Ran a little comparison between eco-goldex, ferro- and ferricyanide

[SaltwaterServr]

I ran all three at 0.2% concentration in 2 liters of water on placer gold we have recovered from about a 20x20' area at one of our mines. Starting pH of 12.01 for each adjusted with NaOH, which is admittedly high for a cyanide leach. Each flask was given 1.506 grams of gold to start which of course is an excess. I ran the leach for 96 hours with a UV-A source lamp at night, with no UV-B wavelengths known as per the manufacturer. Basically it was a reptile basking lamp noted to have UV-A in the spectrum.

I wanted to run this trial based on the discussion of Eco-goldex from back in 2017. It was suggested that since EG mentioned both K3- and K4- as active ingredients, that you'd be better off running a straight leach with ferro- as it was determined that was the principle reagent in the lixiviant. I had come across some literature that had suggested ferro- wasn't considered to favorably as a reagent and that ferri- was a stronger candidate for a leach. Believe that was from the old Cyanide Handbook. The MSDS that came with my purchase of EG didn't mention ferro- at all. Still, I ran all three side by side.

Day 1:

Day 2:

Day 3:

And post-filtration:

Both ferrocyanide and ferricyanide came from Amazon. Below you can see the pricing differences to start. The Eco-Goldex comes in at $11.00 per kilo with shipping to Phoenix, AZ if you buy 25 kg of it like I did.

Potassium ferrocyanide, about $42 per kilo with free shipping:

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

Potassium ferricyanide about $80 with shipping. If you buy 2.5kg from the manufacturer you can get it down to $51 or so. :

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

Results. As expected ferrocyanide ate through more sodium hydroxide due to the formation of hydroferrocyanic acid. It ended at 10.01 or so while Ferri ended at 10.87 and eco-goldex at 10.70.

Remaining gold after filtering and drying:

Potassium ferrocyanide: 1.440 grams

Eco-Goldex: 1.389 grams

Potassium ferricyanide: 1.371 grams

These amounts are very close to each other, but suggest that eco-goldex more closely follows the results of the ferricyanide. When you compare the economics, Eco-goldex is a much much better choice.

 

[anachronism]

Good test. I like that. A lot.

Incidentally EG runs on Ferricyanide.

The mix is bulked up with a range of components including an electrolyte others, some of which actually serve no practical purpose when you analyse them in detail.

NaO 30%

CO(NH2)2 20%

CaO 20%

K3Fe(CN)6 15%

Na2S04 10%

Pb304 < 2%

C6H507Na < 3%

 

[SaltwaterServr]

Edit: My apologies, the percentage is 0.2%, not 2% and has been amended in the original post. 4 grams of each compound was dissolved into 2 liters of water. Any of my professors from college now owe me a nice slap across the face with a wet fish for such an amateur reporting oversight.

 

[Deano]

Good test, worth doing.

Two areas worth noting.

How much of each leachant is actually needed to get the gold recovered, I suspect that you have large excess of leachants, especially the ferro/ferri cyanides.

How do you recover the gold from each leach type, run some tests to see if zinc will do or if you need to use carbon and ash.

Deano

 

[SaltwaterServr]

Good test, worth doing.

Two areas worth noting.

How much of each leachant is actually needed to get the gold recovered, I suspect that you have large excess of leachants, especially the ferro/ferri cyanides.

How do you recover the gold from each leach type, run some tests to see if zinc will do or if you need to use carbon and ash.

Deano

You have me a bit confused on the first question. Are you asking about the potential of adjusting the concentration of each compound to minimize the total volume of solution required to dissolve the total mass of gold I put into each flask? Example, if I ran it at 5% or 50 grams per liter then I'd have a much lower volume waste stream as compare to running it at 0.2% or 4g/l and at the same time I'd be able to dissolve much more gold.

I'm going to test running it with zinc powder for cementation.

The next trial is going to be running it at a much higher concentration, I thought about 2% or 20 g/l for each. Two flasks for each ferri-, ferro-, and goldex. One flask will be air bubbled (sparged with an aquarium bubbler) only, the other will be on a stir plate with the same air injection as well.

The point of all this is that I'm a partner in an start-up mining company here in Arizona. After a good amount of brown field exploration, we're nearing the phase where we're starting prototyping for our ore stream.

Our most favorable property is also the most variable, but we have a lot of rehab to do on it as well. Surface samples run from 0.75 opt for stuff that looks like this:



To 9.875 opt Au and 4.0 opt Ag for this after crushing and blending:



We have also found some sulfides in one old collapsed shaft area that ran 0.57 opt.

Which brings me to these trials. After we pull the gravity recoverable off the tables, we'll have some pretty high grade concentrates left over. Trying to run our leach at a fairly high concentration of cyanide so we can keep the volume down on a 2:1 solution to solids ratio. At those levels of gold, we're going to pretty much need to go with Merrill-Crowe although electrowinning is still being explored.

The next thing I need to get working on is the titration for available CN so we can adjust the solution after zinc back to the appropriate concentrations, and during the gold leach phase as well.

 

[Deano]

I was referring purely to the cost basis in your experiments.

If the ligand concentrations are multiples of that required to solubilise the gold present then trying to compare costings for the different reagents is meaningless unless you know how much unused ligands you still had present at then end of the leach cycle.

I suggest that you try cutting back on all of your ligand types until the recovery is affected, this will give you approximate ligand requirements for each ligand type. Leach times may need to be extended as the ligand concentration is lowered and thus leach rates are also proportionally lowered.

This is economic testing of your leaching agents, it is not efficiency testing of recovery percentages, that is another series of tests.

Deano

 

[SaltwaterServr]

I was referring purely to the cost basis in your experiments.

If the ligand concentrations are multiples of that required to solubilise the gold present then trying to compare costings for the different reagents is meaningless unless you know how much unused ligands you still had present at then end of the leach cycle.

I suggest that you try cutting back on all of your ligand types until the recovery is affected, this will give you approximate ligand requirements for each ligand type. Leach times may need to be extended as the ligand concentration is lowered and thus leach rates are also proportionally lowered.

This is economic testing of your leaching agents, it is not efficiency testing of recovery percentages, that is another series of tests.

Deano

Ah! I see what you mean now.

I could set up the next trial with a titration via silver nitrate/rhodanine at the start, then subsequent titrations every 24 hours until I reach a termination point of the leach, probably the same 96 hours as before. That would give me at least an estimation of consumption of cyanide and what I would need to add back to the leachate to bring it to the original concentration.

More frequent titrations would be of course more desirable but the day job that pays the bills has a say in the matter.

Then to follow on run the next set of trials starting at the 0.2% and then test solutions at half-strengths; 0.2%, 0.1%, 0.05%, 0.025%, 0.0125%, and 0.00625%. Run those concentrations with termination points at 24, 48, 72, and 96 hours. Have to fiddle with the titration a bit to get readings on those lower concentrations. Plot the gold dissolved, remaining ligand in solution.

Those two different trial types should give us some ~good enough~ data sets to work with.

I'm staying with a 4 day maximum leach since I'm generally in the field on the weekends.

Any recommendations or modifications to the above?

 

[Deano]

If you are serious about actual mining then you should look at doing a series of rolling bottle tests, at least 3 splits of ore for each leach type and concentration.

Bottle rolls are usually run as 200g ore with 400 to 600 ml solution in 2 litre bottles.

This will allow you to average out the recovery, high grade gold ores are notorious for large bounce in the numbers.

You can minimise variability by milling the ore to < 100 microns before doing the splits.

Finding what ore sizing you need for processing is another series of tests to be carried out after establishing what reagent levels and times are needed.

Usually you use liquor assays to establish recovered gold grade, running an AA is pretty easy and in alkaline situations there is no need for organic extraction to remove interferents.

You can easily do 24, 36 etc time assays to determine leach times, allow the bottles to stand long enough for the coarser ore particles to settle before sampling as a semi decant sample. You will only need 10 ml of sample per assay.

Look at getting a bare bones type second hand AA, you do not need the more expensive models with sample trains etc.

Using a cyanide probe is easier than titrating and is less liable to errors for an unskilled operator. Check suppliers online for the hand held models.

It may seem a lot of time and expense to go to just for testing but all of this equipment will be used daily on an operating mine.

Way better to face upfront costs than to limp along just hoping when operating.

Most mining failures are from not doing enough test work before the really expensive stage of setting up for actual mining.

Deano

 

[SaltwaterServr]

If you are serious about actual mining then you should look at doing a series of rolling bottle tests, at least 3 splits of ore for each leach type and concentration.

Bottle rolls are usually run as 200g ore with 400 to 600 ml solution in 2 litre bottles.

This will allow you to average out the recovery, high grade gold ores are notorious for large bounce in the numbers.

You can minimise variability by milling the ore to < 100 microns before doing the splits.

Finding what ore sizing you need for processing is another series of tests to be carried out after establishing what reagent levels and times are needed.

Usually you use liquor assays to establish recovered gold grade, running an AA is pretty easy and in alkaline situations there is no need for organic extraction to remove interferents.

You can easily do 24, 36 etc time assays to determine leach times, allow the bottles to stand long enough for the coarser ore particles to settle before sampling as a semi decant sample. You will only need 10 ml of sample per assay.

Look at getting a bare bones type second hand AA, you do not need the more expensive models with sample trains etc.

Using a cyanide probe is easier than titrating and is less liable to errors for an unskilled operator. Check suppliers online for the hand held models.

It may seem a lot of time and expense to go to just for testing but all of this equipment will be used daily on an operating mine.

Way better to face upfront costs than to limp along just hoping when operating.

Most mining failures are from not doing enough test work before the really expensive stage of setting up for actual mining.

Deano

Thank you for the reply, as always.

I've got two companies here in Phoenix that can do the roll bottle tests, and I believe our main assayer has someone down the street from him in Idaho that does it as well. I can ship off a sample of our ore to them, then check it against my results to ascertain any deviations.

Looks like the Hanna Instruments HI98191 is a good meter to pair up with their cyanide electrode coming in at $1300 USD for the pair. Testing range reads from 0 to 260 mg/l.

There are less expensive brands/models but I have domestic servicing if something fails on the unit/probe. I've also used Hanna Instruments in lab settings. We had a few of their meters in one of my biology research labs in college.

From what I can tell, an AAS isn't terribly expensive. A few on ebay for under $1000.00.

The expense isn't a horrible bother at this time; when you have the money for the equipment that's great, and when you don't have the money you start saving for it. Nothing in the mining business seems to be inexpensive and we pretty much knew that going into it.

 

[oro-del-sur]

I'm curious as to what method you used to recover the gold in the tests and any other successes or failures with extraction. I have a 25 kg bag of the Eco-Goldex O series (for high silver ores) and have been doing some testing here in Costa Rica. I don't have enough experience with the science to do much beyond rolling a few 1 kg samples and learning / practicing titration. We have had success with activated carbon, then smelt it with some litharge and cupel it although I'll admit this might not be the best method. The owner of Goldex John Duo told me zinc precipitation requires removal of the oxygen so best to stick with the activated carbon. One problem here is the lack of lab services so we have set up a very basic lab and are doing our own assays, problem is our analytical balance is only .0001 so we get a 3 gram error (although helpful anyway). We will hire someone more professional soon and are saving our money for upgrades as we go along.

This week we may test leach a 100 liter batch of concentrates but I'm still trying to figure out the most practical method to process a few kilos of activated carbon. I've ashed 50g of carbon in my little electric cupel furnace but ashing a few kilos in the open is tricky I can see. We don't have enough knowledge yet to set up and operate a stripper (but want to learn). I have experimented a bit with the SSN leach and was wondering if it might be worth trying. It's very aggressive and my guess is it will strip the gold from the carbon and theoretically allow for zinc or SMB precipitation. Any thoughts about that?

We are an artisanal operation at this point, 10 ton/day using a Chilean style mill for primary grinding and several stone mills (arastras) for secondary grinding and amalgamation. The ores here are high in sulfides. Our results using the Goldex product and our limited skills has been very positive. We are extremely grateful to have access to a product that is not restricted for purchase, transport and handling nor require special permitting to deploy it. For us this is a huge breakthrough. The use of cyanide is strictly prohibited here.