JPS60177192A - Method for separating and recovering gold and silver from waste stripping liquid of gold plating containing co-existing gold and silver - Google Patents

Abstract

PURPOSE:To recover easily gold and silver in short time with good purity by adding a conductive salt and reducing agent to a waste stripping liquid of gold plating and controlling the potential of a cathode to electrodeposit silver first then to electrodeposit gold. CONSTITUTION:A conductive salt such as sodium hydroxide and reducing agent such as formalin soln. are added to a waste stripping liquid of gold plating which is alkaline and has free cyan and oxidizing agent as well as co-existing gold and silver in order to permit the electrolytic treatment thereof. The potential of a cathode is first controlled to the low potential range where silver deposits mainly to electrodeposit silver then the potential of the caqhode is controlled to the high potential range where gold deposits mainly to electrodeposit gold in the stage of subjecting such waste liquid to an electrolytic treatment. The electrodeposited materials having a high ratio of silver and gold are thus respectively obtd.

Description

[Detailed Description of the Invention] The present invention is a method of adding a conductivity salt and a reducing agent to a gold plating stripping waste solution in which gold and silver coexist, and separating and recovering gold and silver by electrolysis using three-electrode potential regulation. It is related to.

It is generally considered difficult to separate gold and silver with high purity from a solution in which gold and silver coexist. However, when attempting to recover gold from semiconductor device parts, gold and silver may coexist at a fairly high concentration in gold plating stripping waste liquid.

In ceramic packages for semiconductor devices, the main body and terminal leads are often connected by silver brazing, and in order to satisfy the properties of the pan cage in the final process, the element attachment part and the terminal This is due to the fact that the lead etc. are plated with gold. In other words, in order to recover as much gold as possible from the element attachment parts, terminal leads, etc., without discarding defective ceramic packages after gold plating, we use alkaline sound-free cyanide, The gold is removed by applying a ceramic package to a stripping solution containing an oxidizing agent, but at the same time, the silver in the silver solder is mixed into the stripping waste solution.

Conventionally, chemical treatment and electrolytic treatment are known as methods for separating and recovering gold and silver from such a cold liquid in which gold and silver coexist. The former involves chemical separation by adding various chemicals, but it involves approximately 30 steps and has the disadvantage of being expensive in terms of chemicals, man-hours, etc., and it is not possible to perform the separation cheaply and quickly. be. In addition, the latter electrolytic treatment has the disadvantage that if electrodeposition is carried out under normal current regulation, gold and silver eutectoid and become difficult to dissolve in chemicals such as aqua regia, making effective separation impossible. be.

The present invention has been made in view of the above-mentioned difficulties, and its purpose is to provide gold plating stripping I11 in which gold and silver coexist, which can separate gold and 612 with high purity in a short time and with less man-hours. The purpose of the present invention is to provide a method for separating and recovering gold and silver from waste liquid, and its characteristics are that the gold plating stripping waste liquid, which is alkaline and contains free cyanide and oxidizing agents, and in which gold and silver coexist, is combined with conductivity salt and reduction. First, the potential of the cathode is controlled to a potential range in which silver is precipitated, and then electrodeposition is carried out by regulating the potential of the cathode to a potential range in which mainly gold is deposited.

Preferred embodiments of the present invention will be described in detail below.

Stripping of gold plating is carried out with a conventional stripping solution, i.e. an alkaline-sound-free stripping solution containing cyanide and an oxidizing agent. A conductivity salt and a reducing agent are added to the waste liquid after using the stripping solution to enable electrolytic treatment.

As the conductivity salt, sodium hydroxide can be suitably used, and as the reducing agent, a polymarine solution can be suitably used. The reducing agent reduces the oxidizing agent remaining in the stripping waste solution and interfering with gold electrodeposition. In the method of the present invention, silver is first deposited in a low potential range, and then gold is deposited in a high potential range. In other words, the difference in deposition potential between silver and gold is utilized. Figure 1 shows
Gold 3.3g/ffi, Silver 1.9g/ff, Copper 1.3g/ffi
j! , nickel 4.1g/j! Add 75 g/f of sodium hydroxide as a conductivity salt and 35 mff/β of a 37% Polmarine solution as a reducing agent to the gold plating stripping waste solution containing
The current-voltage curve when electrolyzed at a bath temperature of 60°C is shown. From this figure, silver mainly begins to precipitate from -0.5V,
-〇, from 9V, gold mainly begins to precipitate, -1,25
It can be seen that water decomposition begins from V. However-
By performing electrodeposition at a low voltage of around 0.5V, for example -0.6V, it is possible to obtain a deposit with a high proportion of silver (approximately 65%). Since this deposit has a high proportion of silver, it is easy to dissolve only the silver with nitric acid and separate it from the gold. Next, by carrying out electrodeposition at a high potential around -0.9V, it is possible to obtain an electrodeposit with a high proportion of gold (approximately 85%). Since this deposit has a high gold ratio, it is easily dissolved in aqua regia. The setting of the cathode potential described above is managed using a reference electrode.

Examples are shown below.

Fri 3.31! /β, silver 1.9 g/' j! , ! P
Sodium hydroxide 75 g/1.37% in stripping waste solution containing I 1.3 g/p, nickel 4.1 g/β
300m j! of each treated solution to which Polmarin solution was added at a concentration of 35nl/A! was placed in an acrylic container, a PT plate was used as the anode, a SUS plate was used as the cathode, a reference electrode was set near the cathode, the cathode potential was set to 10, 6■, and constant potential electrolysis was performed at a bath temperature of 60°C. went. The electrolysis time is determined by the number of coulombs corresponding to the amount of silver in the bath. When the cathode potential is set to 1.0.6V, the current is 5On+A
Therefore, the electrolysis time will be 2.6 hours based on the coulomb number, but considering that the amount of current will decrease slightly:
Time electrolysis was performed. As a result, the amount of silver in the solution to be treated was 74
% was recovered and 21% of gold was recovered.

Next, constant potential electrolysis was carried out at a bath temperature of 60 DEG C. with the cathode potential set at -0.9 .ANG.. As a result, the remaining gold and silver in the solution to be treated were recovered at a recovery rate of nearly 100%.

The ratio of gold and silver in the foil-shaped electrodeposit recovered by setting the cathode potential to 10.6■ is 33% gold and 6% silver.
It was 5%. This foil was heated and melted with nitric acid M (1:1), and the silver was dissolved in a silver nitrate solution for δ11 minutes, so that only gold remained, and gold and silver could be separated and recovered. In addition, the ratio of gold, silver, and copper in the deposits recovered by setting the cathode potential to -0.9■ was 85.7% for gold, 1.9% for silver, and 8.7% for copper. Ta. This foil was melted in regular aqua regia, denitrated, diluted, silver was separated and recovered as silver chloride, and sulfite water was added as a reducing agent to recover only the gold.

As described above, according to the present invention, processing is simplified,
It is effective in that gold and silver can be separated quickly and with high purity, and costs can be reduced.

Although the present invention has been variously explained above with reference to preferred embodiments, the present invention is not limited to these embodiments, and it goes without saying that many modifications can be made without departing from the spirit of the invention. It is.

[Brief explanation of drawings]

FIG. 1 shows a current-voltage curve of a gold plating stripping waste solution in which gold and silver coexist.

Claims (1)

[Claims] 1. A conductivity salt and a reducing agent are added to a gold plating stripping waste solution that is alkaline and contains free cyanide and an oxidizing agent, and in which gold and silver coexist. A gold plating stripping waste liquid in which gold and silver coexist, characterized in that electrodeposition is carried out by regulating the potential range in which silver is deposited, and then electrodeposition is carried out by regulating the potential of the cathode in a potential range in which gold is mainly deposited. A method for separating and recovering gold and silver from 2. Stripped gold plating M in which gold and silver coexist according to claim 1, using sodium hydroxide as a conductivity salt
A method for separating and recovering gold and silver from waste liquid. 3. A method for separating and recovering gold and silver from a gold plating stripping waste solution in which gold and silver coexist according to claim 1 or 2, using a formalin solution as a reducing agent.