GB2058135A

GB2058135A - Process and apparatus for recovering gold and silver

Info

Publication number: GB2058135A
Application number: GB8018550A
Authority: GB
Original assignee: Nanao Kogyo Co Ltd
Current assignee: Nanao Kogyo Co Ltd
Priority date: 1979-06-08
Filing date: 1980-06-05
Publication date: 1981-04-08

Abstract

A process for dissolving and recovering gold and/or silver deposited on materials 7, which comprises contacting said materials with an aqueous solution of cyanide in the presence of air to dissolve said gold and/or silver and then electrolyzing said aqueous solution in a cell 6 to recover said gold and/or silver on a cathode. Gold and/or silver can be dissolved and recovered rapidly and effectively by employing the aqueous solution of cyanide only. <IMAGE>

Description

SPECIFICATION Process and apparatus for recovering gold and silver This invention relates to a process for dissolving and recovering gold and/or silver deposited on materials and an apparatus to practice such process, and more particularly relates to a process in which only a solution of cyanide is used to dissolve and recover gold and/or silver rapidly and effectively and an apparatus to practice the same.

Various materials having gold and/or silver on their surface, such as gold or silver plated wastes, scrap, racks for plating and the like, are often subjected to recovering treatments so as to reuse these precious metals. In conventional processes, gold is dissolved in aqua regia or a cyanide solution containing nitro compounds, and silver is dissolved in nitric acid or other suitable solution, then these metals are recovered from dissolving solutions.

However, it is relatively troublesome to recover gold and/or silver from such solutions, and, for that reason, they are usually received by special refineries to recover the metals. Besides, the waste water containing cyanide and other poisonous compounds is costly to treat.

Accordingly, it is an object of this invention to provide a process for dissolving and recovering gold and/or silver rapidly and effectively.

Another object of this invention is to provide a process in which only a solution of cyanide is used as a dissolving solution.

Still another object of this invention is to provide an apparatus to practice said process efficiently.

According to this invention, these and further objects can be accomplished by providing a process for dissolving and recovering gold and/or silver deposited on materials, which comprises contacting said materials with an aqueous solution of cyanide in the presence of air to dissolve said gold and/or silver and then electrolyzing said aqueous solution to recover said gold and/or silver on a cathode.

Above mentioned objects can be also accomplished, according to one embodiment of this invention, by providing an apparatus which comprises a dissolving chamber for loading materials having gold and/or silver deposited thereon, said chamber being open to the air at upper end thereof, a sprinkler disposed at the top part of said chamber, and an electrolyzer connected with the bottom part of said chamber and provided with an anode and a cathode.Said objects can be accomplished likewise, according to another embodiment of this invention, by providing an apparatus which comprises an electrolyzer provided with an anode and a cathode and filled with an aqueous solution of cyanide, and a porous rotating drum set up in said electrolyzer for loading materials having gold and silver deposited thereon, said electrolyzer being filled with said aqueous solution so that only a part of said materials is soaked therein.According to still another embodiment of this invention, said objects can also be accomplished by providing an apparatus which comprises and electrolyzer provided with an anode and a cathode and filled with an aqueous solution of cyanide, and a basket disposed above the surface of said aqueous solution in said electrolyzer for loading materials having gold and/or silver deposited thereon, said basket being disposed so that it travels vertically and repeatedly whereby said materials in said basket being soaked in said aqueous solution repeatedly.

Brief Description of the Drawing In the accompanying drawing: Fig. 1 shows a schematic illustration of a preferred embodiment of this invention in which a chamber and a sprinkler are employed to load materials and dissolve gold and/or silver; Fig. 2 shows a schematic illustration of a preferred embodiment of this invention in which a porous rotating drum is employed to load materials; Fig. 3 shows a schematic illustration of a preferred embodiment of this invention in which a basket is employed to load materials.

Detailed Description In Fig. 1 there is shown one embodiment of this invention which comprises principally a dissolving chamber 1 open to the air at its upper end, a sprinkler 2 disposed at the top part of this dissolving chamber 1, and an electrolyzer 6 connected with the bottom part 3 of the dissolving chamber 1 and provided with an anode 4 and a cathode 5 on both sides thereof. Materials 7 having gold and/or silver deposited thereon are loaded into the dissolving chamber 1. The materials 7 include gold or silver plated wastes such as scrap or defective of printed circuit which has been nickel then gold plates on brass, plating racks such as silver plating rack, and the like. In Fig. 1, 8 and 9 stand for direct electric source and a switch, respectively.

In the above described apparatus, an aqueous solution of cyanide is sprayed or showered over the materials 7 having gold and/or silver deposited thereon, in the dissolving chamber 1. Since the chamber is open to the air at its upper end, the materials 7 are wetted by the aqueous solution in the presence of air. That is to say, the materials 7 are contacted with air under the wet condition, and the air acts as an oxidizing agent which contributes to a rapid dissolving of deposited gold and/or silver on the materials 7 into the aqueous solution of cyanide. Accordingly, the aqueous cyanide is the only dissolving solution employed.in this invention, which dissolves gold and/or silver rapidly and effectively. Various cyanides, such as sodium cyanide and the like, may be used as a dissolving solution of this invention.

The aqueous solution of cyanide containing dissolved gold and/or silver is introduced to the electrolyzer 6 through the bottom part 3 of the dissolving chamber 1. The electrolyzer 6 has the anode 4 and the cathode 5 on its both side walls.

When the concentration of gold and/or silver in the solution increases enough to electrolyze, the direct electric current is passed by turning on the switch 9, and both metals in the solution are recovered on the cathode 5 as a fine metallic plate, while a gas predominantly consisting of oxygen is generated from the anode 4. Graphite is mainly employed as the anode 4 and stainless steel as the cathode 5.

After the aqueous solution has been treated in the electrolyzer to recover gold and/or silver, it is supplied to the sprinkler 2 by means of a circulating pump 11 disposed at an appropriate position on a conduit 10 connecting the sprinkler 2 and the electrolyzer 6, and is reused to dissolve gold and/or silver As described above, the aqueous solution of cyanide is reusable which results in an economical treatment of gold and/or silver deposited on the materials without any undesirable waste water or environmental pollution.

In Fig. 2 there is shown another embodiment of this invention which comprises an electrolyzer 101 provided with an anode 101a and a cathode 101 b on both side walls thereof, and a porous rotating drum 104 having many holes 103, 103,... 103 set up in the electrolyzer 101 by means of a shaft 102 fixed on the side walls.

Materials 105 having gold and silver deposited thereon are loaded into the rotating drum 104.

The materials 105 to be treated in this apparatus are the same as those described above.

The electrolyzer 101 is filled with an aqueous solution of cyanide 106 so as to soak only a part of the materials 105 in the drum 104. Thus, the materials 105 in the drum 104 are soaked repeatedly in the solution 106 when the drum is rotated by rotating the shaft 104, and gold and/or silver deposited on the materials 105 are dissolved into the solution 106 in the presence of air. As in Fig. 1, the materials 105 are contacted with air under the wet condition, and the air acts as an oxidizing agent which contributes to a rapid dissolving of deposited gold and/or silver Accordingly, the aqueous cyanide is the only dissolving solution in this invention. Any kind of cyanide such as sodium cyanide and the like may be used.When the concentration of gold and/or silver in the solution 106 increases enough to electrolyze, the direct current is applied from an electric source 107 by turning on a switch 108, and both metals in the solution 106 are recovered on the cathode 101 b as a fine metallic plate, while a gas predominantly consisting of oxygen is generated from the anode 101 a. The anode and cathode are the same materials as those used in the apparatus described in Fig. 1.

In Fig. 3 there is shown another embodiment of this invention wherein a basket 109 is employed for loading the materials instead of the rotating drum in the apparatus described above. The electrolyzer 101 provided with the anode 101 a and the cathode 101 b, and the aqueous solution of cyanide 106 are the same as those used in the Fig. 2. The basket 109 is kept above the surface of the solution 106 in the electrolyzer 101 by means of a piece of string 110. By controlling the string 110, the basket 109 travels vertically and the materials 105 loaded therein are soaked in the solution 106 repeatedly. In Fig. 3, the basket 109 in the solution 106 shows a soaked condition.

When the materials 105 are soaked, gold and/or silver deposited thereon are dissolved into the solution 106 in the presence of air. Again, only the aqueous solution of cyanide 106 is employed to dissolve metals rapidly and effectively. The solution 106 containing dissolved gold and/or silver is then similarly electrolyzed as described above.

This invention will be more fully understood by following examples.

EXAMPLE 1 Using scrap of printed circuit which had been plated by nickel then gold on brass, gold on the scrap was dissolved and recovered by means of the apparatus shown in Fig. 1. Each scrap was placed upright on the bottom of the dissolving chamber at 10 mm intervals. Then, 50 g/l solution of NaCN was showered to the scrap in the dissolving chamber at a spraying rate of 10 ml/min. through the spinkler while pumping the solution. Two plates of stainless steel and graphite, 1 dm2 each, were used as the cathode and the anode respectively. Turning on the switch, an electric current of 0.3A was applied to the electrolyzer. After 3 hours, gold was deposited effectively on the cathode.

EXAMPLE 2 In order to dissolve and recover silver deposited on racks for silver plating, the same procedure was repeated using the apparatus and conditions of Example 1. After 3 hours, all silver on the racks was dissolved and was deposited effectively on the cathode of the electrolyzer.

EXAMPLE 3 In the example, the dissolving rate of silver was tested. When a silver plate was treated following the procedure of Example 1, the dissolving rate was 21 micron/hr. at a temperature of 200C.

When silver was dissolved in an aqueous solution of sodium cyanide, conventionally used for silver smelting, with air blowing, the dissolving rate decreased to about one fifth of the present process.

Thus, it is clear that silver is dissolved far more rapidly than the conventional air blowing process.

EXAMPLE 4 Using the apparatus of Fig. 2, the same scrap of printed circuit described in Example 1 was treated to recover gold. The rotating drum was loaded with the scrap, and the electrolyzer was filled with 50 g/l solution of NaCN so as to soak about half of the scrap.

Then, the drum was continued to be rotated slowly until gold deposited on the scrap was dissolved completely into the solution. Plates of stainless steel and graphite 1 dm2 each, were used as the cathode and the anode of the electrolyzer, respectively, and an electric current of 0.3A was applied. After 3 hours, gold was deposited effectively on the cathode.

EXAMPLE 5 Using the apparatus of Fig. 3, the same procedure described in Example 4 was carried out.

The basket was loaded with the scrap of printed circuit, and was soaked in the solution (50 g/l NaCN) repeatedly by controlling the length of the string until gold deposited on the scrap was dissolved completely into the solution. Similar stainless steel and graphite as Example 4 were used as the electrodes and the electric current of 3A was applied to the electrolyzer. After 3 hours, gold was deposited effectively on the cathode.

Claims

1. A process for dissolving and recovering gold and/or silver from materials having gold and/or silver deposited thereon, which comprises contacting said materials with an aqueous solution of cyanide in the presence of air to dissolve said gold and/or silver and then electrolyzing said aqueous solution to recover said gold and/or silver on a cathode.

2. A process claimed in claim 1 wherein said aqueous solution of cyanide is showered or sprayed to said materials to dissolve gold and/or silver.

3. A process claimed in claim 1, wherein said materials are soaked repeatedly in said aqueous solution to dissolve gold and/or silver.

4. An apparatus for dissolving and recovering gold and/or silver from materials having gold and/or silver deposited thereon which comprise a dissolving chamber for loading said materials, said chamber being open to the air at upper end thereof, a sprinkler disposed at the top part of said chamber, and an electrolyzer connected with the bottom part of said chamber and provided with an anode and a cathode, an aqueous solution of cyanide being showered or sprayed to said materials to dissolve gold and/or silver into said aqueous solution in the presence of air, and then said aqueous solution containing dissolved gold and/or silver being introduced through the bottom part of said chamber to said electrolyzer to electrolyze and recover gold and/or silver in said aqueous solution on said cathode.

5. An apparatus claimed in claim 4 wherein said sprinkler is connected to the inner part of said electrolyzer by means of a conduit and a circulating pump is disposed at an appropriate position on said conduit thereby said aqueous solution in said electrolyzer being supplied to said sprinkler and reused.

6. An apparatus for dissolving and recovering gold and/or silver from materials having gold and/or silver deposited thereon which comprises an electrolyzer provided with an anode and cathode and filled with an aqueous solution of cyanide, and a porous rotating drum set up in said electrolyzer for loading said materials, said electrolyzer being filled with said aqueous solution so that only a part of said materials is soaked therein.

7. An apparatus for dissolving and recovering gold and/or silver from materials having gold and/or silver deposited thereon which comprises an electrolyzer provided with an anode and a cathode and filled with an aqueous solution of cyanide, and a basket disposed above the surface of said aqueous solution in said electrolyzer for loading said materials, said basket being so disposed that it travels vertically and repeatedly thereby said materials in said basket being soaked in said aqueous solution repeatedly.