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Want to know more About the Efficiency of "Eco-Goldex" as an alternative to Sodium Cyanid ... (9 replies and 4 comments)
All of the Eco -Goldex type leaches have a mix of various metal leaching agents along with an alkali metal ferrocyanide.
Under the influence of UV light the ferrocyanide will dis-associate into ferric ions and cyanide ligands.
What you then have is a cyanide leach which should be run as a standard cyanide leach, pH 11 etc.
The advantage of these leach formulations is that they are classified as non -hazardous for both storage and transport.
The disadvantages are that you are buying very high priced cyanide when you factor in the % of available cyanide in the leach and that the metals solubilised by the other included leaching agents will load strongly onto carbon.
This not only minimises gold loading onto the carbon but will cause great problems at the carbon stripping stage.
If you think that you will zinc out the gold values then the oxidisers in the leach and the high metal tenors will soon convince you that this is not a winning proposition.
Basically you do not get something for nothing, you will get the advantage of sidestepping cyanide regulations but everything else is downhill.
Deano, I like the way you summed that up. The cyanide alternatives at least offer an option to small / medium scale operators that aren't permitted for cyanide purchase / use. Where I am in Costa Rica the use of cyanide is strictly prohibited but miners need / want to get away from crude amalgamation. We just bought a 25kg bag of the Goldex Os series to do some testing. We are learning.
Are you saying contact with UV light is necessary for the reaction?
Contact with UV light is necessary for the dis-association of the ferrocyanide complex. Sunlight will perform OK, best run as a premix tank specifically for the dis-association stage.
The obvious way to use this type of leaching is to just buy a straight alkali metal ferrocyanide and use that without the extra chemicals you get in the commercial formulations.
These extra chemicals are what gives you the problems.
Hmmm, the manufacturer fails to mention what seems to be a critical detail to obtain best results. i.e. "the pulp requires contact with UV light" ...suggested here as a pretreatment. I have had several conversations with the owner and developer John Guo in Canada. Also not mentioned in the written operation recommendations.
I believe the Eco-Goldex product is a ferricyanide and you suggest using a straight ferrocyanide. I'm not qualified to understand the difference but assume there is a reason.
A straight ferrocyanide may have similar restrictions as cyanide, to purchase, ship handle etc. plus in-country regulations (treated as cyanide perhaps). I wonder.
The “commercial cyanide derivative products” tend to put unwanted metals into solution and require contact with UV light. A straight ferrocyanide still requires contact with UV light but is more selective for gold. Is that correct?
The issue of unwanted metals in solution - to ash the activated carbon and then acid wash to rid the base metals helps resolve this problem? What do you suggest?
The development (or I should say marketing) of these cyanide derivatives is slightly deceiving in performance claims and being touted as an "alternative" to cyanide. But, nothing is for free as you stated. Agreed.
The big issue brewing is what governments will allow as “alternatives” once Minamata kicks in and the international sale / transport of mercury is banned. Millions of small and medium scale miners worldwide will be looking for alternatives. Lixiviation will be high on the list and the cyanide alternatives will be at the top of that list simply because they are available to the general public. A lot of people will be experimenting. We are in that group.
I appreciate your suggestions very much. Thank you.
The difference between ferrocyanide and ferricyanide is that the ferricyanide requires a much stronger source of UV to cause dis-association of the ligand.
Hence the level of UV required for dis-association of ferrocyanide is supplied by sunlight but for ferrocyanide dis-association a stronger UV source is needed.
You will get some dis-association of ferricyanides in sunlight but it is minimal, not what you need for solo leaching purposes.
A disassociated ferro or ferricyanide leach is nothing more than a cyanide leach with all of the operating properties of that leach class.
If you use one of the commercial leaches such as Eco-Goldex you will load very high levels of unwanted metals on your carbon.
You will end up with carbon which has so much junk metal loaded that ashing of this carbon is difficult, wet stripping of the loaded carbon is impossible.
Most of the commercial leach formulations appear to be developed in China, a fair distance to go to lodge any complaints about the recovery stages.
I have no problems with people selling these formulations because any moderately able chemist should be able to isolate the useful components and point out what is useful in these leaches.
I do have a problem when a leach which is sold as a wonder leach has a major problem with its use but this problem is ignored or glossed over.
As of now there are no restrictions on transport and storage of ferro and ferricyanides, how long it will be before this loophole is plugged I have no idea.
Thanks Deano, you give more info in a few posts than most would ever discover searching / testing on their own.
The livelihood of multitudes of small - med scale gold miners around the world depend on finding alternatives to mercury and cyanide. Most everyone I know in these parts are eager and willing.
I agree that the cyanide derivative products exploit a loophole and were likely designed with that intention.
So all ferri-ferro cyanide class leaches require exposure to UV light. How is this accomplished I wonder and is it practical for a 20-30 ton/day operation?
Recovery by what form if not activated carbon or zinc precipitation?
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Eco-Goldex was developed in Canada, corporate headquarters is in Quebec. They claim a strategy partnership with COREM - product manufactured in China.
The JINCHAN product (China) has marketing similar to Eco-Goldex but their MSDS does not list a cyanide derivative as far as I can see. See MSDS following this message.
If you use just a straight ferrocyanide leach then you will have no problems adsorbing the gold onto carbon or zincing the gold out.
Effectively you will just have a straight cyanide leach.
It is only when you use the formulations which solubilise other metals that you run into problems.
As I said earlier, just run a dis-association tank at pH11 in sunlight to have ferrocyanide convert to cyanide. The ferro component will precipitate out as ferric hydroxide leaving you with straight cyanide solution.
The MSDS you sent conveniently does not list the complexed formations of the components in the leach, just the individual totals. This is a fairly standard method of maintaining secrecy of formulation.
Judging by the low ferric level you will have very low cyanide levels in the leach, a very expensive way to complex gold when you look at the cost of the leach in total.
Ok, got it. And it's a brief exposure (on contact) with sunlight or UV is that right? Could be a tank with sunlight shining in the top while being stirred I suppose...or maybe submersing a UV light inside a tank or even passing the solution thru a tube with UV light (like water treatment).
Straight ferrocyanide is available to the public, not hazmat? Can you recommend a specific product and provider in the Americas?
Thanks again, great info. Much appreciated.
Always keep in mind that uv light is adsorbed by water so you are looking at a longer exposure in a stirred tank to ensure that all parts of the liquid spend some time at the exposure surface.
You are looking to buy ferrocyanide by cost, there is no advantage going to grades above industry/commercial.
I have no idea who distributes this product in the Americas, you are just looking for a basic chemical supplier who will sell you a bag but can supply larger quantities if required.
To start with:
I have a scientific background in Mineral Processing
I am working for an active gold mine/processing plant in the EU
I have conducted a number of tests with Eco-Goldex O series as well as CNFree
I am not in any way associated with the supplier of the agent
We are running a flotation plant since 1992. Now, because of the changes in ore mineralogy, we are also looking for an alternative gold leaching agent (cyanide leaching is forbidden by law in Slovakia). We (and also specialized French hydrometallurgical institute) have tried thiosulfate in alkaline media (low recovery) and thiourea in acidic solution. We were quite successful with thiourea in terms of recovery, but due to quite high content of carbonates in the ore, the acid consumption was too high for the process to be economical.
Then we have found out about Eco-Goldex and CNFREE and acquired our samples for testing. From the leaching point of view, I have to say it works - it does leach gold with sufficient recovery. We use doses of about 3 to 6 kg/t of material treated (tested with flotation tailings with 1- 2 g/t Au and also with ore 6 - 10 g/t). Kinetics are quite fast, most of the recoverable gold is leached within 6 hours. We still have to run tests with lower dosages (first tests were started in Q3/2019, so this is still the beginning). All the tests were done indoors in laboratory conditions (2,5 L) without direct sunlight or any UV source.
After reading many comments, I thought there is a great chance that it works based on cyanide leaching. So I have made a few measurements:
- Using ion-selective CN- electrode (ore + water + agent, measured at various times during leaching). Readings were quite high, rising with leaching time and eventually surpassing even the concentration of the agent in solution. This was probably caused by the interference of the electrode with sulfur in the solution. So this method proved to be unreliable in detecting cyanide in the mix.
- High CN- concentrations were also measured using the electrode when the agent was mixed with only water, without any material.
- I have mixed the agent with water (2 g/L) and sent it to an accredited laboratory, where we analyze the water from our tailings pond. The result - free cyanide is under the detection limit.
- I have also purchased laboratory-grade ferrocyanide and ferricyanide. Mixed each with water (2 g/L) and tried the ion-selective electrode. No free cyanide was measured even the next day.
I have analyzed the composition and my guess is that the main working principle is not based on leaching with cyanide, but thiourea in alkaline conditions (also the fast kinetics suggest so).
CONCLUSIONS: Ferrocyanide/Ferricyanide/Eco-Goldex/CNFREE does not dissociate in water to form free cyanide (at least not under normal conditions - leaching in tanks without additional UV light). The action is probably based on thiourea in alkaline conditions with the ferro/ferricyanide as an oxidizing agent. Kinetics are much faster when compared to cyanide (at least with the dosages of several kg/t of material).
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