JPH07165427A - Purification of iron chloride solution - Google Patents

Abstract

PURPOSE:To provide a process for purification of iron chloride solution which can solve the problems in the conventional processes all together such as unsatisfactory separation of impurities and controllability. CONSTITUTION:This purification process is for producing iron oxide of high purity from the waste solution after steel pickling. Iron or iron compound are allowed to contact with the pickling waste solution in the form of iron chloride solution to neutralize free hydrochloric acid until the pH is adjusted to 2 to 4. Then, the pH is adjusted to 2 to 5, as oxygen or an oxygen-containing gas is brought into contact with the neutralized solution to form a precipitation mainly containing 0.5 to 15% of Fe in the solution. The precipitation is removed, and the remaining solution is used as a purified ferrous chloride solution. The oxidation is effected with an oxidizing agent to convert ferrous chloride into ferric chloride, alkali is used to precipitate the ferric chloride. The precipitate is dissolved in hydrochloric acid to give the purified iron chloride solution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is for producing iron oxide for a ferrite raw material containing a small amount of impurities such as Si, Al, P, Na, Ca and B from a hydrochloric acid pickling waste liquid of a steel material such as a steel plate. It relates to a method for purifying an iron chloride solution to be used.

[0002]

2. Description of the Related Art Iron chloride aqueous solution generated as a pickling waste liquid for iron and steel sheets is usually Si, Al, P, Cr, Cu, Ti, N.
Impurities such as a, Ca and B are contained, and when the waste liquid is roasted to produce iron oxide, these impurities remain in the iron oxide. Therefore, when the produced iron oxide is used as a ferrite raw material, the residual impurities cause deterioration of magnetic properties. When used in soft ferrite materials that require miniaturization and high performance, the crystal of ferrite particles is coarsened like Si, P, B, or solid-dissolved in the ferrite crystal like Al. It is necessary to particularly reduce the trace impurities that significantly deteriorate the electrical and magnetic characteristics.

Conventionally, in order to reduce impurities in the steel pickling waste liquid, a coagulation-filtration separation system has been mainly used for the purpose of removing SiO ₂ (Si exists as SiO ₂ ).
The aggregation effect under strongly acidic conditions is not sufficient, and SiO
There was a problem that the removal rate of impurities other than ₂ was low.

To enhance the aggregating effect, JP-A-61-256
In No. 925, iron or iron compound is added to waste acid, and p
A method has been reported in which H is adjusted to 2 to 4 and the precipitated colloidal SiO ₂ compound is precipitated or separated by filtration to reduce SiO ₂ in waste acid. This method focuses only on SiO ₂ as an impurity in the waste acid and does not mention other impurities, and in fact, the effect of removing impurities such as P and Al is low. Further, it is stated that the effect of further reducing SiO ₂ can be achieved by adding iron or an iron compound and then adding ammonia, by the precipitation of iron hydroxide.
After the pH is adjusted by adding iron or an iron compound, ferric hydroxide is less produced, and there is a problem that the effect of removing SiO ₂ , other P, Al and the like is not sufficient.

As a method for utilizing the coprecipitation adsorption effect, in JP-A-63-49294, an alkali is added to the pickling waste liquid to adjust the pH to 3 to 4 to form a ferric hydroxide precipitate. , SiO ₂ is co-precipitated and adsorbed on the precipitate,
We are proposing a method to reduce ₂ . However, since the production amount of ferric hydroxide depends only on the ferric iron content, the effect is small when the ferric iron content is small, and conversely, the iron loss also increases when it is large. Have a problem with.

In JP-A-1-153532, after adding one or more kinds of Al, Cr, V, B and Zn metals to waste acid, the pH is adjusted to 3.5 to 6 by alkali and SiO 2 is added. _{2 In} addition, it has been proposed to coprecipitate and adsorb impurities into metal hydroxide to purify the waste acid, but it has the above-mentioned iron loss problem and further has the cost disadvantage of using expensive metal.

Further, in JP-A-3-5324, iron and an iron compound are added to waste acid, pH is adjusted, and then oxygen or an oxygen-containing gas is blown to form an iron hydroxide hydrate precipitate, which is then hydrated. Due to the adsorption effect of oxidative precipitation, SiO ₂ , etc.,
The reduction of impurities such as P, Al and Cr has been achieved.

However, pH is lowered by oxidation by blowing oxygen-containing gas, it occurs again dissolution of SiO _2, SiO ₂
There is a problem in that the removal effect is a negative aspect. This decrease in pH progresses with the promotion of the formation of hydrous iron oxide precipitates, so the removal effects are contradictory.

Further, in Japanese Patent Application No. 4-120367, an aqueous solution of iron chloride is neutralized with free hydrochloric acid in the solution with iron or an iron compound to adjust the pH to 2 to 4, and then contacted with oxygen or an oxygen-containing gas. While adjusting the pH to 2 to 5 by alkali treatment or the like, 0.5 to 15% of iron (Fe) in the solution is produced as a precipitate containing iron as a main component, and the precipitate is formed. A method of separating and making a purified iron chloride solution and then high-temperature roasting is introduced. However, this method cannot reduce impurities such as B, Ca, and Na that tend to remain on the liquid side.

[0010]

As described above, Japanese Patent Laid-Open Publication No. 61-
No. 256925 has only the effect of removing SiO ₂ , and in JP-A No. 63-49294, it depends on the amount of ferric iron and is inferior in controllability. JP-A-1-153532
In the issue, there was a cost problem. Further, in Japanese Patent Laid-Open No. 3-5324, SiO ₂ is reduced due to a decrease in pH during air oxidation.
There is a problem that the removal effect is reduced. Further, there is a problem that they are not effective against impurities such as B, Na and Ca.

The present invention provides a method for purifying an iron chloride solution, which can solve all the problems of the above-mentioned conventional techniques such as the impurity removal effect and the controllability in the technique of removing impurities in waste acid. The purpose is to do.

[0012]

Means for Solving the Problems In the manufacturing process of iron oxide for a ferrite raw material, the inventors of the present invention have earnestly conducted research on an industrial refining method of an aqueous solution of iron chloride, and as a result, found that the pH effect was found in the first step. SiO ₂ due to coprecipitation adsorption of the precipitate,
Impurities such as P and Al are reduced at the same time, and in the second step, ferric hydroxide is precipitated by pH adjustment after oxidation, and B, Na, and Ca can be reduced by redissolving the precipitate with hydrochloric acid. They have found the present invention and completed the present invention.

That is, according to the present invention, in a method for purifying a pickling waste liquid for producing iron oxide having a higher purity than a steel material pickling waste liquid, iron or an iron compound is contacted with a pickling waste acid which is an iron chloride solution. After neutralizing the free hydrochloric acid and adjusting the pH to 2 to 4, while contacting with oxygen or an oxygen-containing gas, p
By adjusting H to be 2 to 5 by alkali treatment, 0.5 to 15% of iron (Fe) in the solution is produced as a precipitate containing iron as a main component, and the precipitate is separated, A purified ferrous chloride aqueous solution is prepared, and then ferric chloride is oxidized to ferric chloride with an oxidizing agent and neutralized with an alkali to obtain a ferric chloride precipitate. Provided is a method for purifying an iron chloride solution which is dissolved to obtain a purified iron chloride solution.

[0014]

The present invention will be described in more detail below. First,
As described above, the raw material to which the present invention is applied is a hydrochloric acid pickling waste liquid such as a steel plate or an aqueous iron chloride solution such as concentrated waste hydrochloric acid obtained by heating and concentrating the same. They usually contain free hydrochloric acid and are often in a strongly acidic state with a pH below 1.

In the method for purifying the iron chloride solution of the present invention, the above raw materials are used for two-step treatment. The method will be briefly described. In the first stage, after reducing with scraps, etc., oxygen-containing gas is blown in and alkali is added at the same time,
By controlling H, impurities such as SiO ₂ , P and Al are simultaneously reduced. In the second step, ferric iron was changed to ferric iron with an oxidizing agent, and by adding an alkali to control the pH, a ferric hydroxide precipitate was formed, and then the formed precipitate was regenerated into hydrochloric acid. By dissolving, B, Na,
Ca and the like can be reduced, and a purified iron chloride solution can be obtained.

In the first step of this method, the pH is raised by adding iron or an iron compound and Fe ³⁺ + 1 / 2Fe → 3/2
Complete consumption of Fe ^{3+ in} the reaction of Fe ²⁺ . After that, alkali is added while blowing oxygen or oxygen-containing gas to form iron oxide hydroxide and ferric hydroxide precipitate. PH at that time, at the changing of such processing time, but may be controlled in precipitation amount, SiO ₂ others, P, Al,
It has controllability for removing impurities such as Cr.

In the first step of the method of the present invention, free hydrochloric acid is neutralized using iron or an iron compound to adjust the pH to 2
4, preferably adjusted to 2.5 to 3.5. Iron or iron compounds used for neutralization are mill scale, scrap,
An iron source such as iron powder generated in an iron mill can be used. Particularly, metallic iron is advantageous for increasing pH because it rapidly reduces trivalent iron (Fe ³⁺ ) in the liquid. Also, a shape having a larger specific surface area than the reaction rate surface is desirable. pH
2 to 4 is prepared because the effect of reducing impurities cannot be expected at a pH of less than 2, and the time until the pH rises becomes very long at a pH of more than 4, which causes a problem in practical operation.

The above reaction is carried out at 60 ° C. or higher, preferably 80 ° C.
The treatment proceeds rapidly at a temperature of not less than 0 ° C., and the ferrous chloride concentration of the treatment liquid is arbitrary, but it is economically advantageous to handle it at a high concentration (40 wt% or more).

The ferrous chloride aqueous solution thus prepared is separated from the above-mentioned iron or iron compound and sent to the next step.
First, in the first stage, the aqueous solution of ferrous chloride thus obtained is added with an alkali while being in contact with oxygen or an oxygen-containing gas (air is preferable) to prevent pH decrease due to oxygen oxidation, or Control pH to 2-5. As a result, the Fe content in the solution is 0.2
-5% is oxidized to ferric oxide hydroxide (FeOOH) to cause precipitation, and at the same time Fe ³⁺ is produced as hydroxide precipitate,
After coagulation, impurities such as Si, Al and P are coprecipitated / adsorbed and separated by filtration or sedimentation separation (precipitated Fe is 0.5 to 15% of iron content in the liquid).

Here, the pH is adjusted to 2 to 5 by adjusting p
This is because if H5 is exceeded, ferrous hydroxide precipitates and Fe loss is excessive. Further, the amount of Fe as a precipitate is set to 0.5 to 15% of the iron content in the liquid, because if it is less than 0.5%, the effect of removing impurities by coprecipitation cannot be sufficiently obtained, and if it exceeds 15%, Fe loss is large. This is because the yield is reduced.

In the second step, an oxidizing agent is added to the ferrous chloride solution after the first step treatment to obtain a ferric chloride solution. As the oxidant, hydrogen peroxide, coconut powder, etc. can be used. An alkali is added to the solution to control the pH to preferably 3 to 4, and the Fe content in the solution is ferric hydroxide precipitated. If the pH is lower than 3, all the Fe content may not be precipitated as ferric hydroxide precipitate. Also, the pH is 4
If it is larger, the amount of alkali added will be lost.
The purified precipitate is filtered and dehydrated or centrifuged to remove the ferric hydroxide precipitate, and then hydrochloric acid is added to form a ferric chloride solution. The Fe concentration of the solution is arbitrary, but it is desirable to set it to about 20 to 30 g / 100 ml for the efficiency of roasting. Further, regarding the Fe concentration, temperature control is also important at the same time so as not to crystallize. It is preferable that the temperature be 60 ° C. or higher.

As the alkali used in the above steps, ammonia water, NaOH or the like is preferably used.

The impurity removing mechanism of the present invention will be briefly described below. Si exists as SiO ₂ (silica), and mainly exists as silicate ions in the strongly acidic region, but pH 2 to
When neutralized to 5, colloidal polymerization progresses and becomes insoluble as negatively charged colloidal silica.

Al exists as a chloride in a strongly acidic region, but it precipitates as a hydroxide with an increase in pH. C
r, Cu, Ti and the like also exhibit similar behavior.

Regarding P, it dissociates mainly as a phosphate ion (PO ₄ ³⁻ ) in a strongly acidic region, and it is dissolved as a primary salt (Me ⁺ H ₂ PO ₄ ; Me is a metal) with metals. . p
When H is increased to the range of 2 to 5, metals and second salts (M
e ²⁺ H ₂ PO ₄ ), and the third salt (Me ³⁺ H ₂ PO ₄ ).
In particular, the third salt is sparingly soluble and precipitates as a precipitate.

On the other hand, hydrous iron oxide FeOOH and ferric hydroxide Fe (OH) ₃ produced by wet oxidation are structurally porous and have a large surface area, are positively charged in a liquid, and are negatively charged substances such as colloidal silica. It has properties such as lowering the zeta potential for neutralizing and aggregating in a charge-wise manner, easily aggregating with an anionic aggregating agent, and excellent sedimentation and separability and filtration properties.

Impurities such as Na, Ca and B have a particularly low adsorbing effect, and inevitably remain on the liquid side in the above method. In the second step, purification is carried out by utilizing that characteristic.

From the above points, the present inventors should simultaneously utilize the insolubilizing effect of Si, Al, P, etc. by pH adjustment and the coprecipitation / adsorption effect using iron oxide hydroxide and ferric hydroxide as a carrier. , And further, Na, Ca, B, etc. are efficiently left in the liquid side by the method of leaving Si, Al, P,
Impurities such as B, Na and Ca can be removed at a high removal rate.

An example of the flow of the present invention will be described below with reference to FIG. The raw material ferrous chloride aqueous solution is introduced into the reduction (pH adjustment) device 1, and iron or an iron compound (for example, scrap pieces) is added to neutralize free hydrochloric acid to pH 2 to 4.
After that, only the solution is sent to the oxidizer 3 via the buffer tank 2.

Next, in the oxidizing apparatus 3, in parallel with dispersing oxygen or an oxygen-containing gas (eg, air) in the liquid, the pH is maintained or controlled in the range of 2 to 5 by alkali, and the iron oxide hydroxide is obtained. And producing a sedimentation of ferric hydroxide. The precipitates of hydrous iron oxide and ferric hydroxide co-precipitated and adsorbed impurities such as Si, Al and P are aggregated with an anionic polymer flocculant (Miracle Furofuran EA-50 manufactured by Katayama Chemical Co., Ltd.) and thickener 4 After concentrating with
It is dehydrated and separated and discharged as a cake out of the system. On the other hand, an aqueous ferrous chloride solution is obtained from the thickener. An oxidizing agent is added in the oxidizing tank 5 to prepare a ferric chloride solution. Neutralize by adding alkali to the iron chloride solution in the neutralization tank 6 (pH 3-4)
Form a precipitate of iron hydroxide. Iron hydroxide separator 7
The separated neutralization liquid such as Ca, Na and B is drained. The separated iron hydroxide is dissolved in hydrochloric acid in the dissolution tank 8 to obtain a purified iron chloride solution.

[0031]

EXAMPLES The present invention will be specifically described below based on examples.

(Example) Using a steel plate pickling waste liquid as a raw material, a temperature (90 ° C.) was set in a batch type melting tank in which scrap (cold rolled steel plate scrap pieces generated in a steelworks) was filled at 5 times or more of the theoretical consumption amount. The mixture was stirred for 5 hours to neutralize free hydrochloric acid in the raw material and reduce Fe ³⁺ to Fe ²⁺ to adjust the pH to 2.
Adjusted to 7.

Next, after the liquid is separated from the scrap material, the liquid temperature is kept at 70 to 80 ° C. in the oxidation tank for 1 hour during 1 hour.
The same amount of air as the liquid volume was dispersed in the liquid per minute. At the same time, ammonia water is added to prevent the pH from decreasing due to air oxidation or to control the pH to an arbitrary value so that Fe in the solution
2 to 4% of the fraction was allowed to precipitate as a precipitate.

Further, an anionic polymer flocculant (Miracle Furofuran EA-50, manufactured by Katayama Chemical Co., Ltd.) was added with stirring, and then,
The solution was left standing and separated by sedimentation to obtain a ferrous chloride solution. An oxidizing agent (hydrogen peroxide) was added to the solution to oxidize all Fe to Fe ³⁺ . Aqueous ammonia was added to the solution until pH 4 was reached to form an iron hydroxide precipitate. After separating the precipitate by filtration,
It was dissolved in hydrochloric acid to obtain an iron chloride solution. As a result, Table 1 shows the liquid treatment conditions and the impurity concentration after the treatment (typically Si
O ₂ , P, Al, Ca, Na, B) (impurity concentration is converted to iron oxide concentration). Invention Example 1 pH 2.5 during air oxidation, pH 4 during neutralization Invention Example 2 pH 3.5 during air oxidation, pH 4 during neutralization

As comparative examples in the table, iron chloride solution (original sample) for pickling steel sheets and pH after scrap pH adjustment
An example of carrying out retentive oxidation (that is, an example without the second stage of the forced oxidation + neutralization step) is shown. Comparative Example 1 Original Sample Comparative Example 2 pH 2.5 at Air Oxidation, No Post Treatment Comparative Example 3 pH 3.5 at Air Oxidation, No Post Treatment

[0036]

[Table 1]

[0037]

According to the present invention, by treating the waste acid solution in two steps, it becomes possible to control the treatment of the solution, and the impurities (Si, Al, Cr, Cu, Ti, Na, C) in the solution can be controlled.
a, B, etc.) can be removed, and a highly purified iron chloride solution for ferrite production can be prepared.

[Brief description of drawings]

FIG. 1 shows a flow chart of the method of the present invention.

[Explanation of symbols]

 1 Reduction Device 2 Buffer 3 Oxidation Device 4 Thickener 5 Oxidation Tank 6 Neutralization Tank 7 Dehydration Separator 8 Dissolution Tank

Claims (1)

[Claims] 1. A method for purifying a pickling waste liquid for producing iron oxide of higher purity than a steel pickling waste liquid, wherein iron or an iron compound is contacted with a pickling waste acid which is an iron chloride solution to neutralize free hydrochloric acid. After adjusting the pH to 2 to 4 and adjusting the pH to 2 to 5 by contacting with oxygen or oxygen-containing gas by alkali treatment, the iron (Fe) content in the solution is 0.5 to 15 % As a precipitate containing iron as a main component, the precipitate is separated and made into a purified ferrous chloride aqueous solution, and then ferrous chloride is oxidized to ferric chloride with an oxidizing agent, and further alkali A method for purifying a ferric chloride solution, which comprises neutralizing with iron to obtain a ferric chloride precipitate, and dissolving the precipitate with hydrochloric acid to obtain a purified iron chloride solution.