# Activated Carbon Stripping



## Destroyer777 (May 25, 2010)

Hello Everybody,

I have pretty much AC stuff, which contains Au... I need to eluate it first and also precipitate after...
Is anybody know how to do it in the best way?????

I tried two methods yesterday.The first one is: 
1. I've made a column
2. Put dried AC (approx 1kilo) and filled up by 10% solution of HCL (1L, t 40-50C), left it for 15 minutes.
3. Drained solution from the bottom.
4. Partly evaporated, after used small amount of Zinc for precipitation.

Nothing happened....

The second one: I did the same things, but instead of HCL, I used Thiourea (in concentration 90 gr of Thiourea + 20gr HCL per litre of solution).
Result is the same. Zero!

What I did wrong???
Is anybody has experience with Activated Carbon stripping in practice???
Would be very appreciated for any advice....

Best regards,
Denis


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## goldsilverpro (May 25, 2010)

What form of gold was originally run through the carbon? Cyanide complex? Halide complex (Cl, I, or Br)? Thiosulfate? In each case, the removal of the gold from the carbon will be different.

If the gold is in the form of a cyanide complex, I don't think you will ever remove it with acids. I would think that the acid will reduce the cyanide complex to the acid insoluble yellow compound, AuCN. The standard way of eluting the gold cyanide complex from the carbon is by a sodium hydroxide/sodium cyanide solution. This is done at temperatures near boiling and, depending on the strength of the solution, it can take from 1 to 48 hours. Before using the NaOH/NaCN leach, an HCl leach is often first used to remove any acid soluble materials, such as calcium. HCl will not remove the gold. Switching between acids and cyanide can be quite dangerous, due to the production of the extremely poisonous gas, hydrogen cyanide. If you do this, rinse very well in between and use a fume hood.

If gold chloride was originally used, the carbon reduces the gold chloride to gold metal. The gold is often recovered by burning. Other schemes involve first mechanically separating the gold metal from the carbon by abrasion or by such things as ultrasonics. The gold is then recovered by gravity methods.

The following attachments give all of this in more detail.

It seems like you are trying to use the same methods for carbon that work for resins. In the literature, I see no elution methods that are interchangeable between the two.


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## Lou (May 25, 2010)

If he still has it wet in solution and didn't dry it, he can still elute it with HCl.

I'm not a big fan of AC for metals processing. Works nice for decolorizing organics though! Or deodorizing, or removing poisons, etc. 

Refining? Not so much!


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## goldsilverpro (May 25, 2010)

> If he still has it wet in solution and didn't dry it, he can still elute it with HCl.



Lou,

Are you talking about the gold being in the form of a cyanide complex in the carbon? If so, what are the equations involved to leach it out with HCl? What is the efficiency of this? Would you use HCl alone or something like HCl/acetone that is used on resin?


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## Lou (May 27, 2010)

Depending on the carbon, if he had a chloroauric acid solution, the gold may not be reduced. In many cases, it isn't because the activated carbon isn't so activated (most just use it from the can and do not heat and pump on it and cool under H2).


If it were a gold-cyanide complex, he'd have to use very strong, hot HCl to remove the bulk of the cyanide as HCN (not recommended). Even after that, he'd likely be left with gold (I) cyanide which itself is difficult to solvate (need oxidizing acids to do this, or else more sodium cyanide in air).

Efficiency? Depends on the carbon, but generally O.K.; personally, if I were foolish enough to start with AC to begin with, I'd just recover it in quartz combustion boat in a tube furnace with a fine quartz frit to stop ash and go low and slow with the oxygen. It's how I do Pt/C, Pd/C, Rh/C rather than putzing about with leaching it.


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