# Any recommendations of recovery process for large item?



## Trilo68 (Jan 31, 2015)

So i'm a noob to the forum and also to metal recovery and refining. I have been researching into the various methods to recover gold from some items i have. I have not been able to determine the best way to go about it, which is why i would like the opinions of those who have been there before.

On to the items:

The parts are 36" diameter by 21" tall cylinders. The cylinders are made from two sheets of 10ga 304SS with cooling water paths formed in between the two sheets, The inside diameter of the assembly is then nickel plated for a bright finish and then gold plated MIL-G-45204 Type III. I do not know the thickness rating. 

My problem is that cutting them up would be a chore. 10ga 304SS is fairly tough, and each cut would be through two pieces. On the other hand, a bath to handle the entire assembly would be quite large and require a lot of chemical.

One idea i had was a smaller bath with the cylinder on its side which could be rotated as the gold is removed. Again i am not sure how feasible that is so i would like the opinions of those with experience recovering gold.

Thanks in advance.


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## necromancer (Jan 31, 2015)

Trilo68 said:


> One idea i had was a smaller bath with the cylinder on its side which could be rotated as the gold is removed. Again i am not sure how feasible that is so i would like the opinions of those with experience recovering gold.
> 
> Thanks in advance.



this idea will work, try searching for "sulfuric cell" and "reverse electroplating"

you should be able to build one without having to spend to much money.

please make sure you are familiar with all the safety procedures before starting this venture.


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## necromancer (Jan 31, 2015)

forgot this link, you can find plating info here

http://advancedplatingtech.com/gold-plating-services/


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## 4metals (Jan 31, 2015)

Way back when, I had to strip some electroplated cylinders which were even bigger than what you mention, we were stripping a heavy silver electrodeposit and chose an immersion type strip. So if you choose to strip the gold with an immersion stripper it will work for you. 

The strip was in a small heated tank, a 5 gallon bucket will work for you, and the cylinder was laid on its side with a slight downward angle so any liquid in the cylinder would drain by gravity back to the tank. We did lots of these so a fixture was made to hold the cylinder at the right angle so all we had to do was rotate the cylinder manually. 

A pump pumped the strip into the end furthest from the tank and a spray head allowed the strip to cover a wider path in its journey back to the bucket. We rotated the cylinder a few degrees when it was apparent the stripping was complete until the total inner diameter had been stripped. I remember we were able to strip 2 or 3 of these a day this way. 

This method was effective and the flow of fresh solution through the tube kept the stripping rate up and we did not need to add a large tank for the process. If I remember correctly these tubes were over 3 feet in diameter and 10 feet long, but the same technique should work. We did not need heat for silver but for gold you may need a little immersion heater to warm up the strip.


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## necromancer (Jan 31, 2015)

Trilo68 said:


> The cylinders are made from two sheets of 10ga 304SS with cooling water paths formed in between the two sheets



i think this is the problem in question. maybe Trilo68 can upload some pictures ??


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## Trilo68 (Jan 31, 2015)

Image attached.

If one were to use a recirculating system, would you go straight to HCL + NaClO to dissolve the gold from the part? Would this solution dissolve the nickel or attack the SS in the process?

Same for reverse electroplating. How diligent do you need to be as to not start removing the nickel layer as well?

FWIW, i have the appropriate PPE and supplied air full face respirator; however this will be done outside or in an open ended barn so there will be adequate ventilation. I also have both training from previous work using acids and caustics (mainly Hydroflouric and Nitric) for etching and passivating SS, as well as hazmat response training. So yes, the appropriate precautions and protection will be followed.

Thanks for your responses.


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## solar_plasma (Jan 31, 2015)

Whatever way you choose, you could cut a little piece out and try with this. I doubt, that HCl/chlorox would affect the steel. The nickel will get dissolved, but it would not make problems, other than that the waste has to be treated accordingly.

If it where me, I would use a flat tub, about as long and broad as the cylinder is high. Then I would roll the cylinder through my chosen leach, each time the gold has dissolved, a little further. This would give me a more concentrated gold solution and less waste.


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## Trilo68 (Jan 31, 2015)

solar_plasma said:


> If it where me, I would use a flat tub, about as long and broad as the cylinder is high. Then I would roll the cylinder through my chosen leach, each time the gold has dissolved, a little further. This would give me a more concentrated gold solution and less waste.



How deep would you make the solution? 3" or so?


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## solar_plasma (Jan 31, 2015)

The only thing I would want is, that there is at least 1g gold per liter in solution. If possible more.

But if you choose to dissolve the gold this way, try first with a little piece. It is important, that the steel is inert. Otherwise your gold would cement back onto the steel, which would be a headache.


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## justinhcase (Jan 31, 2015)

For large arias of plating I use a sponge made of fiberglass instead of pumping A.R. around.
With good gloves and an effective solution to fumes I leave the bottom of the piece in a small tray of weak A.R.
I then just keep the fiberglass mat wet and move it to the next section when I can see all the Au has been digested.
Wash every thing down well and precipitate as normal.


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## goldsilverpro (Jan 31, 2015)

Type lll plating is pure gold and should strip faster than finger type gold. That would take a giant gold bath just to plate it, although it's very possible that it was brush plated (Google brush plating). Probably the stripping could be done electrolytically with brush de-plating, using EITHER cyanide or strong sulfuric. I would make the wand from rebar and glass wool, using baling wire to secure the glass wool. It would look similar to this without the handle:

http://shop.puregoldplating.co.uk/wp-content/uploads/2012/03/Swab-Thick.jpg

I like the idea of using a sponge (or, scrubber pad) but it would have to be made of plastic (almost any common plastic except nylon!!!). I think Lazersteve did something similar but it was on thin gold. Much, much less solution would be needed. If the gold is thick, it might go slow.


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## Palladium (Jan 31, 2015)

What were these used for or where did they come from? How many? I bet the gold is a thin layer for corrosion purposes only. Those things are probably worth more as jacketed ss than as scrap gold. Wort cooler come to mind.


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## g_axelsson (Jan 31, 2015)

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


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## goldsilverpro (Jan 31, 2015)

Palladium said:


> What were these used for or where did they come from? How many? I bet the gold is a thin layer for corrosion purposes only. Those things are probably worth more as jacketed ss than as scrap gold. Wort cooler come to mind.


I agree. They are pretty neat things.


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## goldsilverpro (Jan 31, 2015)

g_axelsson said:


> 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.
> ...


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.


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## Palladium (Jan 31, 2015)

goldsilverpro said:


> g_axelsson said:
> 
> 
> > 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.
> ...



Yep! It works.


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## g_axelsson (Jan 31, 2015)

Thanks, then I wasn't that far off with my idea. 8) 

I originally thought of this method and used it successfully for treating gold sputtered directly onto aluminum. Nice to hear it can be used for more applications too.

Göran


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## Palladium (Jan 31, 2015)

goldsilverpro said:


> g_axelsson said:
> 
> 
> > 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.
> ...




Recovered copper powder added to the solution until no more red gas, then add a little more. Recover powder proceed to step 2 refining in ar and then on to step 3 ar. It's a 3 step recovery process or a good hcl wash and then ar again. That's why i get 25% for gold filled stainless glasses! It is easier in a way, but more steps.


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## Trilo68 (Jan 31, 2015)

They were used for a vapor deposition process. What you see is what i have.

I don't know the plating method, but it looks very uniform. I have seen copper plated with silver cyanide using a brush, this looks a lot different. Then again that was silver, this is gold; and that was on machined copper, this is on bright nickel. I tried to put one of the brackets (also SS and plated to the same spec) in HCL, H2O and copper chloride (made from HCL + H2O2 +Cu) with a bubbler to etch away the nickel and free the gold. I saw this method on youtube for PCB fingers. At first the solution was very light green from the addition of the copper chloride. The solution has since darkened considerably but is still clear; just a very dark green. Any of the exposed SS has developed a black film, almost like carbon. The SS stays black when wiped, but a lot of the film comes off. When the gold is scratched some flakes off and exposes the blackened SS. There are some flakes floating around and some on the bottom of the container. I am going to try the HCL + bleach to see what happens.

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.

Some pics attached.





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.


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## eastky (Jan 31, 2015)

If those were mine I would see what a wire brush would do to the plating.

I would build a 2X4 frame and cover it in plastic sheeting. Get some 4 inch pvc pipe and a tee or a Y fitting a 90 elbow.
a couple misters from the garden shop and a submersible water pump. A fan to draw the dust through the pipe.

Make sure the guard is on the grinder and turned toward the back of the frame where the pipe is. Keep throwing the dust in the same direction. The gold plating seems to be pretty thick from the piece you have tested. Take your time and you don't have to run the grinder full spend. You want more of a polishing removal speed versus tearing and throwing gold all over the place. 

I really doubt you would need the piping. Seeing that the gold plating is pretty thick from your sample. The gold will most likely ball up and not be a dust.


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## goldsilverpro (Jan 31, 2015)

> 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.


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## kurtak (Feb 1, 2015)

Trilo68 said:


> 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


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## John TG (Feb 1, 2015)

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


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## patnor1011 (Feb 2, 2015)

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:


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## Anonymous (Feb 2, 2015)

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


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## Harold_V (Feb 3, 2015)

kurtak said:


> 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


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## kurtak (Feb 3, 2015)

Harold_V said:


> kurtak said:
> 
> 
> > 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)
> ...



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


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## Trilo68 (Feb 3, 2015)

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.


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## goldsilverpro (Feb 3, 2015)

Small black particles often have PM values.


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## samuel-a (Feb 4, 2015)

goldsilverpro said:


> g_axelsson said:
> 
> 
> > 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.
> ...




Chris,

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


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## goldsilverpro (Feb 4, 2015)

samuel-a said:


> goldsilverpro said:
> 
> 
> > g_axelsson said:
> ...


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.


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## samuel-a (Feb 4, 2015)

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.


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## goldsilverpro (Feb 4, 2015)

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.


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## Lou (Feb 4, 2015)

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


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## g_axelsson (Feb 4, 2015)

goldsilverpro said:


> 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


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## Palladium (Feb 4, 2015)

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


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## Lou (Feb 5, 2015)

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.


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## samuel-a (Feb 5, 2015)

goldsilverpro said:


> 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...




g_axelsson said:


> goldsilverpro said:
> 
> 
> > 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.
> ...



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.


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## samuel-a (Feb 7, 2015)

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.


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