Evaporating cyanide solution.It's safe?

[Joko sulistyo]

Hi all.
I have several kilos of IC legs.After processing gold from the ashes,I always collecting the legs.Now I decide to process them using cyanide method.I have been use this way for pins and boards for several times.But I have questions about my steps in cyanide way.
1)I use potassium cyanide 20 grams per liter water.This is enough?
2)I use lime stone water and when I test with PH paper it's show very high.PH 13.What the effects for stripping?
3)I have no zinc powder.Here is difficult to find Zinc powder.So,I always use evaporation way to recover gold from cyanide gold solution.My step is evaporating my cyanide solution until almost dry (mud).
And then I collect that mud with tissue paper and incinerate the mud until total dry(brown powder).Then I mix the brown powder with borax and soda ash then melting them in my furnace.
When I evaporating the solution,it's produce vapors.How danger this vapor?Yes I do this at open area.But I still worry about this vapors.
I still remember what's mr.GSP said about cyanide.Don't eat it,don't drink it and don't swim it. and I will not.(I miss him.I learn to much from him)
Thank you so much.

 

[Lino1406]

Assuming you have gold + copper +...? cyanide solution, best to cement the gold on copper sheets or foils and evacuate the remaining solutions to an approved site

 

[Joko sulistyo]

Thank you for reply,lino.
How fast copper can cementing gold and silver in base solution?can I use Al foils?

 

[Lino1406]

Al foils is good provided you have nitric acid to dissolve what is not gold

 

[anachronism]

You can even use Aluminium happily if you have no zinc. (And you know what you're doing.)

Edit. Be careful if you have a high pH and you've used NaOH. Try some cooking foil first to see how hard it reacts before really adding a lot because Aluminium and OH ions dont mix well.

Copper is the safest way as Lino said, and Al is a darned good way of getting the last bits out and checking for any residual gold if you don't have an AAS.

 

[Joko sulistyo]

Thank you,jon.
I still confuse about the fume/vapors when I tumbling materials in hot cyanide solution. This vapors safe?

 

[Lino1406]

Now that you already have solution the gas issue is negligible vs. the extraction stage, where (assuming) you used air bubbling with the cyanide. Reducing vs. oxidizing environment

 

[Joko sulistyo]

I use H2O2 not air bubbler.The reaction is very fast.Just 2-3 minutes all gold plated will stripped.How about IC legs?Can cyanide attack gold on them?They are mostly kovar and some of them are copper.Since they come from incineration process,gold plated(the edge of legs) not visible.But I believe still there gold on them.

 

[Lino1406]

Well, air or H2O2 is the moment of oxidizing which can give stinking gases. As for fingers, yes cyanide will take gold, copper, just a matter of time

 

[nickvc]

When you have copper in the mix then cyanide will happily attack that and silver even more especially if you are using high levels of cyanide, the more you use the less selective cyanide becomes.

 

[Joko sulistyo]

High levels of cyanide?How much cyanide?I usually use 20 grams per liter water.I use potassium cyanide and limestone water.That's why the PH too high.I'm a little worry about Hcn that may formed if use just tap water.
Thank's for answer.

 

[Geo]

Will cyanide effect the nickel barrier in case of gold plated pins? If not, only the base metal at the ends of the pins will be effected. Is this correct?

 

[Lino1406]

Electrochemical calculation shows that nickel is attacked even more than gold, silver and copper

 

[g_axelsson]

Then there is an error in those calculations.

Cyanide is selective for gold over nickel in certain circumstances at least, or it would be impossible to leach gold from nickel plated pins.

Did you take in account that a high pH passivates steel

I did some experiments with ferricyanide this summer and this is the result. The pins were gold plate on nickel plate on brass. I used aluminium foils to recover the gold after it was leached from the pins.



Göran

 

[snoman701]

It’s a time/concentration/orp dependent curve. Hot 40g/L sodium cyanide with excess hydrogen peroxide will absolutely dissolve nickel, copper, etc.


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[Lino1406]

Agreed. Passivation, settles this, as part of the nickel becomes solid film nickel hydroxide, concurrently with cyano nickelate ions. Of course, the nickel thickness also is an issue