JPH0657348A - Production of high-purity gold - Google Patents

Abstract

PURPOSE:To easily recover the high-purity gold in a short period of time by reducing aurichloride soln. after precision filtration and stopping the reduction reaction at a specific point of time at the time of producing the high-purity gold directly from the aurichloride soln. by using a reducing agent. CONSTITUTION:The slime obtd. by the electrolysis of silver is subjected to a desilvering treatment by nitric acid extraction. The slime of the desilvering is extracted with hydrochloric acid and hydrogen peroxide to elute gold, by that, the aurichloride soln. is obtd. This soln. is first subjected to coarse sepn. of impurities (about 0.2mu or finer filtration) by precision filtration and thereafter, the reduction is executed by using a reducing agent (sulfurous acid anhydride gas, etc.) and the reduction is stopped at the point of time of 80 to 95%. The amt. of the reducing agent is determined by previously analyzing the concentration of gold. By separately washing the reduced gold obtd. in such a manner, the high-purity gold of about 99.99wt.% or higher is easily obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing high-purity gold, and in particular, it is obtained by desilvering an anode slime obtained by silver electrolysis by nitric acid extraction, and then dissolving gold by hydrochloric acid hydrogen peroxide extraction. The obtained chloroauric acid solution (hereinafter simply referred to as chloroauric acid solution) has a low silver content of 99.9.
It relates to a method for producing high-purity gold of 9% by weight or more.

[0002]

2. Description of the Related Art Conventionally, as a method for producing gold having a purity of 99.99% by weight or more from anode slime from silver electrolysis, an electrolytic refining method by the Wohlwill method has been performed.
In this electrolytic refining method, anode slime from silver electrolysis is treated with nitric acid to dissolve Ag and Pd, and then 95 to 98% by weight of Au,
A raw metal plate for an anode containing 1 to 3% by weight of Ag is electrolyzed using a pure gold plate having a purity of 99.99% by weight or more as a cathode to obtain an electrodeposited metal having a purity of 99.99% by weight or more as a cathode. .
Although high-quality gold can be obtained by this method, problems such as the need to manage the electrolytic solution, the long refining time, and the large amount of energy consumed, resulting in a high labor and cost Have a point. In contrast to such an electrolytic refining method, a method of dissolving gold as a chloroauric acid solution and reducing it to directly produce high-purity gold has been attempted (for example, US Pat. No. 3,892,557). .

However, to reduce gold from a chloroauric acid solution to precipitate gold particles, simple addition of a reducing agent such as sodium sulfite, ferrous salt, hydrogen peroxide, oxalic acid, etc. Impurity elements precipitate and it is difficult to obtain high purity gold of 99.99% by weight or more. Therefore, in the case of producing high-purity gold from a chloroauric acid solution, 99.99% by weight or less of a gold starch containing a small amount of impurities obtained by conventionally adding a reducing agent as described above is melted by heating. It was necessary to carry out electrolysis as an anode for several days, or to re-dissolve the gold precipitate in nitric acid, aqua regia, etc. by applying a great deal of heat for purification. For this reason, the advantage of extracting gold and using a chloroauric acid solution cannot be fully utilized.

Therefore, some improvement measures have been attempted. For example, Japanese Patent Publication No. 59-52218 and Japanese Patent Publication No. 64-3.
As seen in No. 930, a solution of chloroauric acid in which gold is directly eluted from copper electrolytic slime without undergoing silver electrolysis is reduced to a certain range of oxidation-reduction potential and treated with nitric acid to obtain high purity in a short period of time. You have succeeded in earning money.

However, according to this method, the quality of gold as reduced and produced is not 99.99% by weight, and it is achieved after nitric acid treatment and heating and melting. In addition, there is a problem in the process of refining metals other than gold after gold reduction, and the advantage of this method cannot be fully utilized. Further, in Japanese Examined Patent Publication No. 1-33537, 80 to 98% of gold is reduced with a reducing agent to obtain a quality of 99.9.
9% by weight or more of high-purity gold is obtained. However, it became clear that the silver grade did not fall to a satisfactory level.

[0006]

SUMMARY OF THE INVENTION In view of the above-mentioned conventional techniques, the present invention does not require the number of days until gold recovery as in gold electrolysis.
Further, the present invention provides a method for producing high-purity gold that can easily and quickly recover gold without requiring special equipment.

[0007]

In order to achieve the above object, the present invention provides a method for directly producing high-purity gold by reducing a chloroauric acid solution with a known reducing agent. After microfiltration of the acid solution, gold is not completely reduced in order to suppress precipitation of impurity elements, and reduction is stopped when 80 to 95% is reduced. In addition, although 99.99% by weight or more of high-purity gold can be obtained by the above method, in order to obtain high-purity gold with a particularly low silver content, a chloroauric acid solution was previously subjected to the following desilvering treatment before reduction. It is effective to reduce the silver concentration to reduce the concentration. That is, a salt that is easily combined with silver, such as potassium bromide or potassium iodide, is added as a desilvering agent before the reduction, and more desirably, the salt is diluted before the desilvering agent is added or before the reduction, or both. It is suitable.

[0008]

The chloroauric acid solution used in the method of the present invention is obtained by subjecting slime obtained by silver electrolysis to desilvering treatment by nitric acid extraction,
This desilvered slime was obtained by elution of gold by extraction with hydrochloric acid and hydrogen peroxide. This solution is Au100-3
10 g / liter, Ag0.010 to 0.150 g / liter, Pt1 to 3 g / liter, Pd0.1 to 0.5
g / liter, Rh 0.001 to 0.03 g / liter, and the concentration of hydrochloric acid is about 2 to 3N.

First, the impurity element is roughly separated by microfiltration. Impurity elements are dissolved to form colloidal particles or coarse particles in the ionic state or salt form. By carrying out microfiltration, it is possible to remove suspended coarse impurities and relatively large colloidal particles. The term microfiltration as used herein refers to ultrafiltration academically. Although the filtration equipment and the like are not specified, it is preferable that filtration of 0.2 μm or less can be performed in consideration of workability such as filtration speed. Next, the chloroauric acid solution from which impurities have been roughly separated by microfiltration is reduced by 80 to 95% with respect to gold using a known reducing agent, for example, a relatively weak reducing agent such as sulfurous acid gas or sodium sulfite. The end point of this reaction is determined by analyzing the gold concentration in advance and by the amount of reducing agent. The reduced gold thus obtained was filtered and washed to give 99.9.
High-purity gold of 9% by weight or more is obtained. The reason why the reaction is stopped at the time when 80 to 95% is reduced without completely reducing gold is that Pt and P are near the potential at which the reduction precipitation of gold ends.
This is because it is close to the deposition potential of d. Therefore, Pt, Pd
The reduction will be stopped before the reduction rate of gold increases to 100%.
Since the precipitation potential of Pt and Pd is unstable, 80%
In the following, reduction of about 80% is most preferable due to lack of economy. Hereinafter, the insufficient equivalent reduction method in which reduction is stopped before 100% reduction is broadly expressed as 80% reduction even if the reduction rate is not 80%. P by the above method
Although high-purity gold of 99.99% by weight or more can be obtained by suppressing the precipitation of t, Pd, and Rh, silver is precipitated from the early stage of gold reduction, and the silver quality in gold powder is 10 to 100 ppm.

In order to obtain high-purity gold having a lower silver grade, it is effective to reduce the silver concentration by subjecting the chloroauric acid solution to the following desilvering treatment before the reduction.
Therefore, as a desilvering agent, a salt such as potassium bromide or potassium iodide which is easily combined with silver must be added before the reduction. More preferably, it is more effective to dilute before or after the addition of the desilvering agent, or both. The purpose of adding the desilvering agent is to remove silver in the form of a sparingly soluble salt by reacting iodine ions or bromine ions with silver ions. The addition amount of the desilvering agent is determined with respect to the silver equivalent in chloroauric acid, but is not strictly limited. The effect increases in proportion to the amount of the desilvering agent, but the cost and the amount of the desilvering agent also increase, which imposes a burden on the post-process, and therefore, it is preferably 20 to 200.
Double is appropriate. Furthermore, in the case of potassium iodide, the effect of suppressing the mixing of silver is larger than the desilvering effect.

The purpose of the dilution is to lower the acid concentration to lower the solubility of the silver chloride complex dissolved in the liquid and to efficiently carry out the reaction between the iodine ion or the bromine ion and the silver ion. Although the degree of dilution is not limited,
Desirably, the hydrochloric acid concentration is set to 1 N, and there is a balance with the liquid balance such as equipment and liquid treatment, and it is suitable to be 2 or 3 times. By performing these 80% reductions simply or in combination with each other, it is possible to easily obtain a high-purity gold powder having a silver content of 99.99% by weight or more with a low silver content.

[0012]

【Example】

Example 1 Au 337 g / liter, Ag 0.03 g / liter,
Pt 2.3 g / liter, Pd 0.3 g / liter, R
h 0.03 g / liter, hydrochloric acid concentration 2 N, oxidation-reduction potential 800 mV (against silver chloride electrode;
500 ml of a chloroauric acid solution (denoted by V only) was reduced by gradually adding sodium sulfite to gold equivalent. FIG. 1 shows changes in redox potential and changes in concentration of each element in the solution in the reduction reaction of the chloroauric acid solution.
Table 1 shows the analysis value of the reduced gold at each gold reduction rate. Precipitation of Pt, Pd, and Rh is suppressed by stopping the reduction in the middle without reducing gold to 100%,
Although the silver content is slightly high, high-purity gold of 99.99% by weight or more can be obtained.

[0013]

[Table 1]

Example 2 Au chloroauric acid solution 120 containing 310 g / liter, Ag 0.036 g / liter, Pt 2.3 g / liter, Pd 0.3 g / liter, Rh 0.03 g / liter, hydrochloric acid concentration 2.2 N, and redox potential 750 mV. The milliliter was diluted 2-fold, silver equivalents of about 20-fold and 200-fold potassium iodide were added, and after reaction at 80 ° C. for 0.5 h, microfiltration was performed with a membrane filter (0.2 μm). The solution was reduced with 80% gold equivalent of sodium sulfite and the gold dust was separated by filtration. The gold powder was boiled with dilute hydrochloric acid, washed with water and dried. As a result, as shown in Table 2, 99.99 wt%
The above gold powder was obtained.

[0015]

[Table 2]

[0016]

By carrying out the present invention, a high-purity gold powder having a silver content of 99.99% by weight or more and having a low silver content can be easily obtained.

[Brief description of drawings]

FIG. 1 shows changes in redox potential and changes in concentration of each element in a solution in a reduction reaction of a chloroauric acid solution.

[Explanation of symbols]

 1 Redox potential 2 Au concentration 3 Ag concentration 4 Pt concentration 5 Pd concentration 6 Rh concentration

Claims (2)

[Claims] 1. A method for directly producing high-purity gold from a chloroauric acid solution using a reducing agent, wherein the chloroauric acid solution is microfiltered and then the gold reduction reaction is stopped at a point of 80 to 95%. A method for producing high-purity gold, which comprises: 2. A method for directly producing high-purity gold from a chloroauric acid solution by using a reducing agent, wherein a desilvering agent is added to the chloroauric acid solution, and after microfiltration, the gold reduction reaction is carried out. 8
A method for producing high-purity gold, characterized by stopping at 0 to 95%.