JPH0147408B2 - - Google Patents

Description

Detailed Description of the Invention The present invention converts chloride ions (hereinafter referred to as Cl ^- ) contained in iron oxide produced by thermally decomposing an iron chloride solution into sulfur dioxide gas (hereinafter referred to as SO ₂ ). The present invention relates to a method for reducing the amount of water.

Since then, iron oxide, which has been supplied to the market as red iron oxide, has been produced by wet oxidation, dehydration, or roasting of iron sulfate or sulfide ore. After the conversion from the hydrochloric acid method to the hydrochloric acid method, the production of iron oxide using ferrous chloride solution as a raw material has increased.

However, although iron oxide is an important raw material for ferrite cores or pigments for electronic materials, iron oxide produced from iron chloride contains about 0.2 wt% chlorine as chloride ions immediately after thermal decomposition. This Cl ^-
is not preferable when using iron oxide. Therefore, iron oxide is actually subjected to treatments such as washing with water or roasting for the purpose of removing Cl ^- (hereinafter referred to as deCl ^- ). However, in these treatments, it is difficult to remove Cl ^- sufficiently, and there are problems in terms of economics and changes in powder properties, and the water washing method leaves many problems in the wastewater treatment process.

The purpose of the present invention is to fully consider the current situation as described above, and to obtain iron oxide contained in iron oxide powder.
The present invention provides a method for removing Cl ^- . The gist of the present invention is to remove Cl ^- from the iron oxide by keeping iron oxide produced from an iron chloride solution at room temperature to 700°C and passing a medium gas such as air containing SO ₂ through it. This is a method for removing chloride ions from iron oxide powder.

The present invention will be explained in more detail below. We will describe iron oxide (valent) obtained by thermally decomposing ferrous chloride solution at high temperature. Iron oxide α-Fe ₂ O ₃ , which was obtained by thermally decomposing a ferrous chloride solution at a temperature of 500 to 800°C in a fluidized roasting furnace and electrostatically collecting it, had an average particle size of 0.6 to 0.7μ. . X-ray diffraction showed only an α-Fe ₂ O ₃ pattern, and the purity determined by chemical analysis was 99.2 wt% or more. The main impurities are 0.3wt% water and Cl ^- .
0.16wt%, SO ₄ ^2- 0.03wt%, MnO 0.26wt%,
Al ₂ O ₃ is 0.02wt%, CaO is 0.01wt%, SiO,
P, Ti, and Cu were 0.001 to 0.006 wt%. Keep this iron oxide at room temperature ~ 700℃, _SO2 is 0.05~1.5vol
% of mixed air using the flow method. in the air
Figure 1 shows the difference in the amount of Cl ^- remaining in iron oxide powder when SO ₂ is included and when it is not. At this time, the moisture in the air was 0.8 wt%, the SO ₂ gas concentration was 0.4 vol%, and the reaction time was 1 hour. When heated through air only, it gradually decreases as the temperature increases, but
When heated through a medium gas containing SO ₂ , the decrease is already noticeable at room temperature, and at temperatures above 100°C it decreases significantly, and Cl ^- in iron oxide is reduced to 0.04 wt%. Figure 2 shows the relationship between the amount of desorbed Cl ^- and the amount of attached SO ₂ in terms of moles.

Although the molar ratio of Cl ^- /SO ₂ changes depending on the amount of SO ₂ attached, the removal of Cl ^- by SO ₂ is a stoichiometric reaction in this way. It is thought that Cl ^- existing on the surface or inside the iron oxide powder is replaced by SO ₂ having a larger electron affinity and is eliminated. When similar experiments were conducted by varying the amount of moisture in the air from 0 to 10 wt%, the reaction rate was greater when the air contained some moisture.
It was found that the amount of Cl ^- removed also increased. That is, the moisture content in the air is preferably 0.2 to 10 wt%. Also the first
In the figure, it was found that the maximum value of the amount of Cl ^- removed at a temperature around 150°C was a result of the moisture contained in the air or the sample affecting the reaction. If the reaction temperature is 200°C or higher, the longer the reaction time, the more Fe ₂ (SO ₄ ) ₃ will be produced, making it impossible to obtain the intended iron oxide. Under conditions where Fe ₂ (SO ₄ ) ₃ was not produced, the powder properties of iron oxide did not change at all.

The smaller the amount of SO ₂ mixed in the air, the better in terms of workability and economy. The inventors have determined that 0.05~
It was confirmed that there was no difference in the Cl ^- removal effect in the 1.5 vol% range. The exhaust gas after the SO ₂ distribution can be treated in the exhaust gas treatment process after thermal decomposition.

In addition, in the actual process, the iron oxide powder is moved and brought into contact with a medium gas containing SO ₂ using a fluidized bed, rotary reactor, etc., which greatly shortens the deCl ^- treatment time. be able to.

As detailed above, the method of the present invention has a lower Cl ^- removal method than conventional methods of removing Cl - by washing with water or roasting with only air.
Since Cl ^- can be removed at low temperatures, there is no change in powder properties due to treatment, the treatment method is much simpler, and it is an excellent method that does not produce other derivative substances.

The present invention will be described below with reference to Examples.

Example: Concentrate iron works waste acid to reduce iron chloride concentration to approximately 40
% solution at 500-800℃ using a fluidized roasting furnace.
Approximately 2.5 g of iron oxide obtained by thermal decomposition was placed in the center of an opaque quartz reaction tube maintained at 150 ± 5°C in a horizontal electric furnace, and 0.8 g of water containing 0.4 vol% SO ₂ was placed in the center of an opaque quartz reaction tube. 1 by passing wt% air at a flow rate of 180ml/min.
When reacted for a time, the concentration was 0.16wt% before reaction.
Cl ^- decreased to 0.04wt% and SO ₂ was 0.02wt%
increased to 0.17wt%. Average particle size (0.6 μ), specific surface area (4.8 m ² /g), compressed density (2.85
g/cm ³ ) remained unchanged before and after treatment. Also, by heating the same iron oxide through air only,
In order to reduce the Cl ^- amount to 0.04wt%, it is necessary to conduct the process at 700°C for 1 hour, and the grain growth due to sintering is severe. Furthermore, in order to achieve the same Cl ^- removal effect by washing with water, it is necessary to wash 10 times or more using approximately 0.5 g of water per 2.5 g of iron oxide.

Although the powder of α-Fe ₂ O ₃ has been described above, it is of course applicable to γ-Fe ₂ O ₃ and Fe ₃ O ₄ produced by firing iron chloride. In addition to air, inert gases (N ₂ , CO ₂ , Ar, etc.) containing appropriate amounts of oxygen and moisture, and mixtures thereof can also be used as the medium gas.

[Brief explanation of drawings]

FIG. 1 shows the comparison results of heating temperature and amount of residual Cl ^- when SO ₂ -added air and SO ₂ -free air are brought into contact with α-Fe ₂ O ₃ powder containing Cl ^- . Figure 2 shows the relationship between the amount of desorbed Cl ^- and the amount of attached SO ₂ .

Claims (1)

[Claims] 1. Chlorination in iron oxide powder, which is characterized by contacting iron oxide powder produced by thermally decomposing an iron chloride solution with a medium gas containing sulfur dioxide gas at a temperature range of room temperature to 700°C. Method for removing physical ions. 2. A method for removing chloride ions from iron oxide powder according to claim 1, wherein the moisture content in the medium gas is maintained in the range of 0.2 to 10%.