JPH0637307B2 - Method for producing ferrous chloride aqueous solution - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to the production of ferrous chloride aqueous solution, and more specifically to magnetic iron oxide powder for magnetic recording media such as audio tapes, video tapes and magnetic cards. And a method for producing a ferrous chloride aqueous solution suitable as a raw material when producing magnetic iron powder.

[Prior Art] Generally, magnetic iron oxide powder and magnetic iron powder for magnetic recording media used for audio tapes, video tapes, magnetic cards and the like are obtained by a wet method from α-iron oxyhydroxide from an aqueous solution of ferrous chloride. , Γ-iron oxyhydroxide is used as a starting material, and this is sequentially subjected to treatments such as firing (dehydration, baking), reduction, and oxidation to obtain needle-shaped γ-Fe ₂ O ₃ , or its particles. Co-γ-Cobalt-deposited on the surface by cobalt modification treatment
It is manufactured by obtaining Fe ₂ O ₃ or by firing reduction to obtain magnetic iron powder. In this case, the magnetic properties of the obtained magnetic iron oxide powder and magnetic iron powder depend on the properties of the above-mentioned starting material iron oxyhydroxide, for example, the particle size distribution and particle diameter, and therefore, the magnetic oxidation suitable for the magnetic recording medium. In order to obtain iron powder and magnetic iron powder, it is necessary to use starting materials with excellent properties.

[Problems to be Solved by the Invention] With the development of approximations and electronic devices, magnetic iron oxide powders and magnetic iron powders for magnetic recording media are the main materials of the memory, and thus higher performance is required. There is a demand for fine particles having a large axial ratio and a good particle size distribution and excellent dispersibility.

However, when ferric chloride is contained in the aqueous solution of ferrous chloride, which is mainly used as a starting material, ferric oxyhydroxide having non-uniform particle size is produced, which is obtained by dehydration, calcination, reduction and oxidation. The magnetic powder is also affected by this, and only magnetic powder having a non-uniform particle size can be obtained.

Such a phenomenon is unavoidable even if the ferrous chloride aqueous solution generated from the pickling process of steel etc. is mixed with ferric chloride,
It is unavoidable to add stannous chloride solution to reduce ferric iron to ferrous iron as a raw material.

However, with such a conventional method, it is possible to eliminate ferric iron as an impurity that adversely affects the produced iron oxyhydroxide, but other metal elements such as tin are mixed in as impurities. There was a problem inevitable.

In addition, magnetic iron oxide powder has defective products due to particle size etc.
When it is treated with hydrochloric acid to reuse it as an iron source, it becomes ferric chloride. It is necessary to make this ferric chloride high-purity ferrous chloride.

According to the chemical theory, if ferric chloride is reacted with metallic iron, it will react as follows.

That is, according to the formula (3), HCl is chemically not generated or disappeared by the reaction, and ferric chloride should be simply disappeared to produce ferrous chloride.

However, when metallic iron is actually immersed in an aqueous solution of ferric chloride, hydrogen is generated and the pH of the liquid remarkably rises. This is because not all 2H of the formula (1) is stored in the reaction of the formula (2), but a part thereof escapes as H ₂ gas and HCl decreases. Then, ferric iron is not reduced from the vicinity where the pH exceeds 1 to become β-iron oxyhydroxide. This β-
In order to suppress the generation of iron oxyhydroxide, it is necessary to set the pH to 1 or less.

The β-iron oxyhydroxide formed here is extremely fine particles and is not only difficult to filter, but also too fine to make it difficult to control the subsequent firing, reduction and oxidation processes, and the obtained magnetic powder is It is an iron oxyhydroxide having a non-uniform particle size and unsuitable as a raw material for magnetic iron oxide powder or magnetic iron powder for magnetic recording.

Therefore, the present invention is suitable for producing magnetic iron oxide or magnetic iron containing no other metal element such as tin from an aqueous ferric chloride solution or an aqueous ferric chloride solution containing ferrous chloride. The purpose is to produce a ferrous iron aqueous solution.

[Means for Solving the Problems] The inventors of the present invention have made various studies to solve the above problems, but it was found that the object can be achieved by a surprisingly simple means.

That is, metallic iron and hydrochloric acid were added to the ferric chloride aqueous solution,
By reacting at a pH of 1 or less, iron oxyhydroxide having a particle size distribution and particle size suitable for a magnetic recording medium can be obtained.

In this case, the ferric chloride content in the aqueous solution as the raw material is not limited at all, and even in a saturated solution of a pure ferric chloride aqueous solution, ferric chloride aqueous solution contains a small amount of ferric iron. It may be.

The amount of the acid salt to be added is such that the pH of the liquid can be kept at 1 or less during the reduction of all contained ferric ions to ferrous ions. In order to obtain γ-Fe ₂ O ₃ , the produced ferrous chloride aqueous solution is subjected to a step of precipitating iron oxyhydroxide in an oxidized state after neutralizing with an alkali, so that the excess amount of hydrochloric acid is small. Moderate. When the amount of added hydrochloric acid is less than the amount that maintains pH of 1 or less, it is unavoidable that β-iron oxyhydroxide is by-produced. The reduction of ferric ion by metallic iron is from room temperature to 10 at room temperature.
It will be around 0 ° C.

[Operation] Theoretically, it is not possible to make a complete elucidation, but I think as follows.

That is, when hydrochloric acid is added to a ferric chloride aqueous solution and neutralized with metallic iron, ferric chloride becomes ferrous chloride at a lower potential than hydrogen ions become hydrogen, so ferric chloride is preferentially converted to ferrous chloride. Will be reduced. However, when the pH is higher than 1, the following reaction occurs.

FeCl ₃ + 2H ₂ O → FeOOH + 3HCl This reaction proceeds regardless of the redox reaction, and the hydrochloric acid produced here is consumed by reacting with the remaining metallic iron.
H did not change, and the above reaction proceeded further to the right, and β-iron oxyhydroxide was produced more and more. In order to prevent this reaction from occurring, it is necessary to add hydrochloric acid such that the pH does not exceed 1 before the ferric ion is reduced to ferrous ion.

[Example] (1) Ferric chloride 0.6 mol /, ferrous chloride 0.1
27.1 g of concentrated hydrochloric acid was added to the mol / mixed aqueous solution,
The whole was made up to 200 ml and 100 g of metallic iron was added. It was left at room temperature in a nitrogen atmosphere. Fe ²⁺ is 1.0 after 4 hours
It became mol /, and Fe ³⁺ was almost absent (below the detection limit).

(2) Ferric chloride 0.96 mol /, ferrous chloride 0.
To the 23 mol / mixed aqueous solution, 42.1 g of concentrated hydrochloric acid was added to make the whole 200 ml, and 100 g of metallic iron was added.
The temperature was set to 60 ° C. in a nitrogen atmosphere, and after 3 hours, Fe ²⁺ became 1.4 mol /, and Fe ³⁺ was hardly present.

The ferrous chloride solutions obtained in Examples 1 and 2 were highly pure and suitable as a raw material for magnetic iron oxide. That is, γ-iron oxyhydroxide produced from these ferrous chloride aqueous solutions as a raw material is fine, has a large axial ratio, and has a good particle size distribution.
The particles were excellent in dispersibility.

[Effects] As described above, even if ferric chloride is mixed in the ferrous chloride aqueous solution, it should be sufficiently wet to prepare a ferrous chloride aqueous solution that can be used as a raw material for magnetic iron oxide. Can be realized with simple operation and at low cost.

In addition, magnetic iron oxide powders whose particle sizes and the like are out of the standard can be easily produced as a ferrous chloride aqueous solution suitable as a raw material for producing magnetic iron oxide powders.

Claims (2)

[Claims] 1. A method for producing an aqueous solution of ferrous chloride, comprising adding metallic iron and hydrochloric acid to an aqueous solution of ferric chloride and reacting the solution at a pH of 1 or less. 2. The method for producing an aqueous solution of ferrous chloride according to claim 1, which comprises adding metallic iron and hydrochloric acid to an aqueous solution of ferric chloride containing ferrous chloride and reacting them at a pH of 1 or less.