JPS646255B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Traditionally, the recovery or refining of gold from jewelry-like Dore gold or gold alloy scrap required the work of highly specialized and skilled smelters. This is because of the complexity of the processes involved in the work and the dangers inherent in the use of the materials involved in such complex processes. Prior to the late 1970s, gold in its pure state was extracted from ore or solution by alkali sulfide, leaching, or some cyanide, which is extremely toxic and dangerous.

During the late 1970s, the price of gold soared and the use of aqua regia or alkaline cyanide solutions became popular for this purpose. As mentioned above, these prior art processes are extremely dangerous to humans because they involve toxic chemical agents. Those processes are also complex and slow.

In U.S. Pat. No. 4,182,671, an electrolytic gold and silver refining vessel and process is disclosed, in which a solution of apparently concentrated nitric acid and silver nitrate (a toxic substance) as the electrolyte to produce silver at the cathode and gold at the anode of the vessel. are using.

A principal object of the present invention is to improve upon the known prior art relating to gold recovery or refining in general, and in particular as exemplified by the aforementioned U.S. Pat. No. 4,182,671. This improvement is
It includes, among other things, the simplification of the process and the equipment that carries out the process. This process has been made much safer, faster, more economical and more versatile in the present invention, and the process and equipment implementing the invention are only used for refining gold and therefore other Not used for metal smelting. Regarding the device, many of the components required in the prior art were completely eliminated. As a result of this simplification, it is no longer necessary to use highly specialized and highly skilled technicians to monitor the process and equipment, and therefore highly skilled technicians are no longer required for these purposes. does not require. The most important feature of the present invention is the use of a mild nitric acid solution in the electrolytic cell to refine the gold to a purity of 99.9% so that the gold alloy forming the slab anode is free of platinum or other platinum metals.

If the gold alloy, Doerr gold or scrap to be refined contains more than 0.5% platinum, it may require the use of silver that is molten and subsequently recovered, and the use of copper or other non-ferrous metals or alloys of such metals. up to 4.8 carats (20% gold), and the resulting alloy is treated with an aqueous nitric acid solution (H ₂ O ₇ /100-60%) as an electrolyte.
HNO ₃ 40% + solution per EADS ethylene dinitrilotetraacetic acid diridium salt (HO ₂ CCH ₂ ) ₂ N (CH ₂ ) ₂ N
(CH ₂ CO ₂ NA) ₂ 2H ₂ O2g) is cast into a rectangular slab anode for suspension from an anode bar in an electrolytic cell using (CH 2 CO 2 NA) 2 2H 2 O2g). This solution is supplied from a reservoir and then placed in a stainless steel container cathode. A direct current with a current density of ² to 2.5 amps per square inch of anode surface was applied to the cell at a voltage of 3 to 5 volts. A cooling device in the form of a water bucket is used to prevent boiling of the electrolyte solution as a result of the heat generated by this current and voltage.

As a result of electrolysis, base metals such as copper are dissolved in an electrolytic solution. As this occurs, the gold in the slab anode settles as mud or slime to the bottom of the vessel cathode. The solution is then filtered from the slime which is boiled with concentrated nitric acid or plained with ammonia hydroxide. The gold mud is again filtered, washed thoroughly with distilled water, dried and then heated to a molten state and shaped into the desired shape. The resulting gold is 99.9% pure. If platinum or palladium were present in the gold alloy slab anode and a silver addition of the anode metal was made, these platinum metals would have been dissolved in the electrolyte solution. If iridium or some other platinum group metals were present, they would remain in the resulting gold mud or slime and require subsequent processing to remove. Conventionally, silver is recovered by introducing the metal into an electrolyte solution in a holding tank, where the copper is dissolved in NaOH (sodium hydroxide), replacing the silver in the nitrate, yielding the metallic form of silver. Other forms of precipitating silver such as It is a self-contained unit configured to make full use of.
This device consists of seven main components: a DC power supply 10 including a transformer 10a and a rectifier 10b, an electrolytic cell 11, a pollution control device 12, a circulation valve 1
It consists of a cooling device 13 including 3a, a control panel 14, a filtration device 15, and a drying container 16. These main components will be explained further.

As mentioned above, if it contains 0.5% or more of platinum,
This process requires silver addition of the gold alloy to be refined prior to placing the alloy slab anode into the electrolytic cell 11. This process also requires melting the pure gold powder that is ultimately produced after completing all other process steps.

Downsizing to 4.8 carats are accomplished by melting the scrap or precious metal alloy being refined and adding appropriate amounts of non-ferrous metals such as copper or other base metals or alloys. Silver is added when the alloy to be refined contains significant amounts of platinum (0.5% or more). This silver addition ensures uniform blending of gold with other metals.
It is carried out in a melting furnace capable of generating temperatures of approximately 1205°C (2200°C). If necessary, stirring with a graphite rod can be used to ensure this type of formulation. The compounded molten metal is then poured into an open-sided mold, producing approximately 170-200 grams of pure gold per hour (6
In embodiments of the invention that can recover up to 7 oz.
A multi-layer rectangular slab anode measuring 3-7/8 inches by 1/8 inches is formed. The invention is in no way limited to these quantities and dimensions as described above, so that these essential figures may vary widely in practice. Indeed, the flexibility of this process and apparatus compared to known prior art is one of the important features and advantages of the present invention.

In the present invention, it is not necessary to add silver if the gold alloy being refined is free of platinum metal or contains less than 0.5% platinum metal. To make the explanation easier to understand, approximately 835 grams (22 troy ounces) of 14 karat gold
is assumed to be refined. This gold has the following analysis by weight:

Gold = 12.8 troy ounces 14/24 = 12.8/22 Silver = 4.60 troy ounces 5/24 = 4.6/22 Copper = 4.6 troy ounces 5/24 = 4.6/22 If the gold alloy contains less than 0.5% platinum, then 4.8 carats; Alternatively, since silver additions up to 20% are required, a certain amount of copper is added to the melting furnace along with the gold alloy before melting and casting the slab anode to bring about a 1:4 ratio of the weight of existing gold to the weight of silver and copper. must be added.

If 12.8 troy ounces of gold are, as mentioned above,
If 9.2 troy ounces of silver and copper are also present, then 42 ounces of additional copper must be added to the melting furnace. The resulting alloy will have the following composition: That is, Gold = 12.8 troy ounces 4.8/24 = 12.8/63 Silver = 4.6 troy ounces Copper = 45.6 troy ounces 63.0 troy ounces The specific gravity of this metal when cast into a slab is: Gold 12.8 x 10.20 troy ounces / approximately 16.5 cm ³ (cubic 130.56 Silver 4.6 x 5.548 troy ounces / approx. 16.5 cm ³ (cubic inches) = 25.52 Copper 45.6 / 63.0 x 4.710 troy ounces / approx. 16.5 cm ³ (cubic inches) = 214.77 / 370.85 Specific gravity = 370 85 / 63.0 = 5.88 4.8 When approximately 1350 g (36 oz) of karat gold alloy is refined to the above specific gravity, the anodes of the electrolyzer will each be approximately 2.8 cm x 9.8 cm x 0.3 cm (1-1/2 inch x 3-cm).
7 slab sections measuring 7/8 inch x 1/8 inch)
Consisting of 7a. Once they are cast, the slab sections are ready for installation in an electrolytic cell 79, shown in detail in FIGS. 4 and 5.

The DC power supply 10 is derived from a 110 volt three phase 60 cycle semiconductor millicon rectifier 106 capable of delivering 250 amperes at 3 to 5 volts. With this capacity,
This DC power supply is capable of producing a current density of about ² to 2.5 amps per square inch, which is the range required to carry out this process. This current is supplied to the bath 11 via standard electrical connections (FIGS. 4 and 5).

The electrolytic cell 11, which is a key element of the invention, additionally has a removable clean steel anode rod 20 connected conventionally as at 21 to the positive terminal 18, and to the negative terminal 19. It consists of a removable stainless steel container cathode 22 connected in a conventional manner. The vessel 11 has the anode slab portion 17a within a vessel 22 or tank and is centered on a longitudinal axis therein. Preferably, the anode rod 20 is placed about 10-1/2 inches above the floor of the container cathode 22. The anode rod is electrically isolated from the container cathode 22 by conventional means.

The filtration device 15 consists of a 3/8 inch tube 24 inserted into the vessel cathode 22 and having a micron filter 24 at its lower end at the floor of the vessel cathode 22.

A dynamic and reversible pump 25 generates the necessary suction to filter liquid electrolyte and cleaning fluid from the gold slime that forms at the bottom of the vessel cathode 22. The filter is self-cleaning by backflow provided by a reversible pump.

Within the vessel 11 there is an outlet 26 for the fumes generated by the electrochemical reaction of the vessel cathode. A transparent polycarbonate lid 22 covers the vessel 11 and prevents leakage of fumes from the top of the vessel cathode 22, which is open.

The side wall of the vessel cathode is surrounded by a cooling device 13 consisting of a jacket 28 which allows cooling water to pass through during the gold recovery process by opening and closing valves 13a, one of which controls the cooling water. The other one of the valves allows the cooling water to enter and exit the cooling water.
This cooling device dissipates the heat released by the reaction and thus prevents boiling of the electrolyte solution. A heating element 29 fixed to the bottom wall of the container cathode 22 is
The last part of this process works only during the hot nitric acid bath and brings this acid to a boil. Alternatively, an ammonia hydroxide bath can be used without boiling instead of an acid bath.

A plurality of slab anode sections 17a forming a complete slab 17 of silver-doped gold alloy are inserted into titanium clamps 30 (FIG. 5) and these clamps are secured to anode rod 20 as by fastener means 31. inserted into. The electrolyte is now poured into the container cathode 22 and completely covers the slab anode 17. In the illustrated embodiment, there are seven approximately 2.8 cm x 9.8 cm x
It takes 6.5 cm of electrolyte to coat a 0.3 cm (1-1/2 inch x 3-7/8 inch x 1/8 inch) slab section.
The lid 27, which opens and closes with a hinge 32, is closed and a direct current is applied. For this reason, the blower of the pollution control device 2 (not shown) is automatically activated.

As a result of the bath electrochemical process, all the silver and copper in the slab anode 17 is dissolved into the electrolyte solution, so that the refined gold is transferred to the vessel cathode 2.
Fall to the bottom of 2. When the slab anode 17 disappears, no current flows and the precipitated slime-like gold remains at the bottom of the vessel cathode. At this point, filtering device 15 is activated to filter the electrolyte from the gold in the vessel cathode. A 5 micron filter 24 prevents the passage of gold through the filter. Once the used electrolyte has leaked out, the leakage device is shut off and sufficiently concentrated nitric acid or ammonia hydroxide is poured from the overhead reservoir 33 of this device via piping 34 into the container cathode; Coat the gold mud contained in the bottom of the cathode. Usually this requires about 1/2 nitric acid.
The heating element 29 is turned on and boils the nitric acid for about 5 minutes. If ammonia hydroxide is used, no boiling is required as described above. When this process is complete, the filtration device 15 is activated again to filter the spent nitric acid or ammonia hydroxide bath. The filtration device is shut off so that distilled water from the overhead storage tank 33 is drained into a container to wash the gold mud in the filtration device. This wash water is then filtered from the vessel cathode and a second wash of the gold mud with distilled water is carried out followed by filtration of the water from the vessel cathode 22.

The container cathode 22, held by a removable fastener 35, has now been removed from the electrolytic cell 11 and placed in the drying compartment 16 of the apparatus, as can be seen most clearly in FIG. It will be destroyed. Drying continues in the compartment 16 until the water content of the gold mud is low enough to dry the dried gold powder from the container cathode. This operation typically requires 5 to 10 minutes and is followed by closing the lid 36 of the drying compartment. is opened and the container cathode is removed and thus inverted to deposit pure gold powder into the collection container. From this vessel, the gold powder can be placed in the same melting furnace used for silver addition, where the refined gold is brought back to a molten state and thus can be poured into suitable molds.

The pollution control system continuously draws the fumes from the electrolytic cell through water and a caustic stripping solution past the cell outlet 26 to neutralize the NO and NO ₂ fumes. The fumes are drawn by a blower 37a from the outlet 26 to a stainless steel tank 37 containing stripping solution, as shown in FIG. When this solution becomes saturated, it is replaced with fresh solution.

The electrolyte, nitric acid and distilled water removed from the vessel cathode 22 have an amount of silver in the form of a silver nitrate solution at different concentrations, which can be advantageously recovered due to its current market value of $20 per troy ounce. Recovery is carried out by introducing metallic copper or NaOH into the solution in the electrolyte holding tank at the bottom of vessel 11 (FIGS. 2 and 3). Copper replaces silver nitrate, yielding the metallic form of silver. The silver is filtered from the remainder of the solution, washed and dried prior to melting.

The control panel 14 of this device is configured such that whenever the DC power source 10 is activated, the pollution control device 12 is also activated. Also, when the heating element 29 is energized, the pollution control device 12 is automatically turned on. Heating element 29 and DC power supply 10 cannot be turned on at the same time. These electrical control devices are state-of-the-art control devices and therefore do not need to be described in detail.

The reaction occurring in vessel 11 can be described as follows. The nitric acid in the electrolyte and the electrical current passed through the bath during this process oxidize the silver and base metals of the slab anode 17. The following ionic reaction occurs, namely AgAg ⁺ +e ^- CuCu ²⁺ +2e ^- ZnZn ²⁺ +2e ^- MM (ions) + electrons for metal M. The presence of nitric acid in the electrolyte bath causes an electromotive force to act on the slab anode. The anode and cathode receive it. The metal ions formed at the anode migrate to the cathode and discharge their negative charges (electrons), thus becoming copper (Cu), silver (Ag) or zinc (Zn) metal atoms. During this reaction,
The anode metal is turned into an ionized solution. This reaction continues until all the metal within the anode has been converted and the anode has dissolved. Gold, which resists oxidation or loss of electrons under the conditions present, falls to the cathode as slime or mud. In other words, these metal ions move relative to the cathode 22 under the action of the electromotive force applied to the bath and are thus precipitated at the cathode in the ionic reaction described below. That is, Ag+ +e- -Ag Cu+ ² +2e- -Cu Zn+ ² +2e- -Zn Once in contact with the cathode, these metal particles
Reacts with nitric acid to produce multiple nitrates, Ag (NO ₃ ), Cu
(NO ₃ ) ₂ , Zn(NO ₃ ) ₂ , and these nitrates are easily soluble in the water present in the electrolyte. The gold of the slab anode 17 is never oxidized due to its resistance to oxidation. As the anode dissolves in the electrolytic solution, the gold is precipitated as dirt or slime that falls to the floor of the cathode 22, and other metals remain in solution, as described above. The above-mentioned EADS in solution acts as a detergent or emulsifier and prevents refined gold particles falling from the slab anode from becoming suspended in the electrolyte solution. This EADS also prevents polarization that would otherwise prevent this process. Occasionally, the gold of the slab anode may form a screen that prevents the free movement of ions, but because of the voltage applied to bath 11, electrically positive ions can break through this screen.
Therefore, it moves to the cathode 22. When this gold shield is penetrated by ions, this shield becomes
It collapses and falls to the bottom of the container cathode 22 and the process continues until completion. Since the gold is never melted in the process of the present invention, potential loss of the fume gold is prevented. Conventional processing methods result in boiling of the aqua regia that dissolves the gold, resulting in the above losses. The process prevents gold loss caused by failure to precipitate gold from the electrolyte and spillage and/or breakage of glass or ceramic containers used in other processes. .

The present invention, in which the gold is not in solution but is added with silver, is not affected by the amount of silver present in the alloy, and the electrolytic process is dependent on the relative amounts of silver and gold present in the alloy being refined. No need to change fluid. Furthermore, the voltage and current density are less dangerous than in the known prior art. Further, as long as the electrolytic solution 5 is used to process 1 kg of an alloy containing 20% gold, there is no need to replenish the electrolytic solution.

Another important attribute of the present invention is the adaptability of the site to large or small amounts of gold refining or recovery from the alloy. Since there are many variables involved,
Most other processes are not suitable for recovering relatively small amounts of gold from jewelry and the like. While the hot nitric acid method is flexible in this respect, it is extremely slow and labor intensive, thus making it extremely expensive.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a gold recovery device according to the present invention;
Fig. 2 is a front view of the device shown in Fig. 1, Fig. 3 is a side view of the above device, Fig. 4 is an enlarged front view of an electrolytic cell that constitutes a part of this device, and Fig. 5 is an electrolysis cell. It is a side view of a tank. 10... DC power supply, 11... Electrolytic cell, 12... Pollution control device, 13... Cooling device, 14... Control panel, 1
5...Leakage device, 16...Drying container (chamber).

Claims (1)

[Claims] 1. An electrolytic cell having an alloy body containing gold as an anode and a container containing an electrolyte and nitric acid and collecting gold from the anode as a cathode, an electrical connection between an anode terminal and a cathode terminal of the electrolytic cell. a direct current connected to and supplying power, a pollution control control system connected to remove and neutralize toxic fumes from the electrolytic cell during operation of the electrolytic cell, an electrolyte cooling system for the electrolytic cell, and an electrolyte cooling system in the vessel cathode. A gold recovery device comprising an electrolyte filtration device for an electrolytic cell including a filter, a control device electrically connected to a DC power source and a pollution control control device. 2. The gold recovery apparatus according to claim 1, wherein the electric heating element provided on the bottom wall of the container cathode is electrically coupled to the control means. 3. A self-contained unit having a body part containing said tank, said pollution control device and said filtration device and control means, and forming an overhead storage means for electrolyte on said body. The gold recovery device according to paragraph 1. 4. The passing means comprises an electrolyte pump and holding tank means, said passing means being of a type which allows liquid electrolyte to pass through while blocking the passage of refined gold particles which are precipitated at the bottom of the vessel cathode. A gold recovery device according to claim 1, characterized in that: 5. The gold recovery device according to claim 4, wherein the filter comprises a 5 micron filter. 6. Claims characterized in that the fluid cooling device comprises a jacket surrounding the vessel cathode and having a cooling water inlet and an outlet, and a plurality of valves external to the bath for controlling the circulation of cooling water in the jacket. The gold recovery device according to paragraph 1. 7. A drying chamber located laterally in said body portion of said vessel and suitable to receive the vessel cathode in its entirety therein for drying the refined metal of the vessel cathode and draining said vessel after removal of said vessel cathode from said vessel. A gold recovery device according to claim 3, characterized in that it comprises means. 8. A gold recovery device according to claim 1, characterized in that the tank has a transparent lid placed on top to trap fumes. 9. The gold recovery device according to claim 1, wherein the passing means is a reversible means and is therefore self-purifying.