Any recommendations of recovery process for large item?

[goldsilverpro]

Could a wand/mat be used in reverse electroplating? Seems like it would be tough to get the cathode and electrolyte(sulfuric) to conduct well in that instance.

A plating shop I once worked in brush plated gold using the same gold solution that we rack and barrel plated in. We just put some solution in a small beaker, dunked the brush in the solution, and rubbed it on the part. The wand was a carbon rod with a wad of glass wool held on one end with a couple of rubber bands. Real hi-tech. The other end of the rod had the positive lead clamped to it. The negative lead was clamped to the part. Same exact principle of those pen platers used to plate auto emblems.

A brush de-plater using cyanide or sulfuric would work the same way except the polarity would be reversed. The glass wool will hold a lot of solution and keep it conductive. With sulfuric, any small black particles will be gold. Everything, including the beaker of solution, should be in the same plastic tray so you lose nothing.

 

[kurtak]

I should probably start another thread but i also have some contacts out of a 400A contactor. I hear there is cadmium and/or tungsten in them so they cant just be melted down. Is it worth it to refine just these pieces if i do not intend to refine any other silver? There is ~6 oz of material there (pic attached) as is.

Trilo68

Yes those are the tungsten/silver type points - they run between 30 - 40% silver - you have to "boil" them in nitric to leach the silver out of the tungsten - you know they are done leaching when you break them in half & they are black all the way to the center (if there is a whitish silver color in the center they are not done leaching)

the cadmium is in the solder - it will be in your waste after cementing you silver back out of solution

Kurt

 

[John TG]

Trilo
Just wondering if you finished your process or not and if so how much gold did you get?

 

[patnor1011]

I would not process those cylinders. I fell in love with them the second I came here
I can see them being turned to some futuristic piece of furniture, man I would love to have few of them. :lol:

 

[Anonymous]

Patnor is right. They are probably worth far more as furniture.

 

[Harold_V]

Yes those are the tungsten/silver type points - they run between 30 - 40% silver - you have to "boil" them in nitric to leach the silver out of the tungsten - you know they are done leaching when you break them in half & they are black all the way to the center (if there is a whitish silver color in the center they are not done leaching)

I recovered hundreds, if not thousands, of ounces from contacts in my years in the lab. One thing I found to be consistent was that the tungsten/silver contacts have a waffle pattern on the rear, where they are soldered to the buss. If is obvious once the contact has been removed, even if it is still covered with solder.

Harold

 

[kurtak]

Yes those are the tungsten/silver type points - they run between 30 - 40% silver - you have to "boil" them in nitric to leach the silver out of the tungsten - you know they are done leaching when you break them in half & they are black all the way to the center (if there is a whitish silver color in the center they are not done leaching)

I recovered hundreds, if not thousands, of ounces from contacts in my years in the lab. One thing I found to be consistent was that the tungsten/silver contacts have a waffle pattern on the rear, where they are soldered to the buss. If is obvious once the contact has been removed, even if it is still covered with solder.

Harold

Correct (as underlined above)

Contact points are my main source of silver - about 70 - 80% of my silver comes from contacts (I am talking refined silver by the pound - 3 - 4 two pound bars per batch)

What I have noticed is that besides the waffle pattern on the back is that when they are odd shaped (like these are) you can count on them being W/Ag --- I have never had an odd shaped point that was other then W/Ag

On the other hand - when they are round - as a rule they will not be W/Ag - although there is one exception to this rule & that is the "small" round ones that come out of house hold circuit breakers

Square &/or rectangular points could be ether W/Ag or not - in which case the waffle pattern on the back is the dead give away to the W/Ag

Kurt

 

[Trilo68]

I have not processed the cylinders yet as i am trying to figure out the best way to do it. As for use as furniture or something else, they should still be usable after the gold is gone. Personally, i don't find the color of gold to be aesthetically pleasing. I would rater have them in the stainless or brushed nickel finish if they were going to be art/furniture or some other focal point. All of the jewelry i have bought for my wife has been either white gold, platinum, or sterling. My wedding band is titanium/tungsten carbide. But i digress.

So far the HCL+H2O2+bubbler is flaking the gold off of one of the brackets. The solution is very dark green, the exposed SS is black, and there a some black bits in the solution, but for the most part is clear(aside from the gold floating around). This is probably going to take a long time as they have been in there 96+ hours and there is probably 2/3 still unaffected, and don't think it is feasible for these parts.

The HCL + bleach didn't go like i expected. I used 300mL HCL and 50mL bleach for one bracket(approx 5" x 1/2" x 1"). At first the solution rapidly turned gold, which is good. It then started to turn green and kept getting darker. From what i have seen, this usually dissolves the gold with 15-30 minutes. After about 30 min, it didnt look like much gold had been removed, so i added 25mL more bleach. It bubbled but thats about it. I left it in overnight and still had most of the gold on it. Some pieces flaked off and were in the bottom of the container with a lot of black "sand". Some of the gold looks rainbowed, like what happens to SS exhaust pipes. Thats where i left it.

I then made a "wand" from some thick copper and some fiberblass mat wrapped around it. Like suggested, i used that to soak up some sulfuric and started deplating. That took the gold off, turned the solution and the mat black, and made some heat. There was more heat than i was expecting. I noticed that when places on a spot that had not been deplated, the current would go up to about 6A, then drop quickly to around 1-2A when the gold was gone. Now i have to learn how to pull the gold from the sulfuric. I want to make sure i know how this is going to turn out before attempting the large parts.

As for the silver, i dont see the waffle pattern. However since they are odd shaped, they are W/Ag, correct? Pic attached with 3 one way and 3 the other.

Thanks again everyone.

 

[goldsilverpro]

Small black particles often have PM values.

 

[samuel-a]

I've always wondered if an aqua regia prepared with mostly concentrated nitric and just a tiny bit of hydrochloric acid would dissolve the gold and passivate the underlying nickel surface.
The passivated surface (oxide film) should protect the surface from cementing the gold back to the nickel metal.

This is an experiment I've wanted to do but hasn't done yet. If it's a practical way to treat scrap like this remains to be seen.

Göran

Already done it a jillion times. 50% nitric, 3% HCl, remainder tap water, all by volume. Won't touch the stainless. The problem is getting rid of all that nitric so the gold will drop with a sulfite. Sulfamic acid will kill the nitric but it takes a lot of it. Dilute hydrazine hydrate or solid hydrazine sulfate will drop the gold without eliminating the nitric but it's more dangerous. Also, I believe hydrazine is a carcinogen. Works great, though.

Chris,

How about Al as the base material instead of SS?
The plating is as follows: Al --> Ni 50µin --> Au 20µin

 

[goldsilverpro]

I've always wondered if an aqua regia prepared with mostly concentrated nitric and just a tiny bit of hydrochloric acid would dissolve the gold and passivate the underlying nickel surface.
The passivated surface (oxide film) should protect the surface from cementing the gold back to the nickel metal.

This is an experiment I've wanted to do but hasn't done yet. If it's a practical way to treat scrap like this remains to be seen.

Göran

Already done it a jillion times. 50% nitric, 3% HCl, remainder tap water, all by volume. Won't touch the stainless. The problem is getting rid of all that nitric so the gold will drop with a sulfite. Sulfamic acid will kill the nitric but it takes a lot of it. Dilute hydrazine hydrate or solid hydrazine sulfate will drop the gold without eliminating the nitric but it's more dangerous. Also, I believe hydrazine is a carcinogen. Works great, though.

Chris,

How about Al as the base material instead of SS?
The plating is as follows: Al --> Ni 50µin --> Au 20µin

I've never tried stripping Au from Al with this solution, Sam. Worth an experiment. I usually used the sulfuric stripper (reverse plating) for Au on Al.

 

[samuel-a]

Thanks Chris,

I guess an experiment is scheduled. :mrgreen:
The geometry and dimensions of the items makes the stripping cell a bit of a pain. But if all else fails, it would be the way to go.

 

[goldsilverpro]

Another possibility for Au on Al would be a nitric leach to undermine the gold by dissolving the Ni underlayer. I don't think it's possible to electroplate Au directly on Al. At least, I've never seen it done or heard of it being done. Usually, a thin layer of Zn is laid down, then a layer of Ni or Cu, and finally, the Au layer. With Au, the underlayer is most likely Ni because of the migration problems with Cu.

 

[Lou]

To the OP,

What about just cutting these so they unroll in rectangular sheets, making manageable strips, and then just wet sanding them down in a bucket of water?


Lou

 

[g_axelsson]

Another possibility for Au on Al would be a nitric leach to undermine the gold by dissolving the Ni underlayer. I don't think it's possible to electroplate Au directly on Al. At least, I've never seen it done or heard of it being done. Usually, a thin layer of Zn is laid down, then a layer of Ni or Cu, and finally, the Au layer. With Au, the underlayer is most likely Ni because of the migration problems with Cu.

Just as you say, you can't plate gold directly on aluminum and needs one or several metal layers between the Al and Au, but you can sputter coat or evaporate gold directly onto aluminum without any major problems. I have encountered both methods in the heater of early laser printer / copiers.

Gold directly on Al : http://goldrefiningforum.com/phpBB3/viewtopic.php?f=49&t=19177&start=20#p194541
Gold on Al with intermediate layers : http://goldrefiningforum.com/phpBB3/viewtopic.php?f=49&t=19177#p194209

Göran

 

[Palladium]

I have an angle grinder with a diamond wheel and a vacuum attachment that would be the cats meow.

 

[Lou]

I don't even know if that's necessary...hell even steel wool will do the trick.

I just figure that's probably much easier and just as fast.

 

[samuel-a]

Another possibility for Au on Al would be a nitric leach to undermine the gold by dissolving the Ni underlayer. I don't think it's possible to electroplate Au directly on Al. At least, I've never seen it done or heard of it being done. Usually, a thin layer of Zn is laid down, then a layer of Ni or Cu, and finally, the Au layer. With Au, the underlayer is most likely Ni because of the migration problems with Cu.

Thanks Chris,
I have used Nitric quite successfully in terms of stripping the gold foils, but it was too labor intensive to wash each and every piece (i have few hundreds IR reflectors to process).
As far a i could learn, a bright Ni coat is applied and mirror finish Au is deposited in a multi-step process involving sputtering and electrolysis (and perhaps some annealing).
I know Epner and Heraeus are quite big on that...

Another possibility for Au on Al would be a nitric leach to undermine the gold by dissolving the Ni underlayer. I don't think it's possible to electroplate Au directly on Al. At least, I've never seen it done or heard of it being done. Usually, a thin layer of Zn is laid down, then a layer of Ni or Cu, and finally, the Au layer. With Au, the underlayer is most likely Ni because of the migration problems with Cu.

Just as you say, you can't plate gold directly on aluminum and needs one or several metal layers between the Al and Au, but you can sputter coat or evaporate gold directly onto aluminum without any major problems. I have encountered both methods in the heater of early laser printer / copiers.

Gold directly on Al : http://goldrefiningforum.com/phpBB3/viewtopic.php?f=49&t=19177&start=20#p194541
Gold on Al with intermediate layers : http://goldrefiningforum.com/phpBB3/viewtopic.php?f=49&t=19177#p194209

Göran

Right on Goran. I remember this post.
I think this would definitely be the way to go as i have so many units to process and the thin plate just bearly makes it worth my while.
Thanks.

 

[samuel-a]

Well... the nitric based AR indeed leave the Al alone. However, Ni is taken up as well with the gold, which in it self isn't a big issue but the reaction gets quite vigorous as the solution heats up.