# cyanide bombing solution



## greentea (Jul 8, 2008)

Hi guys, I'm new to this forum. I have about 40 gallons of cyanide bombing solution that has been sitting outside in a plastic drum for maybe 15 years or so. I used to bomb a lot of gold back then so I know about the dangers of cyanide. I'm planning on decanting it a few gallons at a time and mixing zinc powder in - then sending the precipitate to a
refiner. I'd done the AR process in the past and don't want to use the strong acids - really, I have no suitable place to use them. Anyone want to give me their opinion about this? Any tips?


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## Lino1406 (Jul 8, 2008)

I suppose you will benefit by
stirring in some caustic before
adding Zn, or Al powder


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## greentea (Jul 8, 2008)

Lino1406 said:


> I suppose you will benefit by
> stirring in some caustic before
> adding Zn, or Al powder




I was thinking of recycling the cyanide so I was hoping the zinc would make the metals drop out and the cyanide would be reuseable? I haven't done this before so I don't know.


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## Lino1406 (Jul 8, 2008)

How to recycle Zn cyanide?


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## greentea (Jul 8, 2008)

Lino1406 said:


> How to recycle Zn cyanide?



By your answer I assume the cyanide will no longer be useful because of the zinc - okay - now, which caustic were you referring to?

Thanks for your help. I only did the AR method once and that was many years ago. I am a novice in regard to these other processes. I'm trying to read a few pages of this board every day to educate myself.


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## Lino1406 (Jul 8, 2008)

You work with cyanide. When you'll take
a sample of your cyanide and add Zn, watch
if there are gas bubbles. If not, stir in some
caustic soda, to accellerate things


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## greentea (Jul 8, 2008)

Lino1406 said:


> You work with cyanide. When you'll take
> a sample of your cyanide and add Zn, watch
> if there are gas bubbles. If not, stir in some
> caustic soda, to accellerate things



Got it, thanks!


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## Lou (Jul 8, 2008)

You should make sure it is basic, at least pH 12 with sodium or potassium hydroxide. Then you add in the zinc. The cyanogold complex will break, and make zinc cyanide. 

The only way to safely recover the cyanide off the zinc (that I can think of) would be to distill off the HCN by making system acidic with sulfuric or phosphoric acid, in a glass setup, either in a hood with traps, or outside on a blustery day. HCN can easily be condensed (pretty light blue liquid). This reacts with sodium or potassium hydroxide to give the cyanide salt. 

If you don't want to mess with AR, then you really don't want to mess with cyanide. 


The cemented gold will still have zinc in it, or it should if you used an excess of zinc like you ought to have done. After you've decanted, filtered, and rinsed the gold with sodium hydroxide, you can remove any last traces of zinc with 20% HCl, keeping in mind that you keep acid away from base.

Melt the gold with sodium nitrate and borax. If your bombing solutions used pure gold you will have a relatively good product.


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## greentea (Jul 8, 2008)

Lou said:


> You should make sure it is basic, at least pH 12 with sodium or potassium hydroxide. Then you add in the zinc. The cyanogold complex will break, and make zinc cyanide.
> 
> The only way to safely recover the cyanide off the zinc (that I can think of) would be to distill off the HCN by making system acidic with sulfuric or phosphoric acid, in a glass setup, either in a hood with traps, or outside on a blustery day. HCN can easily be condensed (pretty light blue liquid). This reacts with sodium or potassium hydroxide to give the cyanide salt.
> 
> ...






Much thanks for the additional information, Lou. I think I'll be okay with the cyanide since I will do the work outside. I worked with it for many years and know the hazards. What I remember about the AR is that it's very corrosive and I really don't want to add even more problems or time in handling this stuff. I plan to neutralize the cyanide with bleach as some here have suggested. Thanks again.


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## Harold_V (Jul 8, 2008)

Lou said:


> Melt the gold with sodium nitrate and borax. If your bombing solutions used pure gold you will have a relatively good product.


Bombing was and is typically used to clean and polish gold alloy, removing traces of fire scale, unless I don't remember things well. In this case, assuming that's correct, there would be copper in solution along with gold and silver. The end product will be contaminated with all of those elements. 

I think I'd do a dilute nitric wash after the values have been cemented with zinc. That way you'd separate silver and copper from the gold, then the silver could be recovered on scrap copper. A wash with HCl would leave the silver behind, likely partially converted to silver chloride. 

All depends on how highly concentrated the bombing solution is whether it would be worth the trouble, considering the relatively low value of silver. Might not be more than a portion of an ounce in solution. 

Harold


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## Lou (Jul 9, 2008)

I'd just oxidize all the crap when I go to melt it. Then shot it and re-refine.

If there were enough silver containing slag, it might be going after.


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## goldsilverpro (Jul 9, 2008)

I wouldn't even consider trying to recover the cyanide, especially through the use of acids. This method should not have been mentioned on this forum. There's no reason to die for a little bit of gold. 

Here's how I would get the gold:

(1) Adjust the pH to 12, or a little higher, with NaOH or KOH. Try not to use an excess. If you do, it will take more zinc in the next step - step (2).

(2) Add 325 mesh zinc dust, in increments, to the solution, with stirring. Don't use solid zinc - the gold will only precipitate on the surface, leaving a lot of undissolved zinc. It should take about 2 oz of Zn for each oz of gold. Zinc dust tends to clump. I break it up by adding it to the solution from a small squeeze type flour sifter. As you stir, the precipitated powder in the solution will be brown, from the gold. When all the gold has dropped, the pptd. powder will appear gray, from the excess zinc. At this point, you should be finished dropping the gold.

(3) Allow the gold powder to settle overnight. It is traditional to hang a zinc bar, or two, in the solution. This prevents gold from redissolving.

(4) Siphon, filter, and rinse well several times with hot water. Try to rinse out as much cyanide as possible.

(5) There will always be excess zinc mixed with the gold. This can be removed with NaOH solution (hot is probably best) or an acid (about 20%HNO3 or 10%H2SO4 - don't use HCl). If you use acid, a fume hood is a must, since traces of cyanide are probably still present and HCN will be created.

(6) Rinse well and dry.


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## Lou (Jul 9, 2008)

Chris's method is probably the best for dealing with it, as he's dealt with such things many, many times.

Harold, GSP, I was in error when I suggested HCl. NaOH or KOH would be better to remove the zinc as zincate. Then nitric to remove the silver and copper.

Copper doesn't dissolve terribly well in cyanide, but silver does. You remember things just fine Harold, bombing is for removing oxides. For some reason I thought this was a plating solution, not a dip.


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## goldsilverpro (Jul 10, 2008)

In step (5) above. If you have much zinc in the gold, the acid will react violently. To tame it down, first cover the sludge with water and then add a small amount of acid, UNDER THE HOOD! When it quits reacting, stir and add another shot of acid. Repeat until an addition of acid gives no reaction.


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## Harold_V (Jul 10, 2008)

goldsilverpro said:


> In step (5) above. If you have much zinc in the gold, the acid will react violently. To tame it down, first cover the sludge with water and then add a small amount of acid, UNDER THE HOOD! When it quits reacting, stir and add another shot of acid. Repeat until an addition of acid gives no reaction.



I processed high grade gold ore with cyanide/bromine, and recovered the values with zinc. I used the exact procedure you mentioned---because the yield contained both silver and gold. Worked perfectly!

Harold


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## PhillipJ (Jul 21, 2008)

Wow. Been a while since I have dropped in at this forum. Been heavy into electroplating the Harley the past six months.

Anyhow. Is the above method the same for a cyanide gold plating solution?

Also, I have a home brew gold plating solution made from potassium ferrocyanide and sodium carbonate and wondering if the above method will work on that too. Raise the pH to 12 and add zinc powder.

That solution worked but was sometimes hard to get it to plate good. Depended on which way the wind was blowing. Pretty soft too.

Phillip


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## Harold_V (Jul 21, 2008)

Hey Phillip! Long time!

As far as I know, you can use zinc to recover the values from those solutions. It's a good idea to have a little free cyanide available to accelerate the conversion. I always added an ounce or so to my rather large volume (approx 15 gallons) of solution when I'd recover the values. Bear in mind, I kept my cyanide level no greater than .02%, so you may not need to add any. Low cyanide is selective when dissolving from ores, leaving copper behind. 

Some types of plating solutions can be troublesome as I recall. Could be GSP may have something to offer in that regard. He has considerable experience in the plating field---as well as in refining. I imagine he's seen it all by now. 

Good to hear from you. 

Harold


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## PhillipJ (Jul 21, 2008)

Thanks for the info Harold. I doubt if I can get ahold of any cyanide if needed. Maybe the potassium ferrocyanide is sort of on the same order but way less toxic. 

I kinda tested smb to drop it out of the potassium ferrocyanide solution but that didn't work. And any acid just turns it blue.

The zinc & sodium hydroxide thing seems worth a try. 

Right now I am plating the most of it out, but have my doubts that it'll all plate out. Used about 15 grams of gold when I made the solution up and now I need that back as I have my eye on some cool wheels for the bike.

I gold plated my brake calipers and some othe small items.


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## Harold_V (Jul 21, 2008)

PhillipJ said:


> I gold plated my brake calipers and some othe small items.


Way cool! Pics?

I plated a couple railroad spikes years ago----with home made electrolyte and a gold anode. Still have the solution and anode-------and one of the spikes! A friend did the nickel base plating, then I pursued the gold. Turned out pretty well for a guy that had never plated anything. 

Harold


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