gas is discharged out of the system before CO ₂ gas and the chemical equilibrium in the reaction is disturbed, resulting in a particle size distribution of the obtained granular goethite particles. Becomes non-uniform, and especially when the temperature exceeds 50 ° C., granular magnetite may be mixed. In addition, if the NH ₃ gas is strongly discharged, the smell of ammonia becomes a problem, so use of NH ₃ gas must be avoided.

Examples of the alkali hydroxide used in the present invention include sodium hydroxide and potassium hydroxide. Alkali hydroxide may be dissolved in water in advance and used as an aqueous solution, or may be added to an aqueous solution of alkali carbonate or a suspension containing the iron-containing precipitate and stirred and dissolved. Ammonia water cannot be used for the same reason as ammonium carbonate.

In the present invention, both alkali carbonate and alkali hydroxide are used in combination, and the alkali hydroxide is
It is added to either the aqueous solution of alkali carbonate or the suspension containing the iron-containing precipitate. When added after starting the stirring under a non-oxidizing atmosphere, the particle size of the obtained granular goethite particles becomes large, and the atomization as the object of the present invention cannot be achieved.

The amount of alkali hydroxide added is in the range of 0.1 to 0.3 mol with respect to 1 mol of the alkali carbonate. It may be less than 0.1 mol, but it is difficult to obtain what is the object of the present invention. If it exceeds 0.3 mol, granular magnetite particles may be mixed in the granular goethite particles, which is not preferable. When magnetite is mixed in the granular goethite fine particles, a uniform particle size distribution cannot be obtained when the granular magnetite fine particles of the present invention are produced. A preferable range is 0.15 to 0.2 mol.

The total amount of both alkalis is more than 1.0 equivalent to Fe ²⁺ in the aqueous ferrous salt solution used. When the amount is 1.0 equivalent or less, a large amount of sulfur content is contained in the obtained granular goethite fine particles, which is not preferable. It is preferably more than 1.0 equivalent and 2.0 equivalents or less. It may exceed 2.0 equivalents but it is not necessary to use an excess of alkali. More preferably 1.3-
It is 1.7 equivalents. The pH value of the reaction solution during the oxidation reaction in this case is in the range of 7.0 to 11.0, preferably 8.0 to 10.0.

The temperature at which the suspension containing the iron-containing precipitate in the present invention is maintained and stirred under a non-oxidizing atmosphere is 50 to 50.
The temperature range is 65 ° C. When the temperature is lower than 50 ° C., the CO ₂ gas in the suspension cannot be sufficiently discharged to the outside of the reaction system, so that the growth of the generated goethite particles in the short axis direction is not sufficiently suppressed and the fine particles are Insufficiency is also insufficient. When the temperature exceeds 65 ° C, granular magnetite particles may be mixed in the granular goethite particles. When magnetite is mixed in granular goethite particles,
When producing the granular magnetite fine particles in the present invention, a uniform particle size distribution cannot be obtained. A preferable temperature range is 50 to 55 ° C.

The time for maintaining and stirring the suspension containing the iron-containing precipitate in the present invention under a non-oxidizing atmosphere is 30 to 30 minutes.
It is 360 minutes. If it is less than 30 minutes, the CO ₂ gas in the suspension cannot be sufficiently discharged to the outside of the reaction system, so that the growth of the generated goethite fine particles in the minor axis direction is not sufficiently suppressed, and the fine particles are not sufficiently suppressed. Insufficiency is also insufficient. Three
It may exceed 60 minutes, but there is no need to unnecessarily lengthen the time. The preferred range is 60 to 240 minutes.

The non-oxidizing atmosphere may be the same as the non-oxidizing atmosphere. By maintaining and stirring in a non-oxidizing atmosphere, growth of goethite particles is suppressed in the short axis direction. Therefore, when maintaining and stirring in an oxidizing atmosphere, the oxidation reaction starts and goethite particles occur. Therefore, the effect of suppressing the short-axis direction becomes insufficient, so it must be avoided.

Examples of the water-soluble silicate used in the present invention include sodium silicate and potassium silicate.

The amount of the water-soluble silicate added is 0.5 to 5.0 atom% in terms of Si with respect to Fe ²⁺ in the ferrous salt aqueous solution. When it is less than 0.5 atom%, the particle size of the obtained granular goethite particles becomes large, and when it exceeds 5.0 atom%, it is present as an unnecessary salt in the obtained granular goethite particles. It is not preferable. The preferable range is 1.5 to 3.5 atomic%.

The time of adding the water-soluble silicate is from the end of the above-mentioned maintenance stirring to the start of the oxidation reaction. As described above, since the growth of goethite particles generated by the maintenance stirring in the short axis direction is suppressed, it is preferable to be from 15 minutes before the start of the oxidation reaction after the termination of the maintenance stirring to immediately before the start of the oxidation reaction. More preferably, it is from 5 minutes before to immediately before the start of the oxidation reaction. When added after the oxidation reaction is started, needle-like particles of goethite particles have already occurred due to the start of the oxidation reaction, and the obtained goethite particles are also not particles, and particles that have a rice grain shape with an axial ratio. Becomes

Further, the water-soluble silicate is previously added to the alkali carbonate aqueous solution or the alkali hydroxide aqueous solution.
When mixed and used, it is difficult to obtain the effect of suppressing growth of goethite particles generated in the short axis direction by maintaining and stirring in a non-oxidizing atmosphere, and atomization becomes insufficient.

It should be noted that the water-soluble silicate is preferably added as an aqueous solution dissolved in water because it is rapidly and uniformly stirred and dispersed in the suspension.

The temperature during the oxidation reaction in the present invention is 50.
The temperature range is -60 ° C. When the temperature is lower than 50 ° C., the crystallinity of the obtained granular goethite fine particles is insufficient, which causes a problem in the production of the granular magnetite fine particles. 6
When the temperature exceeds 0 ° C, granular magnetite particles may be mixed in the obtained granular goethite particles. When magnetite is mixed in the granular goethite fine particles, a uniform particle size distribution cannot be obtained when the granular magnetite fine particles of the present invention are produced. The temperature range is preferably 50 to 55 ° C.

The oxidizing means in the present invention is carried out by passing an oxygen-containing gas (for example, air) through the liquid. Further, mechanical stirring may be accompanied if necessary.

The granular goethite fine particles which are the precursor particles of the granular magnetite fine particles according to the present invention have an average particle diameter of 0.01 to 0.03 μm and a BET specific surface area value of 200 to 300 m ² / g. . 200 m ² / g
If it is less than the above, the desired effect cannot be obtained. 300
If it exceeds m ² / g, the desired product cannot be obtained. The preferable range is 0.012 to 0.
02 μm and a BET specific surface area value of 220 to 270 m
² / g.

Further, the granular goethite fine particle powder contains 0.5 to 5.0 atom% of a silicon compound in terms of Si with respect to all Fe in the granular goethite fine particle powder. 0.
If it is less than 5 atomic%, the BET specific surface area value of the obtained granular goethite fine particle powder will not be 200 m ² / g or more, and the desired fine particle powder cannot be obtained. If it exceeds 5.0 atom%, the silicon compound will be present as an unnecessary salt in the obtained granular goethite fine particle powder, which is not preferable and it is difficult to form a uniform composition.

Next, the production of granular magnetite fine particles according to the present invention will be described.

The above-mentioned granular goethite fine particles are used as the precursor particles of the granular magnetite fine particles according to the present invention.

The ferrous salt aqueous solution in the present invention includes
Examples thereof include ferrous sulfate and ferrous chloride.

The amount of the ferrous iron salt aqueous solution added is 17.0 to 38.0% by weight in terms of Fe with respect to the granular goethite fine particles. When it is less than 17.0% by weight, sufficient magnetite cannot be formed, and the blackness is insufficient.
When it exceeds the weight%, unreacted ferrous hydroxide colloid may be mixed. The preferred range is 25.0-3
It is 6.0% by weight.

Examples of the alkali hydroxide aqueous solution in the present invention include sodium hydroxide, potassium hydroxide, aqueous ammonia and the like.

A suspension containing granular goethite fine particles and a ferrous hydroxide colloid obtained by introducing an aqueous solution of ferrous salt and an aqueous alkali hydroxide solution into the reaction solution containing the particulate goethite fine particles of the present invention and reacting them. The suspension has a pH value of 11
Alkaline exceeding. When the pH value is less than 11, the reaction time becomes long, and unreacted goethite fine particles may remain. Further, the reason for being alkaline is not preferable because acidic ferric hydroxide colloid is not sufficiently generated and ferrous salt remains. Preferred p
The H value is in the range of 12 to 13.5.

The reaction solution containing the granular goethite fine particles after the formation of the granular goethite fine particles is preferably washed with water once to remove the residual alkali carbonate in the reaction liquid, and then the aqueous alkali hydroxide solution is added. . It is also possible to add the aqueous alkali hydroxide solution without removing the remaining alkali carbonate, but in that case, by adding a considerable amount of the aqueous alkali hydroxide solution into the suspension, The value can be greater than 11.

In the present invention, the suspension is 40-100
Heat and stir in the temperature range of ° C. If the temperature is below 40 ° C,
Reactivity is not sufficient and it is difficult to make magnetite. 1
When the temperature exceeds 00 ° C, it is not industrial because an apparatus such as an autoclave is required.

The atmosphere for heating and stirring is a non-oxidizing atmosphere. In the case of an oxidizing atmosphere, the colloidal ferrous hydroxide may be oxidized to inhibit the formation of magnetite in the granular goethite particles.

The filtration, washing with water and drying for obtaining the granular magnetite fine particles may be carried out by a conventional method.

When the granular goethite fine particles are produced,
P, Al, Zn, which are usually added for the purpose of improving the characteristics,
Water-soluble salts such as Ni, Cu, Co, Mn and Cr can also be added. The addition amount of each of the above-mentioned salts to be added is 1.0 to 20.0 atomic% in terms of elements of each salt with respect to Fe ²⁺ in the ferrous iron salt aqueous solution.

[0072]

The operation of the present invention having the above-described structure is as follows.

First, the goethite particles as the precursor particles will be described.

Goethite particles obtained by reacting an aqueous solution of ferrous salt with an aqueous alkaline solution to form a suspension containing an iron-containing precipitate and aerating an oxygen-containing gas in the suspension to carry out an oxidation reaction are Usually, the particles are needle-shaped and have an axial ratio of about 2 or more.

Therefore, the present inventor, when trying to obtain granular goethite fine particles, suppresses the growth of the axial ratio as much as possible and makes it so small that the axial ratio is not recognized.
It was considered that granular goethite fine particles could be obtained by setting the axial ratio to about 1.0 ± 0.2.

The above-mentioned Japanese Patent Publication No. 63-13941 discloses that
It has been shown that the addition of a water-soluble silicate before the oxidation reaction can suppress the growth of the particle size of the obtained goethite particles in the long axis direction. However, as described above, the spindle-shaped goethite particle powder obtained by the method described in the publication has an axial ratio of about 1.5 to 1.0, but a particle size of about 0.15 μm or more, It cannot be said that the particles are the object of the present invention.

According to the results of the experiment conducted by the present inventor, when the water-soluble silicate was added before the stirring under the non-oxidizing atmosphere, the stirring under the stirring under the non-oxidizing atmosphere was performed thereafter. It is difficult to obtain the effect of suppressing the growth of the goethite particles in the short axis direction even if an oxidation reaction is performed, and the atomization becomes insufficient, and the growth of the goethite particles in the long axis direction is suppressed by the water-soluble silicate. It has been confirmed that the action rather causes a phenomenon that promotes growth in the minor axis direction.

On the other hand, in the method described in JP-A-60-141625, the reaction concentration is 0.225 mol / l.
It is a very thin concentration below the range, and the reaction temperature is 5
Although the temperature is 0 ° C. or lower, the reaction temperature in each “Example” of the publication is “20 ° C.”, and the preferable range is 10 to 25 ° C.

However, as described above, the granular goethite fine particles produced at such a reaction concentration and reaction temperature have a particle size distribution as shown in "Fig. 1" of "Example 1" of the same publication. It is hard to say that it is excellent. Moreover, at such a reaction concentration and reaction temperature, it cannot be said to be industrial when productivity and seasonal water temperature are taken into consideration.

Further, even if the oxidation reaction is carried out in the co-existence of a carbonate other than ammonium carbonate and a caustic alkali in the publication, the intended effect of the present invention cannot be expected.
Regarding the description "...", according to the experimental results of the present inventor, when ammonium carbonate is used in the alkaline aqueous solution, NH ₃ which is an ammonia component is gasified and discharged into the atmosphere, and thus the obtained granular goethite fine particles are It has been confirmed that the particle size distribution deteriorates. This is the same when ammonia water is used as the alkali hydroxide.

As described above, the present inventor has thoroughly studied the prior art, and as a result, the method of adding a water-soluble silicate before the oxidation reaction or the method of using both alkali carbonate and alkali hydroxide in combination. It was found that the granular goethite fine particles having an excellent particle size distribution cannot be obtained only by itself.

Therefore, in order to obtain granular goethite fine particles having an excellent particle size distribution, it is necessary to suppress the growth of the produced goethite particles not only in the major axis direction but also in the minor axis direction. , A combination of alkali carbonate and alkali hydroxide, and a water-soluble silicate is added after stirring the suspension containing the iron-containing precipitate in the temperature range of 50 to 65 ° C. under a non-oxidizing atmosphere for a certain period of time. Then
It has been found that by performing an oxidation reaction after that, it is possible to suppress not only the growth of the generated goethite particles in the major axis direction but also the growth in the minor axis direction.

In the method of the present invention, the present inventor believes that the growth of the particle diameter in the minor axis direction can be suppressed as follows.

That is, in the usual reaction for producing goethite particles having a spindle shape, FeCO ₃ is obtained by neutralizing the ferrous salt aqueous solution and the alkaline carbonate aqueous solution.
A suspension containing is produced. When the alkali exceeds 1.0 equivalent, FeCO _{3 in} the suspension reacts and changes to F
It becomes e (OH) ₂ and further reacts to produce FeOOH (goethite) particles. However, FeCO ₃ and Fe (OH) ₂ coexist in the reaction solution during the oxidation reaction, and FeO ₃ FeOO produced when the ratio is high
It can be presumed that the particle size of the H particle grows in the minor axis direction and becomes a spindle-shaped particle having an axial ratio in which the central part of the particle is swollen.

The present inventor has proposed that FeC in the above oxidation reaction
Paying attention to the fact that CO ₂ generated when O ₃ reacts and changes is gasified and discharged to the outside of the reaction system, and to discharge this CO ₂ gas to the outside of the reaction system before the oxidation reaction is performed. I tried.

By maintaining and stirring FeCO _{3 in} the suspension before the oxidation reaction is performed in a non-oxidizing atmosphere, FeCO ₃ in the suspension is reacted to form a reaction system as CO ₂ gas. Discharging outside means that FeCO
Some of ₃ means that the ratio of Fe (OH) ₂ is high for FeCO ₃ was changed to Fe (OH) _2. Fe to FeCO ₃ thus obtained
As a result of carrying out an oxidation reaction by passing an oxygen-containing gas through the suspension having a high ratio of (OH) ₂ , a bulge portion on the minor axis side of the spindle-shaped goethite particles, which is a characteristic of the alkali carbonate-based reaction. Became smaller. This is considered to be the result of suppressing grain growth in the minor axis direction.

Further, by adding alkali hydroxide to alkali carbonate and using both alkalis together, Fe (OH) 2
It is considered that since the alkali ratio of ₂ could be increased, the growth in the minor axis direction could be further suppressed.

Thus, the short axis direction of the goethite particles produced by adding alkali hydroxide to alkali carbonate and using both alkalis together and by maintaining and stirring the suspension in a non-oxidizing atmosphere. Of the present invention by adding a water-soluble silicate that suppresses the growth of the goethite particles in the long axis direction to the suspension after the stirring and suppressing the growth of It was possible to obtain granular goethite fine particles having an excellent particle size distribution.

This can be said to be due to the synergistic effect of the method of using both alkalis, the method of maintaining and stirring in a non-oxidizing atmosphere, and the method of adding a water-soluble silicate to carry out an oxidation reaction.

Next, the production of granular magnetite fine particles according to the present invention using the granular goethite fine particles as precursor particles will be described.

In the reaction for producing the granular magnetite fine particles from the granular goethite fine particles, for example, “... Reactive lepidocrocite particles having high reactivity react with each other to produce granular magnetite core particles in Japanese Patent Laid-Open No. 32324/1993. Then, the growth reaction takes place on the particle surface of the granular magnetite core particles that have already precipitated by reacting the low-reactivity goethite particles. Rarely was it used to produce magnetite particles.

However, in the present invention, due to the large BET specific surface area value of 200 to 300 m ² / g,
As described above, as described in the above “Pigment Dispersion Technology”, “The smaller the particles are, the higher the chemical activity of the particles is.”. Since the granular goethite fine particles having a high activity are used, the granular magnetite fine particles can be easily produced as shown in the examples below.

[0094]

The present invention will be described below with reference to examples and comparative examples.

The BET specific surface area values in Examples and Comparative Examples are MONOSORB MS-11 type (QUATAC).
It was shown by the value measured by HROME.

Particle size of particles, axial ratio (as a measure of sphericalness,
Those having an axial ratio within 1.0 ± 0.2 are considered to be excellent in granular or spherical shape. ) Indicates the average value of the numerical values measured from electron micrographs.

The particle size distribution of the particles is shown by the geometric standard deviation value (σg) obtained by the following method. That is, the particle size of 350 particles shown in an electron micrograph at a magnification of 120,000 is measured, and the actual particle size and the number of particles obtained by calculating from the measured values are calculated according to a statistical method on a log-normal probability paper. The abscissa represents the particle size of the particles, and the ordinate represents the cumulative number of particles belonging to each of the particle size intervals at equal intervals in percentage. Then, the particle diameter values corresponding to the particle numbers of 50% and 84.13% are read from this graph, and the geometric standard deviation value (σg) = major axis diameter (μm) when the number is 50% / number of particles The value was calculated according to the particle diameter (μm) at 84.13%.

The amount of Si contained in the goethite particles or magnetite particles was measured by fluorescent X-ray analysis. Also,
The contents of other elements were also measured by fluorescent X-ray analysis.

The magnetic characteristics of the magnetite particle powder are described in "Vibration sample magnetometer VSM-3S-15" (Toei Industry Co., Ltd.).
Manufactured by K.K.) and applied to an external magnetic field of 5 KOe.

The adsorption capacity was obtained by pressing the particle powders obtained in the examples and comparative examples, crushing them, and crushing them to obtain a particle size of 10 to 20 mesh. Circulation type adsorption rate evaluation device ("Chemical industry data")
vol. No. 20, No. 4, (1985), page 14, evaluation method), and then a tedra bag containing 10 l of a test gas containing hydrogen sulfide having a concentration of 5 ppm was attached to the apparatus. Subsequently, the test gas was circulated by ventilating the sample column at a flow rate of 5 l / min. The circulating test gas was sampled after 120 minutes, and the hydrogen sulfide content concentration in the sampled test gas was shown by the value measured by the gas chromatography method. The smaller the adsorption capacity after 120 minutes, the better the adsorption capacity.

<Production of Goethite Particle Powder> Examples 1 to 4 and Comparative Example 1

Example 1 2.12 mol / l Na was added to a reaction vessel kept at a non-oxidizing atmosphere by flowing N ₂ gas at a rate of 50 l / min.
₂ CO ₃ aqueous solution 14 l and 0.53 mol / l NaO
10 l of H aqueous solution (0.178 mol for Na ₂ CO ₃
Corresponds to. ) Is added (the total amount of Na ₂ CO ₃ and NaOH corresponds to 1.76 equivalents to Fe ²⁺ in the aqueous ferrous salt solution), and then the first content containing 1.33 mol of Fe ²⁺ is added. 15 l of an iron salt aqueous solution (reaction concentration corresponds to 0.5 mol / l) was added and mixed to obtain a suspension containing an iron-containing precipitate at a temperature of 50 ° C.

While continuously blowing N ₂ gas at a rate of 50 l / min into the suspension containing the iron-containing precipitate,
The temperature of this suspension was set to 53 ° C., and the mixture was maintained and stirred for 120 minutes. Then, 1.0 mol / l sodium silicate 0.
2 in terms of Si with respect to Fe ²⁺ in 5l (ferrous salt aqueous solution.
It corresponds to 5 atom%. ) Was added.

Subsequently, 150 l / min of air was bubbled through the suspension for 90 minutes at a temperature of 50 ° C. to produce yellowish brown precipitate particles. The pH value during air ventilation is
It was 9.3 to 9.5.

The yellowish brown precipitate obtained was extracted, filtered, washed with water and dried, and the yellowish brown particle powder was goethite as a result of X-ray diffraction. The electron micrograph (×) shown in FIG.
50000), it consisted of granular particles having an axial ratio of 1.0, and had a particle size of 0.016 μm and a geometric standard deviation value σg of 0.83, which was excellent in particle size distribution. Also, the BET specific surface area value is 203 m ² / g,
Si contained in the granular goethite fine particles was 0.76% by weight.

Examples 2 to 4, Comparative Example 1 Concentration of aqueous ferrous salt solution, type of alkaline carbonate aqueous solution, concentration and usage amount, presence / absence of alkaline hydroxide aqueous solution, type, concentration and usage amount, aqueous ferrous salt solution Alkali ratio to Fe ^{2+ in} the reaction, reaction concentration, atmosphere of reaction vessel (presence or absence of non-oxidizing atmosphere), temperature and maintenance stirring time, kind of water-soluble silicate, addition amount and addition time, water-soluble metal salt Goethite particles were produced in the same manner as in Example 1 except that presence / absence, type, addition amount and addition timing, reaction temperature in the oxidation reaction and air aeration amount were variously changed.

The main manufacturing conditions and various characteristics at this time are shown in Tables 1 to 3.

[0108]

[Table 1]

[0109]

[Table 2]

[0110]

[Table 3]

<Production of Magnetite Particle Powder> Examples 5-8, Comparative Examples 2 and 3;

Example 5 The reaction liquid containing the granular goethite fine particles obtained in Example 1 was bubbled with 50 l / min of N ₂ gas into the reaction vessel to make a non-oxidizing atmosphere, and a yellowish brown precipitate (precipitate) was obtained. In an amount of 1.78 kg in terms of granular goethite fine particles) in a reaction solution containing 7.5 l of 1.33 mol / l ferrous sulfate aqueous solution (50 in terms of Fe of granular goethite fine particles).
Corresponds to% by weight. ) Was added and the liquid temperature was set to 85 ° C.
Next, 2.5 l of 10 mol / l NaOH aqueous solution was added to adjust the pH value to 12.8 to produce ferrous hydroxide colloid, and subsequently, the mixture was heated and stirred at 85 ° C. for 3 hours to produce a black precipitate.

The black precipitate particles thus produced were separated by filtration, washed with water, dried and pulverized by a conventional method. The obtained black fine particle powder was magnetite as a result of X-ray diffraction, and as apparent from the electron micrograph (× 30000) shown in FIG. 2, the particles were particles having an axial ratio of 1.0. The diameter is 0.
The particle size distribution was 028 μm and the geometric standard deviation value σg was 0.82, which was excellent in particle size distribution. Also, the BET specific surface area value is 5
It was 3.2 m ² / g, and Si contained in the granular magnetite fine particle powder was 0.51% by weight.

Comparative Example 2 20 l of an aqueous ferric sulfate solution containing 0.67 mol / l Fe ³⁺ and 0.67 mol / l were placed in a reaction vessel in which 50 l / min of N ₂ gas was passed to make a non-oxidizing atmosphere. 10 l of ferrous sulfate aqueous solution containing Fe ²⁺ (reaction concentration is 0.5 mol / l
And the molar ratio of Fe ³⁺ : Fe ²⁺ = 2: 1. ) And the temperature is raised to 55 ° C., and the mixed iron ion solution is mixed with 20 l of a 2.665 N NaOH aqueous solution at 85 ° C.
aOH corresponds to 1 equivalent to Fe ³⁺ and Fe ²⁺ . )
Was added and stirred, and subsequently, the mixture was heated and stirred in the non-oxidizing atmosphere at a reaction temperature of 80 ° C. for 1 hour to generate black precipitate particles.

The black precipitate particles thus produced were separated by filtration, washed with water, dried and pulverized by a conventional method. The obtained black fine particle powder was magnetite as a result of X-ray diffraction, and as apparent from the electron micrograph (× 50000) shown in FIG. 5, the particles were particles having an axial ratio of 1.0. The diameter is 0.
011 μm, the geometric standard deviation value σg is 0.43, which is inferior to the particle size distribution, and the BET specific surface area value is 98.5 m ² /
g.

Examples 6 to 8 and Comparative Example 3 Type of particles to be treated, reaction temperature atmosphere of reaction vessel in reaction for producing magnetite fine particles, type, concentration and amount of aqueous ferrous salt solution, aqueous alkali hydroxide solution type,
Magnetite particles were produced in the same manner as in Example 5 except that the concentration, the amount used, and the reaction temperature were variously changed.

Table 4 shows the main manufacturing conditions and various characteristics at this time.

[0118]

[Table 4]

[0119]

The granular magnetite fine particle powder according to the present invention is a granular magnetite fine particle powder having a large BET specific surface area and an excellent particle size distribution, as shown in the above-mentioned Examples.

Therefore, the granular magnetite fine particle powder according to the present invention is suitable as a material particle powder for magnetic ink and magnetic toner.

Further, the granular magnetite fine particle powder according to the present invention is suitable as an adsorbent and a deodorant for sulfur oxides, hydrogen sulfide, nitrogen oxides and the like in the air and gas, and
It is also suitable as a material powder for various catalysts.

The granular magnetite fine particle powder according to the present invention is excellent in dispersibility when kneaded with a resin to form a resin molded product or when mixed and dispersed in a vehicle to form a coating material. It is suitable as a granular magnetite fine powder.

[Brief description of drawings]

FIG. 1 is an electron micrograph (× 50000) showing the particle structure of the granular goethite fine particle powder obtained in Example 1.

2 is an electron micrograph (× 30000) showing the particle structure of the granular magnetite fine particle powder obtained in Example 5. FIG.
Is.

FIG. 3 An electron micrograph (× 30000) showing the particle structure of the granular magnetite fine particle powder obtained in Example 6.
Is.

FIG. 4 is an electron micrograph (× 30000) showing the particle structure of the spindle-shaped goethite particle powder obtained in Comparative Example 1.

FIG. 5 is an electron micrograph (× 50000) showing the particle structure of the granular magnetite particle powder obtained in Comparative Example 2.

FIG. 6 is an electron micrograph (× 50000) showing the particle structure of the granular magnetite particle powder obtained in Comparative Example 3.

Claims (1)

[Claims] 1. When a ferrous salt aqueous solution and an alkaline aqueous solution are reacted in a non-oxidizing atmosphere to form a suspension containing an iron-containing precipitate, alkali hydroxide excluding aqueous ammonia is converted to alkali hydroxide excluding ammonium carbonate. The alkali hydroxide is added to either the aqueous solution or the suspension, and the addition amount of the alkali hydroxide is 0.1 to 0.
In the range of 3 mol, the an amount exceeding 1.0 equivalents relative to Fe ²⁺ in said aqueous ferrous salt solution to total amount of both alkali, moreover, Fe ²⁺ of the ferrous salt aqueous solution is the A suspension containing the iron-containing precipitate was prepared by containing the iron-containing precipitate in a concentration range of 0.3 to 0.6 mol / l. The mixture is maintained under stirring in a non-oxidizing atmosphere for 30 to 360 minutes, and then the water-soluble silicate in the suspension is added in an amount of 0.5 to 5 in terms of Si with respect to Fe ²⁺ in the ferrous salt aqueous solution. .0
After adding atomic%, granular goethite fine particles are generated by aerating an oxygen-containing gas in the liquid in the temperature range of 50 to 60 ° C. to perform an oxidation reaction, and then make a non-oxidizing atmosphere, and in this liquid, An aqueous solution of ferrous salt and an aqueous solution of alkali hydroxide are added to react with each other to form an alkaline suspension containing the particulate goethite fine particles and the ferrous hydroxide colloid, and the pH value of the suspension is not higher than 11. A method for producing granular magnetite fine particle powder, which comprises producing granular magnetite fine particles by heating and stirring in a temperature range of 40 to 100 ° C. in an oxidizing atmosphere.