JPH11229053A - Production of high purity gold - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for simply and efficiently producing high purity gold having >=99.999 wt.% purity from a desilverized deposit generated by the nitric acid extraction of silver electrolysis anode slime by a reduction process. SOLUTION: Gold is recovered by adding nitric acid to a chloroauric acid solution of the desilverized deposit to dissolve further gold remaining in a residue to lower free hydrochloric acid concentration, diluting with water >=1.5 times the volume, filtering to remove the residue and reducing to. The quantity of nitric acid to be added is controlled to about 0.1-0.4 liten industrial 63 wt.% nitric acid per 1kg desilverized deposit and the chlorauric acid solution after the addition of nitric acid is preferably kept at 60-90 deg.C for 1-3 hr.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for producing 99.999% by weight of high-purity gold, such as used for bonding wires of electronic materials, by using anode slime obtained by silver electrolysis regardless of electrolytic purification. The present invention relates to a method for producing a precipitate desilvered by nitric acid extraction by a reduction method.

[0002]

2. Description of the Related Art Conventionally, as a method for producing gold having a purity of 99.999% by weight or more from an anode slime of silver electrolysis, an electrolytic refining method by the Wohllwill method is generally performed. In this method, silver anode slime is subjected to a nitric acid extraction treatment to obtain 95 to 98% by weight of Au and 1 to 3% by weight of silver.
After the desilvered precipitate is obtained, this is used as an original metal plate for an anode, and a pure metal plate having a purity of 99.99% by weight or more is used as a cathode and electrolysis is carried out by superimposing an alternating current and a direct current.

However, in this electrolytic refining method, an electrodeposit having a purity of 99.99% by weight or more can be obtained at the cathode, but 99.9% by weight is obtained.
Since the purity does not become 99% by weight or more, it is necessary to carry out electrolytic purification again. Specifically, the obtained electrodeposited metal was used as an original metal plate for an anode, and the chloroauric acid solution in which the electrodeposited metal was dissolved was used as an electrolytic solution. It is intended to obtain electrodeposition of not less than .999% by weight.

In contrast to such an electrolytic purification method, a method for producing high-purity gold by dissolving the above-described desilvered extract obtained by nitric acid extraction with hydrochloric acid and hydrogen peroxide to form a chloroauric acid solution and reducing the solution. (For example, US Patent No. 3)
No. 892557). Further, in this reduction of gold, in order to prevent the reduction deposition potential from approaching gold and to prevent contamination due to the deposition of palladium, the chloroauric acid solution is subjected to microfiltration, and then the reduction reaction of gold is reduced to 80 to 95%. A method for stopping the operation is known (JP-A-6-57348).

[0005]

The above-described electrorefining method of gold can obtain high-grade gold having a purity of 99.999% by weight or more, but requires the management of an electrolytic solution and the time required for the purification. Since it is long, the amount of gold staying in the process increases, consuming a large amount of energy, and the labor and cost associated therewith are extremely large.

On the other hand, the reduction method for obtaining high-purity gold by directly reducing a chloroauric acid solution does not have the same problems as the electrolytic refining method described above, and can obtain 99.99% by weight of reduced gold. However, since the resulting reduced gold contains silver or silica as an impurity in a unit of 10 to 100 ppm, it has been difficult to obtain high-purity gold at a level satisfying a purity of 99.999% by weight.

Specifically, the anodic slime of silver electrolysis is desilvered by extraction with nitric acid, and hydrochloric acid and hydrogen peroxide are added to the desilvered precipitate to dissolve gold.
100 to 300 g / l, Ag: 0.010 to 0.150 g
/ L, Pt: 1-3 g / l, Pd: 0.1-0.5 g /
1, Rh: 0.001 to 0.03 g / l, Si: 0.00
5 to 0.010 g / l and a free hydrochloric acid concentration of 2 to 3 mol / l.

This chloroauric acid solution is subjected to microfiltration, and gold in the solution is reduced to 80 to 95% with a known reducing agent such as hydrazine. When the resulting gold contains 10 to 100 ppm of Ag and Si as main impurities. , A purity of 99.99% by weight is the limit of gold quality, and gold with a higher purity could not be obtained.

The present invention has been made in view of the above circumstances, and has as its object to provide a method for easily and efficiently producing high-purity gold having a purity of 99.999% by weight or more by a reduction method.

[0010]

In order to achieve the above object, the present invention provides a method for dissolving gold with hydrochloric acid and hydrogen peroxide from a desilvered precipitate obtained by extracting nitric acid from a silver electrolytic anode slime with hydrochloric acid and hydrogen peroxide. In the method of reducing and recovering gold from a solution using a reducing agent, nitric acid is added to a chloroauric acid solution before reduction to dissolve the gold remaining in the residue and reduce the free hydrochloric acid concentration in the solution. And a method for producing high-purity gold, which comprises removing a residue by filtration and reducing the same.

In the method of the present invention, the concentration of free hydrochloric acid in the chloroauric acid solution is preferably reduced to 1 mol / liter or less. The amount of nitric acid added to the chloroauric acid solution was 0.1% with 63% by weight of industrial nitric acid per 1 kg of desilvered precipitate.
The volume is preferably 1 to 0.4 liter, and the chloroauric acid solution after addition of nitric acid is preferably maintained at 60 ° C to 90 ° C for 1 to 3 hours.

Further, in the present invention, as described above, the chloroauric acid solution to which nitric acid has been added is diluted to 1.5 times or more with water to further reduce the free hydrochloric acid concentration in the solution. It is preferable to remove the residue by filtration and to reduce the residue.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION In a reaction for dissolving gold in a desilvered precipitate of a silver electrolytic anode slime with hydrochloric acid and hydrogen peroxide, first, as shown in the following chemical formula 1, hydrochloric acid and hydrogen peroxide react to form chlorine. It is considered that the chlorine is generated and then reacts with the gold as shown in the chemical formula 2, so that the gold is dissolved as a chloro complex. Usually, hydrochloric acid and hydrogen peroxide are added in amounts equivalent to 1 to 2 times the amounts required for the reactions shown in Chemical Formulas 1 and 2.

[0014]

Embedded image 3HCl + 1.5H ₂ O ₂ = 3H ₂ O + 1.5Cl ₂

Embedded image Au + 1.5Cl ₂ + HCl = H (AuCl ₄ )

In the above-described gold dissolution reaction using hydrochloric acid and hydrogen peroxide, hydrochloric acid which can be decomposed with hydrogen peroxide and hydrochloric acid which can be consumed by dissolving gold have a limit. About 3 mol / l of free hydrochloric acid remains.
Therefore, the free hydrochloric acid remaining, silver AgCl ₂ ^- to dissolve a chloro complex, in gold deposited in the reduction of post is assumed to be mixed as an impurity. Also,
Silica dissolves in a gel state and is not sufficiently captured even by filtration, so that it is mixed in with gold during reduction, like silver.

Therefore, in the present invention, as shown in the following chemical formula 3, undissolved gold is further dissolved in nitric acid and hydrochloric acid by adding nitric acid to a gold chloride oxidation solution in which gold is dissolved in hydrochloric acid and hydrogen peroxide. Let it. At this time, hydrochloric acid is consumed and the concentration of free hydrochloric acid in the solution decreases, so that the solubility of silver decreases and silver, which is an impurity, can be precipitated. In order to precipitate silver by lowering the solubility of silver, the concentration of free hydrochloric acid in the chloroauric acid solution is preferably 1 mol / l or less, more preferably 0.5 mol / l or less.

[0017]

3HNO ₃ + 13HCl + 4Au = 3NOCl
+ 6H ₂ O + 4H (AuCl ₄ )

The amount of nitric acid to be added in this case is 0.1 to 0.4 liter / 63% by weight of industrial nitric acid based on the desilvered precipitate obtained by extracting the silver electrolytic anode slime with nitric acid.
A range of kg is preferred. The amount of nitric acid added is 0.1 liter /
If it is less than kg, the effect of silver precipitation is not sufficient, and if it is more than 0.4 liter / kg, nitrate is left undesirably generated in a large amount as nitrogen oxide (NOx) when gold is reduced later.

It was further surprisingly found that the addition of nitric acid reduces silica in chloroauric acid solution as well as silver. Although the cause is not clear, it is considered that the silica gel is dehydrated and changes to a form that can be easily removed by the subsequent microfiltration.

In order to promote the reaction of the above formula 3, the temperature of the solution after the addition of nitric acid is preferably maintained at 60 to 90 ° C. If the temperature of the solution is lower than 60 ° C., the reaction does not proceed sufficiently or the reaction takes time,
There is no remarkable difference in the effect even when heating to 0 ° C. or more. The termination of the reaction varies depending on the temperature. In the above temperature range of 60 to 90 ° C., the reaction is usually completed in 1 to 3 hours.

In the present invention, after the addition of nitric acid as described above, the chloroauric acid solution can be further diluted with water. The dilution with water lowers the concentration of free hydrochloric acid and further reduces the solubility of silver, so that desilvering by precipitation proceeds further.
In this case, the concentration of free hydrochloric acid is reduced by increasing the degree of dilution, and the effect of desilvering is obtained with a dilution of about 1.5 times, and other impurity elements are reduced in proportion, but when the degree of dilution increases, It is most desirable to dilute gold about twice as much as gold also has a reduced concentration. Even if the dilution is further increased, the amount of wastewater after gold reduction only increases, and there is no remarkable difference in desilvering.

After adding nitric acid and, if desired, diluting,
The chloroauric acid solution is microfiltered to remove undissolved residues.
The filter medium used in this case is not particularly specified, but a filter medium having a mesh size of about 0.2 μm is preferable in consideration of the capturing of particles and the filtration speed.

The composition of the chloroauric acid solution after such treatment is as follows: Au: 50 to 150 g / l, Ag: ≦ 0.001
g / l, Pt: 0.5-1.5 g / l, Pd: 0.05-1.5
0.3 g / l, Rh: ≤ 0.015 g / l, Si: <0.
002 g / l, and the contents of Ag and Si are significantly reduced. The concentration of free hydrochloric acid in the solution is 0.7 to 1.0.
It is about 0 mol / l.

Thereafter, the gold dissolved in the chloroauric acid solution is precipitated by reduction using a known reducing agent. As the reducing agent, for example, it is preferable to use a relatively weak reducing agent such as hydrazine, sulphite gas or sodium sulphite. Further, by stopping the reduction reaction of gold at the point of 80 to 95%, contamination of impurities such as Pt and Pd can be prevented. The end point of the reduction reaction can be determined in advance by analyzing the gold concentration to determine the amount of the reducing agent to be added, or by determining the oxidation-reduction potential.

[0025]

EXAMPLE 1 A silver electrolytic anode slime was extracted with nitric acid, filtered and subjected to Au: 97.8% by weight, Ag: 0.9% by weight, Pt:
A desilvered precipitate having a composition of 0.7% by weight, Pd: 0.1% by weight, Rh: 0.4% by weight, Si: <0.1% by weight) was obtained. 400 g of the desilvered precipitate was placed in each beaker, 700 ml of 35% by weight hydrochloric acid was added to each beaker, the liquid temperature was adjusted to 40 ° C., and 370 ml of 35% by weight hydrogen peroxide solution was gradually added with a metering pump over 4 hours. Was added and gold was dissolved to obtain a chloroauric acid solution. At this time, the liquid temperature rose to 85 ° C.

To each of the obtained chloroauric acid solutions, 0.1 to 0.4 liters of industrial-grade 63% by weight nitric acid was added per 1 kg of desilvered precipitate as shown in Table 1 below. As one
Hold for hours. Next, water was added so that the volume of the solution was doubled, and the solution was left to cool. Thereafter, the solution was microfiltered with a membrane filter having an aperture of 0.2 μm, and hydrazine in an amount such that 90% of gold in the filtrate was reduced was added to 4% by weight, and gold was reduced and precipitated.

For each sample, the reduced gold thus obtained was collected, washed with warm water and dried, and then the quality of the reduced gold was analyzed. The grades of the obtained reduced gold are summarized in Table 1 below. In addition, as a comparative example, the quality of the obtained reduced gold was analyzed with respect to a sample that was performed in the same manner as described above except that addition of nitric acid and / or dilution with water were not performed.
Are also shown.

[0028]

[Table 1] Reduction of nitric acid added Grade (ppm of impurities) Sample (l / kg) Diluted Au (wt%) Ag Pt Pd Rh Si 1 0.1 Yes 99.999 4 3 1 1 <1 20.2 Yes 99.999 2 3 1 < 1 <1 3 0.3 Yes 99.999 1 1 1 <1 <1 4 0.4 Yes 99.999 1 1 <1 <1 <1 5 0.1 No 99.999 15 3 1 1 2 6 * No No 99.992 51 3 1 1 25 7 * No Yes 99.996 8 1 1 <127 Note: Samples marked with * in the table are comparative examples.

From the results shown in Table 1, it can be seen that all of the samples subjected to the desilvering treatment by adding nitric acid to the chloroauric acid solution have a purity of the recovered reduced gold of 99.999% by weight or more. I understand.

Example 2 Using the same desilvering precipitate obtained by extracting nitric acid from the electrolytic anode slime as in Example 1 above, 25 kg thereof was put into a 150 liter FRP tank, and 44 liters of 35% by weight hydrochloric acid were added.
23 liters of a 35% by weight aqueous hydrogen peroxide solution was added and dissolved. After the liquid temperature was adjusted to 60 ° C., 68% by weight of industrial nitric acid was
One liter was added, and the mixture was stirred until no red gas peculiar to nitrogen oxides was generated.

Thereafter, water was added to dilute to twice the volume, and the mixture was allowed to stand overnight, cooled, coarsely filtered with a Denver filter having a diameter of 60 cm, and then finely filtered with a cartridge filter having openings of 0.2 μm. When the composition of the obtained filtrate was analyzed, Au: 151 g / l, Ag: <1 mg / l, P
t: 423 mg / l, Pd: 99 mg / l, Rh: <1
mg / l, Si: <1 mg / l.

Four liters of the filtrate was taken, and hydrazine diluted to 4% by weight was added in an amount capable of reducing 90% of the gold in the solution to reduce gold. After the reduction, the solution was filtered, washed with depulp with 2 liters of warm water, filtered again to dry the reduced gold, and the quality of the obtained reduced gold was analyzed.
It was 9.999% by weight.

[0033]

According to the present invention, it is impossible to recover high-purity gold by a conventional method without using the conventional gold electrorefining and by a reduction method. Prevention of contamination and high-purity gold of 99.999% or more can be efficiently recovered in a short time by the reduction method.

Claims (5)

[Claims] 1. A method for dissolving gold with hydrochloric acid and hydrogen peroxide from a desilvered precipitate obtained by extracting nitric acid from a silver electrolytic anode slime with nitric acid, and reducing and recovering gold with a reducing agent from the obtained chloroauric acid solution, the method comprising: By adding nitric acid to the chloroauric acid solution of the above, the remaining gold in the residue is dissolved to reduce the free hydrochloric acid concentration in the solution, and then the residue is removed by filtration and reduced. Manufacturing method of high purity gold. 2. The method for producing high-purity gold according to claim 1, wherein the concentration of free hydrochloric acid in the chloroauric acid solution is reduced to 1 mol / liter or less. 3. The amount of nitric acid added is 1 kg of the desilvered precipitate.
The method for producing high-purity gold according to claim 1 or 2, characterized in that the amount of the industrial-grade 63 wt% nitric acid is 0.1 to 0.4 liter. 4. A chloroauric acid solution after addition of nitric acid is heated to 60 ° C. to 9 ° C.
The method for producing high-purity gold according to any one of claims 1 to 3, wherein the method is held at 0 ° C for 1 to 3 hours. 5. The chloroauric acid solution after the addition of nitric acid is mixed with water for 1.5 times.
The method for producing high-purity gold according to any one of claims 1 to 4, wherein after diluting to a volume twice or more, filtration is performed to remove a residue, and reduction is performed.