Request for info, extracting gold in/on magnetite

[Bentfunky]

So, I find that I have quite an interesting challenge and could use some help finding info on topic.

I need to find an efficient way to extract gold from magnetite particles.

For testing, I've been digesting material in aqua regia. This was ok to verify presence of gold and to get some idea of its concentration.

However, I have to admit that this has been a very inefficient process. Multiple days of AR treatment of small samples (few tablespoons) of test material results in only partial gold extraction. I've run the same sample three times through this process, each time extracting about the same amount of gold. I'm sure that gold still remains uncollected.

Moreover, once extracted, gold tend to exist in a colloidal state. This occurs even when dropping gold with copper. Again, not a huge deal when only processing for testing purposes.

However, this experience and reading literature on topic suggest that chemical leaching would be inefficient/inadequate for extracting gold from larger volumes of ferromagnetic concentrates (mostly magnetite). Also, I will admit that I have a visceral dislike of chemical leaching using strong acids or cyanide.

Smelting is likely not an option. Gold concentration isn't high enough to make this efficient either. I'd pretty much need to smelt at temps near 2800 F to ensure gold was extracted from magnetite. I've tried.

Any thoughts on other potential gold extracting methodologies would be much appreciated!

 

[butcher]

Your best bet is using gravity separation to recover any free gold.
Not all black sands will contain gold, it is really dependent on the source of gold.

Smelting with a collector metal would also be an option for any gold that may be locked up in the matrix, which normally will not be worth the cost involved in the recovery.

Attempting to leach black sands with aqua regia will not work, not only wasteful and foolish but can become deadly because of the gaseous products involved.

 

[galenrog]

While gold can occur in magnetite, the likelihood of it being in paying quantities is low. You wrote that you did testing to determine presence of gold. What tests did you perform, and what were the results?

Personally, it the material passes standard field tests for gold, but none is visible, I would have a qualified professional perform an assay.

This may be a case of spending dollars to chase dimes. There are many ways to find gold. Find a few that work for you. Leaching magnetite with AR is a waste of time and resources. As Butcher pointed out, the process can produce some extremely dangerous gasses. Imagine losing 90% of lung function dangerous.

Time for more coffee.

 

[Bentfunky]

While gold can occur in magnetite, the likelihood of it being in paying quantities is low. You wrote that you did testing to determine presence of gold. What tests did you perform, and what were the results?

For purposes of testing for gold and to get a general idea if there is enough to care, I take small sample of material (2 or 3 tablespoons) and place it in warm AR.

Normally, before AR, I clean up samples by removing ferromagnetic material after panning heavies. If large amount of sulfides, material gets roasted. I then place remaining heavies in warm nitric acid to remove base metals (if present) and to oxidize sulfides (if present).

The above doesn’t apply, however, in this case. Gold baring material is an entirely different animal. Gold is contained in magnetite matrix. Upside is that isolating gold baring material is straightforward.

After AR soak, I drop values with copper. This provides info on amount of gold.



As you can see from stannous chloride, I’ve got gold. Haven’t weighed yet, since I’m still working to get most gold from sample material. Mostly, colloidal gold, so will need to redissolve and drop with SMB before weighing.

Definitely enough to be interesting.

 

[cosmetal]

After mechanically processing for free gold, try "cracking" your remaining cons by heating to approx. 1500F and while still hot, throwing them into a tub of water. This helps to release some of the gold from the magnetite. Mechanically process again. This has worked for me and I am always surprised at the amount of free gold that shows up in my pan.

Want "super/super cons"? Mill the cons to +/- 100 mesh and then continue your chemical investigation of the "super/super cons".

Peace and health,
James

 

[Bentfunky]

After mechanically processing for free gold, try "cracking" your remaining cons buy heating to approx. 1500F and while still hot, throwing them into a tub of water. This helps to release some of the gold from the magnetite. Mechanically process again. This has worked for me and I am always surprised at the amount of free gold that shows up in my pan.

Want "super/super cons"? Mill the cons to +/- 100 mesh and then continue your chemical investigation of the "super/super cons".

Peace and health,
James

@cosmetal, I like the super/super cons idea . My magnetite is not very coarse, so milling didn't occur to me. However, now that you mention it, makes a lot of sense! Time to break out the mortal and pestle. I'll grind up the sample material that has already had 3 AR baths. Should make for a good test. If I can raise concentration of free gold enough, smelting becomes an option.

 

[Bentfunky]

Your best bet is using gravity separation to recover any free gold.
Not all black sands will contain gold, it is really dependent on the source of gold.

Smelting with a collector metal would also be an option for any gold that may be locked up in the matrix, which normally will not be worth the cost involved in the recovery.

Attempting to leach black sands with aqua regia will not work, not only wasteful and foolish but can become deadly because of the gaseous products involved.

@butcher, appreciate your comments! I've been smelting here and there for the past couple years. Just recently built a new furnace. It's a beast. I agree, smelting is not an option right now.

Also, agree about not leaching for anything except testing small samples. I am not a fan of that approach in general. I have no idea how people who recycle precious metals from e-waste via leaching don't seriously injure or kill themselves. Many don't seem to use fume hoods!

As mentioned, I don't have much free gold. It's actually in magnetite matrix if you can believe it! Occasionally, gold is big enough that one can actually see it on grains of magnetite. I took a picture a while back using macro lense. I'll post pic if I can find it.

 

[butcher]

Before I spent much time, trouble, money, energy, or fuel into trying to crack those nuts, I would consider taking a good representative sample of the black sands (a good mix not- the heavys from the bottom of the bucket) and only after removing all of the free gold you possible can using gravity methods, send the free gold barren magnetite-hematites samples out for a professional fire assay. Now that you saved money on the information and now have an idea of how much gold per ton of black sands you may expect, you can then begin into looking at the best means to use and at what cost it will take to recover the gold from its matrix bond.

I would almost bet you would profit more from selling the black sands, along with all kinds of different types and styles of fancy equipment, gadgets, and whirly-Gigs along with the parts, consumables, and chemicals for someone else to attempt to recover gold from them, those selling claims and shovels are the ones who profited in the gold rush, not the men trying to get gold out of a magnetite matrix.

Gold has such a beautiful and mystifying reflection of light which pierces its golden glow into the eyes of those of us with gold fever with such fierceness, not only blindly blinding us along with dazzling us, while always making itself out to be much more than it actually is, or maybe it is that it just skews or fevered brains perception of itself with its golden glow, I do not know, who knows, you may get rich off the gold you see in the microscope.
I just do not know of anyone who did get rich smelting magnetite ore except the mining shops selling supplys or even the black sands...

You could always just enjoy its beauty in the microscope and move on to better propects?

 

[Bentfunky]

Before I spent much time, trouble, money, energy, or fuel into trying to crack those nuts, I would consider taking a good representative sample of the black sands (a good mix not- the heavys from the bottom of the bucket) and only after removing all of the free gold you possible can using gravity methods, send the free gold barren magnetite-hematites samples out for a professional fire assay. Now that you saved money on the information and now have an idea of how much gold per ton of black sands you may expect, you can then begin into looking at the best means to use and at what cost it will take to recover the gold from its matrix bond.

I would almost bet you would profit more from selling the black sands, along with all kinds of different types and styles of fancy equipment, gadgets, and whirly-Gigs along with the parts, consumables, and chemicals for someone else to attempt to recover gold from them, those selling claims and shovels are the ones who profited in the gold rush, not the men trying to get gold out of a magnetite matrix.

Gold has such a beautiful and mystifying reflection of light which pierces its golden glow into the eyes of those of us with gold fever with such fierceness, not only blindly blinding us along with dazzling us, while always making itself out to be much more than it actually is, or maybe it is that it just skews or fevered brains perception of itself with its golden glow, I do not know, who knows, you may get rich off the gold you see in the microscope.
I just do not know of anyone who did get rich smelting magnetite ore except the mining shops selling supplys or even the black sands...

You could always just enjoy its beauty in the microscope and move on to better propects?

Right now, I’m just verifying that material is interesting enough to send out for assay.

I’m just about there. Just too easy to see what one wants to see instead of what’s actually there. Costs money when that happens.

I take your underlying point, however. Assuming good values in material, I honestly don’t know how I’d efficiently and safely extract it.

As an update to earlier comments, I ground up previously processed test material to fine powder. Will let it sit in AR for a day or two. Really curious to see results. Hopefully, less colloidal gold. Can’t imagine that tin or other usual suspects remained in test material after first AR bath, so no idea why I’m getting colloidal gold on subsequent AR processing of same material. Just so odd.

 

[cosmetal]

Before I spent much time, trouble, money, energy, or fuel into trying to crack those nuts, I would consider taking a good representative sample of the black sands (a good mix not- the heavys from the bottom of the bucket) and only after removing all of the free gold you possible can using gravity methods, send the free gold barren magnetite-hematites samples out for a professional fire assay. Now that you saved money on the information and now have an idea of how much gold per ton of black sands you may expect, you can then begin into looking at the best means to use and at what cost it will take to recover the gold from its matrix bond.

I would almost bet you would profit more from selling the black sands, along with all kinds of different types and styles of fancy equipment, gadgets, and whirly-Gigs along with the parts, consumables, and chemicals for someone else to attempt to recover gold from them, those selling claims and shovels are the ones who profited in the gold rush, not the men trying to get gold out of a magnetite matrix.

Gold has such a beautiful and mystifying reflection of light which pierces its golden glow into the eyes of those of us with gold fever with such fierceness, not only blindly blinding us along with dazzling us, while always making itself out to be much more than it actually is, or maybe it is that it just skews or fevered brains perception of itself with its golden glow, I do not know, who knows, you may get rich off the gold you see in the microscope.
I just do not know of anyone who did get rich smelting magnetite ore except the mining shops selling supplys or even the black sands...

You could always just enjoy its beauty in the microscope and move on to better propects?

As always, very wise and experienced suggestions.

But, curiosity and experimentation are such seductive, expensive and, sometimes harsh, mistresses.

Wait! I'ts time for me to go "see the elephant" again! https://en.wikipedia.org/wiki/Seeing_the_elephant

Peace and health,
James

 

[butcher]

If you live in a placer mining district you may look into buying black sands from other miners and prospectors (mostly those who are not so good at panning or recovery), and get enough gold using better classifying and gravity methods than those who held the sands before you.

 

[Bentfunky]

If you live in a placer mining district you may look into buying black sands from other miners and prospectors (mostly those who are not so good at panning or recovery), and get enough gold using better classifying and gravity methods than those who held the sands before you.

Unfortunately, while the area where I live is known to have a little gold, there aren't any profitable gold mines, at least none that are active. There are a few old gold mines here and there from late 1800s, early 1900s.

One of @cosmetal's earlier comments is spot on. I derive a lot of enjoyment from the hunt. I'd much rather hunt for my own gold than be practical and benefit from someone else's. Those darn elephant are everywhere!

--Bent

 

[cosmetal]

If you live in a placer mining district you may look into buying black sands from other miners and prospectors (mostly those who are not so good at panning or recovery), and get enough gold using better classifying and gravity methods than those who held the sands before you.

Butcher,

You're reading my mind.

I live in an area surrounded by large bucket-line dredging fields active from the late 1800s to early 1900s. Huge monsters chewed through the alluvial fields surrounding Sacramento and neighboring cities. They were interested in the larger free placer gold and didn't bother with the smaller 1 grain or less fines. Their equipment just "blew" that pesky "stuff" right out of their slucies and back into the tailings piles.

My problem is getting access to the properties. Believe me, I'm working on it. Anyone living in my area that has access to these tailing fields please contact me.

Time to see the Elephant http://explore.museumca.org/goldrush/fever11.html,
James

 

[cosmetal]

If you live in a placer mining district you may look into buying black sands from other miners and prospectors (mostly those who are not so good at panning or recovery), and get enough gold using better classifying and gravity methods than those who held the sands before you.

Unfortunately, while the area where I live is known to have a little gold, there aren't any profitable gold mines, at least none that are active. There are a few old gold mines here and there from late 1800s, early 1900s.

One of @cosmetal's earlier comments is spot on. I derive a lot of enjoyment from the hunt. I'd much rather hunt for my own gold than be practical and benefit from someone else's. Those darn elephant are everywhere!

--Bent

Bent,

Kindred spirit!

Make sure you keep a bag of roasted peanuts in your lab/shop. You never know when the "elephants" might show-up.Your choice - pay their "elephant tax" in peanuts or gold!

Still looking for the Elephant after all these years,
James

 

[butcher]

I remember seeing a few pink ones in my day, never could catch one though.

 

[Bentfunky]

I remember seeing a few pink ones in my day, never could catch one though.

Update on results of grinding concentrates. Worked very well! I cleanly dropped a pretty decent amount of gold using SMB (relative to sample size and number of times material had already been processed). Nice red-brown color. Definitely, time to send some concentrates out for assay.

Interestingly, all the nitric was consumed this time, so I'd need a 5th round of AR if I decided to recover all the gold in sample. Probably, not worth the effort. This round took 4 to 5 milliliters of nitric. For me, that is a lot.

The other big change that I made was not using heat. Just let material sit in AR for a couple/few days. This kept other material such as (likely) palladium from going into solution with the gold. Hence, the much cleaner gold drop.

Now, I'll need to reprocess the material collected from the earlier 3 AR treatments. Results were no where near as clean as this round. Live and learn.

 

[Bentfunky]

Ok, I processed all my sample material and understand the material that I'm working with.

Material is gold, palladium (maybe more than the gold), and (unfortunately) a notable amount of lead. Arrrgggg ... I hate lead! Values are likely enough to keep me looking/testing area.

Assay pending.

 

[cosmetal]

Ok, I processed all my sample material and understand the material that I'm working with.

Material is gold, palladium (maybe more than the gold), and (unfortunately) a notable amount of lead. Arrrgggg ... I hate lead! Values are likely enough to keep me looking/testing area.

Assay pending.

Bent,

Previously. you said "Normally, before AR, I clean up samples by removing ferromagnetic material after panning heavies. If large amount of sulfides, material gets roasted. I then place remaining heavies in warm nitric acid to remove base metals (if present) and to oxidize sulfides (if present)."

Again, I am no chemical expert. So, I'm not trying to be a smart a##. But, I am confused about the lead (Pb). It is my understanding, that, nitric acid (HNO3) will dissolve lead to form Pb(NO3)2. https://en.wikipedia.org/wiki/Compounds_of_lead#:~:text=Metallic%20lead%20is%20attacked%20

The Pb(NO3)2 or "Lead(II) nitrate is an inorganic compound with the chemical formula Pb(NO3)2. It commonly occurs as a colourless crystal or white powder and, unlike most other lead(II) salts, is soluble in water.". https://en.wikipedia.org/wiki/Lead(II)_nitrate

If you washed your sample after the HNO3 dissolve, how can this final test contain "a notable amount of lead"? At this time, I would say that "Assay pending" is a very good choice.

You say that you are located in the US, but, you haven't divulged what state your sample came from. This company is located in Phoenix, AZ and advertise that they can assay and chemically process commercial quantities of black sand concentrates https://tcbinter.com/?page_id=85 I have never used them nor do I know of anyone who has. If you do use them, I hope that you let us know about your experience.

Peace and health,
James

 

[Bentfunky]

Ok, I processed all my sample material and understand the material that I'm working with.

Material is gold, palladium (maybe more than the gold), and (unfortunately) a notable amount of lead. Arrrgggg ... I hate lead! Values are likely enough to keep me looking/testing area.

Assay pending.

Bent,

Previously. you said "Normally, before AR, I clean up samples by removing ferromagnetic material after panning heavies. If large amount of sulfides, material gets roasted. I then place remaining heavies in warm nitric acid to remove base metals (if present) and to oxidize sulfides (if present)."

Again, I am no chemical expert. So, I'm not trying to be a smart a##. But, I am confused about the lead (Pb). It is my understanding, that, nitric acid (HNO3) will dissolve lead to form Pb(NO3)2. https://en.wikipedia.org/wiki/Compounds_of_lead#:~:text=Metallic%20lead%20is%20attacked%20

Peace and health,
James

You are too observant

WRT lead, my answer falls under the heading of being "penny-wise but pound foolish."

The cheapo thought centers of my brain over-rode the logic part. Didn't think that I'd have to worry about lead or some other base metals since I was working with ferromagnetic test material. Lead isn't attracted to magnet. So, I could save a little nitric. Didn't consider that lead might hitch a ride during separation process with magnet. This bit of ground probably has a lot of lead.

In retrospect, a nitric preprocessing step would have been beneficial in any case due to possibly of encountering palladium, which is present in nearby rocks at concentrations of approx 1g/ton.