JPH0712936B2 - Method for producing high-purity iron oxide hydroxide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a hydrochloric acid pickling waste liquid (hereinafter referred to as "pickling waste liquid") generated when a steel material, that is, a steel plate, a mold, a rod, or a wire rod is pickled with hydrochloric acid. ) From a method for producing hydrous iron oxide as a raw material for iron oxide for ferrite.

[Prior Art] There are (a) a roasting method and (b) a neutralization method as a method for producing iron oxide from a pickling waste liquid. Conventionally, there is a roasting method capable of recovering hydrochloric acid together with the production of iron oxide. It has been common practice. However, in the roasting method, the pickling waste liquid is put into a flame of 600 to 800 ° C and pyrolyzed, so that the obtained iron oxide has variations in particle size,
In addition, when used as iron oxide for ferrite, the reactivity is low, and there is concern that pollution may occur due to migration of HCl gas into the gas phase. On the other hand, according to the method of precipitating from an aqueous solution, that is, the so-called neutralization method, it is impossible to recover hydrochloric acid,
It is advantageous because it does not have the drawbacks mentioned above.

In the neutralization method, oxygen gas is introduced into a stock solution containing ferrous ions and an alkaline agent is injected to raise the pH of the stock solution as described in, for example, Japanese Examined Patent Publication No. 21040/1989. It makes it easy to oxidize ferrous ions. As the alkaline agent, sodium salt, ammonium salt, calcium salt and the like can be used. Sodium salt and ammonium salt are expensive, but calcium salt is inexpensive, so only calcium salt can be industrially used. The composition of industrial calcium salts is shown in Table 1.

Conventionally, calcium salts shown in Table 1, particularly slaked lime, have been used as they are as alkaline agents.

[Problems to be solved by the invention]

Generally, pickling waste liquid contains Si, Al, Mn, etc. contained in steel materials. Therefore, iron oxide hydroxide produced from pickling waste liquid, and iron oxide for ferrite produced by firing iron oxide hydroxide. Also, impurities such as Si are mixed in.

Since the quality of iron oxide for ferrite decreases as the amount of impurities contained in iron oxide for ferrite increases, standards for iron oxide for ferrite are set as shown in Table 2. However, generally, if the impurities such as SiO ₂ are 0.1% or less, it can be used as iron oxide for ferrite. In this respect, the composition of iron oxide produced by the roasting method is as shown in Table 3, and thus it can be used as iron oxide for ferrite.

On the other hand, in the neutralization method using an alkaline agent, conventionally, slaked lime (see Table 1) has been generally used as an alkaline agent. However, as described below, mixing of impurities accompanying the use of this slaked lime is a problem. Met. Generally, slaked lime has a particle size of 1 m
It is manufactured by digesting relatively fine powder of quick lime containing quick lime of m or less with groundwater. Therefore, SiO ₂ dissolved in the SiO ₂ and ground water or the like contained in the following fine grain size 1mm enters into slaked lime. This slaked lime is then classified into quality-dependent products with particle sizes of 590 μm or less, 149 μm or less, and 44 μm or less. Although relatively coarse-grained SiO ₂ can be removed by this classification process, fine-grained quick lime with a particle size of 1 mm or less and SiO ₂ dissolved in groundwater etc. are extremely fine, so mixing into each product slaked lime after classification is not possible. It is inevitable.

Therefore, the object of the present invention is to obtain high-purity iron oxide hydroxide with a reduced SiO ₂ content by removing SiO ₂ from the calcium salt alkaline agent.

[Means for solving problems]

The present invention for solving the above problems is a method for producing hydrous iron oxide by a neutralization method using an alkaline agent from an acidic waste liquid containing a ferrous salt, in which quick lime is sieved by dry classification, and a particle size is calculated. It is characterized in that a product having a size of 1 mm or more is obtained, which is digested and then sieved to a particle size of 0.5 mm or less and digested quicklime is used as an alkaline agent.

[Action]

In the present invention, quicklime is used as a starting material for the production of the alkaline agent. Since quick lime has a lower SiO ₂ content than conventional slaked lime (see Table 1), by selecting quick lime as the above raw material, the mixing of SiO ₂ into hydrous iron oxide can be reduced than before. .

Next, among the particles of quick lime, the particle size is 1m with a particularly high SiO ₂ content.
The SiO ₂ content of quick lime is reduced by separating particles of m or less by dry classification.

Further, the classified quicklime is digested to produce digested quicklime. This digested quicklime is a fine powder with a particle size of about 2.5 mm or less.
A relatively coarse-grained (0.5 mm or more) gangue mainly composed of iO ₂ is mixed. Therefore, by removing coarse particles having a particle size of 0.5 mm or more by sieving and classifying particles having a particle size of 0.5 mm or less, digested quick lime with a significantly reduced SiO ₂ amount can be obtained.

If the digested quicklime thus obtained is used as an alkaline agent in the neutralization method, a hydrous iron oxide having a low SiO ₂ content can be obtained.

[Specific configuration of the invention]

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

In the present invention, quicklime (see Table 1) that is industrially used is used as a starting material for producing an alkaline agent. Therefore, the following steps are adopted to reduce the SiO ₂ content from this quicklime.

SiO ₂ contained in quicklime used industrially is especially 1 mm
Especially in less than fine powder. Therefore, first, quick lime is removed by dry classification to remove portions having a particle size of less than 1 mm.

Next, the obtained particles having a particle size of 1 mm or more are digested to produce digested quicklime. This digested quicklime is a fine powder with a particle size of 2.5 mm or less, and among them, those with a relatively large particle size contain SiO ₂ in a gangue state.

Therefore, this digested quicklime is screened to a particle size of 0.5 m
Remove the part that exceeds m, collect the powder with a particle size of less than 0.5 mm,
This is used as an alkaline agent.

Next, the process leading to the completion of the present invention will be described.

In general, hydrous iron oxide obtained by using an alkaline agent in a hydrochloric acid pickling waste liquid of steel contains SiO ₂ as an impurity, and this SiO ₂ is derived from both the waste liquid and the alkaline agent. Therefore, the present inventors have found that the SiO ₂ content in hydrous iron oxide is 0.
SiO _{2 in} alkaline agent required to be within 1%
To know the tolerance limits content, using the apparatus of neutralization method shown in FIG. 2, the SiO ₂ content of SiO ₂ and hydrous oxide in the iron in the SiO ₂ and the alkali agent in the pickling waste I investigated the relationship. That is, in FIG. 2, first, the pickling waste liquid 1 is introduced into the reaction tank 4, the alkali agent 2 is injected from the upper part, and air or oxygen gas 3 is blown from the lower part to sufficiently stir them for reaction. Then, the obtained iron oxide hydroxide slurry is introduced into the sedimentation separation tank 5, and the treated water 6 is discharged from the upper part to the outside of the system.
Part of the hydrous iron oxide sludge obtained from the lower part is in the reaction tank 4
At the same time, the balance 7 is used as the product hydrous iron oxide.

As a result, it was found that when the pH of the slurry in the reaction tank 4 is 5 to 8, all of the SiO ₂ in the pickling waste liquid 1 and the alkaline agent 2 is mixed in the hydrous iron oxide sludge 7. Since it was clarified that all the SiO ₂ entering the reaction system was contained in the hydrous iron oxide, the relationship between the pickling waste liquid, the alkaline agent and the SiO ₂ content in the hydrous iron oxide was determined by mass balance. This relationship is shown in FIG. In the same figure, the case where the SiO ₂ content in hydrous iron oxide is 0.10% is shown by a straight line.

Incidentally, SiO ₂ content in Table 3, namely SiO ₂ content of the hydrous oxide in the iron produced in roasting method, SiO ₂ in the pickling waste
Equal to content. That is, the SiO ₂ content in the pickling waste liquid is 0.04 to 0.07% according to Table 3.

Therefore, the SiO ₂ content in the product hydrous iron oxide is 0.10%.
In order to be within the range, from Fig. 3, SiO ₂ in the alkaline agent
The content must be 0.07% or less. However, conventionally used slaked lime has a SiO ₂ content of 0.12% and 0.07%.
It should not be used because it is above.

Therefore, the present inventors have diligently studied the composition of the calcium salt alkaline agent, and as described below, have a particle size of 1 m.
Classifying quick lime of m or more and using slaked lime obtained by digesting this (hereinafter referred to as "digested quick lime") as an alkaline agent reduces hydrous iron oxide, and thus the SiO ₂ content in iron oxide for product ferrite. It was found to be extremely effective in.

In the present invention, quicklime, which is a starting material, is obtained by crushing limestone mined from a vein into particles having a particle size of 100 mm or less and then removing surface soil adhering to the surface by washing with water and calcining at about 1000 ° C. However, it is difficult to completely remove the topsoil by washing with water, and ash is generated due to the fuel during firing, so that a layer with a high SiO ₂ content is formed on the surface of the quicklime after firing. The thickness of this layer is about 1 mm. The quicklime is subjected to the subsequent crushing and classification steps to give quicklime products of various particle sizes. At that time, the SiO ₂ -rich layer on the surface is scraped to a powder having a particle size of 1 mm or less.

Therefore, in the present invention, quick lime is sieved by dry classification to separate a portion having a particle size of about 1 mm or more to reduce the SiO ₂ content.

Next, digested quicklime is produced by digesting quicklime having a particle size of 1 mm or more obtained by this classification. Table 4 shows an example of the components of this digested quicklime.

Since the SiO ₂ content of digested quicklime As is apparent from Table 4 still high it is necessary to further reduce the amount of SiO _2.

By the way, in the present invention, the digested lime is sieved to a particle size of 0.
The reason why the thickness is 5 mm or less is as follows. That is, the present inventors further investigated the state of existence of SiO ₂ in quicklime in order to reduce the SiO ₂ content of digested quicklime.
As a result, it was discovered that relatively coarse-grained gangue (particle size 0.5 mm or more) mainly composed of SiO ₂ was mixed in the matrix portion of quicklime. Furthermore, it was also found that the origin of the high-SiO ₂ part of the quick lime and the gangue are different, and the shape and grain size are different. However, in the digested quicklime obtained according to the present invention, as is clear from the production method, most of the gangue remains in the digested quicklime. Therefore, by removing the gangue portion from the digested quicklime, the SiO ₂ content in the digested quicklime can be significantly reduced.

Therefore, it is clear that the particle size of digested quick lime is mainly the part with small particle size (particle size 0.2 mm or less) as shown in Fig. 4, but the part with large particle size is mainly gangue. became. Therefore, in order to check the particle size of the gangue, quick lime is mixed and stirred in a hydrochloric acid solution, and then the insoluble matter is separated and the particle size is measured. Most of the insoluble matter in hydrochloric acid is considered to exist in the state of gangue, and the particle size is concentrated in the range of 0.1 to 3 mm.

Therefore, as a result of examining FIG. 4 and FIG. 5, it was judged that it was necessary to classify digested quicklime with a particle size of 0.5 mm or less, preferably 0.2 mm or less.
Table 4 shows the results of examining the SiO ₂ content.

From Table 4, digested quicklime is 500μm, preferably 200μm
It was clarified that the SiO ₂ content of digested quicklime significantly decreased when the particles were classified according to the particle size.

Next, a classification method applicable to the present invention will be described. In general, quicklime is fine powder with a particle size of about 250 μm or less when digested, so gangue can be separated to some extent even by dry classification such as air classification. In fact, in the production of slaked lime, dry classification is usually performed after digestion. To improve the purity.

On the other hand, in wet classification, a large amount of water is added to digested quick lime to classify it into lime milk for classification, so that part of the digested quick lime is dissolved in water and its particle size becomes 149 μm or less. For this reason, it is easy to separate from the gangue, and especially the particle size of classification is 50
By setting the thickness to 0 μm or less, it is possible to relatively easily remove the SiO ₂ content other than the gangue content. Therefore, it is desirable to employ wet classification in the present invention. As a specific example of wet classification, a method of sieving while adding water or a wet classifier, that is, a dynamic type, a mechanical type, a hydraulic type, a moisture type, a centrifugal type, or the like can be used.

〔Example〕

 Next, examples of the present invention will be described.

(Example 1) A lump of quick lime is crushed into a powder, which is subjected to sieving by dry classification, and a coarse portion having a particle diameter of 1000 µm or more is collected,
Digest this. Next, the obtained digested quicklime was wet classified to collect fine parts having a particle size of 500 μm or less.

Then, the neutralization method apparatus shown in FIG. 2 was used to treat the pickling waste liquid of the steel material with the digested quicklime suspension to produce iron oxide hydroxide. Further, after washing the iron oxide hydroxide, 500
Firing at ℃, to produce iron oxide. Si in the obtained iron oxide
When the O ₂ content was analyzed, it was 0.09% in SiO ₂ / Fe ₂ O ₃ . Therefore, this iron oxide can be used for ferrite.

(Example 2) Quicklime powder was produced in the same manner as in Example 1, and a coarse portion having a particle size of 2000 µm or more was fractionated by dry classification.
It was digested to obtain digested quicklime. Next, this digested quicklime was wet classified to collect fine parts having a particle size of 149 μm or less. Next, using this suspension of digested quicklime, iron oxide was prepared from the pickling waste liquid in the same manner as in Example 1, and
The SiO ₂ content was analyzed and found to be 0.08% SiO ₂ / Fe ₂ O ₃ . Therefore, also in this example, iron oxide that can be sufficiently used as iron oxide for ferrite was obtained.

(Comparative Example 1) results except that used to manufacture the iron oxide under the same conditions as in Example 1, was analyzed SiO ₂ content in its hydrated lime shown in Table 1 as it is as an alkaline agent, SiO ₂ / Fe ₂ O ₃
It was 0.15%. This exceeds 0.10% and cannot be used as iron oxide for ferrite.

〔The invention's effect〕

As described above, in the present invention, iron oxide hydroxide having an extremely low SiO ₂ content can be obtained, and high-quality iron oxide for ferrite can be economically obtained by using this as a raw material.

[Brief description of drawings]

FIG. 1 is a process diagram according to the present invention, FIG. 2 is a device diagram for carrying out the present invention, and FIG. 3 is a waste liquid, lime and iron oxide.
FIG. 4 is a diagram showing the relationship of SiO ₂ content, FIG. 4 is a diagram showing the particle size of digested quicklime, and FIG. 5 is a diagram showing the particle size of hydrochloric acid insoluble matter of quicklime. 1 ... hydrochloric acid pickling waste liquid, 2 ... alkali agent, 3 ... air or oxygen gas, 4 ... reaction tank, 5 ... sedimentation / separation tank, 6 ... treated water, 7
… Hydrous iron oxide sludge.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Nobuo Teramoto, 5-15 Kitahama, Higashi-ku, Osaka City, Osaka Prefecture Sumitomo Metal Industries, Ltd. (72) Koichi Hata, 1-3-1, Otemachi, Chiyoda-ku, Tokyo (72) Inventor Toshinori Baba, 4720 Fujisawa, Fujisawa, Kanagawa Prefecture, Ebara Research Institute, Inc. (72) Inventor, Taka Takai, 4720, Fujisawa, Fujisawa, Kanagawa, Japan, Ebara Research Institute, Ltd.

Claims (1)

[Claims] 1. A method for producing iron oxide hydroxide from an acidic waste liquid containing a ferrous salt by a neutralization method using an alkaline agent. Quick lime is sieved by dry classification to obtain particles having a particle size of 1 mm or more. A method for producing a high-purity iron oxide hydroxide with high purity, which comprises using digested quicklime having a particle size of 0.5 mm or less as an alkaline agent after digesting the.