gold extraction from fine carbon

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FPZA

Member
Joined
Jul 10, 2013
Messages
11
Hi there,
I have 200 mtons fine carbon that comes from carbon safety screen. We couldn't use them in cyanide leaching cause they are fine.
The carbon has about 30 ppm gold, 200 ppm siver and 3000 ppm mercury. I extract the mercury in our electrical mercury retort. I tried to extract the gold and silver, the best way is burning the carbon and doing cyanide leach on the ash to extract gold and silver.
I'm looking to find the best technique to burn the carbon. Is there anybody here to help me?
 
FPZA said:
We couldn't use them in cyanide leaching cause they are fine.
Can I ask why you think this is? Is it because of post-leach filtering problems or something else?

If something else, can I suggest SSN (Saturated Saline Nitric] as your leach? This is cheap and let's you get at high purity gold (by solvent extraction) and silver easily. (More so than with cyanide.)
 
Gratilla said:
FPZA said:
We couldn't use them in cyanide leaching cause they are fine.
Can I ask why you think this is? Is it because of post-leach filtering problems or something else?

If something else, can I suggest SSN (Saturated Saline Nitric] as your leach? This is cheap and let's you get at high purity gold (by solvent extraction) and silver easily. (More so than with cyanide.)
Dear Gratilla, Thank you for your reply
I mean we couldn't use them in our gold plant which is a CIL plant due to the screen mesh size. Our screens are 1 mm mesh and the fine carbons are smaller than this size. I got a combination of ash and carbon after gold extraction in our mercury retoprt which contains just 50 ppm gold and 500 ppm silver so I guess Nitric leach isn't good and I should use the cyanide leaching on it.
The leaching isn't a problem now, burning the carbon is my problem. Burning in the retort gives me 30% ash and 70% non burned carbon and isn't a good way. I lose ash when i use burning by the direct flame in a kiln and I have to use cyclone and bag filter after the kiln also i have to scrub the mercury. this is a complicated process design.
 
The carbon that is left over is probably from an incomplete combustion process. The carbon needs oxygen to burn. In the retort it is starved for oxygen so what carbon you have left over is probably because it was oxygen starved. Maybe find a way to tap the retort so you can feed it oxygen. That might eliminate the 2nd burning process and save you from losing mercury downstream that has to be recovered.
 
The carbon that is left over is probably from an incomplete combustion process. The carbon needs oxygen to burn. In the retort it is starved for oxygen so what carbon you have left over is probably because it was oxygen starved. Maybe find a way to tap the retort so you can feed it oxygen. That might eliminate the 2nd burning process and save you from losing mercury downstream that has to be recovered.

...additional you would save a lot of energy. Depending what source the carbon comes from, there could be dissolvable contents in the ashes. I think of potassium carbonate (from plants) or calcium phosphate (animal bones). So, dissolving those contents could reduce the amount of ashes further more. Checking this on a small probe would't hurt. If my guess is right, you are left with a +200 ppm Au concentrate = +0,2g/kg, if it only would be 85% C in your material...maybe even more,since activated carbon is >90% C. Then every method should work for dissolving the gold and you could choose the cheapest. Maybe the 20g Ag/kg should be recovered first, if you don't choose a method, that leaches both Au and Ag at once.

6kg Au, 40kg Ag, 600kg Hg...at all about 300 000 $.....nice

Couldn't the Hg be used to dissolve the Au and Ag? Since you have the facilities to distill Hg, this would be the most economic and ecological method, wouldn't it?

...only thoughts...since you already use cyanide in large scale, there is only left the fact, that you would save energy :)
 
solar_plasma said:
The carbon that is left over is probably from an incomplete combustion process. The carbon needs oxygen to burn. In the retort it is starved for oxygen so what carbon you have left over is probably because it was oxygen starved. Maybe find a way to tap the retort so you can feed it oxygen. That might eliminate the 2nd burning process and save you from losing mercury downstream that has to be recovered.

...additional you would save a lot of energy. Depending what source the carbon comes from, there could be dissolvable contents in the ashes. I think of potassium carbonate (from plants) or calcium phosphate (animal bones). So, dissolving those contents could reduce the amount of ashes further more. Checking this on a small probe would't hurt. If my guess is right, you are left with a +200 ppm Au concentrate = +0,2g/kg, if it only would be 85% C in your material...maybe even more,since activated carbon is >90% C. Then every method should work for dissolving the gold and you could choose the cheapest. Maybe the 20g Ag/kg should be recovered first, if you don't choose a method, that leaches both Au and Ag at once.

6kg Au, 40kg Ag, 600kg Hg...at all about 300 000 $.....nice

Couldn't the Hg be used to dissolve the Au and Ag? Since you have the facilities to distill Hg, this would be the most economic and ecological method, wouldn't it?

...only thoughts...since you already use cyanide in large scale, there is only left the fact, that you would save energy :)

I charge air to thr retort from two 1/2" valves. there are 12 tray in the retort, the carbon which is up in each tray is burned as well and from 3 or 4 cm downer it isn't burned ( the depth in each tray is 10 cm).
I will try potassium carbonate and calcium phosphate to check the effect. good idea, tnx
I havent try mercury to extract the gold from the carbon,but I will try it too. tnx again
Also I have designed a test to leach the fine carbon directly with aqua regia and will inform the group from my conclusion
 
I havent try mercury to extract the gold from the carbon,but I will try it too. tnx again

from the ashes, not from the carbon


Since you can distill Hg and since you are working with cyanide in such a large scale, I hope you have the knowledge and the equipent to do that savely for the environment! What I said are only ideas from a non-expert!
 
solar_plasma said:
I havent try mercury to extract the gold from the carbon,but I will try it too. tnx again

from the ashes, not from the carbon


Since you can distill Hg and since you are working with cyanide in such a large scale, I hope you have the knowledge and the equipent to do that savely for the environment! What I said are only ideas from a non-expert!

Oh! yeah,from the ashes, also mercury on carbons isn't good way cause mercury is adsorbed to carbon in normal temperature.
Gold extraction from the ashes by cyanide is much much cheaper in cost than mercury amalgamation. We have a big gold plant with CIL( carbon in leach) process and our capacity is 3500 mtons ore per day and about 10-11 kg gold. I have safe system for the cyanide leaching.
 
I'm still going to say oxygen deprivation. The carbon being that fine and packed 4 in deep is probably not allowing oxygen to penetrate the materials.
 
And I am still going to say, Palladium is right and a better oxidation would also save energy, since the process would be exotherm.

Another idea, if you would use the carbon for reduction of copper oxide, you could refine the copper in copper cells and get the PMs in the anode slimes....which only makes sense, if you already have the equipment running. :)
 
If you have a problem burning that carbon, mix some sodium nitrate or potassium nitrate with it. Just try heating a small sample of your carbon, once it gets red hot you mix in a little sodium or potassium nitrate and you will see how fast that carbon burns. The nitrate salt gives a source of oxygen so that your carbon can easily burn off. By testing with a small amount you can get an idea of how much you will need to add for bigger volume. I've tried this method... works well
Just for precautions, you should assay that ash / carbon for mercury after retorting to make sure no more mercury is there.
 
santiago said:
If you have a problem burning that carbon, mix some sodium nitrate or potassium nitrate with it. Just try heating a small sample of your carbon, once it gets red hot you mix in a little sodium or potassium nitrate and you will see how fast that carbon burns. The nitrate salt gives a source of oxygen so that your carbon can easily burn off. By testing with a small amount you can get an idea of how much you will need to add for bigger volume. I've tried this method... works well
Just for precautions, you should assay that ash / carbon for mercury after retorting to make sure no more mercury is there.

Dear Santiago
Thank you very much for your advise,I will do it.
 
To burn carbon completely, with no oxygen-deficit, a valuable option would be, to burn it as a coal-water slurry. A google-search with "coal-water slurry fuel" delivers a lot of results about this already developed and practized technology.
If you use your carbon, such as it is, in a "coal-slurry-burner", you would have to treat the off-gasses adequately, in order to remove the mercury and to recover solid ashes (fly-ash), probably by combined washing and filtering procedures.
 
If it were me, I'd heat the carbon with hot caustic soda and use an electroplater at 4 volts DC. :lol:
 
the main thing you have to realize is if your gold is in ionic form adsorbed on carbon surface, or as a very fine metallic particles mixed with fine carbon.

we are working with carbon adsorption and desorption processes in our lab and its highly dependent on pH value, oxidation state of heavy metal and ionic form
another interesting thing is, that its almost impossible to desorb ions of metals ( we are working only with radioactive heavy metals ) completely

according to the facts i wrote above, you have to fit your processing sequence on your situation to achieve desired result
 
Sucho said:
the main thing you have to realize is if your gold is in ionic form adsorbed on carbon surface, or as a very fine metallic particles mixed with fine carbon.

we are working with carbon adsorption and desorption processes in our lab and its highly dependent on pH value, oxidation state of heavy metal and ionic form
another interesting thing is, that its almost impossible to desorb ions of metals ( we are working only with radioactive heavy metals ) completely

according to the facts i wrote above, you have to fit your processing sequence on your situation to achieve desired result

Dear Sucho, It is cyanide-gold complex that was adsorbed to carbon in our gold plant. These are the fine carbones that came out from the process duo to the small size. The best way for the extract is burning the carbon then leach the ashes by cyanide again and extract the gold and silver. as the carbons are hard the burning as also hard. I'm looking for the best way to burn the carbons.
 
I have combined some Sodium Nitrate with the fine carbons and put it in the retort. After 24 hours I saw that the nitrate was molted and the carbon didnt burned as well.
I am burning the carbon in a rotating kiln with direct flame today. The burner uses gas and I charge more air in the kiln to see how the carbons burn.
 
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