JPH059606A - Separation method of gold-silver alloy - Google Patents

Abstract

(57) [Abstract] [Purpose] It is possible to easily separate gold-silver alloys without adjusting the quality of gold-silver alloys, reducing the generation of nitrogen oxides, waste liquid treatment, chemical costs, etc. associated with nitric acid dispensing To provide a way to do. In the method for separating a gold-silver alloy into gold and silver, the step of forming the gold-silver alloy as an anode, electrolyzing it in an iodine compound electrolyte and depositing it on a cathode to form fine particles, and the cathode deposit. Is extracted with an acid having an oxidizing property to separate into gold and silver.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for separating and refining gold and silver. More specifically, the present invention relates to a gold-silver alloy produced in a refining process of precious metals and scraps containing gold and silver represented by jewelry, electrical industry and electronic industry. The present invention relates to a method of separating gold and silver from scraps generated from a gold-silver alloy used for electric parts such as.

[0002]

2. Description of the Related Art The methods for separating and refining metal alloys include the Wall Will method and the nitric acid dispensing method, which are commonly used in the fields of precious metal refining and precious metal recovery.

In the Wall Will method, a rough gold plate containing silver is used as an anode in a hydrochloric acid electrolyte containing gold, gold is dissolved by electrolysis, and then deposited on the cathode. Silver becomes silver chloride and is obtained as anode mud. However, since silver chloride generated on the anode hinders electrolysis, the gold quality of the rough metal plate used for refining must be 95% or more and silver must be 5% or less. Limited to a few.
It is common to separate those containing 5% or more of silver, such as a gold-silver alloy represented by 18 gold, by the nitric acid separation method.

In the nitric acid dispensing method, other metals such as copper and silver are added to a gold-silver alloy and melted in a furnace to adjust the grade of the alloy so that the grade of gold is 20 to 25% or less. Then, when nitric acid is acted on, metals other than gold are dissolved in nitric acid, and gold is separated without being dissolved in nitric acid to obtain a residue. A drawback of the nitric acid dispensing method is that a large amount of nitrogen oxides are generated when nitric acid acts, but here, since the quality is adjusted by adding another metal, the amount of the metal weight of 3 to 3
This means that four times as much metal is dissolved, which further promotes the generation of nitrogen oxides. Further, there is a problem in that it requires time and effort such as adjustment of the quality of the gold-silver alloy, waste liquid treatment and chemical cost.

The inventor believes that if a gold-silver alloy can be finely processed, it can be dissolved in an acid such as aqua regia or nitric acid. Therefore, the gold-silver alloy is obtained by electrolyzing it in an alkali cyanide solution. A method of dissolving the obtained electrolytic precipitate in aqua regia or nitric acid and separating it was examined. However, there are safety-related problems such as the fact that a toxic cyanide compound must be used first, and a toxic hydrogen cyanide gas is generated when the electrolytic precipitate is dissolved in an acid. However, it is not always a good method because it has a drawback that the acid dissolution is not sufficiently performed and a large amount of undissolved residue remains, and that no precious metal components other than gold and silver contained in the gold-silver alloy are not easily recovered.

[0006]

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a method for separating a gold-silver alloy more easily, which makes it unnecessary to adjust the quality of the gold-silver alloy, and the nitric acid dispensing method The purpose is to reduce the problems associated with the process such as generation of nitrogen oxides, waste liquid treatment, and chemical cost. Furthermore, since the use of gold-silver alloys is wide-ranging, valuable platinum and palladium are often contained in addition to gold and silver, and a method applicable to these materials is also provided.

[0007]

According to the present invention, there is provided a step of depositing a gold-silver alloy on a cathode again by electrolyzing in a iodide electrolytic solution using a gold-silver alloy as an anode to process fine particles. A method for separating a noble metal, which comprises a step of treating a precipitate with an acid having an oxidizing property to separate gold and silver.

[0008]

In the method of the present invention, the gold-silver alloy is first processed into fine particles by electrolysis in the iodide electrolytic solution. The gold grade of the gold-silver alloy is preferably in the range of 25 to 95%. The reason is that if it is less than 25%, there is no difference from the above-mentioned nitric acid fractionation method, and if it exceeds 95%, it can be treated by the Wall Will method. However, the method of the present invention is not inapplicable. In addition, since gold and silver alloys are used in a wide variety of cases, valuable platinum and palladium are often contained in addition to gold and silver, and the method of the present invention can be applied to these materials. The use of an iodine compound as the electrolytic solution means that the particles can be finely processed and that they have almost no toxicity. It is preferable to use potassium iodide or sodium iodide as the iodine compound. The electrolytic solution is adjusted to have an iodine compound concentration of 50 to 500 g / l and a hydrogen ion concentration of 4 to 13.0.

There are two methods for using the gold-silver alloy as the anode. One is a method of directly energizing a gold-silver alloy as an electrode plate, and the other is an indirect electrode by placing an insoluble electrode such as a platinum-plated titanium plate as an electrode plate and placing a gold-silver alloy on it. This is a method of making the anode positive. The cathode plate is preferably made of a stainless steel plate or the like, and may be made of a material that is not easily corroded by the electrolytic solution, and may be the insoluble electrode described above. As electrolysis conditions, a current density of approximately ^{2 to} 10 A / dm ² and electrolysis at room temperature to about 70 ° C. are performed.
By electrolysis, gold-silver alloys are deposited on the cathode as particles, but as the quality of gold decreases, it gradually turns dark brown to black.In addition to gold and silver, precious metals such as platinum and palladium,
Base metal such as copper is deposited on the cathode. The difference from the case of using potassium cyanide as the electrolytic solution is the difference in the state of particles and the difference in the electrodeposition of platinum, palladium and the like. Electrodeposited particles in the potassium cyanide electrolytic solution are slightly larger than those in the iodine compound electrolytic solution, and the deposited metal shows a dendrite-like deposition state, but the electrodeposited particles in the iodine compound electrolytic solution are extremely fine and amorphous. It shows the state. It can be said that this difference is the difference in the solubility in the next acid dissolution.
Further, in the potassium cyanide electrolytic solution, platinum and palladium are hardly deposited and remain in the electrolytic solution, but in the iodine electrolytic solution, platinum and palladium are also deposited. Recovery of platinum and palladium from potassium cyanide electrolyte is very difficult and difficult to recover as metallic platinum or metal palladium, so it is easier to process by iodine electrolyte and recover by another method. . In the next step, the cathode deposit is treated with an oxidizing acid to separate gold and silver. This cathode deposit is
It is a fine gold-silver powder that contains palladium and platinum.

There are two methods of treatment, one is a method of treating with nitric acid to extract silver to obtain gold as a residue, which is a preferable method when the grade of gold is low and the grade of silver is high. Another method is to blow gold with aqua regia, chlorine blown into hydrochloric acid, sulfuric acid-salt-nitric acid, etc. to dissolve gold with an acid capable of dissolving gold and leave silver as silver chloride as a residue. so,
This is a preferable method when the quality of gold is high and the quality of silver is low.

In the method using nitric acid, the treatment is performed with nitric acid having a concentration of about 5 to 15 N. Since the cathode precipitate is finely processed, silver in the gold-silver alloy, which is usually difficult to dissolve, is easily dissolved to obtain a silver nitrate solution. The remaining gold can be purified to a purity of 95% or higher by the Wallwil method or the like. Also, silver is made into silver chloride by adding salt, ignited in a crucible containing caustic soda and borax, made into metallic silver, and purified by the Mobius method or the like. When platinum and palladium are contained, most of platinum and palladium are extracted in the nitric acid extract, so the solution after obtaining silver chloride is neutralized and further reduced with sodium borohydride or the like. Depending on the agent, metallic platinum,
It can be easily recovered as metallic palladium. The characteristic of the method using nitric acid is that it is more effective when the grade of gold is low and the grade of silver is high, so even when the grade of gold is below 80%, it is possible to obtain 95 to 98% of gold, Moreover, the extraction ratio of silver becomes high. However, gold grade 98%
To do so, it is necessary to perform extraction multiple times.

Of the methods of dissolving gold with an acid capable of dissolving gold, the method using aqua regia is the simplest, so the explanation will be based on the action when aqua regia is used. This action is almost the same when chlorine is blown into hydrochloric acid, or when an acid capable of dissolving gold such as sulfuric acid-salt-nitric acid is dissolved. Gold in the gold-silver alloy is usually difficult to dissolve, but the cathode precipitate obtained by this method is easily processed in aqua regia because it is finely processed. In the residue, silver chloride is obtained and gold and silver can be separated. Gold in aqua regia is made into metallic gold by a reducing agent such as hydrazine dihydrochloride and oxalic acid, and silver chloride is also ignited in a crucible containing caustic soda and borax to become metallic silver. If platinum and palladium are included,
Since platinum and palladium are extracted into the aqua regia solution, the solution after obtaining gold can be neutralized and further easily recovered as metallic platinum or metallic palladium with a reducing agent such as sodium borohydride. The characteristics of the method using aqua regia are:
It is more effective when the gold grade is high and the silver grade is low, and is particularly preferable when the gold grade exceeds 70%. The reason is that if the amount of silver chloride generated during aqua regia dissolution is small, the filtration is easy and the treatment can be performed in a shorter time.

When the method of the present invention is carried out, it is not necessary to adjust the quality of the gold-silver alloy, and it is not necessary to dissolve the metal added for the quality adjustment, so the amount of chemicals is reduced and the amount of nitrogen oxides generated is also reduced. Will be reduced. For example, 75% gold, silver
When 1 kg of 25% 18-gold alloy is treated, in the conventional nitric acid dispensing method, 2 kg of copper is added to adjust to 3 kg of gold-silver-copper alloy of 25% gold, 8.3% silver and 66.7% copper, and then treated with nitric acid. I will do it,
This is because the method of the present invention only needs to process 1 kg. Further, since the iodine compound electrolyte can be reused, there is a feature that it is sufficient to compensate for a slight decrease due to the operation. Furthermore, the separation ability of gold and silver is high, and the next gold purification,
It has the feature that it can produce raw materials that can be supplied to silver refining equipment. Hereinafter, the implementation of the present invention will be described.

[0014]

Example 1 1.0 kg of gold-silver alloy containing 74.8% gold and 25.0% silver
A plate with a width of 5 cm and a length of 10 cm was used as the anode,
For the cathode, stainless steel plate of the same size (JISSUS304
Electrolysis was performed by applying a direct current of 8 A in an electrolytic solution containing 200 g / l of potassium iodide. Hydrogen generation was observed from the cathode for the first 30 minutes after the start of electrolysis, but as the color of the electrolyte changed from transparent to black brown, hydrogen generation subsided and a black brown electrodeposit started to deposit on the cathode. The obtained electrodeposit was composed of fine particles, and as a result of analysis, water content 31
%, Gold 51.2%, silver 16.5%, and the anode, which is a gold-silver alloy, was dissolved by electrolysis and deposited again on the cathode. After drying the obtained cathode deposit, 1
Take 00 g, add 100 ml of pure water and 150 ml of hydrochloric acid, heat in a beaker, add 40 ml of nitric acid to dissolve aqua regia, dissolve in aqua regia, dilute to about 500 ml, and precipitate by filtration (silver chloride). ) And liquid (gold solution). Gold in the liquid
It contains 74.2g and 0.05g silver, and the precipitate contains 23.7g silver and 0.
It contained 02g. The gold in the liquid was reduced with hydrazine dihydrochloride to obtain 99.8% metallic gold, and the silver in the precipitate was caustic soda and borax in a crucible and heated strongly to give 99.5% metallic silver. I was able to get By the above operation, the gold-silver alloy could be separated into gold and silver.

[0015]

[Prior art example 1] 100g of gold-silver alloy containing 74.8% gold and 25.0% silver
And 300 g of copper are melted in a crucible to reduce the quality of gold to 1/4 (about 19
%) To obtain a thin alloy (thickness: about 0.5 mm) using a rolling machine to make it easy to dissolve in nitric acid. This small piece was put in a beaker, 200 ml of pure water was added, and 400 ml of nitric acid was gradually added dropwise while heating and dissolved. After the dissolution of nitric acid, the residue and the liquid were separated by filtration. The liquid contained 23.5 g of silver, and the residue contained 1.4 g of silver and 74.3 g of gold.
The liquid containing silver was added as salt to precipitate as silver chloride.
Then, silver chloride could be made into 99.8% metallic silver by adding caustic soda and borax in a crucible and heating it strongly. When the residue was also dissolved in the crucible and analyzed, the quality of gold was 96.2%, which contained a large amount of copper in addition to silver.

[0016]

[Prior art example 2] 100g of gold-silver alloy containing 74.8% gold and 25.0% silver
Was processed into a thin plate (thickness: about 1 mm) with a rolling mill, and further cut into small pieces of several cm square with scissors. Put this small piece in a beaker, add 100 ml of pure water and 150 ml of hydrochloric acid, heat in a beaker and add 40 ml of nitric acid to dissolve aqua regia, but the metal surface appears to be covered with white skin and dissolves. I couldn't do that.

[0017]

[Prior art example 3] 100g of gold-silver alloy containing 74.8% gold and 25.0% silver
Was processed into a thin plate (thickness: about 1 mm) with a rolling mill, and further cut into small pieces of several cm square with scissors. The small pieces were placed in a beaker, 100 ml of pure water and 150 ml of nitric acid were added, and the mixture was heated in a beaker to dissolve nitric acid.The metallic luster slightly lost its luster, but the others did not change and could not be dissolved. There wasn't. To treat the same weight of gold-silver alloy in Example 1, 100 g of metal may be treated, but in Example 2,
About four times as much metal must be dissolved. Also, the amount of chemicals used, the amount of nitrogen oxides generated, and the amount of waste liquid generated will increase several times. Furthermore, the method of the present invention was able to obtain higher quality gold.

[0018]

Example 2 Gold 50.3%, Silver 41.0%, Palladium 5.5%,
A 1.0 kg gold-silver alloy containing 1.0% platinum was processed into a plate with a width of 5 cm and a length of 10 cm, which was used as the anode. A stainless steel plate of the same size (JISSUS304) was used as the cathode, containing 500 g / l of potassium iodide. Electrolysis was performed by applying a direct current of 8 A in the electrolytic solution. Hydrogen generation was observed from the cathode for 30 minutes after the start of electrolysis, but as the electrolyte color changed from transparent to black-brown, hydrogen generation subsided and a black-brown electrodeposit began to deposit on the cathode. The obtained electrodeposit was composed of fine particles, and as a result of analysis, moisture was 28%, gold was 32.2%, silver was 29.5%,
It has a composition of 3.0% palladium and 0.6% platinum, and the anode, which is a gold-silver alloy, is dissolved by electrolysis and deposited again on the cathode. After drying the obtained cathode deposit, 100 g of it is taken, 100 ml of pure water and 250 ml of hydrochloric acid are added, heated in a beaker, and 40 ml of nitric acid is added dropwise to dissolve aqua regia. It was diluted and separated by filtration into a precipitate (silver chloride) and a liquid. When filtering,
Filtration was a little difficult and filtration was a little difficult. In the liquid, gold 49.5g, silver 0.10g, palladium 5.4g, platinum 1.2
g, and the precipitate contained 39.5 g of silver and 0.95 g of gold. The gold in the liquid was reduced and precipitated with hydrazine dihydrochloride and then separated by filtration to obtain 99.8% metallic gold. The filtrate was neutralized and treated with a 5% sodium borohydride solution to further reduce the platinum and palladium. The silver in the precipitate was caustic soda and borax in a crucible and heated strongly to obtain 97.0% metallic silver. By the above operation, the gold-silver alloy could be separated into gold and silver.

[0019]

Example 3 Gold 81.0%, Silver 17.0%, Palladium 1.5%,
A 1.0 kg gold-silver alloy containing 0.3% platinum was processed into a plate shape with a width of 5 cm and a length of 10 cm, which was used as the anode. A stainless steel plate of the same size (JISSUS304) was used as the cathode, containing 150 g / l of potassium iodide. Electrolysis was carried out by applying a direct current of 8 A in the electrolytic solution to obtain a cathode deposit of 77.9% gold, 16.8% silver, 1.49% palladium, and 0.26% platinum. 500 g of this cathode precipitate was placed in an evaporation dish, 250 ml of nitric acid and 250 ml of pure water were added, and silver, platinum and palladium were extracted by heating. When this operation was repeated twice, silver, platinum, and palladium were extracted from the noble metals other than gold contained in the cathode deposit. In the residue after nitric acid extraction, gold 97.4%, silver 2.
04%, platinum 0.05%, palladium 0.38%,
90% of impurities other than gold were removed, and the quality of gold was 95% or more, so the purity was sufficient for purification by the Wall-Will method. Example 3 shows that the method of the present invention enables the nitric acid extraction operation to be performed by the method of the present invention even if the quality of the nitric acid was conventionally difficult to extract.

[0020]

Example 4 Similar to Example 3, 81.0% gold, 17.0 silver
%, Palladium 1.5%, platinum 0.3%, gold-silver alloy 1.0
A plate processed to have a width of 5 cm and a length of 10 cm was used as an anode, and the cathode was made of a stainless steel plate of the same size (JISSUS30).
4 products) in an electrolytic solution containing 150 g / l potassium iodide and applying a direct current of 8 A to electrolyze,
A cathode deposit containing 77.9%, silver 16.8%, palladium 1.49%, and platinum 0.26% was obtained. 50 g of this cathode deposit is placed in an evaporation dish,
100 ml of hydrochloric acid and 50 ml of pure water were added, and 25 ml of nitric acid was added dropwise with further heating to dissolve aqua regia. Metal components except silver were extracted into aqua regia and analyzed to find that gold 38.9
g, 0.11 g of platinum, and 0.81 g of palladium. After reducing this solution with hydrazine dihydrochloride to obtain gold powder,
The mixture was neutralized and further reduced with a sodium borohydride solution to obtain a mixed powder of platinum and palladium. Most of the residue when the aqua regia was dissolved was silver chloride, and 8.5 g of metallic silver could be obtained by electrolysis after dissolving in a potassium cyanide solution.

[0021]

Comparative Example 1 Gold 81.0%, Silver 17.0%, Palladium 1.5%,
A 1.0 kg gold-silver alloy containing 0.3% platinum was processed into a plate with a width of 5 cm and a length of 10 cm, which was used as the anode. A stainless steel plate of the same size (JISSUS304) was used as the cathode, and an electrolytic solution containing 150 g / l of potassium cyanide. Then, a direct current of 8 A was applied to carry out electrolysis to obtain a cathode deposit of 79.5% gold, 18.8% silver, 0.02% palladium, and 0.01% platinum. 50 g of this cathode precipitate was placed in an evaporation dish, 100 ml of hydrochloric acid and 50 ml of pure water were added, and 25 ml of nitric acid was added dropwise while heating to dissolve aqua regia. Metal components other than silver were extracted into aqua regia and analyzed, and as a result, 35.2 g of gold was contained, but platinum and palladium were hardly contained. Also, toxic hydrogen cyanide gas was generated when the aqua regia was dissolved. Gold powder could be obtained from this solution by reduction with hydrazine dihydrochloride. Almost all of the residue when dissolved in aqua regia was silver chloride, so when dissolved in a potassium cyanide solution, 1.3 g of what was insoluble in the potassium cyanide solution was contained.
When this insoluble material was analyzed, gold and silver were detected. The metallic silver could be easily recovered from the potassium cyanide solution in which silver chloride was dissolved. Palladium and platinum are accumulated in the electrolytic solution containing potassium cyanide described above,
Since it did not deposit on the cathode, the anode was switched to a platinum-plated titanium plate for electrolysis, but it did not deposit even after a long time.

[0022]

[Comparative Example 2] 50.3% gold, 41.0% silver, 5.5% palladium,
A 1.0 kg gold-silver alloy containing 1.0% platinum was processed into a plate with a width of 5 cm and a length of 10 cm, which was used as the anode. A stainless steel plate of the same size (JISSUS304) was used as the cathode, and an electrolyte containing potassium cyanide 150 g / l. Then, electrolysis was performed by applying a direct current of 8 A to obtain a cathode deposit of 53.1% gold, 45.5% silver, 0.01% palladium, and 0.01% platinum. 50 g of this cathode precipitate was placed in an evaporation dish, 100 ml of hydrochloric acid and 50 ml of pure water were added, and 25 ml of nitric acid was added dropwise while heating to dissolve aqua regia. Metal components other than silver were extracted into aqua regia and analyzed to find that 16.4 g of gold was contained, but platinum and palladium were scarcely contained. Also, toxic hydrogen cyanide gas was generated when the aqua regia was dissolved. Gold powder could be obtained from this solution by reduction with hydrazine dihydrochloride. When the residue obtained by dissolving aqua regia was dissolved in a potassium cyanide solution, 13.5 g of a substance that was insoluble in the potassium cyanide solution was contained. Analysis of this insoluble material revealed that it contained 62.3% gold and 36.9% silver. Palladium and platinum were accumulated in the above-mentioned electrolytic solution containing potassium cyanide, but because they did not deposit on the cathode, the anode was switched to a platinum-plated titanium plate for electrolysis, but it took a long time. Also did not precipitate.

In Comparative Examples 1 and 2, potassium cyanide is used as an electrolytic solution for electrolyzing a gold-silver alloy, but harmful hydrogen cyanide is generated when the aqua regia is dissolved next time, and a cathode precipitate is also generated. It shows that it is difficult to dissolve all the gold in it, and in particular, it can be seen that it becomes difficult to dissolve as the amount of silver in the gold-silver alloy increases. Also, recovery of platinum and palladium becomes more difficult than in the examples.

[0024]

Example 5 Gold 50.3%, Silver 41.0%, Palladium 5.5%,
A 1.0 kg gold-silver alloy containing 1.0% platinum was processed into a plate with a width of 5 cm and a length of 10 cm, which was used as the anode. A stainless steel plate (JISSUS304) of the same size was used as the cathode, containing 500 g / l of potassium iodide. Electrolysis was performed by applying a direct current of 8 A in the electrolytic solution. Hydrogen generation was observed from the cathode for the first 30 minutes after the start of electrolysis, but as the color of the electrolyte changed from transparent to black brown, hydrogen generation subsided and a black brown electrodeposit started to deposit on the cathode. The obtained electrodeposit was composed of fine particles, and as a result of analysis, water content was 28%, gold was 35.0%, silver was 27.5%,
It has a composition of 3.0% palladium and 0.6% platinum, and the anode, which is a gold-silver alloy, is dissolved by electrolysis and deposited again on the cathode. After drying the obtained cathode deposit, 100 g of it was taken, 100 ml of pure water and 250 ml of nitric acid were added, and the mixture was heated in a beaker to perform nitric acid extraction, and then separated by filtration to obtain a precipitate (gold) and a liquid. . Analysis of the gold deposit revealed that the quality was 96.2%. The gold in the gold-silver alloy was of a grade that could be concentrated and directly input into the Wallwil method, and the gold and silver were substantially separated.

[0025]

INDUSTRIAL APPLICABILITY The present invention makes it unnecessary to adjust the quality of a gold-silver alloy, and can reduce the generation of nitrogen oxides associated with the nitric acid dispensing method, waste liquid treatment, chemical costs, etc., and easily separate the gold-silver alloy. .

Claims (4)

[Claims] 1. A method for separating a gold-silver alloy into gold and silver, a step of electrolyzing the gold-silver alloy in an iodine compound electrolyte solution serving as an anode and depositing it on a cathode to process it into fine particles, and the cathode deposit. A method for separating a gold-silver alloy, which comprises a step of extracting the slag with an acid having an oxidizing property to separate into gold and silver. 2. The method of separating a gold-silver alloy according to claim 1, wherein the oxidizing acid is nitric acid and the gold-silver alloy has a gold quality of 80% or less. 3. The oxidative acid is any of aqua regia, chlorine-blown water into hydrochloric acid, and sulfuric acid-salt-nitric acid, and the gold-silver alloy has a gold grade of 70% or more. 1. The method for separating a gold-silver alloy according to 1. 4. The method for separating a gold-silver alloy according to claim 1, wherein the gold-silver alloy contains platinum and palladium.