JPH0323225A - Production of goethite - Google Patents

Abstract

PURPOSE:To obtain goethite reduced in the changes with the lapse of time until the conclusion of reaction in the number of particles and specific surface area, increased in specific surface area, and having uniform particle size distribution by carrying out rapid oxidation directly after the initiation of reaction at the time of oxidizing a hydroxide formed by allowing an aqueous alkali to react with an aqueous solution of ferrous salt. CONSTITUTION:In a method for producing goethite by oxidizing a suspension of hydroxide prepared by allowing an aqueous solution of ferrous salt and an aqueous alkali to react with each other by means of an oxidizing gas, rapid oxidation is carried out based on the curve of the change in the rate of oxidation from Fe<2+> ions to Fe<3+> ions with the lapse of time directly after the initiation of the reaction, by which acicular crystals having 100-120m<2>/g specific surface area and uniform particle size distribution (sigmaL/L<=0.4) are obtained. By carrying out rapid oxidation as first as possible directly after the initiation of oxidizing reaction as mentioned above, goethite reduced in the change in specific surface area as well as in the number of particles with the lapse of time until the conclusion of reaction, increased in specific surface area, and having uniform particle size distribution can be obtained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for producing acicular goethite with a uniform particle size distribution and a large specific surface area.
This invention relates to a method for producing goethite, which is suitable as a raw material for magnetic recording materials that require excellent magnetic properties, such as for video tapes, high-end audio tapes, and high-visibility tapes. [Prior Art and RH] When processing powder raw materials into useful products, the characteristics resulting from the particle morphology play an important role. Even in magnetic materials, 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 type of morphology control, but among them, it is extremely difficult to achieve a specific surface area (hereinafter referred to as Se) of 100 rrf/g or more and a uniform particle size distribution using the BET method. there were. As a method of making the particle size distribution uniform, for example, (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 make goethite; (b) JP-A-53-56196;
No. 3-57200, No. 53-75199, No. 54-2
No. 0998, No. 54-79200, No. 54-9369
In Publication No. 7, etc., a neutralization reaction is carried out in the coexistence of soluble silicate to homogenize a floc of uniform hydroxide, and then a reaction is carried out to uniformly produce acicular goethite particles. Method, (c) JP-A-51-86795, JP-A No. 52-59095
No. 52-59096, No. 52-59097, etc. describe a method of oxidizing ferrous hydroxide to goethite by limiting its oxidation rate to goethite. Kaisho 56-22637, Kaisho 56-2263
Publications such as No. 8 describe methods using seed crystals prepared at room temperature. However, method (a) requires strong stirring for several hours, preferably 2 to 4 hours, and it is difficult to sufficiently homogenize the flocs consisting of uneven ferrous hydroxide particles using only this stirring means. is difficult. In the (b) method, the soluble silicate used is 0.1 to 0.1 to Pe as Si.
It is necessary to use 1.7 at%, and since goethite incorporates silicate and becomes the same form as if it had been diluted with silicate, the magnetic properties deteriorate. In method (c), the oxidation rate must be varied in the dacite production process, which is time consuming and requires delicate control of the oxidation rate. (2) Although seed crystals are used in the method,
Problems include the risk of producing magnetite rather than goethite unless the reaction conditions, especially temperature conditions, are strictly controlled. Furthermore, in these known techniques, the reaction time is long, so the goethite particles obtained are greatly lengthened, and Se=4
It was difficult to produce goethite with a specific surface area of 50r+{/g or more. On the other hand, as a method to increase the specific surface area, (e) JP-A No. 5
As described in No. 9-18119, a hydroxide obtained by reacting a ferrous salt aqueous solution with an alkali aqueous solution is oxidized in a pressurized atmosphere to Se = 50 to 100n.
? Although a method for producing goethite having S/g has been described, there is a limit to making Ss sufficiently large. Furthermore, with known techniques, it is difficult to increase the specific surface area and make the particle size distribution uniform. When the specific surface area is increased, the particle size distribution cannot be controlled, and when the particle size distribution is made uniform, the specific surface area cannot be increased. The chemical reactions that occur during the production of goethite particles are expressed by common inorganic chemistry reaction formulas, and are not technically difficult, but the particles that become the product are (Represented by weight ratio of metal precepts) ■ Specific surface area ■ Particle size distribution (coefficient of variation: σL/L (expressed)), ■ Shape C
It is necessary to control the M ratio (L/D (expressed as 1)) to a predetermined value. However, if it is a general chemical product, it is only necessary to manufacture it by focusing on the
e: Ni-100: 0.5 (IT amount ratio)
, specific surface area: Se=35±1.8, coefficient of variation: σL
/t. -o. ss±0.05, axial ratio; L/D −1
Values such as 1±I (see Fig. L) are specified, 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 while particles are being produced and produced are at least the gas phase of air, the liquid phase of the reaction liquid, and the solid phase of ferrous hydroxide. It is a heterophasic reaction involving four phases consisting of the solid phase-2 of goethite, and the size, shape, and number of particles also change over time. j[It is a complicated phenomenon. Therefore, it has been difficult to produce particles with a predetermined morphology with good reproducibility or to develop particles with excellent performance using purely empirical or qualitative methods. (Means for Solving !III!) 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. As a result of quantitatively organizing the complex phenomena taking place within the reactor, they discovered the surprising fact that the initial oxidation reaction rate has a decisive influence on the above factors. .That is, the first
When goethite is produced by oxidizing the hydroxide obtained by reacting an aqueous iron salt solution with an aqueous alkaline solution, the oxidation rate change curve over time is determined by measuring the total Fe concentration and the amount of change from Fe″′ to Fe′°. , and then calculate the changes over time in the number of particles and the change in specific surface area over time for various forms of changes over time in the oxidation rate, and compare them with the results.The faster the oxidation is performed immediately after the start of the oxidation reaction, the greater the increase in both the number of particles and the specific surface area. It has been found that the change over time until the reaction is completed is small, the specific surface area is large, and the particle size distribution is uniform.In other words, the present invention provides a hydroxide obtained by reacting a ferrous salt aqueous solution with an alkali aqueous solution. In the method for producing goethite by oxidizing a suspension of
Based on the time-course curve of the oxidation rate to iron ions, rapid oxidation is performed immediately after the start of the reaction to increase the specific surface area l00 to 120.
Uniform particle size distribution at ryf/g (σL/L < 0.4)
The present invention provides a method for producing goethite, which is characterized by obtaining needle-like crystals. The present invention will be explained in detail below. To explain the structure of the present invention, in the present invention, p e ! of the ferrous salt aqueous solution used in the reaction! +Ion concentration is 10-50g/j! A certain degree is desirable. A lower concentration is advantageous for rapid oxidation, but from an industrial perspective, it is not preferable to have a concentration of less than 10 g/1 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 is not preferable because the rapid oxidation, which is a feature of the present invention, becomes difficult. In the present invention, the lower the reaction temperature, the faster the oxidation rate and the easier it is to achieve the purpose of the present invention, but since 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 an amount sufficient to replenish the consumption of dissolved oxygen by the normal reaction, and the range is within the range of the above Fe" ion concentration. Te100~2
00N rtt/hr - Kg mol F1°. In the present invention, rapid oxidation refers to an amount of oxidizing gas that is at least greater than this lower limit, but methods of pressurizing the system or increasing the oxygen concentration are also effective ways to achieve rapid oxidation. In addition, during the reaction, Ni, Cr,^1, Mn, CoSZn. ．． T
I. ．． One or two types of sulfates or nitrates such as Si, Mg, etc. are added to 0.3 parts per 100 parts of p e f 4 ions.
It is preferable to add about 3 parts. Further, the optimum range of rapid oxidation time should be determined depending on the composition, concentration, reaction temperature, etc. of the raw materials, but usually about 10 to 30 minutes is desirable. Next, this will be explained in more detail with examples. Example I A caustic soda aqueous solution (concentration 1
．． 8 mol/j! ) Added 3.5 points. From the gas supply means circularly distributed at the bottom of the container, 5 liters of nitrogen gas was supplied.
．． The solution was started to be supplied to the caustic soda aqueous solution at a flow rate of 0 1/■in. While stirring the caustic soda aqueous solution, add ferrous sulfate aqueous solution (4 degrees 0.226 mol #!) 3.5rd
and nitric acid -1-7 Kel (0.0036 mol/1)
280cc. Zinc sulfate (0.0022 mol/I!
) 280cc was added. When a ferrous boronate aqueous solution was added to a large excess of aqueous caustic acid 7 solution, a neutralization reaction occurred instantly and ferrous hydroxide was obtained in a suspended state. An additional 2.0 liters of air was added from the gas supply device that was flowing nitrogen gas into this suspended e-liquid.
N1/win was added and flowed to rapidly oxidize to produce goethite. The temperature of the suspension was maintained at 35 ± 0.5°C from the neutralization reaction to the oxidation reaction. Iron (I) in suspension
The content of I) was measured by the automatic titration method using potassium permanganate to measure the divalent iron concentration and the oxidation rate was determined while the reaction progressed and the supply of oxidizing gas was stopped when the M suspension became bright yellow. Ta. The oxidation rate at this time was over 99.7%.
The container was exposed to atmospheric pressure and left for 1 hour with stirring.
The viscosity after standing was measured with a B-type viscosity needle and was found to be 350 centiboads. The total oxidizing gas supply time was 16 minutes. The slurry consisted of needle-shaped goethite particles, and was washed with water and filtered to obtain a wet cake. A value of 84.4rd/g was obtained as the specific surface area of the goethite particles. The particle size has a long axis/short axis ratio of 9.8, and the length of long yuzu is 0.11.
It was 5ym. Looking at this in terms of particle size distribution, σL/L was 0.40. The results are shown in Table 1. Examples 2-7 Real! In @1, goethite was produced by changing the reaction temperature, oxidation time, and coprecipitated M ratio as shown in Table 1, and keeping all other conditions the same as in Example 1 in Tables 1 and 2. The results are shown in Table 1. Comparative Examples 1 to 4 Goethite was produced under various conditions in the same manner as in the example except that the amount of air was changed and the oxidation rate was relatively slow. The results are shown in Table 2.

[Brief explanation of drawings]

Figure 1 is a model diagram showing goethite particles. In the figure, L is the length of the long sleeve, and L is the length of the short axis.

Claims (1)

[Claims] (1) In 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, ferrous ions are converted to ferric ions. Based on the time-course curve of the oxidation rate to
Uniform particle size distribution at 20m^2/g (σ_L/L≦0.4
) A method for producing goethite, characterized by obtaining needle-like crystals.