Sciencemadness Discussion Board

Gold Via Electrolosis

Ramiel - 13-4-2003 at 21:27

I've been mulling over this mad idea of mine for a little while; how is it best to use an electrolytic cell to get pure gold from:
a) Carrat gold (jewlery etc)
b) Solution

The major stumbling block is that i have basic (year 12 chemistry) knowledge of electrochemisty, hence I don't understand the dynamics of an electrochemical system. What I mean by that is I don't know jack schitt (do you?).

If i were to oxidize a metal chunk containing by weight 18/24 gold, 3/24 copper, 3/24 silver (this should sound familiar!) in a solution of say ammonium nitrate, what might happen? The metal ions are clearly going to be of different valencies, and I don't know if gold even forms a nitrate salt (such is the quality of my education!).

b) seems to be a simple matter of reducing the copper, silver and gold seperately using specific voltages.

any comments or suggestions are most welcome.

Marvin - 14-4-2003 at 09:14

Gold does form salts, like the nitrate, chloride, but to make gold chloride you normally need aqua regia.

To process gold electrolytically, you normally need cyanides which are best avoided under normnal circumstances.

If you have equipment that will melt the alloy, mixing it with a base metal to produce less than 1/4 total gold content and dropping the result into nitric acid will generally produce a brown powder that is pretty pure gold.

If you wanted to try the full method, it starts with cupelation, which involves adding lead to the alloy of gold, silver and base metals, the easily oxidisable lead takes away most of the base impurities in the alloy leaving an alloy of gold and silver.

In more recent times, since the discovery of nitric acid, it was found that adding 3 parts of silver to the resultant alloy (called inquartation) to make sure the gold content was less than 1 in 4, and then dissolving it in nitric acid (called parting) would leave all the gold as a brown powder, and the silver could be recovered from the solution in nitric acid.

If you lack a welder of any sort, then simply dissolving 9ct jewelry in nitric acid should leave the gold, and silver can be precipitated out of solution as the chloride. Its worth saying that the jewelry is probably significantly more expensive than its gold content, and it might be worth asking a local jeweler to sell you scrap gold bits for chemistry testing.

Chris Owen - 20-10-2003 at 19:06

It's been a long since this thread died but I'm new and feel compelled to put in my two cents.

Ramiel, if you're still around, I would first ask why you are doing this.

If you hope to make money doing this, you may be taking the wrong approach. For the small refiner, the old standard aqua regia method is still the state of the art. If you're a real big guy, you can afford a Miller Chlorine/Wohlwill Cell setup. The aqua regia (AR) process, with great care. will produce gold of 99.99% consistent purity, which is required in order to sell at, or near, the market price. If you can't purify to four nines, you may as well sell it as is.

However, if you're just playing around, you've picked an interesting subject. I, too, have dreamed of a nice, clean electrolytic system to replace the smelly, corrosive, fumey AR. The problem is purity. Everything I've tried required an AR step at the end, anyway.

The biggest bottleneck in the AR system is dissolving the gold (some would say filtering), due to the impervious layer of silver chloride that forms on the surfaces, thus hindering the penetration of the acids. It may take 12, or more, hours to dissolve karat gold.

The answer may be to first break it down to powder and upgrade it to about 99% in an electrolytic cell. Then, go after it with AR. The gold powder will literally dissolve in minutes. There are several ways of doing this electrolytically:
1 - In 1940, Western Electric was issued a Patent concerning the electrolytic dissolving of gold, silver, and palladium. They mainly had plated electronic parts in mind. The electrolyte is concentrated sulfuric acid with about 5% water carefully added (If you have someone constantly stir while you slowly dribble in the water, you can get away with this, safely). The sulfuric is usually put into a mild steel tank and the tank, itself, is made the cathode (-). The work is hung in the center and is made the anode. It's very simple. The gold breaks down and settles, as a powder, to the bottom and then is carefully collected, rinsed, and put into AR. Nothing else but Ni or Co will dissolve. These are both poisons and will make the solution stop working. Without Ni or Co, the soln. can be used over and over. It works best for things like electronic pins, which can be tumbled and electrolysed in a plating barrel. Besides the need for electrical contact to each piece, the biggest problem is it's failure to dissolve alloys (as in jewelry scrap). There are, however, additives that can be used to solve these problems. Karat gold could be melted into to a bar and broken down quickly into powder.
2 - A modification of Marvin's inquartation method. Whereas, after inquarting he used nitric acid to leach the other metals away from the gold, you could also leach with an electrolytic nitrate soln. You could bag the impure bar with a poly fabric and collect the gold powder inside the bag and put bag and all in AR. The Cu and Ag will plate poorly at the cathode and could cause a mess.
3 - Cyanide is wonderful when used electrolytically. I miss it. It will effeciently dissolve and plate out a large number of metals, i.e. Au, Ag, Cu, Zn, all of which are in jewelry gold. Cyanide works too good. If you hung a karat gold bar in a cyanide matrix and turned on the juice, it would both dissolve and plate out all of the metals. You'd be back where you started from.
4 - You could use a halide (Cl, Br, I) soln. as the electrolyte. This is the basis of the Wohlwill Cell. Slightly off-purity gold (98%, or so), in bar form, is bagged and suspended in a soln. containing lots of gold chloride and a little bit of HCl. The impure gold is the anode and the cathode is a rectangular piece of four nines gold, rolled thin. All bussing is done with pure silver rods. Nearing 100% efficiency, the gold, Cu, Ni, Pd, and Zn dissolve, but only the gold plates out on the pure gold cathode, that is, until the impurities reach certain levels. This is controlled by periodically removing portions of the solution and replacing it with gold chloride.

Ramiel: Things in your post.
1 - Solutions. 4 common types: bombing, plating, drag-out, and commercial stripping solutions. All contain cyanide in some form and all but the stripper can be plated out, usually with Stainless steel electrodes. You can also "zinc out" the gold - won't work on the stripper. This easy method consists of sprinkling zinc dust on the top of the soln. The zinc dissolves and drops the gold., which settles on the bottom. The soln. is syphoned off and the gold powder is collected, rinsed well, acid treated, and purified using AR.
2 - You're right, gold doesn't form a nitrate and, therefore, doesn't dissolve. The alloy you describe, 18 Kt gold, has too high a gold content to allow the soln. to penetrate and get after the other metals. The gold forms a solid barrier. To attack these metals with nitric acid or an electrolytic nitrate, you must first reduce the gold content to at least 40%. This is done by melting extra Cu or Ag with the bar.
3 - Separating by specific votages (or, current densities) is interesting. I've wanted to try something like this: place the anode and cathode in a tank in this manner: ( . / ) , where the period is the anode, the slash is the cathode, and the parentheses is the tank. Notice that the distance from anode to each point on he cathode varies, progressively. Therefore, the current density along the cathode also varies. The current applied to the top of the slash is less than that at the bottom. Since some different metals will deposit at different current densities, this may afford some separation on the cathode.

Titan - 30-3-2005 at 07:04

Gold-salt water mixture static -coating mixture to laminating for instance metal sufaces.

18/12 gold , 18/12 silver ,13/54 copper salt solution ;) Carrat copper (jewlery sfund sterling)

Tsjerk - 12-4-2006 at 06:23

Quote:
Originally posted by Chris Owen
It's been a long since this thread died but I'm new and feel compelled to put in my two cents.

Ramiel, if you're still around, I would first ask why you are doing this.

If you hope to make money doing this, you may be taking the wrong approach. For the small refiner, the old standard aqua regia method is still the state of the art. If you're a real big guy, you can afford a Miller Chlorine/Wohlwill Cell setup. The aqua regia (AR) process, with great care. will produce gold of 99.99% consistent purity, which is required in order to sell at, or near, the market price. If you can't purify to four nines, you may as well sell it as is.

However, if you're just playing around, you've picked an interesting subject. I, too, have dreamed of a nice, clean electrolytic system to replace the smelly, corrosive, fumey AR. The problem is purity. Everything I've tried required an AR step at the end, anyway.

The biggest bottleneck in the AR system is dissolving the gold (some would say filtering), due to the impervious layer of silver chloride that forms on the surfaces, thus hindering the penetration of the acids. It may take 12, or more, hours to dissolve karat gold.

The answer may be to first break it down to powder and upgrade it to about 99% in an electrolytic cell. Then, go after it with AR. The gold powder will literally dissolve in minutes. There are several ways of doing this electrolytically:
1 - In 1940, Western Electric was issued a Patent concerning the electrolytic dissolving of gold, silver, and palladium. They mainly had plated electronic parts in mind. The electrolyte is concentrated sulfuric acid with about 5% water carefully added (If you have someone constantly stir while you slowly dribble in the water, you can get away with this, safely). The sulfuric is usually put into a mild steel tank and the tank, itself, is made the cathode (-). The work is hung in the center and is made the anode. It's very simple. The gold breaks down and settles, as a powder, to the bottom and then is carefully collected, rinsed, and put into AR. Nothing else but Ni or Co will dissolve. These are both poisons and will make the solution stop working. Without Ni or Co, the soln. can be used over and over. It works best for things like electronic pins, which can be tumbled and electrolysed in a plating barrel. Besides the need for electrical contact to each piece, the biggest problem is it's failure to dissolve alloys (as in jewelry scrap). There are, however, additives that can be used to solve these problems. Karat gold could be melted into to a bar and broken down quickly into powder.
2 - A modification of Marvin's inquartation method. Whereas, after inquarting he used nitric acid to leach the other metals away from the gold, you could also leach with an electrolytic nitrate soln. You could bag the impure bar with a poly fabric and collect the gold powder inside the bag and put bag and all in AR. The Cu and Ag will plate poorly at the cathode and could cause a mess.
3 - Cyanide is wonderful when used electrolytically. I miss it. It will effeciently dissolve and plate out a large number of metals, i.e. Au, Ag, Cu, Zn, all of which are in jewelry gold. Cyanide works too good. If you hung a karat gold bar in a cyanide matrix and turned on the juice, it would both dissolve and plate out all of the metals. You'd be back where you started from.
4 - You could use a halide (Cl, Br, I) soln. as the electrolyte. This is the basis of the Wohlwill Cell. Slightly off-purity gold (98%, or so), in bar form, is bagged and suspended in a soln. containing lots of gold chloride and a little bit of HCl. The impure gold is the anode and the cathode is a rectangular piece of four nines gold, rolled thin. All bussing is done with pure silver rods. Nearing 100% efficiency, the gold, Cu, Ni, Pd, and Zn dissolve, but only the gold plates out on the pure gold cathode, that is, until the impurities reach certain levels. This is controlled by periodically removing portions of the solution and replacing it with gold chloride.

Ramiel: Things in your post.
1 - Solutions. 4 common types: bombing, plating, drag-out, and commercial stripping solutions. All contain cyanide in some form and all but the stripper can be plated out, usually with Stainless steel electrodes. You can also "zinc out" the gold - won't work on the stripper. This easy method consists of sprinkling zinc dust on the top of the soln. The zinc dissolves and drops the gold., which settles on the bottom. The soln. is syphoned off and the gold powder is collected, rinsed well, acid treated, and purified using AR.
2 - You're right, gold doesn't form a nitrate and, therefore, doesn't dissolve. The alloy you describe, 18 Kt gold, has too high a gold content to allow the soln. to penetrate and get after the other metals. The gold forms a solid barrier. To attack these metals with nitric acid or an electrolytic nitrate, you must first reduce the gold content to at least 40%. This is done by melting extra Cu or Ag with the bar.
3 - Separating by specific votages (or, current densities) is interesting. I've wanted to try something like this: place the anode and cathode in a tank in this manner: ( . / ) , where the period is the anode, the slash is the cathode, and the parentheses is the tank. Notice that the distance from anode to each point on he cathode varies, progressively. Therefore, the current density along the cathode also varies. The current applied to the top of the slash is less than that at the bottom. Since some different metals will deposit at different current densities, this may afford some separation on the cathode.

rot - 12-4-2006 at 10:41

It is actually very simple. Treat your alloy with nitric acid. Nitric acid dissolves Copper and silver readily but not gold!. If you make a mixture of Nitric acid and Hydrochloric acid you make aqua regia, the only reagent capable of dissolving gold and platina, IIRC.

Fleaker - 12-4-2006 at 14:39

Aqua regia (NOCl + other NOx) is not the only reagent capable of dissolving gold or platinum, both of which can be extracted with hot halogen gases. However, before you attempt to dissolve gold jewelry scraps, you should, as mentioned above, inquartate (copper or silver can be used) your gold and dilute it down to 6 karat or so, then it can either be dissolved in nitric acid or electrochemically parted in the Wohlwill cell. The Miller process mentioned by Chris Owen is very effective as an upgrading step. The gold, however, should be of 90% purity to make it worthwhile, but more or less, one melts the gold alloy and blows chlorine gas through it, leaving pure gold underneath a chloride gooey crust. That can then go to the refining cell, which, contrary to Chris Owen's belief, is used to achieve gold of very high purity (typically 4 to 5 N).
The use of sulfuric acid in a cell is strictly for stripping gold electroplate, not for achieving an effective parting.

I will try and post pictures of the different processes if I have time.