JPS60255907A - Manufactue of metallic cadmium powder - Google Patents

Abstract

PURPOSE:To manufacture easily active metallic Cd powder having a large specific surface area when Zn is immersed in a CdSO4 soln. to deposit metallic Cd, by adding a substance inhibiting the growth of crystals of deposited metallic Cd to the CdSO4 soln. CONSTITUTION:When Zn is immersed in a CdSO4 soln. to deposite metallic Cd on the Zn surface by a substitution reaction, a substance inhibiting the growth of crystals of deposited metallic Cd is added to the CdSO4 soln. The inhibiting substance includes protein forming lyophilic colloid such as glue, gelatin or albumin, and it is added by <=about 0.4g/l, preferably <=about 0.1g/l. Metallic Cd is deposited in the form of porous fine powder having activity and >=about 1m<2>/g specific surface area and contg. >=about 90% metallic Cd.

Description

[Detailed description of the invention] [Field of invention] The present invention relates to a method for producing metal cadmium powder.

In particular, the present invention relates to a method for easily producing active metal cadmium powder with a large specific surface area.

[Prior art]

Conventionally, as a method for producing metal cadmium using a substitution reaction, a zinc plate is immersed in a cadmium sulfate solution and a substitution reaction (oxidation-reduction reaction, formula (1) below) between Cd ions and Zn ions in the solution is carried out. Therefore, a method is known in which cadmium powder made of dendrites is formed on the surface of a zinc plate and recovered to obtain metal cadmium.

Cd50. +Zn −+ ZnSO4+Cd −1)
However, in the conventional method, in order to obtain metal cadmium in powder form, the above-mentioned sponge is ground into lumps, and then a fine grinder such as a ball mill is used.

It must be ground to a fine particle size.

In particular, when the obtained metal cadmium powder is used as an active material for batteries such as nickel-cadmium batteries, it is required to be active, so at least 1 m"
It is desired to have a specific surface area of /I or more, and therefore it is necessary to carry out the grinding carefully. When used as such an active material, it is desired that the metal cadmium content (metallic Cd content) in the cadmium powder is at least 901 or more.

In order to satisfy these conditions, sufficient pulverization is carried out using the above-mentioned known method until the grain size is reduced to several micrometers or less, and furthermore, in order to prevent oxidation during pulverization, wet pulverization is carried out in, for example, alcohol. Alternatively, in the case of dry pulverization, a number of measures had to be taken, such as carrying out the pulverization in an inert gas.

Therefore, it has been desired to be able to recover fine particulate cadmium powder directly from a solution without using pulverization means.

[Purpose of the invention]

An object of the present invention is to provide a method for producing metal cadmium powder that eliminates the drawbacks of the conventional methods and can recover fine cadmium powder that is fine, has a large specific surface area, and has a high metal cadmium content directly from a solution in which a substitution reaction is carried out. There's K things to do.

The above object is to suppress the crystal growth of metal cadmium precipitated in the cadmium sulfate solution in a method for producing metal cadmium powder through a step of immersing zinc in a cadmium sulfate solution and precipitating metal cadmium through a substitution reaction. This is achieved by having a substance that absorbs water exist.

[Embodiment]

FIG. 1 is a process explanatory diagram of one embodiment of the present invention. The most important point in the steps of the Kinen method is the addition of a substance that has the effect of inhibiting crystal growth to the cadmium sulfate solution used as the replacement liquid. The precipitation process of metallic cadmium in a substitution reaction can be explained by nucleation on the zinc surface at the beginning of one reaction and growth of dendrite crystals as one reaction progresses.

In the case of the known method, most of the precipitated cadmium contributes to the growth of andrite crystals, except at the initial stage of the reaction, forming coarse dendrites, and as a result, the plates of andrite crystals become entangled with each other to form sponges. As mentioned above, the sponge formed here is not easy to grind into fine powder. Therefore, in order to eliminate such drawbacks, the present inventors conducted research to directly precipitate fine powdered cadmium in the substitution reaction, and as a result, they found that a substance that has the effect of inhibiting crystal growth was added to the cadmium sulfate replacement solution. By adding K, the growth of coarse andrite is suppressed,
Furthermore, it was discovered that the fine metal cadmium powder with a large specific surface area can be directly recovered without forming a sponge because the precipitates are easily separated from the zinc surface.90 In the method of the present invention, the crystal growth of dendrites is However, on the other hand, since spontaneous detachment of precipitates from the zinc surface also occurs in a fast cycle, the frequency of nucleation increases and the substitution rate is not inhibited. Due to the nucleation and crystal growth that occur in this rapid cycle, the precipitate does not take on the appearance of a sponge unlike in known methods, but maintains a fine powder form and is deposited at the bottom of the tank used for the substitution reaction, making it easy to recover.

In addition, the collected sediment is easily dispersed in the first washing step and easily separated from substances that can suppress the crystal growth of the metal cadmium, and if it is further dried after K filtration, no pulverization step is required. Metallic cadmium powder can be obtained without Moreover, the powder obtained in this process is fine and each individual powder has a spongy shape.
"Has a specific surface area of 71 or more and has a metallic Cd content of 90
96 or more active.

Used in the present invention. The substance that can suppress the crystal growth of the precipitated metal cadmium is as follows.

(() As a substance capable of forming a lyophilic colloid in a cadmium sulfate solution, 1, for example, glue.

Proteins such as gelatin and aldimine.

(11) Substances that can form salts or complex salts with cadmium include 1, such as caffeine, sulfur-containing amino acids (L-cysteine, cystine, methionine, etc.), and 01D polymer flocculants, such as anionic or nonionic I lyacrylamide. An example of such a flocculant may be mentioned.

The present inventors used thiourea as a substance other than the above.

An example of an aromatic compound having an OH group is α-naphthrol, a polymer substance such as polyvinyl alcohol, and a carbohydrate such as sugar. ing.

The amount of the substance capable of suppressing the crystal growth of metal cadmium is determined appropriately depending on the cadmium concentration of the substitution liquid and the acting force of the substance itself, and is approximately 0.4.
It is desired that 1/ is equal to or less than OIIμ. 0.41! If / is more than .

Although it has the effect of inhibiting crystal growth, the andrite branches exhibit a granular shape and tend to reduce the specific surface area as a whole.
This is because a specific surface area of 1 m''79 or more may not be achieved.

In the present invention, there is no need to particularly limit the cadmium concentration of the cadmium sulfate solution used as the replacement liquid. Concentrations commonly used in known methods, e.g. 40-5011/
It can be arbitrarily selected within the concentration range of 1 or less. As a cadmium source, a natural resource such as an oxide, or a cadmium compound in a somewhat fractionated state can be used.

In the present invention, the precipitates during the substitution reaction naturally separate from the zinc surface, but this natural separation can be done by artificially scraping off the K in a faster cycle or by applying vibration to the immersed zinc plate. In this case, a finer powder with a larger specific surface area can be obtained. This is thought to be due to K accelerating the nucleation cycle on the zinc surface.

In the present invention, the temperature of the substitution liquid does not need to be particularly limited.5 Although the method of the present invention can be sufficiently carried out by the substitution reaction at room temperature, for example, heating to a temperature of 50 to 80°C may be used to control the substitution reaction rate. Operations for increasing productivity by increasing productivity are normally carried out in known methods, and this does not impede the effects of the present invention.

Further, although the form of zinc used in the present invention is not limited, it is preferably in the form of a plate with a smooth surface.

The four methods of the present invention will be explained in more detail with reference to Examples below.

Example 1 Dissolve cadmium oxide with sulfuric acid to obtain a Cd concentration of 4011
/l Thiourea as an organic additive after K adjustment.

L-cysteine, α-naphthol, ? Ten types of anionic flocculants and nonionic flocculants consisting of ribinyl alcohol glue, gelatin, caffein, sand m, and lyacrylamide-based polymers were added at concentrations of o, i, and iyt, respectively, to prepare a replacement liquid. Take 2 t of each substitution liquid into a vessel F)
Four zinc plates each having a size of 100 m x 50 m x 15 tsm T were immersed in the solution, and a substitution reaction was started at room temperature. During the reaction, the immersed zinc plate was occasionally vibrated to remove precipitates. After the substitution reaction is complete,
The precipitate deposited at the bottom of the container is collected, and then washed with water, alkaline, and alcohol in the machine shown in the process shown in Figure 1, filtered, dried at a temperature of 60 to 70°C, and classified with a 350 methane to obtain metal cadmium powder. Obtained.

The properties of the metal cadmium powder obtained by the above operation are shown in Table IK. From Table 1, glue, which is tannokuku substance,
Gelatin was particularly effective, and a specific surface area of 2 m''79 or more was obtained.Other effective materials were 1c and ff lyacrylamide polymers, caffeine, and L-cysteine.

Table-1 * ◎ represents a specific surface area of 2 m'', 41 or more, O represents 1 to 2 points, 2 force 1x represents a specific surface area of 1 m''/l or less.

Example 2 Dissolve cadmium oxide with sulfuric acid and apply 11 degrees Cd to 40Vt
Addition concentration of glue after K adjustment is 0.8, 0.4゜0
．． 2, 0.1, 0.051//l, Toru-sama, 5
[B) ft substitution liquid was prepared. Example 1 for these five types
A similar operation was performed to obtain metallic cadmium powder. The relationship between the amount added and the specific surface area in this case is shown in FIG.

As can be seen from Figure 2, when the Cd concentration is 140 N/l, the addition amount is 0, and the specific surface area is 1 for the following glue addition.
m''/9 or higher, proving to be particularly effective.

Example 3 Dissolve cadmium oxide with sulfuric acid to make Cd concentration 20&/lK
Addition concentration of glue after adjustment is 0.4, 0.2.0.
l.

Four types of replacement liquids were prepared so that the concentration was 0.059/l.

These four foods were subjected to the same operations as in Example 1 and (b) to obtain metal cadmium powder. The relationship between the amount added and the specific surface area in this case is shown in FIG. As can be seen from FIG. 2, in the case of a Cd concentration of 0 2 /A, the specific surface area increases to 1 m''/9 or more when the glue addition amount is 02 ν or less, which proves to be particularly effective.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the manufacturing process of metal cadmium powder in the present invention. Figure 2 shows the displacement liquid Cd1lI degree 401//l
Graph showing the relationship between the amount of glue added and specific surface area in K. FIG. 3 is a graph showing the relationship between the amount of glue added and the specific surface area when the Cd concentration of the replacement liquid is 201/lK. 91 Figure

Claims (9)

[Claims] (1) A method of producing metal cadmium powder through a step of immersing zinc in a cadmium sulfate solution and precipitating metal cadmium by a substitution reaction. A method for producing metal cadmium powder, the special purpose of which is to include a substance capable of suppressing crystal growth of precipitated metal cadmium in the cadmium sulfate solution. (2) Claim No. 1, wherein the substance capable of suppressing the crystal growth of metal cadmium is an R liquid colloid forming substance.
A method for producing metal cadmium powder as described in . (3) The method for producing metal cadmium powder according to claim (2), wherein the lyophilic colloid-forming substance is tan-matrix. (4) The method for producing metal cadmium powder according to claim (3), wherein the tan/liquid substance is glue or gelatin. (5) The method for producing metal cadmium powder according to claim 0, wherein the substance capable of suppressing the crystal growth of metal cadmium is a substance capable of forming a salt or a complex salt with metal cadmium. (6) The method for producing metal cadmium powder according to claim (5), wherein the salt-forming substance is caffeine. (7) The method for producing metal cadmium powder according to claim (5), wherein the complex-forming substance is a sulfur-containing amino acid. (8) The method for producing metal cadmium powder according to claim (1), wherein the substance capable of suppressing crystal growth of metal cadmium is a polymer flocculant. (9) 4 where the polymer flocculant is anionic or nonionic;
+7 A method for producing metal cadmium powder according to claim (8), which is an acrylamide-based flocculant.