Laboratory Testing & General Mineral Processing Engineering

Laboratory Testing & General Mineral Processing Engineering 2017-04-04T06:57:51+00:00
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Gold in sodium cyanide solution (3 replies)

9 months ago
Pauloc 9 months ago

I've dissolved Gold from electronic waste into a solution of sodium cyanide my question is how do I now remove the gold from the liquid safely. At the moment I have about 2 liters of solution

thank in advance Paul 

9 months ago
Wayne 9 months ago
1 like by Cyanide

HI Paul,

Safely is relative, you have already worked with the most dangerous one "NaCN" but no lecture here.

We run a process which uses carbon adsorption and acid stripping followed by electrowinng the dore onto wire mesh then sent for refining.

For your couple of liters this would not be very practical.  I don't think there is a real easy answer to your question although easy is relative to the drive of the person involved.

This link might be worth your while though.



9 months ago
Cyanide 9 months ago

You also may try a Zinc dust precipitation. Here is the Patent

You can get zinc from old batteries. In either cases, since you have a small volume like this, you could burn off the filtered precipitate or loaded carbon = gold.

Also see and

9 months ago
inOr 9 months ago
2 likes by Bob Mathias and David

If you don't want to recycle zinc from other sources, you can buy zinc powder (called "dust") on eBay.  I checked and you can buy 1 lb. for $22-24 for "high purity" product.  You don't really need 99.95% purity though.  That's for chemical laboratories.  I didn't search for "industrial" grade, but you should be able to find zinc at 98%, for example.  Zinc "cementation", as it's called in miner's lingo, is an old technique.  According to one description, the gold cyanide solution was poured over a series of cells containing lumps of zinc (called 'mossy' zinc for some reason).  I guess that the gold precipitated onto the bottom of the cells as a powder and washed out and over the zinc on a screen.  You get the point.

I haven't tried any of this, mind you, but the following should work. Prudence dictates that you experiment with a sample before committing the rest of your gold to the procedure..  

Add the zinc powder, in small batches, to the gold cyanide solution in a flask while stirring.  The zinc should dissolve as it replaces the gold in the cyanide complex.  When it has, add a bit more zinc and so forth until no more will dissolve.  This gives you a rough idea of when all the gold has been removed from the sample.  The entire contents of the flask can then be filtered through paper.  Do not throw the filtrate away just yet.  It might contain some unreacted gold cyanide if you haven't added enough zinc, and you will need to repeat the procedure on the solution to recover that gold.

On the other hand, if you added too much zinc and some remains in the flask together with the gold dust, thoroughly wash the solids on the filter paper with enough water to remove any trace of cyanide. If any cyanide salt remains in the gold-zinc mixture this next step will convert it into lethal hydrogen cyanide gas. I advise that you carry out this step in the open or under a ventilation hood.  Now dry the powder and add to a flask or beaker and add strong hydrochloric acid dropwise until hydrogen stops bubbling.  Don't add anything to the HCl, and the gold will be unaffected by the HCl.  It's a bit complicated, but for small scale applications it should be pretty economical.  All you need is distilled water, zinc, hydrochloric acid, a spare flask and/or beaker, a conical funnel and filter paper.  If you don't have it yet, find C.W. Ammen's book.

P.S.: You might try adding a few drops of strong HCl (50%?) to the dry powder before trying to remove the excess zinc. If it doesn't fizz, there isn't much, if any, zinc contaminating your gold.  If you need more HCl, you can probably get away with adding more than a drop at a time.  When this reaction is complete, add water to the flask to dilute the HCl.  Then filter and wash with distilled water.  Again, save the filtrate until you've determined that you have most of the gold in your final product.  That way, if something goes wrong you still have your gold to recover some other way. 

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