WO2002020857A1

WO2002020857A1 - Method for producing silver having high purity

Info

Publication number: WO2002020857A1
Application number: PCT/JP2001/004296
Authority: WO
Inventors: Yuichiro Shindo
Original assignee: Nikko Materials Company, Limited
Priority date: 2000-09-07
Filing date: 2001-05-23
Publication date: 2002-03-14
Also published as: JP4842426B2; JP2002080919A

Abstract

A method for producing a silver having high purity from a raw material of low grade, characterized in that it comprises dissolving the raw material with a nitric acid solution, adding hydrochloric acid to the resulting mixture to give silver chloride crystals, and reducing the silver chloride crystals. The method allows the production of a high purity silver having a purity of 99.999 % or more without the use of the electrolysis purification method with a simple process and at a low cost.

Description

Manufacturing method of high purity silver

The present invention relates to a method for producing high-purity silver, and more particularly, to a method for producing high-purity silver having a purity of 99.999% or more from low-grade silver-containing raw materials at a low light value.

Rice field

Background art

Generally, high-purity silver is produced from a crude silver raw material by an electrolytic refining method. For example, a lead electrolytic anode slime is used as a starting material, a low-grade coarse silver plate obtained by concentrating silver contained in the anode slime is used as an anode, a silver nitrate solution containing nitric acid is used as an electrolytic solution, and the cathode is electrolyzed. It is manufactured by depositing silver on a plate.

This coarse silver plate contains about 98 to 99% of silver and other trace impurities such as gold, platinum, palladium, bismuth, copper, iron, and tellurium.

In electrolytic refining, as silver is dissolved from the coarse silver plate, trace impurities such as palladium, bismuth, copper, iron, and tellurium contained as the above impurities are also dissolved in the electrolyte, and these impurities in the electrolyte are removed. The concentration increases.

When the impurity concentration of such heavy metals increases, there arises a problem that the purity of the precipitated silver is reduced, or the purity of the silver is reduced by replacing the precipitated silver with the impurities. Therefore, in order to prevent such an increase in the impurity concentration due to heavy metals, a cleaning treatment of the electrolytic tail solution was required.

In the cleaning treatment of this electrolytic tail solution, silver oxide is added to the solution to raise the pH, and the pH is adjusted empirically to an appropriate value. As a precipitate. In the case of work based on such experience, it cannot always be said that an appropriate pH adjustment has been performed. For this reason, there has been a problem that high purity silver of 99.9% or more cannot be stably obtained by the above-mentioned conventional method, and that the yield of silver is low.

It is considered that the above problem is due to the pH not being strictly adjusted.Using a specially designed pH meter, two-step pH adjustment was performed by adding silver oxide, and strict liquid management was performed. For producing high-purity silver (Japanese Unexamined Patent Publication No. 2000-38692). In addition to using the costly electrolytic refining method, the above method requires a further cleaning step of the liquid, and if the purity is to be further increased, the pH meter must be used. There was a problem of the complexity of the process that strict liquid management was required depending on the means such as use, and there was a drawback that the cost became higher accordingly. Disclosure of the invention

The present invention provides a method for solving the above-mentioned problems without using the electrolytic purification method described above. /. An object of the present invention is to provide a method capable of producing the high-purity silver in a simple process and at low cost.

The present invention has found that high purity of silver can be achieved by two acid treatments, and provides the following method.

1. A method for producing high-purity silver from a low-grade silver-containing raw material, in which the raw material is dissolved with nitric acid, and then hydrochloric acid is added to obtain a salt crystal. For producing high-purity silver, characterized by reducing

2. The method for producing high-purity silver according to 1 above, wherein the silver chloride crystals are reduced with hydrogen.

3. The method for producing high-purity silver as described in 1 or 2 above, wherein the reduction is performed at a temperature of 200 ° C. or more.

4. The method for producing high-purity silver according to any one of the above 1 to 3, wherein the purity of the silver obtained after the reduction is 99.999% or more.

5. The method for producing high-purity silver as described in any one of 1 to 4 above, wherein the quality of the silver-containing raw material is 99.9% or less. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is an explanatory view of a purification step of high purity silver of the present invention. Embodiment of the Invention

According to the present invention, 1.2 equivalents or more of nitric acid is added to a low-grade silver-containing raw material having a grade of 99.9% or less, and the silver-containing raw material is dissolved with nitric acid. In this case, if the amount of nitric acid to be added is less than 1.2 equivalents, sufficient dissolution cannot be obtained, so that at least 1.2 equivalents is required. At this time, most of the impurities contained in the silver and the raw materials are dissolved.

Next, 1.2 equivalents or more of hydrochloric acid is added to obtain silver chloride crystals. In this case, silver is selectively converted into silver chloride crystals, and the chloride of impurities in the raw material is dissolved in the aqueous solution, and only silver chloride has no solubility and can be separated efficiently.

Addition of hydrochloric acid requires at least 1.2 equivalents. If it is less than this, the yield of silver chloride becomes poor, which is not preferred.

Next, the obtained silver chloride crystal is reduced with hydrogen at 200 ° C. or more to obtain high-purity silver having a purity of 99.999% or more. In this case, if the temperature is lower than 200 ° C., the reduction efficiency is reduced. Therefore, it is desirable to reduce hydrogen at 200 ° C. or higher.

The impurities separated in the steps of dissolving with nitric acid and obtaining silver chloride crystals contain trace amounts of noble metals, but they are usually discarded because their amounts are extremely small. However, it can be concentrated and collected. The hydrochloric acid generated by the reduction step can be reused in the above-mentioned step of silver chloride using hydrochloric acid.

As shown above, it is possible to achieve high purity of silver by two acid treatments: a process of dissolving the raw material with nitric acid and a process of generating silver chloride with hydrochloric acid. High purity silver with a purity of 9% or more can be obtained. Example

Next, examples will be described. It should be noted that the present embodiment is merely an example of the present invention, and the present invention is not limited to these embodiments. That is, the present invention It includes other aspects and modifications included in the technical idea.

To 100 g of a low-grade (3 N level) silver-containing raw material having the impurity content shown in Table 1, 2 equivalents of 61% nitric acid (14 OmL) was added and dissolved at a temperature of 60 ° C. The impurities contained in the raw materials are palladium 2.Oppm, selenium 1.3ppm, antimony 0.3ppm, copper 1.Oppm, iron 1.Oppm, titanium 1.0ppm, Platinum 0.1 ρ ρm, Rd. 0.1 lp pm,: ^ ¾l. Op pm. Almost all of these impurities were dissolved during nitric acid dissolution.

Next, to this solution was added 36% hydrochloric acid (2 times equivalent, 160 mL) to obtain 130 g of salted silver crystals. At this time, the impurity salt was almost dissolved in the aqueous solution, but only silver chloride was hardly soluble and precipitated as a solid.

The obtained silver chloride crystals were hydrogen reduced at 400 ° C. The yield was 97.8%. High purity silver (after purification) with the impurity content shown in Table 1 was obtained. In addition, it was found that if the temperature is lower than 200 ° C. during the hydrogen reduction, the reduction efficiency decreases, which is not preferable. The hydrochloric acid generated by the reduction step was reused in the above-mentioned step of salting silver with hydrochloric acid.

The noble metal in the impurities separated in the steps of dissolving with nitric acid and obtaining silver chloride crystals is usually discarded because it is a very small amount.However, it is concentrated and converted to ammonium chloroplatinate by, for example, an ammonium chloride reaction. It can be recovered by adsorption to graphite.

As shown in Table 1, the impurities contained in the high-purity silver obtained in this example were palladium 0.02 ppm, selenium 0.01 ppm, antimony 0.03 ppm ヽ copper 0.01 ppm , Iron 0.05 ppm, Titanium 0.01 ppm, Platinum 0.0 lp pm, Rhodium 0.01! 11. The sulfur content was 0.03 ppm.

As described above, it is possible to achieve high purity of silver by two acid treatments: a process of dissolving raw materials with nitric acid and a process of generating silver chloride with hydrochloric acid. Was obtained. P d S e S b C u Fe T i P t Rh S Raw material 2.0 1.3 0.3 1.0 1.0 1.0 0.1 0.1 1.0 After purification 0.02 0.01 0.03 0.01 0.05 <0.01 <0.01 <0.01 <0.03

(p P m) Effect of the invention

INDUSTRIAL APPLICABILITY The present invention has an excellent effect that high-purity silver of 99.999% or more can be purified in two acid treatment steps without using an electrolytic refining method, and can be manufactured stably and at low cost.

Claims

The scope of the claims

1. A method for producing high-purity silver from a low-grade silver-containing raw material, in which the raw material is dissolved with nitric acid, and then hydrochloric acid is added to obtain chloride crystals, and the silver chloride crystals are further reduced. And a method for producing high-purity silver.

2. The method for producing high-purity silver according to claim 1, wherein silver chloride crystals are reduced with hydrogen.

3. The method for producing high dullness silver according to claim 1 or 2, wherein the reduction is carried out at not less than 3.2 ° C.

4. The method for producing high-purity silver according to any one of claims 1 to 3, wherein the purity of the silver obtained after the reduction is 99.999% or more.

5. The method for producing high-purity silver according to any one of claims 1 to 4, wherein the quality of the silver-containing raw material is 99.9% or less.