JPH035326A - Reactor and production of goethite - Google Patents

Abstract

PURPOSE:To improve the uniformity in the grain size distribution of the goethite by supplying an aq. ferrous salt soln. and an aq. alkaline soln. to the reactor provided with an agitating means, a liq. flow control cylinder and a gas introducing means and supplying an oxidizing gas while agitating the solns. to oxide CONSTITUTION:N2 is supplied into the reactor from a gas sparger 5 to replace the internal atmosphere with N2. An aq. alkaline soln. of NaOH, etc., is then supplied from an alkali hydroxide supply port 7, and an aq. soln. of a ferrous salt such as FeSO4 is added from a supply port 6, the solns. are agitated, and air is simultaneously introduced from the gas sparger 5. The liq. reactant is kept at 40 deg.C and oxidized at the rate of 5%/min until when initial 30% oxidation is completed. The amt. of air to be introduced is then decreased, and the oxidation is allowed to proceed at the rate of 3%/min to convert the hydroxide to goethite. After oxidation is finished, the mixture is agitated for about one hour in the atmosphere, and the liq. reactant is discharged from a discharge port 8 and filtered. The precipitate is washed with water and then dried to obtain the fine grains having uniform mol.wt. distribution and having >=100m<2>/g specific surface.

Description

Detailed Description of the Invention [Technical Field] The present invention relates to a stirred tank type gas-liquid mixing reactor and a method for producing fine acicular goethite with a uniform particle size distribution using the reactor, and in particular to a method for producing fine acicular goethite with a uniform particle size distribution. The present invention relates to an apparatus and method for producing goethite suitable as a raw material for recording materials.

"Background technology" When processing powder raw materials into useful products, the properties resulting from the particle form play an important role.In magnetic materials as well, goethite (iron oxyhydroxide), which is the starting material, plays an important role. The morphology of the particles greatly influences the properties of the magnetic recording material obtained from them. Although many studies have been made regarding such morphology control, it has been said that the most difficult task has been to make the particle size and particle size distribution uniform.

As a method for making the particle size distribution uniform, for example,
-21720, JP-A No. 53-56196, JP-A-5
3-53200, JP 53-75199, JP 54-20998, JP 54-79200, JP 54-93697, JP 51-86795, JP 52- No. 59095, JP-A No. 52-59096,
Methods described in publications such as JP-A-52-59097, JP-A-56-22637, and JP-A-56-22638 are known. Broadly speaking, these can be divided into (a) Tokuko Sho 5;
2-21720, a method of vigorously stirring for several hours in a non-oxidizing state to form a uniform hydroxide and then oxidizing it to goethite; (b) JP-A-53-56196, JP-A-53-57200, JP-A-53-75199,
JP-A-54-20998, JP-A-54-79200, JP-A-54-93697, etc. disclose methods of forming uniform flocs of hydroxide by carrying out a neutralization reaction in the coexistence of soluble silicate. A method of achieving uniformity and then carrying out a uniform production reaction of acicular goethite particles, (c) JP-A-51
-86795, JP-A No. 52-59095, JP-A No. 52-59095
No. 2-59096, JP-A No. 52-59097, etc. A method of oxidizing ferrous hydroxide to goethite by limiting the oxidation rate, (d) JP-A No. 56-22637, JP-A-Sho. No. 56-22638 and the like disclose a method using seed crystals prepared at room temperature. However, method (a) requires strong stirring for several hours, preferably 2 to 4 hours, and this stirring method alone is insufficient to homogenize the flocs consisting of non-uniform hydroxide primary particles. difficult to do. In the method (b), the soluble silicate used has an St of 0.1 to 1.
It is necessary to use 7 atomic percent, and since goethite incorporates silicate and becomes the same form as if it had been diluted with silicate, the magnetic properties of iron powder obtained by reducing it by a conventional method In method (c), the oxidation rate must be slowed down and various changes must be made in the goethite manufacturing process, which requires time, and slowing down the oxidation rate leads to particle growth. In the method (d), which cannot overcome the problem of particle miniaturization required as a characteristic of high-density recording materials, although seed crystals are used, the reaction conditions, especially the temperature conditions, are not strictly controlled. If not managed, there is a danger that magnetite will be generated more than goethite. Furthermore, due to the long reaction time of these known techniques, the resulting goethite particles grow large;
The specific surface area (hereinafter referred to as SA) determined by the BET method is 4On (
/g or less, making it difficult to obtain magnetic materials for high-density recording.
Techniques for efficiently manufacturing magnetic materials for high-density recording of 00rrf/H, for example, Japanese Patent Application Laid-Open No. 57-209834,
JP-A-58-32028, JP-A-58-140327
．． The technology was disclosed in Japanese Patent Application Laid-open No. 59-18119.

However, performance requirements for magnetic materials are progressing faster than actual technology progress, and materials for even higher density recording are required. For example, those used in high-definition television video tapes are required to have a specific surface area of 10 On/g or more and an aspect ratio of long side/short side of magnetic material particles of 10 or less, for example, about 7. is a further dramatic improvement on the technology previously filed by the applicant, and makes it possible to stably produce a magnetic material for high-density recording having a specific surface area of 100n(/g or more). In other words, in order to make goethite finer and have a more uniform particle size distribution, it is sufficient to perform Sakae and Sokubrewing, but the need to increase the oxidation rate was disclosed in Japanese Patent Application Laid-open No. 59-181190, which discloses only the technique for obtaining goethite having a specific surface area of less than 100r+(/g). In order to obtain goethite, a fast oxidation reaction rate is required, which is difficult to achieve stably using the stirred tank reactor or bubble column reactor used in conventional technology. .

"Basic idea of the invention" The present invention was made in view of the above requirements, and it is possible to achieve stable high-speed oxidation by improving the contact between the oxidizing gas and the object to be oxidized. I found out.

More specifically, by using a specific reaction device to improve the contact between the oxidizing gas and the oxidized material, and by increasing the reaction rate at the initial stage of the oxidation reaction and achieving high-speed oxidation, the specific surface area is 100n ( The basic idea of the present invention lies in the discovery that fine goethite with a particle size of 1.2 g or more can be stably obtained.

``Detailed Disclosure of the Invention'' That is, the present invention provides a reaction apparatus suitable for producing fine goethite that has been improved to dramatically improve the contact state between gas and liquid, and production of fine goethite using the apparatus. It's a method.

The present invention is a reaction device equipped with a stirring means having at least two or more stages of stirring blades, a liquid flow control cylinder, and a gas introduction means inside a stirred tank reactor, and a reaction device in which goethite is produced using the device. This is a manufacturing method.

As a preferred method for producing goethite, a ferrous salt aqueous solution is added to a reactor equipped with a stirring means having at least two or more stages of stirring blades, a liquid flow control tube, and a gas introduction means inside a stirred tank reactor. This method for producing goethite is characterized by supplying and stirring an aqueous alkaline solution and oxidizing it by supplying an oxidizing gas from a gas introducing means.

A feature of the present invention is that it is a reaction apparatus in which the contact state between gas and liquid is extremely improved, and that by using this reaction apparatus, goethite that is fine and has an excellent uniformity of particle size distribution can be produced.

The present invention will be described below with reference to the drawings.

FIG. 1 shows an example of a reactor according to the present invention. Reference numeral 100 in FIG. 1 shows an example of a stirred tank type reactor. 1 is a stirrer, and stirring blades II 2 and stirring blades 3 are attached in two stages. Preferably, the stirring blades 2 are of the propeller type, and the stirring blades 3 are of the turbine type. The propeller-type blades are preferably used to efficiently circulate the reaction liquid inside and outside the liquid flow control cylinder 4. In the case of FIG. 1, the reaction liquid rises in the liquid flow control cylinder 4, flows downward on the outside thereof, and circulates up and down inside the reactor as a whole. The turbine-type stirring blade 3 is provided in order to efficiently disperse and dissolve the gas supplied from the gas introducing means into the reaction liquid. A liquid flow control tube 4 is provided surrounding the stirring blade and concentrically with the stirrer shaft and the reactor. The liquid flow control cylinder acts as a draft tube and effectively assists the rise of the reaction liquid. One of the features of the present invention is that the use of the liquid flow control cylinder is effective in dispersing gas and liquid, and that the power of the stirrer can be kept low. For example, in the case of a reactor having an internal volume of IIK-II as shown in the Examples below, in order to obtain the stirrer rotation speed of 112 to 450 PPM necessary to sufficiently increase the oxidation rate, An electric motor with moderate power is sufficient. Preferably, a baffle plate is installed inside the liquid flow control cylinder in order to improve the stirring state of the reaction liquid. Liquid flow system? A pipe-shaped gas introduction means 5 is provided at the bottom of the 11-piece. Preferred gas introduction means include:
Holes with a diameter of 2 to 5III11 are drilled downward at equal intervals of 5 to 10 m on the circumference of the pipe (hereinafter referred to as a ring sparger).

This ring sparger is connected to the respective gas supply sources so that both oxidizing gases such as air and oxygen as well as non-oxidizing gases such as nitrogen and inert gases can be supplied to the reaction liquid. Since it is possible to instantly switch and introduce oxidizing gas and non-oxidizing gas, which is preferably present, it is possible to precisely control the temporal change in oxidation rate from the beginning of the oxidation reaction to the end. It is also one of the features of the present invention that it can be done. In addition, the upper part of the reactor is provided with a feed port for raw materials such as ferrous salt and alkali hydroxide, and an exhaust hole (not shown), and the bottom of the reactor is provided with an outlet for taking out the reaction liquid. As a temperature control means for the reactor, a water cooling jacket is preferably attached to the reactor outer cylinder, and although not shown, it is also preferable that a steam inlet for heating is also provided. Water vapor is directly introduced into the reaction liquid to enable rapid heating, and it is designed to be practical as a manufacturing device so as to shorten heating time.It also enables pressurized reactions. Therefore, it is preferable to design the reactor of the present invention in consideration of pressure resistance so as to be able to maintain a pressurized state of several kg/ctAG. This is because performing the oxidation reaction under pressure can avoid flooding of oxidizing gas (hereinafter referred to as oxidizing gas), as disclosed in JP-A-59-18119. This is because the conveniences such as being able to use it efficiently and increasing the oxidation rate, (1) requiring a relatively low amount of alkali hydroxide, and (2) widening the reaction temperature range can also be utilized in the present invention.

The present inventors have found that in order to obtain goethite with a specific surface area of 100rrf/g or more and a uniform particle size distribution, the oxidation rate is 30%.
% or less, the time change in reaction rate is controlled to perform high-speed oxidation of at least 3%/min or more, preferably 5%/min or more. This rate of change is determined by the specific surface area of goethite. Note that the present invention does not aim at obtaining goethite with a specific surface area of less than 100rd/g, but it is intended to obtain goethite with a specific surface area of less than 10.0rd/g as described in the applicant's previous invention. This does not prevent you from obtaining the site in any way. Another feature of the present invention is that goethite with a uniform particle size distribution and a specific surface area of less than 100 rd/g can be effectively obtained by controlling the time change in the reaction rate of the oxidation reaction to be low.

In the present invention, the ferrous salt is a water-soluble iron salt, and sulfates, hydrochlorides, nitrates, etc. are effective, and they are used alone or in combination of two or more.

The quality of these products is sufficient for industrial production.
The effects of the present invention can be exhibited. Furthermore, it is effective as a raw material pretreatment method of the present invention to filter the first fertile salt aqueous solution in which these are dissolved in water through a half-stage ultrafiltration to remove finely insoluble substances. It goes without saying that the present invention, which guarantees stable production of iron, is effective in the reaction of iron alone, but it does not in any way prevent the coexistence of components other than iron, such as nickel, zinc, manganese, It is also effective in producing goethite containing these metal components by oxidizing hydroxides obtained by co-precipitation of chromium and the like. The coexistence of components other than iron has a secondary effect on the shape, specific surface area, etc. of the goethite obtained, and does not impede the effects of the present invention, but may in fact promote the effects.

The alkali hydroxide used in the present invention may be any one as long as it reacts with ferrous salt to produce hydroxide. For example, aqueous solutions of potassium hydroxide, sodium hydroxide, etc. can be effectively used. can.

In the present invention, the oxidizing gas is a gas containing oxygen,
Specifically, oxygen, air, or a mixed gas obtained by diluting these with nitrogen, water vapor, or the like can also be effectively used.

In the present invention, there are no particular limitations on the production conditions for goethite, except for controlling the change in oxidation rate over time in the oxidation reaction of hydroxide.The reaction temperature and reaction pressure are secondary. However, the present invention allows precise control of these manufacturing conditions. For example, if the reaction temperature is lowered or the reaction pressure is increased, the specific surface area of goethite will increase.The reaction temperature is 20-60°C.
The reaction pressure is preferably between 30 and 50°C and is between atmospheric pressure and 50°C.
kg/cjG is sufficient.

"Example 1" A reaction device (hereinafter referred to as the reaction device) was used, which was equipped with a stirring means having at least two or more stages of stirring blades, a liquid flow control tube, and a gas introduction means inside a stirred tank reactor. We carried out the production of game site. Internal volume used: 5rrr
A sectional view of the reactor is schematically shown in FIG. 1. The inside of the reactor was purged with nitrogen by supplying nitrogen from a gas sparger 5. Then, 690 L of an aqueous sodium hydroxide solution (concentration 14.3 mat/L) was added from the alkali hydroxide supply lower. Ferrous sulfate aqueous solution (contains 3 mol and 1 mol of nickel nitrate and zinc sulfate, respectively, per 100 mol of ferrous sulfate, concentration 0.55)
361OL of 4 mol/L) was added from the ferrous salt supply port 6, and air was introduced from the gas sparger 5 at the same time as stirring was started. The oxidation rate was maintained at a time change of 5%/min until the initial 30% oxidation, and then the amount of air introduced was reduced to allow the oxidation reaction to proceed at a rate of 3%/min to convert hydroxide to goethite. I forced it. The temperature of the reaction solution was maintained at 40° C. during the progress of the oxidation reaction. At the end of the reaction, the suspension changed from yellow-brown to bright yellow, confirming that the oxidation reaction was complete. After stirring in the atmosphere for 1 hour, the reaction solution was taken out from the reaction solution outlet 8, filtered, washed with water, and dried at 120"C. This goethite had a specific surface area (by BET method, the same hereinafter) of 102 rrf /g of fine particles,
It had a highly uniform particle size distribution in which the standard deviation of the variation in major axis length/the length of major axis was 0.38.

Furthermore, when the particles were observed using a transmission electron microscope at a magnification of 100,000 times, almost no twins or resin-like particles were observed in the particles.

"Example 2" In Example 1, zinc sulfate was not added and the oxidation rate was changed over time from the initial stage to the end of the reaction at 5%/min, and the reaction temperature was maintained at 35 °C. The other manufacturing conditions were the same as in Example 1.

This goethite is a fine particle with a specific surface area of 106 rrf/H, and the standard deviation of variation in long sleeve length/long axis length is 0.
．． It had a very uniform particle size distribution of 36 mm. Furthermore, when the particles were observed using a transmission electron microscope at a magnification of 100,000 times, almost no twins or resin-like particles were observed in the particles.

"Example 3" In Example 1, zinc sulfate and nickel nitrate were not added, and the oxidation rate was changed over time to 50% from the initial stage.
The rate was 10%/min until the end of the reaction, and then 5%/min until the end of the reaction. To perform a time change of reaction rate of 10%/min, the 0 reaction temperature with oxygen as the oxidizing gas is 3
0'C was maintained. The other manufacturing conditions were the same as in Example 1. This goethite has a specific surface area of 101 rrr/
g of fine particles, and had an extremely uniform particle size distribution in which the standard deviation of variation in long sleeve length/long axis length was 0.39. In addition, when the particles were observed using a transmission electron microscope at a magnification of 10,000 times, almost no twins or resinous particles were observed in the particles.

"Effects of the Invention" As is clear from the above examples, the present invention can be used as a magnetic recording material for high-quality television by performing a high-speed oxidation reaction using a stirred reactor equipped with a liquid flow control tube. This is an excellent method for producing goethite with fineness of 100 rd/g or more and excellent uniformity of particle size distribution, which satisfies performance requirements.The present invention is also a useful technology for controlling the morphology of various fine particles. . That is, metal oxide catalysts,
High-performance ferrite products, pigments for printing inks, magnetic pigments,
This technique is also useful in producing functional particles used in paper-making fillers, photosensitive materials, electrode materials, etc.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of an embodiment of the present invention.
In the figure, 100-...-- Stirred tank reactor, l...
-・・・・・・Stirrer, 2−・・・・・Propeller type stirring blade, 3−・・・・・・Turbine type stirring blade, 4 Liquid flow control cylinder , gas introduction means (gas sparger), 6 ferrous salt supply port, 7 ...... - alkali hydroxide supply port, 8 removal of reaction liquid Show mouth. Drawing figure 1

Claims (2)

[Claims] (1) A reaction device equipped with a stirring means having at least two or more stages of stirring blades, a liquid flow control cylinder, and a gas introduction means inside a stirred tank reactor. (2) A ferrous salt aqueous solution and an alkali aqueous solution are placed in a reactor equipped with a stirring means having at least two or more stages of stirring blades, a liquid flow control tube, and a gas introducing means inside a stirred tank reactor. A method for producing goethite, which comprises supplying and stirring an oxidizing gas from a gas introduction means for oxidation.