Any recommendations of recovery process for large item?

[Trilo68]

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.

 

[necromancer]

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.

 

[necromancer]

forgot this link, you can find plating info here

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

 

[4metals]

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.

 

[necromancer]

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 ??

 

[Trilo68]

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.

 

[solar_plasma]

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.

 

[Trilo68]

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?

 

[solar_plasma]

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.

 

[Justincase]

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.

 

[goldsilverpro]

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.

 

[Palladium]

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.

 

[g_axelsson]

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

 

[goldsilverpro]

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.

 

[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.

 

[Palladium]

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.

Yep! It works.

 

[g_axelsson]

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

 

[Palladium]

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

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.

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.

 

[Trilo68]

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.

 

[eastky]

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.