Hydrometallurgy: Leaching in Heap, Vat, CIL, CIP, Merrill–Crowe, SX Solvent Extraction

Hydrometallurgy: Leaching in Heap, Vat, CIL, CIP, Merrill–Crowe, SX Solvent Extraction

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Acetonitrile leaching of ore (3 replies and 1 comment)

A
Adrian Hall
7 years ago
Adrian Hall 7 years ago

Hi everyone,

I have 200 tonnes of ore that is preg robbing.  The free gold is approx 30% and the preg robbed gold approx 60%.  The remaining 10% is slow leaching preg robbed and locked in either sulphides or silicates.

I had diagnostic leaching testing to confirm the above.  

This ore was cleaned up from a mill where it is suspected activated carbon from the CIP circuit was milled by the ball mill.  So the activated carbon has the same size distribution as the ore.

I tried roasting at 450 degrees C with sodium nitrate as an oxidising agent, however this resulted in only 30% recovery, the same as the free milling component.

Before trying more aggressive roasting conditions, I wondered if it is possible to leach the ore with acetonitrile on a large scale of the lab version.

Has anybody here had any experience with acetonitrile?

Can I use an acetonitile leach after a cyanide leach?

And is there any reason I couldn't heap leach the ore with cyanide first, followed by acetonitrile?

Thanks in advance 

Adrian

Y
Yves
7 years ago
Yves 7 years ago

Hi Adrian,

acetonitrile is a good carbon gold stripper and may well strip the gold on your prerg robbing material but the chemical is expensive and toxic. Why don't you try grind your material finer and then agitate in CIL configuration with activated carbon. Activated carbon has usually a higher gold equilibrium than the natural carbonaceous  preg robbers. Many plants are using this way successfully.

Regards,

 

Yves 

R
Richard S
7 years ago
Richard S 7 years ago
1 like by David

Another possible solution is to try leaching in thiosulfate.  The complex will not absorb onto carbon.  You will need to leach a little longer than cyanide perhaps, however it can be very effective.  You can precipitate leach solution with ven met (stabilized borohydride).  It should be pretty easy to run a bottle roll test to confirm results.  Do not run higher than 45C or it will affect the thiosulfate solution.  This will not leach the 10% of the gold locked in silica or sulfides.  Considering your small tonnage of material, there is not a likely good economic solution to oxidized or grind this material fine enough.

A
Adrian Hall
7 years ago

Hi Richard,

This material came from cleanup from a mill. The grade is coming from loaded carbon. The oxide ore was probably a few g/t. However this goes 60 g/t. Several prospectors have tried to leach this in the past. So the gold is already preg robbed.

Do you think thiosulfate can leach the gold from the carbon?

I dismissed thiosulfate leaching as I thought it may leach the free gold, but not the preg robbed gold.

A
Adrian Hall
7 years ago
Adrian Hall 7 years ago

Hi Yves,

It doesn't contain natural carbonaceous preg robbers. The preg robbing is due to activated carbon.  However this has been through the mill, the carbon is ground.  The grade of the ore is 60 g/t, so I guess it was loaded carbon that contaminated this ore.

I only have one 200 tonne batch to treat.  I read in the Micron elution technique that acetonitrile was more effective at stripping loaded carbon than methanol.  In the Micron technique, the carbon was presoaked with 5% NaCN.  Then elution with 40% w/v methanol.  

However, I don't want to try to use a column as in the Micron method. I have a predominately oxide ore with a P80 less than 1mm.

I was thinking of a heap leach type scenario.  Irrigate first with 5% NaCN, followed by 40% w/v acetonitrile.  The irrigation rate would be very slow as the percolation rate of this material will be quite low.  I would load the gold from step one onto carbon.  For the second step, I was thinking of boiling of the acetonitrile, then direct electrowinning the remaining solution.

I haven't tried to seperate the carbon from the oxide ore yet.   Maybe flotation with diesel could work.

 

 


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