# gold extraction from fine carbon



## FPZA

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?


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## Lino1406

After "extraction" of the mercury how much of it is left?


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## Gratilla

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.)


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## FPZA

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.)
Click to expand...

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.


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## FPZA

Lino1406 said:


> After "extraction" of the mercury how much of it is left?


Dear Lino, Thank you for your question 
about 30% is left.


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## Palladium

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.


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## solar_plasma

> 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


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## FPZA

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
Click to expand...


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


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## solar_plasma

> 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!*


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## FPZA

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!*
Click to expand...


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.


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## solar_plasma

WOW!

It is amazing how many different interesting people one can meet here on the forum.


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## Palladium

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.


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## solar_plasma

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.


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## santiago

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.


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## FPZA

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.


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## freechemist

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.


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## DANCER

If it were me, I'd heat the carbon with hot caustic soda and use an electroplater at 4 volts DC. :lol:


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## Sucho

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


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## FPZA

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.


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## FPZA

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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## solar_plasma

Just another maybe stupid idea (but that's the way a brainstorming works, so why not writing it at the blackboard): 

Maybe you could blend the carbon with a harmless burnable binder and form some kind of briqettes, so the oxigen better can reach into the material.


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## niteliteone

solar_plasma said:


> Just another maybe stupid idea


I hear nothing "stupid" about this idea, I was thinking along the same lines.
Wouldn't adding a touch of powdered Potassium Nitrate , increase oxygen in the mix to help combustion like it does with gun powder ???
Or even using a touch with an Oxidizing flame ???

Please forgive the train of thought, it's past my bed time.


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## santiago

OK,
the carbon should be red-hot when when the nitrate is added. After adding the nitrate it should burn off immediately within minutes.


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## FPZA

santiago said:


> OK,
> the carbon should be red-hot when when the nitrate is added. After adding the nitrate it should burn off immediately within minutes.


I'll try it in my furnace tomorrow.


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## solar_plasma

My last idea would be to build a turbulence chamber furnace. Then catch the gold by a electrostatic particle filter from the cooled down exhaust. Though I am no technician and have no clue how much effort this would take. If you have a regular flow of more material, you could even use the energy to vaporize water and drive some turbines or a steam machine gaining electricity for your plant. Combined heat and power units can be obtained modularly. Small machines are usually fired with gas or wood pellets in europe, the big energy providers often use coalpowder.


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## DANCER

As a pre-teen chemist, I would play with black powder. I made small cherry-bomb like explosives with xxxxxxxxxxxxxxx if not confined, it only burned very rapidly. When confined, it exploded. You might try it on a small sample. :lol:


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## NobleMetalWorks

DANCER said:


> As a pre-teen chemist, I would play with black powder. I made small cherry-bomb like explosives with xxxxxxxxxxxxx. If not confined, it only burned very rapidly. When confined, it exploded. You might try it on a small sample. :lol:



I don't think this is the proper place, nor proper forum to talk about explosives and how to make them. You might want to be careful what you suggest people try. And you might want to think twice about doing what you suggest yourself.

Scott

I agree, and have removed some of the content. We do not promote such activity on this board.

Harold


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## butcher

In Hoke's Book she speaks of recovering gold from high carbon material using litharge, the oxygen in the PbO combines with carbon forming CO2, and the lead collects the gold.


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## sota

dear FPZA I do know how to help you...my company is called Sotagold...visit our website and contact me at my privet email so I know you are real it is [email protected]
we are new in US and we have developed a technology to do exactly what you are asking


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## Palladium

Wow!


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## sota

We specialize in extracting Au from Fine Carbon of any size.
In fact the finer the better ...we use a unique ground breaking technology and able to extract 94-98% of Au from Fine Carbon at very low costs .
Our company is called Sotagold...please visit our website Sotagold.com and for more info email me at KLKNY @hotmail.com 
Thnaks


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## hnk

This is not a new problem, most mines struggle with carbon fines (and extracting Gold from it) that utilise carbon leaching. There is various ways to try and recover the gold, as mentioned above, but you can also try using a fluidized bed hearth. Its a speciality system, and not a home made plant, here is a company that does it: www.macrotec.co.za/gold-recovery

The system recovers about 95% of the Gold from the fine carbon particles at 60kg carbon per hour.


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## tassie73

Hi,

We have a similar issue with fine carbon in our plant. Not sure how you recover the gold in your CIL circuit but we collect all the fine carbon and when we have enough we run it through the elution column to recover the gold and then dispose of the carbon.

Another way you could try to recover the gold and silver is but ashing and then smelting the carbon. I have done this in small batches before. Load up a calcine oven and ash the carbon and then flux and smelt the ashed product.

Good luck, it is not easy.

Chris


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## ericrm

DANCER said:


> If it were me, I'd heat the carbon with hot caustic soda and use an electroplater at 4 volts DC. :lol:



what will happen?


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## Reno Chris

A half burned mixture of ash and carbon is harder to burn than just straight carbon. The ash will automatically limit the oxygen to the carbon by covering it. However full ashing is the first thing you must accomplish. Any carbon present will re-extract the gold if you try to dissolve it in a leach, and any carbon will float on the surface if you try to flux smelt it. 
A rotary kiln is a good idea.
We used to have a business that processed spent carbon from mines. They had a multi stage burner that rotated and stirred the carbon until it was fully 100% ashed. 
Wetting the ash would be a bad idea unless you are going to do some sort of cyanide leach or something like that. It will take a lot of effort to re-dry it if a dry product is what you want to use. 

The gold will be very tiny, so trying to extract with things like metallic mercury would be a waste of time. The business I am familiar with did what was basically a gigantic fire assay on the ash, fluxing it with lead oxide and lead, much like a fire assay, but in the form of a giant 500 pound version. They also had huge cupellation tubs to part the precious metals from the lead. Another option is that you could also do a cyanide leach to re-dissolve it, filter and then use a merril crowe process or electro-winning if you have the equipment and facility to do that - you have a fairly high silver to gold ratio.


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## Reno Chris

> when we have enough we run it through the elution column to recover the gold and then dispose of the carbon.



You know the elution process takes out the majority of the gold out but still leaves a significant amount in the carbon, right? the more times you load the carbon and then strip it, the more gold will be left behind on the carbon each time. The numbers he was mentioning at the beginning of the thread, 30 ppm gold, are consistent with carbon that has already been eluted, but no more gold will come off. Your disposed carbon probably has a similar amount of gold adhering to it.


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## sota

tassie73 said:


> Hi,
> 
> We have a similar issue with fine carbon in our plant. Not sure how you recover the gold in your CIL circuit but we collect all the fine carbon and when we have enough we run it through the elution column to recover the gold and then dispose of the carbon.
> 
> Another way you could try to recover the gold and silver is but ashing and then smelting the carbon. I have done this in small batches before. Load up a calcine oven and ash the carbon and then flux and smelt the ashed product.
> 
> Good luck, it is not easy.
> 
> Chris


dear Tassie our company Sotagold specializes in extracting gold from VERY fine carbon and I believe we can help we are in US...email me at [email protected] if you interested
thanks


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## [email protected]

That's similar to performing electrowing (desorption process of activated carbon), but with more voltage would also be a bit expensive, will depend on how much content metal has coal, for that would have to be heated to over 90 ° C, which desorption is when it starts and then pass by electrowinning (energy consumption, amperage ratings above 1,000), plus the fine coal could swim on the solution and not desorbed well. I say from my experience, since I work long ago in Plants ADR (adsorption-desorption-reactivation of activated carbon), and have that problem of generation of fine coal, and I'm looking for a process that is me profitable to recover the gold is within the coal, although much of the fine coal recovery in the DSM and filter presses.


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## [email protected]

It would be good idea pelletizing fine coal with a binder and sodium or potassium nitrate, then take them to the retort furnace, and then cast in a conventional oven.


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## sparks424

tassie73 said:


> Hi,
> 
> We have a similar issue with fine carbon in our plant. Not sure how you recover the gold in your CIL circuit but we collect all the fine carbon and when we have enough we run it through the elution column to recover the gold and then dispose of the carbon.
> 
> Another way you could try to recover the gold and silver is but ashing and then smelting the carbon. I have done this in small batches before. Load up a calcine oven and ash the carbon and then flux and smelt the ashed product.
> 
> Good luck, it is not easy.
> 
> Chris



but which system do you use to collect those fine carbons from your CIL tank


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## sohwohn

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.


This is genius! I'll definitely try this out soon..!


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## sohwohn

butcher said:


> In Hoke's Book she speaks of recovering gold from high carbon material using litharge, the oxygen in the PbO combines with carbon forming CO2, and the lead collects the gold.


Wow! So PbO is reduced to Pb? Do I get a metal (Pb-alloy) bead from the ashes?


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## PeterM

Sir, your carbon could become soluable with Piranha Solution. 


Use caution it's aggressive on dissolving carbon. 

Good Luck


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## butcher

PeterM,
I have removed the links to the video, the risk to your safety could cost more than gold.

I do not trust luck with safety.


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## baltyboweni

Why don't you just burn and add aqua-regia?


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