JPH04219323A - Production of goethite - Google Patents

Abstract

PURPOSE:To provide a process for producing an acicular goethite having small axial ratio and uniform particle size distribution. CONSTITUTION:Acicular crystal of goethite having an axial ratio (L/D) of 5-6 and uniform particle size distribution (sigmaL/L=0.4 to 0.5) can be produced by continuously mixing and reacting an aqueous solution of a ferrous salt with an aqueous solution of an alkali using a line mixer, quickly mixing an oxidizing gas into the reaction mixture in the subsequent line mixer to quickly oxidize 7-15% of the hydroxide formed by the former reaction, charging the obtained reaction mixture into a subsequent post-reactor and introducing oxidizing gas into the reactor to complete the reaction.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method for producing acicular goethite with a uniform particle size distribution and a small axial ratio L/D, particularly for use in 8mm video tapes, high-grade audio tapes, and high-definition tapes that require high recording density. The present invention relates to a method for producing goethite (FeO.OH), which is suitable as a raw material for magnetic recording materials that require excellent magnetic properties, such as those for tapes.

0002

BACKGROUND OF THE INVENTION When powder raw materials are processed into useful products, the properties resulting from their particle morphology play an important role. In magnetic materials as well, the influence of goethite particles, which are the starting materials, greatly influences the properties of the magnetic materials obtained from them. Many studies have been made regarding this kind of shape control, but the most effective devices for controlling the shape are a ring-shaped perforated nozzle or a device equipped with a perforated plate with many ventilation holes at the bottom. It was common to oxidize ferrous hydroxide to goethite by blowing air, mixing the system and turbulent diffusion.

[0003] When producing goethite particles, the chemical reaction that occurs is expressed by a very common reaction formula of inorganic chemistry.
Technically speaking, it seems not to be that difficult, but the particles that become the product are: ■ Ingredients and composition (expressed in weight ratio of metal components) ■
Specific surface area (1) Particle size distribution (coefficient of variation: expressed as σL/L [-]), and (2) Shape (axial ratio; expressed as L/D [-]) need to be controlled so that they become predetermined values.

[0004]However, while a general chemical product can be manufactured by focusing only on item (■), these particles
For example, Fe:Ni=100:0.5 (weight ratio), specific surface area: S=35±1.8, coefficient of variation: σL/L=0.5
5±0.05, axial ratio; L/D=11±1 (L: long axis, D
: short axis), etc., and manufacturing is required to be controlled so as to satisfy the particle morphology conditions of ■, ■, and ■ in addition to ■.

Although the target chemical reaction itself is simple, the phenomena that actually occur during the generation and growth of particles are at least the gas phase of air, the liquid phase of the reaction liquid, and the solid phase of ferrous hydroxide. −
1. It is a heterophasic reaction involving four phases consisting of solid phase-2 of goethite, and it is an extremely complex phenomenon in which the size, shape, and number of particles change simultaneously over time. Therefore, it has been difficult to produce particles with a predetermined shape with good reproducibility or to develop particles with excellent performance using a mere empirical or qualitative method using the general equipment as described above.

[0006]

[Means for Solving the Problems] In view of the above-mentioned problems, the present inventors have made extensive studies and have discovered the following fact, and have arrived at the present invention. In other words, as a result of using the largest possible reactor and quantitatively organizing the complex phenomena taking place within the reactor, we found that the initial oxidation reaction rate has a decisive influence on the above factors. They discovered the surprising fact that

That is, when goethite is produced by oxidizing the hydroxide obtained by reacting a ferrous salt aqueous solution with an alkaline aqueous solution, the oxidation rate can be determined by measuring the total Fe concentration and the amount of change from Fe2+ to Fe3+. A time-dependent change curve is taken, and when this is used to determine the time-dependent change in the number of particles and the time-dependent change in the axial ratio L/D for various forms of change over time at various oxidation rates, and compared with the results,
It has been found that the faster the oxidation is performed immediately after the start of the oxidation reaction, the smaller the change over time in both the number of particles and the axial ratio L/D until the end of the reaction, the smaller the axial ratio, and the more uniform the particle size distribution.

This means that the more quickly oxidation occurs immediately after ferrous hydroxide is generated, the more Fe2+→
The reaction of Fe3+ progresses rapidly and the surface is covered with goethite, which stops the growth of ferrous hydroxide particles and prevents aggregation with other particles, resulting in uniform particles with a small axial ratio of the goethite particles. It is thought that. However, when carrying out such a reaction, even if a large amount of raw materials are charged all at once into a reactor in a short period of time to achieve the desired rapid oxidation, there is a limit on an industrial scale where the amount of liquid is large.
Adding and mixing 0 tons of raw materials in a few minutes or less not only leads to an increase in the size of the equipment, piping, and valves, but also makes it difficult to remove the reaction heat generated in a short period of time, which is not practical.

[0009] In order to solve this problem, the present inventors
It has been found that if the reaction is carried out in the following manner, raw materials can be charged into the batch reactor relatively slowly, and scale-up to an industrial level is possible.

That is, the present invention provides a method for producing goethite by oxidizing a hydroxide suspension obtained by reacting a ferrous salt aqueous solution with an alkaline aqueous solution with an oxidizing gas. After the aqueous solution and alkaline aqueous solution are continuously mixed and reacted in a line mixer, oxidizing gas is immediately mixed in the next line mixer, and 7 to 15% of the hydroxide produced in the previous reaction is continuously mixed. After rapidly oxidizing to
The obtained reaction mixture was charged into the next post-reactor, the remaining reaction was completed by passing oxidizing gas, and the axial ratio L/D = 5.
The present invention provides a method for producing high-performance goethite, which is characterized by obtaining needle-like crystals with a uniform particle size distribution (σL/L=0.4-0.5) of .about.6.

The present invention will be explained in detail below. To explain the structure of the present invention, in the present invention, the first
An aqueous iron salt solution and an aqueous alkaline solution are continuously supplied to a line mixer at a predetermined flow rate ratio to cause a mixing reaction and obtain a hydroxide suspension. The heat of neutralization accompanying the reaction is removed by providing a jacket on the line mixer and using a refrigerant, or by passing it through a cooler provided after the line mixer.

In the present invention, in order to immediately mix and react the hydroxide suspension obtained in the first stage with the oxidizing gas at a predetermined flow rate ratio, No. No. 1 following the 1-line mixer 12 and cooler. The liquid is passed through the 2-line mixer 13. The transition from the first stage reaction to the second stage reaction is preferably carried out within 5 minutes. It is not preferable to leave the ferrous hydroxide as it is for more than 5 minutes, since the hydroxide will cause crystal growth and/or agglomeration of crystals during that time, making it no longer possible to achieve the purpose of rapid oxidation.

[0013] Furthermore, the oxidation reaction by the line mixer is 2
It is desirable to oxidize 7-15% of the oxide in ~15 minutes. If it takes more than 15 minutes, it is not preferable because crystal growth and/or aggregation of crystals may occur before the surface of the ferrous hydroxide is completely covered with goethite particles. In addition, the axial ratio
Although this does not deviate from the purpose of reducing /D, it is not preferable to carry out economically on a large-scale industrial scale. On the other hand, if the oxidation of the hydroxide is less than 7%, the surface will not be completely covered with goethite particles, which is not preferred for the same reason as mentioned above. Further, it is not necessary to oxidize to 15% or more since the surface of the hydroxide is completely covered with goethite particles for the purpose of rapid oxidation. In the present invention, a predetermined amount of the intermediate reaction solution obtained through the neutralization and oxidation steps in the first-stage flow system is charged into a batch reactor, and the remaining reaction is carried out in a conventional oxidation method.

In the present invention, the Fe2+ ion concentration of the ferrous salt aqueous solution used in the reaction is preferably about 10 to 50 g/l. Lower concentrations are advantageous for rapid oxidation, but
Industrially, it is not preferable to use less than 10 g/l because the volumetric efficiency decreases. On the other hand, if it is too high than 50 g/l, it is advantageous in terms of volumetric efficiency, but it becomes difficult to achieve the rapid oxidation that is a feature of the present invention, which is not preferable.

In the present invention, the lower the reaction temperature, the faster the oxidation rate and the easier it is to achieve the object of the present invention, but it is not economical in terms of energy to use a low-temperature refrigerant.
The temperature is preferably about 50°C. Although there is an optimum value for the oxidizing gas such as air depending on the reaction conditions, it is preferable to aerate in an amount sufficient to replenish the consumption of dissolved oxygen by the normal reaction.
The range is preferably 1 for the above Fe2+ ion concentration.
It is about 00 to 200 Nm3/hr·Kg mol Fe2+. In the present invention, rapid oxidation usually refers to an amount of oxidizing gas passed at least above this lower limit, but methods such as pressurizing the system or increasing the oxygen concentration are also effective in achieving rapid oxidation. be.

Also, during the reaction, Ni, Cr, Al, Mn, Co, Zn, Ti, Si are present as coprecipitates in the ferrous salt aqueous solution.
, one or two of sulfates or nitrates such as Mg
It is preferable to add about 0.3 to 3 parts per 100 parts of e2+ ions. Further, the optimum range of the rapid oxidation time and degree of oxidation should be determined depending on the composition, concentration, reaction temperature, etc. of the raw materials.

[0017]

EXAMPLES Next, examples will be explained in more detail with reference to the drawings. Example 1 A caustic soda aqueous solution (concentration 1.8 mol/l) was passed through the caustic soda aqueous solution supply line 1 at a rate of 14 m3/hr.
In addition, a ferrous sulfate aqueous solution containing nickel nitrate (0.0003 mol/l) and zinc sulfate (0.0002 mol/l) (
Concentration: 0.226 mol/l) was fed at 14 m3/hr through the ferrous sulfate aqueous solution supply line 2 to the No. 1 tube equipped with a jacket cooler. Supplied to a 1-line mixer 12 (residence time 15 seconds). Refrigerant enters through inlet 8 and exits through outlet 9.

Next, No. 1 with a jacket cooler having a refrigerant inlet 10 and a refrigerant outlet 11 was installed. 2 line mixer 1
3 (residence time 13 minutes), the above mixture was added to No. 3 (residence time 13 minutes). Air from 2-line mixer air supply line 3 2.0Nm3
The outlet liquid, which has completed the prescribed reaction, is fed through the reaction vessel supply line 4 into a reaction vessel 14 with an internal volume of 8 m3 equipped with temperature control means and stirring means, and air is supplied at a rate of 2.0 Nm3 /min. Blowing into the reaction vessel 14 from a gas supply means 15 concentrically arranged around the bottom of the reaction vessel 14 via the reaction vessel air supply line 5,
The remaining oxidation reaction proceeded. Note that the reaction vessel 4 is equipped with a reaction slurry outlet 6 and a gas vent 7. From the first stage neutralization reaction to the second stage oxidation reaction, the temperature was 35
It was maintained at ±0.5°C.

The content of iron [II] in the suspension was determined by automatic titration using potassium permanganate to measure the divalent iron concentration and determine the oxidation rate while the reaction progressed and the suspension turned bright yellow. At that point, the supply of oxidizing gas was stopped. The oxidation rate at this time exceeded 99.7%. The container was exposed to atmospheric pressure and left for 1 hour with stirring. The viscosity after standing was 350 centipoise as measured with a B-type viscometer. The total oxidizing gas supply time in the vessel was 40 minutes. The slurry consisted of acicular goethite particles, and was washed with water and then sieved to obtain a wet cake.

[0020]

[Effect of the invention] According to the method of the present invention, it is possible to obtain acicular goethite with a uniform particle size distribution and a small axial ratio L/D. It can be carried out slowly and is suitable for industrial level production.

[Brief explanation of the drawing]

FIG. 1 is a schematic illustration of an apparatus for explaining the implementation of the method of the invention.

[Explanation of symbols]

1 Caustic soda aqueous solution supply line 2 Ferrous sulfate aqueous solution supply line 3 No. 2 line mixer air supply line 4
Reaction vessel supply line 5 Reaction vessel air supply line 6 Reaction slurry outlet 7 Gas vent 8, 10 Refrigerant inlet 9, 11 Refrigerant outlet 12 No. 1 line mixer 13 No. 2-line mixer 14 Reaction vessel 15 Concentric gas supply means

Claims (1)

[Claims] 1. A method for producing goethite by oxidizing a hydroxide suspension obtained by reacting a ferrous salt aqueous solution and an alkaline aqueous solution with an oxidizing gas, comprising:
After continuously mixing and reacting the iron salt aqueous solution and the alkaline aqueous solution in a line mixer, oxidizing gas is immediately mixed in the next line mixer, and 7 of the hydroxides produced in the previous reaction are mixed.
After continuous rapid oxidation of ~15%, the resulting reaction mixture was charged into the next post-reactor and the oxidizing gas was bubbled through to complete the remaining reaction, resulting in an axial ratio L/D=5~ 6. A method for producing high-performance goethite, which is characterized by obtaining acicular crystals with a uniform particle size distribution (σL/L=0.4 to 0.5).