Separating Tungsten from Gold

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dbarrett55

Member
Joined
Jan 22, 2013
Messages
5
Location
San Francisco, CA
I have some scrap metal that is about 50/50 gold/tungsten according to my xray flourescense machine. Does anyone know whether using Nitric acid will disolve the tungsten and leave the gold behind. From all the posts I searched for, it looks like a combination of hydroflouric acid and nitric will dissolve tungsten, but I am not sure how to handle that acid or whether it will also dissolve the gold. Can anyone point me in a direction to separate this alloy. The scrap came from a semiconductor wafer manufacturing machine according to the person I purchased it from.
 
dbarrett55 said:
I have some scrap metal that is about 50/50 gold/tungsten according to my xray flourescense machine. Does anyone know whether using Nitric acid will disolve the tungsten and leave the gold behind. From all the posts I searched for, it looks like a combination of hydroflouric acid and nitric will dissolve tungsten, but I am not sure how to handle that acid or whether it will also dissolve the gold. Can anyone point me in a direction to separate this alloy. The scrap came from a semiconductor wafer manufacturing machine according to the person I purchased it from.
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First, I would take any process that suggests using Hydrofluoric Acid, and throw it right out. Not worth the risk, Hydrofluoric Acid is probably the worst possible, readily available acid you can choose to use. It's one of the few acids that if you get it on a large enough area of your skin, it will kill you, and even if you survive a spill, it is probably likely that the damage will be extremely severe.

Best when you have material this unusual to simply have a refiner/refinery set up top process this type of material do it instead. What you save will be beyond monetary value, it will be you.

Scott
 
Thanks for the info. Since I don't want to take the chance of dying, I think I will avoid the hydroflouric acid. I didn't really want to go down the hydroflouric acid path anyway. Any idea if nitric acid will dissolve the tungsten. I suppose I could just get some 70% nitric and test is with a sample....but if anyone already knows whether it would dissolve the tungsten leaving me the gold, that would be helpful.
 
That is a bizarre alloy, I have never heard about it before. Have you tested it on a fresh surface so it isn't just gold plated tungsten? XRF only sees the surface, not the inside of an object.

Only nitric have very little effect on tungsten, hydrogen peroxide is an order of magnitude faster but still quite slow in dissolving (actually oxidizing). Highest attack rate is at 60 degrees C.

Hot aqua regia attacks tungsten fast, creating a yellow-green oxide layer. If it will stop the reaction or just fall off your alloy I don't know. This is what I would try.

Göran
 
It is a bizarre alloy. According to the guy who cleans the semiconductor machine, the manufacturer was alternately spraying gold and then tungsten. I filed one of the samples significantly to make sure it wasn't just gold plated tungsten and its pretty consistent in the amount of gold and tungsten. Using aqua regia won't help as that will dissolve the gold as well.
 
So it's not alloyed but layered?

There might be several ways to deal with it, if it's layered, depending on what the plating thickness is. I'm kind of curious about the process of plating Tungsten.

Still though, I wouldn't even attempt processing something of this nature myself, I would have someone equipped and experienced in this type of material do it. Gold is worth too much to risk botching a complex job like this sounds it is.

Scott
 
My scrap is about 1mm in thickness but since I really don't know exactly how this scrap came into being, I can't say for sure if it is layered or not. I do know that when I perform xray flourescence before and after numerous filings, it stays pretty consistent in its gold/tungsten content. So if it is layered, the layers are likely only fractions of a micron thick (if not atoms thick, but I am not familiar enough with how semiconductor eqpt makes products to say for sure).
I could also try to melt it and see what results, but that might be a waste of time given tungsten's extremely high melting temp. At the end of the day, I have had some bad experiences with a few refiners when I have sent them this type of material (at times they have claimed 65-70% melt loss) so I am hoping to see how much gold I can extract from a small sample of my batch to see the results. If I can get reasonable results, I am more confident is selling the resulting pure/almost pure gold beads to a refiner without the risk of getting screwed by them.
 
Hi there dbarrett!
It's funny, I just started a project that involves running AR in which there are tungsten components and have just posted my preliminary progress. see my thread "my next learning experience" It's not exactly what you are doing but, I recieved advice from three of our members who seem to have worked with tungsten before,
Glondor
Sam from "gold n scrap"
Lazersteve
Per-haps they would be able to give you sources of info on W/Au
Also;
I don't know what post it was because I was reading everything I could find about W/Au separation on the abouve search bar, but I recall one of the posts said that you could dissolve the tungsten in hot KOH and recover the gold.
Good luck and I'de be interested in what you find out and how it works. post your results.
Hope I helped! artart47
 
If it is flakes from an evaporator then you should be able to break it in smaller pieces and use aqua regia. The layering of pure metals makes it into a sandwich and not an alloy, acid should be able to reach the gold without being blocked by the tungsten. I think that the tungsten will turn into oxide and the gold will go into solution. Then it is just a matter of filtering the gold chloride and drop it.

Göran
 
Hi, I used aqaua regia on gold plated tungsten wire (corona wire 300gms, .002" dia) once, seems like nothing happend to pure tungsten wire underneath and solution came clear dark yellow with dissolved gold. Only slight warm aqua regia was used.
 
Nobody has mentioned it, so it probably won't work, but...Would a solution of AP attack tungsten? If so, that might be the easiest and cheapest solution. Of course, if it works, you can send my "finders fee" check by mail. :^) Good luck and keep us posted.

Bert
 
If it is a sintered product , it may be powdered or atomized , than incinerated a little longer. Stirring the heated powder is needed I guess.

The tungsten exposed will oxidize but the gold won't . One trained could manage the tungsten oxide.

Further recovering of gold should be piece of cake.
 
As far as I know, metallic tungsten can be oxidized to water soluble tungstates, in molten mixtures of alkali hydroxides (-carbonates) and -nitrates. Reactions seem to be strongly exothermic, and difficult to control. Sodium- and potassium tungstates, Na2WO4 and K2WO4 are both salts, highly soluble in water.

US-Patent US4603043 A describes the production of sodium tungstate from tungsten-metal-scrap under controlled conditions.
 

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Thanks everyone for your ideas. I will put one of the samples in Aqua Regia and see if I can get the gold to go into solution completely, see what happens with the W, and then see if I can recover anything! I'll keep you posted.
 
Well, I'll assume, as the last post on this thread was nearly 6 years ago, that there was never a follow up on this thread, and no new info is available.
 

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