JPH05161891A - Method for utilizing waste alkali water solution containing alkali hydroxide - Google Patents

Abstract

PURPOSE:To provide a method for utilizing industrially and economically a waste alkali water soln. contg. an alkali hydroxide. CONSTITUTION:A gas contg. CO2 is passed through a waste alkali water soln. contg. 0.1-8.0mol/l alkali hydroxide to react them to obtain an alkali water soln. contg. an alkali carbonate and then, an iron (II) salt water soln. being equivalent or less to the alkali carbonate contained in the alkali water soln. is added in the alkali water soln. to obtain a suspension contg. FeCO3 and then, after FeCO3 in the suspension is precipitated, supernatant liq. is removed to obtain a high concn. FeCO3 suspension.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of using a waste alkali aqueous solution, which can obtain a suspension containing FeCO ₃ at a high concentration from a waste alkali aqueous solution containing a low concentration of alkali hydroxide, and in particular, The waste alkali aqueous solution generated in the manufacturing process of various iron oxide particle powders for magnetic recording materials can be effectively used.

[0002]

As is well known, as an aqueous waste alkali solution containing a low concentration of alkali hydroxide generated in the production process of various iron oxide particle powders for magnetic recording materials, for example, goethite particles or magnetite particles are produced. The waste alkaline aqueous solution after being subjected to hydrothermal treatment to produce a plate-like Ba ferrite fine particle powder for magnetic recording materials, and a Co coating obtained by heating and reacting the waste alkaline aqueous solution and magnetic iron oxide particles in a highly alkaline aqueous solution. For example, there is a waste alkali aqueous solution after the generation of the stickable magnetic iron oxide particles.

Conventionally, as a method of treating each of the waste alkaline aqueous solutions, waste sulfuric acid or the like is added to each of the waste alkaline aqueous solutions without reusing the alkali component because the alkali concentration of each of the waste alkaline aqueous solutions is thin. It has been harmonized and released to the sea.

[0004]

As described above, the waste alkali aqueous solution containing a low concentration of alkali hydroxide is discarded without being reused, but it is very problematic from the viewpoint of effective utilization of resources. ..

However, as a method for effectively using the waste aqueous alkali solution, for example, Japanese Patent Application Laid-Open No. 49-35900.
A method of cooling the waste alkaline aqueous solution described in Japanese Patent Laid-Open Publication No. 1994-242242 and recovering sodium sulfate having a solubility or higher as crystals is proposed. Since sodium sulfate and the like are separated by cooling after concentrating, the thermal energy required for heating and concentrating becomes considerably expensive, so it is not profitable and is not performed so often.

[0006] The treatment of acidic wastewater includes, for example,
JP-B-37-13054, JP-A-52-1112
For the purpose of recovering Fe ions and the like contained in the wastewater disclosed in JP-A-68 and JP-A-60-90832, an aqueous solution of alkali hydroxide or an aqueous solution of alkali carbonate is added to iron carbonate, iron oxide or Fe ( Technical means for recovering OH) ₂ are known.

[0007] Therefore, the present invention provides a method for effectively and industrially utilizing the aqueous waste alkali solution, in detail, for producing goethite particles or magnetite particles from the aqueous waste alkali solution. It is a technical object to provide a new technical means capable of efficiently obtaining a suspension containing FeCO _{3 in} a high concentration useful as a starting material.

[0008]

The above technical problems can be achieved by the method of the present invention as follows.

That is, the present invention is 0.1-8.0 mol /
1 to 2 in a waste alkali aqueous solution containing 1 liter of alkali hydroxide
A gas containing 0 vol% CO ₂ is passed through the reaction to form an alkali aqueous solution containing an alkali carbonate, and then an aqueous solution of a ferrous salt is added to the alkali aqueous solution in an amount equal to or less than the amount of the alkali carbonate contained in the solution. a suspension containing FeCO ₃ by reacting, then consists in obtaining a high concentration FeCO ₃ suspension by removing the supernatant were allowed to settle FeCO ₃ of the suspension alkali hydroxide It is a method of using a waste alkaline aqueous solution containing.

Next, various conditions for carrying out the method of the present invention will be described.

The waste alkali aqueous solution containing a low concentration of alkali hydroxide used in the present invention may contain alkali hydroxide and alkali carbonate. still,
The alkali hydroxide is sodium hydroxide, potassium hydroxide, ammonium hydroxide and the like, and the alkali carbonate is sodium carbonate, potassium carbonate, ammonium carbonate and the like.

The waste alkaline aqueous solution is, for example,
A suspension containing a ferrous hydroxide colloid obtained by adding an aqueous solution of a ferrous salt and an aqueous solution of an alkali hydroxide equivalent to or more than Fe ^{2+ in the} aqueous solution of the ferrous salt, the suspension comprising: Aqueous waste alkali aqueous solution containing excess alkali hydroxide after generating goethite particles or magnetite particles by carrying out an oxidation reaction by aerating an oxygen-containing gas to oxidize, maghemite particles, magnetite particles and intermediate oxides thereof. Co- ^deposited magnetic iron oxide particles obtained by heat-reacting any of the magnetic iron oxide particles of a certain beltride compound particle in a highly alkaline aqueous solution containing metal ions such as Co ²⁺ and Fe ²⁺ were produced. alkaline suspension containing the the Co ions and Ti ions by waste alkali solution and Ba ions and Fe ³⁺ ions and optionally containing excess alkali hydroxide after, Using an autoclave or the like hydrothermal treatment and waste alkali solution or the like containing excess alkali hydroxide After generating the magnetic recording plate Ba ferrite fine powder can be cited as response device.

The concentration of alkali hydroxide in the aqueous waste alkali solution is 0.1 to 8.0 mol / l. 0.1mo
If it is less than 1 / l, it is not economical because the concentration is too thin and the equipment scale must be increased.
Further, occur simultaneously oxidized FeCO ₃ generation and FeCO ₃ when to produce FeCO _3, undesirably asymmetry crystal particles are formed when producing goethite particles or magnetite particles or the like as a starting material.
When it exceeds 8.0 mol / l, crystals of alkali carbonate are precipitated and troubles such as clogging may occur, which is not preferable. In addition, it is preferable that the concentration of impurities such as Na ₂ SO ₄ contained in the waste alkaline aqueous solution does not precipitate as crystals.

As the gas containing CO ₂ in the present invention, each combustion waste gas generated by burning a fuel such as coal, heavy oil, natural gas, city gas, generator gas, blast furnace gas can be used. .

The CO ₂ concentration of the gas containing CO ₂ used in the present invention is in the range of 1 to 20 vol%. 1v
If it is less than 10% by volume, the equipment scale becomes large, which is not economical, and a concentrated gas exceeding 20% by volume can be used. For example, pure CO ₂ gas can be used, but economically it is not possible to use the atmosphere. It is advantageous to use combustion exhaust gases of various coals and combustion exhaust gases of various petroleum exhausted therein, and CO ₂ in these exhaust gases is usually 20 vol%.
It is below. Above all, it is preferable to use the waste gas of the heavy oil combustion type boiler containing 11 to 14 vol% CO ₂ .

The impurities contained in the waste gas include O ₂ , SOx, NOx and the like. Even if such impurities are contained, high concentration FeCO ₃ obtained by carrying out the present invention is obtained. It does not hinder the production of goethite particles, magnetite particles or the like using the suspension as the starting material.

In the present invention, the flow rate of the gas containing CO ₂ and the aeration time when the alkaline aqueous solution containing alkali carbonate is produced are not particularly limited, and the pH of the alkaline aqueous solution is 11.5-12.3. It is sufficient to ventilate until the range is reached. If the pH is less than 11.5, Na
₂ CO ₃ is mixed with NaHCO ₃ , so FeCO
_At the time of sedimentation of ₃ , foaming and cloudiness of the supernatant occur. When the pH exceeds 12.3, since NaOH remains, Fe (OH) ₂ is generated and sedimentation is delayed, which causes an adverse effect.

In the present invention, the temperature at which an aqueous alkali solution containing an alkali carbonate is produced is set at the aeration of CO ₂
Usually, a range of 25 to 90 ° C. is suitable, though it depends on the temperature of the gas containing Although it can be produced even when the temperature exceeds 90 ° C, it is preferably 90 ° C or lower because the equipment cost and the like increase.

The ferrous salt aqueous solution used in the present invention may be ferrous sulfate, ferrous chloride or the like, and the concentration of the ferrous salt aqueous solution is not particularly limited. However, it is usually about 1.0 to 2.0 mol / l.

In the present invention, the amount of the ferrous salt aqueous solution added to the alkaline aqueous solution containing the alkaline carbonate is equal to or less than the amount of the alkaline carbonate contained in the solution. If the amount exceeds the equivalent, the Fe ²⁺ salt remains in the supernatant, so that it is necessary to treat the supernatant separately. A preferred range is 0.95-1.00 equivalent.

In the present invention, the stirring time for producing the alkaline aqueous solution containing the alkali carbonate depends on the apparatus such as the container and the stirrer, but is preferably in the range of 10 to 60 minutes. If the time is less than 10 minutes, the flocculation with low density of FeCO ₃ remains, so that the sedimentation time is delayed and 6
If it exceeds 0 minutes, flocs having a sufficiently low density of FeCO ₃ are already broken and easily settled, and since oxidation of FeCO ₃ also occurs, asymmetric goethite particles and magnetite particles are generated, which is preferable. Absent.

In the present invention, the concentration of FeCO ₃ in the suspension obtained by allowing the suspension containing FeCO ₃ to stand and removing the supernatant liquid is usually 0.5 to 2.0 mol.
/ L is preferable. If it is less than 0.5 mol / l, the economical effect is reduced due to the thin concentration,
When it exceeds 2.0 mol / l, the high concentration F obtained
Since the viscosity of the eCO ₃ suspension becomes high, when it is used as a starting material to produce goethite or magnetite, the reaction becomes non-uniform and handling becomes difficult.

The above 0.5 to 2.0 mol / l Fe
In producing goethite particles or magnetite particles using a suspension containing CO ₃ as a starting material, for example, JP-A-50-80999 and JP-A-59-23 are used.
A method for obtaining goethite particles by carrying out an oxidation reaction by passing an oxygen-containing gas through a suspension containing FeCO ₃ disclosed in Japanese Patent No. 2922, and JP-A-49-35.
A method of obtaining magnetite particles by performing an oxidation reaction by passing an oxygen-containing gas through a suspension containing FeCO ₃ disclosed in Japanese Unexamined Patent Publication No. 900-9005 and Japanese Unexamined Patent Publication No. 55-109232 may be used. Further, if necessary, after removing the supernatant liquid, an alkaline aqueous solution such as an aqueous solution of an alkaline carbonate or an aqueous solution of an alkali hydroxide or an aqueous solution of a ferrous salt may be added to adjust the alkali equivalent ratio.

[0024]

In [act invention, FeCO ₃ by removing the supernatant were allowed to settle FeCO ₃ in suspension
The concentration can be increased, but this is based on the findings obtained by the following experiments.

First, 40 g / l NaOH and 43 g / l Na ₂ SO ₄ obtained after producing goethite particles were produced.
When an aqueous ferrous salt solution was directly added to a waste alkali aqueous solution containing and to produce Fe (OH) ₂ colloid, as shown in FIG. 1, the obtained Fe (OH) ₂ colloid was precipitated. It took about 100 hours or more (shown as a in FIG. 1), and it took about 50 hours even if a coagulant was added (shown as b in FIG. 1).

Next, a ferrous iron salt aqueous solution is directly added to the waste alkali aqueous solution to generate an Fe (OH) ₂ colloid, and the Fe (OH) ₂ colloid is not precipitated to burn heavy oil having the following composition. Type Boiler Waste Gas Aerated to Fe
As a result of attempting to obtain a suspension containing CO ₃ , an O ₂ gas contained in the boiler waste gas causes an oxidation reaction, resulting in asymmetrical production of goethite particles and magnetite particles which are not suitable for practical use. Weight about air ratio 1.20 waste gas _{^{9450~12900Nm 3 / h O 2 3.8~3.9 vol}} % CO 2 11.8~12.6vol% SOx 19~22 ppm NOx 53~82 ppm Dust 0.003 ~ 0.006 g / Nm ³

After the above experiment, the waste alkali aqueous solution was first ventilated with the boiler waste gas for reaction to obtain an alkali aqueous solution containing Na ₂ CO ₃ . In this case, even if the waste gas contains O ₂ gas, no problem occurs because there are no Fe ions in the waste alkali aqueous solution, and then the ferrous salt aqueous solution is added to contain FeCO ₃ . As a suspension, as shown in FIG.
CO ₃ is allowed to settle in a standing time of about 1 to 2 hours (Fig. 1
(Indicated by c)).

Therefore, in the present invention, FeCO ₃ can be precipitated by allowing a suspension containing FeCO ₃ to stand for a short period of time.
The concentration of CO ₃ can be increased. Also,
Impurities such as Na ₂ SO ₄ contained can be removed considerably together with the supernatant, and the obtained high-concentration FeCO ₃ suspension is used as a starting material to generate goethite particles and magnetite particles with a uniform particle size in a high-concentration reaction. You can

According to the technical means disclosed in Japanese Patent Laid-Open No. 61-48428, it is described that Na ₂ CO ₃ with high purity can be obtained by passing CO ₂ gas through NaOH. There is no disclosure of using the waste alkaline aqueous solution and the waste gas.

[0030]

EXAMPLES Next, according to Examples, Comparative Examples and Reference Examples,
The method of the present invention will be described.

Example 1 40 g / l NaOH and 43 g / l Na ₂ S at 50 ° C.
12. Add to 1000 ml of waste alkali aqueous solution containing O ₄ .
A heavy oil combustion type boiler waste gas containing 5 vol% CO ₂ gas and 3.9 vol% O ₂ gas was aerated at a rate of 35 l / min to adjust the pH value of the waste alkaline aqueous solution to 12.1
As a result, an alkaline aqueous solution containing Na ₂ CO ₃ at 70 ° C. was obtained. To the obtained alkaline aqueous solution containing Na ₂ CO ₃ ,
FeSO ₄ aqueous solution containing Fe ²⁺ 1.5 mol / l 33
3 ml (corresponding to 1.00 equivalent to Na ₂ CO ₃ in the alkaline aqueous solution) was added and stirred for 20 minutes,
A suspension containing 0.375 mol / l FeCO ₃ was produced. A suspension containing the produced FeCO ₃ was allowed to stand for 100 minutes to remove the supernatant 833ml were allowed to settle FeCO ₃ to obtain a suspension containing FeCO ₃ of 1.0 mol / l.

Examples 2-14, Comparative Examples 1-5 Type of waste alkali aqueous solution, type and concentration of alkali hydroxide or carbonate contained, type and concentration of by-product salt contained, amount of the waste alkali used, type of gas containing CO _2, the concentration of CO ₂ gas, the concentration of O ₂ gas, the gas-passing time of an aeration rate and aeration time, pH and liquid temperature after venting,
A suspension containing FeCO ₃ was prepared in the same manner as in Example 1 except that the type of ferrous salt solution, the amount used and the alkali equivalent ratio, the stirring time, the sedimentation time, and the amount of the waste supernatant were changed. Was generated.

The main production conditions and various characteristics of the suspension containing FeCO ₃ at this time are shown in Tables 1 and 2.

[0034]

[Table 1]

In Table 1, the type A of the waste alkali aqueous solution containing the alkali hydroxide is A, the waste alkaline aqueous solution containing the alkali hydroxide after the formation of goethite particles,
B is a waste alkali aqueous solution containing alkali hydroxide after producing Co-deposited magnetic iron oxide particles, and C is a waste alkali solution containing alkali hydroxide after producing plate-like Ba ferrite fine particles for magnetic recording. The aqueous solution, D, is an aqueous alkali hydroxide solution prepared by dissolving an alkali hydroxide in water. Further, the type E of the waste gas containing CO ₂ is the waste gas of the heavy oil combustion type boiler, and the type F is the low concentration CO ₂ gas. Further, G at the aeration time is directly aerated to the waste alkaline aqueous solution, and H is aeration at the waste alkaline aqueous solution by adding the ferrous salt aqueous solution to produce Fe (OH) ₂ colloid.

[0036]

[Table 2]

In Table 2, I of the type of precipitate
FeCO ₃ and J are FeCO ₃ mixed with goethite particles and magnetite particles. Comparative Example 1
Then, FeCO ₃ and Fe (OH) ₂ were oxidized during aeration and the color of the suspension changed. In Comparative Example 2, a lot of bubbles were observed during sedimentation, and the supernatant was cloudy.
In Comparative Example 3, it was allowed to stand for 10 hours, but only half of the sedimented. In Comparative Example 4, sedimentation took 5 hours. In Comparative Example 5, although it settled, the precipitate was oxidized and its color changed.

Reference Example 1 3.0 l of a high concentration FeCO ₃ suspension containing 1.0 mol / l FeCO ₃ obtained in Example 14 was added to Na ₂ CO 3.
Aqueous 2.0 l (Na ₂ CO ₃ containing ₃ 350 g is
This corresponds to 2.1 equivalents to Fe. ) Is added and the temperature is 55
20 l / min of air was bubbled in at 4.5 ° C. for 4.5 hours to produce tan precipitated particles. In addition, p during air ventilation
H was 8-9. The yellowish brown precipitate particles are
The obtained yellowish brown particle powder obtained by filtering, washing with water, drying and pulverizing was goethite as a result of X-ray diffraction, and as shown in the electron micrograph (× 30000) shown in FIG. The particles were spindle-shaped particles having a diameter of 0.27 μm and an axial ratio of 5.3, and the particle sizes were uniform and dendritic particles were not mixed.

Reference Examples 2 to 4 Usage amount of high concentration FeCO ₃ suspension, kind and addition amount of additional alkali or ferrous salt, addition amount of water, reaction concentration, equivalence ratio, reaction temperature and aeration of air Goethite particles or magnetite particles were produced in the same manner as in Reference Example 1 except that the amount was variously changed.

Table 3 shows the main production conditions and various characteristics of the produced particles at this time.

[0041]

[Table 3]

[0042]

EFFECTS OF THE INVENTION According to the method for utilizing an aqueous waste alkali solution containing an alkali hydroxide according to the present invention, the aqueous waste alkali solution can be recycled industrially and economically effectively without discarding it.

Further, by utilizing the boiler waste gas, the high-concentration FeCO ₃ suspension obtained by the present invention is obtained without directly discharging the waste gas containing CO ₂ into the atmosphere, and then the suspension is used. When producing goethite particle powder or magnetite particle powder as a starting material, CO ₂
Because it emits gas, etc., C in the global environment
There is also an effect that it can be used to reduce O ₂ gas and the like.

The high-concentration FeCO obtained by the present invention
_The goethite particle powder or magnetite particle powder produced by using ₃ suspensions as a starting material is also suitable as a pigment powder for paints, a raw material powder for a magnetic particle material for magnetic recording, and a material powder for a magnetic toner.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the sedimentation time and the sedimentation volume of each of the produced suspensions containing FeCO ₃ or Fe (OH) ₂ .

FIG. 2 is an electron micrograph (× 3000) showing the particle structure of the spindle-shaped goethite particle powder obtained in Reference Example 1.
0).

Claims (1)

[Claims] 1. A 1-20 vol% C in a waste alkali aqueous solution containing 0.1-8.0 mol / l alkali hydroxide.
A gas containing O ₂ is ventilated to react to form an alkaline aqueous solution containing an alkali carbonate, and then an aqueous solution of a ferrous salt equal to or less than the amount of the alkali carbonate contained in the alkaline aqueous solution is added and reacted. By FeC
A suspension containing O ₃ and then FeCO ₃ in the suspension
_A method for utilizing a waste alkali aqueous solution containing alkali hydroxide, characterized in that a high-concentration FeCO ₃ suspension is obtained by precipitating ₃ and then removing a supernatant.