JPH10280059A - Separation of gold and silver from noble metal alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To rapidly separate gold and silver without using nitric acid and enable the prevention of environmental pollution and the improvement in cost effectiveness by adding sulfuric acid of a specific concn. to a noble metal alloy mainly contg. gold and silver of anode slime, etc., of copper electrolytic smelting, heating the alloy to melt the silver and separating the melt to a silver sulfate soln. and an unmolten residue contg. the gold. SOLUTION: The noble metal alloy is formed to a shot form of about -10N+30 meshes and the silver is melted by using the sulfuric acid of >=70% (by weight) in concn. and at 150 deg.C. The preferably sulfuric acid concn. and temp. are respectively about 84% and 170 to 180 deg.C. The sulfuric acid is thickened simultaneously with melting of the silver and the unmolten residue contg. The gold is separated. The remaining liquid is thereafter diluted with water to the sulfuric acid concn. of <=70%, by which the silver sulfate is deposited and recovered. On the other hand, the unmolten residue is melted by hydrochloric acid, hydrogen peroxide, gaseous chlorine, etc.; and the melt is treated by a known reduction method or org. solvent method, by which the melt is refined to the gold purity having a market value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for economically separating gold and silver from precious metal alloys containing gold and silver, such as anode slime for copper electrorefining.

[0002]

2. Description of the Related Art For example, gold and silver are contained in anode slime generated by electrolytic copper refining, and gold and silver have been conventionally recovered by treating the anode slime.

As a specific method for recovering the gold and silver, the anode slime is sulfated and roasted to separate copper, and the residue is oxidized and roasted to volatilize and separate selenium. Noble metals such as gold and silver are concentrated in lead by mixing and heating and melting a reducing agent. The obtained noble lead is put into an ash-blowing furnace, heated and melted, and air is blown against the melt to sequentially oxidize and remove the lead and impurities in the noble lead, thereby forming a coarse silver plate mainly containing gold and silver. And

[0004] Silver is separated as electrodeposited silver by subjecting the coarse silver plate containing gold and silver to electrolytic treatment with a Mepiers type silver electrolysis. The anode slime generated by this silver electrolysis is
After silver is dissolved with nitric acid to recover gold, the remaining residue is heated and melted and cast on a gold anode, and the gold is recovered by gold electrolysis. In addition, the solution dissolved in nitric acid contains platinum together with silver,
Platinum group metals such as palladium are similarly dissolved, and silver and platinum groups are purified and recovered from this solution.

In addition to the above-mentioned anode slime for electrolytic copper refining, noble lead obtained by distilling zinc of zinc crust obtained by the Barks method, and gold and silver obtained by processing scraps of electronic equipment in an ash blowing furnace Alloys, etc., are usually thrown into the above ash-blowing furnace and processed together with other noble lead, and after being made into a noble metal alloy, are processed in the same manner as described above to sequentially recover silver and gold. .

[0006]

Considering the refining costs in the above-mentioned method for recovering gold and silver, it can be seen that most of the costs are occupied by gold remaining in the system. That is, the increase in the refining cost is such that the gold in the noble metal alloy treated in the ash blowing furnace becomes an anode slime by silver electrolysis, and further becomes an electrolytic gold having a market value by gold electrolysis through an acid treatment. Because gold is purified in the final step, gold is retained in each of the silver electrolysis step, the anode slime acid treatment step, and the gold electrolysis step.

Therefore, in order to reduce the purification cost,
It is necessary to change the process to separate and recover gold from silver as soon as possible. For example, considering a wet process that does not go through an electrolytic process, the recovery of gold is described in Japanese Patent Publication No. 1-3353.
No. 7 and Japanese Patent Publication No. 64-3930 propose a method of dissolving a gold concentrate with hydrochloric acid, hydrogen peroxide, or chlorine gas, and subjecting the dissolved solution to a reduction treatment. As another method, a method for purifying gold using an organic solvent DBC is also known.

On the other hand, silver can be recovered by dissolving silver once, separating impurities as a hardly soluble compound such as silver chloride or silver sulfate, and leaching with ammonia water to reduce hydrogen. A method of purifying by extracting using a solvent such as an organic phosphorus compound containing sulfur in the molecule known as Cyanex 471X (manufactured by Cytec Corporation) and the like are known.

However, in order to treat the above-mentioned noble metal alloy containing gold and silver simultaneously by the above-described silver recovery method, it is necessary to dissolve silver once. Nitric acid is usually used to dissolve the silver, but a large amount of nitrogen oxides (NO _x ) is generated during the dissolution, and the total nitrogen in the wastewater obtained by treating the solution after the dissolution increases, thereby causing environmental pollution. There was a problem, and there was a drawback that measures for preventing pollution were required.

As described above, the conventional method of recovering gold and silver from a noble metal alloy mainly containing gold and silver, such as an anode slime for copper electrolytic refining, has a high purification cost,
It was not economic. In addition, it is conceivable to recover gold at an early stage to reduce the refining cost, but in that case, since nitric acid is used when silver is dissolved, there is a disadvantage that a new problem of environmental pollution occurs.

The present invention has been made in view of such a conventional situation,
An object of the present invention is to provide a method for separating gold and silver, which can separate gold and silver from a precious metal alloy containing gold and silver at an early stage, is economical, and has no concern about environmental pollution.

[0012]

In order to achieve the above object, the present invention provides a method for separating gold and silver from a noble metal alloy, which comprises adding a concentration of 7 to a noble metal alloy mainly containing gold and silver.
0% by weight or more of sulfuric acid is added and silver is dissolved by heating to a temperature of 150 ° C. or more, and at the same time, sulfuric acid is concentrated.
After separating the undissolved residue containing gold, water is added to the remaining solution so that the sulfuric acid concentration becomes 70% by weight or less, and silver in the solution is precipitated and recovered as silver sulfate.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, in separating gold and silver from a noble metal alloy mainly containing gold and silver such as anode slime for electrolytic copper refining, silver is first dissolved using sulfuric acid. At this time, gold contained in the noble metal alloy is not dissolved in sulfuric acid, and when other noble metals such as platinum and palladium are contained, these noble metals are not dissolved in sulfuric acid but remain in the residue. In this method, since nitric acid is not used for dissolving silver, there is almost no problem of polluting the environment.

In the step of dissolving silver with sulfuric acid, it is preferable to dissolve the noble metal alloy in the form of a shot in order to increase the dissolution rate of silver. The smaller the shot of the noble metal alloy is, the more preferable it is. , A silver leaching rate of 98% or more is obtained.

The reason why the concentration of sulfuric acid used for dissolving silver is set to 70% by weight or more is that the lower the concentration of sulfuric acid, the weaker the ability to dissolve silver. This is because a sulfuric acid concentration of at least 84% by weight is required. The sulfuric acid added to the noble metal alloy is concentrated at the same time as the silver is dissolved by heating, and has a higher concentration than that at the time of addition.

The dissolution rate of silver increases as the dissolution temperature increases, and practically it is necessary to dissolve at a temperature of 150 ° C. or higher. However, if the melting temperature is about 170 to 180 ° C., the silver in the noble metal alloy is sufficiently melted, and even if the temperature is higher than that, it is uneconomical in terms of energy and the concentration of sulfuric acid excessively proceeds too much. Absent. Therefore, the heating temperature for dissolving silver is preferably about 150 to 180 ° C.

After dissolution of the silver, undissolved residues are removed by filtration. Since this residue mainly contains gold, it is then to be dissolved by hydrochloric acid, hydrogen peroxide, chlorine gas or the like according to the above-mentioned usual method for recovering gold, and treated by a known reduction method or an organic solvent method. Gold can be refined to a marketable purity.

On the other hand, the solution remaining after removing the residue is:
It is concentrated sulfuric acid (usually 80% by weight or more) and dissolves silver. As shown in the solubility curve of FIG. 1, since the solubility of silver sulfate extremely decreases at a sulfuric acid concentration of 70% by weight or less, silver sulfate is precipitated by diluting the concentrated sulfuric acid concentration to 70% by weight or less. Can be collected.

The solution remaining after collecting the precipitated silver sulfate is sulfuric acid having a concentration of 70% by weight or less, usually 60 to 70% by weight. By using sulfuric acid of not less than%, it can be repeatedly used for dissolving silver from a noble metal alloy.

[0020]

EXAMPLE 1 A noble metal alloy containing 83.5% by weight of silver, 13.4% by weight of gold, 0.14% by weight of platinum, 0.81% by weight of palladium, and 0.35% by weight of copper was melted by heating. After granulating in a shot shape,
It was sieved to -10 to +18.5 mesh.

Each of the shot-shaped noble metal alloys was
0 g each, 100 g of each was placed in a 1-liter glass beaker, and sulfuric acid having a concentration of 98 wt%
ml, and the liquid temperature was 100 ° C., 130 ° C., 15
The mixture was heated to 0 ° C. and 170 ° C. and stirred for 1 hour.

Thereafter, the mixture was filtered through a glass filter paper to remove undissolved residues. The residue and the solution (filtrate) from which the residue was removed were analyzed to determine the degree of dissolution of each metal element. The results are shown in Table 1 below for each dissolution temperature.

[0023]

[Table 1]

As shown in Table 1 above, the melting temperature was 150
It can be seen that by setting the temperature to not less than ° C., the solubility of silver sharply increases. Also, it can be seen that noble metals other than silver, such as gold, platinum and palladium, do not dissolve in sulfuric acid regardless of the dissolution temperature and remain in the residue. By heating the noble metal alloy together with sulfuric acid to 150 ° C. or more, silver dissolves in sulfuric acid and gold remains in the residue, so that gold and silver can be easily and efficiently separated.

EXAMPLE 2 A noble metal alloy containing 88.2% by weight of silver, 9.7% by weight of gold, 0.14% by weight of platinum, 0.96% by weight of palladium, and 0.81% by weight of copper was heated and melted. After granulating into shots,
It was sieved to -10 to +30 mesh.

100 g of the obtained shot-shaped noble metal alloy
Was placed in a 1 liter glass beaker, 1000 ml of sulfuric acid having a concentration of 70% by weight was added, and the mixture was heated so that the liquid temperature became 170 ° C. and stirred and maintained for 12 hours. During this time, a small amount of the solution was sampled at each time shown in Table 2 below, and the degree of silver dissolution and the degree of sulfuric acid concentration were examined. The results are shown in Table 2 below.

[0027]

[Table 2]

As shown in Table 2, when silver is dissolved at a temperature of 170 ° C. using sulfuric acid having a concentration of 70% by weight,
It turns out that a dissolution time of about 6 hours or more is required. Also, during this dissolution time, 70% by weight initially added
Is concentrated to about 84% by weight.

Further, after the above-mentioned heating and melting were continued for 12 hours, the solution was filtered through a glass filter paper to recover undissolved residues. This residue weighed 11.4 g and was analyzed for its components. As a result, 85.2% by weight of Au, 2.7% by weight of Ag, and Pt:
The composition was 1.23% by weight and Pd: 8.29% by weight, and there was no gold loss. In addition, this residue can be dissolved in hydrochloric acid, hydrogen peroxide, or chlorine gas, and then treated by a known reduction method or an organic solvent method, whereby gold can be purified to a marketable purity. Further, the number of days required for purification can be reduced as compared with the conventional case.

Next, 200 ml of water was added to the solution obtained by filtering the above residue (sulfuric acid concentration: 84% by weight) to dilute silver sulfate, and the solution was filtered again to recover silver sulfate. The precipitated silver sulfate had a very good filterability. The recovered silver sulfate is 11
It was 0 g. Table 3 below shows the compositions of the filtrate after filtering the residue and the filtrate for silver sulfate recovery. Table 4 below
The following shows the quality of the recovered silver sulfate.

[0031]

[Table 3]

[0032]

[Table 4]

As can be seen from the results, the distribution of silver to silver sulfate was 85.8%, and Pd was detected as a main impurity. The silver sulfate can be used as a raw material and subjected to the above-described known reduction method or solvent extraction method to purify silver to a purity having a market value. Further, since the filtrate after the recovery of silver sulfate is sulfuric acid having a concentration of 60 to 70% by weight, it can be used again for dissolving the noble metal alloy by supplementing and adding concentrated sulfuric acid having a concentration of 98% by weight.

[0034]

According to the present invention, the silver in the noble metal alloy containing gold and silver is easily dissolved and the gold is concentrated in the residue, so that the gold and silver can be separated at an early stage to recover the gold. , The purification cost can be reduced.

Further, sulfuric acid used for dissolving silver can be repeatedly used for dissolving silver by replenishing with concentrated sulfuric acid, which is also economical in this respect. Further, since nitric acid is not used for dissolving silver, there is no generation of substances causing environmental pollution such as nitrogen oxides, and therefore, there is no need to provide special equipment for the treatment and the like.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between sulfuric acid concentration and silver solubility.

Claims (2)

[Claims] 1. A sulfuric acid having a concentration of 70% by weight or more is added to a noble metal alloy mainly containing gold and silver, and heated to a temperature of 150 ° C. or more, thereby dissolving the silver and simultaneously concentrating the sulfuric acid. After separating the residue, water is added to the remaining solution so that the sulfuric acid concentration becomes 70% by weight or less, and silver in the solution is precipitated and recovered as silver sulfate. Separation of gold and silver from a noble metal alloy, Method. 2. The method according to claim 1, wherein the remaining solution is mixed with concentrated sulfuric acid and used for dissolving the noble metal alloy after silver sulfate is precipitated and recovered. How to separate gold and silver.