JPH0128112B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an aqueous alkali dicyanauric acid solution, and particularly to a method for producing an aqueous alkali dicyanauric acid solution with high concentration and high purity.

Generally, gold powder, gold plate, etc. are dissolved in an aqueous sodium cyanide solution by the following reaction.

4Au+8NaCN+2H ₂ O+O ₂ → 4NaAu(CN) ₂ +2NaOH This reaction formula can be similarly applied to other potassium cyanide and magnesium cyanide. Further, oxygen in the above reaction formula acts as an oxidizing agent, and normally oxygen in the air is dissolved in water and contributes to the reaction.

Electrolysis is a method of oxidizing gold using electricity. That is, if electrolysis is performed in a sodium cyanide solution using gold as an anode, gold will be eluted by the following anode reaction.

2Au + 4NaCN→ 2NaAu(CN) ₂ +2Na ⁺ +2e In addition, oxygen generated at the anode as a side reaction also contributes to the elution of gold at the anode as sodium dicyanoaurate.

At the cathode, the following electrolysis reaction of water occurs, and sodium hydroxide is produced by the anode reaction and the sum.

2H ₂ O＋2e→H ₂ ↑＋2OH ^- 2Na ⁺ +2OH ^- →2NaOH However, sodium dicyanoaurate (), which is known as a raw material for plating solution and catalyst solution, is prone to reduction and precipitation at the cathode. Since it is a material that easily dissolves, gold eluted at the anode is deposited on the cathode due to the following side reaction.

2NaAu(CN) ₂ +2e →2Au+2NaCN+CN ^- Therefore, when trying to obtain an aqueous solution of sodium dicyanaurate () by electrolysis, gold plates are used as both electrodes, and the polarity of the two electrodes is alternately changed.
The gold was gradually eluted into the sodium cyanide solution by reversing the anode and cathode. However, even with this method, there were problems such as redeposition of gold, poor manufacturing yield, and long melting time. Furthermore, it was not possible to obtain a highly purified solution of sodium dicyanoaurate () containing no sodium hydroxide.

In view of the above-mentioned drawbacks, the present inventor has made extensive research and found that it is possible to produce a highly concentrated and highly purified solution of sodium dicyanaurate () in a short period of time. We have developed a method that can produce an aqueous aqueous solution of dicyanoauric acid by elution.

The present invention relates to a method for producing an aqueous solution of an alkali dicyanoaurate () by eluting gold as an anode in an aqueous alkali cyanide solution by electrolytic action. partitioning the chamber and the cathode chamber,
This is a method for producing an aqueous alkali dicyanoauric acid solution, which is characterized by stirring the surface of an ion exchange membrane on the anode chamber side with an aqueous alkali cyanide solution at a flow rate of 1 cm/sec or more.

This ion exchange membrane is a membrane that blocks dicyanauric acid ions but allows alkali metal ions to freely pass through. For example, the product name: Selemion CMV (manufactured by Asahi Glass Co., Ltd.) is known. . As the anode, a metal plate or an insoluble cage filled with gold pieces or powder is used, and as the cathode, a material such as stainless steel that does not dissolve in an aqueous solution of alkali cyanide or alkali hydroxide is used. The higher the temperature, the better the solubility of the dicyanoauric acid alkali becomes, so the higher the liquid temperature is, the more preferable it is.

However, even if electrolysis is carried out simply through an ion exchange membrane with normal stirring, the current density at the anode will not exceed several A/dm ² because the liquid stagnates on the surface of the ion exchange membrane. Therefore, it is necessary to forcibly stir the liquid on the surface of the ion exchange membrane to constantly clean it so that the liquid does not stagnate, thereby speeding up ion exchange.

Therefore, the liquid must be stirred using a pump at a flow rate of 1 cm/sec or more on the surface of the ion exchange membrane on the anode chamber side. Note that the flow rate on the surface of the ion exchange membrane on the cathode chamber side may be 1 cm/sec or more,
In this case, by making the flow rate on the ion exchange membrane surface on the anode chamber side of the electrolytic cell faster than the flow rate on the cathode chamber side surface, the liquid agitation at the anode will inevitably improve.
The reaction between gold and cyanide ions at the anode can be effectively carried out. Furthermore, if necessary, another new aqueous alkali cyanide solution may be supplied to the surface of the ion exchange membrane to supply the alkali cyanide consumed in dissolving the gold.

By forcibly cleaning the ion exchange membrane surface using the method described above, the anode current density can be increased to 10~
It is now possible to flow a current as high as 100A/ ^dm2 , and as a result, a highly pure and highly concentrated aqueous dicyanoauric acid aqueous solution can be obtained in a short time.
It became possible to elute the gold from the anode in a short time.

Examples of the present invention, conventional examples, and comparative examples will be described below.

Example 1 One 10 kg Au plate (1 cm x 50 cm x 10 cm) was used as an anode, two stainless steel plates were used as cathodes, and the distance between the electrodes was 6.
cm, and the electrolytic cell was divided into three equal parts with an ion exchange membrane (trade name: Selemion CMV) manufactured by Asahi Glass Co., Ltd. interposed between the two electrodes, with the center as an anode chamber. KCN200g/
, put an electrolytic solution with a liquid temperature of 70℃ into an electrolytic tank, and a pump that circulates the anode chamber solution and stirs the liquid on the anode side ion exchange membrane surface, and a cathode chamber solution that circulates and stirs the cathode side ion exchange membrane surface. Two stirring pumps were used. Note that one end of the cathode side pump is separate from the electrolytic cell.
Connected to KCN supply tank 20.

Electrolysis was carried out for 3 hours at an anode current density of 35 A/dm ² , a flow rate of 7 cm/sec on the surface of the ion exchange membrane on the anode side, and a flow rate of 5 cm/sec on the surface of the ion exchange membrane on the cathode side.
8 kg of Au was eluted, and an aqueous potassium dicyanoauric acid solution (PH=12.8) containing 300 g of Au was obtained.

Example 2 The anode current density was 35 A/d in the same manner as in Example 1.
When electrolysis was carried out ^for 3 hours at a flow rate of 8 cm/sec on the surface of the ion exchange membrane on the anode side and 6 cm/sec on the surface of the ion exchange membrane on the cathode side, Au8Kg was eluted and Au300
g/g of potassium dicyanoaurate() aqueous solution (PH
= 12.3) was obtained.

Conventional example Three 3Kg Au plates (0.3cm x 50cm x 10cm) are used as electrodes, and the distance between the electrodes is kept at 6cm. When the center is an anode, both sides are used as the cathode, and when both sides are anode, the center electrode is used as the cathode. Switch the anode and cathode alternately for 15 seconds each so that the polarity changes so that the current density at the anode is 1A/dm ² (even if the current density is increased further, the elution amount will not change and the gold concentration will also increase). ), electrolysis was carried out for 3 hours using electrolyte solution 30 at a temperature of 70°C. Note that no ion exchange membrane was used, and the surface of each electrode plate was stirred at a flow rate of 0.4 cm/sec using a pump. 0.5Kg of Au is eluted by electrolysis,
An aqueous solution of potassium dicyanoaurate (PH=14.2) containing 17 g of Au/au was obtained.

Comparative Example The flow rate on the anode side and the cathode side was 0.4 cm/sec, and the anode current density was 8 A/dm ² (even if the current density was increased further, the elution rate did not increase, only the voltage increased abnormally, and no current could be passed). ) was electrolyzed in the same manner as in Example 1, 1.2 kg of Au was eluted, and Au50
g/g of potassium dicyanoaurate() aqueous solution (PH
= 12.6) was obtained.

As is clear from the above Examples, Conventional Examples, and Comparative Examples, according to the method for producing an aqueous dicyanauric acid aqueous solution of the present invention, a large amount of gold can be eluted in a short time compared to the conventional electrolysis method. Furthermore, a highly purified aqueous alkali dicyanoauric acid solution with a high gold content and low pH can be obtained.

Claims (1)

[Claims] 1 In a method of producing an aqueous solution of alkali dicyanoaurate () by eluting gold as an anode in an aqueous alkali cyanide solution by electrolysis, the anode chamber and the cathode are separated by an ion exchange membrane that shields the alkali dicyanoaurate (). 1. A method for producing an aqueous alkali dicyanoauric acid solution, the method comprising: partitioning the ion-exchange membrane surface on the anode chamber side with an aqueous alkali cyanide solution at a flow rate of 1 cm/sec or more.