Leach process for large quantity of black sands

[goldshark]

Does any body know of a good leaching process for a 5 ton a day operation? Cyanide is very difficult to permit. The sands are predominantly magnetite, but still contain about an ounce per ton in unrecoverable ( by tabling) Au. I haven't done an ICP to see what all contains. This would be processing from multiple areas, on a 5 ton per day basis. Any thoughts would be appreciated, TIA.

 

[orvi]

It would be helpful if you will know if the gold is in the matrix of the black sands (locked in minerals or so), or it is just so small to be tabled/panned efficiently. If it is just a too small mili-gold, I would suggest that flotation unit might be of great help, if tuned right. 5 ton a day require vast quantity of chemicals, and if it wouldn´t be cyanide, then it start to be expensive. With nicely tuned sieve (for smallest fraction) and one/two flotation vat, I think you will be able to do this at good recovery rate.
If it is locked, you will either need to destroy the matrix or dissolve it, which will require additional milling and chemicals. Oz per ton is very nice number tho. Allow to process also by more expensive processes.

 

[kurtak]

goldshark - I am no expert in this field - however I have a friend that ran a fair size placer operation & one night (over a few glasses of whiskey) talked about black sands

From our whiskey clouded talk a couple things I remember

It would be helpful if you will know if the gold is in the matrix of the black sands (locked in minerals or so)

milling the black sands to much finer mesh freed up more gold - by a lot

I would suggest that flotation unit might be of great help

& if I remember right flotation used for ultra fine recovery

I will try to get with him & pick his brain more - may take a few days

Kurt

 

[goldshark]

Thanks all. I grabbed a core out of the tote to have an independent lab give an umpire assay . I viewed the sample under a microscope. It is hard to quantify the distribution, but what I saw was a quantity of fine Au particles, and pyrite. From a previous sample of panned pyrites from this area, I have received assays of 16 ozs. per ton. I will have assays performed on various particle sizes to see where the greater values may be found. All for now, until the assays come back.

 

[Ultrax]

Does any body know of a good leaching process for a 5 ton a day operation? Cyanide is very difficult to permit. The sands are predominantly magnetite, but still contain about an ounce per ton in unrecoverable ( by tabling) Au. I haven't done an ICP to see what all contains. This would be processing from multiple areas, on a 5 ton per day basis. Any thoughts would be appreciated, TIA.

We are taking gold from limonite and magnetite crusts using thiosulfate-ammonium leaching. This is expensive but the most effective method after cyanidation. Unfortunately, acidic ways are not applicable for magnetite. Of course, if you have a technologist who can develop the technology of gold precipitation on anion resins. It's a VERY complex problem. For more than a year we strive to get at least 65%. As the German miners say: Gold wears an iron hat

 

[Alondro]

It's possible if you roast magnetite it will convert into a form that is soluble in HCl. I have a small sample of black sands with gold in them, and I'll be testing that method once I've constructed a simple tube kiln.

 

[orvi]

It's possible if you roast magnetite it will convert into a form that is soluble in HCl. I have a small sample of black sands with gold in them, and I'll be testing that method once I've constructed a simple tube kiln.

5 tons a day dissolving magnetite... From process point of view... I think this way is not very efficient one.
Smelting would also be tough due to iron.

From what I know from my experience, gold isn't locked up in magnetite (at least I never experienced this). So maybe magnetic separation (cheap) could remove some unnecessary mass, high-grading the cons.
Then, also less leachant would be necessary.

Maybe some "hidden" cyanide based leach like EcoGoldex would be applicable - not cheap, not very elegant in some ways but maybe under your legislation, it isn't classified as cyanide

 

[Alondro]

5 tons a day dissolving magnetite... From process point of view... I think this way is not very efficient one.
Smelting would also be tough due to iron.

From what I know from my experience, gold isn't locked up in magnetite (at least I never experienced this). So maybe magnetic separation (cheap) could remove some unnecessary mass, high-grading the cons.
Then, also less leachant would be necessary.

Maybe some "hidden" cyanide based leach like EcoGoldex would be applicable - not cheap, not very elegant in some ways but maybe under your legislation, it isn't classified as cyanide

Maybe very fine milling, down to a powder, would release the tiny gold particles. Smelting with lead as a collector, then cupelling, is also possible. Since it's magnetite, there's not going to be much in the way of sulfides to produce the dreaded matte.

 

[stoneware]

Maybe very fine milling, down to a powder, would release the tiny gold particles. Smelting with lead as a collector, then cupelling, is also possible. Since it's magnetite, there's not going to be much in the way of sulfides to produce the dreaded matte.

Clarkson Rod Mill.

 

[Ultrax]

5 tons a day dissolving magnetite... From process point of view... I think this way is not very efficient one.
Smelting would also be tough due to iron.

From what I know from my experience, gold isn't locked up in magnetite (at least I never experienced this). So maybe magnetic separation (cheap) could remove some unnecessary mass, high-grading the cons.
Then, also less leachant would be necessary.

Maybe some "hidden" cyanide based leach like EcoGoldex would be applicable - not cheap, not very elegant in some ways but maybe under your legislation, it isn't classified as cyanide

EcoGoldex is exactly sodium cyanide (based on XRF analysis) in a shell of organic compounds for transportation. There are no miracles in our business

It is possible to melt magnetite into iron-sodium slag and use lead as a collector in arc ore-thermal furnaces. It is profitable if you have your own electric power plant

 

[stoneware]

 

[goldshark]

It's possible if you roast magnetite it will convert into a form that is soluble in HCl. I have a small sample of black sands with gold in them, and I'll be testing that method once I've constructed a simple tube kiln.

Since Magnetite is FeO, what does a calcining roast do to the Magnetite, if it is already an oxide? Does roasting oxidize the Magnetite further ( FeO2), or are you oxidizing some form of PM's adhered to the surface?

 

[Ultrax]

Roasting with oxidizing of iron: Fe->FeO -> Fe2O3 ->Fe3O4.
Each step of oxidation impairs solubility in acids.

Roasting with reducing of iron: Fe3O4-> Fe2O3 -> FeO ->Fe.
The reducing agent usually is a (C) carbon (as in Primitive Technology video) or hydrogen (H).

Hydrochloric acid is a very expensive way to oxidize iron oxides. Yes, it is considered the most active, but it is almost impossible to achieve complete quantitative dissolution - the excess of concentrated (!) Acid should be from 20 to 30 times. And, of course, closed cover and heating up to 100C! Boiling hydrochloric acid is a very unpleasant substance. And as I already wrote, all iron oxides will NOT dissolve anyway.

 

[stoneware]

Method for the assay and recovery of precious metals

Patent, US5238485A.

Abstract​

Complex ores of the precious metals which also contain iron spinels and similar compounds are assayed and their precious metals content is extracted by subjecting the ores or concentrates thereof together with an iron-embrittling agent to a pyrometallurgical process which reduces at least a major portion of the iron compounds to liquid metallic iron.

The liquid iron serves as a collector metal for the precious metals and, after cooling, the iron is brittle and easily comminuted and can be separated from the precious metals through use of either an electrolytic process or a selective chemical dissolution of the iron and other base metals leaving the precious metals available for analysis and recovery.

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[goldshark]

Sounds expensive. Would it be feasible on a 1 OZ/Troy per ton, with 100 tons or more available?

 

[orvi]

EcoGoldex is exactly sodium cyanide (based on XRF analysis) in a shell of organic compounds for transportation. There are no miracles in our business

It is possible to melt magnetite into iron-sodium slag and use lead as a collector in arc ore-thermal furnaces. It is profitable if you have your own electric power plant

I totally understand that EcoGoldex is only nicely suited cyanide. But if cyanide is hard to permit for him, then EcoGoldex is branded good which you can purchase and use. It says no cyanide, so you will play dumb and if it will work, use that for leaching. It has MSDS, everything, you gear yourself up with some nice PPE, build one vat for treatment of the used liquid and you are done. In the eyes of law, everything nice and green

By the way, how the cyanide is measured by XRF ? I would try Raman or IR spectroscopy first, but by what machine it can be measured ?

 

[Yggdrasil]

I think they usually use AAS or similar to measure the leach.

 

[orvi]

Method for the assay and recovery of precious metals

Patent, US5238485A.

Abstract​

Complex ores of the precious metals which also contain iron spinels and similar compounds are assayed and their precious metals content is extracted by subjecting the ores or concentrates thereof together with an iron-embrittling agent to a pyrometallurgical process which reduces at least a major portion of the iron compounds to liquid metallic iron.

The liquid iron serves as a collector metal for the precious metals and, after cooling, the iron is brittle and easily comminuted and can be separated from the precious metals through use of either an electrolytic process or a selective chemical dissolution of the iron and other base metals leaving the precious metals available for analysis and recovery.

​

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Say we make optimistic 1,5 ton of iron metal from that 5 tons cons... Electrolyse this ammount in a single day would require extreme ammount of electricity. Dissolving 1500 kg of Fe in a day... How ? With what ? What would we do with all that waste ? :/ Assuming 4L of HCL for one kg of iron, that is insane ammount of acid. 6000L for just the dissolution of Fe... Then energy for melting it down, waste treatment wouldnt be cheap also... And then you get 1800USD for the gold. I think this dissolving route is dead end.

 

[orvi]

I think they usually use AAS or similar to measure the leach.

My point is how we determine CN- anion in the powder or solution via XRF. We all know very well that anything below Mg is hard to measure by XRF due to small atomic radius. C and N are way off from the magnesium, much lighter. I am just intrigued how they measured it. Powder diffraction ? Does CN- have specific pattern on powder XRF reading ?

Also, if it is encapsuled CN- with organic additives, how you distinguish carbon from that encapsulation from CN- carbon.

Guys from one mining company tested the EcoGoldex in certified lab by certified methods for CN- detection, but they found no free CN- in the solution. That is why I am intrigued about Ultrax method to prove/disprove free cyanide in EG.

 

[Yggdrasil]

My point is how we determine CN- anion in the powder or solution via XRF. We all know very well that anything below Mg is hard to measure by XRF due to small atomic radius. C and N are way off from the magnesium, much lighter. I am just intrigued how they measured it. Powder diffraction ? Does CN- have specific pattern on powder XRF reading ?

Also, if it is encapsuled CN- with organic additives, how you distinguish carbon from that encapsulation from CN- carbon.

Guys from one mining company tested the EcoGoldex in certified lab by certified methods for CN- detection, but they found no free CN- in the solution. That is why I am intrigued about Ultrax method to prove/disprove free cyanide in EG.

Aah, I see.