Merrill crowe help

[SKH]

For all the old wise men out there. I've been struggling with an ore that is a mix of pyrite and powder gold/silver. It's been tested by two labs. SGS used FAA303 to test a shaker table concentrate for me and got 23g/t gold and almost 4 times more silver.
Then had ALS metallurgy did a bottle roll test just on the pulverized 250 mesh ore and got 3.5 g/t gold and 14 g/t silver.
My problem, I cannot get that out.
Don't know what I'm screwing up.
Took 6kg (13.2lbs) ran it for 24 hrs in the tested leach and used the merrill crowe system to recover.
Filtered with D/E until crystal clear. Then vacuum to 28 inch Hg and no air bubbles visible. Calculate gold quantity and mix 4x zinc plus 0.2x lead nitrate with new leach fluid and mix in under vacuum. Only getting less than half the amount metals as tested.
Please help!!!

 

[4metals]

Have you tested the solution after the zinc recovery that yielded half of your expected recovery? Is the missing Gold and Silver still in solution or still in the ore?

 

[Deano]

Basic metallurgy is to perform your leach and after 24 hours filter the liquor and assay the grade of the filtrate by ICP or AAS. From these numbers you can calculate the leachable grade of your ore.
If you now carry out a zinc recovery from the rest of the filtered liquor and filter out the zinc you can do an analysis of the supposedly barren residual liquor.
If you get gold values in the liquor at this stage you generally have one of two possibilities occurring.
The first is that you have miscalculated the zinc addition level or are using ultra-fine zinc powder which is blocking the solution access to the zinc after a short period.
The second is that you are not using straight cyanide for leaching but are either using a propriety formulation from China or you are adding an oxidiser such as a peroxide which is not affected by your de-airation process.
Doing the above steps will give you the information needed to sort out your problem.
Deano


edited to fix a typo.

 

[zacchy]

You should know that pyrite must be toasted with heat, to release SO2, the iron in pyrite is also cyanicidal, so you must add extra sodium cyanide. But when the laboratory gives you the result, it must tell you the technique they used, to be able to compare results.

 

[SKH]

Basic metallurgy is to perform your leach and after 24 hours filter the liquor and assay the grade of the filtrate by ICP or AAS. From these numbers you can calculate the leachable grade of your ore.
If you now carry out a zinc recovery from the rest of the filtered liquor and filter out the zinc you can do an analysis of the supposedly barren residual liquor.
If you get gold values in the liquor at this stage you generally have one of two possibilities occurring.
The first is that you have miscalculated the zinc addition level or are using ultra-fine zinc powder which is blocking the solution access to the zinc after a short period.
The second is that you are not using straight cyanide for leaching but are either using a propriety formulation from China or you are adding an oxidiser such as a peroxide which is not affected by your de-airation process.
Doing the above steps will give you the information needed to sort out your problem.
Deano


edited to fix a typo.

Hi Deano
Really appreciate your reply.
I am using fine zinc powder but also the Chinese product to leach.
ALS Global has tested ore with both cyanide and Chinese product.
Cyanide gives me a 98% Au recovery but very difficult to get here and the Chinese product 96% Au recovery but very easy to get here. Both over a lab eight hour leach time.
Spoke to Chinese supplier and he said exactly the same as cyanide to recover. Is that correct from your knowledge.

 

[SKH]

You should know that pyrite must be toasted with heat, to release SO2, the iron in pyrite is also cyanicidal, so you must add extra sodium cyanide. But when the laboratory gives you the result, it must tell you the technique they used, to be able to compare results.

Hi Zacchy
Lab only tested sample liquid with AAS to determine grade but no recovery from liquid. Also not using cyanide due to being to difficult to get here. Lab tested without roasting due to very fine free gold available. It's the recovery that's getting me to struggle.

 

[SKH]

Have you tested the solution after the zinc recovery that yielded half of your expected recovery? Is the missing Gold and Silver still in solution or still in the ore?

Thanks for your reply.
I have not tested it yet. I'm not using cyanide but a Chinese product to leach. Trying to establish method for testing of the liquid.

 

[Deano]

If you are using a Chinese product to leach with you are getting not only gold into solution but a wide range of base metals.
Most of these base metals are more chemically reactive than gold and will flood your recovery system with low value product rather than the target metals.
The easiest way to test for gold is to run your leach liquor through AAS, it will cost you to do this through a lab but it will be cheaper than alternative methods. You will probably have trouble with ICP analysis due to the high level of base metals dissolved in the leach liquor, high dilution levels usually result in suspect results.
There are several threads on why not to use Chinese leaching agents, read them and then try using the recommended ferro/ferri cyanide leaches. Read your local MSDS literature on them to assure yourself that they are not on a list of prohibited chemicals.
These are what do the leaching in the Chinese leaches but do not have the metallurgical garbage associated with the Chinese formulations.
Most Chinese leaches also have oxidisers in them, de-aeration will not get rid of them.
These Chinese leaches will also cause major problems with activated carbon processing, gold uptake is crowded out by base metals and stripping is problematic.
Deano

 

[goldshark]

Merrill Crowe process uses Zinc shavings.

 

[SKH]

If you are using a Chinese product to leach with you are getting not only gold into solution but a wide range of base metals.
Most of these base metals are more chemically reactive than gold and will flood your recovery system with low value product rather than the target metals.
The easiest way to test for gold is to run your leach liquor through AAS, it will cost you to do this through a lab but it will be cheaper than alternative methods. You will probably have trouble with ICP analysis due to the high level of base metals dissolved in the leach liquor, high dilution levels usually result in suspect results.
There are several threads on why not to use Chinese leaching agents, read them and then try using the recommended ferro/ferri cyanide leaches. Read your local MSDS literature on them to assure yourself that they are not on a list of prohibited chemicals.
These are what do the leaching in the Chinese leaches but do not have the metallurgical garbage associated with the Chinese formulations.
Most Chinese leaches also have oxidisers in them, de-aeration will not get rid of them.
These Chinese leaches will also cause major problems with activated carbon processing, gold uptake is crowded out by base metals and stripping is problematic.
Deano

Thanks Deano
Any cyanide is just impossible to get here. I have to be state registered to buy HCL.
Will have to investigate a different leach process that can use the merrill crowe system or not. Please advice me

 

[Deano]

Check with your country's restrictions list for ferro/ferri cyanides, usually available as the potassium form.
Most countries have no restrictions on use, transport and storage of these chemicals, I expect that yours will be similar.
These chemicals are usually available through the usual chemical suppliers and require no permitting.
Deano

 

[SKH]

Check with your country's restrictions list for ferro/ferri cyanides, usually available as the potassium form.
Most countries have no restrictions on use, transport and storage of these chemicals, I expect that yours will be similar.
These chemicals are usually available through the usual chemical suppliers and require no permitting.
Deano

Thanks Deano
Will follow-up with my supplier.
That will make recovery so much easier with the Merrill Crowe system.