midas
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gold-clean
hello
My name is Oguz. (Turkey-istanbul) cemist.
gold chain - clening
H2O2 + NaCN + gold ->
Are you know this reaction alternative?
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woelen
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An alternative might be to use sodium thiosulfate instead of sodium cyanide. The thiosulfate is non-toxic, but it appears to work quite well,
especially, when combined with small amounts of copper.
The use of google, with the following keywords may give you useful links: gold thiosulfate leaching.
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enhzflep
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Midas, the process you are describing is reffered to as Cyanide Bombing, or just Bombing. You don't state whether you are cleaing karat gold (as I
assume you are, or 24k gold)
Although not clear on the exact reaction scheme, I can tell you that when bombing karat golds, HCN is produced. This gas is both absorbed into the
solution and expelled as bubbles.
The process has been around since the 1970s, pioneered by a pair of gentlemen whose names escape me at this time. When processing karat golds, if I
recall correctly, the outer layer of the metal is removed - Au, Ag and Cu. Of this outter layer, a proportion of the Au is re-plated automatically,
leading to Gold-enrichment on the surface.
That said, the remaining solution still contains gold in appreciable amounts, and if contemplating this process on an industrial scale, i.e several
times a day for a period of months, one is advised to keep the solution and send it to a refiners.
In Aus, the typical refining cost is ~$200, plus about ~$1 or $1.50 a gram of fine gold recovered. More often than not it is uneconomical to recover
the Ag and Cu from this solution (as a consumer that is, the refiners routinely reclaim these metals to reduce their operating costs.)
This process should always be carried out outside, or failing that, right next to a open
window.
Lastly, if you just want to clean 1 or 2 chains, just dump some NaCN or KCN into some cold water and drop your chains into this solution. This method
takes longer, but avoids the release of copious quantities of HCN. Additionally, it's a slower, more controlled process that reduces weight by 1/100s
of a gram, rather than 1/10s.
If this is still too slow, you may consider electro-stripping - i.e using ~+5-7v, connect the + to the article and - to a stainless-steel teaspoon.
[Edited on 10-5-2006 by enhzflep]
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midas
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we use Cyanide Bombing but they toxid.
H2O2 + NaCN + gold ->
alternative reaction
H2O2 + sodium thiosulfate + gold -> ???
and
how much sodium thiosulfate, h2o2 and water?
thank you
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enhzflep
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In this case, I've been prepared to do some searching for you, since I'm interested myself. As woelen suggested, you should search
for gold thiosulphate leaching - however in the last 5mins i've turned up a number of methods of recovering gold from thiosulfate leaching
solutions. One mentions recovery from a solution containing 0.2Mol/liter of ammonium thiosulfate, however most refferences to the process mention
tightly controlled conditions and/or very high (how high??) concentrations of thiosulfate. (usually uneconomical)
What are you trying to clean them from?
Are they old and tarnished, or are they fresh from soldering, and covered in red fire-scale?
Pottasium dichromate in your pickle will remove fire-scale, as will Nitric. Hell, even dilute Aqua Regia will do it. Personally, I'd be more than
happy to have 5gm KCN in 500ml water with a chain in it overnight in my bedroom while I slept. As I mentioned before, when you avoid the peroxide
there is very minimal gassing - something like what you get from your solder joints if you leave articles in the pickle for too long. i.e hardly
any - maybe 1cc gas for every 10hours from a 100gm 18k hollow rope chain.
Carefull with the dichromate in pickle though - it will slowly disolve diamonds!!!!!
[Edited on 10-5-2006 by enhzflep]
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midas
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I am trying to clean them from gold-clean. (500-1000 gr)
They aren't old and tarnished or they aren't soldering.
They are gold plating (red,green ...) and Rhodium plating.
I will trying Pottasium dichromate procces. Are you waiting enhzflep?
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midas
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Pottasium dichromate is negative.
I will trying 0.2Mol/liter of ammonium thiosulfate.
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enhzflep
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Okay, so dichromates out. Let us know how you get on with the Thiosulfate route.
I should probably mention that we always had extreme dificulty removing rhodium from articles. Cyanide never seemed to touch it, in fact the only way
we were able to removed rhodium plated onto articles was by polishing, or by sending them out to be stripped. Guess that's the downside to plating
with something soo inert 
I don't know what the chemicals used to strip them were, however every time something had rhodium removed commercially, the article would come back
with rather severe pitting on the surface. I.e the article would have an appearance similar to un uncleaned casting!
If the rhodium plated article was a brooch or a Pr of earrings, I'd be tempted to suggest nickel plating, followed by gold of the correct colour.
HOWEVER since you are discussion chains, I would not recommend this route since the article is in a high-wear sitaution, and the article will look
like mokume gane in no time as the different layers of plating wear through.
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