JPH0617236B2 - Method for producing manganese dioxide for dry batteries - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing manganese dioxide for a dry battery.
More specifically, an electrochemically active material suitable for dry cells,
The present invention relates to a method capable of inexpensively producing γ-type manganese dioxide.

2. Description of the Related Art The most common type of dry battery, the cylindrical type (UM-type), mixes MnO ₂ as an active material and acetylene black or graphite powder as a conductive agent together with an electrolytic solution, and then mixes this with a cathode Zn can. It is obtained by wrapping it in kraft paper coated with paste so that it does not come into contact, and inserting a positive electrode carbon rod.

As described above, in the case of a manganese dry battery, manganese dioxide is used as the positive electrode active material, and in order to use this in a dry battery, the content of impurities is small, it is electrochemically active, and the bulk density is large. Moreover, low price is an important requirement.

Conventionally, high quality naturally occurring manganese ore has been used to satisfy these requirements, but this is becoming scarce worldwide, and it is not possible to obtain good quality manganese dioxide for dry batteries from natural ore. It's getting harder. Therefore, electrolytic manganese dioxide has been noticed and widely used as an alternative. This product has a high activity and a large bulk density, and is suitable for the above purpose. However, in order to obtain this, an electrolytic oxidation process is indispensable. Since this process consumes a large amount of power, the product cost is extremely high.

Therefore, many studies have been conducted to obtain manganese dioxide which is inexpensive and has good electrochemical properties. As one of them, it has been reported so far that electrochemically active γ-type manganese dioxide (IV) can be obtained by treating manganese (III) oxide with sulfuric acid. However, most of them are intended to convert low-activity β-type manganese dioxide ore into active manganese dioxide, and the gangue component in the ore remains in the activated manganese dioxide as it is. Since the purity is about 80%, there is a problem in using it as a positive electrode active material for dry batteries.

Further, as a result of such activation treatment, half of the manganese in the raw material ore is converted into manganese sulfate (I
I) results in a significantly low yield and a poor yield.

Mn ₂ O ₃ + H ₂ SO ₄ → MnO ₂ + MnSO ₄ + H ₂ O Therefore, various methods for effectively utilizing this by-product manganese sulfate have been proposed, but none of them are sufficient and are still in practical use. Has not arrived.

Manganese salts synthesized from an aqueous solution of manganese (II) sulfate are all formed as fine particles except for crystals of manganese sulfate, and thus manganese dioxide obtained from them has an apparent density of 0.5 g / cm ³ or less. It is small and has poor filling properties for batteries, and of course, the resulting dry battery has unsatisfactory discharge characteristics.

As one method for solving such a drawback, there is a heaviening method which the present inventors have already applied for as Japanese Patent Application No. 59-76334 (Japanese Patent Application Laid-Open No. 60-221323). That is, in this method, manganese oxide obtained by roasting manganese sulfate is acid-treated with sulfuric acid to give manganese dioxide, and then 0.25 in a powder state.
A manganese dioxide with an apparent density of 1.6 to 2.0 g / cm ^{3 that} is electrochemically active and has excellent packing properties is produced by compressing under a pressure of up to 20 tons / cm ² and crushing to a prescribed particle size. is there.

Furthermore, although there are many papers on the reaction of roasting manganese sulfate crystals to produce Mn ₂ O ₃ and / or Mn ₃ O ₄ , there are very few studies to obtain highly active manganese dioxide for dry batteries, There is a recent one entitled "Manufacture of manganese (IV) oxide for batteries from manganese (II) sulfate" by Koga (Journal of the Chemical Society of Japan, 1983, (1), 18-2).
2).

This document is particularly intended to increase the apparent density, and is characterized in that commercially available manganese sulfate (MnSO ₄ .4-6H ₂ O) is dehydrated to a monohydrate to form a lump. , It is reported that an apparent density of about 0.7 g / cm ³ can be obtained.

That is, after roughly crushing commercially available manganese (II) sulfate, 200 ° C
The sample is heated to a constant weight in, dried, dehydrated, and lumped to form a pulverized sample, which is dried again at 250 ° C. and re-pulverized. The value of the apparent density is almost the same as the value of manganese dioxide obtained by activating the β-type manganese dioxide ore, and the condition as a practical product can be satisfied.
Further, as a result of a discharge test of the thus obtained manganese dioxide in a wet battery, it is superior to electrolytic manganese dioxide in light discharge and gives discharge characteristics equivalent to electrolytic manganese dioxide in heavy discharge.

Problems to be Solved by the Invention As described above, it has become increasingly difficult to obtain high-quality manganese dioxide from natural ores, and for this reason, resource-rich low-activity β-type manganese dioxide ( I
V) Attempts have been made to chemically treat manganese (III) oxide obtained by heat-treating an ore (eg pyrolusite), for example sulfuric acid or nitric acid to obtain electrically active manganese dioxide. ing. However, in this method, since manganese oxide obtained by heat-treating manganese ore is subjected to acid treatment as it is, gangue components and the like contained in the ore remain in the generated manganese dioxide, so that the MnO ₂ grade is Remarkably low, which was insufficient for practical use.

Further, in such an acid treatment of manganese oxide, for example, sulfuric acid treatment, manganese sulfate as a by-product is formed in an equimolar amount with the target manganese dioxide or with Mn ₃ O ₄ in an amount twice as much as the target, so that the efficiency is improved. Is extremely low, which is an industrial disadvantage.

Therefore, it is urgently desired to develop a new method for producing manganese dioxide for a dry battery, which can effectively reuse manganese sulfate as the by-product and can solve the deterioration of quality due to contamination by gangue components and the like. In addition, it is extremely significant in industrially producing inexpensive and high-quality manganese dioxide. The object of the present invention is also such a point.

Means for Solving the Problems The present inventors have proposed a method for obtaining active γ-type manganese dioxide by subjecting manganese (III) oxide obtained by heat-treating β-type manganese (IV) ore and the like to sulfuric acid treatment. In view of the current situation as described above, the problem of deterioration of the quality of the final product due to the mixing of gangue components in the ore is that the sulfuric acid crystallized from the manganese sulfate aqueous solution obtained during the acid treatment is purified. This can be solved by using manganese crystals as the raw material, and in order to make the final product electrochemically active γ-type manganese dioxide, the specific surface area of manganese (III) oxide that is subjected to acid treatment (applied interface) It was found that it is important to suppress the α-formation of manganese dioxide that is generated by making as large as possible.

That is, the method for producing manganese dioxide for dry batteries of the present invention is Mn.
Roasting manganese sulphate crystals mainly composed of SO ₄ · nH ₂ O,
A method for producing manganese dioxide for a dry battery by treating the obtained manganese oxide (MnO _x ) with an acid, wherein the manganese sulfate crystal is preliminarily heated to a temperature within a range of 250 to 500 ° C. and n is 1 or less.
It is characterized in that it is dehydrated to the following and then roasted to reduce the crystal grain size of the MnO _x to 10 μm or less and then subjected to an acid treatment.

Examples of manganese sulfate that can be used in the method of the present invention include MnO ₂ , ores containing MnCO ₃ , manganese sulfate, manganese carbonate roasting, sulfuric acid obtained by acid treatment of Mn ₂ O ₃ obtained by oxidation, etc. The manganese aqueous solution may be purified and crystallized, and both give good results.

The method of the present invention can be carried out according to the steps shown as a flow chart in FIG.

First, manganese sulfate crystals as a raw material are roasted manganese ores to Mn ₂ O ₃ or MnO, and then treated with sulfuric acid to separate into low-grade MnO ₂ and manganese sulfate aqueous solution as in the conventional method, and roasted manganese is used. It can be obtained by further refining and crystallizing the manganese sulfate aqueous solution obtained from the sulfuric acid treatment of ore. Here, as the refining treatment, neutralization with lime or the like and purification with ammonium sulfide or the like are effective, and impurities (As, Fe, Mo, etc.) are advantageously removed by such treatment. Also, crystallization can be carried out, for example, simply by concentrating by heating.

The manganese sulphate crystals thus obtained are generally MnSO ₄ · nH ₂
It contains a large amount of water of crystallization as indicated by O (n = 2 to 4). Then, this was dehydrated to n ≦ 1 and then roasted (900 to 1,100 ° C.) to Mn ₃ O ₄ and further oxidized and roasted (6
(00-900 ° C.) to obtain Mn ₂ O ₃ and treating it with sulfuric acid gives high-quality (not containing gangue components) MnO ₂ .
Here, it is advantageous that the sulfuric acid concentration in the sulfuric acid treatment is in the range of 3N to 36N, and the treatment temperature is in the range of 65 to 100 ° C, and the manganese sulfate aqueous solution formed in this step is recycled. , Subjected to similar treatment and converted to high-quality MnO ₂ .

Action The method of the present invention is an ore containing MnO ₂ , MnCO ₃ , or Mn ₂ O obtained by roasting or oxidizing manganese sulfate or manganese carbonate.
_The acid treatment of ₃ with sulfuric acid is intended to effectively utilize the manganese sulfate aqueous solution by-produced in the step of producing manganese dioxide. For this purpose, the manganese sulfate aqueous solution is purified and crystallized to remove impurities. It is characterized in that it is converted into electrochemically active γ-type manganese dioxide after it is made into a small amount of purified manganese sulfate crystals. However, for that purpose, it is necessary to take various measures in consideration of the following points.

First, the thermal decomposition of manganese (II) sulphate crystal begins near 800 ° C and Mn ₂ O ₃ and / or Mn ₃ O ₄ is produced.
This thermal decomposition reaction is an endothermic reaction, and ordinary manganese sulfate crystals have 2 to 4 water of crystallization. Therefore, a large amount of heat energy is required to remove this crystal water.

Also, when the water of crystallization is released, if it is not promptly removed from the system, it dissolves the manganese sulfate crystals and solidifies them to form lumps, which not only hinders the thermal decomposition reaction of manganese sulfate but also roasts it. Since it sticks in the equipment, special measures are required to prevent this sticking.

Furthermore, in order to obtain manganese dioxide for dry batteries, acid treatment with sulfuric acid is necessary.
It should be manganese oxide whose main component is ₂ O ₃ . Therefore, it is necessary to change Mn ₃ O ₄ to Mn ₂ O ₃ , which can be realized by heating and oxidizing in air at 600 to 900 ° C.
However, this reaction is surface-chemically controlled, and therefore,
In order to accelerate the reaction, it is necessary to make the reaction interface as large as possible.

From the above viewpoints, the inventors of the present invention have variously studied, and removal of water of crystallization is performed by heating the manganese sulfate crystal (MnSO ₄ .nH ₂ O) at a temperature of 250 to 500 ° C. before roasting (dehydration treatment). It has been found that this can be advantageously carried out. In this dehydration treatment, as described above, it is important to quickly remove the separated water of crystallization outside the system, and it is advantageous to use a hot air dryer type with a fluidized bed or a forced agitator. In relation to the above dehydration treatment temperature, when the temperature is higher than 500 ° C, desorption of water of crystallization occurs rapidly, which causes unfavorable solid solution of crystals. On the other hand, when carried out at a temperature lower than 250 ° C. Since the dehydration rate is extremely slow, the efficiency is drastically reduced and the work efficiency is deteriorated.

The manganese sulphate dehydrated according to the invention is shown in the attached FIG.
As can be seen from the comparison between (a), (b) and (c), cracking along the crystal interface occurs with the desorption of water of crystallization. When this manganese sulphate is roasted at 900-1100 ° C, it becomes unit particles along the cracks that occur when the water of crystallization breaks off, and changes into a tuft shape of grapes with a diameter of about 1 μm (Figs. 2 (e) and (f)). reference). On the other hand, when the water of crystallization is manganese sulfate of 2 (Fig. 2 (a)), if it is roasted as it is, the crystals are considerably dissolved as shown in Fig. 2 (d). Recognize.

Thus, according to the present invention, the manganese (III) oxide obtained after roasting by dehydration treatment before roasting is a tufted aggregate of grapes of spherical particles having a unit particle size of 10 μm or less, and is therefore crushed. It is extremely easy to pulverize it. Thus, according to the method of the present invention, since manganese (III) oxide is crushed and pulverized to have a spherical shape of 10 μm or less, the specific surface area is very large, and the γ-type produced by acid treatment with sulfuric acid is formed. The production rate of manganese dioxide is extremely high and active, and unlike the Koga paper, it has excellent heavy discharge characteristics (see FIG. 4). From this point of view, setting the particle size of manganese oxide to 10 μm or less is extremely important in the method of the present invention, and this condition is satisfied in order to obtain highly active γ-type manganese dioxide in a high yield. There is a need.

FIG. 3 shows a comparison of the state changes of manganese sulfate crystals treated according to the method of the present invention and similar crystals treated according to the conventional method. That is, according to the method of the present invention,
The MnSO ₄ crystals crystallized as relatively large crystal grains are cracked by the dehydration treatment, but they remain large-sized crystals by the conventional method (Fig. 3 (a)). Further, in the case of roasting such manganese sulfate, those treated according to the method of the present invention having cracks can be rapidly decomposed, and Mn ₃ O ₄ having a porous fine particle size can be obtained, while The method requires a long time roasting at high temperature, and the product (Mn ₃ O ₄ ) obtained has a large particle size (see FIG. 3 (b)). This is further roasted and converted into Mn ₂ O ₃ as shown in FIG. 3 (c), and the same can be said in this case as in the case of (b). Further, since this roasting treatment is surface chemical reaction rate-determining, Mn ₃ O ₄ → Mn ₂ O ₃ is incomplete in the conventional method, or it becomes an uneconomical treatment with large energy consumption.

Thus, manganese oxide to be subjected to sulfuric acid treatment is obtained, but when operated according to the method of the present invention, high-quality γ-type manganese dioxide is provided at a high yield without problems,
In the case of the conventional method, the reaction is slow and the quality is not so good.

That is, the apparent density is remarkably inferior, and extra operations and treatments are required to improve it.

Examples Hereinafter, the method of the present invention will be described in more detail with reference to examples, but these are examples of the present invention, and the scope of the present invention is not limited to the following examples.

Example 1 Mn ₂ O ₃ obtained by roasting manganese dioxide ore at 900 ° C.
Was treated with sulfuric acid to obtain manganese dioxide. still,
The manganese sulfate aqueous solution produced as a by-product in the above step was neutralized with lime and purified with ammonium sulfide to remove impurities, thereby obtaining a purified manganese sulfate aqueous solution.

The aqueous solution of manganese sulfate thus obtained was heated and concentrated to be crystallized as crystals of manganese sulfate (dihydrate) (see FIG. 2 (a)). Then, the water of crystallization was removed by dehydration at 300 ° C. for 1 hour to obtain a monohydrate salt as shown in FIG. 2 (b). On the other hand, dehydration treatment was carried out at 400 ° C. for 2 hours to obtain a hemihydrate as shown in FIG. 2 (c).

By roasting the three types of manganese sulfate thus obtained at 1,000 ° C. for 1 hour, manganese oxide (Mn ₃ O ₄ ) as shown in FIGS. 2 (d) to (f) is formed, respectively. did. Then
Tufted Mn of Grape Obtained from Dehydrated Manganese Sulfate of Monohydrate
_After oxidizing and roasting ₃ O ₄ in air at 700 ° C. for 2 hours to form Mn ₂ O ₃ , acid treatment with sulfuric acid (concentration: 10 N) was performed, and the obtained manganese dioxide was washed and the pH was adjusted. pressurizing s by condensation, density 1.23 g / cm ³ apparent Fritsch, tap density 2.00 g / cm ³
Of manganese dioxide powder was obtained.

Thus, the discharge characteristics of the manganese dioxide obtained by the method of the present invention, electrolytic manganese dioxide and manganese dioxide obtained by the conventional method (non-dehydration treatment) were examined. The results are shown in Fig. 4. This discharge characteristic is obtained by using the above manganese dioxide in a dry battery (battery size: R20 (single), electrolyte: 30% ZnC).
l ₂ , MnO ₂ filling amount: 30 g / cell) was prepared, and the battery life at the time of heavy load discharge was measured according to a conventional method. That is, the change in the potential with respect to the discharge time when 2 ohm continuous discharge was performed at 20 ° C. was plotted.

As is clear from FIG. 4, according to the manganese dioxide obtained by the method of the present invention, it is possible to achieve discharge characteristics superior to those obtained by the conventional method as well as electrolytic manganese dioxide.

Effects of the Invention As described in detail above, according to the method for producing manganese dioxide for a dry battery of the present invention, before the manganese sulfate crystal as a raw material is roasted to obtain manganese oxide, dehydration treatment is performed under predetermined conditions in advance. However, the particle size of the manganese oxide can be reduced to 10 μm or less before the sulfuric acid treatment by applying a unique device of roasting and then roasting. -Type manganese dioxide can be efficiently obtained. In addition, this manganese dioxide has a better heavy discharge characteristic than conventional electrolytic manganese dioxide, and is extremely useful as a positive electrode active material for dry batteries.

Further, manganese sulfate produced as a by-product from manganese ore or by the sulfuric acid treatment of synthetic manganese oxide can be effectively used, and high-quality γ-type manganese dioxide can be provided at low cost.

[Brief description of drawings]

FIG. 1 is a flow chart for explaining the method of the present invention, and FIGS. 2 (a) to (f) are electron micrographs showing the “particle structure” of the product at each stage of the method of the present invention. (Magnification: × 10,000), and FIGS. 3 (a) to (d) are schematic diagrams showing the states of products obtained by the steps of the method of the present invention and the conventional method in comparison. FIG. 4 is a graph plotting the results of examining the discharge characteristics of manganese dioxide obtained by the method of the present invention and manganese dioxide obtained by the conventional method.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kensaku Murakawa Kensaku Murakawa 1-3, Nishi-Nagasumotodori, Amagasaki City, Hyogo Prefecture Sumitomo Metal Industries, Ltd. Central Research Laboratory (72) Ryohei Ishikawa, Myokogogen Town, Nakakubiki District, Niigata Prefecture Daiji Taguchi 272 Chuo Denki Kogyo Co., Ltd. (72) Inventor Hiroshi Tsukida Myokokogen-cho, Nakakubiki-gun, Niigata Prefectural Taguchi 272 Chuo Denki Kogyo (72) Inventor Hiroshi Ochiai 272 Taguchi, Myokokogen-cho, Nakakubiki-gun Electric Industry Co., Ltd. (72) Inventor Masami Aimi Taguchi 272, Myokokogen-cho, Nakakubiki-gun, Niigata Chuo Electric Industry Co., Ltd. (72) Takahiro Miyashita 272 Taguchi, Myokokogen-cho, Nakakubiki-gun, Niigata Chuo Denki Kogyo Co., Ltd. In-house (72) Inventor Masanori Niiyama 272 Taguchi, Myokokogen-cho, Nakakubiki-gun, Niigata Chuo Electric Industry Co., Ltd. The inner

Claims (3)

[Claims] 1. A manganese sulfate crystal containing MnSO ₄ .nH ₂ O (n = 2 to 4) as a main component at a temperature within a range of 250 to 500 ° C.
Of manganese dioxide having a crystal grain size of 10 μm or less to produce manganese oxide (MnO _x ), and acid-treating the manganese oxide. Method. 2. The manganese sulfate crystal is obtained by purifying and crystallizing an aqueous solution of manganese sulfate obtained by treating Mn ₂ O ₃ or MnO obtained by roasting manganese ore or manganese sulfate or manganese carbonate with sulfuric acid. The method for producing manganese dioxide for a dry battery according to claim 1, characterized in that 3. The roasting is performed at 900-1100 ° C. and 600
The method for producing manganese dioxide for a dry battery according to claim 1 or 2, characterized in that it is carried out in two steps of oxidation roasting at 900 ° C.