Ran an alternative -cyanide leach experiment.

[SaltwaterServr]

Most folks know that when it comes to free-mill gold, you'll get between 35% and 60% of the gravity recoverable fraction with the remainder only available via chemical leaching. Even with mercury, you won't grab the remainder. The options for gold leaching at a commercial level have historically been HCl leaching with a few other alternatives until cyanide came onto the playing field in the late 1800's.

Due to it's toxicity in water it's almost impossible for small scale miners to be able to purchase NaCN or KCN for processing. We're then left with few alternatives that are commercially available.

Eco-Goldex is one commercially available product that is based on potassium ferricyanide. I compared it with a leach of pure potassium ferricyanide and potassium ferrocyanide.

All solutions have 0.2% of their respective compounds, 1.506 grams of gold with no more than .5 grams of picker sized gold per flask. pH is a little high to start, 12.01, but in my experience that would settle down a bit to the mid 11 range. Testing for the rate of cyanogen activity as well as loading capacity of each solution. In layman's terms I was looking for which solution dissolves the gold the fastest and which one will hold the most gold after 72 hours. (turned into 96 hours) You'll be able to tell which one has the most gold in solution by the amount of gold not dissolved in each flash at the end of the experiment period.

Also tracking reagent consumption of the NaOH for each solution, although on the scale most of us will be doing this, that cost is minimal.



End of day 1:



End of day 2:



End of Day 3:



and the resulting remaining gold from each at the end of day 4. O is ferrocyanide, I is ferri, E is eco-goldex. Note the iron left behind in the Goldex. BTW, all gold is from the same spot on one hill in Arizona.




Results of the trial

Remaining gold from the starting point of 1.506 grams per flask:

Ferrocyanide: 1.440 grams
Eco-goldex: 1.389 grams
Ferricyanide: 1.371 grams

Ferrocyanide ate the most sodium hydroxide by far, which is expected as it forms hydroferrocyanic acid in solution.

Now the economics. Ferro and ferri were both reagent grade chemicals, but it's hard to get your hands on lower grade stuff.

Ferro is $42.20 per kilogram with free shipping from amazon through Prime.

https://www.amazon.com/gp/product/B00DYO7VT2/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1

Ferricyanide is much more expensive. I paid $39.84 with shipping (not prime eligible) for only 500 grams. Equivalent price is then about $79, depending on shipping. If you go buy it at the manufacturer's website you can get it for $57.08 per kilo with a 2.5 kg purchase and standard shipping.

https://www.amazon.com/gp/product/B01N1WLBDB/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

and straight from the source:

https://www.sciencecompany.com/NSearch.aspx?keywords=potassium+ferricyanide

Eco-Goldex blows them both away. I bought 25kg of the stuff, and with shipping it came out to $11.00 per kg. Shipping was $50.00 including customs and all that from Canada.

Eco-Goldex's active ingredient is ferricyanide, but they've already processed it and powdered it. The difference is it is coming from China. It's damn hard to beat the economics of it.

Next step, going to pick up some gold foil and run some more tests on Eco-goldex with four different retention times 24 hours, 48, 72 and 96. It'll be sometime next week before I start that.

 

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[The1rod]

Cool experiment, I have been curious about leaching. So did you get the chemicals in a powder form and have to mix them to make the solution in the beakers? If so how much of the chemical did it take to make the 2000ml of solution?

 

[SaltwaterServr]

Cool experiment, I have been curious about leaching. So did you get the chemicals in a powder form and have to mix them to make the solution in the beakers? If so how much of the chemical did it take to make the 2000ml of solution?

For this trial, all were run at 0.2% in 2000ml of solution. Each flask therefore had 4 grams of the respective compounds. These were not stoichiometrically balanced for available -CN, I went with straight weight of each.

 

[Clay Diggins]

You can get the ferri a lot cheaper from a photographic supply company. About $25 a pound in small lots or 1/4 that in 40 pound kegs from Hunt. If you need to do volume one ton will approach $4,000 - $5,000 + shipping with a minimum order a a few tons.

You can recover the ferri and reuse it. It keeps the chemical expense way down. It's really easy to pull the metals out with electro rather than precipitation even zinc can provide the enerygy if you don't have on site power. A little bit of ferri can be a big help late in the flotation process too.

Generally you need to introduce a halogen like bromine, iodine or chlorine in addition to the ferri to get the time down. Even with that I don't see any way primary ferri processing of ore is going to be economical in the long run. Halogens are expensive and the fumes are nearly as bad as cyanide. Do you know of any profitable primary ferri ore processing operations?

Heavy Pans

 

[Nitric]

I'm really dumb to this subject and want to know it. I wish I had the brains that some of you have!!

I don't want to sound stupid but here it goes!! Is what your doing the same idea as Aqua Regia? Could I throw gold and other metals in a solution of this and it would work the same way? Dropping(?) the metals out one by one. Or is this specific to what your doing with rock....

 

[brianc053]

I'm really dumb to this subject and want to know it. I wish I had the brains that some of you have!!

I don't want to sound stupid but here it goes!! Is what your doing the same idea as Aqua Regia? Could I throw gold and other metals in a solution of this and it would work the same way? Dropping(?) the metals out one by one. Or is this specific to what your doing with rock....

Nitric, don't feel dumb - I have a degree in Physics and I still don't understand what's being discussed. At all. (I didn't like Chemistry though...)
- Brian

 

[Mad Machinist]

You can get the ferri a lot cheaper from a photographic supply company. About $25 a pound in small lots or 1/4 that in 40 pound kegs from Hunt. If you need to do volume one ton will approach $4,000 - $5,000 + shipping with a minimum order a a few tons.

You can recover the ferri and reuse it. It keeps the chemical expense way down. It's really easy to pull the metals out with electro rather than precipitation even zinc can provide the enerygy if you don't have on site power. A little bit of ferri can be a big help late in the flotation process too.

Generally you need to introduce a halogen like bromine, iodine or chlorine in addition to the ferri to get the time down. Even with that I don't see any way primary ferri processing of ore is going to be economical in the long run. Halogens are expensive and the fumes are nearly as bad as cyanide. Do you know of any profitable primary ferri ore processing operations?

Heavy Pans

Easy now. We are spending money trying to find a way for the small scale guy to get the most out of a ton of ore.

 

[SaltwaterServr]

You can get the ferri a lot cheaper from a photographic supply company. About $25 a pound in small lots or 1/4 that in 40 pound kegs from Hunt. If you need to do volume one ton will approach $4,000 - $5,000 + shipping with a minimum order a a few tons.

You can recover the ferri and reuse it. It keeps the chemical expense way down. It's really easy to pull the metals out with electro rather than precipitation even zinc can provide the enerygy if you don't have on site power. A little bit of ferri can be a big help late in the flotation process too.

Generally you need to introduce a halogen like bromine, iodine or chlorine in addition to the ferri to get the time down. Even with that I don't see any way primary ferri processing of ore is going to be economical in the long run. Halogens are expensive and the fumes are nearly as bad as cyanide. Do you know of any profitable primary ferri ore processing operations?

Heavy Pans

At $25 a pound with shipping you're at $63.91 per kilo from the site link you provided, which is less than the Amazon.com source but more than the manufacturer's source. I wasn't able to find any company by the name of Hunt that provides ferricyanide, but I only searched few different key words. The Hunt chemical company seems to have been bought out by Fuji, and they don't offer it at all unless their search option doesn't like prussian blue or potassium ferricyanide as the inquiries.

Regardless, Eco-goldex is a ferricyanide leach, as I mentioned. If you were doing bulk processing, you could always buy it through Alibaba, do the same blend that Goldex does, and probably come out cheaper. IIRC, there's already a knock off company supplying the same thing for less than Goldex, but then you're having to do all your own shipping from China.

Either way, the solution is reusable once you determine the amount of cyanogen still available after filtration and gold recovery.

Playing devil's advocate, let's say expected maximum recovery per 4 grams in 0.2% solution is only .1 gram of gold and you couldn't use any of that solution again. For a kilogram of Eco-Goldex, which costs $11.00, you'd be getting 26.5 grams recovered that you couldn't otherwise. That's $1105.00 in gold for $11.00 cyanide cost. Of course you have other costs associated but you're very much playing on the correct side of the ledger.

If you went with Goldex purchased at a metric tonne your cost is around $3-$4 for that same $1105.00 recovered.

Now if you went to straight potassium ferricyanide at the really expensive price I paid from Amazon.com, you're up to 33.75 grams recovery per kilogram of ferri. $1293.00 of gold for let's say $85.00 from Amazon. Again, very much on the good side of the ledger.

This is of course being applied to the fraction of gold in your ore that cannot be recovered by gravity methods. Mercury is out the door and international trade in it is supposedly suspended into the US come 2020. There's little chance any of us have the operational size and capex funds for a traditional cyanide leach operation. Right now, this is pretty much it.

 

[SaltwaterServr]

I'm really dumb to this subject and want to know it. I wish I had the brains that some of you have!!

I don't want to sound stupid but here it goes!! Is what your doing the same idea as Aqua Regia? Could I throw gold and other metals in a solution of this and it would work the same way? Dropping(?) the metals out one by one. Or is this specific to what your doing with rock....

No, AR is a completely different monster in it's selective nature. AR is performing surgery with a laser scalpel, cyanide is performing it with a chainsaw. Cyanide can be slightly tailored by adding say ammonia to suppress copper, but it's not selective at all in a general sense. You can part out certain metals selectively, but I'm more concerned for the use on concentrates of ore after the gravity recoverable fraction has been removed.

 

[Nitric]

No, AR is a completely different monster in it's selective nature. AR is performing surgery with a laser scalpel, cyanide is performing it with a chainsaw. Cyanide can be slightly tailored by adding say ammonia to suppress copper, but it's not selective at all in a general sense. You can part out certain metals selectively, but I'm more concerned for the use on concentrates of ore after the gravity recoverable fraction has been removed.

So this is grabbing and holding the microscopic, not "melting" or disolving?

I won't ask a ton more questions... I'll just keep following the thread and look some up of terms used, I'll have to start crash coursing. I really want to know this kind of stuff.

 

[SaltwaterServr]

So this is grabbing and holding the microscopic, not "melting" or disolving?

I won't ask a ton more questions... I'll just keep following the thread and look some up of terms used, I'll have to start crash coursing. I really want to know this kind of stuff.

Not melting, but dissolving, yes. The cyanogen CN(-) will disassociate from the parent compound. The mechanisms of which are somewhat important as UV-A light is necessary to split CN- from potassium ferricyanide K3[Fe(CN)6] or ferro K4[Fe(CN)6] to form the active radical.

The cyanogen will attack an atom of gold and form one of two cyanide gold complexes; either Au(I) cyanide complex: Au(CN)2- or it forms the Au(III) cyanide complex: Au(CN)4-. Au(I) is much more stable of the two.

For research, a starting point is here with the 100 year old plus Cyanide Handbook:

https://archive.org/details/cyanidehandbook00clenrich/page/n5

and then here:

https://www.amazon.com/Chemistry-Gold-Extraction-Second/dp/0873352408

 

[Nitric]

Not melting, but dissolving, yes. The cyanogen CN(-) will disassociate from the parent compound. The mechanisms of which are somewhat important as UV-A light is necessary to split CN- from potassium ferricyanide K3[Fe(CN)6] or ferro K4[Fe(CN)6] to form the active radical.

The cyanogen will attack an atom of gold and form one of two cyanide gold complexes; either Au(I) cyanide complex: Au(CN)2- or it forms the Au(III) cyanide complex: Au(CN)4-. Au(I) is much more stable of the two.

For research, a starting point is here with the 100 year old plus Cyanide Handbook:

https://archive.org/details/cyanidehandbook00clenrich/page/n5

and then here:

https://www.amazon.com/Chemistry-Gold-Extraction-Second/dp/0873352408

Ya..I'll have to start with the links. You are wayyyyyyyyy over my head!

Thank you!!! For taking the time to explain and give links. I'll check those out.
Thanks again!!!

 

[SaltwaterServr]

Ya..I'll have to start with the links. You are wayyyyyyyyy over my head!

Thank you!!! For taking the time to explain and give links. I'll check those out.
Thanks again!!!

No problem.

Here's another that's helpful.

https://babel.hathitrust.org/cgi/pt?id=mdp.39015004540335;view=1up;seq=8

 

[Clay Diggins]

Ya..I'll have to start with the links. You are wayyyyyyyyy over my head!

Thank you!!! For taking the time to explain and give links. I'll check those out.
Thanks again!!!

Try this link for an introduction to ferricyanide uses. 911 metallurgist is a great site for processing information. You will notice ferricyanide is only used as a auxillary to metal extraction. That's why I asked about mining operations that were using ferricyanide as a primary leach, I don't think it's ever been profitable by itself. It's slow and light sensitive.

Ferricyanide is produced by heating melted iron and cyanide together. A dangerous business as you can imagine. The commercial leach premixes contain more inexpensive sodium hydroxide (lye) than they do ferricyanide which is why they are so much less expensive by weight. Buying ferricyanide and adding the required lye is cheaper and more flexible than the premix but it does take some time and knowledge.

Adding a halogen to the ferricyanide/lye mix speeds things up a lot but it costs more and is a lot less environmentally friendly. Typically bromine is the main halogen leach agent when using ferricyanide but bromine costs more than the ferricyanide in the solution.

Heavy Pans

 

[Nitric]

Try this link for an introduction to ferricyanide uses. 911 metallurgist is a great site for processing information. You will notice ferricyanide is only used as a auxillary to metal extraction. That's why I asked about mining operations that were using ferricyanide as a primary leach, I don't think it's ever been profitable by itself. It's slow and light sensitive.

Ferricyanide is produced by heating melted iron and cyanide together. A dangerous business as you can imagine. The commercial leach premixes contain more inexpensive sodium hydroxide (lye) than they do ferricyanide which is why they are so much less expensive by weight. Buying ferricyanide and adding the required lye is cheaper and more flexible than the premix but it does take some time and knowledge.

Adding a halogen to the ferricyanide/lye mix speeds things up a lot but it costs more and is a lot less environmentally friendly. Typically bromine is the main halogen leach agent when using ferricyanide but bromine costs more than the ferricyanide in the solution.

Heavy Pans

Thank you!!

I have very little chemistry. One thing that I do know is that Cyanide scares me. Lack of knowledge might be the fear. I've been exposed, and burnt every way possible by fuming nitric(think fuming was the term for over 67(?), can't remember) from testing metals. We used the good stuff! Not the diluted down stuff you get in some of the test kits. But Cyanide is something I was told you don't get the same chances and I've never used it for anything.

Anyhow, I'll keep following along in the thread and read the links!!

Thanks again!!!

added...I tried to look "fuming" up. I have no idea where I came up with that. I thought it was 60 something and higher percentage. I guess that's a term used in fuel. So, never mind me......

 

[SaltwaterServr]

Try this link for an introduction to ferricyanide uses. 911 metallurgist is a great site for processing information. You will notice ferricyanide is only used as a auxillary to metal extraction. That's why I asked about mining operations that were using ferricyanide as a primary leach, I don't think it's ever been profitable by itself. It's slow and light sensitive.

Ferricyanide is produced by heating melted iron and cyanide together. A dangerous business as you can imagine. The commercial leach premixes contain more inexpensive sodium hydroxide (lye) than they do ferricyanide which is why they are so much less expensive by weight. Buying ferricyanide and adding the required lye is cheaper and more flexible than the premix but it does take some time and knowledge.

Adding a halogen to the ferricyanide/lye mix speeds things up a lot but it costs more and is a lot less environmentally friendly. Typically bromine is the main halogen leach agent when using ferricyanide but bromine costs more than the ferricyanide in the solution.

Heavy Pans

It is light sensitive, but ferricyanide has been used to speed up KCN and NaCN leaches.

Bottomline, extrapolating from my trial you can get 26.5 grams of gold into solution for $11.00 in goldex costs. That's incredibly promising since that's working on gold that's not recoverable by gravity methods.

How that compares to large operations running 50 tons per hour using traditional cyanide is irrelevant, we as small miners have no other alternatives.

I wouldn't put too much into trying to figure out how much of any given compound is in goldex. One MSDS shows only 10% ferricyanide and 10% of NaO while these are also out there which could be for one of their other formulations:

NaOH ---------------------------------5-10
CO(NH2)3 = Urea--------------------15-30
NaCO3---------------------------------5-10
CaO------------------------------------20
K3Fe(CN)6.10H2O--------------------5-30
Na2SO4--------------------------------2-10
NaBr------------------------------------5-10

and this one too

NaO 30%
CO(NH2)2 20%
CaO 20%
K3Fe(CN)6 15%
Na2S04 10%
Pb304 < 2%
C6H507Na < 3%

Could you make your own cake mix with those as a starting point? Yeah.

Should you? ABSOLUTELY NOT!

Easier to just buy it rather than having to mix and then blend it.

 

[SaltwaterServr]

Deano over on GRF is providing guidance on refining this very rough experiment. Waiting for my titration equipment to come in, as well as the chemicals necessary for the titration itself. Then I can set up the next set of trials to get a much better read on leach times and consumption rates as related to each reagent and various concentrations of each.

 

[pczim]

Great and interesting post. I’m not sure though you can beat cyanide at $3 per kg.

Thank you for posting.

 

[SaltwaterServr]

Great and interesting post. I’m not sure though you can beat cyanide at $3 per kg.

Thank you for posting.

Precisely why it's used as extensively as it is, but its damned tough to get a permit for it in the US.

Considering the potential gold loading rates within the alternative cyanide types as well as recycling the leachate, the economics are screaming for further investigation.

 

[Clay Diggins]

Cyanide is always "recycled" in commercial mining operations. The systems for recovering cyanide are part of the normal process stream for mineral leaching. REDOX - it works both ways, nobody in mining is throwing their chemicals out.

There is no such thing as a "permit" to buy cyanide, you can buy cyanide on the open market in the United States without a permit. The problem you are running into has to do with the companies that sell cyanide. They will only sell to known companies with an established need for cyanide. That's because people use cyanide to kill other people. Chemical companies oddly don't like being associated with enabling murder. Go figure.

If you can show what your use for cyanide is those companies will ship you whatever you need for your project - no permit needed.

Potassium or sodium cyanide is way cheaper, faster, more effective and just as "recyclable" as potassium ferricyanide. I suspect that's why there are no mines of any size using potassium ferricyanide as a primary leach.

I wish you luck on your project. It can be fun to experiment with chemicals. Mining companies try different formulas and processes constantly in an effort to get better recovery and lower their OPEX (economics). I suspect whatever result you obtain will already be well known within the mining industry.

Heavy Pans