JPS6265937A - Production of lepidocrosite - Google Patents

Abstract

PURPOSE:To produce lepidocrosite having uniform crystallinity without coagulation by supplying an oxidative gas, dividedly in 3 stages, to a suspension of ferrous hydroxide. CONSTITUTION:An aq. alkaline soln. or alkaline gas of 0.3-0.7 molar ratio is supplied to an aq. FeCl2 soln. to effect reaction, by which the suspension of Fe(OH)2 is obtd. The oxidative gas is blown to such suspension at 5-50 deg.C so as to attain 1.0V1<v1<1.5V1 to form green rust which is the basic salt contg. hexagonal planar Fe(II) and FE(III); thereafter the oxidative gas is blown thereto to attain 1.5V2<v2<2.5V2 to oxidize the green rust. The suspension essentially consisting of the nuclear crystal of lepidocrosite is obtd. An alkali is then added to such suspension to maintain the pH at 3.2-4.2 and the oxidative gas is supplied thereto so as to attain 1.5V3<v3<2.0V3 [v1-3 is the amt. of the oxidative gas to be blown (l); V1-3 is the theoretically required amt. of the oxidative gas to be supplied (l)], by which the lepidocrosite having the desired grain sizes is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to the production of lepidochrosite (γ-FeOOH), and more particularly, to the production of lepidochrosite (γ-FeOOH). The present invention relates to a method for producing lepidocrocite, which is suitable as a starting material when producing magnetic iron oxide powder for recording media.

(Prior art and interlayer points to be solved) In general, magnetic iron oxide powder for magnetic recording media such as audio tapes, video tapes, and magnetic cards is a-FeOOH (goethite) or 7-FeOOH (lepidochrome). The starting material is γ-Fe2O3 (maghemite), which is sequentially subjected to treatments such as calcination (dehydration, hardening), reduction, and oxidation to obtain acicular γ-Fe2O3 (maghemite), or cobalt is added to the particle surface by cobalt modification treatment. Deposited Co-γ-Fe20. It is manufactured by obtaining In this case, the magnetic properties of the obtained magnetic iron oxide powder depend on the properties of the above-mentioned starting material, so in order to obtain magnetic iron oxide powder suitable for magnetic recording media, it is necessary to use a starting material with excellent properties. be.

In this respect, conventionally, lepidocrocite (γ-FeOOH)
The magnetic iron oxide powder obtained using as a starting material has a
Although the final products, such as magnetic recording media such as audio tapes and video tapes, have excellent magnetic orientation, monodispersity, squareness ratio, and transfer characteristics, they have a problem in that they have a large particle size distribution.

By the way, conventionally, hydroxides obtained by reacting an aqueous solution of a ferrous salt such as ferrous chloride with an aqueous alkali solution have been used. In order to obtain uniform lepidocrocite particles by oxidizing a suspension, it was thought to be extremely important to match the oxidation rate to the crystal growth rate. That is, the oxidation reaction that occurs by supplying an oxidizing gas to the hydroxide suspension does not proceed at the same oxidation reaction rate during the entire reaction process, but the oxidation reaction rate differs depending on the stage. The idea is that it is necessary to control the supply rate of the oxidizing gas into the reaction solution in accordance with the crystal growth rate at each stage.

This method follows the method used in the production of goethite (γ-FeOOH) to produce lepidochrosite (γ-FeOOH).
It is intended to be applied to the production of OOI().

Incidentally, the method of controlling the oxidation rate during the production of goethite is to divide the oxidation of the hydroxide of the ferrous salt into several steps and calculate the amount of oxidation within a certain period of time by calculating the oxidation rate (%) and the number of moles of oxygen introduced. (Japanese Unexamined Patent Publication No. 52-59095, 52
-59096, 52-59097), or when oxidizing the hydroxide of a ferrous salt, a part of the total hydroxide is taken out at a certain frequency into an external container, and an oxidizing gas is supplied to it to oxidize it. Oxidation rate (%) per cycle by circulating
(Japanese Unexamined Patent Publication No. 57-166322,
209834, 58-32028. 58-1403
27), but all of these methods are based on the recognition that matching the oxidation rate to the crystal growth rate is important for making the particle size distribution uniform.

However, in the production method of lepidocrocite, delicate control technology is required to control the supply rate of oxidizing gas in order to match the oxidation rate to the crystal growth rate, and the skill with which the lepidocrocite is produced This results in a large influence on the particle size distribution of the site needle-like crystals. In other words, if the rate of supply of the oxidizing gas into the reaction solution is high, the rate of one reaction increases and the rate of generation of crystal nuclei increases, so that each needle-like crystal is At the same time, the number of nuclei generated during the process increases, so that lepidocrocite needle-like crystals with a large (broad) particle size distribution can be obtained. On the other hand, if the supply rate is slow, the reaction rate will be low and the nucleation rate will be slow, so nucleation will be suppressed during the process, but individual needle crystals will become extremely long needle crystals with a long axis length, and , the tactroid structure (raft-shaped crystal aggregate) peculiar to lepidocrocite further aggregates, resulting in lepidocrocite with poor properties.

The present invention eliminates the drawbacks of the prior art related to lepidocrocite, and makes it possible to easily produce lepidocrocite needle-like crystals with a uniform particle size distribution and uniform particles with good crystallinity without agglomeration. The purpose is to provide a method.

(Means for Solving the Problems) In order to achieve the above object, the present invention divides the oxidation reaction process into three stages in consideration of the generation and growth of green last and lepidic crocite nucleus crystals, and each stage The aim is to appropriately control the supply of oxidizing gases to advance the oxidation reaction.

The present invention will be explained in detail below based on examples.

First, the entire reaction process according to the present invention is divided into three stages as follows.

■1 Prepare an aqueous ferrous chloride solution as a ferrous salt, and add an alkali to the ferrous chloride ratio (mole ratio) R = 0.3
After adding and reacting an alkaline aqueous solution such as caustic alkali, ammonia, etc. and/or ammonia gas under stirring in the range of ~0.7 to form a suspension of ferrous hydroxide,
C1 is a basic salt containing Fe(II) and Fe(m) in the form of a hexagonal plate, which is produced by carrying out an oxidation reaction by supplying an oxidizing gas (air or oxygen) preferably at a temperature of 10 to 30°C. Generates green last. This reaction is referred to as the first stage reaction.

Second Stage Reaction When oxidizing gas is continued to be supplied to the suspension under stirring, the color of the suspension changes from dark blue-green to dark yellow-green to brownish brown as the oxidation progresses. Nucleic crystals of docrosite are generated, resulting in a suspension containing needle-shaped crystals as the main component.

This reaction is referred to as the second stage reaction.

Furthermore, an alkaline aqueous solution or gas (
Gradually add ammonia gas etc. 1) to adjust the pH value to 3.2
While maintaining the pH at ~4.2, continue to supply oxidizing gas, and when the initial amount of ferrous chloride is consumed, the pH value will rise, so when the pH value reaches approximately 5.5. is the end point of the reaction, and the supply of oxidizing gas is stopped. As a result, the nucleus crystals produced in the second stage reaction grow, and lepidocrocite having the desired particle size is obtained. This reaction is referred to as the third stage reaction.

Since the crystal growth rates are different in the above-described first to third stage reactions, in the present invention, the supply amount of the oxidizing gas is controlled to be changed appropriately at each stage. For example, when one reaction system is uniformly stirred and the oxidizing gas blowing rate is kept constant (e.g., 1st stage reaction...about 20Q/m
in, 2nd stage reaction...approx. Based on experiments, it is as follows.

First stage reaction: 1. OV, <U, <1.5V.

Second stage reaction: 1.5V2 (υ, <2.5V2 Second stage reaction: 1.5V, <υ, <2.OV.

Here, vl, {circle around (2)} and V are theoretical values of the oxidizing gas supply amount (Ilk) necessary for the reaction, and can be easily determined as follows.

That is, in the first stage reaction and the second stage reaction, Fe(OH
) is oxidized with an oxidizing gas (air) to form a green rust of basic salt containing Fe(If) and Fe(III) in the first stage, and then in the second stage, this neutral suspension is This is a process of oxidizing green last to generate lepidocrocite nucleus crystals, and the reaction formula is expressed by the following formula.

4Fe(OH) 2+02→4FeOOH+2H,0 Therefore, the theoretical required air supply amount VZ(Q) and V2(2
) is calculated using the following formula.

First stage reaction (2Fe(II)-+Fe(II), F
e(m)): 22.4 X (273+t engineering) V, = aX (total number of moles of Fe(II))
, 21X 273 0 in the second stage reaction (Fe(U), Fe(III)-+2Fe
OOH): 22.4 X (273+t2) y2=bx (total number of moles of Fe(II))
, 21 .0 tl, t2: Temperature of supplied air ('C) In addition, in the third stage reaction, Fe (■) that was not consumed in the first and second stage reactions is oxidized and This is a step of growing the generated nuclear crystals to obtain lepidocrocite having a desired particle size, and the reaction formula is expressed by the following formula.

4 FeCQ, + 8 NaOH+ 02-'p4F
e○○H+ 8 N a CQ + 2 Hz O Therefore, the theoretical required air supply amount v, (Q) is calculated by the following formula.

22.4 X (273+t3) ■, = (total number of moles of Fe(II))
X O, 21
The starting material was diluted to 8.480%. F of this aqueous solution
The number of moles of e(II) is 27.54 moles. To this, a caustic soda solution prepared by dissolving 1.21 kg of NaOH as an alkali in 42.5 Q of water was added at 17°C.
The mixture was further cooled in a jacket and stirred while maintaining the temperature at 17°C. The pH value of the resulting suspension containing Fe(OH)2 as a main component was 7.3.

Compressed air was added to this suspension in the first stage reaction at 20R/win (
20'C), 7.6Q/win (20'C) in the second stage reaction
When oxidation was carried out while blowing from the bottom of the tank at a blowing rate of , it took 16+ minutes for the first stage reaction and 51 minutes for the second stage reaction. However, the end point of the second stage reaction was set at the time when the pH value reached 4. At this time, the alkali addition ratio (molar ratio) R was 0.55.

When the FeO○H nucleus crystals produced in the first and second stage reactions were observed using an electron microscope, they clearly had a particle size in which fine needle-like crystals, which are characteristic of lepidocrocite, were shaped like a raft. It was γ-FeOOH with uniform properties.

Next, switch the blowing gas from air to N2 gas.

The mixture was heated from a liquid temperature of 17°C to 40'C under N2 atmosphere and stirring with a stirrer. After the temperature was raised, the N2 gas was stopped, and as a third stage reaction, a caustic soda solution containing 960 g of NaOH dissolved in 18Q water was gradually added while blowing compressed air from the bottom of the tank at a blowing rate of 2.52 /win (20°C). and the pH value was maintained at 3.6 to grow lepidocrocite nuclei. When the pH value could not be kept constant and reached 5.5, the addition of alkali was stopped and the reaction was terminated. The reaction time required for this was 256 minutes.

From the above, the amount of supplied air υ2, υ at each stage is calculated as follows.

uL/V,=20X16/216.8=1.48,
', a, = 1.48V□v 2/ V2 near, 6 X
51/216.8=1.79,”-u z=1.7
9Vzt+, /V, = 2.5x256/354.7=1
．． 80,", υ3"1.80V3 In addition, the lepidocrocite needles obtained in this example had a good particle size distribution with an average long axis length of 0.97 μm and an average axial ratio of 11.4. They were uniform particles with no separation.

Furthermore, the obtained slurry solution was filtered, washed, and dried, followed by dehydration, roasting (430°C), and reduction (470°C) using conventional methods.
After processing to obtain Fe, ○, and measuring its magnetic properties, coercive force (Hc) = 42506° saturation magnetization (σs
) = 84, 9 emu/g, specific surface area (SSA)
= 30.5 m2/g, which was suitable for magnetic recording J'[11M ([4).

(Comparative Example) The production method was exactly the same as in the above example, except that only the amount of air supplied in the second stage reaction was changed. In other words, the blowing rate is 20 Q/win in the first stage reaction and 20 Q/min in the second stage reaction.
, 2,5Q/In1n was obtained in the third stage reaction.

The reaction time at each stage was 18 min, 38 min, and 252 min, respectively.
It was a minute. From this result, the amount of air blown at each stage is as follows.

u, /V, = 20X18/216.8 = 1.66 -
”, u, = 1.66V.

v2/V2=20X38/216-8=3
−51 −”−u a=3−51 V 2υ, /V3
=2.5X252/354.7=1.78 ,',υ
a” 1, 78 V aThe lepidocrocite needles obtained in this comparative example had an average major axis length of 0.54 μm,
The average axial ratio was 8.2, and the particle size distribution was not very good.

Furthermore, this slurry solution was treated in the same manner as in the above example to obtain Fe, 04, and its magnetic properties were measured; Hc = 375 0;, σ5 = 82.3 emu/g,
5SA=32.1m"7g.

(Effects of the Invention) As detailed above, according to the present invention, since the supply amount of oxidizing gas is appropriately controlled in three stages in the production of lepidocrocite, needle crystals with uniform particle size are produced. In addition, lepidocrocite with excellent properties such as uniform crystallinity and no agglomeration can be produced stably and easily.
This makes it possible to produce magnetic iron oxide powder with excellent properties.

Claims (1)

[Claims] In a method for obtaining lepidocrocite by oxidizing a hydroxide suspension obtained by reacting an aqueous ferrous chloride solution with an aqueous alkaline solution or an alkaline gas with an oxidizing gas, the amount of the oxidizing gas supplied is A method for producing lepidocrocite, which is characterized by appropriately controlling the oxidation reaction in three stages according to the oxidation reaction process.